Annie Michaud

Hypoxaemia enhances peripheral muscle oxidative stress in chronic obstructive pulmonary disease

Background: Because oxidative stress affects muscle function, the underlying mechanism to explain exercise induced peripheral muscle oxidative stress in patients with chronic obstructive pulmonary disease (COPD) is clinically relevant. This study investigated whether chronic hypoxaemia in COPD worsens peripheral muscle oxidative stress and whether an abnormal muscle inflammatory process is associated with it. Methods: Nine chronically hypoxaemic and nine non-hypoxaemic patients performed repeated knee extensions until exhaustion. Biopsy specimens were taken from the vastus lateralis muscle before and 48 hours after exercise. Muscle oxidative stress was evaluated by lipid peroxidation (lipofuscin and thiobarbituric acid reactive substances (TBARs)) and oxidised proteins. Inflammation was evaluated by quantifying muscle neutrophil and tumour necrosis factor (TNF)-α levels. Results: When both groups were taken together, arterial oxygen pressure was positively correlated with quadriceps endurance time (n = 18, r = 0.57; p<0.05). At rest, quadriceps lipofuscin inclusions were significantly greater in hypoxaemic patients than in non-hypoxaemic patients (2.9 (0.2) v 2.0 (0.3) inclusions/fibre; p<0.05). Exercise induced a greater increase in muscle TBARs and oxidised proteins in hypoxaemic patients than in non-hypoxaemic patients (40.6 (9.1)% v 10.1 (5.8)% and 51.2 (11.9)% v 3.7 (12.2)%, respectively, both p = 0.01). Neutrophil levels were significantly higher in hypoxaemic patients than in non-hypoxaemic patients (53.1 (11.6) v 21.5 (11.2) counts per fibre × 10−3; p<0.05). Exercise did not alter muscle neutrophil levels in either group. Muscle TNF-α was not detected at baseline or after exercise. Conclusion: Chronic hypoxaemia was associated with lower quadriceps endurance time and worsened muscle oxidative stress at rest and after exercise. Increased muscle neutrophil levels could be a source of the increased baseline oxidative damage. The involvement of a muscle inflammatory process in the exercise induced oxidative stress of patients with COPD remains to be shown.

Profiling of mRNA Expression in Quadriceps of Patients with COPD and Muscle Wasting

Peripheral muscle wasting is a feature of chronic obstructive pulmonary disease (COPD). Potent therapeutic strategies are needed to improve peripheral muscle mass in these patients. We hypothesized that the evaluation of the mRNA expression profile of quadriceps muscle could be useful in identifying key biochemical pathways involved in the wasting process. We monitored mRNA expression profile of quadriceps muscle in four patients with COPD with muscle atrophy (age: 71.3 ± 2.1 years, mean SD; FEV1 28.3 ± 10.8 % predicted) and four control subjects (age: 66.5 ± 1.3 years) using HuU95v2 gene chips. Fifty-seven mRNAs transcripts (0.5%) were found to be differentially expressed in muscles of COPD patients (i.e., p < 0.01). Among them, forkhead box O -1 and -3 and insulin-like growth factor-1 expressions being significantly elevated in COPD subjects. Concomitantly, a significant reduction in mRNA expression of two myofilament proteins was observed. Energy production appears to be impaired as indicated by the significant rise in nicotinamide N-methyltransferase mRNA expression. This study provides for the first time evidence that genes are selectively expressed in limb muscles of COPD patients and further research need to focus on their functional roles in the pathogenesis of muscle dysfunction.

Atrophy and hypertrophy signalling of the quadriceps and diaphragm in COPD

Background Factors involved in the regulation of muscle mass in chronic obstructive pulmonary disease (COPD) are still poorly understood. Comparing the signalisation involved in muscle mass regulation between two muscles with different levels of activation within the same subjects is an interesting strategy to tease out the impact of local (muscle activity) versus systemic factors in the regulation of muscle mass. A study was undertaken to measure and compare the protein levels of p-AKT, AKT, Atrogin-1, p-p70S6K, p-4E-BP1, p-GSK3β as well as the mRNA expression of Atrogin-1, MuRF1 and FoxO-1 in the quadriceps and the diaphragm of 12 patients with COPD and 7 controls with normal lung function. Methods Diaphragm biopsies were obtained during thoracic surgery and quadriceps samples were obtained from needle biopsies. Protein content and mRNA expression were measured by western blot and quantitative PCR, respectively. Results Increased mRNA expressions of Atrogin-1, MuRF1 and FoxO-1 were found in the quadriceps compared with the diaphragm only in patients with COPD. The quadriceps/diaphragm ratio for MuRF1 was higher in COPD. The protein level of p-p70S6K was decreased in the quadriceps compared with the diaphragm in patients with COPD. The quadriceps/diaphragm ratios of p-p70S6K and p-GSK3β were lower in patients with COPD than in controls. Conclusions These results indicate a greater susceptibility to a catabolic/anabolic imbalance favouring muscle atrophy in the quadriceps compared with the diaphragm in patients with COPD. The balance between the atrophy and hypertrophy signalling is inhomogeneous between respiratory and lower limb muscles, suggesting that local factors are likely to be involved in the regulation of muscle mass in COPD.

COPD results in a reduction in UCP3 long mRNA and UCP3 protein content in types I and IIa skeletal muscle fibers.

PURPOSE Findings recently have shown coupling protein-3 (UCP3) content to be decreased in the skeletal muscle of patients with chronic obstructive pulmonary disease (COPD). Uncoupling protein-3 mRNA exists as two isoforms: long (UCP3L) and short (UCP3S). The UCP3 protein is expressed the least in oxidative and the most in glycolytic muscle fibers. Levels of UCP3 have been associated positively with intramyocellular triglyceride (IMTG) contents in conditions of altered fatty acid metabolism. As a source for muscle free fatty acid metabolism, IMTG is decreased in COPD. The current study completely characterized all the parameters of UCP3 expression (ie, UCP3L and UCP3S mRNA expression in whole muscle samples) and UCP3 protein content as well as IMTG content in the different fiber types in patients with COPD and healthy control subjects. METHODS Using real-time polymerase chain reaction, UCP3 gene expression was quantified. Skeletal muscle fiber type and UCP3 protein and IMTG content were measured using immunofluorescence and Oil red oil staining, respectively. RESULTS The findings showed that UCP3L mRNA expression was 44% lower (P < .005) in the patients with COPD than in the control subjects, whereas the UCP3S mRNA content was similar in the two groups. As compared with control subjects, UCP3 protein content was decreased by 89% and 83% and the IMTG content by 64% and 54%, respectively, in types I and IIa fibers (P < .0167) of patients with COPD, whereas they were unchanged in IIx fibers. CONCLUSIONS The reduced UCP3 and IMTG content in the more oxidative fibers may be linked to the altered muscle fatty acid metabolism associated with COPD. Further studies are required to determine the exact role and clinical relevance of the reduced UCP3 content in patients with COPD.

Rapid, versatile and sensitive method for the quantification of radium in environmental samples through cationic extraction and inductively coupled plasma mass spectrometry

In this study, the method proposed by St-Amant et al. based on ionic chromatography was modified to rapidly quantify 226Ra and 228Ra by inorganic mass spectrometry in a broad variety of matrices at environmental levels. The sample volume loaded on the cationic resin AG50Wx8 was varied to achieve the highest possible adsorption without any significant loss of retention for radium. The pH and volume for the elution steps were optimized to obtain the highest pre-concentration factor and compatibility with plasma-based instruments and to eliminate interference to the maximum extent possible. Finally, inductively coupled plasma mass spectrometry (ICP-MS) instrumental conditions were investigated and optimized for the quantification of radium. An instrumental detection limit of 0.53 pg L−1 in 226Ra and 0.47 pg L−1 in 228Ra were achieved. When combined with the cationic separation procedure for interference removal, the overall method detection limit decreases to 10 fg L−1 in less than 2 hours.