The protein-bound uremic toxin p-cresyl-sulfate promotes intracellular ROS production and lipid peroxidation in 3T3-L1 adipose cells

Patients with chronic kidney disease (CKD) often exhibit increased level of oxidative stress that contribute to the deterioration of renal function and uremic complications. White adipose tissue (WAT) has been recognized as a major site of production of radical oxygen species (ROS) in the context of metabolic diseases. This study was designed to decipher whether the protein bound uremic toxin p-cresyl-sulfate (p-CS) could contribute to ROS production in WAT and promote oxidative stress. Mouse 3T3-L1 adipocytes were incubated for 2 h in culture medium containing 212 μM p-CS, a concentration chosen to mimic levels encountered in end stage renal disease patients or KCl as a control and intracellular ROS production was measured using the fluorescent probe 5-6-carboxy-2',7'-dichlorodihydrofluorescein diacetate. Oxidative insult was estimated by the measurement of malondialdehyde (MDA) content and glutathione content. The effects of probenecid (1 mM) a potent inhibitor of organic anion transporter, apocynin (1 mM) an inhibitor of NADPH oxidase or common antioxidants such as α-tocopherol (2.5 μM), ascorbate (200 μM), and N-acetylcysteine (500 μM) were further evaluated. p-CS triggered a striking increase in ROS production (+228%, p < 0.01), in MDA content (+214%, p < 0.005) and a decrease in glutathione (-47%, P < 0.01). Pre-treatment of cells with probenecid, apocynin or antioxidants prevented the p-CS induced ROS production and oxidative insults. These results suggest that in uremic state, the intracellular accumulation of p-CS in adipose cells could contribute, through an activation of NADPH oxidase, to the redox imbalance often reported in CKD patients.

Abnormalities in Glucose Metabolism, Appetite-Related Peptide Release, and Pro-nflammatory Cytokines Play a Central Role in Appetite Disorders in Peritoneal Dialysis

Background: Appetite disorders are frequent and scantly studied in peritoneal dialysis (PD) patients and are associated with malnutrition and cardiovascular complications. Objective: We investigated the relationship between uremic insulin resistance, pro-inflammatory cytokines, and appetite-related peptides release (ARPr) with eating-behavior disorders in PD patients. Methods: We included 42 PD patients (12 suffering anorexia, 12 obese with high food-intake, and 18 asymptomatic) and 10 controls. We measured blood levels of ARPr including orexigens [neuropeptide-Y (NPY), ghrelin, and nitric-oxide], anorexigens [cholecystokinin, insulin, corticotropin-releasing factor, leptin, and adiponectin (Ad)], and cytokines (TNF-α, sTNFα-R2, and IL-6) both at baseline and after administering a standard-food stimulus (SFS). We also measured the expression of TNF-α, leptin and Ad-encoding mRNAs in abdominal adipose tissue. We compared these markers with eating motivation measured by a Visual Analog Scale (VAS). Results: Anorexics showed both little appetite, measured by a VAS, and low levels of orexigens that remained constant after SFS, coupled with high levels of anorexigens at baseline and after SFS. Obeses showed higher appetite, increased baseline levels of orexigens, lower baseline levels of anorexigens and cytokines and two peaks of NPY after SFS. The different patterns of ARPr and cytokines pointed to a close relationship with uremic insulin resistance. In fact, the euglycemic-hyperglycemic clamp reproduced these disorders. In anorexics, TNF-α fat expression was increased. In obese patients, leptin expression in fat tissue was down-regulated and showed correlation with the appetite. Conclusion: In PD, appetite is governed by substances that are altered at baseline and abnormally released. Such modulators are controlled by insulin metabolism and cytokines and, while anorexics display inflammatory predominance, obese patients predominantly display insulin resistance.

Associations of adiponectin and leptin levels with protein-energy wasting, in end stage renal disease patients

OBJECTIVE

The aim of the study was to examine the prevalence of protein-energy wasting (PEW) in hemodialysis (HD) and peritoneal dialysis (PD) patients in our center and determine whether adiponectin and leptin are involved in the development of PEW.

DESIGN

Prospective (18 months).

SETTING

University Hospital of Heraklion, Crete, Greece.

SUBJECTS

Seventy-four end-stage-renal-disease patients, 47 on HD and 27 on PD.

MAIN OUTCOME MEASURES

At three sequential time points (baseline, 6 and 18 months) anthropometric, nutritional and inflammatory status data were collected. Serum adiponectin and leptin were also assessed at each time point. Patients were allocated to 3 strata according to PEW severity (0, 1-2 and ≥3 criteria for PEW).

RESULTS

Adiponectin and leptin levels were greater among PD compared to HD patients (p≤0.035). Adiponectin levels were incrementally greater across increasing strata of PEW (p≤0.002). Leptin showed the opposite trend, with lower levels in malnourished patients and higher levels in patients with zero PEW criteria (p≤0.042). Alterations of adiponectin levels during the observation period were dependent on PEW stratum (p≤0.021) and mode of dialysis (p≤0.002), after adjustment for age, dialysis vintage, gender and fat mass index. Particularly, adiponectin levels increased over time in HD patients with ≥3 criteria for PEW, whereas adiponectin levels decreased in PD patients with ≥3 criteria for PEW throughout the study. Leptin alterations over time were not affected by dialysis mode or PEW stratification.

CONCLUSIONS

Our study provides evidence that increased adiponectin and decreased leptin levels are independently associated with PEW and thus, poor prognosis.

An Analysis of Anthropometric Indicators and Modifiable Lifestyle Parameters Associated with Hypertensive Nephropathy

The surge in prevalence of chronic noncommunicable diseases like hypertension and chronic kidney disease has been linked with modifiable lifestyle practices and increased body fat. This study sought to compare the association between different modifiable lifestyle practices, adiposity indices, renal function parameters, and hypertension as well as the predictive implications for levels of these parameters in target cardiac organ damage among an urban Ghanaian hypertensive population. Using a hospital-based case-control study design, 241 Ghanaian indigenes from the Kumasi metropolis were recruited for this study. The case group was made up of 180 hypertensives and 61 normotensives served as controls. In addition to sociodemographic data, standard haemodynamic, anthropometric, renal function, and cardiac organ damage assessments were done. The prevalence of chronic kidney disease (CKD) ranged from 13.3% to 16.6% depending on the equation used in estimating the glomerular filtration rate (eGFR). Percentage cluster distribution by chronic kidney disease was observed to be significantly tilted toward the upper quartiles (3rd and 4th) of the haemodynamic parameters measured. Chronic kidney disease was significantly higher among self-reported smokers and alcoholic hypertensives. In this urban population, adiposity was associated with hypertension and renal insufficiency. Chronic kidney disease was associated with hypertension and cardiac abnormalities.

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.

High plasma chemerin is associated with renal dysfunction and predictive for cardiovascular events - Insights from phenotype and genotype characterization

The novel adipokine chemerin, encoded by the RARRES2 gene, has been suggested to be linked to insulin resistance and to the metabolic syndrome (MetS). However, no well-defined cardiovascular profile has been reported and the association with coronary artery disease (CAD) is a matter of debate. Because there is a relation between renal dysfunction and CAD, we analyzed plasma chemerin levels and the estimated glomerular filtration rate (eGFR) in 495 patients undergoing coronary angiography for the evaluation of established or suspected stable CAD. Chemerin levels were higher in patients with Type 2 diabetes mellitus (T2DM, n=111) and the metabolic syndrome (MetS, n=147) than in subjects without T2DM (191.5±72.9 vs. 169.7±64.7ng/ml, p=0.001) or the MetS (201.2±71.0 vs. 163,1ng/ml, p<0.001), but did not differ significantly between patients with significant CAD (n=247) and those without significant CAD (177.1±67.0 vs. 171.7±67.2ng/ml, p=0.193). Analysis of covariance using age, sex, and BMI as covariates showed that chemerin was significantly and independently associated with eGFR (F=49.6, p<0.001). After an 8-year follow-up period, patients with high chemerin levels were more often affected by cardiovascular events (HR=1.72 [95% CI 1.19-2.47], p=0.004), even after appropriate adjustment for age, gender, BMI, as well as eGFR (adjusted HR 1.51 [95% CI 1.03-2.23], p=0.037). Given the cardiometabolic role of chemerin, we also applied a Cardio-Metabo Chip analysis and revealed a genome-wide significant association with SNPs (rs55709438, rs2444030, and rs3098423) located at chromosomal region 15q15-23, which were associated with metabolic traits and eGFR. This study for the first time demonstrates that high chemerin concentrations are significantly associated with renal impairment and predictive of cardiovascular events and that 15q15-23 might have an impact on chemerin levels beyond common genetic variations in RARRES2.

Serum adipokine levels in renal transplant recipients

BACKGROUND

Metabolic syndrome (MS) is a common complication in renal transplant (RTx) recipients. This study aimed to explore the alterations and interrelationship of various adipokines in RTx recipients with and without MS.

METHODS

RTx recipients followed at our hospital were randomly selected for the cross-sectional study of MS. The modified Adult Treatment Panel III criteria adopted for Asian populations were used to define MS. Overnight fasting blood samples were obtained for determination of adipokines, including adiponectin, leptin, resistin, and visfatin. Univariate and multivariate logistic regressions were performed to determine parameters that were associated with serum adipokine levels. Pearson correlation analysis was performed between adipokines.

RESULTS

A total of 280 RTx recipients were enrolled for the study. Seventy-three cases (26.1%) fulfilled the criteria of MS. A significantly higher serum leptin level was found in MS patients (16.61 ± 13.90 vs 8.00 ± 7.42 μg/mL; P < .0001). There was no significant difference in serum levels of adiponectin, resistin, and visfatin between the 2 groups. Serum adiponectin level was positively correlated with serum resistin (r = 0.422; P < .0001) and visfatin levels (r = 0.224; P < .0001). Serum resistin level was positively correlated with serum visfatin level. All but serum visfatin level were negatively correlated with estimated glomerular filtration rate. Univariate logistic regression revealed the following variables to be associated with serum leptin level: metabolic syndrome, sex, body weight, waist circumference, body mass index (BMI), hypertension, serum creatinine, fasting blood sugar, HbA1c, serum triglyceride, and uric acid. Multivariate analysis revealed that sex, body weight, BMI, and serum creatinine were associated with serum leptin level.

CONCLUSIONS

Compared with RTx recipients without MS, patients with MS were associated with significantly higher serum leptin levels and similar adiponectin, resistin, and visfatin levels. A close interrelationship was also found in the serum levels of these adipokines.

White adipose tissue overproduces the lipid-mobilizing factor zinc α2-glycoprotein in chronic kidney disease

Chronic kidney disease (CKD) is frequently associated with protein-energy wasting, a recognized strong predictive factor of mortality. Zinc α2-glycoprotein (ZAG) is a new adipokine involved in body weight control through its lipid-mobilizing activity. Here we tested whether the uremic environment in CKD could alter ZAG production by white adipose tissue and contribute to CKD-associated metabolic disturbances. Compared with normal plasma, uremic plasma induced a significant increase in ZAG synthesis (124%), was associated with a significant increase in basal lipolysis (31%), and significantly blunted lipogenesis (-53%) in 3T3-L1 adipocytes in vitro. In 5/6 nephrectomized rats and mice in vivo, there was a significant decrease in white adipose tissue accretion (-44% and -43%, respectively) and a significantly higher white adipose tissue content of ZAG protein than in sham-operated, pair-fed control animals (498% and 106%, respectively). Subcutaneous white adipose tissue biopsies from patients with end-stage renal disease exhibited a higher content of ZAG (573%) than age-matched controls. Thus, the ZAG content is increased in white adipose tissue from patients or animal models with CKD. Overproduction of ZAG in CKD could be a major contributor to metabolic disturbances associated with CKD.

Is high body mass index independently associated with diminished glomerular filtration rate? An epidemiological study

AIM

To examine whether there is an independent association between body mass index (BMI) and estimated glomerular filtration rate (GFR) in a large primary care population.

METHODS

Anonymous data were sequentially extracted from primary care records between 2006 and 2009 in a primary care population of approximately 220,000 people in Kent, South East UK. Using GFR, BMI, age, gender and comorbidities we examined the association between BMI and GFR. Univariate and multivariate analysis was performed using SPSS(®) (SPSS Inc., Chicago).

RESULTS

Sixty-one thousand six-hundred thirty seven people fulfilled the inclusion criteria. There was no correlation between BMI and GFR on univariate analysis. When stratified by BMI, ANOVA demonstrated a statistically significant difference in GFR across BMI strata (p < 0.001). However the absolute differences in BMI between groups were very small. There was a small association between BMI and GFR on multivariate analysis, much of which was lost on adjustment for confounding variables.

CONCLUSION

These findings suggest that elevated BMI is not a biologically significant predictor of diminished GFR and therefore may be an insufficiently accurate measure of risk for the metabolic syndrome and CKD.

Antilipolytic effect of calcimimetics depends on the allelic variant of calcium-sensing receptor gene polymorphism rs1042636 (Arg990Gly)

Calcium-sensing receptor polymorphism rs1042636 (Arg990Gly) affects the response to the calcimimetic cinacalcet, used to treat hypercalcemia in secondary hyperparathyroidism (sHPT) or parathyroid carcinoma. Carriers of the Arg allelle, show less parathyroid hormone secretion suppression in response to the drug. This effect was reproducible in transfected cultured human embryonic kidney cells, supporting a causal relationship on the protein level. We previously established that cinacalcet has an antilipolytic effect in isolated human adipocytes; however, there were a number of samples that did not respond to the treatment. The present work aimed to investigate whether the variable antilipolytic response to cinacalcet in adipocytes was consistent with the effect reported for the rs1042636 polymorphism. Lipolysis was assessed by measuring glycerol release after exposure to cinacalcet (10 μM) or vehicle in adipocytes isolated from 38 donors. Responsiveness was defined as lipolysis suppression (cinacalcet vs vehicle control) greater than 20%. Genotype analysis showed that 23 adipocyte donors were homozygous for Arg at position 990, 14 heterozygous and 1 homozygous Gly-Gly. Among the Arg homozygotes, one was responsive to cinacalcet, whereas five Gly carriers responded to the calcimimetic. In all, 83% of adipocytes showing response to cinacalcet carried the glycine allele, whereas in 96% of Arg-Arg individuals adipocytes did not respond to the calcimimetic (P=0.027, Fisher's exact test). Confirming sHPT observations, adipocytes from rs1042636 Gly-allele carriers show higher sensitivity to the antilipolytic action of cinacalcet. The potential benefit of cinacalcet as a suppressor of basal lipolysis and free fatty acid release in uremic patients needs to consider the rs1042636 single-nucleotide polymorphism.

Correlates of insulin resistance in older individuals with and without kidney disease

BACKGROUND

Chronic kidney disease (CKD) is associated with insulin resistance (IR). Prior studies have found that in individuals with CKD, leptin is associated with fat mass but resistin is not and the associations with adiponectin are conflicting. This suggests that the mechanism and factors associated with IR in CKD may differ.

METHODS

Of the 2418 individuals without reported diabetes at baseline, participating in the Health, Aging and Body Composition study, a study in older individuals aged 70-79 years, 15.6% had CKD defined as an estimated glomerular filtration rate (eGFR) <60 mL/min/1.73 m(2) based on cystatin C. IR was defined as the upper quartile of the homeostasis model assessment. The association of visceral and subcutaneous abdominal fat, percent body fat, muscle fat, lipids, inflammatory markers and adiponectin were tested with logistic regression. Interactions were checked to assess whether the factors associated with IR were different in those with and without CKD.

RESULTS

Individuals with IR had a lower eGFR (80.7 ± 20.9 versus 75.6 ± 19.6, P < 0.001). After multivariable adjustment, eGFR (odds ratio per 10 mL/min/1.73 m(2) 0.92, 95% confidence interval 0.87-0.98) and CKD (1.41, 1.04-1.92) remained independently associated with IR. In individuals with and without CKD, the significant predictors of IR were male sex, black race, higher visceral fat, abdominal subcutaneous fat and triglycerides. In individuals without CKD, IR was associated with lower high-density lipoprotein and current nonsmoking status in multivariate analysis. In contrast, among individuals with CKD, interleukin-6 (IL-6) was independently associated with IR. There was a significant interaction of eGFR with race and IL-6 with a trend for adionectin but no significant interactions with CKD (P > 0.1). In the fully adjusted model, there was a trend for an interaction with adiponectin for eGFR (P = 0.08) and significant for CKD (P = 0.04 ), where adiponectin was associated with IR in those without CKD but not in those with CKD.

CONCLUSIONS

In mainly Stage 3 CKD, kidney function is associated with IR; except for adiponectin, the correlates of IR are similar in those with and without CKD.

To eat or not to eat: dietary fat in uremia is the question

Although a diet low in protein is well known to reduce the risk of progression in patients with chronic kidney disease (CKD), the impact of dietary fat content and fat quality has largely been ignored. As a reduced protein intake results in an obligatory reduction in energy intake, and as CKD patients often suffer from energy malnutrition, this issue deserves greater attention. The present review aims to summarize what is currently known about dietary fat intake in CKD and suggests areas for further study. We conclude that although overweight per se is an important risk factor for the development of CKD, the role of obesity as a risk factor for complications in manifest CKD remains unclear. Current data support a balanced increase in dietary fat intake in patients with CKD to compensate for reduced energy intake in protein-restricted diets and anorexic patients. However, patients who are obese should be encouraged to lose weight while maintaining or, preferably, increasing muscle mass.

Clinical importance of an elevated circulating chemerin level in incident dialysis patients

BACKGROUND

Circulating chemerin, a novel adipokine linked to obesity, glucose tolerance and hyperlipidaemia, was recently reported to be increased in chronic kidney disease (CKD) patients. We explored possible links between chemerin and various clinical, nutritional and biochemical markers as well as its association with 5-year all-cause mortality.

METHODS

Fasting plasma samples were obtained from 252 CKD Stage 5 patients [median age 56 years, male 61%, glomerular filtration rate (GFR) 7 mL/min] enrolled at the initiation of dialysis. Serum chemerin was measured using commercial ELISA. Chemerin levels were related to clinical status and biomarkers of inflammation, glucose and lipid metabolism and body composition (body mass index and total and truncal fat mass by dual-energy X-ray absorptiometry). Survival, censored for transplantation, was recorded for a follow-up time of 5 years.

RESULTS

In univariate regression, circulating chemerin (119 ± 26 ng/mL) was positively correlated with cholesterol (ρ = 0.21; P = 0.001), triglycerides (ρ = 0.22; P = 0.0007), apolipoprotein B (ρ = 0.33; P < 0.0001), high-sensitivity C-reactive protein (ρ = 0.18; P = 0.006), white blood cell count (ρ = 0.23; P < 0.001), insulin (ρ = 0.18; P < 0.05) and homeostatic model assessment (HOMA) index (ρ = 0.17; P < 0.05), whereas we found a negative correlation with GFR (ρ = -0.28; P = 0.007), high-density lipoprotein cholesterol (ρ = -0.15; P < 0.05) and homocysteine (ρ = -0.25; P = 0.001). Moreover, a high chemerin predicted a better survival (log-rank χ(2) = 3.85; P < 0.05). Also, in a Cox model, adjustments for age, sex and CRP did not alter this finding (hazard ratio = 1.98 [95% confidence interval = 1.13-3.50], P = 0.01). However, adjusting for GFR made the model non-significant.

CONCLUSIONS

We report that, in incident dialysis patients, an elevated chemerin is associated with a survival advantage despite its significant positive association with markers of inflammation and dyslipidaemia.

Asymmetrical dimethylarginine triggers lipolysis and inflammatory response via induction of endoplasmic reticulum stress in cultured adipocytes

Protein energy wasting, a state of decreased stores of body protein and fat, is a risk factor for mortality in advanced chronic kidney disease (CKD). Little is known about the mechanism underlying loss of fat in CKD. Accumulation of asymmetric dimethylarginine (ADMA) is prevalent in advanced CKD. Here we assessed the effect of ADMA on cellular perturbation in cultured 3T3-L1 adipocytes. Exposure of adipocytes to ADMA induced lipolysis and decreased perilipin A, with no alteration of lipases expression or activity. ADMA treatment also upregulated the expression of inflammatory adipocytokines via activation of nuclear factor-kappaB (NF-kappaB). Blocking the inflammatory responses with NF-kappaB inhibitor partly inhibited the ADMA-induced lipolysis. Furthermore, ADMA treatment triggered endoplasmic reticulum (ER) stress, revealed by phosphorylation of PKR-like eukaryotic initiation factor 2alpha kinase, eukaryotic translational initiation factor 2alpha, c-Jun NH2-terminal kinase, and overexpression of glucose-regulated protein 78. Treatment with ER stress inhibitor completely abolished the ADMA-induced lipolysis and inflammatory responses. Moreover, conditioned medium from the ADMA-treated adipocytes increased protein degradation in cultured C2C12 myotubes, suggesting that the ADMA-induced adipocyte perturbation may promote skeletal muscle proteolysis. These data suggest that elevated ADMA promoted the adipocyte perturbation through induction of ER stress, which might have implication for protein energy wasting in CKD.