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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: A Multi-Functional Signaling Molecule with Roles in Gastrointestinal Disease

The survival factor renalase (RNLS) is a recently discovered secretory protein with potent prosurvival and anti-inflammatory effects. Several evolutionarily conserved RNLS domains are critical to its function. These include a 20 aa site that encodes for its prosurvival effects. Its prosurvival effects are shown in GI disease models including acute cerulein pancreatitis. In rodent models of pancreatic cancer and human cancer tissues, increased RNLS expression promotes cancer cell survival but shortens life expectancy. This 37 kD protein can regulate cell signaling as an extracellular molecule and probably also at intracellular sites. Extracellular RNLS signals through a specific plasma membrane calcium export transporter; this interaction appears most relevant to acute injury and cancer. Preliminary studies using RNLS agonists and antagonists, as well as various preclinical disease models, suggest that the immunologic and prosurvival effects of RNLS will be relevant to diverse pathologies that include acute organ injuries and select cancers. Future studies should define the roles of RNLS in intestinal diseases, characterizing the RNLS-activated pathways linked to cell survival and developing therapeutic agents that can increase or decrease RNLS in relevant clinical settings.

Kinetics and equilibria of the reductive and oxidative half-reactions of human renalase with α-NADPH

Renalase is a recently discovered flavoprotein that has been reported to be a hormone produced by the kidney to down-modulate blood pressure and heart rate. The consensus belief has been that renalase oxidizes circulating catecholamine neurotransmitters thereby attenuating vascular tone. However, a convincing in vitro demonstration of this activity has not been made. We have recently discovered that renalase has α-NAD(P)H oxidase/anomerase activity. Unlike most naturally occurring nucleotides, NAD(P)H can accumulate small amounts of the α-anomers that once oxidized are configurationally stable and unable to participate in cellular activity. Thus, anomerization of NAD(P)H would result in a continual loss of cellular redox currency. As such, it appears that the root purpose of renalase is to return α-anomers of nicotinamide dinucleotides to the β-anomer pool. In this article, we measure the kinetics and equilibria of renalase in turnover with α-NADPH. Renalase is selective for the α-anomer, which binds with a dissociation constant of ∼20±3 μM. This association precedes monophasic two-electron reduction of the FAD cofactor with a rate constant of 40.2±1.3 s(-1). The reduced enzyme then delivers both electrons to dioxygen in a second-order reaction with a rate constant of ∼2900 M(-1) s(-1). Renalase has modest affinity for its β-NADP+ product (Kd=2.2 mM), and the FAD cofactor has a reduction potential of -155 mV that is unaltered by saturating β-NADP+. Together these data suggest that the products are formed and released in a kinetically ordered sequence (β-NADP+ then H2O2), however, the reoxidation of renalase is not contingent on the dissociation of β-NADP+. Neither the oxidized nor the reduced form of renalase is able to catalyze anomerization, implying that the redox and anomerization chemistries are inextricably linked through a common intermediate.