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Biomedical subjects

G Ambrosio

Publications and source records attributed to G Ambrosio.

At least 19 recordsLinked to original sources
PubMed1996

Effects of tissue factor induced by oxygen free radicals on coronary flow during reperfusion.

Tissue factor is a transmembrane protein that activates the extrinsic coagulation pathway by binding factor VII. Endothelial cells, being in contact with circulating blood, do not normally express tissue factor. Here we provide evidence that oxygen free radicals induce tissue factor messenger RNA transcription and expression of tissue factor procoagulant activity in endothelial cells in culture. Isolated, perfused rabbit hearts exposed to exogenous oxygen free radicals also showed a marked increase in tissue factor activity within the coronary circulation. Furthermore, in ex vivo and in vivo hearts subjected to ischemia and reperfusion, a condition associated with a production of oxygen free radicals in large amounts, a marked increase in tissue factor activity occurred. This phenomenon could be abolished by oxygen radical scavengers. This increase in tissue factor activity during postischemic reperfusion was accompanied by a significant decrease in coronary flow, suggesting that increase in tissue factor activity with the consequent activation of the coagulation cascade might impair coronary flow during reperfusion and possibly contribute to the occurrence of reperfusion injury.

Animals↗
PubMed1995

Visual dysfunction in patients with mitochondrial myopathies. I. Electrophysiologic impairments.

Seventeen patients with biopsy-confirmed mitochondrial progressive external ophthalmoplegia underwent electroretinography and visual evoked potential testing to checkerboard-reversal stimuli to investigate subclinical visual dysfunction. Seven patients (41%) had impaired Snellen visual acuity that was never less than 0.6. Thirteen patients (76%) showed electroretinographic and/or visual evoked potential alterations, whereas six (35%) showed impairment on both tests. Two patients showed delayed VEP P100 latency without fundus, electroretinographic or visual acuity anomalies. Visual dysfunctions were not related to age at onset and course of the disease.

Adolescent↗
PubMed1995

Visual dysfunction in patients with mitochondrial myopathies. II. Contrast sensitivity function.

Contrast sensitivity function with stationary and temporally modulated (8 Hz) black and white vertical sinusoidal gratings was investigated in 11 patients with biopsy-confirmed mitochondrial progressive external ophthalmoplegia. To evaluate contrast sensitivity function results, the contrast sensitivity versus spatial frequency experimental data for each subject were fitted with a second-order polynomial, and the coefficients of the best-fitting function from normal and patient groups were compared. Patients with progressive external ophthalmoplegia, as a group, showed a decreased sensitivity at the intermediate spatial frequencies (i.e., around 1.4 c/deg) with stationary gratings and through a wider range of spatial frequencies with temporally modulated gratings. These findings were confirmed by analyzing contrast sensitivity functions from each individual. The study showed that contrast sensitivity function detects visual function abnormalities noninvasively in a number of patients with mitochondrial progressive external ophthalmoplegia with unaffected Snellen visual acuity.

Adult↗
PubMed1995

Magnetic resonance imaging in "typical" and "late onset" Friedreich's disease and early onset cerebellar ataxia with retained tendon reflexes.

MRI makes it possible to study the in vivo brain and spinal cord morphology of patients with hereditary ataxia. We performed T1- and T2-weighted studies in eleven patients with Friedreich's disease (FD), five with "late onset" FD and ten with early onset cerebellar ataxia with retained tendon reflexes (EOCA). Cervical cord atrophy was constant in FD and "late onset" FD and often associated with atrophy of the cerebellum and of the brainstem; T2-weighted studies showed posterior column degeneration in the cervical cord. The most frequent finding in EOCA was cerebellar atrophy, pure or associated with cervical cord or brainstem atrophy; the cerebellar atrophy was marked in a few cases and was related to disease duration.

Adolescent↗
PubMed1995

Influence of O2 deprivation, reduced flow, and temperature on release of ANP from rabbit hearts.

The separate effects of hypoxia and ischemia on atrial natriuretic peptide (ANP) release were evaluated in Langendorff-perfused rabbit hearts. Heart rate, coronary flow, and atrial and ventricular volumes were kept constant. Hypoxia was induced for 20 min at room temperature in seven hearts and at 37 degrees C in a second group of seven hearts. A third group of eight hearts was subjected to global ischemia for 20 min by reducing coronary flow to 1 ml/min at room temperature. All hearts were reoxygenated/reperfused at 37 degrees C for 30 min. Hypoxia at 37 degrees C induced a significant increase in ANP release. In contrast, both room temperature hypoxia and ischemia were characterized by a significant decrease in ANP release, despite hemodynamic alterations similar to those recorded during hypoxia at 37 degrees C. Both reoxygenation and reperfusion induced a prompt reversal of the changes of ANP release observed during the period of oxygen deprivation. These data demonstrate that decreased oxygen availability and reduced coronary flow are not the primary factors affecting release of ANP during ischemia and that alterations of myocardial temperature may play a major role in this phenomenon.

Animals↗
PubMed1995

[ECG-dipyridamole and ECG-exercise test in the assessment of ischemic cardiopathy: effects of the acute administration of nitroglycerin].

It is known that intravenous administration of dipyridamole can induce chest pain and ECG signs of ischemia in patients with coronary artery disease. In the present study we evaluated ECG and hemodynamic changes in response to dipyridamole (0.56 mg/kg in 10 min) under basal conditions and 3 hours after administration of nitroglycerin (10 mg/24 h patch) in 14 patients with coronary artery disease. The effects of nitroglycerin were also compared to those induced by the same drug on a bicycle stress test in the same patients. Exercise stress test induced specific ST changes in all patients when performed off-drug. Nitroglycerin administration completely prevented exercise-induced ischemia in 2 patients, and significantly prolonged exercise time in the remaining patients (p < 0.01). This effect was accompanied by a significant increase in heart rate (HR) and rate-pressure product at the threshold of ischemia (HRBP, p < 0.01); furthermore we observed a significant increase in HR at the maximal work load (p < 0.05). In the absence of treatment, dipyridamole infusion induced ST segment changes and/or typical chest pain in 12/14 patients. Moreover we observed a significant increase (p < 0.05) in HR, BP and HRBP during the test with respect to basal conditions. Following nitroglycerin administration, dipyridamole infusion failed to induce ischemia in 4 patients, and the time to ST depression in the remaining 8 patients (459 +/- 69 vs 610 +/- 127 s; p < 0.05) was significantly prolonged.(ABSTRACT TRUNCATED AT 250 WORDS)

Dipyridamole↗
PubMed1995

Protective role of chronic ubiquinone administration on acute cardiac oxidative stress.

Previous studies have shown that acute exogenous administration of coenzyme ubiquinone (CoQ10) can protect the heart against oxidant-mediated injury. The aim of this study was to investigate whether protection against cardiac oxidative stress could be obtained by increasing tissue levels of CoQ10, as achieved by chronic CoQ10 supplementation. Wistar rats were randomly divided into two groups: a control group given standard diet and a test group receiving diet supplemented with CoQ10 (5 mg/kg/day) for 4 weeks. Functional and metabolic changes induced by oxidative stress were investigated in isolated perfused hearts and in papillary muscles. Tissue concentrations of ubiquinones were significantly higher in the left ventricle of treated rats than in controls. H2O2 infusion (60 microM for 60 min) induced marked alterations of both developed pressure, which decreased to -58.8 +/- 16.8% of base line and end-diastolic pressure which increased almost 13-fold. These effects were reduced significantly (P < .05) in hearts from CoQ10-supplemented rats (-13.8 +/- 2.3 and +375.0 +/- 42.5%, respectively). In the same hearts, cumulative release of oxidized glutathione (a specific marker of oxidative stress) was 450.2 +/- 69.2 nmol/g of wet weight in the control group and only 89.6 +/- 22.3 nmol/g of wet weight in treated hearts (P < .01). In papillary muscles, after 60 min of perfusion with H2O2, active tension decreased, largely in controls whereas it was almost unchanged in the treated group (-34.4 +/- 7.5% of baseline vs. -0.1 +/- 0.05%, P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Modulation of platelet function by reactive oxygen metabolites.

Reactive oxygen metabolites have been reported to affect platelet aggregation. However, this phenomenon is still poorly understood. In the present study we investigated the effects of superoxide radical and hydrogen peroxide (H2O2) on platelet function in vitro and correlated those effects to possible changes of platelet concentrations of cyclic nucleotides and thromboxane, since these systems play a key role in the response of platelets to activating stimuli. Human platelets were exposed to xanthine-xanthine oxidase (X-XO), a system that generates both superoxide radicals and H2O2. Sixty seconds of incubation with X-XO impaired aggregation in response to ADP (by 48%), collagen (by 71%), or the thromboxane mimetic U-46619 (by 50%). This effect was reversible and occurred in the absence of cell damage. Impairment of aggregation in platelets exposed to X-XO was due to H2O2 formation, since it was prevented by catalase but not by superoxide dismutase. Similarly, incubation with the pure H2O2 generator glucose-glucose oxidase also markedly inhibited ADP-induced platelet aggregation in a dose-dependent fashion. Impaired aggregation by H2O2 was accompanied by a > 10-fold increase in platelet concentrations of guanosine 3',5'-cyclic monophosphate (cGMP), whereas adenosine 3',5'-cyclic monophosphate levels remained unchanged. The inhibitory role of increased cGMP formation was confirmed by the finding that H2O2-induced impairment of platelet aggregation was largely abolished when guanylate cyclase activation was prevented by incubating platelets with the guanylate cyclase inhibitor, LY-83583. Different effects were observed when arachidonic acid was used to stimulate platelets. Exposure to a source of H2O2 did not affect aggregation to arachidonate. Furthermore, in the absence of exogenous H2O2, incubation with catalase, which had no effects on platelet response to ADP, collagen, or U-46619, virtually abolished platelet aggregation and markedly reduced thromboxane B2 production (to 44% of control) when arachidonic acid was used as a stimulus. In conclusion, our data demonstrate that H2O2 may exert complex effects on platelet function in vitro. Low levels of endogenous H2O2 seem to be required to promote thromboxane synthesis and aggregation in response to arachidonic acid. In contrast, exposure to larger (but not toxic) concentrations of exogenous H2O2 may inhibit aggregation to several agonists via stimulation of guanylate cyclase and increased cGMP formation.

Adenine Nucleotides↗
PubMed1994

A monoclonal antibody against rabbit tissue factor inhibits thrombus formation in stenotic injured rabbit carotid arteries.

Tissue factor (TF) is a transmembrane protein that binds factor VII/VIIa, thus activating the extrinsic blood coagulation pathway. Since this pathway appears to be involved in the formation of intravascular thrombi, the anti-rabbit TF monoclonal antibody, AP-1, was produced and tested as an antithrombotic agent in a rabbit model of recurrent intravascular thrombosis. In this model, a plastic constrictor is positioned around the injured rabbit carotid arteries, and flow is monitored with a Doppler flow probe. This produces cyclic flow variation (CFV) in the carotid artery, which is caused by recurrent formation and dislodgment of thrombi at the site of the stenosis. After monitoring CFV pattern for 30 minutes, AP-1 was infused intravenously into nine rabbits at doses of 0.05 to 1.5 mg/kg body weight, and a control monoclonal antibody that does not react with rabbit TF was infused into four additional rabbits. In all rabbits receiving AP-1, CFV was abolished, and a steady normal blood flow was restored, indicating that thrombus formation had been blocked by AP-1. By contrast, in all rabbits that received the control monoclonal antibody, CFV continued unaltered. There was no change in the partial thromboplastin time and ex vivo platelet aggregation to several different agonists after infusion of AP-1, indicating an absence of systemic effects on the coagulation process. We conclude that activation of the extrinsic coagulation pathway has a key role in triggering intravascular thrombosis and that an anti-TF monoclonal antibody is an effective antithrombotic agent that could have therapeutic potential for humans.

Animals↗
PubMed1994

Oxygen radicals inhibit human plasma acetylhydrolase, the enzyme that catabolizes platelet-activating factor.

Platelet-activating factor (PAF) can exert profound inflammatory effects at very low concentrations. In plasma, PAF is hydrolyzed to lyso-PAF by acetylhydrolase, an enzyme that circulates bound to LDL. Previous studies suggest that oxygen radicals may act synergistically with PAF to potentiate tissue injury. However, mechanisms underlying this interaction have not been elucidated. In this study we investigated whether oxygen radicals may inactivate PAF acetylhydrolase. PAF acetylhydrolase activity was measured in human plasma and purified LDL before and after exposure to radicals (10-20 nmol/min per ml) generated by xanthine/xanthine oxidase. Oxygen radicals induced > 50% loss of PAF acetylhydrolase activity within 60 s and almost complete inactivation by 10 min. This phenomenon was irreversible and independent of oxidative modification of LDL. Inactivation occurred without changes in the affinity constant of the enzyme (Km was 17.9 microM under control conditions and 15.1 microM after exposure to oxygen radicals). Inactivation was prevented by the scavengers superoxide dismutase or dimethylthiourea or by the iron chelator deferoxamine. Thus, superoxide-mediated, iron-catalyzed formation of hydroxyl radicals can rapidly and irreversibly inactivate PAF acetylhydrolase. Since concomitant production of PAF and oxygen radicals can occur in various forms of tissue injury, inactivation of acetylhydrolase might represent one mechanism by which oxygen radicals may potentiate and prolong the proinflammatory effects of PAF.

1-Alkyl-2-acetylglycerophosphocholine Esterase↗
PubMed1994

Myocardial damage during ischaemia and reperfusion.

Large quantities of oxygen free radicals can be generated on reperfusion of the ischemic myocardium. This phenomenon is probably responsible for a specific component of cell damage separate from ischemic injury and may blunt the beneficial effects of thrombolysis. Anti-free radical interventions may reduce the severity of this "reperfusion injury". However, reports of treatment failures indicate that reperfusion injury is a complex phenomenon, and suggest that the beneficial effects of treatment may be critically dependent on factors that are not clearly understood.

Animals↗
PubMed1994

[Protection by blockers against human low density lipoprotein peroxidation induced by oxygen free radicals].

Previous studies in other systems have shown that beta-receptor blockers may effectively inhibit oxygen radical-induced lipid peroxidation. On the other hand, it has been recently proposed that oxygen free radicals can induce peroxidation of human low density lipoproteins (LDL), and that peroxidized LDL may be an atherogenic stimulus. Chemically modified LDL are internalized by macrophages via a specific cell surface receptor that was termed the scavenger receptor. This phenomenon may induce foam cells transformation in vivo. In the present study we investigated whether beta-blockers may reduce oxygen radical-mediated LDL peroxidation. Purified human LDL were oxidized by exposure to oxygen free radicals generated by xanthine (0.2 mM) and xanthine oxidase (100 mU) at 37 degrees C after a pre-incubation (30 min) in presence of different concentrations (from 1 to 30 microM) of acebutolol, metoprolol or propranolol, three agents with a different degree of lipophilicity. Peroxidation was measured from malonyldihaldehyde (MDA) production. Data have shown a significant percent inhibition of MDA formation in presence of beta-blockers (from 33 to 85%). Thus, beta-blockers reduced peroxidation of human LDL in vitro at clinically relevant concentrations. The order of potency appears to follow the degree of lipophilicity. These data suggest that, although beta-blockers are known to adversely effect lipid metabolism, these agents might on the other hand prevent atherogenesis via a mechanism of inhibition of LDL peroxidation in vivo and reduced foam cells formation.

Acebutolol↗
PubMed1994

[The peroxidation of human glycosylated low-density lipoproteins is mediated by the superoxide radical: the protective effects of superoxide dismutase].

Low-density lipoproteins (LDL) oxidized by oxygen radicals are a potent atherogenic stimulus. Chemically modified LDL are internalized by macrophages via a specific cell surface receptor that was termed the scavenger receptor, and could induce foam cell transformation. Post-translational nonenzymatic glycosylation of low density lipoprotein (LDL) occurs in vivo in diabetic patients. Glycosylated LDL (glcLDL) is degraded by macrophages in part by the classic LDL-receptor and in part by the scavenger receptor. This latter mechanism may contribute to the formation of foam cells and acceleration of atherosclerosis in diabetes mellitus. Oxygen free radicals (ORs) could induce LDL peroxidation and subsequent formation of foam cells. Glycosylation may alter protein conformation. A free radical is any chemical species that has an unpaired electron. This property renders it highly chemically reactive. When a radical reacts with a non radical another free radical is generated. This characteristic enables radicals to trigger chain reactions. Oxygen radicals are: superoxide anion (.O2-), hydroxyl radical (.OH) and hydrogen peroxide (H2O2). Thus, the aim of this study was to investigate whether glcLDL are susceptible to peroxidative modification by ORs. GlcLDL was prepared incubating LDL with 40 mM glucose in sterile phosphate-buffer-EDTA 1 mM for 10 days at 37 degrees C. Control LDL (cLDL) was similarly incubated with buffer but without glucose. After this preparation both forms of LDL were oxidized by CuSO4 (15 microM for 20 hours at 37 degrees C) or by xanthine/xanthine oxidase (X:2 mM/XO: 100 mU for 20 hours at 37 degrees C).(ABSTRACT TRUNCATED AT 250 WORDS)

Diabetes Mellitus↗
PubMed1993

Evidence that mitochondrial respiration is a source of potentially toxic oxygen free radicals in intact rabbit hearts subjected to ischemia and reflow.

Previous in vitro studies have shown that isolated mitochondria can generate oxygen radicals. However, whether a similar phenomenon can also occur in intact organs is unknown. In the present study, we tested the hypothesis that resumption of mitochondrial respiration upon reperfusion might be a mechanism of oxygen radical formation in postischemic hearts, and that treatment with inhibitors of mitochondrial respiration might prevent this phenomenon. Three groups of Langendorff-perfused rabbit hearts were subjected to 30 min of global ischemia at 37 degrees C, followed by reflow. Throughout ischemia and early reperfusion the hearts received, respectively: (a) 5 mM KCl (controls), (b) 5 mM sodium amobarbital (Amytal, which blocks mitochondrial respiration at Site I, at the level of NADH dehydrogenase), and (c) 5 mM potassium cyanide (to block mitochondrial respiration distally, at the level of cytochrome c oxidase). The hearts were then processed to directly evaluate oxygen radical generation by electron paramagnetic resonance spectroscopy, or to measure oxygen radical-induced membrane lipid peroxidation by malonyl dialdehyde (MDA) content of subcellular fractions. Severity of ischemia, as assessed by 31P-nuclear magnetic resonance measurements of cardiac ATP, phosphocreatine, and pH, was similar in all groups. Oxygen-centered free radical concentration averaged 3.84 +/- 0.54 microM in reperfused control hearts, and it was significantly reduced by Amytal treatment (1.98 +/- 0.26; p < 0.05), but not by KCN (2.58 +/- 0.96 microM; p = not significant (NS)), consistent with oxygen radicals being formed in the mitochondrial respiratory chain at Site I. Membrane lipid peroxidation of reperfused hearts was also reduced by treatment with Amytal, but not with KCN. MDA content of the mitochondrial fraction averaged 0.75 +/- 0.06 nM/mg protein in controls, 0.72 +/- 0.06 in KCN-treated hearts, and 0.54 +/- 0.05 in Amytal-treated hearts (p < 0.05 versus both groups). Similarly, MDA content of lysosomal membrane fraction was 0.64 +/- 0.09 nM/mg protein in controls, 0.79 +/- 0.15 in KCN-treated hearts, and 0.43 +/- 0.06 in Amytal-treated hearts (p < 0.05 versus both groups). Since the effects of Amytal are known to be reversible, in a second series of experiments we investigated whether transient mitochondrial inhibition during the initial 10 min of reperfusion was also associated with beneficial effects on subsequent recovery of cardiac function after wash-out of the drug. At the end of the experiment, recovery of left ventricular end-diastolic and of developed pressure was significantly greater in those hearts that had been treated with Amytal during ischemia and early reflow, as compared to untreated hearts.(ABSTRACT TRUNCATED AT 400 WORDS)

Adenosine Triphosphate↗
PubMed1993

The functional recovery of post-ischemic myocardium requires glycolysis during early reperfusion.

Glycolysis normally provides only a small fraction of myocardial ATP production, but ATP from glycolysis may be preferentially used to support membrane activities such as ion pumping. Since ion homeostasis is disturbed during ischemia, glycolysis may be particularly important in the recovery of postischemic myocardium. This hypothesis was investigated in isovolumic, isolated rabbit hearts, perfused with 16 mM glucose, 5 mM pyruvate or 5 mM acetate. Global left ventricular function (rate-pressure product, RPP) and unidirectional ATP synthesis rate (P(i)-->ATP flux, 31P NMR) were measured before and after 20 min global ischemia. Control hearts with intact glycolysis were compared with hearts which had glycolysis inhibited by iodoacetate (150 microM), 2-deoxyglucose (10 mM) or prior glycogen depletion. In normal hearts, inhibition of glycolysis had no effect on function when pyruvate or acetate was present as as a carbon substrate. In post-ischemic hearts, reperfusion with glucose (n = 7) resulted in moderate recovery of function to about 65% of pre-ischemic levels after 1 h reperfusion. Administration of iodoacetate at the onset of reperfusion to hearts receiving pyruvate or acetate resulted in much worse functional recovery and a marked rise in left ventricular end-diastolic pressure (LVEDP). With pyruvate (n = 7), RPP recovered to 27% of pre-ischemic levels, while mean LVEDP increased to 34 mmHg (vs 16 mmHg with glucose); with acetate (n = 6), RPP returned to 31% of pre-ischemic levels, while mean LVEDP rose to 32 mmHg. The ratio of P(i)-->ATP flux to atoms of oxygen consumed (P:O ratio) was 2.14 +/- 0.36 in hearts reperfused with iodoacetate and pyruvate, consistent with partial mitochondrial uncoupling. However, if inhibition of glycolysis with iodoacetate was delayed until after 30 min reperfusion, recovery of hearts reperfused with pyruvate was similar to hearts perfused with glucose, and there was no evidence of mitochondrial uncoupling (P:O ratio = 2.95 +/- 0.33). Inhibition of glycolysis during reperfusion with 2-deoxyglucose yielded results similar to reperfusion with iodoacetate. The worst recovery was observed in hearts with combined glycolytic inhibition by pre-ischemic glycogen depletion and iodoacetate during reperfusion (RPP = 13% of pre-ischemic levels). These findings indicate that glycolysis plays a crucial role during early reperfusion in the functional and metabolic recovery of post-ischemic myocardium.

Adenosine Triphosphate↗
PubMed1993

The effects of calcium channel antagonist treatment and oxygen radical scavenging on infarct size and the no-reflow phenomenon in reperfused hearts.

Calcium antagonists reduce ischemic injury, and anti-free-radical interventions may reduce reperfusion injury. However, the effects of treatment with both interventions have never been investigated. In the present study, anesthetized rabbits underwent 30 minutes of coronary artery ligation, which was followed by 5.5 hours of reflow. Eight animals in each group received: (1) the calcium antagonist gallopamil during ischemia, (2) the oxygen radical scavenger superoxide dismutase during reperfusion, (3) combined treatment with gallopamil and superoxide dismutase, and (4) saline solution. All groups were similar with respect to collateral flow during ischemia and extent of risk region. Infarct size averaged 60.2% +/- 5.5% of risk region in controls and was significantly smaller (p < 0.001) in rabbits that were treated with either gallopamil (28.1% +/- 3.4%) of superoxide dismutase (29.3% +/- 3.2%). Little further reduction in infarct size was observed with combination therapy (22.9% +/- 3.2% of risk region; p = NS). Superoxide dismutase had no effects on hemodynamics, whereas gallopamil significantly reduced heart rate, mean arterial pressure, and rate-pressure product. However, the reduction in infarct size that was observed in gallopamil-treated rabbits significantly exceeded the expected value in this group after corrections were made for changes in these determinants of ischemic injury. Therefore we investigated whether other factors may have contributed to the beneficial effects of gallopamil. In vitro the drug had no oxygen radical scavenging activity, nor did it exert antioxidant effects. In addition, gallopamil did not affect neutrophil function. In conclusion, in this acute model myocardial cell necrosis was significantly reduced either by administration of a calcium antagonist during ischemia or by removing oxygen radicals during reperfusion. However, superoxide dismutase administration did not further reduce infarct size when given to animals that had been treated with gallopamil. Since gallopamil has no direct effect on several mechanisms of reperfusion injury, these data suggest that calcium antagonists, by decreasing myocardial oxygen demand during ischemia, may indirectly reduce oxygen radical damage during subsequent reperfusion.

Analysis of Variance↗