Selenium determination in human plasma lipoprotein fractions by mass spectrometry analysis

Previous observations have suggested that lipoproteins may be involved in t he transport of selenium in humans. To further investigate this question, s elenium was measured in lipoprotein fractions isolated from plasma of healt hy adults. A gas chromatographic-mass spectrometric method using the isotop ic dilution technique was developed to ensure a reliable measurement of low amounts of selenium. About 3% of total plasma selenium was bound to lipopr oteins, mainly to the LDL fraction. After solvent fractionation of LDL and HDL, the major part of the selenium was recovered in the protein extract, s uggesting that it may be incorporated in apolipoproteins. The exact form of Se is not yet clearly established. Considering the different Se compounds found in proteins, it is postulated to be selenomethionine, and/or particip ating in a selenium-sulphur bond. This could explain why the amount of sele nium bound to apolipoprotein B in LDL was about twice that which could be e xpected from a random substitution of selenomethionine for methionine. (C) 2000 Elsevier Science S.A. All rights reserved.