Abstract
Ageing is often characterised by nutritional deficiencies and functional alterations of the digestive and immune system. The aim of the present study was to analyse the impact of consumption of conventional milk with A1/A2 beta-casein, compared to milk containing only the A2 beta-casein variant, characterised by a protein profile favouring gut health. Twenty-four ageing Balb-c mice (20 months old) were fed for 4 weeks, with either a control diet (CTRL), a diet supplemented with bovine milk containing A1/A2 beta-casein (A1A2) or a diet containing A2/A2 beta-casein (A2A2). Lymphocyte subpopulations, enzymatic activities, cytokine secretion, gut morphology and histopathological alterations were measured in different gut segments, while short-chain fatty acids (SCFAs) content and microbiota composition were evaluated in faecal samples. The A2A2 group showed higher content of faecal SCFAs (in particular, isobutyrate) of intestinal CD4+ and CD19+ lymphocytes in the intraepithelial compartment and improved villi tropism. The A1A2 group showed higher percentages of intestinal TCRγδ+ lymphocytes. Faecal microbiota identified Deferribacteriaceae and Desulfovibrionaceae as the most discriminant families for the A2A2 group, while Ruminococcaceae were associated to the A1A2 group. Taken together, these results suggest a positive role of milk, in particular when containing exclusively A2 beta-casein, on gut immunology and morphology of an ageing mice model.
Highlights
Milk is an important component of the diet and a source of lipids, carbohydrates, proteins with high biological value, minerals, like calcium, phosphorous, magnesium, several trace elements, like zinc and iodine, as well as B2, B12, D and A vitamins [1]
The aim of the present work was to analyse the effect of consumption of conventional milk, containing the A1/A2 beta-casein variant, compared to milk containing only the A2 beta-casein variant, in an animal model of ageing mice, to assess whether diet supplementation with bovine milk containing different beta-casein profiles could differently impact on gut health, by evaluating gut morphology and enzymatic activity, immunological phenotype, microbiota composition and short-chain fatty acids (SCFAs) production
In order to verify the presence of the two different beta-casein allele variants, the C > A single nucleotide substitution at position 473 of bovine beta-casein sequence was evaluated by an external laboratory using Real-Time PCR in the two milk batches, confirming that A1/A2 beta-casein (A1A2) milk was heterozygous, while A2/A2 beta-casein (A2A2) milk was homozygous for the A2 variant
Summary
Milk is an important component of the diet and a source of lipids, carbohydrates (mainly lactose), proteins with high biological value, minerals, like calcium, phosphorous, magnesium, several trace elements, like zinc and iodine, as well as B2, B12, D and A vitamins [1]. Beta-casein, a 209-amino acid protein, is the second most abundant casein in bovine milk and represents about 30% of total caseins. Several genetic variants of beta-casein have been described (UniProtKB, accession number P02666), among which the most represented are named as A1 and A2. The amount of A1 and A2 beta-casein variants in milk depends on the breed of cattle: African and Asian species produce milk containing only the A2 variant, while European cattle produce mainly A1 beta-casein. The milk commercially produced in many countries contains a mixture of both variants, in different proportions [2]
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