Rationale: The 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, or statins, are important drugs used in the treatment and prevention of cardiovascular disease. Although statins are well tolerated, many patients develop myopathy manifesting as muscle aches and pain. Rhabdomyolysis is a rare but severe toxicity of statins. MG-CoA (3-hydroxy-3-methylglutaryl coenzyme A) reductase inhibitors, statins, are highly effective drugs for the treatment of hypercholesterolemia, a major risk factor of cardiovascular disease. Statins inhibit the synthesis of mevalonate, the rate-limiting step in cholesterol biosynthesis. 1,2 Although statins are generally well tolerated, 3 skeletal muscle side effects are commonly reported among those treated. One such side effect, myalgia, which is defined as muscle aches or weakness in the absence of blood creatine kinase elevation, occurs in 5% to 15% of statin-treated patients. 2,4 -8 In rare cases, potentially life-threatening statin-induced rhabdomyolysis may occur, a condition characterized by acute muscle damage, resulting in pronounced elevation in creatine kinase levels and possible renal failure. 9 The pathophysiology of statin-induced myopathy is not completely understood. The leading mechanism suggests a role for cellular depletion of secondary metabolic intermediates of mevalonate in the development of statin-induced myotoxicity. 10 In addition to decreased cholesterol synthesis, HMG-CoA reductase inhibition by statins causes a commensurate reduction in the levels of downstream metabolic products including isoprenoids, dolichol, and ubiquinone (coenzyme Q10). 10 -13 Among these are the isoprenoid secondary metabolic intermediates geranylgeranylpyrophosphate and farnesylpyrophosphate that are involved in protein isoprenylation and activation of small GTPases such as Rho and Rab. The important role for diminished isoprenylation in the mechanism of statin myotoxicity is related to induction of the muscle atrophy-linked protein atrogin-1. 12 This is highlighted by the findings that supplementation of geranylgeranylpyrophosphate to cultured skeletal myotubes or isolated myofibers treated with statins leads to attenuation of toxicity, 11,13-15 whereas inactivation of a Rab and RhoA induces toxicity. 11,13 Decreased geranylgeranylation of small GT-

Our results demonstrate that PON1 does not mediate clopidogrel active metabolite formation or antiplatelet action, while CYP2C19 activity and genotype remains a predictor of clopidogrel pharmacokinetics and antiplatelet response.

Organic anion transporting polypeptide 2B1 (OATP2B1) is a widely expressed membrane transporter with diverse substrate specificity. In vitro and clinical studies suggest a role for intestinal OATP2B1 in the oral absorption of medications. Moreover, OATP2B1 is highly expressed in hepatocytes where it is thought to promote liver drug clearance. However, until now, a shortcoming of studies implicating OATP2B1 in drug disposition has been a lack of in vivo models. Here, we report the development of a knockout (KO) mouse model with targeted, global disruption of the Slco2b1 gene to examine the disposition of two confirmed mOATP2B1 substrates, namely, fexofenadine and rosuvastatin. The plasma pharmacokinetics of intravenously administered fexofenadine was not different between KO and wildtype (WT) mice. However, after oral fexofenadine administration, KO mice had 70% and 41% lower maximal plasma concentration (C max) and area under the plasma concentration-time curve (AUC 0-last) than WT mice, respectively. In WT mice, coadministration of fexofenadine with grapefruit juice (GFJ) or apple juice (AJ) was associated with reduced C max by 80% and 88%, respectively, while the AUC 0-last values were lower by 35% and 70%, respectively. In KO mice, AJ coadministration reduced oral fexofenadine C max and AUC 0-last values by 67% and 59%, respectively, while GFJ had no effects. Intravenous and oral rosuvastatin pharmacokinetics were similar among WT and KO mice. We conclude that intestinal OATP2B1 is a determinant of oral fexofenadine absorption, as well as a target for fruit juice interactions. OATP2B1 does not significantly influence rosuvastatin disposition in mice. SIGNIFICANCE STATEMENT A novel mouse model with targeted disruption of the Slco2b1 gene revealed that OATP2B1 is a determinant of oral absorption but not systemic disposition of fexofenadine, as well as a target of fruit juice interactions. Rosuvastatin oral and intravenous pharmacokinetics were not dependent on OATP2B1. These findings support the utility of the Slco2b1 KO mouse model for defining mechanisms of drug disposition at the intersection of in vitro and clinical pharmacology.

Folic acid is a vitamin essential for thymidylate and purine synthesis. The human proton-coupled folate transporter (hPCFT) has recently been identified as a pH-dependent folic acid transporter, and mutations in this transporter have been linked to hereditary folic acid malabsorption. In this study, we assessed hPCFT-mediated transport activity in vitro, intersubject variability of intestinal expression in relation to blood folates, and the relationship of proton-pump inhibitor (PPI) therapy on hPCFT expression in vivo. We created a Madin-Darby canine kidney strain II (MDCKII) cell line stably expressing hPCFT to evaluate its drug substrates and inhibitors. Intestinal pinch biopsies (duodenum, ileum, colon) were collected from patients undergoing routine endoscopy procedures, and expressed levels of hPCFT were determined by RT-PCR. When assessed using MDCKII-hPCFT cells, folic acid and methotrexate were found to be high-affinity hPCFT substrates. Sulfasalazine and pyrimethamine were noted to inhibit hPCFT activity with Ki values of 42.3 and 161.7 micromol/l, respectively. hPCFT was localized to the brush-border membrane of enterocytes with highest expression in the duodenum and reduced levels in the ileum and colon. When we assessed hPCFT expression in a subset of patients who were receiving PPI therapy, a near 50% reduction in duodenal hPCFT mRNA expression was noted. These results suggest that hPCFT transporter activity can be modulated by many drugs in clinical use, and expression of this transporter in the gastrointestinal tract is higher in the duodenum than more distal sites (duodenum > ileum > colon). Importantly, we note that PPI drug use appears to be associated with reduced hPCFT expression in vivo.