Possible degradation/biotransformation of lutein in vitro and in vivo: isolation and structural elucidation of lutein metabolites by HPLC and LC-MS (atmospheric pressure chemical ionization)

Metabolites of lutein are highly concentrated in the human macula and are known to provide protection against age-related macular degeneration. The aim of this investigation was to characterize the in vitro oxidation products of lutein obtained through photo-oxidation and to compare them with biologically transformed dietary lutein in intestine, plasma, liver, and eyes of rats. In vivo studies involved feeding rats a diet devoid of lutein for 2 weeks to induce deficiency. Rats were divided into two equal groups (n = 6/group) and received either micellar lutein by gavage for 10 days or diet supplemented with fenugreek leaves as a lutein source for 4 weeks. Lutein metabolites/oxidation products obtained from in vivo and in vitro studies were characterized by HPLC and LC-MS (APCI) techniques to elucidate their structure. The characteristic fragmented ions resulting from photo-oxidation of lutein were identified as 523 (M++H+ − 3CH3), 476 (M++H+ − 6CH3), and 551 (M++H+ − H2O). In the eyes, the fragmented molecules resulting from lutein were 13-Z lutein, 13′-Z lutein, 13-Z zeaxanthin, all-E zeaxanthin, 9-Z lutein, 9′-Z lutein, and 3′-oxolutein. Epoxycarotenoids were identified in liver and plasma, whereas anhydrolutein was identified in intestine. This study emphasizes the essentiality of dietary lutein to maintain its status in the retina.