Effect of Add‐on Aliskiren to Type 1 Angiotensin Receptor Blocker Therapy on Endothelial Function and Autonomic Nervous System in Hypertensive Patients With Ischemic Heart Disease

Abstract

The aim of this study was to evaluate the add‐on effect of aliskiren to valsartan on endothelial‐dependent vasodilation in hypertensive patients with ischemic heart disease (IHD). After 4 weeks of treatment with 80 mg of valsartan, 28 patients were allocated to either continued treatment with valsartan or an add‐on treatment with valsartan plus 150 mg of aliskiren. Aliskiren significantly decreased plasma renin activity, whereas endothelium‐dependent vasodilation measured by flow‐mediated dilation (FMD) did not change. In contrast, heart rate significantly decreased (73.1 ± 9.8 to 66.3 ± 7.0 beats per minute at baseline and 24 weeks, respectively [P = .009]) and the standard deviation of the R‐R intervals (SDNN) significantly increased in the aliskiren group. The add‐on aliskiren to valsartan therapy may not improve endothelial functions, although it significantly reduced resting heart rate via regulation of the autonomic nervous system in hypertensive patients with IHD.

The renin‐angiotensin‐aldosterone system (RAAS) plays a key role in blood pressure (BP) and volume homeostasis. Recent studies have shown that the RAAS is involved in a diverse range of physiological and pathological processes such as vascular growth, remodeling, inflammation, and hypertrophy.1, 2 In addition, it is well known that RAAS activation induces vasoconstriction, thereby contributing to atherosclerosis progression, vascular fibrosis, and endothelial function impairment.

Blocking various steps in the RAAS pathway is assumed to have protective effects against atherosclerosis progression. Angiotensin II (Ang II) increases the production of reactive oxygen species via membrane‐bound nicotinamide adenine dinucleotide phosphate oxidase3 and promotes direct vasoconstriction and vascular fibrosis by inhibiting endothelial nitric oxide synthase (eNOS) activity.4 Aldosterone directly impairs endothelial function by inhibiting eNOS activity.5 The specific blockade of these factors is one of the major therapeutic strategies used against vascular injury in atherosclerosis. Angiotensin‐converting enzyme (ACE) inhibitors interfere with Ang II production by inhibiting Ang I to Ang II conversion; angiotensin receptor blockers (ARBs) block the action of Ang II at the type 1 angiotensin receptor. Both pharmaceutical classes have demonstrated beneficial effects on cardiovascular outcomes in clinical trials.6, 7 Aldosterone blockade also protects against vascular injury in the clinical setting.8

In spite of these therapeutic options, each blockade has its own specific set of problems. Plasma Ang II concentration increases after ARB treatment despite a decrease in aldosterone levels. This may have a detrimental effect on the vasculature.9 In addition, plasma renin activity (PRA) is also increased by both ACE inhibitor and ARB treatment, and renin was recently reported to contribute to cardiovascular disease development.10 Therefore, a strategy against the secondary reactive increase of plasma renin or Ang II during the RAAS blockade may be clinically relevant.

Aliskiren is a direct renin inhibitor (DRI) that blocks the RAAS at the first step in the pathway, reducing PRA and the circulating levels of Ang I, Ang II, and aldosterone.11 Although ACE inhibitors and ARBs increase PRA, aliskiren reduces it by directly inhibiting renin function. Previous clinical trials have demonstrated the beneficial effects of aliskiren on vascular endothelial function and atherosclerotic changes.12 However, the meaning and mechanism of PRA blockade remains unclear. The aim of this study was to evaluate the effect of add‐on aliskiren to pretreatment with valsartan on endothelium‐dependent vasodilation in hypertensive patients with ischemic heart disease (IHD).

Methods

Patients

Hypertensive patients with IHD taking antihypertensive drugs or with a BP >130/80 mm Hg were enrolled in this study. Patients were eligible for study inclusion on the basis of the following criteria: angiographically documented coronary artery disease (>50% luminal diameter narrowing of >1 epicardial coronary arteries on angiography); history of coronary revascularization; and history of myocardial infarction. Exclusion criteria were (1) unstable clinical condition; (2) poorly controlled type 2 diabetes mellitus (hemoglobin A_1c [HbA_1c] >7.5%; National Glycohemoglobin Standardization Program); and (3) moderate renal dysfunction (serum creatinine >1.4 mg/dL). Patients were given detailed explanations of the study protocol, and informed consent was obtained from all participants. The study protocol conformed to the Declaration of Helsinki and was reviewed and approved by the University of Tokyo's institutional review board. This clinical trial was registered with the University Hospital Medical Information Network—Clinical Trials Registry (UMIN–CTR; JPRN–UMIN 000007158).

Study Design

The study protocol is summarized in Figure 1. This study was conducted in 28 patients (26 men and 2 women; mean age, 69±7 years). None of the patients had previously taken an aldosterone blocker. After 4 weeks of treatment with valsartan (80 mg/d), patients were randomly assigned to 24 weeks of treatment with either continued valsartan or valsartan plus aliskiren (150 mg/d). Randomization was performed using the Viedoc electronic data capture system (PCG Solutions, Uppsala, Sweden); a dynamic allocation method was employed after stratification by sex, age, and history of smoking. Endothelial function was measured by flow‐mediated dilation (FMD) at baseline and after 24 weeks of treatment. Concurrently administered antihypertensive drugs were adjusted to maintain normal BP during the study period.

Figure 1.

Experimental design of the study. FMD indicates flow‐mediated dilation.

Assessment of Endothelial Function and Autonomic Nervous System

Endothelial function was assessed by FMD and was measured according to guidelines published by the International Brachial Artery Reactivity Task Force.13 Patients were instructed to abstain from eating, smoking, and consuming caffeine for at least 4 hours and to lie down for 20 minutes prior to the start of the study. The FMD of the brachial artery was evaluated by amplitude and brightness‐mode ultrasonography using a linear‐array 10‐MHz transducer (UNEXEF18G; UNEX, Nagoya, Japan). Baseline diameter measurements were obtained over 30 seconds, before the cuff was inflated to 50 mm Hg above the patient's systolic BP for 5 minutes, and then deflated. The diameter of the brachial artery was continuously recorded for 2 minutes after the cuff was deflated. All diameters were measured during the end‐diastolic phase, which was defined as the start of the R wave on the electrocardiogram (ECG). FMD was calculated as the percentage change in diameter from the baseline value before cuff release to the peak value after cuff release.

The reproducibility of FMD was previously measured (n=14). Intraobserver reliability yielded an intraclass correlation coefficient of 0.968 with a variation of 3.2%. The activity of the autonomic nervous system was evaluated by monitoring the heart rate variability. ECGs were also recorded during FMD measurements using a 3‐lead ECG system and converted to R‐R intervals using the analogue/digital converter built‐in for the ultrasound device (UNEXEF18G, UNEX).14 The standard deviation of the R‐R intervals (SDNN), a parameter of parasympathetic nervous system activity, was calculated using 100 R‐R interval consecutive data.

Blood Collection

Fasting blood samples were collected for analysis, including complete blood cell count, HbA_1c level, serum creatinine level, estimated glomerular filtration rate (eGFR), lipid profile, serum potassium level, C‐reactive protein (CRP) level, and brain natriuretic peptide (BNP) level. Standard laboratory methods at Tokyo University Hospital were used in the analysis.

Statistical Analysis

Data are shown as mean±standard deviation. Baseline and follow‐up analyses were performed between patients in the control and aliskiren groups using Student t test for uncoupled data. Within‐group analyses of the control and aliskiren groups were conducted with the paired t test. Simple linear regression analysis was performed to investigate the association between changes in FMD and clinical variables, including age, systolic BP, diastolic BP, heart rate, complete blood cell count, lipid profile, serum creatinine level, eGFR, serum potassium level, changes in serum potassium level, urinary albumin level, uric acid level, HbA_1c level, CRP level, BNP level, PRA, changes in PRA and plasma aldosterone, changes in plasma aldosterone level, SDNN, and changes in SDNN. A P value of <.05 was considered significant. Data analysis was performed using JMP pro 9 (SAS Institute, Cary, NC).

Results

Patients' Characteristics

Of the 28 patients enrolled in the study, 24 patients completed 24 weeks of treatment (control group, n=13; aliskiren group, n=11). There were no significant differences between the two groups with regard to age, sex, history of smoking, and BP. Endothelial function, calculated by FMD, did not differ between the control and aliskiren groups (control group, 3.8%±2.0%; aliskiren group, 3.9%±1.4%; P=.883) (Table 1).

Table 1.

Baseline Characteristics of Patients and Clinical Variables at Baseline and After 24 Weeks of Treatment

	Control Group (n=13)			Aliskiren Group (n=11)
	Baseline	24 Weeks	P Value	Baseline	24 Weeks	P Value
Age, y	69.5±5.9	–	–	68.5±9.7	–	–
Men	12 (92.3)	–	–	10 (90.9)	–	–
Body mass index, kg/m2	25.7±2.9	–	–	25.2±2.2	–	–
Current smoker	1 (7.7)	–	–	2 (18.1)	–	–
Systolic BP, mm Hg	131.6±13.7	126.7±11.3	.18	136.1±12.9	128.1±17.5	.28
Diastolic BP, mm Hg	72.0±9.7	69.0±12.4	.20	76.4±13.4	73.3±12.7	.45
Heart rate, beats per min	65.4±10.6	67.2±12.4	.67	73.1±9.8	66.3±7.0	.01[Link]
Total cholesterol, mg/dL	162.3±25.6	162.8±25.8	.89	150.6±21.2	169.2±37.6	.03[Link]
HDL cholesterol, mg/dL	53.5±9.6	54.7±11.0	.66	50.8±9.5	55.4±13.5	.05
LDL cholesterol, mg/dL	91.0±18.3	93.3±18.7	.44	82.0±19.3	95.6±33.0	.05
Triglycerides, mg/dL	141.0±58.7	128.6±64.8	.46	138.5±71.2	157.1±166.9	.62
Creatinine, mg/dL	0.9±0.1	0.9±0.1	.64	1.0±0.2	0.9±0.2	.15
eGFR, mL/min/1.73 m2	63.7±9.8	65.3±13.0	.44	62.3±16.7	65.0±16.7	.12
Serum potassium, mEq/L	4.4±0.3	4.2±0.2	.01[Link]	4.3±0.4	4.3±0.3	.38
Urinary albumin, mg/gCr	46.6±56.3	95.3±155.7	.20	208.0±223.0	176.4±250.1	.60
Uric acid, mg/dL	5.6±1.1	5.4±1.2	.27	5.9±1.5	6.0±1.8	.50
HbA1c, %	5.8±0.4	5.7±0.3	.70	5.4±0.6	5.4±0.5	.79
CRP, mg/dL	0.1±0.1	0.1±0.2	.42	0.2±0.4	0.2±0.2	.87
BNP, pg/mL	61.3±47.4	57.8±39.9	.72	46.6±39.9	55.4±61.3	.42

Abbreviations: BNP, brain natriuretic peptide; BP, blood pressure; CRP, C‐reactive protein; eGFR, estimated glomerular filtration rate; FMD, flow‐mediated dilation; HDL, high‐density lipoprotein; LDL, low‐density lipoprotein. Data are shown as mean±standard deviation and the difference between baseline and post‐treatment was analyzed by paired t test. ^a P<.05.

Effect of Aliskiren Addition to Valsartan Pretreatment

We compared clinical variables at baseline with those measured after 24 weeks of treatment (Table 1); systolic BP remained unchanged in both groups. In contrast, heart rate significantly decreased in the aliskiren group (control group, 65.4±10.6 to 67.2±12.4 beats per minute at baseline and 24 weeks, respectively [P=.665]; aliskiren group, 73.1±9.8 to 66.3±7.0 beats per minute at baseline and 24 weeks, respectively [P=.009] (Figure 2a). As indicated in Table 2, none of the patients started β‐blocking agents to lower BP, suggesting that heart rate did not decrease because of other medications than aliskiren. Furthermore, SDNN was significantly increased in the aliskiren group (22.1±8.2 to 32.6±13.3 ms, P=.011), whereas it remained unchanged in the control group (27.1±13.0 to 33.4±19.5 ms, P=.091) (Figure 2a). This suggests that aliskiren in addition to valsartan increases parasympathetic nervous system activity as compared with valsartan alone.

Figure 2.

Changes in heart rate (HR) and the standard deviation of R‐R intervals (SDNN) during the study period (a). Changes in plasma renin activity and plasma aldosterone during the study period (b). Changes in baseline diameter of brachial artery and flow‐mediated dilation (FMD) during the study period (c). These data were measured at baseline (white columns) and after 24 weeks of treatment (black columns). N.S indicates not significant.

Table 2.

Medication During the Study Period

Drug Therapy	Control Group (n=13)	Aliskiren Group (n=11)
Calcium channel blocker	7	9
β‐Blocker	8	5
α‐Blocker	0	0
Diuretics
Loop diuretic	0	0
Aldosterone receptor blocker	0	0
Thiazide diuretic	0	1
Change of medication	1	2
	Amlodipine (10 mg add)	Amlodipine (5 mg add)
		Amlodipine 5 mg to benidipine 8 mg

Basic laboratory parameters remained unchanged after 24 weeks in both groups (eg, lipid profile, renal function, HbA_1c, uric acid level, BNP level, and CRP level). In contrast, PRA significantly decreased in the aliskiren group (4.8±3.4 ng/mL/h to 1.2±1.2 ng/mL/h, P=.002), whereas plasma aldosterone level remained unchanged in both groups (control group, 121.8±40.0 pg/mL to 108.2±38.1 pg/mL, P=.158; aliskiren group, 95.7±32.8 pg/mL to 85.5±27.7 pg/mL, P=.287) (Figure 2b). The lack of change in aldosterone may be the result of pretreatment with valsartan for 4 weeks in both groups. Consequently, endothelial function measured by FMD did not change in either group (control group, 3.8%±2.0% to 3.9%±2.1%, P=.609; aliskiren group, 3.9%±1.4% to 4.0%±1.9%, P=.809) (Figure 2c).

Clinical Variables Associated With the Improvement in FMD

FMD improved in 7 patients in the control group and 4 patients in the aliskiren group. We compared the clinical variables in both populations with improved and unimproved FMD. There were no significant differences between these populations in the control group. However, patients with a low baseline FMD had a significantly improved FMD magnitude after 24 weeks of aliskiren treatment (improved, 3.2%±0.8%; unimproved, 4.9%±0.7%, P=.02). Interestingly, baseline serum potassium levels significantly correlated with the improvement in FMD in the aliskiren group (Figure 3a). A high baseline serum potassium level corresponded with an unresponsive FMD in the group taking add‐on aliskiren. Furthermore, we investigated the clinical variables associated with changes in FMD. In the control group, simple linear regression analysis indicated that changes in SDNN positively correlated with changes in FMD (r=0.615; P=.025), and in the aliskiren group, changes in PRA positively correlated with changes in FMD (r=0.796; P=.018) (Figure 3b). Parameters other than SDNN, PRA, and FMD had no statistically significant correlation ratio in either group.

Figure 3.

Relationship between baseline serum potassium level and improvement in flow‐mediated dilation (FMD). Center line, median; bottom and top of box, 25th to 75th percentiles; whiskers, maximum and minimum data points (a). Simple linear regression analysis for changes in FMD (b). Blue points indicate patients in the control group, whereas red points indicate patients in the aliskiren groups. N.S indicates not significant.

Discussion

In this study, we demonstrated that aliskiren added on to valsartan therapy did not improve endothelial function; however, it induced a significant reduction in resting heart rate via regulation of autonomic nervous system activity in hypertensive patients with IHD. Decreased renin activity alone did not have a sufficient effect on endothelial function, although it demonstrated a marked effect on resting heart rate.

Renin Activity and Endothelial Function

There have been several reports on the effect of aliskiren treatment on vascular function, including endothelial function. Direct renin inhibitor monotherapy using aliskiren and combination therapy with ACE inhibitors or calcium blockers improves endothelial function.15, 16, 17 Virdis and colleagues reported that aliskiren, compared with ramipril, increased nitric oxide availability in forearm resistance arterioles of patients with essential hypertension.12 In addition, aliskiren significantly decreased PRA, compared with ramipril, whereas BP, plasma Ang II level, and plasma aldosterone level remained unchanged. This suggests that improvement of endothelial function was derived from aliskiren‐induced PRA reduction. Furthermore, it has been reported that PRA is directly and independently associated with the occurrence of cardiovascular disease among patients with hypertension,18 and renin inhibition by aliskiren prevents atherosclerosis progression in mice.19 Therefore, aliskiren is assumed to have a beneficial effect on endothelial function by reducing PRA, resulting in a protective effect against atherosclerosis progression. However, aliskiren plus valsartan failed to improve endothelial function in our study, possibly because of a result of the study design or the small sample size. It is also possible that aliskiren has a detrimental effect on endothelial function in specific situations; the beneficial effect of PRA reduction could have been overcome by another mechanism such as RAS‐independent intracellular signaling pathways through (pro)renin receptors ([P]RR), which cannot be blocked by aliskiren.10, 20, 21, 22, 23 In this study, plasma renin concentration (PRC) may have been significantly increased after aliskiren treatment, resulting in a marked enhancement of the (P)RR pathway.11, 24 This effect may exceed the beneficial effect of decreasing PRA on endothelial function. The discrepancy in the effect of aliskiren between previous studies and this present study suggests that both effects derived from increased (pro)renin and reduction of PRA could have resulted in the lack of improvement in endothelial function seen in this study.

Effect of Aliskiren on the Autonomic Nervous System

In the aliskiren group, heart rate was significantly reduced, whereas SDNN was significantly increased, suggesting that aliskiren suppresses sympathetic nervous system activity. There have been some reports on agents that inhibit RAAS activity and interfere with sympathetic hyperactivity in patients with chronic kidney disease.25, 26 Recently, Siddiqi and colleagues27 reported that aliskiren reduces sympathetic nerve activity, quantified by muscle sympathetic nerve activity, in patients with chronic kidney disease. Previous studies have also demonstrated that increased PRA is an independent determinant of reduced high‐frequency power and the square root of the mean of squared differences between adjacent normal R‐R intervals, which were used as an index of parasympathetic nervous system modulation,28 and heart rate was elevated in human renin receptor transgenic rats.29 These reports allow us to hypothesize that the decreased PRA induced by aliskiren reduces heart rate via suppression of the sympathetic nervous system in hypertensive patients with IHD.

Clinical Variables Associated With Change in FMD

It was expected that suppression of sympathetic nervous system activity would improve endothelial function. Moreover, in the control group, changes in SDNN positively correlated with changes in FMD (r=0.615; P=.025) (Figure 3b). This correlative relationship suggests that improvement of endothelial function by blockade of Ang II is primarily derived from the downregulation of sympathetic nervous system activity. In contrast, in the aliskiren group, SDNN did not correlate with changes in FMD, and changes in PRA correlated with changes in FMD. The absence of a correlative relationship between SDNN and FMD suggests that there may be an aliskiren‐induced negative impact on endothelial function that is not mediated via the autonomic nervous system. The beneficial effect of aliskiren add‐on therapy to valsartan on the autonomic nervous system was cancelled by aggravating factors on the endothelium. Therefore, no significant improvement was seen in the FMD values. The correlative relationship between changes in PRA and FMD suggested that increased PRC following aliskiren treatment has a negative effect on endothelial function via the (P)RR pathway.

Interestingly, baseline serum potassium levels were high in patients whose endothelial function did not improve in the aliskiren group despite an increase in SDNN. Baseline serum potassium levels were low in patients with improved endothelial function, indicating that the presence of baseline hyperkalemia predicted worse outcomes of dual‐blockade therapy with valsartan and aliskiren. This result corresponded with the findings of the Aliskiren Trial in Type 2 Diabetes Using Cardiovascular and Renal Disease Endpoints (ALTITUDE) trial, where patients taking aliskiren with high baseline potassium values demonstrated an increased hazard ratio of cardiovascular events.30 It is speculated that hyperkalemia associated with ARB therapy corresponded to a RAAS situation, in which the detrimental results on endothelial function induced by dual therapy of aliskiren and valsartan were observed. This hyperkalemia may be associated with changes in PRA; however, the underlying bridging mechanism between them is yet to be elucidated, and further study is needed to clarify this.

Study Limitations

A notable limitation of the present study is the small sample size. The absence of associations between FMD and ARB monotherapy or dual‐blockade therapy of a DRI and an ARB may be a consequence of the resultant lack of statistical power. However, the improvement in the autonomic nervous system, notably the reduction in heart rate, was statistically significant. The difference between the effect on endothelial function and autonomic nervous system by add‐on aliskiren suggested that the negative result of endothelial function may be derived from another mechanism, such as the RAS‐independent pathway of (P)RR. In addition, we used only 150 mg/d of aliskiren. Several studies have previously used 300 mg/d of aliskiren, and it was reported that aliskiren provides dose‐dependent efficacy in Japanese patients with hypertension.31 Stanton and colleagues have demonstrated that PRA decreased by −83%, −77%, and −60% after treatment with 300 mg/d, 150 mg/d, and 75 mg/d of aliskiren, respectively.32

Conclusions

Reduction in PRA induced by dual‐blockade therapy of valsartan and aliskiren may not have a beneficial effect on endothelial function. However, this dual therapy induced a significant reduction in resting heart rate via regulation of the autonomic nervous system in hypertensive patients with IHD.

J Clin Hypertens (Greenwich). 2014;16:591–598. ©2014 Wiley Periodicals, Inc.