In vitro metabolism of a new neuroprotective agent, KR-31543 in the human liver microsomes: identification of human cytochrome P450.

KR-31543, (2S,3R,4S)-6-amino-4-[N-(4-chlorophenyl)-N-(2-methyl-2H-tetrazol-5-ylmethyl)amino]-3,4-dihydro-2-dimethoxymethyl-3-hydroxy-2-methyl-2H-1-benzopyran, is a new neuroprotective agent for preventing ischemia-reperfusion damage. This study was performed to identify the metabolic pathway of KR-31543 in human liver microsomes and to characterize cytochrome P450 (CYP) enzymes that are involved in the metabolism of KR-31543. Human liver microsomal incubation of KR-31543 in the presence of NADPH resulted in the formation of two metabolites, M1 and M2. M1 was identified as N-(4-chlorophenyl)-N-(2-methyl-2H-tetrazol-5-ylmethyl)amine on the basis of LC/MS/MS analysis with a synthesized authentic standard, and M2 was suggested to be hydroxy-KR-31543. Correlation analysis between the known CYP enzyme activities and the rates of the formation of M1 and M2 in the 12 human liver microsomes have showed significant correlations with testosterone 6beta-hydroxylase activity (a marker of CYP3A4). Ketoconazole, a selective inhibitor of CYP3A4, and anti-CYP3A4 monoclonal antibodies potently inhibited both N-hydrolysis and hydroxylation of KR-31543 in human liver microsomes. These results provide evidence that CYP3A4 is the major isozyme responsible for the metabolism of KR-31543 to M1 and M2.

Pharmacokinetic and pharmacodynamic characterization of gliclazide in healthy volunteers.

Pharmacokinetic and pharmacodynamic properties of gliclazide were studied after an oral administration of gliclazide tablets in healthy volunteers. After an overnight fasting, gliclazide tablet was orally administered to 11 volunteers. Additional 10 volunteers were used as a control group (i.e., no gliclazide administration). Blood samples were collected, and the concentration determined for gliclazide and glucose up to 24 after the administration. Standard pharmacokinetic analysis was carried out for gliclazide. Pharmacodynamic activity of the drug was expressed by increase of glucose concentration (deltaPG), by area under the increase of glucose concentration-time curve (AUC(deltaPG)) or by the difference in increase of glucose concentration (D(deltaPG)) at each time between groups with and without gliclazide administration. Pharmacokinetic analysis revealed that Cmax, Tmax, CL/F (apparent clearance), V/F (apparent volume of distribution) and half-life of gliclazide were 4.69+/-1.38 mg/L, 3.45+/-1.11 h, 1.26+/-0.35 L/h, 17.78+/-5.27 L, and 9.99+/-2.15 h, respectively. When compared with the no drug administration group, gliclazide decreased significantly the AUC(deltaPG) s at 1, 1.5, 2, 2.5, 3 and 4 h (p<0.05). The deltaPGs were positively correlated with AUC(gliclazide) at 1 and 1.5 h (p<0.05), and the correlation coefficient was maximum at 1 h (r = 0.642) and gradually decreased at 4 h after the administration. The AUC(deltaPG)s were positively correlated with AUC(gliclazide) at 1, 2, 3 and 4 h (p<0.05), and the maximum correlation coefficient was obtained at 2 h (r=0.642) after the administration. The D(deltaPG) reached the maximum at 1 h, remained constant from 1 h to 3 h, and decreased afterwards. Therefore, these observations indicated that maximum hypoglycemic effect of gliclazide was reached at approximately at 1.5 h after the administration and the effect decreased, probably because of the homeostasis mechanism, in health volunteers.