Editor-in-Chief articles of choice and comments at the year-end of 2023

As the Editor-in-Chief of World Journal of Gastroenterology, every week prior to a new issue's online publication, I perform a careful review of all encompassed articles, including the title, clinical and/or research importance, originality, novelty, and ratings by the peer reviewers. Based on this review, I select the papers of choice and suggest pertinent changes (e.g., in the title) to the Company Editors responsible for publication. This process, while time-consuming, is very important for assuring the quality of publications and highlighting important articles that Readers may revisit.

Endothelial cells and blood vessels are major targets for COVID-19-induced tissue injury and spreading to various organs

The coronavirus disease 2019 (COVID-19) infected so far over 250 million people and caused the death of over 5 million worldwide. Aging, diabetes, and cardiovascular diseases, conditions with preexisting impaired endothelial functions predispose to COVID-19. While respiratory epithelium is the main route of virus entry, the endothelial cells (ECs) lining pulmonary blood vessels are also an integral part of lung injury in COVID-19 patients. COVID-19 not only affects the lungs and respiratory system but also gastrointestinal (GI) tract, liver, pancreas, kidneys, heart, brain, and skin. Blood vessels are likely conduits for the virus dissemination to these distant organs. Importantly, ECs are also critical for vascular regeneration during injury/lesions healing and restoration of vascular network. The World Journal of Gastroenterology has published in last two years over 67 outstanding papers on COVID-19 infection with a focus on the GI tract, liver, pancreas, etc., however, the role of the endothelial and vascular components as major targets for COVID-19-induced tissue injury, spreading to various organs, and injury healing have not been sufficiently emphasized. In the present article, we focus on these subjects and on current treatments including the most recent oral drugs molnupiravir and paxlovid that show a dramatic, significant efficacy in controlling severe COVID-19 infection.

Melatonin ameliorates aging-related impaired angiogenesis in gastric endothelial cells via local actions on mitochondria and VEGF-survivin signaling

Tissue injury healing is impaired in aging, and this impairment is caused in part by reduced angiogenesis. Melatonin, a neuroendocrine hormone that regulates sleep and circadian rhythm, is also produced in the gastrointestinal tract. The expression of melatonin receptors MT1 and MT2 in gastric endothelial cells and their roles in aging-related impairment of gastric angiogenesis have not been examined. We hypothesized that MT1 and MT2 expression is reduced in gastric endothelial cells of aging rats and that melatonin treatment can upregulate their expression and improve angiogenesis. We examined the expression of MT1 and MT2 in gastric endothelial cells (GECs) isolated from young and aging rats. We also examined the effects of melatonin treatment on angiogenesis, GEC mitochondrial function, expression of vascular endothelial growth factor (VEGF), its signaling receptor (VEGFR-2), and the inhibitor of apoptosis protein, survivin. Young and aging GECs expressed MT1 (in the cytoplasm and mitochondria) and MT2 (in nucleus and mitochondria). In aging GECs, MT1 and MT2 levels, in vitro angiogenesis, and mitochondrial membrane potential were significantly reduced (by 1.5-fold, 1.9-fold, 3.1-fold, and 1.63-fold, respectively) compared with young GECs. Melatonin treatment of aging GECs significantly increased MT1 and MT2 expression compared with the controls, induced nuclear translocation of MT1, and significantly ameliorated the aging-related impairment of angiogenesis and mitochondrial function. Aging GECs have significantly reduced MT1 and MT2 expression, angiogenesis, and mitochondrial membrane potential compared with young GECs. Treatment of aging GECs with melatonin increases expression of VEGF receptor and survivin and ameliorates aging-related impaired angiogenesis and mitochondrial function.NEW & NOTEWORTHY This study showed reduced expression of melatonin receptors MT1 and MT2, angiogenesis, and mitochondrial function in gastric endothelial cells (GECs) isolated from aging rats. Treatment of aging GECs with melatonin increases expression of VEGF receptor and survivin and ameliorates aging-related impaired angiogenesis and mitochondrial function. These studies provide new insight into the mechanisms of the aging-related impairment of angiogenesis and delayed tissue injury healing and provide a rationale for melatonin treatment to reverse these abnormalities.

The Critical Role of Growth Factors in Gastric Ulcer Healing: The Cellular and Molecular Mechanisms and Potential Clinical Implications

In this article we review the cellular and molecular mechanisms of gastric ulcer healing. A gastric ulcer (GU) is a deep defect in the gastric wall penetrating through the entire mucosa and the muscularis mucosae. GU healing is a regeneration process that encompasses cell dedifferentiation, proliferation, migration, re-epithelialization, formation of granulation tissue, angiogenesis, vasculogenesis, interactions between various cells and the matrix, and tissue remodeling, all resulting in scar formation. All these events are controlled by cytokines and growth factors (e.g., EGF, TGFα, IGF-1, HGF, bFGF, TGFβ, NGF, VEGF, angiopoietins) and transcription factors activated by tissue injury. These growth factors bind to their receptors and trigger cell proliferation, migration, and survival pathways through Ras, MAPK, PI3K/Akt, PLC-γ, and Rho/Rac/actin signaling. The triggers for the activation of these growth factors are tissue injury and hypoxia. EGF, its receptor, IGF-1, HGF, and COX-2 are important for epithelial cell proliferation, migration, re-epithelialization, and gastric gland reconstruction. VEGF, angiopoietins, bFGF, and NGF are crucial for blood vessel regeneration in GU scars. The serum response factor (SRF) is essential for VEGF-induced angiogenesis, re-epithelialization, and blood vessel and muscle restoration. Local therapy with cDNA of human recombinant VEGF165 in combination with angiopoietin1, or with the NGF protein, dramatically accelerates GU healing and improves the quality of mucosal restoration within ulcer scars. The future directions for accelerating and improving healing include local gene and protein therapies with growth factors, their combinations, and the use of stem cells and tissue engineering.

NSAID-induced injury of gastric epithelial cells is reversible: roles of mitochondria, AMP kinase, NGF, and PGE2

Nonsteroidal anti-inflammatory drugs (NSAIDs) such as diclofenac (DFN) and indomethacin (INDO) are extensively used worldwide. Their main side effects are injury of the gastrointestinal tract, including erosions, ulcers, and bleeding. Since gastric epithelial cells (GEPCs) are crucial for mucosal defense and are the major target of injury, we examined the extent to which DFN- and INDO-induced GEPC injury can be reversed by nerve growth factor (NGF), 16,16 dimethyl prostaglandin E2 (dmPGE2), and 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR), the pharmacological activator of the metabolic sensor AMP kinase (AMPK). Cultured normal rat gastric mucosal epithelial (RGM1) cells were treated with PBS (control), NGF, dmPGE2, AICAR, and/or NSAID (DFN or INDO) for 1-4 h. We examined cell injury by confocal microscopy, cell death/survival using calcein AM, mitochondrial membrane potential using MitoTracker, and phosphorylation of AMPK by Western blotting. DFN and INDO treatment of RGM1 cells for 2 h decreased mitochondrial membrane potential and cell viability. NGF posttreatment (initiated 1 or 2 h after DFN or INDO) reversed the dissipation of mitochondrial membrane potential and cell injury caused by DFN and INDO and increased cell viability versus cells treated for 4 h with NSAID alone. Pretreatment with dmPGE2 and AICAR significantly protected these cells from DFN- and INDO-induced injury, whereas dmPGE2 and AICAR posttreatment (initiated 1 h after NSAID treatment) reversed cell injury and significantly increased cell viability and rescued the cells from NSAID-induced mitochondrial membrane potential reduction. DFN and INDO induce extensive mitochondrial injury and GEPC death, which can be significantly reversed by NGF, dmPGE2, and AICAR.NEW & NOTEWORTHY This study demonstrated that mitochondria are key targets of diclofenac- and indomethacin-induced injury of gastric epithelial cells and that diclofenac and indomethacin injury can be prevented and, importantly, also reversed by treatment with nerve growth factor, 16,16 dimethyl prostaglandin E2, and 5-aminoimidazole-4-carboxamide ribonucleotide.

Mitochondria in gastric epithelial cells are the key targets for NSAIDs-induced injury and NGF cytoprotection

Gastric epithelial cells are important components of mucosal protection and targets of nonsteroidal anti-inflammatory drugs (NSAIDs)-induced injury. Diclofenac (DFN) is one of the most widely used NSAIDs; however, even its short-term use can induce gastric erosions and ulcers. Nerve growth factor (NGF) has been reported to act not only on neuronal cells but also on endothelial cells; however, its action on gastric epithelial cells is unknown. This study was aimed to determine, whether NGF can protect gastric epithelial cells against DFN-induced injury, and to determine the underlying molecular mechanisms with a focus on mitochondria, survivin, and insulin-like growth factor 1 (IGF-1). Cultured normal rat gastric mucosal epithelial cells 1 (RGM1) were treated with phosphate-buffered saline (PBS; control), NGF (100 ng/mL) and/or DFN (0.25-1.00 mM) for 4 hours. We examined: (1) cell injury by confocal microscopy; (2) cell death/survival using Calcein AM live cell tracking dye; (3) mitochondrial structure and membrane potential function using MitoTracker in live cells; and (4) expression of NGF, its receptor - tropomyosin receptor kinase A (TrkA), survivin and IGF-1 by immunostaining. DFN treatment of RGM1 cells for 4 hours caused extensive cell injury, mitochondrial disintegration, reduced cell viability (from 94 ± 3% in controls to 14 ± 4% in 0.5 mM DFN-treated cells; P < 0.001), and expression of survivin and IGF-1. NGF treatment significantly increased survivin and IGF-1 expression by 41% and 75%, respectively versus PBS controls. Pretreatment with NGF before DFN treatment reduced mitochondrial damage and cell death by 73% and 82%, respectively versus treatment with DFN alone (all P < 0.001). This study also showed the presence of high-affinity TrkA receptors in the plasma membrane and mitochondria of RGM1 cells indicating novel actions of NGF.

Increased susceptibility of aging gastric mucosa to injury and delayed healing: Clinical implications

In this editorial we comment on the article by Fukushi K et al published in the recent issue of the World Journal of Gastroenterology 2018; 24(34): 3908-3918. We focus specifically on the mechanisms of the anti-thrombotic action of aspirin, gastric mucosal injury and aging-related increased susceptibility of gastric mucosa to injury. Aspirin is widely used not only for the management of acute and chronic pain and arthritis, but also importantly for the primary and secondary prevention of cardiovascular events such as myocardial infarcts and strokes. Clinical trials have consistently shown that antiplatelet therapy with long term, low dose aspirin (LDA) - 75 to 325 mg daily, dramatically reduces the risk of non-fatal myocardial infarcts, stroke and mortality in patients with established arterial diseases. However, such treatment considerably increases the risk of gastrointestinal (GI) ulcerations and serious bleeding by > 2-4 fold, especially in aging individuals. This risk is further increased in patients using LDA together with other antiplatelet agents, other nonsteroidal anti-inflammatory agents (NSAIDs) and/or alcohol, or in patients with Helicobacter pylori (H. pylori) infection. Previous studies by our group and others have demonstrated prominent structural and functional abnormalities in gastric mucosa of aging individuals (which we refer to as aging gastric mucosa or “aging gastropathy”) compared to the gastric mucosa of younger individuals. Aging gastric mucosa has impaired mucosal defense, increased susceptibility to injury by a variety of noxious agents such as aspirin, other NSAIDs and ethanol, and delayed and impaired healing of injury. The mechanism underlying these abnormalities of aging gastric mucosa include reduced mucosal blood flow causing hypoxia, upregulation of PTEN, activation of pro-apoptotic caspase-3 and caspase-9, and reduced survivin (anti-apoptosis protein), importin-α (nuclear transport protein), vascular endothelial growth factor, and nerve growth factor. The decision regarding initiation of a long-term LDA therapy should be made after a careful consideration of both cardiovascular and GI risk factors. The latter include a previous history of GI bleeding and/or ulcers, age ≥ 70, male gender, concurrent use of other NSAIDs, alcohol consumption and H. pylori infection. Furthermore, the incidence of GI ulcers and bleeding can be reduced in patients on long term LDA treatment by several measures. Clinicians treating such patients should test for and eradicate H. pylori, instruct patients to avoid alcohol and non-aspirin NSAIDs, including cyclooxygenase-2-selective NSAIDs, and prescribe proton pump inhibitors in patients on LDA therapy. In the future, clinicians may be able to prescribe one of several potential new drugs, which include aspirin associated with phosphatidylcholine (PL2200), which retains all property of aspirin but reduces by approximately 50% LDA-induced GI ulcerations.

To our readers: Important questions from the editors/editorial board

This letter proposes updating the World Journal of Gastroenterology (WJG) with several new items and subsections and seeks the readers’ input for these suggested changes. In order to further enhance the scope of the WJG, to make it more interactive, and to accommodate our readers’ interest, the editors ask the readers for their input regarding potential new proposed changes and new subsections listed below: (1) new subsection - selected highlights from other related Baishideng Publishing Group world series journals; (2) new subsection - challenging images of the week - a quiz with an answer and references on another page; (3) to re-introduce or restore for some issues the cover page on which selected illustration; (4) new subsection - new hypotheses, new concepts and revisiting old concepts in a short, commentary format; (5) preview of the forthcoming issue articles (title and authors); (6) suggestions submitted by the readers - new topics and initiatives; and (7) additional topic area - molecular basis of gastric/liver diseases as an additional area for articles submitted to the journal.

Reduced NGF in Gastric Endothelial Cells Is One of the Main Causes of Impaired Angiogenesis in Aging Gastric Mucosa

BACKGROUND & AIMS

Aging gastric mucosa has increased susceptibility to injury and delayed healing owing to impaired angiogenesis, but the mechanisms are not fully known. We examined whether impairment of angiogenesis in aging gastric mucosa is caused by deficiency of nerve growth factor (NGF) in gastric endothelial cells (ECs), and whether NGF therapy could reverse this impairment.

METHODS

In gastric mucosal ECs (GECs) isolated from young and aging rats we examined the following: (1) in vitro angiogenesis, (2) NGF expression, and (3) the effect of NGF treatment on angiogenesis, GEC proliferation and migration, and dependence on serum response factor. In in vivo studies in young and aging rats, we examined NGF expression in gastric mucosa and the effect of NGF treatment on angiogenesis and gastric ulcer healing. To determine human relevance, we examined NGF expression in gastric mucosal biopsy specimens of aging (≥70 y) and young (≤40 y) individuals.

RESULTS

In cultured aging GECs, NGF expression and angiogenesis were reduced significantly by 3.0-fold and 4.1-fold vs young GECs. NGF therapy reversed impairment of angiogenesis in aging GECs, and serum response factor silencing completely abolished this response. In gastric mucosa of aging rats, NGF expression in GECs was reduced significantly vs young rats. In aging rats, local NGF treatment significantly increased angiogenesis and accelerated gastric ulcer healing. In aging human subjects, NGF expression in ECs of gastric mucosal vessels was 5.5-fold reduced vs young individuals.

CONCLUSIONS

NGF deficiency in ECs is a key mechanism underlying impaired angiogenesis and delayed ulcer healing in aging gastric mucosa. Local NGF therapy can reverse these impairments.

In vitro model of vasculo-angiogenesis: demonstration that bone marrow derived endothelial progenitor cells form new hybrid capillary blood vessels jointly with gastric endothelial cells

Regeneration of blood vessels (neovascularization) is critical for tissue injury healing. The contribution of bone marrow-derived endothelial progenitor cells (BMD-EPCs) to neovascularization during tissue injury healing is not fully elucidated and it is not clear whether BMD-EPCs can form new capillary blood vessels independently or jointly with fully differentiated endothelial cells (ECs). The aim of this study was to establish an in vitro model of vasculogenesis/angiogenesis by co-culture of BMD-EPCs and gastric endothelial cells (GECs) on Matrigel, examine direct interactions of these cells; and, identify the mechanisms involved. We isolated BMD-EPCs and GECs from bone marrow and stomach of rats, respectively. In these cells, we examined the expression of CD34, CD133, CD31, VEGF-R2, stromal derived factor 1 (SDF-1) and CXCR4, and, their ability to form capillary-like tubes when cultured separately or when co-cultured (1:5 ratio) on growth factor-reduced Matrigel. Fluorescence-labeled BMD-EPCs seeded alone on Matrigel formed capillary-like tubes reflecting in vitro vasculogenesis, and when co-cultured with GECs on Matrigel, formed 'hybrid' tubes containing BMD-EPCs nested between GECs thus reflecting in vitro angio-vasculogenesis. These 'hybrid' tubes were 1.5-fold wider (P < 0.001) and had more extensive (5.1-fold increase) loops (P < 0.01) at the junctions of BMD-EPCs and GECs versus tubes formed by GECs alone. GECs expressed SDF-1 that likely mediated homing of BMD-EPCs (which expressed the SDF-1 receptor, CXCR4) and their incorporation during neovascularization. BMD-EPCs can independently form capillary-like tubes on Matrigel, and when co-cultured with fully differentiated ECs on Matrigel, form capillary-like 'hybrid' tubes comprised of both cell types. Both BMD-EPCs and GECs express SDF-1 and CXCR4, which indicate direct paracrine interactions between these cells during neovascularization.

NGF protects endothelial cells from indomethacin-induced injury through activation of mitochondria and upregulation of IGF-1

BACKGROUND/AIMS

Endothelial cells (ECs) lining blood vessels are critical for delivery of oxygen and nutrients to all tissues and organs and play a crucial role in the regeneration of blood vessel following tissue injury. ECs are also major targets of injury by a variety of noxious factors [e.g., ethanol and nonsteroidal anti-inflammatory drugs (NSAIDs) such as aspirin, indomethacin, diclofenac], especially in gastric mucosa that has direct exposure to these agents. In this study, we investigated whether nerve growth factor (NGF) can protect gastric microvascular ECs (GECs) from injury by indomethacin (INDO) and the mechanisms involved.

METHODS

GECs were isolated from rat gastric mucosa and pre-treated with either vehicle or NGF (100ng/ml) for 30min to 4h followed by treatment with vehicle or 0.25mM INDO for 4h.

STUDIES

1) cell viability using Calcein AM live cell tracking dye, 2) mitochondrial structure and function using MitoTracker, molecular probe that stains mitochondria in live cells in a manner dependent on mitochondrial membrane potential (MMP), 3) in vitro angiogenesis - endothelial tube formation on Matrigel, 4) expression and subcellular localization of NGF receptor, TrkA, and 5) expression of IGF-1 protein.

RESULTS

Treatment with INDO reduced GEC viability and in vitro angiogenesis and induced mitochondrial injury and MMP depolarization. NGF pre-treatment protected GECs from INDO-induced injury preventing both INDO-induced MMP depolarization and reduced in vitro angiogenesis. The NGF high affinity receptor, TrkA, was localized in GECs to both cell membrane and mitochondria. NGF treatment of GECs also resulted in increased IGF-1 protein expression.

CONCLUSIONS

1) NGF protects GECs against IND-induced injury. 2) Mitochondria are major targets of both INDO-induced injury and NGF afforded protection of GECs. 3) TrkA expression in the mitochondria of GECs indicates that the protection afforded by NGF is partly mediated by its direct action on mitochondria. 4) NGF prevents MMP depolarization and increases expression of IGF-1 protein in GECs. These studies indicate that NGF may play a protective role against injury to GECs; and, that maintenance of mitochondrial structure and function is one of the mechanisms.

Formation of new blood vessels during gastric ulcer healing. Role of bone marrow derived endothelial progenitor cells

Regeneration of blood vessels (neovascularization) is critical for gastric ulcer (GU) healing. The contributions of bone marrow-derived endothelial progenitor cells (BMD-EPCs) to neovascularization during GU healing are not fully elucidated. Our specific aims were to determine whether in GU, BMD-EPCs are incorporated into blood vessels of GU granulation tissue jointly with ECs, thus forming hybrid vessels; or, form separate vessels consisting of only BMD-EPCs. GUs were induced in rats by serosal application of acetic acid. Vascular cast studies were performed at 7, 21 and 60 days after GU induction and tissue specimens were immunostained for CD34, CD133, VEGFR2, and SDF-1 at 14 days. Human relevance was determined using archival human GU specimens. In rat GU granulation tissue BMD-EPCs constituted 28 ± 3% of all cells lining newly formed blood vessels, and were nested between fully differentiated ECs. In rat GU granulation tissue, expression of stromal derived factor-1 (SDF-1) - the major chemoattractant for BMD-EPCs was strongly upregulated. In human GU specimens, BMD-EPCs were also present in granulation tissue constituting 34 ± 3% of all cells lining blood vessels and jointly formed hybrid vessels with differentiated ECs. Our study uncovered that BMD-EPCs incorporate into newly formed blood vessels in GU granulation tissue; and, together with ECs of pre-existing vessels, contribute to and support neovascularization through vasculogenesis. This study is the first demonstration that vasculogenesis occurs during GU healing in both humans and in rats.

Expression of nerve growth factor in rat stomach. Implications for interactions between endothelial, neural and epithelial cells

This study was aimed to determine the expression and localization of nerve growth factor (NGF) in the gastric mucosa. Transmural gastric specimens were obtained from euthanized rats.

STUDIES

1) expression of NGF and TrkA receptor by Western blotting; 2) histological evaluation of gastric wall architecture; 3) expression of NGF using immunostaining. Immunostaining showed strong and differential expression of NGF in neural elements of gastric myenteric and submucosal plexuses; in epithelial cells: mainly in chief and progenitor cells, in enterochromaffin-like (ECL) cells; and, in endothelial cells (ECs) lining blood vessels. We concluded that NGF expression in neural elements, epithelial cells and endothelial cells of blood vessels indicated a complex local interaction between neural, epithelial and endothelial cells that regulated gastric mucosal homeostasis and, likely, the protection against gastric injury and ulcer healing.

Nerve growth factor is critical requirement for in vitro angiogenesis in gastric endothelial cells

Angiogenesis is critical for the healing of gastric mucosal injury and is considered to be primarily regulated by vascular endothelial growth factor (VEGF), the fundamental proangiogenic factor. The role of nerve growth factor (NGF) in gastric angiogenesis is unknown. We examined the expression of NGF and its TrkA receptor in endothelial cells (ECs) isolated from gastric mucosa of rats (GMECs), the effect of NGF treatment on in vitro angiogenesis in GMECs, and, the mechanisms underlying NGF's proangiogenic actions. Isolated GMECs from Fisher rats were treated with vehicle, NGF (10-1,000 ng/ml), VEGF (20 ng/ml), or NGF+VEGF. To determine whether and to what extent NGF is critical for angiogenesis in GMECs, we silenced NGF expression using specific siRNA and examined in vitro angiogenesis with and without treatment with exogenous NGF and/or VEGF. Treatment of GMECs with NGF significantly increased in vitro angiogenesis similar to that seen in GMECs treated with VEGF. Silencing of NGF in GMECs abolished angiogenesis, and this effect was reversed only by exogenous NGF but not VEGF, which indicates a direct proangiogenic action of NGF on GMECs that is, at least in part, distinct and independent of VEGF. NGF's proangiogenic action on GMECs was mediated via PI3-K/Akt signaling. This study showed for the first time that gastric mucosal ECs express NGF and its receptor TrkA and that NGF is critical for angiogenesis in these cells.

In vivo imaging of porcine gastric enteric nervous system using confocal laser endomicroscopy &molecular neuronal probe

BACKGROUND AND AIM

The gastric enteric nervous system (GENS) is organized into the submucosal plexus and the myenteric plexus that regulate muscle activity and mucosal functions, respectively. A non-invasive, in vivo visualization of GENS was not possible until recent introduction of needle-based confocal laser endomicroscopy (nCLE). Our aim was to determine the feasibility of in vivo visualization of GENS in the porcine stomach using endoscopic ultrasound (EUS) guided nCLE and local injection of molecular neuronal probe NeuroTrace.

METHODS

In anesthetized pigs during endoscopy, NeuroTrace was injected into the submucosa and muscularis propria of distal, and proximal stomach under EUS guidance and nCLE imaging was performed using the Cellvizio AQ Flex probe. After euthanasia, transmural gastric specimens from the areas of NeuroTrace injection were obtained for histology. We performed quantitative analysis of nCLE images recorded during in vivo studies: histologic evaluation of unstained specimens under fluorescence microscope for NeuroTrace localization. We also performed immunostaining of these specimens for nerve growth factor (NGF). In in vitro studies, we examined the uptake of NeuroTrace by glial cells.

RESULTS

The nCLE imaging successfully visualized neuronal cells and nerve fibers in distinctive image patterns. Fluorescence microscopy of mucosal sections showed that in vivo-injected NeuroTrace was retained in GENS components. NGF was strongly expressed in neural and glial cells, and the pattern of NGF staining was similar to that of NeuroTrace staining.

CONCLUSIONS

This study demonstrates for the first time that combined use of EUS-guided nCLE and NeuroTrace is capable to visualize GENS.

EUS-guided in vivo imaging of the porcine esophageal enteric nervous system by using needle-based confocal laser endomicroscopy

BACKGROUND AND AIMS

The GI tract is innervated by the autonomic enteric nervous system, mainly composed of submucosal Meissner's plexus and myenteric Auerbach's plexus, which is essential for motility, blood flow regulation, and secretory functions. In vivo visualization of the esophageal enteric nervous system (EENS) during endoscopy has not been possible without invasive mucosal resection. This study aimed to visualize the EENS without mucosal resection, in vivo by using the novel probe, needle-based confocal laser-induced endomicroscopy (nCLE) with a fluorescence neuronal probe, NeuroTrace, under EUS guidance and to evaluate the feasibility of ex vivo imaging of the neuronal network in submucosal biopsy samples acquired at endoscopy.

METHODS

Four Yorkshire pigs were anesthetized and examined. In vivo experiment: During endoscopy, NeuroTrace was injected into the submucosa and muscularis propria of the middle and distal esophagus under EUS guidance, and nCLE imaging was performed. Ex vivo experiment: Submucosal tissue biopsy specimens from the porcine esophagus were obtained for ex vivo evaluation by using a "through-the-needle" forceps technique. After incubation of the samples in NeuroTrace solution, pCLE was used to visualize the EENS elements in the tissue.

RESULTS

Imaging of the EENS network by using EUS-guided nCLE was successful, both within the submucosa and the muscularis propria, and clearly visualized neuronal cells, glial cells, nerve bundles, and nerve fibers provided distinctive image patterns with excellent imaging quality. The use of the "through-the-needle" forceps technique achieved ex vivo images similar to those acquired in vivo.

CONCLUSIONS

EUS-guided in vivo imaging of the enteric nervous system is feasible without mucosal resection and provides a novel ex vivo imaging alternative for human application. These novel, minimally invasive imaging approaches could be of tremendous diagnostic value to better characterize and explore the EENS of the GI tract.

Role of Dopamine and D2 Dopamine Receptor in the Pathogenesis of Inflammatory Bowel Disease

BACKGROUND

VEGF-induced vascular permeability and blood vessels remodeling are key features of inflammatory bowel disease (IBD) pathogenesis. Dopamine through D2 receptor (D2R) inhibits VEGF/VPF-mediated vascular permeability and angiogenesis in tumor models. In this study, we tested the hypothesis that pathogenesis of IBD is characterized by the disturbance of dopaminergic system and D2R activity.

METHODS

IL-10 knockout (KO) mice and rats with iodoacetamide-induced ulcerative colitis (UC) were treated intragastrically with D2R agonists quinpirole (1 mg/100 g) or cabergoline (1 or 5 µg/100 g). Macroscopic, histologic, and clinical features of IBD, colonic vascular permeability, and angiogenesis were examined.

RESULTS

Although colonic D2R protein increased, levels of tyrosine hydroxylase and dopamine transporter DAT decreased in both models of IBD. Treatment with quinpirole decreased the size of colonic lesions in rats with iodoacetamide-induced UC (p < 0.01) and reduced colon wet weight in IL-10 KO mice (p < 0.05). Quinpirole decreased colonic vascular permeability (p < 0.001) via downregulation of c-Src and Akt phosphorylation. Cabergoline (5 µg/100 g) reduced vascular permeability but did not affect angiogenesis and improved signs of iodoacetamide-induced UC in rats (p < 0.05).

CONCLUSIONS

Treatment with D2R agonists decreased the severity of UC in two animal models, in part, by attenuation of enhanced vascular permeability and prevention of excessive vascular leakage. Hence, the impairment dopaminergic system seems to be a feature of IBD pathogenesis.

Nerve growth factor injected into the gastric ulcer base incorporates into endothelial, neuronal, glial and epithelial cells: implications for angiogenesis, mucosal regeneration and ulcer healing

A previous study has demonstrated that locally administered growth factors such as epidermal growth factor, basic fibroblast growth factor and hepatocyte growth factor can accelerate healing of experimental gastric ulcers in rats. That study indicates that locally administered growth factors can exert potent biological effects resulting in enhanced gastric ulcers healing. However, the fate of injected growth factors, their retention and localization to specific cellular compartments have not been examined. In our preliminary study, we demonstrated that local injection of nerve growth factor to the base of experimental gastric ulcers dramatically accelerates ulcer healing, increases angiogenesis - new blood vessel formation, and improves the quality of vascular and epithelial regeneration. Before embarking on larger, definitive and time sequence studies, we wished to determine whether locally injected nerve growth factor is retained in gastric ulcer's tissues and taken up by specific cells during gastric ulcer healing. Gastric ulcers were induced in anesthetized rats by local application of acetic acid using standard methods; and, 60 min later fluorescein isothiocyanate-labeled nerve growth factor was injected locally to the ulcer base. Rats were euthanized 2, 5 and 10 days later. Gastric specimens were obtained and processed for histology. Unstained paraffin sections were examined under a fluorescence microscope, and the incorporation of fluorescein isothiocyanate-labeled nerve growth factor into various gastric tissue cells was determined and quantified. In addition, we performed immunostaining for S100β protein that is expressed in neural components. Five and ten days after ulcer induction labeled nerve growth factor (injected to the gastric ulcer base) was incorporated into endothelial cells of blood vessels, neuronal, glial and epithelial cells, myofibroblasts and muscle cells. This study demonstrates for the first time that during gastric ulcer healing locally administered exogenous nerve growth factor is retained in gastric tissue and is taken up by endothelial, neural, muscle and epithelial cells. This is likely the basis for the therapeutic action of locally administered nerve growth factor and its stimulation of angiogenesis, tissue regeneration and gastric ulcer healing.

Expression of nerve growth factor, its TrkA receptor, and several neuropeptides in porcine esophagus. Implications for interactions between neural, vascular and epithelial components of the esophagus

This study was aimed to determine the expression and localization of nerve growth factor (NGF) and several neural peptides in porcine esophagus. Transmural esophageal specimens were obtained from euthanized pigs.

STUDIES

1) histologic evaluation, 2) expressions of NGF and its tropomyosin receptor kinase A (TrkA) receptor, calcitonin generelated peptide (CGRP), neuronal nitric oxide synthase (nNOS), and neuronal enolase using immunostaining and quantification of signal distribution and intensity. Immunostaining for NGF, CGRP, nNOS and neuronal specific enolase (NSE) showed their strong and differential expression and localization in the neuronal network. NGF was strongly expressed in the majority of neurons and nerves, distribution of TrkA was complementary; its signal was 1.5-fold weaker P < 0.001 than NGF). Quantitatively the signal intensity was: CGRP > nNOS > NGF > NES > TrkA. In addition to neural structures, nNOS, NGF and TrkA were expressed in keratinocyte progenitor cells of esophageal mucosa and in endothelial cells of blood vessels. We conclude that a strong expression of NGF in majority of esophageal neurons and nerves indicates important, but previously unrecognized regulatory roles in the esophagus; 2) This study showed expression of NGF and some of the neuropeptides in neural elements, keratinocyte progenitor cells and endothelial cells of blood vessels, which indicates local interactions between neural, epithelial and endothelial cells.

Confocal laser endomicroscopy: a new gold standard for the assessment of mucosal healing in ulcerative colitis

BACKGROUND AND AIM

Endoscopic assessment of mucosal healing in ulcerative colitis (UC) is increasingly accepted as a measure of disease activity, therapeutic goal, and the key prognostic indicator. While regular endoscopy evaluates appearance of the mucosal surface, confocal laser endomicroscopy (CLE) enables in vivo visualization of subepithelial mucosa at 1000× magnification during ongoing endoscopy. Our aims were to determine using CLE whether endoscopically normal appearing colonic mucosa in patients with UC in remission (UC-IR) has fully regenerated mucosal structures, resolved inflammation, and to identify the mechanisms.

METHODS

Twelve patients (six controls and six with UC-IR) underwent colonoscopy using CLE and intravenous fluorescein infusion. During colonoscopy, CLE images of colonic mucosa and conventional mucosal biopsies were obtained and evaluated using image-analysis systems. We quantified; (i) regeneration of colonic crypts and blood microvessels; (ii) cyclooxygenase 2 (COX2) expression; (iii) mitochondrial DNA (mtDNA) mutations; (iv) inflammatory infiltration; and (v) vascular permeability (VP).

RESULTS

In control subjects, CLE demonstrated normal colonic crypts and microvasculature. COX2 expression was minimal, and < 7% crypts showed mtDNA mutations. Colonic mucosa of UC-IR patients had impaired and distorted crypt regeneration, increased COX2, 69% crypts with mtDNA mutations, persistent inflammation, and abnormal vascular architecture with increased VP (all P < 0.001 vs normal mucosa).

CONCLUSIONS

(i) Endoscopically normal appearing colonic mucosa of patients with UC-IR remains abnormal: CLE demonstrates impaired crypt regeneration, persistent inflammation, distinct abnormalities in angioarchitecture and increased vascular permeability; molecular imaging showed increased COX2 and mtDNA mutations; (ii) CLE may serve as a new gold standard for the assessment of mucosal healing in UC.

Angiogenesis in gastric mucosa: an important component of gastric erosion and ulcer healing and its impairment in aging

Angiogenesis (also referred to as neovascularization-formation of new blood vessels from existing vessels) is a fundamental process essential for healing of tissue injury and ulcers because regeneration of blood microvessels is a critical requirement for oxygen and nutrient delivery to the healing site. This review article updates the current views on angiogenesis in gastric mucosa following injury and during ulcer healing, its sequential events, the underlying mechanisms, and the impairment of angiogenesis in aging gastric mucosa. We focus on the time sequence and ultrastructural features of angiogenesis, hypoxia as a trigger, role of vascular endothelial growth factor signaling (VEGF), serum response factor, Cox2 and prostaglandins, nitric oxide, and importin. Recent reports indicate that gastric mucosa of aging humans and experimental animals exhibits increased susceptibility to injury and delayed healing. Gastric mucosa of aging rats has increased susceptibility to injury by a variety of damaging agents such as ethanol, aspirin, and other non-steroidal anti-inflammatory drugs because of structural and functional abnormalities including: reduced gastric mucosal blood flow, hypoxia, reduced expression of vascular endothelial growth factor and survivin, and increased expression of early growth response protein 1 (egr-1) and phosphatase and tensin homolog (PTEN). Until recently, postnatal neovascularization was assumed to occur solely through angiogenesis sprouting of endothelial cells and formation of new blood vessels from pre-existing blood vessels. New studies in the last decade have challenged this paradigm and indicate that in some tissues, including gastric mucosa, the homing of bone marrow-derived endothelial progenitor cells to the site of injury can also contribute to neovascularization by a process termed vasculogenesis.

Novel mechanisms and signaling pathways of esophageal ulcer healing: the role of prostaglandin EP2 receptors, cAMP, and pCREB

Clinical studies indicate that prostaglandins of E class (PGEs) may promote healing of tissue injury e.g., gastroduodenal and dermal ulcers. However, the precise roles of PGEs, their E-prostanoid (EP) receptors, signaling pathways including cAMP and cAMP response element-binding protein (CREB), and their relation to VEGF and angiogenesis in the tissue injury healing process remain unknown, forming the rationale for this study. Using an esophageal ulcer model in rats, we demonstrated that esophageal mucosa expresses predominantly EP2 receptors and that esophageal ulceration triggers an increase in expression of the EP2 receptor, activation of CREB (the downstream target of the cAMP signaling), and enhanced VEGF gene expression. Treatment of rats with misoprostol, a PGE1 analog capable of activating EP receptors, enhanced phosphorylation of CREB, stimulated VEGF expression and angiogenesis, and accelerated esophageal ulcer healing. In cultured human esophageal epithelial (HET-1A) cells, misoprostol increased intracellular cAMP levels (by 163-fold), induced phosphorylation of CREB, and stimulated VEGF expression. A cAMP analog (Sp-cAMP) mimicked, whereas an inhibitor of cAMP-dependent protein kinase A (Rp-cAMP) blocked, these effects of misoprostol. These results indicate that the EP2/cAMP/protein kinase A pathway mediates the stimulatory effect of PGEs on angiogenesis essential for tissue injury healing via the induction of CREB activity and VEGF expression.

Increased susceptibility of aging gastric mucosa to injury: The mechanisms and clinical implications

This review updates the current views on aging gastric mucosa and the mechanisms of its increased susceptibility to injury. Experimental and clinical studies indicate that gastric mucosa of aging individuals-“aging gastropathy”-has prominent structural and functional abnormalities vs young gastric mucosa. Some of these abnormalities include a partial atrophy of gastric glands, impaired mucosal defense (reduced bicarbonate and prostaglandin generation, decreased sensory innervation), increased susceptibility to injury by a variety of damaging agents such as ethanol, aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs), impaired healing of injury and reduced therapeutic efficacy of ulcer-healing drugs. Detailed analysis of the above changes indicates that the following events occur in aging gastric mucosa: reduced mucosal blood flow and impaired oxygen delivery cause hypoxia, which leads to activation of the early growth response-1 (egr-1) transcription factor. Activation of egr-1, in turn, upregulates the dual specificity phosphatase, phosphatase and tensin homologue deleted on chromosome ten (PTEN) resulting in activation of pro-apoptotic caspase-3 and caspase-9 and reduced expression of the anti-apoptosis protein, survivin. The imbalance between pro- and anti-apoptosis mediators results in increased apoptosis and increased susceptibility to injury. This paradigm has human relevance since increased expression of PTEN and reduced expression of survivin were demonstrated in gastric mucosa of aging individuals. Other potential mechanisms operating in aging gastric mucosa include reduced telomerase activity, increase in replicative cellular senescence, and reduced expression of vascular endothelial growth factor and importin-α-a nuclear transport protein essential for transport of transcription factors to nucleus. Aging gastropathy is an important and clinically relevant issue because of: (1) an aging world population due to prolonged life span; (2) older patients have much greater risk of gastroduodenal ulcers and gastrointestinal complications (e.g., NSAIDs-induced gastric injury) than younger patients; and (3) increased susceptibility of aging gastric mucosa to injury can be potentially reduced or reversed pharmacologically.