Pivotal Role of the α2A-Adrenoceptor in Producing Inflammation and Organ Injury in a Rat Model of Sepsis

Abstract

BackgroundNorepinephrine (NE) modulates the responsiveness of macrophages to proinflammatory stimuli through the activation of adrenergic receptors (ARs). Being part of the stress response, early increases of NE in sepsis sustain adverse systemic inflammatory responses. The intestine is an important source of NE release in the early stage of cecal ligation and puncture (CLP)-induced sepsis in rats, which then stimulates TNF-α production in Kupffer cells (KCs) through the activation of the α2-AR. It is important to know which of the three α2-AR subtypes (i.e., α2A, α2B or α2C) is responsible for the upregulation of TNF-α production. The aim of this study was to determine the contribution of α2A-AR in this process.Methodology/Principal FindingsAdult male rats underwent CLP and KCs were isolated 2 h later. Gene expression of α2A-AR was determined. In additional experiments, cultured KCs were incubated with NE with or without BRL-44408 maleate, a specific α2A-AR antagonist, and intraportal infusion of NE for 2 h with or without BRL-44408 maleate was carried out in normal animals. Finally, the impact of α2A-AR activation by NE was investigated under inflammatory conditions (i.e., endotoxemia and CLP). Gene expression of the α2A-AR subtype was significantly upregulated after CLP. NE increased the release of TNF-α in cultured KCs, which was specifically inhibited by the α2A-AR antagonist BRL-44408. Equally, intraportal NE infusion increased TNF-α gene expression in KCs and plasma TNF-α which was also abrogated by co-administration of BRL-44408. NE also potentiated LPS-induced TNF-α release via the α2A-AR in vitro and in vivo. This potentiation of TNF-α release by NE was mediated through the α2A-AR coupled Gαi protein and the activation of the p38 MAP kinase. Treatment of septic animals with BRL-44408 suppressed TNF-α, prevented multiple organ injury and significantly improved survival from 45% to 75%.Conclusions/SignificanceOur novel finding is that hyperresponsiveness to α2-AR stimulation observed in sepsis is primarily due to an increase in α2A-AR expression in KCs. This appears to be in part responsible for the increased proinflammatory response and ensuing organ injury in sepsis. These findings provide important feasibility information for further developing the α2A-AR antagonist as a new therapy for sepsis.

The inhibitory effect of ghrelin on sepsis-induced inflammation is mediated by the MAPK phosphatase-1

“…These studies demonstrated that gut is the major source of the increased circulating NE in sepsis. We have also shown that NE induced hepatocellular dysfunction in early sepsis is mediated by the activation of ·2-adrenoceptors (9) and recently we reported that the · 2a form of the receptor mRNA expression is increased in Kupffer cells in response to sepsis (10). In addition, Spengler et al (11) demonstrated that stimulation of ·2 adrenoceptors augments the production of macrophage derived TNF-·.…”

“…The small intestine was exposed and a branch of the superior mesenteric vein was cannulated with a PE-10 catheter. NE at 20 μM in normal saline containing 0.1% ascorbic acid or vehicle (0.1% ascorbic acid in normal saline) was infused into the portal vein at a rate of 13 μl/min for 2 h using Harvard pump as described previously (10). Liver tissues were collected, flash frozen in liquid nitrogen and stored at -80˚C.…”

“…Kupffer cells were isolated from normal rats as previously described (10,21). Briefly, rats were anesthetized with isoflurane inhalation, following midline incision, the portal vein was cannulated and the inferior vena cava was severed.…”

Ventilator-Induced Lung Injury: Mechanisms and Future Therapeutic Interventions

“…Supporting this hypothesis, Miksa et al showed in experimental models of sepsis that an 2A -adrenocepter antagonist reduced plasma levels of aspartate aminotransferase (AST), alanine aminotransferase (ALT) and creatinine, indicative for attenuated liver and kidney injury (Miksa et al, 2009). Moreover, these authors showed that inhibition of 2A -adrenocepter activation significantly improved survival in septic animals from 45 to 75% (Miksa et al, 2009). Another pathway of neuroimmune regulation is considered to be involved in the pathogenesis of VILI and MOF as well.…”

Neural Reflex Control of Inflammation During Sepsis Syndromes

“…Activation of 2-AR results in an increase in cAMP concentrations, which can modulate cytokine expression, i.e., decreasing TNF- and increasing IL-8 (Elenkov & Chrousos, 1999). However, recently was described that 2A-AR stimulation increases TNF- gene expression in Kupffer cells and plasma TNF- during sepsis (Miksa et al, 2009). Thus, through AR stimulation, locally released NE, or circulating catecholamines, affect lymphocyte traffic, circulation, and proliferation, and modulate cytokine production and the functional activity of different lymphoid cells (Elenkov et al, 2000), just as they control heart rate and other vital functions.…”