Inhibitory effects of Agaricus blazei extracts on human myeloid leukemia cells
Introduction
The Basidiomycete fungus Agaricus blazei Murill, an edible mushroom belonging to the Agaricaceae family, is native to southern Brazil and was introduced to Japan around 1950s. It is now commonly cultivated in Japan, China and Brazil (Kuroiwa et al., 2005, Mizuno, 1995). Popularly known as “Himematsutake” or “Brazilian mushroom”, Agaricus blazei has been traditionally used as a health food supplement for the prevention of cancer, diabetes, hyperlipidemia, arteriosclerosis and chronic hepatitis (Kawamura et al., 2005). In recent years, the mushroom is used in Japan as an adjuvant in cancer chemotherapy (Yoshimura et al., 2005).
Extracts of Agaricus blazei were found to inhibit the growth of various types of tumor cells, including sarcoma-180, Lewis lung carcinoma, Ehrlich ascites carcinoma, and Shionogi carcinoma in mice in vivo (Fujimiya et al., 1999, Ito et al., 1997, Ohno et al., 2001, Takaku et al., 2001) and human ovarian cancer HRA cells in vitro (Kobayashi et al., 2005). Mechanistics studies have demonstrated that the anti-tumor activities of Agaricus blazei extracts can be related to induction of apoptosis, cell-cycle arrest, inhibition of tumor-induced neovascularization, immunopotentiation and restoration of tumor-suppressed host immune system (Ebina and Fujimiya, 1998, Fujimiya et al., 1998, Kimura, 2005, Kimura et al., 2004, Kobayashi et al., 2005). Despite these findings, very few studies on the inhibitory effects of Agaricus blazei extracts on human leukemic cells have been reported (Jin et al., 2007, Kawamura and Kasai, 2007).
Most studies on the anti-tumor effect of Agaricus blazei extracts have focused on polysaccharide being the major, if not the only, active component. However, detailed comparison in isolation of anti-tumor components among different extraction and purification methods seemed to be lacking. Hence, it would be difficult to pinpoint if polysaccharides are really the major or the most potential anti-tumor component in Agaricus blazei, even though encouraging results have been obtained with the polysaccharides in previous studies (Kawamura et al., 2005, Lee et al., 2003, Mizuno et al., 1999). Besides, these approaches may have limited the potential of finding other valuable anti-tumor components from the mushroom.
In the present study, an attempt was made to optimize the extraction method for anti-leukemic components from Agaricus blazei using a systematic and bioassay-guided approach. The tumor-selective growth inhibitory activity of the extracts on leukemic cell lines was evaluated in vitro and further confirmed in vivo using tumor-bearing nude mice model. Our study also tried to explain the mechanism of anti-leukemic activity of Agaricus blazei and its active component(s).
Section snippets
Preparation of Agaricus blazei extracts
The Agaricus blazei used in this study was purchased from a commercial farm in Japan (via a local agent), authenticated by a mycology expert and a small sample was deposited as herbarium voucher specimen (no. 2006-3018) in the museum of the Institute of Chinese Medicine, the Chinese University of Hong Kong. Fruiting bodies of the mushroom were cleaned and cut into small pieces for the preparation of various extracts with or without heat using different solvents (ratio of raw materials to
Screening of Agaricus blazei extracts for anti-tumor effects
In vitro MTT-based cytotoxicity test with the human promyelocytic leukemia NB-4 cells was used as a model to determine the anti-tumor potential of different Agaricus blazei extracts and the polysaccharide enriched fractions (Table 1). Our results showed that six Agaricus blazei extracts were found to significantly suppress the growth of NB-4 cells and produced values of concentration for 50% growth inhibition (IC50) at below 250 μg/mL. All of these extracts, except JAB80H, involved the use of
Discussion and conclusion
For decades, extracts of various mushrooms have drawn much attention in complementary and alternative medicine. Most studies on the anti-tumor effect of Agaricus blazei extracts have put emphasis on polysaccharide being the major, if not the only, active component. However, many of these studies have used only one extract derived from a single extraction method that may or may not involve polysaccharide enrichment (Ito et al., 1997, Lee et al., 2003). As other components of the mushroom were
Acknowledgements
This study was supported by HKSAR RGC Competitive Earmarked Research Grant CUHK4531/05M. The authors would like to thank Dr. Zhu L. Yang (Kunming Institute of Botany, the Chinese Academy of Sciences, Kunming, Yunnan, China) who examined and authenticated the Agaricus blazei sample used.
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