PubMed Health⌕ Search

Biomedical subjects

A M Gorman

Publications and source records attributed to A M Gorman.

At least 19 recordsLinked to original sources
PubMed2005

Hypoxia induces neurite outgrowth in PC12 cells that is mediated through adenosine A2A receptors.

Development of the nervous system is a complex process, involving coordinated regulation of diverse cellular processes including proliferation, differentiation and synaptogenesis. Disturbances to brain development such as pre- and perinatal hypoxia have been linked to behavioural and late onset of neurological disorders. This study examines the effect of hypoxia on neurite outgrowth in PC12 cells. Hypoxia not only caused a rapid induction of neurite outgrowth, but also synergistically enhanced nerve growth factor (NGF)-induced neurite outgrowth up to 24 h. Transactivation of TrkA receptors was ruled out since the TrkA inhibitor K252a did not block hypoxia-induced neurite outgrowth. Adenosine deaminase prevented hypoxia-induced neurite outgrowth indicating that the effect is mediated by adenosine. Use of the specific adenosine A2A receptor agonist CGS21680 and antagonist 8-3(chlorostyryl)caffeine demonstrated that activation of this receptor is critical for hypoxia-induced neurite outgrowth. Hypoxia-induced neurite outgrowth was blocked by the adenylate cyclase inhibitor, MDL-12,330A, indicating a role for activation of this enzyme in the pathway. Hypoxia was further shown to cause a decrease in growth-associated protein (GAP)-43 levels and a lack of induction of betaIII tubulin, in contrast to NGF treatment which resulted in increased cellular levels of both of these proteins. These findings suggest that hypoxia induces neurite outgrowth in PC12 cells via a pathway distinct from that activated by NGF. Thus, exposure to hypoxia at critical stages of development may contribute to aberrant neurite outgrowth and could be a factor in the pathogenesis of certain delayed developmental neurological disorders.

Adenosine↗
PubMed2003

On the role of Hsp27 in regulating apoptosis.

Heat shock proteins (Hsps) comprise several different families of proteins that are induced in response to a wide variety of physiological and environmental insults. One such protein which is highly induced during the stress response is a 27-kDa protein, termed Hsp27 whose expression is seen to correlate with increased survival in response to cytotoxic stimuli. It has been shown to prevent cell death by a wide variety of agents that cause apoptosis. Hsp27 is a molecular chaperone with an ability to interact with a large number of proteins. Recent evidence has shown that Hsp27 regulates apoptosis through an ability to interact with key components of the apoptotic signalling pathway, in particular, those involved in caspase activation and apoptosis. This article will review recent advances in the field and will address some of the potential mechanisms by which Hsp27 functions as an anti-apoptotic molecule.

Animals↗
PubMed2001

Apoptotic morphology does not always require caspase activity in rat cerebellar granule neurons.

The death of a cell via apoptosis is characterized by morphological changes including cell shrinkage and nuclear condensation. Intracellularly, proteases, including caspases, are activated. In the present article we have compared the ability of three different neurotoxic agents to induce caspase activity in cerebellar granule cells (CGC). These compounds are the microtubule-disrupting agent colchicine and the oxidative stress-inducing agents hydrogen peroxide and methylmercury (MeHg). We have previously shown that each of these agents causes nuclear changes that are consistent with apoptosis, i.e., induction of chromatin condensation and DNA cleavage into fragments of regular size (700, 300 and 50 kbp). However, only colchicine causes a large increase in caspase activity, as monitored by the ability of whole cell extracts to cleave the synthetic caspase substrate DEVD-MCA. In contrast, MeHg and hydrogen peroxide do not induce any significant increase of DEVDase activity as compared to control cells. Immunocytochemistry confirms that active caspase-3 is abundant only in colchicine-exposed cells. In agreement with these findings, the pan-caspase inhibitor, z-VAD-fmk, is efficient in protecting CGC against colchicine, but not against hydrogen peroxide or MeHg. These data suggest that in CGC the activation of caspases is not always required to induce morphological changes and pattern of DNA fragmentation consistent with apoptosis.

Journal Article↗
PubMed2000

Dexamethasone pre-treatment interferes with apoptotic death in glioma cells.

Glucocorticoids are known to influence the ability of cells to undergo apoptosis, directly inducing apoptosis in thymocytes while inhibiting it in hepatoma and carcinoma cells. Dexamethasone, a synthetic glucocorticoid, is reported to induce partial resistance to certain anticancer drugs in glioma cell lines. In the present study, the effect of dexamethasone on apoptosis of glioma and astrocytoma cell lines was investigated. Exposure of D384 human astrocytoma and C6 rat glioma cells to staurosporine induced apoptosis as judged by the formation of condensed nuclei and caspase activation. Pre-treatment of cells with dexamethasone caused a reduction in staurosporine-induced apoptosis. In addition, dexamethasone also conferred protection against the induction of apoptosis by anticancer agents including camptothecin and etoposide. The protective effect of dexamethasone was dose and time dependent, with maximal protection obtained with concentrations equal to or greater than 100 nM and a pre-incubation period of at least 24h. The earliest significant inhibition was seen with a pre-incubation period of 8h. Co-treatment with the glucocorticoid receptor antagonist RU38486 abolished the effect of dexamethasone, indicating that the protection due to dexamethasone is mediated via this receptor. Dexamethasone was found to induce a time-dependent up-regulation of Bcl-x(L) protein expression. However, the ability of cytochrome c/dATP to activate the caspase cascade in cytosolic extracts of D384 cells was unaffected by prior exposure of the cells to dexamethasone (1 microM) for 48 h. In conclusion, dexamethasone inhibits the induction of apoptosis in astrocytoma cells, probably via an up-regulation of Bcl-x(L), which could prevent cytochrome c release from mitochondria and subsequent caspase activation. Since glucocorticoids are often used in the treatment of gliomas to relieve cerebral oedema, the inhibition of apoptosis by these compounds could potentially interfere with the efficacy of chemotherapeutic drugs.

Animals↗
PubMed1999

Application of a fluorometric assay to detect caspase activity in thymus tissue undergoing apoptosis in vivo.

To date, in vivo apoptosis within the thymus has been assessed using morphological criteria and/or detection of a DNA ladder indicative of oligonucleosomal fragmentation of the DNA. Here, we have used a fluorometric method to investigate activation of the caspase protease family in the thymus following in vivo induction of apoptosis by injection of the synthetic glucocorticoid hydrocortisone. Cleavage of DEVD-MCA by caspase-3 and other group II caspases releases free MCA which can be detected fluorimetrically. We demonstrate a time-dependent increase in DEVD-MCA cleavage activity within this tissue indicating the activation of caspase-3 like enzymes. This activity was inhibited by the specific group II caspase inhibitor DEVD-CHO. The interpretation of increased caspase activity was confirmed by immunoblot analysis to reveal cleavage of the caspase-3 substrate, fodrin. In addition, agarose gel electrophoresis of the DNA yielded a ladder pattern, confirming the occurrence of apoptosis. This study demonstrates that DEVD-MCA cleavage activity may be a useful quantitative method for the analysis of apoptosis in thymus tissue. It is a relatively rapid procedure not requiring thymocyte isolation or gel electrophoresis and detects fairly early biochemical changes occurring during apoptosis. In the present study we have used this method to demonstrate the involvement of caspases in thymocyte apoptotic death induced in vivo by glucocorticoids. Thus, measurement of caspase activity in thymus tissue may have applications for studying the in vivo effects of immunotoxicants.

Animals↗
PubMed1999

Antioxidant-mediated inhibition of the heat shock response leads to apoptosis.

We examined the hypothesis that reactive oxygen species (ROS) contribute to the induction of heat shock proteins (hsps) during stress response. Exposure of HL-60 human myelocytic cells to 42 degrees C induced both hsp72 and hsp27. In the presence of the antioxidant molecules pyrrolidine dithiocarbamate or 1,10-phenanthroline induction of hsp72 and 27 was significantly decreased, while N-acetyl-L-cysteine caused a slight reduction. Prevention of hsp induction was associated with heat sensitization and increased caspase activity, indicating that the cells were undergoing apoptosis. These data suggest that ROS contribute to the induction of hsps and furthermore, that hsp induction and apoptosis are mutually exclusive events within the same cell.

Antioxidants↗
PubMed1999

Cytochrome c release and caspase-3 activation during colchicine-induced apoptosis of cerebellar granule cells.

The microtubule-disrupting agent colchicine is known to be neurotoxic toward certain neuronal populations including cerebellar granule cells (CGCs). In this study we investigated the involvement of cytochrome c release and caspase-3 activation during colchicine-induced CGC apoptosis. Treatment of rat CGCs with 1 micrometer colchicine (for up to 24 h) caused high molecular weight DNA fragmentation and nuclear condensation. An involvement of group II caspases (which includes caspase-3) was demonstrated by the proteolytic degradation of poly(ADP-ribose) polymerase (PARP) after 18 h exposure to colchicine. Colchicine induced a time-dependent increase in Ac-Asp-Glu-Val-Asp-alpha-(4-methyl-coumaryl-7-amide) (DEVD-MCA) cleavage activity in CGCs, which was blocked with a specific, peptide-based, aldehyde inhibitor of group II caspases, i. e. DEVD-CHO. We also observed a time-dependent proteolysis of caspase-3 as judged by the appearance of p17 which is one of the subunits of active caspase-3. Activation of caspase-3 during colchicine-induced apoptosis may be mediated by cytochrome c since there was a close correlation between the time courses of cytochrome c release from the mitochondria and of caspase-3 activation. Furthermore, colchicine-induced apoptosis, as assessed by propidium iodide visualization of the nuclei, could be blocked by the caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp (O-methyl) fluoromethyl ketone.

Amino Acid Chloromethyl Ketones↗
PubMed1998

Apoptosis in neuronal cells: role of caspases.

Apoptosis is a controlled form of cell death involving cascades of degradative events. Proteolysis during apoptosis is largely due to the activity of a family of cysteine proteases called caspases. In recent years different roles for members of this family have been revealed. In the central nervous system caspase-2 is highly expressed in the brain during development although many caspases are expressed at low levels in the adult. However, an involvement of caspases in apoptosis of mature neurons has been demonstrated in vivo, where specific inhibitors of caspases are found to protect against ischemic injury. We have reviewed the evidence for the existence of caspases in the central nervous system and their activation during neuronal cell death.

Animals↗
PubMed1997

Use of flow cytometry techniques in studying mechanisms of apoptosis in leukemic cells.

The use of flow cytometric techniques has significantly aided the rapid advancement of our understanding of the process of apoptosis. Our laboratory is currently involved in investigating the ways in which cells can be induced to die and some of the signals that may be involved. To this end, we are using flow cytometry to detect apoptosis in cell cultures and to measure intracellular changes that occur during apoptosis, in particular, alterations in parameters such as mitochondrial function, oxidative stress, and gene expression. In this review of recent and ongoing research in our laboratory, we outline our studies on mechanisms of apoptosis by cytotoxic drugs, particularly in relation to the involvement of oxidative stress. In addition, we are studying the increased sensitivity to apoptosis seen in K652 cells that have been transfected with the p53 gene.

Animals↗
PubMed1996

Apoptosis -- the story so far....

The process of programmed cell death, or apoptosis, has become one of the most intensively studied topics in biological sciences in the last two decades. Apoptosis as a common and universal mechanism of cell death, distinguishable from necrosis, is now a widely accepted concept after the landmark paper by Kerr, Wyllie and Currie in the early seventies [1]. Different components of the death machinery in eukaryotes are discussed in this issue.

Apoptosis↗
PubMed1996

Reactive oxygen intermediate(s) (ROI): common mediator(s) of poly(ADP-ribose)polymerase (PARP) cleavage and apoptosis.

HL-60 acute myeloblastic and U937 monoblastoid leukaemic cell lines both cleave poly(ADP-ribose)polymerase (PARP), at the onset of apoptosis, in response to a wide range of cytotoxic agents. This appears to be a common feature of leukaemic cell apoptosis. However, in the chronic myelogenous leukaemic (CML) derived cell line, K562, no such cleavage was detectable. This correlated with previous findings that this cell line is particularly resistant to apoptosis induced by cytotoxic agents. Proteolytic cleavage of PARP and the subsequent progression to apoptosis was inhibited by two protease inhibitors NEM and IOD. As both PARP cleavage and DNA fragmentation appeared closely linked in these cell lines, anti-oxidants (previously shown to be effective inhibitors of DNA fragmentation and apoptosis) were also demonstrated to prevent PARP cleavage. These results combine to suggest that ROI may mediate PARP cleavage, DNA fragmentation and the eventual apoptosis of these cells following cytotoxic insult.

Antioxidants↗
PubMed1996

Oxidative stress and apoptosis in neurodegeneration.

The pathogenesis of neurodegenerative diseases such as Parkinson's diseases, amyotrophic lateral sclerosis and Alzheimer's disease is unknown. These diseases are characterized by a slow, progressive loss of particular subsets of neurons. Much evidence has accumulated which supports the hypothesis that oxidative stress and damage by free radicals may play an important part in these diseases. In particular recent studies with the inherited form of amyotrophic lateral sclerosis have revealed mutations in the superoxide dismutase gene, which is one of the cell's main defence mechanisms against oxidative stress. These findings suggest a direct link between oxidative stress and the development of a neurodegenerative disease.

Apoptosis↗
PubMed1996

Donor-to-donor and donor-to-patient transmission of hepatitis C virus.

A patient was reported with suspected acute post-transfusion hepatitis C virus (HCV) infection, 5 months after the transfusion of 2 units of red cells. The archived serum samples of the two implicated donations were retested by the original 3rd-generation assay together with another 3rd-generation assay and RI-BA III, and were tested for HCV RNA using the PCR. Both donations were anti-HCV negative but one was found to be PCR positive. This donor was a regular donor and was identified as the husband of a donor identified 18 months earlier as being HCV positive. This case is an example of transmission of HCV in the window period of infection, and a probable example of the transmission of HCV from wife to husband through intimate contact.

Blood Donors↗
PubMed1996

The repression of apoptosis by activated abl oncogenes in chronic myelogenous leukaemia.

The formation of the unique fusion gene, bcr-abl, and the resultant increase in abl tyrosine kinase activity, is seen as the major driving force in the initiation of chronic myelogenous leukaemia (CML). The deregulation of abl tyrosine kinase activity, brought about by the binding of a portion of the Scr molecule to the SH2 regulatory domain of abl, appears to play a role in promoting resistance to drug-induced apoptosis. Thus the large increase In mature myeloid cells seen in CML could be the direct result of the suppression of apoptosis by the bcr-abl fusion protein. The role and contribution of apoptosis in the progression of CML and the possible role of antisense oligonucleotides to the bcr-abl gene as therapeutic agents is discussed.

Apoptosis↗
PubMed1995

Hepatitis B transmission from contaminated cryopreservation tank.

Over a 25-month period, six multiply transfused patients undergoing cytotoxic treatment for haematological or other malignant disorders developed icteric acute hepatitis B virus (HBV) infection. Bone marrow or peripheral-blood stem cells had been harvested from all six patients and stored in the same cryopreservation tank for possible future transplantation. Human DNA, HBsAg, and HBV DNA with sequences identical to those from four patients with related infections were subsequently found in the liquid nitrogen. Leakage of the cryopreservation bags used to store bone marrow harvested from the first patient when acutely infected with HBV led to contamination of the tank and its contents with HBV and subsequent transmission to patients after transplantation. This incident emphasises the continuing need to screen donors of tissue to be cryopreserved for bloodborne virus infections. It also reinforces the requirement for primary containers used to cryopreserve human tissue to be sealed in a way which prevents exchange of material between the specimen and the liquid nitrogen.

Acute Disease↗
PubMed1995

Excitatory amino acid-induced cytotoxicity in primary cultures of mouse cerebellar granule cells correlates with elevated, sustained c-fos proto-oncogene expression.

An elevated, sustained expression of c-fos mRNA was found in primary cultures of mouse cerebellar granule cells following exposure to toxic concentrations of the excitatory amino acids, L-glutamate, L-homocysteate, S-sulpho-L-cysteine and N-methyl-D-aspartate (NMDA), using leakage of lactate dehydrogenase (LDH) as an indicator of cytotoxicity. In contrast, when used at non-toxic concentrations these compounds induced a rapid and transient increase in c-fos mRNA levels. Both LDH release and elevated, sustained c-fos mRNA induction were blocked (in the case of L-homocysteate) or reduced (in the case of L-glutamate and S-sulpho-L-cysteine) by the selective NMDA receptor antagonist (DL(+/-)-2-amino- 5-phosphonopentanoic acid) whereas 6-cyano-7-nitroquinoxaline-2,3-dione (a selective antagonist at non-NMDA ionotropic receptors) had no effect. These data suggest a role for altered c-fos mRNA expression in excitotoxic mechanisms.

Animals↗