Coxsackievirus Infections and Oxidative Stress as Mediators of Beta Cell Damage

Type I diabetes (T1D) is an autoimmune disease resulting in gradual cell-mediated destruction of insulin producing beta cells in the pancreatic islets of Langerhans. The most plausible environmental triggers to launch and/or accelerate this process in a genetically predisposed organism include enterovirus infections and oxidative stress. Among other enteroviruses the group B of coxsackieviruses is associated with potential beta cell toxicity. Beta cells are weak in antioxidative defense, which makes them hypersensitive to oxidative stress. The viral and oxidative hazards may interact in an additive fashion in suitable conditions and result in cumulative damage. However, prior to the present study the mechanisms of the resulting beta cell damage were poorly characterized. Thus, this study was set to clarify the patterns and consequences of coxsackie B virus infections and the effects of experimental oxidative stress in various cell culture models to understand the mechanistic pattern of beta cell damage and death. The performed experiments were planned with the particular intention to detect different forms of beta cell death due to varying viral and oxidative conditions. We chose the coxsackie B strain (CVB) because of its aggressive nature in cell systems and the previously characterized epidemiologic link to T1D. Acknowledging the inhibitory potential of in vivo conditions we developed two models resembling a slowly progressing coxsackievirus infection first, by restricting the production of viral progeny with a selective inhibitor of viral RNA replication and second, by means of lowering the multiplicity of infection (comparable to the amount of infective viral particles per cell). Hydrogen peroxide was selected to serve as the oxidative stressor because it represents a physiological agent present during most oxidative processes in vivo. L-cysteine, the precursor of the most important intracellular antioxidant glutathione, was chosen to counteract hydrogen peroxide. This study shows that a productive CVB-infection results in lytic beta cell death. When pharmacologically restricted by guanidine-HCl, the viability increases dramatically through decreased necrosis and associates with simultaneous stimulation of apoptotic death. A similar pattern of host cell death characterizes a CVB5 infection of low multiplicity. L-cysteine protects dose-dependently against hydrogen peroxide 5 induced damage. Also apoptosis provoked by a moderate level of hydrogen peroxide is reversed by L-cysteine. The intracellular glutathione content transiently decreases during a low multiplicity CVB5 infection, but shows full recovery at later timepoints. This might imply a more physiological type of damage, which has previously been linked to induction of apoptotic cell death. Furthermore, …