Up-regulation of phospholipid hydroperoxide glutathione peroxidase in rat casein-induced polymorphonuclear neutrophils

Antioxidant enzymes play key roles in the protection of cells from oxidative damage. Little is known, however, about the expression of antioxidants and/or their roles in PMNs (polymorphonuclear leucocytes), which are thought to suffer from oxidative stress in an inflammation site. In the present paper, we report on the regulation of expression of PHGPx (phospholipid hydroperoxide glutathione peroxidase) and cGPx (cytosolic glutathione peroxidase) in rat PMNs in the inflammation site. PHGPx mRNA levels were much lower in casein-induced peritoneal and carrageenan-induced pleural PMNs just after their collection than in peripheral PMNs. cGPx mRNA was also reduced in the casein-induced PMNs, but not in carrageenan-induced PMNs. Both enzymes with decreased levels in the casein-induced PMNs were up-regulated during further 24 h cultivation in vitro and in vivo, with elevation of their protein levels and activities, and reduction of intracellular peroxides. Up-regulation of PHGPx mRNA was attenuated by cycloheximide, a protein synthesis inhibitor, and this effect was cancelled by culturing the cells in the conditioned medium of the cultured casein-induced PMNs. This latter effect was attenuated by pre-treatment with anti-GRO (growth-regulated oncogene) antibody. Recombinant rat GRO could also induce the up-regulation in the presence of cycloheximide, demonstrating that GRO may play an important role in the PHGPx up-regulation of casein-induced PMNs. Production of the lipid mediators leukotriene B₄ and 5-HETE (5-hydroxyeicosatetraenoic acid) was decreased in the cultured casein-induced PMNs exhibiting PHGPx up-regulation. The evidence obtained indicates that PHGPx activity in the activated PMNs would be related to the appearance of the intrinsic function of PMNs in the inflammatory site.