Search PubMed⌕ Search

Biomedical subjects

M S Marber

Publications and source records attributed to M S Marber.

At least 55 records · Page 3Linked to original sources
PubMed1998

The expression of constitutively active isotypes of protein kinase C to investigate preconditioning.

The role of protein kinase C (PKC) in ischemic preconditioning remains controversial because of difficulties with both its measurement and pharmacological manipulation. We investigated preconditioning in isolated neonatal rat cardiocytes by expressing constitutively active isotypes of PKC. Observations at differing durations of simulated ischemia suggested beta-galactosidase (beta-gal) activity reflected viability within transfected myocytes. Preconditioning with 90 min of ischemia significantly increased beta-gal activity and myocyte survival after 6 h of ischemia; an effect abolished by PKC inhibitors. After co-transfection with plasmids encoding beta-gal and either constitutively active mutants of PKC-delta, PKC-alpha, wild type PKC-delta, or empty vector, cardiocytes were subjected to 6 h of ischemia. Only PKC-delta, rendered constitutively active by a limited deletion within the pseudosubstrate domain, consistently increased resistance to simulated ischemia (beta-gal activity was 85.6 +/- 11.9% versus 53.7 +/- 6.5% (p </= 0.01) and dead myocytes 46.8 +/- 3.4% versus 68.7 +/- 2.8% (p </= 0.01)). Since transfection was apparent in only 5-12% of cells, the results suggested a protective bystander effect that was confirmed by co-culture of transfected myocytes with untransfected myocytes. In neonatal cardiocytes expression of active PKC-delta increases resistance to simulated ischemia. This observation may provide further insight into the mechanism and possible avenues for therapeutic exploitation of preconditioning.

Animals↗
PubMed1998

Cardiotrophin-1 induces heat shock protein accumulation in cultured cardiac cells and protects them from stressful stimuli.

Cardiotrophin-1 (CT-1) was originally identified as a molecule capable of inducing cardiac hypertrophy. We show here that treatment of cultured neonatal cardiocytes with CT-1 induces enhanced synthesis of the heat shock proteins hsp70 and hsp90, with hsp70 levels being enhanced three-fold and hsp90 levels being enhanced seven-fold. Such CT-1-treated cells are protected against subsequent exposure to severe thermal or ischaemic stress, as assayed both by measures of total cell death, such as trypan blue exclusion and LDH release, and by measures of apoptosis, such as propidium-iodide-staining and TUNEL-labelling. Hence, CT-1 can induce the protective hsps and protect cardiac cells from diverse stresses.

Animals↗
PubMed1998

beta-Galactosidase staining following intracoronary infusion of cationic liposomes in the in vivo rabbit heart is produced by microinfarction rather than effective gene transfer: a cautionary tale.

The myocardium is a potential target for the expression of exogenous genes to treat inherited and acquired diseases. Although adenovirus-mediated gene transfer has resulted in high-level gene transfer in vivo via direct intramyocardial injection and via a percutaneous intra-arterial route, the time-course of gene expression is limited by host immune responses. It was the aim of this study to test whether cationic liposome-mediated gene transfer, which does not suffer from the aforementioned problems, was feasible in the adult rabbit myocardium via a percutaneous transluminal approach. Doses of plasmid DNA encoding lacZ from 200-800 micrograms complexed to cationic liposomes resulted in X-gal conversion at day 3 with associated myocardial damage. We hypothesised that the damage was associated with macro-aggregates of cationic liposomes-DNA occluding the microcirculation. When such aggregates were excluded no X-gal conversion was seen in vivo. In order to show that X-gal conversion occurs in areas of infarction in the myocardium we caused closed chest infarction by deploying a platinum micro-embolisation coil in the circumflex coronary artery. At day 3 X-gal conversion was observed in the territory supplied by the occluded artery. Thus, microinfarction causes the false positive appearance of gene transfer when using a lacZ reporter gene.

Animals↗
PubMed1998

Reversible left ventricular dysfunction: does it affect clinical practice and does it matter?

There is substantial evidence that many patients with impaired left ventricular function secondary to coronary artery disease may have hibernating or stunned myocardium. The identification of these patients is important, as revascularisation is associated with an improvement in function, and there is some evidence that revascularisation of these patients will actually improve prognosis. The most useful investigations for the identification of reversible left ventricular dysfunction are dobutamine echocardiography, thallium scanning and, although not available in many centres, PET scanning.

Coronary Disease↗
PubMed1998

Myocardial preconditioning: mechanisms and man.

Myocardial preconditioning describes the profound myocardial protection that follows a short episode of sublethal ischaemia. Adenosine is produced in ischaemic myocardium and is thought to be an important trigger of the protective mechanism. The exact pathway awaits full elucidation but activation of G proteins and subsequently protein kinase C appear to be important signals. End effectors responsible for delaying cell death include opening of K+ATP ion channels and the transcription of a family of cytoprotective proteins. Absolute proof that preconditioning occurs in man is still awaited, although cross clamping of the aorta during cardiac surgery, balloon inflation during coronary angioplasty, warm-up angina and preinfarction angina are surrogate models supporting its existence. A clearer understanding of the protective mechanisms involved could lead to the development of novel therapeutic agents that could save the infarcting myocardium.

Animals↗
PubMed1996

Gene delivery to the heart in vivo and to cardiac myocytes and vascular smooth muscle cells in vitro using herpes virus vectors.

Herpes simplex virus 1 (HSV1), while usually thought of as neurotrophic, can also efficiently infect a wide variety of non-neuronal cell types and so might be developed as a vector for gene delivery to non-neuronal as well as neuronal cells. Here we have tested three different disabled HSV vectors for their ability to deliver a lacZ gene to primary cardiac myocytes and vascular smooth muscle cells in vitro, and used the most efficient virus to transfect the rat heart in vivo. We also assessed the degree of cytopathic effect of the various viruses on the cardiac myocytes in vitro by testing the effects on the frequency of beating in synchronously beating myocyte cultures. While an HSV mutant in which the essential immediate-early gene IE2 had been deleted gave high efficiency gene transfer to the cardiac myocytes in vitro and the rat heart in vivo, viruses in which ICP34.5 or ICP34.5 and VMW65 were inactive (and which were also unable to replicate in these cells) gave a much lower efficiency of gene transfer, mirroring the degree of cytopathic effect observed in the beating myocyte cultures. Gene transfer to the vascular smooth muscle cells was considerably less efficient than to the myocytes in all cases. These results indicate that while HSV may be inappropriate for highly efficient gene transfer to the arterial wall, efficient gene transfer can be achieved in the myocardium, and thus that HSV vectors may be suitable for the alteration of cardiac cell physiology in vivo.

Animals↗
PubMed1995

Overexpression of the rat inducible 70-kD heat stress protein in a transgenic mouse increases the resistance of the heart to ischemic injury.

Myocardial protection and changes in gene expression follow whole body heat stress. Circumstantial evidence suggests that an inducible 70-kD heat shock protein (hsp70i), increased markedly by whole body heat stress, contributes to the protection. Transgenic mouse lines were constructed with a cytomegalovirus enhancer and beta-actin promoter driving rat hsp70i expression in heterozygote animals. Unstressed, transgene positive mice expressed higher levels of myocardial hsp70i than transgene negative mice after whole body heat stress. This high level of expression occurred without apparent detrimental effect. The hearts harvested from transgene positive mice and transgene negative littermates were Langendorff perfused and subjected to 20 min of warm (37 degrees C) zero-flow ischemia and up to 120 min of reflow while contractile recovery and creatine kinase efflux were measured. Myocardial infarction was demarcated by triphenyltetrazolium. In transgene positive compared with transgene negative hearts, the zone of infarction was reduced by 40%, contractile function at 30 min of reflow was doubled, and efflux of creatine kinase was reduced by approximately 50%. Our findings suggest for the first time that increased myocardial hsp70i expression results in protection of the heart against ischemic injury and that the antiischemic properties of hsp70i have possible therapeutic relevance.

Animals↗
PubMed1994

Hsp70 in myocardial ischaemia.

Numerous reports suggest that stress protein accumulation confers protection in various mammalian tissues against differing stresses. The purpose of this article is to review the evidence that stress proteins, in particular hsp70, are able to alter the resistance of the heart to subsequent ischaemic and non-ischaemic injury and to discuss the possible physiological basis for this apparent protection. The possible, though unlikely involvement of heat stress proteins in classical ischaemic preconditioning is addressed as is the possibility of their involvement in a delayed second window of protection.

Animals↗
PubMed1994

Preconditioning in isolated superfused rabbit papillary muscles.

Preconditioning has only been demonstrated in arterially perfused myocardium. Our aim was to develop a model of preconditioning in isolated, superfused, isometrically contracting rabbit right ventricular papillary muscle. This would eventually allow us to evaluate isolated human muscles. Papillary muscles were suspended in an organ bath, superfused with oxygenated Tyrode solution, and field stimulated at 1 Hz. Muscles were assigned either to control or to preconditioning groups. Preconditioning was induced with 3 min of rapid pacing (3 Hz) with substrate-free hypoxic buffer and was followed by 15 min of reoxygenation with substrate. Subsequently, both groups were exposed to 45 min of substrate-free hypoxia followed by 120 min of reoxygenation with substrate. Preconditioning protected the myocardium with better recovery of developed force (50.6 +/- 6.7 vs. 27.4 +/- 4.2% of baseline developed force, P < 0.01). This effect could be blocked by 8-(p-sulfophenyl)theophylline (SPT) given during preconditioning at a dose that did not increase hypoxic damage in controls (percent developed force compared to baseline: preconditioned muscles + SPT = 30.9 +/- 2.8% and control muscles + SPT = 27.1 +/- 2.3%). In addition, pretreatment with (-)N6(2-phenylisopropyl)adenosine similarly protected the myocardium (49.5 +/- 5.5% recovery, P < 0.01). We conclude that isolated superfused muscles can be preconditioned. This preconditioning does not depend on coronary flow and involves activation of adenosine receptors.

Animals↗
PubMed1994

Adenosine receptor involvement in a delayed phase of myocardial protection 24 hours after ischemic preconditioning.

BACKGROUND: We previously reported a delayed phase of protection against infarction 24 hours after ischemic preconditioning in the rabbit. In the present study, we investigated the possibility that this "second window of protection," like the well-described early phase of protection in the rabbit, might be associated with adenosine receptor activation. METHODS AND RESULTS: In the first series of experiments, we examined whether adenosine receptor blockade with 8-(p-sulfophenyl)-theophylline (SPT) during preconditioning could abolish the delayed protection against infarction 24 hours later. Open-chest rabbits were subjected to myocardial preconditioning (PC) with the four 5-minute coronary occlusions or they were sham operated on (SHAM). During these procedures, animals received either SPT (PC + SPT, n = 6; and SHAM + SPT, n = 6) or vehicle (PC + VEH, n = 12; and SHAM + VEH, n = 11). Twenty-four hours later, infarct development after a 30-minute coronary occlusion/120-minute reperfusion insult was assessed with triphenyltetrazolium staining. In vehicle-treated rabbits, the infarct-to-risk ratio (I/R) was reduced from 53.6 +/- 5.7% (SHAM + VEH) to 32.9 +/- 4.6% (PC + VEH) (P < .05), clearly indicating a delayed phase of protection. Although I/R was not significantly different between SHAM + VEH (53.6 +/- 5.7%) and SHAM + SPT (61.7 +/- 5.4%), in PC + SPT the delayed protection was abolished (I/R = 56.8 +/- 3.8%). In the second series of experiments, we examined if pharmacological adenosine A1 receptor stimulation could evoke a delayed phase of protection. Conscious rabbits were pretreated with intravenous boluses of saline or the A1 receptor-selective agonist 2-chloro-N6-cyclopentyladenosine (CCPA), and infarct size in response to 30-minute ischemia/120-minute reperfusion was assessed 24 hours later. I/R was 54.5 +/- 2.7% in saline-pretreated controls (n = 12). Pretreatment with 25 micrograms/kg CCPA (n = 6), 50 micrograms/kg CCPA (n = 6), or 100 micrograms/kg CCPA (n = 6) resulted in I/R ratios of 37.1 +/- 4.2% (P < .01), 37.7 +/- 2.2% (P < .01), and 26.3 +/- 5.7% (P < .01), respectively. In both series of experiments, there were no differences in systemic hemodynamics during the infarct protocol, assessed as rate-pressure product, between the different experimental groups. CONCLUSIONS: Twenty-four hours after repetitive brief coronary occlusions, susceptibility to infarction in rabbit myocardium is reduced, an effect that may have clinical relevance. Results of the present study suggest that this second window of protection following preconditioning may, like the early phase of protection, be initiated by an adenosine-related mechanism.

Adenosine↗