Impairment of CYP3A4 capacity in patients receiving danazol therapy: examination on oxidative cortisol metabolism

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.

Evaluation of 6β-hydroxycortisol, 6β-hydroxycortisone, and a combination of the two as endogenous probes for inhibition of CYP3A4 in vivo

An endogenous probe for CYP3A activity would be useful for early identification of in vivo cytochrome P450 (CYP) 3A4 inhibitors. The aim of this study was to determine whether formation clearance (CL(f)) of the sum of 6β-hydroxycortisol and 6β-hydroxycortisone is a useful probe of CYP3A4 inhibition in vivo. In human liver microsomes (HLMs), the formation of 6β-hydroxycortisol and 6β-hydroxycortisone was catalyzed by CYP3A4, and itraconazole inhibited these reactions with half maximal inhibitory concentration (IC(50))(,u) values of 3.1 nmol/l and 3.4 nmol/l, respectively. The in vivo IC(50,u) value of itraconazole for the combined CL(f) of 6β-hydroxycortisone and 6β-hydroxycortisol was 1.6 nmol/l. The greater inhibitory potency in vivo is probably due to circulating inhibitory itraconazole metabolites. The maximum in vivo inhibition was 59%, suggesting that f(m,CYP3A4) for cortisol and cortisone 6β-hydroxylation is ~60%. Given the significant decrease in CL(f) of 6β-hydroxycortisone and 6β-hydroxycortisol after 200-mg and 400-mg single doses of itraconazole, this endogenous probe can be used to detect moderate and potent CYP3A4 inhibition in vivo.

Note in statistical treatment of medical and pharmaceutical data

This study highlights the essential concept in the statistical treatment of medical and pharmaceutical data. To explain the concept, artificial data generated using random numbers was analyzed, and the importance of the confidence interval and distribution of data was shown. Sole use of the standard deviation (SD) is not considered appropriate from the viewpoint of clinical treatment, because many oversights occur. It was shown by considering the confidence interval that such oversights rarely occur, and the safety level is increased. Moreover, the probability of the occurrence of outliers from the average can be calculated by the distribution of data. Thus, pharmacokinetic data for humans were examined. The results for the human data also support the importance of the confidence interval and the distribution of differences between groups.

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.

Effects of growth hormone deficiency and rhGH replacement therapy on the 6beta-hydroxycortisol/free cortisol ratio, a marker of CYP3A activity, in growth hormone-deficient children

OBJECTIVE

To determine the effect of both growth hormone deficiency (GHD) and rhGH replacement therapy on CYP3A activity as well as the potential influence of gender.

METHODS

The sample consisted of 35 GHD children (16 males and 19 females), aged 2.9-13.1 years, and a control group of 35 healthy children matched for age and sex. The urinary ratio 6beta-hydroxycortisol/free cortisol was used as a marker of CYP3A activity. In patients, urine samples were collected at two times, prior to starting rhGH replacement treatment and 30 days after beginning therapy.

RESULTS

A significantly higher metabolic activity in GHD children was observed in relation to controls ( P=0.0001) without sex differences. Paired comparisons demonstrated a sexually dimorphic effect of rhGH therapy on the CYP3A activity. While boys displayed a significant decrease ( P=0.003), girls showed no significantly different values of CYP3A marker ( P>0.05). Unpaired comparison between controls and GHD children after therapy demonstrated absence of significant differences in boys ( P>0.05) and a strikingly higher activity in girls ( P=0.0001).

CONCLUSIONS

The data suggests that: (a) GHD in children increases CYP3A activity in a non-sex-dependent manner, (b) rhGH treatment for 30 days to GHD children results in a sexually dimorphic effect on CYP3A activity, with a significant decrease in males toward normalization in relation to controls and non-significant changes in females. The results of this study may have important clinical implications for GHD children, since changes in CYP3A activity importantly affect the metabolism of both steroid hormones and CYP3A substrate drugs.