Impact of the kidney transplantation on renalase and blood pressure levels in renal transplant donors and recipients

INTRODUCTION AND OBJECTIVES

Prevalence of hypertension increases as glomerular filtration rate (GFR) declines. Renalase metabolizes catecholamines and have an important role in blood pressure (BP) regulation. The purpose of the study was to evaluate the effect of kidney transplantation on renalase levels and BP in kidney donors and recipients.

MATERIALS AND METHODS

Twenty kidney transplant recipients and their donors were included in the study. Serum renalase levels and ambulatory BP values were measured in both donors and recipients before and after transplantation. Factor associated with change in renalase and BP levels were also evaluated.

RESULTS

In donors; mean GFR and hemoglobin levels decreased while night-time systolic blood pressure (SBP) and diastolic blood pressure (DBP) levels and serum renalase levels increased simultaneously after nephrectomy. Day-time SBP and DBP levels did not changed and the night/day ratio of mean arterial pressure (MAP) increased significantly. In recipients, mean GFR increased, while mean serum renalase levels, creatinine and BP levels decreased after transplantation. Correlation analysis revealed that changes in MAP correlated with alteration in serum renalase levels and GFR.

CONCLUSIONS

After transplantation, serum renalase levels increased in donors and decreased in recipients. The renalase levels are associated with change in MAP and circadian rhythm of BP in donors and recipients.

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.

Impact of the kidney transplantation on renalase and blood pressure levels in renal transplant donors and recipients

INTRODUCTION AND OBJECTIVES

Prevalence of hypertension increases as glomerular filtration rate (GFR) declines. Renalase metabolizes catecholamines and have an important role in blood pressure (BP) regulation. The purpose of the study was to evaluate the effect of kidney transplantation on renalase levels and BP in kidney donors and recipients.

MATERIALS AND METHODS

Twenty kidney transplant recipients and their donors were included in the study. Serum renalase levels and ambulatory BP values were measured in both donors and recipients before and after transplantation. Factor associated with change in renalase and BP levels were also evaluated.

RESULTS

In donors; mean GFR and hemoglobin levels decreased while night-time systolic blood pressure (SBP) and diastolic blood pressure (DBP) levels and serum renalase levels increased simultaneously after nephrectomy. Day-time SBP and DBP levels did not changed and the night/day ratio of mean arterial pressure (MAP) increased significantly. In recipients, mean GFR increased, while mean serum renalase levels, creatinine and BP levels decreased after transplantation. Correlation analysis revealed that changes in MAP correlated with alteration in serum renalase levels and GFR.

CONCLUSIONS

After transplantation, serum renalase levels increased in donors and decreased in recipients. The renalase levels are associated with change in MAP and circadian rhythm of BP in donors and recipients.

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.

Urinary renalase concentration in patients with preserved kidney function undergoing coronary angiography

AIM

The purpose of the study was to evaluate urinary renalase concentration before and after coronary angiography/percutaneous coronary interventions (CA/PCI) in patients with coronary artery disease (CAD) and preserved kidney function and verify its potential application as contrast-induced acute kidney injury (CI-AKI) diagnostic marker.

METHODS

This prospective study comprised 95 consecutive patients (69.5% men; median age 65 years) with CAD submitted to elective or urgent CA/PCI. Data regarding 128 clinical variables were obtained. Urine samples were collected on admission and 6 h after CA/PCI and tested for urinary renalase using ELISA method, which was expressed as renalase-to-creatinine ratio. The CI-AKI diagnosis was based on ≥50% relative or ≥0.3 mg/dl absolute increase of serum creatinine concentration 48 h following the procedure.

RESULTS

Nine patients developed CI-AKI (9.5%). In comparison to baseline values, urinary renalase-to-creatinine ratio significantly decreased 6 h following CA/PCI, (2843.6 vs.1540.7 ng/mg, P < 0.0001). Nine patients developed CI-AKI (9.5%).The reduction of renalase level was profound both in CI-AKI (2709.7 vs. 1585.7 ng/mg, P = 0.007) and non-CI-AKI group (2814.9 vs.1561.8 ng/mg, P < 0.0001). There was a trend towards a greater relative decrease of urinary renalase in CI-AKI group (-57.3 vs.-41.8%, P = 0.10). Univariate analysis revealed that both pre- and post-procedural urinary renalase did not predict CI-AKI onset; however, absolute decrease of renalase below 25 percentile was a predictor of CI-AKI (OR = 5.4, 95% CI:1.3-21.9, P = 0.027).

CONCLUSION

Urinary renalase concentration is reduced in the aftermath of CA/PCI, which may be related to CI-AKI development. Further studies are warranted to elucidate the role of urinary renalase as a CI-AKI diagnostic marker.

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.

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.

An Improved Classification of Kidney Function Recovery Using Estimated Glomerular Filtration Rate Slope Post-transplantation

BACKGROUND

The impact of renal function recovery on graft survival was examined using estimated glomerular filtration rate (eGFR) slope after kidney transplantation (GAP classification); this was compared to the conventional classification of immediate graft function (IGF), slow graft function (SGF), and delayed graft function (DGF).

MATERIALS AND METHODS

Overall, 541 cases of cadaveric renal transplants were reviewed from a prospective transplant database. eGFR and its slope were measured using the harmonic mean over the first week post-transplantation. Next, 495 kidney transplant recipients from an independent institution were assessed to determine the prognostic value of graft function based on the eGFR slope.

RESULTS

The main discrimination of eGFR slopes occurred within the first 7 days. Three groups in the GAP classification (Good graft function, Average graft function, Poor graft function) were defined based on eGFR slope tertiles: good graft function (GGF), average graft function (AGF), and poor graft function (PGF) were defined based on the ΔCrCL per day over the first 7 days: <1 mL/min, 1-4 mL/min, and >4 mL/min, respectively. When applied to the validation cohort, the 5-year graft failure was 20% for the PGF group, 4% for the AGF group, and 3% for the GGF group. Multivariable Cox regression analysis demonstrated better prediction of long-term graft function with the new classification (C statistic 0.49 [old)] vs 0.61 [new]).

CONCLUSION

The new GAP criteria were better at predicting long-term graft survival and renal function compared to the conventional classification system, and deserve further consideration in future studies.

[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.

Blood, urine and faecal metabolite profiles in the study of adult renal disease

Chronic kidney disease (CKD) is a major public health burden and to date traditional biomarkers of renal function (such as serum creatinine and cystatin C) are unable to identify at-risk individuals before the disease process is well under way. To help preventive strategies and maximize the potential for effective interventions, it is important to characterise the molecular changes that take place in the development of renal damage. Metabolomics is a promising tool to identify markers of renal disease since the kidneys are involved in the handling of major biochemical classes of metabolites. These metabolite levels capture a snap-shot of the metabolic profile of the individual, allowing for the potential identification of early biomarkers, and the monitoring of real-time kidney function. In this review, we describe the current status of the identification of blood/urine/faecal metabolic biomarkers in different entities of kidney diseases including: acute kidney injury, chronic kidney disease, renal transplant, diabetic nephropathy and other disorders.

Human urinary renalase lacks the N-terminal signal peptide crucial for accommodation of its FAD cofactor

Renalase is a recently discovered secretory protein involved in the regulation of blood pressure. Cells synthesize all known isoforms of human renalase (1 and 2) as flavoproteins. Accommodation of FAD in the renalase protein requires the presence of its N-terminal peptide. However, in secretory proteins, such peptides are usually cleaved during their export from the cell. In the present study, we have isolated human renalase from urinary samples of healthy volunteers and human recombinant renalases 1 and 2 expressed in Escherichia coli cells. In these proteins, we investigated the presence of the renalase N-terminal peptide and the FAD cofactor and performed computer-aided molecular analysis of the renalase crystal structure to evaluate possible consequences of removal of the N-terminal peptide. In contrast to human recombinant renalase isoforms 1 and 2 containing non-covalently bound FAD and clearly detectable N-terminal peptide, renalase purified from human urine lacks both the N-terminal signal peptide and FAD. The computer-aided analysis indicates that the removal of this peptide results in inability of the truncated renalase to bind the FAD cofactor. Thus, our results indicate that human renalase secreted in urine lacks its N-terminal peptide, and therefore catalytic activities of urinary renalase reported in the literature cannot be attributed to FAD-dependent mechanisms. We suggest that FAD-dependent catalytic functions are intrinsic properties of intracellular renalases, whereas extracellular renalases act in FAD- and possibly catalytic-independent manner.

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.

Effect of Salt Intake and Potassium Supplementation on Urinary Renalase and Serum Dopamine Levels in Chinese Adults

Objective: The aim of our study was to assess the effects of altered salt and potassium intake on urinary renalase and serum dopamine levels in humans. Methods: Forty-two subjects (28-65 years of age) were selected from a rural community of northern China. All subjects were sequentially maintained on a low-salt diet for 7 days (3.0 g/day of NaCl), a high-salt diet for an additional 7 days (18.0 g/day of NaCl), and a high-salt diet with potassium supplementation for a final 7 days (18.0 g/day of NaCl + 4.5 g/day of KCl). Results: Urinary renalase excretions were significantly higher during the high-salt diet intervention than during the low-salt diet. During high-potassium intake, urinary renalase excretions were not significantly different from the high-salt diet, whereas they were significantly higher than the low-salt levels. Serum dopamine levels exhibited similar trends across the interventions. Additionally, a significant positive relationship was observed between the urine renalase and serum dopamine among the different dietary interventions. Also, 24-hour urinary sodium excretion positively correlated with urine renalase and serum dopamine in the whole population. Conclusions: The present study indicates that dietary salt intake and potassium supplementation increase urinary renalase and serum dopamine levels in Chinese subjects.

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.