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Sargassum fusiforme polysaccharides (SFPs) are acidic polysaccharides that possess significant medicinal and commercial potential. This review aims to summarize recent advances in the structure, extraction methods, and diverse biological activities of SFPs, including their antioxidant, antitumor, immunomodulatory, antiviral, intestinal flora-regulating, and anti-diabetic properties. The key findings reveal the complex composition of polysaccharides, highlighting alginic acid, fucoidan, and laminaran as the primary constituents, and detailing their structural features. At the same time, the characteristics as well as the advantages and disadvantages of hot water extraction, acid extraction, alkali extraction, ultrasonic extraction, microwave extraction, and enzyme extraction were systematically compared. Finally, this review concludes by emphasizing the necessity for further research to elucidate the structure–function relationships of SFPs, optimize their extraction techniques, and provide a theoretical foundation for subsequent studies.

The high molecular weight and poor solubility of seaweed polysaccharides have limited their function and application. In this study, ultraviolet/hydrogen peroxide (UV/H2O2) treatment was used to prepare low-molecular-weight seaweed polysaccharides from Sargassum fusiforme. The effects of UV/H2O2 treatment on the physicochemical properties and anti-photoaging activity of S. fusiforme polysaccharides were studied. UV/H2O2 treatment effectively degraded polysaccharides from S. fusiforme (DSFPs), reducing their molecular weight from 271 kDa to 26 kDa after 2 h treatment. The treatment did not affect the functional groups in DSFPs but changed their molar percentage of monosaccharide composition and morphology. The effects of the treatment on the anti-photoaging function of S. fusiforme polysaccharides were investigated using human epidermal HaCaT cells in vitro. DFSPs significantly improved the cell viability and hydroxyproline secretion of UVB-irradiated HaCaT cells. In particular, DSFP-45 obtained from UV/H2O2 treatment for 45 min showed the best anti-photoaging effect. Moreover, DSFP-45 significantly increased the content and expression of collagen I and decreased those of pro-inflammatory cytokines, including interleukin-1β, interleukin-6, and tumor necrosis factor-α. Thus, UV/H2O2 treatment could effectively improve the anti-photoaging activity of S. fusiforme polysaccharides. These results provide some insights for developing novel and efficient anti-photoaging drugs or functional foods from seaweed polysaccharides.

Respiratory syncytial virus (RSV) is a leading cause of respiratory tract infections, particularly in infants and the older population, with limited effective treatments available. Cordycepin, lactoferrin, and Sargassum fusiforme polysaccharides (CLS) are natural compounds with antiviral and immunomodulatory properties. This study investigates the therapeutic potential of CLS in RSV infection. A murine model of RSV infection was used to evaluate the effects of CLS. Lung pathology was assessed by lung index, histology, and bronchoalveolar lavage fluid (BALF) albumin and LDH levels. Viral load was measured by RSV mRNA and protein expression. Alveolar macrophage depletion was achieved using clodronate liposomes, and macrophage polarization was analyzed via flow cytometry and RT-qPCR. CLS treatment improved lung pathology, reduced BALF injury markers, and decreased viral load. The therapeutic effects of CLS were abrogated by macrophage depletion, indicating a reliance on alveolar macrophages. CLS promoted M2-like macrophage polarization, increasing M2 markers and reducing M1 markers. , CLS reduced RSV-induced apoptosis and enhanced macrophage proliferation. CLS protects against RSV-induced lung injury by promoting M2-like macrophage polarization and reducing viral load. These findings support CLS as a potential therapeutic for RSV infections.

A low fasting blood glucose level is a common symptom in diabetes patients and can be induced by high-fat diet (HFD) feeding at an early stage, which may play important roles in the development of diabetes, but has received little attention. In this study, five polysaccharides were prepared from Sargassumfusiforme and their effects on HFD-induced fasting hypoglycemia and gut microbiota dysbiosis were investigated. The results indicated that C57BL/6J male mice fed an HFD for 4 weeks developed severe hypoglycemia and four Sargassumfusiforme polysaccharides (SFPs), consisting of Sf-2, Sf-3, Sf-3-1, and Sf-A, significantly prevented early fasting hypoglycemia without inducing hyperglycemia. Sf-1 and Sf-A could also significantly prevent HFD-induced weight gain. Sf-2, Sf-3, Sf-3-1, and Sf-A mainly attenuated the HFD-induced decrease in Bacteroidetes, and all five SFPs had a considerable influence on the relative abundance of Oscillospira, Mucispirillum, and Clostridiales. Correlation analysis revealed that the fasting blood glucose level was associated with the relative abundance of Mucispinllum and Oscillospira. Receiver operating characteristic analysis indicated that Mucispinllum and Oscillospira exhibited good discriminatory power (AUC = 0.745–0.833) in the prediction of fasting hypoglycemia. Our findings highlight the novel application of SFPs (especially Sf-A) in glucose homeostasis and the potential roles of Mucispinllum and Oscillospira in the biological activity of SFPs.

Hematopoietic damage is a serious side effect of cytotoxic drugs, and agents promoting hematopoiesis are quite important for decreasing the death rate in cancer patients. In our previous work, we prepared the simulated digestive product of fucoidan from Sargassum fusiforme, DSFF, and found that DSFF could activate macrophages. However, more investigations are needed to further evaluate whether DSFF could promote hematopoiesis in the chemotherapy process. In this study, the protective effect of DSFF (1.8–7.2 mg/kg, i.p.) on cyclophosphamide-induced hematopoietic damage in mice and the underlying mechanisms were investigated. Our results show that DSFF could restore the numbers of white blood cells, neutrophils, and platelets in the peripheral blood, and could also retard bone marrow cell decrease in mice with cyclophosphamide-induced hematopoietic damage. UPLC/Q-Extraction Orbitrap/MS/MS-based lipidomics results reveal 16 potential lipid biomarkers in a serum that responded to hematopoietic damage in mice. Among them, PC (20:1/14:0) and SM (18:0/22:0) were the key lipid molecules through which DSFF exerted protective actions. In a validation experiment, DSFF (6.25–100 μg/mL) could also promote K562 cell proliferation and differentiation in vitro. The current findings indicated that DSFF could affect the blood cells and bone marrow cells in vivo and thus showed good potential and application value in alleviating the hematopoietic damage caused by cyclophosphamide.

This study used microscopy-based quantitative enumeration to investigate the effects of large-scale Sargassum fusiforme cultivation on coastal water quality and phytoplankton communities. Data from April (cultivation period) and June (non-cultivation period) in 2018 and 2019 showed that cultivation increased pH and dissolved oxygen (DO). It also reduced nitrate–nitrogen (NO3–N), nitrite–nitrogen (NO2–N), phosphate–phosphorus (PO4–P), total phosphorus (TP), and silicate–silicon (SiO3–Si) concentrations. These changes indicate improved coastal water quality from S. fusiforme cultivation. Nutrient levels rose again during the non-cultivation period. This suggests that water purification decreased without cultivation. Cultivation also lowered the dominance of Skeletonema costatum. This led to a more diverse and stable phytoplankton community. Microscopic observation is valuable for quantifying larger phytoplankton species, and plays an important role in ecological monitoring. These findings provide insights for sustainable aquaculture and ecological restoration.

Sargassum fusiforme polysaccharides (SFPs) have multiple activities. The fermentation of S. fusiforme by Lactobacillus can alter its polysaccharide properties and biological activities. In this study, three different Lactobacillus species (Lactobacillus plantarum (LP), Lactobacillus acidophilus (LA), and Lactobacillus rhamnosus (LR)) were selected to ferment S. fusiforme. The polysaccharides SFP (unfermented) and FSFP (fermented by LP, LA, or LR denoted as LP-SFP, LA-SFP, and LR-SFP, respectively) were extracted, and their physicochemical properties and biological activities were investigated. According to the results, fermentation caused significant changes in the physicochemical properties and biological activities of SFP. Specifically, FSFP showed a significant increase in uronic acid and fucose content and a significant decrease in molecular weight; LA-SFP and LR-SFP had stronger DPPH scavenging abilities; LR-SFP had the strongest inhibition of ROS production and cell mortality; LP-SFP and LR-SFP significantly increased SOD activity in zebrafish; LA-SFP had a significant effect on the proliferation of Lactobacillus plantarum; LP-SFP had a significant effect on the proliferation of Lactobacillus rhamnosus; and LA-SFP had a stronger food-excretion-promoting activity. In conclusion, the fermentation of Lactobacillus for the preparation of SFPs can change the physicochemical properties of polysaccharides and has broad potential for improving their biological activity.

Seaweed polysaccharides represent a kind of novel gut microbiota regulator. The advantages and disadvantages of using cecal and fecal microbiota to represent gut microbiota have been discussed, but the regulatory effects of seaweed polysaccharides on cecal and fecal microbiota, which would benefit the study of seaweed polysaccharide-based gut microbiota regulator, have not been compared. Here, the effects of two Sargassum fusiforme polysaccharides prepared by water extraction (SfW) and acid extraction (SfA) on the cecal and fecal microbiota of high-fat diet (HFD) fed mice were investigated by 16S rRNA gene sequencing. The results indicated that 16 weeks of HFD dramatically impaired the homeostasis of both the cecal and fecal microbiota, including the dominant phyla Bacteroidetes and Actinobacteria, and genera Coriobacteriaceae, S24-7, and Ruminococcus, but did not affect the relative abundance of Firmicutes, Clostridiales, Oscillospira, and Ruminococcaceae in cecal microbiota and the Simpson’s index of fecal microbiota. Co-treatments with SfW and SfA exacerbated body weight gain and partially reversed HFD-induced alterations of Clostridiales and Ruminococcaceae. Moreover, the administration of SfW and SfA also altered the abundance of genes encoding monosaccharide-transporting ATPase, α-galactosidase, β-fructofuranosidase, and β-glucosidase with the latter showing more significant potency. Our findings revealed the difference of cecal and fecal microbiota in HFD-fed mice and demonstrated that SfW and SfA could more significantly regulate the cecal microbiota and lay important foundations for the study of seaweed polysaccharide-based gut microbiota regulators.

Brown seaweeds are known as important marine food sources, from which phytosterols have been recognized as functional food components with multiple health-beneficial effects. However, studies on phytosterol extraction and quantitation from edible brown seaweeds are limited. In the present work, extraction methods for seaweed phytosterols were compared and optimized by one-factor-at-one-time method and response surface methodology. Moreover, the quantitation method of total sterols and major sterol components, including fucosterol, saringosterol, and ostreasterol, was established and validated using 1H NMR. Furthermore, the developed extraction and determination methods were applied to investigate three common edible seaweeds from Japan (Hijiki, Wakame, and Kombu). As a result, the finally optimized conditions were ultrasound-assisted extraction with CHCl3-MeOH 2:3 for 15 min followed by saponification with 1.65 mL of 1.85 M KOH for 14.5 h. Based on the developed methods, phytosterols in three seaweeds were compared, and Hijiki showed an abundant total sterol amount (2.601 ± 0.171 mg/g DW), significantly higher than Wakame (1.845 ± 0.137 mg/g DW) and Kombu (1.171 ± 0.243 mg/g DW). Notably, the composition of the sterol components varied in different seaweeds. These findings might help the nutritional investigation and functional food development concerning phytosterols from seaweeds.

Lipid accumulation is a major factor in the development of non‐alcoholic fatty liver disease (NAFLD). Currently, there is a lack of intervention or therapeutic drugs against NAFLD. In this study, we investigated the ability of Sargassum fusiforme polysaccharide (SFPS) to reduce lipid accumulation induced by high sugar in HepG2 cells and Drosophila melanogaster larvae. The results indicated that SFPS significantly (p < .01) decreased the accumulation of lipid droplets in high sugar–induced HepG2 cells. Furthermore, SFPS also suppressed the expression of Srebp and Fas (genes involved in lipogenesis) and increased the expression of PPARɑ and Cpt1 (genes that participated in fatty acid β‐oxidation) in these cells. SFPS markedly reduced the content of triglyceride of the third instar larvae developed from D. melanogaster eggs reared on the high‐sucrose diet. The expression of the Srebp and Fas genes in the larvae was also inhibited whereas the expression of two genes involved in the β‐oxidation of fatty acids, Acox57D‐d and Fabp, was increased in the larval fat body (a functional homolog of the human liver). We also found that SFPS ameliorated developmental abnormalities induced by the high‐sucrose diet. These results of this study suggest that SFPS could potentially be used as a therapeutic agent for the prevention and treatment of NAFLD. In the present study, we first demonstrated that polysaccharide (SFPS) from medicinal and edible brown alga Sargassum fusiform showed lipid‐lowering activity by inhibiting lipogenesis and promoting fatty acid β‐oxidation in vitro and in vivo. We also found that high sugar–induced developmental retardation was ameliorated by SFPS activity. Meanwhile, SFPS is a natural phytochemical that reduces hepatic lipid accumulation, suggesting that it has potential applications in the prevention or treatment of nonalcoholic fatty liver disease and health promotion.