Chronic kidney disease (CKD) perturbs the crosstalk with others organs, with the interaction between the kidneys and the heart having been studied most intensively. However, a growing body of data indicates that there is an association between kidney dysfunction and disorders of the central nervous system. In epidemiological studies, CKD is associated with a high prevalence of neurological complications, such as cerebrovascular disorders, movement disorders, cognitive impairment and depression. Along with traditional cardiovascular risk factors (such as diabetes, inflammation, hypertension and dyslipidaemia), non-traditional risk factors related to kidney damage (such as uraemic toxins) may predispose patients with CKD to neurological disorders. There is increasing evidence to show that uraemic toxins, for example indoxyl sulphate, have a neurotoxic effect. A better understanding of factors responsible for the elevated prevalence of neurological disorders among patients with CKD might facilitate the development of novel treatments. Here, we review (i) the potential clinical impact of CKD on cerebrovascular and neurological complications, (ii) the mechanisms underlying the uraemic toxins’ putative action (based on pre-clinical and clinical research) and (iii) the potential impact of these findings on patient care.

Chronic kidney disease (CKD) is associated with profound vascular remodeling, which accelerates the progression of cardiovascular disease. This remodeling is characterized by intimal hyperplasia, accelerated atherosclerosis, excessive vascular calcification, and vascular stiffness. Vascular smooth muscle cell (VSMC) dysfunction has a key role in the remodeling process. Under uremic conditions, VSMCs can switch from a contractile phenotype to a synthetic phenotype, and undergo abnormal proliferation, migration, senescence, apoptosis, and calcification. A growing body of data from experiments in vitro and animal models suggests that uremic toxins (such as inorganic phosphate, indoxyl sulfate and advanced-glycation end products) may directly impact the VSMCs’ physiological functions. Chronic, low-grade inflammation and oxidative stress—hallmarks of CKD—are also strong inducers of VSMC dysfunction. Here, we review current knowledge about the impact of uremic toxins on VSMC function in CKD, and the consequences for pathological vascular remodeling.

Vascular dysfunction is an essential element found in many cardiovascular pathologies and in pathologies that have a cardiovascular impact such as chronic kidney disease (CKD). Alteration of vasomotricity is due to an imbalance between the production of relaxing and contracting factors. In addition to becoming a determining factor in pathophysiological alterations, vascular dysfunction constitutes the first step in the development of atherosclerosis plaques or vascular calcifications. In patients with CKD, alteration of vasomotricity tends to emerge as being a new, less conventional, risk factor. CKD is characterized by the accumulation of uremic toxins (UTs) such as phosphate, para-cresyl sulfate, indoxyl sulfate, and FGF23 and, consequently, the deleterious role of UTs on vascular dysfunction has been explored. This accumulation of UTs is associated with systemic alterations including inflammation, oxidative stress, and the decrease of nitric oxide production. The present review proposes to summarize our current knowledge of the mechanisms by which UTs induce vascular dysfunction.

Associations of chronic kidney disease (CKD) with metabolic syndrome and cardiovascular disease (CVD) have long been recognized. Until recently, such associations were mainly limited to interrelationships between either heart and kidney, heart and metabolic syndrome, or metabolic syndrome and kidney. It is the merit of the American Heart Association (AHA) to have set up a work group of cardiologists, endocrinologists, and nephrologists for the purpose of combining all 3 disorders in a single entity, as an appreciation of their pathophysiological interrelatedness. To this end, they proposed the term cardiovascular-kidney-metabolic (CKM) syndrome, which reflects multidirectional relationships among metabolic risk factors, CKD, and the cardiovascular system. Following a consensus approach in defining CKM with 5 stages, the work group subsequently developed new risk prediction equations, named predicting risk of CVD events (PREVENT) equations, which included estimated glomerular filtration rate (eGFR) and albuminuria as variables in addition to traditional cardiovascular and metabolic factors. Despite several limitations, this development is a major step forward in cardiovascular risk prediction. Its clinical application should translate into earlier, more appropriate treatment and prevention of CKM syndrome.

Elevated serum urea levels are common in moderate-to-advanced chronic kidney disease (CKD). Several studies have shown that urea is a direct and indirect uraemic toxin, especially with regard to cardiovascular disease. We sought to determine whether serum urea levels are associated with adverse cardiovascular events and death before renal replacement therapy (RRT) in patients with CKD. CKD-REIN is a prospective cohort of CKD nephrology outpatients not receiving maintenance dialysis. The 2507 patients included in the analysis were divided into three groups according to the baseline serum urea level (T1 <10.5, T2 10.5–15.1 and T3 ≥15.1 mmol/L). Cox proportional hazard models were used to estimate hazard ratios (HRs) for first atheromatous or non-atheromatous cardiovascular (CV) events and all-cause mortality before RRT. The models were adjusted for baseline comorbidities, laboratory data and medications. Of the 2507 included patients {median [interquartile range (IQR)] age: 69 [61–77]; mean (standard deviation) estimated glomerular filtration rate (eGFR) 33.5 (11.6) mL/min/1.73 m²}, 54% had a history of cardiovascular disease. After multiple adjustments for CV risk factors (including eGFR), patients in T3 had a higher risk of atheromatous and non-atheromatous CV events than patient in T1 (n events = 451, HR [95% CI]: 1.93 [1.39; 2.69]). The adjusted HRs for death before RRT (n events = 407) were 1.31 [0.97; 1.76] and 1.73 [1.22; 2.45] for patients T2 and those in T3, respectively. Our data suggested that urea is a predictor of CV outcomes beyond CV risk factors including eGFR.