The Effect of a Human Antibacterial Neuropeptide SL-21 on the Expression of Pro-inflammatory Factors in Airway Epithelial Cells

Antimicrobial peptides are evolutionary components of the immune system generated in response to microbial infections. Human catestatin CgA352-372 (SL-21) is an endogenous neuropeptide with multiple biological functions. The present study aimed to further evaluate the immunomodulatory role of SL-21 in innate immunity of lung cells and investigate its impact on the expression level of pro-inflammatory factors. SL-21 neuropeptide, generated from the C-terminus of chromogranin A, was first chemically synthesized by solid-phase method and purified using C-8 semi-preparative RP-HPLC. According to the results of MTT assay, SL-21 showed no significant cytotoxicity effect on human lung epithelial adenocarcinoma cell line (A549) and human fetal lung fibroblast primary cells even at high concentration (< 12 % suppression of the cell growth). Furthermore, SL-21 decreased the expression level of pro-inflammatory factors including interleukine-1 beta (IL-1 beta), IL-6, IL-8, and tumor necrosis factor-alpha in a dose- and time-dependent manner. The results suggest that SL-21 antimicrobial neuropeptide interferes with cytokine network evolving during inflammatory processes of the respiratory tract. Since inflammation has been implicated as one of the main causative factors in human diseases, our findings suggest that potent SL-21 anti-inflammatory properties could be of great significance in the treatment of inflammatory disorders.