Release of wheat gluten exorphins A5 and C5 during in vitro gastrointestinal digestion of bread and pasta and their absorption through an in vitro model of intestinal epithelium

In vitro digestion and fermentation characteristics of eight kinds of pulses and suggestions for different populations

Pulse-based diets are attracting attention for their potential in combating diet-related non-communicable diseases. However, limited research studies have focused on the digestive and fermentative properties of pulses, which are crucial for exerting benefits. Here, we investigated the in vitro digestibility of starch/protein, along with the fermentation characteristics, of eight pulses and their pastes, including white kidney beans, adzuki beans, cowpeas, broad beans, mung beans, chickpeas, white lentils, and yellow peas. The findings indicated that pulse flours and pastes were low GL food (estimated GL < 10) and had a low degree of protein hydrolysis during simulated gastrointestinal digestion. During in vitro fermentation, pulses flours and pastes decreased the fermentation pH, increased the level of short-chain fatty acids (mainly consisting of valeric acid, followed by acetic acid, propionic acid, butyric acid, isobutyric acid, and isovaleric acid), and positively modulated the microbiota composition over time, specifically reducing the ratio of Firmicutes to Bacteroidetes. In addition, we found that boiling could affect the in vitro digestion and fermentation characteristics of pulses, possibly depending on their intrinsic nutrient characteristics. This research could provide a comprehensive summary of the nutrient content, digestibility, and fermentation of eight pulses and their pastes. Guided by factor analysis, for different individuals' consumption, pulses, cowpeas, broad beans, white lentils, and white kidney beans were preferred for diabetic individuals, yellow peas and white lentils were preferred for intestinal homeostasis disorders, and white lentils, broad beans, white kidney beans, and cowpeas were suitable for obese individuals, in which white lentils were considered healthier and suggested for healthy adults.

Gluten Exorphins Promote Cell Proliferation through the Activation of Mitogenic and Pro-Survival Pathways

Celiac disease (CD) is a chronic and systemic autoimmune disorder that affects preferentially the small intestine of individuals with a genetic predisposition. CD is promoted by the ingestion of gluten, a storage protein contained in the endosperm of the seeds of wheat, barley, rye, and related cereals. Once in the gastrointestinal (GI) tract, gluten is enzymatically digested with the consequent release of immunomodulatory and cytotoxic peptides, i.e., 33mer and p31-43. In the late 1970s a new group of biologically active peptides, called gluten exorphins (GEs), was discovered and characterized. In particular, these short peptides showed a morphine-like activity and high affinity for the δ-opioid receptor (DOR). The relevance of GEs in the pathogenesis of CD is still unknown. Recently, it has been proposed that GEs could contribute to asymptomatic CD, which is characterized by the absence of symptoms that are typical of this disorder. In the present work, GEs cellular and molecular effects were in vitro investigated in SUP-T1 and Caco-2 cells, also comparing viability effects with human normal primary lymphocytes. As a result, GEs treatments increased tumor cell proliferation by cell cycle and Cyclins activation as well as by induction of mitogenic and pro-survival pathways. Finally, a computational model of GEs interaction with DOR is provided. Altogether, the results might suggest a possible role of GEs in CD pathogenesis and on its associated cancer comorbidities.

Do gluten peptides stimulate weight gain in humans?

Observations from animal and in vitro laboratory research, and anecdotal evidence, have led to the suggestion that gluten consumption stimulates weight gain by the presence of peptides expressing opioid activity. Another proposed mechanism is that gluten peptides decrease resting energy expenditure resulting in a positive energy balance. In order to induce such effects in vivo, intact food peptides must be absorbed in sufficient quantities, remain intact in the blood for sufficient time to have long‐lasting biological activity and bind to receptors involved in appetite, satiety and energy regulation. However, although peptides from food may pass from the intestine into the blood in extremely low quantities, they are generally rapidly degraded by plasma and vasculum‐bound aminopeptidases, resulting in very short half‐lives and loss of bioactivity. At present, gluten peptide sequences that influence regulators of energy metabolism have not been identified. Furthermore, data on the quantitative absorption of gluten peptides in the blood stream, their stability and lasting bioactivity are also lacking. Therefore, there is no evidence for proposed effects on driving appetite by the brain, nor on energy expenditure and weight gain. Furthermore, the level of overweight observed in various countries appears to be independent of the level of wheat consumption, and abundant observational evidence in humans shows that the levels of gluten consumption are neither related to daily calorie intake nor to BMI. This narrative review therefore discusses the proposed effects of gluten on bodyweight (BW) and putative biological mechanisms in the light of the current evidence.

Model infant biscuits release the opioid-acting peptides milk β-casomorphins and gluten exorphins after in vitro gastrointestinal digestion

Infant biscuits (IBs) are commonly used during the complementary feeding of infants from the 6th month of life. They contain wheat flour and dairy ingredients, which can release the opioid-acting peptides β-casomorphins (BCMs) and gluten exorphins (GEs) after gastrointestinal digestion. In the present study, five model IBs were prepared with or without gluten and different powdered milk derivatives in the formulations. IBs were digested simulating an in vitro static gastrointestinal digestion for infants aged 6-12 months. BCMs and GEs were identified and quantified by UPLC/HR-MS. The amounts of BCM7 and the GE A5 were related to the β-CN and gluten content of the formulations. To date, levels of BCMs and GEs in digests of IBs have not been reported in literature. This work represents an in vitro investigation regarding the release of opioid-acting peptides in IBs. It could add additional knowledge on complementary foods for infant health.

Food-Derived Opioid Peptides in Human Health: A Review

World Health Organization data suggest that stress, depression, and anxiety have a noticeable prevalence and are becoming some of the most common causes of disability in the Western world. Stress-related disorders are considered to be a challenge for the healthcare system with their great economic and social impact. The knowledge on these conditions is not very clear among many people, as a high proportion of patients do not respond to the currently available medications for targeting the monoaminergic system. In addition, the use of clinical drugs is also associated with various side effects such as vomiting, dizziness, sedation, nausea, constipation, and many more, which prevents their effective use. Therefore, opioid peptides derived from food sources are becoming one of the safe and natural alternatives because of their production from natural sources such as animals and plant proteins. The requirement for screening and considering dietary proteins as a source of bioactive peptides is highlighted to understand their potential roles in stress-related disorders as a part of a diet or as a drug complementing therapeutic prescription. In this review, we discussed current knowledge on opioid endogenous and exogenous peptides concentrating on their production, purification, and related studies. To fully understand their potential in stress-related conditions, either as a drug or as a therapeutic part of a diet prescription, the need to screen more dietary proteins as a source of novel opioid peptides is emphasized.

Investigating the Bioaccessibility and Bioavailability of Cadmium in a Cooked Rice Food Matrix by Using an 11-Day Rapid Caco-2/HT-29 Co-culture Cell Model Combined with an In Vitro Digestion Model

Investigating the bioaccessibility and bioavailability of Cd based on real contaminated cooked rice matrixes helps establish an accurate risk assessment method and effectively reduce the digestion and absorption of Cd. An 11-day in vitro rapid Caco-2/HT-29 co-culture cell model was used to establish and evaluate the simulation of the absorption and transport of Cd in the small intestine with a 70:30 Caco-2/HT-29 co-culture ratio and 1.0 mmol L^-1 butyric acid as a differentiation inducer. The bioaccessibility and bioavailability of Cd in cooked rice were studied using the cell model combined with an in vitro digestion model. The bioaccessibility of Cd of each of the three cooked rice samples was significantly higher in the gastric phase (59.04-80.23%) than in the gastrointestinal phase (37.14-52.93%). Despite the extension of the digestion time of the gastrointestinal phase, no significant difference was found among the time points. Results demonstrated that the amount of undigested residue, not the level of Cd contamination, significantly contributed to the bioaccessibility of Cd, which was affected by pH or ion. The absorption rate of Cd (25.08% ± 3.05%) was greater than the values obtained using the pure Caco-2 cell models. The bioavailability of Cd (8.29% ± 1.95%) was almost similar to that of Zn²⁺ (6.66% ± 1.41%) in the cooked rice matrix, indicating that the intestinal epithelium expressed a strong absorptive capacity of Cd during the absorption of essential metallic elements. The 11-day rapid Caco-2/HT-29 co-culture cell model combined with the in vitro digestion model was an efficient tool for studying the bioaccessibility and bioavailability of Cd or other substances in a food matrix to further investigate mechanistic steps and screen a broad set of food matrix factors.

Excess of nutrient-induced morphofunctional adaptation and inflammation degree in a Caco2/HT-29 in vitro intestinal co-culture

OBJECTIVES

The intestinal cell function can be modulated by the type and quantity of nutrients. The aim of this study was to evaluate the effects of an excess of nutrients on intestinal morphofunctional features and a possible association of inflammation in a 70/30 Caco2/HT-29 intestinal in vitro co-culture.

METHODS

An excess of nutrients (EX) was obtained by progressively increasing the medium change frequency with respect to standard cell growth conditions (ST) from confluence (T0) to 15 d after confluence (T15).

RESULTS

In comparison with the ST group, the EX group revealed a maintenance in the number of microvilli, an increase in follicle like-structures and mucus production, and a decrease in the number of tight junction. The specific activity of markers of intestinal differentiation, alkaline phosphatase and aminopeptidase N, and of the enterocyte differentiation specific marker, dipeptidyl peptidase-IV, were progressively raised. The transepithelial electrical resistance, indicative of the co-culture barrier properties, decreased, whereas Lucifer yellow P_app evaluation, an index of the paracellular permeability to large molecules, showed an increase. Reactive oxygen species and nitric oxide production, indicative of an oxidative status, together with interleukin-6, interleukin-8, indicative of a low-grade inflammation, and peptide YY secretion were higher in the EX group than in the ST group. The differences between ST and EX were particularly evident at T15.

CONCLUSION

These data support the suitability of our in vitro gut model for obesity studies at the molecular level and the necessity to standardize the medium frequency change in intestinal culture.

Morphofunctional properties of a differentiated Caco2/HT-29 co-culture as an in vitro model of human intestinal epithelium

An intestinal 70/30 Caco2/HT-29 co-culture was set up starting from the parental populations of differentiated cells to mimic the human intestinal epithelium. Co-culture was harvested at confluence 0 (T0) and at 3, 6, 10, and 14 days post confluence after plating (T3, T6, T10, and T14, respectively) for morphological and functional analysis. Transmission electron microscopy revealed different features from T0 to T14: microvilli and a complete junctional apparatus from T6, mucus granules from T3, as also confirmed by PAS/Alcian Blue staining. The specific activity of alkaline phosphatase (ALP), aminopeptidase N (APN), and dipeptidyl peptidase IV (DPPIV) progressively increased after T0, indicating the acquirement of a differentiated and digestive phenotype. Transepithelial electrical resistance (TEER), indicative of the barrier properties of the monolayer, increased from T0 up to T6 reaching values very similar to the human small intestine. The apparent permeability coefficient for Lucifer Yellow (LY), along with morphological analysis, reveals a good status of the tight junctions. At T14, HT-29 cells reduced to 18.4% and formed domes, indicative of transepithelial transport of nutrients. This Caco2/HT-29 co-culture could be considered a versatile and suitable in vitro model of human intestinal epithelium for the presence of more than one prevalent intestinal cell type, by means of a minimum of 6 to a maximum of 14 post-confluence days obtained without the need of particular inducers of subclones and growth support to reach an intestinal differentiated phenotype.

Thermal treatment reduces gliadin recognition by IgE, but a subsequent digestion and epithelial crossing permits recovery

Wheat is one of the most important crops in the world in terms of human nutrition. With regards to health, some individuals exhibit wheat-related disorders such as food allergy to wheat (FAW). In this disorder, gluten is involved, particularly the gliadins which are among the main proteins responsible for FAW. Food processing, as well as digestibility and intestinal transport are key factors to consider since they may affect the allergenic potential of food allergens. Wheat is always consumed after heat processing and this step may impact epitope accessibility by inducing aggregation and may irreversibly destroy conformational epitopes. Our aim was to investigate the effects of heating and digestion on the structure of well-known allergens (total gliadins and α-gliadins) and their capacity to maintain their allergenic potential after crossing an intestinal barrier. The sizes of the processed (heated and heated/digested) proteins were characterized by laser light scattering and chromatographic reverse phase. The IgE-binding capacities of native and processed proteins were checked using a dot blot with sera from wheat allergenic patients. Furthermore, the abilities of these samples to cross the intestinal barrier and to induce mast cell degranulation were investigated by combining two in vitro cellular models, Caco-2 and RBL-SX38. The heat treatment of total gliadins and α-gliadins induced the production of large aggregates that were hardly recognized by IgE of patients in dot-blot. However, after limited pepsin hydrolysis, the epitopes were unmasked, and they were able to bind IgE again. Native proteins (gliadins and α-type) and processed forms were able to cross the Caco-2 cells in small amount. Permeability studies revealed the capacity of α-gliadins to increase paracellular permeability. In the RBL assay, the total native gliadins were able to trigger cell degranulation, but none of their processed forms. However after crossing the CaCo-2 monolayer, processed gliadins recovered their degranulation capacity to a certain extent. Total native gliadins remained the best allergenic form compared to α-type.

Food-Derived Hemorphins Cross Intestinal and Blood-Brain Barriers In Vitro

A qualitative study is presented, where the main question was whether food-derived hemorphins, i.e., originating from digested alimentary hemoglobin, could pass the intestinal barrier and/or the blood-brain barrier (BBB). Once absorbed, hemorphins are opioid receptor (OR) ligands that may interact with peripheral and central OR and have effects on food intake and energy balance regulation. LLVV-YPWT (LLVV-H4), LVV-H4, VV-H4, VV-YPWTQRF (VV-H7), and VV-H7 hemorphins that were previously identified in the 120 min digest resulting from the simulated gastrointestinal digestion of hemoglobin have been synthesized to be tested in in vitro models of passage of IB and BBB. LC-MS/MS analyses yielded that all hemorphins, except the LLVV-H4 sequence, were able to cross intact the human intestinal epithelium model with Caco-2 cells within 5-60 min when applied at 5 mM. Moreover, all hemorphins crossed intact the human BBB model with brain-like endothelial cells (BLEC) within 30 min when applied at 100 µM. Fragments of these hemorphins were also detected, especially the YPWT common tetrapeptide that retains OR-binding capacity. A cAMP assay performed in Caco-2 cells indicates that tested hemorphins behave as OR agonists in these cells by reducing cAMP production. We further provide preliminary results regarding the effects of hemorphins on tight junction proteins, specifically here the claudin-4 that is involved in paracellular permeability. All hemorphins at 100 µM, except the LLVV-H4 peptide, significantly decreased claudin-4 mRNA levels in the Caco-2 intestinal model. This in vitro study is a first step toward demonstrating food-derived hemorphins bioavailability which is in line with the growing body of evidence supporting physiological functions for food-derived peptides.