Dakin solution alters macrophage viability and function

Background: Macrophages are important in wound defense and healing. Dakin's solution (DS), buffered sodium hypochlorite, has been used since World War I as a topical antimicrobial for wound care. DS has been shown to be toxic to host cells, but effects on immune cells are not well documented. Materials and methods: DS at 0.5%, 0.125%, and ten-fold serial dilutions from 0.25% -0.00025% were evaluated for cellular toxicity on murine macrophages (J774A.1). The effect of DS on macrophage adhesion, phagocytosis, and generation of reactive oxygen species was examined. Macrophage polarization following DS exposure was determined by gene expression using quantitative real-time polymerase chain reaction. Results: Concentrations of DS >0.0025% reduced macrophage viability to <5% in exposure times as short as 30 s. Similarly, phagocytosis of Staphylococcus aureus, Pseudomonas aeruginosa, and Aspergillus flavus were significantly reduced at all tested concentrations by macrophages pretreated with DS. H₂O₂ production was reduced by 8%-38% following treatment with 0.00025%-0.125% DS. Macrophage adherence was significantly increased with >0.0025% DS after 15 min of exposure compared with controls. Quantitative real-time polymerase chain reaction demonstrated that DS exposure resulted in classical macrophage activation, with increased expression of inducible nitric oxide synthase 2, interferon-γ, and interleukin (IL)-1β. Conclusions: DS at clinically used concentrations (0.025%-0.25%) was detrimental to macrophage survival and function. For optimal clinical use, understanding the impact of DS on macrophages is important as depletion may result in impaired pathogen clearance and delayed healing. These findings indicate that 0.00025% DS is a safe starting dose; however, optimal use of DS requires further validation with in vivo models.