A combined casein-free-nicotinamide diet prevents diabetes in the NOD mouse with minimum insulitis.

We have previously shown that diabetes in the NOD mouse can be prevented if mice are placed from weaning on an infant formula diet in which the protein source is replaced with casein hydrolysate (Pregestimil) or soy protein (Prosobee), or if 1% nicotinamide is given in the drinking water. Nicotinamide somewhat suppresses insulitis but the hydrolysed casein formula does not. In this study, Prosobee was given concurrently with oral nicotinamide from weaning and their effects on the development of insulitis and diabetes measured. These effects were also assessed in mice given Prosobee alone from conception (day -20) or from weaning. Unlike the earlier experiments, a marked suppression of insulitis was observed when the diets and nicotinamide were given concurrently (mean insulitis scores +95% confidence intervals (back transformed): day 40 = 0.4% [0.03, 1.17] vs. 12.5% [2.52, 28.40] and at day 90 = 8.8% [3.65, 15.68] vs. 48.1% [33.89, 62.49], P = 0.0001). A similar suppression was observed on day 90 with Pregestimil combined with nicotinamide 7.3% [3.88, 11.70] vs. 43.8% [32.59, 55.35] (P = 0.0001). Qualitatively, introduction of Prosobee from conception appeared to elicit a greater degree of suppression of insulitis than when introduced from day 21. Insulitis lesions were examined immunohistochemically for CD4, CD8 and MAC-1 cells. The proportion of these cells was not different for any regime despite the great differences in total number of inflammatory cells in and around the islets of mice fed the combined diet. All the three dietary treatments (Prosobee from day -20, Prosobee from day 21, Prosobee+nicotinamide from day 21) resulted in substantial protection from diabetes in mice followed until 250 days. We conclude that the complete prevention of diabetes in the NOD mouse fed a casein-free diet together with nicotinamide is accompanied by marked inhibition of insulitis, which is not seen when either dietary agent is introduced alone. The somewhat greater suppression of insulitis in mice given the soy diet from conception compared to those fed from day 21 may indicate that even maternal diet during gestation may influence diabetes outcome in the offspring.

Immunohistochemical analyses of pancreatic macrophages and CD4 and CD8 T cell subsets prior to and following diabetes in the NOD mouse.

CD4 and CD8 T cells and macrophages have been implicated as cellular mediators of beta cell destruction in insulin-dependent diabetes mellitus (IDDM). The ratios of the two T cell subsets were, therefore, quantified in nonobese diabetic (NOD) mouse islets prior to IDDM, at the onset of the disease, and following onset by immunohistochemistry. The number of periislet-, intraislet-, and exocrine-located macrophages were also determined during these stages. At all time points studied (day 90, day 250, at diabetes onset, 4-6 weeks after diabetes), CD4 cells were 2.5 times higher than CD8 cells except at day 250, on which the CD4:CD8 ratio was 3.8. At days 90 and 250, islets were heavily infiltrated with both the T cell subsets associated with lower numbers of macrophages. At onset of the disease and after insulin treatment, although the CD4:CD8 ratios were similar, the absolute numbers of the two subsets were reduced-considerably. At these stages a majority of the islets was atrophied, some were still surrounded by T cells and macrophages and were enriched with glucagon cells. CD4 and CD8 cells were also observed in the exocrine region at the two stages. Macrophages located in the periislet areas were significantly higher in number than in the intraislet positions in all study groups (p = 0.001). They also showed a gradual decline from day 90 to clinical diabetes. Periislet-located macrophages were significantly higher at day 90 than after onset and in control Swiss mice (p < 0.05). The numbers of macrophages in the exocrine areas were similar in all groups of NOD mice. In control Swiss mice they were significantly lower in the periislet, intraislet, and exocrine regions.