The relationship between cotinine concentrations and inflammatory markers among highly secondhand smoke exposed non-smoking adolescents

• We examine the immunomodulatory effect of secondhand smoke exposure in adolescents.
• Cotinine is used as a marker for secondhand smoke exposure.
• IL-4 and IL-6 have weak inverse association with cotinine levels.
• Secondhand smoke may have immunosuppressive effect.

BackgroundSecondhand smoke (SHS) exposure is a risk factor of respiratory, cardiovascular and inflammatory diseases, however its association with inflammatory markers among highly SHS exposed adolescents has not yet been explored.MethodsParticipants included in this study were a subset of 68 non-smoking adolescents, aged 12.5–17.5 from the Healthy Lifestyle in Europe by Nutrition in Adolescence (HELENA) study, recruited from Crete Greece. Smoking and SHS exposure was assessed via serum cotinine concentrations. Cytokines (Interleukin-1β, 2, 4, 5 and 6, tumor necrosis factor-α, interferon-γ, tumor growth factor-β1), immunoglobulins IgG, IgA, IgM, complement factors C3, C4, high sensitivity C-reactive protein, and endothelial inflammatory markers [soluble E-selectin, soluble L-selectin, soluble intercellular adhesion molecules (sICAM-1) and soluble vascular cell adhesion molecules-1 (sVCAM-1)] were assessed. Inflammatory markers in the lower 25th percentile and upper 75th percentile groups of cotinine levels were compared and multivariate linear regression analysis was performed controlling for age, sex and BMI.ResultsCotinine concentrations were notably elevated (geometric mean 0.82 ng/ml, 95%CI 0.62–1.07) in this study population. A significant decrease in IL-4 (130.09 vs. 25.77 pg/ml, p = 0.014) and IL-6 (19.52 vs. 5.52 pg/ml, p = 0.008) concentrations between the upper 75th percentile cotinine level group and lower 25th percentile cotinine level group was observed. In a multivariate linear regression analysis, cotinine concentrations had a weak inverse association with IL-4 and IL-6 (p = 0.028 and p = 0.06) which was not statistically significant when adjusted for multiple comparisons (modified Bonferroni, p > 0.016). No differences in the other variables was noted.ConclusionsAmong highly SHS exposed adolescents, cotinine levels had weak inverse association with IL-4 and IL-6, which did not achieve statistical significance. However, our results potentially indicate an immunosuppressive role of SHS. Further research is warranted to explore this hypothesis.