Immunologically active peptides that accompany hen egg yolk immunoglobulin Y: separation and identification

Age-Dependent Effects of Yolkin on Contact Sensitivity and Immune Phenotypes in Juvenile Mice

Yolkin, an egg yolk immunoregulatory protein, stimulates the humoral but inhibits the cellular immune response in adult mice. The aim of this investigation was to evaluate the effects of yolkin administration on the immune response using a model of juvenile, i.e., 28-day- and 37-day-old, mice. We examined the yolkin influence on the magnitude of the cellular immune response, which was determined as contact sensitivity (CS) to oxazolone (OXA), and the humoral immune response, which was determined as the antibody response to ovalbumin (OVA). Yolkin was administered in drinking water, followed by immunization with OXA or OVA. In parallel, the phenotypic changes in the lymphoid organs were determined following yolkin treatment and prior immunization. The results showed that yolkin had a stimulatory effect on CS in the mice treated with yolkin from the 37th day of life but not from the 28th day of life. In contrast, no regulatory effect of yolkin on antibody production was found in 28-day- and 37-day-old mice. Phenotypic studies revealed significant changes in the content of B cells and T cell subpopulations, including CD4+CD25+Foxp3 regulatory T cells. The association between the effects of yolkin on the magnitude of CS and phenotypic changes in main T- and B-cell compartments, as well the importance of changes in T-regulatory and CD8+ cells in the age categories, are discussed. We conclude that the immunoregulatory effects of yolkin on the generation of CS in mice are age dependent and change from stimulation in juvenile to suppression in adult mice.

Yolkin, a Polypeptide Complex from Egg Yolk, Affects Cytokine Levels and Leukocyte Populations in Broiler Chicken Blood and Lymphoid Organs after In Ovo Administration

Yolkin is a polypeptide complex isolated from hen egg yolk that exhibits immunomodulating properties. The aim of the present study was to determine whether in-ovo-delivered yolkin affects leukocyte populations and cytokine levels in broiler chickens. The experiment was carried out on eggs from Ross 308 broiler breeder birds. Yolkin was administered in ovo on the 18th day of incubation, once, at the following three doses: 1, 10, or 100 µg/egg. The immunological parameters were assessed in 1-, 7-, 14-, 21-, 28-, 35-, and 42-day-old birds kept under farming conditions and routinely vaccinated. The leukocyte populations were determined in the thymus, spleen, and blood. The cytokine (IL-1β, IL-2, IL-6, and IL-10) levels were determined in the plasma of the broiler chickens. Each experimental group included eight birds. The most pronounced effect of yolkin was an increase in the population of T cells, both CD4+ and CD8+, mainly in the blood. This effect on the lymphocyte subsets may be valuable regarding chicken immune responses, mainly against T-dependent antigens, during infection or after vaccination.

Importance for humans of recently discovered protein compounds - yolkin and yolk glycopeptide 40, present in the plasma of hen egg yolk

Vitellogenin (Vt) is considered the primary protein precursor of egg yolk, serving as a source of protein- and lipid-rich nutrients for the developing embryo. However, recent research has revealed that the functions of Vt and Vt-derived polypeptides, such as yolkin (Y) and yolk glycopeptide 40 (YGP40), extend beyond their nutritional roles as a source of amino acids. Emerging evidence has demonstrated that both Y and YGP40 possess immunomodulatory properties and can contribute to host immune defenses. Additionally, Y polypeptides have been shown to exhibit neuroprotective activity, participating in the modulation of neurons' survival and activity, inhibiting neurodegeneration processes, and improving cognitive functions in rats. These non-nutritional functions not only enhance our understanding of the physiological roles of these molecules during embryonic development but also offer a promising basis for the potential application of these proteins in human health.

Mechanism of Molecular Activity of Yolkin-a Polypeptide Complex Derived from Hen Egg Yolk-in PC12 Cells and Immortalized Hippocampal Precursor Cells H19-7

Food-derived bioactive peptides able to regulate neuronal function have been intensively searched and studied for their potential therapeutic application. Our previous study showed that a polypeptide complex yolkin, isolated from hen egg yolk as a fraction accompanying immunoglobulin Y (IgY), improved memory and cognitive functions in rats. However, the mechanism activated by the yolkin is not explained. The goal of the present study was to examine what molecular mechanism regulating brain-derived neurotrophic factor (BDNF) expression is activated by the yolkin complex, using in vitro models of PC12 cell line and fetal rat hippocampal cell line H19-7. It was shown that yolkin increased the proliferative activity of rat hippocampal precursor cells H19-7 cells and upregulated the expression/production of BDNF in a cyclic adenosine monophosphate (cAMP)-response element-binding protein (CREB)-dependent manner. Additionally the upregulation of carboxypeptidase E/neurotrophic factor-α1 (CPE/(NF-α1) expression was shown. It was also determined that upregulation of CREB phosphorylation by yolkin is dependent on cyclic adenosine monophosphate/protein kinase A (cAMP/PKA) and phosphoinositide 3-kinases/protein kinase B (PI3K/Akt) signaling pathway activation. Moreover, the impact of yolkin on the level of intracellular Ca²⁺, nitric oxide, and activation of extracellular signal-regulated kinases 1/2 (ERK 1/2 kinase) was excluded. These results emphasize that yolkin can act comprehensively and in many directions and may participate in the regulation of neurons' survival and activity. Therefore, it seems that the yolkin specimen can be used in the future as a safe, bioavailable, natural nutraceutical helping to improve the cognition of older people.

A Novel Mechanism of Macrophage Activation by the Natural Yolkin Polypeptide Complex from Egg Yolk

Ageing is accompanied by the inevitable changes in the function of the immune system. It provides increased susceptibility to chronic infections that have a negative impact on the quality of life of older people. Therefore, rejuvenating the aged immunity has become an important research and therapeutic goal. Yolkin, a polypeptide complex isolated from hen egg yolks, possesses immunoregulatory and neuroprotective activity. Considering that macrophages play a key role in pathogen recognition and antigen presentation, we evaluated the impact of yolkin on the phenotype and function of mouse bone marrow-derived macrophages of the BMDM cell line. We determined yolkin bioavailability and the surface co-expression of CD80/CD86 using flow cytometry and IL-6, IL-10, TGF-β and iNOS mRNA expression via real-time PCR. Additionally, the impact of yolkin on the regulation of cytokine expression by MAPK and PI3K/Akt kinases was determined. The stimulation of cells with yolkin induced significant changes in cell morphology and an increase in CD80/CD86 expression. Using pharmaceutical inhibitors of ERK, JNK and PI3K/Akt, we have shown that yolkin is able to activate these kinases to control cytokine mRNA expression. Our results suggest that yolkin is a good regulator of macrophage activity, priming mainly the M1 phenotype. Therefore, it is believed that yolkin possesses significant therapeutic potential and represents a promising possibility for the development of novel immunomodulatory medicine.

Comparative N-glycoproteomic analysis of Tibetan and lowland chicken fertilized eggs: Implications on proteins biofunction and species evolution

The characterization and functionality of protein glycosylation among different related species are of common interest. Herein, non-standard quantification and N-glycosylation enrichment technology combined with ultra-high liquid chromatography-tandem mass spectrometry were used to establish detailed N-glycoproteomics of fertilized eggs, and quantitatively compared between Tibetan and lowland chicken. A total of 396N-glycosites from 143 glycoproteins were found. Specifically, compared with lowland chicken egg white, 32N-glycosites of 22 glycoproteins were up-regulated and 57N-glycosites of 25 glycoproteins were down-regulated in Tibetan chicken egg white. Also, 137N-glycosites in 72 glycoproteins showed much higher-degree glycosylation and 36N-glycosites in 15 glycoproteins displayed lower-degree glycosylation in Tibetan chicken egg yolk than those in lowland chicken egg yolk. Through bioinformatic analysis, these varied glycoproteins were highly associated with antifreeze activity, hypoxia adaptation, coagulation cascade, and binding/immunity activities, which may be related to plateau hypoxia and cold stress. PRACTICAL APPLICATIONS: These findings provide a new insight on the role of biological egg N-glycoproteins related to environmental adaptation and evolution, which may be further applied in improving egg processing and human health, by developing biomolecules for food and medical industry.

IgY technology: Methods for developing and evaluating avian immunoglobulins for the in vitro detection of biomolecules

The term “IgY technology” was introduced in the literature in the mid 1990s to describe a procedure involving immunization of avian species, mainly laying hens and consequent isolation of the polyclonal IgYs from the “immune” egg yolk (thus avoiding bleeding and animal stress). IgYs have been applied to various fields of medicine and biotechnology. The present article will deal with specific aspects of IgY technology, focusing on the currently reported methods for developing, isolating, evaluating and storing polyclonal IgYs. Other topics such as current information on isolation protocols or evaluation of IgYs from different avian species are also discussed. Specific advantages of IgY technology (e.g., novel antibody specificities that may emerge via the avian immune system) will also be discussed. Recent in vitro applications of polyclonal egg yolk-derived IgYs to the field of disease diagnosis in human and veterinary medicine through in vitro immunodetection of target biomolecules will be presented. Moreover, ethical aspects associated with animal well-being as well as new promising approaches that are relevant to the original IgY technology (e.g., development of monoclonal IgYs and IgY-like antibodies through the phage display technique or in transgenic chickens) and future prospects in the area will also be mentioned.

C-Terminal Fragment of Vitellogenin II, a Potential Yolkin Polypeptide Complex Precursor Protein-Heterologous Expression, Purification, and Immunoregulatory Activity

The aim of this research was to analyze the heterologous expression, purification, and immunoregulatory activity of recombinant YGP40 (rYGP40), the potential precursor of the yolkin peptide complex. The ygp40 coding sequence was codon optimized, successfully expressed in the E. coli system, and purified from inclusion bodies with a yield of about 1.1 mg/L of culture. This study showed that the protein exhibits immunomodulatory activity, expressed by the stimulation of TNF-α and IL-10 production and nitric oxide induction at a level comparable to that of the natural yolkin peptide complex obtained by other authors from hen egg yolk. At the highest dose of 100 µg/mL, rYGP40 also caused the up-regulation of iNOS expression in murine bone marrow-derived macrophages (BMDM). Moreover, no cytotoxic effects of rYGP40 on the BMDM cell line were observed.

Comparative Studies of Yolkin Preparations Isolated from Egg Yolks of Selected Bird Species

The results of our research have proven that yolkin preparations isolated from eggs of different bird species show a high similarity in polypeptide composition. Despite the small differences in protein patterns, all of yolkin preparations showed also strong immunomodulatory activity, comparable with yolkin obtained previously from hen egg yolk. It can therefore be deducted that the presence of this polypeptide complex in the egg is not accidental and performs an important biological function for developing embryo.

Yolkin Isolated from Hen Egg Yolk as a Natural Immunoregulator, Activating Innate Immune Response in BMDM Macrophages

One of the goals of biomedical sciences is to search and identify natural compounds that are safe, have no side effects, and possess immunostimulatory activity. It has been proven that medicines of natural origin can be effective agents, supporting the therapy of many diseases, not only in the weakened immune system of the body but also in the prevention of many diseases in healthy people. It has been shown that yolkin, a polypeptide complex isolated from hen egg yolk as a fraction accompanying immunoglobulin Y (IgY), possesses potential biological activity. However, the mechanism of its action has not been explained. The objective of this investigation was to examine the molecular mechanisms of innate immune response, activated in response to yolkin, in murine bone marrow-derived macrophages (BMDM). It was shown that yolkin induced phosphorylation of extracellular signal-kinases (ERK1/2) and c-Jun N-terminal kinase (JNK) and upregulated expression and production of type I interferons, TNF-α (tumor necrosis factor α), and nitric oxide (NO), in BMDM cells. Using pharmacological inhibitors of ERK 1/2 and JNK kinases, we revealed that the JNK signaling cascade is required for yolkin-induced inducible NOS expression and upregulation of NO production in mouse macrophages. Using the TLR4-deficient BMDM cell line, we established that yolkin can activate macrophages in a TLR4-dependent manner. It was also shown that NO, TNF-α, and type I IFNs (α/β) produced by BMDM cells in response to yolkin triggered antiviral activity. These data indicate that yolkin affects the regulation of the immune system and antiviral response; therefore, it can be used as an effective immunostimulator of the innate immunity or as a supplement of the conventional therapy of immunodeficiency.

Effects of yolkin on the immune response of mice and its plausible mechanism of action

Yolkin is a product of proteolytic degradation of vitellogenin, a protein contained in eggs' yolk, with already described procognitive properties. Here, we investigated effects of yolkin on the humoral and cellular immune response in mice, phenotype of cells from lymphoid organs and function of innate immunity cells. In vitro studies included effects of yolkin on mitogen-induced thymocyte proliferation, percentage of CD19 cells in bone marrow cells culture, expression of signaling molecules in Jurkat cells, interleukin 2 receptor (IL-2R) subunits in WEHI 231 cells and susceptibility of these cells to anti-Ig-induced cell death. The results showed that repeatable i.p. injections of yolkin stimulated the humoral immune response to sheep red blood cells (SRBC) irrespective of the time of the treatment. On the other hand, yolkin inhibited contact sensitivity to oxazolone. Treatment of mice with yolkin diminished the percentage of double positive cells and increasing the content of single positive CD4+ and CD8+ cells in the thymus. At the same time an increase of percentage of CD19 + B cells in the spleen and mesenteric lymph nodes was observed. In addition, the protein, given i.p., diminished ex vivo ability to synthesize nitric oxide by resident, peritoneal macrophages, stimulated with lipopolisaccharide (LPS). In vitro studies showed that yolkin increased CD19+ cell content in bone marrow cell population. The protein also enhanced proliferation of thymocytes to concanavalin A and stimulated expression of MAP kinases in Jurkat cells. In WEHI 231 B cell line yolkin caused a loss of IL-2R gamma chain expression, correlated with an increased resistance of these cells to proapoptotic action of anti-Ig antibodies. In conclusion, this is a first demonstration of immunotropic properties of yolkin in in vitro and in vivo tests. The results provide evidence for induction of maturation and stimulatory signals in immature T and B cells by the protein, suggesting its potential role in the development of an embryo's immune system.

How Can the Value and Use of Egg Yolk Be Increased?

The major driving force for the egg consumption in the United States over the past few decades was processed egg. However, the consumption of egg through the processed egg reached the plateau in recent years because of the imbalance in the demands between the egg white and yolk products. The consumer demands for egg white products are very high while those for the egg yolk, the co-product of dried egg white, are low because of the negative perceptions on egg yolk. Two key approaches that can be used to increase the value and use of egg yolk are: (1) developing new commodity products by fractionating egg yolk and apply them in various food processing, and (2) separating functional proteins and lipids from yolk and use them as is or further develop functional peptides and functional lipids and use them as pharmaceutical, nutraceutical, and cosmeceutical agents. These approaches can diversify the use of egg yolk, which eventually will help increase the consumption of egg. This review (1) discusses the current use of egg yolk products and the development of new functional commodity products from egg yolk, (2) review the important functional components in egg yolk and overview the current separation methods and their applications, (3) discuss the production of functional peptides and lipids using the separated egg proteins and lipids, and (4) suggest the future directions for the best use of egg yolk components. Development of scale-up production methods, which is vital for the practical applications, is discussed when appropriate.

A simple and rapid method of isolation of active polypeptide complex, yolkin, from chicken egg yolk

A large number of bioactive peptides isolated from natural sources are known to play important physiological roles in the human body. It is possible to use these as alternative therapy agents. One example is yolkin which can be useful as a food supplement, a natural therapeutic agent for preventing and treating cognitive disorders of various origins, preferably in patients with unsatisfactory responses to known therapies. A new simple method of isolation of yolkin based on precipitation with ethanol or acetone was developed. The best precipitation efficiency of both ethanol and acetone was achieved when stirred into the starting material to a final concentration of 70%. These methods preserved the ability of yolkin to stimulate human whole blood cells to release anti-inflammatory cytokines and neurotrophins. At first we indicated that yolkin displayed a potential neuroprotective effect by the ability to stimulate cells to produce pro-survival brain derived neurotrophic factor (BDNF).

Pro-Cognitive Properties of the Immunomodulatory Polypeptide Complex, Yolkin, from Chicken Egg Yolk and Colostrum-Derived Substances: Analyses Based on Animal Model of Age-Related Cognitive Deficits

The study aimed to assess the effect of the polypeptide Y complex (Yolkin), isolated from chicken egg yolk, on behavioural and cognitive functions. It also aimed to compare this activity with colostrum-derived substances (Colostrinin, Coloco), which have a confirmed impact on learning and memory. In the study, the effect of Yolkin, administered to rats of different ages, who performed various tasks involving spatial and episodic memory, motor functions and exploratory behavior, was assessed. The experiment was carried out in rats which were 6 and 12 months old. Two different doses of the studied specimens based on previous comparative studies and two different routes of administration (oral and retroperitoneal) were used. A series of behavioural tests were carried out, including an open field test, a novel object recognition test and a Morris water maze. They were used to evaluate the impact of the studied specimen on improving locomotor function and exploratory behaviour, preventing their decline and assess the functioning of episodic and spatial memory in aging rats. The administration of Yolkin gave distinct effects compared to colostrum-derived substances, although confirmed its suggested pro-cognitive action. Therefore, it may be used to enhance cognitive functions and inhibit the progression of dementia in the course of neurodegenerative disorders.

Peptides accompanying chicken egg yolk IgY--alternative methods of isolation and immunoregulatory activity

In the hen immune system the egg content plays as significant a role in the development of the chick as colostrum does in newborn mammals. One of the most important proteins in this system seems to be the main yolk immunoglobulin IgY. It has been shown that IgY is accompanied by an immunostimulatory polypeptide complex named yolkin. In this report the biological activities of yolkin separated by means of four different procedures are presented. It was shown that yolkin acts as an inducer rather than a modulator of cytokine and nitric oxide release, and does not participate in the protection of cells against destructive effects of reactive oxygen species. However, using the perchloric acid procedure it is possible to obtain a peptide fraction with higher inducing activity, stronger antioxidant properties and ability to decrease the NO level induced by lipopolysaccharide. The results obtained show that it is feasible to select one of the presented methods of yolkin isolation that yields a product of particular activity. The properties of yolk peptides not only indicate their roles in the development of chicks, but can also be useful for the regulation of some immunological disturbances.