Platelet microparticles and hemostatic disturbances in renal insufficiency and cardiovascular disease

Abstract

Background: Chronic kidney disease (CKD) affect up to 10-15% of the population worldwide and is a growing global health problem. Diabetes, hypertension and renal diseases, such as glomerulonephritis, are the major cause of CKD in high- and middle-income countries. CKD is a strong independent risk factor for cardiovascular disease (CVD) and CKD patients do worse after a cardiovascular event. This is only partially explained by traditional risk factors. Several non-traditional risk factors for CVD in CKD are becoming recognised, such as inflammation, oxidative stress, calcium-phosphate metabolism, endothelial dysfunction, malnutrition, anemia, and most recently gut microbiota, all in interplay with accumulating uremic toxins as renal function decline. Hemostatic disturbances including platelet dysfunction are well known in CKD, which is considered a prothrombotic state. However, the paradoxical simultaneous increased risk of bleeding is less understood. Microparticles (MPs) are small sized vesicles (100-1000 nm), which are shed into the circulation from various cells including platelets and endothelial cells due to different stimuli or apoptosis. MPs carry the same surface proteins as their parent cell, and MPs are both markers of disease and can induce inter-cellular cross talk. Platelet MPs (PMPs) are the most abundant MPs in the circulation, and the major significance is their procoagulant activity. MP concentrations are known to correlate with both CKD and CVD. Vitamin D deficiency and endothelial dysfunction is evident early in CKD and are associated with increased risk of CVD. Normal endothelial function is essential for maintained hemostasis. Vitamin D is involved in calcium-phosphate balance and upregulates production of nitric oxide, essential in endothelial function. Endothelial microparticles (EMPs) may have a role in assessing endothelial dysfunction. The overall objective of this PhD project was to elucidate some of the complex mechanism causing CKD patients to suffer such high risk for CVD, with focus on hemostatic disturbances, and platelet and endothelial microparticles.

Methods and results: In study I, hemostasis was studied using a global assay in patients with severe CKD, patients on hemodialysis, and healthy controls The results demonstrated a prothrombotic state and an impaired fibrinolysis in severe CKD, as well as a tighter fibrin network assessed with scanning electron microscopy, despite normal concentrations of endogenous fibrinolysis in hibitors. In study II, platelet and endothelial microparticles were investigated in acute coronary syndrome (ACS) patients with and without CKD, using flow cytometry. PMPs and EMPs concentrations were elevated in severe CKD. Study III, a substudy of the SOLID randomized placebo-controlled trial, where paricalcitol treatment in CKD patients demonstrated beneficial effects on endothelial function and reduced proinflammatory cytokines. In our study, paricalcitol treatment reduced concentrations of intercellular adhesion molecule-1 (ICAM-1) positive MPs. Concentrations of cell-activation induced EMPs and PMPs were maintained in the paricalcitol group. Study IV investigated if biomarkers related to hemostasis, endothelial function and vascular regulation correlated with renal function in a large cohort of ACS patients, and determined their association with outcome in the subgroups with preserved and with reduced renal function. Biomarkers were quantified by proteomic methods. The biomarkers in ACS patients with reduced renal function indicated a prothrombotic state, with altered endothelial function and vascular regulation, and several of these were associated with outcome in this group.

Conclusions: We confirm that CKD is associated with a prothrombotic state, and at the same time an impaired fibrinolysis potentially due to a tighter fibrin network. We show that in ACS patients with CKD, the MP profile indicate higher platelet activation and endothelial dysfunction compared with non-CKD patients, despite concurrent dual antiplatelet and statin treatment. We show that in CKD patients, paricalcitol treatment reduce concentrations of ICAM positive MPs, indicating a less proatherosclerotic endothelium. We found that in a large cohort of ACS patients with reduced renal function, the biomarker profile indicates a prothrombotic state. The biomarkers associated with outcome differ between patients with CKD and non-CKD. This indicate that in the field of biomarkers, it might not be sufficient to adjust for renal function. Rather, when renal failure is established, it could be regarded as a separate disease state with its own distinct pathophysiology.