Actions of β-apo-carotenoids in differentiating cells: Differential effects in P19 cells and 3T3-L1 adipocytes

Abstract

β-Apo-carotenoids, including β-apo-13-carotenone and β-apo-14′-carotenal, are potent retinoic acid receptor (RAR) antagonists in transactivation assays. We asked how these influence RAR-dependent processes in living cells. Initially, we explored the effects of β-apo-13-carotenone and β-apo-14′-carotenal on P19 cells, a mouse embryonal carcinoma cell line that differentiates into neurons when treated with all-trans-retinoic acid. Treatment of P19 cells with either compound failed to block all-trans-retinoic acid induced differentiation. Liquid chromatography tandem mass spectrometry studies, however, established that neither of these β-apo-carotenoids accumulates in P19 cells. All-trans-retinoic acid accumulated to high levels in P19 cells. This suggests that the uptake and metabolism of β-apo-carotenoids by some cells does not involve the same processes used for retinoids and that these may be cell type specific. We also investigated the effects of two β-apo-carotenoids on 3T3-L1 adipocyte marker gene expression during adipocyte differentiation. Treatment of 3T3-L1 adipocytes with either β-apo-13-carotenone or β-apo-10′-carotenoic acid, which lacks RAR antagonist activity, stimulated adipocyte marker gene expression. Neither blocked the inhibitory effects of a relatively large dose of exogenous all-trans-retinoic acid on adipocyte differentiation. Our data suggest that in addition to acting as transcriptional antagonists, some β-apo-carotenoids act through other mechanisms to influence 3T3-L1 adipocyte differentiation.

β-Apo-10′-carotenoids Modulate Placental Microsomal Triglyceride Transfer Protein Expression and Function to Optimize Transport of Intact β-Carotene to the Embryo

“…Also, ␤-apo-14Ј-carotenal effectively inhibited agonist-induced RXR␣, PPAR␣, and PPAR␥ activation, decreasing adipogenesis (16). These cell culture-based experiments demonstrated that specific ␤-apocarotenoids function as nuclear receptor antagonists exerting an anti-vitamin A (retinoic acid) activity (17). Not only apo10AL (42) but also apo10OL (9) was detected in tissues of mice fed BC-containing diets even though the enzymes that could catalyze the conversion of ␤-apocarotenal, the primary asymmetric cleavage product of BC, into ␤-apocarotenol have not been identified.…”

“…This cleavage product can ultimately yield one molecule of retinoic acid; how- ever, it can also function itself as a transcriptional regulator by antagonizing retinoic acid actions (13)(14)(15)(16)(17). We previously showed that 24 h after a single maternal administration of BC at midgestation, Bco2 mRNA levels increased, whereas Bco1 transcription was down-regulated in the placentas of WT dams (25).…”

“…Instead, BCO2, which has a broader substrate specificity than BCO1 (7), seems to prevent toxic accumulation of carotenoids, including BC, in mitochondria where the asymmetric cleavage enzyme is localized (8,12). Interestingly, ␤-apocarotenoids have also been recently found to function as transcriptional regulators, specifically as nuclear receptor antagonists, exerting anti-retinoic acid activities (13)(14)(15)(16)(17). 3 The abbreviations used are: RXR, retinoid X receptor; apoB, apolipoprotein B; apo10AL, ␤-apo-10Ј-carotenal; apo10OL, ␤-apo-10Ј-carotenol; BC, ␤-carotene; BCO1, ␤-carotene 15,15Ј-oxygenase; BCO2, ␤-carotene 9Ј,10Ј-oxygenase; COUP-TFI/II, chicken ovalbumin upstream promoter transcription factor I/II; Cyp26A1, cytochrome p450 family 26 The placenta is a critical organ that during gestation transports BC, among other nutrients, from the maternal bloodstream to the fetal circulation.…”

Role of PPARγ in the nutritional and pharmacological actions of carotenoids

“…β-Apo-10'-carotenoic acid increased expression of LPL and AP2, but did not have a significant influence on expression levels of adiponectin or PPARγ. 88 β-Apo-14'-carotenal, β-apo-14'-carotenoic acid, and β-apo-13-carotenone were demonstrated to be RAR antagonists in transactivation assays. 89 However, β-apo-13-carotenone and β-apo-10'-carotenoic acid lack RAR-antagonist activity.…”

“…They failed to diminish the inhibitory effects of a relatively large dose of exogenous all-trans-RA on adipocyte differentiation. 88 It is evident that β-carotene has a complex influence on PPARγ-regulated pathways controlling adipogenesis. An adipose tissue-specific conversion of β-carotene via carotenoid oxygenases can influence the activities of key transcription factors.…”