The role of reduced oxidative stress and iron in the alterations of polyamine metabolism in hypoxic bovine pulmonary artery smooth muscle cells (PASMC)

We have examined the hypothesis that the reduction of oxidative stress (OS) or cellular iron may mediate hypoxic effect on cellular polyamine regulatory mechanisms and content in PASMC. Confocal scanning laser microscopy showed a decrease in the intensity of 2,7-dichlorofluorescin fluorescence (DCF) in PASMC exposed to hypoxia for 24 hr as compared to normoxic cells, indicating reduction in OS. TBARS assay showed a reduction in lipid peroxidation in hypoxic cells. Treatment with the oxygen radical scavenger, DMTU, or the iron chelator, desferrioxamine (DX) for 24 hr also reduced DCF intensity as compared to control cells. Such as hypoxia, treatment with DX reduced ornithine decarboxylase mRNA content and activity as well as cellular putrescine and spermidine contents. Treatment with DMTU or N-acetylcysteine or inhibitors and uncouplers of oxidative phosphorylation (antimycin, dinitrophenol) also reduced ODC activity. However, different from hypoxia, both DX and DMTU reduced, rather than increased, ¹⁴C-spermidine uptake in PASMC. In contrast to hypoxia, DMTU treatment caused a reduction in the expression of the extracellular matrix protein, tenascin in the condition media of PASMC. Addition of iron reversed the effect of DX and hypoxia on ODC activity, 14C-spermidine uptake, cellular putrescine content and the reduction in DCF intensity. These data suggest that the reduction in oxidative stress or cellular iron may be the cellular mechanism which mediate the effect of hypoxia on polyamine metabolism.