Fat Metabolism and Digestion in Obstructive Sleep Apnea and Chronic Obstructive Pulmonary Disease

Detailed Summary

Obstructive sleep apnea (OSA) is the most common type of sleep apnea and is caused by an obstruction of the upper airways. The obstruction results in periods of intermittent hypoxia and re-oxygenation, which lead to increased oxidative stress, increased inflammation, endothelial dysfunction, and insulin resistance. Chronic obstructive pulmonary disease (COPD) is a lung disease that leads to poor airflow. This disease leads to systemic hypoxia, reduced oxidative capacity, and increased inflammation. The direct cause of OSA and COPD is unclear, but OSA and COPD may be linked to other comorbid conditions such as obesity and type II diabetes. Upon onset of OSA and COPD, metabolic disturbances associated with obesity and type II diabetes can be exacerbated. Obesity is a condition characterized by an increase in visceral fat, elevated plasma levels of free fatty acids, inflammation, and insulin resistance. Although the effects of body fat distribution have not been studied in these patients, an increase in both subcutaneous and abdominal fat mass in non-OSA older women was shown to increase morbidity and mortality. Fat/adipose tissue is an active tissue capable of secreting proinflammatory cytokines such as tumor necrosis factor (TNF)-alpha and interleukin (IL)-6, reactive oxygen species and adipokines. Particularly, abdominal fat is a prominent source of pro-inflammatory cytokines, which contributes to a low grade, chronic inflammatory state in these patients. Additionally, an increased inflammatory state is associated with reduced lean body mass, and together with elevated circulating free fatty acids may increase the occurrence of lipotoxicity and insulin resistance. Thus, increased fat deposition is associated with a poor prognosis in OSA and COPD patients and therefore it is of clinical and scientific importance to understand the changes in fat metabolism and digestion as a result of OSA and COPD. It is therefore our hypothesis that fat synthesis and insulin resistance is increased and whole body protein synthesis is decreased in OSA and COPD patients, leading to a poor prognosis.

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