Protein kinase C modulates the pulmonary inflammatory response in acute pancreatitis

Downregulation of TNF-α/TNF-R1 Signals by AT-Lipoxin A4 May Be a Significant Mechanism of Attenuation in SAP-Associated Lung Injury

Our previous studies verified the potent anti-inflammatory effects against severe acute pancreatitis (SAP) of AT-Lipoxin A4 and their analogues. However, the anti-inflammatory effects of AT-Lipoxin A4 on SAP-associated lung injury are not thoroughly known. We used western blot, polymerase chain reaction (PCR), and immunofluorescence to investigate the downregulation of TNF-α signals in cellular and animal models of SAP-associated lung injury following AT-Lipoxin A4 intervention. In vitro, we found that AT-Lipoxin A4 markedly suppressed protein expression in TNF-α signals in human pulmonary microvascular endothelial cell, such as tumor necrosis factor receptor-associated factor 2 (TRAF2), TNF-R1-associated death domain (TRADD), receptor-interacting protein (RIP), vascular cell adhesion molecule-1 (VCAM-1), and E-selectin. Moreover, AT-Lipoxin A4 inhibited downstream signals activated by TNF-α, including NF-κB/p65, JNK/MAPK, and ERK/MAPK. In vivo, AT-Lipoxin A4 significantly decreased pathological scores of the pancreas and lungs and the serum levels of IL-6 and TNF-α. Immunofluorescence, western blotting, and real-time PCR assay showed that AT-Lipoxin A4 significantly attenuated the expression of TNF-R1, TRADD, TRAF2, and RIP in the lungs of SAP rats. In addition, the activation of NF-κB was also downregulated by AT-Lipoxin A4 administration as compared with SAP rats. AT-Lipoxin A4 could inhibit the production of proinflammatory mediators and activation of TNF-α downstream signals such as NF-κB and MAPK. Downregulation of TNF-α signals by AT-Lipoxin A4 may be a significant mechanism in the attenuation of SAP-associated lung injury.

Protein kinase C and acute respiratory distress syndrome

The acute respiratory distress syndrome (ARDS) is a major public health problem and a leading source of morbidity in intensive care units. Lung tissue in patients with ARDS is characterized by inflammation, with exuberant neutrophil infiltration, activation, and degranulation that is thought to initiate tissue injury through the release of proteases and oxygen radicals. Treatment of ARDS is supportive primarily because the underlying pathophysiology is poorly understood. This gap in knowledge must be addressed to identify urgently needed therapies. Recent research efforts in anti-inflammatory drug development have focused on identifying common control points in multiple signaling pathways. The protein kinase C (PKC) serine-threonine kinases are master regulators of proinflammatory signaling hubs, making them attractive therapeutic targets. Pharmacological inhibition of broad-spectrum PKC activity and, more importantly, of specific PKC isoforms (as well as deletion of PKCs in mice) exerts protective effects in various experimental models of lung injury. Furthermore, PKC isoforms have been implicated in inflammatory processes that may be involved in the pathophysiologic changes that result in ARDS, including activation of innate immune and endothelial cells, neutrophil trafficking to the lung, regulation of alveolar epithelial barrier functions, and control of neutrophil proinflammatory and prosurvival signaling. This review focuses on the mechanistic involvement of PKC isoforms in the pathogenesis of ARDS and highlights the potential of developing new therapeutic paradigms based on the selective inhibition (or activation) of specific PKC isoforms.

Ethyl pyruvate significantly inhibits tumour necrosis factor-α, interleukin-1β and high mobility group box 1 releasing and attenuates sodium taurocholate-induced severe acute pancreatitis associated with acute lung injury

In this study, we examined the effect of ethyl pyruvate (EP) on pulmonary inflammation in rats with severe pancreatitis-associated acute lung injury (ALI). Severe acute pancreatitis (SAP) was induced in rats by the retrograde injection of 5% sodium taurocholate into the pancreatic duct. Rats were randomly divided into the following experimental groups: control group, SAP group and EP-treated group. The tissue specimens were harvested for morphological studies, Streptavidin-peroxidase immunohistochemistry examination. Pancreatic or lung tissue oedema was evaluated by tissue water content. Serum amylase and lung tissue malondialdehyde (MDA) and myeloperoxidase (MPO) were measured. Meanwhile, the nuclear factor-κB (NF-κB) activation, tumour necrosis factor-α (TNF-α), interleukin-1β (IL-1β) levels and HMGB1 protein expression levels in the lung were studied. In the present study, we demonstrated that treatment with EP after SAP was associated with a reduction in the severity of SAP and lung injury. Treatment with EP significantly decreased the expression of TNF-α, IL-1β, HMGB1 and ameliorated MDA concentration, MPO activity in the lung in SAP rats. Compared to SAP group, administration of EP prevented pancreatitis-induced increases in nuclear translocation of NF-κB in the lung. Similarly, treatment with EP significantly decreased the accumulation of neutrophils and markedly reduced the enhanced lung permeability. In conclusion, these results demonstrate that EP might play a therapeutic role in pulmonary inflammation in this SAP model.

Downregulation of HMGB1 protects against the development of acute lung injury after severe acute pancreatitis

OBJECTIVE

To examine the effect of downregulation of high mobility group box 1 (HMGB1) on severe acute pancreatitis (SAP) associated with acute lung injury (ALI), and its subsequent effect on disease severity.

METHODS

Wistar rats were given an IV injection of pRNA-U6.1/Neo-HMGB1, pRNA-U6.1/Neo-vector or saline before induction of SAP. Then, SAP was induced in rats by the retrograde injection of 5% sodium taurocholate into the pancreatic duct. The control group received only a sham operation. Lung and pancreas samples were harvested after induction of SAP. The protein levels of HMGB1, matrix metalloproteinase-9 (MMP-9) and intercellular adhesion molecule-1 (ICAM-1) in lung tissue were investigated. The severity of pancreatic injury was determined by a histological score of pancreatic injury, serum amylase, and pancreatic water content. The lung injury was evaluated by measurement of pulmonary microvascular permeability, lung myeloperoxidase activity and malondialdehyde levels.

RESULTS

The results found that in pRNA-U6.1/Neo-HMGB1 treated rats, serum tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) levels were decreased and the severity of pancreatic tissue injury was less compared with either untreated SAP or pRNA-U6.1/Neo-vector treated rats (P<0.05). The administration of pRNA-U6.1/Neo-HMGB1 in SAP-induced rats downregulated the DNA binding activity of the nuclear factor-kappa B (NF-κB) and the expressions of MMP-9 and ICAM-1 in lung. Thus, compared with the untreated SAP rats, the inflammatory response and the severity of ALI decreased (P<0.05).

CONCLUSIONS

These results demonstrate that HMGB1 could augment Inflammation by inducing nuclear translocation of NF-κB, thus aggratating the severity of SAP associated with ALI.

Lung injury in acute pancreatitis: mechanisms underlying augmented secondary injury

Acute lung injury (ALI) and its more severe form, the acute respiratory distress syndrome (ARDS), are common complications of acute pancreatitis (AP). ALI/ARDS contribute to the majority of AP-associated deaths, particularly in the setting of secondary infection. Following secondary pulmonary infection there can be an exacerbation of AP-associated lung injury, greater than the sum of the individual injuries alone. The precise mechanisms underlying this synergism, however, are not known. In this review we discuss the main factors contributing to the development of augmented lung injury following secondary infection during AP and review the established models of AP in regard to the development of associated ALI.

Upregulation of PIAS1 protects against sodium taurocholate-induced severe acute pancreatitis associated with acute lung injury

The regulator of cytokine signaling known as protein inhibitor of activated STAT-1 (PIAS1) is increasingly understood to have diverse regulatory functions for inflammation, but its effect in inflammatory conditions such as severe acute pancreatitis (SAP) has not previously been reported. The aim of this study was to investigate the effect of upregulation of PIAS1 on SAP associated with acute lung injury (ALI), and its subsequent effect on disease severity. Sprague-Dawley rats were given an IV injection of adenovirus serotype 5 (Ad5)/F35-PIAS1, Ad5/F35-vector or saline before induction of SAP. The control group received only a sham operation. Lung and pancreas samples were harvested 16h after induction. The protein levels of PIAS1 in tissue were investigated. The severity of pancreatic injury was determined by a histological score of pancreatic injury, serum amylase, and pancreatic water content. The lung injury was evaluated by measurement of pulmonary microvascular permeability, lung myeloperoxidase activity and malondialdehyde levels. The survival rates of rats were also analyzed. The results found that in Ad5/F35-PIAS1 treated rats, serum tumor necrosis factor (TNF)-α, interleukin (IL)-1β and IL-6 levels were decreased but showed no influence on the levels of IL-10, and the severity of pancreatic tissue injury was less compared with either untreated SAP or Ad5/F35-vector treated rats (P<0.01). The administration of Ad5/F35-PIAS1 in SAP-induced rats downregulated the activity of the signal transducer and activator of transcription-1 (STAT1) pathway and the expressions of matrix metalloproteinase-9 (MMP-9) and intercellular adhesion molecule (ICAM)-1 protein in lung. Thus, compared with the untreated SAP rats, the inflammatory response and the severity of ALI decreased, and the survival rates increased (P<0.01). These findings suggest that PIAS1 could augment anti-inflammatory activity by inhibiting STAT1, thus attenuating the severity of SAP associated with ALI.

L-Arginine-induced acute pancreatitis results in mild lung inflammation without altered respiratory mechanics

Acute lung injury is a common complication of acute pancreatitis (AP) and contributes to the majority of AP-associated deaths. Although some aspects of AP-induced lung inflammation have been demonstrated, investigation of resultant changes in lung function is limited. The aim of this study was to characterize acute lung injury in L-arginine-induced AP. Seven groups of male Sprague-Dawley rats (n = 4-10/group) received 2 intraperitoneal (i.p.) injections of L-arginine (250 mg/100 g) at 6, 12, 24, 36, 48, or 72 hours before measurement of lung impedance mechanics. Control rats (n = 10) received i.p. saline. Bronchoalveolar lavage (BAL), plasma, and pancreatic and lung tissue were collected to determine pancreatic and lung measures of acute inflammation. AP developed between 6 and 36 hours, as indicated by increased pancreatic abnormal acinar cells, myeloperoxidase (MPO) activity, edema, and plasma amylase activity, before beginning to resolve by 72 hours. In the lung, MPO activity increased (2.4-fold) from 12 hours, followed by a modest increase in lung edema at 48 hours, with increased BAL cell count (2.5-fold) up to 72 hours (P < .05). In contrast, no significant changes in lung mechanics were evident over the same period. Despite measurable lung inflammation, no significant deterioration in respiratory function resulted from L-arginine-induced AP.