PROPHYLACTIC ORAL-ADMINISTRATION OF METABOLICALLY ACTIVE INSULIN ENTRAPPED IN ISOBUTYLCYANOACRYLATE NANOCAPSULES REDUCES THE INCIDENCE OF DIABETES IN NONOBESE DIABETIC MICE

Nonobese diabetic (NOD) mice develop an autoimmune disease with a long prodromal period and constitute a model for investigating the prevent ion of human type 1 diabetes. Since prophylactic insulin injections re duced the incidence of diabetes in NOD mice, we tested a new prophylac tic strategy to prevent diabetes in NOD mice consisting of oral admini stration of insulin, protected in polyalkylcyanoacrylate nanocapsules from degradation in the gastrointestinal tract. In humans, this form o f prophylactic insulin administration would be less constraining than insulin injections. Ninety female NOD mice were randomized at weaning and fed once a week (from 60 to 300 days of age) with insulin nanocaps ules (100 U/kg) or empty nanocapsules. Within the group fed with insul in nanocapsules, the incidence of diabetes was reduced (38% vs 75%; P < 0.02), the onset of disease was delayed (P < 0.02), and the severity of lymphocytic inflammation of endogenous islets was reduced (P < 0.0 3). Although the oral treatment was stopped at 300 days of age, the in cidence of diabetes at 360 days remained lower in mice previously fed insulin nanocapsules (P < 0.02). Previous feedings with insulin nanoca psules did not protect against cyclophosphamide-induced diabetes, sinc e final incidence of diabetes (sum of the incidence during the initial 360 days and the further CY-induced incidence) reached the final inci dence obtained in mice previously fed empty nanocapsules and treated w ith cyclophosphamide. Intestinal absorption of insulin nanocapsules wa s evidenced by HPLC separation of human insulin in NOD sera. During co transfer, T splenocytes from mice fed insulin nanocapsules were able t o reduce the capacity of T cells from diabetic donors to adoptively tr ansfer the disease (P < 0.01). Antigens for islet-cell autoantibodies (ICA) in pancreata from both NOD groups were compared by immunofluores cence with the same ICA-positive human sera to ensure that differences were due to quantitative changes in antigen. These antigens, which co uld serve as an index of a possibly more extended antigen beta-cell re st, were decreased (P < 0.02) and pancreatic insulin content was reduc ed (P < 0.05) in mice fed with insulin nanocapsules, suggesting a mech anism of 'beta cell rest'. To summarize, early feeding with insulin na nocapsules reduces diabetes and insulitis in the NOD mouse model that mimics human type 1 diabetes. This may be due both to generation of ce llular mechanisms that actively suppress disease and a decrease in ant igens which makes beta cells less vulnerable to autoimmune aggression. (C) 1996 Academic Press Limited