Involvement of peritoneal macrophage in the induction of cytotoxicity due to apoptosis in ascitic fluid associated with severe acute pancreatitis

Thymol regulates the functions of immune cells in the rat peritoneal cavity after l-arginine-induced pancreatitis

AIMS

The present study aimed to evaluate the protective action of thymol towards l-arginine-induced acute pancreatitis (AP) by studying the function of rat peritoneal immune cells.

MAIN METHODS

Rat peritoneal exudate cells (PECs), obtained 24 h after the injection of l-arginine (350 mg/100 g of b.w.), were evaluated for mitochondrial activity (MTT assay), adherence capacity (methylene-blue assay), and phagocyte enzyme activity (myeloperoxidase, MPO, assay). The activity of α-amylase and free MPO, as well as the concentration of reactive oxygen species (ROS, i.e. O₂^-), were determined in the peritoneal exudate fluid. Also, serum α-amylase activity determination and pancreatic tissue pathohistological analysis were performed.

KEY FINDING

The administered thymol (50 and 100 mg/kg, per os) caused a significant decrease in the PEC mitochondrial activity and adherence capacity when compared with these functions of PECs isolated from rats with AP. A decrease in cellular MPO activity, as well as in the levels of ROS, α-amylase, and free MPO in peritoneal exudates was found in animals treated with thymol compared to the control animals with AP. Additionally, thymol administration prevented an increase in serum α-amylase activity, accompanied by the decrease in pancreatic tissue damage that follows l-arginine application.

SIGNIFICANCE

The present results showed that thymol exerts significant immunomodulatory properties and a potential to silence PEC functions in inflammatory conditions such as the AP induced by l-arginine.

Abdominal paracentesis drainage attenuates severe acute pancreatitis by enhancing cell apoptosis via PI3K/AKT signaling pathway

Our previous studies have shown that abdominal paracentesis drainage (APD) is a safe and effective strategy for patients with severe acute pancreatitis (SAP). However, the underlying mechanisms behind APD treatment remain poorly understood. Given that apoptosis is a critical pathological response of SAP, we here aim to investigate the effect of APD on cell apoptosis in pancreatic tissues during SAP and to explore its potential molecular mechanism. SAP was induced by 5% sodium-taurocholate retrograde while APD group was inserted a drainage tube into the right lower abdomen of rats immediately after SAP induction. Histopathological staining, serum amylase, endotoxin and inflammatory mediators were measured. Cell apoptosis, apoptosis-related proteins and signaling pathway were also evaluated. Our results demonstrated that APD treatment significantly attenuated pancreatic damage and decreased the serum levels of amylase, endotoxin, TNF-α, IL-1 and IL-6 in rats with SAP. Notably, APD treatment enhanced cell apoptosis and reduced necrosis in pancreatic tissues, as evidenced by Tunnel staining, the increased pro-apoptosis proteins (Cleaved-caspase-3 and bax) and decreased anti-apoptosis protein (Bcl-2). Moreover, the effect of APD on cell apoptosis was further confirmed by the regulatory pathway of PI3K/AKT and NF-kB signaling pathway. These results suggest that APD attenuates the severity of SAP by enhancing cell apoptosis via suppressing PI3K/AKT signaling pathway. Our findings provide new insights for understanding the effectiveness of APD in patients with SAP.

Alcohol and Smoking Mediated Modulations in Adaptive Immunity in Pancreatitis

Pancreatitis is a condition of pancreatic inflammation driven by injury to the pancreatic parenchyma. The extent of acinar insult, intensity, and type of immune response determines the severity of the disease. Smoking, alcohol and autoimmune pancreatitis are some of the predominant risk factors that increase the risk of pancreatitis by differentially influencing the adaptive immune system. The overall decrease in peripheral lymphocyte (T-, B- and (natural killer T-) NKT-cell) count and increased infiltration into the damaged pancreatic tissue highlight the contribution of adaptive immunity in the disease pathology. Smoking and alcohol modulate the responsiveness and apoptosis of T- and B-cells during pancreatic insult. Acute pancreatitis worsens with smoking and alcohol, leading to the development of systemic inflammatory response syndrome and compensatory anti-inflammatory response syndrome, suggesting the critical role of adaptive immunity in fatal outcomes such as multiple organ dysfunction. The presence of CD4⁺ and CD8⁺ T-lymphocytes and perforin-expressing cells in the fibrotic tissue in chronic pancreatitis modulate the severity of the disease. Due to their important role in altering the severity of the disease, attempts to target adaptive immune mediators will be critical for the development of novel therapeutic interventions.

Abdominal paracentesis drainage ameliorates severe acute pancreatitis in rats by regulating the polarization of peritoneal macrophages

AIM

To investigate the role of peritoneal macrophage (PM) polarization in the therapeutic effect of abdominal paracentesis drainage (APD) on severe acute pancreatitis (SAP).

METHODS

SAP was induced by 5% Na-taurocholate retrograde injection in Sprague-Dawley rats. APD was performed by inserting a drainage tube with a vacuum ball into the lower right abdomen of the rats immediately after the induction of SAP. To verify the effect of APD on macrophages, PMs were isolated and cultured in an environment, with the peritoneal inflammatory environment simulated by the addition of peritoneal lavage in complete RPMI 1640 medium. Hematoxylin and eosin staining was performed. The levels of pancreatitis biomarkers amylase and lipase as well as the levels of inflammatory mediators in the blood and peritoneal lavage were determined. The polarization phenotypes of the PMs were identified by detecting the marker expression of M1/M2 macrophages via flow cytometry, qPCR and immunohistochemical staining. The protein expression in macrophages that had infiltrated the pancreas was determined by Western blot.

RESULTS

APD treatment significantly reduced the histopathological scores and levels of amylase, lipase, tumor necrosis factor-α and interleukin (IL)-1β, indicating that APD ameliorates the severity of SAP. Importantly, we found that APD treatment polarized PMs towards the M2 phenotype, as evidenced by the reduced number of M1 macrophages and the reduced levels of pro-inflammatory mediators, such as IL-1β and L-selectin, as well as the increased number of M2 macrophages and increased levels of anti-inflammatory mediators, such as IL-4 and IL-10. Furthermore, in an in vitro study wherein peritoneal lavage from the APD group was added to the cultured PMs to simulate the peritoneal inflammatory environment, PMs also exhibited a dominant M2 phenotype, resulting in a significantly lower level of inflammation. Finally, APD treatment increased the proportion of M2 macrophages and upregulated the expression of the anti-inflammatory protein Arg-1 in the pancreas of SAP model rats.

CONCLUSION

These findings suggest that APD treatment exerts anti-inflammatory effects by regulating the M2 polarization of PMs, providing novel insights into the mechanism underlying its therapeutic effect.

The oncogenic microRNA miR-21 promotes regulated necrosis in mice

MicroRNAs (miRNAs) regulate apoptosis, yet their role in regulated necrosis remains unknown. miR-21 is overexpressed in nearly all human cancer types and its role as an oncogene is suggested to largely depend on its anti-apoptotic action. Here we show that miR-21 is overexpressed in a murine model of acute pancreatitis, a pathologic condition involving RIP3-dependent regulated necrosis (necroptosis). Therefore, we investigate the role of miR-21 in acute pancreatitis injury and necroptosis. miR-21 deficiency protects against caerulein- or L-arginine-induced acute pancreatitis in mice. miR-21 inhibition using locked-nucleic-acid-modified oligonucleotide effectively reduces pancreatitis severity. miR-21 deletion is also protective in tumour necrosis factor-induced systemic inflammatory response syndrome. These data suggest that miRNAs are critical participants in necroptosis and miR-21 enhances cellular necrosis by negatively regulating tumour suppressor genes associated with the death-receptor-mediated intrinsic apoptosis pathway, and could be a therapeutic target for preventing pathologic necrosis.

Anti-inflammatory effects of peritoneal lavage in acute pancreatitis

OBJECTIVES

Intraperitoneal administration of trypsin stimulates the production of cytokines from peritoneal macrophages. Removing the pancreatitis-associated ascitic fluid from the peritoneal cavity may decrease the systemic inflammatory response in acute pancreatitis (AP). We investigated the effect of peritoneal lavage on the systemic inflammatory response in severe AP.

METHODS

Acute pancreatitis was induced in Wistar rats by 5% taurocholate intraductal injection. Peritoneal lavage was performed for 4 hours after onset of AP. At 4 hours after induction of AP, serum samples were assayed for amylase and inflammatory cytokines (tumor necrosis factor α, interleukin-6 [IL-6], and IL-10). Expression of pancreatic cyclooxygenase-2 and inducible nitric oxide synthase, liver mitochondrial function, and pulmonary myeloperoxidase activities were determined.

RESULTS

Peritoneal lavage after AP led to a decrease in serum levels of tumor necrosis factor α and IL-6 and an increase in IL-10. In the pancreas, this treatment reduced cyclooxygenase-2 and inducible nitric oxide synthase expression. Liver mitochondrial dysfunction was also reduced. There were no differences on serum amylase levels and pulmonary myeloperoxidase between groups with AP.

CONCLUSIONS

Peritoneal lavage has a systemic anti-inflammatory effect in severe AP and may be able to decrease the severity of severe AP.

Role of macrophages in the progression of acute pancreatitis

In addition to pancreatic cells, other inflammatory cell populations contribute to the generation of inflammatory mediators during acute pancreatitis. In particular, macrophages could be activated by mediators released during pancreatitis by a damaged pancreas. It has been reported that peritoneal macrophages, alveolar macrophages and Kupffer cells become activated in different stages of severe acute pancreatitis. However, macrophages display remarkable plasticity and can change their physiology in response to environmental cues. Depending on their microenvironmental stimulation, macrophages could follow different activation pathways resulting in marked phenotypic heterogeneity. This ability has made these cells interesting therapeutical targets and several approaches have been assayed to modulate the progression of inflammatory response secondary to acute pancreatitis. However, despite the recent advances in the modulation of macrophage function in vivo, the therapeutical applications of these strategies require a better understanding of the regulation of gene expression in these cells.

Role of triggering receptor expressed on myeloid cells-1 in experimental severe acute pancreatitis

BACKGROUND/PURPOSE

Triggering receptor expressed on myeloid cells-1 (TREM-1) is a regulator of immunity and an amplifier of inflammatory signaling. The aim was to clarify the role of TREM-1 in the pathophysiology of experimental severe acute pancreatitis (SAP).

METHODS

SAP was induced by retrograde injection of 3 and 20% sodium deoxycholate (DCA) into the biliopancreatic ducts in rats (DCA pancreatitis). Soluble TREM-1 levels in serum, ascitic fluid, pancreas, liver and kidney were determined with an established available enzyme-linked immunosorbent assay (ELISA) kit. To clarify the source of soluble TREM-1 in serum and ascitic fluid, peritoneal macrophage depletion was done. Moreover, the effect of blockade of TREM-1 pathway was examined using LP17 (a synthetic TREM-1 inhibitor).

RESULTS

Soluble TREM-1 levels in serum and ascitic fluid were higher in SAP. Membrane-bound TREM-1 protein was increased in pancreas, liver and kidney in SAP. Peritoneal macrophage depletion resulted in the reduction of soluble TREM-1 levels in serum and ascitic fluid. Pretreatment with LP17 improved the hepatic and renal dysfunction (serum aspartate aminotransferase and blood urea nitrogen levels) in SAP.

CONCLUSIONS

TREM-1 may act as an important mediator for inflammation and organ injury in SAP. TREM-1 may be a potential therapeutic target for the development of SAP and associated organ dysfunction.

Ablation of proliferating microglia does not affect motor neuron degeneration in amyotrophic lateral sclerosis caused by mutant superoxide dismutase

Microglial activation is a hallmark of all neurodegenerative diseases including amyotrophic lateral sclerosis (ALS). Here, a detailed characterization of the microglial cell population within the spinal cord of a mouse model of familial ALS was performed. Using flow cytometry, we detected three distinct microglial populations within the spinal cord of mice overexpressing mutant superoxide dismutase (SOD1): mature microglial cells (CD11b(+), CD45(low)), myeloid precursor cells (CD11b(+), CD45(int)), and macrophages (CD11b(+), CD45(high)). Characterization of cell proliferation within the CNS of SOD1(G93A) mice revealed that the expansion in microglial cell population is mainly attributable to the proliferation of myeloid precursor cells. To assess the contribution of proliferating microglia in motor neuron degeneration, we generated CD11b-TK(mut-30); SOD1(G93A) doubly transgenic mice that allow the elimination of proliferating microglia on administration of ganciclovir. Surprisingly, a 50% reduction in reactive microglia specifically in the lumbar spinal cord of CD11b-TK(mut-30); SOD1(G93A) doubly transgenic mice had no effect on motor neuron degeneration. This suggests that proliferating microglia-expressing mutant SOD1 are not central contributors of the neurodegenerative process in ALS caused by mutant SOD1.

Pancreatitis-associated ascitic fluid induces hepatocyte death independent of local cytokines

INTRODUCTION

Kupffer-cell-derived cytokines mediate liver injury, yet macrophage pacification does not abolish hepatocyte injury. We undertook this study to examine the role of pancreatitis-associated ascitic fluid (PAAF) in liver injury.

METHODS

Pathogen-free PAAF was perfused into healthy rat livers in situ for 60 min (n = 5, sham = 5, LPS = 5). AST, ALT, LDH, and TNF were measured in the effluent. Primary cultures of rat Kupffer cells or hepatocytes were treated with PAAF; AST, ALT, LDH, and TNF were measured and cell proliferation was determined by MTT assay. A hepatocyte human cell line (CCL-13) was treated with PAAF and apoptosis was measured by flow cytometry.

RESULTS

Liver perfusion with PAAF induced a >15-fold increase in AST/ALT/LDH (P < 0.001 PAAF vs sham), but not in TNF. In vitro, Kupffer cell viability was sharply reduced by PAAF in a dose-dependent manner; however, 5% PAAF (50% viability) did not induce TNF production from Kupffer cells. PAAF induced a multifold increase in AST/ALT/LDH from fresh hepatocytes (P < 0.001 vs control), which was not attenuated by a protease inhibitor. The CCL-13 cell population was reduced to 15 +/- 2% of baseline by PAAF (P < 0.001 vs control), whereas elastase, trypsin, or TNF had no effect. PAAF increased the percentage of nonviable CCL-13 cells (78 +/- 4% vs 28 +/- 1%, P < 0.001 vs control). Neither protease inhibitor nor heat inactivation of PAAF altered this pattern of hepatocyte death.

CONCLUSION

PAAF induces direct hepatocyte injury and death by heat-stable factors other than pancreatic enzymes but not via local production of Kupffer-cell-derived cytokines.

Peritoneal inflammatory cells in acute pancreatitis: Relationship of infiltration dynamics and cytokine production with severity of illness

BACKGROUND

The purpose of this study was to clarify the still poorly understood dynamics of peritoneal inflammatory cells (PICs) in acute pancreatitis.

METHODS

Acute pancreatitis of 3 different degrees of severity was induced in male Wistar rats. Peritoneal lavage was performed at 1, 6, 12, and 24 hours after the induction, and the fluids collected were analyzed for the number and subpopulation of PICs. The levels of apoptosis and necrosis, cytokines, and bacterial infection were also investigated.

RESULTS

The number of PICs was increased in mild and moderate pancreatitis, and the infiltration of inflammatory cells had occurred. In severe pancreatitis, the number of PICs increased until 6 hours after the induction, but thereafter the number decreased. Infiltration of neutrophils occurred 6 hours after the induction, but it was not sustained thereafter and infiltration of peritoneal macrophages did not occur. Cytokines in the lavage fluid increased in all 3 models during the first 6 hours after the induction. Subsequently, cytokines were reduced in mild and moderate pancreatitis but significantly increased in severe pancreatitis. The level of bacterial infection increased according to the severity.

CONCLUSIONS

The relationship between the PIC dynamics and cytokine levels in severe pancreatitis is very different from that observed in mild or moderate pancreatitis.

Activation of adenosine A2a receptor pathway reduces leukocyte infiltration but enhances edema formation in rat caerulein pancreatitis

INTRODUCTION

Adenosine plays important roles in a variety of pathophysiologic conditions through receptor-mediated mechanisms. Recent studies have shown that adenosine exerts potent anti-inflammatory properties that are chiefly brought about through the occupancy of the A2a receptor.

AIM

To examine the effect of A2a receptor stimulation or inhibition on the pathologic findings during acute pancreatitis.

METHODOLOGY

Rats were randomized into three groups and received a selective A2a receptor agonist CGS-21680 (CGS), a selective A2a antagonist 3,7-dimethyl-1-[2-propynyl]-xanthine (DMPX), or saline. Thirty minutes after the injection, acute pancreatitis was produced in the rats by seven intraperitoneal injections of caerulein. The severity of acute pancreatitis was evaluated by serum amylase activity, pancreas myeloperoxidase (MPO) activity, Evans blue extravasation, and pathologic changes of the pancreas. In addition, we investigated the effects of CGS on the pathologic findings of caerulein pancreatitis induced in neutrophil-depleted rats.

RESULTS

Administration of caerulein produced hyperamylasemia and morphologic changes of the pancreas including interstitial edema, acinar cell vacuolization, and infiltration of inflammatory cells. In CGS-treated rats, the pancreatic edema and the Evans blue extravasation were aggravated significantly compared with those of saline-treated rats, whereas leukocyte infiltration and MPO activity of the pancreas were decreased. In contrast to CGS, administration of DMPX ameliorated the pancreatic edema and Evans blue extravasation. Treatment with CGS accelerated the pancreatic edema in pancreatitis even after the depletion of neutrophils.

CONCLUSION

The activation of adenosine A2a receptors modulates the pathology of acute pancreatitis through at least two diverse properties. One is an anti-inflammatory effect involving neutrophils, and the other is a propagating effect for pancreatic edema formation. The actions of the A2a receptor pathways are unique, and they may have an important role in the progression of acute pancreatitis.

Peripheral lymphocyte reduction in severe acute pancreatitis is caused by apoptotic cell death

To investigate impairment of cellular immunity in severe acute pancreatitis, alterations of peripheral lymphocytes in acute pancreatitis were examined. In 48 patients with severe acute pancreatitis, the mean peripheral lymphocyte count on admission was 959 + 105/mm3, and it was significantly decreased in the patients with subsequent infection (623 +/- 90/mm3 ) in comparison to those without infection (1084 +/- 135/mm(3)). According to an analysis of lymphocyte subsets, although both B and T lymphocytes were decreased in peripheral circulation in the patients with infection, it was primarily CD8-positive lymphocytes that decreased in these subsets. Cell cycle analysis of lymphocytes collected from these patients indicated that apoptotic changes occurred after 24 hours' incubation in lymphocytes from patients with severe pancreatitis but not in lymphocytes from healthy control subjects. In a rat model of experimental necrotizing pancreatitis, total peripheral lymphocytes and T lymphocytes were significantly decreased 5 hours after induction of pancreatitis. In severe pancreatitis, peripheral lymphocytes are eliminated from systemic circulation possibly as a result of apoptosis. It has been suggested that impairment of cellular immunity due to peripheral lymphocyte apoptosis is linked to the development of subsequent infectious complications in acute pancreatitis.

Macrophage-derived transforming growth factor-beta1 induces hepatocellular injury via apoptosis in rat severe acute pancreatitis

BACKGROUND

The mechanism of acute pancreatitis-induced hepatocellular injury is unclear. We have observed hepatocyte apoptosis in rat acute necrotizing pancreatitis. These studies were designed to determine the mediator(s) responsible for hepatocyte apoptosis and to clarify the significance of macrophages as its source.

METHODS

A rat sodium deoxycholate-induced pancreatitis model was used. Immunohistochemical studies for apoptosis-inducing mediators on hepatocytes were examined in the liver and on the peritoneal macrophages. The levels of transforming growth factor-beta1 (TGF-beta1) were also evaluated quantitatively with an enzyme-linked immunosorbent assay. Induction of apoptosis on the hepatocytes was evaluated by in situ nick-end labeling and tissue DNA fragmentation enzyme-linked immunosorbent assay. Finally, the effects of TGF-beta1 neutralization and macrophage depletion were examined.

RESULTS

In the liver and the peritoneal macrophages, strong expression of TGF-beta1 was detected early in the course of pancreatitis. In sodium deoxycholate-induced pancreatitis, the levels of TGF-beta1 were also elevated in the plasma (9.2 +/- 0.8 ng/mL), in the pancreatitis-associated ascitic fluid (11.5 +/- 0.6 ng/mL), and in the liver homogenate (2.8 +/- 0.3 ng/g of liver tissue). Moreover, the amount of fragmented DNA of the liver with pancreatitis was 290% +/- 20% of that with a sham operation and serum alanine aminotransferase levels elevated to 248.2 +/- 67.0 IU/L. TGF-beta1 neutralization partly blocked the positive labeling on the nuclei of the hepatocytes, the elevation of the amounts of fragmented DNA (205% +/- 10% of sham operation), and the serum alanine aminotransferase level (144.2 +/- 14.9 IU/L). On the other hand, the macrophage depletion caused a marked decrease in the TGF-beta1 protein level in the plasma (4.8 +/- 1.2 ng/mL) or in the pancreatitis-associated ascitic fluid (8.0 +/- 1.0 ng/mL). Moreover, the macrophage depletion completely inhibited the elevation of the TGF-beta1 protein level in the liver homogenate (1.5 +/- 0.4 ng/g of liver tissue), and thereafter decreased the amounts of the positive labeling on the nuclei of the hepatocytes and decreased the amount of fragmented DNA (120% +/- 18% of sham operation) and the serum alanine aminotransferase elevation (119.2 +/- 24.2 IU/L).

CONCLUSIONS

In a model of sodium deoxycholate-induced pancreatitis, macrophages are responsible for pancreatitis-induced hepatocellular injury by means of apoptosis, and macrophage-derived TGF-beta1 is one of the major factors inducing the hepatocyte apoptosis.