Brief Introduction
Lentinus edodes (shiitake) is one of the world’s second largest cultivated medicinal and edible mushroom used as ‘Functional foods’ has a long history in oriental folklore for treatment of tum-ors, flu, heart diseases, high blood pressure, obesity, problems related to s-exual dysfunction and ageing, diabetes, liver ailments, respiratory diseases, exhaustion and weakness. L. edodes is among the most valuable medicinal mushroom. It is a source of two well-studied and widely approved polysaccharide medicines: LEM (an acronym for L. edodes mycelia), a protein-bound polysaccharide derived only from the mycelium, and lentinan – a cell-wall branched-Dglucan extracted from both the fruiting body and mycelium. Both compounds are immune system enhancers that demonstrated anticance-r activity. Additionally, L. edodes contains other compounds that inhibit blood aggregation; reduce cholesterol levels, and exhibit antibacterial and antiviral effect. A lignan-rich compound derived from L. edodes mycelium holds a promising factor for treating both hepatitis-B and AIDS. Another anti-tumour active polysaccharide, KS-2, has been isolated from L. edodes mycelia (LEM).

It is a good source of carbohydrate, protein and essential amino acids. It is low in fat, have a high percentage of polyunsaturated fatty acids and also contain many vitamins and minerals. The protein in L. edodes are composed of 18 types of amino acids, including all essential amino acids in ratios similar to that ideal for human nutrition. L. edodes contains significant quantities of vitamins C, B1, B2, B12, niacin, and vitamin D (the highest content of vitamin D of any plant food). L. edodes mushroom-derived polysaccharides, immunomodulating and anticance-r compounds are used in clinical applications as adjuvant to standard chemotherapy. Another potential use for L. edodes is as foodstuff, consumed whole or in concentrated extract or as dietary supplement. There are several types of dietary supplements and medicinal formulations derived from L. edodes: dried and pulverized fruiting bodies, hot water and alcohol extracts of fruiting bodies, biomass or extracts of mycelia, or broth harvested from submerged liquid cultures. Commercial preparations are available as tablets, capsules, or elixirs, and are available in most Asian countries and are increasingly available in USA, New Zealand, Australia, and Europe.

Chemical Constituents
Scientific investigations have led to isolation of many compounds from L. edodes having health promotion activities. Fruit bodies of L. edodes contains 88–92% water, protein, lipids, carbohydrates as well as vitamins and minerals. The mushroom is a good source of vitamins, especially provitamin D2 (ergosterol), which under ultraviolet (UV) light and heat yields calciferol (vitamin D2). It also contains B vitamins, including B1 (thiamine), B2 (riboflavin) and B12 (niacin). The fatty acids account for 3.38% of the total lipids with an appreciable amount of amino acids. In addition to glycogen-like polysaccharides, (1-4)-, (1- 6)–D-glucans and antitum-or polysaccharides, lentinan, (1- 3)-, (1-6)–bonded heteroglucans, heterogalactans, heteromannans, xyloglucans, etc., have been identified. Among the free sugars present are trehalose, glycerol, mannitol, arabitol, mannose, and arabinose. In shiitake mushrooms, dietary fiber consists of water-soluble materials such as -glucan and protein and water-insoluble substances extractable only with salts, acids, and alkalies such as polyuronide (acidic polysaccharide), hemicellulose, -glucan with heterosaccharide chains, lignin, and chitin present as cell wall constituents. The aroma components include alcohols, ketones, sulfides, alkanes, fatty acids, etc. The major volatile flavor contributors are matsutakeol (octen-1- ol-3) and ethyl-n-amyl ketone. The characteristic aroma of shiitake mushrooms was identified as 1, 2, 3, 5, 6- pentathiepane. According to Mizuno, the components responsible for the delicious flavor are monosodium gluta- mate, 50-nucleotides, free amino acids, lower molecular weight peptides, organic acids, and sugars. Their relative ratios are responsible for the variation in flavor naturally seen in this mushroom. Organic acids contributing to the flavor of shiitake mushroom include malic acid, fumaric acid, -keto-glutaric acid, oxalic acid, lactic acid, acetic acid, formic acid, and glycolic acid.

Lentinan is a high molecular weight (5×105 Da); D +20–22° (NaOH) polysaccharide [(C6H10O5)n] extracted from cell wall of fruiting body in a triple helix structure containing only glucose molecules with mostly -(1-3)-glucose linkages in the regularly branched backbone, and -(1-6)- glucose side chains. The configuration of the glucose molecule in a helix structure is considered to be important for the biological and pharmacological activity. Lentinan is completely free of any nitrogen (and thus protein), phosphorus, sulphur and any other atoms except carbon, oxygen and hydrogen. It is water soluble, heat stable and alkali labile.

Pharmacological Effects
L. edodes is one of the well-known macrofungus used in several therapeutic applications. It is the source of several well-studied preparations with proven pharmacological properties. The medicinal properties of L. edodes have been studied since Ming Dynasty (1369-1644). The elders from Japanese Empire considered shiitake as the “elixir of the life” increasing vigor and energy. Antibiotic, anti-carcinogenic, anticancer, antifungal, antibacterial and antiviral, antidiabetic, hypolipidemic compounds have been isolated intracellularly (fruiting body and mycelia) and extracellularly (culture media) from L. edodes. Some of these substances were lentinan, lectin and eritadenine. The shiitake mushroom is used medicinally for diseases involving depressed immune function (including AIDS), cancer, diabetes, environmental allergies, fungal infection, frequent flu and colds, bronchial inflammation, and regulating urinary incontinence. A summary of the therapeutic effects and bioactive compounds of L. edodes which is reported in the literature till 2009 has been represented in Table 5. Major therapeutic effects of this wonderful mushroom are being elaborated below.

1. Antitumor and Anticarcinogenic Activity 
The antitumor polysaccharide ‘Lentinan’ was first isolated and studied by Chihara et al. who demonstrated that its anti-tumor effects were greater than other mushroom polysaccharides and was active for some types of tum-ors. The antitum-or effect of lentinan was confirmed by using Sarcoma-180 transplanted in CD-1/ICD mice [5]. Later, it showed prominent antitumor activity not only against allogenic tum-ors, such as Sarcoma-180, but also against various synergic and autochthonous tumors, and it prevented chemical and viral oncogenesis. The tumor inhibitory effect of lentinan was highly striking. In 1-5 mg/kg x 10 doses, the inhibition ratio was 95 to 97.5%, and in dosages of 0.2 mg/kg x 10, the tumors underwent complete regression in 6 out of 10 mice. Combination treatment of L. edodes mycelium extracts with 5-Fluorouracil represent a novel chemotherapeutic strategy in colon c-ancers and that p53, p21/Cip1 and p27/Kip1 may play some important roles for the involvement in antitum-or activity. Four antitumor (1/3)–D-glucans coded as L-I1, L-I2, L-I3 and L-I4 with high molecular weight (1.47×106 –1.67×106 ) were isolated from four kinds of fruiting bodies of Lentinus edodes. Exo-biopolymer from rice bran cultured with L. edodes [rice bran exo-biopolymer (RBEP)] induced the activation of NK cells in a dose-dependent manner when administrated orally [46]. The carcinostatic effect of lentinan results from the activation of the host’s immune system. ß-D-glucan binds to lymphocyte surfaces or serum-specific proteins, which activate macrophage, T-helper cells, natural killer (NK) cells, and other effector cells. All these increase the production of antibodies as well as interleukins (IL-1, IL-2) and interferon (IFN-) released upon activation of effector cells. The antitumor studies conducted with L. edodes thus far are very interesting and do show a potential for providing therapeutic control of cancer. It is, however, difficult to say whether L. edodes could have preventive effects against cancer when consumed as part of the diet. 

2. Immunomodulating Effects
Lentinus edodes has attracted a lot of attention owing to its immunomodulatory effects. Lentinan is well known as a type of biological response modifier (BRM). Augmentations of NK (Natural Killer), CTL (Cytotoxic T Lymphocyte), LAK (Lymphokine Activated Killer) activities and DTH (Delayed Type Hypersensitivity) responses against tumor antigen were observed after administration of Lentinan. These activities are responsible for the antitum-or effects of lentinan. Antitumor polysaccharide L-II was isolated and purified from the fruiting body of L. edodes. The antitum-or activity of the polysaccharide L-II on micetransplanted sarcoma 180 was mediated by immunomodulation by inducing T-cells and macrophage-dependent immune system responses. Kupfahl et al. evaluated evaluated the effect of lentinan in the well-established model system of the murine Listeria Monocytogenes infection. The results showed that the lentinan enhances the protective CD8 T-cell response against L. monocytogenes probably by a mechanism that involves the IL-12-mediated augmentation of the specific antilisterial CD8 T-cell response Fruit body and mycelial extracts of L. edodes are able to enhance the proliferation of rat thymocytes directly and act as co-stimulators in the presence of the T-mitogen PHA. Many interesting mechanisms of action of Lentinan and possible pathways for inflammatory and immune reactions have been represented.

Pre-treatment of mice with lentinan significantly decreased the parasitemia and increased their survival after infection by Plasmodium yoelii 17XL (P.y17XL). Enhanced IL-12, IFN- and NO production induced by lentinan in spleen cells of infected mice revealed that the Th1 immune response was stimulated against malaria infection. In vitro and in vivo, lentinan enhanced the expression of MHC II, CD80/CD86, and Toll-like receptors (TLR2/TLR4), and increased the production of IL-12 in spleen dendritic cells (DCs) co-cultured with parasitized red blood cells (pRBCs). It was concluded that lentinan has prophylactic potential for the treatment of malaria. The immunomodulation effects of lentinan through oral administration were investigated and the results obtained proved its efficacy, that prefeeding of the mice for 7 days at an optimum dose of 3 mg/mouse was most effective against tumor induction, achieving a tumor inhibition rate (TIR) of 94.44%. Possible immune system regulating actions of lentinan were summarized. 

3. Antimicrobial Activity
Antimicrobial activity has been found in liquid cultures, chloroform, ethyl acetate, water and dried fruit body extracts of L. edodes. These extracts are active against gram positive and gram-negative bacteria, yeasts and mycelial fungi, including dermatophytes and phytopathogens. Mycelial-free culture of L. edodes exhibited greater antimicrobial effect against grampositive than gram-negative bacteria with Bacillus subtilis and Staphylococcus aureus among the most highly inhibited. Antimicrobial compounds isolated from L. edodes liquid cultures include lentinamicin (octa-2, 3-diene-5, 7 diyne-1-ol), -ethyl phenyl alcohol. 

L. edodes had been believed to cure the common cold for hundreds of years. More recently, some scientific evidences have been obtained to support this belief. L. edodes showed an activity (expressed as the percentage decrease in lung lesion score compared with the control) of 46%, which was of the same magnitude as for amantadine hydrochloride, a common drug against influenza (40%). A watery extract from L. edodes was also reported to prevent the multiplication of polio virus. Lentinan enhanced the host resistance against infections with bacteria, fungi, parasites, and viruses, including the agents of AIDS. Lentinan reduced the toxicity of azidothymidine AZT (a drug commonly used for treating HIV carriers and AIDS patients). Prevention of the onset of AIDS symptoms through potentiation of host defense is now being actively investigated both experimentally and clinically. In addition to lentinan, other substances from L. edodes have also been shown to have antiviral activity. The mechanism of their effect is in most cases via induction of interferon. Lentinan has also shown: (a) antiviral activity in mice against VSV (vesicular stomatis virus), encephalitis virus, Abelson virus, an adenovirus type 12; (b) stimulated nonspecific resistance against respiratory viral infection in mice; (c) conferred complete protection against an LD75 challenge dose of virulent mouse influenza A/SW15; (d) increased resistance to the protozoal parasites Schistosoma japanicum, Sch. mansoni; (e) exhibited activity against Mycobacterium tuberculosis bacilli resistant to antituberculosis drugs, Bacillus subtilis, Staphylococcus aureus, Micrococcus lenteus, Candida albicans and Saccharomyces cerevisiae; (f) increased host resistance to infections with potentially lethal Listeria monocytogenes. LEM and a new lignan-rich compound ‘JLS-18’ derived from LEM, blocked the release of infectious Herpes simplex virus in animal and it has been suggested because of its high activity that JLS-18 could be of value in the treatment of hepatitis B and AIDS patients. Water-soluble lignins from EP3 and EPS4 from shiitake mushroom mycelium have shown antiviral effects. 

4. Cardiovascular and Hypolipidemic Activity
Cardiovascular diseases are among the main causes of death in our society and there is a strong correlation between enhanced blood cholesterol levels and the development of such diseases. The popular macrofungus L. edodes, has been shown to produce blood cholesterol lowering compound designated eritadenine [2(R), 3(R)-dihydroxy-4-(9-adenyl)- butyric acid]. The hypocholesterolemic action of this compound has been quite extensively examined in rats. Eritadenine is suggested to accelerate the removal of blood cholesterol either by stimulating tissue uptake or by inhibiting tissue release. It was demonstrated that when rats were fed a diet supplemented with 5% (dry weight) of L. edodes fruiting bodies for 10 weeks the plasma cholesterol levels of the animals decreased significantly. Eritadenine works by lowering levels of all lipoprotein types, i.e., high-density as well as low-density lipoproteins. In addition to animal tests, the effectiveness of L. edodes in lowering blood serum cholesterol was also tested in human subjects. A daily intake of 90 g of fresh shiitake, 9 g of dried shiitake, and 9 g of UV-irradiated dried shiitake for 7 days lowered the mean serum cholesterol levels in young women by 12, 7 and 6%, respectively. All three diets decreased serum cholesterol levels of older persons (60 years of age) by 9% over 7 days. Eritadenine reduces blood serum cholesterol in mice, not by the inhibition of cholesterol biosynthesis, but by the acceleration of the excretion of ingested cholesterol and its metabolic decomposition. It has been shown to lower blood levels of cholesterol and lipids in animals. When added to the diet of rats, eritadenine (0.005%) caused a 25% decrease in total cholesterol in as little as one week. The cholesterol-lowering activity of this substance is more pronounced in rats fed a high fat diet than in those on a low-fat diet. Although feeding studies with humans have indicated a similar effect. The amount of cholesterol reducing agent (eritadenine) in L. edodes, in search of a potential natural medicine against blood cholesterol was quantified. 

5. Antidiabetic Activity
The hypoglycemic effect of an exo-polymer produced from a submerged mycelium culture of L. edodes was investigated in streptozotocin- induced diabetic rats, the administration of the exo-polymer (200 mg/kg BW) reduced the plasma glucose level by as much as 21.5%, and increased plasma insulin by 22.1% as compared to the control group. It also lowered the plasma total cholesterol and triglyceride levels by 25.1 and 44.5%, respectively. The hypoglycemic effect of L. edodes has been also demonstrated and proved its potential in lowering the blood glucose and triglyceride (TG) levels in the serum of rats. It also lowered the plasma total cholesterol and triglyceride levels by 25.1 and 44.5%, respectively. Exopolysaccharide (EPS) produced from submerged mycelial culture of Lentinus species was evaluated for hypogly cemic activity in streptozotocin (STZ)-induced diabetic rats. In dose-dependent study, orally administered L. strigosus EPS, at the dose of 150 mg/kg, exhibited a considerable hypoglycemic effect in STZ-induced diabetic rats. Plasma insulin levels of STZ-induced diabetic rats decreased as compared to control group rats. Although insulin levels slightly increased in the EPS-treated groups. The hypoglycemic potential of the EPS was further supported by histological observations of pancreatic islets of Langerhans.