The effect of six prostaglandins, prostacyclin and iloprost on generation of superoxide anions by human polymorphonuclear leukocytes stimulated by zymosan or formyl-methionyl-leucyl-phenylalanine

Pharmacological evidence that the inhibitory effects of prostaglandin E2 are mediated by the EP2 and EP4 receptors in human neutrophils

Prostaglandin E2 (PGE2) is a recognized inhibitor of granulocyte functions. However, most of the data supporting this was obtained when available pharmacological tools mainly targeted the EP2 receptor. Herein, we revisited the inhibitory effect of PGE2 on reactive oxygen species production, leukotriene biosynthesis, and migration in human neutrophils. Our data confirm the inhibitory effect of PGE2 on these functions and unravel that the effect of PGE2 on human neutrophils is obtained by the combined action of EP2 and EP4 agonism. Accordingly, we also demonstrate that the inhibitory effect of PGE2 is fully prevented only by the combination of EP2 and EP4 receptor antagonists, underscoring the importance of targeting both receptors in the effect of PGE2. Conversely, we also show that the inhibition of ROS production by human eosinophils only involves the EP4 receptor, despite the fact that they also express the EP2 receptor.

Development and Characterization of Biointeractive Gelatin Wound Dressing Based on Extract of Punica granatum Linn

Punica granatum Linn (pomegranate) extracts have been proposed for wound healing due to their antimicrobial, antioxidant, and anti-inflammatory properties. In this work, we designed biointeractive membranes that contain standard extracts of P. granatum for the purpose of wound healing. The used standard extract contained 32.24 mg/g of gallic acid and 41.67 mg/g of ellagic acid, and it showed high antioxidant activity (the concentration of the extract that produces 50% scavenging (IC50) 1.715 µg/mL). Compared to the gelatin-based membranes (GEL), membranes containing P. granatum extracts (GELPG) presented a higher maximal tension (p = 0.021) and swelling index (p = 0.033) and lower water vapor permeability (p = 0.003). However, no difference was observed in the elongation and elastic modulus of the two types of membranes (p > 0.05). Our wound-healing assay showed that a GELPG-treated group experienced a significant increase compared to that of the control group in their wound contraction rates on days 3 (p < 0.01), 7 (p < 0.001), and on day 14 (p < 0.001). The GELPG membranes promoted major histological changes in the dynamics of wound healing, such as improvements in the formation of granular tissue, better collagen deposition and arrangement, and earlier development of cutaneous appendages. Our results suggest that a biointeractive gelatin-based membrane containing P. granatum extracts has a promising potential application for dressings that are used to treat wounds.

Transcriptome Analysis of Paralichthys olivaceus Erythrocytes Reveals Profound Immune Responses Induced by Edwardsiella tarda Infection

Unlike mammalian red blood cells (RBCs), fish RBCs are nucleated and thus capable of gene expression. Japanese flounder (Paralichthys olivaceus) is a species of marine fish with important economic values. Flounder are susceptible to Edwardsiella tarda, a severe bacterial pathogen that is able to infect and survive in flounder phagocytes. However, the infectivity of and the immune response induced by E. tarda in flounder RBCs are unclear. In the present research, we found that E. tarda was able to invade and replicate inside flounder RBCs in both in vitro and in vivo infections. To investigate the immune response induced by E. tarda in RBCs, transcriptome analysis of the spleen RBCs of flounder challenged with E. tarda was performed. Six sequencing libraries were constructed, and an average of 43 million clean reads per library were obtained, with 85% of the reads being successfully mapped to the genome of flounder. A total of 1720 differentially expressed genes (DEGs) were identified in E. tarda-infected fish. The DEGs were significantly enriched in diverse Gene Ontology (GO) terms and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, especially those associated with immunity, disease, and infection. Ninety-one key DEGs involved in 12 immune-related pathways were found to form extensive interaction networks. Twenty-one genes that constituted the hub of the networks were further identified, which were highly regulated by E. tarda and involved in a number of immune processes, notably pathogen recognition and signal transduction, antigen processing and presentation, inflammation, and splicing. These results provide new insights into the immune role of flounder RBCs during bacterial infection.

Glucagon-like peptide-1 receptor signalling reduces microvascular thrombosis, nitro-oxidative stress and platelet activation in endotoxaemic mice

BACKGROUND AND PURPOSE

Excessive inflammation in sepsis causes microvascular thrombosis and thrombocytopenia associated with organ dysfunction and high mortality. The present studies aimed to investigate whether inhibition of dipeptidyl peptidase-4 (DPP-4) and supplementation with glucagon-like peptide-1 (GLP-1) receptor agonists improved endotoxaemia-associated microvascular thrombosis via immunomodulatory effects.

EXPERIMENTAL APPROACH

Endotoxaemia was induced in C57BL/6J mice by a single injection of LPS (17.5 mg kg^-1 for survival and 10 mg kg^-1 for all other studies). For survival studies, treatment was started 6 h after LPS injection. For all other studies, drugs were injected 48 h before LPS treatment.

KEY RESULTS

Mice treated with LPS alone showed severe thrombocytopenia, microvascular thrombosis in the pulmonary circulation (fluorescence imaging), increased LDH activity, endothelial dysfunction and increased markers of inflammation in aorta and whole blood (leukocyte-dependent oxidative burst, nitrosyl-iron haemoglobin, a marker of nitrosative stress, and expression of inducible NOS). Treatment with the DPP-4 inhibitor linagliptin or the GLP-1 receptor agonist liraglutide, as well as genetic deletion of DPP-4 (DPP4^-/- mice) improved all these parameters. In GLP-1 receptor-deficient mice, both linagliptin and liraglutide lost their beneficial effects and improvement of prognosis. Incubation of platelets and cultured monocytes (containing GLP-1 receptor protein) with GLP-1 receptor agonists inhibited the monocytic oxidative burst and platelet activation, with a GLP-1 receptor-dependent elevation of cAMP levels and PKA activation.

CONCLUSIONS AND IMPLICATIONS

GLP-1 receptor activation in platelets by linagliptin and liraglutide strongly attenuated endotoxaemia-induced microvascular thrombosis and mortality by a cAMP/PKA-dependent mechanism, preventing systemic inflammation, vascular dysfunction and end organ damage.

LINKED ARTICLES

This article is part of a themed section on Redox Biology and Oxidative Stress in Health and Disease. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.12/issuetoc.

Prostaglandin E2 promotes M2 polarization of macrophages via a cAMP/CREB signaling pathway and deactivates granulocytes in teleost fish

The profile of prostaglandin (PG) production is determined by the differential expression of the enzymes involved in their production and degradation. Although the production of PGE2 by fish leukocytes has been relatively well studied in several fish species, knowledge of how its production is regulated, its biological activities and the signaling pathways activated by this PG is scant or even contradictory. In this work we show that in the teleost fish gilthead seabream (Sparus aurata L.) macrophages regulate PGE2 release mainly by inducing the expression of the genes encoding the enzymes responsible for its synthesis, while acidophilic granulocytes (AGs) not only induce these genes quickly after activation but also inhibit the expression of the genes encoding the enzymes responsible for PGE2 degradation at later time points. In addition, treatment of macrophages with PGE2 promoted their M2 polarization, which is characterized by high expression levels of interleukin-10, mannose-receptor c-type 1 and arginase 2 genes. In sharp contrast, PGE2 promoted the deactivation of AGs, since it decreased the production of reactive oxygen species and the expression of genes encoding pro-inflammatory cytokines. These differences are the result of the alternative signaling pathways used by PGE2 in macrophages and AGs, a cAMP/CREB signaling pathway operating in macrophages, but not in AGs, downstream of PGE2. Our data identify for the first time a role for professional phagocyte-derived-PGE2 in the resolution of inflammation in fish and highlight key differences in the PGE2 signaling pathway in macrophages and granulocytes.

Anti-Ulcer Efficacy of Soluble Epoxide Hydrolase Inhibitor TPPU on Diclofenac-Induced Intestinal Ulcers

Proton pump inhibitors such as omeprazole (OME) reduce the severity of gastrointestinal (GI) ulcers induced by nonsteroidal anti-inflammatory drugs (NSAIDs) but can also increase the chance of dysbiosis. The aim of this study was to test the hypothesis that preventive use of a soluble epoxide hydrolase inhibitor (sEHI) such as TPPU can decrease NSAID-induced ulcers by increasing anti-inflammatory epoxyeicosatrienoic acids (EETs). Dose- [10, 30, and 100 mg/kg, by mouth (PO)] and time-dependent (6 and 18 hours) ulcerative effects of diclofenac sodium (DCF, an NSAID) were studied in the small intestine of Swiss Webster mice. Dose-dependent effects of TPPU (0.001-0.1 mg/kg per day for 7 days, in drinking water) were evaluated in DCF-induced intestinal toxicity and compared with OME (20 mg/kg, PO). In addition, the effect of treatment was studied on levels of Hb in blood, EETs in plasma, inflammatory markers such as myeloperoxidase (MPO) in intestinal tissue homogenates, and tissue necrosis factor-α (TNF-α) in serum. DCF dose dependently induced ulcers that were associated with both a significant (P < 0.05) loss of Hb and an increase in the level of MPO and TNF-α, with severity of ulceration highest at 18 hours. Pretreatment with TPPU dose dependently prevented ulcer formation by DCF, increased the levels of epoxy fatty acids, including EETs, and TPPU's efficacy was comparable to OME. TPPU significantly (P < 0.05) reversed the effect of DCF on the level of Hb, MPO, and TNF-α Thus sEHI might be useful in the management of NSAID-induced ulcers.

Inhibition of TNF-α, and NF-κB and JNK pathways accounts for the prophylactic action of the natural phenolic, allylpyrocatechol against indomethacin gastropathy

BACKGROUND

The gastro-intestinal disorders, induced by the NSAIDs including indomethacin (IND) remain unresolved medical problems. Herein, we disclose allylpyrocatechol (APC) as a potential agent against IND-gastropathy and rationalize its action mechanistically.

METHODS

Mice were pre-treated with APC for 1h followed by IND (18mgkg(-1)) administration, and the ulcer-prevention capacity of APC was evaluated on the 3rd day by histology. Its effect on the inflammatory (MPO, cytokines, adhesion molecules), ulcer-healing (COX, prostaglandins, growth factors and their receptors) and signaling parameters (NF-κB and MAPKs) were assessed by immunoblots/mRNA, and ELISA at the time points of their maximal changes due to IND administration.

RESULTS

IND induced oxidative stress, triggering mucosal TNF-α that activated NF-κB and JNK MAPK signaling in mice. These increased the pro-inflammatory biochemical parameters, but reduced the healing factors. APC reversed all the adverse effects to prevent gastric ulceration. APC (5mgkg(-1)), trolox (50mgkg(-1)) and NAC (250mgkg(-1)) showed similar protection that was better than that by misoprostol (5μgkg(-1)) and omeprazole (3mgkg(-1)).

CONCLUSIONS

The anti-ulcer effect of APC can be primarily attributed to its antioxidant action that helped in controlling various inflammatory parameters and augmenting angiogenesis.

GENERAL SIGNIFICANCE

Given that APC is an effective, non-toxic antioxidant with appreciable natural abundance, further evaluation of its pharmacokinetics and dynamics would help in promoting it as a new anti-inflammatory agent.

Effect of selenium and grape seed extract on indomethacin-induced gastric ulcers in rats

Indomethacin (IND) is a non-steroid anti-inflammatory agent that is known to induce severe gastric mucosal lesions. In this study, we investigated the protective effect of selenium (SEL), grape seed extract (GSE), and both on IND-induced gastric mucosal ulcers in rats. Sprague-Dawley rats (200-250 g) were given SEL, GSE, and both by oral gavage for 28 days, and then gastric ulcers were induced by oral administration of 25 mg/kg IND. Malondialdehyde (MDA), non-enzymatic (reduced glutathione, GSH) and enzymatic (superoxide dismutase, catalase, and glutathione peroxidase) antioxidants, prostaglandin E2 (PGE2) in gastric mucosa, and serum tumor necrosis factor alpha (TNF-α) were measured. Moreover, gastric ulcer index and preventive index were determined. Indomethacin increased the gastric ulcer index, MDA, TNF-α, and decreased PGE2 and non-enzymatic (GSH) and enzymatic (superoxide dismutase, catalase, and glutathione peroxidase) antioxidants. Pretreatment with SEL, GSE, and both significantly decreased the gastric ulcer index, MDA, and TNF and increased antioxidants and PGE2. Histopathological observations confirm the gastric ulcer index and biochemical parameters. Selenium and GSE have a protective effect against IND-induced gastric ulcers through prevention of lipid peroxidation, increase of GSH, activation of radical scavenging enzymes, PGE2 generation, and anti-inflammatory activity. Co-administration of GSE and SEL is more effective than GSE or SEL alone.

Gallic Acid Enriched Fraction of Phyllanthus emblica Potentiates Indomethacin-Induced Gastric Ulcer Healing via e-NOS-Dependent Pathway

The healing activity of gallic acid enriched ethanolic extract (GAE) of Phyllanthus emblica fruits (amla) against the indomethacin-induced gastric ulceration in mice was investigated. The activity was correlated with the ability of GAE to alter the cyclooxygenase- (COX-) dependent healing pathways. Histology of the stomach tissues revealed maximum ulceration on the 3rd day after indomethacin (18 mg/kg, single dose) administration that was associated with significant increase in inflammatory factors, namely, mucosal myeloperoxidase (MPO) activity and inducible nitric oxide synthase (i-NOS) expression. Proangiogenic parameters such as the levels of prostaglandin (PG) E₂, vascular endothelial growth factor (VEGF), hepatocyte growth factor (HGF), von Willebrand Factor VIII, and endothelial NOS (e-NOS) were downregulated by indomethacin. Treatment with GAE (5 mg/kg/day) and omeprazole (3 mg/kg/day) for 3 days led to effective healing of the acute ulceration, while GAE could reverse the indomethacin-induced proinflammatory changes of the designated biochemical parameters. The ulcer healing activity of GAE was, however, compromised by coadministration of the nonspecific NOS inhibitor, N-nitro-L-arginine methyl ester (L-NAME), but not the i-NOS-specific inhibitor, L-N6-(1-iminoethyl) lysine hydrochloride (L-NIL). Taken together, these results suggested that the GAE treatment accelerates ulcer healing by inducing PGE₂ synthesis and augmenting e-NOS/i-NOS ratio.

Role of neutrophils in acrylonitrile-induced gastric mucosal damage

Acrylonitrile (ACN) is a widely used intermediate in the manufacture of plastics, acrylic fibers, synthetic rubbers and resins that are used in a variety of products including food containers and medical devices. ACN is a possible human carcinogen and a documented animal carcinogen, with the stomach being an important target of its toxicity. ACN has been previously reported to require metabolic activation to reactive intermediates and finally to cyanide (CN⁻). The current study aimed at exploring the potential role of neutrophils in ACN-induced gastric damage in rats. Experimental neutropenia was attained by injecting rats with methotrexate. This significantly ameliorated gastric mucosal injury induced by ACN. This is evidenced by protection against the increase in gastric ulcer index, myeloperoxidase (MPO) activity and CN⁻ level. Also, neutropenia guarded against the decrease in prostaglandin E2 (PGE2), induction of oxidative stress and reduction of total nitrites and alleviated histopathological alterations in rat stomachs. These data indicate that neutrophil infiltration is, at least partly, involved in ACN-induced gastric damage in rats.

Epigallocatechin gallate accelerates healing of indomethacin-induced stomach ulcers in mice

Management of the gastric toxicity of non-steroidal anti-inflammatory drugs (NSAIDs) remains a crucial problem because the commercially available drugs have side effects and are often expensive. Therefore, we examined the potential of the green tea-derived polyphenol epigallocatechin gallate (EGCG) to treat indomethacin-induced stomach ulcers in mice. Administration of indomethacin (18 mg/kg, po) to mice induced ulceration in the glandular portion of the gastric mucosa, accompanied by increased lipid peroxidation (LPO) and protein oxidation and reductions in thiol defense, mucin, cyclooxygenase (COX) expression and prostaglandin (PG) synthesis in the gastric tissues. Daily oral administration of EGCG (2 mg/kg) or omeprazole (3 mg/kg) for 3 days produced similar (≈ 72-75%, p < 0.001) beneficial effects on the acute gastric ulceration. Treatment with the test samples partially reversed all the adverse oxidative effects of indomethacin. In addition, EGCG, but not omeprazole, enhanced expression of the COX isoforms and PG synthesis. The results suggest that the non-toxic and inexpensive tea polyphenol EGCG may be an excellent candidate for further evaluation as a potent anti-ulcer drug.

Black tea and theaflavins assist healing of indomethacin-induced gastric ulceration in mice by antioxidative action

The healing activities of black tea (BT) and the theaflavins (TF) against the indomethacin-induced stomach ulceration were studied in a mouse model. Indomethacin (18 mg/kg, p.o.) administration induced maximum ulceration in the glandular portion of the gastric mucosa on the 3rd day, accompanied by increased lipid peroxidation and protein oxidation, depletion of thiol-defense and mucin, as well as reduced expressions of cyclooxygenases (COX) and prostaglandin (PG) E synthesis in the gastric tissues, and plasma total antioxidant status of mice. Treatment with BT (40 mg/kg), TF (1 mg/kg), and omeprazole (3 mg/kg) produced similar (74%-76%) ulcer healing, as revealed from the histopathological studies. Treatment with all the above samples reversed the adverse oxidative effects of indomethacin significantly. BT and TF also enhanced the PGE synthesis by augmenting the expressions of COX 1 and 2, but did not modulate acid secretion.

Protective effect of palm vitamin E and α-tocopherol against gastric lesions induced by water immersion restraint stress in Sprague-Dawley rats

OBJECTIVE

Stress can lead to various changes in the gastrointestinal tract of rats. The present study was designed to compare the effect of palm vitamin E (PVE) and α-tocopherol (α-TF) supplementations on the gastric parameters important in maintaining gastric mucosal integrity in rats exposed to water immersion restraint stress (WRS). These parameters include gastric acidity, plasma gastrin level, gastric prostaglandin E(2) (PGE(2)), and gastric lesions.

MATERIALS AND METHODS

Sixty male Sprague-Dawley rats (200-250 g) were divided into three equal groups: a control group, which received a normal rat diet (RC), and two treatment groups, receiving oral supplementation of either PVE or α-TF at 60 mg/kg body weight for 28 days. Each group was further divided into two groups: the nonstress and stress groups. The stress groups were subjected to 3.5 h of WRS once at the end of the treatment period. Blood samples were then taken to measure the gastrin level, after which the rats were killed. Gastric juice was collected for measurement of gastric acidity and gastric tissue was taken for measurement of gastric mucosal lesions and PGE(2).

RESULTS

Exposure to stress resulted in the production of gastric lesions. PVE and α-TF lowered the lesion indices as compared to the stress control group. Stress reduced gastric acidity but pretreatment with PVE and α-TF prevented this reduction. The gastrin levels in the stress group were lower as compared to that in the nonstress control. However, following treatment with PVE and α-TF, gastrin levels increased and approached the normal level. There was also a significant reduction in the gastric PGE(2) content with stress exposure, but this reduction was blocked with treatment with both PVE and α-TF.

CONCLUSION

In conclusion, WRS leads to a reduction in the gastric acidity, gastrin level, and gastric PGE(2) level and there is increased formation of gastric lesions. Supplementation with either PVE or α-TF reduces the formation of gastric lesions, possibly by blocking the changes in the gastric acidity, gastrin, and gastric PGE(2) induced by stress. No significant difference between PVE and α-TF was observed.

Healing potential of Picrorhiza kurroa (Scrofulariaceae) rhizomes against indomethacin-induced gastric ulceration: a mechanistic exploration

Background

The present study was undertaken to evaluate the potential of the rhizomes of the Indian medicinal plant, Picrorhiza kurroa in healing indomethacin-induced acute stomach ulceration in mice and examine its capacity to modulate oxidative stress and the levels of prostaglandin (PGE₂) and EGF during the process.

Methods

Male swiss albino mice, ulcerated with indomethacin (18 mg/kg, p. o., single dose) were treated up to 7 days with different doses of the methanol extract of P. kurroa rhizomes (designated as PK). The healing capacity of the most effective dose of PK (20 mg/kg, p. o. × 3 d) was compared with that of omeprazole (Omez) (3 mg/kg, p. o. × 3 d). The effects of the drug-treatment for one and three days on the biochemical parameters were assessed by comparing the results with that of untreated mice of the 1^st and 3^rd day of ulceration. The stomach tissues of the mice were used for the biochemical analysis.

Results

The macroscopic indices revealed maximum ulceration on the 3^rd day after indomethacin administration, which was effectively healed by PK. Under the optimized treatment regime, PK and Omez reduced the ulcer indices by 45.1% (P < 0.01), and 76.3% respectively (P < 0.001), compared to the untreated ulcerated mice.

Compared to the ulcerated untreated mice, those treated with PK for 3 days showed decreased the levels of thiobarbituric acid reactive substances (TBARS) (32.7%, P < 0.05) and protein carbonyl (37.7%, P < 0.001), and increased mucin (42.2%, P < 0.01), mucosal PGE₂ (21.4%, P < 0.05), and expressions of COX-1 and 2 (26.9% and 18.5%, P < 0.05), EGF (149.0%, P < 0.001) and VEGF (56.9%, P < 0.01). Omez reduced the TBARS (29.4%, P < 0.05), and protein carbonyl (38.9%, P < 0.001), and increased mucin (38.3%, P < 0.01), without altering the other parameters significantly.

Conclusion

PK (20 mg/kg, p. o. × 3 days) could effectively heal indomethacin-induced stomach ulceration in mice by reducing oxidative stress, and promoting mucin secretion, prostaglandin synthesis and augmenting expressions of cyclooxygenase enzymes and growth factors.

Healing properties of malabaricone B and malabaricone C, against indomethacin-induced gastric ulceration and mechanism of action

The healing activity of malabaricone B and malabaricone C, the major antioxidant constituents of the spice Myristica malabarica against the indomethacin-induced gastric ulceration in mice has been studied. The histological indices revealed maximum ulceration on the 3rd day after indomethacin administration, which was effectively healed by malabaricone B, malabaricone C (each 10 mg/kg body weight/day) and omeprazole (3 mg/kg body weight/day) for 3 days. Compared to the untreated ulcerated mice, treatment with malabaricone B, malabaricone C and omeprazole reduced the ulcer indices by 60.3% (P<0.01), 88.4% and 86.1% respectively (P<0.001). All the test samples accelerated ulcer healing than observed in natural recovery even after 7 days. Stomach ulceration reduced the total antioxidant status of plasma by 41% (P<0.05), which was significantly increased by malabaricone B (36%, P<0.01), malabaricone C (61%, P<0.001) and omeprazole (53%, P<0.001). Compared to the ulcerated untreated mice, those treated with malabaricone B reduced the levels of thiobarbituric acid reactive substances and protein carbonyls by 17% and approximately 34% respectively (P<0.05), while malabaricone C and omeprazole reduced the parameters almost equally (approximately 30%, P<0.01, and approximately 40%, P<0.01 respectively). Likewise, all the test samples reduced the oxidation of protein and non-protein thiols significantly (P<0.05). The antioxidant activity of the test samples could partly account their healing capacities. However, the differential potency of them was explainable by considering their relative abilities to modulate mucin secretion, PGE(2) synthesis and expression of EGF receptor and COX isoforms, malabaricone C being most effective in controlling all these factors.

The PGE2-induced inhibition of the PLD activation pathway stimulated by fMLP in human neutrophils is mediated by PKA at the PI3-Kgamma level

Prostaglandin E2 (PGE2), an eicosanoid that modulates inflammation, inhibits several chemoattractant-elicited functions in neutrophils such as chemotaxis, production of superoxide anions, adhesion, secretion of cytotoxic enzymes and synthesis of leukotriene B4. We previously reported that PGE2 inhibits the fMLP signaling pathway that leads to PLD activation through suppression of PI3-Kgamma activity and the decreased recruitment to membranes of PLD activation factors, PKC, Rho and Arf-GTPases. This effect is mediated via the EP2 receptors known to raise cAMP in cells. The inhibition of most fMLP-induced functional responses by PGE2 via EP2 receptors is mediated by PKA, except the chemotactic response. We have investigated the role of PKA in the EP2-mediated inhibition of the PLD activation pathway. H-89, a selective PKA pharmacological inhibitor suppressed the inhibitory effects of PGE2 at all stages of the PLD pathway activated by fMLP, i.e. PLD activity, translocation to membranes of PKCalpha, Rho and Arf-GTPases, calcium influx, tyrosine phosphorylation of proteins and finally translocation of p110gamma catalytic subunit of PI3-K to membranes. However, neither PLD nor PI3-Kgamma was substrate of PKA. These data provide evidence that PGE2-stimulated PKA activity regulates the PLD pathway stimulated by fMLP at the level of PI3-Kgamma and that the inhibition of PI3-Kgamma activation by PKA is a complex mechanism that remains to be completely elucidated.

Vascular protection by dietary polyphenols

Consumption of polyphenol-rich foods, such as fruits and vegetables, and beverages derived from plants, such as cocoa, red wine and tea, may represent a beneficial diet in terms of cardiovascular protection. Indeed, epidemiological studies demonstrate a significant inverse correlation between polyphenol consumption and cardiovascular risk. Among the numerous plausible mechanisms by which polyphenols may confer cardiovascular protection, improvement of the endothelial function and inhibition of angiogenesis and cell migration and proliferation in blood vessels have been the focus of recent studies. These studies have indicated that, in addition to and independently from their antioxidant effects, plant polyphenols (1) enhance the production of vasodilating factors [nitric oxide (NO), endothelium-derived hyperpolarizing factor (EDHF) and prostacyclin] and inhibit the synthesis of vasoconstrictor endothelin-1 in endothelial cells; and (2) inhibit the expression of two major pro-angiogenic factors, vascular endothelial growth factor (VEGF) and matrix metalloproteinase-2 (MMP-2) in smooth muscle cells. The mechanisms of these effects involve: (1) in endothelial cells, increased Ca(2+) level and redox-sensitive activation of the phosphoinositide 3 (PI3)-kinase/Akt pathway (leading to rapid and sustained activation of nitric oxide synthase and formation of EDHF) and enhanced expression of nitric oxide synthase; and (2) in smooth muscle cells, both redox-sensitive inhibition of the p38 mitogen-activated protein kinase (p38 MAPK) pathway activation (leading to inhibition of platelet-derived growth factor (PDGF)-induced VEGF gene expression) and redox-insensitive mechanisms (leading to inhibition of thrombin-induced MMP-2 formation). The current evidence suggests that all these mechanisms are triggered by polyphenols with specific structures, although the structural requirements may be different from one effect to the other, and that they all contribute to the vasoprotective, anti-angiogenic, anti-atherogenic, vasorelaxant and anti-hypertensive effects of acute or chronic administration of plant polyphenols found in vivo in animals and in patients.

Aggravation of inflammatory bowel disease by cyclooxygenase-2 inhibitors in rats

The objective of the present study was to determine the effect of a selective cyclooxygenase-2 (COX-2) inhibitor in in-vivo dextran sodium sulfate (DSS)-stimulated distal colon tissues of the rat. Longitudinal colon tissue sections from DSS-treated rats exhibited noticeable inflammation, altered contraction, increased myleoperoxidase activity, and oxidative stress. When the animals were pretreated with celecoxib, a selective COX-2 inhibitor, the flare of the colon was further worsened in terms of all the parameters studied. There was a reduction in PGE2 levels on chronic administration of celecoxib in DSS-treated animals. The results of the present study suggest that COX-2 enzyme and prostaglandins derived from COX-2 might play a defensive role in protecting ulceration of the colon akin to that seen in the upper gastrointestinal tract.

The role of cyclooxygenase inhibition in the effect of alpha-melanocyte-stimulating hormone on reactive oxygen species production by rat peritoneal neutrophils

The effect of alpha-MSH on reactive oxygen species (ROS) production by rat peritoneal neutrophils and the effect of cyclooxygenase (COX) inhibition were investigated using the chemiluminescence (CL) technique. Cells were obtained by peritoneal lavage 4h after administration of oyster glycogen to rats and were stimulated with lipopolysaccharide (LPS) from Salmonella enderitidis and phorbol 12-myristate 13-acetate (PMA). The increasing concentrations of alpha-MSH (10(-12)-10(-6) M) were added to stimulated cells alone or along with the COX inhibitors indomethacin, ketorolac or nimesulide (10(-8)-10(-5) M). Luminol and lucigenin CL levels were significantly increased in cells stimulated with LPS and PMA compared to unstimulated ones. alpha-MSH significantly reduced lucigenin CL values and this effect was completely reversed in the presence of indomethacin (10(-8) and 10(-7) M). In conclusion, alpha-MSH inhibits the production of superoxide radicals by activated rat peritoneal neutrophils and COX contributes to this effect.

Prostaglandin E2 protects gastric mucosal cells from apoptosis via EP2 and EP4 receptor activation

Prostaglandin E(2) (PGE(2)) has a strong protective effect on the gastric mucosa in vivo; however, the molecular mechanism of a direct cytoprotective effect of PGE(2) on gastric mucosal cells has yet to be elucidated. Although we reported previously that PGE(2) inhibited gastric irritant-induced apoptotic DNA fragmentation in primary cultures of guinea pig gastric mucosal cells, we show here that PGE(2) inhibits the ethanol-dependent release of cytochrome c from mitochondria. Of the four main subtypes of PGE(2) receptors, we also demonstrated, using subtype-specific agonists, that EP(2) and EP(4) receptors are involved in the PGE(2)-mediated protection of gastric mucosal cells from ethanol-induced apoptosis. Activation of EP(2) and EP(4) receptors is coupled with an increase in cAMP, for which a cAMP analogue was found here to inhibit the ethanol-induced apoptosis. The increase in cAMP is known to activate both protein kinase A (PKA) and phosphatidylinositol 3-kinase pathways. An inhibitor of PKA but not of phosphatidylinositol 3-kinase blocked the PGE(2)-mediated protection of cells from ethanol-induced apoptosis, suggesting that a PKA pathway is mainly responsible for the PGE(2)-mediated inhibition of apoptosis. Based on these results, we considered that PGE(2) inhibited gastric irritant-induced apoptosis in gastric mucosal cells via induction of an increase in cAMP and activation of PKA, and that this effect was involved in the PGE(2)-mediated protection of the gastric mucosa from gastric irritants in vivo.

Effects of sucralfate on gastric irritant-induced necrosis and apoptosis in cultured guinea pig gastric mucosal cells

We previously reported that several gastric irritants, including ethanol, hydrogen peroxide, and hydrochloric acid, induced both necrosis and apoptosis in cultured gastric mucosal cells. In the present study, we examined the effects of sucralfate, a unique gastroprotective drug, on gastric irritant-induced necrosis and apoptosis produced in vitro. Sucralfate strongly inhibited ethanol-induced necrosis in primary cultures of guinea pig gastric mucosal cells. The preincubation of cells with sucralfate was not necessary for its cytoprotective effect to be observed, thus making its mechanism of action different from that of other gastroprotective drugs. Necrosis of gastric mucosal cells induced by hydrogen peroxide or indomethacin was also suppressed by sucralfate. On the other hand, sucralfate only weakly inhibited ethanol-induced apoptosis. These results suggest that the cytoprotective effect of sucralfate on gastric mucosa in vivo can be explained, at least in part, by its inhibitory effect on gastric irritant-induced necrosis.

Lysophosphatidic acid enhances in vivo infiltration and activation of guinea pig eosinophils and neutrophils via a Rho/Rho-associated protein kinase-mediated pathway

Lysophosphatidic acid (LPA) has been shown to be a chemoattractant in in vitro studies. The present study was carried out to determine whether LPA enhances infiltration of inflammatory cells in in vivo studies with guinea pigs. LPA (1 - 10 microg/ml), when by guinea pigs for 5 min, substantially increased the numbers of eosinophils and neutrophils in the bronchoalveolar lavege fluid (BALF), which was recovered at over 4 h after the inhalation of LPA. Infiltration in BALF was significantly inhibited by inhalation of Y-27632, an inhibitor of Rho-associated protein kinase (ROCK). LPA also increased superoxide production of eosinophils and neutrophils. In contrast, Y-27632 inhibited superoxide production. These findings suggest that LPA may contribute to infiltration and activation of inflammatory cells in bronchial asthma; furthermore, the Rho/ROCK-mediated pathway may be involved.

Prostaglandin D2 and its metabolites induce caspase-dependent granulocyte apoptosis that is mediated via inhibition of I kappa B alpha degradation using a peroxisome proliferator-activated receptor-gamma-independent mechanism

Many inflammatory mediators retard granulocyte apoptosis. Most natural PGs studied herein (e.g., PGE(2), PGA(2), PGA(1), PGF(2 alpha)) either delayed apoptosis or had no effect, whereas PGD(2) and its metabolite PGJ(2) selectively induced eosinophil, but not neutrophil apoptosis. This novel proapoptotic effect does not appear to be mediated via classical PG receptor ligation or by elevation of intracellular cAMP or Ca(2+). Intriguingly, the sequential metabolites Delta(12)PGJ(2) and 15-deoxy-Delta(12,) Delta(14)-PGJ(2) (15dPGJ(2)) induced caspase-dependent apoptosis in both granulocytes, an effect that did not involve de novo protein synthesis. Despite the fact that Delta(12)PGJ(2) and 15dPGJ(2) are peroxisome proliferator-activated receptor-gamma (PPAR-gamma) activators, apoptosis was not mimicked by synthetic PPAR-gamma and PPAR-alpha ligands or blocked by an irreversible PPAR-gamma antagonist. Furthermore, Delta(12)PGJ(2) and 15dPGJ(2) inhibited LPS-induced I kappa B alpha degradation and subsequent inhibition of neutrophil apoptosis, suggesting that apoptosis is mediated via PPAR-gamma-independent inhibition of NF-kappa B activation. In addition, we show that TNF-alpha-mediated loss of cytoplasmic I kappa B alpha in eosinophils is inhibited by 15dPGJ(2) in a concentration-dependent manner. The selective induction of eosinophil apoptosis by PGD(2) and PGJ(2) may help define novel therapeutic pathways in diseases in which it would be desirable to specifically remove eosinophils but retain neutrophils for antibacterial host defense. The powerful proapoptotic effects of Delta(12)PGJ(2) and 15dPGJ(2) in both granulocyte types suggest that these natural products control the longevity of key inflammatory cells and may be relevant to understanding the control and resolution of inflammation.

Prostaglandin biology in inflammatory bowel disease

Similar to in the upper gastrointestinal tract, prostaglandins represent one of the most important components of mucosal defense in the small intestine and colon. The effects of prostaglandins in this context are widespread, ranging from maintenance of blood flow to stimulation of mucus secretion to modulation of the mucosal immune system. There is little doubt that the ability of NSAIDs to cause injury throughout the gastrointestinal tract and to exacerbate IBD is due in large part to the ability of these agents to suppress prostaglandin synthesis. With the advent of selective COX-2 inhibitors, it has become possible to dissect further the roles of prostaglandins in mucosal defense. The weight of evidence collected so far suggests that prostaglandins derived from COX-2 are important in promoting the healing of mucosal injury, in protecting against bacterial invasion, and in down-regulating the mucosal immune system. Suppression of COX-2 in a setting of gastrointestinal inflammation and ulceration has been shown in experimental models to result in impairment of healing and exacerbation of inflammation-mediated injury. In the near future, pharmacologic probes will be available that will permit clinicians to identify better the specific prostaglandin receptors that mediate the effects of this group of mediators on the various aspects of mucosal defense. This identification should permit the development of therapeutic agents that specifically can modulate some aspects of mucosal defense without having undesired effects on other aspects of mucosal function. Such agents may permit clinicians to enhance mucosal repair selectively and to block selectively any contribution of prostaglandins to the pain associated with IBD.

Inflammatory mediators in gastrointestinal defense and injury

Inflammation of the mucosal layer of the gastrointestinal (GI) tract is not only a feature almost always associated with ulceration of those tissues, but it also plays an important role in both the production and healing of the lesions. The mediators that coordinate inflammatory responses also have the capability to alter the resistance of the mucosa to injury induced by noxious substances, while others render the mucosa more susceptible to injury. In this article, we provide a review of the inflammatory mediators that modulate GI mucosal defense. Among the mediators discussed are nitric oxide, the eicosanoids (prostaglandins, leukotrienes, and thromboxanes), neuropeptides, cytokines, and proteinases. Many of these mediators are considered potential therapeutic targets for the treatment of ulcerative diseases of the digestive tract.

Nonsteroidal anti-inflammatory drugs and the gastrointestinal tract. Mechanisms of protection and healing: current knowledge and future research

The resistance of the gastric mucosa to injury is attributable to a series of factors collectively known as "mucosal defense." Many components of mucosal defense are regulated by prostaglandins and nitric oxide (NO). Thus, inhibition of the production of these mediators predisposes the stomach to injury. Administration of these agents, as synthetic prostaglandins or NO donors, can restore mucosal defense and thereby prevent damage induced by several irritants. Repair of gastric ulcers is also influenced by NO and prostaglandins. Furthermore, a variety of growth factors appear to play critical roles in stimulating the formation of granulation tissue (the "foundation" for repair), the formation of new blood vessels, and the proliferation of epithelial cells. Better understanding of the factors that regulate ulcer healing should provide clues for the development of drugs that can produce better "quality" healing of ulcers.

Selective cyclo-oxygenase-2 inhibitors aggravate ischaemia-reperfusion injury in the rat stomach

1. Effects of indomethacin, the selective cyclo-oxygenase (COX)-2 inhibitors NS-398 and DFU, and dexamethasone on gastric damage induced by 30 min ischaemia followed by 60 min reperfusion (I-R) were investigated in rats. Modulation of gastric levels of COX-1 and COX-2 mRNA by I-R was evaluated using Northern blot and reverse transcription-polymerase chain reaction. 2. I-R-induced gastric damage was dose-dependently aggravated by administration of indomethacin (1 - 10 mg kg(-1)), NS-398 (0.4 - 4 mg kg(-1)) or DFU (0.02 - 2 mg kg(-1)) as assessed macroscopically and histologically. 3. Likewise, administration of dexamethasone (1 mg kg(-1)) significantly increased I-R damage. 4. Low doses of 16, 16-dimethyl-prostaglandin(PG)E(2), that did not protect against ethanol-induced mucosal damage, reversed the effects of the selective COX-2 inhibitors, indomethacin and dexamethasone. 5. I-R had no effect on gastric COX-1 mRNA levels but increased COX-2 mRNA levels in a time-dependent manner. Dexamethasone inhibited the I-R-induced expression of COX-2 mRNA. 6. I-R was not associated with a measurable increase in gastric mucosal formation of 6-keto-PGF(1alpha) and PGE(2). PG formation was substantially inhibited by indomethacin (10 mg kg(-1)) but was not significantly reduced by NS-398 (4 mg kg(-1)), DFU (2 mg kg(-1)) or dexamethasone (1 mg kg(-1)). 7. The findings indicate that selective COX-2 inhibitors and dexamethasone markedly enhance gastric damage induced by I-R. Thus, whereas COX-2 has no essential role in the maintenance of gastric mucosal integrity under basal conditions, COX-2 is rapidly induced in a pro-ulcerogenic setting and contributes to mucosal defence by minimizing injury. This suggests that in certain situations selective COX-2 inhibitors may have gastrotoxic effects.

Probucol inhibits oxidized-low density lipoprotein-induced adhesion of monocytes to endothelial cells by reducing P-selectin synthesis in vitro

Probucol (PBC) is an unique antiatherogenic drug producing its effect by antioxidant action rather than hypolipidaemic effect. However, the exact mechanism of its antiatherogenic effect is unclear. Therefore we investigated the PBC effects on the adhesion of monocytes to endothelial cells, an early event in atherogenesis. Monocyte adhesion to cultured pig aortic endothelial cells (EC) was induced by oxidized low density lipoprotein (Ox-LDL). To elucidate the mechanisms of the inhibition on adhesion, PBC effects on the Ox-LDL-induced expression of P-selectin, on the synthesis of von Willebrand factor (vWF) and prostacyclin (PGI2) were examined. The results showed that Ox-LDL enhanced the adhesion of monocytes to EC in a concentration-dependent and time-related manner. PBC 25, 50 and 75 micromol/L inhibited the Ox-LDL-induced adhesion index from 37.3% to 19.7, 16.6 and 14.6% respectively (p all < 0.05), and inhibited the Ox-LDL-induced expression of P-selectin from 293.0 ng/ml to 180.0, 132.9 and 132.6 ng/ml respectively. Furthermore, PBC significantly attenuated the Ox-LDL-impaired synthesis of PGI2 and vWF. These results indicate that PBC may provide a new approach in the prevention of atherosclerosis (AS) by intervention of monocyte adhesion to EC. In conclusion, PBC inhibits the Ox-LDL-induced adhesion of monocytes to EC. This effect is associated with the inhibition of the Ox-LDL-induced expression of P-selectin and the protection on the synthesis of PGI2.

Do E-series prostaglandins and their metabolites influence oxidation of native and glycated low-density lipoproteins?

Oxidation of lipoproteins, and, in particular, low-density lipoproteins (LDL), has been shown to play a significant role in the pathogenesis of atherosclerosis. Oxidized LDL are endocytosed via scavenger receptors to form lipid-laden foam cells. The non-enzymatic reaction of glucose with proteins and lipoproteins results in a modified LDL involved in the pathogenesis of late complications in diabetes mellitus. In the present paper, the influence of various E-series prostaglandins (PGE1; 13,14-dihydro PGE1; 13,14-dihydro 15-keto PGE1; and PGE2) on oxidation of native and glycated LDL was investigated. The effect of these agents in the concentration range from 1 pg/mL to 1.6 micrograms/mL on copper-induced oxidation of native and glycated LDL was tested. The concentration of each agent causing the maximal effect on oxidation of native LDL, as measured by the formation of thiobarbituric acid-reacting substances, was chosen to estimate the effect on 2, 4, 8, and 24 h oxidation of glycated LDL. The study was performed with LDL isolated by sequential ultracentrifugation from normolipidemic individuals. LDL (0.25 mg protein/mL) was oxidatively modified with 5 microM CuSO4. The glycosylation of LDL was performed by incubation of LDL with 500 mM glucose for varying periods of time ranging from 10 to 31 days. Our results show that only 13,14-dihydro PGE1 significantly inhibits copper-induced oxidation of native LDL, while the other examined E-series prostaglandins in vitro are ineffective as reducing agents in LDL-oxidation.

Recombinant human erythropoietin enhances superoxide production by FMLP-stimulated polymorphonuclear leukocytes in hemodialysis patients

Recombinant human erythropoietin (rHuEPO) is a hematopoietic growth factor that has a broad spectrum of action. We have observed the in vivo and in vitro effects of rHuEPO on the superoxide production of circulating polymorphonuclear leukocytes (PMNs) in hemodialysis patients. The PMNs were separated from heparinized blood after dextran sedimentation and Ficoll-Conray centrifugation and stimulated with formyl-methionyl-leucyl-phenylalanine (FMLP), serum-treated zymosan (STZ), or phorbol myristate acetate (PMA). The in vivo study showed that rHuEPO therapy for 12 weeks enhanced the superoxide production by FMLP-stimulated PMNs (P < 0.01). However, no significant changes on superoxide production was found in either STZ- or PMA-stimulated PMNs. Simultaneous measurement of PGE2 production by PMNs in response to all three stimulants did not show any significant changes after rHuEPO therapy. The direct in vitro effect of rHuEPO on PMNs showed that rHuEPO does not enhance the superoxide production by non-stimulated PMNs. However, preincubation of rHuEPO enhanced superoxide production from FMLP- and STZ-stimulated PMNs. Our results indicate that rHuEPO enhanced FMLP-stimulated superoxide production of PMNs both in vivo and in vitro in hemodialysis patients, which may be responsible for the increased oxidant stress in hemodialysis patients after rHuEPO therapy.

Nonsteroidal anti-inflammatory drug-induced gastrointestinal toxicity: new insights into an old problem

Nonsteroidal anti-inflammatory drugs are widely used for the treatment of chronic arthropathies, but their gastrointestinal damage remains a significant limitation to their use. In this review, the pathogenic mechanisms through which these drugs are believed to cause gastrointestinal damage are outlined. A better understanding of the pathogenesis of gastric and intestinal injury has resulted in novel strategies that are being employed to develop nonsteroidal anti-inflammatory drugs that do not have significant adverse effects on the gastrointestinal tract.

Migration of neutrophils from blood to tissue: alteration of modulatory effects of prostanoid on superoxide generation in rabbits and humans

Alteration of neutrophil function is associated with their migration from blood into tissue. We evaluated this alteration in both human and rabbit neutrophils, by comparing the inhibitory effects of prostanoids on formylmethionyl-leucyl-phenylalanine (fMLP)-stimulated superoxide generation in human circulating blood neutrophils with those in saliva, and also comparing rabbit circulating blood neutrophils with those exudated into peritoneal cavity. We showed that EP-receptor agonists (PGE1) EP2/EP3 agonist (misoprostol), EP2-receptor agonist (butaprost) and DP-receptor agonist (PGD2) inhibited fMLP-stimulated superoxide production from human blood neutrophils in a concentration-dependent manner. In contrast, these prostanoids produced a significantly smaller maximum inhibition of fMLP-stimulated superoxide production in salivary neutrophils compared to those in blood neutrophils. Similar differences were observed for rabbit blood and peritoneal neutrophils. The inhibitory effect of EP2 agonist (butaprost) on the fMLP-stimulated superoxide generation in human blood neutrophils was significantly higher than that of EP3 agonist (ONO-AP-324). The EP1 antagonist (SC-51322) and EP4 antagonist (AH23848B) employed in this study could not antagonize the inhibitory effect of PGE2. TP agonist (U-46619) failed to show any inhibitory effect in either blood or salivary neutrophils. These results indicated that EP2 and DP receptors are the primary receptors mediating the prostanoids inhibition of fMLP-stimulated superoxide generation from neutrophils. Furthermore, it can be concluded that neutrophils become less responsive to prostanoids in terms of fMLP-stimulated superoxide production in association with their migration from blood to tissue.

Synergistic inhibition of human polymorphonuclear function by prostaglandin E1 and linsidomine

Polymorphonuclear cells (PMN) are the dominating inflammatory cell population in acute tissue injury and contribute to host-defence mechanisms by formation and release of chemical mediators. The aim of the present study was to investigate whether chemoattractant-induced PMN stimulation can be synergistically antagonized by vasodilatory prostaglandins and nitric oxide (NO), both being formed by the vasculature in inflamed areas. PGE1 (10 nM-10 microM) inhibited concentration-dependently formyl-methionyl-leucyl-phenylalanine (fMLP)-induced beta-glucuronidase and oxygen radical (O2.) release from human PMN. The NO donor linsidomine (100 microM) was ineffective, but significantly enhanced PGE1 effects on oxygen radical generation and enzyme release. The non-selective phosphodiesterase inhibitor 3-isobutyl-l-methylxanthine (IBMX) (0.5 mM) potentiated PGE1 effects on all parameters measured. The combination linsidomine (100 microM) plus IBMX (0.5 mM) did not additionally reduce beta-glucuronidase release, but abolished fMLP-stimulated O2. generation. There was a stimulation of cAMP formation by PGE1 but not by linsidomine, both in the absence and presence of IBMX. It is concluded that the effects of linsidomine on PMN function and its synergism with PGE1 are not tightly correlated with total cAMP accumulation. Alternatively, the inhibition of O2. generation by linsidomine may be related to its ability to modulate the activation of the NADPH oxidase system or to scavenge free oxygen radicals.

Intracolonic administration of zileuton, a selective 5-lipoxygenase inhibitor, accelerates healing in a rat model of chronic colitis

BACKGROUND

5-Lipoxygenase products play a part in inflammatory response.

AIMS

The effect of intracolonic administration of zileuton (a 5-lipoxygenase inhibitor) on colonic damage and eicosanoid local release was assessed in a rat model of colitis.

METHODS

Ninety rats with trinitrobenzenesulphonic acid induced colitis were randomised to receive placebo, 5-aminosalicylic acid (50 mg/kg), or zileuton (50 mg/kg) intracolonically for four weeks. Local eicosanoid release was monitored by intracolonic dialysis throughout the study. The colon was removed for macroscopic and histological assessment at weeks 1, 2, and 4 after colitis induction in 10 rats of each group.

RESULTS

Zileuton significantly reduced macroscopic damage score after four weeks of treatment in comparison with the other two groups (p = 0.034). In addition, zileuton administration significantly increased the intracolonic release of both thromboxane B2 at week 1 (p = 0.05) and prostaglandin E2 at weeks 2 and 4 (p < 0.05). Zileuton and 5-aminosalicylic acid decreased leukotriene B4 release by 90% at day 3.

CONCLUSIONS

Intracolonic zileuton, compared with 5-aminosalicylic acid and placebo, seems to improve the course of the disease in a model of chronic colitis. This effect may be related to an increased and maintained production of prostaglandin E2 together with inhibition of leukotriene B4 synthesis.

Considerations for nonsteroidal anti-inflammatory drug therapy: safety

Although therapeutically beneficial, nonsteroidal anti-inflammatory drugs are associated with serious gastrointestinal side effects, including ulceration, hemorrhage, and perforation. Endoscopic studies indicate that up to 30% of chronic NSAID users will develop gastroduodenal ulceration. Various case-control studies have reported an association between ulcer-related complications or deaths and NSAID use. An imprecise correlation has been found to exist between the presence of NSAID-induced gastrointestinal damage and symptoms, such as dyspepsia and pain. It is now thought that the major deleterious effects of NSAIDs on the gastrointestinal tract are related to the ability of systemically absorbed NSAIDs to alter gastric and duodenal defense mechanisms, primarily via inhibition of mucosal prostaglandin synthesis. Although various therapeutic agents have been investigated for their ability to prevent NSAID-induced ulcers, only the prostaglandin analogue misoprostol has been shown to significantly reduce the incidence of both gastric and duodenal ulcers in NSAID users. Recently, the Misoprostol Ulcer Complications Outcomes Safety Assessment trial demonstrated that misoprostol also reduces the most serious complications of NSAID-induced ulcers, namely bleeding, perforation, and gastric outlet obstruction.

Tumour necrosis factor alpha-induced oxidative burst in neutrophils adherent to fibronectin: effects of cyclic AMP-elevating agents

Human neutrophils, plated on fibronectin-coated polystyrene wells, were found to exhibit a prolonged production of superoxide anion (O2-) in response to tumour necrosis factor-alpha (TNF). The TNF-triggered O2- production was significantly reduced by 10 microM prostaglandin E2 (PGE2), which was ineffective at lower doses. Moreover, the O2- production was slightly reduced by the phosphodiesterase type IV (PDE IV) inhibitor RO 20-1724. When PGE2 and RO 20-1724 were added together to TNF-triggered neutrophils they caused a marked synergistic inhibition of O2- production. The action of PGE2 could be mimicked by forskolin (FK), a well-known direct activator of adenylate cyclase. These results suggest that cyclic AMP (cAMP)-elevating agents (PGE2, FK, RO 20-1724) down-regulate the capacity of adherent neutrophils to mount the respiratory burst in response to TNF. Consistent with this interpretation, PGE2 and RO 20-1724 increased the intracellular levels of cAMP displaying synergistic activity. Moreover, the membrane-permeable analogue of cAMP, dibutyryl cAMP, was found to inhibit the TNF-induced O2- production in a dose-dependent manner. As all the aforementioned cAMP-elevating agents did not affect the O2- production in response to phorbol myristate acetate, they appear to act by interfering with the assembly of the O2(-)-generating NADPH oxidase complex rather than by directly inhibiting the activity of already working oxidase complex. In conclusion, taking into account the TNF capacity to promote PGE2 formation at sites of inflammation, our observations suggest the existence of a negative PGE2-dependent feed-back, potentially capable of controlling the neutrophil response to TNF and susceptible to amplification by PDE IV-inhibiting compounds.

Cyclic AMP-elevating agents down-regulate the oxidative burst induced by granulocyte-macrophage colony-stimulating factor (GM-CSF) in adherent neutrophils

Human neutrophils, plated on fibronectin-precoated wells, were found to release large quantities of superoxide anion (O2-) in response to GM-CSF. O2- production was reduced by prostaglandin E2 (PGE2) and the phosphodiesterase type IV (PDE IV) inhibitor RO 20-1724. Both agents are known to increase intracellular cyclic AMP (cAMP) levels by inducing its production (PGE2) or blocking its catabolism (RO 20-1724). When added in combination, PGE2 and RO 20-1724 had a marked synergistic inhibitory effect, which was reproduced by replacing PGE2 with a direct activator of adenylate cyclase, i.e. forskolin (FK). Moreover, the neutrophil response to GM-CSF was inhibited by a membrane-permeable analogue of cAMP in a dose-dependent manner. As GM-CSF and PGE2 are known to be generated at tissue sites of inflammation, the results suggest the existence of a PGE2-dependent regulatory pathway potentially capable of controlling the neutrophil response to GM-CSF, in turn limiting the risk of local oxidative tissue injury. Moreover, owing to its susceptibility to amplification by RO 20-1724, the PGE2-dependent pathway and in particular PDE-IV may represent a pharmacological target to reduce the generation of histotoxic oxidants by GM-CSF-responding neutrophils.

Eicosanoids, fatty acids and neutrophils: their relevance to the pathophysiology of disease

PUFA and their eicosanoid metabolites are potent biological modifiers. They have beneficial effects in a number of diseases, which may result in part from their direct actions on neutrophils as well as from their ability to modulate eicosanoid biosynthesis. A consideration of their interactions with other cell types, e.g. lymphocytes and macrophages, is beyond the scope of this review. Small alterations in structure can result in large changes in the neutrophil response. This will have important implications for the further development and use of fatty acids for therapeutic purposes.

Review article: new insights into prostaglandins and mucosal defence

A role for prostaglandins in maintaining mucosal integrity in the gastrointestinal tract is well documented. While traditionally the effects of prostaglandins on mucosal blood flow and epithelial function have been regarded as critical in the mechanism of action of these fatty acids, recent evidence that mucosal ulceration is almost invariably associated with mucosal inflammation has caused a re-evaluation of the role of prostaglandins in mucosal defence. This review focuses on the ability of prostaglandins to exert anti-inflammatory, and therefore anti-ulcerogenic, effects in the gastrointestinal tract. These effects of prostaglandins are attributable to their ability to suppress the release of inflammatory mediators and reactive oxygen metabolites from a number of immunocytes, stromal cells and inflammatory cells. There is emerging evidence for cooperative interactions between prostaglandins and nitric oxide in maintaining mucosal integrity. Recent work on the inducible isoform of prostaglandin synthase as it pertains to mucosal defence is also reviewed.

Role of neutrophils in indomethacin-induced gastric mucosal lesions in rats

Nonsteroidal anti-inflammatory drugs (NSAIDs) cause clinically important gastric damage by several mechanisms. In order to evaluate the role of neutrophil infiltration in lesion formation, tissue myeloperoxidase activities were assessed in different gastric layers of the stomach both in rats with normal neutrophil levels and in neutropenic rats. Sprague-Dawley rats were treated either with indomethacin (Indo; 25 mg/kg, s.c.) or the vehicle. A group of rats were made neutropenic by administration of methotrexate (MTX; 2.5 mg/kg i.p.) once a day for 3 days. The stomachs were removed for the determination of lesion index, glutathione, lipid peroxide levels, protein oxidation and tissue myeloperoxidase activities. MTX treatment appeared to reduce neutrophil infiltration significantly while producing insignificant effects on eosinophils and macrophages. Indo administration caused multiple gastric lesions and treatment with MTX significantly reduced lesion index. In rats treated with Indo, neither glutathione nor LP levels showed any significant changes but the protein oxidation was significantly higher than that of other groups. The MPO level of gastric mucosa was increased in Indo-treated rats and reversed by MTX pretreatment. The results of the present study indicate that neutrophil infiltration in the gastric mucosa of rats may be involved in the pathogenesis of NSAID-induced gastric mucosal injury, but no correlation was found between lesion formation and protein oxidation in the gastric mucosa.

Characterization of the PGE receptor subtype mediating inhibition of superoxide production in human neutrophils

1. The aims of this study were to characterize the EP receptor subtype mediating the inhibition of superoxide anion generation by formyl methionyl leucine phenylalanine (FMLP)-stimulated human neutrophils, and to test the hypothesis that adenosine 3':5'-cyclic monophosphate (cyclic AMP) is the second messenger mediating the inhibition of the neutrophil by prostaglandin (PG)E2. 2. PGE2 (0.001-10 microM) inhibited FMLP (100 nM)-induced O2-generation from human peripheral blood neutrophils in a concentration-dependent manner, with an EC50 of 0.15 +/- 0.03 microM, and a maximum effect ranging from 36-84% (mean inhibition of 68.7 +/- 2.5%, n = 32). 3. The EP2-receptor agonists, misoprostol, 11-deoxy PGE1, AH13205 and butaprost, all at 10 microM, inhibited O2- generation, causing 95.5 +/- 2.9%, 56.8 +/- 5.2%, 37.1 +/- 6.6% and 18.9 +/- 4.4% inhibition respectively, the latter two being much less effective than PGE2. Similarly, the EP1-receptor agonist, 17-phenyl PGE2 (10 microM), and the EP3/EP1-receptor agonist, sulprostone (10 microM), also inhibited O2- generation, causing 32.2 +/- 7.0% and 15.3 +/- 3.4% inhibition respectively. 4. The non-selective phosphodiesterase inhibitor, isobutyl methylxanthine (IBMX, 0.25 mM) inhibited the FMLP response by 54.5 +/- 5.0%. In addition, IBMX shifted concentration-effect curves for PGE2, misoprostol, 11-deoxy PGE1, butaprost, and AH 13205 to the left, to give EC50s of 0.04 +/- 0.03 (n = 13), 0.07 +/- 0.03 (n = 4), 0.08 +/- 0.03 (n = 4), 0.33 +/- 0.13 (n = 4) and 0.41 +/- 0.2 microM (n = 3) respectively, allowing equieffective concentration-ratios (EECs, PGE2 = 1) of 11.5, 5.3, 50.7 and 12.7 to be calculated. This agrees well with the relative potencies of these agonists at EP2 receptors.5. By contrast, even in the presence of IBMX (0.25 mM), sulprostone and 17-phenyl PGE2 were only effective at the highest concentration (10 microM), and gave EECs of > 700 and 486 respectively, suggesting that EP1 or EP3 receptors are not involved.6. The selective type IV phosphodiesterase inhibitor, rolipram at 2 and 10 nM did not inhibit the FMLP response, but at the higher concentration of 50 nM, it decreased the FMLP response by 46.6 +/-7.3%.However, rolipram shifted concentration-effect curves for PGE2 to the left to give EC50s of 0.06 +/-0.022,0.015 +/- 0.0, 0.012 +/- 0.006 microM at 2, 10 and 50 nM respectively, compared to the control EC50 of0.27+/- 0.09 microM for PGE2.7. The EP4/TP receptor blocking drug, AH 23848B (10 microM, 10 min) did not inhibit 02- generation by PGE2, but was found to potentiate significantly the effect of PGE2 at the lower concentrations of PGE2 tested (0.001-0.1 microM).8. The adenylate cyclase inhibitor, SQ 22,536 (0.1 mM, 2 min) reduced PGE2-induced inhibition of 02-production, giving an EC50 in the absence of SQ 22,536 of 0.24 +/- 0.1, and 1.9 +/- 1.1 AM in its presence.9. These results suggest that inhibition of superoxide generation by PGE2 is mediated by stimulation ofEP2 receptors and activation of adenylate cyclase, leading to the elevation of intracellular levels of cyclic AMP.

Comparison of the prostaglandin E (EP) receptor of human neutrophils and HL-60 cells differentiated with DMSO

Human promyelocytic leukaemic HL-60 cells can be differentiated with DMSO to become neutrophil-like. In this study, the prostanoid receptors linked to adenylate cyclase have been compared in human neutrophils and in differentiated HL-60 cells. Both cell types appear to express EP2 receptors as recognised by the ability of EP2 agonists and not EP1 or EP3 agonists to increase cell cyclic AMP levels, and the finding that the increase in cyclic AMP induced by PGE2 was not blocked by the EP4 receptor antagonist AH 23,848 (30 microM). Neither cell type appears to express receptors for PGI2, but human neutrophils and not differentiated HL-60 cells express receptors for PGD2. In addition, human neutrophils may contain EP3 receptors linked to a reduction in cyclic AMP levels. The lack of other prostanoid receptors coupled to adenylate cyclase in HL-60 cells suggests that these cells may provide a useful starting point for the cloning of the EP2 receptor.

Characterization of prostanoid receptors on rat neutrophils

1. The effects of various prostanoid agonists have been compared on the increase in intracellular free calcium ([Ca2+]i) and the aggregation reaction of rat peritoneal neutrophils induced by N-formyl-L-methionyl-L-leucyl-L-phenylalanine (FMLP). 2. Prostaglandin E2 (PGE2) and the specific IP-receptor agonist, cicaprost, both inhibited the FMLP-induced increase in [Ca2+]i (IC50 33 nM and 18 nM respectively) and the FMLP-induced aggregation reaction (IC50 5.6 nM and 7.9 nM respectively). PGD2, PGF2 alpha, and the TP-receptor agonist, U 46619, were inactive at the highest concentration tested (1 microM). 3. The EP1-receptor agonist, 17-phenyl-omega-trinor PGE2, and the EP3-receptor agonists, GR 63799X and sulprostone, had no inhibitory effect on FMLP-stimulated rat neutrophils. 4. PGE1 (EP/IP-receptor agonist) and iloprost (IP-receptor agonist) inhibited the FMLP-induced increase in [Ca2+]i with IC50 values of 34 nM and 38 nM respectively. The EP2-receptor agonists, butaprost and misoprostol (1 microM), inhibited both FMLP-stimulated [Ca2+]i and aggregation. However another EP2-receptor agonist, AH 13205, was inactive in both assays. 5. Prostanoid receptors present on rat neutrophils were further characterized by measuring [3H]-adenosine 3':5'-cyclic monophosphate ([3H]-cyclic AMP) accumulation. Only those agonists capable of stimulating [3H]-cyclic AMP accumulation were able to inhibit both FMLP-stimulated [Ca2+]i and aggregation. 6. These results indicate that rat neutrophils possess inhibitory IP and EP-receptors; the relative potencies of PGE2, misoprostol and butaprost are those expected for the EP2-receptor subtype. No evidence for DP, FP, TP or EP1 and EP3-receptors was obtained.

Pro-inflammatory and anti-inflammatory effects of the stable prostaglandin D2 analogue, ZK 118.182

This study examined the pro- and anti-inflammatory effects of the stable prostaglandin (PG) D2 analogue, ZK 118.182 and the mechanism by which prostaglandins may exert their anti-inflammatory activity. Co-injected locally, ZK 118.182, like PGE2 and PGD2, dose-dependently increased plasma leakage induced by intradermal injection of bradykinin in rabbit skin. Infused i.v., ZK 118.182 (0.45 microgram/kg/min), a dose which did not affect systemic blood pressure, inhibited oedema formation in rabbit skin induced by the neutrophil-dependent agonists, formyl-methionyl-leucyl-phenylalanine (FMLP) and leukotriene B4 (LTB4). However, it did not modify plasma leakage induced by the neutrophil-independent mediators, bradykinin and platelet-activating factor (PAF). In contrast, neutrophil accumulation in response to LTB4 and FMLP was not affected in animals infused with ZK 118.182. In vitro, ZK 118.182, like PGE2 and PGD2 inhibited FMLP-induced superoxide anion (O2-) production by rabbit neutrophils. The compound, however, had minimal effects on O2- production induced by phorbol myristate acetate (PMA). ZK 118.182 inhibited to a small extent FMLP but not PMA-induced neutrophil adherence. These results show that depending on the route of administration, the PGD2 analogue, ZK 118.182, exhibits either pro- or anti-inflammatory effects. The anti-inflammatory effect may be related to the ability of the compound to inhibit increased microvascular permeability induced by neutrophil activation without interfering with neutrophil accumulation. This latter effect may be due to the analogue's capacity to suppress neutrophil secretion to a greater extent than neutrophil adherence.

Microvascular changes in liver after ischemia-reperfusion injury. Protection with misoprostol

Morphological changes in the hepatic microvasculature were studied in experimentally induced ischemia-reperfusion injury in the rat using a vascular casting technique. Partial hepatic ischemia was induced for 90 min followed by 24 hr reperfusion. Microvascular casting was performed after 24 hr reperfusion by either intraarterial or intravenous infusion of acrylic resin (Mercox). After corrosion of the tissue, the cast was examined by scanning electron microscopy. Casts of normal livers showed good patency with no evidence of unfilled areas. The mean diameter of sinusoids was 14 +/- 3 microns with those in zone 1 slightly smaller than those in zone 3. Liver casts from rats subjected to ischemia and reperfusion resulted in gross disruption of normal architecture. The common characteristics seen in both prograde and retrograde casts were clusters of closed sinusoids around zones 2 and 3 of the liver acini, which resulted in cavities of various sizes. Varicosities were observed in some areas. The mean diameter of sinusoids in areas of patent microvascular structure (10 +/- 2 microns) was significantly smaller compared to those in normal livers (P < 0.001). Misoprostol given at 1 min before reperfusion markedly reduced the microvascular injury. The hepatic microvascular was generally intact with mild focal unfilled areas. The majority of the sinusoids were of normal size and no clusters of blind ending sinusoids were detected. The present study shows that hepatic ischemia-reperfusion results in extensive microvascular injury in the liver. The protective effects of misoprostol against this injury may occur at the vascular level.

Inhibition of human platelets and polymorphonuclear neutrophils by the potent and metabolically stable prostaglandin D2 analog ZK 118.182

The actions of the novel metabolically stable and selective prostaglandin D2 receptor agonist ZK 118.182 ((5Z,13E)-(9R,11R,15S)-9-chloro-15-cyclohexyl-15- hydroxy-16,17,18,19,20-pentanor-3-oxa-5,13-prostadienoic acid) were studied in human platelets and polymorphonuclear neutrophils in vitro and compared to the naturally occurring agonist prostaglandin D2. ZK 118.182 inhibited collagen and ADP induced platelet aggregation more potently than prostaglandin D2 (IC50: 15 nM versus 60 nM) but was less effective than the stable prostacyclin mimetic iloprost (IC50: 3 nM). The same rank order of potencies was observed for the inhibition of collagen-induced platelet ATP secretion. A dose-dependent activation of adenylate cyclase could be demonstrated by ZK 118.182 which was comparable to that of prostaglandin D2 with respect to the concentration needed for half maximal stimulation (ED50) maximal cAMP level achievable. ZK 118.182 also dose dependently reduced the formyl-methionyl-leucyl-phenylalanine (FMLP) or platelet-activating factor (PAF) induced activation of polymorphonuclear neutrophils. Both, the oxygen burst resulting in the generation of superoxide anions and the degranulation of polymorphonuclear neutrophils accompanied by release of the lysosomal enzyme beta-glucuronidase, were significantly and dose dependently inhibited. ZK 118.182 was more potent than prostaglandin D2 in inhibiting polymorphonuclear neutrophil activation in all tests performed. In summary, ZK 118.182 is a prostaglandin D2 mimetic exerting potent inhibitory effects on human platelets and polymorphonuclear neutrophils.

Skeletal muscle ischemia-reperfusion injury: a review of endothelial cell-leukocyte interactions

Ischemia-reperfusion injury remains a difficult problem facing vascular surgeons because of its associated high morbidity and mortality. The basis for tissue injury during ischemia depends on depletion of tissue oxygen and energy substrates. Cell injury, as documented cellular edema and lysosomal degranulation, begins after only 30 min of ischemia. Irreversible cellular changes occur after 4-6 h of skeletal muscle ischemia. Following acute arterial occlusion, the restoration of blood flow heralds the onset of biochemical events, forming the basis of what is known as the reperfusion syndrome. This tissue injury is maximal in areas with the greatest blood flow during reperfusion. Endothelium-leukocyte interactions play an important role in ischemia-reperfusion injury. Both endothelial and white blood cells have the biochemical machinery and capacity to generate molecular signals, to express adhesion proteins, and to produce toxic metabolic by-products. Since the microcirculatory changes in ischemia-reperfusion injury parallel those seen in inflammation, the leukocyte-endothelial interaction can explain many of the reactions associated with the early phases of ischemia-reperfusion injury.