FREE RADICAL-MEDIATED LIPID-PEROXIDATION IN CELLS - OXIDIZABILITY IS A FUNCTION OF CELL LIPID BIS-ALLYLIC HYDROGEN CONTENT

Oxidizability of lipids in homogeneous solution varies linearly with t he extent of their unsaturation. In vitro cellular, as well as in vivo , studies Of oxidizability have generally relied upon chemical indicat ors of peroxidation such as thiobarbituric acid-reactive substances. T o examine the oxidizability of lipids in cells, we have measured oxyge n uptake and, using electron paramagnetic resonance spin trapping with alpha-(1-oxo-4-pyridyl)-N-tert-butylnitrone (POBN), the real time gen eration of lipid-derived free radicals. We have used our experimental in vitro cellular lipid modification model to examine the rate and ext ent of lipid peroxidation versus the degree of lipid unsaturation in L 1210 murine leukemia cells. Lipid peroxidation was stimulated using th e prooxidants iron, ascorbate, and the ether lipid compound -octadecyl -2-Omethyl-rac-glycero-3-phosphocholine. We did a total cellular lipid analysis to determine the number of lipid carbon-carbon double bonds contained in L1210 cells enriched with eight fatty acids of different degrees of unsaturation. We found in cellular lipids that (i) lipid ch ain length had no apparent effect on the rate or extent of radical for mation; (ii), the maximum amount of lipid radical generated increases with the total number of bis-allylic positions in the cellular lipids; and, most importantly, (iii) the rate of cellular lipid peroxidation increases exponentially with the number of bis-allylic positions. Our quantitative results clearly demonstrate, for the first time, that the number of bis-allylic positions contained in the cellular lipids of i ntact cells determines their susceptibility, i.e., oxidizability, to f ree radical-mediated peroxidative events.