1,25-Dihydroxyvitamin D Modulates Antibacterial and Inflammatory Response in Human Cigarette Smoke-Exposed Macrophages

<div><p>Cigarette smoking is associated with increased inflammation and defective antibacterial responses in the airways. Interestingly, vitamin D has been shown to suppress inflammation and to improve antibacterial defense. However, it is currently unknown whether vitamin D may modulate inflammation and antibacterial defects in human cigarette smoke (CS)-exposed airways. To explore these unresolved issues, alveolar macrophages obtained from non-smoking and smoking subjects as well as human cigarette smoke extract (CSE)-treated THP-1 macrophages were stimulated with 1,25-dihydroxyvitamin D (1,25(OH)₂D) to address inflammatory and antibacterial responses. Although basal levels of inflammatory cytokines and chemokines did not differ between non-smoking and smoking subjects, 1,25(OH)₂D did reduce levels of IL-6, TNF-α and MCP-1 in alveolar macrophages in response to LPS/IFN-γ, although not statistically significant for TNF-α and IL-6 in smokers. CSE did not significantly alter vitamin D metabolism (expression levels of CYP24A1 or CYP27B1) in THP-1 macrophages. Furthermore, stimulation with 1,25(OH)₂D reduced mRNA expression levels and/or protein levels of IL-8, TNF-α and MCP-1 in CSE-treated THP-1 macrophages. 1,25(OH)₂D did not improve defects in phagocytosis of <i>E</i>. <i>coli</i> bacteria or the oxidative burst response in CSE-treated THP-1 macrophages or alveolar macrophages from smokers. However, 1,25(OH)₂D significantly enhanced mRNA expression and/or protein levels of the antimicrobial peptide cathelicidin in alveolar macrophages and THP-1 macrophages, independently of CS exposure. In conclusion, our results provide the first evidence that vitamin D could be a new strategy for attenuating airway inflammation and improving antibacterial defense in CS-exposed airways.</p>