Background & Aims The 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors, or statins, target liver HMG-CoA and are of proven benefit in the prevention of coronary heart disease. Rosuvastatin is an effective statin notable for liver selectivity and lack of significant metabolism. We assessed the extent and relevance of hepatic transporters to rosuvastatin uptake. Methods Transporters involved in rosuvastatin uptake were determined through heterologous expression of multiple human and rat uptake transporters. Human organic anion transporting polypeptide (OATP) 1B1 and sodium-dependent taurocholate cotransporting polypeptide (NTCP) allelic variants were also assessed. Expression of OATP and NTCP messenger RNA and protein was determined from a bank of human liver samples. Results Multiple OATP family members, including 1B1, 1B3, 2B1, and 1A2, were capable of rosuvastatin transport. Naturally occurring polymorphisms in OATP1B1, including *5, *9, *15, and *18, were associated with profound loss of activity toward rosuvastatin. Interestingly, the major human hepatic bile acid uptake transporter NTCP, but not rat Ntcp, also transported rosuvastatin. Human hepatocyte studies suggested that NTCP alone accounted for ∼35% of rosuvastatin uptake. Remarkably, NTCP*2, a variant known to have a near complete loss of function for bile acids, exhibited a profound gain of function for rosuvastatin. Quantitative messenger RNA analysis revealed marked intersubject variability in expression of OATPs and NTCP. Conclusions Multiple transporters mediate the overall hepatic uptake of rosuvastatin, and NTCP may be a heretofore unrecognized transporter important to the disposition of rosuvastatin and possibly other drugs/statins in clinical use. Accordingly, transporter expression and polymorphisms may be key determinants of intersubject variability in response to statin therapy in general.

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.

Background: Many drugs are cosubstrates of cytochrome P450 (CYP) 3A and MDR1; furthermore, their disposition is markedly affected by pretreatment with inducing agents, including St John's wort. Such drug interactions reflect induction of both proteins through a common mechanism involving the steroid X receptor/pregnane X receptor. However, the relative contributions of enhanced metabolism and efflux transport to the overall induction process are unknown.Methods: The effects of 12 days' pretreatment with St John's wort on the disposition of selected in vivo probe drugs were determined in 21 young healthy subjects. Midazolam after oral and intravenous administration was used to assess CYP3A activity in both the intestinal epithelium and the liver, whereas the disposition of fexofenadine after an oral dose was assumed to be a measure of MDR1 function, and the oral plasma concentration‐time profile of cyclosporine (INN, ciclosporin) was considered to reflect both CYP3A and MDR1 activities.Results: St John's wort markedly affected the plasma concentration‐time profiles of all of the drugs, with associated increases in their clearance. With midazolam, the enhancement was considerably less after intravenous administration (approximately 1.5‐fold) than after oral administration (approximately 2.7‐fold), and estimated intestinal and hepatic extraction ratios were higher by approximately 1.2‐ to 1.4‐fold. By contrast, the oral clearances of fexofenadine and cyclosporine were equally increased by approximately 1.6‐fold and 1.9‐fold, respectively; these changes were both statistically less than for midazolam's oral clearance and greater than its estimated intestinal extraction.Conclusions: Although the disposition of all 3 drugs was altered by St John's wort, the extent of induction measured by oral clearance was different with CYP3A activity (midazolam), apparently increasing more than MDR1 function (fexofenadine), whereas with cyclosporine the change in oral clearance appeared to be more closely associated with the increase in MDR1 rather than CYP3A, despite the fact that both proteins are importantly involved in its disposition. These discordances indicate that, although a common molecular mechanism may be involved, the quantitative aspects of induction are complex and depend on the particular drug and the relative contributions of CYP3A and MDR1 in its disposition.Clinical Pharmacology & Therapeutics (2003) 73, 41–50; doi: 10.1067/mcp.2003.10

Background: The efflux transporter P-glycoprotein, a member of the adenosine triphosphate-binding cassette superfamily, is a major determinant of the pharmacokinetics and pharmacodynamics of the opioid loperamide, a well-recognized antidiarrheal agent. Animal studies indicate that P-glycoprotein limits morphine entry into the brain. In this study, the authors examined whether other opioids of importance to anesthesiologists such as fentanyl, sufentanil, and alfentanil, and also morphine-6-glucuronide and morphine-3-glucuronide, are P-glycoprotein substrates and whether, in turn, these opioids act also as P-glycoprotein inhibitors. Methods: The transcellular movement of the various opioids, including loperamide and morphine, was assessed in L-MDR1 (expressing P-glycoprotein) and LLC-PK1 cell monolayers (P-glycoprotein expression absent). A preferential basal-to-apical versus apical-to-basal transport in the L-MDR cells but not the LLC-PK1 cells is seen for P-glycoprotein substrates. In addition, the effect of the various opioids on the transcellular movement of the prototypical P-glycoprotein substrate digoxin was examined in Caco-2 cell monolayers. IC50 values were calculated according to the Hill equation. Results: Loperamide was a substrate showing high dependence on P-glycoprotein in that basal-apical transport was nearly 10-fold greater than in the apical-basal direction in L-MDRI cells. Morphine also showed a basal-to-apical gradient in the L-MDR1 cell monolayer, indicating that it too is a P-glycoprotein substrate, but with less dependence than loperamide in that only 1.5-fold greater basal-apical directional transport was observed. Fentanyl, sufentanil, and alfentanil did not behave as P-glycoprotein substrates, whereas the morphine glucuronides did not cross the cell monolayers at all, whether P-glycoprotein was present or not. Loperamide, sufentanil, fentanyl, and alfentanil inhibited P-glycoprotein-mediated digoxin transport in Caco-2 cells with IC50 values of 2.5, 4.5, 6.5, and 112 microm, respectively. Morphine and its glucuronides (20 microm) did not inhibit digoxin (5 microm) transport in Caco-2 cells, and therefore IC50 values were not determined. Conclusions: Opioids have a wide spectrum of P-glycoprotein activity, acting as both substrates and inhibitors, which might contribute to their varying central nervous system-related effects.