Local IGF Bioactivity Associates with High PAPP-A Activity in the Pericardial Cavity of Cardiovascular Disease Patients

Objective: Pregnancy-associated plasma protein-A (PAPRA) has been suggested as a proatherogenic enzyme by its ability to locally increase insulin-like growth factor (IGF) activity through proteolytic cleavage of IGF binding protein-4 (IGFBP-4). Recently, stanniocalcin-2 (STC2) was discovered as an inhibitor of PAPP-A.This study aimed to investigate IGFBR4, PAPRA, and STC2 as local regulators of IGF bioactivity in the cardiac microenvironment by comparing levels in the pericardial fluid with those in the circulation of patients with cardiovascular disease. Methods: Plasma and pericardial fluid were obtained from 39 patients undergoing elective cardiothoracic surgery, hereof 15 patients with type 2 diabetes. Concentrations of IGF-I, intact and fragmented IGFBR4, PAPP-A, and STC2 were determined by immunoassays and IGF bioactivity by a cell-based assay. Results: In pericardial fluid, the concentrations of total IGF-I, intact IGFBR4, and STC2 were 72 +/- 10%, 91 +/- 5%, and 40 +/- 24% lower than in plasma, while PAPRA was 15 times more concentrated.The levels of the 2 IGFBR4 fragments generated by PAPRA and reflecting PAPP-A activity were elevated by more than 25%. IGF bioactivity was 62 +/- 81% higher in the pericardial fluid than plasma. Moreover, pericardial fluid levels of both IGFBR4 fragments correlated with the concentration of PAPP-A and with the bioactivity of IGF All protein levels were similar in pericardial fluid from nondiabetic and diabetic subjects. Conclusions: PAPP-A increases IGF bioactivity by cleavage of IGFBP-4 in the pericardial cavity of cardiovascular disease patients. This study provides evidence for a distinct local activity of the IGF system, which may promote cardiac dysfunction and coronary atherosclerosis.