The role of novel biomarkers of cardiovascular disease in chronic kidney disease: focus on adiponectin and leptin

Impact of Different Adipose Depots on Cardiovascular Disease

ABSTRACT

Adipose tissue (AT)-derived factors contribute to the regulation of cardiovascular homeostasis, thereby playing an important role in cardiovascular health and disease. In obesity, AT expands and becomes dysfunctional, shifting its secretory profile toward a proinflammatory state associated with deleterious effects on the cardiovascular system. AT in distinct locations (ie, adipose depots) differs in crucial phenotypic variables, including inflammatory and secretory profile, cellular composition, lipolytic activity, and gene expression. Such heterogeneity among different adipose depots may explain contrasting cardiometabolic risks associated with different obesity phenotypes. In this respect, central obesity, defined as the accumulation of AT in the abdominal region, leads to higher risk of cardiometabolic alterations compared with the accumulation of AT in the gluteofemoral region (ie, peripheral obesity). The aim of this review was to provide an updated summary of clinical and experimental evidence supporting the differential roles of different adipose depots in cardiovascular disease and to discuss the molecular basis underlying the differences of adipose depots in the regulation of cardiovascular function.

Advances in Cardiovascular Biomarker Discovery

Cardiovascular diseases are the leading causes of mortality worldwide. Among them, hypertension and its pathological complications pose a major risk for the development of other cardiovascular diseases, including heart failure and stroke. Identifying novel and early stage biomarkers of hypertension and other cardiovascular diseases is of paramount importance in predicting and preventing the major morbidity and mortality associated with these diseases. Biomarkers of such diseases or predisposition to their development are identified by changes in a specific indicator’s expression between healthy individuals and patients. These include changes in protein and microRNA (miRNA) levels. Protein profiling using mass spectrometry and miRNA screening utilizing microarray and sequencing have facilitated the discovery of proteins and miRNA as biomarker candidates. In this review, we summarized some of the different, promising early stage protein and miRNA biomarker candidates as well as the currently used biomarkers for hypertension and other cardiovascular diseases. Although a number of promising markers have been identified, it is unlikely that a single biomarker will unambiguously aid in the classification of these diseases. A multi-marker panel-strategy appears useful and promising for classifying and refining risk stratification among patients with cardiovascular disease.

Epicardial Adipose Tissue, Adiponectin and Leptin: A Potential Source of Cardiovascular Risk in Chronic Kidney Disease

The importance of cardiometabolic factors in the inception and progression of atherosclerotic cardiovascular disease is increasingly being recognized. Beyond diabetes mellitus and metabolic syndrome, other factors may be responsible in patients with chronic kidney disease (CKD) for the high prevalence of cardiovascular disease, which is estimated to be 5- to 20-fold higher than in the general population. Although undefined uremic toxins are often blamed for part of the increased risk, visceral adipose tissue, and in particular epicardial adipose tissue (EAT), have been the focus of intense research in the past two decades. In fact, several lines of evidence suggest their involvement in atherosclerosis development and its complications. EAT may promote atherosclerosis through paracrine and endocrine pathways exerted via the secretion of adipocytokines such as adiponectin and leptin. In this article we review the current knowledge of the impact of EAT on cardiovascular outcomes in the general population and in patients with CKD. Special reference will be made to adiponectin and leptin as possible mediators of the increased cardiovascular risk linked with EAT.

Selected cardiovascular risk factors in early stages of chronic kidney disease

Cardiovascular diseases, including hypertension, congestive heart failure, myocardial infarction, stroke and atherosclerosis, are common in patients with chronic kidney disease. Aside from the standard biomarkers, measured to determine cardiovascular risk, new ones have emerged: markers of oxidative stress, apoptosis, inflammation, vascular endothelium dysfunction, atherosclerosis, organ calcification and fibrosis. Unfortunately, their utility for routine clinical application remains to be elucidated. A causal relationship between new markers and cardiovascular diseases in patients with chronic kidney disease remains to be established. First of all, there is a lack of large, randomized trials. Moreover, most studies focus on patients with end-stage renal disease as well as on dialysed patients. In such patients, cardiovascular diseases are already present and advanced while early detection of cardiovascular disease risk factor in patients with early-stages of chronic kidney disease would allow more precise prognosis and, as a result, changes in treatment algorithm. In this article, we conduct a comprehensive review of literature for publications relating to cardiovascular risk factors in patients with early-stages of chronic kidney disease. Overall, there are many encouraging advances in detection of cardiovascular risk factors that are making the future more promising for patients suffering from chronic kidney disease.

Long Pentraxin 3 as a Broader Biomarker for Multiple Risk Factors in End-Stage Renal Disease: Association with All-Cause Mortality

Persistent inflammation in end-stage renal disease (ESRD) patients is known to underlie the progression of chronic kidney disease and to be associated with multiple risk factors including malnutrition, atherosclerosis, and cardiovascular disease (CVD). The acute-phase protein pentraxin 3 (PTX3) has a proven potential as a local inflammatory biomarker, but its clinical utility in ESRD remains unclear. Circulating levels of PTX3 and classical inflammatory mediators, including the clinical prototypical C-reactive protein (CRP), were assessed in 246 ESRD patients on dialysis and analysed in relation to the lipid profile, adipokine levels, and nutritional, cardiac, and renal fibrosis markers. Occurrence of deaths was recorded for the following year. Contrarily to the classical inflammatory markers, PTX3 levels were negatively correlated with nutritional markers and associated with a less atherogenic lipid profile. Levels of the cardiac and renal fibrosis markers and of the oxidized LDL/LDL-C ratio were found to be independent determinants of PTX3 concentration. When comparing inflammatory mediators, the increase in the PTX3 levels was the only predictor of all-cause mortality in dialysis patients in a survival model adjusted to all markers under study, other than the inflammatory ones, besides common confounding factors in dialysis. Data support the clinical applicability of PTX3 as a broader inflammatory biomarker than the classical ones, presenting a close association with inflammation, malnutrition, CVD, and renal fibrosis and a great potential to predict all-cause mortality in dialysis patients. The pleiotropic character of PTX3 may be of clinical relevance, and it could be targeted to ameliorate the high morbidity and mortality associated with ESRD.

IL 6 but not TNF is linked to coronary artery calcification in patients with chronic kidney disease

INTRODUCTION

Patients with chronic kidney disease (CKD) have a high risk of death mainly due to cardiovascular diseases (CVD). Early risk identification may allow interventions and prevention of fatal events.

OBJECTIVES

The study aim was to assess the usefulness of selected CVD biomarkers as predictors of 5-year mortality in patients with different CKD stages.

PATIENTS AND METHODS

Study included 57 CKD patients: 38 in stage 5 (ESRD), 19 in stage 3 and 4 (CKD3-4), and 19 healthy controls. Blood samples were obtained once to measure fetuin A, adiponectin, leptin, tumor necrosis factor (TNF), interleukin-6 (IL-6), metalloproteinase-9 (MMP9), intracellular-1 (ICAM1) and vascular-1 (VCAM1) adhesion molecules (ELISA or Luminex platform). Computed tomography was performed to assess the calcium score (CS). Patients were prospectively followed for 5 years to evaluate their all-cause mortality.

RESULTS

Serum VCAM1, TNF and IL-6 were significantly higher in more advanced CKD stages. VCAM1 correlated significantly with ICAM1, TNF and IL-6. TNF and IL-6 were also significantly correlated with each other. No significant changes were detected for other markers. IL-6 correlated significantly with CS, age, renal function and CRP. Elevated CS and IL-6 increased over 3 times the 5-year all-cause and cardiovascular mortality risks in patients with CKD or ESRD at baseline.

CONCLUSIONS

IL-6 and CS were significantly associated with 5-year risk of all-cause mortality in CKD patients. Our study suggests an involvement of chronic inflammation linked to coronary artery calcification that is likely to contribute to the cardiovascular mortality in patients with impaired renal function.

Comparison of BMI, waist circumference, and waist-to-height ratio for identification of subclinical cardiovascular risk in pediatric kidney transplant recipients

BACKGROUND

Kidney transplant recipients are at high risk for CV morbidity. However, the measure of obesity that best predicts CV risk has not been established.

OBJECTIVE

A prospective, controlled study was conducted to compare the ability of BMI, WC, and WHr to identify CV risk in pediatric kidney transplant recipients.

METHODS

Transplant recipients, aged 3-20 years, had echocardiogram, CIMT, BMI, WC, WHr, blood pressure, lipids, and leptin measured. Receiver operating characteristic analysis was used to compare the ability of BMI, WC, and WHr to detect a composite adverse CV outcome. Presence of the composite outcome was defined by ≥3 of the following five criteria: (a) LVH, (b) high CIMT, (c) impaired myocardial strain, (d) dyslipidemia, and/or (e) hypertension. Multivariate analysis was conducted by generalized estimating equation regression.

RESULTS

We analyzed 108 visits of 42 transplant recipients. Prevalence of obesity by WHr (43.5%) was higher than BMI (24.1%) and WC (12.0%). Proportion of WHr-obese who met criteria for the adverse CV outcome was higher (62.2%) than BMI (34.6%) and WC-obese (33.3%). Leptin levels were higher in children with obesity. Area under the ROC curve for WHr-obese (0.77) was higher compared to BMI (0.47) and WC (0.48) to detect the CV outcome, P = 0.0006. WHr-obesity was associated with 5.72 increased odds of having the adverse CV outcome, P = 0.0001, while BMI and WC were not significant.

CONCLUSION

WHr is more sensitive than BMI or WC to detect subclinical CV risk and should be included in screening of pediatric kidney transplant recipients.

Cardiometabolic risks vary by weight status in pediatric kidney and liver transplant recipients: A cross-sectional, single-center study in the USA

There is an increasing need to understand long-term metabolic changes and resultant comorbidities because life expectancy is increasing after pediatric kidney and liver transplants. We evaluated differences in classic and novel cardiometabolic biomarkers among obese and normal weight adolescent transplant recipients. We enrolled a total of 80 adolescent (mean±SD, 14.8 years ±3.0) transplant recipients (63 kidney, 17 liver) with mean duration from transplantation of 6.0 (±4.1) years. Among kidney transplant recipients, overweight and obese individuals had higher leptin (16.7 vs 7.5 μg/mL, P<.001), lower HDL (1.1 vs 1.3 mmol/L, P=.02), higher free fatty acid (0.6 vs 0.5 mmol/L, P=.03), higher apoB-to-apoA1 ratio (0.8 vs 0.6, P=.03), and higher glucose (5.8 vs 4.3 mmol/L, P=.03) concentrations compared to normal weight individuals. Regardless of obesity status, over half of all participants (57.5%) were considered at high cardiometabolic risk using consensus guidelines, and this was more pronounced for kidney transplant recipients (61.9%). Post-transplantation adolescents have increased cardiometabolic risk characterized by traditional risk factors of obesity and diabetes. The presence of obesity significantly worsens biomarkers of cardiometabolic risk. Future studies should explore whether treatment of obesity can improve the health and long-term outcomes for children undergoing solid organ transplant.

A prospective evaluation of obesometric parameters associated with renal stone recurrence

INTRODUCTION

Our aim was to evaluate whether obesometric serum hormones and body fat distribution are associated with renal stone recurrence.

METHODS

We conducted a prospective cohort study of participants undergoing renal stone (RS) intervention at a single institution from November 2009-June 2010 and followed them for a median 62 months. Obesometric parameters were measured at baseline, including body mass index (BMI), fasting serum leptin and adiponectin, and proportion of visceral adipose tissue (%VAT) averaged from three fixed axial computed tomography (CT) slices. The primary study outcome was stone recurrence.

RESULTS

A total of 110 participants were enrolled. Elevated %VAT was associated RS recurrence; participants with %VAT in the highest quartile had a five-year stone-free rate of 47.1% compared to 72.2% among other participants (p=0.004). Adjusting for gender, elevated %VAT was independently predictive of renal stone recurrence among initial stone formers (n=74; hazard ratio [HR] 4.53, 95% confidence interval [CI] 1.08-19.02), but not among recurrent stone formers (n=19; HR 0.51, 95% CI 0.054-4.72). Other obesometric factors, including leptin, adiponectin, and BMI, were not significantly predictive of recurrence.

CONCLUSIONS

We report a novel association between an elevated %VAT and stone recurrence. These findings may inform patient counselling and followup regimens. The metabolic basis for these findings requires further investigation.

Adipokines and their Relation to Endothelial Dysfunction in Patients with Chronic Kidney Disease

INTRODUCTION

Chronic Kidney Disease (CKD) patients are at high risk of cardiovascular diseases (CVDs). Reduced nitric oxide (NO) bioavailability is a key element in connecting kidney disease to endothelial dysfunction (ED) and cardiovascular (CV) complications. Further, inflammation is implicated in ED in CKD. Besides these, adipose tissue factors were thought to have a role in inflammation and ED in CKD.

AIM

It is proposed to evaluate the concentration changes of adipokines, inflammatory and ED markers in CKD patients compared to healthy controls. Further, to assess the associations between adipokines, inflammation and ED in CKD patients.

MATERIALS AND METHODS

A total of 120 CKD patients were included and classified into 3 groups based on Glomerular filtration rate (GFR). Group I (n=40) patients had a GFR between 60-119 ml/min/1.73m(2) (stage I, II), group II (n=40) had 15-59 ml/min/1.73m(2) (stage III, IV) and group III (n=40) had <15 ml/min/1.73m(2) (stage V). Forty healthy subjects served as controls. Adiponectin, Leptin, Interleukin-10 (IL-10), Interleukin-6 (IL-6), tumour necrosis factor-α (TNF-α) were estimated by ELISA. High sensitivity C-reactive protein (hsCRP) was estimated by immunoturbidimetry and NO by Griess method.

STATISTICAL ANALYSIS

Mann-Whitney U test was used to compare the difference in variables between controls and CKD patients. One-way ANOVA Kruskalwallis test was used for comparison of variables between groups in CKD patients. Spearman's rank correlation was used to explore the associations between variables. Simple univariate linear regression analysis was used to predict the value of variable from another variable.

RESULTS

A significant increase in leptin, IL-6, TNF-α, IL-6/IL-10 ratio, hsCRP and decrease in adiponectin, IL-10, NO was observed in CKD patients compared to controls (p<0.05). In CKD patients, adiponectin, leptin, IL-6, IL-6/IL-10 ratio, TNF-α were significantly increased and IL-10 levels were decreased from group I to group III (p<0.05). In group III CKD patients IL-6 showed a significant negative correlation with NO (r=-0.557; p=0.005). In linear regression analysis also, IL-6 showed a significant negative association with NO (B±SE=-0.038±0.11; p=0.002) in CKD patients.

CONCLUSION

The present study demonstrates that adipokine levels are altered from initial to final stages of CKD due to renal dysfunction which in association with an exaggerated inflammation may contribute to the ED and CV events.

Cardiovascular biomarkers in chronic kidney disease: state of current research and clinical applicability

The high incidence of cardiovascular events in chronic kidney disease (CKD) warrants an accurate evaluation of risk aimed at reducing the burden of disease and its consequences. The use of biomarkers to identify patients at high risk has been in use in the general population for several decades and has received mixed reactions in the medical community. Some practitioners have become staunch supporters and users while others doubt the utility of biomarkers and rarely measure them. In CKD patients numerous markers similar to those used in the general population and others more specific to the uremic population have emerged; however their utility for routine clinical application remains to be fully elucidated. The reproducibility and standardization of the serum assays are serious limitations to the broad implementation of these tests. The lack of focused research and validation in randomized trials rather than ad hoc measurement of multiple serum markers in observational studies is also cause for concern related to the clinical applicability of these markers. We review the current literature on biomarkers that may have a relevant role in field of nephrology.

Decreased serum level of soluble-leptin-receptor in patients with systemic lupus erythematosus

BACKGROUND

There is some evidence suggesting that leptin and its negative regulator, soluble-leptinreceptor (SLR) may be able to influence inflammatory and autoimmune processes.

METHODS

In this study, several variables including socio-demographics, health-related habits, depression score, serum molecules and blood parameters besides the SLR level were evaluated in patients with SLE (SLE-patients) and healthy controls.

RESULTS

The patients had significantly lower SLR level and higher depression score than the controls and both of these variables have a significant association with the occurrence of disease in logistic regression model. Moreover, the results of Pearson correlation analysis showed that patients' SLR level was negatively correlated with their weights and BDI scores.

CONCLUSION

For the first time, this study indicated a lower level of SLR in SLE-patients and suggested that lower concentrations of SLR in these patients may be implicated in the pathogenesis of SLE.

Differential effect of baseline adiponectin on all-cause mortality in hemodialysis patients depending on initial body mass index. Long-term follow-up data of 4.5 years

OBJECTIVES

We sought to investigate the interaction of adiponectin levels and body mass index (BMI) for predicting all-cause mortality in a cohort of hemodialysis (HD) patients.

DESIGN

Longitudinal, observational cohort study.

SETTING

HD unit.

SUBJECTS

Sixty patients (mean age: 64 ± 13 years, 39 men) with end-stage renal disease on maintenance HD followed up for 4.5 years represented the prospective study cohort.

INTERVENTION

Associations between baseline plasma adiponectin levels and initial BMI with all-cause mortality were assessed taking into account the assumption of nonlinear correlations. The association between adiponectin, BMI, and serum levels of interleukin-10 (IL-10) and interleukin-6 (IL-6) with survival was determined cross-sectionally.

MAIN OUTCOME MEASURE

All-cause mortality.

RESULTS

Nonlinear survival modeling showed that there was a U-shaped association of BMI with all-cause mortality, whereas there was an inverse U-shaped association for plasma adiponectin levels. Using a BMI of 24 kg/m(2) as a cutoff, an interaction effect of BMI on the association between adiponectin and mortality was observed (P = .045). In participants with BMI ≥ 24 kg/m(2), each 15 μg/mL increase in plasma adiponectin levels was associated with a decreased hazard of death (hazard ratio: 0.57, 95% CI: 0.32 to 0.99) in unadjusted analysis. In HD patients with BMI < 24 kg/m(2), no significant association was observed between adiponectin and mortality (P = .989). Cross-sectional analysis showed that in the subgroup of patients in whom the protective effect of adiponectin was observed (BMI ≥ 24 kg/m(2)), a positive linear association existed between adiponectin and IL-10 levels (r = 0.345, P = .027) as well as a negative association with IL-6 levels (r = -0.322, P = .040). No association was observed in patients with BMI < 24 kg/m(2), neither with IL-10 nor with IL-6.

CONCLUSIONS

Obesity possibly modifies the effect of adiponectin on all-cause mortality in HD patients, thus explaining the published conflicting results in recent literature regarding the association of plasma adiponectin levels and mortality in chronic kidney disease patients.

Chronic kidney disease and subclinical lacunar infarction are independently associated with frontal lobe dysfunction in community-dwelling elderly subjects: the Sefuri brain MRI study

Although recent studies have found that chronic kidney disease (CKD) is an independent risk factor for cognitive impairment in population-based cohorts, the mechanisms of cognitive impairment in subjects with CKD are unclear. We examined 503 elderly subjects (mean age: 72.4 years), who were living independently at home without apparent dementia, using MRI. The subject was judged as having frontal lobe dysfunction if the scores on the modified Stroop test were higher than the fifth quintile for each given decade. Serum creatinine values, measured by the enzymatic method, were used for the Japanese equation of estimated glomerular filtration rate (eGFR). Subjects in the frontal lobe dysfunction group tended to have higher blood pressure, lower eGFR and more lacunar infarcts, and were less educated. When possible confounders were entered into the multivariate logistic regression model, the independent predictors of frontal lobe dysfunction were eGFR (odds ratio 0.854; 95% confidence interval (CI) 0.743-0.983 per 10 ml min(-1) per 1.73 m(2)) and the number of lacunar infarction (odds ratio 1.460; 95% CI 1.127-1.892). The mean of the logarithmically transformed Stroop test scores in the eGFR<60 ml min(-1) per 1.73 m(2) group was 1.376 (95% CI 1.301-1.451), which was significantly higher than that (1.250) for the eGFR 60-89 ml min(-1) per 1.73 m(2) group (95% CI 1.215-1.285) (P=0.009) and tended to be higher than that (1.264) for the eGFR ≥90 ml min(-1) per 1.73 m(2) group (95% CI 1.188-1.340) (analysis of covariance, adjusted for age). The present study showed that CKD and subclinical lacunar infarction independently contributed to frontal lobe dysfunction in healthy elderly subjects.

Protein-energy wasting and mortality in chronic kidney disease

Protein-energy wasting (PEW) is common in patients with chronic kidney disease (CKD) and is associated with an increased death risk from cardiovascular diseases. However, while even minor renal dysfunction is an independent predictor of adverse cardiovascular prognosis, PEW becomes clinically manifest at an advanced stage, early before or during the dialytic stage. Mechanisms causing loss of muscle protein and fat are complex and not always associated with anorexia, but are linked to several abnormalities that stimulate protein degradation and/or decrease protein synthesis. In addition, data from experimental CKD indicate that uremia specifically blunts the regenerative potential in skeletal muscle, by acting on muscle stem cells. In this discussion recent findings regarding the mechanisms responsible for malnutrition and the increase in cardiovascular risk in CKD patients are discussed. During the course of CKD, the loss of kidney excretory and metabolic functions proceed together with the activation of pathways of endothelial damage, inflammation, acidosis, alterations in insulin signaling and anorexia which are likely to orchestrate net protein catabolism and the PEW syndrome.

Adiponectin level as a consequence of genetic variation, but not leptin level or leptin: adiponectin ratio, is a risk factor for carotid intima-media thickness

BACKGROUND AND PURPOSE

The adipocytokines adiponectin and leptin have been suggested as risk factors for cardiovascular disease, including stroke, acting through atherosclerosis. However, studies have provided conflicting results in underpowered cohorts with some suggesting that the leptin:adiponectin ratio is a better predictor of risk. We examined these associations with carotid intima-media thickness (IMT), a marker of early atherosclerosis and arterial remodeling and an independent predictor of stroke. We also examined association between genetic variants in the leptin and adiponectin genes and IMT.

METHODS

Adiponectin and leptin levels were determined in 990 individuals from the community Carotid Atherosclerosis Progression Study. Five variants in the gene encoding adiponectin and 7 in the gene encoding leptin were genotyped and their effects on circulating levels assessed. Both were then correlated with IMT.

RESULTS

Adiponectin levels negatively correlated with IMT (-0.079, P=0.013). There was no correlation between leptin levels or leptin:adiponectin ratio and IMT. Two variants in the ADIPOQ gene encoding adiponectin were associated with altered adiponectin levels, 1 of which (rs266729) was associated with IMT. There was also an interaction with body mass index (P=0.019) with the association being present in obese subjects (P=0.02).

CONCLUSIONS

Our results support a causal role for adiponectin in early carotid IMT and suggest it may act through interaction with obesity. In contrast, we found no evidence of a role for leptin and no evidence that leptin:adiponectin ratio is a better predictor of risk that adiponectin levels alone.