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Biomedical subjects

C Michiels

Publications and source records attributed to C Michiels.

At least 73 records · Page 4Linked to original sources
PubMed1993

[Bone metastasis of hepatocellular carcinoma. Apropos of 22 cases].

There have been few studies and case-reports of bone metastases from hepatocellular carcinoma. To determine the characteristics of these metastases, we retrospectively studied 22 patients in whom the diagnosis was established either on the basis of concomitant occurrence of malignant bone lesions and hepatocellular carcinoma in the absence of other detectable malignant disease (n = 15) or on the basis of histological evidence of bone metastasis from an hepatocellular carcinoma (n = 7). There were 21 males and one female. Mean age was 62.5 years. Most patients (88.2%) had chronic alcohol abuse. The bone metastases occurred as the first manifestation of the liver cancer in half the cases (11/22). Time interval between onset of bone symptoms and admission was less than one month in 6 of 11 patients; mean interval was 7.4 weeks. Hepatomegaly was found upon initial physical evaluation in 9 of 11 patients. Pain was the main symptom of bone disease (18/22). Palpable bone masses were found in 6 of 22 patients. Purely osteolytic lesions were seen on roentgenograms in every case; rupture of the cortex and spread to adjacent soft tissues were common findings. The radionuclide bone scan was normal in four of 12 patients. An advanced primary hepatic tumor was found in 84.2% of cases. Histologic examination of bone specimens established the diagnosis of metastasis from a hepatocellular carcinoma in 7 of 9 patients (77.8%). Severe bleeding occurred during one of the nine biopsy procedures. Patients were given symptomatic treatment. Systemic chemotherapy was used in five patients, unsuccessfully. Median survival was three months.

Bone Neoplasms↗
PubMed1993

Effects of naftidrofuryl on hypoxia-induced activation and mortality of human endothelial cells.

The present study was designed to elucidate the possible beneficial effects of naftidrofuryl on ischemia-induced endothelium damage. For this purpose, an in vitro model was developed wherein human endothelial cells isolated from umbilical vein were submitted to hypoxia. Long-term hypoxia incubation (6 h) induced cell mortality, and naftidrofuryl strongly protected endothelial cells against this mortality in a dose-dependent manner and at concentrations as low as 10(-9) M. 66% protection was still observed after 16 h of hypoxia. Naftidrofuryl had to be present during the hypoxia incubation to exert its action; preincubation up to 24 h in the presence of naftidrofuryl could not protect endothelial cells incubated under hypoxia without naftidrofuryl. Short-term hypoxia, which does not induce mortality, strongly activates the endothelial cells with an increase in the cytosolic calcium concentration, in the phospholipase A2 activity, and in the synthesis of prostaglandin and of platelet-activating factor. It also enhances the adherence of polymorphonuclear neutrophils. Naftidrofuryl was able to markedly inhibit this whole cascade of events in a dose-dependent manner. We also demonstrated that naftidrofuryl could block the decrease in ATP concentration that results from the hypoxic conditions. These results indicate that by preserving the energetic level of the cells, naftidrofuryl prevents the activation of endothelial cells and the cell mortality induced by hypoxia. By maintaining an intact endothelium in vivo during ischemia, naftidrofuryl could prevent the further damage induced by leukocyte recruitment and activation.

Adenosine Triphosphate↗
PubMed1993

[Diagnostic modalities and treatment of cancer of the pancreas. Evolution in the population in the department of Côte d'Or from 1976 to 1988].

There is no study establishing time trends for the diagnostic and therapeutic approaches to pancreatic cancer based on population data. The data of the Registry of Digestive Tumors of Côte-d'Or (France) were used to this end in 544 cancers diagnosed between 1976 and 1988. The proportion of the histologically confirmed cases increased annually by 13.4% (P < 0.001). This was mainly due to progress in percutaneous biopsy (+25.7% per year between 1983 and 1988, P < 0.001). As regards the diagnosis, ultrasonography was used more frequently (+21.9% per year, P < 0.001) as well as CT scan since its introduction in 1983 (+19.6% per year, P < 0.001). Pancreatic cancer was diagnosed by sonography in 16.7% of the cases in 1976 and 70.6% in 1988 (mean annual variation: +5.7%, P < 0.001). The proportions for CT scan were 12.8% in 1983 and 23.5% in 1988 (mean annual variation: +3.5%, NS). There was no significant change in the use of retrograde cholangiopancreatography over time. Other diagnosis criteria were less frequently used: laparoscopy was no longer used after 1983 and intraoperative diagnosis was made less frequently (-2.5% per year, P < 0.001). Endoscopy or radiographic data were rarely used as a diagnosis criterion. These changes in approaches to the diagnosis of pancreatic cancer were not accompanied by any progress in diagnosis stage, therapeutic approach or survival suggesting that when clinical symptoms become evident, pancreatic cancer is already advanced. Therapeutic advances, early diagnosis in patient at risk or identification or reasons for pancreatic cancer are the only means of progress in this problem.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1992

Importance of various antioxidant enzymes for cell stability. Confrontation between theoretical and experimental data.

A theoretical model was developed taking into account the production and destruction of oxygen-derived free radicals. The steady state of the system was derived by using the rate equations of these reactions, and the stability of the system was tested. In the simplified model, only one stable steady state was found. However, we know that glutathione peroxidase can be inhibited by hydroperoxides, and, when incorporated into the model, this effect led to a complex situation with the presence of some stable and some unstable domains according to the concentration of either the enzyme or the hydroperoxide. This qualitative description of the system was compared with experimental data on the protection given by three antioxidant enzymes, and concordance of data was found which allows some quantification of the system. A general view of the efficiency of the three antioxidant enzymes and of the stability of the system according to their concentrations could be produced.

Animals↗
PubMed1992

Effect of hypoxia upon intracellular calcium concentration of human endothelial cells.

Ischemia is a situation occurring in several diseases including myocardial infarction and organ transplantation in which oxygenated blood supply is impaired. Ischemia leads to many cellular and tissue modifications, the most important one being cell death. Several explanations have been proposed to account for these modifications and cell death; among them is calcium overload. However, the influence of calcium concentration on the alteration of endothelial cell functions or viability during ischemia are still unknown. We developed here an in vitro model where human endothelial cell monolayers were submitted to hypoxia with or without reoxygenation and variation in calcium concentration was followed using a specific intracellular probe Fura 2. We observed a significant increase of [Ca2+]i during 2 h hypoxia reaching values similar to those observed during agonist stimulation of endothelial cells but far lower than values toxic for the cells. This increase was constant during the hypoxic incubation and was due mainly to an influx of extracellular calcium. Viability was also followed during hypoxia and using calcium channel blockers, we could show that there was no correlation between viability and the rise in calcium concentration. During the reoxygenation period, [Ca2+]i decreased to reach the normal value of resting cells after 45 min, suggesting that cells were still able to recover their calcium homeostasis. The use of a ketone body (beta-hydroxybutyrate) indicated that an energy deficiency was responsible for the hypoxia-induced increase in [Ca2+]i. We actually observed a 43% decrease in ATP concentration after 2 h hypoxia. This decrease was already significant after 30 min which thus precedes the changes in [Ca2+]i. These results show that during hypoxia, energy deficiency led to an increase in [Ca2+]i which is, however, too low to account for the loss of viability but which is within the range of concentrations observed during stimulation of endothelial cells. We propose that such increased intracellular calcium concentrations could play a role in the synthesis of mediators leading to the development of local inflammation.

3-Hydroxybutyric Acid↗
PubMed1992

Human umbilical vein endothelial cells submitted to hypoxia-reoxygenation in vitro: implication of free radicals, xanthine oxidase, and energy deficiency.

Ischemia-reperfusion is observed in various diseases such as myocardium infarct. Different theories have been proposed to explain the reperfusion injury, among them that the free radical generation plays a crucial role. To study the mechanisms of the reperfusion injury, a hypoxia (H)-reoxygenation (R) model upon human umbilical vein endothelial cells in culture was developed in order to mimic the in vivo situation. Different parameters were quantified and compared under H or H/R, and we found that oxygen readmission led to damage amplification after a short hypoxia period. To estimate the importance of various causes of toxicity, the effects of various protective molecules were compared. Different antioxidant molecules, iron-chelating agent, xanthine oxidase inhibitors, and energy-supplying molecules were very efficient protectors. Synergy could also be observed between the antioxidants and the energy-supplying molecules or the xanthine oxidase inhibitors. The toxic effect of O2.(-) could be lowered by the presence of SOD or glutathione peroxidase in the culture medium, whereas glutathione peroxidase was the most efficient enzyme when injected into the cells. The production of O2.(-) and of H2O2 by endothelial cells was directly estimated to be, respectively, of 0.17 and 0.035 mumol/min/mg prot during the R period. O2.(-) production was completely inhibited when allopurinol was added during H and R. In addition, a xanthine oxidase activity of 21.5 10(-6) U/mg prot could be observed by a direct assay in cells after H but not in control cells, thus confirming the previous conclusions of xanthine oxidase as a potent source of free radicals in these conditions. Thanks to the use of cultured human endothelial cells, a clear picture was obtained of the overall process leading to cell degenerescence during the reoxygenation process. We particularly could stress the importance of the low energetic state of these cells, which is a critical factor acting synergistically with the oxidant molecules to injure the cells. These results also open new possibilities for the development of new therapeutics for ischemia.

Cell Hypoxia↗
PubMed1992

The importance of antioxidant enzymes in cellular aging and degeneration.

Aerobic cells contain various amounts of the three main antioxidant enzymes: superoxide dismutase (SOD), catalase and GSH peroxidase. These three enzymes are necessary for cell survival since inhibition of their activity leads to the arrest of cell mitosis and to cell death. Amongst them, GSH peroxidase was shown to be more efficient than catalase and much more than SOD. This result was obtained by comparing the cell protection against oxidative stress after their microinjection in the cytoplasm. With age, the level of these antioxidant enzymes does not change in several experimental models, so that it is not possible to explain the aging process by a lack of protection due to a decrease in the activity of these three enzymes. However, tissues and cells are more susceptible to free radical attacks with age. In order to understand the importance of free radicals in this process, we have to distinguish between their respective effects on cell mitosis, cell death and cell aging. The effects on mitosis and cell death are well described, and the results clearly show a threshold of response which is determined by the antioxidant content of the cell. There is now evidence that short free radical stresses can also speed up the aging of in vitro cultured human fibroblasts. However, such effects are not typical of free radicals but are also obtained with many other deleterious substances so that free radicals have to be considered as one amongst other factors responsible for influencing the evolution of a cell to an older stage or to cell death. The lowering of the general metabolism and of the free energy in old cells are probably the main factors responsible for the increased susceptibility of these cells to stresses such as oxidative stresses.

Aerobiosis↗
PubMed1991

Cytotoxicity of linoleic acid peroxide, malondialdehyde and 4-hydroxynonenal towards human fibroblasts.

Lipid peroxidation occurs during oxidative stress and leads to the formation of various active compounds. However, controversy remains about its importance in the events leading to cell death. One approach to estimate their role in cell death would be to test the toxicity of oxidative products generated during the stress. In this work, three of these products were incubated with human fibroblasts and their toxicities were compared. The three compounds tested are: linoleic acid peroxide (LOOH), malondialdehyde (MDA) and 4-hydroxynonenal (HNE). Three cellular parameters were assayed: viability, DNA synthesis estimated by thymidine incorporation and protein synthesis measured by leucine incorporation. Protection against cellular damages was also tested adding alpha-tocopherol in the culture medium. The results showed that the peroxide was more toxic than HNE and much more than MDA. The possibility of initiation and propagation of the free radical chain reaction could explain this highest toxicity. The fibroblasts seem to be protected by alpha-tocopherol against LOOH. These effects emphasize the crucial role of this lipophilic antioxidant to protect cells against peroxidation damages.

Aldehydes↗
PubMed1991

Association of antioxidant systems in the protection of human fibroblasts against oxygen derived free radicals.

The protection of human diploid fibroblasts against high oxygen tension was investigated using various combinations of the three major antioxidant enzymes: superoxide dismutase, catalase and glutathione peroxidase. alpha-Tocopherol, a well-known hydrophobic antioxidant, was also tested in combination with the different enzymes. Microinjection of solutions containing different combinations of the three enzymes was compared with the injection of each single enzyme. We observed that the protections given by catalase or superoxide dismutase on the one hand, and by glutathione peroxidase on the other hand, were additive. Surprisingly, the combinations of catalase and superoxide dismutase were less effective than catalase alone and was even toxic at low SOD concentrations. Addition of alpha-tocopherol following the injection of any of the three enzymes was highly beneficial, but the strongest synergistic effect was obtained with glutathione peroxidase. These results stress the importance of membrane protection by alpha-tocopherol and indirectly by glutathione peroxidase. They also showed that any injection leading to the decrease in the O2.- or H2O2 concentration combined with one of these two protectors is very beneficial for the cells probably by decreasing the OH concentration. This is also proven by the very good protective effect obtained with desferrioxamine.

Antioxidants↗
PubMed1990

Respiratory activity of isolated rat liver mitochondria following in vitro exposure to oxygen species: a threshold study.

Respiratory activity of isolated rat liver mitochondria was assayed following in vitro exposure to oxygen radicals. Our results show that mitochondrial respiration is more sensitive to O2.(-) than to H2O2. However, ferrous ions drastically enhance the toxicity of the enzymatic system generating H2O2 because of the production of the hydroxyl radicals. A protection against those oxygen species could be given by SOD in the xanthine/xanthine oxidase system and by catalase with the glucose/glucose oxidase system. The most damaging system was the combination of Fe2+ with H2O2. In this case, OH. is formed in a Fenton-like reaction. The fact that the OH. is the most damaging molecule accounts for the finding that catalase and desferrioxamine were efficient protectors in this system. Threshold levels of O2.(-) and H2O2 able to inhibit the mitochondrial respiration have been estimated. It is concluded that under normal respiration such thresholds are not reached in vivo and that the impairment of the mitochondrial respiratory activity does not seem to originate only from the natural free radical production in those organelles. However, if the production of free radicals is such to exceed the defense capability, like under oxidative stress, then the critical threshold can be surpassed and the respiration impaired leading to irreversible damages.

Aging↗
PubMed1990

Glutathione peroxidase, superoxide dismutase, and catalase inactivation by peroxides and oxygen derived free radicals.

Glutathione peroxidase (GPX), superoxide dismutase (SOD) and catalase are the most important enzymes of the cell antioxidant defense system. However, these molecules are themselves susceptible to oxidation. The aim of this work was to estimate to what extent this system could be inactivated by its own substrates. We tested the effect of hydrogen peroxide, cumene hydroperoxide, t-butyl hydroperoxide and hydroxyl and superoxide radicals on GPX, SOD and catalase. For GPX, a 50% inactivation was observed at 10(-1) M (30 min, 37 degrees C) for hydrogen peroxide, 3 x 10(-4) M (15 min, 37 degrees C) for cumene hydroperoxide and 5 x 10(-5) M (11 min, 37 degrees C) for t-butyl hydroperoxide. Unlike the hydroxyl radicals, superoxide anions did not inactivate this enzyme. Catalase was inactivated by hydroxyl radicals and by superoxide anions but organic peroxides had no effect. SOD was inactivated by 50% by hydrogen peroxide at 4 x 10(-4) M (20 min, 37 degrees C), but organic peroxides and hydroxyl radicals were ineffective on this enzyme. Since the three enzymes of the antioxidant system are susceptible to at least one of the oxidative reactive molecules, in the case of high oxidative stresses such an inhibition could take place, leading to an irreversible autocatalytical process in which the production rate of the oxidants will continuously increase, leading to cell death.

Catalase↗
PubMed1990

Comparative study of oxygen toxicity in human fibroblasts and endothelial cells.

The resistance of human pulmonary fibroblasts (WI-38) and human umbilical vein endothelial cells to oxygen toxicity (1 atm O2) was compared. Endothelial cells were more sensitive than fibroblasts. They contained also less antioxidant enzymes except for SOD: respectively 132%, 96%, 70%, 59%, and 21% of the SOD, GSH peroxidase, GSH reductase, catalase, and G6PD content of fibroblasts. However, they contained 1.81-fold more GSH than fibroblasts. Their lower content of antioxidant enzymes can explain their higher sensitivity to oxygen. The efficiency of natural antioxidant molecules and enzymes in the protection of cells incubated 3 days under 1 atm O2 was studied. alpha-tocopherol added in the culture medium led to a significant protection, contrary to the result for ascorbic acid. Microinjection of catalase, SOD, and GSH peroxidase directly into the cells was also tested: the protection was concentration dependent for both types of cells but SOD did not protect the endothelial cells. Lower activities of the other enzymes were needed to achieve protection of the endothelial cells, compared to fibroblasts. Since endothelial cells were also shown to display lower antioxidant enzyme activities, it can be hypothesized that their content is optimized for survival in physiological conditions.

Ascorbic Acid↗
PubMed1990

Importance of a threshold for error accumulation in cell degenerative processes. I. Modulation of the threshold in a model of free radical-induced cell degeneration.

Antioxidant enzymes (catalase, superoxide dismutase and glutathione peroxidase) have been injected into human fibroblasts exposed to 2 atm O2 in order to test if the threshold of oxidative damage versus antioxidant defenses could be modulated and if the damage remains reversible beyond the threshold. Cell damage was estimated by thymidine incorporation and cell survival curves. The proportion of dividing cells, measured by thymidine incorporation, rapidly decreased after O2 incubation: no cells could divide after 15 h of hyperoxia. However, cells incubated for a short time and injected with a high concentration of any of the three enzymes divided like non-oxygen-incubated cells: the enzymes could protect the cells against their loss of division potential. However, when cells were incubated for a longer period and/or when the injected enzyme concentration was lower, cells were either less or not protected and could no longer divide. These results suggest the presence of a threshold for the oxidative damage which cannot be totally repaired and which impairs the cell division; this threshold can, however, be modulated by supplementation of antioxidant enzymes, glutathione peroxidase being the most efficient.

Catalase↗
PubMed1988

Quantitative study of natural antioxidant systems for cellular nitrofurantoin toxicity.

The toxicity of nitrofurantoin was studied on human WI-38 fibroblasts: this chemical was lethal when added at concentrations higher than 5.10(-5) M in the culture medium. The protection afforded by antioxidants was then tested: alpha-tocopherol gave at 10(-4) M a light protection in contrast to ascorbic acid which even became toxic at high concentrations. We also tested catalase, superoxide dismutase and glutathione peroxidase introduced intracellularly by the microinjection technique. On a molecular basis, glutathione peroxidase was 23-times more efficient than catalase and 3000-times more than superoxide dismutase. The results also showed that a similar range of enzyme concentrations was found for the protection against high oxygen pressure. This suggests that, in the case of both oxygen and nitrofurantoin toxicity, the peroxide derivatives are the most toxic intermediates of the free radical attacks.

Antioxidants↗
PubMed1988

Use of the inhibition of enzymatic antioxidant systems in order to evaluate their physiological importance.

Chemical inhibitors of the different antioxidant enzymes were systematically testet either on purified enzymes of after incubation with human fibroblasts in culture. Inhibition values were obtained for catalase with aminotriazole, for superoxide dismutase with diethyldithiocarbamate, for glutathione peroxidase with mercaptosuccinate, for glutathione reductase with bischloroethylnitrosourea and for glutathione synthesis with buthionine sulfoximine. Viability of cells incubated with these inhibitors was then tested under normal conditions and under high oxygen pressure; the data were correlated with the above-mentioned inhibitory values. Cell viability was particularly affected when the glutathione-related enzymes, especially glutathione peroxidase, were inhibited.

Amitrole↗
PubMed1988

Microinjection of antibodies against superoxide dismutase and glutathione peroxidase.

Antibodies were prepared against glutathione peroxidase, superoxide dismutase, and catalase. Inhibition of the enzyme activity was obtained with anti-Gpx and anti-SOD antibodies but not with anti-CAT antibodies. The antibodies were then injected into human fibroblasts and bovine chondrocytes in culture either under normal conditions or under 1 atm of oxygen. The injected anti-Gpx and anti-SOD antibodies increased the mortality rate of the fibroblasts incubated under 1 atm of oxygen. However, when cells were incubated under normal atmosphere, anti-Gpx antibodies inhibited the division while anti-SOD antibodies increased this capacity. Anti-Gpx antibodies injected into chondrocytes decreased their viability. Injection of control antiserum had no effect. These data stress the primary importance of Gpx as antioxidant under all conditions and the relative efficiency of SOD according to the balance between the radical production and the activity of the other antioxidant systems.

Animals↗
PubMed1987

Comparative study of the enzymatic defense systems against oxygen-derived free radicals: the key role of glutathione peroxidase.

Human WI-38 diploid fibroblasts have been cultivated under high toxic O2 pressure, and their survival curves are reported. Superoxide dismutase, catalase, or glutathione peroxidase provided some protection when injected in the cells exposed to O2. This protective effect, recorded after 3 or 4 days of incubation, was the most pronounced when cells were injected just before oxygen exposure. Quantitative injection assays have been performed for the three enzymes. Surprisingly, glutathione peroxidase was found to be much more effective than both catalase and superoxide dismutase, the latter being particularly inefficient.

Catalase↗