Cells before and after treatment with the ethyl acetate extracts of P. betle. MCF-7 cells (1 x 106) were treated with the IC50 concentration (65 g/ml) of the ethyl acetate extract of P. betle for 0, 24 and 48 h. Activity of catalase (Figure 3a), superoxide dismutase (Figure 3b) and glutathione peroxidase (Figure 3c) was determined using commercial assay kits. a indicates significant difference from untreated cells (p<0.05).showing the importance of phenolic compounds as antioxidants [25,26]. Our correlation analyses also support this observation. Indeed, the ethyl acetate extract of P. betle had the highest phenolic content, implying that the Beclabuvir biological activity antioxidant activities may have been contributed by the phenolics. We identified the presence of catechin, morin and quercetin through HPLC analyses. These three compounds are well-known antioxidants and could have contributed to the observed antioxidant activities [27]. Previous studies have identified several phenolic compounds in the leaves of P. betle including -sitosterol, PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/27488460 dotriacontanoic acid, tritriacontane, stearic acid, hydroxychavicol, chevibetol and allylpyrocatechol, together with their glucosides [28,29]. Many of these compounds including chevibetol, hydroxychavicol and allylpyrocatechol have antioxidant activities [30,31]. Studies comparing the anti-proliferative effect of extracts of P. betle leaves on breast cancer cells are lacking. In this study, amongst the four solvent extracts, the ethyl acetate extract had the most potent antiproliferative effect on breast cancer cells and this was observed to be more potent than Scutellaria baicalensis [32] and Patrinia scabiosaefolia [33], popular Chinese medicinal herbs that are traditionally used for treating cancer. Furthermore, the ethyl acetate extract also contained the highest phenolic content and antioxidant activities which could contribute towards the protective effects. A study in China reported a positive correlation between the antioxidant activities of several Chinese medicinal herbs and their anti-cancer effects on MCF-7 cells [3]. Hydroxychavicol, a component of P. betle leaf showed anti-proliferative effect towards oral carcinoma cell line [30] and may have the same anti-proliferative effect against MCF-7 cells. Toxicology studies in rats showed no signs of toxicity and hepatotoxicity of P. betle up to a concentration of 1.5 g/kg body weight, implying its safety against normal cells and its specificity in targetting cancer cells [8]. Epidemiology and clinical studies have revealed the involvement of reactive oxygen species (ROS) in carcinogenesis [34,35]. Tumor cells have increased production of ROS, causing oxidative stress and disturbing the redox state, leading to DNA damage, mutations and altered gene expression which contributes to carcinogenesis. At the same time, cancer cells have reduced capacity to remove ROS due to altered antioxidant defense systems. However, ROS also play important roles in inducing apoptosis, implying an anti-cancer effect. Hence finding the right balance between ROS and antioxidant defense levels in cancer cells is important to ensure that cancer progression can be inhibited while at the same time maintaining apoptosis. For this reason, we investigated the effect of the ethyl acetate extract on antioxidant enzyme levels in MCF-7-Glutathione peroxidase (nmol/min/ml)Catalase (nmol/min/ml)Abrahim et al. BMC Complementary and Alternative Medicine 2012, 12:220 http://www.biomedcentral.com/1472-6882/.