Identification of Two Forms of Human Plasma Renalase, and Their Association With All-Cause Mortality

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.

Renalase Levels are Decreased in Maternal Blood and Placental Tissues in Pregnancies Associated with Preterm Preeclampsia

Preeclampsia (PEC) is a complication of pregnancy associated with hypertension and the risk of eclampsia. The pathophysiology of PEC is unknown and identifying factors associated with PEC during pregnancy is crucial for placental, fetal, and maternal health. Renalase (RNLS) is an anti-inflammatory secretory flavoprotein associated with hypertension. Recent data demonstrated a correlation between maternal serum RNLS and PEC, and work from our group identified RNLS expression in the placenta. However, it remains unknown whether RNLS levels in placenta are altered by preeclampsia. Additionally, it is unclear if there is a differential effect of preterm and term PEC on RNLS. We demonstrate that serum RNLS was reduced in preterm cases of PEC. Similarly, placental RNLS was diminished in the chorion of preterm cases of PEC. However, a reduction of RNLS in the decidua was observed with all cases of PEC, while the levels of RNLS within the placental villi were similar in all cases. Overall, we demonstrate that RNLS correlates with PEC both systemically in maternal serum and locally within the placenta, with variable effects on the different layers of the placenta and more pronounced in preterm cases.

Clinical predictive value of renalase in post-ERCP pancreatitis

BACKGROUND AND AIMS

Plasma levels of renalase decrease in acute experimental pancreatitis. We aimed to determine if decreases in plasma renalase levels after ERCP predict the occurrence of post-ERCP pancreatitis (PEP).

METHODS

In this prospective cohort study conducted at a tertiary hospital, plasma renalase was determined before ERCP (baseline) and at 30 and 60 minutes after ERCP. Native renalase levels, acidified renalase, and native-to-acidified renalase proportions were analyzed over time using a longitudinal regression model.

RESULTS

Among 273 patients, 31 developed PEP. Only 1 PEP patient had a baseline native renalase >6.0 μg/mL, whereas 38 of 242 without PEP had a native renalase > 6.0 μg/mL, indicating a sensitivity of 97% (30/31) and specificity of 16% (38/242) in predicting PEP. Longitudinal models did not show differences over time between groups.

CONCLUSIONS

Baseline native renalase levels are very sensitive for predicting PEP. Further studies are needed to determine the potential clinical role of renalase in predicting and preventing PEP.

Plasma renalase levels are associated with the development of acute pancreatitis

BACKGROUND/OBJECTIVES

Severe acute pancreatitis is associated with significant morbidity and mortality. Identifying factors that affect the risk of developing severe disease could influence management. Plasma levels of renalase, an anti-inflammatory secretory protein, dramatically decrease in a murine acute pancreatitis model. We assessed this response in hospitalized acute pancreatitis patients to determine if reduced plasma renalase levels occur in humans.

METHODS

Plasma samples were prospectively and sequentially collected from patients hospitalized for acute pancreatitis. Two forms of plasma renalase, native (no acid) and acidified, were measured by ELISA and RNLS levels were compared between healthy controls and patients with mild and severe disease (defined as APACHE-II score ≥7) using nonparametric statistical analysis.

RESULTS

Control (33) and acute pancreatitis (mild, 230 (76.7%) and severe, 70 (23.3%) patients were studied. Acidified RNLS levels were lower in pancreatitis patients: Control: 10.1 μg/ml, Mild 5.1 μg/ml, Severe 6.0 μg/ml; p < 0.001. Native RNLS levels were increased in AP: Control: 0.4 μg/ml, Mild 0.9 μg g/ml, Severe 1.2 μg/ml p < 0.001; those with severe AP trended to have higher native RNLS levels than those with mild disease (p = 0.056). In patients with severe AP, higher APACHE-II scores at 24 h after admission correlated with lower acid-sensitive RNLS levels on admission (r = -0.31, p = 0.023).

CONCLUSION

Low plasma acidified RNLS levels, and increased native RNLS levels are associated with AP. Additional studies should assess the clinical correlation between plasma RNLS levels and AP severity and outcomes.

Cardiac-specific renalase overexpression alleviates CKD-induced pathological cardiac remodeling in mice

Introduction

CKD-induced pathological cardiac remodeling is characterized by myocardial hypertrophy and cardiac fibrosis. The available therapeutic options are limited, it is thus urgently needed to identify novel therapeutic targets. Renalase (RNLS) is a newly discovered protein secreted by the kidney and was found beneficial in many renal diseases. But whether it exerts protective effects on cardiac remodeling in CKD remains unclear.

Methods

RNLS knockout (KO) and wild-type (WT) mice were both used to build CKD models and the adeno-associated virus (AAV9) system was used to overexpress RNLS cardiac specifically. Echocardiography was performed to detect cardiac structural changes every 6 weeks until 18 weeks post-surgery. High throughput sequencing was performed to understand the underlying mechanisms and the effects of RNLS on cardiac fibroblasts were validated in vitro.

Results

Knockout of RNLS aggravated cardiac remodeling in CKD, while RNLS cardiac-specific overexpression significantly reduced left ventricular hypertrophy and cardiac fibrosis induced by CKD. The following RNA-sequencing analysis revealed that RNLS significantly downregulated the extracellular matrix (ECM) receptor interaction pathway, ECM organization, and several ECM-related proteins. GSEA results showed RNLS significantly downregulated several profibrotic biological processes of cardiac fibroblasts which were upregulated by CKD, including fibroblast proliferation, leukocyte migration, antigen presentation, cytokine production, and epithelial-mesenchymal transition (EMT). In vitro, we validated that RNLS reduced the primary cardiac fibroblast proliferation and α-SMA expression stimulated by TGF-β.

Conclusion

In this study, we examined the cardioprotective role of RNLS in CKD-induced cardiac remodeling. RNLS may be a potential therapeutic factor that exerts an anti-fibrotic effect in pathological cardiac remodeling.

Renalase and its receptor, PMCA4b, are expressed in the placenta throughout the human gestation

Placental function requires organized growth, transmission of nutrients, and an anti-inflammatory milieu between the maternal and fetal interface, but placental factors important for its function remain unclear. Renalase is a pro-survival, anti-inflammatory flavoprotein found to be critical in other tissues. We examined the potential role of renalase in placental development. PCR, bulk RNA sequencing, immunohistochemistry, and immunofluorescence for renalase and its binding partners, PMCA4b and PZP, were performed on human placental tissue from second-trimester and full-term placentas separated into decidua, placental villi and chorionic plates. Quantification of immunohistochemistry was used to localize renalase across time course from 17 weeks to term. Endogenous production of renalase was examined in placental tissue and organoids. Renalase and its receptor PMCA4b transcripts and proteins were present in all layers of the placenta. Estimated RNLS protein levels did not change with gestation in the decidual samples. However, placental villi contained more renalase immunoreactive cells in fetal than full-term placental samples. RNLS co-labeled with markers for Hofbauer cells and trophoblasts within the placental villi. Endogenous production of RNLS, PMCA4b, and PZP by trophoblasts was validated in placental organoids. Renalase is endogenously expressed throughout placental tissue and specifically within Hofbauer cells and trophoblasts, suggesting a potential role for renalase in placental development and function. Future studies should assess renalase's role in normal and diseased human placenta.

Association of renalase with clinical outcomes in hospitalized patients with COVID-19

Renalase is a secreted flavoprotein with anti-inflammatory and pro-cell survival properties. COVID-19 is associated with disordered inflammation and apoptosis. We hypothesized that blood renalase levels would correspond to severe COVID-19 and survival. In this retrospective cohort study, clinicopathologic data and blood samples were collected from hospitalized COVID-19 subjects (March—June 2020) at a single institution tertiary hospital. Plasma renalase and cytokine levels were measured and clinical data abstracted from health records. Of 3,450 COVID-19 patients, 458 patients were enrolled. Patients were excluded if <18 years, or opted out of research. The primary composite outcome was intubation or death within 180 days. Secondary outcomes included mortality alone, intensive care unit admission, use of vasopressors, and CPR. Enrolled patients had mean age 64 years (SD±17), were 53% males, and 48% non-whites. Mean renalase levels was 14,108·4 ng/ml (SD±8,137 ng/ml). Compared to patients with high renalase, those with low renalase (< 8,922 ng/ml) were more likely to present with hypoxia, increased ICU admission (54% vs. 33%, p < 0.001), and cardiopulmonary resuscitation (10% vs. 4%, p = 0·023). In Cox proportional hazard model, every 1000 ng/ml increase in renalase decreased the risk of death or intubation by 5% (HR 0·95; 95% CI 0·91–0·98) and increased survival alone by 6% (HR 0·95; CI 0·90–0·98), after adjusting for socio-demographics, initial disease severity, comorbidities and inflammation. Patients with high renalase-low IL-6 levels had the best survival compared to other groups (p = 0·04). Renalase was independently associated with reduced intubation and mortality in hospitalized COVID-19 patients. Future studies should assess the pathophysiological relevance of renalase in COVID-19 disease.

Kidney-Targeted Renalase Agonist Prevents Cisplatin-Induced Chronic Kidney Disease by Inhibiting Regulated Necrosis and Inflammation

BACKGROUND

Repeated administration of cisplatin causes CKD. In previous studies, we reported that the kidney-secreted survival protein renalase (RNLS) and an agonist peptide protected mice from cisplatin-induced AKI.

METHODS

To investigate whether kidney-targeted delivery of RNLS might prevent cisplatin-induced CKD in a mouse model, we achieved specific delivery of a RNLS agonist peptide (RP81) to the renal proximal tubule by encapsulating the peptide in mesoscale nanoparticles (MNPs). We used genetic deletion of RNLS, single-cell RNA sequencing analysis, and Western blotting to determine efficacy and to explore underlying mechanisms. We also measured plasma RNLS in patients with advanced head and neck squamous cell carcinoma receiving their first dose of cisplatin chemotherapy.

RESULTS

In mice with CKD induced by cisplatin, we observed an approximate 60% reduction of kidney RNLS; genetic deletion of RNLS was associated with significantly more severe cisplatin-induced CKD. In this severe model of cisplatin-induced CKD, systemic administration of MNP-encapsulated RP81 (RP81-MNP) significantly reduced CKD as assessed by plasma creatinine and histology. It also decreased inflammatory cytokines in plasma and inhibited regulated necrosis in kidney. Single-cell RNA sequencing analyses revealed that RP81-MNP preserved epithelial components of the nephron and the vasculature and suppressed inflammatory macrophages and myofibroblasts. In patients receiving their first dose of cisplatin chemotherapy, plasma RNLS levels trended lower at day 14 post-treatment.

CONCLUSIONS

Kidney-targeted delivery of RNLS agonist RP81-MNP protects against cisplatin-induced CKD by decreasing cell death and improving the viability of the renal proximal tubule. These findings suggest that such an approach might mitigate the development of CKD in patients receiving cisplatin cancer chemotherapy.

RENALASE: DISCOVERY, BIOLOGY, AND THERAPEUTIC APPLICATIONS

While investigating the mechanisms that could mediate the significant burden of cardiovascular complications observed in persons with chronic kidney disease (CKD) and end stage renal disease (ESRD), we identified a previously unknown protein, which we named renalase (RNLS). Over the past 15 years, our understanding of the biology, physiology, and pathophysiology of RNLS has matured. Here we aim to highlight that RNLS is a bifunctional protein. It metabolizes intracellular nicotinamide adenine dinucleotide (NADH), modulates mitochondrial function, and protects energy metabolism. When secreted outside the cell, independent of its enzymatic properties, it functions as a signaling molecule that mediates resistance to stressful stimuli and promotes cell and organ survival. RNLS has been shown to modulate the severity of acute injury to the pancreas, liver, kidney, and heart. It also protects against the development of chronic injury, and here we highlight the potential use of exogenous RNLS peptide agonists to prevent cisplatin-mediated CKD (CP-CKD).

Elevated Levels of Renalase, the β-NAD(P)H Isomerase, Can Be Used as Risk Factors of Major Adverse Cardiovascular Events and All-Cause Death in Patients with Chronic Kidney Disease

BACKGROUND

Renalase is an enzyme and a cytokine involved in cell survival. Since its discovery, associations between it and both cardiovascular and kidney disease have been noted. Recognizing this, we conducted a study in which we followed patients with chronic kidney disease.

MATERIAL AND METHODS

The study involved 90 CKD patients with varying stages of the disease and 30 healthy controls. Renalase was measured with an ELISA kit, and patients were followed-up after a median of 18 months. During the follow-up, we asked about the occurrence of MACE, all-cause mortality and the need for dialysis initiation.

RESULTS

In CKD subgroups, RNSL correlated with all-cause death only in the HD group (Rs = 0.49, p < 0.01). In the whole CKD population, we found a positive correlation of RNSL concentration and both MACE occurrence (Rs = 0.38, p < 0.001) and all-cause death (Rs = 0.34, p < 0.005). There was a significant increase in MACE occurrence probability in patients with elevated renalase levels (>25 μg/mL).

CONCLUSIONS

Elevated renalase levels can be used as a risk factor of MACE in patients with CKD, but its long-term utility needs further research. High renalase levels are a risk factor of death among CKD patients. In HD patients, all deaths were observed among patients with >30 μg/mL; this level could be used as a "red flag" marker in future studies.

Renalase is a novel tissue and serological biomarker in pancreatic ductal adenocarcinoma

Dysregulated expression of the secretory protein renalase can promote pancreatic ductal adenocarcinoma (PDAC) growth in animal models. We characterized renalase expression in premalignant and malignant PDAC tissue and investigated whether plasma renalase levels corresponded to clinical PDAC characteristics. Renalase immunohistochemistry was used to determine the presence and distribution of renalase in normal pancreas, chronic pancreatitis, PDAC precursor lesions, and PDAC tissues. Associations between pretreatment plasma renalase and PDAC clinical status were assessed in patients with varied clinical stages of PDAC and included tumor characteristics, surgical resection in locally advanced/borderline resectable PDAC, and overall survival. Data were retrospectively obtained and correlated using non-parametric analysis. Little to no renalase was detected by histochemistry in the normal pancreatic head in the absence of abdominal trauma. In chronic pancreatitis, renalase immunoreactivity localized to peri-acinar spindle-shaped cells in some samples. It was also widely present in PDAC precursor lesions and PDAC tissue. Among 240 patients with PDAC, elevated plasma renalase levels were associated with worse tumor characteristics, including greater angiolymphatic invasion (80.0% vs. 58.1%, p = 0.012) and greater node positive disease (76.5% vs. 56.5%, p = 0.024). Overall survival was worse in patients with high plasma renalase levels with median follow-up of 27.70 months vs. 65.03 months (p < 0.001). Renalase levels also predicted whether patients with locally advanced/borderline resectable PDAC underwent resection (AUC 0.674; 95%CI 0.42-0.82, p = 0.04). Overall tissue renalase was increased in both premalignant and malignant PDAC tissues compared to normal pancreas. Elevated plasma renalase levels were associated with advanced tumor characteristics, decreased overall survival, and reduced resectability in patients with locally advanced/borderline resectable PDAC. These studies show that renalase levels are increased in premalignant pancreatic tissues and that its levels in plasma correspond to the clinical behavior of PDAC.

Decreased plasma levels of the survival factor renalase are associated with worse outcomes in COVID-19

INTRODUCTION

Renalase (RNLS), a novel secreted plasma flavoprotein, has anti-inflammatory effects in a variety of disease processes. Severe COVID-19 disease is associated with disordered inflammatory responses. We hypothesized that reduced plasma RNLS levels could be a marker of COVID-19 disease severity.

METHODS

Plasma was collected from 51 hospitalized COVID-19 patients and 15 uninfected non-hospitalized controls. Plasma RNLS and cytokine levels were measured and sociodemographic and clinical data were collected from chart review. Data were analyzed using nonparametric analyses and Kaplan Meir curve log rank analysis.

RESULTS

Plasma RNLs levels were negatively correlated with inflammatory markers, including IL-1b, IL-6, and TNFa (p = 0.04, p = 0.03, p = 0.01, respectively). Patients with COVID-19 disease had lower levels of RNLS than controls. Lower levels of RNLS were associated with more severe disease among COVID-19 patients. Low RNLS was also associated with worse survival among COVID-19 patients (HR = 4.54; 95% CI: 1.06-19.43; p = 0.005).

CONCLUSION

Low plasma RNLS levels are associated with severe COVID-19 disease and may be a useful additional biomarker when identifying patients with severe COVID-19 disease. Given RNLS anti-inflammatory properties and negative correlation with inflammatory markers, these findings also suggest evidence of a potential pathophysiological mechanism for severe COVID-19 disease.

The partnership between renalase and ejection fraction as a risk factor for increased cardiac remodeling biomarkers in chronic heart failure patients

Objective: Heart failure (HF) represents a huge socio-economic burden. It has been demonstrated, experimentally, that renalase, a newly discovered protein, prevents cardiac hypertrophy and adverse remodeling, which is seen in HF. We postulated the following aims: to investigate associations of renalase with biomarkers of cardiac remodeling: galectin-3, soluble suppression of tumorigenicity, (sST2), growth differentiation factor 15 (GDF-15) and syndecan-1, myocardial stretch (BNP) and cardio-renal axis (cystatin C) in HF patients with reduced ejection fraction (HFrEF) and preserved ejection fraction (HFpEF) to determine whether renalase, in combination with left ventricular ejection fraction (LVEF), represents a risk factor for plasma elevation in biomarkers.Methods: We classified HF patients (n = 76) according to LVEF (preserved/reduced), applied a median plasma renalase (113 ng/mL) as a cut-off value (low/high) and created four subgroups of HF patients: HFpEF/low renalase (n = 19), HFrEF/low renalase (n = 19), HFrEF/high renalase (n = 32) and HFpEF/high renalase (n = 6). A control group (n = 35) consisted of healthy volunteers.Results: Plasma concentrations of evaluated biomarkers were determined using an ELISA technique and were highest in HF patients with reduced EF (p < .001, respectively), and renalase's positive correlations were obtained relating to all biomarkers: galectin-3 (r = 0.913; p < .001), sST2 (r = 0.965; p < .001), GDF-15 (r = 0.887; p < .001), syndecan-1 (r = 0.922; p < .001), BNP (r = 0.527; p < .001) and cystatin C (r = 0.844; p < .001) and strong and negative correlation with LVEF (r = -0.456, p < .001). Increased renalase, regardless of the EF (preserved/reduced), was shown to be an independent risk factor for an increase in all evaluated cardiac remodeling biomarkers, p < .001, respectively. However, increased renalase and reduced EF was the only independent risk factor for BNP and cystatin C elevation, p < .001, respectively. Results after multivariable adjustments (age/gender) were identical.Conclusion: When elevated plasma renalase and HF are present, regardless of EF being reduced or preserved, that represents a significant risk factor for increase in cardiac remodeling biomarker plasma concentrations. However, only elevated renalase and reduced EF demonstrated significance as a risk factor for BNP and cystatin C plasma elevation. Renalase may be considered a promising molecule for the improved predictive abilities of conventional biomarkers and is worthy of further investigation.