A PHYSIOLOGICAL-ROLE OF PLASMALOGENS - TH E PROTECTION AGAINST OXIDATIVE STRESS AND IODINE EXCESS

Plasmalogens constitute a peculiar class of glycerophospholipids chara cterized by a unique structural feature:a vinyl ether group on the sn- 1 position of glycerol instead of the usual ester function. The specif ic role of plasmalogens, which are especially abundant in brain and he art, has remained elusive for a long time. The ability of reactive oxy gen species such as singlet oxygen to attack vinyl ether groups led to the hypothesis that plasmalogens have all antioxidant function. This is supported by the cleavage of plasmalogens during some forms of oxid ative stress and by the hypersensitivity to oxidants of mutant cells d eficient in plasmalogen synthesis. In a completely different research area, the main iodolipid of the thyroid gland was identified as 2-iodo hexadecanal. This compound is formed via the addition of a peroxidase- generated reactive form of iodine to the vinyl ether group of plasmalo gens, followed by cleavage of this group. As 2-iodohexadecanal mimicks the inhibitory, effects of iodine on adenylyl cyclase and H2O2 produc tion in the thyroid, it is likely to represent the mediator of these w ell-known autoregulatory actions which prevent the development of thyr otoxicosis following: exposure to excess iodine.