L-Fucose-Rich Sulfated Glycans from Edible Brown Seaweed: A Promising Functional Food for Obesity and Energy Expenditure Improvement

Abstract

The global obesity epidemic, exacerbated by the sedentary lifestyle fostered by the COVID-19 pandemic, presents a growing socioeconomic burden due to decreased physical activity and increased morbidity. Current obesity treatments show promise, but they often come with expensive medications, frequent injections, and potential side effects, with limited success in improving obesity through increased energy expenditure. This study explores the potential of a refined sulfated polysaccharide (SPSL), derived from the brown seaweed Scytosiphon lomentaria (SL), as a safe and effective anti-obesity treatment by promoting energy expenditure. Chemical characterization revealed that SPSL, rich in sulfate and L-fucose content, comprises nine distinct sulfated glycan structures. In vitro analysis demonstrated potent anti-lipogenic properties in adipocytes, mediated by the downregulation of key adipogenic modulators, including 5' adenosine monophosphate-activated protein kinase (AMPK) and peroxisome proliferator-activated receptor γ (PPARγ) pathways. Inhibiting AMPK attenuated the anti-adipogenic effects of SPSL, confirming its involvement in the mechanism of action. Furthermore, in vivo studies using zebrafish models showed that SPSL increased energy expenditure and reduced lipid accumulation. These findings collectively highlight the therapeutic potential of SPSL as a functional food ingredient for mitigating obesity-related metabolic dysregulation by promoting energy expenditure. Further mechanistic and preclinical investigations are warranted to fully elucidate its mode of action and evaluate its efficacy in obesity management, potentially offering a novel, natural therapeutic avenue for this global health concern.

Keywords: AMPK; Scytosiphon lomentaria; brown seaweed; energy expenditure; fucoidan; metabolic disorders; sulfated glycans; zebrafish.

Figure 1

Anti-adipogenic effect of the polysaccharide-rich SL hydrolysates using five different enzymes in 3T3-L1 cells. (A) Lipid accumulation percentage in ORO staining in 3T3-L1 cells treated with vehicle and five different samples during adipocyte differentiation and enzymatic hydrolysate yields. NT: untreated; DF: differentiated control; SL: S. lomentaria; Blank: No enzyme-assisted SL hydrolysis; SLA: AMG-assisted SL hydrolysate; SLC: Celluclast-assisted SL hydrolysate; SLT: Termamyl-assisted SL hydrolysate; SLU: Ultraflo-assisted SL hydrolysate; SLV: Viscozyme-assisted SL hydrolysate (n = 4). (B) Adipocyte differentiation rate of each hydrolysate in 3T3-L1 cells under ORO staining. (C) Cell viability of each hydrolysate during adipocyte differentiation (n = 3). Scale bar: 50 μm. ns; not significant. MDI: IBMX, dexamethasone, insulin cocktail. *** p < 0.001 and **** p < 0.0001 vs. DF, ^## p < 0.01 vs. NT, ^$ p < 0.05 and ^$$$ p < 0.001 vs. Blank. All data are presented as means ± SD.

Figure 2

The characterization of sulfated polysaccharides from SLC (SPSL). (A) The percentages of proximate composition rates and neutral monosaccharide compositions were evaluated in SLC and SPSL, respectively. Fuc: L-Fucose, Rha: L-Rhamnose, Ara: L-Arabinose, Gal: L-Galactose, Glu: D-Glucose, Xyl: L-Xylose, Fru: D-Fructose. (B) The percentage of sulfate content in SLC and SPSL. Data are indicated as means ± SD (n = 3). (C) Molecular weight analysis of SPSL. The molecular weight distribution of the SPSL along with SLC was assessed by agarose gel electrophoresis with three different standards known as its molecular weights. MW: 50−500 kDa (Dextran sulfate, D8906, Sigma-Aldrich, MO, USA). MW: 60 kDa (Chondroitin 6-sulfate, D4384, Sigma-Aldrich). MW: 8 kDa (Dextran sulfate, D4911, Sigma-Aldrich). (D) The comparative alignments of FT-IR spectrum from SLC, SPSL, and commercial fucoidan. (E) The chromatogram of SPSL acid hydrolysate for glycan analysis. (F) The percentages of major sulfated glycan constituents in SPSL. **** p < 0.0001 vs. SLC.

Figure 3

The anti-adipogenesis effect of SPSL in 3T3-L1 adipocytes. (A) The percentage of cell viability of the series of doses of SPSL-treated 3T3-L1 adipocytes. (B) The visualization of three different doses of SPSL exposed 3T3-L1 cells by ORO staining. (C) The quantification of lipid accumulation rate by ORO staining in the three different doses of SPSL-exposed 3T3-L1 cells. Scale bar: 50 μm. ns; not significant. MDI: IBMX, dexamethasone, insulin cocktail. ** p < 0.01 and *** p < 0.001 vs. DF; ^#### p < 0.0001 vs. NT. All data are expressed as means ± SD (n = 3).

Figure 4

The adipogenesis modulators were controlled by SPSL treatment in 3T3-L1 adipocytes. (A) The immunoblotting for proteins related to adipogenesis modulation controlled by SPSL treatment. (B) The quantification of changes in PPARγ expressions. (C) The quantification of changes in SREBP-1 expression. (D) The quantification of changes in C/EBPα expression. (E) The quantification of changes in ATGL expression. (F) The quantification of changes in pAMPKα expression. (G) The quantification of changes in pACC expression. MDI: IBMX, dexamethasone, insulin cocktail. * p < 0.05, *** p < 0.001, and **** p < 0.0001. All data are presented as means ± SD (n = 2).

Figure 5

AMPK inhibition decreased the anti-adipogenesis effect of SPSL in adipocytes. (A) The visualization of fully- differentiated 3T3-L1 adipocytes that were incubated SPSL and SPSL + Compound C, respectively. (B) The quantification results of the rate of lipid accumulation in 3T3-L1 adipocytes that were incubated SPSL and SPSL with Compound C, respectively. Scale bar: 100 μm. MDI: IBMX, dexamethasone, insulin cocktail. ** p < 0.01 and **** p < 0.0001 vs. DF; ^#### p < 0.0001 vs. NT, ^$$$$ p < 0.0001 vs. SPSL (±Compound C). All data are presented as means ± SD (n = 3).

Figure 6

Improvement of energy expenditure rate and lipid accumulation in zebrafish by SPSL treatment. (A) The assay for energy expenditure assessment using Alamar Blue staining in a zebrafish model. (B) Energy expenditure levels after 72 h of SPSL treatment. (C) The survival rate of zebrafish exposed to different SPSL concentrations for 72 h. ns; not significant. (D) Oil red O-stained zebrafish were supplemented with an egg yolk along with SPSL in a dose-dependent manner. The blue arrow within blue dash lined box indicates a dorsal aorta portion in zebrafish with 10× magnification. (E) The level of lipid accumulation in zebrafish supplemented an egg yolk for 48 h. (F) The triglyceride level in zebrafish larvae supplemented an egg yolk for 48 h. Scale bar: 500 μm. ^## p < 0.01 and ^#### p < 0.0001 vs. NT; * p < 0.05, ** p < 0.01, and **** p < 0.0001 vs. Blank. All data are presented as means ± SEM (n = 3).