Photodecomposition, photomutagenicity and photocytotoxicity of retinyl palmitate under He–Ne laser photoirradiation and its effects on photodynamic therapy of cancer cells in vitro

• Retinyl palmitate (RP) is a principal storage form of vitamin A.
• No photodecomposition of RP alone under irradiation of He–Ne laser.
• no mutagenicity under laser irradiation in presence or absence of HpD.
• RP alone (1–100 μM) has cytotoxicity on HeLa cells.
• Timing of adding RP before PDT is important since 24 h incubation enhances PDT.

ObjectiveOur aim was to study photodecomposition, photomutagenicity and cytotoxicity of retinyl palmitate (RP), a principal storage form of vitamin A in humans and animals, under He–Ne laser photoirradiation. Moreover, the effect of different concentrations and timing protocol of antioxidants on photodynamic therapy (PDT) is contradictory, so the effect of RP (as antioxidant) on the PDT cytotoxicity was studied.MethodsPhotomutagenicity was tested by Ames test. Photodecomposition was studied by UV–vis spectroscopy. Cytotoxicity was measured with MTT-assay. Moreover, the effect of PDT, using hematoporphyrin derivatives (HpD) as photosensitizer under He–Ne laser irradiation (10 J/cm2), was studied on HeLa cells either with or without RP (1–100 μM) which incubated with the cells for short or long incubation period (1 h or 24 h) prior to PDT.ResultsNo photodecomposition of RP alone was obseved whereas there is a little photodecomposition of RP only in presence of HpD under irradiation with He–Ne laser. Moreover, no photomutagenicity was observed in Salmonella typhimurium strains under laser irradiation in presence or absence of HpD. RP alone (1–100 μM) significantly decrease the viability of HeLa cells. Laser irradiation of HeLa cells pre-incubated with RP alone for 24 h showed further significant decrease in viability of the cells. While RP incubations for 1 h before PDT had slight effect on the cells, 24 h incubation before PDT enhanced the cytotoxicity of PDT on HeLa cells.ConclusionsRP can be used 24 h before PDT to enhance its effects. RP is not mutagenic under irradiation with He–Ne laser.