Polyunsaturated omega-3 fatty acids improve responsiveness to clopidogrel after percutaneous coronary intervention in patients with cytochrome P450 2C19 loss-of-function polymorphism.

BACKGROUND: Antiplatelet properties of omega-3 polyunsaturated fatty acids (PUFA) have been demonstrated in patients with coronary artery disease (CAD). It is unknown whether omega-3 PUFA can enhance platelet inhibition on standard aspirin and clopidogrel treatment in the setting of CYP2C19 loss-of-function polymorphism. AIM: To investigate whether omega-3 PUFA are able to modify platelet responsiveness to clopidogrel therapy in patients with CYP2C19 loss-of-function polymorphism undergoing percutaneous coronary intervention (PCI). METHODS: 63 patients with stable CAD undergoing PCI (48 males, mean age 63.2 ± 9.6 years) were enrolled into an investigator- initiated, prospective, single-centre, double-blind, placebo-controlled, randomised study. Patients on standard dual antiplatelet therapy (aspirin 75 mg daily and clopidogrel 600 mg loading dose followed by 75 mg daily) were assigned to receive the addition of 1 g of omega-3 ethyl esters (n = 33) or placebo (n = 30) for 1 month. Platelet function was measured serially by light transmittance aggregometry in response to 5 and 20 µmol/L ADP at baseline, 12 h, 3-5 days and 30 days after randomisation. CYP2C19*2 was genotyped at baseline. RESULTS: No significant differences were found in baseline variables, including the frequency of CYP2C19 genetic variants. At least one loss-of-function variant of CYP2C19*2 was found in 19 (30.2%) patients. In patients with CYP2C19*1/*2 and *2/*2 variants, maximal platelet aggregation induced by 5 and 20 µmol/L ADP was reduced by 21.4% (p = 0.006) and 14.3% (p = 0.041), respectively, after 1 month of treatment with omega-3 PUFA as compared to placebo. The beneficial effect of omega-3 PUFA was demonstrated in carriers of CYP2C19 loss-of-function polymorphism, whereas no differences in platelet aggregation between the omega-3 PUFA and placebo groups were found in patients with the 1*/1* variant. CONCLUSIONS: The addition of omega-3 ethyl esters significantly potentiates platelet response to clopidogrel after PCI mostly in patients with CYP2C19 loss-of-function polymorphism.

An important role of the SRC family kinase Lyn in stimulating platelet granule secretion.

The Src family kinases (SFKs) have been proposed to play stimulatory and inhibitory roles in platelet activation. The mechanisms for these apparently contradictory roles are unclear. Here we show that SFK, mainly Lyn, is important in stimulating a common signaling pathway leading to secretion of platelet granules. Lyn knock-out or an isoform-nonselective SFK inhibitor, PP2, inhibited platelet secretion of both dense and alpha granules and the secretion-dependent platelet aggregation induced by thrombin, collagen, and thromboxane A(2). The inhibitory effect of Lyn knock-out on platelet aggregation was reversed by supplementing granule content ADP, indicating that the primary role of Lyn is to stimulate granule secretion. Inhibitory effect of PP2 on platelet aggregation induced by thrombin and thromboxane A(2) were also reversed by supplementing ADP. Furthermore, PP2 treatment or Lyn knock-out diminished agonist-induced Akt activation and cyclic GMP production. The inhibitory effect of PP2 or Lyn knock-out on platelet response can be corrected by supplementing cyclic GMP. These data indicate that Lyn stimulates platelet secretion by activating the phosphoinositide 3-kinase-Akt-nitric oxide (NO)-cyclic GMP pathway and also provide an explanation why Lyn can both stimulate and inhibit platelet activation.

Genetic predictors of depressive symptoms in cardiac patients.

Numerous studies suggest that the prevalence of depression is greater among cardiac patients than in the general population. However, little attention has been paid to the possibility of genetic contributions to depressive symptoms in cardiac patients. We conducted a candidate gene study focusing on genes related to inflammation, platelet aggregation, endothelial function and omega-3 fatty acid metabolism as predictors of depressive symptoms among 977 participants with established cardiovascular disease. Results suggested that genetic variation related to endothelial dysfunction is predictive of depressive symptoms and that endothelial dysfunction may be a novel mechanism contributing to depressive symptoms among cardiac patients.

Requirements of SLP76 tyrosines in ITAM and integrin receptor signaling and in platelet function in vivo.

Src homology 2 domain-containing leukocyte phosphoprotein of 76 kD (SLP76), an adaptor that plays a critical role in platelet activation in vitro, contains three N-terminal tyrosine residues that are essential for its function. We demonstrate that mice containing complementary tyrosine to phenylalanine mutations in Y145 (Y145F) and Y112 and Y128 (Y112/128F) differentially regulate integrin and collagen receptor signaling. We show that mutation of Y145 leads to severe impairment of glycoprotein VI (GPVI)-mediated responses while preserving outside-in integrin signaling. Platelets from Y112/128F mice, although having mild defects in GPVI signaling, exhibit defective actin reorganization after GPVI or alpha IIb beta 3 engagement. The in vivo consequences of these signaling defects correlate with the mild protection from thrombosis seen in Y112/128F mice and the near complete protection observed in Y145F mice. Using genetic complementation, we further demonstrate that all three phosphorylatable tyrosines are required within the same SLP76 molecule to support platelet activation by GPVI.

Genetic strain differences in platelet aggregation and thrombus formation of laboratory rats.

Rats are employed to investigate the role of platelets in thrombus formation under flow conditions in vivo and to evaluate the pre-clinical potential of antiplatelet drugs. While Wistar and Sprague-Dawley (SD) strains are commonly used in thrombosis models, a number of rat strains have been established. Each strain possesses genetically unique characteristics such as hypertension, hyperglycemia or hyperlipidemia. The appropriate selection of a strain might have advantages for physiological and pharmacological studies. Comparative investigation of platelet aggregation among laboratory strains of rats is useful for the development of thrombosis models. In the present study, platelet aggregation response in eight laboratory rat strains, ACI, Brown Norway (BN), Donryu, Fischer 344 (F344), LEW, SD, Wistar and WKAH, were compared. Considerable strain differences were observed in ADP-, collagen- and TRAP-induced platelet aggregation. SD and BN are high-platelet-aggregation strains, while F344 and ACI are low-response strains. In the arteriovenous shunt thrombosis model, SD formed larger thrombi than F344 and Wistar rats. In the FeCl(3)-induced thrombosis model with the carotid artery, the time to occlusion of SD was significantly shorter than of F344 and ACI rats. F344 and ACI rats had significantly increased bleeding times compared with SD rat. The present study demonstrates that there are considerable strain differences in platelet aggregation among laboratory rats, which reflect thrombus formation.

Central and peripheral clocks in cardiovascular and metabolic function.

The molecular circadian clock entrains biological rhythms to a 24-hour schedule. Aspects of cardiovascular physiology and, indeed, the incidence of myocardial infarction and stroke are also subject to diurnal variation. The use of rodent models of disrupted clock function has begun to elucidate the role of the molecular clock in the pathophysiology of cardiovascular and metabolic disease.

Molecular and genetic basis for thrombasthenic thrombopathia in otterhounds.

OBJECTIVES: To determine the molecular and genetic basis for thrombasthenic thrombopathia in Otterhounds and establish whether the defect would be best classified as type-I Glanzmann's thrombasthenia. ANIMALS: 57 dogs, including 13 affected Otterhounds, 23 carrier Otterhounds, 17 unaffected Otterhounds, and 4 clinically normal unrelated dogs of other breeds. PROCEDURE: Functional (platelet aggregation, clot retraction, buccal mucosa bleeding time) and biochemical (electrophoresis, flow cytometry, fibrinogen content) analyses were conducted. In addition, first-strand cDNA synthesis from platelet total RNA was performed. Exons of the genes encoding for glycoproteins (GP) IIb and IIIa were amplified in overlapping fashion. The resulting products were excised from agarose gels and sequenced. The sequences obtained were compared with known cDNA sequences for canine GPIIb and GPIIIa. RESULTS: A single nucleotide change at position G1193 (1100) was detected in exon 12 of the gene encoding for platelet GPIIb in 2 affected Otterhounds. Carrier Otterhounds were heterozygous at this position, and 2 unaffected Otterhounds were unchanged. This nucleotide change would result in substitution of histidine for aspartic acid at position 398 (367) within the third calcium-binding domain of GPIIb. CONCLUSIONS AND CLINICAL RELEVANCE: These studies suggest that thrombasthenic thrombopathia of Otterhounds is homologous phenotypically and has a similar molecular basis to type-I Glanzmann's thrombasthenia in humans.

Ultrastructural studies of platelet aggregates from human subjects receiving clopidogrel and from a patient with an inherited defect of an ADP-dependent pathway of platelet activation.

Our study investigated the effect of the antithrombotic drug clopidogrel (75 mg/d for 7 days) on the ultrastructure of platelet aggregates induced by ADP or 2-methylthio-ADP (2-MeS-ADP) in citrated platelet-rich plasma and examined the activation state of the GP IIb/IIIa complexes. Results were compared with those obtained for patient M.L., who has a congenital disorder characterized by a reduced and reversible platelet response to ADP. When untreated normal platelets were stimulated with high-dose ADP, electron microscopy revealed large and stable aggregates often surrounded by a layer of what appeared to be degranulated platelets. The reversible aggregates of platelets from subjects receiving clopidogrel or from patient M.L. did not show this layer. Electron microscopy showed that in both situations, the aggregates were composed of loosely bound platelets with few contact points. Immunogold labeling of ultrathin sections of Lowicryl-embedded aggregates formed by ADP or 2-MeS-ADP showed a much decreased platelet surface staining by (1) a polyclonal anti-fibrinogen antibody and (2) AP-6, a murine anti-ligand-induced binding site monoclonal antibody specific for GP IIb/IIIa complexes occupied with fibrinogen. Similar findings were seen after disaggregation, when many single platelets were present that showed no signs of secretion. Flow cytometry confirmed that the number of ligand-occupied GP IIb/IIIa complexes was much lower on platelets stimulated with ADP or 2-MeS-ADP after clopidogrel treatment. As expected from previous studies, ADP-induced platelet shape change and Ca2+ influx were unaffected by clopidogrel. These results agree with the hypothesis that platelet activation by ADP is biphasic and highlight a receptor-induced activation pathway affected by clopidogrel (or congenitally impaired in patient M.L.) that is necessary for the full activation of GP IIb/IIIa and the formation of stable macroaggregates.