Renal denervation has blood pressure-independent protective effects on kidney and heart in a rat model of chronic kidney disease

The Total Denervation of the Ischemic Kidney Induces Differential Responses in Sodium Transporters' Expression in the Contralateral Kidney in Goldblatt Rats

The Goldblatt model of hypertension (2K-1C) in rats is characterized by renal sympathetic nerve activity (rSNA). We investigated the effects of unilateral renal denervation of the clipped kidney (DNX) on sodium transporters of the unclipped kidneys and the cardiovascular, autonomic, and renal functions in 2K-1C and control (CTR) rats. The mean arterial pressure (MAP) and rSNA were evaluated in experimental groups. Kidney function and NHE3, NCC, ENaCβ, and ENaCγ protein expressions were assessed. The glomerular filtration rate (GRF) and renal plasma flow were not changed by DNX, but the urinary (CTR: 0.0042 ± 0.001; 2K-1C: 0.014 ± 0.003; DNX: 0.005 ± 0.0013 mL/min/g renal tissue) and filtration fractions (CTR: 0.29 ± 0.02; 2K-1C: 0.51 ± 0.06; DNX: 0.28 ± 0.04 mL/min/g renal tissue) were normalized. The Na+/H+ exchanger (NHE3) was reduced in 2K-1C, and DNX normalized NHE3 (CTR: 100 ± 6; 2K-1C: 44 ± 14, DNX: 84 ± 13%). Conversely, the Na+/Cl- cotransporter (NCC) was increased in 2K-1C and was reduced by DNX (CTR: 94 ± 6; 2K-1C: 144 ± 8; DNX: 60 ± 15%). In conclusion, DNX in Goldblatt rats reduced blood pressure and proteinuria independently of GRF with a distinct regulation of NHE3 and NCC in unclipped kidneys.

Salt-Sensitive Hypertension and the Kidney

Salt-sensitive hypertension (SS-HT) is characterized by blood pressure elevation in response to high dietary salt intake and is considered to increase the risk of cardiovascular and renal morbidity. Although the mechanisms responsible for SS-HT are complex, the kidneys are known to play a central role in the development of SS-HT and the salt sensitivity of blood pressure (SSBP). Moreover, several factors influence renal function and SSBP, including the renin-angiotensin-aldosterone system, sympathetic nervous system, obesity, and aging. A phenotypic characteristic of SSBP is aberrant activation of the renin-angiotensin system and sympathetic nervous system in response to excessive salt intake. SSBP is also accompanied by a blunted increase in renal blood flow after salt loading, resulting in sodium retention and SS-HT. Obesity is associated with inappropriate activation of the aldosterone mineralocorticoid receptor pathway and renal sympathetic nervous system in response to excessive salt, and mineralocorticoid receptor antagonists and renal denervation attenuate sodium retention and inhibit salt-induced blood pressure elevation in obese dogs and humans. SSBP increases with age, which has been attributed to impaired renal sodium handling and a decline in renal function, even in the absence of kidney disease. Aging-associated changes in renal hemodynamics are accompanied by significant alterations in renal hormone levels and renal sodium handling, resulting in SS-HT. In this review, we focus mainly on the contribution of renal function to the development of SS-HT.

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.

Cardiorenal damages in mice at early phase after intervention induced by angiotensin II, nephrectomy, and salt intake

The interconnection of heart performance and kidney function plays an important role for maintaining homeostasis through a variety of physiological crosstalk between these organs. It has been suggested that acute or chronic dysfunction in one organ causes dysregulation in another one, like patients with cardiorenal syndrome. Despite its growing recognition as global health issues, still little is known on pathophysiological evaluation between the two organs. Previously, we established a preclinical murine model with cardiac hypertrophy and fibrosis, and impaired kidney function with renal enlargement and increased urinary albumin levels induced by co-treatment with vasopressor angiotensin II (A), unilateral nephrectomy (N), and salt loading (S) (defined as ANS treatment) for 4 weeks. However, how both tissues, heart and kidney, are initially affected by ANS treatment during the progression of tissue damages remains to be determined. Here, at one week after ANS treatment, we found that cardiac function in ANS-treated mice (ANS mice) are sustained despite hypertrophy. On the other hand, kidney dysfunction is evident in ANS mice, associated with high blood pressure, enlarged glomeruli, increased levels of urinary albumin and urinary neutrophil gelatinase-associated lipocalin, and reduced creatinine clearance. Our results suggest that cardiorenal tissues become damaged at one week after ANS treatment and that ANS mice are useful as a model causing transition from early to late-stage damages of cardiorenal tissues.

Renal Denervation Influences Angiotensin II Types 1 and 2 Receptors

The sympathetic and renin-angiotensin systems (RAS) are two critical regulatory systems in the kidney which affect renal hemodynamics and function. These two systems interact with each other so that angiotensin II (Ang II) has the presynaptic effect on the norepinephrine secretion. Another aspect of this interaction is that the sympathetic nervous system affects the function and expression of local RAS receptors, mainly Ang II receptors. Therefore, in many pathological conditions associated with an increased renal sympathetic tone, these receptors' expression changes and renal denervation can normalize these changes and improve the diseases. It seems that the renal sympathectomy can alter Ang II receptors expression and the distribution of RAS receptors in the kidneys, which influence renal functions.

Toward Human Models of Cardiorenal Syndrome in vitro

Heart and kidney diseases cause high morbidity and mortality. Heart and kidneys have vital functions in the human body and, interestingly, reciprocally influence each other’s behavior: pathological changes in one organ can damage the other. Cardiorenal syndrome (CRS) is a group of disorders in which there is combined dysfunction of both heart and kidney, but its underlying biological mechanisms are not fully understood. This is because complex, multifactorial, and dynamic mechanisms are likely involved. Effective treatments are currently unavailable, but this may be resolved if more was known about how the disease develops and progresses. To date, CRS has actually only been modeled in mice and rats in vivo. Even though these models can capture cardiorenal interaction, they are difficult to manipulate and control. Moreover, interspecies differences may limit extrapolation to patients. The questions we address here are what would it take to model CRS in vitro and how far are we? There are already multiple independent in vitro (human) models of heart and kidney, but none have so far captured their dynamic organ-organ crosstalk. Advanced in vitro human models can provide an insight in disease mechanisms and offer a platform for therapy development. CRS represents an exemplary disease illustrating the need to develop more complex models to study organ-organ interaction in-a-dish. Human induced pluripotent stem cells in combination with microfluidic chips are one powerful tool with potential to recapitulate the characteristics of CRS in vitro. In this review, we provide an overview of the existing in vivo and in vitro models to study CRS, their limitations and new perspectives on how heart-kidney physiological and pathological interaction could be investigated in vitro for future applications.

Effects of renal sympathetic denervation on the course of congestive heart failure combined with chronic kidney disease: Insight from studies with fawn-hooded hypertensive rats with volume overload induced using aorto-caval fistula

Background: The coincidence of congestive heart failure (CHF) and chronic kidney disease (CKD) results in poor survival rate. The aim of the study was to examine if renal denervation (RDN) would improve the survival rate in CHF induced by creation of aorto-caval fistula (ACF).Methods: Fawn-hooded hypertensive rats (FHH), a genetic model of spontaneous hypertension associated with CKD development, were used. Fawn-hooded low-pressure rats (FHL), without CKD, served as controls. RDN was performed 4 weeks after creation of ACF and the follow-up period was 10 weeks.Results: We found that intact (non-denervated) ACF FHH exhibited survival rate of 58.8% (20 out of 34 rats), significantly lower than in intact ACF FHL (81.3%, 26/32 rats). In intact ACF FHL albuminuria remained stable throughout the study, whereas in ACF FHH it increased significantly, up to a level 40-fold higher than the basal values. ACF FHL did not show increases in renal glomerular and tubulointerstitial injury as compared with FHL, while ACF FHH exhibited marked increases in kidney injury as compared with FHH. RDN did not improve the survival rate in either ACF FHL or ACF FHH and did not alter the course of albuminuria in ACF FHL. RDN attenuated the albuminuria, but did not reduce the kidney injury in ACF FHH.Conclusions: Our present results support the notion that even modest CKD increases CHF-related mortality. RDN did not attenuate CHF-dependent mortality in ACF FHH, it delayed the progressive rise in albuminuria, but it did not reduce the degree of kidney injury.

Inhibition of α2-adrenoceptor is renoprotective in 5/6 nephrectomy-induced chronic kidney injury rats

In the present study, we investigated the renoprotective effects of long-term treatment with yohimbine, an α2-adrenoceptor inhibitor, in a 5/6 nephrectomy-induced chronic kidney disease (CKD) rat model. Male Sprague-Dawley rats were randomly allocated into the following groups: sham-operated, 5/6-nephrectomized (5/6 Nx), 5/6 Nx + low or high dose of yohimbine (0.3 or 3.0 mg/L in drinking water, respectively), and 5/6 Nx + hydralazine (250 mg/L in drinking water). The 5/6 Nx group presented with renal dysfunction, hypertension, noradrenaline overproduction, and histopathological injuries. Blood pressure decreased in both the yohimbine- and hydralazine-treated groups. Treatment with high dose of yohimbine, but not hydralazine, apparently attenuated urinary protein excretion and noradrenaline concentration of renal venous plasma. Renal fibrosis and upregulated fibrosis-related gene expression were suppressed by high dose of yohimbine. Furthermore, yohimbine, but not hydralazine, treatment ameliorated the urinary concentration ability. These findings suggest that long-term yohimbine treatment can be a useful therapeutic option to prevent the progression of CKD.

Protective Effect of Vitis labrusca Leaves Extract on Cardiovascular Dysfunction through HMGB1-TLR4-NFκB Signaling in Spontaneously Hypertensive Rats

The Vitis labrusca is a grapevine that has antioxidant, neuroprotective, hepatoprotective, and anticarcinogenic activity. However, the effect of Vitis labrusca leaves on the cardiovascular system is yet to be ascertained. The present study was designed to investigate the effects of Vitis labrusca leaves extract (HP1) on cardiovascular remodeling in spontaneously hypertensive rats. Experiments were performed in rats and were randomly divided into the following groups: Wistar Kyoto rat (WKY), normal control group; spontaneously hypertensive rats (SHR), negative control group; SHR + Losa, positive control group (losartan, 10 mg/kg/daily, AT₁ receptor blocker) and SHR + HP1 (100 mg/kg/daily). HP1 was orally administered daily for 4 weeks. The HP1 treatment significantly improved blood pressure, electrocardiographic parameters, and echocardiogram parameters compared to hypertensive rats. Additionally, the left ventricular (LV) remodeling and LV dysfunction were significantly improved in HP1-treated hypertensive rats. Furthermore, an increase in fibrotic area has been observed in hypertensive rats compared with WKY. However, administration of HP1 significantly attenuated cardiac fibrosis in hypertensive rats. Moreover, HP1 suppressed the expression of high mobility group box 1 (HMGB1), toll-like receptor 4 (TLR4), myeloid differentiation primary response 88 (MyD88), nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB), tumor necrosis factor alpha (TNF-α), interleukin-6 (IL-6), receptor for advanced glycation end products (RAGE), and extracellular signal-regulated kinases (ERK1/2) induced by hypertensive rats, resulting in improved vascular remodeling. Therefore, these results suggest that HP1 can improve the cardiovascular remodeling in hypertensive rats, and the mechanisms may be related to the suppressive effect of HP1 on HMGB1-TLR4-NFκB signaling in the cardiovascular system. Thus, the protective role of the traditional herbal medicine HP1 may provide new insights into the development of therapeutic drugs on the development of hypertensive cardiovascular dysfunction.

A role for NPY-NPY2R signaling in albuminuric kidney disease

Neuropeptide Y (NPY) is implicated in many pathological conditions including obesity, diabetes, and insulin resistance. However, a pathogenic role of NPY in kidney disease has not been described. We found that NPY is produced by the podocyte in the glomerulus, and this production decreases in renal disease, in contrast to an increase in circulating NPY levels. In the glomerulus, NPY signals via the NPY receptor 2 (NPY2R) and modulates PI3K, MAPK, and NFAT signaling, along with RNA processing and cell migration and, if prolonged, predicted nephrotoxicity. The pharmacological inhibition of NPY-NPY2R signaling also protected against albuminuria and kidney disease in a mouse model of glomerulosclerosis, suggesting that inhibiting this pathway may be therapeutically beneficial in the prevention of kidney disease.

Albuminuria is an independent risk factor for the progression to end-stage kidney failure, cardiovascular morbidity, and premature death. As such, discovering signaling pathways that modulate albuminuria is desirable. Here, we studied the transcriptomes of podocytes, key cells in the prevention of albuminuria, under diabetic conditions. We found that Neuropeptide Y (NPY) was significantly down-regulated in insulin-resistant vs. insulin-sensitive mouse podocytes and in human glomeruli of patients with early and late-stage diabetic nephropathy, as well as other nondiabetic glomerular diseases. This contrasts with the increased plasma and urinary levels of NPY that are observed in such conditions. Studying NPY-knockout mice, we found that NPY deficiency in vivo surprisingly reduced the level of albuminuria and podocyte injury in models of both diabetic and nondiabetic kidney disease. In vitro, podocyte NPY signaling occurred via the NPY2 receptor (NPY2R), stimulating PI3K, MAPK, and NFAT activation. Additional unbiased proteomic analysis revealed that glomerular NPY-NPY2R signaling predicted nephrotoxicity, modulated RNA processing, and inhibited cell migration. Furthermore, pharmacologically inhibiting the NPY2R in vivo significantly reduced albuminuria in adriamycin-treated glomerulosclerotic mice. Our findings suggest a pathogenic role of excessive NPY-NPY2R signaling in the glomerulus and that inhibiting NPY-NPY2R signaling in albuminuric kidney disease has therapeutic potential.

Histamine receptor agonist alleviates severe cardiorenal damages by eliciting anti-inflammatory programming

Heart failure and chronic kidney disease are major causes of morbidity and mortality internationally. Although these dysfunctions are common and frequently coexist, the factors involved in their relationship in cardiorenal regulation are still largely unknown, mainly due to a lack of detailed molecular targets. Here, we found the increased plasma histamine in a preclinical mouse model of severe cardiac dysfunction, that had been cotreated with angiotensin II (Ang II), nephrectomy, and salt (ANS). The ANS mice exhibited impaired renal function accompanied with heart failure, and histamine depletion, by the genetic inactivation of histidine decarboxylase in mice, exacerbated the ANS-induced cardiac and renal abnormalities, including the reduction of left ventricular fractional shortening and renal glomerular and tubular injuries. Interestingly, while the pharmacological inhibition of the histamine receptor H3 facilitated heart failure and kidney injury in ANS mice, administration of the H3 agonist immethridine (Imm) was protective against cardiorenal damages. Transcriptome analysis of the kidney and biochemical examinations using blood samples illustrated that the increased inflammation in ANS mice was alleviated by Imm. Our results extend the pharmacological use of H3 agonists beyond the initial purposes of its drug development for neurogenerative diseases and have implications for therapeutic potential of H3 agonists that invoke the anti-inflammatory gene expression programming against cardiorenal damages.

Renal sympathetic nerve activation via α2-adrenergic receptors in chronic kidney disease progression

Chronic kidney disease (CKD) is increasing worldwide without an effective therapeutic strategy. Sympathetic nerve activation is implicated in CKD progression, as well as cardiovascular dysfunction. Renal denervation is beneficial for controlling blood pressure (BP) and improving renal function through reduction of sympathetic nerve activity in patients with resistant hypertension and CKD. Sympathetic neurotransmitter norepinephrine (NE) via adrenergic receptor (AR) signaling has been implicated in tissue homeostasis and various disease progressions, including CKD. Increased plasma NE level is a predictor of survival and the incidence of cardiovascular events in patients with end-stage renal disease, as well as future renal injury in subjects with normal BP and renal function. Our recent data demonstrate that NE derived from renal nerves causes renal inflammation and fibrosis progression through alpha-2 adrenergic receptors (α₂-AR) in renal fibrosis models independent of BP. Sympathetic nerve activation-associated molecular mechanisms and signals seem to be critical for the development and progression of CKD, but the exact role of sympathetic nerve activation in CKD progression remains undefined. This review explores the current knowledge of NE-α₂-AR signaling in renal diseases and offers prospective views on developing therapeutic strategies targeting NE-AR signaling in CKD progression.

Heart-kidney interactions: mechanistic insights from animal models

Pathological changes in the heart or kidney can instigate the release of a cascade of cardiorenal mediators that promote injury in the other organ. Combined dysfunction of heart and kidney is referred to as cardiorenal syndrome (CRS) and has gained considerable attention. CRS has been classified into five distinct entities, each with different major pathophysiological changes. Despite the magnitude of the public health problem of CRS, the underlying mechanisms are incompletely understood, and effective intervention is unavailable. Animal models have allowed us to discover pathogenic molecular changes to clarify the pathophysiological mechanisms responsible for heart-kidney interactions and to enable more accurate risk stratification and effective intervention. Here, this article focuses on the use of currently available animal models to elucidate mechanistic insights in the clinical cardiorenal phenotype arising from primary cardiac injury, primary renal disease with special emphasis of chronic kidney disease-specific risk factors, and simultaneous cardiorenal/renocardiac dysfunction. The development of novel animal models that recapitulate more closely the cardiorenal phenotype in a clinical scenario and discover the molecular basis of this condition will be of great benefit.

Renal nerves contribute to hypertension in Schlager BPH/2J mice

Schlager mice (BPH/2J) are hypertensive due to a greater contribution of the sympathetic nervous system (SNS) and renin-angiotensin system (RAS). The kidneys of BPH/2J are hyper-innervated suggesting renal nerves may contribute to the hypertension. We therefore determined the effect of bilateral renal denervation (RD) on hypertension in BPH/2J. Mean arterial pressure (MAP) was measured by radiotelemetry before and for 3 weeks after RD in BPH/2J and BPN/3J. The effects of pentolinium and enalaprilat were examined to determine the contribution of the SNS and RAS, respectively. After 3 weeks, MAP was -10.9 ± 2.1 mmHg lower in RD BPH/2J compared to baseline and -2.1 ± 2.2 mmHg in sham BPH/2J (P < 0.001, n = 8-10). RD had no effect in BPN/3J (P > 0.1). The depressor response to pentolinium was greater in BPH/2J than BPN/3J, but in both cases the response in RD mice was similar to sham. Enalaprilat decreased MAP more in RD BPH/2J compared to sham (-12 vs -3 mmHg, P < 0.001) but had no effect in BPN/3J. RD reduced renal noradrenaline in both strains but more so in BPH/2J. RD reduced renin mRNA and protein, but not plasma renin in BPH/2J to levels comparable with BPN/3J mice. We conclude that renal nerves contribute to hypertension in BPH mice as RD induced a sustained fall in MAP, which was associated with a reduction of intrarenal renin expression. The lack of inhibition of the depressor effects of pentolinium and enalaprilat by RD suggests that vasoconstrictor effects of the SNS or RAS are not involved.

Association of B-Type Natriuretic Peptide Level With Residual Kidney Function in Incident Peritoneal Dialysis Patients

BACKGROUND

Residual kidney function (RKF) is an important factor influencing both technique and patient survival in peritoneal dialysis (PD) patients. B-type natriuretic peptide (BNP) is considered a marker of cardio-renal syndrome. The relationship between BNP and RKF in PD patients remains unclear.

METHODS

We conducted a prospective study of 89 patients who had started and continued PD for 6 months or more in Kyushu University Hospital between June 2006 and September 2015. Participants were divided into low BNP (≤ 102.1 ng/L) and high BNP (> 102.1 ng/L) groups according to median plasma BNP level at PD initiation. The primary outcome was RKF loss, defined as 24-hour urine volume less than 100 mL. We estimated the association between BNP and RKF loss using a Kaplan-Meier method and Cox proportional hazards model and compared the rate of RKF decline between the 2 groups. To evaluate the consistency of the association, we performed subgroup analysis stratified by baseline characteristics.

RESULTS

During the median follow-up of 30 months, 30 patients lost RKF. Participants in the high BNP group had a 5.87-fold increased risk for RKF loss compared with the low BNP group after adjustment for clinical and cardiac parameters. A high plasma BNP level was more clearly associated with RKF loss in younger participants compared with older participants in subgroup analysis.

CONCLUSIONS

B-type natriuretic peptide may be a useful risk marker for RKF loss in PD patients. The clinical importance of plasma BNP level as a marker of RKF loss might be affected by age.

The Impact of the Nitric Oxide (NO)/Soluble Guanylyl Cyclase (sGC) Signaling Cascade on Kidney Health and Disease: A Preclinical Perspective

Chronic Kidney Disease (CKD) is a highly prevalent disease with a substantial medical need for new and more efficacious treatments. The Nitric Oxide (NO), soluble guanylyl cyclase (sGC), cyclic guanosine monophosphate (cGMP) signaling cascade regulates various kidney functions. cGMP directly influences renal blood flow, renin secretion, glomerular function, and tubular exchange processes. Downregulation of NO/sGC/cGMP signaling results in severe kidney pathologies such as CKD. Therefore, treatment strategies aiming to maintain or increase cGMP might have beneficial effects for the treatment of progressive kidney diseases. Within this article, we review the NO/sGC/cGMP signaling cascade and its major pharmacological intervention sites. We specifically focus on the currently known effects of cGMP on kidney function parameters. Finally, we summarize the preclinical evidence for kidney protective effects of NO-donors, PDE inhibitors, sGC stimulators, and sGC activators.

Renal tubular ACE-mediated tubular injury is the major contributor to microalbuminuria in early diabetic nephropathy

Diabetic nephropathy is a major cause of end-stage renal disease in developed countries. While angiotensin-converting enzyme (ACE) inhibitors are used to treat diabetic nephropathy, how intrarenal ACE contributes to diabetic renal injury is uncertain. Here, two mouse models with different patterns of renal ACE expression were studied to determine the specific contribution of tubular vs. glomerular ACE to early diabetic nephropathy: it-ACE mice, which make endothelial ACE but lack ACE expression by renal tubular epithelium, and ACE 3/9 mice, which lack endothelial ACE and only express renal ACE in tubular epithelial cells. The absence of endothelial ACE normalized the glomerular filtration rate and endothelial injury in diabetic ACE 3/9 mice. However, these mice developed tubular injury and albuminuria and displayed low renal levels of megalin that were similar to those observed in diabetic wild-type mice. In diabetic it-ACE mice, despite hyperfiltration, the absence of renal tubular ACE greatly reduced tubulointerstitial injury and albuminuria and increased renal megalin expression compared with diabetic wild-type and diabetic ACE 3/9 mice. These findings demonstrate that endothelial ACE is a central regulator of the glomerular filtration rate while tubular ACE is a key player in the development of tubular injury and albuminuria. These data suggest that tubular injury, rather than hyperfiltration, is the main cause of microalbuminuria in early diabetic nephropathy.

Renal denervation attenuates aldosterone expression and associated cardiovascular pathophysiology in angiotensin II-induced hypertension

The sympathetic nervous system interacts with the renin-angiotensin-aldosterone system (RAAS) contributing to cardiovascular diseases. In this study, we sought to determine if renal denervation (RDN) inhibits aldosterone expression and associated cardiovascular pathophysiological changes in angiotensin II (Ang II)-induced hypertension. Bilateral RDN or SHAM operation was performed before chronic 14-day Ang II subcutaneous infusion (200ng/kg/min) in male Sprague-Dawley rats. Bilateral RDN blunted Ang II-induced hypertension and ameliorated the mesenteric vascular dysfunction. Cardiovascular hypertrophy in response to Ang II was significantly attenuated by RDN as shown by histopathology and transthoracic echocardiography. Moreover, Ang II-induced vascular and myocardial inflammation and fibrosis were suppressed by RDN with concurrent decrease in fibronectin and collagen deposition, macrophage infiltration, and MCP-1 expression. Interestingly, RDN also inhibited Ang II-induced aldosterone expression in the plasma, kidney and heart. This was associated with the reduction of calcitonin gene-related peptide (CGRP) in the adrenal gland. Ang II promoted aldosterone secretion which was partly attenuated by CGRP in the adrenocortical cell line, suggesting a protective role of CGRP in this model. Activation of transforming growth factor-β (TGF-β)/Smad and mitogen-activated protein kinases (MAPKs) signaling pathway was both inhibited by RDN especially in the heart. These results suggest that the regulation of the renal sympathetic nerve in Ang II-induced hypertension and associated cardiovascular pathophysiological changes is likely mediated by aldosterone, with CGRP involvement.

Low-dose hydralazine prevents fibrosis in a murine model of acute kidney injury-to-chronic kidney disease progression

Acute kidney injury (AKI) and progressive chronic kidney disease (CKD) are intrinsically tied syndromes. In this regard, the acutely injured kidney often does not achieve its full regenerative capacity and AKI directly transitions into progressive CKD associated with tubulointerstitial fibrosis. Underlying mechanisms of such AKI-to-CKD progression are still incompletely understood and specific therapeutic interventions are still elusive. Because epigenetic modifications play a role in maintaining tissue fibrosis, we used a murine model of ischemia-reperfusion injury to determine whether aberrant promoter methylation of RASAL1 contributes causally to the switch between physiological regeneration and tubulointerstitial fibrogenesis, a hallmark of AKI-to-CKD progression. It is known that the antihypertensive drug hydralazine has demethylating activity, and that its optimum demethylating activity occurs at concentrations below blood pressure-lowering doses. Administration of low-dose hydralazine effectively induced expression of hydroxylase TET3, which catalyzed RASAL1 hydroxymethylation and subsequent RASAL1 promoter demethylation. Hydralazine-induced CpG promoter demethylation subsequently attenuated renal fibrosis and preserved excretory renal function independent of its blood pressure-lowering effects. In comparison, RASAL1 demethylation and inhibition of tubulointerstitial fibrosis was not detected upon administration of the angiotensin-converting enzyme inhibitor Ramipril in this model. Thus, RASAL1 promoter methylation and subsequent transcriptional RASAL1 suppression plays a causal role in AKI-to-CKD progression.

Chronic Kidney Disease As a Potential Indication for Renal Denervation

Renal denervation is being used as a blood pressure lowering therapy for patients with apparent treatment resistant hypertension. However, this population does not represent a distinct disease condition in which benefit is predictable. In fact, the wide range in effectiveness of renal denervation could be a consequence of this heterogeneous pathogenesis of hypertension. Since renal denervation aims at disrupting sympathetic nerves surrounding the renal arteries, it seems obvious to focus on patients with increased afferent and/or efferent renal sympathetic nerve activity. In this review will be argued, from both a pathophysiological and a clinical point of view, that chronic kidney disease is particularly suited to renal denervation.

Renal Sympathetic Denervation in Rats

Experimental renal sympathetic denervation is a well-established technique. Classically, renal sympathetic denervation is achieved by dorsal rhizotomy. While more recently, direct renal sympathetic denervation is typically applied by stripping all visible renal nerve bundles followed by painting with a solution of 10 % phenol in ethanol to remove the remaining nerves. In clinical settings, a reliable marker of renal sympathetic denervation or renal sympathetic overactivity has not been established. However, in experimental models, successful renal sympathetic denervation is validated by a decrease in renal norepinephrine content levels. This facilitates the assessment of incomplete denervation by technical failure and reinnervation for long-term experimental models. In this chapter, we introduce comprehensive methods for direct renal sympathetic denervation and measurement of renal norepinephrine content levels.

Renal denervation mitigates cardiac remodeling and renal damage in Dahl rats: a comparison with β-receptor blockade

Chronic activation of the sympathetic nervous system (SNS) contributes to cardiac remodeling and the transition to heart failure (HF). Renal sympathetic denervation (RDN) may ameliorate this damage by improving renal function and sympathetic cardioregulation in hypertensive HF patients with renal injury. The efficacy may be comparable to that of chronic β-blocker treatment. Dahl salt-sensitive hypertensive rats were subjected to RDN in the hypertrophic stage. Another group of Dahl rats were subjected to sham operations and treated chronically with vehicle (CONT) or β-blocker bisoprolol (BISO). Neither RDN nor BISO altered the blood pressure; however, BISO significantly reduced the heart rate (HR). Both RDN and BISO significantly prolonged survival (22.2 and 22.4 weeks, respectively) compared with CONT (18.3 weeks). Echocardiography revealed reduced left ventricular (LV) hypertrophy and improved LV function, and histological analysis demonstrated the amelioration of LV myocyte hypertrophy and fibrosis in the RDN and BISO rats at the HF stage. Tyrosine hydroxylase and β1-adrenergic receptor (ADR) expression levels in the LV myocardium significantly increased only in the RDN rats, whereas the α1b-, α1d- and α2c-ADR expression levels increased only in the BISO rats. In both groups, renal damage and dysfunction were also reduced, and this reduction was accompanied by the suppression of endothelin-1, renin and angiotensin-converting enzyme mRNAs. RDN ameliorated the progression of both myocardial and renal damage in the hypertensive rats independent of blood pressure changes. The overall effects were similar to those of β-receptor blockade with favorable effects on HR and α-ADR expression. These findings may be associated with the restoration of the myocardial SNS and renal protection.

Assessment of urinary angiotensinogen as a marker of podocyte injury in proteinuric nephropathies

Urinary protein (UP) is widely used as a clinical marker for podocyte injury; however, not all proteinuric nephropathies fit this model. We previously described the elevation of urinary angiotensinogen (AGT) accompanied by AGT expression by injured podocytes in a nitric oxide inhibition rat model (Eriguchi M, Tsuruya K, Haruyama N, Yamada S, Tanaka S, Suehiro T, Noguchi H, Masutani K, Torisu K, Kitazono T. Kidney Int 87: 116-127, 2015). In this report, we performed the human and animal studies to examine the significance and origin of urinary AGT. In the human study, focal segmental glomerulosclerosis (FSGS) patients presented with higher levels of urinary AGT, corrected by UP, than minimal-change disease (MCD) patients. Furthermore, AGT was evident in podocin-negative glomerular segmental lesions. We also tested two different nephrotic models induced by puromycin aminonucleoside in Wistar rats. The urinary AGT/UP ratio and AGT protein and mRNA expression in sieved glomeruli from FSGS rats were significantly higher than in MCD rats. The presence of AGT at injured podocytes in FSGS rats was detected by immunohistochemistry and immunoelectron microscopy. Finally, we observed the renal tissue and urinary metabolism of exogenous injected human recombinant AGT (which is not cleaved by rodent renin) in FSGS and control rats. Significant amounts of human AGT were detected in the urine of FSGS rats, but not of control rats. Immunostaining for rat and human AGT identified that only rat AGT was detected in injured podocytes, and filtered human AGT was seen in superficial proximal tubules, but not in injured podocytes, suggesting AGT generation by injured podocytes. In conclusion, the urinary AGT/UP ratio represents a novel specific marker of podocyte injury.

Animal Models to Study Links between Cardiovascular Disease and Renal Failure and Their Relevance to Human Pathology

The close association between cardiovascular pathology and renal dysfunction is well documented and significant. Patients with conventional risk factors for cardiovascular disease like diabetes and hypertension also suffer renal dysfunction. This is unsurprising if the kidney is simply regarded as a “modified blood vessel” and thus, traditional risk factors will affect both systems. Consistent with this, it is relatively easy to comprehend how patients with either sudden or gradual cardiac and or vascular compromise have changes in both renal hemodynamic and regulatory systems. However, patients with pure or primary renal dysfunction also have metabolic changes (e.g., oxidant stress, inflammation, nitric oxide, or endocrine changes) that affect the cardiovascular system. Thus, cardiovascular and renal systems are intimately, bidirectionally and inextricably linked. Whilst we understand several of these links, some of the mechanisms for these connections remain incompletely explained. Animal models of cardiovascular and renal disease allow us to explore such mechanisms, and more importantly, potential therapeutic strategies. In this article, we review various experimental models used, and examine critically how representative they are of the human condition.

Direct conscious telemetry recordings demonstrate increased renal sympathetic nerve activity in rats with chronic kidney disease

Chronic kidney disease (CKD) is associated with sympathetic hyperactivity and impaired blood pressure control reflex responses, yet direct evidence demonstrating these features of autonomic dysfunction in conscious animals is still lacking. Here we measured renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) using telemetry-based recordings in a rat model of CKD, the Lewis Polycystic Kidney (LPK) rat, and assessed responses to chemoreflex activation and acute stress. Male LPK and Lewis control animals (total n = 16) were instrumented for telemetric recording of RSNA and MAP. At 12–13 weeks-of-age, resting RSNA and MAP, sympathetic and haemodynamic responses to both peripheral (hypoxia: 10% O₂) and central chemoreflex (hypercapnia: 7% CO₂) activation and acute stress (open-field exposure), were measured. As indicators of renal function, urinary protein (U_Pro) and creatinine (U_Cr) levels were assessed. LPK rats had higher resting RSNA (1.2 ± 0.1 vs. 0.6 ± 0.1 μV, p < 0.05) and MAP (151 ± 8 vs. 97 ± 2 mmHg, p < 0.05) compared to Lewis. MAP was negatively correlated with U_Cr (r = −0.80, p = 0.002) and positively correlated with RSNA (r = 0.66, p = 0.014), with multiple linear regression modeling indicating the strongest correlation was with U_cr. RSNA and MAP responses to activation of the central chemoreflex and open-field stress were reduced in the LPK relative to the Lewis (all p < 0.05). This is the first description of dual conscious telemetry recording of RSNA and MAP in a genetic rodent model of CKD. Elevated RSNA is likely a key contributor to the marked hypertension in this model, while attenuated RSNA and MAP responses to central chemoreflex activation and acute stress in the LPK indicate possible deficits in the neural processing of autonomic outflows evoked by these sympathoexcitatory pathways.