The role of endothelin receptor antagonism in collar-induced intimal thickening and vascular reactivity changes in rabbits

Aggravated endothelial endocrine dysfunction and intimal thickening of renal artery in high-fat diet-induced obese pigs following renal denervation

Background

Renal denervation (RDN) targeting the sympathetic nerves in the renal arterial adventitia as a treatment of resistant hypertension can cause endothelial injury and vascular wall injury. This study aims to evaluate the risk of atherosclerosis induced by RDN in renal arteries.

Methods

A total of 15 minipigs were randomly assigned to 3 groups: (1) control group, (2) sham group, and (3) RDN group (n = 5 per group). All pigs were fed a high-fat diet (HFD) for 6 months after appropriate treatment. The degree of intimal thickening of renal artery and the conversion of endothelin 1 (ET-1) receptors were evaluated by histological staining. Western blot was used to assess the expression of nitric oxide (NO) synthesis signaling pathway, ET-1 and its receptors, NADPH oxidase 2 (NOX2) and 4-hydroxynonenal (4-HNE) proteins, and the activation of NF-kappa B (NF-κB).

Results

The histological staining results suggested that compared to the sham treatment, RDN led to significant intimal thickening and significantly promoted the production of endothelin B receptor (ET_BR) in vascular smooth muscle cells (VSMCs). Western blotting analysis indicated that RDN significantly suppressed the expression of AMPK/Akt/eNOS signaling pathway proteins, and decreased the production of NO, and increased the expression of endothelin system proteins including endothelin-1 (ET-1), endothelin converting enzyme 1 (ECE1), endothelin A receptor (ET_AR) and ET_BR; and upregulated the expression of NOX2 and 4-HNE proteins and enhanced the activation of NF-kappa B (NF-κB) when compared with the sham treatment (all p < 0.05). There were no significant differences between the control and sham groups (all p > 0.05).

Conclusions

RDN aggravated endothelial endocrine dysfunction and intimal thickening, and increased the risk of atherosclerosis in renal arteries of HFD-fed pigs.

The Effects of Calcium Channel Blockers are not Related to their Chemical Structure in the Collar Model of the Rabbit

Placing a silicone collar around the rabbit carotid artery induces intimal thickening, an early stage in atherosclerosis and restenosis. We investigated whether treatment with oral pranidipine, a new potent, long-lasting dihydropyridine calcium channel blocker (CCB), inhibited collar-induced intimal thickening in addition to the changes in vascular reactivity usually observed in this model. Pranidipine treatment did not inhibit collar-induced intimal thickening. Placing the collar around the carotid artery resulted in the characteristic changes in vascular reactivity, such as increased sensitivity to 5-hydroxytryptamine. Treatment with Nω-nitro-l-arginine (100 μM) and pranidipine, however, did not affect collar-induced changes in vascular reactivity. From results of this and previous studies, we conclude that pranidipine does not prevent collar-induced intimal thickening or collar-induced changes in vascular reactivity. Not all CCBs prevent collar-induced intimal thickening, suggesting that the effects of these agents are not related to their chemical structure and/or their calcium channel-blocking actions.

Selective endothelin A receptor antagonism with sitaxentan reduces neointimal lesion size in a mouse model of intraluminal injury

BACKGROUND AND PURPOSE

Endothelin (ET) receptor antagonism reduces neointimal lesion formation in animal models. This investigation addressed the hypothesis that the selective ETA receptor antagonist sitaxentan would be more effective than mixed ETA / B receptor antagonism at inhibiting neointimal proliferation in a mouse model of intraluminal injury.

EXPERIMENTAL APPROACH

Antagonism of ETA receptors by sitaxentan (1-100 nM) was assessed in femoral arteries isolated from adult, male C57Bl6 mice using isometric wire myography. Neointimal lesion development was induced by intraluminal injury in mice receiving sitaxentan (ETA antagonist; 15 mg·kg(-1) ·day(-1) ), A192621 (ETB antagonist; 30 mg·kg(-1) ·day(-1) ), the combination of both antagonists or vehicle. Treatment began 1 week before, and continued for 28 days after, surgery. Femoral arteries were then harvested for analysis of lesion size and composition.

KEY RESULTS

Sitaxentan produced a selective, concentration-dependent parallel rightward shift of ET-1-mediated contraction in isolated femoral arteries. Sitaxentan reduced neointimal lesion size, whereas ETB and combined ETA / B receptor antagonism did not. Macrophage and α-smooth muscle actin content were unaltered by ET receptor antagonism but sitaxentan reduced the amount of collagen in lesions.

CONCLUSIONS AND IMPLICATIONS

These results suggest that ETA receptor antagonism would be more effective than combined ETA /ETB receptor antagonism at reducing neointimal lesion formation.

Prolonged AMP-activated protein kinase induction impairs vascular functions

AMP-activated protein kinase (AMPK) is a regulator of cellular metabolism and is involved in the pathogenesis of several diseases, including type 2 diabetes and cardiovascular diseases. Data showing the effects of AMPK on vasculature are controversial. Therefore, the aim of this study was to determine the impact of prolonged AMPK activation on vascular functions. For this purpose we have examined the role of AMPK in endothelium-dependent and -independent relaxation and vascular contractions. For this, we incubated thoracic aortic rings, from rats, with AMPK activator 5-aminoimidazole-4-carboxamide-1-4-ribofuranoside (AICAR, 500 μmol/L or 2 mmol/L) in the presence or absence of AMPK inhibitor compound C (10 μmol/L). Next, cumulative dose–response curves to acetylcholine (ACh) (10−9−10−4 mol/L), nitroglycerine (NG) (10−9–3 × 10−5 mol/L), and noradrenaline (NA) (10−9−10−4 mol/L) were obtained. Endothelial nitric oxide synthase (eNOS) protein expression was determined. Our results show that endothelium-dependent relaxation was inhibited after AICAR treatment, and that this effect was reversed by AMPK inhibition. Moreover, AICAR enhanced the contractile response to NA and caused a decrease in eNOS protein expression. In conclusion, prolonged AMPK induction causes endothelial impairment, possibly via increased degradation and (or) reduced expression of eNOS.

MMP-2 and MMP-9 Alteration in Response to Collaring in Rabbits: The Effects of Endothelin Receptor Antagonism

Matrix metalloproteinases (MMPs), and, in particular, gelatinases (MMP-2 and MMP-9), have been implicated in vascular cell proliferation and/or migration, contributing to intimal thickening, an essential stage in the development of atherosclerosis and restenosis following balloon angioplasty. Endothelin, a strong chemoatractant and mitogen, has been shown to promote smooth muscle cell proliferation and migration by activating MMPs via endothelin-A (ETA) receptors. The positioning of a soft silicon collar around the left carotid artery in rabbits results in intimal thickening. In this study, we investigate the possible role of gelatinases and the effect of a nonselective ETA/ETB receptor antagonist, TAK-044 (5 mg/kg body weight/day, subcutaneously [sc]), on these enzymes. Our results demonstrated that both MMP-2 and MMP-9 activities increased in response to collaring in placebo group, while treatment with TAK-044 significantly suppressed both gelatinase activities and proMMP-2 levels, and inhibited intimal thickening in collared arteries. These results suggest that either enhanced MMP expression or endothelin receptor antagonism may be involved in the formation of intimal thickening in this model.

Neuroprotective effect of topically applied brimonidine tartrate 0.2% in endothelin-1-induced optic nerve ischaemia model

BACKGROUND

To investigate the neuroprotective effects of topically applied brimonidine tartrate 0.2% (BMD), an alpha(2)-receptor agonist, on the retinal ganglion cell (RGC) layer and inner nuclear layer (INL) of rabbit retina in endothelin-1 (ET-1)-induced optic nerve (ON) ischaemia model.

METHODS

Osmotic minipumps were surgically implanted into one eye of 16 New Zealand Albino rabbits to deliver ET-1 at the constant rate of 0.5 microL/h for 2 weeks. Eyes were divided into four groups. ET-1 was given with (Group 3) and without topical BMD therapy (Group 1). Groups 2 and 4 were taken as controls. Rabbits were sacrificed at day 14. Morphological alterations, total cell number and proportion of cells undergoing apoptosis in INL and RGC layer were assessed by histopathological analysis to determine the survival of the cells of the INL and RGC layer.

RESULTS

Endothelin-1 led to severe reduction of cells in both the RGC layer and INL in Group 1 (P < 0.05). In Group 3, the total cell number and the proportion of cells undergoing apoptosis in the RGC layer were comparable with the control group (Group 4), whereas the former was found to be higher and the latter was found to be lower than those recorded for Group 1. However, the total cell number in the INL was found to be lower in Group 3 compared with that of Group 4, despite topical BMD therapy (P < 0.05).

CONCLUSIONS

Topically applied BMD seems to be neuroprotective and antiapoptotic in the ET-1-induced ON ischaemia model, especially for RGCs. BMD might be used as an adjuvant agent for its neuroprotective effects in hypoxic-ischaemic conditions such as diabetic retinopathy, normotensive glaucoma and other retinal vascular occlusive conditions which require further investigations.