Aquaporins as potential drug targets

Aquaporins in colorectal cancer: exploring their role in tumorigenesis, metastasis, and drug response

Aquaporins (AQPs) are small, integral proteins facilitating water transport across plasma cell membranes in response to osmotic gradients. This family has 13 unique members (AQP0-12), which can also transport glycerol, urea, gases, and other salute small molecules. AQPs play a crucial role in the regulation of different cellular processes, including metabolism, migration, immunity, barrier function, and angiogenesis. These proteins are found to aberrantly overexpress in various cancers, including colorectal cancer (CRC). Growing evidence has explored AQPs as a potential diagnostic biomarker and therapeutic target in different cancers. However, there is no comprehensive review compiling the available information on the crucial role of AQPs in the context of colorectal cancer. This review highlights the significance of AQPs as the biomarker and regulator of tumor cells metabolism. In addition, the proliferation, angiogenesis, and metastasis of tumor cells related to AQPs expression as well as function are discussed. Understanding the AQPs prominent role in chemotherapy resistance is of great importance clinically.

Protective effect of Bifidobacterium animalis CGMCC25262 on HaCaT keratinocytes

Bifidobacteria are the most prevalent members of the intestinal microbiota in mammals and other animals, and they play a significant role in promoting gut health through their probiotic effects. Recently, the potential applications of Bifidobacteria have been extended to skin health. However, the beneficial mechanism of Bifidobacteria on the skin barrier remains unclear. In this study, keratinocyte HaCaT cells were used as models to evaluate the protective effects of the cell-free supernatant (CFS), heat-inactivated bacteria, and bacterial lysate of Bifidobacterium animalis CGMCC25262 on the skin barrier and inflammatory cytokines. The results showed that all the tested samples were able to upregulate the transcription levels of biomarker genes associated with the skin barrier, such as hyaluronic acid synthetase (HAS) and aquaporins (AQPs). Notably, the transcription of the hyaluronic acid synthetase gene-2 (HAS-2) is upregulated by 3~4 times, and AQP3 increased by 2.5 times when the keratinocyte HaCaT cells were co-incubated with 0.8 to 1% CFS. In particular, the expression level of Filaggrin (FLG) in HaCaT cells increased by 1.7 to 2.7 times when incubated with Bifidobacterial samples, reaching its peak at a concentration of 0.8% CFS. Moreover, B. animalis CGMCC25262 also decreased the expression of the proinflammatory cytokine RANTES to one-tenth compared to the levels observed in HaCaT cells induced with tumor necrosis factor alpha (TNF-α) and interferon gamma (IFN-γ). These results demonstrate the potential of B. animalis CGMCC25262 in protecting the skin barrier and reducing inflammatory response.

Toward New AQP4 Inhibitors: ORI-TRN-002

Cerebral edema is a life-threatening condition that can cause permanent brain damage or death if left untreated. Existing therapies aim at mitigating the associated elevated intracranial pressure, yet they primarily alleviate pressure rather than prevent edema formation. Prophylactic anti-edema therapy necessitates novel drugs targeting edema formation. Aquaporin 4 (AQP4), an abundantly expressed water pore in mammalian glia and ependymal cells, has been proposed to be involved in cerebral edema formation. A series of novel compounds have been tested for their potential inhibitory effects on AQP4. However, selectivity, toxicity, functional inhibition, sustained therapeutic concentration, and delivery into the central nervous system are major challenges. Employing extensive density-functional theory (DFT) calculations, we identified a previously unreported thermodynamically stable tautomer of the recently identified AQP4-specific inhibitor TGN-020 (2-(nicotinamide)-1,3,4-thiadiazol). This novel form, featuring a distinct hydrogen-bonding pattern, served as a template for a COSMOsim-3D-based virtual screen of proprietary compounds from Origenis™. The screening identified ORI-TRN-002, an electronic homologue of TGN-020, demonstrating high solubility and low protein binding. Evaluating ORI-TRN-002 on AQP4-expressing Xenopus laevis oocytes using a high-resolution volume recording system revealed an IC50 of 2.9 ± 0.6 µM, establishing it as a novel AQP4 inhibitor. ORI-TRN-002 exhibits superior solubility and overcomes free fraction limitations compared to other reported AQP4 inhibitors, suggesting its potential as a promising anti-edema therapy for treating cerebral edema in the future.

Effects of retinoid-loaded hyaluronic acid nanomicelles on vaginal epithelium in a murine menopause model

PURPOSE

This study aimed to develop hyaluronic acid (HA)-based, retinoic acid (RA)-containing nanomicelles and to investigate the effects of these newly developed nanomicelles on regeneration of the vaginal epithelium and aquaporin 3 (AQP3) expression in a murine menopause model.

MATERIALS AND METHODS

The HA-based, RA-loaded nanomicelles were developed, and the RA-loading rate, encapsulation efficiency, and hydrodynamic diameter were measured. Female BALB/c mice (8 weeks; n=30) were divided into control and experimental groups. Menopause was established in the experimental group by removing both ovaries. The experimental group was further divided into an ovariectomy group, an HA-C18 vehicle group, and an HA-C18-RA group (2.5 µg per mouse); vaginal administration of HA-C18 or HA-C18-RA was performed once daily. After 4 weeks of treatment, murine vaginal tissue was removed, and histological analysis was performed.

RESULTS

Three drug-loaded nanomicelles were synthesized: the RA content in HA-C18-RA-10, HA-C18-RA-20, and HA-C18-RA-30 was 3.13%, 2.52%, and 16.67%, respectively, and the RA encapsulation efficiency was 95.57%, 83.92%, and 93.24%, respectively. In the experimental versus control group, serum estrogen levels were significantly reduced, and the vaginal mucosal epithelial layer was significantly thinner. After 4 weeks of treatment, the thickness of the vaginal mucosal epithelial layer and AQP3 expression was increased in the HA-C18-RA group compared with the HA-C18 vehicle group.

CONCLUSIONS

The newly developed HA-based nanomicelles containing RA resulted in vaginal epithelial recovery and increased AQP3 expression. The results may contribute to the development of functional vaginal lubricants or moisturizers for the treatment of vaginal dryness.

Ablation of AQP5 gene in mice leads to olfactory dysfunction caused by hyposecretion of Bowman's gland

Smell detection depends on nasal airflow, which can make absorption of odors to the olfactory epithelium by diffusion through the mucus layer. The odors then act on the chemo-sensitive epithelium of olfactory sensory neurons (OSNs). Therefore, any pathological changes in the olfactory area, for instance, dry nose caused by Sjögren's Syndrome (SS) may interfere with olfactory function. SS is an autoimmune disease in which aquaporin (AQP) 5 autoantibodies have been detected in the serum. However, the expression of AQP5 in olfactory mucosa and its function in olfaction is still unknown. Based on the study of the expression characteristics of AQP5 protein in the nasal mucosa, the olfaction dysfunction in AQP5 knockout (KO) mice was found by olfactory behavior analysis, which was accompanied by reduced secretion volume of Bowman's gland by using in vitro secretion measure system, and the change of acid mucin in nasal mucus layer was identified. By excluding the possibility that olfactory disturbance was caused by changes in OSNs, the result indicated that AQP5 contributes to olfactory functions by regulating the volume and composition of OE mucus layer, which is the medium for the dissolution of odor molecules. Our results indicate that AQP5 can affect the olfactory functions by regulating the water supply of BGs and the mucus layer upper the OE that can explain the olfactory loss in the patients of SS, and AQP5 KO mice might be used as an ideal model to study the olfactory dysfunction.

Natural phenylethanoid glycosides diuretics derived from Lagopsis supina: Biological activity, mechanism, molecular docking, and structure-activity relationship

Aquaporins (AQPs) and vasopressin type 2 receptor (V2R) play a crucial role in urine excretion and are widely used to explore novel diuretics. In this study, three phenylpropanoids including stachysoside A (L1), acteoside (L2), and glucopyranosyl (1 → 6) martynoside (L3) were isolated from Lagopsis supina (Steph. ex Willd.) lk. -Gal. ex Knorr. Their diuretic activity, mechanism, molecular docking, and structure-activity relationships were explored. The results suggest that L1, L2, and L3 exhibit acute (6 h) and prolonged (6 d) activities including increased urinary excretion volume, diuretic action, and diuretic activity, without affecting the urinary pH and minor altering the electrolyte balance in saline-loaded rats. Further, L1, L2, and L3 significantly reduced the levels of angiotensin II (Ang II), anti-diuretic hormone (ADH), and aldosterone (ALD), AQPs 1-4 and 7, and V2R, and remarkably elevated the atriopeptin (ANP) level. Besides, L1, L2, and L3 obviously suppressed mRNA and protein levels of AQPs 1-4 and 7, and V2R. The hypothetical binding modes of L1, L2, and L3 with these proteins were determined by molecular docking, and a tight structure-activity relationship was also proposed. Collectively, L1, L2, and L3 represent three natively novel phenylethanoid glycoside diuretics, which inhibit AQP and V2R-mediated molecular mechanisms. They are superior to furosemide as long-term diuretics.

Exploring the role of Aquaporins (AQPs) in LPS induced systemic inflammation and the ameliorative effect of Garcinia in male Wistar rat

The Aquaporins (AQPs) could prove to be striking targets of inflammation. The aim of this study was to study the involvement of AQPs and explore the anti-inflammatory activity of Garcinia extract in LPS induced acute systemic inflammation in Wistar rats. Adult male Wistar rats (n = 6) were pretreated with Garcinia orally twice for 7 days, followed by a single intraperitoneal dose (5.5 mg/kgbw) of LPS. Serum ALT, AST, ALP, Creatinine, Urea and BUN, nitric oxide, prostaglandin, cytokine and chemokine levels were measured. LC-MS analysis of Garcinia was performed to identify the phytoconstituents present. The iNOS and COX enzyme activity were determined in the target tissues. qPCR analysis of inos, cox-2 and aqps was performed. Relative protein expression of AQPs was studied by Western blot analysis. Molecular docking studies were performed to study the interaction of garcinol and hydroxycitric acid, the two important phytoconstituents of Garcinia with AQP. The qPCR analysis showed tissue-specific up-regulation of aqp1, aqp3, aqp4 and aqp8 in LPS induced rats. Garcinia extract treatment effectively lowered the mRNA expression of these AQPs. Garcinia extract significantly inhibited the LPS-induced NO, prostaglandin, cytokine and chemokine production in serum and also decreased tissue-specific transcript level of inos and cox-2, thus suggesting the anti-inflammatory role of Garcinia. Also, docking studies revealed interactions of garcinol and hydroxycitric acid with AQP1, 3, 4 and 8. Therefore, the present study suggests the possible involvement of AQP1, 3, 4 and 8 in inflammation and the efficacy of Garcinia extract as an anti-inflammatory agent. Therefore, AQPs can act as prognostic markers of inflammation and can be targeted with Garcinia extract.

Role of ATP-Binding Cassette Transporter Proteins in CNS Tumors: Resistance- Based Perspectives and Clinical Updates

Despite gigantic advances in medical research and development, chemotherapeutic resistance remains a major challenge in complete remission of CNS tumors. The failure of complete eradication of CNS tumors has been correlated with the existence of several factors including overexpression of transporter proteins. To date, 49 ABC-transporter proteins (ABC-TPs) have been reported in humans, and the evidence of their strong association with chemotherapeutics' influx, dissemination, and efflux in CNS tumors, is growing. Research studies on CNS tumors are implicating ABC-TPs as diagnostic, prognostic and therapeutic biomarkers that may be utilised in preclinical and clinical studies. With the current advancements in cell biology, molecular analysis of genomic and transcriptomic interplay, and protein homology-based drug-transporters interaction, our research approaches are streamlining the roles of ABC-TPs in cancer and multidrug resistance. Potential inhibitors of ABC-TP for better clinical outcomes in CNS tumors have emerged. Elacridar has shown to enhance the chemo-sensitivity of Dasatanib and Imatinib in various glioma models. Tariquidar has improved the effectiveness of Temozolomide's in CNS tumors. Although these inhibitors have been effective in preclinical settings, their clinical outcomes have not been as significant in clinical trials. Thus, to have a better understanding of the molecular evaluations of ABC-TPs, as well as drug-interactions, further research is being pursued in research labs. Our lab aims to better comprehend the biological mechanisms involved in drug resistance and to explore novel strategies to increase the clinical effectiveness of anticancer chemotherapeutics, which will ultimately improve clinical outcomes.

Aquaporins in health and disease

Aquaporins (AQPs) are transmembrane channel proteins that mainly facilitate the water translocation through the plasma cell membrane. For several years these proteins have been extensively examined for their biologic role in health and their potential implication in different diseases. Technological improvements associated with the methods employed to evaluate the functions of the AQPs have provided us with significant new knowledge. In this chapter, we will examine the role of AQPs in health and disease based on the latest currently available evidence.

Plant Aquaporins: Diversity, Evolution and Biotechnological Applications

The plasma membrane forms a permeable barrier that separates the cytoplasm from the external environment, defining the physical and chemical limits in each cell in all organisms. The movement of molecules and ions into and out of cells is controlled by the plasma membrane as a critical process for cell stability and survival, maintaining essential differences between the composition of the extracellular fluid and the cytosol. In this process aquaporins (AQPs) figure as important actors, comprising highly conserved membrane proteins that carry water, glycerol and other hydrophilic molecules through biomembranes, including the cell wall and membranes of cytoplasmic organelles. While mammals have 15 types of AQPs described so far (displaying 18 paralogs), a single plant species can present more than 120 isoforms, providing transport of different types of solutes. Such aquaporins may be present in the whole plant or can be associated with different tissues or situations, including biotic and especially abiotic stresses, such as drought, salinity or tolerance to soils rich in heavy metals, for instance. The present review addresses several aspects of plant aquaporins, from their structure, classification, and function, to in silico methodologies for their analysis and identification in transcriptomes and genomes. Aspects of evolution and diversification of AQPs (with a focus on plants) are approached for the first time with the aid of the LCA (Last Common Ancestor) analysis. Finally, the main practical applications involving the use of AQPs are discussed, including patents and future perspectives involving this important protein family.

Lagopsis supina exerts its diuretic effect via inhibition of aquaporin-1, 2 and 3 expression in a rat model of traumatic blood stasis

ETHNOPHARMACOLOGICAL RELEVANCE

Lagopsis supina has been used as a traditional medicinal herb for centuries in China. In folk medicine, it is used for promoting blood circulation and removing blood stasis (PBCRBS), anti-inflammatory and diuretic activities. Modern pharmacological investigation have shown that L. supina have an improvement in blood and lymphatic microcirculation, myocardioprotective, and antioxidative activities. Although the pharmacological research of L. supina was more, there was no report on the diuretic activity.

AIM OF THE STUDY

This study was to evaluate the diuretic activity and the underlying mechanism of an ethanol extract of L. supina (LS) in a rat model of traumatic blood stasis (TBS).

MATERIALS AND METHODS

There were 30 male Sprague-Dawley rats that were randomly assigned to the control group, TBS group, and LS group (10 animals in each group). LS was administered orally (460 mg/kg) once daily for 7 successive days. The control group and TBS group were given an equal amount of 0.3% sodium carboxymethyl cellulose (CMC-Na). For the efficacy evaluation, the urine output volume, the urinary electrolyte concentrations (Na⁺, K⁺, Cl^- and Ca²⁺) and pH value, the levels of angiotensin II (Ang II), atriopeptin (ANP), anti-diuretic hormone (ADH) and aldosterone (ALD), as well as aquaporin (AQP)-1, 2 and 3 protein expressions were detected in a rat model of TBS. The protein expressions of AQP-1, 2 and 3 were detected by quantitative immunohistochemistry (IHC) and Western blot analysis.

RESULTS

In the efficacy evaluation, rat models treated with LS showed a significant increase in the total urine output (p < 0.01). The urinary electrolyte and the acid-base disturbances, including the decrease of Na⁺ and Ca²⁺ levels and the Na⁺/K⁺ value together with the increase in the Cl^- level and the pH value, in the urine of the LS group were compared with the TBS group. Moreover, the levels of Ang II, ADH and ALD of rat model were decreased after being treated with LS (p < 0.05 or p < 0.01), while the ANP level was increased (p < 0.05). In addition, the results of the quantitative IHC and the Western blot analysis showed that the expression levels of AQP-1, 2 and 3 proteins decreased significantly compared with those of the TBS group.

CONCLUSIONS

This is the first reported notable diuretic effect by LS, which probably was through the suppression of the renin-angiotensin-aldosterone system (RAAS) and the regulation of the signaling pathways of AQP-1, 2 and 3 protein expressions. Based on our results, we conclude that L. supina carries out its diuretic effect mainly by down-regulating the levels of AQP-1, 2 and 3 expressions in TBS rat model. These data also embody the traditional Chinese medicine (TCM) application principle of Huo xue li shui. These findings suggest that LS may warrant further evaluation as a possible agent for the diuretic drug in clinical applications. Further research is underway to elucidate the active compounds responsible for the diuretic activity of LS.

Loss of Aquaporin-3 in Placenta and Fetal Membranes Induces Growth Restriction in Mice

Aquaporin (AQP) 3, a facilitated transporter of water and glycerol, expresses in placenta and fetal membranes, but the detailed localization and function of AQP3 in placenta remain unclear. To elucidate a role of AQP3 in placenta, we defined the expression and cellular localization of AQP3 in placenta and fetal membranes, and investigated the structural and functional differences between wild-type and AQP3 null mice. Gestational sacs were removed during mid-gestational period and amniotic fluid was aspirated for measurements of volume and composition. Fetuses with attached placenta and fetal membranes were weighed and processed for histological assessment. AQP3 strongly expressed in basolateral membrane of visceral yolk sac cells of fetal membrane, the syncytiotrophoblasts of the labyrinthine placenta and fetal nucleated red blood cell membrane. Mice lacking AQP3 did not exhibit a significant defect in differentiation of trophoblast stem cells and normal placentation. However, AQP3 null fetuses were smaller than their control litter mates in spite of a decrease in litter size. The total amniotic fluid volume per gestational sac was reduced, but the amniotic fluid-to-fetal weight ratio was increased in AQP3 null mice compared with wild-type mice. Glycerol, free fatty acid and triglyceride levels in amniotic fluid of AQP3 null mice were significantly reduced, whereas lactate level increased when compared to those of wild-type mice. These results suggest a role for AQP3 in supplying nutrients from yolk sac and maternal blood to developing fetus by facilitating transport of glycerol in addition to water, and its implication for the fetal growth in utero.

Revisiting the metabolic syndrome: the emerging role of aquaglyceroporins

The metabolic syndrome (MetS) includes a group of medical conditions such as insulin resistance (IR), dyslipidemia and hypertension, all associated with an increased risk for cardiovascular disease. Increased visceral and ectopic fat deposition are also key features in the development of IR and MetS, with pathophysiological sequels on adipose tissue, liver and muscle. The recent recognition of aquaporins (AQPs) involvement in adipose tissue homeostasis has opened new perspectives for research in this field. The members of the aquaglyceroporin subfamily are specific glycerol channels implicated in energy metabolism by facilitating glycerol outflow from adipose tissue and its systemic distribution and uptake by liver and muscle, unveiling these membrane channels as key players in lipid balance and energy homeostasis. Being involved in a variety of pathophysiological mechanisms including IR and obesity, AQPs are considered promising drug targets that may prompt novel therapeutic approaches for metabolic disorders such as MetS. This review addresses the interplay between adipose tissue, liver and muscle, which is the basis of the metabolic syndrome, and highlights the involvement of aquaglyceroporins in obesity and related pathologies and how their regulation in different organs contributes to the features of the metabolic syndrome.

Endothelial Aquaporins and Hypomethylation: Potential Implications for Atherosclerosis and Cardiovascular Disease

Aquaporins (AQPs) are transmembrane channels that facilitate water and glycerol permeation through cell membranes. Recently, the water channel AQP1 was suggested to contribute to endothelial homeostasis and cardiovascular health. Less is known about endothelial aquaglyceroporins expression and its implication in cardiovascular disease (CVD). We have previously used cultured human endothelial cells under a hypomethylating environment to study endothelial dysfunction and activation, a phenotype implicated in the establishment of atherosclerosis and CVD. Here, we used the same cell model to investigate aquaporin’s expression and function in healthy or pro-atherogenic phenotype. We first confirmed key features of endothelium dysfunction and activation in our cell model, including an augmented endothelial transmigration under hypomethylation. Subsequently, we found AQP1 and AQP3 to be the most predominant AQPs accounting for water and glycerol fluxes, respectively, in the healthy endothelium. Moreover, endothelial hypomethylation led to decreased levels of AQP1 and impaired water permeability without affecting AQP3 and glycerol permeability. Furthermore, TNF-α treatment-induced AQP1 downregulation suggesting that the inflammatory NF-κB signaling pathway mediates AQP1 transcriptional repression in a pro-atherogenic endothelium, a possibility that warrants further investigation. In conclusion, our results add further support to AQP1 as a candidate player in the setting of endothelial dysfunction and CVD.

Aquaporin-Targeted Therapeutics: State-of-the-Field

Drugs targeting aquaporins have broad potential clinical applications, including cancer, obesity, edema, glaucoma, skin diseases and others. The astrocyte water channel aquaporin-4 is a particularly compelling target because of its role of brain water movement, neuroexcitation and glia scarring, and because it is the target of pathogenic autoantibodies in the neuroinflammatory demyelinating disease neuromyelitis optica . There has been considerable interest in the identification of small molecule inhibitors of aquaporins, with various candidates emerging from testing of known ion transport inhibitors, as well as compound screening and computational chemistry. However, in general, the activity of reported aquaporin inhibitors has not been confirmed on retesting, which may be due to technical problems in water transport assays used in the original identification studies, and the challenges in modulating the activity of small, compact, pore-containing membrane proteins. We review here the state of the field of aquaporin-modulating small molecules and biologics, and the challenges and opportunities in moving forward.

SLC3A2 is upregulated in human osteosarcoma and promotes tumor growth through the PI3K/Akt signaling pathway

Growing evidence indicates that SLC3A2 (solute carrier family 3 member 2) is upregulated and correlates with tumor growth in multiple types of cancers, while the role of SLC3A2 in human osteosarcoma (OS) is rarely discussed. Thus, the aim of the present study was to demonstrate the expression of SLC3A2 in human osteosarcoma and reveal its biological function and the underlying mechanisms. RT-PCR, western blot analysis and immunohistochemistry (IHC) were used to assess the expression of SLC3A2 in OS samples and cell lines. Cell cycle, Cell Counting Kit-8 (CCK-8) and colony formation assays were used to test the cell survival capacity. To investigate the potential mechanism by which SLC3A2 regulates OS growth, we used a slide-based antibody array. We demonstrated that SLC3A2 was upregulated in OS cell lines as well as OS tissues. High expression of SLC3A2 was correlated with clinical stage and tumor size in OS. Reduced expression of SLC3A2 inhibited OS cell proliferation through G2/M phase arrest. Most importantly, we found that SLC3A2 may regulate OS growth through the PI3K/Akt signaling pathway. In conclusion, SLC3A2 is upregulated in OS and plays a crucial role in tumor growth. Targeting SLC3A2 may provide a new therapeutic strategy for OS.

Evaluation of The Protective Effect of Hydro-Alcoholic Extract of Raspberry Fruit on Aquaporin1 Expression in Rats Kidney Treated by Methotrexate

OBJECTIVE

Methotrexate (MTX) is an antimetabolite drug commonly prescribed for the various cancers and autoimmune diseases. Despite its considerable therapeutic effects, nephrotoxicity is the most important side-effect of treatment with MTX. Aquaporin1 (AQP1) is a water channel proteins which is present in mammalian kidney. Raspberry fruit with antioxidant properties is able to protect biological systems from the harmful effects of free radicals. The purpose of this study was to investigate the effect of raspberry extract on expression of AQP1 and the MTX-induced nephrotoxicity in rats.

MATERIALS AND METHODS

In this experimental study, 60 adult male Wistar rats were divided into nine groups including control, sham, MTX treated group [single dose of 20 mg/kg of body weight (BW) MTX at the third day], raspberry treated groups [intraperitoneal (I.P) injection of 100, 200, 400 mg/kg of BW raspberry extract for ten consecutive days], MTX and raspberry treated groups. At day 11, rats were sacrificed via chloroform inhalation and kidney tissues were fixed in formalin solution for histological and immunohistochemistry analysis. The serological assays for urea, creatinine, uric acid and interleukin-6 (IL-6) levels were also performed.

RESULTS

MTX elevated serum level of the urea, creatinine, uric acid, IL-6, renal tissue damage and decreased the AQP1 expression level. Raspberry fruit extract improved the kidney function and reduced side effects of MTX in treated rats. Expression of AQP1, in a dose dependent manner was also ameliorated, as compared to control group.

CONCLUSION

According to the findings of this study, it can be concluded that biological activity of compounds presented in raspberry fruit extract especially anthocyanins may have chemo-protective effect on kidney function and AQP1 expression in rats treated by MTX.

Experimental Evaluation of Proposed Small-Molecule Inhibitors of Water Channel Aquaporin-1

The aquaporin-1 (AQP1) water channel is a potentially important drug target, as AQP1 inhibition is predicted to have therapeutic action in edema, tumor growth, glaucoma, and other conditions. Here, we measured the AQP1 inhibition efficacy of 12 putative small-molecule AQP1 inhibitors reported in six recent studies, and one AQP1 activator. Osmotic water permeability was measured by stopped-flow light scattering in human and rat erythrocytes that natively express AQP1, in hemoglobin-free membrane vesicles from rat and human erythrocytes, and in plasma membrane vesicles isolated from AQP1-transfected Chinese hamster ovary cell cultures. As a positive control, 0.3 mM HgCl2 inhibited AQP1 water permeability by >95%. We found that none of the tested compounds at 50 µM significantly inhibited or increased AQP1 water permeability in these assays. Identification of AQP1 inhibitors remains an important priority.

Aquaporins: Their role in gastrointestinal malignancies

Aquaporins (AQPs) are small (~30 kDa monomers) integral membrane water transport proteins that allow water to flow through cell membranes in reaction to osmotic gradients in cells. In mammals, the family of AQPs has thirteen (AQP0-12) unique members that mediate critical biological functions. Since AQPs can impact cell proliferation, migration and angiogenesis, their role in various human cancers is well established. Recently, AQPs have been explored as potential diagnostic and therapeutic targets in gastrointestinal (GI) cancers. GI cancers encompass multiple sites including the colon, esophagus, stomach and pancreas. Research in the last three decades has revealed biological aspects and signaling pathways critical for the development of GI cancers. Since the majority of these cancers are very aggressive and rapidly metastasizes, identifying effective targets is crucial for treatment. Preclinical studies have utilized inhibitors of specific AQPs and knock down of AQP expression using siRNA. Although several studies have explored the role of AQPs in colorectal, esophageal, gastric, hepatocellular and pancreatic cancers, there is no comprehensive review compiling the available information on GI cancers as has been published for other malignancies such as ovarian cancer. Due to the similarities and association of various sites of GI cancers, it is helpful to consider these results collectively in order to better understand the role of specific AQPs in critical GI cancers. This review summarizes the current knowledge of the role of AQPs in GI malignancies with particular focus on diagnosis and therapeutic applications.

Challenges and achievements in the therapeutic modulation of aquaporin functionality

Aquaporin (AQP) water and solute channels have basic physiological functions throughout the human body. AQP-facilitated water permeability across cell membranes is required for rapid reabsorption of water from pre-urine in the kidneys and for sustained near isosmolar water fluxes e.g. in the brain, eyes, inner ear, and lungs. Cellular water permeability is further connected to cell motility. AQPs of the aquaglyceroporin subfamily are necessary for lipid degradation in adipocytes and glycerol uptake into the liver, as well as for skin moistening. Modulation of AQP function is desirable in several pathophysiological situations, such as nephrogenic diabetes insipidus, Sjögren's syndrome, Menière's disease, heart failure, or tumors to name a few. Attempts to design or to find effective small molecule AQP inhibitors have yielded only a few hits. Challenges reside in the high copy number of AQP proteins in the cell membranes, and spatial restrictions in the protein structure. This review gives an overview on selected physiological and pathophysiological conditions in which modulation of AQP functions appears beneficial and discusses first achievements in the search of drug-like AQP inhibitors.

Down-regulated aquaporin 5 inhibits proliferation and migration of human epithelial ovarian cancer 3AO cells

Background

Recent studies suggested that aquaporins 5 (AQP5) was associated with many kinds of cancers and regulated many processes of various kinds of cancer cells. Our previous studies also demonstrated that AQP5 was highly expressed in epithelial ovarian cancer and contributed to the progress of ovarian cancer.

Methods

Lentivirus for knocking-down the expression of AQP5 was prepared and verified by qPCR and Western blotting. Cell counting kit-8 (CCK8) assay and transwell assay were performed to investigate the role of AQP5 on proliferation and migration of 3AO cells. The effects of down-regulating AQP5 on tumorigenesis were tested by tumor xenografts experiments.

Results

An effective lentivirus silencing AQP5 expression was obtained and used in this study. Down-regulating AQP5 inhibited proliferation and migration of cultured human epithelial ovarian cancer 3AO Cell. Furthermore, interfering of AQP5 during tumorigenesis could efficiently decrease the tumor growth in athymic mice.

Conclusions

These findings altogether suggest that AQP5 regulated multi processes in ovarian carcinogenesis and may be an attractive therapeutic target.

Expression of aquaporin proteins in vagina of diabetes mellitus rats

INTRODUCTION

Aquaporins (AQPs) are membrane proteins that facilitate water movement across biological membranes. Vaginal lubrication may be mediated by blood flow and other potential mechanisms related to transudation of fluid. The most common female sexual dysfunction in diabetes is inadequate vaginal lubrication.

AIM

To investigate the expression of AQP1-3 in vaginal tissue of diabetes mellitus rats.

METHODS

Female Sprague-Dawley rats (N = 20) were randomly divided into group A (12-week-old nondiabetic control, N = 5), group B (16-week-old nondiabetes control, N = 5), group C (12-week-old diabetes mellitus rats, N = 5), and group D (16-week-old diabetes mellitus rats, N = 5). Vaginal fluid was measured by fluid weight absorbed by cotton swabs after pelvic nerve electrostimulation and anterior vaginal tissue was dissected for determining the expression of AQP1-3 by immunohistochemical study and Western blot.

MAIN OUTCOME MEASURES

The expression of AQP1-3 was determined in the vagina of diabetes mellitus rats by Western blot.

RESULTS

There are no significant differences in serum estradiol concentrations of rats among these groups (P > 0.05). Vaginal fluid was significantly lower in group C (2.7 ± 0.67 mg) and group D (2.5 ± 1.03 mg) than in group A (5.74 ± 1.23 mg) and group B (5.5 ± 1.08 mg) (P < 0.05), respectively. The protein expressions of AQP1-3 were significantly lower in group C (43.40 ± 4.83, 60.60 ± 12.80, and 59.60 ± 6.95) and group D (20.81 ± 2.86, 47.80 ± 11.43, and 54.20 ± 5.26) than in group A (116.62 ± 3.21, 110.81 ± 8.044, and 108.80 ± 4.97) and group B (122.12 ± 14.54, 111.21 ± 15.07, and 106.40 ± 4.16) (P < 0.05), respectively.

CONCLUSIONS

Decreased vaginal fluid in diabetes mellitus rats after electrostimulation may be partly due to estrogen-independent decreases of AQP1-3 in vaginal tissue.

Development of a Novel Ligand, [C]TGN-020, for Aquaporin 4 Positron Emission Tomography Imaging

Aquaporin 4 (AQP4), the most abundant isozyme of the water specific membrane transporter aquaporin family, has now been implicated to play a significant role in the pathogenesis of various disease processes of the nervous system from epilepsy to Alzheimer’s disease. Considering its clinical relevance, it is highly desirable to develop a noninvasive method for the quantitative analysis of AQP distribution in humans under clinical settings. Currently, the method of choice for such diagnostic examinations continues to be positron emission tomography (PET). Here, we report the successful development of a PET ligand for AQP4 imaging based on TGN-020, a potent AQP4 inhibitor developed previously in our laboratory. Utilizing [¹¹C]-TGN-020, PET images were successfully generated in wild type and AQP4 null mice, providing a basis for future evaluation regarding its suitability for clinical studies.

Surfing the wave, cycle, life history, and genes/proteins expressed by testicular germ cells. Part 4: intercellular bridges, mitochondria, nuclear envelope, apoptosis, ubiquitination, membrane/voltage-gated channels, methylation/acetylation, and transcription factors

As germ cells divide and differentiate from spermatogonia to spermatozoa, they share a number of structural and functional features that are common to all generations of germ cells and these features are discussed herein. Germ cells are linked to one another by large intercellular bridges which serve to move molecules and even large organelles from the cytoplasm of one cell to another. Mitochondria take on different shapes and features and topographical arrangements to accommodate their specific needs during spermatogenesis. The nuclear envelope and pore complex also undergo extensive modifications concomitant with the development of germ cell generations. Apoptosis is an event that is normally triggered by germ cells and involves many proteins. It occurs to limit the germ cell pool and acts as a quality control mechanism. The ubiquitin pathway comprises enzymes that ubiquitinate as well as deubiquitinate target proteins and this pathway is present and functional in germ cells. Germ cells express many proteins involved in water balance and pH control as well as voltage-gated ion channel movement. In the nucleus, proteins undergo epigenetic modifications which include methylation, acetylation, and phosphorylation, with each of these modifications signaling changes in chromatin structure. Germ cells contain specialized transcription complexes that coordinate the differentiation program of spermatogenesis, and there are many male germ cell-specific differences in the components of this machinery. All of the above features of germ cells will be discussed along with the specific proteins/genes and abnormalities to fertility related to each topic.

AQP1 mediates water transport in the carotid body

In this study, we explored the presence of aquaporins (AQPs), a family of membrane water channel proteins, in carotid body (CB) type I chemoreceptor cells. The CB is a polymodal chemoreceptor whose major function is to detect changes in arterial O2 tension to elicit hyperventilation during hypoxia. The CB has also been proposed to function as a systemic osmoreceptor, thus we hypothesized that the presence of AQPs in type I cell membrane may confer higher sensitivity to osmolarity changes and hence accelerate the activation of chemoreceptor cells. We detected the expression of AQP1, AQP7, and AQP8 in the CB and confirmed the location of AQP1 in type I cells. We have also shown that inhibition of AQP1 expression clearly reduced type I cell swelling after a hyposmotic shock, demonstrating that AQP1 has a major contribution in transmembrane water movement in these chemoreceptor cells. Interestingly, CB AQP1 expression levels change during postnatal development, increasing during the first postnatal weeks as the organ matures. In conclusion, in this study, we report the novel observation that AQPs are expressed in the CB. We also show that AQP1 mediates water transport across the cell membrane of type I cells, supporting the contribution of this protein to the osmoreception function of the CB.

P2Y(2) receptors and water transport in the kidney

The kidneys play a critical role in the maintenance of water homeostasis. This is achieved by the inherent architecture of the nephron along with the expression of various membrane transporters and channels that are responsible for the vectorial transport of salt and water. The collecting duct has become a focus of attention by virtue of its ability to transport water independent of solutes (free-water transport), and its apparent involvement in various water balance disorders. It was originally believed that the water transport capability of the collecting duct was solely under the influence of the circulating hormone, arginine vasopressin (AVP). However, during the past decade, locally produced autocrine and/or paracrine factors have emerged as potent modulators of transport of water by the collecting duct. Recently, much attention has been focused on the purinergic regulation of renal water transport. This review focuses on the role of the P2Y(2) receptor, the predominant purinergic receptor expressed in the collecting duct, in the modulation of water transport in physiological and pathophysiological conditions, and its therapeutic potential as a drug target to treat water balance disorders in the clinic. Studies carried out by us and other investigators are unravelling potent interactions among AVP, prostanoid and purinergic systems in the medullary collecting duct, and the perturbations of these interactions in water balance disorders such as acquired nephrogenic diabetes insipidus. Future studies should address the potential therapeutic benefits of modulators of P2Y(2) receptor signalling in water balance disorders, which are extremely prevalent in hospitalised patients irrespective of the underlying pathology.

The solute carrier (SLC) complement of the human genome: phylogenetic classification reveals four major families

Solute carriers (SLCs) is the largest group of transporters, embracing transporters for inorganic ions, amino acids, neurotransmitters, sugars, purines and fatty acids among other substrates. We mined the finished assembly of the human genome using Hidden Markov Models (HMMs) obtaining a total of 384 unique SLC sequences. Detailed clustering and phylogenetic analysis of the entire SLC family showed that 15 of the families place into four large phylogenetic clusters with the largest containing eight SLC families, suggesting that many of the distinct families of SLCs have a common evolutionary origin. This study represents the first overall genomic roadmap of the SLCs providing large sequence sets and clarifies the phylogenetic relationships among the families of the second largest group of membrane proteins.

Membrane domain specificity in the spatial distribution of aquaporins 5, 7, 9, and 11 in efferent ducts and epididymis of rats

Water content within the epididymis of the male reproductive system is stringently regulated to promote sperm maturation. Several members of the aquaporin (AQP) family of water channel-forming integral membrane proteins have been identified in epididymal cells, but expression profiling for this epithelium is presently incomplete, and no AQP isoform has yet been identified on basolateral plasma membranes of these cells. In this study, we explored AQP expression by RT-PCR and light microscopy immunolocalizations using peroxidase and wide-field fluorescence techniques. The results indicate that several AQPs are coexpressed in the epididymis including AQP 5, 7, 9, and 11. Immunolocalizations suggested complex patterns in the spatial distribution of these AQPs. In principal cells, AQP 9 and 11 were present mainly on microvilli, whereas AQP 7 was localized primarily to lateral and then to basal plasma membranes in a region-specific manner. AQP 5 was also expressed regionally but was associated with membranes of endosomes. Additionally, AQPs were expressed by some but not all basal (AQP 7 and 11), clear (AQP 7 and 9), and halo (AQP 7 and 11) cells. These findings indicate unique associations of AQPs with specific membrane domains in a cell type- and region-specific manner within the epididymis of adult animals.

Medical management of brain tumor patients

Brain tumors can present challenging medical problems. Seizures, peritumoral edema, venous thromboembolism, fatigue, and cognitive dysfunction can complicate the treatment of patients who have primary or metastatic brain tumors. Effective medical management results in decreased morbidity and mortality and improved quality of life for affected patients.

Identification of aquaporin 4 inhibitors using in vitro and in silico methods

The in vitro inhibitory effects and in silico docking energies of 18 compounds with respect to aquaporin 4 (AQP4) were investigated. More than half of the compounds tested showed inhibitory activity in the in vitro functional assay and included the 5-HT(1B/1D) agonists sumatriptan, and rizatriptan. Moreover, the observed inhibitory activity of the compounds used in this study at 20 microM showed a strong correlation with their in silico docking energies, r(2)=0.64, which was consistent with that found in previous studies. The AQP4 inhibitory IC(50) values of three compounds, 2-(nicotinamido)-1,3,4-thiadiazole, sumatriptan and rizatriptan, were subsequently found to be 3, 11, and 2 microM, respectively.

Present and future therapeutic strategies in non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is found in individuals who do not drink or abuse alcohol and represents a significant health burden for the general community. NAFLD is often associated with one or more features of the metabolic syndrome and has potential for evolution towards non-alcoholic steatohepatitis (NASH), the necro-inflammatory form of liver steatosis. The most worrisome evolutive events in a subgroup of NASH patients include advanced liver fibrosis, cirrhosis, and hepatocellular carcinoma. Pathophysiology of NAFLD/NASH is complex, but studies point to a pre-eminent role of oxidative stress and lipid peroxidation in the liver, including early mitochondrial dysfunction. Changes follow an insulin resistance status with a background of a chronic pro-inflammatory status due to an excess of visceral adiposity. Although no established therapy exists for NAFLD/NASH, potential therapeutic approaches are discussed in this review.

Topiramate reduced sweat secretion and aquaporin-5 expression in sweat glands of mice

Decreased sweat secretion is a primary side effect of topiramate in pediatric patients, but the mechanism underlying this effect remains unclear. This study aimed to better understand how topiramate decreases sweat secretion by examining its effect on the expression of carbonic anhydrase (CA) II and aquaporin-5 (AQP5), total CA activity, as well as on tissue morphology of sweat glands in mice. Both developing and mature mice were treated with a low (20 mg/kg/day) and high dose (80 mg/kg/day) of topiramate for 4 weeks. Sweat secretion was investigated by an established technique of examining mold impressions of hind paws. CA II and AQP5 expression levels were determined by immunofluorescence and immunoblotting and CA activity by a colorimetric assay. In mature mice, topiramate treatment decreased the number of pilocarpine reactive sweat glands from baseline in both the low and high dose groups by 83% and 75%, respectively. A similar decrease was seen in developing mice. Mature mice with reactive sweat glands that declined more than 25% compared to baseline were defined as anhidrotic mice. These mice did not differ from controls in average secretory coil diameter, CA II expression and CA activity. In contrast, anhidrotic mice did show a reduction in membrane AQP5 expression in sweat glands after topiramate delivery. Thus, sweat secretion and membrane AQP5 expression in mouse sweat glands decreased following topiramate administration. These results suggest dysregulation of AQP5 may be involved in topiramate-induced hypohidrosis and topiramate may serve as a novel therapy for hyperhidrosis.

Distal tubular epithelial cells of the kidney: Potential support for proximal tubular cell survival after renal injury

The tubular epithelium of the kidney is susceptible to injury from many causes, such as ischemia-reperfusion and the associated oxidative stress, nephrotoxins, inflammatory and immune disorders and many others. The outcome is often acute kidney injury, which may progress to chronic kidney disease and fibrosis. Acute kidney injury involves not only direct injury to the distal tubular (DT) and proximal tubular (PT) epithelium during and immediately following the injurious event, but the closely-associated and sometimes dysfunctional renal vascular endothelium also plays an important part in modulating the tubular epithelial injury. In comparison with the PT, the DT epithelium is less sensitive to cell death, especially after ischemic injury. It is more prone to apoptosis than necrosis when it dies, and has key paracrine and autocrine functions in secreting an array of inflammatory, reparative, and survival cytokines that include chemotactic cytokines, polypeptide growth factors, and vasoactive peptides. In a neighborly way, the cytokines and growth factors secreted by the DT epithelium may then act positively on the ischemia-sensitive PT that has receptors to many of these proteins, but may not be able to synthesize them. A more complete understanding of these cellular events will allow protection against nephron destruction, regeneration leading to re-epithelialization of the injured tubules, or prevention of progression to chronic kidney disease. This review looks at these functions in the DT epithelial cells, specifically the cells in the medullary thick ascending limb of the loop of Henle, in contrast with those of the straight segment of the PT.