标题：Mechanism of Action of Panaxytriol on Midazolam 1′-Hydroxylation and 4-Hydroxylation Mediated by CYP3A in Liver Microsomes and Rat Primary Hepatocytes
摘要：In our previous study, panaxytriol (PXT) was shown to enhance midazolam (MDZ) 1′-hydroxylation significantly but to inhibit MDZ 4-hydroxylation. To explore the underlying mechanism, we investigated the effects of PXT on cytochrome P450 3A (CYP3A)-mediated MDZ metabolic pathways using rat liver microsomes (RLM), human liver microsomes (HLM), and rat primary hepatocytes. In the presence of PXT, the V max of 4-OH MDZ decreased from 0.72 to 0.51 nmol/min·mg pro in RLM and from 0.32 to 0.12 nmol/min·mg pro in HLM, and the K m value increased from 5.12 to 7.26 µM in RLM and from 27.87 to 32.80 µM in HLM. But the presence of PXT reduced the K m and increased the V max values of MDZ 1′-hydroxylation in RLM and HLM. Interestingly, the differential effect of PXT on MDZ 4-hydroxylation and 1′-hydroxylation was also observed in primary rat hepatocytes after 45-min culture. PXT did not affect the expression levels of CYP3A1/2 mRNA in rat hepatocytes. With extension of the culture time to 6 h, however, PXT significantly inhibited both MDZ 4-hydroxylation and 1′-hydroxylation, and the expression level of CYP3A1/2 mRNA was decreased to 87% and 80% (CYP3A1) and to 89% and 85% (CYP3A2) of those in controls in the presence of PXT 4.0 and 8.0 µg/mL, respectively. These results suggest that PXT could activate MDZ 1′-hydroxylation but inhibit MDZ 4-hydroxylation by changing the CYP3A enzyme affinity and metabolic rate after a short-term intervention. However, long-term treatment with PXT could inhibit both the 4-hydroxylation and 1′-hydroxylation of MDZ by downregulating CYP3A1/2 mRNA expression.
