Lamba Jatinder, Strom Stephen, Venkataramanan Raman, Thummel Kenneth E, Lin Yvonne S, Liu Wei, Cheng Cheng, Lamba Vishal, Watkins Paul B, Schuetz Erin
Department of Pharmaceutical Sciences, St Jude Children's Research Hospital, Memphis, TN 38105, USA.
Clin Pharmacol Ther. 2006 Apr;79(4):325-38. doi: 10.1016/j.clpt.2005.11.013. Epub 2006 Feb 20.
Variant cytochrome P450 (CYP) 3A4 alleles cannot explain human variation in CYP3A4 expression. This study investigated whether common single-nucleotide polymorphisms (SNPs) in multidrug resistance 1 (MDR1), encoding P-glycoprotein, or the pregnane X receptor (PXR) were associated with basal or inducible CYP3A4 expression.
MDR1 G2677T and C3435T SNPs and a PXR 6-base pair (bp) deletion were genotyped in the deoxyribonucleic acid from 144 human livers in 3 cohorts each phenotyped for basal or rifampin (INN, rifampicin)-inducible hepatic CYP3A4 expression (or both) and in 57 human small bowel biopsy specimens from 3 cohorts each phenotyped for either basal or rifampin-induced CYP3A4 expression (or both).
Hepatic CYP3A4 expression/function was significantly higher in persons homozygous for the MDR1 2677T (Ser893) allele compared with persons homozygous for 2677G (Ala893) in all 3 hepatic cohorts. For example, homozygous MDR1 2677 TT livers had higher midazolam hydroxylase activity than homozygous 2677 GG livers (1831 +/- 1336 pmol x min(-1) x mg protein(-1) versus 1060 +/- 552 pmol x min(-1) x mg protein(-1), P = .03). In 2 of the 3 groups the association was observed in men but not in women. For example, homozygous MDR1 2677 TT male hepatocytes had significantly higher testosterone 6beta-hydroxylase activity compared with homozygous 2677 GG livers (0.120 +/- 0.06 pmol x min(-1) x mg protein(-1) versus 0.069 +/- 0.04 pmol x min(-1) x mg protein(-1), P = .0002). Conversely, rifampin induction of testosterone 6beta-hydroxylation in primary human hepatocytes was significantly higher in persons homozygous for 2677G (12.0 +/- 5.7-fold) compared with MDR1 homozygous TT carriers (7.3 +/- 4.6-fold) (P = .01). Suggestive evidence for higher CYP3A4 expression in MDR1 2677T carriers was also observed in human intestines. CYP3A4 expression was also related to a 6-bp deletion in PXR in 2 of the liver cohorts. Two-factor ANOVA analysis revealed a significant interaction between the MDR1 2677 SNP and the PXR 6-bp deletion influencing CYP3A4 expression (P = .007).
Individuals homozygous for the MDR1 2677T allele show enhanced constitutive CYP3A4 expression in the liver and intestine, as compared with those homozygous for the MDR1 2677G allele, particularly in men. Conversely, the magnitude of CYP3A4 induction by rifampin is greater in persons with the MDR1 2677G allele and is inversely related to baseline CYP3A4 expression. MDR1 likely influences basal CYP3A4 expression by limiting the intracellular concentration of an endogenous regulator. MDR1 genotype may be a useful predictor of basal CYP3A4 and the extent of some CYP3A4-mediated drug interactions in humans. Moreover, the influence of MDR1 genotype on CYP3A4 expression adds additional complexity to determining the relative contribution of the MDR1 alleles to the disposition of substrates shared by CYP3A4 and MDR1/P-glycoprotein.
细胞色素P450（CYP）3A4变异等位基因无法解释人类CYP3A4表达的个体差异。本研究调查了编码P-糖蛋白的多药耐药性1（MDR1）或孕烷X受体（PXR）中的常见单核苷酸多态性（SNP）是否与基础或诱导型CYP3A4表达相关。
对来自3个队列的144例人类肝脏的脱氧核糖核酸进行MDR1 G2677T和C3435T SNP以及PXR 6碱基对（bp）缺失的基因分型，每个队列均针对基础或利福平（国际非专利药品名称，利福平）诱导的肝脏CYP3A4表达（或两者）进行表型分析；并对来自3个队列的57例人类小肠活检标本进行基因分型，每个队列均针对基础或利福平诱导的CYP3A4表达（或两者）进行表型分析。
在所有3个肝脏队列中，与MDR1 2677G（Ala893）纯合子相比，MDR1 2677T（Ser893）等位基因纯合子的肝脏CYP3A4表达/功能显著更高。例如，MDR1 2677 TT纯合子肝脏的咪达唑仑羟化酶活性高于2677 GG纯合子肝脏（1831±1336 pmol·min⁻¹·mg蛋白⁻¹对1060±552 pmol·min⁻¹·mg蛋白⁻¹，P = 0.03）。在3组中的2组中，该关联在男性中观察到，但在女性中未观察到。例如，MDR1 2677 TT纯合子男性肝细胞的睾酮6β-羟化酶活性显著高于2677 GG纯合子肝脏（0.120±0.06 pmol·min⁻¹·mg蛋白⁻¹对0.069±0.04 pmol·min⁻¹·mg蛋白⁻¹，P = 0.0002）。相反，在原代人肝细胞中，利福平诱导的睾酮6β-羟化在2677G纯合子个体中显著更高（12.0±5.7倍），而MDR1 TT纯合子携带者为（7.3±4.6倍）（P = 0.01）。在人类肠道中也观察到MDR1 2677T携带者中CYP3A4表达较高的提示性证据。在2个肝脏队列中，CYP3A4表达也与PXR中的6-bp缺失有关。双因素方差分析显示，MDR1 2677 SNP与PXR 6-bp缺失之间存在显著的相互作用，影响CYP3A4表达（P = 0.007）。
与MDR1 2677G等位基因纯合子相比，MDR1 2677T等位基因纯合子个体在肝脏和肠道中显示出增强的组成型CYP3A4表达，尤其是在男性中。相反，利福平诱导的CYP3A4在MDR1 2677G等位基因个体中幅度更大，且与基线CYP3A4表达呈负相关。MDR1可能通过限制内源性调节因子的细胞内浓度来影响基础CYP3A4表达。MDR1基因型可能是人类基础CYP3A4以及某些CYP3A4介导的药物相互作用程度的有用预测指标。此外，MDR1基因型对CYP3A4表达的影响增加了确定MDR1等位基因对CYP3A4和MDR1/P-糖蛋白共享底物处置的相对贡献的复杂性。
