Renal afferent impulses, the posterior hypothalamus, and hypertension in rats with chronic renal failure

Primary Role of the Kidney in Pathogenesis of Hypertension

Previous transplantation studies and the concept of 'nephron underdosing' support the idea that the kidney plays a crucial role in the development of essential hypertension. This suggests that there are genetic factors in the kidney that can either elevate or decrease blood pressure. The kidney normally maintains arterial pressure within a narrow range by employing the mechanism of pressure-natriuresis. Hypertension is induced when the pressure-natriuresis mechanism fails due to both subtle and overt kidney abnormalities. The inheritance of hypertension is believed to be polygenic, and essential hypertension may result from a combination of genetic variants that code for renal tubular sodium transporters or proteins involved in regulatory pathways. The renin-angiotensin-aldosterone system (RAAS) and sympathetic nervous system (SNS) are the major regulators of renal sodium reabsorption. Hyperactivity of either the RAAS or SNS leads to a rightward shift in the pressure-natriuresis curve. In other words, hypertension is induced when the activity of RAAS and SNS is not suppressed despite increased salt intake. Sodium overload, caused by increased intake and/or reduced renal excretion, not only leads to an expansion of plasma volume but also to an increase in systemic vascular resistance. Endothelial dysfunction is caused by an increased intracellular Na+ concentration, which inhibits endothelial nitric oxide (NO) synthase and reduces NO production. The stiffness of vascular smooth muscle cells is increased by the accumulation of intracellular Na+ and subsequent elevation of cytoplasmic Ca++ concentration. In contrast to the hemodynamic effects of osmotically active Na+, osmotically inactive Na+ stimulates immune cells and produces proinflammatory cytokines, which contribute to hypertension. When this occurs in the gut, the microbiota may become imbalanced, leading to intestinal inflammation and systemic hypertension. In conclusion, the primary cause of hypertension is sodium overload resulting from kidney dysregulation.

Possible organ-protective effects of renal denervation: insights from basic studies

Inappropriate sympathetic nervous activation is the body's response to biological stress and is thought to be involved in the development of various lifestyle-related diseases through an elevation in blood pressure. Experimental studies have shown that surgical renal denervation decreases blood pressure in hypertensive animals. Recently, minimally invasive catheter-based renal denervation has been clinically developed, which results in a reduction in blood pressure in patients with resistant hypertension. Accumulating evidence in basic studies has shown that renal denervation exerts beneficial effects on cardiovascular disease and chronic kidney disease. Interestingly, recent studies have also indicated that renal denervation improves glucose tolerance and inflammatory changes. In this review article, we summarize the evidence from animal studies to provide comprehensive insight into the organ-protective effects of renal denervation beyond changes in blood pressure.

Controversies in Hypertension IV: Renal Denervation

Renal denervation is not a cure for hypertension. Although more recent sham-controlled trials were positive, a significant minority of patients in each trial were unresponsive. The optimal patient or patients need to be defined. Combined systolic/diastolic hypertension appears more responsive than isolated systolic hypertension. It remains uncertain whether patients with comorbidities associated with higher adrenergic tone should be targeted, including obesity, diabetes, sleep apnea, and chronic kidney disease. No biomarker can adequately predict response. A key to a successful response is the adequacy of denervation, which currently cannot be assessed in real time. It is uncertain what is the optimal denervation methodology: radiofrequency, ultrasound, or ethanol injection. Radiofrequency requires targeting the distal main renal artery plus major branches and accessory arteries. Although denervation appears to be safe, conclusive data on quality of life, improved target organ damage, and reduced cardiovascular events/mortality are required before denervation can be generally recommended.

Exploring the Link between Chronic Kidney Disease and Parkinson's Disease: Insights from a Longitudinal Study Using a National Health Screening Cohort

Chronic kidney disease (CKD) and Parkinson's disease (PD) are common illnesses found in the geriatric population. A potential link between CKD and PD emergence has been hypothesized; however, existing conclusions are disputed. In this longitudinal research, we analyzed data acquired from the Korean National Health Insurance Service-Health Screening Cohort. The dataset comprised the health information of 16,559 individuals clinically diagnosed with CKD and 66,236 control subjects of comparable ages, all aged ≥40 years. These subjects participated in health examinations from 2002 to 2019. To assess the correlation between CKD and PD, we employed overlap-weighted Cox proportional hazard regression models. The unadjusted, crude hazard ratio for PD was greater in the CKD group than in the control group (crude hazard ration (HR) 1.20; 95% confidence interval (CI) = 1.04-1.39; p = 0.011). However, the Cox proportional hazard regression analysis, incorporating propensity score overlap weighting, revealed no significant discrepancy after considering confounding variables such as demographic factors, socio-economic status, lifestyle, and concurrent health conditions (adjusted HR (aHR), 1.09; 95% CI = 0.97-1.22; p = 0.147). Subgroup analyses showed a higher probability of PD development among certain CKD individuals, including those who resided in rural areas (aHR, 1.19; 95% CI = 1.03-1.37; p = 0.022), maintained a normal weight (aHR, 1.29; 95% CI = 1.08-1.56; p = 0.006), or had fasting blood glucose levels ≥100 mg/dL (aHR, 1.18; 95% CI = 1.00-1.39; p = 0.046). Therefore, these clinical or environmental factors may influence the incidence of PD in CKD patients. In conclusion, our results suggest that the general CKD population may not exhibit a greater propensity for PD than their non-CKD counterparts. However, this might be contingent upon specific lifestyle and comorbid conditions. Thus, certain lifestyle alterations could be crucial in mitigating the potential manifestation of PD in patients diagnosed with CKD.

Mendelian randomization uncovers a protective effect of interleukin-1 receptor antagonist on kidney function

Interleukins (ILs), key cytokine family of inflammatory response, are closely associated with kidney function. However, the causal effect of various ILs on kidney function needs further investigation. Here we show two-sample summary-level Mendelian randomization (MR) analysis that examined the causality between serum IL levels and kidney function. Genetic variants with strong association with serum IL levels were obtained from a previous genome-wide association study meta-analysis. Summary-level data for estimated glomerular filtration rate (eGFR) were obtained from CKDGen database. As a main MR analysis, multiplicative random-effects inverse-variance weighted method was performed. Pleiotropy-robust MR analysis, including MR-Egger with bootstrapped error and weighted median methods, were also implemented. We tested the causal estimates from nine ILs on eGFR traits. Among the results, higher genetically predicted serum IL-1 receptor antagonist level was significantly associated with higher eGFR values in the meta-analysis of CKDGen and the UK Biobank data. In addition, the result was consistent towards eGFR decline phenotype of the outcome database. Otherwise, nonsignificant association was identified between other genetically predicted ILs and eGFR outcome. These findings support the clinical importance of IL-1 receptor antagonist-associated pathway in relation to kidney function in the general individuals, particularly highlighting the importance of IL-1 receptor antagonist.

Exploring the Link between Chronic Kidney Disease and Alzheimer's Disease: A Longitudinal Follow-Up Study Using the Korean National Health Screening Cohort

Chronic kidney disease (CKD) and Alzheimer's disease (AD) are common chronic diseases in the elderly population. Although a relationship between CKD and the occurrence of AD has been proposed, previous research results have been disputed, and further investigation is necessary to confirm this relationship. In this longitudinal follow-up study, we examined data from the Korean National Health Insurance Service-Health Screening Cohort, consisting of 15,756 individuals with CKD and 63,024 matched controls aged ≥40 years who received health check-ups between 2002 and 2019. Overlap-weighted Cox proportional hazard regression models were exploited to calculate hazard ratios (HRs) for the association between CKD and AD. During the monitoring period, individuals with CKD had a greater incidence of AD than those without CKD (15.80 versus 12.40 per 1000 person years). After accounting for various factors, CKD was significantly associated with a 1.14-fold increased likelihood of developing AD, with a 95% confidence interval ranging from 1.08 to 1.20. In subgroup analysis, this relationship persisted irrespective of age (≥70 or <70), sex, income, smoking status, alcohol consumption, place of residence, or fasting blood glucose level. Additionally, the association between CKD and AD was still evident among patients who were overweight or obese, those with normal blood pressure or cholesterol levels, and those without any other health conditions or with a CCI score of ≥2. These results suggest that CKD could increase the probability of developing AD in the Korean adult population irrespective of demographic or lifestyle conditions. This may make it challenging to predict AD in patients with CKD, emphasizing the importance of frequent AD screening and management.

Effects of renal denervation on cardiovascular, metabolic and renal functions in streptozotocin-induced diabetic rats

Diabetes promotes renal sympathetic hyperactivity, autonomic imbalance, and cardiovascular and renal dysfunction. Bilateral renal denervation (BRD) has emerged as a treatment for diabetes; however, the mechanisms that underlie the beneficial effects of BRD are unknown.

AIMS

The present study evaluated the effects of BRD on autonomic, cardiovascular, metabolic, and renal function in streptozotocin-diabetic rats.

MAIN METHODS

Wistar rats were separated into three experimental groups: control (CTR), diabetic (DM), and diabetic that underwent BRD (DM BRD). BRD was performed two weeks after STZ-diabetes induction, the experiments were performed four weeks after DM induction. This study evaluated sympathetic vasomotor nerve activity in different territories (renal, lumbar and splanchnic), arterial baroreceptor reflex, metabolic and renal function.

KEY FINDINGS

BRD significantly reduced glycemia, glycosuria, albuminuria, and SGLT2 gene expression in the kidney in DM rats. Renal sympathetic nerve activity (rSNA) was significantly increased and splanchnic sympathetic nerve activity (sSNA) was significantly decreased in DM rats, without changes in lumbar sympathetic nerve activity (lSNA). BRD was able to normalize sSNA and significantly increase lSNA in DM rats compared to control rats. Additionally, cardiac baroreceptor sensitivity was impaired in DM rats, and BRD significantly improved baroreflex sensitivity.

SIGNIFICANCE

Our data suggest that renal nerves play an important role in autonomic, cardiovascular, and renal dysfunction in STZ-DM rats. Thus, sympathetic renal hyperactivity should be considered a possible therapeutic target in diabetic patients.

Sympathetic Activation in Hypertensive Chronic Kidney Disease - A Stimulus for Cardiac Arrhythmias and Sudden Cardiac Death?

Studies have revealed a robust and independent correlation between chronic kidney disease (CKD) and cardiovascular (CV) events, including death, heart failure, and myocardial infarction. Recent clinical trials extend this range of adverse CV events, including malignant ventricular arrhythmias and sudden cardiac death (SCD). Moreover, other studies point out that cardiac structural and electrophysiological changes are a common occurrence in this population. These processes are likely contributors to the heightened hazard of arrhythmias in CKD population and may be useful indicators to detect patients who are at a higher SCD risk. Sympathetic overactivity is associated with increased CV risk, specifically in the population with CKD, and it is a central feature of the hypertensive state, occurring early in its clinical course. Sympathetic hyperactivity is already evident at the earliest clinical stage of CKD and is directly related to the progression of renal failure, being most pronounced in those with end-stage renal disease. Sympathetic efferent and afferent neural activity in kidney failure is a crucial facilitator for the perpetuation and evolvement of the disease. Here, we will revisit the role of the feedback loop of the sympathetic neural cycle in the context of CKD and how it may aggravate several of the risk factors responsible for causing SCD. Targeting the overactive sympathetic nervous system therapeutically, either pharmacologically or with newly available device-based approaches, may prove to be a pivotal intervention to curb the substantial burden of cardiac arrhythmias and SCD in the high-risk population of patients with CKD.

The angiotensin II type 1 receptor blocker azilsartan can overwhelm the sympathetic nerve activation stimulated by coadministration of calcium channel blockers

Objective:

In our recent study, non-Gaussianity of heart rate variability (λ_25s), an indicator of sympathetic nerve activity, did not change during two-day treatment with the angiotensin II type 1 receptor blocker (ARB) azilsartan. Coadministration of calcium channel blockers (CCBs) might affect the study results.

Methods:

In this subanalysis, 20 patients with chronic kidney disease (14 men; age 61±15 years) were divided into three groups: patients with coadministration of L-type CCB, patients without coadministration of CCB, and patients with coadministration of sympathoinhibitory (L/T- or L/T/N-type) CCB. λ_25s was calculated separately in daytime and nighttime.

Results:

Daytime λ_25s at baseline was higher in patients with L-type CCB coadministration (0.62±0.18, n = 5) compared with those without CCB (0.49±0.13, n = 11) and those with sympathoinhibitory CCB (0.46±0.06, n = 4). The relationship between the changes in daytime λ_25s and systolic blood pressure was positive in patients with L-type CCB coadministration, whereas the relationship was inverse in the other two groups. A larger decrease in daytime λ_25s was shown in patients with L-type CCB coadministration compared with those in the other two groups.

Conclusions:

CCBs, as well as diuretics, are recommended as second-line antihypertensive agents. Our results suggested that ARBs can overwhelm the activation of sympathetic nerve activity stimulated by coadministration of L-type CCBs.

Arterial Destiffening Starts Early after Renal Artery Denervation

Introduction

Renal artery denervation (RDN) is a new widely discussed method in treatment of hypertension. Most of the RDN studies assessed BP and arterial changes 3 and 6 months after the procedure, but there is a lack of trials that investigated early changes after RDN.

Aim

To investigate aortic stiffness 24-48 hours after the procedure and thus to examine whether RDN might have an early additive value for a cardiovascular risk decline beyond the lowering of blood pressure.

Methods

RDN was performed for 73 patients with resistant hypertension. Arterial stiffness and central haemodynamics were measured before the procedure, the next day after the procedure, and subsequently after 1, 3, 6, and 12 months.

Results

Within 48 hours, RDN significantly reduced aortic pulse wave velocity (AoPWV) from 11.3±2.7 to 10.3±2.6 m/s (p=0.001); reduction was sustained at months 1, 3, 6, and 12. Early changes in the AoPWV value did not correlate with changes in office systolic or diastolic BP (p=0.45; p=0.33). Furthermore, the higher the initial AoPWV value, the greater the reduction of AoPWV observed after 6 months: Q₁ 8.4±1, Δ0.05±1.6 / Q₂ 10.1±0.4, Δ1.1±1.4 / Q₃ 12.2±0.8, Δ1.8±1.7 / Q₄ 15.3±1.7, Δ2.8±2.1 (p=0.002).

Conclusions

Early and sustained effects on AoPWV observed in our study suggest that RDN may have additional effects on reducing arterial stiffness and cardiovascular risk.

Dry-weight reduction improves intradialytic hypertension only in patients with high predialytic blood pressure

BACKGROUND

The aim of this study was to investigate whether additional volume reduction by ultrafiltration can improve blood pressure in patients with intradialytic hypertension (IDH) defined as at least 10 mmHg systolic blood pressure (SBP) rise during hemodialysis.

PATIENTS AND METHODS

This prospective, open-label, single-center study included 11 IDH patients with normal predialytic blood pressure (BP) (group A), 11 IDH patients with high predialytic BP (group B), and 18 patients without IDH as control. Serum angiotensin-II, aldosterone (ALD), angiotensin-converting enzyme, endothelin-1, nitric oxide, and asymmetric dimethylarginine were measured before and after the treatments.

RESULTS

Basic angiotensin-converting enzyme, ALD, endothelin-1, and asymmetric dimethylarginine serum levels were significantly increased in group B compared with control (P < 0.05). On comparing the results from the first and 13th dialysis sessions in group A, the dry weight was reduced by - 0.15 ± 0.16 kg after 12 sessions and the predialytic SBP increased by 3.18 ± 6.25 mmHg before and by 7.37 ± 14.90 mmHg at 4 h during the 13th session. In group B, the dry weight was reduced by 0.67 ± 0.53 kg (P = 0.006 vs. group A) at the 13th session and they had - 12.09 ± 16.20 mmHg less SBP before (P = 0.009 vs. group A) and - 11.82 ± 14.66 mmHg at 4 h of the 13th session. The decrease in dry weight was associated with significantly higher decreases in angiotensin-II and ALD serum levels in group B compared with group A.

CONCLUSION

Reducing fluid overload in IDH patients with high predialytic BP can effectively improve their BP, but had no effect on BP in normal predialytic BP IDH cases.

Renal denervation reduces sympathetic overactivation, brain oxidative stress, and renal injury in rats with renovascular hypertension independent of its effects on reducing blood pressure

The underlying mechanisms by which renal denervation (RD) decreases blood pressure (BP) remain incompletely understood. In this study, we investigated the effects of ischemic kidney denervation on different sympathetic outflows, brain and renal expression of angiotensin-II receptors, oxidative stress and renal function markers in the 2-kidney, 1-clip (2K-1C) rat model. Surgical RD was performed in Wistar male rats 4-5 weeks after clip implantation. After 10 days of RD, BP, and the activity of sympathetic nerves projecting to the contralateral kidney (rSNA) and splanchnic region were partially reduced in 2K-1C rats, with no change in systemic renin-angiotensin system (RAS). To distinguish the effects of RD from the reduction in BP, 2K-1C rats were treated with hydralazine by oral gavage (25 mg/kg/day for 1 week). RD, but not hydralazine, normalized oxidative stress in the sympathetic premotor brain regions and improved intrarenal RAS, renal injury, and proteinuria. Furthermore, different mechanisms led to renal injury and oxidative stress in the ischemic and contralateral kidneys of 2K-1C rats. Injury and oxidative stress in the ischemic kidney were driven by the renal nerves. Although RD attenuated rSNA, injury and oxidative stress persisted in the contralateral kidney, probably due to increased BP. Therefore, nerves from the ischemic kidney at least partially contribute to the increase in BP, sympathetic outflows, brain oxidative stress, and renal alterations in rats with renovascular hypertension. Based on these findings, the reduction in oxidative stress in the brain is a central mechanism that contributes to the effects of RD on Goldblatt hypertension.

Sympathetic overactivity in dialysis patients-Underappreciated and clinically consequential

Cardiovascular morbidity and mortality remain frustratingly common in dialysis patients. A dearth of established evidence-based treatment calls for alternative therapeutic avenues to be embraced. Sympathetic hyperactivity, predominantly due to afferent nerve signaling from the diseased native kidneys, has been established to be prognostic in the dialysis population for over 15 years. Despite this, tangible therapeutic interventions have, to date, been unsuccessful and the outlook for patients remains poor. This narrative review summarizes established experimental and clinical data, highlighting recent developments, and proposes why interventions to ameliorate sympathetic hyperactivity may well be beneficial for this high-risk population.

Role of the Sympathetic Nervous System and Its Modulation in Renal Hypertension

The kidneys are densely innervated with renal efferent and afferent nerves to communicate with the central nervous system. Innervation of major structural components of the kidneys, such as blood vessels, tubules, the pelvis, and glomeruli, forms a bidirectional neural network to relay sensory and sympathetic signals to and from the brain. Renal efferent nerves regulate renal blood flow, glomerular filtration rate, tubular reabsorption of sodium and water, as well as release of renin and prostaglandins, all of which contribute to cardiovascular and renal regulation. Renal afferent nerves complete the feedback loop via central autonomic nuclei where the signals are integrated and modulate central sympathetic outflow; thus both types of nerves form integral parts of the self-regulated renorenal reflex loop. Renal sympathetic nerve activity (RSNA) is commonly increased in pathophysiological conditions such as hypertension and chronic- and end-stage renal disease. Increased RSNA raises blood pressure and can contribute to the deterioration of renal function. Attempts have been made to eliminate or interfere with this important link between the brain and the kidneys as a neuromodulatory treatment for these conditions. Catheter-based renal sympathetic denervation has been successfully applied in patients with resistant hypertension and was associated with significant falls in blood pressure and renal protection in most studies performed. The focus of this review is the neural contribution to the control of renal and cardiovascular hemodynamics and renal function in the setting of hypertension and chronic kidney disease, as well as the specific roles of renal efferent and afferent nerves in this scenario and their utility as a therapeutic target.

Sympathetic Overactivity in Chronic Kidney Disease: Consequences and Mechanisms

The incidence of chronic kidney disease (CKD) is increasing worldwide, with more than 26 million people suffering from CKD in the United States alone. More patients with CKD die of cardiovascular complications than progress to dialysis. Over 80% of CKD patients have hypertension, which is associated with increased risk of cardiovascular morbidity and mortality. Another common, perhaps underappreciated, feature of CKD is an overactive sympathetic nervous system. This elevation in sympathetic nerve activity (SNA) not only contributes to hypertension but also plays a detrimental role in the progression of CKD independent of any increase in blood pressure. Indeed, high SNA is associated with poor prognosis and increased cardiovascular morbidity and mortality independent of its effect on blood pressure. This brief review will discuss some of the consequences of sympathetic overactivity and highlight some of the potential pathways contributing to chronically elevated SNA in CKD. Mechanisms leading to chronic sympathoexcitation in CKD are complex, multifactorial and to date, not completely understood. Identification of the mechanisms and/or signals leading to sympathetic overactivity in CKD are crucial for development of effective therapeutic targets to reduce the increased cardiovascular risk in this patient group.

Renal Denervation Promotes Atherosclerosis in Hypertensive Apolipoprotein E-Deficient Mice Infused with Angiotensin II

Objective: To determine the effect of renal denervation (RDN) on the severity of atherosclerosis and aortic aneurysm in hypertensive mice. Methods: Hypertension, atherosclerosis and aortic aneurysm were induced by subcutaneous infusion of angiotensin II (1 μg/kg/min) for 28 days in apolipoprotein E-deficient mice. RDN was conducted using combined surgical and local chemical denervation. The norepinephrine concentration in the kidney was measured by high-performance liquid chromatography. Blood pressure was measured by the tail-cuff method. Atherosclerosis was assessed by Sudan IV staining of the aortic arch. The aortic diameter was measured by the morphometric method. The mRNA expression of genes associated with atherosclerosis and aortic aneurysm were analyzed by quantitative PCR. Results: RDN decreased the median norepinephrine content in the kidney by 93.4% (n = 5-7, P = 0.003) 5 days after the procedure, indicating that the RDN procedure was successful. RDN decreased systolic blood pressure in apolipoprotein E-deficient mice. Mice that had RDN had more severe aortic arch atherosclerosis (median percentage of Sudan IV positive area: 13.2% in control mice, n = 12, and 25.4% in mice having RDN, n = 12, P = 0.028). The severity of the atherosclerosis was negatively correlated with the renal norepinephrine content (spearman r = -0.6557, P = 0.005). RDN did not affect the size of aortic aneurysms formed or the incidence of aortic rupture in mice receiving angiotensin II. RDN significantly increased the aortic mRNA expression of matrix metalloproteinase-2 (MMP-2). Conclusion: RDN promoted atherosclerosis in apolipoprotein E-deficient mice infused with angiotensin II associated with upregulation of MMP-2. The higher MMP-2 expression could be the results of the greater amount of atheroma in the RDN mice. The findings suggest further research is needed to assess potentially deleterious effects of RDN in patients.

Renal Denervation Improves the Baroreflex and GABA System in Chronic Kidney Disease-induced Hypertension

Hypertensive rats with chronic kidney disease (CKD) exhibit enhanced gamma-aminobutyric acid (GABA)_B receptor function and regulation within the nucleus tractus solitarii (NTS). For CKD with hypertension, renal denervation (RD) interrupts the afferent renal sympathetic nerves, which are connecting to the NTS. The objective of the present study was to investigate how RD improves CKD-induced hypertension. Rats underwent 5/6 nephrectomy for 8 weeks, which induced CKD and hypertension. RD was induced by applying phenol to surround the renal artery in CKD. RD improved blood pressure (BP) by lowering sympathetic nerve activity and markedly restored the baroreflex response in CKD. The GABA_B receptor expression was increased in the NTS of CKD; moreover, the central GABA levels were reduced in the cerebrospinal fluid, and the peripheral GABA levels were increased in the serum. RD restored the glutamic acid decarboxylase activity in the NTS in CKD, similar to the effect observed for central treatment with baclofen, and the systemic administration of gabapentin reduced BP. RD slightly improved renal function and cardiac load in CKD. RD may improve CKD-induced hypertension by modulating the baroreflex response, improving GABA system dysfunction and preventing the development and reducing the severity of cardiorenal syndrome type 4 in CKD rats.

Potential role of endurance training in altering renal sympathetic nerve activity in CKD?

Chronic kidney disease (CKD), is characterized by a progressive loss of renal function and increase in cardiovascular risk. In this review paper, we discuss the pathophysiology of increased sympathetic nerve activity in CKD patients and raise the possibility of endurance exercise being an effective countermeasure to address this problem. We specifically focus on the potential role of endurance training in altering renal sympathetic nerve activity as increased renal sympathetic nerve activity negatively impacts kidney function as well indirectly effects multiple other systems and organs. Recent technological advances in device based therapy have highlighted the detrimental effect of elevated renal sympathetic nerve activity in CKD patients, with kidney function and blood pressure being improved post renal artery nerve denervation in selected patients. These developments provide optimism for the development of alternative and/or complementary strategies to lower renal sympathetic nerve activity. However, appropriately designed studies are required to confirm preliminary observations, as the widespread use of the renal denervation approach to lower sympathetic activity presently has limited feasibility. Endurance training may be one alternative strategy to reduce renal sympathetic nerve activity. Here we review the role of endurance training as a potential alternative or adjunctive to current therapy in CKD patients. We also provide recommendations for future research to assist in establishing an evidence base for the use of endurance training to lower renal sympathetic activity in CKD patients.

Renal denervation enhances GABA-ergic input into the PVN leading to blood pressure lowering in chronic kidney disease

OBJECTIVE

Sympathoexcitation plays an important role in the pathogenesis of hypertension in patients with chronic kidney disease (CKD). The paraventricular nucleus of the hypothalamus (PVN) in the brain controls sympathetic outflow through γ-amino butyric acid (GABA)-ergic mechanisms. Renal denervation (RDN) exerts a long-term antihypertensive effect in hypertension with CKD; however, the effects of RDN on sympathetic nerve activity and GABA-ergic modulation in the PVN are not clear. We aimed to elucidate whether RDN modulates sympathetic outflow through GABA-ergic mechanisms in the PVN in hypertensive mice with CKD.

METHODS AND RESULTS

In 5/6-nephrectomized male Institute of Cancer Research mice (Nx) at 4 weeks after nephrectomy, systolic blood pressure (SBP) was significantly increased, accompanied by sympathoexcitation. The Nx-mice underwent RDN or sham operation, and the mice were divided into three groups (Control, Nx-Sham, and Nx-RDN). At 2 weeks after RDN, SBP was significantly decreased and urinary sodium excretion was increased in Nx-RDN compared with Nx-Sham. Urinary norepinephrine excretion (uNE) levels did not differ significantly between Nx-RDN and Nx-Sham. At 6 weeks after RDN, SBP continued to decrease and uNE levels also decreased in Nx-RDN compared with Nx-Sham. Bicuculline microinjection into the PVN increased mean arterial pressure and lumbar sympathetic nerve activity in all groups. The pressor responses and change in lumbar sympathetic nerve activity were significantly attenuated in Nx-Sham, but were enhanced in Nx-RDN at 6 weeks after RDN.

CONCLUSIONS

The findings from the present study indicate that RDN has a prolonged antihypertensive effect and, at least in the late phase, decreases sympathetic nerve activity in association with enhanced GABA-ergic input into the PVN in mice with CKD.

Does Telomere Shortening Precede the Onset of Hypertension in Spontaneously Hypertensive Mice?

Telomere length is widely considered as a marker of biological aging. Clinical studies have reported associations between reduced telomere length and hypertension. The aim of this study was to compare telomere length in hypertensive and normotensive mice at pre-disease and established disease time points to determine whether telomere length differs between the strains before and after the onset of disease. Genomic DNA was extracted from kidney and heart tissues of 4-, 12-, and 20-week-old male hypertensive (BPH/2J) and normotensive (BPN/3J) mice. Relative telomere length (T/S) was measured using quantitative PCR. Age was inversely correlated with telomere length in both strains. In 4-week-old pre-hypertensive animals, no difference in T/S was observed between BPH/2J and BPN/3J animals in kidney or heart tissue (kidney p = 0.14, heart p = 0.06). Once the animals had established disease, at 12 and 20 weeks, BPH/2J mice had significantly shorter telomeres when compared to their age-matched controls in both kidney (12 weeks p < 0.001 and 20 weeks p = 0.004) and heart tissues (12 weeks p < 0.001 and 20 weeks p < 0.001). This is the first study to show that differences in telomere lengths between BPH/2J and BPN/3J mice occur after the development of hypertension and do not cause hypertension in the BPH/2J mice.

Hypertension: a problem of organ blood flow supply-demand mismatch

This review introduces a new hypothesis that sympathetically mediated hypertensive diseases are caused, in the most part, by the activation of visceral afferent systems that are connected to neural circuits generating sympathetic activity. We consider how organ hypoperfusion and blood flow supply–demand mismatch might lead to both sensory hyper-reflexia and aberrant afferent tonicity. We discuss how this may drive sympatho-excitatory-positive feedback and extend across multiple organs initiating, or at least amplifying, sympathetic hyperactivity. The latter, in turn, compounds the challenge to sufficient organ blood flow through heightened vasoconstriction that both maintains and exacerbates hypertension.

Cardiovascular Autonomic Dysfunction in Chronic Kidney Disease: a Comprehensive Review

Cardiovascular autonomic dysfunction is a major complication of chronic kidney disease (CKD), likely contributing to the high incidence of cardiovascular mortality in this patient population. In addition to adrenergic overdrive in affected individuals, clinical and experimental evidence now strongly indicates the presence of impaired reflex control of both sympathetic and parasympathetic outflow to the heart and vasculature. Although the principal underlying mechanisms are not completely understood, potential involvements of altered baroreceptor, cardiopulmonary, and chemoreceptor reflex function, along with factors including but not limited to increased renin-angiotensin-aldosterone system activity, activation of the renal afferents and cardiovascular structural remodeling have been suggested. This review therefore analyzes potential mechanisms underpinning autonomic imbalance in CKD, covers results accumulated thus far on cardiovascular autonomic function studies in clinical and experimental renal failure, discusses the role of current interventional and therapeutic strategies in ameliorating autonomic deficits associated with chronic renal dysfunction, and identifies gaps in our knowledge of neural mechanisms driving cardiovascular disease in CKD.

Impaired excitability of renal afferent innervation after exposure to the inflammatory chemokine CXCL1

Recently, we showed that renal afferent neurons exhibit a unique firing pattern, i.e., predominantly sustained firing, upon stimulation. Pathological conditions such as renal inflammation likely alter excitability of renal afferent neurons. Here, we tested whether the proinflammatory chemokine CXCL1 alters the firing pattern of renal afferent neurons. Rat dorsal root ganglion neurons (Th11-L2), retrogradely labeled with dicarbocyanine dye, were incubated with CXCL1 (20 h) or vehicle before patch-clamp recording. The firing pattern of neurons was characterized as tonic, i.e., sustained action potential (AP) firing, or phasic, i.e., <5 APs following current injection. Of the labeled renal afferents treated with vehicle, 58.9% exhibited a tonic firing pattern vs. 7.8%, in unlabeled, nonrenal neurons (P < 0.05). However, after exposure to CXCL1, significantly more phasic neurons were found among labeled renal neurons; hence the occurrence of tonic neurons with sustained firing upon electrical stimulation decreased (35.6 vs. 58.9%, P < 0.05). The firing frequency among tonic neurons was not statistically different between control and CXCL1-treated neurons. However, the lower firing frequency of phasic neurons was even further decreased with CXCL1 exposure [control: 1 AP/600 ms (1-2) vs. CXCL1: 1 AP/600 ms (1-1); P < 0.05; median (25th-75th percentile)]. Hence, CXCL1 shifted the firing pattern of renal afferents from a predominantly tonic to a more phasic firing pattern, suggesting that CXCL1 reduced the sensitivity of renal afferent units upon stimulation.

Short-term safety and efficiency of cryoablation for renal sympathetic denervation in a swine model

Background:

Renal sympathetic nerves are involved in the reflective activation of the sympathetic nervous system in circulatory control. Catheter-based renal denervation (RDN) ameliorated treatment-resistant hypertension safely, but 10%–20% of treated patients are nonresponders to radiofrequency denervation. The purpose of this study was to investigate the safety and efficiency of cryoablation for sympathetic denervation in a swine model and to explore a new way of RDN.

Methods:

Seven swines randomly assigned to two groups: Renal cryoablation (CR) group and control group. The control group underwent renal angiogram only. The CR group underwent renal angiogram plus bilateral renal cryoablation. Renal angiograms via femoral were performed before denervation, after denervation and prior to the sacrifice to access the diameter of renal arterial and the pressure of aorta abdominalis. Euthanasia of the swine was performed on 28-day to access norepinephrine (NE) changes of the renal cortex and the changes of renal nerves.

Results:

Cryoablation did not induce severe complications at any time point. There was no significant change in diameter of renal artery. CR reduced systolic blood pressure (BP) from 145.50 ± 9.95 mmHg at baseline to 119.00 ± 14.09 mmHg. There was a slight but insignificant decrease in diastolic BP. The main nerve changes at 28-day consisted of necrosis with perineurial fibrosis at the site of CR exposure in conjunction with the nerve vacuolation. Compared with the control group, renal tissue NE of CR group decreased by 89.85%.

Conclusions:

Percutaneous catheter-based cryoablation of the renal artery is safe. CR could effectively reduce NE storing in the renal cortex, and the efficiency could be maintained 28-day at least.

Pathophysiology of resistant hypertension in chronic kidney disease

Hypertension associated with chronic kidney diseases often is resistant to drug treatment. This review deals with two main aspects of the management of CKD patients with hypertension: the role of sodium/volume and the need for dietary salt restriction, as well as appropriate use of diuretics and what currently is called sequential nephron blockade; the second aspect that is addressed extensively in this review is the role of the sympathetic nervous system and the possible clinical use of renal denervation.

Renal Denervation Prevents Immune Cell Activation and Renal Inflammation in Angiotensin II-Induced Hypertension

RATIONALE

Inflammation and adaptive immunity play a crucial role in the development of hypertension. Angiotensin II and probably other hypertensive stimuli activate the central nervous system and promote T-cell activation and end-organ damage in peripheral tissues.

OBJECTIVE

To determine if renal sympathetic nerves mediate renal inflammation and T-cell activation in hypertension.

METHODS AND RESULTS

Bilateral renal denervation using phenol application to the renal arteries reduced renal norepinephrine levels and blunted angiotensin II-induced hypertension. Bilateral renal denervation also reduced inflammation, as reflected by decreased accumulation of total leukocytes, T cells, and both CD4+ and CD8+ T cells in the kidney. This was associated with a marked reduction in renal fibrosis, albuminuria, and nephrinuria. Unilateral renal denervation, which partly attenuated blood pressure, only reduced inflammation in the denervated kidney, suggesting that this effect is pressure independent. Angiotensin II also increased immunogenic isoketal-protein adducts in renal dendritic cells (DCs) and increased surface expression of costimulation markers and production of interleukin (IL)-1α, IL-1β, and IL-6 from splenic DCs. Norepinephrine also dose dependently stimulated isoketal formation in cultured DCs. Adoptive transfer of splenic DCs from angiotensin II-treated mice primed T-cell activation and hypertension in recipient mice. Renal denervation prevented these effects of hypertension on DCs. In contrast to these beneficial effects of ablating all renal nerves, renal afferent disruption with capsaicin had no effect on blood pressure or renal inflammation.

CONCLUSIONS

Renal sympathetic nerves contribute to DC activation, subsequent T-cell infiltration and end-organ damage in the kidney in the development of hypertension.

The role of the kidney and the sympathetic nervous system in hypertension

Nearly one-third of the world's population has hypertension. The human and societal impact of hypertension is enormous. Primary hypertension accounts for 95 % of cases of hypertension in adults. The pathogenesis of primary hypertension is complex. The kidney and the sympathetic nervous system play important roles in the development and maintenance of hypertension. This review discusses their respective roles, the interaction between the two, implications of sympathetic overactivity in kidney disease and therapeutic interventions that have been developed on the basis of this knowledge, especially modulation of the sympathetic nervous system.

A Salt-Induced Reno-Cerebral Reflex Activates Renin-Angiotensin Systems and Promotes CKD Progression

Salt intake promotes progression of CKD by uncertain mechanisms. We hypothesized that a salt-induced reno-cerebral reflex activates a renin-angiotensin axis to promote CKD. Sham-operated and 5/6-nephrectomized rats received a normal-salt (0.4%), low-salt (0.02%), or high-salt (4%) diet for 2 weeks. High salt in 5/6-nephrectomized rats increased renal NADPH oxidase, inflammation, BP, and albuminuria. Furthermore, high salt activated the intrarenal and cerebral, but not the systemic, renin-angiotensin axes and increased the activity of renal sympathetic nerves and neurons in the forebrain of these rats. Renal fibrosis was increased 2.2-fold by high versus low salt, but intracerebroventricular tempol, losartan, or clonidine reduced this fibrosis by 65%, 69%, or 59%, respectively, and renal denervation or deafferentation reduced this fibrosis by 43% or 38%, respectively (all P<0.05). Salt-induced fibrosis persisted after normalization of BP with hydralazine. These data suggest that the renal and cerebral renin-angiotensin axes are interlinked by a reno-cerebral reflex that is activated by salt and promotes oxidative stress, fibrosis, and progression of CKD independent of BP.

The crosstalk between the kidney and the central nervous system: the role of renal nerves in blood pressure regulation

NEW FINDINGS

What is the topic of this review? This review describes the role of renal nerves as the key carrier of signals from the kidneys to the CNS and vice versa; the brain and kidneys communicate through this carrier to maintain homeostasis in the body. What advances does it highlight? Whether renal or autonomic dysfunction is the predominant contributor to systemic hypertension is still debated. In this review, we focus on the role of the renal nerves in a model of renovascular hypertension. The sympathetic nervous system influences the renal regulation of arterial pressure and body fluid composition. Anatomical and physiological evidence has shown that sympathetic nerves mediate changes in urinary sodium and water excretion by regulating the renal tubular water and sodium reabsorption throughout the nephron, changes in the renal blood flow and the glomerular filtration rate by regulating the constriction of renal vasculature, and changes in the activity of the renin-angiotensin system by regulating the renin release from juxtaglomerular cells. Additionally, renal sensory afferent fibres project to the autonomic central nuclei that regulate blood pressure. Hence, renal nerves play a key role in the crosstalk between the kidneys and the CNS to maintain homeostasis in the body. Therefore, the increased sympathetic nerve activity to the kidney and the renal afferent nerve activity to the CNS may contribute to the outcome of diseases, such as hypertension.

Abnormal neurocirculatory control during exercise in humans with chronic renal failure

Abnormal neurocirculatory control during exercise is one important mechanism leading to exercise intolerance in patients with both end-stage renal disease (ESRD) and earlier stages of chronic kidney disease (CKD). This review will provide an overview of mechanisms underlying abnormal neurocirculatory and hemodynamic responses to exercise in patients with kidney disease. Recent studies have shown that ESRD and CKD patients have an exaggerated increase in blood pressure (BP) during both isometric and rhythmic exercise. Subsequent studies examining the role of the exercise pressor reflex in the augmented pressor response revealed that muscle sympathetic nerve activity (MSNA) was not augmented during exercise in these patients, and metaboreflex-mediated increases in MSNA were blunted, while mechanoreflex-mediated increases were preserved under basal conditions. However, normalizing the augmented BP response during exercise via infusion of nitroprusside (NTP), and thereby equalizing baroreflex-mediated suppression of MSNA, an important modulator of the final hemodynamic response to exercise, revealed that CKD patients had an exaggerated increase in MSNA during isometric and rhythmic exercise. In addition, mechanoreflex-mediated control was augmented, and metaboreceptor blunting was no longer apparent in CKD patients with baroreflex normalization. Factors leading to mechanoreceptor sensitization, and other mechanisms underlying the exaggerated exercise pressor response, such as impaired functional sympatholysis, should be investigated in future studies.

Chronic bilateral renal denervation attenuates renal injury in a transgenic rat model of diabetic nephropathy

Bilateral renal denervation (BRD) has been shown to reduce hypertension and improve renal function in both human and experimental studies. We hypothesized that chronic intervention with BRD may also attenuate renal injury and fibrosis in diabetic nephropathy. This hypothesis was examined in a female streptozotocin-induced diabetic (mRen-2)27 rat (TGR) shown to capture the cardinal features of human diabetic nephropathy. Following diabetic induction, BRD/sham surgeries were conducted repeatedly (at the week 3, 6, and 9 following induction) in both diabetic and normoglycemic animals. Renal denervation resulted in a progressive decrease in systolic blood pressure from first denervation to termination (at 12 wk post-diabetic induction) in both normoglycemic and diabetic rats. Renal norepinephrine content was significantly raised following diabetic induction and ablated in denervated normoglycemic and diabetic groups. A significant increase in glomerular basement membrane thickening and mesangial expansion was seen in the diabetic kidneys; this morphological appearance was markedly reduced by BRD. Immunohistochemistry and protein densitometric analysis of diabetic innervated kidneys confirmed the presence of significantly increased levels of collagens I and IV, α-smooth muscle actin, the ANG II type 1 receptor, and transforming growth factor-β. Renal denervation significantly reduced protein expression of these fibrotic markers. Furthermore, BRD attenuated albuminuria and prevented the loss of glomerular podocin expression in these diabetic animals. In conclusion, BRD decreases systolic blood pressure and reduces the development of renal fibrosis, glomerulosclerosis, and albuminuria in this model of diabetic nephropathy. The evidence presented strongly suggests that renal denervation may serve as a therapeutic intervention to attenuate the progression of renal injury in diabetic nephropathy.

Improvement of albuminuria after renal denervation

OBJECTIVES

The primary objective of this study was the effect of renal denervation (RDN) on elevated urinary albumin-to-creatinine ratio (UACR) in treatment-resistant hypertensive patients. In addition, patients were stratified according their UACR at baseline into micro- (30-300 mg/g, n=37) and macroalbuminuria (≥ 300 mg/g, <2,200 mg/g, n=22).

BACKGROUND

Increased albuminuria indicates cardiovascular and renal damage in hypertension. RDN emerged as an innovative interventional approach to reduce blood pressure (BP) and may thus reduce albumin urinary excretion.

METHODS

Fifty-nine treatment-resistant hypertensive patients with elevated UACR at baseline underwent catheter-based RDN using the Symplicity Flex™ catheter (Medtronic Inc., Santa Rosa, CA).

RESULTS

In the whole and pre-specified subgroups both office and 24-h ambulatory BP were significantly reduced 6 months after RDN. In parallel, a significant reduction in UACR occurred in all patients (160 (65-496) versus 89 (29-319) mg/g creatinine, p<0.001) and in both subgroups (microalbuminuria: 83 (49-153) versus 58 (17-113) mg/g creatinine, p=0.001; macroalbuminuria: (536 (434-1483) versus 478 (109-1080) mg/g creatinine, p<0.001). In accordance, the prevalence of micro- and macroalbuminuria decreased significantly. Regression analysis revealed a modest positive relationship between the decrease of UACR and the fall of systolic BP (β=0.340, p=0.039) independent of renal function. Renal function remained unchanged after RDN.

CONCLUSIONS

In summary, following RDN, the magnitude of albuminuria as well as the prevalence of micro- and macroalbuminuria decreased in treatment-resistant hypertensive patients. Since albuminuria is an independent renal and cardiovascular risk factor, our findings suggest a reduction of renal and cardiovascular risk in these patients.

Ischemia and reactive oxygen species in sympathetic hyperactivity states: a vicious cycle that can be interrupted by renal denervation?

Renal denervation has developed as a new treatment strategy for patients suffering from resistant hypertension. The success of this therapy is due to the fact that sympathetic hyperactivity is involved in the pathogenesis of elevated blood pressure. However, not only the sympathetic nervous system (SNS), but also the renin angiotensin system (RAS) is known to be involved in hypertension. In addition, RAS is involved in other sympathetic hyperactivity states, such as heart failure, chronic kidney disease, insulin resistance and obstructive sleep apnea. Moreover, renal denervation has a beneficial effect on patients suffering from these disease states. Recent research suggested that the production of reactive oxygen species (ROS) is elevated in sympathetic hyperactivity states, and that ROS are able to activate the SNS and local tissue renin angiotensin system. Therefore, this review discusses the possibility of ROS as a common trigger of SNS and RAS activity in sympathetic hyperactivity states, and the effect of renal denervation on this ROS production.

Renal denervation for arrhythmias: hope or hype?

Renal artery denervation (RDN) has been introduced as an ablation procedure that can effectively treat drug-resistant forms of hypertension. The ablative lesions reduce the afferent and efferent sympathetic nerve traffic to and from the kidneys, thus improving blood pressure control. Because of better control of blood pressure, and because the procedure reduces central sympathetic output to sensitive structures within the cardiovascular system, it has been hypothesized that RDN may be a valuable antiarrhythmic intervention. Preliminary results using RDN for atrial fibrillation control are promising. This review focuses on the mechanisms by which RDN may function as an antiarrhythmic treatment and early clinical results.

Endovascular renal denervation: a novel sympatholytic with relevance to chronic kidney disease

Endovascular renal denervation (sympathectomy) is a novel procedure developed for the treatment of resistant hypertension. Evidence suggests that it reduces both afferent and efferent sympathetic nerve activity, which may offer clinical benefit over and above any blood pressure-lowering effect. Studies have shown objective improvements in left ventricular mass, ventricular function, central arterial stiffness, central haemodynamics, baroreflex sensitivity and arrhythmia frequency. Benefits have also been seen in insulin resistance, microalbuminuria and glomerular filtration rate. In chronic kidney disease, elevated sympathetic activity has been causally linked to disease progression and cardiovascular sequelae. Effecting a marked reduction in sympathetic hyperactivity may herald a significant step in the management of this and other conditions. In this in-depth review, the pathophysiology and clinical significance of the sympatholytic effects of endovascular renal denervation are discussed.

Renal Denervation

Resistant hypertension, defined as failure to reach blood pressure (BP) goals despite treatment with ≥3 antihypertensive agents, one of which is a diuretic, bears a significant risk of cardiovascular complications. Strong evidence exists, implicating the overactivation of the sympathetic nervous system (SNS) in the pathogenesis of resistant hypertension through complex neurohormonal interactions. Renal denervation is a novel attractive option to achieve adequate blockade of the sympathetic system, with subsequent BP reductions in patients with resistant hypertension. Data have shown promising results regarding the efficacy of the procedure, maintaining a favorable safety profile. As such, the paradigm of resistant hypertension has expanded in other conditions involving a hyperadrenergic state such as the metabolic syndrome, heart failure, arrhythmias, sleep apnea, and renal failure. This review focuses on the pathophysiological rationale of modifying SNS tone and the evidence of the benefits of such intervention beyond BP control.

International expert consensus statement: Percutaneous transluminal renal denervation for the treatment of resistant hypertension

Catheter-based radiofrequency ablation technology to disrupt both efferent and afferent renal nerves has recently been introduced to clinical medicine after the demonstration of significant systolic and diastolic blood pressure reductions. Clinical trial data available thus far have been obtained primarily in patients with resistant hypertension, defined as standardized systolic clinic blood pressure ≥ 160 mm Hg (or ≥ 150 mm Hg in patients with type 2 diabetes) despite appropriate pharmacologic treatment with at least 3 antihypertensive drugs, including a diuretic agent. Accordingly, these criteria and blood pressure thresholds should be borne in mind when selecting patients for renal nerve ablation. Secondary forms of hypertension and pseudoresistance, such as nonadherence to medication, intolerance of medication, and white coat hypertension, should have been ruled out, and 24-h ambulatory blood pressure monitoring is mandatory in this context. Because there are theoretical concerns with regard to renal safety, selected patients should have preserved renal function, with an estimated glomerular filtration rate ≥ 45 ml/min/1.73 m(2). Optimal periprocedural management of volume status and medication regimens at specialized and experienced centers equipped with adequate infrastructure to cope with potential procedural complications will minimize potential patient risks. Long-term safety and efficacy data are limited to 3 years of follow-up in small patient cohorts, so efforts to monitor treated patients are crucial to define the long-term performance of the procedure. Although renal nerve ablation could have beneficial effects in other conditions characterized by elevated renal sympathetic nerve activity, its potential use for such indications should currently be limited to formal research studies of its safety and efficacy.