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Biomedical subjects

A McGinty

Publications and source records attributed to A McGinty.

At least 19 recordsLinked to original sources
PubMed2006

Circulating markers of prognosis and response to treatment in patients with midgut carcinoid tumours.

BACKGROUND AND AIMS: Midgut carcinoid tumours are uncommon tumours with an unpredictable clinical behaviour and few useful prognostic markers. Somatostatin analogues are widely used in treatment but a survival advantage has not been proven. We analysed features associated with poor prognosis and assessed the clinical implications of the biochemical response to therapy. METHODS: Clinical and biochemical data were collected for patients with midgut carcinoid tumours attending a tertiary referral neuroendocrine clinic from 1978 to 2000. Using death as the end point, univariate and multivariate survival analyses were performed to identify prognostic indicators. The significance of altering biomarkers with therapy was also studied by including repeated measurements of the most prognostic biochemical parameter in a time dependent covariate survival analysis. RESULTS: We identified 139 patients with sufficient data for our analyses. Factors associated with a poor outcome on univariate analysis included: plasma neurokinin A (NKA), urinary 5-hydroxyindolacetic acid output, age, and >/=5 liver metastases. Plasma NKA was the strongest and only independent predictor of outcome on multivariate analysis. Patients in whom NKA continued to rise despite somatostatin analogues had a significantly worse survival than those in whom NKA stabilised or fell (one year survival rate 40% v 87%). Time dependent covariate analysis concluded that survival was better predicted by the most recent plasma NKA value rather than by the initial value. CONCLUSIONS: Plasma NKA is an accurate marker of prognosis for midgut carcinoid tumours. This is the first paper to support a survival advantage in patients in whom plasma NKA is altered by somatostatin analogues.

Adult↗
PubMed2005

An investigation into the role of Bcl-2 in neuroendocrine differentiation.

INTRODUCTION: In addition to its role in apoptosis suppression, Bcl-2 has been reported to be co-expressed with neuroendocrine markers in several tissues, leading to speculation that this oncoprotein may promote neuroendocrine differentiation. AIM: This study investigated whether Bcl-2 modulated neuroendocrine biopeptide expression. METHODS: Levels of chromogranin A, neurone specific enolase, protein gene peptide 9.5, pancreatic polypeptide, and the chromogranin-derived peptides, intervening peptide and vasostatin-1 were examined by immunocytochemistry in rat phaeochromocytoma (PC12) cell lines genetically engineered to over-express Bcl-2 and their mock-transfected controls. Intensity of fluorescence was graded using a semi-quantitative scale from (-) indicating negative expression to (+++) indicating intense positivity. RESULTS: Mann-Whitney U analysis indicated that no significant differences in expression existed between control and Bcl2 over-expressing cell lines for any of the six peptides examined. CONCLUSIONS: The results of this study do not support the hypothesis that Bcl-2 promotes the acquisition of a neuroendocrine phenotype.

Animals↗
PubMed2000

Induction of prostaglandin endoperoxide synthase 2 by mitogen-activated protein kinase cascades.

Prostaglandin endoperoxide synthase (PGHS) catalyses the rate-limiting step in the formation of prostaglandin and thromboxane eicosanoids from arachidonic acid released by phospholipase A(2). Two forms of PGHS exist, PGHS-1 and PGHS-2. PGHS-2, normally absent from cells, is rapidly expressed in response to a wide variety of stimuli and has been implicated in the pathogenesis of colon cancer and several inflammatory diseases. The three principal mitogen-activated protein kinase (MAPK) pathways are the extracellular signal-regulated protein kinase (ERK), the c-Jun N-terminal kinase (JNK) cascade and the p38-MAPK cascade. The present study was undertaken to investigate the putative involvement of the MAPK cascades in PGHS-2 induction. The potential role of ERK in PGHS-2 up-regulation was assessed by using cell lines expressing, both stably and after adenoviral infection, constitutively active forms of its upstream activator MAPK/ERK kinase (MEK1). The possible involvement of JNK and p38-MAPK in positively modulating PGHS-2 transcription was investigated by using adenovirus-mediated transfer of active forms of their respective specific upstream kinases, mitogen-activated protein kinase kinase (MKK) 7 and MKK3/MKK6. ERK activation promoted the induction of PGHS-2 mRNA and protein. Similarly, activation of JNK by Ad-MKK7D and p38-MAPK by Ad-MKK3bE/Ad-MKK6bE resulted in the increased expression of PGHS-2. These results provide evidence that activation of all three of the major mammalian MAPK leads to the induction of PGHS-2 mRNA and protein. Because PGHS-2 is up-regulated by a diverse range of stimuli, both mitogenic and stress-evoking, these results provide evidence that the convergence point of these stimuli could be the activation of one or more MAPK cascade(s).

3T3 Cells↗
PubMed2000

Cyclooxygenase-2 expression inhibits trophic withdrawal apoptosis in nerve growth factor-differentiated PC12 cells.

Cyclooxygenase-2 (Cox-2), an enzyme responsible for catalyzing the committed step in prostanoid biosynthesis, is the product of an immediate early gene capable of being up-regulated by diverse stimuli. Significantly Cox-2 mRNA is absent from rat pheochromocytoma (PC12) cells, both basally and following stimulation with a range of agonists. Using PC12 cells engineered to stably express isopropyl-1-thio-beta-D-galactopyranoside-inducible Cox-2 (PCXII-4), we have investigated the putative effects of Cox-2 expression on differentiation, proliferation, and trophic withdrawal apoptosis. Cox-2 bioactivity had no effect on nerve growth factor-induced differentiation, epidermal growth factor-induced proliferation, or aromatic L-amino acid decarboxylase expression. However, trophic withdrawal apoptosis, induced by the removal of nerve growth factor following differentiation, was markedly reduced in the PCXII-4 when compared with control cells, as assessed by annexin V staining, DNA laddering, and Hoechst 33258 staining. The specificity of this effect was confirmed using two pharmacologically distinct nonsteroidal anti-inflammatory drugs, indomethacin and NS398. Investigations showed that the activity of the pro-apoptotic protease caspase-3 was reduced in PCXII cells. This study demonstrates that Cox-2-derived prostaglandins exert cytoprotective effects in trophic factor withdrawal apoptosis and provides evidence that this is, at least in part, due to suppression of caspase-3 activity.

Animals↗
PubMed2000

The memory enhancing effects of a Ginkgo biloba/Panax ginseng combination in healthy middle-aged volunteers.

The effects of capsules containing 60 mg of a standardised extract of Ginkgo biloba (GK501) and 100 mg of a standardised extract of Panax ginseng (G115) on various aspects of cognitive function were assessed in healthy middle-aged volunteers. A double blind, placebo controlled, 14 week, parallel group, repeated assessment, multi-centre trial of two dosing regimens, 160 mg b.i.d. and 320 mg o.d. was conducted. Two hundred and fifty-six healthy middle-aged volunteers successfully completed the study. On various study days (weeks 0, 4, 8, 12 and 14) the volunteers performed a selection of tests of attention and memory from the Cognitive Drug Research computerised cognitive assessment system prior to morning dosing and again, at 1, 3 and 6 h later. The volunteers also completed questionnaires about mood states, quality of life and sleep quality. The Ginkgo/ginseng combination was found significantly to improve an Index of Memory Quality, supporting a previous finding with the compound. This effect represented an average improvement of 7.5% and reflected improvements to a number of different aspects of memory, including working and long-term memory. This enhancement to memory was seen throughout the 12-week dosing period and also after a 2-week washout. This represents the first substantial demonstration of improvements to the memory of healthy middle-aged volunteers produced by a phytopharmaceutical.

Adult↗
PubMed2000

Cyclooxygenase 2 promotes cell survival by stimulation of dynein light chain expression and inhibition of neuronal nitric oxide synthase activity.

Cyclooxygenase 2 (COX-2) inhibits nerve growth factor (NGF) withdrawal apoptosis in differentiated PC12 cells. The inhibition of apoptosis by COX-2 was concomitant with prevention of caspase 3 activation. To understand how COX-2 prevents apoptosis, we used cDNA expression arrays to determine whether COX-2 regulates differential expression of apoptosis-related genes. The expression of dynein light chain (DLC) (also known as protein inhibitor of neuronal nitric oxide synthase [PIN]) was significantly stimulated in PC12 cells overexpressing COX-2. The COX-2-dependent stimulation of DLC expression was, at least in part, mediated by prostaglandin E(2). Overexpression of DLC also inhibited NGF withdrawal apoptosis in differentiated PC12 cells. Stimulation of DLC expression resulted in an increased association of DLC/PIN with neuronal nitric oxide synthase (nNOS), thereby reducing nNOS activity. Furthermore, nNOS expression and activity were significantly increased in differentiated PC12 cells after NGF withdrawal. This increased nNOS activity as well as increased nNOS dimer after NGF withdrawal were inhibited by COX-2 or DLC/PIN overexpression. An nNOS inhibitor or a membrane-permeable superoxide dismutase (SOD) mimetic protected differentiated PC12 cells from NGF withdrawal apoptosis. In contrast, NO donors induced apoptosis in differentiated PC12 cells and potentiated apoptosis induced by NGF withdrawal. The protective effects of COX-2 on apoptosis induced by NGF withdrawal were also overcome by NO donors. These findings suggest that COX-2 promotes cell survival by a mechanism linking increased expression of prosurvival genes coupled to inhibition of NO- and superoxide-mediated apoptosis.

Animals↗
PubMed1999

Effect of glucose on endothelin-1-induced calcium transients in cultured bovine retinal pericytes.

Published work has shown that endothelin-1-induced contractility of bovine retinal pericytes is reduced after culture in high concentrations of glucose. The purpose of the present study was to establish the profile of endothelin-1-induced calcium transients in pericytes and to identify changes occurring after culture in high concentrations of glucose. Glucose had no effect on basal levels of cytosolic calcium or on endothelin-1-induced calcium release from intracellular stores. However, influx of calcium from the extracellular medium after endothelin-1 stimulation was reduced in pericytes that had been cultured in 25 mM D-glucose. L-type Ca(2+) currents were identified by patch clamping. The L-type Ca(2+) channel agonist, (-)-Bay K8644, caused less influx of calcium from the extracellular medium in pericytes that had been cultured in 25 mM D-glucose than in those cultured with 5 mM D-glucose. However, 3-O-methylglucose, a nonmetabolizable analogue of glucose which can cause glycation, had similar effects to those of high concentrations of glucose. The results suggest that reduced function of the L-type Ca(2+) channel that occurs in bovine retinal pericytes after culture in high concentrations of D-glucose is probably due to glycation of a channel protein.

Animals↗
PubMed1999

Expression of C5a receptor in mouse brain: role in signal transduction and neurodegeneration.

In this study we explored the potential role of the complement derived anaphylatoxin C5a and the expression of its receptor in mouse brain. Using in situ hybridization, we found that C5a receptor messenger RNA is expressed in mouse brain. In response to intraventricular kainic acid injection, there was marked increase in the C5a receptor messenger RNA expression, particularly in hippocampal formation and cerebral cortex. C5a ligand-binding autoradiography confirmed the functional expression and elevation of the C5a receptor post-lesioning. The expression of C5a receptor messenger RNA in brain was confirmed by northern blot hybridization of total RNA from neuronal and glial cells in vitro. Based on these findings we explored the role of C5a in mechanisms of signal transduction in brain cells. Treatment of primary cultures of mouse astrocytes with human recombinant C5a resulted in the activation of mitogen-activated extracellular signal-regulated protein kinase. This response appeared to be mediated by the C5a receptor since astrocyte cultures derived from C5a receptor knockout mice were not responsive to the treatment. Understanding the regulation of C5a receptor in brain and mechanisms by which pro-inflammatory C5a modulates specific signal transduction pathways in brain cells is crucial to studies of inflammatory mechanisms in neurodegeneration.

Animals↗
PubMed1999

Regulation of leukocyte trafficking by lipoxins.

Lipoxins are lipoxygenase interaction products formed by transcellular metabolism during host defence and inflammation. In model systems, lipoxins modulate polymorphonuclear leukocytes (PMN) chemotaxis, adhesion molecule expression, inhibit PMN-endothelial cell adhesion, and attenuate cytokine release from epithelial cells. These observations raise the possibility that lipoxins are 'stop signals' for PMN-mediated tissue injury and promote the resolution of acute inflammation.

Arachidonic Acids↗
PubMed1998

Different activation of mitogen-activated protein kinases in experimental proliferative glomerulonephritis.

Mitogen-activated protein (MAP) kinases are critical for cell signaling goals such as cellular proliferation and induction of apoptosis. We examined whether MAP kinases, as a point of convergence for multiple extracellular stimuli, are activated in proliferative glomerulonephritis (GN) in vivo. Accelerated crescentic anti-glomerular basement membrane (GBM) GN was induced in rats preimmunized with rabbit IgG by administration of rabbit anti-rat GBM serum. Whole cortical tissue and isolated glomeruli were then subjected to kinase activity assays and Western blot analysis. Cortical activity of the archetypal MAP kinase, extracellular signal-regulated kinase (ERK), was increased significantly one, three, and seven days after induction of GN. In contrast, activation of MAP kinases with antiproliferative actions, stress-activated protein kinase, and p38 MAP kinase was detectable only in the early stages of proliferative GN (days one and three), implying that different MAP kinases serve distinct roles in the pathogenesis of GN.

Animals↗
PubMed1998

Leukotrienes and lipoxins: lipoxygenase-derived modulators of leukocyte recruitment and vascular tone in glomerulonephritis.

With the gradual elucidation of the cellular and molecular events that underpin the inflammatory process, the pathogenetic complexities of glomerulonephritis are slowly being unravelled. Lipoxygenase-derived eicosanoids play important counter-regulatory roles within inflamed glomeruli. Leukotrienes, derived from the 5-lipoxygenase pathway, are potent stimuli for leukocyte infiltration, intrarenal vasoconstriction, and mesangial cell contraction in many forms of experimental glomerulonephritis and probably in human disease. The recruitment of 12- and 15-lipoxygenase pathways, particularly during cell-cell interactions, promotes the formation of lipoxins. The latter compounds antagonize many leukotriene effects, attenuate neutrophil recruitment, and are potential 'braking signals' within the inflammatory cascade that promote resolution of inflammation. The generation and metabolism of leukotrienes and lipoxins is regulated independently, and each family of eicosanoids mediates its biological activities through distinct cell surface receptors and signal transduction pathways. Leukotriene biosynthesis inhibitors and leukotriene receptor antagonists are protective in several experimental models of glomerulonephritis. Initial studies with lipoxins and synthetic lipoxin stable analogues suggest that it may be possible to harness this and other putative anti-inflammatory system for therapeutic gain [3,22,92].

Cell Movement↗
PubMed1998

Protein kinases C: potential targets for intervention in diabetic nephropathy.

Protein kinases C are a family of serine threonine protein kinases that play key roles in extracellular signal transduction. Inappropriate activation of protein kinase C has been implicated in the pathophysiology of many diseases, including diabetes mellitus. Indeed, protein kinase C activation may contribute not only to the pathogenesis of diabetic complications such as nephropathy and retinopathy, but also to insulin resistance. Growing awareness that protein kinase C isoforms subserve specific subcellular functions has led to the development of isoform-specific inhibitors, which may be useful investigational tools and therapeutic agents for attenuating the effects of inappropriate protein kinase C activity. Here we review the role played by protein kinases C in diabetic nephropathy and the recent progress that has been made to modulate its activity using specific inhibitors.

Animals↗
PubMed1997

Activation of extracellular signal-regulated kinase in proliferative glomerulonephritis in rats.

Multiple extracellular mitogens are involved in the pathogenesis of proliferative forms of glomerulonephritis (GN). In vitro studies demonstrate the pivotal role of extracellular signal-regulated kinase (ERK) in the regulation of cellular proliferation in response to extracellular mitogens. In this study, we examined whether this kinase, as a convergence point of mitogenic stimuli, is activated in proliferative GN in vivo. Two different proliferative forms of anti-glomerular basal membrane (GBM) GN in rats were induced and whole cortical tissue as well as isolated glomeruli examined using kinase activity assays and Western blot analysis. Administration of rabbit anti-rat GBM serum to rats, preimmunized with rabbit IgG, induced an accelerated crescentic anti-GBM GN. A significant increase in cortical, and more dramatically glomerular ERK activity was detected at 1, 3, and 7 d after induction of GN. Immunization of Wistar-Kyoto rats with bovine GBM also induced a crescentic anti-GBM GN with an increase of renal cortical ERK activity after 4, 6, and 8 wk. ERK is phosphorylated and activated by the MAP kinase/ERK kinase (MEK). We detected a significant increase in the expression of glomerular MEK in the accelerated form of anti-GBM GN, providing a possible mechanism of long-term activation of ERK in this disease model. In contrast to ERK, activation of stress-activated protein kinase was only detectable at early stages of proliferative GN, indicating these related kinases to serve distinct roles in the pathogenesis of GN. Our observations point to ERK as a putative mediator of the proliferative response to immune injury in GN and suggest that upregulation of MEK is involved in the long-term regulation of ERK in vivo.

Animals↗
PubMed1994

Altered endothelin-1 induced contraction and second messenger generation in bovine retinal microvascular pericytes cultured in high glucose medium.

The effect of simulated hyperglycaemia on bovine retinal pericytes was studied following culture of these cells for 10 days under normal (5 mmol/l) and elevated (25 mmol/l) glucose conditions in the absence of endothelial cells. Pericytes cultured under high ambient glucose exhibited both a delayed and reduced contractile response following stimulation with endothelin-1. Stimulation with 10(-7) mol/l endothelin-1 for 30 s caused significant contraction in cells grown in both 5 mmol/l and 25 mmol/l glucose. The former also contracted significantly with 10(-8) mol/l endothelin-1. Further, at all concentrations tested, statistical comparison of the time course of contraction showed a significant difference (p < 0.02) in the reduction of planimetric surface area between the two cell groups. Since neither binding of endothelin-1 nor the number of receptors for this peptide were significantly different (p > 0.1) between bovine retinal pericytes grown for 10 days under normo- or hyperglycaemic conditions, it became apparent that the altered contractility in bovine retinal pericytes following culture in high glucose must be due to post-binding intracellular disturbance(s). Indeed, both basal and 15 s post-stimulation with 10(-8) mol/l endothelin-1, levels of inositol trisphosphate were significantly reduced (p < 0.05 and p < 0.02, respectively) in pericytes cultured for 10 days in 25 mmol/l glucose. These results show that endothelial-independent alterations in contractility of pericytes occur when they are grown in conditions which simulate hyperglycaemia. The results also suggest that the observed attenuation in response to endothelin-1 stimulation evident in pericytes grown under simulated hyperglycaemic conditions is not due to alterations in peptide binding.

Animals↗
PubMed1993

Characterization of the cysteine proteinases of the common liver fluke Fasciola hepatica using novel, active-site directed affinity labels.

The excreted/secreted proteinases of adult and juvenile Fasciola hepatica maintained in vitro were found to hydrolyse the fluorogenic substrates Cbz-Phe-Arg- and Cbz-Arg-Arg-NHMec. This activity was demonstrated to have a classical cysteine proteinase inhibitor profile, with turn-over of both substrates being blocked by pre-incubation with E64 and peptidyl diazomethanes. The Cbz-Arg-Arg-NHMec hydrolysing activity of the mature fluke exhibited an alkaline stability not characteristic of its mammalian lysosomal counterparts. Further, the biotinylated affinity reagents biotin-Phe-Ala-CHN2 and biotin-Phe-Cys(SBzyl)-CHN2 were used to label and characterize these cysteine proteinases in terms of apparent molecular weight and subsite specificity. Adult fluke media were found to contain four species of molecular weights 66, 58, 50 and 25-26 kDa; juvenile media contained three species of molecular weights 66, 54 and 25-26 kDa. The major 25-26 kDa cysteine proteinase common to both stages was shown to have a subsite specificity similar to that of mammalian cathepsin B.

Affinity Labels↗
PubMed1992

The synthesis, kinetic characterization and application of a novel biotinylated affinity label for cathepsin B.

In this study we report on the synthesis, kinetic characterization and application of a novel biotinylated and active-site-directed inactivator of cathepsin B. Thus the peptidyldiazomethane biotinyl-Phe-Ala-diazomethane has been synthesized by a combination of solid-phase and solution methodologies and has been shown to be a very efficient inactivator of bovine and human cathepsin B. The respective apparent second-order rate constants (k0bs./[I]) for the inactivation of the human and bovine enzymes by this reagent, namely approximately 5.4 x 10(4) M-1.min-1 and approximately 7.8 x 10(4) M-1.min-1, compare very favourably with those values determined for the urethane-protected analogue benzyloxycarbonyl-Phe-Ala-chloromethane first described by Green & Shaw [(1981) J. Biol. Chem. 256, 1923-1928], thus demonstrating that the presence of the biotin moiety at the P3 position is compatible with inhibitor effectiveness. The utilization of this reagent for the detection of cathepsin B in electrophoretic gels, using Western blotting and in combination with a streptavidin/alkaline phosphatase detection system, is also demonstrated. Given that the peptidyldiazomethanes exhibit a pronounced reactivity towards cysteine proteinases, we feel that the present label may well constitute the archetypal example of a wide range of reagents for the selective labelling of this class of proteinase, even in a complex biological milieu containing additional classes of proteinases.

Affinity Labels↗