Use of a direct high performance liquid chromatography method for multiple testosterone hydroxylations in studies of microsomal monooxygenase activities

Long-Term Anticonvulsant Therapy Worsens Outcome in Paracetamol-Induced Fulminant Hepatic Failure

1 Paracetamol hepatotoxicity has been found to be potentiated by anticonvulsant drugs in animal experiments; isolated case reports in humans sugest that long-term anticonvulsant therapy may also adversely influence outcome following overdose.

2 We compared the clinical course, after paracetamol overdose, of 18 patients on long-term anticonvulsant therapy with corresponding features in two published series of paracetamol-induced fulminant hepatic failure from this unit: 297 patients seen between 1973 and 1985 and a further 99 between October 1986 and April 1988.

3 Mortality in those patients who were taking anticonvulsants, but who did not receive N-acetylcysteine, was higher than in either of these series (93.3% vs 64.6% and vs 57.9%, P< 0.025). Although not statistically significant, there were also trends towards more severe coma (grade 3 or 4: 93.3% vs 75.4%, 1986-88), acidosis (pH less than 7.30: 40% vs 22.6%, 1973-85) and coagulopathy (prothrombin time greater than 100 s: 53.3% vs 33.7%, 1973-85). In the small number of patients given N-acetylcysteine, mortality was similar to that in the 1986-88 series (1/3 vs 15/42).

4 We conclude that chronic use of anticonvulsants enhances clinical features of paracetamol toxicity and discuss possible mechanisms by which this could be mediated.

Determination of testosterone and 6beta-hydroxytestosterone by gas chromatography-selected ion monitoring-mass spectrometry for the characterization of cytochrome p450 3A activity

A method for the determination of testosterone and its metabolite, 6beta-hydroxytestosterone, in liver microsomal incubates employing gas chromatography with selected ion monitoring mass spectrometric detection (GC-SIM-MS) has been developed. The method is more rapid than previously reported methods. Testosterone and its metabolites are extracted from the incubation mixture in a single step with methylene chloride. The method does not require derivatization and testosterone and its metabolites are separated on a HP-5MS fused-silica capillary column in less than 15 min. The retention times of testosterone (m/z 288), methyltestosterone (m/z 302), and 6beta-hydroxytestosterone (m/z 304) are approximately 12.7, 12.8, and 13.4 min, respectively. There are no interferences from other known CYP450 metabolites of testosterone. In addition, the selectivity and specificity of the mass spectrometer helps eliminate possible interferences from drugs and new chemical entities evaluated using this methodology. Calibration curves for testosterone and 6beta-hydroxytestosterone are linear from 0.25 to 100 microM. Extraction recoveries are better than 92% for both analytes and the internal standard, methyltestosterone. Over the course of five separate runs, within-day and inter-day precision (expressed as relative standard deviation) was less than 5% for all concentrations of testosterone and 6beta-hydroxytestosterone. Accuracies ranged from 95.8 to 105.8% for testosterone and 94.6 to 104.2% for 6beta-hydroxytestosterone. The assay has been used to characterize the CYP3A metabolic activity of multiple preparations of human, rat, and dog liver microsomes.

The effect of budesonide and triamcinolone acetonide on hepatic microsomal testosterone metabolism in the rat

The hepatic microsomal metabolism of testosterone was studied in male rats after treatment with either budesonide or triamcinolone acetonide for 13 weeks. The in vitro metabolism was determined using a testosterone concentration of 35 nM which is comparable to the levels found in plasma. It was shown that the total microsomal testosterone metabolism was decreased in budesonide-treated rats and increased in rats treated with triamcinolone acetonide. The testosterone metabolites produced were measured and thus it was revealed that budesonide treatment brought about its effect through a 50% decrease in the activity of steroid 5 alpha-reductase, but did not affect other reductive enzymes, or the oxidation of testosterone. Triamcinolone acetonide treatment decreased steroid 5 alpha-reductase activity by 95% and also decreased the activities of steroid 3 alpha- and 3 beta-reductases by more than 90%. In addition, treatment with triamcinolone acetonide caused a 50% increase in the oxidative metabolism of testosterone, which resulted in the observed increase in total testosterone metabolism. The presence of 0.1 microM budesonide in the microsomal incubations was without effect on testosterone metabolism. However, 0.1 microM triamcinolone acetonide inhibited testosterone oxidation by 65%, without affecting the reductive pathway of testosterone metabolism.

Genetically engineered V79 Chinese hamster cell expression of purified cytochrome P-450IIB1 monooxygenase activity

Chinese hamster V79 fibroblasts, frequently used as target cells in short-term tests for mutagenicity, do not possess measurable monooxygenase activity; in particular, enzymatic oxidation of testosterone (T) cannot be demonstrated. If these V79 cells, however, had been transfected with the cDNA-encoding rat liver cytochrome P-450IIB1 under control of the SV40 early promoter, they stably expressed monooxygenase activity. These so-called SD1 cells then oxidatively metabolized T at a rate of 27 pmol/mg protein/min, converting it to 16 alpha- and 16 beta-hydroxy-T as well as 4-androsten-3,17-dione as sole metabolites in a ratio of 1.1:1.0:1.6. The regio- and stereoselective conversion of T by SD1 cells, as well as the quantitative distribution of the metabolites, corresponds well with the results reported for pure cytochrome P-450IIB1 in a reconstituted system.

Sex-related difference in oxidative metabolism of testosterone and erythromycin by hamster liver microsomes

The activities of testosterone hydroxylases and erythromycin N-demethylase were significantly higher in liver microsomes from female hamsters than in the male counterparts. SDS-polyacrylamide gel electrophoresis revealed a difference in protein composition between male and female liver microsomes in the molecular mass region comprising cytochrome P-450. Western blot analysis showed further that antibodies to rat male-specific cytochrome P-450 crossreacted with at least two proteins in both male and female hamster microsomes, but one of the female proteins had a different molecular mass from that of the male proteins. It is concluded that sex difference in liver microsomal cytochrome P-450 is not restricted to rats and mice, as has previously been believed.

Effects of ethanol ingestion on the hepatotoxicity and metabolism of paracetamol in mice

The influence of ethanol on paracetamol-induced liver damage was studied in mice and related to changes in microsomal monooxygenases and plasma paracetamol metabolites in the same group of animals. Paracetamol (400 mg/kg body wt, p.o.) was administered alone or simultaneously with ethanol (3 g/kg, p.o.) to mice fed either a chow diet or pretreated for 4 weeks with a liquid diet containing ethanol (20% of energy). Acute ethanol administration protected against paracetamol hepatotoxicity, but this protection was complete only in mice not fed ethanol previously. Acute ethanol administration also appeared to reduce paracetamol monooxygenation in vivo, but ethanol (50 mM) added to microsomal incubations in vitro had no significant effect on paracetamol activation and covalent binding. The chronic ingestion of ethanol in the diet increased paracetamol-related liver damage, but there appeared to be no induction of paracetamol monooxygenation in these animals. We are unable to confirm current concepts that the potentiation of paracetamol hepatotoxicity by chronic ethanol ingestion and its reduction by acute ethanol administration result solely from contrasting effects of ethanol on cytochrome P-450, and alternative explanations are proposed.

The effect of peroxisome proliferators on the metabolism and spectral interaction of endogenous substrates of cytochrome P-450 in rat hepatic microsomes

The peroxisome proliferators clofibric acid and di-(2-ethylhexyl)-phthalate (DEHP) preferentially induced the 12-hydroxylation, compared to the 11-hydroxylation, of lauric acid in rat liver microsomes. A marked increase in the affinity of spectral interaction of this substrate with cytochrome P-450 was also observed. In addition, both clofibric acid and DEHP treatment produced a marked effect on the profile of site- and stereo-specific microsomal metabolites of testosterone. These results demonstrate that both peroxisome proliferators induce similar form(s) of cytochrome P-450 which are active in the metabolism of endogenous substrates of cytochrome P-450. The possible relevance of these findings to the hepatotoxicity of peroxisome proliferators is discussed.