BIOSYNTHESIS AND METABOLISM OF 2-IODOHEXADECANAL IN CULTURED DOG THYROID-CELLS

2-Iodohexadecanal (2-IHDA) is a major thyroid iodolipid. It mimics the main regulatory effects of iodide on thyroid metabolism: inhibition o f H2O2 production and of adenylyl cyclase, The biosynthesis of 2-IHDA and its metabolism have been investigated in cultured dog thyroid cell s maintained in a differentiated state by forskolin, Incubation of the se cells with [9,10-H-3]hexadecan-1-ol or [9,10-H-3]palmitic acid labe led several phospholipids, but [9,10-H-3]hexadecan-1-ol was selectivel y incorporated into plasmenylethanolamine. In the presence of an exoge nous H2O2 generating system (glucose oxidase), iodide induced the prod uction of [9,10-H-3]2-IHDA from [9,10-H-3]hexadecan-1-ol-labeled cells but not from [9,10-H-3]palmitic acid-labeled cells, 2-IHDA was also g enerated during the lactoperoxidase-catalyzed iodination of brain and heart plasmalogens, and of ethyl hexadec-1-enyl ether, a synthetic vin yl ether-containing compound, Taken together, these results show that thyroid 2-IHDA is derived from plasmenylethanolamine via an attack of reactive iodine on the vinyl ether group. 2-Iodohexadecan-1-ol (2-IHDO ) was also detected in these studies; it was formed later than 2-IHDA, and thyroid cells converted exogenous 2-IHDA into 2-IHDO in a time-de pendent way, The ratio of 2-IHDO/2-IHDA increased with H2O2 production and decreased as a function of iodide concentration, An aldehyde-redu cing activity was detected in subcellular fractions of the horse thyro id No formation of 2-iodohexadecanoic acid could be detected, Reductio n into the biologically inactive 2-IHDO is thus a major metabolic path way of 2-IHDA in dog thyrocytes.