Richard A. Bone

Optical density spectra of the macular pigmentin vivo andin vitro

A precise relative optical density spectrum of the macular pigment, based upon its dichroic properties, was determined. The spectrum proved essentially identical to that of liposome-bound zeaxanthin and lutein, a system duplicating the macular pigment and its environment. Substantial agreement was also found with the spectra of Wyszecki and Stiles (1982, Color science: Concepts and methods, quantitative data and formulae. New York: Wiley) and Vos (1972, Institute for Perception, RVO-TNO, IZF 1972-17, Soesterberg, The Netherlands), and the latter is recommended as a standard. For 7 subjects, the pigment density spectrum derived from foveal and extra-foveal sensitivities was compared with the dichroism-based spectrum. Results indicated that the pigment is described by a common distribution of molecular orientations for all subjects.

Macular pigment in henle fiber membranes:A model for Haidinger's brushes

The dichroic properties of lutein, presumed to be the macular pigment, are demonstrated and the structure of Henle fiber membranes is discussed. A consequence of the pigment molecules being incorporated into the bilipid components of these membranes is shown to be the production of Haidingers brushes. Spectra of lutein in association with phospholipid model membranes at different temperatures are presented and these support the theory that such incorporation occurs. Additional experiments test an alternative model for Haidingers brushes and show it to be inconsistent with the spectroscopic properties of lutein.

Epidermal cells functioning as lenses in leaves of tropical rain-forest shade plants

A ray tracing model has been developed to investigate the possible focusing effects of the convexly curved epidermal cell walls which characterize a number of shade-adapted plants. The model indicates that such focusing occurs, resulting in higher photosynthetic photon flux densities at certain locations within the leaf. It is postulated that there will be a corresponding increase in the rate of photosynthesis. In addition, leaf reflectance measurements indicate that this is generally less for the shade plants compared with sun species and would be advantageous in increasing the efficiency of energy capture. Either effect is important for plants which must survive at extremely low light levels.

Macular pigment response to a supplement containing meso-zeaxanthin, lutein and zeaxanthin

BackgroundAge-related macular degeneration (AMD) is a disease with multiple risk factors, many of which appear to involve oxidative stress. Macular pigment, with its antioxidant and light-screening properties, is thought to be protective against AMD. A result has been the appearance of dietary supplements containing the macular carotenoids, lutein and zeaxanthin. More recently, a supplement has been marketed containing, in addition, the third major carotenoid of the macular pigment, meso-zeaxanthin. The purpose of the study was to determine the effectiveness of such a supplement in raising macular pigment density in human subjects.MethodsA 120 day supplementation study was conducted in which 10 subjects were given gel-caps that provided 20 mg/day of predominantly meso-zeaxanthin, with smaller amounts of lutein and zeaxanthin. A second group of 9 subjects were given gel caps containing a placebo for the same 120 day period. Prior to and during the supplementation period, blood serum samples were analyzed by high performance liquid chromatography for carotenoid content. Similarly, macular pigment optical density was measured by heterochromatic flicker photometry. Differences in response between the supplementation and placebo groups were tested for significance using a students t-test.ResultsDuring supplementation with the carotenoids, blood samples revealed the presence of all three carotenoids. Macular pigment optical density, measured at 460 nm, rose at an average rate of 0.59 ± 0.79 milli-absorbance unit/day in the 10 supplemented subjects. This was significantly different from the placebo group (9 subjects) for whom the average rate was -0.17 ± 0.42 milli-absorbance units/day.ConclusionWe have shown for the first time that meso-zeaxanthin is absorbed into the serum following ingestion. The data indicate that a supplement containing predominantly meso-zeaxanthin is generally effective at raising macular pigment density, and may turn out to be a useful addition to the defenses against AMD.

Dose-dependent response of serum lutein and macular pigment optical density to supplementation with lutein esters.

We conducted a study to determine the effect of different doses of a lutein supplement on serum lutein concentration and macular pigment optical density (MPOD). Lutein is one of the major components of human macular pigment. Eighty-seven subjects received daily doses of 5, 10, or 20 mg of lutein, or a placebo, over a 140 day period. Serum lutein concentration was determined by HPLC and MPOD by heterochromatic flicker photometry (HFP). Serum lutein responded positively, except in the placebo group, reaching a plateau that, averaged for each dosage group, was linearly dependent on dose. Likewise MPOD, on average, increased at a rate that varied linearly with dose. For subjects deemed more proficient at HFP, approximately 29% of the variability in MPOD response could be attributed to a linear dependence on the fractional change in serum lutein concentration. We did not detect any significant influence of age on serum lutein uptake or MPOD response.

Improved charge transport of Nb-doped TiO2 nanorods in methylammonium lead iodide bromide perovskite solar cells

Nb-doped rutile nanorod-based methylammonium lead iodide bromide (MAPbI3−xBrx) perovskite solar cells have been developed by integrating an excellent photon-active perovskite sensitizer with the superior electron transporting rutile nanorods. It is found that there are two distinct stages in the formation of the perovskite materials prepared using non-stoichiometric mixed halide precursors, namely the orange colored bromine-rich transient state formed at 105 °C and the dark brown colored iodine-rich crystallized state formed at 155 °C. Optical, compositional, and crystalline properties of the perovskite samples at the two stages are studied by using UV-vis spectroscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction. The mixed halide materials undergo a transition from an intermediate cubic phase to a well-crystallized tetragonal perovskite phase through complicated diffusion, evaporation, and intercalation processes. Furthermore, a well-crystallized mixed halide perovskite is integrated with Nb-doped rutile nanorods and undoped rutile nanorods to fabricate perovskite solid state solar cells. Perovskite solar cells with Nb-doped rutile nanorods have significantly improved performance including the increased short circuit current and open circuit voltage compared to perovskite solar cells with undoped rutile nanorods. The overall power conversion efficiency enhancement of the device with Nb-doped rutile nanorods is over 50% compared with an undoped nanorod-based device, which is attributed to the superior charge collection efficiency of the Nb-doped rutile nanorods as evidenced by the electrochemical impedance measurement.

Denudation Rates, Thermal Evolution, and Preservation of Blueschist Terrains

The erosion of low temperature, high pressure blueschist facies metamorphic rocks presents a number of problems. If their rate of erosion is not sufficiently rapid, then the rise in temperature caused by thermal relaxation and radioactive self heating is great enough to obliterate the original low temperature mineral assemblages. The problem has been investigated using a one dimensional, two layer model to mimic an accretionary prism overlying oceanic lithosphere. The results suggest that, if no erosion takes place, the maximum time that blueschist conditions may exist is about 26 m.y. if levels of radioactive self heating are high, and approximately 100 m.y. if levels are very low. If erosion takes place, the maximum temperature reached by an element of rock is at a higher level in the earths crust than its initial depth of burial. Rocks may re-equilibrate at this temperature or be overprinted by incomplete reactions depending on the temperature rise and rocks involved. This could result in the geothermal profile of metamorphic rocks being concave to the temperature axis, in contrast to the convex shape of the original profile. The minimum erosion rate which would produce no overprint on original assemblages is estimated by us to be about 0.04 cm/year when radioactive self heating is negligible and rises to 0.14 cm/year for higher levels of self heating. Variations of erosion rates during unloading result in different thermal histories. An initial rapid rate of erosion which then slows is less likely to result in an overprint than the converse. Examination of estimates of erosion rates for the present suggests that normal fluvio-glacial erosion rates may be inadequate to successfully exhume blueschist assemblages without overprinting. Unloading may thus be tectonic or quasi-tectonic. This may explain the common association of blueschist blocks within olistostrome and melange like bodies.

ANALYSIS OF ZEAXANTHIN DISTRIBUTION WITHIN INDIVIDUAL HUMAN RETINAS

Publisher Summary This chapter discusses the analysis of zeaxanthin distribution within individual human retinas. In this analysis, sections of individual eyes are analyzed for the content of the three stereoisomers of zeaxanthin, thereby determining their distribution across the retina. Retina contains two isomeric xanthophylls—lutein arid zeaxanthin—with the greatest concentration at the center of the macula and diminishing with eccentricity. The elution order of the three authentic zeaxanthin dicarbamate diastereomer in a racemic mixture is prepared from rhodoxanthin. An analysis of serum zeaxanthin reveals that the serum contains dominantly RR-zeaxanthin. The principal peak was collected and combined with a sample of the racemic mixture. The results and observations support the hypothesis that lutein and/or zeaxanthin undergoes oxidation in the retina followed by nonstereospecific reduction to regenerate the observed suite of stereoisomers. The presence and distribution of these stereoisomers appear to be consistent with, and support, a hypothesis of antioxidant function for the macular carotenoids.

Distribution of macular pigment components, zeaxanthin and lutein, in human retina.

Publisher Summary This chapter discusses the distribution of macular pigment components in human retina. The isomeric dihydroxycarotenoids, zeaxanthin and lutein have been identified as the major constituents of the macular pigment of the human retina. Although these pigments appear to be localized in a small area centered on the fovea, high-performance liquid chromatography (HPLC) has revealed their presence throughout the neural retina. This technique is also sufficiently sensitive to quantify the pigments in neonatal and prenatal eyes. In addition, an alternative approach to determining the distribution of macular pigment carotenoids in the retina is through microspectrophotometry of fixed retinal tissue. Beyond the immediate yellow spot, however, the pigment density appears to be too low for accurate quantitation by this technique. The distribution of individual zeaxanthin diastereoisomers throughout the retina is not known but is currently under investigation. In the macular region, the average ratio of zeaxanthin to mzeaxanthin is found to range from 1.08 to 1.34 to 1.

Linear dichroism and orientational studies of carotenoid Langmuir-Blodgett films

Abstract The linear dichroism of single monolayers of lutein, zeaxanthin and a mixture of lutein and synthetic phosphatidylcholine has been measured. The angle of orientation of the carotenoid molecules was found to lie between 45° and 51° relative to the plane of the solid support. Although the adsorbed monolayers were mostly in a monomeric state, microscopic observations, as well as the II-A isotherms, indicated the existence of crystalline islets. The results have been interpreted in connection with Haidingers polarization brushes.