PREVENTION OF TYPE-I DIABETES IN NONOBESE DIABETIC MICE BY LATE INTERVENTION WITH NONHYPERCALCEMIC ANALOGS OF 1,25-DIHYDROXYVITAMIN D-3 IN COMBINATION WITH A SHORT INDUCTION COURSE OF CYCLOSPORINE-A

In nonobese diabetic (NOD) mice, type I diabetes can be prevented with out generalized immunosuppression by nonhypercalcemic analogs of vitam in D-3 when treatment is started early, i.e. before the autoimmune att ack, reflected by insulitis, occurs. The aim of this study was to inve stigate whether these substances can arrest progression to clinically overt diabetes when administered in a more advanced disease stage, nam ely when the autoimmune attack is on going, reflecting the situation i n prediabetic subjects in whom immune intervention is being considered . We, therefore, evaluated the protective potential of MC1288 (20-epi- 1,25-dihydroxyvitamin D-3) a nonhypercalcemic analog of 1,25-dihydroxy vitamin D-3, both alone and in combination with a short induction cour se of cyclosporin A, in NOD mice that already have insulitis, as demon strated in pancreatic biopsies performed 15 days before the start of t herapy. Subsequently, mice were randomized into a control group, recei ving the treatment vehicle (n = 26), and three treatment groups, recei ving, respectively, 7.5 mg/kg.day cyclosporin A (CyA) from days 85-105 (n = 19), 0.1 mu g/kg.2 days MC1288 from days 85-200 (n = 20), or the combination of these two regimens (n = 20). At the time of the pancre atic biopsy (day 70), insulitis was evenly distributed in all groups, and 27.7% of the islets scored showed signs of destructive insulitis. Diabetes outcome by 200 days was 74% (14 of 19) in the CyA-treated gro up, comparable to the diabetes incidence in control mice (65%; 17 of 2 6; P = NS). Treatment with MC1288 alone could not reduce disease incid ence (70%; 14 of 20), but the combination therapy reduced diabetes inc idence to 35% (7 of 20; P < 0.05 vs. untreated; P < 0.01 vs. CyA group ; P < 0.025 vs. MC1288). All treatments were well tolerated, without m ajor side-effects on calcium or bone metabolism and without signs of g eneralized immunosuppression. Cotransfer experiments could not reveal the induction of suppressor cells. Reverse transcription-PCR on pancre atic tissue revealed significantly lower levels of interferon-gamma an d higher levels of interleukin-4 in the combination group. In conclusi on, nonhypercalcemic analogs of 1,25-dihydroxyvitamin D-3 administered to NOD mice when the autoimmune disease is already active can prevent clinical diabetes when this therapy is combined with a short inductio n course of an immunosuppressant such as CyA.