Opioid and cholecystokinin antagonists alleviate gastric inhibition of food intake by premeal loads of casein in meal-fed rats

Metabolic Syndrome and Biotherapeutic Activity of Dairy (Cow and Buffalo) Milk Proteins and Peptides: Fast Food-Induced Obesity Perspective-A Narrative Review

Metabolic syndrome (MS) is defined by the outcome of interconnected metabolic factors that directly increase the prevalence of obesity and other metabolic diseases. Currently, obesity is considered one of the most relevant topics of discussion because an epidemic heave of the incidence of obesity in both developing and underdeveloped countries has been reached. According to the World Obesity Atlas 2023 report, 38% of the world population are presently either obese or overweight. One of the causes of obesity is an imbalance of energy intake and energy expenditure, where nutritional imbalance due to consumption of high-calorie fast foods play a pivotal role. The dynamic interactions among different risk factors of obesity are highly complex; however, the underpinnings of hyperglycemia and dyslipidemia for obesity incidence are recognized. Fast foods, primarily composed of soluble carbohydrates, non-nutritive artificial sweeteners, saturated fats, and complexes of macronutrients (protein-carbohydrate, starch-lipid, starch-lipid-protein) provide high metabolic calories. Several experimental studies have pointed out that dairy proteins and peptides may modulate the activities of risk factors of obesity. To justify the results precisely, peptides from dairy milk proteins were synthesized under in vitro conditions and their contributions to biomarkers of obesity were assessed. Comprehensive information about the impact of proteins and peptides from dairy milks on fast food-induced obesity is presented in this narrative review article.

Invited review: Potential antiobesity effect of fermented dairy products

The growing prevalence of obesity affects millions of people around the world and has gained increased attention over the years because it is associated with the development of other chronic degenerative diseases. Different organizations recommend lifestyle changes to treat obesity; nevertheless, other strategies in addition to lifestyle changes have recently been suggested. One of these strategies is the use of probiotics in fermented dairy products; however, a need exists to review the different studies available related to the potential antiobesity effect of these products. Because probiotic fermented dairy products that support weight management are not available in the market, there is a great opportunity for the development of functional dairy products with new lactic acid bacteria that may present this added health benefit. Thus, the purpose of this overview is to highlight the importance of probiotic fermented dairy products as potential antiobesogenic functional foods and present in vitro and in vivo studies required before this kind of product may be introduced to the market. Overall, most studies attributed the antiobesity effect of fermented dairy foods to the probiotic strains present; however, bioactive peptides released during milk fermentation may also be responsible for this effect.

Screening ultrafiltration membranes to separate lactose and protein from sheep whey: application of simplified model

Several studies demonstrated that protein from whey milk could be a new strategy to reduce energy intake and increase satiety. Sheep whey has high protein content, but it is also rich in lactose. The aim of this study was to screening different ultrafiltration membranes to separate protein and lactose from sheep whey in one step. Protein was recovered in the concentrate feed, and lactose passed through three membranes and was recovered in the permeate feed. Membranes with different chemical composition and molecular weight cut-offs were assayed, and the influence of operating pressure and lactose concentration feed in the permeate flux and lactose rejection coefficients were studied. Lactose separation was not affected by pressure in GR60PP or GR90PP, and 85% and 80%, respectively of the lactose was separated into permeate feed. When the feed concentration increased, lactose separation remained stable in all three membranes, being GR60PP the most efficient, as 90% of the disaccharides were separated. In all cases 100% of the protein was recovered. Finally, the Spiegler-Kedem-Katchalsky model perfectly fitted the results obtained about lactose rejection coefficients.

Peptides from Natural or Rationally Designed Sources Can Be Used in Overweight, Obesity, and Type 2 Diabetes Therapies

Overweight and obesity are among the most prominent health problems in the modern world, mostly because they are either associated with or increase the risk of other diseases such as type 2 diabetes, hypertension, and/or cancer. Most professional organizations define overweight and obesity according to individual body-mass index (BMI, weight in kilograms divided by height squared in meters). Overweight is defined as individuals with BMI from 25 to 29, and obesity as individuals with BMI ≥30. Obesity is the result of genetic, behavioral, environmental, physiological, social, and cultural factors that result in energy imbalance and promote excessive fat deposition. Despite all the knowledge concerning the pathophysiology of obesity, which is considered a disease, none of the existing treatments alone or in combination can normalize blood glucose concentration and prevent debilitating complications from obesity. This review discusses some new perspectives for overweight and obesity treatments, including the use of the new orally active cannabinoid peptide Pep19, the advantage of which is the absence of undesired central nervous system effects usually experienced with other cannabinoids.

In vitro modulation of gut microbiota by whey protein to preserve intestinal health

The effect of several types of whey milk - cow, sheep, goat and a mixture of them (60 : 20 : 20, respectively) - was assessed in the human gut microbiota. The prebiotic potential of these substrates was evaluated through in vitro gastrointestinal digestion following faecal batch culture fermentations (mimicking colonic fermentation) for 48 hours, using faeces from normal-weight (NW) and obese (OB) donors. Throughout the fermentation process, pH, gas production, short chain and branched fatty acids (SCFA-BCFA) were measured, as well as the changes of microbiota using qPCR. The pH decreased in all whey samples during the fermentation process. Gas production was higher in all whey samples than in controls, especially at 12 hours (p < 0.05). The diversity of SCFA and BCFA production was significantly different between the donors, in particular cow and mixed whey. Whey milk had a strong prebiotic effect on the gut microbiota of NW and OB donors, showing a significant increase of Bifidobacterium (p < 0.05) with cow, sheep and mixed whey and increase in the Lactobacillus group, particularly in OB donors. Bacteria associated with obesity did not show an increase in any of the groups of donors. Therefore, supplementing a diet with these types of whey can selectively stimulate the growth of probiotic bacteria, enhancing SCFA production, which could improve intestinal disorders. In addition, it may be an interesting approach to the prevention of overweight and obesity and related diseases. Whey milk has a potent prebiotic effect. It can selectively stimulate desirable bacteria and SCFA profile, in both OB and NW donors, contributing to improved intestinal health and reducing obesity.

Dietary bioactive peptides: Human studies

Current opinion strongly links nutrition and health. Among nutrients, proteins, and peptides which are encrypted in their sequences and released during digestion could play a key role in improving health. These peptides have been claimed to be active on a wide spectrum of biological functions or diseases, including blood pressure and metabolic risk factors (coagulation, obesity, lipoprotein metabolism, and peroxidation), gut and neurological functions, immunity, cancer, dental health, and mineral metabolism. A majority of studies involved dairy peptides, but the properties of vegetal, animal, and sea products were also assessed. However, these allegations are mainly based on in vitro and experimental studies which are seldom confirmed in humans. This review focused on molecules which were tested in humans, and on the mechanisms explaining discrepancies between experimental and human studies.

Protein Digestion-Derived Peptides and the Peripheral Regulation of Food Intake

The gut plays a central role in energy homeostasis. Food intake regulation strongly relies on the gut-brain axis, and numerous studies have pointed out the significant role played by gut hormones released from enteroendocrine cells. It is well known that digestive products of dietary protein possess a high satiating effect compared to carbohydrates and fat. Nevertheless, the processes occurring in the gut during protein digestion involved in the short-term regulation of food intake are still not totally unraveled. This review provides a concise overview of the current data concerning the implication of food-derived peptides in the peripheral regulation of food intake with a focus on the gut hormones cholecystokinin and glucagon-like peptide 1 regulation and the relationship with some aspects of glucose homeostasis.

In vitrotransport and satiety of a beta-lactoglobulin dipeptide and beta-casomorphin-7 and its metabolites

In vitrotransport of β-CM7 occurs through rapid hydrolysis into three peptide metabolites that transport at variable rates.

Possible role of milk-derived bioactive peptides in the treatment and prevention of metabolic syndrome

The growing prevalence of metabolic syndrome as well as its impact on public health has garnered increased attention in recent years. As a result, metabolic syndrome is now considered one of the world's leading public health problems. Bioactive peptides deriving from milk proteins may play an important role in the prevention and treatment of metabolic syndrome and its complications via several mechanisms, such as the satiety response, the regulation of insulinemia levels and blood pressure, the uptake of free radicals, and alteration of the lipid profile. These peptides can be incorporated into functional foods or administered via nutraceuticals to decrease the risk of obesity, atherogenesis, arterial hypertension, and type 2 diabetes. Recent findings have generated considerable scientific and commercial interest in milk-derived bioactive peptides, leading to numerous publications on the effectiveness of these substances. This review summarizes the current knowledge on bioactive peptides derived from milk proteins and examines the potential value of these peptides in the treatment and prevention of metabolic syndrome and its complications.

Intragastric infusion of pea-protein hydrolysate reduces test-meal size in rats more than pea protein

Because protein hydrolysates are digested faster than the corresponding proteins, they may increase or hasten the acute eating-inhibitory effect of protein. Potential mediating mechanisms include accelerated or greater release of satiating gut peptides and activation of metabolic signals that inhibit eating. We tested these hypotheses in adult male rats that were surgically equipped with intragastric (IG) cannulas and adapted to 30-min test meals at dark onset after 14-h food deprivation. Equiosmotic 12 ml loads of saline-urea control (C), 13.6% pea protein (PP), or 13.6% PP hydrolysate (PPH, DSM/DFS, Delft, The Netherlands) solutions were IG infused in 1 min just before test meals. PPH reduced test-meal size compared to C more than PP (-3.8±0.3 g vs. -2.6±0.4 g; P<0.0001). Plasma glutamate increased more after PPH than PP (P<0.0001). Plasma lactate, alanine, insulin, glucagon, GLP-1 and paracetemol (an index of gastric emptying) all increased similarly, and glucose decreased similarly, after PPH or PP. Finally, PPH still reduced test-meal size more than PP (-4.6±0.3 g vs. -3.1±0.4 g; P<0.001) in rats after subdiaphragmatic vagal deafferentation, indicating that abdominal vagal afferents are not necessary for the eating-inhibitory effects of PP and PPH and, by extension, that gut peptides whose satiating effects depend on intact vagal afferents (e.g., CCK and glucagon) do not play crucial roles. Thus, PPH reduced short-term food intake more than PP under our conditions, but the mechanism(s) involved remain unclear.

Soy protein- and casein-based weaning diets differ in effects on food intake and blood glucose regulation in male Wistar rats

The effect of weaning male Wistar rats to AIN-93G diets based on casein (C) and soy protein (S) on blood glucose and food intake (FI) regulation was determined. In experiment 1, male Wistar rats (n = 21 per group) received either C or S AIN-93G diets for 7 weeks. In experiment 2, 3 groups of rats were formed (n = 21 per group). The C followed by the S diet group (CS) was weaned to the C diet for 6 weeks followed by the S diet for another 7 weeks. Diet sequence was the reverse for the S followed by the C diet group (SC). The control group (CC) received the C diet throughout 13 weeks. Body weight and cumulative FI were not affected by diet in either experiment. In experiment 1, in fasted rats, S preloads reduced FI for 1 hour more in the C diet group (P < .05), but response to C preloads was not affected by diet. A cholecystokinin A receptor blocker prevented FI reduction by S in rats fed C but not S diet (P < .05). At week 7, rats fed the S diet had higher plasma insulin (67%) (P < .005), glucose (30%) (P < .05) and homeostatic model assessment of insulin resistance index (75%) (P < .005). In experiment 2, FI at weeks 6 and 12 was, again, suppressed most strongly by S preloads in rats fed the C diet (P < .05). At week 13, S and C preloads increased insulin and the insulin/glucose ratio (P < .05), but no differences were found due to preload or diet composition. In conclusion, differences in the effects of first diet exposure to the AIN-93G diets on blood glucose did not persist through either diet change or time. In contrast, protein composition of the most recent diet, but not time, affected FI regulation in response to protein preloads.

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.

Whey proteins in the regulation of food intake and satiety

Whey protein has potential as a functional food component to contribute to the regulation of body weight by providing satiety signals that affect both short-term and long-term food intake regulation. Because whey is an inexpensive source of high nutritional quality protein, the utilization of whey as a physiologically functional food ingredient for weight management is of current interest. At present, the role of individual whey proteins and peptides in contributing to food intake regulation has not been fully defined. However, Whey protein reduces short-term food intake relative to placebo, carbohydrate and other proteins. Whey protein affects satiation and satiety by the actions of: (1) whey protein fractions per se; (2) bioactive peptides; (3) amino-acids released after digestion; (4) combined action of whey protein and/or peptides and/or amino acids with other milk constituents. Whey ingestion activates many components of the food intake regulatory system. Whey protein is insulinotropic, and whey-born peptides affect the renin-angiotensin system. Therefore whey protein has potential as physiologically functional food component for persons with obesity and its co-morbidities (hypertension, type II diabetes, hyper- and dislipidemia). It remains unclear, however, if the favourable effects of whey on food intake, subjective satiety and intake regulatory mechanisms in humans are obtained from usual serving sizes of dairy products. The effects described have been observed in short-term experiments and when whey is consumed in much higher amounts.

Effects of bioactive peptides isoleucine-proline-proline (IPP), valine-proline-proline (VPP) and leucine-lysine-proline (LKP) on gene expression of osteoblasts differentiated from human mesenchymal stem cells

Food-derived bioactive peptides are reported to express a variety of functions in vivo. We studied the in vitro effect of three bioactive tripeptides, isoleucine-proline-proline (IPP), valine-proline-proline (VPP) and leucine-lysine-proline (LKP), on osteoblast proliferation and gene expression. We used UMR-106 osteosarcoma cells, human marrow-derived mesenchymal stem cells (hMSC) and osteoblasts differentiated from hMSC. Treatment with 50 mum-IPP increased UMR-106 cell and hMSC proliferation. The gene expression of hMSC-differentiated osteoblasts was analysed by the microarray method. Microarray analysis revealed that IPP up-regulated 270 genes and down-regulated 100 genes. VPP and LKP, by contrast, had a very modest influence on osteoblast gene expression. Real-time PCR confirmed that IPP up-regulated PTHrP, BMP-5 and CREB-5 and down-regulated VDR and caspase-8. IPP possesses potential to increase osteoblast proliferation, differentiation and signalling. Agents that increase the number and function of osteoblasts could improve bone mass and structure, and decrease fracture risk.

Hyperglycemia after protein ingestion concurrent with injection of a GLP-1 receptor agonist in rats: a possible role for dietary peptides

Protein ingestion after injection of the glucagon-like peptide-1 receptor agonist Exendin-4 (Ex-4) causes hyperglycemia in rats. The objectives of this study were to determine the components of protein digestion responsible for this effect and to associate it with changes in the concentrations of other metabolites and hormones. Two experiments were conducted. In the first experiment, food-deprived rats were gavaged with intact whey (WP) or albumin protein, their hydrolysates, amino acid mixtures (1 g/2.5 ml), or water 5 min after injection of either PBS or Ex-4 (0.5 μg/rat). Tail vein blood was analyzed for glucose over 2 h. In the second experiment, food-deprived rats were gavaged with WP with or without Ex-4. Groups of conscious rats were killed by decapitation either before, or at selected times after gavage. Plasma concentrations of glucose, amino acids, free fatty acids (FFA), glycerol, insulin, glucagon, and leptin were measured. In experiment 1, blood glucose was higher when intact proteins and protein hydrolysates, but not amino acid mixtures, were given with than without Ex-4 ( P < 0.05). In experiment 2, concentrations of glucose, FFA, and the ratio of tyrosine to branched-chain amino acid were higher ( P < 0.01), but leptin and essential amino acid concentrations were lower ( P < 0.05), and insulin, glucagon, and glycerol were similar when WP was given with or without Ex-4. We conclude that the hyperglycemia caused by the administration of Ex-4 concurrently with dietary protein arises from the action of peptides released during digestion and their interaction with Ex-4 in the regulation of glucose, fatty acid, and amino acid metabolism.

Cholecystokinin-induced satiety is mediated through interdependent cooperation of CCK-A and 5-HT3 receptors

Recent evidence supports a role for the serotonin-3 (5-HT3) receptors in the modulation of cholecystokinin (CCK)-induced satiation. Likewise, 5-HT's anorectic response has been linked to recruitment of peripheral CCK-A receptors. Evidence to date, however, does not elucidate whether there is a concomitant interaction between CCK-A and 5-HT3 receptors or whether each receptor functions independently in the negative feedback control of food intake elicited by CCK. In the present study, we used selective receptor antagonists to investigate the roles of CCK-A and 5-HT3 receptors in CCK-induced satiation. Intraperitoneal administration of CCK-8 reduced 30-min 15% sucrose intake in a dose-responsive manner. Prior treatment with ondansetron (1.0 mg/kg ip), a highly selective 5-HT3 receptor antagonist, attenuated CCK-induced suppression of food intake in a dose-responsive manner. Pretreatment with lorglumide (1.0 mg/kg ip), a selective CCK-A receptor antagonist, reversed CCK-induced inhibition of sucrose intake. Finally, simultaneous blockade of CCK-A and 5-HT3 receptors by lorglumide and ondansetron, as well as concomitant administration of the two antagonists with CCK, produced a significant synergistic increase in sucrose intake compared with intakes after administration of saline, CCK, or either antagonist alone. These findings support evidence that CCK-A and 5-HT3 receptors cooperate interdependently in control of short-term food intake. Most likely, this interconnection exists through a feed-forward parallel model arising from CCK-A and 5-HT3 receptors, where activation of one system engages the other to intensify the overall satiety signal.

Dietary proteins in the regulation of food intake and body weight in humans

This review presents 4 lines of evidence supporting a role for proteins in the regulation of food intake and maintenance of healthy body weights. It is concluded that the protein content of food, and perhaps its source, is a strong determinant of short-term satiety and of how much food is eaten. Although the role of protein in the regulation of long-term food intake and body weight is less clear, the evidence reviewed suggests that further research to define its role is merited. Such research has the potential to lead to new functional foods, food formulations, and dietary recommendations for achieving healthy body weights.

Enterostatin inhibition of dietary fat intake is dependent on CCK-A receptors

Enterostatin, a pentapeptide released from the exocrine pancreas and gastrointestinal tract, selectively inhibits fat intake through activation of an afferent vagal signaling pathway. This study investigated if the effects of enterostatin were mediated through a CCK-dependent pathway. The series of in vivo and in vitro experiments included studies of 1) the feeding effect of peripheral enterostatin on Otsuka Long Evans Tokushima Fatty (OLETF) rats lacking CCK-A receptors, 2) the effect of CCK-8S on the intake of a two-choice high-fat (HF)/low-fat (LF) diet, 3) the effects of peripheral or central injection of the CCK-A receptor antagonist lorglumide on the feeding inhibition induced by either central or peripheral enterostatin, and 4) the ability of enterostatin to displace CCK binding in a 3T3 cell line expressing CCK-A receptor gene and in rat brain sections. The results showed that OLTEF rats did not respond to enterostatin (300 microg/kg ip) in contrast to the 23% reduction in intake of HF diet in Long Evans Tokushima Otsuka (LETO) control rats. CCK (1 microg/kg ip) decreased the intake of the HF diet in a two-choice diet regime with a compensatory increase in intake of the LF diet. Peripheral injection of lorglumide (300 microg/kg) blocked the feeding inhibition induced by either near-celiac arterial or intracerebroventricular enterostatin, whereas intracerebroventricular lorglumide (5 nmol icv) only blocked the response to intracerebroventricular enterostatin but not to arterial enterostatin. Enterostatin did not bind on CCK-A receptors because neither enterostatin nor its analogs VPDPR and beta-casomorphin displaced [3H]L-364,718 from CCK-A receptors expressed in 3T3 cells or the binding of 125I-CCK-8S from rat brain sections. The data suggest that both the peripheral and central responses to enterostatin are mediated through or dependent on peripheral and central CCK-A receptors.

Exendin-4, a GLP-1 receptor agonist, interacts with proteins and their products of digestion to suppress food intake in rats

This study investigated the hypotheses that dietary proteins suppress food intake partly through the glucagon-like peptide-1 (GLP-1) signaling pathway, and that this effect is mediated by products of protein digestion. The GLP-1 receptor agonist, Exendin-4 (Ex-4) (0.5 micro g/rat), was given intraperitoneally to male Wistar rats, and food intake was measured when Ex-4 was given alone or with preloads of intact whey and casein proteins, their hydrolysates and amino acid mixtures (0.5 g x 4 mL(-1) x rat(-1)). Both Ex-4 and the preloads suppressed food intake (P < 0.05), but the effect of Ex-4 on food intake was reduced when coadministered with the preloads (P < 0.05). Because the effect of Ex-4 was reduced by the protein hydrolysates and by the amino acid preloads, the results support a role for the end products of protein digestion and GLP-1 release in the suppression of food intake in response to protein ingestion. We concluded that the GLP-1 signaling pathway, activated by the release of products of protein digestion, is another mechanism accounting for the reduction of food intake after protein ingestion.

Endogenous opiates and behavior: 2001

This paper is the twenty-fourth installment of the annual review of research concerning the opiate system. It summarizes papers published during 2001 that studied the behavioral effects of the opiate peptides and antagonists. The particular topics covered this year include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology(Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).

Dietary peptides induce satiety via cholecystokinin-A and peripheral opioid receptors in rats

We hypothesized that the digestion of proteins gives rise to peptides that initiate several satiety signals from the gut, and that the signals arising will be dependent on the protein source. The role of peripheral opioid and cholecystokinin (CCK)-A receptors was investigated. Casein, soy protein, and casein and soy hydrolysates were administered to rats by gavage (0.5 g protein/4 mL water). Food intake was measured over 2 h. The opioid receptor antagonist, naloxone methiodide (1.0 mg/kg) given intraperitoneally (i.p.), increased food intake when given at the same time as the hydrolysate preloads, 25 min after the casein preloads and 55 min after the soy protein preloads. The CCK-A receptor antagonist, devazepide (which reverses protein-induced food intake suppression), when given at 0.25 mg/kg, i.p., 60 min before preloads of each of three soy hydrolysates, also blocked suppression of food intake, but the strength and duration of the interaction depended on the preparation. When the two receptor antagonists were both administered with soy or casein preloads, their effects were additive. We conclude that peptides arising from digestion contribute to satiety by independent activation of both opioid and CCK-A receptors.