Effects of Cigarette Smoking on Oxidative Stress, DNA Damage, Immunological Profile, Viral Susceptibility, and Survival in Patients with Chronic Obstructive Pulmonary Disease

Background: Cigarette smoking promotes persistent systemic alterations in COPD, yet the interplay among genetic susceptibility, oxidative stress, immune dysregulation, impaired control of persistent viral replication, and long-term outcomes remains incompletely understood. Methods: We conducted an observational study in 102 patients aged ≥70 years with severe-to-very-severe COPD undergoing pulmonary rehabilitation. Current smokers (n = 38) were compared with never/former smokers (n = 64). Analyses included Chr15q25 genotyping (rs16969968), oxidative stress biomarkers (tail intensity, 8-OHdG, MDA, and bilirubin), hematological and immunological parameters, α7nAChR expression, TTV load as a surrogate marker of immune competence, latent virus prevalence, and five-year survival assessed by multivariable Cox regression. Results: Current smokers exhibited significantly higher DNA damage (tail intensity, p = 0.001; 8-OHdG, p = 0.002), lower bilirubin levels (p = 0.031), increased neutrophil and CD4+ T-cell counts (p = 0.031 and p = 0.028, respectively), altered α7nAChR expression on CD4+ T cells (p = 0.030), and higher TTV load (p = 0.002) than never/former smokers. The rs16969968 AA genotype was more frequent among current smokers. In survival analyses, an elevated WBC count was independently associated with increased mortality risk (HR 1.12, 95% CI 1.01–1.23; p = 0.035), whereas higher bilirubin levels showed a protective association. TTV load, smoking status, and FEV1 were not independently associated with mortality. Conclusions: In severe-to-very-severe COPD, smoking is associated with a distinct biological profile characterized by enhanced oxidative DNA damage, systemic inflammation, immune remodeling, reduced antioxidant defenses, and impaired control of persistent viral replication. WBC and bilirubin emerged as the biomarkers most consistently associated with long-term outcomes. These findings support integrated biological profiling as a tool for risk stratification and precision-guided rehabilitation in advanced COPD.