Abstract
Introduction: Resistant arterial hypertension (RHT) is defined as poor controlled blood pressure (BP) despite optimal doses of three or more antihypertensive agents, including a diuretic. In the development of RHT, hyperactivity of sympathetic (SNS) and renin–angiotensin–aldosterone (SRAA) systems are involved, and SNS is a potent stimulator of vasoactive endothelin-1 (ET-1) peptide. Renal sympathetic denervation (RSD) through disrupting renal afferent and efferent nerves attenuates SNS activity.
Material and methods: We carried out pilot study investigating the effect of RSD on BP and plasma ET-1 levels in consecutive 9 RHT patients (7 male and 2 female, mean age of 56 ± 13.3).
Results: After 12 months of the RSD, we observed a significant reduction of BP office, 24-h ambulatory BP monitoring (ABPM) (p < 0.05, respectively), and “non-dipping” pattern (from 55% to 35%) (p < 0.05). Moreover, RSD significantly decreased plasma ET-1 levels in both renal artery (at right from 21.8 ± 4.1 to 16.8 ± 2.9 pg/ml; p = 0.004; at left from 22.1 ± 3.7 to 18.9 ± 3.3 pg/ml; p = 0.02). We observed positive correlations between plasma renal arteries ET-1 levels and systolic BP values at ABPM [Global-SBP (r = 0.58; p < 0.01), Diurnal-SBP (r = 0.51; p < 0.03) and Nocturnal-SBP (r = 0.58; p < 0.01), respectively].
Discussion: Our data confirmed the positive effects of RSD on BP values in patients with RHT, and showed a possible physio-pathological role of ET-1.
RSD is associated to a significant reduction of plasma ET-1 levels, representing an useful tool into reduction of BP in RHT patients.
KEY MESSAGES
Introduction
Resistant arterial hypertension (RHT) is defined as blood pressure (BP) of >140/90 mmHg in adults despite the treatment with optimal doses of 3 or more antihypertensive agents, one of which is a diuretic (Citation1,Citation2). This definition also includes patients in whom effective BP control requires the use of at least four drugs (Citation3). It is very important to rule out the causes of pseudo-resistance to treatment, which usually include an important technique of BP measurement, non-adherence of the patient, especially regarding therapeutic recommendations, and finally the white coat effects (Citation3).
The pathophysiology of RHT is poorly understood although several suggested mechanisms include: (a) hyperactivity of both sympathetic and renin–angiotensin–aldosterone systems (RAAS) (Citation4,Citation5); (b) arterial stiffness (Citation6), and (c) cardiac hypertrophy (Citation7).
Furthermore, some studies have indicated that sympathetic nervous system (SNS) is a potent stimulator of endothelin-1 (ET-1) production, widespreadly in animal and human tissues, and exerts its hypertensive effects via interaction with the ET system (Citation8,Citation9). ET-1 mRNA transcription is widespread in animal and human tissues, including the heart, lung and adrenals, not only endothelial cells, but many other resident cells such as smooth muscle cells or fibroblasts; these same tissues have high receptor binding ET-1, representing autocrine, and paracrine systems (Citation9). Moreover, ET-1 contributes importantly to the renal mechanisms involved in the control of renal sympathetic nerve activity and maintenance of sodium balance (Citation10).
Recently, renal sympathetic denervation (RSD) using a catheter-based approach, which targets at disrupting renal afferent and efferent nerves thereby attenuating sympathetic nervous activity, is well-known as an innovative method for RHT (Citation11,Citation12).
Based on these aspects we carried out a pilot study investigating the effect of RSD on BP reduction and plasma ET-1 values in a group of RHT patients.
Materials and methods
Participants
A total of 9 patients (7 male/2 female) with RHT were enrolled in this clinical study aimed at assessing the effects of RSD on BP and plasma ET-1 values.
The group study consisted in patients with RHT to undergo RSD in Specialized Center of Secondary Hypertension, Hospital Policlinico Umberto I, University of Rome, “La Sapienza”, Italy. Written informed consent was obtained from all patients.
Patients underwent a complete medical history and physical examination and a comprehensive evaluation of cardiovascular risk factors.
RHT was defined as an office BP (>140/90 mmHg) and a mean 24-h ambulatory BP (ABPM) of more than 130/80 mmHg despite the use of three or more antihypertensive drugs, including a diuretic. In all patients, assessment of kidney and renal artery anatomy was performed using computed tomography angiography.
Exclusion criteria included an estimated glomerular filtration rate (GFR) of loss than 45 ml/min per 1.75 m2 and pregnancy. All patients were studied accurately for excluding all forms of secondary arterial hypertension, including obstructive sleep apnea syndrome. Routine blood tests were performed in all participants prior to RSD ().
Table 1. Demographic, hemodynamic, biochemical, and bioumoral parameters in patients with resistant arterial hypertension (RHT) at diagnosis.
Average sitting office BP was measured after at least 5 min of rest on both arms, and was calculated as the average of three consecutive measurements within a 1-min interval at baseline with a validated device.
ABPM measurement was performed in the non-dominant arm with an oscillometric device (Spacelabs 90217; Spacelabs Healthcare, Snoqualmie, WA). From 06.00 to 11.00 h BP was measured at 20-min intervals and from 23.00 at 06.00 at 30-min intervals. Recordings had to be repeated when loss than 70% of readings were valid. From the recordings 24-h daytime and night-time averages of systolic BP (SBP), diastolic BP (DBP) and heart rate (HR) were calculated. Nocturnal “dipping” was defined as 10–20% decrease of nocturnal BP relative to daytime BP. The category “non-dipper” was defined as 0–10% nocturnal dip. ABPM recordings were performed in all patients 12 months after the intervention of RSD.
After the procedure the patients remained at the antihypertensive drugs that was prescribed prior to the intervention, unless clinically relevant changes in BP dictated medication adaption ().
Table 2. Baseline anti-hypertensive drugs in nine patients with resistant arterial hypertension (RHT) before renal sympathetic denervation (RSD).
Plasma ET-1
Before and after RSD blood sampling to measure plasma ET-1 levels were obtained in ethylenediaminetetraacetic acid (EDTA) from the right and left renal arteries. Moreover, samples at baseline were obtained in the antecubital vein. After high speed centrifugation, the blood samples were stored at −80 °C until assay.
Plasma ET-1 level was determined by specific radioimmunoassay (RIA). In brief, on the day of assay ET-1 was extracted from samples with C18 columns (sep-column) after acidification with 1 ml of 0.1% trifluoroacetic acid (PH 3) and with 60% acetranile. The extracts were evaporated under nitrogen and then arranged with specific RIA (RIK-6901, Peninsula Laboratories, Belmont, CA). Cross reactivities with ET-2 and ET-3 was 7% and 17% with human big endothelin. The assays were performed in duplicate. Interassay and intra-assay coefficient of variations were 13% and 9%, respectively, as we report in our previous study (Citation13). Concentrations of ET-1 were expressed in pg/ml and normal levels ranged from 3.6 and 14 pg/ml.
Catheter-based renal denervation (RSD)
Catheter-based RSD was performed according to standard clinical practice and following the instructions for use of the RSD systems (Medtronic, Santa Rosa, CA). In brief, all patients underwent to renal angiography before performing RSD.
Symplicity flex catheter (Medtronic, Santa Rosa, CA), was advanced into the renal artery and, after connected the device to a radiofrequency generator, radio frequency emission was applied. The treatment was repeated 4–6 times along the length of both main renal arteries (Krum H, Lancet. 2009). Last two patients were treated with the Symplicity Spyral catheter (Medtronic, Santa Rosa, CA).
Statistical analysis
The Sigmastat program was used for statistical analyses (2.0 version, Jandel Scientific, CA). Data are presented as mean ± standard error of the mean unless otherwise indicated.
A comparison between parameters was calculated by paired and unpaired t-test. Regression analysis was used to test correlation between ET-1 plasma levels and BP values. A p value <0.05 was considered statistically significant.
Results
presents baseline clinical characteristics of the nine RHT patients. The group study had a mean age of 56 ± 13.3. At baseline, average office SBP was 163.2 ± 29.9 mmHg, DBP 96.3 ± 19.60 mmHg and HR 68.3 ± 17.7 bpm (). On average, RHT patients were taking 5 ± 0.88 antihypertensive drugs, including angiotensin-converting enzyme inhibitors (ACE-I), angiotensin II receptor blockers (ARB), calcium channel blocker (CCB), diuretics, alfa-blockers, mineralocorticoid receptor antagonists (MRA), and clonidine (). The average serum creatinine of patients at baseline was 0.9 ± 0.25 mg/dl.
presents the mean 24-h ABPM, mean daytime ABPM measurements, and mean nocturnal ABPM measurements at baseline and after 12 months of RSD. At baseline the “non-dipping” pattern was present in 55% of RHT patients and was reduced to 35% after 12 months of RSD (p < 0.05). Moreover the mean of G-SBP, D-SBP and N-SBP was statistically reduced (p < 0.05) after RSD ().
Table 3. Ambulatory monitoring of blood pressure (AMBP) in patients with resistant arterial hypertension (RHT).
The behavior of ET-1 levels is presented in and . The plasma ET-1 levels determined in the right and left renal arteries (21.8 ± 4.1 pg/mL and 22.1 ± 3.7 pg/mL, respectively) were significantly higher (p <0.05) compared to antecubital vein (16.5 ± 3.8 pg/ml). Compared to those at baseline, RSD decreased plasma ET-1 levels from 21.8 ± 4.1 pg/ml to 16.8 ± 2.9 pg/ml at the right renal artery (p < 0.004) and 22.1 ± 3.7 pg/ml to 18.9 ± 3.3 pg/ml at the left renal artery (p < 0.02).
Figure 1. Plasma endothelin-1 (ET-1) levels in RH patients before renal sympathetic denervation (RSD).
Figure 2. The endothelin-1 (ET-1) levels in patients before and after renal sympathetic denervation (RSD).
In , we have reported the assumption of antihypertensive drugs in single patients after RSD; the mean assumption of antihypertensive drugs was 4.44 ± 0.73.
Table 4. Anti-hypertensive drugs in nine patients with resistant arterial hypertension (RHT) patients after renal sympathetic denervation (RSD).
The correlation study revealed a positive correlation between plasma renal arteries ET-1 levels and G-SBP (r = 0.58; p < 0.01), D-SBP (r = 0.51; p < 0.03) and N-SBP (r = 0.58; p < 0.01) values ().
Figure 3. Correlation between plasma renal arteries ET-1 levels during renal sympathetic denervation (RSD) with global (G) diurnal (D) and nocturnal (N) systolic blood pressure (SBP) at ABPM, and office systolic blood pressure.
Moreover, the shows a positive correlation between plasma ET-1 levels and office SBP values (r = 0.46; p < 0.05).
Discussion
Our study for the first time explored the baseline circulating ET-1 levels in RHT patients and the effect of RSD before and after the procedure. The major findings of our study are: (a) the concentrations of plasma ET-1 were significantly higher in RHT patients into renal arteries at baseline compared to antecubital veins, and correlated with office and ABPM-SBP values; (b) after the RSD procedure into renal arteries a significant reduction of plasma ET-1 levels was observed.
RHT is arbitrarily defined when a therapeutic strategy that includes appropriate life-style measures plus a diuretic and two other antihypertensive drugs belonging to different classes at adequate doses (but not necessarily including a mineralocorticoid receptor antagonist) fails to lower SBP and DBP values to 140 and 90 mmHg respectively (Citation1,Citation2). The definition of RHT is prevalently based of office BP measurements, and few reports for a correct diagnosis that excluded white coat hypertension have used the ABPM. Nevertheless, a large study based on the Spanish Ambulatory Pressure Registry counted about 68,000 patients treated for hypertension, 12% of whom were diagnosed with RHT. ABPM confirmed true resistance to treatment in 62.4% of these patients, and the remaining 37.5% the ineffectiveness of the study was to the white-coat effect (Citation14). Therefore, in our study, for diagnosis of true RHT, we used office BP and ABPM measurements, and excluded all secondary forms of arterial hypertension.
Since in some patients the use of maximal doses of antihypertensive drugs and exclusion of the secondary hypertension etiology of hypertension did not result in reaching target BP values, at today the RSD treatment has been shown to reduce BP in these patients (Citation11,Citation12).
In literature an interesting study supports the “proof- of- concept”, showing that the RSD can reduce noradrenaline spillover in patients by 47%, corresponding with sustained reduction of BP up to one year (Citation11).
There is the evidence from observational and intervention studies that ET-1 is involved in RHT (Citation8).
Recently, Lu et al. (Citation15) investigated in 8 Chinese Kunming dogs the effects of RSD (performed at baseline, 30 min, one month and three months after ablation) on plasma ET-1 levels, and showed a significant decrease of plasma ET-1 levels associated to BP reduction.
ET-1 is the most potent endogenous vasoconstrictor and is implicated in the pathogenesis of hypertension (Citation16). In addition, to increasing BP through vasoconstriction, ET-1 also contributes to sodium and water regulation in the kidney and, in the vasculature. ET-1 causes endothelial dysfunction with vascular remodeling, which are both common in hypertension (Citation17). The role of ET-1 in the pathogenesis of hypertension is clearly established. In fact, the plasma or vascular levels of ET-1 are elevated in some forms of hypertension, and studies reported a difference of ET-1 levels between normotensive and hypertensive subjects (Citation18–23). Moreover, clinical trials have attenuated the use of ET receptor antagonists as monotherapy in primary hypertension, and a mixed ET receptor antagonist successfully lowered BP (Citation24).
Two clinical trials were completed in RHT patients administrating a ETA receptor antagonist and the results were undetermined (Citation25,Citation26). However, it was evident from these studies that ET receptor antagonists can reduce BP in this patient group and target BP achieved in many patients who could not previously achieve BP control with three or more antihypertensive drugs.
In addition to endothelial cells, from which ET-1 was generally isolated (Citation16), most cell types within the kidney produce and bind ET-1, with renal tubular epithelial cells, particularly of the inner medullary collecting duct, of major importance (Citation27). ET-1 contributes importantly to the control of renal sympathetic nerve activity and maintenance of sodium and water balance (Citation28). The dysregulation of this mechanism can contribute to arterial hypertension.
As regard relationship between ET-1 and sympathetic nerve activity, in addition to the direct vasoconstrictor actions of ET-1, there is good evidence that ET-1 can increase BP via sympatho-excitatory actions. In fact experimental animal and clinical evidence suggests that overactivity of the SNS and increased levels of ET-1 are directly correlated with BP values and the progression of heart failure disease. In animal study, the non-selective ET receptor antagonist significantly decreased sympathetic nerve activity, suggesting that ET-1 plays an important role in regulating the level of sympathetic nerve activity. ET receptors are present at multiple loci that affect baroreflex control, including the carotid sinus, nucleus tractus solitarius, area postrema, and rostral ventrolateral medulla, suggesting that ET-1 can modulate sympathetic nerve activity through baroreflex function (Citation29).
One of the main question is if RDN can directly induce endothelial damage and subsequently structural and functional changes. In literature there are conflicting results (Citation30–32). Recently Doltra et coll. haven’t found adverse effects on renal arteries evaluated as increase in cross-sectional areas, velocity and flow and a decrease in wall shear stress observed thought magnetic resonance imaging before and after RDN (Citation30). Previously, Weijie et coll have found that renal artery vasodilation, after RDN treatment, could be considered a possible indicator of successful renal nerve damage (Citation31). Conversely, Templin e coll. have found diffuse renal artery constriction and local tissue damage at the ablation site with edema and thrombus formation after RDN, evaluated with optical tomography, and these lesions were not evident at the angiographic evaluation (Citation31). Theoretically the endothelium damage is possible after nerve ablation with radiofrequency, but the conflicting results showed in the literature can be, in part, attributed to different methodologies used (i.e. device, duration of surgery, use of contrast medium during RDN, or saline solution after ablation); further studies as requested to clarify the possible endothelium damage.
The major limitations of our study are the absence of a control group and the limited number of enrolled patients.
In conclusion, our study suggests that an effective RSD is associated to a reduction of plasma ET-1 levels. Our findings could explain how RSD contributes to BP control in RHT patients, through blocking one of the pathophysiologic mechanisms of hypertension. Further studies will be necessary to confirm our results.
Disclosure statement
The authors report no conflicts of interest. The authors alone are responsible for the content and writing of this article.
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