Age-dependent photoionization thresholds of melanosomes and lipofuscin isolated from human retinal pigment epithelium cells

Lian Hong, Jacob Garguilo, Laura Anzaldi, Glenn S. Edwards, Robert J. Nemanich, John D. Simon

Research output: Contribution to journalArticlepeer-review

16 Scopus citations


Melanosomes and lipofuscin were isolated from 14-, 59-, and 76-year-old, human retinal pigment epithelium specimens and examined. The morphological features of these samples were studied by scanning electron microscopy and atomic force microscopy, and the photoionization properties were examined by photoelectron emission microscopy. Ovoid- and rod-shaped melanosomes were observed. The size of the granules and the distribution between the two shapes show no significant age-dependent change. However, there is a higher occurrence of irregularly shaped aggregates of small round granules in older samples which suggests degradation or damage to melanosomes occurs with age. The melanosomes from the 14-year-old donor eye are well characterized by a single photoionization threshold, 4.1 eV, while the two older melanosomes exhibit two thresholds around 4.4 and 3.6 eV. Lipofuscin from both young and old cells show two thresholds, 4.4 and 3.4 eV. The similarity of the potentials observed for aged melanosomes and lipofuscin suggest that the lower threshold in the melanosome sample reflects lipofuscin deposited the surface of the melanosome. The amount, however, is not sufficient to alter the density of the melanosome, and therefore these granules do not separate in a sucrose gradient at densities characteristic of the typical melanolipofuscin granule. These data suggest that thin deposits of lipofuscin on the surface of retinal pigment epithelium melanosomes are common in the aged eye and that this renders the melanosomes more pro-oxidant.

Original languageEnglish (US)
Pages (from-to)1475-1481
Number of pages7
JournalPhotochemistry and photobiology
Issue number6
StatePublished - Nov 2006
Externally publishedYes

ASJC Scopus subject areas

  • Biochemistry
  • Physical and Theoretical Chemistry


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