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Biomedical subjects

D E MacIntyre

Publications and source records attributed to D E MacIntyre.

At least 55 records · Page 3Linked to original sources
PubMed1992

Prevention and reversal of experimental colitis by a monoclonal antibody which inhibits leukocyte adherence.

The role of neutrophils in the pathogenesis of acute colitis was investigated using a rabbit model. Colitis was induced by intracolonic administration of trinitrobenzene sulfonic acid in 30% ethanol. Myeloperoxidase activity was measured at various times after induction of colitis as an index of neutrophil infiltration, and this was confirmed by histology. The permeability of the colonic epithelium to [51Cr]EDTA was also measured at various times after induction of colitis. The most marked increase in neutrophil infiltration of the colon occurred during the period 3-6 h after induction of colitis. This was also the period in which the greatest increase in colonic permeability was observed. Pretreatment with a monoclonal antibody (IB-4) directed against the leukocyte adhesion molecule, CD18, markedly suppressed neutrophil infiltration into the colonic tissue after induction of colitis. This pretreatment also significantly reduced the extent of epithelial injury. Administration of IB-4 to rabbits 12 h after induction of colitis resulted in a rapid decline in tissue myeloperoxidase activity. When measured 12 h after IB-4 administration (3 mg/kg), colonic myeloperoxidase activity was reduced by about 80% compared to the control group treated with the vehicle. These results are consistent with the hypothesis that neutrophils contribute significantly to the epithelial dysfunction that characterizes colitis and suggest that antibodies directed against adhesion molecules may represent a novel approach to the treatment of intestinal inflammatory disorders.

Acute Disease↗
PubMed1992

The role of CD18 in IL-8 induced dermal and synovial inflammation.

1. The intradermal administration of endothelial IL-8 (IL-8(1-77) or monocyte derived IL-8 (IL-8(1-72) to rabbits produced a concentration-dependent increase in plasma extravasation and an accumulation of polymorphonuclear leukocytes (PMNs) when measured over a 3 h time period. When plasma extravasation and PMN accumulation were measured over a 30 min time period no significant increases in PMN accumulation or plasma extravasation were observed in response to IL-8 alone. However, under these conditions, the addition of prostaglandin E2 (100 pmol) produced a significant potentiation of IL-8-induced plasma extravasation. There was no significant difference between the biological activities of IL-8(1-77) and IL-8(1-72). 2. Plasma extravasation and PMN accumulation induced by IL-8 were inhibited in rabbits pretreated with the monoclonal antibody designated IB4 (1 mg kg-1, i.v.) directed against the common beta chain (CD18) of the leukocyte integrins. 3. The intra-articular administration to rabbits of IL-8(1-77) (1 nmol) resulted 24 h later in the appearance of a mixed population of leukocytes (PMNs and mononuclear cells) in synovial lavage fluid. Biochemical analyses revealed the presence of an increased level of sulphated proteoglycans (sPG) and of the metalloproteinase stromelysin. Pretreatment of rabbits with IB4 (3 mg kg-1, i.v.) inhibited the accumulation of PMNs but had no effect on the mononuclear infiltrate nor on the levels of sPG or stromelysin. 4. The intradermal or intra-articular injection of E. coli-derived endotoxin induced similar inflammatory changes to those observed with IL-8.The possibility that the biological activities of IL-8 were attributable to minor contamination with endotoxin is unlikely for two reasons. Firstly, biological effects of endotoxin were observed at levels greater than that contained in the IL-8 preparation. Secondly,reduction of the endotoxin content of the IL-8 preparation by a factor of 10 did not produce a concomitant reduction in the observed biological activity of the IL-8.

Animals↗
PubMed1992

Differing roles for platelet-activating factor during inflammation of the lung and subarachnoid space. The special case of Streptococcus pneumoniae.

Although well-characterized in the lung, the role of platelet-activating factor (PAF) in inflammation in the central nervous system is undefined. Using rabbit models of meningitis and pneumonia, PAF was found to induce significant blood-brain barrier permeability and brain edema at doses five times lower than those required to generate leukocyte recruitment to the subarachnoid space. Both leukocytosis and increased vascular permeability occurred in response to PAF in the lung. Antibody to the CD-18 family of leukocyte adhesion molecules inhibited leukocyte recruitment in response to PAF in the brain (greater than 80%); a similar level of inhibition in the lung required treatment with a combination of a PAF receptor antagonist (L-659,989) and anti-CD18 antibody. Treatment with L-659,989 decreased abnormal cerebrospinal fluid cytochemical values induced by intracisternal challenge with pneumococci but not Haemophilus influenzae, indicating a special role for PAF in pneumococcal disease. Antibodies directed at phosphorylcholine, a unique, shared determinant of bioactivity of PAF and pneumococcal cell wall, obviated the inflammatory potential of both agents. However, no evidence for a direct PAF-like activity of pneumococcal cell wall components was detected in vitro by bioassay using platelets or neutrophils. It is concluded that PAF can induce inflammation in the subarachnoid space. In brain, PAF effects appear to be mediated through CD-18-dependent events, while in lung, PAF effects independent of CD-18 are also evident. At both sites, PAF is of particular clinical importance during inflammation induced by pneumococci apparently due to a unique proinflammatory relationship between the pneumococcal cell wall teichoic acid and PAF.

Animals↗
PubMed1991

5-Lipoxygenase-activating protein is the target of a quinoline class of leukotriene synthesis inhibitors.

An indole class of leukotriene synthesis inhibitors, exemplified by MK-886, which does not directly inhibit 5-lipoxygenase, has been shown to bind to an 18-kDa leukocyte membrane protein and to inhibit 5-lipoxygenase membrane translocation. It was demonstrated that the 18-kDa protein is necessary for the cellular activation of leukotriene synthesis and was named 5-lipoxygenase-activating protein (FLAP). We describe here a class of leukotriene synthesis inhibitors based on a quinoline structure, which is structurally distinct from MK-886. However, similar to MK-886, several quinolines are potent inhibitors of cellular leukotriene synthesis but are poor inhibitors of soluble 5-lipoxygenase. To determine whether FLAP is the protein target of leukotriene synthesis inhibitors of the quinoline class, we investigated the ability of these compounds to inhibit photoaffinity labeling of FLAP and to elute FLAP from indole affinity gels. The abilities of the quinoline inhibitors to interact with FLAP correlated well with their abilities to inhibit leukotriene synthesis in human polymorphonuclear leukocytes. L-674,573, a potent quinoline leukotriene synthesis inhibitor, inhibited indole photoaffinity labeling of FLAP in a concentration-dependent manner. In addition, L-674,573 selectively eluted FLAP from indole affinity gels, in contrast to L-671,480, a quinoline that was inactive as an inhibitor of leukotriene synthesis. When human leukocyte membranes were labeled with the indole photoaffinity probe [125I]L-669,083 and immunoprecipitated with a FLAP antibody, the labeling of FLAP was inhibited by L-674,573 but not by L-671,480. These results suggest a direct binding site for the quinoline leukotriene synthesis inhibitors on FLAP and provide further evidence for the essential role of FLAP in cellular leukotriene synthesis.

5-Lipoxygenase-Activating Proteins↗
PubMed1990

Evidence that circulating 6keto prostaglandin E1 causes the platelet defect of Bartter's syndrome.

Bartter's syndrome is associated with activation of prostaglandin metabolism. In the present study we provide several lines of evidence that a circulating metabolite of prostacyclin, 6ketoPGE1 is responsible for a defect in platelet function present in patients with Bartter's syndrome. In platelet aggregometry studies, plasma from patients contained platelet inhibitory activity which was fully neutralized by coincubation with antibody directed against 6ketoPGE1. Fractionation of lipophilic extracts of plasma by high pressure liquid chromatography yielded a platelet inhibitory fraction which comigrated with authentic 6ketoPGE1 and was neutralized by anti 6ketoPGE1 antibody. Lastly, direct measure of the plasma concentration of 6ketoPGE1 by specific radioimmunoassay indicates a 2-fold increase in patients with Bartter's syndrome (133 +/- 9.1 vs 60.7 +/- 12.3 picograms/ml; p less than 025). These studies provide firm evidence that the platelet dysfunction present in patients with Bartter's syndrome is attributable to an increase in the plasma concentration of 6ketoPGE1. In addition, these data provide further evidence in support of the centrality of activation of prostaglandin metabolism in the pathophysiology of Bartter's syndrome.

Adult↗
PubMed1989

Lack of effect of pertussis toxin on TNF-alpha-induced formation of reactive oxygen intermediates by human neutrophils.

When human PMN were plated on fetal calf serum-coated polystyrene surfaces, addition of TNF-alpha, FMLP or PMA elicited adhesion and H2O2 formation. These effects of TNF-alpha and FMLP, but not of PMA, were impaired by removal of extracellular Ca2+. In addition, H2O2 formation induced by FMLP but not by TNF-alpha or PMA was inhibited by prior treatment with pertussis toxin (250-500 ng/ml). Thus, although the sequelae of TNF-alpha-receptor interaction on human PMN remain to be characterized in detail, they do not involve a pertussis toxin-sensitive GTP-binding protein.

Calcium↗
PubMed1989

2,3-Dihydro-5-benzofuranols as antioxidant-based inhibitors of leukotriene biosynthesis.

The enzymes that catalyze the oxidative metabolism of arachidonic acid have provided fertile ground for the development of useful therapeutic agents for nearly a quarter century. Inhibitors of the enzyme cyclooxygenase prevent the formation of the prostaglandins and thromboxanes and are clinically useful antiinflammatories and peripheral analgesics. More recently it has been discovered that the enzyme 5-lipoxygenase is the first step in the formation of a series of biologically important metabolites of arachidonic acid, the leukotrienes. Evidence suggests that an inhibitor of 5-lipoxygenase may be a useful therapeutic agent in the treatment of asthma, immediate hypersensitivity, and inflammation. Various antioxidants have been examined as inhibitors of 5-lipoxygenase in vitro. We were intrigued by recent reports that the 2,3-dihydro-5-benzofuranol ring system maximizes the stereoelectronic effects necessary for efficient hydrogen atom abstraction by peroxyl radicals. In this study we describe the synthesis of over 50 new 2,3-dihydro-5-benzofuranols and their biological evaluation as inhibitors of leukotriene biosynthesis in isolated human polymorphonuclear leukocytes. We show that the 2,3-dihydro-5-benzofuranol ring system, although not a potent inhibitor of leukotriene biosynthesis in itself, can provide a useful template for the design of antioxidant-based inhibitors of leukotriene biosynthesis. Furthermore, within a structural class the potency of a given analogue can be predicted on the basis of its overall calculated lipophilicity (log P). The data are interpreted in terms of a model in which the observed inhibition by this class of inhibitors is dependent on the intrinsic ability of the antioxidant to reduce the enzyme and on the fraction of the inhibitor that is partitioned into the membrane.

Antioxidants↗
PubMed1989

Evidence for two mechanisms of thrombin-induced platelet activation: one proteolytic, one receptor mediated.

The possibility that thrombin-induced platelet reactivity could occur via both a receptor-related and a proteolytic process was examined. Thrombin elicited the formation of considerably more [32P]phosphatidic acid (an index of phospholipase C catalysed phosphoinositide metabolism) than did platelet activating factor, 5-hydroxytryptamine, ADP, and the thromboxane A2 analogue EP171, when these agents were added either alone or in combination. Co-addition of thrombin and EP171 did not evoke significantly more [32P]phosphatide acid than did thrombin alone. The protease inhibitor leupeptin, decreased but did not abolish [32P]phosphatidic acid formation elicited by either thrombin alone or thrombin in combination with EP171. The serine protease, trypsin, stimulated an increase in [32P]phosphatidic acid and this effect was additive with that of EP171. This augmentation by trypsin of EP171-induced [32P]phosphatidic acid formation was inhibited by leupeptin. These results are consistent with the concept that thrombin-induced activation of phospholipase C occurs by two distinct mechanisms: one via proteolysis, which is sensitive to leupeptin, and the other via receptor activation, a process shared by EP171. The individual components of this dual mechanism can be mimicked by the co-addition of a receptor-directed agonist (EP171) and a proteolytic agent (trypsin).

Adenosine Diphosphate↗
PubMed1988

Agonist-induced calcium flux, phosphoinositide metabolism, aggregation and enzyme secretion in human neutrophils.

Formyl-methionyl-leucyl-phenylalanine (FMLP), platelet activating factor (PAF) and leukotriene B4 (LTB4) are potent activators of human neutrophils. Using human neutrophils prelabelled with the fluorescent indicator dye, Quin 2, or with [32P]-orthophosphate, we examined the effects of these stimuli on intracellular free calcium concentration, [Ca2+]i, and on various indices of phosphoinositide metabolism, including [32P]-phosphatidic acid (PtdA) formation. The concentration-dependence of the observed changed in [Ca2+]i or [32P]-PtdA were then compared to stimulus-induced aggregation and enzyme release (beta-N-acetylglucosaminidase (NAG) and lysozyme). FMLP, PAF and LTB4 caused a concentration-dependent elevation of [Ca2+]i, aggregation and enzyme release. However, unlike FMLP and PAF, LTB4 (less than or equal to 2.5 microM) did not cause significant formation of [32P]-PtdA. The concentration response curves for agonist-induced elevation of [Ca2+]i lie to the left of those for aggregation and enzyme release. FMLP and PAF also caused an elevation of [Ca2+]i at concentrations lower than those required to elicit [32P]-PtdA formation. These observations suggest that [Ca2+]i elevation per se cannot mediate human neutrophil functional responses to FMLP, PAF and LTB4. Consequently there may exist other mediator(s) that act in concert with [Ca2+]i or are triggered by [Ca2+]i elevation to promote human neutrophil activation. Both the elevation of [Ca2+]i and the formation of these putative mediator(s) in response to LTB4 apparently occur independently of inositol phospholipid hydrolysis.

Adult↗
PubMed1987

Effects of protein kinase C activation on human platelet cyclic AMP metabolism.

Treatment of intact human platelets with the tumour-promoting phorbol ester, phorbol 12-myristate 13-acetate (PMA), specifically inhibited PGD2-induced cyclic AMP formation without affecting the regulation of cyclic AMP metabolism by PGI2, PGE1, 6-keto-PGE1, adenosine or adrenaline. This action of PMA was: (i) concentration-dependent; (ii) not mediated by evoked formation or release of endogenous regulators of adenylate cyclase activity (thromboxane A2 or ADP); (iii) mimicked by 1,2-dioctanoylglycerol (DiC8) but not by 4 alpha-phorbol 12,13-didecanoate (which does not activate protein kinase C); (iv) attenuated by Staurosporine. These results indicate that activation of protein kinase C in platelets may provide a regulatory mechanism to abrogate the effects of the endogenous adenylate cyclase stimulant PGD2 without compromising the effects of exogenous stimulants of adenylate cyclase (PGI2, 6-keto-PGE1, adenosine).

Adenosine Diphosphate↗
PubMed1987

Possible mechanisms of the potentiation of blood-platelet activation by adrenaline.

Vasopressin and adrenaline in combination exert synergistic effects on platelet activity. This study investigated the effects of sub-threshold concentrations of adrenaline (0.1-1 microM) on vasopressin (10 nM-1 microM)-induced platelet aggregation, ATP secretion, elevation of cytosolic free Ca2+ concentration ([Ca2+]i) and hydrolysis of inositol phospholipids, monitored as [32P]phosphatidic acid formation. Potentiation of vasopressin-induced aggregation and ATP secretion by adrenaline was accompanied by enhanced elevation of [Ca2+]i and [32P]phosphatidic acid formation. The stimulatory effects of adrenaline on vasopressin-induced platelet activation were mimicked by the combination of the Ca2+ ionophore, ionomycin, and the protein kinase C activator, phorbol 12-myristate 13-acetate, but not by either of these agents alone. These results suggest that the potentiation of vasopressin-induced platelet activation by adrenaline is mediated via enhancement of inositol phospholipid hydrolysis and elevation of [Ca2+]i.

Adenosine Triphosphate↗
PubMed1986

Desensitization and antagonism of vasopressin-induced phosphoinositide metabolism and elevation of cytosolic free calcium concentration in human platelets.

The receptor mechanisms underlying vasopressin-induced human platelet activation were investigated with respect to stimulation of phosphoinositide metabolism and changes in the cytosolic free Ca2+ concentration ([Ca2+]i). Vasopressin stimulated phosphoinositide metabolism, as indicated by the early formation of [32P]phosphatidic acid ([32P]PtdA) and later accumulation of [32P]phosphatidylinositol ([32P]PtdIns). In addition, vasopressin elicited a transient depletion of [glycerol-3H]PtdIns and accumulation of [glycerol-3H]PtdA. The effects of vasopressin on phosphoinositide metabolism were concentration-dependent, with half maximal [32P]PtdA formation occurring at 30 +/- 15 nM-vasopressin. In the presence of 1 mM extracellular free Ca2+, vasopressin induced a rapid, concentration-dependent elevation of [Ca2+]i in quin2-loaded platelets: half-maximal stimulation was observed at 53 +/- 20 nM-vasopressin. The V1-receptor antagonist [1-(beta-mercapto-beta, beta-cyclopentamethylenepropionic acid),2-(O-methyl)tyrosine,8-arginine]-vasopressin selectively inhibited vasopressin (100 nM)-induced [32P]PtdA formation [I50 (concn. giving 50% inhibition) = 5.7 +/- 2.4 nM] and elevation of [Ca2+]i (I50 = 3 +/- 1.5 nM). Prior exposure of platelets to vasopressin rendered them unresponsive, in terms of [32P]PtdA formation and elevation of [Ca2+]i, to a subsequent challenge with vasopressin, but responsive to a subsequent challenge with U44069, a thromboxane-A2 mimetic. These results indicate that vasopressin-induced human platelet activation is initiated by combination with specific V1 receptors on the platelet, and that the sequelae of receptor occupancy (stimulation of phosphoinositide metabolism and elevation of [Ca2+]i) are equally susceptible to inhibition by receptor antagonists and by receptor desensitization.

Arginine Vasopressin↗
PubMed1985

Inhibition of platelet-activating-factor-induced human platelet activation by prostaglandin D2. Differential sensitivity of platelet transduction processes and functional responses to inhibition by cyclic AMP.

It has been proposed that cyclic AMP inhibits platelet reactivity: by preventing agonist-induced phosphoinositide hydrolysis and the resultant formation of 1,2-diacylglycerol and elevation of cytosolic free Ca2+ concentration [( Ca2+]i); by promoting Ca2+ sequestration and/or extrusion; and by suppressing reactions stimulated by (1,2-diacylglycerol-dependent) protein kinase C and/or Ca2+-calmodulin-dependent protein kinase. We used the adenylate cyclase stimulant prostaglandin D2 to compare the sensitivity to cyclic AMP of the transduction processes (phosphoinositide hydrolysis and elevation of [Ca2+]i) and functional responses (shape change, aggregation and ATP secretion) that are initiated after agonist-receptor combination on human platelets. Prostaglandin D2 elicited a concentration-dependent elevation of platelet cyclic AMP content and inhibited platelet-activating-factor(PAF)-induced ATP secretion [I50 (concn. causing 50% inhibition) approximately 2 nM], aggregation (I50 approximately 3 nM), shape change (I50 approximately 30 nM), elevation of [Ca2+]i (I50 approximately 30 nM) and phosphoinositide hydrolysis (I50 approximately 10 nM). A 2-fold increase in cyclic AMP content resulted in abolition of PAF-induced aggregation and ATP secretion, whereas maximal inhibition of shape change, phosphoinositide hydrolysis and elevation of [Ca2+]i required a greater than 10-fold elevation of the cyclic AMP content. This differential sensitivity of the various responses to inhibition by cyclic AMP suggests that the mechanisms underlying PAF-induced aggregation and ATP secretion differ from those underlying shape change. Thus a major component of the cyclic AMP-dependent inhibition of PAF-induced platelet aggregation and ATP secretion is mediated by suppression of certain components of the activation process that occur distal to the formation of DAG or elevation of [Ca2+]i.

Adenosine Triphosphate↗
PubMed1985

Potentiation of adrenaline-induced platelet aggregation by angiotensin II.

The effects of angiotensin II (ANG II) alone and in combination with other agonists on human platelet aggregation, thromboxane B2 (TxB2) and cytosolic [Ca2+]i were investigated. ANG II (10(-11) - 10(-7) M) alone had no direct effect on aggregation, TxB2 production or [Ca2+]i after short- (less than 2 min) or long-term (30 min) incubation. In contrast, low concentrations of ANG II (10(-11) M) enhanced adrenaline-induced platelet aggregation but high concentrations (10(-7) M) had an inhibitory effect. Moreover, ANG II (10(-11) - 10(-7) M) augmented platelet responses to the TxA2 mimetic, U44069. Pretreatment of platelets with flurbiprofen abolished this facilitatory effect of ANG II on adrenaline- but not on U44069-induced platelet aggregation. These results suggest that ANG II stimulation of agonist-induced platelet activation may be due to potentiation of the effects rather than the synthesis of TxA2.

Angiotensin II↗
PubMed1985

Regulation of platelet cytosolic free calcium by cyclic nucleotides and protein kinase C.

PAF elicits a rapid, concentration-dependent elevation of platelet cytosolic free calcium ([Caf]), measured by quin2. Elevation of [Caf] is transient, and the rate of reversal increases with agonist concentration. Adenylate cyclase stimulants (PGI2, PGD2) and 8-bromo cAMP; a guanylate cyclase stimulant (sodium nitroprusside) and 8-bromo cGMP; and a protein kinase C stimulant (phorbol myristate acetate) block the elevation of [Caf] induced by PAF, and accelerate its reversal. These results suggest that cAMP, cGMP and 1,2-diacylglycerol (DAG) could act as second messengers to regulate [Caf] in platelets. As PAF is known to stimulate platelet phosphoinositide hydrolysis (ergo DAG formation) but fails to elevate platelet cAMP or cGMP, it is proposed that DAG, via activation of protein kinase C, may act as an endogenous modulator of platelet [Caf]: an action that contributes to the role of DAG as a bi-directional regulator of platelet reactivity.

Aminoquinolines↗
PubMed1985

Tumour-promoting phorbol esters inhibit agonist-induced phosphatidate formation and Ca2+ flux in human platelets.

Tumour-promoting phorbol esters (phorbol-12-myristate-13-acetate, PMA; phorbol-12,13-dibutyrate, PDBu) but not 4 beta-phorbol, activate protein kinase C. Using human platelets pre-labelled with quin2 or 32PO4 we examined the effects of these compounds on human platelet cytosolic free Ca2+ ([Ca2+]i) and on [32P]phosphatidic acid ([32P]PtdOH). PMA and PDBu, but not 4 beta-phorbol inhibited thrombin-, PAF- and vasopressin-induced elevation of [Ca2+]i and [32P]PtdOH formation. It is suggested that protein kinase C may act to terminate the transduction processes that link receptor occupancy to cellular activation.

Blood Platelets↗