Vascular toxicity of urea, a new "old player" in the pathogenesis of chronic renal failure induced cardiovascular diseases

Uremic Toxins and Cardiovascular System

When chronic kidney disease develops, the capacity of the kidneys to clear metabolic waste products from the body is gradually lost. This process results in the retention of a large array of compounds affecting biochemical and biological functions (uremic toxins), of which several can cause cardiovascular damage. This article reviews the main cardiotoxic mechanisms related to uremic toxin retention (endothelial dysfunction, vascular smooth muscle cell alterations, inflammation, mineral bone disorder, insulin resistance, and thrombogenicity) and the main responsible retention compounds. Therapeutic options are reviewed, such as influencing solute generation by intestinal microbiota.

Modeling Uremic Vasculopathy With Induced Pluripotent Stem Cell-Derived Endothelial Cells as a Drug Screening System

Background: Cardiovascular complications are the leading cause of mortality in patients with chronic kidney disease (CKD). Uremic vasculopathy plays a crucial role in facilitating the progression of cardiovascular complications in advanced CKD. However, the improvement of conventional research methods could provide further insights into CKD.

Objectives: In this study, we aimed to develop a novel model of uremic vasculopathy as a potential drug screening system.

Methods and Results: The effects of uremic serum and different combinations of uremic toxins on induced pluripotent stem cell (iPSC)-derived endothelial cells (ECs) of a normal control and a CKD patient were investigated using several functional assays. We found that a mixture of uremic toxins composed of high urea, creatinine, uric acid, and indoxyl sulfate exerted deleterious effects on normal control iPSC-ECs that were comparable to uremic serum by increasing reactive oxygen species and apoptosis, as well as suppression of tube formation. Additional characterization revealed a potential involvement of dysregulated TGF-β signaling as treatment with either losartan or TGF-β inhibitors led to the attenuation of adverse effects induced by uremic toxins. Importantly, impaired wound healing potential seen in CKD patient-specific iPSC-ECs was rescued by treatment with losartan and TGF-β inhibitors.

Conclusion: Our study demonstrated that simplified uremic toxin mixtures can simulate the uremic micromilieu reproducibly and CKD patient-specific iPSC-ECs can potentially recapitulate susceptibility to uremic vasculopathy. This novel model of uremic vasculopathy may provide a new research tool as a drug screening system.

Risk factors and therapies in vascular diseases: An umbrella review of updated systematic reviews and meta-analyses

Aberrant blood vessel functioning and systemic circulation are key causes for vascular disorders; cardiovascular, cerebrovascular, renal artery stenosis, and peripheral artery diseases. Epidemiological and basic science evidence supported genetic reasons, compounded by obesity, hypercholesterolemia, hypertension, diabetes, and smoking as risk factors. This is an umbrella review of risk factors and therapies in vascular disorders, exploring systematic reviews and meta-analyses studies in PubMed, Cochrane, Embase, and Central published in January 2000-May 2018. We made qualitative eligibility gradation of the articles based on inclusion criteria, and independently extracted descriptive and methodologic data to compile their outcomes. We considered 95% confidence interval and the between-study heterogeneity, designated by I 2 . Overall, we extracted 217 studies of impressive quality and at low risk of bias, including 124, 30, 23, 32, and 8, respectively, for the search terms "cardiovascular," "renal," "cerebral," and "limb ischemia" each in combination with "risk factors" and "therapeutics." Our search on genome-wide analyses revealed genes associated with HDL-cholesterol, matrix metalloproteases, angiogenesis, notch3, renin-angiotensin, apolipoprotein E, insulin, and cytokine levels as critical participants in the pathogenesis of vascular diseases. Hypertension and endothelial growth factor-linked polymorphisms were found to contribute to vascular damage. The studies reinforced that lifestyle and dietary patterns influenced susceptibility of circulatory system diseases. Additionally, endovascular medicines, surgical vascularization, angioplasty, and renal artery stenting appeared as major therapeutic approaches in vascular patients. Altogether, our review offers up-to-date information on pathophysiology of vascular diseases and provides insight into existing research, clinical management and clinical gaps in the field.

Urea Memory: Transient Cell Exposure to Urea Causes Persistent Mitochondrial ROS Production and Endothelial Dysfunction

Urea at post-dialysis levels induces increased ROS in a number of cell types. The aim of this study was to determine whether urea-induced production of ROS remains elevated after urea is no longer present, and, if it does, to characterize its origin and effects. Human arterial endothelial cells were incubated with 20 mM urea for two days, and then cells were incubated for an additional two days in medium alone. Maximal ROS levels induced by initial urea continued at the same level despite urea being absent. These effects were prevented by either MnSOD expression or by Nox1/4 inhibition with GKT13781. Sustained urea-induced ROS caused a persistent reduction in mtDNA copy number and electron transport chain transcripts, a reduction in transcription of mitochondrial fusion proteins, an increase in mitochondrial fission proteins, and persistent expression of endothelial inflammatory markers. The SOD-catalase mimetic MnTBAP reversed each of these. These results suggest that persistent increases in ROS after cells are no long exposed to urea may play a major role in continued kidney damage and functional decline despite reduction of urea levels after dialysis.