Preparation of fatty acid cholesterol ester hydroperoxides by photosensitized oxidation

Cholesteryl nitrolinoleate, a nitrated lipid present in human blood plasma and lipoproteins

Nitric oxide (*NO) and *NO-derived reactive species (e.g., peroxynitrite anion, nitrogen dioxide radical) react with lipids containing unsaturated fatty acids to generate nitrated species. In the present work, we synthesized, characterized, and detected a nitrated derivative of cholesteryl linoleate (Ch18:2) in human blood plasma and lipoproteins using a high-pressure liquid chromatography coupled to electrospray ionization tandem mass spectrometry method. It was synthesized by a reaction of Ch18:2 with nitronium tetrafluoroborate, yielding a species with m/z 711, which is characteristic of the cholesteryl nitrolinoleate (Ch18:2NO2) ammonium adduct. The presence of the nitro group was confirmed by using [15N]nitrite, which gave a product with m/z 712, with the same chromatographic and spectrometric characteristics of those of m/z 711. Furthermore, a C-NO2 structure was also demonstrated in Ch18:2NO2 by infrared analysis (Vmax 1549, 1374 cm-1). A stable product with m/z of 711, showing the same chromatographic characteristics and fragmentation pattern as those of synthesized standard, was found in human blood plasma and lipoproteins of normolipidemic subjects. The presence of this novel nitrogen-containing lipid product in human plasma and lipoproteins could represent a potential indicator of the oxidative/nitrative roles that *NO or its metabolites play during in vivo lipid oxidation, generating a compensatory mechanism of protection in vascular disease.

HeLp, a heme lipoprotein from the hemolymph of the cattle tick, Boophilus microplus

The main protein of the hemolymph of the cattle tick Boophilus microplus has been isolated and shown to be a heme lipoprotein (HeLp). HeLp has an apparent molecular mass of 354,000 and contains two apoproteins (103 and 92 kDa) found in equal amounts. HeLp presents a pI of 5.8 and a density of 1.28 g/ml and contains 33% lipids, containing both neutral lipids and phospholipids, and 3% of sugars. A remarkable feature of HeLp is the abundance of cholesterol ester (35% of total lipids), a lipid not previously reported in invertebrate lipoproteins. Western blot analysis showed HeLp in hemolymph from adult females and males, but not in eggs. Although HeLp contains 2 heme molecules, it is capable of binding 6 additional molecules of heme. Boophilus feeds large amount of blood, and we recently showed that this tick is unable to perform de novo synthesis of heme (Braz, G. R. C., Coelho, H. S. L., Masuda, H., and Oliveira, P. L. (1999) Curr. Biol. 9, 703-706). Injection of tick females with (55)Fe-labeled heme-HeLp indicated that this protein transports heme from hemolymph to tissues. HeLp is suggested to be an essential adaptation to the loss of the heme synthesis pathway.