Long-term outcome of individuals treated with oral insulin: diabetes prevention trial-type 1 (DPT-1) oral insulin trial

Abstract

Objective: To evaluate the long-term intervention effects of oral insulin on the development of type 1 diabetes and to assess the rate of progression to type 1 diabetes before and after oral insulin treatment was stopped in the Diabetes Prevention Trial-Type 1 (DPT-1).

Research design and methods: The follow-up included subjects who participated in the early intervention of oral insulin (1994-2003) to prevent or delay type 1 diabetes. A telephone survey was conducted in 2009 to determine whether diabetes had been diagnosed and, if not, an oral glucose tolerance test (OGTT), hemoglobin A1c (HbA1c), and autoantibody levels were obtained on all subjects who agreed to participate.

Results: Of 372 subjects randomized, 97 developed type 1 diabetes before follow-up; 75% of the remaining 275 subjects were contacted. In the interim, 77 subjects had been diagnosed with type 1 diabetes and 54 of the remainder have had an OGTT; 10 of these were diagnosed with type 1 diabetes, subsequently. Among individuals meeting the original criteria for insulin autoantibodies (IAAs) (≥80 nU/mL), the overall benefit of oral insulin remained significant (P=0.05). However, the hazard rate in this group increased (from 6.4% [95% CI 4.5-9.1] to 10.0% [7.1-14.1]) after cessation of therapy, which approximated the rate of individuals treated with placebo (10.2% [7.1-14.6]).

Conclusions: Overall, the oral insulin treatment effect in individuals with confirmed IAA≥80 nU/mL appeared to be maintained with additional follow-up; however, once therapy stopped, the rate of developing diabetes in the oral insulin group increased to a rate similar to that in the placebo group.

Figure 1

Flow diagram of all subjects recruited into the original DPT-1 study and results of the follow-up study. IVGTT, intravenous glucose tolerance test; T1D, type 1 diabetes.

Figure 2

A: Time to type 1 diabetes for the entire DPT-1 population from 1994 to 2009. B: Time to type 1 diabetes for subjects with a baseline IAA level confirmed ≥80 nU/mL from 1994 to 2009. (A high-quality color representation of this figure is available in the online issue.)

Figure 3

Proportion of subjects with IAA levels confirmed ≥80 nU/mL who are diabetes-free by time of study and after study. A: Oral insulin treatment group (where “on treatment [Trt]” is defined as time receiving oral insulin). B: Placebo group (where “monitored” is defined as time receiving placebo and “not monitored” is defined as time no longer receiving placebo and monitored by study). (A high-quality color representation of this figure is available in the online issue.)

Figure 4

Proportion of subjects with IAA levels not confirmed ≥80 nU/mL who are diabetes-free by time of study and after study. A: Oral insulin treatment group (where “on treatment [Trt]” is defined as time receiving oral insulin). B: Placebo group (where “monitored” is defined as time receiving placebo and “not monitored” is defined as time no longer receiving placebo and monitored by study). (A high-quality color representation of this figure is available in the online issue.)