Prostaglandin E2 elevation of cyclic-AMP in granuloma macrophages at various stages of inflammation: Relevance to anti-inflammatory and immunomodulatory functions

In the carrageenin-induced granuloma of rats the inflammatory tissue growth and macrophage invasion on the one hand and the cyclic-AMP content of the macrophages on the other, display opposite directional changes. Macrophages, isolated from this tissue at different stages of inflammation, were used to examine the effect of prostaglandin E₂ on intracellular levels of c-AMP. It appears that during infiltration of the macrophages into the inflammatory tissue, the sensitivity of adenylate cyclase to activation by PGE₂ increases. Arguments are presented that these observations made , are in direct relevance to the previously described anti-inflammatory effect of PGE on granuloma tissue .     

P2X4 receptors mediate PGE2 release by tissue‐resident macrophages and initiate inflammatory pain

Prostaglandin E2 (PGE2) is a key mediator of inflammation and contributes to pain hypersensitivity by promoting sensory neurons hyperexcitability. PGE2 synthesis results from activation of a multi‐step enzymatic cascade that includes cyclooxygenases (COXs), the main targets of non‐steroidal anti‐inflammatory drugs (NSAIDs). Although NSAIDs are widely prescribed to reduce inflammatory symptoms such as swelling and pain, associated harmful side effects restrict their long‐term use. Therefore, finding new drugs that limit PG production represents an important therapeutic issue. In response to peripheral inflammatory challenges, mice lacking the ATP‐gated P2X4 channel (P2X4R) do not develop pain hypersensitivity and show a complete absence of inflammatory PGE2 in tissue exudates. In resting conditions, tissue‐resident macrophages constitutively express P2X4R. Stimulating P2X4R in macrophages triggers calcium influx and p38 MAPK phosphorylation, resulting in cytosolic PLA2 (cPLA2) activation and COX‐dependent release of PGE2. In naive animals, pain hypersensitivity was elicited by transfer into the paw of ATP‐primed macrophages from wild type, but not P2X4R‐deficient mice. Thus, P2X4Rs are specifically involved in inflammatory‐mediated PGE2 production and might therefore represent useful therapeutic targets.     

Interleukin 1 and prostaglandin production by cells of the mononuclear phagocyte system isolated from mycobacterial granulomas

A study has been made of the activity of interleukin 1 (IL-1) and prostaglandins (PGs) in the culture supernatants from unstimulated and lipopolysaccharide (LPS)-stimulated mycobacteria-induced granuloma cells. Both epithelioid cells from bacillus Calmette-Guerin (BCG)-induced granulomas and macrophages from Mycobacterium leprae-induced granulomas, separated on a fluorescence-activated cell sorter using monoclonal antibody specific to guinea pig macrophages, spontaneously secreted low levels of IL-1 (assayed by thymocyte comitogenic and fibroblast mitogenic activities) into culture supernatants. However, culture supernatants from LPS-stimulated epithelioid cells showed significantly higher IL-1 activity than those from unstimulated cells. In contrast, LPS stimulation of M. leprae granuloma macrophages failed to enhance IL-1 production. Nevertheless, IL-1 activity in the culture supernatants from stimulated mycobacterial granuloma cells of both types was much lower than that from LPS-stimulated peritoneal exudate macrophage culture supernatants. There was no detectable amount of prostaglandin E2 (PGE2) in the culture supernatants from both unstimulated and LPS-stimulated BCG- and M. leprae-induced granuloma cells in comparison to much higher levels of PGE2 produced by unstimulated (0.28-6.2 ng/ml) or LPS-stimulated (greater than 15 ng/ml) peritoneal exudate macrophages. However, BCG granuloma cells either secreted prostaglandin F2 alpha (PGF2 alpha) spontaneously or produced comparable levels of PGF2 alpha to those from peritoneal exudate macrophages on stimulation, while M. leprae granuloma macrophages produced much lower levels of PGF2 alpha.     

Regulation of guinea pig macrophage collagenase production by dexamethasone and colchicine

Previous studies have demonstrated that exposure of guinea pig macrophages to a primary signal, such as lipopolysaccharide (LPS), stimulates the synthesis of prostaglandin E2 (PGE2) which, in turn, elevates cAMP levels resulting in the production of the enzyme, collagenase. The potential of regulating the biochemical events in this activation sequence was examined with the anti-inflammatory agents dexamethasone and colchicine, which suppress the destructive sequelae in chronic inflammatory lesions associated with the degradation of connective tissue. The addition of dexamethasone with LPS to macrophage cultures resulted in a dose-dependent inhibition of PGE2 and collagenase production, which was reversed by the exogenous addition of phospholipase A2. Collagenase production was also restored in dexamethasone-treated cultures by the addition of products normally produced as a result of phospholipase action, such as arachidonic acid, PGE2 or dibutyryl-cAMP. Since the effect of dexamethasone was thus linked to phospholipase A2 inhibition, mepacrine, a phospholipase inhibitor, was also tested. Mepacrine, like dexamethasone, caused a dose-dependent inhibition of PGE2 and collagenase. In addition to corticosteroid inhibition, colchicine was also found to block collagenase production. However, this anti-inflammatory agent had no effect on PGE2 synthesis. Colchicine was effective only when added at the onset of culture and not 24 h later, implicating a role for microtubules in the transmission of the activation signal rather than enzyme secretion. The failure of lumicolchicine to inhibit collagenase activity provided additional evidence that microtubules are involved in the activation of macrophages. These findings demonstrate that dexamethasone and colchicine act at specific steps in the activation sequence of guinea pig macrophages to regulate collagenase production.     

Production of cyclooxygenase products and superoxide anion by macrophages in response to chemotactic factors

Mononuclear phagocytes are known to play a key role in various phlogistic reactions by synthesizing and releasing products that may potentiate or inhibit inflammatory processes. The expression of these products appears to be dependent on the source of the macrophage population as well as the stimulus employed. We have studied superoxide anion (O-2) production as well as the generation of PGE2, PGF2 alpha, and TXB2 from resident, oil-elicited and thioglycollate-induced peritoneal macrophages in mice in the presence and absence of chemotactic peptides. Production of O-2, occurred only in elicited macrophages stimulated with high concentrations of FMLP or C5a; resident cells stimulated with either of the chemotactic peptides were completely unresponsive. Although resident peritoneal macrophages incubated with chemotactic peptides did not generate O-2, these cells did secrete significant levels of PGE2, PGF2 alpha, and TXB2 in response to C5a. FMLP had no stimulatory effect. Elicited macrophages generated increased levels of PGE2 and PGF2 alpha when incubated with C5a. However, production of TXB2 was not stimulated. FMLP was inactive in stimulating PGE2, PGF2 alpha, and TXB2 in all types of macrophages studied. These studies indicate a heterogeneity in the production of inflammatory mediators from various macrophage populations in response to chemotactic factors.     

前列腺素E_1对肺的细胞保护作用

本文观察到体外培养下,前列腺素E_1 可降低豚鼠巨噬细胞和嗜酸粒细胞对肺细胞的细胞毒作用,可抑制肺泡巨噬细胞的吞噬活性,并能降低标记肺细胞的自发[~3H]释放量。前列腺素E_1 对炎症效应细胞的抑制作用和对肺细胞的保护作用有显著的剂量-效应关系。鉴于巨噬细胞在机体防御和炎症反应中的作用极为重要,而激活巨噬细胞可以释放前列腺素E_1,推论在肺部疾病发展过程中,由激活巨噬细胞释放前列腺素使局部浓度增高时,可以负反馈地调整效应细胞的活力,并对正常肺细胞产生细胞保护作用,以减轻炎症效应细胞对肺组织的伤害。     

Surface contact modulation of inflammatory macrophage antibody dependent cytotoxicity and prostanoid release.

Adherence to extracellular matrix proteins modulates the functional and secretory activities of mononuclear phagocytes, although the mechanisms regulating these adherence-dependent changes are poorly understood. In this study, the ability of rat inflammatory peritoneal macrophages (PM) to adhere to an endothelial cell-derived extracellular matrix or a denatured collagen/fibronectin-coated surface and perform antibody dependent cell cytotoxicity (ADCC) and secrete reactive oxygen intermediates was compared with PM adherent to tissue culture plastic. Prostaglandin E2 (PGE2) and thromboxane B2 (TxB2), two major cyclooxygenase products released by inflammatory macrophages, were also measured by PM adherent to the protein coated surfaces. Rat exudate PM were equally adherent to tissue culture plastic or wells coated with either endothelial cell derived matrix or denatured collagen (gelatin)/fibronectin. PM adherent to a denatured collagen/fibronectin-coated wells demonstrated significantly less cytolytic activity (15 +/- 2% lysis) when compared with either tissue culture plastic adherent PM (43 +/- 7% lysis) or PM adherent to extracellular matrix (59 +/- 11% lysis). PM adherent to extracellular matrix released twofold more TxB2 than plastic adherent PM, while PM adherent to denatured collagen/fibronectin released 40% more PGE2 than cells adherent to tissue culture plastic or 80% more PGE2 than PM adherent to the extracellular matrix. PM adherent to denatured collagen/fibronectin release less superoxide anion (27 +/- .9 nmoles/10(6) PM) than PM adherent to either tissue culture plastic (43 +/- 1 nmoles/10(6) PM) or the extracellular matrix (60 +/- 0.5 nmoles/10(6) PM). Furthermore, incubation of plastic adherent PM with exogenous PGE2 reduced superoxide production in a dose-dependent manner. These results demonstrate that the inhibition of ADCC and secretion of reactive oxygen intermediates by PM adherent to a denatured collagen/fibronectin surface correlated with an increased release of the immunosuppressive prostanoid PGE2. Furthermore, the addition of exogenous PGE2 to plastic adherent PM reproduced the depression in ADCC and superoxide anion production observed by PM adherent to a denatured collagen/fibronectin surface. These studies suggest that the increased production and release of PGE2 by inflammatory macrophages adherent to a denatured collagen surface may act to suppress cytotoxic mechanisms and thereby constitutes part of an autocrine feedback mechanism regulating macrophage function during wound injury.     

Liver X receptor ligands inhibit the lipopolysaccharide-induced expression of microsomal prostaglandin E synthase-1 and diminish prostaglandin E2 production in murine peritoneal macrophages

Microsomal prostaglandin E synthase (mPGES)-1, which is dramatically induced in macrophages by inflammatory stimuli such as lipopolysaccharide (LPS), catalyzes the conversion of cyclooxygenase-2 (COX-2) reaction product prostaglandin H(2) (PGH(2)) into prostaglandin E(2) (PGE(2)). The mPGES-1-derived PGE(2) is thought to help regulate inflammatory responses. On the other hand, excess PGE(2) derived from mPGES-1 contributes to the development of inflammatory diseases such as arthritis and inflammatory pain. Here, we examined the effects of liver X receptor (LXR) ligands on LPS-induced mPGES-1 expression in murine peritoneal macrophages. The LXR ligands 22(R)-hydroxycholesterol (22R-HC) and T0901317 reduced LPS-induced expression of mPGES-1 mRNA and mPGES-1 protein as well as that of COX-2 protein. However, LXR ligands did not influence the expression of microsomal PGES-2 (mPGES-2) or cytosolic PGES (cPGES) protein. Consequently, LXR ligands suppressed the production of PGE(2) in macrophages. These results suggest that LXR ligands diminish PGE(2) production by inhibiting the LPS-induced gene expression of the COX-2-mPGES-1 axis in LPS-activated macrophages.     

The proinflammatory effect of prostaglandin E2 in experimental inflammatory bowel disease is mediated through the IL-23-->IL-17 axis

Although Crohn's disease has been traditionally considered to be Th1-mediated, the newly identified Th17 cells emerged recently as crucial participants. Th1/Th17 differentiation is controlled primarily by the IL-12 family of cytokines secreted by activated dendritic cells (DCs) and macrophages. IL-23 and IL-12/IL-27 have opposite effects, supporting the Th17 and Th1 phenotypes, respectively. We found that PGE(2), a major lipid mediator released in inflammatory conditions, shifts the IL-12/IL-23 balance in DCs in favor of IL-23, and propose that high levels of PGE(2) exacerbate the inflammatory process in inflammatory bowel disease through the IL-23-->IL-17 axis. We assessed the effects of PGE(2) on IL-12, IL-27, and IL-23 and found that PGE(2) promotes IL-23, inhibits IL-12 and IL-27 expression and release from stimulated DCs, and subsequently induces IL-17 production in activated T cells. The effects of PGE(2) are mediated through the EP2/EP4 receptors on DCs. In vivo, we assessed the effects of PGE analogs in an experimental model for inflammatory bowel disease and found that the exacerbation of clinical symptoms and histopathology correlated with an increase in IL-23 and IL-17, a decrease in IL-12p35 expression in colon and mesenteric lymph nodes, and a substantial increase in the number of infiltrating neutrophils and of CD4(+)IL-17(+) T cells in the colonic tissue. These studies suggest that high levels of PGE(2) exacerbate the inflammatory process through the preferential expression and release of DC-derived IL-23 and the subsequent support of the autoreactive/inflammatory Th17 phenotype.     

Tumor necrosis factor production by murine resident peritoneal macrophages is enhanced by dietary n-3 polyunsaturated fatty acids

Tumor necrosis factor (TNF) is a macrophage derived peptide that has an antitumor action and modulates immune and inflammatory reactions. Dietary fatty acids may modulate TNF production as dietary n-3 polyunsaturated fatty acids suppress human monocyte TNF production, but enhance its secretion by murine peritoneal macrophages. Mice were maintained for 5 weeks on diets containing different amounts of n-3 and n-6 fatty acids. TNF, PGE2 and 6-keto PGF1 alpha production was monitored following in vitro stimulation of resident peritoneal macrophages with lipopolysaccharide. Macrophages from mice fed the high n-3 diet produced 8-fold more TNF and half the PGE2 produced by macrophages from mice on the other diets. Indomethacin caused an increase in the TNF production by macrophages from mice on all diets but macrophages from mice on the high n-3 diet produced more TNF than macrophages from mice on the other diets. Exogenous PGE2 (100 nM) greatly decreased TNF production by macrophages from mice on all diets, but macrophages from mice on the high n-3 diet secreted 70% more TNF than macrophages from mice fed the other diets, indicating that PGE2 is only partly responsible for the effects observed. The results show that feeding n-3 polyunsaturated fatty acids may cause enhanced TNF production by resident peritoneal macrophages and that PGE2 is partly responsible for the effect.     

Elevated COX2 expression and PGE2 production by downregulation of RXRα in senescent macrophages

Increased systemic level of inflammatory cytokines leads to numerous age-related diseases. In senescent macrophages, elevated prostaglandin E2 (PGE2) production contributes to the suppression of T cell function with aging, which increases the susceptibility to infections. However, the regulation of these inflammatory cytokines and PGE2 with aging still remains unclear. We have verified that cyclooxygenase (COX)-2 expression and PGE2 production are higher in LPS-stimulated macrophages from old mice than that from young mice. Downregulation of RXRα, a nuclear receptor that can suppress NF-κB activity, mediates the elevation of COX2 expression and PGE2 production in senescent macrophages. We also have found less induction of ABCA1 and ABCG1 by RXRα agonist in senescent macrophages, which partially accounts for high risk of atherosclerosis in aged population. Systemic treatment with RXRα antagonist HX531 in young mice increases COX2, TNF-α, and IL-6 expression in splenocytes. Our study not only has outlined a mechanism of elevated NF-κB activity and PGE2 production in senescent macrophages, but also provides RXRα as a potential therapeutic target for treating the age-related diseases.     

Regulation by PGE2 of the production of oxygen intermediates by LPS-activated macrophages

The regulation by prostaglandin E2 (PGE2) of production of oxygen radicals by bacterial lipopolysaccharide-(LPS) activated macrophages was studied in vitro. A 48-hr incubation of murine thioglycollate-elicited macrophages with LPS (0.1 micrograms/ml) resulted in an enhanced ability of these cells to produce oxygen radicals when challenged with phorbol myristate acetate (PMA). Macrophages incubated for 48 hr without LPS did not produce measurable amounts of oxygen radicals when exposed to this triggering stimulus. Thus, PMA-triggered production of oxygen radicals was the result of macrophage activation by LPS. The PMA-triggered production of oxygen radicals by the LPS-activated macrophages was inhibited when PGE2 (10(-5) to 10(-9) M) was present during the incubation with LPS. Inhibition by PGE2 occurred during the early stages of macrophage activation, since the addition of PGE2 24 hr after LPS no longer inhibited the production of oxygen radicals by the macrophages. This inhibitory effect of PGE2 on the LPS-induced activation of macrophages could be reproduced by cyclic-adenosine-monophosphate (cAMP) agonists, such as isoproterenol and cholera toxin as well as by the cAMP analog dibutyryl-cAMP, suggesting a cAMP-mediated mechanism for the inhibitory effect of PGE2 on macrophage activation by LPS. Previous reports have implicated prostaglandins as mediators of destructive processes associated with chronic inflammation. Our findings suggest that PGE2 may, on the other hand, reduce tissue damage in a chronic inflammatory site by inhibiting the production of oxygen radicals by macrophages activated in the sera.     

Prostaglandin E2 suppresses lipopolysaccharide-stimulated IFN-beta production

Macrophages activate the production of cytokines and chemokines in response to LPS through signaling cascades downstream from TLR4. Lipid mediators such as PGE(2), which are produced during inflammatory responses, have been shown to suppress MyD88-dependent gene expression upon TLR4 activation in macrophages. The study reported here investigated the effect of PGE(2) on TLR3- and TLR4-dependent, MyD88-independent gene expression in murine J774A.1 macrophages, as well as the molecular mechanism underlying such an effect. We demonstrate that PGE(2) strongly suppresses LPS-induced IFN-beta production at the mRNA and protein levels. Poly (I:C)-induced IFN-beta and LPS-induced CCL5 production were also suppressed by PGE(2). The inhibitory effect of PGE(2) on LPS-induced IFN-beta expression is mediated through PGE(2) receptor subtypes EP(2) and EP(4), and mimicked by the cAMP analog 8-Br-cAMP as well as by the adenylyl cyclase activator forskolin. The downstream effector molecule responsible for the cAMP-induced suppressive effect is exchange protein directly activated by cAMP (Epac) but not protein kinase A. Moreover, data demonstrate that Epac-mediated signaling proceeds through PI3K, Akt, and GSK3beta. In contrast, PGE(2) inhibits LPS-induced TNF-alpha production in these cells through a distinct pathway requiring protein kinase A activity and independent of Epac/PI3K/Akt. In vivo, administration of a cyclooxygenase inhibitor before LPS injection resulted in enhanced serum IFN-beta concentration in mice. Collectively, data demonstrate that PGE(2) is a negative regulator for IFN-beta production in activated macrophages and during endotoxemia.     

Prostaglandin E2 modulates TNF-alpha-induced MCP-1 synthesis in pancreatic acinar cells in a PKA-dependent manner

Cyclooxygenase (COX)-2 is increased in human chronic pancreatitis. We recently demonstrated in a model of chronic pancreatitis (WBN/Kob rat) that inhibition of COX-2 activity reduces and delays pancreatic inflammation and fibrosis. Monocyte chemoattractant protein (MCP)-1 mRNA and PGE(2) were significantly reduced, correlating with a decreased infiltration of macrophages. MCP-1 plays an important role in the recruitment of macrophages to the site of tissue injury. The aim of our study is to identify mechanisms by which macrophages and acinar cells maintain an inflammatory reaction. The expression profile of E prostanoid receptors EP(1-4) and MCP-1 was analyzed by RT-PCR from pancreatic specimens and AR42J cells. MCP-1 secretion was detected by ELISA from rat pancreatic lobuli. We determined EP(1-4) mRNA levels in WBN/Kob rats with chronic pancreatic inflammation. Individual isoforms were highly increased in rat pancreas, concurrent with MCP-1 mRNA expression. In supernatants of pancreatic lobuli and AR42J cells, MCP-1 was detectable by ELISA. In the presence of TNF-alpha, MCP-1 was upregulated. Coincubation with PGE(2) enhanced the TNF-alpha-induced MCP-1 synthesis significantly. Similarly, TNF-alpha mRNA was synergistically upregulated by TNF-alpha and PGE(2). Furthermore, the synergistic effect of TNF-alpha and PGE(2) was abolished by inhibition of PKA but not of PKC. We conclude that EP receptors are upregulated during chronic pancreatic inflammation. PGE(2) modulates the TNF-alpha-induced MCP-1 synthesis and secretion from acinar cells. This synergistic effect is controlled by PKA. This mechanism might explain the COX-2-dependent propagation of pancreatic inflammation.     

The effect of silica-treated macrophages on the synthesis of collagen and other proteins in vitro

Treatment with SiO₂ releases from peritoneal macrophages a soluble factor which stimulates the synthesis of collagen and other proteins in incubated slices of experimental granulation tissue. This factor can also be obtained by SiO₂-treatment from certain subcellular particles of intact macrophages. A similar agent is released from the macrophages by incubation with rheumatoid synovialtissue extract. Macrophages induced by paraffin or thioglycollate medium cannot be stimulated further by SiO₂. The SiO₂-treated macrophages have no effect on detached matrix-free cells from embryonic-chick tendon or granulation tissue. Another factor from macrophages, present in the 100000 g-supernatant of the homogenate, inhibits the synthesis of collagen in granuloma slices. The synthesis of DNA and RNA in slices is suppressed by the extract from intact macrophages but not affected by preparations obtained with SiO₂. The possible relevance of these findings to lysosomal actions, to the regulation of granuloma formation and to inflammation are discussed.     

EP2 and EP4 receptors on muscularis resident macrophages mediate LPS-induced intestinal dysmotility via iNOS upregulation through cAMP/ERK signals

Intestinal resident macrophages play an important role in gastrointestinal dysmotility by producing prostaglandins (PGs) and nitric oxide (NO) in inflammatory conditions. The causal correlation between PGs and NO in gastrointestinal inflammation has not been elucidated. In this study, we examined the possible role of PGE(2) in the LPS-inducible inducible NO synthase (iNOS) gene expression in murine distal ileal tissue and macrophages. Treatment of ileal tissue with LPS increased the iNOS and cyclooxygenase (COX)-2 gene expression, which lead to intestinal dysmotility. However, LPS did not induce the expression of iNOS and COX-2 in tissue from macrophage colony-stimulating factor-deficient op/op mice, indicating that these genes are expressed in intestinal resident macrophages. iNOS and COX-2 protein were also expressed in dextran-phagocytized macrophages in the muscle layer. CAY10404, a COX-2 inhibitor, diminished LPS-dependent iNOS gene upregulation in wild-type mouse ileal tissue and also in RAW264.7 macrophages, indicating that PGs upregulate iNOS gene expression. EP(2) and EP(4) agonists upregulated iNOS gene expression in ileal tissue and isolated resident macrophages. iNOS mRNA induction mediated by LPS was decreased in the ileum isolated from EP(2) or EP(4) knockout mice. In addition, LPS failed to decrease the motility of EP(2) and EP(4) knockout mice ileum. EP(2)- or EP(4)-mediated iNOS expression was attenuated by KT-5720, a PKA inhibitor and PD-98059, an ERK inhibitor. Forskolin or dibutyryl-cAMP mimics upregulation of iNOS gene expression in macrophages. In conclusion, COX-2-derived PGE(2) induces iNOS expression through cAMP/ERK pathways by activating EP(2) and EP(4) receptors in muscularis macrophages. NO produced in muscularis macrophages induces dysmotility during gastrointestinal inflammation.     

Anti-inflammatory and anti-arthritic effects of new synthetic 3-(4-hydroxyphenyl)-4-(4-thiomethoxyphenyl)-1H-pyrrole-2,5-dione

We previously reported that 3-(4-hydroxyphenyl)-4-(4-thiomethoxyphenyl)-1H-pyrrole-2,5-dione (1, HMP) has a strong inhibitory effect on prostaglandin E(2) (PGE(2)) production. In this study, the anti-inflammatory and anti-arthritic effects of HMP were evaluated on LPS-induced RAW 264.7 macrophages and rats with carrageenan-induced paw edema and adjuvant-induced arthritis (AIA). The attenuation of PGE(2) production by HMP was found to be caused by the inhibition of cyclooxygenase-2 (COX-2) activity, but not COX-1 activity. However, HMP did not affect COX-2 at the protein or mRNA levels, whereas it suppressed the releases and expressions of inflammatory cytokines, such as, interleukin-1β (IL-1β) and IL-6 in LPS-induced macrophages. Furthermore, HMP suppressed LPS-induced nitric oxide (NO) production by down regulating the protein and mRNA expressions of inducible nitric oxide synthase (iNOS). In rats with carrageenan-injected acute inflammation, oral administration of HMP (25 or 50mg/kg, po) reduced paw swelling, and PGE(2) release and myeloperoxidase (MPO) activity in tissue. Furthermore, HMP (25 or 50mg/kg, po) significantly reduced paw swelling, arthritic indices and plasma PGE(2) concentrations in rat with AIA. These results show that HMP reduces swelling in a model acute inflammation and inhibits arthritic responses in a model of chronic inflammation via the inhibition of PGE(2) production. These results suggest that HMP is a potential therapeutic agent for the treatment of arthritis and associated disorders.     

Extracellular matrix-induced cyclooxygenase-2 regulates macrophage proteinase expression

Chronic inflammatory diseases are characterized by the persistent presence of macrophages and other mononuclear cells, tissue destruction, cell proliferation, and the deposition of extracellular matrix (ECM). The tissue degradation is mediated, in part, by enhanced proteinase expression by macrophages. It has been demonstrated recently that macrophage proteinase expression can be stimulated or inhibited by purified ECM components. However, in an intact ECM the biologically active domains of matrix components may be masked either by tertiary conformation or by complex association with other matrix molecules. In an effort to determine whether a complex ECM produced by vascular smooth muscle cells (SMC) regulates macrophage degradative phenotype, we prepared insoluble SMC matrices and examined their ability to regulate proteinase expression by RAW264.7 and thioglycollate-elicited peritoneal macrophages. Here we demonstrate that macrophage engagement of SMC-ECM triggers PKC-dependent activation of MAPK(erk1/2) leading to increased expression of cyclooxygenase (COX)-2 and prostaglandin (PG) E(2) synthesis. The addition of PGE(2) to macrophage cultures stimulates their expression of both urokinase-type plasminogen activator and MMP-9, and the selective COX-2 inhibitor NS-398 blocks ECM-induced proteinase expression. Moreover, ECM-induced PGE(2) and MMP-9 expression by elicited COX-2(-/-) macrophages is markedly reduced when compared with the response of either COX-2(+/-) or COX-2(+/+) macrophages. These data clearly demonstrate that SMC-ECM exerts a regulatory role on the degradative phenotype of macrophages via enhanced urokinase-type plasminogen activator and MMP-9 expression, and identify COX-2 as a targetable component of the signaling pathway leading to increased proteinase expression.