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PubMed2001

Lipofuscin-formation in cultured retinal pigment epithelial cells is related to their melanin content.

Age-related macular degeneration (AMD), the leading cause of blindness in the developed world, is accompanied by degeneration of the retinal pigment epithelial (RPE) cells. There is an inverse correlation between the melanin content of the eye and the incidence of AMD. Lipofuscin (LF)-accumulation in RPE cells accompanies the process of aging, and may also be related to AMD. This study was designed to evaluate the effect of melanin/melanosomes on the rate of LF formation in cultured rabbit and bovine RPE cells subjected to oxidative stress (40% normobaric O(2)) and daily supplementation with photoreceptor outer segments for 4 weeks. The LF content was measured at 0, 2, and 4 weeks in RPE cells from pigmented and albino rabbits, as well as in pigment-rich and pigment-poor bovine cells. Albino rabbit and pigment-poor bovine cells accumulated significantly higher amounts of LF than pigmented rabbit cells and pigment-rich bovine RPE cells after both 2 and 4 weeks of exposure. Autometallography of melanin-containing cells, without previous exposure to ammonium sulfide, showed a positive outcome, indicating either the occurrence of pre-existing iron-sulphur clusters or an extremely high intrinsic reducing capacity. These results suggest that melanin acts as an efficient antioxidant, perhaps by interacting with transition metals.

Animals↗
PubMed2001

Delayed induction of pigmented spots on UVB-irradiated hairless mice.

Human skin exposed to solar radiation for a long time subsequently develops pigmented spots, which are named solar lentigines. Since no animal model of this process is currently available, we attempted to induce similar spots in pigmented hairless mice. The mice were irradiated at 38 or 94 mJ/cm(2) three times/week for various periods of time (1-8 weeks) under an ultraviolet light source (Toshiba FL-SE; UVB). Skin pigmentation of irradiated mice was visually observed and skin color was determined with a colorimeter for 78 weeks. Uniform pigmentation was induced, but persisted only during exposure, disappearing completely within 2 weeks after cessation of exposure. At about 28 weeks after the first exposure, pigmented spots suddenly began to appear. These pigmented spots were less than 2 mm in diameter and light brown in color. The length of the latent period until appearance and the extent of development of these spots were dependent on the exposure period. Histological examination revealed increased numbers of active melanocytes and melanin granules in the affected epidermis. These pigmented spots closely resemble solar lentigines in humans, and the mice should be useful as an animal model of solar lentigines.

Animals↗
PubMed2002

Plumage pigmentation and expression of its regulatory genes during quail development--histochemical analysis using Bh (black at hatch) mutants.

The plumage on the dorsal trunk of normal quail embryos exhibits longitudinal black and brown stripes of pigments produced by melanocytes. However, this pigmentation pattern disappeared in Bh (black at hatch) heterozygous and homozygous embryos because of overall black and brown pigmentation of plumages, respectively. To investigate the mechanisms of the pigment pattern formation of plumage and clarify the roles of the Bh locus in the pattern formation, we examined the expression pattern of genes relating to melanocyte development (Mitf, MelEM antigen, Kitl, Kit and EdnrB2) and melanin pigment production (Dct, Tyrp1, Tyr and Mmp115) in Bh mutant and wild-type embryos throughout development. As a result, we found that MelEM antigen was expressed in melanoblasts committed to produce black pigment before apparent melanogenic gene expression, and that Bh heterozygotes and homozygotes showed abnormal expression patterns of the MelEM antigen. These results indicate that MelEM antigen is a good marker for melanoblasts committed to produce black pigment, and suggests that the Bh locus directs melanocytes to produce eumelanin in proper positions.

Animals↗
PubMed2000

Ectopic pigmentation in Xenopus in response to DCoH/PCD, the cofactor of HNF1 transcription factor/pterin-4alpha-carbinolamine dehydratase.

DCoH, the dimerization cofactor of the HNF-1 homeodomain proteins (hepatocyte nuclear factor-1alpha and beta), is involved in gene expression by associating with these transcription factors. The protein also called PCD for pterin-4alpha-carbinolamine dehydratase is a bifunctional factor as it catalyzes also the regeneration of tetrahydrobiopterin. This coenzyme is used by the enzyme phenylalanine hydroxylase, which generates tyrosine, the precursor of catecholamines and melanin. DCoH/PCD presumably cooperates with other partners, because it is expressed earlier than HNF1 and phenylalanine hydroxylase (PAH) in early vertebrate development. It is also found in cells lacking HNF1 and PAH like skin, brain and the pigmented epithelium of the eye suggesting a yet unknown function. We show that the overexpression of DCoH/PCD in Xenopus induces the formation of ectopic pigment cells in the epidermis, that are visible earlier than the endogenous pigmentation and broader distributed. This ectopic pigmentation is accompanied by an increase in tyrosinase activity and the amount of melanin. Overexpression of DCoH/PCD induces the appearance of pigment cells also in animal cap explants, that normally differentiate into atypical epidermis. DCoH/PCD mutants with impaired carbinolamine dehydratase activity retain the potential to induce pigmentation and we propose therefore that DCoH/PCD is not simply an essential enzyme for melanin biosynthesis, but also a regulator for the differentiation of pigment producing cells.

Animals↗
PubMed1997

A rare form of adult onset leukodystrophy: orthochromatic leukodystrophy with pigmented glia.

BACKGROUND: Orthochromatic leukodystrophy with pigmented glia and scavenger cells is a rare leukodystrophy of unknown etiology. This report describes a 42-year-old man with a history of depression, dementia and parkinsonism having the pathological features of orthochromatic leukodystrophy with pigmented glia. METHODS: We reviewed the clinical history and pathology of autopsy and brain biopsy material. RESULTS: Imaging revealed bilateral cerebral white matter hypodensities. At autopsy, the brain demonstrated a leukodystrophy affecting predominantly the cerebral hemispheres and characterized by demyelination, and cytoplasmic pigment deposits in oligodendroglia and astrocytes. The pigment had the staining properties of ceroid-lipofuschin and on ultrastructural examination was composed of membrane-bound lipid and electron-dense inclusions which had a fingerprint-like pattern. Similar pigment inclusions were not observed on ultrastructural examination of renal, splenic or hepatic tissue obtained at autopsy. The brain biopsy contained cerebral cortex with sparse subcortical white matter in which a few oligodendroglia and fewer astrocytes at the grey/white junctions showed cytoplasmic pigmentary inclusions identical to those described above. However, due to the paucity of white matter in the specimen a definite diagnosis of orthochromatic leukodystrophy with pigmented glia was not made. CONCLUSIONS: The diagnosis of orthochromatic leukodystrophy with pigmented glia and scavenger cells can only be made antemortem if the brain biopsy contains adequate white matter and although a rare condition, it should be considered in the differential diagnosis of an adult onset leukodystrophy.

Adult↗
PubMedDate not supplied

Mutually exclusive expression of the L and M pigment genes in the human retinoblastoma cell line WERI: Resetting by cell division.

The key steps in the evolution of full trichromatic color vision in primates include duplication of the ancestral pigment gene to form the L and M pigment gene array on the X chromosome, mutually exclusive expression of the L and M pigment genes in cone photoreceptors, and formation of a retinal mosaic with randomly distributed L and M cones. Previous work using transgenic mice has indicated that a locus control region adjacent to this array of genes plays an important role in their mutually exclusive expression in respective cone cells (Smallwood et al., 2002). However, the mechanism by which this is accomplished is unknown. We searched for a cellular model system to investigate the mechanism of this mutually exclusive expression. We previously showed that the undifferentiated human retinoblastoma cell line WERI expresses L and M cone opsin but not rod opsin genes. We now show that WERI cells express the L and M pigment genes in a mutually exclusive manner, in that either L or M pigment mRNA is expressed in a single cell. Importantly, clonal analysis showed that single WERI cells that express either L or M generate, upon cell division produce, a mixed population of L- or M-expressing cells. These results indicate, first, that cell division resets L or M pigment gene expression, most likely due to disassembly and reassembly of LCR-promoter DNA-protein complexes during cell division. Second, a retinal mosaic with near-random distribution of L and M cones may have been generated automatically after duplication of the ancestral gene to form the L and M pigment genes. Third, determination of L and M cone identity may not require external molecular cues during differentiation, and is consistent with the idea that L and M cones are not intrinsically different.

Blotting, Northern↗
PubMed1993

Identification of the Cl(-)-binding site in the human red and green color vision pigments.

Chloride ions are known to bind and alter the absorption spectra of some but not all visual pigments. In this report, the human red and green color vision pigments are shown to bind Cl- and to undergo a large red shift in their absorption maxima. Mutation of 18 different positively charged amino acids in these pigments identified two residues, His197 and Lys200, in the Cl(-)-binding site. His197 and Lys200 are strictly conserved in all long-wavelength cone pigments but are absent in all rhodopsins and short-wavelength cone pigments. This fact suggests that the evolutionary branch of the long-wavelength pigments was established when an ancestral pigment acquired the ability to bind Cl- and, as a result, shift the absorption maximum to longer wavelengths.

Amino Acid Sequence↗
PubMed1986

Photosensitivity of 10-substituted visual pigment analogues: detection of a specific secondary opsin-retinal interaction.

The photosensitivities of the bovine rhodopsin and gecko pigment 521 analogues regenerated from C-10-substituted analogues of 11-cis- and 9-cis-retinals were determined by two different methods. A similar reactivity trend was noted for both pigment systems as revealed in the photosensitivity of the gecko pigments and relative quantum yields of the bovine analogues. The 10-fluoro-11-cis photopigments had a photosensitivity less than, but approaching, that of the native (11-cis) visual pigment while the 10-fluoro-9-cis photopigments had a much lower photosensitivity than the parent 9-cis regenerated pigment. The results are interpreted in terms of recently described models of rhodopsin architecture and of the primary molecular reaction of visual pigments to light. The unusually low photoreactivity of the 10-fluoro-9-cis pigment molecule is viewed as the result of a regiospecific hydrogen-bonding interaction of the electronegative fluorine atom to the opsin.

Animals↗
PubMed1989

Analogue pigment studies of chromophore-protein interactions in metarhodopsins.

Several analogue pigments have been prepared containing retinals altered at the cyclohexyl ring or proximal to the aldehyde group in order to examine the role of the chromophore in the formation of the metarhodopsin I and II states of visual pigments. Deletion of the 13-methyl group on the isoprenoid chain did not affect metarhodopsin formation. However, analogue pigments containing chromophores with modified rings did not show the typical absorption changes associated with the metarhodopsin transitions of native or regenerated rhodopsins. In particular, 4-hydroxyretinal pigments did not show clear transitions between the metarhodopsin I and metarhodopsin II states. Pigment formed with an acyclic retinal showed no evidence by absorption spectroscopy of metarhodopsin formation. A retinal altered by substitution of a five-membered ring containing a nitroxide required a more acidic pH than the native pigment for formation of the metarhodopsin II state. ESR data suggest that the ring remains buried within the protein through the metarhodopsin II state. However, the Schiff base linkage is susceptible to hydrolysis of hydroxylamine in the metarhodopsin II state. These data indicate that (1), in the transition from rhodopsin to metarhodopsin II, major protein conformational changes are occurring near the lysine-retinal linkage whereas the ring portion of the chromophore remains deeply buried within the protein and (2) pigment absorptions characteristic of the metarhodopsin I and II states may be due to specific protein-chromophore interactions near the region of the chromophore ring.

Animals↗
PubMed2005

Amino acid residues responsible for the meta-III decay rates in rod and cone visual pigments.

Vertebrate retinas have two types of photoreceptor cells, rods and cones, which contain visual pigments with different molecular properties. These pigments diverged from a common ancestor, and their difference in molecular properties originates from the difference in their amino acid residues. We previously reported that the difference in decay times of G protein-activating meta-II intermediates between the chicken rhodopsin and green-sensitive cone (chicken green) pigments is about 50 times. This difference only originates from the differences of two residues at positions 122 and 189 (Kuwayama, S., Imai, H., Hirano, T., Terakita, A., and Shichida, Y. (2002) Biochemistry 41, 15245-15252). Here we show that the meta-III intermediates exhibit about 700 times difference in decay times between the two pigments, and the faster decay in chicken green can be converted to the slower decay in rhodopsin by replacing the residues in chicken green with the corresponding rhodopsin residues. However, the inverse directional conversion did not occur when the two residues in rhodopsin were replaced by those of chicken green. Analysis using chimerical mutants derived from these pigments has demonstrated that amino acid residues responsible for the slow rhodopsin meta-III decay are situated at several positions throughout the C-terminal half of rhodopsin. Considering that rhodopsins evolved from cone pigments, it has been suggested that the molecular properties of rhodopsin have been optimized by mutations at several positions, and the chicken green mutants at two positions could be rhodopsin-like pigments transiently produced in the course of molecular evolution.

Amino Acid Sequence↗
PubMed1997

Analysis of some optical properties of a native and reconstituted photosystem II antenna complex, CP29: pigment binding sites can be occupied by chlorophyll a or chlorophyll b and determine spectral forms.

The minor photosystem II antenna complex CP29(Lhcb-4) has been reconstituted in vitro with the Lhcb-4 apoprotein, overexpressed in Escherichia coli, and the native pigments. Modulation of the pigment composition during reconstitution yields binding products with markedly different chlorophyll a/b binding ratios even though the total number of bound chlorophylls (a plus b) remains constant at eight. A thermodynamic analysis of steady state absorption and fluorescence spectra demonstrates that all chlorophylls are energetically coupled, while the kinetics of chlorophyll photooxidation indicate that triplet chlorophyll-carotenoid coupling is also conserved during pigment binding in vitro. The influence of the chlorophyll a/b binding ratio on the absorption spectra measured at 72 and 300 K is analyzed for the Qy absorption region. Increased chlorophyll b binding leads to large increases in absorption in the 640-660 nm region, while absorption in the 675-690 nm interval decreases markedly. These changes are analyzed in terms of a Gaussian decomposition description in which the eight subbands display a temperature-dependent broadening in agreement with the weak electron-phonon coupling demonstrated for other antenna chlorophyll spectral forms. In this way, we demonstrate that increased chlorophyll b binding leads to increased absorption intensity associated with the subbands at 640, 648, 655, and 660 nm and decreased intensity for the long wavelength subbands at 678 and 684 nm. The wavelength position of all subbands is unchanged. The above data are interpreted to indicate that CP29 has eight chlorophyll binding sites, many or all of which can be occupied by either chlorophyll a or chlorophyll b according to the conditions in which pigment binding occurs. Chlorophyll b absorption is primarily associated with four subbands located at 640, 648, 655, and 660 nm. The invariance of the wavelength position of the absorption bands in recombinant products with different chlorophyll a/b binding stoichiometries is discussed in terms of the mechanism involved in the formation of spectral bands. We conclude that pigment-protein interactions dominate in the determination of spectral heterogeneity with probably only minor effects on absorption associated with pigment-pigment interactions.

Apoproteins↗
PubMed2003

Highly dispersed green silicate and oxide pigments precipitated from model systems of postgalvanic waste.

A procedure was worked out to obtain highly dispersed green silicate and oxide pigments precipitated from postgalvanic waste. The highly dispersed chromium(III) silicates and oxides were produced from the waste, originating from chromium plating, by reduction of Cr(VI) to Cr(III) employing various reducing agents. All the reductions were conducted in an acidic medium. Solutions of Cr(III), obtained in reducing processes, were employed to precipitate silicate pigments (using sodium metasilicate solution and containing mainly chromium(III) silicates) and oxide pigments (using sodium hydroxide and containing chromium(III) oxides). The precipitated silicates and oxides were subjected to a comprehensive physicochemical analysis (estimating bulk density, capacities to absorb water, dibutyl phthalate, paraffin oil, particle size distribution, and morphology of particle surface). Precipitation process (its parameters) and heating of the reactive mixture exerts a significant effect on the principal physicochemical properties of the pigments. The heating significantly affects first of all color shade of the obtained silicate and oxide pigments as well as their dispersion. Coprecipitated chromium(III) and iron(III) silicates exhibit a brownish color and a reasonably uniform character. Apart from primary agglomerates (in the range of 414-717 nm), they contain small amounts of secondary agglomerates (in the range of 4154-6445 nm). Best physicochemical parameters have been demonstrated by chromium pigments which have been precipitated from chromium solutions reduced using hydrogen peroxide. Chromium(III) oxides deserve particular distinction since their structure includes primary particles, primary agglomerates but is completely free of secondary agglomerates. The pigments manifest a brightly green color and a low capacity to absorb water (100 cm3 x 100 g(-1)). Application of hydrophobicity-inducing agents in the course of precipitation has corrected physicochemical parameters of both the oxides and silicates of chromium(II). Their bulk densities have been clearly decreased (to as low as below 250 g x L(-1) in the case of chromium(III) silicate), while capacities to absorb paraffin oil have increased to as much as 750 cm3 x 100 g(-1) for chromium(II) oxide. The respective particle size distribution has shown a tendency for disappearance of large accumulations of secondary agglomerates.

Carcinogens, Environmental↗
PubMed2001

Physical stability of the blue pigments formed from geniposide of gardenia fruits: effects of pH, temperature, and light.

Fruits of Gardenia jasminoides contain geniposide which can be transformed to blue pigments by a simple modification. Colorless geniposide obtained from gardenia fruits by charcoal and silica gel column chromatographies was hydrolyzed with beta-glucosidase to yield genipin. The resulting genipin was transformed to blue pigments by reaction with amino acids (glycine, lysine, or phenylalanine). The stability of the blue pigments against heat, light, and pH was studied to examine the blue dye for possible use as a value-added food colorant. Thermal degradation reactions at temperatures of 60-90 degrees C were carried out at different pH levels within the range 5.0-9.0 (pH 5.0, acetate buffer; pH 7.0, phosphate buffer; and pH 9.0, CHES buffer). The blue pigments remained stable after 10 h at temperatures of 60-90 degrees C, and in some cases, more new pigments formed. The pigments were more stable at alkaline pH than neutral and acidic pH. Similarly, the pigments were stable under light irradiance of 5000-20 000 lux. In this case, pH effect was not significant.

Drug Stability↗
PubMed2001

Isolation and structures of oligomeric wine pigments by bisulfite-mediated ion-exchange chromatography.

Methods have been developed that are based on cation exchange chromatography in the absence and presence of excess bisulfite for the isolation of wine pigments from Australian red wine and grape marc extract. The pigments were identified using HPLC and electrospray ionization mass spectrometry. The mass spectral data indicate that these pigments are C4-substituted anthocyanins with a tetracyclic structure. The pigments form a series of closely related oligomeric pigments which include those previously described in the literature, such as pigment A and vitisin A, as well as some newly identified pigments.

Chromatography, Ion Exchange↗
PubMed2002

Spectrophotometric determination of yellow pigment content and evaluation of carotenoids by high-performance liquid chromatography in durum wheat grain.

The so-called "yellow pigment" content of durum wheat has been used for a long time as an indicator of the color quality of durum wheat and pasta products. For decades the chemical nature of these pigments has been assigned to carotenoids, mainly to the xanthophyll lutein and its fatty acid esters. The chemical composition of the yellow pigments of eight German durum wheat cultivars was studied. Grains were milled on a laboratory mill. Pigment extraction of millstream fractions was performed according to the optimized ICC standard method 152 procedure, and the chemical composition of the extract was analyzed by isocratic reversed phase high-performance liquid chromatography. all-trans-Lutein ranged from 1.5 to 4 mg kg(-1), and zeaxanthin was found in traces. No lutein esters and carotenes were detected. Surprisingly, the fraction of carotenoids of the complete yellow pigment content amounted to only 30-50% of the yellow pigment quantities, so there are still compounds in durum wheat not yet identified that contribute considerably to the yellow color of the grain extracts. The isolation and chemical identification of those pigments are under investigation.

Carotenoids↗
PubMed2001

A technique for preserving pigmentation in some capsalid monogeneans for taxonomic purposes.

A technique is described to preserve the pigment found in the bodies and the intestine of some brightly coloured and darkly pigmented benedeniine capsalid monogeneans. Previous studies of these pigmented capsalids have proven difficult because the pigmentation usually disappears when the worms are fixed using preservatives containing concentrations of formalin over 5% and/or ethanol, acetic acid, chromic acid, picric acid and mercuric chloride. The technique developed here uses a fixative comprising glycerol, acetone and formalin (GAF). After fixation under light coverslip compression for three minutes, specimens are transferred to absolute acetone for three minutes and cleared in a mixture of nine parts cedar wood oil and one part absolute acetone before mounting in Canada balsam. Processing must be carried out quickly, as these chemicals will cause the pigments to fade if the specimens are exposed to them for too long. Pigmented benedeniines processed using this technique retain the distribution, intensity and colour observed in live worms. The colour and distribution of pigmentation in monogeneans may be of taxonomic importance and this technique aids preparation of whole-mounts suitable for registration as type-material.

Acetone↗
PubMed1999

Indocyanine green angiography of retinal pigment epithelial tears.

PURPOSE: To investigate the fluorescein and indocyanine green (ICG) features before and after retinal pigment epithelial tear. METHODS: Fluorescein and ICG videoangiography were performed in 30 patients affected by age-related macular degeneration either complicated by tear of the retinal pigment epithelium (25 eyes) or by pigment epithelial detachment with pretear characteristics (5 eyes). RESULTS: At the pretear stage fluorescein angiography (FA) showed in all cases signs of occult CNV associated with delayed, slow and uneven filling of the pigment epithelium detachment. In 2 eyes the ICG filling of the retinal pigment epithelial detachment was seen. Progression to the tear stage was seen in 4 eyes where a CNV was evident on ICG angiography; in two eyes within one month after laser photocoagulation. At the tear stage FA showed an area of marked hyperfluorescence with well defined margins. Adjacent to the exposed area the torn RPE was markedly hypofluorescent during all angiographic phases. The bare choroid was always hypo or normofluorescent on ICG angiography. The torn retinal pigment epithelium showed moderate hypofluorescence. The exact seat and extension of CNVs could be visualized in 20 cases (67%; 95% C.I., 50-84%) with ICG angiography vs. 6 cases (20%; 95% C.I., 6-34%) with FA (p<0.001). CONCLUSIONS: ICG angiography did not add anything substantial to the analysis of frank tears. The most useful application of ICG angiography in this disease is the visualization of the seat and extension of the associated CNV In fact, it is well known that laser treatment of a pigment epithelial detachment at the pretear stage may facilitate the development of a tear of the RPE.

Aged↗
PubMed2000

Evolution and development of pigment cells: at the crossroads of the discipline.

The following is a summary of the current state of comparative biology with respect to pigmentation. Recent results from molecular analyses of genes involved in pigmentation in lower vertebrates are compared with similar data from mouse and man. Particular emphasis has been placed on evolutionary and developmental aspects of pigmentation. Recent advances in molecular biology of lower vertebrate pigmentation allow for the comparison of orthologous molecules across a wider range of species than ever before; some of these results are summarized and used to highlight the current state of pigmentation from a comparative perspective. A more cellular, organismal approach is also explored to highlight some important lessons from comparative biology. Lastly, large-scale evolutionary questions are put into a framework that highlights both the differences and similarities between mammals/birds and other vertebrates. It is the opinion of the authors that important, long-standing questions in these areas can now be addressed in ways that have not been possible before. Thus, the discipline is at an exciting crossroads where developmental and evolutionary data can be used to create a unified view of pigment cells and pigments across many species.

Animals↗