Laminaria japonica (LJ) and Hizikia fusiforme (HF) are brown seaweeds known to have various health-promoting effects. In this study, we investigated the anti-diabetic effects and possible mechanism(s) of LJ and HF by using both in vitro and in vivo models. C2C12 myotubes, mouse-derived skeletal muscle cells, treated with LF or HF extracts were used for the in vitro model, and muscle tissues from C57BL/6N mice fed a high-fat diet supplemented with 5% LF or HF for 16 weeks were used for the in vivo model. Although both the LF and HF extracts significantly inhibited α-glucosidase activity in a dose-dependent manner, the HF extract had a superior α-glucosidase inhibition than the LF extract. In addition, glucose uptake was significantly increased by LJ- and HF-treated groups when compared to the control group. Phosphorylation of protein kinase B and AMP-activated protein kinase was induced by LJ and HF in both the vivo and in vitro skeletal muscle models. Furthermore, LJ and HF significantly decreased tumor necrosis factor-α whereas both extracts increased interleukin (IL)-6 and IL-10 production in lipopolysaccharide-stimulated C2C12 myotubes. Taken together, these findings imply that the brown seaweeds LJ and HF could be useful therapeutic agents to attenuate muscle insulin resistance due to diet-induced obesity and its associated inflammation.

Seaweed is known to have various health-promoting effects. However, the mechanisms underlying seaweed’s antidiabetic effects remain unclear. We investigated the potential antidiabetic effects of seaweed water extracts and further examined their mechanism(s) using C2C12 mouse skeletal muscle cells. Briefly, we screened the physiochemical properties of seven seaweed extracts by comparing the antioxidant and α-glucosidase inhibitory effects. Among them, three seaweed extracts, Undaria pinnatifida sporophyll (UPS), Codium fragile (CF), and Gracilaria verrucosa (GV), were selected for further testing of their possible antidiabetic effects with underlying mechanisms using C2C12 myotubes. Consistent with the superior α-glucosidase inhibition of the three seaweed extracts, the extracts also enhanced glucose utilization in myotubes compared to the control. The upregulated glucose uptake by the seaweed extracts was reversed by an AMP-activated protein kinase (AMPK) inhibitor, compound C, in the UPS- and CF-treated groups. Furthermore, all three seaweed extracts significantly promoted the phosphorylation of AMPK which was completely blocked by pretreating with compound C. In addition, all three extracts reduced lipopolysaccharide-simulated TNF-α production in C2C12 cells. Our results demonstrated that all three seaweed extracts exhibited antidiabetic properties through not only the inhibition of glucose absorption but also the promotion of glucose utilization. Moreover, the regulation of inflammatory cytokine production by the extracts suggested their potential anti-inflammatory property which might play a critical role in protecting insulin sensitivity in a chronic inflammatory state. Taken together, UPS, CF, and GV are a promising source to modulate the glucose absorption and utilization in muscle cells partially via the AMPK pathway.

Cardiovascular and metabolic diseases are a leading cause of death worldwide. Epidemiological studies strongly highlight various benefits of consuming colorful fruits and vegetables in everyday life. In this review, we aimed to revisit previous studies conducted in the last few decades regarding green-colored foods and their bioactive compounds in consideration of treating and/or preventing cardiovascular and metabolic diseases. This review draws a comprehensive summary and assessment of research on the physiological effects of various bioactive compounds, mainly polyphenols, derived from green-colored fruits and vegetables. In particular, their health-beneficial effects, including antioxidant, anti-inflammatory, anti-diabetic, anti-obesity, cardioprotective, and lipid-lowering properties, will be discussed. Furthermore, the bioavailability and significance of action of these bioactive compounds on cardiovascular and metabolic diseases will be discussed in detail.