Journal of Medicinal Plants Research Vol. 5(26), pp. 6182-6191, 16 November, 2011 Available online at http://www.academicjournals.org/JMPR ISSN 1996-0875 ©2011 Academic Journals DOI: 10.5897/JMPR11.1114 Full Length Research Paper Effects of selected medicinal plants on human low-density lipoprotein oxidation, 2, 2-diphenyl-1- picrylhydrazyl (DPPH) radicals and human platelet aggregation Fadlina Chany Saputri and Ibrahim Jantan* Drug and Herbal Research Center, Faculty of Pharmacy, Universiti Kebangsaan Malaysia, Jalan Raja Muda Abdul Aziz, 50300 Kuala Lumpur, Malaysia. Accepted 4 October, 2011 The effects of the methanol extracts of 20 selected medicinal plants on free radical scavenging capacity, human low-density lipoprotein (LDL) peroxidation and platelet aggregation were investigated. The antioxidant activity was evaluated using 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging capacity and thiobarbituric acid reactive substances (TBARS) assay with LDL as the oxidation substrate. The antiplatelet activity in human whole blood was investigated using an electrical impedance method. The total phenolic contents (TPC) of the extracts were determined by the Folin- Ciocalteau method. Among the extracts, Phyllanthus amarus and Labisia pumila var. alata possessed potent radical scavenging activity with IC 50 values of 3.4 and 5.7 μg/ml, respectively. The extracts of Zingiber officinale, Curcuma xanthorrhiza and Curcuma domestica showed strong inhibition of LDL peroxidation with IC 50 values ranging from 0.1 to 0.9 μg/ml. The extract of Z. officinale was the most effective sample against platelet aggregation caused by arachidonic acid (AA) and adenosine diphosphate (ADP) with IC 50 values of 10.9 and 7.7 μg/ml, respectively. The Pearson correlation analysis indicated that the TPC of the extracts showed significant positive correlations with DPPH scavenging activity (r = 0.846) and LDL antioxidant activity (r = 0.639) and moderate positive correlations with antiplatelet activities (AA-induced, r = 0.51; ADP-induced, r = 0.40; collagen-induced, r = 0.44). The antioxidant and antiplatelet activities of the plant extracts could partly be due to their TPC. Key words: Medicinal plants, LDL antioxidant activity, antiplatelet activity, DPPH scavenging capacity, total phenolic contents. INTRODUCTION Oxidation of LDL by chain-propagating free radicals has been considered as playing an important role in the initiation and progression of early stage of atherosclerosis and the development of cardiovascular diseases. It is likely that oxidative modifications of LDL involve lipid peroxidation and the modification of apolipoprotein B- 100, followed by macrophage uptake and cell accumulation of cholesterol to generate foam cells, causing early atherosclerotic lesions (Heinecke, 2006). *Corresponding author. E-mail: ibj@pharmacy.ukm.my. Tel: +603 92897315. Fax: +603 26983271 Reduction of LDL oxidation may be one of the most important therapeutic approaches to prevent the development of atherosclerosis. Many antioxidants have been developed to delay or inhibit the oxidation of the biomolecules by terminating the initiation or propagation of the oxidizing chain reactions by free radicals and inhibiting the foam cell formation (Faure et al., 2004). Platelets have also been implicated in the pathogenesis of artherothrombotic conditions and play a key role in acute arterial thrombosis. Platelet aggregation is induced by the action of endogenous agonists such as AA, ADP, platelet activating factor (PAF), thrombin and collagen (Gibbins, 2004). Many epidemiological and biological studies showed that plant-derived polyphenolics are