Mechanistic Study Using Oral Insulin for Immune Efficacy in Secondary Prevention of Type 1 Diabetes

Type 1 diabetes (T1D) is a disease that predominantly affects children. T1D is preceded by islet autoimmunity, which often starts in early childhood and which has a peak incidence at around 1 to 2 years of age. Previous studies show that multiple islet autoantibodies indicate a point of limited return in the path to T1D. Every year, around 10% of multiple islet autoantibody positive children progress from islet autoantibody positivity to symptomatic T1D. Thus, therapy and intervention is needed to change the inevitable path to insulin dependence. Treated should be initiated early when most beta cells are still intact and when the autoimmune process is less advanced may be more effective.

Administration of oral insulin in multiple islet autoantibody-positive children offers the potential for immunological tolerance against beta cells and thereby protect against progression to T1D. Previous studies in rodents had indicated that mucosal administration of insulin is effective in inducing regulatory immune responses that can prevent autoimmune diabetes. Mouse studies indicated that the dose of oral insulin is important. In human studies oral insulin administration shows an excellent safety profile, without adverse side effects at doses between 2.5 and 7.5 mg per day (1-3). The administration of oral insulin (7.5 mg per day) to prediabetic ICA and IAA positive first degree relatives of T1D patients within the DPT-1 study showed no significant beneficial effect in the intention to treat analysis. A sub-analysis of the data, however, showed significant benefit in those relatives with higher titer IAA.

The Pre-POINT study, the first primary autoantigen vaccination dose-finding study in which children with high genetic risk for type 1 diabetes were administered insulin orally daily tested doses (2.5 mg; 7.5 mg; 22.5 mg and 67.5 mg) showed five of six children exposed to a dose of 67.5 mg insulin had evidence of an antibody or T cell response to insulin. The response differed to the typical responses seen in children who develop diabetes in that the antibody responses were of weak affinity and the T cell responses had a preponderance of cells with regulatory T cell phenotypes (37). These results are also encouraging from a safety viewpoint and indicate that oral exposure to insulin at doses that are approximately equivalent to efficacious doses in rodents may promote tolerance in children.

A secondary prevention study using 7.5 mg oral insulin administered daily is currently conducted by the TrialNet Study Group, and includes the Forschergruppe Diabetes, Klinikum rechts der Isar der Technischen Universität München as a study site. Autoantibody, normoglycemic subjects aged 3 to 45 years are treated with oral insulin. In this currently conducted trial there have been no safety issues reported thus far.

The active substance for oral application is human insulin, synthesized in a special non-disease-producing laboratory strain of Escherichia coli bacteria that has been genetically altered by the addition of the gene for human insulin production (Lilly Pharmaceuticals, Indianapolis, Indiana, USA). The physical, chemical and pharmaceutical properties of the human insulin have been well documented by the manufacturer. Oral Insulin will be applied as a capsule containing 7.5 mg of the active substance together with filling substance cellulose and a dose escalation to 67.5 mg of the active substance together with filling substance cellulose. After ingestion, most of the insulin will be degraded by gastric acids. Enteric delivery and systemic availability is therefore unlikely and efficacy of active insulin is likely to be restricted to the oral mucosa.