PHARMACOLOGICAL OVERVIEW OF PROANTHOCYANIDINS FROM THE BARK OF THESPESIA POPULNEA (L.) AS AN ANTIOXIDANT AND CYTOTOXIC AGENT

摘要

The preliminary phytochemical analysis of the aqueous ethanolic extract of the bark of Thespesia populnea (L.) revealed the presence of alkaloids, unsaturated sterols, triterpenes, flavonoids and the absence of anthraquinones. The froth test indicated the presence of saponins. Most importantly this study revealed the presence of proanthocyanidins which has not been reported before. In the present study, ethyl acetate and aqueous soluble proanthocyanidin fractions (EASPA and AQSPA respectively) were extracted and purified by chromatography on Sephadex LH-20. Prussian blue test and acid catalyzed cleavage test revealed that proanthocyanidins have been successfully separated from non-proanthocyanidin phenolics. The yields of purified EASPA and AQSPA fractions were 0.081% and 0.72% (by weight) of the fresh bark. Acid catalyzed cleavage followed by TLC studies of both EASPA and AQSPA fractions showed the presence of two anthocyanidins, cyanidin and delphinidin, suggesting that they are composed of (epi)catechin and (epi)gallocatechin units with (epi)catechin being more abundant compared to the other. This was further confirmed by 13C NMR spectroscopic studies. In addition, 13C NMR spectroscopic studies revealed (epi)catechin to be the epi-isomer. The preliminary antioxidant activity of purified EASPA and AQSPA fractions was determined using the DPPH assay. The IC₅₀ values of EASPA and AQSPA (0.0725 mg/mL and 0.0781 mg/mL respectively) were clearly lower than that of ascorbic acid (0.125 mg/mL), which is an established standard used in antioxidant studies. Thus, proanthocyanidin samples appear to possess better antioxidant capacity than ascorbic acid. In addition, EASPA and AQSPA fractions were shown to mediate cytotoxic activity against MCF 7 cells through SRB assay.