Spatial response of jejunal pacing defined by a novel high-resolution multielectrode array.

Gastric pacing has shown preclinical success in modulating bioelectrical slow-wave activity and has potential as a novel therapy for functional motility disorders. However, the translation of pacing techniques to the small intestine remains preliminary. This paper presents the first high-resolution framework for simultaneous pacing and response mapping of the small intestine. A novel surface-contact electrode array, capable of simultaneous pacing and high-resolution mapping of the pacing response, was developed and applied in vivo on the proximal jejunum of pigs. Pacing parameters including the input energy and pacing electrode orientation were systematically evaluated, and the efficacy of pacing was determined by analyzing spatiotemporal characteristics of entrained slow waves. Histological analysis was conducted to determine if the pacing resulted in tissue damage. A total of 54 studies were conducted on 11 pigs, and pacemaker propagation patterns were successfully achieved at both low (2 mA, 50 ms) and high (4 mA, 100 ms) energy levels with the pacing electrodes oriented in the antegrade, retrograde, and circumferential directions. The high energy level performed significantly better (P = 0.014) in achieving spatial entrainment. Comparable success (greater than 70%) was achieved when pacing in the circumferential and antegrade pacing directions, and no tissue damage was observed at the pacing sites. This study defined the spatial response of small intestine pacing in vivo revealing effective pacing parameters for slow-wave entrainment in the jejunum. Intestinal pacing now awaits translation to restore disordered slow-wave activity associated with motility disorders.NEW & NOTEWORTHY A novel surface-contact electrode array customized for the small intestine anatomy enabled simultaneous pacing and high-resolution response mapping. The spatial response of small intestine bioelectrical activity to pacing was mapped for the first time in vivo. Antegrade and circumferential pacing achieved spatial entrainment over 70% of the time and their induced pattern was held for 4-6 cycles postpacing at high energy (4 mA, 100 ms, at ∼2.7 s which corresponds to 1.1 × intrinsic frequency).

Recording and analysis of slow waves of the small intestine of mice with heart failure.

BACKGROUND: Gastrointestinal (GI) symptoms in heart failure (HF) patients are associated with increased morbidity and mortality. We hypothesized that HF reduces bioelectrical activity underlying peristalsis. In this study, we aimed to establish a method to capture and analyze slow waves (SW) in the small intestine in mice with HF. METHODS: We established a model of HF secondary to coronary artery disease in mice overexpressing tissue-nonspecific alkaline phosphatase (TNAP) in endothelial cells. The myoelectric activity was recorded from the small intestine in live animals under anesthesia. The low- and high-frequency components of SW were isolated in MATLAB and compared between the control (n = 12) and eTNAP groups (n = 8). C-kit-positive interstitial cells of Cajal (ICC) and Pgp9.5-positive myenteric neurons were detected by immunofluorescence. Myenteric ganglia were assessed by hematoxylin and eosin (H&E) staining. RESULTS: SW activity was successfully captured in vivo, with both high- and low-frequency components. Low-frequency component of SW was not different between endothelial TNAP (eTNAP) and control mice (mean[95% CI]: 0.032[0.025-0.039] vs. 0.040[0.028-0.052]). High-frequency component of SW showed a reduction eTNAP mice relative to controls (0.221[0.140-0.302] vs. 0.394[0.295-0.489], p < 0.01). Dysrhythmia was also apparent upon visual review of signals. The density of ICC and neuronal networks remained the same between the two groups. No significant reduction in the size of myenteric ganglia of eTNAP mice was observed. CONCLUSIONS: A method to acquire SW activity from small intestines in vivo and isolate low- and high-frequency components was established. The results indicate that HF might be associated with reduced high-frequency SW activity.

The bioelectrical conduction system around the ileocecal junction defined through in vivo high-resolution mapping in rabbits.

Coordinated contractions across the small and large intestines via the ileocecal junction (ICJ) are critical to healthy gastrointestinal function and are in part governed by myoelectrical activity. In this study, the spatiotemporal characteristics of the bioelectrical conduction across the ICJ and its adjacent regions were quantified in anesthetized rabbits. High-resolution mapping was applied from the terminal ileum (TI) to the sacculus rotundus (SR), across the ICJ and into the beginning of the large intestine at the cecum ampulla coli (AC). Orally propagating slow wave patterns in the SR did not entrain the TI. However, aborally propagating patterns from the TI were able to entrain the SR. Bioelectrical activity was recorded within the ICJ and AC, revealing complex interactions of slow waves, spike bursts, and bioelectrical quiescence. This suggests the involvement of myogenic coordination when regulating motility between the small and large intestines. Mean slow wave frequency between regions did not vary significantly (13.74-17.16 cycles/min). Slow waves in the SR propagated with significantly faster speeds (18.51 ± 1.57 mm/s) compared with the TI (14.05 ± 2.53 mm/s, P = 0.0113) and AC (9.56 ± 1.56 mm/s, P = 0.0001). Significantly higher amplitudes were observed in both the TI (0.28 ± 0.13 mV, P = 0.0167) and SR (0.24 ± 0.08 mV, P = 0.0159) within the small intestine compared with the large intestine AC (0.03 ± 0.01 mV). We hypothesize that orally propagating slow waves facilitate a motor-brake pattern in the SR to limit outflow into the ICJ, similar to those previously observed in other gastrointestinal regions.NEW & NOTEWORTHY Competing slow wave pacemakers were observed in the terminal ileum and sacculus rotundus. Prevalent oral propagation in the sacculus rotundus toward the terminal ileum potentially acts as a brake mechanism limiting outflow. Slow waves and periods of quiescence at the ileocecal junction suggest that activation may depend on the coregulatory flow and distention pathways. Slow waves and spike bursts in the cecum impart a role in the coordination of motility.

Gastrointestinal Myoelectric Measurements via Simultaneous External and Internal Electrodes in Pigs.

INTRODUCTION: Currently, there is no accurate noninvasive measurement system to diagnose gastrointestinal (GI) motility disorders. Wireless skin patches have been introduced to provide an accurate noninvasive measurement of GI myoelectric activity which is essential for developing neuro-stimulation devices to treat GI motility disorders. The aim of this study is to compare the external and internal electrical signal measurements in ambulatory pigs. METHODS: Yucatan pigs underwent placement of internal electrodes on the stomach, small intestine, and colon. Wires were brought through the abdominal wall. Signals were collected by a wireless receptor. Four external patches were placed on the abdominal skin to record the signals simultaneously. Pigs were kept for 6 d while the sensors were continuously recording the data from both systems. RESULTS: Internal sensors detected rich signals from each organ. The stomach had a dominant frequency that ranged from 4 to 4.5 cpm, with occasional higher frequencies at 2, 3 and 4 times that. Small intestine signals had their primary energy in the 12-15 cpm range. Colon signals primarily displayed a dominant broad peak in the 4-6 cpm region. External skin patches detected a substantial fraction of the activities measured by the internal electrodes. A clear congruence in the frequency spectrum was observed between the internal and external readings. CONCLUSIONS: Internally measured myoelectrical signals confirmed different patterns of rhythmic activity of the stomach, small intestine, and colon. Skin patches provided GI myoelectric measurement with a range of frequencies that could be useful in the diagnosis and treatment of motility disorders.

Biomechanical characterization of the small intestine to simulate gastrointestinal tract chyme propulsion.

Regular intestinal motility is essential to guarantee complete digestive function. The coordinative action and integrity of the smooth muscle layers in the small intestine's wall are critical for mixing and propelling the luminal content. However, some patients present gastrointestinal limitations which may negatively impact the normal motility of the intestine. These patients have altered mechanical and muscle properties that likely impact chyme propulsion and may pose a daily scenario for long-term complications. To better understand how mechanics affect chyme propulsion, the propulsive capability of the small intestine was examined during a peristaltic wave along the distal direction of the tract. It was assumed that such a wave works as an activation signal, inducing peristaltic contractions in a transversely isotropic hyperelastic model. In this work, the effect on the propulsion mechanics, from an impairment on the muscle contractile ability, typical from patients with systemic sclerosis, and the presence of sores resultant from ulcers was evaluated. The passive properties of the constitutive model were obtained from uniaxial tensile tests from a porcine small intestine, along with both longitudinal and circumferential directions. Our experiments show decreased stiffness in the circumferential direction. Our simulations show decreased propulsion forces in patients in systemic sclerosis and ulcer patients. As these patients may likely need medical intervention, establishing action concerning the impaired propulsion can help to ease the evaluation and treatment of future complications.

Distal Small Bowel Resection Yields Enhanced Intestinal and Colonic Adaptation.

BACKGROUND: Murine ileocecal resection (ICR) has been used to investigate intestinal adaptation. The established model often includes the sacrifice of significant length of the proximal colon. Here, we optimized a highly selective vascular approach to the ICR, with primary jejunal-colic anastomosis yielding maximal colonic preservation. MATERIALS AND METHODS: Forty C57BL/6 mice underwent a highly vascularly selective ICR. The terminal branches of the ileocecal artery are isolated apart from the mesenteric branches supplying the small bowel to be resected. The distal 50% of small bowel and cecum are resected; a primary jejuno-colonic anastomosis is performed. Animals were sacrificed at postoperative weeks 2 (n = 10) and 10 (n = 29). Proximal 50% small bowel resection (SBR) with jejuno-ileal anastomosis was also performed for comparison. RESULTS: The entire colon (with exception of the cecum) was preserved in 100% of animals. Ninety-seven percent of animals survived to postoperative week 10, and all exhibited structural adaptation in the remnant small intestine epithelium. Crypts deepened by 175%, and villi lengthened by 106%, versus 39% and 29% in the proximal SBR cohort, respectively. Colonic proliferation, structural adaptation, and functional adaptation (measured by p-histone 3, luminal-facing apical crypt border size, and sucrase isomaltase, respectively) were increased in ICR compared with proximal SBR. CONCLUSIONS: Highly selective isolation of the cecal vasculature allows for greater colon preservation and yields enhanced remnant intestine epithelial adaptation. ICR is also associated with greater colonic adaptation and unique plasticity toward an intestinal phenotype. These findings underscore major differences between resection sites and offer insights into the critical adaptive mechanisms in response to massive intestinal loss.

Heterophilic and homophilic cadherin interactions in intestinal intermicrovillar links are species dependent.

Enterocytes are specialized epithelial cells lining the luminal surface of the small intestine that build densely packed arrays of microvilli known as brush borders. These microvilli drive nutrient absorption and are arranged in a hexagonal pattern maintained by intermicrovillar links formed by 2 nonclassical members of the cadherin superfamily of calcium-dependent cell adhesion proteins: protocadherin-24 (PCDH24, also known as CDHR2) and the mucin-like protocadherin (CDHR5). The extracellular domains of these proteins are involved in heterophilic and homophilic interactions important for intermicrovillar function, yet the structural determinants of these interactions remain unresolved. Here, we present X-ray crystal structures of the PCDH24 and CDHR5 extracellular tips and analyze their species-specific features relevant for adhesive interactions. In parallel, we use binding assays to identify the PCDH24 and CDHR5 domains involved in both heterophilic and homophilic adhesion for human and mouse proteins. Our results suggest that homophilic and heterophilic interactions involving PCDH24 and CDHR5 are species dependent with unique and distinct minimal adhesive units.

Clostridioides difficile toxin A-mediated Caco-2 cell barrier damage was attenuated by insect-derived fractions and corresponded to increased gene transcription of cell junctional and proliferation proteins.

Pathogenesis of C. difficile in the intestine is associated with the secretion of toxins which can damage the intestinal epithelial layer and result in diseases such as diarrhoea. Treatment for C. difficile infections consists of antibiotics which, however, have non-specific microbiocidal effects and may cause intestinal dysbiosis which results in subsequent health issues. Therefore, alternative treatments to C. difficile infections are required. We investigated whether different black soldier fly- and mealworm-derived fractions, after applying the INFOGEST digestion protocol, could counteract C. difficile toxin A-mediated barrier damage of small intestinal Caco-2 cells. Treatment and pre-treatment with insect-derived fractions significantly (p < 0.05) mitigated the decrease of the transepithelial electrical resistance (TEER) of Caco-2 cells induced by C. difficile toxin A. In relation to these effects, RNA sequencing data showed an increased transcription of cell junctional and proliferation protein genes in Caco-2 cells. Furthermore, the transcription of genes regulating immune signalling was also increased. To identify whether this resulted in immune activation we used a Caco-2/THP-1 co-culture model where the cells were only separated by a permeable membrane. However, the insect-derived fractions did not change the basolateral secreted IL-8 levels in this model. To conclude, our findings suggest that black soldier fly- and mealworm-derived fractions can attenuate C. difficile induced intestinal barrier disruption and they might be promising tools to reduce the symptoms of C. difficile infections.

Intestinal organoid-based 2D monolayers mimic physiological and pathophysiological properties of the pig intestine.

Gastrointestinal infectious diseases remain an important issue for human and animal health. Investigations on gastrointestinal infectious diseases are classically performed in laboratory animals leading to the problem that species-specific models are scarcely available, especially when it comes to farm animals. The 3R principles of Russel and Burch were achieved using intestinal organoids of porcine jejunum. These organoids seem to be a promising tool to generate species-specific in vitro models of intestinal epithelium. 3D Organoids were grown in an extracellular matrix and characterized by qPCR. Organoids were also seeded on permeable filter supports in order to generate 2D epithelial monolayers. The organoid-based 2D monolayers were characterized morphologically and were investigated regarding their potential to study physiological transport properties and pathophysiological processes. They showed a monolayer structure containing different cell types. Moreover, their functional activity was demonstrated by their increasing transepithelial electrical resistance over 18 days and by an active glucose transport and chloride secretion. Furthermore, the organoid-based 2D monolayers were also confronted with cholera toxin derived from Vibrio cholerae as a proof of concept. Incubation with cholera toxin led to an increase of short-circuit current indicating an enhanced epithelial chloride secretion, which is a typical characteristic of cholera infections. Taken this together, our model allows the investigation of physiological and pathophysiological mechanisms focusing on the small intestine of pigs. This is in line with the 3R principle and allows the reduction of classical animal experiments.

Effects of degree of milling on the starch digestibility of cooked rice during (in vitro) small intestine digestion.

Effects of degree of milling on starch digestibility of cooked rice during (in vitro) small intestine digestion were investigated. By fitting starch digestograms to the logarithm of slope plot and combination of parallel and sequential digestion kinetics model, two starch fractions with distinct digestion rate constants were identified. Results from scanning electronic microscope and confocal laser scanning microscope showed that the rapidly digestible starch fraction (RDF) was mainly composed of gelatinized starch, while the slowly digestible starch fraction (SDF) was consisted of relatively intact starch granules, protein matrix encapsulated starch and starch-protein binary complex. The cooked rice with milling treatment had more loosely packed and larger network cells compared to that for brown rice. Consequentially, the RDF content was decreased, while that for SDF was increased by the milling treatment. These results could help the rice processing industry to develop healthy rice products with desirable starch digestibility.

Simulated digestion and fecal fermentation behaviors of exopolysaccharides from Paecilomyces cicadae TJJ1213 and its effects on human gut microbiota.

This study aimed to explore the in vitro simulated digestion and fecal fermentation behaviors of two purified exopolysaccharide fractions (EPS1 and EPS2) from Paecilomyces cicadae TJJ1213 and its effects on human gut microbiota composition. Results showed that EPS1 and EPS2 could not be digested by saliva-gastrointestinal. After fecal fermentation, however, the molecular weight of EPS1 and EPS2 significantly decreased, and the molar ratios of the monosaccharide composition remarkably changed, indicating that EPS1 and EPS2 could be degraded and consumed by human gut microbiota. Notably, EPS1 and EPS2 could significantly modulate the composition, via increasing the relative abundances of Bacteroides and Phascolarctobacterium and decreasing the pathogenic bacteria Escherichia-Shigella, Klebsiella and Fusobacterium. In addition, EPS1 and EPS2 also could promote the production of short-chain fatty acids during fermentation for 24 h. These results suggested that EPS from Paecilomyces cicadae TJJ1213 can be used as a functional food to improve health and prevent diseases by promoting gut health.

Identification and expression analysis of the ß-defensin genes in the goat small intestine.

Defensins represent a family of cysteine-rich peptides that have broad-spectrum antimicrobial activities and serve as a typical kind of effector molecule in the immunity. Ruminant species have a large number of ß-defensins in the absence of α- and θ-defensins. It is well-known that the genomes of sheep and cattle harbor at least 43 and 57 ß-defensin genes, respectively. However, the repertoire of the goat ß-defensin gene family has not been fully elucidated. In this study, we identified a total of 50 ß-defensins from the goat genome, including 48 functional genes and 2 pseudogenes. Cross-species genomic and evolutionary analyses showed that all of the ß-defensins in goat chromosomes 8, 13 and 23 present one-to-one orthologous relationships to their sheep and cattle counterparts, whereas some ß-defensin genes in goat chromosome 27 are goat-specific. Moreover, we observed that some duplicated genes in goat chromosome 27 may be derived from gene copy number variation, and the annotation of sheep and cattle ß-defensins appears to be incomplete in the genome. Importantly, real-time PCR analysis showed that 17 ß-defensins are expressed in the small intestine with abundant cBD1s expression. These findings significant increased our knowledge of ruminant ß-defensin and provided useful information for genetic studies, as well as providing a foundation for future research exploring the role of defensins in the immune response.

Vitamin A and retinoic acid accelerate the attenuation of intestinal adaptability upon feeding induced by high-fat diet in mice.

With its unique cellular plasticity, the small intestinal mucosa exhibits efficient adaptability upon feeding. However, little is known about the effect of high-fat diet (HFD) feeding on this adaption and its underlying mechanism. Herein, we demonstrated that the cell proliferation ability, mitochondrial morphology, and global transcriptomic profile of the small intestine exhibited a prominent discrepancy between the fasted and refed state in mice, which were markedly attenuated by long-term HFD feeding. The retinol (Vitamin A, VA) metabolism pathway was dramatically affected by HFD feeding in the small intestine. Both VA and its active metabolite retinoic acid (RA), with the administration of lipid micelles, promoted the expression of genes involved in lipid absorption and suppressed the expression of genes involved in the cell proliferation of intestinal organoids. Via chip-qPCR and RT-qPCR, genes involved in lipid metabolism and cell proliferation were target genes of RARα/RXRα in small intestinal organoids treated with RA and lipid micelles. The role of VA in the in vivo attenuation of intestinal adaptability, in response to HFD, was evaluated. Mice were fed a normal chow diet, HFD, or HFD diet supplemented with additional 1.5-fold VA for 12 weeks. VA supplementation in HFD accelerated the attenuation of intestinal adaptability upon feeding induced by HFD, promoted lipid absorption gene expression, and increased body weight and serum cholesterol levels. In conclusion, the discrepancy of the small intestine between the fasted and refed state was dramatically attenuated by HFD feeding, in which VA and RA might play important roles.

Bicarbonate ion transport by the electrogenic Na+ /HCO3- cotransporter, NBCe1, is required for normal electrical slow-wave activity in mouse small intestine.

BACKGROUND: Normal gastrointestinal motility depends on electrical slow-wave activity generated by interstitial cells of Cajal (ICC) in the tunica muscularis of the gastrointestinal tract. A requirement for HCO3- in extracellular solutions used to record slow waves indicates a role for HCO3- transport in ICC pacemaking. The Slc4a4 gene transcript encoding the electrogenic Na+ /HCO3- cotransporter, NBCe1, is enriched in mouse small intestinal myenteric region ICC (ICC-MY) that generate slow waves. This study aimed to determine how extracellular HCO3- concentrations affect electrical activity in mouse small intestine and to determine the contribution of NBCe1 activity to these effects. METHODS: Immunohistochemistry and sharp electrode electrical recordings were used. KEY RESULTS: The NBCe1 immunoreactivity was localized to ICC-MY of the tunica muscularis. In sharp electrode electrical recordings, removal of HCO3- from extracellular solutions caused significant, reversible, depolarization of the smooth muscle and a reduction in slow-wave amplitude and frequency. In 100 mM HCO3- , the muscle hyperpolarized and slow wave amplitude and frequency increased. The effects of replacing extracellular Na+ with Li+ , an ion that does not support NBCe1 activity, were similar to, but larger than, the effects of removing HCO3- . There were no additional changes to electrical activity when HCO3- was removed from Li+ containing solutions. The Na+ /HCO3- cotransport inhibitor, S-0859 (30µM) significantly reduced the effect of removing HCO3- on electrical activity. CONCLUSIONS & INFERENCES: These studies demonstrate a major role for Na+ /HCO3- cotransport by NBCe1 in electrical activity of mouse small intestine and indicated that regulation of intracellular acid:base homeostasis contributes to generation of normal pacemaker activity in the gastrointestinal tract.

Mucin degrader Akkermansia muciniphila accelerates intestinal stem cell-mediated epithelial development.

Mucin-degrading bacteria are densely populated in the intestinal epithelium; however, their interaction with intestinal stem cells (ISCs) and their progeny have not been elucidated. To determine whether mucin-degrading bacteria play a role in gut homeostasis, mice were treated with Akkermansia muciniphila, a specialized species that degrades mucin. Administration of A. muciniphila for 4 weeks accelerated the proliferation of Lgr5+ ISCs and promoted the differentiation of Paneth cells and goblet cells in the small intestine (SI). We found similar effects of A. muciniphila in the colon. The levels of acetic and propionic acids were higher in the cecal contents of A. muciniphila-treated mice than in PBS-treated mice. SI organoids treated with cecal contents obtained from A. muciniphila-treated mice were larger and could be diminished by treatment with G protein-coupled receptor (Gpr) 41/43 antagonists. Pre-treatment of mice with A. muciniphila reduced gut damage caused by radiation and methotrexate. Further, a novel isotype of the A. muciniphila strain was isolated from heathy human feces that showed enhanced function in intestinal epithelial regeneration. These findings suggest that mucin-degrading bacteria (e.g., A. muciniphila) may play a crucial role in promoting ISC-mediated epithelial development and contribute to intestinal homeostasis maintenance.

Salvia miltiorrhiza induces depolarization of pacemaker potentials in murine small intestinal interstitial cells of Cajal via extracellular Ca2+ and Na+ influx.

Interstitial cells of Cajal (ICCs) are pacemaker cells that control smooth muscle contraction in the gastrointestinal (GI) tract. The present study investigated the effects of Salvia miltiorrhiza (SM) on the pacemaker potentials of ICCs from the mouse small intestine in vitro and on GI motility in vivo. The whole­cell patch­clamp configuration was used to record pacemaker potential in ICCs in vitro, and GI motility was investigated in vivo by recording intestinal transit rate (ITR). Using the whole­cell patch­clamp configuration, SM depolarized the pacemaker potentials of ICCs in a dose­dependent manner. Fulvestrant blocked SM­induced effects but 1,3­dihydro­3,3­bis(4­hydroxyphenyl)-7-methyl­2H­indol­2­one did not. Additionally, 4­[2­phenyl-5,7­bis(trifluoromethyl) pyrazolo[1,5­a]pyrimidin­3­yl] phenol blocked SM­induced effects. Intracellular guanosine 5'­O­(2­thiodiphosphate), and pretreatment with extracellular Ca2+­ and Na+­free solutions also blocked SM­induced effects. Furthermore, ITR values were increased by SM in vivo and SM elevated the levels of motilin (MTL). The SM­induced increase in ITR was associated with increased protein expression levels of c­kit and the transmembrane protein 16A (TMEM16A) channel. In addition, SM induced pacemaker potential depolarization through estrogen receptor ß in a G protein­dependent manner via extracellular Ca2+ and Na+ regulation in the murine small intestine in vitro. Moreover, SM increased the ITR in vivo through the MTL hormone via c­kit and TMEM16A­dependent pathways. Taken together, these results suggested that SM may have the ability to control GI motility and could be used as a GI motility regulator.

Feeding management before gastrointestinal studies in pigs.

Pigs are used to model humans in gastrointestinal (GI) studies because of their comparable size, physiology and behaviour: both are monogastric omnivores. A porcine surgical model for testing novel, tethered ultrasound capsule endoscopes (USCE) requires a clean, motile small intestine. Recommendations for human GI tract preparation before the mechanically similar process of video capsule endoscopy describe using oral purgatives, while high-carbohydrate drinks are recommended before colorectal surgery. Reports of the GI preparation of pigs exist but lack technical details, that is, administration, efficacy and side effects. This report details feeding a high-energy liquid diet to 11 female pigs undergoing surgery and USCE which was readily accepted and easily administered, and which produced a clean, motile small intestine and caused no detectable physiological/behavioural abnormalities.

COVID-19 and Hartnup disease: an affair of intestinal amino acid malabsorption.

Since the outbreak of COVID-19, clinicians have tried every effort to fight the disease, and multiple drugs have been proposed. However, no proven effective therapies currently exist, and different clinical phenotypes complicate the situation. In clinical practice, many severe or critically ill COVID-19 patients developed gastrointestinal (GI) disturbances, including vomiting, diarrhoea, or abdominal pain, even in the absence of cough and dyspnea. Understanding the mechanism of GI disturbances is warranted for exploring better clinical care for COVID-19 patients. With evidence collected from clinical studies on COVID-19 and basic research on a rare genetic disease (i.e., Hartnup disorder), we put forward a novel hypothesis to elaborate an effective nutritional therapy. We hypothesize that SARS-CoV-2 spike protein, binding to intestinal angiotensin-converting enzyme 2, negatively regulates the absorption of neutral amino acids, and this could explain not only the GI, but also systemic disturbances in COVID-19. Amino acid supplements could be recommended.Level of evidence No level of evidence: Hypothesis article.

Effects of endogenous proteins on rice digestion during small intestine (in vitro) digestion.

Rices with higher protein contents are nutritionally desirable. This study investigates the effects of endosperm proteins on starch in vitro digestibility in cooked and uncooked rice, and the mechanisms underlying any changes. The composition of rice endosperm proteins and the morphologies of proteins and starch granules were determined by SDS-PAGE and confocal microscopy. Starch molecular fine structure was examined using size-exclusion chromatography. In vitro digestion showed that the digestion rate coefficients (k) of cooked rice flour were significantly lower than those of isolated starch or of a starch-protein mixture. (e.g for samples from SWR4, k is 9.6, 12.9 and 11.6 × 10-2 min-1 for cooked rice flour, isolated starch and starch-protein mixture, respectively). For uncooked samples, digestion rate coefficients were 1.4, 1.5 and 1.8 × 10-2 min-1 for flour, starch-protein mixture and starch, respectively. The digestion rates in cooked samples were higher than those in uncooked samples. This suggests that, in cooked samples, starch digestion rates are more affected by the protein physical barrier than by some chemical effect (e.g. hydrogen bonding between protein and starch), while in uncooked samples, a chemical effect from protein is more pronounced than a physical barrier from protein.

Oxidized phospholipids affect small intestine neuromuscular transmission and serotonergic pathways in juvenile mice.

BACKGROUND: Oxidized phospholipid derivatives (OxPAPCs) act as bacterial lipopolysaccharide (LPS)-like damage-associated molecular patterns. OxPAPCs dose-dependently exert pro- or anti-inflammatory effects by interacting with several cellular receptors, mainly Toll-like receptors 2 and 4. It is currently unknown whether OxPAPCs may affect enteric nervous system (ENS) functional and structural integrity. METHODS: Juvenile (3 weeks old) male C57Bl/6 mice were treated intraperitoneally with OxPAPCs, twice daily for 3 days. Changes in small intestinal contractility were evaluated by isometric neuromuscular responses to receptor and non-receptor-mediated stimuli. Alterations in ENS integrity and serotonergic pathways were assessed by real-time PCR and confocal immunofluorescence microscopy in longitudinal muscle-myenteric plexus whole-mount preparations (LMMPs). Tissue levels of serotonin (5-HT), tryptophan, and kynurenine were measured by HPLC coupled to UV/fluorescent detection. KEY RESULTS: OxPAPC treatment induced enteric gliosis, loss of myenteric plexus neurons, and excitatory hypercontractility, and reduced nitrergic neurotransmission with no changes in nNOS+ neurons. Interestingly, these changes were associated with a higher functional response to 5-HT, altered immunoreactivity of 5-HT receptors and serotonin transporter (SERT) together with a marked decrease in 5-HT levels, shifting tryptophan metabolism toward kynurenine production. CONCLUSIONS AND INFERENCES: OxPAPC treatment disrupted structural and functional integrity of the ENS, affecting serotoninergic tone and 5-HT tissue levels toward a higher kynurenine content during adolescence, suggesting that changes in intestinal lipid metabolism toward oxidation can affect serotoninergic pathways, potentially increasing the risk of developing functional gastrointestinal disorders during critical stages of development.