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Bradykinin (BK) is one of the most important peptide regulating vascular tone, water, and ionic balance in the body, playing a key role in controlling blood pressure. Interestingly, patients with essential hypertension excrete less BK than do normotensive subjects. To elucidate the mechanism by which BK regulates renal water transport, AQP2-transfected collecting duct CD8 cells, expressing the BK receptor (BK2), were used as experimental model. In CD8 cells, BK pretreatment impaired forskolin-induced AQP2 translocation to the apical plasma membrane. To clarify the signal transduction cascade associated with this effect, we first investigated whether BK induced increase in citosolic calcium, via the G protein Gq known to be coupled to BK2 receptor. Spectrofluorometry employing fura-2-AM revealed that 100 nM BK elicited a significant increase in Cai (from 72.8 ± 7.4, to 310.7 ± 43.4 nM, n=6, P which was abolished by the receptor antagonist HOE-140. In renal cells, Gq coupled receptors may activate Rho and its downstream effectors. In CD8 cells it has been shown that forskolin-induced AQP2 translocation is associated with a decrease in Rho activity and depolymerization of F-actin which facilitates the translocation of AQP2 to the plasma membrane. Interestingly, BK treatment in CD8 cells resulted in a significant increase in Rho activity, as assessed by selective pull down experiments. In agreement with these data, BK induced a significant increase of F-actin content as assessed by actin polymerization assay and by immunofluorescence experiments. BK effects on actin assembly were abolished by the BK2 agonist HOE-140. We conclude that the diuretic effect of bradykinin may in part be explained by impairement of AQP2 translocation via activation of Rho and F-actin formation. [ABSTRACT FROM AUTHOR]

The small Rho GTP-binding proteins are important cell morphology, function, and apoptosis regulators. Unlike other Rho proteins, RhoB can be subjected to either geranylgeranylation (RhoB-GG) or farnesylation (RhoB-F), making that the only target of the farnesyltransferase inhibitor (FTI). Fluorescence resonance energy transfer experiments revealed that RhoB is activated by hyperosmolarity. By contrast, hyposmolarity did not affect RhoB activity. Interestingly, treatment with farnesyltransferase inhibitor-277 (FTI-277) decreased the cell size. To evaluate whether RhoB plays a role in volume reduction, renal collecting duct MCD4 cells and Human Kidney, HK-2 were transiently transfected with RhoB-wildtype-Enhance Green Fluorescence Protein (RhoB-wt-EGFP) and RhoB-CLLL-EGFP which cannot undergo farnesylation. A calcein-based fluorescent assay revealed that hyperosmolarity caused a significant reduction of cell volume in mock and RhoB-wt-EGFP-expressing cells. By contrast, cells treated with FTI-277 or expressing the RhoB-CLLL-EGFP mutant did not properly respond to hyperosmolarity with respect to mock and RhoB-wt-EGFP expressing cells. These findings were further confirmed by 3D-LSCM showing that RhoB-CLLL-EGFP cells displayed a significant reduction in cell size compared to cells expressing RhoB-wt-EGFP. Moreover, flow cytometry analysis revealed that RhoB-CLLL-EGFP expressing cells as well as FTI-277-treated cells showed a significant increase in cell apoptosis. Together, these data suggested that: (i) RhoB is sensitive to hyperosmolarity and not to hyposmolarity; (ii) inhibition of RhoB farnesylation associates with an increase in cell apoptosis, likely suggesting that RhoB might be a paramount player controlling apoptosis by interfering with responses to cell volume change., (© 2024 Wiley Periodicals LLC.)

Celiac disease - a prevalent food intolerance - requires strict adherence to a lifelong gluten-free (GF) diet as the only effective treatment. However, GF products often lack soluble fibre and have a high glycaemic index. Consequently, there is a pressing need in the food industry to develop GF products with improved nutritional profiles. In this context, the impact of incorporating orange peel flour (OPF) into muffins undergoing sourdough fermentation was examined, focusing on their technological, antioxidant, and nutritional characteristics. The functional properties of OPF were investigated using human colon carcinoma HCT8 cells as a model system. Treatment with OPF extract demonstrated a notable reduction in malignant cell viability and intracellular ROS levels, indicating potent antioxidant capabilities. Western blot analysis revealed significant alterations in key signalling pathways, including increased phosphorylation of NF-kB at serine 536 and reduced intracellular levels of caspase-3, alongside increased phosphorylation of RIPK3 and MLKL, suggesting potential involvement in necroptosis. OPF incorporation in muffins with sourdough increased antioxidant activity, reduced glycaemic index, and affected the volatile profile. Furthermore, based on simulated colonic fermentation, muffins with OPF showed a slight prebiotic effect, supported by the significant increase in bacillus-shaped lactic acid bacteria and Clostridia population. Overall, OPF-enriched muffins demonstrated considerable antioxidant effects and impacts on cell viability, underscoring their potential as functional ingredients in GF products. These findings signify the prospect of OPF enhancing the nutritional profiles and conferring health benefits of GF muffins.

High concentrations of urinary calcium counteract vasopressin action via the activation of the Calcium-Sensing Receptor (CaSR) expressed in the luminal membrane of the collecting duct cells, which impairs the trafficking of aquaporin-2 (AQP2). In line with these findings, we provide evidence that, with respect to wild-type mice, CaSR knock-in (KI) mice mimicking autosomal dominant hypocalcaemia, display a significant decrease in the total content of AQP2 associated with significantly higher levels of AQP2 phosphorylation at Ser261, a phosphorylation site involved in AQP2 degradation. Interestingly, KI mice also had significantly higher levels of phosphorylated p38MAPK, a downstream effector of CaSR and known to phosphorylate AQP2 at Ser261. Moreover, ATF1 phosphorylated at Ser63, a transcription factor downstream of p38MAPK, was significantly higher in KI. In addition, KI mice had significantly higher levels of AQP2-targeting miRNA137 consistent with a post-transcriptional downregulation of AQP2. In vivo treatment of KI mice with the calcilytic JTT-305, a CaSR antagonist, increased AQP2 expression and reduced AQP2-targeting miRNA137 levels in KI mice. Together, these results provide direct evidence for a critical role of CaSR in impairing both short-term vasopressin response by increasing AQP2-pS261, as well as AQP2 abundance, via the p38MAPK-ATF1-miR137 pathway. KEY POINTS: Calcium-Sensing Receptor (CaSR) activating mutations are the main cause of autosomal dominant hypocalcaemia (ADH) characterized by inappropriate renal calcium excretion leading to hypocalcaemia and hypercalciuria. Current treatments of ADH patients with parathyroid hormone, although improving hypocalcaemia, do not improve hypercalciuria or nephrocalcinosis. In vivo treatment with calcilytic JTT-305/MK-5442 ameliorates most of the ADH phenotypes of the CaSR knock-in mice including hypercalciuria or nephrocalcinosis and reverses the downregulation of the vasopressin-sensitive aquaporin-2 (AQP2) expression, providing direct evidence for a critical role of CaSR in impairing vasopressin response. The beneficial effect of calcilytic in reducing the risk of renal calcification may occur in a parathyroid hormone-independent action through vasopressin-dependent inhibition of cAMP synthesis in the thick ascending limb and in the collecting duct. The amelioration of most of the abnormalities in calcium metabolism including hypercalciuria, renal calcification, and AQP2-mediated osmotic water reabsorption makes calcilytic a good candidate as a novel therapeutic agent for ADH., (© 2024 The Authors. The Journal of Physiology © 2024 The Physiological Society.)

Nephrogenic syndrome of inappropriate antidiuresis (NSIAD) is a rare X-linked disease caused by gain-of-function mutations of arginine vasopressin receptor 2 (V2R). Patients with NSIAD are characterized by the inability to excrete a free water load and by inappropriately increased urinary osmolality despite very low levels of plasma vasopressin, resulting in euvolaemic hyponatraemia. To dissect the signalling downstream V2R constitutively active variants, Flp-In T-REx Madin-Darby canine kidney (FTM) cells, stably transfected with V2R mutants (R137L, R137C and F229V) and AQP2-wt or non-phosphorylatable AQP2-S269A/AQP2-S256A, were used as cellular models. All three activating V2R mutations presented constitutive plasma membrane expression of AQP2-wt and significantly higher basal water permeability. In addition, V2R-R137L/C showed significantly higher activity of Rho-associated kinase (ROCK), a serine/threonine kinase previously suggested to be involved in S269-AQP2 phosphorylation downstream of these V2R mutants. Interestingly, FTM cells expressing V2R-R137L/C mutants and AQP2-S269A showed a significant reduction in AQP2 membrane abundance and a significant reduction in ROCK activity, indicating the crucial importance of S269-AQP2 phosphorylation in the gain-of-function phenotype. Conversely, V2R-R137L/C mutants retained the gain-of-function phenotype when AQP2-S256A was co-expressed. In contrast, cells expressing the F229V mutant and the non-phosphorylatable AQP2-S256A had a significant reduction in AQP2 membrane abundance along with a significant reduction in basal osmotic water permeability, indicating a crucial role of Ser256 for this mutant. These data indicate that the constitutive AQP2 trafficking associated with the gain-of-function V2R-R137L/C mutants causing NSIAD is protein kinase A independent and requires an intact Ser269 in AQP2 under the control of ROCK phosphorylation. KEY POINTS: Nephrogenic syndrome of inappropriate antidiuresis is caused by two constitutively active variant phenotypes of AVPR2, one sensitive to vaptans (V2R-F229V) and the other vaptan resistant (V2R-R137C/L). In renal cells, all three activating arginine vasopressin receptor 2 (V2R) variants display constitutive AQP2 plasma membrane expression and high basal water permeability. In cells expressing V2R-R137L/C mutants, disruption of the AQP2-S269 phosphorylation site caused the loss of the gain-of-function phenotype, which, in contrast, was retained in V2R-F229V-expressing cells. Cells expressing the V2R-F229V mutant were instead sensitive to disruption of the AQP2-S256 phosphorylation site. The serine/threonine kinase Rho-associated kinase (ROCK) was found to be involved in AQP2-S269 phosphorylation downstream of the V2R-R137L/C mutants. These findings might have clinical relevance for patients with nephrogenic syndrome of inappropriate antidiuresis., (© 2023 The Authors. The Journal of Physiology published by John Wiley & Sons Ltd on behalf of The Physiological Society.)

Small cell lung cancer (SCLC) is treated as a homogeneous disease, although the expression of NEUROD1, ASCL1, POU2F3, and YAP1 identifies distinct molecular subtypes. The MYC oncogene, amplified in SCLC, was recently shown to act as a lineage-specific factor to associate subtypes with histological classes. Indeed, MYC-driven SCLCs show a distinct metabolic profile and drug sensitivity. To disentangle their molecular features, we focused on the co-amplified PVT1, frequently overexpressed and originating circular (circRNA) and chimeric RNAs. We analyzed hsa_circ_0001821 (circPVT1) and PVT1/AKT3 (chimPVT1) as examples of such transcripts, respectively, to unveil their tumorigenic contribution to SCLC. In detail, circPVT1 activated a pro-proliferative and anti-apoptotic program when over-expressed in lung cells, and knockdown of chimPVT1 induced a decrease in cell growth and an increase of apoptosis in SCLC in vitro. Moreover, the investigated PVT1 transcripts underlined a functional connection between MYC and YAP1/POU2F3, suggesting that they contribute to the transcriptional landscape associated with MYC amplification. In conclusion, we have uncovered a functional role of circular and chimeric PVT1 transcripts in SCLC; these entities may prove useful as novel biomarkers in MYC-amplified tumors., (© 2022 Wiley Periodicals LLC.)

The deletion of phenylalanine at position 508 (F508del) produces a misfolded CFTR protein that is retained in the ER and degraded. The lack of normal CFTR channel activity is associated with chronic infection and inflammation which are the primary causes of declining lung function in Cystic Fibrosis (CF) patients. Moreover, LPS-dependent oxidative stress downregulates CFTR function in airway epithelial cells. Olive leaf extract (OLE) is used in traditional medicine for its effects, including anti-oxidant and anti-inflammatory ones. We found that OLE decreased the intracellular ROS levels in a dose-response manner in CFBE cells. Moreover, OLE attenuates the inflammatory response to LPS or IL-1β/TNFα stimulation, mimicking the infection and inflammatory status of CF patients, in CFBE and primary nasal epithelial (HNE) cells. Furthermore, we demonstrated that OLE restored the LPS-mediated decrease of Trikfafta TM -dependent F508del-CFTR function in CFBE and HNE cultures. These findings provide strong evidence of OLE to prevent redox imbalance and inflammation that can cause chronic lung damage by enhancing the antioxidant activity and attenuating inflammation in CF airway epithelial cells. Additionally, OLE might be used in combination with CFTR modulators therapy to improve their efficacy in CF patients.

Extracellular vesicles (EVs) have emerged as important players in cell-to-cell communication within the bone marrow (BM) of multiple myeloma (MM) patients, where they mediate several tumor-associated processes. Here, we investigate the contribution of fibroblasts-derived EVs (FBEVs) in supporting BM angiogenesis. We demonstrate that FBEVs' cargo contains several angiogenic cytokines (i.e., VEGF, HGF, and ANG-1) that promote an early over-angiogenic effect independent from EVs uptake. Interestingly, co-culture of endothelial cells from MM patients (MMECs) with FBEVs for 1 or 6 h activates the VEGF/VEGFR2, HGF/HGFR, and ANG-1/Tie2 axis, as well as the mTORC2 and Wnt/β-catenin pathways, suggesting that the early over-angiogenic effect is a cytokine-mediated process. FBEVs internalization occurs after longer exposure of MMECs to FBEVs (24 h) and induces a late over-angiogenic effect by increasing MMECs migration, chemotaxis, metalloproteases release, and capillarogenesis. FBEVs uptake activates mTORC1, MAPK, SRC, and STAT pathways that promote the release of pro-angiogenic cytokines, further supporting the pro-angiogenic milieu. Overall, our results demonstrate that FBEVs foster MM angiogenesis through dual time-related uptake-independent and uptake-dependent mechanisms that activate different intracellular pathways and transcriptional programs, providing the rationale for designing novel anti-angiogenic strategies.

Sex hormones play an important role in the regulation of water homeostasis, and we have previously shown that tamoxifen (TAM), a selective estrogen receptor modulator (SERM), affects the regulation of aquaporin (AQP)-2. In this study, we investigated the effect of TAM on the expression and localization of AQP3 in collecting ducts using various animal, tissue, and cell models. The impact of TAM on AQP3 regulation was studied in rats subjected to 7 days of unilateral ureteral obstruction (UUO), with the rats fed a lithium-containing diet to induce nephrogenic diabetes insipidus (NDI), as well as in human precision-cut kidney slices (PCKS). Moreover, intracellular trafficking of AQP3 after TAM treatment was investigated in Madin-Darby Canine Kidney (MDCK) cells stably expressing AQP3. In all models, the expression of AQP3 was evaluated by Western blotting, immunohistochemistry and qPCR. TAM administration attenuated UUO-induced downregulation of AQP3 and affected the localization of AQP3 in both the UUO model and the lithium-induced NDI model. In parallel, TAM also affected the expression profile of other basolateral proteins, including AQP4 and Na/K-ATPase. In addition, TGF-β and TGF-β+TAM treatment affected the localization of AQP3 in stably transfected MDCK cells, and TAM partly attenuated the reduced AQP3 expression in TGF-β exposed human tissue slices. These findings suggest that TAM attenuates the downregulation of AQP3 in a UUO model and a lithium-induced NDI model and affects the intracellular localization in the collecting ducts.

Renal collecting duct principal cells play a key role in controlling body water balance. Principal cells express the water channels AQP2, AQP3, and AQP4 that mediate renal water reabsorption. AQP3 and AQP4 are expressed at the basolateral membrane constitutively. Conversely, AQP2 is localized in intracellular vesicles and translocates to the plasma membrane under vasopressin action. Stimulation with vasopressin activates the cAMP/PKA signal transduction pathway that induces the redistribution of AQP2 from an intracellular pool to the apical plasma membrane. AQP2 trafficking and function depend on multiple post-translational modifications. Moreover, several proteins control different steps activated by the vasopressin stimulation that triggers the redistribution of the AQP2 vesicles. A-kinase anchoring proteins (AKAPs) together with phosphodiesterases and adenylate cyclases play crucial roles in modulating local changes of cAMP. Soluble N-ethylmaleimide sensitive fusion factor attachment protein receptors (SNARE), cytoskeletal proteins, and the small GTPases of the Rho family regulate the fusion and the endocytotic retrieval of AQP2 vesicles. Abnormal vasopressin signaling and altered AQP2 expression or trafficking can lead to disorders characterized by deregulated mechanisms controlling water homeostasis. This review provides updated data on the molecular signals regulating vasopressin-induced AQP2 trafficking in health and disease., (Copyright © 2022. Published by Elsevier Ltd.)

Vasopressin (AVP) plays a key function in controlling body water and salt balance through the activation of the vasopressin receptors V1aR and V2R. Abnormal secretion of AVP can cause the syndrome of inappropriate antidiuresis that leads to hyponatremia, which is an electrolyte disorder often observed in the elderly hospitalized and oncologic patients. Beyond kidneys, the colonic epithelium modulates water and salt homeostasis. The water channel AQP3, expressed in villus epithelial cells is implicated in water absorption across human colonic surface cells. Here, the action of dDAVP, a stable vasopressin analog, was evaluated on the AQP3 expression and function using human colon HCT8 cells as an experimental model. Confocal and Western Blotting analysis revealed that HCT8 cells express both V1aR and V2R. Long-term (72 h) treatment with dDAVP reduced glycerol uptake and cell viability. These effects were prevented by SR49059, a synthetic antagonist of V1aR, but not by tolvaptan, a specific V2R antagonist. Of note, the SR49059 action was impaired by DFP00173, a selective inhibitor of AQP3. Interestingly, compared to the normal colonic mucosa, in the colon of patients with adenocarcinoma, the expression of V1aR was significantly decreased. These findings were confirmed by gene expression analysis with RNA-Seq data. Overall, data suggest that dDAVP, through the V1aR dependent pathway, reduces AQP3 mediated glycerol uptake, a process that is reversed in adenocarcinoma, suggesting that the AVP-dependent AQP3 pathway may represent a novel target in colon diseases associated with abnormal cell growth., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The handling editor SD declared a past collaboration with the author GT., (Copyright © 2022 Centrone, D’Agostino, Ranieri, Mola, Faviana, Lippolis, Silvestris, Venneri, Di Mise, Valenti and Tamma.)

Exposure to actual or simulated microgravity results in alterations of renal function, fluid redistribution, and bone loss, which is coupled to a rise of urinary calcium excretion. We provided evidence that high calcium delivery to the collecting duct reduces local Aquaporin 2 (AQP2)-mediated water reabsorption under vasopressin action, thus limiting the maximal urinary concentration to reduce calcium saturation. To investigate early renal adaptation into simulated microgravity, we investigated the effects of 10 days of strict bedrest in 10 healthy volunteers. We report here that 10 days of inactivity are associated with a transient, significant decrease (day 5) in vasopressin (copeptin) paralleled by a decrease in AQP2 excretion, consistent with an increased central volume to the heart, resulting in reduced water reabsorption. Moreover, bedrest caused a significant increase in calciuria secondary to bone demineralization paralleled by a decrease in PTH. Urinary osteopontin, a glycoprotein exerting a protective effect on stone formation, was significantly reduced during bedrest. Moreover, a significant increase in adrenomedullin (day 5), a peptide with vasodepressor properties, was observed at day 5, which may contribute to the known reduced orthostatic capacity post-bedrest. We conclude that renal function is altered in simulated microgravity and is associated with an early increase in the risk of stone formation and reduced orthostatic capacity post-bedrest within a few days of inactivity., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Tamma, Di Mise, Ranieri, Centrone, Venneri, D’Agostino, Ferrulli, Šimunič, Narici, Pisot and Valenti.)

Wine production represents an ancient human activity and one of the most economically important markets in Europe. Moreover, the health effects of grapes and related products have been largely demonstrated, and mostly depend on their richness in bioactive molecules such as flavonoid and non-flavonoid phenolic compounds. Italy has the highest global wine production and provides one of the richest grapevine germplasm in the Mediterranean area. In this paper, our attention was focused on the evaluation of the total phenol and anthocyanin content in five autochthonous Apulian grapevine cultivars, in both wines and their non-alcoholic extracts. Moreover, the potential antioxidant effects of the non-alcoholic wine extracts on the cell viability of Caco-2 and HeLa carcinoma cell lines were tested. Finally, for the most promising autochthonous selected cultivars (Negramaro, Nero di Troia and Susumaniello), comparative transcriptomic analysis in berries was performed using high-throughput sequencing technology., Competing Interests: Competing Interests: The authors have declared that no competing interest exists., (© The author(s).)

Desmopressin (dDAVP) is the best characterized analogue of vasopressin, the endocrine regulator of water balance endowed with potent vasoconstrictive effects. Despite the use of dDAVP in clinical practice, ranging from the treatment of nephrogenic diabetes insipidus to bleeding disorders, much remains to be understood about the impact of the drug on endothelial phenotype. The aim of this study was, thus, to evaluate the effects of desmopressin on the viability and function of human pulmonary microvascular endothelial cells (HLMVECs). The results obtained demonstrate that the vasopressor had no cytotoxic effect on the endothelium; similarly, no sign of endothelial activation was induced by dDAVP, indicated by the lack of effect on the expression of inflammatory cytokines and adhesion molecules. Conversely, the drug significantly stimulated the production of nitric oxide (NO) and the expression of the inducible isoform of nitric oxide synthase, NOS2/iNOS. Since the intracellular level of cAMP also increased, we can hypothesize that NO release is consequent to the activation of the vasopressin receptor 2 (V2R)/guanylate cyclase (Gs)/cAMP axis. Given the multifaceted role of NOS2-deriving NO for many physio-pathological conditions, the meanings of these findings in HLMVECs appears intriguing and deserves to be further addressed.

The transport of chloride and bicarbonate across epithelia controls the pH and volume of the intracellular and luminal fluids, as well as the systemic pH and vascular volume. The anion exchanger pendrin (SLC26A4) and the cystic fibrosis transmembrane conductance regulator (CFTR) channel are expressed in the apical membrane of epithelial cells of various organs and tissues, including the airways, kidney, thyroid, and inner ear. While pendrin drives chloride reabsorption and bicarbonate, thiocyanate or iodide secretion within the apical compartment, CFTR represents a pathway for the apical efflux of chloride, bicarbonate, and possibly iodide. In the airways, pendrin and CFTR seems to be involved in alkalinization of the apical fluid via bicarbonate secretion, especially during inflammation, while CFTR also controls the volume of the apical fluid via a cAMP-dependent chloride secretion, which is stimulated by pendrin. In the kidney, pendrin is expressed in the cortical collecting duct and connecting tubule and co-localizes with CFTR in the apical membrane of β intercalated cells. Bicarbonate secretion occurs via pendrin, which also drives chloride reabsorption. A functional CFTR is required for pendrin activity. Whether CFTR stimulates pendrin via a direct molecular interaction or other mechanisms, or simply provides a pathway for chloride recycling across the apical membrane remains to be established. In the thyroid, CFTR and pendrin might have overlapping functions in driving the apical flux of iodide within the follicular lumen. In other organs, including the inner ear, the possible functional interplay between pendrin and CFTR needs to be explored., Competing Interests: The authors declare no conflict of interest., (© 2022 The Author(s). Published by IMR Press.)

Vasopressin (AVP) increases water permeability in the renal collecting duct through the regulation of aquaporin-2 (AQP2) trafficking. Several disorders, including hypertension and inappropriate antidiuretic hormone secretion (SIADH), are associated with abnormalities in water homeostasis. It has been shown that certain phytocompounds are beneficial to human health. Here, the effects of the Olive Leaf Extract (OLE) have been evaluated using in vitro and in vivo models. Confocal studies showed that OLE prevents the vasopressin induced AQP2 translocation to the plasma membrane in MCD4 cells and rat kidneys. Incubation with OLE decreases the AVP-dependent increase of the osmotic water permeability coefficient (Pf). To elucidate the possible effectors of OLE, intracellular calcium was evaluated. OLE increases the intracellular calcium through the activation of the Calcium Sensing Receptor (CaSR). NPS2143, a selective CaSR inhibitor, abolished the inhibitory effect of OLE on AVP-dependent water permeability. In vivo experiments revealed that treatment with OLE increases the expression of the CaSR mRNA and decreases AQP2 mRNA paralleled by an increase of the AQP2-targeting miRNA-137. Together, these findings suggest that OLE antagonizes vasopressin action through stimulation of the CaSR indicating that this extract may be beneficial to attenuate disorders characterized by abnormal CaSR signaling and affecting renal water reabsorption.

Vasopressin is the key hormone involved in water conservation and regulation of water balance, essential for life. In the renal collecting duct, vasopressin binds to the V2 receptor, increasing water permeability through activation of aquaporin-2 redistribution to the luminal membrane. This mechanism promotes rapid water reabsorption, important for immediate survival; however, only recently it has become clear that long-term adverse effects are associated with alterations of the vasopressin-aquaporin-2 pathway, leading to several syndromes associated with water balance disorders. The kidney resistance to the vasopressin action may cause severe dehydration for patients and, conversely, nonosmotic release of vasopressin is associated with water retention and increasing the circulatory blood volume. This chapter discusses the relevance of the altered vasopressin-aquaporin-2 pathway in some diseases associated with water balance disorders, including congenital nephrogenic diabetes insipidus, syndrome of inappropriate secretion of antidiuretic hormone, nephrogenic syndrome of inappropriate antidiuresis, and autosomal dominant polycystic kidney disease. The emerging picture suggests that targeting the vasopressin-AQP2 axis can provide therapeutic benefits in those patients., (Copyright © 2021 Elsevier B.V. All rights reserved.)