Insulin, but not proinsulin C-peptide, enhances platelet fibrinogen binding in vitro in Type 1 diabetes mellitus patients and healthy subjects

Abstract

Introduction: Insulin treatment is essential in Type 1 diabetes mellitus (DM). However, previous studies have shown complex effects of insulin on platelet function. Proinsulin C-peptide has shown beneficial effects in Type 1 DM, but it is not known if it can affect platelet activation. We thus investigated how insulin, C-peptide, and their combination influence platelets from DM patients and healthy subjects. Materials and methods: Hirudinized blood from patients ( n=10) and healthy subjects ( n=10) was preincubated in the absence or presence of insulin (10 and 100 μU/ml), C-peptide (0.3, 1, and 10 nM), or the combination (1 nM C-peptide+100 μU/ml insulin or 10 nM C-peptide+100 μU/ml insulin) and further incubated without or with 10 −6 M ADP. Platelet activation was monitored by platelet fibrinogen binding and P-selectin expression using whole blood flow cytometry. Data are presented as binding index (BI), which integrates the percentage of activated cells and their mean fluorescence intensity. Results: Insulin enhanced ADP-induced platelet fibrinogen binding in both Type 1 DM patients and healthy subjects. For example, ADP-stimulated platelet fibrinogen BI increased from 4.25±0.74 to 8.63±2.00 with 10 μU/ml insulin ( P<.05) in Type 1 DM patients. However, insulin did not increase platelet P-selectin expression. Proinsulin C-peptide did not influence platelet fibrinogen binding or P-selectin expression in either Type 1 DM patients or healthy subjects. The combination of C-peptide and insulin had similar effects as insulin alone. Conclusions: Insulin at physiological concentrations enhances platelet fibrinogen binding in both Type 1 DM patients and healthy subjects, whilst C-peptide does not influence platelet activation.