Abstract
2-Iodohexadecanal (2-IHDA) is a major thyroid iodolipid. It mimics the main regulatory effects of iodide on thyroid metabolism: inhibition of H2O2 production and of adenylyl cyclase. The biosynthesis of 2-IHDA and its metabolism have been investigated in cultured dog thyroid cells maintained in a differentiated state by forskolin. Incubation of these cells with [9,10-3H]hexadecan-1-ol or [9,10-3H]palmitic acid labeled several phospholipids, but [9, 10-3H]hexadecan-1-ol was selectively incorporated into plasmenylethanolamine. In the presence of an exogenous H2O2 generating system (glucose oxidase), iodide induced the production of [9,10-3H]2-IHDA from [9,10-3H]hexadecan-1-ol-labeled cells but not from [9,10-3H]palmitic acid-labeled cells. 2-IHDA was also generated during the lactoperoxidase-catalyzed iodination of brain and heart plasmalogens, and of ethyl hexadec-1-enyl ether, a synthetic vinyl 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-dependent way. The ratio of 2-IHDO/2-IHDA increased with H2O2 production and decreased as a function of iodide concentration. An aldehyde-reducing activity was detected in subcellular fractions of the horse thyroid. No formation of 2-iodohexadecanoic acid could be detected. Reduction into the biologically inactive 2-IHDO is thus a major metabolic pathway of 2-IHDA in dog thyrocytes.
Highlights
It has been known as early as 1955 that the iodinating capacity of the thyroid gland is not restricted to tyrosyl residues in thyroglobulin
In the presence of an exogenous H2O2 generating system, iodide induced the production of [9,10-3H]2-IHDA from [9,10-3H]hexadecan-1-ol-labeled cells but not from [9,10-3H]palmitic acidlabeled cells. 2-IHDA was generated during the lactoperoxidase-catalyzed iodination of brain and heart plasmalogens, and of ethyl hexadec-1-enyl ether, a synthetic vinyl ether-containing compound. 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 detected in these studies; it was formed later than 2-IHDA, and thyroid cells converted exogenous 2-IHDA into 2-IHDO in a time-dependent way
When dog thyrocytes in culture were incubated with radioiodide, they produced two iodolipids co-eluting in RP-HPLC with synthetic 2-IHDA (Fig. 2) and 2-iodooctadecanal
Summary
Materials—1H NMR spectra were recorded in CDCl3 on a Bruker WM 250 spectrometer and are reported in ppm from internal tetramethylsilane on the ␦ scale. Infrared spectra were taken with a Bruker IFS 25 instrument, and the samples were examined as deposited films on NaCl discs or in chloroform solution. Electron impact mass spectra were recorded on a VG Micromass 7070 or on a FISONS VG AUTOSPEC spectrometer. In both cases, peak intensities are expressed as percentages relative to the base peak. Thin layer chromatography analyses were performed on 0.25-mm POLYGRAM silica gel SILG/UV254 precoated plates (MACHEREY NAGEL). Column chromatographies were performed over silica gel (MN Kieselgel 0.04 – 0.063 mm) using flash technique or over florisil 0.15– 0.25 mm (Merck).
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
