Vascular alpha-1D-adrenoceptors are overexpressed in aorta of the aryl hydrocarbon receptor null mouse: role of increased angiotensin II

BMY 7378, a selective α1D-adrenoceptor antagonist, is a new angiotensin converting enzyme inhibitor: In silico, in vitro and in vivo approach

BMY 7378 is a multitarget drug primarily known for its selective antagonism of α1D-adrenoceptors (α1D-AR), exhibiting both hypotensive effects and the ability to prevent or reverse angiotensin II-induced vascular hypertrophy. Notably, BMY 7378 contains a phenylpiperazine moiety, a structural feature associated with angiotensin-converting enzyme (ACE) inhibition. This study aimed to investigate ACE inhibition as a potential pharmacological mechanism of BMY 7378. Using an in silico approach we predicted BMY 7378 interactions with the ACE active site, followed by in vitro activity assays. Additionally, ACE protein expression in the heart was analyzed following four weeks of BMY 7378 treatment in 7-8-month-old spontaneously hypertensive rats (SHR). All assays were benchmarked against captopril, a standard ACE inhibitor. In silico results showed that BMY 7378 binds to the ACE active site, though with reduced interaction with Zn701 (73.7 % compared to captopril), likely due to the pKa of its amino group. The inhibitory concentration 50 (IC50) for BMY 7378 was 136 μM, lower than other reported phenylpiperazine derivatives. Furthermore, BMY 7378 significantly increased ACE expression in the hearts of SHR, with an increase of 8.5-fold compared to captopril. In conclusion, BMY 7378 exhibits dual activity as an α1D-AR antagonist and an ACE inhibitor, making it a promising pharmacological tool for investigating and potentially treating hypertension and its associated cardiovascular complications.

Aryl-hydrocarbon receptor (AhR) activation contributes to high-fat diet-induced vascular dysfunction

BACKGROUND AND PURPOSE

Metabolic and vascular dysfunction are common features of obesity. Aryl hydrocarbons receptors (AhR) regulate lipid metabolism and vascular homeostasis, but whether vascular AhR are activated in obesity or if AhR have protective or harmful effects on vascular function in obesity are not known. Thus, our study addressed whether AhR activation contributes to obesity-associated vascular dysfunction and the mechanisms involved in the AhR effects.

EXPERIMENTAL APPROACH

Male AhRKO (AhR knockout) and WT (wild type) mice were fed either a control or a HF (high-fat) diet for ten weeks. Metabolic and inflammatory parameters were measured in serum and adipose tissue. Vascular reactivity (isometric force) was evaluated using a myography. eNOS and AhR protein expression was determined by Western blot; Cyp1A1 and eNOS gene expression by RT-PCR. Nitric oxide (NO) production was quantified by DAF fluorescence.

KEY RESULTS

HF diet increased serum total, HDL, and LDL cholesterol, as well as vascular AhR protein expression and proinflammatory cytokines in the adipose tissue. HF diet decreased endothelium-dependent vasodilation. AhR deletion protected mice from HF diet-induced dyslipidemia, weight gain, and inflammatory processes. HF diet-induced endothelial dysfunction was attenuated in AhRKO mice. Vessels from AhRKO mice exhibited a greater NO reserve. In cultured endothelial cells, lysophosphatidylcholine (LPC, a major component of LDL and oxLDL) reduced eNOS gene expression and NO production. Antagonism of AhR abrogated LPC effects on endothelial cells and LPC-induced decreased endothelium-dependent vasodilation.

CONCLUSION AND IMPLICATIONS

AhR deletion attenuates HF diet-induced dyslipidemia and vascular dysfunction by improving eNOS/NO signalling. Targeting AhR may prevent obesity-associated vascular dysfunction.

AHR canonical pathway: in vivo findings to support novel antihypertensive strategies

Essential hypertension (HTN) is a disease where genetic and environmental factors interact to produce a high prevalent set of almost indistinguishable phenotypes. The weak definition of what is under the umbrella of HTN is a consequence of the lack of knowledge on the players involved in environment-gene interaction and their impact on blood pressure (BP) and mechanisms. The disclosure of these mechanisms that sense and (mal)adapt to toxic-environmental stimuli might at least determine some phenotypes of essential HTN and will have important therapeutic implications. In the present manuscript, we looked closer to the environmental sensor aryl hydrocarbon receptor (AHR), a ligand-activated transcription factor involved in cardiovascular physiology, but better known by its involvement in biotransformation of xenobiotics through its canonical pathway. This review aims to disclose the contribution of the AHR-canonical pathway to HTN. For better mirror the complexity of the mechanisms involved in BP regulation, we privileged evidence from in vivo studies. Here we ascertained the level of available evidence and a comprehensive characterization of the AHR-related phenotype of HTN. We reviewed clinical and rodent studies on AHR-HTN genetic association and on AHR ligands and their impact on BP. We concluded that AHR is a druggable mechanistic linker of environmental exposure to HTN. We conclude that is worth to investigate the canonical pathway of AHR and the expression/polymorphisms of its related genes and/or other biomarkers (e.g. tryptophan-related ligands), in order to identify patients that may benefit from an AHR-centered antihypertensive treatment.

Chronic diabetes and hypertension impair the in vivo functional response to phenylephrine independent of α1-adrenoceptor expression

Diabetes and hypertension can coexist and exacerbate each other. In the early stages of diabetes, there is a decreased vascular response of the sympathetic nervous system (SNS), probably due to lower expression of α₁-adrenoceptors; however, it is unclear how diabetes in advanced stages changes the functionality of the SNS, especially the expression of α₁-adrenoceptors. Thus, the aim of this work was to analyse the functional response to phenylephrine, a selective α₁-adrenoceptor agonist, and the expression of α₁-adrenoceptors in chronic diabetes and hypertension. Male SHR and WKY rats aged 10-12 weeks were administered either streptozotocin (60 mg/kg i.p.) or a vehicle (control group). Eight weeks after administration, dose-response curves to phenylephrine were generated and the gene and protein expression of α₁-adrenoceptor subtypes (α_1A-, α_1B- and α_1D-adrenoceptors) in the heart and aorta were measured. The response to phenylephrine was diminished in hypertensive rats and in normotensive diabetic rats. The coexistence of both diabetes and hypertension produced an even smaller response to phenylephrine than that observed for each condition separately. In the heart and aorta of diabetic rats, no changes in α_1A-, α_1B- or α_1D-adrenoceptor mRNA expression were observed; however, protein expression was increased, mainly for the α_1D-adrenoceptor. Hypertension increased mRNA and protein expression of α₁-adrenoceptors in a tissue-dependent manner. The coexistence of both diabetes and hypertension produced differences in the regulation of mRNA and protein expression (increase or decrease) in both the heart and aorta. In conclusion, diabetes, hypertension and the coexistence of both pathologies impairs the in vivo response to phenylephrine. However, the differences in α_1A-, α_1B- and α_1D-adrenoceptor expression cannot explain the reduced response to the agonist. This should be further explored in future experiments.

The α1D-adrenoreceptor antagonist BMY 7378 reverses cardiac hypertrophy in spontaneously hypertensive rats

OBJECTIVE

The α1D-adrenoreceptor (α1D-AR) is involved in angiotensin II-induced vascular remodeling and hypertension. Whether α1D-AR plays a role in hypertension-associated cardiac hypertrophy is unclear. Here we investigated effects of BMY 7378, a selective α1D-AR antagonist, on cardiac status in aged spontaneously hypertensive rats (SHR).

METHODS

Male SHR were studied during the phase of developing hypertension (5 and 10 weeks old) and once hypertension was established (20 and 30 weeks old) to assess the evolution of cardiac hypertrophy. Age-matched WKY rats were studied as controls. Thirty-week-old SHR were treated for 4 weeks with BMY 7378 (10 mg/kg per day, o.a.), or captopril (angiotensin-converting enzyme inhibitor, 40 mg/kg per day, o.a.) (as a positive control). Blood pressure and cardiac function were measured in vivo, cardiac hypertrophy by histology, and α1D-AR protein expression by immunofluorescence.

RESULTS

By 30 weeks of age, SHR exhibited significant hypertension and cardiac hypertrophy. BMY 7378 and captopril decreased blood pressure and improved hemodynamic parameters and cardiac function in treated SHR vs. untreated SHR (P < 0.05). Histology showed increased cardiomyocyte size, fibrosis, and left ventricular hypertrophy in SHR hearts. BMY 7378 ameliorated fibrosis and cardiac hypertrophy, but had no effect on cardiomyocyte size in SHR. Effects of BMY 7378 were associated with increased α1D-AR protein expression in SHR.

CONCLUSION

Our data indicate that pharmacological antagonism of α1D-AR reduces blood pressure and associated cardiac hypertrophy in aged SHR. These findings suggest that the α1D-AR plays a pathophysiological role in the development of hypertension and cardiac target organ damage in SHR.

Pupo A. Updates in the function and regulation of α1 -adrenoceptors

α1 -Adrenoceptors are seven transmembrane domain GPCRs involved in numerous physiological functions controlled by the endogenous catecholamines, noradrenaline and adrenaline, and targeted by drugs useful in therapeutics. Three separate genes, whose products are named α1A -, α1B -, and α1D - adrenoceptors, encode these receptors. Although the existence of multiple α1 -adrenoceptors has been acknowledged for almost 25 years, the specific functions regulated by each subtype are still largely unknown. Despite the limited comprehension, the identification of a single class of subtype-selective ligands for the α1A - adrenoceptors, the so-called α-blockers for prostate dysfunction, has led to major improvement in therapeutics, demonstrating the need for continued efforts in the field. This review article surveys the tissue distribution of the three α1 -adrenoceptor subtypes in the cardiovascular system, genitourinary system, and CNS, highlighting the functions already identified as mediated by the predominant activation of specific subtypes. In addition, this review covers the recent advances in the understanding of the molecular mechanisms involved in the regulation of each of the α1 -adrenoceptor subtypes by phosphorylation and interaction with proteins involved in their desensitization and internalization. LINKED ARTICLES: This article is part of a themed section on Adrenoceptors-New Roles for Old Players. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.14/issuetoc.

Aryl Hydrocarbon Receptor: A New Player of Pathogenesis and Therapy in Cardiovascular Diseases

The aryl hydrocarbon receptor (AhR) is a DNA binding protein that acts as a nuclear receptor mediating xenobiotic metabolism and environmental responses. Owing to the evolutionary conservation of this gene and its widespread expression in the immune and circulatory systems, AhR has for many years been almost exclusively studied by the pharmacological/toxicological field for its role in contaminant toxicity. More recently, the functions of AhR in environmental adaption have been examined in the context of the occurrence, development, and therapy of cardiovascular diseases. Increasing evidence suggests that AhR is involved in maintaining homeostasis or in triggering pathogenesis by modulating the biological responses of critical cell types in the cardiovascular system. Here, we describe the structure, distribution, and ligands of AhR and the AhR signaling pathway and review the impact of AhR on cardiovascular physiology. We also discuss the potential contribution of AhR as a new potential factor in the targeted treatment of cardiovascular diseases.

Expression and localization of the AT1 and AT2 angiotensin II receptors and α1A and α1D adrenergic receptors in aorta of hypertensive and diabetic rats

Hypertension and diabetes are multifactorial diseases that frequently coexist and exacerbate each another. During the development of diabetes, the impairment of noradrenergic and renin-angiotensin systems has been reported in the response mediated by α₁-AR and AT₁ receptors. Although their participation in the development of cardiovascular complications is still controversial, some studies have found increased or diminished response to the vasoconstrictive effect of noradrenaline or angiotensin II in a time-dependent manner of diabetes. Thus, the aim of this work was to investigate the possible changes in the expression or localization of α₁-AR (α_1A and α_1D) and angiotensin II receptors (AT₁ and AT₂) in aorta of rats after 4 weeks of the onset of diabetes. In order to be able to examine the expression of these receptors, immunofluorescence procedure was performed in tunica intima and tunica media of histological sections of aorta. Fluorescence was detected by a confocal microscopy. Our results showed that the receptors are expressed in both tunics, where adrenergic receptors have a higher density in tunica intima and tunica media of SHR compared with WKY; meanwhile, the expression of angiotensin II receptors is not modified in both groups of rats. On the other hand, the results showed that diabetes produced an increase or a decrease in the expression of receptors that is not associated to a specific type of receptor, vascular region, or strain of rat. In conclusion, diabetes and hypertension modify the expression of the receptors in tunica intima and tunica media of aorta in a different way.

Effect of inter-renal aortic coarctation-induced hypertension on function and expression of vascular α(1A)- and α(1D)-adrenoceptors

We investigated the effect of inter-renal aortic coarctation on the function and expression of vascular α(1A)- and α(1D)-adrenoceptors and plasma angiotensin II (ATII) in rats. Male Wistar rats, either sham operated (SO), or with aortic coarctation for 7 (AC7) and 14 days (AC14) were used for agonist-induced pressor responses in vehicle (physiological saline)- and antagonist-treated anesthetized animals, immunoblot analysis (α(1A)- and α(1D)-adrenoceptor in aorta and caudal arteries), and immunoassay (plasma ATII). The α(1D)-adrenoceptor antagonist, BMY-7378 (BMY) blocked noradrenaline-induced responses in the order SO > AC7 ≫ AC14; in contrast, the α(1A)-adrenoceptor antagonist RS-100329 (RS), produced a marginal shift to the right of the dose-response curve to noradrenaline, along with a strong decrease of the maximum pressor effect in the order SO > AC7 = AC14. The potency of the α(1A)-adrenoceptor agonist A-61603 increased in rats with AC14, and responses were inhibited by RS in the order AC14 > AC7 > SO. In aorta, α(1D)-adrenoceptor protein increased in AC7 and decreased in AC14; α(1A)-adrenoreceptor protein increased in the caudal artery of AC7 and returned to control values in AC14. Plasma ATII increased in AC7 and AC14, compared with SO rats. These results suggest an early and direct relationship between ATII and α(1D)-adrenoreceptors in the development of hypertension in this experimental model.

The role of endogenous aryl hydrocarbon receptor signaling in cardiovascular physiology

The aryl hydrocarbon receptor (AHR) is an orphan nuclear receptor with a primary function of mediating xenobiotic metabolism through transcriptional activation of Phase I and Phase II drug-metabolizing enzymes. Although no high-affinity physiological activators of AHR have been discovered, the endogenous signaling of the AHR pathway is believed to play an important role in the development and function of the cardiovascular system, based on the observations on ahr gene-deficient mice. The AHR knockout mice develop cardiac hypertrophy, abnormal vascular structure in multiple organs and altered blood pressure depending on their host environment. In this review, the endogenous role of AHR in cardiovascular physiology, including heart function, vascular development and blood pressure regulation has been summarized and discussed.

Angiotensin II modifies the expression of α(1)-adrenoceptors in aorta smooth muscle cells of α(1D)-adrenoceptor knockout mice

1 The effect of angiotensin II (Ang II) on α(1A)-, α(1B)-, and a(1D)-adrenoceptors (α(1)-AR) expression was analyzed in aorta smooth muscle cells obtained from wild-type (WT) and knock out of α(1D)-AR (α(1D)-AR KO) mice. 2 The relative abundance of mRNA for the three α(1)-ARs was determined in WT and α(1D)-AR KO aortic smooth muscle cells. There were no significant differences between WT and α(1D)-AR KO cells. 3 As early as 1 h Ang II increased α(1B)-AR mRNA in WT cells ≈ 2 fold compared with control; in contrast, in α(1D)-AR KO cells the α(1B)-AR transcript was ≈ 50% of control. 4 Western blot assays showed that Ang II incremented protein content for α(1A)-AR, 86% and 107% in WT and α(1D)-AR KO cells, respectively. 5 Protein for α(1B)- and α(1D)-ARs did not change significantly with Ang II in both WT and a(1D)-AR KO cells. 6 The effect of Ang II on α(1B)-AR mRNA seems to be influenced by the absence of α(1D)-AR in aortic smooth muscle cells, which might be important to understand the interactions among α(1)-ARs.

Mechanisms involved in α1B-adrenoceptor desensitization

α(1B)-Adrenergic receptors mediate many of the actions of the natural catecholamines, adrenaline and noradrenaline. They belong to the seven transmembrane domains G protein-coupled receptor superfamily and exert their actions mainly through activation of Gq proteins and phosphoinositide turnover/calcium signaling. Many hormones and neurotransmitters are capable of inducing α(1B)-adrenergic receptor phosphorylation and desensitization; among them: adrenaline and noradrenaline, phorbol esters, endothelin-I, bradykinin, lysophosphatidic acid, insulin, EGF, PDGF, IGF-I, TGF-β, and estrogens. Key protein kinases for these effects are G protein coupled receptor kinases and protein kinase C. The lipid/protein kinase, phosphoinositide-3 kinase also appears to play a key role, acting upstream of protein kinase C. In addition to the agents employed for cells stimulation, we observed that paracrine/autocrine mediators also participate; these processes include EGF transactivation and sphingosine-1-phosphate production and action. The complex regulation of these receptors unlocks opportunities for therapeutic intervention.

An activated renin-angiotensin system maintains normal blood pressure in aryl hydrocarbon receptor heterozygous mice but not in null mice

It has been postulated that fetal vascular abnormalities in aryl hydrocarbon receptor null (ahr(-/-)) mice may alter cardiovascular homeostasis in adulthood. We tested the hypothesis that blood pressure regulation in adult heterozygous mice (ahr(+/-)) would be normal, compared to ahr(-/-) mice, since no vascular abnormalities have been reported in the heterozygote animals. Mean arterial blood pressure (MAP) was measured using radiotelemetry prior to and during treatment with inhibitors of the autonomic nervous system, nitric oxide synthase (NOS), angiotensin converting enzyme (ACE), or endothelin-1 A receptor (ET(A)). Also, indices of renin-angiotensin system (RAS) activation were measured. ahr(+/-) and ahr(-/-) mice were normotensive and hypotensive, respectively, compared to wild-type (ahr(+/+)) littermates. Responses of all genotypes to autonomic nervous system inhibition were normal. ahr(+/-) mice responded normally to NOS inhibition, while the responses of ahr(-/-) mice were significantly blunted. In contrast, ahr(+/-) mice were significantly more responsive to inhibition of ACE, an ET(A) antagonist, or both, while ahr(-/-) mice were significantly less responsive to ACE inhibition and more responsive to an ET(A) antagonist. ahr(+/-) mice also exhibited significant increases in plasma renin and ACE activity, plasma sodium, and urine osmolality, indicative of RAS activation. Thus, normotension in ahr(+/-) mice appears to be maintained by increased RAS and ET-1 signaling, while hypotension in ahr(-/-) mice may result from decreased RAS signaling. In conclusion, despite the lack of overt fetal vascular abnormalities in ahr(+/-) mice, the loss of a single ahr allele has a significant effect on blood pressure regulation.

The unexpected role for the aryl hydrocarbon receptor on susceptibility to experimental toxoplasmosis

The aryl hydrocarbon receptor (AhR) is part of a signaling system that is mainly triggered by xenobiotic agents. Increasing evidence suggests that AhR may regulate immunity to infections. To determine the role of AhR in the outcome of toxoplasmosis, we used AhR−/− and wild-type (WT) mice. Following an intraperitoneal infection with Toxoplasma gondii (T. gondii), AhR−/− mice succumbed significantly faster than WT mice and displayed greater liver damage as well as higher serum levels of tumor necrosis factor (TNF)-α, nitric oxide (NO), and IgE but lower IL-10 secretion. Interestingly, lower numbers of cysts were found in their brains. Increased mortality was associated with reduced expression of GATA-3, IL-10, and 5-LOX mRNA in spleen cells but higher expression of IFN-γ mRNA. Additionally, peritoneal exudate cells from AhR−/− mice produced higher levels of IL-12 and IFN-γ but lower TLR2 expression than WT mice. These findings suggest a role for AhR in limiting the inflammatory response during toxoplasmosis.

α(1D)-Adrenergic receptors constitutive activity and reduced expression at the plasma membrane

Adrenergic receptors are a heterogeneous family of the G protein-coupled receptors that mediate the actions of adrenaline and noradrenaline. Adrenergic receptors comprise three subfamilies (α(1), α(2), and β, with three members each) and the α(1D)-adrenergic receptor is one of the members of the α(1) subfamily with some interesting traits. The α(1D)-adrenergic receptor is difficult to express, seems predominantly located intracellularly, and exhibits constitutive activity. In this chapter, we will describe in detail the conditions and procedures used to determine changes in intracellular free calcium concentration which has been instrumental to define the constitutive activity of these receptors. Taking advantage of the fact that truncation of the first 79 amino acids of α(1D)-adrenergic receptors markedly increased their membrane expression, we were able to show that constitutive activity is present in receptors truncated at the amino and carboxyl termini, which indicates that such domains are dispensable for this action. Constitutive activity could be observed in cells expressing either the rat or human α(1D)-adrenergic receptor orthologs. Such constitutive activity has been observed in native rat arteries and we will discuss the possible functional implications that it might have in the regulation of blood pressure.