ABSTRACT:The breast cancer resistance protein (BCRP) is a member of the ATP-binding cassette transporters. The aim of the present study was to identify genetic variants of BCRP in Koreans and to assess the functional consequences of BCRP polymorphisms. Twenty single nucleotide polymorphisms (SNP), including four nonsynonymous SNP, were identified by DNA sequencing of the BCRP gene in 92 Korean subjects. BCRP V12M, Q141K, P269S, and Q126Stop were detected at frequencies of 23, 28, 0.2, and 1.9%, respectively. These four coding variants were also screened in Chinese and Vietnamese subjects; the allelic frequencies among the three populations were compared; and predictions were made as to the potential frequency of each variant.

CYP2J2 plays important roles in the metabolism of therapeutic drugs, such as astemizole and ebastine, as well as endogenous fatty acids. This study aimed to identify CYP2J2 genetic variants in Koreans and to characterize their functional consequences. From direct sequencing of the CYP2J2 gene, 12 genetic variations, including the two novel nonsynonymous mutations G312R and P351L, were identified from 93 Korean subjects. The two novel CYP2J2 variants were co-expressed with NADPH-cytochrome P450 reductase in Sf9 cells and their catalytic activities were quantified. The recombinant CYP2J2 G312R variant showed almost complete loss of enzymatic activity, as determined by CYP2J2-catalysed astemizole O-demethylation and ebastine hydroxylation. The CYP2J2 P351L variant showed enzymatic activities that were comparable with the wild-type CYP2J2. The reduced CO spectra of the recombinant CYP2J2 proteins suggested no CO binding to the heme in CYP2J2 G312R. In addition, molecular modelling of the three-dimensional structure consistently predicted that there might be spatial hindrance between heme and the bulky side chain of the R312 residue in CYP2J2 G312R variant. The CYP2J2 G312R variant was not found in 192 Chinese, 99 African-Americans, 100 Caucasians and 159 Vietnamese subjects. Two of the 192 Chinese subjects (0.52%) were heterozygous for CYP2J2 P351L. Twelve CYP2J2 variants, including two novel nonsynonymous variants, were identified in a Korean population. The G312R variant is the first nonfunctional CYP2J2 allele to be identified, and is expected to influence the disposition of its substrate therapeutics, as well as endogenous compounds.

ABSTRACT:The objective of this study was to identify CYP3A4 variants in Koreans and to characterize their functional consequences in vitro and in vivo. Four single nucleotide polymorphisms were identified in 50 Koreans by direct DNA sequencing. In an additional genotyping using 248 subjects, CYP3A4*18 was confirmed as the most frequent coding variant in Koreans at 1.7%, and its frequency was similar to that of Asians, suggesting that CYP3A4*18 would be the highest coding variant in Asians. The recombinant CYP3A4.18 protein prepared in baculovirus expression system showed 67.4% lower V max and 1.8-fold higher K m for midazolam 1-hydroxylation compared with the wild type. The mean values of C max and area under the concentration curve (AUC) in the CYP3A4*1/*18 and CYP3A5*1/*3 subjects (n ‫؍‬ 8) were 63% and 32% higher than in CYP3A4*1/*1 and CYP3A5*1/*3 carriers (n ‫؍‬ 8), respectively. Although the in vitro assay exhibited a significant reduction of the enzyme activity for midazolam, the in vivo differences associated with the CYP3A4*1/*18 tend to be low (P < 0.07 in C max and P < 0.09 in AUC). In summary, the heterozygous CYP3A4*1/*18 does not appear to cause a significant change of midazolam disposition in vivo; however, the clinical relevance of CYP3A4*18/*18 remains to be evaluated.CYP3A is the most abundantly expressed subfamily of cytochrome P450 (P450) enzymes in the human liver (Shimada et al., 1994). The CYP3A enzymes are responsible for the metabolism of more than 50% of clinically used drugs (Komori et al., 1990;Guengerich, 1999;Lamba et al., 2002a). Four human CYP3A enzymes, CYP3A4, CYP3A5, CYP3A7, and CYP3A43, have been identified. CYP3A4 is regarded as the most dominant CYP3A enzyme in the liver and small intestine of humans. It has been reported that CYP3A4 expression shows large interindividual variation (Guengerich, 1999;Ozdemir et al., 2000;Lin et al., 2002). These variations can lead to different responses to human drugs that are substrates for CYP3A4. Because approximately 85% of this variability is attributed to genetic factors (Ozdemir et al., 2000), genetic analysis is needed to understand interindividual variability. To date, more than 39 allelic variants have been described (http://www.cypalleles.ki.se/cyp3a4.htm) (Dai et al., 2001;Eiselt et al., 2001;Kuehl et al., 2001;Lamba et al., 2002a;Fukushima-Uesaka et al., 2004). Among the CYP3A4 variants, alleles with nonsynonymous single nucleotide polymorphisms (SNPs), i.e., CYP3A4*2, *4, *5, *6, *17, and *18, have been shown to alter enzyme activity, compared with the wild type (Lee and Goldstein, 2005). Although some CYP3A SNPs exhibited an altered intrinsic clearance of CYP3A substrates in vitro, there have been few data explaining their meaningful influences on its substrate clearance in humans. The CYP3A4*1B promoter SNP has been extensively studied because of its role in transcriptional regulation in vitro. However, no significant change associated with CYP3A4*1B was observed in midazolam (MDZ) clearance (Wandel et al., 2000;Garcia-Martin...

It is well known that the CYP2C19 genetic polymorphism influences the pharmacokinetics and pharmacodynamics of proton pump inhibitors (PPIs), but no report has addressed the effects on ilaprazole, a newly developed PPI. To investigate the effects of the CYP2C19 genetic polymorphism on the disposition and pharmacodynamics of ilaprazole, multiple doses of once-daily 10 mg ilaprazole were repeatedly administered for 7 days to 27 healthy Korean participants, comprising 9 homozygous CYP2C19 extensive metabolizers (homo EMs), 10 heterozygous EMs (hetero EMs), and 8 homozygous poor metabolizers (PMs). The plasma concentration and pharmacodynamic response were measured in the last dose interval. Each genotype group was matched for gender and thus was composed of 4 male and 4 female participants when the analysis was conducted. The pharmacokinetic parameters estimated from the plasma concentrations of ilaprazole and its metabolite ilaprazole sulfone, the serum gastrin level, and the 24-hour intragastric pH were compared among the CYP2C19 genotype groups. No statistically significant differences in the maximum plasma concentration at steady state(C(ss,max)) and the area under the concentration-time curve from zero to 24 hours (AUC(τ)) of ilaprazole and ilaprazole sulfone were observed among the homo EM, hetero EM, and PM CYP2C19 genotypes. In addition, the mean 24-hour intragastric pH, the percentage of time at pH >4, and the AUC(τ) of serum gastrin showed no significant differences among the CYP2C19 genotype groups. The data suggests that the pharmacokinetics and pharmacodynamics of ilaprazole are not significantly influenced by the CYP2C19 genetic polymorphism in healthy participants.

Glucuronidation by UDP-glucuronosyltransferase 2B7 (UGT2B7) has been identified as an important pathway for the elimination of its substrate drugs in humans. Alterations in UGT2B7 function or expression may influence individual variations in drug responses. In an effort to screen for UGT2B7 single nucleotide polymorphisms (SNPs) in Koreans, the UGT2B7 gene was directly sequenced in 50 normal subjects. A total of 19 genetic variations were found: seven in exons, eight in introns, and four in the 5'-untranslated region. The order of the frequency distribution of UGT2B7 variations was: -900A>G, -327G>A, -161C>T, 10539A>G, 10711G>C and 10806T>A (40%); 2099T>A, 2100C>T, 2283A>G and 2316A>G (39%); 12029T>A (37%); 10928C>A (33%); 10541G>A (28%); 10897insA (24%); 372A>G (13%) and 211G>T (12%), as well as other minor alleles with less than 10% frequency. Nineteen variations were used to characterize linkage disequilibrium (LD) structures at the UGT2B7 locus. Eight tagging SNPs in UGT2B7 were determined. Identification of UGT2B7 SNPs with LD and the tagging SNPs lays the foundation for investigating UGT2B7-related genotype/phenotype association studies for Koreans as well as other populations.