Actions of danazol in vivo on cytochrome P-450 and steroidogenic enzymes in rat testis and liver microsomal preparations

Danazol increases the oral bioavailability of midazolam by inactivation of hepatic and intestinal CYP3A in rats

Danazol (DNZ) is a synthetic androgen derivative used for the treatment of intractable hematological disorders. In this study, we investigated the effects of DNZ on CYP3A activity in hepatic and small intestinal microsomes and the pharmacokinetics of midazolam (MDZ), a typical substrate for CYP3A, in rats.MDZ 4-hydroxylation activities in hepatic and small intestinal microsomes significantly decreased 24 h after DNZ (100 mg/kg, i.p.) treatment. Time-dependent inactivation of MDZ 4-hydroxylation activities was noted when microsomes were pre-incubated with DNZ in the presence of a NADPH-generating system.The Western blot analysis indicated that the decrease observed in enzyme activity was not due to changes in the protein expression of CYP3A.In contrast to the intravenous administration, serum MDZ concentrations in DNZ-treated rats were markedly higher than those in control rats when administered orally. DNZ treatment increased MDZ oral bioavailability by approximately 2.5-folds.We herein demonstrated that DNZ increased the bioavailability of orally administered MDZ through irreversible inactivation of hepatic and intestinal CYP3A in rats.

Extended steroid profiling in H295R cells provides deeper insight into chemical-induced disturbances of steroidogenesis: Exemplified by prochloraz and anabolic steroids

Human adrenocortical H295R cells have been validated by the OECD Test Guideline 456 to detect chemicals disrupting testosterone and 17β-estradiol (estradiol) biosynthesis. This study evaluated a novel approach to detect disturbances of steroidogenesis in H295R cells, exemplified by prochloraz and five anabolic steroids. Steroid profiles were assessed by an untargeted LC-MS-based method, providing a relative quantification of 57 steroids annotated according to their accurate masses and retention times. Such a panel of steroids included several mineralocorticoids, glucocorticoids, progestins and adrenal androgens. The coverage of a high number of metabolites in this extended steroid profiling facilitated grouping of chemicals with similar effects and detecting subtler differences between chemicals. It allowed, for example, distinguishing between the effects of turinabol and oxymetholone, supposed to act similarly in a previous characterization including only nine adrenal steroids. Furthermore, the results revealed that product/substrate ratios can provide superior information on altered enzyme activities compared to individual metabolite levels. For example, the 17α-hydroxypregnenolone/pregnenolone ratio was found to be a more sensitive marker for detecting 17α-hydroxylase inhibition by prochloraz than the corresponding individual steroids. These results illustrate that chemical grouping and calculation of product/substrate ratios can provide valuable information on mode-of-action and help prioritizing further experimental work.

New technologies and screening strategies for hepatotoxicity: use of in vitro models

Hepatotoxicity remains a significant cause for drug failures during clinical trials. This is due, in part, to the idiosyncratic nature of toxicity in humans and inherent physiological differences between humans and preclinical species leading to limited correct prediction of adverse responses in humans. To address this issue, robust screening assays are being developed, which have heightened predictive capacity for human hepatotoxicity, and may be utilized throughout the discovery and development phases in conjunction with traditional in vivo methods, for decision making during drug selection and risk assessment. This manuscript describes an example application of in vitro-based strategies using human hepatocyte cultures in lead optimization screening in conjunction with ADME profiling, for evaluation of compound-associated CYP450 induction potential, and the identification of potentially useful biomarkers as predictors of hepatotoxicity for use in vitro, and in preclinical species and humans.

[3H]dexamethasone binding activity in liver microsomes is modulated differently by 17 alpha-alkylated androgens and testosterone in vivo

Rat liver microsomes contain a single class of steroid binding sites, capable of binding various glucocorticoids and progesterone. In a previous article, we have described the in vitro interaction of several androgens with this binding site. Unlike natural androgens, the 17 alpha-alkyl derivatives stanozolol and danazol were capable of interacting with this binding site through a negative allosteric pattern. Now, the effects these steroids exert on the microsomal [3H]dexamethasone binding site have been studied in vivo. The administration of a single dose of stanozolol to rats provoked a significant reduction in the microsomal [3H]dexamethasone binding capacity. This effect was maximal two hr after stanozolol administration and persisted for six hr. The restoration of the [3H]dexamethasone binding level after stanozolol administration was dependent on protein synthesis, since it was blocked by the concomitant administration of cycloheximide. None of the other androgens tested (danazol, methyltestosterone, fluoxymesterone, and testosterone propionate) was capable of provoking a similar effect when administered 2 or 24 hr prior to sacrifice. In rats treated for seven days with a daily dose of diverse androgens and sacrificed 24 hr after the last treatment, none of the 17 alpha-alkyl androgens assayed provoked significant changes in the microsomal [3H]dexamethasone binding level, although stanozolol, danazol, and methyltestosterone provoked a significant increase in glucocorticoid receptor concentration. In contrast, the administration of testosterone propionate provoked a 50% reduction in the [3H]dexamethasone binding level without causing changes in the glucocorticoid receptor concentration. These results provide new evidence on the existence of different effects on the liver of 17 alpha-alkyl androgens, compared to the effects produced by natural androgens.

Serum bile acid concentrations as an indicator of liver dysfunction induced during danazol therapy

The effects of danazol therapy (600 mg/day) on the liver function of 16 women with endometriosis were investigated. The primary bile acids (cholic acid [CA] and chenodeoxycholic acid [CDCA]) were analyzed with radioimmunoassays in the fasting state and after a test meal. Also, the conventional liver function tests were performed. Ultrasonography was used to detect any possible changes in the gallbladder function. The fasting concentrations of CA increased (P less than 0.05) during therapy, while those of CDCA did not change. The ratio of CA/CDCA also increased (P less than 0.001). The maximal response of CA after the test meal increased (P less than 0.01) during the trial. As regards the other liver function tests, only the transaminases significantly increased (P less than 0.01) after 1 month of therapy but showed a tendency to decrease later during the trial. The gallbladder's volume and function did not change. All the parameters studied normalized within 1 month of cessation of danazol therapy. Danazol seems to have a rather mild effect on liver function. The analyzed parameters indicate transient cell wall injury and slight disturbances in liver cell uptake and secretion mechanism and also of synthesis activity.

Danazol inhibits steroidogenesis by the human ovary in vivo

Gonadotropins, estradiol (E2), and the steroid precursors of ovarian estrogen secretion were examined in women on danazol to clarify actions of the medication on hypothalamic-pituitary-ovarian function. Follicle-stimulating hormone was not altered acutely after a single maximal dose or chronically during therapy, whereas a slight but significant increase in luteinizing hormone was noted during the 6 months of treatment. During danazol treatment, there was a blunted response of E2 to injections of human menopausal gonadotropins. The progestin and androgen precursors of E2 were reduced, with the exception of 17-hydroxypregnenolone, which was significantly increased. This 17-hydroxylase enzyme block persisted in spite of dexamethasone suppression of adrenal function. Therefore, the reduced ovarian secretion of E2 in women receiving danazol is due in part to reductions of ovarian precursor steroids for E2 synthesis, consequent to a direct ovarian action of the medication.

Steroid interactions with cytochrome P-450 from testis microsomes

The cytochrome P-450 of gonadal microsomes is an integral component of the steroid converting enzymes, 17 alpha-hydroxylase and 17,20-lyase. Interaction of the steroid substrates with this cytochrome results in a shift in the Soret band as measured by difference spectroscopy. In these studies it is shown that in contrast to placental microsomal cytochrome P-450 which binds C19 steroids, testis microsomal cytochrome P-450 primarily binds C21 steroids. However, addition of a 17 alpha- methyl, 17 beta-acetate or a 17 beta-benzoate group to testosterone permits interaction. The addition of hydroxyl or methyl groups to other positions does not affect binding. The presence of multiple oxygen functions on C21 steroids, as in cortisol and corticosterone, precludes interaction. At least one oxygen function seems necessary for binding as 5 alpha- and 5 beta-pregnane do not bind whereas 20-deoxypregnenolone (5-pregnen-3 beta-ol) does bind. These findings indicate that factors in addition to hydrophobic interactions dictate the binding of steroid substrates to testis microsomal cytochrome P-450.