Review of the potential health impact of β-casomorphins and related peptides

Effect of Genetic Polymorphism of Bovine β-Casein Variants (A1 and A2) on Yoghurt Characteristics

The present study aims to evaluate the physicochemical and sensory characteristics of A2 yoghurts (made with A2A2 β-CN milk), in comparison with Control yoghurts (elaborated from conventional milk, a mixture of A1 and A2 β-CN milk). The pH, acidity, water-holding capacity, spontaneous syneresis, firmness and color of yoghurts were monitored during their cold storage (4 °C) for 35 days. Two independent sensory tests (with expert judges and consumers) were also performed. The A2 yoghurts showed only minor differences in some of their physicochemical and sensory characteristics compared to those made with conventional milk. At specific storage times, the A2 yoghurt exhibited higher levels of acidity, luminosity (L*) and firmness, compared to the Control. No differences were observed in the growth curves of the starter (Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus salivarius subsp. thermophilus) during the yoghurt production, nor in the water-holding capacity or spontaneous syneresis of the two types of gels. Regarding the sensory evaluation of samples, the A2 yoghurts were described as firmer and more adherent (by the expert panel), and brighter and more homogeneous (by the consumers) than the Control. In all cases, both consumers and expert sensory panels showed a preference for the A2 yoghurts. Therefore, these results demonstrate the suitability of A2A2 β-CN milk for producing yoghurts with similar characteristics to those obtained with conventional milk.

The Effect of A2 Milk on Gastrointestinal Symptoms in Comparison to A1/A2 Milk: A Single-center, Randomized, Double-blind, Cross-over Study

β-Casein, a major protein in cow's milk, is divided into the A1 and A2 type variants. Digestion of A1 β-casein yields the peptide β-casomorphin-7 which could cause gastrointestinal (GI) discomfort but A2 milk containing only A2 β-casein might be more beneficial than A1/A2 (regular) milk. The aim of this study was to evaluate the differences in GI discomfort after ingestion of A2 milk and A1/A2 milk. A randomized, double-blind, cross-over human trial was performed with 40 subjects who experienced GI discomfort following milk consumption. For each intervention period, either A2 milk first (A2→A1/A2) or A1/A2 milk was first consumed for 2 weeks (A1/A2→A2) following a 2-week washout period. GI symptom rating scale (GSRS) scores, questionnaire for digestive symptoms, and laboratory tests including fecal calprotectin were evaluated. For symptom analysis, generalized estimating equations gamma model was used. A2 milk increased bloating (P = 0.041) and loose stools (P = 0.026) compared to A1/A2 milk in GSRS. However, A2 milk caused less abdominal pain (P = 0.050), fecal urgency (P < 0.001) and borborygmus (P = 0.007) compared to A1/A2 milk in questionnaire for digestive symptoms. In addition, fecal calprotectin also decreased or less increased after consumption of A2 milk compared to A1/A2 milk (P = 0.030), and this change was more pronounced in males (P = 0.005) than in females. There were no significant adverse reactions during the trial. A2 milk alleviated digestive discomfort in Koreans following A2 milk consumption (ClinicalTrials.gov NCT06252636 and CRIS KCT0009301).

BCM-7: Opioid-like Peptide with Potential Role in Disease Mechanisms

Bovine milk is an essential supplement due to its rich energy- and nutrient-rich qualities. Caseins constitute the vast majority of the proteins in milk. Among these, β-casein comprises around 37% of all caseins, and it is an important type of casein with several different variants. The A1 and A2 variants of β-casein are the most researched genotypes due to the changes in their composition. It is accepted that the A2 variant is ancestral, while a point mutation in the 67th amino acid created the A1 variant. The digestion derived of both A1 and A2 milk is BCM-7. Digestion of A2 milk in the human intestine also forms BCM-9 peptide molecule. The opioid-like characteristics of BCM-7 are highlighted for their potential triggering effect on several diseases. Most research has been focused on gastrointestinal-related diseases; however other metabolic and nervous system-based diseases are also potentially triggered. By manipulating the mechanisms of these diseases, BCM-7 can induce certain situations, such as conformational changes, reduction in protein activity, and the creation of undesired activity in the biological system. Furthermore, the genotype of casein can also play a role in bone health, such as altering fracture rates, and calcium contents can change the characteristics of dietary products. The context between opioid molecules and BCM-7 points to a potential triggering mechanism for the central nervous system and other metabolic diseases discussed.

Health-Related Outcomes and Molecular Methods for the Characterization of A1 and A2 Cow's Milk: Review and Update

A new trend in cow's milk has emerged in the market called type A1 and A2 milk. These products have piqued the interest of both consumers and researchers. Recent studies suggest that A2 milk may have potential health benefits beyond that of A1 milk, which is why researchers are investigating this product further. It is interesting to note that the A1 and A2 milk types have area-specific characteristics compared to breed-specific characteristics. Extensive research has focused on milk derivatives obtained from cow's milk, primarily through in vitro and animal studies. However, few clinical studies have been conducted in humans, and the results have been unsatisfactory. New molecular techniques for identifying A1 and A2 milk may help researchers develop new studies that can clarify certain controversies surrounding A1 milk. It is essential to exercise extreme caution when interpreting the updated literature. It has the potential to spread panic worldwide and have negative economic implications. Therefore, this study aims to investigate the differences between A1 and A2 milk in various research areas and clarify some aspects regarding these two types of milk.

Bovine milk β-casein: Structure, properties, isolation, and targeted application of isolated products

β-Casein, an important protein found in bovine milk, has significant potential for application in the food, pharmaceutical, and other related industries. This review first introduces the composition, structure, and functional properties of β-casein. It then reviews the techniques for isolating β-casein. Chemical and enzymatic isolation methods result in inactivity of β-casein and other components in the milk, and it is difficult to control the production conditions, limiting the utilization range of products. Physical technology not only achieves high product purity and activity but also effectively preserves the biological activity of the components. The isolated β-casein needs to be utilized effectively and efficiently for various purity products in order to achieve optimal targeted application. Bovine β-casein, which has a purity higher than or close to that of breast β-casein, can be used in infant formulas. This is achieved by modifying its structure through dephosphorylation, resulting in a formula that closely mimics the composition of breast milk. Bovine β-casein, which is lower in purity than breast β-casein, can be maximized for the preparation of functional peptides and for use as natural carriers. The remaining byproducts can be utilized as food ingredients, emulsifiers, and carriers for encapsulating and delivering active substances. Thus, realizing the intensive processing and utilization of bovine β-casein isolation. This review can promote the industrial production process of β-casein, which is beneficial for the sustainable development of β-casein as a food and material. It also provides valuable insights for the development of other active substances in milk.

Effects of diets supplemented with bioactive peptides on nutrient digestibility, immune cell responsiveness, and fecal characteristics, microbiota, and metabolites of adult cats

Bioactive peptides (BP) are recognized for their ability to function as antioxidants and maintain lipid stability. They may have positive health effects, including antihypertensive, anti-inflammatory, antimicrobial, osteoprotective, gut health, and immunomodulatory properties, but are poorly tested in cats. Our primary objective was to determine the apparent total tract digestibility (ATTD) of BP-containing kibble diets and assess how the fecal characteristics, metabolites, and microbiota were affected in adult cats. Our secondary objective was to test whether BP could impact blood oxidative stress markers and cytokine concentrations following transport stress. Twelve adult cats (4.83 ± 0.37 yr; 4.76 ± 0.14 kg) were used in a replicated 4 × 4 Latin square design to test four extruded kibble diets: Control (no BP), Chicken (4% chicken BP), Marine1 (2% marine BP), and Marine2 (4% marine BP). Each experimental period lasted 28 d, with a 20-d adaptation phase, 5 d for fecal collection, 2 d for blood collection, and 1 d for transport stress testing (driven in vehicle in individual carriers for 45 min). Salivary cortisol and blood oxidative stress markers and cytokines were measured after transport. Fecal microbiota data were evaluated using 16S rRNA gene amplicon sequencing and QIIME2. All other data were analyzed using the Mixed Models procedure of SAS, with P < 0.05 being considered significant and P < 0.10 considered trends. No differences were observed in animal health outcomes, with all cats remaining healthy and serum metabolites remaining within reference ranges. Cats fed the Marine2 diet had higher (P < 0.05) ATTD of dry matter (84.5% vs. 80.9%) and organic matter (88.3% vs. 85.8%) than those fed the control diet. The ATTD of protein and energy tended to be higher (P < 0.10) for cats fed the Marine2 diet. Fecal characteristics, metabolites, and bacterial alpha and beta diversity measures were not affected by treatment. However, the relative abundances of six bacterial genera were different (P < 0.05) and two bacterial genera tended to be different (P < 0.10) across treatments. Treatment did not alter salivary cortisol, blood oxidative stress markers, or blood cytokines after transport stress. Our data suggest that BP inclusion may increase nutrient digestibility and modify fecal microbiota and immune measures. More testing is required, however, to determine whether BP may provide additional benefits to cats.

Worldwide research on the health effects of bovine milk containing A1 and A2 β-casein: Unraveling the current scenario and future trends through bibliometrics and text mining

The possible adverse effect of consuming bovine milk with A1 β-casein (but not with A2 β-casein) on health aspects due to the release of β-casomorphin-7 (BCM-7) is currently under debate. The aim of this study was to perform a bibliometric analysis of studies extracted from Scopus to explore the relationship between BCM-7, A1 or A2 bovine milk with different aspects of health. Over time, several research groups were formed that are no longer active and although some authors have returned to the field of study, they have focused their efforts mainly on conducting reviews that show the same imprecise conclusions due to the few original articles. Research is concentrated in Europe and Asia, where New Zealand, China and Germany are the countries with the most publications, records and citations on the subject, respectively. On the other hand, no country in Africa or South America has scientific production, which opens the possibility of building collaborations between countries and exploring areas that lack scientific studies. Based on conflicting information from primarily in vitro and animal studies, and limited clinical trials with poor designs, A1 milk presents pro-inflammatory and oxidative activity, but the evidence is insufficient to associate its consumption with negative health effects. However, A2 milk may be better tolerated by the digestive system of some individuals, suggesting its possible modulating role in the intestinal microbiota. Stronger scientific evidence is needed to reach a consensus on whether the presence of β-casein A1 can significantly negatively affect health. The information shown will allow a better understanding of the subject and consumers will be able to make their own decisions regarding A1 or A2 milk.

Proteolysis and therapeutic potential of bioactive peptides derived from Cheddar cheese

Cheddar cheese-derived bioactive peptides are considered a potential component of functional foods. A positive impact of bioactive peptides on diet-related chronic, non-communicable diseases, like obesity, cardiovascular diseases, and diabetes, has been observed. Bioactive peptides possess multifunctional therapeutic potentials, including antimicrobial, immunomodulatory, antioxidant, enzyme inhibitory effects, anti-thrombotic, and phyto-pathological activities against various toxic compounds. Peptides can regulate human immune, gastrointestinal, hormonal, and neurological responses, which play an integral role in the deterrence and treatment of certain diseases like cancer, osteoporosis, hypertension, and other health disorders, as described in the present review. This review summarizes the categories of the Cheddar cheese-derived bioactive peptides, their general characteristics, physiological functions, and possible applications in healthcare.

Identification of stably expressed Internal Control Genes (ICGs) for normalization of expression data in liver of C57BL/6 mice injected with beta casomorphins

In recent years, beta-casomorphin peptides (BCM7/BCM9) derived from the digestion of cow milk have drawn a lot of attention world over because of their proposed impact on human health. In order to evaluate the transcriptional modulation of target genes through RT-qPCR in response to these peptides, availability of appropriate reference or internal control genes (ICGs) will be the key. The present study was planned to identify a panel of stable ICGs in the liver tissue of C57BL/6 mice injected with BCM7/BCM9 cow milk peptides for 3 weeks. A total of ten candidate genes were evaluated as potential ICGs by assessing their expression stability using software suites; geNorm, NormFinder and BestKeeper. The suitability of the identified ICGs was validated by assessing the relative expression levels of target genes, HP and Cu/Zn SOD. Based on geNorm, PPIA and SDHA gene pair was identified to be most stably expressed in liver tissue during the animal trials. Similarly, NormFinder analysis also identified PPIA as the most stable gene. BestKeeper analysis showed crossing point SD value for all the genes in the acceptable range that is closer to 1. Overall, the study identified a panel of stable ICGs for reliable normalization of target genes expression data in mice liver tissues during BCM7/9 peptides trial.

Demographic pattern of A1/A2 beta casein variants indicates conservation of A2 type haplotype across native cattle breeds (Bos indicus) of India

Genetic variations of the beta casein gene hold importance because of their probable association with human health. Comparative sequence analysis of β-casein gene across Indian native, crossbred and exotic breeds in India revealed 15 SNPs and 4 INDELs corresponding to 14 haplotypes. The frequency of A2 type haplotype was maximum (0.941) across all Indian native breeds. Among the 15 variants reported for taurine breeds, only three (A1, A2 and B) were observed in analysed populations. Allelic profiling of A1/A2 β-casein variants in ~ 4000 animals belonging to three cattle types and breeding bulls also revealed the predominance of A2 allele (0.95) in Indian cattle. The high proportion of A2 allele/haplotype indicates that Indian native cattle are the best suited to meet the demands for A2 milk globally. However, a higher percentage of heterozygous genotype (A1A2) in breeding bulls warrants the need to screen sire lines so as to drift the herd towards A2.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03232-0.

A2 Milk and BCM-7 Peptide as Emerging Parameters of Milk Quality

Beta-casein makes up about 30% of the total protein contained in milk and can be present in cows' milk in two distinct forms (A1 or A2) or as a combination of the two. The only difference between these two variants of β-casein (β-CN) is a single amino acid substitution. This results in a different behavior of the protein upon enzymatic cleavage, following human consumption or due to microbial action. In most of the commercially available milk containing A1 or A1/A2 β-CN variants, the β-casomorphin-7 peptide (BCM-7) is released upon digestion and during cheese manufacturing/ripening, while this does not happen with A2 milk. BCM-7 is a known μ-opioid receptor agonist that may influence the gastro-intestinal physiology directly and may also exert effects elsewhere in the body, such as on the cardiovascular, neurological and endocrine systems. The present article is aimed at a revision of prior review papers on the topic, with a focus on the impact of ingestion of A1 β-CN milk and A2 β-CN milk on any health-related outcomes and on the impact of A1 or A2 β-CN variant on technological properties of cows' milk. When systematic reviews were considered, it was possible to conclude that A2 β-CN exerts beneficial effects at the gastrointestinal level compared with A1 β-CN, but that there is no evidence of A1 β-CN having negative effects on human health. Physicochemical differences among cows' milk containing either β-CN A2 or β-CN A1 and their effects on technological properties are discussed.

Fungal Cell Factories for Efficient and Sustainable Production of Proteins and Peptides

Filamentous fungi are a large and diverse taxonomically group of microorganisms found in all habitats worldwide. They grow as a network of cells called hyphae. Since filamentous fungi live in very diverse habitats, they produce different enzymes to degrade material for their living, for example hydrolytic enzymes to degrade various kinds of biomasses. Moreover, they produce defense proteins (antimicrobial peptides) and proteins for attaching surfaces (hydrophobins). Many of them are easy to cultivate in different known setups (submerged fermentation and solid-state fermentation) and their secretion of proteins and enzymes are often much larger than what is seen from yeast and bacteria. Therefore, filamentous fungi are in many industries the preferred production hosts of different proteins and enzymes. Edible fungi have traditionally been used as food, such as mushrooms or in fermented foods. New trends are to use edible fungi to produce myco-protein enriched foods. This review gives an overview of the different kinds of proteins, enzymes, and peptides produced by the most well-known fungi used as cell factories for different purposes and applications. Moreover, we describe some of the challenges that are important to consider when filamentous fungi are optimized as efficient cell factories.

Protein Quality in Infant Formulas Marketed in Brazil: Assessments on Biodigestibility, Essential Amino Acid Content and Proteins of Biological Importance

Infant formulas, designed to provide similar nutritional composition and performance to human milk, are recommended when breastfeeding is not enough to provide for the nutritional needs of children under 12 months of age. In this context, the present study aimed to assess the protein quality and essential amino acid content of both starting (phase 1) and follow-up (phase 2) formulas from different manufacturers. The chemical amino acid score and protein digestibility corrected by the amino acid score were calculated. The determined protein contents in most formulas were above the maximum limit recommended by FAO and WHO guidelines and at odds with the protein contents declared in the label. All infant formulas contained lactoferrin (0.06 to 0.44 g·100 g⁻¹) and α-lactalbumin (0.02 to 1.34 g·100 g⁻¹) below recommended concentrations, whereas ĸ-casein (8.28 to 12.91 g·100 g⁻¹), α-casein (0.70 to 2.28 g·100 g⁻¹) and β-lactoglobulin (1.32 to 4.19 g·100 g⁻¹) were detected above recommended concentrations. Essential amino acid quantification indicated that threonine, leucine and phenylalanine were the most abundant amino acids found in the investigated infant formulas. In conclusion, infant formulas are still unconforming to nutritional breast milk quality and must be improved in order to follow current global health authority guidelines.

A1 and A2 milk caseins-comparative FTIR and spectroflourimetry analysis

Around 35% of the total caseins are β-caseins, which are further classified as A1 β-caseins and A2 β-caseins, based on differences in the amino acid composition of both. A2 is the wild type genetic variant of β-casein while A1 is the mutant. The present study aimed at the isolation of A1 and A2 casein from different cow milk sources and its characterization by using simple chemical techniques, viz. FTIR and spectrofluorimetry. The commercial milk sample from Bos indicus (Gir) (A2) was obtained from Bombay Panjrapole, Mumbai and two commercially available packaged cow milk samples (pasteurized, skimmed) namely from Gokul and Mother Dairy (A1) were also obtained for comparison analysis from the local market. The isolation of casein was performed by standard method and analyzed using SDS-PAGE, FTIR and spectrofluorimetry. There was evidence that the A2 milk lacked histidine and rich in aromatic amino acids like tryptophan using FTIR and spectrofluorimetry techniques.

"A2 milk" authentication using isoelectric focusing and different PCR techniques

Genetic variants of milk proteins have attracted great interest for decades as they are related to important issues such as the composition and technological properties of milk. More recently, an "A1/A2 hypothesis" was developed saying that β-casein variant A1 may be a dietary risk factor for cardiovascular diseases, type 1 diabetes, sudden infant death syndrome and neurological disorders due to the release of β-casomorphin-7, whereas no evidence for such adverse effects was assumed for β-casein A2. Thus, the aim of this study was to adapt and establish analytical methods for the identification of genetic variants of β-casein using isoelectric focusing of milk proteins as well as appropriate PCR techniques. Allele-specific polymerase chain reaction (AS-PCR) proved to be a reliable method for differentiating most common β-casein variants (A1, A2, B, C), amplification-created restriction site (ACRS)-PCR using three different restriction enzymes allowed also the detection of variant A3, and the restriction fragment length polymorphism (RFLP)-PCR method enabled the reliable discrimination between A2 (homozygote/heterozygote) and non-A2 animals. Since traces of β-casein A1 were also found in commercial "A2 milk" in Austria, the authentication of such expensive dairy products is urgently recommended, both by genotyping of all dairy cows at farm level (to confirm that all cows are homozygous β-casein A2A2) and by screening commercial products on the market (to confirm the absence of β-casein variants A1, B, and C in dairy products labelled "A2 milk") to protect consumers from this unexpected fraud.

Potential Protective Protein Components of Cow's Milk against Certain Tumor Entities

Milk and dairy products, especially from cow's milk, play a major role in the daily human diet. It is therefore hardly surprising that the subject of milk is being extensively researched and that many effects of individual milk components have been characterized as a result. With the wealth of results available today, the influence of milk on the development of various types of cancer and, in particular, its often protective effects have been shown both in vitro and in vivo and in the evaluation of large-scale cohort and case-control studies. Various caseins, diverse whey proteins such as α-lactalbumin (α-LA), bovine α-lactalbumin made lethal to tumor cells (BAMLET), β-lactoglobulin (β-LG), or bovine serum albumin (BSA), and numerous milk fat components, such as conjugated linoleic acid (CLA), milk fat globule membrane (MFGM), or butyrate, as well as calcium and other protein components such as lactoferrin (Lf), lactoferricin (Lfcin), and casomorphines, show antitumor or cytotoxic effects on cells from different tumor entities. With regard to a balanced and health-promoting diet, milk consumption plays a major role in a global context. This work provides an overview of what is known about the antitumoral properties of proteins derived from cow's milk and their modes of action.

Bioactive Compounds in Infant Formula and Their Effects on Infant Nutrition and Health: A Systematic Literature Review

Infant formulas are an alternative to replace or supplement human milk when breastfeeding is not possible. The knowledge of human milk's bioactive compounds and their beneficial effects has attracted the interest of researchers in the field of infant nutrition, as well as researchers of technology and food sciences that seek to improve the nutritional characteristics of infant formulas. Several scientific studies evaluate the optimization of infant formula composition. The bioactive compound inclusion has been used to upgrade the quality and nutrition of infant formulas. In this context, the purpose of this systematic literature review is to assess the scientific evidence of bioactive compounds present in infant formulas (α-lactalbumin, lactoferrin, taurine, milk fat globule membrane, folates, polyamines, long-chain polyunsaturated fatty acids, prebiotics, and probiotics) and their effects on infant nutrition and health. Through previously determined criteria, studies published in the last fifteen years from five different databases were included to identify the advances in the optimization of infant formula composition. Over the last few years, there has been optimization of the infant formula composition, not only to increase the similarities in their content of macro and micronutrients but also to include novel bioactive ingredients with potential health benefits for infants. Although the infant food industry has advanced in the last years, there is no consensus on whether novel bioactive ingredients added to infant formulas have the same functional effects as the compounds found in human milk. Thus, further studies about the impact of bioactive compounds in infant nutrition are fundamental to infant health.

Comparative Effects of Milk Containing A1 versus A2 β-Casein on Health, Growth and β-Casomorphin-7 Level in Plasma of Neonatal Dairy Calves

Simple Summary

Bovine milk generally contains two types of the milk protein β-casein, A1 and A2. Enzymatic digestion of the A1 type yields the opioid peptide β-casomorphin-7, which is suggested to adversely affect human and animal health. This study aimed to compare the effects of milk containing either homozygote A1 or A2 β-casein on health and growth parameters in 47 dairy calves during the first three weeks of life. Additionally, we studied, for the first time, the levels of intact β-casomorphin-7 in plasma of calves fed milk of alternative β-casein genotypes. Milk feeding of “A2-milk” led to a lower milk intake and a looser fecal consistency (higher prevalence of diarrhea) compared to “A1-milk”. Nevertheless, weight gains and end weights of calves of both feeding groups were similar, which might be caused by the associated higher protein content of milk containing the A2 variant. Intact β-casomorphin-7 was detected in plasma after A1- and A2-milk consumption, but was almost 5 times higher for A1-calves. In summary, A2-milk minimized the cleavage of the opioid peptide β-casomorphin-7 and might have advantages in the development of pre-weaned dairy calves.

Abstract

Research has shown that digestion of A1 β-casein (β-CN) affects gastrointestinal motility and opioid activity through the release of the peptide β-casomorphin-7 (β-CM7). In the case of the A2 variant, the cleavage of β-CM7 does not occur or occurs at a very low rate. Therefore, the aim of the study was to compare the effects of milk containing either homozygote A1 or A2 β-CN on health and growth parameters of dairy calves. Forty-seven neonatal calves (24 females, 23 males) of the breeds German Holstein (GH, n = 9), German Simmental (GS, n = 33) and their crossing (GH × GS, n = 5) were used in a 21-day feeding study. Fecal score (FS), respiratory frequency (RF), and rectal body temperature (BT) were recorded daily, whereas body weight was measured at birth and at day 21 to estimate the average daily weight gain (ADG). Additionally, blood was collected from calves three times during the experimental period and, for the first time, the respective plasma samples were analyzed for intact β-CM7. Consumption of A2-milk led to a lower daily milk intake (dMI) (p < 0.05). Furthermore, fecal consistency was softer for calves fed A2-milk (p < 0.05). Although 44% of A2-calves had diarrhea or revealed a tendency towards it (FS ≥ 3), A1-calves had a prevalence of 21%. Calves with a FS of 4 were offered an electrolyte solution and received a dietary food supplement for the stabilization of the fluid and electrolyte balance. Nevertheless, similar ADG and end weights (EW) of calves fed A1- or A2-milk (p > 0.05) indicate that A2-milk may compensate higher diarrhea rates and lower dMI due to the associated higher protein content. This is the first report of intact β-CM7 in plasma of calves fed milk of either A1 or A2 β-CN. Evidence from this study suggests that due to the change in the amino-acid sequence, A2-milk might be able to prevent or, at least, to minimize the cleavage of β-CM7 in calves.

Understanding functional implication of β-casein gene variants in four cattle breeds characterized using AmpliSeq approach

Here, we designed a custom panel targeting whole β-casein gene SNPs of zebu and taurine cattle breeds to identify variants and applicability in dairy cattle genotyping. We sequenced two libraries consisting of different pools of primer sets from 95 individuals on the Illumina MiSeq. Consequently, over 92% target regions were amplified and 71 SNPs were available after quality filtering. Only three intronic variants were novel while majority of the identified variants were catalogued in dbSNP as known variants. Identified missense SNPs lead to variant A1/A2, B, F and A3, located in exon 7 only. For confirmation, A1/A2 locus was genotyped using PCR-RFLP. Variant B was observed in all animals, either in homozygous or in heterozygous form. Variants A1, F and A3 predicted to have a deleterious effect on protein function by decreasing the structural stability. Additionally, SIFT score revealed that the A1 variant might affect the protein function.

The protective effects of human milk-derived peptides on the pancreatic islet biology

Several epidemiological studies support the protective role of breastfeeding in reducing the risk for type 1 diabetes. Human breast milk is the perfect nutrition for infants and contains many complex proteins, lipids and carbohydrates. In this study, we examined the physiological effects of human milk-derived opioid peptides, β-casomorphins (BCM), and compared them with bovine-milk-derived opioid peptides on pancreatic hormone regulation and β-cell regeneration. Exposure of wild-type zebrafish embryos to 50 µg/ml of human BCM-5 and -7 from 3 days post fertilisation until 6 days post fertilisation resulted in an increased insulin domain of expression while exposure to bovine BCM-5 and -7 significantly reduced the insulin domain of expression as analysed by whole-mount in situ hybridisation. These changes may be accounted for by reduced insulin expression or β-cell number and were mitigated by the µ-opioid receptor antagonist, naloxone. The effect of BCM on β-cell regeneration was assessed following ablation of β-cells in Tg (ins: CFP-NTR) zebrafish from 3 days post fertilisation to 4 days post fertilisation, followed by exposure of bovine and human BCM-5 and -7 (50 µg/ml) from 4 days post fertilisation until 7 days post fertilisation. The regenerative capacity of β-cells was not impeded following exposure to human BCM-5 and -7, whereas the capacity of β-cells to regenerate following bovine BCM-5 and -7 exposure was reduced. Our data suggest that human BCM-5 and -7 may promote β-cell development and enable the regeneration of β-cells, while the bovine-milk-derived peptides, BCM-5 and -7, play an opposite role. These data may provide some biological explanation for the protective effect of breastfeeding on the development of type 1 diabetes.

The effect of endurance exercise on intestinal integrity in well-trained healthy men

Exercise is one of the external factors associated with impairment of intestinal integrity, possibly leading to increased permeability and altered absorption. Here, we aimed to examine to what extent endurance exercise in the glycogen‐depleted state can affect intestinal permeability toward small molecules and protein‐derived peptides in relation to markers of intestinal function. Eleven well‐trained male volunteers (27 ± 4 years) ingested 40 g of casein protein and a lactulose/rhamnose (L/R) solution after an overnight fast in resting conditions (control) and after completing a dual – glycogen depletion and endurance – exercise protocol (first protocol execution). The entire procedure was repeated 1 week later (second protocol execution). Intestinal permeability was measured as L/R ratio in 5 h urine and 1 h plasma. Five‐hour urine excretion of betacasomorphin‐7 (BCM7), postprandial plasma amino acid levels, plasma fatty acid binding protein 2 (FABP‐2), serum pre‐haptoglobin 2 (preHP2), plasma glucagon‐like peptide 2 (GLP2), serum calprotectin, and dipeptidylpeptidase‐4 (DPP4) activity were studied as markers for excretion, intestinal functioning and recovery, inflammation, and BCM7 breakdown activity, respectively. BCM7 levels in urine were increased following the dual exercise protocol, in the first as well as the second protocol execution, whereas 1 h‐plasma L/R ratio was increased only following the first exercise protocol execution. FABP2, preHP2, and GLP2 were not changed after exercise, whereas calprotectin increased. Plasma citrulline levels following casein ingestion (iAUC) did not increase after exercise, as opposed to resting conditions. Endurance exercise in the glycogen depleted state resulted in a clear increase of BCM7 accumulation in urine, independent of DPP4 activity and intestinal permeability. Therefore, strenuous exercise could have an effect on the amount of food‐derived bioactive peptides crossing the epithelial barrier. The health consequence of increased passage needs more in depth studies.

Clinical evaluation of glutathione concentrations after consumption of milk containing different subtypes of β-casein: results from a randomized, cross-over clinical trial

Abstract

This study reports the plasma glutathione concentrations in a double-blind, randomized, controlled, 2 × 2 cross-over study in which healthy participants consumed conventional milk (2 × 250 mL per day) containing both A1 and A2 types of β-casein, or milk containing only A2 type β-casein. Beta-casomorphin-7 (BCM-7), a peptide uniquely derived from the A1 type of β-casein, was previously reported to downregulate glutathione expression in human gut epithelial and neuronal cell lines by limiting cysteine uptake. The current human study demonstrates that consumption of milk containing only A2 β-casein was associated with a greater increase in plasma glutathione concentrations compared with the consumption of milk containing both β-casein types, and did not increase plasma BCM-7 concentrations compared with the washout diet in the study participants. Thus, milk containing only A2 β-casein and not A1 β-casein has the potential to promote the production of the antioxidant glutathione in humans.

Clinical Trial Registration

ClinicalTrials.gov; identifier: NCT02406469

Electronic supplementary material

The online version of this article (doi:10.1186/s12937-016-0201-x) contains supplementary material, which is available to authorized users.