Desta Zeruesenay, Saussele Tanja, Ward Bryan, Blievernicht Julia, Li Lang, Klein Kathrin, Flockhart David A, Zanger Ulrich M
Division of Clinical Pharmacology, Department of Medicine, Indiana University School of Medicine, 1001 West 10th Street, WD Myers Bldg., W7123, Indianapolis, IN 46202, USA.
Pharmacogenomics. 2007 Jun;8(6):547-58. doi: 10.2217/14622416.8.6.547.
To determine the influence of cytochrome P450 2B6 (CYP2B6) genotype on the rate of oxidative efavirenz metabolism in human liver microsomes.
MATERIALS & METHODS: Formation rates of 8-hydroxyefavirenz, 7-hydroxyefavirenz and 8,14-dihydroxyefavirenz were determined in vitro with efavirenz as a substrate (10 microM) in a large panel of human liver microsomes (n = 87) that were genotyped for variants of the CYP2B6 gene and phenotyped for CYP2B6 protein expression and bupropion hydroxylation.
Efavirenz 8-hydroxylation, the major route of efavirenz clearance, was detected in all samples, exhibiting an overall interindividual variability of 44.7-fold; 8,14-dihydroxyefavirenz and 7-hydroxyefavirenz were also detected in most samples. The formation rate of 8-hydroxyefavirenz correlated significantly with CYP2B6 protein (Spearman's r(S) = 0.54; p < 0.0001) and bupropion hydroxylase activity (r(S) = 0.73; p < 0.0001). Compared with the *1/*1 genotype, efavirenz 8-hydroxylation was significantly lower in samples with *1/*6 and *6/*6 genotype, which also had significantly decreased CYP2B6 protein (Mann-Whitney test, p < 0.05). A decrease in CYP2B6 protein was also observed in samples with *1/*5 and *5/*6 genotypes, but this did not result in significant reduction of efavirenz metabolism, probably due to differences in specific activity of the protein variants. Lower CYP2B6 protein and activity, as well as efavirenz 8-hydroxylation was also found in several samples with rarer genotypes. We found no effect of gender and age on any of the phenotypes tested, but prior exposure to carbamazepine markedly increased CYP2B6 protein expression and activity as well as efavirenz 8-hydroxylation.
We have shown that CYP2B6 genetic polymorphism markedly influences the metabolism of efavirenz in human liver microsomes. Importantly, the CYP2B6*6 allele harboring the SNPs c.516G>T [Q172H] and c.785A>G [K262R] was significantly associated with a pronounced decrease in CYP2B6 expression and activity, as well as a low rate of efavirenz 8-hydroxylation. These results represent a first step towards elucidating the mechanism by which this allele identifies patients exhibiting very high efavirenz plasma concentrations.
确定细胞色素P450 2B6（CYP2B6）基因型对人肝微粒体中依法韦仑氧化代谢速率的影响。
以依法韦仑为底物（10微摩尔），在一大组人肝微粒体（n = 87）中体外测定8-羟基依法韦仑、7-羟基依法韦仑和8,14-二羟基依法韦仑的生成速率，这些肝微粒体针对CYP2B6基因变体进行了基因分型，并针对CYP2B6蛋白表达和安非他酮羟基化进行了表型分析。
在所有样品中均检测到依法韦仑8-羟基化，这是依法韦仑清除的主要途径，个体间总体变异为44.7倍；在大多数样品中也检测到了8,14-二羟基依法韦仑和7-羟基依法韦仑。8-羟基依法韦仑的生成速率与CYP2B6蛋白显著相关（斯皮尔曼r(S)=0.54；p<0.0001）和安非他酮羟化酶活性（r(S)=0.73；p<0.0001）。与*1/*1基因型相比，*1/6和6/6基因型样品中的依法韦仑8-羟基化显著降低，其CYP2B6蛋白也显著减少（曼-惠特尼检验，p<0.05）。在1/5和5/*6基因型样品中也观察到CYP2B6蛋白减少，但这并未导致依法韦仑代谢显著降低，可能是由于蛋白变体的比活性不同。在几种稀有基因型的样品中也发现了较低的CYP2B6蛋白和活性以及依法韦仑8-羟基化。我们发现性别和年龄对所测试的任何表型均无影响，但先前接触卡马西平可显著增加CYP2B6蛋白表达和活性以及依法韦仑8-羟基化。
我们已经表明，CYP2B6基因多态性显著影响人肝微粒体中依法韦仑的代谢。重要的是，携带单核苷酸多态性c.516G>T [Q172H]和c.785A>G [K262R]的CYP2B6*6等位基因与CYP2B6表达和活性的显著降低以及依法韦仑8-羟基化率低显著相关。这些结果代表了阐明该等位基因识别依法韦仑血浆浓度非常高的患者的机制的第一步。
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