Organic anion-transporting polypeptide 1A2 (OATP1A2) is a drug uptake transporter known for broad substrate specificity, including many drugs in clinical use. Therefore, genetic variation in SLCO1A2 may have important implications to the disposition and tissue penetration of substrate drugs. In the present study, we demonstrate OATP1A2 protein expression in human brain capillary and renal distal nephron using immunohistochemistry. We also determined the extent of single nucleotide polymorphisms in SLCO1A2 upon analyses of ethnically defined genomic DNA samples (n = 95 each for African-, Chinese-, European-, and Hispanic-Americans). We identified six nonsynonymous polymorphisms within the coding region of SLCO1A2 (T38C (I13T), A516C (E172D), G559A (A187T), A382T (N128Y), A404T (N135I), and C2003G (T668S)), the allelic frequencies of which appeared to be ethnicity-dependent. In vitro functional assessment revealed that the A516C and A404T variants had markedly reduced capacity for mediating the cellular uptake of OATP1A2 substrates, estrone 3-sulfate and two δ-opioid receptor agonists, deltorphin II, and [d-penicillamine^2,5]-enkephalin. On the other hand, the G559A and C2003G variants appeared to have substrate-dependent changes in transport activity. Cell surface biotinylation and immunofluorescence confocal microscopy suggested that altered plasma membrane expression of the transporter may contribute to reduced transport activity associated with the A516C, A404T, and C2003G variants. The A404T (N135I) variant also showed a shift in the apparent molecular size, indicative of alterations in glycosylation status. Taken together, these data suggest that SLCO1A2 polymorphisms may be an important yet unrecognized contributor to inter-individual variability in drug disposition and central nervous system entry of substrate drugs.

CYP3A activity in adults varies between individuals and it has been suggested that this has a genetic basis, possibly related to variant alleles in CYP3A4 and CYP3A5 genes. Accordingly, genotype-phenotype associations were investigated under constitutive and induced conditions. Midazolam's systemic and oral clearances, and the erythromycin breath test (ERBT) were determined in 57 healthy subjects: 23 (11 men, 12 women) European- and 34 (14 men, 20 women) African-Americans. Studies were undertaken in the basal state and after 14-15 days pretreatment with rifampin. DNA was characterized for the common polymorphisms CYP3A4*1B, CYP3A5*3, CYP3A5*6 and CYP3A5*7 by direct sequencing, and for exon 21 and exon 26 variants of MDR1 by allele-specific, real-time polymerase chain reaction. In 95% of subjects, the basal systemic clearance of midazolam was unimodally distributed and variability was less than four-fold whereas, in 98% of the study population, oral clearance varied five-fold. No population or sex-related differences were apparent. Similar findings were observed with the ERBT. Rifampin pretreatment markedly increased the systemic (two-fold) and oral clearance (16-fold) of midazolam, and the ERBT (two-fold) but the variabilities were unchanged. No associations were noted between these phenotypic measures and any of the studied genotypes, except for oral clearance and its fold-increase after rifampin. These were related to the presence of CYP3A4*1B and the inversely linked CYP3A5*3 polymorphism, with the extent of induction being approximately 50% greater in CYP3A5*3 homozygotes compared to wild-type subjects. In most healthy subjects, variability in intestinal and hepatic CYP3A activity, using midazolam as an in-vivo probe, is modest and common polymorphisms in CYP3A4 and CYP3A5 do not appear to have important functional significance.

This study investigated whether the smokinginducible cytochrome P450 (CYP) 1A2 and the polymorphic CYP2D6 play significant roles in the metabolism of olanzapine and its clinical effects at steady-state treatment. Caffeine and debrisoquine were used as measures of CYP1A2 and CYP2D6, respectively. After drug therapy for 15 days, the effect of olanzapine on the activities of CYP1A2 and CYP2D6 was also examined. Seventeen psychiatric patients (9 men and 8 women) were orally administered olanzapine, at a mean ± standard deviation (SD) dosage of 10 mg/d for all smokers (n = 8) and 7.5 ± 2.5 mg/d (range, 5–10 mg) for nonsmokers (n = 9;p < 0.01). The plasma concentration-to-dose (C:D) ratio was closely correlated to the CYP1A2 activity (r s = −0.89;p < 0.0001). The mean urinary caffeine indexes of nonsmokers and smokers were 17 ± 8 and 101 ± 44, respectively, indicating that smoking had induced a sixfold higher CYP1A2 activity (p < 0.0001). Likewise, the olanzapine plasma C:D ratio (ng·mL·mg) was about fivefold lower in smokers (7.9 ± 2.6) than in nonsmokers (1.56 ± 1.1;p < 0.0001). On day 15 of the antipsychotic therapy, the percentage decrease in Brief Psychiatric Rating Scale (BPRS) total score relative to the predosing score (in the drug-free period) was higher for nonsmokers than for smokers (30.4 ± 10% vs. 12.5 ± 14%;p < 0.01). Six nonsmokers and three smokers experienced side effects with olanzapine. After 15 days of drug treatment, olanzapine had caused significant (p < 0.0001) and substantial CYP1A2 inhibition (by 50%) in comparison with predosing values, and such inhibition can contribute to adverse drug interactions. In conclusion, smoking-induced increased CYP1A2 activity significantly diminished plasma olanzapine concentrations and the antipsychotic effect of the drug. The performance of a simple caffeine test may assist in individualization of the olanzapine dosage.

We retrospectively examined the association of polymorphisms in the CYP3A, CYP2J2, CYP2C8, and ABCB1 genes with pharmacokinetic (PKs) and pharmacodynamic (PDs) parameters of tacrolimus in 103 renal transplant recipients for a period of 1 year. CYP3A5 expressers had lower predose concentrations (C₀)/dose and higher dose requirements than nonexpressers throughout the study. Among CYP3A5*1 carriers, those also carrying the CYP3A4*1B allele showed the lowest C₀/dose, as compared with CYP3A4*1/CYP3A5*3 carriers (54.28 ± 26.45, 59.12 ± 24.00, 62.43 ± 41.12, and 57.01 ± 17.34 vs. 112.37 ± 76.60, 123.21 ± 59.57, 163.34 ± 76.23, and 183.07 ± 107.82 at 1 week, 1 month, 5 months, and 1 year after transplantation). In addition, CYP3A4*1B/CYP3A5*1 carriers showed significantly lower dose-corrected exposure than CYP3A4*1/CYP3A5*1 carriers 1 year after transplantation (57.01 ± 17.34 vs. 100.09 ± 24.78; P = 0.016). Only the ABCB1 TGC (3435-2677-1236) haplotype showed a consistent association with PDs (nephrotoxicity; OR = 4.73; CI: 1.3–16.7; P = 0.02). Our findings indicate that the CYP3A4*1B-CYP3A5*1 haplotype may have a more profound impact in tacrolimus PKs than the CYP3A5*1 allele. This study does not support a critical role of the CYP450 or ABCB1 single nucleotide polymorphisms in the occurrence of toxicity or acute rejection in renal transplant recipients treated with tacrolimus.

The farnesoid X receptor (FXR or NR1H4) is an important bile-acid-activated, transcriptional regulator of genes involved in bile acid, lipid, and glucose homeostasis. Accordingly, interindividual variations in FXR expression and function could manifest as variable susceptibility to conditions such as cholesterol gallstone disease, atherosclerosis, and diabetes. We performed an FXR polymorphism discovery analysis of European-, African-, Chinese-, and Hispanic-Americans and identified two rare gain-of-function variants and a common single nucleotide polymorphism resulting in a G-1T substitution in the nucleotide adjacent to the translation initiation site (FXR*1B) with population allelic frequencies ranging from 2.5 to 12%. In cell-based transactivation assays, FXR*1B (-1T) activity was reduced compared with FXR*1A (-1G). This reduced activity for FXR*1B resulted from neither decreased translational efficiency nor the potential formation of a truncated translational variant. To further define the relevance of this polymorphism, gene expression was examined in a human liver bank to reveal that levels of the FXR target genes small heterodimer partner and organic anion transporting polypeptide 1B3 were significantly reduced in livers harboring an FXR*1B allele. These findings are the first to identify the presence of a common genetic variant in FXR with functional consequences that could contribute to disease risk or therapeutic outcomes.