Extraction, Enrichment, and LC-MSn-Based Characterization of Phlorotannins and Related Phenolics from the Brown Seaweed, Ascophyllum nodosum

Phenolic components from the edible brown seaweed, Ascophyllum nodosum, have been associated with considerable antioxidant activity but also bioactivities related to human health. This study aims to select and identify the main phlorotannin components from this seaweed which have been previously associated with potential health benefits. Methods to enrich phenolic components then further select phlorotannin components from ethanolic extracts of Ascophyllum nodosum were applied. The composition and phenolic diversity of these extracts were defined using data dependent liquid chromatography mass spectroscopic (LC-MSn) techniques. A series of phlorotannin oligomers with apparent degree of polymerization (DP) from 10 to 31 were enriched by solid phase extraction and could be selected by fractionation on Sephadex LH-20. Evidence was also obtained for the presence of dibenzodioxin linked phlorotannins as well as sulphated phlorotannins and phenolic acids. As well as diversity in molecular size, there was evidence for potential isomers at each DP. MS2 fragmentation analyses strongly suggested that the phlorotannins contained ether linked phloroglucinol units and were most likely fucophlorethols and MS3 data suggested that the isomers may result from branching within the chain. Therefore, application of these LC-MSn techniques provided further information on the structural diversity of the phlorotannins from Ascophyllum, which could be correlated against their reported bioactivities and could be further applied to phlorotannins from different seaweed species.

Characteristics of Polyphenolic Content in Brown Algae of the Pacific Coast of Russia

Water and ethanol brown macroalgal extracts of nine species of Laminariales and four species of Fucales of the Pacific coast of Russia were investigated. It has been shown that brown algae species of Agarum, Thalassiophyllum, Fucus and Cystoseira can be a source of the polyphenolic compounds with antioxidant activity. Phenolic content in the ethanol algal extracts (Undaria pinnatifida, Arthrothamnus bifidus, Thalassiophyllum clathrus and Agarum turneri) was 1.1-3.5 times higher than in the water extracts. In Sargassum pallidum and Kjellmaniella crassifolia, the total polyphenolic content was 2.1 and 1.6 times higher, respectively, in water extracts than in ethanol extracts. The maximum radical scavenging activity has been detected in Agarum turneri ethanol extracts (38.8 mg ascorbic acid/g and 2506.8 µmol Trolox equiv/g dry algae). Phlorotannin content varies from 16.8 μg/g dry sample of Costaria costata to 2763.2 μg/g dry sample of Agarum turneri. It is found the content of polyphenolic compounds in brown algae is determined mainly by their species-specificity and by their belonging to the genus. The presence of major phenols in the extract of Thalassiophyllum clathrus, such as phenolic acid (gallic acid), hydroxycinnamic acids (caffeic acid, chlorogenic acid, coumaric acid) and flavonols (kaempferol, quercetin) has been established.

Seaweed Phenolics: From Extraction to Applications

Seaweeds have attracted high interest in recent years due to their chemical and bioactive properties to find new molecules with valuable applications for humankind. Phenolic compounds are the group of metabolites with the most structural variation and the highest content in seaweeds. The most researched seaweed polyphenol class is the phlorotannins, which are specifically synthesized by brown seaweeds, but there are other polyphenolic compounds, such as bromophenols, flavonoids, phenolic terpenoids, and mycosporine-like amino acids. The compounds already discovered and characterized demonstrate a full range of bioactivities and potential future applications in various industrial sectors. This review focuses on the extraction, purification, and future applications of seaweed phenolic compounds based on the bioactive properties described in the literature. It also intends to provide a comprehensive insight into the phenolic compounds in seaweed.

Topical Application of Phlorotannins from Brown Seaweed Mitigates Radiation Dermatitis in a Mouse Model

Radiation dermatitis (RD) is one of the most common side effects of radiotherapy; its symptoms progress from erythema to dry and moist desquamation, leading to the deterioration of the patients’ quality of life. Active metabolites in brown seaweed, including phlorotannins (PTNs), show anti-inflammatory activities; however, their medical use is limited. Here, we investigated the effects of PTNs in a mouse model of RD in vivo. X-rays (36 Gy) were delivered in three fractions to the hind legs of BALB/c mice. Macroscopic RD scoring revealed that PTNs significantly mitigated RD compared with the vehicle control. Histopathological analyses of skin tissues revealed that PTNs decreased epidermal and dermal thickness compared with the vehicle control. Western blotting indicated that PTNs augmented nuclear factor erythroid 2-related factor 2 (NRF2)/heme oxygenase-1 (HO-1) pathway activation but attenuated radiation-induced NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells) and inflammasome activation, suggesting the mitigation of acute inflammation in irradiated mouse skin. PTNs also facilitated fast recovery, as indicated by increased aquaporin 3 expression and decreased γH2AX (histone family member X) expression. Our results indicate that topical PTN application may alleviate RD symptoms by suppressing oxidative stress and inflammatory signaling and by promoting the healing process. Therefore, PTNs may show great potential as cosmeceuticals for patients with cancer suffering from radiation-induced inflammatory side effects such as RD.

Effect of Food Preparations on In Vitro Bioactivities and Chemical Components of Fucus vesiculosus

Fucus vesiculosus is a brown macroalgae used in food and generally considered safe to be consumed, according to EU Directive (EC 258/97). The aim of this study is to analyze the effect of food preparation on F.vesiculosus of different origins on what concerns its chemical constituents and final bioactivities. The aqueous extract of the seaweeds were obtained at different temperatures, similar to food preparation and then purified by SPE. The compound identification was carried out by Liquid Chromatography High Resolution Mass Spectrometry (LC-HRMS/MS) and algae extracts microstructure were observed by Scanning Electron Microscopy (SEM). The activities were determined by using antioxidant activity, inhibition of acetylcholinesterase (AChE) and 3-hidroxi-3-methyl-glutaril-CoA (HMG-CoA) reductase (HMGR) together with Caco-2 cells line simulating the intestinal barrier. The activity of AChE and the HMGR were inhibited by the extracts giving IC₅₀ values of 15.0 ± 0.1 µg/mL and 4.2 ± 0.1 µg/mL, respectively and 45% of the cholesterol permeation inhibition. The main compounds identified were phlorotannins and peptides derivatives. The mode of preparation significantly influenced the final bioactivities. Moreover, the in vitro results suggest that the preparation of F. vesiculosus as a soup could have hypercholesterolemia lowering effect.

In Vitro Anticancer and Radiosensitizing Activities of Phlorethols from the Brown Alga Costaria costata

The anticancer and radiosensitizing effects of high-molecular-weight phlorethols CcPh (Mw = 2520 Da) isolated from the brown algae of Costaria costata on human colorectal carcinoma HCT 116 and HT-29 cells were investigated. Phlorethols CcPh possessed cytotoxic activity against HT-29 (IC50 = 92 μg/mL) and HCT 116 (IC50 = 94 μg/mL) cells. CcPh at non-toxic concentrations inhibited the colony formation in colon cancer cells and significantly enhanced their sensitivity to low non-toxic X-ray irradiation. The combinatory effect of radiation and CcPh was synergistic (Combination index < 0.7). Algal phlorethols might be prospective candidates as radiosensitizers to improve the scheme of radiotherapy.

The Effect of Ensiling on the Nutritional Composition and Fermentation Characteristics of Brown Seaweeds as a Ruminant Feed Ingredient

Simple Summary

In recent years, there has emerged a renewed interest in the inclusion of seaweed as an animal feed ingredient. Due to annual fluctuations in the availability and biochemical composition of seaweeds, effective preservation methods are needed. These are currently restricted to thermal processing methods. Ensiling is a commonly applied preservation technique for terrestrial forages intended for livestock feed but little is known about the characteristics of silage made from seaweeds. This study considered the potential of ensiling two brown seaweed species (Fucus vesiculosus and Saccharina latissimi) with or without the use of a microbial inoculant. The potential applications of seaweed silage as a feed ingredient in ruminant diets were considered. The results showed that, depending on the species, ensiling may be a suitable preservation method for brown seaweeds.

Abstract

Ensiling could be an effective method to preserve seaweeds for animal feed applications, however, there is limited scientific knowledge in this area. Seaweeds are a promising ruminant feed ingredient, in part due to the content of phenolic compounds, which are receiving considerable interest as alternative antimicrobial agents in feed. The aim of the study was to compare the effect of ensiling on the nutritional composition and fermentation characteristics of two brown seaweed species, Fucus vesiculosus (FV) and Saccharina latissimi (SL) with or without the use of a Lactobacillus plantarum (LAB) inoculant. The effect of ensiling on the stability of phlorotannin was also investigated using nuclear magnetic resonance (NMR). After harvesting, the seaweeds were wilted for 24 h and subsequently ensiled in laboratory-scaled silos for 90 days. SL silage showed a stronger fermentation pattern (pH < 4), dominated by lactic acid (50–60 g/kg Dry Matter (DM)), and a slightly higher acetic acid content compared to FV silages (p < 0.05). The fermentability of FV was limited (pH > 4.8) with low lactic acid production (<5 g/kg DM). The addition of the LAB inoculant showed no effect on the fermentation process but a modest effect on the chemical composition of both species was observed after the 90-day ensiling period. The results showed no losses in the nutrient content of FV after ensiling, however losses in the Crude Protein (CP, −32%), ash (−36%), Neutral Detergent Fibre (NDF, −77%) and Acid Detergent Fibre (ADF, −58%) content of SL were observed. The ensiling process had a limited effect on the in vitro true dry matter digestibility and phenolic content of either species. Therefore, ensilage may be a suitable preservation method for the use of brown seaweeds as a ruminant feed; however, species-specific differences were observed.

Activity of Bacteriophage and Complex Tannins against Biofilm-Forming Shiga Toxin-Producing Escherichia coli from Canada and South Africa

Bacteriophages, natural killers of bacteria, and plant secondary metabolites, such as condensed tannins, are potential agents for the control of foodborne pathogens. The first objective of this study evaluated the efficacy of a bacteriophage SA21RB in reducing pre-formed biofilms on stainless-steel produced by two Shiga toxin-producing Escherichia coli (STEC) strains, one from South Africa and the other from Canada. The second objective examined the anti-bacterial and anti-biofilm activity of condensed tannin (CT) from purple prairie clover and phlorotannins (PT) from brown seaweed against these strains. For 24-h-old biofilms, (O113:H21; 6.2 log10 colony-forming units per square centimeter (CFU/cm2) and O154:H10; 5.4 log10 CFU/cm2), 3 h of exposure to phage (1013 plaque-forming units per milliliter (PFU/mL)) reduced (p ≤ 0.05) the number of viable cells attached to stainless-steel coupons by 2.5 and 2.1 log10 CFU/cm2 for O113:H21 and O154:H10, respectively. However, as biofilms matured, the ability of phage to control biofilm formation declined. In biofilms formed for 72 h (O113:H21; 5.4 log10 CFU/cm2 and O154:H10; 7 log10 CFU/cm2), reductions after the same duration of phage treatment were only 0.9 and 1.3 log10 CFU/cm2 for O113:H21 and O154:H10, respectively. Initial screening of CT and PT for anti-bacterial activity by a microplate assay indicated that both STEC strains were less sensitive (p ≤ 0.05) to CT than PT over a concentration range of 25-400 µg/mL. Based on the lower activity of CT (25-400 µg/mL), they were not further examined. Accordingly, PT (50 µg/mL) inhibited (p ≤ 0.05) biofilm formation for up to 24 h of incubation at 22 °C, but this inhibition progressively declined over 72 h for both O154:H10 and O113:H21. Scanning electron microscopy revealed that both SA21RB and PT eliminated 24 h biofilms, but that both strains were able to adhere and form biofilms on stainless-steel coupons at longer incubation times. These findings revealed that phage SA21RB is more effective at disrupting 24 than 72 h biofilms and that PT were able to inhibit biofilm formation of both E. coli O154:H10 and O113:H21 for up to 24 h.

Dieckol, a Major Marine Polyphenol, Enhances Non-Rapid Eye Movement Sleep in Mice via the GABAA-Benzodiazepine Receptor

We had previously demonstrated that phlorotannins, which are marine polyphenols, enhance sleep in mice via the GABA_A-benzodiazepine (BZD) receptor. Among the constituents of phlorotannin, dieckol is a major marine polyphenol from the brown alga Ecklonia cava. Although phlorotannins are known to exert hypnotic effects, the sleep-enhancing effect of dieckol has not yet been determined. We evaluated the effect of dieckol on sleep-wake state of mice by analyzing electroencephalograms (EEGs) and electromyograms. Flumazenil, a GABA_A-BZD antagonist, was used to investigate the molecular mechanism underlying the effects of dieckol on sleep. The polygraphic recordings and corresponding hypnograms revealed that dieckol accelerated the initiation of non-rapid eye movement sleep (NREMS); it shortened sleep latency and increased NREMS duration. According to the change in time-course, dieckol showed sleep-enhancing effects by increasing the amount of NREMS and decreasing wakefulness during the same hours. Additionally, sleep quality was evaluated by analyzing the EEG power density, and dieckol was found to not affect sleep intensity while zolpidem was found to reduce it. Finally, we treated mice with zolpidem or dieckol in combination with flumazenil and found the latter to inhibit the sleep-enhancing effect of dieckol and zolpidem, thereby indicating that dieckol exerts sleep-enhancing effects by activating the GABA_A-BZD receptor, similar to zolpidem. These results implied that dieckol can be used as a promising herbal sleep aid with minimal side effects, unlike the existing hypnotics.

Antimicrobial and Fermentation Potential of Himanthalia elongata in Food Applications

Himanthalia elongata is a brown oceanic seaweed rich in bioactive compounds. It could play an important role in food production because of its antimicrobial and antioxidant properties. Three strains belonging to the Lactobacillus casei group (Lactobacillus casei, Lactobacillus paracasei, and Lactobacillus rhamnosus) and a Bacillus subtilis strain were used for the solid-state fermentation of commercial seaweeds, and bacterial growth was monitored using the plate count method. High-pressure processing (HPP) was also employed (6000 bar, 5 min, 5 °C) before extraction. The antimicrobial activity of the extracts was tested in terms of the main food pathogenic bacteria (Salmonella spp., Listeria monocytogenes, Escherichia coli, Staphylococcus aureus, and Bacillus cereus), and the phenolic content was estimated using the Folin-Ciocalteau method. In addition, targeted UHPLC-MS² methods were used to unravel the profile of phlorotannins. H. elongata allowed the growth of the L. casei group strains and B. subtilis, showing the fermentability of this substrate. Significant antimicrobial activity toward L. monocytogenes was observed in the extracts obtained from unfermented samples, but neither fermentation nor HPP enhanced the natural antimicrobial activity of this seaweed species. The content in the phenolic compounds decreased because of the fermentation process, and the amount of phenolics in both the unfermented and fermented H. elongata extracts was very low. Despite phlorotannins being related to the natural antimicrobial activity of this brown seaweed, these results did not support this association. Even if fermentation and HPP were not proven to be effective tools for enhancing the useful compounds of H. elongata, the seaweed was shown to be a suitable substrate for L. casei group strains as well as for B. subtilis growth, and its extracts exhibited antimicrobial activity toward foodborne pathogens.

Bioactive Compounds from Seaweed with Anti-Leukemic Activity: A Mini-Review on Carotenoids and Phlorotannins

Chronic Myeloid Leukemia (CML) represents 15-20% of all new cases of leukemia and is characterized by an uncontrolled proliferation of abnormal myeloid cells. Currently, the first-line of treatment involves Tyrosine Kinase Inhibitors (TKIs), which specifically inhibits the activity of the fusion protein BCR-ABL. However, resistance, mainly due to mutations, can occur. In the attempt to find more effective and less toxic therapies, several approaches are taken into consideration such as research of new anti-leukemic drugs and "combination chemotherapy" where different drugs that act by different mechanisms are used. Here, we reviewed the molecular mechanisms of CML, the main mechanisms of drug resistance and current strategies to enhance the therapeutic effect of TKIs in CML. Despite major advances in CML treatment, new, more potent anticancer drugs and with fewer side effects are needed. Marine organisms, and particularly seaweed, have a high diversity of bioactive compounds with some of them having anticancer activity in several in vitro and in vivo models. The state-of-art suggests that their use during cancer treatment may improve the outcome. We reviewed here the yet few data supporting anti-leukemic activity of some carotenoids and phlorotannins in some leukemia models. Also, strategies to overcome drug resistance are discussed, particularly the combination of conventional drugs with natural compounds.

The Quest for Phenolic Compounds from Macroalgae: A Review of Extraction and Identification Methodologies

The current interest of the scientific community for the exploitation of high-value compounds from macroalgae is related to the increasing knowledge of their biological activities and health benefits. Macroalgae phenolic compounds, particularly phlorotannins, have gained particular attention due to their specific bioactivities, including antioxidant, antiproliferative, or antidiabetic. Notwithstanding, the characterization of macroalgae phenolic compounds is a multi-step task, with high challenges associated with their isolation and characterization, due to the highly complex and polysaccharide-rich matrix of macroalgae. Therefore, this fraction is far from being fully explored. In fact, a critical revision of the extraction and characterization methodologies already used in the analysis of phenolic compounds from macroalgae is lacking in the literature, and it is of uttermost importance to compile validated methodologies and discourage misleading practices. The aim of this review is to discuss the state-of-the-art of phenolic compounds already identified in green, red, and brown macroalgae, reviewing their structural classification, as well as critically discussing extraction methodologies, chromatographic separation techniques, and the analytical strategies for their characterization, including information about structural identification techniques and key spectroscopic profiles. For the first time, mass spectrometry data of phlorotannins, a chemical family quite exclusive of macroalgae, is compiled and discussed.

Attenuation of Inflammation and Leptin Resistance by Pyrogallol-Phloroglucinol-6,6-Bieckol on in the Brain of Obese Animal Models

Obesity induces inflammation both in the adipose tissue and the brain. Activated macrophage infiltration, polarization of macrophages to a more inflammatory type (M1), and increased levels of pro-inflammatory cytokines are related to brain inflammation, which induces leptin resistance in the brain. Pyrogallol-phloroglucinol-6,6-bieckol (PPB), a compound from Ecklonia cava, has anti-inflammatory effects. In this study, we evaluated the effects of PPB effect M1 polarization and inflammation and its ability to restore the effects of leptin, such as a decrease in appetite and body weight. We administered PPB to diet-induced obesity (DIO) and leptin-deficient (ob/ob) mice, evaluated macrophage activation, polarization, and changes of inflammatory cytokine level in adipose tissue and brain, and determined the effect of PPB on leptin resistance or leptin sensitivity in the brain. The levels of activated macrophage marker, M1/M2, and pro-inflammatory cytokines were increased in the adipose tissue and brain of DIO and ob/ob mice than control. TLR4 expression, endoplasmic reticulum (ER) stress, and NF-κB expression in the brain of DIO and ob/ob mice were also increased; this increase was related to the upregulation of SOCS3 and decreased phosphorylated STAT3, which decreased leptin sensitivity in the brain. PPB decreased inflammation in the brain, restored leptin sensitivity, and decreased food intake and weight gain in both DIO and ob/ob mice.

A critical review of analytical methods used for the chemical characterisation and quantification of phlorotannin compounds in brown seaweeds

INTRODUCTION

Phlorotannins, the phenolic compounds found in brown seaweeds, are a unique and diverse class of compounds showing a huge potential for food and pharmaceutical applications.

OBJECTIVE

This review will give an account of the colorimetric assays used and a discussion of their quantitative and qualitative analytical shortcomings. It will also discuss other more complex and modern analytical chemistry methods that are currently being developed to study phlorotannins. The purpose of this review is to increase awareness of these bioactive compounds and promote further development of robust analytical methods for use in biology, food science, pharmacology and biomedical and cosmeceutical sciences.

RESULTS

Whilst the biological activity and huge commercial potential of the phlorotannins has been widely reported throughout the literature, the chemical structures and reactivity of these compounds is still not well understood. The phlorotannin content of seaweed is usually characterised using colorimetric assays. However, although these methods give a reasonable overall estimation of the total phenolic content, they lack precision and specificity.

CONCLUSION

This review highlights the strengths and weaknesses of commonly used colorimetric assays. Novel techniques are highlighted using more selective chemistry to identify this class of compounds.

Pyrogallol-Phloroglucinol-6,6-Bieckol from Ecklonia cava Attenuates Tubular Epithelial Cell (TCMK-1) Death in Hypoxia/Reoxygenation Injury

The hypoxia/reoxygenation (H/R) injury causes serious complications after the blood supply to the kidney is stopped during surgery. The main mechanism of I/R injury is the release of high-mobility group protein B1 (HMGB1) from injured tubular epithelial cells (TEC, TCMK-1 cell), which triggers TLR4 or RAGE signaling, leading to cell death. We evaluated whether the extracts of Ecklonia cava (E. cava) would attenuate TEC death induced by H/R injury. We also evaluated which phlorotannin-dieckol (DK), phlorofucofuroeckol A (PFFA), pyrogallol phloroglucinol-6,6-bieckol (PPB), or 2,7-phloroglucinol-6,6-bieckol (PHB)-would have the most potent effect in the context of H/R injury. We used for pre-hypoxia treatment, in which the phlorotannins from E. cava extracts were added before the onset of hypoxia, and a post- hypoxia treatment, in which the phlorotannins were added before the start of reperfusion. PPB most effectively reduced HMGB1 release and the expression of TLR4 and RAGE induced by H/R injury in both pre- and post-hypoxia treatment. PPB also most effectively inhibited the expression of NF-kB and release of the inflammatory cytokines TNF-α and IL-6 in both models. PPB most effectively inhibited cell death and expression of cell death signaling molecules such as Erk/pErk, JNK/pJNK, and p38/pp38. These results suggest that PPB blocks the HGMB1-TLR4/RAGE signaling pathway and decreases TEC death induced by H/R and that PPB can be a novel target for renal H/R injury therapy.

Phlorotannins from Ecklonia cava Attenuates Palmitate-Induced Endoplasmic Reticulum Stress and Leptin Resistance in Hypothalamic Neurons

Leptin resistance in the hypothalamus has an essential role in obesity. Saturated fatty acids such as palmitate bind to Toll-like receptor 4 (TLR4) and lead to endoplasmic reticulum (ER) stress and leptin resistance. In this study, we evaluated whether extracts of Ecklonia cava would attenuate the ER stress induced by palmitate and reduce leptin resistance in hypothalamic neurons and microglia. We added palmitate to these cells to mimic the environment induced by high-fat diet in the hypothalamus and evaluated which of the E. cava phlorotannins-dieckol (DK), 2,7-phloroglucinol-6,6-bieckol (PHB), pyrogallol-phloroglucinol-6,6-bieckol (PPB), or phlorofucofuroeckol-A (PFFA)-had the most potent effect on attenuating leptin resistance. TLR4 and NF-κB expression induced by palmitate was attenuated most effectively by PPB in both hypothalamic neurons and microglia. ER stress markers were increased by palmitate and were attenuated by PPB in both hypothalamic neurons and microglia. Leptin resistance, which was evaluated as an increase in SOCS3 and a decrease in STAT3 with leptin receptor expression, was increased by palmitate and was decreased by PPB in hypothalamic neurons. The culture medium from palmitate-treated microglia increased leptin resistance in hypothalamic neurons and this resistance was attenuated by PPB. In conclusion, PPB attenuated leptin resistance by decreasing ER stress in both hypothalamic neurons and microglia.

Brown Macroalgae as Valuable Food Ingredients

Due to the balanced nutritional value and abundance of bioactive compounds, seaweeds represent great candidates to be used as health-promoting ingredients by the food industry. In this field, Phaeophyta, i.e., brown macroalgae, have been receiving great attention particularly due to their abundance in complex polysaccharides, phlorotannins, fucoxanthin and iodine. In the past decade, brown algae and their extracts have been extensively studied, aiming at the development of well-accepted products with the simultaneous enhancement of nutritional value and/or shelf-life. However, the reports aiming at their bioactivity in in vivo models are still scarce and need additional exploration. Therefore, this manuscript revises the relevant literature data regarding the development of Phaeophyta-enriched food products, namely those focused on species considered as safe for human consumption in Europe. Hopefully, this will create awareness to the need of further studies in order to determine how those benefits can translate to human beings.

Phlorotannins with Potential Anti-tyrosinase and Antioxidant Activity Isolated from the Marine Seaweed Ecklonia stolonifera

Compounds were isolated from Ecklonia stolonifera Okamura, a marine brown alga widely consumed as food. Among the isolated compounds, 974-A was demonstrated for the first time to be a potent competitive inhibitor of mushroom tyrosinase activity towards l-tyrosine and l-DOPA (IC₅₀ values = 1.57 ± 0.08 and 3.56 ± 0.22 µM, respectively). Molecular docking simulations clarified that the hydroxyl residues of the isolated compounds formed hydrogen bonds with residues at the catalytic and allosteric sites of tyrosinase, while other residues participated in hydrophobic interactions. Moreover, 974-A, phlorofucofuroeckol-A and eckol reduced the cellular melanin content and tyrosinase activity, and downregulated the expression of melanogenesis enzymes including tyrosinase, tyrosinase-related protein (TRP)-1, and TRP-2 in B16F10 melanoma cells. These compounds also effectively scavenged radicals at the cellular level. Thus, our results revealed that compounds isolated from E. stolonifera are potent tyrosinase inhibitors with potential applications in the cosmetic industry for treatment of hyperpigmentation and for the anti-browning effect in the agricultural field.

Voltammetric, spectroscopic, and cellular characterization of redox functionality of eckol and phlorofucofuroeckol-A: A comparative study

Interest in phlorotannins has increased in recent years largely due to antioxidant capacity, however, the redox mechanism of phlorotannins is still obscure. In the present study, the electrochemical oxidation mechanisms of eckol (EL) and phlorofucofuroeckol-A (PFF-A), two representative phlorotannin compounds, were comparatively analyzed in a wide pH range using cyclic and differential pulse voltammetry as well as spectroscopic assay. The voltammetric study revealed that EL and PFF-A were successively oxidized in three pH-dependent steps. Moreover, it was found that the PFF-A presented a stronger proton and electron transferring activity as compared to EL since PFF-A exhibited lower acid-base dissociation constant (pKa ) value and higher heterogeneous rate constant (kbh ) value in the first oxidation step. These property were further evidenced by comparison of direct antioxidant activity (i.e., superoxide anion and peroxide radicals) as well as indirect antioxidant activity (i.e., mRNA expression of two phase II enzymes) between EL and PFF-A. PRACTICAL APPLICATIONS: Phlorotannins from edible algae have been regarded as novel antioxidants those presented high application potential in food industry. Even though antioxidant activity of phlorotannin compounds have been widely investigated in both in vitro and in vivo studies, very few reports focused on electron transferring functionality which is chemical basis for antioxidant process. Herein, the oxidative mechanisms of two representative phlorotannins were comparatively analyzed using multiple electrochemical methods. This is hopefully to give information on the chemical meaning behind the antioxidant activity of dietary phlorotannins.

Phenolic Content of Brown Algae (Pheophyceae) Species: Extraction, Identification, and Quantification

Over the last few decades, isolations and chemical characterizations of secondary metabolites with proved biological activities have been of interest for numerous research groups across the world. Phenolics, as one of the largest and most widely distributed group of phytochemicals, have gained special attention due to their pharmacological activity and array of health-promoting benefits. Reports on phenolic potentials of marine algae, especially brown algae (Pheophyceae) that are characterized by the presence of phlorotannins, are still scarce. The aim of this review paper is to provide an overview of current knowledge about phenolic potential of different brown algae species (74 species from 7 different orders). Studies on brown algae phenolics usually involve few species, thus the focus of this review is to provide information about the phenolic potential of reported algae species and to get an insight into some issues related to the applied extraction procedures and determination/quantification methods to facilitate the comparison of results from different studies. The information provided through this review should be useful for the design and interpretation of studies investigating the brown algae as a source of valuable phytochemicals.

Slow-Binding Inhibition of Tyrosinase by Ecklonia cava Phlorotannins

Tyrosinase inhibitors improve skin whitening by inhibiting the formation of melanin precursors in the skin. The inhibitory activity of seven phlorotannins (1-7), triphlorethol A (1), eckol (2), 2-phloroeckol (3), phlorofucofuroeckol A (4), 2-O-(2,4,6-trihydroxyphenyl)-6,6'-bieckol (5), 6,8'-bieckol (6), and 8,8'-bieckol (7), from Ecklonia cava was tested against tyrosinase, which converts tyrosine into dihydroxyphenylalanine. Compounds 3 and 5 had IC50 values of 7.0 ± 0.2 and 8.8 ± 0.1 μM, respectively, in competitive mode, with Ki values of 8.2 ± 1.1 and 5.8 ± 0.8 μM. Both compounds showed the characteristics of slow-binding inhibitors over the time course of the enzyme reaction. Compound 3 had a single-step binding mechanism and compound 5 a two-step-binding mechanism. With stable AutoDock scores of -6.59 and -6.68 kcal/mol, respectively, compounds 3 and 5 both interacted with His85 and Asn260 at the active site.

Optimization of Phlorotannins Extraction from Fucus vesiculosus and Evaluation of Their Potential to Prevent Metabolic Disorders

Phlorotannins are phloroglucinol-based phenolic compounds, occurring particularly in brown macroalgae, that have been recognized for their promising bioactive properties. In this study, the extraction of phlorotannins from Fucus vesiculosus was evaluated with particular emphasis on the influential parameters, including the solvent concentration, solvent-solid ratio, extraction temperature and extraction time, using a single-factor design followed by a Box-Behnken design. The maximum total phlorotannin content, determined using the 2,4-dimethoxybenzaldehyde (DMBA) method, corresponded to 2.92 ± 0.05 mg of phloroglucinol equivalents/g dry seaweed (mg PGE/g DS), and was achieved for extracts carried out with acetone 67% (v/v), a solvent-solid ratio of 70 mL/g and temperature at 25 °C. This crude extract, together with a semi-purified phlorotannin fraction, were further evaluated for their anti-enzymatic capacity against α-glucosidase, α-amylase and pancreatic lipase, both showing promising inhibitory effects, particularly against α-glucosidase for which a greater inhibitory effect was observed compared to the pharmaceutical drug acarbose (IC50 = 4.5 ± 0.8 and 0.82 ± 0.3 μg/mL, respectively, against 206.6 ± 25.1 μg/mL). Additionally, the ultra-high-pressure liquid chromatography coupled to mass spectrometry (UHPLC-MS) analysis carried out on the ethyl acetate fraction revealed the presence of fucols, fucophlorethols, fuhalols and several other phlorotannin derivatives. Moreover, possible new phlorotannin compounds, including fucofurodiphlorethol, fucofurotriphlorethol and fucofuropentaphlorethol, have been tentatively identified in this extract. Overall, this study provides evidence that F. vesiculosus phlorotannin-rich extracts hold potential for the management of the activity of α-glucosidase, α-amylase and pancreatic lipase, which are well known to be linked to metabolic disorders such as diabetes and obesity.

Dereplication by High-Performance Liquid Chromatography (HPLC) with Quadrupole-Time-of-Flight Mass Spectroscopy (qTOF-MS) and Antiviral Activities of Phlorotannins from Ecklonia cava

Ecklonia cava is edible seaweed that is found in Asian countries, such as Japan and Korea; and, its major components include fucoidan and phlorotannins. Phlorotannins that are isolated from E. cava are well-known to have an antioxidant effect and strong antiviral activity against porcine epidemic diarrhea virus (PEDV), which has a high mortality rate in piglets. In this study, the bioactive components were determined based on two different approaches: (i) bio-guided isolation using the antiviral activity against the H1N1 viral strain, which is a representative influenza virus that originates from swine and (ii) high-resolution mass spectrometry-based dereplication, including relative mass defects (RMDs) and HPLC-qTOFMS fragmentation analysis. The EC70 fraction showed the strongest antiviral activity and contained thirteen phlorotannins, which were predicted by dereplication. Ten compounds were directly isolated from E. cava extract and then identified. Moreover, the dereplication method allowed for the discovery of two new phlorotannins. The structures of these two isolated compounds were elucidated using NMR techniques and HPLC-qTOFMS fragmentation analysis. In addition, molecular modelling was applied to determine the absolute configurations of the two new compounds. The antiviral activities of seven major phlorotannins in active fraction were evaluated against two influenza A viral strains (H1N1 and H9N2). Six of the compounds showed moderate to strong effects on both of the viruses and phlorofucofuroeckol A (12), which showed an EC50 value of 13.48 ± 1.93 μM, is a potential active antiviral component of E. cava.

Phenolic Compounds from Edible Algae: Bioactivity and Health Benefits

Algae have been consumed for many years in Asian countries; at present, its consumption around the world either as food ingredient or directly as food commodity has increased considerably mainly due to the Asian influence and its cuisine, but also because of the growing interest in the beneficial health effects of algae. Although several biological activities have been attributed to different algae compounds such as pigments, lipids, polysaccharides, fiber, proteins or vitamins, in the present review we will highlight the different phenolic compounds present on seaweeds and their important role in the functional and health effects, paying special attention to the antioxidant, anti-proliferative, anti-obesity and antidiabetic activities.

Dual BACE1 and Cholinesterase Inhibitory Effects of Phlorotannins from Ecklonia cava-An In Vitro and in Silico Study

Alzheimer's disease (AD) is one of the most common neurodegenerative diseases with a multifactorial nature. β-Secretase (BACE1) and acetylcholinesterase (AChE), which are required for the production of neurotoxic β-amyloid (Aβ) and the promotion of Aβ fibril formation, respectively, are considered as prime therapeutic targets for AD. In our efforts towards the development of potent multi-target, directed agents for AD treatment, major phlorotannins such as eckol, dieckol, and 8,8'-bieckol from Ecklonia cava (E. cava) were evaluated. Based on the in vitro study, all tested compounds showed potent inhibitory effects on BACE1 and AChE. In particular, 8,8'-bieckol demonstrated the best inhibitory effect against BACE1 and AChE, with IC50 values of 1.62 ± 0.14 and 4.59 ± 0.32 µM, respectively. Overall, kinetic studies demonstrated that all the tested compounds acted as dual BACE1 and AChE inhibitors in a non-competitive or competitive fashion, respectively. In silico docking analysis exhibited that the lowest binding energies of all compounds were negative, and specifically different residues of each target enzyme interacted with hydroxyl groups of phlorotannins. The present study suggested that major phlorotannins derived from E. cava possess significant potential as drug candidates for therapeutic agents against AD.