Specific inhibition of leukotriene B4 (LTB4)-induced neutrophil emigration by 20-hydroxy LTB4: implications for the regulation of inflammatory responses

Self-extinguishing relay waves enable homeostatic control of human neutrophil swarming

Neutrophils collectively migrate to sites of injury and infection. How these swarms are coordinated to ensure the proper level of recruitment is unknown. Using an ex vivo model of infection, we show that human neutrophil swarming is organized by multiple pulsatile chemoattractant waves. These waves propagate through active relay in which stimulated neutrophils trigger their neighbors to release additional swarming cues. Unlike canonical active relays, we find these waves to be self-terminating, limiting the spatial range of cell recruitment. We identify an NADPH-oxidase-based negative feedback loop that is needed for this self-terminating behavior. We observe near-constant levels of neutrophil recruitment over a wide range of starting conditions, revealing surprising robustness in the swarming process. This homeostatic control is achieved by larger and more numerous swarming waves at lower cell densities. We link defective wave termination to a broken recruitment homeostat in the context of human chronic granulomatous disease.

Self-extinguishing relay waves enable homeostatic control of human neutrophil swarming

Neutrophils exhibit self-amplified swarming to sites of injury and infection. How swarming is controlled to ensure the proper level of neutrophil recruitment is unknown. Using an ex vivo model of infection, we find that human neutrophils use active relay to generate multiple pulsatile waves of swarming signals. Unlike classic active relay systems such as action potentials, neutrophil swarming relay waves are self-extinguishing, limiting the spatial range of cell recruitment. We identify an NADPH-oxidase-based negative feedback loop that is needed for this self-extinguishing behavior. Through this circuit, neutrophils adjust the number and size of swarming waves for homeostatic levels of cell recruitment over a wide range of initial cell densities. We link a broken homeostat to neutrophil over-recruitment in the context of human chronic granulomatous disease.

Exploring human CYP4 enzymes: physiological roles, function in diseases and focus on inhibitors

The cytochrome P450 (CYP)4 family of enzymes are monooxygenases responsible for the ω-oxidation of endogenous fatty acids and eicosanoids and play a crucial part in regulating numerous eicosanoid signaling pathways. Recently, CYP4 gained attention as a potential therapeutic target for several human diseases, including cancer, cardiovascular diseases and inflammation. Small-molecule inhibitors of CYP4 could provide promising treatments for these diseases. The aim of the present review is to highlight the advances in the field of CYP4, discussing the physiology and pathology of the CYP4 family and compiling CYP4 inhibitors into groups based on their chemical classes to provide clues for the future discovery of drug candidates targeting CYP4. Teaser: This review provides an updated view of the physiology and pathology of CYP4 enzymes. CYP4 inhibitors are compiled based on their skeletons to provide clues for the future discovery of drug candidates targeting CYP4.

Inhalation of two putative Gulf War toxins by mice

We employed our inhalation methodology to examine whether biomarkers of inflammation and oxidative stress would be produced in mice following inhalation of aerosols containing carbonaceous particles or the vapor of pesticides prevalent during the first Gulf War. Exposure to two putative Gulf War Illness toxins, fine airborne particles and the pesticide malathion, increased biomarkers of inflammation and oxidative stress in Friend virus B (FVB) female mice. Mice inhaling particles 24 h before had increased lung lavage and plasma Leukotriene B4 (LTB4) (a biomarker of inflammation) and PGF2α (a biomarker of oxidative stress) levels, lung lavage protein and lung lavage lactic dehydrogenase (LDH) levels. These changes were a function of particle density and exposure time. Compared to particle inhalation, mice inhaling malathion 24 h before had small increase in plasma LTB4 and PGF2α levels but no increase in lung lavage LTB4, lung lavage protein, lung lavage LDH, and lung lavage alveolar macrophage (AM) levels compared to unexposed control mice. AM from particle-exposed mice contained phagocytosed particles, while AM from malathion-exposed mice showed no abnormalities. Our results indicate that inhaling particles or malathion can alter inflammatory and oxidative biomarkers in mice and raise the possibility that these toxins may have altered inflammation and oxidative stress biomarkers in Gulf War-exposed individuals.

Altered leukotriene B4 metabolism in CYP4F18-deficient mice does not impact inflammation following renal ischemia

Inflammatory responses to infection and injury must be restrained and negatively regulated to minimize damage to host tissue. One proposed mechanism involves enzymatic inactivation of the pro-inflammatory mediator leukotriene B4, but it is difficult to dissect the roles of various metabolic enzymes and pathways. A primary candidate for a regulatory pathway is omega oxidation of leukotriene B4 in neutrophils, presumptively by CYP4F3A in humans and CYP4F18 in mice. This pathway generates ω, ω-1, and ω-2 hydroxylated products of leukotriene B4, depending on species. We created mouse models targeting exons 8 and 9 of the Cyp4f18 allele that allows both conventional and conditional knockouts of Cyp4f18. Neutrophils from wild-type mice convert leukotriene B4 to 19-hydroxy leukotriene B4, and to a lesser extent 18-hydroxy leukotriene B4, whereas these products were not detected in neutrophils from conventional Cyp4f18 knockouts. A mouse model of renal ischemia-reperfusion injury was used to investigate the consequences of loss of CYP4F18 in vivo. There were no significant changes in infiltration of neutrophils and other leukocytes into kidney tissue as determined by flow cytometry and immunohistochemistry, or renal injury as assessed by histological scoring and measurement of blood urea nitrogen. It is concluded that CYP4F18 is necessary for omega oxidation of leukotriene B4 in neutrophils, and is not compensated by other CYP enzymes, but loss of this metabolic pathway is not sufficient to impact inflammation and injury following renal ischemia-reperfusion in mice.

Intrapulmonary administration of leukotriene B(4) augments neutrophil accumulation and responses in the lung to Klebsiella infection in CXCL1 knockout mice

In prior studies, we demonstrated that 1) CXCL1/KC is essential for NF-κB and MAPK activation and expression of CXCL2/MIP-2 and CXCL5/LPS-induced CXC chemokine in Klebsiella-infected lungs, and 2) CXCL1 derived from hematopoietic and resident cells contributes to host immunity against Klebsiella. However, the role of CXCL1 in mediating neutrophil leukotriene B(4) (LTB(4)), reactive oxygen species (ROS), and reactive nitrogen species (RNS) production is unclear, as is the contribution of these factors to host immunity. In this study, we investigated 1) the role of CXCL1 in LTB(4), NADPH oxidase, and inducible NO synthase (iNOS) expression in lungs and neutrophils, and 2) whether LTB(4) postinfection reverses innate immune defects in CXCL1(-/-) mice via regulation of NADPH oxidase and iNOS. Our results demonstrate reduced neutrophil influx, attenuated LTB(4) levels, and decreased ROS and iNOS production in the lungs of CXCL1(-/-) mice after Klebsiella pneumoniae infection. Using neutrophil depletion and repletion, we found that neutrophils are the predominant source of pulmonary LTB(4) after infection. To treat immune defects in CXCL1(-/-) mice, we intrapulmonarily administered LTB(4). Postinfection, LTB(4) treatment reversed immune defects in CXCL1(-/-) mice and improved survival, neutrophil recruitment, cytokine/chemokine expression, NF-κB/MAPK activation, and ROS/RNS production. LTB(4) also enhanced myeloperoxidase, H(2)O(2,) RNS production, and bacterial killing in K. pneumoniae-infected CXCL1(-/-) neutrophils. These novel results uncover important roles for CXCL1 in generating ROS and RNS in neutrophils and in regulating host immunity against K. pneumoniae infection. Our findings suggest that LTB(4) could be used to correct defects in neutrophil recruitment and function in individuals lacking or expressing malfunctional CXCL1.

Leukotriene inhibition in small animal medicine

Leukotrienes are important mediators of inflammatory and allergic conditions in people and are suspected to play an important role in tumorigenesis and tumor growth of several different tumor types. Based on this, researchers are making great progress in identifying novel pharmacologic targets for several human diseases. Leukotriene inhibition has resulted in therapeutic benefit in clinical trials involving people with osteoarthritis, allergic asthma, and atopic dermatitis. Despite this progress and the possibility that leukotriene inhibition may also play an important therapeutic role in veterinary patients, parallel advances have not yet been made in veterinary medicine. This article summarizes leukotriene function and synthesis. It also reviews the published literature regarding potential therapeutic applications of leukotriene inhibition in both human and veterinary medicine, focusing primarily on osteoarthritis, NSAID induced gastrointestinal mucosal damage, allergic asthma, atopic dermatitis, and cancer.

Increased interleukin-10 production and Th2 skewing in the absence of 5-lipoxygenase

Eicosanoids (prostaglandins and leukotrienes) are important mediators of inflammatory responses. These lipid mediators may also regulate the production of peptide mediators of the immune system. In this study, we investigated the effect of the absence of 5-lipoxygenase (5-LO)-derived leukotrienes on interleukin (IL)-10 production. IL-10 is a key regulator of immune and inflammatory responses, and previous studies have suggested that prostaglandins effect their immunosuppressive functions in part by stimulation of IL-10 production. We therefore investigated whether leukotriene production would have a similar role in regulation of IL-10 production. We have made the striking observation that absence of 5-LO-derived leukotrienes results in increased IL-10 production with a concomitant decrease in the production of pro-inflammatory cytokines, including tumour necrosis factor (TNF)-alpha and IL-12. Moreover, T-cell cytokine production in the absence of 5-LO-derived leukotrienes results in increased IL-4 production and decreased interferon (IFN)-gamma production. This may be in part secondary to increased IL-10 production and its effects on dendritic cell function resulting in altered T-cell differentiation. These findings indicate that, in addition to the central role leukotrienes play in the acute inflammatory response, endogenous leukotrienes are also important regulators of inflammatory cytokine production, via regulation of IL-10 production and in vivo differentiation of T cells.

Up-regulation of prostaglandin biosynthesis by leukotriene C4in elicited mice peritoneal macrophages activated with lipopolysaccharide/interferon-γ

Leukotrienes (LT) and prostaglandins (PG) are proinflammatory mediators generated by the conversion of arachidonic acid via 5-lipoxygenase (5-LO) and cyclooxygenase (COX) pathways. It has long been proposed that the inhibition of the 5-LO could enhance the COX pathway leading to an increased PG generation. We have found that in in vitro models of inflammation, such as mice-elicited peritoneal macrophages activated with lipopolysaccharide (LPS)/interferon-gamma (IFN-gamma), the deletion of the gene encoding for 5-LO or the enzyme activity inhibition corresponded to a negative modulation of the COX pathway. Moreover, exogenously added LTC(4), but not LTD(4), LTE(4), and LTB(4), was able to increase PG production in stimulated cells from 5-LO wild-type and knockout mice. LTC(4) was not able to induce COX-2 expression by itself but rather potentiated the action of LPS/IFN-gamma through the extracellular signal-regulated kinase-1/2 activation, as demonstrated by the use of a specific mitogen-activated protein kinase (MAPK) kinase inhibitor. The LT-induced increase in PG generation, as well as MAPK activation, was dependent by a specific ligand-receptor interaction, as demonstrated by the use of a cys-LT1 receptor antagonist, although also a direct action of the antagonist used, on PG generation, cannot be excluded. Thus, the balance between COX and 5-LO metabolites could be of great importance in controlling macrophage functions and consequently, inflammation and tumor promotion.

Myeloid expression of cytochrome P450 4F3 is determined by a lineage-specific alternative promoter

The cytochrome P450 4F3 (CYP4F3) gene encodes two functionally distinct enzymes that differ only by the selection of exon 4 (CYP4F3A) or exon 3 (CYP4F3B). CYP4F3A inactivates leukotriene B4, a reaction that has significance for controlling inflammation. CYP4F3B converts arachidonic acid to 20-hydroxyeicosatetraenoic acid, a potent activator of protein kinase C. We have previously shown that mRNAs coding for CYP4F3A and CYP4F3B are generated from distinct transcription start sites in neutrophils and liver. We therefore investigated mechanisms that regulate the cell-specific expression of these two isoforms. Initially, we analyzed the distribution of CYP4F3 in human leukocytes and determined a lineage-specific pattern of isoform expression. CYP4F3A is expressed in myeloid cells and is coordinate with myeloid differentiation markers such as CD11b and myeloperoxidase during development in the bone marrow. In contrast, CYP4F3B expression is restricted to a small population of CD3+ T lymphocytes. We identified distinct transcriptional features in myeloid, lymphoid, and hepatic cells that indicate the presence of multiple promoters in the CYP4F3 gene. The hepatic promoter depends on a cluster of hepatocyte nuclear factor sites 123-155 bp upstream of the initiator ATG codon. The myeloid promoter spans 400 bp in a region 468-872 bp upstream of the ATG codon; it is associated with clusters of CACCT sites and can be activated by ZEB-2, a factor primarily characterized as a transcriptional repressor in cells that include lymphocytes. ZEB-2 interacts with C-terminal binding protein and Smads, and this would provide opportunities for integrating environmental signals in myelopoiesis and inflammation.

Distinct roles of eicosanoids in the immune response to viral encephalitis: or why you should take NSAIDS

Prostaglandins (PGs) and leukotrienes (LTs) are important proinflammatory mediators. They are both derived from arachidonic acid (AA). Cyclooxygenase (COX), the key enzyme in transforming AA into PGs, has two isoforms: COX-1 is constitutively expressed, and COX-2, is inducible. Lipoxygenase (5-LO) is the key enzyme for LT production. PGs and LTs have been intensively studied. Release of these molecules is associated with mucus secretion, redness, pain, fever and other inflammatory manifestations. Both PGs and LTs are involved in host defense against various pathogens. In addition to mediating inflammatory symptoms, PGs might suppress some innate immune factors, including nitric oxide (NO) production. PGs also suppress a TH1 response. LTs have pathologic potential, especially in asthma. LTs also have been found to have positive roles in host defense, either against virus or bacteria. Finally, PGs and LTs might regulate the production of each other, possibly at the level of substrate competition by their enzymes. Because they are clinically important molecules, a further understanding of the roles that PGs and LTs played in host defense will have great impact on therapeutic research.

Selective inhibition of COX-2 is beneficial to mice infected intranasally with VSV

Cyclooxygenase (COX) is the key enzyme for prostaglandin (PG) synthesis. PGs are mediators of many critical physiological and inflammatory responses. There are two isoforms, COX-1 and COX-2, both of which are constitutively expressed in the central nervous system (CNS). Studies have shown that COX-1 and COX-2 are involved in physiological and pathological conditions of the brain. However, little is known about the role(s) of COX in the host defense system against a viral infection in the CNS. In this report, we used Vesicular Stomatitis Virus (VSV) induced acute encephalitis to distinguish between the contribution(s) of the two isoforms. COX-2 activity was inhibited with a COX-2 selective drug, celecoxib (Celebrex), and COX-1 was antagonized with SC560. We found that inhibition of COX-2 led to decreased viral titers, while COX-1 antagonism did not have the same effect at day 1 post infection. 5-lipooxygenase (5-LO) expression and neutrophil recruitment in the CNS were increased in celecoxib-inhibited mice. Furthermore, mice treated with celecoxib expressed more Nitric Oxide Synthase-1 (NOS-1), a crucial component of the innate immune system in the restriction of VSV propagation. The expression of type 1 cytokines, IFN-gamma and IL-12, were also increased in celecoxib-treated mice.

Deficiency of 5-lipoxygenase accelerates renal allograft rejection in mice

Acute renal allograft rejection is associated with alterations in renal arachidonic acid metabolism, including enhanced synthesis of leukotrienes (LTs). LTs, the products of the 5-lipoxygenase (5-LO) pathway, are potent lipid mediators with a broad range of biologic activities. Previous studies, using pharmacological agents to inhibit LT synthesis or activity, have implicated these eicosanoids in transplant rejection. To further investigate the role of LTs in acute graft rejection, we transplanted kidneys from CByD2F1 mice into fully allogeneic 129 mice that carry a targeted mutation in the 5lo gene. Unexpectedly, allograft rejection was significantly accelerated in 5-LO-deficient mice compared with wild-type animals. Despite the marked reduction in graft survival, the 5lo mutation had no effect on the hemodynamics or morphology of the allografts. Although LTB4 levels were reduced, renal thromboxane B2 production and cytokine expression were not altered in 5-LO-deficient allograft recipients. These findings suggest that, along with their proinflammatory actions, metabolites of 5-LO can act to enhance allograft survival.

Leukotrienes play protective roles early during experimental VSV encephalitis

Leukotrienes (LT) are potent lipid mediators of inflammation. 5-Lipoxygenase (5-LO) is the key enzyme in the conversion of arachidonic acid to LT. There are four LT: LTB(4), LTC(4), LTD(4) and LTE(4). LT have been extensively studied in airway inflammation but little is known about their roles in viral infection in the CNS. LTB(4) is a chemoattractant for neutrophils. In this work, we studied the roles of LT in acute vesicular stomatitis virus (VSV) encephalitis. Two methods were used to disrupt 5-LO activity: mice were treated with Zileuton, an enzyme antagonist, or 5-LO genetic knockout mice were used. We found that inhibition or deletion of 5-LO resulted in: (a) impaired process of neutrophil infiltration into the CNS early during viral infection; (b) fewer neurons expressed nitric oxide synthase-1 (NOS-1); (c) higher viral titers 1 day after viral infection; and (d) increased disruption of blood brain barrier (BBB). Our studies suggest that LT are important innate immune players during VSV pathogenesis and are beneficial to the host in early control of viral replication in the CNS.

Fas/Apo-1 (CD95)-mediated apoptosis of neutrophils with Fas ligand (CD95L)-expressing tumors is crucial for induction of inflammation by neutrophilic polymorphonuclear leukocytes associated with antitumor immunity

To address how FasL-expressing tumors induce neutrophil emigration and abrogate tumorigenicity, we investigated the behavior of FasLcDNA-transfected hepatoma MH134 (G2) cells injected into wild-type (+) mice, lpr(cg)/lpr(cg) (lpr(cg)) mice with death domain (DD)-mutated Fas, and gld/gld lpr/lpr (gld/lpr) mice with defects in FasL/Fas. G2 cells were eradicated after extensive infiltration of neutrophils around them in + mice but formed tumors without such infiltration in lpr(cg) and gld/lpr mice. Abundant cell debris suggestive of apoptosis of infiltrating neutrophils was found among G2 tumor cells in + mice but a few neutrophils infiltrating among G2 cells were intact in lpr(cg) and gld/lpr mice. Collectively, these results indicate the crucial role of Fas DD in Fas-mediated apoptosis of neutrophils and suggest that apoptosis of neutrophils with FasL-expressing tumors may trigger the extensive infiltration of neutrophils, resulting in violent inflammation and ultimately in the eradication of tumor cells.

Genetic factors determine the contribution of leukotrienes to acute inflammatory responses

Leukotrienes (LT) are potent lipid mediators synthesized by the 5-lipoxygenase pathway of arachidonic acid (AA) metabolism. LT have been implicated in a broad spectrum of inflammatory processes. To investigate the influence of genetic factors on the contribution of LT to acute inflammation, we generated congenic 5-lipoxygenase-deficient 129, C57BL/6 (B6), and DBA/1Lac (DBA) mouse lines. Topical application of AA evoked a vigorous inflammatory response in 129 and DBA mice, whereas only a modest response was seen in B6 animals. The response to AA in 129 and DBA strains is LT dependent. In contrast, LT make little contribution to this response in B6 mice. AA-induced inflammation in B6 mice is prostanoid dependent, since this response was substantially reduced by treating B6 mice with a cyclooxygenase inhibitor. These data suggest that prostanoids are essential for AA-induced cutaneous inflammation in B6 mice, whereas LT are the major mediators of this response in 129 and DBA strains. In contrast, the response to AA in the peritoneal cavity is robust in the 129 and B6 strains, but was significantly blunted in DBA mice, showing that strain differences in the response to AA are tissue specific. Variations in these and other experimental models of inflammation appear to correlate directly with the ability of a particular mouse strain and a specific tissue to respond to LT, specifically LTC4. Taken together, these findings indicate that the relative contribution of prostanoids and LT to inflammatory responses is variable not only between strains but also between different tissues within these inbred mouse lines.

Asthma therapy with agents preventing leukotriene synthesis or action

Elucidation of the biochemistry of leukotriene production and the pharmacology of its actions has led to the development of a number of therapeutic agents shown to be of value in the treatment of asthma. These agents either prevent the synthesis of the leukotrienes, by preventing the action of the 5-lipoxygenase-activating protein or the catalytic action of the 5-lipoxygenase, or by inhibiting the action of leukotrienes at the CysLT1 receptor. Numerous clinical trials in exercise-induced asthma, allergen-induced asthma, aspirin-induced asthma, and spontaneously occurring asthmatic episodes have indicated that these agents are safe and effective asthma treatments.

Deficiency of 5-Lipoxygenase Abolishes Sex-Related Survival Differences in MRL-lpr/lpr Mice

Leukotrienes, the 5-lipoxygenase (5LO) products of arachidonic acid metabolism, have many proinflammatory actions that have been implicated in the pathogenesis of a variety of inflammatory diseases. To investigate the role of LTs in autoimmune disease, we generated an MRL-lpr/lpr mouse line with a targeted disruption of the 5lo gene. MRL-lpr/lpr mice spontaneously develop autoimmune disease that has many features resembling human systemic lupus erythematosus, including sex-related survival differences; female MRL-lpr/lpr mice experience significant early mortality compared with males. Unexpectedly, we found that mortality was accelerated in male 5LO-deficient MRL-lpr/lpr mice compared with male wild-type MRL-lpr/lpr animals. In contrast, the 5lo mutation had no effect on survival in females. Mortality was also accelerated in male MRL-lpr/lpr mice that were treated chronically with a pharmacological inhibitor of LT synthesis. Furthermore, LT-dependent inflammatory responses are enhanced in male MRL-lpr/lpr mice compared with females, and the 5lo mutation has greater impact on these responses in males. Because immune complex-mediated glomerulonephritis is the major cause of death in MRL-lpr/lpr mice and has been related to arachidonic acid metabolites, we also assessed kidney function and histopathology. In male MRL-lpr/lpr mice, renal plasma flow was significantly reduced in the 5lo−/− compared with the 5lo+/+ group, although there were no differences in the severity of renal histopathology, lymphoid hyperplasia, or arthritis between the groups. These findings suggest that the presence of a functional 5lo gene confers a survival advantage on male MRL-lpr/lpr mice and that, when 5LO function is inhibited, either genetically or pharmacologically, this advantage is abolished.

Role of the 5-lipoxygenase-activating protein (FLAP) in murine acute inflammatory responses

Leukotrienes are potent inflammatory mediators synthesized from arachidonic acid (AA) predominately by cells of myeloid origin. The synthesis of these lipids is believed to be dependent not only on the expression of the enzyme 5-lipoxygenase (5-LO), which catalyzes the first steps in the synthesis of leukotrienes, but also on expression of a nuclear membrane protein termed the 5-LO-activating protein (FLAP). To study the relationship of these two proteins in mediating the production of leukotrienes in vivo and to determine whether the membrane protein FLAP has additional functions in various inflammatory processes, we have generated a mouse line deficient in this protein. FLAP-deficient mice develop normally and are healthy. However, an array of assays comparing inflammatory reactions in FLAP-deficient mice and in normal controls revealed that FLAP plays a role in a subset of these reactions. Although examination of DTH and IgE-mediated passive anaphylaxis showed no difference between wild-type and FLAP-deficient animals, mice without FLAP possessed a blunted inflammatory response to topical AA and had increased resistance to platelet-activating factor-induced shock compared to controls. Also, edema associated with Zymosan A-induced peritonitis was markedly reduced in animals lacking FLAP. To determine whether these differences relate solely to a deficit in leukotriene production, or whether they reflect an additional role for FLAP in inflammation, we compared the FLAP-deficient mice to 5-LO-deficient animals. Evaluation of mice lacking FLAP and 5-LO indicated that production of leukotrienes during inflammatory responses is dependent upon the availability of FLAP and did not support additional functions for FLAP beyond its role in leukotriene production.

Effect of SC-41930, a potent selective leukotriene B4 receptor antagonist, in the guinea pig model of middle ear inflammation

Arachidonic acid metabolites such as prostaglandins and leukotrienes have been shown to play an important role in the pathogenesis of otitis media (OM). Among these mediators, leukotriene B4 (LTB4) is one of the most potent inducers of inflammatory processes. SC-41930 has been shown to be a specific LTB4 receptor antagonist both in vitro and in vivo. In this study, anti-inflammatory effects of SC-41930 were investigated in a guinea pig model of OM induced by middle ear (ME) inoculation of killed Staphylococcus aureus. Outcome of treatment was determined by measurement of myeloperoxidase activity in the samples of ME mucosa, evaluation of temporal bone histopathology, and presence of ME fluids. Myeloperoxidase activity in the SC-41930-treated group was found to be significantly lower than that in the control group. Histopathology of temporal bones indicated decreased inflammation in the treated group as compared to the controls. In addition, ME fluids were absent in four out of six treated animals. These results demonstrate that SC-41930 can produce significant anti-inflammatory effects in this model of OM.

Post-capillary venules in the "milky spots" of the greater omentum are the major site of plasma protein and leukocyte extravasation in rodent models of peritonitis

Intraperitoneal injection of inflammatory agents in the mouse and rat causes plasma protein and leukocyte extravasation into the peritoneal cavity. Following an intraperitoneal injection of zymosan A, the milky spots of the omentum were the only abdominal sites detected where intravenously administered Monastral Blue labeled interendothelial cell gaps responsible for plasma extravasation. In addition, when colored microspheres were intraventricularly administered to quantify blood flow, the omentum was the only abdominal organ which showed an increase in blood flow during zymosan A peritonitis. A combination of light and electron microscopy, plus measurement of myeloperoxidase activity (a marker of neutrophil accumulation) demonstrated that the omental milky spots are the major route through which leukocytes migrate into the peritoneal cavity. Identical structures in the pleura likewise are the sites of protein leakage into the pleural cavity. In contrast, selective sites of protein and cellular extravasation could not be detected in the synovial lining of the inflamed knee joint.

Leukotriene B4 plays a critical role in the progression of collagen-induced arthritis

Leukotriene B4 (LTB4) is a product of the 5-lipoxygenase pathway of arachidonic acid metabolism. LTB4 is a potent chemotactic factor for neutrophils and has been postulated to play an important role in a variety of pathological conditions including rheumatoid arthritis (RA), psoriasis, and inflammatory bowel disease. The role of LTB4 in such diseases has not yet been defined but in this paper we provide direct evidence that LTB4 plays a critical role in a murine model of RA. CP-105,696, (+)-1-(3S,4R)-[3-(4-phenylbenzyl)- 4-hydroxychroman-7-yl]cyclopentane carboxylic acid, is an LTB4 receptor antagonist that inhibits LTB4 binding to human neutrophil membranes with an IC50 of 3.7 nM and inhibits LTB4-induced chemotaxis of these cells with an IC50 of 5.2 nM. CP-105,696 inhibits LTB4-induced neutrophil influx in mouse skin when administered orally with an ED50 of 4.2 mg/kg. CP-105,696 had a dramatic effect on both the clinical symptoms and histological changes of murine collagen-induced arthritis when administered at doses of 0.3-10 mg/kg. Inhibition was not associated with suppression of the humoral immune response to collagen and was equally effective if drug treatment was commenced just prior to the onset of arthritis or throughout the experiment. These results suggest that LTB4 receptor antagonists may be effective therapeutic agents for the treatment of RA.

Altered inflammatory responses in leukotriene-deficient mice

Leukotrienes have been implicated in the regulation of immune responses, including inflammation and immediate hypersensitivity reactions. Here, we describe the phenotypic analysis of leukotriene-deficient mice generated by inactivation of the 5-lipoxygenase (5LO) gene. These 5LO(-/-) mice were unable to synthesize detectable levels of leukotrienes and were more resistant to lethal anaphylaxis induced by platelet-activating factor. The intensity of an acute inflammatory response induced by arachidonic acid was similar in 5LO(-/-) mice and controls. However, the response in 5LO(-/-) mice, but not in controls, could be virtually eliminated by a cyclooxygenase inhibitor. These data suggest that inflammatory responses are modulated by arachidonic acid metabolites through a variety of interconnected mechanisms. This has important implications for understanding the early events of an inflammatory response and for designing drugs for use in therapeutic intervention.

Effect of in vivo desensitization to leukotriene B4 on eosinophil infiltration in response to C5a in guinea-pig skin

1. The effect of in vivo desensitization to leukotriene B4 (LTB4) on eosinophil infiltration in response to recombinant C5a was examined in guinea-pig skin. 2. LTB4 (10-300 ng) and C5a (1-10 micrograms) caused a dose-dependent increase in the levels of eosinophil peroxidase activity (a measure of eosinophil infiltration) 4 h after injection into guinea-pig skin. Leukotriene B4 and C5a were approximately equipotent on a molar basis. Platelet activating factor (0.01-10 micrograms) also caused eosinophil accumulation but was much less active than LTB4 or C5a. 3. 20-Hydroxy-LTB4 caused a dose-dependent desensitization of eosinophil responses to LTB4 (ED50 = 1.6 micrograms kg-1, s.c.) and partially reduced responses to C5a. At a dose of 20-hydroxy-LTB4 (10 micrograms) which inhibited responses to LTB4 completely, responses to C5a were reduced by 56.5 +/- 1.8% (n = 5). The structurally related metabolite of 20-hydroxy-LTB4, 20-carboxy-LTB4, which does not cause desensitization to the effects of LTB4, did not inhibit eosinophil infiltration in response to C5a. 4. The LTB4 receptor antagonist, SC-41,930 (10 mg kg-1, p.o.), also inhibited eosinophil accumulation in response to C5a by 63.0 +/- 3.9% (n = 5) at a dose which inhibited responses to LTB4 by 86.5 +/- 1.9% (n = 5). 5. These data indicate that eosinophil infiltration in response to C5a may, in part, be mediated by the generation of secondary chemotactic factors such as LTB4.