Abstract
Background: Non-provitamin A carotenoids astaxanthin (AX) and fucoxanthin (FX) are bioactive molecules that are abundant in seafood. Although their dietary intake is beneficial, only around 10% of ingested carotenoids are absorbed. Recent studies have speculated the role of redundant lipid transporters such as scavenger receptor B1 (SRB1), in carotenoids transport, and this SRB1 transporter is under the control of nuclear transcription factor peroxisome proliferator-activated receptor gamma (PPARγ).

Aims and Objectives: This study aims at investigating the role of SRB1 and its transcriptional regulation by PPARγ, under the influence of selected PPARγ agonists (conjugated linoleic acid [CLA] and pioglitazone [PGZ]) in intestinal uptake of AX and FX.

Materials and Methods: AX and FX were extracted from shrimp carapace and the seaweed Padina tetrastomatica, purified, and purity were assessed. The carotenoids are then gavaged for 14 days, and along with CLA or PGZ. On the 15th day, the animals were sacrificed and tissues were analyzed for carotenoid uptake (liver and serum), protein expression (PPARγ and SRB1) in enterocytes by western blotting and gene expression (PPARα, PPARγ, peroxisome proliferator-activated gamma coactivator 1α, SRB1, and sterol regulatory element-binding protein 1) by quantitative polymerase chain reaction.

Results: The results of the study indicate an increase in intestinal uptake, when coadministered with PPARγ agonists (AXCLA>AXPGZ>AX and FXCLA>FXPGZ>FX), signifying a role of PPARγ in the process. Protein expression of PPARγ in comparison with the control in AXCLA increased (1.4 folds); AX and AXPGZ groups had no change. FX and FXPGZ treatments exhibited half the expression, which was restored in FXCLA (1.1 folds). The SRB1 was decreased in AX and did not change in FX group (0.3 and 1.0 folds, respectively). Although AXCLA group exhibited a decrease in SRB1 expression, when compared to control (0.57 folds), there was an increase in comparison with the AX group. There was a similar increase in FXCLA group (1.3 folds). PGZ treatment did not show any significant change in SRB1 expression either with AX or FX (AXPGZ-1.2 and FX PGZ 1.0 folds). Similarly, gene expression of PPARγ and SRB1 increased in AX (2.0 and 1.57), CLA (2.4 and 3.9), and AXCLA groups (4.9 and 3.0 folds), respectively, with an additive effect in AXCLA.

Conclusion: These results indicate that the absorption of carotenoids is modulated by the PPARγ agonists CLA and PGZ, by altering the protein and gene expression of PPARγ and SRB1, also the carotenoids themselves influence these markers.

Key words: Astaxanthin; Fucoxanthin; Peroxisome Proliferator-Activated Receptors; Scavenger Receptor B1; Bioavailability