Comparative Study on the Antiherpetic Activity of Aqueous and Ethanolic Extracts Derived from Cajanus cajan (L.) Millsp.

Introduction: Aqueous and ethanolic extracts of Cajanus cajan (Fabaceae) were examined in vitro for their antiviral activity against herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2). Materials and Methods: The antiviral activity was determined using a plaque reduction assay. The cytotoxic concentration (CC50) as well as the inhibitory concentration (IC50) of the extracts was determined from dose-response curves. Results: All extracts tested revealed a high antiviral activity against cell-free HSV-1 and HSV-2. The most active one was the Cajanus ethanol extract with IC50 values of 0.022 mu g/ml for HSV-1 and 0.1 mu g/ml for HSV-2. In order to identify the mode of antiviral action, the extracts were added to the host cells or viruses at different stages of infection. HSV-1 and HSV-2 were considerably inactivated when the viruses were pretreated with the extracts for 1 h prior to cell infection. At maximum non-cytotoxic concentrations of the extracts, plaque formation was significantly reduced by 95-99% for HSV-1 and HSV-2. In a time-dependent assay with cell-free HSV-1 over a period of 2 h, a clearly time-dependent effect was demonstrated whereby the Cajanus ethanol extract revealed a much higher activity than the Cajanus aqueous one. Conclusion: The results obtained indicate that the extracts affect HSV before cell adsorption, but have no effect on the intracellular virus replication. According to our findings, a therapeutic application of Cajanus ethanolic extracts containing creme or ointment as antiviral agent in recurrent HSV infection appears to be promising.