Opioid peptides encrypted in intact milk protein sequences

Dietary proteins as determinants of metabolic and physiologic functions of the gastrointestinal tract

Dietary proteins elicit a wide range of nutritional and biological functions. Beyond their nutritional role as the source of amino acids for protein synthesis, they are instrumental in the regulation of food intake, glucose and lipid metabolism, blood pressure, bone metabolism and immune function. The interaction of dietary proteins and their products of digestion with the regulatory functions of the gastrointestinal (GI) tract plays a dominant role in determining the physiological properties of proteins. The site of interaction is widespread, from the oral cavity to the colon. The characteristics of proteins that influence their interaction with the GI tract in a source-dependent manner include their physico-chemical properties, their amino acid composition and sequence, their bioactive peptides, their digestion kinetics and also the non-protein bioactive components conjugated with them. Within the GI tract, these products affect several regulatory functions by interacting with receptors releasing hormones, affecting stomach emptying and GI transport and absorption, transmitting neural signals to the brain, and modifying the microflora. This review discusses the interaction of dietary proteins during digestion and absorption with the physiological and metabolic functions of the GI tract, and illustrates the importance of this interaction in the regulation of amino acid, glucose, lipid metabolism, and food intake.

The influence of μ-opioid receptor agonist and antagonist peptides on peripheral blood mononuclear cells (PBMCs)

Milk is one of the main source of biologically-active peptides that may function as regulatory substances called food hormones. After passing the gut-blood barrier, the μ-opioid receptor agonist and antagonist peptides may become the new factors influencing various functions of the human organism. The aim of the conducted research was to determine the influence of μ-opioid receptor agonist peptides: human and bovine β-casomorphin-7 (h/bBCM-7) and antagonistic peptides: casoxin-6 and- D (CXN-6/D) on proliferation and cytokine secretion of human peripheral blood mononuclear cells (PBMCs). The PBMCs proliferation was measured by the use of the BrdU test, which assesses the DNA synthesis activity and the WST-1 test which assesses the activity of mitochondrial dehydrogenase enzymes. The influence of all the investigated peptides on secretion of IL-4, IL-8, IL-13 and IFN-γ was determined by the use of the ELISA tests. Incubating the cells with the peptides has not caused any changes to their enzymatic activity, which has been proved by a WST-1 test. When using a BrdU test, however, it has been observed that there appear changes to proliferation of PBMCs correlated to amounts of bromodeoxyuridine incorporated into the cellular DNA. Moreover, changes to secretion of IL-4 and IL-13 by the cells under the influence of agonists were detected, as well as changes to secretion of IFN-gamma under the influence of all the examined substances. The obtained results provide information on immunomodulatory effects of food-derived opioid peptides, which may be of clinical significance especially in the case of allergic diseases in newborns.

Principal pathogenetic components and biological endophenotypes in autism spectrum disorders

Autism is a complex neurodevelopmental disorder, likely encompassing multiple pathogenetic components. The aim of this study is to begin identifying at least some of these components and to assess their association with biological endophenotypes. To address this issue, we recruited 245 Italian patients with idiopathic autism spectrum disorders and their first-degree relatives. Using a stepwise approach, patient and family history variables were analyzed using principal component analysis ("exploratory phase"), followed by intra- and inter-component cross-correlation analyses ("follow-up phase"), and by testing for association between each component and biological endophenotypes, namely head circumference, serotonin blood levels, and global urinary peptide excretion rates ("biological correlation phase"). Four independent components were identified, namely "circadian & sensory dysfunction," "immune dysfunction," "neurodevelopmental delay," and "stereotypic behavior," together representing 74.5% of phenotypic variance in our sample. Marker variables in the latter three components are positively associated with macrocephaly, global peptiduria, and serotonin blood levels, respectively. These four components point toward at least four processes associated with autism, namely (I) a disruption of the circadian cycle associated with behavioral and sensory abnormalities, (II) dysreactive immune processes, surprisingly linked both to prenatal obstetric complications and to excessive postnatal body growth rates, (III) a generalized developmental delay, and (IV) an abnormal neural circuitry underlying stereotypies and early social behaviors.

Extrusion texturized dairy proteins: processing and application

The primary proteins in milk, casein and the whey proteins α-lactalbumin and β-lactoglobulin, have a number of health benefits and desirable functional properties. In a twin-screw extruder, mechanical shear forces, heat, and pressure cause considerable changes in the molecular structures of the dairy proteins, a process known as texturization. These changes further impart unique functional properties to dairy proteins, resulting in new protein-based food ingredients. The new functional behavior depends on the extent of texturization and the degree of structural change imparted and is controlled by adjusting parameters such as extrusion temperature and moisture level. Such texturized proteins can be used to produce puffed high-protein snacks. Softer gels and expanded structures can be made using supercritical fluid extrusion and cold extrusion, techniques that avoid elevated temperatures, minimizing possible damage to the nutritive components and functionality of the texturized dairy proteins. The uses of the texturized dairy ingredient in food products with improved functionality and enhanced nutritive profiles are presented.

The bioavailable octapeptide Gly-Ala-Hyp-Gly-Leu-Hyp-Gly-Pro stimulates nitric oxide synthesis in vascular endothelial cells

Gly-Ala-Hyp-Gly-Leu-Hyp-Gly-Pro (GAXGLXGP, X: Hyp), an octapeptide contained in chicken collagen hydrolysate, inhibits angiotensin I-converting enzyme activity in vitro. Intestinal Caco-2 and bovine aortic endothelial cells (BAECs) were used to investigate whether the transported GAXGLXGP improves vascular function. When GAXGLXGP was added to the apical side of Caco-2 monolayers, the intact form of GAXGLXGP was released to the basolateral side without incorporation into the cells. This transport was energy-independent but was associated with tight junction permeability. GAXGLXGP was then added to BAECs, and endothelial nitric oxide (NO) synthase (eNOS) activation was examined. GAXGLXGP at a concentration of 10 microM stimulated production of NO during a 1 h incubation. This event involved phosphorylation of eNOS at Ser(1179) without a change in the total eNOS protein level. These findings indicate that GAXGLXGP absorbed intact through the intestinal epithelium has direct effects on eNOS activity in vascular endothelial cells, leading to NO synthesis, thereby suggesting the potential for improvement in vascular function.

Post-weaning effects of milk and milk components on the intestinal mucosa in inflammation

Many milk-derived components have immunomodulatory and anti-inflammatory properties, and some of these reduce intestinal inflammation when orally administered to animal models of colitis. However, the potential for ruminant milk or milk components to benefit people with intestinal inflammatory disorders (such as Inflammatory Bowel Disease) has not been well-researched. This review describes published research into mechanisms by which ruminant milk and its components may have beneficial effects when consumed by people who have intestinal inflammation.

Type 1 diabetes, the A1 milk hypothesis and vitamin D deficiency

The 'A1' genetic variant of beta-casein in milk has been linked to type 1 diabetes (T1D). The keystone piece of supporting evidence is an ecological study positively correlating the incidence of T1D with amount of A1 beta-casein consumption per capita. Of relevance, A1 beta-casein consumption is also positively correlated with latitude, itself implicated in T1D through vitamin D deficiency. Ecological and biological evidence convincingly implicate vitamin D deficiency in T1D. Latitude is a confounder of the ecological data that underpin the hypothesis that A1 beta-casein in cow's milk is a causative factor in T1D.

Content of beta-casomorphins in milk of women with a history of allergy

The prevalence of food allergies increased over the past decade. Most symptoms of food allergy appear during the first 2 yr of life. The aim of this study was to determine the beta-casomorphin-5 and -7 (BCMs) in colostrum and milk of 12 breast-feeding women with a history and clinical manifestation of food allergy. The results were compared with the data obtained from a control group of healthy age-matched breast-feeding women. The level of BCM in women with food allergy was constant during lactation, whereas the highest level of opioid peptides was found in colostrums of healthy women with a subsequent rapid decrease in mature milk. These differences in BCMs profile between allergic and healthy breast-feeding women suggest that BCM content in the human milk may be an indicator of allergic conditions.

The antihypertensive effect of peptides: a novel alternative to drugs?

Many types of bioactive peptides that inhibit angiotensin I, angiotensin I converting enzyme (ACE) and Ang II type 1 receptor (AT1) in the cardiovascular system contribute to the prevention and treatment of hypertension. These inhibitory peptides are derived from many food proteins or artificial synthetic products. Further research examining the bioavailability of ACE inhibitory peptides will lead to the development of more effective ACE inhibitory peptides and foods. Our research also demonstrates that ACE inhibitory peptide LAP may lower blood pressure with no adverse effects.

Changes of beta-casomorphin content in human milk during lactation

Milk is the best, complete food important for the development and nourishment of a neonate. Except for nutrients, milk contains biologically active opioid peptides derived from beta-casein, named beta-casomorphins (BCMs), which can exert effects in the gastrointestinal tract as well as in the whole body of neonates. The content of beta-casomorphins in human milk during maturation phases has not been studied so far. The aim of this study was to determine the content of beta-casomorphin-5 and -7 in human milk in different phases of lactation. A significantly higher concentration of both beta-casomorphins was found in colostrum than in mature milk. The concentration of beta-casomorphin in milk collected in the second month of lactation was similar to the level obtained in the fourth month of lactation. The content of beta-casomorphins in human milk was observed with the period of lactation. The level of opioid peptides may depend on the function of these peptides in neonate's body and may be associated with the maturation process.

Enzymatic Hydrolysis of Heated Whey: Iron-Binding Ability of Peptides and Antigenic Protein Fractions

This study evaluated the influence of various enzymes on the hydrolysis of whey protein concentrate (WPC) to reduce its antigenic fractions and to quantify the peptides having iron-binding ability in its hydrolysates. Heated (for 10 min at 100 degrees C) WPC (2% protein solution) was incubated with 2% each of Alcalase, Flavourzyme, papain, and trypsin for 30, 60, 90, 120, 150, 180, and 240 min at 50 degrees C. The highest hydrolysis of WPC was observed after 240 min of incubation with Alcalase (12.4%), followed by Flavourzyme (12.0%), trypsin (10.4%), and papain (8.53%). The nonprotein nitrogen contents of WPC hydrolysate followed the hydrolytic pattern of whey. The major antigenic fractions (beta-lactoglobulin) in WPC were degraded within 60 min of its incubation with Alcalase, Flavourzyme, or papain. Chromatograms of enzymatic hydrolysates of heated WPC also indicated complete degradation of beta-lactoglobulin, alpha-lactalbumin, and BSA. The highest iron solubility was noticed in hydrolysates derived with Alcalase (95%), followed by those produced with trypsin (90%), papain (87%), and Flavourzyme (81%). Eluted fraction 1 (F-1) and fraction 2 (F-2) were the respective peaks for the 0.25 and 0.5 M NaCl chromatographic step gradient for analysis of hydrolysates. Iron-binding ability was noticeably higher in F-1 than in F-2 of all hydrolysates of WPC. The highest iron contents in F-1 were observed in WPC hydrolysates derived with Alcalase (0.2 mg/kg), followed by hydrolysates derived with Flavourzyme (0.14 mg/kg), trypsin (0.14 mg/kg), and papain (0.08 mg/kg). Iron concentrations in the F-2 fraction of all enzymatic hydrolysates of WPC were low and ranged from 0.03 to 0.05 mg/kg. Fraction 1 may describe a new class of iron chelates based on the reaction of FeSO4 x 7 H2O with a mixture of peptides obtained by the enzymatic hydrolysis of WPC. The chromatogram of Alcalase F-1 indicated numerous small peaks of shorter wavelengths, which probably indicated a variety of new peptides with greater ability to bind with iron. Alcalase F-1 had higher Ala (18.38%), Lys (17.97%), and Phe (16.58%) concentrations, whereas the presence of Pro, Gly, and Tyr was not detected. Alcalase was more effective than other enzymes at producing a hydrolysate for the separation of iron-binding peptides derived from WPC.

Polymorphism of bovine beta-casein and its potential effect on human health

Proteins in bovine milk are a common source of bioactive peptides. The peptides are released by the digestion of caseins and whey proteins. In vitro the bioactive peptide beta-casomorphin 7 (BCM-7) is yielded by the successive gastrointestinal proteolytic digestion of bovine beta-casein variants A1 and B, but this was not seen in variant A2. In hydrolysed milk with variant A1 of beta-casein, BCM-7 level is 4-fold higher than in A2 milk. Variants A1 and A2 of beta-casein are common among many dairy cattle breeds. A1 is the most frequent in Holstein-Friesian (0.310-0.660), Ayrshire (0.432-0.720) and Red (0.710) cattle. In contrast, a high frequency of A2 is observed in Guernsey (0.880-0.970) and Jersey (0.490-0.721) cattle. BCM-7 may play a role in the aetiology of human diseases. Epidemiological evidence from New Zealand claims that consumption of beta-casein A1 is associated with higher national mortality rates from ischaemic heart disease. It seems that the populations that consume milk containing high levels of beta-casein A2 have a lower incidence of cardiovascular disease and type 1 diabetes. BCM-7 has also been suggested as a possible cause of sudden infant death syndrome. In addition, neurological disorders, such as autism and schizophrenia, seem to be associated with milk consumption and a higher level of BCM-7. Therefore, careful attention should be paid to that protein polymorphism, and deeper research is needed to verify the range and nature of its interactions with the human gastrointestinal tract and whole organism.

Putting microbes to work: Dairy fermentation, cell factories and bioactive peptides. Part II: Bioactive peptide functions

A variety of milk-derived biologically active peptides have been shown to exert both functional and physiological roles in vitro and in vivo, and because of this are of particular interest for food science and nutrition applications. Biological activities associated with such peptides include immunomodulatory, antibacterial, anti-hypertensive and opioid-like properties. Milk proteins are recognized as a primary source of bioactive peptides, which can be encrypted within the amino acid sequence of dairy proteins, requiring proteolysis for release and activation. Fermentation of milk proteins using the proteolytic systems of lactic acid bacteria is an attractive approach for generation of functional foods enriched in bioactive peptides given the low cost and positive nutritional image associated with fermented milk drinks and yoghurt. In Part II of this review, we focus on examples of milk-derived bioactive peptides and their associated health benefits, to illustrate the potential of this area for the design and improvement of future functional foods.

Efficacy of αs1-casein hydrolysate on stress-related symptoms in women

OBJECTIVE

To examine the effects of alpha (s1)-casein hydrolysate on females with stress-related symptoms.

DESIGN

Double-blind, randomized, crossover, placebo-controlled trial.

SETTING

The alpha (s1)-casein hydrolysate was manufactured by INGREDIA (Arras, France) and the placebo was manufactured by DIETAROMA (Bourg, France). Study was designed and performed at PROCLAIM (Rennes, France), and the statistical analyses were performed by D Desor (Nancy, France).

SUBJECTS

A total of 63 female volunteers suffering from at least one disorder that may be related to stress such as anxiety, sleep problems and general fatigue.

INTERVENTIONS

A total of 63 volunteers participated in a double-blind, randomized, crossover, placebo-controlled study. Subjects were randomly allocated to receive either tablets containing alpha (s1)-casein hydrolysate or placebo at the dose of 150 mg/day for 30 days. After a 3 weeks washout period, they were crossed over for a new 30-day period of tablets intake. The outcome measure was a questionnaire including 44 items of symptoms that may be related stress in which the severity of each sign was evaluated using a 10-degree scale. These measures were studied repeatedly at the day of 0, 15 and 30 after the start of each interventional period.

RESULTS

The 30-day treatment by alpha (s1)-casein hydrolysate in females with stress-related symptoms reduced their symptoms, particularly in digestion (P<0.01), cardiovascular (P<0.05), intellectual (P<0.01), emotional (P<0.05) and social problems (P<0.05).

CONCLUSION

This study showed that a 30-day ingestion of alpha (s1)-casein hydrolysate decreased the stress-related symptoms in females suggesting that this product may be used as an effective functional ingredient alleviating such symptoms.

SPONSORSHIP

This study was partially supported by the INGREDIA of France and Neurobiology Research Program from the Korea Ministry of Science and Technology (2004-01757) of Korea.

Interactions between bovine beta-lactoglobulin A and various bioactive peptides as studied by front-face fluorescence spectroscopy

Front-face fluorescence spectroscopy was used for the first time to study the interactions between bovine beta-lactoglobulin variant A (beta-Lg A) and various beta-Lg-derived bioactive peptides. Fluorescence spectra were recorded for beta-Lg A-peptide mixtures at 25 degrees C and pH 6.8 with an excitation wavelength of 290 nm to characterize the molecular environment of tryptophan (Trp) residues present in the protein but absent in the peptides. Spectra remained unchanged following addition of peptides beta-Lg f92-100 and beta-Lg f125-135, while Phe-Phe interaction between beta-Lg f69-83 molecules interfered with analysis. Addition of beta-Lg f102-105 produced a blue shift (3 nm) and a significant increase in fluorescence intensity, while addition of beta-Lg f142-148 also caused a significant increase in fluorescence intensity but accompanied by a red shift (3 nm). These results indicate that the polarity of the Trp environment in the beta-Lg A structure may be modified differently depending on the peptide added.

Ethological comparison of the effects of a bovine αs1-casein tryptic hydrolysate and diazepam on the behaviour of rats in two models of anxiety

A bovine alpha s1-casein tryptic hydrolysate was previously demonstrated to display an anxiolytic-like activity in the conditioned defensive burying and in the elevated plus-maze models when i.p. injected. The present study assessed the anxiolytic-like effects of this tryptic hydrolysate after an oral administration in rats faced to the same behavioural situations using diazepam as a reference. In a first experiment, the behavioural effects of the hydrolysate in the conditioned defensive burying test were investigated at doses ranging 5-50 mg/kg. The results showed that the minimal dose required to elicit an anxiolytic-like activity is 15 mg/kg. In a second experiment, the alpha s1-casein tryptic hydrolysate (15 mg/kg, p.o.) was demonstrated to display an anxiolytic-like activity similar to diazepam (3 mg/kg, p.o.) in the conditioned defensive burying test and the elevated plus-maze. However, the ethological analysis of behaviour indicated that this hydrolysate has a different activity compared to diazepam. While diazepam induced a disinhibition state in rats, possibly related to the risk-taking behaviour observed after a benzodiazepine ingestion in humans, the tryptic hydrolysate did not display such a side effect. These results suggest that the mechanism of action of the bovine alpha s1-casein tryptic hydrolysate may differ from that of diazepam.

A tryptic hydrolysate from bovine milk alphaS1-casein improves sleep in rats subjected to chronic mild stress

The putative effects of a tryptic bovine alphaS1-casein hydrolysate on stress-induced sleep disorders were investigated and their possible link with typical blood stress parameters such as plasma corticosterone concentrations and glycaemia was assessed. Rats were subjected to chronic stress in the form of environmental disturbances, while receiving an oral administration of the alphaS1-casein hydrolysate (CH). Chronic stress significantly reduced sleep duration in control rats during the first 2 days of the stress period, but stress-induced sleep disturbance was prevented in CH-treated rats. Indeed, CH administration allowed the maintenance of slow wave sleep (SWS) duration and even a slight increase in paradoxical sleep (PS) duration in treated rats. Results on plasma corticosterone concentrations and on glycemia values were inconclusive with respect to the implication of the HPA axis in this study. However, the protective effect of the alphaS1-casein hydrolysate on sleep during exposure to our chronic mild stress conditions may be mediated by modulation of the central adrenergic response.

beta-Casomorphin-7 regulates the secretion and expression of gastrointestinal mucins through a mu-opioid pathway

We have recently shown that beta-casomorphin-7, a milk opioid peptide, strongly stimulates mucin secretion in the rat jejunum through a nervous pathway and opioid receptor activation. In this study, the hypothesis that beta-casomorphin-7 may also act directly on intestinal goblet cells was investigated in vitro in rat and human intestinal mucin-producing cells (DHE and HT29-MTX) using quantitative and semiquantitative RT-PCR and ELISA. The presence of mu-opioid receptors was demonstrated in rat goblet cells in the upper half of the colonic crypt and in the two cell lines by immunohistochemistry and RT-PCR. In rat DHE cells, beta-casomorphin-7 increased the expression of rat mucin (rMuc)2 and rMuc3 but not rMuc1, rMuc4, and rMuc5AC. This effect was time and dose dependent, with the maximum of increase in transcripts being noticed for a concentration of 10(-4) M after 2 h of stimulation for rMuc2 (225% of controls) and 4 h of stimulation for rMuc3 (208% of controls). Mucin secretion was maximally increased after 8 h of stimulation. Interestingly, these effects were prevented by pretreatment of the cells with the mu-opioid antagonist cyprodime. In human HT29-MTX cells, beta-casomorphin-7 (10(-4) M) also increased MUC5AC mRNA levels (219% after 24 h of stimulation) and the secretion of this mucin (169% of controls). In conclusion, beta-casomorphin-7 may contribute significantly to mucin production via a direct effect on intestinal goblet cells and the activation of mu-opioid receptors. Because intestinal mucins have a crucial mucosal protective function, dairy products containing beta-casomorphin-7 may improve intestinal protection and could have dietary and health applications.

Thermodynamics of Binding Interactions between Bovine β-Lactoglobulin A and the Antihypertensive Peptide β-Lg f142-148

The binding capacity of bovine beta-lactoglobulin variant A (beta-Lg A) for six peptides derived from beta-Lg was evaluated using an ultrafiltration method under the following conditions: pH 6.8, 40 degrees C, and a beta-Lg A/peptide molar ratio of 1:5. Only peptides beta-Lg f102-105, f142-148, and f69-83 bound in significant amounts to beta-Lg A corresponding to 1.5, 1.1, and 0.7 mol of peptide per mole of beta-Lg A, respectively. The interaction between beta-Lg A and the antihypertensive peptide beta-Lg f142-148 was investigated further by isothermal titration calorimetry. The binding isotherms at pH 6.8 and 25 degrees C confirmed that beta-Lg f142-148 bound to beta-Lg A and that the interaction followed a sequential three-site binding model with constants of association of 2 x 10(3), 1 x 10(3), and 0.4 x 10(3) M(-1) for the first, second, and third binding sites, respectively. The enthalpy of binding was exothermic for the first and second binding sites and endothermic for the third binding site. Binding of the peptide to all three sites was spontaneous as shown by the negative free energy values. These results show for the first time that beta-Lg A can bind bioactive peptides. This potential could be exploited to transport bioactive peptides and protect them in the gastrointestinal tract following their oral administration as nutraceuticals.

Health Implications of Milk Containing β-Casein with the A2Genetic Variant

Milk from dairy cows has long provided a high quality source of protein and selected micronutrients such as calcium to most populations. Recently, a relationship between disease risk and consumption of a specific bovine ss-casein fraction either A1 or A2 genetic variants has been identified. Populations, which consume milk containing high levels of ss-casein A2 variant, have a lower incidence of cardiovascular disease and type 1 diabetes. Furthermore, consumption of milk with the A2 variant may be associated with less severe symptoms of autism and schizophrenia. The mechanism of action focuses on ss-casein A1 and related forms preferentially that are able to produce a bioactive opioid peptide, ss-casomorphin-7 (ss-CM-7) during digestion. Infants may absorb ss-CM-7 due to an immature gastrointestinal tract. Adults, on the other hand, appear to reap the biological activity locally on the intestinal brush boarder. ss-CM-7 can potentially affect numerous opioid receptors in the nervous, endocrine, and immune systems. Whether there is a definite health benefit to milk containing the A2 genetic variant is unknown and requires further investigation.

Effects of a tryptic hydrolysate from bovine milk αS1–casein on hemodynamic responses in healthy human volunteers facing successive mental and physical stress situations

BACKGROUND

Preclinical results in rats have demonstrated anxiolytic-like effects of a tryptic bovine alphaS1-casein hydrolysate.

AIM OF THE STUDY

We investigated the putative effects of this tryptic hydrolysate on systolic (SBP), diastolic (DBP) blood pressures, heart rate (HR) values and plasma cortisol concentrations (CC) in human healthy volunteers facing successive stress situations.

METHODS

The subjects were (double blind) randomly allocated to ingest three times, 12 hours apart, two capsules containing either 200 mg of alphaS1-casein hydrolysate (TS) or bovine skimmed milk powder as a placebo (CS). On the morning of the test day, a first blood sample for baseline measurement of CC was taken before the subjects were submitted to the Stroop test (ST) and, after a 30-min rest, to a Cold Pressor test (CPT). SBP, DBP, and HR were continuously recorded for 5 min before the ST and during each stress situation. A second blood sample was taken 15 min after the end of the CPT condition.

RESULTS

ST and ST + CPT combined test situations increased SBP, DBP and HR. The significant "Treatment x SBP" and "Treatment x DBP" interactions indicated the lower percentage changes in SBP and DBP of the TS. In addition, the results showed a significant decrease of the CC in the TS but not in the CS throughout the ST + CPT combined stress tests. HR remained stable in TS between the initial rest period and the CPT unlike what happened in CS.

CONCLUSION

On the basis of blood pressure and cortisol changes, these results suggest an antistress profile of this alphaS1-casein hydrolysate in human subjects.

Milk bioactive peptides and beta-casomorphins induce mucus release in rat jejunum

Intestinal mucus is critically involved in the protection of the mucosa. An enzymatic casein hydrolysate and beta-casomorphin-7, a mu-opioid peptide generated in the intestine during bovine casein digestion, markedly induce mucus discharge. Because shorter mu-opioid peptides have been described, the effects of the opioid peptides in casein, beta-casomorphin-7, -6, -4, -4NH2 and -3, and of opioid neuropeptides met-enkephalin, dynorphin A and (D-Ala2,N-Me-Phe4,glycinol5)enkephalin (DAMGO) on intestinal mucus secretion were investigated. The experiments were conducted with isolated perfused rat jejunum. Mucus secretion under the influence of beta-casomorphins and opioid neuropeptides administered intraluminally or intra-arterially was evaluated using an ELISA for rat intestinal mucus. Luminal administration of beta-casomorphin-7 (1.2 x 10(-4) mol/L) provoked a mucus discharge (500% of controls) that was inhibited by naloxone, a specific opiate receptor antagonist. Luminal beta-casomorphin-6, -4 and -4NH2 did not modify basal mucus secretion, whereas intra-arterial administration of beta-casomorphin-4 (1.2 x 10(-6) mol/L) induced a mucus discharge. In contrast, intra-arterial administration of the nonopioid peptide beta-casomorphin-3 did not release mucus. Among the opioid neuropeptides, intra-arterial infusion of Met-enkephalin or dynorphin-A did not provoke mucus secretion. In contrast, beta-endorphin (1.2 x 10(-8) to 1.2 x 10(-6) mol/L) induced a dose-dependent release of mucus (maximal response at 500% of controls). DAMGO (1.2 x 10(-6) mol/L), a mu-receptor agonist, also evoked a potent mucus discharge. Our findings suggest that mu-opioid neuropeptides, as well as beta-casomorphins after absorption, modulate intestinal mucus discharge. Milk opioid-derived peptides may thus be involved in defense against noxious agents and could have dietary and health applications.

Beta-casein-derived peptides, produced by bacteria, stimulate cancer cell invasion and motility

In colon cancer, enteric bacteria and dietary factors are major determinants of the microenvironment but their effect on cellular invasion is not known. We therefore incubated human HCT-8/E11 colon cancer cells with bacteria or bacterial conditioned medium on top of collagen type I gels. Listeria monocytogenes stimulate cellular invasion through the formation of a soluble motility-promoting factor, identified as a 13mer beta-casein-derived peptide (HKEMPFPKYPVEP). The peptide is formed through the combined action of Mpl, a Listeria thermolysin-like metalloprotease, and a collagen-associated trypsin-like serine protease. The 13mer peptide was also formed by tumour biopsies isolated from colon cancer patients and incubated with a beta-casein source. The pro- invasive 13mer peptide-signalling pathway implicates activation of Cdc42 and inactivation of RhoA, linked to each other through the serine/threonine p21- activated kinase 1. Since both changes are necessary but not sufficient, another pathway might branch upstream of Cdc42 at phosphatidylinositol 3-kinase. Delta opioid receptor (deltaOR) is a candidate receptor for the 13mer peptide since naloxone, an deltaOR antagonist, blocks both deltaOR serine phosphorylation and 13mer peptide-mediated invasion.

Peptide and amino acid glycation: new insights into the Maillard reaction

Nonenzymatic glycation of proteins, peptides and other macromolecules (the Maillard reaction) has been implicated in a number of pathologies, most clearly in diabetes mellitus. but also in the normal processes of aging and neurodegenerative amyloid diseases such as Alzheimer's. In the early stage, glycation results in the formation of Amadori-modified proteins. In the later stages, advanced glycation end products (AGE) are irreversibly formed from Amadori products leading to the formation of reactive intermediates, crosslinking of proteins, and the formation of brown and fluorescent polymeric materials. Although, the glycation of structural proteins has been attributed a key role in the complications of diabetes, recent attention has been devoted to the physiological significance of glycated peptide hormones. This review focuses on the physico-chemical properties of the Amadori compounds of bioactive peptides of endogenous and exogenous origin, such as Leu-enkephalin and morphiceptin, investigated under different conditions as well as on novel pathways in the Maillard reaction observed from investigating intramolecular events in ester-linked glycopeptides.

Expression of milk-derived antihypertensive peptide in Escherichia coli

Many angiotensin converting enzyme inhibitory peptides (ACEIP) have been identified in recent years. Among all the literatures available thus far, almost all the ACEIP were obtained by means of enzymatic hydrolysis. However, little information was available on antihypertensive peptides obtained by DNA recombination technology. In the present paper, our aims were 1) to establish a new method to produce antihypertensive peptides (AHP), and 2) to study the expression profiles of different host strains (Escherichia coli JM109 and DH5alpha). To achieve these objectives, a DNA fragment encoding the published ACEIP, identified as FFVAPFPEVFGK (known as CEI12) was synthesized, ligated with the expression vector, pQE16, and transformed into E. coli JM109 and DH5alpha. SDS-PAGE analysis and Western-blotting detection demonstrated that the peptide CEI12 (fused with dihydrofolate reductase [DHFR]) was specifically expressed only in E. coli JM109 with IPTG induction. The expression profiles of the AHP CEI12 at different IPTG concentrations and different inducing times demonstrated no significant differences by SDS-PAGE analysis. The expression level of CEI12 (fused with DHFR) was about 500 microg/L culture.

Detection of caseinophosphopeptides in the distal ileostomy fluid of human subjects

Caseinophosphopeptides (CPP) were detected for the first time in ileostomy fluid, collected at 2 h intervals for 10 h post milk and CPP ingestion, from human volunteers with an ileostomy. The level of CPP present in ileostomy fluid obtained from milk-fed volunteers was markedly higher than that from volunteers fed with selected CPP preparations. The findings are based on HPLC analysis in combination with peptide-bound P determination, thin-layer electrophoresis and amino acid analysis, together with ELISA studies using polyclonal antibodies raised against a set of CPP to detect immunoreactive CPP in ileostomy fluid. These procedures allowed the detection of nm concentrations of CPP. CPP, which can be released during intestinal digestion, may function as bioactive constituents and carriers for different minerals, especially Ca, and may be used as ingredients in functional foods or pharmaceutical preparations.

Endogenous opiates: 2000

This paper is the twenty-third installment of the annual review of research concerning the opiate system. It summarizes papers published during 2000 that studied the behavioral effects of the opiate peptides and antagonists, excluding the purely analgesic effects, although stress-induced analgesia is included. The specific topics covered this year include stress; tolerance and dependence; learning, memory, and reward; eating and drinking; alcohol and other drugs of abuse; sexual activity, pregnancy, and development; mental illness and mood; seizures and other neurological disorders; electrical-related activity; general activity and locomotion; gastrointestinal, renal, and hepatic function; cardiovascular responses; respiration and thermoregulation; and immunological responses.