Antiherpes simplex virus type 2 activity of casuarinin from the bark of Terminalia arjuna Linn

Casuarinin, a hydrolyzable tannin isolated from the bark of Terminalia arjuna Linn. (Combretaceae), was investigated for its antiviral activity on herpes simplex type 2 (HSV-2) in vitro. Results showed that the IC(50) of casuarinin in XTT and plaque reduction assays were 3.6+/-0.9 and 1.5+/-0.2 microM, respectively. The 50% cytotoxic concentration for cell growth (CC(50)) was 89+/-1 microM. Thus, the selectivity index (SI) (ratio of CC(50) to IC(50)) of casuarinin was 25 and 59 for XTT and plaque reduction assays, respectively. Casuarinin continued to exhibit antiviral activity even added 12 h after infection. During the attachment assay, casuarinin was shown to prevent the attachment of HSV-2 to cells. Furthermore, casuarinin also exhibited an activity in inhibiting the viral penetration. Interestingly, casuarinin was virucidal at a concentration of 25 microM, reducing viral titers up to 100,000-fold. This study concludes that casuarinin possesses anti-herpesvirus activity in inhibiting viral attachment and penetration, and also disturbing the late event(s) of infection.