Thromboxane synthase is preferentially conserved in activated mouse peritoneal macrophages

Thromboxane synthase deficiency improves insulin action and attenuates adipose tissue fibrosis

Thromboxane A2, an arachidonic acid-derived eicosanoid generated by thromboxane synthase (TBXAS), plays critical roles in hemostasis and inflammation. However, the contribution of thromboxane A2 to obesity-linked metabolic dysfunction remains incompletely understood. Here, we used in vitro and mouse models to better define the role of TBXAS in metabolic homeostasis. We found that adipose expression of Tbxas and thromboxane A2 receptor (Tbxa2r) was significantly upregulated in genetic and dietary mouse models of obesity and diabetes. Expression of Tbxas and Tbxa2r was detected in adipose stromal cells, including macrophages. Furthermore, stimulation of macrophages with interferon-γ or resistin factors known to be upregulated in obesity induced Tbxas and Tbxa2r expression. Mice lacking Tbxas had similar weight gain, food intake, and energy expenditure. However, loss of Tbxas markedly enhanced insulin sensitivity in mice fed a low-fat diet. Improvement in glucose homeostasis was correlated with the upregulated expression of multiple secreted metabolic regulators (Ctrp3, Ctrp9, and Ctrp12) in the visceral fat depot. Following a challenge with a high-fat diet, Tbxas deficiency led to attenuated adipose tissue fibrosis and reduced circulating IL-6 levels without adipose tissue macrophages being affected; however, these changes were not sufficient to improve whole body insulin action. Together, our results highlight a novel, diet-dependent role for thromboxane A2 in modulating peripheral tissue insulin sensitivity and adipose tissue fibrosis.

Specificity of eicosanoid production depends on the TLR-4-stimulated macrophage phenotype

Eicosanoid metabolism differs in profile and quantity between macrophages of different tissue origin and method of elicitation, as well as between primary and immortalized macrophages after activation with inflammatory stimuli. Using a lipidomic approach, we comprehensively analyzed the eicosanoids made by murine RPMs, TGEMs, BMDM, and the macrophage-like cell line RAW after stimulation with the TLR-4-specific agonist KLA. Direct correlation among total COX metabolites, COX side-products (11-HETE, 15-HETE), COX-2 mRNA, and protein at 8 h was found when comparing each cell type. Comprehensive qPCR analysis was used to compare relative transcript levels between the terminal prostanoid synthases themselves as well as between each cell type. Levels of PGE(2), PGD(2), and TxB(2) generally correlated with enzyme transcript expression of PGES, PGDS, and TBXS, providing evidence of comparable enzyme activities. PGIS transcript was expressed only in RPM and TGEM macrophages and at an exceptionally low level, despite high metabolite production compared with other synthases. Presence of PGIS in RPM and TGEM also lowered the production of PGE(2) versus PGD(2) by approximately tenfold relative to BMDM and RAW cells, which lacked this enzyme. Our results demonstrate that delayed PG production depends on the maximal level of COX-2 expression in different macrophages after TLR-4 stimulation. Also, the same enzymes in each cell largely dictate the profile of eicosanoids produced depending on the ratios of expression between them, with the exception of PGIS, which appears to have much greater synthetic capacity and competes selectively with mPGES-1.

Lipoxygenase-derived eicosanoids are involved in the inhibitory effect of Crotalus durissus terrificus venom or crotoxin on rat macrophage phagocytosis

Crotalus durissus terrificus snake venom and its major toxin, crotoxin or type II PLA2 subunit of this toxin, induce an inhibitory effect on spreading and phagocytosis in 2h incubated macrophages. The involvement of arachidonate-derived mediators on the inhibitory action of the venom or toxins on rat peritoneal macrophage phagocytosis was presently investigated. Peritoneal cells harvested from naive rats and incubated with the venom or toxins or harvested from the peritoneal cavity of rats pre-treated with the toxins were used. Zileuton, a 5-lipoxygenase inhibitor but not indomethacin, a cyclooxygenase inhibitor, given in vivo and in vitro abolished the inhibitory effect of venom or toxins on phagocytosis. Resident peritoneal macrophages incubated with the venom or toxins showed increased levels of prostaglandin E2 and lipoxin A4, with no change in leukotriene B4. These results suggest that lipoxygenase-derived eicosanoids are involved in the inhibitory effect of C.d. terrificus venom, crotoxin or PLA2 on macrophage phagocytosis.

Pathway-oriented profiling of lipid mediators in macrophages

Macrophages produce various kinds of lipid mediators including eicosanoids and platelet-activating factor. Since they are produced from common precursors, arachidonic acid-containing phospholipids, regulations of metabolic pathways underlie the patterning of lipid mediator production. Here, we report a pathway-oriented profiling strategy of lipid mediators by a newly developed multiplex quantification system. We profiled mouse peritoneal macrophages in different activation states. The analysis of kinetics revealed the differences in the production time course of various lipid mediators, which also differed by the macrophage types. Scatterplot matrix analysis of the inhibitor study revealed correlations of lipid mediator species. The changes of these correlations provided estimates on the effects of lipopolysaccharide priming. We also found a highly linked production of 11-hydroxyeicosatetraenoic acid and prostaglandin E2, implying the in vivo property of cyclooxygenase-mediated 11-hydroxyeicosatetraenoic acid production. The present approach will serve as a strategy for understanding the regulatory mechanism of lipid mediator production.

Cyclooxygenase Isozymes: The Biology of Prostaglandin Synthesis and Inhibition

Nonsteroidal anti-inflammatory drugs (NSAIDs) represent one of the most highly utilized classes of pharmaceutical agents in medicine. All NSAIDs act through inhibiting prostaglandin synthesis, a catalytic activity possessed by two distinct cyclooxygenase (COX) isozymes encoded by separate genes. The discovery of COX-2 launched a new era in NSAID pharmacology, resulting in the synthesis, marketing, and widespread use of COX-2 selective drugs. These pharmaceutical agents have quickly become established as important therapeutic medications with potentially fewer side effects than traditional NSAIDs. Additionally, characterization of the two COX isozymes is allowing the discrimination of the roles each play in physiological processes such as homeostatic maintenance of the gastrointestinal tract, renal function, blood clotting, embryonic implantation, parturition, pain, and fever. Of particular importance has been the investigation of COX-1 and -2 isozymic functions in cancer, dysregulation of inflammation, and Alzheimer's disease. More recently, additional heterogeneity in COX-related proteins has been described, with the finding of variants of COX-1 and COX-2 enzymes. These variants may function in tissue-specific physiological and pathophysiological processes and may represent important new targets for drug therapy.

The change in leukotrienes and lipoxins in activated mouse peritoneal macrophages

The aim of this study was to investigate to what extent the generation of leukotrienes (LTs) and lipoxins (LXs) was affected by the expression of definite levels of macrophage activation. We used a system of murine peritoneal macrophages at different states of activation consisting in resident macrophages and FCS-, thioglycollate- or Corynebacterium parvum-elicited macrophages. The profile of lipoxygenase metabolites in resident macrophages was characterized by the presence of high levels of 12-HETE, followed by 15-HETE, 5-HETE, LTB(4) and 6-trans-LTB(4), 6-trans-12-epi-LTB(4). A comparable pattern was also found in FCS-elicited macrophages which appeared not to be responsive to the challenge with interferon gamma plus LPS, as measured by the generation of NO and tumor necrosis factor alpha. Resident as well as FCS-elicited macrophages also generated appreciable quantities of LXs (A(4) and B(4)). Thioglycollate-elicited macrophages, which expressed a state of 'responsive' macrophages, showed a block of the LT and LX synthesis. This block was also present in C. parvum-elicited macrophages which expressed a fully 'activated' phenotype, reflected by their capacity of releasing NO and tumor necrosis factor alpha even though they were not challenged. These results provide the first evidence that the level of 'responsive' as well as 'activated' macrophages was associated with of a simultaneous block of LTB(4) and LXs.

Avian macrophage metabolism

This review considers the role of avian macrophages as a source of immune effector and immunoregulatory metabolites. Although considerable attention has been given to the importance of leukocytic cytokines, particularly the monokines such as interleukin-1 (IL-1), interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-alpha), and transforming growth factor-beta (TGF-beta), metabolites produced by macrophages appear to be of equal importance in determining the progression of immune responses. The three metabolite categories that have received the greatest attention are the reactive oxygen species (ROS), the reactive nitrogen intermediates (RNI), and the eicosanoids. Additionally, the xenobiotic metabolites produced via cytochrome P450 activity mediate some immune-environmental interactions. Each of these four metabolite categories is subject to different requirements for metabolite production, and each has distinct effector functions. An understanding of macrophage metabolite regulation could allow improvements in avian health management and production via the effective control of metabolite production. The present review considers prior and recent information on the production of the metabolites by avian macrophages. Additionally, the potential ramifications of metabolite production and regulation are discussed.

Inverse gene expression of prostacyclin and thromboxane synthases in resident and activated peritoneal macrophages

Prostacyclin and thromboxane A2 produced from prostaglandin H2 are known to be important modulators with opposite biological activities. To examine possible roles of these prostanoids in immune responses, we have studied the gene expression of prostacyclin synthase (PGIS) and thromboxane synthase (TXS) in murine resident macrophages or in macrophages elicited with casein or bacillus Calmette-Guérin (BCG). Northern blot analyses showed that the PGIS mRNA was expressed in a decreasing order in the resident, and casein- and BCG-elicited macrophages. In contrast, the TXS mRNA was expressed in an increasing order in the resident, and casein- and BCG-elicited macrophages. On the other hand, the mRNA for cyclooxygenase-2, which produces PGH2 and participates in the production of prostanoids in inflammation, was expressed in both the resident and BCG-elicited macrophages but barely in the casein-elicited cells. In situ hybridization analysis showed that the expression of mRNAs for PGIS and TXS was ascribable not only to the alteration of the expression levels of both mRNAs in the each macrophage but also to the changes in subpopulations of the cells expressing these mRNAs. These observations suggested that the inverse gene expression of PGIS and TXS in macrophages contributes to immune responses by modulating the relative levels of prostacyclin and thromboxane A2.

Differential effects of cyclo-oxygenase pathway metabolites on cytokine production by T lymphocytes

Cyclo-oxygenase pathway metabolites released in the microenvironment by activated platelets and endothelial cells are potential local modulators of the immune response. In the present study, we have investigated the modulatory role of PGE2, iloprost (prostacyclin analogue), U-46619 (thromboxane analogue) on the release of IL-2, IFN-gamma, TNF-alpha and IL-6 by T lymphocytes. Our results show that PGE2 and prostacyclin differ in the regulation of cytokine production. PGE2 inhibited the release of IL-2 and IFN-gamma, while iloprost did not affect their production. The addition of PGE2 or iloprost greatly decreased the amount of TNF-alpha measured in the supernatants, although the rates of inhibition differed according to the kind of stimulation. Unlike that of PGE2, inhibition by iloprost was stronger in alloactivated cultures than in PHA-stimulated ones. In vitro IL-6 production was stimulated by PGE2 in alloactivated cultures and by iloprost, whatever the stimulus. These results are probably due to other cellular subsets contaminating the T-lymphocyte preparations. After complete removal of monocytes from cell cultures, there were inhibitory effects of lloprost and PGE2 on IL-6 released in the supernatants. We did not observe any significant effect of thromboxane analogue on the production of either cytokine.

Discordance between macrophage arachidonate metabolic phenotype and the expression of cytosolic phospholipase A2 and cyclooxygenase

Macrophages (M phi s) exhibit variations in their ability to release and metabolize arachidonate (AA) depending on their state of activation, differentiation, and tissue origin. In order to understand these variations on a molecular level, we determined whether differences in AA release and metabolism by murine peritoneal M phi s could be explained in terms of cytosolic phospholipase A2 (cPLA2) and cyclooxygenase (COX) expression. Resident M phi s exhibited greater COX capacity (conversion of exogenous AA to PGE2) but lower phospholipase (PLase) activity (release of endogenous AA) than elicited M phi s. Activation of resident M phi s in vivo with endotoxin increased both their PLase activity and COX capacity. Despite the observed differences in PLase activity, peritoneal M phi s under all conditions expressed similar amounts of cPLA2 mRNA and protein. All M phi s exhibited COX-1 mRNA and protein (i.e., the constitutive isoform of COX), although elicited M phi s exhibited increased mRNA for COX-1 but decreased levels of protein, relative to resident M phi s. Elicited (but not resident) cells also exhibited COX-2 mRNA but not COX-2 protein (i.e., the inducible form of COX). Despite the increased COX capacity of resident cells with in vivo activation, their expression of COX-2 mRNA and protein was equivalent to that of unactivated cells, becoming apparent only after cell adherence in vitro. In sum, there is no simple relationship between the ability of M phi s to release and metabolize AA, and the expression of cPLA2 or COX isoforms. Moreover, adherence appears to be important for the expression of COX-2 by M phi s.

Toxoplasma gondii alters eicosanoid release by human mononuclear phagocytes: role of leukotrienes in interferon gamma-induced antitoxoplasma activity

Toxoplasma gondii tachyzoites markedly alter the profile of eicosanoids released by human mononuclear phagocytes. Freshly isolated, 2-h adherent human monocytes release both cyclooxygenase (e.g., thromboxane [TX] B2, prostaglandin [PG] E2) and 5-lipoxygenase (e.g., leukotriene [LT] B4, LTC4) products of arachidonic acid metabolism after stimulation by the calcium ionophore A23187 or ingestion of opsonized zymosan particles or heat-killed T. gondii. However, after incubation with viable T. gondii, normal and chronic granulomatous disease monocytes release only the cyclooxygenase products TXB2 and PGE2 and fail to form LTB4, LTC4, or other 5-lipoxygenase products. Monocytes maintained in culture for 5 d lose this capacity to release TXB2 and PGE2 after incubation with T. gondii. T. gondii significantly inhibit calcium ionophore A23187-induced LTB4 release by monocyte-derived macrophages; heat-killed organisms do not affect this calcium ionophore A23187-induced release of LTB4. T. gondii-induced inhibition of LTB4 release by calcium ionophore A23187-stimulated monocyte-derived macrophage is reversed by interferon (IFN)-gamma treatment of the monolayers. LTB4 induced extensive damage to the cellular membranes and cytoplasmic contents of the organisms as observed by transmission electron microscopy. Exogenous LTB4 (10(-6) M) induced intracellular killing of ingested T. gondii by non-IFN-gamma-treated monocyte-derived macrophages. IFN-gamma-induced antitoxoplasma activity in monocyte-derived macrophages was inhibited by the selective 5-lipoxygenase inhibitor zileuton but not by the cyclooxygenase inhibitor indomethacin. These findings suggest a novel role for 5-lipoxygenase arachidonic acid products in human macrophage IFN-gamma-induced antitoxoplasma activity.

Abundant expression of thromboxane synthase in rat macrophages

The cloned cDNA for rat thromboxane (TX) synthase with a size of 1851 bp contained a 1599-bp open reading frame which encoded a 533-amino acid protein sharing 79.7% identity with human TX synthase. RNA blot analysis was carried out with rat cells and tissues. Rat peritoneal macrophages most abundantly expressed mRNA for TX synthase, and its level was not changed by in vivo stimulation of casein. Bone marrow, spleen, lung and thymus also expressed the TX synthase gene. These findings suggest the possibility that TXA2 plays a role in the immune system.

Selective eicosanoid formation during HL-60 macrophage differentiation. Regulation of thromboxane synthase

Earlier studies on HL-60 cells induced to differentiate into macrophages by phorbol esters have shown a selective stimulation of thromboxane (Tx) formation from endoperoxide prostaglandin (PG) H2, indicating that Tx synthesis is regulated at the level of Tx synthase (TxS), one of the peripheral enzymes of the PGH-synthase pathway. We now report on the regulation of TxS during HL-60 macrophage differentiation using monoclonal anti-TxS serum and comparing turnover rates of TxS and its biological activity with those of other enzymes of arachidonic acid metabolism. Western-blot analysis, enzyme-linked immunosorbent assay, immunohistochemical staining and [35S]methionine-labeling experiments suggested a phorbol-ester-dependent early induction of synthesis of TxS. [35S]Methionine incorporation into TxS was stimulated within 4 h after initiation of differentiation and was associated with a major rise in the TxS catalytical activity. Pulse-chase experiments showed a half life for the TxS protein of 16.4 h in both control and phorbol-ester-treated cells. The biological half life of TxS was 10.5 h, as determined by PGH2 incorporation into TxB2 after cycloheximide treatment. In contrast, the biological half lives of PGH synthase, prostacyclin synthase and 5-lipoxygenase were significantly shorter and were 3, 2.5 and 2.5 h, respectively. These results reveal that Tx synthesis in macrophages is mediated by at least two distinct mechanisms; a protein-kinase-C-dependent induction of de novo synthesis of TxS and the selective resistance of the enzyme against the activity of protein kinase C.

Cytokine modulation of immune activation associated suppression of macrophage cyclooxygenase activity in vivo

Intraperitoneal infection with Listeria monocytogenes (LM) results in activation of the peritoneal macrophage population which displays increased surface expression of major histocompatibility (MHC) Class II (Ia) antigen and markedly suppressed prostaglandin (PG) synthesis. We demonstrate here that this decrease in PG production is also seen after treatment by mitogen (Con A) and endotoxin (LPS), and can be explained by reduced cyclooxygenase activity in these cell populations. We show that, whereas Ia expression was augmented at all doses of LM and Con A tested, it displayed a biphasic response to LPS in vivo: increase at the lowest dose and inhibition at higher doses. In order to identify possible endogenous mediators of these responses, we used highly purified preparations of recombinant murine (rMu) cytokines and neutralizing cytokine specific monoclonal antibodies (MAbs) to examine whether interferon-gamma (IFN-gamma) and/or tumor necrosis factor (TNF) down-regulate macrophage cyclooxygenase activity in vivo. We found that IFN-gamma induced Ia expression but had no effect on PG secretion. In contrast, TNF-alpha suppressed PG synthesis and inhibited Ia surface expression. Similarly, in our model of Con A-induced peritoneal macrophage activation, pretreatment of animals with a neutralizing MAb to rMuIFN-gamma completely blocked the induction of Ia positive macrophages by Con A but did not affect Con A-dependent suppression of PG synthesis. Pretreatment with MAb to TNF had no effect on Con A-induced Ia levels, but significantly inhibited suppressed PG synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Enhanced metabolism of arachidonic acid by macrophages from nonobese diabetic (NOD) mice

The inbred nonobese diabetic (NOD) mouse spontaneously develops an autoimmune diabetes, which is now recognized as an experimental model for human type I insulin-dependent diabetes mellitus (IDDM). The autoimmune reaction, specifically directed against pancreatic beta cells (insulitis), involves both macrophages and T lymphocytes. The study of the production of cyclooxygenase and lipoxygenase derivatives of arachidonic acid metabolism shows that in some conditions, and in particular in the presence of zymosan A, macrophages from NOD mice produced significantly more 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) and leukotriene C4 (LTC4) than macrophages from age- and sex-matched C57BL/6 mice. Moreover, zymosan A-stimulated macrophages from NOD females produced significantly more LTC4 than did macrophages from NOD males. These results may be of interest, given the bidirectional relationship between the various cytokines involved in the destruction of beta cells of the islets of Langerhans and different eicosanoids.

Down-regulation of cyclooxygenase product generation by human peritoneal macrophages

Isolated human peritoneal macrophages under resting conditions synthesize and release significant quantities of the cyclooxygenase products prostaglandin E2 (PGE2) and thromboxane B2 (TXB2). These increased linearly with time and were dependent on de novo protein synthesis. Following the addition of calcium ionophore A23187 there was a marked decrease in total generation of immunoreactive cyclooxygenase products. In contrast, there was a concomitant increase in the release of 5-lipoxygenase products. The down-regulation of both PGE2 and TXB2 was not due to diversion of substrate from the cyclooxygenase pathway to the 5-lipoxygenase pathway nor was it due to inhibitory effects of products of the 5-lipoxygenase pathway on the generation of cyclooxygenase products. Instead, the inhibitory effects of A23187 were thought to be due to a down-regulation of cyclooxygenase itself, a hypothesis supported by the finding that TXA2 synthase proved to be unaltered and Western analysis of crude peritoneal macrophage (PM phi) membranes demonstrated lesser quantities of cyclooxygenase in membranes from A23187-treated PM phi than in those prepared from control cells.

Regulation of cyclooxygenase and thromboxane synthase in human monocytes

Stimulation of human monocytes by lipopolysaccharide or phorbol ester resulted in an increase in thromboxane-B2 and prostaglandin-E2 production, whereas interleukin 1, tumour necrosis factor alpha and leukotriene C4 exerted no effects. Inhibitors of protein kinase C suppressed these increases. The activity of cyclooxygenase was induced 3.2-fold by an 8-h stimulation, whereas thromboxane-synthase and prostaglandin-E-isomerase activities remained unchanged. A glucocorticoid, dexamethasone, blocked both basal and induced prostanoid release, as well as cyclooxygenase activity. By immunoprecipitation, we were able to demonstrate an enhanced de novo synthesis of cyclooxygenase protein induced by lipopolysaccharide and phorbol ester. Dexamethasone suppressed cyclooxygenase synthesis, whereas thromboxane synthase was induced. For cyclooxygenase, we calculated a half-life of 3.2 h in human monocytes, and for thromboxane synthase, a half-life of 28 h. These results suggest that the regulation of differential prostanoid production mainly occurs by up and down regulation of cyclooxygenase.

Human platelet-mediated cytotoxicity against Toxoplasma gondii: role of thromboxane

Human platelets, in the absence of antibody, are cytotoxic to tachyzoites of Toxoplasma gondii as determined by vital staining, transmission electron microscopy, and the failure of Toxoplasma to survive and replicate in mice after in vitro interaction of the organisms with platelets. Platelet to T. gondii ratios as low as 1:3 were toxic to the organisms with direct cell-cell contact essential for platelet-mediated cytotoxicity. Adherence of platelets to T. gondii and disruption of surface membranes and cytoplasmic contents of the organisms were observed ultrastructurally. Reactive oxygen species were not implicated in the platelet-mediated toxicity. The interaction of T. gondii with platelets resulted in a marked increase in thromboxane B2 (TXB2) production compared with that by unstimulated platelets. The cyclooxygenase inhibitors acetylsalicylic acid and indomethacin inhibited platelet-mediated cytolytic activity as did the selective TXA2 synthetase inhibitor dazmegrel, indicating a role for thromboxane in the platelet-induced cytotoxicity. Further, toxoplasmacidal activity was retained in the TXA2 synthetase-containing microsomal fractions of platelets disrupted by freezing and thawing; cytolytic activity was absent in microsome-depleted platelet supernatant fractions. Both the TXA2-generating platelet microsome system and a stable TXA2 analogue induced damage to the cellular membranes of the Toxoplasma as noted by transmission electron microscopy. These findings suggest that platelets may play a role in the host defense against Toxoplasma and that release of thromboxane may be important in this cytolytic process.

Fish oil dietary supplementation reduces Ia expression in rat and mouse peritoneal macrophages

Preliminary studies suggest that administration of fish oil fatty acids may be beneficial in several immunological diseases; therefore, we studied the effect of fish oil dietary supplementation on the expression of Ia in stimulated murine peritoneal macrophages. Rats (n = 19) and mice (n = 27) on standard rodent feeding were separated in experimental (E) and control (C) groups that received fish oil or saline solution, respectively, daily for 4 weeks by esophageal gavage. Cholesterol serum levels were significantly lowered by fish oil (E vs C, P less than 0.01). E and C groups were injected intraperitoneally with Listeria monocytogenes (LM) and peritoneal cells were harvested 4 and 7 days after infection. Decreased expression of Ia induced by LM was found in rats (C = 49.68 +/- 5.09%, E = 16.95 +/- 4.3%, P less than 0.01) and mice (C = 47.38 +/- 7.63%, E = 26.66 +/- 1.92%, P less than 0.01). Animals with a more pronounced depression of serum cholesterol (reduction of 44.04 +/- 1.52% of baseline levels) had more depression of Ia expression (6.47 +/- 1.22%, P less than 0.001 vs control). Reduction of Ia expression was not related to PGE2 production by peritoneal cells. Reduction of Ia expression by fish oil could induce down-regulation of antigen presentation and alloreactivity.

Eicosanoid synthesis in human peritoneal macrophages stimulated with S. epidermidis

Peritoneal macrophages isolated from CAPD patients phagocytosed S. epidermidis in a time dependent manner. Coincident with a maximum phagocytic uptake of 56% by 12 hours, there was secretion of a significant amount of neutral protease (1.37 +/- 0.2 mg [3H]-casein degraded/10(6) cells, P = 0.05). In contrast to these delayed effects, coincubation of PMO with S. epidermidis resulted in a significant increase in both LTB4 and LTC4 synthesis above that of controls, with 6.33 +/- 1.20 ng LTB4/10(6) cells (P less than 0.01) and 2.06 +/- 0.68 ng LTC4/10(6) cells (P = 0.014) being generated by three hours. The generation of these lipoxygenase products was both time and dose dependent, and the rapid production and release of the potently chemotactic LTB4 is consistent with the observed clinical response, where a rapid influx of PMN into the peritoneal cavity occurs during episodes of peritonitis, while the generation of LTC4 may contribute to the hyperemia and interstitial edema. In contrast, although there was a time dependent rise in cyclooxygenase product generation by unstimulated cells, a dose dependent inhibition of synthesis was clearly demonstrated when cells were incubated with bacteria, with a mean 40% reduction in generation of PGE2 and a mean 34% reduction in TXB2 generation (P = 0.01 and P less than 0.025, respectively). It was demonstrated that the inhibition was not due to lack of available substrate and that the generation of eicosanoids was unrelated to phagocytosis, bacterial/PMO contact or bacterial surface characteristics. Instead, the observed effect of S. epidermidis on the PMO was attributable to a secreted bacterial product.

Phospholipase A2, an in vivo immunomodulator

Arachidonic acid (AA) can be released from membrane phospholipids by the action of phospholipase A2 (PLA2). There is evidence that unsaturated fatty acids, particularly AA, released from membrane phospholipids are required to activate the respiratory burst of macrophages. The data reported here indicate that peritoneal macrophages harvested 30 min after i.p. injection of PLA2 can phagocytose Candida albicans more efficiently and emit more chemoluminescence (CL) than normal cells when stimulated by zymosan. PLA2 injection also enhances the CL of peritoneal cells from mice already stimulated by immunomodulators such as trehalose dimycolate (TDM), bestatin, or oncostatic drugs such as aclacinomycin (ACM). CL is not sensitive to potassium cyanide (KCN), but is inhibited by catalase, superoxide dismutase (SOD), nordihydroguaiaretic acid (NDGA) and high doses of indomethacin (10(-3) M). In vivo PLA2 treatment stimulates the synthesis of both cyclooxygenase and lipoxygenase derivatives of AA metabolism (PGE2, 6-keto, PGF1 alpha TXB2 and LTC4). Inhibitors of AA metabolism (NDGA, indomethacin) modulate the production of free oxidizing radicals in this experimental model, partly because of their effect on AA metabolism, as determined by the measuring immunoreactive products. However, this work indicates that the effects of these inhibitors, which have been extensively used in CL studies, should be interpreted with caution, since their specificity for AA metabolism is relative.

Altered release of eicosanoids by rat alveolar macrophages during granulomatous pulmonary inflammation

Release of arachidonic acid metabolites (eicosanoids) by alveolar macrophages may be important in regulating pulmonary inflammatory reactions. The purpose of this study was to characterize eicosanoids released by rat alveolar macrophages during the evolution of experimentally induced pulmonary inflammation. Immunization with subcutaneous bacillus Calmette-Guerin (BCG) followed 2 wk later by intravenous BCG challenge resulted in mild granulomatous pulmonary inflammation for up to 30 days. At serial intervals, alveolar macrophages were lavaged from the BCG-treated rats as well as from control normal rats. Lavaged macrophages were cultured in vitro, and culture supernatants were assayed by radioimmunoassay for release of prostaglandin E2 (PGE2), Leukotriene B4 (LTB4), and thromboxane B2 (TXB2). Cells were cultured alone, or with added LPS or calcium ionophore A23187 to stimulate eicosanoid release. During BCG-induced inflammation, spontaneous release of PGE2 and LTB4 was unchanged, while spontaneous release of TXB2 was depressed acutely and then returned to control levels. The capacity of alveolar macrophages to release specific eicosanoids in response to an in vitro stimulus was dramatically altered during the course of BCG-induced inflammation. Stimulated release of PGE2 was transiently increased during acute lung injury, but stimulated release of LTB4 was significantly decreased at all stages of inflammation. Stimulated release of TXB2 was unchanged. These results indicate that during the course of granulomatous pulmonary inflammation there are dynamic changes in the profile of eicosanoids released by alveolar macrophages, both spontaneously and in response to in vitro stimulation. This alteration in the release of eicosanoids by alveolar macrophages may be an important factor in the resolution of pulmonary inflammation.

Pertussis toxin and H-7 distinguish mechanisms involved in eicosanoid release from lipopolysaccharide-primed macrophages. Eicosanoid release from lipopolysaccharide-primed macrophages

Release of eicosanoids is an important response of macrophages to inflammation and bacterial infection. At low concentrations, bacterial lipopolysaccharide (1-2 micrograms/ml) fails to stimulate eicosanoid release in resident peritoneal macrophages but primes the macrophages for a greatly enhanced release of eicosanoids on stimulation with the calcium ionophore A23187 (0.1 microM) or with phorbol 12-myristate 13-acetate (50 nM), an activator of protein kinase C. Incubation of macrophages with Bordetella pertussis toxin, prior to priming with lipopolysaccharide, inhibited the release of both cyclooxygenase and lipoxygenase products upon A23187 stimulation. Pertussis toxin treatment of macrophages had no effect on eicosanoid release when the stimulus was phorbol 12-myristate 13-acetate. The presence of 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7), an effective inhibitor of protein kinase C, during lipopolysaccharide priming and subsequent stimulation significantly inhibited eicosanoid release when phorbol 12-myristate 13-acetate was the stimulus, but did not affect eicosanoid release stimulated by A23187. Based on these results, at least two mechanisms, distinguished by apparent differences in sensitivity to pertussis-toxin-sensitive, guanine-nucleotide-binding proteins and protein kinase C, are involved in eicosanoid secretion by lipopolysaccharide-activated macrophages in response to A23187 and phorbol 12-myristate 13-acetate.

Mononuclear phagocytes and eicosanoids: aspects of their synthesis and biological activities

Mononuclear phagocytes convert arachidonic acid and other unsaturated fatty acids from intracellular sources to a variety of oxygenated metabolites such as prostaglandins and leukotrienes which are secreted into the surrounding medium. Other oxidative products such as hydroxylinoleic acids are reacylated into cellular constituents. The underlying metabolic pathways are activated by numerous stimuli of exogenous or endogenous origin. Depending on the state of activation and cell differentiation, the organ of origin and the nature of the stimulus used, macrophages elaborate a distinct spectrum of oxidative arachidonic acid metabolites. The contribution of these metabolites to the proinflammatory properties of macrophages is twofold: As autocrine signals they modulate the synthesis of diverse macrophage products and they influence cellular functions of other cells such as T-lymphocytes.

Dehydroisoandrosterone prevention of autoimmune disease in NZB/W F1 mice: lack of an effect on associated immunological abnormalities

The effect of dietary dehydroisoandrosterone (DHA) on several immunological abnormalities associated with the development of systemic lupus erythematosus in New Zealand Black/New Zealand White F1 (NZB/W) female mice was examined. Despite the extraordinary benefits in prolonged survival and decreased synthesis of antibodies to double-stranded DNA obtained by adding DHA (0.4% w/v) to the diet fed to these mice (Lucas et al. (1985) J. Clin. Invest. 75, 2091-2093), remarkably small changes in the chemistry and function of the immune system were detected. DHA prevented the increases in spleen mass and in peritoneal cell number which occur with age in NZB/W female mice, but did not prevent the development of hypergammaglobulinemia. DHA did not affect peritoneal macrophage functions as measured by the phagocytosis of opsonized and non-opsonized sheep erythrocytes, or the zymosan-stimulated release of PGE2, 6-ketoPGF1 alpha, TXB2 and LTC4. In spleen, DHA delayed the loss of T-cell mitogenic responses until 5.5 months of age, but did not alter the spleen lymphocyte population.

Prostacyclin release and cytotoxicity of peritoneal cells are inversely related in pregnant and non-pregnant mice infected with herpes simplex virus

Cytotoxicity of peritoneal cells in a HSV-infected murine model is attenuated in late pregnancy. Prostacyclin (PGI2) is elevated at this time in reproductive tissues and has been implicated in the regulation of the immune response. The purpose of this study was to estimate PGI2 in the peritoneal wash or culture supernatants of peritoneal cells obtained from uninfected and HSV-infected pregnant and virgin mice using a radioimmunoassay for 6-keto-prostaglandin F1 alpha. The peritoneal wash of uninfected pregnant and virgin mice contained high levels of 6-keto-PGF1 alpha, 505 +/- 51 pg/100 microliters, (mean +/- S.E., n = 15), and 200 +/- 19 pg/100 microliters, (n = 30), ad did peritoneal effector and target cell cultures (1,159 +/- 118 pg/100 microliters, n = 6, and 1,057 +/- 207 pg/100 microliters, n = 7), respectively. HSV-infection induced in vitro cytotoxicity and suppressed the release of 6-keto-PGF 1 alpha (r = -0.897, P less than 0.05, n = 18). Its concentration was significantly higher (14-fold, P less than .05) in the peritoneal wash, but not in the cell culture, of pregnant (212 +/- 29 pg/100 microliters, n = 19) as compared to virgin mice (18.5 +/- 3.4 pg/100 microliters, n = 27). The levels of 6-keto-PGF1 alpha were inversely correlated (P less than .05) with the combined effects of HSV-infection and cytotoxicity.

Dietary marine lipid does not alter susceptibility of (NZBxNZW)F1 mice to pathogenic microorganisms

Female (NZBxNZW)F1 mice were fed for one month with a diet in which the sources of fat were either melted beef tallow or fish oil, the latter regimen being associated with a marked decrease in the expression of auto-immune disease in these animals. To test whether or not this beneficial effect was associated with an increased risk of infection, animals fed each of these diets were challenged intraperitoneally with graded doses of four different classes of microorganisms: a gram positive bacillus that is an intracellular parasite (Listeria monocytogenes), an exotoxin-producing gram negative bacillus (Pseudomonas aeruginosa), a yeast (Candida albicans), and a herpes group virus (murine cytomegalovirus). There was no difference in the susceptibility of the animals fed the two different diets to any of these infections as shown by either determinations of the LD50 for each organism or by assessment of the times of survival for those animals that did succumb. We conclude that the beneficial anti-inflammatory effects of fish oil diets in these mice are not associated with an increased risk of infection with a variety of microbial agents.

Functional characteristics of macrophages in glomerulonephritis in the rat. O2- generation, MHC class II expression, and eicosanoid synthesis

Macrophage infiltration is important in the pathogenesis of acute proliferative glomerulonephritis (gn). The state of activation of macrophages during gn may be central to their role in injury. To study this, a method for extracting macrophages from nephritic glomeruli in active in situ gn was developed. MHC Class II (Ia) antigen expression, superoxide (O2-) generation, and eicosanoid synthesis were compared with thioglycollate elicited peritoneal macrophages (TEM). At the height of inflammation there were 407 +/- 83 macrophages/glomerulus. Compared with TEM, Ia expression, and in vitro production of O2- were enhanced. Synthesis of prostaglandin E2 was greatly reduced (day 6 gn, 62 +/- 10 ng/mg; TEM 663 +/- 128 ng/mg cell protein). Thromboxane synthesis was relatively conserved (day 6 gn, 109 +/- 28 ng/mg; TEM 201 +/- 53 ng/mg). Leukotriene B4 (LTB4) was undetectable (day 6 gn, less than 13 ng/mg; TEM 119 +/- 56 ng/mg). This large influx of activated macrophages in glomeruli may be fundamental to pathogenesis of glomerular inflammation.

Macrophage heterogeneity in prostaglandins and thromboxane synthesis: differential activation by Fc- and C3b-dependent bacterial phagocytosis

Resident peritoneal macrophages, obtained from rats, were separated into subpopulations by centrifugation on a Percoll discontinuous density gradient. Nine fractions of pure macrophages were isolated. Each subpopulation was studied for Fc- and C3b-dependent bacterial phagocytosis and assayed for the related synthesis of PGE2, TxA2 and PGI2, measured by their stable metabolites TxB2 and 6-Keto-PGF1. The results show that with decreasing density, which corresponds to a greater maturity, the production of PGE2 increases and that of TxB2 and 6-Keto-PGF1 decreases. The cells of low density were mostly stimulated by IgG-opsonized bacteria, whereas those of high density responded preferentially to C3b- opsonized bacteria. This pattern is roughly similar to the one characterizing the phagocytosis via these two receptors although the correlation is not absolute. It can be concluded that enzymes involved in the metabolism of arachidonic acid, as well as receptors for C3b and IgG, are differentially expressed among resident macrophage subpopulations and thus during macrophage maturation.

The production of C3, PGE2 and TxB2 by splenic, alveolar, and peritoneal guinea pig macrophages

The synthesis and release of C3, PGE2, and TxB2 by cultured splenic, alveolar and peritoneal guinea pig macrophages in 24 hour culture was determined. There were significant differences in C3 production among all three sources of macrophages. Splenic macrophages produced significantly less PGE2 than alveolar or peritoneal macrophages. Peritoneal macrophages produced significantly more TxB2 than splenic or alveolar macrophages. The cells from the different sources appear to be different populations of macrophages.

Enhancement of eicosanoid synthesis in mouse peritoneal macrophages by the organic mercury compound thimerosal

Availability of the common precursor arachidonic acid represents the fundamental prerequisite of the cellular eicosanoid synthesis. The amount of free arachidonic acid is regulated not only by phospholipases, which liberate this polyunsaturated fatty acid from lipid pools, but also by the reacylating enzyme acylCoA:lysophosphatide acyltransferase. We have previously shown (Goppelt-Strübe, G., C.-F. Körner, G. Hausmann, D. Gemsa, and K. Resch. Control of Prostanoid Synthesis: Role of Reincorporation of Released Precursor Fatty Acids. Prostaglandins 32:373. 1986.) that the organic mercury compound thimerosal in murine peritoneal macrophages inhibits arachidonic acid reincorporation into cellular lipids, thereby leading to an enhanced prostanoid synthesis. In this report we show that the production of leukotriene C4 was also increased after the addition of thimerosal to mouse peritoneal macrophages in a time and dose dependent manner. Concomitantly, thimerosal led to a significant rise of the intracellular calcium concentration as measured by fura-2 fluorescence. Simultaneous addition of thimerosal and indomethacin or exogeneous arachidonic acid to the cells resulted in a synergistic enhancement of leukotriene C4 synthesis. On the other hand, another sulfhydryl group blocking agent, ethacrynic acid, was found to be ineffective in increasing leukotriene C4 levels even in combination with exogeneous arachidonic acid. Thimerosal therefore provides a helpful tool in studying the basic regulatory mechanisms of the cellular leukotriene synthesis.

Cyclophosphamide modulates arachidonic acid metabolism by peritoneal macrophages

The treatment of mice with a single dose of cyclophosphamide (Cy) (200 mg/kg) enhanced the chemiluminescence (CL) response of peritoneal macrophages (PM) triggered with opsonized zymosan (OpZ). The enhanced CL response could not be attributed to the stimulation of the cyanide-insensitive respiratory burst, since neither superoxide anion release nor immune complex-triggered cytotoxicity, an oxygen-dependent lytic mechanism, were increased in Cy-PM. Then, products of the oxidative metabolism of arachidonic acid were measured. It was found that Cy-PM exhibited increased release of prostaglandin E2 and leukotriene C4 in response to OpZ when compared with resident PM. In contrast, similar levels of thromboxane B2 production were observed in both populations. The activation of macrophage arachidonic acid metabolism reported here may contribute to the immunomodulating action of Cy.

sn-1,2-Diacylglycerols and phorbol diesters stimulate thromboxane synthesis by de novo synthesis of prostaglandin H synthase in human promyelocytic leukemia cells

We studied the regulation of thromboxane (TX) synthesis in promyelocytic leukemia cells during macrophage differentiation. Cells treated with 12-O-tetradecanoylphorbol-13-acetate (TPA) showed rates of TXB2 synthesis from exogenous arachidonic acid that exceeded that of control cells by a factor of up to 81. Cells treated with sn-1,2-dioctanoylglycerol (diC8) showed similarly high TXB2 synthesis rates when diC8 was added concomitantly with a subthreshold concentration of TPA or when given in multiple doses. These activities depended on de novo synthesis of prostaglandin H (PGH) synthase because: microsomal PGH synthase activity showed large increases in Vmax values, and mass measurements of PGH synthase revealed the presence of PGH synthase in differentiating cells whereas the enzyme was undetectable in control cells. These results indicate that macrophage differentiation is associated with stimulation of TXB2 synthesis that requires both activation of protein kinase C and de novo synthesis of PGH synthase.

Interferon-gamma potentiation of lipopolysaccharide-induced eicosanoid release from human monocytes

Interferon-gamma (IFN-gamma) can act to potentiate lipopolysaccharide (LPS)-stimulated processes in mononuclear phagocytes, including interleukin-1 release and tumoricidal activity. The present investigation examined the capacity of IFN-gamma to modulate LPS-stimulated prostaglandin E2 (PGE2) and thromboxane B2 (TxB2) release from counterflow isolated human monocytes. The release of PGE2 and TxB2 was compared for cells incubated with IFN-gamma prior to treatment with LPS and for cells treated simultaneously with IFN-gamma and LPS. Treatment of cells with IFN-gamma prior to stimulation with LPS (10 micrograms/ml, Salmonella typhimurium) resulted in elevated prostaglandin E (by immunoassay) and [3H]PGE2 release from monocytes when compared with LPS-treated cultures. In contrast, IFN-gamma pretreatment did not potentiate labeled or immunoreactive TxB2 release from LPS-treated monocytes. IFN-gamma pretreatment without LPS stimulation did not result in elevated eicosanoid release over controls. In addition, continuous treatment of monocytes with both IFN-gamma and LPS did not result in greater release of PGE2 and TxB2 than the summed individual effects of IFN-gamma and LPS. These results indicate that IFN-gamma selectively potentiates LPS-stimulated arachidonic acid conversion to PGE2 and not TxB2 in human monocytes. This effect was observed only for monocytes pretreated with IFN-gamma prior to stimulation with LPS.

Indomethacin in vivo increases the sensitivity to Listeria infection in mice. A possible role for macrophage thromboxane A2 synthesis

This paper demonstrates that in the presence of indomethacin, a cyclooxygenase inhibitor, 100% of the mice died when infected with live Listeria, whereas none of the animals died in the absence of the drug. The death of the animals correlated with the numbers of bacteria found extraperitoneally in the spleen and not with the Ia expression of the peritoneal macrophages. Increases in the spleen bacterial numbers between mice treated with either indomethacin or a specific thromboxane synthase inhibitor, OKY1581, and those not receiving either drug, were found as early as 2-4 h after infection. The differences in the initial increased bacterial spleen counts in the presence of indomethacin were reversed by administration of a stable thromboxane A2 analog or another potent vasoconstrictor, phenylephrine. Because thromboxane A2 does not regulate macrophage or T cell functions directly (Tripp, C.S., A. Wyche, E.R. Unanue, and P. Needleman, 1986, J. Immunol., In press; and Ceuppens, J.S., S. Vertessen, H. Deckmyn, and J. Vermylen, 1985, Cell Immunol., 90:458-463), but is probably generated at the site of an infection (Tripp, C.S., K.M. Leahy, and P. Needleman, 1985, J. Clin. Invest., 76:898-901), these data suggest an important role for the vasoconstrictive properties of thromboxane A2 in the regulation of immunity to Listeria infection.

Monocyte migration explains the changes in macrophage arachidonate metabolism during the immune response

The profile of arachidonic acid metabolites in resident peritoneal macrophages is distinctly different from the profile of macrophages isolated after an acute bacterial infection. The latter produce decreased prostaglandins E2 and I2 and leukotriene C4 while conserving the synthesis of thromboxane A2. We show here that the initial changes in peritoneal macrophage arachidonate metabolism during the immune response appear to be the result of the large influx of blood monocytes, which have a characteristic metabolism distinct from resident macrophages. We demonstrate that the initial decrease in peritoneal macrophage arachidonate metabolism and the increase in macrophage numbers occur simultaneously after infection with Listeria monocytogenes. Also the macrophage arachidonate metabolism seen at the height of the peritoneal cellular influx is the same as that of purified blood monocytes. Both Listeria peritoneal macrophages and blood monocytes produce equal or greater quantities of thromboxane A2 relative to prostaglandins I2 and E2 or leukotriene C4 whereas resident cells produce 1/10 to 1/25 as much thromboxane A2 compared to the other products. Furthermore, the changes in peritoneal macrophage arachidonate metabolism in response to Listeria infection do not occur if the influx of blood monocytes is stopped by irradiating the mice prior to infection implying that the cellular influx is necessary to see the changes in arachidonate metabolism. Finally, activation of peritoneal macrophages, measured as an increase in Ia expression, occurs 36 hr after the influx of monocytes from the blood and the resultant shift in arachidonate metabolism during Listeria infection.

Differential alteration of lipoxygenase and cyclooxygenase metabolism by rat peritoneal macrophages induced by endotoxin tolerance

Altered macrophage arachidonic acid metabolism may play a role in endotoxic shock and the phenomenon of endotoxin tolerance induced by repeated injections of endotoxin. Studies were initiated to characterize both lipoxygenase and cyclooxygenase metabolite formation by endotoxin tolerant and non-tolerant macrophages in response to 4 different stimuli, i.e. endotoxin, glucan, zymosan, and the calcium ionophore A23187. In contrast to previous reports of decreased prostaglandin synthesis by tolerant macrophages, A23187-stimulated immunoreactive (i) leukotriene (LT)C4/D4 and prostaglandin (PG)E2 production by tolerant cells was greater than that by non-tolerant controls (p less than 0.001). However, A23187-stimulated i-6-keto-PGF1 alpha levels were lower in tolerant macrophages compared to controls. Stimulation of prostaglandin and thromboxane (Tx)B2 synthesis by endotoxin or glucan was significantly less in tolerant macrophages compared to controls (p less than 0.05). iLTC4/D4 production was not significantly stimulated by endotoxin or glucan, but was stimulated by zymosan in the non-tolerant cells. Synthesis of iLTB4 by control macrophages was stimulated by endotoxin (p less than 0.01). These results demonstrate that arachidonic acid metabolism via the lipoxygenase and cyclooxygenase pathways in macrophages is differentially altered by endotoxin tolerance.

Compartmentalized regulation of macrophage arachidonic acid metabolism

We show that downregulation of arachidonic acid (20:4) metabolism which occurs following i.p. injection of C. parvum can occur in a single, localized macrophage population, and is therefore unlikely to be mediated solely by a systemic factor.