Search

Isoprostanes (iPs) are prostaglandin (PG) isomers generated by free radical-catalyzed peroxidation of polyunsaturated fatty acids (PUFAs). Urinary F2-iPs, PGF2α isomers derived from arachidonic acid (AA) are used as indices of lipid peroxidation in vivo. We now report the characterization of two major F3-iPs, 5-epi-8,12-iso-iPF3α-VI and 8,12-iso-iPF3α-VI, derived from the ω-3 fatty acid, eicosapentaenoic acid (EPA). Although the potential therapeutic benefits of EPA receive much attention, a shift toward a diet rich in ω-3 PUFAs may also predispose to enhanced lipid peroxidation. Urinary 5-epi-8,12-iso-iPF3α-VI and 8,12-iso-iPF3α-VI are highly correlated and unaltered by cyclooxygenase inhibition in humans. Fish oil dose-dependently elevates urinary F3-iPs in mice and a shift in dietary ω-3/ω-6 PUFAs is reflected by an increasing slope [m] of the line relating urinary 8, 12-iso-iPF3α-VI and 8,12-iso-iPF2α-VI. Administration of bacterial lipopolysaccharide evokes a reversible increase in both urinary 8,12-iso-iPF3α-VI and 8,12-iso-iPF2α-VI in humans on an ad lib diet. However, while excretion of the iPs is highly correlated (R² median = 0.8), [m] varies by an order of magnitude, reflecting marked inter-individual variability in the relative peroxidation of ω-3 versus ω-6 substrates. Clustered analysis of F2- and F3-iPs refines assessment of the oxidant stress response to an inflammatory stimulus in vivo by integrating variability in dietary intake of ω-3/w-6 PUFAs. [ABSTRACT FROM AUTHOR]

Prostaglandin D2 (PGD2) is a cyclooxygenase (COX) product of arachidonic acid that activates D prostanoid receptors to modulate vascular, platelet, and leukocyte function in vitro. However, little is known about its enzymatic origin or its formation in vivo in cardiovascular or inflammatory disease. 11,15- Dioxo-9α-hydroxy-2,3,4,5-tetranorprostan- 1,20-dioic acid (tetranor PGDM) was identified by mass spectrometry as a metabolite of infused PGD2 that is detectable in mouse and human urine. Using liquid chromatography-tandem mass spectrometry, tetranor PGDM was much more abundant than the PGD2 metabolites, 11βPGF2α and 2,3-dinor-11β-PGF2α, in human urine and was the only endogenous metabolite detectable in mouse urine. Infusion of PGD2 dose dependently increased urinary tetranor PGDM > 2,3-dinor-11β-PGF2α > 11β-PGF2α in mice. Deletion of either lipocalin-type or hemopoietic PGD synthase enzymes decreased urinary tetranor PGDM. Deletion or knockdown of COX-1, but not deletion of COX-2, decreased urinary tetranor PGDM in mice. Correspondingly, both PGDM and 2,3-dinor-11β-PGF2α were suppressed by inhibition of COX-1 and COX-2, but not by selective inhibition of COX-2 in humans. PGD2 has been implicated in both the development and resolution of inflammation. Administration of bacterial lipopolysaccharide coordinately elevated tetranor PGDM and 2,3-dinor-11β-PGF2α in volunteers, coincident with a pyrexial and systemic inflammatory response, but both metabolites fell during the resolution phase. Niacin increased tetranor PGDM and 2,3-dinor-11β-PGF2α in humans coincident with facial flushing. Tetranor PGDM is an abundant metabolite in urine that reflects modulated biosynthesis of PGD2 in humans and mice. [ABSTRACT FROM AUTHOR]

Isoeicosanoids are free radical-catalyzed isomers of the enzymatic products of arachidonic acid. They are formed in situ in cell membranes, are cleaved, circulate, and are excreted in urine. Isomers of prostaglandin F2α, the F2-isoprostanes, have emerged as sensitive indices of lipid peroxidation in vivo. Analogous compounds formed from docosahexaenoic acid (DHA) are termed neuroprostanes and are more abundant than isoprostanes (iPs) in brain. Isofurans are another class of isoeicosanoids characterized by a substituted tetrahydrofuran ring. They are preferentially formed, relative to iPs, under conditions of elevated oxygen tension. Here, we report the discovery of neurofurans (nFs), the analogous family of compounds formed from DHA. Formation of nFs is characterized by mass spectrometry and confirmed by oxidation of DHA in vitro and following CCl4 administration in liver in vivo. It is demonstrated that the levels of nFs are elevated in the brain cortex of a mouse model of Alzheimer disease and are depressed in mouse brain cortex by deletion of p47phox, an essential component of the phagocyte NADPH oxidase. Measurement of the nFs may ultimately prove useful in diagnosis, timing, and selection of dose in the treatment and chemoprevention of neurodegenerative disease. [ABSTRACT FROM AUTHOR]

This report identifies a novel gene encoding 15-oxoprostaglandin-Δ13-reductase (PGR-2), which catalyzes the reaction converting 15-keto-PGE2 to 13,14-dihydro-15-keto-PGE2. The expression of PGR-2 is up-regulated in the late phase of 3T3-L1 adipocyte differentiation and predominantly distributed in adipose tissue. Overexpression of PGR-2 in cells decreases peroxisome proliferator-activated receptor γ (PPARγ)-dependent transcription and prohibits 3T3-L1 adipocyte differentiation without affecting expression of PPARγ. Interestingly, we found that 15-keto-PGE2 can act as a ligand of PPARγ to increase co-activator recruitment, thus activating PPARγ-mediated transcription and enhancing adipogenesis of 3T3-L1 cells. Overexpression of 15-hydroxyprostaglaudin dehydrogenase, which catalyzes the oxidation reaction of PGE2 to form 15-keto-PGE2 significantly increased PPARγ-mediated transcription in a PGE2-dependent manner. Reciprocally, overexpression of wild-type PGR-2, but not the catalytically defective mutant, abolished the effect of 15-keto-PGE2 on PPARγ activation. These results demonstrate a novel link between catabolism of PGE2 and regulation of ligand-induced PPARγ activation. [ABSTRACT FROM AUTHOR]

The prostaglandin G/H synthase enzymes, commonly termed COX-1 and COX-2, differ markedly in their responses to regulatory stimuli and their tissue expression patterns. COX- 1 is the dominant source of ‘housekeeping’ prostaglandins, whereas COX-2 synthesizes prostaglandins of relevance to pain, inflammation, and mitogenesis. Despite these distinctions, the two enzymes are remarkably conserved, and their subcellular distributions overlap considerably. To address the functional interchangeability of the two isozymes, mice in which COX-1 is expressed under COX-2 regulatory elements were created by a gene targeting ‘knock-in’ strategy. In macrophages from these mice, COX-1 was shown to be lipopolysaccharide-inducible in a manner analogous to COX-2 in wild-type macrophages However, COX-1 failed to substitute effectively for COX-2 in lipopolysaccharide-induced prostaglandin E2 synthesis at low concentrations of substrate and in the metabolism of the endocannabinoid 2-arachidonylglycerol. The marked depression of the major urinary metabolite of prostacyclin in COX-2 null mice was only partially rescued by COX-1 knock-in, whereas the main urinary metabolite of prostaglandin E2 was rescued totally. Replacement with COX-1 partially rescued the impact of COX-2 deletion on reproductive function, The renal pathology consequent to COX-2 deletion was delayed but not prevented, whereas the corresponding peritonitis was unaltered, Insertion of COX-1 under the regulatory sequences that drive COX-2 expression indicated that COX-1 can substitute for some COX-2 actions and rescue only some of the consequences of gene disruption. Manipulation of COX-2 also revealed a preference for coupling with distinct downstream prostaglandin synthases in vivo. These mice will provide a valuable reagent with which to elucidate the distinct roles of the COX enzymes in mammalian biology. [ABSTRACT FROM AUTHOR]

Elevated levels of circulating fibrinogen are associated with an increased risk of atherothrombotic diseases although a causative correlation between high levels of fibrinogen and cardiovascular complications has not been established. We hypothesized that a potential mechanism for an increased prothrombotic state is the post-translational modification of fibrinogen by tyrosine nitration. Mass spectrometry identified tyrosine residues 292 and 422 at the carboxyl terminus of the beta-chain as the principal sites of fibrinogen nitration in vivo. Immunoelectron microscopy confirmed the incorporation of nitrated fibrinogen molecules in fibrin fibers. The nitration of fibrinogen in vivo resulted in four distinct functional consequences: increased initial velocity of fibrin clot formation, altered fibrin clot architecture, increased fibrin clot stiffness, and reduced rate of clot lysis. The rate of fibrin clot formation and clot architecture was restored upon depletion of the tyrosine-nitrated fibrinogen molecules. An enhanced response to the knob "B" mimetic peptides Gly-His-Arg-Pro(am) and Ala-His-Arg-Pro(am) suggests that incorporation of nitrated fibrinogen molecules accelerates fibrin lateral aggregation. The data provide a novel biochemical risk factor that could explain epidemiological associations of oxidative stress and inflammation with thrombotic complications.

This report identifies a novel gene encoding 15-oxoprostaglandin-Delta13-reductase (PGR-2), which catalyzes the reaction converting 15-keto-PGE2 to 13,14-dihydro-15-keto-PGE2. The expression of PGR-2 is up-regulated in the late phase of 3T3-L1 adipocyte differentiation and predominantly distributed in adipose tissue. Overexpression of PGR-2 in cells decreases peroxisome proliferator-activated receptor gamma (PPARgamma)-dependent transcription and prohibits 3T3-L1 adipocyte differentiation without affecting expression of PPARgamma. Interestingly, we found that 15-keto-PGE2 can act as a ligand of PPARgamma to increase co-activator recruitment, thus activating PPARgamma-mediated transcription and enhancing adipogenesis of 3T3-L1 cells. Overexpression of 15-hydroxyprostaglandin dehydrogenase, which catalyzes the oxidation reaction of PGE2 to form 15-keto-PGE2, significantly increased PPARgamma-mediated transcription in a PGE2-dependent manner. Reciprocally, overexpression of wild-type PGR-2, but not the catalytically defective mutant, abolished the effect of 15-keto-PGE2 on PPARgamma activation. These results demonstrate a novel link between catabolism of PGE2 and regulation of ligand-induced PPARgamma activation.