Marine microorganisms often produce exopolysaccharides with novel structures and diverse biological activities due to their specific marine environment. The novel active exopolysaccharides from marine microorganisms have become an important research area in new drug discovery, and show enormous development prospects. In the present study, a homogeneous exopolysaccharide from the fermented broth of the mangrove endophytic fungus Penicillium janthinellum N29, designated as PJ1-1, was obtained. The results of chemical and spectroscopic analyses showed that PJ1-1 was a novel galactomannan with a molecular weight of about 10.24 kDa. The backbone of PJ1-1 was composed of →2)-α-d-Manp-(1→, →4)-α-d-Manp-(1→, →3)-β-d-Galf-(1→ and →2)-β-d-Galf-(1→ units with partial glycosylation at C-3 of →2)-β-d-Galf-(1→ unit. PJ1-1 had a strong hypoglycemic activity in vitro, evaluated using the assay of α-glucosidase inhibition. The anti-diabetic effect of PJ1-1 in vivo was further investigated using mice with type 2 diabetes mellitus induced by a high-fat diet and streptozotocin. The results indicated that PJ1-1 markedly reduced blood glucose level and improved glucose tolerance. Notably, PJ1-1 increased insulin sensitivity and ameliorated insulin resistance. Moreover, PJ1-1 significantly decreased the levels of serum total cholesterol, triglyceride and low-density lipoprotein cholesterol, enhanced the level of serum high-density lipoprotein cholesterol and alleviated dyslipidemia. These results revealed that PJ1-1 could be a potential source of anti-diabetic agent.

Polysaccharides derived from green algae have garnered significant attention owing to their distinctive structural characteristics and biological activities. In particular, sulfated polysaccharides from these algae represent a promising frontier in the discovery of novel therapeutic agents. In this present study, a sulfated galactan from Caulerpa taxifolia, designated SGC, was obtained by dilute alkali extraction and chromatographic purification. On the basis of chemical and spectroscopic analyses, the backbone of SGC was constituted by a backbone of →3)-β-d-Galp-(1→ with sulfate substitution at the C-2 and a branch on C-6. The side chains contained →6)-β-d-Galp(2SO₄)-(1→, →6)-β-d-Galp(3OMe)-(1→ and →3)-β-d-Galp(4,6-Pyr)-(1→ units. SGC possessed strong hypoglycemic activity in vitro, as evaluated by an assay of α-amylase inhibition. The anti-diabetic activity of SGC in vivo was further investigated using T2DM mice induced by high-fat diet combined with streptozotocin. The results indicated that SGC markedly restored body weight, reduced fasting blood glucose and possessed a significant glucose-regulating effect. Furthermore, SGC effectively increased insulin sensitivity and mitigated insulin resistance. Additionally, SGC effectively regulated lipid metabolism and alleviated oxidative stress. Notably, SGC ameliorated liver and pancreas damage induced by high-fat diet combined with streptozotocin. The investigation demonstrates that SGC is a unique sulfated galactan and has potential as a novel anti-diabetic agent.

The distinct conditions of the marine habitat drive microorganisms to synthesize exopolysaccharides possessing unique structural features and a broad spectrum of bioactive properties. An extracellular polysaccharide (AVP1) was obtained from the fermented liquid of a marine Aspergillus versicolor CS13 from the Yellow River Delta sediment. AVP1 was characterized as a mannogalactan with a molecular weight of approximately 16.2 kDa and a mannose-to-galactose molar ratio of 1.0: 2.4. The polysaccharide AVP1 was constituted by a backbone of →2)-α-d-Manp-(1→ and →5)-β-d-Galf-(1→ units, and branch at C-6 of →5)-β-d-Galf-(1→ units. The side chains contained →6)-α-d-Manp-(1→ and α-d-Manp-(1→ units. AVP1 possessed an obvious α‑amylase inhibitory activity in vitro. AVP1 significantly enhanced insulin sensitivity and glucose consumption in insulin-resistant (IR)-HepG2 cells, and alleviated sodium palmitate (PA)-induced insulin resistance. Moreover, AVP1 effectively reduced total cholesterol (TC) and triglyceride (TG) levels, while increased the activities of superoxide dismutase (SOD), catalase (CAT) and reduced glutathione (GSH). It also decreased malondialdehyde (MDA) content and reactive oxygen species (ROS) levels, thereby improved lipid metabolism and mitigated oxidative stress in IR-HepG2 cells. These results demonstrated that AVP1 exhibited notable restorative effects in IR-HepG2 cells and possessed strong activity to alleviate insulin resistance in vitro. This study provides a basis for the development of novel marine-derived hypoglycemic agents.