Transient prehypertensive treatment in spontaneously hypertensive rats: A comparison of losartan and amlodipine regarding long-term blood pressure, cardiac and renal protection

Four-week inhibition of the renin-angiotensin system in spontaneously hypertensive rats results in persistently lower blood pressure with reduced kidney renin and changes in expression of relevant gene networks

AIMS

Prevention of human hypertension is an important challenge and has been achieved in experimental models. Brief treatment with renin-angiotensin system (RAS) inhibitors permanently reduces the genetic hypertension of the spontaneously hypertensive rat (SHR). The kidney is involved in this fascinating phenomenon, but relevant changes in gene expression are unknown.

METHODS AND RESULTS

In SHR, we studied the effect of treatment between 10 and 14 weeks of age with the angiotensin receptor blocker, losartan, or the angiotensin-converting enzyme inhibitor, perindopril [with controls for non-specific effects of lowering blood pressure (BP)], on differential RNA expression, DNA methylation, and renin immunolabelling in the kidney at 20 weeks of age. RNA sequencing revealed a six-fold increase in renin gene (Ren) expression during losartan treatment (P < 0.0001). Six weeks after losartan, arterial pressure remained lower (P = 0.006), yet kidney Ren showed reduced expression by 23% after losartan (P = 0.03) and by 43% after perindopril (P = 1.4 × 10-6) associated with increased DNA methylation (P = 0.04). Immunolabelling confirmed reduced cortical renin after earlier RAS blockade (P = 0.002). RNA sequencing identified differential expression of mRNAs, miRNAs, and lncRNAs with evidence of networking and co-regulation. These included 13 candidate genes (Grhl1, Ammecr1l, Hs6st1, Nfil3, Fam221a, Lmo4, Adamts1, Cish, Hif3a, Bcl6, Rad54l2, Adap1, Dok4), the miRNA miR-145-3p, and the lncRNA AC115371. Gene ontogeny analyses revealed that these networks were enriched with genes relevant to BP, RAS, and the kidneys.

CONCLUSION

Early RAS inhibition in SHR resets genetic pathways and networks resulting in a legacy of reduced Ren expression and BP persisting for a minimum of 6 weeks.

Noninvasive Monitoring of Blood Pressure and Heart Rate during Estrous Cycle Phases in Normotensive Wistar-Kyoto and Spontaneously Hypertensive Female Rats

Since 2015, the National Institutes of Health has called for its funded preclinical research to include both male and female subjects. However, much of the basic animal research that has studied heart rate and blood pressure in the past has used male rats. Male rats have been preferred for these studies to avoid the possible complicating effects of the female estrous cycle. The aim of the current study was to determine whether blood pressure and heart rates vary as a function of the estrous cycle phase of young normotensive Wistar-Kyoto (WKY) and Spontaneously Hypertensive (SHR) female rats. Blood pressure and heart rate were measured at the same time of day throughout the estrous cycle by using a noninvasive tail cuff sphygmomano- metric technique. As expected, 16-wk-old female SHR rats had higher blood pressure and heart rates than did age-matched female WKY rats. However, no significant differences in mean, systolic, or diastolic arterial blood pressure or heart rate were detected across the different stages of the estrous cycle in either strain of female rats. Consistent with previous reports, heart rates were higher and showed less variation in the hypertensive SHR female rats as compared with the normotensive WKY female rats. These results indicate that studies measuring blood pressure and heart rate can include young female SHR and WKY rats with no effect of estrous cycle stage.

RAS inhibition in resident fibroblast biology

Angiotensin II (Ang II) is a primary mediator of profibrotic signaling in the heart and more specifically, the cardiac fibroblast. Ang II-mediated cardiomyocyte hypertrophy in combination with cardiac fibroblast proliferation, activation, and extracellular matrix production compromise cardiac function and increase mortality in humans. Profibrotic actions of Ang II are mediated by increasing production of fibrogenic mediators (e.g. transforming growth factor beta, scleraxis, osteopontin, and periostin), recruitment of immune cells, and via increased reactive oxygen species generation. Drugs that inhibit Ang II production or action, collectively referred to as renin angiotensin system (RAS) inhibitors, are first line therapeutics for heart failure. Moreover, transient RAS inhibition has been found to persistently alter hypertensive cardiac fibroblast responses to injury providing a useful tool to identify novel therapeutic targets. This review summarizes the profibrotic actions of Ang II and the known impact of RAS inhibition on cardiac fibroblast phenotype and cardiac remodeling.

Prevalence of AT1R antibody (AT1R-Ab) among Malaysian multi-ethnic population

BACKGROUND

Angiotensin II type 1 receptor antibody (AT1R-Ab) is a non-HLA antibody that has been reported to cause antibody-mediated rejection and graft loss in kidney transplantation. The prevalence of positive AT1R-Ab varies between 8% and 18% in different regions. Thus, this study aims to determine the prevalence of AT1R-Ab among the Malaysian population.

METHODOLOGY

All sera for AT1R-Ab were collected at the University Malaya Medical Centre (UMMC), Kuala Lumpur, Malaysia. The sera were centrifuged and kept refrigerated at -80 °C before being transported to the South Australian Transplantation and Immunogenetics Laboratory (SATIS). Enzyme-linked immunosorbent assay kit (One Lambda) was used for the detection of AT1R-Ab, and it was performed according to the manufacturer's instructions. The level of >17.1 U/mL was considered to be AT1R-Ab positive; 10.0-17.1 U/mL at risk, and <10.0 U/mL negative.

RESULTS

A total of 115 samples were collected from 99 patients pre and post-kidney transplant recipients. From the pre-transplant sera (n = 68) 17.7% were positive, 35.3% were at risk and 47.0% were negative. The positive AT1R-Ab cohort were relatively younger, with a mean age of 34.7 ± 8.3 years old and statistically significant, with a p-value of 0.028. Among the sera that were tested positive, 19.0% were from the Chinese ethnicity, 6.7% from Malay and 16.7% from Indian. There was no difference in the rejection episodes, persistent or de novo HLA-DSA, and graft function between the group (AT1R-Ab negative vs AT1R-Ab at risk and positive) and the results were consistent in a model adjusted for all potential confounders.

CONCLUSION

The prevalence of positive (>17.1 U/mL) pre-transplant AT1R-Ab was 17.7% and 35.3% were at risk (10.0-17.1 U/mL) in our pre-transplant cohort.

Renin-Angiotensin System Inhibition Following Transcatheter Aortic Valve Replacement

BACKGROUND

Several studies have demonstrated the benefits of transcatheter aortic valve replacement (TAVR) in patients with aortic stenosis, but the presence of persistent fibrosis and myocardial hypertrophy has been related to worse prognosis.

OBJECTIVES

The aim of this study was to explore the potential benefits of renin-angiotensin system (RAS) inhibitors on left ventricular remodeling and major clinical outcomes following successful transcatheter aortic valve replacement (TAVR).

METHODS

Patients from 10 institutions with severe aortic stenosis who underwent TAVR between August 2007 and August 2017 were included. All baseline data were prospectively recorded, and pre-specified follow-up was performed. Doses and types of RAS inhibitors at discharge were recorded, and matched comparison according to their prescription at discharge was performed.

RESULTS

A total of 2,785 patients were included. Patients treated with RAS inhibitors (n = 1,622) presented similar surgical risk scores but a higher rate of all cardiovascular risk factors, coronary disease, and myocardial infarction. After adjustment for these baseline differences, reduction of left ventricular volumes and hypertrophy was greater and cardiovascular mortality at 3-year follow-up was lower (odds ratio: 0.59; 95% confidence interval: 0.41 to 0.87; p = 0.007) in patients treated with RAS inhibitors. Moreover, RAS inhibitors demonstrated a global cardiovascular protective effect with significantly lower rates of new-onset atrial fibrillation, cerebrovascular events, and readmissions.

CONCLUSIONS

Post-TAVR RAS inhibitors are associated with lower cardiac mortality at 3-year follow-up and offer a global cardiovascular protective effect that might be partially explained by a positive left ventricular remodeling. An ongoing randomized trial will help confirm these hypothesis-generating findings. (Renin-Angiotensin System Blockade Benefits in Clinical Evolution and Ventricular Remodeling After Transcatheter Aortic Valve Implantation [RASTAVI]; NCT03201185).

Beneficial Cardiovascular Effects of Hydroalcoholic Extract from Crocus Sativus in Hypertension Induced by Angiotensin II

Objectives

Angiotensin II (AngII), a major product of renin-angiotensin system (RAS) has important role in induction of hypertension and antihypertensive effect of several medicinal plant was mediated by effect on this agent. Therefore, this study examined the possible effect of hydroalcoholic extract of Crocus sativus (C. sativus) on hypertension induced by AngII.

Methods

Six groups (n = 6) of rats were used as follow: 1) Control, 2) AngII (300 ng/kg), 3) Losartan (Los, 10 mg/kg) + AngII and 4-6) C. sativus extract (10, 20 & 40 mg/kg,) + AngII. The femoral artery and vein were cannulated for recording cardiovascular parameters and drugs administration, respectively. All drugs were injected intravenously (i.v). Los and all doses of C. sativus injected 10 min before AngII. Systolic blood pressure (SBP), mean arterial blood pressure (MAP) and heart rate (HR) were recorded throughout the experiment and those peak changes (Δ) were calculated and compared to control and AngII.

Results

AngII significantly increased ΔMAP, ΔSBP and ΔHR than control (P < 0. 01 to P < 0.001) and these increments were significantly attenuated by Los. All doses of C. sativus significantly reduced peak ΔMAP, ΔSBP, and ΔHR than AngII group (P < 0. 05 to P < 0.001). In addition, peak ΔMAP, ΔSBP in doses 10 and 20 were significant than Los + AngII group (P < 0.05 to P< 0.01) but in dose 40 only MAP was significant (P < 0.05). Peak ΔHR in all doses of C sativus was not significant than Los+ AngII.

Conclusion

Regarding the improving effect of the C. sativus extract on AngII induced hypertension, it seems that this ameliorating effect partly mediated through inhibition of RAS.

Effect of prehypertensive losartan therapy on AT1R and ATRAP methylation of adipose tissue in the later life of high‑fat‑fed spontaneously hypertensive rats

Hypertension is frequently associated with metabolic disorders. The present study was designed to investigate the long-term effect of prehypertensive losartan therapy on metabolic disorders in high-fat-fed spontaneously hypertensive rats (SHRs), and to examine the role of epigenetic regulation of angiotensin II type 1 receptor (AT1R) and AT1 receptor-associated protein (ATRAP) expression in adipose tissue. A total of 32 4-week-old male SHRs were divided into four groups (n=8 rats/group): Standard chow; standard chow + losartan; high-fat diet; and high-fat diet + losartan. At 10 weeks of age, treatment with losartan was discontinued. Rats were followed up until 26 weeks of age. Obesity, dyslipidemia, hyperglycemia, abnormal adipokine secretion, larger adipocytes and decreased expression of markers of adipocyte differentiation were present in high-fat-fed SHRs, and were attenuated in losartan-treated rats. The increased expression and promoter hypomethylation of AT1R subtype a (AT1aR) in the adipose tissue of high-fat-fed SHRs were reversed by treatment with losartan. No difference was observed in the expression and promoter methylation of AT1R subtype b (AT1bR) among the four groups. Decreased expression and promoter hypermethylation of ATRAP were demonstrated in the adipose tissue of high-fat-fed SHRs. However, losartan made no difference to the expression and promoter methylation of ATRAP. Prehypertensive losartan therapy may relieve metabolic disorders in the later life of high-fat-fed SHRs. Differential epigenetic regulation of AT1aR and ATRAP expression through DNA methylation in adipose tissue may be involved in the long-term beneficial effect.

Vasa recta pericyte density is negatively associated with vascular congestion in the renal medulla following ischemia reperfusion in rats

Recent evidence suggests that a greater density of pericytes in renal cadaveric allografts is associated with better recovery following transplant. The physiological mechanism(s) through which pericyte density may be beneficial is not well understood. The goal of this study was to test the hypothesis that lower medullary pericyte density is associated with greater renal injury following ischemia reperfusion (IR) in a rat model, providing a basis for future studies to better understand pericytes in a pathological environment. To test our hypothesis, we determined the association between medullary pericyte density and renal injury in spontaneously hypertensive rats (SHR) following 45 min of warm bilateral IR. We found that there was a significant negative relationship between pericyte density and plasma creatinine (slope = -0.03, P = 0.02) and blood urea nitrogen (slope = -0.5, P = 0.01) in female but not male SHR. Pericyte density was negatively associated with medullary peritubular capillary (PT) congestion in both sexes following IR (male: slope = -0.04, P = 0.009; female: slope = -0.03, P = 0.0001). To further test this relationship, we used a previously reported method to reduce pericyte density in SHR. Medullary erythrocyte congestion in vasa recta (VR) and PT significantly increased following IR in both sexes when pericyte density was pharmacologically decreased (VR: P = 0.03; PT: P = 0.03). Our data support the hypothesis that pericyte density is negatively associated with the development of IR injury in SHR, which may be mediated by erythrocyte congestion in the medullary vasculature.

Superoxide increases angiotensin II AT1 receptor function in human kidney-2 cells

The redox-sensitive Sp family transcription factor has been linked to the regulation of angiotensin II type 1 receptor (AT1R). However, the exact mechanism of AT1R regulation in renal cells is poorly understood. We tested the specificity of reactive oxygen species (ROS), superoxide vs. hydrogen peroxide (H₂O₂), and the specific role of Sp3 transcription factor, if any, in the regulation of AT1R in human kidney cells (HK2 cells). Superoxide dismutase (SOD) inhibitor diethyldithiocarbamate (DETC), but not H₂O₂ treatment, increased fluorescence levels of superoxide probe dihydroethidium (DHE). H₂O_2, but not DETC, treatment increased the fluorescence of the H₂O₂-sensitive probe dichloro-dihydro-fluorescein (DCFH). These data suggest that SOD inhibition by DETC increases the superoxide but not H₂O₂ and exogenously added H₂O₂ is not converted to superoxide in renal cells. Furthermore, DETC, but not H₂O₂, treatment increased nuclear accumulation of Sp3, which was attenuated with the superoxide dismutase (SOD)-mimetic tempol. DETC treatment also increased AT1R mRNA and protein levels that were attenuated with tempol, whereas H₂O₂ did not have any effects on AT1R mRNA. Moreover, Sp3 overexpression increased, while Sp3 depletion by siRNA decreased, protein levels of AT1R. In addition, Sp3 siRNA in the presence of DETC decreased AT1R protein expression. Furthermore, DETC treatment increased the levels of cell surface AT1R as measured by biotinylation and immunofluorescence studies. Angiotensin II increased PKC activity in vehicle-treated cells that further increased in DETC-treated cells, which was attenuated by AT1R blocker candesartan and SOD-mimetic tempol. Taken together, our results suggest that superoxide, but not H₂O₂, via Sp3 up-regulates AT1R expression and function in the renal cells.

Early treatment with losartan effectively ameliorates hypertension and improves vascular remodeling and function in a prehypertensive rat model

AIMS

Pharmacological treatment of prehypertension may ameliorate hypertension and improve vascular structure and function. This study investigated 1) whether early treatment with either losartan or amlodipine at the onset of prehypertension can prevent hypertension and 2) whether losartan and amlodipine equally improve vascular remodeling and function in a rat model of hypertension.

MATERIALS AND METHODS

Stroke-prone spontaneously hypertensive (SHRSP) rats were administered losartan, amlodipine or saline for 6 or 16weeks at the onset of prehypertension. Wistar-Kyoto rats were used as a control. All groups were observed for 40weeks. Systolic blood pressure was measured using the tail-cuff method. Vascular structure and function were determined by microscopy and vascular ring contractility assays, respectively. Angiotensin II (Ang II) and aldosterone (Aldo) were measured by radioimmunoassays. Angiotensin II type 1 receptor (AT1R) and angiotensin II type 2 receptor (AT2R) expression was measured by western blot.

KEY FINDINGS

Losartan effectively reduced progression from prehypertension to hypertension as well as vascular remodeling and improved vascular contractility in SHRSP rats. Long-term losartan (16weeks) had greater benefits than short-term (6weeks) treatment. Losartan increased Ang II and decreased Aldo levels in the serum and vessel walls of resistance vessels in a time-dependent manner. Losartan significantly decreased AT1R and increased AT2R vascular expression. Amlodipine had no effect on vascular AT1R and AT2R expression.

SIGNIFICANCE

Losartan administered at the onset of prehypertension is more effective than amlodipine in ameliorating hypertension and improving vascular remodeling and function, which is likely mediated by the renin-angiotensin-aldosterone system.

Hypomethylation of Agtrap is associated with long-term inhibition of left ventricular hypertrophy in prehypertensive losartan-treated spontaneously hypertensive rats

Prehypertensive losartan treatment may lead to long‑term inhibition of the development of left ventricular hypertrophy (LVH) in spontaneously hypertensive rats (SHRs). However, the underlying mechanism has yet to be fully elucidated. The aim of the present study was to investigate the expression of angiotensin type 1 receptor-associated protein (ATRAP/Agtrap) and methylation of the Agtrap gene in the myocardium following the withdrawal of treatment. Four‑week‑old SHRs were randomly divided into three groups, and were treated with saline, amlodipine or losartan, respectively, for 6 weeks. Wistar Kyoto rats (WKYs) were used as a control. All rats were followed up regularly until they reached the age of 32 weeks. Systolic blood pressure (SBP), left ventricular mass/body weight (LVM/BW), and cardiac fibrosis and structure were measured. The mRNA and protein expression of ATRAP in the myocardium were determined using reverse transcription‑quantitative polymerase chain reaction and western blot analysis. Methylation of the Agtrap promoter was detected by bisulfite pyrosequencing. Reduced levels of SBP, LVM/BW, cardiac fibrosis and interventricular septum thickness were determined to be maintained only in prehypertensive losartan‑treated SHRs. Whereas, an increased expression of ATRAP mRNA and protein, and hypomethylation of the Agtrap promoter in the myocardium, were demonstrated only in the losartan‑treated SHRs. In conclusion, the results of the present study suggested that the hypomethylation of Agtrap accompanying upregulation of ATRAP expression in the myocardium is associated with the long‑term inhibition of LVH in SHRs with prehypertensive losartan treatment.

Persistent phenotypic shift in cardiac fibroblasts: impact of transient renin angiotensin system inhibition

Fibrotic cardiac remodeling ultimately leads to heart failure - a debilitating and costly condition. Select antihypertensive agents have been effective in reducing or slowing the development of cardiac fibrosis. Moreover, some experimental studies have shown that the reduction in fibrosis induced by these agents persists long after stopping treatment. What has not been as well investigated is whether this transient treatment results in a protection against future fibrotic cardiac remodeling. In the present review, previously published studies are re-examined to assess whether the relative percent increase in collagen deposition over an off-treatment period is attenuated, relative to control, following transient antihypertensive treatment in young or adult rats. Present findings suggest that transient inhibition of the renin angiotensin system (RAS) not only produces a sustained reduction in cardiac fibrosis, but also results in a degree of protection against future collagen deposition. In addition, prior transient RAS inhibition appears to alter the cardiac fibroblast phenotype such that these cells show a muted response to myocardial injury - namely reduced proliferation, chemokine release, and collagen deposition. This review puts forth several potential mechanisms underlying this long-term cardiac protection that is afforded by transient RAS inhibition. Specifically, fibroblast phenotypic change, cardiac fibroblast apoptosis, sustained suppression of the RAS, persistent reduction in left ventricular hypertrophy, and persistent reduction in arterial pressure are each discussed. Identifying the mechanisms ultimately responsible for this change in cardiac fibroblast response to injury, hypertension, and aging may reveal novel targets for therapy.

Long-term prehypertension treatment with losartan effectively prevents brain damage and stroke in stroke-prone spontaneously hypertensive rats

Prehypertension has been associated with adverse cerebrovascular events and brain damage. The aims of this study were to investigate i) whether short- and long-term treatments with losartan or amlodipine for prehypertension were able to prevent blood pressure (BP)-linked brain damage, and ii) whether there is a difference in the effectiveness of treatment with losartan and amlodipine in protecting BP-linked brain damage. In the present study, prehypertensive treatment with losartan and amlodipine (6 and 16 weeks treatment with each drug) was performed on 4-week-old stroke-prone spontaneously hypertensive rats (SHRSP). The results showed that long-term (16 weeks) treatment with losartan is the most effective in lowering systolic blood pressure in the long term (up to 40 weeks follow-up). Additionally, compared with the amlodipine treatment groups, the short- and long-term losartan treatments protected SHRSP from stroke and improved their brains structurally and functionally more effectively, with the long-term treatment having more benefits. Mechanistically, the short- and long-term treatments with losartan reduced the activity of the local renin-angiotensin-aldosterone system (RAAS) in a time-dependent manner and more effectively than their respective counterpart amlodipine treatment group mainly by decreasing AT1R levels and increasing AT2R levels in the cerebral cortex. By contrast, the amlodipine treatment groups inhibited brain cell apoptosis more effectively as compared with the losartan treatment groups mainly through the suppression of local oxidative stress. Taken together, the results suggest that long-term losartan treatment for prehypertension effectively protects SHRSP from stroke-induced brain damage, and this protection is associated with reduced local RAAS activity than with brain cell apoptosis. Thus, the AT1R receptor blocker losartan is a good candidate drug that may be used in the clinic for long-term treatment on prehypertensive populations in order to prevent BP-linked brain damage.