Resveratrol isomeric switching during bioreduction of gold nanoparticles: a gateway for cis-resveratrol

Resveratrol, a polyphenolic and biocompatible molecule, exhibits significant pharmacological effects but has poor bioavailability and metabolic stability. It appears in two isomeric forms trans-(E)-resveratrol (tRes) and cis-(Z)-resveratrol (cRes). Many pharmacological activities studied so far are of tRes and is the most stable, predominant, and natural form. cRes is not commercially available due to difficulty in its purification and hence not explored much for its biological activities. Therefore, our study focuses on investigating the stability and therapeutic potential of cRes through its bio-conjugation to nanomaterial. In this study, tRes reduces gold ions to gold nanoparticles (GNPs) and itself gets oxidized to its isomeric form cRes. The isomeric switching was evidenced through cRes characteristic spectral differences and chromatographic elution pattern. The monodispersed GNPs of 25.6 ± 0.4 nm size was formed having zeta potential of -19 ± 3.82 mV confirming it to be a stable formulation. The stability studies were further extended to be tested under different physiological fluids. The cRes loaded GNPs (cRGNPs) reflecting the biological activity of cRes presented equivalent antioxidant property to that of tRes even at low concentrations. Also, cRGNPs showed the hemocompatibility by presenting no hemotoxicity and simultaneous in vitro anti-hemolytic activity. Therefore, the stability provided to cRes upon conjugating to GNPs can further be exploited to study the biological activities of cRes through its nano-conjugated delivery.