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

Impaired inhibitory reno-renal reflex responses in chronic kidney disease

The renal afferent nerves serve as physiologic regulators of efferent renal sympathetic nerve activity (rSNA) as part of the inhibitory reno-renal reflex. Dysregulation of this reflex response may promote sympathoexcitation and subsequent hypertension under pathologic conditions such as chronic kidney disease (CKD). We have undertaken an in-depth characterization of reno-renal reflex function in CKD using an anesthetized rodent model with concurrent physiological outflows assessed. Using anesthetized male Lewis Polycystic Kidney (LPK) rats and normotensive Lewis controls, we investigated the cardiovascular [blood pressure (BP), heart rate (HR) and sympathetic responses (recorded from renal and splanchnic nerves (r/sSNA)] to renal capsaicin (50 µM) and direct electrical stimulation of the whole renal nerve. In Lewis rats, intra-pelvic renal capsaicin injection resulted in a depressor, bradycardic, and sympathoinhibitory response in sSNA with no significant change in rSNA. In contrast, the same stimulus led to a pressor and sympathoexcitatory response in the LPK group. In Lewis rats, low-intensity electrical stimulation (0.2 ms pulses, 15 μA, 2-40 Hz) of the renal nerve elicited a depressor response and bradycardia with concurrent sympathoexcitation (sSNA), whereas high-intensity (150 µA) stimulation induced a biphasic depressor/pressor response and tachycardia. In LPK rats, low-intensity renal nerve electrical stimulation triggered a biphasic depressor/pressor BP response, tachycardia, and sympathoexcitation. High-intensity stimulation similarly caused a biphasic depressor/pressor BP response and tachycardia. The magnitude of the sSNA response and both phases of the blood pressure response was higher in LPK compared to Lewis. All responses showed some degree of frequency dependency. Our results suggest the inhibitory reno-renal reflex is impaired in CKD, with dominance of excitatory reflex response. However, a depressor component remained that could be targeted using implantable neurotechnologies to lower blood pressure in CKD patients safely and effectively.

Renal denervation for hypertensive heart disease and atrial fibrillation

Accumulating evidence supports the efficacy of renal denervation (RDN) as an antihypertensive treatment. Additionally, several RDN clinical studies, including meta-analyses, have suggested that RDN may potentially have beneficial effects on left ventricular hypertrophy, diastolic function, and new-onset/recurrence of atrial fibrillation (AF), although most studies were not randomized sham-controlled. In particular, the effects of RDN on left ventricular hypertrophy and AF recurrence appear to be relatively evident. Sympathetic activation plays a critical role in the development of hypertension, hypertensive heart disease, and AF. Notably, several studies suggest the cardioprotective effects of RDN even in the absence of significant blood pressure reduction, probably due to its sympathoinhibitory effects. It is imperative to establish the efficacy of RDN in patients with hypertensive heart disease and/or AF, focusing on parameters of sympathetic activity in the clinical setting, including randomized sham-controlled trials. Moreover, further basic research is essential to elucidate the therapeutic mechanisms of RDN beyond blood pressure lowering and the renal nerves-linked pathophysiologies of hypertensive heart disease and AF. This review outlines the effects of renal denervation on hypertensive heart disease, particularly on left ventricular hypertrophy and diastolic function, and on atrial fibrillation. The sympathoinhibitory effect of renal denervation, an important potential mechanism of its beneficial effects on heart disease, is also discussed.

The denervation or activation of renal sympathetic nerve and renal blood flow

The denervation or activation of the sympathetic nerve in the kidney can affect renal hemodynamics. The sympathetic nervous system regulates the physiological functions of the kidneys. Stimulation of sympathetic efferent nerves affects various parameters related to renal hemodynamics, including sodium excretion, renin secretion, and renal blood flow (RBF). Hence, renal sympathetic fibers may also play an essential role in regulating systemic vascular resistance and controlling blood pressure. In the absence of renal nerves, the hemodynamics response to stimuli is negligible or absent. The effect of renal sympathetic denervation on RBF is dependent on several factors such as interspecies differences, the basic level of nerve activity in the vessels or local density of adrenergic receptor in the vascular bed. The role of renal denervation has been investigated therapeutically in hypertension and related disorders. Hence, the dynamic impact of renal nerves on RBF enables using RBF dynamic criteria as a marker for renal denervation therapy.

Vascular Dysfunction in Polycystic Kidney Disease: A Mini-Review

Polycystic kidney disease (PKD) is one of the most common hereditary kidney diseases, which is characterized by progressive cyst growth and secondary hypertension. In addition to cystogenesis and renal abnormalities, patients with PKD can develop vascular abnormalities and cardiovascular complications. Progressive cyst growth substantially alters renal structure and culminates into end-stage renal disease. There remains no cure beyond renal transplantation, and treatment options remain largely limited to chronic renal replacement therapy. In addition to end-stage renal disease, patients with PKD also present with hypertension and cardiovascular disease, yet the timing and interactions between the cardiovascular and renal effects of PKD progression are understudied. Here, we review the vascular dysfunction found in clinical and preclinical models of PKD, including the clinical manifestations and relationship to hypertension, stroke, and related cardiovascular diseases. Finally, our discussion also highlights the critical questions and emerging areas in vascular research in PKD.

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.

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.