Aim: To demonstrate a direct inhibitory effect of cigarette smoke exposure on paraoxonase 1 activity in a murine in vivo model.
Methods: At 8 weeks old, we randomized 10 C57/bl6 mice to an environment consisting of either filtered air or cigarette smoke for 6 months. Smoke exposure (7 hours per day, 5 days per week) was standardized using a model TE-10 smoking machine and adjusted to maintain constant sidestream and mainstream smoke. After 6 months of exposure, we assessed differences in lung air space, cholesterol, lipid, and lipoprotein profiles, as well as paraoxonase activity in mice exposed to cigarette smoke extract compared to unexposed control mice.
Results: Cigarette smoke exposure by the protocol used was sufficient to result in pathologic changes in lung architecture consistent with emphysema. Specifically, we observed that mice exposed to cigarette smoke had a significantly higher mean linear chord length compared to animals that were exposed to filtered air (p<0.02). Despite this exposure, no differences in total HDL-cholesterol levels or HDL-cholesterol sub-fractions (i.e. HDL2 and HDL3 fractions) were noted between smoke-exposed and unexposed animals (p=1.00, 0.6, and 0.4, respectively). Notably, mean HDL-cholesterol levels were identical between groups (92.8 vs 92.8 mg/dL, p=1.0). Paraoxonase activity, however, was markedly reduced in mice exposed to cigarette smoke compared to those who were not exposed (102, SD=9.6 vs 144, SD=4.1 units of activity, respectively, p=0.002).
Conclusion: In this murine model, tobacco smoke exposure directly inhibits paraoxonase activity independently of HDL-cholesterol levels rather than indirectly via reduction in HDL-cholesterol levels.
Keywords: High density lipoprotein; Paraoxonase; antioxidants; tobacco smoke.