Lung ischemia reperfusion injury (LIRI) is a morbid complication following thoracic organ transplantation. The alveolar macrophage (AM) orchestrates early reperfusion events ultimately resulting in florid lung injury via an early proinflammatory burst of TNF and IL-1 which primes surrounding cells such as type 2 pneumocytes (T2P). These studies characterized the effects of AM secretory products on T2P undergoing hypoxia and reoxygenation (H&R).
Primary cultures of AM underwent 2 hrs hypoxia (FIO2 0.5%) followed by up to 4 hrs reoxygenation. AM experimental media was harvested and used for pretreatment of T2P. T2P were pretreated with either unstimulated macrophage media (negative control), or media from macrophages undergoing 2 hrs hypoxia and 15 minutes (HR15) of reoxygenation, or 2 hrs hypoxia and 4 hrs (HR4) reoxygenation. T2P were subsequently exposed to 2 hrs hypoxia and up to 4 hrs reoxygenation. Media was again harvested to quantitate T2P chemokine secretion by ELISA, while EMSA assessed transcription factor transactivation.
ELISAs demonstrated that CINC (p<0.05) and MCP-1 (p<0.05) secretion, but not MIP-1, was significantly increased after 2 hrs hypoxia and 4 hrs reoxygenation in isolated T2P. There was a synergistic increase in expression of CINC and MCP-1 after treatment of T2P with HR15 (p<0.05) and HR4 (p<0.05) macrophage media compared with negative controls. MIP-1, which was not dramatically secreted from isolated T2P, was significantly increased after AM media pretreatment. NFkB transactivation in T2P was increased in the HR15 and HR4 pretreated groups.
These studies demonstrated that secretion of the potent chemokines CINC and MCP-1 is increased in T2P undergoing H&R, and that this expression is synergistically augmented after pretreatment with AM media undergoing previous H&R. Interestingly, MIP-1 secretion from the T2P was significant only after treatment with HR AM media (at levels above that present in isolated AM media). The AM primes alveolar epithelial cells, augmenting their eventual response to oxidative stress.
Nebulized anti-inflammatory strategies targeting AM in thoracic organ donors (during organ procurement) may have dramatic protective effects against LIRI.
A.S. Farivar, None.