Photodynamic inactivation of primary human fibroblasts by methylene blue and toluidine blue O

Abstract

An important determinant of the clinical applicability and value of antimicrobial photodynamic inactivation (PDI) is the cytotoxicity of the treatment to human cells. We evaluated the in vitro cytotoxicity of PDI to primary human fibroblasts using methylene blue (MB) and toluidine blue O (TBO) as the photosensitizers. The primary human fibroblasts were exposed to PDI regimes that were used for the inactivation of methicillin-resistant Staphylococcus aureus (MRSA) and multi-drug resistant Escherichia coli (MDR E. coli). Mitochondrial activity subsequent to exposure was evaluated after 24h using the methylthiazoletetrazolium assay and compared to pretreatment values. Mitochondrial activity of primary human fibroblasts was reduced by 27% after exposure to light (163.8 J/cm(2)) and MB (50 μg/ml). At a TBO concentration previously demonstrated to induce 99.91% and 83.2% reduction in a viable count for MRSA and MDR E. coli, respectively, 39.6% of the fibroblasts were photo-inactivated. Our findings showed that MB/TBO-PDI did not induce significant cytotoxic effects on human fibroblasts in culture.