Mechanism of prostaglandin E2 inhibition of acute changes in vascular permeability

Angioedema and Fatty Acids

Angioedema is a life-threatening emergency event that is associated with bradykinin and histamine-mediated cascades. Although bradykinin-mediated angioedema currently has specific therapeutic options, angioedema is sometimes intractable with current treatments, especially histamine-mediated angioedema, suggesting that some other mediators might contribute to the development of angioedema. Fatty acids are an essential fuel and cell component, and act as a mediator in physiological and pathological human diseases. Recent updates of studies revealed that these fatty acids are involved in vascular permeability and vasodilation, in addition to bradykinin and histamine-mediated reactions. This review summarizes each fatty acid’s function and the specific receptor signaling responses in blood vessels, and focuses on the possible pathogenetic role of fatty acids in angioedema.

Methyl gallate attenuates inflammation induced by Toll-like receptor ligands by inhibiting MAPK and NF-Κb signaling pathways

OBJECTIVE AND DESIGN

Methyl gallate (MG) is a prevalent polyphenol in the plant kingdom, which may be related to the effects of several medicinal plants. Although it is widely reported that polyphenols have therapeutic effects, there are few studies demonstrating that MG has anti-inflammatory action. This study aimed to investigate the molecular mechanism behind the anti-inflammatory activity of MG and its effect on hyperalgesia.

METHODS

Swiss mice were pretreated orally with different doses of MG and subjected to i.pl. injection of zymosan to induce paw edema. RAW264.7 macrophages and BMDMs stimulated with different TLR agonists such as zymosan, LPS, or Pam3CSK₄ were used to investigate the molecular mechanisms of MG RESULTS: MG inhibits zymosan-induced paw edema and hyperalgesia and modulates molecular pathways crucial for inflammation development. Pretreatment with MG inhibited cytokines production and NF-κB activity by RAW 264.7 cells stimulated with zymosan, Pam3CSK₄ or LPS, but not with PMA. Moreover, pretreatment with MG decreased IκB degradation, nuclear translocation of NF-κBp65, c-jun and c-fos and ERK1/2, p38 and JNK phosphorylation.

CONCLUSION

Thus, the results of this study demonstrate that MG has a promising anti-inflammatory effect and suggests an explanation of its mechanism of action through the inhibition of NF-κB signaling and the MAPK pathway.

Role of oxylipins generated from dietary PUFAs in the modulation of endothelial cell function

Oxylipins, which are circulating bioactive lipids generated from polyunsaturated fatty acids (PUFAs) by cyclooxygenase, lipooxygenase and cytochrome P450 enzymes, have diverse effects on endothelial cells. Although studies of the effects of oxylipins on endothelial cell function are accumulating, a review that provides a comprehensive compilation of current knowledge and recent advances in the context of vascular homeostasis is lacking. This is the first compilation of the various in vitro, ex vivo and in vivo reports to examine the effects and potential mechanisms of action of oxylipins on endothelial cells. The aggregate data indicate docosahexaenoic acid-derived oxylipins consistently show beneficial effects related to key endothelial cell functions, whereas oxylipins derived from other PUFAs exhibit both positive and negative effects. Furthermore, information is lacking for certain oxylipin classes, such as those derived from α-linolenic acid, which suggests additional studies are required to achieve a full understanding of how oxylipins affect endothelial cells.

Macrolide antibiotics promote the LPS-induced upregulation of prostaglandin E receptor EP2 and thus attenuate macrolide suppression of IL-6 production

We studied the influence of the inhibitory effect of clarithromycin (CAM) and erythromycin (EM) on the production of macrophage inflammatory protein (MIP)-2, interleukin-6 (IL-6), and prostaglandin E(2) (PGE(2)), as well as PGE(2) receptor (EP(2)) expression, by LPS-stimulated RAW264.7 cells. Production of IL-6 was significantly decreased by treatment with CAM or EM in a dose-dependent manner, but the inhibitory effect of CAM was significantly weaker than that of EM. In contrast, the production of MIP-2 and PGE(2) was inhibited to the same extent by CAM and EM. LPS induced the expression of EP(2) mRNA and its expression was promoted further by treatment with CAM or EM. In particular, CAM significantly upregulated EP(2) mRNA expression compared with that after stimulation by LPS alone. After treatment with a nonselective cyclooxygenase (COX) inhibitor (indomethacin), a selective COX-2 inhibitor (NS398), or an EP(2)/EP(4) receptor antagonist (AH6809), the inhibitory effect of CAM and EM on LPS-induced IL-6 production was equalized. These results indicate that macrolide antibiotics upregulate the expression of EP(2), which then attenuates the suppressive effect on IL-6 production of these antibiotics, suggesting that these drugs have a variable anti-inflammatory effect that could influence host defenses.

The expression of cyclooxygenase and the production of prostaglandin E2 in neutrophils after burn injury and infection

Recent studies have demonstrated that neutrophils have the capacity to produce a variety of cytokines after stimulation. The synthesis and release of prostaglandin E2 (PGE2) via the cyclooxygenase (COX) pathway has been reported to occur in activated neutrophils. In the present study, we sought to determine the status of COX protein synthesis and PGE2 production in murine neutrophils after burn injury. The effect of burn injury on neutrophil COX and PGE2 response to infection or lipopolysaccharide (LPS) was also examined. Peritoneal neutrophils were obtained from BDF1 mice at 4, 18, 24, and 36 hours after a 15% TBSA full-thickness scald burn or sham burn. We found that neutrophils from healthy mice express a low level of COX-2 protein. Neutrophil COX-2 protein expression in burn animals was significantly increased at 4 hours and dramatically decreased at 36 hours after burn injury. Animals 36 hours after burn and topically infected with Pseudomonas Aeruginosa had neutrophil COX-2 expression almost identical to burn injury only. Neutrophils harvested from healthy mice cocultured with LPS (1 microg/ml) had a marked induction of COX-2 protein. Neutrophils 24 hours after burn were unresponsive to LPS-stimulated COX-2 enhancement. COX-1 protein was strongly expressed constitutively and not affected further by burn injury or LPS. The production of PGE2 corresponded with the changes in COX-2 expression for all groups of mice. Our data suggested that neutrophils express both COX-1 and COX-2 and produce PGE2. The effects of burn injury on neutrophil COX-2 protein synthesis and PGE2 production suggest that after burn there is a time-dependent response. Insights into not only the global cellular response to injury and infection but also temporal nature of the response are important in the development of the therapeutic treatment strategies for burn patients.

Schistosoma mansoni activates host microvascular endothelial cells to acquire an anti-inflammatory phenotype

Since endothelial cells (ECs) play a key role in immune defense mechanisms and in immunopathology, we investigated whether the intravascular helminth parasite Schistosoma mansoni could interact with and activate resting ECs in vitro. Microscopic analysis revealed that the lung-stage schistosomula specifically attached to microvascular ECs. This adherence was associated to active cellular processes involving actin filament formation. Since variation of permeability of cultured capillary brain ECs is a good marker for endothelial activation, the transendothelial passage of a low-molecular-weight molecule (inulin) on monolayers of bovine brain capillary ECs (BBCEC) was measured in response to parasites. Schistosomula induced a dramatic decrease in transendothelial permeability, a characteristic marker for the generation of an anti-inflammatory phenotype to ECs. This paracellular barrier enhancing effect on endothelial monolayers was due to a soluble substance(s) (below 1 kDa in size) secreted from S. mansoni schistosomula and not by mechanisms associated to adherence between parasites and ECs. The reinforcement of the endothelial barrier function was accompanied by an elevation of intracellular concentration of cyclic AMP (cAMP). The use of specific kinase inhibitors confirms that schistosomula activate ECs through a cAMP/protein kinase A pathway that leads to an increased phosphorylation of the myosin light-chain kinase. These combined findings suggest that the secretory/excretory products from schistosomula possess anti-inflammatory factor(s) that signal host microvascular endothelium. The immunological consequences of such activation are discussed.