Xenobiotic transporter expression and function in the human mammary gland.

Xenobiotic transport in the mammary gland has tremendous clinical, toxicological and nutritional implications. Mechanisms such as passive diffusion, carrier-mediated transport, and transcytosis mediate xenobiotic transfer into milk. In vivo animal and human studies suggest the functional expression of both xenobiotic and nutrient transporters in the lactating mammary gland and the potential involvement of such systems in the significant accumulation of certain compounds in milk. In vitro cell culture systems provide further evidence for carrier-mediated transport across the lactating mammary epithelium. Additionally, molecular characterization studies indicate the expression of various members of the organic cation transporter, organic anion transporter, organic anion polypeptide transporter, oligopeptide transporter, nucleoside and nucleobase transporter, multidrug resistant transporter, and multidrug resistant-like protein transporter families at the lactating mammary epithelium. The in vivo relevance of the expression of such xenobiotic and nutrient transporters and their involvement in drug disposition at the mammary gland requires investigation.