Knowledge of phytosterol (PS) contents in marine algae is currently lacking compared to those in terrestrial plants. The present studies developed a quantitative 1H NMR method for the determination of the total PSs in Sargassum. The characteristic proton signal H-3α in PSs was used for quantification, and 2,3,4,5-tetrachloro-nitrobenzene was used as an internal standard. Seaweed samples could be recorded directly after total lipid extraction and saponification. The results showed that the PS contents in Sargassum fusiforme (788.89–2878.67 mg/kg) were significantly higher than those in Sargassum pallidum (585.33–1596.00 mg/kg). The variable contents in both species suggested that fixed raw materials are very important for future research and development. Orthogonal projection to latent structures discriminant analysis was carried out in the spectral region of δ 3.00–6.50 in the 1H NMR spectrum. S. fusiforme and S. pallidum could be separated well, and the key sterol marker was fucosterol.Keywords: fucosterol; orthogonal projection to latent structures discriminant analysis; phytosterols; quantitative 1H NMR; Sargassum; seaweed;

Dietary phytosterols have been successfully used for lowering cholesterol levels, which correlates with the fact that some phytosterols are able to act as liver X receptor (LXR) agonists. Sargassum fusiforme is an edible marine seaweed well-known for its antiatherosclerotic function in traditional Chinese medicine. In this study, seven phytosterols including fucosterol (1), saringosterol (2), 24-hydroperoxy-24-vinyl-cholesterol (3), 29-hydroperoxy-stigmasta-5,24(28)-dien-3β-ol (4), 24-methylene-cholesterol (5), 24-keto-cholesterol (6), and 5α,8α-epidioxyergosta-6,22-dien-3β-ol (7) were purified and evaluated for their actions on LXR-mediated transcription using a reporter assay. Among these phytosterols, 2 was the most potent compound in stimulating the transcriptional activities of LXRα by (3.81 ± 0.15)-fold and LXRβ by (14.40 ± 1.10)-fold, respectively. Two epimers of 2, 24(S)-saringosterol (2a) and 24(R)-saringosterol (2b), were subsequently separated by semipreparative high-performance liquid chromatography. Interestingly, 2a was more potent than 2b in LXRβ-mediated transactivation ((3.50 ± 0.17)-fold vs (1.63 ± 0.12)-fold) compared with control. Consistently, 2a induced higher expression levels of LXR target genes including key players in reverse cholesterol transport in six cell lines. These data along with molecular modeling suggested that 2a acts as a selective LXRβ agonist and is a potent natural cholesterol-lowering agent. This study also demonstrated that phytosterols in S. fusiforme contributed to the well-known antiatherosclerotic function.

The chemical composition of monogalactosyldiacylglycerols (MGDGs) from brown alga Sargassum horneri and their inhibitory effects on lipid accumulation were investigated in this study. A total of 10 molecular species of MGDGs were identified using nuclear magnetic resonance, alkaline hydrolysis, gas chromatography–flame ionization detector, and high-performance liquid chromatography–tandem mass spectrometry methods. Individual molecular species of MGDGs, including (2S)-1-O-myristoyl-2-O-palmitoleoyl-3-O-β-d-galactopyranosyl-sn-glycerol (1), (2S)-1-O-myristoyl-2-O-linoleyl-3-O-β-d-galactopyranosyl-sn-glycerol (3), (2S)-1-O-palmitoyl-2-O-linolenoyl-3-O-β-d-galactopyranosyl-sn-glycerol (5), (2S)-1-O-myristoyl-2-O-oleyl-3-O-β-d-galactopyranosyl-sn-glycerol (7), (2S)-1-O-palmitoyl-2-O-palmitoleoyl-3-O-β-d-galactopyranosyl-sn-glycerol (8), (2S)-1-O-palmitoyl-2-O-linoleyl-3-O-β-d-galactopyranosyl-sn-glycerol (9), and (2S)-1-O-palmitoyl-2-O-oleyl-3-O-β-d-galactopyranosyl-sn-glycerol (10), were then furnished using semi-preparative high-performance liquid chromatography, and their inhibitory effects on triglyceride (TG) accumulation and free fatty acid (FFA) levels in 3T3-L1 adipocytes were evaluated. Compounds 3 and 9 showed inhibitory effects on TG and FFA accumulation, with TG levels of 1.568 ± 0.2808 and 1.701 ± 0.1460 μmol/L and FFA levels of 0.149 ± 0.0258 and 0.198 ± 0.0229 mequiv/L, respectively, which were more effective than other compounds. The primary structure–activity relationship suggested that linoleyl [18:2(ω-6)] in the sn-2 position played an important role on triglyceride accumulation inhibition.