Fucoxanthin (Fx) and fucosterol (Fs) are characteristic lipid components of brown seaweeds that afford several health benefits to humans. This article describes the quantitative evaluation of lipids of 15 species of brown seaweeds with specific reference to Fx, Fs, and functional long-chain omega-6/omega-3 polyunsaturated fatty acids (PUFAs). In addition, fatty-acid composition of selected species was also accomplished in the study. Major omega-3 PUFAs in the brown seaweeds analyzed were α-linolenic acid (18:3n-3), octadecatetraenoic acid (18:4n-3), arachidonic acid (20:4n-6), and eicosapentaenoic acid (20:5n-3). Both Fx (mg · g(-1) dry weight [dwt]) and Fs (mg · g(-1) dwt) were determined to be relatively abundant in Sargassum horneri (Turner) C. Agardh (Fx, 3.7 ± 1.6; Fs, 13.4 ± 4.4) and Cystoseira hakodatensis (Yendo) Fensholt (Fx, 2.4 ± 0.9; Fs, 8.9 ± 2.0), as compared with other brown seaweed species. Studies related to seasonal variation in Fx, Fs, and total lipids of six brown algae [S. horneri, C. hakodatensis, Sargassum fusiforme (Harv.) Setch., Sargassum thunbergii (Mertens ex Roth) Kuntze, Analipus japonicus (Harv.) M. J. Wynne, and Melanosiphon intestinalis (D. A. Saunders) M. J. Wynne] indicated that these functional lipid components reached maximum during the period between January and March. The functional lipid components present in these seaweeds have the potential for application as nutraceuticals and novel functional ingredients after their recovery.
Fucoxanthin, a xanthophyll present in brown algae consumed in Eastern Asia, can suppress carcinogenesis and obesity in rodents. We investigated the metabolism, tissue distribution, and depletion of fucoxanthin in ICR mice by comparison with those of lutein. The experiments comprised 14-d dietary supplementation with lutein esters or fucoxanthin, followed by 41- or 28-d, respectively, depletion periods with carotenoid-free diets. After lutein ester supplementation, 3'-hydroxy-ε,ε-caroten-3-one and lutein were the predominant carotenoids in plasma and tissues, accompanied by ε,ε-carotene-3,3'-dione. The presence of these keto-carotenoids in mouse tissues is reported here for the first time, to our knowledge. Lutein and its metabolites accumulated most in the liver (7.51 μmol/kg), followed by plasma (2.11 μmol/L), adipose tissues (1.01-1.44 μmol/kg), and kidney (0.87 μmol/kg). The half-life of the depletion (t(1/2)) of lutein metabolites varied as follows: plasma (1.16 d) < liver (2.63 d) < kidney (4.44 d) < < < adipose tissues (>41 d). Fucoxanthinol and amarouciaxanthin A were the main metabolites in mice fed fucoxanthin and partitioned more into adipose tissues (3.13-3.64 μmol/kg) than into plasma, liver, and kidney (1.29-1.80 μmol/kg). Fucoxanthin metabolites had shorter t(1/2) in plasma, liver, and kidneys (0.92-1.23 d) compared with those of adipose tissues (2.76-4.81 d). The tissue distribution of lutein and fucoxanthin metabolites was not associated with their lipophilicity, but depletion seemed to be slower for more lipophilic compounds. We concluded that mice actively convert lutein and fucoxanthin to keto-carotenoids by oxidizing the secondary hydroxyl groups and accumulate them in tissues.
Apoptosis induced by fucoxanthin in HL-60 cells was associated with a loss of mitochondrial membrane potential at an early stage, but not with an increase in reactive oxygen species. Fucoxanthin treatment caused cleavages of procaspase-3 and poly (ADP-ribose) polymerase without any effect on the protein level of Bcl-2, Bcl-X L , or Bax. Apoptosis induction by fucoxanthin may be mediated via mitochondrial membrane permeabilization and caspase-3 activation.
Neoxanthin, a major carotenoid in green leafy vegetables, was reported to exhibit potent antiproliferative effect via apoptosis induction on human prostate cancer cells. However, the metabolic fate of dietary neoxanthin in mammals remains unknown. In the present study, we investigated the gastrointestinal metabolism of neoxanthin in mice and the in vitro digestion of spinach, and estimated the antiproliferative effect of neoxanthin metabolites on PC-3 human prostate cancer cells. Two hours after the oral administration to mice of purified neoxanthin, unchanged neoxanthin and stereoisomers of neochrome (8'-R/S) were detected in the plasma, liver, and small intestinal contents. To estimate the effect of intragastric acidity on the conversion of dietary neoxanthin into neochrome (epoxide-furanoid rearrangement), spinach was digested in vitro by incubating it with a pepsin-HCl solution at pH 2.0 or 3.0 (gastric phase) followed by a pancreatin-bile salt solution (intestinal phase). Spinach neoxanthin was largely converted into (R/S)-neochrome during the digestion when the gastric phase was set at pH 2.0, whereas the rearrangement was observed to a lesser extent at pH 3.0. (R/S)-neochrome dose-dependently inhibited the proliferation of PC-3 cells as well as neoxanthin at concentrations < or = 20 micromol/L. Although neoxanthin induced evident apoptotic cell death, (R/S)-neochrome inhibited the cell proliferation without obvious apoptosis induction. These results indicate that dietary neoxanthin is partially converted into (R/S)-neochrome by intragastric acidity before intestinal absorption and that (R/S)-neochrome exhibits an antiproliferative effect on PC-3 cells by the induction of cytostasis.
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