BACKGROUND: Nephrogenic diabetes insipidus (NDI) is a rare genetic disease that causes water imbalance. The kidneys play a crucial role in regulating body fluids by controlling water balance through urine excretion. This highlights their essential function in managing the body\'s water levels, but individuals with NDI may have excess urine production (polyuria), that leads to excessive thirst (polydipsia). Untreated affected individuals may exhibit poor feeding and failure to thrive. This disease is caused by mutations in the AVPR2 and the AQP2 genes which have the X-linked and autosomal recessive/dominant inheritance, respectively. Both of these genes are expressed in the kidney.
METHODS: Twelve Iranian patients from 10 consanguineous families were studied in this project. DNA was extracted from the whole blood samples of the patients and their parents. All coding exons and exon-intron boundaries of the AVPR2 and AQP2 genes were sequenced in the affected individuals, and the identified variants were investigated in the parents. All variants were analyzed according to the ACMG (American College of Medical Genetics and Genomics) guidelines.
RESULTS: In this study, 6 different mutations were identified in the patients, including 5 in the AQP2 gene (c.439G>A, c.538G>A, c.140C>T, c.450T>A, and the novel c.668T>C) and 1 in the AVPR2 gene (c.337C>T) in the present study.
CONCLUSIONS: As expected, all the detected mutations in this study were missense. According to the ACMG guideline, the identified mutations were categorized as pathogenic or likely pathogenic. Unlike previous studies which showed more than 90% of mutations were in the AVPR2 gene, and only less than 10% of the mutations were in the AQP2 gene, it was found that more than 90% of our identified mutations located in the AQP2 gene, and only one mutation was observed in the AVPR2 gene, which seems it may be a result of the high rate of consanguineous marriages in the Iranian population. We observed genotype-phenotype correlation in some of our affected individuals, and some of the mutations were observed in unrelated families from same ethnicity which could be suggestive of a founder mutation.

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.

To construct an animal model of atrial fibrillation and observe the effect of acute atrial fibrillation on renal water and sodium metabolism in mice. A total of 20 C57 mice were randomly assigned to 2 groups (n = 10/group): control group (CON) and atrial fibrillation group (AF). The mice model of atrial fibrillation was induced by chlorhexidine gluconate (CG) in combination with transesophageal atrial spacing. The urine of the two groups of mice was collected, and then we calculate the urine volume and urine sodium content. The expression of TGF-β and type III collagen in the atrial myocardium of the two groups was detected by immunohistochemistry and Western Blot. The levels of CRP and IL-6 in blood were observed by ELISA, and the NF-κB, TGF-β, collagen type III, AQP2, AQP3, AQP4, ENaC-β, ENaC-γ, SGK1 and NKCC proteins in the kidneys of the two groups of mice was observed by Western Blot. Compared with CON, the expression of TGF-β and type III collagen in the atrial myocardium of the mice in AF were increased, the levels of CRP and IL-6 in the blood in AF were increased, and the renal NF-κB, TGF-β, type III collagen AQP2, AQP3, ENaC-β, ENaC-γ, SGK1 and NKCC protein expression in AF were up-regulated. The level of urine volume and urine sodium content in AF were significantly reduced. In the acute attack of atrial fibrillation, the formation of renal inflammatory response and fibrosis is activated, and the renal water and sodium metabolism is hindered, which is related to the up-regulated of the expressions of renal NKCC, ENaC and AQPs.

Aurantii Fructus is a commonly used qi-regulating medicinal herb in China. Both traditional Chinese medicine theory and modern experimental research demonstrate that Aurantii Fructus has dryness effect, the material basis of which remains unclear. In recent years, spectrum-effect relationship has been widely employed in the study of active ingredients in Chinese medicinal herbs, the research ideas and methods of which have been constantly improved. Based on the idea of spectrum-effect study, the ultra-high perfor-mance liquid chromatography-quadrupole-time of flight mass spectrometry(UHPLC-Q-TOF-MS) fingerprints of different fractions of Aurantii Fructus extract were established for the identification of total components. Then, the dryness effects of the fractions on normal mice and gastrointestinal motility disorder(GMD) rats were systematically compared. Finally, principal component analysis(PCA), Pearson bivariate correlation analysis and orthogonal partial least squares analysis(OPLS) were integrated to identify the dryness components of Aurantii Fructusextract. The results showed that narirutin, naringin, naringenin, poncirin, oxypeucedanin, and eriodictyol-7-O-glucoside had significant correlations with and contributed to the expression of AQP2 in kidney, AQP3 in colon, and AQP5 in submandibular gland, which were the main dryness components in Aurantii Fructus.

BACKGROUND: Lithium is widely used in the treatment of bipolar disorders and may lead to nephrogenic diabetes insipidus (NDI), following long-term treatment. Metformin is considered the preferred initial therapy for patients with type 2 diabetes mellitus (T2D).
OBJECTIVE: To investigate the protective effect of metformin on the kidney damage caused by lithium administration.
METHODS: Using an animal model of chronic lithium-induced NDI, rats were divided into 4 groups: sham, metformin, lithium, and lithium + metformin. The effects of these treatments were examined using serum electrolytes, blood and tissue total antioxidant status, total oxidant status, the oxidative stress index, urine and blood osmolality, and tissue aquaporin-2 (AQP2) levels. Additionally, histopathological changes, including congestion, hydropic swelling, tubular necrosis, tubular atrophy, and Bowman\'s capsule dilatation, were evaluated. The total histopathological score was obtained by summing the scores for each pathological finding.
RESULTS: In the lithium group, biochemical variables indicating NDI, including sodium, chloride and blood osmolality, increased, and urine osmolality decreased, compared to the sham group. With metformin treatment, the blood osmolality decreased from 328.17 mOsm/kg to 306.33 mOsm/kg, and urine osmolality increased from 349.67 mOsm/kg to 754.50 mOsm/kg (p = 0.004 and p = 0.001, respectively). Tissue AQP2 levels decreased with lithium administration but stabilized with metformin treatment. Additionally, in comparison to the lithium group, the total histopathological score in the metformin group declined from 8.0 to 2.0 (p = 0.002).
CONCLUSIONS: Metformin may help protect the kidneys from lithium-induced NDI through the AQP2 regulating effect and a reduction in oxidative stress.

In this paper, non-equilibrium MD simulations (NEMD) of human aquaporin-2 (AQP2) in the presence of an external static electric field have been performed along + z and - z directions of the pore axis. The impacts of the electric field direction on the gating mechanism corresponding to the selectivity filter (SF) region of AQP2 have been studied. Besides, the effects of applied external electric field on the PMF profile of water molecules translocation, water permeability, and molecules dipole orientation are investigated. Our results showed that when the external electric field is implemented along the + z direction of the channels, the selectivity filter region is kept in the wide conformation for the majority of the time. Therefore, a remarkable increase in the overall water permeability can be seen compared to the case without any external electric field. This is in contrast to the effects of - z-directed electric field on the conformations of the selectivity filter, which induces mostly narrow conformations in this constriction region. A substantial higher energy barrier emerged in the middle of the AQP2\'s pores under the effect of -z-directed electric field in comparison with the zero and + z-directed electric field strengths, which is mainly ascribed to the deviation from bipolar dipole orientation within the AQP2\'s pores.Communicated by Ramaswamy H. Sarma.

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.
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).
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.
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.
Current Controlled Trial NCT04363554 , date of registration: 20.08.2017.

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.
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.
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.
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.
(EU Clinical trials register number: 2015-002585-23 , registered on 5th November 2015).

In order to establish a more perfect evaluation system for dryness effect of Atractylodis Rhizoma, determine the main dry parts of Atractylodis Rhizoma，and further define the mechanism of stir-baked Atractylodis Rhizoma in reducing the dryness. The healthy rats were given with different doses of water extract and volatile oil of raw Atractylodis Rhizoma and stir-baked Atractylodis Rhizoma for 21 days. Based on the theory of the dry-dry and dryness-induced Yin deficiency, the amount of drinking water, tissue morphology of submandibular glands, urine volume and the expression of aquaporin 2 (AQP2) in the kidneys, as well as blood rheology, ratio of cAMP/cGMP in serum and the content of Na⁺-K⁺-ATP enzyme were selected as the evaluation indexes. The results indicated that the rats with high dose volatile oil from raw Atractylodis Rhizoma had a significant increase in the amount of drinking water, urine volume, blood viscosity, ratio of cAMP/cGMP and content of Na⁺-K⁺-ATP enzyme in the serum（P<0.05）as compared with the soybean oil group; meanwhile, atrophy of submandibular acinar gland was obvious，and the expression of aquaporin 2 was reduced significantly（P<0.05）. There were significant differences between volatile oil high dose group of raw Atractylodis Rhizoma and volatile oil high dose group of stir-baked Atractylodis Rhizoma. There was no significant difference between the water extract groups of raw and stir-baked Atractylodis Rhizoma and the saline group. A comprehensive evaluation system for the dryness effect of Atractylodis Rhizoma was established. It was confirmed that the volatile oil part was the main dry part of Atractylodis Rhizoma. It revealed that the mechanism of dryness effect of Atractylodis Rhizoma was not only related to the decrease of the total content of the volatile oil, but also may be related to the transformation of dryness components in the volatile oil. It provides references for the study of material basis of Atractylodis Rhizoma dryness, provides an experimental basis for the clinical application of Atractylodis Rhizoma, further clarifies the mechanism of stir-baked Atractylodis Rhizoma in reducing the dryness, and provides thoughts for the evaluation of other dry traditional Chinese medicines.

Objectives Endolymphatic sac (ELS) pathophysiology in Ménière\'s disease (MD) remains poorly understood. We identified from the literature a group of proteins expressed on the ELS and involved in endolymph volume regulation: aquaporin-2 (AQP2), vasopressin receptor V2R, sodium potassium chloride cotransporter 2 (NKCC2), and transient receptor potential cation channel V4 (TRPV4). Our objective was to determine whether their ELS expression was altered in MD, to better understand the pathophysiology of endolymphatic hydrops. Study Design Prospective case-control study. Setting Tertiary care center. Subjects Twenty-four patients with definite MD undergoing endolymphatic duct blockage surgery were recruited, as well as 23 controls with no history of MD undergoing surgery for vestibular schwannoma (VS). Methods ELS biopsies and blood samples for plasma arginine vasopressin (AVP) were obtained. Immunohistochemistry for AQP2, V2R, NKCC2, and TRPV4 was performed. Slides were scanned digitally for highly sensitive pixel density analysis by specialized software (VIS; Visiopharm). Results Global scores generated by the software represent total and relative protein expression density of 3 staining intensity levels, exclusively on ELS epithelium. AQP2 expression density was significantly elevated in MD compared to VS ( P = .003). There was no significant difference in plasma AVP, V2R, NKCC2, and TRPV4 expression. Conclusion This original study evaluates simultaneous in situ expression of AQP2, V2R, NKCC2, and TRPV4 on the human ELS in MD, with a control group. Our results show only AQP2 upregulation on the ELS of patients with MD. We suggest a constitutively increased expression of AQP2 in MD, independent of its regulatory axis (AVP-V2R). Acquired regulator sequence mutations could support this model.