Gut microbiota composition and immunity of ageing mice supplemented with cow milk containing a different casein profile

Objective: Ageing is characterised by nutritional deficiencies and functional alterations of the digestive and immune system, accompanied by altered gut microbiota composition. Cow milk containing A2 beta-casein was reported to be better tolerated in subjects with unspecific milk intolerance, in comparison to conventional milk containing A1 beta-casein. The aim of this study was to evaluate whether supplementation with milk containing A2 beta-casein could improve gut microbiota composition and immunity in an animal model of aging mice. Methods: Twenty-four, 20 months old Balb-c mice were fed three nutritionally balanced, isocaloric and isoproteic diets: standard (Control) or supplemented with cow milk containing either A1/A2 (Standard milk) or A2/A2 beta-casein (Test milk). At day 30, fecal samples were collected for Next Generation Sequencing (NGS) and HPLC for microbial composition and SCFA analysis, respectively. Lymphocyte subpopulations were evaluated by flow cytometry in jejunum. Results: Beta diversity analysis highlighted specific, significant variations of faecal microbiota composition in Test milk-supplemented mice with respect to the other groups. Comparison of taxonomical assignments among groups identified Lachnospiraceae as characterizing family within the two milk-supplemented mice. Moreover, Test milk-supplemented group showed a higher content of faecal SCFA (in particular, butyrate). Immunological analysis revealed higher percentage of T helper and B lymphocytes, paralleled by decreased numbers of T-cytotoxic lymphocytes, in mice supplemented with Test milk. Conclusions: Taken together, results suggest a positive role of milk containing A2 beta-casein when consumed by aged mice as supplementation, both in terms of increased differentiation of T-helper and B lymphocytes and of higher concentration of beneficial microbiota-derived fermentation products.