Viral mutation accelerated by nitric oxide production during infection in vivo

Nitric oxide (NO), superoxide (O-2(-)), and their reaction product peroxyni trite (ONOO-) are generated in excess during a host's response against vira l infection, and contribute to viral pathogenesis by promoting oxidative st ress and tissue injury. Here we demonstrate that NO and peroxynitrite great ly accelerates the mutation of Sendai virus (SeV), a nonsegmented negative- strand RNA virus, by using green fluorescent protein (GFP) inserted into an d expressed by a recombinant SeV (GFP-SeV) as an indicator for mutation. GF P-SeV mutation frequencies were much higher in the wild-type mice than in t hose lacking inducible NO synthase, suggesting that mutation of the virus i n vivo is NO dependent. High levels of NO and NO-mediated oxidative stress were induced by GFP-SeV infection in the lung of the wild-type mice, but no t in the iNOS-deficient mice, as evidenced by electron spin resonance spect roscopy and immunohistochemical analysis for nitrotyrosine formation as wel l as histopathological examination. Furthermore, peroxynitrite, an NO-deriv ed reactive nitrogen intermediate, enhanced viral mutation in vitro. These results indicate that the oxidative stress induced by NO produced during th e natural course of viral infection increases mutation, expands the quasisp ecies spectrum, and facilitates evolution of RNA viruses.