Due to the medicinal importance of mushrooms, the Romans viewed them as the ―food of the gods‖, and the Chinese viewed them as an ―elixir of life‖ (Mattila; Suonpaa; Piironen, 2000). The benefits of mushroom compounds for different clinical conditions have attracted the interest of the scientific community in the past decade, resulting in efforts to understand the molecular mechanisms responsible for the health benefits of mushrooms (Wasser, 2011).
Studies conducted over the past few decades have shown that mushrooms have a number of nutritional and functional properties that could make a notable contribution to the design of healthy eating patterns (Chang, 1996; Kalogeropoulos et al., 2013). In recent years, to unravel unanswered questions about mushrooms, especially those used in traditional medicine, mushrooms are being investigated due to the many ethnomycological claims for their medicinal value (Chang; Buswell, 2008). This topic has contributed to the great increase in the cultivation of varieties, as many of these varieties are sold as medicines in capsule form (e.g., A. blazei).
Mushrooms contain significant amounts of bioactive substances, such as vitamins and precursors to vitamins, minerals, trace elements and beta-glucans. Moreover, the specific antioxidant properties of mushrooms are attributed primarily to their phenolic content (Kalogeropoulos et al., 2013). Among the potential therapeutic uses of mushrooms are those linked to the anti-tumor activity of many species, as well as other benefits such as antioxidant activity, anti-inflammatory activity, antiviral activity, immunomodulatory activity, the lowering of cholesterol levels and beneficial effects on hypertension and diabetes. Moreover, mushrooms may be used against autoimmune diseases, such as rheumatoid arthritis and lupus (Smith; Rowan; Sullivan, 2002).
As mushrooms represent a source of compounds with pharmacological properties that show potential for the prevention of these diseases, we present several of the principal activities associated with the health effects of mushrooms:
a) Anti-tumor: there is evidence that mushrooms, as a food, play a role in cancer chemoprevention. Although the mechanism of antitumor action is not yet fully known, researchers believe that anticancer activity is associated with cell wall polysaccharides in the fruiting body (fruit) that can stimulate the formation of antibodies that inhibit tumor growth. In this case, the most important known polysaccharide is beta-glucan, which enhances the immune system by increasing the natural defenses of the body (Manzi; Pizzoferrato, 2000; Smith; Rowan; Sullivan, 2002).
b) Diabetes: components derived from mushrooms have been shown to have an effect in the control of diabetes by regulating various pathophysiological pathways related to the onset of the disease (Li et al., 2011; Xiao et al., 2011; Huang et al., 2012). Several antihyperglycemic mechanisms associated with medicinal mushrooms have been investigated, including the improvement of β cells and insulin-releasing activity, antioxidant defenses, the pathways of carbohydrate metabolism and α- glucosidase inhibitory activity of aldose reductase, but more conclusive data are needed (De Silva et al., 2012).
c) Hypertension: several types of mushrooms have shown hypotensive effects when blood pressure is already high (Guillamon et al., 2010). One of these possible effects is related to the low concentration of sodium and the high concentration of potassium (182–395 mg/100 g) in mushrooms (Manzi et al., 1999). Several studies have investigated the anti-hypertensive effects of certain edible mushroom species, e.g., L.
edodes, Ganoderma lucidum, Pleurotus narbonensis and G. frondosa (Guillamon et
al., 2010).
d) Cholesterol: in general, the intake of edible mushrooms reduces cardiovascular risk due to the occurrence of specific substances and other bioactive compounds
(Guillamon et al., 2010). Although the mechanism of action is unclear, the anti- triglyceride and anti-total cholesterol activities of edible mushrooms may be attributable to the fermentation of dietary fiber. Short-chain fatty acids, such as propionate, generated by the bacterial fermentation of dietary fibers have been shown to inhibit hepatic cholesterol synthesis (Chen; Anderson; Jennings, 1984; HARA et al., 1998). It has been suggested that dietary fiber from mushrooms might bind bile acids, reducing their entry into the enterohepatic circulation. This mechanism then produces an increase in gut bile acid secretion (Cheung, 1996). As a result, the liver responds by increasing the hepatic conversion of cholesterol into bile acids, reducing the circulating levels of cholesterol (Jeong et al., 2010). Several studies have shown lipid peroxidation inhibition and a suppression of the activity of HMG-CoA reductase in both normocholestolemic and hypercholesterolemic animal models (Guillamon et al., 2010).
e) Anti-inflammatory: certain species of fungi are known to produce significant anti- inflammatory effects (Jose; Ajith; Janardhanan, 2004; Kim et al., 2004; Lull; Wichers; Savelkoul, 2005), and natural anti-inflammatory substances have been isolated from certain edible mushrooms. In addition, it has been reported that ergosterol and ergosterol peroxide from edible mushrooms can inhibit inflammatory processes (Guillamon et al., 2010).
f) Immune-modulatory: several classes of mushroom compounds, such as proteins, polysaccharides, lipopolysaccharides and glucoproteins, have been classified as molecules that have potent effects on the immune system. They may restore and augment the immunological responses of the host immune effector cells, but they have no direct cytotoxic effect on tumors. The regular intake of mushrooms may enhance the immune response of the human body, thereby increasing resistance to disease and, in certain cases, causing regression of the disease state (Chang; Buswell, 2003; Wasser, 2011).
Medicinal mushrooms present an excellent opportunity for the development of new types of therapies and have been valued for their potential healing properties for centuries (Liu et al., 2012; Pereira et al., 2012). Additional evidence on the beneficial effects of medicinal mushrooms has been obtained through in vitro and animal studies (Badole et al., 2006; Ding et al., 2010). Safety issues in terms of the long-term consumption of mushrooms and inter- crossing or interactions with other drugs also need further clarification. Therefore, future investigations of these topics are necessary to rationalize the use of mushrooms and their products as drugs or nutritional supplements used in potential diabetes treatments (De Silva et al., 2012).