Tissue-derived proinflammatory effect of adenosine A2B receptor in lung ischemia-reperfusion injury

Abstract

Objective: Ischemia-reperfusion injury after lung transplantation remains a major source of morbidity and mortality. Adenosine receptors have been implicated in both pro- and anti-inflammatory roles in ischemia-reperfusion injury. This study tests the hypothesis that the adenosine A(2B) receptor exacerbates the proinflammatory response to lung ischemia-reperfusion injury.

Methods: An in vivo left lung hilar clamp model of ischemia-reperfusion was used in wild-type C57BL6 and adenosine A(2B) receptor knockout mice, and in chimeras created by bone marrow transplantation between wild-type and adenosine A(2B) receptor knockout mice. Mice underwent sham surgery or lung ischemia-reperfusion (1 hour ischemia and 2 hours reperfusion). At the end of reperfusion, lung function was assessed using an isolated buffer-perfused lung system. Lung inflammation was assessed by measuring proinflammatory cytokine levels in bronchoalveolar lavage fluid, and neutrophil infiltration was assessed via myeloperoxidase levels in lung tissue.

Results: Compared with wild-type mice, lungs of adenosine A(2B) receptor knockout mice were significantly protected after ischemia-reperfusion, as evidenced by significantly reduced pulmonary artery pressure, increased lung compliance, decreased myeloperoxidase, and reduced proinflammatory cytokine levels (tumor necrosis factor-α; interleukin-6; keratinocyte chemoattractant; regulated on activation, normal T-cell expressed and secreted; and monocyte chemotactic protein-1). Adenosine A(2B) receptor knockout → adenosine A(2B) receptor knockout (donor → recipient) and wild-type → adenosine A(2B) receptor knockout, but not adenosine A(2B) receptor knockout → wild-type, chimeras showed significantly improved lung function after ischemia-reperfusion.

Conclusions: These results suggest that the adenosine A(2B) receptor plays an important role in mediating lung inflammation after ischemia-reperfusion by stimulating cytokine production and neutrophil chemotaxis. The proinflammatory effects of adenosine A(2B) receptor seem to be derived by adenosine A(2B) receptor activation primarily on resident pulmonary cells and not bone marrow-derived cells. Adenosine A(2B) receptor may provide a therapeutic target for prevention of ischemia-reperfusion-related graft dysfunction in lung transplant recipients.

Figure 1

Pulmonary function after IR. Pulmonary artery pressure, pulmonary compliance and airway resistance were improved after IR in A_2BR^−/− mice compared to WT mice. *p<0.05 versus WT Sham, ^#p<0.05 versus WT IR (n=5/group).

Figure 2

Expression of cytokines in lung BAL fluid after IR. Expression of TNF-α, IL-6, KC (CXCL1), RANTES and MCP-1 were all significantly increased in WT mice after IR versus sham. Cytokine levels in A_2BR^−/− mice after IR were significantly attenuated compared to WT IR. *p<0.05 versus WT Sham, ^#p<0.05 versus WT IR (n=5/group).

Figure 3

Myeloperoxidase (MPO) levels in lung tissue were significantly elevated in WT mice after IR versus sham. MPO levels were significantly reduced in A_2BR^−/− mice after IR compared to WT IR. *p<0.05 versus WT Sham, ^#p<0.05 versus WT IR (n=5/group).

Figure 4

Pulmonary function after IR in bone marrow chimeras. All groups underwent lung IR. Pulmonary artery pressure and pulmonary compliance were significantly improved in A_2BR^−/−→A_2BR^−/− and WT→A_2BR^−/− chimeras compared to WT→WT chimeras (donor→recipient). *p<0.05 versus WT→WT, ^#p<0.05 versus A_2BR^−/−→WT (n=5/group).