Effects of Niflumic Acid on Thrombocytic Cytoplasmic Free Calcium and Platelet Aggregation in Patients with Diabetes Mellitus.

Background: Platelet activation plays an important role in cardiovascular complications which are frequently seen in patients with diabetes mellitus. It has been demonstrated that platelets are hyperactive in diabetes patients and this is supposed to be due to high platelet cytoplasmic free calcium ion concentration ([Ca²⁺]i). There are chloride channels on the membranes of platelets and the activation of chloride channels may participate in the transportation of calcium. Our previous study also showed that niflumic acid (NFA), a chloride channel blocker, can inhibit the elevation of platelet [Ca²⁺]i in healthy volunteers. The goal of this study was to investigate effects of NFA on platelet [Ca²⁺]i and platelet aggregation rate (PAG) in diabetic patients.

Methods: We prospectively enrolled 17 consecutive patients with diabetes mellitus at diagnosis. The control group was formed from 17 healthy volunteers. Platelet [Ca²⁺]i was detected by Fura-2 fluorescent technique and PAG was detected by platelet aggregometer. We studied the effects of NFA, nifedipine, a calcium channel blocker, and their combining effects on platelet [Ca²⁺]i and PAG in diabetic patients.

Results: The PAG, platelet resting [Ca²⁺]i, Ca²⁺ release and Ca²⁺ influx in diabetic patients were significantly higher than control group(P<0.05). NFA and nifedipine reduced the platelet Ca²⁺ influx which induced by thrombin in a dose-dependent manner in diabetic patients. 50% inhibition concentration (IC₅₀₎ of NFA was 50μmol/L. At this concentration, NFA reduced platelet [Ca²⁺]i by (54.7±14.5)% and decreased PAG by (32.3±21.4)%. The IC₅₀ of Nifedipine was 7.5μmol/L. At this concentration, nifedipine reduced platelet [Ca²⁺]i by (17.9±11.9)% and decreased PAG by (32.3±20.4)%. NFA(50μmol/L) combining with nifedipine (7.5μmol/L) inhibited platelet Ca²⁺ influx induced by thrombin in diabetes patients and their effects were independent.

Conclusions: Platelets in patients with diabetes mellitus are hyperactive. NFA reduces the PAG and platelet [Ca²⁺]i influx possibly by blocking the chloride channels on platelet membrane in diabetic patients. There are no interactions between NFA and nifedipine on the movement of platelet [Ca²⁺]i.