Effect of candesartan, a type 1 angiotensin II receptor antagonist, on bronchial hyper-responsiveness to methacholine in patients with bronchial asthma

Targeting the renin angiotensin system for respiratory diseases

Renin-angiotensin system (RAS) plays an indispensable role in regulating blood pressure through its effects on fluid and electrolyte balance. As an aside, cumulative evidence from experimental to clinical studies supports the notion that dysregulation of RAS contributes to the pro-inflammatory, pro-oxidative, and pro-fibrotic processes that occur in pulmonary diseases like asthma, chronic obstructive pulmonary disease (COPD), idiopathic pulmonary fibrosis (IPF), and acute lung injury (ALI). Pharmacological intervention of the various RAS components can be a novel therapeutic strategy for the treatment of these respiratory diseases. In this chapter, we first give a recent update on the RAS, and then compile, review, and analyse recent reports on targeting RAS components as treatments for respiratory diseases. Inhibition of the pro-inflammatory renin, angiotensin-converting enzyme (ACE), angiotensin (Ang) II, and Ang II type 1 receptor (AT1R) axis, and activation of the protective ACE2, AT2R, Ang (1-7), and Mas receptor axis have demonstrated varying degrees of efficacies in experimental respiratory disease models or in human trials. The newly identified alamandine/Mas-related G-protein-coupled receptor member D pathway has shown some therapeutic promise as well. However, our understanding of the RAS ligand-and-receptor interactions is still inconclusive, and the modes of action and signaling cascade mediating the newly identified RAS receptors remain to be better characterized. Clinical data are obviously lacking behind the promising pre-clinical findings of certain well-established molecules targeting at different pathways of the RAS in respiratory diseases. Translational human studies should be the focus for RAS drug development in lung diseases in the next decade.

Hidden Comorbidities in Asthma: A Perspective for a Personalized Approach

Bronchial asthma is the most frequent inflammatory non-communicable condition affecting the airways worldwide. It is commonly associated with concomitant conditions, which substantially contribute to its burden, whether they involve the lung or other districts. The present review aims at providing an overview of the recent acquisitions in terms of asthma concomitant systemic conditions, besides the commonly known respiratory comorbidities. The most recent research has highlighted a number of pathobiological interactions between asthma and other organs in the view of a shared immunological background underling different diseases. A bi-univocal relationship between asthma and common conditions, including cardiovascular, metabolic or neurodegenerative diseases, as well as rare disorders such as sickle cell disease, α1-Antitrypsin deficiency and immunologic conditions with hyper-eosinophilia, should be considered and explored, in terms of diagnostic work-up and long-term assessment of asthma patients. The relevance of that acquisition is of utmost importance in the management of asthma patients and paves the way to a new approach in the light of a personalized medicine perspective, besides targeted therapies.

Nonrespiratory Comorbidities in Asthma

Asthma is a chronic heterogeneous airway disease. Common comorbid conditions are often disproportionately present in severe asthma. Optimal care of patients with asthma requires the recognition and treatment of these comorbid conditions. This review outlines the pathophysiological mechanisms between nonrespiratory comorbid conditions and asthma and their effect on asthma outcomes. They include: type 2 diabetes mellitus, hypertension, atherosclerotic cardiovascular disease, adrenal and thyroid gland diseases, pregnancy, osteoporosis, adverse effects from medications, and mental health disorders. Studies indicate how poor glycemic control of type 2 diabetes mellitus is associated with not only greater health care utilization but poorer asthma outcomes. Also, a large health care claims database indicates that a substantial proportion of pregnant women have uncontrolled asthma and are prescribed suboptimal controller therapy. Additional data about these nonrespiratory comorbidities and medications known to benefit both nonrespiratory comorbidities and asthma are necessary.

ASTHMA: ROLE OF THE ANGIOTENSIN-(1-7)/MAS PATHWAY IN PATHOPHYSIOLOGY AND THERAPY

The incidence of asthma is a global health problem, requiring studies aimed at developing new treatments to improve clinical management, thereby reducing personal and economic burdens on the health system. Therefore, the discovery of mediators that promote anti-inflammatory and pro-resolutive events are highly desirable to improve lung function and quality of life in asthmatic patients. In that regard, experimental studies have shown that the Angiotensin-(1-7)/Mas receptor of the renin-angiotensin system (RAS) is a potential candidate for the treatment of asthma. Therefore, we reviewed findings related to the function of the Angiotensin-(1-7)/Mas pathway in regulating the processes associated with inflammation and exacerbations in asthma, including leukocyte influx, fibrogenesis, pulmonary dysfunction and resolution of inflammation. Thus, knowledge of the role of the Angiotensin-(1-7)/Mas can help pave the way for the development of new treatments for this disease with high morbidity and mortality through new experimental and clinical trials.

Suppressive effects of type I angiotensin receptor antagonists, candesartan and irbesartan on allergic asthma

The effects of candesartan and irbesartan, antagonists of the type I angiotensin II receptor, were investigated on allergic asthma. The antigen-induced degranulation was measured by evaluating β-hexosaminidase activity in vitro. Additionally, a murine ovalbumin-induced allergic asthma model was used to test the in vivo efficacy. It was observed that while candesartan inhibited the antigen-induced degranulation in rat RBL-2H3 mast cells, irbesartan did not. Administration of candesartan and irbesartan decreased the number of immune cells in the bronchoalveolar lavage fluid and reduced the expression of Th2 (IL-4, IL-5, and IL-13) and Th1 cytokines (IL-2 and IFN-γ) in the lung tissues of mice with ovalbumin-induced allergic asthma. Histological studies revealed that both antagonists reduced inflammation and mucin production in the lungs. Therefore, these findings provide evidence that candesartan and irbesartan could have potential applications as anti-allergic agents.

Lung

In the present chapter, we review and summarize current advances on the role of angiotensin-(1-7) [Ang-(1-7)] in the pathophysiology of main lung diseases: pulmonary hypertension (PH), acute respiratory distress syndrome (ARDS), asthma, and pulmonary fibrosis. Understanding the involvement of renin angiotensin system (RAS) in pulmonary inflammation may open new therapeutic possibilities for the treatment of respiratory diseases. Studies to date showed that Ang-(1-7) presents anti-inflammatory, antifibrotic activities and reduces pulmonary remodeling. These actions support the development of new pharmacological therapies based on the increase in Ang-(1-7) in the lungs to improve the treatment of inflammatory diseases.

Angiotensin-(1-7) attenuates airway remodelling and hyperresponsiveness in a model of chronic allergic lung inflammation

BACKGROUND AND PURPOSE

A long-term imbalance between pro- and anti-inflammatory mediators leads to airway remodelling, which is strongly correlated to most of the symptoms, severity and progression of chronic lung inflammation. The Angiotensin-(1-7) [Ang-(1-7)]/Mas receptor axis of the renin-angiotensin system is associated with attenuation of acute and chronic inflammatory processes. In this study, we investigated the effects of Ang-(1-7) treatment in a model of chronic allergic lung inflammation.

EXPERIMENTAL APPROACH

Mice were sensitized to ovalbumin (OVA; 4 injections over 42 days, 14 days apart) and were challenged three times per week (days 21-46). These mice received Ang-(1-7) (1 μg·h(-1) , s.c.) by osmotic mini-pumps, for the last 28 days. Histology and morphometric analysis were performed in left lung and right ventricle. Airway responsiveness to methacholine, analysis of Ang-(1-7) levels (RIA), collagen I and III (qRT-PCR), ERK1/2 and JNK (Western blotting), IgE (elisa), cytokines and chemokines (elisa multiplex), and immunohistochemistry for Mas receptors were performed.

KEY RESULTS

Infusion of Ang-(1-7) in OVA-sensitized and challenged mice decreased inflammatory cell infiltration and collagen deposition in the airways and lung parenchyma, and prevented bronchial hyperresponsiveness. These effects were accompanied by decreased IgE and ERK1/2 phosphorylation, and decreased pro-inflammatory cytokines. Mas receptors were detected in the epithelium and bronchial smooth muscle, suggesting a site in the lung for the beneficial actions of Ang-(1-7).

CONCLUSIONS AND IMPLICATIONS

Ang-(1-7) exerted beneficial attenuation of three major features of chronic asthma: lung inflammation, airway remodelling and hyperresponsiveness. Our results support an important protective role of Ang-(1-7) in lung inflammation.

Vasoactive peptides upregulate mRNA expression and secretion of vascular endothelial growth factor in human airway smooth muscle cells

Airway remodeling and associated angiogenesis are documented features of asthma, of which the molecular mechanisms are not fully understood. Angiotensin (ANG)II and endothelin (ET)-1 are potent vasoconstricting circulatory hormones implicated in asthma. We investigated the effects of ANG II and ET-1 on human airway smooth muscle (ASM) cells proliferation and growth and examined the mRNA expression and release of the angiogenic peptide, vascular endothelial growth factor (VEGF). Serum deprived (48 h) human ASM cells were incubated with ANG II (100 nM) or ET-1 (10 nM) for 30 min, 1, 2, 4, 8, 16, and 24 h and the endogenous synthesis of VEGF was examined in relation to control cells receiving serum free culture medium. ET-1 induced time dependent DNA biosynthesis as determined by [3H]-thymidine incorporation assay. Using northern blot hybridization, we detected two mRNA species of 3.9 and 1.7 kb encoding VEGF in the cultured smooth muscle cells. Both ANG II and ET-1 induced the mRNA expression (two- to threefold) and secretion (1.8- to 2.8-fold) of VEGF reaching maximal levels between 4-8 h of incubation. Induced expression and release of VEGF declined after 8 h of ANG II incubation while levels remained elevated in the case of ET-1. The conditioned medium derived from ET-1-treated ASM cells induced [3H]-thymidine incorporation and cell number in porcine pulmonary artery endothelial as well as human umbilical vein endothelial cells. Moreover, the VEGF tyrosine kinase receptor inhibitor blocked the conditioned medium induced mitogenesis in endothelial cells. Our results suggest a potential role for ANG II and ET-1 in ASM cell growth and upregulation of VEGF that may participate in endothelial cell proliferation via paracrine mechanisms and thus causing pathological angiogenesis and vascular remodelling seen during asthma.

The involvement of type 1a angiotensin II receptors in the regulation of airway inflammation in a murine model of allergic asthma

BACKGROUND

There has been increasing evidence suggesting the involvement of angiotensin II (Ang II) and type 1 Ang II receptors (AT1) in the pathogenesis of bronchial asthma. However, whether such an involvement would promote or suppress the pathophysiology of asthma is controversial.

OBJECTIVE

The aim of this study was to investigate the role of AT1 in the development of allergic airway inflammation.

METHODS

Agtr1a+/+ [wild-type C57BL/6 mice (WT)] and Agtr1a-/- mice [AT1a knockout mice (AT1aKO)] with a genetic background of C57BL/6 were systemically sensitized to ovalbumin (OVA), followed by OVA inhalation. OVA-specific IgE in serum obtained just before the inhalation was measured. Bronchoalveolar lavage (BAL) fluid and lung tissues were obtained at various time-points. Cell numbers and differentiation, and cytokine contents in BAL fluids were determined. Peribronchial accumulation of eosinophils and mucus inclusions in the bronchial epithelium were evaluated in lung tissues stained histochemically. Cell numbers and differentiation in BAL fluids of the mice were also determined after lipopolysaccharide (LPS) inhalation.

RESULTS

The levels of OVA-specific IgE in AT1aKO were significantly higher than those in WT. The numbers of total cell, eosinophils and lymphocytes in BAL fluids 7 days after OVA inhalation in AT1aKO were significantly higher than those in WT. Airway inflammation in bronchial tissues in terms of eosinophil accumulation and mucus hypersecretion in AT1aKO was also stronger than in WT. The contents of IL-4, IL-5 and IL-13, but not IFN-gamma, in BAL fluids of AT1aKO were significantly higher than those of WT. In contrast, neutrophil accumulation in BAL fluids after LPS inhalation was significantly higher in WT than in AT1aKO.

CONCLUSION

AT1a might be involved in the negative regulation of the development of allergic airway inflammation through polarizing the T-helper (Th) balance towards Th1 predominance. Therefore, it would be of clinical importance to investigate the effects of long-term administration of AT1 blockers on the Th1/Th2 balance in hypertensive patients with bronchial asthma.

Candesartan

Candesartan cilexetil is the prodrug of candesartan, an angiotensin II receptor antagonist. Candesartan binds selectively and non-competitively to the angiotensin II receptor type 1, thus preventing the actions of angiotensin II. Clinical trials have demonstrated its efficacy at a dose range of 2 to 32 mg once daily in hypertension of all grades, heart failure, in reducing urinary albumin excretion in diabetes mellitus and in coexisting hypertension and renal failure. Pharmacokinetic properties of candesartan cilexetil in elderly patients are not significantly different from those in younger individuals. Hepatic impairment does not change pharmacokinetics of candesartan cilexetil at doses up to 12 mg/day. No dose adjustment is necessary in patients with mild or moderate renal impairment. Tolerability of candesartan cilexetil is not much different from that of placebo. All adverse events are usually of mild to moderate severity and not dose-related. The most common adverse events were headache, upper respiratory tract infection, back pain, and dizziness. The incidence of these adverse effects, as well as of cough, was similar in patients treated with candesartan cilexetil or placebo. The incidence of adverse events in long-term trials was not different from that in short-term trials. Tolerability of candesartan cilexetil does not differ with either age or gender.

Protective Effects of Angiotensin II Interruption: Evidence for Antiinflammatory Actions

Angiotensin II, the major effector molecule produced from the renin-angiotensin-aldosterone axis, is a vasoconstrictor contributing to hypertension. Evidence indicates, however, that angiotensin II also is a potent proinflammatory mediator with growth and remodeling effects. In vitro and in vivo studies have shown that angiotensin II blockade significantly reduces concentrations of proinflammatory mediators and oxidative stress products in numerous inflammatory models. Interruption of angiotensin II activity with angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers has been beneficial for patients with inflammatory diseases. Much of this benefit occurs independent of the antihypertensive effect of angiotensin II interruption, suggesting a distinctive protective mechanism. Angiotensin II receptor blockers may represent a novel class of antiinflammatory drugs with indications far beyond cardiovascular diseases.