Lysophosphatidylcholine-induced cellular injury in cultured fibroblasts involves oxidative events

Abstract

Lysophosphatidylcholine (lysoPC), formed during LDL oxidation and located within atherosclerotic plaques, induces numerous cellular responses, but via unknown mechanisms. Cellular events involved in sublethal lysoPC-induced injury were examined because these are relevant to mechanisms by which lysoPC alters cell behavior. LysoPC evoked transient membrane permeabilization in fibroblasts within 10 min. Cells underwent reversible rounding within 2 h, returning 3 h later to grossly normal appearance and a normal response to growth stimulation. We asked whether this sublethal permeabilization resulted from physical perturbation of the plasma membrane or if it required cellular events. LysoPC induced leakage of fluorescent dye from unilamellar phospholipid vesicles, suggesting physical membrane perturbation was a significant contributor. To characterize this further we increased the cholesterol content of cells and vesicles to stabilize membranes, and found decreased lysoPC-induced permeabilization in both cell and cell-free systems as cholesterol levels increased. Interestingly, vitamin E, a known antioxidant, blunted lysoPC-induced permeabilization and morphological changes in cells. Thus, lysoPC appeared to cause an unexpected oxidant stress-dependent enhancement of cell injury. To confirm this, several structurally distinct antioxidants, including N, N'-diphenyl-1,4-phenylenediamine, Desferal, Tiron, and 4-hydroxy TEMPO, were applied and these also were inhibitory. Oxidant stress was observed by a lysoPC-induced increase in fluorescence of 5- and 6-carboxy-2',7'-dichlorodihydrofluorescein diacetate, an intracellular marker of reactive oxygen species. Lysophosphatidylethanolamine (lysoPE) caused qualitatively similar morphological changes to cells and induced permeabilization, but injury by lysoPE was not inhibited by antioxidants. These data suggest that generation of intracellular reactive oxygen species follows lysoPC-induced plasma membrane destabilization and that this lysoPC-specific oxidant stress enhances cell injury. This intracellular oxidant stress in response to lysoPC may be an integral part of the multiple influences lysoPC has on gene expression and cell function.