title: Evidence for intracellular aggregation of hypericin and the impact on its photocytotoxicity in PAM 212 murine keratinocytes.
abstract: We have assessed photoinduced toxicity of hypericin in PAM 212 murine keratinocytes and the relationship between concentration, incubation time and light fluence to evaluate the effect of intracellular aggregation at high concentrations. Confocal microscopy was used to establish the subcellular localization of hypericin at 5 and 50 microM and incubation times of 1 and 3 h. From fluorescence uptake time course studies, intracellular hypericin was demonstrated to exist predominantly in the monomeric form for up to 26 h incubation at 5 microM. However, there was a pronounced aggregation effect at 50 microM, with intracellular hypericin fluorescence levels initially showing an increase followed by a decrease with incubation time. This effect was subsequently shown to exert an effect on the phototoxicity of hypericin. On irradiation, the photocytotoxicity for 1 and 7 h incubation with 50 microM hypericin was comparable, whereas using 5 microM the photocytotoxicity showed good correlation with the intracellular fluorescence measurements at 1 and 7 h incubation.
authors.affiliation: National Medical Laser Centre, Royal Free and University College Medical School, Academic Division of Surgical Specialties, University College London, London, UK. t.theodossiou@ucl.ac.uk
authors.forename: Theodossis
authors.initials: T
authors.lastname: Theodossiou
authors.forename: Michael D
authors.initials: MD
authors.lastname: Spiro
authors.forename: Jake
authors.initials: J
authors.lastname: Jacobson
authors.forename: John S
authors.initials: JS
authors.lastname: Hothersall
authors.forename: Alexander J
authors.initials: AJ
authors.lastname: Macrobert
mesh_terms: D000818:Animals; D000873:Anthracenes; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D015603:Keratinocytes / Q000166:cytology / Q000187:drug effects* / Q000528:radiation effects*; D051379:Mice; D018613:Microscopy, Confocal; D010569:Perylene / Q000031:analogs & derivatives* / Q000737:chemistry / Q000633:toxicity; D017319:Photosensitizing Agents / Q000737:chemistry* / Q000633:toxicity*; D013057:Spectrum Analysis
chemical_list: D000873:Anthracenes; D017319:Photosensitizing Agents; D010569:Perylene; C004965:hypericin