ß-Glucans (Beta-Glucans)
are polysaccharides of D-glucose monomers linked by ß-glycosidic bonds. ß-glucans are a diverse group of molecules that can vary with respect to molecular mass, solubility, viscosity, and three-dimensional configuration. They occur most commonly as cellulose in plants, the bran of cereal grains, the cell wall of baker's yeast, certain fungi, mushrooms and bacteria. Some forms of beta glucans are useful in human nutrition as texturing agents and as soluble fiber supplements, but can be problematic in the process of brewing.
Research has shown that insoluble (1,3/1,6) ß-glucan, has greater biological activity than that of its soluble (1,3/1,4) ß-glucan counterparts. The most active forms of ß-glucans are those comprising D-glucose units with (1,3) links and with side-chains of D-glucose attached at the (1,6) position. These are referred to as ß-1,3/1,6 glucan. One of the most common sources of ß(1,3)D-glucan for supplement use is derived from the cell wall of baker’s yeast (Saccharomyces cerevisiae) which are often insoluble.
ß-glucans are known as "biological response modifiers" because of their ability to activate the immune system. Immunologists at the University of Louisville discovered that a receptor on the surface of innate immune cells called Complement Receptor 3 (CR3 or CD11b/CD18) is responsible for binding to beta-glucans, allowing the immune cells to recognize them as "non-self." Several health claims requests were submitted to the EFSA NDA Panel (Dietetic Products, Nutrition and Allergies), related to the role of ß-glucans in "maintenance of normal blood cholesterol concentrations and maintenance or achievement of a normal body weight". In July 2009, the Scientific Committee issued the following statements: On the basis of the data available, the Panel concludes that a cause and effect relationship has been established between the consumption of beta-glucans and the reduction of blood cholesterol concentrations.
In some studies, beta-1,3 glucans enhanced the effects of chemotherapy. In a mouse carcinoma model, beta-1,3 glucans did not reduce tumor incidence but was associated with reduced mortality in combination with cyclophosphamide. In human patients with advanced gastric or colorectal cancer, the administration of beta-1,3 glucans derived from shiitake mushrooms, in conjunction with chemotherapy resulted in prolonged survival times.
A study conducted by the Canadian Department of Defense showed that orally administered yeast ß-glucan given with or without antibiotics protected mice against anthrax infection. A dose of antibiotics along with oral whole glucan particles (2 mg/KG body weight or 20 mg/KG body weight) for eight days prior to infection with Bacillus anthracis protected mice against anthrax infection over the 10-day post-exposure test period. Mice treated with antibiotic alone did not survive.
Early research by Onderdonk et al. investigated the ability of yeast b-glucan to reduce septic infections using in vivo models. Onderdonk et al. found that mice challenged with E. coli or S. aureus bacteria were protected against septic infections when they were injected with PGG-glucan 4–6 hours prior to infection. Work by Kernodle et al. demonstrated that preventative dosing of yeast ß-glucan prior to infection with S. aureus prevented sepsis in a guinea pig model. Research has been conducted in animals on the use of yeast ß-glucans for the treatment and prophylaxis of bacterial sepsis and protection against oxidative organ injury.
For maximal absorption, oral ß(1,3)-D-glucan should be taken on an empty stomach.