HYPEROXIA INCREASES PROTEIN MASS OF 5-LIPOXYGENASE AND ITS ACTIVATING PROTEIN, FLAP, AND LEUKOTRIENE B 4 OUTPUT IN NEWBORN RAT LUNGS

Abstract

In this study, the authors examined in newborn rat lung tissues the release of leukotriene B 4 (LTB 4) from tissue explants in vitro, the protein expression of the LT-synthesizing enzyme, 5-lipoxygenase (5-LO), and its activating protein (FLAP), and the effects of in vivo hyperoxic exposure (>95% O 2) on these parameters. Basal LTB 4 output increased from 0.98 ng/mgDNA/30 min at day 1 to 3.3 ng/mgDNA/30 min at day 28 (P <. 05). Exposure of rat pups to >95% O 2 from days 1 to 7 and 60% O 2 from days 7 to 28 stimulated a 1.6-fold (P <. 05) increase in LTB 4 output, compared to normoxic pups (to 1.6 ng/mgDNA/30 min) by day 1 and on day 7. The calcium ionophore, A23187, caused an increase in LTB 4 output from both exposure groups, but LTB 4 output was consistently greater (P <. 05) from hyperoxia-exposed pups. Western immunoblotting of lung tissue showed that 5-LO and FLAP protein mass increased (P <. 05) from days 4 to 14. Hyperoxia exposure increased the mass of both proteins (P <. 05). Immunohistochemistry localized 5-LO and FLAP mainly to alveolar macrophages on day 14, but some staining was evident in parenchymal tissue. These data show that hyperoxia increases LTB 4 output, as well as protein levels of 5-LO and FLAP, in newborn rat lungs during early postnatal life. Elevated LTB 4 may contribute to the etiology of newborn lung disease.