Systemic inflammation mediates the detrimental effects of obesity on asthma control

Obesity negatively impacts asthma control, but the inflammatory mechanisms are poorly understood.

To explore which systemic inflammatory mediators mediate the effects of obesity on asthma control.

The subjects with stable asthma (n = 108) underwent assessment of clinical characteristics, which included using The Asthma Control Questionnaire (ACQ)-6. Obesity was defined as a body mass index (BMI) of ≥30 kg/m2, overweight was defined as BMI between 25 to 29.9 kg/m2, and lean weight was defined as BMI < 25 kg/m2. Body composition, including fat mass (FM), visceral fat area (VFA), and percentage body fat (PBF) was analyzed by bioimpedance. Serum interleukin (IL) 4, IL-5, IL-8, IL-13, IL-17, chemokine (C-C motif) ligand (CCL) 17, CCL22, leptin, adiponectin, C-reactive protein (CRP), and interferon (IFN) gamma were measured by using ELISA. Linear regression models were fitted according to the Baron and Kenny procedures for mediation analysis.

FM (12.73 ± 3.95 versus 18.59 ± 2.95 versus 27.82 ± 5.17 kg; p < 0.0001), VFA (65.99 ± 23.17 versus 93.96 ± 10.28 versus 123.10 ± 18.34 cm2; p < 0.0001), PBF (23.86 ± 7.46 versus 30.74 ± 5.08 versus 36.21 ± 6.28 %; p = 0.0003) and ACQ-6 values (0.83 [0, 1.17]) versus 1.15 [0.50, 1.75] versus 1.33 [0.83, 1.83] score; p = 0.002) were different among lean (n = 52), overweight (n = 37), and obese (n = 19) subjects. Serum levels of leptin, IL-5, IL-13, IL-17, CCL17, CRP, and IFN-gamma in the obese group were significantly elevated compared with the subjects who were lean or overweight (all p < 0.05). The mediation analyses found that the effect of obesity, assessed by BMI, on ACQ-6 was significantly mediated through IL-13 and CCL17. Furthermore, IL-13 and CCL17 mediated the effects of body composition (FM, VFA and PBF) on ACQ-6. The effects of obesity assessed by body composition, but not by using BMI, on ACQ-6 were mediated by leptin.

Our mediation analysis confirmed that systemic inflammation biomarkers, such as leptin, CCL17, IL-4, and IL-13, mediated the effects of obesity on asthma control. This warrants prospective exploration in this distinct asthma phenotype in the future.