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Contains fulltext : 291310.pdf (Publisher’s version ) (Open Access) Poly- and perfluoroalkyl substances (PFASs) are omnipresent in the environment and have been shown to accumulate in humans. Most PFASs are not biotransformed in animals and humans, so that elimination is largely dependent on non-metabolic clearance via bile and urine. Accumulation of certain PFASs in humans may relate to their reabsorption from the pre-urine by transporter proteins in the proximal tubules of the kidney, such as URAT1 and OAT4. The present study assessed the in vitro transport of 7 PFASs (PFHpA, PFOA, PFNA, PFDA, PFBS, PFHxS and PFOS) applying URAT1- or OAT4-transfected human embryonic kidney (HEK) cells. Virtually no transport of PFASs could be measured in URAT1-transfected HEK cells. All PFASs, except PFBS, showed clear uptake in OAT4-transfected HEK cells. In addition, these in vitro results were further supported by in silico docking and molecular dynamic simulation studies assessing transporter-ligand interactions. Information on OAT4-mediated transport may provide insight into the accumulation potential of PFASs in humans, but other kinetic aspects may play a role and should also be taken into account. Quantitative information on all relevant kinetic processes should be integrated in physiologically based kinetic (PBK) models, to predict congener-specific accumulation of PFASs in humans in a more accurate manner.

BACKGROUND AND OBJECTIVES: The estimated glomerular filtration rate (eGFR) is a crucial parameter in heart failure. Much less is known about the importance of tubular function. We addressed the effect of tubular maximum phosphate reabsorption capacity (TmP/GFR), a parameter of proximal tubular function, in patients with heart failure.DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: We established TmP/GFR (Bijvoet formula) in 2085 patients with heart failure and studied its association with deterioration of kidney function (>25% eGFR decrease from baseline) and plasma neutrophil gelatinase-associated lipocalin (NGAL) doubling (baseline to 9 months) using logistic regression analysis and clinical outcomes using Cox proportional hazards regression. Additionally, we evaluated the effect of sodium-glucose transport protein 2 (SGLT2) inhibition by empagliflozin on tubular maximum phosphate reabsorption capacity in 78 patients with acute heart failure using analysis of covariance.RESULTS: Low TmP/GFR (CONCLUSIONS: TmP/GFR, a measure of proximal tubular function, is frequently reduced in heart failure, especially in patients with more advanced heart failure. Lower TmP/GFR is furthermore associated with future risk of plasma NGAL doubling and worse clinical outcomes, independent of glomerular function.

Rationale: Hypertension is the most important risk factor for cardiovascular and cerebrovascular diseases. Getting deep insight into the pathogenesis of hypertension is necessary. Objective: To investigate the role of ANK (ankyrin) repeat domain 36 ( ANKRD36 ) in hypertension. Methods and Results: We first recruited an essential hypertension cohort and then performed genome-wide transcriptome analysis with peripheral blood mRNA. ANKRD36 was found to be significantly lower expressed in hypertension. The anchorin repeat domain mediates a variety of protein-protein interactions. The ENaC (epithelial sodium channel) genes expression was found upregulated in human umbilical vein endothelial cells with ANKRD36 knockdown by using Affymetrix expression profile chip. In human embryonic kidney epithelial cells and HEK293T (human embryonic kidney cells), ANKRD36 overexpression significantly downregulated expression of ENaC genes, and ANKRD36 knockdown upregulated their expression. The chromosome immunoprecipitation assay and yin yang 1 ( YY1 ) knockdown showed the expression of ENaC was regulated by ANKRD36 via YY1, a dual-function transcription factor ubiquitously expressed in human tissues. Immunocoprecipitation and fluorescence resonance energy transfer assay confirmed the interaction between ANKRD36 and YY1. The nucleo-cytoplasmic ratio of YY1 decreased when ANKRD36 was overexpressed and also increased when ANKRD36 was knocked down. ANK2 domain of ANKRD36 was critical to its interaction with YY1. Ankrd36 knockout mice showed higher blood pressure levels and Na + reabsorption, especially when fed with high-salt diet. Higher expression of ENaC genes was observed in renal tubular epithelial cells from the knockout mice, and Yy1 knockdown mitigated the alteration. Ankrd36 knockout mice also showed more sensitive response to ENaC inhibitor amiloride treatment. Conclusions: We identified that ANKRD36 was involved in blood pressure regulation by interacting with YY1 and then altering expression of ENaC genes. Lower expressed ANKRD36 in hypertension might be a potential therapeutic target, and the application of ENaC inhibitors on hypertension treatment might be extended when serum K + levels are closely monitored.

Magnesium is an essential cofactor in many cellular processes, and aberrations in magnesium homeostasis can have life-threatening consequences. The kidney plays a central role in maintaining serum magnesium within a narrow range (0.70-1.10 mmol/L). Along the proximal tubule and thick ascending limb, magnesium reabsorption occurs via paracellular pathways. Members of the claudin family form the magnesium pores in these segments, and also regulate magnesium reabsorption by adjusting the transepithelial voltage that drives it. Along the distal convoluted tubule transcellular reabsorption via heteromeric TRPM6/7 channels predominates, although paracellular reabsorption may also occur. In this segment, the NaCl cotransporter plays a critical role in determining transcellular magnesium reabsorption. Although the general machinery involved in renal magnesium reabsorption has been identified by studying genetic forms of magnesium imbalance, the mechanisms regulating it are poorly understood. This review discusses pathways of renal magnesium reabsorption by different segments of the nephron, emphasizing newer findings that provide insight into regulatory process, and outlining critical unanswered questions.

Lithium is used in the treatment of bipolar disorder. We previously demonstrated that two types of transporters mediate the tubular reabsorption of lithium in rats, and suggested that sodium-dependent phosphate transporters play a role in lithium reabsorption with high affinity. In the present study, we examined sex differences in lithium reabsorption in rats. When lithium chloride was infused at 60 µg/min, creatinine clearance and the renal clearance of lithium were lower, and the plasma concentration of lithium was higher in female rats. These values reflected the higher fractional reabsorption of lithium in female rats. In rats infused with lithium chloride at 6 µg/min, the pharmacokinetic parameters of lithium examined were all similar in both sexes. The fractional reabsorption of lithium was decreased by foscarnet, a representative inhibitor of sodium-dependent phosphate transporters, in male and female rats when lithium chloride was infused at the low rate. Among the candidate transporters mediating lithium reabsorption examined herein, the mRNA expression of only PiT2, a sodium-dependent phosphate transporter, exhibited sexual dimorphism. The present results demonstrated sex differences in the tubular reabsorption of lithium with low affinity in rats.

Background Dotinurad is a selective urate reabsorption inhibitor (SURI), which selectively inhibits URAT1 to lower serum uric acid levels in patients with hyperuricemia. Herein, the effects of dotinurad were compared among patient groups with different stages of renal dysfunction. Methods Patient data from four clinical trials were pooled and divided into four groups according to the stage of renal dysfunction to compare the effects of dotinurad at different stages. The grouping (stages G1–G3b) was based on the estimated glomerular filtration rate (eGFR) of the patients. In addition, patient data from a long-term study (34 or 58 weeks) were evaluated in the same manner. Results In the pooled analysis, the percentage of patients achieving a serum uric acid level of ≤ 6.0 mg/dL was 64.7–100.0% at a dose of 2 or 4 mg. In the long-term analysis, the percentage of patients achieving a serum uric acid level of ≤ 6.0 mg/dL was 60.0–100.0% at a dose of 2 or 4 mg. Although the outcomes in stage G3b were worse due to higher baseline serum uric acid levels, satisfactory outcomes were observed in all stages. Even in stages G3a and G3b, when renal function declined, the eGFR remained constant throughout the dose period. Conclusion The efficacy of dotinurad was confirmed in hyperuricemic patients with normal renal function (stage G1) and mild to moderate renal dysfunction (stage G2–G3b). Dotinurad was found to be effective in the treatment of hyperuricemia in patients with mild to moderate renal dysfunction.

Background: The transepithelial transport of electrolytes, solutes, and water in the kidney is a well-orchestrated process involving numerous membrane transport systems. Basolateral potassium channels in tubular cells not only mediate potassium recycling for proper Na+,K+-ATPase function but are also involved in potassium and pH sensing. Genetic defects in KCNJ10 cause EAST/SeSAME syndrome, characterized by renal salt wasting with hypokalemic alkalosis associated with epilepsy, ataxia, and sensorineural deafness. Methods: A candidate gene approach and whole-exome sequencing determined the underlying genetic defect in eight patients with a novel disease phenotype comprising a hypokalemic tubulopathy with renal salt wasting, disturbed acid-base homeostasis, and sensorineural deafness. Electrophysiologic studies and surface expression experiments investigated the functional consequences of newly identified gene variants. Results: We identified mutations in the KCNJ16 gene encoding KCNJ16, which along with KCNJ15 and KCNJ10, constitutes the major basolateral potassium channel of the proximal and distal tubules, respectively. Coexpression of mutant KCNJ16 together with KCNJ15 or KCNJ10 in Xenopus oocytes significantly reduced currents. Conclusions: Biallelic variants in KCNJ16 were identified in patients with a novel disease phenotype comprising a variable proximal and distal tubulopathy associated with deafness. Variants affect the function of heteromeric potassium channels, disturbing proximal tubular bicarbonate handling as well as distal tubular salt reabsorption. Keywords: KCNJ10; KCNJ15; KCNJ16; acid-base homeostasis; deafness; distal tubule; hypokalemia; potassium channels; proximal tubule; tubulopathy.

Drug reabsorption following biliary excretion is well-known as enterohepatic recirculation (EHR). Renal tubular reabsorption (RTR) following renal excretion is also common but not easily assessed. Intestinal excretion (IE) and enteroenteric recirculation (EER) have not been recognized as common disposition mechanisms for metabolically stable and permeable drugs. IE and intestinal reabsorption (IR:EHR/EER), as well as RTR, are governed by dug concentration gradients, passive diffusion, active transport, and metabolism, and together they markedly impact disposition and pharmacokinetics (PK) of small molecule drugs. Disruption of IE, IR, or RTR through applications of active charcoal (AC), transporter knockout (KO), and transporter inhibitors can lead to changes in PK parameters. The impacts of intestinal and renal reabsorption on PK are under-appreciated. Although IE and EER/RTR can be an intrinsic drug property, there is no apparent strategy to optimize compounds based on this property. This review seeks to improve understanding and applications of IE, IR, and RTR mechanisms.

Cellular transport systems for both essential and toxic trace elements remain elusive. In our studies on the transport systems for cadmium (Cd), we found that the cellular uptake of Cd is mediated by the transporter for manganese (Mn). We identified ZIP8 and ZIP14, members of the ZIP zinc (Zn) transporter family, as transporters having high affinities for both Cd and Mn. Notably, the uptake of Cd into rice root from soil is mediated by a transporter for Mn as well. We found that ZIP8 is highly expressed at the S3 segment of the kidney proximal tubule and can transport glomerulus-filtered Cd and Mn ions in the lumen into epithelial cells of the proximal tubule, suggesting that ZIP8 has an important role in the renal reabsorption of both toxic Cd and essential Mn. Mutations in ZIP8 and ZIP14 genes were found in humans having congenital disorders associated with the disturbed transport of Mn, although ZIP8 mutation causes whole-body Mn deficiency while ZIP14 mutation causes Mn accumulation in the brain. Mutations in ZnT10, a Zn transporter responsible for Mn excretion, also cause hyperaccumulation of Mn in the brain. Results of genome-wide association studies have indicated that ZIP8 SNPs are involved in a variety of common diseases. Thus, ZIP8, ZIP14, and ZnT10 play crucial roles in the transport of Mn and thereby control Mn- and Cd-related biological events in the body.

Anticholinergics, therapeutic agents for overactive bladder, are clinically suggested to reduce urine output. We investigated whether this effect is due to bladder or kidney urine reabsorption. Various solutions were injected into the bladder of urethane-anesthetized SD rats. The absorption rate for 2 hr was examined following the intravenous administration of the anticholinergics imidafenacin (IM), atropine(AT), and tolterodine(TO). The bilateral ureter was then canulated and saline was administered to obtain a diuretic state. Anticholinergics or 1-deamino-[8-D-arginine]-vasopressin (dDAVP) were intravenously administered. After the IM and dDAVP administrations, the rat kidneys were immunostained with AQP2 antibody, and intracellular cAMP was measured. The absorption rate was ~10% of the saline injected into the bladder and constant even when anticholinergics were administered. The renal urine among peaked 2 hr after the saline administration. Each of the anticholinergics significantly suppressed the urine production in a dose-dependent manner, as did dDAVP. IM and dDAVP increased the intracellular cAMP levels and caused the AQP2 molecule to localize to the collecting duct cells' luminal side. The urinary reabsorption mechanism through the bladder epithelium was not activated by anticholinergic administration. Thus, anticholinergics suppress urine production via an increase in urine reabsorption in the kidneys' collecting duct cells via AQP2.

Sodium-glucose cotransporter-2 inhibitors (SGLT2i) are the latest introduction into the armamentarium of diabetes care in the present decade. By virtue of their beneficial effects, such as blood pressure-lowering, bodyweight reduction and significant renal and cardioprotective effects which extends beyond their glycaemic control effects, SGLT2i have become one of the most preferred oral antihyperglycaemic agents of recent times. However, they can influence tubular handling of electrolytes that can result in some electrolyte disturbances such as alteration in the serum levels of magnesium, potassium and phosphate levels. Some of these changes are mild or transient and may not have significant clinical implications. The underlying putative mechanism(s) responsible for disturbances of electrolytes are yet to be deciphered. In this review, we aim to describe electrolytes and acid–base abnormalities due to SGLT2i as well as to elucidate the underlying mechanism.

International audience; Aims: Interindividual variability in capacity to reabsorb glucose at the proximal renal tubule could contribute to risk of diabetic kidney disease. Our present study investigated, in patients with diabetes, the association between fractional reabsorption of glucose (FRGLU) and degree of renal disease as assessed by urinary albumin excretion (UAE) and estimated glomerular filtration rate (eGFR).Methods: FRGLU [1-(glucose clearance/creatinine clearance)] was assessed in 637 diabetes patients attending our tertiary referral centre, looking for correlations between FRGLU and UAE (normo-, micro-, macro-albuminuria) and Kidney Disease: Improving Global Outcomes (KDIGO) eGFR categories: >90 (G1); 90-60 (G2); 59-30 (G3); and11mmol/L).Results: Median (interquartile range, IQR) FRGLU levels were blood glucose-dependent: 99.90% (0.05) for low (n=106); 99.90% (0.41) for intermediate (n=288); and 96.36% (12.57) for high (n=243) blood glucose categories (P11mmol/L.

Acidosis is associated with E. coli induced pyelonephritis but whether bacterial cell wall constituents inhibit HCO3 transport in the outer medullary collecting duct from the inner stripe (OMCDi) is not known. We examined the effect of lipopolysaccharide (LPS), on HCO3 absorption in isolated perfused rabbit OMCDi. LPS caused a ~ 40% decrease in HCO3 absorption, providing a mechanism for E. coli pyelonephritis-induced acidosis. Monophosphoryl lipid A (MPLA), a detoxified TLR4 agonist, and Wortmannin, a phosphoinositide 3-kinase inhibitor, prevented the LPS-mediated decrease, demonstrating the role of TLR4-PI3-kinase signaling and providing proof-of-concept for therapeutic interventions aimed at ameliorating OMCDi dysfunction and pyelonephritis-induced acidosis.

Inhibitors of sodium–glucose cotransporter 2 (SGLT2) have undoubtedly shifted the paradigm for diabetes medicine and research and, especially, diabetic kidney disease (DKD). The pharmacological action of SGLT2 inhibitors is simply the release of glucose into urine; however, precisely how SGLT2 inhibitors contribute to the health of those with diabetes has still not been completely elucidated. Towards this end, the present review provides a novel insight into the action of SGLT2 inhibitors by highlighting a neglected fuel-burning system found in proximal tubular cells—‘glycolysis’. In addition, exploring the details of the molecular mechanisms and clinical biomarkers of the organ protection conferred by SGLT2 inhibitors is now required to prepare for the next stage of clinical diabetes medicine—the ‘post-SGLT2 inhibitor era’.

Chronic kidney disease (CKD) has significant effects on renal clearance (CLr ) of drugs. Physiologically-based pharmacokinetic (PBPK) models have been used to predict CKD effects on transporter-mediated renal active secretion and CLr for hydrophilic nonpermeable compounds. However, no studies have shown systematic PBPK modeling of renal passive reabsorption or CLr for hydrophobic permeable drugs in CKD. The goal of this study was to expand our previously developed and verified mechanistic kidney model to develop a universal model to predict changes in CLr in CKD for permeable and nonpermeable drugs that accounts for the dramatic nonlinear effect of CKD on renal passive reabsorption of permeable drugs. The developed model incorporates physiologically-based tubular changes of reduced water reabsorption/increased tubular flow rate per remaining functional nephron in CKD. The final adaptive kidney model successfully (absolute fold error (AFE) all < 2) predicted renal passive reabsorption and CLr for 20 permeable and nonpermeable test compounds across the stages of CKD. In contrast, use of proportional glomerular filtration rate reduction approach without addressing tubular adaptation processes in CKD to predict CLr generated unacceptable CLr predictions (AFE = 2.61-7.35) for permeable compounds in severe CKD. Finally, the adaptive kidney model accurately predicted CLr of para-amino-hippuric acid and memantine, two secreted compounds, in CKD, suggesting successful integration of active secretion into the model, along with passive reabsorption. In conclusion, the developed adaptive kidney model enables mechanistic predictions of in vivo CLr through CKD progression without any empirical scaling factors and can be used for CLr predictions prior to assessment of drug disposition in renal impairment.

Significance statement: In conditions when our blood experiences alkalosis, a pronounced kidney response is initiated causing a marked increase of urine base excretion. We recently discovered the cellular physiology of this, which employs fast activation of the base-secreting β-intercalated cells of the collecting duct. This function is fully dependent on the cystic fibrosis transmembrane conductance regulator (CFTR), the anion channel defective in CF. Hence, CF patients and mice cannot efficiently excrete an acute base load. Here, we find that the inability of fast urinary base removal in the CF mouse model causes a marked inhibition of ventilation. This study provides physiological insights into acid–base regulation and may have important implications for CF patients who are already burdened with reduced lung function.Abstract: The lungs and kidneys are pivotal organs in the regulation of body acid–base homeostasis. In cystic fibrosis (CF), the impaired renal ability to excrete an excess amount of HCO3− into the urine leads to metabolic alkalosis. This is caused by defective HCO3− secretion in the β-intercalated cells of the collecting duct that requires both the cystic fibrosis transmembrane conductance regulator (CFTR) and pendrin for normal function. We studied the ventilatory consequences of acute oral base loading in normal, pendrin knockout (KO), and CFTR KO mice. In wild-type mice, oral base loading induced a dose-dependent metabolic alkalosis, fast urinary removal of base, and a moderate base load did not perturb ventilation. In contrast, CFTR and pendrin KO mice, which are unable to rapidly excrete excess base into the urine, developed a marked and transient depression of ventilation when subjected to the same base load. Therefore, swift renal base elimination in response to an acute oral base load is a necessary physiological function to avoid ventilatory depression. The transient urinary alkalization in the postprandial state is suggested to have evolved for proactive avoidance of hypoventilation. In CF, metabolic alkalosis may contribute to the commonly reduced lung function via a suppression of ventilatory drive.

The estimated glomerular filtration rate (eGFR) is a crucial parameter in heart failure. Much less is known about the importance of tubular function. We addressed the effect of tubular maximum phosphate reabsorption capacity (TmP/GFR), a parameter of proximal tubular function, in patients with heart failure.We established TmP/GFR (Bijvoet formula) in 2085 patients with heart failure and studied its association with deterioration of kidney function (25% eGFR decrease from baseline) and plasma neutrophil gelatinase-associated lipocalin (NGAL) doubling (baseline to 9 months) using logistic regression analysis and clinical outcomes using Cox proportional hazards regression. Additionally, we evaluated the effect of sodium-glucose transport protein 2 (SGLT2) inhibition by empagliflozin on tubular maximum phosphate reabsorption capacity in 78 patients with acute heart failure using analysis of covariance.Low TmP/GFR (0.80 mmol/L) was observed in 1392 (67%) and 21 (27%) patients. Patients with lower TmP/GFR had more advanced heart failure, lower eGFR, and higher levels of tubular damage markers. The main determinant of lower TmP/GFR was higher fractional excretion of urea (TmP/GFR, a measure of proximal tubular function, is frequently reduced in heart failure, especially in patients with more advanced heart failure. Lower TmP/GFR is furthermore associated with future risk of plasma NGAL doubling and worse clinical outcomes, independent of glomerular function.

The renal response to acute hyperkalemia is mediated by increased K(+) secretion within the connecting tubule (CNT), flux that is modulated by tubular effects (e.g., aldosterone) in conjunction with increased luminal flow. There is ample evidence that peritubular K(+) blunts Na(+) reabsorption in the proximal tubule, thick ascending Henle limb, and distal convoluted tubule (DCT). Although any such reduction may augment CNT delivery, the relative contribution of each is uncertain. The kidney model of this laboratory was recently advanced with representation of the cortical labyrinth and medullary ray. Model tubules capture the impact of hyperkalemia to blunt Na(+) reabsorption within each upstream segment. However, this forces the question of the extent to which increased Na(+) delivery is transmitted past the macula densa and its tubuloglomerular feedback (TGF) signal. Beyond increasing macula densa Na(+) delivery, peritubular K(+) is predicted to raise cytosolic Cl(−) and depolarize macula densa cells, which may also activate TGF. Thus, although the upstream reduction in Na(+) transport may be larger, it appears that the DCT effect is critical to increasing CNT delivery. Beyond the flow effect, hyperkalemia reduces ammoniagenesis and reduced ammoniagenesis enhances K(+) excretion. What this model provides is a possible mechanism. When cortical [Formula: see text] is taken up via peritubular Na(+)-K(+)([Formula: see text])-ATPase, it acidifies principal cells. Consequently, reduced ammoniagenesis increases principal cell pH, thereby increasing conductance of both the epithelial Na(+) channel and renal outer medullary K(+) channel, enhancing K(+) excretion. In this model, the effect of aldosterone on principal cells, diminished DCT Na(+) reabsorption, and reduced ammoniagenesis all provide relatively equal and additive contributions to renal K(+) excretion. NEW & NOTEWORTHY Hyperkalemia blunts Na(+) reabsorption along the nephron, and increased CNT Na(+) delivery facilitates K(+) secretion. The model suggests that tubuloglomerular feedback limits transmission of proximal effects past the macula densa, so that it is DCT transport that is critical. Hyperkalemia also reduces PCT ammoniagenesis, which enhances K(+) excretion. The model suggests a mechanism, namely, that reduced cortical ammonia impacts CNT transport by raising cell pH and thus increasing both ENaC and ROMK conductance.

Passive permeability is a key property in drug disposition and delivery. It is critical for gastrointestinal absorption, brain penetration, renal reabsorption, defining clearance mechanisms and drug-drug interactions. Passive diffusion rate is translatable across tissues and animal species, while the extent of absorption is dependent on drug properties, as well as in vivo physiology/pathophysiology. Design principles have been developed to guide medicinal chemistry to enhance absorption, which combine the balance of aqueous solubility, permeability and the sometimes unfavorable compound characteristic demanded by the target. Permeability assays have been implemented that enable rapid development of structure-permeability relationships for absorption improvement. Future advances in assay development to reduce nonspecific binding and improve mass balance will enable more accurately measurement of passive permeability. Design principles that integrate potency, selectivity, passive permeability and other ADMET properties facilitate rapid advancement of successful drug candidates to patients.

Sodium glucose transporters (SGLTs) belong to the mammalian solute carrier family SLC5. This family includes 12 different members in human that mediate the transport of sugars, vitamins, amino acids, or smaller organic ions such as choline. The SLC5 family belongs to the sodium symporter family (SSS), which encompasses transporters from all kingdoms of life. It furthermore shares similarity to the structural fold of the APC (amino acid-polyamine-organocation) transporter family. Three decades after the first molecular identification of the intestinal Na+-glucose cotransporter SGLT1 by expression cloning, many new discoveries have evolved, from mechanistic analysis to molecular genetics, structural biology, drug discovery, and clinical applications. All of these advances have greatly influenced physiology and medicine. While SGLT1 is essential for fast absorption of glucose and galactose in the intestine, the expression of SGLT2 is largely confined to the early part of the kidney proximal tubules, where it reabsorbs the bulk part of filtered glucose. SGLT2 has been successfully exploited by the pharmaceutical industry to develop effective new drugs for the treatment of diabetic patients. These SGLT2 inhibitors, termed gliflozins, also exhibit favorable nephroprotective effects and likely also cardioprotective effects. In addition, given the recent finding that SGLT2 is also expressed in tumors of pancreas and prostate and in glioblastoma, this opens the door to potential new therapeutic strategies for cancer treatment by specifically targeting SGLT2. Likewise, further discoveries related to the functional association of other SGLTs of the SLC5 family to human pathologies will open the door to potential new therapeutic strategies. We furthermore hope that the herein summarized information about the physiological roles of SGLTs and the therapeutic benefits of the gliflozins will be useful for our readers to better understand the molecular basis of the beneficial effects of these inhibitors, also in the context of the tubuloglomerular feedback (TGF), and the renin-angiotensin system (RAS). The detailed mechanisms underlying the clinical benefits of SGLT2 inhibition by gliflozins still warrant further investigation that may serve as a basis for future drug development.

BACKGROUND: Hepatocyte NF 4α (Hnf4a) is a major regulator of renal proximal tubule (PT) development. In humans, a mutation in HNF4A impairs PT functions and is associated with Fanconi renotubular syndrome (FRTS). In mice, mosaic deletion of Hnf4a in the developing kidney reduces the population of PT cells, leading to FRTS-like symptoms. The molecular mechanisms underlying the role of Hnf4a in PT development remain unclear. METHODS: The gene deletion tool Osr2Cre removed Hnf4a in developing nephrons in mice, generating a novel model for FRTS. Immunofluorescence analysis characterized the mutant phenotype, and lineage analysis tested whether Cadherin-6 (Cdh6)–expressing cells are PT progenitors. Genome-wide mapping of Hnf4a binding sites and differential gene analysis of Hnf4a mutant kidneys identified direct target genes of Hnf4a. RESULTS: Deletion of Hnf4a with Osr2Cre led to the complete loss of mature PT cells, lethal to the Hnf4a mutant mice. Cdh6(high), lotus tetragonolobus lectin-low (LTL(low)) cells serve as PT progenitors and demonstrate higher proliferation than Cdh6(low), LTL(high) differentiated PT cells. Additionally, Hnf4a is required for PT progenitors to differentiate into mature PT cells. Genomic analyses revealed that Hnf4a directly regulates the expression of genes involved in transmembrane transport and metabolism. CONCLUSIONS: Hnf4a promotes the differentiation of PT progenitors into mature PT cells by regulating the expression of genes associated with reabsorption, the major function of PT cells.

Background: The discovery of Sodium-Glucose co-transporter-2 (SGLT2) inhibitors had rewritten the treatment of diabetes mellitus with an impressive fall in the incidence of death and associated complications. Introduction: The SGLT2 inhibitors by inhibiting the SGLT2 in the proximal nephron, helps in reducing the reabsorption of approximately 90% of the filtered glucose and increased urinary glucose excretion (UGE). Methods: The literature related to SGLT2 inhibitors has been thoroughly explored from various available public domains and reviewed extensively for this article. Detailed and updated information related to SGLT2 inhibitors with a major focus on the recently approved Ertuglifolzin is structured in this review. Result: The present review is an effort to understand the management of diabetes mellitus over the past few decades with a special focus on the role of SGLT2 receptor in the causes of therapeutic and preventive strategies for diabetes mellitus. Pragmatic placement of the currently available Canagliflozin, Dapagliflozin, and Empagliflozin as oral antidiabetic agents has been done. Well accommodated stereochemistry and a high docking score of Ertugliflozin in ligand-receptor simulation studies attribute to its high potency. Conclusion: This review highlights the unique mechanism of SGLT2 Inhibitors coupled with pleiotropic benefits on weight and blood pressure, which make it an attractive choice of therapy to diabetic patients, not controlled by other medications.

Angiotensin II (ANG II) stimulates proximal nephron transport via activation of classical protein kinase C (PKC) isoforms. Acute fructose treatment stimulates PKC and dietary fructose enhances ANG II’s ability to stimulate Na+transport, but the mechanisms are unclear. We hypothesized that dietary fructose enhances ANG II’s ability to stimulate renal proximal tubule Na+reabsorption by augmenting PKC-α activation and increases in intracellular Ca2+. We measured total and isoform-specific PKC activity, basal and ANG II-stimulated oxygen consumption, a surrogate of Na+reabsorption, and intracellular Ca2+in proximal tubules from rats given either 20% fructose in their drinking water (fructose group) or tap water (control group). Total PKC activity was measured by ELISA. PKC-α, PKC-β, and PKC-γ activities were assessed by measuring particulate-to-soluble ratios. Intracelluar Ca2+was measured using fura 2. ANG II stimulated total PKC activity by 53 ± 15% in the fructose group but not in the control group (−15 ± 11%, P < 0.002). ANG II stimulated PKC-α by 0.134 ± 0.026 but not in the control group (−0.002 ± 0.020, P < 0.002). ANG II increased PKC-γ activity by 0.008 ± 0.003 in the fructose group but not in the control group ( P < 0.046). ANG II did not stimulate PKC-β in either group. ANG II increased Na+transport by 454 ± 87 nmol·min−1·mg protein−1in fructose group, and the PKC-α/β inhibitor Gö6976 blocked this increase (−96 ± 205 nmol·min−1·mg protein−1, P < 0.045). ANG II increased intracellular Ca2+by 148 ± 53 nM in the fructose group but only by 43 ± 10 nM in the control group ( P < 0.035). The intracellular Ca2+chelator BAPTA blocked the ANG II-induced increase in Na+transport in the fructose group. We concluded that dietary fructose enhances ANG II’s ability to stimulate renal proximal tubule Na+reabsorption by augmenting PKC-α activation via elevated increases in intacellular Ca2+.

Hypomagnesemia in patients with congenital anomalies of the kidneys and urinary tract or autosomal dominant tubulointerstitial kidney disease is highly suggestive of HNF1B-associated disease. Intriguingly, the frequency of low serum Mg2+ (sMg) level varies and is lower in children than in adults with HNF1B mutations that could be partially due to application of inaccurate normal limit of sMg, irrespective of age and gender. We aimed to re-assess cross-sectionally and longitudinally the frequency of hypomagnesemia in HNF1B disease by using locally derived reference values of sMg. Fourteen children with HNF1B-associated kidney disease were included. Control group comprising 110 subjects served to generate 2.5th percentiles of sMg as the lower limits of normal. In both controls and patients, sMg correlated with age, gender, and fractional excretion of Mg2+. In girls, sMg concentration was higher than in boys when analyzed in the entire age spectrum (p

The diabetic kidney presents excess expression and activity of the SGLT2 transporter of the proximal tubule. This situation increases the renal reabsorption of Na and glucose and reduces their distal supply. In addition to the metabolic effects on the internal environment of this excess reabsorbed glucose, the renal tubule is subjected to glycosylated stress capable of locally activating both apoptosis and inflammasome. The result is a progressive loss of nephron units, activation of transition of mesangial epithelium and collagen deposition. Activation of insulin signalling by the MAP kinase pathway and resistance to the metabolic effects of insulin take place. This is simultaneously combined with afferent vasodilation due to hyperglycaemia, tubuloglomerular feedback inhibition due to reduced distal fluid supply, podocyte dedifferentiation and reduction in their number, the latter effects being due to insulin resistance. The result is self-feeding renal damage, with intraglomerular hyper-pressure, podocyte dedifferentiation, tubular apoptosis, and local and distant activation of inflammasome. All these effects are susceptible to be totally or partially corrected by inhibiting glucose transport via the SGLT transporters.

Kidney size and glomerular filtration rate (GFR) often increase with the onset of diabetes, and elevated GFR is a risk factor for the development of diabetic kidney disease. Hyperfiltration mainly occurs in response to signals passed from the tubule to the glomerulus: high levels of glucose in the glomerular filtrate drive increased reabsorption of glucose and sodium by the sodium–glucose cotransporters SGLT2 and SGLT1 in the proximal tubule. Passive reabsorption of chloride and water also increases. The overall capacity for proximal reabsorption is augmented by growth of the proximal tubule, which (alongside sodium–glucose cotransport) further limits urinary glucose loss. Hyperreabsorption of sodium and chloride induces tubuloglomerular feedback from the macula densa to increase GFR. In addition, sodium–glucose cotransport by SGLT1 on macula densa cells triggers the production of nitric oxide, which also contributes to glomerular hyperfiltration. Although hyperfiltration restores sodium and chloride excretion it imposes added physical stress on the filtration barrier and increases the oxygen demand to drive reabsorption. Tubular growth is associated with the development of a senescence-like molecular signature that sets the stage for inflammation and fibrosis. SGLT2 inhibitors attenuate the proximal reabsorption of sodium and glucose, normalize tubuloglomerular feedback signals and mitigate hyperfiltration. This tubule-centred model of diabetic kidney physiology predicts the salutary effect of SGLT2 inhibitors on hard renal outcomes, as shown in large-scale clinical trials.

The kidneys filter large amounts of glucose. To prevent the loss of this valuable fuel, the tubular system of the kidney, particularly the proximal tubule, has been programmed to reabsorb all filtered glucose. The machinery involves the sodium-glucose cotransporters SGLT2 and SGLT1 on the apical membrane and the facilitative glucose transporter GLUT2 on the basolateral membrane. The proximal tubule also generates new glucose, particularly in the post-absorptive phase but also to enhance bicarbonate formation and maintain acid-base balance. The glucose reabsorbed or formed by the proximal tubule is primarily taken up into peritubular capillaries and returned to the systemic circulation or provided as an energy source to further distal tubular segments that take up glucose by basolateral GLUT1. Recent studies provided insights on the coordination of renal glucose reabsorption, formation, and usage. Moreover, a better understanding of renal glucose transport in disease states is emerging. This includes the kidney in diabetes mellitus, when renal glucose retention becomes maladaptive and contributes to hyperglycemia. Furthermore, enhanced glucose reabsorption is coupled to sodium retention through the sodium-glucose cotransporter SGLT2, which induces secondary deleterious effects. As a consequence, SGLT2 inhibitors are new anti-hyperglycemic drugs that can protect the kidneys and heart from failing. Recent studies discovered unique roles for SGLT1 with implications in acute kidney injury and glucose sensing at the macula densa. This review discusses established and emerging concepts of renal glucose transport, and outlines the need for a better understanding of renal glucose handling in health and disease.

Neutrophil gelatinase-associated lipocalin (NGAL) is a secreted low-molecular weight iron-siderophore-binding protein. NGAL overexpression in injured tubular epithelia partly explains its utility as a sensitive and early urinary biomarker of acute kidney injury (AKI). Herein, we extend mechanistic insights into the source and kinetics of urinary NGAL excretion in experimental AKI. Three models of experimental AKI were undertaken in adult male Wistar rats; renal ischemia-reperfusion injury (IRI) and gentamicin (G) and cisplatin (Cisp) nephrotoxicity. Alongside standard histological and biochemical assessment of AKI, urinary NGAL excretion rate, plasma NGAL concentration, and renal NGAL mRNA/protein expression were assessed. In situ renal perfusion studies were undertaken to discriminate direct shedding of NGAL to the urine from addition of NGAL to the urine secondary to alterations in the tubular handling of glomerular filtrate-derived protein. Renal NGAL expression and urinary excretion increased in experimental AKI. In acute studies in both the IRI and G models, direct renal perfusion with Kreb’s buffer eliminated urinary NGAL excretion. Addition of exogenous NGAL to the Kreb’s buffer circuit, reestablishment of perfusion with systemic blood or reperfusion with renal vein effluent restored high levels of urinary NGAL excretion. Urinary NGAL excretion in AKI arises in large proportion from reduced reabsorption from the glomerular filtrate. Hence, subclinical cellular dysfunction could increase urinary NGAL, particularly in concert with elevations in circulating prerenal NGAL and/or pharmacological inhibition of tubular reabsorption. More granular interpretation of urinary NGAL measurements could optimize the scope of its clinical utility as a biomarker of AKI.

Background: Clinical development of lesinurad, a selective uric acid reabsorption inhibitor, required analysis of lesinurad in plasma from special patient populations. Methods: EMA and FDA bioanalytical method validation guidance have recommended studying matrix effects on quantitation if samples from special patient populations are to be analyzed. In addition to lesinurad (plasma protein binding 98.2%), the matrix effects from special population plasma on the quantitation of verapamil (PPB 89.6%), allopurinol and oxypurinol (PPB negligible) were also investigated. Results: The plasma from special population patients had no matrix effects on the three quantification methods with stable isotope labeled internal standard, protein precipitation extraction, and LC-MS/MS detection. The validated lesinurad plasma quantification method was successfully applied for the pharmacokinetic evaluations to support the clinical studies in renal impaired patients. Conclusion: Special population plasma did not affect quantitation of drugs with a wide range of plasma protein binding levels in human plasma. With the confirmation that there is no impact on quantification from the matrix, the bioanalytical method can be used to support the pharmacokinetic evaluations for clinical studies in special populations.