The effect of temperature on monoxygenase reactions in the microsomal membrane

The effect of temperature on the rates of monoxygenase reactions was studied with microsomes prepared from phenobarbital pretreated rats. The rates of the N-demethylation of ethylmorphine, benzphethamine, aminopyrine, and p-nitroanisole were studied. Breaks at temperatures around 24 degrees C were observed in the Arrhenius plots of all these reactions. The energy of activation of these reactions has values of 10-12 and 19-21 kcal per mol at temperature ranges above and below the break temperature, respectively. The break, however, was not observed if 30% glycerol was added to the microsomes. The Arrhenius plot of the microsomal NADPH-cytochrome c reductase activity also did not show any break. The implications of these observations in relationship to the fluidity of the membrane, the translational mobility of membrane enzymes, and the rate of monoxygenase reactions are discussed.

Estradiol, testosterone, dehydroepiandrosterone and androstenedione: novel derivatives and enantiomers. Interactions with rat liver microsomal cytochrome P450 and antioxidant/radical scavenger activities in vitro

Interactions of 27 steroids, among them 17 derivatives such as ethers, sulfates and amidosulfonates derived from 17 beta- and 17 alpha-estradiol, from testosterone and alpha- and beta-dihydrotesosterone and from dehydroepiandrosterone with rat liver microsomal cytochromes P450 (P450) were investigated in vitro by assessing binding to P450 and effects on P450 mediated monooxygenase functions as measured by different model reactions: ethoxyresorufin O-deethylation (EROD), ethoxycoumarin O-deethylation (ECOD) and ethylmorphine N-demethylation (EMND). With the exception of 17 alpha-estradiol-3-dimethylamidosulfonate, estrone, its -3-methylether and -3-amidosulfonate and testosterone, all other steroids displayed type I or reverse type I binding to P450. All steroids inhibited EROD activity in micromolar concentrations. An additional strong inhibition of ECOD and EMND activities was only demonstrated for the androgens and progestins. Estriol, estrone and mestranol displayed less inhibitory actions on the model reactions than estradiol. No major differences in comparison to the parent compounds were noted with the other derivatives. The only exceptions were 17 beta-(8,9-dehydro-14 alpha,15 alpha-methylene)estradiol, which displayed stronger effects than estradiol, and dehydroepiandrosterone-3-sulfate, which was less effective than dehydroepiandrosterone. Possible antioxidant properties of the steroids were examined by the stimulated lipid peroxidation (LPO), H2O2 production, and lucigenin (LC) and luminol (LM) amplified chemiluminescence (CL) using rat liver microsomes. Additionally, the influence on rat whole blood chemiluminescence (WB-CL) was assessed. All the estrogens, but not their methylethers and amidosulfonates inhibited LPO in micromolar concentrations. The effects on the other oxidase model reactions or on WB-CL were less distinct. Only ethinylestradiol and 17 beta-(8,9-dehydro-14 alpha,15 alpha-methylene)estradiol displayed a strong inhibitory action on all model reactions. With the exception of dehydroepiandrosterone-3-sulfate, which in general had only weak effects, the androgen and progestin derivatives, in contrast, strongly decreased H2O2 formation and LM- and LC-CL, but were mostly ineffective on LPO and WB-CL.

[Involvement of cytochrome P4503A in the monohydroxylation of ring A of praziquantel in rat liver microsomes]

The possibility of involvement of cytochrome P4503A (CYP3A) in the monohydroxylation of the ring A of praziquantel (PZQ) was studied by using CYP3A specific inducer dexamethasone (DEX), specific inhibitor triacetyloeandomycin (TAO) and the activity of erythromycin (ERY) and ethylmorphine (EMP) N-demethylase which are known to be marker for CYP3A enzyme activity as probes. In the liver microsomes obtained from rats pretreated with CYP3A inducer DEX with TAO treatment the content of uncomplexed P450 was decreased, the activity of ERY and EMP N-demethylase ws reduced, and simultaneously, the rate of formation of ring A monohydroxylate of PZQ was inhibited. Ring A monohydroxylate formation was competitively inhibited by TAO and ERY. The rates of ring A monohydroxylate formation were strongly correlated with the activity of N-demethylase of ERY and EMP. These results indicate that CYP3A is involved in the monohydroxylation of the ring A of PZQ.

Transplantation of fetal liver tissue suspension into the spleens of adult syngenic rats: effects of different cytotoxins on cytochrome P450 mediated monooxygenase functions and on oxidative state

Syngenic fetal liver tissue suspensions were transplanted into the spleens of adult male Fisher 344 inbred rats. Four months after surgery, transplant recipients and age matched control rats were treated with different cytotoxins (allyl alcohol [AAL], bromobenzene [BBZ], carbon tetrachloride [CCl4], or thioacetamide [TAA]) or the respective solvents 24 or 48 hours before sacrifice. Effects of the cytotoxins on P450 mediated monooxygenase functions in liver and spleen 9,000 g supernatants were assessed by measuring the model reactions ethoxyresorufin O-deethylation (EROD), ethoxycoumarin O-deethylation (ECOD), pentoxyresorufin O-depentylation (PROD), and ethylmorphine N-demethylation (EMND). Additionally, the influence on the oxidative state was investigated by assessing the liver and spleen tissue content of lipid peroxidation (LPO) products and of reduced and oxidized glutathione (GSH;GSSG). The livers of both solvent treated transplant recipients and control rats displayed regular EROD, ECOD, PROD and EMND activities. After AAL treatment EROD and EMND activities within the livers were not affected, but ECOD and PROD activities were increased. BBZ administration caused a decrease in EROD and EMND activities, ECOD activity remained unaffected, and PROD activity was even increased. CCl4 and TAA administration caused a strong reduction in the activity of all four model reactions. Spleens of control rats displayed almost no P450 mediated monooxygenase functions, independent whether the rats had been treated with the cytotoxins or not. In the transplant containing spleens, however, significant EROD and ECOD, but hardly any PROD or EMND activities were seen. After AAL administration EROD activity was not affected in the transplant containing spleens, but ECOD activity was increased. BBZ treatment led to a decrease in EROD and an elevation in ECOD activity. CCl4 and TAA strongly reduced the activity of both of these model reactions. The tissue content of LPO products within livers and transplant containing spleens was significantly increased after BBZ and CCl4 treatment. An elevation in LPO products was also seen in the spleens of the control rats due to CCl4 administration. Tissue GSH and GSSG content in both livers and transplant containing spleens were strongly reduced after BBZ treatment. After CCl4 administration only a significant decrease in liver GSSG contents was seen. TAA treatment caused a reduction in the GSH and GSSG content in the spleens of both transplant recipients and control rats, but not in the livers. From these results it can be concluded, that the effects of cytotoxins like AAL, BBZ, CCl4 or TAA on P450 dependent monooxygenase functions and on oxidative state are exerted in the ectopic intrasplenic liver cell transplants in a similar way as in normal orthotopic liver.

Changes in rat liver monooxygenase activities after administration of atenolol, nifedipine and diltiazem alone and in combination

The effects of the Ca2+ antagonists nifedipine (NF) and diltiazem (DL) and of the cardioselective beta 1-adrenergic blocking agent atenolol (AT) on the hexobarbital (HB) sleeping time and on the activity of some liver drug-metabolizing enzyme systems in male Wistar rats were studied. Two hours after single oral administration, atenolol (150 mg/kg) did not change hexobarbital sleeping time, while nifedipine (50 mg/kg) and diltiazem (30 mg/kg) prolonged it by 171.2 and 99.6%, respectively. Coadministration of atenolol with diltiazem or with nifedipine significantly prolonged hexobarbital sleep by 205 and 283%, respectively. Administered alone, atenolol decreased the ethylmorphine-N-demethylase (EMND) activity, but the amidopyrine-N-demethylase (APND) activity was not changed in any of the treated groups. Atenolol and nifedipine significantly increased aniline-4-hydroxylase (AH) activity and this effect was also observed with the combinations AT + NF and AT + DL. The NADPH cytochrome P-450 reductase activity was significantly decreased by nifedipine and diltiazem. Only nifedipine increased the total content of cytochrome P-450 (by 23.8%). Atenolol and diltiazem tended to increase the content of cytochrome b5 which was increased by nifedipine by 97.6%. The same effect was observed with the combinations AT + NF and AT + DL. The results suggest that NF, AT + NF and AT + DL produced the manifested changes in hepatic oxidative metabolism. The decreased EMND activity by atenolol, however, and the prolongation of hexobarbital sleeping time by nifedipine, diltiazem and their coadministration with atenolol did not correlate with enhanced microsomal P-450 and b5 content.

Effect of vitamin E on lipid peroxidation and liver monooxigenase activity in experimental influenza virus infection

Influenza virus infection was associated with development of oxidative stress in liver of mice, viz. increase in amount of lipid peroxidation products, decrease in cytochrome P-450 and NADP. H-cytochrome c-reductase activity, and inhibition of liver monooxygenases (aniline hydroxylase, ethylmorphine-N-demethylase, amidopyrine-N-demethylase and analgin-N-demethylase). These effects were most pronounced on the 7th day after virus inoculation as compared to the 5th one. Supplementation of mice with vitamin E before virus inoculation leads to liver protection against oxidative stress and toxicosis. A marked decrease of lipid peroxidation products and an increase of cytochrome P-450 and activities of monooxygenases was established. The stabilizing effect of vitamin E was dose-dependent and was most pronounced on the 5th day after virus inoculation as compared to the 7th one.

Transplantation of fetal liver tissue suspension into the spleens of adult syngenic rats: effects of various mitogens and cytotoxins on cytochrome P450 (P450) isoforms expression and on P450 mediated monooxygenase functions

Syngenic fetal liver tissue suspensions were transplanted into the spleens of adult male Fisher 344 inbred rats. Four months after surgery, transplant recipients and age matched control rats were treated with various mitogens (fluorene [FEN], fluorenone [FON] and 2-acetylaminofluorene [AAF]) or cytotoxins (allyl alcohol [AAL], bromobenzene [BBZ] and carbon tetrachloride [CCl4]) or the respective solvents 24 or 48 hours before sacrifice. The expression of three cytochrome P450 (P450) isoforms, 1A1, 2B1 and 3A2, within spleens and livers was assessed by immunohistochemistry and P450 mediated monooxygenase functions in spleen and liver 9000 g supernatants by the model reactions ethoxyresorufin O-deethylation (EROD), ethoxycoumarin O-deethylation (ECOD), and ethylmorphine N-demethylation (EMND). The orthotopic livers of both solvent treated transplant recipients and control rats displayed only in few lobules a slight P450 1A1, but in all lobules a moderate P450 2B1 and 3A2 expression, all mainly located in the hepatocytes around the central veins. Correspondingly, regular EROD, ECOD and EMND activities were observed. Each of the three mitogens increased the P450 1A1 expression in the hepatocytes of the perivenous zones of the liver lobules. FON administration caused an additional P450 1A1 immunostaining in the periportal areas, and AAF treatment a P450 1A1 expression in bile duct epithelia. Also the staining for P450 2B1 and 3A2 in the hepatocytes of the perivenous and intermediate zones of the liver lobules was intensified after treatment with any of the mitogens. The three model reactions were significantly increased within the livers after FEN and FON administration, whereas after AAF treatment only ECOD was enhanced, EROD remained unaffected and EMND was decreased. The cytotoxin AAL caused small lesions and fatty degeneration of hepatocytes only in some periportal areas. BBZ only produced a perivenous necrosis of single cells, whereas CCl4 caused complete necrosis of the centrilobular parenchyma. Immunohistochemically, AAL administration led to an increase in the P450 2B1 expression in the perivenous hepatocytes, whereas the staining for P450 1A1 was not affected and that for P450 3A2 was even decreased in the periportal areas. Due to AAL treatment EROD and EMND activities were not affected and ECOD activity was increased. BBZ administration caused a P450 1A1 expression in the periportal hepatocytes but a decrease in this staining of the perivenous cells. The number of hepatocytes positively stained for P450 2B1 and 3A2 in the perivenous and intermediate zones was diminished in comparison to the livers of solvent treated rats. After BBZ treatment, EROD and EMND activities were decreased, ECOD activity was not affected. CCl4 administration caused a strong reduction in the expression of all three P450 isoforms and in the activity of all three model reactions. Spleens of control rats displayed almost no P450 isoforms expression and P450 mediated monooxygenase functions, without as well as after treatment with the mitogens or cytotoxins. Similar to adult liver, the hepatocytes in the transplant containing spleens showed nearly no P450 1A1, but a noticeable P450 2B1 and 3A2 expression. No staining was observed within the bile duct cells of the intrasplenic transplants.

Combined effect of propranolol with nifedipine or with diltiazem on rat liver monooxygenase activities

The effects of two Ca2+ antagonists nifedipine (NF) and diltiazem (DL) and of the nonselective beta-adrenergic blocking agent propranolol (PR) on the hexobarbital (HB) sleeping time and on the activity of some liver drug-metabolizing enzyme systems in male Wistar rats were studied. Two h after single oral administration PR (50 mg/kg) did not change HB sleeping time, while NF (50 mg/kg) and DL (30 mg/kg) prolonged it by 171.2 and 99.6%, respectively. Coadmistration of PR with DL or with NF significantly prolonged HB sleep by 240.7 and 129%, respectively. Only NF increased aniline 4-hidroxylase (AH) activity (by 92%) and the total P-450 content (by 24%). PR and NF increased cytochrome b5 content and this effect was also observed with the combinations PR + NF (by 109%) and PR + DL (by 102%). The NADPH cytochrome P-450 reductase activity was significantly decreased by NF and DL and after their combination with PR. The ethymorphine-N-demethylase (EMND) and amidopyrine-N-demethylase (APND) activities were not changed. The effects of PR, NF and DL administrated alone or in combination on liver oxidative metabolism are considered as possible mechanisms of drug interactions.

Testicular toxicity of Di(2-ethylhexyl)phthalate in developing rats

To understand the factors involved in the enhanced testicular toxicity of di(2-ethylhexyl)phthalate (DEHP) in developing animals, po doses of 50, 100, 250 or 500 mg DEHP/kg were administered to 25-d-old albino rats for 30 consecutive days. Activities of testicular and hepatic cytochrome P-450 enzymes were determined. A dose-dependent increase in the activities of lactate dehydrogenase and gamma-glutamyl transpeptidase and a decrease in sorbitol dehydrogenase was observed in the testes. The activity of beta-glucuronidase increased at dosages of 250 and 500 mg/kg, while acid phosphatase decreased. Testes had marked destructive changes in the advanced germ cell layers at dosages of 250 and 500 mg/kg, which supports biochemical studies indicating that DEHP interacts with the maturation process of the testes. The dose-dependent decrease in hepatic cytochrome P-450 levels and the activities of ethylmorphine N-demethylase and aniline hydroxylase suggest that impaired metabolism of DEHP could lead to higher amounts of the diester or its metabolites reaching the testes; this may result in enhanced vulnerability of the testes to DEHP in developing animals.

Differential responses of hepatic monooxygenases and glutathione S-transferases of mice to a combination of cadmium and nickel

The acute combined effects of cadmium (Cd) and nickel (Ni) on hepatic monooxygenase activities (ethylmorphine N-demethylase, EMND; aminopyrine N-demethylase, AMND; aniline 4-hydroxylase, AH), cytochrome P-450, cytochrome b5, microsomal heme and reduced glutathione (GSH) levels and glutathione S-transferase (GST) activities toward several substrates (1-chloro-2,4-dinitrobenzene, CDNB; 1,2-dichloro-4-nitrobenzene, DCNB; ethacrynic acid, EAA; 1,2-epoxy-3-(p-nitrophenoxy)-propane, ENPP) were determined and compared with those of Cd or Ni alone in mice. Male adult mice (25-30 g) were administered either a single dose of Cd (3.58 mg CdCl2.H2O/kg, i.p.) 48 hr prior to killing or a single dose of Ni (59.5 mg NiCl2.H2O/kg, s.c.) 16 hr prior to killing. For the combined treatment, the animals received the single dose of Ni 32 hr after the single dose of Cd and were then killed 16 hr later. Cd treatment alone significantly decreased EMND, AMND, and AH activities and cytochrome P-450 and heme levels as compared with controls. Cytochrome b5 level was not altered by Cd treatment. Cd also inhibited GSH level and the GST activities toward CDNB, EAA and ENPP significantly. No significant change was observed in the GST activity for DCNB by Cd. Ni treatment alone, however, decreased the monooxygenase and GST activities studied, and cytochrome P-450, cytochrome b5, heme and GSH levels significantly. Combined treatment significantly depressed the monooxygenase activities and cytochromes and heme levels. GSH level was not significantly altered.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of spironolactone on dimethyl mercury toxicity. A possible molecular mechanism

The protective activity of spironolactone (CAS 52-01-7) against dimethyl mercury intoxication was studied. Dimethyl mercury increased serum glutamate pyruvate transaminase (SGPT), serum bilirubin, blood urea nitrogen (BUN), and caused impairment of the drug metabolic activity of rat liver in vivo and in vitro. It also caused a severe neuropathy to these animals. Administration of spironolactone caused a reduction of dimethyl mercury toxicity. It decreased the values of SGPT, bilirubin and BUN, and restored the impaired drug metabolism caused by dimethyl mercury. The neuropathy produced after administration of dimethyl mercury was only mildly ameliorated by the treatment with spironolactone. Pregnenolone-16 alpha-carbonitrile (PCN), a potent microsomal enzyme inducer, had only a weak action, with the expected exception of the repair of the impaired drug metabolism of the liver. A mechanism of the protective action of spironolactone against dimethyl mercury intoxication is proposed. It is suggested that both the ability to induce drug metabolizing enzymes, here demethylases, and the capacity to bind to the demethylated metabolite of the organic mercurial, giving a non toxic, easily excretable complex should coexist in the protective molecule.

Age related effects of di(2-ethylhexyl)phthalate on hepatic cytochrome P450 monooxygenases in Wistar rats

Age related response of di(2-ethylhexyl)phthalate (DEHP) was studied by administering the plasticizer (2000 mg/kg, orally) to 3, 6 and 10 week old wistar rats for 1, 7 or 15 days and determining the activity of hepatic P450 monooxygenases. Single administration of DEHP decreased the cytochrome P450 contents and activity of arylhydrocarbon hydroxylase, aniline hydroxylase and ethylmorphine N-demethylase at all the age groups while repeated exposure induced them with maximum alterations occurring in 3 week old rats. Repeated administration for 15 days, on the other hand, caused a decrease in the cytochrome P450 content and the activity of arylhydrocarbon hydroxylase, aniline hydroxylase and ethylmorphine N-demethylase only in the 3 week old rats. The 6 and 10 week old rats exposed to the same schedule of DEHP showed an inhibition in the activity of arylhydrocarbon hydroxylase and an increase in the activity of aniline hydroxylase and ethylmorphine N-demethylase, which was however lower than that seen after 7 days of exposure to DEHP in the respective age group of animals. Our data have indicated the differences in the sensitivity of the P450 monooxygenases towards DEHP and its metabolites amongst 3, 6 and 10 week old animals.

Estrogen, not testosterone, creates male predominance of a P4501-related cytochrome in adult guinea pig adrenals

Guinea pig adrenal microsomes possess a distinctive cytochrome P450 that is immunochemically related to P4501 and correlates with microsomal capacity for xenobiotic metabolism. This 52K protein and the capacity for metabolizing compounds such as ethylmorphine are located in the zona reticularis, are suppressed by ACTH, and are predominant in adult males. The protein is undetectable and the enzyme activity is low in young prepubertal animals. In males, both increase with age. However, in females, the protein remains undetectable, and ethylmorphine demethylase activity remains low into adulthood. Despite this clear sex difference through puberty and into sexual maturity, we recently observed that in female retired breeders, both the 52K cytochrome P450 and the capacity for metabolism of ethylmorphine appear at levels equal to those in males of comparable age. As estrogen levels are low in female retired breeders, we decided to investigate whether estrogen plays a role in maintaining the low levels of this protein and of xenobiotic metabolism seen in younger females. In a series of gonadectomy and hormone replacement experiments, we demonstrated that estrogen suppressed the levels of both protein and enzyme activity in adult guinea pigs. Ovariectomy resulted in the appearance of the 52K cytochrome P450 and of ethylmorphine demethylase in female adrenal microsomes at levels comparable to those seen in adult males. Estrogen replacement suppressed the increase in both protein concentration and enzyme activity. In hemiovariectomized cycling females, compensatory hypertrophy of the remaining ovary occurred, and the characteristic low levels of the 52K P450 and enzyme activity were maintained. Furthermore, estrogen treatment of male guinea pigs suppressed levels of both the 52K P450 and ethylmorphine demethylase activity in male adrenals. These experiments demonstrate that estrogen plays a significant role in the regulation of this protein. Testosterone, on the other hand, was not required to maintain the higher levels of 52K P450 and correlated enzyme activity in adult males. The levels of both were the same in normal, castrated, and sham-operated males, treated with testosterone or vehicle alone or left untreated. In fact, castration of prepubertal males resulted in a rapid rise to adult male levels of both immunodetectable protein and enzyme activity, implying that some suppressive agent of testicular origin effects the gradual increase that normally occurs with age in males.(ABSTRACT TRUNCATED AT 400 WORDS)

Studies on the acute effects of coumarin and some coumarin derivatives in the rat

The mechanism of acute coumarin-induced hepatotoxicity in the rat has been investigated by comparing the effects of coumarin with those of a number of methyl-substituted coumarin derivatives. Male Sprague-Dawley rats were given single ip doses of corn oil (control), coumarin (0.86 and 1.71 mmol/kg body weight), 3,4-dimethylcoumarin (3,4-DMC, 1.71 and 2.57 mmol/kg), 3-, 4- and 6-methylcoumarins (3-MC, 4-MC and 6-MC, 1.71 mmol/kg) and 3- and 4-methyloctahydrocoumarins (3-MOHC and 4-MOHC, 2.57 mmol/kg) and hepatotoxicity assessed after 24 hr. Coumarin administration produced dose-related hepatic necrosis and a marked elevation of plasma alanine aminotransferase and aspartate aminotransferase activities. In contrast, none of the coumarin derivatives examined produced either hepatic necrosis or elevated plasma transaminase activities. Treatment with coumarin reduced hepatic microsomal ethylmorphine N-demethylase and 7-ethoxycoumarin O-deethylase activities, whereas one or both mixed-function oxidases appeared to be induced by treatment with 3,4-DMC, 4-MC, 3-MOHC and 4-MOHC. These results provide further evidence that acute coumarin-induced hepatotoxicity in the rat is due to the formation of a coumarin 3,4-epoxide intermediate. That 3- and/or 4-methyl substitution (i.e. 3-MC, 4-MC and 3,4-DMC) leads to a reduction in coumarin-induced hepatotoxicity, due to diminished formation of 3,4-epoxide intermediates, was confirmed by the results of molecular orbital calculations.

Postnatal development of body mass and of hepatic xenobiotics biotransformation of male rats with low body mass at birth

Body mass gain of male rats with low body mass at birth was lower from birth up to the 5th postnatal day, but higher from the days 5 to 30 in comparison with male litter mates with normal body mass at birth. Absolute body and liver masses were significantly lower up to the 30th postnatal day, but fully improved at adult age. No differences of ethoxycoumarin O-deethylation activities existed between both groups at all ages. Ethylmorphine N-demethylation activity was significantly lower in newborn males with low body mass, but had been fully developed as early as the 5th postnatal day. We conclude that postnatal adaptation of male rats with spontaneous growth retardation at birth is slightly delayed only during the first days of life.

Regioselective O-demethylation of scoparone (6,7-dimethoxycoumarin) to assess cytochrome P450 activities in vitro in rat. Effects of gonadal steroids and the involvement of constitutive P450 enzymes

1. In the rat, scoparone (6,7-dimethoxycoumarin) is regioselectively O-demethylated in vitro by the hepatic cytochrome P450 (P450) system, yielding isoscopoletin and scopoletin. 2. Scoparone has been proposed as an indicator substrate for the assessment of P450 differentiation in vitro in rat. It has been suggested that isoscopoletin formation mainly reflects activity of enzymes of the P4501A subfamily, whereas scopoletin formation has been associated with P4502B activity. 3. In the present study, rate of formation of scopoletin and isoscopoletin were measured in hepatic microsomes from male, female and castrated male rats, in castrates treated with testosterone, in males treated with oestradiol, and in females treated with testosterone. Furthermore, effects of induction by phenobarbital (PB), beta-naphthoflavone (BNF), isoniazid, triacetyloleandomycin, and dexamethasone were studied in both sexes. 4. Scoparone metabolism was partly sex- and steroid-dependent. Variation of isoscopoletin formation with sex or hormonal status correlated well with ethylmorphine demethylation. 5. Scoparone-O-demethylation was regioselectively induced by PB and BNF. Induction effects were not very large and showed no sex differences. 6. Microsomal metabolism of scoparone was partly inhibited by a monoclonal antibody against P4502C11. Scopoletin and isoscopoletin formation were inhibited when ethylmorphine was added to the incubation mixture. Scoparone competitively inhibited testosterone 6 beta-hydroxylation. 7. It is concluded that a number of P450 enzymes, including those which are constitutively expressed, contribute to the biotransformation of scoparone. This lack of selectivity limits the usefulness of scoparone as a general indicator substrate for P450 differentiation in rats.

Sex differences in the diabetes-induced modulation of rat hepatic cytochrome P450 proteins

Sex differences in the diabetes-induced changes in hepatic cytochrome P450 proteins were investigated in rats treated with streptozotocin. Changes in specific cytochrome P450 proteins were monitored using diagnostic substrates and immunologically utilizing specific polyclonal antibodies. When expressed in terms of nmoles of total cytochrome P450, ethoxyresorufin O-deethylase activity was increased by treatment with streptozotocin, the extent of induction being the same in the two sexes. In contrast, lauric acid hydroxylase and ethylmorphine N-demethylase activities were induced only in the male rat. Finally, p-nitrophenol hydroxylase and pentoxyresorufin O-dealkylase were enhanced by the same treatment in both sexes, the effect being more pronounced in the male. These findings indicate that sex-specific changes in certain cytochrome P450 proteins exist in response to insulin-dependent diabetes but these cannot, however, be ascribed to sex differences in the severity of diabetes induced by streptozotocin since the degrees of hyperketonaemia and hyperglycaemia were the same in the two sexes. These are likely to reflect sex-specific differences in growth hormone and triglyceride levels in the diabetic animals.

Comparison of human fetal hepatic and adrenal cytochrome P450 activities with some major gestational steroids and ethylmorphine as substrates

The immunoidentified human fetal liver and adrenal microsomal contents of cytochromes P450IIIA and P450XVIIA1 were compared to the metabolism of steroids and ethylmorphine. In fetal liver microsomes, 16 alpha-hydroxylation of dehydroepiandrosterone (DHA) was catalyzed at a high rate in almost all investigated specimens and accompanied by a high ethylmorphine N-demethylase activity. Progesterone 16 alpha- and 17 alpha-hydroxylation was found only in the livers with the highest DHA 16 alpha-hydroxylation activities, while 21-hydroxylation of progesterone was catalyzed only occasionally in these samples. In fetal adrenal microsomes, 21-hydroxylation of progesterone to 11-desoxycorticosterone (DOC) and 11-desoxycortisol (DOCOL) was catalyzed. In contrast to fetal liver, the adrenals also catalyzed the 17 alpha-hydroxylation of pregnenolone and the formation of DHA from 17 alpha-OH-pregnenolone. 16 alpha-hydroxylation of DHA and ethylmorphine N-demethylation were modest in the adrenals. P450IIIA/HLp was immunoidentified in all investigated liver specimens except two (18/20) in which no ethylmorphine N-demethylation or 16 alpha-hydroxylation of DHA was found. P450XVIIA1 bands were observed in 8/20 blots of liver specimens, but there was no correlation between the density of these bands and the 17 alpha-hydroxylation of progesterone. All 11 fetal adrenal samples catalyzed DHA 16 alpha-hydroxylation, although only 8 were positive for P450IIIA/HLp. All investigated adrenals were positive in regard of the P450XVIIA1 band, except one (8/9) with a low 17 alpha-hydroxylation of progesterone. All adrenal specimens catalyzed 21-hydroxylation of progesterone and contained P450C21 bands in immunoblots and all samples catalyzed the formation of DOC and DOCOL from progesterone. Our findings in the fetal livers show a correlation between the DHA 16 alpha-hydroxylation and immunoidentified P450IIIA/HLp bands. In adrenals, there was a correlation between the immunoidentified P450XVIIA1 bands and the 17 alpha-hydroxylation of progesterone.

Interferon suppresses the isoform-specific activities of hepatic cytochrome P450 in female rats

The results from the present study indicate that rat IFN-gamma decreases hepatic P450 levels and catalytic activities in female rats. The magnitude of the down-regulation of P450 is similar to that found in male rats. Furthermore, the activities of specific P450 isoforms (P4502A1 and P4502C6 and possibly P4502C12, and P4502B1 and 2) are decreased by IFN. Hence, the effect of IFN in female rats appears to involve several, but not all, hepatic P450 isoforms. Both hormone-dependent and hormone-independent isoforms are suppressed by IFN. The mechanism for this effect does not, however, appear to be mediated by changes in serum levels of sex steroids.

Metabolism of diazepam and related benzodiazepines by human liver microsomes

The metabolism of diazepam has been studied in vitro using microsomal preparations from five human livers. An HPLC method was developed for the assay of diazepam, its congeners and its metabolites. Various methods for the incorporation of diazepam into the incubation medium were explored. It was shown that the use of organic solvents or small quantities of hydrochloric acid enhanced the solubility of this substrate. However all of the organic solvents tested were associated with substantial (around 50%) inhibition of metabolism of diazepam by both major pathways (N-demethylation and C3-hydroxylation). The use of hydrochloric acid gave satisfactory solubilization of diazepam, but not of pinazepam, prazepam or halazepam. Detailed metabolic studies were conducted only for diazepam, using neither hydrochloric acid nor organic solvents in the incubation medium. Formation of N-desmethyl-diazepam increased approximately linearly with diazepam concentration to 200 microM, and did not show saturation. Formation of temazepam gave a curved profile over the same range of diazepam concentrations, suggestive of a sigmoidal relationship. Michaelis-Menten parameters could not be determined for either reaction, but intrinsic clearances for N-demethylation varied over a 6-fold range. Diazepam N-demethylation was apparently promoted by the inclusion of temazepam in the incubation medium, while C3-hydroxylation of diazepam was enhanced in the presence of N-desmethyldiazepam. Mephenytoin in the incubation mixture had no effect on diazepam metabolism by either pathway. The present studies have defined some of the methodological problems inherent in in vitro metabolic studies with benzodiazepines, and have shed further light on the metabolism of diazepam in vitro by human liver.

Decrease in the specific forms of cytochrome P-450 in liver microsomes of a mutant strain of rat with hyperbilirubinuria

Eisai-hyperbilirubinuria rats (EHBR) is a mutant originated from Sprague Dawley rats. The activities of UDP-glucuronyltransferase and drug metabolizing enzymes in EHBR were compared with those in Sprague Dawley rats as the control. The activity of aniline hydroxylase was significantly increased in liver microsomes of EHBR whereas the activity of ethylmorphine N-demethylase was found to be significantly decreased in EHBR as compared to control rats. In addition, the activity of testosterone 7 alpha-hydroxylase was increased in EHBR whereas the activity of testosterone 6 beta-hydroxylase was significantly decreased in EHBR as compared to control rats. Western blot analysis of liver microsomes of EHBR with antibodies to P-450IA2, P-450IIB1, P-450IIC11 and P-450IIIA2 showed that the amounts of P-450IIB1 and P-450IIIA2 in liver microsomes were significantly lower in EHBR than in control rats. These results indicated the form-specific alteration in the amounts of cytochrome P-450 in liver microsomes of EHBR.

The effects of peripubertal testosterone on ethylmorphine demethylase activity in adult rats testectomized neonatally

The physiologic activity of ethylmorphine demethylase (EMDM) is 2.5 times greater in adult male rats than in females. Defeminization, effected neonatally by testicular androgens, causes 65% of the increase while masculinization causes the rest. Castration of the intact adult does not alter the defeminized activity of the enzyme but abolishes its masculinized activity. Testosterone restores the latter. Adults that are not defeminized, because of neonatal castration, have enzymes unresponsive to testosterone. Thus, defeminization seems necessary for the expression of masculine activity. This was studied by castrating males at birth (day 1) and implanting capsules of testosterone propionate on day 35. On day 71, the activity had increased 4.4-fold to physiologic levels, compared with rats receiving no steroid (1.9 nmol.min-1.mg-1). Removal of the implant on day 71 decreased the activity on day 84 to that of the no-steroid rats. Thus, defeminization is neither caused by androgen in peripubertal rats nor needed to effect full physiologic activity of the enzyme. The activation of EMDM by peripubertal testosterone may reflect its regulation of growth hormone; first, testosterone (days 35-71) failed to increase enzyme activity in males hypophysectomized on day 35; second, growth hormone infused (5 micrograms.h-1) over days 71-76 blocked the activation, actually decreasing activity 3.7-fold; third, the activity induced by testosterone was further increased (26%) by growth hormone release-inhibiting hormone (5 micrograms.h-1, days 71-76).

The influence of "essential" phospholipids (EPL) on phase-I- and phase-II-reactions and on the glutathione status in the liver of aging rats

"Essential" phospholipids (EPL; polyene-phosphatidylcholine) were administered orally to aging male rats in doses of 100 and 300 mg/kg b.wt. over 10 weeks. One and 7 days after the last treatment cytochrome P-450 concentration, epoxide hydrolase and glutathione-S-transferases were found to be unchanged, but ethylmorphine N-demethylation, ethoxycoumarin O-deethylation and UDP-glucuronosyltransferase activities were enhanced, as were the concentrations of both reduced and oxidized glutathione, the values being similar to those in young adult rats. These results are discussed in terms of an increase in endoplasmic reticulum membrane fluidity.

The influence of the radiation syndrome on cytochrome P450-dependent monooxygenation in rat liver

Cytochrome P-450 concentration and the monooxygenation activities of some cytochrome P-450 forms were determined in rat liver in the course of the acute radiation sickness. Ethylmorphine N-demethylation, ethoxycoumarin, ethoxyresorufin, and pentoxyresorufin O-dealkylation were used as indicator reactions. After radiation a distinct decrease in the hepatic biotransformation capacity can be observed, most pronounced at the climax of the radiation syndrome. Phenobarbital treatment (60 mg/kg b. m. at 3 consecutive days each) increases the concentration and the monooxygenase activities of some cytochrome P-450 forms. The degree of this induction effect is not altered at the third day after radiation, whereas at day 7 no significant inducibility can be observed.

Sex differences in cytochrome P-450-dependent xenobiotic and steroid metabolism in the mature rainbow trout kidney

The rainbow trout kidney during the late reproductive stages was found to exhibit a profound sex-related difference in its capacity to metabolize both xenobiotic model substrates and endogenous steroids. The cytochrome P-450 content of trunk kidney microsomes was 28-fold higher in males than in females. In trunk kidney microsomes, the dealkylation of various 7-alkoxycoumarins was 22- to 38-fold higher in males than in females, whereas ethylmorphine-N-demethylase (EMND) and 7-ethoxyresorufin-O-deethylase (EROD) activities were only slightly higher in males than in females. In contrast to the alkoxycoumarin- and EROD activities, the EMND activity showed considerable activity in the head kidney microsomes and the level was found to be higher in females than in males. Progesterone and androstenedione 16- and 6 beta-hydroxylase activities were present mainly in the male trunk kidney microsomes. On the contrary, the oestradiol 2-hydroxylase was distributed along the whole kidney and showed a 2.8-fold higher activity in the female head kidney than in the male head kidney. The catalytic analysis indicated a differential regulation of trout renal P-450 isoenzymes during sexual maturation. Furthermore, the data presented indicate that the high level of the hemoprotein in male trunk kidney was not a general increased level of the protein, but rather an increase of certain cytochrome P-450 isoenzymes.

Effects of TCDD on vitamin A status and liver microsomal enzyme activities in a TCDD-susceptible and a TCDD-resistant rat strain

To investigate the relationship between vitamin A status and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) lethality, the influence of TCDD on tissue and serum vitamin A levels was determined in the most TCDD-susceptible (Long-Evans) and the most TCDD-resistant (Han/Wistar) rat strains. The TCDD LD50 values of these two strains differ by a factor of more than 300. Groups of three rats per strain were used in a dose-response study (given single ip doses of 0, 4, 40, 400, 800 or 1600 micrograms TCDD/kg body weight and killed on day 11) and in a time-course experiment (given single ip doses of 0, 4 and, in the case of Han/Wistar rats only, 1600 micrograms TCDD/kg body weight, and killed on days 4, 11, 23, 50 and 76). The strains showed similar response over the 76-day study with respect to vitamin A levels in the liver, kidneys, testicles and serum after exposure to a sublethal dose of TCDD (4 micrograms/kg body weight). In contrast, TCDD doses lethal to the Long-Evans strain only (40-1600 micrograms/kg, day 11) markedly increased kidney and serum vitamin A levels in Han/Wistar rats, while they were practically without effect in Long-Evans rats. Hepatic cytochrome P-450 concentration, and the activities of 7-ethoxyresorufin O-deethylase, ethylmorphine N-demethylase, and uridine diphosphate glucuronosyltransferase (towards p-nitrophenol) were affected by the TCDD doses in much the same manner in both strains. These findings show that the correlations between TCDD lethality and changes in vitamin A status found among species of laboratory animals do not hold for Long-Evans and Han/Wistar strains of rat.

Electrophoretic, spectral, catalytic and immunochemical properties of highly purified cytochrome P-450 from sheep lung

1. Cytochrome P-450LgM2 was purified from sheep lung microsomes in the presence of detergents, Emulgen 913 and cholate. 2. The purification procedure involved the chromatography of the detergent solubilized microsomes on DEAE-cellulose and hydroxylapatite. 3. Cytochrome P-450LgM2 was further purified on second DEAE-cellulose and hydroxylapatite columns. 4. The specific content of the highly purified P-450LgM2 was 16-18 nmol P-450/mg protein and purified 164-fold. 5. The yield was 16% of the initial content in microsomes. 6. The SDS-polyacrylamide slab gel electrophoresis (PAGE) of the purified lung cytochrome P-450LgM2 showed one protein band having the monomer molecular weight of 49,500. 7. The absolute CO-difference spectrum of dithionate-reduced P-450LgM2 gave a peak at 451 nm. 8. When sheep lung cytochrome P-450LgM2 and P-450LM2 purified from liver of phenobarbital (PB)-induced rabbit were subjected to Western Blotting and visualized immunochemically with anti-P-450LM2, they showed identical mobilities. 9. P-450LgM2 was found to be very active in N-demethylation of benzphetamine in a reconstituted system containing purified sheep lung reductase and synthetic lipid. 10. Turnover numbers (min-1) for benzphetamine, aniline, ethylmorphine and p-nitrophenol were determined to be 273, 1.2, 15.5 and 1.05, respectively, in a reconstituted microsomal lung monooxygenase system. 11. Spectral, electrophoretic, biocatalytic and immunochemical properties of sheep lung P-450LgM2 were found to be similar to those of P-450 isozyme 2, purified from PB-treated rabbit liver and of rabbit lung microsomes.

Altered carbohydrate, lipid, and xenobiotic metabolism by liver from rats flown on Cosmos 1887

To determine the possible biochemical effects of prolonged weightlessness on liver function, samples of liver from rats that had flown aboard Cosmos 1887 were analyzed for protein, glycogen, and lipids as well as the activities of a number of key enzymes involved in metabolism of these compounds and xenobiotics. Among the parameters measured, the major differences were elevations in the glycogen content and hydroxymethylglutaryl-CoA (HMG-CoA) reductase activities for the rats flown on Cosmos 1887 and decreases in the amount of microsomal cytochrome P-450 and the activities of aniline hydroxylase and ethylmorphine N-demethylase, cytochrome P-450-dependent enzymes. These results support the earlier finding of differences in these parameters and suggest that altered hepatic function could be important during spaceflight and/or the postflight recovery period.

Effects of age, adrenocorticotropin, and dexamethasone on a male-specific cytochrome P450 localized in the inner zone of the guinea pig adrenal

Guinea pig adrenal microsomes have a capacity for xenobiotic metabolism which is localized to the inner zone, greater in adult males then females, greater in older than in younger males, and suppressed by ACTH. In this paper we show that a cytochrome P450 distinct from P450(21) and P450(17) alpha, which is localized to the inner zone, is male specific, increases with age, and is suppressed by ACTH. This is the first report of a sex-dependent cytochrome P450 in the adrenal. It is immunochemically related to the two members of the P450I family, P450 c and d, neither of which has been reported to be hormonally regulated. The correlation of this cytochrome P450 with the ability of the microsomes to metabolize ethylmorphine suggests that it accounts for this capacity. Whether metabolism of foreign compounds and/or male-specific steroid hydroxylation are its functions in vivo remains to be determined.

Influence of prenatal administration of cadmium on postnatal development and inducibility of hepatic monooxygenases in rats

Cadmium inhibits hepatic monooxygenases in rats of different ages. But also in the offspring of dams which had received cadmium during pregnancy changes in biotransformation activities and their inducibilities could be observed. In the 30- and 60-day-old offspring a decrease in the inducibility of ethoxyresorufin O-deethylation by the specific inducer beta-naphthoflavone could be demonstrated, whereas cytochrome P-450 concentration, ethylmorphine N-demethylation and ethoxycoumarin O-deethylation were not influenced.

Effects of tin-porphyrins on developmental changes in hepatic cytochrome P450 content, selected P450-dependent drug-metabolizing enzyme activities and brain glutathione levels in the newborn rat

Sn-mesoporphyrin is considerably more effective than Sn-protoporphyrin in inhibiting bilirubin production in vivo, in the experimental animal. In this study the effects of Sn-mesoporphyrin, administered in doses ranging from 1 to 20 mumol/kg b.w., on the developmental patterns of hepatic cytochrome P450 content and cytochrome P450-dependent drug metabolism in rat neonates were examined at various time points during the 5-week period immediately after birth. No detrimental alterations in cytochrome P450 content or in cytochrome P450-dependent drug metabolism were observed. In addition no deleterious effects were noted on total glutathione content in brain of Sn-mesoporphyrin-treated animals. After single doses of Sn-protoporphyrin of 20, 50 or 100 mumol/kg b.w. were administered at birth, transient decreases in hepatic cytochrome P450 content (days 1 and 2), and ethylmorphine demethylase (days 2 and 5) and 7-ethoxycoumarin deethylase (days 1, 2 and 5) activities were observed in the period immediately after birth. However no sustained alterations in the developmental patterns of these enzymes were observed even at the highest dose (100 mumol/kg b.w.) of Sn-protoporphyrin administered. These findings indicate that in the doses utilized in this study both metalloporphyrins have no long-term effects on cytochrome P450-dependent drug metabolism. Furthermore, in doses up to 20 mumol/kg b.w., neither compound produced any short-term effects on hepatic cytochrome P450 content or functional activity in newborn rats.

Characterization of cytochrome P-450-dependent activities in hagfish, dogfish, perch and spectacle caiman

1. Owing to interest in the original function and evolution of cytochrome P-450 this enzyme system was studied in four species each at different levels on the phylogenetic tree, representing Agnatha, Selachi, Teleostei, and Reptilia. 2. All species contained considerable amounts of hepatic microsomal cytochrome P-450. The content in dogfish, perch and spectacle caiman was 0.2-0.3 while in the dogfish it was 0.6 nmol per mg protein. 3. Hepatic microsomal cytochrome P-450 dependent ethylmorphine demethylase, benzo(a)pyrene hydroxylase, 7-ethoxycoumarin-O-deethylase and 7-ethoxyresorufin-O-deethylase activities have been measured and the assays were carefully characterized with respect to pH-, protein content-, incubation time- and temperature-activity relationships. 4. The study revealed species-dependent differences in the liver microsomal cytochrome P-450 enzyme system, which could be due to differences in cytochrome P-450 composition or in the microenvironment around the enzyme.

Effects of 2-arylbenzimidazoles on rat hepatic microsomal monooxygenase system

1. The effects of eight newly synthesized 2-aryl substituted benzimidazole derivatives on control and phenobarbital (PB) treated rat liver microsomal aniline 4-hydroxylase and ethylmorphine N-demethylase activities, and their binding to control and PB-treated rat liver microsomal oxidized cytochrome P-450 are presented. 2. All compounds inhibited ethylmorphine N-demethylase activity with I50 values ranging from 8.50 x 10(-4) M to 27.83 x 10(-4) M in control and ranging from 2.80 x 10(-4) M to 15.79 x 10(-4) M in PB-treated rats. 3. Aniline 4-hydroxylase activity was inhibited by all of the compounds tested having I50 values in the range of 7.04 x 10(-4) M-31.37 x 10(-4) M in PB-treated rats, but only five of the compounds showed inhibitory activity in control rats. 4. Only a few significant regression coefficients could be found between the parameters of the chemicals studied and their inhibitory patterns. 5. No correlation has been observed between the binding of the derivatives and their inhibitory pattern.

Growth hormone depresses ethylmorphine demethylase activity: correlation with decreased levels of fast-turnover cytochrome P-450 in hypophysectomized female rats

The hepatic monooxygenase system was studied in hypophysectomized female rats infused for 5 days with ovine growth hormone (GH). At 7.5 micrograms.h-1 GH decreased the total cytochrome P-450 by 16%; at 10 micrograms.h-1 it reduced both cytochrome P-450 (31%) and the activity of ethylmorphine demethylase (31%). GH did not alter the activities of NADPH cytochrome c reductase or aniline hydroxylase. The lower GH dose decreased the amount of fast- and slow-turnover P-450 by 11 and 38%, respectively, while the higher dose decreased both by 49%. The loss of demethylase activity therefore correlates with the loss of fast-turnover P-450. This component is relatively more abundant in the female (fast: slow turnover of 4.3) than the male (fast:slow turnover of 2.5). GH did not affect the half-lives of the P-450 components, suggesting that it decreases their synthesis. The P-450 concentration in microsomes from GH-treated animals did not increase after incubation with hemin, suggesting that in vivo the hormone does not lower P-450 synthesis via depression of heme. Puromycin mimicked the effect of GH and when given with the hormone their effects on the P-450 levels were multiplicative (p less than 0.05), suggesting different modes of action and that GH does not decrease P-450 by acting at translation.

Effects of cage beddings on microsomal oxidative enzymes in rat liver

The purpose of the present studies was to evaluate the effects of some commercially available cage beddings on rat liver microsomal cytochrome P-450-dependent drug-metabolizing enzyme, ethylmorphine N-demethylase, and the carcinogen-metabolizing enzyme, benzo(a)pyrene hydroxylase. Sprague-Dawley rats were housed in cages containing cedar chip, corncob or heat-treated pinewood bedding for 3 weeks. Control rats were housed in cages on wire bottom floors containing no bedding material. Rats housed in cages containing cedar chip showed 18, 46 and 49% increases in liver cytochrome P-450 content, ethylmorphine N-demethylase and benzo(a)pyrene hydroxylase activities, respectively. The liver enzyme activities of rats housed in cages containing corncob bedding were similar to those obtained with control rats. In contrast, the pinewood-bedded rats showed a 21% decrease in ethylmorphine N-demethylase activity without affecting cytochrome P-450 content and benzo(a)pyrene hydroxylase activity. Hexobarbital-induced sleep times of the variously bedded rats were similar to those of control animals. These data suggest that the commercial bedding materials differ in their abilities to affect liver microsomal enzymes. Thus, interlaboratory variability in basal enzyme activities reported in the literature may be partly due to bedding materials used in the animal's cages.

Phenacetin O-deethylation by human liver microsomes: kinetics and propranolol inhibition

1. Phenacetin O-deethylation catalysed by human liver microcomes has been examined over a substrate concentration range of 2.5 to 700 microM using preparations of eight human liver samples. Michaelis-Menten kinetics described phenacetin oxidation satisfactorily in five of these samples; apparent Km values were in the range of 17.7 to 38.4 microM. 2. In the three other livers a single rectangular hyperbolic relationship did not describe the substrate saturation data adequately; analyses in these three cases requiring two classes of catalytic site. The apparent Km value for the higher affinity class of site in these three samples was within the range quoted above, but limitations imposed by assay sensitivity and phenacetin solubility obviated accurate characterization of the lower affinity class. 3. Estimates of Vmax for the high affinity class of site in the eight livers varied eleven-fold and there was no correlation between either Km or Vmax and microsomal cytochrome P-450 specific content, NADPH cytochrome c (P-450) reductase specific activity or ethylmorphine demethylase activity. 4. Propranolol was a potent competitive inhibitor of phenacetin deethylation with apparent Ki values of 2 to 7 microM describing its effect on the higher affinity class of activity. Propranolol was also an inhibitor of the lower affinity phenacetin deethylase identified in three of the livers, however the mechanism of inhibition could not be characterized. 5. These data suggest the possibility that propranolol oxidation may be mediated in part, by one or more human liver cytochrome P-450 species catalyzing phenacetin oxidation.

Cadmium sensitivity differences between liver microsomal drug metabolizing enzyme systems of guinea-pig and rat

1. Male guinea-pigs (400-500 g) and rats (225-275 g) were given a single dose of cadmium chloride (CdCl2) (2 mg Cd2+/kg i.p.) and 72 hr later the liver microsomal drug metabolizing enzyme activities and Cd levels of tissues and microsomes were determined. 2. No significant differences were noted between Cd treated and control animal tissue weights of microsomal protein contents in either guinea-pigs or rats. 3. Cd treatment exhibited significant inhibition of the activities of aniline 4-hydroxylase and ethylmorphine N-demethylase and on the levels of cytochrome P-450 and cytochrome b5 of liver of both species but the degree of inhibition were not the same in the species; they were 23, 34, 16 and 10% in guinea-pigs and 58, 57, 25 and 13% in rats, respectively. 4. No activity changes were observed in liver NADPH-cytochrome c reductase of the species by Cd treatment. 5. The duration of hexobarbital sleeping time was significantly prolonged in both species. However, the prolongation was 1.6 fold in guinea-pigs but 3.4 fold in rats. 6. No significant differences were found between either tissue or microsomal Cd levels of guinea-pigs and rats.

Hepatic Ah-receptor levels and the effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on hepatic microsomal monooxygenase activities in a TCDD-susceptible and -resistant rat strain

Previous studies have shown that in two inbred strains of mice, straightforward correlations exist among the number of hepatic Ah-receptors, enzyme inducibility by TCDD, and lethality of TCDD. Here, studies were conducted in two strains of rats (Han/Wistar and Long-Evans) which differ widely in susceptibility to the lethal effects of TCDD, to determine if these are general phenomenona in TCDD toxicity. The total number of specific binding sites (Ah-receptors) for [3H]TCDD proved to be approximately equal in the livers of both rat strains. Likewise, no notable difference was detected in the effect of TCDD on the activities of 7-ethoxyresorufin O-deethylase, 7-ethoxycoumarin O-deethylase, and ethylmorphine N-demethylase or on the amount of cytochrome P-450 in hepatic microsomal fractions. Immunoblot analysis was carried out with monoclonal antibodies (Mabs). Mab 1-7-1 directed against rat liver 3-methylcholanthrene (MC)-inducible P-450 recognized forms P-450c and P-450d in TCDD-treated rats in a dose-dependent fashion and to a similar extent in both strains. In contrast, Mab 2-66-3 (against phenobarbital-inducible P-450) did not recognize any proteins in either strain, confirming the conclusion that TCDD elicits a MC-type induction of hepatic cytochrome P-450 in both strains of rats. Thus, it seems that the correlations observed in mice do not hold in rats and therefore should not be generalized. The parameters measured in the present study are causally unrelated to the mechanism of lethal action of TCDD in these rat strains.

Neonatal programming of ethylmorphine demethylase and corticosteroid 5 alpha-reductase by testosterone, dihydrotestosterone, and estradiol. Effects of an anti-estrogen, an anti-androgen, and an inhibitor of estrogen synthetase

The neonatal imprinting of ethylmorphine demethylase and corticosteroid 5 alpha-reductase was studied. Males, castrated at birth (day 1), were injected (sc) with testosterone, dihydrotestosterone, or estradiol on days 2, 4, and 6 and with testosterone (2 mg/rat/day) on days 50-59. Microsomes were prepared on day 60. All three steroids, at greater than or equal to 0.73 mumol/pup, increased the apparent Vmax and decreased the apparent Km of the demethylase to values that did not differ (p less than 0.05) from those of intact adult males. Analogously, all steroids, at greater than or equal to 0.73 mumol/pup, decreased the apparent Vmax of the reductase to intact male values; its apparent Km was increased to adult male values by both androgens (at greater than or equal to 0.37 mumol/pup) and by estradiol (at greater than or equal to 0.73 mumol/pup). Flutamide (1.45 mumol/pup) failed to alter these effects indicating that androgen receptors are not involved in the imprinting process. Nafoxidine (1.45 mumol/pup) blocked the effects of all three steroids, indicating that androgens and estrogens both imprint via the estrogen receptor. An inhibitor of androgen aromatase, 1,4,6-androstatriene-3, 17 dione, blocked the imprinting effects of testosterone, but not those of dihydrotestosterone. Thus, testosterone is oxidized to estradiol prior to imprinting, while dihydrotestosterone imprints as the parent compound. The latter may reflect a pharmacologic occupancy of the estrogen receptor by dihydrotestosterone.

l-alpha-Acetylmethadol administration to lactating rat dams. Effect on hepatic aniline hydroxylase and ethylmorphine N-demethylase activities in rat pups

l-alpha-Acetylmethadol (LAAM) was administered to lactating rat dams, and subsequent effects on hepatic drug-metabolizing enzymes of their offspring were assessed. Dams were given LAAM or a control solution in their drinking water following parturition and throughout lactation. Hepatic ethylmorphine-N-demethylase (EMDM) and aniline hydroxylase (AH) activities, as well as cytochrome P-450 content, were determined in the offspring at 21-23 days of age, or following sexual maturation (61-64 days). LAAM induced AH and EMDM activities, as well as cytochrome P-450 content in both male and female 21-23-day-old pups compared to controls; these differences were not observed at 61-64 days of age. In addition, normal sex-related differences in EMDM activity were apparent at 61-64 days of age. These results demonstrate the LAAM administration to lactating dams causes hepatic metabolic induction in the sexually immature rat, suggesting that LAAM and/or its metabolites passed to the pups via the milk. These changes, induced by LAAM administered via lactation, are reversible and do not interfere with the normal development of sex-dependent differences in hepatic EMDM activity observed in rats following sexual maturation.

Pyrazole as a modifier of liver microsomal monooxygenase in DBA/2N and AKR/J mice

Effects of pyrazole on liver microsomal monooxygenase was studied in two inbred strains of mice, DBA/2N (D2) and AKR/J (AKR). A selective effect on microsomal monooxygenase was found. In the D2 mouse pyrazole strongly increases the coumarin 7-hydroxylase (CoH) and 7-ethoxycoumarin O-deethylase (ECDE) activities while on the total cytochrome P-450 (P-450) content and ethylmorphine N-demethylase (EMDM) and benzo(a)pyrene hydroxylase (AHH) activities the effect is biphasic (increased with lower doses and decreased with higher). For AKR the effect of pyrazole is different from the D2. The increase of CoH and ECDE is weaker and no biphasic effect for the other three parameters can be seen. Instead only a decrease takes place. The optimal dose of pyrazole for the induction of CoH in the D2 mice is 200 mg/kg once a day during three days. The effect of pyrazole is strongest in animals (D2) of 4-10 weeks old. For young animals (2 weeks old) no effect except of a weak decrease in AHH can be seen. Also for old animals the effect is weak. Recovery of the monooxygenase after pyrazole induction takes place in about 120 hr except for the total P-450 content which is still below normal. No sex dependence in the effect of pyrazole on CoH was found.

Effects of pregnancy on the cytochrome P-450 system in mice

The effects of pregnancy on the hepatic cytochrome P-450-dependent mixed-function monooxygenase system (P-450) from day 6 to day 18 of gestation were examined in the C57BL/6J mouse. Pregnancy induced an initial increase and then a decrease in total P-450 content, a decrease in microsomal aminopyrine-N-demethylase activity, and had no effect on microsomal ethylmorphine-N-demethylase activity. Pregnancy also induced in the C57BL/6J and the DBA/2J mice a new major isozyme of P-450 (P-450gest) as determined by high performance liquid chromatography and gel electrophoresis.

Regulation of heme metabolism and monooxygeneses in liver and kidney: influence of therapeutically used gold compounds

Two gold compounds, gold sodium thiomalate (AuTM) and auranofin (AF) are presently in clinical use in therapy of rheumatoid arthritis. The effects of varying doses of AF administered to rats by either the p.o. or the i.p. route on heme metabolism were determined. Twenty four hours after a single dose of AF, decreases in the sulfhydryl-containing enzymes, delta-aminolevulinic acid dehydratase and ferrochelatase activities were observed in the liver and kidneys. These decreases in heme biosynthetic enzymes were accompanied by decreases in cytochrome P-450-dependent enzymic activities and increases in microsomal heme oxygenase activity. These changes were observed with AF dosages as low as 5 mg/kg, with maximal changes occurring at a p.o. dose of about 15 mg of AF per kg and an i.p. dose of 5 to 10 mg of AF per kg. Dose-response studies with AuTM showed that maximal changes in heme metabolism occur at a lower dose of AF than of AuTM, even though AF was administered p.o. and AuTM was administered parenterally. In addition, the kidneys appeared to be more susceptible to the inhibitory effects of the two chrysotherapeutic agents than did the liver. The present studies demonstrate the p.o. drug AF affects heme metabolism in a manner similar to that reported previously with the parenterally administered AuTM.

Studies on the mechanism of 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU)-induced hepatotoxicity. II. Biochemical and morphological characterization of the injury and its prevention by phenobarbital

The present study characterizes the biochemical, morphological, and histological sites of CCNU-induced hepatotoxicity and investigates the effect of modifiers of drug metabolism on this toxicity. A single oral dose (100 mg/kg) of CCNU caused four- and ninefold increases in serum GOT and GPT respectively 48 h after administration in rats. A 25-fold rise in serum bilirubin, a total loss of bile flow, and a decrease in BSP clearance were also observed. Cytochrome P-450 content and EM-N-demethylase activity were significantly decreased to 88% and 66% of control values respectively. A histopathological time course study of CCNU-induced injury showed a progression of acute inflammation, edema, and fibrin deposition in portal areas over 24 h with necrosis and sloughing of bile duct epithelium at 24 and 36 h. Treatment of rats with PB (40 mg/kg/day for 4 days, i.p.) 24 h prior to CCNU administration protected against CCNU-induced hepatotoxicity. Thus, the levels of serum GOT, GPT, and bilirubin were only 2.5 and 4 times higher than in untreated or PB-treated controls. Histopathological examination also showed reduced severity of bile duct lesions in PB-pretreated animals. In rats receiving both PB and CCNU, bile flow was restored and BSP clearance was increased compared to the CCNU-treated rats. The mixed-function oxidase activity in PB + CCNU-treated rats was not significantly different from that in PB-treated controls. It is concluded that pretreatment of rats with PB can markedly suppress the hepatotoxic manifestations, including histopathological changes, the rise in serum bilirubin, and the cholestasis observed in CCNU-treated rats.

Effects of ascorbic acid supplementation on liver, lung and kidney microsomal drug metabolizing enzymes of the guinea-pig

1. Male guinea-pigs were administered 8, 180 and 360 mg ascorbic acid/day via drinking water for 1 and 2 months. The two high levels of ascorbic acid were not able to produce saturation in either blood or any of the three tissues (liver, lung and kidney) while the lowest ascorbic acid level was sufficient to prevent scurvy. 2. There was no significant differences among the groups receiving three distinct ascorbic acid levels in body weights, tissue weights or protein contents. 3. No significant alterations were observed in microsomal ethylmorphine N-demethylase activity of any of the three tissues among the groups after experimental periods. 4. The two high ascorbic acid levels produced significant increases in liver microsomal aniline 4-hydroxylase activity as compared to the lowest supplementation of ascorbic acid after 2 months. However, no significant enzyme activity changes were found among the groups after 1 month. 5. In lung, after 1 month significant increase was observed in microsomal aniline 4-hydroxylase activity with the two high ascorbic acid levels as compared to the lowest supplementation of ascorbic acid whereas after 2 months no significant changes were observed. 6. Kidney microsomal aniline 4-hydroxylase activity was unaffected by changes in ascorbate status.

Xenobiotic-metabolizing enzyme systems in test fish--II. The ethylmorphine N-demethylase activity of guppy (Poecilia reticulata) liver

The oxidative demethylation of the model substrate ethylmorphine has been characterized for the first time in the liver of a fish (Poecilia reticulata). The enzyme showed maximal activity at 35 degrees C and pH values higher than 8. The values of Km and Vmax for the reaction were 0.83 +/- 0.11 mM and 4.64 +/- 0.81 nmol HCHO/(mg microsomal protein) per min. The activity is attributed to the cytochrome P-450-dependent monoxygenase system, since it is inhibited by CO and requires NADPH; moreover it is inhibited competitively by alpha-naphthoflavone and non-competitively by metyrapone. The enzyme activity is induced by a two-week treatment of fish with phenobarbital and may be associated with a protein band of Mr 54,000.

Induction of cytochrome P-450 in congenic C57BL/6J mice by isosafrole: lack of correlation with the Ah locus

Isosafrole induction of cytochrome P-450 was compared in congenic strains of C57BL/6J mice, one of which expresses normal levels of the Ah receptor [B6(Ahb)], and another that does not contain a measurable receptor concentration [B6(Ahd)]. Using sucrose gradient analysis of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) binding, an Ah receptor concentration of 69.1 +/- 3.8 fmol/mg protein was measured in the hepatic cytosol from B6(Ahb) mice, while no receptor could be detected in the cytosol from B6(Ahd) mice. Isosafrole treatment (75 mg/kg X 3 days) increased the total hepatic microsomal cytochrome P-450 content to the same extent in the two congenic strains. The level of microsomal monooxygenase induction in the isosafrole-treated B6(Ahd) mice was greater than that of B6(Ahb) mice for ethylmorphine N-demethylase and isosafrole metabolite-complex formation, the latter a measure of cytochrome P2-450. In the case of 7-ethoxycoumarin O-deethylase only the isosafrole-treated B6(Ahd) mice had elevated microsomal activity. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) also revealed a similar induction pattern for the two congenic strains, following isosafrole treatment. Thus, the isosafrole treated B6(Ahd) mice produced an equivalent or slightly larger induction of cytochrome P-450 than the B6(Ahb) mice, suggesting that there is no direct role for the Ah receptor in the regulation of these cytochrome P-450 monooxygenase activities by isosafrole.