Quantitative assessment of intestinal stiffness and associations with fibrosis in human inflammatory bowel disease

Asymmetric fluid flow in helical pipes inspired by shark intestines

Unlike human intestines, which are long, hollow tubes, the intestines of sharks and rays contain interior helical structures surrounding a cylindrical hole. One function of these structures may be to create asymmetric flow, favoring passage of fluid down the digestive tract, from anterior to posterior. Here, we design and 3D print biomimetic models of shark intestines, in both rigid and deformable materials. We use the rigid models to test which physical parameters of the interior helices (the pitch, the hole radius, the tilt angle, and the number of turns) yield the largest flow asymmetries. These asymmetries exceed those of traditional Tesla valves, structures specifically designed to create flow asymmetry without any moving parts. When we print the biomimetic models in elastomeric materials so that flow can couple to the structure's shape, flow asymmetry is significantly amplified; it is sevenfold larger in deformable structures than in rigid structures. Last, we 3D-print deformable versions of the intestine of a dogfish shark, based on a tomogram of a biological sample. This biomimic produces flow asymmetry comparable to traditional Tesla valves. The ability to influence the direction of a flow through a structure has applications in biological tissues and artificial devices across many scales, from large industrial pipelines to small microfluidic devices.

Gut mechanoimmunology: Shaping immune response through physical cues

The gut immune system embodies a complex interplay between the gut mucosal barrier, the host's immune cells, and gut microbiota. These components exist within a dynamic environment characterized by a variety of physical cues, e.g., compression, tension, shear stress, stiffness, and viscoelasticity. The physical cues can be modified under specific pathological conditions. Given their dynamic nature, comprehending the specific effects of these physical cues on the gut immune system is critical for pathological and therapeutic studies of intestinal immune-related diseases. This review aims to discuss how physical cues influence gut immunology by affecting the gut mucosal barrier, host immune cells, and gut microbiota, defining this concept as gut mechanoimmunology. This review seeks to highlight that an enhanced understanding of gut mechanoimmunology carries therapeutic implications, not only for intestinal diseases but also for extraintestinal diseases.

Tissue palpation in endoscopy using EIT and soft actuators

The integration of soft robots in medical procedures has significantly improved diagnostic and therapeutic interventions, addressing safety concerns and enhancing surgeon dexterity. In conjunction with artificial intelligence, these soft robots hold the potential to expedite autonomous interventions, such as tissue palpation for cancer detection. While cameras are prevalent in surgical instruments, situations with obscured views necessitate palpation. This proof-of-concept study investigates the effectiveness of using a soft robot integrated with Electrical Impedance Tomography (EIT) capabilities for tissue palpation in simulated in vivo inspection of the large intestine. The approach involves classifying tissue samples of varying thickness into healthy and cancerous tissues using the shape changes induced on a hydraulically-driven soft continuum robot during palpation. Shape changes of the robot are mapped using EIT, providing arrays of impedance measurements. Following the fabrication of an in-plane bending soft manipulator, the preliminary tissue phantom design is detailed. The phantom, representing the descending colon wall, considers induced stiffness by surrounding tissues based on a mass-spring model. The shape changes of the manipulator, resulting from interactions with tissues of different stiffness, are measured, and EIT measurements are fed into a Long Short-Term Memory (LSTM) classifier. Train and test datasets are collected as temporal sequences of data from a single training phantom and two test phantoms, namely, A and B, possessing distinctive thickness patterns. The collected dataset from phantom B, which differs in stiffness distribution, remains unseen to the network, thus posing challenges to the classifier. The classifier and proposed method achieve an accuracy of 93 % and 88.1 % on phantom A and B, respectively. Classification results are presented through confusion matrices and heat maps, visualising the accuracy of the algorithm and corresponding classified tissues.

Hydrogel-Integrated Millifluidic Systems: Advancing the Fabrication of Mucus-Producing Human Intestinal Models

The luminal surface of the intestinal epithelium is protected by a vital mucus layer, which is essential for lubrication, hydration, and fostering symbiotic bacterial relationships. Replicating and studying this complex mucus structure in vitro presents considerable challenges. To address this, we developed a hydrogel-integrated millifluidic tissue chamber capable of applying precise apical shear stress to intestinal models cultured on flat or 3D structured hydrogel scaffolds with adjustable stiffness. The chamber is designed to accommodate nine hydrogel scaffolds, 3D-printed as flat disks with a storage modulus matching the physiological range of intestinal tissue stiffness (~3.7 kPa) from bioactive decellularized and methacrylated small intestinal submucosa (dSIS-MA). Computational fluid dynamics simulations were conducted to confirm a laminar flow profile for both flat and 3D villi-comprising scaffolds in the physiologically relevant regime. The system was initially validated with HT29-MTX seeded hydrogel scaffolds, demonstrating accelerated differentiation, increased mucus production, and enhanced 3D organization under shear stress. These characteristic intestinal tissue features are essential for advanced in vitro models as they critically contribute to a functional barrier. Subsequently, the chamber was challenged with human intestinal stem cells (ISCs) from the terminal ileum. Our findings indicate that biomimicking hydrogel scaffolds, in combination with physiological shear stress, promote multi-lineage differentiation, as evidenced by a gene and protein expression analysis of basic markers and the 3D structural organization of ISCs in the absence of chemical differentiation triggers. The quantitative analysis of the alkaline phosphatase (ALP) activity and secreted mucus demonstrates the functional differentiation of the cells into enterocyte and goblet cell lineages. The millifluidic system, which has been developed and optimized for performance and cost efficiency, enables the creation and modulation of advanced intestinal models under biomimicking conditions, including tunable matrix stiffness and varying fluid shear stresses. Moreover, the readily accessible and scalable mucus-producing cellular tissue models permit comprehensive mucus analysis and the investigation of pathogen interactions and penetration, thereby offering the potential to advance our understanding of intestinal mucus in health and disease.

Kismet/CHD7/CHD8 affects gut microbiota, mechanics, and the gut-brain axis in Drosophila melanogaster

The gut microbiome affects brain and neuronal development and may contribute to the pathophysiology of neurodevelopmental disorders. However, it is unclear how risk genes associated with such disorders affect gut physiology in a manner that could impact microbial colonization and how the mechanical properties of the gut tissue might play a role in gut-brain bidirectional communication. To address this, we used Drosophila melanogaster with a null mutation in the gene kismet, an ortholog of chromodomain helicase DNA-binding protein (CHD) family members CHD7 and CHD8. In humans, these are risk genes for neurodevelopmental disorders with co-occurring gastrointestinal symptoms. We found that kismet mutant flies have a significant increase in gastrointestinal transit time, indicating the functional homology of kismet with CHD7/CHD8 in vertebrates. Rheological characterization of dissected gut tissue revealed significant changes in the mechanics of kismet mutant gut elasticity, strain stiffening behavior, and tensile strength. Using 16S rRNA metagenomic sequencing, we also found that kismet mutants have reduced diversity and abundance of gut microbiota at every taxonomic level. To investigate the connection between the gut microbiome and behavior, we depleted gut microbiota in kismet mutant and control flies and quantified the flies' courtship behavior. Depletion of gut microbiota rescued courtship defects of kismet mutant flies, indicating a connection between gut microbiota and behavior. In striking contrast, depletion of the gut microbiome in the control strain reduced courtship activity, demonstrating that antibiotic treatment can have differential impacts on behavior and may depend on the status of microbial dysbiosis in the gut prior to depletion. We propose that Kismet influences multiple gastrointestinal phenotypes that contribute to the gut-microbiome-brain axis to influence behavior. We also suggest that gut tissue mechanics should be considered as an element in the gut-brain communication loop, both influenced by and potentially influencing the gut microbiome and neurodevelopment.

Computational insights into colonic motility: Mechanical role of mucus in homeostasis and inflammation

Colonic motility plays a vital role in maintaining proper digestive function. The rhythmic contractions and relaxations facilitate various types of motor functions that generate both propulsive and non-propulsive motility modes which in turn generate shear stresses on the epithelial surface. However, the interplay between colonic mucus, shear stress, and epithelium remains poorly characterized. Here, we present a colonic computational model that describes the potential roles of mucus and shear stress in both homeostasis and ulcerative colitis (UC). Our model integrates several key features, including the properties of the mucus bilayer and faeces, intraluminal pressure, and crypt characteristics to predict the time-space mosaic of shear stress. We show that the mucus thickness which could vary based on the severity of UC, may significantly reduce the amount of shear stress applied to the colonic crypts and effect faecal velocity. Our model also reveals an important spatial shear stress variance in homeostatic colonic crypts that suggests shear stress may have a modulatory role in epithelial cell migration, differentiation, apoptosis, and immune surveillance. Together, our study uncovers the rather neglected roles of mucus and shear stress in intestinal cellular processes during homeostasis and inflammation.

Listen to Your Gut: Key Concepts for Bioengineering Advanced Models of the Intestine

The intestine performs functions central to human health by breaking down food and absorbing nutrients while maintaining a selective barrier against the intestinal microbiome. Key to this barrier function are the combined efforts of lumen-lining specialized intestinal epithelial cells, and the supportive underlying immune cell-rich stromal tissue. The discovery that the intestinal epithelium can be reproduced in vitro as intestinal organoids introduced a new way to understand intestinal development, homeostasis, and disease. However, organoids reflect the intestinal epithelium in isolation whereas the underlying tissue also contains myriad cell types and impressive chemical and structural complexity. This review dissects the cellular and matrix components of the intestine and discusses strategies to replicate them in vitro using principles drawing from bottom-up biological self-organization and top-down bioengineering. It also covers the cellular, biochemical and biophysical features of the intestinal microenvironment and how these can be replicated in vitro by combining strategies from organoid biology with materials science. Particularly accessible chemistries that mimic the native extracellular matrix are discussed, and bioengineering approaches that aim to overcome limitations in modelling the intestine are critically evaluated. Finally, the review considers how further advances may extend the applications of intestinal models and their suitability for clinical therapies.

Identifying immune cell infiltration and effective diagnostic biomarkers in Crohn's disease by bioinformatics analysis

Background

Crohn's disease (CD) has an increasing incidence and prevalence worldwide. It is currently believed that both the onset and progression of the disease are closely related to immune system imbalance and the infiltration of immune cells. The aim of this study was to investigate the molecular immune mechanisms associated with CD and its fibrosis through bioinformatics analysis.

Methods

Three datasets from the Gene Expression Omnibus data base (GEO) were downloaded for data analysis and validation. Single sample gene enrichment analysis (ssGSEA) was used to evaluate the infiltration of immune cells in CD samples. Immune cell types with significant differences were identified by Wilcoxon test and Least Absolute Shrinkage and Selection Operator (LASSO) regression analysis. Differentially expressed genes (DEGs) were screened and then subjected to Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) functional correlation analysis, as well as protein-protein interaction (PPI) network analysis. The cytoHubba program and the GSE75214 dataset were used to screen for hub genes and plot Receiver operating characteristic (ROC)curves to screen for possible biomarkers of CD based on diagnostic efficacy. The hub genes of CD were correlated with five significantly different immune cells. In addition, validation was performed by real time quantitative PCR (RT-qPCR) experiments in colonic tissue of CD intestinal fibrosis rats to further identify hub genes that are more related to CD intestinal fibrosis.

Results

The DEGs were analyzed separately by 10 algorithms and narrowed down to 9 DEGs after taking the intersection. 4 hub genes were further screened by the GSE75214 validation set, namely COL1A1, CXCL10, MMP2 and FGF2. COL1A1 has the highest specificity and sensitivity for the diagnosis of CD and is considered to have the potential to diagnose CD. Five immune cells with significant differences were screened between CD and health controls (HC). Through the correlation analysis between five kinds of immune cells and four biomarkers, it was found that CXCL10 was positively correlated with activated dendritic cells, effector memory CD8+ T cells. MMP2 was positively correlated with activated dendritic cells, gamma delta T cells (γδ T) and mast cells. MMP2 and COL1A1 were significantly increased in colon tissue of CD fibrosis rats.

Conclusion

MMP2, COL1A1, CXCL10 and FGF2 can be used as hub genes for CD. Among them, COL1A1 can be used as a biomarker for the diagnosis of CD. MMP2 and CXCL10 may be involved in the development and progression of CD by regulating activated dendritic cell, effector memory CD8+ T cell, γδ T cell and mast cell. In addition, MMP2 and COL1A1 may be more closely related to CD intestinal fibrosis.

Stiffness Restricts the Stemness of the Intestinal Stem Cells and Skews Their Differentiation Toward Goblet Cells

BACKGROUND & AIMS

Fibrosis and tissue stiffening are hallmarks of inflammatory bowel disease (IBD). We have hypothesized that the increased stiffness directly contributes to the dysregulation of the epithelial cell homeostasis in IBD. Here, we aim to determine the impact of tissue stiffening on the fate and function of the intestinal stem cells (ISCs).

METHODS

We developed a long-term culture system consisting of 2.5-dimensional intestinal organoids grown on a hydrogel matrix with tunable stiffness. Single-cell RNA sequencing provided stiffness-regulated transcriptional signatures of the ISCs and their differentiated progeny. YAP-knockout and YAP-overexpression mice were used to manipulate YAP expression. In addition, we analyzed colon samples from murine colitis models and human IBD samples to assess the impact of stiffness on ISCs in vivo.

RESULTS

We demonstrated that increasing the stiffness potently reduced the population of LGR5+ ISCs and KI-67+-proliferating cells. Conversely, cells expressing the stem cell marker, olfactomedin-4, became dominant in the crypt-like compartments and pervaded the villus-like regions. Concomitantly, stiffening prompted the ISCs to preferentially differentiate toward goblet cells. Mechanistically, stiffening increased the expression of cytosolic YAP, driving the extension of olfactomedin-4+ cells into the villus-like regions, while it induced the nuclear translocation of YAP, leading to preferential differentiation of ISCs toward goblet cells. Furthermore, analysis of colon samples from murine colitis models and patients with IBD demonstrated cellular and molecular remodeling reminiscent of those observed in vitro.

CONCLUSIONS

Collectively, our findings highlight that matrix stiffness potently regulates the stemness of ISCs and their differentiation trajectory, supporting the hypothesis that fibrosis-induced gut stiffening plays a direct role in epithelial remodeling in IBD.

Mechanobiological considerations in colorectal stapling: Implications for technology development

Technological advancements in minimally invasive surgery have led to significant improvements in patient outcomes. One such technology is surgical stapling, which has evolved into a key component of many operating rooms by facilitating ease and efficacy in resection and repair of diseased or otherwise compromised tissue. Despite such advancements, adverse post-operative outcomes such as anastomotic leak remain a persistent problem in surgical stapling and its correlates (i.e., hand-sewing), most notably in low colorectal or coloanal procedures. Many factors may drive anastomotic leaks, including tissue perfusion, microbiome composition, and patient factors such as pre-existing disease. Surgical intervention induces complex acute and chronic changes to the mechanical environment of the tissue; however, roles of mechanical forces in post-operative healing remain poorly characterized. It is well known that cells sense and respond to their local mechanical environment and that dysfunction of this "mechanosensing" phenomenon contributes to a myriad of diseases. Mechanosensing has been investigated in wound healing contexts such as dermal incisional and excisional wounds and development of pressure ulcers; however, reports investigating roles of mechanical forces in adverse post-operative gastrointestinal wound healing are lacking. To understand this relationship well, it is critical to understand: 1) the intraoperative material responses of tissue to surgical intervention, and 2) the post-operative mechanobiological response of the tissue to surgically imposed forces. In this review, we summarize the state of the field in each of these contexts while highlighting areas of opportunity for discovery and innovation which can positively impact patient outcomes in minimally invasive surgery.

Bridging the Gap in Ashby's Map for Soft Material Properties for Tissue Engineering

Ashby's map's role in rationally selecting materials for optimal performance is well-established in traditional engineering applications. However, there is a major gap in Ashby's maps in selecting materials for tissue engineering, which are very soft with an elastic modulus of less than 100 kPa. To fill the gap, we create an elastic modulus database to effectively connect soft engineering materials with biological tissues such as the cardiac, kidney, liver, intestine, cartilage, and brain. This soft engineering material mechanical property database is created for widely applied agarose hydrogels based on big-data screening and experiments conducted using ultra-low-concentration (0.01-0.5 wt %) hydrogels. Based on that, an experimental and analysis protocol is established for evaluating the elastic modulus of ultra-soft engineering materials. Overall, we built a mechanical bridge connecting soft matter and tissue engineering by fine-tuning the agarose hydrogel concentration. Meanwhile, a soft matter scale (degree of softness) is established to enable the manufacturing of implantable bio-scaffolds for tissue engineering.

Mechanosensation to inflammation: Roles for YAP/TAZ in innate immune cells

Innate immune cells are responsible for eliminating foreign infectious agents and cellular debris, and their ability to perceive, respond to, and integrate biochemical and mechanical cues from their microenvironment eventually determines their behavior. In response to tissue injury, pathogen invasion, or a biomaterial implant, immune cells activate many pathways to initiate inflammation in the tissue. In addition to common inflammatory pathways, studies have demonstrated the role of the mechanosensitive proteins and transcriptional coactivators YAP and TAZ (YAP/TAZ) in inflammation and immunity. We review our knowledge of YAP/TAZ in controlling inflammation and immunity in innate immune cells. Furthermore, we discuss the roles of YAP/TAZ in inflammatory diseases, wound healing, and tissue regeneration and how they integrate mechanical cues with biochemical signaling during disease progression. Last, we comment on possible approaches that can be exploited to harness the therapeutic potential of YAP/TAZ in inflammatory diseases.

Mechanosensing in macrophages and dendritic cells in steady-state and disease

Macrophages and dendritic cells are myeloid cells that play critical roles in immune responses. Macrophages help to maintain homeostasis through tissue regeneration and the clearance of dead cells, but also mediate inflammatory processes against invading pathogens. As the most potent antigen-presenting cells, dendritic cells are important in connecting innate to adaptive immune responses via activation of T cells, and inducing tolerance under physiological conditions. While it is known that macrophages and dendritic cells respond to biochemical cues in the microenvironment, the role of extracellular mechanical stimuli is becoming increasingly apparent. Immune cell mechanotransduction is an emerging field, where accumulating evidence suggests a role for extracellular physical cues coming from tissue stiffness in promoting immune cell recruitment, activation, metabolism and inflammatory function. Additionally, many diseases such as pulmonary fibrosis, cardiovascular disease, cancer, and cirrhosis are associated with changes to the tissue biophysical environment. This review will discuss current knowledge about the effects of biophysical cues including matrix stiffness, topography, and mechanical forces on macrophage and dendritic cell behavior under steady-state and pathophysiological conditions. In addition, we will also provide insight on molecular mediators and signaling pathways important in macrophage and dendritic cell mechanotransduction.

A rapid high throughput bioprinted colorectal cancer spheroid platform forin vitrodrug- and radiation-response

We describe the development of a high-throughput bioprinted colorectal cancer (CRC) spheroid platform with high levels of automation, information content, and low cell number requirement. This is achieved via the formulation of a hydrogel bioink with a compressive Young's modulus that is commensurate with that of colonic tissue (1-3 kPa), which supports exponential growth of spheroids from a wide range of CRC cell lines. The resulting spheroids display tight cell-cell junctions, bioink matrix-cell interactions and necrotic hypoxic cores. By combining high content light microscopy imaging and processing with rapid multiwell plate bioprinting, dose-response profiles are generated from CRC spheroids challenged with oxaliplatin (OX) and fluorouracil (5FU), as well as radiotherapy. Bioprinted CRC spheroids are shown to exhibit high levels of chemoresistance relative to cell monolayers, and OX was found to be significantly less effective against tumour spheroids than in monolayer culture, when compared to 5FU.

Exercise Training Prevents the Loss of Wall Thickness and Lowers Expression of Alzheimer's Related Proteins in 3xTg Mouse Jejunum

Growing evidence has demonstrated the benefits of regular exercise on cardiovascular, neural, and cognitive function in humans with Alzheimer's disease (AD). However, the consequences of AD on gastrointestinal morphology and the effects of regular exercise, which plays an important role against the development of certain gastrointestinal-related diseases, are still poorly understood. Therefore, to assess the changes in intestinal structure in a mouse model of AD and the impact of exercise, 2-month-old 3xTg-AD male mice were subjected to treadmill running 5 days per week for a period of 5 months. Jejunum from 3xTg-AD mice analyzed by histochemical methods revealed significant alterations in morphology. Compared to age-matched wild-type (WT) mice, villi length and crypt depth were increased, and collagen content of jejunum was elevated in 3xTg-AD mice. Jejunum wall dimensions, expressed as total wall thickness, outer longitudinal thickness, and inner circular thickness were decreased in 3xTg-AD compared to WT. Smooth muscle actin expression in jejunal wall was decreased in 3xTg-AD. Most of these aberrations were improved with exercise. Western blot expression of cyclin dependent kinase 5 (CDK5, involved in neural cell death and hyperphosphorylation of tau), was elevated in 3xTg-AD jejunum. This was associated with a 4-fold increase in tau5 expression. Exercise prevented the increase in expression of CDK5 and tau5. Expression of caspase 3 (an apoptotic marker) was elevated in 3xTg-AD jejunum and exercise prevented this. The results of our study indicate that the abnormalities in jejunum of the 3xTg mouse model of AD were prevented with exercise training.

Autonomous Untethered Microinjectors for Gastrointestinal Delivery of Insulin

The delivery of macromolecular drugs via the gastrointestinal (GI) tract is challenging as these drugs display low stability as well as poor absorption across the intestinal epithelium. While permeation-enhancing drug delivery methods can increase the bioavailability of low molecular weight drugs, the effective delivery of high molecular weight drugs across the tight epithelial cell junctions remains a formidable challenge. Here, we describe autonomous microinjectors that are deployed in the GI tract, then efficiently penetrate the GI mucosa to deliver a macromolecular drug, insulin, to the systemic circulation. We performed in vitro studies to characterize insulin release and assess the penetration capability of microinjectors and we measured the in vivo release of insulin in live rats. We found that the microinjectors administered within the luminal GI tract could deliver insulin transmucosally to the systemic circulation at levels similar to those with intravenously administered insulin. Due to their small size, tunability in sizing and dosing, wafer-scale fabrication, and parallel, autonomous operation, we anticipate that these microinjectors will significantly advance drug delivery across the GI tract mucosa to the systemic circulation in a safe manner.

Mechanoscopy: A Novel Device and Procedure for in vivo Detection of Chronic Colitis in Mice

BACKGROUND

Gut stiffening caused by fibrosis plays a critical role in the progression of inflammatory bowel disease (IBD) and colon cancer. Previous studies have characterized the biomechanical response of healthy and pathological gut, with most measurements obtained ex vivo.

METHODS

Here, we developed a device and accompanying procedure for in vivo quantification of gut stiffness, termed mechanoscopy. Mechanoscopy includes a flexible balloon catheter, pressure sensor, syringe pump, and control system. The control system activates the balloon catheter and performs automated measurements of the gut stress-strain biomechanical response.

RESULTS

A gut stiffness index (GSI) is identified based on the slope of the obtained stress-strain response. Using a colitis mouse model, we demonstrated that GSI positively correlates with the extent of gut fibrosis, the severity of mucosal damage, and the infiltration of immune cells. Furthermore, a critical strain value is suggested, and GSI efficiently detects pathological gut fibrotic stiffening when the strain exceeds this value.

CONCLUSIONS

Based on these results, we envision that mechanoscopy and GSI will facilitate the clinical diagnosis of IBD.

Mechanical forces directing intestinal form and function

The vertebrate intestine experiences a range of intrinsically generated and external forces during both development and adult homeostasis. It is increasingly understood how the coordination of these forces shapes the intestine through organ-scale folding and epithelial organization into crypt-villus compartments. Moreover, accumulating evidence shows that several cell types in the adult intestine can sense and respond to forces to regulate key cellular processes underlying adult intestinal functions and self-renewal. In this way, transduction of forces may direct both intestinal homeostasis as well as adaptation to external stimuli, such as food ingestion or injury. In this review, we will discuss recent insights from complementary model systems into the force-dependent mechanisms that establish and maintain the unique architecture of the intestine, as well as its homeostatic regulation and function throughout adult life.

A Stiff Extracellular Matrix Favors the Mechanical Cell Competition that Leads to Extrusion of Bacterially-Infected Epithelial Cells

Cell competition refers to the mechanism whereby less fit cells (“losers”) are sensed and eliminated by more fit neighboring cells (“winners”) and arises during many processes including intracellular bacterial infection. Extracellular matrix (ECM) stiffness can regulate important cellular functions, such as motility, by modulating the physical forces that cells transduce and could thus modulate the output of cellular competitions. Herein, we employ a computational model to investigate the previously overlooked role of ECM stiffness in modulating the forceful extrusion of infected “loser” cells by uninfected “winner” cells. We find that increasing ECM stiffness promotes the collective squeezing and subsequent extrusion of infected cells due to differential cell displacements and cellular force generation. Moreover, we discover that an increase in the ratio of uninfected to infected cell stiffness as well as a smaller infection focus size, independently promote squeezing of infected cells, and this phenomenon is more prominent on stiffer compared to softer matrices. Our experimental findings validate the computational predictions by demonstrating increased collective cell extrusion on stiff matrices and glass as opposed to softer matrices, which is associated with decreased bacterial spread in the basal cell monolayer in vitro. Collectively, our results suggest that ECM stiffness plays a major role in modulating the competition between infected and uninfected cells, with stiffer matrices promoting this battle through differential modulation of cell mechanics between the two cell populations.

Engineering in vitro immune-competent tissue models for testing and evaluation of therapeutics

Advances in 3D cell culture, microscale fluidic control, and cellular analysis have enabled the development of more physiologically-relevant engineered models of human organs with precise control of the cellular microenvironment. Engineered models have been used successfully to answer fundamental biological questions and to screen therapeutics, but these often neglect key elements of the immune system. There are immune elements in every tissue that contribute to healthy and diseased states. Including immune function will be essential for effective preclinical testing of therapeutics for inflammatory and immune-modulated diseases. In this review, we first discuss the key components to consider in designing engineered immune-competent models in terms of physical, chemical, and biological cues. Next, we review recent applications of models of immunity for screening therapeutics for cancer, preclinical evaluation of engineered T cells, modeling autoimmunity, and screening vaccine efficacy. Future work is needed to further recapitulate immune responses in engineered models for the most informative therapeutic screening and evaluation.

Regenerating dynamic organs using biomimetic patches

The regeneration of dynamic organs remains challenging because they are intrinsically anisotropic and undergo large volumetric deformation during normal or pathological function. This hampers the durability and applicability of regenerative medicine approaches. To address the challenges of organ dynamics, a new class of patches have emerged with anisotropic and auxetic properties that mimic native tissue biomechanics and accommodate volumetric deformation. Here, we outline the critical design, materials, and processing considerations for achieving optimal patch biomechanics according to target pathology and summarize recent advances in biomimetic patches for dynamic organ regeneration. Furthermore, we discuss the challenges and opportunities which, if overcome, would open up new applications in organ regeneration and expedite the clinical translation of patch-based therapeutics.

Immunological Regulation of Intestinal Fibrosis in Inflammatory Bowel Disease

Intestinal fibrosis is a late-stage phenotype of inflammatory bowel disease (IBD), which underlies most of the long-term complications and surgical interventions in patients, particularly those with Crohn's disease. Despite these issues, antifibrotic therapies are still scarce, mainly due to the current lack of understanding concerning the pathogenetic mechanisms that mediate fibrogenesis in patients with chronic intestinal inflammation. In the current review, we summarize recent evidence regarding the cellular and molecular factors of innate and adaptive immunity that are considered critical for the initiation and amplification of extracellular matrix deposition and stricture formation. We focus on the role of cytokines by dissecting the pro- vs antifibrotic components of the immune response, while taking into consideration their temporal association to the progressive stages of the natural history of IBD. We critically present evidence from animal models of intestinal fibrosis and analyze inflammation-fibrosis interactions that occur under such experimental scenarios. In addition, we comment on recent findings from large-scale, single-cell profiling of fibrosis-relevant populations in IBD patients. Based on such evidence, we propose future potential targets for antifibrotic therapies to treat patients with IBD.

TLR4 Deficiency Affects the Microbiome and Reduces Intestinal Dysfunctions and Inflammation in Chronic Alcohol-Fed Mice

Chronic alcohol abuse causes an inflammatory response in the intestinal tract with damage to the integrity of the mucosa and epithelium, as well as dysbiosis in the gut microbiome. However, the role of gut bacteria in ethanol effects and how these microorganisms interact with the immune system are not well understood. The aim of the present study was to evaluate if TLR4 alters the ethanol-induced intestinal inflammatory response, and whether the response of this receptor affects the gut microbiota profile. We analyzed the 16S rRNA sequence of the fecal samples from wild-type (WT) and TLR4-knockout (TLR4-KO) mice with and without ethanol intake for 3 months. The results demonstrated that chronic ethanol consumption reduces microbiota diversity and causes dysbiosis in WT mice. Likewise, ethanol upregulates several inflammatory genes (IL-1β, iNOS, TNF-α) and miRNAs (miR-155-5p, miR-146a-5p) and alters structural and permeability genes (INTL1, CDH1, CFTR) in the colon of WT mice. Our results further demonstrated that TLR4-KO mice exhibit a different microbiota that can protect against the ethanol-induced activation of the immune system and colon integrity dysfunctions. In short, our results reveal that TLR4 is a key factor for determining the gut microbiota, which can participate in dysbiosis and the inflammatory response induced by alcohol consumption.

Current knowledge on the multiform reconstitution of intestinal stem cell niche

The development of “mini-guts” organoid originates from the identification of Lgr5⁺ intestinal stem cells (ISCs) and circumambient signalings within their specific niche at the crypt bottom. These in vitro self-renewing “mini-guts”, also named enteroids or colonoids, undergo perpetual proliferation and regulated differentiation, which results in a high-performance, self-assembling and physiological organoid platform in diverse areas of intestinal research and therapy. The triumphant reconstitution of ISC niche in vitro also relies on Matrigel, a heterogeneous sarcoma extract. Despite the promising prospect of organoids research, their expanding applications are hampered by the canonical culture pattern, which reveals limitations such as inaccessible lumen, confine scale, batch to batch variation and low reproducibility. The tumor-origin of Matrigel also raises biosafety concerns in clinical treatment. However, the convergence of breakthroughs in cellular biology and bioengineering contribute to multiform reconstitution of the ISC niche. Herein, we review the recent advances in the microfabrication of intestinal organoids on hydrogel systems.

Development of Anti-fibrotic Therapy in Stricturing Crohn's Disease: Lessons from Randomized Trials in Other Fibrotic Diseases

Intestinal fibrosis is considered an inevitable complication of Crohn's disease (CD) that results in symptoms of obstruction and stricture formation. Endoscopic or surgical treatment is required to treat the majority of patients. Progress in the management of stricturing CD is hampered by the lack of effective anti-fibrotic therapy; however, this situation is likely to change because of recent advances in other fibrotic diseases of the lung, liver and skin. In this review, we summarized data from randomized controlled trials (RCT) of anti-fibrotic therapies in these conditions. Multiple compounds have been tested for the anti-fibrotic effects in other organs. According to their mechanisms, they were categorized into growth factor modulators, inflammation modulators, 5-hydroxy-3-methylgultaryl-coenzyme A (HMG-CoA) reductase inhibitors, intracellular enzymes and kinases, renin-angiotensin system (RAS) modulators and others. From our review of the results from the clinical trials and discussion of their implications in the gastrointestinal tract, we have identified several molecular candidates that could serve as potential therapies for intestinal fibrosis in CD.

Biomaterials for intestinal organoid technology and personalized disease modeling

Recent advances in intestinal organoid technologies have paved the way for in vitro recapitulation of the homeostatic renewal of adult tissues, tissue or organ morphogenesis during development, and pathogenesis of many disorders. In vitro modelling of individual patient diseases using organoid systems have been considered key in establishing rational design of personalized treatment strategies and in improving therapeutic outcomes. In addition, the transplantation of organoids into diseased tissues represents a novel approach to treat currently incurable diseases. Emerging evidence from intensive studies suggests that organoid systems' development and functional maturation depends on the presence of an extracellular matrix with suitable biophysical properties, where advanced synthetic hydrogels open new avenues for theoretical control of organoid phenotypes and potential applications of organoids in therapeutic purposes. In this review, we discuss the status, applications, challenges and perspectives of intestinal organoid systems emphasising on hydrogels and their properties suitable for intestinal organoid culture. We provide an overview of hydrogels used for intestinal organoid culture and key factors regulating their biological activity. The comparison of different hydrogels would be a theoretical basis for establishing design principles of synthetic niches directing intestinal cell fates and functions. STATEMENT OF SIGNIFICANCE: Intestinal organoid is an in vitro recapitulation of the gut, which self-organizes from intestinal stem cells and maintains many features of the native tissue. Since the development of this technology, intestinal organoid systems have made significant contribution to rapid progress in intestinal biology. Prevailing methodology for organoid culture, however, depends on animal-derived matrices and suffers from variability and potential risk for contamination of pathogens, limiting their therapeutic application. Synthetic scaffold matrices, hydrogels, might provide solutions to these issues and deepen our understanding on how intestinal cells sense and respond to key biophysical properties of the surrounding matrices. This review provides an overview of developing intestinal models and biomaterials, thereby leading to better understanding of current intestinal organoid systems for both biologists and materials scientists.

Engineering mechanobiology through organoids-on-chip: A strategy to boost therapeutics

The mechanical environment of living cells is as critical as chemical signaling. Mechanical stimuli play a pivotal role in organogenesis and tissue homeostasis. Unbalances in mechanotransduction pathways often lead to diseases, such as cancer, cystic fibrosis, and neurodevelopmental disorders. Despite its inherent relevance, there is a lack of proper mechanoresponsive in vitro study systems. In this context, there is an urge to engineer innovative, robust, dynamic, and reliable organotypic technologies to better connect cellular processes to organ-level function and multi-tissue cross-talk. Mechanically active organoid-on-chip has the potential to surpass this challenge. These systems converge microfabrication, microfluidics, biophysics, and tissue engineering fields to emulate key features of living organisms, hence, reducing costs, time, and animal testing. In this review, we intended to present cutting-edge organ-on-chip platforms that integrate biomechanical stimuli as well as novel multicellular culture, such as organoids. We focused on its application in two main fields: precision medicine and drug development. Moreover, we also discussed the state of the art for the development of an engineered model to assess patient-derived tumor organoid metastatic potential. Finally, we highlighted the current drawbacks and emerging opportunities to match the industry needs. We envision the use of mechanoresponsive organotypic-on-chip microdevices as an indispensable tool for precision medicine, drug development, disease modeling, tissue engineering, and developmental biology.

A literature review on large intestinal hyperelastic constitutive modeling

Impacts, traumas and strokes are spontaneously life-threatening, but chronic symptoms strangle patient every day. Colorectal tissue mechanics in such chronic situations not only regulates the physio-psychological well-being of the patient, but also confirms the level of comfort and post-operative clinical outcomes. Numerous uniaxial and multiaxial tensile experiments on healthy and affected samples have evidenced significant differences in tissue mechanical behavior and strong colorectal anisotropy across each layer in thickness direction and along the length. Furthermore, this study reviewed various forms of passive constitutive models for the highly fibrous colorectal tissue ranging from the simplest linearly elastic and the conventional isotropic hyperelastic to the most sophisticated second harmonic generation image based anisotropic mathematical formulation. Under large deformation, the isotropic description of tissue mechanics is unequivocally ineffective which demands a microstructural based tissue definition. Therefore, the information collected in this review paper would present the current state-of-the-art in colorectal biomechanics and profoundly serve as updated computational resources to develop a sophisticated characterization of colorectal tissues.

Bowel stiffness associated with histopathologic scoring of stenosis in patients with Crohn's disease

BACKGROUND AND AIMS

Intestinal stenosis is a common complication of Crohn's Disease (CD). Stenosis is associated with alteration of bowel mechanical properties. This study aims to quantitate the mechanical properties of the intestinal stenosis and to explore associations between histology and mechanical remodeling at stenotic intestinal sites in CD patients.

METHODS

Intestinal segments from stenotic sites were studied in vitro from 19 CD patients. A luminal catheter with a bag was used to stepwise pressurize the intestinal segments from 0-100 cmH₂O with 10 cmH₂O increments. B-mode ultrasound images were obtained at the narrowest part of the stenosis at each pressure level and morphometric parameters were obtained from ultrasound images. The mechanical behavior of the stenotic tissue were characterized by using an isotropic three dimensional strain energy function in Demiray model form, the mechanical constants were obtained by fitting the model to the recorded intraluminal pressure and the inner radius of the stenotic segment of the small bowel. Grading scores were used for histological analysis of inflammation, fibrosis, muscular hypertrophy and adipocyte proliferation in the intestinal layers. The collagen area fraction in intestinal layers was also calculated. Associations between histological and the mechanical constants (stiffness) were analyzed.

RESULTS

Chronic inflammation was mainly located in mucosa whereas fibrosis was found in submucosa. The mechanical remodeling was performed with changed mechanical constants ranged between 0.35-13.68kPa. The mechanical properties changes were associated mainly with chronic inflammation, fibrosis and combination of inflammation and fibrosis (R>0.69, P<0.001). Furthermore, the mechanical properties correlated with the collagen fraction in submucosa and muscular layers (R>0.53, P<0.05).

CONCLUSIONS

We quantitated the intestinal stenosis stiffness. Associations were found between bowel mechanical remodeling and histological changes at the stenotic site in CD patients.

STATEMENT OF SIGNIFICANCE

Although intestinal ultrasonography, CT and MRI can be used to diagnose Crohn's Disease (CD)-associated bowel strictures, these techniques may not have sufficient accuracy and resolution to differentiate predominantly inflammatory strictures from predominantly fibrotic strictures. The present study aims to quantitate the mechanical remodeling of intestinal stenosis and to explore the associations between histological parameters and mechanical properties at the intestinal stenotic sites in CD patients. For the first time, we quantitatively demonstrated that the mechanical properties of the intestinal wall in CD stenosis are associated with the chronic inflammation, fibrosis and collagen fraction in the intestinal layers. The results of this study may facilitate design and development of artificial biomaterials for gastrointestinal organs. The potential clinical implication of this study is that the histological characteristics in patients with CD can be predicted clinically by means of inflammation and fibrosis assessment in conjunction with tissue stiffness measurement.

Multifaceted Design and Emerging Applications of Tissue Adhesives

Tissue adhesives can form appreciable adhesion with tissues and have found clinical use in a variety of medical settings such as wound closure, surgical sealants, regenerative medicine, and device attachment. The advantages of tissue adhesives include ease of implementation, rapid application, mitigation of tissue damage, and compatibility with minimally invasive procedures. The field of tissue adhesives is rapidly evolving, leading to tissue adhesives with superior mechanical properties and advanced functionality. Such adhesives enable new applications ranging from mobile health to cancer treatment. To provide guidelines for the rational design of tissue adhesives, here, existing strategies for tissue adhesives are synthesized into a multifaceted design, which comprises three design elements: the tissue, the adhesive surface, and the adhesive matrix. The mechanical, chemical, and biological considerations associated with each design element are reviewed. Throughout the report, the limitations of existing tissue adhesives and immediate opportunities for improvement are discussed. The recent progress of tissue adhesives in topical and implantable applications is highlighted, and then future directions toward next-generation tissue adhesives are outlined. The development of tissue adhesives will fuse disciplines and make broad impacts in engineering and medicine.

Growth of tumor emboli within a vessel model reveals dependence on the magnitude of mechanical constraint

Tumor emboli-aggregates of tumor cells within vessels-pose a clinical challenge as they are associated with increased metastasis and tumor recurrence. When growing within a vessel, tumor emboli are subject to a unique mechanical constraint provided by the tubular geometry of the vessel. Current models of tumor emboli use unconstrained multicellular tumor spheroids, which neglect this mechanical interplay. Here, we modeled a lymphatic vessel as a 200 μm-diameter channel in either a stiff or soft, bioinert agarose matrix to create a vessel-like constraint model (VLCM), and we modeled colon or breast cancer tumor emboli with aggregates of HCT116 or SUM149PT cells, respectively. The stiff matrix VLCM constrained the tumor emboli to the cylindrical channel, which led to continuous growth of the emboli, in contrast to the growth rate reduction that unconstrained spheroids exhibit. Emboli morphology in the soft matrix VLCM, however, was dependent on the magnitude of mechanical mismatch between the matrix and the cell aggregates. In general, when the elastic modulus of the matrix of the VLCM was greater than the emboli (EVLCM/Eemb > 1), the emboli were constrained to grow within the channel, and when the elastic modulus of the matrix was less than the emboli (0 < EVLCM/Eemb < 1), the emboli bulged into the matrix. Due to a large difference in myosin II expression between the cell lines, we hypothesized that tumor cell aggregate stiffness is an indicator of cellular force-generating capability. Inhibitors of myosin-related force generation decreased the elastic modulus and/or increased the stress relaxation of the tumor cell aggregates, effectively increasing the mechanical mismatch. The increased mechanical mismatch after drug treatment was correlated with increased confinement of tumor emboli growth along the channel, which may translate to increased tumor burden due to the increased tumor volume within the diffusion distance of nutrients and oxygen.

ILC1 drive intestinal epithelial and matrix remodelling

Organoids can shed light on the dynamic interplay between complex tissues and rare cell types within a controlled microenvironment. Here, we develop gut organoid cocultures with type-1 innate lymphoid cells (ILC1) to dissect the impact of their accumulation in inflamed intestines. We demonstrate that murine and human ILC1 secrete transforming growth factor β1, driving expansion of CD44v6+ epithelial crypts. ILC1 additionally express MMP9 and drive gene signatures indicative of extracellular matrix remodelling. We therefore encapsulated human epithelial-mesenchymal intestinal organoids in MMP-sensitive, synthetic hydrogels designed to form efficient networks at low polymer concentrations. Harnessing this defined system, we demonstrate that ILC1 drive matrix softening and stiffening, which we suggest occurs through balanced matrix degradation and deposition. Our platform enabled us to elucidate previously undescribed interactions between ILC1 and their microenvironment, which suggest that they may exacerbate fibrosis and tumour growth when enriched in inflamed patient tissues.

Extracellular Matrix Mechanical Properties and Regulation of the Intestinal Stem Cells: When Mechanics Control Fate

Intestinal stem cells (ISC) are crucial players in colon epithelium physiology. The accurate control of their auto-renewal, proliferation and differentiation capacities provides a constant flow of regeneration, maintaining the epithelial intestinal barrier integrity. Under stress conditions, colon epithelium homeostasis in disrupted, evolving towards pathologies such as inflammatory bowel diseases or colorectal cancer. A specific environment, namely the ISC niche constituted by the surrounding mesenchymal stem cells, the factors they secrete and the extracellular matrix (ECM), tightly controls ISC homeostasis. Colon ECM exerts physical constraint on the enclosed stem cells through peculiar topography, stiffness and deformability. However, little is known on the molecular and cellular events involved in ECM regulation of the ISC phenotype and fate. To address this question, combining accurately reproduced colon ECM mechanical parameters to primary ISC cultures such as organoids is an appropriated approach. Here, we review colon ECM physical properties at physiological and pathological states and their bioengineered in vitro reproduction applications to ISC studies.

Development of an Improved 3D in vitro Intestinal Model to Perform Permeability Studies of Paracellular Compounds

The small intestine is the primary site of drug absorption following oral administration, making paramount the proper monitoring of the absorption process. In vitro tools to predict intestinal absorption are particularly important in preclinical drug development since they are less laborious and cost-intensive and raise less ethical considerations compared to in vivo studies. The Caco-2 model is considered the gold standard of in vitro intestinal models regarding the prediction of absorption of orally delivered compounds. However, this model presents several drawbacks, such as the expression of tighter tight junctions, not being suitable to perform permeability of paracellular compounds. Besides, cells are representative of only one intestinal cell type, without considering the role of non-absorptive cells on the absorption pathway of drugs. In the present study, we developed a new three-dimensional (3D) intestinal model that aims to bridge the gap between in vitro tools and animal studies. Our 3D model comprises a collagen layer with human intestinal fibroblasts (HIFs) embedded, mimicking the intestinal lamina propria and providing 3D support for the epithelium, composed of Caco-2 cells and mucus-producing HT29-MTX cells, creating a model that can better resemble, both in terms of composition and regarding the outcomes of drug permeability when testing paracellular compounds, the human small intestine. The optimization of the collagen layer with HIFs was performed, testing different collagen concentrations and HIF seeding densities in order to avoid collagen contraction before day 14, maintaining HIF metabolically active inside the collagen disks during time in culture. HIF morphology and extracellular matrix (ECM) deposition were assessed, confirming that fibroblasts presented a normal and healthy elongated shape and secreted fibronectin and laminin, remodeling the collagen matrix. Regarding the epithelial layer, transepithelial electrical resistance (TEER) values decreased when cells were in the 3D configuration, comparing with the 2D analogs (Caco-2 and coculture of Caco-2+HT29-MTX models), becoming more similar with in vivo values. The permeability assay with fluorescein isothiocyanate (FITC)–Dextran 4 kDa showed that absorption in the 3D models is significantly higher than that in the 2D models, confirming the importance of using a more biorelevant model when testing the paracellular permeability of compounds.

Human Microphysiological Models of Intestinal Tissue and Gut Microbiome

The gastrointestinal (GI) tract is a complex system responsible for nutrient absorption, digestion, secretion, and elimination of waste products that also hosts immune surveillance, the intestinal microbiome, and interfaces with the nervous system. Traditional in vitro systems cannot harness the architectural and functional complexity of the GI tract. Recent advances in organoid engineering, microfluidic organs-on-a-chip technology, and microfabrication allows us to create better in vitro models of human organs/tissues. These micro-physiological systems could integrate the numerous cell types involved in GI development and physiology, including intestinal epithelium, endothelium (vascular), nerve cells, immune cells, and their interplay/cooperativity with the microbiome. In this review, we report recent progress in developing micro-physiological models of the GI systems. We also discuss how these models could be used to study normal intestinal physiology such as nutrient absorption, digestion, and secretion as well as GI infection, inflammation, cancer, and metabolism.

The myofibroblast at a glance

In 1971, Gabbiani and co-workers discovered and characterized the “modification of fibroblasts into cells which are capable of an active spasm” (contraction) in rat wound granulation tissue and, accordingly, named these cells ‘myofibroblasts’. Now, myofibroblasts are not only recognized for their physiological role in tissue repair but also as cells that are key in promoting the development of fibrosis in all organs. In this Cell Science at a Glance and the accompanying poster, we provide an overview of the current understanding of central aspects of myofibroblast biology, such as their definition, activation from different precursors, the involved signaling pathways and most widely used models to study their function. Myofibroblasts will be placed into context with their extracellular matrix and with other cell types communicating in the fibrotic environment. Furthermore, the challenges and strategies to target myofibroblasts in anti-fibrotic therapies are summarized to emphasize their crucial role in disease progression.

Evaluation of human primary intestinal monolayers for drug metabolizing capabilities

BACKGROUND

The intestinal epithelium is a major site of drug metabolism in the human body, possessing enterocytes that house brush border enzymes and phase I and II drug metabolizing enzymes (DMEs). The enterocytes are supported by a porous extracellular matrix (ECM) that enables proper cell adhesion and function of brush border enzymes, such as alkaline phosphatase (ALP) and alanyl aminopeptidase (AAP), phase I DMEs that convert a parent drug to a more polar metabolite by introducing or unmasking a functional group, and phase II DMEs that form a covalent conjugate between a functional group on the parent compound or sequential metabolism of phase I metabolite. In our effort to develop an in vitro intestinal epithelium model, we investigate the impact of two previously described simple and customizable scaffolding systems, a gradient cross-linked scaffold and a conventional scaffold, on the ability of intestinal epithelial cells to produce drug metabolizing proteins as well as to metabolize exogenously added compounds. While the scaffolding systems possess a range of differences, they are most distinguished by their stiffness with the gradient cross-linked scaffold possessing a stiffness similar to that found in the in vivo intestine, while the conventional scaffold possesses a stiffness several orders of magnitude greater than that found in vivo.

RESULTS

The monolayers on the gradient cross-linked scaffold expressed CYP3A4, UGTs 2B17, 1A1 and 1A10, and CES2 proteins at a level similar to that in fresh crypts/villi. The monolayers on the conventional scaffold expressed similar levels of CYP3A4 and UGTs 1A1 and 1A10 DMEs to that found in fresh crypts/villi but significantly decreased expression of UGT2B17 and CES2 proteins. The activity of CYP3A4 and UGTs 1A1 and 1A10 was inducible in cells on the gradient cross-linked scaffold when the cells were treated with known inducers, whereas the CYP3A4 and UGT activities were not inducible in cells grown on the conventional scaffold. Both monolayers demonstrate esterase activity but the activity measured in cells on the conventional scaffold could not be inhibited with a known CES2 inhibitor. Both monolayer culture systems displayed similar ALP and AAP brush border enzyme activity. When cells on the conventional scaffold were incubated with a yes-associated protein (YAP) inhibitor, CYP3A4 activity was greatly enhanced suggesting that mechano-transduction signaling can modulate drug metabolizing enzymes.

CONCLUSIONS

The use of a cross-linked hydrogel scaffold for expansion and differentiation of primary human intestinal stem cells dramatically impacts the induction of CYP3A4 and maintenance of UGT and CES drug metabolizing enzymes in vitro making this a superior substrate for enterocyte culture in DME studies. This work highlights the influence of mechanical properties of the culture substrate on protein expression and the activity of drug metabolizing enzymes as a critical factor in developing accurate assay protocols for pharmacokinetic studies using primary intestinal cells.

GRAPHICAL ABSTRACT

Advances and Current Challenges in Intestinal in vitro Model Engineering: A Digest

The physiological environment of the intestine is characterized by its variegated composition, numerous functions and unique dynamic conditions, making it challenging to recreate the organ in vitro. This review outlines the requirements for engineering physiologically relevant intestinal in vitro models, mainly focusing on the importance of the mechano-structural cues that are often neglected in classic cell culture systems. More precisely: the topography, motility and flow present in the intestinal epithelium. After defining quantitative descriptors for these features, we describe the current state of the art, citing relevant approaches used to address one (or more) of the elements in question, pursuing a progressive conceptual construction of an "ideal" biomimetic intestinal model. The review concludes with a critical assessment of the currently available methods to summarize the important features of the intestinal tissue in the light of their different applications.

Molecular transport through primary human small intestinal monolayers by culture on a collagen scaffold with a gradient of chemical cross-linking

BACKGROUND

The luminal surface of the small intestine is composed of a monolayer of cells overlying a lamina propria comprised of extracellular matrix (ECM) proteins. The ECM provides a porous substrate critical for nutrient exchange and cellular adhesion. The enterocytes within the epithelial monolayer possess proteins such as transporters, carriers, pumps and channels that participate in the movement of drugs, metabolites, ions and amino acids and whose function can be regulated or altered by the properties of the ECM. Here, we characterized expression and function of proteins involved in transport across the human small intestinal epithelium grown on two different culture platforms. One strategy employs a conventional scaffolding method comprised of a thin ECM film overlaying a porous membrane while the other utilizes a thick ECM hydrogel placed on a porous membrane. The thick hydrogel possesses a gradient of chemical cross-linking along its length to provide a softer substrate than that of the ECM film-coated membrane while maintaining mechanical stability.

RESULTS

The monolayers on both platforms possessed goblet cells and abundant enterocytes and were impermeable to Lucifer yellow and fluorescein-dextran (70 kD) indicating high barrier integrity. Multiple transporter proteins were present in both primary-cell culture formats at levels similar to those present in freshly isolated crypts/villi; however, expression of breast cancer resistance protein (BCRP) and multidrug resistance protein 2 (MRP2) in the monolayers on the conventional scaffold was substantially less than that on the gradient cross-linked scaffold and freshly isolated crypts/villi. Monolayers on the conventional scaffold failed to transport the BCRP substrate prazosin while cells on the gradient cross-linked scaffold successfully transported this drug to better mimic the properties of in vivo small intestine.

CONCLUSIONS

The results of this comparison highlight the need to create in vitro intestinal transport platforms whose characteristics mimic the in vivo lamina propria in order to accurately recapitulate epithelial function.

GRAPHICAL ABSTRACT

The aqueous extract of Phellinus igniarius (SH) ameliorates dextran sodium sulfate-induced colitis in C57BL/6 mice

Phellinus igniarius, which is called Sanghuang in Chinese, is a fungal herb widely used in Traditional Chinese Medicine to treat stomachache, inflammation and tumors. Recent studies have demonstrated the antitumor, anti-diabetic, anti-inflammatory and immunity-modulating activities of P. igniarius. In the present study, we investigated that ameliorating effect of the aqueous extract of P. igniarius fruiting body (SH) on dextran sodium sulfate (DSS)-induced colitis in C57BL/6 mice. Treatment with SH (250 and 400 mg/kg) for 8 weeks effectively alleviated the pathological indicators of colitis such as bodyweight reduction, disease activity index score, shortening of colon length and abnormal colon histology. The plasma levels of lipopolysaccharide (LPS) and inflammatory factors such as interleukin-6 (IL-6), IL-1β and tumor necrosis factor (TNF)-α were all significantly reduced. Supplementation of SH (10 mg/L) also inhibited LPS-elicited IL-1β production by RAW264.7 macrophages. Real-time PCR and western blot showed that treatment with SH significantly inhibited the phosphorylation of nuclear factor kappa B inhibitor alpha (IκBα) and decreased the expression of IL-6/IL-1β-maturation genes such as apoptosis-associated speck-like protein (ASC3) and caspase-1 in the colon of DSS-induced colitis mice. These results suggest that SH is adequate for the treatment of colitis. Inhibiting the expression and release of inflammatory factors may participate in the colitis-ameliorating effect of SH.