Cellular glutathione peroxidase as a predominant scavenger of hydroperoxyeicosatetraenoic acids in rabbit alveolar macrophages

The cytosol of rabbit lung alveolar macrophages contains a high amount of peroxidase, which reduces 5-hydroperoxyeicosatetraenoic acid (5-HPETE) to 5-hydroxyeicosatetraenoic acid (5-HETE) in the presence of glutathione. This peroxidase was purified 69-fold to homogeneity with overall recovery of activity of 18.5%. The molecular mass of the enzyme was approximately 80 kDa by gel filtration, and emerged as a single band at 23.1 kDa under reducing condition by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The amino-terminal sequence of the purified peroxidase was completely identical to the sequence deduced from cellular glutathione peroxidase (cGPx) gene of rabbit liver. No other activity that reduces 5-HPETE to 5-HETE was observed during purification. These results suggest that cGPx plays an important role in metabolism of lipid hydroperoxides, especially HPETE, in lung alveolar macrophages.

Suppression of leukotriene formation in RBL-2H3 cells that overexpressed phospholipid hydroperoxide glutathione peroxidase

The overexpression of phospholipid hydroperoxide glutathione peroxidase (PHGPx) by RBL-2H3 cells was used as the basis for an investigation of the effects of PHGPx on the formation of leukotrienes. The rates of production of leukotriene C4 (LTC4) and leukotriene B4 (LTB4) in cells that overexpressed PHGPx were 8 times lower than those in a control line of cells. The reduction in rates of production of leukotrienes apparently resulted from the increase in the PHGPx activity since control rates of formation of leukotrienes could be achieved in PHGPx-overexpressing cells upon inhibition of PHGPx activity by diethyl malate. The conversion of radioactively labeled arachidonic acid to intermediates in the lipoxygenase pathway, such as 5-hydroxyeicosatetraenoic acid (5-HETE), LTC4, and LTB4, was strongly inhibited in PHGPx-overexpressing cells that had been prelabeled with [14C]arachidonic acid. PHGPx apparently inactivated the 5-lipoxygenase that catalyzed the conversion of arachidonic acid to 5-hydroperoxyeicosatetraenoic acid (5-HPETE) since 5-HPETE is a common precursor of 5-HETE, LTC4, and LTB4. The rates of formation of LTC4 and LTB4 in PHGPx-overexpressing cells returned to control rates upon the addition of a small amount of 12-HPETE. Flow cytometric analysis revealed that the rapid burst of formation of lipid hydroperoxides induced by A23187 was suppressed in PHGPx-overexpressing cells as compared with the control lines of cells. Subcellular fractionation analysis showed that the amount of PHGPx associated with nuclear fractions from PHGPx-overexpressing cells was 3.5 times higher than that from the control line of cells. These results indicate that PHGPx might be involved in inactivation of 5-lipoxygenase via reductions in levels of the fatty acid hydroperoxides that are required for the full activation of 5-lipoxygenase. Thus, in addition to its role as an antioxidant enzyme, PHGPx appears to have a novel function as a modulator of the production of leukotrienes.