Abstract
IMPORTANCE: Cigarette smoking has been associated with risk of neurodegenerative disorders, such as Alzheimer disease. The association between smoking and biomarkers of changes in human cerebrospinal fluid (CSF) is not fully understood. OBJECTIVE: To investigate the association of cigarette smoking with CSF biomarkers of neurodegeneration, neuroinflammation, oxidation, and neuroprotection. DESIGN, SETTING, AND PARTICIPANTS: In this case-control study of 191 adult men in China, biomarkers in the CSF of participants with and without significant cigarette exposure were examined. Participants who did not smoke and had no history of substance use disorder or dependence were assigned to the nonsmoking group. The active smoking group included participants who consumed at least 10 cigarettes per day for 1 year. Five-milliliter samples of CSF were obtained from routine lumbar puncture conducted before anterior cruciate ligament reconstruction surgery. Data collection took place from September 2014 to January 2016, and analysis took place from January to February 2016. EXPOSURES: Cigarette smoking. MAIN OUTCOMES AND MEASURES: CSF levels of β-amyloid 42 (Aβ42), which has diagnostic specificity for Alzheimer disease, tumor necrosis factor alpha (TNFα), brain-derived neurotrophic factor (BDNF), total superoxide dismutase (SOD), and nitric oxide synthase (NOS) were measured. Sociodemographic data and history of smoking were obtained. RESULTS: Of 191 participants, 87 (45.5%) were included in the active smoking group and 104 (54.4%) in the nonsmoking group. Compared with the active smoking group, the nonsmoking group was younger (mean [SD] age, 34.4 [10.5] years vs 29.6 [9.5] years; P = .01), had more education (mean [SD] duration of education, 11.9 [3.1] years vs 13.2 [2.6] years; P = .001), and had lower body mass index (mean [SD], 25.9 [3.6] vs 24.9 [4.0]; P = .005). Comparing the nonsmoking group with the smoking group, mean (SD) CSF levels of Aβ42 (38.0 [25.9] pg/mL vs 52.8 [16.5] pg/mL; P < .001) and TNFα (23.0 [2.5] pg/mL vs 28.0 [2.0] pg/mL; P < .001) were significantly lower, while BDNF (23.1 [3.9] pg/mL vs 13.8 [2.7] pg/mL; P < .001), total SOD (15.7 [2.6] U/L vs 13.9 [2.4] U/L; P < .001), total NOS (28.3 [7.2] U/L vs 14.7 [5.6] U/L; P < .001), inducible NOS (16.0 [5.4] U/L vs 10.3 [2.7] U/L; P < .001), and constitutive NOS (12.4 [6.9] U/mL vs 4.4 [3.9] U/mL) were higher. In addition, in participants in the smoking group who were aged 40 years or older, total SOD levels were negatively correlated with Aβ42 levels (r = -0.57; P = .02). In those who smoked at least 20 cigarettes per day, TNFα levels were positively correlated with Aβ42 levels (r = 0.51; P = .006). The association of TNFα with Aβ42 production was stronger than that of total SOD with Aβ42 production (z = -4.38; P < .001). CONCLUSIONS AND RELEVANCE: This case-control study found that cigarette smoking was associated with at-risk biomarkers for Alzheimer disease, as indicated by higher Aβ42 levels, excessive oxidative stress, neuroinflammation, and impaired neuroprotection found in the CSF of participants in the active smoking group.