SGLT2 inhibition in a kidney with reduced nephron number: modeling and analysis of solute transport and metabolism

ASK1 limits kidney glucose reabsorption, growth, and mid-late proximal tubule KIM-1 induction when diabetes and Western diet are combined with SGLT2 inhibition

Selonsertib is an apoptosis signal-regulating kinase 1 inhibitor (ASK1i) that attenuated the decline in creatinine-based estimated GFR in humans with type 2 diabetes and kidney disease but increased the rate of acute kidney injury. This study explored the individual and combined kidney effects of selonsertib and the antihyperglycemic sodium-glucose cotransporter 2 inhibitor (SGLT2i) dapagliflozin in Western diet-fed male Akita mice, a murine model of early type 1 diabetes mellitus showing signs of systemic but no kidney inflammation. ASK1i reduced elevated plasma levels of proinflammatory cytokines/chemokines (IL-6, MCP1/CCL2, KC/CXCL1, and IP-10/CXCL10) without significantly changing hyperglycemia, glomerular hyperfiltration, and albuminuria or affecting the blood glucose and glomerular hyperfiltration-lowering effect of SGLT2i. A potential sign of tubular stress, SGLT2i modestly upregulated kidney cortex transcription of proinflammatory and profibrotic genes and distal tubule injury marker Ngal. Adding ASK1i to SGLT2i lowered the transcription of many of these genes, including Ngal. However, ASK1i enhanced kidney glucose reabsorption independent of SGLT2i, and combined ASK1i + SGLT2i increased kidney weight by 30%. This was associated with and positively correlated with the upregulation of the tubular stress/injury marker KIM-1, primarily in the mid-to-late proximal tubule. Combined ASK1i + SGLT2i increased the tubular injury score but not signs of kidney inflammation or fibrosis beyond a robust increase in kidney mRNA expression of Il6, Ccl2 (Mcp1), and Timp1, associated with increased plasma IL-6 levels. The data support the hypothesis that housekeeping functions of ASK1 limit glucose reabsorption and the associated growth and cellular stress induced in the mid-to-late proximal tubule by combining hyperglycemia and Western diet with SGLT2 inhibition.NEW & NOTEWORTHY Selonsertib is an apoptosis signal-regulating kinase 1 (ASK1) inhibitor that attenuated creatinine-based eGFR decline in humans with type 2 diabetes and kidney disease but increased acute kidney injury rates. Here, we report evidence in a murine model of early type 1 diabetes mellitus that housekeeping functions of ASK1 limit glucose reabsorption and the associated growth and cellular stress induced in the mid-to-late proximal tubule by combining hyperglycemia and Western diet with SGLT2 inhibition.

Effects of sotagliflozin on kidney and cardiac outcome in a hypertensive model of subtotal nephrectomy in male mice

Dual inhibition of sodium glucose cotransporters 1 and 2 (SGLT1/SGLT2) by sotagliflozin protects the kidney and heart in patients with type 2 diabetes mellitus (T2DM) and chronic kidney disease (CKD). To gain mechanistic insights, the current study aimed to establish a murine model of hypertensive CKD that shows cardio-renal protection by sotagliflozin. Since protection by SGLT2 inhibitors can be diabetes-independent, a nondiabetic murine model of subtotal nephrectomy with angiotensin II infusion-facilitated hypertension was followed for 7 weeks. The model showed 40% lower GFR, doubling in plasma FGF23, 50 mmHg higher systolic blood pressure (SBP), 100-fold increased albuminuria, and robust signs of kidney injury, inflammation, and fibrosis versus sham controls, associated with a 30% larger left cardiac ventricle and wall thickness and upregulation of markers of cardiac overload and fibrosis. Sotagliflozin, initiated 1 week after the last surgery, showed target-engagement evidenced by glucosuria, 9 mmHg lower SBP, temporal reduction in body weight and GFR, and 30% higher plasma GLP1. Sotagliflozin, however, did not improve markers of kidney injury, inflammation, fibrosis, albuminuria, and plasma FGF23, or signs of cardiac overload, fibrosis, or impaired function. Limited sotagliflozin responsiveness may relate to short treatment time, limited metabolic benefits in nondiabetic setting and/or the model's dominant angiotensin II-driven effects/hypertension.

Genetic deletion of the kidney sodium/proton exchanger-3 (NHE3) does not alter calcium and phosphate balance due to compensatory responses

The sodium/proton exchanger-3 (NHE3) plays a major role in acid-base and extracellular volume regulation and is also implicated in calcium homeostasis. As calcium and phosphate balances are closely linked, we hypothesized that there was a functional link between kidney NHE3 activity, calcium, and phosphate balance. Therefore, we examined calcium and phosphate homeostasis in kidney tubule-specific NHE3 knockout mice (NHE3loxloxPax8 mice). Compared to controls, these knockout mice were normocalcemic with no significant difference in urinary calcium excretion or parathyroid hormone levels. Thiazide-induced hypocalciuria was less pronounced in the knockout mice, in line with impaired proximal tubule calcium transport. Knockout mice had greater furosemide-induced calciuresis and distal tubule calcium transport pathways were enhanced. Despite lower levels of the sodium/phosphate cotransporters (NaPi)-2a and -2c, knockout mice had normal plasma phosphate, sodium-dependent 32Phosphate uptake in proximal tubule membrane vesicles and urinary phosphate excretion. Intestinal phosphate uptake was unchanged. Low dietary phosphate reduced parathyroid hormone levels and increased NaPi-2a and -2c abundances in both genotypes, but NaPi-2c levels remained lower in the knockout mice. Gene expression profiling suggested proximal tubule remodeling in the knockout mice. Acutely, indirect NHE3 inhibition using the SGLT2 inhibitor empagliflozin did not affect urinary calcium and phosphate excretion. No differences in femoral bone density or architecture were detectable in the knockout mice. Thus, a role for kidney NHE3 in calcium homeostasis can be unraveled by diuretics, but NHE3 deletion in the kidneys has no major effects on overall calcium and phosphate homeostasis due, at least in part, to compensating mechanisms.

Insightful Perspectives on Sodium-glucose Co-transporter 2 Inhibitors: Navigating Safety Updates and Beyond

SGLT2 (Sodium-Glucose Co-transporter 2) inhibitors, also known as gliflozin class, are a novel family of oral drugs being used to treat type 2 diabetes. SGLT2 inhibitors can work alone or in conjunction with other medications. This class includes five drugs, including canagliflozin, ertugliflozin, sotagliflozin, dapagliflozin, and empagliflozin. SGLT2 inhibitors inhibit the SGLT2 cotransporter in the proximal tubules of the kidney, reducing glucose and sodium reabsorption. It promotes the elimination of sugar in urine (diabetes mellitus) and lowers blood sugar levels. SGLT2 inhibitors also have pleiotropic effects on cardiac and renal function, broadening their therapeutic applications in heart failure. Despite the clinical benefits, regulators have placed secondary warnings in product information since the medications first hit the market. SGLT2 inhibitors, in particular, have had a significant impact on a variety of risk factors. This can lead to hypoglycaemia, urinary tract infections, diabetic ketoacidosis, lower limb amputation, and fractures. Although some of these events are uncommon, they can lead to severe and deadly consequences; therefore, patients must be closely monitored. In general, SLGT2 inhibitors are an efficient diabetes treatment with strong cardiovascular and renal protection and a favourable safety overview. This review sought to summarise the safety overview of commercially available SGLT2 inhibitors.

Glomerular pressure and tubular oxygen supply: a critical dual target for renal protection

The primary treatment goal of chronic kidney disease (CKD) is preserving renal function and preventing its progression to end-stage renal disease. Glomerular hypertension and tubular hypoxia are critical risk factors in CKD progression. However, the renal hemodynamics make it difficult to avoid both factors due to the existence of peritubular capillaries that supply oxygen to the renal tubules downstream from the glomerulus through the efferent arteriole. In the treatment strategies for balancing glomerular pressure and tubular oxygen supply, afferent and efferent arterioles of the glomerulus determine glomerular filtration rate and blood flow to the peritubular capillaries. Therefore, sodium-glucose cotransporter 2 inhibitors and angiotensin receptor-neprilysin inhibitors as well as classical renin-angiotensin system inhibitors, which can change the diameter of afferent and/or efferent arterioles, are promising options for balancing this dual target and achieving renal protection. This review focuses on the clinical importance of glomerular pressure and tubular oxygen supply and proposes an effective treatment modality for this dual target.

Water and sodium conservation response induced by SGLT2 inhibitor ipragliflozin in Dahl salt-sensitive hypertensive rats

Sodium-glucose cotransporter 2 (SGLT2) inhibitors increase urine volume with glucosuria and natriuresis. We recently reported that osmotic diuresis by the SGLT2 inhibitor ipragliflozin induces fluid homeostatic action via the stimulation of fluid intake and vasopressin-induced water reabsorption in euvolemic rats. However, the effects of SGLT2 inhibitors on these parameters in hypervolemic animals remain unclear. In this study, Dahl salt-sensitive hypertensive rats, a hypervolemic rat model, were fed a low-salt (0.3%) or high-salt (8%) diet for 14 days, then divided into vehicle or ipragliflozin (0.01%) groups. During 7 days of treatment, the high-salt diet groups significantly increased fluid intake and urine volume. In the ipragliflozin groups, fluid intake and urine volume increased by 63% and 235%, respectively, in rats fed a normal-salt diet and by 46% and 72%, respectively, in rats fed a high-salt diet. Ipragliflozin increased urinary vasopressin by 200% and solute-free water reabsorption by 196% in the normal-salt group but by only 44% and 38%, respectively, in the high-salt group. A high-salt diet significantly increased fluid balance (fluid intake - urine volume) and Na+ balance (Na+ intake - urinary Na+), but ipragliflozin did not change fluid and Na+ balance in normal- or high-salt groups. A high-salt diet significantly increased systolic blood pressure, but ipragliflozin did not significantly change systolic blood pressure in normal- or high-salt groups. In conclusion, SGLT2 inhibitor ipragliflozin did not change fluid and Na+ balance regardless of basal fluid retention, suggesting the potential of SGLT2 inhibitors to maintain body water and Na+.

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

BACKGROUND

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?

GOAL

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.

RESULTS

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.

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.

Sodium-glucose cotransporter-2 inhibitors and abnormal serum potassium: a real-world, pharmacovigilance study

BACKGROUND

New trials indicated a potential of sodium-glucose cotransporter-2 inhibitors (SGLT2i) to reduce hyperkalemia, which might have important clinical implications, but real-world data are limited. Therefore, we examined the effect of SGLT2i on hyper- and hypokalemia occurrence using the FDA adverse event reporting system (FAERS).

METHODS

The FAERS database was retrospectively queried from 2004q1 to 2021q3. Disproportionality analyses were performed based on the reporting odds ratio (ROR) and 95% confidence interval (CI).

RESULTS

There were 84 601 adverse event reports for SGLT2i and 1 321 186 reports for other glucose-lowering medications. The hyperkalemia reporting incidence was significantly lower with SGLT2i than with other glucose-lowering medications (ROR, 0.83; 95% CI, 0.79-0.86). Reductions in hyperkalemia reports did not change across a series of sensitivity analyses. Compared with that with renin-angiotensin-aldosterone system inhibitors (RAASi) alone (ROR, 4.40; 95% CI, 4.31-4.49), the hyperkalemia reporting incidence was disproportionally lower among individuals using RAASi with SGLT2i (ROR, 3.25; 95% CI, 3.06-3.45). Compared with that with mineralocorticoid receptor antagonists (MRAs) alone, the hyperkalemia reporting incidence was also slightly lower among individuals using MRAs with SGLT-2i. The reporting incidence of hypokalemia was lower with SGLT2i than with other antihyperglycemic agents (ROR, 0.79; 95% CI, 0.75-0.83).

CONCLUSION

In a real-world setting, hyperkalemia and hypokalemia were robustly and consistently reported less frequently with SGLT2i than with other diabetes medications. There were disproportionally fewer hyperkalemia reports among those using SGLT-2is with RAASi or MRAs than among those using RAASi or MRAs alone.

Early changes in estimated glomerular filtration rate post-initiation of empagliflozin in EMPEROR-Preserved

AIMS

Renal function (estimated glomerular filtration rate [eGFR]) changes early after the introduction of empagliflozin have not been described in heart failure with preserved ejection fraction (HFpEF). The aim of this study was to describe early eGFR changes, assess its determinants and its clinical impact on cardiovascular and renal outcomes in patients with HFpEF enrolled in EMPEROR-Preserved.

METHODS AND RESULTS

Estimated glomerular filtration rate changes (absolute and relative) from randomization to week 4 were calculated and landmark analyses performed. Initial eGFR change was available in 5836 patients (97.5% of the population). Empagliflozin induced a mean eGFR change of -3.2 ml/min/1.73 m2 versus placebo from baseline to week 4. After week 4, in the empagliflozin group, the risk of the primary outcome (composite of heart failure hospitalization or cardiovascular death), cardiovascular, all-cause mortality and sustained ≥50% eGFR decrease or end-stage renal disease (ESRD) did not differ by eGFR change levels. In contrast, in the placebo group, patients included in the tertile with most profound eGFR decrease (i.e. ≥5.1% from baseline) had a higher risk of the primary outcome (hazard ratio [HR] 1.46, 95% confidence interval [CI] 1.17-1.82), cardiovascular mortality (HR 1.38, 95% CI 1.01-1.89) and sustained ≥50% eGFR decrease or ESRD (HR 2.20, 95% CI 1.20-4.04) versus tertile with eGFR increase.

CONCLUSION

An initial relatively small eGFR decrease may be expected after empagliflozin initiation. Such small eGFR decrease was not associated with adverse cardiovascular outcomes with empagliflozin. In contrast, eGFR decrease was associated with poor cardiovascular outcomes with placebo.

Nascent shifts in renal cellular metabolism, structure, and function due to chronic empagliflozin in prediabetic mice

Sodium-glucose cotransporter, type 2 inhibitors (SGLT2i) are emerging as the gold standard for treatment of type 2 diabetes (T2D) with renal protective benefits independent of glucose lowering. We took a high-level approach to evaluate the effects of the SGLT2i, empagliflozin (EMPA) on renal metabolism and function in a prediabetic model of metabolic syndrome. Male and female 12-wk-old TallyHo (TH) mice, and their closest genetic lean strain (Swiss-Webster, SW) were treated with a high-milk-fat diet (HMFD) plus/minus EMPA (@0.01%) for 12-wk. Kidney weights and glomerular filtration rate were slightly increased by EMPA in the TH mice. Glomerular feature analysis by unsupervised clustering revealed sexually dimorphic clustering, and one unique cluster relating to EMPA. Periodic acid Schiff (PAS) positive areas, reflecting basement membranes and mesangium were slightly reduced by EMPA. Phasor-fluorescent life-time imaging (FLIM) of free-to-protein bound NADH in cortex showed a marginally greater reliance on oxidative phosphorylation with EMPA. Overall, net urine sodium, glucose, and albumin were slightly increased by EMPA. In TH, EMPA reduced the sodium phosphate cotransporter, type 2 (NaPi-2), but increased sodium hydrogen exchanger, type 3 (NHE3). These changes were absent or blunted in SW. EMPA led to changes in urine exosomal microRNA profile including, in females, enhanced levels of miRs 27a-3p, 190a-5p, and 196b-5p. Network analysis revealed "cancer pathways" and "FOXO signaling" as the major regulated pathways. Overall, EMPA treatment to prediabetic mice with limited renal disease resulted in modifications in renal metabolism, structure, and transport, which may preclude and underlie protection against kidney disease with developing T2D.NEW & NOTEWORTHY Renal protection afforded by sodium glucose transporter, type 2 inhibitors (SGLT2i), e.g., empagliflozin (EMPA) involves complex intertwined mechanisms. Using a novel mouse model of obesity with insulin resistance, the TallyHo/Jng (TH) mouse on a high-milk-fat diet (HMFD), we found subtle changes in metabolism including altered regulation of sodium transporters that line the renal tubule. New potential epigenetic determinants of metabolic changes relating to FOXO and cancer signaling pathways were elucidated from an altered urine exosomal microRNA signature.

Metabolic Communication by SGLT2 Inhibition

BACKGROUND

SGLT2 (sodium-glucose cotransporter 2) inhibitors (SGLT2i) can protect the kidneys and heart, but the underlying mechanism remains poorly understood.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

How the kidney regulates magnesium: a modelling study

The kidneys are crucial for maintaining Mg2+ homeostasis. Along the proximal tubule and thick ascending limb, Mg2+ is reabsorbed paracellularly, while along the distal convoluted tubule (DCT), Mg2+ is reabsorbed transcellularly via transient receptor potential melastatin 6 (TRPM6). TRPM6 and other renal transporter expressions are regulated by sex hormones. To investigate renal Mg2 handling, we have developed sex-specific computational models of electrolyte transport along rat superficial nephron. Model simulations indicated that along the proximal tubule and thick ascending limb, Mg2+ and Na+ transport occur parallelly, but they are dissociated along the DCT. In addition, our models predicted higher paracellular Mg2+ permeability in females to attain similar cortical thick ascending limb fractional Mg2+ reabsorption in both sexes. Furthermore, DCT fractional Mg2+ reabsorption is higher in females than in males, allowing females to better fine-tune Mg2+ excretion. We validated our models by simulating the administration of three classes of diuretics. The model predicted significantly increased, marginally increased and significantly decreased Mg2+ excretions for loop, thiazide and K-sparing diuretics, respectively, aligning with experimental findings. The models can be used to conduct in silico studies on kidney adaptations to Mg2+ homeostasis alterations during conditions such as pregnancy, diabetes and chronic kidney disease.

Empagliflozin in Heart Failure: Regional Nephron Sodium Handling Effects

SIGNIFICANCE STATEMENT

The effect of sodium-glucose cotransporter-2 inhibitors (SGLT2i) on regional tubular sodium handling is poorly understood in humans. In this study, empagliflozin substantially decreased lithium reabsorption in the proximal tubule (PT) (a marker of proximal tubular sodium reabsorption), a magnitude out of proportion to that expected with only inhibition of sodium-glucose cotransporter-2. This finding was not driven by an "osmotic diuretic" effect; however, several parameters changed in a manner consistent with inhibition of the sodium-hydrogen exchanger 3. The large changes in proximal tubular handling were acutely buffered by increased reabsorption in both the loop of Henle and the distal nephron, resulting in the observed modest acute natriuresis with these agents. After 14 days of empagliflozin, natriuresis waned due to increased reabsorption in the PT and/or loop of Henle. These findings confirm in humans that SGLT2i have complex and important effects on renal tubular solute handling.

BACKGROUND

The effect of SGLT2i on regional tubular sodium handling is poorly understood in humans but may be important for the cardiorenal benefits.

METHODS

This study used a previously reported randomized, placebo-controlled crossover study of empagliflozin 10 mg daily in patients with diabetes and heart failure. Sodium handling in the PT, loop of Henle (loop), and distal nephron was assessed at baseline and day 14 using fractional excretion of lithium (FELi), capturing PT/loop sodium reabsorption. Assessments were made with and without antagonism of sodium reabsorption through the loop using bumetanide.

RESULTS

Empagliflozin resulted in a large decrease in sodium reabsorption in the PT (increase in FELi=7.5%±10.6%, P = 0.001), with several observations suggesting inhibition of PT sodium hydrogen exchanger 3. In the absence of renal compensation, this would be expected to result in approximately 40 g of sodium excretion/24 hours with normal kidney function. However, rapid tubular compensation occurred with increased sodium reabsorption both in the loop ( P < 0.001) and distal nephron ( P < 0.001). Inhibition of sodium-glucose cotransporter-2 did not attenuate over 14 days of empagliflozin ( P = 0.14). However, there were significant reductions in FELi ( P = 0.009), fractional excretion of sodium ( P = 0.004), and absolute fractional distal sodium reabsorption ( P = 0.036), indicating that chronic adaptation to SGLT2i results primarily from increased reabsorption in the loop and/or PT.

CONCLUSIONS

Empagliflozin caused substantial redistribution of intrarenal sodium delivery and reabsorption, providing mechanistic substrate to explain some of the benefits of this class. Importantly, the large increase in sodium exit from the PT was balanced by distal compensation, consistent with SGLT2i excellent safety profile.

CLINICAL TRIAL REGISTRY NAME AND REGISTRATION NUMBER

ClinicalTrials.gov ( NCT03027960 ).

Sex differences in renal transporters: assessment and functional consequences

Mammalian kidneys are specialized to maintain fluid and electrolyte homeostasis. The epithelial transport processes along the renal tubule that match output to input have long been the subject of experimental and theoretical study. However, emerging data have identified a new dimension of investigation: sex. Like most tissues, the structure and function of the kidney is regulated by sex hormones and chromosomes. Available data demonstrate sex differences in the abundance of kidney solute and electrolyte transporters, establishing that renal tubular organization and operation are distinctly different in females and males. Newer studies have provided insights into the physiological consequences of these sex differences. Computational simulations predict that sex differences in transporter abundance are likely driven to optimize reproduction, enabling adaptive responses to the nutritional requirements of serial pregnancies and lactation - normal life-cycle changes that challenge the ability of renal transporters to maintain fluid and electrolyte homeostasis. Later in life, females may also undergo menopause, which is associated with changes in disease risk. Although numerous knowledge gaps remain, ongoing studies will provide further insights into the sex-specific mechanisms of sodium, potassium, acid-base and volume physiology throughout the life cycle, which may lead to therapeutic opportunities.

Coupling of renal sodium and calcium transport: a modeling analysis of transporter inhibition and sex differences

Ca2+ transport along the nephron occurs via specific transcellular and paracellular pathways and is coupled to the transport of other electrolytes. Notably, Na+ transport establishes an electrochemical gradient to drive Ca2+ reabsorption. Hence, alterations in renal Na+ handling, under pathophysiological conditions or pharmacological manipulations, can have major effects on Ca2+ transport. An important class of pharmacological agent is diuretics, which are commonly prescribed for the management of blood pressure and fluid balance. The pharmacological targets of diuretics generally directly facilitate Na+ transport but also indirectly affect renal Ca2+ handling. To better understand the underlying mechanisms, we developed a computational model of electrolyte transport along the superficial nephron in the kidney of a male and female rat. Sex differences in renal Ca2+ handling are represented. Model simulations predicted in the female rat nephron lower Ca2+ reabsorption in the proximal tubule and thick ascending limb, but higher reabsorption in the late distal convoluted tubule and connecting tubule, compared with the male nephron. The male rat kidney model yielded a higher urinary Ca2+ excretion than the female model, consistent with animal experiments. Model results indicated that along the proximal tubule and thick ascending limb, Ca2+ and Na+ transport occurred in parallel, but those processes were dissociated in the distal convoluted tubule. Additionally, we conducted simulations of inhibition of channels and transporters that play a major role in Na+ and Ca2+ transport. Simulation results revealed alterations in transepithelial Ca2+ transport, with differential effects among nephron segments and between the sexes.NEW & NOTEWORTHY The kidney plays an important role in the maintenance of whole body Ca2+ balance by regulating Ca2+ reabsorption and excretion. This computational modeling study provides insights into how Ca2+ transport along the nephron is coupled to Na+. Model results indicated that along the proximal tubule and thick ascending limb, Ca2+ and Na+ transport occur in parallel, but those processes were dissociated in the distal convoluted tubule. Simulations also revealed sex-specific responses to different pharmacological manipulations.

Efficacy and Safety of Esaxerenone in Hypertensive Patients with Diabetes Mellitus Undergoing Treatment with Sodium-Glucose Cotransporter 2 Inhibitors (EAGLE-DH)

INTRODUCTION

The EAGLE-DH study assessed the efficacy and safety of esaxerenone in hypertensive patients with diabetes mellitus receiving sodium-glucose cotransporter 2 (SGLT2) inhibitors.

METHODS

In this multicenter, open-label, prospective, interventional study, esaxerenone was started at 1.25 or 2.5 mg/day and could be gradually increased to 5 mg/day on the basis of blood pressure (BP) and serum potassium levels. Oral hypoglycemic or antihypertensive medications prior to obtaining consent was continued. Data were evaluated in the total population and creatinine-based estimated glomerular filtration rate (eGFR) subcohorts (eGFR ≥ 60 mL/min/1.73 m2 [G1-G2 subcohort] and 30 to < 60 mL/min/1.73 m2 [G3 subcohort]).

RESULTS

In total, 93 patients were evaluated (G1-G2, n = 49; G3, n = 44). Morning home systolic/diastolic BP values (SBP/DBP) were significantly reduced from baseline to week 12 (- 11.8 ± 10.8/- 5.1 ± 6.3 mmHg, both P < 0.001) and week 24 (- 12.9 ± 10.5/- 5.7 ± 6.3 mmHg, both P < 0.001). Similar results were observed in both eGFR subcohorts. The urinary albumin-to-creatinine ratio significantly decreased from baseline to week 24 in the total population (geometric percentage change, - 49.1%, P < 0.001) and in both eGFR subcohorts. The incidences of treatment-emergent adverse events (TEAEs) and drug-related TEAEs were 45.2% and 12.9%, respectively; most were mild or moderate. Serum potassium levels increased over the first 2 weeks of esaxerenone treatment, gradually decreased by week 12, and remained constant to week 24. One patient in the G1-G2 subcohort had serum potassium levels ≥ 5.5 mEq/L. No patients had serum potassium ≥ 6.0 mEq/L.

CONCLUSION

Esaxerenone effectively lowered BP, was safe, and showed renoprotective effects in hypertensive patients with diabetes mellitus receiving treatment with SGLT2 inhibitors. Esaxerenone and SGLT2 inhibitors did not interfere with either drug's efficacy and may reduce the frequency of serum potassium elevations, suggesting they are a compatible combination.

CLINICAL TRIAL REGISTRATION

jRCTs031200273.

Efficacy and Safety of Sodium-Glucose Cotransporter-2 Inhibitors in Nondiabetic Patients with Chronic Kidney Disease: A Review of Recent Evidence

Background

Sodium-glucose cotransporter-2 inhibitors (SGLT2i) were initially developed as glucose-lowering agents in patients with type-2 diabetes. However, available data from clinical trials and meta-analyses suggest that SGLT2i have pleiotropic benefits in reducing mortality and delaying the progression of chronic kidney disease (CKD) in both diabetic and nondiabetic patients. Thus, we herein review the current evidence regarding the efficacy and safety of SGLT2i in patients with nondiabetic CKD and appraise the recently reported clinical trials that might facilitate the management of CKD in routine clinical practice.

Summary

The benefits of SGLT2i on nondiabetic CKD are multifactorial and are mediated by a combination of mechanisms. The landmark DAPA-CKD trial revealed that dapagliflozin administered with renin-angiotensin system blockade drugs reduced the risk of a sustained decline (at least 50%) in the estimated glomerular filtration rate, end-stage kidney disease, or death from cardiorenal causes. The recent EMPA-KIDNEY trial showed that empagliflozin therapy led to a lower risk of progression of kidney disease or death from cardiovascular causes. These benefits were consistent in patients with and without diabetes. Moreover, a meta-analysis of DAPA-HF and EMPEROR-Reduced trials confirmed reductions in the combined risk of cardiovascular death or worsening heart failure including composite renal endpoint.

Key Messages

Considering the robust data available from DAPA-CKD, EMPA-KIDNEY, and other trials such as EMPEROR-Preserved, DIAMOND that included nondiabetic patients, it may be necessary to update current guidelines to include SGLT2i as a first-line therapy for CKD and reevaluate current CKD therapeutic approaches.

Mathematical modeling of calcium homeostasis in female rats: An analysis of sex differences and maternal adaptations

Calcium plays a vital role in various biological processes, including muscle contractions, blood clotting, skeletal mineralization, and cell signaling. While extracellular calcium makes up less than 1% of total body calcium, it is tightly regulated since too high or too low extracellular calcium concentration can have dangerous effects on the body. Mathematical modeling is a well-suited approach to investigate the complex physiological processes involved in calcium regulation. While mathematical models have been developed to study calcium homeostasis in male rats, none have been used to investigate known sex differences in hormone levels nor the unique physiological states of pregnancy and lactation. Calcitriol, the active form of vitamin D, plays a key role in intestinal calcium absorption, renal calcium reabsorption, and bone remodeling. It has been shown that, when compared to age-matched male rats, females have significantly lower calcitriol levels. In this study we first seek to investigate the impact of this difference as well as other known sex differences on calcium homeostasis using mathematical modeling. Female bodies differ from male bodies in that during their lifetime they may undergo massive adaptations during pregnancy and lactation. Indeed, maternal adaptations impact calcium regulation in all mammals. In pregnant rodents, intestinal absorption of calcium is massively increased in the mother's body to meet the needs of the developing fetus. In a lactating rodent, much of the calcium needs of milk are met by bone resorption, intestinal absorption, and renal calcium reabsorption. Given these observations, the goal of this project is to develop multi-scale whole-body models of calcium homeostasis that represents (1) how sex differences impact calcium homeostasis in female vs. male rats and (2) how a female body adapts to support the excess demands brought on by pregnancy and lactation. We used these models to quantify the impact of individual sex differences as well as maternal adaptations during pregnancy and lactation. Additionally, we conducted "what if" simulations to test whether sex differences in calcium regulation may enable females to better undergo maternal adaptations required in pregnancy and lactation than males.

Functional and Clinical Importance of SGLT2-inhibitors in Frailty: From the Kidney to the Heart

SGLT2 (sodium-glucose cotransporter 2) enables glucose and sodium reabsorption in the kidney. SGLT2-inhibitors (also known as gliflozins, which include canagliflozin, dapagliflozin, empagliflozin, and ertugliflozin) act by increasing glycosuria, thereby reducing glycemia. These drugs are critical to reach and keep glycemic control, a crucial feature, especially in patients with comorbidities, like frail individuals. Several studies evaluated the effects of SGLT2-inhibitors in different settings beyond diabetes, revealing that they are actually pleiotropic drugs. We recently evidenced the favorable effects of SGLT2-inhibition on physical and cognitive impairment in frail older adults with diabetes and hypertension. In the present overview, we summarize the latest clinical and preclinical studies exploring the main effects of SGLT2-inhibitors on kidney and heart, emphasizing their potential beneficial actions in frailty.

Sodium-glucose cotransporter-2 inhibitors in heart failure: Potential decongestive mechanisms and current clinical studies

Congestion is a key pathophysiological feature of heart failure (HF) syndrome that drives most of the clinical manifestations of acute HF and is related with poor quality of life and outcomes. Therefore, safe and effective decongestion is an important therapeutic target in the management of acute HF and despite the use of guideline-recommended loop diuretics, adequate decongestion is not always achieved in patients with acute HF. Recently, sodium-glucose cotransporter-2 (SGLT-2) inhibitors have been shown to provide clinical benefits across a broad spectrum of patients with HF, including consistent reduction in the risk of acute HF episodes. While the exact mechanisms underlying these benefits remain a matter of debate, a growing body of evidence suggests that effective decongestion may be partly responsible, especially in the setting of acute HF. In this review, we discuss the potential decongestive mechanisms of SGLT-2 inhibitors, such as osmotic diuresis, natriuresis, preservation of glomerular filtration and facilitation of interstitial drainage, which can collectively translate into effective and safe decongestion. Furthermore, we provide a comprehensive review of up-to-date clinical data of SGLT-2 inhibitor use in the acute HF population.

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.

Renal Oxygen Demand and Nephron Function: Is Glucose a Friend or Foe?

The kidneys and heart work together to balance the body's circulation, and although their physiology is based on strict inter dependence, their performance fulfills different aims. While the heart can rapidly increase its own oxygen consumption to comply with the wide changes in metabolic demand linked to body function, the kidneys physiology are primarily designed to maintain a stable metabolic rate and have a limited capacity to cope with any steep increase in renal metabolism. In the kidneys, glomerular population filters a large amount of blood and the tubular system has been programmed to reabsorb 99% of filtrate by reabsorbing sodium together with other filtered substances, including all glucose molecules. Glucose reabsorption involves the sodium-glucose cotransporters SGLT2 and SGLT1 on the apical membrane in the proximal tubular section; it also enhances bicarbonate formation so as to preserve the acid-base balance. The complex work of reabsorption in the kidney is the main factor in renal oxygen consumption; analysis of the renal glucose transport in disease states provides a better understanding of the renal physiology changes that occur when clinical conditions alter the neurohormonal response leading to an increase in glomerular filtration pressure. In this circumstance, glomerular hyperfiltration occurs, imposing a higher metabolic demand on kidney physiology and causing progressive renal impairment. Albumin urination is the warning signal of renal engagement over exertion and most frequently heralds heart failure development, regardless of disease etiology. The review analyzes the mechanisms linked to renal oxygen consumption, focusing on sodium-glucose management.

[Finerenone cardiorenal effects and its placement in treatment of chronic kidney disease in patients with type 2 diabetes mellitus: A review]

Chronic kidney disease (CKD) is one of the most common complications of diabetes mellitus and an independent risk factor for cardiovascular disease. Despite guideline-directed therapy of CKD in patients with type 2 diabetes, the risk of renal failure and cardiovascular events still remains high. To date, current medications for CKD haven't reduced enough the residual risk associated with inflammation and fibrosis in patients with type 2 diabetes. Here, in this review we present the results of FIDELIO-DKD, FIGARO-DKD trials and their pooled analysis FIDELITY, aimed to evaluate the effectiveness and safety of selective non-steroidal mineralocorticoid receptor antagonist finerenone in patients with type 2 diabetes with wide range stages of CKD. Modern pathophysiological aspects of mineralocorticoid receptor hyperactivation and features of their blockade by steroidal and nonsteroidal mineralocorticoid receptor antagonists are considered, differences in pharmacological effects between them are also discussed, finerenone benefits and its adverse events, demonstrated in randomized clinical trials are considered here. The probable mechanisms of early and delayed action of finerenone, which were realized in beneficial cardiovascular and renal outcomes in patients with type 2 diabetes with CKD, are presented here. Practical points for finerenone initiation and titration are indicated, aimed to minimize the hyperkalemia risk. Current guidelines for CKD treatment in patients with type 2 diabetes are analyzed, the finerenone placement in combined nephroprotective therapy is determined.

Influence of administration time and sex on natriuretic, diuretic, and kaliuretic effects of diuretics

Sex differences in renal function and blood pressure have been widely described across many species. Blood pressure dips during sleep and peaks in the early morning. Similarly, glomerular filtration rate, filtered electrolyte loads, urine volume, and urinary excretion all exhibit notable diurnal rhythms, which reflect, in part, the regulation of renal transporter proteins by circadian clock genes. That regulation is sexually dimorphic; as such, sex and time of day are not two independent regulators of kidney function and blood pressure. The objective of the present study was to assess the effect of sex and administration time on the natriuretic and diuretic effects of loop, thiazide, and K⁺-sparing diuretics, which are common treatments for hypertension. Loop diuretics inhibit Na⁺-K⁺-2Cl^- cotransporters on the apical membrane of the thick ascending limb, thiazide diuretics inhibit Na⁺-Cl^- cotransporters on the distal convoluted tubule, and K⁺-sparing diuretics inhibit epithelial Na⁺ channels on the connecting tubule and collecting duct. We simulated Na⁺ transporter inhibition using sex- and time-of-day-specific computational models of mouse kidney function. The simulation results highlighted significant sex and time-of-day differences in the drug response. Loop diuretics induced larger natriuretic and diuretic effects during the active phase. The natriuretic and diuretic effects of thiazide diuretics exhibited sex and time-of-day differences, whereas these effects of K⁺-sparing diuretics exhibited a significant time-of-day difference in females only. The kaliuretic effect depended on the type of diuretics and time of administration. The present computational models can be a useful tool in chronotherapy, to tailor drug administration time to match the body's diurnal rhythms to optimize the drug effect.NEW & NOTEWORTHY Sex influences cardiovascular disease, and the timing of onset of acute cardiovascular events exhibits circadian rhythms. Kidney function also exhibits sex differences and circadian rhythms. How do the natriuretic and diuretic effects of diuretics, a common treatment for hypertension that targets the kidneys, differ between the sexes? And how do these effects vary during the day? To answer these questions, we conducted computer simulations to assess the effects of loop, thiazide, and K⁺-sparing diuretics.

Is there any robust evidence showing that SGLT2 inhibitor use predisposes to acute kidney injury?

A novel class of oral glucose lowering drugs, sodium-glucose co-transporter type 2 inhibitors (SGLT2is), has shown additional beneficial effects on body weight, serum uric acid levels, blood pressure, and cardiac and renal function. Conflicting data have been published regarding the potential risk of acute kidney injury (AKI) when using SGLT2is. Aim of this manuscript was to review the current literature on this issue. SGLT2is induce a mild acute decline in estimated glomerular filtration rate, attributed to the effect of proximal tubular natriuresis on tubuloglomerular feedback through increased macula densa sodium delivery, leading to afferent arteriole vasoconstriction and reduced intraglomerular pressure. This functional effect with a subsequent rise in serum creatinine fulfills the creatinine-based criteria for AKI, as defined in clinical practice and trial settings. Other proposed potential mechanisms as to how SGLT2is lead to AKI include osmotic diuresis leading to volume depletion, increased urinary uric acid levels, intratubular oxidative stress, local inflammation and tubular injury. Despite the warning published by the US Food and Drug Administration in 2016 about a potential risk of AKI and the report of some clinical cases of AKI after treatment with SGLT2is, large observational real-life retrospective studies, randomized controlled trials and propensity-matched analyses of data from clinical practice unambiguously demonstrate that SGLT2is are safe for the kidney and do not predispose to AKI. In conclusion, while we can probably stop worrying about AKI risk when using SGLT2is, the question whether these agents should be withheld in the presence of clinical situations at high risk for AKI remains unaddressed.

Renoprotective effects of empagliflozin in type 1 and type 2 models of diabetic nephropathy superimposed with hypertension

Diabetes, hypertension, and aging are major contributors to cardiovascular and chronic kidney disease (CKD). Sodium/glucose cotransporter 2 (SGLT2) inhibitors have become a preferred treatment for type II diabetic patients since they have cardiorenal protective effects. However, most elderly diabetic patients also have hypertension, and the effects of SGLT2 inhibitors have not been studied in hypertensive diabetic patients or animal models. The present study examined if controlling hyperglycemia with empagliflozin, or given in combination with lisinopril, slows the progression of renal injury in hypertensive diabetic rats. Studies were performed using hypertensive streptozotocin-induced type 1 diabetic Dahl salt-sensitive (STZ-SS) rats and in deoxycorticosterone-salt hypertensive type 2 diabetic nephropathy (T2DN) rats. Administration of empagliflozin alone or in combination with lisinopril reduced blood glucose, proteinuria, glomerular injury, and renal fibrosis in STZ-SS rats without altering renal blood flow (RBF) or glomerular filtration rate (GFR). Blood pressure and renal hypertrophy were also reduced in rats treated with empagliflozin and lisinopril. Administration of empagliflozin alone or in combination with lisinopril lowered blood glucose, glomerulosclerosis, and renal fibrosis but had no effect on blood pressure, kidney weight, or proteinuria in hypertensive T2DN rats. RBF was not altered in any of the treatment groups, and GFR was elevated in empagliflozin-treated hypertensive T2DN rats. These results indicate that empagliflozin is highly effective in controlling blood glucose levels and slows the progression of renal injury in both hypertensive type 1 and type 2 diabetic rats, especially when given in combination with lisinopril to lower blood pressure.

Sex differences in circadian regulation of kidney function of the mouse

Kidney function is regulated by the circadian clock. Not only do glomerular filtration rate and urinary excretion oscillate during the day, but the expressions of several renal transporter proteins also exhibit circadian rhythms. Interestingly, the circadian regulation of these transporters appears to be sexually dimorphic. Thus, the goal of the present study was to investigate the mechanisms by which the kidney function of the mouse is modulated by sex and time of day. To accomplish this, we developed the first computational models of epithelial water and solute transport along the mouse nephrons that represent the effects of sex and the circadian clock on renal hemodynamics and transporter activity. We conducted simulations to study how the circadian control of renal transport genes affects overall kidney function and how that process differs between male and female mice. Simulation results predicted that tubular transport differs substantially among segments, with relative variations in water and Na+ reabsorption along the proximal tubules and thick ascending limb tracking that of glomerular filtration rate. In contrast, relative variations in distal segment transport were much larger, with Na+ reabsorption almost doubling during the active phase. Oscillations in Na+ transport drive K+ transport variations in the opposite direction. Model simulations of basic helix-loop-helix ARNT like 1 (BMAL1) knockout mice predicted a significant reduction in net Na+ reabsorption along the distal segments in both sexes, but more so in males than in females. This can be attributed to the reduction of mean epithelial Na+ channel activity in males only, a sex-specific effect that may lead to a reduction in blood pressure in BMAL1-null males.NEW & NOTEWORTHY How does the circadian control of renal transport genes affect overall kidney function, and how does that process differ between male and female mice? How does the differential circadian regulation of the expression levels of key transporter genes impact the transport processes along different nephron segments during the day? And how do those effects differ between males and females? We built computational models of mouse kidney function to answer these questions.

Renoprotective Effects of SGLT2 Inhibitors

SGLT2 inhibitors can protect the kidneys of patients with and without type 2 diabetes from failing. This includes blood glucose dependent and independent mechanisms. SGLT2 inhibitors lower glomerular pressure and filtration, thereby reducing the physical stress on the filtration barrier and the oxygen demand for tubular reabsorption. This improves cortical oxygenation, which, together with lesser tubular glucotoxicity and improved mitochondrial function and autophagy, can reduce proinflammatory and profibrotic signaling and preserve tubular function and GFR in long term. By shifting transport downstream, SGLT2 inhibitors may mimic systemic hypoxia and stimulate erythropoiesis, which improves oxygen delivery to the kidney and other organs.

Sex and species differences in epithelial transport in rat and mouse kidneys: Modeling and analysis

The goal of this study was to investigate the functional implications of sex and species differences in the pattern of transporters along nephrons in the rat and mouse kidney, as reported by Veiras et al. (J Am Soc Nephrol 28: 3504–3517, 2017). To do so, we developed the first sex-specific computational models of epithelial water and solute transport along the nephrons from male and female mouse kidneys, and conducted simulations along with our published rat models. These models account for the sex differences in the abundance of apical and basolateral transporters, glomerular filtration rate, and tubular dimensions. Model simulations predict that 73% and 57% of filtered Na+ is reabsorbed by the proximal tubules of male and female rat kidneys, respectively. Due to their smaller transport area and lower NHE3 activity, the proximal tubules in the mouse kidney reabsorb a significantly smaller fraction of the filtered Na+, at 53% in male and only 34% in female. The lower proximal fractional Na+ reabsorption in female kidneys of both rat and mouse is due primarily to their smaller transport area, lower Na+/H+ exchanger activity, and lower claudin-2 abundance, culminating in significantly larger fractional delivery of water and Na+ to the downstream nephron segments in female kidneys. Conversely, the female distal nephron exhibits a higher abundance of key Na+ transporters, including Na+-Cl− cotransporters in both species, epithelial Na+ channels for the female rat, and Na+-K+-Cl−cotransporters for the female mouse. The higher abundance of transporters accounts for the enhanced water and Na+ transport along the female rat and mouse distal nephrons, relative to the respective male, resulting in similar urine excretion between the sexes. Model simulations indicate that the sex and species differences in renal transporter patterns may partially explain the experimental observation that, in response to a saline load, the diuretic and natriuretic responses were more rapid in female rats than males, but no significant sex difference was found in mice. These computational models can serve as a valuable tool for analyzing findings from experimental studies conducted in rats and mice, especially those involving genetic modifications.

SGLT2 Inhibitors in Patients with Chronic Kidney Disease and Heart Disease: A Literature Review

Sodium-glucose transport protein 2 inhibitors, commonly referred to as SGLT2i, are a group of prescription pharmaceuticals that are approved by the United States Food and Drug Administration for use with diet and exercise to lower blood glucose in adults with type 2 diabetes. Diabetes is a well-recognized major contributor to cardiovascular and renal disease burden. In addition to blood glucose control, SGLT2i have been shown to provide significant cardiovascular and renoprotective benefits in patients with and without diabetes. In this review, we describe current evidence related to the renal and cardiovascular benefits of using SGLT2i.

Mechanisms of cardio-renal protection of sodium-glucose cotransporter-2 inhibitors

Sodium-glucose cotransporter-2 inhibitors (SGLT2i) are glucose-lowering drugs used in the treatment of type 2 diabetes (T2D) that have shown additional cardiac and renal benefits. The mechanisms of SGLT2i-mediated cardiorenal protection include blood pressure lowering and endothelial function improvements, enhancement of cardiac and renal hemodynamics, optimization of energetic efficiency through metabolic changes and cellular ion exchanges, reduction of inflammation and oxidative stress with consequent fibrosis reduction, and sympathetic activity modulation. This review explores the most recent data regarding the physiological mechanisms of SGLT2i cardiac and renal benefits, which lie at the root of the solid clinical evidence on cardiorenal protection, making SGLT2i a promising new pharmacological approach to the treatment of patients at high risk of cardiorenal syndrome.

Empagliflozin and serum potassium in heart failure: an analysis from EMPEROR-Pooled

AIMS

Hyperkalaemia frequently leads to interruption and discontinuation of neurohormonal antagonists, which may worsen heart failure prognosis. Some studies suggested that sodium-glucose cotransporter 2 inhibitors reduce hyperkalaemia, an effect that may have important clinical implications. This analysis evaluates the effect of empagliflozin on the occurrence of hyper- and hypokalaemia in HF.

METHODS AND RESULTS

EMPEROR-Pooled (i.e. EMPEROR-Reduced and EMPEROR-Preserved combined) included 9583 patients with available serum potassium levels at baseline (98.6% of the total EMPEROR-Pooled population, n = 9718). Hyperkalaemia was identified by investigators' reports of adverse events, and by a laboratory serum potassium value above 5.5 mmol/L and 6.0 mmol/L. The main outcome was a composite of investigator-reported hyperkalaemia or initiation of potassium binders. Patients with high potassium at baseline were more frequently diagnosed with diabetes and ischaemic HF aetiology and had lower left ventricular ejection fraction and estimated glomerular filtration rate but were more frequently treated with sacubitril/valsartan or mineralocorticoid receptor antagonists. Empagliflozin (compared with placebo) reduced the composite of investigator-reported hyperkalaemia or initiation of potassium binders [6.5% vs. 7.7%, hazard ratio (HR) 0.82, 95% confidence interval (CI) 0.71-0.95, P = 0.01]. Empagliflozin reduced hyperkalaemia rates regardless of the definition used (serum potassium >5.5 mmol/l: 8.6% vs. 9.9%, HR 0.85, 95% CI 0.74-0.97, P = 0.017; serum potassium >6.0 mmol/l: 1.9% vs. 2.9%, HR 0.62, 95% CI 0.48-0.81, P < 0.001). The incidence of hypokalaemia (investigator-reported or serum potassium <3.0 mmol/l) was not significantly increased with empagliflozin.

CONCLUSIONS

Empagliflozin reduced the incidence of hyperkalaemia without significant increase in hypokalaemia.

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.

Determining risk factors for triple whammy acute kidney injury

Concurrent use of a diuretic, a renin-angiotensin system (RAS) inhibitor, and a non-steroidal anti-inflammatory drug (NSAID) significantly increases the risk of acute kidney injury (AKI). This phenomenon is known as "triple whammy". Diuretics and RAS inhibitors, such as an angiotensin converting enzyme (ACE) inhibitor or angiotensin receptor blocker, are often prescribed in tandem for the treatment of hypertension, whereas some NSAIDs, such as ibuprofen, are available over the counter. As such, concurrent treatment with all three drugs is common. The goals of this study are to better understand the mechanisms underlying the development of triple whammy AKI and to identify physiological factors that may increase an individual's susceptibility. To accomplish these goals, we utilize sex-specific computational models of long-term blood pressure regulation. These models include variables describing the heart and circulation, kidney function, sodium and water reabsorption in the nephron and the RAS and are parameterized separately for men and women. Hypertension is modeled as overactive renal sympathetic nervous activity. Model simulations suggest that low water intake, the myogenic response, and drug sensitivity may predispose patients with hypertension to develop triple whammy-induced AKI. Triple treatment involving an ACE inhibitor, furosemide, and NSAID results in blood pressure levels similar to double treatment with ACEI and furosemide. Additionally, the male and female hypertensive models act similarly in most situations, except for the ACE inhibitor and NSAID double treatment.

SGLT2 Inhibitors: Benefits for CKD and Cardiovascular Disease in Type 2 Diabetes

PURPOSE OF REVIEW

Over the past few decades, multiple glucose lowering therapies have been developed, but until now, no single drug has proven to both decrease cardiovascular mortality and improve renal outcomes. The purpose of this review is to outline the key findings of the recent major outcome clinical trials on SGLT2 inhibitors, review the indications for their use, and improve adoption of these medications in patients with type 2 diabetes mellitus (T2DM).

RECENT FINDINGS

Recent studies have shown a benefit for SGLT2 inhibitors in patients with heart failure (HF) and kidney disease both in the presence and absence of T2DM. Additional benefits also include improvements in fluid status, blood pressure, serum uric acid levels, and weight loss. Available data suggests that SGLT2 inhibitors should be used in all eligible patients with HFrEF and/or CKD with albuminuria to decrease progression of CKD, hospitalizations for heart failure, major atherosclerotic cardiovascular events, and cardiovascular death, with and without T2DM.

SGLT2 inhibition potentiates the cardiovascular, renal and metabolic effects of sGC stimulation in hypertensive rats with prolonged exposure to high fat diet

Prolonged high-fat diet (HFD) accelerates the cardiovascular, renal, and metabolic dysfunction in hypertensive rats with altered renal development (ARDev). Soluble guanylate cyclase (sGC) stimulation or sodium-glucose cotransporter 2 (SGLT2) inhibition may improve cardiovascular, renal, and metabolic function in settings of hypertension and obesity. This study examined whether 6 wk treatment with an SGLT2 inhibitor (empagliflozin, 7 mg/kg/day) enhances the cardiovascular, renal, and metabolic effects of a sGC stimulator (praliciguat, 10 mg/kg/day) in hypertensive rats with ARDev and prolonged exposure to HFD. Arterial pressure (AP), renal vascular resistance (RVR), fat abdominal volume (FAV), insulin resistance, leptin and triglycerides levels, and intrarenal infiltration of inflammatory cells were higher, but cardiac output and creatinine clearance were lower in hypertensive rats (n = 15) than in normotensive rats (n = 7). Praliciguat administration (n = 10) to hypertensive rats reduced (P < 0.05) AP, FAV, plasma concentrations of leptin and triglycerides, and increased (P < 0.05) cardiac output and creatinine clearance. Empagliflozin administration (n = 8) only increased (P < 0.05) glucosuria and creatinine clearance and decreased (P < 0.05) plasma leptin and triglycerides concentrations in hypertensive rats. Simultaneous administration of praliciguat and empagliflozin (n = 10) accelerated the decrease in AP, improved glucose tolerance, reduced (P < 0.05) incremental body weight gain, and decreased (P < 0.05) insulin resistance index, RVR, and the infiltration of T-CD3 lymphocytes in renal cortex and renal medulla. In summary, the combined administration of praliciguat and empagliflozin leads to a greater improvement of the cardiovascular, renal, and metabolic dysfunction secondary to prolonged exposure to HFD in hypertensive rats with ARDev than the treatment with either praliciguat or empagliflozin alone.

NEW & NOTEWORTHY This is the first study, to our knowledge, showing that SGLT2 inhibition potentiates the beneficial cardiovascular, renal, and metabolic effects elicited by sGC stimulation in hypertensive rats with prolonged high-fat diet. The effects of the simultaneous administration of praliciguat and empagliflozin are greater than those elicited by either one alone. The effects of the simultaneous treatment may be related to a greater reduction in the inflammatory status.

Sex-Specific Computational Models of Kidney Function in Patients With Diabetes

The kidney plays an essential role in homeostasis, accomplished through the regulation of pH, electrolytes and fluids, by the building blocks of the kidney, the nephrons. One of the important markers of the proper functioning of a kidney is the glomerular filtration rate. Diabetes is characterized by an enlargement of the glomerular and tubular size of the kidney, affecting the afferent and efferent arteriole resistance and hemodynamics, ultimately leading to chronic kidney disease. We postulate that the diabetes-induced changes in kidney may exhibit significant sex differences as the distribution of renal transporters along the nephron may be markedly different between women and men, as recently shown in rodents. The goals of this study are to (i) analyze how kidney function is altered in male and female patients with diabetes, and (ii) assess the renal effects, in women and men, of an anti-hyperglycemic therapy that inhibits the sodium-glucose cotransporter 2 (SGLT2) in the proximal convoluted tubules. To accomplish these goals, we have developed computational models of kidney function, separate for male and female patients with diabetes. The simulation results indicate that diabetes enhances Na+ transport, especially along the proximal tubules and thick ascending limbs, to similar extents in male and female patients, which can be explained by the diabetes-induced increase in glomerular filtration rate. Additionally, we conducted simulations to study the effects of diabetes and SGLT2 inhibition on solute and water transport along the nephrons. Model simulations also suggest that SGLT2 inhibition raises luminal [Cl-] at the macula densa, twice as much in males as in females, and could indicate activation of the tubuloglomerular feedback signal. By inducing osmotic diuresis in the proximal tubules, SGLT2 inhibition reduces paracellular transport, eventually leading to diuresis and natriuresis. Those effects on urinary excretion are blunted in women, in part due to their higher distal transport capacity.

The mixed blessing of AMPK signaling in Cancer treatments

Background

Nutrient acquisition and metabolism pathways are altered in cancer cells to meet bioenergetic and biosynthetic demands. A major regulator of cellular metabolism and energy homeostasis, in normal and cancer cells, is AMP-activated protein kinase (AMPK). AMPK influences cell growth via its modulation of the mechanistic target of Rapamycin (mTOR) pathway, specifically, by inhibiting mTOR complex mTORC1, which facilitates cell proliferation, and by activating mTORC2 and cell survival. Given its conflicting roles, the effects of AMPK activation in cancer can be counter intuitive. Prior to the establishment of cancer, AMPK acts as a tumor suppressor. However, following the onset of cancer, AMPK has been shown to either suppress or promote cancer, depending on cell type or state.

Methods

To unravel the controversial roles of AMPK in cancer, we developed a computational model to simulate the effects of pharmacological maneuvers that target key metabolic signalling nodes, with a specific focus on AMPK, mTORC, and their modulators. Specifically, we constructed an ordinary differential equation-based mechanistic model of AMPK-mTORC signaling, and parametrized the model based on existing experimental data.

Results

Model simulations were conducted to yield the following predictions: (i) increasing AMPK activity has opposite effects on mTORC depending on the nutrient availability; (ii) indirect inhibition of AMPK activity through inhibition of sirtuin 1 (SIRT1) only has an effect on mTORC activity under conditions of low nutrient availability; (iii) the balance between cell proliferation and survival exhibits an intricate dependence on DEP domain-containing mTOR-interacting protein (DEPTOR) abundance and AMPK activity; (iv) simultaneous direct inhibition of mTORC2 and activation of AMPK is a potential strategy for suppressing both cell survival and proliferation.

Conclusions

Taken together, model simulations clarify the competing effects and the roles of key metabolic signalling pathways in tumorigenesis, which may yield insights on innovative therapeutic strategies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-022-09211-1.

Extending the ambit of SGLT2 inhibitors beyond diabetes: a review of clinical and preclinical studies on non-diabetic kidney disease

BACKGROUND

Sodium-glucose cotransporter-2 inhibitors (SGLT2i) are novel antidiabetic agents with overwhelming cardiorenal protection. Recent trials focusing on the nephroprotective role of SGLT2i have underscored its success as a phenomenal agent in halting the progression of kidney disease in patients with and without Type 2 diabetes mellitus. Multitudes of pleiotropic effects on tubules have raised hopes for reasonable nephroprotection beyond the purview of the hyperglycemic milieu.

AREA COVERED

This review summarizes various animal and human data as evidence for the utility of SGLT2i in non-diabetic chronic kidney disease (CKD). Web-based medical database entries were searched. On the premise of existing evidence, we have discussed mechanisms likely contributing to nephroprotection by SGLT2i in patients with non-diabetic CKD.

EXPERT OPINION

Further elucidation of mechanisms of nephroprotection offered by SGLT2i is required to extend its use as a nephroprotective agent. The use of non-traditional markers of kidney damage in future studies would improve the evaluation of their role in attenuating CKD progression. Emerging animal data support the early use of SGLT2i in states of modest proteinuria for superior outcomes. Future long-term trials in patients should aim to address the time of intervention with SGLT2i during the natural disease course of CKD for best outcomes.

High-Salt Attenuates the Efficacy of Dapagliflozin in Tubular Protection by Impairing Fatty Acid Metabolism in Diabetic Kidney Disease

High-salt intake leads to kidney damage and even limits the effectiveness of drugs. However, it is unclear whether excessive intake of salt affects renal tubular energy metabolism and the efficacy of dapagliflozin on renal function in diabetic kidney disease (DKD). In this study, we enrolled 350 DKD patients and examined the correlation between sodium level and renal function, and analyzed influencing factors. The results demonstrated that patients with macroalbuminuria have higher 24 h urinary sodium levels. After establishment of type 2 diabetes mellitus model, the animals received a high-salt diet or normal-salt diet. In the presence of high-salt diet, the renal fibrosis was aggravated with fatty acid metabolism dysregulation. Furthermore, Na+/K+-ATPase expression was up-regulated in the renal tubules of diabetic mice, while the fatty acid metabolism was improved by inhibiting Na+/K+-ATPase of renal tubular epithelial cells. Of note, the administration with dapagliflozin improved renal fibrosis and enhanced fatty acid metabolism. But high salt weakened the above-mentioned renal protective effects of dapagliflozin in DKD. Similar results were recapitulated in vitro after incubating proximal tubular epithelial cells in high-glucose and high-salt medium. In conclusion, our results indicate that high salt can lead to fatty acid metabolism disorders by increasing Na+/K+-ATPase expression in the renal tubules of DKD. High salt intake diminishes the reno-protective effect of dapagliflozin in DKD.

Renoprotective Role of Hypoxia-Inducible Factors and the Mechanism

BACKGROUND

The kidney requires abundant blood supply, and oxygen is transmitted by diffusion through blood vessels. Most physiological metabolism of the kidney depends on oxygen, so it is very sensitive to oxygen. An increasing pool of evidence suggests that hypoxia is involved in almost all acute and chronic kidney diseases (CKDs). Vascular damage, tubular injury, and fibrosis are the main pathologies associated during hypoxia. Hypoxia-inducible factors (HIFs) are the main mediators during hypoxia, but their functions remain controversial. This article reviewed recent studies and described its mechanisms on renoprotection.

SUMMARY

HIF is degraded rapidly during under normal oxygen. But under hypoxia, HIFs accumulate and many target genes are regulated by HIFs. Homeostasis during injury is maintained through these genes. Pretreatment of HIF can protect the kidney from acute hypoxia and can improve repair, but HIF's role in CKD and in renal tumor is still controversial. Due to its mechanism in kidney disease, many drugs toward HIFs are widely researched, even some of which have been used in clinical or in clinical research.

KEY MESSAGES

In this review, we described the known physiological mechanisms, target genes, and renal protective roles of HIFs, and we discussed several drugs that are researched due to such renal protective roles.

Renal Tubular Handling of Glucose and Fructose in Health and Disease

The proximal tubule of the kidney is programmed to reabsorb all filtered glucose and fructose. Glucose is taken up by apical sodium-glucose cotransporters SGLT2 and SGLT1 whereas SGLT5 and potentially SGLT4 and GLUT5 have been implicated in apical fructose uptake. The glucose taken up by the proximal tubule is typically not metabolized but leaves via the basolateral facilitative glucose transporter GLUT2 and is returned to the systemic circulation or used as an energy source by distal tubular segments after basolateral uptake via GLUT1. The proximal tubule generates new glucose in metabolic acidosis and the postabsorptive phase, and fructose serves as an important substrate. In fact, under physiological conditions and intake, fructose taken up by proximal tubules is primarily utilized for gluconeogenesis. In the diabetic kidney, glucose is retained and gluconeogenesis enhanced, the latter in part driven by fructose. This is maladaptive as it sustains hyperglycemia. Moreover, renal glucose retention is coupled to sodium retention through SGLT2 and SGLT1, which induces secondary deleterious effects. SGLT2 inhibitors are new anti-hyperglycemic drugs that can protect the kidneys and heart from failing independent of kidney function and diabetes. Dietary excess of fructose also induces tubular injury. This can be magnified by kidney formation of fructose under pathological conditions. Fructose metabolism is linked to urate formation, which partially accounts for fructose-induced tubular injury, inflammation, and hemodynamic alterations. Fructose metabolism favors glycolysis over mitochondrial respiration as urate suppresses aconitase in the tricarboxylic acid cycle, and has been linked to potentially detrimental aerobic glycolysis (Warburg effect). © 2022 American Physiological Society. Compr Physiol 12:2995-3044, 2022.

Adaptive Changes in single-nephron GFR, Tubular Morphology, and Transport in a Pregnant Rat Nephron: Modeling and Analysis

Normal pregnancy is characterized by massive increases in plasma volume and electrolyte retention. Given that the kidneys regulate homeostasis of electrolytes and volume, the organ undergoes major adaptations in morphology, hemodynamics, and transport to achieve the volume and electrolyte retention required in pregnancy. These adaptations are complex, sometimes counterintuitive, and not fully understood. In addition, the demands of the developing fetus and placenta change throughout the pregnancy. For example, during late pregnancy, K⁺ retention and thus enhanced renal K⁺ reabsorption is required despite many kaliuretic factors. The goal of this study is to unravel how known adaptive changes along the nephrons contribute to the ability of the kidney to meet volume and electrolyte requirements in mid- and late pregnancy. We developed computational models of solute and water transport in the superficial nephron of the kidney of a rat in mid- and late pregnancy. The mid-pregnant and late-pregnant rat superficial nephron models predict that morphological adaptations and increased activity of the sodium hydrogen exchanger 3 (NHE3) and epithelial sodium channel (ENaC) are essential for enhanced Na⁺ reabsorption observed during pregnancy. Model simulations showed that for sufficient K⁺ reabsorption, increased H ⁺-K ⁺-ATPase activity and decreased K⁺ secretion along the distal segments is required in both mid- and late-pregnancy. Furthermore, certain known sex differences in renal transporter pattern (e.g., the higher NHE3 protein abundance but lower activity in the proximal tubules of virgin female rats compared to male) may serve to better prepare the female for the increased transport demand in pregnancy.

Sodium-glucose cotransporter-2 inhibitors and non-steroidal mineralocorticoid receptor antagonists: Ushering in a new era of nephroprotection beyond renin-angiotensin system blockade

The therapeutic options for preventing or slowing the progression of chronic kidney disease (CKD) have been thus far limited. While angiotensin converting enzyme inhibitors (ACEi) and angiotensin receptor blockers (ARBs) are, without a doubt, safe and effective drugs, a significant proportion of patients with CKD still progress to end-stage kidney disease. After decades of negative trials, nephrologists have finally found cause for optimism with the introduction of sodium-glucose cotransporter-2 (SGLT2) inhibitors and non-steroidal mineralocorticoid receptor antagonists (MRAs). Recent trials such as EMPA-REG OUTCOME and CREDENCE have provided evidence of the renal benefits of SGLT2 inhibitors, which have now found widespread acceptance as first-line agents for diabetic CKD, in addition to ACEi/ARBs. Considering results from the DAPA-CKD study, it is expected that their use will soon be expanded to other causes of albuminuric CKD as well, although confirmation from further trials, such as the EMPA-KIDNEY study is awaited. Likewise, although the role of mineralocorticoid receptor overactivation in CKD progression has been known for decades, it is only now with the FIDELIO-DKD study that we have evidence of benefits of MRAs on hard renal endpoints, specifically in patients with diabetic CKD. While further research is ongoing, given the evidence of synergism between the three drug classes, it is foreseeable that a combination of two or more of these drugs may soon become the standard of care for CKD, regardless of underlying aetiology. This review describes pathophysiologic mechanisms, current evidence and future perspectives on the use of SGLT2 inhibitors and novel MRAs in CKD.

Sex differences in solute and water handling in the human kidney: Modeling and functional implications

The kidneys maintain homeostasis by controlling the amount of water and electrolytes in the blood. That function is accomplished by the nephrons, which transform glomerular filtrate into urine by a transport process mediated by membrane transporters. We postulate that the distribution of renal transporters along the nephron is markedly different between men and women, as recently shown in rodents. We hypothesize that the larger abundance of a renal Na+ transport in the proximal tubules in females may also better prepare them for the fluid retention adaptations required during pregnancy and lactation. Also, kidneys play a key role in blood pressure regulation, and a popular class of anti-hypertensive medications and angiotensin converting enzymes (ACE) inhibitors have been reported to be less effective in women. Model simulations suggest that the blunted natriuretic and diuretic effects of ACE inhibition in women can be attributed, in part, to their higher distal baseline transport capacity.

Modeling within-Host SARS-CoV-2 Infection Dynamics and Potential Treatments

The goal of this study was to develop a mathematical model to simulate the actions of drugs that target SARS-CoV-2 virus infection. To accomplish that goal, we have developed a mathematical model that describes the control of a SARS-CoV-2 infection by the innate and adaptive immune components. Invasion of the virus triggers the innate immunity, whereby interferon renders some of the target cells resistant to infection, and infected cells are removed by effector cells. The adaptive immune response is represented by plasma cells and virus-specific antibodies. The model is parameterized and then validated against viral load measurements collected in COVID-19 patients. We apply the model to simulate three potential anti-SARS-CoV-2 therapies: (1) Remdesivir, a repurposed drug that has been shown to inhibit the transcription of SARS-CoV-2, (2) an alternative (hypothetical) therapy that inhibits the virus' entry into host cells, and (3) convalescent plasma transfusion therapy. Simulation results point to the importance of early intervention, i.e., for any of the three therapies to be effective, it must be administered sufficiently early, not more than a day or two after the onset of symptoms. The model can serve as a key component in integrative platforms for rapid in silico testing of potential COVID-19 therapies and vaccines.

A Computational Model of Kidney Function in a Patient with Diabetes

At the onset of diabetes, the kidney grows large and the glomerular filtration rate becomes abnormally high. These structural and hemodynamics changes affect kidney function and may contribute to the development of chronic kidney disease. The goal of this study is to analyze how kidney function is altered in patients with diabetes and the renal effects of an anti-hyperglyceamic therapy that inhibits the sodium-glucose cotransporter 2 (SGLT2) in the proximal convoluted tubules. To accomplish that goal, we have developed a computational model of kidney function in a patient with diabetes and conducted simulations to study the effects of diabetes and SGLT2 inhibition on solute and water transport along the nephrons. Simulation results indicate that diabetes-induced hyperfiltration and tubular hypertrophy enhances Na+ transport, especially along the proximal tubules and thick ascending limbs. These simulations suggest that SGLT2 inhibition may attenuate glomerular hyperfiltration by limiting Na+-glucose transport, raising luminal [Cl-] at the macula densa, restoring the tubuloglomerular feedback signal, thereby reducing single-nephron glomerular filtration rate.

A kidney perspective on the mechanism of action of sodium glucose co-transporter 2 inhibitors

Sodium glucose co-transporter (SGLT) 2 inhibitors reduce the risk of kidney failure in patients with and without type 2 diabetes (T2D). Although the precise underlying mechanisms for these nephroprotective effects are incompletely understood, various hypotheses have been proposed including reductions in intraglomerular pressure through restoration of tubuloglomerular feedback, blood pressure reduction and favorable effects on vascular function, reduction in tubular workload and hypoxia, and metabolic effects resulting in increased autophagy. Here, we review these mechanisms, which may also explain the beneficial effects of SGLT2 inhibitors on kidney function in patients without T2D.