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BE Britigan, TL Roeder and DM Shasby
Research Service, VA Medical Center, Iowa City, IA.
Spin trapping, a sensitive and specific means of detecting free radicals,
is optimally performed on cell suspensions. This makes it unsuitable for
the study of adherent endothelial cell monolayers because disrupting the
monolayer to induce a cell suspension could introduce confounding factors.
This problem was eliminated through the use of endothelial cells that were
grown to confluence on microcarrier beads. Using the spin trap
5,5-dimethyl-1-pyrroline-N-oxide (DMPO), the nature of free radical species
generated by suspensions of microcarrier bead adherent porcine pulmonary
endothelial cells under various forms of oxidant stress was examined.
Exposure of these endothelial cells to paraquat resulted in the spin
trapping of superoxide (.O2-). Endothelial cell incubation in the presence
of either bolus or continuous fluxes of hydrogen peroxide (H2O2) yielded
spin trap evidence of hydroxyl radical formation, which was preventable by
pretreating the cells with deferoxamine. Chromium oxalate which eliminates
extracellular electron paramagnetic resonance spectrometry (EPR) signals,
prevented the detection of DMPO spin adducts generated by paraquat but not
H2O2-treated endothelial cells. When endothelial cells were coincubated
with PMA-stimulated monocytes evidence of both .O2- and hydroxyl radical
production was detected, whereas with PMA- stimulated neutrophils only .O2-
production could be confirmed. Neutrophil elastase, cathepsin G, and the
combination of PMA and A23187 have previously been suggested to induce
endothelial cell oxy-radical generation. However, exposure of endothelial
cells to each of these agents did not yield DMPO spin adducts or
cyanide-insensitive endothelial cell O2 consumption. These data indicate
that endothelial cell exposure: to paraquat induces extracellular .O2-
formation; to H2O2 leads to intracellular hydroxyl radical production; and
to elastase, cathepsin G, or A23187/PMA does not appear to cause oxy-
radical generation.
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