Role of toll-like receptor 4 in the pathophysiology of severe acute pancreatitis in mice

Toll-like receptor 4 in pancreatic damage and immune infiltration in acute pancreatitis

Acute pancreatitis is a complex inflammatory disease resulting in extreme pain and can result in significant morbidity and mortality. It can be caused by several factors ranging from genetics, alcohol use, gall stones, and ductal obstruction caused by calcification or neutrophil extracellular traps. Acute pancreatitis is also characterized by immune cell infiltration of neutrophils and M1 macrophages. Toll-like receptor 4 (TLR4) is a pattern recognition receptor that has been noted to respond to endogenous ligands such as high mobility group box 1 (HMGB1) protein and or exogenous ligands such as lipopolysaccharide both of which can be present during the progression of acute pancreatitis. This receptor can be found on a variety of cell types from endothelial cells to resident and infiltrating immune cells leading to production of pro-inflammatory cytokines as well as immune cell activation and maturation resulting in the furthering of pancreatic damage during acute pancreatitis. In this review we will address the various mechanisms mediated by TLR4 in the advancement of acute pancreatitis and how targeting this receptor could lead to improved outcomes for patients suffering from this condition.

Intestinal TLR4 deletion exacerbates acute pancreatitis through gut microbiota dysbiosis and Paneth cells deficiency

Toll-like receptor 4 (TLR4) has been identified as a potentially promising therapeutic target in acute pancreatitis (AP). However, the role of intestinal TLR4 in AP and AP-associated gut injury remains unclear. This study aimed to explore the relationship between intestinal TLR4 and gut microbiota during AP. A mouse AP model was establish by intraperitoneal injection of L-arginine. Pancreatic injury and intestinal barrier function were evaluated in wild-type and intestinal epithelial TLR4 knockout (TLR4ΔIEC) mice. Gut microbiota was analyzed by 16S rRNA sequencing. Quadruple antibiotics were applied to induce microbiota-depleted mice. Differentially expressed genes in gut were detected by RNA sequencing. L. reuteri treatment was carried out in vivo and vitro study. Compared with wild-type mice, AP and AP-associated gut injury were exacerbated in TLR4ΔIEC mice in a gut microbiota-dependent manner. The relative abundance of Lactobacillus and number of Paneth cells remarkably decreased in TLR4ΔIEC mice. The KEGG pathway analysis derived from RNA sequencing suggested that genes affected by intestinal TLR4 deletion were related to the activation of nod-like receptor pathway. Furthermore, L. reuteri treatment could significantly improve the pancreatic and intestinal injury in TLR4ΔIEC mice through promoting Paneth cells in a NOD2-dependent manner. Loss of intestinal epithelial TLR4 exacerbated pancreatic and intestinal damage during AP, which might be attributed to the gut microbiota dysbiosis especially the exhausted Lactobacillus. L. reuteri might maintain intestinal homeostasis and alleviate AP via Paneth cells modulation.Abbreviations: AP Acute pancreatitis, TLR4 Toll-like receptor 4, IL-1β Interleukin-1β, IL-6 Interleukin-6, TNF-α Tumor necrosis factor-α, SIRS Systematic inflammatory response syndrome, LPS Lipopolysaccharides, SPF Specific pathogen-free, ZO-1 Zonula occludens-1, CON Control, H&E Hematoxylin and eosin, FISH Fluorescence in situ hybridization, DAPI 4',6-diamidino-2-phenylindole, PCoA Principal co-ordinates analysis, SCFA Short chain fatty acid, LEfSe Linear discriminant analysis Effect Size, ANOVA Analysis of variance, F/B Firmicutes/Bacteroidetes, PCA Principal component analysis, NOD2 Nod-like receptor 2, ABX antibiotics, PCNA proliferating cell nuclear antigen.

Pyroptosis in acute pancreatitis and its therapeutic regulation

Pyroptosis defines a new type of GSDMs-mediated programmed cell death, distinguishes from the classical concepts of apoptosis and necrosis-mediated cell death and is prescribed by cell swelling and membrane denaturation, leading to the extensive secretion of cellular components and low-grade inflammatory response. However, NLRP3 inflammasome activation can trigger its downstream inflammatory cytokines, leading to the activation of pyroptosis-regulated cell death. Current studies reveal that activation of caspase-4/5/11-driven non-canonical inflammasome signaling pathways facilitates the pathogenesis and progression of acute pancreatitis (AP). In addition, a large number of studies have reported that NLRP3 inflammasome-dependent pyroptosis is a crucial player in driving the course of the pathogenesis of AP. Excessive uncontrolled GSDMD-mediated pyroptosis has been implicated in AP. Therefore, the pyroptosis-related molecule GSDMD may be an independent prognostic biomarker for AP. The present review paper summarizes the molecular mechanisms of pyroptotic signaling pathways and their pathophysiological impacts on the progress of AP. Moreover, we briefly present some experimental compounds targeting pyroptosis-regulated cell death for exploring novel therapeutic directions for the treatment and management of AP. Our review investigations strongly suggest that targeting pyroptosis could be an ideal therapeutic approach in AP.

Liver injury associated with acute pancreatitis: The current status of clinical evaluation and involved mechanisms

Acute pancreatitis (AP) is a very common acute disease, and the mortality rate of severe AP (SAP) is between 15% and 35%. The main causes of death are multiple organ dysfunction syndrome and infections. The mortality rate of patients with SAP related to liver failure is as high as 83%, and approximately 5% of the SAP patients have fulminant liver failure. Liver function is closely related to the progression and prognosis of AP. In this review, we aim to elaborate on the clinical manifestations and mechanism of liver injury in patients with AP.

Cytokine signature for predicting new-onset prediabetes after acute pancreatitis: A prospective longitudinal cohort study

BACKGROUND/PURPOSE

Acute inflammation of the pancreas often leads to metabolic sequelae, the most common of which is new-onset prediabetes (and, ultimately, diabetes). However, there is a lack of studies on predictors of this sequela. The aim was to investigate whether cytokines/chemokines measured at baseline are predictive of new-onset prediabetes after acute pancreatitis (NOPAP).

METHODS

This was a prospective longitudinal cohort study (as part of the LACERTA project) that included 68 individuals with non-necrotising acute pancreatitis who had no diabetes mellitus. Of them, 17 individuals had prediabetes at baseline and during follow-up, 37 individuals had normoglycaemia at baseline and during follow-up, and 14 individuals had normoglycaemia at baseline and developed NOPAP during follow-up. A commercially available human cytokine/chemokine multiplex kit was used to measure a total of 28 analytes at baseline. Multinomial regression analyses were conducted to investigate the associations between the cytokines/chemokines and the three study groups.

RESULTS

Interleukin-1β and interferon γ significantly predicted progression to NOPAP with an odds ratio (95% confidence interval) of 1.097 (1.002, 1.201) and 1.094 (1.003, 1.192), respectively (after accounting for age, sex, body mass index, and aetiology of acute pancreatitis). None of the studied cytokines/chemokines showed statistically significant associations with the antecedent prediabetes group (after accounting for the above covariates).

CONCLUSION

Elevated levels of interleukin-1β and interferon γ in acute pancreatitis individuals with normoglycaemia at baseline may predict progression to NOPAP during follow-up.

Abdominal paracentesis drainage attenuates intestinal inflammation in rats with severe acute pancreatitis by inhibiting the HMGB1-mediated TLR4 signaling pathway

BACKGROUND

Our previous studies confirmed that abdominal paracentesis drainage (APD) attenuates intestinal mucosal injury in rats with severe acute pancreatitis (SAP), and improves administration of enteral nutrition in patients with acute pancreatitis (AP). However, the underlying mechanisms of the beneficial effects of APD remain poorly understood.

AIM

To evaluate the effect of APD on intestinal inflammation and accompanying apoptosis induced by SAP in rats, and its potential mechanisms.

METHODS

SAP was induced in male adult Sprague-Dawley rats by 5% sodium taurocholate. Mild AP was induced by intraperitoneal injections of cerulein (20 μg/kg body weight, six consecutive injections). Following SAP induction, a drainage tube connected to a vacuum ball was placed into the lower right abdomen of the rats to build APD. Morphological changes, serum inflammatory mediators, serum and ascites high mobility group box protein 1 (HMGB1), intestinal barrier function indices, apoptosis and associated proteins, and toll-like receptor 4 (TLR4) signaling molecules in intestinal tissue were assessed.

RESULTS

APD significantly alleviated intestinal mucosal injury induced by SAP, as demonstrated by decreased pathological scores, serum levels of D-lactate, diamine oxidase and endotoxin. APD reduced intestinal inflammation and accompanying apoptosis of mucosal cells, and normalized the expression of apoptosis-associated proteins in intestinal tissues. APD significantly suppressed activation of the intestinal TLR4 signaling pathway mediated by HMGB1, thus exerting protective effects against SAP-associated intestinal injury.

CONCLUSION

APD improved intestinal barrier function, intestinal inflammatory response and accompanying mucosal cell apoptosis in SAP rats. The beneficial effects are potentially due to inhibition of HMGB1-mediated TLR4 signaling.

The Role of TLR-4 and Galectin-3 Interaction in Acute Pancreatitis

Toll-like receptor-4 (TLR-4) is a member of evolutionarily conserved type I transmembrane proteins that can initiate sterile inflammatory cascade in the pancreas. Expression of TLR-4 is up-regulated in pancreatic tissue, as well as, on peripheral blood innate immune cells in human and experimental models of acute pancreatitis. TLR-4 plays important pro-inflammatory roles during development of acute pancreatitis: it recognize alarmins released from injured acinar cells and promotes activation and infiltration of innate immune cells after the premature and intraacinar activation of tripsinogen. Galectin-3 is β-galactoside-binding lectin that plays pro-inflammatory roles in a variety autoimmune diseases, acute bacterial infections and during tumorigenesis. It is reported that Galectin-3 is alarmin in experimental models of neuroinflammation and binds to TLR-4 promoting the pro-inflammatory phenotype of microglia. Also, in experimental model of acute pancreatitis Galectin-3 is colocalized with TLR-4 on innate inflammatory cells resulted in enhanced production of inflammatory cytokines, TNF-α and IL-1β, increased infiltration of pro-inflammatory N1 neutrophils, macrophages and dendritic cells and increased damage of pancreatic tissue. This review paper discusses the role of TLR-4/Gal-3 axis in the pathogenesis of acute pancreatitis.

Single immunoglobulin and Toll‑interleukin‑1 receptor domain containing molecule protects against severe acute pancreatitis in vitro by negatively regulating the Toll‑like receptor‑4 signaling pathway: A clinical and experimental study

Single immunoglobulin and Toll-interleukin-1 receptor domain-containing molecule (SIGIRR) is a specific inhibitor of IL-1R and Toll-like receptor (TLR) signaling and considered a potential target for the treatment of inflammatory diseases. Pathogenic mechanisms associated with the TLR4 signaling pathway have a critical role in the development of severe acute pancreatitis (SAP). The aim of the present study was to determine the role of SIGIRR in the regulation of TLR4 signaling during the progression of SAP. Pancreatitis-associated ascitic fluid (PAAF) was collected from patients with SAP. Murine RAW264.7 macrophages were transfected with a SIGIRR overexpression plasmid and co-cultured with the PAAF from the donors in order to evaluate the effect of SIGIRR in vitro. The mRNA expression of TLR4, SIGIRR and other key downstream signaling molecules was quantified using semi-quantitative PCR with agarose gel electrophoresis. Furthermore, the levels of pro-inflammatory cytokines in the culture supernatant were detected using ELISA. In contrast to SIGIRR, the mRNA expression levels of TLR4, myeloid differentiation factor 88 (MyD88), IL-1R-associated kinase-1 (IRAK-1) and TNF receptor-associated factor-6 (TRAF-6) were significantly increased in RAW264.7 cells following treatment with PAAF. Furthermore, TLR4, MyD88, IRAK-1 and TRAF-6 mRNA levels were significantly downregulated following SIGIRR overexpression and PAAF treatment in RAW264.7 cells. The levels of IL-2, IL-12, IL-17 and IFN-γ in the culture supernatant were also significantly decreased, while IL-10 levels were increased. Overall, SIGIRR negatively regulated the TLR4 signaling pathway to protect against the development of SAP in an in vitro model. Therefore, SIGIRR may represent a promising therapeutic target for SAP.

NLRP3 Inflammasome-Mediated Inflammation in Acute Pancreatitis

The discovery of inflammasomes has enriched our knowledge in the pathogenesis of multiple inflammatory diseases. The NLR pyrin domain-containing protein 3 (NLRP3) has emerged as the most versatile and well-characterized inflammasome, consisting of an intracellular multi-protein complex that acts as a central driver of inflammation. Its activation depends on a tightly regulated two-step process, which includes a wide variety of unrelated stimuli. It is therefore not surprising that the specific regulatory mechanisms of NLRP3 inflammasome activation remain unclear. Inflammasome-mediated inflammation has become increasingly important in acute pancreatitis, an inflammatory disorder of the pancreas that is one of the fatal diseases of the gastrointestinal tract. This review presents an update on the progress of research into the contribution of the NLRP3 inflammasome to acute pancreatic injury, examining the mechanisms of NLRP3 activation by multiple signaling events, the downstream interleukin 1 family of cytokines involved and the current state of the literature on NLRP3 inflammasome-specific inhibitors.

Combinatory antibiotic treatment protects against experimental acute pancreatitis by suppressing gut bacterial translocation to pancreas and inhibiting NLRP3 inflammasome pathway

Gut bacterial translocation following impaired gut barrier is a critical determinant of initiating and aggravating acute pancreatitis (AP). Antibiotic combination (ABX; vancomycin, neomycin and polymyxin b) is capable of reducing gut bacteria, but its efficacy in AP prevention and the underlying mechanism have not been investigated yet. AP was induced in BALB/c mice by caerulein (CAE) hyperstimulation. We found that ABX supplementation attenuated the severity of AP as evidenced by reduced pancreatic oedema and myeloperoxidase activity. The protective effect was also confirmed by improved histological morphology of the pancreas and decreased pro-inflammatory markers (IL-1β, TNF-α, MCP-1) in pancreas. ABX administration inhibits the activation of colonic TLR4/NLRP3 inflammasome pathway. Subsequently, down-regulated NLRP3 resulted in decreased colonic pro-inflammation (IL-1β, IL-6, MCP-1) and enhanced gut physical barrier as evidenced by up-regulation of tight junction proteins including occludin, claudin-1 and ZO-1, as well as improved histological morphology of the colon. Together, combinatory ABX therapy inhibited the translocation of gut bacteria to pancreas and its amplification effects on pancreatic inflammation by inhibiting the pancreatic NLRP3 pathway, and inhibiting intestinal-pancreatic inflammatory responses. The current study provides the basis for potential clinical application of ABX in AP.

Effect of Endotoxemia in Suckling Rats on Pancreatic Integrity and Exocrine Function in Adults: A Review Report

Background. Endotoxin (LPS), the component of Gram-negative bacteria, is responsible for sepsis and neonatal mortality, but low concentrations of LPS produced tissue protection in experimental studies. The effects of LPS applied to the suckling rats on the pancreas of adult animals have not been previously explored. We present the impact of neonatal endotoxemia on the pancreatic exocrine function and on the acute pancreatitis which has been investigated in the adult animals. Endotoxemia was induced in suckling rats by intraperitoneal application of LPS from Escherichia coli or Salmonella typhi. In the adult rats, pretreated in the early period of life with LPS, histological manifestations of acute pancreatitis have been reduced. Pancreatic weight and plasma lipase activity were decreased, and SOD concentration was reversed and accompanied by a significant reduction of lipid peroxidation products (MDA + 4 HNE) in the pancreatic tissue. In the pancreatic acini, the significant increases in protein signals for toll-like receptor 4 and for heat shock protein 60 were found. Signal for the CCK1 receptor was reduced and pancreatic secretory responses to caerulein were diminished, whereas basal enzyme secretion was unaffected. These pioneer studies have shown that exposition of suckling rats to endotoxin has an impact on the pancreas in the adult organism.

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.

NAD+ augmentation ameliorates acute pancreatitis through regulation of inflammasome signalling

Acute pancreatitis (AP) is a complicated disease without specific drug therapy. The cofactor nicotinamide adenine dinucleotide (NAD⁺) is an important regulator of cellular metabolism and homeostasis. However, it remains unclear whether modulation of NAD⁺ levels has an impact on caerulein-induced AP. Therefore, in this study, we investigated the effect of increased cellular NAD⁺ levels on caerulein-induced AP. We demonstrated for the first time that the activities and expression of SIRT1 were suppressed by reduction of intracellular NAD⁺ levels and the p53-microRNA-34a pathway in caerulein-induced AP. Moreover, we confirmed that the increase of cellular NAD⁺ by NQO1 enzymatic action using the substrate β-Lapachone suppressed caerulein-induced AP with down-regulating TLR4-mediated inflammasome signalling, and thereby reducing the inflammatory responses and pancreatic cell death. These results suggest that pharmacological stimulation of NQO1 could be a promising therapeutic strategy to protect against pathological tissue damage in AP.

Knockdown of Myeloid Differentiation Factor 88 Attenuates Lipopolysaccharide-Induced Inflammatory Response in Pancreatic Ductal Cells

OBJECTIVES

The aim of the study was to explore the potential role of myeloid differentiation factor 88 (MyD88), which acts as an adaptor in the TLR4 signalling pathway, in immune responses of the pancreatic duct during acute pancreatitis.

METHODS

Primary cultures of pancreatic duct epithelial cells from Wistar rats and cultures of the pancreatic ductal ARIP cell line were treated with lipopolysaccharide (LPS), and expression of toll-like receptor 4 mRNA was determined using real-time PCR, expression of MyD88 protein using Western blot, and levels of inflammatory cytokines using enzyme-linked immunosorbent assay. These experiments were repeated using ARIP cells in which MyD88 expression was stably knocked down.

RESULTS

Toll-like receptor 4 and MyD88 expression were similar between pancreatic duct epithelial cells and ARIP cells after LPS stimulation. Myeloid differentiation factor 88 knockdown led to significantly lower levels of inflammatory cytokines after LPS induction in ARIP cells.

CONCLUSIONS

Myeloid differentiation factor 88 knockdown attenuates LPS-induced inflammatory responses in pancreatic ductal cells, suggesting that the MyD88 pathway plays a critical role in their immune defense activity.

The effect of lornoxicam on TLR2 and TLR4 messenger RNA expression and tumor necrosis factor-α, interleukin-6, and interleukin-8 secretion in patients with systemic complications of acute pancreatitis

OBJECTIVES

To assess the effects of the cyclooxygenase-1/cyclooxygenase-2 inhibitor lornoxicam on systemic complications in patients with acute pancreatitis, Toll-like receptor (TLR)2 and TLR4 messenger RNA expression, and cytokine secretion (IL-6, IL-8, tumor necrosis factor-α).

METHODS

Adult patients with acute pancreatitis were randomized to standard therapy or standard therapy plus lornoxicam. Standard therapy included analgesics, spasmolytics, octreotide, pantoprazole, and intravenous fluids. The TLR2 and TLR4 expression levels and TLR2- and TLR4-mediated cytokine production in peripheral blood mononuclear cells were assessed in patients with severe complications and in healthy volunteers (n = 15).

RESULTS

A total of 334 patients received standard therapy (n = 246) or standard therapy plus lornoxicam (n = 88), 172 (51.5%) of whom developed systemic complications. Occurrence of complications was higher with standard therapy compared with lornoxicam (57.3% versus 35.2%; P = 0.00034), as was mortality (19.1% versus 6.8%; P = 0.006). The TLR2 and TLR4 expression and TLR2 and TLR4-mediated cytokine production were significantly higher in patients with systemic complications of acute pancreatitis compared with healthy volunteers. Relative TLR2 expression and cytokine production were significantly reduced in patients receiving lornoxicam versus standard therapy.

CONCLUSIONS

The use of lornoxicam at the onset of acute pancreatitis decreased TLR2 and TLR4 expression and the production of proinflammatory cytokines, thereby reducing the risk of systemic complications and mortality.

Sterile inflammation in the liver and pancreas

The ability of tissue injury to result in inflammation is a well-recognized phenomenon and is central to a number of common liver and pancreatic diseases including alcoholic steatohepatitis and pancreatitis, as well as drug-induced liver injury, non-alcoholic steatohepatitis, and pancreatitis from other causes. The requirements of extracellular damage-associated molecules and a cytosolic machinery labeled the inflammasome have been established in in vitro culture systems and in vivo disease models. This has provided a generic insight into the pathways involved, and the challenge now is to understand the specifics of these mechanisms in relation to the particular insults and organs involved. One reason for the excitement in this field is that a number of therapeutic candidates such a toll-like receptor antagonists and interleukin-1R antagonists are either approved or in clinical trials for other indications.

Association of endotoxin and endothelin-1 with acute kidney injury in patients with acute pancreatitis

AIM: To investigate the association of endotoxin and endothelin-1 with acute kidney injury in patients with acute pancreatitis (AP).

METHODS: Fifty-two AP patients with acute kidney injury and equal number of AP patients without acute kidney injury were enrolled in this study. Blood samples were obtained from all patients for laboratory analysis of liver function, renal function, electrolytes, procalcitonin (PCT) and endothelin-1 (ET-1).

RESULTS: The SIRS score showed no significant difference between cases and controls (2.66 ± 0.86 vs 2.30 ± 1.00, t = 1.90, P > 0.05), indicating that both groups suffered from systemic inflammatory response. The levels of PCT (23.24 ng/mL vs 0.23 ng/mL, Z = -7.31, P < 0.05) , ET-1 (7.61 pg/mL ± 2.17 pg/mL vs 2.34 pg/mL ± 1.28 pg/mL, t = 4.98, P < 0.05), urea (Z = -2.17), creatinine (Z = -7.69) and cystatin C (Z = -8.39) were significantly higher in cases than in controls. The mortality and improvement rates also differed significantly between cases and controls (36.5% vs 5.8%; 21.2% vs 94.2%, χ² = 141.92, P < 0.05).

CONCLUSION: Endotoxin and ET-1 are closely associated with the development of acute kidney injury possibly by inducing severe renal vasoconstriction.

Effect of short-term intermittent peritoneal lavage on immune function in rats with early severe acute pancreatitis

AIM: To analyze the role of Toll-like receptor 4 (TLR4), soluble CD14 (sCD14) on monocyte-macrophage cell surface, and nuclear factor kB (NF-kB) in immune mechanisms involved in the therapeutic effect of peritoneal lavage against L-arginine-induced severe acute pancreatitis in rats.

METHODS: Severe acute pancreatitis was induced in rats by intraperitoneal injection of L-arginine (3.5 g/100 g) at a concentration of 70 g/L. Forty-eight rats were randomly divided into three groups: severe acute pancreatitis group (for testing at 12, 24, and 36 h, 6 rats per subgroup), control group (12, 24, and 36 h, 4 rats per subgroup), and lavage group (12, 24, and 36 h, 6 rats per subgroup). Rats of the severe acute pancreatitis group were killed at 12, 24 and 36 h after modeling. Rats of the control group were also killed at the above point of time after intraperitoneal injection of normal saline. Rats of the lavage group were catheterized in the upper and lower abdomen for peritoneal lavage at 1 h after modeling (100 mL, once per 6 h, lavage speed at 60 drops/min; 12 h subgroup, twice, 24 h subgroup 4 times, 36 h group 6 times). After the lavage was finished, the rats were killed. The contents of serum amylase and lipase and the concentrations of TLR4 and sCD14 in the blood were determined, and histopathological changes and expression levels of NF-kB in the pancreatic tissue were observed.

RESULTS: The rat model of severe acute pancreatitis was successfully replicated by intraperitoneal injection of L-arginine. The contents of serum amylase and lipase in the lavage group were significantly lower those in the severe acute pancreatitis group (12 h: 1 253.3 ± 195.2 vs 1 953.3 ± 316.9, 20.0 ± 6.5 vs 86.3 ± 36.8; 24 h: 2 299.2 ± 416.4 vs 4 047.7 ± 589.3, 33.7 ± 15.5 vs 238.2 ± 73.2; 36 h: 1 581.3 ± 391.6 vs 2 327.8 ± 354.6, 22.0 ± 9.3 vs 158.3 ± 38.5, all P < 0.05), but showed no significant difference compared to the control group (all P > 0.05). Pathological changes in the pancreatic tissue in the lavage group were significantly improved compared to the severe acute pancreatitis group and control group (both P < 0.05). The concentrations of TLR4 and sCD14 in the blood were significantly lower in the lavage group than in the severe acute pancreatitis group (P < 0.05), but showed no statistically significant difference compared with the control group at various time points. Expression of NF-kB in the pancreatic tissue was lower in the lavage group than that in the severe acute pancreatitis group, but was almost undetectable in the control group.

CONCLUSION: Short-term intermittent peritoneal lavage has a remarkable inhibitory effect on immune function in rats with early severe acute pancreatitis.

Controversial role of toll-like receptors in acute pancreatitis

Acute pancreatitis (AP) is a common clinical condition with an incidence of about 300 or more patients per million annually. About 10%-15% of patients will develop severe acute pancreatitis (SAP) and of those, 10%-30% may die due to SAP-associated complications. Despite the improvements done in the diagnosis and management of AP, the mortality rate has not significantly declined during the last decades. Toll-like receptors (TLRs) are pattern-recognition receptors that seem to play a major role in the development of numerous diseases, which make these molecules attractive as potential therapeutic targets. TLRs are involved in the development of the systemic inflammatory response syndrome, a potentially lethal complication in SAP. In the present review, we explore the current knowledge about the role of different TLRs that have been described associated with AP. The main candidate for targeting seems to be TLR4, which recognizes numerous damage-associated molecular patterns related to AP. TLR2 has also been linked with AP, but there are only limited studies that exclusively studied its role in AP. There is also data suggesting that TLR9 may play a role in AP.

Trypsin inhibits lipopolysaccharide signaling in macrophages via toll-like receptor 4 accessory molecules

AIMS

To examine the role of trypsin in the immune response of macrophages and to determine whether protease-activated receptors (PARs) are involved in the effects of trypsin.

MAIN METHODS

We used RAW264.7 cells and peritoneal macrophages isolated from C57BL/6 wild-type mice, PAR2 knockout mice, and ddY mice. Macrophages were stimulated with lipopolysaccharide (LPS) in the presence or absence of trypsin, thrombin, and PAR subtype-specific agonists (PARs-AP). Activation of macrophages was quantified by nitric oxide production and expression of inflammatory mediators, such as inducible nitric oxide synthase, interleukin-1β, and interleukin-6. To clarify the effect of trypsin on LPS receptors, we also investigated the expression of toll-like receptor 4 (TLR4), soluble MD-2 (sMD-2), membrane-bound MD-2 (mMD-2), soluble CD14 (sCD14), and membrane-bound CD14 (mCD14). To directly investigate the effect of trypsin on CD14 protein, we expressed recombinant CD14 protein.

KEY FINDINGS

Trypsin inhibited LPS-induced nitric oxide production and expression of inducible nitric oxide synthase, interleukin-1β, and interleukin-6. The same inhibitory effects of trypsin were observed in wild-type macrophages and in PAR2 knockout macrophages. Furthermore, the other PAR agonists, thrombin, PAR1-AP, PAR2-AP, and PAR4-AP, did not mimic the effect of trypsin. Although trypsin did not affect TLR4 or mMD-2 expression, sCD14, mCD14, and sMD-2 expressions were decreased by trypsin. Furthermore, trypsin also degraded recombinant CD14 protein.

SIGNIFICANCE

Trypsin inhibited LPS signaling PAR-independently via degradation of TLR4 accessory molecules. This observation provides a better understanding of the complicated immune response in acute pancreatitis.

Long-lasting effect of infant rats endotoxemia on heat shock protein 60 in the pancreatic acinar cells: involvement of toll-like receptor 4

Introduction. Lipopolysaccharide endotoxin (LPS) is responsible for septic shock and multiorgan failure, but pretreatment of rats with low doses of LPS reduced pancreatic acute damage. Aim. We investigated the effects of the endotoxemia induced in the early period of life on Toll-like receptor 4 (TLR4), heat shock protein 60 (HSP60) and proapoptotic Bax, caspase-9 and -3 or antiapoptotic Bcl-2 protein expression in the pancreatic acinar cells of adult animals. Material and Methods. Newborn rats (25 g) were injected with endotoxin (Escherichia coli) for 5 consecutive days. Two months later, pancreatic acinar cells were isolated from all groups of animals and subjected to caerulein stimulation (10⁻⁸ M). Protein expression was assessed employing Western blot. For detection of apoptosis we have employed DNA fragmentation ladder assay. Results. Preconditioning of newborn rats with LPS increased TLR4, Caspase-9 and -3 levels, but failed to affect basal expression of HSP60, Bax, and Bcl-2. Subsequent caerulein stimulation increased TLR4, Bcl-2, and caspases, but diminished HSP60 and Bax proteins in pancreatic acinar cells. Endotoxemia dose-dependently increased TLR4, Bax, HSP60, and both caspases protein signals in the pancreatic acini, further inhibiting antiapoptotic Bcl-2. Conclusions. Endotoxemia promoted the induction of HSP60 via TLR4 in the infant rats and participated in the LPS-dependent pancreatic tissue protection against acute damage.

Sterile inflammatory response in acute pancreatitis

The initial injury in acute pancreatitis is characteristically sterile and results in acinar cells necrosis. Intracellular contents released from damaged cells into the extracellular space serve as damage-associated molecular patterns (DAMPs) that trigger inflammation. There is increasing evidence that this sterile inflammatory response mediated through DAMPs released from necrotic acinar cells is a key determinant of further pancreatic injury, remote organ injury, and disease resolution in experimental models. A number of DAMPS, including high-mobility group box protein 1, DNA, adenosine triphosphate and heat shock protein 70, have been shown to have a role in experimental pancreatitis. Many of these DAMPs are also detectable in the human pancreatitis. Genetic deletion and pharmacologic antagonism demonstrate that specific DAMP receptors, including Toll-like receptor (TLR) 4, TLR9, and P2X7, are also required for inflammation in experimental acute pancreatitis. Downstream DAMP-sensing components include nod-like receptor protein 3, caspase 1, interleukin-1β (IL-1), IL-18, and IL-1 receptor, and also are required for full experimental pancreatitis. These DAMP-mediated pathways provide novel therapeutic targets using antagonists of TLRs and other receptors.

Toll-like receptor 4 signaling pathway and pancreatitis

The pathogenesis of pancreatitis has long been a hot topic in basic and clinical research but is still not fully clarified. Toll-like receptor 4 (TLR4) recognizes the lipopolysaccharide (LPS) of Gram-negative bacteria and stimulates the synthesis and release of inflammatory cytokines through activation of the NF-κB signaling pathway, which ultimately results in inflammatory responses that involve multiple organs. Animal and clinical studies have shown that the TLR4 signal pathway plays an important role in the development of tissue injury during acute pancreatitis (AP) and up-regulation of TLR4 and the TLR4 signaling pathway contributes to the development of multiple organ dysfunction syndrome (MODS) associated with severe acute pancreatitis (SAP) by increasing proinflammatory cytokines. Therefore, further studies are required to clarify the role of the TLR 4 signaling pathway in the pathogenesis of pancreatitis to explore novel methods for treating this disease.

TLR4 but not TLR2 regulates inflammation and tissue damage in acute pancreatitis induced by retrograde infusion of taurocholate

OBJECTIVE

Neutrophil infiltration is a key regulator in the pathophysiology of acute pancreatitis (AP), although the impact of Toll-like receptors (TLRs) in AP remains elusive. The aim of this study was to define the role of TLR2 and TLR4 in leukocyte recruitment and tissue damage in severe AP.

EXPERIMENTAL DESIGN

AP was induced by retrograde infusion of sodium taurocholate into the pancreatic duct in wild-type, TLR2- and TLR4-deficient mice. Samples were collected 24 h after induction of AP.

RESULTS

Taurocholate challenge caused a clear-cut pancreatic damage characterized by increased acinar cell necrosis, neutrophil infiltration, focal hemorrhage and edema formation, as well as increased levels of blood amylase and CXCL2 (macrophage inflammatory protein-2) in the pancreas and serum. Moreover, challenge with taurocholate increased activation of trypsinogen in the pancreas. Notably, TLR2 gene-deficient mice exhibited a similar phenotype to wild-type mice after challenge with taurocholate. In contrast, tissue damage, pancreatic and lung myeloperoxidase (MPO) activity, serum and pancreatic levels of CXCL2 as well as blood amylase were significantly reduced in TLR4-deficient mice exposed to taurocholate. However, taurocholate-induced activation of trypsinogen was intact in TLR4-deficient mice.

CONCLUSION

Our data suggest a role for TLR4 but not TLR2 in the pathogenesis of severe AP in mice.

Possible role of toll-like receptor 4 in acute pancreatitis

Because the mechanism underlying the development of acute pancreatitis (AP) has not yet been fully clarified, it has been a hot but difficult topic in basic and clinical research for a long time. Currently, the dominant hypothesis for the pathogenesis of AP is that it is a disease of self-digestive acute chemical inflammation induced by trypsin activation. As proteins to trigger the inflammatory response cascade, Toll-like receptors (TLRs), especially TLR4, provide a new clue for studying the pathogenesis of AP from the source. Some studies have found that when TLR4 is activated by certain factors, it can amplify an inflammatory effect and aggravate the body's inflammatory response through a series of signal transduction. Toll-like receptor 4 may play an important role in the synthesis and release of proinflammatory cytokines, and the up-regulation of the TLR4 gene may be related with the development and progression of multiple organ injury during AP. As the "gate" of inflammatory response, TLR4 may be closely associated with the development and progression of multiple organ injury during AP. Understanding the roles of TLR4 in AP will help to further clarify the pathogenesis of AP and to search a new target for the treatment of AP.

Toll-like receptors as therapeutic targets in gastrointestinal diseases

IMPORTANCE OF THE FIELD

Toll-like receptors (TLRs) are innate immunity receptors that recognize several different antigens, initiating immunological/inflammatory responses. Recent evidence associates numerous pathophysiological processes and diseases with dysregulated activation of these receptors, conferring a potential therapeutic value to their modulation.

AREAS COVERED IN THIS REVIEW

The aim of this systematic review that covers literature from the past 10 years is to address the role of TLRs in the pathophysiology of gastrointestinal (GI) diseases as well as the therapeutic potential of modulating TLRs' signaling pathways in GI pathology.

WHAT THE READER WILL GAIN

This review shows that TLRs play an important role in the pathophysiology of several GI diseases and that modulating TLRs signaling pathways may have an enormous therapeutic potential. Different methods for modulation of TLRs' activity in GI tract, with direct agonists/antagonists but also with non-specific substances, like antibiotics or probiotics, are presented.

TAKE HOME MESSAGE

Even though TLRs modulators have been used for therapy in some GI diseases, further research, particularly in humans, is needed in order to establish the precise role of the different TLRs in the diverse GI diseases and to motivate clinical trials that consider TLRs as therapeutic targets in GI pathology.

TRAF6 as the key adaptor of TLR4 signaling pathway is involved in acute pancreatitis

OBJECTIVES

To study the potential role of tumor necrosis factor receptor-associated factor 6 (TRAF6) as the key adaptor of the toll-like receptor 4 (TLR4) signaling pathway in acute pancreatitis (AP) in mice.

METHODS

Acute pancreatitis was induced by 7 intraperitoneal injections of cerulein in TLR4-deficient (TLR4-Def) and TLR4 wild-type (TLR4-WT) mice. Inflammatory severity was scored and evaluated based on pathological study. TRAF6 expression was determined by reverse transcriptase polymerase chain reaction, Western blot, and immunohistochemistry.

RESULTS

Acute pancreatitis was successfully induced in both mice strains, but the inflammatory progression was different. In TLR4-Def mice, pancreatic inflammation was blunt and mild first, then became increasingly intensive and peaked at the later stage, whereas in the TLR4-WT mice, the response was fast initiated and peaked at the early stage of AP, then alleviated gradually. TRAF6 expression in TLR4-Def mice was significantly higher than that in the TLR4-WT mice. Immunohistochemistry located TRAF6 expressed mainly in the pancreatic acinar cells.

CONCLUSIONS

The TLR4-TRAF6 signaling pathway is critically involved in AP. Other signaling pathways beyond TLR4 may participate in the pancreatic inflammatory process via TRAF6. As a convergence point of the TLR4-dependent and the TLR4-independent signaling pathways, TRAF6 plays an important role in AP.

Effects of Salvia miltiorrhizae on ICAM-1, TLR4, NF-kappaB and Bax proteins expression in multiple organs of rats with severe acute pancreatitis or obstructive jaundice

To observe the protective effects of Salvia miltiorrhizae injection on multiple organs of rats with SAP or OJ. Two hundred eighty-eight rats were used for SAP-associated experiments and OJ-associated experiments. The rats were randomly divided into sham-operated, model control and treated group. According to the different time points after operation, the SAP rats in each group were subdivided into 3, 6 and 12 h groups while the OJ rats were divided into 7, 14, 21 and 28 days groups. The mortality rates, pathological changes and ICAM-1 (only in lung), TLR4 (only in liver), Bax and NF-kappaB proteins expression in multiple organs (liver, kidney, lung, intestinal mucosa, spleen, thymus and lymph nodes) were observed, respectively. The mortality rates of treated groups decreased in both SAP and OJ experiments. Compared to model control group, the pathological changes can be seen in treated groups including; (1) the pathological changes of multiple organs in SAP and OJ experiments were improved, the pathological severity scores of kidney (at 6 h), intestinal mucosa (at 12 h), spleen (at 6 and 12 h), thymus (at 3 and 6 h) and lymph nodes (at 3 and 6 h) in SAP experiment and of liver (on 21 and 28 days), lung (21 days), intestinal mucosa (on 21 and 28 days) and spleen (on 21 and 28 days) in OJ experiment significantly declined (P < 0.05 or P < 0.01); (2) the positive rate of Bax protein in pancreas (at 3 h) and liver (on 6 and 12 h) in SAP experiment and in liver (on 28 days), kidney (on 21 days), and thymus (on 28 days) in OJ experiment were significantly lower (P < 0.05 or P < 0.01); (3) the positive rate of NF-kappaB in liver (at 12 h) and kidney (at 6 h) in SAP experiment and in liver (on 21 days), kidney (on 28 days), intestinal mucosa (on 28 days) and thymus (on 14 days) in OJ experiment significantly decreased (P < 0.05). (4) the positive rate of ICAM-1 in lungs (at 12 h) in SAP experiment was significantly less (P < 0.05). Salvia miltiorrhizae injection can protect multiple organs of SAP or OJ rats and inhibit the expression of ICAM-1, TLR4, NF-kappaB and regulate Bax proteins. Salvia miltiorrhizae may relieve the inflammation response and enhance the immunity function of SAP and OJ rats.

Effect of salvia miltiorrhizae on the expressions of TLR4 protein in the liver of rats with SAP or OJ

To investigate the effect of salvia miltiorrhizae on the expressions of TLR4 protein in the liver of rats with severe acute pancreatitis (SAP) and obstructive jaundice (OJ), and explore the protective mechanism of salvia miltiorrhizae on the liver of rats. A total of 288 mice was used in SAP- (n = 108) and OJ-associated experiments (n = 180). The rats were randomly divided into sham-operated, model control and treated group. Based on the different time points after operation, these groups were subdivided into 3, 6 and 12 h subgroups (SAP rats, n = 12) or 7, 14, 21 and 28 days subgroups (OJ rats, n = 15). At the corresponding time points after operation, blood and liver specimens were collected to determine the contents of endotoxin and TNF-alpha in the blood as well as the expression levels of TLR4 protein in the liver. Compared with the corresponding model control group, though the number of dead SAP or OJ rats in the treated group declined, no statistical difference was noted; The levels of plasma endotoxin in SAP (at 6 and 12 h) or OJ rats in the treated group decreased significantly (P < 0.001 and P < 0.01, respectively); The levels of serum TNF-alpha in SAP (at 12 h) or OJ rats (on 14 days) declined (P < 0.001 and P < 0.01, respectively); The staining intensity as well as the product of staining intensity and positive rate of TRL4 protein only significantly declined on 7 and 28 days in OJ rats (P < 0.01). On 7 days, treated group in positive rate of TLR4 protein were significantly lower than that in model control group (P < 0.01). The pathological changes in different treated groups of SAP and OJ rats were improved. Salvia miltiorrhizae is able to reduce the levels of plasma endotoxin and inhibit effectively the expressions of TLR4 protein in the liver of SAP or OJ rats, thereby decreasing inflammatory reaction and exerting protective effect on liver function.

Toll-like receptors and their role in gastrointestinal disease

The innate immune response to invading pathogens is centred upon a family of non-clonal, germline-encoded pattern recognition receptors (PRRs), the Toll-like receptors (TLRs). These provide specificity for a vast range of microbial pathogens, and offer an immediate anti-microbial response system. Thirteen mammalian TLRs have been described; 10 are expressed in humans, each responsible for the recognition of distinct, invariant microbial structures originating from bacteria, viruses, fungi and protozoa. The two most thoroughly studied are TLR4 and TLR2, the PRRs for Gram-negative and Gram-positive bacterial products, respectively. TLR4 is also the major receptor recognising endogenous ligands released from damaged or dying cells. Activation of a TLR by its relevant ligand rapidly ignites a complex intracellular signaling cascade that ultimately results in upregulation of inflammatory genes and production of proinflammatory cytokines, interferons and recruitment of myeloid cells. It also stimulates expression, upon antigen presenting cells, of co-stimulatory molecules required to induce an adaptive immune response. Whilst a robust TLR response is critical for survival and defence against invading pathogens, inappropriate signaling in response to alterations in the local microflora environment can be detrimental. Such 'unhelpful TLR responses' could form the basis for a large number of gastrointestinal and liver disorders, including inflammatory bowel disease, viral hepatitis, autoimmune liver diseases and hepatic fibrosis. As our understanding of TLRs expands, the pathogenesis of a number of gastrointestinal disorders will be further elucidated, and this offers potential for specific therapies aimed directly at TLR signaling.

Potential role of the TLR4/IRAK-4 signaling pathway in the pathophysiology of acute pancreatitis in mice

OBJECTIVE AND DESIGN

Toll-like receptor 4 (TLR4) is potentially associated with acute pancreatitis (AP), but its exact role remains controversial. IL-1 receptor-associated kinase 4 (IRAK-4) is a common mediator of Toll-like receptors pathways, with an essential role in transducing downstream signals. This study investigates the potential role of the TLR4 pathway, in particular IRAK-4, in a murine model of AP.

METHODS

Acute pancreatitis was induced in wild-type and TLR4-deficient mice by intraperitoneal injections of caerulein (50 microg/kg). Pancreatic pathological scores and myeloperoxidase activity were dynamically measured, along with pancreatic TLR4 and IRAK-4 mRNA and protein.

RESULTS

In wild-type mice, pathological scores and myeloperoxidase activity were rapidly increased at 1, 2 and 4 h, followed by alleviation at 12 and 24 h. In TLR4-deficient mice, they were slightly increased within 2 h, but became more severe at 12 and 24 h. IRAK-4 mRNA and protein were significantly down-regulated at 1, 2 and 4 h in wild-type mice. Unexpectedly, TLR4-deficient mice showed more profound reductions of IRAK-4 mRNA and protein at the same time.

CONCLUSIONS

TLR4 deficiency delayed the initiation of pancreatitis, implying a potential role for TLR4 during AP. IRAK-4 might function during AP, but independently of TLR4.

Therapeutic effect of sandostatin with salviae miltiorrhizae on experimental severe acute pancreatitis

AIM: To study therapeutic effects of sandostatin (SS) with salviae miltiorrhizae (SM) on experimental acute necrotizing pancreatitis (ANP).

METHODS: ANP models were induced by retrograde injection of 15 g/L sodium deoxycholate. Forty rats and one hundred fifty mice were randomly divided into five groups: ANP group, sham group, SS group, SM group and combination group with fifty mice and eight rats in each group respectively. Three-day mortality rate of mice was estimated. Serum amylase, NO, endotoxin, TNF-α and IL-6 24 h after the injection were measured and pancreatic histological changes were examined using light microscopy.

RESULTS: Compared with sham group, 3-d mortality rate in mice, amylase, NO, endotoxin, TNF-α and IL-6 of rats in 24 h ANP group were significantly higher (83.3% vs 0.0%, 1521.3 ± 57.9 U/dL vs 659.5 ± 58.7 U/dL, 115.2 ± 9.7 mmol/L vs 34.3 ± 2.1 mmol/L, 0.438 ± 0.137 EU/mL vs 0.029 ± 0.012 EU/mL, 191.7 ± 14.1 ng/L vs 47.5 ± 5.8 ng/L, 152.4 ± 14.7 ng/L vs 41.7 ± 5.8 ng/L, all P < 0.01), and the damage to pancreatic tissue observed by light microscopy was more severe. Compared with ANP group, the above-mentioned indexes of SM group, SS group and combination group were obviously improved (P < 0.05), especially in combination group (P < 0.05).

CONCLUSION: The therapeutic effect of sandostatin with salviae miltiorrhizae inoidesellis on ANP is superior to western medicine or traditional Chinese medicine used alone.

The toll-like receptor signaling molecule Myd88 contributes to pancreatic beta-cell homeostasis in response to injury

Commensal flora and pathogenic microbes influence the incidence of diabetes in animal models yet little is known about the mechanistic basis of these interactions. We hypothesized that Myd88, an adaptor molecule in the Toll-like-receptor (TLR) pathway, regulates pancreatic beta-cell function and homeostasis. We first examined beta-cells histologically and found that Myd88-/- mice have smaller islets in comparison to C57Bl/6 controls. Myd88-/- mice were nonetheless normoglycemic both at rest and after an intra-peritoneal glucose tolerance test (IPGTT). In contrast, after low-dose streptozotocin (STZ) challenge, Myd88-/-mice had an abnormal IPGTT relative to WT controls. Furthermore, Myd88-/- mice suffer enhanced beta-cell apoptosis and have enhanced hepatic damage with delayed recovery upon low-dose STZ treatment. Finally, we treated WT mice with broad-spectrum oral antibiotics to deplete their commensal flora. In WT mice, low dose oral lipopolysaccharide, but not lipotichoic acid or antibiotics alone, strongly promoted enhanced glycemic control. These data suggest that Myd88 signaling and certain TLR ligands mediate a homeostatic effect on beta-cells primarily in the setting of injury.

Increased levels of soluble triggering receptor expressed on myeloid cells-1 in patients with acute pancreatitis

OBJECTIVE

To determine the contribution of triggering receptor expressed on myeloid cells (TREM)-1 in acute pancreatitis (AP).

DESIGN

Prospective study.

SETTING

General intensive care unit at Kobe University Hospital.

PATIENTS

Forty-eight patients with AP and seven patients as control.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

We measured serum concentrations of soluble TREM-1 (sTREM-1) at the time of admission by enzyme-linked immunoadsorbent assay. Serum sTREM-1 levels increased significantly in AP (63 +/- 11 pg/mL) and correlated with Ranson score (R = .628, p < .001) and Acute Physiology and Chronic Health Evaluation II score (R = .504, p < .001). Serum TREM-1 levels were higher in patients with early organ dysfunction (which occurred within 7 days after onset) than those without early organ dysfunction (101 +/- 19 vs. 25 +/- 4 pg/mL, p < .001). Incidences of early organ dysfunction in patients whose serum sTREM-1 levels were < or = 40 and > 40 pg/mL were 17% and 83%, respectively (p < .001). The usefulness of serum sTREM-1 in detecting early organ dysfunction was superior to that of C-reactive protein, interleukin-6, interleukin-8, Ranson score, and Acute Physiology and Chronic Health Evaluation II score. Serum sTREM-1 levels decreased with resolution of early organ dysfunction.

CONCLUSIONS

Serum sTREM-1 levels were significantly increased and correlated with disease severity and early organ dysfunction in patients with AP. Serum sTREM-1 level may be a useful marker for early organ dysfunction in AP.