Insulin prophylaxis down-regulates islet antigen expression and islet autoimmunity in the low-dose STZ mouse model of diabetes

The aims of this study were to evaluate in an autoimmune diabetes animal model [low-dose streptozotocin (LD-STZ) mouse] (a) the efficacy of a prophylactic insulin treatment as a diabetes prevention tool, and (b) its possible mechanisms through both the insulitis evaluation and islets antigen expression, Diabetes was induced in male C57B16/J mice with STZ (50 mg/kg b/w for five consecutive days); insulin (1 U/day) was injected subcutaneously for ten consecutive days before the induction of diabetes and for a further ten days. Seventy-one male C57B16/J mite were grouped as follows: Group I (n = 25) made diabetic with i,p, STZ, Group 2 (n = 21) made diabetic with i,p, STZ and injected subcutaneously with insulin, Group 3 (It = 15) injected with insulin, while Group 4 (n = 10) comprised normal animals as controls. The animals of each group were killed at two intervals: half of them at day 12 and the remainder at day 24 from the beginning of the STZ treatment. A significant reduction of glycemia levels and insulitis severity was observed between mice of Group 1 vs. Group 2 at day 12 and day 24, Down-regulation of islet antigen expression (insulin, A2B5, GM2-1, ICA Ag) was achieved even without a complete metabolic suppression of beta-cell activity. In conclusion, prophylactic insulin treatment is effective to reduce glycemia levels and insulitis severity and down-regulates islet antigen expression in the LD-STZ model.