Studies on the mechanism of sex difference in drug-oxidizing activity of liver microsomes

Metabolism of territrem a in liver microsomes from wistar rats: 2. Sex differences and regulation with gonadal hormones and phenobarbital

The aim of the present study was to assess the effects of sex difference on metabolism of territrem A (TRA) by liver microsomes from 7-wk-old Wistar rats. Metabolism of TRA to 2-dihydro-4beta-demethylterritrem A (MA2) through 4beta-hydroxymethyl-4beta-demethylterritrem A (MA1) and 4beta-oxo-4beta-demethylterritrem A (MAX) was observed in intact male rats. However, in intact female rats only MA1 was formed, although the amount of MA, formed in females was much less than in males. Phenobarbital pretreatment enhanced this step and was not affected by gonadectomy. In the gonadectomized rats of both sexes, MA2 was formed from TRA when the animals were further treated by testosterone and was significantly enhanced by treatment with phenobarbital. However, estradiol treatment or estradiol in combination with phenobarbital treatment did not affect MA2 formation from TRA in gonadectomized rats.

Effects of the estrous cycle and the gender differences on hepatic drug-metabolising enzyme activities

The aim of the present study was to investigate the effects of the estrous cycle and physiological dose of estradiol (E2) and the gender difference on several hepatic drug-metabolising enzyme activities. Eight-week old female Sprague-Dawley rats at different stages of the estrous cycle [proestrous (P), estrous (E), and diestrous (D)] and 8-week old male rats were used in this study (n = 5, respectively). Serum E2 level at D was higher than that at E and lower than that at P. The hepatic cytochrome P450 content, aniline hydroxylase, ethoxycoumarin O-deethylase and aminopyrine N-demethylase activities in male were significantly higher than those in female at any stage of the estrous cycle and these activities in female remained unchanged during the estrous cycle. Neither the estrous cycle nor the gender difference affected the cytochrome b5 content. NADPH-cytochrome c reductase (fPT) activity at P was similar to that in male, and was significantly higher than that in E and D. fPT activity was increased by the administration of physiological dose of E2 in ovariectomized rats. Uridine diphosphate glucuronyltransferase (UDP-GT) activity at E was significantly lower than that at P or D and that activity in female was significantly lower than that in male. These results indicate that the estrous cycle, especially serum E2 level, may affect both fPT and UDP-GT activities.

Sex-related differences of hepatic microsomal mixed function oxidase system and antibody production in broilers implanted with corticosterone and/or fed ascorbic acid

1. Most of the components of the mixed function oxidase (MFO) in hepatic microsomes were reduced by corticosterone implants, and the degree of the reduction in females and at an older age was greater than those in males and at a younger age. 2. Ascorbic acid (AA) prevented the reduction in the MFO caused by corticosterone implants. 3. The activities of aniline hydroxylase and aminopyrine N-demethylase were enhanced by corticosterone implants regardless of AA supplementation. 4. The activity of NADPH-cytochrome c reductase in male broiler was greater than that in females under normal conditions. 5. Corticosterone implants and dietary AA had less influence on the antibody production, especially to T-cell dependent antigen.

Regulation of the expression of the sex-specific isoforms of cytochrome P-450 in rat liver

The hepatic metabolism of steroid hormones and of xenobiotics frequently depends on the expression of the sex-specific isoforms of cytochrome P-450 and on differences in sex hormones. Following biochemical, immunological and molecular biological investigations, it was shown that in adult rat liver there exist at least four male-specific and one female-specific isoforms of cytochrome P-450. The designation of these sex-specific genes is IIC11, IIIA2, IIC13 and IIA2 in males, and IIC12 in females. The irreversible programming of the expression of these isoforms of cytochrome P-450 in adulthood occurs during the perinatal period of life, and is named enzyme imprinting. One of the main factors that regulates the expression of the sex-specific isoforms of cytochrome P-450 is the level of androgens in the blood. Castration of adult rats decreased the level of the male isoforms of cytochrome P-450 and the activity of the monooxygenase enzyme system that remained higher than in intact females. The mechanism of enzyme imprinting can be explained as follows: neonatal androgens program the secretion of hypothalamic hormones, somatostatin and growth-hormone-releasing factor. These factors determine the type of growth hormone secretion in adult rats, and this controls the type of sex-specific isoforms of cytochrome P-450 expressed in adulthood. Metabolic regulation similar to that outlined above was shown to occur for several metabolism-dependent chemical carcinogens. Such a pathway may explain the different sensitivity displayed by male and female rats to treatment with these carcinogenic agents. One possible way of modulating the expression of some isoforms of cytochrome P-450 in adult rats is by treating neonates with specific xenobiotics that change the constitutive expression of neonatal androgens. It appears that this enzyme imprinting plays an important role in determining the individual sensitivity to the carcinogenic effects of chemicals.

Indium selectively increases the cytochrome P-450 dependent O-dealkylation of coumarin derivatives in male mice

Indium pretreatment of rats and mice has been reported to decrease the concentration of cytochrome P-450, thereby reducing the activity of some cytochrome P-450 dependent enzymatic reactions. The present study reveals that pretreatment of C57Bl/6JHan mice of both sexes with one s.c. dose of 120 mg of In2(SO4)3.5 H2O per kg of body weight decreases the concentration of cytochrome P-450 to about 65% of control levels. Neither cytochrome b5 nor NADPH-cytochrome P-450 reductase is affected. Hepatic microsomal ethoxyresorufin O-deethylase activity declines to about 75% of control values. In contrast, with coumarin substrates, a sex dependence in the direction of change is observed: in female mice indium decreases the activity to about 75%, whereas in males it enhances the activity to 140%. Moreover, with 7-(methoxy-14C)coumarin as substrate, indium-pretreated male mice exhale about 180% and females about 65% of 14CO2 compared to the corresponding controls. A close correlation between the in vivo and in vitro effects of indium on the metabolism of the coumarin derivatives is suggested. After isolation and purification of cytochrome P-450, SDS-PAGE indicates in indium-pretreated male mice an intensification of a 48.5 kDa protein band which is decreased in females. Immunological studies using antibodies raised against control female cytochrome P-450 show cross reactivity among all microsomes used in these experiments. High percentages of inhibition occur in microsomes with high molecular activity towards coumarin derivatives. The in vitro kinetics of antibody-inhibited O-deethylation of 7-ethoxycoumarin seems to obey a non- or partial-competitive type of inhibition. Indium pretreatment of mice produces sex-dependent effects on the metabolism of coumarin derivatives.

Sex-related differences in NADPH-dependent lipid peroxidation induced by cadmium

Male and female rats were dosed once a day for 2 days with injections of 1.5 mg Cd/kg. Formation of thiobarbituric acid reactive substances (TBA-RS) was significantly increased in male rat liver but not in the females. NADPH-dependent lipid peroxidation in vitro in microsomes derived from untreated rat liver was greater in males than in females. Furthermore, addition of cadmium (Cd) to microsomes isolated from male rat liver produced a dose-dependent potentiation of NADPH-dependent lipid peroxidation from low concentrations of Cd. In microsomes derived from females a significant increase in lipid peroxidation was observed only at high Cd concentrations. NADPH-dependent lipid peroxidation enhanced by Cd was greater in the males than in the females. These data suggest that a sex-related difference in the ability of Cd to induce lipid peroxidation in vivo in rat liver appears to be mediated partly through differences in hepatic microsomal NADPH-dependent lipid peroxidation.

Hepatotoxicity and metabolism of acetaminophen in male and female rats

This present study was designed to assess the role of metabolic and pharmacokinetic factors in the lower susceptibility of female rats compared to male rats to xenobiotics metabolized by the cytochrome P-450-dependent mixed-function oxidase (MFO) system. Adult intact male and female Sprague-Dawley rats were administered labeled acetaminophen (1 g/kg body weight + 5 microCi [3H]acetaminophen) after an overnight fast. They were bled and killed at 0.5, 1, 2, 3, 6, 12, 24, and 36 h after drug administration. The percentage of [3H]acetaminophen radioactivity remaining in blood, liver, GI tract, and excreted in the urine was determined at all time intervals. Plasma prothrombin time and serum transaminases were determined as indices of hepatotoxicity. Hepatic GSH and glycogen were assayed. Total urinary acetaminophen and its metabolites and the molar percent of various metabolites excreted during the first 6 h were determined. Castrated male and ovariectomized female rats and their respective controls were also given acetaminophen (APAP) and were killed 24 h later to determine hepatotoxicity. The extent of hepatic damage in the intact male rats was greater and appeared sooner than in the female rats. Hepatic GSH and glycogen were depleted earlier in female rats. The percent of the administered dose excreted in the urine during the first 6 h was 17.5 for the male rat versus 24.5 for the female rat. While the APAP glucuronide conjugate concentration was significantly higher, the APAP sulfate conjugate concentration was lower in the female than it was in the male rat. Although peak radioactivity in serum was reached by 30 min in both male and female rats, suggesting quick intestinal absorption, it was significantly higher in female rats and was associated with decreased intestinal and hepatic levels and increased urinary excretion when compared to male rats. While castration of male rats decreased susceptibility to hepatotoxicity, ovariectomy of female rats tended to increase susceptibility to hepatotoxicity in comparison to their respective controls. Our data suggest that aside from the reported sex differences in the cytochrome P-450-dependent MFO enzymes, there are significant differences in GSH utilization. There are also significant changes in glucuronidation and sulfation pathways, as well as in the pharmacokinetics of acetaminophen, which tend to protect female rats against acetaminophen hepatotoxicity.

Potentiation of CCl4 hepatotoxicity and lethality by chlordecone in female rats

Female Sprague-Dawley rats (175-200 g) were maintained on a commercial powdered rat chow containing 0 or 10 ppm chlordecone (Kepone; CD). On day 15 of the dietary protocol, a single dose of CCl4 (5-100 microliters/kg) was administered i.p. in corn oil vehicle. Controls received corn oil vehicle only. Twenty-four hours after CCl4 administration, hepatotoxicity was assessed using biochemical, functional, and histopathological parameters. Serum enzymes (GPT, GOT, ICD and OCT) were elevated in a dose related manner in the animals receiving CD-CCl4 combination. CCl4 alone at the doses used had no marked effect. Centrilobular necrosis was observed in the animals receiving CD-CCl4 combination. Biliary excretion of phenolphthalein glucuronide (PG) and the rate of bile flow were decreased in a dose-dependent manner. Forty-eight hour LD50 of CCl4 was decreased 26-fold by CD pretreatment. These results indicate that CD potentiates CCl4 toxicity in female rats as well. Since the hepatic functional status is greatly compromised, the CD potentiated lethality is preceded by hepatic failure. Furthermore, female rats are sensitized to smaller doses of CCl4 in comparison to male rats.

Influence of estradiol and testosterone on cytochrome P-450 and monooxygenase activity in immature brook trout, Salvelinus fontinalis

Levels of hepatic microsomal cytochrome P-450 were depressed by administration of estradiol-17 beta and were elevated by administration of testosterone in both male and female juvenile brook trout (Salvelinus fontinalis). Treatment-associated changes in the levels of other microsomal electron transfer components in liver did not reflect the changes in cytochrome P-450 content and were also distinct from the changes in these components in kidney. Electrophoretic analysis of hepatic microsomes revealed that estradiol treatment reduced the amounts of several proteins including some heme-staining protein at 56,000 daltons, possibly containing cytochrome P-450. Hepatic microsomal benzo[a]pyrene hydroxylase and the response to 7,8-benzoflavone in vitro were affected little by steroid treatment, and ethoxyresorufin O-deethylase activity could not be detected in any of the samples. Hepatic microsomes metabolized testosterone to a suite of products including 6 beta-hydroxytestosterone (the major metabolite) and 16 beta-hydroxytestosterone, plus as many as eleven unknown metabolites. Estradiol-17 beta treatment depressed the rates of testosterone metabolism and particularly the rates of 6 beta-hydroxylase activity but did not affect 16 beta-hydroxylase activity. Both activities were largely unaffected by testosterone. The results are consistent with the idea that both androgens and estrogens regulate the levels of hepatic cytochrome P-450 in brook trout and that the effect, at least of estradiol-17 beta, involves regulation of forms that function in specific hydroxylation of testosterone. The significance of these effects and whether factors additional to steroids are involved in this regulation of hepatic cytochromes P-450 in fish remain to be established.

Cytochrome P-450 as a determinant of sex difference of drug metabolism in the rat

1. Recent advances in the studies of sex-related differences of drug metabolism in the rat are described. Experiments with novel substrates have provided new insights into the sex differences of drug metabolism. 2. One of each form of cytochrome P-450, P-450-male and P-450-female, from liver microsomes of male and female rats, respectively, were purified to electrophoretic homogeneity. 3. These forms of cytochrome P-450 are distinguishable from each other in their catalytic, physical and immunochemical properties. 4. The use of antibodies to the two forms of cytochrome P-450 shows that P-450-male and P-450-female, present in rat-liver microsomes, are dependent on sex hormones. 5. In addition, evidence for the involvement of multiple forms of cytochrome P-450 in the occurrence of the sex difference has been presented.

Role of biotransformation in the potentiation of halocarbon hepatotoxicity by 2,5-hexanedione

2,5-Hexanedione (2,5-HD) pretreatment potentiated CHCl3-induced hepatotoxicity. 2,5-HD significantly increased hepatic cytochrome P-450, NADPH cytochrome c reductase, aniline hydroxylation, p-nitroanisole O-demethylation, and aminopyrine N-demethylation in both male and female mice. 2,5-HD pretreatment potentiated CHCl3-induced centrilobular necrosis and increased serum alanine amino transferase (ALT) activity by 20 times more than CHCl3 alone. Similarly, 2,5-HD pretreatment potentiated CDCl3-induced hepatotoxicity as well as CCl4-induced hepatotoxicity in male mice, but did not potentiate trichloroethylene-, 1,1,2-trichloroethane-, or perchloroethylene-induced hepatotoxicity. In female mice, 2,5-HD pretreatment potentiated CHCl3- and CDCl3-induced hepatotoxicity as well as trichloroethylene-, 1,1,2-trichloroethane-, and carbon tetrachloride-induced hepatotoxicity, but not perchloroethylene-induced hepatotoxicity. 2,5-HD pretreatment had no preferential effect on either CHCl3- or CDCl3-induced hepatotoxicity in females. However, phenobarbital pretreatment did differentiate CHCl3- and CDCl3-induced hepatotoxicity in females. 2,5-HD-induced potentiation of halocarbon hepatotoxicity is sex dependent.

Inducibility of aryl hydrocarbon hydroxylase in BALB/c/ki mice exposed to urban air pollution

In two separate experiments BALB/c/ki mice were exposed to urban air pollution. Mice exposed to clean air served as controls. In both experiments there were no obvious quantitative or qualitative differences in lung or liver tissue examined by light microscopy. In both experiments higher aryl hydrocarbon hydroxylase activities and higher trace metal concentrations were observed in the mice exposed to polluted urban air. These data are interpreted in terms of health hazards of urban air pollutants.

Drug metabolism under pathological and abnormal physiological states in animals and man

The activity of microsomal drug-metabolizing enzymes is altered by several pathological or abnormal physiological states, such as changes in nutritional status, liver, heart or kidney diseases, hormonal disturbances, pregnancy, tumour-bearing state, adjuvant arthritis, changes in reticuloendothelial system and environmental factors (stress, irradiation, heavy metals). The activities of other metabolic pathways, such as glucuronidation, sulphate conjugation, acetylation and alcohol oxidation are generally affected to lesser extents. Rats are most commonly used in drug metabolism studies, and it is important to know that the activity of most of the microsomal drug-metabolizing enzymes is higher in males than in females through androgen action which is readily impaire drug-metabolizing enzymes in male rats are thus manifested by two mechanisms; one is by impairment of androgen action and the other is by depression of the basic enzymic activity. Therefore, those effects of pathological states, observed only in male rats but not in females, are generally not seen in other species of animals, including man. The effects of starvation, hyperthyroidism, adrenal insufficiency, diabetes and morphine administration are cases where changes in metabolism are due solely to impairment of androgen action. In other pathological cases, those drug-metabolizing enzymes showing sex differences are depressed more markedly in male rats than those showing no clear sex difference. The author therefore recommends the use of female rats in the evaluation of the effects of pathological states on hepatic microsomal drug-metabolizing enzymes. Generally, changes in activity of the hepatic enzymes reflect closely the changes in the rates of drug metabolism in vivo. However, the protein-binding of drugs, hepatic blood flow and renal function are also known to affect the rate of drug metabolism and excretion in vivo, and therefore changes of these factors in pathological states should also be taken into consideration.

Kinetic studies on sex difference in susceptibility to chronic benzene intoxication--with special reference to body fat content

The sex difference in the susceptibility to haematopoietic disorders induced by benzene was studied kinetically with a special reference to its relation with the body fat content. In rats of both sexes with a large body fat content, benzene was eliminated more slowly and remained in the body for a longer time than in rats with a small body fat content. In accord with this finding, the decrease in white blood cell numbers during a chronic benzene exposure was observed only in the groups of rats which had a large volume of fat tissue. In an experimental human exposure, the elimination of benzene was slower in the females than in the males. The kinetic study revealed that the slower elimination in the females is due primarily to the bulky distribution of body fat tissue in that sex. From these results obtained from the experimental exposure of men and rats to benzene, it was concluded that the human female, with her massive body fat tissue, shows an inherent disposition to be susceptible to a chemical such as benzene which has a high affinity with fat tissue.