Biological effects and metabolic interactions after chronic and acute administration of 4-methylpyrazole and ethanol to rats

Computational identification of potential bioactive compounds from Triphala against alcoholic liver injury by targeting alcohol dehydrogenase

Alcoholic liver injury resulting from excessive alcohol consumption is a significant social concern. Alcohol dehydrogenase (ADH) plays a critical role in the conversion of alcohol to acetaldehyde, leading to tissue damage. The management of alcoholic liver injury encompasses nutritional support and, in severe cases liver transplantation, but potential adverse effects exist, and effective medications are currently unavailable. Natural products with their potential benefits and historical use in traditional medicine emerge as promising alternatives. Triphala, a traditional polyherbal formula demonstrates beneficial effects in addressing diverse health concerns, with a notable impact on treating alcoholic liver damage through enhanced liver metabolism. The present study aims to identify potential active phytocompounds in Triphala targeting ADH to prevent alcoholic liver injury. Screening 119 phytocompounds from the Triphala formulation revealed 62 of them showing binding affinity to the active site of the ADH1B protein. Promising lipid-like molecule from Terminalia bellirica, (4aS, 6aR, 6aR, 6bR, 7R, 8aR, 9R, 10R, 11R, 12aR, 14bS)-7, 10, 11-trihydroxy-9-(hydroxymethyl)-2, 2, 6a, 6b, 9, 12a-hexamethyl-1, 3, 4, 5, 6, 6a, 7, 8, 8a, 10, 11, 12, 13, 14b-tetradecahydropicene-4a-carboxylic acid showed high binding efficiency to a competitive ADH inhibitor, 4-Methylpyrazole. Pharmacokinetic analysis further confirmed the drug-likeness and non-hepatotoxicity of the top-ranked compound. Molecular dynamics simulation and MM-PBSA studies revealed the stability of the docked complexes with minimal fluctuation and consistency of the hydrogen bonds throughout the simulation. Together, computational investigations suggest that (4aS, 6aR, 6aR, 6bR, 7R, 8aR, 9R, 10R, 11R, 12aR, 14bS)-7, 10, 11-trihydroxy-9-(hydroxymethyl)-2, 2, 6a, 6b, 9, 12a-hexamethyl-1, 3, 4, 5, 6, 6a, 7, 8, 8a, 10, 11, 12, 13, 14b-tetradecahydropicene-4a-carboxylic acid from the Triphala formulation holds promise as an ADH inhibitor, suggesting an alternative therapy for alcoholic liver injury.

From Ethanol to Salsolinol: Role of Ethanol Metabolites in the Effects of Ethanol

In spite of the global reputation of ethanol as the psychopharmacologically active ingredient of alcoholic drinks, the neurobiological basis of the central effects of ethanol still presents some dark sides due to a number of unanswered questions related to both its precise mechanism of action and its metabolism. Accordingly, ethanol represents the interesting example of a compound whose actions cannot be explained as simply due to the involvement of a single receptor/neurotransmitter, a scenario further complicated by the robust evidence that two main metabolites, acetaldehyde and salsolinol, exert many effects similar to those of their parent compound. The present review recapitulates, in a perspective manner, the major and most recent advances that in the last decades boosted a significant growth in the understanding on the role of ethanol metabolism, in particular, in the neurobiological basis of its central effects.

Fenofibrate--a lipid-lowering drug--reduces voluntary alcohol drinking in rats

The administration of disulfiram raises blood acetaldehyde levels when ethanol is ingested, leading to an aversion to alcohol. This study was aimed at assessing the effect of fenofibrate on voluntary ethanol ingestion in rats. Fenofibrate reduces blood triglyceride levels by increasing fatty acid oxidation by liver peroxisomes, along with an increase in the activity of catalase, which can oxidize ethanol to acetaldehyde. UChB drinker rats were allowed to consume alcohol 10% v/v freely for 60 days, until consumption stabilized at around 7 g ethanol/kg/24 h. About 1-1.2 g ethanol/kg of this intake is consumed in the first 2 h of darkness of the circadian cycle. Fenofibrate subsequently administered (50 mg/kg/day by mouth [p.o.]) for 14 days led to a 60-70% (p < 0.001) reduction of 24-h ethanol consumption. When ethanol intake was determined within the first 2 h of darkness, the reduction was 85-90% (p < 0.001). We determined whether animals chronically allowed access to ethanol and subsequently treated with fenofibrate, would a) increase liver catalase activity, and b) increase blood acetaldehyde levels after a 24-h ethanol deprivation and the subsequent administration of 1 g ethanol/kg. The oral administration of 1 g ethanol/kg produced a rapid increase in blood (arterial) acetaldehyde in fenofibrate-treated animals versus controls also administered 1 g/kg ethanol (70 μM vs. 7 μM; p < 0.001). Liver catalase activity following fenofibrate treatment was increased 3-fold (p < 0.01). Other hepatic enzymes responsible for the metabolism of ethanol (alcohol dehydrogenase and aldehyde dehydrogenase) remained unchanged. No liver damage was induced, as measured by serum glutamic-pyruvic transaminase (GPT) activity. The effect of fenofibrate in reducing alcohol intake was fully reversible. Overall, in rats allowed chronic ethanol intake, by mouth (p.o.), fenofibrate administration increased liver catalase activity and reduced voluntary ethanol intake. The administration of 1 g ethanol/kg (p.o.) to these animals increased blood acetaldehyde levels in fenofibrate-treated animals, suggesting the possible basis for the reduction in ethanol intake.

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.

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.

Bradycardia and hypotension associated with fomepizole infusion during hemodialysis

We report a case of hypotension and bradycardia associated with intravenous fomepizole infusion.

CASE REPORT

A 59-year-old man presented to hospital 10 hours after ethylene glycol ingestion with ataxia, slurred speech, metabolic acidosis, heart rate 70/min, blood pressure 160/100 mmHg. Treatment with hemodialysis and fomepizole began 7.5 hours after admission. Severe bradycardia (29/min) and hypotension (69 mmHg systolic) occurred immediately following a 30 minute intravenous infusion of the first (19 mg/kg) fomepizole dose, but rapidly corrected with 1 mg atropine. Transient bradycardia (48/min) and hypotension (89/57 mmHg) recurred immediately after the second (10 mg/kg) fomepizole dose, also given during dialysis.

DISCUSSION

Hemodialysis may cause a drop in blood pressure and heart rate; however, the close temporal relationship with fomepizole infusions, dose-related symptom intensity and recurrence with rechallenge suggest a causal relationship with fomepizole. Hemodialysis, acidosis and high initial fomepizole dose may have enhanced patient susceptibility, as a post-dialysis fomepizole dose was well tolerated.

CONCLUSION

Fomepizole may precipitate bradycardia and/or hypotension during hemodialysis. Monitor vital signs closely during and immediately after infusion.

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.

Pretreatment of CD-1 mice with 4-methylpyrazole blocks toxicity from the gamma-hydroxybutyrate precursor, 1,4-butanediol

1,4-Butanediol (1,4-BD) is the dihydroxy precursor of gamma-hydroxybutyrate (GHB), a popular recreational drug that has been banned by the United States Food and Drug Administration (FDA) and controlled as a federal schedule I drug. 1,4-BD is enzymatically converted in vivo to GHB by alcohol dehydrogenase (ADH), and overdoses can result in coma, severe respiratory depression, bradycardia, hypothermia, seizures, and death. Presently, there is no antidote. We pretreated CD-1 mice with the ADH antagonist, 4-methylpyrazole (4-MP), to determine if blocking ADH can prevent or decrease toxicity from 1,4-BD overdose. Pretreatment with 4-MP increased the Toxic Dose-50 (TD(50)) of 1,4-BD for the righting reflex from 585 mg/kg (95% CI, 484-707 mg/kg) in control mice to 5,550 mg/kg (95% CI, 5,353-5,756 mg/kg) in pretreated mice. Pretreatment with 4-MP also increased the TD(50) of 1,4-BD for the rotarod test from 163 mg/kg (95% CI, 136-196 mg/kg) in control mice to 4,900 mg/kg (95% CI, 4,812-4,989 mg/kg) in pretreated mice. Pretreatment with 4-MP significantly decreased the toxicity of 1,4-BD in CD-1 mice, presumably by inhibiting its ADH biotransformation to GHB. 4-MP warrants further investigation as a potential antidote for this increasingly abused drug.

The mode of toxic action of the pesticide gliftor: the metabolism of 1,3-difluoroacetone to (-)-erythro-fluorocitrate

The biochemical toxicology of 1,3-difluoroacetone, a known metabolite of the major ingredient of the pesticide Gliftor (1,3-difluoro-2-propanol), was investigated in vivo and in vitro. Rat kidney homogenates supplemented with coenzyme A, ATP, oxaloacetate, and Mg2+ converted 1,3-difluoroacetone to (-)-erythro-fluorocitrate in vitro. Administration of 1,3-difluoroacetone (100 mg kg(-1) body weight) to rats in vivo resulted in (-)-erythro-fluorocitrate synthesis in the kidney, which was preceded by an elevation in fluoride levels and followed by citrate accumulation. Animals dosed with 1,3-difluoroacetone did not display the 2-3 hour lag phase in either (-)-erythro-fluorocitrate synthesis or in citrate and fluoride accumulation characteristic of animals dosed with 1,3-difluoro-2-propanol. We demonstrate that the conversion of 1,3-difluoro-2-propanol to 1,3-difluoroacetone by an NAD+-dependent oxidation is the rate-limiting step in the synthesis of the toxic product, (-)-erythro-fluorocitrate from 1,3-difluoro-2-propanol. Prior administration of 4-methylpyrazole (90 mg kg(-1) body weight) was shown to prevent the conversion of 1,3-difluoro-2-propanol (100 mg kg(-1) body weight) to (-)-erythro-fluorocitrate in vivo and to eliminate the fluoride and citrate elevations seen in 1,3-difluoro-2-propanol-intoxicated animals. However, administration of 4-methylpyrazole (90 mg kg(-1) body weight) to rats 2 hours prior to 1,3-difluoroacetone (100 mg kg(-1) body weight) was ineffective in preventing (-)-erythro-fluorocitrate synthesis and did not diminish fluoride or citrate accumulation in vivo. We conclude that the prophylactic and antidotal properties of 4-methylpyrazole seen in animals treated with 1,3-difluoro-2-propanol derive from its capacity to inhibit the NAD+-dependent oxidation responsible for converting 1,3-difluoro-2-propanol to 1,3-difluoroacetone in the committed step of the toxic pathway.

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.

American Academy of Clinical Toxicology Practice Guidelines on the Treatment of Ethylene Glycol Poisoning. Ad Hoc Committee

Fomepizole (4-methylpyrazole, 4-MP, Antizol) is a potent inhibitor of alcohol dehydrogenase that was approved recently by the US Food and Drug Administration (FDA) for the treatment of ethylene glycol poisoning. Although ethanol is the traditional antidote for ethylene glycol poisoning, it has not been studied prospectively. Furthermore, the FDA has not approved the use of ethanol for this purpose. Case reports and a prospective case series indicate that the intravenous (i.v.) administration of fomepizole every 12 hours prevents renal damage and metabolic abnormalities associated with the conversion of ethylene glycol to toxic metabolites. Currently, there are insufficient data to define the relative role of fomepizole and ethanol in the treatment of ethylene glycol poisoning. Fomepizole has clear advantages over ethanol in terms of validated efficacy, predictable pharmacokinetics, ease of administration, and lack of adverse effects, whereas ethanol has clear advantages over fomepizole in terms of long-term clinical experience and acquisition cost. The overall comparative cost of medical treatment using each antidote requires further study.

Fomepizole for the treatment of ethylene glycol poisoning. Methylpyrazole for Toxic Alcohols Study Group

BACKGROUND

Ethylene glycol poisoning causes metabolic acidosis and renal failure and may cause death. The standard treatment is inhibition of alcohol dehydrogenase with ethanol, given in intoxicating doses, and adjunctive hemodialysis. We studied the efficacy of fomepizole, a new inhibitor of alcohol dehydrogenase, in the treatment of ethylene glycol poisoning.

METHODS

We administered intravenous fomepizole to 19 patients with ethylene glycol poisoning (plasma ethylene glycol concentration, > or =20 mg per deciliter [3.2 mmol per liter]). Patients who met specific criteria also underwent hemodialysis. Treatment was continued until plasma ethylene glycol concentrations were less than 20 mg per deciliter. Acid-base status, renal function, the kinetics of fomepizole, and ethylene glycol metabolism were assessed at predetermined intervals.

RESULTS

Fifteen of the patients initially had acidosis (mean serum bicarbonate concentration, 12.9 mmol per liter). Acid-base status tended to normalize within hours after the initiation of treatment with fomepizole. One patient with extreme acidosis died. In nine patients, renal function decreased during therapy; at enrollment, all nine had high serum creatinine concentrations and markedly elevated plasma glycolate concentrations (> or =97.7 mg per deciliter [12.9 mmol per liter]). None of the 10 patients with normal serum creatinine concentrations at enrollment had renal injury during treatment; all 10 had plasma glycolate concentrations at or below 76.8 mg per deciliter (10.1 mmol per liter). Renal injury was independent of the initial plasma ethylene glycol concentration. The plasma concentration of glycolate and the urinary excretion of oxalate, the major metabolites of ethylene glycol, uniformly fell after the initiation of fomepizole therapy. Few adverse effects were attributable to fomepizole.

CONCLUSIONS

In patients with ethylene glycol poisoning, fomepizole administered early in the course of intoxication prevents renal injury by inhibiting the formation of toxic metabolites.

Anesthetic potencies of n-alkanols: results of additivity and solubility studies suggest a mechanism of action similar to that for conventional inhaled anesthetics

The mechanism by which n-alkanols produce anesthesia and the characteristics relevant to those mechanisms (e.g., lipid solubilities versus potencies) remain unknown. Accordingly, we determined potencies (minimum alveolar anesthetic concentration [MAC]) and solubilities of normal methanol, ethanol, butanol, hexanol, and octanol. We also determined the additivity of these alkanols with a conventional anesthetic (desflurane) and the additivity of methanol with butanol. Finally, we determined whether alkanol metabolism influences alkanol potencies. MAC for methanol, ethanol, butanol, hexanol, and octanol (0.00200, 0.000989, 0.000133, 0.0000214, and 0.00000117 atm, respectively) increased with an increasing solubility in olive oil (olive oil/gas partition coefficients 48.6, 108, 1,650, 11,600, and 93,500, respectively) and octanol (octanol/gas partition coefficients 163, 1,150, 22,900, 135,000, and 4,140,000) to give a product of MAC x solubility for olive oil approximately 10 times less (values of 0.10-0.25) than that expected from the Meyer-Overton hypothesis (compared with conventional inhaled anesthetics). There was less deviation for octanol, but the results were more variable. Inhibition of methanol and butanol metabolism by 4-methylpyrazole did not alter MAC. Methanol, ethanol, butanol, hexanol, and octanol had approximately additive anesthetic effects with desflurane, with some small but statistically significant deviations both above and below additivity. In the presence of 0.5 MAC of desflurane, we needed to add 0.4-0.6 MAC of each alkanol to inhibit the movement of 50% of the rats in response to noxious stimulation. Similarly, the effects of methanol and butanol were additive (with each other). The saline/gas partition coefficient for each alkanol was high (3700, 2650, 1400, 900, and 709 for methanol through octanol), which indicates high polarity. We conclude that the potent anesthetic effects of normal alkanols may result from an affinity to both polar and nonpolar phases. Our finding of additivity of alkanols with each other is consistent with a common mechanism of action. Similarly, the finding of additivity or slight deviations from additivity for alkanols with desflurane is consistent with mechanisms of action that have much in common.

Kinetic interactions between 4-methylpyrazole and ethanol in healthy humans

4-Methylpyrazole (4-MP), a potent inhibitor of alcohol dehydrogenase activity, is a candidate to replace ethanol as the antidote for methanol and ethylene glycol intoxications, because it has a longer duration of action and apparently fewer adverse effects. To study a probable mutual inhibitory effect between ethanol and 4-MP on their elimination, two studies were performed in healthy human volunteers using double-blind crossover designs. In study A1 4-MP in the presumed therapeutic dose range of 10 to 20 mg/kg caused a 40% reduction in the rate of elimination of ethanol in 12 subjects given 0.5 to 0.7 g/kg of ethanol. These data suggest that such doses of 4-MP inhibit alcohol dehydrogenase activity in humans in vivo and would be effective at blocking methanol or ethylene glycol metabolism. In study B, ethanol (0.6 g/kg followed by 0.2 g/kg twice) significantly decreased the rate of elimination of 4-MP (5 mg/kg, given intravenously to four subjects). These moderate doses of ethanol also inhibited the rate of urinary excretion of 4-carboxypyrazole, the primary metabolite of 4-MP in humans. Data suggest that ethanol inhibits 4-MP metabolism, thereby increasing the duration of therapeutic blood levels of 4-MP in the body. This mutual interaction may have clinical implications, because most self-poisoned patients have also ingested ethanol. Theoretically, methanol and ethylene glycol might also show such interactions with 4-MP.

Alcohols synergize with NGF to induce early differentiation of PC12 cells

The role of alcohols in affecting neuromorphogenesis was investigated in a single cell type, pheochromocytoma (PC12). The effect of ethanol at physiological concentrations in this system leads to enhanced morphological and functional differentiation in combination with nerve growth factor (NGF). PC12 cells treated with a suboptimal concentration of NGF (30 ng/ml) and an alcohol (87 mM) underwent rapid morphological differentiation which was dependent upon the side chain length of the alcohol MeOH less than EtOH less than PrOH less than BuOH. Pyrazole at either 5 or 10 mM had no effect on alcohol induced neurite extension. Assessment of the degree of differentiation promoted by the various alcohols was quantified by an increase in neurite extension, a decrease in the incorporation of [3H]thymidine, an increase in acetylcholine esterase (AChE) activity and immunostaining with neuron specific enolase. Thus, alcohols may function in a specific manner by interacting with transmembrane signalling pathways which promote gene expression and neuronal differentiation.

Effects of 4-methylpyrazole, methanol/ethylene glycol antidote, in healthy humans

4-Methylpyrazole (4-MP), an inhibitor of alcohol dehydrogenase, may be useful for the treatment of methanol and ethylene glycol intoxications. A placebo-controlled, double blind, multiple dose, sequential, ascending-dose study has been performed to determine the tolerance of 4-MP in healthy volunteers. Oral loading doses of 4-MP were followed by supplemental doses every 12 h through 5 days, producing plasma levels in the therapeutic range. A slight, transient elevation in one or both serum transaminase values was observed in 6 of the 15 subjects treated with 4-MP. This effect was not dose related nor apparently mediated through a hypersensitivity reaction. Serum triglyceride levels were increased in 30% of 4-MP treated subjects, but also in 25% of the placebo subjects. 4-MP treatment did not produce any other significant changes in objective clinical parameters nor in subjective side effects. The results suggest that a mild, transient increase in liver function tests might be observed in some subjects treated with multiple doses of 4-MP. Nevertheless, the slower elimination rate and lesser degree of toxicity of 4-MP would make it preferable to ethanol in therapy of these poisonings.

Non-linear kinetics of 4-methylpyrazole in healthy human subjects

In order to evaluate the pharmacokinetic profile of the alcohol dehydrogenase inhibitor 4-methylpyrazole 4-MP, a placebo-controlled, double-blind, single-dose, randomized, sequential, ascending-dose "Phase-I study" was performed in healthy male volunteers at dose levels of 10 (n = 4), 20 (n = 4), 50 (n = 4) and 100 mg.kg-1 (n = 3). In the 10 and 20 mg.kg-1 group, the elimination of 4-MP from the plasma followed non-linear kinetics with mean rates of concentration decline of 3.66 and 5.05 mumol.l-1.h-1, respectively. In the two highest dose groups, the elimination also appeared to be non-linear although the patterns were not followed long enough to confirm this. The mean rates of concentration decline at the higher doses were significantly increased, up to 14.9 mumol.l-1.h-1 at 100 mg.kg-1. The average renal clearance of 4-MP was low, 0.016 ml.min-1.kg-1, and only 3% of the administered dose was excreted unchanged in the urine, indicating metabolism as the major route of elimination. Because of the apparently unusual kinetics following single dose treatment, thorough multiple dose studies need to be carried out to determine a safe dosage regimen for 4-MP.

4-Methylpyrazole: a controlled study of safety in healthy human subjects after single, ascending doses

4-Methylpyrazole (4-MP), an inhibitor of alcohol dehydrogenase, is a possible future drug for the treatment of methanol and ethylene glycol intoxications and the severe ethanol-disulfiram reaction. Therefore a placebo-controlled, double-blind, single-dose, randomized, sequential, ascending-dose "Phase I study" was performed in healthy volunteers in order to determine the tolerance of 4-MP at dose levels of 10 (n = 4), 20 (n = 4), 50 (n = 4), and 100 mg/kg (n = 3). Along with each dose group, there were two placebos except with the 100 mg/kg group where there was only one placebo. In the 10 and 20 mg/kg group there were no side-effects in any subject. At the 50 mg/kg level, three out of four subjects experienced slight to moderate nausea and dizziness from 0 to 2.5 h after dosing. In the 100 mg/kg group all three subjects reported side-effects like nausea, dizziness, and vertigo, that were short-lived in two subjects, but lasted up to 30 h in one subject. The study was stopped after evaluation of the latter subject, so fewer subjects were completed in this last group. Despite these subjective side-effects, there were no significant changes in objective clinical parameters like pulse, blood pressure, body temperature, or blood and urine chemistries. We conclude that at a single dose of 4-MP (10-20 mg/kg) producing plasma levels within a probable therapeutic range, no side-effects were attributed to 4-MP.

Distribution of oral 4-methylpyrazole in the rat: inhibition of elimination by ethanol

4-Methylpyrazole (4-MP), a potent competitive inhibitor of alcohol dehydrogenase activity, is being studied as a therapeutic agent for methanol and ethylene glycol poisoning. In order to evaluate the distribution of 4-MP using doses in the potentially therapeutic range, male Sprague-Dawley rats were administered 4-MP orally at zero time in doses of 5, 10, or 20 mg/kg. Half of the rats were also treated orally at 0, 1, 2, and 3 h with ethanol (1 g/kg each h) and half with glucose in isocaloric amounts. At doses of 10 and 20 mg/kg, 4-MP elimination appeared to be saturated, with an elimination rate of 10 mumol/L/h. Elimination at 5 mg/kg was non-conclusive as to the order. The rate of 4-MP elimination was decreased about 50% by concomitant administration of ethanol. Urinary excretion of unchanged 4-MP accounted for only about 1% of the dose; the amount excreted unchanged was significantly increased by ethanol administration. The results demonstrate the mutual inhibition of metabolism by ethanol and 4-methylpyrazole, which may explain why the inhibition of ADH by 4-MP can be longer than that predicted by the elimination rate of 4-MP alone.

Blood acetaldehyde and the ethanol-induced increase in splanchnic circulation

Acute oral administration of ethanol significantly increases (50-60%) portal blood flow to the liver. As earlier studies have indicated that this effect is maximal at concentrations of ethanol that saturate the alcohol dehydrogenase (ADH) system and is blocked by the ADH inhibitor 4-methylpyrazol, we investigated the possible role of acetaldehyde, a product in the ADH reaction, as a mediator of this effect. In the first series of experiments it was shown that, contrary to expectations, cyanamide administration prior to alcohol suppressed fully the effect of ethanol on portal blood flow without altering it in the absence of ethanol [ethanol = 69.5 +/- 5.6; ethanol + cyanamide 42.9 +/- 2.4; control = 43.0 +/- 3.0; cyanamide = 55.1 +/- 3.7 ml X min-1 X (kg body wt)-1]. Arterial blood concentrations of acetaldehyde were elevated from 3.6 +/- 0.3 microM in the presence of ethanol to 293 +/- 48 microM in the presence of ethanol + cyanamide. Infusion of acetaldehyde either into the left ventricle, resulting in arterial blood acetaldehyde levels of 227 +/- 77 microM, or into the portal circulation, resulting in arterial blood levels of 198 +/- 40 microM, did not modify portal blood flow or splanchnic hemodynamics, nor the effect of ethanol per se. The combination of cyanamide + ethanol significantly reduced total peripheral resistance (from 28 +/- 3 to 19 +/- 2 dyne X cm X sec-5), while neither ethanol or cyanamide per se, nor acetaldehyde affected total peripheral resistance. Data suggest that acetaldehyde is not involved in the ethanol-mediated increase in portal vein flow. Further studies indicate that the effects of cyanamide in suppressing the ethanol-induced increase in portal blood flow and increasing total peripheral resistance appear to be related to an ethanol-cyanamide interaction which is independent of the acetaldehyde levels in the circulation.

Non-specific prolongation of the effects of general depressants by pyrazole and 4-methylpyrazole

The liver alcohol dehydrogenase inhibitors, pyrazole and 4-methylpyrazole, have been tested for their ability to prolong drug-induced sleep times in mice. Both drugs (at 1 mmol kg-1 i.p.) prolonged the duration of loss of righting reflex following chloral hydrate, pentobarbitone, barbitone, temazepam and halothane, but not diethyl ether. This suggests that the effects of these pyrazoles are not specific to the inhibition of liver alcohol dehydrogenase.

Methanol and ethylene glycol poisonings. Mechanism of toxicity, clinical course, diagnosis and treatment

Methanol and ethylene glycol poisonings share many characteristics both clinically and biochemically. Both alcohols are metabolised via alcohol dehydrogenase to their toxic metabolites. Methanol is slowly metabolised to formaldehyde which is rapidly metabolised to formate, the metabolite mainly responsible for methanol toxicity. Formate metabolism depends upon the folate pool which is small in primates compared with other animals. Therefore, formate accumulates in primates during methanol intoxication and is mainly responsible for the metabolic acidosis in the early stage of intoxication. In late stages lactate may also accumulate, mainly due to formate inhibition of the respiratory chain. This tissue hypoxia caused by formate may explain the ocular as well as the general toxicity. Ethylene glycol is metabolised more rapidly than methanol, via alcohol dehydrogenase to glycolaldehyde which is rapidly metabolised to glycolate, the metabolite mainly responsible for the metabolic acidosis in ethylene glycol poisoning. Glycolate is metabolised by various pathways, including one to oxalate which rapidly precipitates with calcium in various tissues and in the urine. Ethylene glycol toxicity is complex and not fully understood, but is mainly due to the severe metabolic acidosis caused by glycolate and to the calcium oxalate precipitation. The clinical course in both poisonings is initially characterised by the development of metabolic acidosis following a latent period, which is more pronounced in methanol poisoning and is the time taken for both alcohols to be metabolised to their toxic metabolites. In methanol poisoning there are usually visual symptoms progressing to visual impairment, whereas ethylene glycol victims develop renal and cardiopulmonary failure. Prognosis is excellent in both poisonings provided that there is early treatment with alkali to combat acidosis, ethanol as an antimetabolite, and haemodialysis to remove the alcohols and their toxic metabolites. Ethanol is also metabolised by alcohol dehydrogenase, but has a much higher affinity for this enzyme than methanol and ethylene glycol. Presence of ethanol will therefore inhibit formation of toxic metabolites from methanol and ethylene glycol. Due to competition for the enzyme, the therapeutic ethanol concentration depends on the concentration of the other two alcohols, but a therapeutic ethanol concentration around 22 mmol/L (100 mg/dl) is generally recommended. Most patients are, however, admitted at a late stage to hospitals not capable of performing analyses of these alcohols or their specific metabolites on a 24-hour basis.(ABSTRACT TRUNCATED AT 400 WORDS)

4-Methylpyrazole may be an alternative to ethanol therapy for ethylene glycol intoxication in man

4-Methylpyrazole (4 MP) is a strong inhibitor of alcohol dehydrogenase. Its use in acute ethylene glycol (EG) or methanol intoxication has been suggested in experimental studies about its efficacy and safety. We report three cases of accidental intoxication with ethylene glycol in man treated orally with 20 mg/kg/day of 4 MP. The treatment was maintained until plasma EG concentrations became unmeasurable. The patients were admitted early during the course of the poisoning. Their neurological status was good. A slight metabolic acidosis observed in two cases was easily corrected and did not recur. Renal function remained normal in all cases. No patient underwent hemodialysis. On admission plasma EG concentrations were 24.2 mmol/l, 13 mmol/l and 9.7 mmol/l respectively. Plasma EG half-lives were 14.5, 11.5 and 14.75 hours respectively. Plasma oxalate concentrations and the rate of urine oxalate elimination, determined in two patients, were high on admission but quickly returned to normal. Concerning possible side effects of 4 MP, a skin rash was observed in one patient and a possible eosinophilia in the others. These three cases suggest that 4 MP may decrease the metabolic consequences of EG poisoning in man and may be of therapeutic value when administered early during the course of the intoxication before coma, seizures and organic renal failure have occurred.

Interaction of pyrazole and 4-methylpyrazole with hepatic microsomes: effect on cytochrome P-450 content, microsomal oxidation of alcohols, and binding spectra

Microsomes isolated from rats treated with either pyrazole or 4-methylpyrazole, potent inhibitors of alcohol dehydrogenase, catalyzed the oxidation of ethanol and 2-butanol at rates 2-3-fold higher than saline controls. Time course experiments and dose-response experiments indicated that an increase in the microsomal oxidation of alcohols could be observed 24 hr after a single treatment with 200 mg/kg body weight of either pyrazole or 4-methylpyrazole, and after 2 or 3 days of treatment with 50 mg/kg of either of these compounds. The pyrazole treatment did not change the activity of NADPH-cytochrome P-450 reductase, the content of cytochrome P-450, or the oxidation of aminopyrine. Hence, microsomal oxidation of alcohols was increased by the pyrazole treatment whether results were expressed "per mg of protein" or "per nmol of P-450." Microsomes from the pyrazole-treated rats displayed an increase in binding spectrum with ethanol as the substrate as compared to controls, as well as type 2 binding spectrum with dimethyl sulfoxide and 2-butanol. These results suggest the possibility that pyrazole may induce an alcohol-preferring P-450 isozyme. By contrast, the 4-methylpyrazole treatment, besides increasing the oxidation of alcohols, also increased the oxidation of aminopyrine and the content of cytochrome P-450. The increase in the oxidation of alcohols and aminopyrine was primarily due to the increase in content of P-450 produced by the 4-methylpyrazole treatment. Binding spectra with dimethyl sulfoxide and 2-butanol were also observed after 4-methylpyrazole treatment; however, the 2-butanol-binding spectrum was a modified type 1 spectrum, not type 2.(ABSTRACT TRUNCATED AT 250 WORDS)

Voluntary consumption of ethanol and its consequences in C57 mice treated with 4-methylpyrazole

Daily injections of the alcohol dehydrogenase inhibitor 4-methylpyrazole (4MP) were administered to C57BL/6J mice offered continuous free access to food, water and 10% v/v ethanol. There was a significant correlation (r = -0.82) between the rate of ethanol consumption during pretreatment and the effect of 4MP on subsequent intake. Mice drinking more than 2.5 g/kg per day decreased their intake, while subjects drinking less than this amount increased the quantity of ethanol self-administered. The elevated concentrations of plasma ethanol which resulted from voluntary consumption were sufficient to produce intoxication but did not induce physical dependence. Presenting mice with 10% ethanol as their only fluid or offering them a choice of water and saccharin-sweetened ethanol increased intake but failed to raise plasma ethanol to the concentrations observed in mice offered unflavored ethanol and water, and treated with 4MP. The evidence suggests that plasma ethanol does not limit voluntary drinking in untreated mice and that concentrations of 135 to 250 mg/dl are not avoided by C57 mice in a free-choice situation.

Effect of triiodothyronine on alcohol dehydrogenase and aldehyde dehydrogenase activities in rat liver. Implications for the control of ethanol metabolism

Treatment of rats with 20 micrograms of 3,3',5-triiodo-L-thyronine (T3) per 100 g body wt for a period of 6 days led to a 45% decrease in total liver alcohol dehydrogenase and a 36% decrease in total liver aldehyde dehydrogenase. Most of the latter decrease was directly attributable to a 57% fall in the level of the physiologically-important low Km mitochondrial isoenzyme. The high Km isoenzyme of the postmitochondrial and soluble fractions was much less affected by T3-treatment. T3, at concentrations up to 0.1 mM, did not inhibit the activity of aldehyde dehydrogenase in vitro. Despite these large losses of the two enzymes most intimately involved in ethanol metabolism, the rate of ethanol elimination in vivo was the same in T3-treated and control animals. Moreover, there was no difference between the two groups in the susceptibility of ethanol elimination to inhibition by 4-methylpyrazole, making it unlikely that an alternative route of ethanol metabolism had been significantly induced by treatment with T3. As it had been suggested that T3 might create a "hypermetabolic state" in which constraints normally imposed on alcohol dehydrogenase and aldehyde dehydrogenase are removed thereby compensating for any loss in total enzymic activity, 2,4-dinitrophenol (0.1 mmoles/kg body wt) was administered to rats in order to raise the general metabolic rate. However, the uncoupler proved to be lethal to T3-treated animals and did not stimulate ethanol elimination in controls. The results do not support the notion that ethanol elimination in vivo is normally governed either by the level of alcohol dehydrogenase or by that of hepatic aldehyde dehydrogenase. However, the mode of control remains unclear.

Suppression of acetaldehyde accumulation by 4-methylpyrazole in alcohol-hypersensitive Japanese

Alcohol-sensitive Japanese subjects with facial flushing and an increase in heart rate during ethanol intoxication exhibited marked individual variation in accumulation of acetaldehyde. This variation correlated well with the intensity of the above mentioned physiological responses. Oral pretreatment with 10 mg/kg 4-methylpyrazole, which inhibited the ethanol elimination rate by 15-25%, strongly suppressed both acetaldehyde accumulation and the associated responses. Under this condition, the sensitivity to acetaldehyde appeared to be reduced, and the correlation between the acetaldehyde level and the physiological responses disappeared. The effectiveness of even a low dose of 4-methylpyrazole suggests its clinical usefulness for alleviation of acute acetaldehyde toxicity in alcohol-hypersensitive Japanese individuals as well as in disulfiram-treated alcoholics.

Increased microsomal oxidation of alcohols after pyrazole treatment and its similarities to the induction by ethanol consumption

Microsomes isolated from rats treated for 3 days with 200 mg/kg body wt. per day of pyrazole, a potent inhibitor of alcohol dehydrogenase, catalyzed the oxidation of ethanol and 2-butanol at rates 2-3-fold higher than saline controls. This increase was blocked by carbon monoxide, and was not associated with an increase in the oxidation of aminopyrine or in the content of cytochrome P-450, suggesting the possibility of an induction of an alcohol-preferring cytochrome P-450 by pyrazole. Microsomes from the pyrazole-treated rats displayed a stereochemical preference for the oxidation of the (+)-2-butanol isomer over the (-)-2-butanol isomer, which was blocked by carbon monoxide, and also displayed a type-2 binding spectrum with dimethylsulfoxide or 2-butanol. No such spectrum was found with the saline controls. These properties are similar to those which are observed with microsomes from chronic ethanol-fed rats. These similarities suggest the possibility that pyrazole treatment may induce a cytochrome P-450 isozyme with properties similar to the ethanol-inducible cytochrome P-450.

Studies on the effect of 4-methylpyrazole on methanol poisoning using the monkey as an animal model: with particular reference to the ocular toxicity

Young cynomolgus monkeys (Macaca fascicularis) were chosen as a model to investigate the ocular toxicity in animals poisoned with methanol and treated with 4-methylpyrazole (4-MP). The metabolism of methanol in the monkey was investigated after administration of 4-MP. Plasma levels of methanol, formic acid, 4-MP and 4-hydroxy-MP (4-OH-MP) were determined. After intramuscular injection, 4-MP was rapidly absorbed and depressed the elimination rate of methanol as well as the accumulation of formate in the blood. The results show the same great individual variations in monkeys as in humans regarding the susceptibility to methanol poisoning. Administration of a single dose of 5 g/kg induces a serious intoxication in most monkeys, causing death to some of them. Two monkeys receiving a single dose of 6 g/kg of methanol developed a serious initial inebriation and were treated with 4-MP. These monkeys survived and showed no signs of toxicity on ocular examinations which included ophtalmoscopy and electroretinogram (ERG) recordings.

Analysis of 4-methylpyrazole in plasma and urine by gas chromatography with nitrogen-selective detection

A simple, sensitive, and specific gas chromatographic method for the quantitation of 4-methylpyrazole in plasma and urine is described. Samples containing 4-methylpyrazole, with 3-methylpyrazole as the internal standard, are extracted into ether and the concentrated ethereal extracts are chromatographed on a Carbowax 20M column using nitrogen-selective detection. Standard curves are linear and reproducible over the range of 25-1000 ng/mL for plasma and 0.5-5 micrograms/mL for urine. Recovery of 4-methylpyrazole is complete from plasma and urine, and the overall between-day coefficient of variation is within 6.0%. No interference is observed from the extractive constituents of plasma and urine. The assay method is suitable for an examination of 4-methylpyrazole disposition in animals and humans.

A simple procedure using 4-methylpyrazole for developing tolerance and other chronic alcohol effects

Young rats given ethanol chronically by gradually increasing the concentration in the drinking fluid to 17.5% reached a maximal daily consumption of 15-17 g ethanol/kg body wt., which corresponded to 35-40% of their energy intake. This chronic treatment was markedly potentiated by additional supplementation of the drinking fluid with a low dose of the alcohol dehydrogenase inhibitor 4-methylpyrazole. Rats on this regimen exhibited higher and more sustained blood ethanol levels. Consequently, more pronounced functional and metabolic tolerance developed and more frequent signs of physical dependence was observed than in rats drinking only ethanol solution. Simple provision of drinking fluid supplemented with ethanol and 4-methylpyrazole appears to provide a nutritionally adequate and easy way to produce tolerance and other chronic alcohol effects.

Normal electroretinogram and no toxicity signs after chronic and acute administration of the alcohol dehydrogenase inhibitor 4-methylpyrazole to the cynomolgus monkey (Macaca fascicularis)--a possible new treatment of methanol poisoning

High doses of 4-methylpyrazole (4-MP) could be administered to monkeys in long- and short-term experiments without yielding any general toxicity or any toxic influence on the retinal photoreceptors, the conduction of impulses through the retina or on the activity in the inner nuclear layer detectable by recording the electroretinogram (ERG). Both series included a low dose (20 mg/kg) and a high dose level (100 mg/kg), the former being a tentative therapeutic dose. In the first series the substance was administered for 6 weeks and the toxicity regarding clinical signs, hematology and blood chemistry, and gross and microscopic pathology evaluated. Furthermore ophthalmoscopy with assessment of the fundus structures and recordings of the ERG were performed. The second series was mainly concerned with revealing of any direct effect of 4-MP on the ERG. Because of the low toxicity of 4-MP and its powerful inhibitory capacity on alcohol dehydrogenase, the substance should prove a potential tool in clinical alcohol research and an effective antidote in clinical situations where inhibition of alcohol dehydrogenase (ADH) is the key to a successful outcome of, for example, methanol and ethylene glycol poisoning.

High pressure liquid chromatographic assay of 4-methylpyrazole. Measurements of plasma and urine levels

4-Methylpyrazole (4-MP), a potent competitive inhibitor of alcohol dehydrogenase activity, has potential usefulness as a treatment means for methanol and ethylene glycol poisoning as well as severe disulfiram-ethanol interactions. Further study of the safety and metabolism of 4-MP in human subjects is needed before it can be used in such therapies. An HPLC assay has been developed to measure 4-MP levels in plasma and urine samples. The method was sensitive enough to quantitate 4-MP in an amount as low as 0.1 nmol. Recovery of 4-MP from spiked urine and plasma samples was greater than 90%. 4-MP levels in the plasma and urine of rats injected with an oral dose of 50 mg/kg of body weight were determined; the detectability limit in these samples was about 3 microM. The method is easy to perform and thus has practical application for research laboratories dealing with ethanol metabolism and clinical laboratories desiring to monitor 4-MP levels.

Elevated concentrations of ethanol in plasma do not suppress voluntary ethanol consumption in C57BL mice

The 24-hr patterns of ethanol intake and resulting concentrations of ethanol in plasma are described for male C57BL/6J mice given free access to water and a 10% v/v solution of ethanol. Animals treated with the alcohol dehydrogenase inhibitor 4-methylpyrazole developed peak plasma concentrations of 116 +/- 20 mg/100 ml, while controls given daily injections of saline exhibited peak plasma concentrations of 11 +/- 7 mg/100 ml. Ethanol consumption as measured by total daily intake and preference was not significantly different in the two groups of mice. The absence of an effect on ethanol consumption despite a tenfold difference in peak plasma levels suggests that concentrations of circulating ethanol within the range observed do not limit voluntary consumption of ethanol.

Evaluation of the differential in vivo toxic effects of ethanol and acetaldehyde on the hypothalamic-pituitary-gonadal axis using 4-methylpyrazole

4-Methylpyrazole (4-MP) blocks ethanol (ETOH) oxidation by inhibiting alcohol dehydrogenase (ADH). Because ADH has been identified and shown to be active in the testes, we examined the effect of ETOH + 4-MP in the ETOH-fed rat model. Weanling rats were divided into four groups of 15 rats each and fed a liquid diet: group I received ETOH (5% v/v) + 4-MP (1.34 mM); group II was pair-fed the diet containing only 4-MP and isocalorically matched to group I; group III received ETOH diet; and group IV was pair-fed isocalorically to match group III. Using two-way analysis of variance for nonorthogonal data, the results were analyzed to examine both ETOH and 4-MP as the main treatment and to test for interaction. Both ETOH and 4-MP produced significant main treatment effects with significant interaction on liver/body ratio, testes weight expressed as per cent of normal, and plasma luteinizing hormone levels, and without interaction on plasma testosterone concentrations.

Uninterrupted prolonged ethanol oxidation as a main pathogenetic factor of alcoholic liver damage: evidence from a new liquid diet animal model

Marked fatty infiltration and degenerative or mild inflammatory changes including eosinophilic cytoplasmic degeneration in centrilobular cells and focal inflammatory changes with cell necrosis were observed in livers of rats maintained for 12 weeks on a nutritionally adequate and balanced liquid ethanol diet. The animals continuously oxidized ethanol due to the supplementation of the diet with a low dose of 4-methylpyrazole (4-MP, an alcohol dehydrogenase inhibitor), that decreased ethanol elimination by about 20%. In other, equicalorically pair-fed groups of rats receiving (a) a similar ethanol-containing liquid diet without 4-MP or (b) a diet with 4-MP and 20% less ethanol, only a few minor changes were seen. The liver histology of rats pair-fed a control diet with a 4 times higher doses of 4-MP was completely normal. The results indicate that the prolonged imbalance of hepatic metabolism due to the uninterrupted oxidation of ethanol is a crucial factor in the development of alcoholic liver injury.

Inhibition of testosterone production by rat Leydig cells with ethanol and acetaldehyde: prevention of ethanol toxicity with 4-methylpyrazole

The toxic effects of ethanol and acetaldehyde on testosterone biosynthesis were examined in vitro using isolated Leydig cells prepared from adult rat testes. The ability of 4-methylpyrazole, an inhibitor of alcohol dehydrogenase, to prevent the toxic effects of ethanol on testosterone production was investigated. Ethanol was found to inhibit gonadotropin-stimulated testosterone production in a dose dependent fashion. Concentrations of ethanol (25 mg/100 reduce testosterone levels by 44% as compared to the controls. Acetaldehyde at micromolar concentrations also inhibited testosterone biosynthesis. The addition of 4-methylpyrazole to the culture medium prevented the toxic effects of ethanol as determined by testosterone production. These studies suggest that ethanol per se may not directly inhibit testosterone biosynthesis. Rather, it would appear that acetaldehyde, the first product of ethanol metabolism, may be responsible for the toxic effects of ethanol upon Leydig cells at least in vitro.

Mechanism of the protective action of thiol compounds in ethanol-induced liver injury

The protective action of cysteine or mercaptopropionylglycine (MPG) in acute ethanol-induced liver injury has been investigated in the rat. Cysteine accelerated clearance of ethanol and acetaldehyde from blood and liver and prevented an increase in hepatic content of triglyceride and serum ornithine carbamoyl transferase activity. MPG accelerated clearance of ethanol and acetaldehyde less efficiently but prevented an increase in these variables to the same degree. The mode of action of thiol compounds in acute ethanol-induced liver injury has been discussed.

Methanol poisoning

Methanol poisoning is an uncommon but an extremely hazardous intoxication. Since methanol is a versatile fuel and is having increasing usage in an energy-conscious society, a high index of suspicion and swift laboratory confirmation is essential in managing this poisoning. Methanol poisoning may occur in sporadic or epidemic circumstances. Chronic exposure may occur in the occupational setting. Man is uniquely susceptible to methanol toxicity, perhaps dependent upon folate metabolism. Classic symptoms of methanol toxicity can only occur in laboratory animals who are rendered folate deficient. Folate may be useful in humans enhancing removal of the toxic products of methanol poisoning. The enzyme responsible for metabolism of methanol is alcohol dehydrogenase. Ethanol has a higher affinity for this enzyme and is preferentially metabolized. Simultaneous ethanol and methanol administration may confuse the onset of the intoxication. Pyrazoles may also be used to inhibit alcohol dehydrogenase thus preventing the intoxication. The most important initial symptom of methanol poisoning is visual disturbance. The symptoms may be delayed up to 24 hours after ingestion due to simultaneous alcohol administration and metabolic processes. Laboratory evidence of severe metabolic acidosis with increased anion and osmolar gaps strongly suggest the clinical diagnosis. There may be an important association between mean corpuscular volume which is significantly higher in cases of severe methanol poisoning than in mild cases.(ABSTRACT TRUNCATED AT 250 WORDS)