Michèle Ramonatxo

l-Arginine Decreases Inflammation and Modulates the Nuclear Factor-κB/Matrix Metalloproteinase Cascade in Mdx Muscle Fibers

Duchenne muscular dystrophy (DMD) is a lethal, X-linked disorder associated with dystrophin deficiency that results in chronic inflammation, sarcolemma damage, and severe skeletal muscle degeneration. Recently, the use of L-arginine, the substrate of nitric oxide synthase (nNOS), has been proposed as a pharmacological treatment to attenuate the dystrophic pattern of DMD. However, little is known about signaling events that occur in dystrophic muscle with l-arginine treatment. Considering the implication of inflammation in dystrophic processes, we asked whether L-arginine inhibits inflammatory signaling cascades. We demonstrate that L-arginine decreases inflammation and enhances muscle regeneration in the mdx mouse model. Classic stimulatory signals, such as proinflammatory cytokines interleukin-1beta, interleukin-6, and tumor necrosis factor-alpha, are significantly decreased in mdx mouse muscle, resulting in lower nuclear factor (NF)-kappaB levels and activity. NF-kappaB serves as a pivotal transcription factor with multiple levels of regulation; previous studies have shown perturbation of NF-kappaB signaling in both mdx and DMD muscle. Moreover, L-arginine decreases the activity of metalloproteinase (MMP)-2 and MMP-9, which are transcriptionally activated by NF-kappaB. We show that the inhibitory effect of L-arginine on the NF-kappaB/MMP cascade reduces beta-dystroglycan cleavage and translocates utrophin and nNOS throughout the sarcolemma. Collectively, our results clarify the molecular events by which L-arginine promotes muscle membrane integrity in dystrophic muscle and suggest that NF-kappaB-related signaling cascades could be potential therapeutic targets for DMD management.

l-arginine improves dystrophic phenotype in mdx mice

A possible treatment for Duchenne muscular dystrophies would be to compensate for dystrophin loss by increasing the expression of utrophin, another cytoskeletal protein of the muscle membrane. We previously found that L-arginine, the substrate for nitric oxide synthase, significantly increased utrophin level in muscle and targeted it to the sarcolemma. Here, we have addressed the expected benefit in the mdx mice. Magnetic resonance imaging of lower limbs revealed a 35% reduction of the necrotic zones, confirmed by histological staining of muscles. This regression of the necrosis was also supported by the drastic reduction of Evans blue incorporation, a cell impermeable dye. The creatine kinase level in the serum decreased by 57%. Utrophin level increased 2- to 3-fold in muscles. Beta-dystroglycan was relocalised with utrophin to the membrane. In the diaphragm, the most affected muscle in mdx mice, the isometric tension increased by 30%, with regression of collagen and of cytoplasmic lipid overloading. Finally, molsidomine, a therapeutic agent that is converted to a NO donor, also attenuated the dystrophic phenotype. Our results suggest that pharmacological activators of the NO pathway may constitute a realistic treatment for Duchenne and Becker muscular dystrophies.

Dose-dependent effect of individualized respiratory muscle training in children with Duchenne muscular dystrophy.

The aim of this study was to evaluate the effects of low intensity, home inspiratory muscle training on respiratory muscle endurance in children with Duchenne muscular dystrophy, using a double-blind protocol. The originality aspect of this study is the use of a reproducible method of endurance and of the same method for evaluation and training. We studied eight trained children (mean age 14.7+/-4.5 years) and eight control children (mean age, 12.6+/-1.8 years). For 6 weeks, children breathed twice a day for 10 min through a valve with either 30% (training group) or less than 5% (control group) of their maximum inspiratory pressure (P(imax)). The results showed (1) a 46% improvement in the time limit after training in the training group and no change in the control group and (2) a significant correlation between the total time of respiratory muscle training and the percentage of endurance improvement in the training group. We conclude that specific training improves respiratory muscle endurance in Duchenne muscular dystrophy and the effectiveness of training appears to be dependent on the quantity of training.

Diaphragm Movement Before and After Cholecystectomy: A Sonographic Study

Respiratory disorders after abdominal surgery are commonly explained by changes in diaphragmatic movement that are difficult to demonstrate and quantify. Our aim was thus to quantify these changes using a noninvasive method. We used M-mode sonography for the prospective study to measure diaphragmatic amplitude in 14 patients before and after cholecystectomy. During quiet breathing, the diaphragm inspiratory amplitude (DIA) was significantly decreased after surgery from 1.4 ± 0.2 cm to 1 ± 0.1 cm and from 1.6 ± 0.3 cm to 1.2 ± 0.3 cm in the Laparoscopic and Open Cholecystectomy groups, respectively. The total time cycle of diaphragmatic motion decreased significantly in the two groups. The DIA also decreased significantly during deep breathing after cholecystectomy from 6.0 ± 0.8 cm to 3.0 ± 1.8 cm and from 6.1 ± 1.3 cm to 3.1 ± 1.6 cm in the Laparoscopic and Open Cholecystectomy groups, respectively. The six patients who underwent spirometric examination showed, during quiet breathing, a significant decrease in DIA without change in tidal volume, i.e., 0.51 ± 0.08 L to 0.45 ± 0.08 L. We found a significant decrease in DIA after cholecystectomy and a significant interindividual correlation between DIA during deep inspiration and inspiratory capacity. Using M-mode sonography techniques, we were able to demonstrate changes in diaphragmatic mobility after laparoscopic or open cholecystectomy.

Non-invasive quantification of diaphragm kinetics using m-mode sonography.

PurposeThe standard conditions of spirometry (i.e., wearing a noseclip and breathing through a mouthpiece and a pneumotachograph) are likely to alter the ventilatory pattern. We used “time-motion” mode (M-mode) sonography to assess the changes in diaphragm kinetics induced by spirometry dunng quiet breathing.MethodsAn M-mode sonographic study of the nght diaphragm was performed before and dunng standard spirometry in eight patients without respiratory disease (age 34 to 68 yr).ResultsDuring spirometry, the diaphragm inspiratory amplitude (DIA) increased from 1.34 ± 0.18 cm to 1.80 ± 0.18 cm (P = 0.007), whereas the diaphragmatic mspiratory time (T1 diaph) increased from 1.27 ± 0.15 to 1.53 ± 0.23 sec, (P = 0.015), without change in diaphragmatic total time interval (Ttot diaph). Therefore, the diaphragm duty cycle (T1 diaph /Ttot diaph) increased from 38% ± 1% to 44% ± 4% (P = 0.023). The diaphragm inspiratory (DIV) and expiratory (DEV) motion velocity increased (P = 0.007).ConclusionM-mode sonography enabled us to demonstrate that the weanng of a nose clip and breathing through a mouthpiece and a pneumotachograph induce measurable changes in diaphragm kinetics.RésuméObjectifLes conditions de la spirométne standard (c.-à-d. le port du pince-nez et la respiration à travers un embout buccal et un pneumotacographe) sont susceptibles d’altérer la morphologie de la ventilation. Nous avons utilisé le mode «temps-amplitude» (mode M) de la sonographie pour évaluer les changements de la cinétique diaphragmatique provoqués par la spirométne pendant la respiration de repos.RésultatsPendant la spirométne, l’amplitude mspiratoire diaphragmatique augmentait de 1, 34 ± 0, 18 à 1, 80 ± 0, 18 cm (P = 0, 007), alors que le temps diaphragmatique mspiratoire (T1 diaph) augmentait de 1, 27 ± 0, 15 à 1, 53 ± 0, 23 sec (P = 0, 015), sans changement du temps diaphragmatique total (Ttot diaph). Par conséquent, le temps de l’activité diaphragmatique (T1 diaph/Ttot diaph) augmentait de 38 ± 1 % à 44 ± 4% (P = 0, 023). La vélocité de l’amplitude mspiratoire et expiratoire augmentait (P = 0, 007).ConclusionLa sonographie en mode M nous a permis de démontrer que le port du pince-nez et la respiration à travers un embout buccal et un pneumotacographe provoquent des changements tangibles de la cinétique diaphragmatique.

A standardized method for the evaluation of respiratory muscle endurance in patients with Duchenne muscular dystrophy

The aim of the study was to develop a standardized method using controlled breathing to quantify respiratory muscle endurance in children with Duchenne muscular dystrophy (DMD) and to test its reproducibility. In 10 DMD patients, all between 10 and 14 years (mean age, 11.5 +/- 1.5 years), except for two patients of 20 and 22 years, and 10 healthy children (mean age, 12 +/- 1 years), we measured the maximal time (Tlim) that a threshold load fixed at 35% of the individual maximal inspiratory pressure (Pimax) could be tolerated. We asked the children to maintain their rest breathing pattern until exhaustion using visual feedback and an auditory signal. The mean Tlim in the DMD children was 4.45 +/- 1.45 min and values were reproducible. All healthy children were able to obtain Tlim values greater than 30 min. The respiratory muscles of DMD children are more susceptible to fatigue than those of healthy subjects. This method should be satisfactory for estimating the effect of treatment and for the specific training of respiratory muscles in DMD patients without significant learning disability.

Determinants of the tension-time index of inspiratory muscles in children with cystic fibrosis

Nutritional status and chronic pulmonary hyperinflation can alter respiratory muscle function in cystic fibrosis (CF). This study investigated: 1) whether inspiratory muscle function is reduced in children with stable CF in comparison with healthy controls; and 2) the mechanisms leading to inspiratory muscle weakness, which probably predispose to respiratory muscle fatigue. We determined the tension‐time index of the inspiratory muscles (TTMUS) noninvasively at rest in 16 children with mild to moderate CF (mean age, 11 ± 2 years) and 10 healthy controls (mean age, 11 ± 2 years). The TTMUS was determined as follows: TTMUS = TI/TTOT · PI/PIMAX, where PI is the mean inspiratory pressure estimated from the measure of mouth occlusion pressure (P0.1), PIMAX is the maximal inspiratory pressure, and TI/TTOT is the duty cycle. The results showed similar nutritional status in both groups, as well as mild to moderate airway obstruction, hyperinflation, and trapped gas in the CF group. In this group only, a significant inverse relationship was found between T1/TTOT and P1/PIMAX[TITTOT = 0.482 ‐ (0.388PI/PIMAX), r = −0.53; p < 0.05]. The patients also had a greater TTMUS (TTMUS = 0.087 ± 0.030 in CF vs. 0.056 ± 0.014 in controls, P < 0.01) that increased with decreasing lean body mass (r = −0.70, P < 0.005), with increasing percent predicted functional residual capacity (r = 0.70, P < 0.05). and increasing volumes of trapped gas (r = 0.77, P < 0.01). The multiple linear regression analysis for these factors was significant (R2 = 0.84, P < 0.01); however, the partial regression coefficient was significant only for lean body mass (r2 = 0.60, P < 0.05). Therefore, muscle mass appeared as the strongest determinant of TTMUS in CF. This study used a noninvasive method to assess the inspiratory muscle performance in children with CF. The results suggest impairment in inspiratory muscle function in these children despite good nutritional status and only mild to moderate alteration in pulmonary function tests. In addition, we were able to investigate some of the determinants of inspiratory muscle weakness, namely, muscle mass, hyperinflation, and trapped gas, and found that muscle mass played a predominant role. Pediatr. Pulmonol. 1997; 23:336–343.

Ventilatory response of prepubertal boys and adults to carbon dioxide at rest and during exercise

SummaryThe aim of this study was to determine whether the greater ventilation in children at rest and during exercise is related to a greater CO2 ventilatory response. The CO2 ventilatory response was measured in nine prepubertal boys [10.3 years (SD 0.1)] and in 10 adults [24.9 years (SD 0.8)] at rest and during moderate exercise (

Alteration of the Piglet Diaphragm Contractility In Vivo and Its Recovery after Acute Hypercapnia

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