Purpose: The xanthophyll carotenoids lutein and zeaxanthin, along with their major metabolites, meso-zeaxanthin, and 3'-oxolutein, are highly concentrated in the human macula. In addition to these two metabolites, there are still others that have not yet been identified. A highly sensitive HPLC-mass spectral method was used to identify and quantify a new xanthophyll metabolite that increases with age.
Methods: Maculae (4-mm diameter) from donor eyes free of ocular disease were procured from the local eye bank. The carotenoid extracts from each tissue sample were analyzed by HPLC coupled with an in-line single quadrupole mass spectrometer in a positive ion atmospheric pressure chemical ionization mode. The elution profile, visible absorption spectra and mass spectra were compared to synthetic standards to identify the ocular carotenoids and their metabolites.
Results: Along with 3'-oxolutein and meso-zeaxanthin, a relatively nonpolar zeaxanthin derivative was identified, with m/z 582.5 and spectral properties similar to those of dietary zeaxanthin. This compound was identified as 3-methoxyzeaxanthin (3-MZ) based on elution profile, absorption spectra, and mass spectra in comparison to a synthetic standard. 3-MZ increased with age (P < 0.001) and was not detectable in peripheral retina or in nonretinal tissues.
Conclusions: Identification of 3-MZ in the macula of aged donors indicates that O-methylation of carotenoids is a potential biomarker for aging and age-related ocular disorders.