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Biomedical subjects

J Guignard

Publications and source records attributed to J Guignard.

At least 19 recordsLinked to original sources
PubMed1989

Production of free radicals arising from the surface activity of minerals and oxygen. Part I. Iron mine ores.

The excess incidence of lung cancers observed in many metal mines probably is not only correlated with radioactivity but also with the inhaled dusts. In an attempt to determine a possible mechanism of carcinogenicity related to the surface activity of dusts, using the spin-trapping agent and ESR spectroscopy, one can demonstrate that some mineral dusts from iron ore mines are very active in an oxidative process in aqueous medium, implying the formation of radical oxygen species on reducing surface sites of the solid. This reducing surface activity of the dusts depends on the presence of Fe2+ ion in the lattice and on the process of activation and passivation of the surface sites. The more simple process of activation is the dissolution of the oxidized coating on the particle surface. Among the oxides, oxyhydroxides, carbonates, and silicates, the magnesium-iron phyllosilicates (chlorite, biotite, berthierine) appear the most active. The siderite FeCO3 is also active, but the iron oxides and oxyhydroxides are generally nonactive.

Free Radicals↗
PubMed1989

Production of free radicals arising from the surface activity of minerals and oxygen. Part II. Arsenides, sulfides, and sulfoarsenides of iron, nickel, and copper.

The excess incidence of lung cancers observed in metallic mines other than iron mines probably can be correlated not only to radioactivity, but also to dust pollution. The present work investigates the role of surface properties of sulfides and arsenides, which are present in metal mines, in oxidizing mechanisms capable of inducing oxidative stress and, possibly, of participating in carcinogenesis. Using added spin-trapping agent followed by ESR spectroscopy, it was observed that nickel and copper arsenides can be very active in the oxidation of formate or DMSO, by reducing the oxygen dissolved in a cell-free medium. Sulfides, on the other hand, are not active, except for the iron sulfides, which are very active as an air-aged powder. The process of activation and rendering the particle surface passive was investigated. Surface dissolution and moderate grinding were found to be activating factors, while air-aging generally rendered the particle surface passive. The critical factor in determining activity is the availability of reducing species of iron, copper, or nickel on the surface of the minerals.

Arsenates↗
PubMed1989

Production of oxygen radicals by the reduction of oxygen arising from the surface activity of mineral fibres.

According to certain hypotheses, the production of oxygen radicals within the biological medium (the phenomenon of oxidative stress) may play an important role in fibrosis and in certain steps of carcinogenesis. The mineral fibres of various materials are capable of participating in this phenomenon, owing to the reducing nature of their surface activity, so that OH. radicals can be produced from oxygen in 3 steps. The surface activity of inorganic materials which are insoluble or only very slightly soluble is due to the presence of electron donor active sites, generally linked to Fe2+ ions found in the neighbourhood of the surface. In biological systems, these sites may emerge on the surface as a result of the partial dissolution of the particle, the action of a biological reducing agent, the phenomenon of deposition on the surfaces or cation exchange. We have explored the reducing properties of the surfaces of a certain number of mineral fibres, in aqueous buffer medium, by electron paramagnetic resonance (EPR) measurement of the adduct with the radical-trapping agent 5,5'-dimethyl-l-pyrrolidine-N-oxide (DMPO), produced from the radicals initially formed (OH. or R.). We have found certain fibres to be highly effective in producing radicals from dissolved oxygen (Canadian chrysotile, nemalite, freshly ground amphiboles) while others have little effect. The reducing activity of certain fibres may be markedly increased by prior treatment in the presence of a ferrous salt (as in the case of erionite) or by the addition of glutathione to the reaction medium (as in the case of UICC crocidolite). It is suggested that the carcinogenic activity of certain inorganic materials at the pulmonary level is the result of their surface reducing properties. These reducing properties may either be present at the time of inhalation or acquired in the biological medium. This hypothesis is not in conflict with the observation of the role of the dimensional characteristics of fibres in mesothelioma.

Asbestos↗
PubMed1986

Studies on surface properties of asbestos. IV. Catalytic role of asbestos in fluorene oxidation.

To determine whether asbestos is a basic catalyst, catalytic oxidation of fluorene to fluorenone in a heterogeneous system was tested. It was shown that oxidation was quantitatively possible on the surface of all basic minerals, such as asbestos (chrysotile and crocidolite) and magnesia, but was not possible with acidic mineral materials such as silica. The effects of different factors are discussed.

Adsorption↗
PubMed1985

[Hospitals transfers of children of Maghreb countries. Reflections on current problems and short- and long-term solutions].

Every year, several thousands of North African children receive transfers to France for hospitalization. The need for these medical transfers is linked to a rapidly expending population, improving diagnostic techniques and inadequate therapeutic technology. Affected children are referred most often for cardiac and oncological diseases. Efforts have been made to discern the medical indications for such transfers, to facilitate the acceptance by social aid agencies and to provide the best possible psychosocial and educational settings for the children involved. Yet, many problems remain, such as advanced disease states and associated diseases at the time of transfer, affective disorders, worsened by the prolonged stay in hospital. Solutions must be found for these problems. Examples would include close collaboration between referred North African and French medical teams, and the existence in France of cultural environment sensitive to the needs to the North African patients. Because transfers are responsible for a high financial and affective cost, and for a dependent relationship between countries, long-term solutions must be considered and could include the transfer of technology and cooperation in research rather than medical care.

Africa, Northern↗
PubMed1977

[The value of early routine radiological examination following esophagectomy for carcinoma of the lower third of the esophagus].

An early upper gastrointestinal series may be carried out on a routine basis after recovery of the postoperative ileus and makes it possible to confirm the good quality of the anastomoses or, by contrast, reveal a benign fistula. Under some circumstances, it may be carried out very early following the development of postoperative complications: pain, fever, respiratory, circulatory and renal insufficiency or in the presence of abnormal discharge from the drains. It then shows whether this complication is due to an oesophagomediastinal or pleural fistula.

Adult↗
PubMed1977

[Pulmonary complications of esophagectomy for carcinoma of the middle third of the esophagus].

The authors studied 20 patients undergoing operation for a carcinoma of the middle third of the oesophagus during the period January 1972 to April 1975. Postoperative pulmonary complications are extremely common in such patients. All the patients had pulmonary function study results which were compatible with this type of surgery. All underwent resection with oesophagogastric anastomosis via a left thoracophrenolaparotomy. Of the 20 patients, 14 suffered from one or more episodes of acute respiratory insufficiency, some related to pneumonia. On the basis of various associated clinical, radiological, biological, evolutive and histopathological criteria, five types of pulmonary complication were distinguished: 1-Shock lung; 2-Infective pneumonia; 3-Traumatic pulmonary disease; 4-Acute cor pulmonale; 5-Lung disease of undetermined origin. Twelve patients died as a result of pulmonary complications, 11 early (before the 16th day). One patient only died as a result of rupture of the oesophagogastric anastomosis.

Esophageal Neoplasms↗
PubMed1974

[Immune deficiencies].

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Blood Protein Electrophoresis↗