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.

Relationship between intracellular protein denaturation and irreversible inactivation of Saccharomyces pastorianus by low-pressure carbon dioxide microbubbles

To clarify the relationship between irreversible inactivation and intracellular protein denaturation of Saccharomyces pastorianus by low-pressure carbon dioxide microbubbles (CO₂ MB) treatment, a storage test of S. pastorianus cells treated with CO₂ MB was performed, and the effect on the intracellular protein was investigated. In the storage test, the S. pastorianus population, which decreased below the detection limit by CO₂ MB treatment at a temperature of 45 and 50°C (MB45 and MB50), and thermal treatment at a temperature of 80°C (T80), remained undetectable during storage for 3 weeks at 25°C. However, 4.1- and 1.3-logs of the S. pastorianus populations, which survived after CO₂ MB treatment at temperatures of 35 and 40°C (MB35 and MB40), increased gradually during storage for 3 weeks at 25°C. Insolubilization of intracellular proteins in S. pastorianus increased with increasing the temperature of CO₂ MB treatment. Activity of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) identified as one of the insolubilized proteins increased at MB35 and MB40 than non-treatment but disappeared at MB45 and MB50, and T80. Therefore, it was revealed that S. pastorianus cells inactivated below the detection level by CO₂ MB treatment did not regrow and that the denaturation of intracellular proteins of S. pastorianus was caused by CO₂ MB and thermal treatments. Furthermore, it was suggested that denaturation of intracellular vital enzymes was an important factor for achieving irreversible inactivation of S. pastorianus by CO₂ MB and thermal treatments.

Inactivation mechanism of the membrane protein diacylglycerol kinase in detergent solution

We have examined the irreversible inactivation mechanism of the membrane protein diacylglycerol kinase in the detergents n-octyl-beta-D-glucopyranoside (OG) at 55 degrees C and n-decyl-maltopyranoside (DM) at 80 degrees C. Under no inactivation conditions did we find any direct evidence for the chemical modifications that are commonly found in soluble proteins. Moreover, protein inactivated at 55 degrees C in OG could be reactivated by an unfolding and refolding protocol, suggesting that the protein is inactivated by a stable conformational change, not a covalent modification. We also found that the inactivation rate decreased with both increasing protein concentration and increasing thermodynamic stability, consistent with an inactivation pathway involving transient dissociation and/or unfolding of the protein. Our results suggest that the primary cause of diacylglycerol kinase inactivation is not low solubility, but poor intrinsic stability in the detergent environment.