Evaluation of the context of downstream N- and free N-glycomic alterations induced by swainsonine in HepG2 cells.

Swainsonine (SWA), a potent inhibitor of class II α-mannosidases, is present in a number of plant species worldwide and causes severe toxicosis in livestock grazing these plants. The mechanisms underlying SWA-induced animal poisoning are not fully understood. In this study, we analyzed the alterations that occur in N- and free N-glycomic upon addition of SWA to HepG2 cells to understand better SWA-induced glycomic alterations. After SWA addition, we observed the appearance of SWA-specific glycomic alterations, such as unique fucosylated hybrid-type and fucosylated M5 (M5F) N-glycans, and a remarkable increase in all classes of Gn1 FNGs. Further analysis of the context of these glycomic alterations showed that (fucosylated) hybrid type N-glycans were not the precursors of these Gn1 FNGs and vice versa. Time course analysis revealed the dynamic nature of glycomic alterations upon exposure of SWA and suggested that accumulation of free N-glycans occurred earlier than that of hybrid-type N-glycans. Hybrid-type N-glycans, of which most were uniquely core fucosylated, tended to increase slowly over time, as was observed for M5F N-glycans. Inhibition of swainsonine-induced unique fucosylation of hybrid N-glycans and M5 by coaddition of 2-fluorofucose caused significant increases in paucimannose- and fucosylated paucimannose-type N-glycans, as well as paucimannose-type free N-glycans. The results not only revealed the gross glycomic alterations in HepG2 cells induced by swainsonine, but also provide information on the global interrelationships between glycomic alterations.