Up-regulation of renal Mdr1 and Mrp2 transporters during amiodarone pretreatment in rats

Transporter-mediated drug-drug interactions: advancement in models, analytical tools, and regulatory perspective

Drug-drug interactions mediated by transporters are a serious clinical concern hence a tremendous amount of work has been done on the characterization of the transporter-mediated proteins in humans and animals. The underlying mechanism for the transporter-mediated drug-drug interaction is the induction or inhibition of the transporter which is involved in the cellular uptake and efflux of drugs. Transporter of the brain, liver, kidney, and intestine are major determinants that alter the absorption, distribution, metabolism, excretion profile of drugs, and considerably influence the pharmacokinetic profile of drugs. As a consequence, transporter proteins may affect the therapeutic activity and safety of drugs. However, mounting evidence suggests that many drugs change the activity and/or expression of the transporter protein. Accordingly, evaluation of drug interaction during the drug development process is an integral part of risk assessment and regulatory requirements. Therefore, this review will highlight the clinical significance of the transporter, their role in disease, possible cause underlying the drug-drug interactions using analytical tools, and update on the regulatory requirement. The recent in-silico approaches which emphasize the advancement in the discovery of drug-drug interactions are also highlighted in this review. Besides, we discuss several endogenous biomarkers that have shown to act as substrates for many transporters, which could be potent determinants to find the drug-drug interactions mediated by transporters. Transporter-mediated drug-drug interactions are taken into consideration in the drug approval process therefore we also provided the extrapolated decision trees from in-vitro to in-vivo, which may trigger the follow-up to clinical studies.

Modulation of P-glycoprotein efflux pump: induction and activation as a therapeutic strategy

P-glycoprotein (P-gp) is an ATP-dependent efflux pump encoded by the MDR1 gene in humans, known to mediate multidrug resistance of neoplastic cells to cancer therapy. For several decades, P-gp inhibition has drawn many significant research efforts in an attempt to overcome this phenomenon. However, P-gp is also constitutively expressed in normal human epithelial tissues and, due to its broad substrate specificity, to its cellular polarized expression in many excretory and barrier tissues, and to its great efflux capacity, it can play a crucial role in limiting the absorption and distribution of harmful xenobiotics, by decreasing their intracellular accumulation. Such a defense mechanism can be of particular relevance at the intestinal level, by significantly reducing the intestinal absorption of the xenobiotic and, consequently, avoiding its access to the target organs. In this review, the current knowledge on this important efflux pump is summarized, and a new focus is brought on the therapeutic interest of inducing and/or activating P-gp for limiting the toxicity caused by its substrates. Several in vivo and in vitro studies validating the use of such a therapeutic strategy are discussed. An extensive literature search for reported P-gp inducers/activators and for the experimental models used in their characterization was conducted. Those studies demonstrate that effective antidotal pathways can be achieved by efficiently promoting the P-gp-mediated efflux of deleterious xenobiotics, resulting in a significant reduction in their intracellular levels and, consequently, in a significant reduction of their toxicity.

Ivermectin exposure leads to up-regulation of detoxification genes in vitro and in vivo in mice

The biodisposition of the antiparasitic drug ivermectin in host and parasite is decisive for its efficacy and strongly depends on the efflux by ATP-Binding Cassette (ABC) transporters and on its biotransformation by cytochromes P450. The purpose of this study was to evaluate, in vitro and in vivo, the ivermectin ability in modulating the expression of the most important genes involved in drug detoxification. Gene expression of ABC transporters and cytochromes was evaluated by RT-qPCR in murine hepatic and intestinal cell lines exposed to increasing ivermectin doses, and in liver and intestine of mice orally administered with single or repeated therapeutic doses of ivermectin (0.2 mg/kg). Plasma, brain, liver and intestinal concentrations of ivermectin and its main metabolite were measured by HPLC in ivermectin-treated mice. In hepatocyte cell line, ivermectin up-regulated expression of Abcb1a, Abcb1b, Abcc2, Cyp1a1, Cyp1a2, Cyp2b10; while Abcb1a, Abcb1b, Abcg2, Cyp1a1, Cyp1a2, Cyp2b10 and Cyp3a11 levels were induced in intestinal cell line. In mice, repeated administration of ivermectin induced the expression of Abcb1a, Abcc2, Cyp1a1 and Cyp2b10 in intestine while only Cyp3a11 was induced in liver. Compared with single administration, repeated ivermectin administration lowered plasma, liver and intestine drug concentration, while increasing main metabolite content in plasma and intestine. These findings can be regarded as a warning that repeated ivermectin exposure is able to induce detoxification systems in mammals that may lead to subtherapeutic drug concentration. This may also be an important consideration in the assessment of drug-drug interaction and toxicity for other ABC transporters and CYP450s substrates.

P-gp efflux pump inhibition potential of common environmental contaminants determined in vitro

Across different species, cellular efflux pumps such as P-glycoprotein (P-gp; also termed multidrug resistance protein 1 [MDR1]) serve as a first line of defense by transporting toxic xenobiotics out of the cell. This mechanism is also active in aquatic organisms such as mussels, fish, and their larvae. Modulation of this resistance mechanism by chemical agents occurring in the environment could result in either higher or lower internal concentrations of toxic or endogenous compounds in cells. The aim of the present study was to explore and quantify the inhibition of the P-gp efflux pumps by several ubiquitous aquatic contaminants. The calcein-acetoxymethyl ester (calcein-AM) assay commonly used in pharmacological research was established with P-gp-overexpressing Madin-Darby canine kidney cells (MDCKII-MDR1) in a 96-well plate, avoiding extra washing, centrifugation, and lysis steps. This calcein-AM-based P-gp cellular efflux pump inhibition assay (CEPIA) was used to study the inhibition by commonly occurring environmental contaminants. Among others, the compounds pentachlorophenol, perfluorooctane sulfonate, and perfluorooctanoate strongly inhibited the P-gp-mediated efflux of calcein-AM while the chloninated alkanes did not seem to interact with the transporter. The fact that common pollutants can be potent modulators of the efflux transporters is a motive to further study whether this increases the toxicity of other contaminants present in the same matrices.

Rapid stimulating effect of the antiarrhythmic agent amiodarone on absorption of organic anion compounds

In a clinical setting, changes in pharmacokinetics due to drug-drug interactions can often directly affect the therapeutic safety and efficacy of drugs. Recently, interest has been shown in drug-drug interactions in the intestine. It is now recognized that changes in the functions of drug transporters substantially influence the absorption of administered drugs from the intestine. Amiodarone (AMD) is a potent drug used in the treatment of serious supraventricular and ventricular tachyarrhythmias. Despite its potent pharmacological effects, its wide clinical use is precluded by drug-drug interactions. In this study, we characterized the transporter function between AMD and various compounds in human intestinal model Caco-2 cells. AMD significantly and rapidly increased the uptake of [(3)H]estrone-3-sulfate (E-3-S) for 5 min. The apical-to-basal transport of [(3)H]E-3-S was significantly increased by AMD. The AMD-stimulated [(3)H]E-3-S uptake was inhibited by organic anion transporting polypeptide (OATP) substrates. Caco-2 cells treated with AMD showed increased OATP2B1 expression on the cell surface. AMD also increased the absorption of sulfobromophthalein (BSP), which is a typical organic anion compound, and the expression level of Oatp2b1 at the membrane in in vivo experiments. The results indicate that AMD induces OATP2B1/Oatp2b1 expression at the membrane in the intestine and enhances absorption of organic anion compounds.

Tissue-specific alterations in expression and function of P-glycoprotein in streptozotocin-induced diabetic rats

AIM

To investigate the changes of expression and function of P-glycoprotein (P-GP) in cerebral cortex, hippocampus, liver, intestinal mucosa and kidney of streptozocin-induced diabetic rats.

METHODS

Diabetic rats were prepared via a single dose of streptozocin (65 mg/kg, ip). Abcb1/P-GP mRNA and protein expression levels in tissues were evaluated using quantitative real time polymerase chain reaction (QRT-PCR) analysis and Western blot, respectively. P-GP function was investigated via measuring tissue-to-plasma concentration ratios and body fluid excretion percentages of rhodamine 123.

RESULTS

In 5- and 8-week diabetic rats, Abcb1a mRNA levels were significantly decreased in cerebral cortices and intestinal mucosa, but dramatically increased in hippocampus and kidney. In liver, the level was increased in 5-week diabetic rats, and decreased in 8-week diabetic rats. Abcb1b mRNA levels were increased in cerebral cortex, hippocampus and kidney, but reduced in liver and intestinal mucosa in the diabetic rats. Western blot results were in accordance with the alterations of Abcb1a mRNA levels in most tissues examined. P-GP activity was markedly decreased in most tissues of diabetic rats, except kidney tissues.

CONCLUSION

Alterations in the expression and function of Abcb1/P-GP under diabetic conditions are tissue specific, Abcb1 specific and diabetic duration-dependent.