Incidence of VTE in Patients With OSA: A Cohort Study.

BACKGROUND: Previous studies suggesting that OSA may be an independent risk factor for VTE have been limited by reliance on administrative data and lack of adjustment for clinical variables, including obesity. RESEARCH QUESTION: Does OSA confer an independent risk of incident VTE among a large clinical cohort referred for sleep-disordered breathing evaluation? STUDY DESIGN AND METHODS: We analyzed the clinical outcomes of 31,309 patients undergoing overnight polysomnography within a large hospital system. We evaluated the association of OSA severity with incident VTE, using Cox proportional hazards modeling accounting for age, sex, BMI, and common comorbid conditions. RESULTS: Patients were of mean age 50.4 years, and 50.1% were female. There were 1,791 VTE events identified over a mean follow-up of 5.3 years. In age- and sex-adjusted analyses, each 10-event/h increase in the apnea-hypopnea index was associated with a 4% increase in incident VTE risk (hazard ratio [HR], 1.04; 95% CI, 1.02-1.06). After adjusting for BMI, this association disappeared (HR, 1.01; 95% CI, 0.99-1.03). In contrast, nocturnal hypoxemia had an independent association with incident VTE. Patients with > 50% sleep time spent with oxyhemoglobin saturation < 90% are at 48% increased VTE risk compared with those without nocturnal hypoxemia (HR, 1.48; 95% CI, 1.16-1.69). INTERPRETATION: In this large cohort, we found that patients with more severe OSA as measured by the apnea-hypopnea index are more likely to have incident VTE. Adjusted analyses suggest that this association is explained on the basis of confounding by obesity. However, severe nocturnal hypoxemia may be a mechanism by which OSA heightens VTE risk.

Hypoxia-Inducible Factors and Cancer.

PURPOSE OF REVIEW: Hypoxia inducible factors (HIFs) mediate the transcription of hundreds of genes that allow cells to adapt to hypoxic environments. In this review, we summarize the current state of knowledge about mechanisms of HIF activation in cancer, as well as downstream cancer-promoting consequences such as altered substrate metabolism, angiogenesis, and cell differentiation. In addition, we examine the proposed relationship between respiratory-related hypoxia, HIFs, and cancer. RECENT FINDINGS: HIFs are increased in many forms of cancer, and portend a poor prognosis and response to therapy. CONCLUSION: HIFs play a critical role in various stages of carcinogenesis. HIF and its transcription targets may be useful as biomarkers of disease and therapeutic targets for cancer.

Obstructive Sleep Apnea Dynamically Increases Nocturnal Plasma Free Fatty Acids, Glucose, and Cortisol During Sleep.

Context: Obstructive sleep apnea (OSA) is associated with diabetes and cardiovascular disease. This association may be related to metabolic changes that transpire during sleep in OSA. Objective: To examine the impact of OSA, elicited by cessation of continuous positive airway pressure (CPAP), on frequently sampled nocturnal metabolic markers including plasma free fatty acids (FFAs), glucose, insulin, triglycerides (TGs), cortisol, and lactate, as well as glucose production, oral glucose tolerance, blood pressure (BP), endothelial function, cholesterol, and high-sensitivity C-reactive protein (hsCRP). Design and Setting: Randomized crossover trial of CPAP vs CPAP withdrawal. Patients: Thirty-one patients with moderate to severe OSA acclimated to CPAP. Intervention: Patients underwent attended polysomnography while sleeping with therapeutic CPAP, or after CPAP withdrawal, in random order. Venous blood was sampled at ∼20-minute intervals on both nights. In 11 patients, we assessed glucose kinetics with an infusion of 6,6-[2H2]glucose. Results: CPAP withdrawal caused recurrence of OSA associated with hypoxemia, sleep disruption, and heart rate (HR) elevation. CPAP withdrawal dynamically increased nocturnal FFA (P = 0.007), glucose (P = 0.028), and cortisol (P = 0.037), in proportion to respiratory event frequency, HR elevation, or sleep fragmentation. Diabetes predisposed to glucose elevation. CPAP withdrawal also increased systolic BP (P = 0.017) and augmentation index (P = 0.008), but did not affect insulin, TGs, glucose production, oral glucose tolerance, cholesterol, or hsCRP. Conclusion: OSA recurrence during CPAP withdrawal increases FFA and glucose during sleep, associated with sympathetic and adrenocortical activation. Recurring exposure to these metabolic changes may foster diabetes and cardiovascular disease.

Adipose HIF-1α causes obesity by suppressing brown adipose tissue thermogenesis.

Hypoxia-inducible factor-1α (HIF-1α) in adipose tissue is known to promote obesity. We hypothesized that HIF-1α interferes with brown fat thermogenesis, thus decreasing energy expenditure. To test this hypothesis, we compared transgenic mice constitutively expressing HIF-1α in adipose tissues (HIF-1α++) at usual temperature (22 °C), where brown fat is somewhat active, or at thermoneutrality (30 °C), where brown fat is minimally active. HIF-1α++ mice or control litter mates were separated into room temperature (22 °C) or thermoneutrality (30 °C) groups. We assessed weight gain, food intake, calorimetry, activity, and oxygen consumption and transcriptional changes in isolated white and brown adipocytes. At 22 °C, HIF-1α++ mice exhibited accelerated weight gain, cold and glucose intolerance, hyperglycemia, and decreased energy expenditure without changes in food intake or activity. These changes were absent or minimal at thermoneutrality. In brown adipocytes of HIF-1α++ mice, oxygen consumption decreased ~50 % in association with reduced mitochondrial content, uncoupling protein 2, and peroxisome proliferator-activated receptor gamma coactivator 1 (PGC-1α). In conclusion, adipose HIF-1α overexpression inhibits thermogenesis and cellular respiration in brown adipose tissue, promoting obesity in the setting of reduced ambient temperature. KEY MESSAGE: Constitutive HIF-1α activation in adipose tissue promotes weight gain in mice. The weight gain is associated with reduced brown adipose tissue function and oxygen consumption. Reduced oxygen consumption may be mediated by reductions in mitochondria.