Fractionated Dairy Cow Milk β-Casein Enhances Affinity of the Jejunal Alkaline Phosphatase for Hydrolyzing ATP in Piglets Fed Liquid Formulas

Some bioactive peptides originating from β-casein have been shown to be resistant to enzymatic digestion in the gastrointestinal tract and to influence immunological responses. Intestinal alkaline phosphatase (IAP), a critical anti-inflammatory mediator, can catalyze the hydrolytic dephosphorylation of endotoxin lipopolysaccharides (LPS) and other emblematic members of pathogen-associated-molecular patterns (PAMPs) such as ATP, therefore preventing gut dysbiosis and disorders. Objectives of this study were to determine responses in the enzyme kinetics, including affinity (Km) and maximum activity (Vmax) of IAP in hydrolyzing ATP, in piglets fed liquid formulas with varying levels of β-casein. Three formulas were formulated, including a control formula containing whey protein as the sole source of protein, and two testing formulas containing total casein to whey protein ratio (%) of 40:60, but differing in β-casein at 3.51 and 4.36% (on air-dry basis), respectively. Contents of all other dietary nutrients, including ME, CP, minerals and vitamins, were formulated to be equal among the three formulas. A total of 24 colostrum-suckled 3-d-old piglets were randomly assigned to the three formulas, housed individually in metabolic crates, and fed their assigned formulas for 18 d according to a randomized block design. Piglets were euthanized at the end of their study periods and the proximal jejunal tissue samples were collected. Each kinetic experiment was conducted with homogenized porcine jejunal samples (about 5 μg protein each incubation) and 11 gradient concentrations of ATP, ranging 0 – 1.25 mM in incubation media in 4 replicates at pH 7.4 and 37⁰C. The kinetics (parameter estimates ± SE, P < 0.05, R² = 0.66 – 0.93 for equations; n = 44) of jejunal IAP in hydrolyzing dephosphorylation of ATP were obtained, including Vmax values (ug/mg protein·min) of 4.39 ± 0.12, 2.90 ± 0.07, and 2.17 ± 0.14; and Km values (mM,) of 0.070 ± 0.008, 0.056 ± 0.006, and 0.046 ± 0.013 in the control, the 3.51%-β-casein, and the 4.36%-β-casein formulas, respectively. Pooled t-test comparisons showed although the Vmax values were reduced (P < 0.05) by dietary β-casein feeding, the Km value of the control group was higher (P < 0.05) than the 3.51%-β-casein group by 20%, and the 4.36%-β-casein group by 52%, respectively. Results of this study suggest dietary β-casein affects the jejunal IAP functionality. Dietary inclusion of β-casein at 3.51-4.36% has been demonstrated to increase IAP affinity for dephosphorylation of ATP, potentially protecting neonatal piglets from gut dysbiosis and inflammation.