Inhibition of lysosomal degradative functions in RPE cells by a retinoid component of lipofuscin.

Purpose: To investigate the effect of the lipofuscin component N-retinylidene-N-retinylethanolamine (A2-E) on degradative functions of lysosomes in human retinal pigment epithelial (RPE) cells and to evaluate its mechanism of action.

Methods: A2-E was coupled to low-density lipoprotein (LDL). Human RPE cell cultures were loaded with the A2-E/LDL complex, and controls were run with medium containing LDL alone.

Lipofuscin in the retina: quantitative assay for an unprecedented autofluorescent compound (pyridinium bis-retinoid, A2-E) of ocular age pigment.

The pyridinium bis-retinoid, A2-E, has been discovered as one of the major autofluorescent components of retinal pigment epithelial lipofuscin. Due to its chemical characteristics, A2-E may contribute to cellular and molecular changes leading to age-related macular degeneration. Because A2-E is the first lipofuscin component that has been identified, purified, and its structure analysed, it represents an important marker molecule for studying lipofuscin formation under various conditions.

The photochemistry of human retinal lipofuscin as studied by EPR.

Fluorescent material generated in the human retina accumulates within lipofuscin (HLF) granules of the retinal pigment epithelium (RPE) during aging. We have been investigating the possible light-induced contribution of these fluorophores to various diseases including age-related macular degeneration. Our studies have shown that some of the fluorescent components of HLF are products of the reaction of retinaldehyde with ethanolamine and that synthetic mixtures of this reaction can serve as a useful model for photophysical studies.

Photophysical studies on human retinal lipofuscin.

Fluorescent material generated in the human retina accumulates within lipofuscin granules of the retinal pigment epithelium (RPE) during aging. Its presence has been suggested to contributed to various diseases including age-related macular degeneration. Because this material absorbs light at wave lengths as long as 550 nm, photophysical studies were performed to determine whether lipofuscin could contribute to light damage and to determine if its composition is similar to a synthetically prepared lipofuscin.

Lipofuscin fluorophore inhibits lysosomal protein degradation and may cause early stages of macular degeneration.

One of the autofluorescent compounds that accumulates within the lipofuscin granules of the human retinal pigment epithelium (RPE) has now been identified as a quaternary nitrogen-containing cationic amphiphile (the bis-retinoid pyridinium salt, A2-E). Experimental evidence suggests that it may be responsible for lipofuscinogenesis in the RPE through its ability to inhibit lysosomal proteolysis. Furthermore, it may be involved in the events that trigger the changes leading to age-related macular degeneration (AMD), the leading cause of untreatable blindness in the elderly.

Retinal age pigments generated by self-assembling lysosomotropic detergents.

A universal biomarker of cellular ageing in eukaryotic postmitotic cells is the appearance over time of autofluorescent lysosomal residual bodies called age pigments or lipofuscin granules. Their role in the process of cellular ageing has been debated without resolution. Neither the identity nor mechanism of formation of the fluorophores has been definitively determined.

Retinal light damage reduces autofluorescent pigment deposition in the retinal pigment epithelium.

Lipofuscin in the retinal pigment epithelium (RPE) is thought to be derived from phagocytosed photoreceptor outer segment disc membranes. Based on this hypothesis, one would predict that the rate of lipofuscin deposition in the RPE would be proportional to the density of photoreceptor cells in the retina. In previous studies it was demonstrated that specific loss of photoreceptor cells due to a genetic defect resulted in a substantial decrease in the rate of age-related lipofuscin accumulation in the RPE.

Failure of vitamin E to protect the retina against damage resulting from bright cyclic light exposure.

Cumulative light-mediated damage to the retina over a long time period may be involved in the development of age-related retinopathies. Light is thought to produce retinal damage by initiating autoxidative reactions among the molecular components of the retina. Experiments were therefore conducted (1) to confirm that long-term differences in cyclic light intensity affect the rate of age-related photoreceptor cell loss from the retina; and (2) to determine whether the antioxidant, vitamin E, is an effective inhibitor of damage to the retina by bright cyclic light.

The autofluorescent products of lipid peroxidation may not be lipofuscin-like.

The fluorescent molecules of cellular age pigment granules (lipofuscin) are commonly thought to be end products of membrane lipid autoxidation. Lipofuscin fluorophores of the retinal pigment epithelium (RPE) appear to be derived from photoreceptor outer segment membranes. Experiments were therefore conducted to determine whether the in vitro oxidation of retinal homogenates would generate fluorophores similar to the naturally occurring lipofuscin fluorophores of the RPE.

Fluorophores of the human retinal pigment epithelium: separation and spectral characterization.

Ten fluorescent fractions originating from the chloroform extracts of retinal pigment epithelial (RPE) cells of human donor eyes (ages 52-98 yr) have been separated and characterized by UV-vis absorbance and corrected fluorescence spectroscopy. The semipurified fluorophores fall into four categories based upon their spectral properties: green-emitting fluorophores, a golden yellow-emitting fluorophore, yellow-green-emitting fluorophores and orange-red-emitting fluorophores. All share common absorbance peaks around 280- and 330 nm, and the orange-red-emitting fluorophores also exhibit a strong absorbance peak at 420 nm.

Characterization of disease-specific brain fluorophores in ceroid-lipofuscinosis.

By isolating and identifying the molecular components of the storage material in the ceroid-lipofuscinoses, it should be possible to elucidate the metabolic basis for these diseases. Using brains of English setter dogs afflicted with a form of this disorder, the autofluorescent storage granules have been isolated and subjected to extraction with chloroform-methanol. A significant amount of autofluorescent material was solubilized by this procedure.

Lipofuscin autofluorescence: evidence for vitamin A involvement in the retina.

A lipofuscin-like autofluorescence develops in the degenerating photoreceptor cells of the RCS rat, a strain with inherited retinal dystrophy. In animals with normal retinas, age-related lipofuscin accumulation in the eye is restricted to the retinal pigment epithelium (RPE). Previous investigations have established that RPE lipofuscin accumulation in the normal rat retina can be reduced by dietary vitamin A deficiency.

Influence of early photoreceptor degeneration on lipofuscin in the retinal pigment epithelium.

Experiments were conducted to evaluate the role played by photoreceptor cells in the accumulation of age pigment, or lipofuscin, in the retinal pigment epithelium (RPE). The age-related accumulation of RPE lipofuscin was compared between rats with hereditary photoreceptor degeneration (RDY) and congenic rats with normal retinas. In the RDY animals, the age-related increase in RPE lipofuscin content was substantially less than in normal controls.

The fate of the phagosome: conversion to 'age pigment' and impact in human retinal pigment epithelium.

Phagosomes are converted to phagolysosomes and then to residual bodies (also known as lipofuscin granules or age pigment). Lipofuscin granules of retinal pigment epithelial (RPE) cells of single human eyes were isolated and analysed for enzyme content and fluorescence spectra. The granules are low in lysosomal enzymes and they fluoresce yellow-gold.

Lipofuscin: resolution of discrepant fluorescence data.

Lipofuscin granules (age pigments) emit yellow light under ultraviolet excitation in the fluorescence microscope. The reported blue emission maximum of extracts of lipofuscin-laden cells may result from instrumental bias. The major fluorescent components that accumulate with age in these lysosomal residual bodies of human retinal pigment epithelium are yellow-emitting fluorophores.

Immunoglobulin classes of antibodies to Aspergillus fumigatus in patients with pulmonary aspergillosis.

An indirect immunofluorescence test was used to determine the titre and immunoglobulin classes of antibodies to Aspergillus fumigatus in human serum. In 15 patients with aspergillosis, significant titres of IgG but not IgA or IgM antibodies were found. The IgG, IgA and IgM fractions of serum from 2 patients with aspergillosis were separated.