Transport of Amentoflavone Across the Blood-Brain Barrier in vitro

Abstract

The biflavone amentoflavone is an ingredient of Hypericum perforatum L. (Clusiaceae), a plant which is widely used for the treatment of mild to moderate depression. Amentoflavone inhibits the binding of flumazenil to the benzodiazepine binding site of the GABA_A-receptor (IC₅₀ = 14.9 nM). Since it has to pass the blood-brain barrier (BBB) before reaching this receptor, the penetration of [³ H]-amentoflavone through BBB was studied in an in vitro model consisting of primary cell cultures of porcine brain capillary endothelial cells (BCEC). Concentration-dependent uptake (37 - 2000 nM) was neither saturable nor temperature-sensitive indicating passive diffusion as the major uptake mechanism. This finding was confirmed by transport experiments through BCEC monolayers (> 2 % of applied dose was transported after 30 min). Co-administration of Hypericum extract increased amentoflavone transport significantly (amentoflavone alone: permeability coefficient P_app = 4.59·10^-6 cm/s; co-administrated sucrose: P_app = 3.22·10^-6 cm/s; amentoflavone together with hypericum: P_app = 6.74·10^-6 cm/s, co-administrated sucrose P_app = 5.49·10^-6 cm/s) indicating that Hypericum constituents enhance amentoflavone transport possibly by modulating paracellular permeability. Experiments with the P-glycoprotein (P-gp) overexpressing cell line P388-MDR showed that amentoflavone uptake was significantly enhanced by addition of the P-gp inhibitor verapamil, suggesting a P-gp mediated back-transport out of the cells. In conclusion, our findings show, that amentoflavone is able to pass the blood-brain barrier in vitro by passive diffusion.

Amentoflavone - blood-brain barrier - Hypericum perforatum - Clusiaceae -  transport - P-glycoprotein

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