Glucose absorption from starchy food has only been described with small amounts ingested ( approx... more Glucose absorption from starchy food has only been described with small amounts ingested ( approximately 20-75 g). Our aim was to describe total plasma (Ra) and exogenous glucose (Ra(exo)) appearance, glucose release from the liver (HGP), and the metabolic response after ingestion of 5 g polished or parboiled rice/kg body mass. Gas exchange and urea excretion were monitored in 8 healthy subjects before (3.5 h) and after (8 h) ingestion of rice intrinsically labeled with (13)C; [6,6-(2)H(2)]glucose was infused for the measurement of Ra, Ra(exo), and HGP. Changes in plasma glucose, insulin, lactate, and free fatty acids and the increase in Ra(exo) and Ra ( approximately 200%) and the decrease in HGP ( approximately 90%) were not significantly different (P > 0.05) after ingestion of either rice. Glucose oxidation was not significantly different (111.6 +/- 8.2 compared with 89.0 +/- 11.3 g; P = 0.13), but fat oxidation was significantly lower (9.9 +/- 1.7 compared with 21.3 +/- 4.0 g...
The chemical forms of inorganic carbon, CO2 or HCO3-, incorporated during photosynthesis in photo... more The chemical forms of inorganic carbon, CO2 or HCO3-, incorporated during photosynthesis in photoautotrophic Euphorbia characias cell suspension cultures were determined in experiments using 13CO2 and a mass spectrometry technique. From the equations of the CO2 hydration reaction, a kinetic model was first developed, and the effect of photosynthesis on the external CO2 concentration was simulated. It was predicted from this model that CO2 and HCO3- uptakes could be differentiated by recording only the CO2 variation rate in the external medium, successively in absence then in presence of an exogenous carbonic anhydrase activity. The results obtained with either CO2-grown or air-grown photoautotrophic cells were in good agreement with the model and demonstrated that CO2 was the sole species taken up during photosynthesis. In addition no accumulation of inorganic carbon within the cells was observed in the light. Similarly, in dark, CO2 was the only species released by respiration in t...
The fast development of sensitive molecular diagnostic tools is currently paving the way for a pe... more The fast development of sensitive molecular diagnostic tools is currently paving the way for a personalized medicine. A new class of ultrasensitive magnetic resonance imaging (MRI) T2 -contrast agents based on magnetosomes, magnetite nanocrystals biomineralized by magnetotactic bacteria, is proposed here. The contrast agents can be injected into the blood circulation and detected in the picomolar range. Purified magnetosomes are water-dispersible and stable within physiological conditions and exhibit at 17.2 T a transverse relaxivity r2 four times higher than commercial ferumoxide. The subsequent gain in sensitivity by T2 (*) -weighted imaging at 17.2 T of the mouse brain vasculature is evidenced in vivo after tail vein injection of magnetosomes representing a low dose of iron (20 μmoliron kg(-1) ), whereas no such phenomenon with the same dose of ferumoxide is observed. Preclinical studies of human pathologies in animal models will benefit from the combination of high magnetic fiel...
ABSTRACT Photoautotrophic, photomixotrophic and heterotrophic cell suspension cultures of Euphorb... more ABSTRACT Photoautotrophic, photomixotrophic and heterotrophic cell suspension cultures of Euphorbia characias were analysed for fatty acid composition of their neutral lipids. Contents in exponential and stationary phases of growth were compared to those of seeds, leaves and calli from which cell suspensions were derived. Quantitatively, on a dry weight basis, neutral lipid amounts varied in the different cells from 15 to 40% of that in the leaves (5.14 mg per g dry wt) but they were very low compared to that in the seeds (330 mg per g dry wt). The highest values were observed during the exponential phase of growth with photosynthetic cell suspensions. Qualitatively, fatty acid distribution was similar in photoautotrophic cell suspensions and leaves with a high content of linolenic acid. The linolenic acid/linoleic acid ratio decreased from photoautotrophic to heterotrophic cell suspensions. In seeds, the maximal amount of linoleic acid is reached while linolenic acid almost disappears. The desaturation of C18 fatty acids is closely linked with the development of the photosynthetic apparatus and with a low growth rate.
Mycotoxins are secondary metabolites of filamentous fungi which can cause a wide range of systemi... more Mycotoxins are secondary metabolites of filamentous fungi which can cause a wide range of systemic effects. Human health effects of inhaled mycotoxins remain poorly documented, despite the large amounts present, associated with air-borne particles. Among these mycotoxins, sterigmatocystin is one of the most prevalent. Because its chemical structure is close to that of the aflatoxins, we studied its metabolism and its cellular consequences when in contact with the airway epithelium, using the mass spectral signature from the 10% (13)C uniformly enriched sterigmatocystin. The metabolism was studied in vitro, using recombinant cytochrome P450s enzymes, and in porcine tracheal epithelial cell (PTEC) primary cultures at an air-liquid interface. The metabolites were analyzed by high-performance liquid chromatography coupled with tandem mass spectrometry detection. Expressed enzymes and PTECs were exposed to uniformly (13)C-enriched sterigmatocystin to confirm the relationship between sterigmatocystin and its metabolites because this isotopic cluster shape is conserved for all metabolites and their product ions. Incubation of sterigmatocystin with recombinant cytochrome P450 1A1 led to the formation of three metabolites identified as monohydroxysterigmatocystin, dihydroxysterigmatocystin and one glutathione adduct, the latter after the formation of a transient intermediate. In the PTEC cultures, sterigmatocystin metabolism resulted in a glucuro-conjugate. Two other products were detected, a sulfo-conjugate and a glucuro-conjugate of hydroxysterigmatocystin upon cytochrome P450 1A1 induction. This is the first study to report sterigmatocystin metabolism in airway epithelium, and it suggests that, contrary to the aflatoxins, sterigmatocystin is mainly detoxified into its conjugates and is unable to produce significant amounts of reactive metabolites in respiratory cells, at least in pigs.
The effects of factors influencing sunflower protoplast isolation yield, plating efficiency (PE) ... more The effects of factors influencing sunflower protoplast isolation yield, plating efficiency (PE) and the early differentiation into embryoids (embryogenic capacity, EC) have been studied. Only hypocotyl-derived protoplasts divided. The variations of PE and EC in the various treatments did not seem to be linked to the protoplast yields. From statistical analysis of the data, we concluded that, the sunflower genotype,
Studying lignin-biosynthetic-pathway mutants and transgenics provides insights into plant respons... more Studying lignin-biosynthetic-pathway mutants and transgenics provides insights into plant responses to perturbations of the lignification system, and enhances our understanding of normal lignification. When enzymes late in the pathway are downregulated, significant changes in the composition and structure of lignin may result. NMR spectroscopy provides powerful diagnostic tools for elucidating structures in the difficult lignin polymer, hinting at the chemical and biochemical changes that have occurred. COMT (caffeic acid O-methyl transferase) downregulation in poplar results in the incorporation of 5-hydroxyconiferyl alcohol into lignins via typical radical coupling reactions, but post-coupling quinone methide internal trapping reactions produce novel benzodioxane units in the lignin. CAD (cinnamyl alcohol dehydrogenase) downregulation results in the incorporation of the hydroxycinnamyl aldehyde monolignol precursors intimately into the polymer. Sinapyl aldehyde cross-couples 8-O-4 with both guaiacyl and syringyl units in the growing polymer, whereas coniferyl aldehyde cross-couples 8-O-4 only with syringyl units, reflecting simple chemical cross-coupling propensities. The incorporation of hydroxycinnamyl aldehyde and 5-hydroxyconiferyl alcohol monomers indicates that these monolignol intermediates are secreted to the cell wall for lignification. The recognition that novel units can incorporate into lignins portends significantly expanded opportunities for engineering the composition and consequent properties of lignin for improved utilization of valuable plant resources.
Journal of Labelled Compounds and Radiopharmaceuticals, 2007
ABSTRACT Due to their low concentrations in biological matrices, mycotoxin analyses often encount... more ABSTRACT Due to their low concentrations in biological matrices, mycotoxin analyses often encounter detection and quantification problems, especially for toxicokinetic studies. We have developed a strategy to produce in a single process, several fungi secondary metabolites uniformly enriched with (13)C, (15)N stable isotopes in their 'natural' composition. This includes: (1) a plant culture in the presence of 10%, 50% or 100% (13)CO(2) as the only source of carbon, and in the presence or not of 10% (15)N-enriched nitrogen salts as expected wheat or maize uniformly incorporate enriched isotopes into their bioproducts; (2) a subsequent solid culture of different filamentous fungi on plant biomass led to the production of a 'natural' mixture of isotopes-enriched mycotoxins - these compounds exhibit a characteristic isotopic cluster, which can be easily detected by mass spectrometry. As an example, we achieved 10% uniformly (13)C-enriched zearalenone, deoxynivalenol and mycophenolic acid by growing Fusarium graminearum or Penicillium brevicompactum on 10% (13)C enriched wheat seeds and 3 to 10% (13)C, (15)N uniformly enriched fumonisins from Fusarium verticillioides cultures on maize seeds or straw. These compounds were used for metabolism and transport studies in mammals either in vitro or in vivo and analysed by MS and MSn spectra of the isotopic cluster but also by (13)C, (15)N NMR. Moreover, such isotopic pattern enrichment can be used for quantitative evaluations of mycotoxins transport across mammalian biological membranes, alone or in their 'natural' conditions in the presence of other fungi secondary metabolites. Finally, we used such enriched compounds with high reliability in order to study zearalenone metabolism but these enriched compounds would also be used as internal standards to quantify zearalenone or fumonisins in contaminated food samples.
Glucose absorption from starchy food has only been described with small amounts ingested ( approx... more Glucose absorption from starchy food has only been described with small amounts ingested ( approximately 20-75 g). Our aim was to describe total plasma (Ra) and exogenous glucose (Ra(exo)) appearance, glucose release from the liver (HGP), and the metabolic response after ingestion of 5 g polished or parboiled rice/kg body mass. Gas exchange and urea excretion were monitored in 8 healthy subjects before (3.5 h) and after (8 h) ingestion of rice intrinsically labeled with (13)C; [6,6-(2)H(2)]glucose was infused for the measurement of Ra, Ra(exo), and HGP. Changes in plasma glucose, insulin, lactate, and free fatty acids and the increase in Ra(exo) and Ra ( approximately 200%) and the decrease in HGP ( approximately 90%) were not significantly different (P > 0.05) after ingestion of either rice. Glucose oxidation was not significantly different (111.6 +/- 8.2 compared with 89.0 +/- 11.3 g; P = 0.13), but fat oxidation was significantly lower (9.9 +/- 1.7 compared with 21.3 +/- 4.0 g...
The chemical forms of inorganic carbon, CO2 or HCO3-, incorporated during photosynthesis in photo... more The chemical forms of inorganic carbon, CO2 or HCO3-, incorporated during photosynthesis in photoautotrophic Euphorbia characias cell suspension cultures were determined in experiments using 13CO2 and a mass spectrometry technique. From the equations of the CO2 hydration reaction, a kinetic model was first developed, and the effect of photosynthesis on the external CO2 concentration was simulated. It was predicted from this model that CO2 and HCO3- uptakes could be differentiated by recording only the CO2 variation rate in the external medium, successively in absence then in presence of an exogenous carbonic anhydrase activity. The results obtained with either CO2-grown or air-grown photoautotrophic cells were in good agreement with the model and demonstrated that CO2 was the sole species taken up during photosynthesis. In addition no accumulation of inorganic carbon within the cells was observed in the light. Similarly, in dark, CO2 was the only species released by respiration in t...
The fast development of sensitive molecular diagnostic tools is currently paving the way for a pe... more The fast development of sensitive molecular diagnostic tools is currently paving the way for a personalized medicine. A new class of ultrasensitive magnetic resonance imaging (MRI) T2 -contrast agents based on magnetosomes, magnetite nanocrystals biomineralized by magnetotactic bacteria, is proposed here. The contrast agents can be injected into the blood circulation and detected in the picomolar range. Purified magnetosomes are water-dispersible and stable within physiological conditions and exhibit at 17.2 T a transverse relaxivity r2 four times higher than commercial ferumoxide. The subsequent gain in sensitivity by T2 (*) -weighted imaging at 17.2 T of the mouse brain vasculature is evidenced in vivo after tail vein injection of magnetosomes representing a low dose of iron (20 μmoliron kg(-1) ), whereas no such phenomenon with the same dose of ferumoxide is observed. Preclinical studies of human pathologies in animal models will benefit from the combination of high magnetic fiel...
ABSTRACT Photoautotrophic, photomixotrophic and heterotrophic cell suspension cultures of Euphorb... more ABSTRACT Photoautotrophic, photomixotrophic and heterotrophic cell suspension cultures of Euphorbia characias were analysed for fatty acid composition of their neutral lipids. Contents in exponential and stationary phases of growth were compared to those of seeds, leaves and calli from which cell suspensions were derived. Quantitatively, on a dry weight basis, neutral lipid amounts varied in the different cells from 15 to 40% of that in the leaves (5.14 mg per g dry wt) but they were very low compared to that in the seeds (330 mg per g dry wt). The highest values were observed during the exponential phase of growth with photosynthetic cell suspensions. Qualitatively, fatty acid distribution was similar in photoautotrophic cell suspensions and leaves with a high content of linolenic acid. The linolenic acid/linoleic acid ratio decreased from photoautotrophic to heterotrophic cell suspensions. In seeds, the maximal amount of linoleic acid is reached while linolenic acid almost disappears. The desaturation of C18 fatty acids is closely linked with the development of the photosynthetic apparatus and with a low growth rate.
Mycotoxins are secondary metabolites of filamentous fungi which can cause a wide range of systemi... more Mycotoxins are secondary metabolites of filamentous fungi which can cause a wide range of systemic effects. Human health effects of inhaled mycotoxins remain poorly documented, despite the large amounts present, associated with air-borne particles. Among these mycotoxins, sterigmatocystin is one of the most prevalent. Because its chemical structure is close to that of the aflatoxins, we studied its metabolism and its cellular consequences when in contact with the airway epithelium, using the mass spectral signature from the 10% (13)C uniformly enriched sterigmatocystin. The metabolism was studied in vitro, using recombinant cytochrome P450s enzymes, and in porcine tracheal epithelial cell (PTEC) primary cultures at an air-liquid interface. The metabolites were analyzed by high-performance liquid chromatography coupled with tandem mass spectrometry detection. Expressed enzymes and PTECs were exposed to uniformly (13)C-enriched sterigmatocystin to confirm the relationship between sterigmatocystin and its metabolites because this isotopic cluster shape is conserved for all metabolites and their product ions. Incubation of sterigmatocystin with recombinant cytochrome P450 1A1 led to the formation of three metabolites identified as monohydroxysterigmatocystin, dihydroxysterigmatocystin and one glutathione adduct, the latter after the formation of a transient intermediate. In the PTEC cultures, sterigmatocystin metabolism resulted in a glucuro-conjugate. Two other products were detected, a sulfo-conjugate and a glucuro-conjugate of hydroxysterigmatocystin upon cytochrome P450 1A1 induction. This is the first study to report sterigmatocystin metabolism in airway epithelium, and it suggests that, contrary to the aflatoxins, sterigmatocystin is mainly detoxified into its conjugates and is unable to produce significant amounts of reactive metabolites in respiratory cells, at least in pigs.
The effects of factors influencing sunflower protoplast isolation yield, plating efficiency (PE) ... more The effects of factors influencing sunflower protoplast isolation yield, plating efficiency (PE) and the early differentiation into embryoids (embryogenic capacity, EC) have been studied. Only hypocotyl-derived protoplasts divided. The variations of PE and EC in the various treatments did not seem to be linked to the protoplast yields. From statistical analysis of the data, we concluded that, the sunflower genotype,
Studying lignin-biosynthetic-pathway mutants and transgenics provides insights into plant respons... more Studying lignin-biosynthetic-pathway mutants and transgenics provides insights into plant responses to perturbations of the lignification system, and enhances our understanding of normal lignification. When enzymes late in the pathway are downregulated, significant changes in the composition and structure of lignin may result. NMR spectroscopy provides powerful diagnostic tools for elucidating structures in the difficult lignin polymer, hinting at the chemical and biochemical changes that have occurred. COMT (caffeic acid O-methyl transferase) downregulation in poplar results in the incorporation of 5-hydroxyconiferyl alcohol into lignins via typical radical coupling reactions, but post-coupling quinone methide internal trapping reactions produce novel benzodioxane units in the lignin. CAD (cinnamyl alcohol dehydrogenase) downregulation results in the incorporation of the hydroxycinnamyl aldehyde monolignol precursors intimately into the polymer. Sinapyl aldehyde cross-couples 8-O-4 with both guaiacyl and syringyl units in the growing polymer, whereas coniferyl aldehyde cross-couples 8-O-4 only with syringyl units, reflecting simple chemical cross-coupling propensities. The incorporation of hydroxycinnamyl aldehyde and 5-hydroxyconiferyl alcohol monomers indicates that these monolignol intermediates are secreted to the cell wall for lignification. The recognition that novel units can incorporate into lignins portends significantly expanded opportunities for engineering the composition and consequent properties of lignin for improved utilization of valuable plant resources.
Journal of Labelled Compounds and Radiopharmaceuticals, 2007
ABSTRACT Due to their low concentrations in biological matrices, mycotoxin analyses often encount... more ABSTRACT Due to their low concentrations in biological matrices, mycotoxin analyses often encounter detection and quantification problems, especially for toxicokinetic studies. We have developed a strategy to produce in a single process, several fungi secondary metabolites uniformly enriched with (13)C, (15)N stable isotopes in their 'natural' composition. This includes: (1) a plant culture in the presence of 10%, 50% or 100% (13)CO(2) as the only source of carbon, and in the presence or not of 10% (15)N-enriched nitrogen salts as expected wheat or maize uniformly incorporate enriched isotopes into their bioproducts; (2) a subsequent solid culture of different filamentous fungi on plant biomass led to the production of a 'natural' mixture of isotopes-enriched mycotoxins - these compounds exhibit a characteristic isotopic cluster, which can be easily detected by mass spectrometry. As an example, we achieved 10% uniformly (13)C-enriched zearalenone, deoxynivalenol and mycophenolic acid by growing Fusarium graminearum or Penicillium brevicompactum on 10% (13)C enriched wheat seeds and 3 to 10% (13)C, (15)N uniformly enriched fumonisins from Fusarium verticillioides cultures on maize seeds or straw. These compounds were used for metabolism and transport studies in mammals either in vitro or in vivo and analysed by MS and MSn spectra of the isotopic cluster but also by (13)C, (15)N NMR. Moreover, such isotopic pattern enrichment can be used for quantitative evaluations of mycotoxins transport across mammalian biological membranes, alone or in their 'natural' conditions in the presence of other fungi secondary metabolites. Finally, we used such enriched compounds with high reliability in order to study zearalenone metabolism but these enriched compounds would also be used as internal standards to quantify zearalenone or fumonisins in contaminated food samples.
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Papers by Michel Pean