Expression of inducible nitric oxide synthase in experimental viral myocarditis

Nitric oxide (NO) is an important bioactive molecule with regulatory, cytot oxic or cytoprotective properties. In virus-induced myocarditis, NO mediate s host defense mechanisms against the infection or causes cardiac dysfuncti ons. NO is synthesized from L-arginine by the enzyme nitric oxide synthase (NOS). The expression of the inducible form of the nitric oxide synthase (i NOS) is regulated by cytokines, involved in the complex myocardial immune r esponse to enterovirus infections. The present study was undertaken to characterize the role of iNOS and NO in the murine model of viral myocarditis induced by coxsackievirus B3 (CVB3). In response to CVB3 infection we investigated the time course of iNOS indu ction in correlation with cytokine mRNA expression (TNF-alpha, IL-1, IFN- g amma, TGP-beta) in the heart of NMRI mice by RT-PCR. Positive PCR signals for viral RNA were found in the acute and chronic stag e of disease by seminested PCR, indicating the persistence of viral genome. We found distinct expression of iNOS at all time points (1, 2, 3, 4, 7, 14 , 28, 56, 98 days post infection [p. i.]). Higher iNOS mRNA levels were ide ntified between days 4 until 28 p. i. in comparison to day 56 and 98 p. i. using densitometric values. The mRNA of the inflammatory cytokines TNF-alph a, IL-1 alpha, IFN-gamma appeared at days i, 4, and 7 p. i., peaked at day 7 p, i. and persisted until day 98 p. i. Similar like the iNOS mRNA pattern was the expression profile of TGF-beta. Using in situ hybridization and im munohistochemistry iNOS was localized in infiltrates, vascular endothelial cells, smooth muscle cells, myocytes and throughout the interstitial spaces between myocardial fibers in the heart sections of NMRI mice. Increased le vels of NO were measured as total nitrate/nitrite concentration in the sera of mice from day 7 until day 28 p. i.