SC-41930: an inhibitor of leukotriene B4-stimulated human neutrophil functions

SC-41930 was evaluated for effects on human neutrophil chemotaxis and degranulation. At concentrations up to 100 microM, SC-41930 alone exhibited no effect on neutrophil migration, but dose-dependently inhibited neutrophil chemotaxis induced by leukotriene B4 (LTB4) in a modified Boyden chamber. Concentrations of SC-41930 from 0.3 microM to 3 microM competitively inhibited LTB4-induced chemotaxis with a pA2 value of 6.35. While inactive at 10 microM against C5a-induced chemotaxis, SC-41930 inhibited N-formyl-methionyl-leucyl-phenylalanine (fMLP)-induced chemotaxis, with 10 times less potency than against LTB4-induced chemotaxis. SC-41930 inhibited [3H]LTB4 and [3H]fMLP binding to their receptor sites on human neutrophils with KD values of 0.2 microM and 2 microM, respectively. SC-41930 also inhibited neutrophil chemotaxis induced by 20-OH LTB or 12(R)-HETE. At concentrations up to 10 microM, SC-41930 alone did not cause neutrophil degranulation, but inhibited LTB4-induced degranulation in a noncompetitive manner. SC-41930 also inhibited fMLP- or C5a-induced degranulation, but was about 8 and 10 times less effective for fMLP and C5a, respectively. The results indicate that SC-41930 is a human neutrophil LTB4 receptor antagonist with greater specificity for LTB4 than for fMLP or C5a receptors.

In vitro effects of leukotriene B4 (LTB4) on canine PMN effector function(s)

The canine has become an accepted research model for the examination of a number of human clinical conditions. Despite it's status as a research model, little is known regarding the peripheral effects of inflammatory mediator substances. Products of arachidonic acid metabolism (leukotrienes) are reported capable of altering leukocyte functions. Because of the emerging importance of the canine research model and leukotrienes we examined the effects of leukotriene B4 (LTB4) on several in vitro functions of isolated canine peripheral polymorphonuclear leukocytes (PMN). Changes in forward angle light scatter properties of the cells were used as one measure of PMN activation. Other functional changes examined following LTB4 pretreatment included chemotactic capability, the electrophysiological state of the cell plasma membrane, and the metabolic oxidative response (i.e. H2O2 production). Random cellular movement of PMNs increased by 120% and 72% following preincubation with 10(-7) and 10(-9) M LTB4, respectively. LTB4 between 10(-7) and 10(-13) M did not significantly alter cellular resting membrane potential. Between 10(-7) and 10(-9) M LTB4 elicited significant levels of cellular H2O2 production. Although significant, H2O2 production was less than 40% that induced by phorbol myristate acetate (PMA). In numerous respects, canine in vitro PMN responses parallel previous reports of human cell function(s) in the presence of inflammatory mediators and may represent an attractive alternative for investigation of PMN dysfunctions.

Polymorphonuclear leukocytes cap a derivative of wheat germ agglutinin upon stimulation with formyl peptide and C5a but not leukotriene B4

Previously, we reported that a derivative of wheat germ agglutinin (termed WGA-D) specifically inhibits human polymorphonuclear leukocyte (PMN) chemotaxis to FMLP by blocking reexpression (or recycling) of formyl peptide receptors. WGA-D (? formyl peptide receptor probe) binds to a protein on the PMN membrane that exhibits the same m.w. as the formyl peptide receptor. Since clustering (i.e., capping) of ligand-receptor complexes most likely precedes their internalization, we examined the ability of normal and stimulated PMN to cap fluoresceinated WGA-D. We found that, in contrast to capping of fluoresceinated Con A, PMN cap WGA-D in a chemotactic factor-specific fashion. Fluoresceinated WGA-D (5.0 to 20 micrograms/ml) alone did not induce either PMN shape changes (i.e., activation) or capping. Both FMLP (1 to 1000 nM) and human C5a (0.1 to 1.0 nM) induced PMN to polarize and to cap bound WGA-D, in a concentration-dependent fashion. Interestingly, leukotriene B4 (LTB4) (5.0 nM), while inducing the same degree of PMN polarization as FMLP (100 nM) and C5a (0.5 nM), failed to induce PMN to cap bound WGA-D. In contrast, FMLP (100 nM), C5a (0.5 nM), and LTB4 (5.0 nM) induced PMN to cap bound fluoresceinated Con A (10 micrograms/ml) to the same extent. The effect of suboptimal concentrations of FMLP and C5a on capping of WGA-D by PMN was additive. LTB4 did not enhance either FMLP or C5a-induced capping of WGA-D by PMN. Also, FMLP and C5a (but not LTB4) were capable of inducing both desensitization and cross-desensitization of WGA-D capping by PMN. Studies using rhodamine-labeled WGA-D and a fluoresceinated analog of FMLP revealed that both capped to the same place on the PMN membrane. Thus, the data suggest that WGA-D binds to a site on the PMN membrane that is either the FMLP receptor or very closely associated with it.

Neutrophil Mac-1 and MEL-14 adhesion proteins inversely regulated by chemotactic factors

The neutrophil Mac-1 and gp100MEL-14 adhesion proteins are involved in neutrophil extravasation during inflammation. Both the expression and activity of Mac-1 are greatly increased after neutrophil activation. In contrast, neutrophils shed gp100MEL-14 from the cell surface within 4 minutes after activation with chemotactic factors or phorbol esters, releasing a 96-kilodalton fragment of the antigen into the supernatant. Immunohistology showed that gp100MEL-14 was downregulated on neutrophils that had extravasated into inflamed tissue. The gp100MEL-14 adhesion protein may participate in the binding of unactivated neutrophils to the endothelium; rapid shedding of gp100MEL-14 may prevent extravasation into and damage of normal tissues by activated neutrophils.

Sequential patterns of eicosanoid, platelet, and neutrophil interactions in the evolution of the fulminant post-traumatic adult respiratory distress syndrome

Thirty multiply injured blunt-trauma patients at high risk for development of ARDS (multisystem trauma including more than one organ or extremity, Injury Severity Score of 26 or more, hypotension and need for 1500 mL or more blood within the first hour after admission, and PaO2 less than or equal to 70 torr) were studied sequentially with blood and physiologic evaluations beginning immediately after injury and every eight hours for eight days, or until death, to study the evolution of the ARDS process. Mixed venous blood samples were obtained for eicosanoids PGE2, PGF2 alpha, thromboxane B2, PGI2 (6-KetoPGF1 alpha) and leukotriene B4 (LTB4). Platelet (PLAT), and neutrophil (WBC) counts were also done and plasma elastase was measured. At 7:00 AM each day patient neutrophils were obtained for a study of zymosan-activated superoxide production using a chemiluminescence assay. These data were correlated with physiologic measurements of the Respiratory Index (RI), per cent pulmonary shunt (QS/QT), and respiratory compliance measures. Seven patients developed a fulminant post-traumatic ARDS syndrome within 96 hours after injury. Twelve patients without ARDS developed sepsis (TS) four or more days after injury, and 11 had uncomplicated postinjury courses (TR). Compared to both TR and TS, ARDS had a significant (p less than 0.01) rise in neutrophil superoxide production beginning on day 2 through day 4 after injury. This was preceded by rises in PGE2 and LTB4, which were significantly correlated with subsequent falls in PLAT and WBC and rises in TXB2, PGF1, and superoxide production and followed by increases in RI, QS/QT, and a fall in compliance. The significant difference in the pattern and sequence of events in ARDS compared to TR and TS patients suggests that in ARDS the earliest event may be related to peripheral release of PGE2 and LTB4 due to platelet activation and lung sequestration with release of PGF2 alpha, and by aggregation and leukocyte adherence with release of elastase. However, fulminant ARDS mortality appears to be related to the subsequent amplification of the LTB4 leukocyte activation with superoxide production that does not achieve significance before the second day after injury and rises to a maximum by day 4 after injury. These data suggest that post-trauma ARDS follows a different evolutionary pattern than that reported in animal models and is also different from that seen in human TS or TR patients.(ABSTRACT TRUNCATED AT 400 WORDS)

Biphasic accumulation of leukocytes in rat cardiac infarct tissue caused by leukotriene B4 and complement

An initial increase (3-12 hr) in the polymorphonuclear leukocytes (PMN) counts after ligation of the rat left main coronary artery was reduced by 49.4% (at 12 hr) by a 5-lipoxygenase inhibitor, AA-861 (80 mg/kg, p.o., 1 hr before ligation). Depletion of the complement components induced by cobra venoma factor (CVF) (i.v.), given one day before, resulted in significant reduction in the PMN accumulation after 12 hr (by 63.6% at 24 hr). The combined treatment (CVF+AA-861) suppressed the PMN accumulation by 69.7% (24 hr). The infarct size at 48 hr was also reduced by approximately 36% by either AA-861, CVF or combined treatments.

Role of leukotriene B4 in the pathogenesis of Klebsiella pneumoniae-induced bovine mastitis

Mastitis was induced in 4 lactating cows by inoculation of Klebsiella pneumoniae (10(7) organisms/ml) via the teat canal. Sterile isotonic saline solution (1 ml) was instilled into designated control quarters via the teat canal. Changes in milk leukotriene B4 and C4 (LTB4, LTC4) concentrations, milk somatic cell counts, and milk bovine serum albumin concentration were monitored over a 24-hour postinoculation period. Milk LTB4 concentration before inoculation in control quarters and quarters later to be infected was 376 +/- 45 and 326 +/- 56 pg/ml of milk, respectively. A significant (P less than 0.05) increase in milk LTB4 concentration in the infected quarters was first observed at postinoculation hour 6, and milk LTB4 concentration in infected quarters generally remained significantly high through postinoculation hour 14. Thereafter, milk LTB4 concentration in infected quarters was not significantly different from the concentration in control quarters. Measurable amounts of LTC4 were not detected in the milk of either control or infected quarters. Milk bovine serum albumin concentration in the infected quarters generally was high throughout the study, as were milk somatic cell counts. The results of this study suggested that LTB4 contributes to the pathogenesis of bovine mastitis.

The use of fish oil in bronchial asthma

A fish-oil enriched diet has potential in modulating the humoral and inflammatory components of the allergic response by inhibiting the generation of pro-inflammatory mediators derived from arachidonic acid and by reducing the production of PAF-acether. In addition, EPA suppresses the responses of target cells and tissues. Studies in bronchial asthma confirm the anti-inflammatory potential of a fish-oil enriched diet. Dietary supplementation with EPA in subjects with asthma led to changes in leukocyte mediator generation and chemotactic responses. There was also a significant attenuation of the late asthmatic response to inhaled antigen. Further studies are needed to determine the full potential of such diets in effecting changes in the clinical aspects of allergic disease.

[Regulation of the immune response using leukotrienes]

Leukotrienes are derived from lipoxygenation in position 5 of arachidonic acid. They have numerous biological activities, mainly in inflammatory processes. During the last few years, however, it has become quite evident that they also possess a potential for immunoregulation. In particular, LTB4 can induce suppressor cells, activate the synthesis and production of lymphokines such as interleukin 2 or interferon-gamma, stimulate the production of interleukin 1 by monocytes or macrophages, and activate cytotoxic cells against virus-infected or tumor target cells. These findings suggest that LTB4 can play an important role in the interaction between inflammatory and immune phenomena.

Modulation of the migration and chemotaxis of PMN cells by hyaluronic acid

Hyaluronic acid (HA) has a dose-related inhibiting effect on the migration and chemotaxis of polymorphonuclear leucocytes (PMN) in vitro. These effects were measured with a new indirect quantitative assay. On average 1 mg HA/ml causes an inhibition to about 80% of the control (spontaneous migration). This effect increased progressively with an increasing HA concentration, and with 4 mg HA/ml only about 19% of the PMN were able to migrate in the in vitro system. Similar results were obtained in the presence of a potent chemotactic factor (leukotriene B4 [LTB4]). In the mean 1 ng LTB4/ml alone stimulated the chemotaxis of PMN by a factor of 3 compared to the spontaneous migration. The highest HA concentration (4 mg/ml) reduced the number of migrating PMN cells to about 17%. From these experiments it may be concluded that the HA in the synovial fluid of the healthy joint has a protective effect against the invasion of PMN cells. This functions is disturbed in inflamed joints by the decrease in the HA concentration and possibly by its depolymerization. The intraarticular application of high molecular weight HA might be an important therapeutic regimen to restore the natural barrier against PMN migration, also in the presence of chemotactic factors and could therefore be helpful for interrupting the inflammatory cascade.

Postischemic renal injury is mediated by neutrophils and leukotrienes

Neutrophils have been implicated as central mediators in myocardial and skeletal muscle ischemia-reperfusion injury. This study tests whether these cellular elements and the chemoattractant leukotriene (LTB4) play a role in postischemic renal failure. Anesthetized rats underwent 45 min of left renal pedicle clamping. Five minutes after reperfusion, LTB4 levels were elevated to 1.42 ng/ml (P less than 0.05); thromboxane (Tx)B2 was 2,840 pg/ml, higher than 503 pg/ml in sham controls (P less than 0.05); renal artery blood flow was 67% of preclamping values at 1 min of reperfusion compared with 111% in sham (P less than 0.05). At 24 h, creatinine levels were 4.6 mg/dl (P less than 0.05). At 24 h, creatinine levels were 4.6 mg/dl (P less than 0.05); histology showed acute tubular necrosis (ATN). Neutrophil depletion by rabbit antiserum (n = 8) led during reperfusion to reduced LTB4 and TxB2 levels, 1.04 ng/ml and 1.043 pg/ml (P less than 0.05); increased renal blood flow of 174% (P less than 0.05); reduced creatinine levels of 1.8 mg/dl (P less than 0.05); and limited ATN. Pretreatment with diethycarbamazine prevented the increases in LTB4 and TxB2 (P less than 0.05), increased renal blood flow (P less than 0.05), minimized creatinine increase to 1.7 mg/dl (P less than 0.05), and reduced ATN. These data indicate that neutrophils and LTB4 play a role in ischemia-induced Tx synthesis and mediate postischemic renal injury.

Leukotrienes but not complement mediate limb ischemia-induced lung injury

Reperfusion after limb ischemia leads to sequestration of polymorphonuclear leukocytes (PMN) in the lungs and to leukocyte- (WBC) and thromboxane- (Tx) dependent respiratory dysfunction. This study examines the intermediary role of the chemoattractants leukotriene (LT)B4 and complement (C) fragments. Anesthetized sheep with chronic lung lymph fistulae underwent 2 hours of tourniquet ischemia of both hind limbs. In untreated controls (n = 7), 1 minute after tourniquet release, mean pulmonary artery pressure (MPAP) rose from 13 to 38 mmHg (p less than 0.05) and returned to baseline within 30 minutes. Pulmonary artery wedge pressure was unchanged from 3.6 mmHg. There were increases in plasma LTB4 levels from 2.46 to 9.34 ng/ml (p less than 0.01), plasma TxB2 levels from 211 to 735 pg/ml (p less than 0.05), and lung lymph TxB2 from 400 to 1005 pg/ml (p less than 0.05). C3 levels were 96% of baseline values. Thirty minutes after reperfusion, lung lymph flow (QL) increased from 4.3 to 8.3 ml/30 minutes (p less than 0.05), lymph/plasma protein ratio was unchanged from 0.6, and the lymph protein clearance increased from 2.6 to 4.6 ml/30 minutes (p less than 0.05), data consistent with increased microvascular permeability. WBC count fell within the first hour from 6853 to 3793/mm3 (p less than 0.01). Lung histology showed leukosequestration, 62 PMN/10 high-power fields (HPF) and proteinaceous exudates. In contrast to this untreated ischemic group, animals treated with the lypoxygenase inhibitor diethylcarbamazine (n = 5) demonstrated a blunted reperfusion-induced rise in MPAP to 17 mmHg (p less than 0.05). There were no increases in LTB4, TxB2, QL or lymph protein clearance (p less than 0.05). WBC count was unchanged and lung leukosequestration was reduced to 40 PMN/10 HPF (p less than 0.05). Decomplementation with cobra venom factor (n = 4) resulted in plasma C3 levels, 10% of baseline, but tourniquet release still led to pulmonary hypertension, elevated LTB4, TxB2 levels, and a decline in WBC count similar to that of untreated ischemic control animals. Histology showed 46 PMN/10 HPF sequestered in the lungs. Further, bilateral hind limb ischemia in either genetically sufficient (n = 10) or deficient (n = 10) C5 mice led to significant lung leukosequestration of 108 and 106 PMN/10 HPF, respectively, compared with 42 and 47 PMN/10 HPF in sham C5(+) and C5 (-) mice (n = 20) (p less than 0.01). These results suggest that the lung leukosequestration and increased microvascular permeability after lower torso ischemia are mediated by the chemotactic agent LTB4, but not by the complement system.

Leukotriene release enhancing factor. Purification, specific allergen induction, and further biologic properties

Human PBMC cultured with PHA produced a factor which enhanced neutrophil LTB4 production. After progressive purification by gel filtration and chromatofocusing, leukotriene release enhancing factor (LREF) gave a single band on SDS-PAGE corresponding to a Mr of 60 kDa and a isoelectric point of 5.0 to 5.2. Human T lymphocytes were identified as a source of LREF because a long term human CD4+ T cell line, specific for house dust mite (Dermatophagoides farinae) generated leukotriene release enhancing activity (LREA) when stimulated with the inducing Ag together with irradiated accessory cells. Cultures of accessory cell and Ag alone did not induce neutrophil activation. Similarly, control cultures using an irrelevant allergen (grass pollen) failed to produce this activity. Stimulation of PBMC with anti-CD3 mAb also generated LREA. LREA had other neutrophil-associated biologic activities. These included the enhancement of neutrophil adherence to nylon wool, increased cytotoxicity of opsonised schistosomula of Schistosoma mansoni and upregulation of C receptors (CR1 and CR3). LREA had minimal neutrophil chemotactic activity. Therefore, LREF has potential as a mediator of inflammation and provides a link between lipid mediators, neutrophils, and cell-mediated immunity in the context of allergic diseases.

Leukotriene B4 as a mediator of early and late reactions to antigen in humans: the effect of systemic glucocorticoid treatment in vivo

The role played by leukotriene B4 (LTB4) in human allergic reactions has been the subject of recent interest and speculation. To characterize further the role of this mediator, we quantitated LTB4 levels in nasal washing by radioimmunoassay in 13 atopic subjects during immediate and late reactions after nasal antigen challenge while the subjects were taking placebo or prednisone (20 mg every 8 hours for 48 hours) in a double-blind, placebo-controlled, crossover protocol and compared these levels with levels of seven nonatopic subjects undergoing similar nasal antigen challenge. Nasal antigen challenge of atopic subjects resulted in an increase in LTB4 levels during the immediate reaction in 10 of 13 subjects (9/13 with a greater than 50% increase over baseline) with no similar increase observed in nonatopic subjects (p less than 0.05). An increase in LTB4 levels was observed in 12/13 atopic subjects (6/13 with greater than 50% increase over a second baseline) during late time periods (p less than 0.05), which was associated with an influx of neutrophils (from 65,000 +/- 43,000 to 1,246,000 +/- 829,000; p less than 0.05). However, nonatopic subjects appeared to demonstrate a similar late increase in LTB4 levels. High-performance liquid chromatography analysis of immunoreactive LTB4 demonstrated that 84% of immunoreactive LTB4 coeluted with the biologically isomer during the immediate reaction, whereas 44% to 61% coeluted with the biologically active isomer during late reactions. Steroid pretreatment had no effect on either the early or late increase in LTB4 levels or on the neutrophil influx observed during the late reaction.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacological manipulation of inflammation in rabbit hydronephrosis: effects of a combined cyclooxygenase/lipoxygenase inhibitor ethoxyquin, a thromboxane synthase inhibitor RS-5186 and a PAF antagonist L-659,989

The rabbit hydronephrotic kidney (HNK) is a model of renal inflammation characterized by a marked increase in arachidonic acid metabolism that is temporally associated with an inflammatory cell influx into the injured tissue. The HNK exhibits an exaggerated elaboration of eicosanoids ex vivo in response to either bradykinin or the inflammatory cell agonist n-formyl-methionyl-leucyl-phenylalanine (fMLP) compared with the unobstructed contralateral kidney. To pharmacologically manipulate inflammatory cell influx into the HNK we administered ethoxyquin (200 mg/kg p.o.), a combined cyclooxygenase/lipoxygenase inhibitor, RS-5186 (10 mg/kg p.o.), a thromboxane synthase inhibitor or L-659,989 (5 mg/kg p.o.), a platelet activating factor antagonist, before and at various times during the development of hydronephrosis. Only ethoxyquin reduced inflammatory cell influx into the HNK and thereby prevented the enhancement of microsomal cyclooxygenase activity and attenuated the elaboration of eicosanoids ex vivo. Collectively, these results suggest a primary role of an eicosanoid, possibly leukotriene B4, but not thromboxane A2 or the chemotactic phospholipid, platelet activating factor, as a mediator of inflammatory cell influx resulting from ureter obstruction.

Identification of leukotriene B4 as the neutrophil chemotactic factor released by antigen challenge from passively sensitized guinea pig lungs

Neutrophils are prominent in some IgE-mediated allergic reactions and may contribute to the pathophysiology of immediate hypersensitivity. Antigen challenge of fragments of guinea pig lung tissue that were passively sensitized with IgE or IgG antibody evoked the release of neutrophil chemotactic activity (NCA) in parallel with histamine. The NCA released from lung tissue by both IgG- and IgE-dependent stimulation coeluted from a column of Sephacryl S-300 with synthetic leukotriene B4 (LTB4). The NCA in eluates from the Sephacryl S-300 column contained LTB4, as determined by high-performance liquid chromatography and specific radioimmunoassay, in quantities that accounted for the observed chemoattractant activity in the eluates. Furthermore, the NCA of supernatants from antigen-challenged lung fragments was reduced by a mean of 80% after absorption with a monoclonal antibody to LTB4. LTB4 thus constitutes the major functional constituent of NCA released after anaphylactic challenge of IgE- and IgG-sensitized guinea pig lung tissue.

From eosinophil chemotactic factor of anaphylaxis to leukotriene B4--chemistry, biology and functional significance of eosinophil chemotactic leukotrienes in dermatology

The present paper examines evidence for the identity of low molecular weight eosinophil chemotactic factor (ECF) and of leukotriene B4 (LTB4) and its metabolites. Total congruity between the two entities is found regarding (1) cells of origin; (2) conditions for in vitro generation and pharmacological modulation; (3) physiochemical properties; (4) in vitro chemotaxis towards human monocytes, fibroblasts and guinea pig eosinophils; (5) in vivo activities in humans, and (6) occurrence of the factors in various dermatological diseases. Quantitative differences were observed only for in vitro neutrophil migration which may be due to neutrophil chemotactic mono-HETEs and possibly platelet activating factor in the ECF preparations. The name ECF should therefore be replaced by LTB4 and its metabolites, as has happened for SRS which is now called LTC4/D4.

Receptor antagonism of leukotriene B4 myotropic activity by the 2,6 disubstituted pyridine analog U-75302: characterization on lung parenchyma strips

Leukotriene B4 constricts guinea pig lung parenchyma strips in a concentration-dependent manner. The LTB4 structural analog U-75302, 6-(6-[3-hydroxy-1E,5 Z-undecadienyl]-2-pyridinyl)-1,5-hexanediol, was a partial agonist in this system with a potency 300-1000 times less than LTB4. U-75302 constricted lung parenchyma strips only at concentrations greater than 0.3 microM. At concentrations lacking agonist activity U-75302 was an effective antagonist, displacing the LTB4 dose-response curve. Half-maximal responses required 0.10 microM LTB4 in the presence of 0.3 microM U-75302 and 0.01-0.02 microM LTB4 in its absence. The maximal force of contraction was unaffected at this concentration. Concurrent with antagonism of the myotropic response, U-75302 inhibited the LTB4-dependent release of thromboxane B2 from lung parenchyma. This effect was attributable to receptor antagonism, not enzymatic inhibition of phospholipase, cyclooxygenase, or thromboxane synthase. For instance, 0.3 microM U-75302 did not inhibit thromboxane B2 formation by lung parenchyma stimulated with calcium ionophore A23187 and it did not inhibit thromboxane B2 formation by human platelets stimulated with arachidonic acid. U-75302 selectively antagonized the activity of LTB4 and not other myotropic agonists including the thromboxane A2 mimetic U-46619, LTC4, LTD4, AGEPC, PGF2 alpha, and histamine. Receptor antagonists of leukotriene B4 may have multiple beneficial effects on asthmatic or respiratory disorders. These include (i) direct antagonism of LTB4 myotropic actions; (ii) antagonism of LTB4-dependent mediator release; and (iii) antagonism of LTB4 chemotactic action associated with leukocyte infiltration during anaphylactic late phase reactions.

Modulation of plasma exudation by PGE2 and that of leukocyte migration by LTB4 in inflammatory models

Des-Phe8-Arg9-BK could be detected in the entire course of rat carrageenin pleurisy up to 24 h, together with a reduction of the residual levels of high molecular weight kininogen and prekallikrein. On the basis of this continuous release of bradikinin, prostaglandin E2 was released up to 5 h in the pleural exudate and enhanced the plasma leakage. In rat cardiac infarction, the initial increase in the number of polymorphonuclear leukocytes in the cardiac tissue was accompanied by leukotriene B4 in the tissue and this was followed by the second increase and activation of the complement system.

Role of arachidonic acid metabolites in allergen-induced late responses

The sheep model of allergic airway disease shares many pathophysiological similarities with allergic airway disease in humans. Studies performed in this animal model present strong evidence that the release of arachidonic acid metabolites plays an important role in the development of late bronchial responses to antigen challenge. The release of leukotrienes through the lipoxygenase pathway during the acute bronchial obstruction after inhalation of Ascaris suum antigen represents the key factor for the initiation of the subsequent events, namely the late phase response and the bronchial hyperreactivity. If this hypothesis can be substantiated in patients with bronchial asthma then pharmacologic modification of the lipoxygenase pathway and/or products may be important in the treatment of asthma.

Comparative studies of human eosinophil migration towards platelet-activating factor and leukotriene B4

Peripheral-blood polymorphonuclear cells from 36 donors with or without eosinophilia were studied for their in vitro responsiveness towards a wide range of concentrations of leukotriene B4 (LTB4) and platelet-activating factor (PAF). The mean percentage of migrated eosinophils was 17.6 for PAF, 21.1 for LTB4, 20.1 for buffer controls with cells from eosinophil patients, and 1.1 for PAF, 8.9 for LTB4 and 3.2 for buffer control with noneosinophil donors. The quantitative response of eosinophils towards PAF was lower than that towards LTB4 on a molar basis. The data showed high interindividual variations for eosinophil responsiveness towards mediators and buffer and suggest disease-dependent alterations of receptor expression or of basic metabolic activity of eosinophils as possible reasons for this variability.

Leukotrienes and macrophage activation: augmented cytotoxic activity and enhanced interleukin 1, tumor necrosis factor and hydrogen peroxide production

Leukotrienes (LT), and in particular LTB4, are potent inflammatory mediators and immunomodulators. In its interactions with leukocytes, LTB4 can activate numerous functions of neutrophils and modulate the activities of various lymphocyte subsets. LTB4 can also augment macrophage and monocyte cytotoxic activities and enhance their production of hydrogen peroxide and the monokines interleukin 1 and tumor necrosis factor. These observations allow a more detailed understanding of the effects of LTB4 on cellular immune and inflammatory functions.

Leukotriene C4 production from human eosinophils in vitro. Role of eosinophil chemotactic factors on eosinophil activation

We studied the role of naturally occurring eosinophil chemotactic factors on leukotriene (LT)C4 production from highly purified (87.1 +/- 2.4%) normodense eosinophils. Platelet activating factor (PAF) directly induced LTC4 production from eosinophils in a dose (10(-9) to 10(-5) M) and a time-dependent manner. PAF (10(-5) M) induced 0.74 +/- 0.08 ng of LTC4 production/10(6) eosinophils. However, lyso-PAF, eosinophil chemotactic factor of anaphylaxis, and LTB4 failed to induce LTC4 production within the tested range. Furthermore, the pre-incubation of eosinophils with 5 micrograms/ml of cytochalasin B did not alter the chemotactic factor-induced LTC4 production. When eosinophils were stimulated by the submaximal concentration (1 microgram/ml) of calcium ionophore A23187, the pre-incubation of eosinophils with 10(-6) M or 10(-5) M of PAF, or 10(-5) M of eosinophil chemotactic factor of anaphylaxis significantly enhanced LTC4 production up to 163.9 +/- 17.5% (p less than 0.05), 279.2 +/- 32.9% (p less than 0.01) and 165.2 +/- 21.2% (p less than 0.05) of the control, respectively. However, the pre-incubation with lyso-PAF or LTB4 failed to enhance A23187-induced LTC4 production. The pre-incubation of eosinophils with phosphatidyl serine also failed to enhance A23187-induced LTC4 production. However, the direct stimulation of protein kinase C by PMA enhanced the submaximal concentration of A23187-induced LTC4 production from eosinophils up to 179.5 +/- 20.9% (p less than 0.05) of the control. Our findings indicate that PAF and ECF-A work not only as chemotactic factors but also induce a functionally active state of eosinophils probably through their post-receptor mechanisms, and contribute to the inflammatory processes.

Glucocorticoid-induced lymphoma cell growth inhibition: the role of leukotriene B4

Glucocorticoid-sensitive murine S49.1 lymphoma cells respond in a biphasic way to the steroid challenge. The first effect of corticosteroids is to induce a reversible growth inhibition, which is probably permissive for the following cytolysis. Distinct mechanisms for the two effects are likely. Since dilution of S49.1 lymphoma cultures resulted in a drastic reduction of the proliferation rate, which could be overcome by the addition of conditioned medium, the proliferation appears to depend on the presence of autocrine growth factors. Therefore, the cytostatic effect of corticosteroids could possibly be attributable to an interference with the production of endogenous growth factors. Analysis of the growth-promoting activity in culture supernatant showed that the critical growth factor in diluted cultures is an arachidonic acid metabolite, the leukotriene B4. The role of leukotriene B4 in S49.1 cell proliferation received further support from the finding that while nordihydroguaiaretic acid, an inhibitor of the lipoxygenase pathway which is necessary for leukotriene formation blocked lymphoma multiplication, indomethacin, an inhibitor of cyclooxygenase activity, did not affect proliferation. Quantitation of the leukotriene B4 content of dexamethasone-treated vs. untreated cultures revealed an almost complete inhibition of leukotriene production, pointing to the significance of this mechanism for the glucocorticoid-induced lymphoma growth inhibition. Moreover, these findings offer a new approach to increase the therapeutic effectiveness of glucocorticoid therapy of steroid-sensitive leukemias and lymphomas.

Lipoxygenase products in experimental septic arthritis in dogs

Induction of an experimental septic arthritis was performed in the juvenile dog knee by an intra-articular injection with Staphylococcus aureus. From plasma, lipoxygenase (LO) products of arachidonic acid were separated by reversed-phase high-performance liquid chromatography (RP-HPLC) after extraction of lipids. The plasma samples did not contain UV-detectable amounts of LO products other than the LTB4 metabolite 20-COOH-LTB4, and 12-HETE. Small amounts of chemokinetically active material were found coeluting with the eluate fraction of 20-COOH-LTB4, LTB4 and 12-HETE after RP-HPLC. After 48 hours of septic arthritis, resulting in a massive acute joint inflammation, no significant changes in LO products were observed.