Early Proximal Tubule Research Articles

State-of-the-Art-Review: Mechanisms of Action of SGLT2 Inhibitors and Clinical Implications.

Inhibitors of the Na+-coupled glucose transporter SGLT2 (SGLT2i) primarily shift the reabsorption of large amounts of glucose from the kidney's early proximal tubule to downstream tubular segments expressing SGLT1, and the non-reabsorbed glucose is spilled into the urine together with some osmotic diuresis. How can this protect the kidneys and heart from failing as observed in individuals with and without type 2 diabetes? Mediation analyses identified clinical phenotypes of SGLT2i associated with improved kidney and heart outcome, including a reduction of plasma volume or increase in hematocrit, and lowering of serum urate levels and albuminuria. This review outlines how primary effects of SGLT2i on the early proximal tubule can explain these phenotypes. The physiology of tubule-glomerular communication provides the basis for acute lowering of GFR and glomerular capillary pressure, which contributes to lowering of albuminuria but also to long term preservation of GFR, at least in part by reducing kidney cortex oxygen demand. Functional co-regulation of SGLT2 with other sodium and metabolite transporters in the early proximal tubule explains why SGLT2i initially excrete more sodium than expected and are uricosuric, thereby reducing plasma volume and serum urate. Inhibition of SGLT2 reduces early proximal tubule gluco-toxicity and by shifting transport downstream may simulate "systemic hypoxia", and the resulting increase in erythropoiesis, together with the osmotic diuresis, enhances hematocrit and improves blood oxygen delivery. Cardio-renal protection by SGLT2i is also provided by a fasting-like and insulin-sparing metabolic phenotype and, potentially, by off-target effects on the heart and microbiotic formation of uremic toxins.

#3115 Effectiveness of SGLT2 inhibitors in patients with glomerulonephritis: a single center experience

Abstract Background and Aims Sodium-glucose cotransporter 2 (SGLT2) inhibitors have become widely used in recent years because of favorable outcomes on kidney function in people with diabetes mellitus and chronic kidney disease (CKD). The main effect of SGLT2 inhibitors is inhibiting sodium and glucose reabsorption, acting precisely in the early proximal tubule of the renal nephron. Although these drugs developed as glucose-lowering agents for their capability to induce glycosuria, cardiovascular outcome studies found that the reduction in kidney function was significantly delayed, and the incidence of severe decline in kidney function was reduced in patients taking SGLT2 inhibitors. Later on, these outcomes were confirmed by the results of the DAPA-CKD, EMPA-KIDNEY, and CREDENCE studies, which were specific outcome trials in patients with CKD. However, data about the use of SGLT2 inhibitors in patients with glomerulonephritis at routine clinical practice are still limited. The purpose of this study is to investigate the impact of SGLT2 inhibitors use in patients with glomerulonephritis. Method Patients diagnosed with biopsy-proven GN who continued their routine follow-up in Etlik City Hospital nephrology clinic were retrospectively examined. Patients with a steroid treatment history for GN were excluded from this study. We identified 29 patients who were treated with SGLT2 inhibitors for proteinuria. We analyzed the baseline characteristics, comorbidities, GN types, and laboratory parameters (baseline, sixth and twelfth months at the follow-up). Each patient was matched to the control with a similar baseline feature under conservative therapy (n = 29). Both patient groups were treated in line with the KDIGO glomerulonephritis guideline and were received RAAS blockers at the maximum tolerated dose. According to baseline levels, the reduction rate in proteinuria and eGFR of the sixth and twelfth months were calculated as percentages. The study was performed in accordance with the Declaration of Helsinki. The local ethical committee approved the study design. Results Our study involved 58 patients diagnosed with 32 (55%) IgA nephropathy, 16 (28%) with membranous nephropathy, and 10 (17%) with focal segmental glomerulosclerosis. In the treatment group, 23 (79%) patients used dapagliflozin, and 6 (21%) used empagliflozin as SGLT2 inhibitors. Baseline proteinuria levels at [1940 (1780-2700 mg/d) vs. 1890 (1670-2400 mg/d); p = 0.8], eGFRs [60 (44-82) vs. 64 (46-80) ml/min/1.73 m2; p = 0.8] and serum albumin levels (39.6 ± 0.3 vs. 39.1 ± 0.2; p = 0.4) were similar between both groups. The proteinuria reduction rate in the sixth month was 34% (27.3-40.5) for the treatment group and 12% (6.9-20.7) for the control group (<0.0001). Besides, the reduction rate was still higher in the treatment group at the 12th month [50.5% (39-52.6) vs. 26.3% (17.2-35.4); p ≤ 0.0001]. eGFR declining rate at 6th months and 12th months were lower in SGLT2 group than the control group [3.1% (0-6.2) vs. 8.6% (4.1-16.6); p = 0.004 and 0.8% (0-5) vs. 5.9% (3.3-15.2); 0.005, respectively] (Table 1). Proteinuria levels at 6th months were 1170 (970-1890) mg/d and 1730 (1180-2100) mg/d for treatment and control group, respectively. At 12th months, median proteinuria level of SGLT2 group was 940 (840-1480) mg/d and control group was 1250 (1120- 2040) mg/d (Fig. 1). Conclusion In this study with a well-matched control group, we found that SGLT2 inhibitors demonstrate efficacy in mitigating the decline in estimated GFR and reducing albuminuria in patients with GN. However, randomized-controlled trials are still required specific to patients with GN.

Sox9-coordinated cellular neighborhoods generate fibrosis

Poorly regenerative organs deposit scar tissue to mend damage. Aggarwal etal. establish that transient Sox9 activity is necessary for early proximal tubule epithelial regeneration, while Trogisch etal. and Aggarwal etal. show that persistent Sox9 activity in epithelial and endothelial cells activates fibroblasts creating fibrotic microdomains in multiple organs.

How can inhibition of glucose and sodium transport in the early proximal tubule protect the cardiorenal system?

What mechanisms can link the inhibition of sodium-glucose cotransporter 2 (SGLT2) in the early proximal tubule to kidney and heart protection in patients with and without type 2 diabetes? Due to physical and functional coupling of SGLT2 to other sodium and metabolite transporters in the early proximal tubule (including NHE3, URAT1), inhibitors of SGLT2 (SGLT2i) reduce reabsorption not only of glucose, inducing osmotic diuresis, but of other metabolites plus of a larger amount of sodium than expected based on SGLT2 inhibition alone, thereby reducing volume retention, hypertension and hyperuricemia. Metabolic adaptations to SGLT2i include a fasting-like response, with enhanced lipolysis and formation of ketone bodies that serve as additional fuel for kidneys and heart. Making use of the physiology of tubulo-glomerular communication, SGLT2i functionally lower glomerular capillary pressure and filtration rate, thereby reducing physical stress on the glomerular filtration barrier, tubular exposure to albumin and nephrotoxic compounds, and the oxygen demand for reabsorbing the filtered load. Together with reduced gluco-toxicity in the early proximal tubule and better distribution of transport work along the nephron, SGLT2i can preserve tubular integrity and transport function and, thereby, glomerular filtration rate in the long-term. By shifting transport downstream, SGLT2i may simulate systemic hypoxia at the oxygen sensors in the deep cortex/outer medulla, which stimulates erythropoiesis and, together with osmotic diuresis, enhances hematocrit and thereby improves oxygen delivery to all organs. The described SGLT2-dependent effects may be complemented by off-target effects of SGLT2i on the heart itself and on the microbiome formation of cardiovascular-effective uremic toxins.

Metabolic Communication by SGLT2 Inhibition.

SGLT2 (sodium-glucose cotransporter 2) inhibitors (SGLT2i) can protect the kidneys and heart, but the underlying mechanism remains poorly understood. To gain insights on primary effects of SGLT2i that are not confounded by pathophysiologic processes or are secondary to improvement by SGLT2i, we performed an in-depth proteomics, phosphoproteomics, and metabolomics analysis by integrating signatures from multiple metabolic organs and body fluids after 1 week of SGLT2i treatment of nondiabetic as well as diabetic mice with early and uncomplicated hyperglycemia. Kidneys of nondiabetic mice reacted most strongly to SGLT2i in terms of proteomic reconfiguration, including evidence for less early proximal tubule glucotoxicity and a broad downregulation of the apical uptake transport machinery (including sodium, glucose, urate, purine bases, and amino acids), supported by mouse and human SGLT2 interactome studies. SGLT2i affected heart and liver signaling, but more reactive organs included the white adipose tissue, showing more lipolysis, and, particularly, the gut microbiome, with a lower relative abundance of bacteria taxa capable of fermenting phenylalanine and tryptophan to cardiovascular uremic toxins, resulting in lower plasma levels of these compounds (including p-cresol sulfate). SGLT2i was detectable in murine stool samples and its addition to human stool microbiota fermentation recapitulated some murine microbiome findings, suggesting direct inhibition of fermentation of aromatic amino acids and tryptophan. In mice lacking SGLT2 and in patients with decompensated heart failure or diabetes, the SGLT2i likewise reduced circulating p-cresol sulfate, and p-cresol impaired contractility and rhythm in human induced pluripotent stem cell-derived engineered heart tissue. SGLT2i reduced microbiome formation of uremic toxins such as p-cresol sulfate and thereby their body exposure and need for renal detoxification, which, combined with direct kidney effects of SGLT2i, including less proximal tubule glucotoxicity and a broad downregulation of apical transporters (including sodium, amino acid, and urate uptake), provides a metabolic foundation for kidney and cardiovascular protection.

SGLT2 inhibitors for patients with type 2 diabetes and CKD: a narrative review.

Sodium-glucose co-transporter 2 (SGLT2) inhibitors have recently emerged as an effective means to protect kidney function in people with type 2 diabetes and chronic kidney disease (CKD). In this review, we explore the role of SGLT2 inhibition in these individuals. SGLT2 inhibitors specifically act to inhibit sodium and glucose reabsorption in the early proximal tubule of the renal nephron. Although originally developed as glucose-lowering agents through their ability to induce glycosuria, it became apparent in cardiovascular outcome trials that the trajectory of kidney function decline was significantly slowed and the incidence of serious falls in kidney function was reduced in participants receiving an SGLT2 inhibitor. These observations have recently led to specific outcome trials in participants with CKD, including DAPA-CKD, CREDENCE and EMPA-KIDNEY, and real-world studies, like CVD-REAL-3, that have confirmed the observation of kidney benefits in this setting. In response, recent KDIGO Guidelines have recommended the use of SGLT2 inhibitors as first-line therapy in patients with CKD, alongside statins, renin-angiotensin-aldosterone system inhibitors and multifactorial risk factor management as indicated. However, SGLT2 inhibitors remain significantly underutilized in the setting of CKD. Indeed, an inertia paradox exists, with patients with more severe disease less likely to receive an SGLT2 inhibitor. Concerns regarding safety appear unfounded, as acute kidney injury, hyperkalaemia, major acute cardiovascular events and cardiac death in patients with CKD appear to be lower following SGLT2 inhibition. The first-in-class indication of dapagliflozin for CKD may begin a new approach to managing kidney disease in type 2 diabetes.

Critical Analysis of the Effects of SGLT2 Inhibitors on Renal Tubular Sodium, Water and Chloride Homeostasis and Their Role in Influencing Heart Failure Outcomes.

SGLT2 (sodium-glucose cotransporter 2) inhibitors interfere with the reabsorption of glucose and sodium in the early proximal renal tubule, but the magnitude and duration of any ensuing natriuretic or diuretic effect are the result of an interplay between the degree of upregulation of SGLT2 and sodium-hydrogen exchanger 3, the extent to which downstream compensatory tubular mechanisms are activated, and (potentially) the volume set point in individual patients. A comprehensive review and synthesis of available studies reveals several renal response patterns with substantial variation across studies and clinical settings. However, the common observation is an absence of a large acute or chronic diuresis or natriuresis with these agents, either when given alone or combined with other diuretics. This limited response results from the fact that renal compensation to these drugs is rapid and nearly complete within a few days or weeks, preventing progressive volume losses. Nevertheless, the finding that fractional excretion of glucose and lithium (the latter being a marker of proximal sodium reabsorption) persists during long-term treatment with SGLT2 inhibitors indicates that pharmacological tolerance to the effects of these drugs at the level of the proximal tubule does not meaningfully occur. This persistent proximal tubular effect of SGLT2 inhibitors can be hypothesized to produce a durable improvement in the internal set point for volume homeostasis, which may become clinically important during times of fluid expansion. However, it is difficult to know whether a treatment-related change in the volume set point actually occurs or contributes to the effect of these drugs to reduce the risk of major heart failure events. SGLT2 inhibitors exert cardioprotective effects by a direct effect on cardiomyocytes that is independent of the presence of or binding to SGLT2 or the actions of these drugs on the proximal renal tubule. Nevertheless, changes in the volume set point mediated by SGLT2 inhibitors might potentially act cooperatively with the direct favorable molecular and cellular effects of these drugs on cardiomyocytes to mediate their benefits on the development and clinical course of heart failure.

Tracing causes of tubule atrophy in vivo

Acute kidney injury (AKI) is a known risk factor for chronic kidney disease (CKD). The mechanisms for AKI-CKD transition may involve failed tubule repair and progressive interstitial fibrosis but are incompletely understood. Which events lead to failed tubule repair? Can injury spread over time? And are these processes steered by myofibroblasts and fibrotic tissue remodeling?Here, we combined serial intravital 2-photon microscopy and a novel model of partial ischemia-reperfusion injury (partial IRI), which allowed us to investigate injured tissue alongside uninjured tissue in the same kidney and over time. Thus, we occluded only one branch of the left renal artery for 21 min, rendering half the kidney ischemic. We then tracked tubule necrosis and remodeling alongside myofibroblast dynamics for up to 3 weeks. Necrotic cell death was detected by in vivo propidium iodide staining. PDGFRβ-CreERT2-Salsa6F mice (N=5) identified main myofibroblast precursor cells, by tdTomato-expression. Myofibroblast-differentiation was confirmed by ex vivo αSMA staining. Proximal tubule (PT) function was assessed by in vivo uptake of fluorescent albumin.Necrotic cell death was solely detectable upon reperfusion. Border areas in between post-ischemic and non-ischemic tissue presented severely necrotic PTs alongside uninjured PTs. From 1 day after partial IRI, we observed formation of granular casts in the lumen of necrotic tubules, which 1-2 days later also appeared in initially non-necrotic PTs downstream. Tubule necrosis and granular cast accumulation preceded thinned epithelium that lacked albumin endocytosis (day 3-7) and recruitment of myofibroblasts (peaking D4-10). Of note, non-necrotic tubules, without granular cast accumulation, didn’t remodel nor recruit myofibroblasts.Among all remodeling tubule segments, 24% turned atrophic. Importantly, preceding necrotic cell death was higher in atrophic than in recovering tubules (55±13% vs. 39±18% necrotic cells/total segment cell number, (mean±SD), p<.0001). Preceding granular casts accounted for 38±15% vs. 12±11% (mean ±SD) of the luminal area in atrophic and recovering tubules, respectively (p<.0001). Ex vivo staining for pro-fibrotic VCAM-1 demonstrated selective positivity in atrophic tubules, which appeared scattered at D8 while at D21, entire atrophic tubules stained positive (n=3, each). Consistently, we detected persistent myofibroblast enclosure of atrophic tubule, while recruitment around recovered PTs resolved by day 14 (50±21% vs. 23±18% of coverage, p<.001).Tracking the same tubules in vivo and over time, we demonstrated early proximal tubule necrosis, which induced luminal granular cast formation and injury propagation. These events preceded myofibroblast accumulation and predicted tubule atrophy. We further documented de novo expression of pro-inflammatory VCAM-1 and persistent myofibroblast recruitment selectively in atrophic tubules, suggesting an active role of this tubule state in AKI-CKD transition. Novo Nordisk Foundation, Augustinus Foundation, Aarhus University Research Foundation (AUFF) 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.

USE OF SODIUM-GLUCOSE TRANSPORT PROTEIN 2 (SGLT2) INHIBITORS IN DIABETIC KIDNEY DISEASE (DKD)

SGLT2 inhibitors have emerged as a major disease-modifying therapy for preventing the development of chronic kidney disease (CKD). These agents can be used to prevent the decline in renal function through the reduction of glomerular hypertension mediated through tubuloglomerular feedback apart from their effects on glycemic control. The indications for SGLT2 inhibitors have evolved based on growing evidence from randomized controlled trials and broadly fit into five categories, including: glycemic control/metabolic risk, reduced ASCVD, heart failure, diabetic kidney disease with albuminuria, and nondiabetic CKD with albuminuria. . The initial trial was performed in patients with relatively good overall renal function, although sub-analyses suggest that the beneficial effect may extend to patients with CKD. SGLT2 inhibitors block glucose reabsorption in the renal tubules and are effective in reducing glucose levels based on the amount of glucose filtered, thereby increasing the glomerular filtration rate. The greatest transport burden on the diabetic kidney is in the early proximal tubule. SGLT2 inhibitors make the transport load more evenly distributed between the tubular segments. In addition, the total tubular transport load is reduced by lowering GFR. The SGLT2 inhibitory effect helps maintain mitochondrial function and tubular cell metabolism which can maintain tubular function and GFR in the long term.

Empagliflozin increases kidney weight due to increased cell size in the proximal tubule S3 segment and the collecting duct.

The inhibition of renal SGLT2 glucose reabsorption has proven its therapeutic efficacy in chronic kidney disease. SGLT2 inhibitors (SGLTi) have been intensively studied in rodent models to identify the mechanisms of SGLT2i-mediated nephroprotection. So far, the overwhelming effects from clinical trials, could only partially be reproduced in rodent models of renal injury. However, a commonly disregarded observation from these studies, is the increase in kidney weight after SGLT2i administration. Increased kidney mass often relies on tubular growth in response to reabsorption overload during glomerular hyperfiltration. Since SGLT2i suppress hyperfiltration but concomitantly increase renal weight, it seems likely that SGLT2i have a growth promoting effect on the kidney itself, independent of GFR control. This study aimed to investigate the effect of SGLT2i on kidney growth in wildtype animals, to identify enlarged nephron segments and classify the size increase as hypertrophic/hyperplastic growth or cell swelling. SGLT2i empagliflozin increased kidney weight in wildtype mice by 13% compared to controls, while bodyweight and other organs were not affected. The enlarged nephron segments were identified as SGLT2-negative distal segments of proximal tubules and as collecting ducts by histological quantification of tubular cell area. In both segments protein/DNA ratio, a marker for hypertrophic growth, was increased by 6% and 12% respectively, while tubular nuclei number (hyperplasia) was unchanged by empagliflozin. SGLT2-inhibition in early proximal tubules induces a shift of NaCl resorption along the nephron causing compensatory NaCl and H2O reabsorption and presumably cell growth in downstream segments. Consistently, in collecting ducts of empagliflozin-treated mice, mRNA expression of the Na+-channel ENaC and the H2O-channels Aqp-2/Aqp-3 were increased. In addition, the hypoxia marker Hif1α was found increased in intercalated cells of the collecting duct together with evidence for increased proton secretion, as indicated by upregulation of carbonic anhydrases and acidified urine pH in empagliflozin-treated animals. In summary, these data show that SGLT2i induce cell enlargement by hypertrophic growth and possibly cell swelling in healthy kidneys, probably as a result of compensatory glucose, NaCl and H2O hyperreabsorption of SGLT2-negative segments. Particularly affected are the SGLT2-negative proximal tubules (S3) and the collecting duct, areas of low O2 availability.

Sodium-glucose cotransporter 2 inhibitor ameliorates high fat diet-induced hypothalamic-pituitary-ovarian axis disorders.

High-fat diet (HFD) consumption is known to be associated with ovulatory disorders among women of reproductive age. Previous studies in animal models suggest that HFD-induced microglia activation contributes to hypothalamic inflammation. This causes the dysfunction of the hypothalamic-pituitary-ovarian (HPO) axis, leading to subfertility. Sodium-glucose cotransporter 2 (SGLT2) inhibitors are a novel class of lipid-soluble antidiabetic drugs that target primarily the early proximal tubules in kidney. Recent evidence revealed an additional expression site of SGLT2 in the central nervous system (CNS), indicating a promising role of SGLT2 inhibitors in the CNS. In type 2 diabetes patients and rodent models, SGLT2 inhibitors exhibit neuroprotective properties through reduction of oxidative stress, alleviation of cerebral atherosclerosis and suppression of microglia-induced neuroinflammation. Furthermore, clinical observations in patients with polycystic ovary syndrome (PCOS) demonstrated that SGLT2 inhibitors ameliorated patient anthropometric parameters, body composition and insulin resistance. Therefore, it is of importance to explore the central mechanism of SGLT2 inhibitors in the recovery of reproductive function in patients with PCOS and obesity. Here, we review the hypothalamic inflammatory mechanisms of HFD-induced microglial activation, with a focus on the clinical utility and possible mechanism of SGLT2 inhibitors in promoting reproductive fitness.

Aristolochic acid-induced nephropathy is attenuated in mice lacking the neutral amino acid transporter B0AT1 (Slc6a19).

B0AT1 (Slc6a19) mediates absorption of neutral amino acids in the small intestine and in the kidneys, where it is primarily expressed in early proximal tubules (S1-S2). To determine the role of B0AT1 in nephropathy induced by aristolochic acid (AA), which targets the proximal tubule, littermate female B0AT1-deficient (Slc6a19-/-), heterozygous (Slc6a19+/-), and wild-type (WT) mice were administered AA (10 mg/kg ip) or vehicle every 3 days for 3 wk, and analyses were performed after the last injection or 3 wk later. Vehicle-treated mice lacking Slc6a19 showed normal body and kidney weight and plasma creatinine versus WT mice. The urinary glucose-to-creatinine ratio (UGCR) and urinary albumin-to-creatinine ratio (UACR) were two to four times higher in vehicle-treated Slc6a19-/- versus WT mice, associated with lesser expression of early proximal transporters Na+-glucose cotransporter 2 and megalin, respectively. AA caused tubular injury independently of B0AT1, including robust increases in cortical mRNA expression of p53, p21, and hepatitis A virus cellular receptor 1 (Havcr1), downregulation of related proximal tubule amino acid transporters B0AT2 (Slc6a15), B0AT3 (Slc6a18), and Slc7a9, and modest histological tubular damage and a rise in plasma creatinine. Absence of B0AT1, however, attenuated AA-induced cortical upregulation of mRNA markers of senescence (p16), inflammation [lipocalin 2 (Lcn2), C-C motif chemokine ligand 2 (Ccl2), and C-C motif chemokine receptor 2 (Ccr2)], and fibrosis [tissue inhibitor of metallopeptidase 1 (Timp1), transforming growth factor-β1 (Tgfb1), and collagen type I-α1 (Col1a1)], associated with lesser fibrosis staining, lesser suppression of proximal tubular organic anion transporter 1, restoration of Na+-glucose cotransporter 2 expression, and prevention of the AA-induced fivefold increase in the urinary albumin-to-creatinine ratio observed in WT mice. The data suggest that proximal tubular B0AT1 is important for the physiology of renal glucose and albumin retention but potentially deleterious for the kidney response following AA-induced kidney injury.NEW & NOTEWORTHY Based on insights from studies manipulating glucose transport, the hypothesis has been proposed that inhibiting intestinal uptake or renal reabsorption of energy substrates has unique therapeutic potential to improve metabolic disease and kidney outcome in response to injury. The present study takes this idea to B0AT1, the major transporter for neutral amino acids in the intestine and kidney, and shows that its absence attenuates aristolochic acid-induced nephropathy.

The Pathophysiological Basis of Diabetic Kidney Protection by Inhibition of SGLT2 and SGLT1.

SGLT2 inhibitors can protect the kidneys of patients with and without type 2 diabetes mellitus and slow the progression towards end-stage kidney disease. Blocking tubular SGLT2 and spilling glucose into the urine, which triggers a metabolic counter-regulation similar to fasting, provides unique benefits, not only as an anti-hyperglycemic strategy. These include a low hypoglycemia risk and a shift from carbohydrate to lipid utilization and mild ketogenesis, thereby reducing body weight and providing an additional energy source. SGLT2 inhibitors counteract hyperreabsorption in the early proximal tubule, which acutely lowers glomerular pressure and filtration and thereby reduces the physical stress on the filtration barrier, the filtration of tubule-toxic compounds, and the oxygen demand for tubular reabsorption. This improves cortical oxygenation, which, together with lesser tubular gluco-toxicity and improved mitochondrial function and autophagy, can reduce pro-inflammatory, pro-senescence, and pro-fibrotic signaling and preserve tubular function and GFR in the long-term. By shifting transport downstream, SGLT2 inhibitors more equally distribute the transport burden along the nephron and may mimic systemic hypoxia to stimulate erythropoiesis, which improves oxygen delivery to the kidney and other organs. SGLT1 inhibition improves glucose homeostasis by delaying intestinal glucose absorption and by increasing the release of gastrointestinal incretins. Combined SGLT1 and SGLT2 inhibition has additive effects on renal glucose excretion and blood glucose control. SGLT1 in the macula densa senses luminal glucose, which affects glomerular hemodynamics and has implications for blood pressure control. More studies are needed to better define the therapeutic potential of SGLT1 inhibition to protect the kidney, alone or in combination with SGLT2 inhibition.

Efficacy of Initiating Sodium Glucose Co Transporter 2 Inhibitor (SGLT2I) for Treatment of Type II Diabetes Mellitus

Sodium glucose co-transporter 2 (SGLT 2) inhibitors are hypoglycemic agents that have action on kidneys. They cause increased excretion of glucose via kidneys by reducing its absorption. In healthy individuals, kidneys filter almost all of the glucose and return it back into circulation, excreting only a minimum amount in the urine. This reabsorption is facilitated by SGLT 2 receptors which are found in early proximal tubule, with some assistance by sodium glucose co-transporter 1 (SGLT 1). In patients with type 2 diabetes mellitus (T2DM), activity of SGLT 2 is increased. This results in increased absorption of glucose in the bloodcausing further hyperglycemia. Objectives: To determine the efficacy of initiating sodium glucose co transporter2 inhibitor (SGLT2i) in patients with type 2 diabetes mellitus. Study design: Descriptive, case series study Study duration:28th April 2020 to 27th October 2020. Settings: Department of Medicine, Aziz Fatima hospital, Faisalabad and Diabetes & Endocrinology Ward of Hayatabad Medical Complex, Peshawar Materials & Methods: 150 patients with T2D aged between 18 to 60 years. Patients with pregnancy, CHF, those who had received an oral hypoglycemic medication other than metformin for more than 14 days were excluded. All the patients were given Dapagliflozin 10 mg once daily for 26 weeks. For evaluation of HbA1c, blood sampleswere checked and reported by pathologist at hospital. Efficacy was assessed after 26 weeks of treatment. Results:In this study, participants were in the age range from 18 to 60 years with mean age of 40.77 ± 9.42 years. Eighty three patients (55.33%) were between 18 to 40 years of age. Out of 150 patients, 93 (62.0%) were male and 57 (38.0%) were females with male to female ratio 1.6:1. In our study, efficacy of initiating sodium glucose co transporter -2 inhibitor (SGLT2i) in patients of type 2 diabetes mellitus was found in 65 (43.33%) patients. Conclusion: This study concluded that “the efficacy of initiating sodium glucose co transporter - 2 inhibitor (SGLT2i) in patients of type 2 diabetes mellitus is quite high.” Keywords: type 2 diabetes mellitus, sodium glucose co transporter -2 inhibitor,efficacy

SGLT2 Inhibitors: Physiology and Pharmacology.

SGLTs are sodium glucose transporters found on the luminal membrane of the proximal tubule, where they reabsorb some 180 g (1 mol) of glucose from the glomerular filtrate each day. The natural glucoside phlorizin completely blocks glucose reabsorption. Oral SGLT2 inhibitors are rapidly absorbed into the blood stream, where theyremain in the circulation for hours. On glomerular filtration, they bind specifically to SGLT2 in the luminal membrane of the early proximal tubule to reduce glucose reabsorption by 50%-60%. Because of glucose excretion, these drugs lower plasma glucose and glycosylated hemoglobin levels in patients with type 2 diabetes mellitus. The drugs also protect against heart and renal failure. The aim of this review is to summarize what is known about the physiology of renal SGLTs and the pharmacology of SGLT drugs.

High glucose-induced Smad3 linker phosphorylation and CCN2 expression are inhibited by dapagliflozin in a diabetic tubule epithelial cell model.

Background: In the kidney glucose is freely filtered by the glomerulus and, mainly, reabsorbed by sodium glucose cotransporter 2 (SGLT2) expressed in the early proximal tubule. Human proximal tubule epithelial cells (PTECs) undergo pathological and fibrotic changes seen in diabetic kidney disease (DKD) in response to elevated glucose. We developed a specific in vitro model of DKD using primary human PTECs with exposure to high D-glucose and TGF-β1 and propose a role for SGLT2 inhibition in regulating fibrosis. Methods: Western blotting was performed to detect cellular and secreted proteins as well as phosphorylated intracellular signalling proteins. qPCR was used to detect CCN2 RNA. Gamma glutamyl transferase (GT) activity staining was performed to confirm PTEC phenotype. SGLT2 and ERK inhibition on high D-glucose, 25 mM, and TGF-β1, 0.75 ng/ml, treated cells was explored using dapagliflozin and U0126, respectively. Results: Only the combination of high D-glucose and TGF-β1 treatment significantly up-regulated CCN2 RNA and protein expression. This increase was significantly ameliorated by dapagliflozin. High D-glucose treatment raised phospho ERK which was also inhibited by dapagliflozin. TGF-β1 increased cellular phospho SSXS Smad3 serine 423 and 425, with and without high D-glucose. Glucose alone had no effect. Smad3 serine 204 phosphorylation was significantly raised by a combination of high D-glucose+TGF-β1; this rise was significantly reduced by both SGLT2 and MEK inhibition. Conclusions: We show that high D-glucose and TGF-β1 are both required for CCN2 expression. This treatment also caused Smad3 linker region phosphorylation. Both outcomes were inhibited by dapagliflozin. We have identified a novel SGLT2 -ERK mediated promotion of TGF-β1/Smad3 signalling inducing a pro-fibrotic growth factor secretion. Our data evince support for substantial renoprotective benefits of SGLT2 inhibition in the diabetic kidney.

Hnf1b haploinsufficiency differentially affects developmental target genes in a new renal cysts and diabetes mouse model.

ABSTRACTHeterozygous mutations in HNF1B cause the complex syndrome renal cysts and diabetes (RCAD), characterized by developmental abnormalities of the kidneys, genital tracts and pancreas, and a variety of renal, pancreas and liver dysfunctions. The pathogenesis underlying this syndrome remains unclear as mice with heterozygous null mutations have no phenotype, while constitutive/conditional Hnf1b ablation leads to more severe phenotypes. We generated a novel mouse model carrying an identified human mutation at the intron-2 splice donor site. Unlike heterozygous mice previously characterized, mice heterozygous for the splicing mutation exhibited decreased HNF1B protein levels and bilateral renal cysts from embryonic day 15, originated from glomeruli, early proximal tubules (PTs) and intermediate nephron segments, concurrently with delayed PT differentiation, hydronephrosis and rare genital tract anomalies. Consistently, mRNA sequencing showed that most downregulated genes in embryonic kidneys were primarily expressed in early PTs and the loop of Henle and involved in ion/drug transport, organic acid and lipid metabolic processes, while the expression of previously identified targets upon Hnf1b ablation, including cystic disease genes, was weakly or not affected. Postnatal analyses revealed renal abnormalities, ranging from glomerular cysts to hydronephrosis and, rarely, multicystic dysplasia. Urinary proteomics uncovered a particular profile predictive of progressive decline in kidney function and fibrosis, and displayed common features with a recently reported urine proteome in an RCAD pediatric cohort. Altogether, our results show that reduced HNF1B levels lead to developmental disease phenotypes associated with the deregulation of a subset of HNF1B targets. They further suggest that this model represents a unique clinical/pathological viable model of the RCAD disease.

Glucose Metabolism in the Kidney: Neurohormonal Activation and Heart Failure Development.

The liver is not the exclusive site of glucose production in humans in the postabsorptive state. Robust data support that the kidney is capable of gluconeogenesis and studies have demonstrated that renal glucose production can increase systemic glucose production. The kidney has a role in maintaining glucose body balance, not only as an organ for gluconeogenesis but by using glucose as a metabolic substrate. The kidneys reabsorb filtered glucose through the sodium‐glucose cotransporters sodium‐glucose cotransporter (SGLT) 1 and SGLT2, which are localized on the brush border membrane of the early proximal tubule with immune detection of their expression in the tubularized Bowman capsule. In patients with diabetes mellitus, the renal maximum glucose reabsorptive capacity, and the threshold for glucose passage into the urine, are higher and contribute to the hyperglycemic state. The administration of SGLT2 inhibitors to patients with diabetes mellitus enhances sodium and glucose excretion, leading to a reduction of the glycosuria threshold and tubular maximal transport of glucose. The net effects of SGLT2 inhibition are to drive a reduction in plasma glucose levels, improving insulin secretion and sensitivity. The benefit of SGLT2 inhibitors goes beyond glycemic control, since inhibition of renal glucose reabsorption affects blood pressure and improves the hemodynamic profile and the tubule glomerular feedback. This action acts to rebalance the dense macula response by restoring adenosine production and restraining renin‐angiotensin‐aldosterone activation. By improving renal and cardiovascular function, we explain the impressive reduction in adverse outcomes associated with heart failure supporting the current clinical perspective.

Sodium/glucose cotransporter 2 is expressed in choroid plexus epithelial cells and ependymal cells in human and mouse brains.

Diabetes mellitus (DM) is now recognized as one of the risk factors for Alzheimer's disease (AD), and the disease‐modifying effects of anti‐diabetic drugs on AD have recently been attracting great attention. Sodium/glucose cotransporter 2 (SGLT2) inhibitors are a new class of anti‐diabetic drugs targeting the SGLT2/solute carrier family 5 member 2 (SLC5A2) protein, which is known to localize exclusively in the brush border membrane of early proximal tubules in the kidney. However, recent data suggest that it is also expressed in other tissues. In the present study, we investigated the expression of SGLT2/SLC5A2 in human and mouse brains. Immunohistochemical staining of paraffin sections from autopsied human brains and C3H/He mouse brains revealed granular cytoplasmic immunoreactivity in choroid plexus epithelial cells and ependymal cells. Immunoblot analysis of the membrane fraction of mouse choroid plexus showed distinct immunoreactive bands at 70 and 26 kDa. Band patterns around 70 kDa in the membrane fraction of the choroid plexus were different from those in the kidney. Reverse transcription‐polymerase chain reaction analysis confirmed the expression of Slc5a2 mRNA in the mouse choroid plexus. Our results provide in vivo evidence that SGLT2/SLC5A2 is expressed in cells facing the cerebrospinal fluid, in addition to early proximal tubular epithelial cells. These findings suggest that SGLT2 inhibitors may have another site of action in the brain. The effects of SGLT2 inhibitors on brain function and AD progression merit further investigation to develop better treatment options for DM patients.

Absence of Na‐Glucose Cotransporter SGLT2 Does Not Protect the Kidney in a Murine Model of Renal Ischemia‐Reperfusion Injury

The renal Na‐glucose cotransporter SGLT2 reabsorbs most of the filtered glucose in the early proximal tubule. Inhibitors of SGLT2 are glucosuric and form a new class of anti‐hyperglycemic drugs that have been proposed to reduce the risk of acute kidney injury (AKI). Here we tested whether genetic deletion of SGLT2 (KO) alters the initial kidney injury or the subsequent recovery following renal ischemia‐reperfusion (IR).Male KO and wild‐type (WT) mice (C57BL/6J) underwent sham surgery (Sham) or IR (25 min of bilateral renal artery clamping) under ketamine/xylazine anesthesia, while body temperature was maintained at 36–37°C (n=7–15/group). Urine and blood were collected at several time points. GFR was measured 14 days after IR by plasma elimination kinetics of FITC‐sinistrin in conscious mice. Kidneys were harvested 23 days after IR for renal gene expression analysis by RT‐qPCR, blinded histological analysis, and KIM‐1 and CD31 immunostaining.Plasma creatinine increased to similar levels on day 1 after IR in KO‐IR and WT‐IR (2.0±0.2 vs 1.9±0.3 mg/dL, NS) vs Sham groups (0.14±0.01 vs 0.11±0.01 mg/dL, NS). This was associated with a similar increase in urinary KIM‐1 to creatinine ratio, a marker of proximal tubule injury, and similarly reduced urine osmolality and increased plasma osmolality in KO‐IR and WT‐IR, potentially indicating impaired urine concentration. Fractional urinary glucose excretion increased from 27 to 62% in KO‐IR and from 0.1 to 20% in WT‐IR, indicating impaired tubular glucose reabsorption via SGLT1 in KO‐IR. Overall, the data indicated similar initial kidney impairment in response to IR between genotypes. In the recovery phase, GFR remained reduced on day 14 in both KO‐IR and WT‐IR (2.4±0.2 vs 2.8±0.3 μL/min/g BW, NS) vs Sham groups (12±1 vs 12±1 μL/min/g BW, NS). On day 23, plasma creatinine (0.28±0.03 vs 0.32±0.03 mg/dL, NS) was partially and similarly restored in KO‐IR and WT‐IR. Urine osmolality and renal mRNA expression of Na‐2Cl‐K cotransporter NKCC2 and renin were similarly reduced vs Sham groups, suggesting sustained impairment of thick ascending limb function. Renal mRNA expression of markers of injury, inflammation, oxidative stress, and fibrosis, (KIM‐1, NGAL, MCP‐1, NOX2, type 1 collagen, TGFB1) was similarly increased in KO‐IR and WT‐IR vs Sham groups. This was associated with similar localization and enhanced abundance of KIM‐1‐positive cells and an increased histological damage score in kidneys of IR groups. Renal CD31‐positive area and Vegfa mRNA expression were similarly reduced in KO‐IR and WT‐IR vs Sham groups suggesting similar degree of capillaries loss.The data indicate that genetic deletion of SGLT2 did not protect the kidneys in the initial injury phase or the subsequent recovery phase in a mouse model of ischemia‐reperfusion‐induced acute kidney injury, including effects on glomerular and tubular function as well as markers of inflammation, fibrosis and endothelial integrity.Support or Funding InformationNIH R01DK106102, R01DK112042, P30DK079337, and the Department of Veterans Affairs