Three male volunteers ingested a single meal containing a 100 mg dose of astaxanthin consisting of 74% all-E, 9% 9Z-, 17% 13Z-astaxanthin (3R,3'R-, 3R,3'S; meso-, and 3S,3'S-astaxanthin in a 1:2:1 ratio). Plasma astaxanthin concentration-time curves were monitored over 72 hours. 13Z-Astaxanthin accumulated selectively, whereas the 3 and 3'R/S astaxanthin distribution was similar to that of the experimental meal. Results indicate that a selective process increases the relative proportion of astaxanthin Z-isomers compared to the all-E-astaxanthin during blood uptake and that astaxanthin E/Z isomers have similar pharmacokinetics.

Caco-2 human intestinal cells were seeded in a 24-well plate at a density of 8 * 10^4 cells/well. Only differentiated enterocytes display in unchanged transepithelial electrical resistance values (TEER) were used in the experiment. Caco-2 cells were washed twice with Dulbecco’s modified Eagle’s medium (DMEM) media without fetal bovine serum (FBS); then 250 micro-L of freshly prepared 9Z-astaxanthin dissolved in DMSO containing dMEM media (final concentration of 0.5 micro-M) without FBS added to inserts and incubated at 37 deg-C for 1, 3, 6, 12, or 24 hours. DMEM medium (750 micro-L) without FBS was added in the basolateral side. After incubation, TEER values were detected to ensure the integrity of the monolayer; then, media from both sides of the insets were collected, washed, lysed and prepared for HPLC under nitrogen gas. Cellular uptake efficiency and transport efficiency were expressed as the percentage of 9Z-astaxanthin detected inside Caco-2 cells and that in the basolateral compartment to the originally added 9Z-astaxanthin in the apical side. Cellular uptake began significantly at 3 h, and the absorption efficiency increased drastically at 12 h for and continued to increase until 24 h. The absorption efficiency of 9Z-astaxanthin was 7.12% in 24 hours, with a general time-dependent trend.