High Interleukin (IL)-6 is Associated with Lower Lung Function and Increased Likelihood of Metabolic Dysfunction in Asthma

Introduction: Asthma is a complex condition characterized by airway inflammation. Interleukin-6 (IL-6) plays a significant role in asthma pathogenesis through its effects on T cells and its association with pro-inflammatory responses. Both lung and circulating IL-6 levels are elevated in asthma. IL-6 is positively associated with disease severity, frequent exacerbations, and impaired lung function, all of which can be observed clinically. We developed an IL-6 cut-off model to examine the association between high IL-6, race, high body mass index (BMI), metabolic disease, and asthma severity as assessed by reduced lung function.

Methods: This study utilized the Coronary Artery Risk Development in Young Adults (CARDIA) database, comprised of 5115 adults, to investigate the relationship between IL-6 levels, asthma, race, and metabolic dysfunction. A "healthy" subset of 427 patients was used to compute the IL-6 cut-off. IL-6 levels within detection limits (0.15-12 pg/mL) were analyzed. The IL-6 cut-off was determined using the 95th percentile of log-transformed IL-6 values for lean (BMI < 25) and healthy individuals. Specific cut-offs were established for racial groups. Statistical analyses involved comparing patient characteristics between high and low IL-6 groups, regression analyses, and assessment of factors influencing lung function changes.

Results: Using an IL-6 cut-off of 4.979 pg/mL, the cohort was divided into high and low IL-6 groups. High IL-6 correlated with Black race, higher BMI, hypertension, and markers of metabolic dysfunction, e.g., elevated HbA1c, C-reactive protein (CRP), and reduced lung function. Multivariable analysis linked high IL-6 with male gender, high BMI, Black race, HbA1c, CRP, and inversely with lung function and total cholesterol. Obesity showed a consistent positive association with elevated IL-6, regardless of the presence or absence of asthma. Patients with asthma and high IL-6 were more likely to be Black and showed increased CRP. Lung function was lowest in non-lean, high IL-6 patients with asthma, with similar trends in non-lean (BMI ≥ 25) patients without asthma.

Conclusion: This study underscores the significant association between IL-6, asthma, obesity, and metabolic dysfunction. Elevated IL-6 correlates with asthma severity, particularly in individuals with obesity. Future research should explore anti-IL-6 therapies for specific phenotypes, such as obesity-related asthma. These findings advance our understanding of asthma and the role of IL-6 in its pathogenesis.