Cross-over study comparing effects of treatment with an angiotensin converting enzyme inhibitor and an angiotensin II type 1 receptor antagonist on cardiovascular changes in hypertension

Vascular structural and functional changes: their association with causality in hypertension: models, remodeling and relevance

Essential hypertension is a complex multifactorial disease process that involves the interaction of multiple genes at various loci throughout the genome, and the influence of environmental factors such as diet and lifestyle, to ultimately determine long-term arterial pressure. These factors converge with physiological signaling pathways to regulate the set-point of long-term blood pressure. In hypertension, structural changes in arteries occur and show differences within and between vascular beds, between species, models and sexes. Such changes can also reflect the development of hypertension, and the levels of circulating humoral and vasoactive compounds. The role of perivascular adipose tissue in the modulation of vascular structure under various disease states such as hypertension, obesity and metabolic syndrome is an emerging area of research, and is likely to contribute to the heterogeneity described in this review. Diversity in structure and related function is the norm, with morphological changes being causative in some beds and states, and in others, a consequence of hypertension. Specific animal models of hypertension have advantages and limitations, each with factors influencing the relevance of the model to the human hypertensive state/s. However, understanding the fundamental properties of artery function and how these relate to signalling mechanisms in real (intact) tissues is key for translating isolated cell and model data to have an impact and relevance in human disease etiology. Indeed, the ultimate aim of developing new treatments to correct vascular dysfunction requires understanding and recognition of the limitations of the methodologies used.

The association of angiotensin-converting enzyme with biomarkers for Alzheimer's disease

Introduction

Lower angiotensin-converting enzyme (ACE) activity could increase the risk of Alzheimer’s disease (AD) as ACE functions to degrade amyloid-β (Aβ). Therefore, we investigated whether ACE protein and activity levels in cerebrospinal fluid (CSF) and serum were associated with CSF Aβ, total tau (tau) and tau phosphorylated at threonine 181 (ptau).

Methods

We included 118 subjects from our memory clinic-based Amsterdam Dementia Cohort (mean age 66 ± 8 years) with subjective memory complaints (n = 40) or AD (n = 78), who did not use antihypertensive drugs. We measured ACE protein levels (ng/ml) and activity (RFU) in CSF and serum, and amyloid β_1–42, tau and ptau (pg/ml) in CSF.

Results

Cross-sectional regression analyses showed that ACE protein level and activity in CSF and serum were lower in patients with AD compared to controls. Lower CSF ACE protein level, and to a lesser extent serum ACE protein level and CSF ACE activity, were associated with lower CSF Aβ, indicating more brain Aβ pathology; adjusted regression coefficients (B) (95% CI) per SD increase were 0.09 (0.04; 0.15), 0.06 (0.00; 0.12) and 0.05 (0.00; 0.11), respectively. Further, lower CSF ACE protein level was associated with lower CSF tau and ptau levels; adjusted B’s (95% CI) per SD increase were 0.15 (0.06; 0.25) and 0.17 (0.10; 0.25), respectively.

Conclusions

These results strengthen the hypothesis that ACE degrades Aβ. This could suggest that lowering ACE levels by for example ACE-inhibitors might have adverse consequences for patients with, or at risk for AD.

Endothelin-1 modulates angiotensin II in the development of hypertension in fructose-fed rats

Two of the most potent vasoconstrictors, endothelin-1 (ET-1) and angiotensin II (Ang II), are upregulated in fructose hypertensive rats. It is unknown whether an interrelationship exists between these peptides that may contribute to the development of fructose-induced hypertension. The objective of this study was to investigate the existence of an interaction between the endothelin and renin angiotensin systems that may play a role in the development of fructose-induced hypertension. High fructose feeding and treatment with either bosentan, a dual endothelin receptor antagonist, or with L-158,809, an angiotensin type 1 receptor antagonist, were initiated simultaneously in male Wistar rats. Systolic blood pressure, fasted plasma parameters, insulin sensitivity, plasma Ang II, and vascular ET-1-immunoreactivity were determined following 6 weeks of high fructose feeding. Rats fed with a high fructose diet exhibited insulin resistance, hyperinsulinemia, hypertriglyceridemia, hypertension, and elevated plasma Ang II. Treatment with either bosentan or L-158,809 significantly attenuated the rise in blood pressure with no effect on insulin levels or insulin sensitivity in fructose-fed rats. Bosentan treatment significantly reduced plasma Ang II levels, while L-158,809 treatment significantly increased vascular ET-1-immunoreactivity in fructose-fed rats. Thus, treatment with the endothelin receptor antagonist prevented the development of fructose-induced hypertension and decreased plasma Ang II levels. These data suggest that ET-1 contributes to the development of fructose-induced hypertension through modulation of Ang II levels.

Alterations in hypertensive arteries

Mentoring in academia is often carried out in an informal way depending on individuals and circumstances. I was quite fortunate to make the acquaintance of Professor E.E. Daniel when I was making a transition from my research in entomology to biomedical sciences. Here I recount some of that experience, and describe some of the lessons I have learned from this experience, as my tribute to Dr. Daniel on the occasion of his 80th birthday.

Control of vascular changes by renin–angiotensin–aldosterone system in salt-sensitive hypertension

The purpose of this study was to investigate the role of the renin-angiotensin-aldosterone system in hypertension development and cardiovascular structural changes in a salt-sensitive hypertensive model induced by capsaicin (CAP). Newborn male Wistar rats were injected with either capsaicin or vehicle. After weaning at 3 weeks, these rats were divided into the following six treatment groups: capsaicin plus high-salt diet (CAP+HS), control plus high-salt diet (CON+HS), control plus normal salt diet (CON+NS), capsaicin plus high-salt diet and telmisartan (CAP+HS+T, 10 mg/kg/day), capsaicin plus high-salt diet and perindopril (CAP+HS+P, 2 mg/kg/day), and capsaicin plus high-salt diet and spironolactone (CAP+HS+S, 80 mg/kg/day). Treatment with different salt diets and drugs was initiated at 3 weeks of age and lasted 18 weeks. We found that beginning at the second week after the initiation of the treatment, blood pressure became significantly higher in CAP+HS than in other groups, accompanied by the development of cardiac hypertrophy. Treatment with telmisartan, perindopril or spironolactone prevented the development of hypertension in the CAP+HS group. Cardiac hypertrophy was prevented in the perindopril treatment group. The medial thickness, media-to-lumen ratio and cross-sectional area of the thoracic, renal and mesenteric arteries were significantly increased in CAP+HS than in other groups. Lumen diameter was similar in all the vessels among all the groups. Treatment with telmisartan, perindopril or spironolactone prevented the development of vascular remodeling, as found in the CAP+HS group. Beginning at 8 weeks after the initiation of the salt diet treatment (11 weeks of age), blood pressure also became higher in CON+HS than in CON+NS, but lower than CAP+HS. Structural changes of vessels were also present in CON+HS, but the degree of change was less when compared with CAP+HS. We conclude that neonatal treatment with capsaicin plus a high-salt diet, and a high-salt diet alone both induced hypertension development in normal Wistar rats, which are associated with cardiovascular remodeling. The renin-angiotensin-aldosterone system is involved in this salt-sensitive model because treatment that interfered with this system also prevented the development of hypertension and vascular remodeling.

Cardiovascular status following combined angiotensin-converting enzyme and AT1 receptor inhibition in conscious spontaneously hypertensive rats

1. Combined treatment of spontaneously hypertensive rats (SHR) with AT1 receptor antagonists and angiotensin-converting enzyme (ACE) inhibitors has been shown to reduce mean arterial pressure (MAP) more than monotherapy with either agent. The aims of the present study were to investigate the effects of chronic dual renin-angiotensin system (RAS) inhibition using non-hypotensive doses of the AT1 receptor antagonist candesartan cilexetil and the ACE inhibitor perindopril on cardiovascular function and structure. 2. Adult male SHR, aged 15 weeks, were divided into four groups: (i) candesartan cilexetil (0.5 mg/kg per day in drinking water); (ii) perindopril (0.3 mg/kg per day in drinking water); (iii) combined treatment (dual RAS inhibition); or (iv) the appropriate vehicle (0.1% ethanol/0.1% polyethylene glycol/1.5 mmol/l sodium bicarbonate dissolved in water for candesartan cilexetil; distilled water for perindopril). Systolic blood pressure was measured weekly using the tail-cuff method and urinary microalbuminuria was measured fortnightly. 3. After 4 weeks, rats were instrumented for intravenous drug administration and measurement of MAP. At this time, the cardiovascular effects of angiotensin (Ang) I and AngII (5-20 ng) and sodium nitroprusside (SNP) and acetylcholine (ACh; 1-5 micro g) were assessed. In addition, left ventricular : bodyweight and media : lumen ratios were determined as indices of cardiac and vascular hypertrophy, respectively. 4. Candesartan cilexetil and perindopril alone had minimal effect on MAP when measured both directly and indirectly, whereas direct MAP was significantly decreased in the combined treatment group (131 +/- 6 mmHg; P < 0.05) compared with the vehicle group (156 +/- 9 mmHg). Pressor responses to AngI were significantly decreased in all groups compared with the vehicle-treated group and pressor responses to AngII were significantly decreased in the candesartan cilexetil-treated (P < 0.01) and combined treatment groups (P < 0.01) compared with the vehicle-treated group. Depressor responses to ACh and SNP were not significantly affected by any of the antihypertensive therapies compared with vehicle-treated SHR. 5. Vascular hypertrophy was significantly decreased in the candesartan cilexetil and combined groups compared with the vehicle-treated group, whereas cardiac hypertrophy was reduced, with the rank order of effect being: dual RAS inhibition > perindopril > candesartan cilexetil. Urinary albumin tended to decrease with dual RAS inhibition, but was not significantly affected by this short-term treatment. 6. These results demonstrate the efficacy of low-dose dual RAS inhibition as an antihypertensive modality, at least in SHR, not only in reducing arterial pressure, but also in improving cardiovascular structure.

Angiotensin II type 2 receptor blockade partially negates antihypertrophic effects of type 1 receptor blockade on pressure-overload rat cardiac hypertrophy

We investigated the effects of angiotensin II type 2 (AT2) receptor blockade on the antihypertrophic effects of type 1 receptor (AT1) blockade in pressure-overload cardiac hypertrophy in adult rats. Cardiac hypertrophy was induced by banding the abdominal aorta above the renal arteries. The rats were treated with either an AT1 receptor antagonist TCV-116 (TCV, 10 mg/kg/day), an AT2 receptor antagonist PD123319 (PD, 20 mg/kg/day), or both for 4 weeks after the aortic banding. We measured systolic and diastolic blood pressure (BP), body weight (BW), left ventricular weight (LVW), and serum and cardiac angiotensin converting enzyme (ACE) activities. Aortic banding increased BP and LVW/BW, and TCV reversed both these increases. PD affected neither BP nor LVW/BW. TCV+PD reversed the increase in BP but not LVW/BW. Thus, PD was considered to counteract the antihypertrophic effect of TCV without affecting BP. All three treatments reduced cardiac ACE activity without affecting serum ACE activity. Our data demonstrated that AT2 receptor blockade negates the antihypertrophic effects of AT1 receptor blockade in an adult rat model of pressure-overload cardiac hypertrophy. AT2 receptors may mediate the signaling pathways involved in growth inhibition, which could counteract mediation of the cellular growth signaling pathways by AT1 receptors.

Ontogenetic aspects of hypertension development: analysis in the rat

In this review, we attempt to outline the age-dependent interactions of principal systems controlling the structure and function of the cardiovascular system in immature rats developing hypertension. We focus our attention on the cardiovascular effects of various pharmacological, nutritional, and behavioral interventions applied at different stages of ontogeny. Several distinct critical periods (developmental windows), in which particular stimuli affect the further development of the cardiovascular phenotype, are specified in the rat. It is evident that short-term transient treatment of genetically hypertensive rats with certain antihypertensive drugs in prepuberty and puberty (at the age of 4-10 wk) has long-term beneficial effects on further development of their cardiovascular apparatus. This juvenile critical period coincides with the period of high susceptibility to the hypertensive effects of increased salt intake. If the hypertensive process develops after this critical period (due to early antihypertensive treatment or late administration of certain hypertensive stimuli, e.g., high salt intake), blood pressure elevation, cardiovascular hypertrophy, connective tissue accumulation, and end-organ damage are considerably attenuated compared with rats developing hypertension during the juvenile critical period. As far as the role of various electrolytes in blood pressure modulation is concerned, prohypertensive effects of dietary Na+ and antihypertensive effects of dietary Ca2+ are enhanced in immature animals, whereas vascular protective and antihypertensive effects of dietary K+ are almost independent of age. At a given level of dietary electrolyte intake, the balance between dietary carbohydrate and fat intake can modify blood pressure even in rats with established hypertension, but dietary protein intake affects the blood pressure development in immature animals only. Dietary protein restriction during gestation, as well as altered mother-offspring interactions in the suckling period, might have important long-term hypertensive consequences. The critical periods (developmental windows) should be respected in the future pharmacological or gene therapy of human hypertension.