The ABCG2 Transporter Affects Plasma Levels, Tissue Distribution and Milk Secretion of Lumichrome, a Natural Derivative of Riboflavin

The ABCG2 membrane transporter affects bioavailability and milk secretion of xenobiotics and natural compounds, including vitamins such as riboflavin. We aimed to characterize the in vitro and in vivo interaction of ABCG2 with lumichrome, the main photodegradation product of riboflavin, which has proven in vitro anti-cancer activity and a therapeutical role in antibacterial photodynamic therapy as an efficient photosensitizer. Using MDCK-II polarized cells overexpressing murine Abcg2 and human ABCG2 we found that lumichrome was efficiently transported by both variants. After lumichrome administration to wild-type and Abcg2^-/- mice, plasma AUC_{20-120 min} was 1.8-fold higher in Abcg2^-/- mice compared with wild-type mice. The liver and testis from Abcg2^-/- mice showed significantly higher lumichrome levels compared with wild-type, whereas lumichrome accumulation in small intestine content of wild-type mice was 2.7-fold higher than in Abcg2^-/- counterparts. Finally, a 4.1-fold-higher lumichrome accumulation in milk of wild-type versus Abcg2^-/- mice was found. Globally, our results show that ABCG2 plays a crucial role in plasma levels, tissue distribution and milk secretion of lumichrome potentially conditioning its biological activity.