Kidney protective bioactivity guided investigation for isolation and mechanism of Sulfated heterpolysaccharide from Laminarina japonica

A new sulfated polysaccharide (SP7) was obtained and purified from Laminarina japonica with the guidance of kidney protective activity. Analysis of physicochemical features exhibited that SP7 consisted of mannose, amino glucose, rhamnose, glucuronic acid, galactose and fucose at a ratio of 0.82:3.05:2.68:3.11:5.86:1. SP7 had the molecular weight of 4.2   kDa. Cyclophosphamide (CTX) induced oxidative kidney damage mice was used to test the activity and mechanism of SP7 in vivo. Metabolites of CTX caused the over production of reactive oxygen species (ROS). It was found that SP7 inhibited 10   mg/kg CTX-induced renal oxidative damage in mice model. After intraperitoneal injection of SP7 at a dose of 20   mg/kg each day, ferritin heavy chain 1 (FTH1) and glutathione peroxidase 4 (GPX4) protein expression were largely increased ( P < 0.05). TCMK-1 cells incubated with erastin were built as ferroptosis model. Intracellular malondialdehyde (MDA) level was decreased by SP7 treatment time and concentration dependently ( P < 0.05). Electron microscopy showed mitochondria in SP7 treated cells had a 41% increase in length. Test of labile iron pool (LIP) exhibited a 31% decrease of iron concentration in SP7 treated cells. All results proved SP7 would inhibit ferroptosis via downregulating ferritinophagy, which led to a large decrease in kidney oxidative damage.