Effect of acetone administration on renal, pulmonary and hepatic monooxygenase activities in hamster

Stabilization of cytochrome P4502E1 protein by ethanol in primary hamster hepatocyte cultures

We report the effect of ethanol on monooxygenase activities in primary hamster hepatocyte cultures maintained on collagen-coated dishes. The addition of 50mM ethanol to cell cultures both from control and ethanol pretreated animals almost completely maintained, at least for 72hr, the P4502E1-dependent aniline hydroxylase (AnH) activity and the 2E1 immunodetectable apoprotein content at the levels of the corresponding 4-hr plated hepatocytes. On the contrary, other P450-dependent monooxygenase activities, as assayed by testosterone hydroxylases, kept decreasing falling-after 72hr of culture-to the levels of the 4-hr plated hepatocytes. In both cases, in the absence of ethanol, a rapid decline of AnH activities and 2E1 apoprotein contents were also observed, attaining undetectable levels at 72hr. The hybridizable 2E1 mRNA also rapidly declined in both cultures, but such decline was not significantly altered by the presence of 50mM ethanol in the culture medium. Furthermore, we show that P4502E1 in the liver possesses a rapid degradation phase with a half-life of about 6hr. Thus, in the hamster, P4502E1 appears regulated at post-translational level, as in rat, probably by a protein stabilization mechanism.

Influence of vehicle, distant topical delivery, and biotransformation on the chemopreventive activity of apigenin, a plant flavonoid, in mouse skin

PURPOSE

This study was designed to (a) establish a short-term in vivo system to evaluate topical formulations of apigenin, (b) determine whether apigenin should be topically delivered to the local skin tissue or systemic circulation, (c) investigate if biotransformation was involved in apigenin's chemopreventive activity.

METHODS

The effect of topical applied apigenin in acetone/DMSO (A/D, 9:1) on the promotion of skin tumorigenesis was studied. The influence of apigenin in DMSO, A/D (4:1), and propylene glycol/DMSO (PG/D, 4:1) on 12-O-tetradecanoylphorbol-13 acetate (TPA) induced ornithine decarboxylase (ODC) activity was compared. Distant topical delivery of apigenin was conducted on abdominal skin and ODC activity was monitored in dorsal skin. Potential glucuronidation/sulfation of apigenin in intact skin was assessed by measuring isolated apigenin before and after enzyme hydrolysis with glucuronidase/sulfatase. The epidermal extracts from apigenin-treated SENCAR mice were analyzed for metabolites by HPLC.

RESULTS

Apigenin (5 mumol) in A/D did not significantly reduce skin tumor incidence in contrast to previous data with DMSO. Inhibition of TPA-induced ODC by apigenin in three vehicles was in the order of DMSO > A/D > PG/D. TPA-induced ODC in dorsal skin was not inhibited by apigenin delivered from abdominal skin. The quantity of apigenin recovered from epidermal extract was not different before and after beta-glucuronidase/sulfatase treatment. Metabolites were not observed in the HPLC profiles of epidermal extracts from apigenin treated mice.

CONCLUSIONS

(a) The short-term TPA-induced ODC was validated for evaluating topical formulations of apigenin. (b) Topical delivery of apigenin should target the local skin tissue. (c) Glucuronidation/sulfation appeared not to be involved in apigenin's chemopreventive activity.

Induction and suppression of renal and hepatic cytochrome P450-dependent monooxygenases by acute and chronic streptozotocin diabetes in hamsters

The acute and chronic effects of streptozotocin diabetes on kidney and liver microsomal monooxygenases were studied using hamsters 2 days and 6 weeks following treatment with the diabetogen, respectively. Acute diabetes increased aniline hydroxylation and N-nitrosodimethylamine demethylation, decreased pentoxyresorufin O-dealkylation, without affecting benzo(a)pyrene hydroxylation and 7-ethoxycoumarin O-deethylation in kidney and liver microsomes. The effects of chronic diabetes on the microsomal monooxygenases were similar to the effects of acute diabetes, except that the chronic diabetic condition markedly decreased benzo(a)pyrene and 7-ethoxycoumarin oxidations in kidney microsomes. Total cytochrome P450 content and NADPH-cytochrome P450 reductase activity in kidney and liver microsomes of the diabetic hamsters were similar to the controls. Gel electrophoresis of microsomes from control and streptozoptocin treated hamster tissues revealed that diabetes enhanced the intensity of protein band(s) in the P450 molecular weight region. Immunoblotting of microsomal proteins showed that acute and chronic streptozotocin diabetes induced proteins immunorelated to P450s 2E1 and 1A in kidney and liver. In marked contrast, the acute and chronic diabetic conditions decreased the level of a P450 2B-immunorelated protein(s) in kidney and liver. The present study demonstrates that acute and chronic streptozotocin diabetes has the ability to induce P450 2E1 and 1A and suppress P450 2B in hamster kidney and liver and that the hamster monooxygenase responds to diabetes differently from the rat enzyme.

Purification and characterization of hepatic P-450IIE1 from acetone-treated mice

A new cytochrome P-450 isozyme (Mr = 52,000) was purified to apparent electrophoretic homogeneity from hepatic microsomes of mice treated with acetone and its biochemical, spectral, and immunological properties characterized. Several criteria indicated that the purified cytochrome was distinct from the known mouse P-450 isozymes. The absolute spectrum of its oxidized form indicated that it was in the high spin state. In a reconstituted system, it showed low catalytic activities towards 7-ethoxycoumarin, aminopyrine, and coumarin, whereas it catalyzed the oxidation of aniline, acetone, dimethylnitrosamine with high turnover number. The mouse enzyme was immunoreactive with polyclonal antibodies against rat P-450IIE1 and exhibited an NH2-terminal aminoacid sequence with a high homology to that of rat-P-450IIE1. Based upon the above catalytic, spectral, immunological and structural properties, the purified mouse P-450 appears to be the ortholog of previously described P-450IIE1(s) of other species.

Purification and characterization of an acetone-inducible cytochrome P-450 from hamster liver microsomes

A form of cytochrome P-450 has been purified to electrophoretic homogeneity from the hepatic microsomes of Syrian golden hamsters treated with acetone. This P-450 form, designated ha P-450j, had an M(r) of approximately 55,000, bound dimethyl sulphoxide and exhibited a CO-reduced absorbance maximum at 451 nm. The absolute spectra of its oxidized form indicated that ha P-450j was predominantly in the low-spin state. In a reconstituted system, ha P-450j showed relatively low catalytic activities towards 7-ethoxycoumarin, 7-ethoxyresorufin, aminopyrine, ethylmorphine and benzphetamine, whereas it catalysed the oxidation of aniline, acetone and thiobenzamide with a high catalytic-centre activity. In addition, ha P-450j catalysed at a high rate the high-affinity component of dimethylnitrosamine N-demethylase; in contrast, only the low-affinity component of diethylnitrosamine N-de-ethylase was efficiently catalysed. The addition of cytochrome b5 to the reconstitution system decreased the Km value for dimethylnitrosamine N-demethylase by a factor of 5 and increased the Vmax. value, and slightly enhanced the other activities. Thiobenzamide and diethyldithiocarbamate were found to be the most effective inhibitors of the ha-P-450j-dependent aniline hydroxylation. Polyclonal antibodies against rat P-450j recognized ha P-450j in immunoblots of control and treated hamster liver microsomes. Treatment of hamsters with acetone increased the apparent abundance of ha P-450j in microsomes, whereas phenobarbital and beta-naphthoflavone did not induce it. Analysis of N-terminal amino acid sequences demonstrated that ha P-450j has a high degree of sequence identity with rat P-450j. All the evidence presented in this study indicates that ha P-450j could represent the hamster orthologue of the previously described CYP2E1(s) of other species.