Nitric oxide (NO) is an important mediator of diverse physiological and pathological responses. NO-induced oxidative stress has been proposed in the pathogenesis of muscle tissue damage in inclusion-body myositis (IBM), which is characterized by deposition of beta-amyloid protein (Abeta) in vacuolated muscle fibres. To determine whether Abeta can induce NO production in skeletal muscle, we stimulated C2C12 mouse skeletal muscle cells in vitro with Abeta[1-42] or Abeta[25-35] peptides in the presence or absence of interferon gamma (IFN-gamma). Neither Abeta peptides nor IFN-gamma were able to stimulate nitrite (NO(2)(-)) production by C2C12 cells when given alone. However, combination of IFN-gamma with either Abeta[1-42] or Abeta[25-35] resulted in significant NO(2)(-) release into cell-free supernatants. Northern blot analysis of RNA obtained from Abeta/IFN-gamma-stimulated C2C12 cells revealed increased mRNA accumulation of inducible nitric oxide synthase (iNOS). Moreover, approximately 4% of muscle cells incubated with Abeta peptides and IFN-gamma showed ultrastructural features of DNA fragmentation. These findings, taken together, indicate that the association of Abeta with IFN-gamma stimulates NO(2)(-) production via induction of iNOS gene expression in skeletal muscle cells, with occasional evidence for nuclear changes suggesting apoptotic morphology. These data further support a role for Abeta deposition in the pathogenesis of postulated oxidative damage in IBM.