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Obesity and respiration

Obesity alters structure of lungs causing inflammation

Build up of adipose cells in the lungs (Credit: University of Western Australia)
Using dyes to help visualise the structures of 1,373 airways under a microscope, they identified and quantified any fatty tissue present

Adipose tissue accumulates in the walls of lungs, altering the normal structure of the airways causing inflammation in the lungs, according to researchers from University of Western Australia. They also reported that the amount of fat present increased in line with increasing BMI.

Study co-author, Associate Professor Peter Noble from UWA's School of Human Sciences said the research team studied the structure of airways within our lungs and how these changed in people with respiratory disease. The paper, ‘Fatty Airways: Implications for Obstructive Disease’, was published in the European Respiratory Journal.

"Looking at samples of lung, we spotted fatty tissue that had built up in the airway wall. We wanted to see if this accumulation was correlated with body weight."

The research team, which also included Sir Charles Gairdner Hospital, Telethon Kids Institute, University of Auckland and University of Calgary, examined post-mortem samples of lung that had been donated for research and stored in the Airway Tissue Biobank.

They studied samples from 52 people, including 15 who had no reported asthma, 21 who had asthma but died of other causes and 16 who died of asthma. Using dyes to help visualise the structures of 1,373 airways under a microscope, they identified and quantified any fatty tissue present. They compared this data with each person's BMI.

BMI ranged from 15 to 45 and was greater in nonfatal (p<0.05) subjects. Adipose tissue was identified in the outer wall of large airways (per mm of basement membrane perimeter (Pbm)>6mm), but was rarely seen in small airways (Pbm<6 mm). Adipose tissue area correlated positively with BMI and airway wall thickness in all groups. Densities of neutrophils correlated with adipose tissue area in control subjects (Pbm>6 mm, p=0.04) and both neutrophils and eosinophils in FA (Pbm>12 mm, p<0.01).

“These data show that adipose tissue is present within the airway wall and is related to BMI, wall thickness and the number of inflammatory cells,” the paper concluded. “The accumulation of airway adipose tissue in overweight individuals may therefore contribute to airway pathophysiology.”

Noble said researchers had suggested that the link might be explained by the direct pressure of excess weight on the lungs or by a general increase in inflammation created by excess weight.

"This study suggests that another mechanism is also at play," he said. "We've found that excess fat accumulates in the airway walls where it takes up space and seems to increase inflammation within the lungs. We think this is causing a thickening of the airways that limits the flow of air in and out of the lungs, and that could at least partly explain an increase in asthma symptoms."

The team is looking for new ways to study and measure fatty tissue in the lungs. They want to confirm the relationship with respiratory disease and to find out whether the effect can be reversed by weight loss therapy.

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