Evaluation of the toxicity of concentrated barley β-glucan in a 28-day feeding study in Wistar rats
Introduction
Oats and barley have long been known to lower serum cholesterol concentrations in animal models of hypercholesterolemia (De Groot et al., 1963). Consumption of these cereal grains has also demonstrated cholesterol-lowering activity in humans (Judd and Truswell, 1981, Anderson et al., 1984, Newman et al., 1989a, Newman et al., 1989b, Kestin et al., 1990, McIntosh et al., 1991, Ripsin et al., 1992, Lupton et al., 1994, Ikegami et al., 1996, Kahlon and Chow, 1997). However, consumption of relatively large amounts is required to produce clinically relevant reductions (Braaten et al., 1994). Therefore, many studies have been conducted to identify components present in these grains to which cholesterol-lowering activity could be attributable. Several substances have been identified that possess cholesterol-lowering activities (e.g. tocotrienols: Peterson and Qureshi, 1997, Qureshi et al., 1980, Qureshi et al., 1986). However, it is the bran fractions to which the cholesterol-lowering activity has most consistently been associated (Kirby et al., 1981, Anderson et al., 1984, Anderson et al., 1990, Anderson et al., 1991), more specifically, to the β-glucan component (Davidson et al., 1991, Braaten et al., 1994).
Relative to other cereal grains, oat bran contains high concentrations of soluble fiber of which a considerable proportion is β-glucan (>50%: Asp et al., 1992, Aman and Graham, 1987). The concentration of β-glucan in barley appears to be even higher than that of oats (Aman and Graham, 1987, Newman et al., 1992). Chemically, β-glucans are a heterogeneous group of water-soluble endospermic cell-wall polysaccharides consisting of (1→3,1→4)-β-d-linked glucose units (Wood et al., 1989). The β-glucan from barley and oats appears to be chemically indistinguishable (Jeraci and Lewis, 1989).
Concentrated preparations of oat β-glucan have demonstrated cholesterol-lowering activity in humans and animal models of hypercholesterolemia (Kirby et al., 1981, Davidson et al., 1991, Knuckles et al., 1992, Jonnalagadda et al., 1993, Kahlon et al., 1993, Braaten et al., 1994, Zhang et al., 1994, Yokoyama et al., 1998, Onning et al., 1999), as have similar products prepared from barley (Newman et al., 1989a, Newman et al., 1989b, Knuckles et al., 1992, Wang et al., 1992, Kahlon et al., 1993, German et al., 1996, Maqueda de Guevara et al., 2000). A recent study comparing β-glucan-enriched fractions from oats and barley in hypercholesterolemic hamsters demonstrated that the cholesterol-lowering activity of β-glucan from oats and barley was nearly identical (B. Delaney et al., unpublished data, 2002).
These studies suggest that β-glucan-enriched soluble fiber from barley may be useful in controlling elevated serum cholesterol concentrations in humans and an interesting commercial product. Although barley itself and foods containing soluble fibers are not considered unsafe, little toxicological information is available regarding the safety following repeated exposure to concentrate enriched in β-glucan. In the present study, the toxicity of a water-extracted β-glucan-enriched soluble fiber from barley (Barley Betafiber) was evaluated in a 28-day feeding study in Wistar rats. This study was conducted in accordance with OECD Guideline for Testing Chemicals n. 407 (adopted July 27, 1995) and in compliance with the OECD Principles of Good Laboratory Practice.
Section snippets
Preparation of β-glucan enriched soluble fiber concentrate
β-Glucan from hulless barley (Azhul variety) was extracted by a process similar to that of Aman and Hesselman (1985) but without the amyloglucosidase treatment step. The composition of the concentrated β-glucan product (Barley Betafiber, Cargill, Inc., Wayzata, MN) is presented in Table 1.
Analysis of β-glucan in barley concentrate and rat feed
β-Glucan in the barley concentrate was quantified enzymatically (McCleary, 1985) using a Megazyme β-glucan mixed linkage assay kit. β-Glucan-enriched soluble fiber samples were milled to pass through a 0.5-mm
Analysis of β-glucan in rat feed
The concentration of β-glucan was determined in the different feed samples blended with the indicated concentration of the (Barley Betafiber). Limited specificity of the analytic method was observed since control diets appeared to possess approximately 0.7% β-glucan (Table 2). This observation indicated either that a small amount of glucose was released by the enzymatic treatment during the analysis or that the dietary blend did contain a small amount of β-glucan. Following correction for the
Discussion
Oats and barley lower serum cholesterol concentration in humans (Judd and Truswell, 1981, Anderson et al., 1984, Newman et al., 1989a, Newman et al., 1989b, Kestin et al., 1990, McIntosh et al., 1991, Ripsin et al., 1992, Lupton et al., 1994, Ikegami et al., 1996, Kahlon and Chow, 1997). This activity is attributable to the soluble fiber fraction of these cereal grains, more specifically, to the β-glucan component (Davidson et al., 1991, Braaten et al., 1994). The β-glucan in oats and barley
References (54)
- et al.
Dietary nonstarch polysaccharides interact with cholesterol and fish oil in their effects on plasma lipids and hepatic lipoprotein receptor activity in rats
Journal of Nutrition
(1993) - et al.
An enzymatic method for analysis of total mixed-linkage β-glucans in cereal grains
Journal of Cereal Science
(1985) - et al.
Lipid responses of hypercholesterolemic men to oat-bran and wheat bran intake
American Journal of Clinical Nutrition
(1991) - et al.
Hypocholesterolemic effects of oat-bran or bean intake for hypercholesterolemic men
American Journal of Clinical Nutrition
(1984) - et al.
Cholesterol lowering effect of rolled oats
Lancet
(1963) - et al.
Determination of the soluble fiber components(1→3; 1→4)-β-D-glucans and pectins
Animal Feed Science and Technology
(1989) - et al.
Plasma total and lipoprotein cholesterol, liver cholesterol and fecal cholesterol excretion in hamsters fed fiber diets
Journal of Nutrition
(1993) - et al.
The effects of rolled oats on blood lipids and fecal steroid excretion in man
American Journal of Clinical Nutrition
(1981) - et al.
Comparative effects of three cereal grains in plasma lipids, blood pressure, and glucose metabolism in mildly hypercholesterolemic men
American Journal of Clinical Nutrition
(1990) - et al.
Oat-bran intake selectively lowers serum low-density lipoprotein cholesterol concentrations of hypercholesterolemic men
American Journal of Clinical Nutrition
(1981)
Cholesterol-lowering effect of barley bran flour and oil
Journal of the American Dietetic Association
Barley and wheat foodsinfluence on plasma cholesterol concentrations in hypercholesterolemic men
American Journal of Clinical Nutrition
The structure of an inhibitor of cholesterol biosynthesis isolated from barley
Journal of Biological Chemistry
Regulation of lipid metabolism in chicken liver by dietary cereals
Journal of Nutrition
Effect of orally administered β-glucan on macrophage function in mice
Scandinavian Journal of Immunology
Barley β-glucans alter intestinal viscosity and reduce plasma cholesterol concentration in chicks
Journal of Nutrition
Analysis of total and insoluble mixed-linked (1→3)(1→4)-β-D-glucans in barley and oats
Journal of Agricultural and Food Chemistry
Soluble fiber: Hypocholesterolemic effects and proposed mechanisms
Variation in bietary fibre, β-glucan, starch, protein, fat, and hull content of oats grown in Sweden 1987-1989
European Journal of Clinical Nutrition
Interaction of dietary cholesterol with cholate in ratseffect on serum cholesterol, liver cholesterol, and liver function
Nutrition Reports International
Lysosomal glycosidases in mouse peritoneal macrophages stimulated in vitro with soluble and insoluble glycans
Journal of Leukocyte Biology
Oat β-glucan reduces blood cholesterol concentration in hypercholesterolemic subjects
European Journal of Clinical Nutrition
A β-Glucan inhibitable receptor on human monocytesits identity with the phagocytic receptor for particulate activators of the alternative complement pathway
Journal of Immunology
Isolation and characterization of β-glucan receptors on human macronuclear phagocytes
Journal of Experimental Medicine
The hypocholesterolemic effects of β-glucan in oatmeal and oat bran
Journal of the American Medical Association
Cited by (40)
Mushroom β-glucan and polyphenol formulations as natural immunity boosters and balancers: nature of the application
2023, Food Science and Human WellnessCitation Excerpt :Mycoceutical formulations based on β-glucans are generally considered safe. Consumption of concentrated β-glucan was not associated with any obvious signs of toxicity [56,102]. Adverse events and consequences of treatment with mushroom polysaccharide-based nutraceuticals were poorly reported and appeared to be rare.
Subchronic toxicity and genotoxicity studies of Hericium erinaceus β-glucan extract preparation
2022, Current Research in ToxicologyAssessment of toxicological potential of sodium carboxymethyl beta-glucan, a novel beta-glucan
2021, Food and Chemical ToxicologyBeta-glucan
2021, Nutraceuticals and Health CareSubchronic toxicity and genotoxicity studies of Antrodia mushroom β-glucan preparation
2018, Regulatory Toxicology and Pharmacology
- 1
Present address: Land O'Lakes, Inc., PO Box 64101, St. Paul, MN 55164-0101, USA.