No abstract

Dairy is one of the main sources for high quality protein in the human diet. Processing may, however, cause denaturation, aggregation, and chemical modifications of its amino acids, which may impact protein quality. This systematic review covers the effect of milk protein modifications as a result of heating, on protein digestion and its physiological impact. A total of 5363 records were retrieved through the Scopus database of which a total of 102 were included. Although the degree of modification highly depends on the exact processing conditions, heating of milk proteins can modify several amino acids. In vitro and animal studies demonstrate that glycation decreases protein digestibility, and hinders amino acid availability, especially for lysine. Other chemical modifications, including oxidation, racemization, dephosphorylation and cross-linking, are less well studied, but may also impact protein digestion, which may result in decreased amino acid bioavailability and functionality. On the other hand, protein denaturation does not affect overall digestibility, but can facilitate gastric hydrolysis, especially of b-lactoglobulin. Protein denaturation can also alter gastric emptying of the protein, consequently affecting digestive kinetics that can eventually result in different post-prandial plasma amino acid appearance. Apart from processing, the kinetics of protein digestion depend on the matrix in which the protein is heated. Altogether, protein modifications may be considered indicative for processing severity. Controlling dairy processing conditions can thus be a powerful way to preserve protein quality or to steer gastrointestinal digestion kinetics and subsequent release of amino acids. Related physiological consequences mainly point towards amino acid bioavailability and immunological consequences.

In Ca2+‐transporting epithelia, calbindin‐D28K (CaBP28K) facilitates Ca2+ diffusion from the luminal Ca2+ entry side of the cell to the basolateral side, where Ca2+ is extruded into the extracellular compartment. Simultaneously, CaBP28K provides protection against toxic high Ca2+ levels by buffering the cytosolic Ca2+ concentration ([Ca2+]i) during high Ca2+ influx. CaBP28K consistently colocalizes with the epithelial Ca2+ channel TRPV5, which constitutes the apical entry step in renal Ca2+‐transporting epithelial cells. Here, we demonstrate using protein‐binding analysis, subcellular fractionation and evanescent‐field microscopy that CaBP28K translocates towards the plasma membrane and directly associates with TRPV5 at a low [Ca2+]i. 45Ca2+ uptake measurements, electrophysiological recordings and transcellular Ca2+ transport assays of lentivirus‐infected primary rabbit connecting tubule/distal convolute tubule cells revealed that associated CaBP28K tightly buffers the flux of Ca2+ entering the cell via TRPV5, facilitating high Ca2+ transport rates by preventing channel inactivation. In summary, CaBP28K acts in Ca2+‐transporting epithelia as a dynamic Ca2+ buffer, regulating [Ca2+] in close vicinity to the TRPV5 pore by direct association with the channel.

Background Presumed benefits of human milk (HM) in avoiding rapid infancy weight gain and later obesity could relate to its nutrient composition. However, data on breast milk composition and its relation with growth are sparse. Objective We investigated whether short-chain fatty acids (SCFAs), known to be present in HM and linked to energy metabolism, are associated with infancy anthropometrics. Methods In a prospective birth cohort, HM hindmilk samples were collected from 619 lactating mothers at 4–8 wk postnatally [median (IQR) age: 33.9 (31.3–36.5) y, body mass index (BMI) (kg/m2): 22.8 (20.9–25.2)]. Their offspring, born at 40.1 (39.1–41.0) wk gestation with weight 3.56 (3.22–3.87) kg and 51% male, were assessed with measurement of weight, length, and skinfold thickness at ages 3, 12, and 24 mo, and transformed to age- and sex-adjusted z scores. HM SCFAs were measured by 1H-nuclear magnetic resonance spectroscopy (NMR) and GC-MS. Multivariable linear regression models were conducted to analyze the relations between NMR HM SCFAs and infancy growth parameters with adjustment for potential confounders. Results NMR peaks for HM butyrate, acetate, and formic acid, but not propionate, were detected. Butyrate peaks were 17.8% higher in HM from exclusively breastfeeding mothers than mixed-feeding mothers (P = 0.003). HM butyrate peak values were negatively associated with changes in infant weight (standardized B  = −0.10, P = 0.019) and BMI (B = −0.10, P = 0.018) between 3 and 12 mo, and negatively associated with BMI (B = −0.10, P = 0.018) and mean skinfold thickness (B = −0.10, P = 0.049) at age 12 mo. HM formic acid peak values showed a consistent negative association with infant BMI at all time points (B < = −0.10, P < = 0.014), whereas HM acetate was negatively associated with skinfold thickness at 3 mo (B = −0.10, P = 0.028) and 24 mo (B = −0.10, P = 0.036). Conclusions These results suggest that HM SCFAs play a beneficial role in weight gain and adiposity during infancy. Further knowledge of HM SCFA function may inform future strategies to support healthy growth.

In the intestinal mucosa, retinoic acid (RA) is a critical signaling molecule. RA is derived from dietary vitamin A (retinol) through conversion by aldehyde dehydrogenases (aldh). Reduced levels of short-chain fatty acids (SCFAs) are associated with pathological microbial dysbiosis, inflammatory disease, and allergy. We hypothesized that SCFAs contribute to mucosal homeostasis by enhancing RA production in intestinal epithelia. With the use of human and mouse epithelial cell lines and primary enteroids, we studied the effect of SCFAs on the production of RA. Functional RA conversion was analyzed by Adlefluor activity assays. Butyrate (0-20 mM), in contrast to other SCFAs, dose dependently induced aldh1a1 or aldh1a3 transcript expression and increased RA conversion in human and mouse epithelial cells. Epithelial cell line data were replicated in intestinal organoids. In these organoids, butyrate (2-5 mM) upregulated aldh1a3 expression (36-fold over control), whereas aldh1a1 was not significantly affected. Butyrate enhanced maturation markers (Mucin-2 and villin) but did not consistently affect stemness markers or other Wnt target genes (lgr5, olfm4, ascl2, cdkn1). In enteroids, the stimulation of RA production by SCFA was mimicked by inhibitors of histone deacetylase 3 (HDAC3) but not by HDAC1/2 inhibitors nor by agonists of butyrate receptors G-protein-coupled receptor (GPR)43 or GPR109A, indicating that butyrate stimulates RA production via HDAC3 inhibition. We conclude that the SCFA butyrate inhibits HDAC3 and thereby supports epithelial RA production.