Studies on the purification of polysaccharides separated from Tremella fuciformis and their neuroprotective effect

The present study aimed to investigate the protective effect of purified polysaccharides from Tremella fuciformis against glutamate-induced cytotoxicity in differentiated PC12 (DPC12) cells. The aqueous extract of Tremella fuciformis was purified using a DEAE-52 cellulose anion exchange column and a Sepharose G-100 column, respectively. A fraction termed TL04 with a 2,033 kDa molecular weight was obtained. The backbone of TL04 is composed of (1 -> 2)- and (1 -> 4)-linked-mannose and (1 -> 3)-linked-glucans. Results revealed that TL04 treatment improved cell viability and suppressed reactive oxygen species accumulation, lactose dehydrogenase release and caspase-3 activity, and ameliorated mitochondrial abnormal alteration caused by glutamate. TL04 pretreatment enhanced the level of B-cell lymphoma 2 (Bcl-2), and suppressed Bax expression and cytochrome c (Cyto C) release in glutamate-treated cells. Exposure to glutamate strongly increased the activity of caspase-8, caspase-9 and caspase-3, which were significantly reversed by TL04 pretreatment. The presence of Ac-DEVD-CHO (a caspase-3 inhibitor) markedly enhanced the potency of TL04 in improving the viability of glutamate-exposed DPC12 cells. Collectively, the results demonstrated that the purified polysaccharides separated from Tremella fuciformis (TL04) possess a neuroprotective effect against glutamate-induced DPC12 cell damage predominantly through the caspase-dependent mitochondrial pathway. The present study provides an experimental foundation supporting purified TL04 as a potential therapeutic agent for neurodegenerative diseases.