User:Richard T Murray/Aspartame: Difference between revisions

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Aspartame is an artificial sweetener par excellence, in terms of its world market share, coupled with 26 years of intractable, polarized controversy about its safety, since its approval by the USA FDA for dry foods in July, 1981, and then for beverages in July, 1983.
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As a dipeptide, its molecule is made of two normal, essential amino acids, phenylalanine (50 % by weight) and aspartic acid, (39 %), loosely bound together by a smaller methyl unit (11 %).
''Article temporarily moved to [[Aspartame/Draft]] pending revisioning.''
 
At temperatures above body heat, and at low levels of acidity (PH), and soon after ingestion, it readily splits and releases its three components, which follow largely independent paths in humans. Each molecule of aspartame releases one molecule of each of the three parts.
 
The methyl unit becomes methanol, better known as wood alcohol, CH3OH, which is uaually an impurity in alcohol beverages, especially dark wines and liquors, at a level above 100 mg/l, one part in 10,000 by weight.  Methanol itself is not very toxic.  Its harm results from the production of formaldehyde and formic acid.
 
An enzyme, alcohol dehydrogenase, converts most methanol in blood into formaldehyde, a toxin, and much of the formaldehyde is soon made into formic acid, another toxin, and much of that eliminated as water and carbon dioxide.
 
However, the enzyme first is tied up with any available ethanol, C2H5OH, turning it into acetaldehyde, also toxic, until, after all the available ethanol is gone,  the enzyme then quickly turns any methanol into formaldehyde.
 
Two teams published research in 1987 and 2005, showing that methanol in alcohol beverages taken before bedtime, resulted in hangover symptoms in healthy young male students as long as 13 hours later, when the ethyl alcohol was all gone, but the remaining methanol was rapidly becoming formaldehyde.
 
The aspartame content of two liters diet soda, 5.6 12-oz cans, is 1,120 mg, releasing 11 % as 123 mg methanol.  Usually, there is not a concurrent larger amount of ethanol taken, which would prevent the production of formaldehyde.  So, the methanol from any aspartame is quickly turned into formaldehyde.
 
An expert review by a competent, unbiased team led by M. Bouchard, 2001, cites references, many from aspartame industry funded studies, states that about 30 - 40 % of the methanol remains in the body as
unknown, durable reaction products.
 
J. Nutrition 1973 Oct; 103(10): 1454-1459.
Metabolism of aspartame in monkeys.
Oppermann JA, Muldoon E, Ranney RE.
Dept. of Biochemistry, Searle Laboratories,
Division of G.D. Searle and Co. Box 5110, Chicago, IL 60680
 
They found that about 70 % of the radioactive methanol in aspartame put into the stomachs of 3 to 7 kg monkeys was eliminated within 8 hours, with little additional elimination, as carbon dioxide in exhaled air and as water in the urine
 
They did not report any studies on the distribution of radioactivity in body tissues, except that blood plasma proteins after 4 days held 4 % of the initial methanol.
 
The low oral dose of aspartame and for methanol was 0.068 mmol/kg, about 1 part per million [ppm]
of the acute toxicity level of 2,000 mg/kg, 67,000 mmol/kg, used by McMartin (1979).
 
Two L daily use of diet soda provides 123 mg methanol, 2 mg/kg for a 60 kg person, a dose of 67 mmole/kg, a thousand times more than the dose in this study.
 
By eight hours excretion of the dose in air and urine had leveled off at 67.1 +-2.1 % as CO2 in the exhaled air and 1.57+-0.32 % in the urine, so 68.7 % was excreted, and 31.3 % was retained.
 
This data is the average of 4 monkeys.  "...the 14C in the feces was negligible."
 
"That fraction not so excreted (about 31%) was converted to body constituents through the one-carbon metabolic pool."  "All radioactivity measurements were counted to +-1 % accuracy..."
 
The abstract ends, "It was concluded that aspartame was digested to its three constituents that were then absorbed as natural constituents of the diet."
 
http://groups.yahoo.com/group/aspartameNM/message/1286
methanol products (formaldehyde and formic acid) are main cause of
alcohol hangover symptoms [same as from similar amounts of methanol, the
11% part of aspartame]: YS Woo et al, 2005 Dec: Murray 2006.01.20
 
Addict Biol. 2005 Dec;10(4): 351-5.
Concentration changes of methanol in blood samples during
an experimentally induced alcohol hangover state.
Woo YS, Yoon SJ, Lee HK, Lee CU, Chae JH, Lee CT, Kim DJ.
Chuncheon National Hospital, Department of Psychiatry,
The Catholic University of Korea, Seoul, Korea. [ Han-Kyu Lee ]
 
A hangover is characterized by the unpleasant physical and mental symptoms that occur between 8 and 16 hours after drinking alcohol.
After inducing experimental hangover in normal individuals, we measured the methanol concentration prior to and after alcohol consumption and we assessed the association between the hangover condition
and the blood methanol level.
A total of 18 normal adult males participated in this study.
They did not have any previous histories of psychiatric or medical disorders.
The blood ethanol concentration prior to the alcohol intake (2.26+/-2.08) was not significantly different from that 13 hours after the alcohol consumption (3.12+/-2.38).
However, the difference of methanol concentration between the day of experiment (prior to the alcohol intake) and the next day (13 hours after the alcohol intake) was significant (2.62+/-1.33/l vs. 3.88+/-2.10/l, respectively).
A significant positive correlation was observed between the changes of blood methanol concentration
and hangover subjective scale score increment when covarying for the changes of blood ethanol level (r=0.498, p<0.05).
This result suggests the possible correlation of methanol as well as its toxic metabolite to hangover. PMID: 16318957
 
[ The "toxic metabolite" of methanol is formaldehyde, which in turn
partially becomes formic acid -- both potent cumulative toxins
that are the actual cause of the toxicity of methanol.]
 
http://health.groups.yahoo.com/group/aspartameNM/message/1143
http://www.toxsci.oupjournals.org/cgi/content/full/64/2/169
 
"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)."
 
"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."
 
http://groups.yahoo.com/group/aspartameNM/message/1143
methanol (formaldehyde, formic acid) disposition: Bouchard M et al, full
plain text, 2001: substantial sources are degradation of fruit pectins,
liquors, aspartame, smoke: Murray 2005.04.02
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,  [email protected]
Robert C. Brunet, ##  [email protected]
Pierre-Olivier Droz, #
and Gaétan Carrier *  [email protected]
* 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
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.
Received May 10, 2001; accepted August 28, 2001
 
ABSTRACT
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.
 
"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."
 
"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."
 
"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)."
 
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