Organic anion transporting polypeptide 1B1: a genetically polymorphic transporter of major importance for hepatic drug uptake.

The importance of membrane transporters for drug pharmacokinetics has been increasingly recognized during the last decade. Organic anion transporting polypeptide 1B1 (OATP1B1) is a genetically polymorphic influx transporter expressed on the sinusoidal membrane of human hepatocytes, and it mediates the hepatic uptake of many endogenous compounds and xenobiotics. Recent studies have demonstrated that OATP1B1 plays a major, clinically important role in the hepatic uptake of many drugs. A common single-nucleotide variation (coding DNA c.521T>C, protein p.V174A, rs4149056) in the SLCO1B1 gene encoding OATP1B1 decreases the transporting activity of OATP1B1, resulting in markedly increased plasma concentrations of, for example, many statins, particularly of active simvastatin acid. The variant thereby enhances the risk of statin-induced myopathy and decreases the therapeutic indexes of statins. However, the effect of the SLCO1B1 c.521T>C variant is different on different statins. The same variant also markedly affects the pharmacokinetics of several other drugs. Furthermore, certain SLCO1B1 variants associated with an enhanced clearance of methotrexate increase the risk of gastrointestinal toxicity by methotrexate in the treatment of children with acute lymphoblastic leukemia. Certain drugs (e.g., cyclosporine) potently inhibit OATP1B1, causing clinically significant drug interactions. Thus, OATP1B1 plays a major role in the hepatic uptake of drugs, and genetic variants and drug interactions affecting OATP1B1 activity are important determinants of individual drug responses. In this article, we review the current knowledge about the expression, function, substrate characteristics, and pharmacogenetics of OATP1B1 as well as its role in drug interactions, in parts comparing with those of other hepatocyte-expressed organic anion transporting polypeptides, OATP1B3 and OATP2B1.

Different effects of the ABCG2 c.421C>A SNP on the pharmacokinetics of fluvastatin, pravastatin and simvastatin.

AIMS: This study aimed to investigate possible effects of the ABCG2 c.421C>A (p.Gln141Lys; rs2231142) genotype on fluvastatin, pravastatin and simvastatin pharmacokinetics. MATERIALS & METHODS: In a crossover study, five healthy volunteers with the ABCG2 c.421A/A genotype, four with the c.421C/A genotype and 23 with the c.421C/C genotype ingested a single 40-mg dose of fluvastatin, pravastatin and simvastatin, with a washout period of 1 week. Plasma statin concentrations were measured up to 12 h. RESULTS: The estimated marginal mean area under the plasma concentration-time curve from 0 h to infinity (AUC(0-infinity)) of fluvastatin was 97% (p = 0.015) or 72% (p = 0.009) larger in participants with the A/A genotype than in those with the C/A or C/C genotype. The AUC(0-infinity) of simvastatin lactone was 111% (p = 0.005) larger in participants with the A/A genotype than in participants with the C/C genotype. The simvastatin acid:lactone AUC(0-infinity) ratio was 46% (p = 0.017) smaller in individuals with the A/A genotype than in those with the C/C genotype. The ABCG2 genotype had no significant effect on simvastatin acid or pravastatin pharmacokinetics. CONCLUSIONS: Genetic variability in ABCG2 markedly affects the pharmacokinetics of fluvastatin and simvastatin lactone, but has no significant effect on pravastatin or active simvastatin acid. Genotyping for ABCG2 in addition to SLCO1B1 and ABCB1 polymorphisms could help in predicting statin pharmacokinetics when selecting a statin and its dose for an individual patient.

Effect of SLCO1B1 polymorphism on the plasma concentrations of bile acids and bile acid synthesis marker in humans.

BACKGROUND AND OBJECTIVE: Organic anion transporting polypeptide 1B1 (OATP1B1, encoded by SLCO1B1) is a sinusoidal influx transporter of human hepatocytes. Our aim was to characterize the role of OATP1B1 in the hepatic uptake of bile acids in vivo. METHODS: Fasting blood samples were drawn from 24 healthy volunteers with SLCO1B1 c.388AA-c.521TT (*1A/*1A) genotype, eight with c.388GG-c.521TT (*1B/*1B) genotype, 24 with c.521TC genotype, and nine with c.521CC genotype. Plasma concentrations of 15 endogenous bile acids, their synthesis marker, and cholesterol were determined by liquid chromatography-tandem mass spectrometry. RESULTS: The concentrations of ursodeoxycholic acid, glycoursodeoxycholic acid, chenodeoxycholic acid, and glycochenodeoxycholic acid were approximately 50-240% higher in individuals with the SLCO1B1 c.521CC, c.521TC, or c.388AA-c.521TT genotype than in those with the c.388GG-c.521TT genotype (P<0.05), with the largest differences seen between the c.521CC and c.388GG-c.521TT individuals. The concentration of tauroursodeoxycholic acid was approximately 120% higher in individuals with the c.521TC genotype and that of taurochenodeoxycholic acid 110% higher in individuals with the c.521CC or c.521TC genotype than in those with the c.388GG-c.521TT genotype (P<0.05). The cholic acid concentration was approximately 30% higher in individuals with the c.521CC or c.388AA-c.521TT genotype than in those with the c.388GG-c.521TT genotype (P<0.05), but its conjugates remained unaffected by the genotype. The bile acid synthesis marker 7alpha-hydroxy-4-cholesten-3-one/cholesterol concentration ratio was 62 or 45% higher in the c.388AA-c.521TT participants than in the c.388GG-c.521TT or c.521TC participants, respectively (P<0.05). CONCLUSION: SLCO1B1 polymorphism considerably affects the disposition of several endogenous bile acids and bile acid synthesis marker, indicating that OATP1B1 plays an important role in the hepatic uptake of bile acids in vivo in humans.

Polymorphism of the hepatic influx transporter organic anion transporting polypeptide 1B1 is associated with increased cholesterol synthesis rate.

We investigated the influence of SLCO1B1 polymorphism on cholesterol synthesis and absorption during baseline, and as affected by statins. In a crossover study, 32 healthy volunteers with different SLCO1B1 genotypes ingested a single dose of fluvastatin, pravastatin, simvastatin, rosuvastatin, and atorvastatin. Plasma total cholesterol, and cholesterol synthesis and absorption markers were measured before statin administration and up to 12 h thereafter. The mean fasting baseline plasma desmosterol to cholesterol ratio was 40% higher in participants with the SLCO1B1 c.521CC variant genotype than in those with the c.521TT genotype (P=0.043). The genotype had no significant effect on cholesterol absorption markers. All statins decreased lathosterol and avenasterol to cholesterol ratios, but no significant differences in the response existed between SLCO1B1 genotypes. In conclusion, the low activity SLCO1B1 c.521CC genotype is associated with an increased cholesterol synthesis rate. The short-term effects of statins on cholesterol homeostasis were not associated with the SLCO1B1 polymorphism.

Global analysis of genetic variation in SLCO1B1.

INTRODUCTION: Organic anion transporting polypeptide 1B1 (OATP1B1), encoded by the SLCO1B1 gene, mediates the hepatic uptake of endogenous compounds and xenobiotics, including drugs. The aim of this study was to investigate the diversity of the SLCO1B1 gene at the global level. MATERIALS AND METHODS: Distribution of SLCO1B1 alleles was determined in 941 individuals from 52 populations comprising Africa, the Middle East, Asia, Europe, Oceania and the Americas. DNA samples were genotyped at 12 variant sites spanning the entire gene by TaqMan 5 nuclease allelic discrimination assays. RESULTS: The frequency of the low-activity c.521T>C variant varied markedly between populations. The lowest frequencies were observed in Oceania (0.0%; 95% CI: 0.0-6.4%) and sub-Saharan Africa (1.9%; 95% CI: 0.7-4.8%), and the highest frequencies observed in American native populations (24%; 95% CI: 18-32%) and Europe (18%; 95% CI: 14-23%). Moreover, the c.521C allele (r = 0.505, p < 0.001) and the *1B (c.388G-c.521T; r = -0.405, p = 0.006) and *15 (c.388G-c.521C; r = 0.510, p < 0.001) haplotype frequencies correlated significantly with latitude in the northern hemisphere. Overall, SLCO1B1 genetic distances correlated significantly with geographic distances between populations, assuming likely routes of human migration out of Africa via five waypoints (r = 0.235, p = 0.001). SLCO1B1 diversity was generally far greater within than between populations. CONCLUSION: Functionally significant variants of SLCO1B1 are widely distributed and occur at high frequencies around the world. SLCO1B1 diversity is greater within than between populations, and genetic variation in SLCO1B1 is generally similar to that observed for other autosomal markers. However, selective pressure may have acted on SLCO1B1 during human dispersal favoring low-activity variants in the north.

SLCO1B1 polymorphism markedly affects the pharmacokinetics of simvastatin acid.

BACKGROUND AND OBJECTIVE: Organic anion transporting polypeptide 1B1 (OATP1B1) is an uptake transporter located at the sinusoidal membrane of human hepatocytes. This study aimed to investigate the effects of genetic polymorphism in the SLCO1B1 gene encoding OATP1B1 on the pharmacokinetics of simvastatin. METHODS: Four healthy volunteers with the homozygous SLCO1B1 c.521CC genotype, 12 with the heterozygous c.521TC genotype and 16 with the homozygous c.521TT genotype (controls) were recruited. Each study participant ingested a single 40-mg dose of simvastatin. Plasma concentrations of simvastatin (inactive lactone) and its active metabolite simvastatin acid were measured for 12 h. RESULTS: The AUC0-infinity of simvastatin acid was 120 and 221% higher in participants with the SLCO1B1 c.521CC genotype than in those with the c.521TC and c.521TT (reference) genotypes, respectively (P<0.001). The Cmax of simvastatin acid was 162 and 200% higher in participants with the c.521CC genotype than in those with the c.521TC and c.521TT genotypes (P<0.001). The Cmax of simvastatin acid occurred earlier in participants with the c.521CC and c.521TC genotypes than in those with the c.521TT genotype (P<0.05). No association existed between the SLCO1B1 genotype and the elimination half-life of simvastatin acid. Moreover, no statistically significant association was seen between the SLCO1B1 genotype and the pharmacokinetics of simvastatin lactone. CONCLUSIONS: SLCO1B1 polymorphism markedly affects the pharmacokinetics of active simvastatin acid, but has no significant effect on parent simvastatin. Raised plasma concentrations of simvastatin acid in patients carrying the SLCO1B1 c.521C variant allele may enhance the risk of systemic adverse effects during simvastatin treatment. In addition, reduced uptake of simvastatin acid by OATP1B1 into the liver in patients with the c.521C allele could reduce its cholesterol-lowering efficacy.

SLCO1B1 polymorphism and sex affect the pharmacokinetics of pravastatin but not fluvastatin.

OBJECTIVE: Pravastatin is a hydrophilic substrate and fluvastatin a lipophilic substrate of the hepatic uptake transporter organic anion transporting polypeptide 1B1 encoded by SLCO1B1. Our aim was to compare the effects of SLCO1B1 polymorphism on the pharmacokinetics of pravastatin and fluvastatin. METHODS: We recruited 4 healthy volunteers (3 men and 1 woman) with the homozygous SLCO1B1 c.521CC genotype, 12 (7 men and 5 women) with the heterozygous c.521TC genotype, and 16 (8 men and 8 women) with the homozygous c.521TT genotype (control subjects). In a crossover study each subject ingested a single 40-mg dose of fluvastatin and pravastatin with a washout period of at least 1 week. Plasma fluvastatin and pravastatin concentrations were measured for 12 hours. RESULTS: In men with the c.521CC genotype, the mean peak concentration in plasma and area under the plasma concentration-time curve from time 0 to infinity of pravastatin were 274% (95% confidence interval [CI], 92%-456%; P = .001) and 232% (95% CI, 74%-391%; P = .002) greater than those in men with the c.521TT genotype and 120% (95% CI, 11%-230%; P = .026) and 102% (95% CI, 3%-200%; P = .040) greater than those in men with the c.521TC genotype. In addition, women with the c.521TT genotype had a 147% (95% CI, 12%-281%; P = .028) greater peak concentration in plasma and a 142% (95% CI, 7%-242%; P = .034) greater area under the plasma concentration-time curve from time 0 to infinity than men with the c.521TT genotype. The pharmacokinetic variables of pravastatin were approximately similar among women with different SLCO1B1 genotypes. No significant differences were seen in the pharmacokinetics of fluvastatin between subjects with different SLCO1B1 genotypes or between the sexes. CONCLUSIONS: SLCO1B1 polymorphism has a large effect on the pharmacokinetics of pravastatin but not fluvastatin. This suggests that the lipophilic fluvastatin can penetrate the hepatocyte plasma membrane via passive diffusion or that uptake transporters other than organic anion transporting polypeptide 1B1 mainly mediate its hepatic uptake. Moreover, the results suggest that sex may affect the pharmacokinetics of pravastatin and possibly the functional consequences of SLCO1B1 polymorphism.

Association of genetic polymorphism in ABCC2 with hepatic multidrug resistance-associated protein 2 expression and pravastatin pharmacokinetics.

OBJECTIVE: Our aim was to investigate possible effects of sequence variations in ABCC2, encoding the multidrug resistance-associated protein 2 (MRP2), on the pharmacokinetics of the MRP2 substrate pravastatin. METHODS: Deoxyribonucleic acid samples of 41 healthy volunteers, in whom SLCO1B1 single nucleotide polymorphisms (SNPs) and haplotypes had previously been found to be associated with increased plasma pravastatin concentrations, were investigated. Each study participant had ingested a single 40-mg dose of pravastatin followed by blood sampling for pharmacokinetic characterization in standardized conditions. The exons, exon-intron boundaries, promoter region and 3'-untranslated region of the ABCC2 gene of six individuals with the highest and six individuals with the lowest pravastatin area under the plasma concentration-time curve (AUC) values were sequenced. RESULTS: Of the 26 sequence variations found, the synonymous c.1446C>G SNP was observed heterozygously in three (50%) of the six individuals with a low pravastatin AUC and in none (0%) of the six individuals with a high AUC (P=0.06 for allele frequency). The remaining 29 participants were then also genotyped for c.1446C>G, but none of them carried the SNP. In addition, the effect of c.1446C>G on MRP2 mRNA expression was investigated in 93 human liver samples. A multiple linear regression analysis in the 41 participants with pravastatin pharmacokinetic data indicated that the ABCC2 c.1446C>G SNP and the previously identified SLCO1B1 haplotype *17 were independent predictors of the AUC0-12 and Cmax of pravastatin (r=32 and 29%, respectively) (P<0.01). In the participants heterozygous for the ABCC2 c.1446C>G SNP (n=3), who were not carriers of the SLCO1B1*17 haplotype, the AUC0-12 and Cmax of pravastatin were 67 and 68% lower than in those carrying neither the SLCO1B1*17 haplotype nor the ABCC2 c.1446C>G SNP (n=35) (P<0.05). MRP2 mRNA expression was 95% higher in livers with the c.1446CG genotype (n=7) than in those with the c.1446CC genotype (n=86) (P<0.05). CONCLUSIONS: These results support the idea that the ABCC2 c.1446C>G SNP is associated with reduced systemic exposure to pravastatin as a consequence of increased MRP2 expression. The underlying mechanism may involve either a modulating effect of the SNP on mRNA stability or linkage to other polymorphism(s) acting at the transcriptional level.

Frequencies of single nucleotide polymorphisms and haplotypes of organic anion transporting polypeptide 1B1 SLCO1B1 gene in a Finnish population.

OBJECTIVE: Organic anion transporting polypeptide 1B1 (OATP1B1) is a drug uptake transporter located at the sinusoidal membrane of hepatocytes. Our aim was to establish high-throughput genotyping assays for the major known single nucleotide polymorphisms (SNP) in the SLCO1B1 gene encoding OATP1B1 and to investigate the frequencies of SNPs and haplotypes of SLCO1B1 in a large Caucasian population. METHODS: Distribution of SLCO1B1 alleles was determined in 468 healthy Finnish Caucasian subjects at 11 variant sites spanning the entire gene by using allelic discrimination with TaqMan 5' nuclease assays. RESULTS: The allelic frequencies of SLCO1B1 SNPs were 9.7% for g.-11187G>A, 0.4% for g.-11110T>G, 8.0% for g.-10499A>C, 46.2% for c.388A>G, 13.1% for c.411G>A, 13.1% for c.463C>A, 20.2% for c.521T>C, 53.2% for c.571T>C, 46.4% for c.597C>T, 4.0% for c.1929A>C and 48.8% for c.*439T>G. Altogether, 26 haplotypes were statistically inferred. The most common haplotype, with a frequency of 35.6%, contained variant allele C at position c.571, but had the reference nucleotide at all other positions investigated. The functionally significant c.521T>C SNP existed in four major haplotypes, which could be differentiated by the g.-11187G>A, g.-10499A>C and c.388A>G SNPs. The frequencies of these haplotypes were 7.9% for g.-11187G/g.-10499C/c.388G/c.521C (*16), 6.9% for AAGC (*17), 2.7% for GAAC (*5) and 2.4% for GAGC (*15). CONCLUSION: Sequence variations of SLCO1B1 occur at high frequencies in the Caucasian population. Further studies are needed to characterise the effects of SLCO1B1 haplotypes, especially *16, *17, *15 and *5, on drug pharmacokinetics and response, and to determine the frequencies of SLCO1B1 SNPs and haplotypes in different populations.

Itraconazole, gemfibrozil and their combination markedly raise the plasma concentrations of loperamide.

OBJECTIVE: Loperamide is biotransformed in vitro by the cytochromes P450 (CYP) 2C8 and 3A4 and is a substrate of the P-glycoprotein efflux transporter. Our aim was to investigate the effects of itraconazole, an inhibitor of CYP3A4 and P-glycoprotein, and gemfibrozil, an inhibitor of CYP2C8, on the pharmacokinetics of loperamide. METHODS: In a randomized crossover study with 4 phases, 12 healthy volunteers took 100 mg itraconazole (first dose 200 mg), 600 mg gemfibrozil, both itraconazole and gemfibrozil, or placebo, twice daily for 5 days. On day 3, they ingested a single 4-mg dose of loperamide. Loperamide and N-desmethylloperamide concentrations in plasma were measured for up to 72 h and in urine for up to 48 h. Possible central nervous system effects of loperamide were assessed by the Digit Symbol Substitution Test and by subjective drowsiness. RESULTS: Itraconazole raised the peak plasma loperamide concentration (Cmax) 2.9-fold (range, 1.2-5.0; P < 0.001) and the total area under the plasma loperamide concentration-time curve (AUC(0-infinity)) 3.8-fold (1.4-6.6; P < 0.001) and prolonged the elimination half-life (t(1/2)) of loperamide from 11.9 to 18.7 h (P < 0.001). Gemfibrozil raised the Cmax of loperamide 1.6-fold (0.9-3.2; P < 0.05) and its AUC(0-infinity) 2.2-fold (1.0-3.7; P < 0.05) and prolonged its t(1/2) to 16.7 h (P < 0.01). The combination of itraconazole and gemfibrozil raised the Cmax of loperamide 4.2-fold (1.5-8.7; P < 0.001) and its AUC(0-infinity) 12.6-fold (4.3-21.8; P < 0.001) and prolonged the t(1/2) of loperamide to 36.9 h (P < 0.001). The amount of loperamide excreted into urine within 48 h was increased 3.0-fold, 1.4-fold and 5.3-fold by itraconazole, gemfibrozil and their combination, respectively (P < 0.05). Itraconazole, gemfibrozil and their combination reduced the plasma AUC(0-72) ratio of N-desmethylloperamide to loperamide by 65%, 46% and 88%, respectively (P < 0.001). No significant differences were seen in the Digit Symbol Substitution Test or subjective drowsiness between the phases. CONCLUSION: Itraconazole, gemfibrozil and their combination markedly raise the plasma concentrations of loperamide. Although not seen in the psychomotor tests used, an increased risk of adverse effects should be considered during concomitant use of loperamide with itraconazole, gemfibrozil and especially their combination.

Comparison of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) as inhibitors of cytochrome P450 2C8.

Statins are involved in different types of drug interactions. Our objective was to study the effect of statins on cytochrome P450 (CYP) 2C8-mediated paclitaxel 6 alpha-hydroxylation by incubating paclitaxel and statins (0--100 microM) with pooled human liver microsomes. Simvastatin, lovastatin, atorvastatin and fluvastatin were the most potent inhibitors of CYP2C8 activity with K(i) (IC(50)) values of 7.1 (9.6) muM, 8.4 (15) microM, 16 (38) microM and 19 (37) microM, respectively. Cerivastatin, simvastatin acid and lovastatin acid were less potent inhibitors with K(i) (IC(50)) values ranging from 32 to 55 (30--67) microM. Rosuvastatin and pravastatin showed no appreciable effect on CYP2C8 activity even at 100 microM. In conclusion, all the statins tested, except rosuvastatin and pravastatin, had a significant inhibitory effect on the activity of CYP2C8 in vitro. Because many of the statins accumulate in the liver and because also their metabolites may inhibit CYP2C8 activity, in vivo studies are needed to investigate a possible interaction of simvastatin, lovastatin, atorvastatin and fluvastatin with CYP2C8 substrate drugs.