Neutralizing Staphylococcus aureus PAMPs that Trigger Cytokine Release from THP-1 Monocytes

Innate immunity has considerable specificity and can discriminate between individual species of microbes. In this regard, pathogens are "seen" as dangerous to the host and elicit an inflammatory response capable of destroying the microbes. This immune discrimination is achieved by toll-like receptors on host cells recognizing pathogens, such as Staphylococcus aureus, and microbe-specific pathogen-associated molecular pattern (PAMP) molecules, such as lipoteichoic acid (LTA). PAMPs impede wound healing by lengthening the inflammatory phase of healing and contributing to the development of chronic wounds. Preventing PAMPs from triggering the release of inflammatory cytokines will counteract the dysregulation of inflammation. Here, we use ELISA to evaluate the use of cationic molecules branched polyethylenimine (BPEI), PEGylated BPEI (PEG-BPEI), and polymyxin-B to neutralize anionic LTA and lower levels of TNF-α cytokine release from human THP-1 monocytes in a concentration-dependent manner. Additional data collected with qPCR shows that BPEI and PEG-BPEI reduce the expression profile of the TNF-α gene. Similar effects are observed for the neutralization of whole-cell S. aureus bacteria. In vitro cytotoxicity data demonstrate that PEGylation lowers the toxicity of PEG-BPEI (IC₅₀ = 2661 μm) compared to BPEI (IC₅₀ = 853 μM) and that both compounds are orders of magnitude less toxic than the cationic antibiotic polymyxin-B (IC₅₀ = 79 μM). Additionally, the LTA neutralization ability of polymyxin-B is less effective than BPEI or PEG-BPEI. These properties of BPEI and PEG-BPEI expand their utility beyond disabling antibiotic resistance mechanisms and disrupting S. aureus biofilms, providing additional justification for developing these agents as wound healing therapeutics. The multiple mechanisms of action for BPEI and PEG-BPEI are superior to current wound treatment strategies that have a single modality.