Intraperitoneal insulin delivery to patients with type 1 diabetes results in higher serum IGF-I bioactivity than continuous subcutaneous insulin infusion.

OBJECTIVE: Type 1 diabetes (T1D) is associated with low IGF-I and altered levels of IGF-binding proteins (IGFBPs) in plasma. This may be of importance for insulin sensitivity and the risk of developing diabetic complications. We hypothesized that IGF-I bioactivity is affected by the route of insulin administration and that continuous intraperitoneal insulin infusion (CIPII) has a more pronounced effect than continuous subcutaneous insulin infusion (CSII). DESIGN AND METHODS: We compared 10 patients with T1D on CIPII with 20 age- and sex-matched patients on CSII. Blood sampling was carried out 7-9 am after an overnight fast. All patients were C-peptide negative. IGF-I bioactivity was measured in vitro using a specific IGF-I kinase receptor activation (KIRA) assay. IGF-I was also measured by immunoassay together with IGF-II, IGFBP-1 and IGFBP-2.
RESULTS: When compared with subcutaneous insulin, intraperitoneal insulin resulted in (CIPII vs CSII) higher IGF-I bioactivity (1·83 ± 0·76 vs 1·16 ± 0·24 μg/l; P = 0·02), IGF-I (120 ± 35 vs 81 ± 19 μg/l; P = 0·01) and IGF-II (1050 ± 136 vs 879 ± 110 μg/l; P = 0·02). By contrast, log-transformed IGFBP-1 was reduced (P = 0·013), whereas log-transformed IGFBP-2 was not different (P = 0·12). There was a positive correlation between IGF bioactivity and IGF-I (r = 0·69; P < 0·001) and an inverse correlation between IGF-I bioactivity and log10 IGFBP-1 (r = -0·68, P < 0·001).
CONCLUSION: The in vitro IGF-I bioactivity was higher in patients treated with CIPII compared with CSII supporting the theory that the route of insulin administration is of importance for the activity of the IGF system. Intraperitoneal insulin administration may therefore be beneficial by correcting the alterations of the IGF system in T1D.