OBJECTIVES:Various pharmacological effects including antioxidant property of Portulaca oleracea L. were reported previously. In the present study, the effect of the extract of the plant and its constituent, α-linolenic acid (ALA), on oxidant and antioxidant markers of PHA/non-stimulated human mononuclear cells was evaluated.MATERIALS AND METHODS:The effect of 10, 40, and 160 μg/ml of P. oleracea and 5, 15, and 45 μg/ml of ALA or dexamethasone (0.1 mM) on nitric oxide (NO), malondialdehyde (MDA), total thiol (SH), superoxide dismutase (SOD), and catalase (CAT) in the supernatant of phytohemagglutinin-A (PHA)- and nonstimulated lymphocytes was examined (n = 6 for each group).RESULTS:In nonstimulated cells, dexamethasone, high concentration of the extract (160 μg/ml), and ALA (45 μg/ml) significantly increased thiol, CAT, and SOD values. Dexamethasone and high concentration of ALA significantly reduced MDA value (P < 0.01 to P < 0.001). However, the levels of NO and MDA due to dexamethasone and 160 μg/ml of the extract and 15 and 45 μg/ml of ALA treatment were also reduced in PHA-stimulated cells (P < 0.001 for all cases). Treatment of stimulated lymphocyte by dexamethasone and two higher concentrations of the extract and ALA also leads to increased levels of thiol, CAT, and SOD (P < 0.05 to P < 0.001).CONCLUSIONS:P. oleracea and ALA, as well as dexamethasone, decreased NO and MDA levels but increased antioxidant agents in human lymphocytes. These results suggest that P. oleracea and ALA may have therapeutic effect in diseases associated with enhancement of oxidation agents as an antioxidant agent.