Cytochrome B5 Content Research Articles

Activity of Liver Cytochrome P-450-Dependent Monooxygenase System in Morphine-dependent Rats

Young female Wistar rats were injected intraperitoneally with increasing doses of morphine (9-45 mg/kg b.w. twice a day) for 14 days. The activities of the cytochrome P-450-dependent monooxygenase system and microsomal electron transport chain I were determined. Long-term morphine treatment decreased significantly cytochrome P-450 content, while it did not affect microsomal electron transport chain I. A decrease in cytochrome b5 content was accompanied by a compensatory increase in the activity of NADH-cytochrome b5 reductase. Both 4-aminopyrine N-demethylase activity and aniline hydroxylase activity decreased after morphine treatment (48% and 70%, respectively, when compared with controls).

The Role of Cytochrome b5 in the Biosynthesis of Androgens by Human P450c17

Human cytochrome b5 has a profound effect on the 17,20-lyase activities catalyzed by purified, human cytochrome P450c17. It enhances the conversion of 17α-hydroxypregnenolone to dehydroepiandrosterone by 13-fold and the conversion of 17α-hydroxyprogesterone to androstenedione by at least 10-fold. This latter activity is virtually undetectable in the absence of cytochrome b5. Other activities catalyzed by P450c17 include 17α-hydroxylation of progesterone and pregnenolone and are much less influenced by cytochrome b5. The conversion of pregnenolone to 17α-hydroxypregnenolone is increased by 2-fold, while that of progesterone to 17α-hydroxyprogesterone is unchanged. These studies using purified systems suggest that cytochrome b5 plays a role in regulating the activities of P450c17 to optimize the balance between sex hormone synthesis and glucocorticoid synthesis. In particular, they indicate that in human testes which contains a high b5/P450 ratio, 17α-hydraxyprogesterone can serve as an intermediate in testosterone production, rather than being a dead-end product, or stated another way, because of the relatively high concentration of cytochrome b5 in the human testis, both the Δ4 and the Δ5 steroidogenic pathways can lead to testosterone production.

Effect of nifedipine, verapamil and diltiazem on the enzyme-inducing activity of phenobarbital and beta-naphthoflavone

1. 1. The effects of three calcium antagonists (CA), nifedipine (NF), verapamil (V) and diltiazem (DL) on the enzyme-inducing activity of phenobarbital (PB) and β-naphthoflavone (β-NF) were measured by hexobarbital (HB) sleeping time, benzphetamine-N-demethylase (BND) ethoxycourmarin-O-deethylase (ECOD) and ethoxyresorufin-O-deethylase (EROD) activities, as well as by the cytochrome P-450 and cytochrome b5 content. 2. 2. NF, V and DL at oral doses of 100, 80 and 60 mg/kg administered 1 hr before PB additionally shortened the HB sleeping time. 3. 3. Single administration of calcium antagonists on the background of developed PB-provoked enzyme induction prolonged the PB-shortened hexobarbital sleeping time. 4. 4. Three day administration of NF, V and DL plus PB slightly decreased the enzyme-inducing effect of PB on BND activity and cytochrome P-450 and cytochrome b5 content. 5. 5. NF and V administered only once after PB-provoked enzyme induction increased the PB enzyme-inducing effect on BND activity and on the content of cytochrome P-450. DL decreased the PB-induced BND activity and cytochrome P-450 and cytochrome b5 content. 6. 6. The calcium antagonists studied affected the enzyme-inducing activity of β-NF to a lesser extent when compared to PB. Only NF was found to potentiate the enzyme-inducing effect of β-NF on the EROD activity and on the cytochrome P-450 content.

Effect of cyclophosphamide administration on the activity and relative content of hepatic P4502D1 in rat.

1. The effects of the administration of the anticancer and immunosuppressive drug, cyclophosphamide, to the rat on hepatic P4502D1 activity and content in the microsomal fraction have been examined. 2. Liver microsomes were obtained from male Hooded Wistar rats administered a single dose (i.p.) of saline or cyclophosphamide (200 mg/kg). Rats receiving cyclophosphamide were killed 1, 4, 7, 10 or 14 days after cyclophosphamide administration. The O-demethylation of dextromethorphan to dextrorphan was used to monitor 2D1 activity. 3. The mean Vmax for dextrorphan formation was reduced significantly (p < 0.0001) 7, 10 and 14 days after cyclophosphamide administration compared with the control group (control, 0.32 +/- 0.07; 7-day, 0.20 +/- 0.08; 10-day, 0.11 +/- 0.02; and 14-day group, 0.15 +/- 0.02 nmol/mg/min). 4. Western blotting revealed that there was a significant reduction (p < 0.0005) in the microsomal relative 2D1 content 10 days after cyclophosphamide administration compared with the control group (control, 1.25 +/- 0.44; and 10-day group, 0.65 +/- 0.14). 5. The activity of reduced nicotinamide adenine dinucleotide phosphate P450 reductase was significantly reduced (p < 0.0001) 7, 10 and 14 days following cyclophosphamide administration (control, 215 +/- 24; 7-day, 102 +/- 20; 10-day, 59 +/- 4 and 14-day group, 76 +/- 8 nmol/mg/min). Cytochrome b5 content was significantly reduced (p < 0.0001) 7 and 10 days following cyclophosphamide administration (control, 0.46 +/- 0.13; 7-day, 0.28 +/- 0.07 and 10-day group, 0.20 +/- 0.03 nmol/mg). 6. The significant reductions in the activity of rat hepatic microsomal 2D1 following cyclophosphamide administration, as seen by the alterations in mean Vmax for dextrorphan formation, do not appear to be due to a single factor, but may result from a combination of several events, including reductions in relative 2D1 content, reduced nicotinamide adenine dinucleotide phosphate P450-reductase activity and cytochrome b5 content.

Effect of Chloroquine on Rat Liver Microsomes.

Alterations in liver microsomal drug-metabolizing enzymes and phospholipids following oral administration of chloroquine to rats for 14 days were investigated. An increase in cytochrome P450 and cytochrome b5 contents and an increase in the activities of NADPH cytochrome c reductase and NADH microsomal cytochrome reductase were observed. A decrease in cholesterol and an increase in phospholipids were noted in the microsomal membranes, which altered the membrane fluidity, which may be of importance in controlling different membrane functions. The increase in different fractions of microsomal phospholipid is probably due to an increased incorporation of acetate into phospholipids.

Liver enzyme activities after multiple administration of nifedipine in mice.

The effect of multiple nifedipine administration on hexobarbital sleeping time, liver monooxygenase and synthetase activities, lipid peroxidation and microsomal membrane fluidity were studied in male albino mice. The drug was administered orally at a dose of 25 mg/kg daily for 14 and 21 days. Nifedipine caused enzyme induction, demonstrated by shortened hexobarbital sleeping time, enhanced ethylmorphine N-demethylase, aniline 4-hydroxylase, ethoxycoumarine O-deethylase, UDP-glucuronyl transferase, glutathione S-transferase and NADPH-cytochrome c reductase activities and increased content of cytochrome P450 and cytochrome b5. This effect persisted until the 7th day after the last dose of nifedipine. There were no changes in lipid peroxidation and fluidity of the microsomal membranes after 14-day nifedipine administration. The increased cytochrome P450 content and drug metabolizing enzyme activities could be not associated with changes in these liver microsomal membrane properties.

Stimulatory effects of lung cytochrome b5 on benzphetamine N-demethylation in a reconstituted system containing lung cytochrome P450 LgM2

1. 1. Cytochrome b5 was partially purified from sheep lung microsomes in the presence of detergents Emuigen 913 and cholate by three consecutive DEAE-cellulose and Sephadex G-100 gel filtration chromatographies. 2. 2. The specific content ofcytochrome b5 was 16.5 nmol/mg protein and purified cytochrome b5 fractions were free of cytochrome P450, NADPH-cytochrome P450 reductase and NADH-cytochrome b5 reductase activities. 3. 3. The influences of increasing concentrations of lung cytochrome b5 on benzphetamine N-demethylation reactions were examined in four different reconstitution systems containing lung cytochrome P 450 LgM2, lung cytochrome P450 reductase and lipid. In each system concentration of reductase was doubled with respect to former system. 4. 4. In all systems cytochrome b 5 stimulated benzphetamine Ndemethylase activity especially when cytochrome b5 was present at 0.5:1 molar ratio with respect to cytochrome / P450 LgM2. 5. 5. Besides, the greatest fold of increase in benzphetamine N-demethylation activity due to addition of cytochrome b5 was observed in System 1 with the lowest concentration of reductase.

Catalytic and Immunochemical Characterization of Hepatic Microsomal Cytochromes P450 in Beluga Whale ( Delphinapterus leucas)

Understanding the effects of environmental contaminants on cetaceans and other marine mammals will require information on the biochemistry of xenobiotic metabolism in these species. We characterized the hepatic microsomal cytochrome P450 system in beluga whales ( Delphinapterus leucas) from the Canadian Arctic. The content of native P450 averaged 0.203 and 0.319 nmol/mg microsomal protein, cytochrome b5 content averaged 0.199 and 0.236 nmol/mg, and rates of NADPH-cytochrome c reductase were 79 and 76 nmol/min/mg, for females and males respectively. Ethoxyresorufin O-deethylase (EROD), pentoxyresorufin O-depentylase (PROD), and benzo[ a]pyrene (BP) hydroxylase (AHH) activities were significantly greater in males than in females, and were highly correlated with one another ( r 2 between 0.853 and 0.912). HPLC analysis of in vitro BP metabolites revealed benzo-ring (7,8- and 9,10-) dihydrodiols, consistent with activation of this compound, as well as 4,5-dihydrodiol,3-OH-, 7-OH-, and 9-OH-BP and 1,6- and 3,6-quinones. Estradiol 2-hydroxylase activity did not differ between sexes, and rates did not correlate with those of the other activities. Antibodies against scup P450B (an apparent teleost CYP2B) and rat CYP2B1 did not recognize proteins in beluga liver microsomes, but there was a protein detected by antibodies to PB-inducible rabbit CYP2B4. Antibodies to ethanol and ketone-inducible rat CYP2E1 reacted with two proteins in beluga liver microsomes. Antibodies specific to hydrocarbon-inducible CYP1A1 and/or CYP1A2 forms showed a single protein band, apparently more closely related to CYP1A1. The content of CYP1A was fivefold greater in male than in female beluga. CYP1A content was highly correlated with EROD, PROD, and AHH activities, suggesting that this P450 form is a primary catalyst for these reactions in beluga. CYP1A content and activity were highly correlated with the concentrations in blubber of non- ortho and mono- ortho PCB congeners, compounds that induce CYP1A in other mammals. These results indicate that a CYP1A is a catalyst for the metabolism of aromatic hydrocarbon pollutants in the beluga whale, and strongly suggest that this protein is induced in these organisms by environmental contaminants, including PCBs. The results support the measurement of CYP1A expression as a biomarker of exposure to inducers in marine mammals. The full functional and evolutionary relationships of beluga CYP1A and of beluga proteins immunologically related to other P450 forms are uncertain.

Biomonitoring of pollution: the hepatic cytochrome P-450 enzyme system in the feral mouse Apodemus flavicollis as indicator

The aim of the present study was to find a suitable wild-rodent to be used as terrestrial bioindicator. The wild mice were trapped at three sites around Vienna and at a fourth location in the countryside. Apodemus flavicollis, the yellow-necked mouse, was the most frequently captured mouse at all four sites. For each sample hepatic microsomal protein content, cytochromes b5 and P450, and enzyme catalytic activities-ECOD, EROD, BROD and PROD were measured. Except for one male urban group no significant differences between rural and urban groups in ECOD activity were observed. Increased cytochrome b5 and P450 contents per mg of microsomal protein were found in one of the male and all the three female urban groups. However the alkoxyresorufin O-dealkylase activities were significantly increased in both sexes of the three city groups. These results suggest that induction of cytochrome P450IA and P450IIB families has occurred in urban populations, indicating a possible pollution with halogenated dioxins and furans, PCBs, PAHs etc. The data show that induction of hepatic mixed function oxidase (HMFO) activity in the feral mouse Apodemus flavicollis can be successfully used as a terrestrial bioindicator for pollution monitoring.

Effects of in vivo benzo(a)pyrene treatment on liver microsomal mixed-function oxidase activities of gilthead seabream ( Sparus aurata)

Benzo(a)pyrene [B(a)P] treatment of gilthead seabream, 25 mg/kg, i.p. for 5 consecutive days, did not cause any significant changes in ethylmorphine N-demethylase and aniline 4-hydroxylase activities of liver microsomes. The same treatment did not alter the liver microsomal cytochrome b5 content, NADH-cytochrome b5 reductase and NADPH-cytochrome P450 reductase activities. However, benzo(a)pyrene treatment caused a 2–3-fold increase in 7-ethoxyresorufin O-deethylase (7-EROD) activity of gilthead seabream liver microsomes. Although, upon treatment, total cytochrome P450 content of liver microsomes increased about 1.7-fold in 1990 fall, no such increase was observed in spring 1991. However, a new cytochrome P450 with an apparent M r of 58,000 was observed on SDS-PAGE of liver microsomes obtained from benzo(a)pyrene treated gilthead seabream. Besides, in vitro addition of 0.2 × 10 −6 M benzo(a)pyrene to the incubation mixture inhibited 7-ethoxyresorufin O-deethylase activity by 93%. Gilthead seabream liver microsomal 7-ethoxyresorufin O-deethylase activity was characterized with respect to substrate concentration, amount of enzyme, type of buffer used, incubation period and temperature.

In-vitro evidence for the regulation of 17,20-lyase activity by cytochrome b5 in adrenocortical adenomas from patients with Cushing's syndrome.

The electron transfer system molecules, NADPH-cytochrome P450 reductase (Red) and cytochrome b5 (b5) are known to increase the relative activity of 17,20-lyase to 17 alpha-hydroxylase in vitro. Consistent with this hypothesis, we have reported recently that adrenocortical adenomas from patients with Cushing's syndrome that produced exceptionally high concentrations of androgens also contained more b5 mRNA as well as greater 17,20-lyase activity than adenomas that produced low concentrations of androgens. This finding was suggestive but inconclusive in linking b5 functionally to this difference in adenoma 17,20-lyase activity. In the present study, we have extended this finding by examining the effect of b5 on microsomal 17,20-lyase activity using an antibody against cytochrome b5. Biochemical quantitation of the content of b5 and Red activity in the microsomal fraction of the tumours and determination of 17,20-lyase activity in the microsomes in the presence or absence of an antibody against b5. Seven patients with a clinical diagnosis of Cushing's syndrome secondary to benign adrenocortical adenoma were studied. The microsomal activities of 17 alpha-hydroxylase, 17,20-lyase and 3 beta-hydroxysteroid dehydrogenase were measured by in-vitro enzyme assay with thin layer chromatography. Microsomal Red activity was assayed by measuring NADPH-dependent cytochrome c reduction reaction. Cytochrome b5 concentration was determined by spectrophotometric analysis. An in-vitro enzyme assay of microsomal fractions from the adenoma showed that the 17,20-lyase activities of two adenomas that produced high concentrations of adrenal androgen were threefold greater than those of five other adenomas that produced low concentrations of androgens. Cytochrome b5 concentrations were greater in the two adenomas with high 17,20-lyase activity than in the other adenomas, while no significant difference in Red activity was observed among all the adenomas. The increased 17,20-lyase activity in the two adenomas was partially but significantly antagonized by an antibody against b5. These results suggest that differences in tissue b5 are functionally associated with differences in 17,20-lyase activity in adrenocortical adenomas in Cushing's syndrome, resulting in a dissociated secretion of cortisol and androgens in some patients.

Aztreonam decreases hepatic microsomal cytochrome P450 in cynomolgus monkeys.

We examined the effect of successive administrations of aztreonam, which is used clinically as an antibiotic, on the mixed function oxidase system in non-human primates. Treatment of cynomolgus monkeys with aztreonam at doses of between 40 and 300 mg/kg for 4 weeks resulted in a significant decrease in the content of hepatic microsomal P450. On the other hand, no significant change was observed in hepatic cytochrome b5 content and NADPH-cytochrome c (P450) reductase activity following treatment with aztreonam. The activity of testosterone 6 beta-hydroxylase, but not 2 beta- and 16 alpha-hydroxylases in hepatic microsomes, was decreased following the treatment of cynomolgus monkeys with aztreonam. The content of P450 CMLc, which is classified into the 3A subfamily, was also decreased by aztreonam treatment although the content of P450 CMLb, which is a 2A enzyme in cynomolgus monkeys, was unchanged. From these results, we concluded that aztreonam decreased P450 CMLc in hepatic microsomes of cynomolgus monkeys.

Alterations in rat hepatic drug metabolism during pregnancy and lactation

The hepatic microsomal drug metabolism during pregnancy and lactation was studied. Four days post partum, the concentrations of cytochrome P450 and cytochrome b5 were reduced by 50% when compared with pregnant rats, at day 10 of gestation. Within this time period the N-demethylation of aminopyrine, the rate of aldrin epoxidation and the N-demethylation of demethylnitrosamine was reduced by 53, 74 and 21%, respectively. However, the rates of ethoxyresorufin-O-deethylation did not differ amongst both groups and the deethylation of 4-nitroanisole and the 4-hydroxylation of aniline was increased by 71 and 31%, respectively in lactating rats. Furthermore, the activities of UDP-glucuronyltransferase and glutathione 5-transferase were increased by 21 and 27%, but those of epoxide hydrolase were reduced by 85%. Western immunoblot analysis of microsomal proteins obtained from pregnant and lactating rats shows that only proteins encoded by the genes of CYP2C6 and CYP3A1 are expressed at detectable levels, whereas the expression of CYP1A1, CYP1A2, CYP2A1, CYP2B1, CYP2E1 and CYP4A1 was not detectable in pregnant and lactating rats at a protein loading of 3 μg total protein per well. In contrast, in northern blot hybridization experiments, detectable amounts of mRNA of the above named isoenzymes were measurable, but at varying intensities. Based on the northern blot hybridization analysis, an approximate 4-fold and 3-fold increase in CYP2A1 mRNA and CYP3A1 mRNA was found, when lactating rats were compared with female controls or pregnant rats, at day 10 of gestation.

High expression of cytochrome b5 in adrenocortical adenomas from patients with Cushing's syndrome associated with high secretion of adrenal androgens.

The mechanism of dissociated secretion between adrenal androgens and cortisol observed in several clinical situations remains unclear. We investigated whether the electron transfer systems NADPH-cytochrome P450 reductase and cytochrome b5, both of which had been shown to increase 17,20-lyase activity in vitro, were involved in the reaction selectivity between 17 alpha-hydroxylase and 17,20-lyase in adrenocortical adenomas obtained from eight patients with Cushing's syndrome producing different concentrations of adrenal androgen. In vitro enzyme assay using microsomal fraction of adenoma indicated that all adenomas from seven patients showed almost the same degree of 17 alpha-hydroxylase and 3 beta-hydroxysteroid dehydrogenase (3 beta HSD) activities. However, the 17,20-lyase activities of two adenomas producing high concentrations of adrenal androgens were 3-fold greater than those of other five adenomas producing low concentrations of adrenal androgens. The mRNA concentrations of cytochrome P45017 alpha and 3 beta HSD were approximately the same in all adenomas, whereas those of cytochrome b5 in two adenomas possessing high 17,20-lyase activities were greater than those in other adenomas. The increased levels of cytochrome b5 in the two adenomas were further confirmed at the protein level using Western blot analysis of the microsomal fraction. No significant expression of NADPH-cytochrome P450 reductase was detected in any of the adenomas by Northern blot analysis. These results suggest that the difference in the concentration of cytochrome b5 in adrenal adenomas from patients with Cushing's syndrome may partially account for the difference in the amount of adrenal androgens produced by the tumors.

On the enzyme-inducing action of calcium antagonists.

The effects of three calcium antagonists, nifedipine (NF), verapamil (V) and diltiazem (DL), on rat liver monooxygenases were studied. The drugs were administered in oral doses of 50, 40 and 30 mg/kg daily for 3 weeks in male Wistar rats. NF and V shortened the hexobarbital (HB) sleeping time and increased benzphetamin-N-demethylase (BND), ethylmorphine-N-demethylase (EMND), aniline hydroxylase (AH), ethoxycoumarine-O-deethylase (ECOD), ethoxyresorufin-O-deethylase (EROD) and NADPH-cytochrome c reductase activities and the content of cytochrome P-450 and microsomal heme, but did not change the content of cytochrome b5. The data suggest that these calcium antagonists exert an enzyme-inducing effect on the hepatic monooxygenases. DL significantly increased only the EROD and NADPH-cytochrome c reductase activities and shortened HB sleeping time to a lesser extent, suggesting a weaker enzyme-inducing effect as compared to NF and V. The three drugs increased the delta-aminolevulinic acid (ALA) synthetase activity and decreased heme oxygenase (HO) activity. The increased cytochrome P-450 content is probably due to the increased synthesis and the decreased breakdown of this hemoprotein.

Alterations in hepatic biochemistry of mice intoxicated with MIC, carbaryl and thiram.

The effect of different doses of methyl isocyanate (MIC), carbaryl and thiram on liver microsomal mixed-function oxygenases (MFO) was studied in adult Swiss Portan mice by intraperitoneal (i.p.) injection for different durations. The LD50 dose of all three toxicants after 0.75 h of administration could increase cytochrome P-450 and cytochrome b5 contents (82-143%), and the 1/4 LD50 of these compounds could elicit the same effect after 168 h (168-393%). The 1/4 LD50 dose of thiram decreased the cytochrome P-450 content below the control level (69.62%) in 0.75 h and the same dose of MIC could decrease the cytochrome P-450 level by 40% compared to the control after 3 days of consecutive injection. The activities of drug-metabolizing enzymes (aminopyrine demethylase--NADH and NADPH-linked--and aniline hydroxylase) were found to increase with all three compounds in general. Marked changes in the activity of the marker enzyme glucose-6-phosphatase were also seen after i.p. injection if MIC, carbaryl and thiram. These findings suggested that these compounds were hepatotoxic, which could be due to their carbamylating nature.

The prolongation effect on the duration of pentobarbital anesthesia by submaxillariectomy in male rats

The present study was performed to investigate the effects of submaxillariectomy (Subx) on the anesthetic effect (sleeping time) of pentobarbital, the concentration-time profile of plasma pentobarbital and the hepatic drug metabolizing enzyme systems in male rats of the Donryu strain. Subx was performed when the rats were 60 days old. Subx prolonged the duration of pentobarbital (30 mg/kg, i.p.) anesthesia at 10, 23 and 43 days after the operation, respectively. At 43 days after Subx, the plasma pentobarbital concentration was higher in the Subx group until 30 min after the administration. There was no significant difference in the hepatic microsomal cytochrome P-450 content between the Subx and control groups. Cytochrome b5 content, aminopyrine N-demethylase and aniline hydroxylase activities were increased significantly in the Subx group. The activity of heme oxygenase, the rate limiting enzyme in the heme catabolic pathway, tended to increase in the Subx group. Furthermore, the activity of delta-aminolevulinic acid synthetase, the rate limiting enzyme in the heme synthetic pathway, was significantly decreased to 51 percent of the control group by Subx. These results may suggest that the prolongation of the duration of pentobarbital anesthesia is caused by Subx due to the change in the pharmacokinetics of pentobarbital, especially the inhibitory effects of the hepatic pentobarbital metabolizing enzyme system.

Suppression of liver microsomal drug-metabolizing enzyme activities in adult female rats pretreated with cannabidiol.

The suppression by cannabidiol (CBD) of the liver microsomal drug-metabolizing enzyme activities in female rats was demonstrated and its mechanism was examined. Pretreatment of rats with CBD (10 mg/kg, i.p.) caused temporary decreases in contents of cytochrome P450 (P450) and b5 and NADPH-cytochrome c (P450) reductase activity compared with values from the vehicle control group. p-Nitroanisole O-demethylase, aniline hydroxylase, d-benzphetamine N-demethylase and delta 9-tetrahydrocannabinol 11-hydroxylase were also decreased by the CBD pretreatment. The latter two activities took a longer time to return to control levels than the former two. However, the CBD pretreatment, which reduced the protein level of P450 UT-2 (CYP2C11) in adult male rats, did not decrease the protein level of P450 F-1 (CYP2C6) or F-2 (CYP2C12) in liver microsomes from female rats. These results suggest that the mechanisms by which CBD suppresses liver microsomal drug-metabolizing enzyme activities are different in male and female rats.

Effects of in vivo benzene treatment on cytochrome P450 and mixed-function oxidase activities of gilthead seabream ( sparus aurata) liver microsomes

1. Treatment of gilthead seabream ( Spams aurata) with benzene 0.6 ml/kg/day, s.c., for four consecutive days resulted in a marked 78% and 73% decrease in total cytochrome P450 content and 7-ethoxyresorufin O-deethylase activity of liver microsomes, respectively. 2. In contrast, benzene treatment did not affect aniline 4-hydroxylase, ethylmorphine N-demethylase and cytochrome b5 content of fish liver microsomes, significantly. 3. The study revealed a distinct difference in the mixed-function oxidation of xenobiotics in mammalian and fish liver microsomes in response to benzene treatment.

Musk xylene is a novel specific inducer of cytochrome P-450IA2

The effect of musk xylene on contents of both cytochrome P-450IA1 and cytochrome P-450IA2 in rat liver was investigated using Western blotting analysis. Rats were treated i.p. for five consecutive days with either 50, 100 or 200 mg musk xylene/kg body weight. Musk xylene increased both total cytochrome P-450 and cytochrome b5 contents in rat liver microsomes. Musk xylene induced cytochrome P-450IA2 (384 pmol/mg protein) strongly and preferentially and the ratio of cytochrome P450IA2/P-450IA1 was about 12 at the lowest dose tested. Musk xylene also induced the cytochrome P-450IA1 dose-dependently, but these extents were very small (32–174 pmol/mg protein). These results suggest that musk xylene may be a more specific inducer for cytochrome P-450IA2 than any other inducers reported.