Free-radical scavenging activities of Himalayan rhododendrons

Reactive oxygen species can damage cellular biomolecules leading to degenerative diseases. Phenols, a major group of phytochemicals with antioxidant properties, can help inactivate them. To find the antioxidant potential of the genus Rhododendron, its 21 species were studied for their total phenolic content (TPC), flavonoids and antioxidant activity (AOA). TPC varied from 37.3 to 208.9 mg/g, flavonoids from 11.5 to 137.1 mg/g and AOA from 30.4 to 97.4%. R. baileyii, R. camellieflorum, R. campanulatum, R. cilliatum, R. cinnabarinum, R. griffithianum, R. lepidotum, R. niveum, R. sallignum and R. virgatum were found to have high TPC (91.4-208.9 mg/g), AOA (71.5-97.4%) and free radical scavenging activity, as evident from their low IC₅₀ (inhibitory concentration, 0.07-0.19 mg/ml), low EC₅₀ (efficiency concentration, 3.28-8.26 mg/mg), and high ARP (antiradical power, 12.10-30.48), compared to reference standard. R. griffithianum, R. lepidotum and R. virgatum showed better ferrous-ion chelating capacity and inhibition of lipid peroxidation than that of standards, BHT and quercetin. They also showed better reducing power and inhibition of both site-specific and non site-specific hydroxyl radicals-induced deoxyribose degradation than those of other species. R. camellieflorum, R. campanulatum, R. griffithianum, R. lepidotum and R. virgatum were potential scavengers of superoxide anions and also showed significant protection of DNA damage induced by free radicals. Promising species were also subjected to HPLC and MS/MS, which showed the presence of phenolic acids (gallic, caffeic, chlorogenic, ellagic and protocatechuic acids) and flavonoids (quercetin, kaempferol and rutin).