Synthesis and intestinal transport of the iron chelator maltosine in free and dipeptide form

Role of Proteins in the Formation of Melanoidins during Coffee Roasting

The objective of the study was to investigate structural changes in the protein-rich, high-molecular-weight fraction of coffee during roasting and their contribution to the melanoidin formation in the course of the Maillard reaction. For this purpose, high- and low-molecular-weight fractions of one raw and five coffee beans with an increased roasting degree were analyzed in terms of general (color, molecular weight, functionality, elemental composition) and specific parameters (amino acid composition, Maillard reaction products). It could be demonstrated that the high -molecular-weight fraction undergoes significant changes during roasting, where proteins appear to play an important role in melanoidin formation due to their diverse nucleophilic side chains. Modification of the amino acid side chains with known Maillard reaction products (MRPs) occurs in the early stages of roasting and decreases rapidly as color development progresses. The decrease suggests that MRPs are involved in further reactions and thus extend the functionality of the amino acid side chains, opening further possibilities for protein modification. Overall, the large number of reaction pathways leads to the formation of a well-mixed, continuous melanoidin spectrum covering a wide range of molecular masses. In this process, cross-linking and fragmentation reactions oppose each other, leading to an approximation of the molecular weight.

The Intake of Dicarbonyls and Advanced Glycation Endproducts as Part of the Habitual Diet Is Not Associated with Intestinal Inflammation in Inflammatory Bowel Disease and Irritable Bowel Syndrome Patients

A Western diet comprises high levels of dicarbonyls and advanced glycation endproducts (AGEs), which may contribute to flares and symptoms in inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS). We therefore investigated the intake of dietary dicarbonyls and AGEs in IBD and IBS patients as part of the habitual diet, and their association with intestinal inflammation. Food frequency questionnaires from 238 IBD, 261 IBS as well as 195 healthy control (HC) subjects were used to calculate the intake of dicarbonyls methylglyoxal, glyoxal, and 3-deoxyglucosone, and of the AGEs Nε-(carboxymethyl)lysine, Nε-(1-carboxyethyl)lysine and methylglyoxal-derived hydroimidazolone-1. Intestinal inflammation was assessed using faecal calprotectin. The absolute dietary intake of all dicarbonyls and AGEs was higher in IBD and HC as compared to IBS (all p < 0.05). However, after energy-adjustment, only glyoxal was lower in IBD versus IBS and HC (p < 0.05). Faecal calprotectin was not significantly associated with dietary dicarbonyls and AGEs in either of the subgroups. The absolute intake of methylglyoxal was significantly higher in patients with low (<15 μg/g) compared to moderate calprotectin levels (15−<50 μg/g, p = 0.031). The concentrations of dietary dicarbonyls and AGEs generally present in the diet of Dutch patients with IBD or IBS are not associated with intestinal inflammation, although potential harmful effects might be counteracted by anti-inflammatory components in the food matrix.

Amino acids and glycation compounds in hot trub formed during wort boiling

The aim of this study was to investigate the amino acid composition and the amount of individual glycation compounds in hot trub formed during boiling of wort prepared from different malts. Compared to the initial amino acid composition of the used malts, some Maillard reaction products (namely MG-H1, pyrraline) and hydrophobic amino acids (leucine, isoleucine, valine, phenylalanine) accumulated in the hot trub, whereas hydrophilic amino acids remained in the boiled wort. For MG-H1, a threefold increase was observed during wort boiling, whereas the other Maillard reaction products, namely CML, CEL, pyrraline and maltosine increased only slightly (1.1–2-fold). Furosine as a hallmark for peptide-bound Amadori compounds showed a small decrease. The results suggest that mainly glycated amino acids derived from small dicarbonyl compounds such as methylglyoxal and glyoxal are formed during wort boiling. Furthermore, the studies indicate that the modification of the protein structure as a result of the Maillard reaction has an influence on the hydration of the denatured proteins during the wort boiling process, thus affecting the coagulation process and, therefore, precipitation of the hot trub. The work carried out contributes to the understanding of the chemical reactions influencing the amino acid and Maillard reaction product transfer from malt to beer.

Graphical abstract

Elucidation of the non-volatile fingerprint in oven headspace vapor from bread roll baking by ultra-high resolution mass spectrometry

Untargeted research on vapor arising during the thermal processing of food has so far focused on volatile aroma compounds. In this study, we present an oven atmosphere sampling strategy to trap headspace aerosols along with semi- and non-volatile molecules liberated during the baking of wheat bread rolls. The collected vapor condensate was analyzed for its molecular fingerprinting using direct infusion ultra-high resolution mass spectrometry. We detected up to 4,700 molecular species in a vapor sample from bread rolls baked at 230 °C for 15 min. Beyond the global profiling of the underlying matrix, our method can follow complex reaction cascades during the baking process, such as the formation of advanced glycation end-products like maltosine through the interface of trapped vapor. Further, process parameters such as baking temperature and duration were used to model the dynamic liberation of molecules to the oven atmosphere by a response surface methodology approach.

Hydroxypyridinone-Based Iron Chelators with Broad-Ranging Biological Activities

Iron plays an essential role in all living cells because of its unique chemical properties. It is also the most abundant trace element in mammals. However, when iron is present in excess or inappropriately located, it becomes toxic. Excess iron can become involved in free radical formation, resulting in oxidative stress and cellular damage. Iron chelators are used to treat serious pathological disorders associated with systemic iron overload. Hydroxypyridinones stand out for their outstanding chelation properties, including high selectivity for Fe³⁺ in the biological environment, ease of derivatization, and good biocompatibility. Herein, we overview the potential for multifunctional hydroxypyridinone-based chelators to be used as therapeutic agents against a wide range of diseases associated either with systemic or local elevated iron levels.

Dietary Advanced Glycation Endproducts and the Gastrointestinal Tract

The prevalence of inflammatory bowel diseases (IBD) is increasing in the world. The introduction of the Western diet has been suggested as a potential explanation of increased prevalence. The Western diet includes highly processed food products, and often include thermal treatment. During thermal treatment, the Maillard reaction can occur, leading to the formation of dietary advanced glycation endproducts (dAGEs). In this review, different biological effects of dAGEs are discussed, including their digestion, absorption, formation, and degradation in the gastrointestinal tract, with an emphasis on their pro-inflammatory effects. In addition, potential mechanisms in the inflammatory effects of dAGEs are discussed. This review also specifically elaborates on the involvement of the effects of dAGEs in IBD and focuses on evidence regarding the involvement of dAGEs in the symptoms of IBD. Finally, knowledge gaps that still need to be filled are identified.

Function, Regulation, and Pathophysiological Relevance of the POT Superfamily, Specifically PepT1 in Inflammatory Bowel Disease

Mammalian members of the proton-coupled oligopeptide transporter family are integral membrane proteins that mediate the cellular uptake of di/tripeptides and peptide-like drugs and couple substrate translocation to the movement of H⁺ , with the transmembrane electrochemical proton gradient providing the driving force. Peptide transporters are responsible for the (re)absorption of dietary and/or bacterial di- and tripeptides in the intestine and kidney and maintaining homeostasis of neuropeptides in the brain. These proteins additionally contribute to absorption of a number of pharmacologically important compounds. In this overview article, we have provided updated information on the structure, function, expression, localization, and activities of PepT1 (SLC15A1), PepT2 (SLC15A2), PhT1 (SLC15A4), and PhT2 (SLC15A3). Peptide transporters, in particular, PepT1 are discussed as drug-delivery systems in addition to their implications in health and disease. Particular emphasis has been placed on the involvement of PepT1 in the physiopathology of the gastrointestinal tract, specifically, its role in inflammatory bowel diseases. © 2018 American Physiological Society. Compr Physiol 8:731-760, 2018.

Protein Hydrolysates as Promoters of Non-Haem Iron Absorption

Iron (Fe) is an essential micronutrient for human growth and health. Organic iron is an excellent iron supplement due to its bioavailability. Both amino acids and peptides improve iron bioavailability and absorption and are therefore valuable components of iron supplements. This review focuses on protein hydrolysates as potential promoters of iron absorption. The ability of protein hydrolysates to chelate iron is thought to be a key attribute for the promotion of iron absorption. Iron-chelatable protein hydrolysates are categorized by their absorption forms: amino acids, di- and tri-peptides and polypeptides. Their structural characteristics, including their size and amino acid sequence, as well as the presence of special amino acids, influence their iron chelation abilities and bioavailabilities. Protein hydrolysates promote iron absorption by keeping iron soluble, reducing ferric iron to ferrous iron, and promoting transport across cell membranes into the gut. We also discuss the use and relative merits of protein hydrolysates as iron supplements.

Unique Pattern of Protein-Bound Maillard Reaction Products in Manuka (Leptospermum scoparium) Honey

As a unique feature, honey from the New Zealand manuka tree (Leptospermum scoparium) contains substantial amounts of dihydroxyacetone (DHA) and methylglyoxal (MGO). Although MGO is a reactive intermediate in the Maillard reaction, very little is known about reactions of MGO with honey proteins. We hypothesized that the abundance of MGO should result in a particular pattern of protein-bound Maillard reaction products (MRPs) in manuka honey. A protein-rich high-molecular-weight fraction was isolated from 12 manuka and 8 non-manuka honeys and hydrolyzed enzymatically. By HPLC-MS/MS, 8 MRPs, namely, N-ε-fructosyllysine, N-ε-maltulosyllysine, carboxymethyllysine, carboxyethyllysine (CEL), pyrraline, formyline, maltosine, and methylglyoxal-derived hydroimidazolone 1 (MG-H1), were quantitated. Compared to non-manuka honeys, the manuka honeys were characterized by high concentrations of CEL and MG-H1, whereas the formation of N-ε-fructosyllysine was suppressed, indicating concurrence reactions of glucose and MGO at the ε-amino group of protein-bound lysine. Up to 31% of the lysine and 8% of the arginine residues, respectively, in the manuka honey protein can be modified to CEL and MG-H1, respectively. CEL and MG-H1 concentrations correlated strongly with the MGO concentration of the honeys. Manuka honey possesses a special pattern of protein-bound MRPs, which might be used to prove the reliability of labeled MGO levels in honeys and possibly enable the detection of fraudulent MGO or DHA addition to honey.

Free and Protein-Bound Maillard Reaction Products in Beer: Method Development and a Survey of Different Beer Types

The Maillard reaction is important for beer color and flavor, but little is known about the occurrence of individual glycated amino acids in beer. Therefore, seven Maillard reaction products (MRPs), namely, fructosyllysine, maltulosyllysine, pyrraline, formyline, maltosine, MG-H1, and argpyrimidine, were synthesized and quantitated in different types of beer (Pilsner, dark, bock, wheat, and nonalcoholic beers) by HPLC-ESI-MS/MS in the multiple reaction monitoring mode through application of the standard addition method. Free MRPs were analyzed directly. A high molecular weight fraction was isolated by dialysis and hydrolyzed enzymatically prior to analysis. Maltulosyllysine was quantitated for the first time in food. The most important free MRPs in beer are fructosyllysine (6.8-27.0 mg/L) and maltulosyllysine (3.7-21.8 mg/L). Beer contains comparatively high amounts of late-stage free MRPs such as pyrraline (0.2-1.6 mg/L) and MG-H1 (0.3-2.5 mg/L). Minor amounts of formyline (4-230 μg/L), maltosine (6-56 μg/L), and argpyrimidine (0.1-4.1 μg/L) were quantitated. Maltulosyllysine was the most significant protein-bound MRP, but both maltulosyllysine and fructosyllysine represent only 15-60% of the total protein-bound lysine-derived Amadori products. Differences in the patterns of protein-bound and free individual MRPs and the ratios between them were identified, which indicate differences in their chemical, biochemical, and microbiological stabilities during the brewing process.

3-Hydroxypyridinone derivatives as metal-sequestering agents for therapeutic use

Although iron is one of the most important metal ions for living organisms, it becomes toxic when in excess or misplaced. This review presents a glance at representative examples of hydroxypyridinone-based chelators, which have been recently developed as potential clinically useful drugs for metal overload diseases, mostly associated with excess of iron but also other hard metal-ions. It also includes a detailed discussion on the factors assisting chelator design strategy toward fulfillment of the most relevant biochemical properties of hydroxypyridinone chelators, highlighting structure-activity relationships and a variety of potential clinical applications, beyond chelatotherapy. This study appears as a response to the growing interest on metal chelation therapy and opens new perspectives of possible applications in future medicine.

Stability of Individual Maillard Reaction Products in the Presence of the Human Colonic Microbiota

Maillard reaction products (MRPs) are taken up in substantial amounts with the daily diet, but the majority are not transported across the intestinal epithelium. The aim of this study was to obtain first insights into the stability of dietary MRPs in the presence of the intestinal microbiota. Four individual MRPs, namely, N-ε-fructosyllysine (FL), N-ε-carboxymethyllysine (CML), pyrraline (PYR), and maltosine (MAL), were anaerobically incubated with fecal suspensions from eight human volunteers at 37 °C for up to 72 h. The stability of the MRPs was measured by HPLC with UV and MS/MS detections. The Amadori product FL could no longer be detected after 4 h of incubation. Marked interindividual differences were observed for CML metabolism: Depending on the individual, at least 40.7 ± 1.5% of CML was degraded after 24 h of incubation, and the subjects could thus be tentatively grouped into fast and slow metabolizers of this compound. PYR was degraded by 20.3 ± 4.4% during 24 h by all subjects. The concentration of MAL was not significantly lowered in the presence of fecal suspensions. In no case could metabolites be identified and quantified by different mass spectrometric techniques. This is the first study showing that the human colonic microbiota is able to degrade selected glycated amino acids and possibly use them as a source of energy, carbon, and/or nitrogen.

Drug transport via the intestinal peptide transporter PepT1

The focus of this review is on the pharmaceutical relevance of the intestinal peptide transporter PepT1. The review is limited to the progress made in the field over the past two years. Much of this progress is being driven by the prevailing view that PepT1 can be used for drug delivery purposes. Studies have indeed shown that several drugs, prodrugs and drug candidates gain entry into the systemic circulation via PepT1. Very recent examples are prodrugs of zanamivir, oseltamivir and didanosine.

Transport of the areca nut alkaloid arecaidine by the human proton-coupled amino acid transporter 1 (hPAT1)

Objectives

The pyridine alkaloid arecaidine is an ingredient of areca nut preparations. It is responsible for many physiological effects observed during areca nut chewing. However, the mechanism underlying its oral bioavailability has not yet been studied. We investigated whether the H+-coupled amino acid transporter 1 (PAT1, SLC36A1), which is expressed in the intestinal epithelium, accepts arecaidine, arecoline, isoguvacine and other derivatives as substrates.

Methods

Inhibition of l-[3H]proline uptake by arecaidine and derivatives was determined in Caco-2 cells expressing hPAT1 constitutively and in HeLa cells transiently transfected with hPAT1-cDNA. Transmembrane transport of arecaidine and derivatives was measured electrophysiologically in Xenopus laevis oocytes.

Key findings

Arecaidine, guvacine and isoguvacine but not arecoline strongly inhibited the uptake of l-[3H]proline into Caco-2 cells. Kinetic analyses revealed the competitive manner of l-proline uptake inhibition by arecaidine. In HeLa cells transfected with hPAT1-cDNA an affinity constant of 3.8 mm was obtained for arecaidine. Electrophysiological measurements at hPAT1-expressing X. laevis oocytes demonstrated that arecaidine, guvacine and isoguvacine are transported by hPAT1 in an electrogenic manner.

Conclusion

We conclude that hPAT1 transports arecaidine, guvacine and isoguvacine across the apical membrane of enterocytes and that hPAT1 might be responsible for the intestinal absorption of these drug candidates.