Sodium Cotransport Research Articles

EFFECT OF GLIFLOZINS ON RENAL DYSFUNCTION IN CHRONIC HEART FAILURE WITH ANEMIA

In the article, the effect of standard treatments containing gliflozin, i.e. glucose sodium cotransporter type 2 inhibitor dapagliflozin-forsi, on kidney function in particular on glomerular filtration rate and collagen Ⅳ indicators in urine, was studied in the article. In the group of patients who received dapagliflozin, a significant decrease in the amount of collagen Ⅳ in urine after the first month of treatment confirmed the effective effect of the drug on fibrosis processes in the kidney.

THE ROLE OF ANGIOTENSIN-CONVERTING ENZYME INHIBITORS AND GLIFLOZINS IN THE TREATMENT OF CHRONIC HEART FAILURE WITH ANEMIA

The article compares the effect of standard treatments containing gliflozins, i.e. glucose sodium cotransporter type 2 inhibitor dapagliflozin (forsiga) on hematological changes, intracardiac hemodynamics, kidney function, in particular glomerular filtration rate and collagen Ⅳ indicators in urine in patients with chronic heart failure anemia studied. The increase in erythropoietin levels in the group of patients who received dapagliflozin after treatment is related to the effect of the drug on stimulating the production of erythropoietin in the kidney. It is also confirmed that the effective reduction of the amount of collagen Ⅳ in the urine after the treatment has an effective effect of the drug on the fibrosis processes in the kidney.

Hipertensión arterial y riñón

Hypertension (HT) is the main cause of death in the world. It is maintained thanks to the dysfunction of different organs and systems that normally take part in controlling blood pressure (BP) to ensure adequate perfusion of the tissues. The kidneys are the main regulators of BP over the long-term. A strict balance between the production and metabolism of vasoactive substance that regulate the excretion of water and sodium through the renin-angiotensin-aldosterone system (RAAS) modulates BP. Nevertheless, new mechanisms described in the last decade could also explain the variability of BP in patients. The overexpression of sodium cotransporters at renal level seems to escape from the regulatory effect of the RAAS. Moreover, the immune system and intestinal microbiota seem to play an important and newly discovered role. The production of certain inflammatory cytokines promotes the tubular reabsorption of sodium and the intrarenal over-activation of the RAAS. The proliferation of fermicutes, proteobacterias and Prevotella in subjects with salt-sensitive HT predisposes them to more difficult control of BP. Studying these new mechanisms may not only discover new treatment targets, as it may also explain why the improvement in BP control was not enough to reduce the comorbidities and cardiovascular risk associated with HT.

Aberrant adaptation of the inner medullary collecting ducts results in sodium retention and hypernatremia in a thick ascending limb specific Myh9 and Myh10 conditional knockout mouse model

Sodium reabsorption in the thick ascending limb (TAL) epithelium is essential to generate and sustain the interstitial osmotic gradient, which facilitates water reabsorption in the adjacent collecting duct system. Impaired TAL function can compromise this gradient and lead to electrolyte imbalance. Our previous work demonstrated that pan renal tubular conditional genetic inactivation of nonmuscle myosin II genes Myh9&10 in adult mice results in progressive kidney disease of TAL origin with aberrant regulation of TAL proteins U MOD and NKCC2 (Otterpohl et al; 2020). To confirm the cell-autonomous role for NM2 proteins in adult TAL epithelial cells, we generated a TAL-specific conditional knockout mouse model of Myh9&10 using the UMOD->CreERT2 mouse line (cKO). Genetic inactivation of Myh9&10 in the TAL was induced at 5 weeks of age with tamoxifen injections. Age matched control and cKO littermates were part of every cohort. Mice underwent metabolic, histologic, immunohistochemical, and biochemical analyses at varying time points until moribund. Development of progressive kidney disease in cKO mice was indicated by increasing levels of blood urea nitrogen, serum creatinine, and the tubular injury marker NGAL. Our results show that cKO females experience significant loss of weight at 12 weeks of age and are moribund between 13 – 14 weeks, while cKO males survive up to 25 weeks. Interestingly, female cKO mice exhibit hypernatremia at 12 weeks of age and male cKO mice between 16 - 20 weeks of age. We analyzed NKCC2 protein levels in whole kidney lysates and a drastic reduction was evident in both female and male cKO mice by 9 weeks of age, therefore hypernatremia was unexpected. We examined if the hypernatremia in TAL-Myh9&10 cKO mice is due to tubular adaptation in the distal nephron and/or the collecting duct segments. Systematic analysis of sodium cotransporters and channels in the distal nephron and collecting duct segments revealed an increase in NCC/pNCC levels in males and a decrease in females when compared with age matched control littermates. No apparent volume loss (increased urine output) has been observed in the female mice. Additionally, immunostaining experiments showed aberrant increase in expression of ENaC gamma in the inner medullary collecting duct cells in female and not male mice by 9-weeks of age. ENaC expression is limited to cortical collecting duct and the connecting segment under normal conditions in the mouse kidney. Consistent with this, our control mice do not have ENaC gamma expression in the inner medullary collecting ducts. Further experiments are underway to determine the cellular state/identity of these ENaC expressing inner medullary collect duct cells. These experiments confirm the critical role for Myh9&10 proteins in TAL tubule NKCC2 transport, and reveal novel, sex specific, adaptive mechanisms in distal nephron and collecting ducts in response to compromised NKCC2 transport within the TAL. NIDDK RO1 DK131020-01A1 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

RETRACTED: The adaptive mechanism of halophilic Brachybacterium muris in response to salt stress and its mitigation of copper toxicity in hydroponic plants

Serious environmental pollution of heavy metals has attracted people's attention in recent years and halophiles seem to be potential bioremediation in the controlling of heavy metals contamination. In this study, the adaptive mechanism of halophilic Brachybacterium muris (B. muris) in response to salt stress and its mitigation of copper (Cu) toxicity in hydroponic plants were investigated. The cell morphology was observed using transmission electron microscopy. The cell membrane composition and fluidity were examined by the combination of gas chromatography, gas chromatography-mass spectrometry, ultra-high performance liquid chromatography-mass spectrometry, and fluorescence spectrophotometry. Moreover, the metabolic pathways of B. muris in response to salt stress were analyzed using the prokaryotic transcriptomics approach. A hydroponic co-culture model was further conducted to explore the effects of B. muris on wheat seedlings subjected to Cu toxicity. It was found that B. muris can respond to high osmotic pressure by improving the cell membrane fluidity, altering the cell morphology and cell membrane compositions. The proportion of unsaturated fatty acids, phosphatidylethanolamine, and phosphatidylinositol in B. muris cell membranes increased significantly, while zymosterol, fecosterol, and ergosterol contents decreased under a high salinity situation. Further transcriptomic analysis showed that genes encoding L-glutamate synthase, glutamate ABC transporter ATP-binding protein, and sodium cotransporter were up-regulated, indicating that both the synthesis and transport of glutamate were significantly enhanced under high osmotic pressure. Additionally, B. muris alleviated the inhibitory effect of Cu2+ on wheat seedlings' growth, causing a 30.14% decrease in H2O2 content and a significant increase of 83.86% and 45.96% in POD activity and GSH content in wheat roots, respectively. The findings of this study suggested that the salt-tolerant B. muris may serve as a promising strategy for improving the bioremediation of metal-contaminated saline water and soils.

Thick ascending limb specific inactivation of Myh9and Myh10 results in progressive kidney disease with sexually dimorphic sodium transport regulation

Mutations in MYH9 gene that encodes for actin associated molecular motor nonmuscle myosin II (NM2) result in kidney disease in some patients. Based on our previous work that demonstrated a novel role for NM2 motors, we hypothesized that NM2 genes might play a critical role in renal epithelial transport. To test our hypothesis, we generated pan renal tubular conditional knockout (cKO) of Myh9&10 in adult mice that resulted in progressive kidney disease of TAL origin with aberrant transport of TAL cargoes UMOD and NKCC2 (Otterpohl et al; 2020). To confirm the cell‐autonomous role for NM2 proteins in adult TAL epithelium, we generated a TAL‐specific cKO mouse model of Myh9&10using a TAL specific cre transgenic mice, UMOD‐>CreERT2. Cre transgene was induced at 5 weeks of age with tamoxifen injections, age matched control and cKO littermates were part of every cohort. The mice underwent metabolic, histologic, immunohistochemical, and biochemical analysis at varying time points until moribund. The TAL‐specific Myh9&10 cKO mice develop progressive kidney disease indicated by increase in BUN and serum creatinine as well as increasing levels of the tubular injury marker, NGAL. Our results show that Myh9&10 TAL‐ cKO females had significant loss of weight at 12 weeks, the female cKO animals became moribund between 13 – 14 weeks, while the male cohorts survive up to 25 weeks. Histology confirmed the tubulointerstitial disease in Myh9&10 TAL‐cKO with dilated tubules and cellular infiltration. Urine pH declined starting at 9‐weeks of age in females and 12‐week in males. Interestingly, female cKO mice have hypernatremia at 12‐weeks of age compared to male mice which maintain normal sodium levels. Since the pan renal tubular Myh9&10 cKO exhibited loss of NKCC2 leading to salt wasting, this result was unexpected. We analyzed NKCC2 protein levels in kidney lysates, loss of NKCC2 was evident in both female and male Myh9&10 TAL‐cKO. We also observe significant decline in serum potassium levels in 7.5‐week females. We speculated that the hypernatremia in TAL‐Myh9&10 cKO females is due to tubular adaptation in the distal nephron and the collecting duct. Characterization of sodium cotransporters and channels in distal nephron and collecting duct segment revealed an increase in NCC/pNCC levels in males and a decrease in females. Immunostaining experiments showed increase in ENaC gamma expression in the cortical collecting ducts of the females. This could potentially explain the hypernatremia and early morbidity observed in Myh9&10 TAL‐cKO females. We speculate that females upregulate ENaC gamma to compensate for loss of NKCC2, instead males upregulate NCC/pNCC that prevents their early lethality. These experiments confirm the critical role for Myh9&10 proteins in TAL tubule and identify a novel, sex specific tubular adaptation mechanisms. NM2 motor regulating the unique, TAL‐specific sodium cotransporter is intriguing and warrants further analysis. Our model also provides a good resource for understanding the sex‐specific differences of sodium handling and potentially clarify mechanisms underlying Type I Bartter Syndrome.

Cerebrovascular Complications of Diabetes: SGLT-2 Inhibitors as a Promising Future Therapeutics.

Sodium-Glucose co-transporter inhibitors are a novel class of drugs widely used in the treatment of type 2 diabetes mellitus medical management. This class of drugs has a simple mechanism of action by which they decrease blood glucose levels. They prevent the uptake or re-absorption of glucose in the blood by inhibiting the SGLT2 co-transport channels located in the renal proximal convoluted tubule. Since SGLT2 is the low affinity, high capacity glucose transporter, it allows the co-transport of sodium and glucose through it. SGLT2s are accountable for around 90% of the renal glucose reuptake. Cerebrovascular complications or accidents (CVAs) are the world's leading cause of mortality, resulting in around 6 million deaths annually. Diabetics are prone to develop mitochondrial dysfunction and neurodegeneration due to hyperglycemia and oxidative stress end products. Due to hyperglycemic condition in diabetes, it is always an elevated risk of cerebrovascular dysfunction due to hyperglycemia as it includes endothelial dysfunction, atherosclerosis, hypercoagulability, oxidative stress, renal reperfusion injury which may lead to neuronal degeneration and cognitive impairment. A diabetic individual is more prone to develop risk factors for transient ischemic attacks than a non-diabetic patient. These inhibitors reduce hyperglycemia by blocking renal glucose reabsorption, therefore promoting an increase in renal glucose excretion. This review discusses the potential role of SGLT2 inhibitors in treating CVAs associated with T2DM.

GSK-3β inhibitor TDZD-8 prevents reduction of aquaporin-1 expression via activating autophagy under renal ischemia reperfusion injury.

Renal ischemia/reperfusion (I/R) injury is a main cause of acute kidney injury (AKI). Aquaporin (AQP)-1 water channel in the kidney is critical for the maintenance of water homeostasis and the urinary concentrating ability. Increasing evidence supports an important role of autophagy in the pathogenesis of AKI induced by renal I/R. The purpose of the present study is to investigate whether activation of autophagy prevents downregulation of AQP1 protein induced by renal I/R and potential molecular mechanisms. Renal I/R induced consistently reduced protein expression of AQP1, 2, and 3, as well as sodium cotransporters Na+ -K+ -2Cl- cotransporter and α-Na,K-ATPase, which was associated with increased urine output and decreased creatinine clearance in rats. Renal I/R also suppressed autophagy and increased inflammatory responses in the kidney. 4-Benzyl-2-methyl-1,2,4-thiadiazolidine-3,5-dione (TDZD-8), the glycogen synthase kinase-3β inhibitor, ameliorated renal injury under I/R, activated autophagy and markedly increased expression of AQPs and sodium transporters in the kidney, which was associated with improved urine output and creatinine clearance in rats. Hypoxia/reoxygenation (H/R) induced suppression of autophagy and downregulation of AQP1 in murine inner medullary collecting duct 3 (IMCD3) cells, which was fully prevented by TDZD-8 treatment. Inhibition of autophagy by 3-methyladenine or Atg5 gene knockdown attenuated recovery of AQP1 protein expression induced by TDZD-8 in IMCD3 cells with H/R. Interleukin-1 beta (IL-1β) decreased the abundance of AQP1 protein in IMCD3 cells. H/R induced increases in protein expression of nod-like receptor pyrin domain-containing 3 and IL-1β, which was reversed by TDZD-8. In conclusion, TDZD-8 treatment prevented downregulation of AQP1 expression under renal I/R injury, likely via activating autophagy and decreasing IL-1β production.

Proposed mechanisms of systemic cardiovascular action of gliflosins

The literature review is devoted to the study of the mechanisms of the cardioprotective action of a new class of glucose-lowering drugs glyflozins, which inhibit the joint transport of sodium and glucose in the proximal renal tubules. The large-scale clinical trials carried out in recent years have demonstrated the beneficial effect of these compounds not only on glycemic control, but also on the progression of heart failure in patients with diabetes mellitus. Analysis of literature data shows that the effect under consideration is due to both the positive systemic cardiovascular and direct cardiotropic action of the drugs. The first part of the review examines the systemic effect of drugs, including their diuretic, natriuretic and antihypertensive effects, increased hematocrit, vascular effects that influence arterial stiffness, smooth muscle tone, and endothelial dysfunction. The metabolic effects of type 2 sodium and glucose co-transport inhibitors are discussed separately, including an increase in lipolysis, the role of glucagon and activation of ketogenesis, and their contribution to the development of a probable cardioprotective effect.

Fibroblast growth factor 23-Klotho and hypertension: experimental and clinical mechanisms.

Hypertension (HTN) and chronic kidney disease (CKD) are increasingly recognized in pediatric patients and represent risk factors for cardiovascular morbidity and mortality later in life. In CKD, enhanced tubular sodium reabsorption is a leading cause of HTN due to augmented extracellular fluid volume expansion. The renin-angiotensin-aldosterone system (RAAS) upregulates various tubular sodium cotransporters that are also targets of the hormone fibroblast growth factor 23 (FGF23) and its co-receptor Klotho. FGF23 inhibits the activation of 1,25-dihydroxyvitamin D that is a potent suppressor of renin biosynthesis. Here we review the complex interactions and disturbances of the FGF23–Klotho axis, vitamin D, and the RAAS relevant to blood pressure regulation and discuss the therapeutic strategies aimed at mitigating their pathophysiologic contributions to HTN.

Protein Kinase A‐mediated Regulation of SLC5A8 Surface Expression

SLC5A8 (solute carrier gene family 5A, member 8) encodes the sodium monocarboxylate transporter, SMCT1. SMCT1 mediates cotransport of sodium and monocarboxylates, such as short chain fatty acids, in many tissues, including thyroid, kidney, and colon. Inspection of SMCT1’s primary amino acid sequence identifies not only a carboxyl terminus post‐synaptic density/discs large/zona occuldens 1 (PDZ) binding motif postulated to be important in macromolecular transport protein complexing, but also consensus sites for phosphorylation by multiple classes of kinases. Notably, SMCT1 contains a single protein kinase A (PKA) consensus site: RRMT (amino acids 50–53), with T53 potentially functioning as the site of phosphorylation. The present study considers the hypothesis that PKA regulates SMCT1 surface expression, as reported for the sodium‐glucose cotransporter (SGLT1, the product of the SLC5A1 gene). The following experiments test whether elimination of the phosphorylation site disrupts PKA‐mediated regulation of surface expression. Using site‐directed mutagenesis, we disrupted the consensus motif and concomitantly disabled phosphorylation by replacing T53 with an alanine residue (T53A). To facilitate downstream assays, we generated T53A on the background of a human SMCT1 expression construct containing an amino‐terminus, extracellular hemagglutinin (HA) tag. In transiently expressing COS‐7 cells, surface luminescence measurements confirmed T53A resides in the cell surface at levels similar to wild‐type SMCT1, and immunoblot measurements indicate similar total expression levels. Wild‐type SMCT1‐expressing cells displayed increased luminescence signal (~20%) subsequent to forskolin (10 μM) treatment to stimulate adenylate cyclase and activate PKA, consistent with augmented surface expression. In contrast, cells expressing T53A were indifferent to forskolin treatment. As an independent measure of surface expression, plans are underway to perform cell‐surface immunoprecipitation (CS‐IP) experiments. Taken together, these data suggest that, although constitutive plasma membrane residency does not depend on an intact PKA consensus site, forskolin‐activated, PKA‐dependent phosphorylation can increase SMCT1 levels in the plasma membrane, and thereby augment potential transport capacity.Support or Funding InformationNIH/NIGMS Award 1R15GM101674‐01A1 (to PF)

Hepsin-mediated Processing of Uromodulin is Crucial for Salt-sensitivity and Thick Ascending Limb Homeostasis

Uromodulin is a zona pellucida-type protein essentially produced in the thick ascending limb (TAL) of the mammalian kidney. It is the most abundant protein in normal urine. Defective uromodulin processing is associated with various kidney disorders. The luminal release and subsequent polymerization of uromodulin depend on its cleavage mediated by the serine protease hepsin. The biological relevance of a proper cleavage of uromodulin remains unknown. Here we combined in vivo testing on hepsin-deficient mice, ex vivo analyses on isolated tubules and in vitro studies on TAL cells to demonstrate that hepsin influence on uromodulin processing is an important modulator of salt transport via the sodium cotransporter NKCC2 in the TAL. At baseline, hepsin-deficient mice accumulate uromodulin, along with hyperactivated NKCC2, resulting in a positive sodium balance and a better adaptation to water deprivation. In conditions of high salt intake, defective uromodulin processing predisposes hepsin-deficient mice to a salt-wasting phenotype, with a decreased salt sensitivity. These modifications are associated with intracellular accumulation of uromodulin, endoplasmic reticulum-stress and signs of tubular damage. These studies expand the physiological role of hepsin and uromodulin and highlight the importance of hepsin-mediated processing of uromodulin for kidney tubule homeostasis and salt sensitivity.

Slc4a8 in the Kidney: Expression, Subcellular Localization and Role in Acid Base Homeostasis and Salt Reabsorption

BackgroundThe sodium‐dependent bicarbonate transporter Slc4a8 (a.k.a NDCBE) mediates the co‐transport of sodium and bicarbonate in exchange for chloride. It is abundantly detected in the brain, with low expression levels in the kidney. The cell distribution and subcellular localization of Slc4a8 in the kidney and its role in acid/base and electrolyte homeostasis has been the subject of conflicting reports. There are no conclusive localization or functional studies to pinpoint the location and demonstrate the function of Slc4a8 in the kidney.MethodsMolecular techniques, including in situ hybridization and RT‐PCR, were performed on kidney sections and tagged epitopes were used to examine the membrane targeting of Slc4a8 in polarized kidney cells. Crispr/Cas9 was used to generate and examine Slc4a8 KO mice.ResultIn situ hybridization and Zonal distribution studies showed no expression for Slc4a8 (NDCBE) in the cortex or in cortical collecting ducts (CCD). Slc4a8 was predominantly detected in the outer and inner medullary collecting ducts (OMCD and IMCD), and was targeted to the basolateral membrane of osmotically tolerant MDCK cells when confocal microscopy images were acquired. Slc4a8 KO mice did not show any abnormal salt or bicarbonate wasting under baseline conditions or in response to bicarbonate loading, salt restriction or furosemide‐induced diuresis.ConclusionsSlc4a8 (NDCBE) is absent in the CCD and is predominantly localized on the basolateral membrane of medullary collecting duct cells. Further, Slc4a8 deletion does not cause any acid base or electrolyte abnormality in pathophysiologic states such as furosemide‐induced salt wasting or salt restriction. We suggest that Slc4a8 is likely involved in intracellular pH and volume regulation in medullary collecting duct cells.Support or Funding InformationMerit Review 5 I01 BX001000‐06 award from the Department of Veterans Affairs, and funds from the Center on Genetics of Transport and Epithelial Biology at the University of Cincinnati.

Effects of dietary glucose and sodium chloride on intestinal glucose absorption of common carp (Cyprinus carpio L.)

The co-transport of sodium and glucose is the first step for intestinal glucose absorption. Dietary glucose and sodium chloride (NaCl) may facilitate this physiological process in common carp (Cyprinus carpio L.). To test this hypothesis, we first investigated the feeding rhythm of intestinal glucose absorption. Carps were fed to satiety once a day (09:00 a.m.) for 1 month. Intestinal samples were collected at 01:00, 05:00, 09:00, 13:00, 17:00 and 21:00. Result showed that food intake greatly enhanced sodium/glucose cotransporter 1 (SGLT1) and glucose transporter type 2 (GLUT2) expressions, and improved glucose absorption, with highest levels at 09:00 a.m.. Then we designed iso-nitrogenous and iso-energetic diets with graded levels of glucose (10%, 20%, 30%, 40% and 50%) and NaCl (0%, 1%, 3% and 5%), and submitted to feeding trial for 10 weeks. The expressions of SGLT1 and GLUT2, brush border membrane vesicles (BBMVs) glucose transport and intestinal villus height were determined after the feeding trial. Increasing levels of dietary glucose and NaCl up-regulated mRNA and protein levels of SGLT1 and GLUT2, enhanced BBMVs glucose transport in the proximal, mid and distal intestine. As for histological adaptive response, however, high-glucose diet prolonged while high-NaCl diet shrank intestinal villus height. Furthermore, we also found that higher mRNA levels of SGLT1 and GLUT2, higher glucose transport capacity of BBMVs, and higher intestinal villus were detected in the proximal and mid intestine, compared to the distal part. Taken together, our study indicated that intestinal glucose absorption in carp was primarily occurred in the proximal and mid intestine, and increasing levels of dietary glucose and NaCl enhanced intestinal glucose absorption in carp.

A Review of the Efficacy and Safety of Sodium-Glucose Cotransporter 2 Inhibitors: A Focus on Diabetic Ketoacidosis.

Diabetes is a complex, chronic medical condition affecting 29.1 million people in the United States (9.3% of the population) and is projected to affect one in three Americans by 2050 if the current trend continues (1). Diabetes management can be challenging, often requiring multiple therapeutic agents as the disease progresses. Current guidelines recommend metformin as first-line pharmacological therapy for the treatment of type 2 diabetes. Multiple second-line options are available for patients whose A1C goal is not achieved with monotherapy, and selection should be based on patient- and drug-specific factors. Sodium–glucose cotransporter 2 (SGLT2) inhibitors, the newest U.S. Food and Drug Administration (FDA)–approved oral antidiabetic agents, are among these options for patients with type 2 diabetes. Canagliflozin, dapagliflozin, and empagliflozin are the currently available SGLT2 inhibitors in the United States (2,3). Sodium–glucose cotransporter 1 (SGLT1) is predominantly located in the small intestine, but is also expressed in the kidneys, trachea, heart, and colon (4,5). In the kidneys, SGLT1 is primarily located in the S3 segment of the proximal convoluted tubule (PCT) (4). SGLT2 is expressed in the kidneys and primarily located in the S1 and S2 segments of the PCT (4,5). In normoglycemic adults, about 180 g of glucose (Figure 1) is filtered per day in the glomerulus, and most is reabsorbed (4,6). In people with diabetes, reabsorption of glucose is increased compared to people without diabetes (7,8). SGLT1 and SGLT2 are located in the apical membrane and facilitate the transport of glucose with sodium from the renal tubular lumen into the cells (Figure 2) (4). FIGURE 1. Structures of glucose, phlorizin, canagliflozin, dapagliflozin, and empagliflozin. FIGURE 2. Cotransport of glucose and sodium by SGLT1 and SGLT2 in the PCT. Phlorizin (Figure 1), an O -glucose derivative/ O -glycoside, was discovered in …

Membrane-bound pyrophosphatases acquired twice the physiological sodium and proton co-transport function

Membrane-bound pyrophosphatases acquired twice the physiological sodium and proton co-transport function

Diuretic Action of Sodium-Glucose Cotransporter 2 Inhibitors and Its Importance in the Management of Heart Failure.

Primarily, the sodium-glucose cotransporter 2 (SGLT2) inhibitors suppress the cotransport of glucose and sodium from the tubular lumen of the proximal tubules to the blood, and excrete glucose into the urine. Therefore, glucose and caloric balances become negative, reducing both the blood glucose level and insulin secretion. On the other hand, the proximal tubular fluid, constituted with low chloride concentration because of SGLT2 inhibition, is transferred to the loop of Henle. Under low chloride conditions, the reabsorption mechanisms in the loop of Henle do not work, similar to when loop diuretics are given. Subanalysis data on heart failure (HF) from the EMPA-REG OUTCOME trials are discussed, assuming that SGLT2 inhibitors are loop diuretics. Renin-angiotensin system inhibitors and β-blockers contribute to prognostic improvements of HF, independent of SGLT2 inhibitors, and therefore, both regimens are essential for the treatment of HF. On the other hand, the prognostic improvements by SGLT2 inhibitors are not significant under treatment including conventional diuretics such as loop diuretics and aldosterone antagonists, suggesting that the prognostic improvement in HF by SGLT2 inhibitors is mostly through their diuretic action. (Circ J 2016; 80: 2277-2281).

The Benefits of SGLT2 Inhibitors in Cardiovascular Prevention, Glycemic Control and Weight Loss, in the Treatment of Diabetes

The sodium and glucose co-transporter inhibitors type 2 (SGLT2) comprises a new class of hypoglycemic drugs to control type 2 diabetes mellitus, in an attempt to add new non-existing benefits to the so far arising classes. Regarding this new class of drugs, represented by dapaglifozin, canaglifozin and empaglifozin, it is important to highlight the benefits brought by these medications to combat hyperglycemia with insulin-independent mechanisms that are beyond glucose reduction, such as cardiovascular events prevention, reduction in HbA1c, weight loss and blood pressure lowering. Recently, a relevant study (Empa-Reg) brought hope and set the spotlight on the prevention of cardiac events among diabetic patients, which is the main cause of mortality within this group. However, despite coming out as a good treatment option, SGLT2 inhibitors are under constant clinical research and, as a new drug, it should be carefully carried out regarding the long-term effects of glycosuria and other possible side effects, such as the observed increase in the incidence of bladder, breast cancer and bone fractures, which require further studies. Therefore, these compounds might represent a landmark approach for the treatment of diabetes.

Abstract 405: Novel Signaling Mechanisms by Which Intracellular Angiotensin II Induces Na + /HCO 3 - CotransporterExpression In The Proximal Tubule of The Kidney

Previous studies have shown that endocrine and/or paracrine angiotensin II (ANG II) plays an important role in the regulation of sodium and bicarbonate reabsorption in the proximal tubule of the kidney. However, it is not known whether intracellular (or intracrine) ANG II also plays a role in these responses in the proximal tubule. The present study tested the hypothesis that overexpression of an intracellular cyan fluorescent fusion protein of ANG II (ECFP/ANG II) in the proximal tubule of the kidney induces the expression of the Na + /HCO 3 - cotransporter via MAPK- and NF-kB signaling pathways. To test the hypothesis, transport-competent mPCTs from wild-type and type 1a ANG II receptor-deficient mice (AT 1a -KO) were transfected with ECFP/ANG II, and treated with the AT 1 receptor blocker losartan, the MEK1/MEK2 inhibitor U0126, or the NF-κB inhibitor RO 106-9920. In wild-type mPCT cells, the expression of ECFP/ANG II more than doubled total and/or phosphorylated NHE3 antiporter and Na + /HCO 3 - cotransporter proteins (p<0.01). These response were accompanied by more than threefold increases in phospho-ERK 1/2, p65 subunit of NF-κB, and phospho-IKKα/β (Ser 176/180) proteins (p<0.01). Pretreatment of mPCT cells with losartan, U0126, or RO 106-9920 significantly blocked the effects of ECFP/ANG II (p<0.01). Furthermore, the effects of ECFP/ANG II were significantly attenuated in mPCT cells of AT 1a -KO mice (p<0.01),. In wild-type C57BL/6J mice, adenovirus-mediated overexpression of ECFP/ANG II selectively in the proximal tubule of the kidney, driven by the sodium and glucose cotransporter 2 (sglt2) promoter, significantly increased blood pressure, total and/or phosphorylated NHE3 and Na + /HCO 3 - proteins, and proximal tubular lithium reabsorption (p<0.01). These responses to ECFP/ANG II as observed in C57BL/6J mice were also attenuated in AT 1a -KO mice (p<0.01). Our results strongly suggest that intracellular ANG II may induce NHE3 and Na + /HCO 3 - expression, and increase proximal tubular sodium and bicarbonate reabsorption via AT 1a receptor-mediated activation of MAP kinases ERK 1/2 and NF-κB signaling pathways.

The role of amiloride‐insensitive sodium transport in alveolar fluid homeostasis (695.2)

Under both normal and pathological conditions, the lung fluid balance across the alveolar epithelial barrier is mainly regulated by active sodium transporters. Previous work has largely focused on the critical role of ENaC, yet ~60% of alveolar fluid clearance in rats or humans is amiloride insensitive. We decided to explore the role of the amiloride‐insensitive sodium cotransporters SGLT1 (Na+‐glucose co‐transporter 1) and SNATs (Na+‐coupled neutral amino acid transporters) in the intact lung. In isolated perfused rat lungs, we determined alveolar fluid clearance (AFC) using a double indicator dilution technique and probed for the role of SGLT1 and SNATs by addition of appropriate cotransporter substrates or inhibitors. While addition of the SNAT substrate L‐alanine did not affect basal AFC, it rescued AFC in lungs pre‐treated with amiloride, and this response was blocked by the SNAT inhibitor HgCl2. Analysis of bronchoalveolar lavage fluid revealed > 2‐fold of L‐alanine in the epithelial lining fluid compared to plasma level. RT‐PCR identified mRNAs for all 6 SNAT isoforms in whole lung, yet in alveolar epithelial cells, only SNAT 2 and 5 mRNA and protein were detected. In contrast, no functional involvement of SGLT1 in AFC was detected. These results indicate a new role for SNATs in AFC which becomes unmasked when ENaC is inhibited. SNAT2 and SNAT5 may represent novel targets for the resolution of pulmonary edema.Grant Funding Source: Funded by CIHR MOP # 245251