Effects of acyclovir on nitric oxide and cell death in herpesvirus type 1 and 2 infected HEp-2 cells

Abstract number: 1134_03_307

Baskin H., Yazici Z., Baskin Y., Olgun N., Ozkul A., Bahar I.H.

Objectives:  

Herpesviruses are among the most ‘successful’ human pathogens. Inhibition of apoptosis is a common strategy of viral pathogenesis that favors virus replication and may contribute to oncogenesis. The herpes simplex viruses 1 and 2 (HSV1, HSV2) code for a variety of proteins that cooperate in blocking apoptosis triggered by virus infection. Nitric oxide (NO), a potentially toxic signal molecule, has been implicated in a wide range of diverse pathophysiological process. The crosstalk between cell destructive and protective signaling pathways, their activation or inhibition under the modulatory influence of NO will determine the possible role of NO in apoptotic cell death and/or survival. Acylovir's effect mechanism targets at the viral DNA polymerase, acts as a chain terminator. Its first phosphorylation step is catalyzed by the virus encoded thymidine kinase. Acyclovir's interactions with cell death and NO seem to be very important because of ‘post treatmental cognitive functions’that may be encountered due to treatment processes for encephalitis, meningitis cases.

Methods:  

HEp-2 cells were infected by HSV1 (KOS strain) (and UV-inactivated Mock of the same strain) and HSV2 (G strain) (and UV-inactivated Mock of the same strain). Infected cells were treated by non apoptotic doses of acyclovir (48.8; 24.4; 12.2; 6.1; 3; 1.5 mg/mL), respectively. Following 24 hours of infection cells were detected by Hoechst 33342 and propidium iodide for apoptosis/necrosis, and culture supernatants by Griess reagent for NO.

Results:  

NO responses were significantly higher in HSV 1 infected cells in 48.4; 24.4; 12.2, but after 6.1, in 3 and in 1.5 NO responses were higher in HSV2 infected cells. Also in HSV1 infected cells with 48.4; 24.4; 12.2 doses of acyclovir, apoptotic responses were higher than HSV2. But necrosis responses were significantly higher in HSV2 infected cells (48.8; 24.4; 12.2; 6.1; 3 mg /mL).

Conclusion:  

In this study, it is shown that there are significant differences between HSV 1 and 2 in apoptosis/necrosis, and NO responses. It is assumed that involvement of acyclovir in doses higher than 6 mg/mL may trigger the necrotic pathway in HSV2 infected cells, the same compound seems to cause statistically significant higher NO response in HSV1 infected cells in contrast to those infected with HSV2. These results deserve further studies in order to explain the effects of acyclovir in treatment processes especially in ‘cognitive functions’.