Formation of highly reactive A-ring and J-ring isoprostane-like compounds (A4/J4-neuroprostanes) in vivo from docosahexaenoic acid.
Free radical-initiated oxidant injury and lipid peroxidation have been implicated in a number of neural disorders. Docosahexaenoic acid is the most abundant unsaturated fatty acid in the central nervous system. We have shown previously that this 22-carbon fatty acid can yield, upon oxidation, isoprostane-like compounds termed neuroprostanes, with E/D-type prostane rings (E(4)/D(4)-neuroprostanes). Eicosanoids with E/D-type prostane rings are unstable and dehydrate to cyclopentenone-containing compounds possessing A-type and J-type prostane rings, respectively. We thus explored whether cyclopentenone neuroprostanes (A(4)/J(4)-neuroprostanes) are formed from the dehydration of E(4)/D(4)-neuroprostanes. Indeed, oxidation of docosahexaenoic acid in vitro increased levels of putative A(4)/J(4)-neuroprostanes 64-fold from 88 +/- 43 to 5463 +/- 2579 ng/mg docosahexaenoic acid. Chemical approaches and liquid chromatography/electrospray ionization tandem mass spectrometry definitively identified them as A(4)/J(4)-neuroprostanes. We subsequently showed these compounds are formed in significant amounts from a biological source, rat brain synaptosomes. A(4)/J(4)-neuroprostanes increased 13-fold, from a basal level of 89 +/- 72 ng/mg protein to 1187 +/- 217 ng/mg (n = 4), upon oxidation. We also detected these compounds in very large amounts in fresh brain tissue from rats at levels of 97 +/- 25 ng/g brain tissue (n = 3) and from humans at levels of 98 +/- 26 ng/g brain tissue (n = 5), quantities that are nearly an order of magnitude higher than other classes of neuroprostanes. Because of the fact that A(4)/J(4)-neuroprostanes contain highly reactive cyclopentenone ring structures, it would be predicted that they readily undergo Michael addition with glutathione and adduct covalently to proteins. Indeed, incubation of A(4)/J(4)-neuroprostanes in vitro with excess glutathione resulted in the formation of large amounts of adducts. Thus, these studies have identified novel, highly reactive A/J-ring isoprostane-like compounds that are derived from docosahexaenoic acid in vivo.
Departments of Medicine, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA.
Samuel S
SS
Fam
Laine J
LJ
Murphey
Erin S
ES
Terry
William E
WE
Zackert
Yan
Y
Chen
Ling
L
Gao
Saurabh
S
Pandalai
Ginger L
GL
Milne
L Jackson
LJ
Roberts
Ned A
NA
Porter
Thomas J
TJ
Montine
Jason D
JD
Morrow
D000818:Animals; D001921:Brain / Q000378:metabolism; D002845:Chromatography; D002851:Chromatography, High Pressure Liquid; D002855:Chromatography, Thin Layer; D003517:Cyclopentanes / Q000737:chemistry; D018736:DNA Adducts; D004281:Docosahexaenoic Acids / Q000737:chemistry* / Q000494:pharmacology; D005609:Free Radicals / Q000378:metabolism; D006801:Humans; D007477:Ions; D028421:Isoprostanes / Q000737:chemistry* / Q000378:metabolism*; D008297:Male; D008956:Models, Chemical; D010100:Oxygen / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D013237:Stereoisomerism; D013574:Synaptosomes / Q000378:metabolism; D013997:Time Factors
D003517:Cyclopentanes; D018736:DNA Adducts; D005609:Free Radicals; D007477:Ions; D028421:Isoprostanes; D004281:Docosahexaenoic Acids; C013905:cyclopentenone; D010100:Oxygen