N-(Heteroaryl)thiophene sulfonamides as angiotensin AT2 receptor ligands

Two series of N-(heteroaryl)thiophene sulfonamides, encompassing either a methylene imidazole group or a tert-butylimidazolylacetyl group in the meta position of the benzene ring, have been synthesized. An AT2R selective ligand with a Ki of 42 nM was identified in the first series and in the second series, six AT2R selective ligands with significantly improved binding affinities and Ki values of <5 nM were discovered. The binding modes to AT2R were explored by docking calculations combined with molecular dynamics simulations. Although some of the high affinity ligands exhibited fair stability in human liver microsomes, comparable to that observed with C21 undergoing clinical trials, most ligands displayed a very low metabolic stability with t½ of less than 10 min in human liver microsomes. The most promising ligand, with an AT2R Ki value of 4.9 nM and with intermediate stability in human hepatocytes (t½ = 77 min) caused a concentration-dependent vasorelaxation of pre-contracted mouse aorta.

Novel AT2R agonist, β-Pro7Ang III, is cardio- and vaso-protective in diabetic spontaneously hypertensive rats

Stimulation of the angiotensin II type 2 receptor (AT2R) evokes protective effects in various cardiovascular diseases. Thus, this study aimed to investigate the effects of AT2R stimulation, with or without AT1R blockade, in a model of hypertension with concomitant type 1 diabetes mellitus (T1DM). Spontaneously hypertensive rats (SHRs) were given either citrate or a single dose of streptozotocin (STZ; 55 mg/kg, i.p.) to induce diabetes. After 4 weeks of diabetes, animals were administered either a vehicle (saline), AT2R agonist, β-Pro7Ang III (0.1 mg/kg/day via osmotic mini-pump), AT1R blocker, candesartan (2 mg/kg/day via drinking water), or a combination of both for a further 8 weeks. β-Pro7Ang III treatment had no effect on blood pressure, but attenuated the significant increase in cardiac interstitial collagen and protein expression of fibrotic and inflammatory markers, and superoxide levels that was evident in diabetic SHRs. These effects were not observed with candesartan, despite its blood pressure lowering effects. Although β-Pro7Ang III had no effect on aortic fibrosis, it significantly attenuated MCP-1 protein expression and superoxide levels when compared to both the non-diabetic and diabetic SHRs, to a similar extent as candesartan. In both the heart and vasculature, the effects of β-Pro7Ang III in combination with candesartan were similar to those of β-Pro7Ang III alone, and superior to candesartan alone. It was concluded that in hypertension with concomitant diabetes, AT2R stimulation with a novel ligand alone, or in combination with AT1R blockade, improved the cardiac and vascular structural changes that were strongly associated with inflammation and oxidative stress, independent of blood pressure regulation.

Long-term dietary nitrate supplementation slows the progression of established atherosclerosis in ApoE-/- mice fed a high fat diet

BACKGROUND AND AIMS

Atherosclerosis is associated with a reduction in the bioavailability and/or bioactivity of endogenous nitric oxide (NO). Dietary nitrate has been proposed as an alternate source when endogenous NO production is reduced. Our previous study demonstrated a protective effect of dietary nitrate on the development of atherosclerosis in the apoE-/- mouse model. However most patients do not present clinically until well after the disease is established. The aims of this study were to determine whether chronic dietary nitrate supplementation can prevent or reverse the progression of atherosclerosis after disease is already established, as well as to explore the underlying mechanism of these cardiovascular protective effects.

METHODS

60 apoE-/- mice were given a high fat diet (HFD) for 12 weeks to allow for the development of atherosclerosis. The mice were then randomized to (i) control group (HFD + 1 mmol/kg/day NaCl), (ii) moderate-dose group (HFD +1 mmol/kg/day NaNO3), or (iii) high-dose group (HFD + 10 mmol/kg/day NaNO3) (20/group) for a further 12 weeks. A group of apoE-/- mice (n = 20) consumed a normal laboratory chow diet for 24 weeks and were included as a reference group.

RESULTS

Long-term supplementation with high dose nitrate resulted in ~ 50% reduction in plaque lesion area. Collagen expression and smooth muscle accumulation were increased, and lipid deposition and macrophage accumulation were reduced within atherosclerotic plaques of mice supplemented with high dose nitrate. These changes were associated with an increase in nitrite reductase as well as activation of the endogenous eNOS-NO pathway.

CONCLUSION

Long-term high dose nitrate significantly attenuated the progression of established atherosclerosis in the apoE-/- mice fed a HFD. This appears to be mediated in part through a XOR-dependent reduction of nitrate to NO, as well as enhanced eNOS activation via increased Akt and eNOS phosphorylation.

The single-chain relaxin mimetic, B7-33, maintains the cardioprotective effects of relaxin and more rapidly reduces left ventricular fibrosis compared to perindopril in an experimental model of cardiomyopathy

The hormone, relaxin (RLX), exerts various organ-protective effects independently of etiology. However, its complex two-chain and three disulphide bonded structure is a limitation to its preparation and affordability. Hence, a single chain-derivative of RLX, B7-33, was developed and shown to retain the anti-fibrotic effects of RLX in vitro and in vivo. Here, we determined whether B7-33 could retain the other cardioprotective effects of RLX, and also compared its therapeutic efficacy to the ACE inhibitor, perindopril. Adult male 129sv mice were subjected to isoprenaline (ISO; 25 mg/kg/day, s.c)-induced cardiomyopathy, then s.c-treated with either RLX (0.5 mg/kg/day), B7-33 (0.25 mg/kg/day; equivalent dose corrected for MW) or perindopril (1 mg/kg/day) from days 7-14 post-injury. Control mice received saline instead of ISO. Changes in animal body weight (BW) and systolic blood pressure (SBP) were measured weekly, whilst cardiomyocyte hypertrophy and measures of vascular dysfunction and rarefaction, left ventricular (LV) inflammation and fibrosis were assessed at day 14 post-injury. ISO-injured mice had significantly increased LV inflammation, cardiomyocyte hypertrophy, fibrosis, vascular rarefaction and aortic contractility in the absence of any changes in BW or SBP at day 14 post-injury. Both B7-33 and RLX equivalently reduced LV fibrosis and normalised the ISO-induced LV inflammation and cardiomyocyte hypertrophy, whilst restoring blood vessel density and aortic contractility. Comparatively, perindopril lowered SBP and the ISO-induced LV inflammation and vascular rarefaction, but not fibrosis or hypertrophy. As B7-33 retained the cardioprotective effects of RLX and provided rapid-occurring anti-fibrotic effects compared to perindopril, it could be considered as a cost-effective cardioprotective therapy.

Relaxin Inhibits the Cardiac Myofibroblast NLRP3 Inflammasome as Part of Its Anti-Fibrotic Actions via the Angiotensin Type 2 and ATP (P2X7) Receptors

Chronic NLRP3 inflammasome activation can promote fibrosis through its production of interleukin (IL)-1β and IL-18. Conversely, recombinant human relaxin (RLX) can inhibit the pro-fibrotic interactions between IL-1β, IL-18 and transforming growth factor (TGF)-β1. Here, the broader extent by which RLX targeted the myofibroblast NLRP3 inflammasome to mediate its anti-fibrotic effects was elucidated. Primary human cardiac fibroblasts (HCFs), stimulated with TGF-β1 (to promote myofibroblast (HCMF) differentiation), LPS (to prime the NLRP3 inflammasome) and ATP (to activate the NLRP3 inflammasome) (T+L+A) or benzoylbenzoyl-ATP (to activate the ATP receptor; P2X7R) (T+L+Bz), co-expressed relaxin family peptide receptor-1 (RXFP1), the angiotensin II type 2 receptor (AT2R) and P2X7R, and underwent increased protein expression of toll-like receptor (TLR)-4, NLRP3, caspase-1, IL-1β and IL-18. Whilst RLX co-administration to HCMFs significantly prevented the T+L+A- or T+L+Bz-stimulated increase in these end points, the inhibitory effects of RLX were annulled by the pharmacological antagonism of either RXFP1, AT2R, P2X7R, TLR-4, reactive oxygen species (ROS) or caspase-1. The RLX-induced amelioration of left ventricular inflammation, cardiomyocyte hypertrophy and fibrosis in isoproterenol (ISO)-injured mice, was also attenuated by P2X7R antagonism. Thus, the ability of RLX to ameliorate the myofibroblast NLRP3 inflammasome as part of its anti-fibrotic effects, appeared to involve RXFP1, AT2R, P2X7R and the inhibition of TLR-4, ROS and caspase-1.

Relaxin Attenuates Organ Fibrosis via an Angiotensin Type 2 Receptor Mechanism in Aged Hypertensive Female Rats

Background

The antifibrotic effects of recombinant human relaxin (RLX) in the kidney are dependent on an interaction between its cognate receptor (RXFP1) and the angiotensin type 2 receptor (AT₂R) in male models of disease. Whether RLX has therapeutic effects, which are also mediated via AT₂R, in hypertensive adult and aged/reproductively senescent females is unknown. Thus, we determined whether treatment with RLX provides cardiorenal protection via an AT₂R-dependent mechanism in adult and aged female stroke-prone spontaneously hypertensive rats (SHRSPs).

Methods

In 6-month-old (6MO) and 15-month-old ([15MO]; reproductively senescent) female SHRSP, systolic BP (SBP), GFR, and proteinuria were measured before and after 4 weeks of treatment with vehicle (Veh), RLX (0.5 mg/kg per day s.c.), or RLX+PD123319 (AT₂R antagonist; 3 mg/kg per day s.c.). Aortic endothelium-dependent relaxation and fibrosis of the kidney, heart, and aorta were assessed.

Results

In 6MO SHRSP, RLX significantly enhanced GFR by approximately 25% (P=0.001) and reduced cardiac fibrosis (P=0.01) as compared with vehicle-treated counterparts. These effects were abolished or blunted by PD123319 coadministration. In 15MO females, RLX reduced interstitial renal (P=0.02) and aortic (P=0.003) fibrosis and lowered SBP (13±3 mm Hg; P=0.04) relative to controls. These effects were also blocked by PD123319 cotreatment (all P=0.05 versus RLX treatment alone). RLX also markedly improved vascular function by approximately 40% (P<0.001) in 15MO SHRSP, but this was not modulated by PD123319 cotreatment.

Conclusions

The antifibrotic and organ-protective effects of RLX, when administered to a severe model of hypertension, conferred cardiorenal protection in adult and reproductively senescent female rats to a great extent via an AT₂R-mediated mechanism.

In Aged Females, the Enhanced Pressor Response to Angiotensin II Is Attenuated By Estrogen Replacement via an Angiotensin Type 2 Receptor-Mediated Mechanism

[Figure: see text].

Simultaneous targeting of oxidative stress and fibrosis reverses cardiomyopathy-induced ventricular remodelling and dysfunction

BACKGROUND AND PURPOSE

Oxidative stress and fibrosis are hallmarks of cardiomyopathy-induced heart failure yet are not effectively targeted by current frontline therapies. Here, the therapeutic effects of the anti-oxidant, N-acetylcysteine (NAC), were compared and combined with an acute heart failure drug with established anti-fibrotic effects, serelaxin (RLX), in a murine model of cardiomyopathy.

EXPERIMENTAL APPROACH

Adult male 129sv mice were subjected to repeated isoprenaline (25 mg·kg^-1 )-induced cardiac injury for five consecutive days and then left to undergo fibrotic healing until Day 14. Subgroups of isoprenaline-injured mice were treated with RLX (0.5 mg·kg^-1 ·day^-1 ), NAC (25 mg·kg^-1 ·day^-1 ) or both combined, given subcutaneously via osmotic minipumps from Day 7 to 14. Control mice received saline instead of isoprenaline.

KEY RESULTS

Isoprenaline-injured mice showed increased left ventricular (LV) inflammation (~5-fold), oxidative stress (~1-2.5-fold), cardiomyocyte hypertrophy (~25%), cardiac remodelling, fibrosis (~2-2.5-fold) and dysfunction by Day 14 after injury. NAC alone blocked the cardiomyopathy-induced increase in LV superoxide levels, to a greater extent than RLX. Additionally, either treatment alone only partly reduced several measures of LV inflammation, remodelling and fibrosis. In comparison, the combination of RLX and NAC prevented the cardiomyopathy-induced LV macrophage infiltration, remodelling, fibrosis and cardiomyocyte size, to a greater extent than either treatment alone after 7 days. The combination therapy also restored the isoprenaline-induced reduction in LV function, without affecting systolic BP.

CONCLUSION AND IMPLICATIONS

These findings demonstrated that the simultaneous targeting of oxidative stress and fibrosis is key to treating the pathophysiology and dysfunction induced by cardiomyopathy.

N-(Methyloxycarbonyl)thiophene sulfonamides as high affinity AT2 receptor ligands

A series of meta-substituted acetophenone derivatives, encompassing N-(alkyloxycarbonyl)thiophene sulfonamide fragments have been synthesized. Several selective AT2 receptor ligands were identified, among those a tert-butylimidazole derivative (20) with a K_i of 9.3 nM, that demonstrates a high stability in human liver microsomes (t_½ = 62 min) and in human hepatocytes (t_½ = 194 min). This methyloxycarbonylthiophene sulfonamide is a 20-fold more potent binder to the AT2 receptor and is considerably more stable in human liver microsomes, than a previously reported and broadly studied structurally related AT₂R prototype antagonist 3 (C38). Ligand 20 acts as an AT₂R agonist and caused an AT₂R mediated concentration-dependent vasorelaxation of pre-contracted mouse aorta. Furthermore, in contrast to imidazole derivative C38, the tert-butylimidazole derivative 20 is a poor inhibitor of CYP3A4, CYP2D6 and CYP2C9. It is demonstrated herein that smaller alkyloxycarbonyl groups make the ligands in this series of AT₂R selective compounds less prone to degradation and that a high AT2 receptor affinity can be retained after truncation of the alkyloxycarbonyl group. Binding modes of the most potent AT₂R ligands were explored by docking calculations combined with molecular dynamics simulations.

Relaxin Can Mediate Its Anti-Fibrotic Effects by Targeting the Myofibroblast NLRP3 Inflammasome at the Level of Caspase-1

Introduction

The NLRP3 inflammasome produces interleukin (IL)-1β and IL-18, which when chronically activated by transforming growth factor (TGF)-β1, contribute to fibrosis. The recombinant form of the anti-fibrotic hormone, relaxin (RLX), suppresses the pro-fibrotic influence of TGF-β1 and toll-like receptor (TLR)-4 on NLRP3 inflammasome priming and activity in human cardiac myofibroblasts and mice with cardiomyopathy. However, whether RLX also modulates components of the myofibroblast NLRP3 inflammasome remains unknown.

Methods and Results

Stimulation of a human dermal fibroblast (HDF) cell line with TGF-β1 [5 ng/ml; to promote myofibroblast (HDMF) differentiation], LPS (100 ng/ml; to prime the NLRP3 inflammasome) and ATP (5 mM; to activate the NLPR3 inflammasome) (T+L+A) significantly increased NLRP3 inflammasome priming and activity after 8 and 72 h; and α-SMA expression (myofibroblast differentiation) and collagen-I deposition after 72 h. siRNA-induced knock-down of NLRP3 inflammasome priming components (NLRP3, ASC, caspase-1) in T+L+A-stimulated HDMFs for 24 h, completely knocked-down each component after 72 h. RLX (100 ng/ml) administration to T+L+A-stimulated HDMFs after control, NLRP3 or ASC siRNA transfection, equivalently suppressed IL-1β, pro-IL-18, α-SMA, and collagen-I protein levels (by 40%–50%; all p<0.05 vs. T+L+A) after 72 h, as determined by Western blotting. These RLX-induced effects were abrogated by siRNA knock-down of caspase-1.

Conclusion

The anti-fibrotic actions of RLX appear to require modulation of caspase-1 within the myofibroblast NLRP3 inflammasome.

A Novel Epigenetic Drug-Eluting Balloon Angioplasty Device: Evaluation in a Large Animal Model of Neointimal Hyperplasia

PURPOSE

Drug-eluting balloon catheters (DEBc) coated with paclitaxel (PTX) have been associated with potential safety concerns. An efficacious but less toxic balloon coating may reduce these outcomes. We evaluated a novel DEBc, Epi-Solve, coated with metacept-3 (MCT-3), a member of the histone deacetylase inhibitor (HDACi) class of epigenetic agents, in a large animal model of neointimal hyperplasia (NIH).

METHODS

Plain balloon angioplasty (PABA) catheters were ultrasonically coated with MCT-3 to generate Epi-Solve DEBc. An ovine model of NIH formation was established utilising partial left common carotid artery (LCA) ligation. Twenty-eight days post neointima (NI) induction, PABA, Epi-Solve or PTX-coated DEBc were deployed at the site of induced NI formation. Twenty-eight days post-intervention, ligated vessels were evaluated for attenuation of NI formation, gene expression profiles and immunohistochemical analysis.

RESULTS

Epi-Solve DEBc demonstrated attenuation of NIH over no intervention and a trend to inhibition of NIH over PABA. Gene expression analysis and immunohistochemical studies identified significant anti-proliferative and anti-inflammatory signatures and reduced vascular endothelial cell activation compared to PABA.

CONCLUSIONS

Epi-Solve is a novel HDACi-coated DEBc which demonstrates significant anti-proliferative and anti-inflammatory signatures and reduced vascular endothelial cell activation compared to PABA in an ovine model and may afford endothelial protection.

Serelaxin and the AT2 Receptor Agonist CGP42112 Evoked a Similar, Nonadditive, Cardiac Antifibrotic Effect in High Salt-Fed Mice That Were Refractory to Candesartan Cilexetil

Fibrosis is involved in the majority of cardiovascular diseases and is a key contributor to end-organ dysfunction. In the current study, the antifibrotic effects of recombinant human relaxin-2 (serelaxin; RLX) and/or the AT₂R agonist CGP42112 (CGP) were compared with those of the established AT₁R antagonist, candesartan cilexetil (CAND), in a high salt-induced cardiac fibrosis model. High salt (HS; 5%) for 8 weeks did not increase systolic blood pressure in male FVB/N mice, but CAND treatment alone significantly reduced systolic blood pressure from HS-induced levels. HS significantly increased cardiac interstitial fibrosis, which was reduced by either RLX and/or CGP, which were not additive under the current experimental conditions, while CAND failed to reduce HS-induced cardiac fibrosis. The antifibrotic effects induced by RLX and/or CGP were associated with reduced myofibroblast differentiation. Additionally, all treatments inhibited the HS-induced elevation in tissue inhibitor of matrix metalloproteinases-1, together with trends for increased MMP-13 expression, that collectively would favor collagen degradation. Furthermore, these antifibrotic effects were associated with reduced cardiac inflammation. Collectively, these results highlight that either RXFP1 or AT₂R stimulation represents novel therapeutic strategies to target fibrotic conditions, particularly in HS states that may be refractory to AT₁R blockade.

Serelaxin inhibits the profibrotic TGF-β1/IL-1β axis by targeting TLR-4 and the NLRP3 inflammasome in cardiac myofibroblasts

The recombinant form of the peptide hormone relaxin, serelaxin (RLX), mediates its anti-fibrotic actions by impeding the profibrotic activity of cytokines including TGF-β1 and IL-1β. As IL-1β can be produced by the nucleotide-binding oligomerization domain, leucine-rich repeat and pyrin domains-containing protein 3 (NLRP3) inflammasome, this study determined whether RLX targeted the inflammasome to inhibit the profibrotic TGF-β1/IL-1β axis in primary human cardiac myofibroblasts (HCMFs) in vitro and in mice with isoproterenol (ISO)-induced cardiomyopathy in vivo. HCMFs stimulated with TGF-β1 (5 ng/ml), LPS (100 ng/ml), and ATP (5 mM) (T+L+A) for 8 h, to induce the NLRP3 inflammasome, demonstrated significantly increased protein expression of markers of NLRP3 priming (NLRP3, apoptosis-associated speck-like protein containing a C-terminal caspase-recruitment domain, procaspase-1) and activity (IL-1β, IL-18). After 72 h, there was significantly increased neuronal NOS (nNOS), TLR-4, procaspase-1, myofibroblast differentiation, and collagen-I deposition. These measures, along with interstitial TGF-β1 expression and collagen deposition, were also increased in the left ventricle (LV) of ISO-injured mice 14 d postinjury. RLX [16.8 nM (100 ng/ml) in vitro; 0.5 mg/kg per day in vivo] inhibited T+L+A- and ISO-induced TLR-4 expression, NLRP3 priming, IL-1β, IL-18, myofibroblast differentiation, and interstitial collagen deposition at the time points studied, via the promotion of nNOS; with the NLRP3- and IL-1β-inhibitory effects of RLX in HCMFs being abrogated by pharmacological blockade of nNOS or TLR-4. Comparatively, the small molecule NLRP3 inhibitor, N-{[(1,2,3,5,6,7-hexahydro-s-indacen-4-yl)amino]carbonyl}-4-(1-hydroxy-1-methylethyl)-2-furansulfonamide (1 μM in vitro, 10 mg/kg/d in vivo), inhibited components of the NLRP3 inflammasome in vitro and in vivo and ISO-induced interstitial LV fibrosis in vivo but did not affect nNOS, TLR-4, myofibroblast differentiation, or myofibroblast-induced collagen deposition. Hence, RLX can inhibit the TGF-β1/IL-1β axis via a nNOS-TLR-4-NLRP3 inflammasome-dependent mechanism on cardiac myofibroblasts.-Cáceres, F. T., Gaspari, T. A., Samuel, C. S., Pinar, A. A. Serelaxin inhibits the profibrotic TGF-β1/IL-1β axis by targeting TLR-4 and the NLRP3 inflammasome in cardiac myofibroblasts.

Abstract 131: Insulin Regulated Aminopeptidase Inhibitors are More Effective Than the ACE Inhibitor, Perindopril in Preventing Unilateral Ureteral Obstruction-Induced Renal Fibrosis in Mice

New strategies are needed to combat pathological organ fibrosis that leads to end stage organ failure. We have identified the enzyme insulin regulated aminopeptidase (IRAP) as one such promising new target, with IRAP KO mice completely protected, and pharmacological inhibition of IRAP reversing, age-induced cardiac fibrosis. However, the effect of IRAP inhibition in renal fibrosis is unknown. Therefore the objective of this study was to: (1) compare anti-fibrotic efficacy of 2 chemically distinct IRAP inhibitors, HFI-419 and SJM4-164 to the ACE inhibitor, perindopril (PER) in a murine model of unilateral ureteral obstructive (UUO)-induced renal fibrosis; and (2) investigate role of IRAP substrates in mediating ant-fibrotic effect of IRAP inhibitors. Male C57Bl/6J mice (8 weeks old) were assigned to one of the following 7 day protocols (n=6/gp): sham, UUO+Veh, UUO+HFI (0.72mg/kg/d), UUO+SJM (0.72mg/kg/d), or UUO+PER (1mg/kg/d). IRAP substrate involvement was determined using specific receptor blockers for the oxytocin receptor (OTR; Atosiban; 0.6mg/kg/d) or the AT2 receptor (AT2R; PD123319; 10mg/kg/d). Interstitial fibrosis was significantly increased in UUO+Veh-injured kidneys compared to sham (% positive staining: UUO=5.9±0.7 vs Sham=1.2±0.3; p<0.05). HFI and SJM treatment were equally effective in preventing UUO-induced increase in interstitial renal fibrosis (% positive staining: HFI=2.5±0.3, SJM=2.8±0.3, all p<0.05 vs UUO). PER had no effect on UUO-induced increase in interstitial renal fibrosis (PER=6.6±0.7), however it was as effective as the IRAP inhibitors in reducing markers of inflammation, including NFκB activation and macrophage infiltration. The anti-fibrotic effects produced with IRAP inhibition were prevented by OTR or AT2R blockade (% positive staining: OTR=5.0±0.55, AT2R=6±0.8). Overall, this study demonstrated greater reno-protection with IRAP inhibition compared to that achieved using an ACE inhibitor, with IRAP inhibitors exhibiting potent anti-fibrotic and anti-inflammatory effects. Moreover, for the first time we show that the anti-fibrotic effects of IRAP inhibition involve activation of receptors associated with endogenous IRAP substrates.

Abstract 016: Combined AT 2 Receptor Stimulation/ AT 1 Receptor Blockade Does Not Cause Renal Dysfunction

Combined ACE inhibition and angiotensin type 1 receptor (AT 1 R) blockade (dual RAS) blockade) causes renal failure which limits their combined use. Angiotensin type 2 receptor (AT 2 R) stimulation evokes renoprotective effects but potential adverse renal effects in drug combination are not known. We examined the effects of the AT 2 R agonist compound 21 (C21) combined with either candesartan cilexetil or perindopril on renal function in a preclinical model that is predictive of clinical outcome. Adult (~25 week-old) male SHR were placed on a normal salt (0.35%, n=8) or a low salt (LS; 0.05%) diet for 17 days with rats on a LS diet randomised to receive one of the following treatments for the final 10 days: untreated (n=8); C21 (0.3mg/kg/d s.c., n=5); candesartan (2 mg/kg/d, n=6); perindopril (0.5mg/kg/d, n=5); C21+candesartan (n=8); C21+perindopril (n=5); or candesartan+perindopril (dual RAS blockade, n=7). Systolic arterial pressure (SBP) was measured via tail cuff at days 0, 7 and 17. At the end of the treatment, renal function was assessed by measuring plasma creatinine, urea, K+ and glomerular filtration rate (GFR) in conscious rats via transdermal assessment of elimination half-life kinetics of FITC-sinistrin (3-5mg/100g i.v.). Candesartan (-43±10 mmHg) or perindopril (-49±12 mmHg) reduced SBP to a similar extent alone or combined with C21, whereas dual RAS blockade markedly reduced SBP (-115±14 mmHg; P<0.01 versus all groups). Plasma creatinine (424 ±65 μmol/L), urea (>50 mmol/L cut-off) and K+ (5.94 ±0.82 mmol/L) levels were all significantly elevated by dual RAS blockade compared with untreated SHR on normal diet (creatinine 39 ±2 μmol/L; urea 7.08±0.22 mmol/L; K+ 4.23±0.13 mmol/L; all P<0.01) or LS diet (creatinine 29 ±2 μmol/L; urea 5.2±0.57 mmol/L; K+ 4.29±0.17 mmol/L; all P<0.01), whereas plasma measurements for C21+candesartan and C21+perindopril were similar to control groups. Estimated GFR in LS group (1.18±0.06 ml/min/100g BW) was similar to other groups except during dual RAS blockade where GFR was markedly impaired (0.32±0.10 ml/min/100g BW; P<0.01 versus LS). Collectively, these data suggest that, unlike dual RAS blockade, an AT 2 R agonist combined with either ACE inhibition or AT 1 R blockade is not likely to cause renal dysfunction.

Anti-fibrotic Potential of AT2 Receptor Agonists

There are a number of therapeutic targets to treat organ fibrosis that are under investigation in preclinical models. There is increasing evidence that stimulation of the angiotensin II type 2 receptor (AT₂R) is a novel anti-fibrotic strategy and we have reviewed the published in vivo preclinical data relating to the effects of compound 21 (C21), which is the only nonpeptide AT₂R agonist that is currently available for use in chronic preclinical studies. In particular, the differential influence of AT₂R on extracellular matrix status in various preclinical fibrotic models is discussed. Collectively, these studies demonstrate that pharmacological AT₂R stimulation using C21 decreases organ fibrosis, which has been most studied in the setting of cardiovascular and renal disease. In addition, AT₂R-mediated anti-inflammatory effects may contribute to the beneficial AT₂R-mediated anti-fibrotic effects seen in preclinical models.

Low dose dietary nitrate improves endothelial dysfunction and plaque stability in the ApoE-/- mouse fed a high fat diet

BACKGROUND

Nitric oxide (NO) is an important vascular signalling molecule. NO is synthesised endogenously by endothelial nitric oxide synthase (eNOS). An alternate pathway is exogenous dietary nitrate, which can be converted to nitrite and then stored or further converted to NO and used immediately. Atherosclerosis is associated with endothelial dysfunction and subsequent lesion formation. This is thought to arise due to a reduction in the bioavailability and/or bioactivity of endogenous NO.

AIM

To determine if dietary nitrate can protect against endothelial dysfunction and lesion formation in the ApoE^-/- mouse fed a high fat diet (HFD).

METHODS AND RESULTS

ApoE^-/- fed a HFD were randomized to receive (i) high nitrate (10mmol/kg/day, n=12), (ii) moderate nitrate (1mmol/kg/day, n=8), (iii) low nitrate (0.1mmol/kg/day, n=8), or (iv) sodium chloride supplemented drinking water (control, n=10) for 10 weeks. A group of C57BL6 mice (n=6) received regular water and served as a healthy reference group. At 10 weeks, ACh-induced vessel relaxation was significantly impaired in ApoE^-/- mice versus C57BL6. Mice supplemented with low or moderate nitrate showed significant improvements in ACh-induced vessel relaxation compared to ApoE^-/- mice given the high nitrate or sodium chloride. Plaque collagen expression was increased and lipid deposition reduced following supplementation with low or moderate nitrate compared to sodium chloride, reflecting increased plaque stability with nitrate supplementation. Plasma nitrate and nitrite levels were significantly increased in all three groups fed the nitrate-supplemented water.

CONCLUSION

Low and moderate dose nitrate significantly improved endothelial function and atherosclerotic plaque composition in ApoE^-/- mice fed a HFD.

NOX1 deficiency in apolipoprotein E-knockout mice is associated with elevated plasma lipids and enhanced atherosclerosis

Nicotinamide adenine dinucleotide phosphate oxidases (NOX) are enzymes that generate reactive oxygen species (ROS). NOX2 activity in the vascular wall is elevated in hypercholesterolemia, and contributes to oxidative stress and atherogenesis. Here we examined the role of another NOX isoform, NOX1, in atherogenesis in apolipoprotein E-knockout (APOE(-/-)) mice fed a Western diet for 14 weeks. Although NOX1 mRNA expression was unchanged in aortas from APOE(-/-) versus wild-type mice, expression of the NOX1-specific organizer, NOXO1, was diminished, consistent with an overall reduction in NOX1 activity in APOE(-/-) mice. To examine the impact of a further reduction in NOX1 activity, APOE(-/-) mice were crossed with NOX1(-/y) mice to generate NOX1(-/y)/APOE(-/-) double-knockouts. NOX1 deficiency in APOE(-/-) mice was associated with 30-50% higher plasma very-low-density lipoprotein (VLDL)/LDL and triglyceride levels (P < 0.01). Vascular ROS levels were also elevated by twofold in NOX1(-/y)/APOE(-/-) versus APOE(-/-) mice (P < 0.05), despite no changes in expression of other NOX subunits. Although en face analysis of the descending aorta revealed no differences in plaque area between NOX1(-/y)/APOE(-/-) and APOE(-/-) mice, intimal thickening in the aortic sinus was increased by 40% (P < 0.05) in the double-knockouts. Moreover, NOX1 deficiency was associated with a less stable plaque phenotype; aortic sinus lesions contained 60% less collagen (P < 0.01), 40% less smooth muscle (P < 0.01), and 2.5-fold higher levels of matrix metalloproteinase-9 (P < 0.001) than lesions in APOE(-/-) mice. Thus, these data, which suggest a protective role for NOX1 against hyperlipidemia and atherosclerosis in APOE(-/-) mice, highlight the complex and contrasting roles of different NOX isoforms (e.g., NOX2 versus NOX1) in vascular pathology.

Vasoprotective and atheroprotective effects of angiotensin (1-7) in apolipoprotein E-deficient mice

OBJECTIVE

To evaluate the effectiveness of long-term angiotensin (Ang) (1-7) treatment to inhibit the progression of atherosclerosis in apolipoprotein E-deficient (ApoE(-/-)) mice.

METHODS AND RESULTS

Ang (1-7) is a heptapeptide fragment that has been proposed to counterregulate the Ang II proatherogenic effects. The effect of long-term 4-week Ang (1-7) treatment on both inhibition of atherosclerotic lesion development and improvement of endothelial function was examined in apolipoprotein E(-/-) mice that had been fed an atherogenic high-fat (21%) diet for 16 weeks. Chronic Ang (1-7) treatment significantly improved endothelial function, an effect reversed with either angiotensin type 2 (AT(2)) or Mas receptor blockade. In these vessels, Ang (1-7) treatment significantly decreased superoxide production and increased endothelial nitric oxide synthase immunoreactivity when compared with vehicle treatment. These effects were blocked by both AT(2) and Mas receptor antagonists. Lesion development, assessed as both fatty deposits (oil red O) and intima to media ratio, was also significantly decreased with Ang (1-7) treatment compared with respective controls. Cotreatment with either AT(2) or Mas receptor antagonists reversed Ang (1-7)-mediated reduction in lesion development.

CONCLUSIONS

Long-term Ang (1-7) treatment caused both vasoprotection, via improvement in endothelial function, and atheroprotection, with a reduction in lesion progression in a model of atherosclerosis. These effects appear to be mediated by the restoration of nitric oxide bioavailability and involve a complex interaction of both Mas and AT(2) receptors.

AT2 receptors: functional relevance in cardiovascular disease

The renin angiotensin system (RAS) is intricately involved in normal cardiovascular homeostasis. Excessive stimulation by the octapeptide angiotensin II contributes to a range of cardiovascular pathologies and diseases via angiotensin type 1 receptor (AT₁R) activation. On the other hand, tElsevier Inc.he angiotensin type 2 receptor (AT₂R) is thought to counter-regulate AT₁R function. In this review, we describe the enhanced expression and function of AT₂R in various cardiovascular disease settings. In addition, we illustrate that the RAS consists of a family of angiotensin peptides that exert cardiovascular effects that are often distinct from those of Ang II. During cardiovascular disease, there is likely to be an increased functional importance of AT₂R, stimulated by Ang II, or even shorter angiotensin peptide fragments, to limit AT₁R-mediated overactivity and cardiovascular pathologies.

A novel histone deacetylase inhibitor reduces abdominal aortic aneurysm formation in angiotensin II-infused apolipoprotein E-deficient mice

BACKGROUND/AIMS

Aberrant expression of components of the matrix metalloproteinase (MMP) enzyme system is implicated in abdominal aortic aneurysm (AAA) formation. We aimed to investigate the influence of a novel histone deacetylase (HDAC) inhibitor (HDACi) metacept-1 (MCT-1), previously documented to reduce MMP expression, on HDAC activity and MMP expression in aortic smooth muscle cells and the in vivo incidence of AAAs.

METHODS

Western blot and gelatin zymography were used to determine HDAC activity and MMP-2 expression and activity in rat (rVSMCs) and human aortic vascular smooth muscle cells (hVSMCs) in vitro. In vivo AAAs were generated using apolipoprotein E-deficient mice infused with angiotensin (Ang) II. Immunohistochemistry detected MMP-2 and -9 expression in AAA tissue samples.

RESULTS

In vitro, MCT-1 inhibited HDAC activity in rVSMCs, and MMP-2 expression and proteolytic activity in hVSMCs. In vivo, Ang II treatment alone exhibited an AAA incidence of 84%. Doxycycline decreased the incidence of AAAs to 50%. Importantly, MCT-1 reduced AAA incidence to approximately 44%. MMP-2 and -9 immunoreactivity was reduced in MCT-1-treated aortic tissue.

CONCLUSION

The novel HDACi MCT-1 inhibits MMP expression and AAA incidence suggesting this compound may warrant further investigation in the context of AAA biology.

Atrial Natriuretic Peptide Preserves Endothelial Function during Intimal Hyperplasia

BACKGROUND

Atrial and C-type natriuretic peptides (ANP and CNP), acting through different receptors, have antiproliferative effects in vitro. Beneficial effects of CNP in vivo on early atherosclerosis have been described, but it is not known if ANP is antiproliferative in vivo. In the present study, the effects of chronic in vivo ANP were tested and compared with CNP on endothelial dysfunction and intimal thickening caused by peri-arterial collars.

METHODS

Non-occlusive collars were placed bilaterally around the common carotid arteries of rabbits. One collar was filled with saline vehicle. The contralateral collar was filled with ANP or CNP (1 or 10 microM, n = 5-7) with slow replacement of peptide via mini-pump (1 or 10 fmol/h).

RESULTS

After 7 days, endothelium-dependent vasorelaxation in saline-collared arteries was 33 +/- 3% of maximum [averaged over 0.03-1 muM acetylcholine (ACh)] compared to 64 +/- 2% in normal (uncollared) arteries (p < 0.05, n = 23). In vivo ANP restored the ACh relaxation to normal (e.g., 57 +/- 6%, 1 microM ANP), similar to effects seen with CNP in vivo. Endothelium-independent vasorelaxation of collared-vessels was not altered by either peptide. Intimal hyperplasia induced by the collars was not prevented by peri-arterial natriuretic peptides. In additional rabbits (n = 6), CNP (100 pmol/h) given directly into the lumen of collared carotid arteries for 7 days reduced neointima formation by 16 +/- 5% (p < 0.05), whereas ANP given intraluminally (100 pmol/h; n = 6) did not.

CONCLUSIONS

The more potent actions of CNP on vascular smooth muscle cell migration and proliferation (established in vitro) may explain differences between the peptides on intimal hyperplasia in vivo. The major hallmark of atherosclerosis and restenosis, endothelial dysfunction, was prevented by chronic, peri-arterial administration of ANP or CNP.

Angiotensin-(1-7) acts as a vasodepressor agent via angiotensin II type 2 receptors in conscious rats

Given that angiotensin-(1-7) (Ang-[1-7]) has been frequently reported to exert direct in vitro vascular effects but less often in vivo, we investigated whether a vasodepressor effect of Ang-(1-7) could be unmasked acutely in conscious spontaneously hypertensive rats (SHR) against a background of angiotensin II type 1 (AT1) receptor blockade. Mean arterial pressure (MAP) and heart rate were measured over a 5-day protocol in various groups of rats randomized to receive the following drug combinations: saline, AT1 receptor (AT1R) antagonist candesartan (0.01 or 0.1 mg/kg IV) alone, Ang-(1-7) (5 pmol/min) alone, candesartan plus Ang-(1-7), and candesartan plus Ang-(1-7) and angiotensin II type 2 (AT2) receptor (AT2R) antagonist PD123319 (50 microg/kg per minute). In Wistar-Kyoto (WKY) rats, saline, Ang-(1-7), or candesartan alone caused no significant alteration in MAP, whereas Ang-(1-7) coadministered with candesartan caused a marked, sustained reduction in MAP. A similar unmasking of a vasodepressor response to Ang-(1-7) during AT1R blockade was observed in SHR. Moreover, the AT(2)R antagonist PD123319 markedly attenuated the enhanced depressor response evoked by the Ang-(1-7)/candesartan combination in SHR and WKY rats, whereas in other experiments, the putative Ang-(1-7) antagonist A-779 (5 and 50 pmol/min) did not attenuate this vasodepressor effect. In separate experiments, the bradykinin type 2 receptor antagonist HOE 140 (100 microg/kg IV) or the NO synthase inhibitor Nomega-nitro-L-arginine methyl ester (1 mg/kg IV) abolished the depressor effect of Ang-(1-7) in the presence of candesartan. Collectively, these results suggest that Ang-(1-7) evoked a depressor response during AT1R blockade via activation of AT2R, which involves the bradykinin-NO cascade.

Differential regulation by AT(1) and AT(2) receptors of angiotensin II-stimulated cyclic GMP production in rat uterine artery and aorta

1. In the present study we determined whether angiotensin II (Ang II) could increase cyclic GMP levels in two blood vessels that exhibit markedly different angiotensin II receptor subtype expression: rat uterine artery (UA; AT(2) receptor-predominant) and aorta (AT(1) receptor-predominant), and investigated the receptor subtype(s) and intracellular pathways involved. 2. UA and aorta were treated with Ang II in the absence and presence of losartan (AT(1) antagonist; 0.1 microm), PD 123319 (AT(2) antagonist; 1 microm), NOLA (NOS inhibitor; 30 microm), and HOE 140 (B(2) antagonist; 0.1 microm), or in combination. 3. Ang II (10 nm) induced a 60% increase in UA cyclic GMP content; an effect that was augmented with PD 123319 and HOE 140 pretreatment, and abolished by cotreatment with losartan, as well as by NOLA. 4. In aorta, Ang II produced concentration-dependent increases in cyclic GMP levels. Unlike effects in UA, these responses were abolished by PD 123319 and by NOLA, whereas losartan and HOE 140 caused partial inhibition. 5. Thus, in rat UA, Ang II stimulates cyclic GMP production through AT(1) and, to a less extent, AT(2) receptors. In rat aorta, the Ang II-mediated increase in cyclic GMP production is predominantly AT(2) receptor-mediated. In both preparations, NO plays a critical role in mediating the effect of Ang II, whereas bradykinin has differential roles in the two vessels. In UA, B(2) receptor blockade may result in a compensatory increase in cyclic GMP production, whilst in aorta, bradykinin accounts for approximately half of the cyclic GMP produced in response to Ang II.

Angiotensin AT2 receptors: cardiovascular hope or hype?

British Journal of Pharmacology (2003) 140, 809–824. doi:10.1038/sj.bjp.0705448

Type-C natriuretic peptide prevents development of experimental atherosclerosis in rabbits

1. We investigated the effect of local administration of type-C natriuretic peptide (CNP) on the endothelial dysfunction and development of an atheroma-like neointima induced by a peri-arterial collar in rabbits. 2. Peri-arterial collars were placed on both common carotid arteries allowing local treatment of the collared region with either CNP (10 micromol/L) or saline. After 7 days, uncollared (control) and collared sections were taken from both arteries for pharmacological and morphological analysis. 3. Application of the collar markedly attenuated (P < 0.05) endothelium-dependent vasorelaxation induced by acetylcholine (ACh); inhibition of 5-hydroxytryptamine contraction was 80+/-5% in control sections compared with 44+/-4% in collared sections from the same arteries. Local infusion of CNP (10 micromol/L) into the collar restored ACh-induced vasorelaxation (74+/-3% from collared arteries + CNP vs 77+/-2% from control sections from the same arteries). 4. Type-C natriuretic peptide treatment also reduced (P < 0.05) intimal thickening compared with contralateral collared arteries (intima/media ratio 0.06+/-0.01 vs 0.16+/-0.01). 5. These results provide evidence that locally administered CNP is effective in preventing the endothelial dysfunction and development of a neointima in this model.