RESEARCH – May 2014

Glucose impairs inhibition of platelet aggregation by COX inhibitors and L-arginine

Authors: Vilja Mardla, Ebe Rooks, Gennadi Kobzar, Nigulas Samel

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BACKGROUND. Hyperglycaemia has been found to cause increased platelet activity and, as a result, antiplatelet drugs, including aspirin, suppress thrombi formation insufficiently. High blood glucose concentration might be one of the possible factors that cause aspirin resistance. Aspirin treatment reduces cardiovascular events incompletely in patients suff ering from diabetes.

AIM. The main purpose of this study was to analyse the effect of glucose on the effect of COX inhibitors and L-arginine in platelets of healthy subjects and patients suffering from diabetes mellitus.

METHODS. Citrated venous blood was collected from healthy volunteers and from patients suffering from diabetes. Plateletrich plasma (PRP) was obtained after the centrifugation of citrated blood at 160 x g for 10 min at room temperature. The suspension of washed platelets (WP) was prepared as described previously using EDTA and indomethacin to protect the platelets from activation during the washing procedure.

The platelets were counted in a Swelab cell counter and adjusted to a final concentration of 250 x 109 cells/L. Platelet aggregation was measured by a photometric method in a Chrono-Log aggregometer.

RESULTS. In healthy subjects, glucose added in PRP for 15 min impaired the aspiriin inhibition of platelet aggregation induced by ADP in a concentration-dependent way. A similar effect was observed with another COX inhibitor, indomethacin, instead of aspirin. Also, glucose impaired L-arginine inhibition of platelet aggregation. Blood plasma was found to be not responsible for the effect of glucose on platelets. In the PRP of healthy subjects with normal concentration of glucose (5.6 mM), aspirin (0.2 mM) inhibited ADP-induced platelet aggregation by 41 ± 5 % while with 13 mM of glucose the inhibition was only 19 ± 8 %. In patients suffering from diabetes, with 13 mM of glucose in blood, the same concentration of aspirin added in vitro in PRP had no noticeable effect on platelet aggregation. Glucose did not impair the inhibition of ADP-induced aggregation by sodium nitroprusside in the PRP of either healthy subjects or diabetic patients.

CONCLUSION. Glucose attenuates the effect of COX inhibitors and L-arginine on platelets. The results suggest that glucose impaired platelet aggregation inhibition through COX and L-arginine:NO pathway. Long-term exposure of glucose to platelets in diabetic patients has a stronger impeding effect on platelet inhibition caused by aspiriin compared with short-term exposure of glucose in experimental conditions.