RESUMO
BACKGROUND: Concomitant use of clarithromycin (CAM) and rifampicin (RFP) for the treatment of pulmonary Mycobacterium avium complex (MAC) disease affects the systemic concentrations of both drugs due to CYP3A4-related interactions. To date, however, there has been no report that investigates the long-term relationship between the drug concentrations, CYP3A4 activity, and clinical outcomes. Our aim was to investigate the time course of the drug levels in long-term treatment of subjects with pulmonary MAC disease, and examine the correlation of these concentrations with CYP3A4 activity and clinical outcomes. METHODS: Urine and blood samples from nine outpatients with pulmonary MAC disease were collected on days 1, 15, and 29 (for four subjects, sample collections were continued on days 57, 85, 113, 141, 169, 225, 281, 337, and 365). Serum drug concentrations and urinary levels of endogenous cortisol (F) and 6 beta-hydroxycortisol (6ßOHF), the metabolite of F by CYP3A4, were measured, and evaluated 6ßOHF/F ratio as a CYP3A4 activity marker. In addition, the clinical outcomes of 4 subjects were evaluated based on examination of sputum cultures and chest images. RESULTS: The mean 6ßOHF/F ratio increased from 2.63 ± 0.85 (n = 9) on the first day to 6.96 ± 1.35 on day 15 and maintained a level more than double initial value thereafter. The serum CAM concentration decreased dramatically from an initial 2.28 ± 0.61 µg/mL to 0.73 ± 0.23 µg/mL on day 15. In contrast, the serum concentration of 14-hydroxy-CAM (M-5), the major metabolite of CAM, increased 2.4-fold by day 15. Thereafter, both CAM and M-5 concentrations remained constant until day 365. The explanation for the low levels of serum CAM in pulmonary MAC disease patients is that RFP-mediated CYP3A4 induction reached a maximum by day 15 and remained high thereafter. Sputum cultures of three of four subjects converted to negative, but relapse occurred in all three cases. CONCLUSIONS: Our study demonstrated that serum CAM concentrations in pulmonary MAC disease patients were continuously low because of RFP-mediated CYP3A4 induction, which may be responsible for the unsatisfactory clinical outcomes.
RESUMO
Thermolysin is remarkably activated and stabilized by neutral salts, and surface charges are suggested important in its activity and stability. The effects of introducing negative charge into the molecular surface on its activity and stability are described. Seven serine residues were selected, and each of them was changed for aspartate by site-directed mutagenesis in a thermolysin mutant. In the hydrolysis of N-[3-(2-furyl)acryloyl]-glycyl-l-leucine amide, the k(cat)/K(m) values of all mutants were almost similar to that of the wild-type enzyme (WT). However, those of six out of seven mutants were enhanced 17-19 times with 4 M NaCl, being slightly higher than WT. The remaining casein-hydrolyzing activities of the S53D and S65D mutants (Ser53 and Ser65 are replaced with Asp, respectively) after 30-min incubation with 10 mM CaCl(2) at 85 degrees C were 78 and 63%, being higher than those of WT (51%) and the other mutants (35-53%). S53D was stabilized with increase in the enthalpy change of activation for thermal inactivation while S65D was with decrease in the entropy change of activation. The stability of WT was enhanced by CaCl(2) and reached the level of S53D and S65D at 100 mM, suggesting that S53D and S65D might be stabilized by reinforcement of the Ca(2+)-binding structures.