Urinary Aquaporin-2 Research Articles

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.

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. 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. 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 120min 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. 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.

Short-term impact of kampo goreisan in patients with congestive heart failure refractory to tolvaptan-incorporated medical therapy.

We often encounter patients with congestive heart failure refractory to conventional diuretics therapy. Kampo goreisan (Tsumura &Co. Tokyo, Japan) is receiving great concern in mediating body water balance, particularly for such a cohort. However, its detailed biological mechanism remains uncertain. Patients who received goreisan to treat congestive heart failure refractory to tolvaptan-incorporated medical therapy were prospectively included and observed for one week during the therapeutic period. The change in urine biomarkers during the first 24h was assessed as a primary concern. Baseline factors associated with an increase in urine volume during the first 24h were investigated as a secondary concern. A total of 18 patients were included. Median age was 81 (77, 86) and 12 (67%) were men. During the first 24h after the initiation of goreisan, urine cyclic AMP tended to decrease, urine aquaporin-2 decreased significantly, urine osmolality decreased significantly, and urine volume tended to increase. Baseline higher common logarithm of plasma B-type natriuretic peptide was associated with any increases in urine volume during the first 24h with an odds ratio of 73.2 (95% confidence interval 1.04-5149, p = 0.048). Baseline plasma B-type natriuretic peptide level had a positive correlation with a change in urine volume between baseline and day 1 (r = 0.533, p = 0.026). Goreisan may increase urine volume even in patients with congestive heart failure refractory to tolvaptan-incorporated medical therapy by modulating aquaporin-2 systems in the collecting duct, particularly in individuals with advanced heart failure accompanying significant congestion. Goreisan may have a regulatory effect on body fluid, rather than just forcing aquaresis.

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

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). 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. 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. 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 controlled hypotensive hemorrhage on plasma sodium levels in anesthetized pigs: An exploratory study.

Perioperative hyponatremia, due to non-osmotic release of the antidiuretic hormone arginine vasopressin, is a serious electrolyte disorder observed in connection with many types of surgery. Since blood loss during surgery contributes to the pathogenesis of hyponatremia, we explored the effect of bleeding on plasma sodium using a controlled hypotensive hemorrhage pig model. After 30-min baseline period, hemorrhage was induced by aspiration of blood during 30 min at mean arterial pressure <50 mmHg. Thereafter, the animals were resuscitated with retransfused blood and a near-isotonic balanced crystalloid solution and monitored for 180 min. Electrolyte and water balances, cardiovascular response, renal hemodynamics, and markers of volume regulation and osmoregulation were investigated. All pigs (n = 10) developed hyponatremia. All animals retained hypotonic fluid, and none could excrete net-free water. Urinary excretion of aquaporin 2, a surrogate marker of collecting duct responsiveness to antidiuretic hormone, was significantly reduced at the end of the study, whereas lysine vasopressin, i.e., the pig antidiuretic hormone remained high. In this animal model, hyponatremia developed due to net positive fluid balance and generation of electrolyte-free water by the kidneys. A decreased urinary aquaporin 2 excretion may indicate an escape from antidiuresis.

Correlation between serum copeptin and urinary aquaporin-2 levels in children with primary monosymptomatic nocturnal enuresis.

To determine the utility of serum copeptin and urinary aquaporin-2 (AQP2) levels in diagnosing primary monosymptomatic nocturnal enuresis (PMNE) in children. This study comprised 58 children (30 males and 28 females), aged 9.7 (±2.9) years with PMNE enuresis. Another 29 children (16 males and 13 females) aged 10.2 (±3.3) without nocturnal enuresis (NE) were recruited as a control group. History taking, clinical examination, and assessment of serum copeptin (blood) and AQP-2 levels (urine) were performed in all participants. Serum levels of copeptin, potassium and urinary AQP-2, and urine creatinine levels were lower in the PMNE group compared to the control group (p < 0.001 for all). No significant differences in body mass index, urine specific gravity, serum sodium, serum creatinine, or estimated glomerular filtration rate were observed between groups. This study evaluated both serum copeptin and AQP-2 levels in healthy and enuretic children. In this study, serum levels of copeptin (blood) and AQP2 (urine) were significantly lower in enuretic patients compared to healthy controls. Further, the measurement of urinary AQP-2 levels is more practical than serum copeptin levels due to lower invasiveness.

PS-BPB05-3: SERINE PROTEASE INHIBITION EXERTS AQUARETIC EFFECT AND DECREASES URINARY EXOSOMAL AQP2 LEVELS

Objective: Serine proteases (SPs) play pivotal roles in various physiological processes. In the kidney, it is reported that the epithelial sodium channel (ENaC) is activated via the proteolytic cleavage of α and γ subunits by SPs. We previously reported that a synthetic SP inhibitor camostat mesilate (CM) suppressed the cleavage of γENaC, thereby decreasing sodium reabsorption and blood pressure in aldosterone-infused rats. These results suggest the important roles of SPs within the kidney in the regulation of sodium homeostasis and blood pressure. Here, we aimed to identify novel physiological roles of SPs in the renal tubule and understand the mechanism of actions of SP inhibitors by administering CM into healthy rats. Design and method: Six-week-old male Sprague-Dawley rats were divided into control and CM groups. CM group rats were subcutaneously implanted with sustained-release pellets of CM (14 mg/day). After 24 h urine collection was performed, rats were sacrificed at day 7 to obtain blood and kidney samples. Urine volume was measured during the experimental period, and blood and urinary electrolytes, blood vasopressin, and renal tissue osmolality were measured. Protein expression of SPs and aquaporin-2 (AQP2) was analyzed by Western blotting. Results: CM significantly increased urine volume by approximately two-fold throughout the experimental period [urine volume (mL/day): control, 15.5 ± 2.4; CM, 30.6 ± 5.8], in a urinary sodium and osmolyte excretion-independent manner, which indicated that free water excretion had occurred. The vasopressin, potassium, and calcium levels in the blood and osmolality in the inner medulla, which affect free water reabsorption in the renal tubule, remained unchanged after CM administration. CM decreased urinary exosomal AQP2 excretion, suggesting that the AQP2 activity was suppressed in the collecting duct. These changes were reversed by the infusion of desmopressin. Such water diuretic action caused by CM was independent of its action on prostasin and TMPRSS4, which are serine proteases associated with sodium and water homeostasis, respectively. Conclusion: Our results revealed the association of SP inhibition with free water diuresis in the kidney and demonstrated that CM administration resulted in the downregulation of AQP2. The current findings suggest that SP inhibitors could become a new class of aquaretic drugs.

Impact of Goreisan upon aquaporin-2-incorporated aquaresis system in patients with congestive heart failure.

We often encounter patients with congestive heart failure refractory to conventional diuretics therapy, and Kampo Goreisan is receiving great concern to mediate body water balance particularly for such a cohort. However, its detailed biological mechanism remains uncertain. We had two hospitalized patients with congestive heart failure receiving tolvaptan. Following the administration of Goreisan, both urine cyclic adenosine monophosphate concentration and urine aquaporin-2 concentration decreased, accompanied by incremental diluted urine volume. Although further studies are warranted to establish therapeutic strategy, Goreisan might be a promising therapeutic tool for those with congestive heart failure refractory to conventional diuretics including tolvaptan, via pleiotropic effects including suppression of aquaporin-incorporated water reabsorption system.

Evidence for a Prehypertensive Water Dysregulation Affecting the Development of Hypertension: Results of Very Early Treatment of Vasopressin V1 and V2 Antagonism in Spontaneously Hypertensive Rats.

In addition to long-term regulation of blood pressure (BP), in the kidney resides the initial trigger for hypertension development due to an altered capacity to excrete sodium and water. Betaine is one of the major organic osmolytes, and its betaine/gamma-aminobutyric acid transporter (BGT-1) expression in the renal medulla relates to interstitial tonicity and urinary osmolality and volume. This study investigated altered water and sodium balance as well as changes in antidiuretic hormone (ADH) activity in female spontaneously hypertensive (SHR) and normotensive Wistar Kyoto (WKY) rats from their 3–5 weeks of age (prehypertensive phase) to SHR’s 28–30 weeks of age (established hypertension-organ damage). Young prehypertensive SHRs showed a reduced daily urine output, an elevated urine osmolarity, and higher immunostaining of tubule BGT-1, alpha-1-Na-K ATPase in the outer medulla vs. age-matched WKY. ADH circulating levels were not different between young prehypertensive SHR and WKY, but the urine aquaporin2 (AQP2)/creatinine ratio and labeling of AQP2 in the collecting duct were increased. At 28–30 weeks, hypertensive SHR with moderate renal failure did not show any difference in urinary osmolarity, urine AQP2/creatinine ratio, tubule BGT-1, and alpha-1-Na-K ATPase as compared with WKY. These results suggest an increased sensitivity to ADH in prehypertensive female SHR. On this basis, a second series of experiments were set to study the role of ADH V1 and V2 receptors in the development of hypertension, and a group of female prehypertensive SHRs were treated from the 25th to 49th day of age with either V1 (OPC21268) or V2 (OPC 41061) receptor antagonists to evaluate the BP time course. OPC 41061-treated SHRs had a delayed development of hypertension for 5 weeks without effect in OPC 21268-treated SHRs. In prehypertensive female SHR, an increased renal ADH sensitivity is crucial for the development of hypertension by favoring a positive water balance. Early treatment with selective V2 antagonism delays future hypertension development in young SHRs.

Altered arginine vasopressin-cyclic AMP-aquaporin 2 pathway in patients with chronic kidney disease.

In the collecting ducts of the kidney, arginine vasopressin (AVP), cyclic adenosine monophosphate (cAMP), and aquaporin 2 (AQP2) play a pivotal role in maintaining fluid volume and serum osmolality in humans. However, their association among those with chronic kidney disease (CKD) remains uncertain. We prospectively included the out-patients with CKD and measured osmolality-related biomarkers including plasma AVP, urine cAMP, urine AQP2, and urine osmolality levels. Association among these parameters at each CKD stage was investigated. A total of 121 patients were included (median age 71years old [61-78], 89 men, estimated glomerular filtration ratio 28.6 [16.4-45.3] mL/min/1.73m2). Serum osmolality increased as CKD progression, accompanying incremental plasma AVP levels, whereas urine cAMP, urine AQP2, and urine osmolality decreased as CKD progression. At advanced CKD stage, urine cAMP remained low irrespective of the AVP stimulation, whereas urine cAMP levels varied according to the levels of plasma AVP at less advanced CKD stage. The associations between urine cAMP and urine AQP2 and between urine AQP2 and urine osmolality remained preserved irrespective of the CKD stages. Vasopressin type-2 receptor seems to be particularly impaired in patients with advanced CKD, whereas the signal cascade of the downstream of vasopressin type-2 receptor is relatively preserved. Urine cAMP might be a promising marker to estimate the residual function of the collecting duct.

Predictive Value of Urinary Aquaporin 2 for Acute Kidney Injury in Patients with Acute Decompensated Heart Failure.

Acute kidney injury (AKI) is frequently encountered in people with acute decompensated heart failure (ADHF) and is associated with increased morbidity and mortality. Early detection of a urinary biomarker of kidney injury might allow a prompt diagnosis and improve outcomes. Levels of urinary aquaporin 2 (UAQP2), which is also associated with several renal diseases, are increased with ADHF. We aimed to determine whether UAQP2 predicted AKI in patients with ADHF. We conducted a prospective observation study in the coronary care unit (CCU) in a tertiary care university hospital in Taiwan. Individuals with ADHF admitted to the CCU between November 2009 and November 2014 were enrolled, and serum and urinary samples were collected. AKI was diagnosed in 69 (36.5%) of 189 adult patients (mean age: 68 years). Area under the receiver operating characteristic curve (AUROC) of biomarkers was evaluated to evaluate the diagnostic power for AKI. Both brain natriuretic peptide and UAQP2 demonstrated acceptable AUROCs (0.759 and 0.795, respectively). A combination of the markers had an AUROC of 0.802. UAQP2 is a potential biomarker of AKI in CCU patients with ADHF. Additional research on this novel biomarker is required.

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.

Urinary Aquaporin 2 as a Potential Indicator Predicting Tolvaptan Response in Patients With ADPKD

IntroductionTolvaptan is used to treat autosomal dominant polycystic kidney disease (ADPKD) because it inhibits binding of the antidiuretic hormone vasopressin to the vasopressin V2 receptor (V2R), which suppresses the insertion of preformed water channel aquaporin 2 (AQP2) molecules in the luminal membrane of the collecting duct cells.MethodsThis single-center, prospective observational cohort study investigated whether decreased AQP2 elimination in urine affects the renal prognosis of patients who received tolvaptan. We selected 92 patients with ADPKD who were administered tolvaptan in our hospital. We evaluated correlations between changes in urinary AQP2 (U-AQP2) and clinical parameters and the annual change in total kidney volume (TKV) and estimated glomerular filtration rate (eGFR) as renal prognostic factors using univariable and multivariable multiple regression analyses.ResultsThe observation period was 2.4 ± 1.5 years. U-AQP2 per milligram of urinary creatinine (U-AQP2/Cr) decreased from 67.8 ± 50.6 to 20.7 ± 15.1 fmol/mg urinary creatinine after 1 month of tolvaptan treatment. This initial change in U-AQP2/Cr was correlated with high baseline U-AQP2/Cr, low baseline eGFR, and a large initial change in eGFR (baseline to 1 month). The initial change in U-AQP2/Cr (baseline to 1 month) was strongly correlated with the annual change in TKV and eGFR in multivariable analysis.ConclusionInitial decrease in U-AQP2/Cr in the first month of treatment reflects the pharmacologic effect of tolvaptan and could be an indicator of renal prognosis during tolvaptan treatment.

Tolvaptan in Hyponatremia – A Pharmacologic approach

Tolvaptan is the first orally active vasopressin receptor 2 antagonist approved by FDA in 2009 for the treatment of clinically significant hypervolemic and euvolemic hyponatremia associated with heart failure, syndrome of inappropriate antidiuretic hormone secretion, liver cirrhosis. Binding of vasopressin to V2 receptors which are located on renal collecting duct cells were competitively inhibited by Tolvaptan thus prevents vasopressin-mediated activation of these receptors and leads to an increase in the water permeability of the collecting duct causing an increase in the concentration of urine, results in an increase in free water clearance, a decrease in urine osmolality and a fall in serum sodium concentration. Tolvaptan is different from other conventional diuretics because it does not stimulate the sodium channel and increases free water excretion without affecting urinary sodium and potassium excretion. It is metabolized principally via the cytochrome P 450 (CYP 3A) isoenzymes and is eliminated by routes other than renal. Concurrent administration of tolvaptan with ketoconazole or other strong CYP 3A inhibitor decrease the total clearance of tolvaptan and increases tolvaptan concentrations. Urine sodium potassium ratio, weight loss, soluble CD14, urinary aquaporin 2 levels are known predictors of tolvaptan response. Tolvaptan is associated with decreased cost and high effectiveness.

Renal expression and urinary excretion of aquaporin-2 in postobstructive uropathy in rats.

This work assessed the time course of water renal management together with aquaporin-2 (AQP2) kidney expression and urinary AQP2 levels (AQP2u) in obstructive nephropathy. Adult male Wistar rats were monitored after 1, 2, and 7days of bilateral ureteral release (bilateral ureteral obstruction (BUO); BUO-1, BUO-2 and BUO-7). Renal water handling was evaluated using conventional clearance techniques. AQP2 levels were assessed by immunoblotting and immunohistochemical techniques. AQP2 expression in apical membranes was downregulated in BUO-1 rats and upregulated both in BUO-2 and BUO-7 animals. AQP2 protein expression in whole cell lysate fraction from kidney cortex and medulla were significantly decreased in all the experimental groups. Concomitantly, mRNA levels of AQP2 decreased in renal medulla of all groups and in renal cortex from BUO-1; however, in renal cortex from BUO-2 and BUO-7 a recovery and an increase in the level of AQP2 mRNA were, respectively, observed. BUO-7 group showed a significant increase in AQP2u. The alterations observed in apical membranes AQP2 expression could explain, at least in part, the evolution time of water kidney management in the postobstructive phase of BUO. Additionally, the AQP2u increase after 7 days of ureteral release may be postulated as a biomarker of improvement in the kidney function.

Urine concentrating defect as presenting sign of progressive renal failure in Bardet-Biedl syndrome patients.

BackgroundUrine concentrating defect is a common dysfunction in ciliopathies, even though its underlying mechanism and its prognostic meaning are largely unknown. This study assesses renal function in a cohort of 54 Bardet–Biedl syndrome (BBS) individuals and analyses whether renal hyposthenuria is the result of specific tubule dysfunction and predicts renal disease progression.MethodsThe estimated glomerular filtration rate (eGFR), urine albumin:creatinine ratio (ACR) and maximum urine osmolality (max-Uosm) were measured in all patients. Genetic analysis was conducted in 43 patients. Annual eGFR decline (ΔeGFR) was measured in patients with a median follow-up period of 6.5 years. Urine aquaporin-2 (uAQP2) excretion was measured and the furosemide test was performed in patients and controls.ResultsAt baseline, 33 (61.1%), 12 (22.2%) and 9 (16.7%) patients showed an eGFR >90, 60–90 and <60 mL/min/1.73 m2, respectively; 27.3% showed an ACR >30 mg/g and 55.8% of patients showed urine concentrating defect in the absence of renal insufficiency. Baseline eGFR, but not max-Uosm, correlated negatively with age. Conversely, truncating mutations affected max-Uosm and showed a trend towards a reduction in eGFR. Max-Uosm correlated with ΔeGFR (P < 0.005), suggesting that urine concentrating defect may predict disease progression. uAQP2 excretion and Na+ and Cl− fractional excretion after furosemide did not differ between hyposthenuric patients and controls, suggesting that specific collecting duct and thick ascending limb dysfunctions are unlikely to play a central role in the pathogenesis of hyposthenuria.ConclusionsHyposthenuria is a warning sign predicting poor renal outcome in BBS. The pathophysiology of this defect is most likely beyond defective tubular function.

A Comparison of Urine Dilution Ability between Adult Dominant Polycystic Kidney Disease, Other Chronic Kidney Diseases, and Healthy Control Subjects: A Case-Control Study.

The final dilution of urine is regulated via aquaporin-2 water channels in the distal part of the nephron. It is unclear whether urine dilution ability in autosomal dominant polycystic kidney disease patients (ADPKD patients) 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 dilution ability in ADPKD patients compared to non-ADPKD patients and healthy controls. Methods. Eighteen ADPKD, 16 non-ADPKD patients (both with chronic kidney disease, stage I-IV), and 18 healthy controls received an oral water load of 20 ml/kg body weight. Urine was collected in 7 consecutive periods. We measured free water clearance (CH2O), urine osmolality, urine output, fractional excretion of sodium, urine aquaporin2 (u-AQP2), and urine epithelial sodium channel (u-ENaC). Blood samples were drawn four times (at baseline, 2 h, 4 h, and 6 hours after the water load) for analyses of plasma osmolality, vasopressin, renin, angiotensin II, and aldosterone. Brachial and central blood pressure was measured regularly during the test. Results. The three groups were age and gender matched, and the patient groups had similar renal function. One hour after water load, the ADPKD patients had an increased CH2O compared to non-ADPKD patients (2.97 ± 2.42 ml/min in ADPKD patients vs. 1.31 ± 1.50 ml/min in non-ADPKD patients, p0.029). The reduction in u-AQP2 and u-ENaC occurred earlier in ADPKD than in non-ADPKD patients. Plasma concentrations of vasopressin, renin, angiotensin II, and aldosterone and blood pressure measurements did not show any differences that could explain the deviation in urine dilution capacity between the patient groups. Conclusions. ADPKD patients had a higher CH2O than non-ADPKD patients after an oral water load, and u-AQP2 and u-ENaC were more rapidly reduced than in non-ADPKD patients. Thus, urine-diluting capacity may be better preserved in ADPKD patients than in non-ADPKD patients.

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.

Secondary oxalosis induced by xylitol concurrent with lithium-induced nephrogenic diabetes insipidus: a case report

BackgroundXylitol is an approved food additive that is widely used as a sweetener in many manufactured products. It is also used in pharmaceuticals. Secondary oxalosis resulting from high dietary oxalate has been reported. However, reported cases of oxalosis following xylitol infusion are rare.Case presentationA 39-year-old man with a 16-year history of organic psychiatric disorder was hospitalized for a laparoscopic cholecystectomy because of cholecystolithiasis. He had been treated with several antipsychotics and mood stabilizers, including lithium. The patient had polyuria (> 4000 mL/day) and his serum sodium levels ranged from 150 to 160 mmol/L. Urine osmolality was 141 mOsm/L, while serum arginine vasopressin level was 6.4 pg/mL. The patient was diagnosed with nephrogenic diabetes insipidus (NDI), and lithium was gradually discontinued. Postoperative urine volumes increased further to a maximum of 10,000 mL/day, and up to 10,000 mL/day of 5% xylitol was administered. The patient’s consciousness level declined and serum creatinine increased to 4.74 mg/dL. This was followed by coma and metabolic acidosis. After continuous venous hemodiafiltration, serum sodium improved to the upper 140 mmol/L range and serum creatinine decreased to 1.25 mg/dL at discharge. However, polyuria and polydipsia of approximately 4000 mL/day persisted. Renal biopsy showed oxalate crystals and decreased expression of aquaporin-2 (AQP2) in the renal tubules. Urinary AQP2 was undetected. The patient was discharged on day 82 after admission.ConclusionsOur patient was diagnosed with lithium-induced NDI and secondary oxalosis induced by excess xylitol infusion. NDI became apparent perioperatively because of fasting, and an overdose of xylitol infusion led to cerebrorenal oxalosis. Our patient received a maximum xylitol dose of 500 g/day and a total dose of 2925 g. Patients receiving lithium therapy must be closely monitored during the perioperative period, and rehydration therapy using xylitol infusion should be avoided in such cases.

Podocyte stress and detachment measured in urine are related to mean arterial pressure in healthy humans

Hypertension-associated progressive glomerulosclerosis is a significant driver of both de novo and all-cause chronic kidney disease leading to end-stage kidney failure. The progression of glomerular disease proceeds via continuing depletion of podocytes from the glomeruli into the ultrafiltrate. To non-invasively assess injury patterns associated with mean arterial pressure (MAP), we conducted an observational study of 87 healthy normotensive individuals who were cleared for living kidney donation. Urine pellet podocin and aquaporin2 mRNAs normalized to the urine creatinine concentration (UPod:Creat ratio and UAqp2:Creat ratio) were used as markers of podocyte detachment and tubular injury, respectively. The ratio of two podocyte mRNA markers, podocin to nephrin (UPod:Neph) as well as the ratio of podocin to the tubular marker aquaporin2 (UPod:Aqp2) estimated the relative rates of podocyte stress and glomerular vs. tubular injury. The MAP was positively correlated with the UPod:Neph and UPod:Aqp2, thereby confirming the relationship of MAP with podocyte stress and the preferential targeting of the glomerulus by higher MAP. In multivariable linear regression analysis, both UPod:Neph and UPod:Creat, but not UAqp2:Creat or proteinuria, were both significantly related to a range of normal MAP (70 to 110 mmHg). Systolic, as opposed to diastolic or pulse pressure was associated with UPod:Creat. Thus, higher podocyte stress and detachment into the urine are associated with MAP even in a relatively "normal" range of MAP. Hence, urine pellet mRNA monitoring can potentially identify progression risk before the onset of overt hypertension, proteinuria or chronic kidney disease.

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.