Abstract
BACKGROUND: Link Samahan® (LS), a product of Link Natural Products (Pvt) Limited, Sri Lanka contains extracts of 14 medicinal plants. It is used as a prophylactic against cold and cold related symptoms. It has immunomodulatory activity, specifically enhancing the humoral immune response. OBJECTIVE: To investigate the anti-inflammatory activity (AIA) of LS and related mechanisms. MATERIALS AND METHODS: In vivo AIA was assessed by the inhibition of carrageenan-induced rat paw-edema. Mechanisms of AIA were assessed in vitro by the inhibition of reactive oxygen species (ROS) and reactive nitrogen species (RNS) production and expression of inducible nitric oxide synthase (iNOS) gene using rat peritoneal cells. RESULTS: LS showed an increasing inhibition in rat paw-edema up to 5 h compared to the biphasic pattern exhibited by the reference drug, Indomethacin. Inhibition by LS at the 1(st) and 3(rd)-5(th) hours (44.7% and 73.0-74.6%) was comparable to indomethacin (47.4% and 83.6-76.5%; p > 0.05) whereas at the 2(nd) hour, LS exhibited a significantly higher inhibition compared to indomethacin (66.7% vs 28.6%; p < 0.05). LS treatment significantly inhibited the ROS (superoxide; 47.2 ± 0.86%; p < 0.05) and RNS (nitrite; 54.0 ± 0.40%; p < 0.05) production in rat peritoneal cells. Further, specific inhibition of iNOS gene expression in rat peritoneal cells resulted in a significant reduction in RNS production whereas LS had lesser or no inhibitory effect on endothelial NOS and neuronal NOS gene expression. CONCLUSION: LS has potent anti-inflammatory activity and selective inhibition of iNOS activity. AIA of LS shown here supports its use as a prophylactic against cold and cold related symptoms.