Diabetic nephropathy is associated with increased urine excretion of proteases plasmin, prostasin and urokinase and activation of amiloride-sensitive current in collecting duct cells

Amiloride Reduces Urokinase/Plasminogen-Driven Intratubular Complement Activation in Glomerular Proteinuria

SIGNIFICANCE STATEMENT

Proteinuria predicts accelerated decline in kidney function in CKD. The pathologic mechanisms are not well known, but aberrantly filtered proteins with enzymatic activity might be involved. The urokinase-type plasminogen activator (uPA)-plasminogen cascade activates complement and generates C3a and C5a in vitro / ex vivo in urine from healthy persons when exogenous, inactive, plasminogen, and complement factors are added. Amiloride inhibits uPA and attenuates complement activation in vitro and in vivo . In conditional podocin knockout (KO) mice with severe proteinuria, blocking of uPA with monoclonal antibodies significantly reduces the urine excretion of C3a and C5a and lowers tissue NLRP3-inflammasome protein without major changes in early fibrosis markers. This mechanism provides a link to proinflammatory signaling in proteinuria with possible long-term consequences for kidney function.

BACKGROUND

Persistent proteinuria is associated with tubular interstitial inflammation and predicts progressive kidney injury. In proteinuria, plasminogen is aberrantly filtered and activated by urokinase-type plasminogen activator (uPA), which promotes kidney fibrosis. We hypothesized that plasmin activates filtered complement factors C3 and C5 directly in tubular fluid, generating anaphylatoxins, and that this is attenuated by amiloride, an off-target uPA inhibitor.

METHODS

Purified C3, C5, plasminogen, urokinase, and urine from healthy humans were used for in vitro / ex vivo studies. Complement activation was assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, immunoblotting, and ELISA. Urine and plasma from patients with diabetic nephropathy treated with high-dose amiloride and from mice with proteinuria (podocin knockout [KO]) treated with amiloride or inhibitory anti-uPA antibodies were analyzed.

RESULTS

The combination of uPA and plasminogen generated anaphylatoxins C3a and C5a from intact C3 and C5 and was inhibited by amiloride. Addition of exogenous plasminogen was sufficient for urine from healthy humans to activate complement. Conditional podocin KO in mice led to severe proteinuria and C3a and C5a urine excretion, which was attenuated reversibly by amiloride treatment for 4 days and reduced by >50% by inhibitory anti-uPA antibodies without altering proteinuria. NOD-, LRR- and pyrin domain-containing protein 3-inflammasome protein was reduced with no concomitant effect on fibrosis. In patients with diabetic nephropathy, amiloride reduced urinary excretion of C3dg and sC5b-9 significantly.

CONCLUSIONS

In conditions with proteinuria, uPA-plasmin generates anaphylatoxins in tubular fluid and promotes downstream complement activation sensitive to amiloride. This mechanism links proteinuria to intratubular proinflammatory signaling. In perspective, amiloride could exert reno-protective effects beyond natriuresis and BP reduction.

CLINICAL TRIAL REGISTRY NAME AND REGISTRATION NUMBER

Increased Activity of a Renal Salt Transporter (ENaC) in Diabetic Kidney Disease, NCT01918488 and Increased Activity of ENaC in Proteinuric Kidney Transplant Recipients, NCT03036748 .

Protease-Activated Receptor 1-Mediated Damage of Podocytes in Diabetic Nephropathy

There is clinical evidence that increased urinary serine proteases are associated with the disease severity in the setting of diabetic nephropathy (DN). Elevation of serine proteases may mediate [Ca2+]i dynamics in podocytes through the protease-activated receptors (PARs) pathway, including associated activation of nonspecific cation channels. Cultured human podocytes and freshly isolated glomeruli were used for fluorescence and immunohistochemistry stainings, calcium imaging, Western blot analysis, scanning ion conductance microscopy, and patch clamp analysis. Goto-Kakizaki, Wistar, type 2 DN (T2DN), and a novel PAR1 knockout on T2DN rat background rats were used to test the importance of PAR1-mediated signaling in DN settings. We found that PAR1 activation increases [Ca2+]i via TRPC6 channels. Both human cultured podocytes exposed to high glucose and podocytes from freshly isolated glomeruli of T2DN rats had increased PAR1-mediated [Ca2+]i compared with controls. Imaging experiments revealed that PAR1 activation plays a role in podocyte morphological changes. T2DN rats exhibited a significantly higher response to thrombin and urokinase. Moreover, the plasma concentration of thrombin in T2DN rats was significantly elevated compared with Wistar rats. T2DNPar1-/- rats were embryonically lethal. T2DNPar1+/- rats had a significant decrease in glomerular damage associated with DN lesions. Overall, these data provide evidence that, during the development of DN, elevated levels of serine proteases promote an excessive [Ca2+]i influx in podocytes through PAR1-TRPC6 signaling, ultimately leading to podocyte apoptosis, the development of albuminuria, and glomeruli damage.

ARTICLE HIGHLIGHTS

Increased urinary serine proteases are associated with diabetic nephropathy. During the development of diabetic nephropathy in type 2 diabetes, the elevation of serine proteases could overstimulate protease-activated receptor 1 (PAR1). PAR1 signaling is involved in the development of DN via TRPC6-mediated intracellular calcium signaling. This study provides fundamental knowledge that can be used to develop efficient therapeutic approaches targeting serine proteases or corresponding PAR pathways to prevent or slow the progression of diabetes-associated kidney diseases.

Circulating extracellular vesicles in human cardiorenal syndrome promote renal injury in a kidney-on-chip system

BACKGROUNDCardiorenal syndrome (CRS) - renal injury during heart failure (HF) - is linked to high morbidity. Whether circulating extracellular vesicles (EVs) and their RNA cargo directly impact its pathogenesis remains unclear.METHODSWe investigated the role of circulating EVs from patients with CRS on renal epithelial/endothelial cells using a microfluidic kidney-on-chip (KOC) model. The small RNA cargo of circulating EVs was regressed against serum creatinine to prioritize subsets of functionally relevant EV-miRNAs and their mRNA targets investigated using in silico pathway analysis, human genetics, and interrogation of expression in the KOC model and in renal tissue. The functional effects of EV-RNAs on kidney epithelial cells were experimentally validated.RESULTSRenal epithelial and endothelial cells in the KOC model exhibited uptake of EVs from patients with HF. HF-CRS EVs led to higher expression of renal injury markers (IL18, LCN2, HAVCR1) relative to non-CRS EVs. A total of 15 EV-miRNAs were associated with creatinine, targeting 1,143 gene targets specifying pathways relevant to renal injury, including TGF-β and AMPK signaling. We observed directionally consistent changes in the expression of TGF-β pathway members (BMP6, FST, TIMP3) in the KOC model exposed to CRS EVs, which were validated in epithelial cells treated with corresponding inhibitors and mimics of miRNAs. A similar trend was observed in renal tissue with kidney injury. Mendelian randomization suggested a role for FST in renal function.CONCLUSIONPlasma EVs in patients with CRS elicit adverse transcriptional and phenotypic responses in a KOC model by regulating biologically relevant pathways, suggesting a role for EVs in CRS.TRIAL REGISTRATIONClinicalTrials.gov NCT03345446.FUNDINGAmerican Heart Association (AHA) (SFRN16SFRN31280008); National Heart, Lung, and Blood Institute (1R35HL150807-01); National Center for Advancing Translational Sciences (UH3 TR002878); and AHA (23CDA1045944).

Oral Furosemide and Hydrochlorothiazide/Amiloride versus Intravenous Furosemide for the Treatment of Resistant Nephrotic Syndrome

BACKGROUND

Data on diuretic treatment in nephrotic syndrome (NS) are scarce. Our goal was to assess the non-inferiority of the combined oral diuretics (furosemide/hydrochlorothiazide/amiloride) compared to intravenous (i.v.) furosemide in patients with NS and resistant edema.

METHODS

We conducted a prospective randomized trial on 22 patients with resistant nephrotic edema (RNE), defined as hypervolemia and a FENa < 0.2%. Based on a computer-generated 1:1 randomization, we assigned patients to receive either intravenous furosemide (40 mg bolus and then continuous administration of 5 mg/h) or oral furosemide (40 mg/day) and hydrochlorothiazide/amiloride (50/5 mg/day) for a period of 5 days. Clinical and laboratory measurements were performed daily. Hydration status was assessed by bioimpedance on day 1 and at the end of day 5 after treatment initiation. The primary endpoint was weight change from baseline to day 5. Secondary endpoints were hydration status change measured by bioimpedance and safety outcomes (low blood pressure, severe electrolyte disturbances, acute kidney injury and worsening hypervolemia).

RESULTS

Primary endpoint analysis showed that after 5 days of treatment, there was a significant difference in weight change from baseline between groups [adjusted mean difference: -3.33 kg (95% CI: -6.34 to -0.31), p = 0.03], with a higher mean weight change in the oral diuretic treatment group [-7.10 kg (95% CI: -18.30 to -4.30) vs. -4.55 kg (95%CI: -6.73 to -2.36)]. Secondary endpoint analysis showed that there was no significant difference between groups regarding hydration status change [adjusted mean difference: -0.05 L (95% CI: -2.6 to 2.6), p = 0.96], with a mean hydration status change in the oral diuretic treatment group of -4.71 L (95% CI: -6.87 to -2.54) and -3.91 L (95% CI: -5.69 to -2.13) in the i.v. diuretic treatment group. We observed a significant decrease in adjusted mean serum sodium of -2.15 mmol/L [(95% CI: -4.25 to -0.05), p = 0.04]), favored by the combined oral diuretic treatment [-2.70 mmol/L (95% CI: -4.89 to -0.50) vs. -0.10 mmol/L (95%CI: -1.30 to 1.10)]. No statistically significant difference was observed between the two groups in terms of adverse events.

CONCLUSIONS

A combination of oral diuretics based on furosemide, amiloride and hydrochlorothiazide is non-inferior to i.v. furosemide in weight control of patients with RNE and a similar safety profile.

A Serine Protease Inhibitor, Camostat Mesilate, Suppresses Urinary Plasmin Activity and Alleviates Hypertension and Podocyte Injury in Dahl Salt-Sensitive Rats

In proteinuric renal diseases, the serine protease (SP) plasmin activates the epithelial sodium channel (ENaC) by cleaving its γ subunit. We previously demonstrated that a high-salt (HS) diet provoked hypertension and proteinuria in Dahl salt-sensitive (DS) rats, accompanied by γENaC activation, which were attenuated by camostat mesilate (CM), an SP inhibitor. However, the effects of CM on plasmin activity in DS rats remain unclear. In this study, we investigated the effects of CM on plasmin activity, ENaC activation, and podocyte injury in DS rats. The DS rats were divided into the control diet, HS diet (8.0% NaCl), and HS+CM diet (0.1% CM) groups. After weekly blood pressure measurement and 24-h urine collection, the rats were sacrificed at 5 weeks. The HS group exhibited hypertension, massive proteinuria, increased urinary plasmin, and γENaC activation; CM treatment suppressed these changes. CM prevented plasmin(ogen) attachment to podocytes and mitigated podocyte injury by reducing the number of apoptotic glomerular cells, inhibiting protease-activated receptor-1 activation, and suppressing inflammatory and fibrotic cytokine expression. Our findings highlight the detrimental role of urinary plasmin in the pathogenesis of salt-sensitive hypertension and glomerular injury. Targeting plasmin with SP inhibitors, such as CM, may be a promising therapeutic approach for these conditions.

Amiloride evokes significant natriuresis and weight loss in kidney transplant recipients with and without albuminuria

Albuminuria in kidney transplant recipients (KTRs) is associated with hypertension and aberrant glomerular filtration of serine proteases that may proteolytically activate the epithelial Na+ channel (ENaC). The present nonrandomized, pharmacodynamic intervention study aimed to investigate if inhibition of ENaC increases Na+ excretion and reduces extracellular volume in KTRs dependent on the presence of albuminuria. KTRs with and without albuminuria (albumin-to-creatinine ratio > 300 mg/g, n = 7, and <30 mg/g, n = 7, respectively) were included and ingested a diet with fixed Na+ content (150 mmol/day) for 5 days. On the last day, amiloride at 10 mg was administered twice. Body weight, 24-h urine electrolyte excretion, body water content, and ambulatory blood pressure as well as plasma renin, angiotensin II, and aldosterone concentrations were determined before and after amiloride. Amiloride led to a significant decrease in body weight, increase in 24-h urinary Na+ excretion, and decrease in 24-h urinary K+ excretion in both groups. Urine output increased in the nonalbuminuric group only. There was no change in plasma renin, aldosterone, and angiotensin II concentrations after amiloride, whereas a significant decrease in nocturnal systolic blood pressure and increase in 24-h urine aldosterone excretion was observed in albuminuric KTRs only. There was a significant correlation between 24-h urinary albumin excretion and amiloride-induced 24-h urinary Na+ excretion. In conclusion, ENaC activity contributes to Na+ and water retention in KTRs with and without albuminuria. ENaC is a relevant pharmacological target in KTRs; however, larger and long-term studies are needed to evaluate whether the magnitude of this effect depends on the presence of albuminuria.NEW & NOTEWORTHY Amiloride has a significant natriuretic effect in kidney transplant recipients (KTRs) that relates to urinary albumin excretion. The epithelial Na+ channel may be a relevant direct pharmacological target to counter Na+ retention and hypertension in KTRs. Epithelial Na+ channel blockers should be further investigated as a mean to mitigate Na+ and water retention and to potentially obtain optimal blood pressure control in KTRs.

Intrarenal Mechanisms of Sodium-Glucose Cotransporter-2 Inhibitors on Tubuloglomerular Feedback and Natriuresis

When sodium-glucose cotransporter-2 (SGLT2) inhibitors were first introduced a decade ago, no one expected them to have substantial effects beyond their known glucose-lowering effects, until the emergence of evidence of their robust renal and cardiovascular benefits showing that they could attenuate progression of kidney disease, irrespective of diabetes, as well as prevent the development of acute kidney injury. Still, the precise and elaborate mechanisms underlying the major organ protection of SGLT2 inhibitors remain unclear. SGLT2 inhibitors inhibit the reabsorption of sodium and glucose in the proximal tubule of the kidney and then recovers tubuloglomerular feedback, whereby SGLT2 inhibitors reduce glomerular hyperfiltration. This simple demonstration of their beneficial effects has perplexed experts in seeking more plausible and as yet undisclosed explanations for the whole effects of SGLT2 inhibitors, including metabolism reprogramming and the modulation of hypoxia, inflammation, and oxidative stress. Given that the renal benefits of SGLT2 inhibitors in patients with kidney disease but without diabetes were comparable to those seen in patients with diabetes, it may be reasonable to keep the emphasis on their hemodynamic actions. In this context, the aim of the present review is to provide a comprehensive overview of renal hemodynamics in individuals with diabetes who are treated with SGLT2 inhibitors, with a focus on natriuresis associated with the regulation of tubuloglomerular feedback and potential aquaresis. Throughout the discussion of alterations in renal sodium and water transports, particular attention will be given to the potential enhancement of adenosine and its receptors following SGLT2 inhibition.

TRAIL and EGFR Pathways Targeting microRNAs are Predominantly Regulated in Human Diabetic Nephropathy

BACKGROUND

Unbiased microRNA profiling of renal tissue and urinary extracellular vesicles (uEVs) from diabetic nephropathy (DN) subjects may unravel novel targets with diagnostic and therapeutic potential. Here we used the miRNA profile of uEVs and renal biopsies from DN subjects available on the GEO database.

METHODS

The miR expression profiles of kidney tissue (GSE51674) and urinary exosomes (GSE48318) from DN and control subjects were obtained by GEO2R tools from Gene Expression Omnibus (GEO) databases. Differentially expressed miRNAs in DN samples, relative to controls, were identified using a bioinformatic pipeline. Targets of miRs commonly regulated in both sample types were predicted by miRWalk, followed by functional gene enrichment analysis. Gene targets were identified by MiRTarBase, TargetScan and MiRDB.

RESULTS

Eight miRs, including let-7c, miR-10a, miR-10b and miR-181c, were significantly regulated in kidney tissue and uEVs in DN subjects versus controls. The top 10 significant pathways targeted by these miRs included TRAIL, EGFR, Proteoglycan syndecan, VEGF and Integrin Pathway. Gene target analysis by miRwalk upon validation using ShinyGO 70 targets with significant miRNA-mRNA interaction.

CONCLUSION

In silico analysis showed that miRs targeting TRAIL and EGFR signaling are predominately regulated in uEVs and renal tissue of DN subjects. After wet-lab validation, the identified miRstarget pairs may be explored for their diagnostic and/or therapeutic potential in diabetic nephropathy.

The serine protease plasmin plays detrimental roles in epithelial sodium channel activation and podocyte injury in Dahl salt-sensitive rats

Salt-sensitive hypertension is associated with poor clinical outcomes. The epithelial sodium channel (ENaC) in the kidney plays pivotal roles in sodium reabsorption and blood pressure regulation, in which its γ subunit is activated by extracellular serine proteases. In proteinuric nephropathies, plasmin filtered through injured glomeruli reportedly activates γENaC in the distal nephron and causes podocyte injury. We previously reported that Dahl salt-sensitive (DS) rats fed a high-salt (HS) diet developed hypertension and proteinuria along with γENaC activation and that a synthetic serine protease inhibitor, camostat mesilate, mitigated these changes. However, the role of plasmin in DS rats remained unclear. In this study, we evaluated the relationship between plasmin and hypertension as well as podocyte injury and the effects of plasmin inhibitors in DS rats. Five-week-old DS rats were divided into normal-salt diet, HS diet, and HS+plasmin inhibitor (either tranexamic acid [TA] or synthetic plasmin inhibitor YO-2) groups. After blood pressure measurement and 24 h urine collection over 5 weeks, rats were sacrificed for biochemical analyses. The HS group displayed severe hypertension and proteinuria together with activation of plasmin in urine and γENaC in the kidney, which was significantly attenuated by YO-2 but not TA. YO-2 inhibited the attachment of plasmin(ogen) to podocytes and alleviated podocyte injury by inhibiting apoptosis and inflammatory/profibrotic cytokines. YO-2 also suppressed upregulation of protease-activated receptor-1 and phosphorylated ERK1/2. These results indicate an important role of plasmin in the development of salt-sensitive hypertension and related podocyte injury, suggesting plasmin inhibition as a potential therapeutic strategy.

Transforming Growth Factorβ1 Overexpression Is Associated with Insulin Resistance and Rapidly Progressive Kidney Fibrosis under Diabetic Conditions

Diabetes mellitus is a global health problem. Diabetic nephropathy is a common complication of diabetes mellitus and the leading cause of end-stage renal disease. The clinical course, response to therapy, and prognosis of nephropathy are worse in diabetic than in non-diabetic patients. The role of transforming growth factorβ1 in kidney fibrosis is undebatable. This study assessed whether the overexpression of transforming growth factorβ1 is associated with insulin resistance and the rapid progression of transforming growth factorβ1-mediated nephropathy under diabetic conditions. Diabetes mellitus was induced with streptozotocin in wild-type mice and transgenic mice with the kidney-specific overexpression of human transforming growth factorβ1. Mice treated with saline were the controls. Glucose tolerance and kidney fibrosis were evaluated. The blood glucose levels, the values of the homeostasis model assessment for insulin resistance, and the area of kidney fibrosis were significantly increased, and the renal function was significantly impaired in the diabetic transforming growth factorβ1 transgenic mice compared to the non-diabetic transgenic mice, diabetic wild-type mice, and non-diabetic mice. Transforming growth factorβ1 impaired the regulatory effect of insulin on glucose in the hepatocyte and skeletal muscle cell lines. This study shows that transforming growth factorβ1 overexpression is associated with insulin resistance and rapidly progressive kidney fibrosis under diabetic conditions in mice.

Expression of growth arrest specific 1 (Gas1) in the distal tubules and collecting ducts in normal kidney and in the early stages of diabetic nephropathy

The Growth Arrest-Specific protein 1 (Gas1) has been recently described in kidney as an endogenous inhibitor of cell proliferation in mesangial cells and with an important role in the maintenance of nephron progenitor cells. Furthermore, the expression of Gas1 was demonstrated in NCAM + progenitor parietal cells of Bowman's capsule. Thus, the aim of this study was to analyze the expression of Gas1 in the collecting ducts (CD) of healthy rats and to examine whether high glucose levels modify its expression during the early stages of diabetes in STZ-treated rats. Immunofluorescence reveals that principal cells AQP2 + express Gas1 in both healthy and diabetic conditions. Western blot from enriched fractions of medullary CD suggests that diabetes promotes the increase of Gas1. AQP2 + cells are also positive for the expression of CD24 and CD1133 in diabetic rats. In addition, diabetes modifies the cell morphology in the CD and favors the increase of principal cells (AQP2+/Gas1+), induces a significant decrease of intercalated cells (V-ATPase+/Gas1-) and the presence of intermediate cells (Gas1+/V-ATPase+) which express both principal and intercalated cell markers. The expression of Gas1 in the distal tubules was also determined by immunofluorescence, western blot and ELISA in diabetic rats. The results identify Gas1 as a specific marker of principal cells in healthy and diabetic rats and suggest that diabetes promotes the expression of Gas1. Gas1 may have an important role in the maintenance and differentiation to principal cells in the CD during early stages of diabetes.

Mining the Biomarker Potential of the Urine Peptidome: From Amino Acids Properties to Proteases

Native biofluid peptides offer important information about diseases, holding promise as biomarkers. Particularly, the non-invasive nature of urine sampling, and its high peptide concentration, make urine peptidomics a useful strategy to study the pathogenesis of renal conditions. Moreover, the high number of detectable peptides as well as their specificity set the ground for the expansion of urine peptidomics to the identification of surrogate biomarkers for extra-renal diseases. Peptidomics further allows the prediction of proteases (degradomics), frequently dysregulated in disease, providing a complimentary source of information on disease pathogenesis and biomarkers. Then, what does urine peptidomics tell us so far? In this paper, we appraise the value of urine peptidomics in biomarker research through a comprehensive analysis of all datasets available to date. We have mined > 50 papers, addressing > 30 different conditions, comprising > 4700 unique peptides. Bioinformatic tools were used to reanalyze peptide profiles aiming at identifying disease fingerprints, to uncover hidden disease-specific peptides physicochemical properties and to predict the most active proteases associated with their generation. The molecular patterns found in this study may be further validated in the future as disease biomarker not only for kidney diseases but also for extra-renal conditions, as a step forward towards the implementation of a paradigm of predictive, preventive and personalized (3P) medicine.

Zymogen-locked mutant prostasin (Prss8) leads to incomplete proteolytic activation of the epithelial sodium channel (ENaC) and severely compromises triamterene tolerance in mice

AIM

The serine protease prostasin (Prss8) is expressed in the distal tubule and stimulates proteolytic activation of the epithelial sodium channel (ENaC) in co-expression experiments in vitro. The aim of this study was to explore the role of prostasin in proteolytic ENaC activation in the kidney in vivo.

METHODS

We used genetically modified knockin mice carrying a Prss8 mutation abolishing proteolytic activity (Prss8-S238A) or a mutation leading to a zymogen-locked state (Prss8-R44Q). Mice were challenged with low sodium diet and diuretics. Regulation of ENaC activity by Prss8-S238A and Prss8-R44Q was studied in vitro using the Xenopus laevis oocyte expression system.

RESULTS

Co-expression of murine ENaC with Prss8-wt or Prss8-S238A in oocytes caused maximal proteolytic ENaC activation, whereas ENaC was activated only partially in oocytes co-expressing Prss8-R44Q. This was paralleled by a reduced proteolytic activity at the cell surface of Prss8-R44Q expressing oocytes. Sodium conservation under low sodium diet was preserved in Prss8-S238A and Prss8-R44Q mice but with higher plasma aldosterone concentrations in Prss8-R44Q mice. Treatment with the ENaC inhibitor triamterene over four days was tolerated in Prss8-wt and Prss8-S238A mice, whereas Prss8-R44Q mice developed salt wasting and severe weight loss associated with hyperkalemia and acidosis consistent with impaired ENaC function and renal failure.

CONCLUSION

Unlike proteolytically inactive Prss8-S238A, zymogen-locked Prss8-R44Q produces incomplete proteolytic ENaC activation in vitro and causes a severe renal phenotype in mice treated with the ENaC inhibitor triamterene. This indicates that Prss8 plays a role in proteolytic ENaC activation and renal function independent of its proteolytic activity.

Importance of extracellular vesicles in hypertension

Hypertension affects approximately 1.13 billion adults worldwide and is the leading global risk factor for cardiovascular, cerebrovascular, and kidney diseases. There is emerging evidence that extracellular vesicles participate in the development and progression of hypertension. Extracellular vesicles are membrane-enclosed structures released from nearly all types of eukaryotic cells. During their formation, extracellular vesicles incorporate various parent cell components, including proteins, lipids, and nucleic acids that can be transferred to recipient cells. Extracellular vesicles mediate cell-to-cell communication in a variety of physiological and pathophysiological processes. Therefore, studying the role of circulating and urinary extracellular vesicles in hypertension has the potential to identify novel noninvasive biomarkers and therapeutic targets of different hypertension phenotypes. This review discusses the classification and biogenesis of three EV subcategories (exosomes, microvesicles, and apoptotic bodies) and provides a summary of recent discoveries in the potential impact of extracellular vesicles on hypertension with a specific focus on their role in the blood pressure regulation by organs-artery and kidney, as well as renin-angiotensin-system.

Exosomes: Biomarkers and Therapeutic Targets of Diabetic Vascular Complications

Diabetic vascular complications (DVC) including macrovascular and microvascular lesions, have a significant impact on public health, and lead to increased patient mortality. Disordered intercellular cascades play a vital role in diabetic systemic vasculopathy. Exosomes participate in the abnormal signal transduction of local vascular cells and mediate the transmission of metabolic disorder signal molecules in distant organs and cells through the blood circulation. They can store different signaling molecules in the membrane structure and release them into the blood, urine, and tears. In recent years, the carrier value and therapeutic effect of exosomes derived from stem cells have garnered attention. Exosomes are not only a promising biomarker but also a potential target and tool for the treatment of DVC. This review explored changes in the production process of exosomes in the diabetic microenvironment and exosomes' early warning role in DVC from different systems and their pathological processes. On the basis of these findings, we discussed the future direction of exosomes in the treatment of DVC, and the current limitations of exosomes in DVC research.

Plasminogenuria is associated with podocyte injury, edema, and kidney dysfunction in incident glomerular disease

Urinary plasminogen/plasmin, or plasmin (ogen) uria, has been demonstrated in proteinuric patients and exposure of cultured podocytes to plasminogen results in injury via oxidative stress pathways. A causative role for plasmin (ogen) as a "second hit" in kidney disease progression has yet to have been demonstrated in vivo. Additionally, association between plasmin (ogen) uria and kidney function in glomerular diseases remains unclear. We performed comparative studies in a puromycin aminonucleoside (PAN) nephropathy rat model treated with amiloride, an inhibitor of plasminogen activation, and measured changes in plasmin (ogen) uria. In a glomerular disease biorepository cohort (n = 128), we measured time-of-biopsy albuminuria, proteinuria, and plasmin (ogen) uria for correlations with kidney outcomes. In cultured human podocytes, plasminogen treatment was associated with decreased focal adhesion marker expression with rescue by amiloride. Increased glomerular plasmin (ogen) was found in PAN rats and focal segmental glomerulosclerosis (FSGS) patients. PAN nephropathy was associated with increases in plasmin (ogen) uria and proteinuria. Amiloride was protective against PAN-induced glomerular injury, reducing CD36 scavenger receptor expression and oxidative stress. In patients, we found associations between plasmin (ogen) uria and edema status as well as eGFR. Our study demonstrates a role for plasmin (ogen)-induced podocyte injury in the PAN nephropathy model, with amiloride having podocyte-protective properties. In one of the largest glomerular disease cohorts to study plasminogen, we validated previous findings while suggesting a potentially novel relationship between plasmin (ogen) uria and estimated glomerular filtration rate (eGFR). Together, these findings suggest a role for plasmin (ogen) in mediating glomerular injury and as a viable targetable biomarker for podocyte-sparing treatments.

Plasminogen Deficiency and Amiloride Mitigate Angiotensin II-Induced Hypertension in Type 1 Diabetic Mice Suggesting Effects Through the Epithelial Sodium Channel

Background Diabetic nephropathy is a common diabetes mellitus complication associated with hypertension, proteinuria, and excretion of urinary plasmin that activates the epithelial sodium channel, ENaC, in vitro. Here we hypothesized that the deletion of plasminogen and amiloride treatment protect against hypertension in diabetes mellitus. Methods and Results Male plasminogen knockout (plasminogen-deficient [Plg^-/-]) and wild-type mice were rendered diabetic with streptozotocin. Arterial blood pressure was recorded continuously by indwelling catheters before and during 10 days of angiotensin II infusion (ANGII; 30-60 ng/kg per minute). The effect of amiloride infusion (2 mg/kg per day, 4 days) was tested in wild-type, diabetic ANGII-treated mice. Streptozotocin increased plasma and urine glucose concentrations and 24-hour urine albumin and plasminogen excretion. Diabetic Plg^-/- mice displayed larger baseline albuminuria and absence of urine plasminogen. Baseline mean arterial blood pressure did not differ between groups. Although ANGII elevated blood pressure in wild-type, diabetic wild-type, and Plg^-/- control mice, ANGII did not change blood pressure in diabetic Plg^-/- mice. Compared with ANGII infusion alone, wild-type ANGII-infused diabetic mice showed blood pressure reduction upon amiloride treatment. There was no difference in plasma renin, ANGII, aldosterone, tissue prorenin receptor, renal inflammation, and fibrosis between groups. Urine from wild-type mice evoked larger amiloride-sensitive current than urine from Plg^-/- mice with or without diabetes mellitus. Full-length γ-ENaC and α-ENaC subunit abundances were not changed in kidney homogenates, but the 70 kDa γ-ENaC cleavage product was increased in diabetic versus nondiabetic mice. Conclusions Plasmin promotes hypertension in diabetes mellitus with albuminuria likely through the epithelial sodium channel.

Elevated Plasmin(ogen) as a Common Risk Factor for COVID-19 Susceptibility

Patients with hypertension, diabetes, coronary heart disease, cerebrovascular illness, chronic obstructive pulmonary disease, and kidney dysfunction have worse clinical outcomes when infected with SARS-CoV-2, for unknown reasons. The purpose of this review is to summarize the evidence for the existence of elevated plasmin(ogen) in COVID-19 patients with these comorbid conditions. Plasmin, and other proteases, may cleave a newly inserted furin site in the S protein of SARS-CoV-2, extracellularly, which increases its infectivity and virulence. Hyperfibrinolysis associated with plasmin leads to elevated D-dimer in severe patients. The plasmin(ogen) system may prove a promising therapeutic target for combating COVID-19.

Roles for Exosome in Various Kidney Diseases and Disorders

Exosome is a nanoscale vesicle with a size range of 30–100 nm. It is secreted from cell to extracellular space by exocytosis after fusion of multivesicular body (MVB) (formed by endocytic vesicles) with plasma membrane. Exosome plays several important roles in cellular homeostasis and intercellular communications. During the last two decades, exosome has acquired a wide attention to explore its additional roles in various aspects of cell biology and function in several organ systems. For the kidney, several lines of evidence have demonstrated 1that exosome is involved in the renal physiology and pathogenic mechanisms of various kidney diseases/disorders. This article summarizes roles of the exosome as the potential source of biomarkers, pathogenic molecules, and therapeutic biologics that have been extensively investigated in many kidney diseases/disorders, including lupus nephritis (LN), other glomerular diseases, acute kidney injury (AKI), diabetic nephropathy (DN), as well as in the process of renal fibrosis and chronic kidney disease (CKD) progression, in addition to polycystic kidney disease (PKD), kidney transplantation, and renal cell carcinoma (RCC). Moreover, the most recent evidence has shown its emerging role in kidney stone disease (or nephrolithiasis), involving inflammasome activation and inflammatory cascade frequently found in kidney stone pathogenesis.

Urinary extracellular vesicles: Origin, role as intercellular messengers and biomarkers; efficient sorting and potential treatment options

Urinary extracellular vesicles (uEVs) are a heterogenous group of vesicles consisting mainly of microvesicles and exosomes that originate predominantly (99.96%) from kidney, the urinary tract epithelium and the male reproductive tract. Secreted EVs contain molecular cargo from parental cells and provide an attractive source for biomarkers, a potential readout of physiological and pathophysiological mechanisms, and events associated with the urinary system. uEVs are readily enriched and isolated from urine samples and we review 6 standard methods that allow for downstream analysis of the uEV cargo. Although the use of uEVs as a surrogate readout for physiological changes in tissue protein levels is widespread, the protein abundance in uEVs is affected significantly by mechanisms that regulate protein sorting and secretion in uEVs. Data suggest that baseline kidney tissue and uEV levels of apical membrane-associated electrolyte transport proteins are not directly related in human patients. Recent evidence indicates that EVs may contribute to physiological and pathophysiological intercellular signalling and EVs confer protection against renal ischemia-reperfusion injury. The therapeutic use of EVs as information carriers has mainly been explored in vitro and a major hurdle lies in the translation of the in vitro findings into an in vivo setting. Thus, the EV research field is moving from a technical focus to a more physiological focus, allowing for a deeper understanding of human physiology, development of diagnostic tools and potential treatment strategies for precision medicine.

Dietary Na+ intake in healthy humans changes the urine extracellular vesicle prostasin abundance while the vesicle excretion rate, NCC, and ENaC are not altered

Low Na+ intake activates aldosterone signaling, which increases renal Na+ reabsorption through increased apical activity of the NaCl cotransporter (NCC) and the epithelial Na+ channel (ENaC). Na+ transporter proteins are excreted in urine as an integral part of cell-derived extracellular vesicles (uEVs). It was hypothesized that Na+ transport protein levels in uEVs from healthy humans reflect their physiological regulation by aldosterone. Urine and plasma samples from 10 healthy men (median age: 22.8 yr) were collected after 5 days on a low-Na+ (70 mmol/day) diet and 5 days on a high-Na+ (250 mmol/day) diet. uEVs were isolated by ultracentrifugation and analyzed by Western blot analysis for EV markers (CD9, CD63, and ALIX), transport proteins (Na+-K+-ATPase α1-subunit, NCC, ENaC α- and γ-subunits, and aquaporin 2), and the ENaC-cleaving protease prostasin. Plasma renin and aldosterone concentrations increased during the low-Na+ diet. uEV size and concentration were not different between diets by tunable resistive pulse sensing. EV markers ALIX and CD9 increased with the low-Na+ diet, whereas CD63 and aquaporin 2 excretion were unchanged. Full-length ENaC γ-subunits were generally not detectable in uEVs, whereas ENaC α-subunits, NCC, and phosphorylated NCC were consistently detected but not changed by Na+ intake. Prostasin increased with low Na+ in uEVs. uEV excretion of transporters was not correlated with blood pressure, urinary Na+ and K+ excretion, plasma renin, or aldosterone. In conclusion, apical Na+ transporter proteins and proteases were excreted in uEVs, and while the excretion rate and size of uEVs were not affected, EV markers and prostasin increased in response to the low-Na+ diet.

Urokinase-type plasminogen activator contributes to amiloride-sensitive sodium retention in nephrotic range glomerular proteinuria in mice

AIM

Activation of sodium reabsorption by urinary proteases has been implicated in sodium retention associated with nephrotic syndrome. The study was designed to test the hypothesis that nephrotic proteinuria in mice after conditional deletion of podocin leads to urokinase-dependent, amiloride-sensitive plasmin-mediated sodium and water retention.

METHODS

Ten days after podocin knockout, urine and faeces were collected for 10 days in metabolic cages and analysed for electrolytes, plasminogen, protease activity and ability to activate γENaC by patch clamp and western blot. Mice were treated with amiloride (2.5 mg kg^-1 for 2 days and 10 mg kg^-1 for 2 days) or an anti-urokinase-type plasminogen activator (uPA) targeting antibody (120 mg kg^-1 /24 h) and compared to controls.

RESULTS

Twelve days after deletion, podocin-deficient mice developed significant protein and albuminuria associated with increased body wt, ascites, sodium accumulation and suppressed plasma renin. This was associated with increased urinary excretion of plasmin and plasminogen that correlated with albumin excretion, urine protease activity co-migrating with active plasmin, and the ability of urine to induce an amiloride-sensitive inward current in M1 cells in vitro. Amiloride treatment in podocin-deficient mice resulted in weight loss, increased sodium excretion, normalization of sodium balance and prevention of the activation of plasminogen to plasmin in urine in a reversible way. Administration of uPA targeting antibody abolished urine activation of plasminogen, attenuated sodium accumulation and prevented cleavage of γENaC.

CONCLUSIONS

Nephrotic range glomerular proteinuria leads to urokinase-dependent intratubular plasminogen activation and γENaC cleavage which contribute to sodium accumulation.

Regulating ENaC's gate

Epithelial Na⁺ channels (ENaCs) are members of a family of cation channels that function as sensors of the extracellular environment. ENaCs are activated by specific proteases in the biosynthetic pathway and at the cell surface and remove embedded inhibitory tracts, which allows channels to transition to higher open-probability states. Resolved structures of ENaC and an acid-sensing ion channel revealed highly organized extracellular regions. Within the periphery of ENaC subunits are unique domains formed by antiparallel β-strands containing the inhibitory tracts and protease cleavage sites. ENaCs are inhibited by Na⁺ binding to specific extracellular site(s), which promotes channel transition to a lower open-probability state. Specific inositol phospholipids and channel modification by Cys-palmitoylation enhance channel open probability. How these regulatory factors interact in a concerted manner to influence channel open probability is an important question that has not been resolved. These various factors are reviewed, and the impact of specific factors on human disorders is discussed.

Is urinary excretion of plasminogen associated with development of pre-eclampsia? An observational, explorative case-control study

OBJECTIVES

Pre-eclampsia (PE) is characterised by renal glomerular endotheliosis and injury to the glomerular filtration barrier with proteinuria. Patients with PE display aberrant filtration of the plasma proenzyme plasminogen which is activated, in the tubular fluid, to plasmin. Plasmin may activate the epithelial sodium channel and cause impaired sodium excretion and contribute to hypertension. An explorative study was conducted to test the association between urinary total plasminogen/plasmin and the development of PE. A positive association was hypothesised.

DESIGN

An observational, explorative, nested case-control study of healthy pregnant women.

SETTINGS

A Danish County hospital. Samples were collected between 2001 and 2004.

PARTICIPANTS

1631 healthy pregnant women participated. Urine samples were collected longitudinally six times during pregnancy. 30 developed PE (cases) and were compared with 146 randomly selected healthy pregnant women (controls).

PRIMARY OUTCOME

The association between total plasminogen/plasmin excreted in the urine and PE development is expressed by ORs. Total urinary excretion of plasminogen/plasmin was defined by the urine plasminogen-plasmin/creatinine ratio.

SECONDARY OUTCOME

The association between urine (u)-albumin/creatinine ratio, u-aldosterone/creatinine ratio and PE development is expressed by ORs. The correlation between urinary (u-) plasmin and u-aldosterone concentration is expressed as a correlation coefficient.

RESULTS

The development of PE in late pregnancy was associated with increased levels of the urine plasminogen-plasmin/creatinine ratio (OR=2.35; 95% CI: 1.12 to 4.93; p<0.05).U-aldosterone/creatinine ratio did not predict PE at any time. U-albumin/creatinine ratio was positively associated with the development of PE from gestational week 33 (OR=14.04; 95% CI: 2.56 to 76.97; p<0.01) and in week 33-35 (OR=14.15; 95% CI: 3.44 to 58.09; p<0.001) and after gestational week 36, respectively.

CONCLUSION

Aberrant filtration of plasminogen may contribute to the pathophysiological features of impaired sodium excretion and hypertension associated with PE late in pregnancy. However, increased urinary albumin levels reveal stronger associations with PE development compared with urinary plasminogen levels.

Proteasuria-The impact of active urinary proteases on sodium retention in nephrotic syndrome

Sodium retention and extracellular volume expansion are typical features of patients with nephrotic syndrome. In recent years, from in vitro data, endoluminal activation of the epithelial sodium channel (ENaC) by aberrantly filtered serine proteases has been proposed as an underlying mechanism. Recently, this concept was supported in vivo in nephrotic mice that were protected from proteolytic ENaC activation and sodium retention by the use of aprotinin for the pharmacological inhibition of urinary serine protease activity. These and other findings from studies in both rodents and humans highlight the impact of active proteases in the urine, or proteasuria, on ENaC-mediated sodium retention and edema formation in nephrotic syndrome. Targeting proteasuria could become a therapeutic approach to treat patients with nephrotic syndrome. However, pathophysiologically relevant proteases remain to be identified. In this review, we introduce the concept of proteasuria to explain tubular sodium avidity and conclude that proteasuria can be considered as a key mechanism of sodium retention in patients with nephrotic syndrome.

Ion channels and transporters in diabetic kidney disease

Type 1 and 2 diabetes mellitus are major medical epidemics affecting millions of patients worldwide. Diabetes mellitus is the leading cause of diabetic kidney disease (DKD), which is the most common cause of end-stage renal disease (ESRD). DKD is associated with significant changes in renal hemodynamics and electrolyte transport. Alterations in renal ion transport triggered by pathophysiological conditions in diabetes can exacerbate hypertension, accelerate renal injury, and are integral to the development of DKD. Renal ion transporters and electrolyte homeostasis play a fundamental role in functional changes and injury to the kidney during DKD. With the large number of ion transporters involved in DKD, understanding the roles of individual transporters as well as the complex cascades through which they interact is essential in the development of effective treatments for patients suffering from this disease. This chapter aims to gather current knowledge of the major renal ion transporters with altered expression and activity under diabetic conditions, and provide a comprehensive overview of their interactions and collective functions in DKD.

Palmitate Stimulates the Epithelial Sodium Channel by Elevating Intracellular Calcium, Reactive Oxygen Species, and Phosphoinositide 3-Kinase Activity

Previous studies indicate that the epithelial sodium channel (ENaC) in the kidney is upregulated in diabetes mellitus. Here, we show that ENaC single-channel activity in distal nephron cells was significantly increased by palmitate, a free fatty acid which is elevated in diabetes mellitus. We also show that palmitate increased intracellular Ca²⁺ and that after chelating intracellular Ca²⁺ with BAPTA-AM, palmitate failed to affect ENaC activity. Treatment of the cells with 2-aminoethoxydiphenyl borate (2-APB, an inhibitor of IP₃ receptors) abolished the elevation of both intracellular Ca²⁺ and ENaC activity. Treatment of the cells with apocynin (an NADPH oxidase inhibitor), dithiothreitol/NaHS (reducing agents), or LY294002 (a phosphoinositide 3-kinase (PI3K) inhibitor) prevented palmitate-induced ENaC activity, whereas thimerosal (an oxidizing agent) mimicked the effects of palmitate on ENaC activity. However, these treatments did not alter the levels of intracellular Ca²⁺, indicating that elevation of reactive oxygen species (ROS) and activation of PI3K are downstream of the signaling cascade. Since we have shown that ROS stimulate ENaC by activating PI3K, these data together suggest that palmitate first elevates intracellular Ca²⁺, then activates an NADPH oxidase to elevate intracellular ROS and PI3K activity, and finally increases ENaC activity via the activated PI3K.

Pre-eclampsia is associated with altered expression of the renal sodium transporters NKCC2, NCC and ENaC in urinary extracellular vesicles

Pre-eclampsia is a hypertensive disorder of pregnancy characterised by hypertension and sodium retention by the kidneys. To identify changes in sodium uptake proteins in the tubules of the distal nephron, we studied their expression in urinary extracellular vesicles or exosomes (uEVs). Urine was collected from women with pre-eclampsia or during normal pregnancy, and from healthy non-pregnant controls. uEVs were isolated by centrifugation and analyzed by Western blot. Expression, proteolytic cleavage and phosphorylation was determined by densitometric analysis normalized to the exosome marker CD9. Results showed a significant increase in phosphorylation of the activating S130 site in NKCC2, the drug target for frusemide, in women with pre-eclampsia compared with normal pregnant women. Phosphorylation of the activating sites T101/105 in NKCC2 was similar but the activating T60 site in NCC, the drug target for thiazide diuretics, showed significantly less phosphorylation in pre-eclampsia compared with normal pregnancy. Expression of the larger forms of the α subunit of ENaC, the drug target for amiloride, was significantly greater in pre-eclampsia, with more fragmentation of theγ subunit. The differences observed are predicted to increase the activity of NKCC2 and ENaC while reducing that of NCC. This will increase sodium reabsorption, and so contribute to hypertension in pre-eclampsia.

The Absence of the ACE N-Domain Decreases Renal Inflammation and Facilitates Sodium Excretion during Diabetic Kidney Disease

BACKGROUND

Recent evidence emphasizes the critical role of inflammation in the development of diabetic nephropathy. Angiotensin-converting enzyme (ACE) plays an active role in regulating the renal inflammatory response associated with diabetes. Studies have also shown that ACE has roles in inflammation and the immune response that are independent of angiotensin II. ACE's two catalytically independent domains, the N- and C-domains, can process a variety of substrates other than angiotensin I.

METHODS

To examine the relative contributions of each ACE domain to the sodium retentive state, renal inflammation, and renal injury associated with diabetic kidney disease, we used streptozotocin to induce diabetes in wild-type mice and in genetic mouse models lacking either a functional ACE N-domain (NKO mice) or C-domain (CKO mice).

RESULTS

In response to a saline challenge, diabetic NKO mice excreted 32% more urinary sodium compared with diabetic wild-type or CKO mice. Diabetic NKO mice also exhibited 55% less renal epithelial sodium channel cleavage (a marker of channel activity), 55% less renal IL-1β, 53% less renal TNF-α, and 53% less albuminuria than diabetic wild-type mice. This protective phenotype was not associated with changes in renal angiotensin II levels. Further, we present evidence that the anti-inflammatory tetrapeptide N-acetyl-seryl-asparyl-lysyl-proline (AcSDKP), an ACE N-domain-specific substrate that accumulates in the urine of NKO mice, mediates the beneficial effects observed in the NKO.

CONCLUSIONS

These data indicate that increasing AcSDKP by blocking the ACE N-domain facilitates sodium excretion and ameliorates diabetic kidney disease independent of intrarenal angiotensin II regulation.

Hydronephrosis is associated with elevated plasmin in urine in pediatric patients and rats and changes in NCC and γ-ENaC abundance in rat kidney

Obstruction of urine flow at the level of the pelvo-ureteric junction (UPJO) and subsequent development of hydronephrosis is one of the most common congenital renal malformations. UPJO is associated with development of salt-sensitive hypertension, which is set by the obstructed kidney, and with a stimulated renin-angiotensin-aldosterone system (RAAS) in rodent models. This study aimed at investigating the hypothesis that 1) in pediatric patients with UPJO the RAAS is activated before surgical relief of the obstruction; 2) in rats with UPJO the RAAS activation is reflected by increased abundance of renal aldosterone-stimulated Na transporters; and 3) the injured UPJO kidney allows aberrant filtration of plasminogen, leading to proteolytic activation of the epithelial Na channel γ-subunit (γ-ENaC). Hydronephrosis resulting from UPJO in pediatric patients and rats was associated with increased urinary plasminogen-to-creatinine ratio. In pediatric patients, plasma renin, angiotensin II, urine and plasma aldosterone, and urine soluble prorenin receptor did not differ significantly before or after surgery, or compared with controls. Increased plasmin-to-plasminogen ratio was seen in UPJO rats. Intact γ-ENaC abundance was not changed in UPJO kidney, whereas low-molecular cleavage product abundance increased. The Na-Cl cotransporter displayed significantly lower abundance in the UPJO kidney compared with the nonobstructed contralateral kidney. The Na-K-ATPase α-subunit was unaltered. Treatment with an angiotensin-converting enzyme inhibitor (8 days, captopril) significantly lowered blood pressure in UPJO rats. It is concluded that the RAAS contributes to hypertension following partial obstruction of urine flow at the pelvo-ureteric junction with potential contribution from proteolytic activation of ENaC.

Urinary Plasmin(ogen) as a Prognostic Factor for Hypertension

Introduction

Plasmin and its precursor, plasminogen, are detectable in urine from patients with glomerular disease. Urinary plasmin(ogen) levels correlate with blood pressure (BP) and may contribute to renal Na⁺ retention by activating the epithelial Na⁺ channel (ENaC). In a longitudinal nested-cohort study, we asked whether urinary plasmin(ogen) levels predict subsequent increase in BP, incident hypertension, or mortality in subjects with type I diabetes, who often develop proteinuria.

Methods

The Pittsburgh Epidemiology of Diabetes Complications (EDC) study followed up type I diabetic subjects for 25 years. Urine specimens from 70 subjects with a spectrum of baseline urinary albumin levels were examined. Outcomes included increased BP after 2 years (≥1 SD over baseline systolic or diastolic BP, examined via logistic regression), 25-year incident hypertension (≥140/90 mm Hg or initiating BP-lowering medications), and all-cause or cardiovascular mortality, examined using Cox regression.

Results

Subjects experiencing a 2-year increase in BP had higher baseline urinary plasmin(ogen)/creatinine levels (uPl/Cr) than other subjects (P = 0.04); the difference in baseline urinary albumin/creatinine levels (uAlb/Cr) was similar (P = 0.07). Baseline uPl/Cr was associated with increased 25-year hypertension incidence (hazard ratio = 2.05, P = 0.001), all-cause mortality (HR = 2.05, P = 0.01) and cardiovascular mortality (HR = 3.30, P = 0.005), although not independent of uAlb/Cr.

Conclusion

This is the first long-term prospective study addressing clinical outcomes associated with increased urinary plasmin(ogen). Findings are consistent with a role for plasmin(ogen) in promoting increased BP, but also demonstrate the difficulty in distinguishing effects due to plasmin(ogen) from those of albuminuria.

Liddle's-like syndrome associated with nephrotic syndrome secondary to membranous nephropathy: the first case report

Background

Liddle’s syndrome is a rare monogenic form of hypertension caused by truncating or missense mutations in the C termini of the epithelial sodium channel (ENaC) β or γ subunits. Patients with this syndrome present with early onset of hypertension, hypokalemia, metabolic alkalosis, hyporeninemia and hypoaldosteronism, and a potassium-sparing diuretics (triamterene or amiloride) can drastically improves the disease condition. Although elderly patients having these characteristics were considered to have Liddle’s syndrome or Liddle’s-like syndrome, no previous report has indicated that Liddle’s-like syndrome could be caused by nephrotic syndrome of primary glomerular disease, which is characterized by urinary excretion of > 3 g of protein/day plus edema and hypoalbuminemia, or has explained how the activity function of ENaC could be affected in the setting of high proteinuria.

Case presentation

A 65-year-old Japanese man presented with nephrotic syndrome. He had no remarkable family history, but had a medical history of hypertension and hyperlipidemia. On admission, hypertension, spironolactone-resistant hypokalemia (2.43 mEq/l), hyporeninemic hypoaldosteronism, and metabolic alkalosis, which suggested Liddle’s syndrome, were observed. Treatment with triamterene together with a steroid for nephrotic syndrome resulted in rapid and remarkable effective on improvements of hypertension, hypokalemia, and edema of the lower extremities. Renal biopsy revealed membranous nephropathy (MN) as the cause of nephrotic syndrome, and advanced gastric cancer was identified on screening examination for cancers that could be associated with the development of MN. After total gastrectomy, triamterene was not required and proteinuria decreased. A mutation in the β or γ subunits of the ENaC gene was not identified.

Conclusion

We reported for the first time a case of Liddle’s-like syndrome associated with nephrotic syndrome secondary to MN. Aberrant activation of ENaC was suggested transient during the period of high proteinuria, and the activation was reversible with a decrease in proteinuria.

Albuminuria in kidney transplant recipients is associated with increased urinary serine proteases and activation of the epithelial sodium channel

Albuminuria predicts adverse renal outcome in kidney transplant recipients. The present study addressed the hypothesis that albuminuria is associated with increased urine serine proteases with the ability to activate the epithelial sodium channel (ENaC) and with greater extracellular volume and higher blood pressure. In a cross-sectional design, kidney transplant recipients with ( n = 18) and without ( n = 19) albuminuria were included for office blood pressure measurements, estimation of volume status by bioimpedance, and collection of spot urine and plasma samples. Urine was analyzed for serine proteases and for the ability to activate ENaC current in vitro. Urine exosome protein was immunoblotted for prostasin and γ-ENaC protein. In the present study, it was found that, compared with nonalbuminuria (8.8 mg/g creatinine), albuminuric (1,722 mg/g creatinine) kidney transplant recipients had a higher systolic and diastolic blood pressure, despite receiving significantly more antihypertensives, and a greater urinary total plasminogen, active plasmin, active urokinase-type plasminogen activator, and prostasin protein abundance, which correlated significantly with u-albumin. Fluid overload correlated with systolic blood pressure, urinary albumin/creatinine, and plasminogen/creatinine. Urine from albuminuric kidney transplant recipients evoked a greater amiloride- and aprotinin-sensitive inward current in single collecting duct cells (murine cell line M1). γENaC subunits at 50 and 75 kDa showed increased abundance in urine exosomes from albuminuric kidney transplant recipients when compared with controls. These findings show that albuminuria in kidney transplant recipients is associated with hypertension, ability of urine to proteolytically activate ENaC current, and increased abundance of γENaC. ENaC activity could contribute to hypertension and adverse outcome in posttransplant proteinuria.

Urine albumin is a superior predictor of preeclampsia compared to urine plasminogen in type I diabetes patients

Pregnant women with type I diabetes mellitus (T1DM) are at increased risk of developing preeclampsia (PE). Plasminogen is aberrantly filtrated from plasma into tubular fluid in PE patients and activated to plasmin. Plasmin activates the epithelial sodium channel in the collecting ducts potentially causing impaired sodium excretion, suppression of the renin-angiotensin-aldosterone system, and hypertension in PE. The objective of the study was to test whether urinary total plasmin(ogen)/creatinine ratio and plasma concentration of aldosterone were better predictors of PE in pregnant women with T1DM compared with urine albumin and haemoglobin A_1C. The design was a longitudinal observational study of 88 pregnant T1DM patients at 2 Danish centers. Spot urine- and blood samples were collected at gestational weeks 12, 20, 28, 32, and 36. U-plasmin(ogen)/creatinine ratio increased during pregnancy. In gestational week 36, the ratio was significantly increased in the T1DM patients developing PE (P < .05). P-aldosterone was significantly increased in gestational week 20 in the group developing PE (P < .05). U-albumin/creatinine ratio was significantly increased and predicted PE at all tested gestational ages. U-albumin/creatinine ratio had a stronger association with the development of PE compared to u-total plasmin(ogen)/creatinine ratio and p-aldosterone. The positive association between u-total plasmin(ogen) and development of PE late in pregnancy is compatible with involvement in PE pathophysiology. The significance of albumin in urine emphasizes the importance of preventing renal complications when planning pregnancy in patients with type I diabetes.

Epithelial Na+ Channel Regulation by Extracellular and Intracellular Factors

Epithelial Na⁺ channels (ENaCs) are members of the ENaC/degenerin family of ion channels that evolved to respond to extracellular factors. In addition to being expressed in the distal aspects of the nephron, where ENaCs couple the absorption of filtered Na⁺ to K⁺ secretion, these channels are found in other epithelia as well as nonepithelial tissues. This review addresses mechanisms by which ENaC activity is regulated by extracellular factors, including proteases, Na⁺, and shear stress. It also addresses other factors, including acidic phospholipids and modification of ENaC cytoplasmic cysteine residues by palmitoylation, which enhance channel activity by altering interactions of the channel with the plasma membrane.

Urinary peptidomics analysis reveals proteases involved in diabetic nephropathy

Mechanisms underlying the onset and progression of nephropathy in diabetic patients are not fully elucidated. Deregulation of proteolytic systems is a known path leading to disease manifestation, therefore we hypothesized that proteases aberrantly expressed in diabetic nephropathy (DN) may be involved in the generation of DN-associated peptides in urine. We compared urinary peptide profiles of DN patients (macroalbuminuric, n = 121) to diabetic patients with no evidence of DN (normoalbuminuric, n = 118). 302 sequenced, differentially expressed peptides (adjusted p-value < 0.05) were analysed with the Proteasix tool predicting proteases potentially involved in their generation. Activity change was estimated based on the change in abundance of the investigated peptides. Predictions were correlated with transcriptomics (Nephroseq) and relevant protein expression data from the literature. This analysis yielded seventeen proteases, including multiple forms of MMPs, cathepsin D and K, kallikrein 4 and proprotein convertases. The activity of MMP-2 and MMP-9, predicted to be decreased in DN, was investigated using zymography in a DN mouse model confirming the predictions. Collectively, this proof-of-concept study links urine peptidomics to molecular changes at the tissue level, building hypotheses for further investigation in DN and providing a workflow with potential applications to other diseases.

Restoration of plasma markers of liver and kidney functions/integrity in alloxan-induced diabetic rabbits by aqueous extract of Pleurotus tuberregium sclerotia

The effect of aqueous extract of the sclerotia of Pleurotus tuberregium on the plasma electrolytes, and markers of liver and kidney functions/integrity of normal and alloxan-induced rabbits was investigated. Diabetes mellitus was induced by injection of alloxan (120mg/kg body weight), via the marginal ear vein. The extract was administered orally at 100, 200 and 300mg/kg (both to normal and diabetic rabbits), and metformin at 50mg/kg. Gas chromatographic-flame ionization detector analysis of the extract revealed the presence of twelve known phenolic acids, consisting mainly of caffeic acid (80.24%), chlorogenic acid (11.08%), piperic acid (6.11%), sinapinic acid (2.14%) and ferulic acid (0.34%). Compared to test control, the treatment significantly (p<0.05) lowered plasma activities of alkaline phosphatase, gamma glutamyltransferase, and alanine and aspartate transaminases. Also lowered were plasma unconjugated/conjugated bilirubin ratio and concentrations of urea, blood urea nitrogen, creatinine, sodium, and total and unconjugated bilirubin. It however, significantly (p<0.05) raised plasma potassium and calcium levels. Therefore, the modulation of plasma sodium and potassium is an indication of the diuretic potential of the extract. In addition, the extract had no deleterious effect on the liver and kidney of the treated animals, at least at the doses administered in this study.

Significant natriuretic and antihypertensive action of the epithelial sodium channel blocker amiloride in diabetic patients with and without nephropathy

OBJECTIVE

Diabetic nephropathy is associated with aberrant glomerular filtration of serine proteases. The study was designed to test the hypothesis that the epithelial sodium channel is activated proteolytically by urine plasmin in diabetic nephropathy and mediates renal sodium retention.

METHODS

In an open-label intervention study on type 1 diabetes patients on standardized NaCl intake (200 mmol/day) with (n = 15) and without diabetic nephropathy (control, n = 12), urinary Na excretion in response to oral amiloride (20 or 40 mg/day for 2 days) was compared.

RESULTS

A total of 27 patients completed the study and nine diabetic nephropathy and eight control study participants were compliant (24-h urine Na excretion of 200 mmol ± 30%). Amiloride increased significantly total and fractional Na excretion in both groups. Total natriuresis and weight loss were significantly larger in the control group compared with diabetic nephropathy at day 1 of amiloride, whereas fractional Na excretion did not differ. Amiloride intervention increased plasma renin concentration only in diabetic nephropathy group; it reduced SBP in both groups, whereas DBP was reduced in diabetic nephropathy group only. Albuminuria was reduced significantly by amiloride in diabetic nephropathy group. Urine total amiloride concentration was not different between groups (12 ± 1 and 16 ± 1 μmol/l, respectively). Urine total plasminogen and active plasmin were reduced after amiloride in diabetic nephropathy.

CONCLUSION

Amiloride increased renal Na excretion, reduced blood pressure, albuminuria, and total and active plasmin in urine. It is concluded that epithelial sodium channel is an attractive target to attain blood pressure control in long-term type I diabetes with no enhanced activity associated with nephropathy.

Treatment of Disorders of Sodium Balance in Chronic Kidney Disease

Extracellular fluid volume expansion is nearly universal in patients with CKD. Such volume expansion has features similar to the syndrome of heart failure with preserved ejection fraction, which not only leads to symptoms but can also lead to further organ damage. Unique treatment challenges are present in this patient population, including low glomerular filtration, which limits sodium chloride filtration, intrinsic tubule predisposition to sodium chloride retention, and proteinuria. In addition, pharmacokinetic considerations alter the disposition of diuretics in patients with CKD and nephrotic syndrome. Maintaining extracellular fluid volume near to normal is often necessary for hypertension treatment in this population, but it may also help prevent progressive cardiovascular and kidney damage. Although powerful diuretics can often accomplish this goal, this often comes at a cost of competing adverse effects. An approach to reduce extracellular fluid volume while avoiding adverse effects, therefore, requires a nuanced yet aggressive therapeutic approach.

Trial of Amiloride in Type 2 Diabetes with Proteinuria

Introduction

Renal sodium (Na⁺) retention and extracellular fluid volume expansion are hallmarks of nephrotic syndrome, which occurs even in the absence of activation of hormones that stimulate renal Na⁺ transporters. Plasmin-dependent activation of the epithelial Na⁺ channel has been proposed to have a role in renal Na⁺ retention in the setting of nephrotic syndrome. We hypothesized that the epithelial Na⁺ channel inhibitor amiloride would be an effective therapeutic agent in inducing a natriuresis and lowering blood pressure in individuals with macroscopic proteinuria.

Methods

We conducted a pilot double-blind randomized cross-over study comparing the effects of daily administration of either oral amiloride or hydrochlorothiazide to patients with type 2 diabetes and macroscopic proteinuria. Safety and efficacy were assessed by monitoring systolic blood pressure, kidney function, adherence, weight, urinary Na⁺ excretion, and serum electrolytes. Nine subjects were enrolled in the trial.

Results

No significant difference in systolic blood pressure or weight was seen between subjects receiving hydrochlorothiazide and those receiving amiloride (P ≥ 0.15). Amiloride induced differences in serum potassium (P < 0.001), with a 0.88 ± 0.30 mmol/l greater acute increase observed. Two subjects developed acute kidney injury and hyperkalemia when treated with amiloride. Four subjects had readily detectable levels of urinary plasminogen plus plasmin, and 5 did not. Changes in systolic blood pressure in response to amiloride did not differ between individuals with versus those without detectable urinary plasminogen plus plasmin.

Discussion

In summary, among patients with type 2 diabetes, normal renal function, and proteinuria, there were reductions in systolic blood pressure in groups treated with hydrochlorothiazide or amiloride. Acute kidney injury and severe hyperkalemia were safety concerns with amiloride.

Albuminuria is associated with an increased prostasin in urine while aldosterone has no direct effect on urine and kidney tissue abundance of prostasin

The proteinase prostasin is a candidate mediator for aldosterone-driven proteolytic activation of the epithelial sodium channel (ENaC). It was hypothesized that the aldosterone-mineralocorticoid receptor (MR) pathway stimulates prostasin abundance in kidney and urine. Prostasin was measured in plasma and urine from type 2 diabetic patients with resistant hypertension (n = 112) randomized to spironolactone/placebo in a clinical trial. Prostasin protein level was assessed by immunoblotting in (1) human and rat urines with/without nephrotic syndrome, (2) human nephrectomy tissue, (3) urine and kidney from aldosterone synthase-deficient (AS^-/-) mice and ANGII- and aldosterone-infused mice, and in (4) kidney from adrenalectomized rats. Serum aldosterone concentration related to prostasin concentration in urine but not in plasma. Plasma prostasin concentration increased significantly after spironolactone compared to control. Urinary prostasin and albumin related directly and were reduced by spironolactone. In patients with nephrotic syndrome, urinary prostasin protein was elevated compared to controls. In rat nephrosis, proteinuria coincided with increased urinary prostasin, unchanged kidney tissue prostasin, and decreased plasma prostasin while plasma aldosterone was suppressed. Prostasin protein abundance in human nephrectomy tissue was similar across gender and ANGII inhibition regimens. Prostasin urine abundance was not different in AS^-/- and aldosterone-infused mice. Prostasin kidney level was not different from control in adrenalectomized rats and AS^-/- mice. We found no evidence for a direct relationship between mineralocorticoid receptor signaling and kidney and urine prostasin abundance. The reduction of urinary prostasin in spironolactone-treated patients is most likely the result of an improved glomerular filtration barrier function and generally reduced proteinuria.

Urinary Exosomes and Their Cargo: Potential Biomarkers for Mineralocorticoid Arterial Hypertension?

Arterial hypertension (AHT) currently affects approximately 40% of adults worldwide, and its pathological mechanisms are mainly related to renal, vascular, and endocrine systems. Steroid hormones as aldosterone and cortisol are highly relevant to human endocrine physiology, and also to endocrine hypertension. Pathophysiological conditions, such as primary aldosteronism, affect approximately 10% of patients diagnosed with AHT and are secondary to a high production of aldosterone, increasing the risk also for cardiovascular damage and heart diseases. Excess of aldosterone or cortisol increases the activity of the mineralocorticoid receptor (MR) in epithelial and non-epithelial cells. Current research in this field highlights the potential regulatory mechanisms of the MR pathway, including pre-receptor regulation of the MR (action of 11BHSD2), MR activating proteins, and the downstream genes/proteins sensitive to MR (e.g., epithelial sodium channel, NCC, NKCC2). Mineralocorticoid AHT is present in 15-20% of hypertensive subjects, but the mechanisms associated to this condition have been poorly described, due mainly to the absence of reliable biomarkers. In this way, steroids, peptides, and lately urinary exosomes are thought to be potential reporters of biological processes. This review highlight exosomes and their cargo as potential biomarkers of metabolic changes associated to mineralocorticoid AHT. Recent reports have shown the presence of RNA, microRNAs, and proteins in urinary exosomes, which could be used as biomarkers in physiological and pathophysiological conditions. However, more studies are needed in order to benefit from exosomes and the exosomal cargo as a diagnostic tool in mineralocorticoid AHT.

Urinary Excretion of Kidney Aquaporins as Possible Diagnostic Biomarker of Diabetic Nephropathy

Diabetic nephropathy (DN) is a microangiopathic complication of diabetes mellitus (DM) affecting one-third of diabetic patients. The large variability in the clinical presentation of renal involvement in patients with DM makes kidney biopsy a prerequisite for a correct diagnosis. However, renal biopsy is an invasive procedure associated with risk of major complications. Numerous studies aimed to identify a noninvasive biomarker of DN but, so far, none of these is considered to be sufficiently specific and sensitive. Water channel aquaporins (AQPs), expressed at the plasma membrane of epithelial tubular cells, are often dysregulated during DN. In this work, we analyzed the urine excretion of AQP5 and AQP2 (uAQP5 and uAQP2), via exosomes, in 35 diabetic patients: 12 normoalbuminuric with normal renal function (DM), 11 with proteinuric nondiabetic nephropathy (NDN), and 12 with histological diagnosis and classification of DN. ELISA and WB analysis independently showed that uAQP5 was significantly increased in DN patients. Interestingly, linear regression analysis showed a positive correlation between uAQP5 and the histological class of DN. The same analysis, focusing on uAQP2, showed comparable results. Taken together, these data suggest a possible use of AQP5 and AQP2 as novel noninvasive biomarkers to help in classifying the clinical stage of DN.

Diuretic Resistance

Diuretic resistance is defined as a failure to achieve the therapeutically desired reduction in edema despite a full dose of diuretic. The causes of diuretic resistance include poor adherence to drug therapy or dietary sodium restriction, pharmacokinetic issues, and compensatory increases in sodium reabsorption in nephron sites that are not blocked by the diuretic. To illustrate the pathophysiology and management of diuretic resistance, we describe a patient with nephrotic syndrome. This patient presented with generalized pitting edema and weight gain despite the use of oral loop diuretics. Nephrotic syndrome may cause mucosal edema of the intestine, limiting the absorption of diuretics. In addition, the patient's kidney function had deteriorated, impairing the tubular secretion of diuretics. He was admitted for intravenous loop diuretic treatment. However, this was ineffective, likely due to compensatory sodium reabsorption by other tubular segments. The combination of loop diuretics with triamterene, a blocker of the epithelial sodium channel, effectively reduced body weight and edema. Recent data suggest that plasmin in nephrotic urine can activate the epithelial sodium channel, potentially contributing to the diuretic resistance in this patient. This case is used to illustrate and review the mechanisms of, and possible interventions for, diuretic resistance.