INDUCIBLE NITRIC-OXIDE SYNTHASE (INOS) IN PANCREATIC-ISLETS OF NONOBESE DIABETIC MICE - IDENTIFICATION OF INOS-EXPRESSING CELLS AND RELATIONSHIPS TO CYTOKINES EXPRESSED IN THE ISLETS

Inflammatory cytokines and nitric oxide (NO) are candidate mediators o f pancreatic islet beta-cell destruction in insulin-dependent diabetes mellitus. In this study, we used a semiquantitative PCR assay to meas ure levels of messenger RNA (mRNA) expression of the inflammatory cyto kines, interleukin-1 alpha (IL-1 alpha), tumor necrosis factor-alpha, and interferon-gamma (IFN gamma), and of the inducible form of NO synt hase (iNOS) in mononuclear leukocytes isolated from pancreatic islets of autoimmune diabetes-prone nonobese diabetic (NOD) female mice. We f ound that mRNA levels of iNOS, IL-1 alpha, and IFN gamma in islet mono nuclear leukocytes increased from 5 weeks of age to onset of diabetes (>13 weeks of age). To determine whether increased iNOS, IL-1 alpha, a nd IFN gamma mRNA expressions were related to diabetes development, we compared mRNA levels of these molecules in mononuclear leukocytes fro m islets of 12-week-old diabetes-prone NOD female mice and three group s of 12-week-old mice with low diabetes risk: NOD female mice injected with complete Freund's adjuvant at 4 weeks of age, NOD male mice, and BALB/c female mice that do not develop diabetes. We found that iNOS, IL-1 alpha, and IFN gamma mRNA levels were higher in mononuclear leuko cytes from islets of diabetes-prone NOD female mice than in those from mice in the low risk groups. Also, iNOS mRNA levels in individual mic e correlated with IL-1 alpha and IFN gamma mRNA levels. By using speci fic antibodies and immunohistochemical methods, we localized iNOS in m acrophages as well as in beta-cells of islets from diabetes-prone NOD female mice. These findings suggest that IL-1 alpha and IFN gamma may promote islet beta-cell destruction at least in part by up-regulating iNOS expression and NO production by both macrophages and beta-cells i n the islets of autoimmune diabetes-prone NOD mice.