Anti-proliferative and pro-apoptotic activities of fractions of Pleurotus ostreatus were examined using HT-29 colon cancer cells in vitro. A hot-water-soluble fraction of the mycelium of the liquid cultured mushroom was partially isolated and chemically characterized as a low-molecular-weight alpha-glucan. HT-29 cells were exposed to the different isolates and significant inhibition of proliferation was obtained in a dose-dependent manner. Proliferation inhibition was shown to be the result of apoptotic induction because the pro-apoptotic molecules Bax and cytosolic cytochrome-c were upregulated. Fluorescence-activated cell sorter analyses of polysaccharide-treated HT-29 cells showed a high percentage of Annexin-positive cells. Here, we describe a newly identified low-molecular-weight alpha-glucan with promising anti-tumorigenic properties, and demonstrate its direct effect on colon cancer cell proliferation via induction of programmed cell death.

Pleurotus ostreatus is an edible mushroom that also has high medicinal values. In this study, P. ostreatus was tested for its ability to inhibit the growth of fungi and bacteria. The freeze-dried fruiting body, broth from submerged culture, and mycelial biomass of P. ostreatus were extracted using alcohols and water as solvents. The extracts were then tested for their antimicrobial activity against the growth of fungi and bacteria. It was observed that the water extract from fruiting bodies had the strongest effect in inhibiting the growth of most fungi. The most sensitive test microfungi to the inhibition were Candida albicans, Cryptococcus humicola, and Trichosporon cutaneum, and the most sensitive test bacteria were Staphylococcus aureus followed by Escherichia coli. Water extracts from culture broth or mycelial biomass were moderately inhibitive to the growth of fungi and bacteria. The alcohol-based solvents from all samples had much less antimicrobial activity against most test microorganisms. An antimicrobial compound was purified from the water extracts of fruiting bodies with Sephadex G 100 column chromatography and characterized by infrared absorption spectrum (IR), nuclear magnetic resonance (NMR), and mass spectroscopic analysis. We have identified this compound to be 3-(2-aminopheny1thio)-3-hydroxypropanoic acid. This purified compound had a minimum inhibitory concentration of 30µg/mL and 20 µg/mL against the growth of fungi and bacteria, respectively.

Twenty species of edible mushrooms and three purified mushroom polysaccharides were screened for their antitumor potential on human androgen-independent cancer PC-3 cells. A water-soluble extract (POE) prepared from the fresh oyster mushroom Pleurotus ostreatus produced the most significant cytotoxicity on PC-3 cells among the mushroom species tested. At the same time, POE induced a rapid apoptosis on PC-3 cells detected with annexin V-fluorescein isothiocyanate flow cytometry when the cells were exposed to POE (150 microg/mL) for 2 hours. Induced apoptosis was also confirmed by DNA fragment terminal deoxynucleotidyl transferase-mediated X-dUTP nick end labeling staining while POE (200 microg/mL) was added to PC-3 cells for 6 hours. Both cytotoxicity and induced apoptosis mediated by POE in PC-3 cells are dose-dependent. Interestingly, PC-3 cells appeared to be more sensitive to POE in anchorage-independent growth condition. Tumor colony-forming efficiency was dramatically reduced to 4.5% or 0.5% in POE (60 or 120 microg/mL)-supplemented soft agar medium compared with that of POE-free medium (defined as 100%). Temperature in POE processing plays a decisive role for the cytotoxic activity. Bioactivity of POE was eliminated by exposure to high temperature (80 degrees C) for 2 hours; however, it remained stable at a series temperatures of below 40 degrees C. The active fraction POE-F2 was analyzed and identified by size exclusion of high performance liquid chromatography and the CellTiter 96 AQueous Cell Proliferation Assay (Promega, Madison, WI). Since POE-F2 is also sensitive to heat and has strong 280 nm absorption, the results imply that active compounds recovered from P. ostreatus are water-soluble proteins or polypeptides.

Mushrooms are a source of dietary fiber (DF) with a cholesterol-lowering effect. However, their underlying mechanisms are poorly understood. The effect of DF-enriched fractions from three mushrooms species on cholesterol-related expression was studied in vitro. The Pleurotus ostreatus DF fraction (PDF) was used in mice models to assess its potential palliative or preventive effect against hypercholesterolemia. PDF induced a transcriptional response in Caco-2 cells, suggesting a possible cholesterol-lowering effect. In the palliative setting, PDF reduced hepatic triglyceride likely because Dgat1 was downregulated. However, cholesterol-related biochemical data showed no changes and no relation with the observed transcriptional modulation. In the preventive setting, PDF modulated cholesterol-related genes expression in a manner similar to that of simvastatin and ezetimibe in the liver, although no changes in plasma and liver biochemical data were induced. Therefore, PDF may be useful reducing hepatic triglyceride accumulation. Because it induced a molecular response similar to hypocholesterolemic drugs in liver, further dose-dependent studies should be carried out.

BACKGROUND:Functional foods are extensively studied for their cancer preventive effects. In the present study, we compared the anti-cancer activity of aqueous extracts of three species of mushrooms including: Pleurotus ostreatus (PAE), Auricularia polytricha (AAE) and Macrolepiota procera (MAE) on COLO-205 cells.

METHODS:Various in vitro approaches were performed to investigate the most potential mushroom variety that possesses maximum cytotoxic, anti-proliferative and apoptosis inducing properties. MTT assay was used to assess cytotoxicity. IC50 values were obtained and further used to perform clonogenic survival, wound scratch and apoptosis assays. Gene expression studies of apoptosis and cell cycle related studies were performed by reverse transcriptase PCR, followed by estimation of DNA content by flow cytometric analysis.

RESULTS:Our study showed that PAE acts as the most prominent inducer of cancer cell death as compared to other species. Therefore, we performed expression studies for apoptosis and cell cycle to understand the genes which are responsible for their profound activities. Expression studies illustrated increased levels of caspase-9 (1 to 2.1, P<0.01), caspase-3 (1 to 1.7, P<0.01) and Bax (1 to 1.4, P<0.05) genes followed by decreased levels of Bcl-2 (1 to 0.44, P<0.05) gene with PAE treatment and this was attributed to the activation of intrinsic pathway. Along with apoptosis, an arrest at Go/G1 phase was observed through flow cytometric analysis followed by increased expression of inhibitors of cyclin dependent kinases (CKIs), p16 (1 to 1.5, P<0.05) and p21 (1 to 2.4, P<0.01).

CONCLUSION:This study exemplifies the effectiveness of PAE and may serve as a potential therapeutic agent.

In spite of the global consumption of mushrooms, only two epidemiological studies demonstrated an inverse correlation between mushroom intake and the risk of cancer. Therefore, in the present study we evaluated whether extracts from edible mushrooms Agaricus bisporus (portabella), Flammulina velutipes (enoki), Lentinula edodes (shiitake) and Pleurotus ostreatus (oyster) affect the growth of breast and colon cancer cells. Here, we identified as the most potent, P. ostreatus (oyster mushroom) which suppressed proliferation of breast cancer (MCF-7, MDA-MB-231) and colon cancer (HT-29, HCT-116) cells, without affecting proliferation of epithelial mammary MCF-10A and normal colon FHC cells. Flow cytometry revealed that the inhibition of cell proliferation by P. ostreatus was associated with the cell cycle arrest at G0/G1 phase in MCF-7 and HT-29 cells. Moreover, P. ostreatus induced the expression of the tumor suppressor p53 and cyclin-dependent kinase inhibitor p21(CIP1/WAF1), whereas inhibited the phosphorylation of retinoblastoma Rb protein in MCF-7 cells. In addition, P. ostreatus also up-regulated expression of p21 and inhibited Rb phosphorylation in HT-29 cells, suggesting that that P. ostreatus suppresses the proliferation of breast and colon cancer cells via p53-dependent as well as p53-independent pathway. In conclusion, our results indicated that the edible oyster mushroom has potential therapeutic/preventive effects on breast and colon cancer.