Eiichi Kotake-Nara

Absorption and Metabolism of Xanthophylls

Dietary carotenoids, especially xanthophylls, have attracted significant attention because of their characteristic biological activities, including anti-allergic, anti-cancer, and anti-obese actions. Although no less than forty carotenoids are ingested under usual dietary habits, only six carotenoids and their metabolites have been found in human tissues, suggesting selectivity in the intestinal absorption of carotenoids. Recently, facilitated diffusion in addition to simple diffusion has been reported to mediate the intestinal absorption of carotenoids in mammals. The selective absorption of carotenoids may be caused by uptake to the intestinal epithelia by the facilitated diffusion and an unknown excretion to intestinal lumen. It is well known that β-carotene can be metabolized to vitamin A after intestinal absorption of carotenoids, but little is known about the metabolic transformation of non provitamin A xanthophylls. The enzymatic oxidation of the secondary hydroxyl group leading to keto-carotenoids would occur as a common pathway of xanthophyll metabolism in mammals. This paper reviews the absorption and metabolism of xanthophylls by introducing recent advances in this field.

Characterization of Apoptosis Induced by Fucoxanthin in Human Promyelocytic Leukemia Cells

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-XL, or Bax. Apoptosis induction by fucoxanthin may be mediated via mitochondrial membrane permeabilization and caspase-3 activation.

Effects of fats and oils on the bioaccessibility of carotenoids and vitamin E in vegetables.

The low bioavailability of lipophilic micronutrients is mainly caused by their limited solubilization to an aqueous micelle, which hinders their ability to be taken up by the intestines. Bioaccessibility is the ratio of the solubilized portion to the whole amount ingested. We evaluated in this study the effects of individual fats and oils and their constituents on the bioaccessibility of carotenoids and vitamin E in vegetables by simulated digestion. Various fats and oils and long-chain triacylglycerols enhanced the bioaccessibility of β-carotene present in spinach, but not of lutein and α-tocopherol, which are less hydrophobic than β-carotene. Free fatty acid, monoacylglycerol, and diacylglycerol also enhanced the bioaccessibility of β-carotene present in spinach. In addition to the long-chain triacylglycerols, their hydrolyzates formed during digestion would facilitate the dispersion and solubilization of β-carotene into mixed micelles. Dietary fats and oils would therefore enhance the bioaccessibility of hydrophobic carotenes present in vegetables.

Effects of Mixed Micellar Lipids on Carotenoid Uptake by Human Intestinal Caco-2 Cells

We reported previously that lysophosphatidylcholine remarkably enhanced β-carotene uptake from bile acid-mixed micelles by human intestinal Caco-2 cells. In the present study, we evaluated how mixed micelle components other than phospholipids, viz., fatty acids, monoolein, and cholesterol, affect carotenoid uptake by Caco-2 cells. Each component influenced the β-carotene uptake in a different way depending on micellar composition. Oleic acid at 200 µM significantly enhanced uptake in the absence of lysophosphatidylcholine. Cholesterol at 40 µM significantly reduced uptake in the presence of lysophosphatidylcholine, while no reduction was found in the presence of 200 µM oleic acid. Facilitated diffusion was suggested partly to mediate uptake in mixed micelles, except for mixed micelles containing 200 µM oleic acid. Uptake mediated by facilitated diffusion was approximately 20% of total uptake. Mixed micellar lipids have the potential to modify intestinal uptake.

Effect of Glycerophospholipid Class on the β-Carotene Uptake by Human Intestinal Caco-2 Cells

The effects were evaluated of various glycerophospholipids on the uptake of β-carotene solubilized in mixed micelles by human intestinal Caco-2 cells. Phosphatidylethanolamine markedly enhanced the transfer of β-carotene from the micelles to the cells, whereas phosphatidylcholine suppressed it. All the lysoglycerophospholipids enhanced the transfer, irrespective of the polar head group. Glycerophospholipids therefore have the potential to modify the intestinal absorption of carotenoids.

Re-evaluation of the rin mutation and the role of RIN in the induction of tomato ripening

Tomato (Solanum lycopersicum) rin mutants completely fail to ripen: they do not produce red pigmentation, soften or induce an ethylene burst. Therefore, RIN has long been believed to function as a major regulator that is essential for the induction of ripening. Here, we provide evidence contradicting this concept of RIN function, showing induction of fruit ripening in the absence of RIN. A CRISPR/Cas9-mediated RIN-knockout mutation did not repress initiation of ripening and the mutant fruits showed moderate red colouring. Moreover, inactivation of the rin mutant allele partially restored the induction of ripening. Therefore, RIN is not required for the initiation of ripening and rin is not a null mutation, but rather is a gain-of-function mutation that produces a protein that actively represses ripening. Since the discovery of the rin mutant a half-century ago, many models have depicted RIN as indispensable for the induction of ripening; these models should be reconsidered in light of these results.RIN has long been considered a major regulator for ripening induction in tomato as rin mutants fail to ripen. Now, a study shows that the rin allele is a gain-of-function, rather than null, mutation. RIN is not required for ripening initiation.

A 3-hydroxy β-end group in xanthophylls is preferentially oxidized to a 3-oxo ε-end group in mammals

We previously found that mice fed lutein accumulated its oxidative metabolites (3′-hydroxy-ε,ε-caroten-3-one and ε,ε-carotene-3,3′-dione) as major carotenoids, suggesting that mammals can convert xanthophylls to keto-carotenoids by the oxidation of hydroxyl groups. Here we elucidated the metabolic activities of mouse liver for several xanthophylls. When lutein was incubated with liver postmitochondrial fraction in the presence of NAD+, (3′R,6′R)-3′-hydroxy-β,ε-caroten-3-one and (6RS,3′R,6′R)-3′-hydroxy-ε,ε-caroten-3-one were produced as major oxidation products. The former accumulated only at the early stage and was assumed to be an intermediate, followed by isomerization to the latter. The configuration at the C3′ and C6′ of the ε-end group in lutein was retained in the two oxidation products. These results indicate that the 3-hydroxy β-end group in lutein was preferentially oxidized to a 3-oxo ε-end group via a 3-oxo β-end group. Other xanthophylls such as β-cryptoxanthin and zeaxanthin, which have a 3-hydroxy β-end group, were also oxidized in the same manner as lutein. These keto-carotenoids, derived from dietary xanthophylls, were confirmed to be present in plasma of normal human subjects, and β,ε-caroten-3′-one was significantly increased by the ingestion of β-cryptoxanthin. Thus, humans as well as mice have oxidative activity to convert the 3-hydroxy β-end group of xanthophylls to a 3-oxo ε-end group.

Lysoglyceroglycolipids Improve the Intestinal Absorption of Micellar Fucoxanthin by Caco-2 Cells

To improve the intestinal absorption of fucoxanthin, we evaluated the effects of dietary glyceroglycolipids on the uptake and secretion of fucoxanthin solubilized in mixed micelles by human intestinal Caco-2 cells. Although digalactosyldiacylglycerol and sulfoquinovosyldiacylglycerol suppressed fucoxanthin uptake and secretion, their lyso-types, digalactosylmonoacylglycerol and sulfoquinovosylmonoa cylglycerol, remarkably enhanced them. Thus, some dietary glyceroglycolipids may be potential enhancers of fucoxanthin bioavailability in humans.

Egg white hydrolysate inhibits oxidation in mayonnaise and a model system

The flavor deterioration of mayonnaise is induced by iron, which is released from egg yolk phosvitin under acidic conditions and promotes lipid oxidation. To prevent oxidative deterioration, natural components, rather than synthetic chemicals such as ethylenediaminetetraacetic acid have been required by consumers. In the present study, we evaluated the inhibitory effects of three egg white components with the same amino acid composition, namely egg white protein, hydrolysate, and the amino acid mixture, on lipid oxidation in mayonnaise and an acidic egg yolk solution as a model system. We found that the hydrolysate had the strongest inhibitory effect on lipid oxidation among the three components. The mechanism underlying the antioxidant effect was associated with Fe2+-chelating activity. Thus, egg white hydrolysate may have the potential as natural inhibitors of lipid oxidation in mayonnaise.

The content and distribution of steryl ferulates in wheat produced in Japan

Oryzanol contained in rice bran is a complex mixture of steryl ferulates (SFs) with many identified health benefits. Recently, SF has been shown to exist in other cereals such as wheat, rye, and corn. In this study, SFs in several wheats produced in Japan were analyzed. For instance, SF content of whole wheat grain, Yumekaori (Japan) was 15.2 ± 1.4 mg-oryzanol-equivalent/100 g grain, while that of the imported one, 1CW (Canada) was 11.4 ± 1.3 mg-oryzanol-equivalent/100 g grain. The main SF components in the examined wheats were campesteryl ferulate, campestanyl ferulate, and sitostanyl ferulate. SF distribution in whole wheat grain was investigated using 14 fractions produced by a conventional test milling machine. SF was intensively accumulated in the four bran fractions (24 − 95 mg-oryzanol-equivalent/100 g bran fraction). These results suggest that the wheat bran would be an important source of SF.