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Biomedical subjects

S J Martin

Publications and source records attributed to S J Martin.

At least 73 records · Page 4Linked to original sources
PubMed1996

In vitro synergy testing of macrolide-quinolone combinations against 41 clinical isolates of Legionella.

Combination antimicrobial therapy against Legionella species has not been well studied. Several quinolones have activity against Legionella strains, which prompted this in vitro search for a synergistic combination with the macrolides. By a checkerboard assay, erythromycin, clarithromycin, and azithromycin, each in combination with ciprofloxacin and levofloxacin, were tested for synergy against 46 isolates of Legionella. The agar dilution method was employed using buffered charcoal-yeast extract media. A final inoculum of 10(4) CFU per spot was prepared from 24-h growth of each isolate. Plates were incubated at 35 degrees C for 48 h. Synergy, partial synergy, additive effect, or indifference was observed for all combinations of antibiotics tested. There was no antagonism observed. Synergy occurred to a significantly greater extent for the clarithromycin-levofloxacin (P = 0.0001) and azithromycin-levofloxacin (P = 0.003) combinations versus erythromycin-levofloxacin. The azithromycin-ciprofloxacin combination demonstrated significantly greater synergy than did either erythromycin-ciprofloxacin (P = 0.003) or clarithromycin-ciprofloxacin (P = 0.001). The newer macrolides clarithromycin and azithromycin may be more active in combination with a fluoroquinolone than is erythromycin.

Anti-Bacterial Agents↗
PubMed1996

Enzymatic debridement for necrotic wounds.

In a randomised, double-blind, controlled trial, a comparison was made of the relative efficacy of using streptokinase/streptodornase (Varidase) in a hydrogel (KY Jelly) or the hydrogel alone in the debridement of Grade IV pressure sores. Seventeen subjects aged 57-94 years (mean age 81) took part; 21 sores were studied, 11 of which were randomised to the enzyme treatment regime. Both treatments led to eschar removal; fewer days were needed in the hydrogel-only group (mean 8.1 days, sd 1.8) compared to the enzyme/hydrogel group (mean 11.8 days, sd 2.9), but this was not statistically significant. The results suggest that the use of hydrogel alone may be a cost-effective alternative to the use of streptokinase/streptodornase and hydrogel in the treatment of these wounds.

Cost-Benefit Analysis↗
PubMed1995

Cell-free reconstitution of Fas-, UV radiation- and ceramide-induced apoptosis.

Cell-free systems are valuable tools for the dissection of complex cellular processes. Here we show that cytoplasmic extracts from cells exposed to anti-Fas antibody or UV radiation contain an activity capable of reproducing morphological changes typical of apoptosis in nuclei added to these extracts, as well as internucleosomal cleavage of DNA and proteolysis of a protein known to be cleaved during the apoptosis of intact cells. Extracts from control cell populations were inactive in this respect. These effects were partly blocked by the addition of purified Bcl-2 protein or a competitive inhibitor peptide of interleukin-1 beta-converting enzyme to the extracts. Furthermore, apoptotic activity was induced in cytoplasmic extracts from untreated cells by the addition of ceramide, a lipid second messenger implicated recently in apoptosis signaling. These extracts should prove highly useful in the dissection of molecular events that occur during apoptosis.

Animals↗
PubMed1995

Early redistribution of plasma membrane phosphatidylserine is a general feature of apoptosis regardless of the initiating stimulus: inhibition by overexpression of Bcl-2 and Abl.

A critical event during programmed cell death (PCD) appears to be the acquisition of plasma membrane (PM) changes that allows phagocytes to recognize and engulf these cells before they rupture. The majority of PCD seen in higher organisms exhibits strikingly similar morphological features, and this form of PCD has been termed apoptosis. The nature of the PM changes that occur on apoptotic cells remains poorly defined. In this study, we have used a phosphatidylserine (PS)-binding protein (annexin V) as a specific probe to detect redistribution of this phospholipid, which is normally confined to the inner PM leaflet, during apoptosis. Here we show that PS externalization is an early and widespread event during apoptosis of a variety of murine and human cell types, regardless of the initiating stimulus, and precedes several other events normally associated with this mode of cell death. We also report that, under conditions in which the morphological features of apoptosis were prevented (macromolecular synthesis inhibition, overexpression of Bcl-2 or Abl), the appearance of PS on the external leaflet of the PM was similarly prevented. These data are compatible with the notion that activation of an inside-outside PS translocase is an early and widespread event during apoptosis.

ATP Binding Cassette Transporter, Subfamily B↗
PubMed1995

Regulation of the Fas apoptotic cell death pathway by Abl.

Relatively little is known about oncogene involvement in the regulation of Fas-mediated apoptosis. Inhibition of Fas-induced cell death by the bcl-2 oncogene has been demonstrated to be only partial. In light of a growing body of evidence for the Abl kinase as a negative regulator of cell death, we sought to determine whether Abl expression could protect against Fas-mediated cell death. To address this question, we utilized two separate strategies. In the first, we expressed human Fas in K562, a chronic myelogenous leukemia cell line, which constitutively expresses bcr-abl and examined the effects of Fas ligation in these cells. Fas-positive K562 transformants (K562.Fas) were found to be protected against Fas-mediated cell death. However, down-regulation of Bcr-Abl protein levels in K562.Fas cells using antisense oligonucleotides targeted to bcr-abl mRNA rendered these cells highly susceptible to Fas-induced death. In the second approach we utilized a Fas-positive HL-60 cell line, which we transfected with a temperature-sensitive mutant of v-Abl. HL-60.v-Ablts transfectants were found to be protected from Fas-induced apoptosis at the permissive but not the restrictive temperature for the Abl kinase. Taken together, these observations identify the Abl kinase as a negative regulator of Fas-mediated cell death. Since Abl was also found to block apoptosis mediated by ceramide, a recently proposed downstream effector of the apoptotic pathway initiated by Fas, we propose that Abl exerts its protective effects downstream of the early Fas-initiated signaling events.

Antigens, Surface↗
PubMed1995

Proteolysis of fodrin (non-erythroid spectrin) during apoptosis.

Several recent studies have implicated proteases as important triggers of apoptosis. Thus far, substrates that are cleaved during apoptosis have been elusive. In this report we demonstrate that cleavage of alpha-fodrin (non-erythroid spectrin) accompanies apoptosis, induced by activation via the CD3/T cell receptor complex in a murine T cell hybridoma, ligation of the Fas (CD95) molecule on a human T cell lymphoma line and other Fas-expressing cells, or treatment of cells with staurosporine, dexamethasone, or synthetic ceramide. Furthermore, inhibition of activation-induced apoptosis by pretreatment of T hybridoma cells with antisense oligonucleotides directed against c-myc also inhibited fodrin proteolysis, confirming that this cleavage process is tightly coupled to apoptosis. Fodrin cleavage during apoptosis may have implications for the membrane blebbing seen during this process.

Animals↗
PubMed1995

Cell-autonomous Fas (CD95)/Fas-ligand interaction mediates activation-induced apoptosis in T-cell hybridomas.

A number of murine T-cell hybridomas undergo apoptosis within a few hours of activation by specific antigens, mitogens, antibodies against the T-cell antigen receptor, or a combination of phorbol ester and calcium ionophore. This phenomenon has been extensively studied as a model for clonal deletion in the immune system, in which potentially autoreactive T cells eliminate themselves by apoptosis after activation, either in the thymus or in the periphery. Here we show that the Fas/CD95 receptor, which can transduce a potent apoptotic signal when ligand, is rapidly expressed following activation of T-cell hybridomas, as is its functional, membrane-bound ligand. Interference with the ensuing Fas/Fas-ligand interaction inhibits activation-induced apoptosis. Because T-cell receptor ligation can induce apoptosis in a single T hybridoma cell, we suggest that the Fas/Fas-ligand interaction can induce cell death in a cell-autonomous manner.

Animals↗
PubMed1995

The killer and the executioner: how apoptosis controls malignancy.

An escalating research effort focused on apoptotic cell death continues to chip away at the central mechanisms of this intriguing process. One of the areas in which this research has already yielded fundamental insights is in the analysis of oncogenesis, where defects in cell death can have profound effects. Recent progress has been made in understanding the processes of apoptosis induction, transduction, and effect (or 'execution'), especially with respect to our understanding of malignancy, hyperplasia and related phenomena.

Animals↗
PubMed1995

Inhibition of ceramide-induced apoptosis by Bcl-2.

Ceramide, a long chain sphingolipid that is generated intracellularly upon hydrolysis of membrane-associated sphingomyelin, has recently been implicated as a second messenger-like molecule that is produced distal to ligation of the tumour necrosis factor receptor type 1 (TNFR1), as well as the related Fas (CD95/Apo-1) molecule. It is well established that ligation of TNFR1 or Fas leads to apoptosis in most cases. Furthermore, it has also recently been demonstrated that exposure to cell-permeable synthetic ceramides can result in apoptosis in many cases. These and other observations have led to the hypothesis that accumulation of intracellular ceramide may be a common element of several pathways that result in apoptosis. Here we show that exposure to synthetic ceramides triggers apoptosis in the human T lymphoblastoid cell lines, CEM and Jurkat, and that overexpression of the apoptosis-repressor protein, Bcl-2, renders these cells resistant to the apoptosis-inducing effects of ceramide, as well as to several other stimuli. Since exposure to ceramides can result in either cell proliferation, differentiation, cycle arrest, or death, the level of Bcl-2 expression in a cell may be an important factor in determining the outcome of signals that result in intracellular generation of this sphingolipid.

Journal Article↗
PubMed1995

Th1 cells specific for HIV-1 gag p24 are less efficient than Th0 cells in supporting HIV replication, and inhibit virus replication in Th0 cells.

This report provides three lines of evidence to suggest that T-helper type 1 (Th1) and type 0 (Th0) cells could play an opposing role in acquired immune deficiency syndrome (AIDS). Using a panel of Th1 and Th0 clones specific for human immunodeficiency virus-1 (HIV-1) gag p24, derived from seronegative volunteers immunized with gag p24: Ty virus-like particles, a Th1 clone specific for tuberculin (PPD), and a Th0 clone derived by random activation from the same volunteer, we have demonstrated the following differences in the capacity of these clones to regulate the in vitro replication of HIV. (1) Th1 clones were less efficient than Th0 clones in supporting HIV replication, both in their resting state (by 10-1000-fold) and after antigen activation (by five to 100-fold). Furthermore, the infectious titre of HIV recovered from the Th0 population was more than 1000-fold higher than virus from the Th1 population, and the number of HIV-infected Th0 cells was five to 16 times higher than the number of infected Th1 cells. (2) Antigen- or mitogen-activated Th1, but not Th0 clones, inhibited HIV in bystander CEM-4 cells. Th1 cells also inhibited HIV in autologous and allogeneic Th0 cells. The level of inhibition in these experiments ranged from 50% to 100% and was three to 10-fold higher and more sustained in the presence of p24-specific clones compared to the PPD-specific Th1 clone. The capacity of Th1 cells to inhibit HIV in neighbouring cells was also reflected in the reduced replication of HIV in the clones immediately after antigen activation compared to unstimulated cells. Kinetic studies of virus production, cytokine release and proliferation showed that inhibition of HIV was associated with peak cytokine release and preceeded proliferation. (3) The Th1 clones had higher cytolytic potential than the Th0 clones. Therefore, the HIV inhibitory activity of Th1 cells could be partly due to cell to cell killing. These data demonstrate the opposing effects of Th1 and Th0 cells on the in vitro replication of HIV, and suggest that Th1 cells might be important in immunity whereas Th0/Th2 cells might lay a role in promoting disease.

CD4-Positive T-Lymphocytes↗
PubMed1994

HIV-1 infection of human CD4+ T cells in vitro. Differential induction of apoptosis in these cells.

The H9 and CEM CD4+ T cell lines were infected with HIV-1 (NY5/LAV-1 isolate) and monitored for losses in cell viability, syncytium formation, and internucleosomal DNA cleavage (a marker for apoptosis). H9 cells were found to undergo cell death via apoptosis as a result of HIVNY5 infection, but this effect was not apparent in CEM cell cultures. The differential effects of HIV-1NY5 in terms of its apoptosis-inducing properties correlated with the relative abilities of H9 and CEM cells in supporting replication of this HIV-1 isolate, since infected CEM cell cultures produced 10-fold lower levels of HIV-1 p24 protein, and very few of these cells stained positive for cell-associated p24 by comparison with H9 cell cultures infected at the same multiplicity of infection. Furthermore, a different HIV-1 isolate (RF), which replicated equally efficiently in both H9 and CEM cells, produced similar levels of apoptosis in these cultures. HIV-1NY5 was also found to be capable of inducing apoptosis in purified peripheral blood CD4+ T cells as well as inhibiting anti-CD3-driven proliferation of these cells. In contrast, incubation of purified CD8+ T cells with HIV-1NY5 under similar conditions produced no cytopathic effects. Substantial levels of apoptosis were also recorded in HIV-1NY5-infected PHA blasts cell cultures. Soluble rHIV-1IIIB type CHO-derived gp120 was found to mimic the effects of HIV in terms of inhibition of anti-CD3/TCR mAb-induced proliferation of T cells, but apoptosis was not detected in gp120-treated T cell cultures whether cross-linked or used in conjunction with anti-CD3 mAb or not. We conclude therefore that both HIV-1NY5 and HIV-1RF isolates have the capacity to directly trigger apoptotic cell death in CD4+ T cells and that this appears to be at least partly associated with the efficiency of virus replication in these cells.

Apoptosis↗