Hepatoprotective constituents of the edible brown alga Ecklonia stolonifera on tacrine-induced cytotoxicity in Hep G2 cells

Effects of Ecklonia stolonifera Extract on Metabolic Dysregulation in High-Fat Diet-Induced Obese Mice

This study aimed to test the hypothesis that long-term and low-dose supplementation with an ethanol extract of Ecklonia stolonifera may confer protection against high-fat diet (HFD)-induced obesity in mice. Male C57BL/6J mice were divided into two groups, one of which was fed an HFD (40 kcal% fat) and the other an HFD+E. stolonifera (0.006%, w/w, ∼5 mg/kg body weight/day) for 16 weeks. E. stolonifera supplementation significantly reduced body weight from week 3 and until the end of the experiment. E. stolonifera-supplemented mice also exhibited lower fat mass (epididymal, perirenal, and mesenteric fat) and smaller adipocyte size than HFD control mice. The two groups displayed similar food intakes, but E. stolonifera markedly decreased lipogenesis and increased lipolysis and fatty acid oxidation in adipose tissue. Moreover, E. stolonifera significantly decreased plasma and hepatic lipid levels, hepatic lipid droplet accumulation, plasma aminotransferase levels, and liver weight by decreasing lipogenesis and increasing fatty acid oxidation. As E. stolonifera-supplemented mice showed improvements in hyperglycemia, insulin resistance, and inflammation, compared to control mice, it is possible that the beneficial effects of E. stolonifera on obesity might be associated with decreased inflammation and insulin resistance. Collectively, these results indicate that E. stolonifera could be used as a novel means of preventing and treating obesity and obesity-related metabolic disorders.

Preventive and therapeutic use of herbal compounds against doxorubicin induced hepatotoxicity: a comprehensive review

Doxorubicin (DOX) is associated with numerous acute and chronic dose-related toxicities including hepatotoxicity. This adverse reaction may limit the use of other chemotherapeutic agents with hepatic excretion, and so, its prevention is an important issue. The aim of this study was to conduct a comprehensive review of in vitro, in vivo and human studies regarding the protective effects of synthetic and naturally-occurring compounds against DOX-induced liver injury. The search was conducted in Embase, PubMed, and Scopus databases using the following keywords: "doxorubicin," "Adriamycin," "hepatotoxicity," "liver injury," "liver damage," and "hepatoprotective," and all articles published in English were included without time restriction. Forty eligible studies to the end of May 2022 finally were reviewed. Our results demonstrated that all of these drugs, except acetylsalicylic acid, had considerable hepatoprotective effects against DOX. In addition, none of the studied compounds attenuated the antitumor efficacy of DOX treatment. Silymairn was the only compound which is assessed in human studies and showed promising preventive and therapeutic effects. Altogether, our results demonstrated that most of compounds with antioxidant, anti-apoptosis, and anti-inflammatory properties are efficacious against DOX-induced hepatotoxicity and may be considered as a potential adjuvant agent for prevention of hepatotoxicity in cancer patients, after fully been assessed in well-designed large clinical trials.

In-Depth Understanding of Ecklonia stolonifera Okamura: A Review of Its Bioactivities and Bioactive Compounds

Ecklonia stolonifera Okamura (ES) is mainly distributed in the coastal areas of the middle Pacific, around Korea and Japan, and has a long-standing edible value. It is rich in various compounds, such as polysaccharides, fatty acids, alginic acid, fucoxanthin, and phlorotannins, among which the polyphenol compound phlorotannins are the main active ingredients. Studies have shown that the extracts and active components of ES exhibit anti-cancer, antioxidant, anti-obesity, anti-diabetic, antibacterial, cardioprotective, immunomodulatory, and other pharmacological properties in vivo and in vitro. Although ES contains a variety of bioactive compounds, it is not widely known and has not been extensively studied. Based on its potential health benefits, it is expected to play an important role in improving the nutritional value of food both economically and medically. Therefore, ES needs to be better understood and developed so that it can be utilized in the development and application of marine medicines, functional foods, bioactive substances, and in many other fields. This review provides a comprehensive overview of the bioactivities and bioactive compounds of ES to promote in-depth research and a reference for the comprehensive utilization of ES in the future.

Polyopes affinis Suppressed IFN-γ- and TNF-α-Induced Inflammation in Human Keratinocytes via Down-Regulation of the NF-κB and STAT1 Pathways

Polyopes affinis is a red algal species commonly found on the South coast and near Jeju Island, Korea. This study aimed to determine whether P. affinis extracts can inhibit the pathogenesis of T-helper-2 (Th2)-mediated inflammation in a human keratinocyte cell line of atopic dermatitis (AD). Cells were incubated with 10 ng/mL of interferon gamma (IFN-γ) and 10 ng/mL of tumor necrosis factor-alpha (TNF-α) at various concentrations of PAB (10, 30, and 60 µg/mL) and PAA (100, 500, and 1000 µg/mL) extracts. A gene-ontology (GO)-enrichment analysis revealed that PAB significantly enriched the genes associated with biological processes such as cell adhesion, immune response, inflammation, and chemokine-mediated pathways. PAB suppressed the expression of the secretory proteins and mRNAs that are associated with the thymus and the production of activation-regulated chemokines (TARC/CCL17) and macrophage-derived chemokines (MDC/CCL22). The effect of the extract on mitogen-activated protein kinases (MAPKs) was related to its inhibition of TARC/CCL17 and MDC/CCL22 production by blocking NF-κB and STAT1 activation. These results suggest that seaweed extract may improve AD by regulating pro-inflammatory chemokines. In conclusion, we first confirmed the existence of phloroglucinol, a polyphenol formed from a precursor called phlorotannin, which is present in PAB, and this result proved the possibility of PAB being used as a treatment for AD.

Pharmacological Applications of Phlorotannins: A Comprehensive Review

BACKGROUND

Seaweeds, including marine brown algae, are traditional food sources in Asia. Phlorotannins, as the product of the polyketide pathway, are mainly found in brown algae. Different properties have been attributed to this group of marine products ranging from antiallergic to anticancer activity. Mechanism of action is not obvious for all these properties, but there are some explanations for such effects.

OBJECTIVE

The current study aimed to review the phlorotannins and to assess the beneficial uses in medicine.

METHODS

Different databases were explored with the exact terms "Phlorotannin", "Seaweed" and "Brown Algae". Data assembly was finalized by June 2019. The papers showing the effects of phlorotannins in medicine were gathered and evaluated for further assessment.

RESULTS

General physiological aspects of phlorotannins were firstly evaluated. Different arrays of pharmacological properties ranging from anti-diabetic activity to cancer treatment were found. The mechanism of action for some of these beneficiary properties has been confirmed through rigorous examinations, but there are some features with unknown mechanisms.

CONCLUSION

Phlorotannins are characterized as a multifunctional group of natural products. Potential antioxidant characteristics could be attributed to preventive and/or their curative role in various diseases.

A review on phytoconstituents of marine brown algae

Background

From the last few years, the development and discovery of bioactive compounds and their potential properties from marine algae have been enhanced significantly. The coastal area is a huge storehouse for propitious algae. It has been the genuine reality that the consequence of marine algae as a source of different compounds is increasing.

Main body

Numerous advanced research devices are available for the discovery of synthetic compounds but still many researchers are working on natural bioactive compounds to discover their biological properties, which are useful to society. Marine algae are taking the preponderance of consideration from investigators owing to its phenomenon of biological activity like anti-cancer, anti-viral, cholesterol-reducing, and many more. A variety of compounds are collected from algae with specific purposes as they remain in an extremely ambitious and hard state; this condition is responsible for the synthesis of very particularly effective bioactive compounds. The present article is concentrating on the brown algae of the Gujarat coast, phlorotannins, polyphenol, phytosterol from brown algae, and their various applications. The main importance has been given to the secondary metabolites and various applications of marine brown algae.

Conclusion

From this review, it can be concluded that the prominent bioactive compounds from brown algae can cure many serious diseases. Besides, the potential biological activities of a special bioactive compound may represent the interest in the industry of pharmaceuticals, cosmeceutical, and functional foods.

Potential Anti-Aging Substances Derived from Seaweeds

Aging is a major risk factor for many chronic diseases, such as cancer, cardiovascular disease, and diabetes. The exact mechanisms underlying the aging process are not fully elucidated. However, a growing body of evidence suggests that several pathways, such as sirtuin, AMP-activated protein kinase, insulin-like growth factor, autophagy, and nuclear factor erythroid 2-related factor 2 play critical roles in regulating aging. Furthermore, genetic or dietary interventions of these pathways can extend lifespan by delaying the aging process. Seaweeds are a food source rich in many nutrients, including fibers, polyunsaturated fatty acids, vitamins, minerals, and other bioactive compounds. The health benefits of seaweeds include, but are not limited to, antioxidant, anti-inflammatory, and anti-obese activities. Interestingly, a body of studies shows that some seaweed-derived extracts or isolated compounds, can modulate these aging-regulating pathways or even extend lifespans of various animal models. However, few such studies have been conducted on higher animals or even humans. In this review, we focused on potential anti-aging bioactive substances in seaweeds that have been studied in cells and animals mainly based on their anti-aging cellular and molecular mechanisms.

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.

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.

Characterizing Eckol as a Therapeutic Aid: A Systematic Review

The marine biosphere is a treasure trove of natural bioactive secondary metabolites and the richest source of structurally diverse and unique compounds, such as phlorotannins and halo-compounds, with high therapeutic potential. Eckol is a precursor compound representing the dibenzo-1,4-dioxin class of phlorotannins abundant in the Ecklonia species, which are marine brown algae having a ubiquitous distribution. In search of compounds having biological activity from macro algae during the past three decades, this particular compound has attracted massive attention for its multiple therapeutic properties and health benefits. Although several varieties of marine algae, seaweed, and phlorotannins have already been well scrutinized, eckol deserves a place of its own because of the therapeutic properties it possesses. The relevant information about this particular compound has not yet been collected in one place; therefore, this review focuses on its biological applications, including its potential health benefits and possible applications to restrain diseases leading to good health. The facts compiled in this review could contribute to novel insights into the functions of eckol and potentially enable its use in different uninvestigated fields.

Protective Effect of Eckol against Acute Hepatic Injury Induced by Carbon Tetrachloride in Mice

Several in vitro studies have shown the potential hepatoprotective properties of eckol, a natural phlorotannin derived from the brown alga. However, the in vivo hepatoprotective potential of eckol has not been determined. In this study, we performed an in vivo study to investigate the protective effect of eckol and its possible mechanisms on the carbon tetrachloride (CCl₄)-induced acute liver injury model in mice. Results revealed that eckol pre-treatment at the dose of 0.5 and 1.0 mg/kg/day for 7 days significantly suppressed the CCl₄-induced increases of alanine transaminase (ALT) and aspartate aminotransferase (AST) levels in serum and meliorated morphological liver injury. Terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling (TUNEL) analysis showed that the number of positive apoptotic hepatocytes in the eckol-treated group was lower than that in the CCl₄ model group. Western blotting analysis also demonstrated the enhanced expression of bcl-2 and suppressed expression of cleaved caspase-3 by eckol. The CCl₄-induced oxidative stress in liver was significantly ameliorated by eckol, which was characterized by reduced malondialdehyde (MDA) formations, and enhanced superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) activities and glutathione (GSH) content. Moreover, the CCl₄-induced elevations of pro-inflammatory cytokines tumor necrosis factor (TNF)-α, interleukin (IL)-1β and IL-6 were markedly suppressed in the eckol-treated group. However, eckol enhanced the level of IL-10, a potent anti-inflammatory cytokine, and recruited CD11c⁺ dendritic cells into the liver tissues of CCl₄-treated mice. These results indicated that eckol has the protective effect on CCl₄-induced acute liver injury via multiple mechanisms including anti-apoptosis, anti-oxidation, anti-inflammation and immune regulation.

Recent advances in pharmacological research on Ecklonia species: a review

The genus Ecklonia (Lessoniaceae, Phaeophyceae), commonly called kelp (brown algae), is abundant on the coasts of Japan and Korea. During the past few decades, Ecklonia species have received tremendous attention for their wide range of therapeutic properties and multiple health benefits, such as great nutritional value and being rich in vitamins, minerals, dietary fiber, proteins, and polysaccharides. Several novel functional ingredients with diversified biological activities have been isolated and possess antimicrobial, antiviral, hepatoprotective, cardioprotective, anti-inflammatory, neuroprotective, anticarcinogenic, immunomodulatory, hypolipidemic, anti-diabetic, and antioxidant therapeutic properties. The present review discusses the phytochemical, pharmacological, therapeutic, nutritional, and health benefits of different species of genus Ecklonia, as well as their use in the prevention of disease and maintenance of good health.

Hepatoprotective Effect of Gallotannin-enriched Extract Isolated from Gall on Hydrogen Peroxide-induced Cytotoxicity in HepG2 Cells

Background:

Gall (Galla Rhois [GR]) is known to have antibacterial, anti-inflammatory, antimetastatic, and anti-invasion activities and exert hepatoprotective effects. However, the hepatoprotective effects of gallotannin-enriched GR (GEGR) and their mechanisms have not yet been investigated.

Objective:

The potential protective effect of GEGR against hepatotoxicity induced by hydrogen peroxide (H₂O₂) was investigated.

Materials and Methods:

Changes in cell viability, apoptosis protein expression, and reactive oxygen species (ROS) generation were determined in HepG2 cells that were pretreated with four different concentrations of GEGR (6.25–50 μg/ml) for 24 h before H₂O₂ exposure.

Results:

GEGR consisted of gallotannin (69.2%), gallic acid (26.6%), and methyl gallate (4.2%) and showed remarkable 2,2-diphenyl-1-picrylhydrazyl scavenging activity (inhibitory concentration 50% = 0.212 μg/ml). The lethal dose 50% and effective dose 50% values for the response of HepG2 cells to GEGR were determined to be 178 and 6.85 μg/ml, respectively. Significant reductions in the immunofluorescence intensity indicating apoptosis were also detected in the nuclei of HepG2 cells stained with 4’,6-diamidino-2-phenylindole and Annexin V after GEGR treatment. The Bax/Bcl-2 ratio and active caspase-3 level were higher in H₂O₂ + vehicle-treated cells. However, these levels gradually decreased to those of the No-treated group in the GEGR pretreated group even though little or no decrease was observed in response to low GEGR concentrations. Furthermore, the GEGR pretreated group showed a reduced level of 2’,7’-dichlorofluorescein diacetate stained cells, indicating ROS generation relative to the H₂O₂ + vehicle-treated group.

Conclusion:

The results of this study provide strong evidence that GEGR can prevent cell death induced by H₂O₂ in HepG2 cells through the induction of antioxidant conditions.

SUMMARY

The gallotannin (69.2%), gallic acid (26.6%), and methyl gallate (4.2%) are the main constituents of water extracts of GR

GEGR was more potent in DPPH scavenging, and gallotannin contributes to this extract activity

GEGR significantly reduced the increase of apoptosis, Bax/Bcl-2 ratio, and active caspase-3 level after H2O2 treatment

GEGR pretreatment showed protection against H₂O₂-induced ROS production in DCFH-DA staining analysis.

Abbreviations used: COX: Cyclooxygenase; DAPI: 4’,6-diamidino-2-phenylindole; DMSO: Dimethyl sulfoxide; DPPH: 2,2-diphenyl-1-picrylhydrazyl; GEGR: Gallotannin-enriched Galla Rhois; GR: Galla Rhois; HPLC: High-performance liquid chromatography; H₂O₂: Hydrogen peroxide; MMP: Metallopeptidase; MTT: 3-(4,5 dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide; ROS: Reactive oxygen species; UV-Vis: Ultraviolet-visible.

Evaluation of the inhibitory effects of eckol and dieckol isolated from edible brown alga Eisenia bicyclis on human monoamine oxidases A and B

Eckol and dieckol are important phlorotannins found in edible brown algae including Eisenia bicyclis, Ecklonia stolonifera, and others. Inhibition of monoamine oxidase (MAO) play an important role in the early management of Parkinson's disease (PD). The aim of this study was to determine the effectiveness of eckol and dieckol isolated from the methanolic extract of E. bicyclis against PD by the inhibition of human MAO-A and MAO-B (hMAO-A and hMAO-B). A sensitive enzyme-based chemiluminescent assay and kinetics methods were used to investigate enzyme inhibition and mode of inhibition. A molecular docking simulation was performed to clarify the binding characteristics of eckol and dieckol to hMAO-A and hMAO-B. The results suggested that methanolic extract of E. bicyclis and its isolated phlorotannins, eckol and dieckol, have potent inhibitory activity against hMAO-A and hMAO-B. The enzyme-based kinetics results demonstrated eckol mixed and non-competitive inhibition of hMAO-A and hMAO-B, respectively, while dieckol non-competitively inhibited both hMAOs. Molecular docking simulation predicted that eckol and dieckol exhibit higher binding affinity towards hMAO-A and hMAO-B through hydrogen bonding and hydrophobic interactions. These findings implicate eckol and dieckol as inhibitors of hMAOs that might be of potential value in the management of PD.

Protective Effects of Ecklonia stolonifera Extract on Ethanol-Induced Fatty Liver in Rats

Chronic alcohol consumption causes alcoholic liver disease, which is associated with the initiation of dysregulated lipid metabolism. Recent evidences suggest that dysregulated cholesterol metabolism plays an important role in the pathogenesis of alcoholic fatty liver disease. Ecklonia stolonifera (ES), a perennial brown marine alga that belongs to the family Laminariaceae, is rich in phlorotannins. Many studies have indicated that ES has extensive pharmacological effects, such as antioxidative, hepatoprotective, and antiinflammatory effects. However, only a few studies have investigated the protective effect of ES in alcoholic fatty liver. Male Sprague-Dawley rats were randomly divided into normal diet (ND) (fed a normal diet for 10 weeks) and ethanol diet (ED) groups. Rats in the ED group were fed a Lieber-DeCarli liquid diet (containing 5% ethanol) for 10 weeks and administered ES extract (50, 100, or 200 mg/kg/day), silymarin (100 mg/kg/day), or no treatment for 4 weeks. Each treatment group comprised of eight rats. The supplementation with ES resulted in decreased serum levels of triglycerides (TGs), total cholesterol, alanine aminotransferase, and aspartate aminotransferase. In addition, there were decreases in hepatic lipid and malondialdehyde levels. Changes in liver histology, as analyzed by Oil Red O staining, showed that the ES treatment suppressed adipogenesis. In addition, the ES treatment increased the expression of fatty acid oxidation-related genes (e.g., PPAR-α and CPT-1) but decreased the expression of SREBP 1, which is a TG synthesis-related gene. These results suggest that ES extract may be useful in preventing fatty acid oxidation and reducing lipogenesis in ethanol-induced fatty liver.

MicroRNA134 Mediated Upregulation of JNK and Downregulation of NFkB Signalings Are Critically Involved in Dieckol Induced Antihepatic Fibrosis

Though Dieckol, a phlorotannin of Ecklonia cava, was known to have antioxidant, anticancer, antidiabetic, and anti-inflammatory effects, the underlying antifibrotic mechanism of Dieckol still remains unclear until now. Thus, in the current study, the inhibitory mechanism of Dieckol on liver fibrosis was elucidated mainly in hepatic stellate cells (HSCs). Dieckol exerted cytotoxicity in LX-2, HSC-T6, and HepG2 cells with the reduced fibrosis features of large, spread out, and flattened polygonal shapes in LX-2 cells compared to untreated control. Dieckol attenuated the expression of α-SMA and TGF-β1, increased sub-G1 phase population, and induced caspase-3 activation and cleavages of PARP in HSCs. Furthermore, Dieckol decreased phosphorylation of ERK, p38, AKT, NF-kB, and IkB and activated the microRNA(miR)134 level and JNK phosphorylation in HSCs. Conversely, JNK inhbitor SP600125 reversed the effect of Dieckol on PARP, p-NF-kB, α -SMA, and p-JNK in LX-2 cells. Likewise, miR134 overexpression mimic enhanced phosphorylation of JNK and NF-kB and reduced the expression of α-SMA and PARP cleavage, while miR134 inhibitor reversed the ability of Dieckol to cleave PARP and attenuate the expression of α-SMA in LX-2 cells. Overall, our findings suggest that Dieckol suppresses liver fibrosis via caspase activation and miR134 mediated JNK activation and NF-kB inhibition.

Protective effect of fucosterol isolated from the edible brown algae, Ecklonia stolonifera and Eisenia bicyclis, on tert-butyl hydroperoxide- and tacrine-induced HepG2 cell injury

OBJECTIVES

Fucosterol is the primary sterol found in brown algae. Recently, considerable interest has been generated regarding fucosterol due to its potential antioxidant, anti-inflammatory and antidiabetic effects. The aim of this study was to investigate the protective effects of fucosterol on tert-butyl hydroperoxide (t-BHP)- and tacrine-induced oxidative stress in HepG2 cells.

METHODS

Fucosterol by itself exhibited no cytotoxicity at concentrations below 100 μm by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay. The increased intracellular reactive oxygen species (ROS) and decreased glutathione levels observed in t-BHP- and tacrine-treated HepG2 cells were ameliorated by fucosterol pretreatment, indicating that the protective effects of fucosterol are mediated by the induction of cellular defence mechanisms against oxidative stress. Moreover, elevated alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels in tacrine-treated mice were significantly reduced after oral administration of fucosterol.

KEY FINDINGS

The hepatoprotective effects of fucosterol may occur via an increase in the hepatic level of glutathione and a decrease in ROS production, thereby preventing hepatic damage and the resultant increases in ALT and AST activity.

CONCLUSION

These results suggest that fucosterol may be an effective hepatoprotective agent that could be useful for preventive therapies against oxidative stress-related hepatotoxicity.

Protective effect of the edible brown alga Ecklonia stolonifera on doxorubicin-induced hepatotoxicity in primary rat hepatocytes

OBJECTIVES

As part of our efforts to isolate anti-hepatotoxic agents from marine natural products, we screened the ability of 14 edible varieties of Korean seaweed to protect against doxorubicin-induced hepatotoxicity in primary rat hepatocytes.

METHODS

Among the crude extracts of two Chlorophyta (Codium fragile and Capsosiphon fulvescens), seven Phaeophyta (Undaria pinnatifida, Sargassum thunbergii, Pelvetia siliquosa, Ishige okamurae, Ecklonia cava, Ecklonia stolonifera and Eisenia bicyclis), five Rhodophyta (Chondrus ocellatus, Gelidium amansii, Gracilaria verrucosa, Symphycladia latiuscula and Porphyra tenera), and the extracts of Ecklonia stolonifera, Ecklonia cava, Eisenia bicyclis and Pelvetia siliquosa exhibited significant protective effects on doxorubicin-induced hepatotoxicity, with half maximal effective concentration (EC50) values of 2.0, 2.5, 3.0 and 15.0 μg/ml, respectively.

KEY FINDINGS

Since Ecklonia stolonifera exhibits a significant protective potential and is frequently used as foodstuff, we isolated six phlorotannins, including phloroglucinol (1), dioxinodehydroeckol (2), eckol (3), phlorofucofuroeckol A (4), dieckol (5) and triphloroethol-A (6). Phlorotannins 2 ∼ 6 exhibited potential protective effects on doxorubicin-induced hepatotoxicity, with corresponding EC50 values of 3.4, 8.3, 4.4, 5.5 and 11.5 μg/ml, respectively.

CONCLUSION

The results clearly demonstrated that the anti-hepatotoxic effects of Ecklonia stolonifera and its isolated phlorotannins are useful for further exploration and development of therapeutic modalities for treatment of hepatotoxicity.

Anti-adipogenic activity of the edible brown alga Ecklonia stolonifera and its constituent fucosterol in 3T3-L1 adipocytes

Fucosterol is a sterol metabolite of brown algae and regulates genes involved with cholesterol homeostasis. As a part of our continuous search for anti-obesity agents from natural marine sources, the anti-adipogenic activities of Ecklonia stolonifera and its sterol, fucosterol, were evaluated for the inhibition of adipocyte differentiation and lipid formation. Oil Red O staining was used to evaluate triglyceride contents in 3T3-L1 pre-adipocytes primed by differentiation medium (DM) I and DM II. The methanolic extract of E. stolonifera showed strong anti-adipogenic activity, and was thus fractionated with several solvents. Among the tested fractions, the dichloromethane (CH2Cl2) fraction was found to be the most active fraction, with significant inhibition (40.5 %) of intracellular lipid accumulation at a non-toxic concentration, followed by the ethyl acetate fraction (30.2 %) at the same concentration, while the n-butanol and water fractions did not show inhibitory activity within the tested concentrations. The strong anti-adipogenic CH2Cl2-soluble fraction was further purified by a repeated chromatography to yield fucosterol. Fucosterol reduced lipid contents in a concentration-dependent manner without showing any cytotoxicity. Fucosterol treatment also yielded a decrease in the expression of the adipocyte marker proteins peroxisome proliferator-activated receptor γ (PPARγ) and CCAAT/enhancer-binding protein α (C/EBPα) in a concentration-dependent manner. Taken together, these results suggest that fucosterol inhibits expression of PPARγ and C/EBPα, resulting in a decrease of lipid accumulation in 3T3-L1 pre-adipocytes, indicating that the potential use of E. stolonifera and its bioactive fucosterol as an anti-obesity agent.

Effects of laver extracts on adhesion, invasion, and migration in SK-Hep1 human hepatoma cancer cells

The laver (Porphyra tenera), red seaweed, has been reported to have anticancer activity, but little is known about its molecular mechanisms of action. The objective of this study was to determine the effects of laver extract on cancer cell proliferation, invasion, and metastasis in SK-Hep1 cells using migration and invasion assays. We also investigated the relationship of MMP-2/-9 and TIMP-1/-2 expression at both the protein and gene level in SK-Hep1 human hepatoma carcinoma cells after laver extract treatment. Laver extract inhibited cancer cell growth in a dose-dependent manner. In an invasion assay conducted in Transwell chambers, laver extract showed 19.6 and 27.2% inhibition of cancer cell at 200 and 400 μg/mL, respectively, compared to the control. The mRNA levels of both MMP-2 and MMP-9 were down-regulated by laver extract treatment in a dose-dependent manner. Laver extract, at 400 μg/mL, was inhibited by MMP-2 and MMP-9 expressions by 70.1 and 77.0%, respectively. An inverse relationship in the mRNA contents of MMP-2/-9 and TIMP-1/-2 expressions in SK-Hep1 cells was found by laver extract treatment. Our results demonstrate antimetastatic properties of laver extract in inhibiting the adhesion, invasion, and migration of SK-Hep1 human hepatoma cancer cells.

Phlorotannins isolated from the edible brown alga Ecklonia stolonifera exert anti-adipogenic activity on 3T3-L1 adipocytes by downregulating C/EBPα and PPARγ

The dramatic increase in obesity-related diseases emphasizes the need to elucidate the cellular and molecular mechanisms underlying fat metabolism. Inhibition of adipocyte differentiation has been suggested to be an important strategy for preventing or treating obesity. In our previous study, we characterized an Ecklonia stolonifera extract and non-polar fractions thereof, including dichloromethane and ethyl acetate fractions. We showed that these fractions inhibited adipocyte differentiation and lipid formation/accumulation in 3T3-L1 preadipocytes, as assessed by Oil Red O staining. As part of our ongoing search for anti-obesity agents derived from E. stolonifera, in this work, we characterized five known phlorotannins, including phloroglucinol, eckol, dieckol, dioxinodehydroeckol, and phlorofucofuroeckol A, all of which were isolated from the active ethyl acetate fraction of E. stolonifera. We determined the chemical structures of these phlorotannins through comparisons of published nuclear magnetic resonance (NMR) spectral data. Furthermore, we screened these phlorotannins for their abilities to inhibit adipogenesis over a range of concentrations (12.5-100 μM). Of these five phlorotannins, phloroglucinol, eckol, and phlorofucofuroeckol A significantly concentration-dependently inhibited lipid accumulation in 3T3-L1 cells without affecting cell viability. In addition, the five isolated phlorotannins also significantly reduced the expression levels of several adipocyte marker genes, including proliferator activated receptor γ (PPARγ) and CCAAT/enhancer-binding protein α (C/EBPα), although they did so to different extents. These results suggest that the molecular weight of a phlorotannin is an important factor affecting its ability to inhibit adipocyte differentiation and modulate the expression levels of adipocyte marker genes.

Antiulcer, wound healing and hepatoprotective activities of the seaweeds Gracilaria crassa, Turbinaria ornata and Laurencia papillosa from the southeast coast of India

Seaweeds have bioactive compounds of interest in the pharmaceutical industry. In India, seaweeds are used exclusively for phycocolloids production and have not yet received consideration as a dietary supplement. So, it has become imperative to explore the biomedical potential of seaweeds and promote their utilization as a functional food. The seaweeds Turbinaria ornata, Gracillaria crassa and Laurencia papillosa, collected from the Tuticorin coast of the Southeast coast of India and selected based on preliminary screening, were extracted with acetone and evaluated for antiulcer, wound healing and hepatoprotective activities. L. papillosa showed the highest level of gastric protection activity (81%) at 200 mg/kg, comparable to the standard drug ranitidine (90%). G. crassa followed with 76%. G. crassa and L. papillosa, showed marked wound-healing activity. G. crassa at 200 mg/kg, showed a marked effect on the serum marker enzymes indicating prominent hepatoprotective activity. The noteworthy wound-healing and hepato-protective properties of G. crassa besides anti-ulcer activity next to L. papillosa were indicative of its potential for further consideration.

Anti-inflammatory activity of edible brown alga Eisenia bicyclis and its constituents fucosterol and phlorotannins in LPS-stimulated RAW264.7 macrophages

Although individual phlorotannins contained in the edible brown algae have been reported to possess strong anti-inflammatory activity, the responsible components of Eisenia bicyclis have yet to be fully studied. Thus, we evaluated their anti-inflammatory activity via inhibition against production of lipopolysaccharide (LPS)-induced nitric oxide (NO) and tert-butylhydroperoxide (t-BHP)-induced reactive oxygen species (ROS), along with suppression against expression of inducible nitric oxide synthase (iNOS), and cyclooxygenase-2 (COX-2), in RAW 264.7 cells. The anti-inflammatory activity potential of the methanolic extract and its fractions of E. bicyclis was in the order of dichloromethane>methanol>ethyl acetate>n-butanol. The strong anti-inflammatory dichloromethane fraction was further purified to yield fucosterol. From the ethyl acetate fraction, six known phlorotannins were isolated: phloroglucinol, eckol, dieckol, 7-phloroeckol, phlorofucofuroeckol A and dioxinodehydroeckol. We found that these compounds, at non-toxic concentrations, dose-dependently inhibited LPS-induced NO production. Fucosterol also inhibited t-BHP-induced ROS generation and suppressed the expression of iNOS and COX-2. These results indicate that E. bicyclis and its constituents exhibited anti-inflammatory activity which might attribute to inhibition of NO and ROS generation and suppression of the NF-κB pathway and can therefore be considered as a useful therapeutic and preventive approach to various inflammatory and oxidative stress-related diseases.

Determination of major phlorotannins in Eisenia bicyclis using hydrophilic interaction chromatography: seasonal variation and extraction characteristics

In this study, a hydrophilic interaction chromatography (HILIC) condition was developed for the simultaneous determination of five major phlorotannins from an extract of Eisenia bicyclis (Kjellman) Setchell with good linearity (r(2)>0.999). Based on this method, the seasonal variations and extraction characteristics, in terms of total extraction yield and the content of the phlorotannins, were investigated under various extraction conditions. In results, the yields and phlorotannins were increased two-to-four times in summer (June-October) and then, were decreased to normal levels in winter (November-March). In the extraction of E. bicyclis, ethanol percentage in water, extraction time and washing time significantly affected the yield of the extract and the phlorotannins, whereas the temperature and the sample/solvent ratio impacted the extraction to a lesser degree. These results will be useful information in the application of this macroalga in the commercial areas related to nutraceuticals, pharmaceuticals, and cosmeceuticals.

Anti-inflammatory activity of edible brown alga Saccharina japonica and its constituents pheophorbide a and pheophytin a in LPS-stimulated RAW 264.7 macrophage cells

Anti-inflammatory activity of Saccharina japonica and its active components was evaluated via in vitro inhibitory activities against lipopolysaccharide (LPS)-induced nitric oxide (NO) production, inducible nitric oxide synthase (iNOS), and cyclooxygenase-2 (COX-2) expression in RAW 264.7 murine macrophage cells. Since the methanolic extract of S. japonica showed strong anti-inflammatory activity, it was fractionated with several solvents. Among the fractions, the ethyl acetate fraction demonstrated the highest inhibition of LPS-induced NO production (IC50=25.32μg/mL), followed by the CH2Cl2 fraction (IC50=75.86μg/mL). Considering the yield and anti-inflammatory potential together, the CH2Cl2 fraction was selected for chromatographic separation to yield two active porphyrin derivatives, pheophorbide a and pheophytin a, together with an inactive fucoxanthin. In contrast to fucoxanthin, pheophorbide a and pheophytin a showed dose-dependent inhibition against LPS-induced NO production at nontoxic concentrations in RAW 264.7 cells. Both compounds also suppressed the expression of iNOS proteins, while they did not inhibit the COX-2 expression in LPS-stimulated macrophages. These results indicate that pheophorbide a and pheophytin a are two important candidates of S. japonica as anti-inflammatory agents which can inhibit the production of NO via inhibition of iNOS protein expression. Thus, these compounds hold great promise for use in the treatment of various inflammatory diseases.

Hepatoprotection by chemical constituents of the marine brown alga Spatoglossum variabile: a relation to free radical scavenging potential

CONTEXT

In the course of searching hepatoprotective agents from natural sources, the protective effect of chemical constituents of the marine brown alga Spatoglossum variabile Figaro et DE Notar (Dictyoaceae) against CCl₄-induced liver damage in Wistar rats was investigated. The compounds were first investigated for in vitro radical scavenging potential and were also tested for β-glucuronidase inhibition to further explore the relationship between hepatoprotection and antiradical potential.

METHODS

The compounds cinnamic acid esters 1 and 2 and aurone derivatives 3 and 4 were first investigated for in vitro radical scavenging potential against 1,1-diphenyl-2-picrylhydrazyl radicals (DPPH), and superoxide anion radicals. In vivo hepatoprotective studies were performed in seven groups (n = 6) of Wistar rats. The test groups were pretreated with compounds (10 mg/kg body weight, po) orally for 30 min before the intraperitoneal administration of a dose of 20% CCl₄ diluted with dietary cooking oil. Moreover, compounds were also tested for β-glucuronidase inhibition to explore the relationship between hepatoprotection and radical scavenging potential.

RESULTS

The test compounds 1-4 were found to exhibit antiradical activity against 1,1-diphenyl-2-picrylhydrazyl radicals with IC₅₀ values ranging between 54 and 138 µM, whereas aurone derivatives 3 and 4 additionally exhibited superoxide anion scavenging effects with IC₅₀ values of 95 and 87 µM, respectively. In addition, these compounds were found to be weak inhibitors of xanthine oxidase (IC₅₀ ≥1000 µM). In animal model, pretreatment with compounds 2-4 significantly blocked the CCl₄-induced increase in the levels of the serum biochemical markers.

CONCLUSION

It appears that the hepatoprotection afforded by these compounds was mainly due to their radical scavenging activity that protected the cells from the free radicals generated by CCl₄-induced hepatotoxicity.

Anti-inflammatory effects of phlorofucofuroeckol B-rich ethyl acetate fraction obtained from Myagropsis myagroides on lipopolysaccharide-stimulated RAW 264.7 cells and mouse edema

Myagropsis myagroides has been used as a Chinese medicine and its extract has shown various biological activities, however, its anti-inflammatory mechanism remains unknown. In this study, we investigated the inhibitory effects of the ethyl acetate fraction of M. myagroides (EFM) on the production of inflammatory mediators and pro-inflammatory cytokines in lipopolysaccharides (LPS)-stimulated RAW 264.7 cells. EFM significantly inhibited LPS-induced production of nitric oxide (NO), prostaglandin E(2), and pro-inflammatory cytokines in a dose-dependent manner and suppressed the production of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 in RAW 264.7 cells. Inhibitory effect of EFM on iNOS expression and NO production was further confirmed using LPS-activated mouse peritoneal macrophages. EFM treatment strongly suppressed the activation of nuclear factor-kappa B (NF-κB) by suppressing phosphorylation of Akt and extracellular signal-regulated kinases (ERKs). EFM as well as phlorofucofuroeckol B (PFF-B), a major compound isolated from EFM, reduced ear edema induced by phorbol 12-myristate 13-acetate in mice. These results indicate that the anti-inflammatory effect of EFM, rich in PFF-B, on LPS-stimulated macrophages is regulated by the inhibition of NF-κB pathway through the inhibition of ERKs and Akt phosphorylation in LPS-stimulated macrophage cells.

Cytoprotective effects of phlorofucofuroeckol A isolated from Ecklonia stolonifera against tacrine-treated HepG2 cells

We have recently reported that phlorofucofuroeckol A isolated from Ecklonia stolonifera showed potential antioxidative and anti-inflammatory properties in LPS-stimulated macrophages. This study aims to investigate the cytoprotective effect of phlorofucofuroeckol A and to characterize its molecular mechanisms using tacrine-treated HepG2 cells. Phlorofucofuroeckol A showed a cytoprotective effect against tacrine-treated HepG2 cells in a dose-dependent manner (EC(50): 5.7±0.5 μM). Increased intracellular reactive oxygen species (ROS) by tacrine were decreased by phlorofucofuroeckol A. The cytotoxicity of tacrine to HepG2 cells was associated with upregulations of Fas and JNK phosphorylation resulted in the caspase activations and apoptosis. Phlorofucofuroeckol A inhibited the phosphorylation of JNK and the expression of Fas-mediated apoptotic proteins including Fas ligand, cleaved caspase-8, cleaved caspase-3, and poly (ADP-ribose) polymerase. In addition, treatment of phlorofucofuroeckol A regulated the release of cytochrome c from mitochondria to cytosol in a dose-dependent manner in tacrine-treated HepG2 cells. Furthermore, pretreatment of an inhibitor of JNK, SP600125, downregulated Fas and cleaved caspase-3 without change of ROS productions in tacrine-treated HepG2 cells. In conclusion, our study demonstrated that phlorofucofuroeckol A regulates Fas-mediated apoptosis via inhibition of ROS productions and inhibition of JNK phosphorylation in tacrine-treated HepG2 cells.

Dioxinodehydroeckol inhibits melanin synthesis through PI3K/Akt signalling pathway in α-melanocyte-stimulating hormone-treated B16F10 cells

Antimelanogenic activity has previously been reported in ethyl acetate fraction of Ecklonia stolonifera. In this study, using the isolated dioxinodehydroeckol from the fraction, we sought to investigate an antimelanogenic signalling pathway in α-melanocyte-stimulating hormone (α-MSH)-stimulated B16F10 melanoma cells. Treatment with dioxinodehydroeckol inhibited the cellular melanin contents and expression of melanogenesis-related proteins, including microphthalmia-associated transcription factor (MITF), tyrosinase and tyrosinase-related proteins TRP-1 and TRP-2. Moreover, dioxinodehydroeckol stimulated phosphorylation of Akt in a dose-dependent manner without affecting phosphorylation of ERK. These data suggest that dioxinodehydroeckol reduces melanin synthesis through the MITF regulation dependent upon PI3K/Akt signalling pathway.

Isolation and identification of phlorotannins from Ecklonia stolonifera with antioxidant and hepatoprotective properties in tacrine-treated HepG2 cells

Four kinds of phlorotannins having antioxidant activity were isolated from the ethyl acetate fraction of Ecklonia stolonifera ethanolic extract. The structures of the phlorotannins were determined on the basis of spectroscopic evidence, including 1D and 2D nuclear magnetic resonance. The isolated phlorotannins showed potential radical-scavenging activities against 2,2-diphenyl-1-picrylhydrazyl and suppressed the intracellular reactive oxygen species in tacrine-treated HepG2 cells. Among them, eckol and 2-phloroeckol showed hepatoprotective activity in tacrine-treated HepG2 cells; however, phlorofucofuroeckol B and 6,6'-bieckol did not show the activity, even though having high antioxidant activity. Both eckol and 2-phloroeckol inhibited the expression of Fas-mediated cell-death proteins, including tBid, caspase-3, and poly(ADP-ribose) polymerase, and suppressed the release of cytochrome c from mitochondria to cytosol in a dose-dependent manner in tacrine-treated HepG2 cells. These results suggest that eckol and 2-phloroeckol are the principal hepatoprotective constituents of the ethyl acetate fraction of E. stolonifera ethanolic extract.

Effects of 12-week oral supplementation of Ecklonia cava polyphenols on anthropometric and blood lipid parameters in overweight Korean individuals: a double-blind randomized clinical trial

The effects of 12-week supplementation with a polyphenol extract from Ecklonia cava (ECP) on anthropometry, serum biochemistry and hematology have been investigated. Ninety-seven overweight male and female adults (average age 40.5 ± 9.2 yr and body mass index (BMI) of 26.5 ± 1.6 kg/m²) were enrolled in a randomized, double-blind, placebo-controlled trial with parallel-group design. Subjects were randomly allocated into three groups designated as PC (placebo), LD (low-dose, 72 mg-ECP/day) and HD (high-dose, 144 mg-ECP/day). Both LD and HD groups showed significant decreases in BMI, body fat ratio, waist circumference, waist/hip ratio, total cholesterol, low-density lipoprotein (LDL) cholesterol, total cholesterol/high-density lipoprotein (HDL) cholesterol and atherogenic index (AI) after 12 weeks, as compared with the placebo group. The HD group also showed a significant increase in serum HDL cholesterol as compared with the placebo group. Only the HD group showed significant decreases in serum glucose and systolic blood pressure after 12 weeks. There was no significant adverse event related with ingestion of ECP, and serum biochemical and hematological parameters were maintained within normal range during the intervention period. In conclusion, these results demonstrated that ECP supplementation significantly contributed to lowering body fat and serum lipid parameters such as total and LDL cholesterols with dose dependence. Further studies using different populations, dosages or biological markers are highly recommended to better understand the physiological features of this polyphenol.

Isolation of phlorotannins from Eisenia bicyclis and their hepatoprotective effect against oxidative stress induced by tert-butyl hyperoxide

Eisenia bicyclis (Kjellman) Setchell is a common brown alga that inhabits the middle Pacific coast around Korea and Japan. In this study, the ethanol extract and its serial solvent fractions were prepared from fresh E. bicyclis, and their hepatoprotective effects were investigated against hepatotoxicity in tert-butyl hyperoxide(t-BHP)-injured HepG2 cells. When these samples were used at a dose of 10-40 μg/mL⁻¹, they significantly protected the t-BHP-induced cell death in HepG2 cells. Among fractions, ethyl acetate fraction (EF) and n-butanol extract (BF) exhibited potent hepatoprotective activities (62.60% for EF and 64.86% for BF) in t-BHP-injured HepG2 cells at a concentration of 10 μg/mL⁻¹. To find the potential factors for this activity, the samples were characterized on total phenolics, chlorophylls, carotenoids, and radical scavenging activity. Among them, EF showed the highest content of total phenolics and the strongest antioxidant activity both in on- and offline assays. Five phlorotannin compounds, oligomers of phloroglucinol, were isolated chromatographically from this fraction and structurally identified by (1)H-NMR and liquid chromatography-electrospray ionization-mass spectrometry analyses as eckol(1), 6,6'-bieckol(2), 8,8'-bieckol(3), dieckol(4), and phlorofucofuroeckol A(5). Compound 5 among five purified compounds showed the strongest protective activity (45.54%) at a concentration of 10 μM. At the high dose (40 μM), the protective activities of three compounds (compound 2, 4, and 5) were higher than that of quercetin treated with 10 μM concentration. Therefore, we can speculate that they can be developed as potential candidates for natural hepatoprotective agents.

Potential pharmacological applications of polyphenolic derivatives from marine brown algae

Recently, the isolation and characterization of the biologically active components from seaweeds have gained much attention from various research groups across the world. The marine algae have been studied for biologically active components and phlorotannins are one among them. Among marine algae, brown algal species such as Ecklonia cava, Eisenia arborea, Ecklonia stolinifera and Eisenia bicyclis have been studied for their potential biological activities. Majority of the investigations on phlorotannins derived from brown algae have exhibited their potentiality as antioxidant, anti-inflammatory, antidiabetic, antitumor, antihypertensive, anti-allergic, hyaluronidase enzyme inhibition and in matrix metalloproteinases (MMPs) inhibition activity. In this review, we have made an attempt to discuss the potential biological activities of phlorotannins from marine brown algae and their possible candidature in the pharmaceutical applications.

Phlorofucofuroeckol A inhibits the LPS-stimulated iNOS and COX-2 expressions in macrophages via inhibition of NF-κB, Akt, and p38 MAPK

We have recently reported that phlorofucofuroeckol A isolated from the edible brown algae Ecklonia stolonifera showed potential antioxidative and anti-inflammatory properties in macrophage stimulated by LPS treatments. In this study, we further investigated the pharmacological characteristic of phlorofucofuroeckol A in regulations of inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX)-2 through regulatory and signaling pathways using LPS-treated RAW 264.7 cells. Treatment with 20 μM of phlorofucofuroeckol A significantly decreased levels of iNOS and COX-2 mRNA induced by LPS stimulation. As results, levels of pro-inflammatory cytokines such as interleukin (IL)-1β, IL-6 and tumor necrosis factor (TNF)-α were significantly reduced by treatments of phlorofucofuroeckol A in LPS-stimulated RAW 264.7 cells. Phlorofucofuroeckol A inhibited promoter activities of inflammatory-mediators (iNOS and COX-2) and transcriptional factors (nuclear factor-κB, NF-κB, and AP-1) in LPS-treated RAW 264.7 cells. Moreover, phlorofucofuroeckol A inhibited activation of Akt and p38 MAPK in LPS-treated RAW 264.7 cells. These results indicate that the phlorofucofuroeckol A regulates iNOS and COX-2 expressions through the NF-κB-dependent transcriptional control associated with inhibition of multiple signaling proteins, suggesting potential candidates of phloroglucinol derivatives for treatments of inflammatory diseases.

Protein tyrosine phosphatase 1B and α-glucosidase inhibitory Phlorotannins from edible brown algae, Ecklonia stolonifera and Eisenia bicyclis

The present work investigates protein tyrosine phosphatase 1B (PTP1B) and the α-glucosidase inhibitory activities of two edible brown algae, Ecklonia stolonifera and Eisenia bicyclis, as well as in their isolated phlorotannins. Since the individual extracts and fractions showed significant inhibitory activities, column chromatography was performed to isolate six phlorotannins, phloroglucinol (1), dioxinodehydroeckol (2), eckol (3), phlorofurofucoeckol-A (4), dieckol (5), and 7-phloroeckol (6). Phlorotannins 3-6 were potent and noncompetitive PTP1B inhibitors with IC(50) values ranging from 0.56 to 2.64 µM; 4-6 exhibited the most potent α-glucosidase inhibition with IC(50) values ranging from 1.37 to 6.13 µM. Interestingly, 4 and 6 were noncompetitive, while 5 exhibited competitive inhibition in an α-glucosidase assay. E. stolonifera and E. bicyclis as well as their isolated phlorotannins therefore possessed marked PTP1B and α-glucosidase inhibitory activities; this could lead to opportunities in the development of therapeutic agents to control the postprandial blood glucose level and thereby prevent diabetic complications.

Biological importance of marine algae

Marine organisms are potentially prolific sources of highly bioactive secondary metabolites that might represent useful leads in the development of new pharmaceutical agents. Algae can be classified into two main groups; first one is the microalgae, which includes blue green algae, dinoflagellates, bacillariophyta (diatoms)… etc., and second one is macroalgae (seaweeds) which includes green, brown and red algae. The microalgae phyla have been recognized to provide chemical and pharmacological novelty and diversity. Moreover, microalgae are considered as the actual producers of some highly bioactive compounds found in marine resources. Red algae are considered as the most important source of many biologically active metabolites in comparison to other algal classes. Seaweeds are used for great number of application by man. The principal use of seaweeds as a source of human food and as a source of gums (phycocollides). Phycocolloides like agar agar, alginic acid and carrageenan are primarily constituents of brown and red algal cell walls and are widely used in industry.

Antidiabetic and antioxidant effects of polyphenols in brown alga Ecklonia stolonifera in genetically diabetic KK-A(y) mice

The dietary intake and control of blood glucose levels are very important in hyperglycemic patients and alpha-glucosidase inhibitors are a cost-effective means to preventing the progression of diabetes. In search of a natural inhibitor from food materials, alpha-glucosidase inhibitory activity and the anti-hyperglycemic effects of a brown alga, Ecklonia stolonifera, were investigated using non-insulin dependent diabetic mice. Methanolic extract of E. stolonifera (MEE), which contains a high content of polyphenols, showed strong inhibition of alpha-glucosidase in vitro. Male KK-A(y) mice, a genetically non-insulin dependent diabetic model, showed hyperglycemia with aging, but the ingestion of MEE suppressed the increase in plasma glucose and lipid peroxidation levels in unfasted KK-A(y) mice dose dependently. In KK-A(y) mice, which were fed the MEE diet for 4 weeks, MEE moderated the elevation of plasma glucose levels after the oral administration of maltose. The polyphenols in MEE were estimated to be phlorotannins by HPLC-PDA and LC/MS analyses. These results demonstrate that E. stolonifera, seaweed typically used as a health food, has strong antidiabetic and antioxidant effects in vivo, thus, it may have beneficial properties in the prevention of diabetes and could be useful in the development of an antidiabetic pharmaceutical and functional food.

Anti-hyperlipidemic effect of an edible brown algae, Ecklonia stolonifera, and its constituents on poloxamer 407-induced hyperlipidemic and cholesterol-fed rats

We conducted this study to isolate novel anti-hyperlipidemic agents derived from natural marine products. To accomplish this, we investigated the effects of ethanolic (EtOH) extracts of Ecklonia stolonifera and its phlorotannin constituents, eckol and dieckol, on serum lipid levels in rats with hyperlipidemia that was induced by a high-cholesterol diet or poloxamer 407. Treatment with the EtOH extracts of E. stolonifera and its phlorotannin-rich ethyl acetate (EtOAc) and n-butanol (n-BuOH) fractions induced a significant reduction in triglycerides (TG), total cholesterol (TC), and low-density lipoprotein-cholesterol (LDL-C) levels, as well as a significant increase in the high-density lipoprotein-cholesterol (HDLC) level in hyperlipidemic rats. However, treatment with the water (H(2)O) fraction did not exert any significant effects on the serum levels of hyperlipidemic rats. In addition, eckol and dieckol isolated from the active EtOAc fraction induced a significant reduction in serum TG, TC, and LDL-C levels, as well as in the atherogenic index (A.I.). Furthermore, treatment with dieckol induced a greater decrease in the serum TG, TC, and LDL-C levels of hyperlipidemic rats than eckol or lovastatin, as well as an increase in the serum HDL-C levels. Taken together, these results suggest that phlorotannins such as eckol and dieckol have the potential for use for the prevention of hyperlipidemic atherosclerosis.

Marine natural products

This review covers the literature published in 2005 for marine natural products, with 704 citations (493 for the period January to December 2005) referring to compounds isolated from marine microorganisms and phytoplankton, green algae, brown algae, red algae, sponges, coelenterates, bryozoans, molluscs, tunicates and echinoderms. The emphasis is on new compounds (812 for 2005), together with their relevant biological activities, source organisms and country of origin. Biosynthetic studies, first syntheses, and syntheses that lead to the revision of structures or stereochemistries, have been included.