Structural characterization, antioxidant activity, and protective effect against hydrogen peroxide-induced oxidative stress of chemically degraded Gracilaria fisheri sulfated galactans

Sulfated polysaccharides (SPs) possess an extensive range of biological activities, such as the inhibition of oxidation, correlated with their molecular weight (MW) and chemical structure. In this study, we used the trifluoroacetic acid (TFA) controlled degradation method to degrade sulfated galactans (SG) isolated from Gracilaria fisheri and evaluated the antioxidant and protective effects of the low molecular weight SG (LMSG) against H2O2 on fibroblast cells for the first time. Degradation of native SG (NSG) with an initial MW of 217.45 kDa using different concentrations of TFA resulted in five degraded NSG with MW of 97.23, 62.26, 30.74, 2.63, and 2.59 kDa. The reduction in MW was positively correlated with TFA concentrations. Chemical structure analyses using FTIR and NMR indicated that the TFA degradation process did not significantly change the LMSG polysaccharide main chain but did change the functional groups. LMSG exhibited higher scavenging activities and enhanced the cellular activities of GSH, CAT, and SOD enzymes. Moreover, LMSG activated Nrf-2/ARE signaling and increased expression of antioxidant genes CAT and SOD, which corresponded to increased protective effects against H2O2-induced ROS generation in fibroblast cells. The study reveals modification of NSG by acid TFA degradation resulted in the creation of LMSG, which showed greater antioxidant activity.