Hepatic Microsomal Enzyme Induction Research Articles

Induction of hepatic microsomal drug-metabolizing enzymes by sulfur-containing metabolites of chlorinated benzenes in rats

3,5-Dichlorophenyl methyl sulfide and its oxidized compounds, metabolites of m-dichlorobenzene, increased the activity of aniline hydroxylase and aminopyrine N-demethylase and the content of cytochromes P-450 and b 5 in rat liver microsomes. Hexobarbital sleeping time was reduced by these three compounds. After the administration of the sulfide to rats, 3,5-dichlorophenyl methyl sulfone appeared in blood, liver, and kidneys, and remained detectable in the blood and the tissues between 120 and 240 hr. The sulfone was considered to play a principal role in the induction by these compounds. Other chlorophenyl methyl sulfones also showed similar induction activity.

Hepta-, hexa-, tetra- and dichloronaphthalene congeners as inducers of hepatic microsomal drug-metabolizing enzymes

Pretreatment of immature male Wistar rats with 1,2,3,4,5,6,7-hepta-, 1,2,3,4,5,6,8-hepta- and 1,2,3,4,5,6-hexachloronaphthalene resulted in the induction of several hepatic microsomal drug-metabolizing enzymes. The enzymic activities, reduced cytochrome P-450: CO and ethylisocyanide binding difference spectra and electrophoretic mobilities of the induced microsomal proteins were comparable to those observed after administration of the classical inducer of microsomal aryl hydrocarbon hydroxylase, 3-methylcholanthrene. The 1,2,3,4,5,6,7-heptachloronaphthalene congener, which is fully substituted in the lateral 2,3,6 and 7 positions, was more potent than the 1,2,3,4,5,6,8-hepta- and the 1,2,3,4,5,6-hexachloronaphthalene congeners which contain only 3 lateral chloro substituents. 1,2,3,4-Tetra- and several lower chlorinated naphthalenes were inactive as inducers of microsomal aryl hydrocarbon hydroxylase. The effects of structure on the induction activities of the polychlorinated naphthalenes were similar to those observed for other halogenated aryl hydrocarbons.

Rat hepatic microsomal enzyme induction by pretreatment with toxaphene and toxaphene fractions.

The levels of hepatic microsomal induction caused by toxaphene were determined. Young Sprague-Dawley rats (70 g) were administered toxaphene (ip injection, daily for 5 d) at 0, 5, 25, and 100 mg/kg. All doses caused increases in liver/body weight ratio, cytochrome P-450 level, aminopyrine demethylation, and aldrin epoxidation. The aldrin epoxidase activity increased almost 700% at the 100-mg/kg dose. Toxaphene was separated into nonpolar (S-A) and polar (S-B) fractions and administered as before at 25 mg/kg. All treatments caused significant increases in cytochrome P-450, aminopyrine demethylation, and aldrin epoxidation. A comparison of the treatments, however, did not reveal any significant differences between the treatments.

Investigation of the interaction between Probon and indomethacin in rats.

The toxic side-effects and anti-inflammatory activity of combination treatment of Sprague-Dawley rats with indomethacin and Probon, a new type of analgesic, were investigated. Following four weeks of treatment with a combination of these two drugs, the characteristic gastrointestinal side-effect of indomethacin was markedly reduced. Mortality resulting from administration of the drug combination was significantly lower than that resulting from indomethacin treatment alone. The reduced toxicity of indomethacin in combination with Probon is probably due to a change in metabolism produced by the hepatic microsomal enzyme inducer, Probon. The anti-inflammatory effect was also investigated using a contact thermographic method following one, three or seven days pretreatment. The advantage of this combination is that, using a higher dose of indomethacin in combination with the minor analgesic, we could achieve a more reliable anti-inflammatory effect together with a pain-killing action.

Plasma high-density lipoproteins and liver lipids and proteins in man. Relation to hepatic histology and microsomal enzyme induction.

The association of high-density lipoproteins (HDL) in plasma with liver lipids and proteins was investigated in 28 subjects with diagnostic liver biopsy. Lipids and proteins were evaluated in relation to hepatic histology and microsomal enzyme induction, assessed by liver cytochrome P-450. Moderate-severe hepatic parenchymal changes were associated with low liver phospholipids, protein and cytochrome P-450, low plasma HDL cholesterol (HDL-C), and high hepatic triglycerides. Liver microsomal induction accompanying anticonvulsant therapy was associated with high liver phospholipids and protein, high plasma HDL-C, apoproteins A-I and A-II, and high HDL-C/total cholesterol (T-C) ratio. HDL-C, A-I and the HDL-C/T-C ratio were directly proportional to liver phospholipids, protein and cytochrome P-450, inversely related to hepatic triglycerides. Increases in hepatic phospholipids and protein, characteristic of microsomal induction, may lead to the elevation of plasma HDL apoprotein and HDL-C levels and HDL-C/T-C ratios, and thus reduce the risk of coronary heart disease.

Serum LDL cholesterol, the LDL/HDL cholesterol ratio and liver microsomal enzyme induction evaluated by antipyrine kinetics

The association of serum LDL and HDL cholesterol with hepatic microsomal enzyme induction, assessed by plasma antipyrine kinetics was investigated in 30 epileptics. Patients on enzyme-inducing anticonvulsants had reduced LDL/HDL cholesterol ratios and elevated HDL cholesterol concentrations and HDL/total cholesterol ratios, indicating a cholesterol transfer from LDL to HDL. Strong hepatic microsomal enzyme induction was associated with reduced LDL cholesterol. The LDL/HDL cholesterol ratio was negatively proportional and the HDL/total cholesterol ratio positively proportional to the antipyrine clearance rate. Epileptics, particularly those with a high antipyrine clearance, had a cholesterol distribution pattern characteristic of a low probability of developing coronary atherosclerosis. The results support the view that hepatic microsomal enzyme induction favourably alters the cholesterol distribution in the body.

Unidirectional Cross-Tolerance Between the Carbamate Insecticide Propoxur and the Organophosphate Disulfoton in Mice

Previous studies have shown that subchronic treatment of mice with the organophosphate insecticide, disulfoton, or the carbamate insecticide, propoxur, leads to the development of tolerance to their toxicity. Tolerance to disulfoton was due to a decrease in the number of muscarinic cholinergic receptors, while tolerance to propoxur appeared to be due to an induction of hepatic microsomal enzymes. In the present study we investigated if cross-tolerance between disulfoton and propoxur would occur. Cross-tolerance was evaluated by measuring acute toxicities, cholinesterase and carboxylesterase inhibition and hypothermic and antinociceptive effects. Mice tolerant to propoxur were cross-tolerant to the hypothermic and anticholinesterase effects of disulfoton. Similarly, when mice were pretreated with the microsomal enzyme inducer, phenobarbital, the toxicity of disulfoton was decreased. Mice made tolerant to disulfoton were cross-tolerant to the organophosphate chlorpyrifos, but were more sensitive than controls to the toxicity of propoxur. The acute toxicity of the organophosphate malathion was also increased in disulfoton-tolerant mice. Propoxur is metabolized by mixed function oxidases and possibly by a carboxylesterase. While hepatic microsomal enzymes appeared to be unchanged in disulfoton-tolerant mice, brain and liver carboxylesterase activities were significantly inhibited. Pretreatment of mice with the specific carboxylesterase inhibitor triorthotolylphosphate is known to greatly potentiate the toxicity of malathion and also potentiated, to a lesser extent, the toxicity of propoxur.(ABSTRACT TRUNCATED AT 250 WORDS)

Anticonvulsant potency of common antiepileptic drugs in the gerbil.

In gerbils, 'minor' (myoclonic) and 'major' (clonic-tonic) seizures were induced by blowing at the animals with compressed air. The anticonvulsant ED50 of the following drugs was determined after oral administration against both types of seizures: phenytoin, phenobarbital, carbamazepine, sodium valproate, ethosuximide, and diazepam. Valproate, ethosuximide, and diazepam were most potent against 'minor' seizures which could not or only partially be suppressed by phenytoin or carbamazepine, respectively. The 'grand mal' drugs phenytoin, phenobarbital, and carbamazepine were, on the other hand, more potent against 'major' than against 'minor' seizures. When phenobarbital was administered for several days, a strong induction of hepatic microsomal enzymes occurred.

Vitamin D from skin: contribution to vitamin D status compared with oral vitamin D in normal and anticonvulsant-treated subjects.

1. The plasma 25-hydroxycholecalciferol [25-(OH)D3] response to measured u.v. irradiation applied thrice weekly for 10 weeks was investigated in normal and in anticonvulsant-treated subjects. 2. Levels of plasma 25-(OH)D3 achieved after u.v. irradiation were similar in both normal and anticonvulsant-treated subjects, suggesting that hepatic microsomal enzyme induction does not lead to low plasma 25-(OH)D3 concentrations. 3. Cholecalciferol was present in plasma of normal subjects in a very low concentrations (less than 5.0 nmol/l) and did not increase until plasma 25-(OH)D3 levels exceeded 62.5 nmol/l. 4. Cholecalciferol occurred in significant concentrations in plasma during whole body u.v. irradiation or during oral dosage of 62.5 nmol (100 i.u) or more daily. 5. Plasma 25-(OH)D3 concentrations reached a steady state after 5-6 weeks of u.v. irradiation or of oral intake within the usual intake range. 6. Cholecalciferol synthesis in skin calculated from the steady-state equation was 0.0015 +/- 0.0008 nmol/mJ. 7. Cholecalciferol synthesis in skin was also calculated from the oral dosage required to yield the same plasma 25-(OH)D3 concentration as u.v. irradiation and was 0.0024 +/- 0.0018 nmol/mJ. 8. Rates of cholecalciferol synthesis calculated from these data suggest that many of the population of England receive insufficient u.v. irradiation to maintain vitamin D status throughout the year.

Relationship between plasma high-density lipoprotein cholesterol and anticonvulsant levels in epileptics.

Plasma high-density lipoprotein (HDL) cholesterol is a recognized negative risk factor for coronary heart disease. In this study, therapy with phenytoin alone, carbamazepine alone, and phenytoin in combination with phenobarbital was associated with elevated plasma HDL cholesterol concentrations. The highest HDL cholesterol levels were seen in subjects treated with the combination of phenytoin and phenobarbital. Plasma HDL cholesterol levels were proportional to the serum phenobarbital and carbamazepine concentrations. In subjects treated with phenytoin alone, low plasma HDL cholesterol levels were associated with low drug concentrations. The results suggest direct links running from the serum anticonvulsant levels to the extent of hepatic microsomal enzyme induction, and further to the plasma HDL cholesterol concentrations.

Acute and subacute toxicity of octachlorostyrene in the rat.

This study was designed to investigate the acute and subacute toxicity of octachlorostyrene (OCS), a demonstrated environmental pollutant in fish from the Great Lakes and off the Norwegian coast in Europe. In an acute study, groups of 10 male rats were given by gavage single doses of OCS at 1300, 1690, 2190, 2850, or 3710 mg/kg and killed 14 d later. Octachlorostyrene at a dose of 1690 mg/kg and higher caused increased liver weight, increased hepatic microsomal aniline hydroxylase and aminopyrine demethylase activities, and increased serum cholesterol and uric acid levels. Only mild histological changes were seen in the thyroid of the treated animals. In a subacute study, groups of 10 male and female rats were fed diets containing 0.5, 5.0, 50 or 500 ppm OCS for 28 d. Growth rate and food consumption were not affected by treatment. Liver hypertrophy and hepatic microsomal enzyme induction were observed in animals fed 50 ppm OCS or higher. Elevations in serum cholesterol, total protein, potassium, and sorbitol dehydrogenase (SDH) occurred in rats fed the 500 ppm diet. Histological changes occurred in the liver and thyroid of rats exposed to as low as 5.0 ppm OCS. The OCS residues accumulated in the fat and liver in a dose-dependent manner. These data suggest that OCS can produce biochemical and histological changes in rats after administration of a single oral dose and/or when fed in the diet.

Hepatic microsomal enzyme induction by aroclors 1248 and 1254 in cynomolgus monkeys

Aroclors 1248 (2 mg/kg body weight) and 1254 (5 mg/kg body weight) produced a 3-methylcholanthrene type of mixed-function oxidase induction, in the livers of adult female cynomolgus monkeys after 69–122 days of dosing, when the animals were moribund. Both Aroclor 1248 and 1254 produced a mixed pattern of induction in mouse liver 66 hr after ip treatment with 1000 mg/kg body weight including changes characteristic of 3-methylcholanthrene-type induction. However the same dose of Aroclor 1016 did not produce 3-methylcholanthrene-type enzyme induction in mice. The results in adult monkeys are consistent with the hypothesis that PCB isomers capable of inducing aryl hydrocarbon hydroxylase and causing a ‘blue’ shift in the cytochrome peak, are associated with increased toxicity. However the lack of response with Aroclor 1016 in mice suggests that the reported toxicity of this aroclor to infant monkeys may not result from isomers producing a 3-methylcholanthrene-like effect.

Serial PBB levels, PCB levels, and clinical chemistries in Michigan's PBB cohort.

Half of a cohort of 3683 Michigan residents exposed to polybrominated biphenyls (PBBs) in 1973 and 1974 had 2 serum PBB determinations at a 1- or 2-yr interval. The median decrease in serum PBB levels during both 1- and 2-yr intervals was 1 microgram/L. The geometric mean serum polychlorinated biphenyl (PCB) level (6.3 microgram/L) exceeded that of PBB (4.1 micrograms/L), although the range of PCB levels (smaller than 1-57 microgram/L) was narrower than that of PBB levels (smaller than 1-3150 micrograms/L). Mean PCB and PBB levels were higher for males, and mean PCB levels increased with age. In a subgroup with higher-than-average PBB levels, serial clinical chemistry tests during 4 different years showed no consistent significant correlation with serum PBB levels. Tests with greater sensitivity and specificity for hepatic microsomal enzyme induction and thyroid status are needed in future evaluations of the most highly exposed subgroup of the cohort.

Phenobarbital pharmacokinetics and salivary and serum concentrations in pregnancy.

The pharmacokinetics and the ratio between salivary and serum concentrations of phenobarbital (PB) were determined in 10 women undergoing treatment in late pregnancy. An approximately 2.5-fold variation was measured in the apparent relative clearance rates of PB in the women studied. The means of the total clearance rate (0.255 L/h), the relative clearance rate (4.0 ml/h/kg of body weight), the elimination half-life (95 h), the elimination rate constant (0.0071/h), and the apparent volume of distribution (35.49 L) were within the ranges observed in nonpregnant subjects. The PB concentration in saliva was 34% of that in serum. Salivary and serum levels of PB correlated closely with each other. Serum gamma-glutamyl transpeptidase activity increased, and total bilirubin concentrations decreased during PB treatment, both of which can be linked to the PB-caused hepatic microsomal enzyme induction phenomenon. The variation in clearance rate emphasizes the importance of close monitoring of PB treatment of pregnant women. The results suggest that salivary PB measurements can be used with sufficient accuracy to predict PB concentrations in the serum and to optimize PB treatment during pregnancy.

Induction of mixed function oxidases by petroleum in the American eel, Anguilla rostrata.

American eels, Anguilla rostrata, were exposed to crude oil by ingestion of a 10, 100, or 500 microliters/kg fish dose per day for five days. Depuration was followed for an additional twelve days. All oil doses caused an induction of hepatic microsomal enzymes, maximally by three days of exposure. Benzo(a)pyrene hydroxylase (BaPH) showed a dose related response, with greater induction at 100 microliters/kg than at the other doses. The highest dose was hepatotoxic. Cytochrome P-450 induction was dose independent, and remained induced maximally for the entire experimental period, in contrast to BaPH which declined in activity. Reaction optimum for BaPH was at pH 7.5 and 27 degrees C. A study of tissue distribution showed the liver to account for nearly all BaPH activity. A significant increase in the protein content of the hepatic postmitochondrial fraction of oil-exposed fish was also observed.

Plasma high-density lipoproteins and hepatic microsomal enzyme induction. Relation to histological changes in the liver.

The relationship between high-density lipoproteins (HDL) in plasma and hepatic structure and microsomal function has been investigated in 54 patients undergoing diagnostic liver biopsy. Plasma HDL cholesterol and major apoproteins were correlated with hepatic histology and microsomal enzyme activity assessed directly as liver cytochrome P-450 concentration and indirectly by plasma antipyrine clearance rate. HDL cholesterol, the concentrations of apoproteins A-I and A-II, the HDL cholesterol/total cholesterol ratio and cytochrome P-450 were low in subjects with moderate or severe hepatic fatty infiltration or cirrhosis when compared with the values for subjects with a normal live. HDL cholesterol and apoprotein A-I and the HDL cholesterol/total cholesterol ratio were directly proportional to the amount of non-fatty parenchyma in the livers. Subjects with a normal liver undergoing treatment with enzyme-inducing drugs, such as phenytoin, phenobarbital and primidone, had higher HDL cholesterol, apoproteins A-I and A-II, HDL cholesterol/total cholesterol ratio, cytochrome P-450 and antipyrine clearance rate than subjects not receiving such therapy. Treatment with inducers appeared to have compensated for the effect of liver disease in lowering plasma HLD. In the entire population, and also in subjects not taking inducing drugs, when considered separately, plasma HDL cholesterol, apoproteins A-I and A-II and the HDL cholesterol/total cholesterol ratio were significantly correlated with cytochrome P-450 concentration. In subjects on enzyme inducers, HDL cholesterol and apoprotein A-I levels and the HDL cholesterol/total cholesterol ratio were proportional to the magnitude of the induction. Serum triglycerides were inversely proportional to the measures of liver microsomal enzyme activity. The lipoprotein pattern, high HDL cholesterol and apoproteins A-I and A-II, and high HDL cholesterol/total cholesterol ratio that accompany microsomal induction are characterized by a reduced risk of atherosclerotic vascular disease and a prolonged expectation of life. The plasma changes presumably reflect the effect of enzyme inducers, such as phenytoin and phenobarbital on hepatic lipids and proteins.

Hepatic microsomal enzyme induction by aroclors 1248 and 1254 in cynomolgus monkeys

Aroclors 1248 (2 mg/kg body weight) and 1254 (5 mg/kg body weight) produced a 3-methylcholanthrene type of mixed-function oxidase induction, in the livers of adult female cynomolgus monkeys after 69–122 days of dosing, when the animals were moribund. Both Aroclor 1248 and 1254 produced a mixed pattern of induction in mouse liver 66 hr after ip treatment with 1000 mg/kg body weight including changes characteristic of 3-methylcholanthrene-type induction. However the same dose of Aroclor 1016 did not produce 3-methylcholanthrene-type enzyme induction in mice. The results in adult monkeys are consistent with the hypothesis that PCB isomers capable of inducing aryl hydrocarbon hydroxylase and causing a ‘blue’ shift in the cytochrome peak, are associated with increased toxicity. However the lack of response with Aroclor 1016 in mice suggests that the reported toxicity of this aroclor to infant monkeys may not result from isomers producing a 3-methylcholanthrene-like effect.

Inhibition of liver regeneration by chronic alcohol administration.

Liver regeneration is the common mechanism whereby a patient recovers form a liver injury. In the western world, ethanol is the single most important aetiological factor associated with liver disease, and it appears crucial to determine if ethanol interferes with liver regeneration. We studied the response to a 70% hepatectomy in 240 rats receiving a nutritionally adequate diet containing 36% of their calories as ethanol for three weeks and their pair-fed controls receiving a liquid diet where ethanol is isocalorically replace with carbohydrates. Criteria of liver regeneration were: incorporation of 3H-thymidine in hepatocyte DNA (cpm/10 microgram DNA) and number of hepatocyte labelled nuclei on autoradiography per 100 high power fields. Controls displayed the usual response with peak activity of liver regeneration at 24 hours. Consumption of ethanol was associated with a statistically significant reduction of liver regeneration by both criteria for up to 72 hours after a 70% hepatectomy and delayed the peak of regenerative activity by 24 hours. This inhibiting effect was not related to the presence of alcohol in blood nor to hepatic microsomal enzyme induction by ethanol nor to widespread necrosis of hepatocytes. This effect was reversible after one week of abstinence. This impairment of liver cell renewal by ethanol may be of major significance in the severity and outcome of alcohol-related liver injury.

EFFECTS OF THE INHALATION OF ENFLURANE ON HEPATIC MICROSOMAL ENZYMATIC ACTIVITIES IN THE RAT

We have investigated the possible hepatic microsomal enzyme induction effect of enflurane, administered by inhalation in anaesthetic doses for periods of 1 h a day. In 15 experimental groups, differing from one another in anaesthetics concentration (1, 2 and 3% enflurane) and in the number of days of treatment (3, 7, 10, 14, 21 and 24) we found (1) no alteration either in the ratio of liver to body weight or in the microsomal protein content; (2) no modifications in aniline hydroxylase activity; (3) a decrease in the aminopyrine demethylase activity after a number of exposures, varying with the dose.

Enzyme induction and hepatic glycerolipid synthesis in rats treated with 3-methylcholanthrene.

Fasting male rats fed 3-methylcholanthrene in a daily dose of 40 mg . kg body weight-1 gave evidence of hepatic microsomal enzyme induction after 3 days through significantly increased hepatic aryl hydrocarbon hydroxylase activity, cytochrome P448 content, and characteristic changes in microsomal proteins analysed by sodium dodecyl sulfate--polyacrylamide gel electrophoresis. Concomitantly, activities of aminopyrine N-demethylase and microsomal gamma-glutamyltransferase, which are increased in phenobarbital-treated rats, significantly declined. In contrast to phenobarbital, which has been previously shown to increase hepatic triacylglycerol content and in vitro glycerolipid synthesis, 3-methylcholanthrene did not affect hepatic triacylglycerol content, but did inhibit glycerolipid synthesis by cell-free preparations of rat liver and significantly reduced serum triacylglycerol concentration. Thus, the two prototypical drugs inducing characteristically different changes in microsomal enzyme and hemoprotein response also seem to differ in their effect upon another important microsomal function, hepatic glycerolipid synthesis.