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

Coexistence of Cardiovascular Risk Factors and Blood Renalase Concentration

Cardiovascular diseases (CVDs) are one of the biggest health challenges facing health systems around the world. There are certain risk factors (CVRFs) that contribute to CVD. Risk factors associated with lifestyle such as tobacco consumption are particularly essential. Renalase is a recently discovered flavoprotein that may be involved in the progression of cardiometabolic diseases. The aim of the study was to investigate the relation between CVRFs and blood renalase concentration (BRC). The study group consisted of 96 people (51% women) who were hospitalized in the internal medicine department. CVRFs were measured using the AHA Life 7 scale. The E3109Hu ELISA kit was used to assess BRC. We found higher BRC in groups with a lower number of CVRFs (p < 0.05). We found a negative correlation between BRC and the number of CVRFs (r = -0.41). With the regression analysis, obesity, smoking, and a lack of physical activity (LoPE) were independently associated with lower blood renalase concentration. ROC analysis indicated the highest accuracy of BRC < 38.98 ng/mL in patients with ≥5 CVRFs. In conclusion, patients with a higher number of CVRFs had lower BRCs. The CVRFs particularly associated with a lower BRC were obesity, smoking, and LoPE.

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

Renalase: a novel regulator of cardiometabolic and renal diseases

Renalase is a ~38 kDa flavin-adenine dinucleotide (FAD) domain-containing protein that can function as a cytokine and an anomerase. It is emerging as a novel regulator of cardiometabolic diseases. Expressed mainly in the kidneys, renalase has been reported to have a hypotensive effect and may control blood pressure through regulation of sympathetic tone. Furthermore, genetic variations in the renalase gene, such as a functional missense polymorphism (Glu37Asp), have implications in the cardiovascular and renal systems and can potentially increase the risk of cardiometabolic disorders. Research on the physiological functions and biochemical actions of renalase over the years has indicated a role for renalase as one of the key proteins involved in various disease states, such as diabetes, impaired lipid metabolism, and cancer. Recent studies have identified three transcription factors (viz., Sp1, STAT3, and ZBP89) as key positive regulators in modulating the expression of the human renalase gene. Moreover, renalase is under the post-transcriptional regulation of two microRNAs (viz., miR-29b, and miR-146a), which downregulate renalase expression. While renalase supplementation may be useful for treating hypertension, inhibition of renalase signaling may be beneficial to patients with cancerous tumors. However, more incisive investigations are required to unravel the potential therapeutic applications of renalase. Based on the literature pertaining to the function and physiology of renalase, this review attempts to consolidate and comprehend the role of renalase in regulating cardiometabolic and renal disorders.

Aerobic Exercise Training Improves Renal Injury in Spontaneously Hypertensive Rats by Increasing Renalase Expression in Medulla

We aimed to examine the effects of aerobic exercise training on renal function in spontaneously hypertensive rats (SHR) and elucidate their possible mechanisms. Adult male SHR and age-matched Wistar-Kyoto rats (WKY) were divided into four groups: WKY sedentary group, SHR sedentary group, low-intensity training group, and medium-intensity training group. Using molecular and biochemical approaches, we investigated the effects of 14-week training on renalase (RNLS) protein levels, renal function, and apoptosis and oxidative stress modulators in kidney tissues. In vitro, angiotensin II (Ang II)-induced human kidney proximal epithelial cells (HK-2) were treated with RNLS, and changes in apoptosis and oxidative stress levels were observed. Our results show that moderate training improved renal function decline in SHR. In addition, aerobic exercise therapy significantly increased levels of RNLS in the renal medulla of SHR. We observed in vitro that RNLS significantly inhibited the increase of Ang II-inducedapoptosis and oxidative stress levels in HK-2. In conclusion, aerobic exercise training effectively improved renal function in SHR by promoting RNLS expression in the renal medulla. These results explain the possible mechanism in which exercise improves renal injury in hypertensive patients and suggest RNLS as a novel therapy for kidney injury patients.

Roles and mechanisms of renalase in cardiovascular disease: A promising therapeutic target

Cardiovascular disease (CVD) is prevalent worldwide and remains a leading cause of death. Although substantial progress has been made in the diagnosis and treatment of CVD, the prognosis remains unsatisfactory. Renalase is a newly discovered cytokine that is synthesized by the kidney and then secreted into blood. Numerous studies have suggested the efficacy of renalase in treating CVD by metabolizing catecholamines in the circulatory system. As a new biomarker of heart disease, renalase is normally recognized as a signalling molecule that activates cytoprotective intracellular signals to lower blood pressure, protect ischaemic heart muscle and promote atherosclerotic plaque stability in CVD, which subsequently improves cardiac function. Due to its important regulatory role in the circulatory system, renalase has gradually become a potential target in the treatment of CVD. This review summarizes the structure, mechanism and function of renalase in CVD, thereby providing preclinical evidence for alternative approaches and new prospects in the development of renalase-related drugs against CVD.

Serum Renalase Levels Are Predicted by Brain-Derived Neurotrophic Factor and Associated with Cardiovascular Events and Mortality after Percutaneous Coronary Intervention

Circulating brain-derived neurotrophic factor (BDNF) predicts survival rate in patients with coronary artery disease (CAD). We examined the relationship between BDNF and renalase before and after percutaneous coronary intervention (PCI) and the role of renalase in patients with CAD. Serum BDNF and renalase levels were determined using blood samples collected before and after PCI. Incident myocardial infarction, stroke, and mortality were followed up longitudinally. A total of 152 patients completed the assessment. BDNF levels were not significantly changed after PCI compared to baseline levels (24.7 ± 11.0 vs. 23.5 ± 8.3 ng/mL, p = 0.175), although renalase levels were significantly reduced (47.5 ± 17.3 vs. 35.9 ± 11.3 ng/mL, p < 0.001). BDNF level before PCI was an independent predictor of reduction in renalase (95% confidence interval (CI): −1.371 to −0.319). During a median 4.1 years of follow-up, patients with serum renalase levels of ≥35 ng/mL had a higher risk of myocardial infarction, stroke, and death than those with renalase of <35 ng/mL (hazard ratio = 5.636, 95% CI: 1.444–21.998). In conclusion, our results show that serum BDNF levels before PCI were inversely correlated with the percentage change in renalase levels after PCI. Nevertheless, post-PCI renalase level was a strong predictor for myocardial infarction, stroke, and death.

A new method for quantitative determination of renalase based on mass spectrometric determination of a proteotypic peptide labelled with stable isotopes

RATIONALE

Renalase is a recently discovered kidney secretory protein, which is considered as an important component involved in blood pressure regulation. Although altered levels of renalase have been detected in plasma and urine of patients with various kidney diseases, there is certain inconsistency of changes in the renalase levels reported by different laboratories. The latter is obviously associated with the use of the ELISA as the only available approach for quantitative analysis of renalase. Thus there is a clear need for the development of antibody-independent approaches for renalase quantification.

METHODS

We have developed a new method for quantitative determination of human renalase, which is based on mass spectrometric detection of a proteotypic peptide containing С-terminal ¹³ C¹⁵ N-labelled lysine. It corresponds to a tryptic peptide of human renalase, which has been previously detected in most mass spectrometric determinations of this protein.

RESULTS

Using the labelled peptide H-EGDCNFVAPQGISSIIK-OH, corresponding to positions 100-116 of the human renalase sequence, as an internal standard and recombinant human renalase we have generated a calibration curve, which covered the concentration range 0.005-50 ng/mL with a limit of quantitation of 5 pg/mL. Using this calibration curve we were able to detect urinary renalase only after enrichment of initial urinary samples by ammonium sulfate precipitation (but not in untreated urine).

CONCLUSIONS

Results of our study indicate that quantitative determination of renalase based on mass spectrometric detection of a proteotypic peptide labelled with stable isotopes gives significantly lower values of this protein in human urine than those reported in the literature and based on the ELISA.

Synergistic effect of renalase and chronic kidney disease on endothelin-1 in patients with coronary artery disease ‒ a cross-sectional study

Endothelin-1 (ET-1) is associated with endothelial dysfunction and vasoconstriction. Increased circulating ET-1 levels are associated with long-term cardiovascular mortality. Renalase, released from kidney, metabolizes catecholamines and regulates blood pressure. An increase in circulating renalase levels has been reported in patients with chronic kidney disease (CKD) and is associated with coronary artery disease (CAD). We hypothesized the existence of a synergistic effect of serum renalase levels and CKD on ET-1 levels in patients with CAD. We evaluated 342 non-diabetic patients with established CAD. ET-1 and renalase levels were measured in all patients after an overnight fast. Patients with CKD had higher ET-1 (1.95 ± 0.77 vs. 1.62 ± 0.76 pg/ml, P < 0.001) and renalase levels (46.8 ± 17.1 vs. 33.9 ± 9.9 ng/ml, P < 0.001) than patients without CKD. Patients with both CKD and high renalase levels (>the median of 36.2 ng/ml) exhibited the highest serum ET-1 (P value for the trend <0.001). According to multivariate linear regression analysis, the combination of high serum renalase levels with CKD was a significant risk factor for increased serum ET-1 levels (regression coefficient = 0.297, 95% confidence interval = 0.063‒0.531, P = 0.013). In conclusion, our data suggest a synergistic effect of high serum renalase levels and CKD on increases in ET-1 levels in patients with established CAD.

Functional polymorphism of the renalase gene is associated with cardiac hypertrophy in female patients with aortic stenosis

Renalase decreases circulating catecholamines concentration and is important in maintaining primary cellular metabolism. Renalase acts through the plasma membrane calcium ATPase 4b in the heart, which affects pressure overload but not exercise induced heart hypertrophy. The aim of this study was to test the association between a functional polymorphism Glu37Asp (rs2296545) of the renalase gene and left ventricular hypertrophy in a large cohort of patients with aortic stenosis. The study group consisted of 657 patients with aortic stenosis referred for aortic valve replacement. Preoperative echocardiographic assessment was performed to obtain cardiac phenotypes. Generalized-linear models were implemented to analyze data using crude or full model adjusted for selected clinical factors. In females, the Asp37 variant of the Glu37Asp polymorphism was associated with higher left ventricular mass (p = 0.0021 and p = 0.055 crude and full model respectively), intraventricular septal thickness (p = 0.0003 and p = 0.0143) and posterior wall thickness (p = 0.0005 and p = 0.0219) all indexed to body surface area, as well as relative wall thickness (p = 0.001 and p = 0.0097). No significant associations were found among the male patients. In conclusion, we have found the association of the renalase Glu37Asp polymorphism with left ventricle hypertrophy in large group of females with aortic stenosis. The Glu37Asp polymorphism causes not only amino-acid substitution in FAD binding domain but may also change binding affinity of the hypoxia- and hypertrophy-related transcription factors and influence renalase gene expression. Our data suggest that renalase might play a role in hypertrophic response to pressure overload, but the exact mechanism requires further investigation.

The enzyme: Renalase

Within the last two years catalytic substrates for renalase have been identified, some 10 years after its initial discovery. 2- and 6-dihydronicotinamide (2- and 6-DHNAD) isomers of β-NAD(P)H (4-dihydroNAD(P)) are rapidly oxidized by renalase to form β-NAD(P)⁺. The two electrons liberated are then passed to molecular oxygen by the renalase FAD cofactor forming hydrogen peroxide. This activity would appear to serve an intracellular detoxification/metabolite repair function that alleviates inhibition of primary metabolism dehydrogenases by 2- and 6-DHNAD molecules. This activity is supported by the complete structural assignment of the substrates, comprehensive kinetic analyses, defined species specific substrate specificity profiles and X-ray crystal structures that reveal ligand complexation consistent with this activity. This apparently intracellular function for the renalase enzyme is not allied with the majority of the renalase research that holds renalase to be a secreted mammalian protein that functions in blood to elicit a broad array of profound physiological changes. In this review a description of renalase as an enzyme is presented and an argument is offered that its enzymatic function can now reasonably be assumed to be uncoupled from whole organism physiological influences.

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.

Renalase as a Novel Biomarker for Evaluating the Severity of Hepatic Ischemia-Reperfusion Injury

Hepatic ischemia-reperfusion (I/R) injury is a serious complication in clinical practice. However, no efficient biomarkers are available for the evaluation of the severity of I/R injury. Recently, renalase has been reported to be implicated in the I/R injury of various organs. This protein is secreted into the blood in response to increased oxidative stress. To investigate the responsiveness of renalase to oxidative stress, we examined the changes of renalase in cell and mouse models. We observed a significant increase of renalase expression in HepG2 cells in a time- and dose-dependent manner when treated with H₂O₂. Renalase expression also increased significantly in liver tissues that underwent the hepatic I/R process. The increased renalase levels could be efficiently suppressed by antioxidants in vitro and in vivo. Furthermore, serum renalase levels were significantly increased in the mouse models and also efficiently suppressed by antioxidants treatment. The variation trends are consistent between renalase and liver enzymes in the mouse models. In conclusion, renalase is highly sensitive and responsive to oxidative stress in vitro and in vivo. Moreover, renalase can be detected in the blood. These properties make renalase a highly promising biomarker for the evaluation of the severity of hepatic I/R injury.

[The history of renalase from amine oxidase to a a-NAD(P)H-oxidase/anomerase]

Renalase is a recently discovered secretory protein, which plays a certain (still poorly understood) role in regulation of blood pressure. The review summarizes own and literature data accumulated since the first publication on relanase (2005). Initial reports on FAD-dependent amine oxidase activity of this protein were not confirmed in independent experiments performed in different laboratories. In addition, proposed amine oxidase activity of circulating extracellular renalase requires the presence of FAD, which has not been detected either in blood or urinary renalase. Moreover, renalase excreted into urine lacks its N-terminal peptide, which is ultimately needed for accommodation of the FAD cofactor. Results of the Aliverti's group on NAD(P)H binding by renalase and weak diaphorase activity of this protein stimulated further studies of renalase as NAD(P)H oxidase catalyzing reaction of catecholamine co-oxidation. However, physiological importance of such extracellular catecholamine-metabolizing activity (demonstrated in one laboratory and not detected in another laboratory) remains unclear due to existence of much more active enzymatic systems (e.g. neutrophil NAD(P)H oxidase, xanthine oxidase/xanthine) in circulation, which can perform such co-oxidation reactions. Recently a-NAD(P)H oxidase/anomerase activity of renalase, which also pomotes oxidative conversion of b-NADH isomers inhibiting activity of NAD-dependent dehydrogenases, has been described. However, its possible contribution to the antihypertensive effect of renalase remains unclear. Thus, the antihypertensive effect of renalase still remains a phenomenon with unclear biochemical mechanim(s) and functions of intracellular and extracellular (circulating) renalases obviously differ.

Circulating renalase, catecholamines, and vascular adhesion protein 1 in hypertensive patients

The aim of the study was to estimate and correlate circulating levels of renalase, vascular adhesion protein-1 (VAP-1), catecholamines in patients with primary hypertension. The renalase, VAP-1, and catecholamines concentration was estimated in 121 hypertensive patients. The correlation between renalase, VAP-1 levels and catecholamine concentration in blood, blood pressure control, pharmacological therapy, and medical history were taken in to consideration. The median office blood pressure was 145.5/86 mm Hg and was significantly higher than the median home blood pressure measurement value, which was 135/80 mm Hg, P < .05. Circulating renalase and VAP-1 (Me 9.57 μg/mL and Me = 326.7 ng/mL) levels were significantly higher in patients with hypertension comparing to healthy individuals (3.83 μg/mL and 248.37 ng/mL, P < .05). The correlation between renalase and noradrenalin concentration in blood was observed (r = 0.549; P < .05), also the correlation between VAP-1 and noradrenaline was noticed (r = 0.21, P = .029). Renalase level was higher in patients with coronary artery disease and correlated with decreased ejection fraction. VAP-1 concentration correlated also with left ventricular ejection fraction (r = -0.23, P = .013). Hypertensive patients with diabetes mellitus had almost statistically significant higher VAP-1 concentration compared with hypertensive patients without diabetes mellitus (Me = 403.22 ng/mL vs. Me = 326,68 ng/mL, P = .064). In multiple regression analysis, renalase was predicted by plasma dopamine and norepinephrine as also diastolic office blood pressure and left ventricle ejection fraction. Circulating renalase and VAP-1 levels are elevated in patients with poor blood pressure control. Its correlation with noradrenalin concentration need further studies to find out the role of renalase as also VAP-1 in pathogenesis and treatment of hypertension.

Bacterial Renalase: Structure and Kinetics of an Enzyme with 2- and 6-Dihydro-β-NAD(P) Oxidase Activity from Pseudomonas phaseolicola

Despite a lack of convincing in vitro evidence and a number of sound refutations, it is widely accepted that renalase is an enzyme unique to animals that catalyzes the oxidative degradation of catecholamines in blood in order to lower vascular tone. Very recently, we identified isomers of β-NAD(P)H as substrates for renalase (Beaupre, B. A. et al. (2015) Biochemistry, 54, 795-806). These molecules carry the hydride equivalent on the 2 or 6 position of the nicotinamide base and presumably arise in nonspecific redox reactions of nicotinamide dinucleotides. Renalase serves to rapidly oxidize these isomers to form β-NAD(P)⁺ and then pass the electrons to dioxygen, forming H₂O₂. We have also shown that these substrate molecules are highly inhibitory to dehydrogenase enzymes and thus have proposed an intracellular metabolic role for this enzyme. Here, we identify a renalase from an organism without a circulatory system. This bacterial form of renalase has the same substrate specificity profile as that of human renalase but, in terms of binding constant (K(d)), shows a marked preference for substrates derived from β-NAD⁺. 2-dihydroNAD(P) substrates reduce the enzyme with rate constants (k(red)) that greatly exceed those for 6-dihydroNAD(P) substrates. Taken together, k(red)/K(d) values indicate a minimum 20-fold preference for 2DHNAD. We also offer the first structures of a renalase in complex with catalytically relevant ligands β-NAD⁺ and β-NADH (the latter being an analogue of the substrate(s)). These structures show potential electrostatic repulsion interactions with the product and a unique binding orientation for the substrate nicotinamide base that is consistent with the identified activity.

Renalase does not catalyze the oxidation of catecholamines

It is widely accepted that the function of human renalase is to oxidize catecholamines in blood. However, this belief is based on experiments that did not account for slow, facile catecholamine autoxidation reactions. Recent evidence has shown that renalase has substrates with which it reacts rapidly. The reaction catalyzed defines renalase as an oxidase, one that harvests two electrons from either 2-dihydroNAD(P) or 6-dihydroNAD(P) to form β-NAD(P)(+) and hydrogen peroxide. The apparent metabolic purpose of such a reaction is to avoid inhibition of primary dehydrogenase enzymes by these β-NAD(P)H isomers. This article demonstrates that renalase does not catalyze the oxidation of neurotransmitter catecholamines. Using high-performance liquid chromatography we show that there is no evidence of consumption of epinephrine by renalase. Using time-dependent spectrophotometry we show that the renalase FAD cofactor spectrum is unresponsive to added catecholamines, that adrenochromes are not observed to accumulate in the presence of renalase and that the kinetics of single turnover reactions with 6-dihydroNAD are unaltered by the addition of catecholamines. Lastly we show using an oxygen electrode assay that plasma renalase activity is below the level of detection and only when exogenous renalase and 6-dihydroNAD are added can dioxygen be observed to be consumed.

The catalytic function of renalase: A decade of phantoms

Ten years after the initial identification of human renalase the first genuinely catalytic substrates have been identified. Throughout the prior decade a consensus belief that renalase is produced predominantly by the kidney and catalytically oxidizes catecholamines in order to lower blood pressure and slow the heart has prevailed. This belief was, however, based on fundamentally flawed scientific observations that did not include control reactions to account for the well-known autoxidation of catecholamines in oxygenated solutions. Nonetheless, the initial claims have served as the kernel for a rapidly expanding body of research largely predicated on the belief that catecholamines are substrates for this enzyme. The proliferation of scientific studies pertaining to renalase as a hormone has proceeded unabated despite well-reasoned expressions of dissent that have indicated the deficiencies of the initial observations and other inconsistencies. Our group has very recently identified isomeric forms of β-NAD(P)H as substrates for renalase. These substrates arise from non-specific reduction of β-NAD(P)(+) that forms β-4-dihydroNAD(P) (β-NAD(P)H), β-2-dihydroNAD(P) and β-6-dihydroNAD(P); the latter two being substrates for renalase. Renalase oxidizes these substrates with rate constants that are up to 10(4)-fold faster than any claimed for catecholamines. The electrons harvested are delivered to dioxygen via the enzyme's FAD cofactor forming both H2O2 and β-NAD(P)(+) as products. It would appear that the metabolic purpose of this chemistry is to alleviate the inhibitory effect of β-2-dihydroNAD(P) and β-6-dihydroNAD(P) on primary metabolism dehydrogenase enzymes. The identification of this genuinely catalytic activity for renalase calls for re-evaluation of much of the research of this enzyme, in which definitive links between renalase catecholamine consumption and physiological responses were reported. This article is part of a Special Issue entitled: Physiological enzymology and protein functions.