| Summary: | 博士 === 國立中興大學 === 食品暨應用生物科技學系所 === 101 === Fucoxanthin, one of the most abundant carotenoids found in Undaria pinnatifida and belongs to the class of non-provitamin A carotenoids, is a class of 40-carbon organic molecules that consists of xanthophyll groups. It also has unique structures such as allenic bond, α, β-unsaturated carbonyl, and some oxygenic functional groups, including 5,6-monoepoxide, hydroxyl, carbonyl. Studies have shown that fucoxanthin has a number of biological activities, such as antioxidation, anti-inflammation, anticancer, anti-obesity, anti-diabetics, anti-angiogenesis and anti-mutagenesis.
Although fucoxanthin has been shown to cause apoptosis and cell cycle arrest in cancer cells, the mechanisms underlying the anti-cancer effects of fucoxanthin still remain unclear. Herein, we first investigated the effect of fucoxanthin on cell cycle arrest and gap junctional intercellular communication (GJIC) in SK-Hep-1 human hepatoma cells and murine embryonic hepatic (BNL CL.2) cells. We found that fucoxanthin (1–20 μM) strongly and concentration-dependently inhibited the proliferation of SK-Hep-1 cells at 24 h of incubation, whereas it only slightly inhibited the cell proliferation of BNL CL.2 cells. In SK-Hep-1 cells, fucoxanthin caused cell cycle arrest at G0/G1 phase and induced cell apoptosis, as evidenced by increased sub-G1 cells and induction of DNA strand breaks. In addition, fucoxanthin significantly enhanced GJIC of SK-Hep-1 cells and increased protein and mRNA expressions of connexin 43 (Cx43) and connexin 32 (Cx32) in SK-Hep-1 cells but not in BNL CL.2 cells. Moreover, fucoxanthin markedly increased the concentration of intracellular calcium levels in SK-Hep-1 cells. We concluded that fucoxanthin possesses anti-proliferative effect against SK-Hep-1 cells by upregulation of Cx32 and Cx43 expression, thus enhances GJIC of SK-Hep-1 cells. Such actions were accompanied by an increase of the intracellular calcium level, which may then cause cell cycle arrest and apoptosis.
Much evidence indicates that phytochemicals found in fruit and vegetables exhibit chemoprevention and anti-drug resistance potential. However, it is unclear whether fucoxanthin itself is capable of overcoming drug resistance. Therefore, we investigated whether fucoxanthin may overcome drug resistance through attenuation of rifampin-induced cytochrome P450 3A (CYP3A4) and multiple drug resistance 1 (MDR1) gene expression via pregnane X receptor (PXR)-mediated pathways in HepG2 hepatoma cells. We found that fucoxanthin (1-10 μM) significantly attenuated rifampin (20 μM)-induced CYP3A4 and MDR1 mRNA and CYP3A4 protein expression. Mechanistically, fucoxanthin strongly attenuated the PXR- , constitutive androstane receptor (CAR)- and rPXR-mediated CYP3A4 promoter activity in HepG2 cells. Moreover, we found that fucoxanthin significantly decreased the interaction between PXR and steroid receptor coactivator-1 (SRC-1), a PXR co-activator. Thus, fucoxanthin exhibits anti-drug resistance potential and that the effect is likely associated with attenuated interaction between PXR and SRC-1, thereby potentially preventing activation of PXR-mediated CYP3A4 promoter activity, leading to inhibition of PXR-regulated gene expression including CYP3A4 and MDR1. The results suggest a potentially important new therapeutic strategy of fucoxanthin as an adjuvant to prevent drug-resistance in patients receiving chronic therapy with PXR agonists.
The combination of anti-cancer drugs with nutritional/food factors is a potential strategy for improving the efficacy of chemotherapy. Among the anti-cancer drugs, cisplatin is a platinum-containing anticancer drug that has been shown to enhance DNA repair and to inhibit cell apoptosis, leading to drug resistance. Thus, we investigated the anti-proliferative effects of a combination of fucoxanthin and cisplatin in human hepatoma HepG2 cells. We found that fucoxanthin (1-10 μΜ) pre-treatment for 24 h followed by cisplatin (10 μΜ) for 24 h significantly decreased cell proliferation, as compared with cisplatin treatment alone. Mechanistically, we showed that fucoxanthin attenuated cisplatin-induced NFkB expression and enhanced NFkB-regulated Bax/Bcl-2 mRNA ratio. Fucoxanthin also decreased DNA repair related gene expression, such as excision repair cross complementation 1 (ERCC1) and thymidine phosphorylase (TP) through regulation of ERK, p38 and PI3K/AKT, thus rendering cancer cells sensitive to apoptosis induced by cisplatin. The results suggest that the combined treatment of fucoxanthin and cisplatin may provide a novel therapeutic approach to decrease cisplatin-induced drug resistance.
In summary, this dissertation research demonstrates that (1) fucoxanthin possesses anti-proliferative effect and anti-drug resistance potential in human hepatoma cells; (2) the combined treatment of fucoxanthin and anti-cancer drugs could lead to potentially important new therapeutic strategy against human hepatoma cells.
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