Photoinactivation of bacteria by lumichrome: Influence of formulation and preparation method.
Introduction: Lumichrome, a photodegradation product of riboflavin, is an endogenous compound in humans. The compound is more photostable and a more efficient photogenerator of singlet oxygen than riboflavin. It absorbs radiation in the UVA and blue light region, which can be an advantage in aPDT of superficial infections.
Aims and objectives: The aim of this study was to investigate the aPDT effect of various lumichrome pharmaceuticals formulations on bacteria in vitro.
Material & methods: Solutions of lumichrome (10-5 – 10-3M) were prepared in plain PBS, in PBS-cosolvents solutions or in formulations containing cyclodextrins or polyoxamers. Supersaturated solutions of lumichrome in PBS were prepared via the cosolvent and solvent evaporation method. The antibacterial effect of selected lumichrome preparations was studied in vitro against plaktonic Gram-positive and Gram-negative bacteria. The light dose used was ≈ 13 J/cm² and the lamp emitted mainly in the range 340–440 nm.
Results & discussion: Lumichrome was tenfold more phototoxic against Gram-positive than Gram-negative bacteria. The effect was independent of the formulation. When the concentration of lumichrome was enhanced less effect was obtained, probably due to a very high absorbance that blocks the radiation from reaching all the bacteria (inner filter effect).
Conclusion: The study demonstrates the possible utility of lumichrome as a UVA–blue light photosensitizer. The formulation needs to be optimized to improve the photoinactivation of Gram-negative bacteria.
Authors: Victoria J. Valerón Bergh1, Ellen Bruzell2, Anne Bee Hegge1, Hanne Hjorth Tønnesen1.
Affiliations: 1School of Pharmacy, University of Oslo, Norway, and 2 Nordic Institute of Dental Materials (NIOM), Norway.