Glucagonlike peptide 2 protects intestinal barrier in severe acute pancreatitis through regulating intestinal epithelial cell proliferation and apoptosis

Qingyi decoction attenuates intestinal epithelial cell injury via the calcineurin/nuclear factor of activated T-cells pathway

BACKGROUND

Recent studies have demonstrated that dysfunction of the intestinal barrier is a significant contributing factor to the development of severe acute pancreatitis (SAP). A stable intestinal mucosa barrier functions as a major anatomic and functional barrier, owing to the balance between intestinal epithelial cell (IEC) proliferation and apoptosis. There is some evidence that calcium overload may trigger IEC apoptosis and that calcineurin (CaN)/nuclear factor of activated T-cells (NFAT) signaling might play an important role in calcium-mediated apoptosis.

AIM

To investigate the potential mechanisms underlying the therapeutic effect of Qingyi decoction (QYD) in SAP.

METHODS

A rat model of SAP was created via retrograde infusion of sodium deoxycholate. Serum levels of amylase, tumor necrosis factor (TNF-α), interleukin (IL)-6, D-lactic acid, and diamine oxidase (DAO); histological changes; and apoptosis of IECs were examined in rats with or without QYD treatment. The expression of the two subunits of CaN and NFAT in intestinal tissue was measured via quantitative real-time polymerase chain reaction and western blotting. For in vitro studies, Caco-2 cells were treated with lipopolysaccharide (LPS) and QYD serum, and then cell viability and intracellular calcium levels were detected.

RESULTS

Retrograde infusion of sodium deoxycholate increased the severity of pancreatic and intestinal pathology and the levels of serum amylase, TNF-α, and IL-6. Both the indicators of intestinal mucosa damage (D-lactic acid and DAO) and the levels of IEC apoptosis were elevated in the SAP group. QYD treatment reduced the serum levels of amylase, TNF-α, IL-6, D-lactic acid, and DAO and attenuated the histological findings. IEC apoptosis associated with SAP was ameliorated under QYD treatment. In addition, the protein expression levels of the two subunits of CaN were remarkably elevated in the SAP group, and the NFATc3 gene was significantly upregulated at both the transcript and protein levels in the SAP group compared with the control group. QYD significantly restrained CaN and NFATc3 gene expression in the intestine, which was upregulated in the SAP group. Furthermore, QYD serum significantly decreased the LPS-induced elevation in intracellular free Ca²⁺ levels and inhibited cell death.

CONCLUSION

QYD can exert protective effects against intestinal mucosa damage caused by SAP and the protective effects are mediated, at least partially, by restraining IEC apoptosis via the CaN/NFATc3 pathway.

Supplementation of Dietary Quercetin and Vitamin E Promotes the Intestinal Structure and Immune Barrier Integrity in Aged Breeder Hens

In aged animals, the physiological functions of the gastrointestinal tract (GIT) are reduced. Dietary intervention is necessary to re-activate GIT functions. The objective of this study was to investigate the impacts of dietary combination of quercetin (Q) and vitamin E (VE) on the intestinal structure and barrier integrity in aged breeder chickens. A sum of 400 (65-wks-old) Tianfu breeder hens were randomly allotted into four (4) groups with four (4) replicates, and fed with basal diet; basal diet supplemented with 0.4g/kg of Q; basal diet supplemented with 0.2g/kg of VE; and basal diet supplemented with the combination of Q (0.4 g/kg) and VE (0.2 g/kg) for 14 weeks. At the end of the 14^th week, serum and gut segments were collected from eight hens per group for analyses. The results showed that Q+VE exerted synergistic effects on intestinal morphology by promoting villi height and crypt depth (P < 0.05), as well as mitigated the intestinal inflammatory damage of the aged hens, but decreased the concentration of serum D-lactate and diamine oxidase; and increased the levels of secretory immunoglobulin A (sIgA) and Mucin-2 mRNA (P < 0.05). Furthermore, the mRNA expression of intestinal tight junction proteins including occludin, ZO1, and claudin-1 was increased by Q+VE (P < 0.05). Moreover, Q+VE decreased the mRNA expression of the pro-inflammatory genes (TNF-α, IL-6, and IL-1β), and increased the expression of anti-inflammatory genes (IL-10 and IL-4) (P < 0.05). These results were consistent with the mRNA expression of Bax and Bcl-2. In addition, Q+VE protected the small intestinal tract from oxidative damage by increasing the levels of superoxide dismutase, total antioxidant capacity, glutathione peroxidase, catalase (P < 0.05), and the mRNA expression of SOD1 and GPx-2. However, Q+VE decreased malondialdehyde levels in the intestine compared to the control (P < 0.05). These results indicated that dietary Q+VE improved intestinal function in aged breeder hens, by protecting the intestinal structure and integrity. Therefore, Q+VE could act as an anti-aging agent to elevate the physiological functions of the small intestine in chickens.

Glucagon-Like Peptide-2 Modulates Enteric Paneth Cells Immune Response and Alleviates Gut Inflammation During Intravenous Fluid Infusion in Mice With a Central Catheter

Background: Glucagon-like peptide-2 (GLP-2) has protective effects on gastrointestinal functions. Our previous study found that GLP-2 could significantly reduce intestinal permeability and bacterial translocation in total parenteral nutrition (TPN) animal model. However, the effects of GLP-2 on the impairment of the intestinal Paneth cells immune function and gut inflammation during intravenous fluid infusion mainly consisted of nutritional materials is currently scattered.

Objective: The current study was aimed to investigate the efficacy of the GLP-2 in alleviating gut inflammation and modulating enteric Paneth cells immune response in parenterally fed mice and its underlying mechanisms.

Methods: Thirty-six male ICR mice underwent venous catheterization were divided into 3 groups: Chow, TPN, and TPN+GLP-2 groups. GLP-2 was administered intravenously at 60 μg/day for 5 days. The small intestine tissue and serum samples were collected on the 7th day.

Results: Compared with the TPN group, the expression of tight junction proteins occludin and claudin-1 were significantly increased in the TPN+GLP-2 group. In addition, the expression of lysozyme, sPLA2, insulin-like growth factor-1, and epithelial protection and repair genes were improved in the TPN+GLP-2 group. The levels of IL-6 and TNF-α proteins and mRNAs in the ileum tissues were remarkably reduced in the TPN+GLP-2 group, while IL-10 protein and mRNA level were elevated in the TPN+GLP-2 group (all p < 0.05). Moreover, the TPN+GLP-2 group has higher levels of serum endotoxin, D-lactic acid, and MPO than those of the TPN group.

Conclusions: GLP-2 alleviated gut inflammation and improved enteric Paneth cells immune responses through intravenous fluid infusion, possibly by improving the functioning of epithelial protection and repair, and reducing mucosal inflammatory responses.

Effect of silymarin on intestinal injury and PI3K/Akt and NF-κB signaling pathways in rats with severe acute pancreatitis

BACKGROUND

Acute pancreatitis is a very common clinical acute abdomen. Excessive release of inflammatory factors can damage the intestinal mucosa, induce cell apoptosis, and accelerate the course of the disease. Silymarin has anti-oxidative, immunoregulatory, anti-inflammatory, liver-protecting, anti-tissue fibrosis, and other effects. However, there is no relevant research on the effect of silymarin on the intestinal injury in severe acute pancreatitis.

AIM

To study the effects of silymarin on intestinal injury and PI3K/Akt and NF-κB signaling pathways in rats with severe acute pancreatitis.

METHODS

Rats were divided into a control group, a severe acute pancreatitis (SAP) model group, and low-, medium, and high-dose silymarin groups (severe acute pancreatitis rats given 60, 120 , and 240 mg/kg silymarin, respectively). Rats treated with glutamine (1.5 g/kg) were used as positive controls. The death of rats was recorded. Serum amylase and lipase levels were detected using an automatic biochemical analyzer. Serum IL-1β and TNF-α levels were detected by ELISA. Pancreatic and ileal pathology scores were scalculated. The expression of Bcl-2, Bax, PI3K, p-PI3K, Akt, p-Akt, NF-κBp65, and Bcl-2 in ileal tissues was detected by Western blot. TUNEL method was used to detect cell apoptosis in ileal tissues.

RESULTS

The SAP group, control group, and low-, medium, and high-dose silymarin groups had 3, 0, 2, 1, and 0 deaths, respectively. Compared with the control group, the levels of serum amylase, lipase, IL-1β, and TNF-α , the pancreatic and ileal pathology scores, the levels of Bax, p-PI3K/PI3K, p-Akt/Akt, and NF-κBp65, and the apoptosis index increased, while Bcl-2 protein expression decreased in the SAP group. Compared with the SAP group, the levels of serum amylase, lipase, IL-1β, and TNF-αased, the pancreatic and ileal pathology scores, the levels of Bax, p-PI3K/PI3K, p-Akt/Akt, and NF-κBp65 protein levels, and the apoptosis index gradually decreased, while Bcl-2 protein expression gradually increased in the low-, medium, and high-dose silymarin groups. Compared with the SAP group, the serum levels of amylase, lipase, IL-1β, and TNF-α, the pancreatic and ileal pathology scores, the levels of Bax, p-PI3K/PI3K, p-Akt/Akt, and NF-κBp65, and the apoptosis index decreased, while Bcl-2 protein expression increased in the glutamine group.

CONCLUSION

Silymarin can reduce intestinal injury in rats with SAP, inhibit inflammation, reduce cell apoptosis, and inhibit the activation of the PI3K/Akt and NF-κB signaling pathways.

Effect of Boron on Microstructure, Immune Function, Expression of Tight Junction Protein, Cell Proliferation and Apoptosis of Duodenum in Rats

Boron is an essential trace element for animals. Appropriate boron supplementation can produce beneficial effects on the animal body, while a high dose of boron has adverse and even toxic effects. Our aim was to investigate the impact of different doses of boron on the microstructure of duodenum in rats, expression of secretory immunoglobulin A (SIgA) and tight junction protein, cell proliferation and apoptosis. Eighty newly weaned clean Sprague-Dawley (SD) rats were given distilled water supplemented with 0, 10, 20, 40, 80, 160, 320, and 640 mg/L of boron for 60 days. We found that supplementation of 40 and 80 mg/L boron could increase the height of duodenal villi and the crypt depth, the number of intraepithelial lymphocytes (IELs) and goblet cells, the expression of SIgA, Zonula occludens-1 (ZO-1) and occludin, and proliferating cell nuclear antigen (PCNA) in duodenum of rats; decrease expression of Caspase-3 mRNA and the number of Caspase-3-positive cells, but supplementation of 320 and 640 mg/L boron could have the opposite effect in these indexes. The results showed that supplemented with 40 and 80 mg/L of boron could improve the structure and function of duodenum, while supplemented with 320-640 mg/L had a significant inhibitory effect.

4-Phenylbutyric Acid Attenuates Endoplasmic Reticulum Stress-Mediated Intestinal Epithelial Cell Apoptosis in Rats with Severe Acute Pancreatitis

OBJECTIVES

The present study aimed to determine whether intestinal epithelial cell (IECs) apoptosis could be induced by endoplasmic reticulum stress (ERS) in severe acute pancreatitis (SAP), and the role of chemical chaperone 4-phenylbutyric acid (4-PBA) in SAP-associated intestinal barrier injury.

METHODS

Twenty-four male Sprague Dawley rats were randomly divided into three groups: the sham operation group, the SAP group, and the SAP model plus 4-PBA treatment group (4-PBA group). A rat model of SAP was induced by retrograde injection of 5% sodium taurocholate (STC) into the biliopancreatic duct; in the 4-PBA group, 4-PBA was injected intraperitoneally at a dose of 50 mg/kg body weight for 3 days before modeling.

RESULTS

The results indicated that 4-PBA attenuated the following: (1) pancreas and intestinal pathological injuries, (2) serum TNF-α, IL-1β, and IL-6, (3) serum DAO level, serum endotoxin level, (4) the apoptosis of IECs, (5) ER stress markers (caspase-12, CHOP, GRP78, PERK, IRE1α, ATF6) and caspase-3 expression in intestinal. However, the serum AMY, LIPA levels, and the expression of caspase-9, caspase-8 were just slightly decreased.

CONCLUSIONS

ERS may be considered a predominant pathway, which is involved in the apoptosis of IECs during SAP. Furthermore, 4-PBA protects IECs against apoptosis in STC-induced SAP by attenuating the severity of ERS.

Effect of Aging and Glucagon-like Peptide 2 on Intestinal Microbiota in SD Rats

Recent research suggests that intestinal microbiota affect the aging process. Glucagon-like peptide 2 (GLP-2), a growth factor found in the intestinal mucosal epithelium, reduces intestinal permeability and affects intestinal microbiota. The relationship between aging, GLP-2, and intestinal microbiota are still not well understood. The current study examined the influence of aging and GLP-2 on the intestinal microbiota of rats. Twelve 3-month old male SD rats were randomly divided into two groups: a young control group (group C) and a young GLP-2 treatment group (group G). Twelve 26-month old male SD rats were randomly divided into two groups: an aged control group (group L) and an aged GLP-2 treatment group (group T). GLP-2 was intraperitoneally injected into rats from group G and group T for 14 days. Plasma GLP-2 concentration was evaluated by ELISA tests. Fresh intestinal stool samples were collected from each group and total fecal bacterial genomic DNA was extracted from the associated rats. The bacterial composition of fecal samples was analyzed by Miseq high-throughput sequencing and comparison with SRA databases. Overall, the diversity of intestinal microbiota significantly decreases with age in SD rats, while GLP-2 has no significant effect on the diversity of intestinal microbiota. Upon aging, there is a reduction in probiotic bacteria and a concomitant increase in pathogenic bacteria in rats. Treatment with GLP-2 results in a significant reduction in the prevalence of pathogenic bacterial genera and an increase in some potential benefit bacteria in aged rats. In addition, treatment with GLP-2 results in an increase in several probiotics and a reduction in the prevalence of pathogenic bacterial genera in young rats.

Glucagon-Like Peptide-2 Improve Intestinal Mucosal Barrier Function in Aged Rats

Glucagon-like peptide-2 (GLP-2) plays a major role in repairing impaired intestinal mucosa, but its mechanism in the improvement of intestinal barrier function during the aging process remains unclear. In this study, 26-month-old male Sprague-Dawley rats were randomized to control group and GLP-2 group treated with a dose of 250 μg•kg-1•d-1 by intraperitoneal injection. After 14 days of treatment, intestinal mucosal morphometric changes were observed by light microscopy and transmission electron microscopy (TEM). Small intestinal permeability was evaluated by fluorescein isothiocyanate (FITC)-labeled dextran. The mRNA and protein expression of Zonula Occludens-1 (ZO-1), occludin, claudin-1 and the GLP-2 receptor (GLP-2R) were detected by Real-time PCR and Western blot. Our results showed that GLP-2 administration significantly improved the age-related atrophy of intestinal mucosa and villi and increased small intestinal permeability. The mRNA and protein expression of ZO-1and occludin in ileum were up regulated in the GLP-2-treated old rats. In addition, the serum GLP-2 levels were negatively correlated with small intestinal permeability measured by FITC-dextran levels (r=-0.610, P<0.01). Taking all these data together, it is concluded that GLP-2 improved small intestinal epithelial barrier function in aged rats mainly by facilitating intestinal mucosa growth, alleviating the increased small intestinal permeability and increasing ZO-1 and occludin expression. Our observations provide evidence for the clinical significance of GLP-2 in preventing the intestinal epithelial barrier dysfunction during aging.

Blockade of high-mobility group box 1 attenuates intestinal mucosal barrier dysfunction in experimental acute pancreatitis

The release of inflammatory cytokines, that plays a dominant role in local pancreatic inflammation and systemic complications in severe acute pancreatitis (SAP). High-mobility group box 1 (HMGB1) is implicated in the mechanism of organ dysfunction and bacterial translocation in SAP. This current study aims to investigate possible role of HMGB1 in the intestinal mucosal barrier dysfunction of SAP, and the effect of anti-HMGB1 antibody treatment in intestinal mucosal injury in SAP. Our data revealed that the HMGB1 expression was significantly increased in AP mice induced by caerulein and LPS, and the inhibition of HMGB1 played a protective role in intestinal mucosal barrier dysfunction, reduced the serum level of other proinflammatory cytokines include IL-1β, IL-6, TNF-α. Next we investigated the downstream receptors involving in HMGB1 signaling. We found that the expressions of toll-like receptor (TLR) 4 and TLR9 were elevated in ileum of AP mice, the administration of HMGB1 neutralizing antibody significantly reduced the TLR4 and TLR9 expression. It was concluded that HMGB1 contributed the mechanism to the intestinal mucosal barrier dysfunction during AP. Blockade of HMGB1 by administration of HMGB1 neutralizing antibody may be a beneficial therapeutic strategy in improving intestinal mucosal barrier dysfunction in SAP.

Effects of flavonoids on intestinal inflammation, barrier integrity and changes in gut microbiota during diet-induced obesity

Diet-induced obesity is associated with low-grade inflammation, which, in most cases, leads to the development of metabolic disorders, primarily insulin resistance and type 2 diabetes. Although prior studies have implicated the adipose tissue as being primarily responsible for obesity-associated inflammation, the latest discoveries have correlated impairments in intestinal immune homeostasis and the mucosal barrier with increased activation of the inflammatory pathways and the development of insulin resistance. Therefore, it is essential to define the mechanisms underlying the obesity-associated gut alterations to develop therapies to prevent and treat obesity and its associated diseases. Flavonoids appear to be promising candidates among the natural preventive treatments that have been identified to date. They have been shown to protect against several diseases, including CVD and various cancers. Furthermore, they have clear anti-inflammatory properties, which have primarily been evaluated in non-intestinal models. At present, a growing body of evidence suggests that flavonoids could exert a protective role against obesity-associated pathologies by modulating inflammatory-related cellular events in the intestine and/or the composition of the microbiota populations. The present paper will review the literature to date that has described the protective effects of flavonoids on intestinal inflammation, barrier integrity and gut microbiota in studies conducted using in vivo and in vitro models.

GLP-2 Prevents Intestinal Mucosal Atrophy and Improves Tissue Antioxidant Capacity in a Mouse Model of Total Parenteral Nutrition

We investigated the effects of exogenous glucagon-like peptide-2 (GLP-2) on mucosal atrophy and intestinal antioxidant capacity in a mouse model of total parenteral nutrition (TPN). Male mice (6–8 weeks old) were divided into three groups (n = 8 for each group): a control group fed a standard laboratory chow diet, and experimental TPN (received standard TPN solution) and TPN + GLP-2 groups (received TPN supplemented with 60 µg/day of GLP-2 for 5 days). Mice in the TPN group had lower body weight and reduced intestinal length, villus height, and crypt depth compared to the control group (all p < 0.05). GLP-2 supplementation increased all parameters compared to TPN only (all p < 0.05). Intestinal total superoxide dismutase activity and reduced-glutathione level in the TPN + GLP-2 group were also higher relative to the TPN group (all p < 0.05). GLP-2 administration significantly upregulated proliferating cell nuclear antigen expression and increased glucose-regulated protein (GRP78) abundance. Compared with the control and TPN + GLP-2 groups, intestinal cleaved caspase-3 was increased in the TPN group (all p < 0.05). This study shows GLP-2 reduces TPN-associated intestinal atrophy and improves tissue antioxidant capacity. This effect may be dependent on enhanced epithelial cell proliferation, reduced apoptosis, and upregulated GRP78 expression.

Endoplasmic reticulum stress may not be involved in intestinal epithelial cell apoptosis in experimental acute pancreatitis

OBJECTIVES

To investigate whether endoplasmic reticulum (ER) stress is activated in the intestinal epithelium of acute pancreatitis (AP), and whether it is one of the inducing factors of the intestinal epithelial cell apoptosis in AP.

METHODS

Twenty-four rats were randomly divided into two groups. AP was induced via retrograde injection of 3 % sodium taurocholate into the pancreatic duct. As a control group, rats received a sham operation. Forty-eight hours after the operation, the ultrastructural changes of ileal epithelial cells were investigated by transmission electron microscope. The protein expressions of GRP78, CHOP, caspase-12, and JNK in the ileal epithelium were determined by immunohistochemistry, and apoptosis was determined by TdT-mediated dUTP nick end labeling. The mRNA expressions of GRP78, CHOP, caspase-12, and JNK in the ileal epithelium were determined using quantitative RT-PCR.

RESULTS

The ileal epithelium in rats with AP had significantly higher apoptotic cells compared with that of the control rats (P < 0.05). ER stress was activated in the ileal epithelium, which was characterized by dilated, irregular ER and upregulated expressions of GRP78 mRNA and protein. The mRNA and protein expressions of CHOP, caspase-12, and JNK in rats with AP were similar to that in the control rats (P > 0.05).

CONCLUSIONS

ER stress is induced in intestinal epithelium during AP; however, ER stress is not likely to be involved in the apoptosis of the intestinal epithelium during AP.

Small intestinal smooth muscle cell apoptosis in rats with severe acute pancreatitis

AIM: To investigate whether small intestinal smooth muscle cell apoptosis occurs in rats with severe acute pancreatitis (SAP) and the underlying mechanism.

METHODS: Male SD rats were randomly divided into a sham operation group (SO) and an SAP group. SAP was induced by injecting 3.8% sodium taurocholate solution into the subcapsular region of the pancreas of SD rats. Rats in the SO group were injected with 1 mL/kg normal saline. Forty-eight hours later, pancreatic pathological changes and the transit rate of the small bowel were determined. Cell apoptosis, expression of adenine nucleotide translocator (ANT) mRNA, mitochondrial membrane potential, and cytochrome C (Cyt-C) protein expression in the small intestinal smooth muscle were determined by TUNEL method, RT-PCR, flow cytometry and immunohistochemistry, respectively.

RESULTS: Compared with rats in the SO group, rats in the SAP group developed typical SAP symptoms, with a higher pancreatic pathology score (6.85 ± 1.21 vs 1.13 ± 0.91, P < 0.001). Compared with rats in the SO group, the transit rate of the small intestine was significantly lower (55.91% ± 2.93% vs 68.9% ± 5.69%, P < 0.05), the apoptosis of smooth muscle cells in the small intestine increased significantly (0.056 ± 0.184 vs 0.029 ± 0.038, P < 0.05), the expression of ANT mRNA and Cyt-C protein (0.024 ± 0.001 vs 0.057 ± 0.168, P < 0.001) in the smooth muscle of the small intestine increased significantly, and the mitochondrial membrane potential decreased significantly (5.07 ± 0.92 vs 2.40 ± 0.50, P < 0.05) in the SAP group.

CONCLUSION: The mitochondrial signal transduction pathway contributes to smooth muscle cell apoptosis in the small intestine, which may play a role in small intestinal motility dysfunction in SAP rats.

Time course of intestinal barrier function injury in a sodium taurocholate-induced severe acute pancreatitis in rat model

OBJECTIVE

The aims of this study were to clarify the kinetics of intestinal barrier function impairment in sodium taurocholate-induced severe acute pancreatitis (SAP) models and to explore an appropriate concentration of sodium taurocholate and a suitable time point for further study.

METHODS

In total, 104 rats were randomly divided into four groups: the normal control group (n = 8) receiving no treatment, the sham-operation group (n = 32), the 2.5% and 5% sodium taurocholate-treated SAP groups (n = 32 for each group) which were induced via a retrograde injection of 2.5% or 5% sodium taurocholate into the pancreatic duct. Histological examination, serum D-lactate and endotoxin levels and the incidence of bacteria translocation were recorded to assess the intestinal mucosal injury.

RESULTS

Pancreatitis models were successfully established in both the 2.5% and 5% sodium taurocholate-treated groups. The dosage of sodium taurocholate used to induce pancreatitis was positively correlated with the degree of intestinal mucosal injury. The most severe damage to intestinal barrier was observed 24 h after surgery in the 2.5% sodium taurocholate-treated group and 48 h after surgery in the 5% sodium taurocholate-treated group, respectively.

CONCLUSION

Based on the success rate of the model, the mortality and the impairment of intestinal barrier function, we conclude that 24 h after a retrograde injection of 2.5% sodium taurocholate may be the most appropriate time point to study intestinal barrier injury in SAP rats.