ANTIOXIDANT AND CARDIOPROTECTIVE PROPERTIES OF LEAF EXTRACTS OF MISTLETOES (GLOBIMETULA CUPULATA (DC) van Tiegh) FROM COCOA AND KOLANUT TREES

Abstract

In this study, leaf extracts of African mistletoes (Globimetula cupulata) growing on cocoa and kolanut trees [traditionally used as diuretics and antihypertensive agent] were assessed for their phytochemical constituents, in-vitro antioxidant activities and antioxidant effects on ischemia-induced oxidative damage to the heart. Crude extracts and fractions of cocoa and kolanut mistletoes were evaluated for total polyphenols, flavonoids, flavonols, proanthocyanidins as well as total antioxidant and nitric oxide scavenging activities. The hearts of male Wistar albino rat [n = 12, body mass 120 – 150g] were perfused according to the Langendorff’s technique. One ml of graded concentrations (1, 3, 5, 10, 30, and 50μg/ml) of crude extracts of cocoa or kolanut mistletoes were successively administered and effects of the extracts on heart rate and force of contraction were evaluated. Another 24 hearts divided into 4 groups of 6 hearts per group were used for biochemical assay. In group 1 (control), no ischaemia was induced; hearts were simply perfused. In group 2, ischaemia was induced for 20 mins while hearts reperfused for 50mins. In groups 3 and 4, ischaemia was induced and heart reperfused for 50 mins; during reperfusion, 1 ml of 3 μg/ml of cocoa or kolanut mistletoe extract was administered. Effluents were collected in all the four groups for 50 mins and the following biochemical parameters were evaluated from the effluents: flow rate, nitrite level, activities of superoxide dismutase (SOD) and Catalase (CAT), Malondialdehyde (MDA) levels, and total protein. The results of the findings showed presence of flavonoids, flavonols and proanthocyanidins in the extracts and fractions. The samples extracts and fractions exhibited antioxidant activities. The extracts of cocoa and kolanut mistletoes lowered the force of contraction, heart rate and flow rate. The addition of 50 μg/ml of cocoa or kolanut mistletoes collapsed the hearts. The nitrite levels and flow rates were significantly higher (P <0.005) in treated groups compared with non-treated ischaemic group. Higher catalase activity was observed in group treated with kolanut mistletoe extract compared with non-treated ischaemic group. SOD activity was significantly higher (P < 0.005) in control and treated groups compared with non-treated ischaemic group. Higher levels of MDA were observed in non-treated ischaemic group compared with control and treated groups. Negative chronotropic and inotropic effects produced by the extracts supported the use of the plants as antihypertensive agents. Effects of the extracts on the catalase and superoxide dismutase activities during reperfusion suggested that they may be protecting the heart antioxidant activities. The effects on nitrite level and flow rate might be an evidence of anti-ischaemia activity. The results of this study suggest that the phytochemicals in the plant might be responsible for their antioxidant and cardioprotective activities.