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M A Lindsay

Publications and source records attributed to M A Lindsay.

At least 19 recordsLinked to original sources
PubMed2004

Mammalian Sterile20-like kinase 1 and the regulation of apoptosis.

Mammalian Sterile20-like kinase 1 (Mst1) is a ubiquitously expressed serine/threonine kinase which represents a member of the rapidly expanding family of enzymes related to the yeast Sterile20 kinase. Although the physiological function of Mst1 and its role in intracellular signalling is still unclear, reports to date suggest that Mst1, similar to its yeast homologue, operates in the MAPK (mitogen-activated protein kinase) pathway and, in this capacity, may represent a putative MAPK kinase kinase kinase. Moreover, there is abundant evidence for a role of this enzyme in apoptosis, where not only is it a target for caspases, but may also serve as an activator of these proteases to amplify the apoptotic signalling pathway. This paper reviews the investigations that have led to our current understanding of the mechanisms by which Mst1 may be activated and thereby contribute to apoptosis.

Apoptosis↗
PubMed2001

Pharmacological comparison of LTB(4)-induced NADPH oxidase activation in adherent and non-adherent guinea-pig eosinophils.

1. Leukotriene B(4) (LTB(4)) stimulation of guinea-pig peritoneal eosinophils, induced a biphasic activation of the NADPH oxidase composed of a rapid (<3 min) phase mediated by non-adherent cells and a sustained (3 - 120 min) phase mediated by CD11b/CD18 adherent eosinophils. Studies were undertaken to compare the intracellular mechanism that mediate these responses. 2. SB 203580 and PP1, inhibitors of p38 mitogen-activated protein (MAP) kinase and the src-family protein tyrosine kinases, respectively caused concentration-dependent attenuation of both the rapid (SB203580: pD(2)=-6.31; PP1: pD(2)=-5.50) and sustained (SB203580: pD(2)=-6.50; PP1: pD(2)=-5.73) phases. Similarly, the MAP kinase kinase-1 inhibitor, PD098059 produced partial inhibition of the both phases of superoxide generation. 3. The protein kinase C (PKC) inhibitors Ro-31 8220, GF 109203X and Gö 6976 attenuated the rapid NADPH oxidase response (pD(2)s=-6.10, -6.72, -6.15 respectively) and, to a lesser extent, (pD(2)s=-5.54, -6.02, -6.51 respectively) the sustained phase. 4. An inhibitor of phosphatidylinositol 3-kinase (PtdIns 3-kinase), wortmannin caused concentration dependent attenuation of the sustained (pD(2)=-8.68) but not rapid phase of superoxide generation. In contrast, the syk kinase inhibitor, piceatannol abolished the rapid (pD(2)=-6.43) but not sustained respiratory responses. 5. This study demonstrates that LTB(4)-induced superoxide generation from adherent and non-adherent eosinophils is mediated via both common (p38 MAP kinase, MEK-1, PKC and the src kinases) and divergent intracellular pathways (syk kinases and PtdIns 3-kinase). This suggests the possibility of therapeutic intervention to selective attenuate activation of adherent tissue eosinophils.

Androstadienes↗
PubMed2000

Pleiotropic role of lyn kinase in leukotriene B(4)-induced eosinophil activation.

The authors have examined the role of the src-family of protein tyrosine kinases in leukotriene B(4) (LTB(4))-induced activation of guinea-pig eosinophils. Western blot analysis identified the src-like protein tyrosine kinases p53(lyn), p56(lyn), p56/59(hck), p55(fgr), and p56(lck) whereas p60(src), p62(yes), p55(blk), and p59(fyn) were not detected. LTB(4) promoted a rapid increase in p53/56(lyn) activity in eosinophils, which peaked at 5 seconds and remained elevated at 60 seconds; hck, fgr, and lck were not activated. A role for p53/56(lyn) in eosinophil activation was investigated with the use of the src-selective inhibitor PP1 (1 micromol/L to 10 micromol/L), which attenuated LTB(4)-stimulated p53/56(lyn) activity and the phosphorylation of extracellular signal-regulated kinase-2 in intact cells. At comparable concentrations, PP1 was also shown to attenuate LTB(4)-induced nicotinamide adenine dinucleotide phosphate (reduced form) (NADPH) oxidase activation, chemotaxis, and Ca(++)-dependent [(3)H]arachidonic acid (AA) release. Moreover, an inhibitor of mitogen-activated protein kinase kinase-1, PD 098059, significantly inhibited LTB(4)-induced chemotaxis but had no effect on oxidant production or [(3)H]AA release. Collectively, these results implicate lyn kinase in LTB(4)-induced eosinophil activation through the recruitment of divergent cell-signaling pathways.

Animals↗
PubMed2000

The MAP kinase inhibitors, PD098059, UO126 and SB203580, inhibit IL-1beta-dependent PGE(2) release via mechanistically distinct processes.

1. In common with human bronchial epithelial cells, pulmonary A549 cells release prostaglandin (PG) E(2) in response to pro-inflammatory cytokines. We have therefore used these cells to examine the effect of the selective mitogen activated protein (MAP) kinase inhibitors; PD098059, a mitogen activated and extracellular regulated kinase kinase (MEK) 1 inhibitor, UO126, a dual MEK1 & MEK2 inhibitor, and SB203580, a p38 MAP kinase inhibitor in the IL-1beta-dependent release of PGE(2). 2. Following IL-1beta treatment the extracellular regulated kinases (ERKs) and the p38 MAP kinases were rapidly phosphorylated. 3. PD09059, UO126 and SB203580 prevented IL-1beta-induced PGE(2) release at doses that correlated closely with published IC(50) values. Small or partial effects at the relevant doses were observed on induction of cyclo-oxygenase (COX) activity or COX-2 protein suggesting that the primary effects were at the level of arachidonate availability. 4. Neither PD098059 nor SB203580 showed any effect on IL-1beta-induced arachidonate release. We therefore speculate that the MEK1/ERK and p38 kinase cascades play a role in the functional coupling of arachidonate release to COX-2. 5. In contrast, UO126 was highly effective at inhibiting IL-1beta-dependent arachidonate release, implicating MEK2 in the activation of the PLA(2) that is involved in IL-1beta-dependent PGE(2) release. 6. We conclude that the MEK1, MEK2 and p38 MAP kinase inhibitors, PD098059, UO126 and SB203580, are highly potent in respect of inflammatory PG release. Finally, we conclude that these inhibitors act via mechanistically distinct processes, which may have anti-inflammatory benefits.

Arachidonic Acid↗
PubMed2000

Extracellular signal-regulated kinase 1/2 control Ca(2+)-independent force development in histamine-stimulated bovine tracheal smooth muscle.

The role of extracellular signal-regulated kinase (ERK)-1 and ERK-2 in controlling histamine-induced tone in bovine trachealis was investigated. PD 098059, an inhibitor of mitogen-activated protein kinase kinase (MKK)-1, had no effect on the histamine concentration-response relationship that described contraction. However, in the presence of EGTA, PD 098059 produced a parallel 5 fold rightwards shift of the histamine concentration-response curve without reducing the maximum response. The beta(2)-adrenoceptor agonist, procaterol, also displaced the histamine-concentration response curve to the right but the effect was much greater than that evoked by PD 098059, non-competitive and seen in the absence and presence of EGTA. A low basal level of pERK-1 and pERK-2 was always detected in untreated trachealis, which was significantly higher in EGTA-treated tissues and inhibited by PD 098059 and procaterol. Histamine markedly enhanced the phosphorylation of ERK-1 and ERK-2 by a mechanism that was also enhanced by EGTA and significantly attenuated by procaterol and PD 098059. Neither cholera toxin nor SP:-8-Br-cAMPS mimicked the ability of procaterol to dephosphorylate ERK. Similarly, neither pertussis toxin (PTX) nor RP:-8-Br-cAMPS, an inhibitor of cyclic AMP-dependent protein kinase (PKA), affected basal pERK levels or antagonized the inhibitory effect of procaterol. These data implicate the MKK-1/ERK signalling cascade in Ca(2+)-independent, histamine-induced contraction of bovine trachealis. In addition, the ability of procaterol to dephosphorylate ERK in an RP:-8-Br-cAMPS- and PTX-insensitive manner suggests that this may contribute to the anti-spasmogenic activity of beta(2)-adrenoceptor agonists by activating a novel PKA-independent pathway.

Animals↗
PubMed2000

p38 MAP kinase and MKK-1 co-operate in the generation of GM-CSF from LPS-stimulated human monocytes by an NF-kappa B-independent mechanism.

1. The extent to which the p38 mitogen-activated protein (MAP) kinase and MAP kinase kinase (MKK)-1-signalling pathways regulate the expression of granulocyte/macrophage colony-stimulating factor (GM-CSF) from LPS-stimulated human monocytes has been investigated and compared to the well studied cytokine tumour necrosis factor-alpha (TNF alpha). 2. Lipopolysaccharide (LPS) evoked a concentration-dependent generation of GM-CSF from human monocytes. Temporally, this effect was preceded by an increase in GM-CSF mRNA transcripts and abolished by actinomycin D and cycloheximide. 3. LPS-induced GM-CSF release and mRNA expression were associated with a rapid and time-dependent activation of p38 MAP kinase, ERK-1 and ERK-2. 4. The respective MKK-1 and p38 MAP kinase inhibitors, PD 098059 and SB 203580, maximally suppressed LPS-induced GM-CSF generation by >90%, indicating that both of these signalling cascades co-operate in the generation of this cytokine. 5. Electrophoretic mobility shift assays demonstrated that LPS increased nuclear factor kappa B (NF-kappa B) : DNA binding. SN50, an inhibitor of NF-kappa B translocation, abolished LPS-induced NF-kappaB : DNA binding and the elaboration of TNFalpha, a cytokine known to be regulated by NF-kappaB in monocytes. In contrast, SN50 failed to affect the release of GM-CSF from the same monocyte cultures. 6. Collectively, these results suggest that the generation of GM-CSF by LPS-stimulated human monocytes is regulated in a co-operative fashion by p38 MAP kinase- and MKK-1-dependent signalling pathways independently of the activation of NF-kappa B.

Enzyme Inhibitors↗
PubMed2000

Delayed eosinophil apoptosis in asthma.

BACKGROUND: Eosinophilic inflammation of the airways is a key characteristic of asthma. A defect in apoptosis might contribute to the chronic tissue eosinophilia associated with asthma. OBJECTIVE: Our purpose was to examine whether the rate of apoptosis differs between peripheral blood eosinophils from asthmatic patients and healthy volunteers. METHODS: Peripheral blood was obtained from volunteers with asthma and from control volunteers. Eosinophils were isolated by CD16-negative selection to >99% purity and were cultured for 48 hours. The number of apoptotic eosinophils in the culture was assessed by flow cytometric analysis of relative DNA content in propidium iodide-stained cells. Eosinophil apoptosis is expressed as apoptosis index (number of apoptotic cells/total number of cells). RESULTS: Eosinophils from asthmatic patients not taking steroid medication survived longer (apoptosis index 0.25) than those of healthy control subjects (apoptosis index 0.40, P <.05). In contrast, the rate of apoptosis in eosinophils from patients concurrently taking steroids (apoptosis index 0.46) is higher than that of those not using steroids (P <.01) and not different from that of healthy subjects. To assess whether endogenous IL-3, IL-5, and GM-CSF production contributes to the delayed eosinophil apoptosis, the effects of the corresponding neutralizing antibodies were studied on eosinophil longevity. Neutralization of GM-CSF, but not of IL-3 or IL-5, increased slightly but significantly (P <.01) the rate of apoptosis in eosinophils obtained from patients with asthma. To assess whether beta(2)-agonist medication could contribute to the observed differences, we determined the in vitro effects of albuterol, fenoterol, and salmeterol on eosinophil apoptosis. All beta(2)-agonists inhibited eosinophil apoptosis by 12% to 19%. A possibility existed that a prior in vivo exposure to IL-5, GM-CSF, or beta(2)-agonists would explain the observed difference. To study this, eosinophils were incubated with GM-CSF, IL-5, and albuterol for 2 to 3 hours, followed by washout of the added compounds, and were subsequently cultured for 48 hours. However, an exposure to GM-CSF (7 pmol/L) or IL-5 (10 pmol/L) for 15 to 180 minutes was not a sufficient signal to prevent eosinophil apoptosis. In contrast, exposure to albuterol (100 nmol/L) for 120 minutes was sufficient to induce a significant (P <.05) decrease in eosinophil apoptosis. CONCLUSIONS: The results suggest that eosinophil apoptosis is delayed in asthma. This delay may be partly explained by production of GM-CSF. The in vitro effects of beta(2)-agonists suggest that beta(2)-agonist use might contribute to the prolonged eosinophil survival through inhibition of apoptosis and thus may worsen eosinophilia in asthmatic patients. Use of inhaled glucocorticoids seems to totally reverse the delayed eosinophil apoptosis in asthma.

Adrenal Cortex Hormones↗
PubMed2000

Chemotherapy of breast cancer: are the taxanes going to change the natural history of breast cancer?

Among the novel chemotherapeutic drugs introduced in the last decade, taxanes have emerged as the most powerful compounds and results available to date suggest that they will be remembered in the future as the breast cancer chemotherapy of the 1990s. The two taxanes (paclitaxel, Taxol, Bristol-Myers Squibb and docetaxel, Taxotere, Rhône-Poulenc Rorer) share some characteristics, but are also significantly different both in preclinical profile and, most importantly, in clinical characteristics. The main clinical differences are related to their different efficacy-toxicity ratio in relation to dose and schedule; the differing integrability of paclitaxel and docetaxel in anthracycline-taxane containing regimens, secondary to major differences in pharmacokinetic interactions between each taxane and the anthracyclines, and; the potential differences in level of synergism between each taxane and herceptin (HeR2Neu antibody/trastuzumab, Genentech/Roche). In clinical practice, the taxanes are now standard therapy in metastatic breast cancer after prior chemotherapy, in particular anthracyclines, has failed. Their role in combination with anthracyclines in first-line therapy of advanced breast cancer is emerging and sheds new light on the potential role of taxanes in the adjuvant setting. However, the impact of taxanes on the natural history of breast cancer is yet to be defined, despite the trend of results suggesting that these agents have the potential for significant improvements in advanced and, most importantly, adjuvant therapy of breast cancer. The results of all completed or ongoing Phase III trials in first-line metastatic and the adjuvant setting will help determine if taxanes will further improve the outcome of breast cancer or not.

Animals↗
PubMed1999

Role of arachidonic acid in leukotriene B(4)-induced guinea-pig eosinophil homotypic aggregation.

The activation of eosinophils with the lipid mediator, leukotriene B(4), induces their homotypic aggregation. Upon activation with leukotriene B(4), eosinophils release a significant amount of arachidonic acid, a process dependent on the activation of phospholipase A(2). Here, we have evaluated whether arachidonic acid could induce aggregation of eosinophils and whether the release of arachidonic acid mediated the aggregation induced by leukotriene B(4). The exogenous administration of arachidonic acid induced a concentration-dependent eosinophil homotypic aggregation. Pretreatment of eosinophils with a 5-lipoxygenase inhibitor or a leukotriene B(4) receptor antagonist abrogated arachidonic-acid-induced aggregation. Arachidonic acid induced a significant increase in leukotriene B(4) levels and desensitised leukotriene B(4)-induced aggregation in a dose-dependent manner. Moreover, this desensitisation was effectively reversed by a 5-lipoxygenase inhibitor. However, arachidonic acid failed to induce a rise in intracellular Ca(2+) in eosinophils and failed to desensitise these cells to rises in intracellular Ca(2+) induced by leukotriene B(4). Pretreatment of eosinophils with the phospholipase A(2) inhibitor, mepacrine, inhibited the aggregation responses induced by 1 nM leukotriene B(4) by approximately 50% but had no significant effect on the other concentrations of leukotriene B(4) tested (0.1 to 100 nM). In conclusion, arachidonic acid stimulates eosinophil aggregation indirectly via the release of leukotriene B(4). Although a significant amount of arachidonic acid is released in response to activation of eosinophils with leukotriene B(4), the arachidonic acid released does appear to play a major role in mediating leukotriene B(4)-induced eosinophil aggregation.

Animals↗
PubMed1999

'Outside-in' signalling mechanisms underlying CD11b/CD18-mediated NADPH oxidase activation in human adherent blood eosinophils.

1 Incubation of human eosinophils in BSA-coated tissue culture plates resulted in time-dependent adhesion and attendant activation of the NADPH oxidase that were both inhibited (by >85%) by blocking antibodies raised against CD11b and CD18. 2 SB 203580, an inhibitor of p38 mitogen-activated protein (MAP) kinase, did not influence adhesion but inhibited superoxide anion generation (pIC50=-6.57). 3 PP1, an inhibitor of the src-family of protein tyrosine kinases, inhibited adhesion and CD11b/CD18-mediated superoxide anion generation with similar potencies (pEC50s=-5.53 and -5.99 respectively) suggesting that inhibition of the NADPH oxidase was a direct consequence of blocking adhesion. 4 The protein kinase C (PKC) inhibitors Ro-31 8220 (broad spectrum inhibitor), GF 109203X (inhibitor of conventional and novel isoforms) and Gö 6976 (inhibitor of conventional isoforms) suppressed adhesion-dependent NADPH oxidase activation (pIC50s=-6.61, -6.05 and -4.89 respectively) without affecting adhesion. Based upon the selectivity of these drugs PKCdelta and PKCepsilon are implicated in the suppression of oxidant production. 5 Wortmannin, an inhibitor of phosphatidylinositol 3-kinase (PtdIns 3-kinase), abolished superoxide anion production in adherent eosinophils (pEC50=-9.06). Similarly, CD11b/CD18-dependent adhesion was suppressed with the same potency (pEC50=-9.29) although the maximum effect did not exceed 50% implying that wortmannin also had an affect on those processes that govern adhesion-driven oxidase activation. 6 PD 098059 and piceatannol, inhibitors of MAP kinase kinase-1 and the syk tyrosine kinase respectively, had no effect on CD11b/CD18-mediated adhesion or NADPH oxidase activation. 7 The results of this study demonstrate that human eosinophils adhere to BSA-coated plastic by a CD11b/CD18-dependent mechanism, which is responsible for activation of the NADPH oxidase. Although the signalling pathway(s) utilized by CD11b/CD18 is still to be elucidated, the data presented herein implicate p38 MAP kinase, novel PKCs and PtdIns 3-kinase.

Androstadienes↗
PubMed1999

Expression and activation of protein kinase C-zeta in eosinophils after allergen challenge.

Protein kinase (PK) C is an increasingly diverse family of enzymes that has been implicated in a range of cellular functions within the eosinophil. Using isoform-specific polyclonal antibodies, we have explored the expression of PKC isoforms in circulating eosinophils. Initial studies demonstrated the presence of the alpha, betaI, betaII, and zeta and the low-level expression of the delta, epsilon, iota, and micro isoforms but no detectable expression of the gamma, eta, and theta isoforms in both normal and asthmatic subjects. There was no difference in the total protein expression between these two groups. Subsequent studies examined the expression and activation of PKC isoforms in circulating eosinophils from asthmatic patients before and 24 h after a late asthmatic response to an inhaled allergen. Cellular fractionation showed PKC-alpha and PKC-betaII to be mainly located in the cytosol, whereas PKC-betaI was constitutively more expressed in the membrane. No changes in expression or subcellular localization of these isoforms were seen after allergen challenge. In contrast, PKC-zeta expression was increased after allergen challenge, and we demonstrated a significant PKC-zeta translocation to the membrane, in keeping with activation of the enzyme. Our results suggest that 24 h after allergen exposure of asthmatic patients, there is increased expression and activation of eosinophil PKC-zeta that correlates with late asthmatic responses recorded between 4 and 10 h postallergen challenge.

Adult↗
PubMed1999

The academic global virtual concept in clinical cancer research and its application to breast cancer: The Breast Cancer International Research Group.

In contrast to previous decades, the 1990s have witnessed an increase of new agents with significant activity in breast cancer, including chemotherapy, hormone therapy, and, more recently, biologic modifiers. All information appears to confirm that such a trend will persist and even accelerate in the coming decades. Unless clear strategies of development for new drugs are strictly followed, it will become difficult to adequately assess the many new agents with potentially important activity against breast cancer, and patient access may become a limiting key factor. The academic, global virtual concept is calling for the definition of a new relationship between the pharmaceutical industry and clinical researchers. The main aspect is related to the creation of partnerships with an academically controlled global strategy of development for promising new agents, in which the quality and independence of processes (adjuvant setting, for example) are critical. The means are based on the globalization of patient access (worldwide network) and the virtuality of the approach (modern means of communication as well as access to subgroups of patients). The Breast Cancer International Research Group is the first academic global virtual cooperative group in breast cancer and is making contributions in the development of new drugs, such as taxanes, new antiestrogens, and new cytokines.

Academic Medical Centers↗
PubMed1999

SB 203580, an inhibitor of p38 mitogen-activated protein kinase, enhances constitutive apoptosis of cytokine-deprived human eosinophils.

The role of p38 mitogen-activated protein (MAP) kinase, and extracellular-regulated protein kinase -1 and -2 in regulating constitutive apoptosis and interleukin (IL)-5-induced survival of human eosinophils have been investigated. Two populations of donors were identified whose eosinophils, in the absence of exogenous cytokines, underwent apoptosis at different rates. Eosinophils were thus arbitrarily classified as either "fast"- or "slow"-dying cells, where greater or less than 15% of the cells were apoptotic at 2 days, respectively. The selective p38 MAP kinase inhibitor, SB 203580, increased constitutive eosinophil apoptosis in both populations (EC(50) approximately 2 microM) as evinced from morphological analysis, flow cytometry, and DNA laddering. The ability of SB 203580 to kill eosinophils was not due to nonspecific toxicity or through the inhibition of prostanoid or leukotriene production. Exposure of eosinophils to IL-5, at a concentration (10 pM) that enhanced survival maximally, abolished SB 203580-induced apoptosis. In contrast PD 098059, which selectively blocks MAP kinase kinase (MEK) 1, did not affect apoptosis of fast- or slow-dying eosinophils, or the enhanced survival of cells effected by IL-5. Collectively, these results suggest that: 1) the basal activity of p38 MAP kinase may regulate the survival of cytokine-deprived eosinophils through inhibition of apoptosis, 2) the enhancement of eosinophil survival effected by IL-5 is mediated by a mechanism(s) divorced from the activation of p38 MAP kinase, and 3) neither spontaneous eosinophil apoptosis nor their enhanced survival by IL-5 involves the activation of MEK-1.

Apoptosis↗
PubMed1998

Leukotriene B4 activates the NADPH oxidase in eosinophils by a pertussis toxin-sensitive mechanism that is largely independent of arachidonic acid mobilization.

Experiments were designed to investigate whether leukotriene (LTB4) receptors can couple directly to phospholipase A2 (PLA2) in guinea pig eosinophils and the role of endogenous arachidonic acid (AA) in LTB4-induced activation of the NADPH oxidase. LTB4 (EC50 approximately 16 nM) and AA (EC50 approximately 6 microM) generated hydrogen peroxide (H2O2) in a concentration-dependent manner and at an equivalent maximum rate (5-6 nmol/min/10(6) cells). LTB4 stimulated PLA2 over a similar concentration range that activated the NADPH oxidase, although kinetic studies revealed that the release of [3H]AA (t1/2 approximately 2 s) preceded H2O2 generation (t1/2 > 30 s). Pretreatment of eosinophils with pertussis toxin abolished the increase in inositol(1,4,5)trisphosphate mass, [Ca2+]c, [3H]AA release, and H2O2 generation evoked by LTB4. Qualitatively identical results were obtained in eosinophils in which phospholipase C (PLC) was desensitized by 4beta-phorbol 12,13-dibutyrate with the exception that [3H]AA release was largely unaffected. Additional studies performed with the protein kinase C inhibitor, Ro 31-8220, and under conditions in which Ca2+ mobilization was abolished, provided further evidence that LTB4 released [3H]AA independently of signal molecules derived from the hydrolysis of phosphatidylinositol(4,5)bisphosphate by PLC. Pretreatment of eosinophils with the PLA2 inhibitor, mepacrine, abolished LTB4-induced [3H]AA release at a concentration that inhibited H2O2 by only 36%. Collectively, the results of this study indicate that agonism of LTB4 receptors on guinea pig eosinophils mobilizes AA by a mechanism that does not involve the activation of PLC. In addition, although LTB4 effectively stimulated PLA2, a central role for AA in the activation of the NADPH oxidase was excluded.

Animals↗
PubMed1998

Role of the mitogen-activated protein kinases and tyrosine kinases during leukotriene B4-induced eosinophil activation.

Exposure of guinea-pig eosinophils to leukotriene B4 (LTB4; 1 microM) resulted in a rapid generation of H2O2 (index of NADPH oxidase activation), stimulated [3H]arachidonic acid (AA) release (index of phospholipase A2 activity), and promoted CD18-dependent homotypic aggregation. Under similar conditions, LTB4 (1 microM) induced a rapid activation of extracellular-regulated kinases-1 and 2 (ERK-1/2) but not c-jun N-terminal kinases 46 and 54 (JNK-46/54) or p38 mitogen-activated protein kinase (p38 MAP kinase). To examine the role of ERK-1/2 in the mechanism of eosinophil activation, a selective inhibitor of MAP kinase kinase-1/2 (MEK-1/2), PD098059, was employed. However, PD 098059 at concentrations that attenuated ERK-1/2 activation had no significant affect on eosinophil activation. In contrast, a role for tyrosine kinases in LTB4-induced eosinophil activation was suggested by studies with the tyrosine kinase inhibitors, herbimycin A and lavendustin A. However, the results of those experiments implied divergent pathways for the control of eosinophil responses because the inhibitors were more effective at attenuating H2O2 generation than [3H]AA release, and had little effect on homotypic aggregation.

Animals↗
PubMed1998

Role of arachidonic acid and its metabolites in the priming of NADPH oxidase in human polymorphonuclear leukocytes by peritoneal dialysis effluent.

Peritoneal dialysis effluent (PDE) contains a low-molecular-weight solute that will activate and prime the NADPH oxidase of human neutrophils via a phospholipase A2 (PLA2)-dependent mechanism. Since the products of PLA2 are known to activate and prime the oxidase we have investigated their role in the dialysis effluent-mediated activation and priming of human neutrophils. NADPH oxidase activity of PDE-primed and -unprimed neutrophils was measured by lucigenin-enhanced chemiluminescence in the presence of known inhibitors of the arachidonic acid cascade. Incubation of neutrophils with the nonselective PLA2 inhibitor quinacrine (0 to 100 microM) reduced oxidase activity in both primed and unprimed cells. Furthermore, primed cells were more sensitive to the action of quinacrine than were unprimed cells. We were unable to determine the relative roles of secretory PLA2 (sPLA2) and cytosolic PLA2 (cPLA2) since the selective sPLA2 inhibitor scalaradial (0 to 100 microM) inhibited oxidase activity in both groups of cells by similar degrees, while the specific cPLA2 inhibitor AACO-CF3 (0 to 50 microM) failed to affect activity in either group. Inhibition of platelet-activating factor (PAF), cycloxygenase, and 5-lipoxygenase-activating protein by hexanolamino-PAF (0 to 25 microM), flurbiprofen (0 to 25 microM), and MK886 (0 to 5 microM), respectively, had no effect upon oxidase activity. However, the direct inhibition of 5-lipoxygenase by caffeic acid or lipoxin A4 resulted in a similar concentration-dependent attenuation of oxidase activity in both primed and unprimed cells. Leukotriene B4 (LTB4) release from primed neutrophils was comparable to that from unprimed cells with the exception of phorbol myristate acetate-stimulated cells, which released fivefold more LTB4 than control. Taken together, these results suggest that it is arachidonic acid per se, and not its metabolites, that is important in priming of the neutrophil NADPH oxidase by dialysis effluent.

Anti-Inflammatory Agents↗