| Popis: |
Drug transporters play important role in carrying their substrates accross different barriers, and are an important factor of drug bioavailability. They can act as uptake or efflux transporters. Most efflux transporters belong to the ATP-binding cassette (ABC) superfamily of membrane proteins which may influence the intracellular concentration of numerous compounds in a variety of cells and tissues. They are expressed in the apical membranes of many barrier tissues such as the intestine, liver, blood-brain barrier, kidney, placenta, thus contributing to plasma and cerebrospinal fluid, but also to intracellular drug disposition. Of particular interest for drug dispositions are ABCB1 (for digoxin, HIV protease inhibitors, some antiepileptics, antidepressants, antipsychotics, immunosuppressants ; ABCC2 (anticancer drugs like methotrexate, cisplatin, irinotecan, antibiotics), ABCG2 (anticancer drugs, fluvastatin, cimetidin). Variability in their expression and activity due to genetic polymorphisms can cause treatment failures and adverse drug reactions. The main uptake carrier systems are organic anion transporters (OATP). OATP1B1 (coded by SLCO1B1 gene) is a polymorphic influx transporter expressed on the sinusoidal membrane of human hepatocytes where it mediates the hepatic uptake of different endogenous compounds and xenobiotics. A common SNP c.521T>C in the SLCO1B1 decreases the transporting activity of OATP1B1, resulting in increased plasma concentrations of drug-substrates like statins. This polymorphism enhances the risk of statin- induced myopathy and even of rhabdomyolysis. Some SLCO1B1 variants can also influence the clearence of methotrexate, and increase the risk of gastrointestinal toxicity. Among other drugs recognized as OATP1B1 substrates are mycophenolic acid, sirolimus, valsartan, enalapril, torsemide, rifampin, cephalosporins, HIV protease inhibitors, methotrexate and irinotecan. |
