Abstract
Aleurone, a layer of the bran fraction, is deemed to be responsible for the positive health effects associated with the consumption of whole-grain products. Studies on rodents, pigs, and humans report beneficial effects of aleurone in five main areas: the reduction of oxidative stress, immunomodulatory effects, modulation of energy management, digestive health, and the storage of vitamins and minerals. Our study is the first aleurone supplementation study performed in horses. The aim of this study was to investigate the effect of an increase in the dose levels of aleurone on the postprandial glucose-insulin metabolism and the gut microbiome in untrained healthy horses. Seven adult Standardbred horses were supplemented with four different dose levels of aleurone (50, 100, 200, and 400 g/day for 1 week) by using a Latin square model with a 1-week wash out in between doses. On day 7 of each supplementation week, postprandial blood glucose-insulin was measured and fecal samples were collected. 16S ribosomal RNA (rRNA) gene sequencing was performed and QIIME2 software was used for microbiome analysis. Microbial community function was assessed by using the predictive metagenome analysis tool Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) and using the Metacyc database of metabolic pathways. The relative abundancies of a pathway were analyzed by using analysis of composition of microbiomes (ANCOM) in R. There was a significant dose-dependent increase in the postprandial time to peak of glucose (p = 0.030), a significant delay in the time to peak of insulin (p = 0.025), and a significant decrease in both the insulin peak level (p = 0.049) and insulin area under the curve (AUC) (p = 0.019) with increasing dose levels of aleurone, with a consideration of 200 g being the lowest significant dose. Alpha diversity and beta diversity of the fecal microbiome showed no significant changes. Aleurone significantly decreased the relative abundance of the genera Roseburia, Shuttleworthia, Anaerostipes, Faecalibacter, and Succinovibrionaceae. The most pronounced changes in the relative abundance at phyla level were seen in Firmicutes and Verrucomicrobia (downregulation) and Bacteroidetes and Spirochaetes (upregulation). The PICRUSt analysis shows that aleurone induces a downregulation of the degradation of L-glutamate and taurine and an upregulation of the three consecutive pathways of the phospholipid membrane synthesis of the Archaea domain. The results of this study suggest a multimodal effect of aleurone on glucose-insulin metabolism, which is most likely to be caused by its effect on feed texture and subsequent digestive processing; and a synergistic effect of individual aleurone components on the glucose-insulin metabolism and microbiome composition and function.
Highlights
Fold change (FC) 0.042) and the L-glutamate degradation VIII pathway (W = 226 ≥ W0.7; FC 0.054) were decreased as well. This is the first study focusing on the effects of aleurone supplementation in horses
A Latin square model was applied in seven horses to study the effect of different doses of aleurone on the postprandial glucose and insulin metabolism as well as the gut microbiome
The delayed time to peak of postprandial glucose has not been explored in many studies, which focus on the supplementation of aleurone or one of its components [78]
Summary
Whole-grain products have been incorporated in human and animal diets for some decades, which meet the conventional nutritional needs such as dietary fiber content and allow for an improvement of gut microbiome, a stimulation of increased metabolic health, lower risk of cardiovascular disease mortality, and a lower risk of cancer [1,2,3,4,5,6,7,8].Aleurone is known as the layer within the bran fraction of wheat, rye and oat, that is deemed to be responsible for positive health effects associated with the consumption of whole-grain products [9,10,11]. Aleurone comprises a single-cell layer located between the endosperm and the seed coat of the wheat kernel [12, 13]. The predominant function inside the wheat kernel is to regulate the exchange of nutrients that are stored inside the endosperm to allow for the seed embryo germination [14, 15]. Advanced milling and dry-fractionation techniques have been developed to separate the aleurone from the bran fraction [(20–22); Bühler Group, Switzerland]. This allows for a selective incorporation of pure aleurone in both food and feed [23]. Based on the applied fractionation technique, aleurone is available in different purity forms: Aleurone Standard Preparation 1 (ASP01) or a more purified form ASP-02 [(24); Table 1]
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