Abstract
Background: Host-derived (LL-37) and synthetic (WLBU-2) cationic antimicrobial peptides (CAPs) are known for their membrane-active bactericidal properties. LL-37 is an important mediator for immunomodulation, while the mechanism of action of WLBU-2 remains unclear. Objective: To determine if WLBU-2 induces an early proinflammatory response that facilitates bacterial clearance in cystic fibrosis (CF). Methods: C57BL6 mice were given intranasal or intraperitoneal 1×10 6 cfu/mL Pseudomonas aeruginosa (PA) and observed for 2h, followed by instillation of LL-37 or WLBU-2 (2-4mg/kg) with subsequent tissue collection at 24h for determination of bacterial colony counts and quantitative RT-PCR measurement of cytokine transcripts. CF airway epithelial cells (IB3-1, ΔF508/W1282X) were cultured in appropriate media with supplements. WLBU-2 (25μM) was added to the media with RT-PCR measurement of TNF-α and IL-1β transcripts after 20, 30, and 60min. Flow cytometry was used to determine if WLBU-2 assists in cellular uptake of Alexa 488-labeled LPS. Results: In murine lung exposed to intranasal or intraperitoneal WLBU-2, there was a reduction in the number of surviving PA colonies compared to controls. Murine lung exposed to intraperitoneal WLBU-2 showed fewer PA colonies compared to LL-37. After 24h WLBU-2 exposure, PA-induced IL-1β transcripts from lungs showed a twofold decrease (p<0.05), while TNF-α levels were unchanged. LL-37 did not significantly change transcript levels. In IB3-1 cells, WLBU-2 exposure resulted in increased TNF-α and IL-1β transcripts that decreased by 60min. WLBU-2 treatment of IB3-1 cells displayed increased LPS uptake, suggesting a potential role for CAPs in inducing protective proinflammatory responses. Taken together, the cytokine response, LPS uptake, and established antimicrobial activity of WLBU-2 demonstrate its ability to modulate proinflammatory signaling as a protective mechanism to clear infection. Conclusions: The immunomodulatory properties of WLBU-2 reveal a potential mechanism of its broad-spectrum antibacterial activity and warrant further preclinical evaluation to study bacterial clearance and rescue of chronic inflammation.
Highlights
Cationic antimicrobial peptides (CAPs) are one effector of the innate immune response, the “first line of defense” against a pathogenic insult
WLBU-2-exposed cells showed significantly less IL-8 promoter activity compared to LL-37-exposed cells (p
Using equimolar (25μM) peptide concentrations in LPS-stimulated cells, WLBU-2 showed less LPS-induced IL-8 reporter activity compared to LL-37 after 4h
Summary
Cationic antimicrobial peptides (CAPs) are one effector of the innate immune response, the “first line of defense” against a pathogenic insult They are ancient, structurally diverse elements of the immune responses of all living species. These molecules typically have broad-spectrum antimicrobial activity with conserved recognition patterns to molecules such as lipopolysaccharide (LPS) and lipoteichoic acid. After 24h WLBU-2 exposure, PA-induced IL-1β transcripts from lungs showed a twofold decrease (p
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