The effect of pH on hypochlorite-induced peroxidation of phospholipid liposomes

In order to make a further sight into mechanism of hypochlorite (HOCl/OCl-)-induced lipid peroxidation we investigated the effect of pH of incubation medium on accumulation of lipid peroxidation products and also on kinetics of HOCl/OCl- decay and disappearance of double bonds during incubation of egg yolk phosphatidylcholine liposomes with hypochlorite. On the one hand, the increase in pH values led to decrease of the rate of a reaction of hypochlorite with double bonds of phosphatidylcholine acyl chains and, on the other hand, to increase in accumulation of primary (conjugated dienes and lipid peroxides) and secondary (TBA-reactive substances) products of lipid peroxidation. The present data and our previous results allow to suppose that besides the electrophilic addition of HOCl to double bonds another reaction of HOCl/OCl- with some lipid intermediate occurs that leads to initiation of free radical processes of lipid peroxidation. This reaction increases in velocity as pH rises at least in the range from 6,50 to 8,15. The role of intermediate may be performed by organic hydroperoxides which are known to be present in some proportion in lipid phase in vivo.