Effects of renal denervation on the kidney: albuminuria, proteinuria, and renal function

Renal denervation has attracted attention as a novel antihypertensive treatment for hypertensive patients who are poorly controlled by medicine. Clinical studies have shown the antihypertensive effects of renal denervation in patients with treatment-resistant hypertension. However, renal denervation potentially has other beneficial effects, such as improving glucose metabolism and cardioprotection beyond its antihypertensive effects. In this mini-review article, we summarize and discuss the effects of renal denervation on proteinuria, albuminuria, and renal function based on the recent findings of clinical studies, and review the renoprotective effects of renal denervation.

Water Conservation Overrides Osmotic Diuresis During SGLT2 Inhibition in Patients With Heart Failure

BACKGROUND

Sodium-glucose cotransporter 2 inhibitors are believed to improve cardiac outcomes due to their osmotic diuretic potential.

OBJECTIVES

The goal of this study was to test the hypothesis that vasopressin-driven urine concentration overrides the osmotic diuretic effect of glucosuria induced by dapagliflozin treatment.

METHODS

DAPA-Shuttle1 (Hepato-renal Regulation of Water Conservation in Heart Failure Patients With SGLT-2 Inhibitor Treatment) was a single-center, double-blind, randomized, placebo-controlled trial, in which patients with chronic heart failure NYHA functional classes I/II and reduced ejection fraction were randomly assigned to receive dapagliflozin 10 mg daily or placebo (1:1) for 4 weeks. The primary endpoint was change from baseline in urine osmolyte concentration. Secondary endpoints included changes in copeptin levels and solute free water clearance.

RESULTS

Thirty-three randomized, sodium-glucose cotransporter 2 inhibitor-naïve participants completed the study, 29 of whom (placebo: n = 14; dapagliflozin: n = 15) provided accurate 24-hour urine collections (mean age 59 ± 14 years; left ventricular ejection fraction 31% ± 9%). Dapagliflozin treatment led to an isolated increase in urine glucose excretion by 3.3 mmol/kg/d (95% CI: 2.51-4.04; P < 0.0001) within 48 hours (early) which persisted after 4 weeks (late; 2.7 mmol/kg/d [95% CI: 1.98-3.51]; P < 0.0001). Dapagliflozin treatment increased serum copeptin early (5.5 pmol/L [95% CI: 0.45-10.5]; P < 0.05) and late (7.8 pmol/L [95% CI: 2.77-12.81]; P < 0.01), leading to proportional reductions in free water clearance (early: -9.1 mL/kg/d [95% CI: -14 to -4.12; P < 0.001]; late: -11.0 mL/kg/d [95% CI: -15.94 to -6.07; P < 0.0001]) and elevated urine concentrations (late: 134 mmol/L [95% CI: 39.28-229.12]; P < 0.01). Therefore, urine volume did not significantly increase with dapagliflozin (mean difference early: 2.8 mL/kg/d [95% CI: -1.97 to 7.48; P = 0.25]; mean difference late: 0.9 mL/kg/d [95% CI: -3.83 to 5.62]; P = 0.70).

CONCLUSIONS

Physiological-adaptive water conservation eliminated the expected osmotic diuretic potential of dapagliflozin and thereby prevented a glucose-driven increase in urine volume of approximately 10 mL/kg/d · 75 kg = 750 mL/kg/d. (Hepato-renal Regulation of Water Conservation in Heart Failure Patients With SGLT-2 Inhibitor Treatment [DAPA-Shuttle1]; NCT04080518).

Effects of D-allose on ATP production and cell viability in neonatal rat cardiomyocytes

2-Deoxy-d-glucose (2DG) induces anticancer effects through glycolytic inhibition but it may raise the risk of arrhythmia. The rare monosaccharide d-allose also has anticancer properties, but its cardiac effects are unknown. We examined the effects of d-allose on adenosine triphosphate (ATP) production in neonatal rat cardiomyocytes. We showed that 25 mM d-allose selectively reduced glycolytic ATP, but had minimal impact on mitochondrial ATP, while 1 mM 2DG strongly inhibited both. Furthermore, d-allose had less impact on cell viability and was less cytotoxic than 2DG; neither compound caused apoptosis. Thus, d-allose selectively diminished glycolytic ATP production with no apparent effects on cardiomyocytes.

Potential Role of the Skin in Hypertension Risk Through Water Conservation

Previous basic and clinical investigations have identified various pathogenic factors and determinants of risk that contribute to hypertension. Nevertheless, the pathogenesis of hypertension has not been fully elucidated. Moreover, despite the availability of antihypertensive medications for the management of blood pressure, treatments that address the full spectrum of the pathophysiological defects underpinning hypertension remain to be identified. To further investigate the mechanisms of primary hypertension, it is imperative to consider novel potential aspects, such as fluid management by the skin, in addition to the conventional risk factors. There is a close association between body fluid regulation and blood pressure, and the kidney, which, as the principal organ responsible for body fluid homeostasis, is the primary target for research in the field of hypertension. In addition, the skin functions as a biological barrier, potentially contributing to body fluid regulation. In this review, we propose the hypothesis that changes in skin water conservation are associated with hypertension risk based on recent findings. Further studies are required to clarify whether this novel hypothesis is limited to specific hypertension or applies to physiological blood pressure regulation.

Comparison of the effects of renal denervation at early or advanced stages of hypertension on cardiac, renal, and adipose tissue pathology in Dahl salt-sensitive rats

Renal denervation (RDN) has emerged as a novel therapy for drug-resistant hypertension. We here examined the effects of RDN at early versus advanced stages of hypertension on blood pressure and organ pathology in rats with salt-sensitive hypertension. Dahl salt-sensitive (DahlS) rats fed an 8% NaCl diet from 6 weeks of age were subjected to RDN (surgical ablation and application of 10% phenol in ethanol) or sham surgery at 7 (early stage) or 9 (advanced stage) weeks and were studied at 12 weeks. RDN at early or advanced stages resulted in a moderate lowering of blood pressure. Although RDN at neither stage affected left ventricular (LV) and cardiomyocyte hypertrophy, it ameliorated LV diastolic dysfunction, fibrosis, and inflammation at both stages. Intervention at both stages also attenuated renal injury as well as downregulated the expression of angiotensinogen and angiotensin-converting enzyme (ACE) genes and angiotensin II type 1 receptor protein in the kidney. Furthermore, RDN at both stages inhibited proinflammatory gene expression in adipose tissue. The early intervention reduced both visceral fat mass and adipocyte size in association with downregulation of angiotensinogen and ACE gene expression. In contrast, the late intervention increased fat mass without affecting adipocyte size as well as attenuated angiotensinogen and ACE gene expression. Our results thus indicate that RDN at early or late stages after salt loading moderately alleviated hypertension and substantially ameliorated cardiac and renal injury and adipose tissue inflammation in DahlS rats. They also suggest that cross talk among the kidney, cardiovascular system, and adipose tissue may contribute to salt-sensitive hypertension. Supposed mechanism for the beneficial effects of RDN on hypertension and target organ damage in DahlS rats. RDN at early or late stages after salt loading moderately alleviated hypertension and substantially ameliorated renal injury in DahlS rats. Cross talk among the kidney, cardiovascular system, and adipose tissue possibly mediated by circulating RAS may contribute to salt-sensitive hypertension. LV; left ventricular, NE; norepinephrine, RAS; renin-angiotensin system, RDN; renal denervation.

2023 update and perspectives

Total 276 manuscripts were published in Hypertension Research in 2022. Here our editorial members picked up the excellent papers, summarized the current topics from the published papers and discussed future perspectives in the sixteen fields. We hope you enjoy our special feature, 2023 update and perspectives in Hypertension Research.

Revisiting blood pressure and body fluid status

Homeostasis of body fluid is a key component for maintaining health. An imbalance of body sodium and water causes various pathological states, such as dehydration, volume overload, hypertension, cardiovascular and renal diseases, and metabolic disorders. Conventional concepts regarding physiology and pathophysiology of body sodium and water balance have been established by several assumptions. These assumptions are that the kidneys are the master regulator of body sodium and water content, and that sodium moves inside the body in parallel with water. However, recent clinical and basic studies have proposed alternative concepts. These concepts are that body sodium and water balance are regulated by various organs and multiple factors, such as physical activity and the environment, and that sodium accumulates locally in tissues independently of the blood status and/or water. Various concerns remain unclear, and the regulatory mechanism of body sodium, fluid, and blood pressure needs to be readdressed. In the present review article, we discuss novel concepts regarding the regulation of body sodium, water, and blood pressure with a particular focus on the systemic water conservation system and fluid loss-triggered elevation in blood pressure.

Possible contribution of phosphate to the pathogenesis of chronic kidney disease in dolphins

This study aimed to investigate whether phosphate contributes to the pathogenesis of chronic kidney disease (CKD) in dolphins. Renal necropsy tissue of an aged captive dolphin was analyzed and in vitro experiments using cultured immortalized dolphin proximal tubular (DolKT-1) cells were performed. An older dolphin in captivity died of myocarditis, but its renal function was within the normal range until shortly before death. In renal necropsy tissue, obvious glomerular and tubulointerstitial changes were not observed except for renal infarction resulting from myocarditis. However, a computed tomography scan showed medullary calcification in reniculi. Micro area X-ray diffractometry and infrared absorption spectrometry showed that the calcified areas were primarily composed of hydroxyapatite. In vitro experiments showed that treatment with both phosphate and calciprotein particles (CPPs) resulted in cell viability loss and lactate dehydrogenase release in DolKT-1 cells. However, treatment with magnesium markedly attenuated this cellular injury induced by phosphate, but not by CPPs. Magnesium dose-dependently decreased CPP formation. These data support the hypothesis that continuous exposure to high phosphate contributes to the progression of CKD in captive-aged dolphins. Our data also suggest that phosphate-induced renal injury is mediated by CPP formation in dolphins, and it is attenuated by magnesium administration.

Possible renoprotective mechanisms of SGLT2 inhibitors

Treatment with a sodium glucose cotransporter 2 (SGLT2) inhibitor in patients with chronic kidney disease reduces the renal risk independent of changes in blood glucose concentrations and blood pressure. However, the precise mechanism responsible for this SGLT2 inhibitor-induced renoprotective effect is unclear. We have previously shown that SGLT2 inhibitors induce antihypertensive effects with decreased sympathetic nerve activity, which is associated with transient natriuresis. Furthermore, treatment with an SGLT2 inhibitor improves renal ischemia by producing vascular endothelial growth factor-a in the renal tubules. Other studies have suggested that ketone body production, changes in glomerular hemodynamics, and intrarenal metabolic changes and a reduction in oxidative stress due to decreased tubulointerstitial glucose levels may also be involved in the renoprotective effects of SGLT2 inhibitors. In this review, we summarize the mechanism responsible for the SGLT2 inhibitor-induced renoprotective effects, including our recent hypothesis regarding an “aestivation-like response,” which is a biological defense response to starvation.

Blood pressure adaptation in vertebrates: Comparative biology

With evolution from water to land, the osmotic regulation of body fluids and cardiovascular systems of vertebrates evolved to cope with dryness and gravity. While aquatic vertebrates can use buoyancy to compensate for the effects of gravity, terrestrial vertebrates cannot, and must circulate blood throughout their body - a necessity that likely led to the development of strong hearts and high blood pressure. These changes may be supported by anatomical evolution of the cardiovascular system and by functional evolution, with alterations in hormonal systems. Thus, during the evolution of terrestrial animals, increased performance of body functions to endure harsher environments was required, necessitating increased blood pressure. In an age of overeating and insufficient exercise, modern man does not fully utilize the high levels of physical functions acquired through evolution. Drastic changes in our living environment cause hypertension, the pathogenesis of which remains unknown. To survive in new environments, as might be expected in outer space or underwater, an understanding is required of how changes in blood pressure have occurred that enabled adaptation through evolution in vertebrates.

Hepatocellular carcinoma induces body mass loss in parallel with osmolyte and water retention in rats

AIMS

The number of cancer survivors with cardiovascular disease is increasing. However, the effect of cancer on body fluid regulation remains to be clarified. In this study, we evaluated body osmolyte and water imbalance in rats with hepatocellular carcinoma.

MAIN METHODS

Wistar rats were administered diethylnitrosamine, a carcinogenic drug, to establish liver cancer. We analyzed tissue osmolyte and water content, and their associations with aldosterone secretion.

KEY FINDINGS

Hepatocellular carcinoma rats had significantly reduced body mass and the amount of total body sodium, potassium, and water. However, these rats had significantly increased relative tissue sodium, potassium, and water content per tissue dry weight. Furthermore, these changes in sodium and water balance in hepatocellular carcinoma rats were significantly associated with increased 24-h urinary aldosterone excretion. Supplementation with 0.25% salt in drinking water improved body weight reduction associated with sodium and water retention in hepatocellular carcinoma rats, which was suppressed by treatment with spironolactone, a mineralocorticoid receptor antagonist. Additionally, the urea-driven water conservation system was activated in hepatocellular carcinoma rats.

SIGNIFICANCE

These findings suggest that hepatocellular carcinoma induces body mass loss in parallel with activation of the water conservation system including aldosterone secretion and urea accumulation to retain osmolyte and water. The osmolyte and water retention at the tissue level may be a causative factor for ascites and edema formation in liver failure rats.

Sodium/glucose cotransporter 2 and renoprotection: From the perspective of energy regulation and water conservation

Sodium/glucose cotransporter 2 (SGLT2) is a renal low-affinity high-capacity sodium/glucose cotransporter expressed in the apical membrane of the early segment of proximal tubules. SGLT2 reabsorbs filtered glucose in the kidney, and its inhibitors represent a new class of oral medications used for type 2 diabetes mellitus, which act by increasing glucose and sodium excretion in urine, thereby reducing blood glucose levels. However, clinical trials showed marked improvement of renal outcomes, even in nondiabetic kidney diseases, although the underlying mechanism of this renoprotective effect is unclear. We showed that long-term excretion of salt by the kidneys, which predisposes to osmotic diuresis and water loss, induces a systemic body response for water conservation. The energy-intensive nature of water conservation leads to a reprioritization of systemic body energy metabolism. According to current data, use of SGLT2 inhibitors may result in similar reprioritization of energy metabolism to prevent dehydration. In this review article, we discuss the beneficial effects of SGLT2 inhibition from the perspective of energy metabolism and water conservation.

Abstract 23: Body Fluid And Sodium Loss Leads To Aldosterone Hypersecretion And Muscle Catabolism In Hepatocellular Carcinoma Rats

Background: The number of cancer survivors coincides with cardiovascular diseases is increasing, therefore, we are promoting the concept of “Onco-Hypertension” to clarify the mechanism linking cancer and blood pressure. In this study, we evaluated body osmolyte and water imbalance in hepatocellular cancer (HCC) model rats.

Methods: Wistar rats were administered diethylnitrosamine (DEN) (1.5 μg/day, p.o.), a carcinogenic drug, for 8 weeks to establish liver cancer. Three weeks after the completion of DEN administration, we investigated blood pressure, tissue osmolyte and water content, and its association with aldosterone secretion.

Results: HCC rats significantly reduced blood pressure, skin sodium, potassium, and water content. In the carcass (muscle + bone), dry weight, sodium, potassium, and water content were dramatically reduced without changing bone mass in HCC rats, suggesting that HCC causes muscle wasting to supply osmolyte and water for the dehydrated organs. These osmolytes and water loss were significantly associated with increased urinary aldosterone excretion. Supplementation of 0.25% salt water to drink improved body sodium and water loss and muscle wasting in HCC rats, which were completely suppressed by treatment with spironolactone (75 mg/kg/day, p.o.), a mineralocorticoid receptor (MR) blocker.

Conclusion: These findings suggest that HCC causes body osmolyte and water loss, which leads to aldosterone hypersecretion and muscle catabolism to compensate for dehydration. A relatively small amount of salt supplement ameliorates the HCC-induced dehydration and muscle wasting via aldosterone/MR-mediated sodium and water restoration.

Renal NG2-expressing cells have a macrophage-like phenotype and facilitate renal recovery after ischemic injury

Pericytes play an important role in the recovery process after ischemic injury of many tissues. Brain pericytes in the peri-infarct area express macrophage markers in response to injury stimuli and are involved in neovascularization. In the kidney, nerve/glial antigen 2 (NG2)⁺ pericytes have been found to accumulate after renal injury. These accumulated NG2⁺ cells are not involved in scar formation. However, the role of accumulated NG2⁺ cells in injured kidneys remains unknown. Here, using a reversible ischemia-reperfusion (I/R) model, we found that renal NG2⁺ cells were increased in injured kidneys and expressed macrophage markers (CD11b or F4/80) on day 3 after reperfusion. Isolated NG2⁺ cells from I/R kidneys also had phagocytic activity and expressed anti-inflammatory cytokine genes, including mannose receptor and IL-10. These macrophage-like NG2⁺ cells did not likely differentiate into myofibroblasts because they did not increase α-smooth muscle actin expression. Intravenous transfusion of renal NG2⁺ cells isolated from donor mice on day 3 after reperfusion into recipient mice on day 1 after I/R surgery revealed that NG2⁺ cell-injected mice had lower plasma blood urea nitrogen, reduced kidney injury molecule-1 mRNA expression, ameliorated renal damage, and reduced cellular debris accumulation compared with PBS-injected mice on day 5 after reperfusion. In conclusion, these data suggest that renal NG2⁺ cells have an M2 macrophage-like ability and play a novel role in facilitating the recovery process after renal I/R injury.NEW & NOTEWORTHY Brain pericytes have macrophage-like activities after injury. However, such properties of pericytes in peripheral tissues have not been investigated. Here, we provide evidence that nerve/glial antigen 2-positive cells increase after renal injury. The population of nerve/glial antigen 2-positive cells, which does not increase expression of myofibroblast-associated gene, express macrophage markers and anti-inflammatory cytokine genes, have phagocytic activity, and play a role in renal recovery after kidney injury.

Effects of molidustat, a hypoxia-inducible factor prolyl hydroxylase inhibitor, on sodium dynamics in hypertensive subtotally nephrectomized rats

Hypoxia-inducible factor prolyl hydroxylase (HIF-PHD) inhibitors were developed for treatment of renal anemia. Patients applicable for HIF-PHD inhibitor treatment experience complications such as chronic kidney disease, whereby water and electrolyte homeostasis is disrupted. The effects of hypoxia-inducible factor stabilization on salt accumulation in the setting of reduced renal function remain unclear. In the present study, we investigated the effect of a HIF-PHD inhibitor, molidustat, on salt distribution and excretion in rats with subtotal nephrectomy-induced chronic kidney disease. Male Wistar rats were subjected to 5/6 nephrectomy. After confirming blood pressure elevation (>150 mmHg, at 4 weeks after surgery), rats were treated with molidustat. After 1 week of treatment, molidustat did not significantly improve blood cell volume or blood pressure. Distribution of sodium, potassium, and water in skin, carcass, and bone samples was not affected by molidustat. Furthermore, molidustat had no significant effect on urinary sodium excretion or concentration in response to acute oral salt loading (1 g/kg). In conclusion, molidustat did not affect distribution or excretion of salt in rats subjected to a model of nephron loss.

Abnormal neonatal sodium handling in skin precedes hypertension in the SAME rat

We discovered high Na⁺ and water content in the skin of newborn Sprague–Dawley rats, which reduced ~ 2.5-fold by 7 days of age, indicating rapid changes in extracellular volume (ECV). Equivalent changes in ECV post birth were also observed in C57Bl/6 J mice, with a fourfold reduction over 7 days, to approximately adult levels. This established the generality of increased ECV at birth. We investigated early sodium and water handling in neonates from a second rat strain, Fischer, and an Hsd11b2-knockout rat modelling the syndrome of apparent mineralocorticoid excess (SAME). Despite Hsd11b2^−/− animals exhibiting lower skin Na⁺ and water levels than controls at birth, they retained ~ 30% higher Na⁺ content in their pelts at the expense of K⁺ thereafter. Hsd11b2^−/− neonates exhibited incipient hypokalaemia from 15 days of age and became increasingly polydipsic and polyuric from weaning. As with adults, they excreted a high proportion of ingested Na⁺ through the kidney, (56.15 ± 8.21% versus control 34.15 ± 8.23%; n = 4; P < 0.0001), suggesting that changes in nephron electrolyte transporters identified in adults, by RNA-seq analysis, occur by 4 weeks of age. Our data reveal that Na⁺ imbalance in the Hsd11b2^−/− neonate leads to excess Na⁺ storage in skin and incipient hypokalaemia, which, together with increased, glucocorticoid-induced Na⁺ uptake in the kidney, then contribute to progressive, volume contracted, salt-sensitive hypertension. Skin Na⁺ plays an important role in the development of SAME but, equally, may play a key physiological role at birth, supporting post-natal growth, as an innate barrier to infection or as a rudimentary kidney.

[Protective role of SGLT2 inhibition against the kidney disease]

Physiologically, urine from the subject with normal kidney function does not contain detectable level of glucose unless otherwise renal glycosuria. Sodium glucose transporter (SGLT) families in proximal tubules of the kidney play detrimental role to reabsorb the filtered glucose. Recently, the inhibitors for the SGLT2 are available for clinical use for purposing the urinary glucose excretion and lowering blood glucose level. Unexpectedly, the SGLT2 inhibitors have become famous for its cardio-renal protective effects with unknown mechanism. We have so far explored how its inhibition changes cell fate, how the drug affects glucose uptake in non-diabetic kidney, and if the drug suppresses the development of fibrosis. In this review, we will summarize our findings and provide the remaining questions.

Adaptive physiological water conservation explains hypertension and muscle catabolism in experimental chronic renal failure

Aim

We have reported earlier that a high salt intake triggered an aestivation‐like natriuretic‐ureotelic body water conservation response that lowered muscle mass and increased blood pressure. Here, we tested the hypothesis that a similar adaptive water conservation response occurs in experimental chronic renal failure.

Methods

In four subsequent experiments in Sprague Dawley rats, we used surgical 5/6 renal mass reduction (5/6 Nx) to induce chronic renal failure. We studied solute and water excretion in 24‐hour metabolic cage experiments, chronic blood pressure by radiotelemetry, chronic metabolic adjustment in liver and skeletal muscle by metabolomics and selected enzyme activity measurements, body Na⁺, K⁺ and water by dry ashing, and acute transepidermal water loss in conjunction with skin blood flow and intra‐arterial blood pressure.

Results

5/6 Nx rats were polyuric, because their kidneys could not sufficiently concentrate the urine. Physiological adaptation to this renal water loss included mobilization of nitrogen and energy from muscle for organic osmolyte production, elevated norepinephrine and copeptin levels with reduced skin blood flow, which by means of compensation reduced their transepidermal water loss. This complex physiologic‐metabolic adjustment across multiple organs allowed the rats to stabilize their body water content despite persisting renal water loss, albeit at the expense of hypertension and catabolic mobilization of muscle protein.

Conclusion

Physiological adaptation to body water loss, termed aestivation, is an evolutionary conserved survival strategy and an under‐studied research area in medical physiology, which besides hypertension and muscle mass loss in chronic renal failure may explain many otherwise unexplainable phenomena in medicine.

Aestivation motifs explain hypertension and muscle mass loss in mice with psoriatic skin barrier defect

AIM

Recent evidence suggests that arterial hypertension could be alternatively explained as a physiological adaptation response to water shortage, termed aestivation, which relies on complex multi-organ metabolic adjustments to prevent dehydration. Here, we tested the hypothesis that chronic water loss across diseased skin leads to similar adaptive water conservation responses as observed in experimental renal failure or high salt diet.

METHODS

We studied mice with keratinocyte-specific overexpression of IL-17A which develop severe psoriasis-like skin disease. We measured transepidermal water loss and solute and water excretion in the urine. We quantified glomerular filtration rate (GFR) by intravital microscopy, and energy and nitrogen pathways by metabolomics. We measured skin blood flow and transepidermal water loss (TEWL) in conjunction with renal resistive indices and arterial blood pressure.

RESULTS

Psoriatic animals lost large amounts of water across their defective cutaneous epithelial barrier. Metabolic adaptive water conservation included mobilization of nitrogen and energy from muscle to increase organic osmolyte production, solute-driven maximal anti-diuresis at normal GFR, increased metanephrine and angiotensin 2 levels, and cutaneous vasoconstriction to limit TEWL. Heat exposure led to cutaneous vasodilation and blood pressure normalization without parallel changes in renal resistive index, albeit at the expense of further increased TEWL.

CONCLUSION

Severe cutaneous water loss predisposes psoriatic mice to lethal dehydration. In response to this dehydration stress, the mice activate aestivation-like water conservation motifs to maintain their body hydration status. The circulatory water conservation response explains their arterial hypertension. The nitrogen-dependency of the metabolic water conservation response explains their catabolic muscle wasting.

Cardioprotective Effects of a Nonsteroidal Mineralocorticoid Receptor Blocker, Esaxerenone, in Dahl Salt-Sensitive Hypertensive Rats

We investigated the effects of esaxerenone, a novel, nonsteroidal, and selective mineralocorticoid receptor blocker, on cardiac function in Dahl salt-sensitive (DSS) rats. We provided 6-week-old DSS rats a high-salt diet (HSD, 8% NaCl). Following six weeks of HSD feeding (establishment of cardiac hypertrophy), we divided the animals into the following two groups: HSD or HSD + esaxerenone (0.001%, w/w). In survival study, all HSD-fed animals died by 24 weeks of age, whereas the esaxerenone-treated HSD-fed animals showed significantly improved survival. We used the same protocol with a separate set of animals to evaluate the cardiac function by echocardiography after four weeks of treatment. The results showed that HSD-fed animals developed cardiac dysfunction as evidenced by reduced stroke volume, ejection fraction, and cardiac output. Importantly, esaxerenone treatment decreased the worsening of cardiac dysfunction concomitant with a significantly reduced level of systolic blood pressure. In addition, treatment with esaxerenone in HSD-fed DSS rats caused a reduced level of cardiac remodeling as well as fibrosis. Furthermore, inflammation and oxidative stress were significantly reduced. These data indicate that esaxerenone has the potential to mitigate cardiac dysfunction in salt-induced myocardial injury in rats.

Organ protection by SGLT2 inhibitors: role of metabolic energy and water conservation

Therapeutic inhibition of the sodium-glucose co-transporter 2 (SGLT2) leads to substantial loss of energy (in the form of glucose) and additional solutes (in the form of Na⁺ and its accompanying anions) in urine. However, despite the continuously elevated solute excretion, long-term osmotic diuresis does not occur in humans with SGLT2 inhibition. Rather, patients on SGLT2 inhibitor therapy adjust to the reduction in energy availability and conserve water. The metabolic adaptations that are induced by SGLT2 inhibition are similar to those observed in aestivation - an evolutionarily conserved survival strategy that enables physiological adaptation to energy and water shortage. Aestivators exploit amino acids from muscle to produce glucose and fatty acid fuels. This endogenous energy supply chain is coupled with nitrogen transfer for organic osmolyte production, which allows parallel water conservation. Moreover, this process is often accompanied by a reduction in metabolic rate. By comparing aestivation metabolism with the fuel switches that occur during therapeutic SGLT2 inhibition, we suggest that SGLT2 inhibitors induce aestivation-like metabolic patterns, which may contribute to the improvements in cardiac and renal function observed with this class of therapeutics.

Sodium Handling and Interaction in Numerous Organs

Salt (NaCl) is a prerequisite for life. Excessive intake of salt, however, is said to increase disease risk, including hypertension, arteriosclerosis, heart failure, renal disease, stroke, and cancer. Therefore, considerable research has been expended on the mechanism of sodium handling based on the current concepts of sodium balance. The studies have necessarily relied on relatively short-term experiments and focused on extremes of salt intake in humans. Ultra-long-term salt balance has received far less attention. We performed long-term salt balance studies at intakes of 6, 9, and 12 g/day and found that although the kidney remains the long-term excretory gate, tissue and plasma sodium concentrations are not necessarily the same and that urinary salt excretion does not necessarily reflect total-body salt content. We found that to excrete salt, the body makes a great effort to conserve water, resulting in a natriuretic-ureotelic principle of salt excretion. Of note, renal sodium handling is characterized by osmolyte excretion with anti-parallel water reabsorption, a state-of-affairs that is achieved through the interaction of multiple organs. In this review, we discuss novel sodium and water balance concepts in reference to our ultra-long-term study. An important key to understanding body sodium metabolism is to focus on water conservation, a biological principle to protect from dehydration, since excess dietary salt excretion into the urine predisposes to renal water loss because of natriuresis. We believe that our research direction is relevant not only to salt balance but also to cardiovascular regulatory mechanisms.

Crucial Role of AIM/CD5L in the Development of Glomerular Inflammation in IgA Nephropathy

BACKGROUND

IgA nephropathy (IgAN) begins with aberrant IgA deposition in glomeruli, progresses to IgM/IgG/complement codeposition, and results in chronic inflammation and glomerular damage. However, the mechanism that drives such phlogogenic cascade has been unclear. Recently, apoptosis inhibitor of macrophage (AIM) protein was shown to modulate macrophages' function in various pathologic conditions, thereby profoundly affecting the progression of renal disorders, including AKI. A spontaneous IgAN model, grouped ddY (gddY) mouse, revealed the requirement of AIM for the overall inflammatory glomerular injury following IgA deposition.

METHODS

We established an AIM-deficient IgAN model (AIM ^-/- gddY) using CRISPR/Cas9 and compared its phenotype with that of wild-type gddY with or without recombinant AIM administration. An IgA-deficient IgAN model (IgA ^-/- gddY) was also generated to further determine the role of AIM.

RESULTS

In both human and murine IgAN, AIM colocalized with IgA/IgM/IgG in glomeruli, whereas control kidneys did not exhibit AIM deposition. Although AIM ^-/- gddY showed IgA deposition at levels comparable with those of wild-type gddY, they did not exhibit glomerular accumulation of IgM/IgG complements, CD45⁺ leukocyte infiltration, and upregulation of inflammatory/fibrogenic genes, indicating protection from glomerular lesions and proteinuria/hematuria. Recombinant AIM administration reconstituted the IgAN phenotype, resulting in IgM/IgG/complement IgA codeposition. Neither spontaneous IgM/IgG codeposition nor disease was observed in IgA ^-/- gddY mice.

CONCLUSIONS

AIM may contribute to stable immune complex formation in glomeruli, thereby facilitating IgAN progression. Therefore, AIM deposition blockage or disassociation from IgM/IgG may present a new therapeutic target on the basis of its role in IgAN inflammation initiation.

Renal sympathetic nerve activity regulates cardiovascular energy expenditure in rats fed high salt

We recently reported that a 4% high-salt diet + saline for drinking (HS + saline) leads to a catabolic state, reduced heart rate, and suppression of cardiovascular energy expenditure in mice. We suggested that HS + saline reduces heart rate via the suppression of the sympathetic nervous system to compensate for the high salt intake-induced catabolic state. To test this hypothesis, we directly measured renal sympathetic nerve activity (RSNA) in conscious Sprague-Dawley (SD) rats using a radiotelemetry system. We confirmed that HS + saline induced a catabolic state. HS + saline decreased heart rate, while also reducing RSNA in SD rats. In contrast, Dahl salt-sensitive (DSS) rats exhibited no change in heart rate and increased RSNA during high salt intake. Renal denervation significantly decreased heart rate and attenuated the catabolic state independent of blood pressure in DSS rats fed HS + saline, suggesting that salt-sensitive animals were unable to decrease cardiovascular energy consumption due to abnormal renal sympathetic nerve activation during high salt intake. These findings support the hypothesis that RSNA mediates heart rate during high salt intake in SD rats. However, the insensitivity of heart rate and enhanced RSNA observed in DSS rats may be additional critical diagnostic factors for salt-sensitive hypertension. Renal denervation may benefit salt-sensitive hypertension by reducing its effects on catabolism and cardiovascular energy expenditure.

HIF1A and NFAT5 coordinate Na+-boosted antibacterial defense via enhanced autophagy and autolysosomal targeting

Infection and inflammation are able to induce diet-independent Na+-accumulation without commensurate water retention in afflicted tissues, which favors the pro-inflammatory activation of mouse macrophages and augments their antibacterial and antiparasitic activity. While Na+-boosted host defense against the protozoan parasite Leishmania major is mediated by increased expression of the leishmanicidal NOS2 (nitric oxide synthase 2, inducible), the molecular mechanisms underpinning this enhanced antibacterial defense of mouse macrophages with high Na+ (HS) exposure are unknown. Here, we provide evidence that HS-increased antibacterial activity against E. coli was neither dependent on NOS2 nor on the phagocyte oxidase. In contrast, HS-augmented antibacterial defense hinged on HIF1A (hypoxia inducible factor 1, alpha subunit)-dependent increased autophagy, and NFAT5 (nuclear factor of activated T cells 5)-dependent targeting of intracellular E. coli to acidic autolysosomal compartments. Overall, these findings suggest that the autolysosomal compartment is a novel target of Na+-modulated cell autonomous innate immunity. Abbreviations: ACT: actins; AKT: AKT serine/threonine kinase 1; ATG2A: autophagy related 2A; ATG4C: autophagy related 4C, cysteine peptidase; ATG7: autophagy related 7; ATG12: autophagy related 12; BECN1: beclin 1; BMDM: bone marrow-derived macrophages; BNIP3: BCL2/adenovirus E1B interacting protein 3; CFU: colony forming units; CM-H2DCFDA: 5-(and-6)-chloromethyl-2',7'-dichlorodihydrofluorescein diacetate, acetyl ester; CTSB: cathepsin B; CYBB: cytochrome b-245 beta chain; DAPI: 4,6-diamidino-2-phenylindole; DMOG: dimethyloxallyl glycine; DPI: diphenyleneiodonium chloride; E. coli: Escherichia coli; FDR: false discovery rate; GFP: green fluorescent protein; GSEA: gene set enrichment analysis; GO: gene ontology; HIF1A: hypoxia inducible factor 1, alpha subunit; HUGO: human genome organization; HS: high salt (+ 40 mM of NaCl to standard cell culture conditions); HSP90: heat shock 90 kDa proteins; LDH: lactate dehydrogenase; LPS: lipopolysaccharide; Lyz2/LysM: lysozyme 2; NFAT5/TonEBP: nuclear factor of activated T cells 5; MΦ: macrophages; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MFI: mean fluorescence intensity; MIC: minimum inhibitory concentration; MOI: multiplicity of infection; MTOR: mechanistic target of rapamycin kinase; NaCl: sodium chloride; NES: normalized enrichment score; n.s.: not significant; NO: nitric oxide; NOS2/iNOS: nitric oxide synthase 2, inducible; NS: normal salt; PCR: polymerase chain reaction; PGK1: phosphoglycerate kinase 1; PHOX: phagocyte oxidase; RFP: red fluorescent protein; RNA: ribonucleic acid; ROS: reactive oxygen species; sCFP3A: super cyan fluorescent protein 3A; SBFI: sodium-binding benzofuran isophthalate; SLC2A1/GLUT1: solute carrier family 2 (facilitated glucose transporter), member 1; SQSTM1/p62: sequestosome 1; ULK1: unc-51 like kinase 1; v-ATPase: vacuolar-type H+-ATPase; WT: wild type.

α-Lipoic acid exerts a primary prevention for the cardiac dysfunction in aortocaval fistula-created rat hearts

Aim

α-Lipoic acid exerts a powerful antioxidant effect by acting as a free radical scavenger and inducing endogenous antioxidants such as vitamin E and glutathione. In the present study, we examined the effects of α-lipoic acid on cardiac dysfunction in rat hearts with aortocaval fistulae.

Main methods

Aortocaval fistulae were created between the abdominal aorta and inferior vena cava in male rats. Hemodynamic parameters were measured 14 days after surgery using an intravascular pressure transducer, and then these hearts were harvested for tissue weight measurement, pathological evaluation, and mRNA isolation.

Results

In vehicle-treated rats, left ventricular end-diastolic pressure and left ventricular weight significantly increased at 14 days after fistula creation. Fistula-creation resulted in expression of 4-hydroxy-2-nonenal, NADPH oxidase subunit p67^phox and BNP mRNA in a time-dependent manner in the left ventricle.

Long-term treatment (initiated 2 days before surgery, and continued for 14 days after fistula creation; days -2 to 14) with α-lipoic acid (30 mg/kg/day) markedly suppressed the increases in left and right ventricular weight, and left ventricular end-diastolic pressure. α-Lipoic acid treatment from days -2 to 14 prominently prevented the expression of 4-hydroxy-2-nonenal and NADPH oxidase subunit p67^phox, and significantly raised BNP mRNA levels. Short-term treatment with α-lipoic acid from day - 2 to 7 was effective in preventing cardiac enlargement and dysfunction, similar to long-term treatment, but treatment from days 7–14 was not effective.

Conclusions

Treatment with α-lipoic acid can prevent cardiac hyperplasia and dysfunction, probably by inhibiting superoxide production and enhancing BNP mRNA expression in an early phase after fistula creation.

Abstract P169: Renal Denervation Attenuates a Catabolic State in Mice Fed High Salt

Introduction: We recently reported that kidneys accumulate urea as an alternative osmolyte in the renal medulla to concentrate sodium into the urine during high salt intake. This urea-driven water conservation process is coupled with the energy-intensive nature of hepatic urea production, which leads to a catabolic state in mice fed high salt. In this study, we examined the effects of renal denervation on the salt-driven catabolic state since previous studies found that the renal sympathetic nervous system regulates urinary sodium excretion and energy metabolism of some organs such as liver and muscle.

Methods: Sham-operated (sham) or renal denervated (RDX) male C57/B6J mice were fed on 0.3% NaCl diet with tap water (NS) or 4% NaCl high salt diet + 0.9% NaCl water to drink (HS) for 4 consecutive weeks (ad libitum), followed by 2 weeks of pair-feeding to match energy intake in all groups. We measured daily food intake and body weight, 24 hours urinary sodium excretion, body sodium content, and activity of liver arginase, a urea producing enzyme.

Results: NS + sham and HS + sham mice showed similar body weight gain (NS + sham: +3.6 ± 0.2, HS + sham: +3.4 ± 0.2 g) during ad libitum feeding although HS significantly increased food intake (NS + sham: 3.1 ± 0.04, HS + sham: 3.3 ± 0.04 g/day). After the pair-feeding, HS mice significantly decreased their body weight (NS + sham: +0.9 ± 0.07, HS + sham: -0.6 ± 0.05 g) and increased liver arginase activity (NS + sham: 3792 ± 322, HS + sham: 5412 ± 499 units/L/tissue), confirming the high salt-induced catabolic hepatic urea production. On the other hand, HS did not increase food intake (NS + RDX: 3.2 ± 0.1, HS + RDX: 3.1 ± 0.01 g/day) and liver arginase activity (NS + RDX: 3599 ± 316, HS + RDX: 3363 ± 369 units/L/tissue) in RDX group. In addition, HS + RDX mice did not show pair feeding-induced body weight loss (NS + RDX: +0.6 ± 0.3, HS + RDX: +0.3 ± 0.3 g). HS + RDX mice did not alter 24 hours urinary sodium excretion (HS + sham: 135 ± 6.3, HS + RDX: 142 ± 13 mmol/d/kg) and body sodium content (HS + sham: 0.15 ± 0.003, HS + RDX: 0.15 ± 0.006 mmol/d/kg) compared with HS + sham mice.

Conclusion: These findings suggest that renal denervation attenuates the HS-induced body weight loss and catabolic urea production independently of urinary sodium excretion.

Abstract P220: High Salt Intake Induces Catabolism Accompanied by Hepatic Urea Osmolyte Production and Decreases Renal Sympathetic Nerve Activity

Introduction: We have recently reported that high salt intake induces the energy-intensive nature of hepatic urea osmolyte production that accompanied the decrease in heart rate (HR). These findings suggest that high salt intake decreases sympathetic nerve activity to reduce cardiovascular energy expenditure for the hepatic urea production. Therefore, we examined the effects of high salt intake on renal sympathetic nerve activity (RSNA) by using a radiotelemetry system in rats.

Methods: We inserted the radiotelemetry system into male Sprague Dawley (SD) rats for recording RSNA and HR. After 2 weeks recovery, we fed the rats 0.3% NaCl diet (NS) with tap water to drink (NS + tap), 4% NaCl diet with tap water (HS + tap), and 4% NaCl diet with saline (HS + saline) for 4 days in this order, and kept monitoring their HR and RSNA. In the separate experiment, we also fed male SD rats NS + tap or HS + saline for 6 consecutive weeks to confirm a catabolic state in HS + saline rats.

Results: Rats exhibited marked reductions in RSNA and HR during HS + saline phase compared with other phases. HS + saline rats significantly decreased body weight (369±35 g) compared with NS + tap rats (405±48 g) despite of the similar daily food intake (18.5±1.3 vs. 19.2±1.6 g/day). And HS + saline rats increased liver arginase, a urea producing enzyme, activity (1561±121 units/L/mg) compared with NS + tap rats (1337±131 units/L/mg) at 6 weeks after the feeding.

Conclusion: High salt intake decreased RSNA accompanied by the catabolic urea production in rats. These findings suggest that the sympathetic nervous system is one of the key regulators to reduce cardiovascular energy expenditure, which could support the energy-intensive nature of hepatic urea production in high salt-fed rats.

A novel approach to adenine-induced chronic kidney disease associated anemia in rodents

To date, good experimental animal models of renal anemia are not available. Therefore, the purpose of this study was to establish a novel approach to induce chronic kidney disease (CKD) with severe anemia by oral administration of adenine in rodents. Adenine was administered to 6-week-old male C57BL/6 mice (25 and 50 mg/kg body weight) by oral gavage daily for 28 days. Serum creatinine and BUN as well as hematocrit, hemoglobin (Hb) and plasma erythropoietin (EPO) levels were monitored to assess renal function and anemia, respectively. Adenine at 25 mg/kg for 28 days slightly increased plasma creatinine levels, but did not induce anemia. In contrast, 50 mg/kg of adenine daily for 28 days showed severe renal dysfunction (plasma creatinine 1.9 ± 0.10 mg/dL) and anemia (hematocrit 36.5 ± 1.0% and EPO 28 ± 2.4 pg/mL) as compared with vehicle-treated mice (0.4 ± 0.02 mg/dL, 49.6 ± 1.6% and 61 ± 4.0 pg/mL, respectively). At the end of experiment, level of Hb also significantly reduced in 50 mg/kg adenine administration group. Remarkable histological changes of kidney tissues characterized by interstitial fibrosis and cystic appearance in tubules were observed in 50 mg/kg of adenine treatment group. These results have demonstrated that oral dosing with adenine at 50 mg/kg for 28 days is suitable to induce a stable anemia associated with CKD in mice.

High salt intake reprioritizes osmolyte and energy metabolism for body fluid conservation

Natriuretic regulation of extracellular fluid volume homeostasis includes suppression of the renin-angiotensin-aldosterone system, pressure natriuresis, and reduced renal nerve activity, actions that concomitantly increase urinary Na+ excretion and lead to increased urine volume. The resulting natriuresis-driven diuretic water loss is assumed to control the extracellular volume. Here, we have demonstrated that urine concentration, and therefore regulation of water conservation, is an important control system for urine formation and extracellular volume homeostasis in mice and humans across various levels of salt intake. We observed that the renal concentration mechanism couples natriuresis with correspondent renal water reabsorption, limits natriuretic osmotic diuresis, and results in concurrent extracellular volume conservation and concentration of salt excreted into urine. This water-conserving mechanism of dietary salt excretion relies on urea transporter-driven urea recycling by the kidneys and on urea production by liver and skeletal muscle. The energy-intense nature of hepatic and extrahepatic urea osmolyte production for renal water conservation requires reprioritization of energy and substrate metabolism in liver and skeletal muscle, resulting in hepatic ketogenesis and glucocorticoid-driven muscle catabolism, which are prevented by increasing food intake. This natriuretic-ureotelic, water-conserving principle relies on metabolism-driven extracellular volume control and is regulated by concerted liver, muscle, and renal actions.

Increased salt consumption induces body water conservation and decreases fluid intake

BACKGROUND

The idea that increasing salt intake increases drinking and urine volume is widely accepted. We tested the hypothesis that an increase in salt intake of 6 g/d would change fluid balance in men living under ultra-long-term controlled conditions.

METHODS

Over the course of 2 separate space flight simulation studies of 105 and 205 days' duration, we exposed 10 healthy men to 3 salt intake levels (12, 9, or 6 g/d). All other nutrients were maintained constant. We studied the effect of salt-driven changes in mineralocorticoid and glucocorticoid urinary excretion on day-to-day osmolyte and water balance.

RESULTS

A 6-g/d increase in salt intake increased urine osmolyte excretion, but reduced free-water clearance, indicating endogenous free water accrual by urine concentration. The resulting endogenous water surplus reduced fluid intake at the 12-g/d salt intake level. Across all 3 levels of salt intake, half-weekly and weekly rhythmical mineralocorticoid release promoted free water reabsorption via the renal concentration mechanism. Mineralocorticoid-coupled increases in free water reabsorption were counterbalanced by rhythmical glucocorticoid release, with excretion of endogenous osmolyte and water surplus by relative urine dilution. A 6-g/d increase in salt intake decreased the level of rhythmical mineralocorticoid release and elevated rhythmical glucocorticoid release. The projected effect of salt-driven hormone rhythm modulation corresponded well with the measured decrease in water intake and an increase in urine volume with surplus osmolyte excretion.

CONCLUSION

Humans regulate osmolyte and water balance by rhythmical mineralocorticoid and glucocorticoid release, endogenous accrual of surplus body water, and precise surplus excretion.

FUNDING

Federal Ministry for Economics and Technology/DLR; the Interdisciplinary Centre for Clinical Research; the NIH; the American Heart Association (AHA); the Renal Research Institute; and the TOYOBO Biotechnology Foundation. Food products were donated by APETITO, Coppenrath und Wiese, ENERVIT, HIPP, Katadyn, Kellogg, Molda, and Unilever.

Abstract P245: High-salt Diet Induces Catabolic Urea Formation and Muscle Wasting to Enable Renal Salt Concentration

Background: We showed previously that a high salt diet (HSD) increases cortisol levels in man. We hypothesized HSD induces catabolic urea generation to facilitate renal water conservation during dietary salt excretion.

Methods: 16 male mice were pair-fed either a low-salt diet (<0.1% NaCl plus tap water) or a HSD (4% NaCl plus 0.9% saline water) for two weeks. We investigated urinary concentration, body weight, MRI lean body mass, tissue urea levels, and enzymatic urea and creatine generation in liver, skeletal muscle, skin and kidney.

Results: HSD increased renal Na clearance, decreased urea clearance and resulted in urinary Na concentration. HSD reduced body weight and lean body mass, indicating catabolic muscle wasting. This catabolic state was paralleled by urea accumulation and increased arginase activity in liver and in skeletal muscle, while renal urea excretion was reduced. Expression of L-arginine:glycine amidinotransferase (AGAT), which generates the creatine precursor guanidino-acetate and is representative for anabolic liver/muscle metabolism, was selectively reduced in the livers of HSD mice.

Conclusion: HSD induces urea production and body urea accumulation to allow for water-economizing urinary Na concentration. The liver regulates Na homeostasis and induces catabolism by favoring urea over creatine production. Catabolic skeletal muscle serves as a glutamine reservoir for urea generation in HSD mice, resulting in sarcopenia.

Perspectives: Cachexia is associated with increased cardiovascular mortality and heart failure in humans. Our findings link this condition to catabolic urea osmolyte generation for maintaining Na balance.

Antihypertensive action of soluble epoxide hydrolase inhibition in Ren-2 transgenic rats is mediated by suppression of the intrarenal renin-angiotensin system

The aim of the present study was to evaluate the hypothesis that the antihypertensive effects of inhibition of soluble epoxide hydrolase (sEH) are mediated by increased intrarenal availability of epoxyeicosatrienoic acids (EETs), with consequent improvement in renal haemodynamic autoregulatory efficiency and the pressure-natriuresis relationship. Ren-2 transgenic rats (TGR), a model of angiotensin (Ang) II-dependent hypertension, and normotensive transgene-negative Hannover Sprague-Dawley (HanSD) rats were treated with the sEH inhibitor cis-4-(4-(3-adamantan-1-yl-ureido)cyclohexyloxy)benzoic acid (c-AUCB; 26 mg/L) for 48 h. Then, the effects on blood pressure (BP), autoregulation of renal blood flow (RBF) and glomerular filtration rate (GFR), and on the pressure-natriuresis relationship in response to stepwise reductions in renal arterial pressure (RAP) were determined. Treatment with c-AUCB did not significantly change BP, renal autoregulation or pressure-natriuresis in normotensive HanSD rats. In contrast, c-AUCB treatment significantly reduced BP, increased intrarenal bioavailability of EETs and significantly suppressed AngII levels in TGR. However, treatment with c-AUCB did not significantly improve the autoregulatory efficiency of RBF and GFR in response to reductions of RAP and to restore the blunted pressure-natriuresis relationship in TGR. Together, the data indicate that the antihypertensive actions of sEH inhibition in TGR are predominantly mediated via significant suppression of intrarenal renin-angiotensin system activity.

Chelation of dietary iron prevents iron accumulation and macrophage infiltration in the type I diabetic kidney

We previously reported that the functional deletion of p21, a cyclin-dependent kinase inhibitor, in mice attenuated renal cell senescence in streptozotocin (STZ)-induced type 1 diabetic mice. In the present study, we investigated the effect of iron chelation on renal cell senescence and inflammation in the type 1 diabetic kidney. STZ-treated mice showed increase in iron accumulation, tubular cell senescence and macrophage infiltration at week 28 in the kidney. Administering deferasirox, which removes only dietary iron, significantly attenuated iron accumulation in proximal tubules and the number of infiltrating F4/80-positive cells without effecting blood glucose, hematocrit or hemoglobin levels. In contrast however, deferasirox did not influence renal cell senescence. The lack of p21 decreased the renal tubular iron accumulation and did not change tubular cell senescence. Interestingly, the STZ-treated animals showed an increase in p16, another cyclin-dependent kinase inhibitor. The results suggest that type 1 diabetes increases renal tubular iron accumulation and macrophage infiltration through a p21-dependent mechanism, and that the chelation of dietary iron attenuates these responses.

Inhibition of soluble epoxide hydrolase is renoprotective in 5/6 nephrectomized Ren-2 transgenic hypertensive rats

1. The aim of the present study was to test the hypothesis that increasing kidney tissue concentrations of epoxyeicosatrienoic acids (EETs) by preventing their degradation to the biologically inactive dihydroxyeicosatrienoic acids (DHETEs) using blockade of soluble epoxide hydrolase (sEH) would attenuate the progression of chronic kidney disease (CKD).

2. Ren-2 transgenic rats (TGR) after 5/6 renal mass reduction (5/6 NX) served as a model of CKD associated with angiotensin (Ang) II-dependent hypertension. Soluble epoxide hydrolase was inhibited using cis-4-[4-(3-adamantan-1-yl-ureido)cyclohexyloxy]benzoic acid (c-AUCB; 3 mg/L drinking water) for 20 weeks after 5/6 NX. Sham-operated normotensive transgene-negative Hannover Sprague-Dawley (HanSD) rats served as controls.

3. When applied in TGR subjected to 5/6 NX, c-AUCB treatment improved survival rate, prevented the increase in blood pressure, retarded the progression of cardiac hypertrophy, reduced proteinuria and the degree of glomerular and tubulointerstitial injury and reduced glomerular volume. All these organ-protective actions were associated with normalization of the intrarenal EETs : DHETEs ratio, an index of the availability of biologically active EETs, to levels observed in sham-operated HanSD rats. There were no significant concurrent changes of increased intrarenal AngII content.

4. Together, these results show that 5/6 NX TGR exhibit a profound deficiency of intrarenal availability of active epoxygenase metabolites (EETs), which probably contributes to the progression of CKD in this model of AngII-dependent hypertension, and that restoration of intrarenal availability of EETs using long-term c-AUCB treatment exhibits substantial renoprotective actions.

Hyperglycemia causes cellular senescence via a SGLT2- and p21-dependent pathway in proximal tubules in the early stage of diabetic nephropathy

AIMS

Kidney cells in patients with diabetic nephropathy are reported to be senescent. However, the mechanisms that regulate cellular senescence in the diabetic kidney are still unknown. In the present study, we evaluated the contribution of high glucose to renal cell senescence in streptozotocin (STZ)-induced diabetic mice.

METHODS

Non-diabetic and streptozotocin (STZ, 10mgkg(-1)day(-1) for 7days, i.p.)-induced type 1 diabetic C57BL/6J mice and cultured human proximal tubular cells were used in this study.

RESULTS

Hyperglycemia dramatically increased the renal expression of p21 but not other CDK inhibitors such as p16 and p27 at 4weeks after STZ injection. These changes were accompanied by an increase in senescence-associated β-galactosidase staining in tubular epithelial cells. Administration of insulin at doses that maintained normoglycemia or mild hypoglycemia suppressed the changes induced by STZ. Insulin did not affect the senescent markers in non-diabetic mice. Exposure of cultured human proximal tubular cells to 25mmol/L, but not 8mmol/L, glucose medium increased the expression of senescence markers, which was suppressed by knock-down of p21 or sodium glucose cotransporter (SGLT) 2.

CONCLUSIONS

These results suggest that hyperglycemia causes tubular senescence via a SGLT2- and p21-dependent pathway in the type 1 diabetic kidney.

Vasoprotective effects of an endothelin receptor antagonist in ovariectomized female rats

AIMS

The effects of hormone replacement therapy with estrogen on cardiovascular disease in postmenopausal women are still controversial. In the present study, we examined the effects of an endothelin (ET) receptor antagonist (ERA) and/or angiotensin receptor blocker (ARB) on neointimal formation following vascular injury in ovariectomized (OVX) female rats.

MAIN METHODS

Female rats were divided into intact female and OVX groups. The right carotid artery was subjected to balloon injury, and harvested 2 weeks later.

KEY FINDINGS

In the intact female groups, treatment with ARB (L-158809; 1 mg/kg/day) for two weeks after the injury significantly decreased neointimal formation, whereas treatment with the ERA (J-104132; 10 mg/kg/day) did not affect neointimal formation. On the other hand, the ERA markedly decreased neointimal formation after the injury in the OVX groups; however, neointimal formation was not significantly improved by the ARB treatment. In addition, the combined treatment with 17β-estradiol (20 μg/kg/day) or the ERA and ARB markedly suppressed neointimal formation after the balloon injury in the OVX groups, whereas no combinational effects were observed due to the combined treatment with 17β-estradiol and the ERA.

SIGNIFICANCE

These results suggest that ERAs have estrogen-like vasoprotective effects on neointimal formation following balloon injury in OVX rats. ERAs may be useful as an alternative therapy to prevent vascular disease in postmenopausal women.

Abstract 505: An Iron Chelator, Deferasirox, Prevents Renal Iron Accumulation and Macrophage Infiltration But Not Cell Senescence in Type 1 Diabetic Mice

We previously reported that streptozotocin (STZ)-induced type 1 diabetes caused renal tubular cell senescence through blood glucose- and p21-dependent pathway at week 4 of STZ administration in mice. We investigated the involvement of the cell senescence on accumulation of iron in the renal tubular cells in the present study. STZ mice (n=5) did not show the significant iron accumulation in the kidney at week 4. STZ mice (n=10) showed increases in renal tubular iron accumulation (Perl’s Prussian blue: 278.1±71.9 fold vs. non-diabetic control, p<0.01), F4/80-positive macrophage infiltration (2.6±0.6 fold vs. non-diabetic control, p<0.01), and cell senescence (senescence-associated β galactosidase: 3.7±0.4 fold, p16 mRNA: 2.3±0.2 fold vs. non-diabetic control, respectively, p<0.01, respectively) at week 28. Administering oral iron chelator, deferasirox (10 mg/kg/day, n=10), that removes only dietary iron, significantly attenuated the iron accumulation (38.1±12.4 fold vs. non-diabetic control, n.s.) in proximal tubules and the F4/80-positive cells number (1.3±0.3 fold, vs. non-diabetic control, n.s.) without the effect on blood glucose, hematocrit and hemoglobin levels. On the other hand, deferasirox did not affect renal cell senescence (senescence-associated β galactosidase: 3.9±0.5 fold, p16 mRNA: 2.4±0.3 fold vs. non-diabetic control, respectively, n.s.). The functional deletion of p21, a cyclin-dependent kinase inhibitor, in mice decreased the renal tubular iron accumulation (14.0±5.5 fold vs. non-diabetic control, p<0.01), and did not change the cell senescence at week 28. The animals showed an increase in p16, another cyclin-dependent kinase inhibitor, suggesting that p16 rather than p21 plays important role on cell senescence in the kidney of STZ mice at this time point. The results indicate that the chelation of dietary iron attenuates renal iron accumulation and macrophage infiltration through p21-dependent pathway in STZ mice. It seems likely that there is little interaction between renal tubular cell senescence and iron accumulation in the type 1 diabetic kidney.

Abstract 284: P21 is Essential for the Beneficial Effects of Renal Ischemic Preconditioning in Ischemic Acute Kidney Injury

We previously reported that p21, a cell cycle regulator, plays important roles in chronic hypertensive renal injury. However, the roles of renal p21 in acute kidney injury, a life-threatening disease that can occur independently of the pathological background of patients (whether renal p21 is up-regulated or not), have not been fully clarified yet. In the present study, we evaluated the role of p21 in acute kidney injury and the effects of ischemic preconditioning (IPC). The mice lacking functional p21 (p21-KO) and its wild-type control underwent renal ischemia followed by reperfusion (I/R) with or without ischemic preconditioning. IPC attenuated I/R injury in wild-type mice, but not in p21-KO mice. Moreover, IPC increased the renal expression of p21 prior to I/R compared with sham surgery (p21/β-actin, sham: 1.00±0.18 fold, IPC: 4.12±0.32 fold, n=6, p<0.01). Immunohistochemisty (IHC) for p21 showed that there was an increase in the number of p21-positive tubular cells in mice that underwent I/R with and without IPC, and that the p21 immunoreactivity was increased in the nuclei of tubular cells, suggesting the effects on cell cycle. IPC decreased the number of proliferating tubular cells before I/R (0.24±0.11 fold vs. sham group, p<0.01) and increased it at 24 h after I/R (1.66±0.03 fold vs. sham group, p<0.01) in the kidney of wild-type mice. In p21-KO mice, IPC did not change the number of proliferating cells before I/R (0.99±0.10 fold, vs. sham group), and decreased it after I/R (0.53±0.08 fold, vs. sham group, p<0.01). Flow cytometry showed that IPC increased the number of cells in the G1 phase of cell cycle before I/R compared with sham surgery. Additionally, intravital imaging in combination with the mice that express mKO2, a fluorescent protein, at G1 phase of cell cycle showed that IPC increased the number of mKO2-positive cells in the proximal tubules. In conclusion, renal p21 is essential for the beneficial effects of renal IPC. Transient cell cycle arrest by IPC through a p21-dependent pathway seems to be important for recovering tubular cell proliferation after I/R.

Aldosterone induces p21-regulated apoptosis via increased synthesis and secretion of tumour necrosis factor-α in human proximal tubular cells

1. Aldosterone has been shown to mediate p21-dependent cellular senescence in rat kidney proximal tubules in vivo and in cultured human proximal tubular cells. The p21-induced senescent cells express higher levels of apoptotic cytokines, such as tumour necrosis factor (TNF)-α compared with non-senescent cells. The aim of the present study was to investigate the hypothesis that aldosterone increases proximal tubular apoptosis by increasing the secretion of apoptosis-inducing factors through a p21-dependent mechanism. 2. Human proximal tubular cells were incubated with aldosterone (10 nmol/L) and cell senescence was detected by senescence-associated β-galactosidase staining and expression of p21. Apoptosis was analysed by terminal deoxyribonucleotidyl transferase-mediated dUTP-digoxigenin nick end-labelling and annexin/propidium iodide staining, whereas p21 localization was determined by immunofluorescence. 3. Exposure of cells to aldosterone for 3 or 5 days increased senescence-associated β-galactosidase staining, p21 and TNF-α mRNA expression and secretion of TNF-α into the culture medium. These changes were abolished by gene silencing of p21. Aldosterone failed to increase the number of apoptotic cells on day 3, but did increase them on day 5. A neutralizing antibody against TNF-α prevented the aldosterone-induced apoptotic changes. Aldosterone did not affect localization of p21. 4. These findings indicate that aldosterone increases TNF-α synthesis and secretion in proximal tubular cells via p21/senescence-dependent cell phenotypic changes and that the TNF-α secreted plays an important role as a paracrine factor in mediating cell apoptosis, indicating a possible involvement in aldosterone-induced renal damage.