Effects of insulin on platelet and leukocyte activity in whole blood

Diabetes mellitus (DM) is associated with platelet and leukocyte dysfunction. Previous observations with regard to insulin effects on platelet and leukocyte function are less than consistent. We thus investigated the effects of insulin on platelets and leukocytes, as well as on platelet-leukocyte interactions in whole blood. Hirudinized whole blood from 20 healthy subjects was preincubated at 37 degrees C in the absence or presence of insulin (30 and 300 microU/ml), and further incubated without or with adenosine diphosphate (ADP) (10(-5) M) or N-formyl-methionyl-leucyl-phenylalanine (fMLP) (10(-7) M), respectively. Platelet P-selectin expression, platelet fibrinogen binding, single platelet and platelet-platelet aggregate (PPA) counts, and leukocyte CD11b expression and superoxide anion production were monitored by flow cytometry. Insulin decreased single platelet counts (P<0.05) and increased PPAs (P<0.01) at 300 microU/ml in unstimulated samples, but did not significantly influence the P-selectin expression or fibrinogen binding of single platelets. Insulin also enhanced ADP-induced platelet aggregation, seen as an augmented decrease of single platelet counts. Insulin (30 microU/ml) increased leukocyte CD11b mean fluorescence intensity (MFI) in unstimulated, as well as fMLP- and ADP-stimulated samples (P<0.05 for all). fMLP-induced superoxide anion (O(2)(-)) production was, however, attenuated by insulin. Furthermore, fMLP-activation of leukocytes was associated with enhanced platelet fibrinogen binding and P-selectin expression. In conclusion, clinically relevant concentrations of insulin enhance platelet aggregability and leukocyte CD11b expression, but attenuate leukocyte respiratory burst activity. Our results suggest that insulin may modulate thrombotic and inflammatory processes in vivo in a complex manner.