Meridian Medical Group

Functional Properties of Edible Mushrooms by Dr. Raymond Chang, M.D., F.A.C.P.

Commonly known mushrooms that are both edible and have functional properties include Auricularia (mu-er),Flammulina (enokitake), Grifola (rnaitake), Hericium, Lentinus (shiitake), Pleurotus (oyster), and Tremella (yiner). Most edible mushrooms, however, do not have medicinal value (e.g., Agaricus bisporus), and some medicinal mushrooms (e.g. Ganoderma, Coriolus) are not edible. Of the

10,000 known species of mushrooms, it is currently thought that

700 are edible and >200 may have medicinal value, although only a small percentage of these mushrooms are available to the consumer.1

Although many cultures have used mushrooms as both food and medicine, the use of mushrooms as a functional food is most notable in the East, where application of mushrooms to maintain health was formally recorded as early as 100 AD in China. Mushrooms have been incorporated into health tonics, tinctures, teas, soups, arid healthful food dishes, as well as herbal formulas. Within the framework of traditional medicine, mushrooms have been applied to lubricate the lungs (Tremella fuciformis), tonify the kidneys (Cordyceps sinensis), reduce excessive dampness (Grifola umbellate), and invigorate the spleen (Poria cocos). More recently, functional mushrooms have been shown to modulate the immune system, lower blood pressure and blood lipid concentrations, and inhibit tumors, inflammation, and microbial action. I will discuss the shiitake (Lentinus edodes) as a model of the functional mushrooms with demonstrated bioactivity because it is widely consumed as a food in the East and increasingly in the West, arid extensive research on its bioactivity has led to the isolation of pure compounds that have reached pharmaceutical status.

Shiitake as a Model for Functional Mushrooms
Shiitake is the common Japanese name for Lentinus edodes, and is also the common name now used in the West. Indigenous to Asia, shiitake is now cultivated and is the second most commonly produced edible mushroom in the world .2 Besides being a culinary delicacy, there is a long tradition of use of shiitake as medicine in Asia, dating back >2000 years.

Shiitake contains protein (26% of dry weight) , 3 lipids (primarily linoleic acid); carbohydrate; fiber; minerals; vitamins B-1, B-2, and C; and ergosterol , 4 the D provitamin. Besides its nutritive content several important compounds have been isolated from shiitake that have immunomodulatory, lipid-lowering, and antimicrobial properties. These include lentinan, Lentinus edodes mycelium (LEM), KS-2, and eritadenine. Of these, lentinan is the most studied.

In 1969, Ikekawa et al .5 noted that a water extract of shiitake fruiting bodies could inhibit transplanted tumors in mice. Around the same time, Chihara et al .6 isolated an antitumor polysaccharide from shiitake and named it lentinan. The molecular formula for lentinan is (C6H10O5)n, and the mean molecular mass is 500 kDa. Lentinan is a D-glucan as shown by electrophoresis, ultracentrifugation, and other instrumental analyses, Its structure was confirmed as ( 1, 3)-D-glucopyranan with a branched chain of (1,6)-monoglycosyl, showing a right-handed triple helix. 7 ,8 Lentinan has been found to activate macrophages, Tlymphocytes, and other immune effector cells that modulate the release of cytokines, which may in turn account for its indirect antitumor and antimicrobial properties .9

The antitumor effects of lentinan are believed to be a result of immunopotentiation, which has been demonstrated in allogeneic, syngeneic, and autologous rodent tumor test systems and confirmed in randomized, controlled clinical trials in humans.10 For example, Taguchi 11 reported significant improvement(p<0.01) in survival in patients with advanced gastric cancer who were treated with lentinan and chemotherapy compared with those treated with chemotherapy alone. The antimicrobial effects of lentinan are also believed to be enacted via immunologic potentiation of host defenses, which has been demonstrated against bacterial, viral, and parasitic infections.12

Other biologically active polysaccharide fractions have also been conjugate as its major active constituent. 13 It is active orally, and has been studied mostly for its antiviral properties, In a clinical trial of 4O patients with chronic hepatitis B, LEM improved liver function and reduced viremia, 14 More interestingly, LEM has been shown to inhibit human immunodeficiency virus (HIV) infection in vitro 15 and may hove promise as a therapy for acquired immunodeficiency syndrome. Another compound isolated from shiitake is eritadenine, which has been shown to lower serum cholesterol and lipid concentrations in various studies in rodents. 16,17 Besides the well-studied compounds just discussed, other potentially beneficial compounds have been found in shiitake. One example is thioproline, which blocks the formation of carcinogenic N-nitroso compounds.18

A purified compound is very different from the whole mushroom, however, and the inevitable questions that follow are whether eating the whole mushroom has preventive or therapeutic value, and if so, how much mushroom should be consumed and in what form. For shiitake, researchers found that the powdered mushroom fruit bodies given to rats as 10-20% of their diet inhibited transplanted tumors, 19,20 and small studies have demonstrated lipid-lowering effects consumption of 9 g of dried mushrooms or 90 g of fresh mushrooms.21

The content and potency of bioactive ingredients may differ depending on how the mushroom is prepared and ingested. For example, the anticarcinogenic thioproline content varies from undetectable amounts in fresh shiitake, to 134 mg/100 g of dried shiitake, to 843 mg/100 g of boiled shiitake.18 As is the case for most plants and herbs, the specific strain, growing conditions, and other environmental factors will also significantly affect the taste, form, and substance of the mushroom, as well as affect the bioactive content.22

Summary
Edible mushrooms such as shiitake may have important salutary effects on health or even in treating disease. A mushroom characteristically contains many different bioactive compounds with diverse biological activity, and the content and bioactivity of these compounds depend on how the mushroom is prepared and consumed. It is estimated that

5O% of the annual 5 million metric tons of cultivated edible mushrooms contain functional "nutraceutical" or medicinal properties.2 In order of decreasing cultivated tonnage, Lentinus (shiitake), Pleurotus (oyster),Auricularia (mu-er), Flammulina (enokitake), Tremella (yin-er) Hericium, and Grifola (maitake) mushrooms have various degrees of immunomodulatory, lipid-lowering, antitumor, and other beneficial or therapeutic health effects without any significant toxicity.

Although the data for this functional food class are not as strong as those for other functional foods such as cruciferous vegetables, because of their potential usefulness in preventing or treating serious health conditions such as cancer, acquired immune deficiency syndrome (AIDS), and hypercholesterolemia. Functional mushrooms deserve further serious investigation. Additionally, there is a need for epidemiological evidence of the role of this functional food class.