The autocrine regulation of insulin-like growth factor-1 in human brain of Alzheimer's disease.

Abstract Background Insulin-like growth factor (IGF) binding protein (IGFBP)−3 and cyclic Glycine-Proline (cGP) regulate circulating IGF-1 function that is associated with cognition. The association between IGF-1 function and Alzheimer’s disease (AD) remains inconclusive. This study evaluated the changes of IGFBPs and cGP, and their effects on the bioavailability and function of IGF-1 in human brain of AD cases. Methods Using biological and mathematic analysis we measured the concentrations of total, bound and unbound forms of IGF-1, IGFBPs and cGP in the inferior-frontal gyrus and middle-frontal gyrus of human AD (n = 15) and control cases (n = 15). The association between the changes of total concentration of these peptides and total protein concentration in brain tissues were also analyzed. Results The unbound bioavailable IGF-1 was lower whereas the bound cGP and IGFBP-3 were higher in AD than the control cases. Total protein that was lower in AD than control cases, was negatively associated with cGP concentration of control cases and with IGFBP-3 concentration of AD cases. Conclusions The results provide direct evidence for IGF-1 deficiency in AD brain due to lower bioavailable IGF-1. The increase of bound IGFBP-3 impaired autocrine regulation. The increase of bound cGP is an autocrine response to improve the bioavailability and function of IGF-1 in AD brain. Availability of data and material All data generated or analysed during this study are included in this published article. Additional datasets analysed during the current study available from the corresponding author on reasonable request.