Renalase Activity Research Articles

Effect of flaxseed on systemic inflammation and oxidative stress in diabetic rats with or without chronic kidney disease.

BackgroundDiabetes mellitus (DM) and chronic kidney disease (CKD) are common causes of morbidity and mortality. Flaxseed contains several bioactive compounds that have been shown to possess anti-inflammatory and antioxidative properties. The aim of the present study was to investigate the possible effect of flaxseed in diabetic rats with adenine–induced CKD.MethodsMale Wister rats (n = 48) were randomly divided into seven equal groups and treated for 33 consecutive days as follows: G1: control. G2 adenine, G3: streptozotocin (STZ), G4: flaxseed, G5: adenine+flaxseed, G6: STZ+flaxseed, G7: adenine+STZ+flaxseed). DM or CKD were experimentally induced by a single intraperitoneal injection of streptozotocin (STZ) or by adenine via oral gavage, respectively.ResultsRats fed adenine alone exhibited several changes including decreased body weight, increased food and water intake and urine output, increased urinary albumin/creatinine ratio. They also showed an increase in plasma urea and, creatinine, indoxyl sulfate, neutrophil gelatinase-associated lipocalin and cystatin C, and a decrease in renalase activity. These were associated with significant changes in inflammatory and oxidative biomarkers, e.g., increase in 8-isoprostane, 8 -hydroxy -2-deoxy guanosine and decrease in antioxidant enzymes, as well as increase in interleukins 1β and 6, and NF-κB, and a decrease in interlukin-10. Histopathologically, there was increased tubular necrosis and fibrosis. Concomitant administration of adenine and STZ further worsened the renal damage induced by adenine alone. Flaxseed significantly ameliorated the changes caused by adenine and STZ, given either singly or in combination.ConclusionThese findings suggest that flaxseed is a potential therapeutic agent in attenuating the progression of CKD in diabetes.

Renalase—A new understanding of its enzymatic and non‐enzymatic activity and its implications for future research

Renalase was first described in 2005 and since then it became an object of scientific interest because of its proposed ability to catalyse circulating neurotransmitters and its promising antihypertensive effects. However, further research on the enzymatic activity of renalase did not confirm these initial findings and yielded that renalase serves to oxidize isomeric forms of β-NAD(P)H and recycle them by forming β-NAD(P)+. Moreover, in contrast to initial assumptions, it is indicated that renalase's enzymatic activity is confined to the cell and that extracellular renalase loses its enzymatic properties. These new reports led scientists to question as to whether renalase, as an enzyme, still has the potential to influence various systemic physiological responses (e.g. blood pressure). It was also put into question whether many physiological discoveries published based on the notion that renalase is secreted into the blood and acts by oxidation of catecholamines can still be considered valid. In this article, we attempt to review the literature to confront these doubts and find further possible directions of research on the importance of renalase. Our aim was to evaluate recent reports of non-enzymatic activity for renalase.

The Effect of Renalase rs2576178 and rs10887800 Polymorphisms on Ischemic Stroke Susceptibility in Young Patients (

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

Renalase: Gene polymorphism and its association with hypertension in some diseases

Hypertension is a significant public health problem due to its high prevalence and association with increased risk of cardiovascular disease (CVD), and thus the major cause of death in developed countries. Most of diabetes mellitus and hemodialysis patients are expected to have hypertension and of around 10% of pregnant women have hypertension, which increases preeclampsia; the most important medical problem that threatened the life of maternal and neonatal. Previous studies showed that genetic factors could play an important role in predicting hypertension. Recently, a novel soluble flavin adenine dinucleotide (FAD)-dependent amine oxidase, called renalase, found to decrease blood pressure by degrading catecholamines. It is secreted by the kidney and is found in the heart, small intestine, skeletal muscle, endothelium, and nervous system. Renalase polymorphism of the renalase gene may affect the renalase activity and increase susceptibility to some diseases. This review highlights the structure, function, polymorphisms of renalase, and its association with hypertension in hemodialysis, cardiovascular, preeclampsia, and diabetes mellitus patients. As a conclusion, the rs10887800, rs2576178, and rs2296545 renalase gene polymorphism could thus be a risk factor for hypertension.

Associations between renalase concentration and the occurrence of selected diseases.

Renalase is a recently identified flavoprotein oxidase, secreted mainly by the kidneys, which takes part in the degradation of catecholamines. The catecholamine inactivating effect results in the modulation of the sympathetic system tension and, consequently, in a decrease of blood pressure, myocardial contractility, heart rate, and vascular tone. Besides its enzymatic capacity, renalase shows cytoprotective properties by activating mitogen-activated protein kinase (MAPK) pathway. Several single nucleotide polymorphisms (SNPs) of the renalase gene have been identified, of which the most widely studied in relation to the development of selected diseases are rs2296545, rs10887800, and rs2576178. Numerous publications prove the contribution of renalase to the occurrence of cardiovascular diseases, kidney diseases, ischaemic stroke, diabetes type 1 and 2, as well as female infertility and schizophrenia. Further extended research into the various mechanisms of renalase activity may result in the use of this oxidase or its analogues as a therapeutic and/or diagnostic tool.

Atorvastatin and losartan may upregulate renalase activity in hypertension but not coronary artery diseases: The role of gene polymorphism.

The aim is to explore the treatment effect of coronary artery disease (CAD) and hypertension on plasma levels of renalase activity and also the possible association of renalase rs10887800 gene polymorphism with CAD and hypertension. A total of 286 patients who received coronary angiography were included in the study. Subjects were divided into four groups including (1) hypertensive with no CAD (H-Tens, n = 60); (2) CAD with hypertension (CAD + H-Tens, n = 71); (3) CAD with no hypertension (CAD, n = 61); and (4) nonhypertensive with no CAD as a control group (Con, n = 69). The plasma renalase activity was measured using the Amplex Red Monoamine Oxidase Assay Kit. Renalase rs10887800 single-nucleotide polymorphisms (SNPs) were genotyped by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method. Atorvastatin (P = 0.005), losartan (P < 0.001), and captopril (P = 0.001) were administered significantly more in case groups compared with the Con group. Significant higher and lower levels of renalase activity were observed in H-Tens and CAD patients compared with control subjects (P < 0.001 for both comparisons). Furthermore, no significant differences were obtained in the risk or protective effects of renalase rs10887800 SNP against hypertension and/or CAD in both recessive and dominant genetic models (P > 0.05). According to the findings of the present study, atorvastatin and losartan therapy assumes considerable significance in alleviating hypertension, but not CAD, by increasing the renalase activity. Furthermore, it was found that renalase rs10887800 is less likely a predisposing factor for susceptibility to hypertension and/or CAD in an Iranian southeast population.

Relationship between microRNA-146a expression and plasma renalase levels in hemodialyzed patients.

BackgroundmicroRNA (miRNA) belongs to the non-coding RNAs family responsible for the regulation of gene expression. Renalase is a protein composed of 342 amino acids, secreted by the kidneys and possibly plays an important role in the regulation of sympathetic tone and blood pressure. The aim of the present study was to investigate plasma renalase concentration, and explore the relationship between miRNA-146a-5p expression and plasma renalase levels in hemodialyzed patients.MethodsThe study population comprised 55 subjects who succumbed to various cardiac events, 27 women and 28 men, aged 65–70 years. The total RNA including miRNA fraction was isolated using QiagenmiRNEasy Serum/Plasma kit according to the manufacturer’s protocol. The isolated miRNAs were analyzed using a quantitative polymerase chain reaction (qRT-PCR) technique. The plasma renalase levels were measured using a commercial ELISA kit.ResultsIn the group of patients with high levels of renalase, higher miRNA-146a expression was found, compared with those with low concentration of renalase. Patients with simultaneous low miRNA-146a expression and high level of renalase were confirmed to deliver a significantly longer survival time compared with other patients.ConclusionsmiRNA-146a and plasma renalase levels were estimated as independent prognostic factors of hemodialyzed patients’ survival time. Patients with low miRNA-146a expression demonstrated a significantly longer survival time in contrast to the patients with a high expression level of miRNA-146a. Moreover, a significantly longer survival time was found in patients with high renalase activity compared with patients with low activity of the enzyme.

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.

PP.LB02.27

Objective: Renalase is an enzyme that circulates in the blood and modulates the cardiac function, sympathetic tone and systemic blood pressure. It can be synthesized in the kidneys, liver and cardiomyocytes. The active enzyme degrades circulating catecholamines, causing a significant fall in blood pressure. Changes in renalase concentration in hemodialysis patients may explain the frequent occurrence of hypertension among patients with end-stage kidney disease. The aim of this study was to asses’ serum renalase levels in hemodyalisis patients and apparently healthy subjects, and association of renalase and blood pressure in patients group. Design and method: 160 subjects were recruited in the study: 120 with end-stage renal disease, divided into two groups, according to their blood pressures (normotensive and hypertensive), and 40 apparently healthy individuals matched in age and sex. Blood pressure was measured before and after a hemodialysis session. The target values, according to ESH/ESC guidelines, were lower than 140/90 mmHg before, and 130/90 mmHg after hemodialysis. The blood for the estimating serum renalase concentration was taken before dialysis. Enzyme-linked immunosorbent assay (ELISA) kit with monoclonal antibody specific to renalase, was used. Results: Mean serum renalase levels in normotensive as well as hypertensive hemodialysis patients were significantly higher compared to control group {89.32 (45.77–170.22) and 42.7 (32.79–63.35) μg/ml, respectively; p < 0.0005}. No significant difference of renalase levels among normotensive and hypertensive patients was noted {64.04 (40.76–173.84) and 91.86 (56.77–149.75.35)μg/ml; (p > 0.05)}. There was a highly significant difference between systolic and diastolic pressure measured before and after the dialysis in normotensive and hypertensive groups of patients (p < 0.0005). It was noted that there is a significant, negatively directed association between patients’ age at the beginning of dialysis and the duration of hemodialysis. Also, the correlation between blood pressure and renalase activity among normotensive and hypertensive hemodialysis patients was not shown (p > 0.05). Conclusions: Further studies are needed to define the role of renalase and its complex pathophysiological link with blood pressure regulation, kidney function and sympathetic tone. Renalase may become a new therapeutic target that leads to a better prognosis for patients with end-stage kidney disease.

Assessment of Renalase Activity on Catecholamines Degradation

Renalase was recently described as a new flavoprotein that functions as FAD/NADH-dependent oxidase and, in contrast to other monoamine oxidases, is secreted into plasma and urine. Recombinant renalase was found to exert powerful and rapid hypotensive effects when administered intravenously on rats and this was suggested to be mediated by circulating catecholamines degradation. However there is no concrete evidence that directly supports the hypothesis that renalase metabolizes catecholamines. In this study we aimed to evaluate the catecholamines-degrading renalase activity by three different technical approaches: 1) Amplex Red Monoamine Oxidase Assay, which evaluates the rate of resaruzin reduction by renalase oxidative activity; 2) assessment of catecholamines consumptions by high-pressure liquid chromatography (HPLC) with electrochemical-detection (ED) and 3) assessment of product formation by HPLC with photodiode array-detection (DAD). Using the Amplex Red MAO Assay, all three catecholamines were degraded by recombinant renalase overtime, being adrenaline the preferred substrate, followed by noradrenaline and dopamine. In addition using HPLC-ED, it was observed the consumption of all three catecholamines by recombinant renalase, which were oxidized to the correspondent aminochromes, as observed by DAD. However the role of renalase as catalyzer of aminochromes production is still undefined. In summary, the data presented in this study propose by different methodologies the involvement of renalase in catecholamine metabolization.

Plasma renalase in chronic kidney disease: differences and similarities between humans and rats.

Renalase was described in 2005 as a new flavoprotein expressed mainly in the kidney that functions as a flavin adenine dinucleotide (FAD)- and nicotinamide adenine dinucleotide (NADH)-dependent amine oxidase. In contrast to other monoamine oxidases, renalase can be secreted into both plasma and urine where it has been suggested to metabolise catecholamines and contribute to blood pressure control. Renalase was first reported to be undetectable in patients with chronic kidney disease (CKD) and end-stage renal disease (ESRD), suggesting a causal link between the reduced plasma renalase levels, increased plasma catecholamine, and heightened cardiovascular risk that are well documented in this population. Plasma renalase deficiency has been consistently reported in studies using animal models of CKD. However, in studies with 3/4 nephrectomised (3/4nx) rats, the reduced circulating renalase levels were accompanied by increased plasma renalase activity that appeared to be related to decreased inhibition of circulating enzyme. By contrast, a series of recent studies in human subjects provides evidence suggesting that plasma renalase levels are negatively correlated with renal function. Though, similar to that found in the rat remnant kidney, the increased plasma renalase activity in patients with ESRD was associated with decreased inhibition of the circulating enzyme.

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.

Plasma and urine renalase levels and activity during the recovery of renal function in kidney transplant recipients

Renalase is a recently described enzyme secreted by the kidney into both plasma and urine, where it was suggested to degrade catecholamines contributing to blood pressure control. While there is a controversy regarding the relationship between renal function and plasma renalase levels, there is virtually no data in humans on plasma renalase activity as well as on both urine renalase levels and activity. We prospectively examined the time course of plasma and urine renalase levels and activity in 26 end-stage renal disease (ESRD) patients receiving a cadaver kidney transplant (cadaver kidney recipients [CKR]) before surgery and during the recovery of renal function up to day 90 post transplant. The relationship with sympathetic and renal dopaminergic activities was also evaluated. The recovery of renal function in CKR closely predicted decreases in plasma renalase levels (r = 0.88; P < 0.0001), urine renalase levels (r = 0.75; P < 0.0001) and urine renalase activity (r = 0.56; P < 0.03), but did not predict changes in plasma renalase activity (r = -0.02; NS). Plasma norepinephrine levels positively correlated with plasma renalase levels (r = 0.64, P < 0.002) as well as with urine renalase levels and activity (r = 0.47 P < 0.02; r = 0.71, P < 0.0005, respectively) and negatively correlated with plasma renalase activity (r = -0.57, P < 0.002). By contrast, plasma epinephrine levels positively correlated with plasma renalase activity (r = 0.67, P < 0.0001) and negatively correlated with plasma renalase levels (r = -0.62, P < 0.003). A significant negative relationship was observed between urine dopamine output and urine renalase levels (r = -0.48; P < 0.03) but not with urine renalase activity (r = -0.33, NS). We conclude that plasma and urine renalase levels closely depend on renal function and sympathetic nervous system activity. It is suggested that epinephrine-mediated activation of circulating renalase may occur in renal transplant recipients with good recovery of renal function. The increase in plasma renalase activity observed in ESRD patients and renal transplant recipients can be explained on the basis of reduced inhibition of the circulating enzyme.

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 Is an α-NAD(P)H Oxidase/Anomerase

Renalase is a protein hormone secreted into the blood by the kidney that is reported to lower blood pressure and slow heart rate. Since its discovery in 2005, renalase has been the subject of conjecture pertaining to its catalytic function. While it has been widely reported that renalase is the third monoamine oxidase (monoamine oxidase C) that oxidizes circulating catecholamines such as epinephrine, there has been no convincing demonstration of this catalysis in vitro. Renalase is a flavoprotein whose structural topology is similar to known oxidases, lysine demethylases, and monooxygenases, but its active site bears no resemblance to that of any known flavoprotein. We have identified the catalytic activity of renalase as an α-NAD(P)H oxidase/anomerase, whereby low equilibrium concentrations of the α-anomer of NADPH and NADH initiate rapid reduction of the renalase flavin cofactor. The reduced cofactor then reacts with dioxygen to form hydrogen peroxide and releases nicotinamide dinucleotide product in the β-form. These processes yield an apparent turnover number (0.5 s(-1) in atmospheric dioxygen) that is at least 2 orders of magnitude more rapid than any reported activity with catechol neurotransmitters. This highly novel activity is the first demonstration of a role for naturally occurring α-NAD(P)H anomers in mammalian physiology and the first report of a flavoprotein catalyzing an epimerization reaction.

Letter on ‘Sodium-dependent modulation of systemic and urinary renalase expression and activity in the rat remnant kidney’

Letter on ‘Sodium-dependent modulation of systemic and urinary renalase expression and activity in the rat remnant kidney’

Letter on ‘Sodium-dependent modulation of systemic and urinary renalase expression and activity in the rat remnant kidney’

Letter on ‘Sodium-dependent modulation of systemic and urinary renalase expression and activity in the rat remnant kidney’

Sodium-dependent modulation of systemic and urinary renalase expression and activity in the rat remnant kidney

The present study examined the influence of high-sodium intake on systemic and urinary renalase levels and activity in 3/4 nephrectomized (3/4nx) and Sham rats. The reduced circulating renalase levels in 3/4nx rats during normal-sodium intake were accompanied by increased plasma renalase activity. The sodium-induced increase of blood pressure in 3/4nx rats was accompanied by significant decreases in circulating renalase levels and activity as well as by a significant decrease in cardiac renalase levels in 3/4nx rats but not in Sham rats. During normal-sodium intake, no significant differences were observed in either urine renalase levels or activity between 3/4nx and Sham rats, not withstanding the ∼75% decrease in daily urine dopamine output observed in the rat remnant kidney. During high-sodium intake, urinary renalase levels increased in both 3/4nx and Sham groups by three-fold whereas urinary renalase activity increased in 3/4nx and Sham rats by greater than twelve-fold and greater than four-fold, respectively. This was accompanied by sodium-induced increases in daily urinary dopamine output in both 3/4nx and Sham rats by ∼2.3-fold and ∼1.6-fold, respectively. The reduced circulating renalase levels in 3/4nx rats are accompanied by increased plasma renalase activity, which appears to be related with decreased inhibition of the circulating enzyme. Differences in systemic and urinary renalase levels and activity between 3/4nx and Sham rats during high-sodium intake may contribute to activation of the sympathetic nervous system, hypertension and enhanced cardiovascular risk in CKD but do not appear to account for the decrease in renal dopaminergic activity in the rat remnant kidney.

Expression and tissue localization of renalase, a novel soluble FAD-dependent protein, in reproductive/steroidogenic systems

Renalase was initially identified in human kidney as a soluble monoamine oxidase. Here we show that renalase is predominantly expressed in reproductive/steroidogenic systems, with particularly substantial expression in oocytes, granulosa, interstitial and luteal cells of ovary, spermatogenic cells of testis, and cortex of adrenal gland, suggesting its function(s) in maturation of germ cells and steroid hormone regulation. Renalase expression increases in testes and ovaries as mice develop and its expression is further enhanced in the ovaries of pregnant mice, indicating an activity of renalase in reproduction. Gonadotropin-releasing hormone (GnRH) antagonist, cetrorelix, repressed renalase expression in mice ovaries and testes, suggesting that steroids regulate renalase expression. Leptin is an effector and modulator of steroid hormones and reproduction. Surprisingly, knockout of leptin causes a dramatic increase of renalase expression in mice testes. Taken together, our results suggest that reproductive/steroidogenic systems are also the sources for renalase secretion and renalase may play a critical role in reproduction and hormone regulation. This provides a novel insight into understanding the function of renalase.

FAD-Binding Site and NADP Reactivity in Human Renalase: A New Enzyme Involved in Blood Pressure Regulation

Renalase is a recently discovered flavoprotein that regulates blood pressure, regulates sodium and phosphate excretion, and displays cardioprotectant action through a mechanism that is barely understood to date. It has been proposed to act as a catecholamine-degrading enzyme, via either O 2-dependent or NADH-dependent mechanisms. Here we report the renalase crystal structure at 2.5 Å resolution together with new data on its interaction with nicotinamide dinucleotides. Renalase adopts the p-hydroxybenzoate hydroxylase fold topology, comprising a Rossmann-fold-based flavin adenine dinucleotide (FAD)-binding domain and a putative substrate-binding domain, the latter of which contains a five-stranded anti-parallel β-sheet. A large cavity (228 Å 3), facing the flavin ring, presumably represents the active site. Compared to monoamine oxidase or polyamine oxidase, the renalase active site is fully solvent exposed and lacks an ‘aromatic cage’ for binding the substrate amino group. Renalase has an extremely low diaphorase activity, displaying lower k cat but higher k cat/ K m for NADH compared to NADPH. Moreover, its FAD prosthetic group becomes slowly reduced when it is incubated with NADPH under anaerobiosis, and binds NAD + or NADP + with K d values of ca 2 mM. The absence of a recognizable NADP-binding site in the protein structure and its poor affinity for, and poor reactivity towards, NADH and NADPH suggest that these are not physiological ligands of renalase. Although our study does not answer the question on the catalytic activity of renalase, it provides a firm framework for testing hypotheses on the molecular mechanism of its action.