Background and objective: Identification of smokers having predisposition to COPD is important for early intervention to reduce the huge global burden of the disease. Using a guinea pig model, we have shown that p-benzoquinone (p-BQ) derived from cigarette smoke (CS) in the lung is a causative factor for CS-induced emphysema. p-BQ is also derived from CS in smokers and it elicits the production of anti-p-BQ antibody in humans. We therefore hypothesized that anti-p-BQ antibody might have a protective role against COPD and could be used as a predictive biomarker for COPD in smokers. The objective of this study was to compare the serum anti-p-BQ antibody level between smokers with and without COPD for the evaluation of the hypothesis.
Methods: Serum anti-p-BQ antibody concentrations of current male smokers with (n=227) or without (n=308) COPD were measured by an indirect enzyme-linked immunoabsorbent assay (ELISA) developed in our laboratory. COPD was diagnosed by spirometry according to Global Initiative for Chronic Obstructive Lung Disease (GOLD) guidelines.
Results and discussion: A significant difference was observed in the serum anti-p-BQ antibody level between smokers with and without COPD (Mann-Whitney U-test =4,632.5, P=0.000). Receiver operating characteristic (ROC) curve analysis indicated that the ELISA had significant precision (area under the curve [AUC] =0.934, 95% confidence interval [CI]: 0.913-0.935) for identifying smokers with COPD from their low antibody level. The antibody cutoff value of 29.4 mg/dL was constructed from the ROC coordinates to estimate the risk for COPD in smokers. While 90.3% of smokers with COPD had a low antibody value (≤29.4 mg/dL), the majority (86.4%) of smokers without COPD had a high antibody value (≤29.4 mg/dL); 13.6% of current smokers without COPD having an antibody level below this cutoff value (odds ratio [OR] =59.3, 95% CI: 34.15-101.99) were considered to be at risk for COPD.
Conclusion and future directions: Our results indicate that serum anti-p-BQ antibody level may be used as a biomarker to identify asymptomatic smokers at risk for COPD for early intervention of the disease.
Keywords: COPD; anti-p-benzoquinone antibody; biomarker; cigarette smoke; enzyme-linked immunosorbent assay (ELISA).