Platelet surface receptor activation in patients with chronic renal failure on hemodialysis, peritoneal dialysis and those with successful kidney transplantation

Hormones, age, and sex affect platelet responsiveness in vitro

BACKGROUND

Female sex confers a survival advantage following severe injury in the setting of trauma-induced coagulopathy, with female platelets having heightened responsiveness likely due to estrogen. The effects of testosterone on platelet biology are unknown, and platelets express both estradiol and androgen receptors on the plasma membrane. We hypothesize testosterone decreases platelet responses in vitro, and there are baseline differences in platelet function and metabolism stratified by sex/age.

STUDY DESIGN AND METHODS

Apheresis platelets were collected from: older males (OM) ≥45 years, younger males (YM) <45 years, older females (OF) ≥54 years, and younger females (YF) <54 years, and testosterone and estradiol were measured. Platelets were incubated with testosterone (5.31 ng/ml), estradiol (105 pg/ml) or vehicle and stimulated with buffer, adenosine diphosphate (20 μM), platelet activating factor (2 μM), or thrombin (0.3 U/ml). Aggregation, CD62P surface expression, fibrinogen receptor surface expression, and platelet mitochondrial metabolism were measured.

RESULTS

Testosterone significantly inhibited aggregation in OF and OM (p < .05), inhibited CD41a expression in YF, YM, and OM (p < .05), and affected a few of the baseline amounts of CD62P surface expression but not platelet activation to platelet-activating factor and adenosine diphosphate, and variably changed platelet metabolism.

DISCUSSION

Platelets have sex- and age-specific aggregation, receptor expression, and metabolism. Testosterone decreases platelet function dependent on the stimulus, age, and sex. Similarly, platelet metabolism has varying responses to sex hormones with baseline metabolic differences dependent upon sex and age.

PPARγ in Ischemia-Reperfusion Injury: Overview of the Biology and Therapy

Ischemia-reperfusion injury (IRI) is a complex pathophysiological process that is often characterized as a blood circulation disorder caused due to various factors (such as traumatic shock, surgery, organ transplantation, burn, and thrombus). Severe metabolic dysregulation and tissue structure destruction are observed upon restoration of blood flow to the ischemic tissue. Theoretically, IRI can occur in various tissues and organs, including the kidney, liver, myocardium, and brain, among others. The advances made in research regarding restoring tissue perfusion in ischemic areas have been inadequate with regard to decreasing the mortality and infarct size associated with IRI. Hence, the clinical treatment of patients with severe IRI remains a thorny issue. Peroxisome proliferator-activated receptor γ (PPARγ) is a member of a superfamily of nuclear transcription factors activated by agonists and is a promising therapeutic target for ameliorating IRI. Therefore, this review focuses on the role of PPARγ in IRI. The protective effects of PPARγ, such as attenuating oxidative stress, inhibiting inflammatory responses, and antagonizing apoptosis, are described, envisaging certain therapeutic perspectives.

Platelet activation, coagulation activation and C-reactive protein in simultaneous samples from the vascular access and peripheral veins of haemodialysis patients

INTRODUCTION

Most studies of haemodialysis (HD) patients compare venous blood samples from controls with samples from the vascular access (VA) of HD patients. We hypothesised that VA samples may be more prothrombotic compared with venous samples.

METHODS

Samples were taken simultaneously from the VA and the contralateral antecubital vein, from 26 patients immediately before HD. Platelet function was assessed by (1) flow cytometric measurement of P-selectin expression and fibrinogen binding (±ADP) and 2) Ultegra rapid platelet function assay. Plasma soluble P-selectin, von Willebrand factor antigen, high sensitivity C-reactive Protein (hs-CRP), thrombin-antithrombin III complex and D-dimer measured by ELISA.

RESULTS

Thrombin receptor activating peptide-induced platelet aggregation (P < 0.001) and hs-CRP (P < 0.001) were higher in VA compared with venous samples. Unstimulated platelet fibrinogen binding (P = 0.016) and ADP-stimulated P-selectin expression (P = 0.008) were lower in VA compared with venous samples. The significant difference in hsCRP persisted when patients taking and not taking antiplatelet therapy were analysed separately, but platelet activation remained significantly different only in the nonantiplatelet group.

CONCLUSION

There are statistically significant differences between sampling sites, although samples from the VA do not appear to be more pro-thrombotic. Future studies comparing HD patients with controls should ensure uniformity of sampling sites to prevent inaccurate conclusions being drawn.

Increased nitric oxide production in platelets from severe chronic renal failure patients

Nitric oxide (NO) production occurs through oxidation of the amino acid L-arginine by NO synthase (NOS). NO inhibits platelet activation by increasing the levels of cyclic guanosine monophosphate (cGMP), thus maintaining vascular homeostasis. Our group previously demonstrated (da Silva et al. 2005) an enhancement of the L-arginine-NO-cGMP pathway in platelets taken from chronic renal failure (CRF) patients on haemodialysis associated with reduced platelet aggregation. We investigate the platelet L-arginine-NO-cGMP pathway, platelet function, and inflammation from patients in CRF on conservative treatment. A total of 42 CRF patients and 42 controls (creatinine clearance = 27 ± 3 vs. 93 ± 1 mL per min per 1.73 m2, respectively) participated in this study. NOS activity and expression and cGMP concentration were measured in platelets. Platelet aggregation induced by collagen or ADP was evaluated and plasma levels of fibrinogen were determined by the Clauss method. A marked increase in basal NOS activity was seen in undialysed CRF patients compared with controls, accompanied by an elevation of fibrinogen plasma levels. There were no differences in expression of NOS and in cGMP levels. In this context, platelet aggregation was not affected. We provide the first evidence of increased intraplatelet NO biosynthesis in undialysed CRF patients, which can be an early marker of future haemostatic abnormalities during dialysis treatment.

Low responsiveness to clopidogrel increases risk among CKD patients undergoing coronary intervention

Patients with CKD are at higher risk for major events after percutaneous coronary intervention (PCI) compared with subjects with normal renal function. The aims of this study were to evaluate responsiveness to clopidogrel in patients with CKD and to examine the effect of antiplatelet drug response on post-PCI outcome. We retrospectively evaluated a consecutive cohort of 1567 patients with symptomatic coronary artery disease undergoing PCI, 648 (41%) of whom had stage 3 to 5 CKD. We assessed responsiveness to clopidogrel by ADP-induced platelet aggregation after oral administration of a 600-mg clopidogrel loading dose and 100 mg of aspirin. In a multivariate survival analysis that included 1335 (85%) of the cohort, stage 3 to 5 CKD and low response to clopidogrel were independent predictors of the primary end point (composite of myocardial infarction, ischemic stroke, and death within 1 year). In summary, a low response to clopidogrel might be an additional risk factor for the poorer outcomes in patients with stage 3 to 5 CKD compared with patients with better renal function.

Increased coated-platelet levels in chronic haemodialysis patients

AIM

To determine if levels of coated-platelets, which are potentially pro-thrombotic, are increased in end-stage renal disease patients on haemodialysis, a condition associated with high cardiovascular disease risk.

METHODS

In a cross-sectional observational study, coated-platelet levels were measured by flow cytometry in 25 end-stage renal failure haemodialysis patients and 25 controls without renal disease. Associations between coated-platelet levels and clinical and biochemical factors relevant to renal and cardiovascular disease were evaluated.

RESULTS

Mean +/- SD coated-platelet levels were higher in the dialysis group than in the control group (39.3+/-14.3% vs 30.9+/-10.3%, P=0.02). The number of subjects with high coated-platelet levels (>40%) was larger in the dialysis than in the control group (13/25 vs 4/25, chi(2) test, P=0.007). On univariate analysis, coated-platelet levels correlated with serum C-reactive protein levels in renal failure (r=0.47, P=0.02) and inversely with white cell count in the control group (r= -0.60, P=0.001). Coated-platelet levels were higher in dialysis patients reporting alcohol abstinence than among those reporting 'social' drinking (44.3+/-12.6 vs 28.8+/-13.5%, P=0.01). Age, gender, body weight, smoking, diabetes, lipid levels and lipid-lowering drugs were not associated with coated-platelet levels (all P>0.05).

CONCLUSION

Coated-platelet levels are increased in haemodialysis patients relative to subjects with normal renal function, and are related to inflammation and alcohol abstinence. Other vascular risk factors, such as smoking, lipids and diabetes, were not related to coated-platelet levels. Coated-platelets may be implicated in the increased thrombosis and vascular risk in end-stage renal disease.

The Residual Platelet Aggregation after Deployment of Intracoronary Stent (PREDICT) score

BACKGROUND

Recent studies suggest a high interindividual variability of response to clopidogrel associated with adverse cardiovascular outcome. Different clinical factors are considered to influence a persistent residual platelet aggregation (RPA) despite conventional antiplatelet therapy.

OBJECTIVES

To investigate clinical factors that affect RPA after 600-mg clopidogrel loading in a large unselected cohort of patients with symptomatic CAD.

METHODS

The study population included a consecutive cohort of 1,092 patients treated with coronary stenting for stable angina and acute coronary syndromes (ACS). Residual platelet activity was assessed by ADP (20 micromol L(-1))-induced platelet aggregation >or= 6 h after LD. Eleven clinical factors were included in the primary analysis.

RESULTS

In multivariate regression analysis increased RPA was significantly influenced by ACS, reduced LV-function, diabetes mellitus, renal failure (creatinine > 1.5 mg dL(-1)), and age > 65 years. In a factor-weighed model the risk for high RPA increased with higher score levels (OR for patients with a score of 1-3, 1.21, 95% CI 0.7-2.1; score 4-6, OR 2.0, 95% CI 1.17-3.5; P = 0.01; score 7-9, OR 3.3, 95% CI 1.8-6.0). During a 30-day follow-up the incidence of major adverse events was higher in patients with RPA in the upper tertile (4.8% vs. 2.5% in the 2nd and 1.5% in the 1st tertile; P < 0.05).

CONCLUSIONS

The PREDICT score provides a good tool to estimate residual platelet activity after clopidogrel LD by easily available patient details. Additionally, we demonstrate its association with short-term outcome. Thus, patients with a high score may benefit from intensified antiplatelet therapy by improved platelet inhibition and risk reduction for thromboischemic events.

Oxidatively-modified and glycated proteins as candidate pro-inflammatory toxins in uremia and dialysis patients

End stage renal disease (ESRD) patients accumulate blood hallmarks of protein glycation and oxidation. It is now well established that these protein damage products may represent a heterogeneous class of uremic toxins with pro-inflammatory and pro-oxidant properties. These toxins could be directly involved in the pathogenesis of the inflammatory syndrome and vascular complications, which are mainly sustained by the uremic state and bioincompatibility of dialysis therapy. A key underlying event in the toxicity of these proteinaceous solutes has been identified in scavenger receptor-dependent recognition and elimination by inflammatory and endothelial cells, which once activated generate further and even more pronounced protein injuries by a self-feeding mechanism based on inflammation and oxidative stress-derived events. This review examines the literature and provides original information on the techniques for investigating proteinaceous pro-inflammatory toxins. We have also evaluated therapeutic - either pharmacological or dialytic - strategies proposed to alleviate the accumulation of these toxins and to constrain the inflammatory and oxidative burden of ESRD.

Platelet activity and serum homocysteine levels in patients with end-stage renal failure with regard to dialysis modality

BACKGROUND

Recent evidence suggests that the activation of platelets and their interaction with circulating cells are important independent risk factors for atherosclerosis. In non-uremic patients with symptomatic peripheral vascular disease, a relationship between serum homocysteine (Hcy) levels and platelet activity had been reported. The purposes of this study were to evaluate of effects of dialysis modality on platelet activity in patients with end-stage renal failure and to investigate the relationship between platelet activity, Hcy, and left ventricular hypertrophy (LVH).

MATERIAL AND METHODS

In age and sex matched 19 healthy subjects, 20 hemodialysis (HD) patients, and 18 continuous ambulatory peritoneal dialysis (CAPD) patients, the expression of platelet surface receptors CD41, CD61, CD42a, and CD62P were investigated. CD62P expression was statistically significantly increased in HD patients compared with CAPD patients and controls (34.4 +/- 22.5%; 17.3 +/- 19.6%, 12.0 +/- 15.6%, respectively, p < 0.05), but not in CAPD patients compared with controls. There was a positive correlation between CD62 expression and duration of dialysis in HD patients (r = 0.498, p = 0.026). Mean plasma Hcy levels in dialysis patients were higher than reference levels. However, we could not find any relationship between CD62 expression, Hcy, and LVH in both groups (p > 0.05).

CONCLUSIONS

Hemodialysis and peritoneal dialysis (PD) have a different impact on the expression of CD62: peritoneal dialysis seems to have a more favorable effect. It may be possible that the differences in biocompatibility between PD and HD potentially contribute to differences in CD62 expression.