Immunoexpression of interleukin-1 beta in pancreatic islets of NOD mice during cyclophosphamide-accelerated diabetes: co-localization in macrophages and endocrine cells and its attenuation with oral nicotinamide

During insulin-dependent diabetes mellitus, islet invading immune cells des troy beta cells over a prolonged asymptomatic pre-diabetic period. Cytokine s synthesised and secreted by specific immune cells within the islet infilt rate may be crucial effectors of beta cell destruction or protection during the disease. Interleukin-1 beta may be a key cytokine which may act in con cert with other cytokines in initiating and/or promoting beta cell destruct ion. We have examined this hypothesis in NOD mice by assessing the intra-is let expression and co-localization of interleukin-1 beta at different time- points following cyclophosphamide administration. We have also tested the e ffects of long-term oral nicotinamide given to NOD mice in suppressing intr a-islet expression of the cytokine in this accelerated model. Cyclophosphamide was administered to day 95 female NOD mice. Pancreatic tis sues were examined by dual-label confocal immunofluorescence microscopy for the expression and co-localization of interleukin-1 beta at days 0, 4, 7, 11 and at onset of diabetes (day 14). Diabetes developed in 7/11 mice 14 da ys after administration of cyclophosphamide while nicotinamide completely p revented the disease. At day 0, interleukin-beta immunolabelling was observ ed in selective intra-islet macrophages, several somatostatin cells and in a few beta cells. However, at day 4, it was seen mostly in somatostatin and some beta cells. At day 7, an increasing number of interleukin-1 beta cell s were observed within the islets and co-localized to several somatostatin cells, beta cells and macrophages. The mean number of intra-islet interleuk in-1 beta cells reached a peak at day 11 and was significantly higher than at day 7 (p = 0.05) and at day 14 (onset of diabetes; p = 0.03). At day 11, interleukin-1 beta immunolabelling was also present in selective macrophag es which co-expressed inducible nitric oxide synthase. At onset of diabetes , some macrophages, residual beta cells and somatostatin cells showed immun olabelling for the cytokine. Exposure of NOD mice to oral nicotinamide was associated with a considerably reduced expression of interleukin-1 beta cel ls within the islet at day 11 (p = 0.002). We conclude that cylophosphamide treatment enhances the expression of interleukin-1 beta in selective macro phages, somatostatin and beta cells during the course of the disease. Its e xpression reaches a maximum immediately prior to onset of diabetes. Interle ukin-1 beta present in intra-islet macrophages, somatostatin and beta cells may influence its expression by autocrine and paracrine means. Interleukin -1 beta expression within islet macrophages may also up-regulate inducible nitric oxide synthase within the same macrophage or adjacent macrophage pop ulations. These intra-islet molecular events may corroborate with other loc al cytotoxic processes leading to beta cell destruction. Oral nicotinamide may attenuate intra-islet expression of interleukin-1 beta and thus inducib le nitric oxide synthase during prevention of Type 1 diabetes in this anima l model. The expression of interleukin-1 beta in specific islet endocrine c ell-types shown in this study requires furtherbreak investigation.