Abstract
Purpose:
To determine the bioavailability of deuterium-labelled (3R)-β-cryptoxanthin-D2 and (3R,6'R)-α-cryptoxanthin-D2 in serum, liver, and retinas of Japanese quail and to investigate whether these carotenoids that are absorbed into ocular tissues of humans, can also be absorbed into eye tissues of a non-primate animal model for metabolic studies.
Methods:
The serum, liver, retinas, RPE, and lens from 13 Japanese quail after 4 weeks of daily supplementation with 0.25 mg mixture of synthetic (3R)-β-cryptoxanthin-D2 (79%) and (3R,6'R)-α-cryptoxanthin-D2 (21%) were extracted and analyzed by normal phase and reversed phase HPLC.
Results:
(3R)-β-cryptoxanthin-D2 and (3R,6'R)-α-cryptoxanthin-D2 were detected in serum, liver, and retinas of the quail but not in RPE and lens. The serum carotenoids were identified as (3R)-β-cryptoxanthin-D2 (20%), (3R,6'R)-α-cryptoxanthin-D2 (14%), lutein (41%), and zeaxanthin (25%). The liver of quails contained nearly equal levels of (3R)-β-cryptoxanthin-D2 and (3R,6'R)-α-cryptoxanthin-D2 while lutein and zeaxanthin were not detected. The composition of carotenoids in the retina was: (3R)-β-cryptoxanthin-D2 (4%), (3R,6'R)-α-cryptoxanthin-D2 (8%), lutein (40%), and zeaxanthin (48%).
Conclusions:
The distribution of carotenoids in serum of quail suggest a significantly higher ratio of α-cryptoxanthin to β-cryptoxanthin in compare to the ratio of these carotenoids in the supplements provided to these birds. These carotenoids are almost equally distributed in the liver. However, the ratio of α-cryptoxanthin to β-cryptoxanthin in the retina is 2:1, suggesting a preferential absorption and transport of the former into the retina. Surprisingly, these carotenoids were not detected in the RPE. This could be due to the low levels of these carotenoids in this tissue. The levels of lutein and zeaxanthin in the retina of quail were consistent with our earlier analysis of these carotenoids in which we showed a nearly 1:1 ratio for these carotenoids in the retina. The serum of quail showed a higher concentration of lutein relative to zeaxanthin. This study clearly demonstrates that α-cryptoxanthin and β-cryptoxanthin are absorbed into serum, liver, and retina of quail. The fact that the level of β-cryptoxanthin in retina is half of that of α-cryptoxanthin also suggests that there is no in vivo conversion of the latter to the former carotenoid.
Keywords: 444 carotenoids/carotenoid binding proteins •
587 macular pigment