Urinary hyaluronidase activity is closely related to vasopressinergic system following an oral water load in men: a potential role in blood pressure regulation and early stages of hypertension development.

Introduction: Blood pressure (BP) regulation is a complex process involving several factors, among which water-sodium balance holds a prominent place. Arginin-vasopressin (AVP), a key player in water metabolism, has been evoked in hypertension development since the 1980s, but, to date, the matter is still controversial. Hyaluronic acid metabolism has been reported to be involved in renal water management, and AVP appears to increase hyaluronidase activity resulting in decreased high-molecular-weight hyaluronan content in the renal interstitium, facilitating water reabsorption in collecting ducts. Hence, our aim was to evaluate urinary hyaluronidase activity in response to an oral water load in hypertensive patients (HT, n=21) compared to normotensive subjects with (NT+, n=36) and without (NT-, n=29) a family history of hypertension, and to study its association with BP and AVP system activation, expressed by serum copeptin levels and urine Aquaporin 2 (AQP2)/creatinine ratio. Methods: Eighty-six Caucasian men were studied. Water load test consisted in oral administration of 15-20 ml of water/kg body weight over 40-45 min. BP, heart rate, serum copeptin, urine hyaluronidase activity and AQP2 were monitored for 4 hours. Results: In response to water drinking, BP raised in all groups with a peak at 20-40 min. Baseline levels of serum copeptin, urinary hyaluronidase activity and AQP2/creatinine ratio were similar among groups and all decreased after water load, reaching their nadir at 120 min and then gradually recovering to baseline values. Significantly, a blunted reduction in serum copeptin, urinary hyaluronidase activity and AQP2/creatinine ratio was observed in NT+ compared to NT- subjects. A strong positive correlation was also found between urinary hyaluronidase activity and AQP2/creatinine ratio, and, although limited to the NT- group, both parameters were positively associated with systolic BP. Discussion: Our results demonstrate for the first time the existence in men of a close association between urinary hyaluronidase activity and vasopressinergic system and suggest that NT+ subjects have a reduced ability to respond to water loading possibly contributing to the blood volume expansion involved in early-stage hypertension. Considering these data, AVP could play a central role in BP regulation by affecting water metabolism through both hyaluronidase activity and AQP2 channel expression.

Diurnal rhythm of urinary aquaporin-2 in children with primary monosymptomatic nocturnal enuresis.

Background/aim: Nocturnal enuresis can be frustrating for children and their families as the child ages. Our aim is to evaluate urine aquaporin 2 (AQP-2) as a noninvasive biomarker of water balance in children with primary monosymptomatic nocturnal enuresis (PMNE). Material and methods: The study included 90 children; sixty-eight children suffering from PMNE aged (9.57 ± 2.16) years and 22 healthy children with good toilet control, matched sex and age. All enuretic children were subjected to complete history taking, clinical evaluation, and bed wetting diary. Serum arginine vasopressin (AVP) and urine AQP-2 were tested in the morning (at 9-11 am) and evening (at 9-11 pm). Blood urea, creatinine, Na, glucose, urine osmolality, Ca/Cr, Alb/Cr and specific gravity were tested simultaneously. Results: Serum AVP, urine AQP-2, and urine osmolality were statistically lower in patients than controls. Patients had a significantly lower level of night serum AVP concentrations, urine AQP-2, and urine osmolality than the corresponding morning level. Urine AQP-2 was significantly correlated with urine osmolality (p < 0.05). AQP-2 had a sensitivity of 90% and a specificity of 70%. However, no statistically significant correlation was found between serum AVP and urine AQP-2. Conclusion: Primary monosymptomatic nocturnal enuresis in children could be associated with reduction of urine excretion of AQP-2 at night. Urine AQP-2 is significantly correlated with urine osmolality. Therefore, it may be a noninvasive biomarker of hydration status in children with PMNE, with good sensitivity and specificity.

Effect of the DASH diet on the sodium-chloride cotransporter and aquaporin-2 in urinary extracellular vesicles.

The dietary approach to stop hypertension (DASH) diet combines the antihypertensive effect of a low sodium and high potassium diet. In particular, the potassium component of the diet acts as a switch in the distal convoluted tubule to reduce sodium reabsorption, similar to a diuretic but without the side effects. Previous trials to understand the mechanism of the DASH diet were based on animal models and did not characterize changes in human ion channel protein abundance. More recently, protein cargo of urinary extracellular vesicles (uEVs) has been shown to mirror tissue content and physiological changes within the kidney. We designed an inpatient open label nutritional study transitioning hypertensive volunteers from an American style diet to DASH diet to examine physiological changes in adults with stage 1 hypertension otherwise untreated (Sacks FM, Svetkey LP, Vollmer WM, Appel LJ, Bray GA, Harsha D, Obarzanek E, Conlin PR, Miller ER 3rd, Simons-Morton DG, Karanja N, Lin PH; DASH-Sodium Collaborative Research Group. N Engl J Med 344: 3-10, 2001). Urine samples from this study were used for proteomic characterization of a large range of pure uEVs (small to large) to reveal kidney epithelium changes in response to the DASH diet. These samples were collected from nine volunteers at three time points, and mass spectrometry identified 1,800 proteins from all 27 samples. We demonstrated an increase in total SLC12A3 [sodium-chloride cotransporter (NCC)] abundance and a decrease in aquaporin-2 (AQP2) in uEVs with this mass spectrometry analysis, immunoblotting revealed a significant increase in the proportion of activated (phosphorylated) NCC to total NCC and a decrease in AQP2 from day 5 to day 11. This data demonstrates that the human kidney's response to nutritional interventions may be captured noninvasively by uEV protein abundance changes. Future studies need to confirm these findings in a larger cohort and focus on which factor drove the changes in NCC and AQP2, to which degree NCC and AQP2 contributed to the antihypertensive effect and address if some uEVs function also as a waste pathway for functionally inactive proteins rather than mirroring protein changes.NEW & NOTEWORTHY Numerous studies link DASH diet to lower blood pressure, but its mechanism is unclear. Urinary extracellular vesicles (uEVs) offer noninvasive insights, potentially replacing tissue sampling. Transitioning to DASH diet alters kidney transporters in our stage 1 hypertension cohort: AQP2 decreases, NCC increases in uEVs. This aligns with increased urine volume, reduced sodium reabsorption, and blood pressure decline. Our data highlight uEV protein changes as diet markers, suggesting some uEVs may function as waste pathways. We analyzed larger EVs alongside small EVs, and NCC in immunoblots across its molecular weight range.

Peak Lag Between Plasma Vasopressin and Urine Aquaporin-2 Following Cardiac Surgery.

Tolvaptan, a vasopressin type-2 receptor antagonist, is utilized to ameliorate fluid retention following cardiac surgery. However, the optimal timing of tolvaptan administration considering novel biomarkers remains unknown. We prospectively included patients who underwent cardiac surgery between 2016 and 2020. We measured perioperative trends of free water reabsorption mediators including plasma arginine vasopressin and urine aquaporin-2. A total of 20 patients (68 [60, 75] years old, 18 men) were included. Urine volume decreased gradually after the initial 3 hours following cardiac surgery. The plasma arginine vasopressin level increased significantly with a peak at postoperative 6 hours, whereas the urine aquaporin-2 level increased later with a delayed peak at postoperative 12 hours. As a result, urine aquaporin-2 relative to the plasma arginine vasopressin level, which represents the activity of the collecting ducts and indicates predicted responses to tolvaptan, was a minimum at postoperative 6 hours. Tolvaptan administration immediately after cardiac surgery might not be recommended given the transient refractoriness to tolvaptan probably due to the stunning of kidney collecting ducts.

Reduced urinary release of AQP1- and AQP2-bearing extracellular vesicles in patients with advanced chronic kidney disease.

Although several studies have shown that release of water channel proteins, aquaporin 1 (AQP1) and AQP2 in urinary extracellular vesicles (uEV-AQP1 and -AQP2), were altered in experimental kidney injury models, their release in human chronic kidney disease (CKD) has been largely unexplored. The aim of the present study was to clarify whether the release of uEV-AQP1 and -AQP2 is altered in patients with CKD. Urine samples were collected from 15 healthy volunteers (normal group) and 62 CKD patients who were categorized into six glomerular filtration rate (GFR) categories (G1, G2, G3a, G3b, G4, and G5) in between 2005 and 2016 at Miyazaki Prefectural Miyazaki Hospital, Japan. uEV-proteins were evaluated by immunoblot analysis. The release of AQP1 and AQP2 were significantly decreased in patients with both CKD G4 and G5, in comparison with the normal group. The area under the receiver operating characteristic (ROC) curve (AUC) values for AQP1 and AQP2 in patients with CKD G4 and G5 were 0.926 and 0.881, respectively. On the other hand, the AUC values in patients with CKD G1-G3 were 0.512 for AQP1 and 0.680 for AQP2. Multiple logistic regression analysis showed that AQP1 and AQP2 in combination were useful for detecting CKD G4 and G5, with a higher AUC value of 0.945. These results suggest that the release of uEV-AQP1 and -AQP2 was decreased in patients with CKD G4 and G5, and these proteins might be helpful to detect advanced CKD.

Oligosaccharides composition of Descurainiae sophia exerts anti-heart failure by improving heart function and water-liquid metabolism in rats with heart failure.

PURPOSE: To investigate the protective effect of Oligosaccharides composition of Descurainiae sophia on doxorubicin-induced heart failure in rats, and to study its mechanism. METHOD: A rat model of heart failure was established in 180-220 g male Sprague-Dawley rats by low-dose intraperitoneal injection of doxorubicin for 6 weeks. Four weeks after continuous administration, echocardiography was used to detect left ventricular end diastolic diameter (LVEDD) and end systolic diameter (LVESD) in each group, and left ventricular short axis shortening rate (LVFS) and ejection fraction (LVEF) were calculated. ELISA method was used to detecte the levels of atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), troponin I (cTnI), creatine kinase (CK), angiotensin II (Ang II), aldosterone (ALD), arginine pressurization AVP, Renin, Endothelin (ET-1), Nitric Oxide (NO), AQP2 in urine. 6 h cumulative urine output was measured by metabolic cage method after administration for 3 weeks. The urine osmotic pressure was measured by freezing point method. The expression of AQP2 protein in kidney was detected by Western blot method. The changes of myocardial morphology were observed. RESULTS: Compared with the normal control group, the heart rate of the model group was significantly increased (P < 0.01). LVESD and LVEDD were significantly increased (P < 0.01), LVEF and LVFS were significantly decreased (P < 0.01). The levels of CK, cTnI, NO, ET-1, BNP, ANP, ALD, AngII, Renin, AQP2, AVP and osmotic pressure were significantly increased (P < 0.01). Urine output was significantly decreased (P < 0.01). The heart HE showed obvious lesions. Compared with the model group, the Oligosaccharides composition of Descurainiae sophia significantly reduced the heart rate (P < 0.05), decreased LVESD and LVEDD (P < 0.01 or P < 0.05), and increased LVFS and LVEF values (P < 0.01). Oligosaccharides composition of Descurainiae sophia could significantly improve pathological damage of the heart, decrease the levels of cTnI, BNP, AngII, ALD, Renin, AVP in the serum, osmotic pressure and AQP2in the urine (P < 0.01 or P < 0.05), down-regulate the expression of AQP2 protein in the renal(P < 0.01), increase urine volume (P < 0.05). CONCLUSION: Oligosaccharides composition of Descurainiae sophia can significantly improve cardiac function and the disorder of water metabolism in rats with heart failure. Oligosaccharides composition of Descurainiae sophia exerts anti- heart failure through the RAAS system and the arginine vasopressin system.

Urine concentration ability is reduced to the same degree in adult dominant polycystic kidney disease compared with other chronic kidney diseases in the same CKD-stage and lower THAN in healthy control subjects - a CASE control study.

BACKGROUND: Concentration of the urine is primarily regulated via vasopressin dependent aquaporin-2 water channels in the apical membrane of kidney principal cells. It is unclear whether urine concentration ability in ADPKD differs from other patients with similar degree of impaired renal function (non-ADPKD patients). The purpose of this case control study was to measure urine concentration ability in ADPKD patients compared to non-ADPKD patients and healthy controls. METHODS: A seventeen hour long water deprivation test was carried out in 17 ADPKD patients (CKD I-IV), 16 non-ADPKD patients (CKD I-IV), and 18 healthy controls. Urine was collected in 4 consecutive periods during water deprivation (12 h, 1 h, 2 h and 2 h, respectively) and analyzed for osmolality (u-Osm), output (UO), fractional excretion of sodium (FENa), aquaporin2 (u-AQP2) and ENaC (u-ENaC). Blood samples were drawn trice (after 13-, 15-, and 17 h after water deprivation) for analyses of osmolality (p-Osm), vasopressin (p-AVP), and aldosterone (p-Aldo). RESULTS: U-Osm was significantly lower and FENa significantly higher in both ADPKD patients and non-ADPKD patients compared to healthy controls during the last three periods of water deprivation. During the same periods, UO was higher and secretion rates of u-AQP2 and u-ENaC were lower and at the same level in the two groups of patients compared to controls. P-AVP and p-Osm did not differ significantly between the three groups. P-Aldo was higher in both groups of patients than in controls. CONCLUSIONS: Urine concentration ability was reduced to the same extent in patients with ADPKD and other chronic kidney diseases with the same level of renal function compared to healthy controls. The lower urine excretion of AQP2 and ENaC suggests that the underlying mechanism may be a reduced tubular response to vasopressin and aldosterone. TRIAL REGISTRATION: Current Controlled Trial NCT04363554 , date of registration: 20.08.2017.

Aquaporin-2 and NKCC2 expression pattern in patients with hepatosplenic schistosomiasis.

OBJECTIVE: Schistosoma mansoni infection is considered a public health problem. Glomerular involvement in schistosomiasis is a well-documented complication, especially in hepatosplenic schistosomiasis (HSS). However, renal tubular function is poorly understood. The aim of this study was to investigate, through urinary exosomes, tubular transporters functionally in HSS patients. METHODS: Cross-sectional study of 20 HSS patients who had isolated exosomes from urine samples. Protease inhibitor was added in the urine samples who were immediately frozen at -80 °C for further exosomes isolation. After urine had thawed, urinary exosomes were obtained using extensive vortexing, centrifugation and ultracentrifugation steps of urine. Urinary transporters expression from exosomes was evaluated by western blot, including NHE3, AQP2 and NKCC2. Charge amounts for gel electrophoresis were adjusted by urinary creatinine concentration of each patient to avoid urinary concentration bias. All protein expression of HSS patients was relative to healthy controls. RESULTS: The expression of aquaporin-2 (AQP2) was lower in HSS patients than in controls (46.8 ± 40.7 vs. 100 ± 70.2%, P = 0.03) and the expression of the NKCC2 co-transporter was higher (191.7 ± 248.6 vs. 100 ± 43.6%, P = 0.02). CONCLUSIONS: The decrease of AQP2 and the increase of NKCC2 expression in HSS patients seem to be involved with the inability of urinary concentration in these patients. These data show renal tubular abnormalities in HSS patients without manifest clinical disease.

OBJECTIF: L'infection à Schistosoma mansoni est considérée comme un problème de santé publique. L'atteinte glomérulaire dans la schistosomiase est une complication bien documentée, en particulier dans la schistosomiase hépatosplénique (SH). Cependant, la fonction tubulaire rénale est mal connue. Le but de cette étude était d'étudier, par le biais d'exosomes urinaires, les transporteurs tubulaires fonctionnellement chez les patients atteints de SH. MÉTHODES: Il s'agit d'une étude transversale sur 20 patients atteints de SH qui avaient des exosomes isolés d'échantillons d'urine. Un inhibiteur de protéase a été ajouté dans les échantillons d'urine qui ont été immédiatement congelés à -80°C pour un isolement supplémentaire des exosomes. Après décongélation de l'urine, des exosomes urinaires ont été obtenus en utilisant des étapes étendues de vortex, de centrifugation et d'ultracentrifugation d'urine. L'expression des transporteurs urinaires d'exosomes a été évaluée par western blot, y compris NHE3, AQP2 et NKCC2. Les quantités de charge pour l'électrophorèse sur gel ont été ajustées par la concentration de créatinine urinaire de chaque patient pour éviter un biais de concentration urinaire. Toute expression protéique des patients atteints de SH était relative à celle de témoins sains. RÉSULTATS: L'expression de l'aquaporine-2 (AQP2) était plus faible chez les patients SH que chez les témoins (46,8 ± 40,7 vs 100 ± 70,2%, P = 0,03) et l'expression du co-transporteur NKCC2 était plus élevée (191,7 ± 248,6 vs 100 ± 43,6%, P = 0,16). CONCLUSIONS: La diminution de l'AQP2 et l'augmentation de l'expression de NKCC2 chez les patients SH semblent être impliquées dans l'incapacité de concentration urinaire chez ces patients. Ces données montrent des anomalies tubulaires rénales chez les patients SH sans maladie clinique manifeste.

Phosphorylation profile of human AQP2 in urinary exosomes by LC-MS/MS phosphoproteomic analysis.

BACKGROUND: Aquaporin-2 (AQP2) is a key water channel protein which determines the water permeability of the collecting duct. Multiple phosphorylation sites are present at the C-terminal of AQP2 including S256 (serine at 256 residue), S261, S264 and S/T269, which are regulated by vasopressin (VP) to modulate AQP2 trafficking. As the dynamics of these phosphorylations have been studied mostly in rodents, little is known about the phosphorylation of human AQP2 which has unique T269 in the place of S269 of rodent AQP2. Because AQP2 is excreted in urinary exosomes, the phosphoprotein profile of human AQP2 can be easily examined through urinary exosomes without any intervention. METHODS: Human urinary exosomes digested with trypsin or glutamyl endopeptidase (Glu-C) were examined by the liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) phosphoproteomic analysis. RESULTS: The most dominant phosphorylated AQP2 peptide identified was S256 phosphorylated form (pS256), followed by pS261 with less pS264 and far less pT269, which was confirmed by the western blot analyses using phosphorylated AQP2-specific antibodies. In a patient lacking circulating VP, administration of a VP analogue showed a transient increase (peak at 30-60 min) in excretion of exosomes with pS261 AQP2. CONCLUSION: These data suggest that all phosphorylation sites of human AQP2 including T269 are phosphorylated and phosphorylations at S256 and S261 may play a dominant role in the urinary exosomal excretion of AQP2.

Decreased Excretion of Urinary Exosomal Aquaporin-2 in a Puromycin Aminonucleoside-Induced Nephrotic Syndrome Model.

Urinary exosomes, small extracellular vesicles present in urine, are secreted from all types of renal epithelial cells. Aquaporin-2 (AQP2), a vasopressin-regulated water channel protein, is known to be selectively excreted into the urine through exosomes (UE-AQP2), and its renal expression is decreased in nephrotic syndrome. However, it is still unclear whether excretion of UE-AQP2 is altered in nephrotic syndrome. In this study, we examined the excretion of UE-AQP2 in an experimental rat model of nephrotic syndrome induced by the administration of puromycin aminonucleoside (PAN). Rats were assigned to two groups: a control group administered saline and a PAN group given a single intraperitoneal injection of PAN (125 mg/kg) at day 0. The experiment was continued for 8 days, and samples of urine, blood, and tissue were collected on days 2, 5, and 8. The blood and urine parameters revealed that PAN induced nephrotic syndrome on days 5 and 8, and decreases in the excretion of UE-AQP2 were detected on days 2 through 8 in the PAN group. Immunohistochemistry showed that the renal expression of AQP2 was decreased on days 5 and 8. The release of exosomal marker proteins into the urine through UEs was decreased on day 5 and increased on day 8. These data suggest that UE-AQP2 is decreased in PAN-induced nephrotic syndrome and that this reflects its renal expression in the marked proteinuria phase after PAN treatment.

Perioperative urinary excretion of aquaporin-2 dependent upon vasopressin in cardiac surgery.

Aquaporin-2 is found in the apical cell membranes of the principal cells of the collecting duct of the kidney. Plasma arginine vasopressin has been reported to be markedly elevated during cardiac surgery. However fluctuations in urine aquaporin-2 levels have never been reported. We aimed to determine the responses of urine aquaporin-2 and evaluated the relationship between urine aquaporin-2 and plasma arginine vasopressin levels during perioperative periods in cardiac surgical patients. Eight patients undergoing elective isolated aortic valve replacement in normothermia were enrolled prospectively. Blood and urine samples were collected preoperatively and on postoperative days 1, 4, and 7. Patients received furosemide and spironolactone, as needed, during the clinical course; tolvaptan was not needed. Median plasma arginine vasopressin levels [with interquartile range] significantly increased to 1.5 [1.3-2.0], 15.3 [11.4-22.2]*, 2.2 [2.1-2.3], 1.7 [1.5-1.9] pg/mL preoperatively, on postoperative days 1, 4, and 7, respectively (*: p = 0.0001). Similarly, levels of urine aquaporin-2 markedly increased in 3.4 [1.9-5.6], 25.8 [18.4-33.5]**, 9.3 [5.9-14.0], 5.4 [5.3-6.1] (ng/mL), respectively (**p = 0.0004). A significant correlation between plasma arginine vasopressin and urine aquaporin-2 was observed during the entire investigation (R2 = 0.616, p < 0.0001). Plasma arginine vasopressin and urine aquaporin-2 levels were significantly elevated on postoperative day 1 in patients who underwent aortic valve replacement with cardiopulmonary bypass. A significant correlation between plasma arginine vasopressin and urine aquaporin-2 was observed. Urine aquaporin-2 should be further investigated as a potential biomarker for postoperative cardiac dysfunction.

Release of urinary aquaporin-2-bearing extracellular vesicles is decreased in pregnant Japanese Black cattle.

Aquaporin-2 (AQP2), a vasopressin-regulated water channel, plays an important role in renal water homeostasis. It has been reported that the level of AQP2 in human urine is altered during pregnancy. However, little is known about the level of urinary AQP2 in pregnant cattle. In this study, we examined the level of AQP2-bearing extracellular vesicles (uEV-AQP2), which account for most urinary AQP2, in both heifers and cows during the gestational and postpartum periods. The level of uEV-AQP2 was significantly decreased during gestation in comparison with the other cattle examined. Similarly, the levels of EV marker proteins in uEVs, including tumor susceptibility gene 101 (TSG101) protein and apoptosis-linked gene 2-interacting protein X (ALIX), were significantly decreased during gestation. There were significant correlations between the levels of uEV-AQP2 and uEV-TSG101, or uEV-ALIX. Immunohistochemistry data from pregnant and non-pregnant cattle supported the notion that the level of uEV-AQP2 was decreased during gestation. These data indicate that the level of uEV-AQP2 is decreased in pregnant cattle, possibly through a decrease in both the number of EVs released into the urine and renal AQP2 expression.

Effect of 3% saline and furosemide on biomarkers of kidney injury and renal tubular function and GFR in healthy subjects - a randomized controlled trial.

BACKGROUND: Chloride is speculated to have nephrotoxic properties. In healthy subjects we tested the hypothesis that acute chloride loading with 3% saline would induce kidney injury, which could be prevented with the loop-diuretic furosemide. METHODS: The study was designed as a randomized, placebo-controlled, crossover study. Subjects were given 3% saline accompanied by either placebo or furosemide. Before, during and after infusion of 3% saline we measured glomerular filtration rate (GFR), fractional excretion of sodium (FENa), urinary chloride excretion (u-Cl), urinary excretions of aquaporin-2 (u-AQP2) and epithelial sodium channels (u-ENaCγ), neutrophil gelatinase-associated lipocalin (u-NGAL) and kidney injury molecule-1 (u-KIM-1) as marker of kidney injury and vasoactive hormones: renin (PRC), angiotensin II (p-AngII), aldosterone (p-Aldo) and arginine vasopressin (p-AVP). Four days prior to each of the two examinations subjects were given a standardized fluid and diet intake. RESULTS: After 3% saline infusion u-NGAL and KIM-1 excretion increased slightly (u-NGAL: 17 ± 24 during placebo vs. -7 ± 23 ng/min during furosemide, p = 0.039, u-KIM-1: 0.21 ± 0.23 vs - 0.06 ± 0.14 ng/ml, p <  0.001). The increase in u-NGAL was absent when furosemide was given simultaneously, and the responses in u-NGAL were not significantly different from placebo control. Furosemide changed responses in u-KIM-1 where a delayed increase was observed. GFR was increased by 3% saline but decreased when furosemide accompanied the infusion. U-Na, FENa, u-Cl, and u-osmolality increased in response to saline, and the increase was markedly pronounced when furosemide was added. FEK decreased slightly during 3% saline infusion, but simultaneously furosemide increased FEK. U-AQP2 increased after 3% saline and placebo, and the response was further increased by furosemide. U-ENaCγ decreased to the same extent after 3% saline infusion in the two groups. 3% saline significantly reduced PRC, p-AngII and p-Aldo, and responses were attenuated by furosemide. p-AVP was increased by 3% saline, with a larger increase during furosemide. CONCLUSION: This study shows minor increases in markers of kidney injury after 3% saline infusion Furosemide abolished the increase in NGAL and postponed the increase in u-KIM-1. The clinical importance of these findings needs further investigation. TRIAL REGISTRATION: (EU Clinical trials register number: 2015-002585-23 , registered on 5th November 2015).

A bell-shaped pattern of urinary aquaporin-2-bearing extracellular vesicle release in an experimental model of nephronophthisis.

The DBA/2-FG pcy (pcy) mouse is a model of human nephronophthisis, a recessive cystic kidney disease. Renal expression of aquaporin-2 (AQP2), a water channel protein, has been shown to be altered in pcy mice. However, the relationship between the renal expression and its release in urinary extracellular vesicles (uEV-AQP2), which account for most urinary AQP2, in pcy mice has remained largely unknown. In this study, we examined age-related alterations of this relationship in pcy mice. In comparison with control mice, pcy mice after the age of 14 weeks showed defective urinary concentration ability with an increase in urinary volume. Interestingly, the release of uEV-AQP2 increased progressively up to the age of 16 weeks, but at 21 weeks the release did not significantly differ from that in control mice (i.e., a bell-shaped pattern was evident). Similar results were obtained for uEV marker proteins, including tumor susceptibility gene 101 (TSG101) protein and apoptosis-linked gene 2-interacting protein X (Alix). Immunoblot analysis revealed that renal AQP2 expression increased progressively from 11 weeks, and immunohistochemistry showed that this increase was possibly due to an increase in the number of AQP2-positive cells. Analysis of mRNAs for seven types of AQP expressed in the kidney supported this notion. These data suggest that the level of uEV-AQP2 does not simply mirror the renal expression of AQP2 and that the altered release of uEV-AQP2 in pcy mice depends on the numbers of both renal AQP2-positive cells and EVs released into the urine.

An Early Decrease in Release of Aquaporin-2 in Urinary Extracellular Vesicles After Cisplatin Treatment in Rats.

Aquaporin-1 (AQP1) and AQP2 are important proteins involved in the regulation of renal water handling. Both AQPs have been found in urinary extracellular vesicles (uEVs) (uEV-AQP1 and -AQP2). Cisplatin, an antineoplastic agent, is known to down-regulate renal AQP1 and AQP2. However, the effect of cisplatin on the release of uEV-AQP1 and -AQP2 is largely unknown. In this study, we examined whether treatment of rats with cisplatin affected the release of uEV-AQP1 and -AQP2. Blood tests indicated that renal function was little altered at 24 h after cisplatin treatment but thereafter decreased dramatically at all of the other time points examined. Release of uEV-AQP1 was slightly increased at 24 h and decreased at 168 h. On the other hand, release of uEV-AQP2 was decreased dramatically at 24 h, and the decrease was maintained during the experimental period. These data suggest that uEV-AQP2 can be used to detect early renal impairment due to cisplatin. Furthermore, a combination of uEV-AQP2 and -AQP1 may be useful for estimation of cisplatin-induced renal injury in a stage-dependent manner.

AQP2 in human urine is predominantly localized to exosomes with preserved water channel activities.

BACKGROUND: AQP2 water channel is critical for urinary concentration in the kidney. Interestingly, AQP2 is abundantly excreted in the urine as extracellular vesicles (EVs), which is known to be a useful biomarker for water-balance disorders although the character of AQP2-enriched EVs is poorly understood including water channel function. METHODS: Human urine EVs were obtained by a differential centrifugation method. AQP2-bearing EVs were isolated by immunoprecipitation with an AQP2-specific antibody, and the proteins in the EVs were analyzed by LC-MS/MS proteomic analysis. Osmotic water permeability (Pf) of the AQP2-rich EVs was measured by a stopped-flow method monitoring scattered light intensity in response to outwardly directed osmotic gradient. RESULTS: Sequential centrifugation of human urine showed that AQP2 was present predominantly (80%) in low-density EVs (160,000 g), whereas negligible amount in high-density EVs (17,000 g). Proteomic analysis of the AQP2-bearing EVs identified 137 proteins, mostly in the endosome pathway, including the components of ESCRT (endosomal sorting complex required transporter)-I, II, III. Pf value of the 160,000 g EVs was 4.75 ± 0.38 × 10-4 cm s-1 (mean ± SE) with the activation energy of 3.51 kcal mol-1 which was inhibited with 0.3 mM HgCl2 by 63%, suggesting a channel-mediated water transport. Moreover, Pf value showed a significant correlation with the abundance of AQP2 protein in EVs. CONCLUSION: Taken together, AQP2 is localized predominantly to urinary exosomes with preserved water channel activities.

Characterization of urinary exosomal release of aquaporin-1 and -2 after renal ischemia-reperfusion in rats.

Acute kidney injury (AKI) is an important risk factor for the development of chronic kidney disease (CKD), and an alteration in renal water handling has been observed during the transition of AKI to CKD. Urinary exosomal release of aquaporin-1 (AQP1) and AQP2, important proteins for renal water handling, has recently been reported to predict their levels of renal expression. Therefore, we examined the patterns of urinary exosomal release of AQP1 and AQP2, and the exosomal marker proteins tumor susceptibility 101 protein (TSG101) and ALG-2 interacting protein X (Alix), in the acute and chronic phases following induction of AKI by renal bilateral ischemia/reperfusion (I/R) in rats. Blood tests and histological examinations indicated that AKI occurred before at 7 days after renal I/R ( day 7) and that renal fibrosis developed progressively thereafter. Immunoblotting demonstrated significant decreases in the urinary exosomal release of AQP1 and AQP2 during severe AKI. Urinary exosomal release of Alix and TSG101 was significantly increased on day 7. These data were also confirmed in rats with unilateral renal I/R causing more serious AKI. Urinary exosomal release of either the Ser-256- or Ser-269-phosphorylated form of AQP2, both of which are involved in apical trafficking of AQP2, was positively correlated with that of total AQP2. These results suggest that urinary exosomal release of AQP1 and AQP2 is reduced in I/R-induced AKI, whereas that of Alix and TSG101 is increased in the initial phase of renal fibrosis. Furthermore, apical trafficking of AQP2 appears to be related to urinary exosomal release of AQP2.

Effects of sodium nitrite on renal function and blood pressure in hypertensive vs. healthy study participants: a randomized, placebo-controlled, crossover study.

OBJECTIVE: Nitric oxide is a key player in regulating vascular tone. Impaired endothelial nitric oxide synthesis plays an important role in hypertension. Replenishing of nitric oxide by sodium nitrite (NaNO2) has not been investigated in patients with essential hypertension (EHT). We aimed to determine the effects of NaNO2 on blood pressure (BP) and renal sodium and water regulation in patients with EHT compared with healthy control study participants (CON). METHODS: In a placebo-controlled, crossover study, we infused 240 µg NaNO2/kg/h or isotonic saline for 2 h in 14 EHT and 14 CON. During infusion, we measured changes in brachial and central BP, free water clearance, fractional sodium excretion, and urinary excretion rate of γ-subunit of the epithelial sodium channel (U-ENaCγ), and aquaporin-2 (U-AQP2). RESULTS: Placebo-adjusted brachial SBP decreased 18 mmHg (P < 0.001) during NaNO2 infusion in EHT and 12 mmHg (P < 0.001) in CON (Pbetween = 0.024). Brachial DBP and central SBP decreased equally in both groups during NaNO2. In EHT, we found a decrease in U-ENaCγ during NaNO2 infusion. In both groups, we observed a decrease in fractional sodium excretion, free water clearance, and U-AQP2 during NaNO2 infusion. CONCLUSION: This study demonstrated an augmented BP-lowering effect of NaNO2 in patients with EHT. We observed an antinatriuretic and antidiuretic effect of NaNO2 in both groups, and a decrease in U-ENaCγ, solely in EHT. In both groups, we detected a nonvasopressin mediated decrease in U-AQP2, which is most likely compensatory to the decline in diuresis.