Xanthophylls increased HDLC level and nuclear factor PPARγ, RXRγ and RARα expression in hens and chicks
Carotenoids play an important role in immune and antioxidant functions. Actually, non‐provitamin A carotenoids were as active, and at times more active, than β‐carotene in enhancing cell‐mediated and humoral immune response in animals and humans (Chew & Park, 2004). Our previous study also showed that xanthophylls elevated anti‐inflammatory cytokine expression, decreased proinflammatory cytokine expression and enhanced antioxidant ability in hens and chicks (Gao et al., 2012, 2013). However, the related molecular mechanisms need further investigation.
Several carotenoid metabolites were shown to modulate the activity of various transcription systems. These include ligand‐activated nuclear receptors, such as the retinoic acid receptor (RAR), retinoid X receptor (RXR), peroxisome proliferator‐activated receptor (PPAR) and oestrogen receptor (Sharoni et al., 2012). Similarly, other antioxidants, such as vitamin E, were reported to regulate nuclear receptor activity (Azzi et al., 2004). Nuclear receptors can regulate immune function through repression of nuclear factor kappa B (NF‐κB) signalling and inflammatory cytokine production in human, rat and pigs (Garcia‐Bueno et al., 2005; Simone et al., 2011; Zhan et al., 2009). Thus, we speculate that the anti‐inflammatory effects of xanthophylls in chickens may be due to the change of nuclear receptor expression, such as PPAR, RXR and RAR.
A crosstalk between lipid homoeostatic and carotenoid metabolic pathways has recently emerged (Ford, Elsen, & Erdman, 2013). Dietary xanthophylls seem to participate in the primary defence mechanism of high‐density lipoprotein against oxidative stress and may also be expected to affect lipid metabolism and maintain favourable blood lipid profile (Aizawa & Inakuma, 2009). It is reported that dietary lutein and zeaxanthin were positively related to high‐density lipoprotein (HDL) level in serum (Loane, Nolan, & Beatty, 2010; Renzi, Hammond, Dengler, & Roberts, 2012). Therefore, the aims of current study were to determine whether lutein and zeaxanthin could regulate lipid profile (triglyceride, TG; cholesterol, CHO; high‐density lipoprotein cholesterol, HDLC; and low‐density lipoprotein cholesterol, LDLC) and gene expression of nuclear factor (PPARγ, PPAR gamma coactivator 1 alpha (PGC1α), RXRγ and RARα) in liver, duodenum, jejunum and ileum of hens and chicks.