Acetaminophen metabolism and cytotoxicity in PC12 cells transfected with cytochrome P4502E1.

Although a number of studies confirm the important role of metabolites in the cytotoxicity of acetaminophen, its precise mechanisms remain unknown. Acetaminophen is metabolized by microsomal enzymes. Cytochrome P4502E1 (CYP2E1) mediated N-hydroxylation results in the formation of N-acetyl-benzo-quinoneimine, a highly reactive intermediate. We examined biochemical parameters related to necrotic and apoptotic processes in acetaminophen-exposed PC12 cells is and in a PC12 cell line genetically engineered to express human CYP2E1. Both the [3H]thymidine incorporation test and the protein assay uniformly showed dose- and time-related significant growth retardation in both cell lines exposed to the drug. This was more evident in CYP2E1-transfected cells. Moreover, the cytotoxic effect of acetaminophen was increased as evidenced by lactate dehydrogenase activity in the culture medium. Both random oligonucleotide primed synthesis assay and enzyme-linked immunosorbent assay revealed significant DNA fragmentation in both cell lines, which was greater in transfected cells, reaching about 11% of total cellular DNA. These results were confirmed by flow cytometry and microscopic examination of cell nuclei. Intracellular calcium levels were increased only in transfected cells, approximately threefold when 5 mM acetaminophen was administered for 48 h. These results indicate the cytotoxic effects of acetaminophen via apoptosis, necrosis, and growth retardation. While the precise mechanism remains obscure, it seems that DNA fragmentation and apoptotic cascade represent a preliminary biochemical event in acute cell death, and that acetaminophen bio-transformation by CYP2E1 stimulates this pathway.

Interaction between two probes used for phenotyping cytochromes P4501A2 (caffeine) and P4502E1 (chlorzoxazone) in humans.

The first steps in the metabolism of caffeine and chlorzoxazone are primarily catalysed by CYP1A2 and CYP2E1, respectively. Accordingly, these compounds have been developed as metabolic probes for non-invasive phenotyping of these two P450s. Their specificities, however, have been shown to overlap. In this study, 140 mg of caffeine and 500 mg of chlorzoxazone were administered alone or together in 16 healthy subjects under standardized conditions. The metabolites of these two probes were measured in the blood and also in the urine for caffeine. CYP1A2 activity was determined either by the paraxanthine/caffeine ratio in the blood or by the usual caffeine metabolic ratio in the urine. The CYP2E1 activity was determined by the 6-OH-chlorzoxazone/chlorzoxazone ratio in blood. CYP1A2 activities measured in blood and urine were highly significantly correlated. CYP2E1 activity was not modified when chlorzoxazone was given together with caffeine. In contrast, an inhibition of CYP1A2 by chlorzoxazone was demonstrated by a 16% decrease in the caffeine metabolic ratio in urine when both caffeine and chlorzoxazone were given together. Under the same conditions, the paraxanthine/caffeine ratio in plasma also decreased by about 20%. These results were confirmed in vitro by the incubation of 1 mM caffeine with human hepatic liver microsomes in the presence of 0.4 mM chlorzoxazone. The overall metabolism of caffeine decreased by 38% compared to controls incubated without chlorzoxazone.(ABSTRACT TRUNCATED AT 250 WORDS)

Cytochrome P450 2E1 genotype and chlorzoxazone metabolism in healthy and alcoholic Caucasian subjects.

Susceptibility to cancer or ethanol-related liver diseases may be associated with a large variability in cytochrome P450 2E1 activity. This variability may be of genetic origin or reflect environmental factors. To test the role of genetics, the phenotype and genotype of this enzyme were determined in 42 non-alcoholic and 74 alcoholic patients hospitalized for detoxification treatment. Chlorzoxazone metabolism was used to assess CYP2E1 phenotype. Restriction length fragment polymorphisms with Rsa I or Pst I, and Dra I endonucleases were used to determine the two mutant alleles, Pst I/Rsa I-c2 and Dra I-C. A significant gender difference in basal CYP2E1 activity was observed in non-smoking controls (p < 0.05) but not in alcoholics or smokers. Subjects heterozygous for the C or c2 mutated allele did not show any difference in CYP2E1 activity at the basal level, compared with the wild type homozygotes. Conversely, patients with the mutated genotype appeared less inducible than the others after ethanol induction (p < 0.01).

Folic acid deficiency and neutrophil dysfunction.

Polymorphonuclear leukocyte functions were studied in 92 patients with protein-calorie malnutrition. Serum folic acid levels were higher than 3 ng/ml in 38 patients and 3 ng/ml or less in 54 patients. Significant differences were found between these two groups of patients with regard to phagocytosis (81.5 +/- 1.9 versus 69.2 +/- 2.0 percent, p less than 0.001) and bactericidal ability (90.6 +/- 1.1 versus 84.5 +/- 2.3 percent, p less than 0.05). Correction of folic acid deficiency in 22 patients was associated with recovery of normal phagocytosis (p less than 0.001) but not bactericidal function. Adding folic acid to the serum of eight patients also restored normal phagocytic function (p less than 0.001). A correlation was found in vivo and in vitro between changes over time in folic acid levels and in phagocytosis.

Effect of the length of alkyl chain on the cytochrome P450 dependent metabolism of N-diakylnitrosamines.

Liver microsomes from control and treated rats (P4501A, 2B, 2E1-induced) metabolize at variable metabolic rates eight N-nitroso-di-n-alkylamines, including five symmetrical (N-nitroso-dimethyl, -diethyl, -dipropyl, -dibutyl and -diamyl-amines) and four asymmetrical (N-nitrosomethylethyl, methylpropyl, methylbutyl, and methylamyl-amines), into aldehydes. Thus, the longer the alkyl chain of symmetrical N-nitrosamines, the smaller was the metabolic rate of the corresponding aldehyde formation. The chain length of the alkyl group of N-nitroso-methylalkylamines modified the oxidation of the alkyl moiety: the oxidation by CYP2E1 decreased as the n-alkyl chain length increased and conversely for the oxidation by CYP1A and CYP2B. Finally, the longer the n-alkyl chain length of asymmetrical N-nitrosamines, the greater was the oxidation of methyl groups.

Hydroxylation of carbon atoms of the alkyl chain of symmetrical N-nitrosodialkylamines by rat liver microsomes.

Liver microsomal preparations from control and treated rats (cytochromes P450 1A, 2B, 3A and 2E1-induced) metabolized at variable metabolic rates three nitrosodialkylamines (N-nitroso-dipropyl, dibutyl and diamyl-amines) into aldehydes and hydroxy-nitrosamines. The longer the alkyl chain, the smaller was the metabolic rate of the alpha-hydroxylation of alkyl chain yielding aldehyde and the greater was the metabolic rate of the corresponding (omega-1)-hydroxyl metabolite formation. Thus, the (omega-1) hydroxylation of the alkyl chain was the major metabolic pathway of N-nitrosodiamylamine (NDAA) so far as it represented 22-fold the alpha-hydroxylation. The balance between beta to omega hydroxylation and alpha-hydroxylation depends upon the alkyl chain length and also on specific P450 isoform induction.

Induction of liver and kidney CYP1A1/1A2 by caffeine in rat.

Caffeine metabolism by hepatic microsomal P450 enzymes is well documented in experimental animals and humans. However, its induction effect on P450 enzymes has not been thoroughly studied. In a preliminary experiment, the time-dependent incubation of 1 mM caffeine with rat hepatocyte culture resulted in an increase of its own metabolic rate. The dose-dependent expression of rat hepatic and renal cytochromes (CYP) 1A1/1A2 was then investigated after per os administration of caffeine. P450 expression was monitored by using specific enzymatic activities and Northern blot analysis. Caffeine caused a dose-dependent elevation of hepatic CYP1A1/1A2 activities in microsomal preparations, which ranged from 1.7- to 6-fold for ethoxyresorufin O-deethylase and 3- to 8.9-fold for methoxy-resorufin O-demethylase according to the dose regimen of 50 and 150 mg caffeine/kg/day for 3 days, respectively. Northern blot analysis demonstrated that caffeine treatment increased liver CYP1A1 and CYP1A2 mRNA levels over the dose regimen of 50-150 mg caffeine/kg/day for 3 days, respectively. The result of this study demonstrates that caffeine increases its own metabolism in a dose-dependent manner and induces CYP1A1/1A2 expression through either transcriptional activation or mRNA stabilization.

Assessment of cytochrome P4502E1 induction in alcoholic patients by chlorzoxazone pharmacokinetics.

Chlorzoxazone is mainly metabolized to 6-hydroxychloroxazone (6-OHchlorzoxazone) by the ethanol-inducible cytochrome P450 2E1 (CYP2E1). To evaluate the impact of ethanol consumption on the enzyme induction, the pharmacokinetics of chlorozoxazone 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 was 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 6-OHchlorzoxazone/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 controls (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.

Cytochrome P450 4A and 2E1 expression in human kidney microsomes.

Laurate and arachidonate omega and (omega-1)-hydroxylase activities, cytochrome P450 2E1 (CYP2E1), and CYP4A content were measured in 18 human kidney microsomal samples. The rates of laurate and arachidonate were found to be very different from those measured in human liver samples, with a laurate omega/omega-1 ratio of approximately 22 in human kidney vs 0.75 in human liver. Immunoblot analysis of the 18 human kidney microsomal samples identified 1 CYP4A electrophoretic band, but CYP2E1 was not detectable in human kidney, contrary to liver. Laurate and arachidonate omega-hydroxylase activities were significantly correlated with CYP4A content (r = 0.86 and 0.75, respectively). Polyclonal antirat CYP2E1 antibody did not affect omega-hydroxylase activity, whereas the polyclonal antirat CYP4A1 antibody inhibited it by 60%. These results suggest that, in contrast to other species, human kidney microsomes do not contain significant amounts of CYP2E1, but possess CYP4A and fatty acid omega-hydroxylase activity.

Validation of the (omega-1)-hydroxylation of lauric acid as an in vitro substrate probe for human liver CYP2E1.

The (omega-1)-hydroxylation of lauric acid (11-OH-LA), a model substrate of fatty acids, was previously shown to be due to CYP2E1 in rat liver microsomes. The present study examined changes in hepatic CYP2E1 content and 11-OH-LA in a panel of 29 human liver microsomes. The 11-OH-LA activity was strongly correlated with the CYP2E1 content, quantitated by immunoblot (r = 0.75) and with four monooxygenase activities known to be mediated by CYP2E1: chlorzoxazone-6-hydroxylation (r = 0.73), 4-nitrophenol hydroxylation (r = 0.84), N-nitrosodimethylamine demethylation (r = 0.79) and n-butanol oxidation (r = 0.73). The (omega-1)-hydroxylation of lauric acid was inhibited by ethanol (Ki = 3.5 mM), acetone (IC50 = 10 mM) dimethylsulfoxide, chlorzoxazone (competitive inhibitors of CYP2E1), diethyldithiocarbamate, and diallylsulfide (both selective mechanism-based inactivators of CYP2E1). The weak value of ethanol Ki on the (omega-1)-hydroxylation of lauric acid suggested that low levels of alcohol could modify fatty acid metabolism in the liver. Furafylline and gestodene, suicide substrates of CYP1A and CYP3A4, respectively, did not modify the 11-hydroxylation of lauric acid. Polyclonal antibody directed against rat CYP2E1 inhibited the formation of 11-OH-LA without affecting 12-OH-LA activity. Taken together, these results suggest that CYP2E1 is involved in the (omega-1)-hydroxylation of lauric acid in human liver microsomes, and omega-hydroxylation is mediated by another enzyme. Finally, the use of yeasts and mammalian cells genetically engineered for expression of 9 human P450s demonstrated that CYP2E1 was the one enzyme involved in the (omega-1)-hydroxylation of lauric acid.

The effect of chronic alcohol administration on platelet [(3)H]5-hydroxytryptamine uptake and membrane lipid composition.

Platelets are widely used as peripheral models for neuronal amine uptake. Their similarity with the neurosecretory activity of nerve cells, along with similar types and activities of receptors, have prompted many investigators to postulate similar pathological abnormalities in platelets during CNS disease. Ethanol and evening primrose oil (EPO) were chronically administered alone or in combination to rats in a nutritionally balanced liquid milk diet. The platelet phospholipid composition was not altered after the chronic administration of ethanol. However ethanol significantly decreased the levels of arachidonate in platelet membranes. Administration of EPO alone significantly increased the levels of linoleic acid. Platelet 5-HT uptake was measured. The affinity of these uptake sites were unaltered, while the uptake rate, V(max), was decreased by ethanol but this decrease was attenuated by the concomitant administration of EPO. The administration of EPO attenuated some of the detrimental effects due to ethanol.

Acetaldehyde cytotoxicity in cultured rat astrocytes.

The effect of acetaldehyde on astrocytes have been investigated because not only do they play an important role in brain maturation but also recent reports have shown their delayed proliferation following both 'in vivo' and 'in vitro' ethanol exposure. Biochemical parameters related to apoptotic and necrotic processes were examined in primary cultures of rat astrocytes exposed for 4 days to acetaldehyde generated from ethanol by co-cultured alcohol dehydrogenase-transfected Chinese hamster ovary cells. Acetaldehyde levels in the culture media attained concentrations of approximately 450 microM. To study ethanol effects, alcohol oxidation was inhibited by 4-methylpyrazole (an inhibitor of alcohol dehydrogenase). Acetaldehyde but not ethanol increased intracellular calcium levels by 155%. Moreover, significant DNA fragmentation was detected using a random oligonucleotide primed synthesis assay, by flow cytometry and when using agar gel electrophoresis. Transglutaminase activity was elevated in the cells treated with acetaldehyde but when acetaldehyde formation was inhibited by 4-methylpyrazole the enzyme activity was unaffected. Nitrate levels in the culture media were unchanged. Additionally, microscopic examination of cell nuclei revealed chromatin condensation in astrocytes exposed to acetaldehyde. It can be concluded, that in 'in vitro' acetaldehyde exposed rat astrocytes apoptotic pathways are activated.

Changes in neutral lipids in brain synaptosomes of rats after chronic administration of ethanol.

Rats were chronically treated with ethanol in a liquid milk diet for 21 days so that the animals consumed 10 +/- 1 g/kg ethanol daily. Following decapitation, the cortex and hippocampus were removed and a synaptosomal fraction prepared from the cortex. After chronic administration of ethanol, a significant decrease in the cholesterol esters:cholesterol ratio was found in the cortical synaptosomes and a decrease was found in the linoleate content of the cholesterol esters fraction. The composition of the pool of free fatty acids remained unchanged. These results are in agreement with those previously reported which show that following its chronic administration, ethanol decreases polyunsaturated fatty acid composition of phospholipids in the synaptosomal fraction and increases the saturated and monounsaturated fatty acids in cholesterol esters.

The effect of a putative antidepressant, an O2-substituted derivative of barbitone on apomorphine induced hypomotility.

The effects of the chronic administration of barbitone and its O2-substituted isopropyl derivative (O2IB) was studied on the hypomotility induced in rats by the acute administration of a low dose of apomorphine. Neither drug was found to selectively antagonize the hypomotility caused by acute apomorphine administration. No correlation could be found between the behavioural effects of the barbiturates and changes in the concentrations of biogenic amines and GABA in four discrete brain regions. The results of this study do not support the conclusions of previous acute studies in which O2IB has been shown to have an antidepressant profile.

Attenuation of the effects of chronic ethanol administration in the brain lipid content of the developing rat by an oil enriched in gamma linolenic acid.

Chronic ethanol administration to adult rats results in an increase in the linolenic (18:2) to arachidonic (20:4) acid ratios in brain phospholipids. Administration of a diet rich in essential fatty acids can reverse some of the effects of chronic ethanol administration on neuronal membranes. In this study we investigated the effect of ethanol on the neuronal membranes of rat pups and also the effect of the concomitant administration of gamma linolenic acid (18:3) as a component of Evening Primrose Oil (EPO). We found an increase in the concentration of several saturated fatty acids that are components of the phospholipids and a decrease in the mono- and polyunsaturated fatty acid content. EPO was found to attenuate the effect of ethanol in inhibiting the synthesis of polyunsaturated fatty acids. These effects of EPO are probably a direct consequence of the essential fatty acids in the oil circumventing the inhibitory effects of ethanol on polyunsaturated fatty acid synthesis.

Effects of an oil enriched in gamma linolenic acid on locomotor activity and behaviour in the Morris Maze, following in utero ethanol exposure in rats.

Ethanol is known to decrease the quantity of polyunsaturated fatty acids in brain membranes possibly as the repercussion of an inhibition of delta-5- and delta-6-desaturases. Consequently behavioural changes may occur. Evening Primrose Oil (EPO) which is rich in gamma linolenic acid (10% 8:3 (n-6)) was proposed to try to circumvent these deleterious effects of ethanol. An animal model of the foetal alcohol syndrome was used in which ethanol was administered throughout gestation and into the weaning period, in a milk diet. EPO was administered concurrently with ethanol to establish the effect of this essential fatty acid and ethanol on the animal's behaviour. Animals were tested at approximately 60 days of age for their responses in two different behavioural paradigms, i.e. the stressful memory task of the Morris Maze and the non-stressful activity monitor. In this study we report an increase in learning ability in male (Control-EPO and alcohol-EPO versus their control: P less than 0.00001 and P less than 0.01, respectively) and female rats (Control-EPO and alcohol-EPO versus control: P less than 0.0001 and P less than 0.00001, respectively) after administration of EPO. It was also found that ethanol plus EPO administration consistently raised the activity scores of the rats in the activity monitor (daytime activity scores for male and female rats were P less than 0.00001 and P less than 0.0001, respectively), while ethanol alone decreased the scores (male and female rats P less than 0.00001 and P less than 0.01, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Acetaldehyde adducts with serum proteins are not responsible for decreased drug binding in alcoholic patients.

Decreased plasma binding of phenytoin and diazepam has previously been described in patients with alcoholic liver diseases. It has been attributed to hypoalbuminemia, endogenous displacers and/or qualitative changes in albumin such as formation of adducts with acetaldehyde, a highly reactive metabolite of ethanol. In the present report this hypothesis was tested. After treating the sera with activated charcoal to remove the endogenous displacers and adjusting albumin concentration to a constant level, the binding parameters of both drugs, phenytoin and diazepam, were determined in 14 healthy men and 16 alcoholic patients by equilibrium dialysis. In these conditions, no significant difference in the number of binding sites nor in the affinity constant was observed, which suggests that acetaldehyde adducts with proteins do not contribute, to a major extent, to the defect of drug binding observed in alcoholic patients.

[A detailed lipidograph: enzymatic determination of cholesterol, phospholipids and glycerides in plasma lipoprotein after a cellulose acetate electrophoretic procedure (author's transl)]. / Lipidogramme détaillé: évaluation enzymatique du cholestèrol, des phospholipides et des glycerides après électrophorèse du plasma sur acétate de cellulose.

The specific determination of cholesterol and its evaluation in lipoproteins separated by cellulose acetate electrophoresis is described. Using this technique, the authors extended the specific lipid determinations to phospholipids and glycerides. The precision, linearity, accuracy of the methods are satisfactory for fractions greater than 10%. Phospholipids and cholesterol values in alpha lipoproteins are compared with those obtained in the supernatant by concanavalin A precipitation; the differences between the two methods are not significant. We suggest using these three enzymatic determinations to produce a detailed lipidograph. For a selected population, the lipid values in each fraction (expressed in g/l and in mmol/l) were close to those given in the literature. We compared our lipidograph, expressed in SI units, with the Oil Red O stained lipidograph; the difference was not significant.

Interaction of methadone with substrates of human hepatic cytochrome P450 3A4.

Methadone, a synthetic drug, is one of the most widely used drugs for opiate dependency treatment. This drug has been demonstrated to be extensively metabolized by cytochrome P450 3A4 in human liver microsomes. Thus, the aim of this in vitro study was to determine if methadone is an inhibitor of other P450s characterized by their specific catalytic activities. Enzymatic activities specific to P450 2E1, P450 1A, P450 2B and P450 2C were not inhibited by methadone. Conversely, nifedipine oxidation, mediated by cytochrome P450 3A4, was potently inhibited by methadone by a mixed-type inhibition mechanism with a Ki of 100 microM. Fluvoxamine, a new antidepressant, was shown to be a potent mixed-type inhibitor of methadone N-demethylation with a Ki of 7 microM. Finally, methadone appears to be a mixed-type inhibitor and not a suicide inhibitor of cytochrome P450 3A family. Accordingly, caution should be advised in the clinical use of methadone when other drugs are administered that are able to induce or inhibit P450 3A4, such as rifampicin or nifedipine, diazepam and fluvoxamine.

Caffeine increases its own metabolism through cytochrome P4501A induction in rats.

Caffeine is one of the most widely used - and maybe abused - xenobiotic compounds in the world. If numerous pharmacological properties of caffeine have been reported, the effects of caffeine treatment on the hepatic drug-metabolizing enzyme system have been scarcely studied. Pretreatment of rats for 3 days with 150 mg/kg/day of caffeine dramatically increased P4501A and P4502B dependent catalytic activities determined in vitro. Furthermore, N-demethylations and C-8 oxidation of caffeine were increased by about 2 fold by caffeine treatment. Immunoblot analysis demonstrated that the liver contents of P4501A2 and P4502B1/2B2, known to be involved in these monooxygenase activities, increased also by about 2 fold. Cytochrome P4503A1 and 2E1 were not modified. Taken together, there data suggest that caffeine increases its own metabolism through P4501A induction.