Fetal polymorphisms at the ABCB1-transporter gene locus are associated with susceptibility to non-syndromic oral cleft malformations

ATP-binding cassette (ABC) proteins in the placenta regulate fetal exposure to xenobiotics. We hypothesized that functional polymorphisms in ABC genes influence risk for non-syndromic oral clefts (NSOC). Both family-based and case–control studies were undertaken to evaluate the association of nine potentially functional single-nucleotide polymorphisms within four ABC genes with risk of NSOC. Peripheral blood DNA from a total of 150 NSOC case-parent trios from Singapore and Taiwan were genotyped, as was cord blood DNA from 189 normal Chinese neonates used as controls. In trios, significant association was observed between the ABCB1 single-nucleotide polymorphisms and NSOC (P<0.05). Only ABCB1 rs1128503 retained significant association after Bonferroni correction (odds ratio (OR)=2.04; 95% confidence interval (CI)=1.42–2.98), while rs2032582 and rs1045642 showed nominal significance. Association with rs1128503 was replicated in a case–control analysis comparing NSOC probands with controls (OR=1.58; 95% CI=1.12–2.23). A comparison between the mothers of probands and controls showed no evidence of association, suggesting NSOC risk is determined by fetal and not maternal ABCB1 genotype. The two studies produced a combined OR of 1.79 (95% CI=1.38–2.30). The T-allele at rs1128503 was associated with higher risk. This study thus provides evidence that potentially functional polymorphisms in fetal ABCB1 modulate risk for NSOC, presumably through suboptimal exclusion of xenobiotics at the fetal–maternal interface

The H2 Receptor Antagonist Nizatidine is a P-Glycoprotein Substrate: Characterization of its Intestinal Epithelial Cell Efflux Transport

The aim of this study was to elucidate the intestinal epithelial cell efflux transport processes that are involved in the intestinal transport of the H2 receptor antagonist nizatidine. The intestinal epithelial efflux transport mechanisms of nizatidine were investigated and characterized across Caco-2 cell monolayers, in the concentration range 0.05–10 mM in both apical–basolateral (AP–BL) and BL–AP directions, and the transport constants of P-glycoprotein (P-gp) efflux activity were calculated. The concentration-dependent effects of various P-gp (verapamil, quinidine, erythromycin, ketoconazole, and cyclosporine A), multidrug resistant-associated protein 2 (MRP2; MK-571, probenecid, indomethacin, and p-aminohipuric acid), and breast cancer resistance protein (BCRP; Fumitremorgin C) inhibitors on nizatidine bidirectional transport were examined. Nizatidine exhibited 7.7-fold higher BL–AP than AP–BL Caco-2 permeability, indicative of net mucosal secretion. All P-gp inhibitors investigated displayed concentration-dependent inhibition on nizatidine secretion in both directions. The IC50 of verapamil on nizatidine P-gp secretion was 1.2 × 10−2 mM. In the absence of inhibitors, nizatidine displayed concentration-dependent secretion, with one saturable (Jmax = 5.7 × 10−3 nmol∙cm−2∙s−1 and Km = 2.2 mM) and one nonsaturable component (Kd = 7 × 10−4 μL∙cm−2∙s−1). Under complete P-gp inhibition, nizatidine exhibited linear secretory flux, with a slope similar to the nonsaturable component. Vmax and Km estimated for nizatidine P-gp-mediated secretion were 4 × 10−3 nmol∙cm−2∙s−1 and 1.2 mM, respectively. No effect was obtained with the MRP2 or the BCRP inhibitors. Being a drug commonly used in pediatrics, adults, and elderly, nizatidine susceptibility to efflux transport by P-gp revealed in this paper may be of significance in its absorption, distribution, and clearance, as well as possible drug–drug interactions