HYPOCHLORITE-INDUCED PEROXIDATION OF EGG-YOLK PHOSPHATIDYLCHOLINE IS MEDIATED BY HYDROPEROXIDES

Using a chemiluminescent method, the consumption of HOCl/OCl- was inve stigated during interaction with liposomes prepared from dimyristoyolp hosphatidylcholine (DMPC) or egg yolk phosphatidylcholine (EYPC). The concentration of HOCl/OCl- decreased with time in the suspension of EY PC that contain unsaturated lipids and did not change in DMPC Liposome suspensions. HOCl/OCl- was consumed more rapidly in peroxidized EYPC. The amount of double bonds was lowered by 40% in peroxidized liposome s and decreased by approximately one-third under the action of HOCl/OC l- in both native and peroxidized EYPC samples. Second-order rate cons tants for the interaction between HOCl and phospholipid double bonds o f 0.50 M(-1)s(-1) were calculated for native EYPC on basis of the cons umption of HOCl/OCl- or fr om the decrease in concentration of double bonds. in peroxidized EYPC this reaction constant was similar as deter mined following changes in double bonds. It is concluded that the cons umption of HOCl/OCl-increased in peroxidized liposomes due to addition al reactions with lipid peroxidation products. tert-Butyl hydroperoxid e and cumene hydroperoxide, or organic peroxides or epoxides (cis-9,10 -epoxystearic acid; cholesterol-5 alpha,6 alpha-epoxide; trans-2,3-epo xy-butane; cis-2,3-epoxy-butane) were incorporated into liposomes and investigated in respect to their ability (1) to increase the consumpti on of HOCl/OCl- in DMPC liposomes, (2) to generate a non-enhanced chem iluminescence with HOCl/OCl- and (3) to evoke an accumulation of Lipid peroxidation products (TEARS) in EYPC Liposomes in the absence and pr esence of NaOCl. None of peroxides or epoxides tested showed any effec t on the consumption of HOCl/OCl- or the generation of chemiluminescen ce. Nor increase of TEARS both in the absence or presence of HOCl/OCl- . In contrast, tert-butyl hydroperoxide and cumene hydroperoxide incre ased the consumption of HOCl/OCl in DMPC Liposomes and mediated a high er accumulation of TEARS in EYPC Liposomes in the presence of HOCl/OCL - over the control. These data suggest that lipid peroxidation in EYPC can be initiated by the reaction of HOCl/OCL- with organic hydroperox ides.