Endotoxemia in transgenic mice overexpressing human glutathione peroxidases.

In response to endotoxemia induced by administration of lipopolysaccharide, a complex series of reactions occurs in mammalian tissues. During this inflammation response, cells produce different mediators, such as reactive oxygen species, a number of arachidonic acid metabolites, and cytokines. The reactive oxygen species thus generated have been suggested to produce tissue injury as a result of macromolecular damage or by interfering with regulatory processes. They may also act as important signaling molecules to induce redox-sensitive genes. We report here that transgenic mice overexpressing 2 major forms of human glutathione peroxidases (GPs), intra- and extracellular GP, are able to modulate host response during endotoxemic conditions. We show that these animals have a decreased hypotension and increased survival rate after administration of a high dosage of lipopolysaccharide. Overexpression of GPs alters vascular permeability and production of cytokines (interleukin-1 beta and tumor necrosis factor-alpha) and NO, affects arachidonic acid metabolism, and inhibits leukocyte migration. These results suggest an important role for peroxides in pathogenesis during endotoxemia, and GPs, by regulating their level, may prove to be good candidates for antioxidant therapy to protect against such injury.

5-oxo-6,8,11,14-eicosatetraenoic acid is a potent stimulator of L-selectin shedding, surface expression of CD11b, actin polymerization, and calcium mobilization in human eosinophils.

5-oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE) is a metabolite of arachidonic acid formed by the oxidation of 5-hydroxy-6,8,11, 14-eicosatetraenoic acid by a highly specific dehydrogenase. 5-oxo-ETE is a chemoattractant for both neutrophils and eosinophils. Although it is not as effective as leukotriene B4 (LTB4) and platelet-activating factor (PAF) in stimulating neutrophil migration, we found that it is considerably more active than these and a variety of other lipid mediators as an eosinophil chemoattractant. Moreover, low concentrations of 5-oxo-ETE appear to enhance the responsiveness of these cells to PAF. The objectives of the current investigation were to identify rapid responses induced in eosinophils by 5-oxo-ETE that might be related to the infiltration of these cells into tissues. We found that 5-oxo-ETE is more effective than PAF and LTB4 in inducing both L-selectin shedding and actin polymerization in human eosinophils, whereas PAF is the most active of these mediators in stimulating calcium mobilization. The complementary effects of 5-oxo-ETE and PAF on actin polymerization and calcium mobilization may explain their synergistic effect on eosinophil migration. 5-oxo-ETE and PAF were equipotent in stimulating the surface expression of the beta2-integrin CD11b, but were slightly less potent than LTB4. 5-oxo-ETE- induced actin polymerization was subject to homologous but not heterologous desensitization. It was not prevented by incubation of eosinophils with inhibitors of protein kinase C (staurosporine), mitogen-activated protein kinase kinase (PD98059), or phosphatidylinositol-3-kinase (wortmannin). In conclusion, 5-oxo-ETE is a potent activator of human eosinophils and may be an important regulator of tissue infiltration of these cells.

Effects of a fish-oil and vegetable-oil formula on aggregation and ethanolamine-containing lysophospholipid generation in activated human platelets and on leukotriene production in stimulated neutrophils.

The effects of consuming a liquid formula containing either fish oil enriched in omega-3 fatty acids or vegetable oil enriched in oleic acid was evaluated in 20 male subjects randomly allocated into two groups over a 42-d period. A decrease in collagen-induced aggregation by using washed platelet suspensions was found in both groups after nutritional supplementation. A considerable rise in omega-3 and a decrease in omega-6 fatty acids occurred in the platelet phospholipid with fish-oil consumption. The degree of eicosapentaenoic acid (EPA, 20:5n-3) enrichment (fish-oil group) was dramatically greater in the ether-containing plasmenylethanolamine (13.5 mol% of fatty acids; mol% of fatty acids = moles per 100 moles of total fatty acids) than in phosphatidylethanolamine (2.8 mol%) or phosphatidylcholine (2.9 mol%). Neither treatment significantly influenced the agonist-induced accumulation of lysoplasmenylethanolamine as derived via phospholipase A2 hydrolysis of plasmenylethanolamine. HPLC measurements of eicosanoid production in A23187-stimulated neutrophils revealed a considerable decrease in the formation of arachidonic acid-derived leukotriene B4 (LTB4), by 41%, and 5-HETE (5-hydroxyeicosatetraenoic acid), by 30%, in the fish-oil group along with the appearance of the corresponding EPA-derived products [LTB5 and 5-HEPE (5-hydroxyeicosapentaenoic acid)]. No such alterations in the formation of lipoxygenase products were found with the vegetable oil treatment.

Synthesis of prostaglandins and thromboxane B2 by cholesterol-fed rabbits.

Alterations in the synthesis of thromboxane A2 (TxA2) and prostacyclin have been implicated in the development of atherosclerosis. We measured the amounts of the degradation products of these substances, TxB2 and 6-oxo-prostaglandin F1 alpha (6-oxo-PGF1 alpha), respectively, as well as PGE2, that were synthesized by slices and the luminal surfaces of aortas from rabbits fed either a control diet or a diet supplemented with cholesterol and peanut oil. For these studies, we developed conditions that were designed to minimize the autoinactivation of cyclooxygenase during removal and preparation of the tissue. Pretreatment of aortas with a medium containing ibuprofen and EDTA resulted in an approximately twofold increase in 6-oxo-PGF1 alpha production upon subsequent incubation. Despite the increased lipid peroxidation associated with atherosclerotic lesions, we observed no changes in either aortic 6-oxo-PGF1 alpha production or in the levels of its major urinary metabolite, 2,3-dinor-6-oxo-PGF1 alpha, after as long as 15 weeks of dietary supplementation with cholesterol and peanut oil. Similarly, synthesis of PGE2 by aortic slices and the aortic lumen was the same in cholesterol-fed and control rabbits. In contrast to aortic 6-oxo-PGF1 alpha and PGE2 synthesis, there was a dramatic 10-fold increase in TxB2 released from slices of thoracic aorta after 15 weeks on the atherogenic diet. This was much greater than the approximately twofold increase in the synthesis of TxB2 by the luminal surface of the thoracic aorta, suggesting that the primary site of TxB2 synthesis in the aorta is in the inner part of the blood vessel.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of selenium-deficient diets on the production of prostaglandins and other oxygenated metabolites of arachidonic acid and linoleic acid by rat and rabbit aortae.

Selenium is an essential component of glutathione peroxidase, which reduces free and esterified hydroperoxides of polyunsaturated fatty acids. Adequate glutathione peroxidase activity could be important for the maintenance of prostacyclin synthesis by blood vessels, since hydroperoxides can inhibit the formation of this substance. We have investigated the effects of dietary selenium deficiency on glutathione peroxidase activity and the synthesis of 6-oxoprostaglandin F1 alpha and monohydroxy and trihydroxy metabolites of polyunsaturated fatty acids by aorta. The latter products can be formed either by the actions of cyclooxygenase or lipoxygenase or by lipid peroxidation. Aortic glutathione peroxidase activity was reduced by over 80% by feeding rats a selenium-deficient diet for 4 weeks, and to undetectable levels after 6 weeks. There were no appreciable differences in the levels of free and esterified oxygenated metabolites of linoleic acid or arachidonic acid between the control and treated groups after 4 weeks. However, after 6 weeks, there were modest, but statistically significant reductions in the formation of 6-oxoprostaglandin F1 alpha and monohydroxy products formed by cyclooxygenase. On the other hand, the amounts of esterified 18:2 metabolites appeared to be higher in aortae from animals on the selenium-deficient diet, although only the increase in esterified 9-hydroxy-10,12-octadecadienoic acid was statistically significant. These results suggest that selenium deficiency can affect the formation of prostacyclin and other oxygenated metabolites of polyunsaturated fatty acids by aorta, possibly by increasing lipid peroxidation. However, the differences between control and selenium-deficient rats after 6 weeks were not very dramatic, in spite of the fact that glutathione peroxidase activity was undetectable. It would therefore appear that additional mechanisms are also involved in controlling the levels of lipid hydroperoxides in aorta.