Allabi Aurel C, Gala Jean-Luc, Horsmans Yves
Centre d' Investigations Cliniques et de Recherches Thérapeutiques, Covè, Republic of Benin.
Pharmacogenet Genomics. 2005 Nov;15(11):779-86. doi: 10.1097/01.fpc.0000174787.92861.91.
The genetically polymorphic cytochrome P450 2C9 (CYP2C9) metabolizes many important drugs. Among them, phenytoin has been used as a probe to determine CYP2C9 phenotype by measuring the urinary excretion of its major metabolite, S-enantiomer of 5-(4-hydroxyphenyl)-5-phenylhydantoin (p-HPPH). Phenytoin pharmacokinetic is also dependent on the activity of CYP2C19 and p-glycoprotein (ABCB1). To determine the influence of CYP2C9, CYP2C19 and ABCB1 genetic polymorphisms on phenytoin metabolism in a Black population, 109 healthy Beninese subjects received a single 300 mg oral dose of phenytoin. Blood was drawn 4 h after drug intake and urine was collected during the first 8 h. Plasma phenytoin and urine S- and R-enantiomers of p-HPPH were determined by high-performance liquid chromatography. Urinary excretion of (S)-p-HPPH [defined as urinary volumex(S)-p-HPPH urinary concentration] and PMR (defined as the ratio of p-HPPH in urine to 4 h phenytoin plasma concentration), both markers of CYP2C9 activity, were used to determine the functional relevance of new variants of CYP2C9 (*5, *6, *8, *9 and 11) in this population. Plasma phenytoin concentration was significantly associated with ABCB1 haplotype/genotype (P=0.05, Kruskal-Wallis test) and levels increased significantly in the genotype order: wild-type, T3421A and Block-2 genotypes (P=0.015, Jonckheere-Terpstra test). Urinary excretion of (S)-p-HPPH and PMR were significantly associated with the CYP2C9 genotype (P=0.001, analysis of variance (ANOVA) and P<0.0001, Kruskal-Wallis test, respectively) and decreased in the order: CYP2C91/1, CYP2C91/9, CYP2C99/9, CYP2C91/8, CYP2C98/9, CYP2C99/11, CYP2C91/5, CYP2C96/9, CYP2C91/6, CYP2C98/11, CYP2C95/8 and CYP2C95/6 (P<0.001, Jonckheere-Terpstra test). A combined analysis of CYP2C9, 2C19 and ABCB1 revealed that only ABCB1 predicted phenytoin concentration at 4 h and explained 8% of the variability (r=0.08, P=0.04). On the other hand, only CYP2C9 was predictive for the urinary excretion of (S)-p-HPPH and PMR (r=0.21, P=0.001 and r=0.25, P<0.001, respectively). Furthermore, significant relation was found between urinary excretion of (R)-p-HPPH and CYP2C9 genotype (P=0.035) and levels significantly increased in the genotype order: CYP2C91/9, CYP2C91/1, CYP2C99/11, CYP2C91/8 and CYP2C91/5 (P<0.001, Jonckheere-Terpstra test). In summary, the present study demonstrates that, in a Black population, CYP2C95, *6, *8 and 11 variants, but not CYP2C99, are associated with a decreased phenytoin metabolism. The data also confirm the limited contribution of MDR1 gene to inter-individual phenytoin pharmacokinetic variation.
基因多态性细胞色素P450 2C9（CYP2C9）可代谢多种重要药物。其中，苯妥英已被用作一种探针，通过测量其主要代谢产物5 -（4 - 羟基苯基）- 5 - 苯基乙内酰脲（p - HPPH）的S - 对映体的尿排泄量来确定CYP2C9表型。苯妥英的药代动力学也取决于CYP2C19和P - 糖蛋白（ABCB1）的活性。为了确定CYP2C9、CYP2C19和ABCB1基因多态性对黑人人群中苯妥英代谢的影响，109名健康的贝宁受试者口服了300 mg单次剂量的苯妥英。服药4小时后采集血液，并在最初8小时内收集尿液。通过高效液相色谱法测定血浆中的苯妥英以及尿液中p - HPPH的S - 和R - 对映体。（S）- p - HPPH的尿排泄量[定义为尿量×（S）- p - HPPH尿浓度]和PMR（定义为尿中p - HPPH与4小时苯妥英血浆浓度的比值），这两个CYP2C9活性的标志物，被用于确定该人群中CYP2C9新变体（5、6、8、9和11）的功能相关性。血浆苯妥英浓度与ABCB1单倍型/基因型显著相关（P = 0.05，Kruskal - Wallis检验），并且在基因型顺序中显著升高：野生型、T3421A和Block - Ⅱ基因型（P = 0.015，Jonckheere - Terpstra检验）。（S）- p - HPPH的尿排泄量和PMR与CYP2C9基因型显著相关（分别为P = 0.001，方差分析（ANOVA）和P < 0.0001，Kruskal - Wallis检验），并且按以下顺序降低：CYP2C91/1、CYP2C91/9、CYP2C99/9、CYP2C91/8、CYP2C98/9、CYP2C99/11、CYP2C91/5、CYP2C96/9、CYP2C91/6、CYP2C98/11、CYP2C95/8和CYP2C95/6（P < 0.001，Jonckheere - Terpstra检验）。对CYP2C9、2C19和ABCB1的联合分析表明，只有ABCB1可预测4小时时的苯妥英浓度，并解释了8%的变异性（r = 0.08，P = 0.04）。另一方面，只有CYP2C9可预测（S）- p - HPPH的尿排泄量和PMR（分别为r = 0.21，P = 0.001和r = 0.25，P < 0.001）。此外，发现（R）- p - HPPH的尿排泄量与CYP2C9基因型之间存在显著关系（P = 0.035），并且在基因型顺序中水平显著升高：CYP2C91/9、CYP2C91/1、CYP2C99/11、CYP2C91/8和CYP2C91/（P < 0.001，Jonckheere - Terpstra检验）。总之，本研究表明，在黑人人群中，CYP2C95、6、8和11变体，而非CYP2C99，与苯妥英代谢降低相关。数据还证实了MDR1基因对个体间苯妥英药代动力学变异的贡献有限。
