African plants for inhibition of necrotic enzymes from snake venom

Snakebites are categorized as 'a neglected tropical disease' by WHO and as many snakebites occur in parts of the world where antiserum therapy is not easily accessible, and antiserum may not provide protection against local tissue damage, an alternative is needed. Plant-based medicines are an affordable and accessible treatment for the socio-economically challenged people in tropical areas. A total of 226 extracts from 94 different plant species from three countries, Mali, Democratic Republic of Congo and South Africa were tested in Phospholipase A2 (PLA2), proteases and hyaluronidase enzyme assays. These enzymes are closely involved in envenomation as they induce a localized effect and facilitate the spread of toxins into the system. Hence, inhibition of these enzymes will minimize local tissue damage. Bitis arietans and Naja nigricollis venom were used as enzyme sources in the assays. Of the tested extracts 40 plant species had an inhibition of more than 90% in one or more assays. Dose-response curves were established and IC₅₀ values calculated. One ethanol extract in the B. arietans hyaluronidase assay, 10 water extracts and 13 ethanol extracts in the N. nigricollis hyaluronidase assay, 11 ethanol extracts and one water extract in the B. arietans PLA2 activity assay had IC₅₀ values below 100 µg/ml. Many of the extracts with inhibitory effect contain tannins. Tannins interact with enzymes from snake venom by non-specific binding to the proteins. To investigate if the plant extracts with IC₅₀ values below 100 µg/ml contained specific inhibitors against hyaluronidase, protease or PLA2 enzymes the tannins were removed. Eighteen plant species retained their inhibitory effect after tannin removal, and of these six extracts showed IC₅₀ values below 100 µg/ml. As four of the six plants are widely distributed in close proximity to B. arietans and N. nigricollis, a potential inhibitor is accessible for many people in Sub-Saharan Africa.