Effects of the NHE-1 inhibitor cariporide alone or together with the P2Y(12) antagonist AR-C 69331 MX on CD62p expression and formation of platelet-leukocyte aggregates

The sodium-hydrogen exchanger isoform 1 (NHE-1) contributes to platelet activation at elevated pH. Effects of NHE-1 inhibitors on platelet degranulation and formation of proinflammatory and procoagulatory platelet-leukocyte aggregates (PLA) and possible interactions with P2Y(12) inhibitors-which also affect platelet degranulation-have not been investigated. Whole blood from healthy human subjects was incubated with the NHE-1 inhibitor cariporide and the P2Y(12) inhibitor AR-C 69331 MX at clinically reasonable concentrations, in the presence of normal pH or in a propionate model to activate the NHE-1 (approximately pH 7.0). The degranulation marker CD62p, the expression of the activated GPIIb/IIIa receptor (PAC-1), and formation of platelet-leukocyte (monocyte) aggregates (PLA) was assessed by flow cytometry. Cariporide at concentrations up to 20 mug/ml had no effects on ADP- (5 muM) or TRAP- (2 muM) induced CD62p expression or PLA formation at normal pH. At pH 7.0 and stimulation with ADP, PLA decreased from 64 +/- 24% (control) to 47 +/- 23% under cariporide at 2 mug/ml (p < 0.05), and the MFI of PLA (i.e. the platelet mass attached at monocytes) decreased from 547 +/- 203 to 360 +/- 96 units (p < 0.05). PAC-1 MFI decreased from 66 +/- 23 to 34 +/- 18 units (p < 0.05) after ADP and from 74 +/- 29 to 42 +/- 17 units (p < 0.05) after TRAP, respectively. AR-C 69331 MX (10 nM) had inhibitory effects on all parameters irrespectively of the pH, and the combination of both agents at pH 7.0 shows additive effects. In conclusion, our investigation points to-perhaps clinically relevant-effects of NHE-1 inhibition on the degranulation of platelets and formation of platelet-leukocyte aggregates. (C) 2003 Elsevier Ltd. All rights reserved.