Applied nutritional investigationPlasma levels of amino acids and hypermetabolism in patients with chronic obstructive pulmonary disease☆
Introduction
Weight loss is common in patients with chronic obstructive pulmonary disease (COPD).1 Epidemiologic studies have suggested that weight loss is generally associated with high rates of mortality and morbidity.1, 2 Therefore, nutritional assessment and nutritional support should be parts of the management of patients with COPD. Recent studies have suggested that nutritional intervention may correct the weight loss associated with improvement in respiratory muscle function.3, 4, 5 In patients with COPD, muscle weakness and an impaired exercise tolerance also occur,6 suggesting disturbances in intermediary protein metabolism. However, no specific nutritional regimen in terms of protein or nitrogen sources has been recommended because the characteristic nutritional and metabolic abnormalities related to protein metabolism have not been clearly identified in COPD patients. A previous study has shown that the serum level of albumin is normal or only marginally decreased in COPD patients.7 A recent study by our laboratory demonstrated a significant decrease in lean body mass evaluated by dual-energy x-ray absorptiometry in COPD patients.8
Because amino acids are basic units of proteins and they mediate intermediary metabolism, analysis of the plasma levels of free amino acids may be useful for determining the characteristics of nitrogen metabolism and thus of protein malnutrition. However, data on the plasma levels of amino acids in patients with COPD are limited.9, 10 Moreover, the number of subjects in the previous studies was small and the results were inconsistent. Studies on the pathophysiologic role of branched-chain amino acids (BCAAs) suggest that they may serve as an energy substrate and may regulate the degradation and synthesis of muscle protein in hepatic disorders and a variety of stress-related conditions.11, 12 Our preliminary study7 suggested a decreased level of BCAAs in patients with COPD, but possible roles of BCAAs in relation to pathophysiology remain undefined. Previous studies4, 13, 14 have also suggested that a hypermetabolic state in part contributes to weight loss in COPD patients, but its relation to amino-acid levels and weight loss has not been fully clarified. In the present study, we evaluated the nutritional status and measured the plasma levels of amino acids to determine the relation between these factors and pulmonary function and the derangement in energy metabolism, assessed in terms of the resting energy expenditure (REE), in patients with stable COPD.
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Subjects
We studied 30 ambulatory outpatients with stable COPD (29 male, 1 female; age 64 ± 13 y, mean ± SD). COPD was diagnosed based on clinical and radiographic criteria according to the guidelines of the American Thoracic Society.15 We excluded patients with other possible causes of weight loss, including diabetes, endocrine disorders, malabsorption syndrome, neoplastic diseases, infectious diseases, and liver diseases. Patients were receiving inhaled anticholinergic drugs. None of them required
Nutritional assessment
The mean %IBW was significantly lower in COPD patients than in the control subjects (Table I). Anthropometric measurements also suggested that body fat stores (%TSF) and muscle mass (%AMC) were depleted in about half of the studied COPD patients (47% and 65%, respectively). There was no significant difference in the mean serum level of albumin and transferrin between patients and control subjects. Levels of prealbumin and retinol-binding protein were significantly lower in patients than in
Discussion
In the present study, we found a significant decrease in the plasma level of BCAAs and various disturbances in other amino acids in patients with COPD. The significant differences in those amino acids also were found between underweight COPD patients and normal-weight patients. Our study also suggested the relation of a decreased level of BCAAs to weight loss, decrease in FEV1 and PImax, and elevated REE in our patients. To our knowledge, the present investigation and those of Hofford et al.9
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This study was supported by grants from the Japanese Ministry of Health and Welfare.