Exposure of endothelial cells to oxidized low-density lipoprotein (oxLDL) leads to diverse cellular effects, including induction of the intracellular antioxidant GSH. It is not known whether lipid-or protein-derived oxidation products cause GSH induction and whether this involves increased activity of the key enzyme in its synthesis, glutamate—cysteine ligase (GCL). Furthermore, the effect of oxLDL exposure on the cell's ability to combat oxidative stress has not been previously examined. In the present study we found that, in bovine aortic endothelial cells, LDL or 1-palmitoyl-2-arachidonyl phosphatidylcholine oxidized by different reactive oxygen and nitrogen species induced GSH synthesis. However, prevention of GSH synthesis during exposure to oxLDL caused extensive cell death. The mediator causing GSH induction was shown to be a polar lipid and resulted in the increased activity of GCL as well as increased protein levels of the regulatory subunit of GCL. Pretreatment with both oxLDL and the polar lipid subfraction of the oxLDL protected cells against the toxicity of 2,3-dimethoxynaphthoquinone (DMNQ), a superoxide- and H2O2-forming compound. The potential of a low level of lipid peroxidation products to initiate cytoprotective pathways are discussed.
Abbreviations used: oxLDL, oxidized low-density lipoprotein; nLDL, native LDL; GCL, glutamate—cysteine ligase (γ-glutamylcysteine synthetase, EC 184.108.40.206); PAPC, 1-palmitoyl-2-arachidonyl phosphatidylcholine; DMNQ, 2,3-dimethoxynaphthoquinone; MPO, myeloperoxidase; GCLC, GCL catalytic subunit; SIN-1, 3-morpholinosyndnonimine; BHT, butylated hydroxytoluene; DTPA, diethylenetriaminepenta-acetic acid; REM, relative electrophoretic mobility; POPC, 1-palmitoyl-2-oleoyl phosphatidylcholine; LOOH, lipid hydroperoxide; BAEC, bovine aortic endothelial cells; GCLM, GCL modifier subunit; lysoPC, lysophosphatidylcholine; 13-HPODE, (13S)-hydroperoxyoctadecadienoic acid; HNE, 4-hydroxynonenal; EpRE, electrophile-responsive element; HO-1, haem oxygenase-1; PGJs, J-series of prostaglandins; LDH, lactate dehydrogenase; LPS, lipopolysaccharide; BSO, buthionine sulphoximine; FOX, ferrous-ion-mediated oxidation of Xylenol Orange.
These authors made an equal contribution to this paper.