Intracellular Antioxidant Activity is Necessary to Modulate the Macrophage Response to Endotoxin

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Abstract
The tissue-fixed macrophage (Mφ) is a key cell in the coordination of the excessive systemic immunoinflammatory response underlying the adult respiratory distress syndrome (ARDS). Macrophage-generated reactive oxygen intermediates (ROIs) are involved in both tissue destruction via lipid peroxidation and in the activation of these inflammatory cells. It is unclear whether oxidant-induced activation involves an extracellular effect and membrane destabilization or occurs through intracellular alteration of the redox state and direct involvement as second messengers. In this study, we compare the differential effects of known intracellular vs. extracellular antioxidants on the Mφresponse to endotoxin. Rabbit alveolar Mφ were obtained by bronchoalveolar lavage and exposed to either the extracellular antioxidants [vitamin C (VC) (10–1000 μm), Trolox (100–1000 μM, superoxide dismutase (SOD) (10–500 μM))] or the intracellular antioxidants [N-acetylcysteine (NAC) (0.1–10 mM) or butylated hydroxyanisole (BHA) (10–200 μM)] for 1 h. Cells were subsequently stimulated with lipopolysaccharide at 10 ng/mL. After 18 h, supernatants were analyzed for tumor necrosis factor (TNF) and F2 isoprostane (F2ISP) production and cellular monolayers for procoagulant activity (PCA). A dose response inhibition of both TNF and PCA production was demonstrated after both NAC and BHA pretreatment but not with VC, Trolox, or SOD. In addition, northern blots revealed inhibition of TNF mRNA production by both NAC and BHA. F2ISP, a marker of membrane lipid peroxidation, was inhibited by BHA and Trolox but not NAC, VC, or SOD. In conclusion, antioxidants that are incorporated intracellularly are expected to be beneficial in the treatment of excessive inflammatory responses through the interruption of redox dependent signal transduction pathways and subsequent modulation of the Mφ proinflammatory response.