Inhibition of Protein Phosphorylation in Macrophages by Antioxidants

Abstract

It has been shown that a wide variety of antioxidants inhibits macrophage scavenger and polylactosamine receptor activities. The activity of macrophage scavenger receptors to take up oxidized low density liporprotein is also inhibited by protein kinase inhibitors but enhanced by protein phosphatase inhibitors. We studied whether the antioxidants including lipid-soluble phenolic, water-soluble phenolic, glutathione-related and ascorbic acid-related antioxidants were effective to inhibit protein phosphorylation of macrophages. Lower than 100 μM of α-tocopherol, probucol, propyl gallate, nordihydroguaiaretic acid, curcumin, quercetin and Trolox inhibited total protein phosphorylation of thioglycollate-induced mouse macrophages as assessed by H₃³²PO₄ incorporation. Lower than 1 mM of α-tocopherol, probucol, butylated hydroxytoluene, curcumin, catechin, epicatechin, epigallocatechin, epicatechin gallate, epigallocatechin gallate, glutathione, glutathione isopropyl ester, N-acetylcysteine, ascorbic acid, erythorbic acid and dehydroascorbic acid inhibited protein tyrosine phosphorylation of macrophages in the presence of vanadate, a protein tyrosine phosphatase inhibitor, as assessed by Western-blot analysis using anti-phosphotyrosine IgG monoclonal antibody. Most of the antioxidants inhibited protein tyrosine phosphorylation of epidermal growth factor (EGF) receptor of A431 cells in a cell-free system. Oxidative satus of macrophages examined by using dihydrorhodamine 123, and all the catechins reduced their oxidative status. Above results suggest that oxidative stress in macrophages maintain or enhance protein phosphorylation, and that antioxidants reduce protein phosphorylation and the receptor activities by reducing oxidative status.