https://pubs.rsc.org/en/content/articlepdf/2019/NP/C8NP00092A

Marine natural products.

Seaweed is more than the wrap that keeps rice together in sushi. Seaweed biomass is already used for a wide range of other products in food, including stabilising agents. Biorefineries with seaweed as feedstock are attracting worldwide interest and include low-volume, high value-added products and vice versa. Scientific research on bioactive compounds in seaweed usually takes place on just a few species and compounds. This paper reviews worldwide research on bioactive compounds, mainly of nine genera or species of seaweed, which are also available in European temperate Atlantic waters, i.e. Laminaria sp., Fucus sp., Ascophyllum nodosum, Chondrus crispus, Porphyra sp., Ulva sp., Sargassum sp., Gracilaria sp. and Palmaria palmata. In addition, Undaria pinnatifida is included in this review as this is globally one of the most commonly produced, investigated and available species. Fewer examples of other species abundant worldwide have also been included. This review will supply fundamental information for biorefineries in Atlantic Europe using seaweed as feedstock. Preliminary selection of one or several candidate seaweed species will be possible based on the summary tables and previous research described in this review. This applies either to the choice of high value-added bioactive products to be exploited in an available species or to the choice of seaweed species when a bioactive compound is desired. Data are presented in tables with species, effect and test organism (if present) with examples of uses to enhance comparisons. In addition, scientific experiments performed on seaweed used as animal feed are presented, and EU, US and Japanese legislation on functional foods is reviewed.

Bioactive compounds in seaweed: functional food applications and legislation

Amongst the diverse and potent biological activities of free fatty acids (FFAs) is the ability to kill or inhibit the growth of bacteria. The antibacterial properties of FFAs are used by many organisms to defend against parasitic or pathogenic bacteria. Whilst their antibacterial mode of action is still poorly understood, the prime target of FFA action is the cell membrane, where FFAs disrupt the electron transport chain and oxidative phosphorylation. Besides interfering with cellular energy production, FFA action may also result from the inhibition of enzyme activity, impairment of nutrient uptake, generation of peroxidation and auto-oxidation degradation products or direct lysis of bacterial cells. Their broad spectrum of activity, non-specific mode of action and safety makes them attractive as antibacterial agents for various applications in medicine, agriculture and food preservation, especially where the use of conventional antibiotics is undesirable or prohibited. Moreover, the evolution of inducible FFA-resistant phenotypes is less problematic than with conventional antibiotics. The potential for commercial or biomedical exploitation of antibacterial FFAs, especially for those from natural sources, is discussed.

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Antibacterial free fatty acids: activities, mechanisms of action and biotechnological potential

The inhibitory activity of six groups of flavonoids against yeast and rat small intestinal alpha-glucosidases and porcine pancreatic alpha-amylase was compared, and chemical structures of flavonoids responsible for the inhibitory activity were evaluated. Yeast alpha-glucosidase was potently inhibited by the anthocyanidin, isoflavone and flavonol groups with the IC50 values less than 15 microM. The following structures enhanced the inhibitory activity: the unsaturated C ring, 3-OH, 4-CO, the linkage of the B ring at the 3 position, and the hydroxyl substitution on the B ring. Rat small intestinal alpha-glucosidase was weakly inhibited by many flavonoids, and slightly by the anthocyanidin and isoflavone groups. 3-OH and the hydroxyl substitution on the B ring increased the inhibitory activity. In porcine pancreatic alpha-amylase, luteolin, myricetin and quercetin were potent inhibitors with the IC50 values less than 500 microM. The 2,3-double bond, 5-OH, the linkage of the B ring at the 3 position, and the hydroxyl substitution on the B ring enhanced the inhibitory activity, while 3-OH reduced it.

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Inhibition of α-Glucosidase and α-Amylase by Flavonoids

In the last three decades the discovery of metabolites with biological activities from macroalgae has increased significantly. However, despite the intense research effort by academic and corporate institutions, very few products with real potential have been identified or developed. Based on Silverplatter MEDLINE and Aquatic Biology, Aquaculture & Fisheries Resources databases, the literature was searched for natural products from marine macroalgae in the Rhodophyta, Phaeophyta and Chlorophyta with biological and pharmacological activity. Substances that currently receive most attention from pharmaceutical companies for use in drug development, or from researchers in the field of medicine-related research include: sulphated polysaccharides as antiviral substances, halogenated furanones from Delisea pulchra as antifouling compounds, and kahalalide F from a species of Bryopsis as a possible treatment of lung cancer, tumours and AIDS. Other substances such as macroalgal lectins, fucoidans, kainoids and aplysiatoxins are routinely used in biomedical research and a multitude of other substances have known biological activities. The potential pharmaceutical, medicinal and research applications of these compounds are discussed.

Medicinal and pharmaceutical uses of seaweed natural products: A review

Potent α-glucosidase inhibitors purified from the red alga Grateloupia elliptica

In a previous report, we discussed an extract from a marine red alga, Amphiroa zonata, which shows selective cytotoxic activity to human leukemic cells, but no cytotoxicity to normal human dermal fibroblast (HDF) cells in vitro. In this study, we identified palmitic acid, a selective cytotoxic substance from the marine algal extract, and investigated its biological activities. At concentrations ranging from 12.5 to 50 micrograms/ml, palmitic acid shows selective cytotoxicity to human leukemic cells, but no cytotoxicity to normal HDF cells. Furthermore, palmitic acid induces apoptosis in the human leukemic cell line MOLT-4 at 50 micrograms/ml. Palmitic acid also shows in vivo antitumor activity in mice. One molecular target of palmitic acid in tumor cells is DNA topoisomerase I, however, interestingly, it does not affect DNA topoisomerase II, suggesting that palmitic acid may be a lead compound of anticancer drugs.

Antitumor activity of palmitic acid found as a selective cytotoxic substance in a marine red alga.

alpha-Glucosidase inhibitory activity was found in aqueous methanol extracts of tochu-cha, dried leaves of Eucommia ulmoides (Eucommiaceae). Five active principles against yeast enzyme were isolated and characterized. Among them, quercetin (1, Ki: 8.5 x 10(-6) M) was considered to contribute mostly to the activity of the tochu leaves. In regard to an animal alpha-glucosidase, rat intestinal sucrase activity was also inhibited by 1.

Isolation and Identification of α-Glucosidase Inhibitors from Tochu-cha (Eucommia Ulmoides)

The apoptosis-inducing effect of fucoxanthin on human leukemic HL-60 cells was investigated. Fucoxanthin, which was obtained from the brown alga Undaria pinnatifida, inhibited the proliferation of HL-60 cells and induced DNA fragmentation on agarose gel electrophoresis, a typical characteristic feature of apoptotic cells. The results of sandwich ELISA using anti-biotin-antibody and anti-DNA-antibody also demonstrated DNA fragmentation in accordance with the increase in fucoxanthin concentration and incubation time. Since the level of DNA fragmentation did not increase after 24 h incubation, fucoxanthin appeared to have some effect on cell cycle. In contrast, β-carotene did not show an apoptosis-inducing effect on HL-60 cells. These results suggested that a carotenoid structure might be crucial for inducing apoptosis.

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Apoptosis-Inducing Effect of Fucoxanthin on Human Leukemia Cell Line HL-60

Two novel bromophenols (1 and 2) were isolated from an extract of a red alga, Odonthalia corymbifera, together with a known bromophenol (3). The novel bromophenols were determined as 4-bromo-2,3-di...

Hideyuki Kurihara

Papers

Potent α-glucosidase inhibitors purified from the red alga Grateloupia elliptica

Antitumor activity of palmitic acid found as a selective cytotoxic substance in a marine red alga.

Isolation and Identification of α-Glucosidase Inhibitors from Tochu-cha (Eucommia Ulmoides)

Apoptosis-Inducing Effect of Fucoxanthin on Human Leukemia Cell Line HL-60

Two new bromophenols from the red alga odonthalia corymbifera