Changes in membrane microenvironment and signal transduction in platelets from NIDDM patients—a pilot study

Background : Non-insulin-dependent diabetes mellitus (NIDDM) is characterized by the presence of abnormally active platelets in the circulation, leading to increased incidence of thrombotic complications. In this study, we have attempted to understand the pathophysiology of the platelets in NIDDM. Methods : Platelet aggregation was induced by thrombin receptor-activating peptide or epinephrine. Membrane fluidity was derived from the steady-state fluorescence anisotropy of diphenylhexatriene incorporated in the membrane. The phosphotyrosine content of the platelet proteins was probed using specific monoclonal antibodies. The extent of calpain activity was assessed from the proteolysis of calpain substrates. Results : Aggregation was significantly enhanced ( p <0.001) in the platelets obtained from the cases of NIDDM. Anisotropy measurements reflected a significant increase in the microviscosity of platelet membranes from 3.315 (±0.103) in the control to 4.153 (±0.119) in NIDDM. Proteins of relative mobilities of 131, 100, 47 and 38 kDa were found to remain phosphorylated on tyrosine in the resting platelets obtained from NIDDM patients, while they were not phosphorylated in the control counterparts. This was associated with heightened activity of the calcium-dependent thiol protease, calpain, in NIDDM. Conclusions : Taken together, these data indicated significant changes in the signaling mechanism in the platelets obtained from NIDDM, which could lead to platelet hyperactivity in this disease.