In the present study, we isolated and purified one polysaccharide (TRP) from Trametes robiniophila, which had a backbone of 1,3,6- and 1,4-linked glucpyranosyl moieties, with 1-linked arabinofuranosyl and galactopyranosyl terminal at the O-3 position of 1,3,6-linked glucpyranosyl residues. TRP was further evaluated for its antitumor activity against xenografted U-2 OS osteosarcoma in BALB/c nude mice together with the possible mechanism of action. We found that oral administration of TRP significantly suppressed U-2 OS tumor growth in mice via the induction of apoptosis, as evidenced by the increased number of TUNEL-positive cells in tumor tissues. Moreover, TRP administration increased the levels of the proapoptotic Bax protein and decreased the level of the antiapoptotic Bcl-2 protein, thus resulting in a rise of Bax/Bcl-2 ratio. Furthermore, the protein expression of caspase-9, caspase-3 and cleaved PARP became evident in tumor tissues from mice following TRP treatment, but caspase-8 keep unchanged. Besides, overexpression of metadherin (MTDH) was attenuated in tumor tissues of TRP-fed mice. Taken together, these findings suggest that the TRP-induced apoptosis of tumor tissues is through a mitochondria-mediated intrinsic apoptotic pathway.
Keywords: Apoptosis; Polysaccharide; Trametes robiniophila; U-2 OS human osteosarcoma cells; Xenograft tumor.
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