A live show in the stomach : Monitoring in vitro and in vivo human gastric digestion with MRI

A better understanding of the gastric digestion of solid food will allow for a more thorough exploration of the relationship between food properties and physiological mechanisms underlying digestion of nutrients. The breakdown of food structures has mainly been studied via in vitro models. However, these results have been verified only to a limited extent in vivo. This limitation necessitates the investigation of the potential use of non-invasive approaches to bridge the link between in vivo and in vitro digestion research. Thus, this thesis aimed to investigate the potential of magnetic resonance (MR) techniques in monitoring gastric digestion of solid food in static, (semi-)dynamic in vitro models and in humans.The work began with a well-controlled in vitro static digestion model in Chapter 2. We explored the use of time-domain nuclear magnetic resonance (TD-NMR) and magnetic resonance imaging (MRI) to monitor the gastric digestion of whey protein (solution and gel). During digestion, free amino groups (-NH2 groups) and protein concentrations in the supernatant were measured. Transverse relaxation time (T2) values of the digestion mixture were determined by TD-NMR and MRI, and transverse relaxation rate (R2 = T2-1) was calculated. Subsequently, relative amplitudes (TD-NMR) for different T2 values and T2 distribution (MRI) were determined. For the solution, protein concentration and T2 did not change during digestion. For the gels, water in both supernatant and gel phase could be discriminated on the basis of their T2 values. During digestion, R2 of the supernatant correlated positively with the protein (-NH2 groups) concentration in the supernatant. MRI T2-mapping showed similar associations between R2 of supernatant and protein (-NH2 groups) concentration. Thus, R2 was shown to be a useful marker to monitor in vitro gastric digestion of whey protein gels and TD-NMR measurements contributed to interpreting MRI data.TD-NMR results from Chapter 2 showed that water transportation (namely swelling) took place during digestion and may be of great importance for digestion rate. Therefore, we investigated the effect of swelling on gastric digestion of protein gels in Chapter 3. Whey protein gels with NaCl concentrations of 0-0.1 M were used as model foods. Young’s modulus, swelling ratio, acid uptake and digestion rate of the gels were measured. Pepsin transport was monitored by confocal laser scanning microscopy using green fluorescent protein (GFP), which has a similar size as pepsin. We observed that an increase of NaCl in gels corresponded with increased Young’s modulus, reduced swelling and slower digestion. Additionally, a reduction of acid transport was observed, as well as a reduction of GFP both at the surface and in the gels. This shows that swelling affects digestion rate not only by enhancing acid diffusion but also by modulating partitioning of pepsin at the food-gastric fluid interface and thereby the total amount of pepsin in food particle. This perspective on swelling provides new insight for designing food with a specific digestion rate for targeted dietary demands.The work in Chapter 2 was performed under static conditions. Thus, further work was conducted in Chapter 4. We developed a novel MRI-compatible semi-dynamic gastric simulator (MR-GAS) that includes gastric secretion, emptying and mixing, and applied it to investigate the potential of relaxation rates in monitoring digestion. During protein gel digestion, pH and protein hydrolysis were measured. R2 and R1 (= T1-1) of the supernatant were measured by time-domain nuclear magnetic resonance (TD-NMR) and MRI. With TD-NMR, 99% of the variance in R2 and 96% of the variance in R1 could be explained as a function of protein concentration and [H+]. With MRI, the explained variances were 99% for R2 and 60% for R1. From these analyses, the obtained equations enabled the prediction of protein concentration and pH with measured R2 and R1 values. This shows that MR-GAS model may be used in a clinical MRI scanner to monitor gastric digestion under in vitro dynamic circumstances, by measuring R2 and R1. These results underscored the potential of MRI to monitor nutrient hydrolysis and pH changes in in vivo studies. Therefore, in Chapter 5, we conducted a human randomized cross-over trial in which we assessed the effect of food hardness and protein content on gastric emptying and additionally investigated the application of the T1 and T2 to monitor in vivo gastric digestion.The trial was conducted with 18 healthy males provided with three gels differing in hardness and protein content: a soft gel with low protein content (Soft-LP), a hard gel with low protein content (Hard-LP), and a hard gel with high protein content (Hard-HP). Before and after ingestion, abdominal MRI scans and appetite and well-being ratings were obtained until t = 85 min after the start of ingestion. At t = 100 min participants ate an ad libitum lunch. Overall, gastric content volume was different among the treatments: High-HP < Soft-HP < Soft-LP. Mean T2 and T1 of the measured stomach content decreased after ingestion from baseline and then gradually increased from 15 min onwards. The treatments resulted in different T1 and T2 values: Hard-HP < Soft-HP < Soft-LP, although not all the time points differed significantly. The high protein content was the main factor in delaying gastric emptying and high hardness was the secondary factor. T1 and T2 measurements can provide extra information on the dilution and digestion taking place in the stomach. This study suggests the potential of MRI parameters for providing more insights on in vivo digestion, and their results may contribute to linking in vitro and in vivo digestion research.Finally, Chapter 6 discusses findings from in vitro models to in vivo human trials in this thesis. It provides an overview of the application of MR techniques to measure gastric digestion, the added value of MRI measurements for digestion research, and the effects of food properties on gastric digestion. To conclude, MR techniques can provide molecular-level and quantitative information on protein hydrolysis in solid food through T1 and T2 measurements. Moreover, the findings from this thesis can aid in informing in vitro and in silico models and bridging the link between in vitro and in vivo digestion research.&nbsp

Monitoring food digestion with magnetic resonance techniques

This review outlines the current use of magnetic resonance (MR) techniques to study digestion and highlights their potential for providing markers of digestive processes like texture changes and nutrient breakdown. In vivo digestion research can be challenging due to practical constraints and biological complexity. Therefore, digestion is primarily studied using in vitro models. These would benefit from further in vivo validation. Nuclear magnetic resonance (NMR) is widely used to characterize food systems. Magnetic resonance imaging (MRI) is a related technique that can be used to study both in vitro model systems and in vivo gastro-intestinal processes. MRI allows visualisation and quantification of gastric processes like gastric emptying and coagulation. Both MRI and NMR scan sequences can be configured to be sensitive to different aspects of gastric or intestinal contents. For example, magnetization transfer (MT) and chemical exchange saturation transfer (CEST) can detect proton (H+) exchange between water and proteins. MRI techniques have the potential to provide molecular-level and quantitative information on in vivo gastric (protein) digestion. This requires careful validation in order to understand what these MR markers of digestion mean in a specific digestion context. Combined with other measures they can be used to validate and inform in vitro digestion models. This may bridge the gap between in vitro and in vivo digestion research and can aid the optimization of food properties for different applications in health and disease

The importance of swelling for in vitro gastric digestion of whey protein gels

In this paper we report the importance of swelling on gastric digestion of protein gels, which is rarely recognized in literature. Whey protein gels with NaCl concentrations 0–0.1 M were used as model foods. The Young's modulus, swelling ratio, acid uptake and digestion rate of the gels were measured. Pepsin transport was observed by confocal laser scanning microscopy using green fluorescent protein (GFP). With the increase of NaCl in gels, Young's modulus increased, swelling was reduced and digestion was slower, with a reduction of acid transport and less GFP present both at surface and in the gels. This shows that swelling affects digestion rate by enhancing acid diffusion, but also by modulating the partitioning of pepsin at the food-gastric fluid interface and thereby the total amount of pepsin in the food particle. This perspective on swelling will provide new insight for designing food with specific digestion rate for targeted dietary demands.</p

Fiber templated epitaxially grown composite membranes: from thermal insulation to infrared stealth

Thermal insulation materials show a substantial impact on civil and military fields for applications. Fabrication of efficient, flexible, and comfortable composite materials for thermal insulation is thereby of significance. Herein, a “fiber templated epitaxial growth” strategy was adopted to construct PAN@LDH (PAN = polyacrylonitrile; LDH = layered double hydroxides) composite membranes with a three-dimensional (3D) network structure. The PAN@LDH showed an impressive temperature difference of 28.1 °C as a thermal insulation material in the hot stage of 80 °C with a thin layer of 0.6 mm. Moreover, when a human hand was covered with 3 layers of the PAN@LDH-70% composite membrane, it was rendered invisible under infrared radiation. Such excellent performance can be attributed to the following reasons: (1) the hierarchical interfaces of the PAN@LDH composite membrane reduced thermal conduction, (2) the 3D network structure of the PAN@LDH composite membranes restricted thermal convection, and (3) the selective infrared absorption of LDHs decreased thermal radiation. When modified with Dodecyltrimethoxysilane (DTMS), the resulting PAN@LDH@DTMS membrane can be used under high humidity conditions with excellent thermal insulation properties. As such, this work provides a facile strategy for the development of high-performance thermal insulation functional membranes

Exploring in vitro gastric digestion of whey protein by time-domain nuclear magnetic resonance and magnetic resonance imaging

Gastric digestion is crucial for protein breakdown. Although it has been widely studied with in vitro models, verification in vivo remains a big challenge. Magnetic resonance imaging (MRI) has the potential to bridge this gap. Our objective was to use the transverse relaxation time (T2) and rate (R2 = T2 −1) to monitor hydrolysis of protein-rich food during in vitro gastric digestion. Whey protein solution and heat-induced hydrogels were digested by means of simulated gastric fluid (SGF). Free amino groups (–NH2 groups) and protein concentration in the supernatant were measured. T2 and R2 of the digestion mixture were determined by time-domain nuclear magnetic resonance (TD-NMR) and MRI. Subsequently, relative amplitudes (TD-NMR) for different T2 values and T2 distribution (MRI) were determined. For the solution, protein concentration and T2 did not change during digestion. For the gels, water in supernatant and gel phase could be discriminated on the basis of their T2 values. During digestion, R2 of supernatant correlated positively with protein (–NH2 groups) concentration in SGF. Also, the decrease in relative amplitude of gel fraction correlated linearly with the increase of supernatant protein concentration. MRI T2-mapping showed similar associations between R2 of supernatant and protein (–NH2 groups) concentration. In conclusion, T2-measurements by TD-NMR and MRI can be used to monitor in vitro gastric digestion of whey protein gels; TD-NMR measurements contributed to interpreting the MRI data. Thus, MRI has high potential for monitoring in vivo gastric digestion and this should be further pursued

Exploring in vitro gastric digestion of whey protein by time-domain nuclear magnetic resonance and magnetic resonance imaging

Gastric digestion is crucial for protein breakdown. Although it has been widely studied with in vitro models, verification in vivo remains a big challenge. Magnetic resonance imaging (MRI) has the potential to bridge this gap. Our objective was to use the transverse relaxation time (T2) and rate (R2 = T2 −1) to monitor hydrolysis of protein-rich food during in vitro gastric digestion. Whey protein solution and heat-induced hydrogels were digested by means of simulated gastric fluid (SGF). Free amino groups (–NH2 groups) and protein concentration in the supernatant were measured. T2 and R2 of the digestion mixture were determined by time-domain nuclear magnetic resonance (TD-NMR) and MRI. Subsequently, relative amplitudes (TD-NMR) for different T2 values and T2 distribution (MRI) were determined. For the solution, protein concentration and T2 did not change during digestion. For the gels, water in supernatant and gel phase could be discriminated on the basis of their T2 values. During digestion, R2 of supernatant correlated positively with protein (–NH2 groups) concentration in SGF. Also, the decrease in relative amplitude of gel fraction correlated linearly with the increase of supernatant protein concentration. MRI T2-mapping showed similar associations between R2 of supernatant and protein (–NH2 groups) concentration. In conclusion, T2-measurements by TD-NMR and MRI can be used to monitor in vitro gastric digestion of whey protein gels; TD-NMR measurements contributed to interpreting the MRI data. Thus, MRI has high potential for monitoring in vivo gastric digestion and this should be further pursued.</p

Storage Duration Prediction for Long-Expired Frozen Meat Exceeding State Reserve Time via Swept-Source Optical Coherence Tomography (SS-OCT) under Low-Frequency Electric Field

Storage duration detection for frozen meat, especially meat exceeding the state reserve time several times, has always been a big challenge in food safety inspection. Under long freezing times, the physical and chemical properties of meat change complexly. In this paper, the SS-OCT detection method under a low-frequency electric field is firstly (to our knowledge) applied to the predict storage durations of long-expired frozen meat. The average normalized cross-correlation (ANCC) is put forward as a comprehensive parameter to reflect both the electric–kinetic and optical properties of meat’s biological changes. A monotonically increasing inversion rule between ANCC and the storage duration of frozen meat is found after investigating 3840 pork samples, the frozen storage durations of which were from 1 to 13 months. To verify the correctness and accuracy of our method, nine groups of long-expired frozen pork samples were investigated. The maximum relative error for their storage durations is less than 5.71%, which means that our SS-OCT method under a low-frequency electric field is promising in providing a rapid on-site storage duration detection method without any complicated laboratory pretreatments for food safety inspection

Tailoring the multiscale mechanics of tunable decellularized extracellular matrix (dECM) for wound healing through immunomodulation

With the discovery of the pivotal role of macrophages in tissue regeneration through shaping the tissue immune microenvironment, various immunomodulatory strategies have been proposed to modify traditional biomaterials. Decellularized extracellular matrix (dECM) has been extensively used in the clinical treatment of tissue injury due to its favorable biocompatibility and similarity to the native tissue environment. However, most reported decellularization protocols may cause damage to the native structure of dECM, which undermines its inherent advantages and potential clinical applications. Here, we introduce a mechanically tunable dECM prepared by optimizing the freeze-thaw cycles. We demonstrated that the alteration in micromechanical properties of dECM resulting from the cyclic freeze-thaw process contributes to distinct macrophage-mediated host immune responses to the materials, which are recently recognized to play a pivotal role in determining the outcome of tissue regeneration. Our sequencing data further revealed that the immunomodulatory effect of dECM was induced via the mechnotrasduction pathways in macrophages. Next, we tested the dECM in a rat skin injury model and found an enhanced micromechanical property of dECM achieved with three freeze-thaw cycles significantly promoted the M2 polarization of macrophages, leading to superior wound healing. These findings suggest that the immunomodulatory property of dECM can be efficiently manipulated by tailoring its inherent micromechanical properties during the decellularization process. Therefore, our mechanics-immunomodulation-based strategy provides new insights into the development of advanced biomaterials for wound healing