Prevention and regression of hypertension: role of renal microvascular protection

Elevated Vascular Sympathetic Neurotransmission and Remodelling Is a Common Feature in a Rat Model of Foetal Programming of Hypertension and SHR

Hypertension is of unknown aetiology, with sympathetic nervous system hyperactivation being one of the possible contributors. Hypertension may have a developmental origin, owing to the exposure to adverse factors during the intrauterine period. Our hypothesis is that sympathetic hyperinnervation may be implicated in hypertension of developmental origins, being this is a common feature with essential hypertension. Two-animal models were used: spontaneously hypertensive rats (SHR-model of essential hypertension) and offspring from dams exposed to undernutrition (MUN-model of developmental hypertension), with their respective controls. In adult males, we assessed systolic blood pressure (SBP), diastolic blood pressure (DBP), heart rate (HR), sympathetic nerve function (3H-tritium release), sympathetic innervation (immunohistochemistry) and vascular remodelling (histology). MUN showed higher SBP/DBP, but not HR, while SHR exhibited higher SBP/DBP/HR. Regarding the mesenteric arteries, MUN and SHR showed reduced lumen, increased media and adventitial thickness and increased wall/lumen and connective tissue compared to respective controls. Regarding sympathetic nerve activation, MUN and SHR showed higher tritium release compared to controls. Total tritium tissue/tyrosine hydroxylase detection was higher in SHR and MUN adventitia arteries compared to respective controls. In conclusion, sympathetic hyperinnervation may be one of the contributors to vascular remodelling and hypertension in rats exposed to undernutrition during intrauterine life, which is a common feature with spontaneous hypertension.

Activation of the intestinal tissue renin-angiotensin system by transient sodium loading in salt-sensitive rats

BACKGROUND

The renal tissue renin-angiotensin system is known to be activated by salt loading in salt-sensitive rats; however, the response in other organs remains unclear.

METHOD

Spontaneously hypertensive rats were subjected to normal tap water or transient high-salt-concentration water from 6 to 14 weeks of age and were thereafter given normal tap water. From 18 to 20 weeks of age, rats given water with a high salt concentration were treated with an angiotensin II type 1 receptor blocker, valsartan.

RESULTS

Sustained blood pressure elevation by transient salt loading coincided with a persistent decrease in the fecal sodium content and sustained excess of the circulating volume in spontaneously hypertensive rats. Administration of valsartan sustainably reduced the blood pressure and normalized the fecal sodium levels. Notably, transient salt loading persistently induced the intestinal tissue renin-angiotensin system and enhanced sodium transporter expression exclusively in the small intestine of salt-sensitive rats, suggesting the potential connection of intestinal sodium absorption to salt sensitivity.

CONCLUSION

These results reveal the previously unappreciated contribution of the intestinal tissue renin-angiotensin system to sodium homeostasis and blood pressure regulation in the pathophysiology of salt-sensitive hypertension.

Nrf2-related gene expression is impaired during a glucose challenge in type II diabetic rat hearts

Diabetic hearts are susceptible to damage from inappropriate activation of the renin angiotensin system (RAS) and hyperglycemic events both of which contribute to increased oxidant production. Prolonged elevation of oxidants impairs mitochondrial enzyme function, further contributing to metabolic derangement. Nuclear factor erythriod-2-related factor 2 (Nrf2) induces antioxidant genes including those for glutathione (GSH) synthesis following translocation to the nucleus. We hypothesized that an acute elevation in glucose impairs Nrf2-related gene expression in diabetic hearts, while AT1 antagonism would aid in Nrf2-mediated antioxidant production and energy replenishment. We used four groups (n = 6-8/group) of 25-week-old rats: 1) LETO (lean strain-control), 2) type II diabetic OLETF, 3) OLETF + angiotensin receptor blocker (ARB; 10 mg olmesartan/kg/d × 8 wks), and 4) ARBM (4 weeks on ARB, 4 weeks off) to study the effects of acutely elevated glucose on cardiac mitochondrial function and Nrf2 signaling in the diabetic heart. Animals were gavaged with a glucose bolus (2 g/kg) and groups were dissected at T0, T180, and T360 minutes. Nrf2 mRNA was 32% lower in OLETF rats compared to LETO and remained suppressed in response to glucose. LETO Nrf2 mRNA increased 25% at T360 in response to glucose while no changes were observed in diabetic hearts. GCLC and GCLM mRNA decreased in diabetic hearts 33% and 44% respectively and remained suppressed in response to glucose while ARB treatment increased GCLM transcripts 90% at T180. These data illustrate that during T2DM and in response to glucose, cardiac Nrf2's adaptive response to environmental stressors such as glucose is impaired in diabetic hearts and that ARB treatment may aid Nrf2's impaired dynamic response.

Angiotensin-converting enzyme inhibitors reduce mortality compared to angiotensin receptor blockers: Systematic review and meta-analysis

Background There are few reviews comparing the long-term outcomes of the use of angiotensin-converting enzyme inhibitors or angiotensin II receptor blockers in a hypertensive population because both are effective in reducing blood pressure. None of them compared angiotensin-converting enzyme inhibitors or angiotensin II receptor blockers with a placebo group in patients with essential hypertension, because few studies exist with this design. Methods A systematic search of PUBMED, LILACS, SCIELO, ICTRP, Cochrane, EMBASE and ClinicalTrials.gov from 1 January 2000 until 31 December 2015 selected prospective studies that reported an association between the use of angiotensin-converting enzyme inhibitors or angiotensin II receptor blockers in the following cardiovascular outcomes: heart failure/hospitalisation, stroke, acute myocardial infarction, total cardiovascular deaths, total deaths and total outcomes. Summary odds ratios (ORs) and 95% confidence intervals (CIs) were combined by using a fixed-effects model. Results Seventeen studies ( n = 73,761) were included of which 12 studies were randomly assigned to angiotensin II receptor blocker therapy ( n = 24,697) and five to angiotensin-converting enzyme inhibitors ( n = 12,170). Angiotensin-converting enzyme inhibitors proved to be significant in reducing total deaths (OR 0.85, 95% CI 0.78-0.93) and cardiovascular deaths (OR 0.77, 95% CI 0.69-0.87). Angiotensin II receptor blocker therapy did not show a reduction in total deaths (OR 1.02, 95% CI 0.96-1.09) or cardiovascular deaths (OR 0.95, 95% CI 0.86-1.06). For acute myocardial infarction, stroke and heart failure/hospitalisation, the reductions were significant for both classes. Conclusion Angiotensin-converting enzyme inhibitor or angiotensin II receptor blocker use is similar in preventing major cardiovascular outcomes regarding acute myocardial infarction, stroke and heart failure/hospitalisation. However, the use of angiotensin-converting enzyme inhibitors is more effective in reducing total deaths and cardiovascular deaths than angiotensin II receptor blockers.

Clinical significance of 'cardiometabolic memory': a systematic review of randomized controlled trials

'Cardiometabolic memory' has been proposed based on clinical evidence to explain how, even after the cessation of a clinical trial, the superiority of one treatment over the outcome persists. To understand the cardiometabolic memory phenomenon, we performed a systematic review of randomized controlled trials (RCTs) using PubMed in August 2016. The search terms 'randomized controlled trial', 'post-trial follow-up' and 'diabetes, hypertension or dyslipidemia' were used, and articles published after the year 2000 were searched. We judged the memory phenomenon to be positive when the cardiovascular outcome at the end of the post-trial follow-up period in the intervention group was significantly superior even though the favorable control of a risk factor (blood glucose, blood pressure or lipid level) during the trial period was lost after the cessation of the intervention. Among 907 articles retrieved in the initial screening, 21 articles were judged as describing a positive memory phenomenon. Eight, six and seven of the articles concerned diabetes, hypertension and dyslipidemia, respectively. Transient intensive glucose lowering rather easily induced memory for the suppression of diabetic microangiopathies, while memory for the suppression of macroangiopathies tended to be first evident in the post-trial follow-up period. Transient intensive blood pressure lowering was generally effective in the formation of memory for the suppression of cardiovascular events and had an especially strong impact on risk reduction of chronic heart failure. Transient intensive LDL cholesterol lowering clearly had a long-term beneficial effect on risk reduction of cardiovascular events. Our systematic review revealed the clinical relevance of cardiometabolic memory.

Metoprolol restores expression and vasodilatation function of AT2R in spontaneously hypertensive rats

Angiotensin II type 2 receptor (AT2R) is thought as an important regulatory target during antihypertensive treatment but its role in vasomotor regulation remains controversial. The interactional relationship between the sympathetic nervous systems and the renin-angiotensin-aldosterone system (RAS) has been revealed but poorly investigated. This work was designed to explore the effect of metoprolol (MET) treatment on the RAS, especially the expression and vasomotor function of AT2R, in spontaneously hypertensive rats (SHR). The results showed that upregulated renin activity and Ang II concentration of plasma in SHR were inhibited by MET treatment. In isolated superior mesenteric arteries from both Wistar-Kyoto rats and SHR, Ang II perfusion induced vasodilatation after AT1R inhibition by telmisartan, although the vasodilatation was harmed in SHR. Furthermore, AT2R inhibitor PD123319 arrested the vasodilatation induced by Ang II. SHR received MET exerted improved vasodilatation mediated by AT2R (47.29% ± 5.16% vs. 24.99% ± 4.93% for MET and SHR, respectively; P < 0.05). Western blot analysis showed that MET restored expression of AT2R in SHR, which may contribute to MET's antihypertensive effect. These results suggested an impact of β-adrenergic blocker on RAS and supported an important role of AT2R in antihypertensive treatment.

Feasibility of regression of hypertension using contemporary antihypertensive agents

BACKGROUND

Recently, we reported that transient treatment of genetically hypertensive rats with high-dose angiotensin receptor blocker (ARB) causes regression of established hypertension. In this study, we investigated whether treatment with candesartan or nifedipine controlled-release (CR) resulted in a sustained regression of hypertension in humans.

METHODS

Patients aged 30 to 59 years with untreated stage 1 essential hypertension and a family history of hypertension were treated with the antihypertensive agents candesartan (n = 124) or nifedipine CR (n = 120). After 1 year of treatment (phase 1), the medications were tapered and discontinued (phase 2). During phase 2, home and office blood pressures were monitored for another year to assess posttreatment reoccurrence of stage 1 hypertension.

RESULTS

In phase 1, after 1 year of treatment a similarly substantial BP decrease was seen in the candesartan (-24.5/16.1 mm Hg) and nifedipine (-26.8/18.0 mm Hg) groups. In phase 2 there was a substantial reoccurrence of hypertension; at the study end, only 1 patient was able to continue without antihypertensive medication. However, a Kaplan-Meier analysis revealed a significant delay of reoccurrence of hyper tension (P = 0.0001) in the candesartan group.

CONCLUSIONS

One year of treatment with candesartan or nifedipine CR was not associated with marked regression of hypertension in humans at the standard doses used in this trial. However, withdrawal of candesartan was associated with a slightly longer delay before restarting medications. Further studies with larger doses of candesartan given over a longer time are required to determine whether such a regimen may induce sustainable and clinically relevant reversal of hypertension and alteration in its natural history.

Pre-hypertension: another 'pseudodisease'?

Hypertension is one of the most important and common cardiovascular risk factors. Defining the level at which blood pressure starts causing end-organ damage is challenging, and is not easily answered. The threshold of blood pressure defining hypertension has progressively been reduced over time, from systolic >160 mmHg to >150 mmHg, then to >140 mmHg; and now even blood pressures above 130 to 120 mmHg are labeled as 'pre-hypertension' by some expert committees. Are interest groups creating another 'pseudodisease' or is this trend scientifically justified? A recent meta-analysis published in BMC Medicine by Huang et al. clearly indicates that pre-hypertension (120 to 140/80 to 90 mmHg) is a significant marker of increased cardiovascular risk. This raises the question as to whether we now need to lower the threshold of 'hypertension' (as opposed to 'pre-hypertension') to >120/80 mmHg, redefining a significant proportion of currently healthy people as 'patients' with an established disease. These data need to be interpreted with some caution. It is controversial whether pre-hypertension is an independent risk factor or just a risk marker and even more controversial whether treatment of pre-hypertension will lower cardiovascular risk. Please see related research: http://www.biomedcentral.com/1741-7015/11/177.

Prepubertal angiotensin blockade exerts long-term therapeutic effect through sustained ATRAP activation in salt-sensitive hypertensive rats

OBJECTIVE

We previously showed that the molecule interacting with Ang II type 1 receptor (AT1R), ATRAP, promotes AT1R internalization and attenuates AT1R-mediated pathological responses. In this study we examined whether the regulation of renal ATRAP expression is related to the development of salt-induced hypertension and renal injury as well as to the beneficial effects of AT1R blockade.

METHODS AND RESULTS

Dahl Iwai salt-sensitive hypertensive and Dahl Iwai salt-resistant rats were divided into six groups for the administration of vehicle or olmesartan either continuously from 3 to 16 weeks, or transiently from weaning to puberty (3-10 weeks), and fed high salt diet from 6 to 16 weeks. In Dahl Iwai salt-sensitive rats, not only continuous, but also prepubertal olmesartan treatment improved hypertension at 15 weeks. Renal ATRAP expression was suppressed in vehicle-treated Dahl Iwai salt-sensitive rats, concomitant with up-regulation of renal oxidative stress, inflammation and fibrosis-related markers such as p22phox, TGF-β, fibronectin, monocyte chemotactic protein-1 and type 1 collagen. However, prepubertal as well as continuous olmesartan treatment recovered the suppressed renal ATRAP expression and inhibited the renal activation of p22phox, TGF-β, fibronectin, MCP-1 and type 1 collagen. In Dahl Iwai salt-resistant rats, such suppression of renal ATRAP expression or induction of renal pathological responses by salt loading was not observed.

CONCLUSIONS

These results indicate that prepubertal transient blockade of AT1R signaling exerts a long-term therapeutic effect on salt-induced hypertension and renal injury in Dahl Iwai salt-sensitive rats, partly through a sustained enhancement of renal ATRAP expression, thereby suggesting ATRAP a novel molecular target in salt-induced hypertension and renal injury.

Vaccination against the angiotensin type 1 receptor for the prevention of L-NAME-induced nephropathy

Previous studies have shown that renin-angiotensin (Ang) system vaccines may be effective for the treatment of hypertension, but their efficacy for the prevention of renal disease is unclear. The aim of this study was to compare the effects of an Ang II type 1 (AT1) receptor vaccine with an Ang II receptor blocker (ARB) and a vasodilator on blood pressure (BP) and renal injury in the L-NAME nephropathy model. Male spontaneously hypertensive rats (SHRs) were divided into six groups and treated transiently with three injections of vehicle or AT1 receptor vaccine (0.1 mg) at age 4, 6 and 8 weeks, or continuously with candesartan cilexetil (0.1 mg kg(-1) per day) or hydralazine hydrochloride (5 mg kg(-1) per day), then administered NG-nitro-L-arginine methyl ester (L-NAME) from age 18 to 21 weeks to induce renal injury. Vaccination against the AT1 receptor caused a significant increase in AT1 receptor titers, and a sustained decrease in BP. L-NAME treatment resulted in a marked increase in proteinuria in the control groups, which was completely suppressed in the AT1 vaccine-treated group, and glomerular injury scores were also significantly decreased. Real-time RT-PCR and immunofluorescence studies revealed increased renin mRNA, and increased glomerular expression of nephrin. Comparable results were seen in rats treated continuously with the ARB candesartan, but not with hydralazine. These results suggest that transient AT1 vaccination is as effective as continuous treatment with ARB, not only for the attenuation of hypertension, but also for the prevention of L-NAME-induced nephropathy in SHR.

Expression of angiotensin II type 1 receptor-interacting molecule in normal human kidney and IgA nephropathy

The intrarenal renin-angiotensin system plays a crucial role in the regulation of renal circulation and sodium reabsorption through the activation of vascular, glomerular, and tubular angiotensin II type 1 (AT(1)) receptor signaling. We previously cloned a molecule that specifically interacted with the murine AT(1) receptor to inhibit AT(1) receptor signaling, which we named ATRAP (for AT(1) receptor-associated protein). Since murine ATRAP was shown to be highly expressed in the kidney, in the present study we investigated expression and distribution of human ATRAP in normal kidney and renal biopsy specimens from patients with IgA nephropathy. In the normal human kidney, both ATRAP mRNA and protein were widely and abundantly distributed along the renal tubules from Bowman's capsule to the medullary collecting ducts. In all renal tubular epithelial cells, the ATRAP protein colocalized with the AT(1) receptor. In renal biopsy specimens with IgA nephropathy, a significant positive correlation between ATRAP and AT(1) receptor gene expression was observed. There was also a positive relationship between tubulointerstitial ATRAP expression and the estimated glomerular filtration rate in patients with IgA nephropathy. Furthermore, we examined the function of the tubular AT(1) receptor using an immortalized cell line of mouse distal convoluted tubule cells (mDCT) and found that overexpression of ATRAP by adenoviral gene transfer suppressed the angiotensin II-mediated increases in transforming growth factor-β production in mDCT cells. These findings suggest that ATRAP might play a role in balancing the renal renin-angiotensin system synergistically with the AT(1) receptor by counterregulatory effects in IgA nephropathy and propose an antagonistic effect of tubular ATRAP on AT(1) receptor signaling.