Abstract
Acute respiratory distress syndrome (ARDS) is a life-threating lung condition resulting from a direct and indirect injury to the lungs [1, 2]. Pathophysiologically it is characterized by an acute alveolar damage, an increased permeability of the microvascular-barrier, leading to protein-rich pulmonary edema and subsequent impairment of arterial oxygenation and respiratory failure [1]. This study examined the role of extracellular ATP in recruiting inflammatory cells to the lung after induction of acute lung injury with lipopolysaccharide (LPS). However, the precise mechanism is poorly understood. Our objective was to investigate the functional role of the P2X7 receptor in the pathogenesis of acute respiratory distress syndrome (ARDS/ acute lung injury (ALI)) in vitro and in vivo. We show that intratracheally applied LPS causes an acute accumulation of ATP in the BALF (bronchoalveolar lavage) and lungs of mice. Prophylactic and therapeutic inhibition of P2X7R signalling by a specific antagonist and knock-out experiments was able to ameliorate the inflammatory response demonstrated by reduced ATP-levels, number of neutrophils and concentration of pro-inflammatory cytokine levels in the BALF. Experiments with chimeric mice showed that P2X7R expression on immune cells was responsible for the observed effect. Consistently, the inflammatory response is diminished only by a cell-type specific knockdown of P2X7 receptor on non-stationary immune cells. Since the results of BALF from patients with acute ARDS or pneumonia simulated the in vivo data after LPS exposure, the P2X7 receptor may be a new therapeutic target for treatment in acute respiratory distress syndrome (ARDS/ALI).
Highlights
According to the revised Berlin definition, the term acute respiratory distress syndrome (ARDS/acute lung injury (ALI)) describes an acutely developing and progressive hypoxic respiratory failure characterized by bilateral lung infiltrates on chest radiograph that cannot be explained by heart failure or a hypervolemic state [3,4,5]
Adenosine triphosphate (ATP) concentrations were markedly elevated in Bronchoalveolar lavage fluid (BALF) of patients with Acute respiratory distress syndrome (ARDS) compared with normal control subjects (Figure 1A)
To elucidate a possible role of Purinergic-type 2-receptor (P2R) signalling in the observed ATP and neutrophil accumulation in patients with ALI/ARDS we analysed ATP-Levels and cell counts in BALF in mice
Summary
According to the revised Berlin definition, the term acute respiratory distress syndrome (ARDS/ALI) describes an acutely developing and progressive hypoxic respiratory failure characterized by bilateral lung infiltrates on chest radiograph that cannot be explained by heart failure or a hypervolemic state [3,4,5] This definition includes the formerly separate concept of acute lung injury (ALI) within the ARDS entity. Though novel therapeutic strategies including extracorporal membrane oxygenation have led to improved survival, the mortality of the most severe ARDS cases remains unacceptably high around 50–60% [6, 7]. Besides being characterized by more severe inflammation, shock and metabolic acidosis, this hyperinflammatory phenotype is associated with worse clinical outcome including a higher mortality despite usual therapeutic strategies [9]
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