Three male volunteers consumed a meal containing a 10-mg dose of astaxanthin from astaxanthin diesters, followed by a meal with a dose of 100 mg astaxanthin four weeks later. HPLC analysis of the astaxanthins showed 95.2% all-E-, 1.2% 9Z- and 3.6% 13Z-astaxanthin, of (3R,3'R)-, (3R,3'S; meso)- and (3S,3'S)-astaxanthin in a 31:49:20 ratio. Plasma astaxanthin time curves were measured over 76 hours post meal. The (3R,3'R)-astaxanthin optical isomer accumulated selectively in plasma compared to the (3R,3'S)- and (3S,3'S)-isomers, and comprised 54% of total astaxanthin in the blood and only 31% of total astaxanthin in the administered dose.

Human colon cancer cells HCT116 and H29 were cultured with RPMI1640 media supplemented with 5% heat-inactivated fetal bovine serum, 100 U/mL of penicillin, and 0.1 mg/mL of streptomycin at 37 deg-C in a 5% CO2 atmosphere. Cells were seeded in 96-well plates. After 24 hours, media was exchanged with 200 micro-L of complete media by the presence of serial concentrations (R, R)-astaxanthin (4, 6, 8, 10, 12, 14 and 16 micro-M) for 24, 48, and 72 hours. After the specified time the culture media was hanged with MTT-containing medium and assayed for cell viability. (R, R)-astaxanthin inhibited HCT116 and HT29 colon cancer cell growth in a dose-dependent and time-dependent manner. The inhibitory rate was dramatically enhanced by increases in concentration and extension of treatment time. The IC50 of (R, R)-astaxanthin after 72 hours was 7.48 micro-M.