Methanol poisoning. I. The role of formic acid in the development of metabolic acidosis in the monkey and the reversal by 4-methylpyrazole

Awareness raising and dealing with methanol poisoning based on effective strategies

Intoxication with methanol most commonly occurs as a consequence of ingesting, inhaling, or coming into contact with formulations that include methanol as a base. Clinical manifestations of methanol poisoning include suppression of the central nervous system, gastrointestinal symptoms, and decompensated metabolic acidosis, which is associated with impaired vision and either early or late blindness within 0.5-4 h after ingestion. After ingestion, methanol concentrations in the blood that are greater than 50 mg/dl should raise some concern. Ingested methanol is typically digested by alcohol dehydrogenase (ADH), and it is subsequently redistributed to the body's water to attain a volume distribution that is about equivalent to 0.77 L/kg. Moreover, it is removed from the body as its natural, unchanged parent molecules. Due to the fact that methanol poisoning is relatively uncommon but frequently involves a large number of victims at the same time, this type of incident occupies a special position in the field of clinical toxicology. The beginning of the COVID-19 pandemic has resulted in an increase in erroneous assumptions regarding the preventative capability of methanol in comparison to viral infection. More than 1000 Iranians fell ill, and more than 300 of them passed away in March of this year after they consumed methanol in the expectation that it would protect them from a new coronavirus. The Atlanta epidemic, which involved 323 individuals and resulted in the deaths of 41, is one example of mass poisoning. Another example is the Kristiansand outbreak, which involved 70 people and resulted in the deaths of three. In 2003, the AAPCC received reports of more than one thousand pediatric exposures. Since methanol poisoning is associated with high mortality rates, it is vital that the condition be addressed seriously and managed as quickly as feasible. The objective of this review was to raise awareness about the mechanism and metabolism of methanol toxicity, the introduction of therapeutic interventions such as gastrointestinal decontamination and methanol metabolism inhibition, the correction of metabolic disturbances, and the establishment of novel diagnostic/screening nanoparticle-based strategies for methanol poisoning such as the discovery of ADH inhibitors as well as the detection of the adulteration of alcoholic drinks by nanoparticles in order to prevent methanol poisoning. In conclusion, increasing warnings and knowledge about clinical manifestations, medical interventions, and novel strategies for methanol poisoning probably results in a decrease in the death load.

Acute and chronic blood serum proteome changes in patients with methanol poisoning

Twenty-four blood serum samples from patients with acute methanol poisoning (M) from the mass methanol poisoning outbreak in the Czech Republic in 2012 were compared with 46 patient samples taken four years after poisoning (S) (overlap of 10 people with group M) and with a control group (C) of 24 samples of patients with a similar proportion of chronic alcohol abuse. When comparing any two groups, tens to hundreds of proteins with a significant change in concentration were identified. Fifteen proteins showed significant changes when compared between any two groups. The group with acute methanol poisoning showed significant changes in protein concentrations for at least 64 proteins compared to the other groups. Among the most important identified proteins closely related to intoxication are mainly those involved in blood coagulation, metabolism of vitamin A (increased retinol-binding protein), immune response (e.g., increased complement factor I, complement factors C3 and C5), and lipid transport (increased apolipoprotein A I, apolipoprotein A II, adiponectin). For blood coagulation, the most affected proteins with significant changes in the methanol poisoning group were von Willebrand factor, carboxypeptidase N, alpha-2-antiplasmin (all increased), inter-alpha-trypsin inhibitor heavy chain H4, kininogen-1, plasma serine protease inhibitor, plasminogen (all decreased). However, heparin administration used for the methanol poisoning group could have interfered with some of the changes in their concentrations. Data are available via ProteomeXchange with the identifier PXD035726.

Risk factors associated with mortality in patients with methanol poisoning: a retrospective study

Aim: Methanol poisoning (MP) is an essential medical problem worldwide, and despite advances in diagnosis and treatment, the mortality rate in these cases is high. This study aimed to evaluate the clinical and laboratory factors to determine in-hospital mortality in patients with MP. Methods: This single-center, retrospective, observational study was conducted with adult 65 MP cases visiting the emergency department (ED) of a tertiary training and research hospital between January 01, 2017, and February 01, 2022. Data were statistically compared between survivors and non-survivors. Results: The in-hospital mortality rate was 41.5%. The rate of cases with respiratory distress, low Glasgow coma scale (GCS) (≤8), and delayed arrival to the hospital (>24 hours) was higher in the group of non-survivors compared to the group of survivors. Non-survivors had a higher anion gap (30.5 mEq/L vs. 25.5mEq/L), base excess (-25.0 mmol/L vs. -18.6 mmol/L), lactate (10.2 mmol/L vs. 2.2 mmol/L) levels, and lower pH (6.76 vs. 7.14) and bicarbonate (6.3 mmol/L vs. 10.3 mmol/L) levels than survivors (p

Methanol poisoning outbreak in Saudi Arabia: a case series

Background

Outbreaks of methanol poisoning have been described in the medical literature in different regions around the world. Even though in Saudi Arabia a few outbreaks of methanol poisoning have occurred, they remain undocumented. Herein, we describe several cases of methanol poisoning in Saudi Arabia with the goal of increasing awareness about the dangers of methanol poisoning among healthcare staff.

Case presentation

Nine middle-aged Saudi patients (five men aged 24, 26, 27, 36, and 49 years and four females aged 19, 20, 24, and 25 years) were admitted to our emergency department after alcohol consumption. All patients presented with severe metabolic acidosis and some visual impairment. Treatment was initiated based on the clinical suspicion of methanol intoxication because of laboratory test limitations and time constraints. Patients showed improvement and favorable hospital outcomes after aggressive empirical treatment.

Conclusions

Many social and cultural factors influence the lack of reporting of methanol poisoning cases in Saudi Arabia. We believe it is important to document these outbreaks to increase the knowledge among healthcare providers and promote public health awareness. A high index of suspicion and the development of local public health networks to monitor, survey, follow-up, and facilitate data exchange can help healthcare providers recognize and aggressively treat affected individuals. Early empiric and aggressive management can greatly decrease morbidity and mortality despite challenges and limited resources.

One metal-ion-regulated AgTNPs etching sensor array for visual discrimination of multiple organic acids

The detection and discrimination of organic acids (OAs) is of great importance in the early diagnosis of specific diseases. In this study, we established an effective visual sensor array for the identification of OA. This is the first time, to our best knowledge, that metal ions were used to regulate the etching of silver triangular nanoprisms (AgTNPs) in an OA discrimination sensor array. The sensor array was based on the oxidation etching of AgTNPs by three metal ions (Mn²⁺, Pb²⁺, and Cr³⁺) and accelerated etching of AgTNPs by OA. The introduction of metal ions alone led to a slight wavelength shift of the AgTNPs colloid solution, signifying the incomplete etching of the AgTNPs. Nevertheless, when metal ions and OA were introduced simultaneously to the solution, a significant blueshift of the localized surface plasmon resonance peak was detected, and a color change of the AgTNPs was observed, which were the consequences of morphological transitions of the AgTNPs. The addition of different OA accelerated AgTNPs etching in varying degrees, generating diverse colorimetric response patterns (i.e., RGB variations) as "fingerprints" associated with each specific organic acid. Pattern recognition algorithms and neural network simulation were employed to further data analysis, indicating the outstanding discrimination capability of the provided array for eight OA at the 33 µM level. Moreover, excellent results of selective experiments as well as real samples tests demonstrate that our proposed method possesses great potential for practical applications.

Biochemical mechanism underlying the pathogenesis of diabetic retinopathy and other diabetic complications in humans: the methanol-formaldehyde-formic acid hypothesis

Hyperglycemia in diabetic patients is associated with abnormally-elevated cellular glucose levels. It is hypothesized that increased cellular glucose will lead to increased formation of endogenous methanol and/or formaldehyde, both of which are then metabolically converted to formic acid. These one-carbon metabolites are known to be present naturally in humans, and their levels are increased under diabetic conditions. Mechanistically, while formaldehyde is a cross-linking agent capable of causing extensive cytotoxicity, formic acid is an inhibitor of mitochondrial cytochrome oxidase, capable of inducing histotoxic hypoxia, ATP deficiency and cytotoxicity. Chronic increase in the production and accumulation of these toxic one-carbon metabolites in diabetic patients can drive the pathogenesis of ocular as well as other diabetic complications. This hypothesis is supported by a large body of experimental and clinical observations scattered in the literature. For instance, methanol is known to have organ- and species-selective toxicities, including the characteristic ocular lesions commonly seen in humans and non-human primates, but not in rodents. Similarly, some of the diabetic complications (such as ocular lesions) also have a characteristic species-selective pattern, closely resembling methanol intoxication. Moreover, while alcohol consumption or combined use of folic acid plus vitamin B is beneficial for mitigating acute methanol toxicity in humans, their use also improves the outcomes of diabetic complications. In addition, there is also a large body of evidence from biochemical and cellular studies. Together, there is considerable experimental support for the proposed hypothesis that increased metabolic formation of toxic one-carbon metabolites in diabetic patients contributes importantly to the development of various clinical complications.

Comparing N-acetylcysteine and 4-methylpyrazole as antidotes for acetaminophen overdose

Acetaminophen (APAP) overdose can cause hepatotoxicity and even liver failure. N-acetylcysteine (NAC) is still the only FDA-approved antidote against APAP overdose 40 years after its introduction. The standard oral or intravenous dosing regimen of NAC is highly effective for patients with moderate overdoses who present within 8 h of APAP ingestion. However, for late-presenting patients or after ingestion of very large overdoses, the efficacy of NAC is diminished. Thus, additional antidotes with an extended therapeutic window may be needed for these patients. Fomepizole (4-methylpyrazole), a clinically approved antidote against methanol and ethylene glycol poisoning, recently emerged as a promising candidate. In animal studies, fomepizole effectively prevented APAP-induced liver injury by inhibiting Cyp2E1 when treated early, and by inhibiting c-jun N-terminal kinase (JNK) and oxidant stress when treated after the metabolism phase. In addition, fomepizole treatment, unlike NAC, prevented APAP-induced kidney damage and promoted hepatic regeneration in mice. These mechanisms of protection (inhibition of Cyp2E1 and JNK) and an extended efficacy compared to NAC could be verified in primary human hepatocytes. Furthermore, the formation of oxidative metabolites was eliminated in healthy volunteers using the established treatment protocol for fomepizole in toxic alcohol and ethylene glycol poisoning. These mechanistic findings, together with the excellent safety profile after methanol and ethylene glycol poisoning and after an APAP overdose, suggest that fomepizole may be a promising antidote against APAP overdose that could be useful as adjunct treatment to NAC. Clinical trials to support this hypothesis are warranted.

Analysis of Fomepizole Elimination in Methanol- and Ethylene Glycol-Poisoned Patients

INTRODUCTION

Fomepizole is an anti-metabolite therapy that is used to diminish the toxicity from methanol or ethylene glycol. Although its elimination kinetics have been well described in healthy human subjects, the elimination in poisoned patients have only been described in a few isolated cases. This study was designed to relate the elimination of fomepizole in a series of poisoned patients to that in healthy humans.

METHODS

Plasma samples from 26 patients in the clinical trials of the use of fomepizole for methanol and ethylene glycol poisoning were analyzed for fomepizole concentrations. The elimination of fomepizole was assessed after individual doses, both during and without intermittent hemodialysis.

RESULTS

In methanol- and ethylene glycol-poisoned patients, fomepizole had a volume of distribution of 0.66-0.68 L/kg. After repeated doses of fomepizole, the minimum trough concentration averaged 86-109 µmol/L, which is 10 times higher than the minimum therapeutic concentration. In healthy human subjects, fomepizole elimination follows Michaelis-Menten kinetics and has been calculated as zero-order elimination rates. Zero-order elimination rates averaged 13 and 17 μmol/L/h in methanol and ethylene glycol patients, respectively, compared to 6-19 μmol/L/h in healthy subjects. Elimination during intermittent hemodialysis followed first-order kinetics, with a half-life of 3 h.

CONCLUSIONS

Plasma concentrations during the repeated dosing confirmed that the recommended dosing schedule, with and without intermittent hemodialysis, maintained therapeutic concentrations throughout the treatments. Fomepizole elimination in poisoned patients at therapeutic plasma concentrations appears be similar to that reported previously in healthy human subjects.

Fomepizole dosing during continuous renal replacement therapy - an observational study

BACKGROUND

Fomepizole is the preferred antidote for treatment of methanol and ethylene glycol poisoning, acting by inhibiting the formation of the toxic metabolites. Although very effective, the price is high and the availability is limited. Its availability is further challenged in situations with mass poisonings. Therefore, a 50% reduced maintenance dose for fomepizole during continuous renal replacement therapy (CRRT) was suggested in 2016, based on pharmacokinetic data only. Our aim was to study whether this new dosing for fomepizole during CRRT gave plasma concentrations above the required 10 µmol/L. Secondly, we wanted to study the elimination kinetics of fomepizole during CRRT, which has never been studied before.

METHODS

Prospective observational study of adult patients treated with fomepizole and CRRT. We collected samples from arterial line (pre-filter) = plasma concentration, post-filter and dialysate for fomepizole measurements. Fomepizole was measured using high-pressure liquid chromatography with a reverse phase column.

RESULTS

Ten patients were included in the study. Seven were treated with continuous veno-venous hemodialysis (CVVHD) and three with continuous veno-venous hemodiafiltration (CVVHDF). Ninety-eight percent of the plasma samples were above the minimum plasma concentration of 10 µmol/L. Fomepizole was removed during CRRT with a median saturation/sieving coefficient of 0.85 and dialysis clearance of 28 mL/min.

CONCLUSION

Fomepizole was eliminated during CCRT. The new dosing recommendations for fomepizole and CRRT appeared safe, by maintaining the plasma concentration above the minimum value of 10 µmol/L. Based on these data, the fomepizole maintenance dose during CRRT could be reduced to half as compared to intermittent hemodialysis.

Formaldehyde Reacts with Amino Acids and Peptides with a Potential Role in Acute Methanol Intoxication

Methanol, an aliphatic alcohol widely used in the industry, causes acute and chronic intoxications associated with severe long-term health damage, including permanent visual impairment, brain damage, mainly necrosis of the basal ganglia and high mortality due to cancer. However, the role of formaldehyde, an intermediate metabolite of methanol oxidation, in methanol toxicity remains unclear. Thus, we studied the reactivity of several amino acids and peptides in the presence of formaldehyde by identifying products by direct infusion electrospray high-resolution mass spectrometry (MS) and matrix-assisted laser desorption-ionization MS. Cysteine, homocysteine and two peptides, CG and CGAG, provided cyclic products with a +12 amu mass shift with respect to the original compounds. The proposed structures of the products were confirmed by high-resolution tandem MS. Moreover, the formation of the products with +12 amu mass shift was also shown for two biologically relevant peptides, fragments of ipilimumab, which is a human IgG1 monoclonal antibody against cytotoxic T-lymphocyte-associated protein 4. Overall, our experimental results indicate that formaldehyde reacts with some amino acids and peptides, yielding covalently modified structures. Such chemical modifications may induce undesirable changes in the properties and function of vital biomolecules (e.g., hormones, enzymes) and consequently pathogenesis.

Late Functional and Morphological Findings after Methylalcohol Poisoning

AIM

The aim of the study was to determine the morphological and functional findings in a patient after methanol poisoning. Examination methods: The patient (male, 38 years old) was suffered methanol poisoning in eight years ago (2012). The following tests and examinations were performed: neurological visual field XR test (Medmont M700), retinal nerve fibre layer (RNFL), ganglion cell complex (GCC) and peripapillary vessel density (all using Avanti RTvue, Optovue), pattern electroretinography (PERG) and pattern visual evoked potential (PVEP) examination according to ISCEV methodology (Roland Consult Instrument) and brain MRI examination (Philips Achieva Dstream 3 T).

RESULTS

The biggest changes were found in RNFL and VD. PERG also showed damage to retinal ganglion cell axons. In left eye we determined decrease in oscillations (in comparison with contralateral eye) at N35-P50 and P50-N95. VEPs in both eyes were significantly reduced, almost inconspicuous in the left eye. Extension of latency time of P100 was not identified. Functional MRI showed a bilateral decrease in voxel activity with a greater decrease in the left eye. There were postmalatical changes in the dorsal parts of the putamen on MRI. The width of the optic nerve and chiasm was physiological.

CONCLUSION

Asymmetric damaging of RNFL and cortical centres of the brain were determined. We registered large pathological changes in VD, which are probably responsible for the deepening of optic nerve excavation and further loss of nerve fibers of retinal ganglion cells, which have not yet been described in the literature. Following these results is possible to define direct damage of nerve structures and blood vessels by toxins of methanol metabolism in the acute stage and upcoming reparation processes in following periods.

Folate as an Adjuvant Therapy in Methanol Poisoning

Folate and its derivatives have long been used as an adjunctive treatment in methanol poisoning. Methanol is ultimately metabolized to formate, the toxic compound. The accumulation of formate can lead to acidemia, retinal damage, visual impairment, and death. Formate is converted to carbon dioxide and water in a folate-dependent manner, and folate is often given in cases of methanol poisoning. In this paper, the evidence for folate as an adjunctive therapy in methanol poisoning is reviewed.

Derivation of safe exposure levels for potential migration of formaldehyde into food

Polyoxymethylene (POM) is a polymer of formaldehyde used inter alia for kitchenware and food processing machines. By migration into food, consumers may be exposed to small additional amounts of formaldehyde in food. In order to address such potential exposures, Specific Migration Limits are derived using all studies with oral exposure in mammals and birds. The assessment is not only based on local irritation observed in a 2-year rat study that has previously served to calculate acceptable exposure levels, but also on systemic effects, namely on effects on the kidney in adult rats and testes in birds before sexual maturity. At the relatively high oral exposure levels (up to 2000 ppm in drinking water) long-term effects caused by formic acid, the first step metabolite of formaldehyde, such as acidosis, cannot be excluded. The lowest Specific Migration Limit of 2.74 mg/dm², corresponding to 16.5 mg formaldehyde/kg food, is based upon kidney effects in rats, leading to potential exposures that range between 2900 and 4400 times below the endogenous turnover of formaldehyde. Lastly, a recent migration study with POM showed that migration of formaldehyde into food simulants is over an order of magnitude below the lowest Specific Migration Limit derived herein.

FASD: folic acid and formic acid — an unholy alliance in the alcohol abusing mother

Alcohol consumption during pregnancy remains a significant cause of preventable birth defects and developmental disabilities; however, the mechanism of toxicity remains unclear. Methanol is present as a congener in many alcoholic beverages and is formed endogenously. Because ethanol is preferentially metabolized over methanol, it has been found in the sera and cerebro-spinal fluid of alcoholics. Toxicity resulting from methanol has been attributed to formic acid. Formic acid is present in significantly higher quantities in the biofluids of alcoholics. These higher levels can be cytotoxic and cause neuronal cell death. However, the adverse effects can be mitigated by adequate levels of hepatic folic acid, because formic acid elimination depends on folic acid. During pregnancy, folate concentrations are at least 2-fold higher in cord blood then in maternal blood, owing to increased folate requirements. The reverse has been demonstrated in pregnancies with alcohol abuse, suggesting downregulation of folate transporters and low fetal folate levels. Moreover, formic acid can cross the placenta and its adverse effects can be mitigated by folic acid. Thus, the combination of low fetal folate levels and presence of formic acid form a potent cytotoxic combination that may play a significant role in the etiology of fetal alcohol spectrum disorder.

Antidotes for poisoning by alcohols that form toxic metabolites

The alcohols, methanol, ethylene glycol and diethylene glycol, have many features in common, the most important of which is the fact that the compounds themselves are relatively non-toxic but are metabolized, initially by alcohol dehydrogenase, to various toxic intermediates. These compounds are readily available worldwide in commercial products as well as in homemade alcoholic beverages, both of which lead to most of the poisoning cases, from either unintentional or intentional ingestion. Although relatively infrequent in overall occurrence, poisonings by metabolically-toxic alcohols do unfortunately occur in outbreaks and can result in severe morbidity and mortality. These poisonings have traditionally been treated with ethanol since it competes for the active site of alcohol dehydrogenase and decreases the formation of toxic metabolites. Although ethanol can be effective in these poisonings, there are substantial practical problems with its use and so fomepizole, a potent competitive inhibitor of alcohol dehydrogenase, was developed for a hopefully better treatment for metabolically-toxic alcohol poisonings. Fomepizole has few side effects and is easy to use in practice and it may obviate the need for haemodialysis in some, but not all, patients. Hence, fomepizole has largely replaced ethanol as the toxic alcohol antidote in many countries. Nevertheless, ethanol remains an important alternative because access to fomepizole can be limited, the cost may appear excessive, or the physician may prefer ethanol due to experience.

Analysis of methanol and its derivatives in illegally produced alcoholic beverages

INTRODUCTION

Illegal alcohol production remains as a common issue worldwide. Methanol poisoning mostly occurs because of the methanol used in production of counterfeit alcohol instead of ethyl alcohol due to its low price or by drinking the liquids containing methyl alcohol. Pectolytic enzymes results in an increase of methanol levels in many fermentation products such as ciders or wines. Methanol poisonings are infrequently encountered in forensic medicine practice. However, sporadic cases due to methanol intoxication as well as epidemic cases have been reported. In this study, we aimed to identify existence of methanol and its metabolites in illegally produced alcoholic beverages used in Antakya region.

MATERIAL AND METHODS

Twelve legally produced alcohol samples and Fifty-six different illegally produced alcohol samples were collected from the markets and local producers. Existence of methanol, formic acid, methyl amine, methyl formate and trioxan were determined using GC-MS method in these samples.

RESULTS

Fifty-six different illegal alcohol samples were analyzed in this study and methanol was detected in 39 (75%) of samples. Formic acid was detected in 3, formamide in 1, methyl amine in 6, methyl formate in 10 and trioxan in 2 samples.

CONCLUSION

Overwhelming majority of illegal alcoholic beverages was detected to contain methanol. Interestingly this study also revealed the presence of trioxane, which has not previously reported among toxic agents in illegal alcohol samples.

Rapid screening and analysis of alcohol dehydrogenase binders from Glycyrrhiza uralensis root extract using functionalized magnetic nanoparticles coupled with HPLC−MS/MS

Alcohol dehydrogenase (ADH) is a key enzyme that converts ethanol into acetaldehyde. Its binders could be used to efficiently treat human toxic alcohol poisoning and suppress the acetaldehyde accumulation in alcohol hypersensitive alcoholics. In the present study, a new assay based on ADH-functionalized magnetic nanoparticles coupled with high-performance liquid chromatography − tandem mass spectrometry (HPLC−MS/MS) was developed for the rapid screening and identification of ADH binders. ADH was immobilized on silica-coated Fe3O4 magnetic nanoparticles via covalent bonds and the synthesized nanoparticles were characterized by TEM, XRD, FT-IR, and VSM. The amount of bound ADH onto magnetic nanoparticles was 80.6 μg/mg. The optimum temperature and pH for the enzymatic activity of immobilized ADH were 25 °C and 7.0, respectively. The relative activity of immobilized ADH remained 68.14% after 10 times of recycle, which exhibited good durability. Nine compounds with ADH-binding activity were screened and identified in Glycyrrhiza uralensis root extracts, among which seven compounds were first screened and identified. Experimental results proved that the proposed method could rapidly screen ADH binders from complex mixtures.

Methanol and ethylene glycol intoxication

Accidental or intentional ingestion of substances containing methanol and ethylene glycol can result in death, and some survivors are left with blindness, renal dysfunction, and chronic brain injury. However, even in large ingestions, a favorable outcome is possible if the patient arrives at the hospital early enough and the poisoning is identified and appropriately treated in a timely manner. This review covers the common circumstances of exposure, the involved toxic mechanisms, and the clinical manifestations, laboratory findings, and treatment of methanol and ethylene glycol intoxication.

Formate can differentiate between hyperhomocysteinemia due to impaired remethylation and impaired transsulfuration

Formate can differentiate between hyperhomocysteinemia due to impaired remethylation and impaired transsulfuration. Am J Physiol Endocrinol Metab 301: E000-E000, 2011. First published September 20, 2011; 10.1152/ajpendo.00345.2011.-We carried out a (1)H-NMR metabolomic analysis of sera from vitamin B(12)-deficient rats. In addition to the expected increases in methylmalonate and homocysteine (Hcy), we observed an approximately sevenfold increase in formate levels, from 64 μM in control rats to 402 μM in vitamin B(12)-deficient rats. Urinary formate was also elevated. This elevation of formate could be attributed to impaired one-carbon metabolism since formate is assimilated into the one-carbon pool by incorporation into 10-formyl-THF via the enzyme 10-formyl-THF synthase. Both plasma and urinary formate were also increased in folate-deficient rats. Hcy was elevated in both the vitamin B(12)- and folate-deficient rats. Although plasma Hcy was also elevated, plasma formate was unaffected in vitamin B(6)-deficient rats (impaired transsulfuration pathway). These results were in accord with a mathematical model of folate metabolism, which predicted that reduction in methionine synthase activity would cause increased formate levels, whereas reduced cystathionine β-synthase activity would not. Our data indicate that formate provides a novel window into cellular folate metabolism, that elevated formate can be a useful indicator of deranged one-carbon metabolism and can be used to discriminate between the hyperhomocysteinemia caused by defects in the remethylation and transsulfuration pathways.

Metabolic mechanisms of methanol/formaldehyde in isolated rat hepatocytes: carbonyl-metabolizing enzymes versus oxidative stress

Methanol (CH(3)OH), a common industrial solvent, is metabolized to toxic compounds by several enzymatic as well as free radical pathways. Identifying which process best enhances or prevents CH(3)OH-induced cytotoxicity could provide insight into the molecular basis for acute CH(3)OH-induced hepatoxicity. Metabolic pathways studied include those found in 1) an isolated hepatocyte system and 2) cell-free systems. Accelerated Cytotoxicity Mechanism Screening (ACMS) techniques demonstrated that CH(3)OH had little toxicity towards rat hepatocytes in 95% O(2), even at 2M concentration, whereas 50 mM was the estimated LC(50) (2h) in 1% O(2), estimated to be the physiological concentration in the centrilobular region of the liver and also the target region for ethanol toxicity. Cytotoxicity was attributed to increased NADH levels caused by CH(3)OH metabolism, catalyzed by ADH1, resulting in reductive stress, which reduced and released ferrous iron from Ferritin causing oxygen activation. A similar cytotoxic mechanism at 1% O(2) was previous found for ethanol. With 95% O(2), the addition of Fe(II)/H(2)O(2), at non-toxic concentrations were the most effective agents for increasing hepatocyte toxicity induced by 1M CH(3)OH, with a 3-fold increase in cytotoxicity and ROS formation. Iron chelators, desferoxamine, and NADH oxidizers and ATP generators, e.g. fructose, also protected hepatocytes and decreased ROS formation and cytotoxicity. Hepatocyte protein carbonylation induced by formaldehyde (HCHO) formation was also increased about 4-fold, when CH(3)OH was oxidized by the Fenton-like system, Fe(II)/H(2)O(2), and correlated with increased cytotoxicity. In a cell-free bovine serum albumin system, Fe(II)/H(2)O(2) also increased CH(3)OH oxidation as well as HCHO protein carbonylation. Nontoxic ferrous iron and a H(2)O(2) generating system increased HCHO-induced cytotoxicity and hepatocyte protein carbonylation. In addition, HCHO cytotoxicity was markedly increased by ADH1 and ALDH2 inhibitors or GSH-depleted hepatocytes. Increased HCHO concentration levels correlated with increased HCHO-induced protein carbonylation in hepatocytes. These results suggest that CH(3)OH at 1% O(2) involves activation of the Fenton system to form HCHO. However, at higher O(2) levels, radicals generated through Fe(II)/H(2)O(2) can oxidize CH(3)OH/HCHO to form pro-oxidant radicals and lead to increased oxidative stress through protein carbonylation and ROS formation which ultimately causes cell death.

Formate concentrations in plasma from patients poisoned with methanol

Formate and methanol were quantified in blood samples from 11 untreated methanol-poisoned subjects. The range for whole blood methanol concentrations was 0-137 mmol/l and for plasma formate concentrations 0.4-17.1 mmol/l. Simultaneously determined acid-base status and serum electrolyte concentrations allowed assessment of the relative importance of formate accumulation for the acidosis. The plasma formate concentration was highly correlated to both the calculated anion gap (r = 0.833), the bicarbonate concentration (r = 0.852) and the negative base excess (r = 0.865). The accumulation of formate fully accounted for the increase in the anion gap and the fall in plasma bicarbonate, whereas the negative base excess values were about 22% higher than the plasma formate concentration. We conclude that formate accumulation is the main or only reason for acidosis in the early, uncomplicated stages of methanol poisoning. Lactate may appear at more advanced stages.

Anion and osmolal gaps in the diagnosis of methanol and ethylene glycol poisoning

The diagnostic value of determination of the anion and osmolal gaps was studied in 6 patients poisoned with methanol and in 5 poisoned with ethylene glycol. Increased osmolal gap was present on admission in all patients, whereas increased anion gap was present in all except one. In the methanol-poisoned patients the mean blood values were: pH 7.27, anion gap 24 mmol/l, osmolal gap 81 mosmol/kg H2O, methanol 67 mmol/l, ethanol 11 mmol/l and in the ethylene glycol-poisoned patients: pH 6.93, anion gap 38 mmol/l, osmolal gap 35 mosmol/kg H2O and ethylene glycol 24 mmol/l. In the absence of alcoholic acidosis or diabetic coma the finding of a simultaneous increase in both the anion and osmolal gaps indicates methanol or ethylene glycol poisoning. Thus determinations of the anion and osmolal gaps are mandatory whenever facing metabolic acidosis of unknown etiology.

Toxicokinetics of formate during hemodialysis

During hemodialysis in a methanol poisoned patient, formate elimination followed first order kinetics with a plasma half-life of formate of 165 min. The mean dialysator (1.6 m2) clearance of formate was 148 ml/min (n = 8, SD +/- 11, range 128-161) at a blood flow of 215 ml/min. By applying first order kinetics, a volume of distribution of 0.5 l/kg was found, assuming that the dialysator clearance equals the total body clearance of formate. Formate, the main toxic agent in methanol poisoning, is thus probably more effectively removed by hemodialysis than methanol. This fact, and the very slow endogenous methanol elimination during appropriate ethanol treatment, should be considered when deciding on the treatment of a methanol poisoned patient presenting with metabolic acidosis.

Fomepizole: a critical assessment of current dosing recommendations

Fomepizole, 4-methylpyrazole (4-MP), is a competitive antagonist of alcohol dehydrogenase with a binding affinity >8000 times that of ethanol. The drug is currently labeled by the United States Food and Drug Administration for the treatment of adult patients with known or suspected ethylene glycol or methanol poisoning. Fomepizole's wide therapeutic dose range and safety profile confer several advantages over standard ethanol therapy for the treatment of toxic alcohol exposures, including the lack of ethanol-associated side effects. Published data and data obtained from the drug's manufacturer implies that the dose escalation after 48 hours is to compensate for fomepizole-induced increased body clearance resulting from autoinduction of the cytochrome P450 (CYP) drug metabolizing enzyme CYP2E1. However, we were unable to identify any evidence of fomepizole's metabolism occurring via CYP2E1 in humans while the data most frequently cited as evidence for induction do not appear to support this claim. Based on this data along with the apparent zero-order kinetics, the current dose increase recommendations may be unnecessary and considering the safety margin described for fomepizole, an extremely conservative constant higher dose administered every 12 hours would appear to assure efficacy and tolerability. Despite the evidence, dose changes should only be implemented after careful clinical trials.

Acceleration of ethanol and acetaldehyde oxidation by D-glycerate in rats

The aim of the present study was to investigate whether d-glycerate (glycerate) could accelerate ethanol and acetaldehyde (AcH) oxidation in vivo in rats by circumventing the rate-limiting step, that is, the reoxidation of the reduced form of nicotinamide adenine dinucleotide. Male rats belonging to the ANA (Alko, nonalcohol) and AA (Alko, alcohol) rat lines were challenged with 1.2 g ethanol per kilogram with or without glycerate administration (0.1-1.0 g/kg). Blood ethanol, blood AcH, and liver free glycerol concentrations were determined during ethanol intoxication. Glycerate treatment, regardless of the dose, accelerated ethanol elimination by approximately 25% (P < .001) in the ANA animals. Glycerate also accelerated the AcH oxidation, but perhaps not as much as the ethanol oxidation, as indicated by a trend toward elevated AcH levels. In the experiments with the AA rats, glycerate treatment elevated hepatic free glycerol levels by about 50% (P < .05) during alcohol intoxication. The acceleration of ethanol and AcH oxidation in conjunction with elevated glycerol levels by the treatment with glycerate supports the hypothesis that the aldehyde dehydrogenase-mediated AcH oxidation can be coupled with the reduction of glycerate to d-glyceraldehyde catalyzed by the same enzyme. Such a coupling should increase the availability of the oxidized form of nicotinamide adenine dinucleotide and thus accelerate both ethanol and AcH oxidation. Further studies are needed to investigate how the AcH could be even more efficiently oxidized to reduce the harmful effects of ethanol-derived AcH.

Deadly pediatric poisons: nine common agents that kill at low doses

More than 97% of pediatric exposures reported to the AAPCC in 2001 had either no effect or mild clinical effects. Despite the large number of exposures, only 26 of the 1074 reported fatalities occurred in children younger than age 6. These findings reflect the fact that, in contrast to adolescent or adult ingestions, pediatric ingestions are unintentional events secondary to development of exploration behaviors and the tendency to place objects in the mouth. Ingested substances typically are nontoxic or ingested in such small quantities that toxicity would not be expected. As a result, it commonly is believed that ingestion of one or two tablets by a toddler is a benign act and not expected to produce any consequential toxicity. Select agents have the potential to produce profound toxicity and death, however, despite the ingestion of only one or two tablets or sips. Although proven antidotes are a valuable resource, their value is diminished if risk after ingestion is not adequately appreciated and assessed. Future research into low-dose, high-risk exposures should be directed toward further clarification of risk, improvements in overall management strategies,and, perhaps most importantly, prevention of toxic exposure through parental education and appropriate safety legislation.

NTP-CERHR Expert Panel report on the reproductive and developmental toxicity of methanol

The National Toxicology Program (NTP) and the National Institute of Environmental Health Sciences (NIEHS) established the NTP Center for the Evaluation of Risks to Human Reproduction (CERHR) in June 1998. The purpose of the Center is to provide timely, unbiased, scientifically sound evaluations of human and experimental evidence for adverse effects on reproduction, including development, caused by agents to which humans may be exposed. Methanol was selected for evaluation by the CERHR based on high production volume, extent of human exposure, and published evidence of reproductive or developmental toxicity. Methanol is used in chemical syntheses and as an industrial solvent. It is a natural component of the human diet and is found in consumer products such as paints, antifreeze, cleaning solutions, and adhesives. It is used in race car fuels and there is potential for expanded use as an automobile fuel. This evaluation is the result of a 10-month effort by a 12-member panel of government and non-government scientists that culminated in a public Expert Panel meeting. This report has been reviewed by CERHR staff scientists, and by members of the Methanol Expert Panel. Copies have been provided to the CERHR Core Committee, which is made up of representatives of NTP-participating agencies. This report is a product of the Expert Panel and is intended to (1). interpret the strength of scientific evidence that a given exposure or exposure circumstance may pose a hazard to reproduction and the health and welfare of children; (2). provide objective and scientifically thorough assessments of the scientific evidence that adverse reproductive/development health effects are associated with exposure to specific chemicals or classes of chemicals, including descriptions of any uncertainties that would diminish confidence in assessment of risks; and (3). identify knowledge gaps to help establish research and testing priorities. The expert panel report becomes a central part of the subsequent NTP-CERHR Monograph. Each monograph includes the NTP Brief on the chemical under evaluation, the expert panel report, and all public comments on the expert panel report. The NTP Brief contains the NTP's conclusions on the potential for exposure to result in adverse effects on human development and reproduction. It is based on the expert panel report, public comments on the report, and relevant data published after the expert panel report was completed. NTP-CERHR Monographs are publicly available and are transmitted to appropriate health and regulatory agencies.

Formate, the toxic metabolite of methanol, in cultured ocular cells

Methanol has neurotoxic actions on the human retina due to its metabolite, formic acid, which is a mitochondrial toxin. In methanol poisoned animals, morphologic changes were seen both in retinal photoreceptors and in cells of the underlying retinal pigment epithelium (RPE). Here the effects of formate exposure on the two retinal cell types were analyzed in more detail in vitro using photoreceptor (661W) and RPE (ARPE-19) cell lines. Cells were exposed for time courses from minutes to days to sodium formate at pH 7.4 or to formic acid at pH 6.8, to simulate the metabolic acidosis that accompanies methanol poisoning. Formate accumulation, cellular ATP, cytotoxicity (lactate dehydrogenase (LDH) release) and cell phenotype were analyzed. Formate accumulated with a similar biphasic pattern in both cell types, and to similar levels whether delivered as sodium formate or as formic acid. ATP changes with sodium formate treatment differed between cell types with only 661W cells showing a rapid (within minutes), transient ATP increase. The subsequent ATP decrease was earlier in 661W cells (6 h) than the ATP decrease in ARPE-19 cells (24 h), and although both cell types showed evidence of cytotoxicity, the effects were greater for 661W cells. Both cell types showed enhanced morphologic and biochemical changes with formic acid treatment including earlier and/or greater effects on ATP depletion and cytotoxicity; again effects were more pronounced in 661W cells. Formate therefore is toxic for both cell lines, with 661W cells exhibiting greater sensitivity. Medium pH also appears to play a significant role in formate toxicity in vitro.

Formamides mimic aldehydes and inhibit liver alcohol dehydrogenases and ethanol metabolism

Formamides are unreactive analogues of the aldehyde substrates of alcohol dehydrogenases and are useful for structure-function studies and for specific inhibition of alcohol metabolism. They bind to the enzyme-NADH complex and are uncompetitive inhibitors against varied concentrations of alcohol. Fourteen new branched chain and chiral formamides were prepared and tested as inhibitors of purified Class I liver alcohol dehydrogenases: horse (EqADH E), human (HsADH1C*2), and mouse (MmADH1). In general, larger, substituted formamides, such as N-1-ethylheptylformamide, are better inhibitors of HsADH1C*2 and MmADH1 than of EqADH, reflecting a few differences in amino acid residues that change the sizes of the active sites. In contrast, the linear, alkyl (n-propyl and n-butyl) formamides are better inhibitors of EqADH and MmADH1 than of HsADH1C*2, probably because water disrupts van der Waals interactions. These enzymes are also inhibited strongly by sulfoxides and 4-substituted pyrazoles. The structure of EqADH complexed with NADH and (R)-N-1-methylhexylformamide was determined by x-ray crystallography at 1.6 A resolution. The structure resembles the expected Michaelis complex with NADH and aldehyde, and shows for the first time that the reduced nicotinamide ring of NADH is puckered, as predicted for the transition state for hydride transfer. Metabolism of ethanol in mice was inhibited by several formamides. The data were fitted with kinetic simulation to a mechanism that describes the non-linear progress curves and yields estimates of the in vivo inhibition constants and the rate constants for elimination of inhibitors. Some small formamides, such as N-isopropylformamide, may be useful inhibitors in vivo.

American Academy of Clinical Toxicology practice guidelines on the treatment of methanol poisoning

EPIDEMIOLOGY

Almost all cases of acute methanol toxicity result from ingestion, though rarely cases of poisoning have followed inhalation or dermal absorption. The absorption of methanol following oral administration is rapid and peak methanol concentrations occur within 30-60minutes.

MECHANISMS OF TOXICITY

Methanol has a relatively low toxicity and metabolism is responsible for the transformation of methanol to its toxic metabolites. Methanol is oxidized by alcohol dehydrogenase to formaldehyde. The oxidation of formaldehyde to formic acid is facilitated by formaldehyde dehydrogenase. Formic acid is converted by 10-formyl tetrahydrofolate synthetase to carbon dioxide and water. In cases of methanol poisoning, formic acid accumulates and there is a direct correlation between the formic acid concentration and increased morbidity and mortality. The acidosis observed in methanol poisoning appears to be caused directly or indirectly by formic acid production. Formic acid has also been shown to inhibit cytochrome oxidase and is the prime cause of ocular toxicity, though acidosis can increase toxicity further by enabling greater diffusion of formic acid into cells.

FEATURES

Methanol poisoning typically induces nausea, vomiting, abdominal pain, and mild central nervous system depression. There is then a latent period lasting approximately 12-24 hours, depending, in part, on the methanol dose ingested, following which an uncompensated metabolic acidosis develops and visualfunction becomes impaired, ranging from blurred vision and altered visual fields to complete blindness.

MANAGEMENT

For the patient presenting with ophthalmologic abnormalities or significant acidosis, the acidosis should be corrected with intravenous sodium bicarbonate, the further generation of toxic metabolite should be blocked by the administration of fomepizole or ethanol and formic acid metabolism should be enhanced by the administration of intravenous folinic acid. Hemodialysis may also be required to correct severe metabolic abnormalities and to enhance methanol and formate elimination. For the methanol poisoned patient without evidence of clinical toxicity, the first priority is to inhibit methanol metabolism with intravenous ethanol orfomepizole. Although there are no clinical outcome data confirming the superiority of either of these antidotes over the other, there are significant disadvantages associated with ethanol. These include complex dosing, difficulties with maintaining therapeutic concentrations, the need for more comprehensive clinical and laboratory monitoring, and more adverse effects. Thus fomepizole is very attractive, however, it has a relatively high acquisition cost.

CONCLUSION

The management of methanol poisoning includes standard supportive care, the correction of metabolic acidosis, the administration of folinic acid, the provision of an antidote to inhibit the metabolism of methanol to formate, and selective hemodialysis to correct severe metabolic abnormalities and to enhance methanol and formate elimination. Although both ethanol and fomepizole are effective, fomepizole is the preferred antidote for methanol poisoning.

Formate kinetics in methanol poisoning

OBJECTIVE

We sought to describe the kinetics, dialysis clearance, and laboratory markers of formate (FA), the toxic metabolite of methanol (meOH).

METHODS

Data were obtained from a prospective, multicenter study of fomepizole +/- dialysis for methanol poisoning. Inclusion criteria confirmed methanol exposure or suspicion of exposure plus either acidemia or abnormal osmolar gap. Dialysis indications were [meOH] > 50 mg/dL, pH < 7.1, refractory acidosis, or visual toxicity. Serial plasma formate, methanol, pH, and electrolyte measurements were made. Formate was determined by gas chromatography. Endogenous and dialysis elimination half-lives were calculated as t(1/2) = 0.693/Ke, with Ke (elimination constant) derived from the slope of log (FA) vs. time. Half-lives were compared with an unpaired Student's t-test. Dialysis clearance was calculated using the Fick Principle. Pearson correlation analysis compared initial formate with initial pH, serum bicarbonate, and anion gap.

RESULTS

Eleven patients were treated in the study. Eight had detectable formate with mean [FA] of 15.1 mmol/L (range 0.5-34.8). Endogenous elimination half-life was 205 +/- 90 minutes. Elimination half-life during dialysis (n = 5) was 150 +/- 37 minutes, which was not different (t = 0.22; NS). The overall dialysis formate clearance rate was 223 +/- 25 mL/min. Correlation coefficients were: pH vs. formate r2 = 0.93; bicarbonate vs. formate r2 = 0.81; and anion gap vs. formate r2 = 0.76 (all p < 0.05).

CONCLUSIONS

Although dialysis clears formate, it did not significantly enhance endogenous elimination in our series of patients. Low pH, low bicarbonate, and elevated anion gap correlate independently with formate presence.

Aspartame: review of safety

Over 20 years have elapsed since aspartame was approved by regulatory agencies as a sweetener and flavor enhancer. The safety of aspartame and its metabolic constituents was established through extensive toxicology studies in laboratory animals, using much greater doses than people could possibly consume. Its safety was further confirmed through studies in several human subpopulations, including healthy infants, children, adolescents, and adults; obese individuals; diabetics; lactating women; and individuals heterozygous (PKUH) for the genetic disease phenylketonuria (PKU) who have a decreased ability to metabolize the essential amino acid, phenylalanine. Several scientific issues continued to be raised after approval, largely as a concern for theoretical toxicity from its metabolic components--the amino acids, aspartate and phenylalanine, and methanol--even though dietary exposure to these components is much greater than from aspartame. Nonetheless, additional research, including evaluations of possible associations between aspartame and headaches, seizures, behavior, cognition, and mood as well as allergic-type reactions and use by potentially sensitive subpopulations, has continued after approval. These findings are reviewed here. The safety testing of aspartame has gone well beyond that required to evaluate the safety of a food additive. When all the research on aspartame, including evaluations in both the premarketing and postmarketing periods, is examined as a whole, it is clear that aspartame is safe, and there are no unresolved questions regarding its safety under conditions of intended use.

An in vivo ESR spin-trapping study: free radical generation in rats from formate intoxication--role of the Fenton reaction

Electron spin resonance spectroscopy has been used to study free radical generation in rats with acute sodium formate poisoning. The in vivo spin-trapping technique was used with alpha-(4-pyridyl-1-oxide)-N-t-butylnitrone (POBN), which reacts with free radical metabolites to form radical adducts, which were detected in the bile and urine samples from Fischer rats. The use of [(13)C]-sodium formate and computer simulations of the spectra identified the 12-line spectrum as arising from the POBN/carbon dioxide anion radical adduct. The identification of POBN/*CO(2)(-) radical adduct provides direct electron spin resonance spectroscopy evidence for the formation of *CO(2)(-) radicals during acute intoxication by sodium formate, suggesting a free radical metabolic pathway. To study the mechanism of free radical generation by formate, we tested several known inhibitors. Both allopurinol, an inhibitor of xanthine oxidase, and aminobenzotriazole, a cytochrome P450 inhibitor, decreased free radical formation from formate, which may imply a dependence on hydrogen peroxide. In accord with this hypothesis, the catalase inhibitor 3-aminotriazole caused a significant increase in free radical formation. The iron chelator Desferal decreased the formation of free radicals up to 2-fold. Presumably, iron plays a role in the mechanism of free radical generation by formate via the Fenton reaction. The detection of formate free radical metabolites generated in vivo and the key role of the Fenton reaction in this process may be important for understanding the pathogenesis of both formate and methanol intoxication.

Treatment of methanol and isopropanol poisoning with intravenous fomepizole

CASE REPORT

We report a case of mixed methanol and isopropanol poisoning in a patient who refused dialysis but agreed to treatment with intravenous fomepizole. The patient was asymptomatic on arrival, with initial blood methanol and isopropanol concentrations of 146 mg/dL and 39 mg/dL, respectively. Blood ethanol was undetectable. The patient was treated with fomepizole twice daily intravenously until blood methanol was undetectable. No side effects of therapy, other than transient eosinophilia, were observed. The evolution was uneventful and no metabolites of either alcohol were detected at any time during the hospitalization. The decay of plasma methanol and isopropanol under fomepizole treatment were well described by first-order kinetics. The plasma elimination half-lives of methanol and isopropanol were 47.6 hours and 27.7 hours, respectively. Fomepizole appears to have been effective in blocking the toxic metabolism of both methanol and isopropanol and was associated with a favorable outcome.

Fomepizole for the treatment of methanol poisoning

BACKGROUND

Methanol poisoning may result in metabolic acidosis, blindness, and death. The inhibition of alcohol dehydrogenase is fundamental to the treatment of methanol poisoning. We performed a multicenter study to evaluate fomepizole, an inhibitor of alcohol dehydrogenase, in the treatment of patients with methanol poisoning.

METHODS

We administered intravenous fomepizole to 11 consecutive patients who presented with methanol poisoning at a participating center. Serial clinical and laboratory studies, including measurements of plasma formic acid and fomepizole, were performed. The outcomes measured were the preservation of visual acuity, the resolution of metabolic acidosis, the inhibition of formic acid production, the achievment of therapeutic plasma concentrations of fomepizole with the dosing regimen, residual illness or disability, and death.

RESULTS

Plasma formic acid concentrations were detectable in eight patients, and these concentrations were closely correlated with the initial arterial pH values (r=0.92, P<0.001). In response to fomepizole, plasma formic acid concentrations fell and metabolic abnormalities resolved in all patients. Nine patients survived. Seven patients initially had visual abnormalities, but at the end of the trial no surviving patient had any detectable visual deficits related to methanol poisoning. Fomepizole had few adverse effects. The two patients who died had anoxic brain injury that was present at the time of enrollment. During treatment, methanol had an elimination half-life of 54 hours.

CONCLUSIONS

Fomepizole appears to be safe and effective in the treatment of methanol poisoning.

Proposal for reference concentrations (RfC) for inhalation exposure to methanol

A tentative reference concentration (RfC) for methanol in ambient air, i.e. an exposure concentration below which adverse effects are not expected to occur, was derived from the analysis of the toxicological data available in the literature. Well-documented studies that correlate environmental levels of methanol with observed toxic effects have not been found in the literature, nor have any long-term epidemiological studies of chronic low-level occupational exposure been found. Assessment of RfC for acute inhalation exposure is based on a human study (n=26 subjects) with a 'tentative' NOAEL of 262 mg/m(3). The calculated RfC for 1 h exposure is 104.8 mg/m(3). The RfC is given a low confidence rating as there was only one methanol concentration used. A well designed study on monkeys served as the basis for the assessment of RfC for chronic inhalation exposure. In this study, 13.1 and 131 mg/m(3) were considered as NOAEL and LOAEL, respectively. The calculated RfC is 0.38 mg/m(3). The overall database is weak, lacking data on reproductive and developmental endpoints in human or non-human primates. Nevertheless, the RfC is given a medium confidence rating because of the strength of the principal study.

Protective effect of N-acetylcysteine on reduced glutathione, reduced glutathione-related enzymes and lipid peroxidation in methanol intoxication

The primary metabolic appropriation of methanol is oxidation to formaldehyde and then to formate. These processes are accompanied by formation of superoxide anion and hydrogen peroxide. This paper reports data on the effect of N-acetylcysteine (NAC) on reduced glutathione (GSH) and on activity of some GSH-metabolising enzymes in the liver, erythrocytes and serum of rats intoxicated with methanol (3 g/kg b.w.) during 7 days after intoxication. Methanol administration, increasing concentration of the lipid peroxidation products, decreased the liver glutathione-peroxidase and glutathione reductase (GSSG-R) activities, GSH concentration and total antioxidant status (TAS). The use of NAC after methanol ingestion apparently diminished lipid peroxidation, elevated the GSH level in the liver and erythrocytes, and increased activity of GSH-related enzymes in the serum, erythrocytes and in the liver. These results suggest that NAC exerts its protective effect by acting as a precursor for glutathione, the main low molecular antioxidant and as a free radical scavenger.