SHarris%UNCAMULT.BITNET@oac.ucla.edu (Steve Harris) (01/05/90)
Regarding the item in AIDS TREATMENT NEWS, Issue #92, December 1, 1989 on the use of N-acetylcysteine (NAC) for HIV-positive subjects: =================================================================== "The researchers reported that glutathione levels in blood plasma of symptom-free HIV-positive subjects were found to be only 30 percent of those of uninfected controls ... Fluid from the lungs, obtained by bronchoalveolar lavage, was also tested for glutathione, and persons with HIV were found to have 60 percent of normal levels." =================================================================== And from AIDS TREATMENT NEWS, Issue #88, October 6, 1989: =================================================================== "Pathogenesis has been defined as "the origin and development of a disease." In AIDS research, a remarkable ignorance of pathogenesis has been widely tolerated, probably because of an unbalanced research focus on HIV and the search for a magic bullet to kill it. NAC appears to work (if it does) not by killing the virus directly, but rather by correcting biochemical imbalances which occur in the course of the illness, and which then cause other problems, including further viral growth." =================================================================== The salient question is then: What is the source of the biochemical imbalance which depresses glutathione levels in HIV-positive individuals? There is little dispute that individuals with AIDS experience severe colonization by opportunistic organisms including the yeast Candida albicans. Such infections have normally been attributed to the immunosuppressed state, however, and little attention has been focused on the metabolic impact of advancing fungal overgrowth prior to its clinical manifestation. The literature does contain some clues regarding a possible link between acetaldehyde formation resulting from biochemical fermentation activities typical of this yeast species and the disruption of glutathione metabolism and a host of other body processes essential to proper immune function. ================================================================== Truss, C. O. Metabolic abnormalities in patients with chronic candidiasis - the acetaldehyde hypothesis J. Orthomolecular Psychiatry (1984) 13(2) : 66-92 o ... of the various fungi living in the human body, Candida albicans is quantitatively the most important, since it colonizes the entire intestinal tract and vagina, lives on skin, and may infect nails. (p.67) o ... Candida albicans ... growth is strongly stimulated by antibiotics, contraceptive hormones, and immunosuppressant drugs. (p.67) o ... because of its universal presence in the human body, commonly used diagnostic techniques reveal little about this condition ... (p.68) o ... acetaldehyde, produced in the intestine by the anaerobic fermentation of sugars by Candida albicans, is the principal mediator of metabolic disturbances surfacing clinically as the symptoms of this condition. (p.68) o Patients with an overgrowth of yeast in the intestine exhibit much gas formation following the ingestion of sugar or digestible carbohydrates. (p.68) o ... abdominal distention, excess flatus, and belching. The metabolism of sugar by yeasts releases carbon dioxide (CO2), whether this be under anaerobic (fermentation) or aerobic conditions. (p.68) o In yeasts, pyruvate is produced from sugar by glycolysis, just as in human cells. If oxygen is not available, many species of yeast decarboxylate the pyruvate to acetaldehyde, which is then reduced to ethanol. If oxygen is present, pyruvate is oxidatively decarboxylated to acetyl Co-enzyme A (acetyl CoA), and acetaldehyde and ethanol are not formed. (p.68) o Most strains of Candida albicans, however, are not able to convert acetaldehyde to ethanol to any significant degree, but can under anaerobic conditions convert pyruvate to acetaldehyde. (p.68) o ... two pathways for the generation of acetaldehyde by Candida albicans: (1) the conversion of pyruvate to acetaldehyde when oxygen is not available and (2) the conversion of ethanol (exogenous or endogenous) to acetaldehyde when oxygen is available. (p.69) o ... major mechanism for the disposition of aldehydes in the body is oxidation by means of aldehyde dehydrogenase. This takes place primarily in the liver, although other tissues to some extent aid in this process. When the aldehyde is acetaldehyde, the oxidation product is acetate, which binds to Co-enzyme A (Co A). (p.69) o ... the production of a large amount of acetaldehyde can occur without its being detectable in the bloodstream. (p.69) o A strong affinity exists between acetaldehyde and tissues. This rests at least in part on its ability to bind to sulfhydryl and amine groups. Such binding delays the accumulation in the blood of this toxin, and also protects it from oxidation by aldehyde dehydrogenase. (p.69) o ... binding to amine and sulfhydryl groups will be cumulative when it is generated chronically, even though in small amount. (p.70) o ... allow contact with enzymes, and with constituents of the intestinal wall, liver cells, and portal blood. The latter would include nutrients as well as serum proteins, the latter having been found to bind acetaldehyde. (p.70) o ... presence of acetaldehyde in the intestine, the intestinal wall, and in the portal blood would afford many opportunities for its binding to such substances as nutrients, enzymes, vitamins, and polypeptides. If formed high in the intestinal tract, acetaldehyde could react with digestive enzymes in the small intestine. (p.70) o Many of the metabolic disturbances caused by acetaldehyde have been attributed to its strong affinity for sulfhydryl (-SH) and amine groups, and to the increase in the ratio of NADH to NAD that results from the oxidation of acetaldehyde by aldehyde dehydrogenase. (p.70) o The condensation of an aldehyde and an amine results in the formation of a Schiff base. (p.70) o Pyridoxal phosphate (vitamin B-6) is normally protected from degradation by its binding to the amine group of lysine residues of proteins, including serum proteins and hemoglobin. Acetaldehyde may, by binding preferentially to these residues, displace pyridoxal phosphate and result in its increased destruction, and in abnormally low blood levels of this co-enzyme. (p.71) o Acetaldehyde may also bind to the amine group of neurotransmitters to form complex compounds that may function as "false neurotransmitters". (p.71) o ... the tetrahydroisoquinoline that results from the condensation of dopamine and acetaldehyde is salsolinol. Condensation of acetaldehyde with indolealkylamines leads to the formation of tetrahydro-B-carbolines. o Aldehydes react with sulfhydryl groups to form hemiacetals. The -SH group is active in many metabolic steps. For example, it is involved in the first oxidative step of glycolysis, being essential to the activity of glyceraldehyde dehydrogenase, the enzyme that catalyzes the conversion of glyceraldehyde 3-phosphate to 1,3 diphosphoglycerate. The sulfhydryl group is also the active site of Co-enzyme A (CoA). It is the -SH site of CoA that binds the acetyl group to form acetyl CoA. (p.71) o CoA serves as carrier of the acetyl groups that are derived from carbohydrates, fats, and certain amino acids. Thus acetyl CoA is the point of convergence in the metabolism of the three classes of food, for their subsequent entry into and further oxidation by the citric acid cycle. Acetyl CoA also provides the two carbon units from which are synthesized fatty acids, ketones, and cholesterol and steroid hormones, and it donates the acetyl group required for the synthesis of acetylcholine and other substances. (p.71) o ... acetaldehyde induces a dose-dependent suppression of acetyl CoA activity. (p.71) o ... decreased respiration in these tissues, oxygen consumption falling in parallel with the declining level of acetyl CoA as the concentration of acetaldehyde increased. (p.71) o When the ratio of NADH/NAD increases, many secondary abnormalities occur. (p.71) o When either ethanol or acetaldehyde is oxidized by its respective dehydrogenase, NAD is converted to NADH. (p.71) o Increase in the ratio of lactate to pyruvate ... conversion of galactose to glucose is inhibited by NADH ... altered metabolism of serotonin. The 5-HIAA (oxidative) pathway is inhibited by NADH ... citric acid cycle is inhibited by NADH ... inhibition of glycolysis by NADH at the first oxidative step ... elevation of blood uric acid secondary to the elevated lactate levels caused by NADH excess ... oxidative phosphorylation is inhibited by acetaldehyde. This is reversed by NAD. (p.72) o Depression of GLUTATHIONE in the liver, possibly as a result of the binding of acetaldehyde to its cysteine component. Glutathione is important in the removal of toxic free-radicals; a reduction in glutathione may damage membranes. Lipid peroxidation and decreased GSH (reduced glutathione) occurred in animals following chronic ethanol intake. (p.72) o ... increased lactate associated with the high NADH/NAD ratio. This leads to an increase in peptidyl proline hydroxylase activity, favoring collagen deposition in other tissues as well as in the liver. (p.73) o ... acetaldehyde is known to cause increased rigidity of Rbc membranes ... (p.73) o ... certain important amino acids the abnormalities were severe ... (p.73) o Strikingly low are certain non-essential amino acids that derive their carbon skeletions from intermediates in the citric acid cycle: glutamate, asparagine (p.73) o Ethanolamine levels generally are elevated, while those for phosphoethanolamine tend to be low. Since ethanolamine normally is converted to phosphoethanolamine, these results suggest a block in this pathway. (p.75) o ... impairment in the synthesis of non-essential amino acids, particularly those synthesized from citric acid cycle intermediates. Such interconversions as ethanolamine to phosphoethanolamine, and aspartate to asparagine, appear inhibited. Attention is called to the very low levels of glutamate and glutamine, the donors of amine groups in transamination reactions. (p.75) o In the omega six series the levels of the shorter chain fatty acids were elevated, while the levels of the longer chain fatty acids into which these are normally converted were depressed. Particularly striking were the very low levels of 22:5 omega six fatty acids. (p.75) o ... impairment of the elongation reaction for which acetyl CoA furnishes the two-carbon units. (p.81) o Acetaldehyde impairs protein synthesis and secretion. Its binding to amine groups in Schiff base formation could interfere with transamination reactions involved in the synthesis of non-essential amino acids. Also, if by inhibition of acetyl CoA it depressed the citric acid cycle, acetaldehyde could induce a deficiency of the citric acid cycle intermediates that furnish the carbon skeletons of the non-essential amino acids. (p.82) o In patients with chronic candidiasis, diminished flexibility of Rbc membranes resulted in a decrease in filterability of intact red blood cells. (p.83) o Acetaldehyde has been shown to have a different effect on intestinal microvillus membrane vesicles than on Rbc membranes ... increase in the fluidity of these membranes, with an associated dissipation of the Na+ gradient, and an inhibition of carrier function. These studies indicated that the permeability of these membranes increased upon exposure to acetaldehyde. (p.85) o ... extreme intolerance to formaldehyde. Since it also binds to sulfhydryl and amine groups, and in general exhibits toxicity similar to that of acetaldehyde, the effects of these two aldehydes should be additive. (p.90) o The requirement for the continuous removal of acetaldehyde should to some degree diminish the capacity of the liver to cope with formaldehyde. (p.90) o Acetylcholine is the neurotransmitter at both sympathetic and parasympathetic synapses of the autonomic nervous system, and also mediates the action of post-ganglion parasympathetic neurons. Acetaldehyde is a potent synaptic blocking agent ... (p.90) =================================================================== If the yeast is a source of acetaldehyde in vivo, then a truly vicious cycle of immunosuppressive disturbances leading to additional yeast overgrowth and increasing acetaldehyde production would be established. The net result would be a progressively decreasing competence in handling all forms of infectious agents including the HIV virus. One would expect then that this cycle could be impacted by the introduction of exogenous sulfhydryl compounds to complex with acetaldehyde and protect the sulfhydryls in critical molecular structures such as gluthathione and acetyl coenzyme A. =================================================================== Cederbaum, A. I. Rubin, E. Protective effect of cysteine on the inhibition of mitochondrial functions by acetaldehyde Biochem. Pharmacology (1976) 25 : 963-973 o Acetaldehyde, which is produced during ethanol metabolism in the liver, is a toxic compound, with numerous effects on mitochondrial functions. (p.963) o Acetaldehyde depressed oxygen consumption with NAD+-dependent substrates and inhibited energy transduction and utilization by the mitochondria ... acetaldehyde depressed CO2 production from fatty acids and several citric acid cycle intermediates. (p.963) o Thiols apparently participate in many mitochondrial active sites and functions, e.g. oxidative phosphorylation, active accumulation of Mg2+, the active site of coupling factor B, NADH and succinic dehydrogenases, the active site of the phosphate carrier and the adenine nucleotide translocase. It has been claimed that acetaldehyde interacts with CoASH. It seemed possible, therefore, that some of the effects of acetaldehyde on mitochondrial functions may be related to a reaction between acetaldehyde and thiols. (p.963) o Aldehydes react quite readily with mercaptans. In the case of cysteine, ring closure can occur with the consequent formation of thiazolidines. (p.963) o Cysteine could complex with acetaldehyde to form the hemiacetal, which upon cyclization, would form 2-methylthiazolidine-4-carboxylic acid ... cysteine was claimed to protect against death from acetaldehyde toxicity in vivo. (p.963) o Acetaldehyde is a potent inhibitor of [14]CO2 production from fatty acids ... acetaldehyde was considerably more inhibitory toward fatty acid oxidation than were comparable concentrations of acetate. (p.964) o Acetaldehyde depressed [14]CO2 production from several citric acid cycle intermediates, with a major site of inhibition in the alpha-ketoglutarate-succinate span of the cycle. (p.965) o ... in general, amounts of cysteine equimolar to those of acetaldehyde are required for complete protection. Very high concentrations of acetaldehyde inhibited numerous mitochondrial functions, apparently owing to nonspecific interactions and damage to the mitochondria. (p.966) o ... the inhibition by acetaldehyde is not easily reversible, possibly because acetaldehyde forms a strong complex with a mitochondrial receptor. (p.966) o Acetaldehyde was previously shown to be particularly inhibitory toward energy-dependent oxygen consumption associated with the oxidation of NAD+-dependent substrates ... cysteine relieved the inhibition of the state 3 oxidation of all NAD+-dependent substrates tested. (p.967) o ... inhibition of glutamate oxidation by acetaldehyde. (p.968) o ... slight protective effect of mercaptoethanol or glutathione was considerably less than observed for cysteine and mercaptoethylamine. (p.968) o Cystine (3.3mM) produced no relief of the inhibition by acetaldehyde. (p. 968) o Cysteine could complex with acetaldehyde to form 2-methylthiazolidine-4-carboxylic acid. Free sulfhydryl groups can be readily detected by use of the reagent, dithionitrobenzoic acid (Ellman's reagent). (p.970) o Acetaldehyde readily interacts with semicarbazide to form a semicarbazone... (p.970) o The cysteine-acetaldehyde complex appeared stable, since there was no release of acetaldehyde from the complex, in the presence of semicarbazide even after prolonged periods of incubation. (p.970) o ... strong inhibitor of NAD+-dependent state 3 oxygen consumption; glutamate oxidation is depressed to a greater extent than that of succinate. Energy utilization is also inhibited by acetaldehyde, as evidenced by the decrease in respiratory control, P/O and ADP/O ratios, as well as the decrease in the rate of phosphorylation. Fatty acid oxidation is also reduced by acetaldehyde, owing to a variety of effects, including inhibition of beta-oxidation, citric acid cycle activity, and the respiratory-phosphorylation chain. (p.970) o ... acetaldehyde may inhibit mitochondrial functions by interacting with essential thiols; thus, externally added thiols might be effective in protecting against the inhibition by acetaldehyde. (p.970) o ... a free SH and a free amino group in close proximity protect against inhibition by acetaldehyde. Thus, beta-mercaptoethylamine is as effective as cysteine in relieving the inhibition by acetaldehyde. The carboxyl group of cysteine apparently plays no significant role in the interaction with acetaldehyde. (p.971) o The need for the thiol group is suggested by the fact that compounds with free amino and free carboxyl groups (glycine or alanine) provide no relief of the acetaldehyde-induced inhibition. The importance of the amino group is suggested by the observation that thiols with free hydroxyl groups(mercaptoethanol or thioglycerol) are less effective than cysteine or beta-mercaptoethylamine in providing a protective effect. Glutathione, which has a free SH and a free amino group, is not as effective as cysteine. The amino and thiol groups are further apart in glutathione than in cysteine, suggesting the necessity for the proximity of both ligands for maximum protection. (p.971) o ... protective effect of cysteine was mimicked by other thiols, whereas d1sulfides were ineffective. (p.971) o ... the decrease in glutathione content found after a single administration of a large amount of alcohol may be due, in part, to interaction of glutathione with acetaldehyde generated from the oxidation of ethanol. (p.972) =================================================================== Sprince, H. Parker, C. M. Smith, G. G. Gonzales, L. J. Protective action of ascorbic acid and sulfur compounds against acetaldehyde toxicity: implications in alcoholism and smoking Agents and Actions (1975) 5(2) : 164-173 o ... the reduced forms of L-ascorbic acid, L-cysteine FB, L-glutathione, and N-acetyl-L-cysteine (NAC) gave marked protection in rats against the anesthetic and lethal effects of acetaldehyde. (p.166) o ... certain combinations of above test compounds with ascorbic acid some of which at the doses used are more effective than any single component alone. (p.167) o ... at high oral doses (2 mM/kg), L-ascorbic acid and certain sulfhydryl compounds give marked protection against acetaldehyde toxicity and lethality, whereas their oxidized counterparts do not. (p.167) o ... direct protective action against acetaldehyde toxicity and lethality can be obtained with certain naturally-occurring metabolites, namely L-ascorbic acid, L-cysteine, and thiamin, preferably in combination at reduced dose levels. (p.167) o ... [depressed] ascorbic acid levels ... could be induced by elevated acetaldehyde levels releasing catecholamines which, in turn, stimulate increased utilization of ascorbic acid for their resynthesis. (p.168) o Acetaldehyde in common with other aldehydes, might be involved in such an oxidation possibly by way of hemiacetal formation with the hydroxyl groups of ascorbic acid in the 2,3 position. (p.168) o Chemically, L-cysteine by way of its (-SH) group complexes with acetaldehyde to form L-2-methylthiaolidine-4-carboxylic acid (L-MTCA) by way of an intermediary hemiacetal or Schiff base ... (p.168) o ... cysteine can protect Coenzyme A against acetaldehyde inhibition by complexing preferentially with acetaldehyde. (p.168) o ... reduced glutathione, homocysteine, and N-acetyl-cysteine (NAC) could also complex with acetaldehyde by virtue of their free (-SH) groups. N-acetyl-L-cysteine is a well-known mycolytic agent capable of liquefying mucus and secretions associated with pulmonary disorders. (p.168) o Biochemically, it [acetaldehyde] has been demonstrated to give a 'browning reaction' with proteins, involving amino groups, guanidyl groups, and crosslinkage formation. Immunologically, it like formaldehyde, has been found to act at low concentrations on antibodies and presumably also on antigens. With certain antibodies (antipneumococcus serum and diphtheria antitoxin), solubilization of the antibody by the aldehydic group occurs with resultant loss of antibody protective power in the living animal. (p.170) o ... acetaldehyde (and other aldehydes) can react with proteins slowly and irreversibly to result in adverse functional changes in these proteins, for example in reduced enzymatic activity or reduced metal-binding capacity. Such changes slow and irreversible at the molecular level over a period of years could lead to adverse tissue changes and eventually organ dysfunction. (p.170) =================================================================== In summary, it would appear that depressed glutathione levels could conceivably result from the in vivo acetaldehyde-forming decarboxylation of dietary carbohydrates by yeasts of the genus Candida. The efficacy of N-acetylcysteine would then be related to its ability to form a stable complex with acetaldehyde thus affording protection for the numerous vulnerable sulfhydryl structures essential to proper metabolic function of which glutathione is only one.