Thrombin-induced platelet aggregation, phosphoinositide metabolism and protein phosphorylation in NIDDM patients treated by diet, sulphonylurea or insulin

Abstract

We studied thrombin-induced metabolism of phosphoinositide, protein phosphorylation and platelet aggregation in platelets from 32 NIDDM patients and 12 control subjects. To clarify the effect of diet, sulphonylureas, or insulin treatment, the subjects were divided into three groups based on the type of treatment. Thrombin-induced platelet aggregation was measured with an aggregometer. Low-dose thrombin (0.25 U/ml)-stimulated platelet aggregation in diabetic patients was significantly increased compared with the control subjects. Platelet aggregation in the sulphonylurea and insulin groups was significantly lower than in the diet group. On the other hand, in platelets incubated with [32P]orthophosphate, thrombin-induced incorporation of 32P radioactivity into phosphatidic acid (PA) was significantly lower in the sulphonylurea and insulin groups than in the diet group. Thrombin-induced incorporation of [32P] radioactivity into phosphatidylinositol (PIP) for 10 s was significantly higher in the sulphonylurea group than in the diet group. There were no differences in thrombin-induced 47 kDa protein phosphorylation between platelets from the diet, sulphonylurea, or insulin groups. These results suggest that sulphonylureas and insulin induce suppression of thrombin-induced activation of phospholipase C, which mediates hydrolysis of PIP and PIP2 and production of PA, which leads to inhibition of platelet aggregation.

Increased platelet aggregation in diabetic patients with microangiopathy despite good glycemic control

“…The maximal platelet aggregation values induced by low-dose thrombin (<0.5 U/ml) in the present patients were dramatically increased compared with healthy controls or type 2 diabetic patients as previously described 6 (Figure 2). Neither ADP-induced nor collagen-induced platelet aggregation was increased in the present patients (data not shown).…”

“…The values of 12 healthy control subjects and 32 type 2 diabetic patients were determined previously. 6 The presented patients exhibited elevated platelet aggregation in low dose thrombin. diabetic patients, especially in the patients with severe retinopathy.…”

“…5 We previously reported that thrombin-induced breakdown of phosphoinositides is increased in platelets from diabetic subjects with retinopathy. 6 In this study, we examined platelet aggregation, small G protein, phosphatidylinositol 3-kinase (PI3-kinase) and protein kinase C (PKC) in patients with diabetic retinopathy, despite achieving excellent glycemic control during the whole observation period.…”

Increased Osteopontin Levels in the Vitreous of Patients with Diabetic Retinopathy

“…Ishizuka et al [17] reported that the thrombininduced breakdown of phosphoinositides is increased in platelets from diabetic subjects with retinopathy. Furthermore, low-dose thrombin-stimulated platelet aggregation in diabetic patients was greatly elevated compared with healthy control subjects [18] .…”