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Structure and Conformation of the Carotenoids in Human Retinal Macular Pigment.

Arteni AA, Fradot M, Galzerano D, Mendes-Pinto MM, Sahel JA, Picaud S, Robert B, Pascal AA - PLoS ONE (2015)

Bottom Line: In addition, analysis of the ν4 Raman band indicates that these carotenoids are present in a specific, constrained conformation in situ, consistent with their binding to specific proteins as postulated in the literature.We discuss how these conclusions relate to the function of these pigments in macular protection.We also address the possibilities for a more accurate, consistent measurement of MP levels by Raman spectroscopy.

View Article: PubMed Central - PubMed

Affiliation: Institute for Integrative Biology of the Cell (I2BC) & Institut de Biologie et de Technologies de Saclay, CEA, UMR 8221 CNRS, Université Paris Saclay, Gif-sur-Yvette, France.

ABSTRACT
Human retinal macular pigment (MP) is formed by the carotenoids lutein and zeaxanthin (including the isomer meso-zeaxanthin). MP has several functions in improving visual performance and protecting against the damaging effects of light, and MP levels are used as a proxy for macular health-specifically, to predict the likelihood of developing age-related macular degeneration. While the roles of these carotenoids in retinal health have been the object of intense study in recent years, precise mechanistic details of their protective action remain elusive. We have measured the Raman signals originating from MP carotenoids in ex vivo human retinal tissue, in order to assess their structure and conformation. We show that it is possible to distinguish between lutein and zeaxanthin, by their excitation profile (related to their absorption spectra) and the position of their ν1 Raman mode. In addition, analysis of the ν4 Raman band indicates that these carotenoids are present in a specific, constrained conformation in situ, consistent with their binding to specific proteins as postulated in the literature. We discuss how these conclusions relate to the function of these pigments in macular protection. We also address the possibilities for a more accurate, consistent measurement of MP levels by Raman spectroscopy.

No MeSH data available.


Related in: MedlinePlus

Resonance Raman spectra of MP carotenoids in vitro.Room temperature spectra in the 900–1650 cm-1 region are shown for zeaxanthin (red) and lutein (blue) in THF, excited at 488.0 nm. Inset: detail of the ν1 region.
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pone.0135779.g002: Resonance Raman spectra of MP carotenoids in vitro.Room temperature spectra in the 900–1650 cm-1 region are shown for zeaxanthin (red) and lutein (blue) in THF, excited at 488.0 nm. Inset: detail of the ν1 region.

Mentions: Resonance Raman is a vibrational spectroscopy, giving precise molecular details of structure, interactions and environment for the molecule under study. The resonance Raman spectra of carotenoid molecules usually comprise four groups of bands, termed ν1 to ν4 (see Fig 2). The ν1 band, arising from conjugated C = C stretching modes, yields direct access to the extent of the carotenoid conjugated chain. Together with the structure of ν2 (i.e. how many satellites are observed in this spectral region), it may also be used to determine the molecular configuration (trans/cis) of the scattering carotenoid. Additional information can be obtained through study of the ν4 band, around 950 cm-1, which arises from out-of-plane motions of the H nuclei along the conjugated chain. In perfectly planar molecules, these modes are not coupled with the electronic transition (which is oriented along the plane of the molecule) and as a result they exhibit no resonance enhancement—the intensity of this band is thus extremely weak. However, ν4 gains intensity when the carotenoid is distorted out of the plane, e.g. due to steric hindrance within a protein binding pocket. The intensity of this band thus yields information about the planarity of the carotenoid molecule.


Structure and Conformation of the Carotenoids in Human Retinal Macular Pigment.

Arteni AA, Fradot M, Galzerano D, Mendes-Pinto MM, Sahel JA, Picaud S, Robert B, Pascal AA - PLoS ONE (2015)

Resonance Raman spectra of MP carotenoids in vitro.Room temperature spectra in the 900–1650 cm-1 region are shown for zeaxanthin (red) and lutein (blue) in THF, excited at 488.0 nm. Inset: detail of the ν1 region.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4552419&req=5

pone.0135779.g002: Resonance Raman spectra of MP carotenoids in vitro.Room temperature spectra in the 900–1650 cm-1 region are shown for zeaxanthin (red) and lutein (blue) in THF, excited at 488.0 nm. Inset: detail of the ν1 region.
Mentions: Resonance Raman is a vibrational spectroscopy, giving precise molecular details of structure, interactions and environment for the molecule under study. The resonance Raman spectra of carotenoid molecules usually comprise four groups of bands, termed ν1 to ν4 (see Fig 2). The ν1 band, arising from conjugated C = C stretching modes, yields direct access to the extent of the carotenoid conjugated chain. Together with the structure of ν2 (i.e. how many satellites are observed in this spectral region), it may also be used to determine the molecular configuration (trans/cis) of the scattering carotenoid. Additional information can be obtained through study of the ν4 band, around 950 cm-1, which arises from out-of-plane motions of the H nuclei along the conjugated chain. In perfectly planar molecules, these modes are not coupled with the electronic transition (which is oriented along the plane of the molecule) and as a result they exhibit no resonance enhancement—the intensity of this band is thus extremely weak. However, ν4 gains intensity when the carotenoid is distorted out of the plane, e.g. due to steric hindrance within a protein binding pocket. The intensity of this band thus yields information about the planarity of the carotenoid molecule.

Bottom Line: In addition, analysis of the ν4 Raman band indicates that these carotenoids are present in a specific, constrained conformation in situ, consistent with their binding to specific proteins as postulated in the literature.We discuss how these conclusions relate to the function of these pigments in macular protection.We also address the possibilities for a more accurate, consistent measurement of MP levels by Raman spectroscopy.

View Article: PubMed Central - PubMed

Affiliation: Institute for Integrative Biology of the Cell (I2BC) & Institut de Biologie et de Technologies de Saclay, CEA, UMR 8221 CNRS, Université Paris Saclay, Gif-sur-Yvette, France.

ABSTRACT
Human retinal macular pigment (MP) is formed by the carotenoids lutein and zeaxanthin (including the isomer meso-zeaxanthin). MP has several functions in improving visual performance and protecting against the damaging effects of light, and MP levels are used as a proxy for macular health-specifically, to predict the likelihood of developing age-related macular degeneration. While the roles of these carotenoids in retinal health have been the object of intense study in recent years, precise mechanistic details of their protective action remain elusive. We have measured the Raman signals originating from MP carotenoids in ex vivo human retinal tissue, in order to assess their structure and conformation. We show that it is possible to distinguish between lutein and zeaxanthin, by their excitation profile (related to their absorption spectra) and the position of their ν1 Raman mode. In addition, analysis of the ν4 Raman band indicates that these carotenoids are present in a specific, constrained conformation in situ, consistent with their binding to specific proteins as postulated in the literature. We discuss how these conclusions relate to the function of these pigments in macular protection. We also address the possibilities for a more accurate, consistent measurement of MP levels by Raman spectroscopy.

No MeSH data available.


Related in: MedlinePlus