Tubular Sodium Reabsorption Research Articles

Acromegaly and it's cardiovascular implications

Acromegaly is a chronic and slowly progressive disease that results from the hypersecretion of growth hormone (GH) and consequently insulin-like growth factor type 1 (IGF-1), due to a GH-secreting pituitary adenoma in 95-98% of cases. There are several complications or co-morbidities associated with acromegaly, the most frequent being cardiovascular, metabolic and neoplastic. The cardiovascular complications of acromegaly go from arterial hypertension to a peculiar form of cardiomyopathy and are the result of the long-standing exposure to high GH and IGF-1 levels. The pathophysiology of these complications is complex and includes an increased tubular reabsorption of sodium and the direct effects of GH and IGF-1 on the endothelium and the cardiac tissue itself. Frequently, the cardiovascular comorbidities of acromegaly occur concomitantly with metabolic complications such as diabetes and respiratory abnormalities such as the sleep apnea syndrome. In this brief review we analyze the pathophysiology, the clinical manifestations and the management of the cardiovascular complications of acromegaly.

Current Understanding of Pressure Natriuresis.

Pressure natriuresis refers to the concept that increased renal perfusion pressure leads to a decrease in tubular reabsorption of sodium and an increased sodium excretion. The set point of blood pressure is the point at which pressure natriuresis and extracellular fluid volume are in equilibrium. The term "abnormal pressure natriuresis" usually refers to the expected abnormal effect of a certain level of blood pressure on sodium excretion. Factors that cause abnormal pressure natriuresis are known. Sympathetic nerve system, genetic factors, and dietary factors may affect an increase in renal perfusion pressure. An increase in renal perfusion pressure increases renal interstitial hydrostatic pressure (RIHP). Increased RIHP affects tubular reabsorption through alterations in tight junctional permeability to sodium in proximal tubules, redistribution of apical sodium transporters, and/or release of renal autacoids. Renal autocoids such as nitric oxide, prostaglandin E2, kinins, and angiotensin II may also regulate pressure natriuresis by acting directly on renal tubule sodium transport. In addition, inflammation and reactive oxygen species may mediate pressure natriuresis. Recently, the use of new drugs associated with pressure natriuretic mechanisms, such as angiotensin receptor neprilysin inhibitor and sodium glucose co-transporter 2 inhibitors, has been consistently demonstrated to reduce mortality and hypertension-related complications. Therefore, the understanding of pressure natriuresis is gaining attention as an antihypertensive strategy. In this review, we provide a basic overview of pressure natriuresis to the target audience of nephrologists.

AT II Receptor Blockade and Renal Denervation: Different Interventions with Comparable Renal Effects?

Background: Angiotensin II (Ang II) and the renal sympathetic nervous system exert a strong influence on renal sodium and water excretion. We tested the hypothesis that already low doses of an Ang II inhibitor (candesartan) will result in similar effects on tubular sodium and water reabsorption in congestive heart failure (CHF) as seen after renal denervation (DNX). Methods: Measurement of arterial blood pressure, heart rate (HR), renal sympathetic nerve activity (RSNA), glomerular filtration rate (GFR), renal plasma flow (RPF), urine volume, and urinary sodium. To assess neural control of volume homeostasis, 21 days after the induction of CHF via myocardial infarction rats underwent volume expansion (0.9% NaCL; 10% body weight) to decrease RSNA. CHF rat and controls with or without DNX or pretreated with the Ang II type-1 receptor antagonist candesartan (0.5 ug i.v.) were studied. Results: CHF rats excreted only 68 + 10.2% of the volume load (10% body weight) in 90 min. CHF rats pretreated with candesartan or after DNX excreted from 92 to 103% like controls. Decreases of RSNA induced by volume expansion were impaired in CHF rats but unaffected by candesartan pointing to an intrarenal drug effect. GFR and RPF were not significantly different in controls or CHF. Conclusion: The prominent function of increased RSNA – retaining salt and water – could no longer be observed after renal Ang II receptor blockade in CHF rats.

Congestive nephropathy: a neglected entity? Proposal for diagnostic criteria and future perspectives.

Venous congestion has emerged as an important cause of renal dysfunction in patients with cardiorenal syndrome. However, only limited progress has been made in differentiating this haemodynamic phenotype of renal dysfunction, because of a significant overlap with pre‐existing renal impairment due to long‐term hypertension, diabetes, and renovascular disease. We propose congestive nephropathy (CN) as this neglected clinical entity. CN is a potentially reversible subtype of renal dysfunction associated with declining renal venous outflow and progressively increasing renal interstitial pressure. Venous congestion may lead to a vicious cycle of hormonal activation, increased intra‐abdominal pressure, excessive renal tubular sodium reabsorption, and volume overload, leading to further right ventricular (RV) stress. Ultimately, renal replacement therapy may be required to relieve diuretic‐resistant congestion. Effective decongestion could preserve or improve renal function. Congestive acute kidney injury may not be associated with cellular damage, and complete renal function restoration may be a confirmatory diagnostic criterion. In contrast, a persistently low renal perfusion pressure might induce renal dysfunction and histopathological lesions with time. Thus, urinary markers may differ. CN is mostly seen in biventricular heart failure but may also occur secondary to pulmonary arterial hypertension and elevated intra‐abdominal pressure. An increase in central venous pressure to >6 mmHg is associated with a steep decrease in glomerular filtration rate. However, the central venous pressure range that can provide an optimal balance of RV and renal function remains to be determined. We propose criteria to identify cardiorenal syndrome subgroups likely to benefit from decongestive or pulmonary hypertension‐specific therapies and suggest areas for future research.

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

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

Stimulation of Structural and Functional Recovery of the Kidney in Rats with Postischemic Acute Renal Failure of Different Severity by Embryonic Protein-Peptide Complex Therapy.

In male rats, acute renal failure was simulated by clamping the vascular pedicle of the left kidney for 60 or 90 min and right-sided nephrectomy. In the control series, no therapy was performed. In the experimental series, the animals were daily injected subcutaneously with Cellex, a protein-peptide complex (PPC) chromatographically isolated from the brain tissue of pig embryos with a molecular weight of its components from 10 to 250 kDa. PPC was administered 5 times a week (10 injections) in a dose of 0.1 ml/kg (0.1 mg active substance per 1 kg body weight). Ischemia of a single kidney led to the development of acute renal failure, more severe after 90-min ischemia. PPC therapy reduced the severity of functional disorders mainly at the early stages (3 and 7 days) with normalization of blood concentrations of urea and creatinine, creatinine clearance, tubular reabsorption of sodium and calcium, including the cases with 90-min ischemia, which did not occur in the control series. PPC therapy also contributed to hypertrophy of many glomeruli, prevented the development of glomerulosclerosis, and reduced damage to the epithelium of the renal tubules. At the same time, neither pronounced lymphohistiocytic infiltration, nor focal nephrosclerosis typical of control series were observed.

Abstract P147: Attenuation Of Diuretic And Natriuretic Responses To Acute Saline Volume Expansion In Mice Pre-treated With Tumor Necrosis Factor-alpha (TNFα) Inhibitor, Etanercept.

High salt intake induces an immune response that activates the mononuclear phagocyte system (MPS) cells to produce TNFα. We have previously demonstrated that intravenous infusion of TNFα in mice induces diuresis and natriuresis by inhibiting renal tubular sodium reabsorption. We hypothesize that the intravenous saline infusion can also induce the production of TNFα from MPS cells and such increase in TNFα influences saline induced natriuresis in the kidney. To examine this hypothesis, we measured the changes in TNFα levels in plasma and in urinary excretion rate (U TNFα V) during intravenous infusion of isotonic saline (0.9% NaCl), first at euvolemic condition (3 μL/min for 60 min; Baseline period) and then at an enhanced infusion rate (12 μL/min for 90 min; Volume expansion period) in anesthetized mice (n=5). Renal blood flow (RBF) and glomerular filtration rate (GFR) were measured by PAH and inulin clearances respectively. TNFα concentration in plasma and urine samples were determined using ELISA kit (Ebioscience, Woburn, MA). TNFα level in plasma collected during baseline period was undetectable, however, TNFα was increased to 3.7±1.3 pg/mL during volume expansion (VE) period. Baseline U TNFα V level was 0.01±0.002 pg/min/g (kidney wt), which was increased to 0.11±0.03 pg/min/g (P<0.05) during VE period. VE increased urine flow (V, 5.4±0.5 to 22.0±5.1 μL/min/g; P<0.05) and sodium excretion (U Na V; 0.54±0.19 to 4.84 ±1.16 μmol/min/g; P<0.05) without significant changes in RBF (7.1±1.0 to 6.0±1.8 mL/min/g) and GFR (1.18±0.11 to 0.94±0.28 mL/min/g). Interestingly, the diuretic and natriuretic responses to VE were markedly attenuated in mice (n=5) pretreated with a TNFα inhibitor, etanercept (ETN; 0.5 mg/kg intraperitoneally once daily for 3 days prior to the experiment day). VE induced changes in ETN treated mice are as follows: V, 5.9±0.65 to 7.9 ±1.6 μL/min/g; U Na V, 0.43±0.6 to 1.1±0.28 μmol/min/g; RBF, 5.4±0.4 to 6.6±0.9 mL/min/g and GFR, 0.87±0.09 to 0.98±0.13 mL/min/g. These findings demonstrate for the first time that an intravenous saline volume infusion resulted an increase in TNFα level in plasma and in urine. These results strongly suggest a physiological role for TNFα in regulating renal excretory function during saline volume expansion.

Sodium-glucose cotransporter 2 inhibitors (SGLT2i): renal implications

Type 2 diabetes mellitus (DM2) is a chronic condition that affects more than 400 million individuals worldwide. In DM2 patients, an appropriate glycemic control slows the onset and delays the progression of all its micro and macrovascular complications. Even though there are several glucose-lowering drugs, only approximately half of patients achieve glycemic control, while undesirable adverse effects (e.g., low serum glucose) normally affect treatment. Therefore, there is a need for new types of treatments. Sodium-glucose cotransporter 2 inhibitors (SGLT2i) have just been developed for treating DM2. Renal hyperfiltration as a marker of increased intraglomerular pressure in diabetic patients, and the role of renin-angiotensin-aldosterone system (RAAS) in this phenomenon have been studied. Nevertheless, RAAS blockade does not completely reduce hyperfiltration or diabetic renal damage. In this sense, the contribution of renal tubular factors to the hyperfiltration state, including sodium-glucose cotransporter (SGLT), has been currently studied. SGLT2i reduce proximal tubular sodium reabsorption, therefore increasing distal sodium delivery to the macula densa, causing tubule-glomerular feedback activation, afferent vasoconstriction, and reduced hyperfiltration in animal models. In humans, SGLT2i was recently shown to reduce hyperfiltration in normotensive, normoalbuminuric patients suffering from type 1 diabetes mellitus. In DM2 clinical trials, SGLT2 is associated with significant hyperfiltration and albuminuria reduction. The aim of this article is to compile the information regarding SGLT2i drugs, emphasizing its mechanism of renal repercussion.

Isotonic saline infusion increases plasma and urinary levels of tumor necrosis factor‐alpha (TNFα) in mice; evidence for a physiological role of this cytokine in regulating renal function during saline volume expansion.

Although TNFα is considered to play its role in many pathological conditions, the physiological role of this cytokine in regulating many organs’ function including the kidney is increasingly recognized in recent days. Chronic high salt (HS) intake in diet induces an immune response that activates the mononuclear phagocyte system (MPS) cells to release TNFα that appears in the circulation in its soluble form (sTNFα). It has been shown that HS (4% NaCl) diet alone for 2 weeks increased MPS cell infiltration in the renal tissue in mice and this is associated with increases in the circulating sTNFα level in the plasma (Singh et al‐2013). It was also demonstrated that 1% salt added to the drinking water for 3 days in mice increases the urinary excretion rate of sTNFα indicating that its release in the kidney from the infiltrated MPS cells occur even at the early stage of HS intake (Hao et al‐2013). We have previously demonstrated that intravenous infusion of recombinant TNFα in mice induces natriuretic response by inhibiting tubular sodium reabsorption (Shahid et al‐2008; Majid‐2011). We hypothesize that the intravenous saline infusion can also induce the production of sTNFα from activated MPS cells due to an increase in salt content in immune tissues and such increase in sTNF influences saline induced natriuretic response in the kidney. To examine this hypothesis, we measured the changes in sTNFα levels in plasma and urinary excretion rate (UTNFαV) during intravenous infusion of isotonic saline (0.9% NaCl), first at euvolemic conditions (3 μL/min for 60 min; Baseline period) and then at an enhanced infusion rate (12 μL/min for 90 min; saline volume infusion period) in anesthetized mice (n=5). The concentration of sTNFα in plasma and urine samples were determined using ELISA kit (Ebioscience, Woburn, MA) for measuring this cytokine. Baseline level of plasma sTNFα was undetectable, however, the level was increased to 3.7±1.3 pg/mL during saline volume infusion period. Baseline UTNFαV level was 0.01±0.002 pg/min/g of kidney wt, which was increased to 0.11±0.03 pg/min/g (P<0.05) during volume infusion period. In another group of mice (n=5) pretreated with a TNFα inhibitor, etanercept (0.5 mg/kg intraperitoneally once daily for 3 days prior to the experiment day), it was observed that this increase in UTNFαV during saline volume infusion period was markedly attenuated (0.003±0.002 to 0.006±0.004 pg/min/g; P=n.s.). The usual natriuretic response (0.5±0.2 to 3.8 ±1.1 μmol/min/g; P<0.05) to saline volume infusion observed in control mice was seen markedly attenuated (0.4±0.1 to 0.8±0.3 μmol/min/g; P=n.s.) in etanercept pretreated mice. These findings demonstrate for the first time that an intravenous saline volume infusion resulted an increase in sTNFα level in plasma and in urine. These results strongly suggest a physiological natriuretic role for sTNFα in regulating renal excretory function during saline volume expansion.

Interplay of adenosine monophosphate-activated protein kinase/sirtuin-1 activation and sodium influx inhibition mediates the renal benefits of sodium-glucose co-transporter-2 inhibitors in type 2 diabetes: A novel conceptual framework.

Long-term treatment with sodium-glucose co-transporter-2 (SGLT2) inhibitors slows the deterioration of renal function in patients with diabetes. This benefit cannot be ascribed to an action on blood glucose, ketone utilization, uric acid or systolic blood pressure. SGLT2 inhibitors produce a striking amelioration of glomerular hyperfiltration. Although initially ascribed to an action of these drugs to inhibit proximal tubular glucose reabsorption, SGLT2 inhibitors exert renoprotective effects, even in patients with meaningfully impaired levels of glomerular function that are sufficient to abolish their glycosuric actions. Instead, the reduction in intraglomerular pressures may be related to an action of SGLT2 inhibitors to interfere with the activity of sodium-hydrogen exchanger isoform 3, thereby inhibiting proximal tubular sodium reabsorption and promoting tubuloglomerular feedback. Yet, experimentally, such an effect may not be sufficient to prevent renal injury. It is therefore noteworthy that the diabetic kidney exhibits an important defect in adenosine monophosphate-activated protein kinase (AMPK) and sirtuin-1 (SIRT1) signalling, which may contribute to the development of nephropathy. These transcription factors exert direct effects to mute oxidative stress and inflammation, and they also stimulate autophagy, a lysosomally mediated degradative pathway that maintains cellular homeostasis in the kidney. SGLT2 inhibitors induce both AMPK and SIRT1, and they have been shown to stimulate autophagy, thereby ameliorating cellular stress and glomerular and tubular injury. Enhanced AMPK/SIRT1 signalling may also contribute to the action of SGLT2 inhibitors to interfere with sodium transport mechanisms. The dual effects of SGLT2 inhibitors on AMPK/SIRT1 activation and renal tubular sodium transport may explain the protective effects of these drugs on the kidney in type 2 diabetes.

Pathways of hepatic and renal damage through non-classical activation of the renin-angiotensin system in chronic liver disease.

In liver cirrhosis, renin-angiotensin system (RAS) activation sustains renal sodium retention and hepatic fibrogenesis. New information has recently enlivened the traditional concept of RAS. For instance, renin and prorenin bind their ubiquitous receptors, resulting in the local production of angiotensin (Ang) II; increased serum calcium and calcimimetic agents, through stimulation of extracellular calcium-sensing receptors (CaSR), blunt renin production and lead to natriuretic effects in human and experimental cirrhosis. Alongside systemic production, there is Ang II tissue production within various organs through RAS enzymes different from angiotensin-converting enzyme (ACE), that is chymase, tissue plasminogen activator and several cathepsins. In experimental cirrhosis, inhibition of chymase leads to natriuretic and hepatic antifibrotic effects, without changes in systemic haemodynamics. In the kidney, local RAS coordinates proximal and distal tubular sodium reabsorption. However, renalase, whose plasma and tissue levels are severely altered in experimental cirrhosis, degrades systemic and renal tubule catecholamines, antagonizing the effects of renal RAS. Angiotensinogen-derived natriuretic and vasodilating peptides (Ang1-9, Ang1-7, Ang3-8) and their receptors have been described. Receptor agonists or antagonists are available to affect portal hypertension and sodium retention in cirrhosis. ACE2-dependent generation of Ang1-7 may inhibit experimental liver fibrosis. inhibition of Ang1-7 clearance by means of neprilysin blockade has portal hypotensive and natriuretic effects. Ang1-12, whose production renin does not regulate, is converted to several different angiotensin peptides via chymase. Finally, Ang II behaves as either an antinatriuretic or a natriuretic agent, based on the tissue content of AT1 R and AT2 R receptors, their ratio being prone to pharmacological modulation.

Antihypertensive Treatment Guided by Gene Profiling. The First Randomised Clinical Proof of Concept Trial Proving Feasibility in Man, Comparing Rostafuroxin with Losartan

Background: The feasibility of an individual's genetic background to guide antihypertensive drug treatment to replace the current one-size-fits-all strategy remains to be proven. Activation of the Na-K pump signalling pathway by proteins encoded by genetic variants of adducin and enzymes involved in the endogenous ouabain synthesis and transport lead to increased renal tubular sodium reabsorption, volume expansion and hypertension. Rostafuroxin is a powerful, safe and selective inhibitor of these mechanisms. This study is aimed at evaluating whether rostafuroxin is more effective than losartan in reducing blood pressure in carriers of these gene variants. Methods: In a parallel-group, double-masked, randomised phase 2 trial, 13 Italian and 15 Taiwanese centres enrolled never-treated (naive) patients with office blood pressure ranging from 140 to 169 mmHg systolic (OSBP) and from 85 to 100 mmHg diastolic (ODBP) blood pressure, respectively. After stratification for country and genetic background (variants in ADD1, ADD3, ABCB1/MDR1, HSD3B1, and LSS genes grouped in profile 2 (P2), as described in the previous OASIS-HT study or with the addition of other gene variants grouped in the profile 1(P1) , patients were randomised using a computerised random function to rostafuroxin 6 γ (in Italy only), 50 γ or 500 γ or losartan 50 mg, all once daily. The OSBP change two months after randomisation was the primary endpoint. The study is registered with ClinicalTrials.gov, NCT03217825 and with EudraCT number, 2010-022073-34. Findings: Of 902 screened patients, 171/470 (36·4%) were enrolled in Italy and 107/432 (24·8%) in Taiwan, of whom two Italian and five Taiwanese were excluded. In Caucasians carrying P2a, from a baseline around 150 mmHg, OSBP significantly (p value from=0.002 to <0.001) decreased in mmHg (95% confidence interval) 10·8 (4·0-17·5), 23·0 (16·0-29·9), 17·4 (11·0-23·7), and 13·2 (7·2-19·2) on 6, 50 and 500 γ rostafuroxin and 50 mg losartan, respectively. The between-group differences (rostafuroxin 50 γ minus losartan) was 9·8 (0·6-19·0) with p=0·038 and 13·4 (25·4-2·5) with p=0·031 in P2a and LSS 2254524 AA carriers respectively, but not for the other rostafuroxin doses (p=0·319). Chinese with corresponding genetic background, had similar OSBP fall to that of Caucasians with losartan but no change with rostafuroxin. Serious adverse events: none in Caucasian and one in Chinese. Interpretation: The tendency towards a bell-shaped OSBP dose-response curve in Caucasians with a maximum at 50 γ is in line with previous observations and represents the first proof-of-concept in humans that genetic profiling may in the future guide antihypertensive drug treatment. This opens new perspectives for drugs design, based on genetically encoded variability in proteins causally involved in the pathogenesis of hypertension. Funding: CVie Therapeutics and Windtree Therapeutics. Declaration of Interest: GB, as it may be seen from the introduction and discussion, this study is the last of a long series aimed at detecting a target “causal” molecular mechanism(s) of hypertension amenable to be “corrected” by a small molecule in patients. To this end, GB was employee of the Universita Vita Salute San Raffaele, Milano and consultant of pharmaceutical companies, that changed over time (Prassis Sigma Tau; CVie Therapeutics, Taipei; Windtree Therapeutics, Warrington, USA), receiving a salary from the former and a consultancy from the latters, this being well known to both parties. In 2015, as Emeritus Professor, GB changed his position from consultant to employee at CVie Therapeutics first and at Windtree Therapeutics later. PF is consultant of CVie Therapeutics, Taipei, Taiwan first, and then of Windtree Therapeutics, Warrington, PA, USA. LC and SC received personal fees from CVie Therapeutics, Taipei, Taiwan. LFL was employee of CVie Therapeutics Taipei Taiwan. BL was CEO of CVie therapeutics Taipei Taiwan. CVie Therapeutis and Windree Therapeutics paid research grants for this study to the Institutions of GAS, NG, RB, CEC, TDW, and KLW, PM. DC, JAS and CL have no conflicts of interest to declare. Ethical Approval: Local ethics committees approved the research protocol.

PKB is a central molecule in the modulation of Na+-ATPase activity by albumin in renal proximal tubule cells

Evidence points to a possible role of tubular sodium reabsorption in worsening renal injury. Proximal tubule (PT) albumin overload is a critical process in the development of tubule-interstitial injury (TII), and consequently in progression of renal disease. We studied the possible correlation between changes in albumin concentration in the lumen of PT with modification of Na+-ATPase activity. An albumin overload animal model and LLC-PK1 cells as a model of PT cells were used. Albumin overload was induced by intraperitoneal injection of BSA in 14-week-old male Wistar rats. An increase in sodium clearance, fractional excretion of sodium, proteinuria, ratio between urinary protein and creatinine, and albuminuria were observed. These observations indicate that there could be a correlation between an increase in albumin in the lumen of PTs and renal sodium excretion. We observed that the activity of both Na+-ATPase and (Na++K+)ATPase decreased in the renal cortex of an albumin overload animal model. Using LLC-PK1 cells as a model of PT cells, inhibition of Na+-ATPase activity was observed with higher albumin concentrations, similar to that observed in the animal model. The inhibition of protein kinase B by higher albumin concentration was found to be a critical step in the inhibition of Na+-ATPase activity. Interestingly, activation of the ERK1/2/mTORC1/S6K pathway was required for protein kinase B inhibition. This mechanism leads to a decrease in protein kinase C activity and, consequently to inhibition of Na+-ATPase activity. Taken together, our results indicate that the molecular mechanism underlying the modulation of PT Na+-ATPase activity by albumin overload involves activation of the ERK1/2/mTORC1/S6K pathway, which leads to inhibition of the mTORC2/PKB/PKC pathway. Our findings contribute to better understanding regarding handing of renal Na+ induced by albumin overload in the lumen of PTs and, consequently, in the progression of renal disease.

Abstract 081: Ghrelin is Produced by the Kidney and Mediates Distal Tubular Sodium Reabsorption in Rats

Ghrelin is a 28-amino acid peptide hormone that exerts powerful appetite-stimulating effects. Ghrelin receptor expression has been reported in the collecting duct, but the role of ghrelin in the kidney is unknown. The present studies confirmed ghrelin mRNA expression in inner medullary collecting duct cells (N=6) using RT PCR and sequencing of the 320-bp PCR product. Ghrelin peptide expression was also confirmed in these cells using immunohistochemistry and flow cytometry. To test intrarenal ghrelin action, 12-week-old uninephrectomized female Sprague-Dawley rats (N=26) received 3 bolus injections of ghrelin siRNA (N=7) or scrambled siRNA (N=7) into the renal interstitial (RI) space of the remaining kidney, each injection 48h apart. Following the last injection, rats received three, 1h RI infusions of 5% dextrose in water. Mean arterial pressure (MAP), urine sodium (Na + ) excretion (U Na V), glomerular filtration rate (GFR), fractional excretion of Na + (FE Na ), and fractional excretion of lithium (FE Li ) were calculated. In a separate set of rats, renal blood flow (RBF) was measured for 1h (N=6 for both ghrelin siRNA and scrambled siRNA). RI ghrelin siRNA-infused rats demonstrated significantly higher U Na V compared to scrambled siRNA-infused rats for all 3 periods (0.29±0.06 vs. 0.09±0.01, 0.35±0.09 vs. 0.11±0.03, and 0.27±0.07 vs. 0.09±0.02 μmol/min; P&lt;0.01, P&lt;0.05, and P&lt;0.05 respectively) and significantly increased FE Na compared to scrambled siRNA infused rats (0.26±0.05 vs. 0.11±0.02, 0.35±0.06 vs. 0.11±0.03, and 0.24±0.04 vs. 0.10±0.03%; P&lt;0.05, P&lt;0.01, and P&lt;0.05 respectively). There were no differences in in GFR, FE Li , MAP, or RBF. Since the increase in U Na V was not accompanied by similar increases in GFR, the effect of renal ghrelin inhibition suggested a tubular rather than hemodynamic, mechanism of action. To localize the specific tubular site, events distal to the renal proximal tubule were identified by changes in FE Na that occurred independently of changes in FE Li . RI ghrelin siRNA significantly increased FE Na without altering FE Li , suggesting distal nephron-dependent Na + reabsorption. Together, these data introduce ghrelin as a novel intrarenal peptide responsible for tonic Na + reabsorption at the level of the distal nephron.

Role of carbonic anhydrase in acute recovery following renal ischemia reperfusion injury.

Ischemia reperfusion (IR) injury can cause acute kidney injury. It has previously been reported that kidney oxygen consumption (QO2) in relation to glomerular filtration rate (GFR), and thus tubular sodium load, is markedly increased following IR injury, indicating reduced electrolyte transport efficiency. Since proximal tubular sodium reabsorption (TNa) is a major contributor to overall kidney QO2, we investigated whether inhibition of proximal tubular sodium transport through carbonic anhydrase (CA) inhibition would improve renal oxygenation following ischemia reperfusion. Anesthetized adult male Sprague Dawley rats were administered the CA inhibitor acetazolamide (50 mg/kg bolus iv), or volume-matched vehicle, and kidney function, hemodynamics and QO2 were estimated before and after 45 minutes of unilateral complete warm renal ischemia. CA inhibition per se reduced GFR (-20%) and TNa (-22%), while it increased urine flow and urinary sodium excretion (36-fold). Renal blood flow was reduced (-31%) due to increased renal vascular resistance (+37%) without affecting QO2. IR per se resulted in similar decrease in GFR and TNa, independently of CA activity. However, the QO2/TNa ratio following ischemia-reperfusion was profoundly increased in the group receiving CA inhibition, indicating a significant contribution of basal oxygen metabolism to the total kidney QO2 following inhibition of proximal tubular function after IR injury. Ischemia increased urinary excretion of kidney injury molecule-1, an effect that was unaffected by CA. In conclusion, this study demonstrates that CA inhibition further impairs renal oxygenation and does not protect tubular function in the acute phase following IR injury. Furthermore, these results indicate a major role of the proximal tubule in the acute recovery from an ischemic insult.

Urinary extracellular vesicles: the mothership connection.

Urinary extracellular vesicles: the mothership connection.

Role of sodium/glucose cotransporter inhibition on a rat model of angiotensin II\u2013dependent kidney damage

BackgroundRenal proximal tubular sodium and glucose reabsorption are regulated by the sodium-glucose cotransporter (SGLT2). Changes in this transporter can play a role in hyperglycaemia and reactive oxygen species (ROS) production. We demonstrated increased glucose absorption in proximal tubule membrane vesicles and increased expression of SGLT2 in hypertensive rats. Here we investigated Angiotensin II (Ang II) -dependent SGLT2 expression induction and the role of SGLT2 induction in the development of Ang II-dependent kidney damage. The aim of this study was to determine whether SGLT2 induction by Ang II is associated with Ang II-dependent kidney damage. We propose the following objectives a) to demonstrate that Ang II induces SGLT2 expression and b) to demonstrate that prevention of SGLT2 expression and activity prevent Ang II-induced kidney damage.MethodsWe used chronic Ang II infusion as a model of kidney damage in male Wistar rats and evaluated systolic blood pressure by telemetric methods. SGLT2 mRNA and protein expression were evaluated by PCR and immunoblotting. SGLT2 activity was evaluated in brush border membrane vesicles by measuring glucose uptake. ROS production was measured by confocal microscopy. The glomerular filtration rate (GFR) was evaluated by the inulin excretion method, and urinary protein excretion was evaluated by the Bradford method. Biological parameter evaluations were performed, after two weeks of infusion of Ang II. We compared the effects of Angiotensin II (AT1) receptor blockade by Losartan and SGLT2 inhibition by Empagliflozin both as monotherapy treatments and in combination on the development of kidney damage.ResultsChronic Ang II infusion led to a blood pressure elevation and increased SGLT2 mRNA expression and activity as well as kidney damage, as reflected by increased ROS production, decreased GFR and increased urinary protein excretion. AT1 receptor blockade prevented all these changes. By contrast, SGLT2 inhibition did not affect blood pressure and had a small effect on kidney damage. However, the combination of both drugs resulted in the potentiation of the effects observed by AT1 receptor blockade alone.ConclusionsWe suggest that Ang II-dependent increased SGLT2 induction is one mechanism by which Ang II induces kidney damage.

Effects of Dapagliflozin on Volume Status When Added to Renin-Angiotensin System Inhibitors.

Sodium glucose co-transporter 2 (SGLT2) inhibitors reduce the risk of heart and kidney failure in patients with type 2 diabetes, possibly due to diuretic effects. Previous non-placebo-controlled studies with SGLT2 inhibitors observed changes in volume markers in healthy individuals and in patients with type 2 diabetes with preserved kidney function. It is unclear whether patients with type 2 diabetes and signs of kidney damage show similar changes. Therefore, a post hoc analysis was performed on two randomized controlled trials (n = 69), assessing effects of dapagliflozin 10 mg/day when added to renin–angiotensin system inhibition in patients with type 2 diabetes and urinary albumin-to-creatinine ratio ≥30 mg/g. Blood and 24-h urine was collected at the start and the end of treatment periods lasting six and 12 weeks. Effects of dapagliflozin compared to placebo on various markers of volume status were determined. Fractional lithium excretion, a marker of proximal tubular sodium reabsorption, was assessed in 33 patients. Dapagliflozin increased urinary glucose excretion by 217.2 mmol/24 h (95% confidence interval (CI): from 155.7 to 278.7, p < 0.01) and urinary osmolality by 60.4 mOsmol/kg (from 30.0 to 90.9, p < 0.01), compared to placebo. Fractional lithium excretion increased by 19.6% (from 6.7 to 34.2; p < 0.01), suggesting inhibition of sodium reabsorption in the proximal tubule. Renin and copeptin increased by 46.9% (from 21.6 to 77.4, p < 0.01) and 33.0% (from 23.9 to 42.7, p < 0.01), respectively. Free water clearance (FWC) decreased by −885.3 mL/24 h (from −1156.2 to −614.3, p < 0.01). These changes in markers of volume status suggest that dapagliflozin exerts both osmotic and natriuretic diuretic effects in patients with type 2 diabetes and kidney damage, as reflected by increased urinary osmolality and fractional lithium excretion. As a result, compensating mechanisms are activated to retain sodium and water.

Obesity, kidney dysfunction and hypertension: mechanistic links.

Excessive adiposity raises blood pressure and accounts for 65-75% of primary hypertension, which is a major driver of cardiovascular and kidney diseases. In obesity, abnormal kidney function and associated increases in tubular sodium reabsorption initiate hypertension, which is often mild before the development of target organ injury. Factors that contribute to increased sodium reabsorption in obesity include kidney compression by visceral, perirenal andrenal sinus fat; increased renal sympathetic nerve activity (RSNA); increased levels of anti-natriuretic hormones, such as angiotensin II and aldosterone; and adipokines, particularly leptin. The renal and neurohormonal pathways of obesity and hypertension are intertwined. For example, leptin increases RSNA by stimulating the central nervous system proopiomelanocortin-melanocortin 4 receptor pathway, and kidney compression and RSNA contribute to renin-angiotensin-aldosterone system activation. Glucocorticoids and/or oxidative stress may also contribute to mineralocorticoid receptor activation in obesity. Prolonged obesity and progressive renal injury often lead to the development of treatment-resistant hypertension. Patient management therefore often requires multiple antihypertensive drugs and concurrent treatment of dyslipidaemia, insulin resistance, diabetes and inflammation. If more effective strategies for the prevention and control of obesity are not developed, cardiorenal, metabolic and other obesity-associated diseases could overwhelm health-care systems in the future.

Acute SGLT2 Inhibition and the Pressure Natriuresis Response in Rats with Type 1 Diabetes

Increasing blood pressure (BP) induces natriuresis due to downregulation of sodium transport in the proximal tubule. This pressure natriuresis (PN) response influences long‐term BP. Type‐1 diabetic (T1DM) patients show enhanced tubular sodium reabsorption and high BP. We have found that tubular sodium reabsorption is not modulated by BP in T1DM rats. The molecular mechanism of impaired PN is unknown but the sodium‐glucose cotransporter SGLT2 is a plausible candidate and inhibitors acutely induce diuresis in T1DM rats. This study tested the hypothesis that SGLT2 inhibition with dapagliflozin would improve the acute PN response in T1DM rats.T1DM was induced in male Sprague‐Dawley rats by streptozotocin (30–45mg/kg IP; plasma glucose 13.3–&gt;35mmol). After 3 weeks rats were anaesthetised with Inactin (120mg/kg, IP). The jugular vein was cannulated and isotonic saline (containing FITC‐inulin and p‐amino hippurate for measurement of glomerular filtration rate (GFR) and renal plasma flow (RPF)) was infused. Rats were randomly allocated to receive either dapagliflozin (50mg/kg; n=7) or saline vehicle (n=7) and after an equilibration period and baseline urine collection, BP was increased by sequential arterial ligation of first the coeliac and mesenteric arteries and then the distal aorta and the natriuretic response was measured. Experiments were performed under a single blind and rats were euthanised by an overdose of anaesthetic. Data are mean +SD and comparisons were made by 2‐way ANOVA. GFR and RPF were not different between treatment groups and were unaffected by the experimentally‐induced rise in BP, consistent with autoregulation. In vehicle‐treated rats, incremental rises in BP increased urine flow rate from a baseline of 6 ± 3 to a peak of 51 ± 28μl/min/gkw (P&lt;0.01), sodium excretion from 1.7 ± 0.5 to 16.7 ± 1.4 μmol/min/gkw (P&lt;0.01) and fractional sodium excretion from 0.2 ± 7.6 to 5.4 ± 4.5% (P&lt;0.01). The dapaglifozin‐treated rats responded to increasing pressure with a diuresis and natriuresis but the peak absolute (3.8 ± 4.1μmol/min/gkw; P=0.010) and fractional (15.2 ± 8.0%; P=0.018) sodium excretion were significantly lower than in the vehicle‐ group. Dapagliflozin increased urinary glucose excretion from 0.1 ± 0.2 to 0.4 ± 0.2μmol/min/gkw: glucose excretion was not modified by increasing BP in either group. Although dapagliflozin increased urine flow and glucose excretion at steady‐state BP, it did not enhance the acute PN response in T1DM rats. Thus, impaired PN in T1DM does not reflect increased SGLT2 activity.Support or Funding InformationBritish Heart Foundation studentship FS/16/54/32730 &amp; Kidney Research UK Project Grant RP2/2014This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.