Biomedical subjects

E Le Rumeur

Publications and source records attributed to E Le Rumeur.

At least 19 recordsLinked to original sources

PubMed2003

1H NMR structural characterization of the cytochrome c modifications in a micellar environment.

The interaction of cytochrome c with micelles of sodium dodecyl sulfate was studied by proton NMR spectroscopy. The protein/micelles ratio was found to be crucial in controlling the extent of the conformational changes in the heme crevice. Over a range of ratios between 1:30 and 1:60, the NMR spectra of the ferric form display no paramagnetic signals due to a moderately fast exchange between intermediate species on the NMR time scale. This is consistent with an interconversion of bis-histidine derivatives (His18-Fe-His26 and His18-Fe-His33). Further addition of micelles induces a high-spin species that is proposed to involve pentacoordinated iron. The resulting free binding site, also encountered in the ferrous form, is used to complex exogenous ligands such as cyanide or carbon monoxide. Attribution of the heme methyls was performed by means of exchange spectroscopy through ligand exchange or electron transfer. The heme methyl shift pattern of the micellar cyanocytochrome in the ferric low spin form is different from the pattern of both the native and the cyanide cytochrome c adduct, in the absence of micelles, reflecting a complete change of the heme electronic structure. Analysis of the electron self-exchange reaction between the two redox states of the micellar cyanocytochrome c yields a rate constant of 2.4 x 10(4) M(-1) s(-1) at 298 K, which is surprisingly close to the value observed in the native protein.

Animals↗

PubMed2003

MRI texture analysis on texture test objects, normal brain and intracranial tumors.

Texture analysis was performed in three different MRI units on T1 and T2-weighted MR images from 10 healthy volunteers and 63 patients with histologically confirmed intracranial tumors. The goal of this study was a multicenter evaluation of the usefulness of this quantitative approach for the characterization of healthy and pathologic human brain tissues (white matter, gray matter, cerebrospinal fluid, tumors and edema). Each selected brain region of interest was characterized with both its mean gray level values and several texture parameters. Multivariate statistical analyses were then applied in order to discriminate each brain tissue type represented by its own set of texture parameters. Texture analysis was previously performed on test objects to evaluate the method dependence on acquisition parameters and consequently the interest of a multicenter evaluation. Even obtained on different sites with their own acquisition routine protocol, MR brain images contain textural features that can reveal discriminant factors for tissue classification and image segmentation. It can also offer additional information in case of undetermined diagnosis or to develop a more accurate tumor grading.

Adult↗

PubMed2001

Sarcolemma phospholipid structure investigated by immunogold electron microscopy and (31)P NMR spectroscopy with lanthanide ions.

The biological functions of plasma membranes depend greatly on the biophysical properties resulting from protein and phospholipid structure. We investigated the phospholipid structure of the normal sarcolemma membrane, which is known to be highly dysfunctional in myopathies. Combining electron microscopy and (31)P nuclear magnetic resonance (NMR) spectroscopy on isolated sarcolemma vesicles, we find that (i) the sarcolemma vesicles maintain the in-vivo cellular sidedness, (ii) the phospholipid mobility is close to that observed in model membranes (similar lateral diffusion coefficients and spin-lattice T(1) relaxation times). Using broad-band and magic angle spinning (31)P NMR spectroscopy with lanthanide ions (Pr(3+)), it is possible to quantify the distribution of phospholipids between internal and external membrane layers, showing that the trans-bilayer distribution is highly asymmetrical.

Cell Polarity↗

PubMed2000

Role of the mode of sensory stimulation in presurgical brain mapping in which functional magnetic resonance imaging is used.

OBJECT: The aim of this study was to evaluate different types of sensory stimulation used to distinguish between microvasculature and venous drainage on functional magnetic resonance (fMR) images with blood oxygen level-dependent (BOLD) contrast. METHODS: Seven volunteers received three sensory stimulations. One consisted of small discontinuous automated pokes to the ventral aspect of the right thumbtip. The other two were delivered by the investigator, who vigorously brushed the ventral aspect of the right thumbtip either alone or in combination with the thenar region. Seven contiguous axial slices of the head were acquired using echoplanar fMR imaging during each mode of stimulation. Boxcar analysis and Student's t-test were performed. Cluster analysis was used to determine significant differences between rest and activation phases. The major findings were 1) that a discontinuous sensory stimulation involving a small skin area was able to evoke a limited activated area in the postcentral gyrus with a low activation index (AI [2%]); 2) that this limited activated area was included in the activated area elicited by the continuous sensory stimulations; and 3) that this also evoked multiple activated areas exhibiting AIs of either approximately 2% or greater than 5%. This indicated that the limited discontinuous tactile stimulation evoked a BOLD-contrast fMR image essentially of microvasculature, whereas the more extensive continuous stimulations evoked a BOLD-contrast fMR image in both microvasculature and venous drainage. CONCLUSIONS: Different sensory stimulations are necessary to differentiate primary sensory cortex from venous drainage for presurgical brain mapping.

Adult↗

PubMed1999

Static and magic angle spinning (31)P NMR spectroscopy of two natural plasma membranes.

Static and magic angle spinning (31)P NMR spectroscopy was used for the first time in natural plasma membranes from erythrocytes and skeletal muscle to study phospholipid arrangement and composition. Typical static powder-like spectra were obtained showing that phospholipids were in a bilayer arrangement. Magic angle spinning narrowed spectra into two components. The first one corresponded to phosphatidylcholine and the second one to the other phospholipids with intensities in agreement with the known phospholipid composition. These findings show that NMR data previously acquired using model membranes can be transposed to studies on phospholipids in their natural environment.

Animals↗

PubMed1999

Kinetics of PCr to ATP and beta-ATP to beta-ADP phosphoryl conversion are modified in working rat skeletal muscle after training.

Kinetics of phosphoryl transfers from PCr to gamma-ATP and from beta-ATP to beta-ADP were measured by magnetization transfer in an in vivo 31P NMR experiment in working rat skeletal hind leg muscles. Two groups were examined. One group was submitted to a 6-week training program of treadmill running. The other group was composed of sedentary animals. Metabolic oxidative capacity and mechanical performance were improved greatly by training as shown previously. Phosphoryl transfer of PCr-->gamma-ATP or beta-ATP-->beta-ADP total fluxes were identical in resting trained and untrained muscles. Under stimulation, the flux of creatine kinase transfer was significantly inhibited by 23% compared with resting level in untrained muscles; by contrast, it was not inhibited and maintained at the high resting level in trained muscles. Thus physiological changes probably linked to a decrease of the production of anions, which could inhibit creatine kinase, were able to maintain creatine kinase flux. The flux of beta-ATP to beta-ADP transfer were enhanced largely in working muscles from 1.4+/-0.8 and 2+/-0.8 at rest to 4+/-1.6 and 6.6+/-2.7 mM s(-1) for untrained and trained muscles respectively; the effect was more pronounced in trained than in untrained muscles. These results showed an acceleration of phosphoryl turnover in working muscles after training, which could contribute to improve oxidative and mechanical performances. Such kinetic measurements of phosphoryl conversion may provide information on ATP turnover in pathophysiologic situations where ADP accumulates because of impaired ATP synthesis (mitochondrial myopathies, lower perfusion level).

Adenosine Diphosphate↗

PubMed1999

Comparison of automated and visual texture analysis in MRI: characterization of normal and diseased skeletal muscle.

Automated magnetic resonance imaging (MRI) texture analysis was compared with visual MRI analysis for the diagnosis of skeletal muscle dystrophy in 14 healthy and 17 diseased subjects. MRI texture analysis was performed on 8 muscle regions of interest (ROI) using four statistical methods (histogram, co-occurrence matrix, gradient matrix, runlength matrix) and one structural (mathematical morphology) method. Nine senior radiologists assessed full leg transverse slice images and proposed a diagnosis. The 59 extracted texture parameters for each ROI were statistically analyzed by Correspondence Factorial Analysis. Non-parametric tests were used to compare diagnoses based on automated texture analysis and visual analysis. Texture analysis methods discriminated between healthy volunteers and patients with a sensitivity of 70%, and a specificity of 86%. Comparison with visual analysis of MR images suggests that texture analysis can provide useful information contributing to the diagnosis of skeletal muscle disease.

Adolescent↗

PubMed1999

Mitochondrial creatine kinase functional development in post-natal rat skeletal muscle. A combined polarographic/31P NMR study.

Mitochondrial creatine kinase (Mi-CK) function in viable mitochondria from developing rat skeletal muscle was assessed both by polarographic measurements of creatine-induced respiration and 31P NMR spectroscopy measurements of phosphocreatine (PCr) synthesis. Creatine-induced respiration was observed in very young rats and increased by 50% to 35 days of age. PCr synthesis was present in 7 day old animals and increased by 300% reaching levels measured in 35 day and adult muscle. Unlike reports showing Mi-CK enzymatic activities but no mitochondrial function in several situations, a concomitant progression of enzymatic activity and mitochondrial function was evidenced during the developmental stages of skeletal muscle Mi-CK in altricious animals. These results correlated with the progressive pattern of muscle differentiation during development of motricity in such animals. The observation that Mi-CK is functional in skeletal muscle mitochondria very early after birth, strongly favors the notion that adaptations in skeletal muscle of Mi-CK knock-out mice occur early.

Animals↗

PubMed1998

The use of phosphocreatine plus ADP as energy source for motility of membrane-deprived trout spermatozoa.

Live trout spermatozoa initiate flagellar motility for a short period of time (30 s at 18 degrees C), during which their mean beat frequency (BF) decreases steadily from 60 to 20 Hz; motility then stops abruptly. When demembranated, the motility of axonemes lasts much longer, up to 20 min, with high beat frequency, provided that ATP (millimolar concentration) and cAMP (micromolar) are added. In the present paper, the motility of demembranated trout sperm was investigated in the absence of added ATP in various incubation conditions relative to other substrates. Without the addition of exogenous creatine kinase, the addition of phosphocreatine (PCr) and ADP shows the appearance of a progressive activation of all sperm models with BF increasing with time up to high values. Without the addition of cAMP, the BF increases to lower values but flagella propagated poorly coordinated waves for only a few min. Similar progressive activation is also observed when only ADP is added (without any previous in vivo activation) and BF increases up to moderate values. In this latter case, no activation occurs without addition of cAMP. The respective roles of creatine kinase and adenylate kinase in this process were investigated by addition of specific inhibitors such as fluorodinitrobenzene and P1,P5-di(adenosine-5')pentaphosphate in the above described conditions. We conclude from these observations that all the elements necessary for a coupling between ADP/PCr/creatine kinase on one hand and ATP/ADP/dynein on the other appear to be present in trout spermatozoa: thus the existence of a shuttle sustaining this coupling is strongly suggested.

Adenosine Diphosphate↗

PubMed1997

Kinetics of ATP to ADP beta-phosphoryl conversion in contracting skeletal muscle by in vivo 31P NMR magnetization transfer.

The rate constant of the beta-adenosine triphosphate to beta-adenosine diphosphate conversion was measured using 31P nuclear magnetic resonance magnetization transfer in resting and contracting in vivo rat skeletal muscle. Theoretically, the rate constant should be the sum of the rate constants of the reactions catalyzing ATP-ADP exchange. In resting muscle, the conversion rate constant was 0.4 s-1 and beta-ATP intrinsic T1 was 1.7 s. The velocity of conversion was 3.8 mM s-1. During stimulation, phosphocreatine fell to 36% and ATP to 82% of initial values. The rate constant and velocity of beta-phosphoryl conversion increased to 0.8 s-1 and 6.3 mM s-1, respectively, but did not reach expected levels, i.e. the product of the ATP concentration with the sum of pseudo first-rate constants of the individual reactions. These conversion velocities should be higher than reverse creatine kinase velocities, previously measured to be 10 mM s-1 in resting muscle and 7.5 mM s-1 in contacting muscle and confirmed in this work. The discrepancy between expected and observed data could be due either to compartmentation of part of the beta-ATP in pools exchanging slowly with the bulk of cellular ATP, or to ADP binding to macromolecules thus preventing full ADP saturation during magnetization transfer.

Adenosine Diphosphate↗

PubMed1996

Phosphocreatine synthesis by isolated rat skeletal muscle mitochondria is not dependent upon external ADP: a 31P NMR study.

Phosphocreatine synthesis by mitochondria isolated from rat skeletal muscle was determined in presence of inorganic phosphate, creatine, and either ATP or ADP, using 31P NMR spectroscopy in a new protocol maintaining mitochondria for several hours in a well-coupled state. Maximal velocity of phosphocreatine synthesis was identical with 0.4 mM of ADP or 0.5 mM ATP at a rate of 0.063 mM/min. External ATP and ADP were always present in the spectra, demonstrating that in skeletal muscle cells as in heart muscle cells, mitochondrial creatine kinase coupled to translocase has a very strong amplifying effect on oxidative phosphorylation and converts external inorganic phosphate and creatine into phosphocreatine without net adenine nucleotide consumption. Therefore, adenine nucleotides can be considered as cofactors rather than regulators of mitochondria metabolism. This is in agreement with the "phosphocreatine-circuit" theory.

Adenosine Diphosphate↗

PubMed1996

Improvement of muscular oxidative capacity by training is associated with slight acidosis and ATP depletion in exercising muscles.

Metabolic and mechanical properties of female rat skeletal muscles, submitted to endurance training on a treadmill, were studied by a 60-min in vivo multistep fatigue test. 31P-NMR was used to follow energy metabolism and pH. Mechanical performance was greatly improved in trained muscles. The oxidative capacity of the skeletal muscles was evaluated from the relationship between ADP calculated from the creatine kinase equilibrium and work and from the measure of the rate of phosphocreatine (PCr) resynthesis following exercise. In trained muscles, ADP production was lower per unit of mechanical performance, showing an improvement of oxidative metabolism. However, the PCr resynthesis rate was not modified. Slight acidosis and ATP depletion were observed from the beginning of the fatigue test. These modifications suggest changes of the creatine kinase equilibrium favoring mitochondrial ATP production. Our results indicate that muscle status improvement could be accompanied by ATP depletion and minimal acidosis during contraction; this would be of particular importance for objective evaluation of muscle regeneration processes and of gene therapy in muscle diseases.

Acidosis↗

PubMed1996

Effects of dimethylformamide on in vivo fatigue and metabolism in rat skeletal muscle measured by 31P-NMR.

Dimethylformamide (DMF) is widely used as an industrial solvent in spite of well-established hepatotoxicity and adverse effects on in vitro muscle contractility. The doses used in the studies describing these effects were higher than the doses required to solubilize drugs to be injected at very low levels and the potential effects of DMF at very low levels has not yet been explored. The goal of this work was to study the effects of an acute, low dose of DMF (3 mu/100 g body weight, administered i.p.) on mechanical parameters and energy metabolism of contracting rat skeletal muscle. Metabolic changes were followed by 31P nuclear magnetic resonance spectroscopy. Tension was significantly lower during the fatigue test in DMF-treated rats than in controls. Phosphomonoesters and inorganic phosphorus level were lower, and intracellular pH was higher in DMF-treated rats than in controls, showing that energy metabolism was activated to a lesser degree, in relation with the lower mechanical performance, after DMF. Skeletal muscle is a target organ for dimethylformamide which has a major effect on muscle contractility by decreasing the tension developed. The effects of DMF suggest that it is unsuitable for use as a drug vehicle for in vivo injections, even at a very low nonhepatotoxic doses.

Animals↗

PubMed1995

In vivo evidence of abnormal mechanical and oxidative functions in the exercised muscle of dystrophic hamsters by 31P-NMR.

Mechanical properties and metabolic adaptation to exercise in skeletal muscle of dystrophic hamsters were studied with an in vivo 31P-NMR multistep fatigue test. Three successive 20-min steps with increasing rhythms of tetanic stimulation were followed by a 20-min recovery period. Fatigue in dystrophic hamsters (DH) developed more rapidly and was greater than in normal hamsters (NH); total mechanical performance per min increased step by step in NH while it decreased in DH, showing a progressive mechanical impairment of the dystrophic muscles. ADP and PCr recovery rates were significantly reduced in DH muscles. Acidosis appeared in both DH and NH and persisted in DH throughout the test, suggesting reduced mitochondrial oxidative capacity of the dystrophic muscle. The pH recovery rate was reduced in DH muscles suggesting a reduction in export protons capacity. These results provide evidence of impaired mitochondrial function and intracellular ionic regulation in the dystrophic muscle, associated with the lack of dystrophin and dystrophin-associated glycoproteins in the DH.

Analysis of Variance↗

PubMed1994

Multiparametric classification of muscle T1 and T2 relaxation times determined by magnetic resonance imaging. The effects of dynamic exercise in trained and untrained subjects.

Muscle relaxation times can now be measured accurately with magnetic resonance imaging (MRI), distinguishing working muscles from non-working muscles. A correlation between T2 increase and work intensity has been shown in healthy volunteers. The small amount of data on T1 relaxation times is contradictory. In addition, all the published studies have concerned short-duration exercise in subjects of unknown training level. The goals of this study were (i) to determine T1 and T2 variations in thigh muscles after long dynamic exercise, (ii) to analyse the effects of training and (iii) to determine the relationship between power output and relaxation times after exercise. Sedentary men, soccer players and tri-athletes performed submaximal dynamic exercise at a constant heart rate for 15 min. MRI was performed before and 5 min after the end of exercise. The results showed (i) that T1 increased in parallel to T2 in anterior thigh muscles and (ii) that multiple correspondence analysis and hierarchical ascending classification can discriminate three subjects classes according to power output, training level and relaxation times, which fitted well with our three groups of subjects.

Adolescent↗

PubMed1992

Creatine kinase activity in rat skeletal muscle with intermittent tetanic stimulation.

ATP synthesis from PCr through creatine kinase reaction was measured in vivo in rat leg muscle using 31P NMR magnetization transfer and progressive saturation. Both techniques determined a spin-lattice relaxation time for PCr of 3 s at rest and an identical forward rate constant of 0.22-0.26 s-1. In stimulated muscles, magnetization transfer showed that flux was not changed with a steady-state PCr of 54% of initial level. During stimulation inducing a PCr decrease to 38% of initial value, flux was significantly lowered by 30%. These findings could result from an accumulation of ions and water increases or from compartmentation of ATP and PCr in different pools either in the muscle cell or in the different muscle fibers. In addition, these results could reinforce the hypothesis against a crucial role for creatine kinase shuttle in the ATP supply in skeletal muscle.

Adenosine Triphosphate↗

PubMed1991

Lipoproteins in heart transplantation: proton magnetic resonance spectroscopy of plasma.

Despite the major improvement in immunosuppressive therapy, noninvasive detection of heart graft rejection remains a challenge. As lipoproteins are involved in several immunomodulation mechanisms, we studied their proton NMR spectra in plasma from patients after heart transplantation. NMR data were compared to clinical and functional evaluation of rejection process. The total linewidth (TLW) of methyl and methylene peaks, mainly arising from lipoproteins, were significantly lower for patients without a rejection process than for patients before surgery and patients with evidences of a rejection process. When TLW values are referred to TLW on the 8th day for each patient, the sensitivity and the specificity of the test are increased, with resulting positive and negative predictive values of 90 and 91%, respectively. The results obtained on more than 400 samples from 46 patients justify the use of proton NMR spectroscopy as a clinical tool.

Graft Rejection↗

PubMed1990

Assessment of intracellular magnesium depletion in rat striated muscle by in vivo 31P NMR.

Previous in vivo studies have demonstrated that alpha, beta, and gamma ATP chemical shifts measured by 31P NMR spectroscopy can be used to determine intracellular magnesium in erythrocytes, but up to now such results have not been confirmed in striated muscle in vivo. We report beta ATP chemical-shift in vivo measurements revealing the depletion of free intracellular magnesium in striated muscle of rats fed a magnesium deficient diet.

Animals↗