Biology and Chemistry of Beta Glucan Volume Title: Beta-Glucan, Structure, Chemistry and Specific Application

Glucans are most widespread fungal polysaccharides. Isolation of fungal glucans from raw materials requires special intervention to remove other compounds, i.e., proteins, lipids, polyphenols, as well as other polysaccharides. Purity control and structural identification of isolated polysaccharides are necessary for quality estimation of the isolation and purification processes or their specific steps. Modern chemical, spectroscopic and separation methods are able to assist solving these tasks and possess information about the structure of fungal glucans. Organic elemental analysis gives information about elements present in native glucans. Occasional presence of nitrogen could be explained by the contribution of nitrogen-containing compounds like proteins and chitin (chitosan). Total and/or reducing sugars, uronic acids, chitin and/or proteins are commonly estimated to evaluate glucan purity. Gel permeation (size-exclusion) chromatography, laser light scattering and viscometry give information about homogeneity, molecular weight distribution and branching. Monosaccharide composition is usually determined by total hydrolysis under strongly acidic conditions at elevated temperature followed by chromatographic separation of released simple sugars. FTIR and NMR spectroscopy are powerful tools in analysis of purity and structure of fungal glucans. Exact configuration of these polysaccharides can be deduced from the results of sugar linkage analysis and correlation NMR spectra.

The ability of yeast cell wall fractions to stimulate immunity and increase resistance to disease is well documented. For more than fifty years we have known that the immune stimulating activity of yeast cell walls is primarily due to the (1→3,1→6)-β-Dglucans (hereafterβ-glucans), which are important structural components of the cell wall. Evidence indicates that the bioactivity of β -D-glucans is intimately linked to the structure and physicochemical properties of these complex carbohydrate polymers. Virtually all natural product β -glucan isolates are a distribution of glucan polymers with varying polymer lengths, varying molecular weight and, in most cases, differences in branching frequency, length of side chain branches and solution conformation. This level of structural complexity and variability presents a number of challenges to investigators attempting to understand the chemistry and biology of glucans. Herein, we describe the physicochemical analysis, structural chemistry and quantification of glucans derived from natural sources. This work has not only advanced our understanding of these intriguing and medically important biomolecules, but it has also provided a foundation for the development of methods for the total organic synthesis of bioactive β -glucan oligosaccharides. The availability of synthetic β -glucan oligosaccharides of defined structure and composition may herald a new era in the field of glucan biology.

The synthesis of β-(1→3)-glucans is at present has more than a chemical challenge. The discovery of their biological properties found development for new anticancer therapies, the efficient preparation of pure and structurally well-defined β-(1→3)-glucans has generated interest in the glycochemist community. This chapter highlights recent strategies that not only yielded the target biomolecules but have also drawn attention on basic limitations. It also shows how it is possible to strengthen the activity of β-glucans by conjugation to non saccharidic derivatives.

The lightning progress in the understanding of enzymatic mechanisms, democratization of molecular biology tools and their introduction in chemistry laboratories, the pressure of green chemistry notions leading to the need for alternative sustainable and more environmentally friendly approaches, and probably economic factors as well, all these parameters allowed the development of new synthetic strategies based on biocatalysis. This chapter is dedicated to the use of glucosyl hydrolases and some of their mutants, i.e., glucosynthases and thioligases, to the preparation of β-(1,3)-(thio)glucosides.

Photodynamic therapy (PDT) combines a drug or photosensitizer with a specific type of light to eradicate cancer cells. The cellular damage induced by PDT leads to activation of the DNA damage repair, which is an important factor for modulating tumor sensitivity to this treatment. β-Glucans bind complement receptor 3 on the effector cells, thereby activating them to kill tumor cells during PDT. Here, the hypothesis that adjuvant therapy with β-glucans would increase the efficacy of PDT resulting in pronounced necrosis of PDT-treated tumors and suppression of the DNA damage repair system is discussed.

Environmental exposure to β-glucan is ubiquitous. A review of different cellular reactions induced by β-glucan demonstrates a complex pattern of inflammatory reactions depending upon the molecular structure, the dose, and the duration of exposure. Epidemiological data suggest that airways inflammation, atopy, hypersensitivity pneumonitis, and sarcoidosis are related to β-glucan exposure although causality cannot be ascertained. Treatment and health promotion benefits by β-glucan are less clear cut.

Our knowledge of β-glucan effects on invertebrate immunity is still limited. However, more attention is being focused due to the ongoing importance of invertebrate farming for agricultural and nutritional exploitation. Aquacultures of shrimp and shellfish represent an important source of human nutrition and unprecedented growth of aquaculture production in the past decade has caused an increased demand in the prevention of infectious diseases among farmed animals. As a result, new ways to improve the resistance and treatment of diseases are being researched.

Administration of β-glucans through immersion, dietary inclusion, or injection was found to enhance many innate immune responses, resistance to bacterial and viral infections, resistance to pathological and environmental stresses, and growth performance in many shrimp species. This chapter focuses on the efficacy of the glucan administration: (1) as influenced by types of glucans, methods of administration, and shrimp species; (2) on shrimp bacterial and viral diseases as well as humoral and cellular immune responses; (3) on expression of defense-related genes; and (4) on growth and stress tolerance of shrimp. Despite that β-glucan administration is fairly effective in stimulating immune response activities and diseases resistance, the practice of dietary inclusion or drug immersion is not widely practiced in shrimp farms and feed mills, mostly because of the cost of the treatment. Development of more cost-effective glucans as well as more efficient administration methods will facilitate the routinely and prophylactic use of β-glucans as the immunostimulants of shrimp.