Functional evaluation of the grafted wall with porcine-derived small intestinal submucosa (SIS) to a stomach defect in rats

Stomach engineering: region-specific characterization of the decellularized porcine stomach

PURPOSE

Patients affected by microgastria, severe gastroesophageal reflux, or those who have undergone subtotal gastrectomy, have commonly described reporting dumping syndromes or other symptoms that seriously impair the quality of their life. Gastric tissue engineering may offer an alternative approach to treating these pathologies. Decellularization protocols have great potential to generate novel biomaterials for large gastric defect repair. There is an urgency to define more reliable protocols to foster clinical applications of tissue-engineered decellularized gastric grafts.

METHODS

In this work, we investigated the biochemical and mechanical properties of decellularized porcine stomach tissue compared to its native counterpart. Histological and immunofluorescence analyses were performed to screen the quality of decellularized samples. Quantitative analysis was also performed to assess extracellular matrix composition. At last, we investigated the mechanical properties and cytocompatibility of the decellularized tissue compared to the native.

RESULTS

The optimized decellularization protocol produced efficient cell removal, highlighted in the absence of native cellular nuclei. Decellularized scaffolds preserved collagen and elastin contents, with partial loss of sulfated glycosaminoglycans. Decellularized gastric tissue revealed increased elastic modulus and strain at break during mechanical tensile tests, while ultimate tensile strength was significantly reduced. HepG2 cells were seeded on the ECM, revealing matrix cytocompatibility and the ability to support cell proliferation.

CONCLUSION

Our work reports the successful generation of acellular porcine gastric tissue able to support cell viability and proliferation of human cells.

Tissue Engineering for Gastrointestinal and Genitourinary Tracts

The gastrointestinal and genitourinary tracts share several similarities. Primarily, these tissues are composed of hollow structures lined by an epithelium through which materials need to flow with the help of peristalsis brought by muscle contraction. In the case of the gastrointestinal tract, solid or liquid food must circulate to be digested and absorbed and the waste products eliminated. In the case of the urinary tract, the urine produced by the kidneys must flow to the bladder, where it is stored until its elimination from the body. Finally, in the case of the vagina, it must allow the evacuation of blood during menstruation, accommodate the male sexual organ during coitus, and is the natural way to birth a child. The present review describes the anatomy, pathologies, and treatments of such organs, emphasizing tissue engineering strategies.

Regenerative medicine for the upper gastrointestinal tract

The main surgical strategy for gastrointestinal tract malignancy is en bloc resection, which consists of not only resection of the involved organs but also simultaneous resection of the surrounding or adjacent mesenteries that contain lymph vessels and nodes. After resection of the diseased organs, the defect of the gastrointestinal conduit is replaced with organs located downstream, such as the stomach and jejunum. However, esophageal and gastric reconstruction using these natural substitutes is associated with a diminished quality of life due to the loss of the reserve function, damage to the antireflux barrier, and dumping syndrome. Thus, replacement of the deficit after resection with the patient's own regenerated tissue to compensate for the lost function and tissue using regenerative medicine will be an ideal treatment. Many researchers have been trying to construct artificial organs through tissue engineering techniques; however, none have yet succeeded in growing a whole organ because of the complicated functions these organs perform, such as the processing and absorption of nutrients. While exciting results have been reported with regard to tissue engineering techniques concerning the upper gastrointestinal tract, such as the esophagus and stomach, most of these achievements have been observed in animal models, and few successful approaches in the clinical setting have been reported for the replacement of mucosal defects. We review the recent progress in regenerative medicine in relation to the upper gastrointestinal tract, such as the esophagus and stomach. We also focus on the functional capacity of regenerated tissue and its role as a culture system to recapitulate the mechanisms underlying infectious disease. With the emergence of technology such as the fabrication of decellularized constructs, organoids and cell sheet medicine, collaboration between gastrointestinal surgery and regenerative medicine is expected to help establish novel therapeutic modalities in the future.

Extracellular Matrix Bioscaffolds for Building Gastrointestinal Tissue

Regenerative medicine is a rapidly advancing field that uses principles of tissue engineering, developmental biology, stem cell biology, immunology, and bioengineering to reconstruct diseased or damaged tissues. Biologic scaffolds composed of extracellular matrix have shown great promise as an inductive substrate to facilitate the constructive remodeling of gastrointestinal (GI) tissue damaged by neoplasia, inflammatory bowel disease, and congenital or acquired defects. The present review summarizes the preparation and use of extracellular matrix scaffolds for bioengineering of the GI tract, identifies significant advances made in regenerative medicine for the reconstruction of functional GI tissue, and describes an emerging therapeutic approach.

The extracellular matrix of the gastrointestinal tract: a regenerative medicine platform

The synthesis and secretion of components that constitute the extracellular matrix (ECM) by resident cell types occur at the earliest stages of embryonic development, and continue throughout life in both healthy and diseased physiological states. The ECM consists of a complex mixture of insoluble and soluble functional components that are arranged in a tissue-specific 3D ultrastructure, and it regulates numerous biological processes, including angiogenesis, innervation and stem cell differentiation. Owing to its composition and influence on embryonic development, as well as cellular and organ homeostasis, the ECM is an ideal therapeutic substrate for the repair of damaged or diseased tissues. Biologic scaffold materials that are composed of ECM have been used in various surgical and tissue-engineering applications. The gastrointestinal (GI) tract presents distinct challenges, such as diverse pH conditions and the requirement for motility and nutrient absorption. Despite these challenges, the use of homologous and heterologous ECM bioscaffolds for the focal or segmental reconstruction and regeneration of GI tissue has shown promise in early preclinical and clinical studies. This Review discusses the importance of tissue-specific ECM bioscaffolds and highlights the major advances that have been made in regenerative medicine strategies for the reconstruction of functional GI tissues.

Extensive regeneration of the stomach using bioabsorbable polymer sheets

BACKGROUND

The growing prevalence of endoscopic surgery in recent years has led to the minimization of postoperative scarring. However, this procedure does not allow for the regeneration of the resected digestive tract, which compromises the postoperative maintenance of digestive function. In this preliminary study, we developed an artificial gastric wall (AGW) using bioabsorbable polymer (BAP), and evaluated the ability of this BAP patch to repair and regenerate a widely defective gastric wall in an animal model.

METHODS

Pigs were laparotomized under general anesthesia. An 8 × 8-cm, round portion of the anterior gastric wall was excised and replaced by an AGW. The AGW was composed of a copolymer comprising 50% lactic acid and 50% caprolactone. The animals were relaparotomized 4, 8, or 12 weeks after implantation, after which they underwent resection of the entire stomach for gross and histologic evaluation of the graft sites.

RESULTS

All recipient pigs survived until killing. By 4-8 weeks, the graft site revealed progressively fewer mucosal defect after each day. Moreover, the grafted area was indistinguishable from the native stomach 12 weeks after AGW implantation. The structures of the regenerated mucous membrane and muscle layers were identical to those of the native stomach. Furthermore, proton pumps were found in the regenerated tissue.

CONCLUSION

The BAP sheets helped to restore extensive gastric defects without causing any deformation. The use of BAP sheets may become a new therapeutic method that prevents alterations of gastric volume after extensive gastrectomy for stomach cancer and other diseases.

Bio-sheet graft therapy for artificial gastric ulcer after endoscopic submucosal dissection: an animal feasibility study

BACKGROUND

Various bio-sheet grafts have been attempted either to accelerate healing of artificial ulcers or to prevent adverse events after endoscopic submucosal dissection (ESD), but neither prospective nor mechanistic studies were available.

OBJECTIVE

To evaluate the substantial effect of a bio-sheet graft on artificial ulcer healing and its feasibility as an endoscopic treatment modality.

DESIGN

Preclinical, in vivo animal experiment and proof-of-concept study.

SETTING

Animal laboratory.

SUBJECTS

Three mini-pigs, Sus scrofa, mean age 14 months.

INTERVENTION

Multiple ulcers sized 2.5 cm in diameter were generated by ESD in 3 mini-pigs and were assigned randomly into the following 3 groups; control group, bio-sheet group, or combination (bio-sheet plus drug) group. Bio-sheet grafts or bio-sheet plus drug combinations were applied on the artificial ulcers immediately after the ESD.

MAIN OUTCOME MEASUREMENTS

Feasibility and efficacy of endoscopic bio-sheet graft therapy for the management of artificial ulcers and the evaluation of healing conditions based on histology changes in the remaining gastric bed tissues harvested from the stomachs.

RESULTS

Thirty-three ESD specimens were obtained. On an image analysis of the ratio of healed area in the remaining gastric bed tissue compared with the matched dissected gastric mucosa, the control group showed the most significant improvement in healing activity among the 3 groups (P < .05), whereas the severity of inflammation in the remaining ulcer tissue was significantly attenuated in bio-sheet and combination groups (P < .05).

LIMITATIONS

Animal model.

CONCLUSION

Although the bio-sheet grafts provided physical protection from gastric acid attack as reflected in the attenuated inflammation on the ulcer beds, unexpected delayed ulcer healing was noted in the bio-sheet graft group because of its physical hindrance of the healing process.

Proposal of intestinal tissue engineering combined with Bianchi's procedure

AIM

The aim of this study is to examine the feasibility of the small intestinal submucosa (SIS) when the longitudinal staples during Bianchi's procedure are replaced with SIS graft.

METHODS

The mesentery of the bowel was separated based on the bifurcated vessels in five beagles. A 2×7-cm longitudinal half of the bowel was excised and the defect was repaired using SIS with similar blood supply in Bianchi's operation. Six months later, intestinal motility in the SIS-grafted area was recorded. Tissue preparations were obtained from the reorganized area. An organ bath technique with electrical field stimulation was applied. Both the native small intestine and grafted area were morphologically investigated using immunohistochemistry.

MAIN RESULTS

All dogs survived and thrived with no anastomotic leakage. Isoperistaltic migrating contractility during fasting was observed through the grafted segment including the reorganized area. The SIS-reorganized tissue contracted in response to an acetylcholine agonist and electrical field stimulation. The mucosa was covered with normal epithelium. Reorganization of neural and smooth muscle cells was observed.

CONCLUSIONS

SIS has the potential for use as a scaffold that promotes the formation of a physical and physiological neointestine. Our present proposal approaches a novel surgical treatment in patients with short bowel syndrome.

The use of murine-derived fundic organoids in studies of gastric physiology

KEY POINTS

An in vitro approach to study gastric development is primary mouse-derived epithelium cultured as three-dimensional spheroids known as organoids. We have devised two unique gastric fundic-derived organoid cultures: model 1 for the expansion of gastric fundic stem cells, and model 2 for the maintenance of mature cell lineages. Organoids maintained in co-culture with immortalized stomach mesenchymal cells express robust numbers of surface pit, mucous neck, chief, endocrine and parietal cells. Histamine induced a significant decrease in intraluminal pH that was reversed by omeprazole in fundic organoids and indicated functional activity and regulation of parietal cells. Localized photodamage resulted in rapid cell exfoliation coincident with migration of neighbouring cells to the damaged area, sustaining epithelial continuity. We report the use of these models for studies of epithelial cell biology and cell damage and repair.

ABSTRACT

Studies of gastric function and disease have been limited by the lack of extended primary cultures of the epithelium. An in vitro approach to study gastric development is primary mouse-derived antral epithelium cultured as three-dimensional spheroids known as organoids. There have been no reports on the use of organoids for gastric function. We have devised two unique gastric fundic-derived organoid cultures: model 1 for the expansion of gastric fundic stem cells, and model 2 for the maintenance of mature cell lineages. Both models were generated from single glands dissociated from whole fundic tissue and grown in basement membrane matrix (Matrigel) and organoid growth medium. Model 1 enriches for a stem cell-like niche via simple passage of the organoids. Maintained in Matrigel and growth medium, proliferating organoids expressed high levels of stem cell markers CD44 and Lgr5. Model 2 is a system of gastric organoids co-cultured with immortalized stomach mesenchymal cells (ISMCs). Organoids maintained in co-culture with ISMCs express robust numbers of surface pit, mucous neck, chief, endocrine and parietal cells. Histamine induced a significant decrease in intraluminal pH that was reversed by omeprazole in fundic organoids and indicated functional activity and regulation of parietal cells. Localized photodamage resulted in rapid cell exfoliation coincident with migration of neighbouring cells to the damaged area, sustaining epithelial continuity. Thus, we report the use of these models for studies of epithelial cell biology and cell damage and repair.

Repair of gastric defects with an equine pericardial patch

PURPOSES

The objective of this study was to test the efficacy of an equine pericardial patch for repairing full-thickness defects of the stomach wall.

METHODS

Circular defects, 1.5 cm in diameter, were created on the anterior wall of the stomach of 12 female New Zealand rabbits. The defects were repaired by an equine pericardial patch. After euthanasia at different time intervals (3 days to 8 weeks) a macroscopic evaluation of the abdominal cavity (including adhesion scoring), mechanical testing and a histological examination of the stomach were performed.

RESULTS

The animals survived the surgical procedure and underwent an uneventful recovery until euthanasia. None of the patches failed. Adhesions were observed in all animals and were significant in 3/12 animals. Bursting pressure testing indicated that the repair was durable and that adequate strength to prevent patch failure was achieved by the second week. A histological examination showed gradual narrowing of the perforation site by mucosal and limited muscular regeneration.

CONCLUSIONS

The equine pericardial patch was successfully used to repair a gastric defect in our experimental model, and it seems that it could have potential as a material suitable for further research concerning the repair of upper gastrointestinal defects.

Influence of mesenchymal stem cells on stomach tissue engineering using small intestinal submucosa

Small intestinal submucosa (SIS) is a biodegradable collagen-rich matrix containing functional growth factors. We have previously reported encouraging outcomes for regeneration of an artificial defect in the rodent stomach using SIS grafts, although the muscular layer was diminutive. In this study, we investigated the feasibility of SIS in conjunction with mesenchymal stem cells (MSCs) for regeneration of the gastrointestinal tract. MSCs from the bone marrow of green fluorescence protein (GFP)-transgenic Sprague-Dawley (SD) rats were isolated and expanded ex vivo. A 1 cm whole-layer stomach defect in SD rats was repaired using: a plain SIS graft without MSCs (group 1, control); a plain SIS graft followed by intravenous injection of MSCs (group 2); a SIS graft co-cultured with MSCs (group 3); or a SIS sandwich containing an MSC sheet (group 4). Pharmacological, electrophysiological and immunohistochemical examination was performed to evaluate the regenerated stomach tissue. Contractility in response to a muscarinic receptor agonist, a nitric oxide precursor or electrical field stimulation was observed in all groups. SIS grafts seeded with MSCs (groups 3 and 4) appeared to support improved regeneration compared with SIS grafts not seeded with MSCs (groups 1 and 2), by enabling the development of well-structured smooth muscle layers of significantly increased length. GFP expression was detected in the regenerated interstitial tissue, with fibroblast-like cells in the seeded-SIS groups. SIS potently induced pharmacological and electrophysiological regeneration of the digestive tract, and seeded MSCs provided an enriched environment that supported tissue regeneration by the SIS graft in the engineered stomach.

Extracellular matrices for gastrointestinal surgery: Ex vivo testing and current applications

AIM: To assess the effects of bile and pancreatic juice on structural and mechanical resistance of extracellular matrices (ECMs) in vitro.

METHODS: Small-intestinal submucosa (SIS), porcine dermal matrix (PDM), porcine pericardial matrix (PPM) and bovine pericardial matrix (BPM) were incubated in human bile and pancreatic juice in vitro. ECMs were examined by macroscopic observation, scanning electron microscopy (SEM) and testing of mechanical resistance.

RESULTS: PDM dissolved within 4 d after exposure to bile or pancreatic juice. SIS, PPM and PDM retained their integrity for > 60 d when incubated in either digestive juice. The effect of bile was found to be far more detrimental to mechanical stability than pancreatic juice in all tested materials. In SIS, the loss of mechanical stability after incubation in either of the digestive secretions was less distinct than in PPM and BPM [mFmax 4.01/14.27 N (SIS) vs 2.08/5.23 N (PPM) vs 1.48/7.89 N (BPM)]. In SIS, the extent of structural damage revealed by SEM was more evident in bile than in pancreatic juice. In PPM and BPM, structural damage was comparable in both media.

CONCLUSION: PDM is less suitable for support of gastrointestinal healing. Besides SIS, PPM and BPM should also be evaluated experimentally for gastrointestinal indications.

Evidence of innervation following extracellular matrix scaffold-mediated remodelling of muscular tissues

Naturally occurring porcine-derived extracellular matrix (ECM) has successfully been used as a biological scaffold material for site-specific reconstruction of a wide variety of tissues. The site-specific remodelling process includes rapid degradation of the scaffold, with concomitant recruitment of mononuclear, endothelial and bone marrow-derived cells, and can lead to the formation of functional skeletal and smooth muscle tissue. However, the temporal and spatial patterns of innervation of the remodelling scaffold material in muscular tissues are not well understood. A retrospective study was conducted to investigate the presence of nervous tissue in a rat model of abdominal wall reconstruction and a canine model of oesophageal reconstruction in which ECM scaffolds were used as inductive scaffolds. Evidence of mature nerve, immature nerve and Schwann cells was found within the remodelled ECM at 28 days in the rat body wall model, and at 91 days post surgery in a canine model of oesophageal repair. Additionally, a microscopic and morphological study that investigated the response of primary cultured neurons seeded upon an ECM scaffold showed that neuronal survival and outgrowth were supported by the ECM substrate. Finally, matricryptic peptides resulting from rapid degradation of the ECM scaffold induced migration of terminal Schwann cells in a concentration-dependent fashion in vitro. The findings of this study suggest that the reconstruction of tissues in which innervation is an important functional component is possible with the use of biological scaffolds composed of extracellular matrix.