Bioactive polysaccharides from medicinal mushrooms: A review on their isolation, structural characteristics and antitumor activity

Mushrooms either alone or in combination with conventional cancer treatment have been enhanced the efficacy of chemotherapy and radiotherapy improving the patients' quality of life. These therapy effects have been attributed to polysaccharides; the most potent compounds found in the fungi kingdom. Due to their wide range of biological activity and the backbone of glucose residues linked by β-(1 → 3)-glycosidic bonds, often with attached side-chain glucose residues joined by β-(1 → 6) linkages, the mushroom's polysaccharides, particularly the β-glucans, are the most versatile metabolites. Lentinan, D-fraction, and schizophyllan from Lentinula edodes, Grifola frondosa, and Schizophyllum commune, respectively are well-known β-glucans, however, the precise immunomodulation and anticancer mechanisms of action remain to be uncovered. According to several studies, β-glucan can interact with certain receptors on macrophages and dendritic cells, such as dectin-1 and TLRs, producing different cytokines and, in turn, indirectly activating other immune cells including T and B cells. Moreover, recent findings have proved that β-glucans have a direct cytotoxic effect on cancer cells suppressing proliferation and enhancing apoptosis possibly via multiple pathways such as PI3K/Akt/mTOR, NF-κB-, ERK-, ERα-, caspase- and p53-dependent pathways. Indeed, this study intends to provide information on the lentinan, D-fraction, and schizophyllan by examining the extraction procedures, chemical composition, and immunostimulatory and antitumoral biological activities. Future research directions should be directed toward improving the validity and reliability of randomized trials to confirm the potential role of β-glucans on the immune system and as anticancer therapy.