Table 2 shows the NO radical-scavenging activities of the plant extracts. The EC50 values were higher compared to the DPPH – and O2–scavenging values, indicating that higher concentrations of the plant extracts were needed to inhibit the NO radicals. The NO -scavenging activities of the plant extracts did not follow the same pattern as the previous antioxidant assays. Among all the extracts, four extracts exhibited strong NO
-scavenging activities, with EC50 values below 350 μg/ml. The extracts were ethanol leaf (Kedah) (EC50: 213 μg/ml) > ethyl acetate leaf (Kelantan) (EC50: 222 μg/ml) > ethyl BAY 73-4506 price acetate leaf (Kedah) (EC50: 308 μg/ml) > water leaf (Kelantan) (EC50: 329 μg/ml). The activities of these extracts were higher than those of common plants, including various parts of red maple (Acer rubrum) extracts (EC50: 0.4–1.5 mg/ml) ( Royer, Diouf, & Stevanovic, 2011) selleck chemical and the leaves of Symplocos cochinchinensis (EC50: 0.87 mg/ml) ( Sunil & Ignacimuthu, 2011). The NO radical-scavenging activities of the plant extracts also followed a concentration-dependent pattern (Fig. 3a–d). The inhibition
reactions were especially rapid at lower concentrations (<100 μg/ml), slowing down considerably at higher concentrations (>400 μg/ml). The sequence of potency of the extracts differed slightly from those in the other antioxidant assays. In this assay, the ethanol and ethyl acetate extracts of the leaves had high NO -scavenging activities whereas the water extracts, which had high ferric reducing, DPPH, ABTS and O2–radical-scavenging activities were less reactive. Activities of the four most active extracts listed above were lower than those of rutin
(EC50: 194 μg/ml) but higher than those of gallic acid (EC50: 393 μg/ml) and BHT (EC50: 860 μg/ml), implying their potencies. Generally, the leaf extracts from both Kedah and Kelantan had better NO radical-scavenging activities than had the stem extracts. Unlike previous antioxidant assays, the inhibitory activities of the extracts on the NO radicals, in most cases, did not show a levelling off with increasing concentration, indicating that inhibition was still occurring, although at a much reduced rate. Ascorbic FAD acid, however, showed initial inhibition of the NO radicals (26%), up to a concentration of 125 μg/ml, after which negative activity was observed at higher concentrations, suggesting a pro-oxidant effect. Although nitrite ( NO2-) is the final product in this assay, nitrate ( NO3-) may also be generated (Magalhães, Segundo, Reis, & Lima, 2008) which may react with ascorbic acid to form nitrous acid which can subsequently transform to nitric oxide, leading to reduced inhibition of the NO radicals. Pearson correlation analyses were done to predict the relationship between the antioxidant compounds and antioxidant activities (Table 3).