Chapter 11: Endogenous Singlet Oxygen Photosensitizers in Mammalians

Mammalians are frequently exposed to different radiation sources that emit different spectra ranging from the ultraviolet to the infrared. The cells of tissue contain various molecules and some of them may act as endogenous photosensitizers. These specific molecules transfer the absorbed radiation to molecular oxygen that is excited from its ground state to the first singlet state generating highly reactive singlet oxygen (¹O₂). ¹O₂ is an important biochemical intermediate in multiple biological processes. Most of the known endogenous photosensitizers generate ¹O₂ with UVA and partially with visible irradiation. However, many of these photosensitizers also absorb UVB radiation, sometimes to a higher extent as compared to UVA or visible radiation. Thus, UVB-induced ¹O₂ might play an additional, important role for the mechanisms of oxidative tissue damage. Endogenous photosensitizers may change its chemical structure under UV irradiation that may affect ¹O₂ generation.