Anti-HSV-1 activity of Euclea natalensis

The inhibitory effect of crude extracts of Euclea natalensis A. DC. and a naphthoquinone, diospyrin, isolated from this species, was investigated against herpes simplex virus Type 1 (HSV-1) for activity by in vitro studies on primary vervet monkey kidney (VK) cells. Cell toxicity was monitored by determining the effect of the extracts and diospyrin on the monolayers of VK cells. The dose of the plant samples that inhibited 50% cell growth (ID50) after the incubation period was 0.1mg ml(-1) and 0.2mg ml(-1) for acetone and water extracts, respectively. Diospyrin exhibited an ID, of 0.02mg ml(-1) on VK cells. The water extract from the roots of the plant was the least toxic to cell cultures and inhibited the replication of HSV-1 moderately at a concentration of 0.2mg ml(-1). Diospyrin had no inhibitory effect against the virus. However, acetone extracts inhibited the replication of the virus at concentrations ranging from 0.1mg ml(-1) to 0.02mg ml(-1), as shown by the reduction of virus- induced cytopathogenic effects and the protection of cells in a cell viability assay.