CKD-associated Cardiovascular Disease Research Articles

Lipidomic approaches to dissect dysregulated lipid metabolism in kidney disease.

Dyslipidaemia is a hallmark of chronic kidney disease (CKD). The severity of dyslipidaemia not only correlates with CKD stage but is also associated with CKD-associated cardiovascular disease and mortality. Understanding how lipids are dysregulated in CKD is, however, challenging owing to the incredible diversity of lipid structures. CKD-associated dyslipidaemia occurs as a consequence of complex interactions between genetic, environmental and kidney-specific factors, which to understand, requires an appreciation of perturbations in the underlying network of genes, proteins and lipids. Modern lipidomic technologies attempt to systematically identify and quantify lipid species from biological systems. The rapid development of a variety of analytical platforms based on mass spectrometry has enabled the identification of complex lipids at great precision and depth. Insights from lipidomics studies to date suggest that the overall architecture of free fatty acid partitioning between fatty acid oxidation and complex lipid fatty acid composition is an important driver of CKD progression. Available evidence suggests that CKD progression is associated with metabolic inflexibility, reflecting a diminished capacity to utilize free fatty acids through β-oxidation, and resulting in the diversion of accumulating fatty acids to complex lipids such as triglycerides. This effect is reversed with interventions that improve kidney health, suggesting that targeting of lipid abnormalities could be beneficial in preventing CKD progression.

Fractalkine (CX3CL1) and Its Receptor CX3CR1: A Promising Therapeutic Target in Chronic Kidney Disease?

Innate immune cells are key contributors to kidney inflammation and fibrosis. Infiltration of the renal parenchyma by innate immune cells is governed by multiple signalling pathways. Since the discovery of the chemokine fractalkine (CX3CL1) and its receptor, CX3CR1 over twenty years ago, a wealth of evidence has emerged linking CX3CL1-CX3CR1 signalling to renal pathologies in both acute and chronic kidney diseases (CKD). However, despite the extent of data indicating a pathogenic role for this pathway in kidney disease and its complications, no human trials of targeted therapeutic agents have been reported. Although acute autoimmune kidney disease is often successfully treated with immunomodulatory medications, there is a notable lack of treatment options for patients with progressive fibrotic CKD. In this article we revisit the CX3CL1-CX3CR1 axis and its functional roles. Furthermore we review the accumulating evidence that CX3CL1-CX3CR1 interactions mediate important events in the intra-renal pathophysiology of CKD progression, particularly via recruitment of innate immune cells into the kidney. We also consider the role that systemic activation of the CX3CL1-CX3CR1 axis in renal disease contributes to CKD-associated cardiovascular disease. Based on this evidence, we highlight the potential for therapies targeting CX3CL1 or CX3CR1 to benefit people living with CKD.

Uraemic solutes as therapeutic targets in CKD-associated cardiovascular disease.

Chronic kidney disease (CKD) is characterized by the retention of a myriad of solutes termed uraemic (or uremic) toxins, which inflict damage to several organs, including the cardiovascular system. Uraemic toxins can induce hallmarks of cardiovascular disease (CVD), such as atherothrombosis, heart failure, dysrhythmias, vessel calcification and dysregulated angiogenesis. CVD is an important driver of mortality in patients with CKD; however, reliance on conventional approaches to managing CVD risk is insufficient in these patients, underscoring a need to target risk factors that are specific to CKD. Mounting evidence suggests that targeting uraemic toxins and/or pathways induced by uraemic toxins, including tryptophan metabolites and trimethylamine N-oxide (TMAO), can lower the risk of CVD in patients with CKD. Although tangible therapies resulting from our growing knowledge of uraemic toxicity are yet to materialize, a number of pharmacological and non-pharmacological approaches have the potential to abrogate the effects of uraemic toxins, for example, by decreasing the production of uraemic toxins, by modifying metabolic pathways induced by uraemic toxins such as those controlled by aryl hydrocarbon receptor signalling and by augmenting the clearance of uraemic toxins.

Periostin contributes to renal and cardiac dysfunction in rats with chronic kidney disease: Reduction of PPARα

POSTN knockdown inhibits the formation of NLRP3 inflammasome in rat myocardium.Periostin (POSTN), an extracellular matrix protein, and peroxisome proliferator-activated receptor alpha (PPARα), a ligand-activated nuclear transcription factor, are reported to be involved in renal and cardiac dysfunction associated with chronic kidney disease (CKD), respectively. This study is performed to investigate how POSTN-PPARα axis affects the progress of CKD. In vivo, adenovirus particles containing POSTN short hairpin RNA (Ad-shPOSTN) were intravenously given to Sprague Dawley rats following 5/6 nephrectomy. The effects of Ad-shPOSTN on CKD and CKD-associated cardiovascular disease were evaluated. In vitro, NRK-52E renal tubular epithelial cells were infected with Ad-shPOSTN or Ad-POSTN (overexpression) to explore whether POSTN affected collagen deposition by regulating PPARα. We found that POSTN expression was upregulated, while PPARα was downregulated in the injured renal and left ventricular tissues of nephrectomized rats. Ad-shPOSTN improved renal function, prevented cardiac dysfunction, and attenuated organ fibrosis in nephrectomized rats. The expression levels of renal and myocardial PPARα were increased following Ad-shPOSTN administration. Furthermore, POSTN silencing suppressed the formation of NOD-like receptor family pyrin domain containing 3 (NLRP3) inflammasome in the myocardium: the levels of NLRP3, anti-apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC), cleaved caspase 1, mature interleukin (IL)-1β and IL-18 were reduced. In NRK-52E cells, forced overexpression of POSTN directly inhibited PPARα expression and induced collagen deposition. WY14643, a PPARα agonist, suppressed POSTN-induced collagen deposition. In summary, our study demonstrates that POSTN negatively regulates PPARα expression. Targeting POSTN-PPARα axis may present a novel protective intervention to alleviate CKD and CKD-associated cardiac dysfunction.

Adenine-induced chronic kidney disease in rats.

Many animal models have been developed to study the causes and treatments of chronic kidney disease (CKD) in humans, an insidious disease resulting from kidney injury and characterized by persistent functional decline for more than 3 months, with or without evidence of structural deficit. The eventual outcome of CKD may be end-stage kidney disease (ESKD), where patients need dialysis or transplantation to survive. Cardiovascular disease is accelerated in patients with CKD and contributes to increased mortality, with the relationship between CKD and cardiovascular disease being bi-directional. Most animal models do not mimic the complexity of the human disease as many do not develop CKD-associated cardiovascular disease. The adenine diet model of CKD in rodents is an exception. The original adenine diet model produced rapid-onset kidney disease with extensive tubulointerstitial fibrosis, tubular atrophy, crystal formation and marked vessel calcification. Since then, lower adenine intake in rats has been found to induce slowly progressive kidney damage and cardiovascular disease. These chronic adenine diet models allow the characterization of relatively stable kidney and cardiovascular disease, similar to CKD in humans. In addition, interventions for reversal can be tested. Here the key features of the adenine diet model of CKD are noted, along with some limitations of other available models. In summary, the data presented here support the use of chronic low-dose adenine diet in rats as an easy and effective model for understanding human CKD, especially the links with cardiovascular disease, and developing potential therapeutic interventions.

Chronic kidney disease-associated cardiovascular disease: scope and limitations of animal models.

Chronic kidney disease (CKD) is a heterogeneous range of disorders affecting up to 11% of the world's population. The majority of patients with CKD die of cardiovascular disease (CVD) before progressing to end-stage renal disease. CKD patients have an increased risk of atherosclerotic disease as well as a unique cardiovascular phenotype. There remains no clear aetiology for these issues and a better understanding of the pathophysiology of CKD-associated CVD is urgently needed. Although nonanimal studies can provide insights into the nature of disease, the whole-organism nature of CKD-associated CVD means that high-quality animal models, at least for the immediate future, are likely to remain a key tool in improving our understanding in this area. We will discuss the methods used to induce renal impairment in rodents and the methods available to assess cardiovascular phenotype and in each case describe the applicability to humans.

The flavonoid rutin improves kidney and heart structure and function in an adenine-induced rat model of chronic kidney disease

Many foods contain rutin, a flavonoid with many health benefits. Here we tested rutin to reverse chronic kidney disease (CKD) and associated cardiovascular disease, using an established rodent model with adenine diet (0.25%) over 16weeks. Rutin was added to the diet for the final 8weeks. We measured kidney function (blood urea nitrogen/BUN, plasma creatinine/PCr, plasma uric acid, proteinuria); kidney structure (tubular damage, fibrosis, inflammation); cardiovascular function and structure (blood pressure, left ventricular stiffness, vascular responses, echocardiography, histology); and biomarkers for oxidative stress (HO-1), inflammation (PLA-2, TNF-α) and fibrosis (TGF-β). Adenine diet increased CKD characteristics (tubulointerstitial atrophy and fibrosis, inflammation, proteinuria, BUN, PCr, uric acid) and CKD-associated cardiovascular disease. Rutin improved kidney and heart structure and function, decreased HO-1 and PLA-2 expression, but did not reduce TGF-β or TNF-α. Decreased expression of HO-1 and PLA-2 appears to be a mechanistic pathway for reno- and cardioprotection.

Arterial and Cellular Inflammation in Patients with CKD.

CKD associates with a 1.5- to 3.5-fold increased risk for cardiovascular disease. Both diseases are characterized by increased inflammation, and in patients with CKD, elevated C-reactive protein level predicts cardiovascular risk. In addition to systemic inflammation, local arterial inflammation, driven by monocyte-derived macrophages, predicts future cardiovascular events in the general population. We hypothesized that subjects with CKD have increased arterial and cellular inflammation, reflected by 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography computed tomography (PET/CT) of the arterial wall and a migratory phenotype of monocytes. We assessed 18F-FDG uptake in the arterial wall in 14 patients with CKD (mean±SD age: 59±5 years, mean±SD eGFR: 37±12 ml/min per 1.73 m2) but without cardiovascular diseases, diabetes, or inflammatory conditions and in 14 control subjects (mean age: 60±11 years, mean eGFR: 86±16 ml/min per 1.73 m2). Compared with controls, patients with CKD showed increased arterial inflammation, quantified as target-to-background ratio (TBR) in the aorta (TBRmax: CKD, 3.14±0.70 versus control, 2.12±0.27; P=0.001) and the carotid arteries (TBRmax: CKD, 2.45±0.65 versus control, 1.66±0.27; P<0.001). Characterization of circulating monocytes using flow cytometry revealed increased chemokine receptor expression and enhanced transendothelial migration capacity in patients with CKD compared with controls. In conclusion, this increased arterial wall inflammation, observed in patients with CKD but without overt atherosclerotic disease and with few traditional risk factors, may contribute to the increased cardiovascular risk associated with CKD. The concomitant elevation of monocyte activity may provide novel therapeutic targets for attenuating this inflammation and thereby preventing CKD-associated cardiovascular disease.

Abstract 637: Hyperhomocysteinemia-mediated sCD40L induction and CD16 + CD40 + Monocyte Differentiation in Chronic Kidney Disease

Chronic kidney disease (CKD) with uremia is associated with high mortality of cardiovascular disease (CVD) and Hyperhomocysteinemia (HHcy) is highly prevalent in uremic CKD patients. Elevated inflammatory monocyte (MC) is a cellular hallmark of chronic inflammation and CVD. Here we investigated mechanism in uremia-associated HHcy on MC differentiation in CKD-associated CVD. Data base mining revealed that CD40 is induced in MC from CKD subjects and associated with CVD, inflammatory disease and MC activation. Blood samples were obtained from 28 vascular disease patients with or without CKD. By flow cytometric analysis using CD14+ as a MC marker, we observed inflammatory CD16+ MC is increased in CVD, whereas CD40+ MC and CD16+CD40+ MC are increased in CKD-associated CVD. CD40+ MC expresses T cell activation markers CD86, HLA-DR, adhesion receptor CD62L, and chemokine receptor Ccr2. Plasma CD40L levels are increased in CVD, positively correlated with CD16+ MC. Interestingly, plasma Hcy levels are increased in CKD-associated CVD, positively correlated with cellular Hcy, plasma creatinine, CD16+CD40+ MC, and negatively correlated with S-adenosylmethionine/S-adenosylhomocysteine (SAM/SAH), an indicator of methylation. In addition, MC and T cell inflammatory cytokines TNFα, IL-6, and IFN[[Unable to Display Character: &amp;#612;]] are induced in CKD-associated CVD subjects. Next, we examined mechanism of CD16+CD40+ MC differentiation using cultured human peripheral blood mononuclear cells (hPBMC). CKD serum, Hcy, and CD40L induced CD16+CD40+ MC differentiation, which were prevented by folic acid and CD40L antibody. IFN[[Unable to Display Character: &amp;#1003;]], TNFα, and IL-6 synergistically induced CD16+CD40+ MC differentiation, which was blocked by neutralizing antibodies to TNFα and IL-6. Hcy inhibited DNA methyltransferase 1 activity in isolated human blood MC. Finally, by gene analysis and pyrosequencing, we identified that the core promoter of CD40 gene is located at sole CpG island and hypomethylated at p65 consensus element in WBC from CKD-associated CVD subjects with low SAM/SAH ratio. In conclusion, we identified CD16+CD40+ MC as a novel inflammatory MC subset which is increased in uremic HHcy-associated CVD. CD16+CD40+ MC differentiation may be due to CD40 promoter DNA hypomethylation.

Serum sclerostin and adverse outcomes in nondialyzed chronic kidney disease patients.

The chronic kidney disease (CKD)-mineral and bone disorder (MBD) syndrome is an important contributor to the CKD-associated cardiovascular disease and high mortality rates. Sclerostin, a protein synthesized in osteocytes, is a potent downregulator of bone metabolism and a novel candidate for the bone-vascular axis in CKD patients. We tested whether serum sclerostin values are predictive for all-cause mortality and cardiovascular events (CVEs) in a CKD population. Serum sclerostin was obtained from 173 CKD (stage 3-5) and 47 control patients, and its concentration was correlated with estimated glomerular filtration rate and to mineral and vascular abnormalities that are present in the CKD evolution. All-cause mortality and CVEs were also analyzed in relation to serum sclerostin values. Patients with CKD showed higher sclerostin levels (median 63.5 pmol/L vs 52 pmol/L, P < .001) than controls, with values progressively higher across the CKD stages. In univariate analysis, serum sclerostin concentrations were correlated with gender, estimated glomerular filtration rate, flow-mediated dilatation, and endothelium-independent vasodilatation as markers of endothelial dysfunction and with different serum CKD-MBD-associated parameters. However, in multivariate analysis, only gender, fibroblast growth factor-23, phosphate, flow-mediated dilatation, and cholesterol remained significantly associated with sclerostin levels. During the observational period, there were 19 deaths and 50 CVEs. In survival analysis, different sclerostin levels were associated with all-cause mortality and CVEs in these patients. This is the first study that shows that serum sclerostin values are associated, even after multiple adjustments, with fatal and nonfatal CVEs in a nondialyzed CKD population.

Massive analysis of cDNA Ends (MACE) and miRNA expression profiling identifies proatherogenic pathways in chronic kidney disease

Epigenetic dysregulation contributes to the high cardiovascular disease burden in chronic kidney disease (CKD) patients. Although microRNAs (miRNAs) are central epigenetic regulators, which substantially affect the development and progression of cardiovascular disease (CVD), no data on miRNA dysregulation in CKD-associated CVD are available until now. We now performed high-throughput miRNA sequencing of peripheral blood mononuclear cells from ten clinically stable hemodialysis (HD) patients and ten healthy controls, which allowed us to identify 182 differentially expressed miRNAs (e.g., miR-21, miR-26b, miR-146b, miR-155). To test biological relevance, we aimed to connect miRNA dysregulation to differential gene expression. Genome-wide gene expression profiling by MACE (Massive Analysis of cDNA Ends) identified 80 genes to be differentially expressed between HD patients and controls, which could be linked to cardiovascular disease (e.g., KLF6, DUSP6, KLF4), to infection / immune disease (e.g., ZFP36, SOCS3, JUND), and to distinct proatherogenic pathways such as the Toll-like receptor signaling pathway (e.g., IL1B, MYD88, TICAM2), the MAPK signaling pathway (e.g., DUSP1, FOS, HSPA1A), and the chemokine signaling pathway (e.g., RHOA, PAK1, CXCL5). Formal interaction network analysis proved biological relevance of miRNA dysregulation, as 68 differentially expressed miRNAs could be connected to 47 reciprocally expressed target genes. Our study is the first comprehensive miRNA analysis in CKD that links dysregulated miRNA expression with differential expression of genes connected to inflammation and CVD. After recent animal data suggested that targeting miRNAs is beneficial in experimental CVD, our data may now spur further research in the field of CKD-associated human CVD.

Sevelamer and CKD-associated cardiovascular disease: going further, but far from there

Cardiovascular disease is a major complication of chronic kidney disease (CKD), and current data support its link to mineral metabolism disturbances. However, there is an intense debate over whether CKD-mineral and bone disorder therapy could change the cardiovascular burden in CKD. The study by Maizel and colleagues shows the benefits of a phosphate binder, sevelamer, for the progression of aortic stiffness and endothelial dysfunction as well as left ventricular dysfunction and hypertrophy in mice with CKD.

Clinical relevance of epigenetic dysregulation in chronic kidney disease-associated cardiovascular disease

Across the spectrum of clinical medicine, the field of epigenetics has gained substantial scientific interest in recent years. Epigenetics refers to modifications in gene expression which are not explained by changes in DNA sequence. Classical components of epigenetic regulation comprise DNA methylation, histone modifications and RNA interference. In chronic kidney disease (CKD), several features of uraemia, such as hyperhomocysteinemia and inflammation, may contribute to changes in epigenetic gene regulation. It has been suggested that these changes may affect genes related to cardiovascular disease. Thereby, a uraemia-associated disturbance in epigenetic regulation may contribute to the substantial increase in cardiovascular morbidity in CKD patients. The present review aims to summarize current knowledge of epigenetic dysregulation in cardiovascular disease from a nephrological perspective, with a special focus on DNA methylation. We first describe the impact of altered epigenetic regulation in non-CKD-associated arteriosclerosis, and next characterize uraemic features which may affect epigenetic gene regulation in the context of cardiovascular disease. Finally, we conclude that substantial additional work is needed before epigenetic regulatory mechanisms may become therapeutic targets in CKD-associated cardiovascular disease.

Indoxyl Sulfate Counteracts Endothelial Effects of Erythropoietin Through Suppression of Akt Phosphorylation

Erythropoietin (EPO) is used to treat anemia in patients with chronic kidney disease (CKD). A wide variation in individual response to EPO, however, is often observed, causing EPO resistance. EPO exhibits not only hematopoietic but also extra-hematopoietic functions such as endothelial effects. Indoxyl sulfate, a uremic toxin, is involved in endothelial dysfunction, and consequently, the pathogenesis of CKD-associated cardiovascular disease. The aim of the present study was to determine the effect of indoxyl sulfate on the extra-hematopoietic functions of EPO in human umbilical vein endothelial cells (HUVECs). HUVECs were incubated with or without indoxyl sulfate or an Akt inhibitor, and then stimulated with or without EPO. Indoxyl sulfate suppressed EPO-induced survival/proliferation, anti-apoptosis function, phosphorylation of endothelial nitric oxide synthase, and the expression of thrombospondin-1, an erythroid-stimulating factor, in HUVECs. Although EPO induced phosphorylation of both Akt and extracellular signal-regulated kinases (ERK) in HUVECs, indoxyl sulfate suppressed phosphorylation of Akt but not ERK. An Akt kinase inhibitor or Akt small interfering RNA suppressed all the EPO-induced cellular effects in HUVECs. As a site of action of indoxyl sulfate on EPO signaling, indoxyl sulfate attenuated EPO-induced tyrosine phosphorylation of EPO receptor (EPOR) in HUVECs. Indoxyl sulfate negatively regulates the EPOR-Akt pathway in endothelial cells, and might contribute to EPO resistance and endothelial dysfunction in patients with CKD.

SuperTAG Methylation-specific Digital Karyotyping Reveals Uremia-induced Epigenetic Dysregulation of Atherosclerosis-Related Genes

Accelerated atherosclerosis is a hallmark of chronic kidney disease (CKD). Although the role of epigenetic dysregulation in atherosclerosis is increasingly appreciated, only a few studies focused on epigenetics in CKD-associated cardiovascular disease, virtually all of which assessed epigenetic dysregulation globally. We hypothesized that gene-specific epigenetic dysregulation in CKD exists, affecting genes pertinent to inflammation and atherosclerosis. Ten clinically stable patients undergoing hemodialysis therapy and 10 healthy age- and sex-matched controls were recruited. Genome-wide analysis of DNA methylation was performed by SuperTAG methylation-specific digital karyotyping, in order to identify genes differentially methylated in CKD. Analysis of 27 043 436 tags revealed 4288 genomic loci with differential DNA methylation (P<10(-10)) between hemodialysis patients and control subjects. Annotation of UniTags to promoter databases allowed us to identify 52 candidate genes associated with cardiovascular disease and 97 candidate genes associated with immune/infection diseases. These candidate genes could be classified to distinct proatherogenic processes, including lipid metabolism and transport (eg, HMGCR, SREBF1, LRP5, EPHX2, and FDPS), cell proliferation and cell-cycle regulation (eg, MIK67, TP53, and ALOX12), angiogenesis (eg, ANGPT2, ADAMTS10, and FLT4), and inflammation (eg, TNFSF10, LY96, IFNGR1, HSPA1A, and IL12RB1). We provide a comprehensive analysis of genome-wide epigenetic alterations in CKD, identifying candidate genes associated with proatherogenic and inflammatory processes. These results may spur further research in the field of epigenetics in kidney disease and point to new therapeutic strategies in CKD-associated atherosclerotic disease.

Meniscal Tear — A Common Finding with Often Troublesome Consequences: Figure 1

CKD associates with a 1.5- to 3.5-fold increased risk for cardiovascular disease. Both diseases are characterized by increased inflammation, and in patients with CKD, elevated C-reactive protein level predicts cardiovascular risk. In addition to systemic inflammation, local arterial inflammation, driven by monocyte-derived macrophages, predicts future cardiovascular events in the general population. We hypothesized that subjects with CKD have increased arterial and cellular inflammation, reflected by ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography computed tomography (PET/CT) of the arterial wall and a migratory phenotype of monocytes. We assessed ¹⁸F-FDG uptake in the arterial wall in 14 patients with CKD (mean±SD age: 59±5 years, mean±SD eGFR: 37±12 ml/min per 1.73 m²) but without cardiovascular diseases, diabetes, or inflammatory conditions and in 14 control subjects (mean age: 60±11 years, mean eGFR: 86±16 ml/min per 1.73 m²). Compared with controls, patients with CKD showed increased arterial inflammation, quantified as target-to-background ratio (TBR) in the aorta (TBR_max: CKD, 3.14±0.70 versus control, 2.12±0.27; <i>P</i>=0.001) and the carotid arteries (TBR_max: CKD, 2.45±0.65 versus control, 1.66±0.27; <i>P</i>&lt;0.001). Characterization of circulating monocytes using flow cytometry revealed increased chemokine receptor expression and enhanced transendothelial migration capacity in patients with CKD compared with controls. In conclusion, this increased arterial wall inflammation, observed in patients with CKD but without overt atherosclerotic disease and with few traditional risk factors, may contribute to the increased cardiovascular risk associated with CKD. The concomitant elevation of monocyte activity may provide novel therapeutic targets for attenuating this inflammation and thereby preventing CKD-associated cardiovascular disease.