Alamandine attenuates sepsis-associated cardiac dysfunction via inhibiting MAPKs signaling pathways

Abstract

Sepsis-induced myocardial dysfunction represents a major cause of death. Alamandine is an important biologically active peptide. The present study evaluated whether alamandine improves cardiac dysfunction, inflammation, and apoptosis, and affects the signaling pathways involved in these events. Experiments were carried out in mice treated with lipopolysaccharide (LPS) or alamandine, and in neonatal rat cardiomyocytes. Alamandine increased the ejection fraction and fractional shortening, both of which were decreased upon LPS infusion in mice. LPS and alamandine reduced blood pressure, and increased the expression of inducible nitric oxide synthase (iNOS) and endothelial NOS (eNOS) in the heart in mice. The LPS-induced decrease in α-myosin heavy chain (MHC) and β-MHC, and increase in S100 calcium binding protein A8 (S100A8) and S100A9, were reversed by alamandine pre-treatment. Alamandine pre-treatment prevented LPS-induced myocardial inflammation, apoptosis and autophagy. LPS increased p-ERK, p-JNK, and p-p38 levels, which were inhibited by alamandine. Dibutyryl cyclic AMP (db-cAMP) increased p-ERK, p-JNK, and p-p38 levels, and reversed the inhibitory effects of alamandine on the LPS-induced increase in p-ERK, p-JNK, and p-p38. Moreover, db-cAMP reduced the expression of α-MHC and β-MHC in cardiomyocytes, and reversed the almandine-induced attenuation of the LPS-induced decrease in α-MHC and β-MHC. These results indicate that alamandine attenuates LPS-induced cardiac dysfunction, resulting in increased cardiac contractility, and reduced inflammation, autophagy, and apoptosis. Furthermore, alamandine attenuates sepsis induced by LPS via inhibiting the mitogen-activated protein kinases (MAPKs) signaling pathways.

Introduction

Sepsis, a common cause of death in intensive care units, is a systemic response to infection that causes a potentially damaging inflammatory response [1,2]. Cardiac dysfunction and impaired contractility develop during sepsis in both humans and rodents [3,4]. Sepsis increases caspase activity [5], and myocardial apoptosis contributes to sepsis-induced cardiac dysfunction [6]. Increased production of tumor necrosis factor (TNF)-α and interleukin (IL)-1β also contributes to cardiac dysfunction during sepsis [7,8].

Alamandine, a novel component of the renin-angiotensin system (RAS), is formed by decarboxylation of angiotensin (Ang) 1–7 or hydrolysis of Ang A [9]. Recent studies have demonstrated a strong association between the RAS and the inflammatory process [[10], [11], [12]]. Ang II induces a pro-inflammatory environment characterized by the production of inflammatory chemokines and cytokines [13]. RAS also plays an important role in sepsis. Meta-analysis confirmed that the angiotensin-converting enzyme I/D polymorphism is associated with sepsis risk [14]. Sepsis causes a significant increase in the levels of pro-inflammatory cytokines (TNF-α, IL-1β, and IL-6), whereas administration of the renin inhibitor raliskiren decreased the levels of these cytokines [15]. However, it is unknown whether alamandine is involved in sepsis induced by LPS.

Alamandine induces AMPK/nitric oxide (NO) signaling to counterregulate Ang II induced hypertrophy [16]. The signaling pathways associated with mitogen-activated protein kinases (MAPKs), nuclear factor kappa B (NF-κB), and p53 are important signal transduction pathways that mediate sepsis [17,18]. It has been reported that the phosphorylation levels of extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), p38, and inhibitor of kappa B alpha (IκBα) levels were increase in response to LPS treatment in cardiomyocytes [19]. However, whether alamandine attenuates the sepsis induced by LPS via inhibition of MAPKs pathways remains unclear. The present study was designed to determine the role of alamandine in the regulation of sepsis induced by LPS and the signaling pathways involved in this process.