Oral Presentation 18th International Congress on Photobiology 2024

Visible light excites lipofuscin and induces photoaging in skin cells (#120)

Mauricio Baptista 1
  1. University of Sao Paulo, Sao Paulo, SP, Brazil

Lipofuscin is a yellow-brown cross-linked granular material, which is resistant to enzymatic hydrolysis and accumulates in various tissues, as a result of the normal aging process, consequently, it has been called the aging pigment. It is composed of highly oxidized proteins (30-70%), lipids (20-50%), and carbohydrates (4-7%) (1). Lipofuscinogenisis has been linked to the failure in the homeostasis of the skin redoxome, favoring the accumulation of reactive electrophiles in lysosomes, such as 4-hydroxy- 2-nonenal (HNE), which favors the crosslink of the oxidized molecules(2). The chelating properties of lipofuscin also favors the incorporation of metal cations (up to 2%), especially iron. Excitation of lipofuscin with UVA, blue, or green light results in yellow/blue fluorescence. After light absorption, lipofuscin also act as a potent photosensitizer, generating excited states such as triplet excited states and singlet oxygen (1O2) as well as a variety of radicals, accelerating the photodamage on the pigment´s vicinity (3). Lipofuscin-like granules have been identified in keratinocytes exposed to UVA, turning these cells hyper-sensitive to broad spectra Visible Light (VL) and causing exposed cells to accumulate mutagenic DNA lesions (4).   The damage in nuclear DNA is correlated with the accumulation of 1O2 – induced 8-oxo-dG and other oxidation products, as well as single and double-strand breaks. The phototoxicity action spectra of VL in keratinocytes demonstrated that the mutagenic potential of violet (408 nm) and blue (466 nm) light is much larger than those induced by green and red light. The violet/blue component of VL behaves similarly to UVA in keratinocytes, producing fpg-sensitive mutagenic lesions and inhibiting the autophagic flux (5). In conclusion, lipofuscin accumulation can occur in human skin as a consequence of sun bathing with classical sun screen, i.e., those that do not offer broad-band (specially efficient UVA and blue light) photoprotection. Public and health professionals should be aware that the excess of visible light exposure can have nasty consequences to the human skin.

  1. (1) Bastos, Quina & Baptista. Endogenous Photosensitizers in Human Skin Chem Rev 2023, 123, 9720. (2) Schalka et al, The Skin Redoxome. JEADV 2022, 36,181-195. (3) Tonolli et al Lipofuscin Generated by UVA Exposure makes Human Skin Keratinocytes Sensitive to Visible Light. JID 2017, 137, 2447. (4) Tonolli et al. Lipofuscin in keratinocytes: Production, properties, and consequences of the photosensitization with visible light. FRBM 2020, 160, 277-292. (5) Tonolli et al. The phototoxicity action spectra of visible light in HaCaT keratinocytes, JPPB 2023, 243, 112703.