Edible Mushrooms and Beta-Glucans: Impact on Human Health

Abstract

Mushroom cell walls are rich in β-glucans, long or short-chain polymers of glucose subunits with β-1,3 and β-1,6 linkages, that are responsible for the linear and branching structures, respectively. β-glucans from cereals, at variance, have no 1,6 linkages nor branching structures. Both immunomodulatory and anti-inflammatory effects of mushrooms have been described using purified β-glucans or fungi extracts on cellular and experimental models; their potential clinical use has been tested in different conditions, such as recurrent infections of the respiratory tract or complications of major surgery. Another promising application of β-glucans is on cancer, as adjuvant of conventional chemotherapy. β-glucans may protect the cardiovascular system, ameliorating glucose, lipid metabolism, and blood pressure: these activities, observed for oat and barley β-glucans, require confirmation in human studies with mushroom β-glucans. On the other hand, mushrooms may also protect the cardiovascular system via a number of other components, such as bioactive phenolic compounds, vitamins, and mineral elements. The growing knowledge on the mechanism(s) and health benefits of mushrooms is encouraging the development of a potential clinical use of β-glucans, and also to further document their role in preserving health and prevent disease in the context of healthy lifestyles.

Keywords: cancer adjuvant; cardiometabolic system; healthy diet; immune modulation; microbiota; mushrooms; β-glucans.

Figure 1

Chemical structures of β-glucans. The side branches of mushroom β-glucans (A) are attached to the β-1,3-D-glucan main chain by a β-1,6 linkage, and may consist of one or several β-D-glucose units; cereal β-glucans (B) are linear and consist of D-glucose molecules linked by 1,3 β- and 1,4 β- linkages.

Figure 2

Schematic effect of β-glucans on immune and cancer cells. β-glucans are captured by the macrophages via the Dectin-1 receptor with or without TLR-2/6, internalized, fragmented into smaller fragments, carried to the marrow and endothelial reticular system and subsequently released. These small β-glucan fragments are eventually taken up by circulating granulocytes, monocytes or macrophages via the complement receptor (CR)3 and the immune responses turned include phagocytosis of the monoclonal antibody tagged tumor cells. From [37] with permission.

Figure 3

Schematic mechanisms of effect of dietary intake of β-glucans on cholesterol balance. β-glucans increase the production of short-chain fatty acids (SCFA) by intestinal microflora fermentation: SCFA inhibit cholesterol levels by acting on its synthesis, through inhibition of the hydroxymethylglutaryl-coenzyme A (HMG-CoA) reductase, and by increasing LDL-cholesterol catabolism. In addition, β-glucans, by forming a gel on the mucosal surface of the bowel, inhibit intestinal resorption of biliary salts, cholesterol, and fats and stimulate neo-synthesis of biliary salts in the liver.