Photobiology of lipofuscin granules in the retinal pigment epithelium cells of the eye: norm, pathology, age.

Lipofuscin granules (LGs) are accumulated in the retinal pigment epithelium (RPE) cells. The progressive LG accumulation can somehow lead to pathology and accelerate the aging process. The review examines composition, spectral properties and photoactivity of LGs isolated from the human cadaver eyes. By use of atomic force microscopy and near-field microscopy, we have revealed the fluorescent heterogeneity of LGs. We have discovered the generation of reactive oxygen species by LGs, and found that LGs and melanolipofuscin granules are capable of photoinduced oxidation of lipids. It was shown that A2E, as the main fluorophore (bisretinoid) of LGs, is much less active as an oxidation photosensitizer than other fluorophores (bisretinoids) of LGs. Photooxidized products of bisretinoids pose a much greater danger to the cell than non-oxidized one. Our studies of the fluorescent properties of LGs and their fluorophores (bisretinoids) showed for the first time that their spectral characteristics change (shift to the short-wavelength region) in pathology and after exposure to ionizing radiation. By recording the fluorescence spectra and fluorescence decay kinetics of oxidized products of LG fluorophores, it is possible to improve the methods of early diagnosis of degenerative diseases. Lipofuscin ("aging pigment") is not an inert "slag". The photoactivity of LGs can pose a significant danger to the RPE cells. Fluorescence characteristics of LGs are a tool to detect early stages of degeneration in the retina and RPE.

Ommochromes from the Compound Eyes of Insects: Physicochemical Properties and Antioxidant Activity.

The objective of this study was screening of ommochromes from the compound eyes of insects and comparison of their antioxidant properties. Ommochromes were isolated in preparative quantities from insects of five different families: Stratiomyidae, Sphingidae, Blaberidae, Acrididae, and Tenebrionidae. The yield of ommochromes (dry pigment weight) was 0.9-5.4% of tissue wet weight depending on the insect species. Isolated pigments were analyzed by high-performance liquid chromatography and represented a mixture of several ommochromes of the ommatin series. The isolated ommochromes displayed a pronounced fluorescence with the emission maxima at 435-450 nm and 520-535 nm; furthermore, the emission intensity increased significantly upon ommochrome oxidation with hydrogen peroxide. The ommochromes produced a stable EPR signal consisting of a singlet line with g = 2.0045-2.0048, width of 1.20-1.27 mT, and high concentration of paramagnetic centers (> 1017 spin/g dry weight). All the investigated ommochromes demonstrated high antiradical activity measured from the degree of chemiluminescence quenching in a model system containing luminol, hemoglobin, and hydrogen peroxide. The ommochromes strongly inhibited peroxidation of the photoreceptor cell outer segments induced by visible light in the presence of lipofuscin granules from the human retinal pigment epithelium, as well as suppressed iron/ascorbate-mediated lipid peroxidation. The obtained results are important for understanding the biological functions of ommochromes in invertebrates and identifying invertebrate species that could be used as efficient sources of ommochromes for pharmacological preparations to prevent and treat pathologies associated with the oxidative stress development.

The fluorescence lifetime of lipofuscin granule fluorophores contained in the retinal pigment epithelium cells from human cadaver eyes in normal state and in the case of visualized pathology.

A comparative analysis of fluorescence lifetime of lipofuscin granule fluorophores contained in the retinal pigment epithelium cells from human cadaver eyes in normal state and in the case of visualized pathology was carried out. Measurements of fluorescence lifetimes of bis-retinoids and their photooxidation and photodegradation products were carried out using the method of counting time-correlated photons. Comparative analysis showed that, in the case of visualized pathology, the contribution of photooxidation and photodegradation products of bis-retinoids to the total fluorescence of the retinal pigment epithelium cell suspension increases in comparison with the norm.

Femtosecond and Picosecond Dynamics of Recombinant Bacteriorhodopsin Primary Reactions Compared to the Native Protein in Trimeric and Monomeric Forms.

Photochemical reaction dynamics of the primary events in recombinant bacteriorhodopsin (bRrec) was studied by femtosecond laser absorption spectroscopy with 25-fs time resolution. bRrec was produced in an Escherichia coli expression system. Since bRrec was prepared in a DMPC-CHAPS micelle system in the monomeric form, its comparison with trimeric and monomeric forms of the native bacteriorhodopsin (bRtrim and bRmon, respectively) was carried out. We found that bRrec intermediate I (excited state of bR) was formed in the range of 100 fs, as in the case of bRtrim and bRmon. Further processes, namely the decay of the excited state I and the formation of intermediates J and K of bRrec, occurred more slowly compared to bRtrim, but similarly to bRmon. The lifetime of intermediate I, judging from the signal of ΔAESA(470-480 nm), was 0.68 ps (78%) and 4.4 ps (22%) for bRrec, 0.52 ps (73%) and 1.7 ps (27%) for bRmon, and 0.45 ps (90%) and 1.75 ps (10%) for bRtrim. The formation time of intermediate K, judging from the signal of ΔAGSA(625-635 nm), was 13.5 ps for bRrec, 9.8 ps for bRmon, and 4.3 ps for bRtrim. In addition, there was a decrease in the photoreaction efficiency of bRrec and bRmon as seen by a decrease in absorbance in the differential spectrum of the intermediate K by ~14%. Since photochemical properties of bRrec are similar to those of the monomeric form of the native protein, bRrec and its mutants can be considered as a basis for further studies of the mechanism of bacteriorhodopsin functioning.

Estimation of fluorescence lifetime of lipofuscin fluorophores contained in lipofuscin granules of retinal pigment epithelium of human cadaver eyes without signs of pathology.

The fluorescence lifetimes of lipofuscin fluorophores contained in chloroform extracts from retinal pigment epithelium (RPE) of human cadaver eyes without signs of pathology were evaluated by single photon counting. The comparison of fluorescence lifetimes of N-retinylidene-N-retinylethanolamine (A2E) and its photooxidation and photodegradation products has been carried out. It was shown that the contribution of A2E to the total fluorescence of chloroform extract from lipofuscin granules is not major. The results are important for the improvement of noninvasive diagnostic method of degenerative diseases of the retina and RPE-fundus autofluorescence (FAF).

Study of visual pigment rhodopsin supramolecular organization in photoreceptor membrane by small-angle neutron scattering method with contrast variation.

Supramolecular organization of rhodopsin in the photoreceptor membrane was investigated by small-angle neutron scattering method. The experiments, which were performed with mixtures of heavy/light water as solvent (contrast variation method), were aimed at obtaining information about the lipid and protein components of the photoreceptor disc membrane separately. It was shown that the packaging density of the rhodopsin molecules in the photoreceptor membrane was unusually high: the distance between the centers of the molecules was approximately 56 Å. The probability of the monomeric state of rhodopsin molecules in the photoreceptor membrane, according to the data obtained, is rather high.