Factors influencing milk osteopontin concentration based on measurements from Danish Holstein cows

An expert panel on the adequacy of safety data and physiological roles of dietary bovine osteopontin in infancy

Human milk, due to its unique composition, is the optimal standard for infant nutrition. Osteopontin (OPN) is abundant in human milk but not bovine milk. The addition of bovine milk osteopontin (bmOPN) to formula may replicate OPN's concentration and function in human milk. To address safety concerns, we convened an expert panel to assess the adequacy of safety data and physiological roles of dietary bmOPN in infancy. The exposure of breastfed infants to human milk OPN (hmOPN) has been well-characterized and decreases markedly over the first 6 months of lactation. Dietary bmOPN is resistant to gastric and intestinal digestion, absorbed and cleared from circulation within 8-24 h, and represents a small portion (<5%) of total plasma OPN. Label studies on hmOPN suggest that after 3 h, intact or digested OPN is absorbed into carcass (62%), small intestine (23%), stomach (5%), and small intestinal perfusate (4%), with <2% each found in the cecum, liver, brain, heart, and spleen. Although the results are heterogenous with respect to bmOPN's physiologic impact, no adverse impacts have been reported across growth, gastrointestinal, immune, or brain-related outcomes. Recombinant bovine and human forms demonstrate similar absorption in plasma as bmOPN, as well as effects on cognition and immunity. The panel recommended prioritization of trials measuring a comprehensive set of clinically relevant outcomes on immunity and cognition to confirm the safety of bmOPN over that of further research on its absorption, distribution, metabolism, and excretion. This review offers expert consensus on the adequacy of data available to assess the safety of bmOPN for use in infant formula, aiding evidence-based decisions on the formulation of infant formula.

Analytical Ultracentrifugation-Calibrated Anion-Exchange Chromatography for Sensitive and Intact Determination of Osteopontin in Infant Formula and Dairy Products

Osteopontin is a crucial protein ingredient that has been applied in fortified dairy products and infant formula. It has great significance to infant gut health and brain development. However, current techniques including enzyme-linked immunosorbent assay and liquid chromatography coupled with mass spectrometry are still facing the bottleneck of low sensitivity and indirect quantification. Moreover, the unavailable certified commercial OPN standard hinders its accurate quantification. Herein, a novel method of anion-exchange chromatography was established to determine OPN concentration in several dairy matrices. The polarity-reversed capillary isoelectric focusing was utilized to measure the exact isoelectric point (pI) to support method development for OPN separation. Analytical ultracentrifugation was used to calibrate the purity of intact OPN to develop an in-house reference standard. The method showed the merits of limits of detection to 0.04 mg/100 g, relative standard deviation of reproducibility <5% for 13 out of 14 tested matrices, and an average recovery rate of 101.3%. This method has shown the potential to be adopted as an international standard method for the quantification of intact OPN in infant formula and dairy products.

Milk Osteopontin and Human Health

Osteopontin (OPN) is a multifunctional protein found in all vertebrates. OPN is expressed in many different cell types, and is consequently found in most tissues and physiological secretions. OPN is involved in a multitude of biological processes, such as activation and regulation of the immune system; biomineralization; tissue-transformative processes, including growth and development of the gut and brain; interaction with bacteria; and many more. OPN is found in the highest concentrations in milk, where it is believed to initiate and regulate developmental, immunological and physiological processes in infants who consume milk. Processes for the isolation of bovine OPN for use in infant formula have been developed, and in recent years, many studies have investigated the effects of the intake of milk OPN. The purpose of this article is to review and compare existing knowledge about the structure and function of milk OPN, with a particular focus on the effects of milk OPN on human health and disease.

Naturally Occurring N-Terminal Fragments of Bovine Milk Osteopontin Are Transported across Models of the Intestinal Barrier

Osteopontin (OPN) is a bioactive integrin-binding protein found in high concentrations in milk, where it is present both as a full-length protein and as several N-terminally derived fragments. OPN resists gastric digestion, and via interaction with receptors in the gut or by crossing the intestinal barrier into circulation, ingested milk OPN may influence physiological processes. The aim of this study was to investigate OPN interaction with intestinal cells and its transport across models of the intestinal barrier. Immunodetection of OPN incubated with Caco-2 cells at 4 °C and 37 °C showed that OPN binds to the intestinal cells, but it is not internalised. Transepithelial transport was studied using mono- and co-cultures of Caco-2 cells and mucus-producing HT29-MTX cells in transwell membranes. OPN was shown to cross the barrier models in a time-, temperature-, and energy-dependent process inhibited by wortmannin, indicating that the transport takes place via the transcytosis pathway. Analyses of the naturally occurring milk mixture of full-length and N-terminal fragments showed that the N-terminal fragments of OPN bound intestinal cells most effectively and that the fragments were transported across the intestinal membrane models. This suggests that proteolytic processing of OPN increases its biological activity after ingestion.

Milk Osteopontin for Gut, Immunity and Brain Development in Preterm Pigs

Deficient levels of milk osteopontin (OPN) in infant formula may partly account for developmental differences between infants fed formula or maternal milk. We hypothesized that a milk diet supplemented with bovine milk OPN improves gut, immunity and brain development and tested this in a preterm pig model. Preterm pigs delivered by cesarean section (90% gestation) were fed raw bovine milk (CON, n = 19) or the same diet supplemented with a physiologically relevant dose of OPN (46 mg/(kg·d), n = 16). Endpoints related to clinical outcomes, systemic immunity and neurocognitive development were assessed during the study and gut tissues were collected at Day 19. Growth pattern, early motor development and most systemic immune parameters were similar between OPN and CON pigs. The OPN pigs had higher villus-to-crypt ratios than CON pigs and higher monocyte and lymphocyte counts on Day 8. Gut digestive and absorptive functions and cognitive performance (T-maze test) were similar between OPN and CON pigs. In conclusion, dietary supplementation with OPN above basal bovine milk levels induced minor improvements in gut structure and systemic immunity without any effects on cognitive performance. The minimal levels of OPN in infant formula to secure optimal adaptation in the immediate neonatal period remain to be determined.