Breast cancer resistance protein (BCRP), multidrug resistance associated protein 2 (MRP2) and P-glycoprotein (P-gp) are ABC transporters that are expressed in the intestine, where they are involved in the efflux of many drugs from enterocytes back into the intestinal lumen. The inhibition of BCRP, MRP2, and P-gp can result in enhanced absorption and exposure of substrate drugs. Food additives are widely used by the food industry to improve the stability, flavor, and consistency of food products. Although they are considered safe for consumption, their interactions with intestinal transporters are poorly characterized. Therefore, in this study, selected food additives, including preservatives, colorants, and sweeteners, were studied in vitro for their inhibitory effects on intestinal ABC transporters. Among the studied compounds, several colorants were able to inhibit BCRP and MRP2, whereas P-gp was fairly insensitive to inhibition. Additionally, one sweetener was identified as a potent inhibitor of BCRP. Dose-response studies revealed that the IC values of the inhibitors were lower than the estimated intestinal concentrations after the consumption of beverages containing food colorants. This suggests that there is potential for previously unrecognized transporter-mediated food additive-drug interactions.

Xanthine oxidase inhibitors febuxostat and allopurinol are commonly used in the treatment of gout. Febuxostat inhibits the breast cancer resistance protein (BCRP) in vitro. Rosuvastatin is a BCRP substrate and genetic variability in BCRP markedly affects rosuvastatin pharmacokinetics. In this study, we investigated possible effects of febuxostat and allopurinol on rosuvastatin pharmacokinetics. In a randomized crossover study with 3 phases, 10 healthy volunteers ingested once daily placebo for 7 days, 300 mg allopurinol for 7 days, or placebo for 3 days, followed by 120 mg febuxostat for 4 days, and a single 10 mg dose of rosuvastatin on day 6. Febuxostat increased the peak plasma concentration and area under the plasma concentration-time curve of rosuvastatin 2.1-fold (90% confidence interval 1.8-2.6; P = 5 × 10 −5) and 1.9-fold (1.5-2.5; P = 0.001), but had no effect on rosuvastatin half-life or renal clearance. Allopurinol, on the other hand, did not affect rosuvastatin pharmacokinetics. In vitro, febuxostat inhibited the ATP-dependent uptake of rosuvastatin into BCRP-overexpressing membrane vesicles with a half-maximal inhibitory concentration of 0.35 µM, whereas allopurinol showed no inhibition with concentrations up to 200 µM. Taken together, the results suggest that febuxostat increases rosuvastatin exposure by inhibiting its BCRP-mediated efflux in the small intestine. Febuxostat may, therefore, serve as a useful index inhibitor of BCRP in drug-drug interaction studies in humans. Moreover, concomitant use of febuxostat may increase the exposure to BCRP substrate drugs and, thus, the risk of dose-dependent adverse effects. Gout is an increasingly common condition, and the most common form of inflammatory arthritis in developed countries. The main cause of gout is chronic hyperuricemia. Elevated serum uric acid concentration leads to accumulation of monosodium urate in joints, where urate crystals cause an extremely painful inflammatory arthritis and recurrent gout flares. Risk factors for gout include obesity, renal failure, genetic variability, diet, medications, such as diuretics, and excessive consumption of alcohol. 1-4 The increasing prevalence rates of gout worldwide are concordant with the role of lifestyle in its development. Allopurinol is the first-line treatment of chronic hyperuricemia and gout. It is used as a long-term medication to prevent attacks of gout and avoid permanent damage to the joints. Being a nonselective inhibitor of the xanthine oxidase enzyme, allopurinol prevents biotransformation of

Previous studies have shown that lipid-lowering statins are transported by various ATP-binding cassette (ABC) transporters. However, due to varying methods, it is difficult to compare the transport profiles of statins. Therefore, we investigated the transport of ten statins or statin metabolites by six ABC transporters using human embryonic kidney cell-derived membrane vesicles. The transporter protein expression levels in the vesicles were quantified with liquid chromatography-tandem mass spectrometry, and used to scale the measured clearances to tissue levels. In our study, apically expressed breast cancer resistance protein (BCRP) and P-glycoprotein (P-gp) transported atorvastatin, fluvastatin, pitavastatin, and rosuvastatin. Multidrug resistance-associated protein 3 (MRP3) transported atorvastatin, fluvastatin, pitavastatin, and to a smaller extent, pravastatin. MRP4 transported fluvastatin and rosuvastatin. The scaled clearances suggest that BCRP contributes to 84-90% and 82% of the total active efflux of rosuvastatin in the small intestine and the liver, respectively.For atorvastatin, the corresponding values for P-gp-mediated efflux were 32-73% and 56%, respectively. MRP3, on the other hand, may contribute to 33-38% and 35-51% of total active efflux of atorvastatin, fluvastatin, and pitavastatin in jejunal enterocytes and liver hepatocytes, respectively.These data indicate that BCRP may play an important role in limiting the intestinal absorption and facilitating the biliary excretion of rosuvastatin and that P-gp may restrict the intestinal absorption and mediate the biliary excretion of atorvastatin. Moreover, the basolateral MRP3 may enhance the intestinal absorption and sinusoidal hepatic efflux of several statins. Taken together, the data show that statins differ considerably in their efflux transport profiles.

Glucuronidation and sulfation are the most typical phase II metabolic reactions of drugs. The resulting glucuronide and sulfate conjugates are generally considered inactive and safe. They may, however, be the most prominent drug-related material in the circulation and excreta of humans. The glucuronide and sulfate metabolites of drugs typically have limited cell membrane permeability and subsequently, their distribution and excretion from the human body requires transport proteins. Uptake transporters, such as organic anion transporters (OATs and OATPs), mediate the uptake of conjugates into the liver and kidney, while efflux transporters, such as multidrug resistance proteins (MRPs) and breast cancer resistance protein (BCRP), mediate expulsion of conjugates into bile, urine and the intestinal lumen. Understanding the active transport of conjugated drug metabolites is important for predicting the fate of a drug in the body and its safety and efficacy. The aim of this review is to compile the understanding of transporter-mediated disposition of phase II conjugates. We review the literature on hepatic, intestinal and renal uptake transporters participating in the transport of glucuronide and sulfate metabolites of drugs, other xenobiotics and endobiotics. In addition, we provide an update on the involvement of efflux transporters in the disposition of glucuronide and sulfate metabolites. Finally, we discuss the interplay between uptake and efflux transport in the intestine, liver and kidneys as well as the role of transporters in glucuronide and sulfate conjugate toxicity, drug interactions, pharmacogenetics and species differences.

Estrone, estradiol and estriol are endogenous human estrogens that are rapidly conjugated with glucuronic acid in both intestinal and hepatic epithelial cells. The resulting glucuronides, estrone-3-glucuronide (E-G), estradiol-3- and 17-glucuronides (E-3G and E-17G), as well as estriol-3- and 16-glucuronides (E-3G and E-16G) are found in human plasma and urine. Unlike E-17G, the efflux transport of other estrogen glucuronides by human transporters has not yet been investigated comprehensively. We have studied the transport of E-G, E-3G, E-3G, E-16G and estrone-3-sulfate (E-S), another important estrogen conjugate, using the vesicular transport assay with recombinant human MRP2, MRP3, MRP4, MDR1 and BCRP that were expressed in insect cells. The transport screening assays revealed that whereas E-S was a good and specific substrate for BCRP, the less transporter-specific conjugates, E-G and E-3G, were still transported by BCRP at 10-fold higher rates than E-S. BCRP also transported E-16G at higher rates than the studied MRPs, while it transported E-3G at lower rates than MRP3. MRP2 exhibited lower or equal transport rates of E-G, E-3G, E-3G and E-16G in comparison to MRP3 and BCRP in the screening assays, mainly due to its high K values, between 180 and 790 μM. MRP3 transported all the tested glucuronides at rather similar rates, at K values below 20 μM, but lower V values than other transporters. In the case of E-3G, MRP3 was the most active transporter in the screening assay. MRP4 transported only E-16G at considerable rates, while none of the tested estrogen conjugates was transported by MDR1 at higher rates than control vesicles. These new results, in combination with previously reported in vivo human data, stimulate our understanding on the substrate specificity and role of efflux transporters in disposition of estrogen glucuronides in humans.

This study aimed to comprehensively investigate the in vitro metabolism of statins. The metabolism of clinically relevant concentrations of atorvastatin, fluvastatin, pitavastatin, pravastatin, rosuvastatin, simvastatin and their metabolites were investigated using human liver microsomes (HLMs), intestine microsomes (HIMs), liver cytosol, and recombinant cytochrome P450 (CYP) enzymes. We also determined the inhibitory effects of statin acids on their pharmacological target, 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase. In HLMs, statin lactones were metabolized to a much higher extent than their acid forms. Atorvastatin lactone and simvastatin (lactone) showed extensive metabolism (intrinsic clearance (CL int ) values of 3,700 and 7,400 µl/min/mg), while the metabolism of the lactones of 2-hydroxyatorvastatin, 4-hydroxyatorvastatin, and pitavastatin was slower (CL int 20-840 µl/min/mg). The acids had CL int values in the range <0.1-80 µl/min/mg. In HIMs, only atorvastatin lactone and simvastatin (lactone) exhibited notable metabolism, with CL int values corresponding to 20% of those observed in HLMs. CYP3A4/5 and CYP2C9 were the main statin-metabolizing enzymes. The majority of the acids inhibited HMG-CoA reductase with 50% inhibitory concentrations of 4-20 nM. The present comparison of the metabolism and pharmacodynamics of the various statins using identical methods provides a strong basis for further application, e.g., comparative systems pharmacology modelling.

Multidrug resistance associated protein 2 (MRP2/ABCC2) is a membrane transport protein that can potentially affect the disposition of many substrate drugs and their metabolites. Recently, we studied the interaction of a library of 432 compounds with ABCC2, and the structure-activity relationship (SAR) of a subset of 64 compounds divided into four scaffolds (Wissel, G. et al., 2015. Bioorg Med Chem., 23(13), pp.3513–25). We have now expanded this test set by investigating 114 new compounds, of which 71 are representative of the previous four scaffolds and 43 compounds belong to a new scaffold. Interaction with ABCC2 was assessed by measuring the compounds effect on 5(6)-carboxy-2′,7′-dichlorofluorescein transport in the vesicular transport assay. In line with our previous study, we observed that anionic charge is not essential for inhibition of ABCC2 transport, even though it often increases the inhibitory activity within the analogue series. Additionally, we found that halogen substitutions often increase the inhibitory activity. The results confirm the importance of structural features such as aromaticity and lipophilicity for ABCC2 inhibitory activity.

Biologicals are important ocular drugs that are be delivered using monthly and bimonthly intravitreal injections to treat retinal diseases, such as age-related macular degeneration. Long acting delivery systems are needed for prolongation of their dosing interval. Intravitreal biologicals are eliminated from the eye via the aqueous humor outflow. Thus, the anterior and posterior segments are exposed to the drug. We utilized a kinetic simulation model to estimate protein drug concentrations in the vitreous and aqueous humor after bolus injection and controlled release administration to the vitreous. The simulations predicted accurately the experimental levels of 5 biologicals in the vitreous and aqueous humor. The good match between the simulations and experimental data demonstrated almost complete anterior segment bioavailability, and major dose sparing with ocular controlled release systems. Overall, the model is a useful tool in the design of intraocular delivery of biologicals.