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

Astaxanthin exists as multiple stereoisomers owing to chiral carbons, with (3<i>S</i>,3'<i>S</i>) (<i>S</i>) and (3<i>R</i>,3'<i>R</i>) (<i>R</i>) 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 (ΔΔ<i>G</i> = -1.39 kcal/mol) of (<i>S</i>)-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 (<i>S</i>)-enantiomer uptake than (<i>R</i>)-counterpart (<i>P</i> < 0.05). <i>In situ</i> model further revealed superior absorption rate and permeability for (<i>S</i>)-astaxanthin. Critically, the CD36-specific inhibitor sulfo-<i>N</i>-succinimidyl oleate considerably inhibited (<i>S</i>)-astaxanthin absorption in the duodenum and jejunum by 83.78 and 84.01%, respectively, which were notably higher than the inhibitions of (<i>R</i>)-form (49.16 and 36.24%, <i>P</i> < 0.01). This work provides the first evidence that CD36 mediates stereospecific (<i>S</i>)-astaxanthin transport, advancing chiral carotenoid research.