Bioactive peptides derived from human milk proteins — mechanisms of action

Necrotizing enterocolitis: new insights into pathogenesis and mechanisms

Necrotizing enterocolitis (NEC) is the most frequent and lethal disease of the gastrointestinal tract of preterm infants. At present, NEC is thought to develop in the premature host in the setting of bacterial colonization, often after administration of non-breast milk feeds, and disease onset is thought to be due in part to a baseline increased reactivity of the premature intestinal mucosa to microbial ligands as compared with the full-term intestinal mucosa. The increased reactivity leads to mucosal destruction and impaired mesenteric perfusion and partly reflects an increased expression of the bacterial receptor Toll-like receptor 4 (TLR4) in the premature gut, as well as other factors that predispose the intestine to a hyper-reactive state in response to colonizing microorganisms. The increased expression of TLR4 in the premature gut reflects a surprising role for this molecule in the regulation of normal intestinal development through its effects on the Notch signalling pathway. This Review will examine the current approach to the diagnosis and treatment of NEC, provide an overview of our current knowledge regarding its molecular underpinnings and highlight advances made within the past decade towards the development of specific preventive and treatment strategies for this devastating disease.

Temporal Changes of Protein Composition in Breast Milk of Chinese Urban Mothers and Impact of Caesarean Section Delivery

Human breast milk (BM) protein composition may be impacted by lactation stage or factors related to geographical location. The present study aimed at assessing the temporal changes of BM major proteins over lactation stages and the impact of mode of delivery on immune factors, in a large cohort of urban mothers in China. 450 BM samples, collected in three Chinese cities, covering 8 months of lactation were analyzed for α-lactalbumin, lactoferrin, serum albumin, total caseins, immunoglobulins (IgA, IgM and IgG) and transforming growth factor (TGF) β1 and β2 content by microfluidic chip- or ELISA-based quantitative methods. Concentrations and changes over lactation were aligned with previous reports. α-lactalbumin, lactoferrin, IgA, IgM and TGF-β1 contents followed similar variations characterized by highest concentrations in early lactation that rapidly decreased before remaining stable up to end of lactation. TGF-β2 content displayed same early dynamics before increasing again. Total caseins followed a different pattern, showing initial increase before decreasing back to starting values. Serum albumin and IgG levels appeared stable throughout lactation. In conclusion, BM content in major proteins of urban mothers in China was comparable with previous studies carried out in other parts of the world and C-section delivery had only very limited impact on BM immune factors.

Opioid peptides and gastrointestinal symptoms in autism spectrum disorders

Autism spectrum disorders (ASDs) are characterized by deficits in the individual's ability to socialize, communicate, and use the imagination, in addition to stereotyped behaviors. These disorders have a heterogenous phenotype, both in relation to symptoms and regarding severity. Organic problems related to the gastrointestinal tract are often associated with ASD, including dysbiosis, inflammatory bowel disease, exocrine pancreatic insufficiency, celiac disease, indigestion, malabsorption, food intolerance, and food allergies, leading to vitamin deficiencies and malnutrition. In an attempt to explain the pathophysiology involved in autism, a theory founded on opioid excess has been the focus of various investigations, since it partially explains the symptomatology of the disorder. Another hypothesis has been put forward whereby the probable triggers of ASDs would be related to the presence of bacteria in the bowel, oxidative stress, and intestinal permeability. The present update reviews these hypotheses.

Breast Milk from Frequent Trans Fatty Acid Consumers Shows High Triglyceride and Glucose Levels, but Low Cholesterol and Apolipoprotein A-I levels, with Resulting Impaired In Vitro Zebrafish Embryo Growth and Survival

BACKGROUND

It is well known that breast milk is the best nutritional source for infant growth. However, there has been no information about the quality of breast milk from individuals who daily consume a trans fatty acid (TFA)-enriched diet.

SUBJECTS AND METHODS

We performed compositional and functional analyses with breast milk from lactating mothers, in terms of lipid content and zebrafish embryo survivability, among individuals who daily consumed TFA-enriched food (n = 5), normal diet as control (n = 5), and powder formula (n = 5).

RESULTS

In lipid content of breast milk, the control group showed 2.5- and 4.5-fold higher cholesterol content than the TFA group and infant formula, respectively. The TFA group and infant formula showed 1.8- and 2.0-fold higher triglyceride (TG) than the control group. Moreover, the TFA group and formula showed 1.4- and 4.8-fold higher glucose levels compared with control. The TFA group also showed 25% lower protein content than control. Microinjection with breast milk (50 nL) from the TFA group showed significantly lower zebrafish embryo survivability (50% ± 4%) compared with the control (66% ± 5%), whereas microinjection with formula showed the lowest survivability (39% ± 5%) with the slowest developmental speed. Immunodetection revealed that breast milk from the TFA group showed smaller-sized apoA-I (25.5 ± 0.6 kDa) than that from the control group (27.5 ± 1.5 kDa), whereas formula did not contain apoA-I. Larger apoA-I size in breast milk was directly associated with higher embryo survivability.

CONCLUSIONS

Breast milk from the TFA group showed increased TG and loss of cholesterol, lactalbumin (14 kDa), and apoA-I proteins, resulting in functional impairment of development and growth.

Overview of Lactoferrin as a Natural Immune Modulator

Lactoferrin is thought to be the most polyvalent protein present in host defense against tissue injuries and infections in vertebrates. Owing to the propensity of its basic N-terminal domain to interact with various microbial and host targets, lactoferrin not only has antimicrobial properties, but also modulates the innate and adaptive immune responses. Lactoferrin may indeed up- and downregulate immune cell activation, migration, and growth. Whereas the immunomodulatory properties of lactoferrin are evidenced from in vivo studies using either lactoferrin-knockout, lactoferrin-overexpressing transgenic models, and dietary lactoferrin, few mechanisms from in vitro studies have been proposed to explain these properties. The best characterized lactoferrin targets are negatively charged molecules. They encompass pro-inflammatory microbial molecules, such as pathogen-associated molecular patterns (eg, lipopolysaccharide), but also host components such as DNA, the glycosaminoglycan chains of proteoglycans, and surface cell receptors. Signaling through these receptors is thought to be the main lever used by lactoferrin to influence immune cells and cytokine-balance-controlling cell activity. This article aims to review our current understanding, though incomplete, of the many ways lactoferrin influences the complex immune machinery and the known and putative mechanisms that may explain its properties.

A narrative review of the associations between six bioactive components in breast milk and infant adiposity

OBJECTIVE

This narrative review examines six important non-nutritive substances in breast milk, many of which were thought to have little to no biological significance. The overall objective is to provide background on key bioactive factors in breast milk believed to have an effect on infant outcomes (growth and body composition).

METHODS

The evidence for the effects of the following six bioactive compounds in breast milk on infant growth outcomes are reviewed: insulin, leptin, adiponectin, ghrelin, interleukin-6, and tumor necrosis factor-α.

RESULTS

The existing literature on the effects of breast milk insulin, ghrelin, interleukin-6, and tumor necrosis factor-α and their associations with infant growth and adiposity is sparse. Of the bioactive compounds reviewed, leptin and adiponectin are the most researched. Data reveal that breast milk adiponectin has negative associations with growth in infancy.

CONCLUSIONS

There is a need for innovative, well-designed studies to improve causal inference and advance our understanding in the effects of breast milk and its components on offspring growth and body composition. The recommendations provided, along with careful consideration of both known and unknown factors that affect breast milk composition, will help improve, standardize, and ultimately advance this emergent field.

Effect of processing on polyamine content and bioactive peptides released after in vitro gastrointestinal digestion of infant formulas

This study examined the influence of processing on polyamines and peptide release after the digestion of a commercial infant formula designed for children during the first months of life. Polyamine oxidase activity was not suppressed during the manufacturing process, which implicates that polyamine concentrations were reduced over time and during infant formula self-life. In gel electrophoresis, in vitro gastrointestinal digestion of samples with reduced amount of enzymes and time of digestion shows an increase in protein digestibility, reflected in the increase in nonprotein nitrogen after digestion and the disappearance of β-lactoglobulin and α-lactalbumin bands in gel electrophoresis. Depending on the sample, between 22 and 87 peptides were identified after gastrointestinal digestion. A peptide from β-casein f(98-105) with the sequence VKEAMAPK and antioxidant activity appeared in all of the samples. Other peptides with antioxidant, immunomodulatory, and antimicrobial activities were frequently found, which could have an effect on infant health. The present study confirms that the infant formula manufacturing process determines the polyamine content and peptidic profile after digestion of the infant formula. Because compositional dissimilarity between human milk and infant formula in polyamines and proteins could be responsible for some of the differences in health reported between breast-fed and formula-fed children, these changes must be taken into consideration because they may have a great effect on infant nutrition and development.

Lactation and Intestinal Microbiota: How Early Diet Shapes the Infant Gut

Breast milk is a multifunctional biofluid that provides nutrients along with highly diverse non-nutritive bioactive components such as antibodies, glycans, bacteria, and immunomodulatory proteins. Research over the past decade has confirmed the essential role of breast milk bioactives in the establishment a healthy intestinal microbiota within the infant. The intestinal microbiota of an exclusively breastfed baby is dominated by several species of Bifidobacteria - the most influential member of which is Bifidobacterium longum subspecies infantis (B. infantis) - and is referred to as the milk-oriented microbiome (MOM). MOM is associated with reduced risk of infection in infancy as well as a reduced risk of certain chronic illnesses in adulthood. Establishment and persistence of MOM is dependent on the selective digestion of complex sugar structures in breast milk that are otherwise indigestible to the infant by B. infantis and its relatives. This review focuses primarily on the influence of breast milk glycans and glycosylated proteins on the development of the intestinal microbiome, and how maternal phenotype may influence the development of MOM providing a framework to understand how variation in diet shapes a protective intestinal microbiome.

Bioactive peptides released by in vitro digestion of standard and hydrolyzed infant formulas

Hydrolyzed infant formulas serve as appropriate nutritional sources for infants afflicted with cow's milk allergy, and milk proteins in hydrolyzed formulas are industrially hydrolyzed extensively or partially. To investigate whether industrial hydrolysis may modulate the digestive trajectory of milk proteins, thereby releasing different profiles of bioactive peptides compared with standard formulas, both standard and hydrolyzed formulas were subjected to in vitro digestion and formation of bioactive peptides were compared. One standard, one extensively hydrolyzed, and one partially hydrolyzed infant formula were digested in vitro with pepsin and pancreatin, taking into account the higher gastric pH of infants, and the digesta were subjected to peptidomic analysis. The standard formula released a larger variety of bioactive peptides than from the hydrolyzed formulas, indicating that industrial hydrolysis of milk proteins may generally attenuate their indigenous bioactivities such as antibacterial, immuno-regulatory, and anti-oxidative activities. Conversely, industrial hydrolysis may facilitate the formation of bioactive peptides from hydrophobic proteins/regions such as β-LG and the "strategic zone" of β-CN, which encrypt bioactive peptides including a dipeptidyl dipeptidase-4-inhibitory, hypocholesterolemic, and opioid peptides. Infants fed hydrolyzed infant formulas may be influenced by milk protein-derived bioactive peptides in a manner different from those fed standard formula.

Bioactive properties of milk proteins in humans: A review

Many studies have demonstrated that milk protein consumption has benefits in terms of promoting human health. This review assesses the intervention studies which have evaluated potential health enhancing effects in humans following the ingestion of milk proteins. The impact of milk protein ingestion has been studied to asses their satiating, hypotensive, antimicrobial, anti-inflammatory, anticancer, antioxidant and insulinotropic properties as well as their impact on morphological modifications (e.g., muscle and fat mass) in humans. Consistent health promoting effects appear to have been observed in certain instances (i.e., muscle protein synthesis, insulinotropic and hypotensive activity). However, controversial outcomes have also been reported (i.e., antimicrobial, anti-inflammatory, anticancer and antioxidant properties). Several factors including interindividual differences, the timing of protein ingestion as well as the potency of the active components may explain these differences. In addition, processing conditions have been reported, in certain instances, to affect milk protein structure and therefore modify their bioactive potential. It is thought that the health promoting properties of milk proteins are linked to the release of bioactive peptides (BAPs) during gastrointestinal digestion. There is a need for further research to develop a more in-depth understanding on the possible mechanisms involved in the observed physiological effects. In addition, more carefully controlled and appropriately powered human intervention studies are required to demonstrate the health enhancing properties of milk proteins in humans.

Effects of cow milk versus extensive protein hydrolysate formulas on infant cognitive development

Little research has focused on infant developmental effects, other than growth, of formulas that differ substantially in the form of protein. To examine development of infants fed formulas differing in free amino acid content, we randomized 0.5-month-old infants (n = 79) to either a control group who fed only cow milk formula (CMF) during the first 8 months (CMF8), or to one of two experimental groups: one experimental group fed extensively protein hydrolyzed formula (EHF) for 1-3 months during first 4.5 months (EHF1-3) of life, and the other fed EHF for 8 months (EHF8). The Mullen Scales of Early Learning were administered monthly from 1.5 to 8.5 months to assess fine (FM) and gross (GM) motor control, receptive (RL) and expressive (EL) language, visual reception (VR), and an early learning composite (ELC). Across the 5.5-8.5-month time period, when compared to CMF8 infants, GM scores in EHF1-3 infants averaged 1.5 points higher (95 % CI 0.1, 3.0) and in EHF8 infants 2.2 points higher (95 % CI 0.3, 4.0). Similarly, VR scores averaged 1.9 points higher (95 % CI 0.1, 3.8) in EHF1-3 infants and 2.2 points higher (95 % CI -0.2, 4.5) in EHF8 infants. EHF8 infants' RL scores averaged 1.8 points lower (95 % CI 0.1, 3.6) than CMF8 infants. These data suggest that the form of protein in infant formula may impact cognitive development and that the higher free amino acid content in breast milk may be a contributing factor to the differential cognitive development between breastfed and CMF-fed infants.

CLINICAL TRIAL REGISTRATION

clinicaltrials.gov NCT00994747.

Characterization of the bovine milk proteome in early-lactation Holstein and Jersey breeds of dairy cows

Milk is a highly nutritious natural product that provides not only a rich source of amino acids to the consumer but also hundreds of bioactive peptides and proteins known to elicit health-benefitting activities. We investigated the milk protein profile produced by Holstein and Jersey dairy cows maintained under the same diet, management and environmental conditions using proteomic approaches that optimize protein extraction and characterization of the low abundance proteins within the skim milk fraction of bovine milk. In total, 935 low abundance proteins were identified. Gene ontology classified all proteins identified into various cellular localization and function categories. A total of 43 low abundance proteins were differentially expressed between the two dairy breeds. Bioactive proteins involved in host-defense, including lactotransferrin (P=0.0026) and complement C2 protein (P=0.0001), were differentially expressed by the two breeds, whereas others such as osteopontin (P=0.1788) and lactoperoxidase (P=0.2973) were not. This work is the first to outline the protein profile produced by two important breeds of dairy cattle maintained under the same diet, environment and management conditions in order to observe likely true breed differences. This research now allows us to better understand and contrast further research examining the bovine proteome that includes these different breeds.

BIOLOGICAL SIGNIFICANCE

Within the last decade, the amount of research characterizing the bovine milk proteome has increased due to growing interest in the bioactive proteins that are present in milk. Proteomic analysis of low abundance whey proteins has mainly focused on human breast milk; however, previous research has highlighted the presence of bioactive proteins in bovine milk. Recent publications outlining the cross-reactivity of bovine bioactive proteins on human biological function highlight the need for further investigation into the bovine milk proteome. The rationale behind this study is to characterize and compare the low abundance protein profile in the skim milk fraction produced from Holstein and Jersey breeds of dairy cattle, which are two major dairy cattle breeds in the USA. A combination of fractionation strategies was used to efficiently enrich the low abundance proteins from bovine skim milk for proteomic profiling. A total of 935 low abundance proteins were identified and compared between the two bovine breeds. The results from this study provide insight into breed differences and similarities in the milk proteome profile produced by two breeds of dairy cattle.

Dairy foods and dairy proteins in the management of type 2 diabetes: a systematic review of the clinical evidence

Type 2 diabetes mellitus (T2DM) is a growing public health concern affecting hundreds of millions of people worldwide and costing the global economy hundreds of billions of dollars annually. This chronic disease damages the blood vessels and increases the risk of other cardiometabolic ailments such as cardiovascular disease and stroke. If left unmanaged it can also lead to nerve damage, kidney damage, blindness, and amputation. For the most part, many of these symptoms can be prevented or reduced through simple dietary modifications and proper nutrition. Therefore, identifying relatively inexpensive and easily implementable dietary modifications for the prevention and management of T2DM is of considerable value to human health and healthcare modalities around the globe. Protein-rich dairy products have consistently been shown in epidemiologic studies to be beneficial for reducing the risk of developing T2DM. The clinical evidence regarding both dairy foods and dairy proteins (i.e., casein and whey protein) have shown promise for improving insulin secretion in individuals with T2DM. However, the clinical research on dairy protein supplementation in subjects with T2DM has been limited to acute studies. These studies have been mostly descriptive and have not been focused on important T2DM endpoints such as prevention, management, or treatment. Long-term studies are clearly needed to help researchers and medical professionals better understand the effects of consistent dairy protein intake on the metabolic health of humans with T2DM.

Bioactive peptides released from in vitro digestion of human milk with or without pasteurization

BACKGROUND

Pasteurized donor human milk (HM) serves as the best alternative for breast-feeding when availability of mother's milk is limited. Pasteurization is also applied to mother's own milk for very low birth weight infants, who are vulnerable to microbial infection. Whether pasteurization affects protein digestibility and therefore modulates the profile of bioactive peptides released from HM proteins by gastrointestinal digestion, has not been examined to date.

METHODS

HM with and without pasteurization (62.5 °C for 30 min) were subjected to in vitro gastrointestinal digestion, followed by peptidomic analysis to compare the formation of bioactive peptides.

RESULTS

Some of the bioactive peptides, such as caseinophosphopeptide homologues, a possible opioid peptide (or propeptide), and an antibacterial peptide, were present in undigested HM and showed resistance to in vitro digestion, suggesting that these peptides are likely to exert their bioactivities in the gastrointestinal lumen, or be stably transported to target organs. In vitro digestion of HM released a large variety of bioactive peptides such as angiotensin I-converting enzyme-inhibitory, antioxidative, and immunomodulatory peptides. Bioactive peptides were released largely in the same manner with and without pasteurization.

CONCLUSION

Provision of pasteurized HM may be as beneficial as breast-feeding in terms of milk protein-derived bioactive peptides.

Clustering analyses in peptidomics revealed that peptide profiles of infant formulae are descriptive

Prompted by the accumulating evidence on bioactive moieties of milk-derived peptides, novel methods were applied to compare the peptide composition among commercially available hydrolysate formulations and to determine batch-to-batch variations of protein hydrolysate products. Despite the availability of general methods to measure, for example, the degree of hydrolysis and peptide mass distribution at a high level, the objective of this study was to more qualitatively compare peptide sequences and composition. By a comprehensive approach combining peptidomics technologies and multivariate clustering analyses, the peptide profiles of different hydrolyzed milk protein formulations were compared. Moreover, peptide profiles of various hydrolysate batches that had been produced over a period of 5 years were included. Coupling of identified peptide sequences to the position in their corresponding milk proteins produced numerical datasets that subsequently were utilized for multivariate data analyses. These analyses revealed that batch-to-batch variation in the peptide profiles of a specific extensively hydrolyzed casein preparation was low. Moreover, extensive multivariate evaluations revealed that the peptide profiles of different commercially available hydrolyzed milk protein formulations provided a descriptive and distinct signature. Overall, the described methodology may contribute to the field of peptide research as observed dissimilarities in peptide profiles of similar products may be related to differences in their overall functionality.

Bioactive Functions of Milk Proteins: a Comparative Genomics Approach

The composition of milk includes factors required to provide appropriate nutrition for the growth of the neonate. However, it is now clear that milk has many functions and comprises bioactive molecules that play a central role in regulating developmental processes in the young while providing a protective function for both the suckled young and the mammary gland during the lactation cycle. Identifying these bioactives and their physiological function in eutherians can be difficult and requires extensive screening of milk components that may function to improve well-being and options for prevention and treatment of disease. New animal models with unique reproductive strategies are now becoming increasingly relevant to search for these factors.

Differential temporal expression of milk miRNA during the lactation cycle of the marsupial tammar wallaby (Macropus eugenii)

BACKGROUND

Lactation is a key aspect of mammalian evolution for adaptation of various reproductive strategies along different mammalian lineages. Marsupials, such as tammar wallaby, adopted a short gestation and a relatively long lactation cycle, the newborn is immature at birth and significant development occurs postnatally during lactation. Continuous changes of tammar milk composition may contribute to development and immune protection of pouch young. Here, in order to address the putative contribution of newly identified secretory milk miRNA in these processes, high throughput sequencing of miRNAs collected from tammar milk at different time points of lactation was conducted. A comparative analysis was performed to find distribution of miRNA in milk and blood serum of lactating wallaby.

RESULTS

Results showed that high levels of miRNA secreted in milk and allowed the identification of differentially expressed milk miRNAs during the lactation cycle as putative markers of mammary gland activity and functional candidate signals to assist growth and timed development of the young. Comparative analysis of miRNA distribution in milk and blood serum suggests that milk miRNAs are primarily expressed from mammary gland rather than transferred from maternal circulating blood, likely through a new putative exosomal secretory pathway. In contrast, highly expressed milk miRNAs could be detected at significantly higher levels in neonate blood serum in comparison to adult blood, suggesting milk miRNAs may be absorbed through the gut of the young.

CONCLUSION

The function of miRNA in mammary gland development and secretory activity has been proposed, but results from the current study also support a differential role of milk miRNA in regulation of development in the pouch young, revealing a new potential molecular communication between mother and young during mammalian lactation.

Troubled sleep: Night waking, breastfeeding and parent-offspring conflict

Disrupted sleep is probably the most common complaint of parents with a new baby. Night waking increases in the second half of the first year of infant life and is more pronounced for breastfed infants. Sleep-related phenotypes of infants with Prader-Willi and Angelman syndromes suggest that imprinted genes of paternal origin promote greater wakefulness whereas imprinted genes of maternal origin favor more consolidated sleep. All these observations are consistent with a hypothesis that waking at night to suckle is an adaptation of infants to extend their mothers’ lactational amenorrhea, thus delaying the birth of a younger sib and enhancing infant survival.