Title : Untargeted metabolomics of plasma and saliva: Insights into smoking associated COPD pathophysiology
Abstract:
Chronic obstructive pulmonary disease (COPD) is a progressive lung disorder characterized by airflow limitation, chronic inflammation, and loss of elastic recoil, leading to reduced forced expiratory volume (FEV) and impaired lung emptying during expiration. It is the third leading cause of mortality worldwide, accounting for approximately 3.7 million deaths annually. India bears highest burden, contributing ~15% of global COPD cases and ~30% of COPD-related deaths. COPD is influenced by multiple risk factors, including cigarette smoking, air pollution, biomass burning, fossil fuel exposure, and genetic predispositions such as α-antitrypsin deficiency. Among these, cigarette smoking accounts for nearly 90% of COPD cases. Despite the metabolic complexity of COPD, the metabolite profiles across COPD subgroups, such as smokers, ex-smokers, and non-smokers remain unexplored in blood plasma. In addition to this, non-invasive and less complex bio fluids serve as effective matrix to investigate the metabolic profile. Saliva is a promising, non-invasive bio-fluid that reflects systemic metabolic changes, yet its potential in COPD is largely underexplored. In this study, we performed untargeted GC-MS based metabolomics of plasma and saliva in COPD patients (smokers, ex-smokers, and non-smokers) to identify distinct metabolic signatures and associated pathways that differentiate COPD subgroups at the molecular level. We observed elevated oxidative stress level in COPD subgroups, by measuring GSH/GSSG ratio, and plasma lipid peroxidation. RBC membrane fluidity was observed to be reduced which further indicates perturbation in membrane lipids. The multivariate PCA and PLS-DA analysis of plasma and saliva metabolites showed the clear distinction between the patient subgroups. We observed significant alteration in metabolites in plasma and saliva sample of COPD patients compared to the healthy individuals. Pathway analysis indicated significant perturbations in key metabolic pathways, including biosynthesis of fatty acids, glycosylphosphatidylinositol (GPI) anchor, arginine, and TCA. Biomarker analysis revealed significant metabolites and lipids with AUC > 0.8 such as Fumaric acid, scylloinositol, Palmitic acid, methyl stearate, Arachidic acids etc. Additionally, correlation analysis of spirometer data shows positive and negative correlation with altered metabolites. Overall, we observed the effect of smoking on COPD progression and staging in terms of differential expression of their metabolites. Our study reveals that smoker and ex-smoker with COPD has severely altered metabolome profile than non-smoker with COPD suggesting that cigarette smoke plays crucial role in severity of disease.
