Hormones in milk

A Comprehensive Review of Bovine Colostrum Components and Selected Aspects Regarding Their Impact on Neonatal Calf Physiology

Colostrum contains macro- and micronutrients necessary to meet the nutritional and energy requirements of the neonatal calf, bioactive components that intervene in several physiological aspects, and cells and microorganisms that modulate the calf's immune system and gut microbiome. Colostrum is sometimes mistaken as transition milk, which, although more nutritive than whole milk, has a distinct biochemical composition. Furthermore, most research about colostrum quality and colostrum management focuses on the transfer of maternal IgG to the newborn calf. The remaining components of colostrum and transition milk have not received the same attention, despite their importance to the newborn animal. In this narrative review, a large body of literature on the components of bovine colostrum was reviewed. The variability of these components was summarized, emphasizing specific components that warrant deeper exploration. In addition, the effects of each component present in colostrum and transition milk on several key physiological aspects of the newborn calf are discussed.

Type 1 diabetes and pregnancy: An update on glucose monitoring and insulin treatment

The relevance of type 1 diabetes during pregnancy stems from its impact on the health of mother and offspring and its increasing prevalence. Glycemic control during pregnancy is one of the main risk factors for adverse events. Besides, treatment becomes a major challenge not only due to the modifications in insulin requirements due to changes in hormones and cytokines but also to the stricter control targets. Given the recent appearance of new ultra-rapid and basal insulin analogues and the constant evolution of technology to treat people with diabetes, we review these aspects in relation to the treatment of women with type 1 diabetes during pregnancy.

New Achievements in High-Pressure Processing to Preserve Human Milk Bioactivity

High-pressure processing (HPP) is a non-thermal technology that is being increasingly applied in food industries worldwide. It was proposed that this method could be used as an alternative to holder pasteurization (HoP; 62.5°C, 30 min) in milk banks but its impact on the immunologic, enzymatic and hormonal components of human milk has not yet been evaluated in detail. The aim of our study was to compare the effects of HPP in variants: (1) 600 MPa, 10 min (2) 100 MPa, 10 min, interval 10 min, 600 MPa, 10 min (3) 200 MPa, 10 min, interval 10 min, 400 MPa, 10 min (4) 200 MPa, 10 min, interval 10 min, 600 MPa, 10 min in temperature range 19-21°C and HoP on the leptin, adiponectin, insulin, hepatocyte growth factor (HGF), lactoferrin and IgG contents in human milk. HoP was done at the Regional Human Milk Bank in Warsaw at the Holy Family Hospital on S90 Eco pasteurizer (Sterifeed, Medicare Colgate Ltd). Apparatus U4000/65 (Unipress Equipment, Poland) was used for pascalization. Milk samples were obtained from women during 2-6 weeks of lactation. Post-treatment culture showed no endogenous bacterial contamination in any tested option. Concentrations of selected components were determined using ELISA tests. The level of all analyzed components were significantly decreased by HoP: leptin 77.86%, adiponectin 32.79%, insulin 32.40%, HGF 88.72%, lactoferrin 60.31@.%, IgG 49.04%. All HPP variants caused an increase in leptin concentration, respectively (1) 81.79% (2) 90.01% (3) 86.12% (4) 47.96%. Retention of insulin after HPP was (1) 88.20% (2) 81.98% (3) 94.76% (4) 90.31% HGF (1) 36.15% (2) 38.81% 97.15% (3) 97.15% (4) 43.02%, lactoferrin (1) 55.78% (2) 57.63% (3) 78.77% (4) 64.75%. Moreover, HPP variant as 200 + 400 MPa preserved IgG (82.24%) better than HoP and resulted not statistically significant change of adiponectin level (38.55%) compare to raw milk. Our results showed that HPP leads to preservation of adipokines, growth factor, and lactoferrin, IgG much better or comparable with HoP.

Human milk insulin is related to maternal plasma insulin and BMI: but other components of human milk do not differ by BMI

Background

The impact of maternal BMI and insulin sensitivity on bioactive components of human milk (HM) is not well understood. As the prevalence of obesity and diabetes rises, it is increasingly critical that we understand how maternal BMI and hormones associated with metabolic disease relate to concentrations of bioactive components in HM.

Methods

This longitudinal cohort design followed 48 breastfeeding mothers through the first four months of lactation, collecting fasting morning HM samples at 2-weeks and 1, 2, 3, and 4-months, and fasting maternal blood at 2-weeks and 4-months. Insulin, glucose, adipokines leptin and adiponectin, appetite regulating hormone ghrelin, marker of oxidative stress 8OHdG, and inflammatory cytokines (IL-6, IL-8, and TNF-a) were measured in HM and maternal plasma.

Results

26 normal weight (NW) (BMI=21.4±2.0 kg/m²), and 22 overweight/obese (OW/Ob) (BMI=30.4±4.2 kg/m²) were followed. Of all HM analytes measured, only insulin and leptin were different between groups - consistently higher in the OW/Ob group (leptin: p<0.001; insulin: p<0.03). HM insulin was 98% higher than maternal plasma insulin at 2-weeks and 32% higher at 4-months (p<0.001). Maternal fasting plasma insulin and HOMA-IR were positively related to HM insulin at 2-weeks (p<0.001, R²≥0.38, n=31), and 4-months (p≤0.005, R²≥0.20, n=38).

Conclusions

The concentrations of insulin in HM are higher than in maternal plasma and are related to maternal BMI and insulin sensitivity. With the exception of leptin, there were minimal other differences observed in HM composition across a wide range in maternal BMI.

Impact of colostrum and plasma immunoglobulin intake on hippocampus structure during early postnatal development in pigs

The first milk, colostrum, is an important source of nutrients and an exclusive source of immunoglobulins (Ig), essential for the growth and protection from infection of newborn pigs. Colostrum intake has also been shown to affect the vitality and behaviour of neonatal pigs. The objective of this study was to evaluate the effects of feeding colostrum and plasma immunoglobulin on brain development in neonatal pigs. Positive correlations were found between growth, levels of total protein and IgG in blood plasma and hippocampus development in sow-reared piglets during the first 3 postnatal days. In piglets fed an elemental diet (ED) for 24h, a reduced body weight, a lower plasma protein level and a decreased level of astrocyte specific protein in the hippocampus was observed, as compared to those that were sow-reared. The latter was coincident with a reduced microgliogenesis and an essentially diminished number of neurons in the CA1 area of the hippocampus after 72h. Supplementation of the ED with purified plasma Ig, improved the gliogenesis and supported the trophic and immune status of the hippocampus. The data obtained indicate that the development of the hippocampus structure is improved by colostrum or an Ig-supplemented elemental diet in order to stimulate brain protein synthesis and its development during the early postnatal period.

Colostrogenesis: IgG1 transcytosis mechanisms

Biological transport of intact proteins across epithelial cells has been documented for many absorptive and secretory tissues. Immunoglobulins were some of the earliest studied proteins in this category. The transcellular transport (transcytosis) of immunoglobulins in neonatal health and development has been recognized; the process is especially significant with ungulates because they do not transcytose immunoglobulins across the placenta to the neonate. Rather, they depend upon mammary secretion of colostrum and intestinal absorption of immunoglobulins in order to provide intestinal and systemic defense until the young ungulate develops its own humoral defense mechanisms. The neonatal dairy calf's ability to absorb immunoglobulins from colostrum is assisted by a ~24 h "open gut" phenomenon where large proteins pass the intestinal epithelial cells and enter the systemic system. However, a critical problem recognized for newborn dairy calves is that an optimum mass of colostrum Immunoglobulin G (IgG) needs to be absorbed within that 24 h window in order to provide maximal resistance to disease. Many calves do not achieve the optimum because of poor quality colostrum. While many studies have focused on calf absorption, the principal cause of the problem resides with the extreme variation (g to kg) in the mammary gland's capacity to transfer blood IgG1 into colostrum. Colostrum is a unique mammary secretory product that is formed during late pregnancy when mammary cells are proliferating and differentiating in preparation for lactation. In addition to the transcytosis of immunoglobulins, the mammary gland also concentrates a number of circulating hormones into colostrum. Remarkably, the mechanisms in the formation of colostrum in ungulates have been rather modestly studied. The mechanisms and causes of this variation in mammary gland transcytosis of IgG1 are examined, evaluated, and in some cases, explained.

Turning acne on/off via mTORC1

Over the past 10 years, the increase in comprehension of the mechanisms behind acne has been truly exponential. Starting with the ethnological work of Cordain, accelerated by the epidemiological work of Adebamowo, supported by the clinical trials of Smith and Mann, Kwon, DiLandro and others, the interface of diet and acne is coming into focus. Melnik now presents an exceptional pair of papers that illustrate for dermatologists what translational research is all about. The Western diet, the role of dairy, FoxO1 and mTORC1, the interplay of agonists and antagonists, therapeutics present and future – the jigsaw puzzle is coming together.

Nursing during the first two days of life is essential for the expression of proteins important for growth and remodeling of the neonatal porcine cervix

The neonatal porcine cervix is sensitive to hormones, including relaxin (RLX), from birth. Whether nursing is required to establish the cervical developmental program or to determine cervical developmental trajectory is unknown. The objective of study 1 was to determine effects of age and nursing on expression of molecular markers and mediators of porcine cervical growth and remodeling from birth to postnatal day (PND) 2 and to document effects of RLX treatment during this period on expression of targeted gene products in nursed vs. replacer-fed gilts. Study 2 was conducted to determine effects of age at first nursing and duration of nursing from birth on expression of targeted transcripts or proteins at PND 14. Nursing supported cervical estrogen receptor-α, vascular endothelial growth factor, matrix metalloproteinase (MMP)9, and antiapoptotic B-cell lymphoma-2 protein expression on PND 2. These proteins were undetectable in replacer-fed gilts. Returning replacer-fed gilts to nursing after PND 2 did not restore cervical expression of these proteins by PND 14. RLX increased (P < 0.05) cervical estrogen receptor-α, vascular endothelial growth factor, and B-cell lymphoma-2 protein in nursed gilts, MMP2 protein in nursed and replacer-fed gilts, and decreased (P < 0.05) pro-MMP9 protein in nursed gilts, and RXFP1 mRNA levels in nursed and replacer-fed gilts at PND 2. Replacer feeding for 2 wk from birth increased (P < 0.05) RXFP1 mRNA levels on PND 14. Results support the lactocrine hypothesis for maternal programming of neonatal tissues. Nursing from birth is required to establish the neonatal cervical developmental program and to maintain cervical developmental trajectory to PND 14.

Analysis of insulin in human breast milk in mothers with type 1 and type 2 diabetes mellitus

Despite the important role that insulin plays in the human body, very little is known about its presence in human milk. Levels rapidly decrease during the first few days of lactation and then, unlike other serum proteins of similar size, achieve comparable levels to those in serum. Despite this, current guides for medical treatment suggest that insulin does not pass into milk, raising the question of where the insulin in milk originates. Five mothers without diabetes, 4 mothers with type 1, and 5 mothers with type 2 diabetes collected milk samples over a 24-hour period. Samples were analysed for total and endogenous insulin content and for c-peptide content. All of the insulin present in the milk of type 1 mothers was artificial, and c-peptide levels were 100x lower than in serum. This demonstrates that insulin is transported into human milk at comparable concentration to serum, suggesting an active transport mechanism. The role of insulin in milk is yet to be determined; however, there are a number of potential implications for the infant of the presence of artificial insulins in milk.

New developments in our understanding of acne pathogenesis and treatment

Interest in sebaceous gland physiology and its diseases is rapidly increasing. We provide a summarized update of the current knowledge of the pathobiology of acne vulgaris and new treatment concepts that have emerged in the last 3 years (2005-2008). We have tried to answer questions arising from the exploration of sebaceous gland biology, hormonal factors, hyperkeratinization, role of bacteria, sebum, nutrition, cytokines and toll-like receptors (TLRs). Sebaceous glands play an important role as active participants in the innate immunity of the skin. They produce neuropeptides, excrete antimicrobial peptides and exhibit characteristics of stem cells. Androgens affect sebocytes and infundibular keratinocytes in a complex manner influencing cellular differentiation, proliferation, lipogenesis and comedogenesis. Retention hyperkeratosis in closed comedones and inflammatory papules is attributable to a disorder of terminal keratinocyte differentiation. Propionibacterium acnes, by acting on TLR-2, may stimulate the secretion of cytokines, such as interleukin (IL)-6 and IL-8 by follicular keratinocytes and IL-8 and -12 in macrophages, giving rise to inflammation. Certain P. acnes species may induce an immunological reaction by stimulating the production of sebocyte and keratinocyte antimicrobial peptides, which play an important role in the innate immunity of the follicle. Qualitative changes of sebum lipids induce alteration of keratinocyte differentiation and induce IL-1 secretion, contributing to the development of follicular hyperkeratosis. High glycemic load food and milk may induce increased tissue levels of 5alpha-dihydrotestosterone. These new aspects of acne pathogenesis lead to the considerations of possible customized therapeutic regimens. Current research is expected to lead to innovative treatments in the near future.

Insulin-like growth factors (IGFs), IGF binding proteins, and other endocrine factors in milk: role in the newborn

The role of colostrum and milk in the neonate has been chiefly recognized as a comprehensive nutrient foodstuff. In addition, the provision of colostrum-the first milk-for early immune capacity has been well documented for several species. Colostrum is additionally a rich and concentrated source of various factors that demonstrate biological activity in vitro. Three hypotheses have been proposed for the phenotypic function of these secreted bioactive components: (1) only mammary disposal, (2) mammary cell regulation, and (3) neonatal function [gastrointestinal tract (GIT) or systemic]. Traditionally, it was assumed that the development of the GIT is preprogrammed and not influenced by events occurring in the intestinal lumen. However, a large volume of research has demonstrated that colostrum (or milk-borne) bioactive components can basically contribute to the regulation of GIT growth and differentiation, while their role in postnatal development at physiological concentrations has remained elusive. Much of our current understanding is derived from cell culture and laboratory animals, but experimentation with agriculturally important species is taking place. This chapter provides an overview of work conducted primarily in neonatal calves and secondarily in other species on the effects on neonates of selected peptide endocrine factors (hormones, growth factors, in part cytokines) in colostrum. The primary focus will be on insulin-like growth factors (IGFs) and IGF binding proteins (IGFBPs) and other bioactive peptides, but new interest and concern about steroids (especially estrogens) in milk are considered as well.

Environmental chemicals in human milk: a review of levels, infant exposures and health, and guidance for future research

The aim of this review is to introduce the reader to various science and policy aspects of the topic of environmental chemicals in human milk. Although information on environmental chemicals in human milk has been available since the 1950s, it is only relatively recently that public awareness of the issue has grown. This review on environmental chemicals in human milk provides a resource summarizing what is currently known about levels and trends of environmental chemicals in human milk, potential infant exposures, and benefits of breast-feeding relative to the risks of exposures to environmental chemicals. The term "environmental chemicals," as it pertains to human milk, refers to many classes of exogenous chemicals that may be detected in human milk. For example, pharmaceutical agents and alcohol are environmental chemicals that have been found in human milk. Other chemicals, such as heavy metals and volatile organic compounds, have also been detected in human milk. Most research on environmental chemicals in human milk has concentrated on persistent, bioaccumulative, and toxic (PBT) chemicals. In this review, a description of human milk is provided, including a brief review of endogenous substances in human milk. Determinants of levels of PBTs are discussed, as are models that have been developed to predict levels of PBTs in human milk and associated body burdens in breast-feeding infants. Methodologies for human milk sampling and analysis, and concepts for consideration in interpretation and communication of study results, as developed by the Technical Workshop on Human Milk Surveillance and Research for Environmental Chemicals in the United States are described. Studies which have compared the health risks and benefits associated with breast-feeding and formula-feeding are discussed.

Mammary physiology and milk secretion

The presence of drugs or other potentially toxic materials in milk is an obvious public health risk, especially to infants and neonates. There is also increasing concern that human breast cancer is principally epigenetic in origin and results from environmentally produced lesions. Little is known about the mechanisms by which toxic substances enter milk or mammary tissue but knowledge of these processes is important to toxicologists and researchers involved in drug design and metabolism. Five general pathways have been described for transport of proteins, lipids, ions, nutrients and water into milk. Four of these pathways are transcellular, involving transport across at least two membrane barriers; the fifth is paracellular and allows direct exchange of interstitial and milk components. Solute transport by these pathways is mediated by a diverse, and complex array of transport and secretory processes that are regulated by hormonal, developmental, and physiological factors. Current research is beginning to define the mechanisms underlying some of these processes, however the regulation and coordination of solute transport mechanisms remains poorly understood. In this article we review our current understanding of the normal solute transport and secretory processes involved in milk production, and discuss potential regulatory mechanisms.

Enteral administration of hematopoietic growth factors in the neonatal intensive care unit

By 20 wk of gestation, the human fetal gastrointestinal (GI) tract morphologically resembles that of the term infant, but functional development is limited before 26 wk. By 30 wk of gestation, the fetus has the capacity for limited digestion and enteral absorption. GI growth and development continue postnatally. Trophic factors, including nutrients, peptides, hormones and growth factors, are recognized as having important influences on the morphology and histology of the developing GI tract. Other trophic factors are important in adaptation and repair following injury. Many such factors are provided in utero via amniotic fluid swallowing and later by human colostrum and milk.

CONCLUSION

This review discusses cytokines with known GI trophic effects, either in vitro or in vivo, and focuses on those cytokines that have been used in the neonatal intensive care unit.

Human milk surveillance and research of environmental chemicals: concepts for consideration in interpreting and presenting study results

This article describes issues related to the interpretation, presentation, and use of data from human milk surveillance and research studies. It is hoped that researchers conducting human milk studies in the future will consider these concepts when formulating study conclusions and presenting data. The key issues discussed are; (1) communication of information on human milk constituents to health care providers and the public; (2) complexities associated with assessing risks and benefits when comparing breast-feeding and formula-feeding; (3) use of human milk information for trends analysis and assessment of the efficacy of restrictions on use/release of chemicals in the environment; and (4) risk assessment and regulatory decision-making concepts regarding environmental chemicals in human milk. As researchers conduct surveillance and research involving human milk, it is of the utmost importance that the results of these studies are provided with information on risk and benefits that place the data in perspective, so that those involved in decision making regarding infant nutrition (e.g., expectant mothers, physicians, midwives, nurses, and lactation consultants) can appropriately interpret the research data.

Is milk a conduit for developmental signals?

The diverse role of milk in the neonate is slowly expanding beyond nutritional and immunological borders to include possible developmental roles for the numerous hormones and growth factors found in this medium. Yet, despite the growing list of milk-borne factors, the precise impact of each of these on the neonate remains to be elucidated. The focus of this review is to summarize studies from our laboratory which demonstrate clearly that milk-borne factors play an obligatory role in the postnatal development of at least one organ, the anterior pituitary gland.

Vesicular transport of soluble substances into mouse milk

Utilizing a novel protocol to study transport of substances into mouse milk in situ, we have shown that many "fluid-phase" markers are taken up by mammary epithelial cells and deposited in milk. Since the tight junctions are closed and impermeable even to small molecules, extra-alveolar substances (those not synthesized by the alveolar cells) must be transported into the milk by the epithelial cells themselves. The markers we have used include dextran, lucifer yellow dye, horseradish peroxidase, and albumin. Using these markers and immunostaining for endogenous proteins, we have visualized transcytotic vesicles involved in transporting these markers to milk.

Epidermal growth factor reduces the development of necrotizing enterocolitis in a neonatal rat model

Necrotizing enterocolitis (NEC) is the most common gastrointestinal disease of prematurely born infants. Maternal milk plays an important protective role against NEC development and is the major source of epidermal growth factor (EGF) for neonates. The aim of this study was to examine the effect of orally administered EGF on the incidence of NEC in a neonatal rat model. Newborn rats were artificially fed either with growth factor-free rat milk substitute (RMS) or RMS supplemented with 500 ng/ml of EGF (RMS+EGF). Experimental NEC was induced by exposure to asphyxia and cold stress. Development of NEC was evaluated by gross and histological scoring of damage in the ileum. Ileal EGF receptor (EGF-R), EGF, and transforming growth factor-alpha mRNA expression was assessed by RT competitive-PCR, and the EGF-R was localized by immunohistochemistry. EGF supplementation of formula reduced the incidence and severity of NEC in rats (13/16 RMS vs. 4/13 RMS+EGF). Ileal EGF-R mRNA expression was markedly increased in the RMS group compared with RMS+EGF. Enhanced EGF-R expression in the RMS group was localized predominantly in the epithelial cells of injured ileum. These data suggest a new potential therapeutic approach for the prevention and treatment of NEC.

Does breast-feeding protect against childhood obesity?

The impact of breast-feeding on overweight and obesity in children at school entry was assessed in a cross sectional study in Bavaria in 1997. The school entry health examination enrolled 134,577 children. Data on early feeding were collected in two rural districts (eligible population n=13,345). The analyses were confined to 5 or 6 year old children with German nationality. The main outcome measures were overweight (BMI>90th percentile for all German children seen at the 1997 school entry health examination in Bavaria) and obesity (BMI>97th percentile). Information on breast-feeding was available for 9206 children of whom 56% had been breast-fed for any length of time. In non breast-fed children the upper tail of the BMI distribution was enlarged as compared to the breast-fed children whereas the median was almost identical. The prevalence of obesity in children who had never been breast-fed was 4.5% as compared to 2.8% in ever breast-fed children. A clear dose response effect for the duration of breast-feeding on the prevalence of obesity was found: 3.8%, 2.3%, 1.7% and 0.8% for exclusive breast-feeding for up to 2, 3 to 5, 6 to 12 and more than 12 months, respectively. The results for overweight were very similar. The protective effect of beast feeding on overweight and obesity could not be explained by differences in social class or lifestyle. The adjusted odds ratios of breast-feeding for any length of time was 0.71 (95% CI 0.56-0.90) for obesity and 0.77 (95%CI 0.66-0.88) for overweight. This data set did not allow to adjust for maternal weight, an important risk factor for obesity in children. Maternal overweight, however, could not explain the effect of breastfeeding on overweight and obesity in a similar study. The reduction in the risk for overweight and obesity is therefore more likely to be related to the properties of human milk than to factors associated with breast-feeding. The potential relevance of different components of human milk for the observed reduction in the risk for overweight and obesity is discussed. The preventive effect of breast-feeding on overweight and obesity is an important additional argument for the promotion of breast-feeding in industrialised countries.

Milk protein-derived opioid receptor ligands

Milk is mammalian characteristic and is of particular importance for humans: Mother's milk or its substitutes from cows' milk are absolutely essential nutriments for the neonate and cows' milk also represents a basic foodstuff for adults. However, in addition to their well-known nutritive role, milk constituents apparently are also able to carry specific information from the milk producer's to the milk receiver's organism: Thus, a number of milk protein fragments has been shown to behave like opioid receptor ligands able to address opioidergic systems in the adult's or in the neonate's organism. With respect to the proteins, which they are derived off these peptides have been named alpha-casein exorphins or casoxin D (alpha-casein), beta-casomorphins or beta-casorphin (beta-casein), casoxin or casoxin A, B, or C (k-casein), alpha-lactorphins (alpha-lactalbumin), beta-lactorphin (beta-lactoglobulin) or lactoferroxins (lactoferrin). Only casoxins and lactoferroxins display antagonistic properties; the other peptides behave like opioid receptor agonists. Most of the information available so far has been collected about beta-casomorphins. These peptides obviously can be released from beta-casein in the adult's or in the neonate's organism, where they might elicit opioid effects in the frame of a regulatory role as "food hormones". Several synthetic beta-casomorphin derivatives have been shown to be highly specific and potent mu-type opioid receptor ligands which frequently have been used as standard tools in opioid research.

Apelin, the natural ligand of the orphan receptor APJ, is abundantly secreted in the colostrum

By using a strategy that we have developed to search for the ligands of orphan seven-transmembrane-domain receptors [S. Hinuma et al., Nature 393 (1998) 272-276], we have recently identified a natural ligand, apelin, for the orphan 7TMR, APJ [K. Tatemoto et al., Biochem. Biophys. Res. Commun. 251 (1998) 471-476]. In this paper, we isolated rat and mouse apelin cDNAs, and analyzed the tissue distribution of apelin mRNA in rats. Although apelin mRNA was widely detected in a variety of tissues, the highest expression of apelin mRNA was detected in the mammary gland of pregnant rats. In the mammary gland, biologically active apelin and its mRNA considerably increased during pregnancy and lactation, and reached a maximal level around parturition. Moreover, a large amount of apelin (14-93 pmol/ml) was found to be secreted in the bovine colostrum, and it was still detectable even in commercial bovine milk. Since apelin partially suppressed cytokine production by mouse spleen cells in response to T cell receptor/CD3 cross-linking, the oral intake of apelin in the colostrum and milk might modulate immune responses in neonates.

Identification of minor proteins of human colostrum and mature milk by two-dimensional electrophoresis

Two-dimensional electrophoresis (2-DE) followed by electroblotting and microsequencing is considered to be the most powerful method for the isolation and characterization of proteins. In this paper, we report the separation and determination of the N-terminal and/or internal amino acid sequences of the minor proteins of human colostral and mature milk by 2-DE and microsequencing. In order to analyze the minor proteins of human milk, we use immunoabsorbents to remove three major proteins, alpha-lactalbumin, lactoferrin and secretory immunoglobulin A. The major proteins removed by this process accounted for about 79 and 93% of the total whey proteins of mature and colostral milk, respectively. The remaining milk proteins were then separated by isoelectric focusing gel electrophoresis between pH 3 and 10, and subjected to 12.5% sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Approximately 400 spots were detected in both colostral and mature milk by silver staining after 2-DE. Twenty-two major, well-resolved proteins (out of 400) were microsequenced (N-termini as well as internal). These include fatty acid binding protein, beta 2-microglobulin, complement C4, clusterin, alpha 1-antritrypsin, lysozyme C, alpha- and beta-casein, prealbumin, serotransferrin, fructose-bisphosphate aldolase A, and beta-casein fragments. No major differences in the protein patterns were observed between the minor proteins of colostrum and mature milk, indicating that the minor proteins remained relatively constant during lactation. These results suggest that the minor milk proteins are important for the health and development of breast-fed infants throughout lactation.

Stability and distribution of orally administered epidermal growth factor in neonatal pigs

Stability and distribution of orally administered epidermal growth factor (EGF) were examined in newborn and 5-day-old pigs. Forty-five minutes after oral administration of iodine-125 labeled EGF, 60 and 50% of the radioactivity administered were recovered from the internal organs in newborn and 5-day-old pigs, respectively. In both age groups, over 95% of the recovered radioactivity was found in the gastrointestinal tract, of which 78-86% was found in the luminal contents with the remaining found in the gastrointestinal wall. Within the gastrointestinal tract, 65-71% of radioactivity was found in the stomach, 27-30% in the proximal and mid small intestine and 3-4% was found in the distal part of the small intestine. There were no significant differences in the overall distribution of orally administered radioactivity between two age groups. Based on liquid chromatography and trichloroacetic acid precipitation, a substantial amount of EGF recovered from the luminal contents (63-86%) and the gastrointestinal wall (42-81%) remained "intact". The receptor binding ability of the EGF recovered from the gastric contents was 96-102% comparable to the native EGF tracer. The receptor binding ability remained high (40-58%) in the proximal small intestinal lumen and it decreased to 15% in the distal small intestinal lumen in newborn pigs. In 5-day-old pigs, EGF recovered from the small intestinal contents had 5 to 24% receptor binding ability when compared with native EGF tracer. The receptor binding ability of the EGF recovered from all other organs was below 5% with an exception of the gastric wall, from which recovered EGF retained 9 to 26% receptor binding ability. These results indicate that most of orally ingested EGF remained in the gastrointestinal tract in neonatal pigs 45 min after oral ingestion, and significant amount of the ingested EGF remained biologically active. It suggests that milk-borne EGF can survive in the gastrointestinal tract and may play a role in regulating gut development in neonatal animals.

Atrial natriuretic peptide and endothelin concentrations in human milk during postpartum lactation

Milk samples from lactating women (n = 24) were examined for atrial natriuretic peptide (ANP) and endothelin-1 (ET-1) content throughout the first 3 months postpartum. Samples were collected at the beginning (foremilk) and towards the end (hindmilk) of nursing. ANP was detected in the milk samples. A value of 9.4 +/- 1.8 pmol/l (mean +/- SEM) was observed on the third day postpartum. No significant variations in concentrations were observed during the 3 months examined. Foremilk and hindmilk ANP concentrations were also similar. ET-1, as previously reported, is present in the milk of lactating women. According to our observations, the concentration of ET-1 varies during the first 3 postpartum months. The highest concentrations were observed on the third day (10.2 +/- 1.8 pmol/l) of lactation, decreasing to 4.5 +/- 0.8 pmol/l after 1 week (p < 0.05) and to 2.0 +/- 0.3 pmol/l, at 1 month postpartum (p < 0.05), this level being maintained for up to 3 months postpartum. Foremilk samples on the third day postpartum contained significantly higher concentrations of ET-1, compared to hindmilk samples (10.2 +/- 1.8 vs 7.7 +/- 1.2 pmol/l, p < 0.05). The stable levels of ANP and the initial high and subsequently decreasing levels of ET-1 in human milk, during the first 3 months postpartum, suggest that these peptides might be of importance either in the lactating mammary gland or in the suckling newborn.

A milk-borne factor inhibits mammotrope differentiation in the neonatal rat

Within the first few days of neonatal life in the rat, a milk-borne peptide is transferred to the neonatal circulation and transported to the pituitary gland where it acts directly to induce final differentiation of mammotropes. As we were attempting to purify this stimulatory peptide, we separated an antagonistic activity that serves as the focus of the present study. Milk obtained on days 2-3 of lactation was subjected to pH fractionation followed by acetone precipitation to yield two fractions that stimulated and inhibited, respectively, mammotrope differentiation in cultures of neonatal pituitary cells. The stimulatory agent more than doubled the proportion of prolactin secretors in those cultures, whereas the inhibitory agent exerted the opposite effect when tested alone. Moreover, the inhibitory agent severely attenuated mammotrope differentiation evoked by the stimulatory fraction or by basic FGF, an established inducer of this developmental phenomenon. The discovery of a milk-borne inhibitor, coupled with the previously described milk stimulatory factor, indicates that maternal control of mammotrope differentiation is considerably more sophisticated than previously believed.

Insulin-like growth factors in milk and mammary gland

Milk contains insulin-like growth factor I and II (IGF-I and IGF-II) and four IGF binding proteins (IGFBP). Their concentrations are highest prepartum and early postpartum, coinciding with maximal proliferation of mammary cells and the time when the infant gut is the least developed. This has lead to the suggestion that IGFs may be important for the growth and development of the mammary gland and that IGFs in milk play a role in promoting development of the gastrointestinal tract of the newborn. IGF-I and, to a lesser extent, IGF-II can stimulate milk yield and blood flow in goats when infused directly into the mammary gland, suggesting they may also be important in supporting established lactation. Thus IGFs may have a dual function in the mammary gland, establishing and maintaining the maternal mammary system and, once secreted into milk, supporting gastrointestinal development in the newborn.