Carpagnano and colleagues1–
recently reported in CHEST (October 2002) a significant increase in 8-isoprostane and interleukin (IL)-6 levels in the exhaled breath condensate of obstructive sleep apnea (OSA) patients compared with that of obese subjects. In the article, they referred to a close correlation between IL-6 levels and obesity, stating “The higher concentration of this cytokine in obese subjects compared to control subjects…. ” Apart from the increased concentration of this cytokine, its function in obesity is complicated. IL-6 is expressed not only in adipose tissues,3
but also in neurons of hypothalamic nuclei, which regulate body composition,4–5
as well as in nonneurons such as astrocytes, microglia, and brain endothelial cells.6–
A recent study by Wallenius and coworkers7
demonstrated that IL-6 knockout mice developed mature-onset obesity. The obesity was concomitant with decreased glucose tolerance and increased circulatory triglyceride levels in females, as well as increased leptin levels and leptin insensitivity in older mice of both genders. Interestingly, intracerebroventricular IL-6 injection, but not intraperitoneal IL-6 injection, increased energy expenditure, suggesting that centrally acting IL-6 exerts antiobesity effects.