The link between obesity and lung diseases, such as asthma, has been recognized by biomedical researchers for more than 10 years. However, efforts to determine the actual mechanisms involved, as well as effective treatments for this population, have proven difficult. Building on surprising 2011 study results – that asthma in obese individuals is due to a combination of the effects of weight on airway function and metabolic changes in fat affecting the airways –University of Vermont Associate Professor Anne Dixon, M.A., B.M., B.Ch., and colleagues, recently reported another critical discovery in the October 1, 2012 American Journal of Respiratory and Critical Care Medicine. The new results show that the adipose – or fat – tissue around the abdomen appears to play a role in abnormal airway function in obese individuals.
Both of the group’s studies included study participants undergoing bariatric (weight loss) surgery. In the latest study article, the authors write that their objective was to determine if inflammation in adipose tissue in obesity is related to late-onset asthma, and associated with increased markers of airway inflammation and reactivity.
The 2012 study included 15 obese control women and 11 women with asthma. All of the participants with asthma had adult-onset asthma, and tended to be older and significantly heavier than the control subjects. The researchers followed the study participants for twelve months following bariatric surgery, comparing markers in adipose tissue and the airways from the participants with asthma and control subjects, and noted any changes experienced by the participants with asthma over time. After 12 months, the authors report, the subjects with asthma had an average weight loss of 28.4 +/- 16.5 kilos (62.6 +/- 36.4 pounds), and asthma control and airway hyper-responsiveness (AHR) improved significantly. What was not anticipated by the investigators was the fact that these asthmatics had little in the way of airway inflammation typically seen in asthma. Their airway cells expressed receptors for factors produced by adipose tissue, and this was closely related to their airway reactivity. This suggests that proteins excreted by adipose tissue that affect metabolism and other processes may be important mediators of airway disease in obesity through direct effects on the airway rather than by enhancing the type of airway inflammation that is usually seen in asthma.
“Our group has really helped develop the idea that there are two distinct forms of asthma occurring in the setting of obesity,” explains Dixon, who serves as chief of pulmonary and critical care medicine at the UVM College of Medicine and Fletcher Allen Health Care. “There are people with early onset allergic asthma that develop obesity as they grow older and another group that develops late-onset asthma as a consequence of obesity. The two groups are quite different in terms of their disease, and the abdominal fat may be particularly important in those developing asthma later in life.”
In addition to Dixon, who serves as senior author on the American Journal of Respiratory and Critical Care Medicine study, coauthors include first author Olga Sideleva, Ph.D., UVM post-doctoral associate in pulmonary disease and critical care medicine; Benjamin Suratt, M.D., UVM associate professor of medicine; Kendall Black, UVM senior lab/research technician in pulmonary and critical care medicine; W. Gabriel Tharp, UVM M.D.-Ph.D student; Patrick Forgione, M.D., UVM associate professor of surgery; Oliver Dienz, Ph.D., UVM assistant professor of medicine; Charles Irvin, Ph.D., professor of medicine and director, Vermont Lung Center; and Richard Pratley, M.D., professor at Florida Hospital/Sanford-Burnham Transitional Research Institute., and former UVM faculty member.
The team is sharing their research expertise across the globe. In October, Dixon was invited to deliver the keynote presentation at the Newcastle Asthma meeting, an annual meeting held in Newcastle, Australia. In addition, Dixon co-edited a new book, titled Obesity and Lung Disease: A Guide to Management (Humana Press; 2013 edition, released September 10, 2012), which features multiple contributors from the UVM College of Medicine.