Resolvins, docosatrienes, and neuroprotectins, novel omega-3-derived mediators, and their aspirin-triggered endogenous epimers: an overview of their protective roles in catabasis

Regiochemistry of Neuroprostanes Generated from the Peroxidation of Docosahexaenoic Acid in Vitro and in Vivo

Isoprostanes (IsoPs) are isomers of prostaglandins that are generated from the free radical-initiated peroxidation of arachidonic acid (C20.4 omega-6). IsoPs exert potent bioactivity and are regarded as the "gold standard" to assess oxidative stress in various human diseases. Analogously, autoxidation of docosahexaenoic acid (DHA, C22.6 omega-3) generates an array of IsoP-like compounds that are termed neuroprostanes (NPs). A major class of NPs identified in vitro and in vivo contains F-type prostane rings and are know as F4-NPs. A number of different F4-NP regioisomers are formed from the peroxidation of DHA. Among the eight possible regioisomeric groups, we hypothesize that 4- and 20-series NPs are generated in greater amounts than other classes because the precursors that lead to regioisomers other than those of the 4- and 20-series can be further oxidized to form novel dioxolane-IsoP-like compounds, analogous to those generated from arachidonate. Various mass spectrometric approaches, including electron capture atmospheric pressure chemical ionization mass spectrometry, were utilized to analyze NPs formed in vitro and in vivo based on their characteristic fragmentation in the gas phase. Experimental results were consistent with our hypothesis that 4- and 20-series NP regioisomers are preferentially generated. The discovery of regioselectivity in the formation of NPs will allow studies of the biological activities of NPs to focus on the more abundantly generated compounds to determine their role in modulating the pathophysiological consequences of DHA oxidation and oxidant stress.

Rainbow trout (Oncorhynchus mykiss) brain cells biosynthesize novel docosahexaenoic acid-derived resolvins and protectins-Mediator lipidomic analysis

Docosahexaenoic acid (DHA; C22:6 n-3) is an abundant fatty acid in fish phospholipids. In the present study, we employed liquid chromatography-ultraviolet spectrometry-tandem mass spectrometry and dissociated rainbow trout (Oncorhynchus mykiss) brain cells to determine whether fish utilize endogenous DHA to produce the recently uncovered novel lipid mediators termed the resolvins and protectins, generated by mammalian cells [Serhan CN, Hong S, Gronert K, et al. Resolvins: a family of bioactive products of omega-3 fatty acid transformation circuits initiated by aspirin treatment that counter proinflammation signals. J Exp Med 2002; 196:1025-37; Hong S, Gronert K, Devchand P, Moussignac R-L, Serhan, CN. Novel docosatrienes and 17S-resolvins generated from docosahexaenoic acid in murine brain, human blood, and glial cells. J Biol Chem 2003;278:14677-87]. Trout brain cells biosynthesize a range of recently identified di- and tri-hydroxy-containing bioactive products from endogenous sources of DHA when challenged in vitro. We identified neuroprotectin D1, resolvin D5, resolvin D1 and resolvin D2 from trout brain cells. Each compound was identified on the basis of its characteristic physical chemical properties that included MS, MS-MS, UV spectra and chromatographic behavior. The monohydroxy products from DHA, signatures of DHA conversion by lipoxygenases, were also identified. These included both 14S-hydroxy-docosahexaenoic acid and 17S-hydroxy-docosahexaenoic acid. The biosynthesis of these novel bioactive lipid mediators, namely resolvins and protectins, by fish cells provides the first evidence for the conservation of these structures from fish to humans as chemical signals in diverse biological systems.

Does fish oil supplementation in pregnancy reduce the risk of allergic disease in infants?

PURPOSE OF REVIEW

Parallel increases in many inflammatory diseases over the last 40 years suggest that common environmental changes are promoting inflammatory immune responses and/or inhibiting the processes that normally keep these in check. One key change during this period has been declining intakes of anti-inflammatory dietary factors, including omega-3 polyunsaturated fatty acids (n-3 PUFA). As allergic diseases often first manifest in early infancy, prevention strategies need to be targeted early, even in utero. This review will examine recent evidence for the use of fish oil during this early period as a primary prevention strategy for allergic disease.

RECENT FINDINGS

N-3 PUFA have well documented anti-inflammatory effects in vitro and have also been demonstrated to have health benefits in a range of chronic inflammatory diseases, including cardiovascular disease, rheumatoid arthritis and diabetes, supporting their role in modulating inflammation in vivo. Although the effects of fish oil supplementation in established allergic disease are less convincing, there is accumulating evidence that dietary n-3 PUFA may have greater effects before allergic responses are established.

SUMMARY

Supplementation of the maternal diet in pregnancy with n-3 PUFA may provide a non-invasive intervention with significant potential to prevent the development of allergic and possibly other immune-mediated diseases.

Resolvin E1, an endogenous lipid mediator derived from omega-3 eicosapentaenoic acid, protects against 2,4,6-trinitrobenzene sulfonic acid-induced colitis

Resolvin E1 (RvE1; 5S,12R,18R-trihydroxyeicosapentaenoic acid) is an antiinflammatory lipid mediator derived from omega-3 fatty acid eicosapentaenoic acid (EPA). At the local site of inflammation, aspirin treatment enhances EPA conversion to 18R-oxygenated products, including RvE1, which carry potent antiinflammatory signals. Here, we obtained evidence for reduced leukocyte infiltration in a mouse peritonitis model, where the administration of EPA and aspirin initiated the generation of RvE1 in the exudates. Similar results were obtained with the administration of synthetic RvE1, which blocked leukocyte infiltration. RvE1 also protected against the development of 2,4,6-trinitrobenzene sulfonic acid-induced colitis. The beneficial effect was reflected by increased survival rates, sustained body weight, improvement of histologic scores, reduced serum anti-2,4,6-trinitrobenzene sulfonic acid IgG, decreased leukocyte infiltration, and proinflammatory gene expression, including IL-12 p40, TNF-alpha, and inducible nitric oxide synthase. Thus, the endogenous lipid mediator RvE1 counter-regulates leukocyte-mediated tissue injury and proinflammatory gene expression. These findings show an endogenous mechanism that may underlie the beneficial actions of omega-3 EPA and provide targeted approaches for the treatment of intestinal inflammation.

Controlling inflammation: a fat chance?

The inflammatory response protects the body against infection and injury but can itself become deregulated with deleterious consequences to the host. It is now clear that several endogenous biochemical pathways activated during defense reactions can counterregulate inflammation. New experimental evidence adds resolvin E1 to this group of endogenous inhibitors and provides further rationale for the beneficial effects of dietary supplementation with fish oils. It also highlights an unexpected twist in the pharmacology of aspirin.

Human paraoxonases (PON1, PON2, and PON3) are lactonases with overlapping and distinct substrate specificities

The paraoxonase (PON) gene family in humans has three members, PON1, PON2, and PON3. Their physiological role(s) and natural substrates are uncertain. We developed a baculovirus-mediated expression system, suitable for all three human PONs, and optimized procedures for their purification. The recombinant PONs are glycosylated with high-mannose-type sugars, which are important for protein stability but are not essential for their enzymatic activities. Enzymatic characterization of the purified PONs has revealed them to be lactonases/lactonizing enzymes, with some overlapping substrates (e.g., aromatic lactones), but also to have distinctive substrate specificities. All three PONs metabolized very efficiently 5-hydroxy-eicosatetraenoic acid 1,5-lactone and 4-hydroxy-docosahexaenoic acid, which are products of both enzymatic and nonenzymatic oxidation of arachidonic acid and docosahexaenoic acid, respectively, and may represent the PONs' endogenous substrates. Organophosphates are hydrolyzed almost exclusively by PON1, whereas bulky drug substrates such as lovastatin and spironolactone are hydrolyzed only by PON3. Of special interest is the ability of the human PONs, especially PON2, to hydrolyze and thereby inactivate N-acyl-homoserine lactones, which are quorum-sensing signals of pathogenic bacteria. None of the recombinant PONs protected low density lipoprotein against copper-induced oxidation in vitro.

Clues for new therapeutics in osteoporosis and periodontal disease: new roles for lipoxygenases?

Lipoxygenase (LOX) pathways are well appreciated for their ability to regulate key events contributing to the cardinal signs of inflammation. Recent evidence indicates that LOX genes are associated with osteoporosis. Also, overexpression of the 15-LOX Type 1 in transgenic rabbits leads to a reduced inflammatory phenotype and protection from periodontal disease, as well as atherosclerosis. Osteoporosis and inflammation-associated bone degradation, such as periodontitis, affect many individuals worldwide and are known to have pathogenesis that involves local mediators via communication between osteoclasts and osteoblasts during osteogenesis. Evidence has emerged indicating that LOX gene expression is associated with reduced bone strength in murine models of osteoporosis. Overexpression of the 15-LOX gene and its products, such as lipoxins, confers endogenous anti-inflammation. This article discusses the recent findings that may link aberrant LOX pathway expression in these diseases, suggesting new avenues for therapeutic approaches via activation of endogenous pathways for resolution of local inflammation.

Long-chain polyunsaturated fatty acids in childhood developmental and psychiatric disorders

Both omega-3 and omega-6 long-chain PUFA (LC-PUFA) are crucial to brain development and function, but omega-3 LC-PUFA in particular are often lacking in modern diets in developed countries. Increasing evidence, reviewed here, indicates that LC-PUFA deficiencies or imbalances are associated with childhood developmental and psychiatric disorders including ADHD, dyslexia, dyspraxia, and autistic spectrum disorders. These conditions show a high clinical overlap and run in the same families, as well as showing associations with various adult psychiatric disorders in which FA abnormalities are already implicated, such as depression, other mood disorders, and schizophrenia. Preliminary evidence from controlled trials also suggests that dietary supplementation with LC-PUFA might help in the management of these kinds of childhood behavioral and learning difficulties. Treatment with omega-3 FA appears most promising, but the few small studies published to date have involved different populations, study designs, treatments, and outcome measures. Large-scale studies are now needed to confirm the benefits reported. Further research is also required to assess the durability of such treatment effects, to determine optimal treatment compositions and dosages, and to develop reliable ways of identifying those individuals most likely to benefit from this kind of treatment. Childhood developmental and psychiatric disorders clearly reflect multifactorial influences, but the study of LC-PUFA and their metabolism could offer important new approaches to their early identification and management. Heterogeneity and comorbidity are such, however, that a focus on specific traits or symptoms may prove more fruitful than an exclusive reliance on current diagnostic categories.