α-Tocopherol Inhibits the Respiratory Burst in Human Monocytes

• Published in: The Journal of biological chemistry Vol. 273; no. 49; p. 32801
• Main Authors: Odile Cachia, Jamel El Benna, Eric Pedruzzi, Bernard Descomps, Marie-Anne Gougerot-Pocidalo, Claude-Louis Leger
• Format: Journal Article
• Language: English
• Published: American Society for Biochemistry and Molecular Biology 04.12.1998
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.273.49.32801

Vitamin E (α-tocopherol), one of the most important natural antioxidants, is assumed to be beneficial in the prevention of cardiovascular diseases. α-Tocopherol exhibits acyl-peroxyl-radical scavenger properties and exerts cell-mediated actions in the hemovascular compartment, such as inhibition of superoxide anion (O⨪ 2 ) production by leukocytes. The aim of this study was to examine the mechanism underlying the inhibitory effect of α-tocopherol on O⨪ 2 production by human monocytes. In activated monocytes O⨪ 2 is produced by the NADPH-oxidase enzyme complex. The oxidase activation elicited by phorbol myristate acetate (PMA) requires membrane translocation of several cytosolic factors. We found that in human PMA-stimulated adherent monocytes, α-tocopherol (but not β-tocopherol) inhibited O⨪ 2 production in intact cells but had no effect on a membrane preparation containing activated NADPH-oxidase, suggesting that α-tocopherol impairs the assembly process of the enzyme complex. We showed that translocation and phosphorylation of the cytosolic factor p47 phox were reduced in monocytes preincubated with α-tocopherol. We verified that the tryptic phosphopeptide map of monocyte p47 phox was similar to that of neutrophil p47 phox , indicating that several serine residues were phosphorylated. Peptides whose phosphorylation is dependent on protein kinase C (PKC) were phosphorylated to a lesser degree when p47 phox was immunoprecipitated from α-tocopherol-treated monocytes. In vitro , the activity of PKC from monocytes was inhibited by α-tocopherol in a specific manner compared with that of β-tocopherol or Trolox®. Membrane translocation of PKC was not affected. These results show that α-tocopherol inhibits O⨪ 2 production by human adherent monocytes by impairing the assembly of the NADPH-oxidase and suggest that the inhibition of phosphorylation and translocation of the cytosolic factor p47 phox results from a decrease in PKC activity.