Interaction of sanguinarine and its dihydroderivative with the Na+/K+-ATPase. Complex view on the old problem

The effects of sanguinarine (SG) and its metabolite dihydrosanguinarine (DHSG) on Na+/K+-ATPase were investigated using fluorescence spectroscopy. The results showed that the enzyme in E1 conformation can bind both charged and neutral (pseudobase) forms of SG with a KD = 7.2 ± 2.0 μM or 11.7 ± 0.9 μM, while the enzyme in E2 conformation binds only the charged form of SG with a KD = 4.7 ± 1.1 μM. Fluorescence quenching experiments suggest that the binding site in E1 conformation is located on the surface of the enzyme for both forms but the binding site in E2 conformation is protected from the solvent. We found no evidence for interaction of Na+/K+-ATPase and DHSG. This implies that any in vivo effect of SG attributable to inhibition of Na+/K+-ATPase can be considered only prior to SG → DHSG transformation in the gastro-intestinal tract and/or blood. Hence, Na+/K+-ATPase inhibition will be effective in SG topical application but its duration will be very limited in SG oral or parenteral administration.