Intestinal Absorption of Dietary Astaxanthin Mediated by Cluster-Determinant 36 (CD36) Presents Stereoisomeric Selectivity In Vitro and In Vivo

Astaxanthin exists as multiple stereoisomers owing to chiral carbons, with (3S,3'S) (S) and (3R,3'R) (R) as the major natural enantiomer. The differential bioactivity of these isomers implies potential stereoselective absorption. However, whether cluster-determinant 36 (CD36), a key transporter of astaxanthin, exhibits such stereospecificity remains unclear. Herein, molecular docking and alanine scanning mutagenesis revealed a higher affinity (ΔΔG = -1.39 kcal/mol) of (S)-astaxanthin for CD36, attributed to a unique hydrogen bond with ASN53 and critical interactions with PHE300, LEU328, and PHE430. Subsequent CD36-overexpressing cells showed 14.44% higher (S)-enantiomer uptake than (R)-counterpart (P < 0.05). In situ model further revealed superior absorption rate and permeability for (S)-astaxanthin. Critically, the CD36-specific inhibitor sulfo-N-succinimidyl oleate considerably inhibited (S)-astaxanthin absorption in the duodenum and jejunum by 83.78 and 84.01%, respectively, which were notably higher than the inhibitions of (R)-form (49.16 and 36.24%, P < 0.01). This work provides the first evidence that CD36 mediates stereospecific (S)-astaxanthin transport, advancing chiral carotenoid research.