Reabsorption In Proximal Tubule Research Articles

Role of the sympathetic nervous system in regulation of the sodium glucose cotransporter 2.

The sympathetic nervous system (SNS) regulates glucose metabolism in various organs including the kidneys. The sodium glucose cotransporter 2 (SGLT2) mediates glucose reabsorption in renal proximal tubules and its inhibition has been shown to improve glucose control, cardiovascular and renal outcomes. We hypothesized that SNS-induced alterations of glucose metabolism may be mediated via regulation of SGLT2. We used human renal proximal tubule cells to investigate the effects of noradrenaline on SGLT2 regulation. Mice fed a high-fat diet were oral gavaged with dapagliflozin and the expression of noradrenaline and tyrosine hydroxylase was measured in the kidney and heart. Noradrenaline treatment resulted in a pronounced increase in SGLT2 and interleukin (IL)-6 expression in HK2 cells and promoted translocation of SGLT2 to the cell surface. In vivo, dapagliflozin treatment resulted in marked glucosuria in high-fat diet-fed mice. SGLT2 inhibition significantly reduced high-fat diet-induced elevations of tyrosine hydroxylase and noradrenaline in the kidney and heart. We also aimed to assess the levels of hypertension-related cytokines in the kidneys of our mice treated with and without dapagliflozin. Excitingly, we demonstrate that SGLT2 inhibition with dapagliflozin promoted a trend towards reduced tumour necrosis factor-alpha and elevated IL-1β protein levels in the kidney. Our in-vitro and in-vivo studies provide first evidence for an important cross-talk between the SNS and SGLT2 regulation that may not only account for SNS-induced alterations of glucose metabolism but potentially contribute to cardiovascular and renal protection observed with SGLT2 inhibitors.

Effect of rMnSOD on Sodium Reabsorption in Renal Proximal Tubule in Ochratoxin A-Treated Rats.

Ochratoxin A (OTA) is a mycotoxin produced by Aspergillus and Penicillium that represent toxic real threat for human beings and animal health. In this study we evaluated the effect of a new recombinant mitochondrial manganese containing superoxide dismutase (rMnSOD) on oxidative stress and on the alterations of fluid reabsorption in renal proximal tubule (PT) as possible causes of OTA nephrotoxicity. Finally, we have measured the concentration of O2- in the kidney through dihydroethidium assay (DHE) and nitric oxide (NO) concentration through nitrites and nitrates assay. Male Sprague Dawley rats weighing 120-150 g were treated for 14 days by gavage, as follows: Control group, 12 rats received a corresponding amount of saline solution (including 10% DMSO); rMnSOD group, 12 rats treated with rMnSOD (10 µg/kg bw); OTA group, 12 rats treated with OTA (0.5 mg/kg bw) dissolved in 10% DMSO and then scaled to required volume with corn oil; rMnSOD + OTA, 12 rats treated with rMnSOD (10 µg/kg bw) plus OTA (0.5 mg/kg bw). Our results have shown that rMnSOD restores the alteration of reabsorption in PT in rats treated with OTA plus rMnSOD, probably through the response to pressure natriuresis, where nitric oxide plays a key role. Moreover, rMnSOD prevents the nephrotoxicity induced by OTA probably restoring the balance between superoxide and NO that is most probably the cause of hypertension and renal functional alterations through the inhibition of NO synthase. In conclusion these data provide important information for understanding of mechanism of toxic action of OTA. J. Cell. Biochem. 119: 424-430, 2018. © 2017 Wiley Periodicals, Inc.

Cyanide-Nitroprusside Colorimetric Assay: A Rapid Colorimetric Screen for Urinary Cystine.

Cystinuria is an autosomal recessive disorder resulting in poor proximal tubule reabsorption of cystine in the nephron, increasing the risk of cystine stone formation. A fast, inexpensive assay to screen for urinary cystine is needed because cystine stones are difficult to noninvasively differentiate from more common calcium-containing ones. Tandem mass spectrometry (MS/MS) is sensitive and specific but is labor-intensive and costly. Alternatively, a colorimetric assay is fast and cost-effective; however, creatinine interference is an issue. A published cyanide-nitroprusside colorimetric assay was modified for a high-throughput microplate format. Creatinine interference was reduced using 0.1 mol/L PBS and a standard reaction time of 60 s and was further corrected using a formula derived from the slope of multiple creatinine standard curves. The limit of blank was determined to be 2.6 mg/L, the limit of detection 11.9 mg/L, and the limit of quantitation 15.3 mg/L. The analytic measurement range was established as 15.3-100 mg/L cystine. Intraassay and interassay CV was calculated to be 9.6% and 8.0%, respectively, for a high-level cystine concentration (83.6 mg/L). Low-level cystine (36.4 mg/L) intraassay and interassay CV was determined to be 18.1% and 17.6%, respectively. Passing-Bablok regression analysis of colorimetric vs LC-MS/MS results revealed a slope of 1.10 and y intercept of -7.14 mg/L, with an overall bias of 2% by Bland-Altman plot analysis. We analytically validated a rapid colorimetric assay suitable to quantify urinary cystine. The effect of thiol drugs on this assay remains to be determined.

Effects of Reactive Oxygen Species on Tubular Transport along the Nephron.

Reactive oxygen species (ROS) are oxygen-containing molecules naturally occurring in both inorganic and biological chemical systems. Due to their high reactivity and potentially damaging effects to biomolecules, cells express a battery of enzymes to rapidly metabolize them to innocuous intermediaries. Initially, ROS were considered by biologists as dangerous byproducts of respiration capable of causing oxidative stress, a condition in which overproduction of ROS leads to a reduction in protective molecules and enzymes and consequent damage to lipids, proteins, and DNA. In fact, ROS are used by immune systems to kill virus and bacteria, causing inflammation and local tissue damage. Today, we know that the functions of ROS are not so limited, and that they also act as signaling molecules mediating processes as diverse as gene expression, mechanosensation, and epithelial transport. In the kidney, ROS such as nitric oxide (NO), superoxide (O2−), and their derivative molecules hydrogen peroxide (H2O2) and peroxynitrite (ONO2−) regulate solute and water reabsorption, which is vital to maintain electrolyte homeostasis and extracellular fluid volume. This article reviews the effects of NO, O2−, ONO2−, and H2O2 on water and electrolyte reabsorption in proximal tubules, thick ascending limbs, and collecting ducts, and the effects of NO and O2− in the macula densa on tubuloglomerular feedback.

MicroRNA-148b regulates megalin expression and is associated with receptor downregulation in mice with unilateral ureteral obstruction.

Megalin is a multiligand, endocytic receptor that is important for the normal, proximal tubule reabsorption of filtered proteins, hormones, enzymes, essential nutrients, and nephrotoxins. Megalin dysfunction has been associated with acute, as well as chronic kidney diseases. Tubular proteinuria has been observed following unilateral ureteral obstruction (UUO), suggesting megalin dysfunction; however, the pathophysiological mechanism has not been determined. To identify potential regulators of megalin expression, we examined renal microRNAs (miRNAs) expression and observed an upregulation of microRNA-148b (miR-148b) in obstructed mouse kidneys 7 days after UUO, which was associated with a significant reduction in proximal tubule megalin expression and accumulation of megalin ligands. By in silico miRNA target prediction analysis, we identified megalin messenger RNA (mRNA) as a potential target of miR-148b and confirmed using a dual-luciferase reporter assay that miR-148b targeted the 3'-untranslated region of the megalin gene. Transfection of LLC-PK1 cells with miR-148b mimic reduced endogenous megalin mRNA and protein levels in a concentration-dependent manner, while transfection with miR-148b inhibitor resulted in an increase. Our findings suggest that miR-148b directly downregulates megalin expression and that miR-148b negatively regulates megalin expression in UUO-induced kidney injury. Furthermore, the identification of a miRNA regulating megalin expression may allow for targeted interventions to modulate megalin function and proximal tubule uptake of proteins, as well as other ligands.

Na/K-ATPase Signaling and Salt Sensitivity: The Role of Oxidative Stress.

Other than genetic regulation of salt sensitivity of blood pressure, many factors have been shown to regulate renal sodium handling which contributes to long-term blood pressure regulation and have been extensively reviewed. Here we present our progress on the Na/K-ATPase signaling mediated sodium reabsorption in renal proximal tubules, from cardiotonic steroids-mediated to reactive oxygen species (ROS)-mediated Na/K-ATPase signaling that contributes to experimental salt sensitivity.

Phosphaturic mesenchymal tumor (PMT): Exceptionally rare disease, yet crucial not to miss

Phosphaturic mesenchymal tumors (PMTs) are very rare tumors which are frequently associated with Tumor Induced Osteomalacia (TIO), a paraneoplastic syndrome that manifests as renal phosphate wasting. The tumor cells produce a peptide hormone-like substance known as fibroblast growth factor 23 (FGF23), a physiologic regulator of phosphate levels. FGF23 decreases proximal tubule reabsorption of phosphates and inhibits 1-α-hydroxylase, which reduces levels of 1-α, 25-dihydroxyvitamine D3. Thus, overexpression of FGF23 by the tumor cells leads to increased excretion of phosphate in the urine, mobilization of calcium and phosphate from bones, and the reduction of osteoblastic activity, ultimately resulting in widespread osteomalacia. Patients typically present with gradual muscular weakness and diffuse bone pain from pathologic fractures. The diagnosis is often delayed due to the non-specific nature of the symptoms and lack of clinical suspicion. While serum phosphorus and FGF23 testing can assist in making a clinical diagnosis of PMT, the responsible tumor is often difficult to locate. The pathologic diagnosis is often missed due to the rarity of PMTs and histologic overlap with other mesenchymal neoplasms. While patients can experience severe disabilities without treatment, excision is typically curative and results in a dramatic reversal of symptoms. Histologically, PMT has a variable appearance and can resemble other low grade mesenchymal tumors. Even though very few cases of PMT have been reported in the world literature, it is very important to consider this diagnosis in all patients with hypophosphatemic osteomalacia. Here we present a patient who suffered for almost 5 years without a diagnosis. Ultimately, the PMT was located on a 68Ga-DOTA TATE PET/CT scan and subsequently confirmed by histologic and immunohistologic study. Interestingly, strong positivity for FGFR1 by IHC might be related to the recently described FN1-FGFR1 fusion. Upon surgical removal, the patient’s phosphate and FGF23 levels returned to normal and the patient’s symptoms resolved.

Infrared vibrational spectroscopy: a rapid and novel diagnostic and monitoring tool for cystinuria.

Cystinuria is the commonest inherited cause of nephrolithiasis (~1% in adults; ~6% in children) and is the result of impaired cystine reabsorption in the renal proximal tubule. Cystine is poorly soluble in urine with a solubility of ~1 mM and can readily form microcrystals that lead to cystine stone formation, especially at low urine pH. Diagnosis of cystinuria is made typically by ion-exchange chromatography (IEC) detection and quantitation, which is slow, laboursome and costly. More rapid and frequent monitoring of urinary cystine concentration would significantly improve the diagnosis and clinical management of cystinuria. We used attenuated total reflection - Fourier transform infrared spectroscopy (ATR-FTIR) to detect and quantitate insoluble cystine in 22 cystinuric and 5 healthy control urine samples. Creatinine concentration was also determined by ATR-FTIR to adjust for urinary concentration/dilution. Urine was centrifuged, the insoluble fraction re-suspended in 5 μL water and dried on the ATR prism. Cystine was quantitated using its 1296 cm−1 absorption band and levels matched with parallel measurements made using IEC. ATR-FTIR afforded a rapid and inexpensive method of detecting and quantitating insoluble urinary cystine. This proof-of-concept study provides a basis for developing a high-throughput, cost-effective diagnostic method for cystinuria, and for point-of-care clinical monitoring

Protein Carbonylation of an Amino Acid Residue of the Na/K-ATPase α1 Subunit Determines Na/K-ATPase Signaling and Sodium Transport in Renal Proximal Tubular Cells.

BackgroundWe have demonstrated that cardiotonic steroids, such as ouabain, signaling through the Na/K‐ATPase, regulate sodium reabsorption in the renal proximal tubule. By direct carbonylation modification of the Pro222 residue in the actuator (A) domain of pig Na/K‐ATPase α1 subunit, reactive oxygen species are required for ouabain‐stimulated Na/K‐ATPase/c‐Src signaling and subsequent regulation of active transepithelial 22Na+ transport. In the present study we sought to determine the functional role of Pro222 carbonylation in Na/K‐ATPase signaling and sodium handling.Methods and ResultsStable pig α1 knockdown LLC‐PK1‐originated PY‐17 cells were rescued by expressing wild‐type rat α1 and rat α1 with a single mutation of Pro224 (corresponding to pig Pro222) to Ala. This mutation does not affect ouabain‐induced inhibition of Na/K‐ATPase activity, but abolishes the effects of ouabain on Na/K‐ATPase/c‐Src signaling, protein carbonylation, Na/K‐ATPase endocytosis, and active transepithelial 22Na+ transport.ConclusionsDirect carbonylation modification of Pro224 in the rat α1 subunit determines ouabain‐mediated Na/K‐ATPase signal transduction and subsequent regulation of renal proximal tubule sodium transport.

Carbonylation Modification Regulates Na/K-ATPase Signaling and Salt Sensitivity: A Review and a Hypothesis.

Na/K-ATPase signaling has been implicated in different physiological and pathophysiological conditions. Accumulating evidence indicates that oxidative stress not only regulates the Na/K-ATPase enzymatic activity, but also regulates its signaling and other functions. While cardiotonic steroids (CTS)-induced increase in reactive oxygen species (ROS) generation is an intermediate step in CTS-mediated Na/K-ATPase signaling, increase in ROS alone also stimulates Na/K-ATPase signaling. Based on literature and our observations, we hypothesize that ROS have biphasic effects on Na/K-ATPase signaling, transcellular sodium transport, and urinary sodium excretion. Oxidative modulation, in particular site specific carbonylation of the Na/K-ATPase α1 subunit, is a critical step in proximal tubular Na/K-ATPase signaling and decreased transcellular sodium transport leading to increases in urinary sodium excretion. However, once this system is overstimulated, the signaling, and associated changes in sodium excretion are blunted. This review aims to evaluate ROS-mediated carbonylation of the Na/K-ATPase, and its potential role in the regulation of pump signaling and sodium reabsorption in the renal proximal tubule (RPT).

Mathematical Model‐based Analysis of the Acute and Chronic Mechanisms of Diabetic Hyperfiltration

An increase in glomerular filtration rate (GFR) in early diabetes has been associated with development and progression of diabetic kidney disease. Our understanding of the mechanisms responsible for hyperfiltration and subsequent renal injury is incomplete, but may be critical for developing new approaches to prevent diabetic kidney disease. The tubular hypothesis of hyperfiltration proposes that hyperfiltration is initiated by a primary increase in sodium (Na) reabsorption in the proximal tubule (PT), due to tubular growth and increased Na‐glucose cotransport.The renal response to a primary increase in PT Na reabsorption likely involves multiple mechanisms over both the acute and chronic timescales. A more complete understanding of the relative contributions of the driving mechanisms, as well as the relationship between the acute and chronic response, is needed to better understand how diabetic hyperfiltration is initiated and maintained. In this study, we utilized an integrated mathematical model of the renal vasculature, tubular Na and fluid handling, and systemic blood volume regulation to investigate the mechanisms responsible for the hyperfiltration response to increased Na reabsorption in the PT.We find that both tubuloglomerular feedback (TGF) and decreased PT pressure likely contribute to the acute GFR response to increased PT reabsorption. However, these mechanisms and the acute GFR rise appear insufficient to fully return Na balance. Additional adaptations must occur chronically to restore Na balance – either distal Na reabsorption must be reduced to compensate for the increased PT reabsorption, or GFR must be further augmented to match Na excretion to intake. We find that when preglomerular autoregulation is intact, modest distal reductions in Na reabsorption can fully compensate, with no further increase in GFR needed. The distal effect is driven by true pressure‐natriuresis, but regulation by renal sympathetic nerve activity and the renin angiotensin aldosterone system moderate this effect and allow Na homeostasis with minimal increases in blood pressure. However, when preglomerular autoregulation or downregulation of distal Na reabsorption is impaired (as has been proposed in diabetes), Na balance is returned through a further increase in glomerular pressure/GFR.In summary, these results suggest that the hyperfiltration response to a primary increase in PT Na reabsorption is multifactorial. While the acute response is likely dominated by TGF and tubular pressure changes, impaired renal autoregulation and impaired pressure natriuresis/ neurohumoral distal Na transport regulation contribute to the magnitude of the chronic hyperfiltration response and the associated increase in glomerular pressure. In other words, improving preglomerular autoregulation and/or restoring renal Na transport regulation may attenuate hyperfiltration/glomerular hypertension and thereby the drive to renal damage long‐term. An interactive interface to the model is available at qsp.engr.uga.edu:3838/Hyperfiltration_EB.

Ipragliflozin, a sodium-glucose cotransporter 2 inhibitor, ameliorates the development of liver fibrosis in diabetic Otsuka Long-Evans Tokushima fatty rats.

It is widely understood that insulin resistance (IR) critically correlates with the development of liver fibrosis in several types of chronic liver injuries. Several experiments have proved that anti-IR treatment can alleviate liver fibrosis. Sodium-glucose cotransporter 2 (SGLT2) inhibitors comprise a new class of antidiabetic agents that inhibit glucose reabsorption in the renal proximal tubules, improving IR. The aim of this study was to elucidate the effect of an SGLT2 inhibitor on the development of liver fibrosis using obese diabetic Otsuka Long-Evans Tokushima fatty (OLETF) rats and their littermate nondiabetic Long-Evans Tokushima Otsuka (LETO) rats. Male OLETF and LETO rats were intraperitoneally injected with porcine serum twice a week for 12weeks to augment liver fibrogenesis. Different concentrations of ipragliflozin (3 and 6mg/kg) were orally administered during the experimental period. Serological and histological data were examined at the end of the experimental period. The direct effect of ipragliflozin on the proliferation of a human hepatic stellate cell (HSC) line, LX-2, was also evaluated in vitro. OLETF rats, but not LETO rats, received 12weeks of porcine serum injection to induce severe fibrosis. Treatment with ipragliflozin markedly attenuated the development of liver fibrosis and expression of hepatic fibrosis markers, such as alpha smooth muscle actin, collagen 1A1, and transforming growth factor beta (TGF-β), and improved IR in a dose-dependent manner in OLETF rats. In contrast, the proliferation of LX-2 in vitro was not affected, suggesting that ipragliflozin had no significant direct effect on the proliferation of HSCs. In conclusion, our dataset suggests that an SGLT2 inhibitor could alleviate the development of liver fibrosis by improving IR in naturally diabetic rats. This may provide the basis for creating new therapeutic strategies for chronic liver injuries with IR.

Ipragliflozin Improves Hepatic Steatosis in Obese Mice and Liver Dysfunction in Type 2 Diabetic Patients Irrespective of Body Weight Reduction.

Type 2 diabetes mellitus (T2DM) is associated with a high incidence of non-alcoholic fatty liver disease (NAFLD) related to obesity and insulin resistance. Currently, medical interventions for NAFLD have focused on diet control and exercise to reduce body weight, and there is a requirement for effective pharmacological therapies. Sodium-glucose cotransporter 2 (SGLT2) inhibitors are oral antidiabetic drugs that promote the urinary excretion of glucose by blocking its reabsorption in renal proximal tubules. SGLT2 inhibitors lower blood glucose independent of insulin action and are expected to reduce body weight because of urinary calorie loss. Here we show that an SGLT2 inhibitor ipragliflozin improves hepatic steatosis in high-fat diet-induced and leptin-deficient (ob/ob) obese mice irrespective of body weight reduction. In the obese mice, ipragliflozin-induced hyperphagia occurred to increase energy intake, attenuating body weight reduction with increased epididymal fat mass. There is an inverse correlation between weights of liver and epididymal fat in ipragliflozin-treated obese mice, suggesting that ipragliflozin treatment promotes normotopic fat accumulation in the epididymal fat and prevents ectopic fat accumulation in the liver. Despite increased adiposity, ipragliflozin ameliorates obesity-associated inflammation and insulin resistance in epididymal fat. Clinically, ipragliflozin improves liver dysfunction in patients with T2DM irrespective of body weight reduction. These findings provide new insight into the effects of SGLT2 inhibitors on energy homeostasis and fat accumulation and indicate their potential therapeutic efficacy in T2DM-associated hepatic steatosis.

Novel cystine transporter in renal proximal tubule identified as a missing partner of cystinuria-related plasma membrane protein rBAT/SLC3A1

Heterodimeric amino acid transporters play crucial roles in epithelial transport, as well as in cellular nutrition. Among them, the heterodimer of a membrane protein b(0,+)AT/SLC7A9 and its auxiliary subunit rBAT/SLC3A1 is responsible for cystine reabsorption in renal proximal tubules. The mutations in either subunit cause cystinuria, an inherited amino aciduria with impaired renal reabsorption of cystine and dibasic amino acids. However, an unsolved paradox is that rBAT is highly expressed in the S3 segment, the late proximal tubules, whereas b(0,+)AT expression is highest in the S1 segment, the early proximal tubules, so that the presence of an unknown partner of rBAT in the S3 segment has been proposed. In this study, by means of coimmunoprecipitation followed by mass spectrometry, we have found that a membrane protein AGT1/SLC7A13 is the second partner of rBAT. AGT1 is localized in the apical membrane of the S3 segment, where it forms a heterodimer with rBAT. Depletion of rBAT in mice eliminates the expression of AGT1 in the renal apical membrane. We have reconstituted the purified AGT1-rBAT heterodimer into proteoliposomes and showed that AGT1 transports cystine, aspartate, and glutamate. In the apical membrane of the S3 segment, AGT1 is suggested to locate itself in close proximity to sodium-dependent acidic amino acid transporter EAAC1 for efficient functional coupling. EAAC1 is proposed to take up aspartate and glutamate released into luminal fluid by AGT1 due to its countertransport so that preventing the urinary loss of aspartate and glutamate. Taken all together, AGT1 is the long-postulated second cystine transporter in the S3 segment of proximal tubules and a possible candidate to be involved in isolated cystinuria.

SGLT2 Inhibitors: Glucotoxicity and Tumorigenesis Downstream the Renal Proximal Tubule?

At present, diabetes mellitus is the main cause of end-stage renal disease. Effective glycaemic management is the most powerful tool to delay the establishment of diabetic complications, such as diabetic kidney disease. Together with reducing blood glucose levels, new anti-diabetic agents are expected not only to control the progression but also to restore known defects of the diabetic kidney. Sodium-glucose co-transporter 2 (SGLT2) inhibitors are promising anti-diabetic agents that reduce hyperglycaemia by impairing glucose reabsorption in proximal tubule of the kidney and increasing glucosuria. SGLT2 inhibitors have shown to reduce glucotoxicity in isolated proximal tubule cells and also to attenuate expression of markers of overall kidney damage in experimental animal models of diabetes, but the actual renoprotective effect for downstream nephron segments is still unknown and deserves further attention. Here, we briefly discuss possible undesired effects of enhanced glucosuria and albuminuria in nephron segments beyond the proximal tubule after SGLT2 inhibitor treatment, offering new lines of research to further understand the renoprotective action of these anti-diabetic agents. Strategies blocking glucose reabsorption by renal proximal tubule epithelial cells (RPTEC) may be protective for RPTEC, but downstream nephron segments will still be exposed to high glucose and albumin levels through the luminal face. The actual effect of constant enhanced glucosuria over distal nephron segments remains to be established. J. Cell. Physiol. 231: 1635-1637, 2016. © 2015 Wiley Periodicals, Inc.

Abstract 16993: Sex Differences in Renal Transporter Profile Indicate Lower Proximal Reabsorption in Females

Females have lower blood pressure than males before menopause, blunted hypertensive response to AngII, and a leftward shift in pressure natriuresis. Estrogen decreases renal ACE and AT1R and increases NO and AT2R. At the renal transporter level, distal tubule Na+-Cl- cotransporter (NCC) is upregulated by estrogen and more abundant in females, while the loop of Henle (LH) Na+-K+-2Cl- cotransporter (NKCC2) is less abundant. This study aimed to compare female to male apical Na+ transporters’ abundance, distribution, phosphorylation and cleavage and to determine the functional consequences of the differences. Sprague Dawley rats were fasted overnight then fed a 0%KCl meal before termination. The figure displays relative abundance of total and modified (P -phosphorylated, CL-cleaved, FL-full length) transporters expressed along the nephron in females versus males (defined as 1.0), determined by quantitative immunoblotting. Lower abundance of NaPi2, villin, myosin VI, together with higher NHE3-P (inactivation marker) suggest less proximal tubule (PT) reabsorption in females. Confocal immunohistochemistry confirmed that NHE3 localized to the base of the PT microvilli in females (not males) and endogenous CLi+, a marker of volume leaving the PT, was twice as high in females than males. While LH NKCC2 and its regulatory kinase SPAK were not significantly different, distal NCC, and activated NCC-P were more abundant in females, although thiazide sensitive natriuresis was not greater. ENaC α and γ subunits were more activated (-CL) in females. A saline challenge (7% of b.w. saline, i.p.) demonstrated that females excreted a saline load more rapidly than males. Taken together, these results suggest that lower proximal transporters and reabsorption provoke a volume load dependent elevation in NCC and ENaC. This profile in females likely facilitates pressure natriuresis and maintains lower blood pressures.

The Protective Effect of Apocynin on Cyclosporine A-Induced Hypertension and Nephrotoxicity in Rats.

Cyclosporine A (CsA) is the prototype of immunosuppressant drugs that has provided new perspectives in human and veterinary medicine to prevent organ transplant rejection and to treat certain autoimmune diseases and dermatologic diseases. Unfortunately, the treatment with CSA is often limited by severe adverse effects such as hypertension and nephrotoxicity. Some data suggest that reactive oxygen species (ROS) and the oxidative stress play an important role in its pathogenesis, in particular the superoxide (O2 (-)) that is the most powerful free radical generated by nicotinamide adenine dinucleotide phosphate (NADPH) oxidase present mainly in the kidney. The present study has been designed to investigate the role of Apocynin a selective inhibitor of NADPH oxidase activity on cyclosporine-induced adverse effect. In this study, we have evaluated the effect of CsA, used alone or in association with Apocynin on blood pressure (BP), on glomerular filtration rate (GFR), on absoluted fluid reabsorption (Jv) in proximal tubule (PT), on O2 (-) concentration, and on nitric oxide (NO) production. We have demonstrated that CsA administration increases superoxide concentration in the aorta, decreases the NO concentration, reduces GFR and the Jv in PT, and induces a significant increase in BP. Moreover, we have shown that Apocynin treatment restores these hemodynamic alterations, as well as NO and superoxide productions. In conclusion, the reported data indicate that CsA induced nephrotoxicity and hypertension are related to NADPH oxidase activity, in fact Apocynin protects the kidney function and BP from toxic effects induced by CsA through the inhibition of NADPH oxidase activity.

A comprehensive review of the pharmacodynamics of the SGLT2 inhibitor empagliflozin in animals and humans.

Empagliflozin (formerly known as BI 10773) is a potent, competitive, and selective inhibitor of the sodium glucose transporter SGLT2, which mediates glucose reabsorption in the early proximal tubule and most of the glucose reabsorption by the kidney, overall. Accordingly, empagliflozin treatment increased urinary glucose excretion. This has been observed across multiple species including humans and was reported under euglycemic conditions, in obesity and, most importantly, in type 2 diabetic patients and multiple animal models of type 2 diabetes and of type 1 diabetes. This led to a reduction in blood glucose, smaller blood glucose excursions during oral glucose tolerance tests, and, upon chronic treatment, a reduction in HbA1c in animal models and patients. In rodents, such effects were observed in early and late phases of experimental diabetes and were associated with preservation of pancreatic β-cell function. Combination studies in animals demonstrated that beneficial metabolic effects of empagliflozin may also manifest when added to other types of anti-hyperglycemic treatments including linagliptin and pioglitazone. While some anti-hyperglycemic drugs lead to weight gain, empagliflozin treatment was associated with reduced body weight in normoglycemic obese and non-obese animals despite an increased food intake, largely due to a loss of adipose tissue; on the other hand, empagliflozin preserved body weight in models of type 1 diabetes. Empagliflozin improved endothelial dysfunction in diabetic rats and arterial stiffness, reduced blood pressure in diabetic patients, and attenuated early signs of nephropathy in diabetic animal models. Taken together, the SGLT2 inhibitor empagliflozin improves glucose metabolism by enhancing urinary glucose excretion; upon chronic administration, at least in animal models, the reductions in blood glucose levels are associated with beneficial effects on cardiovascular and renal complications of diabetes.

Parathyroid hormone inhibition of Na+/H+ exchanger 3 transcription: Intracellular signaling pathways and transcription factor expression

The main transport mechanism of reabsorption of sodium bicarbonate and fluid in the renal proximal tubules involves Na+/H+ exchanger 3 (NHE3), which is acutely and chronically downregulated by parathyroid hormone (PTH). Although PTH is known to exert an inhibitory effect on NHE3 expression and transcription, the molecular mechanisms involved remain unclear. Here, we demonstrated that, in opossum kidney proximal tubule (OKP) cells, PTH-induced inhibition of Nhe3 gene promoter occurs even in the core promoter that controls expression of the reporter gene. We found that inhibition of the protein kinase A (PKA) and Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathways transformed PTH from an inhibitor of promoter activity into an activator of that same activity, as did point mutations in the EGR1, Sp1, and Sp3 binding consensus elements in the promoter. In nuclear extracts of PTH-treated OKP cells, we also observed increased expression of EGR1 mRNA and of some Sp3 isoforms. Electrophoretic mobility shift assay showed a supershift of the −61 to −42-bp probe with an anti-EGR1 antibody in PTH-treated cells, suggesting that EGR1 binding is relevant for the inhibitory activity of PTH. We conclude that PTH-induced inhibition of NHE3 transcription is related to higher EGR1 expression; to EGR1 binding to the proximal and core promoters; and to PKA and JAK/STAT pathway activation. This mechanism might be responsible, at least in part, for lower NHE3 expression and sodium reabsorption in renal proximal tubules in the presence of high PTH levels.

Intravital Imaging of the Kidney in Salt‐Sensitive Hypertension

Previous studies performed in rat kidneys shed light on the complexities of glomerular filtration of albumin and reabsorption at the proximal tubule (PT). It is now established that both PT reabsorption and transcytosis and glomerular filtration are responsible for determining the extent of albuminuria. Since hypertension is one of the most prevalent diseases worldwide, and is a major risk factor for developing albuminuria and renal failure, we investigated the mechanisms leading to albuminuria in the kidney of a rat model of salt‐sensitive hypertension, the Dahl SS rat. To determine the relative contributions of the glomerulus and PT to albuminuria in the SS rat, we applied the novel intravital two‐photon imaging to investigate the changes in renal function that occur during the development of salt‐sensitive hypertension (at 3, 7 and 14 days of high salt (HS) diet). Our results indicate that high amounts of albumin are filtered at the glomerulus in SS rats fed a low salt (LS) diet (GSCalb = 0.0155). Following HS diet consumption for 14 days, we observed significant elevations in blood pressure and albuminuria, increased prevalence of white blood cells (WBCs) within the kidneys (+Δ1.33 WBCs/image), and significant tubular damage as indicated by increased abundance of cast material (+Δ2.20 casts/image), compared to LS‐fed rats. We also observed a 57% increase in glomerular sieving of albumin (GSCalb = 0.0244) and a 58% reduction in PT reabsorption of albumin. Collectively, these results indicate that both the glomerulus and PT contribute to albuminuria in SS hypertensive rats.