Cardiovascular co-morbidity in chronic kidney disease: Current knowledge and future research needs

Oxidative Stress and Cardiovascular Complications in Chronic Kidney Disease, the Impact of Anaemia

Patients with chronic kidney disease (CKD) have significant cardiovascular morbidity and mortality as a result of risk factors such as left ventricular hypertrophy (LVH), oxidative stress, and inflammation. The presence of anaemia in CKD further increases the risk of LVH and oxidative stress, thereby magnifying the deleterious consequence in uraemic cardiomyopathy (UCM), and aggravating progression to failure and increasing the risk of sudden cardiac death. This short review highlights the specific cardio-renal oxidative stress in CKD and provides an understanding of the pathophysiology and impact of uraemic toxins, inflammation, and anaemia on oxidative stress.

Benefit of Apabetalone on Plasma Proteins in Renal Disease

INTRODUCTION

Apabetalone, a small molecule inhibitor, targets epigenetic readers termed BET proteins that contribute to gene dysregulation in human disorders. Apabetalone has in vitro and in vivo anti-inflammatory and antiatherosclerotic properties. In phase 2 clinical trials, this drug reduced the incidence of major adverse cardiac events in patients with cardiovascular disease. Chronic kidney disease is associated with a progressive loss of renal function and a high risk of cardiovascular disease. We studied the impact of apabetalone on the plasma proteome in patients with impaired kidney function.

METHODS

Subjects with stage 4 or 5 chronic kidney disease and matched controls received a single dose of apabetalone. Plasma was collected for pharmacokinetic analysis and for proteomics profiling using the SOMAscan 1.3k platform. Proteomics data were analyzed with Ingenuity Pathway Analysis to identify dysregulated pathways in diseased patients, which were targeted by apabetalone.

RESULTS

At baseline, 169 plasma proteins (adjusted P value <0.05) were differentially enriched in renally impaired patients versus control subjects, including cystatin C and β2 microglobulin, which correlate with renal function. Bioinformatics analysis of the plasma proteome revealed a significant activation of 42 pathways that control immunity and inflammation, oxidative stress, endothelial dysfunction, vascular calcification, and coagulation. At 12 hours postdose, apabetalone countered the activation of pathways associated with renal disease and reduced the abundance of disease markers, including interleukin-6, plasminogen activator inhibitor-1, and osteopontin.

CONCLUSION

These data demonstrated plasma proteome dysregulation in renally impaired patients and the beneficial impact of apabetalone on pathways linked to chronic kidney disease and its cardiovascular complications.

Mismatch between stiffness in elastic and muscular arteries as a predictor of vascular calcification in dialysis patients

BACKGROUND

Vascular calcification is one of the risk factors for arterial stiffness in patients with chronic kidney disease. We hypothesized that a mismatch between elastic and muscular arteries, represented as pulse wave velocity (PWV) ratio, could depict the extent of vascular calcification in end-stage renal disease. We also aimed to compare the predictive PWV ratio value to other factors possibly related to vascular calcification in dialysis population.

METHODS

In this cross-sectional study, in 60 chronic dialysis patients without previous cerebrovascular events, cardiovascular disease and events or clinically evident peripheral artery disease (ankle-brachial index >0.9), carotid-femoral and carotid-radial PWV as well as central hemodynamic parameters were measured by applanation tonometry (SphygmoCor). The PWV ratio using carotid-femoral PWV divided by carotid-radial PWV was calculated. Each patient underwent blood tests and chest X-ray for aortic arch calcification scoring. Two experienced radiologists blinded to patient's medical data evaluated chest X-rays (Cohen's kappa coefficient 0.76) and calculated how many sectors were calcified (Ogawa et al. in Hemodial Int 13:301-306, 2009). Differently scored chest X-rays were repeatedly reviewed and a consensus was reached.

RESULTS

The study population consisted of 31 (51.7%) males and 29 (48.3%) females, mean age 52.73 ± 13.76 years. Increased risk for aortic arch calcification was associated with higher PWV ratio even after adjustment for age, height, heart rate, ferritin level and C-reactive protein level (OR 2.59E+04, 95% CI 2.43E+01, 2.65E+09, p = 0.021). PWV ratio together with above-mentioned variables could predict the presence of aortic arch calcification with specificity of 93% (95% CI 78, 99%) and sensitivity of 53% (95% CI 34, 72%).

CONCLUSION

The elastic and muscular arteries' stiffness mismatch was strongly associated with the extent of aortic arch calcification in this dialysis population and had better calcification predictive value compared to other demographic, hemodynamic and biochemical markers.

Association between uremic toxin-anthranilic acid and fibrinolytic system activity in predialysis patients at different stages of chronic kidney disease

PURPOSE

Chronic kidney disease (CKD) is an estimated risk factor for increased mortality and morbidity due to fibrinolytic system disturbances. Progressive loss of renal function leads to retention of uremic toxins. Anthranilic acid (AA) is a tryptophan-derived uremic toxin with multidirectional properties that can affect the hemostatic system. The goal of this study was to examine the association between AA and the parameters of fibrinolysis at different stages of CKD.

METHODS

Patients with CKD were divided into two groups: mild-to-moderate (n = 20) and severe-to-end-stage CKD (n = 28). Seventeen healthy volunteers served as an additional control group. Parameters of fibrinolysis, inflammation, and monocytes activation were determined by ELISA immune-enzymatic kits. AA levels were evaluated using high-performance liquid chromatography.

RESULTS

AA concentration and parameters of fibrinolysis: urokinase-type plasminogen activator (uPA), its soluble receptor (suPAR), tissue plasminogen activator (tPA), tissue plasminogen activator inhibitor-1 (PAI-1) and plasmin-antiplasmin complex (PAP) were significantly elevated in the CKD groups compared with the controls. The markers of inflammation, monocyte activation, and impaired kidney function were also increased in those with CKD. AA was positively correlated with the uPA/suPAR system in the early stages of CKD, whereas during severe-to-end-stage CKD, inverse relationships were observed between AA, tPA and PAI-1. Additionally, AA was an independent variable associated with tPA in patients with CKD overall and with uPA levels in the mild-to-moderate CKD group.

CONCLUSIONS

Obtained results suggest for the first time the association between AA and the fibrinolytic system in CKD patients. The distinct relationship between AA and individual parameters of fibrinolysis appears to be dependent on CKD stage.

Impaired renal function and dysbiosis of gut microbiota contribute to increased trimethylamine-N-oxide in chronic kidney disease patients

Chronic kidney disease (CKD) patients have an increased risk of cardiovascular diseases (CVDs). The present study aimed to investigate the gut microbiota and blood trimethylamine-N-oxide concentration (TMAO) in Chinese CKD patients and explore the underlying explanations through the animal experiment. The median plasma TMAO level was 30.33 μmol/L in the CKD patients, which was significantly higher than the 2.08 μmol/L concentration measured in the healthy controls. Next-generation sequence revealed obvious dysbiosis of the gut microbiome in CKD patients, with reduced bacterial diversity and biased community constitutions. CKD patients had higher percentages of opportunistic pathogens from gamma-Proteobacteria and reduced percentages of beneficial microbes, such as Roseburia, Coprococcus, and Ruminococcaceae. The PICRUSt analysis demonstrated that eight genes involved in choline, betaine, L-carnitine and trimethylamine (TMA) metabolism were changed in the CKD patients. Moreover, we transferred faecal samples from CKD patients and healthy controls into antibiotic-treated C57BL/6 mice and found that the mice that received gut microbes from the CKD patients had significantly higher plasma TMAO levels and different composition of gut microbiota than did the comparative mouse group. Our present study demonstrated that CKD patients had increased plasma TMAO levels due to contributions from both impaired renal functions and dysbiosis of the gut microbiota.

Level of inflammatory factors in chronic hemodialysis patients with and without cardiovascular disease

Background:

Considering the existence of controversies about the predictive value of inflammatory markers for cardiovascular disease (CVD), we aimed to compare the level of high-sensitivity C-reactive protein (hs-CRP) and interlukin-6 (IL-6) level in chronic hemodialysis (HD) patients with and without CVD.

Materials and Methods:

In this historical cohort study, HD patients with and without CVD disease were enrolled. The presence of CVD risk factors, level of inflammatory factors including IL-6 and hs-CRP as well as lipid levels, fasting blood sugar, and other biochemical factors were compared in two studied groups.

Results:

During the study, eighty HD patients with (n = 40) and without (n = 40) CVD were enrolled. Diabetes was more prevalent among HD patients with CVD than those without CVD (P < 0.05). The level of IL-6 and hs-CRP were not different in two studied groups (P > 0.05). Univariate analysis of variance test indicated that there was not any significant relationship between hs-CRP and CVD (P > 0.05).

Conclusion:

The findings indicated that the level of inflammatory factors including hs-CRP and IL-6 are not significantly different in HD patients with and without CVD. However, for obtaining more definite conclusion in this field and evaluation their predicting role in this field, it is recommended to study other novel inflammatory markers as well as the additive effect of the inflammatory factors with traditional ones in larger sample size and longer follow-up.

Intravital imaging of the kidney in a rat model of salt-sensitive hypertension

Hypertension is one of the most prevalent diseases worldwide and a major risk factor for renal failure and cardiovascular disease. The role of albuminuria, a common feature of hypertension and robust predictor of cardiorenal disorders, remains incompletely understood. The goal of this study was to investigate the mechanisms leading to albuminuria in the kidney of a rat model of hypertension, the Dahl salt-sensitive (SS) rat. To determine the relative contributions of the glomerulus and proximal tubule (PT) to albuminuria, we applied intravital two-photon-based imaging to investigate the complex renal physiological changes that occur during salt-induced hypertension. Following a high-salt diet, SS rats exhibited elevated blood pressure, increased glomerular sieving of albumin (GSC_alb = 0.0686), relative permeability to albumin (+Δ16%), and impaired volume hemodynamics (-Δ14%). Serum albumin but not serum globulins or creatinine concentration was decreased (-0.54 g/dl), which was concomitant with increased filtration of albumin (3.7 vs. 0.8 g/day normal diet). Pathologically, hypertensive animals had significant tubular damage, as indicated by increased prevalence of granular casts, expansion and necrosis of PT epithelial cells (+Δ2.20 score/image), progressive augmentation of red blood cell velocity (+Δ269 µm/s) and micro vessel diameter (+Δ4.3 µm), and increased vascular injury (+Δ0.61 leakage/image). Therefore, development of salt-induced hypertension can be triggered by fast and progressive pathogenic remodeling of PT epithelia, which can be associated with changes in albumin handling. Collectively, these results indicate that both the glomerulus and the PT contribute to albuminuria, and dual treatment of glomerular filtration and albumin reabsorption may represent an effective treatment of salt-sensitive hypertension.

Cardiovascular risk is similar in patients with glomerulonephritis compared to other types of chronic kidney disease: a matched cohort study

Background

Patients with chronic kidney disease (CKD) due to glomerulonephritis (GN) are thought to be at high risk for cardiovascular disease (CVD). However, no study has examined whether GN directly contributes to CV risk beyond the effects conferred by pre-existing traditional risk factors and level of renal function.

Methods

Matched cohort study using the previously described prospective CanPREDDICT study cohort. 2187 patients with CKD (eGFR 15–45 ml/min/m²) from 25 Canadian centres were divided into GN vs non-GN cause of CKD. Patients on immunotherapy for GN were not included in the study. Standardized measures of CV risk factors, biomarkers and CV outcomes were recorded over 3 years of follow-up, with the primary outcome measure being time to first all-cause CV event.

Results

In the overall cohort, CV events occurred in 25 (8.7%) of the GN group and 338 (17.8%) of the non-GN group (HR 0.45, 95% CI 0.30–0.67, p < 0.01). In a Cox regression multivariable model that included age, sex, prior diabetes and CVD, baseline eGFR and onset of renal replacement therapy, the risk of CV events was similar in the GN and non-GN groups (HR 0.71, 95% CI 0.47–1.08, p = 0.11). GN and non-GN patients were matched by age and using a propensity score including sex, prior diabetes and CVD and baseline eGFR. In the matched group, the risk of CV events was similar in GN vs non-GN patients (N = 25/271 (9.2%) in both groups, HR 1.01, 95% CI 0.05–1.77, p = 0.9). An interaction analysis showed that CRP, ACR and troponin conferred differing amounts of CV risk in the GN and non-GN groups.

Conclusions

Patients with advanced CKD due to GN have a high 8.7% absolute 3-year risk of CVD, attributable to prior CV risk factors and level of kidney function rather than the GN disease itself.

Electronic supplementary material

The online version of this article (doi:10.1186/s12882-017-0511-z) contains supplementary material, which is available to authorized users.

Does apical periodontitis have systemic consequences? The need for well-planned and carefully conducted clinical studies

Apical periodontitis, infection of the root canal system, may have systemic consequences. This proposal has been brought forward many times in dentistry literature but the general consensus is that there is no scientific basis for an association between endodontic infections and general health. This opinion paper argues that, in order to obtain such a scientific basis, or to rule out the issue all together, we need carefully designed longitudinal challenge model (that is, intervention) studies in which we follow specific biomarkers of inflammation. These biomarkers can be those that are currently being substantiated in chronic inflammation and low-grade inflammation studies in medicine and nutritional science, where the presence of these inflammatory disorders is linked to systemic outcomes. A list of suggested biomarkers has been included.

Low molecular weight fucoidan protects renal tubular cells from injury induced by albumin overload

Albuminuria is a causative and aggravating factor for progressive renal damage in chronic kidney disease (CKD). The aim of this study was to determine if low molecular weight fucoidan (LMWF) could protect renal function and tubular cells from albumin overload caused injury. Treatment with 10 mg/g bovine serum albumin caused renal dysfunction, morphological changes, and overexpression of inflammation and fibrosis associated proteins in 129S2/Sv mice. LMWF (100 mg/kg) protected against kidney injury and renal dysfunction with decreased blood creatinine by 34% and urea nitrogen by 25%, increased creatinine clearance by 48%, and decreased significantly urinary albumin concentration. In vitro proximal tubule epithelial cell (NRK-52E) model showed that LMWF dose-dependently inhibited overexpression of proinflammatory and profibrotic factors, oxidative stress and apoptosis caused by albumin overload. These experimental results indicate that LMWF protects against albumin overload caused renal injury by inhibiting inflammation, fibrosis, oxidative stress and apoptosis, which suggests that LMWF could be a promising candidate drug for preventing CKD.

The cytoskeleton as a novel target for treatment of renal fibrosis

The incidence of chronic kidney disease (CKD) is increasing, with an estimated prevalence of 12% in the United States (Synder et al., 2009). While CKD may progress to end-stage renal disease (ESRD), which necessitates renal replacement therapy, i.e. dialysis or transplantation, most CKD patients never reach ESRD due to the increased risk of death from cardiovascular disease. It is well-established that regardless of the initiating insult - most often diabetes or hypertension - fibrosis is the common pathogenic pathway that leads to progressive injury and organ dysfunction (Eddy, 2014; Duffield, 2014). As such, there has been extensive research into the molecular and cellular mechanisms of renal fibrosis; however, translation to effective therapeutic strategies has been limited. While a role for the disruption of the cytoskeleton, most notably the actin network, has been established in acute kidney injury over the past two decades, a role in regulating renal fibrosis and CKD is only recently emerging. This review will focus on the role of the cytoskeleton in regulating pro-fibrotic pathways in the kidney, as well as data suggesting that these pathways represent novel therapeutic targets to manage fibrosis and ultimately CKD.

Deficient serum 25-hydroxyvitamin D is associated with an atherogenic lipid profile: The Very Large Database of Lipids (VLDL-3) study

BACKGROUND

Cross-sectional studies have found an association between deficiencies in serum vitamin D, as measured by 25-hydroxyvitamin D (25[OH]D), and an atherogenic lipid profile. These studies have focused on a limited panel of lipid values including low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), and triglycerides (TG).

OBJECTIVE

Our study examines the relationship between serum 25(OH)D and an extended lipid panel (Vertical Auto Profile) while controlling for age, gender, glycemic status, and kidney function.

METHODS

We used the Very Large Database of Lipids, which includes US adults clinically referred for analysis of their lipid profile from 2009 to 2011. Our study focused on 20,360 subjects who had data for lipids, 25(OH)D, age, gender, hemoglobin A1c, insulin, creatinine, and blood urea nitrogen. Subjects were split into groups based on serum 25(OH)D: deficient (<20 ng/mL), intermediate (≥ 20-30 ng/mL), and optimal (≥ 30 ng/mL). The deficient group was compared to the optimal group using multivariable linear regression.

RESULTS

In multivariable-adjusted linear regression, deficient serum 25(OH)D was associated with significantly lower serum HDL-C (-5.1%) and higher total cholesterol (+9.4%), non-HDL-C (+15.4%), directly measured LDL-C (+13.5%), intermediate-density lipoprotein cholesterol (+23.7%), very low-density lipoprotein cholesterol (+19.0%), remnant lipoprotein cholesterol (+18.4%), and TG (+26.4%) when compared with the optimal group.

CONCLUSION

Deficient serum 25(OH)D is associated with significantly lower HDL-C and higher directly measured LDL-C, intermediate-density lipoprotein cholesterol, very low-density lipoproteins cholesterol, remnant lipoprotein cholesterol, and TG. Future trials examining vitamin D supplementation and cardiovascular disease risk should consider using changes in an extended lipid panel as an additional outcome measurement.

The Role of the Gut Microbiome on Chronic Kidney Disease

Chronic kidney disease (CKD) is estimated to affect nearly 500 million people worldwide and cardiovascular (CV) disease is a major cause of death in this population. However, therapeutic interventions targeting traditional CV risks are not effective at lowering the incidence of CV events or at delaying the progression of the disease in CKD patients. In recent years, disturbances of normal gut microbiome were recognized in the pathogenesis of diverse chronic diseases. Gut dysbiosis is being unraveled in CKD and pointed as a nontraditional risk factor for CV risk and CKD progression. The most often reported changes in gut microbiome in CKD are related to the lower levels of Bifidobacteriaceae and Lactobacillaceae and to higher levels of Enterobacteriaceae. Although metagenomics brought us an amplified vision on the microbial world that inhabits the human host, it still lacks the sensitivity to characterize the microbiome up to species level, not revealing alterations that occur within specific genus. Here, we review the current state-of-the-art concerning gut dysbiosis in CKD and its role in pathophysiological mechanisms in CKD, particularly in relation with CV risk. Also, the strategies towards prevention and treatment of gut dysbiosis in CKD progression will be discussed.

Pharmacological induction of ferritin prevents osteoblastic transformation of smooth muscle cells

Vascular calcification is a frequent complication of atherosclerosis, diabetes and chronic kidney disease. In the latter group of patients, calcification is commonly seen in tunica media where smooth muscle cells (SMC) undergo osteoblastic transformation. Risk factors such as elevated phosphorus levels and vitamin D3 analogues have been identified. In the light of earlier observations by our group and others, we sought to inhibit SMC calcification via induction of ferritin. Human aortic SMC were cultured using β-glycerophosphate with activated vitamin D3 , or inorganic phosphate with calcium, and induction of alkaline phosphatase (ALP) and osteocalcin as well as accumulation of calcium were used to monitor osteoblastic transformation. In addition, to examine the role of vitamin D3 analogues, plasma samples from patients on haemodialysis who had received calcitriol or paricalcitol were tested for their tendency to induce calcification of SMC. Addition of exogenous ferritin mitigates the transformation of SMC into osteoblast-like cells. Importantly, pharmacological induction of heavy chain ferritin by 3H-1,2-Dithiole-3-thione was able to inhibit the SMC transition into osteoblast-like cells and calcification of extracellular matrix. Plasma samples collected from patients after the administration of activated vitamin D3 caused significantly increased ALP activity in SMC compared to the samples drawn prior to activated vitamin D3 and here, again induction of ferritin diminished the osteoblastic transformation. Our data suggests that pharmacological induction of ferritin prevents osteoblastic transformation of SMC. Hence, utilization of such agents that will cause enhanced ferritin synthesis may have important clinical applications in prevention of vascular calcification.

An Increase of Plasma Advanced Oxidation Protein Products Levels Is Associated with Cardiovascular Risk in Incident Peritoneal Dialysis Patients: A Pilot Study

Advanced oxidation protein products (AOPPs) are considered as markers and even mediators of the proinflammatory effect of oxidative stress in uremia. We hypothesized that an increase of oxidative stress associated with peritoneal dialysis (PD), estimated by the variation of plasma AOPPs over time, might be associated with cardiovascular (CV) risk and overall prognosis. In 48 PD patients, blood samples were collected on two occasions: the first one in the first six months after starting PD therapy and the second one, one year after. The plasma AOPPs level variation over the first year on PD was significantly associated with CV antecedents and also with CV prognosis. In those patients in whom the AOPPs levels increased more than 50% above the baseline value, a significant association with past and future CV disease was confirmed. These patients had 4.7 times greater risk of suffering later CV disease than those with a smaller increase, even after adjusting for previous CV history. Our data suggest that the increase of AOPPs plasma level over the first year on PD is conditioned by CV antecedents but also independently predicts CV prognosis. AOPPs plasma levels seem to represent the CV status of PD patients with sufficient sensitivity to identify those with a clearly sustained higher CV risk.

Metabolic biomarkers for chronic kidney disease

Chronic kidney disease (CKD) is an increasingly recognized burden for patients and health care systems with high (and growing) global incidence and prevalence, significant mortality, and disproportionately high treatment costs. Yet, the available diagnostic tools are either impractical in clinical routine or have serious shortcomings impeding a well-informed disease management although optimized treatment strategies with proven benefits for the patients have become available. Advances in bioanalytical technologies have facilitated studies that identified genomic, proteomic, and metabolic biomarker candidates, and confirmed some of them in independent cohorts. This review summarizes the CKD-related markers discovered so far, and focuses on compounds and pathways, for which there is quantitative data, substantiating evidence from translational research, and a mechanistic understanding of the processes involved. Also, multiparametric marker panels have been suggested that showed promising diagnostic and prognostic performance in initial analyses although the data basis from prospective trials is very limited. Large-scale studies, however, are underway and will provide the information for validating a set of parameters and discarding others. Finally, the path from clinical research to a routine application is discussed, focusing on potential obstacles such as the use of mass spectrometry, and the feasibility of obtaining regulatory approval for targeted metabolomics assays.