Fucoidan from sea cucumber protects against high-fat high-sucrose diet-induced hyperglycaemia and insulin resistance in mice

A comprehensive review of sulfated fucan from sea cucumber: Antecedent and prospect

Sulfated fucan from sea cucumber is mainly consists of L-fucose and sulfate groups. Recent studies have confirmed that the structure of sulfated fucan mainly consists of repeating units, typically tetrasaccharides. However, there is growing evidence indicating the presence of irregular domains with heterogeneous units that have not been extensively explored. Moreover, as a key contributor to the nutritional benefits of sea cucumbers, sulfated fucan demonstrates a range of biological activities, such as anti-inflammatory, anticancer, hypolipidemic, anti-hyperglycemic, antioxidant, and anticoagulant properties. These biological activities are profoundly influenced by the structural features of sulfated fucan including molecular weight and distribution patterns of sulfate groups. The latest research indicates that sulfated fucan is dispersed in the extracellular matrix of the body wall of sea cucumbers. This article aimed to review the research progress on the in-situ distribution, structures, structural elucidation strategies, functions, and structure-activity relationships of sulfated fucan, especially in the last decade. It also provided insights into the major challenges and potential solutions in the research and development of sulfated fucan. Moreover, the fucanase and carbohydrate binding modules are anticipated to play pivotal roles in advancing this field.

Anti-obesity and anti-diabetic bioactive peptides: A comprehensive review of their sources, properties, and techno-functional challenges

The scourge of obesity arising from obesogens and poor dieting still ravages our planet as half of the global population may be overweight and obese by 2035. This metabolic disorder is intertwined with type 2 diabetes (T2D), both of which warrant alternative therapeutic options other than clinically approved drugs like orlistat with their tendency of abuse and side effects. In this review, we comprehensively describe the global obesity problem and its connection to T2D. Obesity, overconsumption of fats, the mechanism of fat digestion, obesogenic gut microbiota, inhibition of fat digestion, and natural anti-obesity compounds are discussed. Similar discussions are made for diabetes with regard to glucose regulation, the diabetic gut microbiota, and insulinotropic compounds. The sources and production of anti-obesity bioactive peptides (AOBPs) and anti-diabetic bioactive peptides (ADBPs) are also described while explaining their structure-function relationships, gastrointestinal behaviors, and action mechanisms. Finally, the techno-functional applications of AOBPs and ADBPs are highlighted.

Structural investigation of Fun168A unraveling the recognition mechanism of endo-1,3-fucanase towards sulfated fucan

BACKGROUND

Sulfated fucan has gained interest due to its various physiological activities. Endo-1,3-fucanases are valuable tools for investigating the structure and establishing structure-activity relationships of sulfated fucan. However, the substrate recognition mechanism of endo-1,3-fucanases towards sulfated fucan remains unclear, limiting the application of endo-1,3-fucanases in sulfated fucan research.

SCOPE AND APPROACH

This study presented the first crystal structure of endo-1,3-fucanase (Fun168A) and its complex with the tetrasaccharide product, utilizing X-ray diffraction techniques. The novel subsite specificity of Fun168A was identified through glycomics and nuclear magnetic resonance (NMR).

KEY FINDINGS AND CONCLUSIONS

The structure of Fun168A was determined at 1.92 Å. Residues D206 and E264 acted as the nucleophile and general acid/base, respectively. Notably, Fun168A strategically positioned a series of polar residues at the subsites ranging from -2 to +3, enabling interactions with the sulfate groups of sulfated fucan through salt bridges or hydrogen bonds. Based on the structure of Fun168A and its substrate recognition mechanisms, the novel subsite specificities at the -2 and +2 subsites of Fun168A were identified. Overall, this study provided insight into the structure and substrate recognition mechanism of endo-1,3-fucanase for the first time and offered a valuable tool for further research and development of sulfated fucan.

Potential Application of Marine Fucosyl-Polysaccharides in Regulating Blood Glucose and Hyperglycemic Complications

Diabetes mellitus (DM) has become the world's third major disease after tumors and cardiovascular disease. With the exploitation of marine biological resources, the efficacy of using polysaccharides isolated from marine organisms in blood glucose regulation has received widespread attention. Some marine polysaccharides can reduce blood glucose by inhibiting digestive enzyme activity, eliminating insulin resistance, and regulating gut microbiota. These polysaccharides are mainly fucose-containing sulphated polysaccharides from algae and sea cucumbers. It follows that the hypoglycemic activity of marine fucosyl-polysaccharides is closely related to their structure, such as their sulfate group, monosaccharide composition, molecular weight and glycosidic bond type. However, the structure of marine fucosyl-polysaccharides and the mechanism of their hypoglycemic activity are not yet clear. Therefore, this review comprehensively covers the effects of marine fucosyl-polysaccharides sources, mechanisms and the structure-activity relationship on hypoglycemic activity. Moreover, the potential regulatory effects of fucosyl-polysaccharides on vascular complications caused by hyperglycemia are also summarized in this review. This review provides rationales for the activity study of marine fucosyl-polysaccharides and new insights into the high-value utilization of marine biological resources.

Characterization of an endo-1,3-fucanase from marine bacterium Wenyingzhuangia aestuarii: The first member of a novel glycoside hydrolase family GH174

Sulfated fucans are important marine polysaccharides with various biological and biomedical activities. Fucanases are favorable tools to establish the structure-activity relationships of sulfated fucans. Herein, gene fun174A was discovered from the genome of marine bacterium Wenyingzhuangia aestuarii OF219, and none of the pre-defined glycosidic hydrolase domains were predicted in the protein sequence of Fun174A. Recombinant Fun174A demonstrated a low optimal reaction pH at 5.5. It might degrade sulfated fucans in an endo-processive manner. Glycomics and NMR analyses proved that it specifically hydrolyzed α-1,3-l-fucoside bonds between 2-O-sulfated and non-sulfated fucose residues in the sulfated fucan from sea cucumber Isostichopus badionotus. D119, E120 and E218 were critical for the activity of Fun174A, as identified by site-directed mutagenesis. Three homologs of Fun174A were confirmed to exhibit endo-1,3-fucanase activities. The novelty on sequences of Fun174A and its homologs reveals a new glycoside hydrolase family, GH174.

Discovery of a sulfated fucan-specific carbohydrate-binding module: The first member of a new carbohydrate-binding module family

Sulfated fucan is an important functional polysaccharide with various physiological activities. Carbohydrate-binding module (CBM) is a representative class of carbohydrate-binding protein, which could be employed as a favorable tool for the investigations and applications of polysaccharides. Nevertheless, only one confirmed sulfated fucan-binding CBM has been hitherto reported. In the present study, an unknown domain with a predicted β-sandwich fold was discovered from a fucanase Fun174A, and further cloned and heterologously expressed in Escherichia coli. The expressed protein Fun174A-CBM displayed a specific binding capacity to sulfated fucan. The bio-layer interferometry assays showed that the protein could bind to the sulfated fucan tetrasaccharide with an affinity constant of 2.83 × 10^-4 M. Fun174A-CBM shared no significant sequence similarity to any identified CBMs, indicating that it represents a new CBM family. The discovery of Fun174-CBM and the novel CBM family would be beneficial to the investigations of sulfated fucan-binding proteins.

Sulfated fucan could serve as a species marker of sea cucumber with endo-1,3-fucanase as the essential tool

In the past few decades, sulfated fucan from sea cucumber had attracted considerable interest owing to its abundant physiological activities. Nevertheless, its potential for species discrimination had not been investigated. Herein, particular attention was given to sea cucumber Apostichopus japonicus, Acaudina molpadioides, Holothuria hilla, Holothuria tubulosa, Isostichopus badionotus and Thelenota ananas to examine the feasibility of sulfated fucan as a species marker of sea cucumber. The enzymatic fingerprint suggested that sulfated fucan exhibited significant interspecific discrepancy and intraspecific stability, which revealed that sulfated fucan could serve as the species marker of sea cucumber, by utilizing the overexpressed endo-1,3-fucanase Fun168A and the ultra-performance liquid chromatography-high resolution mass spectrum. Moreover, oligosaccharide profile of sulfated fucan was determined. The oligosaccharide profile combined with hierarchical clustering analysis and principal components analysis further confirmed that sulfated fucan could serve as a marker with a satisfying performance. Besides, load factor analysis showed that the minor structure of sulfated fucan also contributed to the sea cucumber discrimination, besides the major structure. The overexpressed fucanase played an indispensable role in the discrimination, due to its specificity and high activity. The study would lead to a new strategy for species discrimination of sea cucumber based on sulfated fucan.

Therapeutic Effect of Fucoidan on Metabolic Diseases: Experimental Data and Clinical Evidence

The rising prevalence of metabolic diseases represents a major challenge to public health worldwide. Therefore, there is a strong need to conduct research on the effectiveness of complementary and alternative therapies for metabolic disorders. Fucoidan is a fucose-enriched and sulfated polysaccharide extracted from ubiquitous brown seaweed. The antihypertensive, antidiabetic, antiobesity, and hypolipidemic effects of fucoidan have been reported in preclinical research and clinical trials. This study aims to review the mechanisms of action and the experimental and clinical use of different types of fucoidan for the treatment of metabolic diseases.

Structure and hypoglycemic effect of a neutral polysaccharide isolated from sea cucumber Stichopus japonicus

In addition to its high nutritious value, sea cucumber has been recognized by folk medicine for a long time. This study investigated the structure and hyperglycemic activity of a neutral polysaccharide (NPsj) from sea cucumber Stichopus japonicus, whose molecular weight was determined as 301.75 kDa by HPGPC method. Monosaccharide composition analysis indicated that NPsj is a glucan. The structure of NPsj was obtained by combining the analysis of methylation analysis, FTIR, NMR, periodate oxidation, Smith degradation and ESI-MS, which is mainly composed of (1 → 4)-α-d-glucoses with β-d-glucose(1→) branches substituted at O-6 every 7-9 of 1,4 linked glucoses. An in vitro insulin resistance Hep G2 cells model and a 3 T3-L1 cells model were established, and the NPsj has significant effect to increase glucose consumption with no toxicity at 10-100 μg/mL. Furthermore, NPsj upregulates the phosphorylation of Akt1 and down-regulated GSK3β, and then reduces the phosphorylation of GS, indicating its mechanism of ameliorating insulin resistance via Akt/GSK3β/GS signaling pathway.

Hypolipidemic effect of chromium-modified enzymatic product of sulfated rhamnose polysaccharide from Enteromorpha prolifera in type 2 diabetic mice

Sulfated rhamnose polysaccharide (SRP) derived from Enteromorpha prolifera is a metal-ion chelating agent that could potentially be used to treat diabetes. The aim of our study was to determine the effect of a variant of SRP on DIABETES. First, we synthesized and characterized SRPE-3 chromium(III) [SRPE-3-Cr(III)] complex using an enzymatic method. The maximum chelation rate was 18.2% under optimal chelating conditions of pH 6.0, time 4 h, and temperature 60 °C. Fourier transform infrared spectroscopy results showed important sites for Cr(III)-binding were O-H and C=O groups. We then studied the hypolipidemic effects of SRPE-3-Cr(III) on type 2 diabetes mellitus (T2DM) induced by a high-fat, high-sucrose diet (HFSD). Decreased blood glucose content, body fat ratio, serum TG, TC, LDL-C, and increased serum HDL-C were observed after treatment with SRPE-3-Cr(III). In addition, SRPE-3-Cr(III) significantly reduced leptin, resistin, and TNF-α levels, and increased adiponectin contents relative to T2DM. Histopathology results also showed that SRPE-3-Cr(III) could alleviate the HFSD-lesioned tissues. SRPE-3-Cr(III) also improved lipid metabolism via a reduction in aspartate aminotransferase, alanine aminotransferase, fatty acid synthase, and acetyl-CoA carboxylase activities in the liver. SRPE-3-Cr(III) at low doses exhibited better lipid-lowering activities, hence, could be considered to be a novel compound to treat hyperlipidemia and also act as an anti-diabetic agent.

Fucoidan ameliorates glucose metabolism by the improvement of intestinal barrier and inflammatory damage in type 2 diabetic rats

It has been reported that fucoidan possesses anti-diabetic activities by inhibiting α-glucosidase activity, improving β-cell dysfunction, and enhancing insulin sensitivity. However, as a macromolecular carbohydrate, fucoidan is rarely absorbed and indigestible in gastrointestinal tract. The study aimed to explore whether the fucoidan can regulate glucose metabolism by improving intestinal barrier and inflammation in type 2 diabetes mellitus (T2DM) rats. A high-fat diet combined with streptozotocin was used to induce T2DM rats. Different doses of fucoidan (50, 100 and 200 mg/kg) were administered respectively by lavage to T2DM rats for 8 weeks and saline was given to controls. The results showed that in addition to hyperglycemia and hyperlipidemia, T2DM rats were also characterized by increased intestinal permeability and proinflammatory cytokines. Notably, fucoidan reduced fasting blood glucose and insulin resistance index along with alleviated the accumulation of proinflammatory cytokines in T2DM rats. Furthermore, fucoidan repaired the intestinal barrier function, which was accompanied by the up-regulation of tight junction proteins and the improvement of intestinal inflammation via inhibiting TLR4/NF-κB signaling. Meanwhile, fucoidan also mitigated the liver damage, and alleviated insulin resistance by activating PI3K/AKT signaling. Collectively, these findings supported the potential of fucoidan to be used as a functional ingredient to prevent T2DM.

Seaweeds as Ingredients to Lower Glycemic Potency of Cereal Foods Synergistically-A Perspective

Seaweeds are traditional food ingredients mainly in seaside regions. Modern food science and nutrition researchers have identified seaweed as a source of functional nutrients, such as dietary soluble and insoluble fibers, proteins, omega-3 fatty acids, prebiotic polysaccharides, polyphenols, and carotenoids. Owing to the rich nutrients, seaweeds and seaweed extract can be used as functional ingredients by modifying the nutrients composition to reduce the proportion of available carbohydrates, delaying the gastric emptying time and the absorption rate of glucose by increasing the digesta viscosity, and attenuating the digesting rate by blocking the activity of digestive enzymes. This review presents the concept of using seaweed as unconventional ingredients that can function synergistically to reduce the glycemic potency of cereal products.

Antidiabetic potential of seaweed and their bioactive compounds: a review of developments in last decade

Diabetes Mellitus is a public health problem worldwide due to high morbidity and mortality rate associated with it. Diabetes can be managed by synthetic hypoglycemic drugs, although their persistent uses have several side effects. Hence, there is a paradigm shift toward the use of natural products having antidiabetic potential. Seaweeds, large marine benthic algae, are an affluent source of various bioactive compounds, including phytochemicals and antioxidants thus exhibiting various health promoting properties. Seaweed extracts and its bioactive compounds have antidiabetic potential as they inhibit carbohydrate hydrolyzing enzymes in vitro and exhibit blood glucose lowering effect in random and post prandial blood glucose tests in vivo. In addition, they have been associated with reduced weight gain in animals probably by decreasing mRNA expression of pro-inflammatory cytokines with concomitant increase in mRNA expression levels of anti-inflammatory cytokines. Their beneficial effect has been seen in serum and hepatic lipid profile and antioxidant enzymes indicating the protective role of seaweeds against free radicals mediated oxidative stress induced hyperglycemia and associated hyperlipidemia. However, the detailed and in-depth studies of seaweeds as whole, their bioactive isolates and their extracts need to be explored further for their health benefits and wide application in food, nutraceutical and pharmaceutical industries.

Fucoidan protects pancreas and improves glucose metabolism through inhibiting inflammation and endoplasmic reticulum stress in T2DM rats

It is important to maintain the normal function of pancreas in the prevention and intervention of type 2 diabetes mellitus (T2DM). This study was undertaken to explore the protective effects...

Low Molecular Weight, 4-O-Sulfation, and Sulfation at Meta-Fucose Positively Promote the Activities of Sea Cucumber Fucoidans on Improving Insulin Resistance in HFD-Fed Mice

Fucoidans from sea cucumber (SC-FUC) have been proven to alleviate insulin resistance in several species. However, there are few studies that clarify the relationship between their structure and bioactivity. The present study evaluated the influence of molecular weight (Mw), sulfation concentrations (Cs), and sulfation position on improving insulin resistance using SC-FUC. Results showed that fucoidans with lower Mw exerted stronger effects. Having a similar Mw, Acaudina molpadioides fucoidans (Am-FUC) with lower Cs and Holothuria tubulosa fucoidans with higher Cs showed similar activities. However, Isostichopus badionotus fucoidans (higher Cs) activity was superior to that of low-Mw Thelenota ananas fucoidans (Ta-LFUC, lower Cs). Eliminating the effects of Mw and Cs, the bioactivity of Am-FUC with sulfation at meta-fucose exceeded that of Ta-FUC with sulfation at ortho-position. Moreover, the effects of Pearsonothuria graeffei fucoidans with 4-O-sulfation were superior to those of Am-LFUC with 2-O-sulfation. These data indicate that low Mw, 4-O-sulfation, and sulfation at meta-fucose contributed considerably to insulin resistance alleviation by SC-FUC, which could accelerate the development of SC-FUC as a potential food supplement to alleviate insulin resistance.

Acaudina molpadioides mediates lipid uptake by suppressing PCSK9 transcription and increasing LDL receptor in human liver cells

Acaudina molpadioides has been long used as traditional medicinal resources and reported to demonstrate various important bioactivities such as anticoagulation, antithrombosis, anti-hyperglycemia and anticancer. However, its lipid lowering activity is yet to be fully explored. Proprotein convertase subtilisin/kexin type 9 (PCSK9) is an enzyme that enhances the lysosomal degradation of hepatic low density lipoprotein receptor (LDLR) resulting in excessive accumulation of the plasma levels of LDL-cholesterols (LDL-C) which subsequently accelerate atherosclerosis. In the present study, A. molpadioides fractions were subjected to promoter-reporter luciferase assay to determine its role as PCSK9 inhibitors. It was found both fractions (EFA and EFB) reduced the transcriptional activity of PCSK9 promoter. Among the seven 5′end deletion constructs of PCSK9 promoter, fragments D1 (−1,711/−94), D3 (−709/−94) and D4 (−440/−94), were suppressed in the presence of both fractions whereas D2 (−1,214/−94), and, D6 (−351/−94) as well as D7 (−335/−94) were inhibited only by EFA and EFB, respectively. Further transcription factor binding sites prediction using MatInspector software discovered various potential cis-regulatory elements namely, PPAR, KLFs, RBPJ-kappa and SREBP that may potentially be involved in ameliorating the transcriptional activity of PCSK9. Immunofluorescence staining was used to evaluate the effects of both fractions on LDL-C and LDLR. Results showed that levels of LDL-C uptake in EFA-treated cells were 69.1% followed by EFB at 32.6%, as compared to untreated control after 24 h treatment. The LDLR protein distribution was induced by 62.41% and 32.2%, which corresponded to an increase in LDL-C uptake in both EFA and EFB treatment, respectively. Hence, the inhibition of PCSK9 by bioactive compounds in EFA and EFB could be another promising therapeutic agent in reducing the cholesterol levels and atherosclerosis by targeting PCSK9.

Utilizing heterologously overexpressed endo-1,3-fucanase to investigate the structure of sulfated fucan from sea cucumber (Holothuria hilla)

Sea cucumber sulfated fucan (SC-FUC) attracted increasing interests in the recent decades. Endo-1,3-fucanase has been employed in the structural clarification and structure-function relationship investigations of SC-FUC. Nevertheless, the preparation of wild-type endo-1,3-fucanase is costly and time-consuming, which hinders its further utilization. In this study, a heterologously overexpressed endo-1,3-fucanase (FunA) was introduced into structural identification of SC-FUC. FunA was efficiently prepared within one day and utilized in the investigation of sulfated fucan from sea cucumber Holothuria hilla (Hh-FUC). By using enzymatic degradation, glycomics and NMR analysis, the major structure of Hh-FUC was identified to be composed of a tetrasaccharide repeating unit →3-α-l-Fucp-1 → 3-α-l-Fucp2,4(OSO₃^-)-1 → 3-α-l-Fucp2(OSO₃^-)-1 → 3-α-l-Fucp2(OSO₃^-)-1→. Due to the efficient acquisition of enzyme and the superior oligosaccharide recovery, 0.6 mL of E. coli broth and 10 mg of Hh-FUC were sufficient for the structural identification. The results demonstrated the superiority of heterologously overexpressed fucanase over its wild-type enzyme in structural investigation of sulfated fucan.

Hypoglycemic and hypolipidemic effects of total glycosides of Cistanche tubulosa in diet/streptozotocin-induced diabetic rats

ETHNOPHARMACOLOGICAL RELEVANCE

Cistanche tubulosa (Schrenk) R. Wight (Orobanchaceae) is a frequently prescribed component in many traditional herbal prescriptions which are used to treat diabetes in China. In recent studies, the antidiabetic activity of Cistanche tubulosa extracts have been confirmed. However, no systematic investigation has been reported on the total glycosides of Cistatnche tubulosa (TGCT).

AIM OF THE STUDY

The present study aimed to investigate the hypoglycemic and hypolipidemic effects of TGCT and the potential mechanisms in diet/streptozotocin (STZ)-induced diabetic rats, and to chemically characterize the main constituents of TGCT.

MATERIALS AND METHODS

The major constituents of TGCT were characterized by HPLC/Q-TOF-MS and the analytical quantification was performed with HPLC-DAD. Type 2 diabetic rats were induced by high-fat high-sucrose diet (HFSD) and a single injection of STZ (30 mg/kg). TGCT (50 mg/kg, 100 mg/kg and 200 mg/kg) or metformin (200 mg/kg) were orally administered for 6 weeks. Body weight and calorie intake were monitored throughout the experiment. Fasting plasma glucose (FPG), oral glucose tolerance test (OGTT), area under curve of glucose (AUC-G), glycosylated hemoglobin (HbA1c), fasting insulin, serum C-peptide, glycogen content and insulin sensitivity index were tested. The levels of phosphorylated protein kinase B and phosphorylated glycogen synthase kinase 3β, the activities of hexokinase and pyruvate kinase were assayed. Meanwhile, the changes in serum lipid profiles, superoxide dismutase, glutathione peroxidase, malondialdehyde and inflammatory factors were measured. Histological of pancreas were also evaluated by haematoxylin-eosin stain.

RESULTS

Our investigation revealed the presence of phenylethanoid glycosides (PhGs): echinacoside (500.19 ± 11.52 mg/g), acteoside (19.13 ± 1.44 mg/g) and isoacteoside (141.82 ± 5.78 mg/g) in TGCT. Pharmacological tests indicated that TGCT significantly reversed STZ-induced weight loss (11.1%, 200 mg/kg); decreased FPG (56.4%, 200 mg/kg) and HbA1c (37.4%, 200 mg/kg); ameliorated the OGTT, AUC-G and insulin sensitivity; increased glycogen content (40.8% in liver and 52.6% in muscle, 200 mg/kg) and the activities of carbohydrate metabolizing enzymes; regulated lipid profile changes and the activities of antioxidant enzymes; diminished serum markers of oxidative stress and inflammation in a dose-dependent manner (p < 0.05).

CONCLUSIONS

This study confirmed that TGCT was an effective nutritional agent for ameliorating hyperglycemia and hyperlipidemia in diet/STZ-induced diabetic rats, which might be largely attributed to the activities of TGCT on inhibitions of oxidative stress and inflammation.

Overview of key molecular and pharmacological targets for diabetes and associated diseases

Diabetes epidemiological quantities are demonstrating one of the most important communities' health worries. The essential diabetic difficulties are including cardiomyopathy, nephropathy, inflammation, and retinopathy. Despite developments in glucose decreasing treatments and drugs, these diabetic complications are still ineffectively reversed or prohibited. Several signaling and molecular pathways are vital targets in the new therapies of diabetes. This review assesses the newest researches about the key molecules and signaling pathways as targets of molecular pharmacology in diabetes and diseases related to it for better treatment based on molecular sciences. The disease is not cured by current pharmacological strategies for type 2 diabetes. While several drug combinations are accessible that can efficiently modulate glycemia and mitigate long-term complications, these agents do not reverse pathogenesis, and in practice, they are not established to modify the patient's specific molecular profiling. Therapeutic companies have benefited from human genetics. Genome exploration, which is agnostic to the information that exists, has revealed tens of loci that impact glycemic modulation. The physiological report has begun to examine subtypes of diseases, illustrate heterogeneity and propose biochemical therapeutic pathways.

Fucoidan Structure and Its Impact on Glucose Metabolism: Implications for Diabetes and Cancer Therapy

Fucoidans are complex polysaccharides derived from brown seaweeds which consist of considerable proportions of L-fucose and other monosaccharides, and sulphated ester residues. The search for novel and natural bioproduct drugs (due to toxicity issues associated with chemotherapeutics) has led to the extensive study of fucoidan due to reports of it having several bioactive characteristics. Among other fucoidan bioactivities, antidiabetic and anticancer properties have received the most research attention in the past decade. However, the elucidation of the fucoidan structure and its biological activity is still vague. In addition, research has suggested that there is a link between diabetes and cancer; however, limited data exist where dual chemotherapeutic efforts are elucidated. This review provides an overview of glucose metabolism, which is the central process involved in the progression of both diseases. We also highlight potential therapeutic targets and show the relevance of fucoidan and its derivatives as a candidate for both cancer and diabetes therapy.

Structure-function relationship analysis of fucoidan from sea cucumber (Holothuria tubulosa) on ameliorating metabolic inflammation

The structure-function relationships of sea cucumber fucoidan has been seldom investigated. In this study, the effect of fucoidan which extracted from sea cucumber Holothuria tubulosa (Ht-FUC) with different molecular weight and chain conformation (Ht1/2/3/4) in metabolic inflammation was investigated. A co-cultured system comprising adipocytes and macrophages was used to explore the impact in vitro. The high-fat high-sucrose diet (HFD)-fed obese mice model was established to verified the effect of Ht-FUC in vivo. The results demonstrated that all examined Ht-FUC attenuated the productions of inflammatory cytokines, promoted the M2 phenotypic polarization of co-cultured macrophage by activating PPARγ. Furthermore Ht-FUC impressed lipolysis of the co-cultured adipocytes by inhibiting TLR4/NF-κB-dependent pathway. In vivo, Ht-FUC especially reduced serum inflammation level, attenuated M1/M2 polarization of liver Kupffer cells, and attenuated inflammatory infiltration of epididymal adipose tissue. Consistently, Ht3 played the best effect, and may be more beneficial for the intervention of metabolic disease. PRACTICAL APPLICATIONS: In this study, the structure-function relationships of fucoidan extracted from Holothuria tubulosa (Ht-FUC) on ameliorating metabolic inflammation was investigated for the first time. In this research, we reported that Ht-FUC ameliorating metabolic inflammation by improving FFA-induced macrophage polarization and lipolysis in both co-cultured system and obese mice. The study provides some theoretical basis for the high-value utilization of Ht-FUC with different molecular weight.

Multifunctional role of fucoidan, sulfated polysaccharides in human health and disease: A journey under the sea in pursuit of potent therapeutic agents

Fucoidan is a complex polysaccharide (molecular weight 10,000-100,000 Da) derived from brown algae which comprises of L-fucose and sulfate groups have potential as therapeutic diligences against several human diseases. The fucoidan has expanded a widespread range of pharmacological properties as an anti-inflammatory, anticoagulant, antiangiogenic, immunomodulatory, anti-adhesive, anticancer, antidiabetic, antiviral and anti-neurodegenerative agents owing to their diverse chemical conformation and potent antioxidant activity. The antioxidant and immunomodulatory activities of the fucoidan contribute towards their disease preventive potency through dynamic modulation of key intracellular signalling pathways, regulation of ROS accumulation, and maintenance of principal cell survival and death pathways. Additionally, it also reduces cancer-associated cachexia. Despite the wide range of therapeutic potency, the fucoidan is heavily regarded as an unexplored plethora of druggable entities in the current situation. The isolation, screening, biological application, pre-clinical, and clinical assessment along with large scale cost-effective production remain a foremost task to be assessed. Moreover, the chemical synthesis of the present bioactive drug with confirmational rearrangement for enhanced availability and bioactivity also need tenacious investigation. Hence, in the present review, we give attention to the source of isolation of fucoidan, their principle strategic deployment in disease prevention, and the mechanistic investigation of how it works to combat different diseases that can be used for future therapeutic intervention.

Toxicological evaluation of Sargassum Wightii greville derived fucoidan in wistar rats: Haematological, biochemical and histopathological evidences

Objective

The present study aimed to investigate the acute and subacute toxicity profile of fucoidan obtained from Sargassum wightii Greville, a brown marine algae in order to assess its safety.

Methods

Fucoidan was isolated from Sargassum wightii Greviile and subjected to FTIR analysis to confirm the functional groups. In acute toxicity study, a single dose of fucoidan (2000 mg/kg) was orally administered to three female rats as per OECD guideline 423. OECD guidelines 407 was adopted for subacute toxicity study. Fucoidan was orally administered to male and female rats at doses of 100, 200 and 400 mg/kg. Hematological, biochemical and histopathological analyses were carried out.

Results

FTIR analysis confirmed the presence of major functional groups. The animals did not show any remarkable toxic signs or mortality in acute toxicity study at single oral administration of fucoidan at the dose of 2000 mg/kg bodyweight. In subacute toxicity, no statistically significant difference in body weight, relative weight of vital organs, food and water intake compared to the control group was observed. Serum glucose and cholesterol showed a statistically significant reduction at all the doses when compared to normal control and the reduction was in a dose dependent manner. There were no other changes observed in biochemical or haematological parameters. Histopathological analysis showed no significant toxic signs at organ levels in treated groups when compared to normal control.

Conclusions

Based on the results obtained from acute and subacute toxicity study, fucoidan is considered to be safe in the models tested, which encourages its long term administration for medicinal uses. This study supports the application of fucoidan as a traditional medicine.

Studying the effects of sea cucumber ovum powder on nonalcoholic fatty liver disease by proteomics techniques in a rat model

Sea cucumber is a valuable marine food that has antioxidant, anti-diabetic, and anti-obesity functionalities. Sea cucumber ovum (SCO) may contain functional components, however, it is considered to be a waste product during industrial processing. In order to make good use of SCO, this work investigated the effects of freeze-dried SCO powder on NAFLD, using a rat model, through iBT labeling proteomics techniques, tracking changes in the hepatic protein profiles of rats whose diets were supplemented with SCO powder. Male rats were fed with standard food, a high fat diet (HFD), or a HFD supplemented with 150 mg per kg BW or 450 mg per kg BW SCO powder for 6 weeks. Compared with the HFD, low-dose SCO supplementation in the diet could significantly reduce body weight gain and liver weight. Furthermore, in total, 5922 proteins were identified, and 767 proteins were found to be significantly different proteins (p < 0.05) among all four groups. Most of the significantly different proteins were related to apoptosis and lipid metabolism. Fadd, Dci, and Aif1 have been identified as key proteins in the pathways related to apoptosis, lipid metabolism, and inflammation. The results in this study provide an overview of the SCO-induced changes in the liver proteome of NAFLD, which may help us to understand the molecular mechanism behind the effects of SCO on the alleviation of NAFLD.

Sulfated fucan/fucosylated chondroitin sulfate-dominated polysaccharide fraction from low-edible-value sea cucumber ameliorates type 2 diabetes in rats: New prospects for sea cucumber polysaccharide based-hypoglycemic functional food

Sulfated fucan chondroitin sulfate-dominated polysaccharide fraction from low-edible-value sea cucumber may be a good alternative to high-edible-value sea cucumber-derived polysaccharide for application in hypoglycemic functional foods. To evaluate the potential effect of low-edible-value sea cucumber-derived polysaccharide fraction on type 2 diabetes (T2DM), two sulfated fucan/fucosylated chondroitin sulfate-dominated polysaccharide fractions screening from 10 global commercial low-edible-value sea cucumber species were investigated to identify their anti-diabetics efficacies using a high-fat diet and streptozotocin-induced T2DM rat model. Sulfated fucan-dominated polysaccharide fraction from Thelenota ananas and fucosylated chondroitin sulfate-dominated polysaccharide fraction from Cucumaria frondosa ameliorated hyperglycemia, restored hypertriglyceridemia and hypercholesterolemia, decreased inflammatory status and oxidative stress, protected against liver injury, as well as improved insulin resistance and promoted accumulation of hepatic glycogen by activating IRS/PI3K/AKT signaling and regulating GSK-3β gene expression in T2DM rats. The current findings provide an available strategy for the commercialization of sea cucumber polysaccharide based-hypoglycemic functional food.

Egg oil from Portunus trituberculatus alleviates insulin resistance through activation of insulin signaling in mice

Marine bioactive lipids have been utilized to overcome insulin resistance. However, oil from swimming crab has never been studied. Here, we analyzed the constituents of egg oil from Portunus trituberculatus (Pt-egg oil) and investigated its protective effects against insulin resistance in mice on a high-fat diet. The results showed that Pt-egg oil contained 52.05% phospholipids, 8.61% free fatty acids (especially eicosapentaenoic acid and docosahexaenoic acid), 32.38% triglyceride, 4.79% total cholesterol, and ditissimus astaxanthin. Animal experiments showed that Pt-egg oil significantly mitigated insulin resistance and was associated with reductions in blood glucose, insulin, glucose tolerance, insulin tolerance, serum lipids, and hepatic glycogen. Pt-egg oil activated the phosphatidylinositol 3-hydroxy kinase (PI3K)/protein kinase B (Akt)/glucose transporter 4 pathway in skeletal muscle both at the transcriptional level and at the translational level. Pt-egg oil also promoted hepatic glycogen synthesis through activation of the PI3K/Akt/glycogen synthase kinase-3 beta pathway. These indicate that Pt-egg oil can be used as an alternative to marine bioactive lipids to improve insulin resistance.

Therapeutic Effects of Fucoidan: A Review on Recent Studies

Fucoidan is a polysaccharide largely made up of l-fucose and sulfate groups. Fucoidan is favorable worldwide, especially amongst the food and pharmaceutical industry as a consequence of its promising therapeutic effects. Its applaudable biological functions are ascribed to its unique biological structure. Classical bioactivities associated with fucoidan include anti-oxidant, anti-tumor, anti-coagulant, anti-thrombotic, immunoregulatory, anti-viral and anti-inflammatory effects. More recently, a variety of in vitro and in vivo studies have been carried out to further highlight its therapeutic potentials. This review focuses on the progress towards understanding fucoidan and its biological activities, which may be beneficial as a future therapy. Hence, we have summarized in vitro and in vivo studies that were done within the current decade. We expect this review and a variety of others can contribute as a theoretical basis for understanding and inspire further product development of fucoidan.

Biological Activities of Fucoidan and the Factors Mediating Its Therapeutic Effects: A Review of Recent Studies

The marine acid polysaccharide fucoidan has attracted attention from both the food and pharmaceutical industries due to its promising therapeutic effects. Fucoidan is a polysaccharide that mainly consists of L-fucose and sulphate groups. Its excellent biological function is attributed to its unique biological structure. Classical activities include antitumor, antioxidant, anticoagulant, antithrombotic, immunoregulatory, antiviral and anti-inflammatory effects. More recently, fucoidan has been shown to alleviate metabolic syndrome, protect the gastrointestinal tract, benefit angiogenesis and bone health. This review focuses on the progress in our understanding of the biological activities of fucoidan, highlighting its benefits for the treatment of human disease. We hope that this review can provide some theoretical basis and inspiration for the product development of fucoidan.

Sulfated polysaccharide from sea cucumber modulates the gut microbiota and its metabolites in normal mice

Sulfated polysaccharide from sea cucumber (SCSP) has been demonstrated with various health effects, the mechanism of which, however, remains poorly understood. This study aimed to investigate the possible mechanism exhibited by gut microbiota in response to SCSP. BALB/c mice were fed diets supplemented with SCSP and depolymerized SCSP (d-SCSP) for 42 days. The microbiota composition, short chain fatty acids (SCFAs), lipopolysaccharide-binding protein (LBP), body weight and gut tissue index were analyzed. Results revealed that both SCSP and d-SCSP positively regulated the gut microbiota as indicated by the enriched microbiota diversity, SCFA-producing bacteria and sulfide-degrading bacteria, and decreased harmful bacteria. Moreover, SCSP and d-SCSP not only significantly improved the levels of microbial metabolites including SCFAs and LBP, but also effectively adjusted body weight and gut tissue index. The microbial metabolites were identified to strongly correlate with the growth performance using Pearson's correlation coefficient. We further showed that the modulating effect of SCSP on the gut microbiota was altered by free-radical depolymerization, while the microbial metabolites and related growth performance were not. These findings suggest that SCSP can be used as a gut microbiota manipulator for health promotion and alter the gut microbiota in a molecular weight (Mw) dependent manner.

Sialoglycoprotein from Gadous morhua eggs improve high bone turnover activity via down-regulating BMP-2/Smads and Wnt/β-catenin signal pathways

Abstract

The effect of sialoglycoprotein isolated from Gadous morhua eggs (Gm-SGP) on ovariectomized (OVX) induced osteoporosis, which is characterized by high bone turnover activity was investigated. Results revealed that Gm-SGP significantly increased bone mineral density, enhanced bone biomechanical properties and repaired the microstructure of the trabecular bone. Also, the treatment with Gm-SGP remarkably decreased biochemical marker contents or activities, such as serum BALP, PICP, BMP-2, TrACP, Cath-K, urine Ca and P, leading to the reduction in bone turnover. The elevation in the rate of bone formative process contributed in the increase of bone turnover. Both BMP-2/Smads and Wnt/β-catenin signaling pathways played an important role in osteogenesis. Gm-SGP suppressed the key factors expression in these two pathways such as BMP-2, Smad1, Smad4, Lrp-5b, Runx2, Osx, ALP, Col1, OCN and β-catenin. These findings might provide some theoretical basis for the application of Gm-SGP as a potential anti-osteoporotic drug or as functional food.

Graphical Abstract

Sialoglycoprotein isolated from eggs of Carassius auratus promotes fracture healing in osteoporotic mice

In this study, open tibial fracture surgery was performed on mice with ovariectomy induced osteoporosis to investigate the effect of a treatment with sialoglycoprotein isolated from Carassius auratus eggs (Ca-SGP) on fracture healing. Dynamic histological analysis showed that Ca-SGP promoted the generation of cartilage callus on day 5 post-surgery, then facilitated the transformation of the cartilage callus to bony callus on days 11 and 24 post-surgery, and enhanced the remodeling of bony callus on 35 day post-surgery. Moreover, Ca-SGP significantly decreased the secretion of TNF-α and IL-1β in serum on day 5 post-surgery, thus inhibiting the negative spread of the inflammatory reaction. On day 11 post-surgery, Ca-SGP clearly decreased the serum level and the mRNA expression of Aggrecan but also increased the secretion and the expression of VEGF and MMP13, thus promoting the degradation of the cartilage matrix and vascular invasion. On day 24 post-surgery, Ca-SGP remarkably increased the mRNA expression of osteogenesis markers Col1a and OCN, and increased callus BV/TV and Tb.N, this facilitating the formation of woven bone. On day 35 post-surgery, Ca-SGP enhanced the transformation of woven bone into lamellar bone and improved the callus biomechanical property. In conclusion, Ca-SGP promoted fracture healing in osteoporotic mice by accelerating endochondral ossification.

A fucoidan from sea cucumber Pearsonothuria graeffei with well-repeated structure alleviates gut microbiota dysbiosis and metabolic syndromes in HFD-fed mice

A high-fat diet (HFD) has been a major contributor to increasing morbidity caused by metabolic syndromes.

Sialoglycoprotein isolated from the eggs of Gadus morhua enhances fracture healing in osteoporotic mice

Osteoporosis is a common disease in the elderly, which is related to fracture healing delay. In this study, the effects of treatment with sialoglycoprotein isolated from the eggs of Gadus morhua (Gm-SGP) on tibial fracture healing in ovariectomized (OVX) osteoporotic female C57BL/6J mice for 56 days post-fracture were investigated. The result showed that Gm-SGP treatment significantly increased serum angiogenic factors and bone formation markers on day 5 and 11 post-fracture when compared with the OVX group. In addition, histological results in the Gm-SGP group showed a stronger endochondral ossification, a stronger bony consolidation and a stronger bony callus remodeling capability on day 11, 24 and 35 post-fracture, respectively, in comparison with the OVX group. Meanwhile, micro-computerized tomography revealed that the Gm-SGP group had stronger bony callus remodeling capability as evidenced by higher BV/TV and Tb.N but lower Tb.Sp and shorter lengths of callus maximum cross section than the OVX group on day 24 post-fracture. Besides, the tibial callus bending stiffness was significantly enhanced in the Gm-SGP group as compared with the OVX group on day 56 post-fracture. Moreover, gene expression suggested that Gm-SGP promoted vascular invasion and endochondral ossification on day 11 post-fracture as well as bone formation on day 11 and 24 post-fracture via up-regulating the expression of angiogenesis factors (including VEGF, PDGF and Ang1), entochondrostosis factors (including Col2a1, Aggrecan, Col10a1 and MMP-13) and osteogenesis markers (including Col1a1, BMP-2 and OCN). This research suggests that Gm-SGP significantly improve fracture healing which is delayed by OVX-induced osteoporosis. The present study may contribute to providing important implications for the utilization of Gm-SGP from fish eggs as a functional food to enhance fracture healing.

A high fat diet enriched with sea cucumber gut powder provides cardio-protective and anti-obesity effects in C57BL/6 mice

We have previously reported that sea cucumber (SC) inhibits fat accumulation and insulin resistance in 3T3-L1 cells. The present study investigated the anti-obesity and cardio-protective effects of SC freeze-dried gut powder using C57BL/6 as an animal model. Male mice were fed a normal chow diet, a high fat diet (HFD) or a HFD enriched with 2.5, 5 or 7.5% SC gut powder for 4, 8 and 12weeks. Diets enriched with SC caused a significant reduction in body weight gain and fat weight, compared to the HFD, without affecting food intake. Both 2.5% and 5% SC treatment showed a significant reduction in plasma glucose, triacylglycerol (TG), total cholesterol (TC) and non-esterified fatty acids, compared to the HFD. However, animals fed the 7.5% SC diet showed an increase in liver weight, liver TG and TC, compared to the HFD diet. Diets enriched with 2.5% SC caused an increase in adiponectin mRNA expression in adipose tissue and reduced plasma interleukin-6, compared to the HFD diet. Fecal cholesterol excretion increased after 2.5% SC treatment, coinciding with an increase in ATP-binding cassette-5 and -8 mRNA expression in the small intestine. Although both 2.5 and 5% SC treatment caused weight and fat reduction to a similar extent, 2.5% SC was more effective at improving the metabolic profile. None of the tested SC doses caused any toxic effects. Our findings demonstrate for the first time that SC freeze-dried gut powder has the potential as a nutraceutical to target obesity and related disorders.

Effects of Low-Molecular-Weight Fucoidan and High Stability Fucoxanthin on Glucose Homeostasis, Lipid Metabolism, and Liver Function in a Mouse Model of Type II Diabetes

The combined effects of low-molecular-weight fucoidan (LMF) and fucoxanthin (Fx) in terms of antihyperglycemic, antihyperlipidemic, and hepatoprotective activities were investigated in a mouse model of type II diabetes. The intake of LMF, Fx, and LMF + Fx lowered the blood sugar and fasting blood sugar levels, and increased serum adiponectin levels. The significant decrease in urinary sugar was only observed in LMF + Fx supplementation. LMF and Fx had ameliorating effects on the hepatic tissue of db/db mice by increasing hepatic glycogen and antioxidative enzymes, and LMF was more effective than Fx at improving hepatic glucose metabolism. As for glucose and lipid metabolism in the adipose tissue, the expression of insulin receptor substrate (IRS)-1, glucose transporter (GLUT), peroxisome proliferator-activated receptor gamma (PPARγ), and uncoupling protein (UCP)-1 mRNAs in the adipose tissue of diabetic mice was significantly upregulated by Fx and LMF + Fx, and levels of inflammatory adipocytokines, such as adiponectin, tumor necrosis factor-α (TNF-α), and interleukin-6 (IL-6), were significantly modulated only by LMF + Fx supplementation. The efficacy of LMF + Fx supplementation on the decrease in urinary sugar and on glucose and lipid metabolism in the white adipose tissue of db/db mice was better than that of Fx or LMF alone, indicating the occurrence of a synergistic effect of LMF and Fx.

Hypoglycemic effect of D-chiro-inositol in type 2 diabetes mellitus rats through the PI3K/Akt signaling pathway

In this investigation, a model of type 2 diabetes mellitus (T2DM) was used on Sprague-Dawley (SD) rats to clarify more details of the mechanism in the therapy of T2DM. D-chiro-inositol (DCI) was administrated to the diabetic rats as two doses [30, 60 mg/(kg·body weight·day)]. The biochemical indices revealed that DCI had a positive effect on hypoglycemic activity and promoted the glycogen synthesis. The rats in DCI high-dosage group had a blood glucose reduction rate of 21.5% after 5 weeks of treatment, and had insulin content in serum about 15.3 ± 2.37 mIU/L which was significantly decreased than diabetes control group. Real-time polymerase chain reaction (RT-PCR) results revealed that DCI gave a positive regulation on glycogen synthase (GS) and protein glucose transporter-4 (Glut4). Western blotting suggested that DCI could up-regulated the expression of the phosphatidylinositol-3-kinase (PI3K) p85, PI3Kp110, GS as well as the phosphorylation of protein kinase B (Akt) both in the liver and the skeletal muscle. The results also revealed that DCI enhanced the Glut4 expression on skeletal muscle. Above all, DCI played a positive role in regulating insulin-mediated glucose uptake through the PI3K/Akt signaling pathway in T2DM rats.