title: Competitive quenching: a possible novel approach in protecting RPE cells from damage during PDT.
abstract: OBJECTIVE
  The purpose of this study is to demonstrate feasibility of using our novel concept, termed competitive quenching, for protecting the choroidal extravascular compartment and retinal pigment epithelium (RPE) from verteporfin (VP)-induced phototoxicity using hypericin. Furthermore, we aim to achieve partitioning of the quencher, hypericin, in the extravascular space and VP within the microvascular compartment of the chorio-retinal complex in vivo.
  
  
  METHODS
  We protect RPE cells from damage inflicted by photoactivated VP by introducing hypericin into these cells prior to photosensitization to quench the photosensitizing activity of VP. Cell protection levels were measured by MTT and Hemacolor viability assays. Wavelength range used for VP photoexcitation (700 +/- 40 nm) excludes the absorption range of hypericin, preventing the latter from photoactivation. Pharmacokinetic conditions, in which hypericin spreads throughout the choroidal and retinal extravascular space while VP is confined to the vasculature, are delineated using double-fluorescence imaging.
  
  
  RESULTS
  Cell viability increased 3- to 5-fold when 10-20 microM hypericin were present in RPE cells during photosensitization with 0.1-0.5 microM VP. VP fluorescence intensity was unchanged by the presence of hypericin in the cells. Hypericin administered intravenously to rats was confined to the choroidal vasculature after 15 min to 2 hr. Subsequently, hypericin partitioned to the choroidal and retinal extravascular space. VP administered at this time was confined to the microvasculature.
  
  
  CONCLUSIONS
  RPE and choroid may potentially be protected by compartmentalizing hypericin to the extravascular compartment while VP administered shortly before photosensitization is confined to the microvasculature. Adverse photodynamic therapy (PDT) damage to choroidal tissues adjacent to neovasculature targeted for photoablation have the potential of being prevented by competitive quenching with hypericin.
authors: Department of Ophthalmology, Beilinson Medical Center, Tel-Aviv University School of Medicine, Tel Aviv, Israel.
authors: Dov
authors: D
authors: Weinberger
authors: Yonina
authors: Y
authors: Ron
authors: Moshe
authors: M
authors: Lusky
authors: Dan
authors: D
authors: Gaaton
authors: Arie
authors: A
authors: Orenstein
authors: Michael
authors: M
authors: Blank
authors: Mathilda
authors: M
authors: Mandel
authors: Tamar
authors: T
authors: Livnat
authors: Tilda
authors: T
authors: Barliya
authors: Gad
authors: G
authors: Lavie
mesh_terms: D000818:Animals; D000873:Anthracenes; D002460:Cell Line; D002470:Cell Survival; D020256:Choroidal Neovascularization / Q000188:drug therapy / Q000378:metabolism; D019610:Cytoprotection; D008297:Male; D010084:Oxidation-Reduction; D010569:Perylene / Q000031:analogs & derivatives* / Q000493:pharmacokinetics / Q000494:pharmacology*; D010778:Photochemotherapy; D017319:Photosensitizing Agents / Q000493:pharmacokinetics / Q000633:toxicity*; D010857:Pigment Epithelium of Eye / Q000187:drug effects* / Q000473:pathology; D011166:Porphyrins / Q000493:pharmacokinetics / Q000633:toxicity*; D011817:Rabbits; D051381:Rats; D017208:Rats, Wistar; D012160:Retina / Q000378:metabolism; D013778:Tetrazolium Salts / Q000378:metabolism; D013844:Thiazoles / Q000378:metabolism; D000077362:Verteporfin
chemical_list: D000873:Anthracenes; D017319:Photosensitizing Agents; D011166:Porphyrins; D013778:Tetrazolium Salts; D013844:Thiazoles; D000077362:Verteporfin; D010569:Perylene; C004965:hypericin; C022616:thiazolyl blue