Structural characterization and hypoglycemic effect of green alga Ulva lactuca oligosaccharide by regulating microRNAs in Caenorhabditis elegans

The novel oligosaccharides from Ulva lactuca were obtained and characterized by nuclear magnetic resonance, Fourier-transformed infrared and liquid chromatography-quadrupole time-of-flight tandem mass spectrometry. U. lactuca oligosaccharides were composed by beta-D-Glcp-(1 -> 4)-alpha-L-Rhap (2So(3)(-))-(1 -> 2)-beta-D-GlcpA-(1 -> 6)-beta-D-Galp-(1 -> 5)-alpha-L-Arap-(1 -> and alpha-L-Rhap-(1 -> 2)-alpha-L-Rhap(3So(3)(-))-(1 -> 6)-beta-D-Glcp-(1 -> 2)-beta-D-Xylp-(1 -> with a branch of beta-D-GlcpA that connected in C4 of beta-D-Glcp, respectively. After U. lactuca oligosaccharide treatment, the mean lifespan, glucose levels, and insulin resistance were improved in Caenorhabditis elegans. It has significantly enhanced the total superoxide dismutase levels and ameliorated the intracellular reactive oxygen species accumulation. U. lactuca oligosaccharides could prevent the DNA and mitochondrial damage induced by high glucose. The gene expression levels of abnormal dauer formation 16 (DAF-16), protein kinase B (AKT-1), protein skinhead-1 (SKN-1), adenosine monophosphate-activated kinase 2 (AAK-2), DAF-15, and superoxide dismutase 3 (SOD-3) were up-regulated though inhibiting the expressions of miR-48-5p, miR-67-3p, miR-124-3p, and miR-85-3p, while the gene expression levels of DAF-2, LEThal 363 (LET-363), and signal element on X 1 (SEX-1) were also up-regulated. U. lactuca oligosaccharides might be applied in the functional foods to improve glucose metabolism disorders and antioxidant systems in vivo mediated by modulation of microRNAs.