Sodium Solutions Research Articles

Effect of Modified Hydroxyapatite Nanoparticles on Sodium and Calcium Cation-Contaminated Bentonite-Water Solutions at High Temperatures

Effect of Modified Hydroxyapatite Nanoparticles on Sodium and Calcium Cation-Contaminated Bentonite-Water Solutions at High Temperatures

Development of compositions of slag-alkaline binding materials for pavement products

In this work, blast furnace granulated slag of the Kamet-Stal plant was investigated. It was established that the slag belongs to the basic ones. According to the quality factor, the slag belongs to grade 1 and can be used to fabricate slag-alkaline binding material by the alkaline method of activation. A significant part of the slag is in an X-ray amorphous state, which contributes to the production of strong cement stone in the late stages of hardening. The crystalline phases of the slag exhibit weak binding properties and provide strength to the hardened slag-alkaline binding material. To activate the slag and plasticize the composition, portland cement and clay were introduced into it, sodium liquid glass, caustic soda solution and soda ash solution being used as an alkaline sealer. The exclusion of clay from the basic composition leads to an increase in strength almost twice due to additional activation of slag with portland cement. A significant drawback in this case is the numerous precipitates that appear on the samples already on the first day of hardening. Thus, for accelerated curing times, increased mechanical strength, reduction in the amount of leaching and a significant reduction in the cost of finished products, we suggested the composition containing 91 wt.% slag; 6 wt.% clay; and 3 wt.% portland cement closed with a solution of liquid glass with a modulus of 2.3 and a density of 1300 kg/m3.

Ceramic Materials with a Prescribed Phase Composition Based on Hydroxyapatite Powder Processed in Dihydrogen Phosphate Solutions of Ammonium, Sodium, and Potassium

Ceramic Materials with a Prescribed Phase Composition Based on Hydroxyapatite Powder Processed in Dihydrogen Phosphate Solutions of Ammonium, Sodium, and Potassium

Xianglian Zhixie Tablet Antagonizes Dextran Sulfate Sodium-Induced Ulcerative Colitis by Attenuating Systemic Inflammation and Modulating Gut Microbiota.

Xianglian Zhixie Tablet (XLZXT), a classical traditional Chinese medicine formulation, is commonly used to treat Ulcerative Colitis (UC) in China. However, the therapeutic mechanisms of XLZXT for UC have yet to be fully understood. This study aimed to investigate the curative benefits of XLZXT and its associated mechanisms for healing UC in mice. In the present study, the 1% dextran sulfate sodium (DSS) solution was used to establish the UC model in C57BL/6N mice. To investigate the therapeutic effects of XLZXT on DSS-induced UC mice, several parameters were measured, including DAI score, colon length, spleen index, pathological changes in colon tissue, and levels of inflammatory factors in plasma and colon tissue. By investigating the gut microbiota, assessing the levels of intestinal mucosal protein expression, and looking at the proteins involved in the TLR4/MyD88/NF-B p65 signaling pathway, the mechanisms of XLZXT impact on UC were investigated. Mouse feces were examined for patterns of gut microbiota expression using high-throughput sequencing of 16S rRNA. XLZXT effectively alleviated UC symptoms and colon pathological damage in DSS-induced UC mice. It improved body weight loss, stool consistency, and hematochezia, while also repairing colon damage. Moreover, it down-regulated pro-inflammatory cytokines (such as TNF-α, IL-1β, and IL-6), and up-regulated anti-inflammatory cytokines (such as IL-10). XLZXT also increased the expression of MUC-2, Occludin and ZO-1, while decreasing the expression of NF-κB, MyD88 and TLR4. Additionally, it regulated gut microbiota disorder by increasing the abundance of beneficial bacteria and reducing the adhesion of intestinal harmful bacteria. XLZXT demonstrated therapeutic effects on DSS-induced UC mice. The mechanisms may be associated with repairing the intestinal mucosal barrier, regulating the TLR4/MyD88/NF-κB p65 signaling pathway, and restoring the balance of gut microbiota.

Repairing effects of Lactobacillus acidophilus on ceftriaxone-induced intestinal dysbacteriosis in mice

To investigate the repairing effect of Lactobacillus acidophilus LA11-Only on ceftriaxone induced intestinal micronbiota imbalance in mice and its alleviating effect on lipid metabolism. A total of 30 SPF BALB/c male mice were randomly divided into control group(10) and model group(20). The model group was given ceftriaxone sodium solution by gavage for a week to create a mouse model of antibiotic flora disorder. The natural recovery group(10) was given 10% skimmed milk solution by gavage, and the LA11-Onlly group was given Lactobacillus acidophilus skimmed milk solution(1.0×10~9CFU/mL). Two weeks later, the feces were collected aseptically.16S rRNA sequencing technology and ultra-high-performance liquid chromatography combined with mass spectrometry(UPLC-MS) were used to analyze the repair effect of LA11-Onlly on antibiotic induced bacterial flora disorder and lipid metabolism in mice. After ceftriaxone treatment, the diversity of intestinal microbiota in mice decreased, and there was a significant difference in the composition of flora compared with the control group; After treatment with LA11-Onlly, the Alpha diversity increased, the abundance of beneficial bacteria such as Lactobacillus and Butyricicoccus increased, and the composition of flora was closer to the control group; At the same time, the concentration of short chain fatty acids(SCFAs) increased in varying degrees. Compared with the natural recovery group, the levels of butyric acid and valeric acid in LA11-Onlly group increased significantly, close to the same level as the control group. Lactobacillus acidophilus LA11-Onlly probiotics can inhibit the growth of harmful bacteria by regulating the diversity and community composition of intestinal microbiota, promote the increase of the concentration of SCFAs, and alleviate the damage of antibiotics to the body.

Influence of Microplastics on Morphological Manifestations of Experimental Acute Colitis.

Microplastic pollution poses a threat to human health. It is possible that the increase in the incidence of inflammatory bowel disease is associated with exposure to microplastics. We investigated the effect of the consumption of polystyrene microparticles with a diameter of 5 μm at a dose of 2.3 mg/kg/day for 6 weeks on morphological changes in the colons of healthy male C57BL/6 mice and of mice with acute colitis induced by a 1% dextran sulfate sodium solution (DSS). In healthy mice, microplastics caused an increase in the number of endocrine cells, an increase in the content of highly sulfated mucins in goblet cells, an increase in the number of cells in the lamina propria, and a decrease in the volume fraction of macrophages. Microplastic consumption caused more severe acute colitis, which is characterized by a greater prevalence of ulcers and inflammation and a decrease in the content of neutral mucins in goblet cells.

Sorption of cesium from strongly alkaline solutions on a modi ed ferrocyanide sorbent «fersal»

The sorption of cesium from solutions of sodium and potassium nitrates, sodium hydroxide, and also from a model solution simulating alkaline high-level waste (HLW) of FSUE PO «Mayak» on various resorcinolformaldehyde sorbents (RFS), on sorbent based on a boron-containing polymer of the Clevasol brand and on sorbent of the Fersal brand based on modi ed nickel ferrocyanide was studied under batch conditions. It is shown that in all the media studied, the Fersal sorbent has the best sorption-selective characteristics with respect to cesium. During the sorption of cesium from a model solution of HLW under dynamic conditions, the volume of the passed solution to 1% breakthrough for the Fersal sorbent is 127 bed volumes (b.v.). The puri cation resource of the other studied sorbents is 3-4 times less. Desorption of cesium from the Fersal sorbent can be carried out by passing 9-10 b.v. 7.5 mol/dm3 HNO3, however, in this case, the sorbent granules are destroyed, which does not allow it to be reused. It is concluded that the Fersal sorbent is the most promising for the treatment of alkaline HLW.

Synthesis of a Cation-Exchange Resin by Inverse Suspension Polymerization for Lactoferrin Extraction from Whey.

Lactoferrin (LF), the main iron-binding protein of milk, has important nutritional, biological, and pharmaceutical properties. It is an essential nutritional component of newborn diets and also for adult health. Small amounts of lactoferrin can be found in whey, a nutritionally and biologically useful byproduct of the dairy industry. Although the amount of lactoferrin in whey is less than that in other sources like milk and bovine colostrum, the extraction of LF from this underused source has many economic and environmental benefits. The most common technique for the isolation of LF from dairy products is the use of cation-exchange resins. Here, we present the synthesis of a strong cation-exchange resin for the extraction of high-purity lactoferrin from whey. This resin was synthesized by inverse suspension copolymerization of aqueous solutions of sodium 2-acrylamido-2-methyl-1-propanesulfonate and N,N-methylenebisacrylamide in corn oil. The adsorption efficiency of this resin showed selective extraction of lactoferrin from four different whey sources. The adsorption efficiency of lactoferrin from these whey samples ranged from 93.8 to 97.4%.

An eco-friendly strategy for grafting keratin onto polyacrylonitrile fabrics using bi-functional amino acids as coupling agents

Although it is widely used in the textile and apparel fields, polyacrylonitrile (PAN) fabrics have a hydrophobic surface susceptible to the creation of electrostatic charges (ESC). Herein, an eco-friendly method for improving some properties of PAN fabrics is proposed. PAN fabrics were hydrolyzed by a caustic soda solution to create carboxylic groups along their macromolecular chains. The hydrolyzed fabrics were treated with the amino acid lysine or glutamic acid, followed by the proteinic biopolymer keratin, using either the exhaustion or pad-dry-cure method. The used keratin was extracted from waste coarse wool fleece and characterized using amino acid analysis and SDG-PAGE electrophoresis. The effect of keratin concentration, reaction temperature, and duration on the weight gain of the treated fabrics was used to assign the optimum treatment conditions. The treated PAN fabric exhibited excellent wettability, antistatic properties, and improved resistance to UV rays without having a negative effect on the fabric’s strength. The mechanism of the reaction between PAN fabric and the aforementioned reagents was proposed and supported by both 13C-NMR and FTIR spectroscopy. The effects of the applied reagent on some of the inherent properties of PAN fabrics were examined. The finished fabrics were durable to repeated washings up to 20 cycles, as indicated by the fabric’s wettability and resistance to UV rays. Scanning electron microscopy was used to confirm the coating of the treated PAN fabrics with a layer of keratin.

A new rat model of chronic relapsing ulcerative colitis with traditional Chinese medicine syndrome of yang deficiency and dampness stagnation

IntroductionChronic relapsing ulcerative colitis (CRUC) is classified as an inflammatory bowel disease, and traditional Chinese medicine (TCM) has been recognized for its therapeutic benefits in treating CRUC. According to TCM principles, the prevailing syndromes in CRUC are yang deficiency and dampness stagnation (YDDS). The objective of this study is to establish a novel animal model of CRUC exhibiting the YDDS syndrome. MethodsInitially, the rats were administered hydrocortisone succinate sodium through subcutaneous injection, followed by the administration of senna folium granule solution. Subsequently, the rats underwent three cycles of dextran sulfate sodium solution ingestion. ResultsUpon completion of the modeling process, it was observed that the disease activity index, colonic mucosal damage index score, colon weight/length ratio, colonic histopathology score, and tissue damage index scores of the model rats were elevated, while the colon length and spleen index exhibited a decrease compared to the control group. The pathological alterations in the model rats included the presence of shallow or deep ulcers and acute or chronic inflammation throughout the process of CRUC modeling. Additionally, our findings indicate a correlation between the proximity of the ulcer to the anal verge, the severity of the lesion, and the presence of precancerous glands, glandular disappearance, crypt abscesses, and tissue destruction. Furthermore, the expression levels of IL6, IL10, IFNG, and TNFA in the colon tissues were significantly elevated in the model rats compared to the control group. Notably, the end-stage lesions observed in CRUC exhibited greater severity when compared to those observed in cases of acute ulcerative colitis. DiscussionIn conclusion, we have successfully developed a rat model of CRUC with YDDS syndrome, which can be utilized to investigate the effectiveness and underlying mechanisms of TCM in treating CRUC.

Huanglian Ganjiang decoction alleviates ulcerative colitis by restoring gut barrier via APOC1-JNK/P38 MAPK signal pathway based on proteomic analysis

Ethnopharmacological relevanceUlcerative colitis (UC) is a kind of chronic intestinal inflammation accompanied with abdominal pain, diarrhea and hematochezia. Huanglian Ganjiang decoction (HGD) derived from “Beiji Qianjin Yao Fang” was used for UC patients clinically. However, the specific mechanism of HGD in treating UC remain unclear. Aim of studyOur study devoted to demonstrating the therapeutic effect of HGD for colitis and clarifying the underlying mechanism. Materials and methodsUPLC-MS was carried out to identify the ingredients of HGD. UC mice were induced by giving 3% dextran sulfate sodium (DSS) solution for one week and treated by HGD for another week. Body weight fluctuation, disease activity index (DAI), colon length and pathological change of colon tissues were observed to evaluate therapeutical effect of HGD. ELISA and qPCR were carried out to estimate the inflammatory state. Western blot, qPCR and immunofluorescence were used to access the expression of tight junction proteins. Tandem mass tag (TMT)-Based proteomics and network pharmacology was launched to screen and predict the potential targets and pathway regulated by HGD. ResultsBased on the UPLC-MS/MS analysis, 100 components were identified in HGD. After 7-day treatment, HGD significantly alleviated colitis-associated symptoms including body weight loss, shorted colon, increase of DAI score, histopathologic lesions. HGD also reduced inflammatory cytokines IL-6 and IL-1β levels, increased the number of goblet cells and restored tight junction proteins Occludin, Claudin-1 in colon. Network pharmacology study predicted that tight junction and MAPK pathway might be affected by HGD in colitis mice. APOC1 was screened out as key target in HGD-treated mice using TMT-based proteomics study. Further Western blot results showed that HGD reduced expressions of APOC1, p-P38 and p-JNK. ConclusionHGD improves general symptoms of colitis mice at medium and high doses, which may be associated with restoring tight junction and intestinal barrier integrity and function through suppression of APOC1-JNK/P38 MAPK signal pathway.

Artificial tears: Promising treatment or silent threat to public health?

Dry Eye Disease (DED) is a multifactorial chronic inflammatory condition of the corneal surface, attributed to insufficient or low-quality production of tears, accounting for 5-50% of the cases globally. Artificial tears are the first line of treatment as they reduce ocular surface tension, and improve film stability and optical quality. EzriCare Artificial Tears are preservative-free, multi-dose, readily accessible eye drops containing carboxymethylcellulose sodium solution (10 mg in 1 ml) aiming for relief against DED. This article discusses the public health challenges faced by the use of EzriCare Artificial Tears and emphasizes the need for alternative therapies for the effective management of DED. We searched for articles documenting the incidence of the current multi-drug resistant P. aeruginosa strain outbreak caused by the use of preservative-free artificial tears and the challenges faced through the use of artificial tears on PubMed, and Google Scholar. EzriCare and other preservative-free artificial tears have been reported to pose a serious public health risk as they have been found to be the commonly used product among the people infected with the current multi-state outbreak of the multi-drug resistant P. aeruginosa strain. The current multi-state outbreak of the multi-drug resistant P. aeruginosa strain has raised concerns about the safe use of other artificial products. It is high time that further trials should be conducted on other alternative strategies and evaluate the safety and efficacy of nanotechnology in the treatment of dry eye disease.

Tributyrin alleviates gut microbiota dysbiosis to repair intestinal damage in antibiotic-treated mice.

Tributyrin (TB) is a butyric acid precursor and has a key role in anti-inflammatory and intestinal barrier repair effects by slowly releasing butyric acid. However, its roles in gut microbiota disorder caused by antibiotics remain unclear. Herein, we established an intestinal microbiota disorder model using ceftriaxone sodium via gavage to investigate the effects of different TB doses for restoring gut microbiota and intestinal injury. First, we divided C57BL/6 male mice into two groups: control (NC, n = 8) and experimental (ABx, n = 24) groups, receiving gavage with 0.2 mL normal saline and 400 mg/mL ceftriaxone sodium solution for 7 d (twice a day and the intermediate interval was 6 h), respectively. Then, mice in the ABx group were randomly split into three groups: model (M, 0.2 mL normal saline), low TB group (TL, 0.3 g/kg BW), and high TB group (TH, 3 g/kg BW) for 11 d. We found that TB supplementation alleviated antibiotics-induced weight loss, diarrhea, and intestinal tissue damage. The 16S rRNA sequence analysis showed that TB intervention increased the α diversity of intestinal flora, increased potential short-chain fatty acids (SCFAs)-producing bacteria (such as Muribaculaceae and Bifidobacterium), and inhibited the relative abundance of potentially pathogenic bacteria (such as Bacteroidetes and Enterococcus) compared to the M group. TB supplementation reversed the reduction in SCFAs production in antibiotic-treated mice. Additionally, TB downregulated the levels of serum LPS and zonulin, TNF-α, IL-6, IL-1β and NLRP3 inflammasome-related factors in intestinal tissue and upregulated tight junction proteins (such as ZO-1 and Occludin) and MUC2. Overall, the adjustment ability of low-dose TB to the above indexes was stronger than high-dose TB. In conclusion, TB can restore the dysbiosis of gut microbiota, increase SCFAs, suppress inflammation, and ameliorate antibiotic-induced intestinal damage, indicating that TB might be a potential gut microbiota modulator.

Metal Exchangeability in the REE-Enriched Biogenic Mn Oxide Birnessite from Ytterby, Sweden

A black substance exuding from fractures was observed in 2012 in Ytterby mine, Sweden, and identified in 2017 as birnessite with the composition Mx[Mn(III,IV)]2O4∙(H2O)n. M is usually calcium and sodium, with x around 0.5. The Ytterby birnessite is unique, with M being calcium, magnesium, and also rare earth elements (REEs) constituting up to 2% of the total metal content. The biogenic origin of the birnessite was established in 2018. Analysis of the microbial processes leading to the birnessite formation and the REE enrichment has continued since then. The process is fast and dynamic, as indicated by the depletion of manganese and of REE and other metals in the fracture water during the passage over the precipitation zone in the mine tunnel. Studies of the exchangeability of metals in the structure are the main objective of the present program. Exposure to solutions of sodium, calcium, lanthanum, and iron led to exchanges and altered distribution of the metals in the birnessite, however, generating phases with almost identical structures after the exchanges, and no new mineral phases were detected. Exchangeability was more efficient for trivalent elements (REE) over divalent (calcium) and monovalent (sodium) elements of a similar size (ionic radii 90–100 pm).

Ligninsulfonate-based hydrogel films for ion sensing

The manufacturing of sensors based on sustainable and renewable materials is becoming increasingly important to achieve independence from fossil raw materials. It is known that hydrogels based on lignin, the polyphenolic biopolymer in lignocellulosic biomass, are able to react to environmental influences such as pH value, temperature or ion concentration. This effect can be used for sensor applications. For this purpose, ligninsulfonate hydrogel was simultaneously generated and bound to glass surfaces via a two-step synthesis. First, the etched oxide substrates were silanized using (3-acryloxypropyl)methyldimethoxysilane (APMDMS). Thereafter, the hydrogel was bound to the surface via a radical polymerization process. Here, the lignosulfonate solution, which included the crosslinker polyethyleneglycoldiacrylate (PEGDA) and ascorbic acid, was applied directly to the functionalized surface.The functionalized surface was analyzed using XPS, AFM, SEM, ATR-IR, profilometer, contact angle, and QCM. The layer thickness was found to vary between 1.8–8.6 µm as a function of the amount of precursor lignin solution applied. The porous structure exhibited pore sizes of 4–6 µm.For the sensor tests, solutions of sodium(I) and magnesium(II) salts at different concentrations were used. The hydrogels reacted with shrinking and swelling processes, depending on the selected cation and its concentration. This effect was reproducible over several cycles and the initial state could be reestablished at the end of the tests.

Efficacy of mixed diclofenac solutions against root canal biofilms.

The objective of this research was to evaluate the efficacy of diclofenac sodium solutions, with or without cetrimide (CTR) added, against polymicrobial root canal biofilms grown in dentin specimens. The study groups were: (1) 5% diclofenac sodium (DCS); (2) 2.5% DCS; (3) 2.5% DCS + 0. 2% CTR; (4) 2.5% DCS + 0.4% CTR and (5) 0.9% saline solution (SS) as the control. After 5 min of solution contact with the biofilms, the antimicrobial activity was evaluated by means of the adenosine triphosphate (ATP) assay as well as confocal laser scanning microscopy (CLSM). Microbial quantification was indicated as the percentage reduction of relative light units (RLUs) for the ATP assay, the Log10 total biovolume and the viability percentage (green cells) for CLSM. Solutions of 2.5% DCS + 0.4% CTR and 5% DCS showed the highest antimicrobial efficacy. Cetrimide increased the antibiofilm activity of diclofenac sodium against endodontic biofilms.

A novel correlation of bubble aspect ratio through analysis of gas/shear-thinning liquid two-phase flow in a bubble column

Gas/shear-thinning liquid two-phase flow is often involved in the petroleum, chemical, and food industries, with the bubble shape playing a vital role in the theoretical analysis and numerical simulation of the flow. This study investigates the bubble shape variation in a shear-thinning liquid (carboxymethyl cellulose sodium solution) under the bubble swarm condition using high-speed imaging and a bubble recognition algorithm. The results show that trailing bubbles accelerate as they rise along the flow path of leading bubbles. During acceleration, the bubbles are subjected to lateral forces that cause them to deform from an oblate spheroid to a prolate spheroid. The effect of the shear-thinning property is enhanced owing to the increased superficial gas velocity and solution concentration, leading to an increase in the number of prolate spherical bubbles. Considering the significant difference in energy transfer in the flow fields around oblate and prolate particles, new aspect ratio correlations were developed for the two shapes based on the correlations of Re·Eo derived from the Newtonian fluid case. Compared to the previous correlation developed by assuming that the two shapes have the same aspect ratio, the proposed method significantly improves the prediction accuracy of the bubble aspect ratio for a shear-thinning fluid case.

A brief history of crystalloids: the origin of the controversy.

Fluid resuscitation with crystalloids has been used in humans for more than 100 years. In patients with trauma, sepsis or shock of any etiology, they can help modify the clinical course of the illness. However, these solutions are medications which are not side-effect free. Recently, they have been questioned in terms of quantity (fluid overload) and their composition. The most frequently used crystalloids, both in high and low-income countries, are 0.9% normal saline (NS) and Ringer's lactate. The first descriptions of the use of sodium and water solutions in humans date from the cholera epidemic which spread throughout Europe in 1831. The composition of the fluids used by medical pioneers at that time differs greatly from the 0.9% NS used routinely today. The term "physiological solution" referred to fluids which did not cause red blood cell hemolysis in amphibians in in vitro studies years later. 0.9% NS has an acid pH, a more than 40% higher chloride concentration than plasma and a strong ion difference of zero, leading many researchers to consider it an unbalanced solution. In many observational studies and clinical trials, this 0.9% NS composition has been associated with multiple microcirculation and immune response complications, acute kidney injury, and worse clinical outcomes. Ringer's lactate has less sodium than plasma, as well as other electrolytes which can cause problems in patients with traumatic brain injury. This review provides a brief summary of the most important historical aspects of the origin of the most frequently used intravenous crystalloids today.

Safety of troclosene sodium solution in decontamination of wounds: A prospective clinical and laboratory study.

Debate persists regarding the safety of hypochlorite-containing solutions in the decontamination of infected wounds. In 2006, the Israeli Ministry of Health withdrew licensing approval for troclosene sodium as a wound irrigation solution. The aim of this prospective clinical and laboratory study was to investigate the safety of troclosene sodium solution for decontamination of infected wounds. Troclosene sodium solution was used to treat 30 patients with 35 infected skin wounds of various etiologies and body areas, over a treatment period of 8 days. Data were gathered according to a prospectively designed protocol including general findings, wound-specific observations on Day 1 and Day 8 and laboratory parameters on Day 1 and Day 8. Wound swabs and tissue biopsy for culture were taken on Day 1 and Day 8. Statistical analysis was executed. Tests were 2-sided and p values of <0.05 were considered statistically significant. Eighteen males and 12 females, with 35 infected skin wounds were enrolled. There were no adverse clinical events. No significant changes were observed in general clinical observations. Statistically significant improvements were observed in: pain (p < 0.0001); edema (p < 0.0001); area of wound covered by granulation tissue (p < 0.0001); exudate (p < 0.0001); and erythema (p = 0.002). Prior to treatment, bacteria were demonstrated on microscopy or on culture in 90% of wound samples. On Day 8, this frequency reduced to 40%. There were no abnormal laboratory tests. Serum sodium concentration increased significantly between Day 1 and Day 8, whilst serum concentration of urea and concentrations of thrombocytes, leucocytes and neutrophils showed statistically significant reductions, but all values remained within normal laboratory ranges throughout the study period. Troclosene sodium solution is clinically safe in the management of infected wounds. These findings were presented to the Israel Ministry of Health and as a result, troclosene sodium was re-approved and licensed for decontamination of infected wounds in Israel.

Collective Domain Motion Facilitates Water Transport in SGLT1.

The human sodium-glucose cotransporter protein (SGLT1) is an important representative of the sodium solute symporters belonging to the secondary active transporters that are critical to the homeostasis of sugar, sodium, and water in the cell. The underlying transport mechanism of SGLT1 is based on switching between inward- and outward-facing conformations, known as the alternating access model, which is crucial for substrate transport, and has also been postulated for water permeation. However, the nature of water transport remains unclear and is disputed along the passive and active transport, with the latter postulating the presence of the pumping effect. To better examine the water transport in SGLT1, we performed a series of equilibrium all-atom molecular dynamics simulations, totaling over 6 μs of sample representative conformational states of SGLT1 and its complexes, with the natural substrates, ions, and inhibitors. In addition to elucidating the basic physical factors influencing water permeation, such as channel openings and energetics, we focus on dynamic flexibility and its relationship with domain motion. Our results clearly demonstrate a dependence of instantaneous water flux on the channel opening and local water diffusion in the channel, strongly supporting the existence of a passive water transport in SGLT1. In addition, a strong correlation found between the local water diffusion and protein domain motion, resembling the "rocking-bundle" motion, reveals its facilitating role in the water transport.