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Biomedical subjects

F Seguin

Publications and source records attributed to F Seguin.

At least 19 recordsLinked to original sources
PubMed2004

A newborn piglet study of moderate hypoxic-ischemic brain injury by 1H-MRS and MRI.

Cerebral hypoxia-ischemia (HI) is an important cause of perinatal brain damage in the term newborn. The areas most affected are the parasagittal regions of the cerebral cortex and, in severe situations, the basal ganglia. The aim of this study was to show that the newborn piglet model can be used to produce neuropathology resulting from moderate HI insult and to monitor damage for 7 days. Two acute cerebral HI were induced in newborn Large White piglets by reducing the inspired oxygen fraction to 4% and occluding the carotid arteries. Newborn piglets were resuscitated, extubated and monitored for 7 days. (31)P magnetic resonance spectroscopy (MRS) offers the ability to monitor the severity of the HI insults. Lactate (Lac) was detected in the HI group at 2 h, 3 days and 5 days after insult by (1)H MRS. Lac/n-acetylaspartate and Lac/choline and Lac/creatine ratios increased significantly (p < 0.01) in the HI group 2 h after HI insults and remained high over 7 days. For the HI group, mean T(2) values increased significantly in the parietal white matter (subcortical) for 5 days after HI insult [117.5 (+/-7.4) to 158.5 (+/-19.2) at T+3 days, 167.7 (+/-15.4) at T+5 days and 160.9 (+/-10.1) at T+7 days (p < 0.01)]. This newborn piglet model of moderate HI brain injury with reproducible cerebral damage could be use as reference for the study of neuroprotective strategy for a period of 7 days.

Animals↗
PubMed2002

Analysis of the variations of follicular fluid composition during follicular growth and maturation in the mare using proton nuclear magnetic resonance (1H NMR).

Follicular development and ovulatory processes in mammals involve local biochemical changes as a result of substantial modifications in cellular metabolism, the most well known of which is steroid variation. In the present study, the intrafollicular variation of several other components was studied using proton nuclear magnetic resonance ((1)H NMR). This approach made it possible to demonstrate that the intrafollicular biochemical content changes during follicular growth and maturation. Follicular fluid was aspirated by ovarian puncture of the dominant follicle at various physiological stages of its development: early dominant, late dominant and preovulatory. Serum samples were collected during each puncture session. (1)H NMR was used to evaluate intrafollicular and circulating glycoconjugates (sugar chains and N-acetyl groups), lipoproteins (CH(3) and CH(2) groups), glucose metabolites (trimethylamines, acetate and lactate), amino acids (glutamine/glutamate and alanine), creatine/creatinine and polyamines. Follicular fluids were assayed by radioimmunoassay for oestradiol and progesterone contents. The intrafollicular contents of alanine and lipoproteins (CH(3) groups) decreased in the dominant follicle during growth, whereas concentrations of progesterone and oestradiol increased significantly. After injection of gonadotrophin to induce ovulation, follicular maturation was characterized by a decrease in glycoconjugates (sugar chains), trimethylamines and acetate, a decrease in oestradiol concentration, and a further increase in CH(3) groups of lipoproteins and progesterone. The results from the present study showed a clear correlation between the intrafollicular content of alanine and that of oestradiol. A correlation between progesterone and glycoconjugates (sugar chains) was also observed. Therefore, (1)H NMR was shown to be effective for studying specific changes in the biochemical composition of the follicular fluid that occur during follicular development. For the first time, the variation of several compounds (glycoconjugates, lipoproteins, glucose metabolites, amino acids and polyamines) in relation to growth and maturation was demonstrated. Some of these changes could be of crucial importance for follicular maturation and ovulation as well as for oocyte maturation and further fertilization.

Alanine↗
PubMed2001

Effects of atrazine and nicosulfuron on phytoplankton in systems of increasing complexity.

We have tested the sensitivity of phytoplankton to the herbicides atrazine and nicosulfuron in experiments conduced in increasingly complex systems, from single strain phytoplankton cultures (microplates) to mesocosms mimicking whole ecosystems. The endpoints used to assess sensitivity to atrazine and nicosulfuron were total biomass increase, photosynthetic efficiency, and community diversity, depending on the system considered. Nicosulfuron appeared to be very much less toxic to phytoplankton than atrazine, in accord with the planned changes in agricultural practices to reduce the effects of surface water contamination on aquatic biota. Nevertheless, nicosulfuron had significant effects in some systems (principally microcosms), whereas the single monocultures were almost insensitive to it. This points out the inaccuracy of standardized toxicity test on phytoplanktonic algae alone for predicting the effects of xenobiotics on natural communities and the need for tests in microcosms and mesocosms to obtain reliable evidence about the toxicity of a given chemical on freshwater aquatic ecosystems.

Atrazine↗
PubMed2000

Characterization of retinoic acid receptor-deficient keratinocytes.

Retinoids are essential for normal epidermal growth and differentiation and show potential for the prevention or treatment of various epithelial neoplasms. The retinoic acid receptors (RARalpha, -beta, and -gamma) are transducers of the retinoid signal. The epidermis expresses RARgamma and RARalpha, both of which are potential mediators of the effects of retinoids in the epidermis. To further investigate the role(s) of these receptors, we derived transformed keratinocyte lines from wild-type, RARalpha, RARgamma, and RARalphagamma null mice and investigated their response to retinoids, including growth inhibition, markers of growth and differentiation, and AP-1 activity. Our results indicate that RARgamma is the principle receptor contributing to all-trans-retinoic acid (RA)-mediated growth arrest in this system. This effect partially correlated with inhibition of AP-1 activity. In the absence of RARs, the synthetic retinoid N-(4-hydroxyphenyl)-retinamide inhibited growth; this was not observed with RA, 9-cis RA, or the synthetic retinoid (E)-4-[2-(5, 5, 8, 8 tetramethyl-5,6,7,8-tetrahydro-2-naphthalenyl)-1-propenyl] benzoic acid. Finally, both RARalpha and RARgamma differently affected the expression of some genes, suggesting both specific and overlapping roles for the RARs in keratinocytes.

Animals↗
PubMed2000

1H-NMR and (31)P-NMR analysis of energy metabolism of quiescent and motile turbot (Psetta maxima) spermatozoa.

31P-NMR and (1)H-NMR were used to monitor changes of several compounds with high-energy bonds and metabolites prior to and after the initiation of motility of turbot spermatozoa (Psetta maxima). The obtained (31)P-NMR spectra revealed the presence of phosphomonoesters, phosphodiester, intracellular inorganic phosphate (Pi), phosphocreatine (PCr), and free nucleotide triphosphate. Following the activation of motility, the di- and tri-phosphate nucleotides, PCr, phosphomonoesters levels dropped while Pi levels increased. A significant increase of lactate was also seen at the end of the swimming phase. The compositions of seminal fluid and urine were also determined. Lipoproteins, formic acid, amino acid, and citric acid were detected in seminal fluid. Dimethyl amine, trimethylamine, and trimethylamine oxyde were found in urine. These data suggest that at least a part of the energy required during the swimming phase results from anaerobic fermentation and oxidative phosphorylation. J. Exp. Zool. 286:513-522, 2000.

Animals↗
PubMed1999

Nucleotide content, oxidative phosphorylation, morphology, and fertilizing capacity of turbot (Psetta maxima) spermatozoa during the motility period.

The interdependence between motility, respiration, ATP production, and utilization was investigated in intact spermatozoa of turbot (Psetta maxima), a marine teleost. When spermatozoa were diluted in a hyperosmotic medium (>300 mOsmol/kg), they immediately became motile, and the intracellular concentration of ATP as well as the adenylate energy charge ratio dropped concomitant with the straight-line velocity. The ADP and AMP levels increased from 1.4 to 8.0 nmole/10(8) cells and from 0.6 to 6.0 nmole/10(8) cells, respectively. Moreover, 31P-NMR spectra recorded prior to the swimming phase revealed the presence of phosphomonoesters (PMEs) and phosphodiesters (PDEs), intracellular inorganic phosphate (Pi), and phosphocreatine (PCr). At the end of the motility period, PCr, PDE, and PME decreased, while the Pi level increased markedly. Following initiation of motility, O2 consumption of spermatozoa increased from 34.9 to 124.8 O2 nmole/10(9) spermatozoa/min. FCCP, an uncoupler of oxidative phosphorylation, did not significantly affect the respiratory rate of motile spermatozoa. Ouabain, a specific inhibitor of (Na+/K+)/ATPase, slightly decreased the respiration rate of motile spermatozoa, indicating that the major part of ATP catabolism was linked to dynein ATPase. Inhibitors of the respiratory chain (KCN, NaN3, NaHCO3-, oligomycin) reduced sperm respiration, percentage of motile cells, velocity, and adenylate contents. Following the reactivation of motility of demembranated spermatozoa, KCN, NaN3, NaHCO3- altered the flagellar beat frequency, demonstrating that these respiratory inhibitors possess action sites other than mitochondria. Mitochondrial oxidative phosphorylation is highly requested to produce energy required during motion. Nevertheless it is insufficient to maintain endogenous ATP stores. A second phase of motility was induced by a transfer of exhausted spermatozoa into an ionic medium of low osmolality (200 mOsmol/kg) for 30 min. Spermatozoa, once reactivated in AM, recovered 55% of initial motility and 31% of initial fertilization rate. In hypo-osmotic medium, mitochondrial oxidative phosphorylation also induced ATP regeneration. Following activation of movement, several morphological changes were observed in the mitochondria and the midpiece.

Adenine Nucleotides↗
PubMed1999

Cellular signalling and free-radical modulating activities of the novel peptidomimetic L-glutamyl-histamine.

A novel histamine-containing peptidomimetic, L-glutamyl-histamine (L-Glu-Hist), has been synthesized and characterized as a possible cytokine mimic which might lead to cellular responses of improved specificity. The energy-minimized 3-D conformations of L-Glu-Hist derived from its chemical structure stabilize Fe2+-chelating complexes. L-Glu-Hist concentration-dependently accelerates a decrease in ferrous iron in ferrous sulfate solution and shows ferroxidase-like activity at concentrations less than 3 mM in the phenanthroline assay, whereas in the concentration range 3-20 mM it restricts the availability of Fe2+ to phenanthroline by chelation of iron ions. At low concentrations (less than or about 1 mM), L-Glu-Hist stimulates peroxidation of phosphatidylcholine in liposomes catalyzed by a superoxide anion radical (O2)-generating system (Fe2+ + ascorbate) and, at high concentrations (*10 mM), it suppresses lipid peroxidation (LPO) in liposomes. The stimulation of LPO by L-Glu-Hist is related to its ability at low concentrations (*0.05 mM) to release O2 free radicals as determined by the superoxide dismutase-inhibitable reduction of cytochrome c. The release of O2 by L-Glu-Hist might result from its ferroxidase-like activity, while its inhibition of LPO is due to chelation of Fe2+, prevention of the formation of free radicals, and degradation of lipid hydroperoxides at 5-20 mM L-Glu-Hist concentrations. L-Glu-Hist releases O2 at concentrations which stimulate [3H]thymidine incorporation into DNA and proliferation of mouse spleen lymphocytes and also of mononuclear cells from human blood. The induction of lymphocyte proliferation by L-Glu-Hist is dose-dependent in the 0.01-0.05 mM concentration range, although the maximal stimulation of LPO in the O2-dependent system is observed at higher L-Glu-Hist concentrations (*1 mM). Thus, low concentrations of oxygen free radicals released by L-Glu-Hist may provide a very fast, specific, and sensitive trigger for lymphocyte proliferation and immunoregulation.

Animals↗
PubMed1998

Quantification by magnetic resonance spectroscopy of metabolites in seminal plasma able to differentiate different forms of azoospermia.

The aim was to determine whether proton magnetic resonance spectroscopy (1H-MRS) of metabolites such as glycerophosphorylcholine (GPC), choline, citrate and lactate in human seminal plasma can be used to differentiate (i) different azoospermic patients and (ii) different forms of spermatogenic failure including those who had undergone radiation therapy or chemotherapy. Semen samples were provided by men with obstructive azoospermia and spermatogenic failure who had serum follicle stimulating hormone (FSH) values within the normal range and either more or less than normal. Four prominent constituents of seminal plasma were identified by 1H-MRS: GPC, choline, citrate and lactate. The peak area ratios of choline/citrate as well as choline/lactate were significantly different (P < 0.01) between groups with spermatogenic failure and obstructive azoospermia. When the serum FSH values were normal in men with spermatogenic failure and obstructive azoospermia, a significant difference was found in the GPC/choline ratio (P < 0.001). When the FSH values were normal, the GPC/choline ratio appeared to be a very important parameter able to differentiate not only between cases of spermatogenic failure and obstructive azoospermia but also between different forms of spermatogenic failure. These results demonstrate the potential use of 1H-MRS on human seminal plasma in a new approach in the management of male infertility.

Antineoplastic Agents↗
PubMed1995

T1 mapping from spin echo and stimulated echoes.

We present an imaging method to obtain a map of the spin-lattice relaxation time. Images were acquired with the same spatial resolution and in the same time as for a regular spin-echo acquisition. The sequence was based on the simultaneous acquisition of a spin echo and several stimulated echoes with the same intensity except for T1 weighting which increases with the interval between the excitation pulse and the readout pulse. T1 values obtained on phantoms were compared to those from the inversion-recovery method and show the accuracy (2%) and the precision (5%) of the method. T1 images of the brain of a healthy volunteer are presented and demonstrate the ability of the method to obtain T1 mapping in vivo in 12 min and without susceptibility artifacts. In vivo and in vitro results were compared to those obtained by a TOMROP sequence in the same acquisition time.

Biophysical Phenomena↗
PubMed1994

31P and 13C nuclear magnetic resonance studies of macrophages.

Biochemical events associated with differentiation and activation of monocyte-macrophage cell lines are of major interest in the understanding of pathophysiological processes as well as in research on immunopharmacological modulation of these cells. Nuclear magnetic resonance is the technique of choice for kinetic studies of metabolic events under such experimental conditions. This approach was used with the P388-D1 model of mature macrophages. Cells primed in vivo were triggered in vitro during NMR analysis and the results were compared to those from chemiluminescence tests performed simultaneously. Three preliminary phases were achieved: (i) 31P and 13C NMR spectroscopy of perchloric acid extracts, (ii) optimization of culture and perfusion conditions with validation of macrophage viability and functionality, and (iii) development of a data processing technique to improve the time resolution of kinetic studies. Based on their phosphocreatine content, cells primed in vivo exhibited maturation than control cells. After the respiratory burst of primed macrophages was triggered by concanavalin A, 31P NMR spectra reflected both a transient increase in ADP phosphorylation and intracellular acidification. 13C NMR studies indicated an acceleration of metabolism following in vitro triggering. The phenomenon was associated with an increased glucose consumption, implicating the hexose monophosphate shunt. These occurred concomitantly with the appearance of new peaks attributed to phosphorylated sugars.

Animals↗
PubMed1994

Acquisition of spin echo and stimulated echo by a single sequence: application to MRI of diffusion.

A new method is described to measure the restricted diffusion coefficient with magnetic resonance imaging. The two images necessary to calculate the diffusion image are obtained with a simultaneous acquisition of a spin-echo and a stimulated echo, and so, in half the time needed by usual spin-echo or stimulated echo method. A different diffusion contrast is created on each echo. A map of an estimate of the diffusion coefficient and an estimation of T1 value are obtained with only one experiment. The accuracy of the method has been evaluated on phantom and results are in agreement with values found in previous papers and with measurements performed with a usual spin-echo method. Furthermore, in vivo measurements have shown that this method can be used without electrocardiogram triggering.

Brain↗
PubMed1993

Radiofrequency map of an NMR coil by imaging.

We propose a new imaging method to obtain a map of the radiofrequency (RF) field amplitude over a sample. The sequence contains three RF pulses (alpha, 2 alpha, and alpha) and produces two images by a classical spin echo and a stimulated echo. A third image is computed and gives the distribution of the flip angle alpha, and so the RF amplitude, over the sample. The accuracy of the flip angle determination is verified on an homogeneous sample and results show a good correlation between experimental and theoretical flip angles in the range of 50 degrees to 130 degrees. Experiments with a surface coil and a resonator show the method is available in an inhomogeneous RF field. Images obtained on the calf of a volunteer confirms the independence of the computed RF distribution from proton density, T1, or T2 contrast.

Humans↗
PubMed1993

1H nuclear magnetic resonance studies of seminal plasma from fertile and infertile men.

Glycerylphosphorylcholine (GPC), glycerylphosphorylethanolamine (GPE), citrate, and lactate content of human seminal plasma was analysed by measuring the peak area of 1H nuclear magnetic resonance (NMR) spectra in samples from four groups of patients: 21 spermatogenic failure subjects; 14 obstructive azoospermic subjects (vasectomized); seven patients presenting very severe oligoasthenozoospermia (OAT) and 18 normozoospermic subjects (control). The peak areas for GPC, citrate and lactate in seminal plasma were significantly smaller for patients with azoospermia than for the control group: 16.79, 8.18 and 2.28 versus 23.38, 10.58 and 4.30, respectively (P < 0.01). The peak area ratios for citrate:lactate and GPC:lactate were significantly different (P < 0.01) between the control group and the spermatogenic failure or obstructive azoospermia groups. A significant difference was also found in GPE:GPC peak intensity ratio between spermatogenic failure and obstructive azoospermia subjects (P < 0.001). These results provide some quantitative markers which may be used for examining infertility by using 1H NMR of seminal plasma samples.

Biomarkers↗
PubMed1993

[Investigation of seminal plasma. Value of nuclear magnetic resonance].

The purpose of this study was to investigate whether the measurement by NMR of some biochemical markers such as glycerylphosphorylcholine (GPC), glycerylphosphorylethanolamine (GPE), citrate, and lactate in human seminal plasma may be able to differentiate spermatogenic failure from obstructive azoospermia. The peak area ratios citrate/lactate, between normozoospermic and spermatogenic failure or obstructive azoospermia groups were significantly different. We have also found significant differences in GPE/GPC peak intensity ratio between spermatogenic failure men and obstructive azoospermia patients (P < 0.001). This ratio appears to be a very important parameter to differentiate spermatogenic failure from obstructive azoospermia. These results demonstrate the potential use of 1H NMR on human seminal plasma in male infertility evaluation and such analysis may be used to elucidate the molecular basis of the human pathologic seminal plasma disturbances.

Anticoagulants↗
PubMed1991

Biochemical events occurring during the respiratory burst of macrophages: A 31P and 13C NMR study.

In a previous study, 31P NMR revealed that an intracellular acidification occurred during the respiratory burst of P388 D1 macrophages, but this NMR technique could not provide information about the localization of this event in cells. However, using a fluorescent pH-dependent probe, it was confirmed that this transient pH decrease does not occur in the cytosol but more probably occurs in relation to the function of endocytic vesicles. A 31P NMR study allowed us to evidence a transient increase in ADP phosphorylation at the beginning of the respiratory burst, possibly in connection with the initiation of the oxidase complex involved in superoxide anion production. A 13C NMR study of perchloric acid extracts from in vivo primed cells revealed an increase in glucose consumption due to Con A triggering. Sugar phosphates, which must be considered markers of the hexose monophosphate shunt involved in the respiratory burst, were also observed upon this activation process.

Adenosine Diphosphate↗
PubMed1990

31P NMR study of intracellular pH during the respiratory burst of macrophages.

The metabolic events occurring during the respiratory burst of macrophages previously primed in vivo with lipopolysaccharide were studied by 31P nuclear magnetic resonance, using the P388D1 cell line as a model of the mature macrophages. Using perchloric acid extracts, the presence of phosphocreatine was shown in the primed cells, indicating that in control P388 D1 macrophages, in which no phosphocreatine was seen, in vivo maturation was incomplete. The cells primed in vivo exhibited greater maturation than the control cells, as well as greater creatine kinase activity. Perfusion of gel-embedded macrophages allowed the monitoring of phosphorylated metabolite peak intensities and of the intracellular pH. After the respiratory burst of the primed macrophages had been triggered by concanavalin A, these intensities did not alter significantly, but the intracellular pH decreased. 31P NMR spectra reflected transient acidification in the primed cells, possibly due to the formation of endocytic vesicles and their fusion with lysosomes.

Animals↗