Testosterone (TST) and midazolam (MDZ) are widely used as probes to detect CYP3A4/5 activity, but the data acquired with these two substrates do not correlate well at the microsomal level (per milligram of microsomal protein), and the reason is unclear. In this study, CYP3A4/5 activity was probed with TST and MDZ at the microsomal and enzyme levels (per picomole of CYP3A4/5) in 72 human liver samples. Correlation coefficients were lower in V_max and CL_int at the microsomal level, as compared with those at the enzyme level (V_max 0.658 vs 0.883; CL_int no correlation vs 0.796). Compared with TST, MDZ was found to correlate better with the content of CYP3A4/5 (no correlation vs 0.431) and CYP3A5 (no correlation vs 0.447), and huge variations in enzyme content existed among different genotypes, which explained the lower degree of correlation at the microsomal level. In addition, different genotypes had varying effects on activity at the enzyme level, whereas the difference between activity at the enzyme level probed with TST and that probed with MDZ was not obvious (P > 0.05), indicating that the effect of gene polymorphisms on correlation between activity probed with these two substrates was limited at the enzyme level. In conclusion, our study demonstrates a high degree of correlation between CYP3A4/5 activity probed with TST and MDZ at the enzyme level but not at the microsomal level and allows us to correctly understand the influence of gene polymorphisms on the correlations.

中文翻译：

---

CYP3A4 / 5活性与睾丸激素和咪达唑仑探测：在微粒体和酶水平的两个底物之间的相关性。

睾丸激素（TST）和咪达唑仑（MDZ）被广泛用作检测CYP3A4 / 5活性的探针，但用这两种底物获得的数据在微粒体水平（每毫克微粒体蛋白）上没有很好的相关性，原因尚不清楚。在这项研究中，在72个人类肝样品中，在微粒体和酶水平（CYP3A4 / 5的每个picomole）上用TST和MDZ检测了CYP3A4 / 5的活性。与酶水平相比，微粒体水平的V _max和CL _int相关系数较低（V _max为0.658 vs 0.883； CL _int没有相关性vs.0.796）。与TST相比，发现MDZ与CYP3A4 / 5（无相关性，相对于0.431）和CYP3A5（无相关性，相对于0.447）的含量具有更好的相关性，并且不同基因型之间的酶含量存在巨大差异，这说明相关性较低。在微粒体水平上。此外，不同的基因型对酶水平的活性有不同的影响，而用TST探测的酶水平和用MDZ探测的酶水平的活性之间的差异并不明显（P> 0.05），表明基因多态性对这两种底物探测的活性之间相关性的影响在酶水平上受到限制。总之，我们的研究表明，在酶水平而不是微粒体水平，TST和MDZ探测到的CYP3A4 / 5活性之间存在高度相关性，使我们能够正确理解基因多态性对相关性的影响。