5-aminolevulinic acid (5-ALA) is a non-proteinogenic amino acid. Several reports show its beneficial effects, such as antiviral activity against COVID-19, anticancer effects, and a reduction in fatigue. In addition, 5-ALA acts as a precursor to a photosensitizer used for photodynamic therapy; however, 5-ALA may cause DNA damage in mammalian cells. In this study, we evaluated the effect of blue light and 5-ALA on DNA damage using mouse melanoma cells and human keratinocyte cell lines. We performed comet assays to assess DNA double-strand breaks (DSB) and single-strand breaks (SSB). Our results demonstrate that genomic DNA of both cancer cells and non-cancer cells was severely damaged by blue light irradiation in the presence of 5-ALA.

Several studies have suggested the potential benefits of 5-aminolevulinic acid (5-ALA)-based photodynamic therapy (PDT). 5-ALA is a precursor of heme, which generates reactive oxygen species (ROS) following photoirradiation. Some reports indicate that blue light induces intracellular ROS production. In the present study, we elucidated the effects of blue light and 5-ALA on DNA integrity in B16F1 murine melanoma and human keratinocyte HaCaT cells using a variety of comet assay techniques. Co-treatment with blue light and 5-ALA significantly decreased cell viability in both cell lines. A neutral comet assay was performed to assess DNA double-strand break (DSB) formation and blue light and 5-ALA caused DSBs. We also performed an alkali comet assay to detect single-strand breaks (SSB) and alkali labile sites (ALS). The results indicated that 5-ALA accelerated blue light-induced SSB formation. In addition, modified comet assays were done using two types of enzymes to evaluate oxidative DNA damages. The results indicated that blue light and 5-ALA generated oxidized purine and pyrimidines in both cell lines. In summary, co-treatment with 5-ALA and photoirradiation may cause unexpected DNA damage in cells and tissues.