Modulation of P-Glycoprotein mediated efflux by Nigerian plant extracts used in the management of diabetes

The use of herbal medicines alongside conventional drugs for the therapeutic management of diseases is common practice particularly in chronic conditions. A recent field study carried out in Nigeria showed that more than 50% of diabetic patients co-administer herbal preparations with their prescription medicines, thereby raising the risks of herb-drug interactions.

Thirty medicinal plants traditionally used for the management of diabetes in different areas of Nigeria were collected during the field work for in-vitro pharmacokinetic investigations to identify potential herb-drug interactions. The ability of these plants to modulate the effect of the intestinal efflux transporter P-glycoprotein (P-gp) was determined in Caco-2 cells using the fluorescent P-gp substrate, rhodamine-123.

At concentrations ≤100µg/ml, aqueous extracts of Annona senegalensis, Bridelia ferruginea and Khaya senegalensis significantly inhibited the efflux of accumulated rhodamine-123 from the cells. The inhibition was either comparable or much higher than that produced by 20µM verapamil, a known P-gp inhibitor. Aqueous extracts of Syzygium guineense and Isoberlinia doka on the other hand enhanced the efflux of rhodamine-123 from the cells.

These results suggest the possibility of interactions when these extracts are co-administered with prescription medicines which are also P-gp substrates such as glibenclamide.