Structure and Conformation of the Carotenoids in Human Retinal Macular Pigment

PLoS One. 2015 Aug 27;10(8):e0135779. doi: 10.1371/journal.pone.0135779. eCollection 2015.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Humans
  • Lutein / chemistry*
  • Lutein / metabolism
  • Macular Pigment / analysis*
  • Molecular Conformation
  • Retinal Pigments / chemistry*
  • Retinal Pigments / metabolism
  • Spectrum Analysis, Raman
  • Zeaxanthins / chemistry*
  • Zeaxanthins / metabolism

Substances

  • Macular Pigment
  • Retinal Pigments
  • Zeaxanthins
  • Lutein

Grant support

This work was supported by the European Research Council (http://erc.europa.eu/) through the Advanced Grant PHOTPROT (contract number 267333, to BR); the French Infrastructure for Integrated Structural Biology https://www.structuralbiology.eu/networks/frisbi (grant number ANR-10-INSB-05-01, to BR); and the CEA interdisciplinary program Technology for Health (MEDIASPEC project, to BR). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.