In vitro studies (human cell lines)
A very recent study has demonstrated that agaritine purified from Agaricus blazei Murrill exerts anti-tumour activity against leukemic cells (Endo et al., 2010). In this study, a hot water extract of Agaricus blazei Murrill (ABM) powder was fractionated by HPLC based on the anti-tumour activity against leukemic cells in vitro. The purified substance was identified as agaritine, beta-N-(gamma-l(+)-glutamyl)-4(hydroxymethyl) phenylhydrazine, having a molecular mass of 267Da. This compound inhibited the proliferation of leukemic cell lines such as U937, MOLT4, HL60 and K562, but showed no significant effect on normal lymphatic cells. The authors concluded that agaritine has direct anti-tumour activity against leukemic tumor cells in vitro which is in contrast to the carcinogenic activity previously ascribed to this compound. The data also showed that this activity was distinct from that of beta-glucan, which indirectly suppresses proliferation of tumour cells. These data by Endo et al provide support for the conclusion of a recent review that agaritine from consumption of cultivated Agaricus bisporus mushrooms poses no known toxicological risk to healthy humans (Roupas et al., 2010).
Agaricus bisporus extracts have been shown to inhibit cell proliferation of HL-60 leukemia cells via the induction of apoptosis (Jagadish et al., 2009). A fraction from Agaricus blazei has also been shown to induce HL-60 cell apoptosis and the combined effect of down-regulation of telomerase activity and up-regulation of mRNA expression of the caspase-3 gene could be the primary mechanism of induction of apoptosis (programmed cell death) (Gao et al., 2007). Apoptosis by Agaricus blazei on human leukemic U937 cells has also been demonstrated via similar mechanisms (regulation of Bcl-2 and caspase-3) (Jin et al., 2007). Inhibitory effects of Agaricus blazei extracts on human myeloid leukemia cells NB-4 and K-562 cells have also been reported (Kim et al., 2009a). Apoptotic cell death of human leukaemia U937 cells by ubiquinone9 purified from Pleurotus eryngii has also been reported (Bae et al., 2009). Ubiquinone-9-induced cell death was characterised with the cleavage of poly (ADP-ribose) polymerase and pro-caspase 3.
Proliferation of human leukemic U937 cells has been shown to be significantly inhibited by conditioned medium of human peripheral blood mononuclear cells stimulated with cold-water extracts (10-800 µg/mL of medium) of dietary mushrooms, Hypsizigus mamoreus, Agrocybe aegerite and Flammulina velutipes (Ou et al., 2005). A glycoprotein extracted from the golden oyster mushroom Pleurotus citrinopileatus has also been reported to exhibit a growth inhibitory effect against U937 leukemia cells (Chen et al., 2009b).
Gamma-L-glutaminyl-4-hydroxybenzene, a stable phenol found in high concentrations in the gill tissue of Agaricus bisporus has been shown to be capable of selectively inhibiting DNA synthesis in L1210 leukemia cells (FitzGerald et al., 1984).
A novel ribonuclease, from fresh fruiting bodies of the edible mushroom Hypsizigus marmoreus, with anti-proliferative activity against the L1210 leukemia cell line has also been purified (Guan et al. 2007). A thermostable ribosome-inactivating protein with a molecular weight of 20kDa, isolated from fruiting bodies of Hypsizigus marmoreus has also been shown to have anti-proliferative activity against mouse leukemia cells and human leukemia and hepatoma cells (Lam and Ng, 2001).
Coriolus versicolor (CV), also known as Trametes versicolor, has been evaluated for its cytotoxic activities on a B-cell lymphoma (Raji) and two human promyelocytic leukemia (HL-60, NB-4) cell lines. The results demonstrated that CV extract at 50 to 800µg/ml dose-dependently suppressed the proliferation of Raji, NB-4, and HL-60 cells by more than 90%. The extract however did not exert any significant cytotoxic effect on the normal liver cell line WRL when compared with a chemotherapeutic anti-cancer drug, mitomycin C, confirming the tumourselective cytotoxicity. Nucleosome production in HL-60, NB-4 and Raji cells was significantly increased by 3.6-, 3.6- and 5.6-fold respectively upon the treatment of CV extract, while no significant nucleosome production was detected in extract-treated WRL cells. The CV extract was found to selectively and dose-dependently inhibit the proliferation of lymphoma and leukemic cells possibly via an apoptosis-dependent pathway (Lau et al., 2004).
Hypsiziprenol A(9) is a polyterpene isolated from the fruiting body of Hypsizigus marmoreus which has been shown to inhibit the growth of HL-60 cells by inducing apoptosis that is mediated through mitochondrial membrane potential loss and caspase activation (Mizumoto et al., 2008). Similar inhibitory effects on the proliferation of HL-60 human pre-myelocytic leukemia cells has been demonstrated by cultivated mycelium of Cordyceps sinensis (Wu et al., 2007b).
Lucidenic acids isolated from Ganoderma lucidum (YK-02) decreased cell population growth of HL-60 cells. Treatment of HL-60 cells with lucidenic acid A, C, and N caused cell cycle arrest in the G1 phase. Lucidenic acid B-induced apoptosis involved release of mitochondria cytochrome c and subsequently induced the activation of caspase-9 and caspase-3, which were followed by cleavage of poly(ADP-ribose) polymerase (PARP). Pretreatment with a general caspase-9 inhibitor (Z-LEHD-FMK) and caspase-3 inhibitor (Z-DEVD-FMK) prevented lucidenic acid B from inhibiting cell viability in HL-60 cells (Hsu et al., 2008b). Further work by the same group has also shown that Ganoderma lucidum polysaccharides induce macrophage-like differentiation inhuman leukemia THP-1 cells via caspase and p53 a ctivation (Hsu et al., 2009). Ganoderma lucidum has also been shown to induce apoptosis in NB4 human leukemia cells and to affect the signal transduction kinases Akt and Erk (Calvino et al., 2010).
Dried powder of cultured Cordyceps sinensis mycelium has also shown cytotoxic effects towards promyelocytic leukemia HL-60 cells via a suggested dependency on sterol constituents and the activation of caspases-3/7 (Matsuda et al., 2009).