PROTECTION BY SELENOPROTEIN-P IN HUMAN PLASMA AGAINST PEROXYNITRITE-MEDIATED OXIDATION AND NITRATION

In order to study functions of selenoprotein P in human plasma, its le vel was lowered via two techniques, chromatography on Sepharose-bound heparin, or immunoprecipitation; Western blot analysis showed that bot h techniques were effective at substantially lowering selenoprotein P levels in plasma. When peroxynitrite was infused to maintain a 0.9 mu M steady-state concentration, plasma made deficient in selenoprotein P diminished benzoate hydroxylation significantly less than control pla sma. Similar differences were found for protein 3-nitrotyrosine format ion, determined by Western blot analysis. Conversely, in a selenoprote in P-enriched plasma preparation obtained via heparin-Sepharose chroma tography, protection against benzoate hydroxylation was above controls . Likewise, a supernatant from control plasma that had been exposed to anti-selenoprotein P antibodies was less efficient in preventing oxid ation and nitration reactions of peroxynitrite than the supernatant fr om plasma exposed to a non-specific antibody (rabbit anti-sheep IgG). These data demonstrate a role of selenoprotein P in human plasma in th e defense against peroxynitrite.