Calcium ionophore synergizes with bacterial lipopolysaccharides in activating macrophage arachidonic acid metabolism

Identification of Serum-Predictive Biomarkers for Subclinical Mastitis in Dairy Cows and New Insights into the Pathobiology of the Disease

Targeted direct injection/liquid chromatography coupled to tandem mass spectrometry-based metabolomics was employed to identify metabolite alterations that could differentiate subclinical mastitis (SCM) from control (CON) dairy cows at -8, -4, disease diagnosis, +4 and +8 wks relative to parturition. We identified and measured 128 metabolites in the serum. Univariate analysis revealed significant alterations of serum metabolites at all five time points studied. By applying multivariate analyses including principle component analysis and partial least squares-discriminant analysis, some of the metabolites were found to have the strongest power for discriminating the SCM from CON cows. The top five metabolites with the greatest variable importance in projection values were selected as potential biomarkers for SCM. A set of five serum metabolites including lysine, ornithine, isoleucine, LysoPC a C17:0, and leucine at -8 wks and five other metabolites including lysine, leucine, isoleucine, kynurenine, and sphingomyelin (SM) C26:0 at -4 wks prepartum were determined as predictive biomarkers for SCM, which provided highly predictive capabilities with AUC (area under the curve) at 1.00. Five metabolites including lysine, leucine, isoleucine, kynurenine, and SM C26:1 in the serum were identified as diagnostic biomarkers for SCM with the AUC of 1.00. Moreover, we observed that distinct metabolic pathways were affected in SCM cows including lysine degradation, biotin, cysteine, methionine, and glutathione metabolism, valine, leucine, and isoleucine biosynthesis and degradation, and aminoacyl-tRNA biosynthesis prior to and during the occurrence of the disease. Results of this study showed that metabolomics analyses can be used to identify susceptible cows to SCM starting from -8 and -4 wks prepartum and that blood can be used to diagnose cows with SCM.

Long-term stimulation of toll-like receptor-2 and -4 upregulates 5-LO and 15-LO-2 expression thereby inducing a lipid mediator shift in human monocyte-derived macrophages

Macrophage polarization switches during the course of inflammation along with the lipid mediators released. We investigated the lipid mediator formation in human monocyte-derived macrophages during in vitro differentiation and pathogen stimulation. For this, peripheral blood monocytes were differentiated into M1 (CSF-2/IFNγ) or M2 (CSF-1/IL-4) macrophages followed by stimulation with the toll-like receptor (TLR) ligands zymosan (TLR-2), Poly(I:C) (TLR-3) or bacterial lipopolysaccharides (TLR-4) mimicking fungal, viral and bacterial infection, respectively. Expression of enzymes involved in lipid mediator formation such as 5- and 15-lipoxygenases (LO), the 5-LO activating protein and cyclooxygenase-2 (COX-2) was monitored on mRNA and protein level and lipid mediator formation was assessed. In addition, cytokine release was measured. In vitro differentiation of human peripheral blood monocytes to M1 and M2 macrophages considerably attenuated 5-LO activity. Furthermore, while TLR-2 and -4 stimulation of M1 macrophages primarily triggered pro-inflammatory cytokines and lipid mediators, persistent stimulation (16 h) of human M2 macrophages induced a coordinated upregulation of 5- and 15-LO-2 expression. This was accompanied by a marked increase in IL-10 and monohydroxylated 15-LO products in the conditioned media of the cells. After additional stimulation with Ca²⁺ ionophore combined with supplementation of arachidonic, eicosapentaenoic and docosahexaenoic acid these cells also released small amounts of SPM such as lipoxins and resolvins. From this we conclude that activation of TLR-2 or -4 triggers the biosynthesis of pro-inflammatory 5-LO and COX-2 derived lipid mediators in human monocyte-derived M1 macrophages while persistent stimulation of M2 macrophages induces a shift towards pro-resolving 15-LO derived oxylipins.

Significance of arachidonic acid in ocular infections and inflammation

Innate immune responses in the cornea mainly play an important role to mobilize multiple interrelated pathways of corneal lipid, which involve in inflammatory corneal diseases. Signaling lipid mediators derived from arachidonic acid (AA) control cell proliferation, apoptosis, metabolism, and migration, are known as eicosanoids, phosphoinositides, sphingolipids, and fatty acids. Emerging evidences have highlighted the implication of lipid mediators in both injury and repair mechanisms in the cornea. Recently, the role of AA and its metabolites to induce proinflammatory mediators and inflammatory cell infiltration in the pathogen-infected cornea and to cause severe keratitis have been revealed. In this review, we focus on the novel roles of AA downstream signaling in the corneal inflammatory diseases and also the biological relevance of AA signaling in the therapeutic strategies for targeting sight-threatening diseases.

Metabolomics-lipidomics of eicosanoids and docosanoids generated by phagocytes

Lipid mediators derived from essential fatty acids, such as arachidonic acid, play important roles in physiologic and pathophysiologic processes. Prostaglandins, thromboxane, and leukotrienes are well-known eicosanoids that play critical roles in hemodynamics and inflammation. New families of mediators were recently uncovered that constitute a new genus stimulating resolution of acute inflammation, and are organ-protective. These include the resolvins (E-series and D-series), protectins (neuroprotectin D1/protectin D1), and maresins biosynthesized from omega-3 essential fatty acids. Phagocytes play major roles in tissue homeostasis and have a high capacity to produce these mediators, which depend on their tissue and state of activation. It is important to select appropriate methods for identifying target mediators and pathway biomarkers. In this unit, we review state-of-the-art approaches to identify and profile eicosanoid and docosanoid pathways, including specialized pro-resolving mediators resolvins, protectins, and maresins, in relation to their biosynthesis and inactivation by neutrophils and macrophages.

Ketamine inhibits endotoxin-induced inositol 1,4,5-triphosphate in rat ventricular cardiomyocytes

OBJECTIVE

To investigate the effect of ketamine on endotoxin modulation of inositol 1,4,5-triphosphate (IP3) formation in cardiomyocytes.

DESIGN

A prospective observational cell culture study.

SETTING

A research laboratory in the University of Hirosaki School of Medicine.

MATERIALS

Neonatal rat cardiomyocytes.

INTERVENTION

We investigated bradykinin-induced IP3 production in the presence of lipopolysaccharide (LPS) and the effect of ketamine on the LPS modulation of IP3 formation. The LPS modulation of IP3 formation was measured in the presence of BM13177 (a thromboxane A2 (TXA2) receptor inhibitor) or GDPbetaS (a GTP-binding protein inhibitor). U46619 (a TXA2 agonist)-induced IP3 production was measured in the presence of ketamine, and the ketamine modulation of U46619-induced IP3 production was measured in the presence of W7 (a Ca2+ releasing agent) and verapamil (a Ca2+ channel blocker).

RESULTS

One micromole ketamine significantly attenuated the LPS-induced IP3 production from 763.8+/-34.6 to 461.6+/-65.1 pmol mg protein(-1). Ten micromoles of BM13177 or 1 mM GDPbetaS significantly blocked LPS modulation of bradykinin-induced IP3 production from 786.0+/-33.8 to 218.6+/-21.6 and 226.8+/-25.4 pmol mg protein(-1). One micromole of ketamine significantly decreased U46619-induced IP3 production from 857.3+/-45.0 to 632.9+/-64.5 pmol mg(-1) protein. The ketamine inhibition of U46619-induced IP3 production was enhanced by W7 and inhibited by verapamil.

CONCLUSION

Ketamine decreased LPS-induced IP3 formation and the ketamine inhibition was associated with inhibition of the TXA2-IP3 sequence. Inhibition of TXA2 by ketamine was associated with a decrease in intracellular Ca2+.

Mature macrophage cell lines exhibit variable responses to LPS

Bacterial lipopolysaccharide (LPS) is a potent activator of cells of the macrophage/monocyte lineage. Two mature macrophage cell lines, P388D1 and RAW264.7, exhibit very different biological responses to LPS. Although RAW264.7 cells release arachidonic acid from phospholipid in response to LPS stimulation, P388D1 cells do not respond in this manner. However, LPS primes P388D1 cells to release arachidonic acid in response to other stimuli. The goal of this work is to contrast the biochemical events that occur in LPS-treated P388D1 and RAW264.7 macrophages. Enzyme assays indicate that LPS treatment induces the activation of cytosolic PLA2 in RAW264.7, but not in P388D1 cells. Phorbol ester (PMA), a receptor-independent stimulus, also fails to induce arachidonic acid release from P388D1 cells, suggesting that these cells may have a defect in the signal transduction machinery that is common to LPS and PMA. This hypothesis is supported by the observation that the expression of the LPS receptors CD14 and CD11b/CD18 is similar on P388D1 and RAW264.7 cells. Western blot analyses indicate that the erk kinases are activated upon LPS treatment of RAW264.7 but not P388D1 cells. LPS-induced arachidonic acid release is reduced in cells treated with the MEK inhibitor PD98059, suggesting that activated erk kinases mediate the phosphorylation and activation of cPLA2 in this system. Interestingly, the p42 isoform of erk (erk2) appears to be activated in resting P388D1 cells. This observation indicates that the MAP kinase cascade may be constitutively activated in P388D1 cells which may in turn limit their ability to respond to LPS. Together, these data provide evidence that mature macrophages from different sources can exhibit variable responses to LPS and highlight the danger of making generalizations regarding the effects of LPS on macrophages.

Modulation by dantrolene of endotoxin-induced interleukin-10, tumour necrosis factor-alpha and nitric oxide production in vivo and in vitro

1. Intracellular calcium has been suggested to be an important mediator of the cellular response in endotoxaemia and shock. Dantrolene is an agent that interferes with intracellular calcium fluxes resulting in a decreased availability of calcium in the cytoplasm. Here we have investigated the effect of dantrolene on lipopolysaccharide (LPS)-induced production of interleukin-10 (IL-10), tumour necrosis factor-alpha (TNF-alpha), and nitric oxide (NO) in mice and in cultured RAW 264.7 macrophages in vitro. 2. In BALB/c mice, LPS-induced plasma IL-10 levels were significantly enhanced by pretreatment with dantrolene (20 mg kg(-1), i.p.) (P < 0.005 at the 90 min time-point). On the other hand, dantrolene pretreatment suppressed circulating TNF-alpha and nitrite/nitrate (breakdown products of NO) concentrations. However, dantrolene had no effect on LPS-induced plasma interleukin-6 (IL-6) levels (67.22+/-5.51 ng ml(-1) in vehicle-pretreated mice and 62.22+/-3.66 ng ml(-1) in dantrolene-pretreated mice, n = 9). 3. Dantrolene inhibited TNF-alpha and NO production in C57BL/6 IL-10+/+ mice, as well as in their IL-10 deficient counterparts (C57BL/6 IL-10(0/0)). 4. In RAW 264.7 macrophages, dantrolene (10-300 microM) reduced IL-10, TNF-alpha, and nitrite (breakdown product of NO) production elicited by LPS (10 microg ml(-1)). Dantrolene (300 microM) did not affect the LPS-induced nuclear translocation of transcription factor nuclear factor kappaB in these cells. 5. Although LPS failed to alter the intracellullar concentration of calcium in single macrophages loaded with Fura-2, dantrolene caused a significant decrease of the basal calcium level as determined 30 min after dantrolene treatment (P < 0.005). ATP (1 mM) caused a rapid rise in intracellular calcium levels in both dantrolene-pretreated and vehicle-pretreated cells. 6. These results indicate that unlike the secretion of TNF-alpha and NO, IL-10 production is differentially regulated in vitro and in vivo. The decrease of plasma levels of the pro-inflammatory mediators TNF-alpha and NO, and increase in circulating IL-10 concentrations by dantrolene suggest that this drug might offer a new therapeutic approach in inflammatory diseases and septic shock.

Endotoxin priming of thromboxane-related vasoconstrictor responses in perfused rabbit lungs

In prior studies of perfused lungs, endotoxin priming markedly enhanced thromboxane (Tx) generation and Tx-mediated vasoconstriction in response to secondarily applied bacterial exotoxins. The present study addressed this aspect in more detail by employing precursor and intermediates of prostanoid synthesis and performing functional testing of vasoreactivity and measurement of product formation. Rabbit lungs were buffer perfused in the absence or presence of 10 ng/ml endotoxin. Repetitive intravascular bolus applications of free arachidonic acid provoked constant pulmonary arterial pressor responses and constant release reactions of TxA2 and prostaglandin (PG) I2 in nonprimed lungs. Within 60-90 min of endotoxin recirculation, which provoked progressive liberation of tumor necrosis factor-alpha but did not effect any hemodynamic changes by itself, both pressor responses and prostanoid release markedly increased, and both events were fully blocked by cyclooxygenase (Cyclo) inhibition with acetylsalicylic acid (ASA). The unstable intermediate PGG2 provoked moderate pressor responses, again enhanced by preceding endotoxin priming and fully suppressed by ASA. Vasoconstriction also occurred in response to the direct Cyclo product PGH2, again amplified after endotoxin pretreatment, together with markedly enhanced liberation of TxA2 and PGI2. In the presence of ASA, the priming-related increase in pressor responses and the prostanoid formation were blocked, but baseline vasoconstrictor responses corresponding to those in nonprimed lungs were maintained. Pressor responses to the stable Tx analog U-46619 were not significantly increased by endotoxin pretreatment, but some generation of TxA2 and PGI2 was also noted under these conditions. We conclude that endotoxin priming exerts profound effects on the lung vascular prostanoid metabolism, increasing the readiness to react with Tx-mediated vasoconstrictor responses to various stimuli, suggesting that enhanced Cyclo activity is an important underlying event.

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.

Intracellular (polymorphonuclear) magnesium content in patients with bronchial asthma between attacks

Previous studies have demonstrated the role of polymorphonuclears in asthma, the importance of increases in intracellular concentrations of ionized calcium in the release of chemical mediators, the role of magnesium as natural calcium channel blocker, and the importance of magnesium deficiency in plasma histamine concentration and in tissue prostanoid concentration. The objective of our study was to measure the polymorphonuclear magnesium content in patients with asthma in the interval between attacks. We measured the polymorphonuclear magnesium content, and serum and erythrocyte sodium, calcium, and magnesium concentrations in 21 healthy volunteers and 50 patients with different types of asthma. In our patients, the polymorphonuclear magnesium content was lower than in the control group (P < 0.001), while magnesium levels in erythrocytes and serum and the levels of other ions in erythrocytes and serum were normal. This is the first report to document low polymorphonuclear magnesium content in patients with bronchial asthma. The reduction of polymorphonuclear magnesium content may have an important role in the pathogenesis of asthma.

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.

The role of cyclic AMP in the lipopolysaccharide-induced suppression of thymidine kinase activity in macrophage

We observed that lipopolysaccharide (LPS, 1 micrograms/ml) can suppress [3H]thymidine incorporation into acid-insoluble fraction in a mouse macrophage cell line J774 (over 70% at 6 h) without affecting the uptake of [3H]thymidine or DNA polymerase activity. Paralleling this suppression, a decrease in the thymidine kinase (TK) activity, but not of thymidine monophosphate (TMP) kinase and thymidine diphosphate (TDP) kinase, was observed. LPS dose-dependently increased intracellular cAMP levels to about 3.5-times basal at 6 h, proportionally to the decrease of the TK activity. Elevation of intracellular cAMP by several reagents also decreased TK activity. Apparently LPS treatment elevates cAMP concentration by decreasing the low Km cAMP phosphodiesterase activity (58% at 6 h). The time course of cAMP-dependent protein kinase (PK-A) activity during the first 6 h after LPS treatment correlated with that of cAMP concentration. Treatment with a PK-A inhibitor restored about 63% of LPS-induced reduction of TK activity at 6 h. At longer times, however, there was a discrepancy between the change of cAMP concentration or PK-A activity and the reduction of TK activity. Therefore, protein kinase activation caused by the accumulation of intracellular cAMP probably triggers some mechanism responsible for the reduction of the TK activity.

Endotoxin "priming" potentiates lung vascular abnormalities in response to Escherichia coli hemolysin: an example of synergism between endo- and exotoxin

The pore-forming hemolysin of Escherichia coli (HlyA), an important virulence factor in extraintestinal E. coli infections, causes thromboxane generation and related vasoconstriction in perfused rabbit lungs (Seeger, W., H. Walter, N. Suttorp, M. Muhly, and S. Bhakdi. 1989. J. Clin. Invest. 84:220). We investigated the influence of pulmonary vascular "priming" with endotoxin on the responsiveness of the lung to a low-dose HlyA challenge. Rabbit lungs were perfused with Krebs Henseleit buffer containing 0.1-100 ng/ml Salmonella abortus equii lipopolysaccharide (LPS) for 60-180 min. This treatment caused protracted release of tumor necrosis factor into the recirculating medium, but did not induce significant alterations of pulmonary hemodynamics and fluid balance. At a dose of 1 ng/ml, HlyA elicited only moderate thromboxane release (< 200 pg/ml) and pulmonary artery pressure increase (< or = 6 mmHg) in control lungs. Acceleration and potentiation of both the metabolic and vasoconstrictor response occurred in lungs primed with LPS. This priming effect displayed dose (threshold integral of 0.1-1 ng/ml LPS) and time dependencies (threshold integral of 60-90 min LPS incubation). Maximum thromboxane release and pulmonary artery pressure increase surpassed the responses to HlyA in nonprimed lungs by more than 15-fold. Cyclooxygenase inhibition and thromboxane-receptor antagonism blocked these effects. These data demonstrate that LPS priming synergizes with HlyA challenge to provoke vascular abnormalities that are possibly relevant to the pathogenesis of organ failure in severe local and systemic infections.

Bacterial lipopolysaccharide primes human neutrophils for enhanced release of arachidonic acid and causes phosphorylation of an 85-kD cytosolic phospholipase A2

Production of leukotriene B4 (LTB4) by human neutrophils (PMN) in response to different stimuli is increased after pretreatment with lipopolysaccharides (LPS). We have analyzed the steps in arachidonic acid (AA) metabolism affected by LPS by examining release of AA and its metabolites from [3H]AA prelabeled PMN. Pretreatment of PMN for 60 min with up to 1 microgram/ml of LPS alone had no effect, but release of [3H]AA was stimulated up to fivefold during subsequent stimulation with a second agent. In the absence of LPS-binding protein (LBP), priming was maximal after pretreatment of PMN with 10 ng of LPS/ml for 60 min; in the presence of LBP maximal priming occurred within 45 min at 0.1 ng of LPS/ml and within 15 min at 100 ng of LPS/ml. Treatment of PMN with 10 ng of LPS/ml also increased uptake of opsonized zymosan by up to 60%. Phospholipids are the source of released [3H]AA. No release was observed from [14C]oleic acid (OA)-labeled PMN suggesting that phospholipolysis may be specific for [3H]AA-labeled phospholipid pools. Cytosol from PMN primed with LPS contains two to three times the phospholipase A2 (PLA2) activity of control PMN, against 1-palmitoyl-[2-14C]arachidonoyl-phosphatidylcholine. This activity is Ca2+ dependent and dithiothreitol resistant. LPS priming is accompanied by reduced migration during SDS-PAGE of an 85-kD protein, identified as a cytosolic PLA2. The extent and kinetics of this effect of LPS on cPLA2 parallel the priming of [3H]AA release, both depending on LPS concentration either with or without LBP. These findings suggest that priming by LPS of AA metabolism by PMN includes phosphorylation of an AA-phospholipid-selective cytosolic PLA2 that is dissociated from activation until a second stimulus is applied.

Zanvil Alexander Cohn 1926-1993

Zanvil Alexander Cohn, an editor of this Journal since 1973, died suddenly on June 28, 1993. Cohn is best known as the father of the current era of macrophage biology. Many of his scientific accomplishments are recounted here, beginning with seminal studies on the granules of phagocytes that were performed with his close colleague and former editor of this Journal, James Hirsch. Cohn and Hirsch identified the granules as lysosomes that discharged their contents of digestive enzymes into vacuoles containing phagocytosed microbes. These findings were part of the formative era of cell biology and initiated the modern study of endocytosis and cell-mediated resistance to infection. Cohn further explored the endocytic apparatus in pioneering studies of the mouse peritoneal macrophage in culture. He described vesicular inputs from the cell surface and Golgi apparatus and documented the thoroughness of substrate digestion within lysosomal vacuoles that would only permit the egress of monosaccharides and amino acids. These discoveries created a vigorous environment for graduate students, postdoctoral fellows, and junior and visiting faculty. Some of the major findings that emerged from Cohn's collaborations included the radioiodination of the plasma membrane for studies of composition and turnover; membrane recycling during endocytosis; the origin of the mononuclear phagocyte system in situ; the discovery of the dendritic cell system of antigen-presenting cells; the macrophage as a secretory cell, including the release of proteases and large amounts of prostaglandins and leukotrienes; several defined parameters of macrophage activation, especially the ability of T cell-derived lymphokines to enhance killing of tumor cells and intracellular protozoa; the granule discharge mechanism whereby cytotoxic lymphocytes release the pore-forming protein perforin; the signaling of macrophages via myristoylated substrates of protein kinase C; and a tissue culture model in which monocytes emigrate across tight endothelial junctions. In 1983, Cohn turned to a long-standing goal of exploring host resistance directly in humans. He studied leprosy, focusing on the disease site, the parasitized macrophages of the skin. He injected recombinant lymphokines into the skin and found that these molecules elicited several cell-mediated responses. Seeing this potential to enhance host defense in patients, Cohn was extending his clinical studies to AIDS and tuberculosis. Zanvil Cohn was a consummate physician-scientist who nurtured the relationship between cell biology and infectious disease.(ABSTRACT TRUNCATED AT 400 WORDS)

Endotoxin primes perfused rabbit lungs for enhanced vasoconstrictor response to staphylococcal alpha-toxin

The major pore-forming exotoxin of Staphylococcus aureus, staphylococcal alpha-toxin, causes thromboxane-mediated pulmonary hypertension and prostanoid-independent protracted vascular leakage in perfused rabbit lungs. We asked whether lung responsiveness to the staphylococcal agent would be altered by a preceding period of endotoxin priming. Isolated rabbit lungs were perfused with Krebs-Henseleit buffer in the presence or absence of 100 ng/ml Salmonella abortus equii endotoxin for up to 5 h. The lipopolysaccharide exposure evoked the release of large quantities of tumor necrosis factor into the vascular and alveolar spaces but did not significantly alter pulmonary artery pressure, organ weight, or the repeatedly assessed capillary filtration coefficient (Kfc). Two and 4 h after endotoxin administration, alpha-toxin (10 to 30 ng/ml) was bolus-injected into the pulmonary artery. Toxin-evoked prostanoid generation (TxB2, 6-keto-PGF1 alpha) and pressor responses were markedly accelerated and enhanced in endotoxin-primed lungs, both for the 2 h and the 4 h priming period. No significant influence of endotoxin was noted when applied simultaneously with alpha-toxin. Cyclooxygenase inhibition suppressed the alpha-toxin-evoked pressure rise in both endotoxin-primed and nonprimed lungs. Endotoxin priming did not influence the alpha-toxin-induced protracted increase in Kfc values, assessed in the presence of cyclooxygenase inhibition. We conclude that endotoxin primes rabbit lungs for enhanced prostanoid generation and pulmonary hypertension in response to S. aureus alpha-toxin. Such cooperativity of endotoxin priming and exotoxin triggering may be relevant in critically ill patients suffering from both endotoxemia and gram-positive sepsis.

Microbial cell-wall contaminants in peptides: a potential source of physiological artifacts

Microbial cell-wall products (MCWP) such as endotoxins are easily introduced into peptides produced under standard laboratory conditions. Because these products stimulate the induction of cytokines and other mediators, which, in turn, trigger a broad range of physiological responses. MCWP in peptide preparations are potential sources of artifacts. This brief tutorial outlines the physical/chemical nature of MCWP, some of their sources, their physiological effects, and a simple method to control for them in some peptide preparations.

In vivo effect of lipopolysaccharide on alveolar and peritoneal macrophages of rats: superoxide anion generation and 5-lipoxygenase metabolism of arachidonic acid

Influences of the intravenous administration of Escherichia coli lipopolysaccharide, 3 mg/kg, on the production of superoxide anion (O2-) and 5-lipoxygenase metabolites of arachidonic acid (AA) were evaluated in alveolar macrophages (AM) and peritoneal macrophages (PM) on days 1 and 3 after injection. The dose selected was that found to induce a significant leakage of [125I]bovine serum albumin in the pulmonary vasculature. AM obtained 1 day after LPS injection generated smaller amounts of O2- on stimulation with C5a but generated similar amounts with wheat germ lectin (WGA) or AA compared with control AM. This result suggested a prior complement activation. On day 3, on the contrary, their production of O2- significantly exceeded that by control AM with either of the three stimuli. PM collected on day 1 after LPS injection generated a significantly greater amount of O2- on stimulation with either WGA or AA than did control PM. The amount of O2-, however, decreased from day 1 to day 3. AM collected 1 day after the injection of LPS generated significantly more leukotriene B4 (LTB4) and 5-HETE on stimulation with A23187 alone and in combination with AA than did the cells from untreated rats. Such activities returned to the control levels in the AM collected on day 3. In contrast, the PM collected on day 1 produced amounts of LTB4 and 5-HETE similar to those of the control PM, but the cells on day 3 produced significantly more LTB4.(ABSTRACT TRUNCATED AT 250 WORDS)

MacMARCKS, a novel member of the MARCKS family of protein kinase C substrates

MARCKS is a specific protein kinase C (PKC) substrate that binds both calmodulin and actin and is phosphorylated during phagocyte activation, neurosecretion, and growth factor-dependent mitogenesis. We report here on MacMARCKS, a MARCKS homolog, whose synthesis is dramatically increased in macrophages when these cells are exposed to bacterial lipopolysaccharide. We have purified rabbit MacMARCKS and cloned its cDNA from rabbit and mouse. The effector domains of MacMARCKS and MARCKS are nearly identical, and both proteins bind calmodulin in a phosphorylation-regulated manner. MacMARCKS and MARCKS also share a second, highly conserved region also found in the internalization domain of the mannose-6-phosphate receptor. Our data suggest the existence of a family of PKC substrates that are targeted to different subcellular locations and that function to integrate PKC and calcium/calmodulin-dependent signals in the control of the plastic actin cytoskeleton.

The effect of calcium mobilization on LPS-induced IL-1 beta production depends on the differentiation stage of the monocytes/macrophages

The role of elevated intracellular calcium concentration [Ca2+]i in the LPS-induced activation of interleukin-1 beta (IL-1 beta) production was examined in cells representing different stages of myeloid differentiation (undifferentiated monocytic leukaemia cell line THP-1, THP-1 cells induced to adherent, macrophage-like cells by phorbol ester treatment and normal peripheral blood-derived adherent monocytes). LPS did not elevate the [Ca2+]i as measured by the Fura-2 fluorescence technique. When these cells were stimulated with LPS in the presence of the calcium ionophore A23187, a clear increase in the IL-1 beta protein production was observed in the undifferentiated THP-1 cells but not in the more differentiated cell types. This ionophore-induced increase was also seen in the IL-1 beta mRNA levels. Thus these data confirm the previous findings demonstrating that elevation of [Ca2+]i is not involved in the LPS-dependent signal transmission. However, the LPS-induced signals are greatly potentiated by the elevated [Ca2+]i, but only in undifferentiated monocytic cells.

Modulation of effects of lipopolysaccharide on macrophages by a major outer membrane protein of Proteus mirabilis as measured in a chemiluminescence assay

Our previous studies have shown that a major protein isolated from purified cell walls of Proteus mirabilis (39-kDa protein) is a strong modulator of the specific immune responses to lipopolysaccharide (LPS) from this bacterium. When the protein is mixed with LPS before immunization of mice, the responses of antibody-producing cells specific for LPS are greatly enhanced and converted predominantly to the immunoglobulin G isotype. In the present study, the immunomodulating effects of the 39-kDa protein were tested at the level of interaction of LPS with macrophages. Activation of macrophages was determined by measuring the production of oxygen radicals in a chemiluminescence assay with lucigenin as the amplifier. LPS from P. mirabilis induced strong oxidative metabolism in both peritoneal and bone marrow-derived murine macrophages. These responses were inhibited in a dose-dependent manner by mixing LPS with increasing amounts of the protein. In contrast, bovine serum albumin and methylated bovine serum albumin enhanced the response of macrophages dramatically when complexed with LPS. The inhibiting activity of the 39-kDa protein was also observed with LPS from Escherichia coli K-12.

Leukotrienes do not regulate interleukin 1 production by activated macrophages

The objective of this work was to investigate the role of leukotrienes in the production of IL-1 by activated human peripheral blood monocytes and mouse peritoneal macrophages. Using overnight adherent macrophages, stimulation with lipopolysaccharide or zymosan caused a time-dependent increase in IL-1 production. LTC4 was detected and preceded IL-1 production only in zymosan-treated macrophages. Lipopolysaccharide did not stimulate macrophages to produce LTC4. Zymosan-stimulated LTC4 production was inhibited by the lipoxygenase inhibitors, ICI207968 (3.20 microM), nordihydroguaiaretic acid (0.22 microM), phenidone (4.60 microM), REV5901 (0.20 microM), and the Merck 5-lipoxygenase "translocation inhibitor" MK886 (0.02 microM) with IC50 values as shown in parenthesis. However, none of these inhibitors reduced IL-1 production at concentrations which completely inhibited leukotriene synthesis. Taken together, these results do not support a role for leukotrienes in the production of IL-1 by zymosan-activated macrophages.

Primed stimulation of isolated perfused rabbit lung by endotoxin and platelet activating factor induces enhanced production of thromboxane and lung injury

Bacterial sepsis often precedes the development of the adult respiratory distress syndrome (ARDS) and bacterial endotoxin (LPS) produces a syndrome similar to ARDS when infused into experimental animals. We determined in isolated, buffer-perfused rabbit lungs, free of plasma and circulating blood cells that LPS synergized with platelet activating factor (PAF) to injure the lung. In lungs perfused for 2 h with LPS-free buffer (less than 100 pg/ml), stimulation with 1, 10, or 100 nM PAF produced transient pulmonary hypertension and minimal edema. Lungs perfused for 2 h with buffer containing 100 ng/ml of Escherichia coli 0111:B4 LPS had slight elevation of pulmonary artery pressure (PAP) and did not develop edema. In contrast, lungs exposed to 100 ng/ml of LPS for 2 h had marked increases in PAP and developed significant edema when stimulated with PAF. LPS treatment increased capillary filtration coefficient, suggesting that capillary leak contributed to pulmonary edema. LPS-primed, PAF-stimulated lungs had enhanced production of thromboxane B2 (TXB) and 6-keto-prostaglandin F1 alpha (6KPF). Indomethacin completely inhibited PAF-stimulated production of TXB and 6KPF in control and LPS-primed preparations, did not inhibit the rise in PAP produced by PAF in control lungs, but blocked the exaggerated rise in PAP and edema seen in LPS-primed, PAF-stimulated lungs. The thromboxane synthetase inhibitor dazoxiben, and the thromboxane receptor antagonist, SQ 29,548, similarly inhibited LPS-primed pulmonary hypertension and edema after PAF-stimulation. These studies indicate that LPS primes the lung for enhanced injury in response to the physiologic mediator PAF by amplifying the synthesis and release of thromboxane in lung tissue.

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.

Complex effects of in vitro hyperoxia on alveolar macrophage arachidonic acid metabolism

Metabolites of arachidonic acid (AA) released into bronchoalveolar lavage fluid of animals exposed to hyperoxia have previously been implicated as mediators of pulmonary oxygen toxicity. The alveolar macrophage (AM) represents an important potential source of these eicosanoids. We have therefore investigated the effects of in vitro hyperoxia (95% O2/5% CO2) versus normoxia (95% air/5% CO2) on the metabolism of AA in the AM of the rat. Exposure to 95% O2 for up to 72 h did not impair the viability or affect the protein content of cultured AMs. Hyperoxia for 24 to 72 h increased the accumulation of free AA liberated from endogenous stores in cultures of resting AMs. Despite this increase in free AA, no changes in synthesis of thromboxane B2, prostaglandin (PG) E2, PGF2 alpha, leukotriene (LT) B4, or LTC4 were observed in resting AMs exposed to hyperoxia for up to 72 h. This was not due to degradation of eicosanoids in hyperoxia. However, formation of cyclooxygenase metabolites from exogenously supplied AA was reduced in hyperoxia-incubated AMs, suggesting that hyperoxia inhibited the cyclooxygenase enzyme. In AMs stimulated with calcium ionophore A23187, both AA release and synthesis of cyclooxygenase and lipoxygenase eicosanoids were augmented after incubation in hyperoxia for 24 to 72 h. The increase in A23187-stimulated LTB4 synthesis caused by hyperoxia was inhibited by the antioxidants catalase, superoxide dismutase, and the intracellular cysteine loading agent L-2-oxothiazolidine-4-carboxylic acid, suggesting that the augmentation by hyperoxia of A23187-induced AA metabolism was mediated by reactive oxygen metabolites. Thus, hyperoxia has complex effects on AA metabolism in the AM, which include the ability to augment the release of AA and formation of bioactive eicosanoids. These findings support a possible role for eicosanoid synthesis by the AM in the pathogenesis of oxygen toxicity of the lung.

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.

Properties of isolated red pulp macrophages from mouse spleen

Dense monolayers of large, adherent macrophages were prepared from the red pulp of mouse spleen. These sinus-lining phagocytes resembled liver Kupffer cells in morphology, as well as expression of F4/80 and class II MHC antigens and receptors for IgG. C3-coated red cells attached at low levels to spleen macrophages, but attachment and endocytosis were enhanced on fibronectin-coated surfaces. The ionophore A23187 induced spleen macrophages to synthesize prostaglandin E2, but like Kupffer cells, spleen macrophages did not synthesize leukotrienes and made relatively small amounts of HETE and 12-hydroxyheptadecanoic acid. Resident spleen macrophages did not produce H2O2, but splenic inflammatory cells, induced by infection of animals with Listeria monocytogenes, actively released H2O2. We conclude that the functional properties of resident, sinusoidal-lining macrophages in liver and spleen are similar to one another but distinct from other pools of phagocytes.