title: Dynamic analyses reveal cytoprotection by RPE melanosomes against non-photic stress.
abstract: OBJECTIVE
  Isolated melanosomes are known to have antioxidant properties but whether the granules perform an antioxidant function within cells is unclear. The aim of this study was to determine whether retinal pigment epithelium (RPE) melanosomes are competent to protect cultured cells against non-photic oxidative stress induced by treatment with H(2)O(2).
  
  
  METHODS
  Porcine melanosomes, either untreated or irradiated with visible light to simulate age-related melanin photobleaching, were introduced by phagocytosis into ARPE-19 cells. Cells were treated with H(2)O(2) using two delivery methods: as a pulse, or by continuous generation following addition of glucose oxidase to the medium. Cell survival in melanosome-containing cells was compared to survival in cells containing phagocytosed control latex beads using two real-time cell death assays.
  
  
  RESULTS
  Following H(2)O(2) delivery by either method, greater resistance to critical concentrations of H(2)O(2) was seen for cells containing melanosomes than for cells containing beads. Melanosome-mediated protection manifested as a delay in the time of onset of cell death and a slower rate of cell death over time. Photobleaching diminished the stress resistance conferred by the pigment granules. Individual cells in co-cultures were differentially sensitive to oxidative stress depending upon their particle content. Additional features of the time course of the cell death response were revealed by the dynamic analyses conducted over hours post oxidant treatment.
  
  
  CONCLUSIONS
  The results show, for the first time, that melanosomes perform a cytoprotective function within cultured cells by acting as an antioxidant. The outcomes imply that melanosomes perform functions within RPE cells aside from those related to light irradiation, and also suggest that susceptibility to ubiquitous pro-oxidizing agents like H(2)O(2) is partly determined by discrete features of individual RPE cells such as their granule content.
authors: Department of Ophthalmology, Medical College of Wisconsin, Milwaukee, WI 53226-4812, USA. jburke@mcw.edu
authors: Janice M
authors: JM
authors: Burke
authors: Patrycja
authors: P
authors: Kaczara
authors: Christine M B
authors: CM
authors: Skumatz
authors: Mariusz
authors: M
authors: Zareba
authors: Michael W
authors: MW
authors: Raciti
authors: Tadeusz
authors: T
authors: Sarna
mesh_terms: D000818:Animals; D000975:Antioxidants / Q000494:pharmacology*; D002478:Cells, Cultured; D018920:Coculture Techniques; D019610:Cytoprotection; D005949:Glucose Oxidase / Q000378:metabolism; D006801:Humans; D006861:Hydrogen Peroxide / Q000009:adverse effects; D008027:Light; D008268:Macular Degeneration / Q000378:metabolism* / Q000473:pathology; D008543:Melanins / Q000378:metabolism; D020460:Melanosomes / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D008863:Microspheres; D018384:Oxidative Stress; D010587:Phagocytosis / Q000187:drug effects / Q000528:radiation effects; D038761:Photobleaching / Q000528:radiation effects; D011419:Propidium / Q000032:analysis; D055213:Retinal Pigment Epithelium / Q000378:metabolism* / Q000473:pathology; D013050:Spectrometry, Fluorescence; D013552:Swine
chemical_list: D000975:Antioxidants; D008543:Melanins; D011419:Propidium; D006861:Hydrogen Peroxide; D005949:Glucose Oxidase