ABSTRACT
Indian systems of medicine such as ayurveda, siddha, and unani have been practiced for several centuries for the prevention and therapy of chronic diseases. A number of medicinal plants have been identified for this purpose with different therapeutic properties. We have chosen three medicinal plants known for their various therapeutic effects and studied their antioxidant abilities at different levels as a possible mechanism to explain the reported therapeutic properties. The plants used in our studies and their respective effects are: Terminalia arjuna
(arjun) for cardioprotection, Plumbago zeylanica
(chitrak) for neuroprotection, and Pleurotus roseus
(a medicinal mushroom) for anticancer properties. The antioxidant effects of the preparations used for therapeutic applications as well as the active ingredients (wherever possible) were examined at different levels using studies on radical formation, radical scavenging, and inhibition of membrane damage. Mechanisms of protection were also studied by pulse radiolysis of active components. The results obtained showed that aqueous and ethanolic extracts of P. zeylanica
have high activities in FRAP (ferric reducing antioxidant power), DPPH (1,1
′
-diphenyl-2-picrylhydrazyl), and ABTS (2,2
′
-azinobis-3-ethylbenzthiazoline-6-sulfonic acid) assays. The ethanolic extract of P. roseus
has high activities in DPPH and ABTS assays. The various extracts of T. arjuna
showed moderate antioxidant activities in these assays. The studies on the inhibitory effect on lipid peroxidation induced by radiation, peroxynitrite, ascorbate-Fe
, and AAPH [2,2
′
-azobis (amidinopropane) dihydrochloride] in rat liver mitochondria, brain mitochondria, or cardiac homogenate also revealed significant protective abilities. Extracts of T. arjuna
were effective against peroxidation induced by AAPH and radiation, and the extracts of P. zeylanica
were protective against damage induced by ascorbate-Fe
. When we examined the antioxidant effects of baicalein from T. arjuna
and plumbagin from P. zeylanica
in different model systems, they proved to be very potent antioxidants. Their reaction with biologically relevant radicals was also examined by the special technique of pulse radiolysis. Plumbagin was more reactive towards thiyl radicals, whereas baicalein was more effective against hydroxyl radical. They were also effective against peroxyl radicals derived from different sources. The results obtained showed that the various extracts and active ingredients from these medicinal plants have significant antioxidant effects up to varying degrees in the relevant model systems at different levels of protection. These antioxidant abilities may at least in part explain the reported therapeutic effects of these medicinal plants.
