ANTIVIRAL EFFECT OF ORYZACYSTATIN, A PROTEINASE-INHIBITOR IN RICE, AGAINST HERPES-SIMPLEX VIRUS TYPE-1 IN-VITRO AND IN-VIVO

Oryzacystatin (OC) is the first-described cystatin originating from ri ce seed; it consists of two molecular species, OC-I and OC-LI, which h ave antiviral action against poliovirus in vitro (H. Kondo, S. Ijiri, K. Abe, H. Maeda, and S. Arai, FEBS Lett. 299:48-50, 1992), In the exp eriments reported here, we investigated the effects of OC-I and OC-II on the replication of herpes simplex virus type 1 (HSV-1) in vitro and in vivo, HSV-1 was inoculated onto monolayers of monkey kidney epithe lial cells (CV-1 cells) at a multiplicity of infection of 0.1 PFU per cell. After adsorption of the virus onto cells, the cultures were incu bated in the presence of either OC-I or OC-II in the concentration ran ge of 1.0 to 300 mu M, and the supernatant virus yield was quantitated at 24 h. The effective concentration for 90% inhibition of HSV-1 was 14.8 mu M, while a cytotoxic effect on CV-1 cells without infection of HSV-1 was not observed below 500 mu M OC-I, Therefore, the apparent i n vitro chemotherapeutic index was estimated to be more than 33, In th e mouse model of HSV-1-induced keratitis and encephalopathy, topical a dministration of OC-I to the mouse cornea produced a significant decre ase in virus production in the cornea (mean virus yields: 3.11 log(10) PFU in the treated group and 4.37 log(10) PFU in the control group) a nd significant improvement in survival rates (P = 0.01). The in vivo a ntiherpetic effect of OC-I was comparable to that of acyclovir, indica ting that topical treatment of HSV-1 infection in humans with OC-I mig ht be possible. Our data also suggest the importance of some thiol pro teinases, which may be derived from either the host's cells or HSV-1, during the replication process of HSV-1.