Transport Mechanisms Of Several Chiral Drugs And Rutin Deca (H-) Sulfonate Sodium In Caco-2 Cell Model

Absorption from the gastrointestinal tract is the first step governing the entry of a drug into the circulation and, eventually, its tissue distribution. Caco-2 cell monolayers have been widely accepted as an in vitro model system to evaluate the intestinal drug absorption and transport mechanism. Using this model system, we studied the transport characteristics of several chiral drugs and determined a drug candidate's absorption potential as follows. All these studies might help us to understand the stereoselective transport of chiral drugs, elucidate drug-transporter interaction and design drugs with favorable bioavailability.1. Stereoselective and multiple carrier-mediated transport of cetirizine across Caco-2 cell monolayers with potential drug interactionThe study was designed to explore potential transport mechanisms of cetirizine enantiomers across Caco-2 cell monolayers. In the concentration range studied (4.0 ~ 80.0 μmol/L), cetirizine displayed polarized transport with the permeability in the secretory direction being 1.4- to 7.2-fold higher than that in the absorptive direction. The transport kinetic parameters indicated that multiple efflux transporters participated in the transport process and R-cetirizine and S-cetirizine were transported distinctively different from each other. In the presence of inhibitors of P-glycoprotein (P-gp) and multi drug resistance-associated protein (MRP), the absorptive transport was enhanced and secretory efflux was diminished. When verapamil, indomethacin and probenecid were present, the difference in the absorptive permeability of R- and S-cetirizine substantially intensified, whereas MK-571, the specific MRP1/2 inhibitor eliminated the difference completely. Furthermore, the transport characteristics of cetirizine enantiomers were altered in the presence of P-gp substrate ranitidine, In conclusion, the results indicated that there were several efflux transporters including P-gp and MRP participating the absorption and efflux of cetirizine, which showed enantioselectivity in the transmembrane process. In addition, cetirizine-druginteractions mediated by transporters could modify the absorption and the systemic toxicity of this commonly used HI antagonist.2. Stereoselective modulation of ABC transporters by cetirizine enantiomers in Caco-2 cellsSince ABC transporters play an important role in pharmacokinetics such as drug absorption and excretion processes, the study aimed to investigate factors regulating their function and expression. Using Caco-2 cells, which are widely utilized as a model of intestinal epithelial cells, the effects of cetirizine enantiomers on transporters (P-gp, MRPl, MRP2 and MRP3) were examined by assessing the growth inhibition by paclitaxel, the transport characteristics of the P-gp substrate Rhodamine-123 and MRP substrate doxorubicin, and the expression level of mRNA and protein, respectively. Caco-2 cells pretreated with R-cetirizine (100.0 μmol/L, 200.0 μmol/L) reduced its sensitivity to paclitaxel, enhanced the efflux of substrates, and up-regulated the mRNA levels and P-gp expression. Meanwhile, S-cetirizine enhanced Caco-2's sensitivity to paclitaxel, weakened substrates' polarized transport, and down-regulated the mRNA levels and P-gp expression. These results suggested that cetirizine regulated ABC transporters in an enantioselective manner. R-cetirizine played as an inducer of P-gp and MRPs while S-cetirizine acted as an inhibitor of these transporters.3. Determination of the stereoselectivity of chiral drugs transport across caco-2 cell monolayersChoosing eight beta-adrenergic blockers (atenolol, sotalol, celiprolol, carvedilol, esmolol, metoprolol, propranolol and propafenone) as model drugs, the study focused on the transepithelial transport of chrial drug enantiomers in Caco-2 cell model system. The separation and quantitation of enantiomers were performed by RP-HPLC with the use of GITC as a pre-column derivatizing agent. Bi-directional transport studies demonstrated that there was a correlation between drug's lipophilicity and its permeability. Enantioselectivity was observed in the transport of esmolol, which hassomething to do with its hydrolysis by esterases in Caco-2 cell monlayers. Furthermore, the polarized transport of celiprolol and carvedilol showed significant enantioselectivity. By developing the comparative model of P-gp, we inferred that P-gp might participate in the transport of celiprolol and carvedilol in a chirally discriminative way.4. Transport characteristics of rutin deca (H-) sulfonate sodium across Caco-2 cell monolayersCaco-2 cells were utilized to evaluate the transepithelial transport characteristics of rutin deca (H-) sulfonate sodium (RDS), a drug candidate against HIV. Bi-directional transport study of RDS demonstrated the apparent permeability (Papp) in the secretory direction was 1.4 ~ 4.5-fold greater than the corresponding absorptive Papp at concentrations ranging from 50.0 ~ 2000 μmol/L. The transport of RDS was shown to be concentration-, temperature-, and pH-dependent. In the presence of cyclosporin A (CsA) and verapamil, potent inhibitors of P-gp/MRP, the absorptive transport was enhanced and secretory efflux was diminished. RDS significantly reduced the efflux ratio of the P-gp substrate rhodamine-123 in a fashion indicative of P-gp activity suppression, while rhodamine-123 competitively inhibited the polarized transport of the compound. In conclusion, the results indicated that RDS was likely a substrate of P-gp. Several efflux transporters including P-gp participated in the absorption and efflux of RDS and they might play significant roles in limiting the oral absorption of this hydrophilic macromolecular compound. These observations offered important information for the pharmacokinetics of RDS.