Renalase, Stroke, and Hypertension in Hemodialyzed Patients

The early diagnostic value of serum renalase level in diabetic kidney disease and diabetic macroangiopathy: a retrospective case-control study

Background

Diabetic kidney disease (DKD) is a severe complication of diabetes mellitus and is associated with an increased risk of end-stage renal disease (ESRD) and cardiovascular events. Early diagnosis and monitoring of DKD are crucial for implementing appropriate interventions. This study aimed to investigate the relationship between serum renalase (RNLS) levels, DKD, and diabetic macroangiopathy in patients with type 2 diabetes mellitus (T2DM).

Objectives

This study aims to evaluate the diagnostic value of serum renalase levels in DKD and diabetic macroangiopathy.

Design

This is a retrospective case-control study.

Methods

A total of 233 participants were recruited for the study, including 115 T2DM patients without DKD or diabetic retinopathy, and 118 T2DM patients with DKD. Serum RNLS levels were measured using an enzyme-linked immunosorbent assay. Kidney function parameters and diabetic macroangiopathy risk factors were evaluated in relation to serum RNLS levels.

Results

Serum RNLS levels were significantly higher in DKD patients compared to T2DM controls (34.82 (31.68, 39.37) vs 30.52 (28.58, 33.16), p < 0.01). Multiple linear regression analysis indicated that kidney function parameters and carotid intima-media thickness were independently related to RNLS levels. The study population was divided into four groups: no DKD and no diabetic macroangiopathy, DKD without diabetic macroangiopathy, diabetic macroangiopathy without DKD, and both DKD and diabetic macroangiopathy. Analysis results showed that patients with both DKD and diabetic macroangiopathy had the highest RNLS levels. Receiver operating characteristic curve analysis demonstrated the diagnostic value of RNLS for DKD (0.76 (95% confidence interval (CI) = 0.70-0.82, p < 0.01)) and diabetic macroangiopathy (0.75 (95% CI = 0.66-0.84, p < 0.01)).

Conclusion

Circulating RNLS levels were significantly increased in patients with DKD and diabetic macroangiopathy, suggesting that RNLS may serve as an early diagnostic marker.

Renalase Potential as a Marker and Therapeutic Target in Chronic Kidney Disease

Hypertension and cardiovascular disease are prominent features of chronic kidney disease, and they are associated with premature mortality and progression toward end-stage kidney disease. Renalase, an enzyme secreted predominantly by the kidney and identified in 2005, seems to be one of the missing pieces in the puzzle of heart and kidney interaction in chronic kidney disease by lowering blood pressure and reducing the overactivity of sympathetic tone. This review aims to summarize evidence from clinical studies performed on subjects with CKD in order to explore the value of renalase as a marker and/or a therapeutic target in this disease.

Association Between Renalase Gene Polymorphism (rs2296545) and Hypertension in Egyptian Chronic Kidney Disease Patients

Background Renalase gene polymorphisms are associated with an increased risk of essential hypertension, chronic kidney disease (CKD), heart disease, diabetes, and stroke. One of these polymorphisms is a common missense (rs2296545) polymorphism, which was reported to be related to hypertension. The aim of this work was to investigate the possible relation between renalase gene polymorphism (rs2296545) and hypertension in patients with CKD patients. Subjects and methods Ninety patients were included in this case-control study: 30 normotensive CKD patients, 30 hypertensive CKD patients, and 30 apparently healthy controls. Genomic deoxyribonucleic acid (DNA) was extracted from peripheral whole blood, and renalase gene (rs2296545) polymorphism was genotyped in all patients and controls by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Odds ratios (OR) and their 95% CIs were calculated. Results We found that the CC genotype and the C allele renalase (rs2296545) were statistically associated with the risk of CKD (OR= 9.4; 95%CI 1.2-7.2; P= 0.036) and (OR= 3.78; 95%CI 1.57-9.08; P= 0.003), respectively. There was a statistically significant difference between the hypertensive CKD patients and the controls regarding the CC genotypes and the C allele, (26.7% versus 3.3%, P= 0.018) and (40% versus 11.7%, P< 0.001) for the CC genotype and the C allele, respectively. The mean values of systolic and diastolic blood pressure were higher in the normotensive CKD patients with the CC genotype compared to other genotypes (P= 0.014 and P= 0.022, respectively) and also were higher in hypertensive CKD patients with the CC genotype when compared to other genotypes (P= 0.001 for both). Conclusion This study demonstrated a statistically significant increase in the renalase gene (rs2296545) CC genotype and the C allele in CKD patients, especially hypertensive CKD.

Selenoprotein P, Peroxiredoxin-5, Renalase and Selected Cardiovascular Consequences Tested in Ambulatory Blood Pressure Monitoring and Echocardiography

This study aimed to assess the relationship between chosen antioxidants, namely selenoprotein P (SELENOP), peroxiredoxin-5 (Prdx-5), renalase and selected cardiovascular consequences tested in ambulatory blood pressure monitoring (ABPM) and echocardiography (ECHO). In our work, cardiovascular consequences refer to higher mean blood pressure (MBP) and pulse pressure (PP) on ABPM, as well as to left atrial enlargement (LAE), left ventricular hypertrophy (LVH) and lower left ventricular ejection fraction (LVEF%) on ECHO. The study group consisted of 101 consecutive patients admitted to the Department of Internal Medicine, Occupational Diseases and Hypertension to verify the diagnosis of Obstructive Sleep Apnoea (OSA). Each patient underwent full polysomnography, blood tests, ABPM and ECHO. Both selenoprotein-P and renalase levels correlated with different ABPM and ECHO parameters. We found no correlation between the peroxiredoxin-5 level and none of the tested parameters. We point to the possible application of SELENOP plasma-level testing in the initial selection of high cardiovascular-risk patients, especially if access to more advanced examinations is limited. We further suggest SELENOP measurement as a possible indicator of patients at increased left ventricular hypertrophy risk who should be of particular interest and may benefit from ECHO testing.

Levels of Serum and Urine Catecholaminergic and Apelinergic System Members in Acute Ischemic Stroke Patients

Objective: To compare levels of catecholaminergic system members, renalase, cerebellin, and their substrates, epinephrine, norepinephrine, and dopamine, and apelinergic system members, apelin, elabela, and nitric oxide in the blood and urine of patients with acute ischemic stroke and healthy controls. Materials and Methods: 42 patients with acute ischemic stroke and 42 age and sex-matched healthy controls were included in the study. Blood and urine samples were collected simultaneously and within the first 24 hours after the onset of acute stroke clinical manifestations and were measured using an ELISA method. Results: The levels of serum and urine cerebellin, renalase, epinephrine, norepinephrine, dopamine, apelin, elebela, and nitric oxide were similar in ischemic stroke and in control groups (P>0.05). Strong correlations were found between renalase, cerebellin, and catecholamine levels in serum and urine (p

Associations of Renalase With Blood Pressure and Hypertension in Chinese Adults

Objective

Renalase, a novel secretory flavoprotein with amine oxidase activity, is secreted into the blood by the kidneys and is hypothesized to participate in blood pressure (BP) regulation. We investigated the associations of renalase with BP and the risk of hypertension by examining renalase single nucleopeptide polymorphism (SNPs), serum renalase levels, and renal expression of renalase in humans.

Methods

① Subjects (n = 514) from the original Baoji Salt-Sensitive Study cohort were genotyped to investigate the association of renalase SNPs with longitudinal BP changes and the risk of hypertension during 14 years of follow-up. ② Two thousand three hundred and ninety two participants from the Hanzhong Adolescent Hypertension Study cohort were used to examine the association of serum renalase levels with hypertension. Renalase expression in renal biopsy specimens from 193 patients were measured by immunohistochemistry. ③ Renalase expression was compared in hypertensive vs. normotensive patients.

Results

① SNP rs7922058 was associated with 14-year change in systolic BP, and rs10887800, rs796945, rs1935582, rs2296545, and rs2576178 were significantly associated with 14-year change in diastolic BP while rs1935582 and rs2576178 were associated with mean arterial pressure change over 14 years. In addition, SNPs rs796945, rs1935582, and rs2576178 were significantly associated with hypertension incidence. Gene-based analysis found that renalase gene was significantly associated with hypertension incidence over 14-year follow-up after adjustment for multiple measurements. ② Hypertensive subjects had higher serum renalase levels than normotensive subjects (27.2 ± 0.4 vs. 25.1 ± 0.2 μg/mL). Serum renalase levels and BPs showed a linear correlation. In addition, serum renalase was significantly associated with the risk of hypertension [OR = 1.018 (1.006–1.030)]. ③ The expression of renalase in human renal biopsy specimens significantly decreased in hypertensive patients compared to non-hypertensive patients (0.030 ± 0.001 vs. 0.038 ± 0.004).

Conclusions

These findings indicate that renalase may play an important role in BP progression and development of hypertension.

The Effect of Renalase rs2576178 and rs10887800 Polymorphisms on Ischemic Stroke Susceptibility in Young Patients (<50 Years): A Case-Control Study and In Silico Analysis

Background

Ischemic stroke (IS) is the most common form of cerebrovascular accident which its precise etiology remains mysterious. Renalase is a catecholamine-degrading enzyme playing a major role in blood pressure control. Recent studies show the effect of renalase activity on various diseases like IS. In the current study, we examined the possible effects of renalase gene (RNLS) rs2576178 and rs10887800 variants at the 5′-flanking and intron 6 regions on IS, respectively.

Methods

One hundred and fifty-four IS patients younger than 50 years and 165 age- and sex-matched controls were recruited in the study. For genotyping of rs2576178 and rs10887800 variants, the PCR-RFLP method was used.

Results

The RNLS rs10887800 AG genotype was more repeated in IS patients, but the difference was marginally nonsignificant (P = 0.054). This variant was associated with IS in the overdominant model, and the AG genotype is associated with a1.6-fold increased risk of IS compared to AA+ GG genotypes (OR = 1.6, 95% CI: 1-2.5, P = 0.033). No relationship was observed between RNLS rs2576178 polymorphism and IS in all genetic models. The findings of the haplotype and combination effects of rs10887800 and rs2576178 variants on IS showed no significant association. The in silico analysis showed no effect of rs2576178 and rs10887800 polymorphisms in the RNA structure, but the alteration of RNA sequence in rs2576178 results in the lack of a MBNL1 protein binding site.

Conclusions

RNLS rs10887800 but not rs2576178 polymorphism was associated with IS susceptibility in the overdominant model (AG vs AA+ GG genotypes).

The Effect of Bilateral Nephrectomy on Renalase and Catecholamines in Hemodialysis Patients

Background/Aims: Renalase is an enzyme with monoamine oxidase activity that metabolizes catecholamines; therefore, it has a significant influence on arterial blood pressure regulation and the development of cardiovascular diseases. Renalase is mainly produced in the kidneys. Nephrectomy and hemodialysis (HD) may alter the production and metabolism of renalase. The aim of this study was to examine the effect of bilateral nephrectomy on renalase levels in the serum and erythrocytes of hemodialysis patients. Methods: This study included 27 hemodialysis patients post-bilateral nephrectomy, 46 hemodialysis patients without nephrectomy but with chronic kidney disease and anuria and 30 healthy subjects with normal kidney function. Renalase levels in the serum and erythrocytes were measured using an ELISA kit. Results: Serum concentrations of renalase were significantly higher in post-bilateral nephrectomy patients when compared with those of control subjects (101.1 ± 65.5 vs. 19.6 ± 5.0; p < 0.01). Additionally, renalase concentrations, calculated per gram of hemoglobin, were significantly higher in patients after bilateral nephrectomy in comparison with those of healthy subjects (994.9 ± 345.5 vs. 697.6 ± 273.4, p = 0.015). There were no statistically significant differences in plasma concentrations of noradrenaline or adrenaline. In contrast, the concentration of dopamine was significantly lower in post-nephrectomy patients when compared with those of healthy subjects (116.8 ± 147.7 vs. 440.9 ± 343.2, p < 0.01). Conclusions: Increased serum levels of renalase in post-bilateral nephrectomy hemodialysis patients are likely related to production in extra-renal organs as a result of changes in the cardiovascular system and hypertension.

Circulating Renalase as Predictor of Renal and Cardiovascular Outcomes in Pre-Dialysis CKD Patients: A 5-Year Prospective Cohort Study

Chronic kidney disease (CKD) is an independent risk factor for adverse cardiovascular and cerebrovascular events (MACCEs), and mortality since the earlier stages. Therefore, it is critical to identify the link between CKD and cardiovascular risk (CVR) through early and reliable biomarkers. Acknowledging that CKD and CKD progression are associated with increased sympathetic tone, which is implicated in CVR, and that renalase metabolizes catecholamines, we aimed to evaluate the relationship between renalase serum levels (RNLS) and cardiovascular and renal outcomes. The study included 40 pre-dialysis CKD patients (19F:21M) with median age of 61 (IQ 45–66) years. At baseline, we measured RNLS as well as routine biomarkers of renal and cardiovascular risk. A prospective analysis was performed to determine whether RNLS are associated with CKD progression, MACCEs, hospitalizations and all-cause mortality. At baseline, the median level of RNLS and median estimated glomerular filtration rate (eGFR) were 63.5 (IQ 48.4–82.7) µg/mL and 47 (IQ 13–119) mL/min/1.73 m², respectively. In univariate analysis, RNLS were strongly associated with eGFR, age and Charlson Index. Over the course of a mean follow-up of 65 (47 to 70) months, 3 (7.5%) deaths, 2 (5%) fatal MACCEs, 17 (42.5%) hospital admissions occurred, and 16 (40%) patients experienced CKD progression. In univariate analysis, RNLS were associated with CKD progression (p = 0.001), hospitalizations (p = 0.001) and all-cause mortality (p = 0.022) but not with MACCEs (p = 0.094). In adjusted analysis, RNLS predicted CKD progression and hospitalizations regardless of age, Charlson comorbidity index, cardiovascular disease, hypertension, diabetes and dyslipidemia. Our results suggest that RNLS, closely related with renal function, might have a potential role as predictor of renal outcomes, hospitalizations, and mortality in pre-dialysis CKD patients.

Relationship between Renalase Expression and Kidney Disease: an Observational Study in 72 Patients Undergoing Renal Biopsy

The relationship between the levels of renalase and changes in proteinuria, hypertension, renal function, renal tubular epithelial cell apoptosis and B-cell lymphoma-2 (Bcl-2) expression was investigated in patients (chronic nephritis, primary nephrotic syndrome or other kidney disease) that underwent renal biopsy. The study group comprised 72 patients undergoing renal biopsy. Patient profiles and renal function were collected. Concentrations of renalase and Bcl-2 were measured by immunohistochemistry. Tubular injury was detected by periodic acid Schiff staining (PAS) and renal tubular epithelial cell apoptosis was assessed by TUNEL assay. The expression of renalase was significantly lower in renal biopsy specimens than in normal kidney tissues. There was a positive linear relationship between renalase and some serum and cardiac indices; a negative correlation was found between age, eGFR, Ccr and 24-h urinary protein. Renal tubule injury index and tubular epithelial cell apoptosis index showed a negative linear correlation with renalase. The results showed that renalase probably increased the expression of Bcl-2. By two independent samples t-test, renalase levels were significantly increased in the non-hypertension group than in the hypertension group. One-way ANOVA showed that renalase expression was higher in samples with Lee's grade III than in those with Lee's grade V. The expression of renalase was significantly decreased in patients who underwent renal biopsy, and was also associated with blood and renal function. The research proved that renalase may reduce renal tubular injury and apoptosis of renal tubular epithelial cells through the mitochondrial apoptosis pathway, finally achieving the purpose of delaying the progress of renal failure.

Hypertension in dialysis patients: a consensus document by the European Renal and Cardiovascular Medicine (EURECA-m) working group of the European Renal Association - European Dialysis and Transplant Association (ERA-EDTA) and the Hypertension and the Kidney working group of the European Society of Hypertension (ESH)

In patients with end-stage renal disease treated with hemodialysis or peritoneal dialysis, hypertension is very common and often poorly controlled. Blood pressure (BP) recordings obtained before or after hemodialysis display a J-shaped or U-shaped association with cardiovascular events and survival, but this most likely reflects the low accuracy of these measurements and the peculiar hemodynamic setting related with dialysis treatment. Elevated BP by home or ambulatory BP monitoring is clearly associated with shorter survival. Sodium and volume excess is the prominent mechanism of hypertension in dialysis patients, but other pathways, such as arterial stiffness, activation of the renin-angiotensin-aldosterone and sympathetic nervous systems, endothelial dysfunction, sleep apnea and the use of erythropoietin-stimulating agents may also be involved. Nonpharmacologic interventions targeting sodium and volume excess are fundamental for hypertension control in this population. If BP remains elevated after appropriate treatment of sodium-volume excess, the use of antihypertensive agents is necessary. Drug treatment in the dialysis population should take into consideration the patient's comorbidities and specific characteristics of each agent, such as dialysability. This document is an overview of the diagnosis, epidemiology, pathogenesis and treatment of hypertension in patients on dialysis, aiming to offer the renal physician practical recommendations based on current knowledge and expert opinion and to highlight areas for future research.

Hypertension in dialysis patients: a consensus document by the European Renal and Cardiovascular Medicine (EURECA-m) working group of the European Renal Association-European Dialysis and Transplant Association (ERA-EDTA) and the Hypertension and the Kidney working group of the European Society of Hypertension (ESH)

In patients with end-stage renal disease (ESRD) treated with haemodialysis or peritoneal dialysis, hypertension is common and often poorly controlled. Blood pressure (BP) recordings obtained before or after haemodialysis display a J- or U-shaped association with cardiovascular events and survival, but this most likely reflects the low accuracy of these measurements and the peculiar haemodynamic setting related to dialysis treatment. Elevated BP detected by home or ambulatory BP monitoring is clearly associated with shorter survival. Sodium and volume excess is the prominent mechanism of hypertension in dialysis patients, but other pathways, such as arterial stiffness, activation of the renin-angiotensin-aldosterone and sympathetic nervous systems, endothelial dysfunction, sleep apnoea and the use of erythropoietin-stimulating agents may also be involved. Non-pharmacologic interventions targeting sodium and volume excess are fundamental for hypertension control in this population. If BP remains elevated after appropriate treatment of sodium and volume excess, the use of antihypertensive agents is necessary. Drug treatment in the dialysis population should take into consideration the patient's comorbidities and specific characteristics of each agent, such as dialysability. This document is an overview of the diagnosis, epidemiology, pathogenesis and treatment of hypertension in patients on dialysis, aiming to offer the renal physician practical recommendations based on current knowledge and expert opinion and to highlight areas for future research.

Rs10887800 renalase gene polymorphism influences the level of circulating renalase in patients undergoing hemodialysis but not in healthy controls

Background

Human renalase (RNLS), a recently identified flavoprotein with oxidoreductase activity, is secreted into blood by kidneys and metabolizes circulating catecholamines. Recent studies have revealed that common polymorphisms in RNLS gene might affect the risk of several cardiovascular conditions in hemodialyzed patients. However, the exact mechanism underlying this link remains unclear. The study aims to investigate the association between RNLS gene polymorphisms and plasma renalase level in ESKD patients undergoing hemodialysis (HD group) and healthy controls (HC).

Methods

A total of 309 hemodialyzed patients and 90 controls were enrolled in the study. All the participants were genotyped for two RNLS SNPs (rs2576178 and rs10887800) using PCR-RFLP method. Plasma renalase concentrations were determined by enzyme-linked immunosorbent assay (USCN Life Science Inc., Wuhan, China). The IBM SPSS Statistics for Windows, version 20 (IBM Corp., Armonk, NY, USA) was used for statistical analyses.

Results

Genotype distribution and allele frequencies of studied SNPs did not differ between two analyzed groups, p > .050. RNLS concentration in HD group (33.54 μg/mL) was significantly higher than in HC (13.16 μg/mL), p < .001. HD patients with rs10887800AA genotype had lower renalase level (29.32 μg/mL) compared to those with AG (34.52 μg/mL), p < .010 and GG genotype (35.91 μg/mL), p < .010. No significant differences in plasma RNLS between rs10887800AG and GG carriers were observed, p > .050. Interestingly, in HC group rs10887800 polymorphism did not influence RNLS concentration. Rs2576178 SNP did not affect the level of plasma RNLS either in HD group or in HC.

Conclusion

Rs10887800 polymorphic variant of RNLS gene influences the level of circulating RNLS in patients undergoing hemodialysis, and thus elucidates the potentially functional relevance of this polymorphism in HD population.

Increased serum renalase in peritoneal dialysis patients: Is it related to cardiovascular disease risk?

BACKGROUND

Renalase, with possible monoamine oxidase activity, is implicated in degradation of catecholamines; which suggests novel mechanisms of cardiovascular complications in patients with chronic kidney diseases. Epicardial adipose tissue (EAT) has been found to correlate with cardiovascular diseases (CVD) in dialysis patients. The present study aimed to evaluate the association of serum renalase levels with EAT thickness and other CVD risk factors in peritoneal dialysis (PD) patients.

METHODS

The study included 40 PD patients and 40 healthy controls. All subjects underwent blood pressure and anthropometric measurements. Serum renalase was assessed by using a commercially available assay. Transthoracic echocardiography was used to measure EAT thickness and left ventricular mass index (LVMI) in all subjects.

RESULTS

The median serum renalase level was significantly higher in the PD patients than in the control group [176.5 (100-278.3) vs 122 (53.3-170.0)ng/ml] (p=0.001). Renalase was positively correlated with C-reactive protein (r=0.705, p<0.001) and negatively correlated with RRF (r=-0.511, p=0.021). No correlation was observed between renalase and EAT thickness or LVMI. There was a strong correlation between EAT thickness and LVMI in both the PD patients and the controls (r=0.848, p<0.001 and r=0.640, p<0.001 respectively).

CONCLUSIONS

This study indicates that renalase is associated with CRP and residual renal function but not with EAT thickness as CVD risk factors in PD patients.

Age influence on renalase and catecholamines concentration in hypertensive patients, including maintained dialysis

BACKGROUND

Hypertension in elderly patients is one of the main problems in cardiovascular diseases. The sympathetic nervous system hyperactivity seen in older patients is a known risk factor for hypertension and other cardiovascular events as well as chronic kidney disease. Renalase, secreted by the kidney and circulated in blood, may regulate the sympathetic tone by catecholamine degradation and in this way has an impact on cardiovascular and renal complications.

OBJECTIVE

To assess the impact of age on renalase and catecholamine concentration in hypertensive patients, including those on dialyses and its possible relation to blood pressure control and cardiovascular disease.

METHODS

The study cohort of 211 patients was divided into two groups according to age below 65 years (range 19-64) and above 65 years (range 65-86). The older group represented 38% of the whole studied population and 75% of them were dialyzed. The two groups of different ages were also divided into dialysis and nondialysis subgroups. The serum renalase, dopamine, and norepinephrine concentration together with blood pressure value and echocardiography were assessed.

RESULTS

Patients aged 65 years and more had higher renalase (20.59 vs 13.14 µg/mL, P=0.02) and dopamine (41.71 vs 15.46 pg/mL, P<0.001) concentration as well as lower diastolic blood pressure (75.33 vs 85 mmHg, P=0.001), advanced abnormalities in echocardiography, and more often suffered from diabetes and coronary artery disease. The significant correlation between age and renalase (r=0.16; P=0.019), norepinephrine (r=0.179; P=0.013), and dopamine (r=0.21; P=0.003) was found in the whole study population. In the nondialysis subgroup, 44% had chronic kidney disease, mostly in the stage 2 (83%). There was a significantly higher norepinephrine concentration (1.21 vs 0.87 ng/mL; P=0.008) in older patients of that population. In the dialysis subgroup, there were no differences between renalase and catecholamine level but older participants had lower diastolic blood pressure (69 vs 78 mmHg, P=0.001) and ejection fraction (51% vs 56.8%, P=0.03).

CONCLUSION

The elevated renalase level in older hypertensive patients is related rather to kidney function and cardiovascular diseases than to age itself. Thus, renalase appears to be the possible new marker of these indications in this special population.

Association of Renalase SNPs rs2296545 and rs2576178 with the Risk of Hypertension: A Meta-Analysis

Background/Aims

Two renalase single nucleotide polymorphisms (SNPs) rs2296545 and rs2576178 have been reported to be associated with the susceptibility to hypertension (HT). Given the inconsistent results, we conducted a meta-analysis to assess the association between these two SNPs and the risk of HT.

Methods

Electronic databases were systematically searched to find relevant studies. Subgroup analysis was conducted according to the different concomitant diseases and ethnicities in the study population. Pooled odds ratios (OR) and 95% confidence intervals (CI) were calculated using fixed-effect or random-effect models.

Results

A total of six case–control studies on rs2296545 and six studies on rs2576178 were included. In the combined analysis, results showed a significant association between SNP rs2296545 and risk of HT in all genetic models (dominant model CG+CC/GG: OR = 1.43, 95% CI = 1.24–1.65; recessive model CC/CG+GG: OR = 1.36, 95% CI = 1.09–1.69; codominant model CC/GG: OR = 1.63, 95% CI = 1.20–2.20, CG/GG: OR = 1.30, 95% CI = 1.12–1.52; allelic model C/G: OR = 1.29, 95% CI = 1.10–1.51). In subgroup analysis, we observed a significant association between rs2296545 and risk of essential HT. Although we did not observe an association between rs2576178 polymorphism and HT in the combined analysis, an increased risk was observed in the essential HT patients versus healthy controls (subgroup 1) analysis under the dominant, recessive, and codominant genetic models.

Conclusions

Renalase gene rs2296545 polymorphism is significantly associated with increased risk of HT, whereas rs2576178 polymorphism may not be associated with the susceptibility to HT.

Increased serum renalase in hemodialysis patients: is it related to left ventricular hypertrophy?

INTRODUCTION

Left ventricular hypertrophy (LVH) is one of the most common cardiac abnormalities in patients with end stage renal disease (ESRD). Hypertension, diabetes, increased body mass index, gender, age, anemia, and hyperparathyroidism have been described as risk factors for LVH in patients on dialysis. However, there may be other risk factors which have not been described yet. Recent studies show that renalase is associated with cardiovascular events. The aim of this study was to reveal the relation between renalase, LVH in patients under hemodialysis (HD) treatment.

METHODS

The study included 50 HD patients and 35 healthy controls. Serum renalase levels and left ventricle mass index (LVMI) were measured in all participants and the relation between these variables was examined.

FINDINGS

LVMI was positively correlated with dialysis vintage and C-reactive protein (CRP) (r = 0.387, p = 0.005 and r = 0.597, p < 0.001, respectively) and was negatively correlated with residual diuresis and hemoglobin levels (r = -0.324, p = 0.022 and r = -0.499, p < 0.001, respectively). There was no significant association of renalase with LVMI in the HD patients (r = 0.263, p = 0.065). Serum renalase levels were significantly higher in HD patients (212 ± 127 ng/mL) compared to controls (116 ± 67 ng/mL) (p < 0.001). Renalase was positively correlated with serum creatinine and dialysis vintage (r = 0.677, p < 0.001 and r = 0.625, p < 0.001, respectively).

DISCUSSION

In our study, LVMI was correlated with dialysis vintage, residual diuresis, CRP, and hemoglobin. LVMI tends to correlate with renalase and this correlation may be significant in studies with more patient numbers. The main parameters affecting renalase levels are dialysis vintage and serum creatinine.

Renalase attenuates hypertension, renal injury and cardiac remodelling in rats with subtotal nephrectomy

Chronic kidney disease is associated with higher risk of cardiovascular complication and this interaction can lead to accelerated dysfunction in both organs. Renalase, a kidney-derived cytokine, not only protects against various renal diseases but also exerts cardio-protective effects. Here, we investigated the role of renalase in the progression of cardiorenal syndrome (CRS) after subtotal nephrectomy. Sprague-Dawley rats were randomly subjected to sham operation or subtotal (5/6) nephrectomy (STNx). Two weeks after surgery, sham rats were intravenously injected with Hanks' balanced salt solution (sham), and STNx rats were randomly intravenously injected with adenovirus-β-gal (STNx+Ad-β-gal) or adenovirus-renalase (STNx+Ad-renalase) respectively. After 4 weeks of therapy, Ad-renalase administration significantly restored plasma, kidney and heart renalase expression levels in STNx rats. We noticed that STNx rats receiving Ad-renalase exhibited reduced proteinuria, glomerular hypertrophy and interstitial fibrosis after renal ablation compared with STNx rats receiving Ad-β-gal; these changes were associated with significant decreased expression of genes for fibrosis markers, proinflammatory cytokines and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase components. At the same time, systemic delivery of renalase attenuated hypertension, cardiomyocytes hypertrophy and cardiac interstitial fibrosis; prevented cardiac remodelling through inhibition of pro-fibrotic genes expression and phosphorylation of extracellular signal-regulated kinase (ERK)-1/2. In summary, these results indicate that renalase protects against renal injury and cardiac remodelling after subtotal nephrectomy via inhibiting inflammation, oxidative stress and phosphorylation of ERK-1/2. Renalase shows potential as a therapeutic target for the prevention and treatment of CRS in patients with chronic kidney disease.

Pathophysiology of resistant hypertension in chronic kidney disease

Hypertension associated with chronic kidney diseases often is resistant to drug treatment. This review deals with two main aspects of the management of CKD patients with hypertension: the role of sodium/volume and the need for dietary salt restriction, as well as appropriate use of diuretics and what currently is called sequential nephron blockade; the second aspect that is addressed extensively in this review is the role of the sympathetic nervous system and the possible clinical use of renal denervation.

Identification of a receptor for extracellular renalase

Background

An increased risk for developing essential hypertension, stroke and diabetes is associated with single nucleotide gene polymorphisms in renalase, a newly described secreted flavoprotein with oxidoreductase activity. Gene deletion causes hypertension, and aggravates acute ischemic kidney (AKI) and cardiac injury. Independent of its intrinsic enzymatic activities, extracellular renalase activates MAPK signaling and prevents acute kidney injury (AKI) in wild type (WT) mice. Therefore, we sought to identity the receptor for extracellular renalase.

Methods and Results

RP-220 is a previously identified, 20 amino acids long renalase peptide that is devoid of any intrinsic enzymatic activity, but it is equally effective as full-length recombinant renalase at protecting against toxic and ischemic injury. Using biotin transfer studies with RP-220 in the human proximal tubular cell line HK-2 and protein identification by mass spectrometry, we identified PMCA4b as a renalase binding protein. This previously characterized plasma membrane ATPase is involved in cell signaling and cardiac hypertrophy. Co-immunoprecipitation and co-immunolocalization confirmed protein-protein interaction between endogenous renalase and PMCA4b. Down-regulation of endogenous PMCA4b expression by siRNA transfection, or inhibition of its enzymatic activity by the specific peptide inhibitor caloxin1b each abrogated RP-220 dependent MAPK signaling and cytoprotection. In control studies, these maneuvers had no effect on epidermal growth factor mediated signaling, confirming specificity of the interaction between PMCA4b and renalase.

Conclusions

PMCA4b functions as a renalase receptor, and a key mediator of renalase dependent MAPK signaling.

Renalase: its role as a cytokine, and an update on its association with type 1 diabetes and ischemic stroke

PURPOSE OF REVIEW

Remarkable progress has been achieved over the past 2 years in understanding the cellular actions of renalase, its pathophysiology and potential therapeutic utility.

RECENT FINDINGS

There has been a paradigm shift in our thinking about the mechanisms underlying the cellular actions of renalase. We now understand that, independent of its enzymatic properties, renalase functions as a signaling molecule, a cytokine that interacts with a yet-to-be identified plasma membrane receptor(s) to activate protein kinase B and the mitogen-activated protein kinase pathway. These signaling properties are critical to its cytoprotective effects. New information regarding renalase's enzymatic function as an α-nicotinamide adenine dinucleotide oxidase/anomerase will be reviewed. Lastly, we will discuss the association of certain single nucleotide polymorphisms in the renalase gene with type 1 diabetes and with ischemic stroke, and the clinical implications of these findings.

SUMMARY

The consistent association of renalase single nucleotide polymorphisms and the development of type 1 diabetes is a great interest particularly because we now understand that renalase functions as a cytokine. Future work on renalase should focus on exploring the identity of its receptor(s), and its potential role as an immune modulator.

Renalase, kidney and cardiovascular disease: are they related or just coincidentally associated?

Cardiovascular diseases, including hypertension are the leading cause of death in the developed countries. Diabetes and chronic kidney disease became also more prevalent reaching almost the level of epidemy. Researchers are looking eagerly for the new risk and/or pathogenetic factors, as well as therapeutic option in these disease. It has been suggested that human kidney releases a protein named renalase into the bloodstream. It is supposed to be an enzyme which breaks down catecholamines in the blood circulation and regulate blood pressure. However, there were several doubts whether renalase exerts monoaminooxidase activity, or if it is monoaminooxidase at all. Recently, a hypothesis that it is also a cytokine was postulated. Studies on renalase polymorphisms in hypertension, cardiovascular disease or diabetes are inconsistent. Similarly, there are several discrepancies in the animal on the possible role of renalase in hypertension and cardiovascular diseases. Some studies report a protective role of renalase in acute kidney injury, whereas others showed that renalase levels were mainly dependent on kidney function, indicating rather a role of kidney in excretion of this substance. Moreover, validated assays are needed to evaluate renalase levels and activity. On one hand a deeper and more accurate link between renalase and cardiovascular diseases require further profound research, on the other hand whether or not renalase protein could be a new therapeutic target in these pathologies should also be considered. Whether renalase, discovered in 2005, might be a Holy Grail of hypertension, linking kidney and cardiovascular diseases, remains to be proven.

Metabolic function for human renalase: oxidation of isomeric forms of β-NAD(P)H that are inhibitory to primary metabolism

Renalase is a recently identified flavoprotein that has been associated with numerous physiological maladies. There remains a prevailing belief that renalase functions as a hormone, imparting an influence on vascular tone and heart rate by oxidizing circulating catecholamines, chiefly epinephrine. This activity, however, has not been convincingly demonstrated in vitro, nor has the stoichiometry of this transformation been shown. In prior work we demonstrated that renalase induced rapid oxidation of low-level contaminants of β-NAD(P)H solutions ( Beaupre, B. A. et al. (2013) Biochemistry 52 , 8929 - 8937 ; Beaupre, B. A. et al. (2013) J. Am. Chem. Soc . 135 , 13980 - 13987 ). Slow aqueous speciation of β-NAD(P)H resulted in the production of renalase substrate molecules whose spectrophotometric characteristics and equilibrium fractional accumulation closely matched those reported for α-anomers of NAD(P)H. The fleeting nature of these substrates precluded structural assignment. Here we structurally assign and identify two substrates for renalase. These molecules are 2- and 6-dihydroNAD(P), isomeric forms of β-NAD(P)H that arise either by nonspecific reduction of β-NAD(P)(+) or by tautomerization of β-NAD(P)H (4-dihydroNAD(P)). The pure preparations of these molecules induce rapid reduction of the renalase flavin cofactor (230 s(-1) for 6-dihydroNAD, 850 s(-1) for 2-dihydroNAD) but bind only a few fold more tightly than β-NADH. We also show that 2- and 6-dihydroNAD(P) are potent inhibitors of primary metabolism dehydrogenases and therefore conclude that the metabolic function of renalase is to oxidize these isomeric NAD(P)H molecules to β-NAD(P)(+), eliminating the threat they pose to normal respiratory activity.

Renalase, a new secretory enzyme: Its role in hypertensive-ischemic cardiovascular diseases

Abstract Renalase, a novel amine oxidase, is mainly expressed in the kidney, heart, and skeletal muscle. It has been known to degrade circulating catecholamines and plays a crucial role in human diseases. Recent studies have demonstrated its structure, unique bioactivities, function, and the gene polymorphisms in human diseases. In this review, we summarize the effects of renalase on hypertension, myocardial ischemia, acute kidney injury (AKI), ischemic stroke, cardiac dysfunction, organ transplantation, and diabetes mellitus reported in numerous studies.

Renalase prevents AKI independent of amine oxidase activity

AKI is characterized by increased catecholamine levels and hypertension. Renalase, a secretory flavoprotein that oxidizes catecholamines, attenuates ischemic injury and the associated increase in catecholamine levels in mice. However, whether the amine oxidase activity of renalase is involved in preventing ischemic injury is debated. In this study, recombinant renalase protected human proximal tubular (HK-2) cells against cisplatin- and hydrogen peroxide-induced necrosis. Similarly, genetic depletion of renalase in mice (renalase knockout) exacerbated kidney injury in animals subjected to cisplatin-induced AKI. Interestingly, compared with the intact renalase protein, a 20-amino acid peptide (RP-220), which is conserved in all known renalase isoforms, but lacks detectable oxidase activity, was equally effective at protecting HK-2 cells against toxic injury and preventing ischemic injury in wild-type mice. Furthermore, in vitro treatment with RP-220 or recombinant renalase rapidly activated Akt, extracellular signal-regulated kinase, and p38 mitogen-activated protein kinases and downregulated c-Jun N-terminal kinase. In summary, renalase promotes cell survival and protects against renal injury in mice through the activation of intracellular signaling cascades, independent of its ability to metabolize catecholamines, and we have identified the region of renalase required for these effects. Renalase and related peptides show potential as therapeutic agents for the prevention and treatment of AKI.

Renalase in hypertension and kidney disease

Renalase, a recently discovered flavoprotein, which is strongly expressed in the kidney and heart, effectively metabolizes catecholamines. It was discovered during the search to identify proteins secreted by the kidney that could help explain the high incidence of cardiovascular disease in patients with chronic kidney disease. Recent advances have led to more detailed knowledge of its biology, structure, enzymatic activity, mechanisms of action, associations with human disease states and potential therapeutic value. In this study, we review these advances with a focus on hypertension and kidney disease.

Renalase's expression and distribution in renal tissue and cells

To study renalase's expression and distribution in renal tissues and cells, renalase coded DNA vaccine was constructed, and anti-renalase monoclonal antibodies were produced using DNA immunization and hybridoma technique, followed by further investigation with immunological testing and western blotting to detect the expression and distribution of renalase among the renal tissue and cells. Anti-renalase monoclonal antibodies were successfully prepared by using DNA immunization technique. Further studies with anti-renalase monoclonal antibody showed that renalase expressed in glomeruli, tubule, mesangial cells, podocytes, renal tubule epithelial cells and its cells supernatant. Renalase is wildly expressed in kidney, including glomeruli, tubule, mesangial cells, podocytes and tubule epithelial cells, and may be secreted by tubule epithelial cells primarily.

Renalase, hypertension, and kidney - the discussion continues

Hypertension and cardiovascular complications are very common in chronic kidney disease (CKD). Overactivation of sympathetic nervous system is also widely recognized in CKD. Renalase may play an important role in the control of blood pressure (BP) by its regulatory function of catecholamine metabolism. Renalase could be synthesized not only by the kidney but also by cardiomyocytes, liver, and adipose tissue. It probably exerts a hypotensive action, at least in animal models. Whether it metabolizes catecholamines remains to be proved. Another issue that remains to be resolved is the relationship between renalase and renal natriuresis and phosphaturia. In this review, the updated experimental and clinical data on renalase are presented and possible interactions with the endothelium are discussed. Renalase is "a new postulated therapeutic target." Proof of concept studies are needed to define the pathophysiological link between the kidney, sympathetic tone, BP, and cardiovascular complications.