Expression, regulation and function of Aquaporin-3 in colonic epithelial cells

Dynamics and metabolic effects of intestinal gases in healthy humans

Many living beings use exogenous and/or endogenous gases to attain evolutionary benefits. We make a comprehensive assessment of one of the major gaseous reservoirs in the human body, i.e., the bowel, providing extensive data that may serve as reference for future studies. We assess the intestinal gases in healthy humans, including their volume, composition, source and local distribution in proximal as well as distal gut. We analyse each one of the most abundant intestinal gases including nitrogen, oxygen, nitric oxide, carbon dioxide, methane, hydrogen, hydrogen sulfide, sulfur dioxide and cyanide. For every gas, we describe diffusive patterns, active trans-barrier transport dynamics, chemical properties, intra-/extra-intestinal metabolic effects mediated by intracellular, extracellular, paracrine and distant actions. Further, we highlight the local and systemic roles of gasotransmitters, i.e., signalling gaseous molecules that can freely diffuse through the intestinal cellular membranes. Yet, we provide testable hypotheses concerning the still unknown effects of some intestinal gases on the myenteric and submucosal neurons.

The Potential Application of Aloe Barbadensis Mill. as Chinese Medicine for Constipation: Mini-Review

Aloe barbadensis Mill. has a long history of medicinal use in the annals of traditional Chinese medicine, wherein it has garnered considerable renown. Its multifaceted therapeutic properties, characterized by its anti-inflammatory and antibacterial attributes, alongside its established efficacy as a laxative agent, have been extensively documented. This review commences with an exploration of the nomenclature, fundamental characteristics, and principal constituents of Aloe barbadensis Mill. responsible for its laxative effects. Subsequently, we delve into an extensive examination of the molecular mechanisms underlying Aloe barbadensis Mill.'s laxative properties, types of constipation treatments, commercially available preparations, considerations pertaining to toxicity, and its clinical applications. This review aims to serve as a comprehensive reference point for healthcare professionals and researchers, fostering an enhanced understanding of the optimal utilization of Aloe barbadensis Mill. in the treatment of constipation.

Intestinal polyphenol antioxidant activity involves redox signaling mechanisms facilitated by aquaporin activity

Ascertaining whether dietary polyphenols evoke an antioxidant or prooxidant activity, which translates to a functional role required to maintain intestinal cell homeostasis continues to be an active and controversial area of research for food chemists and biochemists alike. We have proposed that the paradoxical function of polyphenols to autoxidize to generate H2O2 is a required first step in the capacity of some plant phenolics to function as intracellular antioxidants. This is based on the fact that cell redox homeostasis is achieved by a balance between H2O2 formation and subsequent outcomes of antioxidant systems function. Maintaining optimal extracellular and intracellular H2O2 concentrations is required for cell survival, since low levels are important to upregulate endogenous antioxidant capacity; whereas, concentrations that go beyond homeostatic control typically result in an inflammatory response, growth arrest, or eventual cell death. Aquaporins (AQPs) are a family of water channel membrane proteins that facilitate cellular transportation of water and other small molecule-derived solutes, such as H2O2, in all organisms. In the intestine, AQPs act as gatekeepers to regulate intracellular uptake of H2O2, generated from extracellular polyphenol autoxidation, thus enabling an intracellular cell signaling responses to mitigate onset of oxidative stress and intestinal inflammation. In this review, we highlight the potential role of AQPs to control important underlying mechanisms that define downstream regulation of intestinal redox homeostasis, specifically. It has been established that polyphenols that undergo oxidation to the quinone form, resulting in subsequent adduction to a thiol group on Keap1-Nrf2 complex, trigger Nrf2 activation and a cascade of indirect intracellular antioxidant effects. Here, we propose a similar mechanism that involves H2O2 generated from specific dietary polyphenols with a predisposition to undergo autoxidation. The ultimate bioactivity is regulated and expressed by AQP membrane function and thus, by extension, represents expression of an intracellular antioxidant chemoprotection mechanism.

Mid-old cells are a potential target for anti-aging interventions in the elderly

The biological process of aging is thought to result in part from accumulation of senescent cells in organs. However, the present study identified a subset of fibroblasts and smooth muscle cells which are the major constituents of organ stroma neither proliferative nor senescent in tissues of the elderly, which we termed "mid-old status" cells. Upregulation of pro-inflammatory genes (IL1B and SAA1) and downregulation of anti-inflammatory genes (SLIT2 and CXCL12) were detected in mid-old cells. In the stroma, SAA1 promotes development of the inflammatory microenvironment via upregulation of MMP9, which decreases the stability of epithelial cells present on the basement membrane, decreasing epithelial cell function. Remarkably, the microenvironmental change and the functional decline of mid-old cells could be reversed by a young cell-originated protein, SLIT2. Our data identify functional reversion of mid-old cells as a potential method to prevent or ameliorate aspects of aging-related tissue dysfunction.

Time-dependent laxative effect of sennoside A, the core functional component of rhubarb, is attributed to gut microbiota and aquaporins

ETHNOPHARMACOLOGICAL RELEVANCE

Sennoside A is a natural anthraquinone component mainly derived from rhubarb and has been routinely used as a clinical stimulant laxative. However, long-term application of sennoside A may lead to drug resistance and even adverse reactions, thus limiting its clinical use. Therefore, to reveal the time-dependent laxative effect and potential mechanism of sennoside A is of critical importance.

AIM OF THE STUDY

This study was conducted to investigate the time-dependent laxative effect of sennoside A and unveil its underlying mechanism from the perspective of gut microbiota and aquaporins (AQPs).

MATERIALS AND METHODS

Based on a mouse constipation model, 2.6 mg/kg sennoside A was administered orally for 1, 3, 7, 14 and 21 days, respectively. The laxative effect was assessed by the fecal index and fecal water content, the histopathology of the small intestine and colon was evaluated by hematoxylin-eosin staining. Gut microbiota changes was observed by 16S rDNA sequencing, and colonic AQPs expression was analyzed by quantitative real-time polymerase chain reaction and western blotting. Partial least-squares regression (PLSR) was used to screen out the effective indicators contributing to the laxative effect of sennoside A. The effective indicators were then fitted to time by a drug-time curve model to analyze the trend of efficacy of sennoside A, and the optimal time of administration was derived by comprehensive analysis with a three-dimensional (3D) time-effect image.

RESULTS

Sennoside A had a significant laxative effect at 7 days of administration with no pathological changes in the small intestine or colon; however, at 14 or 21 days of administration, the laxative effect diminished and slight damage to the colon was observed. Sennoside A affects the structure and function of gut microbes. The alpha diversity showed that the abundance and diversity of gut microorganisms reached the highest value after 7 days of administration. Partial least squares discriminant analysis showed that the composition of the flora was close to normal when administered for less than 7 days, but was closest to the composition of constipation over 7 days. The expression of aquaporin 3 (AQP3) and aquaporin 7 (AQP7) decreased gradually after the administration of sennoside A, with the lowest expression at 7 days, and then increased gradually afterwards, while the expression of aquaporin 1 (AQP1) was the opposite. The PLSR results showed that AQP1, AQP3, Lactobacillus, Romboutsia, Akkermansia and UCG_005 contributed more to the laxative effect of the fecal index, and after fitting with the drug-time curve model, each index showed a trend of increasing and then decreasing. The comprehensive evaluation of the 3D time-effect image concluded that the laxative effect of sennoside A reached its best after 7 days of administration.

CONCLUSION

Sennoside A should be used in regular dosages for less than one week, as it provides significant relief of constipation and exhibits no colonic damage within 7 days of administration. In addition, Sennoside A exerts its laxative effect by regulating gut microbiota of Lactobacillus Romboutsia, Akkermansia and UCG_005 and water channels of AQP1 and AQP3.

Protective effects of Liupao tea against high-fat diet/cold exposure-induced irritable bowel syndrome in rats

Liupao tea as a type of dark tea can relieve irritable bowel syndrome by regulating gut microbiota, but the mechanism has not been fully explained. An ultra-high performance liquid chromatography along with quadrupole time of flight tandem mass spectrometry was used to analyze the phytochemicals in Liupao tea. Then, we explored the effects of Liupao tea against IBS. From the results of chemical analysis, we identified catechins, polyphenols, amino acids, caffeine, polysaccharides and other components in Liupao tea. The open-field test, gastrointestinal function-related indexes, histochemical assays, measurements of cytokine and aquaporin 3 (AQP3), and determination of serum metabolites were utilized to monitor the physiological consequences of Liupao tea administration in rats with irritable bowel syndrome. The results showed that Liupao tea had a significant protective effect on irritable bowel syndrome. Liupao tea increased locomotive velocity while reducing interleukin-6, interleukin-1β, and tumor necrosis factor-α levels, as well as gastrointestinal injury. Moreover, Liupao tea increased the AQP3 levels of renal tissues but reduced the AQP3 levels of gastrointestinal tissues. Liupao tea reduced the Firmicutes/Bacteroides ratio and significantly reconstructed the microbial pattern. Liupao tea relieved irritable bowel syndrome by repairing gastrointestinal dysfunction, regulating the secretion of pro-inflammatory cytokines, modulating water metabolism, and restoring microbial homeostasis.

Adaptive Selection in the Evolution of Aquaglyceroporins in Mammals

Aquaporins (AQPs) are integral membrane proteins responsible for water transport across cellular membranes in both prokaryotes and eukaryotes. A subfamily of AQPs, known as aquaglyceroporins (AQGPs), facilitate the transport of small solutes such as glycerol, water, and other solutes across cellular membranes. These proteins are involved in a variety of physiological processes, such as organogenesis, wound healing, and hydration. Although AQPs have been studied extensively in different species, their conservation patterns, phylogenetic relationships, and evolution in mammals remain unexplored. In the present study, 119 AQGP coding sequences from 31 mammalian species were analysed to identify conserved residues, gene organisation, and most importantly, the nature of AQGP gene selection. Repertoire analysis revealed the absence of AQP7, 9, and 10 genes in certain species of Primates, Rodentia, and Diprotodontia, although not all three genes were absent in a single species. Two Asparagine-Proline-Alanine (NPA) motifs located at the N- and C-terminal ends, aspartic acid (D) residues, and the ar/R region were conserved in AQP3, 9, and 10. Six exons encoding the functional MIP domain of AQGP genes were found to be conserved across mammalian species. Evolutionary analysis indicated signatures of positive selection in AQP7, 9, and 10 amongst different mammalian lineages. Furthermore, substitutions of certain amino acids located close to critical residues may alter AQGP functionality, which is crucial for substrate selectivity, pore formation, and transport efficiency required for the maintenance of homeostasis in different mammalian species.

Arctiin alleviates functional constipation by enhancing intestinal motility in mice

Functional constipation (FC), a common symptom that is primarily associated with intestinal motility dysfunction, is a common problem worldwide. Arctiin (Arc) is a lignan glycoside isolated from the Chinese herbal medicine Arctium lappa L., which is a health food in China. The present study aimed to evaluate the laxative effects of Arc against FC in mice. A model of FC induced by loperamide (5 mg/kg) was established in male Institute of Cancer Research (ICR) mice. Arc was administered at a dose of 100 mg/kg as a protective agent. The faecal status, intestinal motility and histological analyses were evaluated. Furthermore, the levels of gastrointestinal motility-associated neurotransmitters, such as motilin (MTL), nitric oxide (NO), and brain-derived neurotrophic factor (BDNF) and the protective effect of Arc on interstitial cells of Cajal (ICC) were assessed. Arc treatment reversed the loperamide-induced reduction in faecal number and water content and the intestinal transit ratio in ICR mice. Histological analysis confirmed that Arc administration mitigated colonic injury. Moreover, Arc treatment increased levels of motilin and brain-derived neurotrophic factor while decreasing nitric oxide levels and ICC injury in the colon of FC mice. Arc decreased inflammation induction and aquaporin expression levels. Owing to its pro-intestinal motility property, Arc was shown to have a protective effect against FC and may thus serve as a promising therapeutic strategy for the management of FC.

Aquaporins: A new target for traditional Chinese medicine in the treatment of digestive system diseases

Aquaporins (AQPs) are a family of transmembrane proteins expressed in various organ systems. Many studies have shown that the abnormal expression of AQPs is associated with gastrointestinal, skin, liver, kidneys, edema, cancer, and other diseases. The majority of AQPs are expressed in the digestive system and have important implications for the physiopathology of the gastrointestinal tract as well as other tissues and organs. AQP regulators can prevent and treat most gastrointestinal-related diseases, such as colorectal cancer, gastric ulcer, and gastric cancer. Although recent studies have proposed clinically relevant AQP-targeted therapies, such as the development of AQP inhibitors, clinical trials are still lacking and there are many difficulties. Traditional Chinese medicine (TCM) has been used in China for thousands of years to prevent, treat and diagnose diseases, and is under the guidance of Chinese medicine (CM) theory. Herein, we review the latest research on the regulation of AQPs by TCMs and their active components, including Rhei Radix et Rhizoma, Atractylodis macrocephalae Rhizoma, Salviae miltiorrhizae Radix et Rhizoma, Poria, Astragali radix, and another 26 TCMs, as well as active components, which include the active components include anthraquinones, saponins, polysaccharides, and flavonoid glycosides. Through our review and discussion of numerous studies, we attempt to explore the regulatory effects of TCMs and their active components on AQP expression in the corresponding parts of the body in terms of the Triple Energizer concept in Chinese medicine defined as "upper energizer, middle energizer, and lower energizer,"so as to offer unique opportunities for the development of AQP-related therapeutic drugs for digestive system diseases.

Insight into the Mammalian Aquaporin Interactome

Aquaporins (AQPs) are a family of transmembrane water channels expressed in all living organisms. AQPs facilitate osmotically driven water flux across biological membranes and, in some cases, the movement of small molecules (such as glycerol, urea, CO₂, NH₃, H₂O₂). Protein-protein interactions play essential roles in protein regulation and function. This review provides a comprehensive overview of the current knowledge of the AQP interactomes and addresses the molecular basis and functional significance of these protein-protein interactions in health and diseases. Targeting AQP interactomes may offer new therapeutic avenues as targeting individual AQPs remains challenging despite intense efforts.

dDAVP Downregulates the AQP3-Mediated Glycerol Transport via V1aR in Human Colon HCT8 Cells

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.

Treatment of Gastrointestinal Disorders-Plants and Potential Mechanisms of Action of Their Constituents

The worldwide prevalence of gastrointestinal diseases is about 40%, with standard pharmacotherapy being long-lasting and economically challenging. Of the dozens of diseases listed by the Rome IV Foundation criteria, for five of them (heartburn, dyspepsia, nausea and vomiting disorder, constipation, and diarrhoea), treatment with herbals is an official alternative, legislatively supported by the European Medicines Agency (EMA). However, for most plants, the Directive does not require a description of the mechanisms of action, which should be related to the therapeutic effect of the European plant in question. This review article, therefore, summarizes the basic pharmacological knowledge of synthetic drugs used in selected functional gastrointestinal disorders (FGIDs) and correlates them with the constituents of medicinal plants. Therefore, the information presented here is intended as a starting point to support the claim that both empirical folk medicine and current and decades-old treatments with official herbal remedies have a rational basis in modern pharmacology.

A systems-level analysis of bile acids effects on rat colon epithelial cells

Bile acid diarrhea is a chronic condition caused by increased delivery of bile acids to the colon. The underlying mechanisms remain to be elucidated. To investigate genes involved in bile acid diarrhea, systems-level analyses were used on a rat bile acid diarrhea model. Twelve male Wistar Munich rats, housed in metabolic cages, were fed either control or bile acid-mixed (1% wt/wt) diets for 10 days. Food intake, water intake, urine volume, body weight, and fecal output were monitored daily. After euthanasia, colonic epithelial cells were isolated using calcium chelation and processed for systems-level analyses, that is, RNA-sequencing transcriptomics and mass spectrometry proteomics. Bile acid-fed rats suffered diarrhea, indicated by increased drinking, feces weight, and fecal water content compared with control rats. Urine output was unchanged. With bile acid feeding, RNA-sequencing revealed 204 increased and 401 decreased mRNAs; mass spectrometry revealed 183 increased and 111 decreased proteins. Among the altered genes were genes associated with electrolyte and water transport (including Slc12a7, Clca4, and Aqp3) and genes associated with bile acid transport (Slc2b1, Abcg2, Slc51a, Slc51b, and Fabps). Correlation analysis showed a significant positive correlation (Pearson's r = 0.28) between changes in mRNA expression and changes in protein expression. However, caution must be exercised in making a direct correlation between experimentally determined transcriptomes and proteomes. Genes associated with bile acid transport responded to bile acid feeding, suggesting that colonic bile acid transport also occur by regulated protein facilitated mechanisms in addition to passive diffusion. In summary, the study provides annotated rat colonic epithelial cell transcriptome and proteome with response to bile acid feeding.NEW & NOTEWORTHY Feeding rats with a bile acid caused changes in fecal output, underlining this bile acid diarrhea model's usefulness. Colonic epithelial expression of genes associated with facilitated transport of bile acids was altered during bile acid feeding. The study raises the possibility of regulated colonic transepithelial transport of bile acids in response to luminal bile acids. In addition, this study provides annotated rat colonic epithelial cell transcriptome and proteome with response to bile acid feeding.

AQP3 and AQP5-Potential Regulators of Redox Status in Breast Cancer

Breast cancer is still one of the leading causes of mortality in the female population. Despite the campaigns for early detection, the improvement in procedures and treatment, drastic improvement in survival rate is omitted. Discovery of aquaporins, at first described as cellular plumbing system, opened new insights in processes which contribute to cancer cell motility and proliferation. As we discover new pathways activated by aquaporins, the more we realize the complexity of biological processes and the necessity to fully understand the pathways affected by specific aquaporin in order to gain the desired outcome-remission of the disease. Among the 13 human aquaporins, AQP3 and AQP5 were shown to be significantly upregulated in breast cancer indicating their role in the development of this malignancy. Therefore, these two aquaporins will be discussed for their involvement in breast cancer development, regulation of oxidative stress and redox signalling pathways leading to possibly targeting them for new therapies.