Role of PPARγ in the nutritional and pharmacological actions of carotenoids

Abstract:

Peroxisome proliferator-activated receptor gamma (PPARγ) has been shown to play an important role in the biological effects of carotenoids. The PPARγ-signaling pathway is involved in the anticancer effects of carotenoids. Activation of PPARγ partly contributes to the growth-inhibitory effects of carotenoids (β-carotene, astaxanthin, bixin, capsanthin, lutein, and lycopene) on breast cancer MCF7 cells, leukemia K562 cells, prostate cancer (LNCaP, DU145, and PC3 cells), and esophageal squamous cancer EC109 cells. PPARγ is the master regulator of adipocyte differentiation and adipogenesis. Downregulated PPARγ and PPARγ-target genes have been associated with the suppressive effects of β-carotene and lycopene on 3T3L1 and C3H10T1/2 adipocyte differentiation and adipogenesis. β-Carotene is cleaved centrally into retinaldehyde by BCO1, the encoding gene being a PPARγ-target gene. Retinaldehyde can be oxidized to retinoic acid and also be reduced to retinol. β-Carotene can also be cleaved asymmetrically into β-apocarotenals and β-apocarotenones by BCO2. The inhibitory effects of β-carotene on the development of adiposity and lipid storage are dependent substantially on BCO1-mediated production of retinoids. The effects of β-carotene on body adiposity were absent in BCO1-knockout mice. Retinoid metabolism is connected with the activity of PPARγ in the control of body-fat reserves. Retinoic acid, retinaldehyde, retinol, and β-apocarotenals exert suppressive effects on preadipocyte differentiation and adipogenesis via downregulation of PPARγ expression in cell culture. The molecular mechanisms underlying retinoic acid effects on adipose-tissue biology and the development of adiposity remain poorly understood. Adiposity can be affected by retinoids through long-lasting effects at critical developmental stages. Retinol saturase increases PPARγ-transcriptional activity and adipocyte differentiation. Other carotenoids that have been reported to suppress adipocyte differentiation and lipid accumulation in the main via modulation of PPARγ and PPARγ-target genes include astaxanthin, bixin, norbixin, β-cryptoxanthin, fucoxanthin and its metabolites, lycopene, apo-10’-lycopenoic acid, siphonaxanthin, and neoxanthin, except paprika pigments. Lutein, lycopene, and paprika carotenoids reduce proinflammatory cytokine levels by an induction of PPARγ in immune tissues and cells. Lycopene, apo-10’-lycopenoic acid, and astaxanthin might prevent atherosclerosis through modifying cholesterol metabolism via increasing PPARγ expression in macrophages.

Keywords::

• carotenoids
• PPARγ
• anti-cancer
• anti-obesity
• antiatherosclerosis

Disclosure

The authors report no conflicts of interest in this work.