Healthcare associated infections (HAI) pose a major threat to patients admitted to hospitals and infection rates following orthopaedic arthroplasty surgery are as high as 4%, while the infection rates are even higher after revision surgery. 405 nm high-intensity narrow spectrum (HINS) light has been proven to reduce environmental contamination in hospital isolation rooms, and there is potential to develop this technology for application in orthopaedic surgery. Cultured rat osteoblasts were exposed to 405 nm light to investigate if bactericidal doses of the light could be used safely in the presence of mammalian cells. Cell viability was measured by MTT reduction and microscopy techniques, function by alkaline phosphatase activity, and proliferation by the BrdU assay. 405 nm light exposures of up to a dose of 36 J/cm² had no significant effect on osteoblast cell viability while exposure of a variety of clinically related bacteria, to 36 J/cm² resulted in up to 100% kill. High irradiance 405 nm light exposures (54 J/cm²) significantly affected the osteoblast cell viability indicating dose dependency. 405 nm light exposure involved reactive oxygen species (ROS) production in both mammalian and bacterial cells, as shown by fluorescence generated from 6-carboxy-2’,7’-dichlorodihydrofluorescein diacetate dye. Light treated osteoblast cells showed a decrease in intracellular reduced glutathione content and a corresponding increase in the efflux of oxidised glutathione, both indicating oxidative damage. The mammalian cells were significantly protected from dying at 54 J/cm2 by catalase, which detoxifies H₂O₂. Bacterial cells were significantly protected by sodium pyruvate (H₂O₂ scavenger) and by a combination of free radical scavengers (sodium pyruvate, dimethyl thiourea (.OH scavenger), catalase) at 162 and 324 J/cm².Thus the cytotoxic mechanism of 405 nm light in mammalian cells and bacteria could be oxidative stress involving predominantly H₂O₂ generation, with other ROS contributing to the damage.The cell viability and cytotoxicity results suggest that 405 nm light could be used for continual patient safe decontamination during orthopaedic replacement surgeries and further development of this light technology is encouraged.
|Date of Award||19 May 2016|
- University Of Strathclyde
|Sponsors||University of Strathclyde & EPSRC (Engineering and Physical Sciences Research Council)|
|Supervisor||Mary Grant (Supervisor) & Michelle Maclean (Supervisor)|