Biosynthetic pathway and health benefits of fucoxanthin, an algae-specific xanthophyll in brown seaweeds

Abstract

Fucoxanthin is the main carotenoid produced in brown algae as a component of the light-harvesting complex for photosynthesis and photoprotection. In contrast to the complete elucidation of the carotenoid biosynthetic pathways in red and green algae, the biosynthetic pathway of fucoxanthin in brown algae is not fully understood. Recently, two models for the fucoxanthin biosynthetic pathway have been proposed in unicellular diatoms; however, there is no such information for the pathway in brown seaweeds to date. Here, we propose a biosynthetic pathway for fucoxanthin in the brown seaweed, Ectocarpus siliculosus, derived from comparison of carotenogenic genes in its sequenced genome with those in the genomes of two diatoms, Thalassiosira pseudonana and Phaeodactylum tricornutum. Currently, fucoxanthin is receiving attention, due to its potential benefits for human health. Therefore, new knowledge regarding the medical and nutraceutical properties of fucoxanthin from brown seaweeds is also summarized here.

Figure 1

Molecular structure of fucoxanthin.

Figure 2

Thin-layer chromatography (TLC) analysis of carotenoids in seaweeds. Total lipids were extracted from the green seaweed, Ulva pertusa (Upe), red seaweeds, Bangia fuscopurpurea (Bf) and Porphyra yezoensis (Py), and brown seaweeds, Ectocarpus siliculosus (Es) and Undaria pinnatifida (Upi), with methanol. To detect each carotenoid contained in algae, total lipids were developed on a silica gel TLC plate with petroleum ether: acetone (7:3, v/v). We have confirmed that violaxanthin and fucoxanthin can be distinguished by UV-Vis spectrum.

Figure 3

Predicted carotenoid biosynthetic pathway in seaweeds. Red, green and brown boxes reveal the pathway in red, green and brown seaweeds, respectively. The pathways for biosynthesis of zeaxanthin and lutein in red seaweeds and neoxanthin in green seaweeds are proposed based on genomic sequences from Cyanidioschyzon merolae and Chlamydomonas reinhardtii. The color overlapping the name of each carotenoid corresponds to its visible color. The symbol * indicates enzymes unidentified in seaweeds.

Figure 4

Two different hypotheses regarding the biosynthetic pathways for fucoxanthin. (A) Diadinoxanthin hypothesis: β-carotene is converted to fucoxanthin and diatoxanthin from diadinoxanthin; (B) Neoxanthin hypothesis: β-carotene is converted to fucoxanthin and diadinoxanthin from neoxanthin.

Figure 5

Anti-obesity effects of fucoxanthin on diabetic/obese mice. (A) Body weight of diabetic/obese KK-A^y mice and lean C57BL/6J mice after four weeks of feeding of diets with/without 0.2% fucoxanthin; (B) White adipose tissue weight of KK-A^y mice fed the diet with 0.2% fucoxanthin for two weeks. *p < 0.05 compared with controls.