Estimated proinsulin processing activity of prohormone convertase (PC) 1/3 rather than PC2 is decreased in pancreatic β-cells of type 2 diabetic patients

[摘要] References(16)Cited-By(3)Type 2 diabetic (T2D) patients exhibit fasting relative hyperproinsulinemia owing to pancreatic β-cell dysfunction.To clarify the mechanism underlying this hyperproinsulinemic state, we evaluated the activities of the endopeptidases prohormone convertase (PC) 1/3 and PC2 in T2D patients.Fasting blood levels of intact proinsulin (IPI), total proinsulin (t-PI) and C-peptide were measured simultaneously, and intravenous glucagon loading was performed to investigate the dynamics of circulating proinsulin-related molecules released from pancreatic β-cells in 12 healthy volunteers and 18 T2D patients.Taking advantage of the 95% cross-reactivity between proinsulin and des-31,32-proinsulin (des-31,32-PI) with the human proinsulin radioimmunoassay kit used in this study, we estimated PC1/3 and PC2 activities using the following formulas: des-31,32-PI = (t-PI–IPI)/0.95; PC1/3 activity = des-31,32-PI/IPI; and PC2 activity = C-peptide/des-31,32-PI.C-peptide responses to glucagon were slightly lower among T2D patients.IPI and the IPI/C-peptide ratio were significantly higher in T2D patients (p<0.05 and p<0.01, respectively).There was no difference in des-31,32-PI levels or PC2 activity between the two groups.However, PC1/3 activity was significantly lower in T2D patients than in the control group (p<0.01).We propose that decreased activity of PC1/3 rather than PC2 in pancreatic β-cells is involved in the impaired proinsulin processing, resulting in elevated IPI levels in T2D patients.

[学科分类] 内分泌与代谢学

[关键词] Insulin secretion;Insulin biosynthesis;Proinsulin