Prostaglandin E2 inhibits the release of tumor necrosis factor-alpha, rather than interleukin 1 beta, from human macrophages

Direct and indirect modulation of LPS-induced cytokine production by insulin in human macrophages

Overweight and obesity are accompanied by insulin resistance, impaired intestinal barrier function resulting in increased lipopolysaccharide (LPS) levels, and a low-grade chronic inflammation that results in macrophage activation. Macrophages produce a range of interleukins as well as prostaglandin E₂ (PGE₂). To cope with insulin resistance, hyperinsulinemia develops. The purpose of the study was to elucidate how LPS, insulin and PGE₂ might interact to modulate the inflammatory response in macrophages. Human macrophages were either derived by differentiation from U937 cells or isolated from blood mononuclear cells. The macrophages were stimulated with LPS, insulin and PGE₂. Insulin significantly enhanced the LPS-dependent expression of interleukin-1β and interleukin-8 on both the mRNA and protein levels. Additionally, insulin increased the LPS-dependent induction of enzymes involved in the PGE₂-synthesis and the production of PGE₂ by macrophages. PGE₂ in turn further enhanced the LPS-dependent expression of cytokines via its G_s-coupled receptors EP2 and EP4, the latter of which appeared to be more relevant. The combination of all three stimuli resulted in an even higher induction than the combination of LPS plus insulin or LPS plus PGE₂. Thus, the compensatory hyperinsulinemia might directly and indirectly enhance the LPS-dependent cytokine production in obese individuals.

Dendritic Cells as Arbiters of Peritoneal Immune Responses

During the past few years, there has been a substantial increase in the understanding of innate immunity. Dendritic cells are emerging as key players in the orchestration of this early phase of immune responses, with a role that will translate into the subsequent type of adaptive immune response against infection. Here we provide an overview of dendritic cell differentiation and function, with particular emphasis on those features unique to the immune defense of the peritoneal cavity and in the context of peritoneal dialysis-associated immune responses. The reader is referred to the primary references included in the accompanying list for specific details in this fascinating field.

Bioactive Lipids in Age-Related Disorders

Our own studies and those of others have shown that defects in essential fatty acid (EFA) metabolism occurs in age-related disorders such as obesity, type 2 diabetes mellitus, hypertension, atherosclerosis, coronary heart disease, immune dysfunction and cancer. It has been noted that in all these disorders there could occur a defect in the activities of desaturases, cyclo-oxygenase (COX), and lipoxygenase (LOX) enzymes leading to a decrease in the formation of their long-chain products gamma-linolenic acid (GLA), arachidonic acid, eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA) and docosahexaenoic acid (DHA). This leads to an increase in the production of pro-inflammatory prostaglandin E2 (PGE2), thromboxanes (TXs), and leukotrienes (LTs) and a decrease in anti-inflammatory lipoxin A4, resolvins, protectins and maresins. All these bioactive molecules are termed as bioactive lipids (BALs). This imbalance in the metabolites of EFAs leads to low-grade systemic inflammation and at times acute inflammatory events at specific local sites that trigger the development of various age-related disorders such as obesity, type 2 diabetes mellitus, hypertension, coronary heart disease, atherosclerosis, and immune dysfunction as seen in rheumatoid arthritis, lupus, nephritis and other localized inflammatory conditions. This evidence implies that methods designed to restore BALs to normal can prevent age-related disorders and enhance longevity and health.

Fever and sickness behavior: Friend or foe?

Fever has been recognized as an important symptom of disease since ancient times. For many years, fever was treated as a putative life-threatening phenomenon. More recently, it has been recognized as an important part of the body's defense mechanisms; indeed at times it has even been used as a therapeutic agent. The knowledge of the functional role of the central nervous system in the genesis of fever has greatly improved over the last decade. It is clear that the febrile process, which develops in the sick individual, is just one of many brain-controlled sickness symptoms. Not only will the sick individual appear "feverish" but they may also display a range of behavioral changes, such as anorexia, fatigue, loss of interest in usual daily activities, social withdrawal, listlessness or malaise, hyperalgesia, sleep disturbances and cognitive dysfunction, collectively termed "sickness behavior". In this review we consider the issue of whether fever and sickness behaviors are friend or foe during: a critical illness, the common cold or influenza, in pregnancy and in the newborn. Deciding whether these sickness responses are beneficial or harmful will very much shape our approach to the use of antipyretics during illness.

Effects of carnitine and its congeners on eicosanoid discharge from rat cells: implications for release of TNFalpha

THE acyl carrier coenzyme A (CoA) is involved in fatty acid metabolism. The carnitine/CoA ratio is of particular importance in regulating the transport of long-chain fatty acids into mitochondria for oxidation. Also CoA has a role in the formation and breakdown of products from both the cyclooxygenase and lipoxygenase pathways of the precursor arachidonic acid. In the present study the effect of 4 days feeding of 300 mg/kg/day of L-carnitine, acetyl Lcarnitine and propionyl L-carnitine on the basal and calcium ionophore (A23187) stimulated release of arachidonic acid metabolites from rat carrageenin elicited peritoneal cells was investigated. There were two series of experiments carried out. In the first, the harvested peritoneal cell population consisted of less than 90% macrophages and additional polymorphonuclear (PMN) leucocytes. The basal release of prostaglandin E₂ (PGE₂), 6-ketoprostaglandin F_1α (6-keto-PGF_1α) and leukotriene B₄ (LTB₄) was stimulated by all treatments. The A23187 stimulated release of 6-keto-PGF_1α and LTB₄ was increased by all three compounds. The 6-keto-PGF_1α:TxB₂ and 6-keto-PGF_1α:LTB₄ ratios were increased by carnitine treatment. These results suggested that carnitine could modify the macrophage component of an inflammatory site in vivo. In the second series of experiments the harvested cell population was highly purified (>95% macrophages) and none of the compounds fed to the rats caused a change of either eicosanoid or TNFα formation. Moreover the 6-keto-PGF_1α:TxB₂ and 6-keto-PGF_1α:LTB₄ ratios were not enhanced by any of the compounds tested. It is conceivable that in the first series the increased ratios 6-keto-PGF_1α:TxB₂ and 6-keto-PGF_1α:LTB₄ reflected the effect of carnitine or its congeners on PMN leucocytes rather than on macrophages.

Interactions between rnacrophage cytokines and eicosanoids in expression of antitumour activity

Cytokines and eicosanoid products of macrophages play an essential role in expression of antitumour activity of macrophages either in a cell-to-cell contact system between the effector and the target cell or as cell-free soluble products. In this review the relationship between three main monokines, namely TNF-α, IL-1 and IL-6 and the interrelationship between these monokines and eicosanoids (PGE₂, PGI₂, LTB₄, LTC₄) in their production and in expression of antitumour activity is discussed. Emphasis is given to the effect of tumour burden on production of the monokines and of the eicosanoids and on the production of these compounds by the tumour cells. Finally, the therapeutic implications drawn from animal studies and clinical trials is discussed.

LPS-induced serum TNF production and lethality in mice: effect of L-carnitine and some acyl-derivatives

The effect of L-carnitine and some of its acyl derivatives on serum TNF production and lethality in a murine experimental endotoxin shock model was investigated. In some instances, serum IL-6 production was also evaluated. In this experimental model, C57BL/6 mice received 30 mg/kg LPS (E. cell 055:B5) injected intraperitoneally, while L-carnitine and its derivatives were administered according to different schedules. Serum levels of TNF and IL-6 were evaluated 1 h following LPS injection. The treated animals were also monitored daily for differences in body temperature, feeding, and survival for 10 days after LPS injection. Although some derivatives were able to significantly affect TNF production, the marked decrease in serum TNF levels of LPS-treated mice was not paralleled by a substantial increase in survival.

The local inflammatory responses to infection of the peritoneal cavity in humans: their regulation by cytokines, macrophages, and other leukocytes

Studies on infection-induced inflammatory reactions in humans rely largely on findings in the blood compartment. Peritoneal leukocytes from patients treated with peritoneal dialysis offer a unique opportunity to study in humans the inflammatory responses taking place at the site of infection. Compared with peritoneal macrophages (pMϕ) from uninfected patients, pMϕ from infected patients display ex vivo an upregulation and downregulation of proinflammatory and anti-inflammatory mediators, respectively. Pro-IL-1β processing and secretion rather than synthesis proves to be increased in pMϕ from infectious peritonitis suggesting up-regulation of caspase-1 in vivo. A crosstalk between pMϕ, γδ T cells, and neutrophils has been found to be involved in augmented TNFα expression and production during infection. The recent finding in experimental studies that alternatively activated macrophages (Mϕ2) increase by proliferation rather than recruitment may have significant implications for the understanding and treatment of chronic inflammatory conditions such as encapsulating peritoneal sclerosis (EPS).

Studies on the role of acid sphingomyelinase and ceramide in the regulation of tumor necrosis factor alpha (TNFalpha)-converting enzyme activity and TNFalpha secretion in macrophages

Acid sphingomyelinase (ASMase) has been proposed to mediate lipopolysaccharide (LPS) signaling in various cell types. This study shows that ASMase is a negative regulator of LPS-induced tumor necrosis factor alpha (TNFalpha) secretion in macrophages. ASMase-deficient (asm(-/-)) mice and isolated peritoneal macrophages produce severalfold more TNFalpha than their wild-type (asm(+/+)) counterparts when stimulated with LPS, whereas the addition of exogenous ceramides or sphingomyelinase reduces the differences. The underlying mechanism for these effects is not transcriptional but post-translational. The TNFalpha-converting enzyme (TACE) catalyzes the maturation of the 26-kDa precursor (pro-TNFalpha) to an active 17-kDa form (soluble (s)TNFalpha). In mouse peritoneal macrophages, the activity of TACE was the rate-limiting factor regulating TNFalpha production. A substantial portion of the translated pro-TNFalpha was not processed to sTNFalpha; instead, it was rapidly internalized and degraded in the lysosomes. TACE activity was 2-3-fold higher in asm(-/-) macrophages as compared with asm(+/+) macrophages and was suppressed when cells were treated with exogenous ceramide and sphingomyelinase. Indirect immunofluorescence analyses revealed distinct TNFalpha-positive structures in the close vicinity of the plasma membrane in asm(-/-) but not in asm(+/+) macrophages. asm(-/-) cells also had a higher number of early endosomal antigen 1-positive early endosomes. Experiments that involved inhibitors of TACE, endocytosis, and lysosomal proteolysis suggest that in the asm(-/-) cells a significant portion of pro-TNFalpha was sequestered within the early endosomes, and instead of undergoing lysosomal proteolysis, it was recycled to the plasma membrane and processed to sTNFalpha.

Activation of cytosolic phospholipase A2alpha in resident peritoneal macrophages by Listeria monocytogenes involves listeriolysin O and TLR2

Eicosanoid production by macrophages is an early response to microbial infection that promotes acute inflammation. The intracellular pathogen Listeria monocytogenes stimulates arachidonic acid release and eicosanoid production from resident mouse peritoneal macrophages through activation of group IVA cytosolic phospholipase A2 (cPLA2alpha). The ability of wild type L. monocytogenes (WTLM) to stimulate arachidonic acid release is partially dependent on the virulence factor listeriolysin O; however, WTLM and L. monocytogenes lacking listeriolysin O (DeltahlyLM) induce similar levels of cyclooxygenase 2. Arachidonic acid release requires activation of MAPKs by WTLM and DeltahlyLM. The attenuated release of arachidonic acid that is observed in TLR2-/- and MyD88-/- macrophages infected with WTLM and DeltahlyLM correlates with diminished MAPK activation. WTLM but not DeltahlyLM increases intracellular calcium, which is implicated in regulation of cPLA2alpha. Prostaglandin E2, prostaglandin I2, and leukotriene C4 are produced by cPLA2alpha+/+ but not cPLA2alpha-/- macrophages in response to WTLM and DeltahlyLM. Tumor necrosis factor (TNF)-alpha production is significantly lower in cPLA2alpha+/+ than in cPLA2alpha-/- macrophages infected with WTLM and DeltahlyLM. Treatment of infected cPLA2alpha+/+ macrophages with the cyclooxygenase inhibitor indomethacin increases TNFalpha production to the level produced by cPLA2alpha-/- macrophages implicating prostaglandins in TNFalpha down-regulation. Therefore activation of cPLA2alpha in macrophages may impact immune responses to L. monocytogenes.

Alumina particles influence the interactions of cocultured osteoblasts and macrophages

The purpose of the current study was to evaluate the effects of alumina particles on secretion of several cytokines involved in bone resorption in cocultures of macrophages and osteoblasts. To distinguish the contribution of each individual cell type, we have established a heterologous in vitro system that makes use of mouse J774 cells and primary cultured human osteoblasts. J744 cells decreased the production of TNF-alpha when they were cocultured with osteoblasts. Treatment of J744 cells with alumina particles increased TNF-alpha secretion, but the induction was lower when cells were cocultured with osteoblasts. Secretion of IL-6 by J744 cells was very low, and increased in the presence of osteoblasts. Alumina particles were only able to stimulate the release of IL-6 by J744 cells when cells were cocultured with osteoblasts. On the other hand, incubation of osteoblasts with alumina particles enhanced the release of IL-6 and GM-CSF. Coculturing osteoblasts with J744 cells induced them to release IL-6 and GM-CSF, and treatment with alumina further increased the secretion of both mediators by osteoblasts. According to these in vitro results, it seems rather plausible that alumina particles are able to initiate an inflammatory response in vivo.

Cyclooxygenase inhibition in human monocytes increases endotoxin-induced TNF alpha without affecting cyclooxygenase-2 expression

Human endotoxin-stimulated adherent monocytes were used in order to determine whether or not NSAIDs influence cyclooxygenase-2 and/or tumor necrosis factor (TNF)alpha expression within the range of inhibitor concentrations that are required to suppress prostaglandin biosynthesis. Exogenous prostaglandin E(2) (IC(50)<5 nM) inhibited endotoxin-induced TNFalpha mRNA and protein while, up to 1 microM, it did not significantly affect cyclooxygenase-2 mRNA expression. Similar results were obtained using the membrane-permeable cAMP analogue db-cAMP, which caused preferential inhibition of TNFalpha expression. Indomethacin or lysine-acetylsalicylic acid concentration-dependently inhibited prostaglandin E(2) biosynthesis and, at concentrations causing near-complete inhibition, enhanced TNFalpha mRNA and protein expression without significantly influencing cyclooxygenase-2 mRNA. In addition, by facilitating endotoxin-induced TNFalpha expression, indomethacin or lysine-acetylsalicylic acid counteracted dexamethasone-induced inhibition of TNFalpha biosynthesis, thereby exhibiting an effect opposite to that of exogenous prostaglandin E(2). The results suggest that in human endotoxin-stimulated monocytes, NSAIDs can enhance TNFalpha expression through inhibition of cyclooxygenase and the resulting decrease in prostanoid biosynthesis.

LiveStaphylococcus aureusand bacterial soluble factors induce different transcriptional responses in human airway cells

To characterize the response of respiratory epithelium to infection by Staphylococcus aureus ( S. aureus), human airway cells were incubated for 1 to 24 h with a supernatant of a S. aureus culture (bacterial supernatant), then profiled with a pangenomic DNA microarray. Because an upregulation of many genes was noticed around 3 h, three independent approaches were then used to characterize the host response to a 3-h contact either with bacterial supernatant or with live bacteria: 1) a DNA microarray containing 4,200 sequence-verified probes, 2) a semiquantitative RT-PCR with a set of 537 pairs of validated primers, or 3) ELISA assay of IL-8, IL-6, TNFα, and PGE2. Among others, Fos, Jun, and EGR-1 were upregulated by the bacterial supernatant and by live bacteria. Increased expression of bhlhb2 and Mig-6, promoter regions which harbor HIF responding elements, was explained by an increased expression of the HIF-1α protein. Activation of the inducible form of cyclooxygenase, COX-2, and of the interleukins IL-1, IL-6, and IL-8, as well as of the NF-κB pathway, was observed preferentially in cells in contact with bacterial supernatant. Early infection was characterized by an upregulation of anti-apoptotic genes and a downregulation of pro-apoptotic genes. This correlated with a necrotic, rather than apoptotic cell death. Overall, this first global description of an airway epithelial infection by S. aureus demonstrates a larger global response to bacterial supernatant (in term of altered genes and variation factors) than to exponentially growing live bacteria.

Immunomodulatory activity of TNF-alpha during acute liver injury induced by D-galactosamine and its protection by PGE1 in rats

Tumour necrosis factor-alpha (TNF-alpha) mediates hepatocyte cell death by D-galactosamine (D-GalN) and its protection by prostaglandin E(1) (PGE(1)). The activation of immune system plays an important role in the development of liver injury. TNF-alpha and PGE(1) regulate the activity and cytokine release of different inflammatory cells. The present study was undertaken to determine if the noxious or hepatic protective properties of TNF-alpha during D-GalN-induced liver injury was related to an alteration by PGE(1) of the immunoregulatory activity of TNF-alpha. The role of TNF-alpha was assessed by anti-TNF-alpha antibodies to D-GalN-treated rats in the presence or absence of PGE(1). D-GalN enhanced the percentage of monocytes and T lymphocytes in the total peripheral blood mononuclear cells (PBMCs). D-GalN enhanced the activation degree of monocytes, but reduced that of T lymphocytes. D-GalN also enhanced TNF-alpha, IL-1alpha, IL-6 and IFN-gamma concentrations in blood. Anti-TNF-alpha antibodies abolished all immunological changes and greatly reduced liver damage induced by D-GalN. The protection by PGE(1) against D-GalN liver injury was associated with an increase in TNF-alpha concentration and a reduction of IL-1alpha and IL-6. These changes were associated with a reduction of monocyte activation degree and a recovery of that of T lymphocytes. Although anti-TNF-alpha antibodies abolished the protection by PGE(1) against D-GalN-liver injury, they did not essentially counteract the effect of the prostanoid in all immunological parameters studied. The present study showed that the protection against D-GalN liver damage by PGE(1) or anti-TNF-alpha was associated with similar effects on the inflammatory parameters studied. Nevertheless, the abolishment of liver protection by PGE(1) with anti-TNF-alpha in D-GalN-treated rats in the presence of a protective cytokine profile suggests that the release of TNF-alpha induced by PGE(1) pre-administration was exerting a direct protective effect on hepatocytes against D-GalN injury. Consequently, the effect of PGE(1) on inflammatory parameters studied during liver injury was unrelated to TNF-alpha.

Effect of intrarectal prostaglandin E2 analogue (enprostil) on trinitrobenzenesulphonic acid-induced colitis in rats

Prostaglandins exert a protective effect on colonic mucosa in experimentally induced colitis. This study investigated the effect of enprostil, a prostaglandin E2 (PGE2) analogue, on trinitrobenzenesulphonic acid (TNBS)-induced colitis in rats. Each rat received a rectal enema containing TNBS (30 mg), followed 24 h later by intrarectal once-daily enprostil (200 microg). Enprostil-treated and control rats were killed on day 3 (enprostil group, n = 5; control, n = 6) or day 10 (enprostil group, n = 5; control, n = 5) after TNBS treatment. The area of damaged mucosa of the colon was measured relative to the total colonic area. We also determined the macroscopic score of mucosal damage, and measured PGE2, 6-keto-prostaglandin F1alpha (6-keto-PGF1alpha) and thromboxane B2 (TXB2) concentration in portal vein blood samples. Enprostil significantly reduced both the area of damaged mucosa (including the ulcer area) and the macroscopic score after 3 days' treatment compared with control. Similarly, enprostil significantly reduced plasma concentration of PGE2, 6-keto-PGF1alpha and TXB2 during the acute phase at day 3 of treatment compared with control, but not at day 10. These results suggest that PGE2 enema may have therapeutic potential for treating patients with proctitis or left-sided colitis.

In vitro secretion of cytokines and prostaglandin-E2 by monocytes from lung cancer patients

Monocytes (MO) from cancer patients present functional abnormalities, such as an altered secretion of soluble factors. In the present study, our aim was to evaluate the levels of interleukin-1beta (IL-1beta), tumour necrosis factor-alpha (TNF-alpha) and prostaglandin-E2 (PGE2) secreted in vitro by MO from lung cancer patients (LCP), spontaneously or after stimulation with lipopolysaccharide (LPS). Results showed that cytokine secretion was higher for MO from LCP than for MO from healthy controls, while in the 25% of the patients analysed, an absence of response to LPS treatment was found.

Inhibition of TNF-alpha produced by Kupffer cells protects against the nonspecific liver toxicity of immunotoxin anti-Tac(Fv)-PE38, LMB-2

LMB-2 (anti-Tac(Fv)-PE38) is a recombinant immunotoxin composed of the Fv fragment of the anti-Tac Ab fused to a 38-kDa form of Pseudomonas: exotoxin A. Recent clinical trials showed that LMB-2 is a promising agent for the treatment of patients with Tac-positive leukemia or lymphoma. One major side effect that needs to be overcome is nonspecific liver toxicity. In the current study, we have analyzed the mechanism of this toxicity using a mouse model. Mice that were injected with a lethal dose of LMB-2 showed severe hepatic necrosis. Immunohistochemistry revealed that LMB-2 accumulated in Kupffer cells in the liver, suggesting that the damage to the hepatocytes was indirect. When we examined the effects of LMB-2 on peritoneal macrophages, cells in the same lineage as Kupffer cells, we found that LMB-2 induced the production of TNF-alpha by these cells. Following LMB-2 administration to mice, the levels of TNF-alpha in the liver increased to very high levels, whereas the rise in serum levels was modest. In addition, the LMB-2-induced liver toxicity was blocked by a specific TNF binding protein (TNFsRp55). Liver toxicity was also blocked by indomethacin, which also blocked the rise of TNF-alpha in the liver. Both TNFsRp55 and indomethacin treatment protected mice against a lethal dose of LMB-2. These data indicate that TNF-alpha produced in the liver by Kupffer cells has an important causal role in the nonspecific liver toxicity of LMB-2. These findings have important clinical implications for the use of immunotoxins in the therapy of patients with cancer.

Oxidant stress and essential fatty acids in patients with risk and established ARDS

Oxygen free radicals are important mediators of both physiological and pathological events. In acute lung injury, the activated lymphocytes stimulate tumor necrosis factor (TNF) and other cytokines. These lymphokines augment free radical generation by polymorphonuclear leukocytes (PMNLs), macrophages and other cells which may ultimately produce acute respiratory distress syndrome (ARDS). This is supported by our results presented here in that there is a significant increase in lipid peroxidation products in patients with established ARDS. The amount of lipid peroxidation was significantly higher in the established ARDS group compared to patients who are at risk for ARDS. Nitric oxide concentrations were significantly decreased in established ARDS compared to the control and those who are at risk for ARDS. Fatty acid analysis of the plasma phospholipid fraction revealed a significant decreased in linoleic acid, gamma-linolenic acid, dihomo-gamma-linolenic acid and arachidonic acid levels of n-6 series and alpha-linolenic acid, eicosapentaenoic acid, docosa-hexanenoic acid of n-3 series. Patients who are at risk for ARDS have decreased levels of gamma-linolenic acid of the n-6 series, alpha-linolenic acid and eicosapentaenoic acid of the n-3 series. These results suggest that lipid peroxides and alteration in essential fatty acid metabolism may have a role in the pathogenesis of ARDS.

Hyperlipoproteinemia affects cytokine production in whole blood samples ex vivo. The influence of lipid-lowering therapy

Low-density lipoprotein (LDL)-receptor deficient mice, thus hypercholesterolemic, combine protection against infection with an ex vivo two- to threefold higher pro-inflammatory cytokine production in macrophages. A pro-inflammatory cytokine profile ex-vivo is also associated with survival of gram-negative sepsis in man. We hypothesized that high lipoprotein levels would be associated with a pro-inflammatory cytokine production and could explain the resistance to fatal infection. We treated 10 patients with familial hypercholesterolemia (FH) with HMG-CoA reductase inhibitors, and 13 patients with endogenous hypertriglyceridemia (HTG) with fibrates. Blood samples were stimulated ex vivo with lipopolysaccharide (LPS), to assess the cytokine production capacity. FH patients had significantly lower tumor necrosis factor-alpha (TNF-alpha) production, compared to normolipidemic controls (P=0. 001). Lipid lowering treatment in FH patients did not affect TNF-alpha production. HTG patients showed significantly higher TNF-alpha production at baseline than matched normolipidemic controls (P<0.001), while lowering of serum triglycerides in these patients resulted in a significant decrease in TNF-alpha production (P=0.019). The IL-10 production was not affected. These data refute our hypothesis that high LDL-cholesterol levels are associated with a pro-inflammatory cytokine production capacity. In contrast, the study suggests that very-low-density lipoprotein (VLDL) in hypertriglyceridemic patients augments TNF-alpha production.

Coculture system to assess biocompatibility of candidate orthopaedic materials

When examining the biocompatibility of materials for orthopaedic use, it is important to examine the in vitro response of osteoblasts and macrophages to the material. The purpose of the current study was to develop an in vitro system that more accurately models the dynamic macrophage and osteoblast interactive response to biomaterials. A filter coculture system was designed that enables two cell types to be separated, while permitting cellular mediators to diffuse through its porous membrane. Using the filter coculture system, macrophage and osteoblast interaction in response to polymethylmethacrylate particle exposure was examined. As a marker of bone resorption potential, the level of prostaglandin E2 released from the macrophage and osteoblast coculture was compared with traditionally used in vitro culture systems. Cells interacting in the filter coculture system were found to produce prostaglandin E2 levels significantly greater than those of traditional conditioned media transfer systems. This filter coculture system offers an in vitro model that accounts for the continual cell to cell mediator interaction of two cell types simultaneously exposed to an implant material. This system may be useful in examining the biocompatibility of candidate materials at the bone interface, and thus elucidating the mechanisms of material induced bone resorption.

The pathobiology of osteoarthritis and the rationale for the use of pentosan polysulfate for its treatment

OBJECTIVES

Structure-modifying osteoarthritis (OA) drugs (SMOADs) may be defined as agents that reverse, retard, or stabilize the underlying pathology of OA, thereby providing symptomatic relief in the long-term. The objective of this review was to evaluate the literature on sodium pentosan polysulfate (NaPPS) and calcium pentosan polysulfate (CaPPS), with respect to the pathobiology of OA to ascertain whether these agents should be classified as SMOADs.

METHODS

Published studies on NaPPS and CaPPS were selected on the basis of their relevance to the known pathobiology of OA, which also was reviewed.

RESULTS

Both NaPPS and CaPPS exhibit a wide range of pharmacological activities. Of significance was the ability of these agents to support chondrocyte anabolic activities and attenuate catabolic events responsible for loss of components of the cartilage extracellular matrix in OA joints. Although some of the anti-catabolic activities may be mediated through direct enzyme inhibition, NaPPS and CaPPS also have been shown to enter chondrocytes and bind to promoter proteins and alter gene expression of matrix metalloproteinases and possibly other mediators. In rat models of arthritis, NaPPS and CaPPS reduced joint swelling and inflammatory mediator levels in pouch fluids. Moreover, synoviocyte biosynthesis of high-molecular-weight hyaluronan, which is diminished in OA, was normalized when these cells were incubated with NaPPS and CaPPS or after intraarticular injection of NaPPS into arthritic joints. In rabbit, canine, and ovine models of OA, NaPPS and CaPPS preserved cartilage integrity, proteoglycan synthesis, and reduced matrix metalloproteinase activity. NaPPS and CaPPS stimulated the release of tissue plasminogen activator (t-PA), superoxide dismutase, and lipases from vascular endothelium while concomitantly decreasing plasma levels of the endogenous plasminogen activator inhibitor PAI-1. The net thrombolytic and lipolytic effects exhibited by NaPPS and CaPPS may serve to improve blood flow through subchondral capillaries of OA joints and improve bone cell nutrition. In geriatric OA dogs, NaPPS and CaPPS reduced symptoms, as well as normalized their thrombolytic status, threshold for platelet activation, and plasma triglyceride levels. These hematologic parameters were shown to be abnormal in OA animals before drug treatment. Similar outcomes were observed in OA patients when CaPPS or NaPPS were given orally or parenterally in both open and double-blind trials.

CONCLUSIONS

The data presented in this review support the contention that NaPPS and CaPPS should be classified as SMOADs. However, additional long-term clinical studies employing methods of assessing joint structural changes will be needed to confirm this view.

Increased prostacyclin and PGE2 stimulated cAMP production by macrophages from endotoxin-tolerant rats

Sublethal administration of lipopolysaccharide (LPS) renders rats tolerant to multiple lethal stimuli. Tolerant macrophages exhibit differential alterations in LPS-stimulated cytokine and inflammatory mediator release. Increased cAMP levels stimulated by PGE2 or prostacyclin (PGI2) result in differential effects on LPS-induced cytokine release and protect against the pathophysiological changes of endotoxemia. In the present studies, we sought to determine whether PGE2- and PGI2-stimulated cAMP levels are altered in tolerant macrophages. Incubation of macrophages with cicaprost or 11-deoxy-PGE1 in the presence of phosphodiesterase inhibitors resulted in significantly higher (2.5- to 6.5-fold) cAMP concentrations in tolerant macrophages compared with control. In contrast, isoproterenol-stimulated cAMP levels were not significantly different between control and tolerant cells. Also, incubation of tolerant macrophages with LPS did not result in significantly elevated cAMP levels. Prostacyclin (IP) receptor mRNA levels were significantly increased in tolerant cells compared with controls, whereas [3H]PGE2 binding and PGE2 EP4 receptor mRNA levels were not significantly changed. These studies suggest that LPS tolerance induces selective alterations in eicosanoid regulation of cAMP formation.

IL-17 Stimulates the Production and Expression of Proinflammatory Cytokines, IL-β and TNF-α, by Human Macrophages

IL-17 is a newly described, T cell-derived cytokine with ill-defined physiologic properties. As such, we examined the release of proinflammatory mediators by human macrophages in response to recombinant human (rh) IL-17. IL-1β and TNF-α expression and synthesis were up-regulated by rhIL-17 in a dose (ED50 was 50 ± 9 ng/ml)- and time-dependent fashion, with cytokine accumulation reaching a zenith after 9 h. Release of IL-6, PGE2, IL-10, IL-12, IL-1R antagonist, and stromelysin was also stimulated by rhIL-17. IL-1β and TNF-α mRNA expression levels were controlled by rhIL-17 in a complex manner with an initial 30-min inhibitory phase, and then up-regulation beginning at 1 h and reaching a plateau at about 3 h. The latter expression pattern closely mirrored the nuclear accumulation of the transcription factor nuclear factor-κB. cAMP mimetics isobutyl-1-methylxanthine (IBMX), forskolin, PGE2, and cholera toxin reversed rhIL-17-induced release of TNF-α, but had no consistent effect on induced IL-1β synthesis. Induced release of TNF-α was also inhibited by serine/threonine protein kinase inhibitors KT-5720 (protein kinase A) and Calphostin C (protein kinase C), mitogen-activated protein kinase kinase inhibitor PD098059, and a nonspecific tyrosine kinase inhibitor, genistein. Calphostin C alone abrogated the rhIL-17-induced release of IL-1β. The antiinflammatory cytokines IL-4 (p &lt; 0.01) and IL-10 (p &lt; 0.02) completely reversed rhIL-17-stimulated IL-1β release, while IL-13 and TGF-β2 were partially effective (59 and 43% diminution, respectively). IL-10 exerted a significant suppressive effect on IL-17-induced TNF-α release (99%, p &lt; 0.02), while the inhibitory effects of IL-4, IL-13, and TGF-β2 on TNF-α secretion were partial (48, 10, and 23%, respectively). The data suggest a pivotal role for IL-17 in initiating and/or sustaining an inflammatory response.

Effect of PGE1 on TNF-alpha status and hepatic D-galactosamine-induced apoptosis in rats

Prostaglandin E1 has hepatoprotective properties in several clinical and experimental models of liver dysfunction. Hepatotoxicity induced by D-galactosamine (D-GalN) is a suitable animal model of human acute hepatic failure. The aim of the study was to investigate if prostaglandin E1 (PGE1) protection against hepatic D-GalN-induced apoptosis was related to tumour necrosis factor-alpha (TNF-alpha) content in serum. This cytokine is associated with in vitro apoptosis and general inflammatory disorders. In this study, PGE1 was administered 30 min before D-GalN to rats. In other experiments, several doses of TNF-alpha were administered 15min after PGE1 to D-Ga1N-treated rats. Several parameters related to apoptosis and necrosis were measured by flow cytometry, gel electrophoresis, biochemical analysis, and optical and electron microscopy. Tumour necrosis factor-alpha was quantified by competitive enzyme-linked immunosorbent assay (ELISA). PGE1 by itself did not modify the cell cycle of hepatocytes and liver toxicity, but increased TNF-alpha in serum in comparison with the control group. D-Galactosamine increased the percentage of hepatocytes in apoptosis and in the S phase of the cell cycle, and decreased those in G0/G1. Such an increase of hepatocytes in apoptosis was correlated with a higher number of apoptotic bodies and DNA fragmentation in liver than control samples. Also, D-GalN increased alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase and TNF-alpha in serum compared with the control group. Pre-administration of PGE1 to D-GalN-treated rats reduced all the parameters of apoptosis and necrosis in liver, and increased additionallyTNF-alpha content in serum. In those experiments where low doses of TNF-alpha were administered to PGE1 and D-GalN-treated rats an inverse relationship appeared between TNF-alpha and ALT content in serum. In conclusion, the protective effects of PGE1 on D-GalN-induced apoptosis may be linked to its capacity to modulate cell division and/or its immunomodulatory activity. In this sense, our experimental results suggest that TNF-alpha could be involved in protection or exacerbation of liver damage in relation to the pathophysiological status of the liver.

Epinephrine inhibits endotoxin-induced IL-1 beta production: roles of tumor necrosis factor-alpha and IL-10

Epinephrine has been found to inhibit the production of the proinflammatory cytokine tumor necrosis factor (TNF)-alpha and to enhance the production of anti-inflammatory cytokine interleukin (IL)-10. To determine the effect of epinephrine on IL-1 beta production, the following experiments were performed: 1) blood obtained from subjects at 4-21 h after the start of a continuous infusion of epinephrine (30 ng.kg-1.min-1) produced less IL-1 beta after ex vivo stimulation with lipopolysaccharide (LPS), compared with blood drawn from subjects infused with saline; 2) in whole blood in vitro, epinephrine caused a dose-dependent decrease in LPS-induced IL-1 beta production, which was likely mediated via adrenergic receptors; and 3) inhibition of TNF and enhancement of IL-10 both contributed to epinephrine-induced inhibition of IL-1 beta production. Epinephrine, either endogenously produced or administered as a component of sepsis treatment, may attenuate excessive activity of proinflammatory cytokines early in the course of systemic infection.

Regulation of macrophage cytokine production by prostaglandin E2. Distinct roles of cyclooxygenase-1 and -2

Prostaglandin E2 (PGE2) modulates a variety of physiological processes including the production of inflammatory cytokines. There are two cyclooxygenase (Cox) enzymes, Cox-1 and Cox-2, that are responsible for initiating PGE2 synthesis. These isozymes catalyze identical biosynthetic reactions but are regulated by different mechanisms in the cell. This report examines differences in the roles of Cox-1 and Cox-2 in regulating cytokine synthesis in macrophages. We employed agents that selectively modulate the activity of each isozyme and measured their effects on synthesis of interleukin (IL)-6, IL-1, and tumor necrosis factor-alpha by peritoneal macrophages. Among these three cytokines, only IL-6 synthesis was stimulated by production of endogenous PGE2. This effect was specifically linked to activation of Cox-2 and not Cox-1. The specificity derives, partly, from the timing of the production of PGE2 following stimulation of each isozyme and from induction of ancillary signals that control the response to PGE2. The experimental findings demonstrate that the effects of Cox-1 and Cox-2 activity on macrophage IL-6 synthesis are segregated. This provides a mechanism for IL-6 to be induced selectively during inflammation.

The mechanisms of action of disease-modifying antirheumatic drugs: a review with emphasis on macrophage signal transduction and the induction of proinflammatory cytokines

1. Rheumatoid arthritis (RA) is probably the most common source of treatable disability. A major problem in modern rheumatology is that the mechanism(s) of action of the currently used disease-modifying antirheumatic drugs (DMARDs) remain unclear. Many of these drugs entered rheumatology mainly through clinical intuition and have been used for decades. 2. The former T-cell-centered paradigm of rheumatoid inflammation has given way to a model of inflammation highlighting the macrophage and its proinflammatory cytokines. In particular, tumor necrosis factor alpha (TNF-alpha) has gained prominence as a central proinflammatory mediator in RA, and antibodies against TNF-alpha have been successfully used in patients with RA. 3. This review will summarize the recent advances in determining the mechanisms of action of the currently used DMARDs, with particular emphasis on their effects on the induction of TNF-alpha and interleukin 1 (IL-1) in mononuclear phagocytes. Although some DMARDs, such as auranofin, antimalarials and tenidap, act as inhibitors of the induction of these cytokines in monocytes or macrophages or both, other drugs, such as methotrexate, D-penicillamine and aurothiomalate, do not seem to affect either TNF-alpha or IL-1. 4. The drugs' effects on proinflammatory cytokine induction are correlated to those on other macrophage responses.

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.

Staphylococcal exoproducts down-regulate cyclooxygenase 1 and 2 in peritoneal macrophages

Peritoneal macrophages (PMOs) are important components of the host defense against microbial infection in patients undergoing continuous ambulatory peritoneal dialysis (CAPD). Incubation of human PMOs with cell-free supernatant (BFS), prepared from Staphylococcus aureus, inhibited prostaglandin E2 (PGE2) and thromboxane B2 (TXB2) production. Slot-blot analysis of cyclooxygenase-1 (Cox-1) and Cox-2 demonstrated a decrease in both Cox-1 (29%) and, to a greater extent, Cox-2 (65%) protein expression after BFS stimulation. When competitive polymerase chain reaction (PCR) was used, the peak levels of Cox-1 and Cox-2 messenger ribonucleic acid (mRNA) in unstimulated PMOs were 0.304+/-0.13 pmol/L and 9.61+/-2.84 pmol/L (mean+/-SEM, n = 3), respectively. After exposure of samples to BFS for 30 minutes, the level of Cox-2 mRNA was reduced to 0.59+/-0.449 pmol/L (16-fold reduction, p < 0.05), and the level of Cox-1 mRNA was reduced to 0.02+/-0.002 pmol/L (15-fold reduction, p < 0.05). In contrast, these same PMOs showed an increased expression of IL-6 mRNA and increased secretion of IL-6 protein. These results indicate that prostaglandin production in PMOs is regulated by alterations in both immunoreactive Cox-1 and Cox-2. The down-regulation of Cox metabolism in these cells is primarily related to the delayed and depressed increase in the Cox-2 gene product.

Selective enhancement by serum factors of cyclic AMP accumulation in rat microglial cultures

Using purified microglial cultures obtained from the neonatal rat brain we found that media containing fetal calf serum (as well as human, horse and goat sera) enhanced by about 3-fold the accumulation of cyclic AMP induced by the beta-adrenergic agonist isoproterenol and did not affect in a significant way that induced by the direct adenylyl cyclase stimulator forskolin. The effect of fetal calf serum was (i) dose dependent, and statistically significant also at serum concentrations below 1%; (ii) rapidly lost (half life of about 15 min) when the serum-containing medium was exposed to microglia, astrocytes or neuroblastoma cells; (iii) present also when cyclic AMP accumulation was enhanced by prostaglandin E2 or by cholera toxin; (iv) absent on basal cyclic AMP levels. When media containing fetal calf serum or the other mammalian sera mentioned above were tested on astrocyte cultures, an inhibitory, rather than enhancing activity on cyclic AMP levels was observed, indicating that the facilitatory factor(s) present in serum acts specifically on microglial cells. Moreover, in astrocytes the effect of serum was identical when tested on basal and on isoproterenol or forskolin-stimulated cyclic AMP levels. Thus, the mechanism of cyclic AMP inhibition in astrocytes is unrelated to the mechanism of activation in microglia. Our observations suggest that serum contains factor(s), promptly cleared by different cell types. Such factors may interact with so far unidentified microglial receptors responsible for a facilitation of G protein-mediated activation of adenylyl cyclase. Regulation of the cyclic AMP cascade at this step has not been described previously, and may be important for the modulation of microglial functions controlled by the cyclic nucleotide.

Pharmacologic inhibition of particulate-induced bone resorption

In this study, a rat calvaria/macrophage co-culture model was used to study the effects of various agents upon bone resorption induced by macrophage exposure to bone cement particles. The experimental group consisted of calvaria bone disks set in tissue culture medium on stainless-steel platforms into wells with macrophages adherent to the bottom which are exposed to the particles. Tumor necrosis factor alpha (TNF-alpha), prostaglandin E2 (PGE2), and calcium 45 (Ca45 were released in significant amounts in this system. Interleukin 1 alpha (IL-1 alpha) was not detected. Indomethacin inhibited the production of PGE2, but did not affect TNF release or inhibit the release of Ca45. Anti-TNF antibody neutralized the presence of TNF to undetectable levels, but did not affect PGE2 release or inhibit Ca45 release. The addition of calcitonin did not inhibit Ca45 release by calvaria. In contrast, the addition of disodium pamidronate, a member of the bisphosphonate family, was effective in inhibiting the release of Ca45 even after 96 h of incubation. In prior studies, incubation of calvaria in conditioned medium from macrophages exposed to cement particles led to resorption through a mechanism which is dependent upon TNF production by macrophages, and PGE2 production by cells in bone. In this two-way system, in which macrophages and cells in bone are allowed to interact, this dependency was no longer evident. Pamidronate was the only agent tested which suppressed the increase in bone resorption associated with macrophage exposure to bone cement particles to levels which were not significantly different from unexposed calvaria. By delaying or preventing bone resorption associated with macrophage exposure to bone cement particles, bisphosphonates may have a clinical role in cemented joint arthroplasty by decreasing the rate or incidence of aseptic loosening and prolonging implant longevity.

Increased lipopolysaccharide-induced tumour necrosis factor levels and death in hypercholesterolaemic rabbits

Nutritional-induced hypercholesterolaemia in New Zealand rabbits causes increased susceptibility to experimental infections. Rabbits fed cholesterol (0.5 g%) for 8 weeks were injected intravenously with varying doses of Escherichia coli 0127: B8 lipopolysaccharide (LPS; 3-100 micrograms/kg). The levels of cholesterol, triglycerides, tumour necrosis factor (TNF), and the survival rates of treated rabbits were then measured. Rabbits fed either normal chow or chow impregnated with sesame oil were used as controls. LPS induced higher serum TNF levels in hypercholesterolaemic rabbits than in normal rabbits or rabbits fed with chow containing sesame oil. TNF levels rose faster in hypercholesterolaemic rabbits than in normal rabbits, reaching maximum levels at 60 min and 120 min, respectively, after LPS injection. The survival rate of hypercholesterolaemic rabbits (1/11) was lower than in normal rabbits (6/7) or rabbits fed with the sesame oil chow (4/4) at the higher LPS doses. No death occurred at lower doses. One possible interpretation of these results, also supported by neutralization experiments, is that increased TNF secretion in hypercholesterolaemic rabbits raises the host's susceptibility to experimental endotoxaemia and possibly to Gram-negative infection.

Immunomodulatory spectrum of lipids associated with Mycobacterium avium serovar 8

Lipid fractions obtained from Mycobacterium avium serovar 8 were assessed for the ability to affect various immune functions of human peripheral blood mononuclear cells (PBM). Lipids included a total lipid fraction and fractions eluted from silicic acid column separation of that total lipid fraction, using chloroform and chloroform-methanol combinations. Lipid fractions were assayed for total carbohydrate and total 6-deoxyhexose content and were assessed for the ability to influence human macrophage function and the capacity to induce secretion of prostaglandin E2 (PGE2) and tumor necrosis factor alpha in PBM. The total lipid and serovar-specific glycopeptidolipid (GPL) fractions both induced significant levels of tumor necrosis factor alpha, as well as PGE2, in PBM exposed to a sublethal concentration of 100 micrograms lipid per 2 x 10(6) cells. In addition, the same concentrations of the 5 to 7% and GPL fractions induced significant levels of leukotriene B4 in PBM. Comparison of carbohydrate and 6-deoxyhexose contents of each fraction suggested a relationship to carbohydrate content and ability of fractions to induce immune modulator secretion. Analysis of GPL fractions from M. avium serovars 4 and 20 revealed that those GPL lacked the ability to induce PGE2. These results are explained by considering the difference in the carbohydrate residues of the oligosaccharide moieties.

Staphylococcal glycocalyx activates macrophage prostaglandin E2 and interleukin 1 production and modulates tumor necrosis factor alpha and nitric oxide production

We have examined the effect of staphylococcal glycocalyces on the ability of murine peritoneal macrophages to produce prostaglandin E2 (PGE2) and the inflammatory cytokines interleukin 1 (IL-1) and tumor necrosis factor alpha (TNF-alpha) and to generate nitric oxide. Glycocalyx partially purified under endotoxin-free conditions from defined liquid medium cultures of Staphylococcus lugdunensis or Staphylococcus epidermidis was a strong stimulator of PGE2 and IL-1 production. The addition of 10 to 100 micrograms of glycocalyx per ml induced levels of IL-1 and PGE2 production similar to that induced by 0.1 to 1 micrograms of Escherichia coli lipopolysaccharide (LPS) per ml. In contrast, glycocalyx induced ninefold less TNF-alpha and three- to fourfold less nitrite than LPS. A modulatory effect was suggested by the observation that the amount of TNF-alpha and nitrite generated remained constant whether the macrophages were stimulated with 10 or 100 micrograms of glycocalyx per ml. A selective modulation of macrophage activation was confirmed by the demonstration that costimulation of macrophages with both glycocalyx and LPS resulted in a reduction in TNF-alpha and nitrite generation relative to stimulation with LPS alone even though costimulation had no effect on PGE2 production and increased IL-1 production. Involvement of PGE2 in this modulatory effect was suggested by the ability of indomethacin to augment glycocalyx-stimulated TNF-alpha production and to reverse the inhibitory effect of glycocalyx on LPS induction of TNF-alpha production. However, the inability of indomethacin to reverse the inhibitory effect of glycocalyx on LPS-induced nitric oxide generation suggests that the selective modulation of macrophage function by glycocalyx may be more complex than increased sensitivity to PGE2 feedback inhibition.

Pentoxifylline prevents indomethacin induced acute gastric mucosal damage in rats: role of tumour necrosis factor alpha

Neutrophil adherence within the gastric microcirculation is thought to be a major step in the pathogenesis of gastric mucosal damage induced by indomethacin. Pentoxifylline, a methylxanthine derivative, prevents leukocyte adherence to vascular endothelium and protects organs from shock by reducing tumour necrosis factor alpha (TNF alpha) concentrations. Rats were treated with 20 mg/kg oral indomethacin, pretreated with vehicle or with four different doses of pentoxifylline intraperitoneally, and killed after three hours. The gross gastric mucosal injury, neutrophil margination into the gastric microcirculation, mucosal concentrations of 6-keto-prostaglandin F1 alpha (PGF1 alpha), and PGE2 and serum TNF alpha values were measured. Whether the pentoxifylline induced protection involved nitric oxide mediated pathways or gastric acid secretion was evaluated. The data indicate that pentoxifylline reduces indomethacin induced mucosal damage and neutrophil margination in a dose dependent manner without exerting any effect on gastric mucosal prostaglandin concentrations. The maximally effective dose (200 mg/kg) of pentoxifylline reduced gastric damage by 90% and slightly stimulated acid secretion. The effect of pentoxifylline was not affected by pretreatment with the nitric oxide inhibitor. Pentoxifylline prevented the indomethacin induced increase in TNF alpha concentrations in a dose dependent fashion. Serum TNF alpha values were 30.5 (7.0) IU/ml (mean (SEM)) in rats treated with indomethacin alone and 5.0 (2.5) IU/ml (p < 0.01) in rats treated with indomethacin plus 200 mg/kg pentoxifylline. Pentoxifylline, therefore, prevents the acute gastric mucosal damage and neutrophil margination induced by indomethacin and reduces indomethacin induced release of TNF alpha.

Prostaglandin E2 suppresses phytohemagglutinin-induced immune responses of normal human mononuclear cells by decreasing intracellular glutathione generation, but not due to increased DNA strand breaks or apoptosis

Prostaglandin E2 (PGE2) at concentrations more than 1 x 10(-8) M markedly suppressed the cell proliferation and release of soluble molecules of interleukin-2 receptor (sIL-2R), CD4 (sCD4) and CD8 (sCD8) from phytohemagglutinin (PHA)-stimulated normal human mononuclear cells (MNC) in a dose-related manner. To further elucidate the subcellular mechanism of the inhibitory effect of PGE2 on PHA-stimulated MNC, intracellular concentration of glutathione (GSH) in PHA-stimulated MNC was sequentially measured from day 1 to day 3 by enzymic method. Furthermore, the effect of PGE2 on nuclear DNA including DNA strand breaks in alkali treatment and DNA fragmentation (apoptosis) of PHA-stimulated MNC were also measured. We found intracellular GSH levels were significantly decreased in the early stage of lymphocyte activation (day 1), but no evidence of increased DNA strand breaks or apoptotic process appeared in 3-day culture. In addition, butathione sulfoximine (a specific GSH inhibitor) and dibutyryl cyclic AMP also exhibited both proliferation inhibition and GSH-decreasing effects on PHA-stimulated MNC as well as PGE2. These results suggest that the immunosuppressive effect of PGE2 is mediated by the decreased generation of intracellular GSH, but not by the increased DNA strand breaks or apoptotic mechanism in the cells.

The effects of beta 2-adrenoceptor agonists and a corticosteroid, budesonide, on the secretion of inflammatory mediators from monocytes

1. The in vitro effects of the beta 2-adrenoceptor agonists (1 x 10(-9)-10(-5) M), terbutaline, salmeterol, and formoterol, on the release of inflammatory mediators, i.e. the eicosanoids leukotriene B4 (LTB4) and prostaglandin E2 (PGE2) and the cytokine interleukin-1 beta (IL-1 beta), were assessed in cultures of human blood monocytes. For comparison, the effects of a 5-lipoxygenase inhibitor, BW A4C (1 x 10(-9)-10(-5) M), and a corticosteroid, budesonide (1 x 10(-10)-10(-5) M) were also examined. Sotalol was used to investigate whether the actions of beta 2-agonists were mediated through beta-adrenoceptors. 2. Terbutaline, like budesonide, had no significant effect on LTB4 release, whereas BW A4C (IC50 = 2 x 10(-8) M) was a potent inhibitor. All concentrations of formoterol approximately halved the LTB4 secretion, whereas high concentrations (1 x 10(-7)-10(-5) M) only, of salmeterol, inhibited release. Only salmeterol, at high concentrations (greater than 1 x 10(-6) M), lowered the secretion of PGE2 in monocyte cultures. Formoterol and salmeterol reduced the secretion of IL-1 beta only at the highest dose (1 x 10(-5) M). In contrast, budesonide (greater than or equal to 1 x 10(-9) M) was a potent suppressant of this secretion. 3. Treatment of monocyte cultures with sotalol (1 x 10(-5) M) did not significantly antagonize the inhibitory effects of salmeterol and formoterol. These results suggest that the inhibitory action of these beta 2-agonists on the release of eicosanoids or IL-1 beta, is not mediated via beta 2-adrenoceptors.4. This study does not support a therapeutic importance of the anti-release effects of beta2-agonists since high concentrations were generally required. Furthermore, the anti-secretory action of beta2-agonists was distinct from that of corticosteroids.

Induction of two K+ currents by complement component C5a in mouse macrophages

Puff application of complement component C5a (5 x 10(-8) M) onto peritoneal macrophages from thioglycollate-stimulated mice induced two kinds of outward current at a holding potential of -68 mV, a slowly-rising sustained outward current and a spike-like transient outward current. Quinidine (2 x 10(-4) M) and tetraethylammonium (10(-2) M) partially suppressed both types of outward current. Charybdotoxin (2 x 10(-6) M) markedly suppressed the spike-like outward current. Reversal potentials in bath solutions of different external K+ concentrations were dependent only on K+ concentrations. The transient current was not suppressed in Ca(2+)-free EGTA-containing solution, but was completely abolished in BAPTA-containing solution. One kind of single channel responding to C5a, which has a single-channel conductance of 29 pS, was recorded from cell-attached patches. These results suggest that C5a activates a Ca(2+)-dependent and another type of K+ current.