Renal sensory and sympathetic nerves reinnervate the kidney in a similar time-dependent fashion after renal denervation in rats

Long-Term Safety and Efficacy of Transcatheter Microwave and Radiofrequency Denervation in a Chronic Ovine Model

BACKGROUND

Transcatheter renal denervation (RDN) has had inconsistent efficacy and concerns for durability of denervation. We aimed to investigate long-term safety and efficacy of transcatheter microwave RDN in vivo in normotensive sheep in comparison to conventional radiofrequency ablation.

METHODS AND RESULTS

Sheep underwent bilateral RDN, receiving 1 to 2 microwave ablations (maximum power of 80-120 W for 240 s-480 s) and 12 to 16 radiofrequency ablations (180 s-240 s) in the main renal artery in a paired fashion, alternating the side of treatment, euthanized at 2 weeks (acute N=15) or 5.5 months (chronic N=15), and compared with undenervated controls (N=4). Microwave RDN produced substantial circumferential perivascular injury compared with radiofrequency at both 2 weeks [area 239.8 (interquartile range [IQR] 152.0-343.4) mm2 versus 50.1 (IQR, 32.0-74.6) mm2, P <0.001; depth 16.4 (IQR, 13.9-18.9) mm versus 7.5 (IQR, 6.0-8.9) mm P <0.001] and 5.5 months [area 20.0 (IQR, 3.4-31.8) mm2 versus 5.0 (IQR, 1.4-7.3) mm2, P=0.025; depth 5.9 (IQR, 1.9-8.8) mm versus 3.1 (IQR, 1.2-4.1) mm, P=0.005] using mixed models. Renal denervation resulted in significant long-term reductions in viability of renal sympathetic nerves [58.9% reduction with microwave (P=0.01) and 45% reduction with radiofrequency (P=0.017)] and median cortical norepinephrine levels [71% reduction with microwave (P <0.001) and 72.9% reduction with radiofrequency (P <0.001)] at 5.5 months compared with undenervated controls.

CONCLUSIONS

Transcatheter microwave RDN produces deep circumferential perivascular ablations without significant arterial injury to provide effective and durable RDN at 5.5 months compared with radiofrequency RDN.

Characterization of a phenol-based model for denervation of the abdominal aorta and its implications for aortic remodeling

Objective

Sympathetic innervation plays a pivotal role in regulating cardiovascular health, and its dysregulation is implicated in a wide spectrum of cardiovascular diseases. This study seeks to evaluate the impact of denervation of the abdominal aorta on its morphology and wall homeostasis.

Methods

Male and female Sprague-Dawley rats (N = 12), aged 3 months, underwent midline laparotomy for infrarenal aorta exposure. Chemical denervation was induced via a one-time topical application of 10% phenol (n = 6), whereas sham controls received phosphate-buffered saline (n = 6). Animals were allowed to recover and subsequently were sacrificed after 6 months for analysis encompassing morphology, histology, and immunohistochemistry.

Results

At 6 months post-treatment, abdominal aortas subjected to phenol denervation still exhibited a significant reduction in nerve fiber density compared with sham controls. Denervated aortas demonstrated reduced intima-media thickness, increased elastin fragmentation, decreased expression of vascular smooth muscle proteins (α-SMA and MYH11), and elevated adventitial vascular density. Sex-stratified analyses revealed additional dimorphic responses, particularly in aortic collagen and medial cellular density in female animals.

Conclusions

Single-timepoint phenol-based chemical denervation induces alterations in abdominal aortic morphology and vascular remodeling over a 6-month period. These findings underscore the potential of the sympathetic nervous system as a therapeutic target for aortic pathologies.

Clinical Relevance

Aortic remodeling remains an important consideration in the pathogenesis of aortic disease, including occlusive, aneurysmal, and dissection disease states. The paucity of medical therapies for the treatment of aortic disease has driven considerable interest in elucidating the pathogenesis of these conditions; new therapeutic targets are critically needed. Here, we show significant remodeling after phenol-induced denervation with morphologic, histologic, and immunohistochemical features. Future investigations should integrate sympathetic dysfunction as a potential driver of pathologic aortic wall changes with additional consideration of the sympathetic nervous system as a therapeutic target.

Renal denervation restores biomechanics of carotid arteries in a rat model of hypertension

The prevalence of hypertension increases with aging and is associated with increased arterial stiffness. Resistant hypertension is presented when drug treatments fail to regulate a sustained increased blood pressure. Given that the mechanisms between the sympathetic nervous system and the kidney play an important role in blood regulation, renal denervation (RDN) has emerged as a therapeutic potential in resistant hypertension. In this study, we investigated the effects of RDN on the biomechanical response and microstructure of elastic arteries. Common carotid arteries (CCA) excised from 3-month, 8-month, and 8-month denervated rats were subjected to biaxial extension-inflation test. Our results showed that hypertension developed in the 8-month-old rats. The sustained elevated blood pressure resulted in arterial remodeling which was manifested as a significant stress increase in both axial and circumferential directions after 8 months. RDN had a favorable impact on CCAs with a restoration of stresses in values similar to control arteries at 3 months. After biomechanical testing, arteries were imaged under a multi-photon microscope to identify microstructural changes in extracellular matrix (ECM). Quantification of multi-photon images showed no significant alterations of the main ECM components, elastic and collagen fibers, indicating that arteries remained intact after RDN. Regardless of the experimental group, our microstructural analysis of the multi-photon images revealed that reorientation of the collagen fibers might be the main microstructural mechanism taking place during pressurization with their straightening happening during axial stretching.

Renal denervation restores biomechanics of carotid arteries in a rat model of hypertension

The prevalence of hypertension increases with aging and is associated with increased arterial stiffness. Resistant hypertension is presented when drug treatments fail to regulate a sustained increased blood pressure. Given that the mechanisms between the sympathetic nervous system and the kidney play an important role in blood regulation, renal denervation (RDN) has emerged as a therapeutic potential in resistant hypertension. In this study, we investigated the effects of RDN on the biomechanical response and microstructure of elastic arteries. Common carotid arteries (CCA) were excised from 3-, 8- and 8-month-old denervated rats, and subjected to biaxial extension-inflation test. Our results showed that hypertension developed in the 8-month-old rats. The sustained elevated blood pressure resulted in arterial remodeling which was manifested as a significant stress increase in both axial and circumferential directions after 8 months. RDN had a favorable impact on CCAs with a restoration of stresses in values similar to control arteries at 3 months. After biomechanical testing, arteries were imaged under a multi-photon microscope to identify microstructural changes in extracellular matrix (ECM). Quantification of multi-photon images showed no significant alterations of the main ECM components, elastic and collagen fibers, indicating that arteries remained intact after RDN. Regardless of the experimental group, our microstructural analysis of the multi-photon images revealed that reorientation of the collagen fibers might be the main microstructural mechanism taking place during pressurization with their straightening happening during axial stretching.

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.

Sympathetic Modulation in Cardiac Arrhythmias: Where We Stand and Where We Go

The nuance of autonomic cardiac control has been studied for more than 400 years, yet little is understood. This review aimed to provide a comprehensive overview of the current understanding, clinical implications, and ongoing studies of cardiac sympathetic modulation and its anti-ventricular arrhythmias' therapeutic potential. Molecular-level studies and clinical studies were reviewed to elucidate the gaps in knowledge and the possible future directions for these strategies to be translated into the clinical setting. Imbalanced sympathoexcitation and parasympathetic withdrawal destabilize cardiac electrophysiology and confer the development of ventricular arrhythmias. Therefore, the current strategy for rebalancing the autonomic system includes attenuating sympathoexcitation and increasing vagal tone. Multilevel targets of the cardiac neuraxis exist, and some have emerged as promising antiarrhythmic strategies. These interventions include pharmacological blockade, permanent cardiac sympathetic denervation, temporal cardiac sympathetic denervation, etc. The gold standard approach, however, has not been known. Although neuromodulatory strategies have been shown to be highly effective in several acute animal studies with very promising results, the individual and interspecies variation between human autonomic systems limits the progress in this young field. There is, however, still much room to refine the current neuromodulation therapy to meet the unmet need for life-threatening ventricular arrhythmias.

Emerging topics on renal denervation in hypertension: anatomical and functional aspects of renal nerves

Inappropriate sympathetic activation is closely associated with the development and progression of hypertension. Renal denervation (RDN) is a neuromodulation therapy performed using an intraarterial catheter in patients with hypertension. Recent randomized sham-operated controlled trials have shown that RDN has significant antihypertensive effects that last for at least 3 years. Based on this evidence, RDN is nearly ready for general clinical application. On the other hand, there are remaining issues to be addressed, including elucidation of the precise antihypertensive mechanisms of RDN, the appropriate endpoint of RDN during the procedure, and the association between reinnervation after RDN and the long-term effects of RDN. This mini review focuses on studies implicating anatomy of the renal nerves, which consist of afferent or efferent and sympathetic or parasympathetic nerves, the response of blood pressure to renal nerve stimulation, and reinnervation of renal nerves after RDN. A comprehensive understanding of the anatomical and functional aspects of the renal nerves and the antihypertensive mechanisms of RDN, including its long-term effects, will enhance our ability to incorporate RDN into strategies to treat hypertension in clinical practice. This mini review focuses on studies implicating anatomy of the renal nerves, which consist of afferent or efferent and sympathetic or parasympathetic nerves, the response of blood pressure to renal nerve stimulation, and reinnervation of renal nerves after renal denervation. Whether the ablation site is sympathetic dominant or parasympathetic dominant, and afferent dominant or efferent dominant, would in turn determine the final output of renal denervation. BP: blood pressure.

Effect of renal denervation for patients with isolated systolic hypertension: a systematic review and meta-analysis

BACKGROUND

Renal denervation (RDN) is a promising treatment based on catheter intervention for patients with refractory hypertension. However, the effect in patients with isolated systolic hypertension (ISH) remains controversial. The aim of this meta-analysis was to determine the blood pressure lowing effect of RDN in patients with ISH compared with combined systolic/diastolic hypertension (CH) patients.

METHODS

PubMed, Embase, Cochrane and ClinicalTrials.gov were searched for prospective clinical studies that included RDN. The outcomes of interest were the change of 24-hour ambulatory systolic blood pressure (SBP) from baseline. We used the fixed effects model to calculate weighted mean difference (WMD) with 95% confidence interval (CI).

RESULTS

Six trials were included, with 1405 participants, including 597 patients with ISH and 808 patients with CH. Mean follow-up was five months. The reduction of 24-hour ambulatory SBP was significantly greater for the CH patients than the ISH patients (WMD = 3.89, 95% CI: 2.32-5.45, P < 0.0001). RDN also showed a greater reduction in office SBP in the CH patients compared to the ISH patients (WMD = 10.24, 95% CI: 4.24-15.74, P = 0.0003). And the effect was independent of age, length of follow-up, and ablation device.

CONCLUSIONS

RDN provides superior blood pressure control in the CH patients compared with the ISH patients, and the CH patients may be the best suitable population for which RDN is indicated.

Novel Invasive Methods as the Third Pillar for the Treatment of Essential Uncontrolled Hypertension

Pharmacologic therapies remain the treatment of choice for patients with essential hypertension, as endorsed by international guidelines. However, several cases warrant additional modalities, such as invasive antihypertensive therapeutics. The major target of these interventions is the modulation of the sympathetic nervous system, which is a common pathophysiologic mechanism in essential hypertension. In this narrative review, we elaborate on the role of invasive antihypertensive treatments with a focus on renal denervation, stressing their potential as well as the drawbacks that prevent their widespread implementation in everyday clinical practice. In the field of renal denervation, several trials have shown significant and sustained reductions in the level of office and ambulatory blood pressure, regardless of the type of energy that was used (radiofrequency or ultrasound). Critically, renal denervation is considered a safe intervention, as evidenced by follow-up data from large clinical trials. Baroreflex activation therapy may result in enhanced parasympathetic nervous system activation, thus lowering blood pressure levels. Along the same lines, carotid body ablation could also produce a significant antihypertensive effect, which has not been tested in appropriately designed randomized trials. Moreover, cardiac neuromodulation therapy could prove efficacious by altering the duration of the atrioventricular interval in order to regulate the preload of the left ventricle and, therefore, lower blood pressure.

Catheter-based renal denervation in Chinese patients with chronic kidney disease and uncontrolled hypertension

Sympathetic activation contributes to the progression of hypertension and chronic kidney disease (CKD). Ablation of renal sympathetic nerves lowers blood pressure (BP) and preserves renal function in patients with CKD and uncontrolled hypertension by reducing sympathetic nerve activity. But whether this approach is safe and effective in Chinese patients with CKD is unknown. We performed an observational study of eight patients with CKD stages from 1 to 5, office BP ≥150/90 mmHg, while on at least three antihypertensive drug classes including a diuretic, and diagnosis confirmed by 24 h ambulatory systolic BP measurement ≥135 mmHg. All patients underwent catheter-based renal denervation (RDN) using a newly designed RDN System (Golden Leaf Medtech, Shanghai, China). For up to 6 months after RDN, BP was monitored and renal function was assessed. Mean baseline office BP was 165.0 ± 13.9/97.8 ± 5.5 mmHg, despite treatment with three antihypertensive drugs. Six months after RDN, office BP was reduced by 22.1 ± 12.0 (P = .002)/11.0 ± 8.8 mmHg (P = .012) and average 24 h ambulatory BP by 18 ± 13.7 (P = .01)/9.3 ± 7.7 mmHg (P = .016). After RDN, heart rate and estimated glomerular filtration rate (GFR) had no significant change compared with before RDN. In Chinese patients with CKD, our observational pilot study found that treating hypertension with RDN lowers BP while not affecting renal function. Brief Abstract: We performed RDN in eight Chinese patients with hypertension and CKD. The results showed that RDN lowered blood pressure of these patients significantly and eGFR was stable. No obvious adverse event was observed.

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.

Histological evidence supporting the durability of successful radiofrequency renal denervation in a normotensive porcine model

BACKGROUND

Sustained blood pressure reductions after radiofrequency (RF) renal denervation (RDN) have been reported to 3 years in patients with uncontrolled hypertension. However, mechanistic data to support procedural durability are lacking. We aimed to quantify the long-term nerve anatomic and functional effects of RF RDN in a preclinical model.

METHODS

Bilateral RF RDN was performed in 20 normotensive swine. Renal tissue samples were obtained in the RDN-treated groups at 7 ( n  = 6), 28 ( n  = 6), and 180 days ( n  = 8) postprocedure for quantification of cortical norepinephrine (NE) levels and renal cortical axon density. Tissue fibrosis, necrosis and downstream nerve fiber atrophy (axonal loss) were also scored for each sample. Three additional untreated groups ( n  = 6, n  = 6 and n  = 8, respectively) served as control.

RESULTS

Pathologic nerve changes were characterized by necrosis in the ablated region at 7 days that partially resolved by 28 days and fully resolved at 180 days. Axonal loss was apparent within and downstream to the ablation regions and was evident at 7, 28 and 180 days in the main vessel and branch vessels. Consequently, renal cortical axon density and corresponding cortical NE levels were significantly reduced at 7 days in the RDN vs. control group and remained suppressed at 180 days.

CONCLUSIONS

Reductions in renal NE, cortical axon density and downstream axonal loss caused by axonal destruction persisted through 180 days post-RDN in a normotensive swine model. These results suggest functional nerve regrowth after RF RDN is unlikely and support published clinical evidence that the procedure results in durable blood pressure reduction.

Renal Sympathetic Denervation for Hypertension

Arterial hypertension is the most prevalent global modifiable risk factor for cardiovascular morbidity and mortality. Despite the availability of numerous pharmacologic treatments, many patients do not achieve guideline-recommended blood pressure targets. Therefore, renal sympathetic denervation (RDN), a process in which catheter-directed techniques are used to ablate portions of the renal artery to reduce sympathetic activity, has been extensively investigated as a complementary and nonpharmacologic approach for the treatment of arterial hypertension. This review seeks to discuss the pathophysiological rationale of this strategy, to survey its history and development, and to highlight the current clinical evidence and possible future directions of its employment. In sum, RDN has demonstrated itself to be a safe and well-tolerated endovascular intervention that can reliably contribute to improved blood pressure control and, perhaps ultimately, significant cardiovascular prognosis.

Nerve regeneration in transplanted organs and tracer imaging studies: A review

The technique of organ transplantation is well established and after transplantation the patient might be faced with the problem of nerve regeneration of the transplanted organ. Transplanted organs are innervated by the sympathetic, parasympathetic, and visceral sensory plexuses, but there is a lack of clarity regarding the neural influences on the heart, liver and kidneys and the mechanisms of their innervation. Although there has been considerable recent work exploring the potential mechanisms of nerve regeneration in organ transplantation, there remains much that is unknown about the heterogeneity and individual variability in the reinnervation of organ transplantation. The widespread availability of radioactive nerve tracers has also made a significant contribution to organ transplantation and has helped to investigate nerve recovery after transplantation, as well as providing a direction for future organ transplantation research. In this review we focused on neural tracer imaging techniques in humans and provide some conceptual insights into theories that can effectively support our choice of radionuclide tracers. This also facilitates the development of nuclear medicine techniques and promotes the development of modern medical technologies and computer tools. We described the knowledge of neural regeneration after heart transplantation, liver transplantation and kidney transplantation and apply them to various imaging techniques to quantify the uptake of radionuclide tracers to assess the prognosis of organ transplantation. We noted that the aim of this review is both to provide clinicians and nuclear medicine researchers with theories and insights into nerve regeneration in organ transplantation and to advance imaging techniques and radiotracers as a major step forward in clinical research. Moreover, we aimed to further promote the clinical and research applications of imaging techniques and provide clinicians and research technology developers with the theory and knowledge of the nerve.

Contribution of Afferent Renal Nerves to Cystogenesis and Arterial Pressure Regulation in a Preclinical Model of Autosomal Recessive Polycystic Kidney Disease

Polycystic kidney disease (PKD) is the most common inheritable cause of kidney failure, and the underlying mechanisms remain incompletely uncovered. Renal nerves contribute to hypertension and chronic kidney disease - frequent complications of PKD. There is limited evidence that renal nerves may contribute to cardiorenal dysfunction in PKD, and no investigations of the role of sympathetic versus afferent nerves in PKD. Afferent renal nerve activity (ARNA) is elevated in models of renal disease and fibrosis. However, it remains unknown if this is true in PKD. We tested the hypothesis that ARNA is elevated in a preclinical model of autosomal recessive PKD (ARPKD), and that targeted renal nerve ablation would attenuate cystogenesis and cardiorenal dysfunction. We tested this by performing a total (T-RDNx) or afferent (A-RDNx) denervation in 4-week-old male and female PCK rats, then quantifying renal and cardiovascular responses 6 weeks following treatment. Cystogenesis was attenuated with A-RDNx and T-RDNx vs. sham controls, highlighting a crucial role for renal afferent nerves in cystogenesis. In contrast, blood pressure was improved with T-RDNx but not A-RDNx. Importantly, treatments produced similar results in both males and females. Direct renal afferent nerve recordings revealed that ARNA was 2-fold greater in PCK rats vs. non-cystic controls and was directly correlated to cystic severity. To our knowledge, we are the first to demonstrate that PCK rats have greater ARNA than non-cystic, age-matched controls. The findings of these studies support a novel and crucial role for renal afferent innervation in cystogenesis in the PCK rat.

Brain-heart communication in health and diseases

Tight connections between the brain and heart have attracted a considerable amount of attention. This review focuses on the anatomical (extrinsic cardiac autonomic nervous system and intrinsic cardiac autonomic nervous system) and functional (neuroendocrine-heart axis and neuroimmune-heart axis) connections between the brain and heart, the linkage between central nervous system diseases and cardiovascular diseases, the harm of sympathetic hyperactivity to the heart, and current neuromodulation therapies. Depression is a comorbidity of cardiovascular diseases, and the two are causally related. This review summarizes the mechanisms and treatment of depression and cardiovascular diseases, providing theoretical evidence for basic research and clinical studies to improve treatment options.

Renal denervation: basic and clinical evidence

Renal nerves have critical roles in regulating blood pressure and fluid volume, and their dysfunction is closely related with cardiovascular diseases. Renal nerves are composed of sympathetic efferent and sensory afferent nerves. Activation of the efferent renal sympathetic nerves induces renin secretion, sodium absorption, and increased renal vascular resistance, which lead to increased blood pressure and fluid retention. Afferent renal sensory nerves, which are densely innervated in the renal pelvic wall, project to the hypothalamic paraventricular nucleus in the brain to modulate sympathetic outflow to the periphery, including the heart, kidneys, and arterioles. The effects of renal denervation on the cardiovascular system are mediated by both efferent denervation and afferent denervation. The first half of this review focuses on basic research using animal models of hypertension and heart failure, and addresses the therapeutic effects of renal denervation for hypertension and heart failure, including underlying mechanisms. The second half of this review focuses on clinical research related to catheter-based renal denervation in patients with hypertension. Randomized sham-controlled trials using second-generation devices, endovascular radiofrequency-based devices and ultrasound-based devices are reviewed and their results are assessed. This review summarizes the basic and clinical evidence of renal denervation to date, and discusses future prospects and potential developments in renal denervation therapy for cardiovascular diseases.

Enhanced Expression and Function of Renal SGLT2 (Sodium-Glucose Cotransporter 2) in Heart Failure: Role of Renal Nerves

BACKGROUND

Recent clinical studies demonstrate that SGLT2 (sodium-glucose cotransporter 2) inhibitors ameliorate heart failure (HF). The present study was conducted to assess the expression and function of renal SGLT2 and the influence of enhanced renal sympathetic tone in HF.

METHODS

Four weeks after coronary artery ligation surgery to induce HF, surgical bilateral renal denervation (RDN) was performed in rats. Four groups of rats (Sham-operated control [Sham], Sham+RDN, HF and HF+RDN; n=6/group) were used. Immunohistochemistry and Western blot analysis were performed to evaluate the renal SGLT2 expression. One week after RDN (5 weeks after induction of HF), intravenous injection of SGLT2 inhibitor dapagliflozin were performed to assess renal excretory responses. In vitro, human embryonic kidney cells were used to investigate the fractionation of SGLT2 after norepinephrine treatment.

RESULTS

In rats with HF, (1) SGLT2 expression in the proximal tubule of the kidney was increased; (2) the response of increases in urine flow, sodium excretion, and glucose excretion to dapagliflozin were greater; and (3) RDN attenuated renal SGLT2 expression and normalized renal functional responses to dapagliflozin. In vitro, norepinephrine promoted translocation of SGLT2 to the cell membrane.

CONCLUSIONS

These results indicate that the enhanced tonic renal sympathetic nerve activation in HF increases the expression and functional activity of renal SGLT2. Potentiated trafficking of SGLT2 to cell surface in renal proximal tubules mediated by norepinephrine may contribute to this functional activation of SGLT2 in HF. These findings provide critical insight into the underlying mechanisms for the beneficial effects of SGLT2 inhibitors on HF reported in the clinical studies.

Renal denervation inhibits the renin-angiotensin-aldosterone system in spontaneously hypertensive rats

This study was conducted to explore the effect of renal denervation (RDN) on the renin-angiotensin-aldosterone system (RAAS) in spontaneously hypertensive rats (SHRs). Our experimental rats were randomly divided into the RDN group conducted by painting 10% phenol on the bilateral renal nerves (RDNX), the shamoperation group simply painting with saline (Sham), and the normotension control group (WKY) following all the animal blood and tissues of kidney, hypothalamus, and adrenal gland collected and examined 2 weeks after RDN operation. We found that the aldosterone (ALD) levels in serum and tissues all decreased in the RDNX group compared with the Sham group (p < .05). Meantime, the expression of angiotensin II type1 receptor (AT1R) mRNA also exhibited significantly reduced by 2.22-fold in the RDNX group compared to the Sham group identical to the expression of AT1R protein in the renal cortex and outer stripe of the outer medulla (OSOM) subjected to denervation surgery, which manifested the lower ATIR protein expression than the Sham group (p < .05). Besides, the expression of angiotensin II (Ang II) protein in the cortex , OSOM, and inner stripe of the outer medulla were all attenuated by RDN in comparison with the Sham group (p < .05). RDN reduced intrarenal RAAS and circulating RAAS to lower blood pressure and repair renal function.

Renal Denervation Mitigated Fecal Microbiota Aberrations in Rats with Chronic Heart Failure

Background

Changes in the composition and diversity of gut microbiota, which can be altered by autonomic nerve activity, contribute to the development of heart failure (HF). Renal denervation (RDN) can improve cardiac function by reducing sympathetic nerve activity. However, whether the beneficial role of RDN on HF is related to gut microbiota is unknown.

Methods

Thirty rats were assigned to a control, HF (with induced transverse aortic constriction (TAC)), RDN (with RDN induced 10 weeks after TAC), Nog (HF rats with Nogo-P4-administered 8 weeks after RDN), and NEP (HF rats with NEP1-40-administered 8 weeks after RDN) group. Then, 16SrRNA amplicon sequencing and analyses of fecal samples were performed.

Results

Beta diversity analyses revealed that compared to the HF group, the RDN, Nog, and NEP groups clustered closer to the control group. The Firmicutes/Bacteroidetes ratio was reduced in the HF group (1.59) compared with the control group (3.21) and was significantly decreased compared to the Nog (7.19), RDN (6.20), and NEP (4.42) groups. At the genus level, the HF group showed decreased abundances of Lactobacillus and Alistipes and increased abundances of Bacteroides and Clostridium compared with the control group. The abundances of Lactobacillus and Alistipes were increased, and those of Bacteroides and Clostridium were decreased in the RDN, Nog, and NEP groups compared to the HF group. However, no differences were observed between the three groups that underwent RDN. The microbial function showed the same tendency.

Conclusions

RDN reversed the abnormal changes in the gut microbiome in HF rats. Inhibition of reinnervation after RDN did not affect intestinal bacteria.

The influence of inhibiting renal neural regeneration on the efficacy of renal denervation to chronic heart failure

Aims

Some studies support the occurrence of nerve regeneration in renal arteries after renal denervation (RDN). But it is unclear whether inhibiting reinnervation after RDN is beneficial to enhancing the effect of RDN on chronic heart failure (CHF).

Methods and results

Chronic heart failure Sprague Dawley rats induced by transverse aortic constriction were administered with the analogue of Nogo‐B (Nogo group) or its antagonist (NEP group) respectively after RDN. Echocardiography, messenger RNA, and protein expression of calcitonin gene‐related peptide (CGRP) in renal artery and nerves surrounding renal artery were detected. Relative protein expression of CGRP was significantly decreased in the Nog group compared with the RDN group (0.64 ± 0.51 vs. 1.68 ± 1.07, P = 0.048). The number of nerves surrounding renal artery was higher in the NEP group than in the Nog group. Left ventricular end‐systolic volume and diameter (LVVs and LVDs) were greatly decreased, and left ventricular ejection fraction (LVEF) and fractional shortening (FS) increased significantly in the RDN, Nog and NEP groups when compared with the HF group (all P < 0.05). No significant differences were observed in left ventricular end‐diastolic volume and diameter; LVDs; LVVs; FS; LVEF; and the levels of plasma renin, noradrenaline, and N‐terminal pro‐B‐type natriuretic peptide among three groups: the RDN, Nog, and NEP groups.

Conclusions

Reinnervation of renal artery occurred in CHF rats after RDN, which had no effect on therapeutic role of RDN in CHF, and inhibiting this neural regeneration had no clinical significance and did not affect the efficacy of RDN to CHF.

Renal Deafferentation Prevents Progression of Hypertension and Changes to Sympathetic Reflexes in a Rabbit Model of Chronic Kidney Disease

[Figure: see text].

Evidence of Reduced Efferent Renal Sympathetic Innervation After Chemical Renal Denervation in Humans

BACKGROUND

Renal denervation (RDN) is effective at lowering blood pressure. However, it is unknown if ablative procedures elicit sympathetic denervation of the kidneys in humans. The aim of this investigation was to assess sympathetic innervation of the renal cortex following perivascular chemical RDN, which may be particularly effective at ablating perivascular efferent and afferent nerves.

METHODS

Seven hypertensive patients (4F:3M; 50-65 years) completed PET-CT sympathetic neuroimaging of the renal cortex using 11C-methylreboxetine (11C-MRB, norepinephrine transporter ligand) and 6-[18F]-fluorodopamine (18F-FDA; substrate for the cell membrane norepinephrine transporter) before and 8 weeks after chemical RDN (Peregrine System Infusion Catheter, Ablative Solutions; n = 4; 2F:2M) or control renal angiography (n = 3; 2F:1M). Patients completed physiological phenotyping including 24-hour ambulatory blood pressure, hemodynamics, muscle sympathetic nerve activity, and 24-hour urine collection.

RESULTS

RDN decreased 11C-MRB-derived radioactivity by ~30% (Δ  11C-MRB/chamber: -0.95 a.u. confidence interval (CI): -1.36 to -0.54, P = 0.0002), indicative of efferent RDN. In contrast, 18F-FDA-derived radioactivity increased (Δ  18F-FDA/chamber: 2.72 a.u. CI: 0.73-4.71, P = 0.009), consistent with reduced vesicular turnover. Controls showed no change in either marker. Ambulatory systolic pressure decreased in 3 of 4 patients (-9 mm Hg CI: -27 to 9, P = 0.058), and central systolic pressure decreased in all patients (-23 mm Hg CI: -51 to 5, P = 0.095).

CONCLUSIONS

These results are the first to show efferent sympathetic denervation of the renal cortex following RDN in humans. Further studies of mechanisms underlying variable blood pressure lowering in the setting of documented RDN may provide insights into inconsistencies in clinical trial outcomes.

CLINICAL TRIALS REGISTRATION

Trial Number NCT03465917.

Sodium-glucose cotransporter 2 inhibition prevents renal fibrosis in cyclosporine nephropathy

AIMS

Sodium-glucose cotransporter 2 (SGLT2) inhibitors, a new class of antidiabetic drugs, are nephroprotective in case of diabetes, but whether a similar beneficial effect may be detectable also in case of chronic non-diabetic kidney diseases remains still unknown. The aim of this study was to evaluate the effects of empagliflozin, a SGLT-2 inhibitor, on the progression of cyclosporine nephropathy, in the absence of diabetes.

METHODS

Sprague Dawley rats (n = 27) have been fed with low-salt diet starting 10 days before the beginning and finished at the end of the experimental period. Cyclosporine-A (CsA, 15 mg/kg/day, intraperitoneal injection, n = 8) and CsA plus empagliflozin (Empa, 10 mg/kg/day, per os, n = 7) were administered for 4 weeks. The control groups were treated with placebo (Control, n = 7) or empagliflozin (Control + Empa, n = 5). Blood pressure (plethysmographic method) was measured at the beginning and at the end of the experimental period. At the end of the experimental protocol, the kidneys were excised for histomorphometric analysis of renal fibrosis and for immunohistochemical evaluation of inflammatory infiltrates (monocytes/macrophages), type I and type IV collagen expression, and tyrosine hydroxylase expression, used as marker of sympathetic nerve activity.

RESULTS

CsA-treated rats showed a significant increase (p < 0.01) in blood pressure, which was reduced by administration of empagliflozin (p < 0.05). CsA administration caused an increase in glomerular and tubulo-interstitial fibrosis (p < 0.05), renal inflammatory infiltrates (p < 0.05), type I and type IV collagen expression (p < 0.01), and tyrosine hydroxylase expression (p < 0.01) as compared to the control rats and control + Empa-treated rats. Treatment with empagliflozin in CsA-treated rats reduced glomerular (p < 0.01) and tubulo-interstitial fibrosis (p < 0.05), type I and type IV collagen expression (p < 0.01), inflammatory cell infiltration (p < 0.01) and tyrosine hydroxylase expression (p < 0.05), as compared to rats treated with CsA.

CONCLUSION

Empagliflozin administration caused a reduction in blood pressure in CsA-treated rats and showed a protective effect on CsA nephropathy by decreasing renal fibrosis, type I and type IV collagen expression, macrophage infiltration and tyrosine hydroxylase expression. These data suggest that empagliflozin promotes nephroprotection also in non-diabetic kidney disease.

Renal denervation does not affect hypertension or the renin-angiotensin system in a rodent model of juvenile-onset polycystic kidney disease: clinical implications

We examined the effect of total and afferent renal denervation (RDN) on hypertension and the renin-angiotensin system (RAS) in a rodent model of juvenile-onset polycystic kidney disease (PKD). Lewis Polycystic Kidney (LPK) and control rats received total, afferent or sham RDN by periaxonal application of phenol, capsaicin or normal saline, respectively, and were monitored for 4-weeks. Afferent RDN did not affect systolic blood pressure (SBP) determined by radiotelemetry in either strain (n = 19) while total RDN significantly reduced SBP in Lewis rats 4-weeks post-denervation (total vs. sham, 122 ± 1 vs. 130 ± 2 mmHg, P = 0.002, n = 25). Plasma and kidney renin content determined by radioimmunoassay were significantly lower in LPK vs. Lewis (plasma: 278.2 ± 6.7 vs. 376.5 ± 11.9 ng Ang I/ml/h; kidney: 260.1 ± 6.3 vs. 753.2 ± 37.9 ng Ang I/mg/h, P < 0.001, n = 26). These parameters were not affected by RDN. Intrarenal mRNA expression levels of renin, angiotensinogen, angiotensin-converting enzyme (ACE)2, and angiotensin II receptor type 1a were significantly lower, whereas ACE1 expression was significantly higher in the LPK vs. Lewis (all P < 0.05, n = 26). This pattern of intrarenal RAS expression was not changed by RDN. In conclusion, RDN does not affect hypertension or the RAS in the LPK model and indicates RDN might not be a suitable antihypertensive strategy for individuals with juvenile-onset PKD.

Sympathetic innervation of the mouse kidney and liver arising from prevertebral ganglia

The sympathetic nervous system (SNS) plays a crucial role in the regulation of renal and hepatic functions. Although sympathetic nerves to the kidney and liver have been identified in many species, specific details are lacking in the mouse. In the absence of detailed information of sympathetic prevertebral innervation of specific organs, selective manipulation of a specific function will remain challenging. Despite providing major postganglionic inputs to abdominal organs, limited data are available about the mouse celiac-superior mesenteric complex. We used tyrosine hydroxylase (TH) and dopamine β-hydroxylase (DbH) reporter mice to visualize abdominal prevertebral ganglia. We found that both the TH and DbH reporter mice are useful models for identification of ganglia and nerve bundles. We further tested if the celiac-superior mesenteric complex provides differential inputs to the mouse kidney and liver. The retrograde viral tracer, pseudorabies virus (PRV)-152 was injected into the cortex of the left kidney or the main lobe of the liver to identify kidney-projecting and liver-projecting neurons in the celiac-superior mesenteric complex. iDISCO immunostaining and tissue clearing were used to visualize unprecedented anatomical detail of kidney-related and liver-related postganglionic neurons in the celiac-superior mesenteric complex and aorticorenal and suprarenal ganglia compared with TH-positive neurons. Kidney-projecting neurons were restricted to the suprarenal and aorticorenal ganglia, whereas only sparse labeling was observed in the celiac-superior mesenteric complex. In contrast, liver-projecting postganglionic neurons were observed in the celiac-superior mesenteric complex and aorticorenal and suprarenal ganglia, suggesting spatial separation between the sympathetic innervation of the mouse kidney and liver.

Impact of Renal Pelvic Denervation on Systemic Hemodynamics and Neurohumoral Changes in a Porcine Model

INTRODUCTION

The blood pressure (BP) response to arterial renal denervation (RDN) is variable.

METHODS

This study examined the effectiveness of renal pelvic denervation (RPD) on BP, heart rate (HR), norepinephrine (NE), and histopathology in 42 swine. NE levels were measured immediately, 7, 14, 30, and 90 days after RPD. Intra-arterial BP and HR were measured throughout RPD and after 14 days in 5 swine.

RESULTS

During the procedure, RPD immediately reduced systolic BP (-20.6 ± 18.3 mm Hg), diastolic BP (-6.0 ± 8.3 mm Hg), and HR (-5.4 ± 5.6 bpm), which remained decreased at follow-up. The porcine kidneys had a mean NE reduction of 76% directly post procedure and 60% after 7 days, 64% after 14 days, 57% after 30 days, and 65% after 90 days. Histopathological examination confirmed nerve ablation.

CONCLUSIONS

These preliminary findings suggest that the renal pelvis nerve ablation is an encouraging target for RDN. Clinical trials are required to test the feasibility of RPD in human hypertension.

The Effects of Renal Nerve Denervation on Blood Pressure and Target Organs in Different Hypertensive Rat Models

Background

Hypertension contributes to the progression of cardiac remodeling and renal damage. In turn, renal sympathetic hyperactivation showed elevated sympathetic nervous system activity and led to blood pressure increase in certain patients. The purpose of this study was to observe the effect of renal nerve denervation on blood pressure and target organ changes in two hypertensive rat models.

Methods

Hypertensive rats were randomly divided into a renal denervation (RDN) group and sham operation group. Wistar–Kyoto (WKY) rats of the same age were set as the baseline control group. In the secondary hypertension model, SD rats were randomly divided into five groups. Blood pressure and bodyweight were measured every week until they were euthanized.

Results

The two rat models underwent RDN at key timepoints. At these timepoints, the hearts and kidneys were collected for norepinephrine and angiotensin II measurements and histological analysis.

Conclusion

RDN performed before development of hypertension showed a significant antihypertensive effect on the secondary hypertension model.

Device Therapy of Hypertension

In the past decade, efforts to improve blood pressure control have looked beyond conventional approaches of lifestyle modification and drug therapy to embrace interventional therapies. Based upon animal and human studies clearly demonstrating a key role for the sympathetic nervous system in the etiology of hypertension, the newer technologies that have emerged are predominantly aimed at neuromodulation of peripheral nervous system targets. These include renal denervation, baroreflex activation therapy, endovascular baroreflex amplification therapy, carotid body ablation, and pacemaker-mediated programmable hypertension control. Of these, renal denervation is the most mature, and with a recent series of proof-of-concept trials demonstrating the safety and efficacy of radiofrequency and more recently ultrasound-based renal denervation, this technology is poised to become available as a viable treatment option for hypertension in the foreseeable future. With regard to baroreflex activation therapy, endovascular baroreflex amplification, carotid body ablation, and programmable hypertension control, these are developing technologies for which more human data are required. Importantly, central nervous system control of the circulation remains a poorly understood yet vital component of the hypertension pathway and mandates further investigation. Technology to improve blood pressure control through deep brain stimulation of key cardiovascular control territories is, therefore, of interest. Furthermore, alternative nonsympathomodulatory intervention targeting the hemodynamics of the circulation may also be worth exploring for patients in whom sympathetic drive is less relevant to hypertension perpetuation. Herein, we review the aforementioned technologies with an emphasis on the preclinical data that underpin their rationale and the human evidence that supports their use.

Selective afferent renal denervation mitigates renal and splanchnic sympathetic nerve overactivity and renal function in chronic kidney disease-induced hypertension

BACKGROUND

Clinical and experimental evidence have shown that renal denervation, by removing both the sympathetic and afferent nerves, improves arterial hypertension and renal function in chronic kidney disease (CKD). Given the key role of renal sympathetic innervation in maintaining sodium and water homeostasis, studies have indicated that the total removal of renal nerves leads to impaired compensatory mechanisms during hemodynamic challenges.

METHOD

In the present study, we hypothesized that afferent (or sensory) fibers from the diseased kidney contribute to sympathetic overactivation to the kidney and other target organ, such as the splanchnic region, contributing to hypertension in CKD. We used a method to remove selectively the afferent renal fibers (periaxonal application of 33 mmol/l capsaicin) in a rat model of CKD, the 5/6 nephrectomy.

RESULTS

Three weeks after afferent renal denervation (ARD), we found a decrease in mean arterial pressure (∼15%) and normalization in renal and splanchnic sympathetic nerve hyperactivity in the CKD group. Interestingly, intrarenal renin--angiotensin system, as well as renal fibrosis and function and proteinuria were improved after ARD in CKD rats.

CONCLUSION

The findings demonstrate that afferent fibers contribute to the maintenance of arterial hypertension and reduced renal function that are likely to be mediated by increased sympathetic nerve activity to the renal territory as well as to other target organs in CKD.

The current status of renal denervation for the treatment of arterial hypertension

Despite the availability of safe and effective antihypertensive drugs, blood pressure (BP) control to guideline-recommended target values is poor. Several device-based therapies have been introduced to lower BP. The most extensively investigated approach is catheter-based renal sympathetic denervation (RDN), which aims to interrupt the activity of afferent and efferent renal sympathetic nerves by applying radiofrequency energy, ultrasound energy, or injection of alcohol in the perivascular space. The second generation of placebo-controlled trials have provided solid evidence for the BP-lowering efficacy of radiofrequency- and ultrasound-based RDN in patients with and without concomitant pharmacological therapy. In addition, the safety profile of RDN appears to be excellent in all registries and clinical trials. However, there remain unsolved issues to be addressed. This review summarizes the rationale as well as the current evidence and discusses open questions and possible future indications of catheter-based RDN.

Correlated Sensory and Sympathetic Innervation Between the Acupoint BL23 and Kidney in the Rat

Objective: To investigate the sensory and sympathetic innervations associated with both acupoint “Shenshu” (BL23) and kidney in the rat for insight into the neuronal correlation between the Back-Shu Point and its corresponding visceral organ.

Methods: The BL23 and kidney were selected as the representative acupoint and visceral organ in this study, in which their local nerve fibers were examined by using double fluorescent immunohistochemistry with calcitonin gene-related peptide (CGRP) and tyrosine hydroxylase (TH). Meanwhile, their neuronal correlation in the dorsal root ganglia (DRGs), spinal cord, and sympathetic (paravertebral) chain were investigated using a double fluorescent neural tracing technique with Alexa Fluor 488 and 594 conjugates with cholera toxin subunit B (AF488/594-CTB).

Results: The local tissue of acupoint BL23 and the fibrous capsule of kidney distributed abundantly with CGRP- and TH-positive nerve fibers, corresponding to their sensory and sympathetic innervation. On the other hand, the sensory neurons associated with acupoint BL23 and kidney were labeled with AF488/594-CTB and distributed from thoracic (T) 11 to lumbar (L) 3 DRGs and from T10 to L2 DRGs, respectively, in which some of them in T12-T13 DRGs were simultaneously labeled with both AF488/594-CTB. Also, postganglionic neurons associated with both acupoint BL23 and kidney were found in the sympathetic chain at the same spinal segments but separately labeled with AF488-CTB and AF594-CTB.

Conclusion: Our study demonstrates the neural characteristics of the acupoint BL23 and kidney in the rat from the perspective of neurochemistry and neural pathways, providing an example for understanding the neuronal correlation between the Back-Shu Points and their corresponding visceral organs. These results suggest that the stimulation of the Back-Shu Points may regulate the activities of the target-organs via the periphery sensory and sympathetic pathways.

The involvement of renal afferents in the maintenance of cardiorenal diseases

Elevated sympathetic vasomotor activity is a common feature of cardiorenal diseases. Therefore, the sympathetic nervous system is an important therapeutic target, particularly the fibers innervating the kidneys. In fact, renal denervation has been applied clinically and shown promising results in patients with hypertension and chronic kidney disease. However, the underlying mechanisms involved in the cardiorenal protection induced by renal denervation have not yet been fully clarified. This mini-review highlights historical and recent aspects related to the role of renal sensory fibers in the control of cardiorenal function under normal conditions and in experimental models of cardiovascular disease. Results have demonstrated that alterations in renal sensory function participate in the maintenance of elevated sympathetic vasomotor activity and cardiorenal changes; as such, renal sensory fibers may be a potential therapeutic target for the treatment of cardiorenal diseases. Although it has not yet been applied in clinical practice, selective afferent renal denervation may be promising, since such an approach maintains efferent activity and can provide more refined control of renal function compared with total renal denervation. However, more studies are needed to understand the mechanisms by which renal afferents partially contribute to such changes, in addition to the need to evaluate the safety and advantages of the approach for application in the clinical practice.

Sympathetic Nervous System Contributions to Hypertension: Updates and Therapeutic Relevance

The sympathetic nervous system plays a pivotal role in the long-term regulation of arterial blood pressure through the ability of the central nervous system to integrate neurohumoral signals and differentially regulate sympathetic neural input to specific end organs. Part 1 of this review will discuss neural mechanisms of salt-sensitive hypertension, obesity-induced hypertension, and the ability of prior experiences to sensitize autonomic networks. Part 2 of this review focuses on new therapeutic advances to treat resistant hypertension including renal denervation and carotid baroactivation. Both advances lower arterial blood pressure by reducing sympathetic outflow. We discuss potential mechanisms and areas of future investigation to target the sympathetic nervous system.

Renal Sympathetic Nerve-Derived Signaling in Acute and Chronic kidney Diseases

The kidney is innervated by afferent sensory and efferent sympathetic nerve fibers. Norepinephrine (NE) is the primary neurotransmitter for post-ganglionic sympathetic adrenergic nerves, and its signaling, regulated through adrenergic receptors (AR), modulates renal function and pathophysiology under disease conditions. Renal sympathetic overactivity and increased NE level are commonly seen in chronic kidney disease (CKD) and are critical factors in the progression of renal disease. Blockade of sympathetic nerve-derived signaling by renal denervation or AR blockade in clinical and experimental studies demonstrates that renal nerves and its downstream signaling contribute to progression of acute kidney injury (AKI) to CKD and fibrogenesis. This review summarizes our current knowledge of the role of renal sympathetic nerve and adrenergic receptors in AKI, AKI to CKD transition and CKDand provides new insights into the therapeutic potential of intervening in its signaling pathways.

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.

Device-Based Neuromodulation for Resistant Hypertension Therapy

Despite availability of effective drugs for hypertension therapy, significant numbers of hypertensive patients fail to achieve recommended blood pressure levels on ≥3 antihypertensive drugs of different classes. These individuals have a high prevalence of adverse cardiovascular events and are defined as having resistant hypertension (RHT) although nonadherence to prescribed antihypertensive medications is common in patients with apparent RHT. Furthermore, apparent and true RHT often display increased sympathetic activity. Based on these findings, technology was developed to treat RHT by suppressing sympathetic activity with electrical stimulation of the carotid baroreflex and catheter-based renal denervation (RDN). Over the last 15 years, experimental and clinical studies have provided better understanding of the physiological mechanisms that account for blood pressure lowering with baroreflex activation and RDN and, in so doing, have provided insight into which patients in this heterogeneous hypertensive population are most likely to respond favorably to these device-based therapies. Experimental studies have also played a role in modifying device technology after early clinical trials failed to meet key endpoints for safety and efficacy. At the same time, these studies have exposed potential differences between baroreflex activation and RDN and common challenges that will likely impact antihypertensive treatment and clinical outcomes in patients with RHT. In this review, we emphasize physiological studies that provide mechanistic insights into blood pressure lowering with baroreflex activation and RDN in the context of progression of clinical studies, which are now at a critical point in determining their fate in RHT management.

Afferent innervation of the ischemic kidney contributes to renal dysfunction in renovascular hypertensive rats

The ablation of renal nerves, by destroying both the sympathetic and afferent fibers, has been shown to be effective in lowering blood pressure in resistant hypertensive patients. However, experimental studies have reported that the removal of sympathetic fibers may lead to side effects, such as the impairment of compensatory cardiorenal responses during a hemodynamic challenge. In the present study, we evaluated the effects of the selective removal of renal afferent fibers on arterial hypertension, renal sympathetic nerve activity, and renal changes in a model of renovascular hypertension. After 4 weeks of clipping the left renal artery, afferent renal denervation (ARD) was performed by exposing the left renal nerve to a 33 mM capsaicin solution for 15 min. After 2 weeks of ARD, we found reduced MAP (~ 18%) and sympathoexcitation to both the ischemic and contralateral kidneys in the hypertensive group. Moreover, a reduction in reactive oxygen species was observed in the ischemic (76%) and contralateral (27%) kidneys in the 2K1C group. In addition, ARD normalized renal function markers and proteinuria and podocin in the contralateral kidney. Taken altogether, we show that the selective removal of afferent fibers is an effective method to reduce MAP and improve renal changes without compromising the function of renal sympathetic fibers in the 2K1C model. Renal afferent nerves may be a new target in neurogenic hypertension and renal dysfunction.

Sensory signals mediating high blood pressure via sympathetic activation: role of adipose afferent reflex

Blood pressure regulation in health and disease involves a balance between afferent and efferent signals from multiple organs and tissues. Although there are numerous reviews focused on the role of sympathetic nerves in different models of hypertension, few have revised the contribution of afferent nerves innervating adipose tissue and their role in the development of obesity-induced hypertension. Both clinical and basic research support the beneficial effects of bilateral renal denervation in lowering blood pressure. However, recent studies revealed that afferent signals from adipose tissue, in an adipose-brain-peripheral pathway, could contribute to the increased sympathetic activation and blood pressure during obesity. This review focuses on the role of adipose tissue afferent reflexes and briefly describes a number of other afferent reflexes modulating blood pressure. A comprehensive understanding of how multiple afferent reflexes contribute to the pathophysiology of essential and/or obesity-induced hypertension may provide significant insights into improving antihypertensive therapeutic approaches.

Is Aberrant Reno-Renal Reflex Control of Blood Pressure a Contributor to Chronic Intermittent Hypoxia-Induced Hypertension?

Renal sensory nerves are important in the regulation of body fluid and electrolyte homeostasis, and blood pressure. Activation of renal mechanoreceptor afferents triggers a negative feedback reno-renal reflex that leads to the inhibition of sympathetic nervous outflow. Conversely, activation of renal chemoreceptor afferents elicits reflex sympathoexcitation. Dysregulation of reno-renal reflexes by suppression of the inhibitory reflex and/or activation of the excitatory reflex impairs blood pressure control, predisposing to hypertension. Obstructive sleep apnoea syndrome (OSAS) is causally related to hypertension. Renal denervation in patients with OSAS or in experimental models of chronic intermittent hypoxia (CIH), a cardinal feature of OSAS due to recurrent apnoeas (pauses in breathing), results in a decrease in circulating norepinephrine levels and attenuation of hypertension. The mechanism of the beneficial effect of renal denervation on blood pressure control in models of CIH and OSAS is not fully understood, since renal denervation interrupts renal afferent signaling to the brain and sympathetic efferent signals to the kidneys. Herein, we consider the currently proposed mechanisms involved in the development of hypertension in CIH disease models with a focus on oxidative and inflammatory mediators in the kidneys and their potential influence on renal afferent control of blood pressure, with wider consideration of the evidence available from a variety of hypertension models. We draw focus to the potential contribution of aberrant renal afferent signaling in the development, maintenance and progression of high blood pressure, which may have relevance to CIH-induced hypertension.

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.

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.

Role of capsaicin sensitive sensory nerves in ischemia reperfusion-induced acute kidney injury in rats

Acute kidney injury (AKI) is a common kidney disorder which is associated with a high risk of mortality. Extensive evidence revealed the participation of renal afferent sensory nerves in the pathophysiology of renal ischemia reperfusion (IR) injury, however the role of these nerves in renal IR injury is controversial and remains to be further explored. Here, we report that capsaicin sensitive sensory nerves and neuropeptides prevented renal damage in AKI induced by IR injury. The sensory afferent degeneration model was established by injecting 50 mg/kg of capsaicin to male neonatal rats and verified by the tail flick test and reduced sensory neuropeptide of substance P and calcitonin gene related peptide in spinal cord, dorsal root ganglion and kidney after 12 weeks. Then, a model of renal IR injury was established. The sensory afferent degeneration in the AKI group increased the level of serum creatinine, NGAL and KIM-1, aggravated to some extent renal pathological damage, and enhanced the proinflammatory cytokines expressions and tubular cell apoptosis. In addition, it was also discovered that the level of phospho-ERK/ERK (p-ERK/ERK) showed an increase in spinal cord and kidney after degeneration of capsaicin sensitive sensory nerves. In conclusion, the degeneration of sensory nerves aggravated IR-induced AKI in rats, and the activated ERK signaling in spinal cord and kidney after sensory afferent degeneration might be the possible mechanism in the aggravated renal injury.

Effects of renal denervation on blood-pressure response to hemorrhagic shock in spontaneously hypertensive rats

PURPOSE

Renal denervation (RD) has been demonstrated to be an effective approach to reduce blood pressure for those with resistant hypertension. Yet, we aimed to explore the effect and possible mechanism of RD on blood-pressure response to hemorrhagic shock in spontaneously hypertensive rats.

METHODS

A total of 48 male spontaneously hypertensive rats were randomized to three groups: study group, sham-operation group and control group. RD was achieved by cutting off renal nerves and swabbing phenol on it. Ten weeks after RD, 8 rats in each group were sacrificed to collect the kidney and heart tissues. The remaining rats were subjected to an operation to induce hemorrhagic shock which would lead to 40% loss of total blood volume, and observed for 120 min. The serum concentration of norepinephrine was measured before and three weeks after RD.

RESULTS

The blood-pressure and norepinephrine levels were reduced significantly after RD (p < 0.05). Systolic blood pressure and diastolic blood pressure of the surgery group were higher than those in the sham and control groups at 15, 30 and 45 min after hemorrhagic shock (p < 0.05), while no significant difference was observed at 60, 90 and 120 min (p > 0.05). Additionally, the beta-1 adrenergic receptor (β1-AR) in the study group was significantly higher than those in the other two groups (p < 0.05) after hemorrhagic shock.

CONCLUSION

This study demonstrated that RD could to some extent improve blood-pressure response to hemorrhagic shock in an established model of severe hemorrhagic shock in spontaneously hypertensive rats. The mechanism might be associated with up-regulation of β1-AR.

Cellular and molecular mechanisms of kidney fibrosis

Renal fibrosis is the final pathological process common to any ongoing, chronic kidney injury or maladaptive repair. It is considered as the underlying pathological process of chronic kidney disease (CKD), which affects more than 10% of world population and for which treatment options are limited. Renal fibrosis is defined by excessive deposition of extracellular matrix, which disrupts and replaces the functional parenchyma that leads to organ failure. Kidney's histological structure can be divided into three main compartments, all of which can be affected by fibrosis, specifically termed glomerulosclerosis in glomeruli, interstitial fibrosis in tubulointerstitium and arteriosclerosis and perivascular fibrosis in vasculature. In this review, we summarized the different appearance, cellular origin and major emerging processes and mediators of fibrosis in each compartment. We also depicted and discussed the challenges in translation of anti-fibrotic treatment to clinical practice and discuss possible solutions and future directions.