Rapid adhesive responses of endothelial cells and of neutrophils induced by leukotriene B4 are mediated by leucocytic adhesion protein CD18

New and promising type of leukotriene B4 (LTB4) antagonists based on the 1,4-benzodioxine structure

New leukotriene B4 (LTB4) antagonists have been synthesized that can be considered as potential anti-inflammatory drugs. Structures containing the dioxygenated nucleus of 1,4-benzodioxine constitute a potential group of leukotriene B4 (LTB4) antagonists. The objective of this study was to access efficient and selective LTB4 antagonists as a way to elucidate the role of LTB4 in inflammatory processes and therefore allow the development of new types of structures based on 1,4-benzodioxine. Forty-one new 1,4-benzodioxine molecules substituted at different positions of the heterocyclic nucleus were synthesized to determine the minimum structural requirements by studying structure-activity relationships. Eighteen of them were tested in vitro and in vivo for their anti-inflammatory activity related to the antagonist character of LTB4. Pharmacological tests have shown satisfactory in vitro activity for compounds 24b, 24c and 24e with IC50's of 288, 439, 477 nM respectively. The results of the in vivo tests, carried out with the compound that presented greater activity in the in vitro tests 24b, have shown significant anti-inflammatory properties.

The Role of Leukotrienes in Controlling Postischemic Skeletal Muscle Function

This study investigates the role of leukotrienes in controlling postischemic alterations in skeletal muscle edema and viability. In a rodent model of six-hour unilateral hindlimb ischemia and four-hour reperfusion, gastrocnemius muscle edema (GME, wet:dry weight ratio) and viability (GMV, nitroblue tetrazolium) were assessed and indices calculated to compare results from the reperfused limb with those from the contralateral normal limb. The influence of leukotrienes B 4 (LTB4) and C4D4E4 (peptidoleukotrienes, PLT) on these changes was assessed by employing specific receptor antagonists (RA) to these mediators, infused intravenously from thirty minutes prior to and throughout reperfusion. Normal (N; ten-hour general anesthesia, no ischemia) and ischemic animals (I; six-hour ischemia only) did not develop either muscle edema or necrosis (GME-N: 1.00 [0.98-1.01], I: 1.01 [0.99-1.03]; GMV-N: 1.00 [1.00-1.00], I: 1.00 [1.00-1.00]) while control animals (C; ischemia and reperfusion alone) demonstrated both (GME: 1.23 [1.09-1.37]; GMV: 0.53 [0.33-0.61]; P<0.01 vs N,I). In rats receiving the LTB4 RA (SC 41930, 1 mg/kg) muscle viability was preserved, GMV: 1.00 (1.00-1.00), P<0.01 vs C and muscle edema reduced (GME: 1.08 [1.05-1.10], P<0.01 vs C). In contrast the PLT RA (ICI 198615, 550 μg/kg) promoted a further deterioration in viability (GMV: 0.29 [0.17-0.33], P<0.05 vs C; P<0.01 vs N,I) with no amelioration of edema (GME: 1.26 [1.20-1.31], ns vs C). These results demonstrate that postischemic skeletal muscle injury is controlled by leukotrienes, with PLT having a beneficial role and LTB4 appearing to enhance reperfusion injury.

Plasma eicosanoid profiles determined by high-performance liquid chromatography coupled with tandem mass spectrometry in stimulated peripheral blood from healthy individuals and sickle cell anemia patients in treatment

Eicosanoids play an important role in homeostasis and in the pathogenesis of various human diseases. Pharmacological agents such as Ca(2+) ionophores and Ca(2+)-ATPase inhibitors, as well as natural agonists such as formylmethionine-leucyl-phenylalanine (fMLP), can stimulate eicosanoid biosynthesis. The aims of this work were to develop a method to determine the eicosanoid profile of human plasma samples after whole blood stimulation and to assess differences between healthy and sick individuals. For this purpose, a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was partially validated for the quantification of 22 eicosanoids using human plasma from healthy volunteers. In addition, we optimized a method for the stimulation of eicosanoids in human whole blood. LC-MS/MS analyses were performed by negative electrospray ionization and multiple reaction monitoring. An assumption of linearity resulted in a regression coefficient ≥0.98 for all eicosanoids tested. The mean intra-assay and inter-assay accuracy and precision values had relative standard deviations and relative errors of ≤15%, except for the lower limit of quantification, where these values were ≤20%. For whole blood stimulation, four stimuli (fMLP, ionomycin, A23187, and thapsigargin) were tested. Results of the statistical analysis showed that A23187 and thapsigargin were potent stimuli for the production or liberation of eicosanoids. We next compared the eicosanoid profiles of stimulated whole blood samples of healthy volunteers to those of patients with sickle cell anemia (SCA) under treatment with hydroxyurea (HU) or after chronic red blood cell (RBC) transfusion. The results indicate that the method was sufficient to find a difference between lipid mediators released in whole blood of SCA patients and those of healthy subjects, mainly for 5-HETE, 12-HETE, LTB4, LTE4, TXB2, and PGE2. In conclusion, our analytical method can detect significant changes in eicosanoid profiles in stimulated whole blood, which will contribute to establishing the eicosanoid profiles associated with different inflammatory and infectious diseases.

Regulatory mechanism of pyrrolidine dithiocarbamate is mediated by nuclear factor-κB and inhibits neutrophil accumulation in ARDS mice

The aim of the present study was to investigate the regulatory mechanism of nuclear factor (NF)-κB on polymorphonuclear neutrophil (PMN) accumulation and the inflammatory response in lung tissues with acute respiratory distress syndrome (ARDS), as well as the therapeutic effect of pyrrolidine dithiocarbamate (PDTC). Mouse models of ARDS were established by intraperitoneal injection of lipopolysaccharide (LPS). BALB/c mice were divided into control, LPS and PDTC + LPS groups. The expression of PMN adhesion molecules, CD11b/CD18 and intercellular adhesion molecule-1 (ICAM-1), were detected by immunohistochemistry, while the protein expression levels of NF-κB p65 in the lung tissue were analyzed by western blot analysis. In addition, flow cytometry was used to investigate the apoptosis rate of PMNs in the bronchoalveolar fluid, and the expression levels of interleukin (IL)-1β, IL-8 and tumor necrosis factor (TNF)-α and myeloperoxidase (MPO) activity were also determined. Following an intraperitoneal injection of LPS, alveolar septum rupture, pulmonary interstitial hyperemia and PMN infiltration in the alveolar was observed. The protein expression of p65 in the pulmonary cytoplasm decreased, while the expression of p65 in the nucleus increased. The levels of IL-8, IL-1β and TNF-α increased and the high expression status was maintained for 24 h. As the time increased, CD11b/CD18 and ICAM-1 expression increased, as well as MPO activity, while the apoptosis of PMNs was delayed. Compared with the LPS group, the expression of p65 in the pulmonary cytoplasm and the PMN apoptosis rate increased following PDTC intervention, while the expression of p65 in the nucleus decreased, as well as the expression levels of the cytokines and MPO activity. Therefore, PDTC reduced the production of inflammatory cytokines via the NF-κB pathway, which reduced the activation of PMNs in the lung tissue and promoted PMN apoptosis.

Therapeutic effects of pyrrolidine dithiocarbamate on acute lung injury in rabbits

BACKGROUND

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) is an early characteristic of multiple organ dysfunction, responsible for high mortality and poor prognosis in patients. The present study aims to evaluate therapeutic effects and mechanisms of pyrrolidine dithiocarbamate (PDTC) on ALI.

METHODS

Alveolar-arterial oxygen difference, lung tissue edema and compromise, NF-κB activation in polymorphonuclear neutrophil (PMN), and systemic levels of tumor necrosis factor-alpha (TNFa) and intercellular adhesion molecule-1 (ICAM-1) in rabbits induced by the intravenous administration of lipopolysaccharide (LPS) and treated with PDTC. Production of TNFa and IL-8, activation of Cathepsin G, and PMNs adhesion were also measured.

RESULTS

The intravenous administration of PDTC had partial therapeutic effects on endotoxemia-induced lung tissue edema and damage, neutrophil influx to the lung, alveolar-capillary barrier dysfunction, and high systemic levels of TNFa and ICAM-1 as well as over-activation of NF-κB. PDTC could directly and partially inhibit LPS-induced TNFa hyper-production and over-activities of Cathepsin G. Such inhibitory effects of PDTC were related to the various stimuli and enhanced through combination with PI3K inhibitor.

CONCLUSION

NF-κB signal pathway could be one of targeting molecules and the combination with other signal pathway inhibitors may be an alternative of therapeutic strategies for ALI/ARDS.

Sickle acute lung injury: role of prevention and early aggressive intervention strategies on outcome

Acute chest syndrome in sickle cell disease is a form of acute lung injury that may progress to acute respiratory distress syndrome and death. Despite recent advances in diagnosis and treatment that have resulted in improved survival in sickle cell disease, acute chest syndrome remains the most common cause of death in this population. The current standards of treatment for acute chest syndrome have been reviewed. Biomedical re-search forms the basis for sound clinical decision making and implementation of interventions that target prevention, diagnosis, and effective treatment options. Although current clinical trials are ongoing to address several new potential therapeutic options,more research using preventative and interventional strategies in sickle acute lung injury is warranted.

Melatonin effect on endothelial cells reduces vascular permeability increase induced by leukotriene B4

The aim of this study was to investigate the effect of melatonin on the inflammatory increase in vascular permeability. Vascular permeability was stimulated by a nonspecific pro-inflammatory agent (carrageenan), by drugs that disrupt endothelial cells junction (histamine, serotonin or bradykinin) or drugs that promote neutrophil recruitment (leukotriene B4 or N-formyl-methionyl-leucyl-phenylalanine fMLP). Vascular permeability was measured by Evan's blue dye extravasation after simultaneous injection of melatonin and the pro-inflammatory drugs in rat dorsal skin. Melatonin only reduced the increase in vascular permeability induced by leukotriene B4, which activates both neutrophil and endothelial cells. The neutrophil expression of CD18 induced by leukotriene B4 or fMLP was not changed by melatonin. On the other hand, melatonin inhibited the leukotriene B4-induced endothelial cells hyperadhesiveness. Our findings suggest that vascular permeability reduction induced by local melatonin injection is mediated by a reduction of endothelial cells ability to interact with neutrophils.

Characterization of certain inflammatory variables in the peripheral blood of clinically healthy dogs

Many laboratory techniques have been developed to study and quantify the inflammatory response, including the release of acid hydrolase enzymes, leukotriene B(4) (LTB(4)) production, reactive oxygen species (ROS) production and complement conversion studies. Although extensively studied in human health and disease, the relevance of such tests in the dog is largely unknown. After isolation of the peripheral blood mononuclear cell (PBMC) and polymorphonuclear cell (PMN) fractions from the peripheral blood of 38 clinically healthy dogs, values for ROS production were similar for both cell fractions when measured by luminol-enhanced chemiluminescence (17,853+/-9,695 U/10(6) cells versus 19,138+/-14,569 U/10(6) cells for the PBMC (n=38) and PMN (n=18) fractions, respectively). However, the mean time taken to reach maximum chemiluminescence was noticeably shorter in the PBMC fraction (5.1+/-3.3 versus 10.7+/-2.5 min for PBMCs (n=36) and PMNs (n=18), respectively). Intracellular concentrations of beta-glucuronidase, beta-galactosidase and N-acetyl-beta-glucosaminidase were assayed by spectrofluorometry. Mean values for all three enzymes were higher in PBMCs (n=31-35) than in PMNs (n=10-14). Both cell fractions released 20% of the intracellular enzyme concentration when stimulated with opsonized zymosan. Following incubation with A23187 (1 microM), mean LTB(4) production was higher in PBMCs (4.45+/-2.92 ng/10(6) cells; n=27) than in PMNs (0.96+/-2.22 ng/10(6) cells; n=13) using a validated high performance liquid chromatography (HPLC) assay. Immunoprecipitation studies revealed that the mean percentage conversion of C3 to C3b following stimulation with opsonized zymosan was 57.3+/-13.4% (n=36). The results provide normal values for clinically healthy dogs that may subsequently be used in future studies investigating dogs with various inflammatory disorders.

Microvascular in vivo assessment of reperfusion injury: significance of prostaglandin E1 and I2 in postischemic “no-reflow” and “reflow-paradox”

BACKGROUND

Microvascular ischemia-reperfusion (I/R) injury is characterized by failure of capillary perfusion ("no-reflow") and reoxygenation-associated phenomena ("reflow-paradox"), including activation of leukocyte-endothelium interaction with cytotoxic mediator-induced loss of endothelial integrity. The objectives of this study were to elucidate the impact of both prostaglandins E(1) (PGE(1)) and I(2) (PGI(2)) in microvascular reperfusion injury, with special focus on the distinct pathophysiology of no-reflow- and reflow-paradox phenomena.

MATERIALS AND METHODS

By use of the hamster dorsal skinfold preparation and in vivo fluorescence microscopy, the microcirculation of a striated skin muscle was assessed before 4 h of pressure-induced ischemia and 0.5, 2, and 24 h after onset of reperfusion.

RESULTS

I/R was characterized by enhanced leukocyte-endothelium interaction in postcapillary venules, increase of macromolecular leakage, and reduction of functional capillary perfusion (P < 0.05). Intravenous 2-h infusion of PGE(1), starting with onset of reperfusion, reduced leukocyte adhesion and macromolecular leakage in postcapillary venules during early reperfusion (P < 0.05), while 6-h infusion, given during ischemia and early reperfusion, showed no significant effects. PGI(2) infusion also attenuated postischemic leukocyte adhesion, which was significant by a 6-h prolonged administration (P < 0.05), but did not influence the increase of microvascular permeability. Both prostaglandins were unable to prevent the postischemic failure of capillary perfusion (no-reflow).

CONCLUSIONS

Both prostaglandins did not significantly influence postischemic no-reflow phenomena, but appeared as potent inhibitors of reflow-paradox under the experimental circumstances of this study.

Activated polymorphonuclear cells increase sickle red blood cell retention in lung: role of phospholipids

This study investigates the role of the activated polymorphonuclear cell (APMN) products on sickle red blood cell (SRBC) retention/adherence in the pulmonary circulation. Isolated rat lungs were perfused with (51)Cr-labeled normal RBCs (NRBC) or SRBCs (10% hematocrit) suspensions +/- PMNs. Specific activities of lung and perfusate were measured and retention (the number of SRBC/g lung) was calculated. SRBC retention was 3.5 times greater than NRBC retention. PMN activation was required to increase SRBC retention. Supernatants from APMN increased SRBC retention, which suggested soluble products such as oxidants, PAF, and/or leukotriene (LTB(4)) are involved. Heat inactivation of PMN NADPH oxidase had no effect on retention. Whereas neither platelet-activating factor (PAF) nor LTB(4) (secreted by APMN) increased SRBC retention, PAF+LTB(4) did. The PAF antagonist, WEB-2170, attenuated SRBC retention mediated by PAF+LTB(4) and APMNs. Similarly, zileuton (5-lipoxygenase inhibitor) attenuated APMN-mediated SRBC retention. We conclude the concomitant release of PAF and LTB(4) from APMN is involved in the initiation of microvascular occlusion by SRBCs in the perfused rat lung.

Human umbilical vein endothelial cells generate leukotriene C4 via microsomal glutathione S-transferase type 2 and express the CysLT(1) receptor

Certain immunocompetent myeloid cells, such as eosinophils, basophils and mast cells, have a large capacity to synthesize the potent proinflammatory and spasmogenic mediator leukotriene (LT) C4 via a specific microsomal glutathione S-transferase (MGST) termed LTC4 synthase (LTC4S). Here, we report that MGST2, a distant homologue of LTC4S, is abundantly expressed in Human umbilical vein endothelial cells (HUVEC) and converts LTA4 into a single product, LTC4. Thus, using Northern blot, RT-PCR, Western blot, and enzyme activity assays, we show that MGST2 is the main, if not the only, enzyme that converts LTA4 into LTC4 in membrane preparations of HUVEC. In fact, we failed to detect any expression of LTC4S, MGST1 or MGST3 in these cells, indicating that MGST2 is a critical enzyme for transcellular LTC4 biosynthesis in the vascular wall. Unlike LTC4S, MGST2 prefers the naturally occurring free acid of LTA4 over the methyl ester as substrate and is also susceptible to product inhibition with an IC50 of about 1 microM for LTC4. Moreover, HUVEC were found to express the CysLT1 receptor in line with a paracrine and autocrine role for cysteinyl-leukotrienes in endothelial cell function.

Taurine attenuates LPS-induced rolling and adhesion in rat microcirculation

BACKGROUND

Adhesion of polymorphonuclear leukocytes (PMN) to endothelial cells and subsequent transendothelial migration are an early key events in the inflammatory response and play an important part in the pathogenesis of septic shock, contributing to vascular and tissue injury. Taurine (2-aminoethanesulfonic acid) is a sulphur-containing beta amino acid. It is a known antioxidant, possesses antimicrobial properties, and has previously been shown to be protective to the endothelium both in vivo and in vitro. The aim of this study was to determine if pretreatment with taurinewould attenuate the lipopolysaccharide (LPS)-induced increase in leukocyte-endothelial interactions and microvascular permeability during endotoxemia.

MATERIALS AND METHODS

Male Sprague-Dawley rats (300-350 g) were randomized into three groups: (1) Control, (2) LPS, and (3) LPS + Taurine groups. Taurine was administered orally as a 4% solution. Endotoxemia was induced using Escherichia Coli endotoxin (Serotype 0.55 B5)-15 mg/kg via a slow intravenous infusion. Using mesenteric postcapillary venules (28-32-microm diameter) the number of adherent and migrated leukocytes and their rolling velocity were measured by intravital microscopy at baseline and subsequently at 10, 30, 60, and 90 min post administration of LPS.

RESULTS

Following administration of LPS there was a reduction in leukocyte rolling velocity at 30, 60 and 90 min. This was accompanied by a significant increase in the number of adherent leukocytes at 10, 30, 60 and 90 min. Transendothelial migration was significantly increased at 90 min. Taurine significantly attenuated the LPS-induced reduction in leukocyte rolling velocity at 10 and 30 min and the number of adherent leukocytes at all time points. Taurine also attenuated the LPS-induced increase in transendothelial migration at 90 min.

CONCLUSIONS

These results demonstrate that taurine ameliorates endotoxin-induced leukocyte-endothelial cell interactions associated with sepsis, thereby suggesting that taurine may have a therapeutic role in the preventionof endothelial damage in sepsis.

VML 295 (LY-293111), a novel LTB4 antagonist, is not effective in the prevention of relapse in psoriasis

Leukotriene B4 (LTB4) receptor antagonists have been the subject of several studies in the treatment of inflammatory diseases, including psoriasis. A novel oral LTB4 antagonist, VML 295 (LY-293111) has recently been developed and has a pronounced effect on epidermal inflammatory parameters. However, oral treatment of psoriasis for 4 weeks did not result in a decrease in disease severity. The present study was performed in order to investigate whether prolonged treatment with VML 295 up to 8 weeks has a beneficial effect on the overall severity of psoriasis. Moreover, we studied to what extent VML 295 is able to prevent relapse in psoriasis. In the present study, 35 patients with stable chronic plaque psoriasis were included. A representative plaque of at least 16 cm2 was initially treated with clobetasol-17-propionate lotion under hydrocolloid occlusion in all patients. Clearance was achieved within 6 weeks in 31 patients. After clearance, the patients were randomized to treatment and received oral VML 295 capsules 200 mg twice daily or placebo for 8 weeks. Twenty-five patients completed the study. The psoriasis area and severity index (PASI) was assessed before treatment, at clearance, and on days 15, 29, 43 and 5 7 of the treatment period. Biopsies were taken from the treated lesion before treatment, after clearance and at relapse, and cells were analysed by flow cytometry with markers for differentiation (keratin 10), inflammation (vimentin), and proliferation (DNA content). After 8 weeks of treatment, 14 of 15 VML 295-treated patients had relapsed and 11 of 16 placebo-treated patients had relapsed. A total of six patients were withdrawn. The time to relapse and the number of relapsed patients was not significantly different comparing the treatment groups. There was no significant difference in PASI scores between VML 295-treated patients and placebo-treated patients after 8 weeks of treatment. Flow cytometric parameters for differentiation, inflammation and proliferation did not show significant differences between VML 295- and placebo-treated patients. We conclude that oral VML 295 (LY-293111) is not effective in preventing relapse in psoriasis, either clinically or at the cellular level, and that in our group of patients VML 295 had no beneficial effect on overall psoriasis severity. Moreover, we conclude that further development of LTB4 modulating drugs for the treatment of psoriasis is not indicated.

Elevated cytosolic phospholipase A2 expression and activity in human neutrophils during sepsis

Sepsis is defined as the systemic inflammatory response to infection. Phospholipase A2 (PLA2) plays an important role in inflammation processes by initiating the production of inflammatory mediators. The role of cytosolic PLA (cPLA2) has not yet been identified in inflammatory and infectious disease clinical settings. The aim of the present research was to determine whether cPLA2 activity has a role during sepsis. Since neutrophil activation has been documented during sepsis, these cells were chosen as a model to evaluate the function of cPLA2 in this clinical setting. cPLA2 was studied at 3 levels: activity, protein expression, and messenger RNA (mRNA). Neutrophils from 32 septic patients with and without bacteremia were examined. cPLA2 activity was measured using labeled phosphatidyl choline vesicles as a substrate, and total PLA2 was determined by the release of labeled arachidonic acid from prelabeled cells. A significant increase in cPLA2activity, protein expression, and total PLA2 activity in neutrophils was detected during sepsis. mRNA levels, detected by reverse transcriptase–polymerase chain reaction, were significantly higher during sepsis, indicating that the increase in the amount of cPLA2 is regulated on the mRNA level. The significant elevation of cPLA2 activity and expression in neutrophils during sepsis suggests that this enzyme plays a major role in neutrophil function in this clinical setting.

The reported clinical utility of taurine in ischemic disorders may reflect a down-regulation of neutrophil activation and adhesion

The first publications regarding clinical use of taurine were Italian reports claiming therapeutic efficacy in angina, intermittent claudication and symptomatic cerebral arteriosclerosis. A down-regulation of neutrophil activation and endothelial adhesion might plausibly account for these observations. Endothelial platelet-activating factor (PAF) is a crucial stimulus to neutrophil adhesion and activation, whereas endothelial nitric oxide (NO) suppresses PAF production and acts in various other ways to antagonize binding and activation of neutrophils. Hypochlorous acid (HOCl), a neutrophil product which avidly oxidizes many sulfhydryl-dependent proteins, can be expected to inhibit NO synthase while up-regulating PAF generation; thus, a vicious circle can be postulated whereby HOCl released by marginating neutrophils acts on capillary or venular endothelium to promote further neutrophil adhesion and activation. Taurine is the natural detoxicant of HOCl, and thus has the potential to intervene in this vicious circle, promoting a less adhesive endothelium and restraining excessive neutrophil activation. Agents which inhibit the action of PAF on neutrophils, such as ginkgolides and pentoxifylline, have documented utility in ischemic disorders and presumably would complement the efficacy of taurine in this regard. Fish oil, which inhibits endothelial expression of various adhesion factors and probably PAF as well, and which suppresses neutrophil leukotriene production, may likewise be useful in ischemia. These agents may additionally constitute a non-toxic strategy for treating inflammatory disorders in which activated neutrophils play a prominent pathogenic role. Double-blind studies to confirm the efficacy of taurine in symptomatic chronic ischemia are needed.

Effects of antirheumatic drugs on adhesiveness of endothelial cells and neutrophils

Because disease-modifying antirheumatic drugs might exert part of their effects on adhesion of polymorphonuclear neutrophils (PMN) to endothelial cells, this being the first step for PMN migration to inflammatory lesions, we evaluated such drug effects in vitro. Gold sodium thiomalate (GSTM) impaired the ability of interleukin 1beta (IL-1beta)-stimulated human umbilical vein endothelial cells (HUVEC) to express E-selectin and to bind PMN but had no effect on the expression of intercellular adhesion molecule 1 (ICAM-1) or on hyperadhesivity of N-formyl-methionyl-leucyl-phenylalanine (fMLP)-stimulated PMN. Auranofin (AF) interacted with HUVEC and PMN adhesiveness but in opposite directions: this drug hampered IL-1beta-induced HUVEC hyperadhesiveness and expression of E-selectin and intercellular adhesion molecule 1, but augmented PMN adherence and CD18 expression. The net effect of auranofin was a reduction of cytokine-driven adhesiveness and enhancement of formylpeptide-induced adhesion. Salazopyrin did not affect HUVEC or PMN adhesiveness or E-selectin and intercellular adhesion molecule 1 expression. Thus, the gold-containing drugs modulated HUVEC and PMN adhesiveness by different mechanisms but ones involving surface adhesion molecules.

Investigation on a novel and specific leukotriene B4 receptor antagonist in the treatment of stable plaque psoriasis

The aim of the present study was to investigate the efficacy and clinical tolerability of the specific leukotriene B4 receptor antagonist VML295 in the treatment of stable plaque psoriasis. Immunohistochemical and flow cytometrical methods were used to assess the effects on inflammation and epidermal proliferation. VML295 in the treatment of chronic plaque psoriasis was shown to be safe and well tolerated. After treatment, there was a statistically significant difference between patients treated with VML295 and patients treated with placebo with respect to the leukotriene B4-induced CD11b up-regulation on the cell surface of polymorphonuclear leukocytes derived from peripheral blood. Ex vivo CD11b up-regulation in the VML295-treated group was completely inhibited after 7 days of treatment (P = 0.001). This effect persisted until the end of the treatment period (P = 0.004 on day 15 and P < 0.0001 after 4 weeks), whereas CD11b up-regulation in the placebo group remained unaffected. There was no statistically significant difference in the median psoriasis area and severity index between the treatment groups at the end of the treatment period. During treatment, no significant histological changes were observed in the markers for cutaneous inflammation and epidermal proliferation. Although not statistically significant, a tendency for the increased expression of some markers of cutaneous inflammation and epidermal proliferation was observed after 1 week of treatment with VML295, and a decreased expression of these markers was seen after 4 weeks of treatment with VML295. This observation could indicate anti-inflammatory effects of VML295 appearing between 2 and 4 weeks after the start of treatment.

The peroxisome proliferator-activated receptor alpha (PPARalpha) ligand WY 14,643 does not interfere with leukotriene B4 induced adhesion of neutrophils to endothelial cells

Peroxisome proliferator-activated receptors (PPAR) control discrete genes involved in fatty acid and lipid metabolism. Recently, it was suggested that activation of the alpha isoform of PPAR by the potent proinflammatory mediator leukotriene B4 (LTB4) enhanced degradation of this eicosanoid, offersuggesting a new aspect of down-regulation of inflammation. Here, we studied whether PPARalpha activation (by means of the selective agonist WY 14,643) of endothelial cells, pivotal in the regulation of inflammatory responses, interfered with LTB4 induced adhesion of PMN neutrophil granulocytes in vitro. When endothelial cells were treated with WY 14,643 prior to activation with LTB4 (or fMLP, IL-1beta or TNFalpha, as controls) we could not document any effect on the number of adhering PMN or duration of the response. Thus, this study provides no evidence indicating a regulatory function of PPARalpha in LTB4 induced adhesive interactions between endothelial cells and neutrophils.

The CD11b/CD18-integrin in the pathogenesis of psoriasis

The aim of the present investigation was to study the distribution of CD11b, CD18, and ICAM-1 over the various cell populations present in the margin zone of the actively spreading psoriatic lesion and distant uninvolved psoriatic skin. This study was performed in order to obtain more insight in the relevance of these receptor molecules in the early phase of psoriatic plaque development. Skin biopsies were taken and inflammation markers were assessed using immunohistochemical techniques. All dermal changes in the margin zone preceded those in the epidermis. In the margin zone the most peripheral change was a decrease in dermal ICAM-1-expression, followed by an increase in dermal CD11b-expression. CD11b-positive cells showed a different tissue distribution from polymorphonuclear leukocytes and were more abundantly present, suggesting significant amounts of CD11b-bearing cell populations other than polymorphonuclear leukocytes in the early phase of psoriasis. Decreased numbers of CD18-positive cells in distant uninvolved skin suggest the existence of a selective modulating mechanism altering the trafficking of myeloid subpopulations. Polymorphonuclear leukocytes appeared to invade the skin well after the appearance of CD11b- and CD18-positive cells.

The role of selectins and CD18 in leukotriene B4-mediated white blood cell emigration in human skin grafts transplanted on SCID mice

The purpose of this study was to examine the role of selectins and CD18 cell adhesion molecules (CAMs) in inflammation induced by injection of leukotriene B4 (LTB4) into human skin. To accomplish this, the expression of CAMs and the ability of specific antibodies against CAMs to block white blood cell (WBC) transmigration were studied in an in vivo model consisting of human skin transplanted onto mice with the severe combined immune deficiency (SCID) mutation. The results indicate that LTB4-induced WBC transmigration in the human/SCID model is rapid and pronounced; however, it is not accompanied by a significant upregulation of the baseline expression of endothelial P-selectin, E-selectin, ICAM-1 or VCAM-1. An anti-murine CD18 mAb markedly inhibited white cell infiltration (89% inhibition) confirming the importance of beta 2 integrins in the process. The role of selectins was also examined. MEL-14, a bioactive antibody against murine L-selectin inhibited transmigration by 66%. A significant, but smaller, effect (39% inhibition) was observed by blocking E-selectin function. These results indicate that LTB4-induced inflammation does not require upregulation of endothelial CAM expression and, in contrast to TNF alpha-induced transmigration, is only partially blocked by anti-E-selectin antibodies.

Effects of leukotriene C4 and D4, histamine and bradykinin on cytosolic calcium concentrations and adhesiveness of endothelial cells and neutrophils

We compared the effects of leukotrienes B4, C4 and D4 (LTB4, C4 and D4) in vitro, as well as of histamine and bradykinin, on adhesive interactions between cultured umbilical vein endothelial cells (HUVEC) and polymorphonuclear neutrophils (PMN) and on cytosolic calcium transients, [Ca(2+)](i), in vitro. LTB4, but not LTC4 or LTD4 (at 1-100 nM), increased HUVEC adhesiveness for PMN, maximally 2.8 fold; in addition, PMN adhesion was augmented by LTB4 (but not by LTC4 and LTD4) to a plastic surface. Rapid, but smaller increments of HUVEC (but not of PMN) adhesiveness were induced by histamine and bradykinin (at 10 microM). Nonetheless, LTC4 and LTD4 (at 100 nm) induced rapid rises of [Ca(2+)](i) in HUVEC, whereas approximately 100-fold higher concentrations were needed of histamine and bradykinin for similar rises. In PMN LTD4 (and LTB4) induced rapid increases of [Ca(2+)](i), whereas no significant effect was seen with LTC4, histamine or bradykinin. The [Ca(2+)](i) responses to LTC4 and LTD4 were inhibited by the peptidoleukotriene receptor blocker SKF 104,353. Thus, LTB4 and the peptidoleukotrienes display disparate profiles as inducers of adhesion and calcium transients in PMN and HUVEC, indicating discrete differences in the stimulus response coupling for these closely related leukotrienes.

Tepoxalin blocks neutrophil migration into cutaneous inflammatory sites by inhibiting Mac-1 and E-selectin expression

Inflammation is characterized by the migration of polymorphonuclear leukocytes from the vasculature into the tissue causing profound injury. Adhesion and migration of neutrophils across the vascular bed are governed by a series of complex events including cytokine/chemokine production which in turn orchestrates the temporal expression of a cohort of adhesion molecules mediating the migration. Many of these adhesion molecules and their inducers are under the control of inflammatory response transcriptional factors such as NF kappa B and AP-1. Recently we showed tepoxalin, previously known as a dual cyclooxygenase/lipoxygenase (CO/LO) inhibitor, to be a potent inhibitor of NF kappa B-induced transcription in vitro. In this study, we demonstrated that when administered in vivo, tepoxalin but not naproxen (a nonsteroidal anti-inflammatory drug, NSAID) or zileuton (an LO inhibitor), effectively inhibits neutrophil migration into inflammatory sites in murine skin stimulated by either lipopolysaccharide (LPS) or tumor necrosis factor-alpha. Immunohistochemical analysis indicates that 10-50 mg/kg of tepoxalin inhibits neutrophil migration. It also effectively blocks the upregulation of Mac-1 (CD11b/CD18) on neutrophils. Quantitative polymerase chain reaction Mac-1 analysis shows that LPS-induced transcription of E-selectin mRNA was dramatically suppressed by both 25 and 50 mg/kg of tepoxalin, whereas the level of ICAM-1 was only affected by 50 mg/kg of tepoxalin. Since it has been documented that the expression of E-selectin and Mac-1 is regulated either directly or indirectly by the transcription factor NF kappa B, our studies provide in vivo evidence that tepoxalin is a potent inhibitor of NF kappa B-mediated events in animal models and this novel molecular mechanism clearly defines it as a new class of anti-inflammatory compounds.

Development and characterization of essential fatty acid deficiency in human endothelial cells in culture

We induced an essential fatty acid deficiency (EFAD) in human umbilical vein endothelial cells by culture in medium with 20% (vol/vol) delipidated fetal calf serum. EFAD, reflected by decreased cellular linoleic acid (18:2 omega 6) and arachidonic acid (20:4 omega 6) and emergence of the oleic acid derivative 5,8,11-eicosatrienoic acid (20:3 omega 9; Mead's acid), was evident after 1 week of culture and became pronounced after 2 weeks. Beyond that time point, control cells (cultured in 20% normal fetal calf serum) grew deficient of 18:2 omega 6, and EFAD cells died. 18:2 omega 6 addition to EFAD cells resulted in dose-dependent increases of 18:2 omega 6 and 20:4 omega 6. 20:4 omega 6 or 5,8,11,14,17-eicosapentaenoic acid (20:5 omega 3) additions resulted in normalization of these acids, and conversion of 20:5 omega 3 to 4,7,10,13,16,19-docosahexaenoic acid (22:6 omega 3) was noted. Agonist-induced increases in concentrations of prostacycline (prostaglandin I2; PGI2) and cytosolic Ca2+, [Ca2+]i, were reduced in EFAD cells and not restored by 18:2 omega 6 or 20:4 omega 6 additions. Change of the medium in EFAD cultures 1 day before the experiments decreased 20:3 omega 9 and normalized the PGI2 production and [Ca2+]i changes, whereas addition of 20:3 omega 9 to control cells impaired the [Ca2+]i response, indicating a suppressive effect of 20:3 omega 9. Thus, EFAD in endothelial cells is associated with abnormalities of eicosanoid and second-messenger production partly attributable to 20:3 omega 9 accumulation. Moreover, the gradual emergence of 18:2 omega 6 deficiency in regularly grown control cells underlines the need for careful analysis of fatty acids in long-term cell cultures.

Cortical hypoperfusion after global forebrain ischemia in rats is not caused by microvascular leukocyte plugging

BACKGROUND AND PURPOSE

We tested the hypothesis that cerebral hypoperfusion after experimental global cerebral ischemia is caused by plugging of the microcirculation with activated leukocytes using in vivo microscopic observation of the behavior of leukocytes in the cortical microcirculation during the transition from postischemic hyperperfusion to hypoperfusion.

METHODS

Anesthetized and ventilated rats (n = 24) were equipped with a closed cranial window. Physiological variables and cortical regional cerebral blood flow (laser-Doppler flowmetry) were measured continuously. Leukocytes were labeled intravitally with rhodamine 6G and visualized in the microcirculation of the brain surface and outer layers of the cortex with confocal laser scanning microscopy from preischemia to 4 hours after reperfusion that followed 10 minutes of global cerebral ischemia (rCBF < 10% of control).

RESULTS

In controls (n = 8), there were no signs of leukocyte activation over the 4-hour observation period. In ischemic rats (n = 16), during the transition from hyperperfusion to hypoperfusion there was no change in the behavior of leukocytes. Most notably, no capillary pluggers were seen. In the postischemic period only a slight increase of the number of leukocytes rolling along or sticking to the venular endothelium was seen, and very few capillaries were plugged by leukocytes. Extravasation of leukocytes into the brain tissue was observed in 8 rats beginning 2 hours after ischemia with a variable degree between animals.

CONCLUSIONS

Because there was only mild activation of leukocyte-endothelium interaction within the first hours of reperfusion after 10 minutes of global forebrain ischemia, because no leukocytes plugged superficial cortical capillaries during the transition from hyperperfusion to hypoperfusion, and because the regional cerebral blood flow transition was very rapid, we speculate that leukocyte plugging is not responsible for the early cortical hypoperfusion seen after brief global ischemia in rats.

Lipoxin A4 induces neutrophil-dependent cytotoxicity for human endothelial cells

The authors have assessed the capacity of neutrophil granulocytes (PMN) to kill cultured human umbilical-vein endothelial cells (HUVEC) in vitro (as release of 51Cr) in response to the recently described double dioxygenation product of arachidonic acid, lipoxin A4 (LXA4). LXA4 conferred a marked cytotoxicity, whereas formyl-methionyl-leucyl-phenylalanine (fMLP) was less potent. The LXA4 and fMLP effects were dose dependent, with a maximum at 100 nM (which caused 2.7- and 2.3-fold increases of 51Cr release, respectively, relative to buffer-treated controls). The LXA4 and fMLP responses increased with the PMN concentration, depended on the fetal calf serum concentration, incubation temperature and duration and the presence of calcium and magnesium ions.

Remodeling of neutrophil phospholipids with 15(S)-hydroxyeicosatetraenoic acid inhibits leukotriene B4-induced neutrophil migration across endothelium

5-Lipoxygenase products, such as leukotrienes, are important stimuli for leukocyte-mediated tissue injury in acute inflammation. 15-Hydroxyeicosatetraenoic acid (15-HETE) is an eicosanoid generated by a variety of cell types via the actions of 15-lipoxygenases and, in addition, cyclooxygenases and epoxygenases. 15-HETE levels are frequently elevated at sites of inflammation, and extracellular 15(S)-HETE is esterified rapidly into neutrophil (PMN) phospholipids in vitro to levels that are comparable with arachidonic acid. We present evidence that remodeling of PMN phospholipids with 15(S)-HETE stereoselectively inhibits PMN migration across endothelium in response to leukotriene B4 (LTB4) and other chemoattractants. Esterified 15(S)-HETE causes a striking reduction in the affinity of LTB4 cell-surface receptors for their ligand and inhibition of LTB4-triggered stimulus-response coupling. As a result of these actions, esterified 15(S)-HETE attenuates the cytoskeletal rearrangements and CD11/CD18-mediated adhesive events that subserve directed locomotion of PMN across endothelium. These observations indicate that products of the 5-lipoxygenase and 15-lipoxygenase pathways can exert counterbalancing influences on PMN trafficking across endothelium. They suggest that 15(S)-HETE may be a potent endogenous inhibitor of PMN-endothelial interactions in vivo and serve to limit or reverse acute inflammation.

Leukocyte/endothelial interactions and blood-brain barrier permeability in rats during cerebral superfusion with LTB4

The experimental study analyses the vasomotor response (change of diameter of pial arterioles and venules), and blood-brain barrier function of the pia-arachnoidea at the rat brain surface before, during and after cerebral superfusion with 1.5 or 15.0 nM LTB4 in mock CSF. Leukocyte dynamics were studied by assessment of their centerline velocity, of rolling along ("roller") and attachment to ("sticker") the venular wall of white blood cells intravitally stained by Rhodamin 6G. Superfusion of the brain with LTB4 at both dose levels led to dilation of arterioles to 130% (p < 0.001), while of venules to 117% (p < 0.001) of control. The centerline velocity of leukocytes increased from 0.7 to 0.9 mm/s, however, only after superfusion with LTB4 at the high dose level. LTB4 induced a dose-dependent rolling (p < 0.01) and sticking of leukocytes (p < 0.001). Yet, a delay of about 60 min between cerebral administration of LTB4 and the maximal response of leukocyte rolling and sticking was observed. Whereas the blood-brain barrier was not opened by cerebral superfusion with 1.5 or 15.0 nM LTB4, for i.v. Na(+)-fluorescein, barrier leakage was promptly induced by 30.0 nM. The present findings demonstrate that cerebral administration of LTB4 by superfusion of the exposed brain surface is eliciting a pronounced vasomotor response, whereas the induction of leukocyte/endothelial interactions is less impressive.

Ischemia reperfusion injury: a review

Ischemia reperfusion injury is reviewed in the context of the evolution of flap research over the past decade. A description of the clinical relevance of this field is presented and the possible etiologies are reviewed. The pathophysiology of this injury is then explored in some detail. Both skin and myocutaneous flaps, in a variety of animal models, are discussed. Research performed in vitro, as well as in other organ systems similarly affected by ischemia and reperfusion, is also examined. Particular attention is placed on the function of several newly described inflammatory mediators where it appears relevant to future research and treatment in the field of reconstructive microsurgery.

Leukotriene B4-induced hyperadhesiveness of endothelial cells for neutrophils: relation to CD54

Leukotriene B4 (LTB4) induced an in vitro transient state of hyperadhesiveness in cultured human umbilical vein endothelial cells (HUVEC), leading to a 2.2-fold increase in the binding of neutrophil granulocytes (PMN), which was less than that conferred by platelet activating factor (PAF) though more than thrombin did (3.4- or 2.0-fold increases, respectively). This study concerns the role of the adhesive molecules CD18 and CD54 for the LTB4- (as well as thrombin- and PAF-) induced endothelial hyperadhesiveness. The MoAbs 60.3 (to the CD18 molecule on PMN) and 84H10 (to one epitope of CD54 on the HUVEC) blocked the adherence of PMN to LTB4-treated HUVEC, whereas MoAb LB-2 (directed at another CD54 epitope) failed to do so. MoAb 84H10 blocked 43% of the thrombin-induced hyperadhesiveness, whereas the PAF response was unaffected. Thus, LTB4-induced HUVEC hyperadhesiveness may therefore be related to a specific domain on the CD54 (or on an antigenically related molecule) as well as being dependent on CD18, whereas the involvement of CD54 was much less or non-existent for the thrombin and PAF responses, respectively.

Role of oxygen radicals in the microcirculatory manifestations of postischemic injury

Reperfusion after transient tissue ischemia constitutes an irrevocable need to preserve tissue viability. However, release of prolonged ischemia will either result in failure of the microcirculation to reperfusion (no-reflow) and thus the prolongation of hypoxia, or in restoration of blood flow resulting in reoxygenation of the inflicted tissue. While ischemia damages the tissue primarily through hypoxia-induced depletion of energy stores, reoxygenation paradoxically contributes to tissue damage through the formation of oxygen radicals, the release of chemoattractant mediators (TNF, IL-1, LTB4), and the activation of circulating polymorphonuclear leukocytes (PMNs). Through the action of chemoattractant mediators and the upregulation of leukocytic (CD11/CD18) and endothelial adhesion receptors (ICAM, GMP-140), activated PMNs adhere to the endothelium, release further chemoattractants and oxygen radicals and undertain a vicious circle, which will ultimately result in further tissue damage. Both the no-reflow phenomenon and the events initiated by reflow--termed herein as the reflow-paradox--contribute to the failure of the nutritive microvascular perfusion and loss of tissue viability following ischemia and reperfusion.

Dietary fish oil reduces leukocyte/endothelium interaction following systemic administration of oxidatively modified low density lipoprotein

BACKGROUND

In vitro and in vivo experiments have demonstrated the role of oxidatively modified low density lipoprotein (oxLDL) in eliciting leukocyte/endothelium interaction during early atherogenesis.

METHODS AND RESULTS

In the present study we investigated the effect of dietary fish oil on oxLDL-induced leukocyte/endothelium interaction using intravital fluorescence microscopy in the dorsal skinfold chamber model in awake Syrian golden hamsters. Hamsters were fed for 4 weeks prior to the experiments with either standard laboratory chow or a diet supplemented with 5% of a fish oil concentrate (18% eicosapentaenoate, 12% docosahexaenoate). The efficacy of the fish oil diet was demonstrated by the incorporation of fish oil-derived omega-3 fatty acids into plasma, leukocyte, and erythrocyte lipids. In control hamsters (n = 7) and fish oil-fed hamsters (n = 7), leukocyte/endothelium interaction was assessed in the time course after intravenous injection of human LDL (4 mg/kg), oxidized by 7.5 microM Cu2+ (6 hours, 37 degrees C). In control hamsters, injection of oxLDL elicited the rolling and sticking of leukocytes to the endothelium of arterioles and postcapillary venules with a maximum 15 minutes after injection (arterioles: from 3 +/- 1 to 91 +/- 25 cells/mm2 at 15 minutes; venules: from 13 +/- 6 to 150 +/- 46 cells/mm2 at 15 minutes; mean +/- SD). This phenomenon was significantly reduced in fish oil-fed hamsters, where 15 minutes after injection of oxLDL leukocyte sticking reached a maximum of only 15 +/- 7 and 20 +/- 5 cells/mm2 in arterioles and postcapillary venules, respectively (p less than 0.01 versus control animals).

CONCLUSIONS

The results of the present study suggest that inhibition of leukocyte/endothelium interaction may be one of the mechanisms by which dietary fish oil exerts its protective effects on experimental and clinical atherogenesis.

Reassessment of two Boyden chamber methods for measuring canine neutrophil migration: the leading front and the lower surface count assays

Laboratory investigation of neutrophil locomotion has attracted a great deal of attention owing to its potential usefulness to veterinary clinical medicine. Two of the most important principles for measurement of chemotaxis are the leading front and lower surface count techniques. The latter assay has become increasingly popular following the introduction of multi-well chambers utilizing polycarbonate filters. In the present study, this method was compared quantitatively and qualitatively to the leading front assay. Further, the potential usefulness of a simple shape-change assay as a rapid measure of chemotactic activation of neutrophils was assessed and compared with the migration assays. It was concluded that the two migration assays are superior to the shape-change assay, even though both suffer from certain methodological drawbacks. This may be relevant to the elucidation of clinical cases of neutrophil dysfunction.

Dietary fish oil blocks the microcirculatory manifestations of ischemia-reperfusion injury in striated muscle in hamsters

Epidemiologic observations and experimental studies have demonstrated a protective effect of dietary fish oil on the clinical manifestations of ischemia-reperfusion injury. To investigate the underlying mechanisms, we used the dorsal skinfold chamber model for intravital fluorescence microscopy of the microcirculation in striated muscle of awake hamsters. In control hamsters (n = 7), reperfusion after a 4-hr pressure-induced ischemia to the muscle tissue elicited the adhesion of fluorescently stained leukocytes to the endothelium of postcapillary venules, capillary obstruction, and the break-down of endothelial integrity. These microvascular manifestations of ischemia-reperfusion injury were significantly attenuated in animals (n = 7) when fed with a fish oil-enriched diet for 4 weeks prior to the experiments. In leukocyte total lipids, the fish oil diet resulted in a substantial displacement of arachidonic acid, the precursor of the potent adhesion-promoting leukotriene (LT) B4, by fish oil-derived eicosapentaenoic acid, the precursor of biologically less potent LTB5, emphasizing the mediator role of LTB4 in ischemia-reperfusion injury. These results suggest that the preservation of microvascular perfusion by dietary fish oil contributes to its protective effects on the clinical manifestations of ischemia-reperfusion injury.

Leukotrienes as mediators in ischemia-reperfusion injury in a microcirculation model in the hamster

Leukotriene (LT)B4 promotes leukocyte chemotaxis and adhesion to the endothelium of postcapillary venules. The cysteinyl leukotrienes, LTC4, LTD4, and LTE4, elicit macromolecular leakage from this vessel segment. Both leukocyte adhesion to the endothelium and macromolecular leakage from postcapillary venules hallmark the microcirculatory failure after ischemia-reperfusion, suggesting a role of leukotrienes as mediators of ischemia-reperfusion injury. Using the dorsal skinfold chamber model for intravital fluorescence microscopy of the microcirculation in striated muscle in awake hamsters and sequential RP-HPLC and RIA for leukotrienes, we demonstrate in this study that (a) the leukotrienes (LT)B4 and LTD4 elicit leukocyte/endothelium interaction and macromolecular leakage from postcapillary venules, respectively, that (b) leukotrienes accumulate in the tissue after ischemia and reperfusion, and that (c) selective inhibition of leukotriene biosynthesis (by MK-886) prevents both postischemic leukotriene accumulation and the microcirculatory changes after ischemia-reperfusion, while blocking of LTD4/E4 receptors (by MK-571) inhibits postischemic macromolecular leakage. These results demonstrate a key role of leukotrienes in ischemia-reperfusion injury in striated muscle in vivo.

The effect of 20-trifluoromethyl leukotriene B4 on neutrophil functional responses

20-trifluoromethyl-leukotriene B4 (20CF3-LTB4) is a stable derivative of leukotriene B4 (LTB4) that is not subjected to omega-oxidation to less active metabolites. 20CF3-LTB4 was as potent as LTB4 as a chemotactic, adhesion-promoting and aggregatory agent for human neutrophils, but had only 11 +/- 3% of the ability to induce an oxidative response. Nonetheless, both compounds were equally efficient in order to confer a rapid and monophasic increment of the concentration of cytosolic calcium. The kinetics of the calcium, aggregatory and chemiluminescent responses to 20CF3-LTB4 were similar to that of LTB4. These findings suggest that the insertion of the trifluoromethyl group into the LTB4 molecule causes a shift of the biological activity profile, suggesting that 20CF3-LTB4 binds mainly to high affinity LTB4 receptors. Moreover, the similarity of the response kinetics of LTB4 and 20CF3-LTB4 suggests that the mechanism for the rapid and transient responses of LTB4 is not due to its omega-oxidation.

Recombinant human interleukin-8 is a potent activator of canine neutrophil aggregation, migration, and leukotriene B4 biosynthesis

Interleukin-8 (IL-8), formerly known as NAP-1, is formed by a variety of cells upon stimulation with IL-1 or tumor necrosis factor (TNF). The biologic activity of the cytokine involves activation of almost every neutrophil function studied so far in different species. In the present study, we compared the effects of recombinant human IL-8 (rIL-8) and the lipid mediators, leukotriene B4 (LTB4) and platelet-activating factor (PAF), on neutrophil functions in dogs. All three chemotactic factors induced neutrophil aggregation and chemotaxis, with rIL-8 being far more potent than LTB4 and PAF. The migration induced by rIL-8 was significantly greater than that observed towards LTB4 and PAF. In the aggregation assay, rIL-8 was shown for the first time to be a potent stimulant. The aggregation response was more persistent than that obtained with LTB4 and PAF and the potency of rIL-8 was greater. An intradermal dose-response study showed that rIL-8 is an extremely potent inducer of selective neutrophil infiltration in canine skin. The infiltration was more pronounced than following injection of LTB4 or PAF. It was proposed that the superior effect of rIL-8 was caused by a synergistic effect between injected rIL-8 and LTB4, which was shown to be produced in biologically active amounts by canine neutrophils stimulated with rIL-8. From a therapeutic point of view, the simultaneous presence of rIL-8 and LTB4 in inflammatory skin diseases highlights the need to develop drugs that inhibit the production and/or effect of both mediators.

Leukocyte-cell adhesion: a molecular process fundamental in leukocyte physiology

Leukocyte-cell adhesion is a form of physical contact characterized by fast (firm) stickiness between the cells. To analyze the biology and molecular basis of this process, an adhesion-specific assay was developed: the phorbol ester-induced aggregation of human lymphocytes. This rapid and antigen-independent intercellular adhesion requires cellular metabolism, an intact cytoskeleton and extracellular divalent cations, and is mediated by preformed cell-surface proteins referred to as CAMs. Phorbol ester also induces aggregation of monocytes and granulocytes, as well as adhesion of T lymphocytes to either B cells or monocytes and of the leukocytes to vascular endothelial cells. By using the adhesion-specific assay and blocking monoclonal antibodies, several CAMs have been identified, namely the Leu-CAM family (CD11a-c/CD18) and ICAM-1 (CD54). The Leu-CAM family is composed of Leu-CAMa (CD11a/CD18), Leu-CAMb (CD11b/CD18) and Leu-CAMc (CD11c/CD18), three glycoprotein heterodimers made of a common beta-chain and distinct alpha-chains. ICAM-1 is an adhesive ligand for Leu-CAMa. Expression and use of the various CAMs is selective in different types of leukocytes. The Leu-CAMs have been purified and partially characterized. CD18, whose gene is on human chromosome 21, contains 5-6 N-linked complex-type oligosaccharides, and CD11 binds Ca++. Another adhesion pathway is mediated by CD2 and CD58. CD2, a glycoprotein selectively expressed by T cells, is a receptor for CD58, a cell-surface adhesive ligand with broad tissue distribution. Antibodies to the latter CAMs do not block the phorbol ester-induced lymphocyte aggregation. Adhesion is involved in a large variety of leukocyte functions. Anti-Leu-CAM antibodies block induction of IL-2 production and lymphocyte proliferation. Lymphocyte-mediated cytotoxicity is also inhibited. Endogenous NK and LAK cells use Leu-CAMs, ICAM-1 and CD2, and sometimes RGD receptors, to bind and kill tumor cells. Endogenous compounds such as H2O2 and LTB4 also induce Leu-CAM-dependent adhesion in monocytoid cells and granulocytes, respectively, and degranulation of the latter cells is enhanced by the adhesion process. Homologous CAMs have been identified in rabbit and mouse. In in vivo studies in the former species, anti-Leu-CAM antibodies block adhesion of leukocytes to vascular endothelium and thereby their migration into extravascular tissues. The antibodies thus inhibit granulocyte accumulation and plasma leakage in inflammatory lesions, and induce lympho- and granulocytosis, indicating that cell-adhesion contributes to the distribution of leukocytes in the body.(ABSTRACT TRUNCATED AT 400 WORDS)