A gene encoding a carotenoid cleavage dioxygenase class 1 enzyme (FaCCD1) was identified among a strawberry fruit expressed sequence tag collection. The full-length cDNA was isolated, and the expression profiles along fruit receptacle development and ripening, determined by quantitative real time polymerase chain reaction, showed that FaCCD1 is a ripening-related gene that reaches its maximal level of expression in the red fully ripe stage. FaCCD1 was expressed in Escherichia coli, and the products formed by the recombinant protein through oxidative cleavage of carotenoids were identified by liquid chromatography-mass spectrometry and gas chromatography-mass spectrometry analyses. The FaCCD1 protein cleaves zeaxanthin, lutein, and beta-apo-8'-carotenal in vitro. Although beta-carotene is not a good substrate for FaCCD1 in vitro, the expression of FaCCD1 in an engineered carotenoid-producing E. coli strain caused the degradation of beta-carotene in vivo. Additionally, the carotenoid profile in strawberry was analyzed by high-performance liquid chromatography-photodiode detection, and a correlation between the increase of the expression level of FaCCD1 during ripening and the decrease of the lutein content suggests that lutein could constitute the main natural substrate of FaCCD1 activity in vivo.
Antioxidant properties of carotenoids are thought to be at least partly responsible for the protective effects of fruits and vegetables rich in carotenoids against colon cancer. There are large amounts of in vitro data supporting this hypothesis. But there is little known about the antioxidant effects of carotenoid-rich food in vivo particularly in the gastrointestinal tract. In a randomized, crossover trial, healthy men (n = 22) who were consuming a low-carotenoid diet drank 330 mL/d tomato juice or carrot juice for 2 wk. Antioxidant capacity was assessed by the "lag time" of ex vivo LDL oxidation induced by copper and lipid peroxidation as determined by measurements of malondialdehyde (MDA) in plasma and feces using HPLC with fluorescence detection. Although consumption of both carotenoid-rich juices for 2 wk increased the carotenoid level in plasma and feces (P < 0.001), the antioxidant capacity of LDL tended to be increased by only approximately 4.5% (P = 0.08), and lipid peroxidation in the men's plasma and feces was not affected. Thus, processes other than lipid peroxidation could be responsible for the preventive effects of tomatoes and carrots against colon cancer.
Flavonoids are secondary plant metabolites included in our diet but are also provided in a growing number of supplements. They are suggested to interact with intestinal transport systems including phospho-glycoprotein (P-gp) which mediates the efflux of a variety of xenobiotics back into the gut lumen. In human intestinal Caco-2 cells, we tested the effects of 14 different flavonoids on P-gp expression in vitro. Protein expression levels were quantified by Western blotting, flow cytometry, and real-time PCR. Except apigenin, all flavonoids at concentrations of 10 microM increased P-gp expression in Western blotting experiments when cells were exposed to the compounds over 4 wk. Flavone was one of the most effective P-gp inducers in Caco-2 cells and its effects were, therefore, also assessed for changes in P-gp in vivo in the gastrointestinal tract of C57BL/6 mice. P-gp expression was significantly increased by flavone (400 mg/kg body weight x day over 4 wk) in the small intestine but not in the colon which displayed intrinsically the highest expression level. In conclusion, the increase in P-gp expression caused by flavonoids in intestinal epithelial cells in vitro and also in vivo may serve as an adaptation and defense mechanism limiting the entry of lipophilic xenobiotics into the organism.
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