Myeloperoxidase-derived HOCl targets tissue-and lipoprotein-associated plasmalogens to generate ␣-chlorinated fatty aldehydes, including 2-chlorohexadecanal. Under physiological conditions, 2-chlorohexadecanal is oxidized to 2-chlorohexadecanoic acid (2-ClHA). This study demonstrates the catabolism of 2-ClHA by -oxidation and subsequent ␤-oxidation from the -end. Mass spectrometric analyses revealed that 2-ClHA is -oxidized in the presence of liver microsomes with initial -hydroxylation of 2-ClHA. Subsequent oxidation steps were examined in a human hepatocellular cell line (HepG2). Three different ␣-chlorinated dicarboxylic acids, 2-chlorohexadecane-(1,16)-dioic acid, 2-chlorotetradecane-(1,14)-dioic acid, and 2-chloroadipic acid (2-ClAdA), were identified. Levels of 2-chlorohexadecane-(1,16)-dioic acid, 2-chlorotetradecane-(1,14)-dioic acid, and 2-ClAdA produced by HepG2 cells were dependent on the concentration of 2-ClHA and the incubation time. Synthetic stable isotope-labeled 2-ClHA was used to demonstrate a precursorproduct relationship between 2-ClHA and the ␣-chlorinated dicarboxylic acids. We also report the identification of endogenous 2-ClAdA in human and rat urine and elevations in stable isotopelabeled urinary 2-ClAdA in rats subjected to intraperitoneal administration of stable isotope-labeled 2-ClHA. Furthermore, urinary 2-ClAdA and plasma 2-ClHA levels are increased in LPStreated rats. Taken together, these data show that 2-ClHA is -oxidized to generate ␣-chlorinated dicarboxylic acids, which include ␣-chloroadipic acid that is excreted in the urine.

This article is available online at http://www.jlr.org phospholipids and cholesterol esters, both playing structural functions without being related to energy metabolism ( 3 ). As elements of the nervous system, ocular tissues, such as the optic nerve and the neural retina, display similar composition ( 5-7 ). In mammalian cell membranes, phospholipids also comprise ether-linked species containing either an alkyl-ether or a vinyl-ether bond at the sn-1 position of glycerol ( 3,5,8 ). The vinyl-ether-linked species include a carbon-carbon double bond next to the ether linkage in comparison to the ether forms. Vinyl-ether bearing phospholipids are termed as plasmalogens and are found in numerous mammalian cell types, including the retina ( 9-11 ), mostly in the forms of phosphatidylcholines (PC) and phosphatidylethanolamines (PE). In plasmalogens, the sn-2 position of glycerol backbone is usually occupied by PUFAs, whereas the sn-1 position is linked to vinyl-ether moieties with 16 to 18 carbon. The biological functions of plasmalogens are still unclear, although it has been reported that the presence of plasmalogens in membrane affects its fl uidity and fusion ( 8 ). Due to the high PUFA content of plasmalogens, they are also considered as reservoirs of PUFAs, which can be used by a plasmalogen-specifi c phospholipase A2 (iPLA2) ( 12, 13 ) to liberate free fatty acids in order to be further metabolized into second messenger molecules, such as prostaglandins and thromboxanes ( 14, 15 ). The alteration of cellular plasmalogen content has been associated with several human disorders and diseases, such as rhizomelic chondrodysplasia punctata Type 2, Alzheimer's disease, Down syndrome, Zellweger syndrome, and primary open-angle glaucoma ( 8,(16)(17)(18).Although PC and PE are the major phospholipid classes containing plasmalogens, vinyl-ether bearing phospholipids can also appear in the form of phosphatidylserine (PS). The nervous system is an organ with the second highest concentration of lipids, only exceeded by adipose tissue. Nervous tissues contain about 50 to 60% of their dry weight as lipids, and approximately 35 to 40% of these lipids are polyunsaturated fatty acids (PUFAs) ( 1-4 ). The majority of these lipids appear as PUFA-rich-membrane

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Negative ion mass spectrometric techniques for compounds having good ionization properties, such as pentafluorobenzyl derivatives, are believed to be more sensitive than positive ion methods. In this study we develop a technique of quantification of long-chain aldehydes by analysis of their pentafluorobenzyl oxime derivatives utilizing gas chromatography-mass spectrometry in the negative ion chemical ionization mode. We establish that separation of plasmalogens prior to pentafluorobenzyl derivatization is essential and achieve this separation over a silica column. We further demonstrate the sensitivity of this method and utilize this technique to identify increases in hexadecanal and octadecanal in 3-aminotriazole treated human neutrophils.