Effects of Russell's viper venom on mediator production in cultured human umbilical vein endothelial cells

Abstract

Hemodynamic alterations in Russell's viper envenomation are the result of interactions of various vasoactive mediators and perhaps proinflammatory cytokines. Since vascular endothelium is likely to be exposed to high concentrations of the venom and the endothelial cell itself not only plays an important role in the physiologic control of the circulation, but also play a role in inflammation with the synthesis and secretion of proinflammatory cytokines. It was therefore, the objective of this study to determine the effects of Russell's viper venom (RVV) on proinflammatory cytokine production by cultured human umbilical vein endothelial cells (HUVEC) and the release of endothelium-derived substances. Endothelial cells were isolated from freshly obtained human umbilical cord vein and grown in tissue culture to confluence as a homogeneous population. Cells were then incubated at 37°C under 5 per cerit CO2 with RVV (0.2, 1.0, 5.0, and 25.0 μg/ml) or lipopolysaccharide (LPS, 10 μg/ml) for 3,6,12 and 24 hours. After an indicated time, the levels of endothelin-1 (ET-1); 6-keto-PGF1α (a stable metabolite of PGI2) tumor necrosis factor-α (TNF-α); interleukin-1β (IL-1β); and interleukin-6 (IL-6) in supernatants were measured by using ELISA or EIA. The effect of RVV or LPS on cell viability was also measured using MTT assay. The results showed copious amounts of ET-1 production irrespectively with the presence of RVV or LPS. Whereas, production of PGI2 (measured as 6-keto-PGF1α, a stable metabolite) was increased significantly higher in the RVV- and LPS-treated EC than in the control EC. However, TNF-a and IL-6 productions were not different among these groups. The levels of IL-1β were very low, although IL-1β was detectable in the group treated with RVV at a concentration of 25.0 μg/ml. In conclusion, RVV upto 25 μg/ml stimulated PGI2 production by cultured HUVEC. This effect was unlikely related to production of proinflammatory cytokines since LPS or RVV is not sufficient per se to elevate a substantial amount of EC-derived cytokines. The higher amount of IL-6 compared to TNF-α and IL-1β may be produced through other pathways apart from production via a cascade of cytokines. This is the first report showing that RVV upto 25 μg/ml has no effect on prominent proinflammatory cytokine production by HUVEC. However, in blood circulation, the major source of cytokines production is monocyte-macrophage lineage cell. Thus, RVV in blood circulation may activate the production of proinflammatory cytokines mainly from those cells and subsequently induce toxicity.