Received: 19 September, 2009. Accepted: 8 June, 2010. Original Research Paper International Journal of Biomedical and Pharmaceutical Sciences ©2010 Global Science Books In Vitro Antioxidant Activity and Polyphenolic Contents of Rauvolfia tetraphylla L., Rhinacanthus nasutus Kurz. and Solena amplexicaulis (Lam.) Vellingiri Maheshu • Jagathala Mahalingam Sasikumar * • Deivamarudhachalam Teepica Priya Darsini • G. Smilin Bell Aseervatham Department of Biotechnology, Karpagam University, Coimbatore 641 021, Tamil Nadu, India Corresponding author: * jmsashikumar@yahoo.co.in ABSTRACT Methanol extracts of the leaves of Rauvolfia tetraphylla L., Rhinacanthus nasutus Kurz. and Solena amplexicaulis (Lam.) were evaluated for their antioxidant activity. The extracts were investigated for total phenolic and flavonoid contents, antihemolytic activity, reducing power capacity and radical scavenging activity towards DPPH and ABTS radicals. The total phenol content was in the range of 25-41.7 mg gallic acid equivalent/g dry weight (DW) of sample and the total flavonoid content varied from 10.2-25.8 mg quercetin equivalent/g of DW sample. The antioxidant activity was expressed as IC 50 values. The IC 50 values of DPPH activity for R. tetraphylla, R. nasutus and S. amplexicaulis extracts were 170, 230 and 190 μg extract/ml, respectively. The IC 50 values of ABTS scavenging (80-120 μg extract/ml) and antihemolytic activity (135-157 μg extract/ml) were calculated. The IC 50 value of reducing power activity for R. tetraphylla extract was 200 μg extract/ml while R. nasutus and S. amplexicaulis extracts at a concentration of 250 μg/ml did not reach 50% of reducing capacity. In the present study, linear regression analysis of antihemolytic, DPPH and reducing power activities with total phenol and flavonoid contents were evaluated and showed a positive correlation (R 2 > 0.735). However, no correlation was found between ABTS activity and polyphenol content. The results confirm that polyphenols in methanol extracts of plants are largely responsible for their antioxidant activities. _____________________________________________________________________________________________________________ Keywords: ABTS + cation scavenging activity, antihemolytic activity, DPPH-RSA, total flavonoid content, total phenolics content INTRODUCTION In living organisms reactive oxygen species (ROS) and reactive nitrogen species (RNS) can form in different ways (Halliwell 1994). ROS and RNS have been implicated in more than 100 diseases, including malaria, acquired im- munodeficiency syndrome, heart disease, stroke, arterioscle- rosis, diabetes and cancer (Duh 1998; Samak et al. 2009). When produced in excess, ROS can cause tissue injury, whilst, tissue injury can itself cause ROS generation (Tepe et al. 2005). Nevertheless, all aerobic organisms, including human beings, have antioxidant defenses that protect against oxidative damage and numerous damage removal and repair enzymes to remove or repair damaged molecules (Sun et al. 1998; Ridha et al. 2007). However, the natural antioxidant mechanisms can be inefficient, hence dietary intake of antioxidant compounds becomes important (Duh 1998; Espin et al. 2000). Recently there has been a surge of interest in the therapeutic potentials of medicinal plants as antioxidants in reducing such free radical induced tissue injury (Pourmorad et al. 2006). Investigations for phenolic compounds in medicinal herbs have gained importance due to their high antioxidative activity and large number of reports has demonstrated that these compounds are of great value in preventing the onset or progression of many human diseases (Chang et al. 2007). Several plants have been in- vestigated in the search for novel antioxidants. Therefore, research into the determination of natural antioxidant poten- tial from medicinal plant is warranted. Medicinal plants which were studied in the present in- vestigation, Rauvolfia tetraphylla L. (Apocyanaceae), Rhi- nacantus nasutus Kurz. (Acanthaceae) and Solena amplexi- caulis (Lam.) Gandhi (Cucurbitaceae). R. nasutus, are widely distributed in South China and India, and have been cultivated for use in the treatment of hepatitis, diabetes, hypertension, cancer (Siripong et al. 2006) skin diseases (Sendl et al. 1996; Wu et al. 1998) and immunomodulatory effect (Punturee et al. 2005). Rhinacanthus plant is well known as the sources of flavonoids, steroids, triterpenoids, anthraquinones, lignans and especially naphthoquinone analoges (Kupradinun et al. 2009). The methanolic extract of aerial parts showed hepatoprotective and free radical sca- venging activities (Suja et al. 2004). Naphthoquinone and rhinacanthone compounds have been reported to possess in vitro antiproliferative activity towards various cancer cells and activity against Dalton’s lymphoma ascitic cells (Thi- rumrugan et al. 1994; Gotoh et al. 2004; Siripong et al. 2006). R. tetraphylla is medicinally important in the treat- ment of cardiovascular diseases, hypertension, psychiatric diseases, cholera and intestinal disorders (Anonymous 1969; Anitha and Ranjithakumari 2006). Leaves and callus extracts of R. tetraphylla are found to possess antimicrobial activity (Shariff et al. 2006) S. amplexicaulis is useful in anorexia, dyspepsia, flatulence, asthma, cardiac disorder, bronchitis, vomiting, hepatosplenomegaly, hemorrhoids, constipation, gonorrhoea and spermatorrhoea (Warrier et al. 1996). A detailed review of the literature afforded no infor- mation on the antioxidant potential of these plants. There- fore, the present study aims to assess the antioxidant acti- vity and to measure crude polyphenolic contents of the aforesaid plants. MATERIALS AND METHODS Chemicals and supplies All chemicals used, including the solvents, were of analytical grade. 1,1-Diphenyl-2-picryl hydrazyl (DPPH), 2, 2’-azinobis-3- ®