Xenobiotic metabolizing enzymes, especially CYP1A1 and GSTM1, are involved in the activation and ... more Xenobiotic metabolizing enzymes, especially CYP1A1 and GSTM1, are involved in the activation and conjugation of PAHs and are controlled by polymorphic genes. PAHs released from diesel emissions in many cities of the world, especially in developing countries, contribute significantly to the toxic effects of airborne inhalable particles. We have evaluated the gene-environment interaction in Santiago of Chile, studying the contribution of CYP1A1 and GSTM1 polymorphisms on 1-OH-P urinary levels used as the PAHs exposure biomarker. The study was performed on 59 diesel exposed (38 diesel revision workers and 21 subjects working in an urban area as established street vendors) and 44 non-exposed subjects living in a rural area. The 1-OH-P urinary levels of the urban (P=0.043) and rural (P=0.040) populations showed, without considering the genotypes, significant differences between smokers and non-smokers, but no significant differences were found between smokers and non-smokers among the diesel plant workers (P=0.33). Non-smoking subjects of the diesel plants and the urban area showed similar 1-OHP levels (P=0.466) which were significantly higher than those of the subjects living in the rural area (P<0.05). When 1-OH-P levels were related with genotypes, an association was observed for the CYP1A1*2A genotype, so that the diesel-exposed workers carrying the CYP1A1*2A allele showed significantly higher 1-OH-P levels than the subjects from the rural area with the same genotype (P=0.008). On the other hand, there was no significant correlation between urinary 1-OH-P levels and GSTM1 null genotype, although higher levels of the urinary metabolite were found in individuals carrying the combined CYP1A1*2A and GSTM1 null genotype (P=0.055). These results may suggest an association between levels of the exposure biomarker 1-OH-P and presence of the CYP1A1*2A genotype, a potential genetic susceptibility biomarker which might be useful in identifying individuals at higher risk among people exposed to high PAH levels in diesel exhaust.
Summary— Cytochrome P450 2E1 (CYP2E1) is a phase I detoxification enzyme, which is induced by chr... more Summary— Cytochrome P450 2E1 (CYP2E1) is a phase I detoxification enzyme, which is induced by chronic alcohol consumption. It is involved in the activation of numerous carcinogens and in the production of free radicals. As it has previously been shown to be induced in diabetic and obese rats, the aim of this study was to investigate its induction level in poorly-controlled diabetics and in obese patients (Body Mass Index > 30 kg/m2). CYP2E1 activity was determined in 35 diabetic and 17 obese patients by using the in vivo chlorzoxazone hydroxylation test. Even though the glucidic parameters were highly disturbed (mean fasting glycemia > 7.9 mmol/L, post prandial glycemia > 12.2 mmol/L and fructosamine > 326 μmol/L), CYP2E1 activity was not enhanced either in insulin-dependent diabetics (IDDs, n = 7) nor in non-obese non-insulin-dependent diabetics (NTTDDs, n = 15) when compared to controls (n = 42) (0.21 ± 0.03, 0.33 ± 0.03 and 0.30 ± 0.02, respectively, mean ± SEM). However, this activity was lower in IDDs when compared to NIDDs (P < 0.05). In obese patients, with (n = 13) or without (n = 17) NIDD mellitus, CYP2E1 activity was increased by a mean of 40% when compared to controls. In addition, positive correlations were found in all subjects (controls or patients, n = 74) between CYP2E1 activity and serum cholesterol (r = 0.42, P < 0.0001), triglycerides (r = 0.44, P < 0.0001) and BMI (r = 0.36, P < 0.001). Accordingly, subjects with cholesterol and/or triglyceride serum levels above 6.4 and 1.8 mmol/L, respectively, displayed a mean increase of 40% of their CYP2E1 activity vs subjects within the above values. It is believed that individuals with increased CYP2E1 activity are more susceptible to the adverse effects of CYP2E1-mediated activation of toxins and carcinogens.
Chlorzoxazone is mainly metabolized to 6-hydroxychlorzoxazone (6-OHchlorzoxazone) by the ethanol-... more Chlorzoxazone is mainly metabolized to 6-hydroxychlorzoxazone (6-OHchlorzoxazone) by the ethanol-inducible cytochrome P450 2E1 (CYP2E1). To evaluate the impact of ethanol consumption on the enzyme induction, the pharmacokinetics of chlorzoxazone and 6-OHchlorzoxazone were studied in alcoholic and control subjects. Fifteen alcoholic male inpatients (all smokers, daily intake 333 ± 191 g of absolute ethanol) and 20 healthy male volunteers (10 smokers and 10 non-smokers, weekly intake <100 g of absolute ethanol) participated in this study. Following a 12 hr fasting period, each subject was orally administered 500 mg of chlorzoxazone. Venous blood and urine samples were collected over a 10 hr period. Areas under the curve of plasma concentration versus time (AUC) of chlorzoxazone and 6-OHchlorzoxazone were calculated. The total plasma clearance of chlorzoxazone was measured as the dose/AUC ratio. The mean total plasma clearance was not different between smoker and non-smoker controls but it was enhanced by 73% in alcoholic patients. These results indicate a negligible and non-significant effect of cigarette smoking in controls but an increased metabolism of chlorzoxazone in alcoholic patients (P < 0.05). This increase was corroborated by the 2-fold enhancement of the 6OH-chlorzoxazone/chlorzoxazone AUC ratio, compared to controls. A good correlation was found between this AUC ratio and the 6-OHchlorzoxazone/chlorzoxazone concentration ratio at t = 2 hr in patients and in control (r = 0.88 and 0.85, respectively, P < 0.01). The concentration ratio increased by 150% in alcoholic patients and decreased by 65% in the seven alcoholics tested after 7 days of alcohol abstinence. It is therefore concluded that the 6-OHchlorzoxazone/chlorzoxazone concentration ratio at t = 2 hr could constitute a simple and non-traumatic marker of CYP2E1 induction.
Alcoholism-clinical and Experimental Research, 1992
The capacity for the brain to produce acetaldehyde (AcHO) from ethanol was determined in rat brai... more The capacity for the brain to produce acetaldehyde (AcHO) from ethanol was determined in rat brain homogenates. Rat brains were perfused with saline-heparin solution and homogenized in a phosphate buffer. Varying amounts of tissue were incubated with ethanol (0–100 mM) for periods of up to 60 min. The reaction was stopped by the addition of desferrioxamine and ice-cold perchloric acid. Supernatants were treated with dinitrophenylhydrazine reagent, extracted with isooctane in the presence of an internal standard, and the derivatives were separated by HPLC.The addition of 4-methyl pyrazole (an alcohol dehydrogenase inhibitor) or metyrapone (a cytochrome P450 inhibitor) had no effect on the amount of recovered AcHO. On the other hand, treatment with the catalase inhibitors sodium azide, cyanamide, or 3-amino-1,2,4-triazole blocked the production of AcHO while the addition of exogenous peroxide or a peroxide-generating system enhanced the production of AcHO. Overall, these results suggest that AcHO may be produced in the brain during alcohol intoxication, through the action of the enzyme catalase.
Alcoholism-clinical and Experimental Research, 1990
The capacity of liver microsomes to oxidize various substrates known to be specific of alcohol-in... more The capacity of liver microsomes to oxidize various substrates known to be specific of alcohol-inducible cytochrome P-450 was studied in rats treated with different xenobiotics such as 3-methyl-cholanthrene, phenobarbital, acetone, and ethanol. Analysis of results showed a significantly marked increase following ethanol and acetone treatments of the p-nitrophenol hydroxylation (283 ± 19% and 304 ± 21%), N-nitrosodimethylamine (NDMA) demethylation (280 ± 105% and 228 ± 95%), benzene hydroxylation (258 ± 60% and 236 ± 61%), butanol oxidation (173 ± 34% and 154 ± 32%), aniline hydroxylation (147 ± 22% and 95 ± 8%), and ether de-ethylation (95 ± 17% and 83 ± 17%) and a not significant increase of N-nitrosodiethylamine (NDEA) de-ethylation (34 ± 11% and 9 ± 8%) in rat microsomes, respectively, versus control animals (mean ± SD, values expressed as nmol/min/nmole P-450). All of these activities significantly decreased after 3-MC treatment, except for the p-nitrophenol hydroxylation. PB treatment markedly enhanced NDEA de-ethylation, p-nitrophenol, and benzene hydroxylations (106 ± 38%, 109 ± 14%, and 153 ± 62%, respectively) versus controls. These results suggest that NDMA and especially 1-butanol are the most specific and useful probes of alcohol-inducible cytochrome P-450 in crude liver microsomes.
Many investigators have reported an association between genetic polymorphisms of cytochromes P-45... more Many investigators have reported an association between genetic polymorphisms of cytochromes P-450 CYP2E1, CYP1A1 or glutathione S-transferase Mu (GSTM1) and susceptibility to lung cancer. However, pronounced interethnic variations have been described in the frequencies of these polymorphisms, especially between Asians and Caucasians. The present study was set up to establish CYP2E1 (c1, c2 and C, D), CYP1A1 (m1, m2 and Ile, Val) and GSTM1 (null) allelic frequencies in Chileans (n=96) who are an admixture of Native Americans and Caucasians (Spaniards). The rare allele frequencies were found to be 0.15 (c2), 0.21 (C), 0.23 (m2), 0.32 (Val) and 0.21 ('null' genotype). These values are significantly higher than those of Caucasians except for the GSTM1 'null' genotype and suggest differences in susceptibility to lung cancer between both populations.
Alcoholism-clinical and Experimental Research, 1996
Genetic polymorphisms of various cytochromes P450 have recently been described and could be impli... more Genetic polymorphisms of various cytochromes P450 have recently been described and could be implicated in the individual susceptibility of alcoholics to ethanol-related diseases. Rsal and Dral polymorphisms of CYP2E1 and Mspl polymorphism of CYP1A1 were studied in 260 controls and 511 alcoholic patients, without any clinical symptoms (n= 202) or with various ethanol-related diseases (n= 309), such as liver cirrhosis (n= 110), esophageal cancer (n= 62), upper aerodigestive tract cancer (n= 96), and other miscellaneous diseases (n= 41). Frequencies of the mutated alleles were found to be 2.5% (Rsal), 7.9% (Dral), and 8.7% (Mspl) in controls; 4%, 14.1%, and 12% in alcoholics without clinical symptoms; and 3.1%, 12.5%, and 11.2% in alcoholics with ethanol-related diseases. The only significant difference was found in the Dral polymorphism, whose frequency was enhanced in alcoholics with (p < 0.05) or without ethanol-related diseases (p < 0.01) when compared with controls. No differences were found between alcoholics without clinical symptoms and alcoholics with cirrhosis, esophageal cancer, or upper aerodigestive tract cancer. However, in liver cirrhosis and in ethanol-related cancers, the rare Dral-C allele was three times less frequent in patients under the age of 45 than in older patients, suggesting a protective role for this allele. In conclusion, our data indicate that the aforementioned mutations do not play a critical role in the development of cirrhosis, esophageal cancer, or upper aerodigestive tract cancers in Caucasians.
Chlormethiazole is a sedative and anticonvulsive drug used in the treatment of alcohol withdrawal... more Chlormethiazole is a sedative and anticonvulsive drug used in the treatment of alcohol withdrawal. Because it had been reported that chlormethiazole inhibits the alcohol-inducible cytochrome P450 2E1 in rat liver, we investigated the in vivo and in vitro effect of this drug on cytochrome P450 2E1 in human beings. The activity of this cytochrome was assessed using chlorzoxazone as a probe. The 6-hydroxychlorzoxazone- chlorzoxazone blood concentration ratio, reflecting the cytochrome P450 2E1 activity, was determined in 10 controls and in 24 alcoholic patients who had entered a hospital for detoxification. Alcoholic patients were administered either chlormethiazole (1.3-2.3 g/d) or chlorazepate (100-300 mg/d) as a sedative. Cytochrome P450 2E1 activity was significantly increased in alcoholic patients treated with chlorazepate (1.16 ± 0.40 vs. 0.27 ± 0.03, P < .05). In contrast, chlormethiazole treatment inhibited chlorzoxazone hydroxylation almost totally (0.046 ± 0.03, P < .001). After 7-14 days of ethanol withdrawal, alcoholic patients treated with chlorazepate had ratio values similar to those of controls (0.31 ± 0.05), whereas values from alcoholic patients treated with chlormethiazole remained low (0.049 ± 0.01) even though chlormethiazole doses were gradually decreased. Pharmacokinetic studies in controls showed that chlormethiazole-mediated inhibition was present even when chlormethiazole was not detectable in the blood. In addition, the effect of chlormethiazole on cytochrome P450 2E1 was studied in vitro using human liver microsomes. Dixon plot analyses showed a noncompetitive inhibition (Ki = 12 µmol/L). These data clearly show that chlormethiazole is an efficient inhibitor of chlorzoxazone metabolism and thus of cytochrome P450 2E1 activity in human beings. Because cytochrome P450 2E1 induction after chronic ethanol consumption has detrimental effects on the liver through free radical formation, treatment of alcohol detoxification with chlormethiazole may be beneficial.
Xenobiotic metabolizing enzymes, especially CYP1A1 and GSTM1, are involved in the activation and ... more Xenobiotic metabolizing enzymes, especially CYP1A1 and GSTM1, are involved in the activation and conjugation of PAHs and are controlled by polymorphic genes. PAHs released from diesel emissions in many cities of the world, especially in developing countries, contribute significantly to the toxic effects of airborne inhalable particles. We have evaluated the gene-environment interaction in Santiago of Chile, studying the contribution of CYP1A1 and GSTM1 polymorphisms on 1-OH-P urinary levels used as the PAHs exposure biomarker. The study was performed on 59 diesel exposed (38 diesel revision workers and 21 subjects working in an urban area as established street vendors) and 44 non-exposed subjects living in a rural area. The 1-OH-P urinary levels of the urban (P=0.043) and rural (P=0.040) populations showed, without considering the genotypes, significant differences between smokers and non-smokers, but no significant differences were found between smokers and non-smokers among the diesel plant workers (P=0.33). Non-smoking subjects of the diesel plants and the urban area showed similar 1-OHP levels (P=0.466) which were significantly higher than those of the subjects living in the rural area (P<0.05). When 1-OH-P levels were related with genotypes, an association was observed for the CYP1A1*2A genotype, so that the diesel-exposed workers carrying the CYP1A1*2A allele showed significantly higher 1-OH-P levels than the subjects from the rural area with the same genotype (P=0.008). On the other hand, there was no significant correlation between urinary 1-OH-P levels and GSTM1 null genotype, although higher levels of the urinary metabolite were found in individuals carrying the combined CYP1A1*2A and GSTM1 null genotype (P=0.055). These results may suggest an association between levels of the exposure biomarker 1-OH-P and presence of the CYP1A1*2A genotype, a potential genetic susceptibility biomarker which might be useful in identifying individuals at higher risk among people exposed to high PAH levels in diesel exhaust.
Summary— Cytochrome P450 2E1 (CYP2E1) is a phase I detoxification enzyme, which is induced by chr... more Summary— Cytochrome P450 2E1 (CYP2E1) is a phase I detoxification enzyme, which is induced by chronic alcohol consumption. It is involved in the activation of numerous carcinogens and in the production of free radicals. As it has previously been shown to be induced in diabetic and obese rats, the aim of this study was to investigate its induction level in poorly-controlled diabetics and in obese patients (Body Mass Index > 30 kg/m2). CYP2E1 activity was determined in 35 diabetic and 17 obese patients by using the in vivo chlorzoxazone hydroxylation test. Even though the glucidic parameters were highly disturbed (mean fasting glycemia > 7.9 mmol/L, post prandial glycemia > 12.2 mmol/L and fructosamine > 326 μmol/L), CYP2E1 activity was not enhanced either in insulin-dependent diabetics (IDDs, n = 7) nor in non-obese non-insulin-dependent diabetics (NTTDDs, n = 15) when compared to controls (n = 42) (0.21 ± 0.03, 0.33 ± 0.03 and 0.30 ± 0.02, respectively, mean ± SEM). However, this activity was lower in IDDs when compared to NIDDs (P < 0.05). In obese patients, with (n = 13) or without (n = 17) NIDD mellitus, CYP2E1 activity was increased by a mean of 40% when compared to controls. In addition, positive correlations were found in all subjects (controls or patients, n = 74) between CYP2E1 activity and serum cholesterol (r = 0.42, P < 0.0001), triglycerides (r = 0.44, P < 0.0001) and BMI (r = 0.36, P < 0.001). Accordingly, subjects with cholesterol and/or triglyceride serum levels above 6.4 and 1.8 mmol/L, respectively, displayed a mean increase of 40% of their CYP2E1 activity vs subjects within the above values. It is believed that individuals with increased CYP2E1 activity are more susceptible to the adverse effects of CYP2E1-mediated activation of toxins and carcinogens.
Chlorzoxazone is mainly metabolized to 6-hydroxychlorzoxazone (6-OHchlorzoxazone) by the ethanol-... more Chlorzoxazone is mainly metabolized to 6-hydroxychlorzoxazone (6-OHchlorzoxazone) by the ethanol-inducible cytochrome P450 2E1 (CYP2E1). To evaluate the impact of ethanol consumption on the enzyme induction, the pharmacokinetics of chlorzoxazone and 6-OHchlorzoxazone were studied in alcoholic and control subjects. Fifteen alcoholic male inpatients (all smokers, daily intake 333 ± 191 g of absolute ethanol) and 20 healthy male volunteers (10 smokers and 10 non-smokers, weekly intake <100 g of absolute ethanol) participated in this study. Following a 12 hr fasting period, each subject was orally administered 500 mg of chlorzoxazone. Venous blood and urine samples were collected over a 10 hr period. Areas under the curve of plasma concentration versus time (AUC) of chlorzoxazone and 6-OHchlorzoxazone were calculated. The total plasma clearance of chlorzoxazone was measured as the dose/AUC ratio. The mean total plasma clearance was not different between smoker and non-smoker controls but it was enhanced by 73% in alcoholic patients. These results indicate a negligible and non-significant effect of cigarette smoking in controls but an increased metabolism of chlorzoxazone in alcoholic patients (P < 0.05). This increase was corroborated by the 2-fold enhancement of the 6OH-chlorzoxazone/chlorzoxazone AUC ratio, compared to controls. A good correlation was found between this AUC ratio and the 6-OHchlorzoxazone/chlorzoxazone concentration ratio at t = 2 hr in patients and in control (r = 0.88 and 0.85, respectively, P < 0.01). The concentration ratio increased by 150% in alcoholic patients and decreased by 65% in the seven alcoholics tested after 7 days of alcohol abstinence. It is therefore concluded that the 6-OHchlorzoxazone/chlorzoxazone concentration ratio at t = 2 hr could constitute a simple and non-traumatic marker of CYP2E1 induction.
Alcoholism-clinical and Experimental Research, 1992
The capacity for the brain to produce acetaldehyde (AcHO) from ethanol was determined in rat brai... more The capacity for the brain to produce acetaldehyde (AcHO) from ethanol was determined in rat brain homogenates. Rat brains were perfused with saline-heparin solution and homogenized in a phosphate buffer. Varying amounts of tissue were incubated with ethanol (0–100 mM) for periods of up to 60 min. The reaction was stopped by the addition of desferrioxamine and ice-cold perchloric acid. Supernatants were treated with dinitrophenylhydrazine reagent, extracted with isooctane in the presence of an internal standard, and the derivatives were separated by HPLC.The addition of 4-methyl pyrazole (an alcohol dehydrogenase inhibitor) or metyrapone (a cytochrome P450 inhibitor) had no effect on the amount of recovered AcHO. On the other hand, treatment with the catalase inhibitors sodium azide, cyanamide, or 3-amino-1,2,4-triazole blocked the production of AcHO while the addition of exogenous peroxide or a peroxide-generating system enhanced the production of AcHO. Overall, these results suggest that AcHO may be produced in the brain during alcohol intoxication, through the action of the enzyme catalase.
Alcoholism-clinical and Experimental Research, 1990
The capacity of liver microsomes to oxidize various substrates known to be specific of alcohol-in... more The capacity of liver microsomes to oxidize various substrates known to be specific of alcohol-inducible cytochrome P-450 was studied in rats treated with different xenobiotics such as 3-methyl-cholanthrene, phenobarbital, acetone, and ethanol. Analysis of results showed a significantly marked increase following ethanol and acetone treatments of the p-nitrophenol hydroxylation (283 ± 19% and 304 ± 21%), N-nitrosodimethylamine (NDMA) demethylation (280 ± 105% and 228 ± 95%), benzene hydroxylation (258 ± 60% and 236 ± 61%), butanol oxidation (173 ± 34% and 154 ± 32%), aniline hydroxylation (147 ± 22% and 95 ± 8%), and ether de-ethylation (95 ± 17% and 83 ± 17%) and a not significant increase of N-nitrosodiethylamine (NDEA) de-ethylation (34 ± 11% and 9 ± 8%) in rat microsomes, respectively, versus control animals (mean ± SD, values expressed as nmol/min/nmole P-450). All of these activities significantly decreased after 3-MC treatment, except for the p-nitrophenol hydroxylation. PB treatment markedly enhanced NDEA de-ethylation, p-nitrophenol, and benzene hydroxylations (106 ± 38%, 109 ± 14%, and 153 ± 62%, respectively) versus controls. These results suggest that NDMA and especially 1-butanol are the most specific and useful probes of alcohol-inducible cytochrome P-450 in crude liver microsomes.
Many investigators have reported an association between genetic polymorphisms of cytochromes P-45... more Many investigators have reported an association between genetic polymorphisms of cytochromes P-450 CYP2E1, CYP1A1 or glutathione S-transferase Mu (GSTM1) and susceptibility to lung cancer. However, pronounced interethnic variations have been described in the frequencies of these polymorphisms, especially between Asians and Caucasians. The present study was set up to establish CYP2E1 (c1, c2 and C, D), CYP1A1 (m1, m2 and Ile, Val) and GSTM1 (null) allelic frequencies in Chileans (n=96) who are an admixture of Native Americans and Caucasians (Spaniards). The rare allele frequencies were found to be 0.15 (c2), 0.21 (C), 0.23 (m2), 0.32 (Val) and 0.21 ('null' genotype). These values are significantly higher than those of Caucasians except for the GSTM1 'null' genotype and suggest differences in susceptibility to lung cancer between both populations.
Alcoholism-clinical and Experimental Research, 1996
Genetic polymorphisms of various cytochromes P450 have recently been described and could be impli... more Genetic polymorphisms of various cytochromes P450 have recently been described and could be implicated in the individual susceptibility of alcoholics to ethanol-related diseases. Rsal and Dral polymorphisms of CYP2E1 and Mspl polymorphism of CYP1A1 were studied in 260 controls and 511 alcoholic patients, without any clinical symptoms (n= 202) or with various ethanol-related diseases (n= 309), such as liver cirrhosis (n= 110), esophageal cancer (n= 62), upper aerodigestive tract cancer (n= 96), and other miscellaneous diseases (n= 41). Frequencies of the mutated alleles were found to be 2.5% (Rsal), 7.9% (Dral), and 8.7% (Mspl) in controls; 4%, 14.1%, and 12% in alcoholics without clinical symptoms; and 3.1%, 12.5%, and 11.2% in alcoholics with ethanol-related diseases. The only significant difference was found in the Dral polymorphism, whose frequency was enhanced in alcoholics with (p < 0.05) or without ethanol-related diseases (p < 0.01) when compared with controls. No differences were found between alcoholics without clinical symptoms and alcoholics with cirrhosis, esophageal cancer, or upper aerodigestive tract cancer. However, in liver cirrhosis and in ethanol-related cancers, the rare Dral-C allele was three times less frequent in patients under the age of 45 than in older patients, suggesting a protective role for this allele. In conclusion, our data indicate that the aforementioned mutations do not play a critical role in the development of cirrhosis, esophageal cancer, or upper aerodigestive tract cancers in Caucasians.
Chlormethiazole is a sedative and anticonvulsive drug used in the treatment of alcohol withdrawal... more Chlormethiazole is a sedative and anticonvulsive drug used in the treatment of alcohol withdrawal. Because it had been reported that chlormethiazole inhibits the alcohol-inducible cytochrome P450 2E1 in rat liver, we investigated the in vivo and in vitro effect of this drug on cytochrome P450 2E1 in human beings. The activity of this cytochrome was assessed using chlorzoxazone as a probe. The 6-hydroxychlorzoxazone- chlorzoxazone blood concentration ratio, reflecting the cytochrome P450 2E1 activity, was determined in 10 controls and in 24 alcoholic patients who had entered a hospital for detoxification. Alcoholic patients were administered either chlormethiazole (1.3-2.3 g/d) or chlorazepate (100-300 mg/d) as a sedative. Cytochrome P450 2E1 activity was significantly increased in alcoholic patients treated with chlorazepate (1.16 ± 0.40 vs. 0.27 ± 0.03, P < .05). In contrast, chlormethiazole treatment inhibited chlorzoxazone hydroxylation almost totally (0.046 ± 0.03, P < .001). After 7-14 days of ethanol withdrawal, alcoholic patients treated with chlorazepate had ratio values similar to those of controls (0.31 ± 0.05), whereas values from alcoholic patients treated with chlormethiazole remained low (0.049 ± 0.01) even though chlormethiazole doses were gradually decreased. Pharmacokinetic studies in controls showed that chlormethiazole-mediated inhibition was present even when chlormethiazole was not detectable in the blood. In addition, the effect of chlormethiazole on cytochrome P450 2E1 was studied in vitro using human liver microsomes. Dixon plot analyses showed a noncompetitive inhibition (Ki = 12 µmol/L). These data clearly show that chlormethiazole is an efficient inhibitor of chlorzoxazone metabolism and thus of cytochrome P450 2E1 activity in human beings. Because cytochrome P450 2E1 induction after chronic ethanol consumption has detrimental effects on the liver through free radical formation, treatment of alcohol detoxification with chlormethiazole may be beneficial.
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