Biomedical subjects

M Rózanowska

Publications and source records attributed to M Rózanowska.

7 recordsLinked to original sources

PubMed2001

Retinal photodamage.

The retina represents a paradox, in that, while light and oxygen are essential for vision, these conditions also favour the formation of reactive oxygen species leading to photochemical damage to the retina. Such light damage seems to be multi-factorial and is dependent on the photoreactivity of a variety of chromophores (e.g., vitamin A metabolites, lipofuscin, melanin, flavins, porphyrins, carotenoids) endogenous to the retina. The aim of this article is to provide a detailed review of our current understanding of the photochemistry and photobiology of these chromophores and to consider how they may contribute to retinal ageing and pathology.

Adaptation, Physiological↗

PubMed2001

Probing the spatial dependence of the emission spectrum of single human retinal lipofuscin granules using near-field scanning optical microscopy.

The emission spectra of single lipofuscin granules are examined using spectrally resolved confocal microscopy and near-field scanning optical microscopy (NSOM). The emission spectrum varies among the granules examined revealing that individual granules are characterized by different distributions of fluorophores. The range of spectra observed is consistent with in vivo spectra of human retinal pigment epithelium cells. NSOM measurements reveal that the shape of the spectrum does not vary with position within the emissive regions of single lipofuscin granules. These results suggest that the relative distribution of fluorophores within the emissive regions of an individual granule is homogeneous on the spatial scale approximately 150 nm.

Humans↗

PubMed1999

Free radical scavenging properties of melanin interaction of eu- and pheo-melanin models with reducing and oxidising radicals.

The human skin and eye melanin is commonly viewed as an efficient photoprotective agent. To elucidate the molecular mechanism of the melanin-dependent photoprotection, we studied the interaction of two synthetic melanins, dopa-melanin and cysteinyldopa-melanin, with a wide range of oxidising and reducing free radicals using the pulse radiolysis technique. We have found that although both types of free radicals could efficiently interact with the synthetic melanins, their radical scavenging properties depended, in a complex way, on the redox potential, the electric charge and the lifetime of the radicals. Repetitive pulsing experiments, in which the free radicals, probing the polymer redox sites, were generated from four different viologens, indicated that the eumelanin model had more reduced than oxidised groups accessible to reaction with the radicals. Although with many radicals studied, melanin interacted via simple one-electron transfer processes, the reaction of both melanins with the strongly oxidising peroxyl radical from carbon tetrachloride, involved radical addition. Our study suggests that the free radical scavenging properties of melanin may be important in the protection of melanotic cells against free radical damage, particularly if the reactive radicals are generated in close proximity to the pigment granules.

Free Radical Scavengers↗

PubMed1998

Blue light-induced singlet oxygen generation by retinal lipofuscin in non-polar media.

Accumulation of lipofuscin (LF) is a prominent feature of aging in the human retinal pigment epithelium (RPE) cells. This age pigment exhibits substantial photoreactivity, which may increase the risk of retinal photodamage and contribute to age-related maculopathy. In a previous study, we detected singlet oxygen generation by lipofuscin granules excited with blue light. In this paper we investigated the ability of hydrophobic components of lipofuscin to photogenerate singlet oxygen in non-polar environments. Singlet oxygen was detected directly by monitoring its characteristic phosphorescence at ca 1270 nm. The action spectrum of singlet oxygen formation indicated that this process was strongly wavelength-dependent and its efficiency decreased with increasing wavelength by a factor of ten, comparing 420 nm and 520 nm. The quantum yield of singlet oxygen increased with increasing concentration of oxygen. Using laser flash photolysis we studied the possible mechanism of singlet oxygen formation. The observed transient, with a broad absorption spectrum peaking at around 440 nm, was identified as a triplet with lifetime ca 11 microseconds. It was quenched by both molecular oxygen and beta-carotene with concomitant formation of a beta-carotene triplet state. These results indicate the potential role of hydrophobic components of lipofuscin in blue light-induced damage to the RPE.

Aged↗

PubMed1997

The role of retinal pigment epithelium melanin in photoinduced oxidation of ascorbate.

To determine the role of major chromophores of the human retinal pigment epithelium (RPE) in photooxidation of ascorbate, we monitored spectrophotometrically rates of ascorbate depletion, induced by blue light, in suspensions of human RPE melanin, melanolipofuscin and lipofuscin and in preparation of pigmented and nonpigmented bovine RPE cells. The results clearly show that melanin is the key retinal pigment responsible for the photosensitized oxidation of exogenous ascorbate. To elucidate the mechanism of the photooxidation process, we used purified RPE melanin granules and synthetic dopa (dihydroxyphenylalanine) melanin and employed electron spin resonance (ESR) spectroscopy, ESR oximetry and oxidase electrode. Our data indicate that photoinduced melanin radicals oxidize ascorbate via one-electron transfer reaction. The reduced melanin is reoxidized by molecular oxygen with the formation of superoxide anion and hydrogen peroxide, while the ascorbate radicals decay by disproportionation. Because in the absence of oxygen, no measurable oxidation of ascorbate is observed, it can be concluded that melanin acts as an electron transfer agent. Biological implications of this study remain unclear; however, the formation of oxygen-reactive species that accompany melanin-mediated photooxidation of ascorbate may represent a potential risk to the RPE that should be minimized by yet unknown cellular mechanisms.

Animals↗

PubMed1995

Blue light-induced reactivity of retinal age pigment. In vitro generation of oxygen-reactive species.

Exposure of the eye to intense light, particularly blue light, can cause irreversible, oxygen-dependent damage to the retina. However, no key chromophores that trigger such photooxidative processes have been identified yet. We have found that illumination of human retinal pigment epithelium (RPE) cells with light induces significant uptake of oxygen that is both wavelength- and age-dependent. Analysis of photoreactivity of RPE cells and their age pigment lipofuscin indicates that the observed photoreactivity in RPE cells is primarily due to the presence of lipofuscin, which, under aerobic conditions, generates several oxygen-reactive species including singlet oxygen, superoxide anion, and hydrogen peroxide. We have also found that lipofuscin-photosensitized aerobic reactions lead to enhanced lipid peroxidation as measured by accumulation of lipid hydroperoxides and malondialdehyde in illuminated pigment granules. Hydrogen peroxide is only a minor product of aerobic photoexcitation of lipofuscin. We postulate that lipofuscin is a potential photosensitizer that may increase the risk of retinal photodamage and contribute to the development of age-related maculopathy.

Aged↗

PubMed1992

Quantification of neutral red pinocytosis by small numbers of adherent cells: comparative studies.

A colorimetric assay has been developed for studies on neutral red (NR) pinocytosis by small numbers (below 2 x 10(5)) of adherent cells cultured in 96 well plates. The NR uptake per cell mass was much higher in the sea urchin perivisceral adherent cells and human HL-60 cell line monolayers than in the murine and Atlantic salmon macrophages. The apparent difference points to the usefulness of this novel assay in comparative studies.

Animals↗