Investigation of photoexcited states in porcine eumelanin through their transient radical products.

Time-resolved electron paramagnetic resonance was used to monitor the photochemistry of radical pairs from melanin in porcine retinal pigment epithelial cells on the sub-microsecond time scale. Two distinct signals were found: one of enhanced absorption/emission at early times and one mostly emissive at later times. The emissive character of the longer lived feature suggests participation of an excited triplet precursor, something not generally thought to exist in melanins.

Photoprotection by porcine eumelanin against singlet oxygen production.

Melanin, a major pigment found in retinal pigment epithelium (RPE) cells, is considered to function in dual roles, one protective and one destructive. By quenching free radical species and reactive oxygen species (ROS) melanin counteracts harmful redox stress. However, melanin is also thought to be capable of creating ROS.

AcrySof Natural filter decreases blue light-induced apoptosis in human retinal pigment epithelium.

Purpose: The effect of AcrySof filter (UV light-filtering chromophore; Alcon) and AcrySof Natural filter (UV- and blue light-filtering chromophores) on blue light-induced apoptosis in human retinal pigment epithelial (RPE) cells was evaluated.

Design: Laboratory investigation

Clinical Relevance: Acrysof Natural filter reduces the blue-light toxicity in RPE cells and may have a positive impact on age-related macular degeneration (AMD).

Methods: RPE cells were exposed to blue light (430-450 nm) in the presence of either the AcrySof (UV only) filter or Acrysof Natural (UV and blue light) filter for 10 days.

Photoprotection of human retinal pigment epithelium cells against blue light-induced apoptosis by melanin free radicals from Sepia officinalis.

Cultured retinal pigment epithelium (RPE) cells can phagocytize large foreign particles. Heterogeneous melanin aggregates from Sepia officinalis, a species of cuttlefish, were fed to cultured human RPE cells to produce cells laden with Sepia melanin. Blue light-induced apoptosis (BLIA) assays were performed by flow cytometry on parallel cultures consisting of RPE cells isolated from independent eyes and evenly divided into two cultures, one fed Sepia melanin and one containing only native melanin.

Time-resolved detection of melanin free radicals quenching reactive oxygen species.

Melanin, a ubiquitous, heterogeneous biological polymer composed of many different monomers, contains a population of stationary, intrinsic semiquinone-like radicals. Additional extrinsic semiquinone-like radicals are reversibly photogenerated with visible or UV irradiation. The free radical chemistry of melanin is complex and not well characterized, especially the photochemistry of melanin in the presence of oxygen.

Melanin photoprotection in the human retinal pigment epithelium and its correlation with light-induced cell apoptosis.

Time-resolved electron paramagnetic resonance (TREPR) spectroscopy was used to study melanin free radicals in human retinal pigment epithelium (RPE) cells and tyrosine-derived synthetic melanin. TREPR signal traces from RPE cells reveal in vivo light-induced melanin free radical photochemistry in more detail than previously known. Electron spin polarization reflecting a non-Boltzmann population within the energy levels of the spin system is observed in RPE cells as the result of the triplet state photoproduction and subsequent disappearance of free radicals in the melanin polymer.

Trypan blue induces apoptosis in human retinal pigment epithelial cells.

Purpose: To examine whether trypan blue dye induces apoptosis in human retinal pigment epithelium cells.

Design: Laboratory investigation.

Methods: Pure cultures of human retinal pigment epithelium cells were isolated.

The effect of type I and II interferons on human fetal retinal pigment epithelium-induced apoptosis in Jurkat T cells.

Purpose: To examine the regulatory effects of interferon (IFN)-alpha, IFN-gamma, transforming growth factor (TGF)-beta, and tumor necrosis factor (TNF)-alpha on human fetal retinal pigment epithelial (HFRPE) cell-induced apoptosis of human Jurkat T (Jkt) cells.

Methods: Pure cultures of HFRPE cells were isolated. The cells were precultured with medium alone or with addition of IFN-alpha, IFN-gamma, TNF-alpha, or TGF-beta for 72 hours.