The incomplete inhibition of platelet function by acetylsalicylic acid (ASA), despite the patients are receiving therapeutic doses of the drug ('aspirin-resistance'), is caused by numbers of risk factors. In this study we verified the idea that plasma homocysteine (Hcy) contributes to 'aspirin-resistance' in patients with coronary artery disease (CAD) and with or without type 2 diabetes mellitus (T2DM). A cross-designed randomized controlled intervention study has been performed (126 CAD pts incl. 26 with T2DM) to determine whether increasing ASA dose from 75mg to 150mg daily may result in the increased antiplatelet effect, in the course of four-week treatment. Platelet response to collagen (coll) or arachidonic acid (AA) was monitored with whole blood aggregometry, plasma thromboxane (Tx), and Hcy levels were determined immunochemically. The ASA-mediated reductions in platelet response to coll (by 12±3%) or AA (by 10±3%) and in plasma Tx (by 20±9%; p<0.02 or less) were significantly greater for higher ASA dose and significantly correlated with plasma Hcy, which was significantly lower in "good" ASA responders compared to "poor" responders (p<0.001). Higher plasma Hcy appeared a significant risk factor for blood platelet refractoriness to low ASA dose (OR=1.11; ±95%CI: 1.02-1.20, p<0.02, adjusted to age, sex and CAD risk factors). Hcy diminished in vitro antiplatelet effect of low ASA concentration and augmented platelet aggregation (by up to 62% (p<0.005) for coll and up to 15% (p<0.005) for AA), whereas its acetyl derivative acted oppositely. Otherwise, Hcy intensified antiplatelet action of high ASA. Hyperhomocysteinaemia may be a novel risk factor for the suppressed blood platelet response to ASA, and homocysteine may act as a specific sensitizer of blood platelets to some agonists. While homocysteine per se acts as a proaggregatory agent to blood platelets, its acetylated form is able to reverse this effect. Thus, these findings reveal a possibly new challenging potential of the acetylating properties of ASA therapy.
Keywords: (N-α-(9-fluorenylmethoxycarbonyl)-S-trityl-l-homocysteine); 1,4-bis(5-phenyl-2-oxazolyl)benzene; 2,5-diphenyloxazole; 5,5′-dithiobis(2-nitrobenzoic acid); A(max); AA; ACE; ADMA; ADP; ASA; AUC; AcHTL; Acetylhomocysteine; BCA; BMI; BSA; Blood platelet reactivity; CABG; CAD; CI; COX-1; CS; CVD; Coronary artery disease; DCM; DIPEA; DL-N-acetylhomocysteine thiolactone; DL-homocysteine thiolactone hydrochloride; DMF; DMSO; DTNB; F; FAK; Fmoc-Hcy(Trt)-OH; Glu; HDL; HTL; HbA(1c); Hcy; Homocysteine; IQR; LAR; LDL; M; MI; Me; N,N-diisopropylethylamine; N,N-dimethylformamide; NADPH; OR; PAFAH I; PBS; PCI; PON1; POPOP; PPAR; PPO; Platelet protein acetylation; R(S); RT; Rac1; Ras-related C3 botulinum toxin substrate 1; SASAR; SD; SDS; Spearman's rank correlation coefficient; Std; T2DM; TFA; TIA; TNBS; Tx(B(2)); WBEA; acetylsalicylic acid; adenosine-5′-diphosphate; angiotensin converting enzyme; arachidonic acid; area under (aggregometric) curve; asymmetric dimethylarginine; bicinchoninic acid; body mass index; bovine serum albumin; cardiovascular disease; coll; collagen; comprehensive score of blood platelet response to agonists; confidence interval; coronary artery bypass grafting surgery; coronary artery disease; cyclooxygenase-1 (prostaglandin G/H synthase 1); dichloromethane; dimethylsulfoxide; female; focal adhesion kinase; glutamic acid (glutamate); glycated haemoglobin; high-density lipoproteins; high-sensitivity C-reactive protein; homocysteine; hs-CRP; interquartile range; laboratory ASA (aspirin) resistance; low-density lipoproteins; male; maximal aggregation; median; myocardial infarction; n.s.; non-significant; odds ratio; paroxonase; percutaneous coronary intervention; peroxisome proliferator-activated receptor; phosphate buffered saline; picrylsulfonic acid, 2,4,6-trinitrobenzenesulfonic acid; platelet-activating factor acetylhydrolase I; reduced nicotinamide adenine dinucleotide phosphate; room temperature; sodium dodecyl sulfate; standard deviation; standardized value; suboptimal ASA response; thromboxane (B(2)); transient ischaemic attack; trifluoroacetic acid; type 2 diabetes mellitus; whole blood electrical (impedance) aggregometry; ‘Aspirin-resistance’.
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