Loading ...
Sorry, an error occurred while loading the content.

antiseptic? antifungal? antiviral? methanol (formaldehyde, formic acid) disposition: Bouchard M et al, full plain text, 2001: substantial sources are degradation of fruit pectins, liquors, aspartame, smoke: Murray 2005.01.05 rmforall

Expand Messages
  • Rich Murray
    http://groups.yahoo.com/group/aspartameNM/message/1143 antiseptic? antifungal? antiviral? methanol (formaldehyde, formic acid) disposition: Bouchard M et al,
    Message 1 of 1 , Jan 5, 2005
    View Source
    • 0 Attachment
      http://groups.yahoo.com/group/aspartameNM/message/1143
      antiseptic? antifungal? antiviral? methanol (formaldehyde, formic acid)
      disposition: Bouchard M et al, full plain text, 2001: substantial sources
      are degradation of fruit pectins, liquors, aspartame, smoke: Murray
      2005.01.05 rmforall

      An earnest medical layman, I have been writing careful reviews of mostly
      mainstream medical research on aspartame toxicity for six years.

      In recent months I have become aware that evidence strongly shows that
      substantial methanol and thus formaldehyde and formic acid are released into
      humans from degradation of the pectins from fruits and vegetables by
      bacteria in the colon in many people. Whatever the source, the biochemical
      dispositions of methanol and its inevitable products, formaldehyde and
      formic acid, both potent, cumulative toxins, are actually largely unknown,
      according to the expert comprehensive review by Bouchard M et al, 2001.

      "Experimental studies on the detailed time profiles following controlled
      repeated exposures to methanol are lacking."

      "Thus, in monkeys and plausibly humans, a much larger fraction of body
      formaldehyde is rapidly converted to unobserved forms rather than passed on
      to formate and eventually CO2."

      "However, the volume of distribution of formate was larger than that of
      methanol, which strongly suggests that formate distributes in body
      constituents other than water, such as proteins."

      Their comprehensive review shows that there is little information about the
      details of methanol (formaldehyde and formic acid) dispositions in humans
      for long-term, chronic exposures. Their full text is given later in this
      post.

      Research on hangovers, largely caused by the conversion of methanol impurity
      in alcohol drinks into formaldehyde after about eight hours, after most of
      the ethanol has been eliminated, shows that a quarter to a half of those who
      get inebriated do not get hangovers. This shows very large individual
      variation in vulnerability to formaldehyde toxicity, so as a corollary,
      probably there will be many who are not markedly vulnerable to aspartame.

      I suggest that natural selection has given humans complex biochemical
      systems to store the large amounts of formaldehyde generated from pectins
      and to use them to attack pathogens. So far, I have not found any strong
      research to support this hypothesis. I hope to write a useful summary
      in the next few weeks.

      There are many substances, such as folic acid, that protect against
      formaldehyde toxicity.

      This long, complex review presents mainstream evidence for several
      ubiquitous, substantial sources of methanol and its inevitable chain of
      products, formaldehyde and formic acid, which I will initialize as "MCC",
      for Methanol Chain Compounds.

      Monte WC in his seminal summary review (1984) mentions that humans are
      uniquely vulnerable to the conversion of methanol into formaldehyde:

      "Fruit and vegetables contain pectin with variable methyl ester content.
      However, the human has no digestive enzymes for pectin (6, 25)
      particularly the pectin esterase required for its hydrolysis to methanol
      (26)."

      "Humans, due perhaps to the loss of two enzymes during evolution, are
      more sensitive to methanol than any laboratory animal; even the monkey
      is not generally accepted as a suitable animal model (42)."

      "The methyl ester bond of phenyalanine is the first
      to cleave due to its susceptibility to pancreatic enzymes (40).
      This is highly unusual; the methyl esters
      associated with pectin for instance
      are completely impervious to all human digestive enzymes (6)."

      "The greater toxicity of methanol to man is deeply rooted in the limited
      biochemical pathways available to humans
      for detoxification. The loss of uricase (EC 1.7.3.3.),
      formyl-tetrahydrofolate synthetase (EC 6.3.4.3.) (42)
      and other enzymes (18) during evolution sets man apart from all
      laboratory animals including the monkey (42)."

      "The importance of ethanol as an antidote to methanol toxicity in humans
      is very well established in the literature (46, 55). The timely
      administration of ethanol is still considered a vital part of methanol
      poisoning management (11, 12, 19, 20, 50). Ethanol slows the rate of
      methanol's conversion to formaldehyde and formate, allowing the body
      time to excrete methanol in the breath and urine. Inhibition is seen in
      vitro even when the concentration of ethyl alcohol was only 1/16th that
      of methanol (62). The inhibitory effect
      is a linear function of the log of the
      ethyl alcohol concentration, with a 72% inhibition rate at only
      a 0.01 molar concentration of ethanol (2, 46).

      Oxidation of methanol, like that of ethanol, proceeds independently of
      the blood concentration, but at a rate only one seventh (20) to one
      fifth (12) that of ethanol.

      Folacin [ folic acid ] may play an important role in the metabolism of
      methanol by catalyzing the elimination of formic acid (41).
      If this process proves to be as protective for humans
      as has been shown in other organisms (50, 38)
      it may account, in part, for the tremendous variability of
      human responses to acute methanol toxicity. Folacin is a nutrient
      often found lacking in the normal human diet, particularly during
      pregnancy and lactation (14)."

      It is well known that our primate ancestors were highly adapted to a diet of
      fruits and vegetables, and thus had the enzyme systems to prevent toxicity
      from the inevitable methanol content and from methanol from the degradation
      of pectins by bacteria in the colon.

      Humans have been living in groups in lifelong close proximity with fire and
      smoke, a potent source of formaldehyde, for about 2 million years. Fire has
      ever since been essential for survival, as has been intimate enclosed group
      living, especially as homo erectus, Neanderthals, and moderns successively
      adapted to very cold habitats.

      Yet formaldehyde is among the most potent of toxins, and cumulative to boot.
      Yet intimate enclosed group living in a variety of environments promotes
      extreme exposure to a variety of contagious, infectious diseases. And yet,
      humans lack two enzymes that protect against Methanol Chain Compounds
      toxicities. What is an obvious evolutionary explanation for this?

      MCC toxicities must serve to prevent and treat contagious infections from
      bacteria, fungi, parasites, and possibly viruses. This would generate a
      potent positive selection pressure to cause humans to evolve the ability to
      have increased MCC exposures, and to be multiply adapted to tolerate MC
      toxicities.

      Wine and beer serve throughout history to protect against water bourne
      pathogens. For centuries formaldehyde has been used to protect medical
      scientists from highly infected cadaver tissues. What is the scientific
      literature about MCC and the various groups of contagious infectious agents?
      It is a testable hypothesis as to whether MCC in many types of people, with
      the inevitable complex variations of genetics and diet, impede many simple
      infectious agents more than they harm critical body processes in complex
      human cells.

      It may be that MCC are important unexamined co-factors that strongly affect
      research and treatment of many infectious diseases.

      We might find, for instance, that in many humans some infections cause
      reduction of folic acid or folate levels, and thus increased MCC levels.

      Many traditional societies treat diseases with exposure to smoke, whether in
      a hut with a wood fire, or in a temple with incense. Likewise, alcohol
      drinks have been widely used as remedies. Did the daily ration of grog in
      the British Navy serve to reduce infections in the close and dirty confines
      of life on wooden ships? In the trenches of World War I, the British also
      had a daily ration -- were their rates of infection lower
      than for troops that had little liquor?

      These questions throw an entirely new light, expansive, tantalizing, and
      unifying, on the often contentious and poorly researched issues of MCC
      toxicity, especially the aspartame controversy. It would also be ironic,
      but typical of the actual complex evolution of science, for tobacco and wood
      smoke to be shown to have some benefits for infectious diseases.

      http://groups.yahoo.com/group/aspartameNM/message/1140
      EPA Preliminary Remedial Goals, PRGs, 2003 Oct, air and tap water --
      methanol, formaldehyde, formic acid -- not mentioned is methanol from
      aspartame, dark wines and liquors: Murray 2004.11.20 rmforall

      http://groups.yahoo.com/group/aspartameNM/message/1141
      Nurses Health Study can quickly reveal the extent of aspartame (methanol,
      formaldehyde, formic acid) toxicity: Murray 2004.11.21 rmforall

      The Nurses Health Study is a bonanza of information about the health of
      probably hundreds of nurses who use 6 or more cans daily of diet soft
      drinks -- they have also stored blood and tissue samples from their immense
      pool of subjects.

      Dark wines and liquors, as well as aspartame, provide similar levels of
      methanol, above 100 mg daily, for long-term heavy users. Methanol is
      inevitably largely turned into formaldehyde, and thence largely into formic
      acid. Both products are toxic, and at this level of use, about 2 L daily,
      almost six 12-oz cans of diet drink, are above recent lifetime EPA [ PRG ]
      safety limits in tap water for methanol and formaldehyde of respectively,
      for a 60 kg person, 30 mg and 9 mg daily.

      The immediate health effects for dark wines and liquors are the infamous
      "morning after" hangover, for which many informed experts cite as the major
      cause the conversion of the methanol impurity, over one part in ten thousand
      (red wine has 128 mg/L methanol), into formaldehyde and formic acid.
      Everyone knows the complex progression of symptoms at this level of
      long-term, chronic toxicity.

      Aspartame reactors have a very similar progression.

      If 1% of all people exposed to alcohol and/or aspartame are heavy users with
      symptoms, then there would easily be about 2 million cases in the USA alone.

      This is a public health emergency.

      At the very least, professionals and the public should be alerted to
      investigate their own exposure, and be given a chance to try a very safe,
      simple, inexpensive treatment for complex, intractable, progressive
      symptoms -- reducing or eliminating their intake.

      There are as well, many safe substances that prevent or treat the
      toxicities -- for example, high folic acid levels expedite the elimination
      of formaldehyde.

      These toxicities are largely uncontrolled co-factors that affect every
      disease and must confuse and impede many health research programs on all
      levels.

      People in high-pressure, critical occupations, such as pilots, nuclear plant
      operators, and national leaders, should certainly be alerted.

      Also, two careful studies show substantial methanol release from degradation
      of pectins by bacteria in the colon from fruits and vegetables -- a topic
      that deserves careful, thorough research.

      Due to my bias, based on detailed reviews by Monte WC (1984) and by Mark D.
      Gold (2003), for months I have been discounting the startlingly high
      methanol levels reported in the abstract for Lindinger W (1997). I have
      been reducing the values in their abstract from g to mg, an unwarrented
      "correction" by a factor of a thousand, only to find that the full text
      study and their many related studies supply expert, robust results:

      Alcohol Clin Exp Res. 1997 Aug; 21(5): 939-43.
      Endogenous production of methanol after the consumption of fruit.
      Lindinger W, Taucher J, Jordan A, Hansel A, Vogel W.
      Institut fur Ionenphysik, Leopold Franzens Universitat Innsbruck, Austria.

      After the consumption of fruit, the concentration of methanol in the human
      body increases by as much as an order of magnitude.
      This is due to the degradation of natural pectin (which is esterified with
      methyl alcohol) in the human colon.
      In vivo tests performed by means of proton-transfer-reaction mass
      spectrometry show that consumed pectin in either a pure form (10 to 15 g)
      or a natural form (in 1 kg of apples) induces a significant increase of
      methanol in the breath (and by inference in the blood) of humans.
      The amount generated from pectin (0.4 to 1.4 g)
      is approximately equivalent to the total daily endogenous production
      (measured to be 0.3 to 0.6 g/day)
      or that obtained from 0.3 liters of 80-proof brandy
      (calculated to be 0.5 g). [ 1667 mg methanol per liter of brandy ]
      This dietary pectin may contribute to the development
      of nonalcoholic cirrhosis of the liver. PMID: 9267548

      Alcohol Clin Exp Res. 1995 Oct; 19(5): 1147-50.
      Methanol in human breath.
      Taucher J, Lagg A, Hansel A, Vogel W, Lindinger W.
      Institut fur Ionenphysik, Universitat Innsbruck, Austria.

      Using proton transfer reaction-mass spectrometry for trace gas analysis of
      the human breath, the concentrations of methanol and ethanol have been
      measured for various test persons consuming alcoholic beverages and various
      amounts of fruits, respectively.
      The methanol concentrations increased from a natural (physiological) level
      of approximately 0.4 ppm up to approximately 2 ppm a few hours after eating
      about 1/2 kg of fruits,
      and about the same concentration was reached after drinking of 100 ml brandy
      containing 24% volume of ethanol and 0.19% volume of methanol.
      [ 24 ml = 61 g ethanol, and 0.19 ml = 0.34 g = 340 mg methanol ]
      PMID: 8561283

      I urge Channing Laboratory and its participating universities to rapidly
      mount an in-house study to study the Nurses Health Study database for the
      hundreds of nurses who are long-term users, above 6 cans diet drinks daily,
      for correlations with every disease, as well as ubiquitous co-factors like
      wine and liquor, cigarette smoke, and fruits and vegetables. It could
      vastly serve the world public health to make the initial findings widely
      available immediately. The disparaged issue of aspartame toxicity could be
      swiftly made legitimate, and the resulting progress on all levels remarkably
      accelerated.

      A single scientist could do this.

      Comments pro and con are welcome. A convenient venue would be the moderated
      newsgroup: bionet.toxicology.

      Rich Murray, MA Room For All rmforall@...
      1943 Otowi Road, Santa Fe, New Mexico 87505 USA 505-501-2298
      http://groups.yahoo.com/group/aspartameNM/messages
      137 members, 1,143 posts in a public searchable archive
      **************************************************************

      http://groups.yahoo.com/group/aspartameNM/message/957
      safety of aspartame Part 1/2 12.4.2: EC HCPD-G SCF:
      Murray 2003.01.12 rmforall EU Scientific Committee on Food, a whitewash

      http://groups.yahoo.com/group/aspartameNM/message/1045
      http://www.holisticmed.com/aspartame/scf2002-response.htm
      Mark Gold exhaustively critiques European Commission Scientific
      Committee on Food re aspartame ( 2002.12.04 ): 59 pages, 230 references

      "C. Public Relations, Aspartame, Methanol, and Formaldehyde

      Before we discuss what little the Committee did say related to aspartame and
      formaldehyde, it is important to answer all of the typical public relations
      statements from the manufacturer and their consultants who claim there is no
      problem with aspartame and formaldehyde. The answers provided below will be
      brief. Much more detailed and referenced answers can be found at ATIC (2001)
      on the Internet at:
      [ http://www.holisticmed.com/aspartame/abuse/methanol.html ].

      Chart of Aspartame Manufacturer Public Relations Statements
      Related to Methanol and Formaldehyde

      Manufacturer Claim --- Independent Response

      Methanol is found in fruits and alcoholic beverages at higher levels than in
      aspartame products. --- Alcoholic beverages contain large amounts of
      ethanol (a protective factor) which allows methanol to be excreted before
      much of it is converted into formaldehyde (Leaf 1952, Liesivuori 1991, Roe
      1982).

      Fruit juices have protective factors as well that prevent formaldehyde
      poisoning. Fruit juices produce enough methanol to "qualify as significantly
      methanol-contaminated liquor" (Lindinger 1997) -- more methanol than what
      causes chronic health problems in occupational exposure (Kazeniac 1970,
      Kavet 1990, Frederick 1984, Kingsley 1954-55). Since we do not see chronic
      poisoning from fruit juices, they must contain protective factors as well.
      Fruit juices have ethanol as well as other possible protective factors."


      http://groups.yahoo.com/group/aspartameNM/message/870
      Aspartame: Methanol and the Public Interest 1984: Monte:
      Murray 2002.09.23 rmforall

      Dr. Woodrow C. Monte Aspartame: methanol, and the public health.
      Journal of Applied Nutrition 1984; 36 (1): 42-54.
      (62 references) Professsor of Food Science [retired 1992]
      Arizona State University, Tempe, Arizona 85287 woodymonte@...
      ***********************************************************

      [ Comments by Rich Murray are in square bracketts. Without changing text,
      except for omitting long equations, figures, and tables, spacing has been
      added to give emphasis and increase readability. Following are some
      specific extracts. ]

      "That substantial amounts of methanol metabolites or by-products are
      retained for a long time is verified by Horton et al. (1992) who estimated
      that 18 h following an iv injection of 100 mg/kg of 14C-methanol in male
      Fischer-344 rats, only 57% of the dose was eliminated from the body.

      From the data of Dorman et al. (1994) and Medinsky et al. (1997), it can
      further be calculated that 48 h following the start of a 2-h inhalation
      exposure to 900 ppm of 14C-methanol vapors in female cynomolgus monkeys,
      only 23% of the absorbed 14C-methanol was eliminated from the body.

      These findings are corroborated by the data of Heck et al. (1983) showing
      that 40% of a 14C-formaldehyde inhalation dose remained in the body 70 h
      postexposure."

      "Exposure to methanol also results from the consumption of certain
      foodstuffs (fruits, fruit juices, certain vegetables, aspartame sweetener,
      roasted coffee, honey) and alcoholic beverages (Health Effects Institute,
      1987; Jacobsen et al., 1988)."

      [ It's unusual for a mainstream journal article to mention "fruits, fruit
      juices, certain vegetables, aspartame sweetener' and "alcoholic beverages"
      to be methanol sources. ]

      "However, the severe toxic effects are usually associated with the
      production and accumulation of formic acid, which causes metabolic acidosis
      and visual impairment that can lead to blindness and death at blood
      concentrations of methanol above 31 mmol/l (Røe, 1982; Tephly and McMartin,
      1984; U.S. DHHS, 1993).

      Although the acute toxic effects of methanol in humans are well documented,
      little is known about the chronic effects of low exposure doses, which are
      of interest in view of the potential use of methanol as an engine fuel and
      current use as a solvent and chemical intermediate.

      Gestational exposure studies in pregnant rodents (mice and rats) have also
      shown that high methanol inhalation exposures (5000 or 10,000 ppm and more,
      7 h/day during days 6 or 7 to 15 of gestation) can induce birth defects
      (Bolon et al., 1993; IPCS, 1997; Nelson et al., 1985)."

      "The corresponding average elimination half-life of absorbed methanol
      through metabolism to formaldehyde was estimated to be 1.3, 0.7-3.2, and 1.7
      h."

      [ This shows for ingested methanol from the readily released 11% methanol
      component of aspartame diet sodas, that by three half-lives,
      3 X 1.7 h = 5.1 hr, 7/8 = 88 % of the methanol would be substantially turned
      into formaldehyde.

      In dark wines and liquors, the conversion of methanol impurity, about one
      part in ten thousand, into formaldehyde and then formic acid is prevented
      for many hours, as the responsible enzyme is taken up by the remaining
      ethanol. When after many hours all the ethanol is metabolized, the
      conversion of the remaining methanol into formaldehyde and formic acid is
      the major cause of the many difficult symtoms of "morning after" hangover. ]

      "Inversely, in monkeys and in humans, a larger fraction of body burden of
      formaldehyde is rapidly transferred to a long-term component.
      The latter represents the formaldehyde that (directly or after oxidation to
      formate) binds to various endogenous molecules..."

      "Animal studies have reported that systemic methanol is eliminated mainly by
      metabolism (70 to 97% of absorbed dose) and only a small fraction is
      eliminated as unchanged methanol in urine and in the expired air (< 3-4%)
      (Dorman et al., 1994; Horton et al., 1992).

      Systemic methanol is extensively metabolized by liver alcohol dehydrogenase
      and catalase-peroxidase enzymes to formaldehyde, which is in turn rapidly
      oxidized to formic acid by formaldehyde dehydrogenase enzymes (Goodman and
      Tephly, 1968; Heck et al., 1983; Røe, 1982; Tephly and McMartin, 1984).

      Under physiological conditions, formic acid dissociates to formate and
      hydrogen ions.

      Current evidence indicates that, in rodents, methanol is converted mainly by
      the catalase-peroxidase system whereas monkeys and humans metabolize
      methanol mainly through the alcohol dehydrogenase system (Goodman and
      Tephly, 1968; Tephly and McMartin, 1984).

      Formaldehyde, as it is highly reactive, forms relatively stable adducts with
      cellular constituents (Heck et al., 1983; Røe, 1982)."

      "The whole body loads of methanol, formaldehyde, formate, and unobserved
      by-products of formaldehyde metabolism were followed.

      Since methanol distributes quite evenly in the total body water, detailed
      compartmental representation of body tissue loads was not deemed necessary."

      "According to model predictions, congruent with the data in the literature
      (Dorman et al., 1994; Horton et al., 1992), a certain fraction of
      formaldehyde is readily oxidized to formate, a major fraction of which is
      rapidly converted to CO2 and exhaled, whereas a small fraction is excreted
      as formic acid in urine.

      However, fits to the available data in rats and monkeys of Horton et al.
      (1992) and Dorman et al. (1994) show that, once formed, a substantial
      fraction of formaldehyde is converted to unobserved forms.

      This pathway contributes to a long-term unobserved compartment.

      The latter, most plausibly, represents either the formaldehyde that
      (directly or after oxidation to formate) binds to various endogenous
      molecules (Heck et al., 1983; Røe, 1982)
      or is incorporated in the tetrahydrofolic-acid-dependent one-carbon pathway
      to become the building block of a number of synthetic pathways (Røe, 1982;
      Tephly and McMartin, 1984).

      That substantial amounts of methanol metabolites or by-products are retained
      for a long time is verified by Horton et al. (1992) who estimated that 18 h
      following an iv injection of 100 mg/kg of 14C-methanol in male Fischer-344
      rats, only 57% of the dose was eliminated from the body.

      From the data of Dorman et al. (1994) and Medinsky et al. (1997), it can
      further be calculated that 48 h following the start of a 2-h inhalation
      exposure to 900 ppm of 14C-methanol vapors in female cynomolgus monkeys,
      only 23% of the absorbed 14C-methanol was eliminated from the body.

      These findings are corroborated by the data of Heck et al. (1983) showing
      that 40% of a 14C-formaldehyde inhalation dose remained in the body 70 h
      postexposure.

      In the present study, the model proposed rests on acute exposure data, where
      the time profiles of methanol and its metabolites were determined only over
      short time periods (a maximum of 6 h of exposure and a maximum of 48 h
      postexposure).

      This does not allow observation of the slow release from the long-term
      components.

      It is to be noted that most of the published studies on the detailed
      disposition kinetics of methanol regard controlled short-term (iv injection
      or continuous inhalation exposure over a few hours) methanol exposures in
      rats, primates, and humans (Batterman et al., 1998; Damian and Raabe, 1996;
      Dorman et al., 1994; Ferry et al., 1980; Fisher et al., 2000; Franzblau et
      al., 1995; Horton et al., 1992; Jacobsen et al., 1988; Osterloh et al.,
      1996; Pollack et al., 1993; Sedivec et al., 1981; Ward et al., 1995; Ward
      and Pollack, 1996).

      Experimental studies on the detailed time profiles following controlled
      repeated exposures to methanol are lacking."

      "Thus, in monkeys and plausibly humans, a much larger fraction of body
      formaldehyde is rapidly converted to unobserved forms rather than passed on
      to formate and eventually CO2."

      "However, the volume of distribution of formate was larger than that of
      methanol, which strongly suggests that formate distributes in body
      constituents other than water, such as proteins.

      The closeness of our simulations to the available experimental data on the
      time course of formate blood concentrations is consistent with the volume of
      distribution concept (i.e., rapid exchanges between the nonblood pool of
      formate and blood formate)."

      "Also, background concentrations of formate are subject to wide
      interindividual variations (Baumann and Angerer, 1979; D'Alessandro et al.,
      1994; Franzblau et al., 1995; Heinrich and Angerer, 1982; Lee et al., 1992;
      Osterloh et al., 1996; Sedivec et al., 1981)."

      [ There's an on-going debate as to how much of methanol toxicity and
      genotoxicity is due to its formaldehyde or formic acid products, along with
      a dearth of evidence about the actual biochemical disposition in specific
      tissues of people exposed long-term to chronic doses, as in the case of
      alcoholics or aspartame reactors.

      Fully 11% of aspartame is methanol -- 1,120 mg aspartame in 2 L diet soda,
      almost six 12-oz cans, gives 123 mg methanol (wood alcohol). However,
      about 30% of the methanol remains in the body as cumulative durable toxic
      metabolites of formaldehyde and formic acid, 37 mg daily, a gram every
      month, accumulating in and affecting every tissue.

      If only 10% of the methanol accumulates daily as formaldehyde, that would
      give 12 mg daily formaldehyde accumulation -- about 60 times more than the
      0.2 mg from 10% retention of the 2 mg EPA daily limit for formaldehyde in
      drinking water.

      Bear in mind that the EPA limit for formaldehyde in drinking water is
      1 ppm, or 2 mg daily for a typical daily consumption of 2 L of water.

      http://groups.yahoo.com/group/aspartameNM/message/835
      ATSDR: EPA limit 1 ppm formaldehyde in drinking water July 1999:
      Murray 2002.05.30 rmforall

      This is the same limit published May 2, 2002 for California.

      http://groups.yahoo.com/group/aspartameNM/message/1108
      faults in 1999 July EPA 468-page formaldehyde profile:
      Elzbieta Skrzydlewska PhD, Assc. Prof., Medical U. of Bialystok, Poland,
      abstracts -- ethanol, methanol, formaldehyde, formic acid, acetaldehyde,
      lipid peroxidation, green tea, aging, Lyme disease:
      Murray 2004.08.08 rmforall

      Herein I offer abstracts and three full texts of dozens of studies by a
      world-class biochemist and her associates, mostly experiments with rats, on
      ethanol toxicity since 1984 and methanol toxicity since 1993. Enough
      details are provided to show the competency and credibility of E.
      Skrzydlewska and her colleagues over two decades, and to make access to
      their literature more convenient for professionals.

      It is important that many of her studies suggest that many safe substances
      may prevent or treat toxicity from methanol and its inevitable toxic human
      body products, formaldehyde and formic acid:

      N-acetylcysteine (2000); U-83836E containing a trolox ring (1997);
      green tea (2004); vitamins E, C, A, and beta-carotene (2004);
      glutathione (2001); N-Acetylcysteine (NAC) (2001); melatonin (2001);
      low and medium levels of cysteine (1990).


      http://taylorandfrancis.metapress.com/openurl.asp?genre=article&eissn=1537-6524&volume=13&issue=4&spage=277

      Toxicology Mechanisms and Methods
      Publisher: Taylor & Francis Health Sciences, part of the Taylor & Francis
      Group Issue: Volume 13, Number 4 / Oct-Dec 2003 Pages: 277 - 293

      Toxicological and Metabolic Consequences of Methanol Poisoning
      Elzbieta Skrzydlewska, Assoc. Professor, MSc, PhD,
      Deputy Dean of Faculty of Pharmacy,
      Head of Department of Analytical Chemistry, Medical University of Bialystok,
      Mickiewicza 2A 15-230 Bialystok 8, P.O. Box 14, Poland
      skrzydle@...
      http://www.amb.edu.pl/en/sites/university.html dzss@...
      Kilinskiego 1 15-089 Bialystok, Poland fax (48 85)7485408

      Abstract:
      Methanol, when introduced into all mammals, is oxidized into formaldehyde
      and then into formate, mainly in the liver.

      Such metabolism is accompanied by the formation of free radicals.

      In all animals, methanol oxidation, which is relatively slow, proceeds via
      the same intermediary stages, usually in the liver,
      and various metabolic systems are involved in the process, depending on the
      animal species.

      In nonprimates, methanol is oxidized by the catalase-peroxidase system,
      whereas in primates, the alcohol dehydrogenase system takes the main role in
      methanol oxidation.

      The first metabolite (formaldehyde is rapidly oxidized by formaldehyde
      dehydrogenase) is the reduced glutathione (GSH)-dependent enzyme.

      Generated formic acid is metabolized into carbon dioxide with the
      participation of H4folate and two enzymes, 10-formyl H4folate synthetase and
      dehydrogenase,
      whereas nonprimates oxidize formate efficiently.

      Humans and monkeys possess low hepatic H4folate and 10-formyl H4folate
      dehydrogenase levels
      and are characterized by the accumulation of formate after methanol
      intoxication.

      The consequences of methanol metabolism and toxicity distinguish the human
      and monkey from lower animals.

      Formic acid is likely to be the cause of the metabolic acidosis and ocular
      toxicity in humans and monkeys,
      which is not observed in most lower animals.

      Nevertheless, chemically reactive formaldehyde and free radicals may damage
      most of the components of the cells of all animal species, mainly proteins
      and lipids.

      The modification of cell components results in changes in their functions.

      Methanol intoxication provokes a decrease in the activity and concentration
      of antioxidant enzymatic as well as nonenzymatic parameters,
      causing enhanced membrane peroxidation of phospholipids.

      The modification of protein structure by formaldehyde as well as by free
      radicals results changes in their functions,
      especially in the activity of proteolytic enzymes and their inhibitors,
      which causes disturbances in the proteolytic-antiproteolytic balance toward
      the proteolytics and
      enhances the generation of free radicals.

      Such a situation can lead to destructive processes because components of the
      proteolytic-antiproteolytic system during enhanced membrane lipid
      peroxidation may penetrate from blood into extracellular space, and an
      uncontrolled proteolysis can occur.

      This applies particularly to extracellular matrix proteins.

      Keywords: Free Radicals, Methanol Metabolism, Methanol Poisoning,
      Proteases, Protease Inhibitors ]
      *************************************************************

      http://www.toxsci.oupjournals.org/cgi/content/full/64/2/169

      Toxicological Sciences 64, 169-184 (2001)
      Copyright © 2001 by the Society of Toxicology

      BIOTRANSFORMATION AND TOXICOKINETIC

      A Biologically Based Dynamic Model for Predicting the Disposition of
      Methanol and Its Metabolites in Animals and Humans

      Michèle Bouchard *, #,1, bouchmic@...

      Robert C. Brunet, # brunet@...

      Pierre-Olivier Droz, #

      and Gaétan Carrier* gaetan.carrier@...

      * Department of Environmental and Occupational Health, Faculty of Medicine,
      Université de Montréal, P.O. Box 6128, Main Station, Montréal, Québec,
      Canada, H3C 3J7;

      # Institut Universitaire romand de Santé au Travail, rue du Bugnon 19,
      CH-1005, Lausanne, Switzerland, and

      # Département de Mathématiques et de Statistique and Centre de Recherches
      Mathématiques, Faculté des arts et des sciences, Université de Montréal,
      P.O. Box 6128, Main Station, Montréal, Québec, Canada, H3C 3J7

      NOTES

      1 To whom correspondence should be addressed at Département de santé
      environnementale et santé au travail, Université de Montréal, P.O. Box 6128,
      Main Station, Montréal, Québec, H3C 3J7, Canada. Fax: (514) 343-2200.
      E-mail: bouchmic@...

      Received May 10, 2001; accepted August 28, 2001

      ABSTRACT
      TOP
      ABSTRACT
      INTRODUCTION
      METHOD AND MODEL PRESENTATION
      RESULTS
      DISCUSSION
      APPENDIX
      REFERENCES

      A multicompartment biologically based dynamic model was developed to
      describe the time evolution of methanol and its metabolites in the whole
      body and in accessible biological matrices of rats, monkeys, and humans
      following different exposure scenarios.
      The dynamic of intercompartment exchanges was described mathematically by a
      mass balance differential equation system.
      The model's conceptual and functional representation was the same for rats,
      monkeys, and humans, but relevant published data specific to the species of
      interest served to determine the critical parameters of the kinetics.
      Simulations provided a close approximation to kinetic data available in the
      published literature.

      The average pulmonary absorption fraction of methanol was estimated to be
      0.60 in rats, 0.69 in monkeys, and 0.58-0.82 in human volunteers.

      The corresponding average elimination half-life of absorbed methanol through
      metabolism to formaldehyde was estimated to be 1.3, 0.7-3.2, and 1.7 h.

      Saturation of methanol metabolism appeared to occur at a lower exposure in
      rats than in monkeys and humans.
      Also, the main species difference in the kinetics was attributed to a
      metabolism rate constant of whole body formaldehyde to formate estimated to
      be twice as high in rats as in monkeys.

      Inversely, in monkeys and in humans, a larger fraction of body burden of
      formaldehyde is rapidly transferred to a long-term component.
      The latter represents the formaldehyde that (directly or after oxidation to
      formate) binds to various endogenous molecules
      or is taken up by the tetrahydrofolic-acid-dependent one-carbon pathway to
      become the building block of synthetic pathways.

      This model can be used to quantitatively relate methanol or its metabolites
      in biological matrices to the absorbed dose and tissue burden at any point
      in time in rats, monkeys, and humans for different exposures, thus reducing
      uncertainties in the dose-response relationship, and animal-to-human and
      exposure scenario comparisons.

      The model, adapted to kinetic data in human volunteers exposed acutely to
      methanol vapors, predicts that 8-h inhalation exposures ranging from 500 to
      2000 ppm, without physical activities, are needed to increase concentrations
      of blood formate and urinary formic acid above mean background values
      reported by various authors (4.9-10.3 and 6.3-13 mg/liter, respectively).

      This leaves blood and urinary methanol concentrations as the most sensitive
      biomarkers of absorbed methanol.
      Key Words: methanol; formaldehyde; formate; toxicokinetics; modeling;
      animals; humans.

      Methanol is widely used as an industrial solvent and chemical intermediate
      (Kavet and Nauss, 1990).

      It has also received serious consideration as an alternative automotive fuel
      or fuel additive (Health Effects Institute, 1987).

      Inhalation is a major route of human exposure to methanol in the
      occupational and general environments although skin exposure can occur in
      certain industrial settings (Baumann and Angerer, 1979; Downie et al 1992;
      Heinrich and Angerer, 1982; Kawai et al., 1991).

      Exposure to methanol also results from the consumption of certain foodstuffs
      (fruits, fruit juices, certain vegetables, aspartame sweetener, roasted
      coffee, honey) and alcoholic beverages (Health Effects Institute, 1987;
      Jacobsen et al., 1988).

      The toxic effects of acute exposures to high methanol doses in humans are
      well documented (Liesivuori and Savolainen, 1991; Røe, 1982; Tephly and
      McMartin, 1984; U.S. DHHS, 1993).
      Neurological effects, such as the initial transient depression of the
      central nervous system, have generally been reported at blood concentrations
      of methanol above 6 mmol/l (U.S. DHHS, 1993).

      However, the severe toxic effects are usually associated with the production
      and accumulation of formic acid, which causes metabolic acidosis and visual
      impairment that can lead to blindness and death at blood concentrations of
      methanol above 31 mmol/l (Røe, 1982; Tephly and McMartin, 1984; U.S. DHHS,
      1993).

      Although the acute toxic effects of methanol in humans are well documented,
      little is known about the chronic effects of low exposure doses, which are
      of interest in view of the potential use of methanol as an engine fuel and
      current use as a solvent and chemical intermediate.

      Gestational exposure studies in pregnant rodents (mice and rats) have also
      shown that high methanol inhalation exposures (5000 or 10,000 ppm and more,
      7 h/day during days 6 or 7 to 15 of gestation) can induce birth defects
      (Bolon et al., 1993; IPCS, 1997; Nelson et al., 1985).

      The potential deleterious effects of methanol have prompted extensive
      research on its uptake and disposition in animals and humans.

      This has led to the findings that pulmonary absorption of methanol is very
      rapid and absorption fraction ranges from about 60 to 85% depending on the
      species (Dorman et al., 1994; Fisher et al., 2000; Horton et al., 1992).

      Due to the high water solubility of methanol, the distribution of absorbed
      methanol in the tissues of the body is a function of their relative water
      content (Sejersted et al., 1983).

      Animal studies have reported that systemic methanol is eliminated mainly by
      metabolism (70 to 97% of absorbed dose) and only a small fraction is
      eliminated as unchanged methanol in urine and in the expired air (< 3-4%)
      (Dorman et al., 1994; Horton et al., 1992).

      Systemic methanol is extensively metabolized by liver alcohol dehydrogenase
      and catalase-peroxidase enzymes to formaldehyde, which is in turn rapidly
      oxidized to formic acid by formaldehyde dehydrogenase enzymes (Goodman and
      Tephly, 1968; Heck et al., 1983; Røe, 1982; Tephly and McMartin, 1984).

      Under physiological conditions, formic acid dissociates to formate and
      hydrogen ions.

      Current evidence indicates that, in rodents, methanol is converted mainly by
      the catalase-peroxidase system whereas monkeys and humans metabolize
      methanol mainly through the alcohol dehydrogenase system (Goodman and
      Tephly, 1968; Tephly and McMartin, 1984).

      Formaldehyde, as it is highly reactive, forms relatively stable adducts with
      cellular constituents (Heck et al., 1983; Røe, 1982).

      It can also enter, directly or after oxidation to formate, the
      tetrahydrofolic-acid-dependent one-carbon pathway to become the building
      block of many synthetic pathways (Røe, 1982; Tephly and McMartin, 1984).

      The detoxification of formate occurs mainly by a tetrahydrofolate-dependent
      multistep pathway to carbon dioxide (CO2) (McMartin et al., 1977; Palese and
      Tephly, 1975).

      A small percentage of body formate is also eliminated directly in the urine
      (Dorman et al., 1994; Horton et al., 1992).

      Marked species differences in methanol toxicity and metabolism have been
      reported.
      Primates and humans appear to be more susceptible to the acute toxicity of
      methanol than rodents (Tephly and McMartin, 1984).
      This has been mainly attributed to the slower metabolism and elimination
      rate of formate in larger species (Tephly and McMartin, 1984).

      Based on the available toxicokinetic data of methanol in rats, mice,
      monkeys, and humans, toxicokinetic processes were described in the past
      using classic 1 to 3 compartmental models with saturable elimination
      (Batterman et al., 1998; Damian and Raabe, 1996; Dorman et al., 1994; Nihlén
      and Droz, 2000; Pollack and Brouwer, 1996; Pollack et al., 1993; Ward et
      al., 1995; Ward and Pollack, 1996).
      Physiologically based pharmacokinetic (PBPK) models for methanol in animals
      and humans were also developed (Fisher et al., 2000; Horton et al., 1992;
      Perkins et al., 1995; Ward et al., 1997).

      Recently, a different type of multicompartment modeling approach has been
      developed to describe the disposition kinetics of polychlorinated
      dibenzo-dioxins and furans (PCDD and PCDFs) (Carrier et al., 1995a,b),
      azinphosmethyl and its alkylphosphate metabolites (Carrier and Brunet,
      1999), and methyl mercury and its inorganic metabolites (Carrier et al.,
      2001a,b).
      This type of biologically based dynamic model is a refinement of classic
      compartment models, but is closer to biological processes and enables
      simulations for a variety of exposure scenarios in different species.
      This heuristic approach allows essential characteristics of
      intercompartmental transfer processes to be captured using a minimum of
      parameters and without the need for extensive knowledge of all the
      physiological processes.
      The ultimate goal of this approach is to develop a robust human
      toxicokinetic model based on human data, thus avoiding as much as possible
      uncertainties associated with animal to human extrapolations.

      The objective of the present study was to develop and validate such a
      biologically based dynamic model to describe the time evolution of methanol
      and its metabolites in the whole body, and in accessible biological matrices
      (blood, urine, and expired air), and allow links to be made between the
      different compartments.

      This model is constructed by establishing the overall biological
      determinants of methanol disposition in animals and humans, taking into
      account the different time-scales involved in the biological processes.
      The model parameters specific to the species of interest are then determined
      from direct fits to the in vivo time course data of methanol and its
      metabolites in blood and excreta (urine and expired air), available in the
      published literature.

      Model Development

      A toxicokinetic, biologically based, dynamic model was developed to describe
      the time evolution of methanol biodisposition in the animal (rat and monkey)
      and human body.
      The modeling process can be described in four steps:
      (1) the conceptual and functional representation of the model,
      (2) the determination of parameters,
      (3) the simulation of the kinetic profile, and
      (4) the validation of the model.

      Conceptual and functional representation.

      The disposition kinetics of methanol and its metabolites following exposure
      to methanol was modeled using a multicompartment dynamic system, described
      mathematically by a system of coupled differential equations.
      The model conceptual and functional representation is depicted in Figure 1.
      It aims to be sufficiently detailed to describe the available in vivo data
      provided by Horton et al. (1992) on the disposition kinetics of methanol and
      its metabolites in rats.
      It was then verified that it described equally well the monkey and human
      kinetic behavior (Dorman et al., 1994; Osterloh et al., 1996; Sedivec et
      al., 1981).

      View larger version (30K):
      [in this window]
      [in a new window]
      FIG. 1. Conceptual representation of methanol kinetics.
      Symbols are described in Table 1.

      The whole body (blood and tissues) and the excretory routes (urine and
      exhaled air) were each represented by a compartment.
      The whole body loads of methanol, formaldehyde, formate, and unobserved
      by-products of formaldehyde metabolism were followed.

      Since methanol distributes quite evenly in the total body water, detailed
      compartmental representation of body tissue loads was not deemed necessary.

      Formaldehyde in the whole body was also represented as a separate
      compartment although its metabolism rate is too rapid to allow its
      quantification (half-life of about 1.5 min according to McMartin et al.
      [1979] and Tephly and McMartin [1984]).
      It can be shown that, under such fast breakdown, only formaldehyde
      partitioning between formate and other by-products is relevant to the
      unfolding of the dynamics.
      The respiratory tract was further represented as a separate compartment
      since it is the route of entry of inhaled methanol.
      Excretion compartments were the methanol in the exhaled air, the urinary
      methanol, the urinary formic acid, the CO2 in the exhaled air, and the
      excreted unobserved metabolites.
      The dynamic of intercompartment exchanges was then described mathematically
      by a mass balance differential equation system (see Appendix).
      Essentially, the rates of change in the amounts of methanol and its
      metabolites in a given compartment were described as the difference between
      compartment rates of uptake and loss.
      (Symbols used in the functional representation of the model are presented in
      Table 1.)
      Solving numerically the system of differential equations yielded the time
      courses of methanol and its metabolites in the different compartments.

      View this table:
      [in this window]
      [in a new window]
      TABLE 1 Symbols Used in the Conceptual and Functional Representation of the
      Model

      It should also be mentioned that metabolism was considered to follow
      Michaelis-Menten kinetics.
      However, only in the case of methanol metabolism to formaldehyde was a
      saturation constant introduced since, with the exposure dose range used in
      the studies on which the model is based, no saturation of formate or CO2
      metabolism was apparent (Dorman et al., 1994; Horton et al., 1992; Osterloh
      et al., 1996 Sedivec et al., 1981).

      Determination of the parameters.

      Unknown parameters were estimated individually from a statistical best-fit
      to the experimental data specific to the species of interest, by using the
      explicit solutions of subsystems of differential equations when possible
      (see Appendix). A professional edition of a MathCad software was used for
      this purpose (MathSoft Inc., Cambridge, MA).

      Rat parameters.

      Parameters to be determined were the intercompartment transfer rate
      coefficients and metabolism rate constants. Data of Horton et al. (1992) in
      male Fischer-344 rats exposed to a single iv dose of 100 mg per kg of body
      weight of 14C-methanol (n = 4) were used to determine the rat parameters.

      Blood concentration-time profiles (expressed in mg/l) and cumulative urinary
      excretion time courses of 14C-methanol and 14C-formate (expressed in µmol)
      were determined by these authors as well as the cumulative exhalation time
      courses of 14C-methanol and 14CO2 (expressed in µmol).

      In the current study, for the fitting of experimental data and to determine
      parameters, all the experimental values were converted to burdens expressed
      in moles.
      It was then verified that the mass balance was maintained at all time
      points. Also, reported blood concentration values were converted to whole
      body burdens by multiplication by the apparent volume of distribution (Vd).
      In rats, the apparent volume of distribution of methanol (VdMeOH) was
      determined so that the initial experimental concentration of methanol in
      blood at time t = 5 min, when converted in terms of burden, gives the iv
      dose (700 µmol) reported by Horton et al. (1992).

      Monkey parameters.

      To adapt the model to monkey data, only the values of the intercompartment
      transfer rates and metabolism constants needed to be modified.
      Using the same approach as in rats, transfer parameters values of the
      general model solutions were estimated individually by best-fits, using
      MathCad, to the available experimental data of Dorman et al. (1994).
      These authors exposed 4 adult female cynomolgus monkeys (Macaca
      fascicularis, 3-5.5 kg) by inhalation to 900 ppm of 14C-methanol for 2 h.
      Blood concentration-time profiles of 14C-methanol and 14C-formate (expressed
      in µmol/l) were determined as well as the cumulative urinary excretion of
      14C-methanol and 14C-formate 48-h postexposure (expressed in µmol).
      The time courses of 14C-methanol and 14CO2 exhalation rates (µmol/min) were
      also established.
      For the determination of the parameter values, the latter rates were
      converted to cumulative excretion.
      The pulmonary ventilation rate of female cynomolgus monkeys used in the
      model was that reported by Dorman et al. (1994), that is on average 33 l/h
      or 0.56 l/min (equivalent to 0.033 m3/h or 0.8 m3/day).
      In monkeys, the apparent volume of distribution of methanol was calculated
      by best-fit of the following equation to the data observed during the
      constant inhalation built up of methanol blood concentration (B(t)):

      [ long equation ]

      where kelim is the sum of all rates of methanol elimination (metabolism,
      exhalation, and urinary excretion).

      Human parameters.

      When possible, the constants were determined using the available human data.
      This includes the pulmonary absorption fraction of methanol, the pulmonary
      ventilation rate, the apparent volume of distribution of methanol, the
      metabolism rate constant kmet of whole body methanol to formaldehyde, and
      the transfer rate constant km of whole body methanol to urine.
      The other constant parameters were left as determined in monkeys, which are
      considered as good surrogates to humans for the study of methanol kinetics.

      Pulmonary absorption fraction of methanol used in the model adapted to
      humans was that reported by Sedivec et al. (1981).

      The human value was nonetheless close to that determined in rats and
      monkeys.
      Human pulmonary ventilation rate used in the model was that reported by
      Sedivec et al. (1981), that is on average 10.8 l/min.

      The apparent volume of distribution of methanol was that reported in the
      literature, hence, corresponds to the volume of human body fluids (liters),
      expressed per kilogram of body weight.
      This value is about the same as that determined using the experimental
      monkey data.

      The constant parameter kmet was determined from a best-fit to the blood
      concentration-time profile of methanol in human volunteers exposed to 200
      ppm of methanol vapors for 4 h, as determined by Osterloh et al. (1996).

      The km value was determined by adjustment to the data of Sedivec et al.
      (1981) on the urinary excretion time course curves of methanol in volunteers
      during and following an 8-h inhalation exposure to 300 mg/m3 of methanol
      vapors.

      The experimental data of Sedivec et al. (1981) on the time evolution of
      urinary methanol concentrations were converted to cumulative urinary
      excretion of methanol (in µmol) by considering an average time-dependent
      fraction of a daily urinary excretion of 1.5 l (Knuiman et al., 1986).

      Model simulation.

      Once the parameters were determined individually by statistical fits to the
      experimental data, mathematical resolution of the complete model, as
      represented by the system of differential equations, was performed by the
      numerical Runge-Kutta method.
      Model resolution and simulations were also conducted using Mathcad software.
      This allows prediction of the time evolution of methanol and its metabolites
      in the different model compartments.
      In the model, the exposure dose was converted in µmoles for both the iv and
      inhalation exposures.
      Thus, whole body burdens and amounts excreted in urine and in the exhaled
      air are first expressed in µmoles.
      In order to simulate the blood concentrations of methanol or formate as a
      function of time, the amounts in the whole body predicted by the model were
      simply divided by the respective apparent volume of distribution.
      For rats and monkeys, the apparent volume of distribution of formate (VdFA)
      was estimated using a conservation of mass equation for formate burden, and
      by a best-fit to the observed time course of experimental blood
      concentration values of formate.
      For monkeys, this amounts to 6 times the apparent volume of distribution of
      methanol.
      For humans, the same multiple was used.

      To simulate the concentration-time profile of methanol in urine, predicted
      excretion rates (dM(t)/dt = km x X(t), expressed in µmol/min) were divided
      by the urinary flow rate (l/min).
      To simulate the concentration-time profile of methanol in the exhaled air,
      predicted exhalation rates (dE(t)/dt = kre x L(t) + kex x X(t), expressed in
      µmol/min) were divided by the pulmonary ventilation rate (m3/min).

      Simulations of exposure scenarios, where continuous or intermittent doses
      are administered through time, were performed by introducing a nonhomogenous
      term, g(t), describing these time varying inputs (see Appendix).
      Simulations can also be conducted for different routes of exposure (iv,
      inhalation).

      Model Validation

      The model developed using the previously mentioned data was validated using
      a new set of experimental data.
      This includes the kinetic time profiles presented in the inhalation studies
      of Horton et al. (1992) in rats and monkeys and Batterman et al. (1998) in
      human volunteers.
      Also, some human data of Sedivec et al. (1981) not used in the development
      of the model served to validate the model.

      Validation using inhalation data of Horton et al. (1992) in rats.

      The model developed using the iv data of Horton et al. (1992) in rats was
      validated with the inhalation data of the same authors, on the blood
      concentration-time profile of methanol during and following 6-h inhalation
      exposures to 200, 1200, and 2000 ppm of methanol in male Fischer-344 rats (n
      = 4 per group).

      For those simulations, the average pulmonary ventilation rate used was 40
      ml/min (equivalent to 0.0021 m3/h or 0.051 m3/day) for the 200 ppm dose, 40
      ml/min (equivalent to 0.0024 m3/h or 0.058 m3/day) for the 1200 ppm dose,
      and 60 ml/min (equivalent to 0.0033 m3/h or 0.080 m3/day) for the 2000 ppm
      dose to obtain the best-fit to the experimental data as compared to the
      average value of 3.04 l/h or 50 ml/min (equivalent to 0.0030 m3/h or 0.073
      m3/day) reported by Horton et al. (1992).

      Validation using inhalation data of Horton et al. (1992) in monkeys.

      The model adapted to the monkey data of Dorman et al. (1996) was validated
      using the data of Horton et al. (1992) on the blood concentration-time
      profile of methanol in 3 young adult male rhesus monkeys (Macaca mulatta,
      5-7 kg) exposed to methanol vapor concentrations of 200, 1200, or 2000 ppm
      for 6 h.

      For these simulations, the average pulmonary ventilation rate was that
      reported by Horton et al. (1992), that is 48.9 l/h or 0.81 l/min (equivalent
      to 0.049 m3/h or 1.2 m3/day).

      Validation using inhalation data of Sedivec et al. (1981) and Batterman et
      al. (1998) in humans.

      The data of Sedivec et al. (1981) on the urinary excretion time course
      curves of methanol in volunteers during and following 8-h inhalation
      exposures to 102 and 205 mg/m3 of methanol vapors were used in the
      validation process of the model for humans.

      The model adapted to human data was also validated using the data of
      Batterman et al. (1998) on the time-dependent disposition of methanol in
      blood, urine, and breath of volunteers exposed to methanol vapor
      concentration of 800 ppm for periods of 0.5, 1, and 2 h.

      Batterman et al. (1998) presented their data as urinary and exhaled
      concentration-time profiles (expressed in mg/l and ppm, respectively).
      Although in this article the time courses of methanol cumulative excretion
      in urine and exhaled air are usually presented to insure mass balance
      conservation, it was also verified that the model gave a good prediction of
      the overall concentration-time profiles of methanol in urine and exhaled air
      (data not shown).
      To obtain a good fit on both the concentration values and cumulative
      burdens, a time-dependent fraction of a daily urinary excretion of 2.4 l for
      the 30 min and 2 h exposures and of 2.7 l for the 1 h exposure had to be
      considered.
      It has been reported that the daily personal urine volume may commonly vary
      from 0.6 l to more than 2.5 l (Knuiman et al., 1986).
      The average pulmonary ventilation rate used was 11.3, 8.4, and 10.8 l/min
      for the 30 min, 1 h, and 2 h exposures, respectively, to obtain a best-fit
      to the exhalation data.
      These latter rates are in the value range reported by Sedivec et al. (1981;
      average [range]: 10.8 [8.4-13.8] l/min).

      Model Developed Using the IV Data of Horton et al. (1992) in Male
      Fischer-344 Rats

      Table 2 presents the rat parameter values of the model determined using the
      data of Horton et al. (1992) in male Fischer rats exposed via iv to 100 mg
      of 14C-labeled methanol per kg of body weight (see Table 1 for the
      description of symbols).

      Figures 2 and 3 show that these parameter values allowed to reproduce
      closely the data presented by Horton et al. (1992) on the time courses of
      blood concentrations of methanol and formate as well as on the cumulative
      urinary excretion of methanol and formate and the cumulative exhalation of
      methanol and CO2.

      View this table:
      [in this window]
      [in a new window]
      TABLE 2 Numerical Values of Constant Parameters Used in the Model Adjusted
      to Male Fischer-344 rat, Female Cynomolgus Monkey, and Human Data

      View larger version (15K):
      [in this window]
      [in a new window]

      FIG. 2. Model simulations (lines) compared with experimental data of Horton
      et al. (1992) on the concentration-time courses of methanol (crossbars) and
      formate (circles) in blood over 10 h following a single iv dose of 100 mg/kg
      of 14C-labeled methanol in male Fischer-344 rats.
      Each point represents mean value of experimental data (n = 4).

      View larger version (15K):
      [in this window]
      [in a new window]

      FIG. 3. (A) Model simulations (lines) compared with experimental data of
      Horton et al. (1992) on the cumulative urinary excretion profiles of
      methanol (crossbars) and formate (circles) over 18 h following a single iv
      dose of 100 mg/kg of 14C-labeled methanol in male Fischer-344 rats.
      Each point represents mean value of experimental data (n = 4).

      (B) Model simulations (lines) compared with experimental data of Horton et
      al. (1992) on the cumulative exhalation profiles of methanol (crossbars) and
      CO2 (squares) over 18 h following a single iv dose of 100 mg/kg of
      14C-labeled methanol in male Fischer-344 rats.
      Each point represents mean value of experimental data (n = 4).

      The estimated average Michaelis-Menten affinity constant value reported in
      Table 2 and determined using the iv data (Km-IV of 770 µmol, which
      represents the body burden of methanol corresponding to half of the maximal
      velocity for methanol metabolism) shows that when injecting 100 mg/kg of
      14C-methanol to Fischer rats (700 µmol), metabolism is not yet saturated.
      From the product of Km-IV and kmet, an average Vmax value of 411 µmol/h can
      be calculated.
      The model predicts that methanol elimination from the whole body is quite
      rapid (mean elimination half-life of 1.3 h) and that, on average, only 0.01%
      of methanol remains in the unchanged form 18 h following iv injection of 100
      mg/kg of 14C-methanol in rats.
      Peak levels of free formaldehyde in the whole body are reached 0.5 h
      postdosing, at which time formaldehyde burden represents on average 3.2% of
      the injected dose.
      Virtually no free formaldehyde remains in the body 18 h postexposure.
      The metabolism of methanol to formaldehyde (kmet) is predicted to be the
      rate limiting step in the whole body elimination kinetics of free
      formaldehyde.
      Indeed, the biotransformation of formaldehyde to its by-products is
      estimated to be very rapid (kform + koth being very large) compared to
      methanol metabolism to formaldehyde (kmet), as apparent when comparing
      reports of McMartin et al. (1979) and Horton et al. (1992).
      On the other hand, according to model predictions, peak levels of unbound
      formate in the whole body are reached only 3-3.5 h postexposure where
      average formate burden represents 20.1% of injected 14C-methanol.
      Eighteen h postexposure, on average 0.5% of the dose remains in the body as
      free formate.
      Initial build-up of unbound formate in the body prior to attrition is
      dependent on the fact that the metabolism rate constant of formaldehyde to
      formate (kform) is very rapid (average half-life of about 10 min) compared
      to the major elimination route of formate, the metabolism rate to CO2 and
      subsequent exhalation (kCO2), for which a mean half-life of 2.2 h can be
      calculated.
      Since the urinary excretion of formate is negligible compared to CO2
      exhalation, the former contributes only marginally to the whole body time
      course of formate.
      In fact, the model predicts that on average 48.8% of the 14C-methanol iv
      dose is eliminated as exhaled CO2 as compared to 1.7% as urinary formate,
      which is congruent with the experimental results of Horton et al. (1992).

      In comparison, it is estimated from the model that on average 0.8% of the
      dose is excreted as unchanged methanol in the urine and 2.4% of body
      methanol is exhaled unchanged again in accordance with the experimental data
      of Horton et al. (1992).

      Model Validation Using the Inhalation Data of Horton et al. (1992) in
      Fischer-344 Rats

      With the parameter values determined using the iv data of Horton et al.
      (1992), the model was applied to another set of data from the same authors
      on the blood concentration-time profiles of methanol during and following
      6-h inhalation exposures to 200, 1200, and 2000 ppm of methanol in male
      Fischer-344 rats.
      It gave a good prediction of the time-course curves for the 2 lowest doses
      but underestimated the blood concentrations for the 2000 ppm dose (data not
      shown).
      Thus, a new value of the saturation constant Km was estimated from a
      statistical best-fit on the blood concentration-time profile data of Horton
      et al. (1992) in male Fischer-344 rats exposed by inhalation to 2000 ppm of
      methanol vapors for 6 h (Km-Inh) (see Table 2).
      This Km-Inh value was about 3 times smaller than that determined with the iv
      data (on average 235 µmol).
      Thus, after inhalation exposure to 2000 ppm, saturation of methanol
      metabolism appears to occur at a lower body burden.
      With this Km-Inh value, a Vmax of 125 µmol/h was calculated. Using this
      newly determined Km constant for an inhalation exposure, the proposed model
      provided a close approximation to the data of Horton et al. (1992) on the
      blood concentration-time profiles of methanol in male Fischer-344 rats
      exposed to vapor concentrations of 200, 1200, and 2000 ppm of methanol for 6
      h (Fig. 4).

      View larger version (18K):
      [in this window]
      [in a new window]

      FIG. 4. Model simulations (lines) compared with experimental data of Horton
      et al. (1992) on the time courses of methanol concentrations in blood during
      and following 6-h inhalation exposures to 200 (diamonds), 1200 (crossbars),
      and 2000 (squares) ppm of methanol vapors in male Fischer-344 rats.
      Each point represents mean value of experimental data (n = 4).

      Model Adapted to Female Cynomolgus Monkey Data of Dorman et al. (1994)

      Using the conceptual and functional representation of the model established
      with rat data, the model was adapted to monkeys by adjusting parameters
      values (see Table 2), through a statistical best-fit, to the data of Dorman
      et al. (1994) in female cynomolgus monkeys exposed by inhalation to methanol
      vapors.

      As observed in rats, pulmonary absorption of methanol was estimated to be
      very rapid (a few minutes) as compared to the metabolism rate constant kmet
      of whole body methanol to formaldehyde.
      The predicted pulmonary absorption fraction of methanol in monkeys was in
      the same range as that determined in rats.
      The estimated monkey constant kmet was however 1.8 times higher than in
      rats. Interestingly, contrary to the rat, according to the data of Dorman et
      al. (1994), no saturation of methanol metabolism was apparent in monkeys
      even after a 2-h inhalation exposure to 2000 ppm.
      Further comparison of monkey and rat parameter values shows that the
      estimated monkey metabolism rate constant kform of whole body formaldehyde
      to formate was 2.0 times lower than that of rats.
      This was also the case for exhalation rate constant kex of absorbed methanol
      (1.8 times).
      The monkey kCO2 value, which represents a combined metabolism rate constant
      of whole body formate to CO2 and transfer rate constant of CO2 to the
      exhaled air, was estimated to be 2.6 times higher than in rats.
      As observed with the rat data of Horton et al. (1992), no saturation of
      formaldehyde or formate metabolism was apparent from the data of Dorman et
      al. (1994).
      It is also noteworthy that the estimated monkey transfer rate constant ku of
      whole body formate to urine was 5.4 times lower than in rats and the monkey
      transfer rate constant km of whole body methanol to urine was 12.8 times
      smaller than that obtained for rats.
      The estimated monkey apparent volume of distribution of methanol and
      formate, expressed in liters per kilogram of body weight, were only slightly
      lower than those of the rats (1.2 and 1.4 times, respectively).

      With the parameter values described in Table 2, Figure 5 shows that the
      model provides a close approximation to the data obtained by Dorman et al.
      (1994) on the blood concentration-time profiles of methanol and formate as
      well as the time dependent variations in methanol and CO2 exhalation rates
      over the 8-h period following the beginning of a 2-h inhalation exposure to
      900 ppm of 14C-methanol in adult female cynomolgus monkeys.

      Although the corresponding detailed urinary excretion profiles of methanol
      and formate were not depicted by Dorman et al. (1994), cumulative excretion
      of methanol and formate in urine was reported.
      The model succeeded in reproducing closely these values (0.43 µmol predicted
      as compared to 0.41 µmol observed on average for urinary methanol, and 1.12
      µmol predicted as compared to 1.15 µmol observed on average for urinary
      formate).

      View larger version (16K):
      [in this window]
      [in a new window]
      FIG. 5. (A) Model simulations (lines) compared with experimental data of
      Dorman et al. (1994) on the time courses of methanol (crossbars) and formate
      (circles) concentrations in blood during and following a 2-h inhalation
      exposure to 900 ppm of 14C-methanol in adult female cynomolgus monkeys
      (Macaca fascicularis). Each point represents mean value of experimental data
      (n = 4). (B) Model simulations (lines) compared with experimental data of
      Dorman et al. (1994) on the time courses of methanol (crossbars) and CO2
      (squares) exhalation rates during and following a 2-h inhalation exposure to
      900 ppm of 14C-methanol i
      (Message over 64 KB, truncated)
    Your message has been successfully submitted and would be delivered to recipients shortly.