EPITHELIAL PERMEABILITY INDUCED BY NEUTROPHIL TRANSMIGRATION IS POTENTIATED BY HYPOXIA - ROLE OF INTRACELLULAR CAMP

Mucosal tissues, such as the lung and intestine, are primary targets f or ischemic damage. Under these conditions, neutrophil (polymorphonucl ear leukocyte; PMN) infiltration into the protective epithelium has be en implicated as a pathophysiologic mediator. Because PMN transepithel ial migration results in increased paracellular permeability, and beca use our previous data revealed that epithelial hypoxia enhances PMN tr ansmigration, we hypothesized that macromolecular permeability may be altered in epithelium exposed to hypoxia and reoxygenation (H/R) in th e presence of PMNs. Human intestinal epithelia (T84) were grown on per meable supports, exposed to cellular hypoxia (pO(2) 20 torr) for 0-72 hr, and examined for increases in PMN-evoked permeability by using sta ndard flux assays. Increasing epithelial hypoxia potentiated PMN-induc ed permeability of labeled paracellular tracers (size range 3-500 kD). Such increases were blocked by monoclonal antibody (mAb) to the PMN i ntegrin CD11b (82 +/- 1% decreased compared with control mAb) and were partially blocked by anti-CD47 mAb (51 +/- 1%). Assessment of barrier recovery revealed that monolayers exposed to H/R were significantly d iminished in their ability to reseal following PMN transmigration (rec overy of 36 +/- 6% in H/R vs. 94 +/- 2% in normoxic controls). Because intracellular cyclic AMP (cAMP) has been demonstrated to regulate epi thelial permeability, and because PMN-derived compound(s), (i.e., 5'-a denosine monophosphate; AMP) elevate epithelial cAMP, we examined the impact of hypoxia on epithelial cAMP responses. These experiments reve aled that hypoxic epithelia were diminished in their ability to genera te cAMP, and pharmacologic elevation (8-bromo-cAMP) of intracellular c AMP in hypoxic cells normalized both PMN-induced permeability changes and restoration of barrier function. These results support a role for PMN in increased intestinal permeability associated with reperfusion i njury and imply a substantial role for cAMP signaling in maintenance o f permeability during PMN transmigration. (C) 1998 Wiley-Liss, Inc.