Studies on bioconverted phytopharmaceuticals of Cardiospermum halicacabum

Abstract

Balloon vine (Cardiospermum halicacabum) of sapindaceae family is extensively used in ayurvedic system of medicine for inflammatory diseases. Previous studies had shown that the extracts of this plant exhibit anti inflammatory activity. They reduce the activity of PLA2 involved in the inflammatory process. The active constituent in this plant responsible for PLA2 inhibition was not known till date. The present study which involved soaking of PLA2 crystals in the aqueous extract and subsequent X-ray diffraction indicated the compound binding to the active site to be berberine, an alkaloid. Subsequent binding studies with berberine purified from Cardiospermum halicacabum and PLA2 by Surface Plasmon Resonance proved that the equilibrium dissociation constant or KD which is inversely proportional to binding strength is of the order of 10-8 M, implies a very strong binding affinity between these two molecules. Berberine was biotransformed by a fungus Rhizopus oryzae and the products formed were found to be hydroxy derivatives of berberine formed by the demethylation of methoxy groups present in berberine. Molecular docking, enzyme kinetic studies and Surface Plasmon Resonance studies proved that the derivatives of berberine formed had higher PLA2 inhibitory activity than native berberine. It was proved experimentally by X-ray crystallography that biotransformed berberine namely dihydroxyberberine was bound to PLA2 in a longitudinally inverted manner with respect to the binding of native berberine. New interactions formed between the two molecules, as a result of this inverted binding, enhanced the PLA2 inhibitory activity of the derivative with respect to the native berberine molecule.