The role of oxygen radicals in experimental acute pancreatitis

Oxygen-derived free radicals mediate an important step in the initiation of experimental acute pancreatitis. Thereby, it seems that these reactive oxygen metabolites are generated at an early stage of disease. The source of the enhanced production of oxygen radicals still remains unclear. Experimentally, the efficiency of scavenger treatment varied between different models, whereby these differences depended on the experimental model and not on the form of pancreatitis which was induced. Most studies pretreated the experimental animals before inducing acute pancreatitis. This does not mirror the clinical reality, since patients are admitted to the hospital after onset of the disease. It was shown in Cerulein pancreatitis, however, that scavenger treatment also mitigated the pancreatic tissue damages after induction of acute pancreatitis. Moreover, antioxidant treatment also attenuated the extrapancreatic complications, thus improving the final outcome of the disease. The first indirect observations also suggest that in human acute recurrent and chronic pancreatitis, oxygen free radicals are generated and add to the damages seen. Therefore, well-defined controlled clinical studies with patients suffering from acute pancreatitis are needed to validate the role of oxygen radicals in this disease.     

The role of neutral endopeptidase in caerulein-induced acute pancreatitis

Substance P (SP) is well known to promote inflammation in acute pancreatitis (AP) by interacting with neurokinin-1 receptor. However, mechanisms that terminate SP-mediated responses are unclear. Neutral endopeptidase (NEP) is a cell-surface enzyme that degrades SP in the extracellular fluid. In this study, we examined the expression and the role of NEP in caerulein-induced AP. Male BALB/c mice (20-25 g) subjected to 3-10 hourly injections of caerulein (50 μg/kg) exhibited reduced NEP activity and protein expression in the pancreas and lungs. Additionally, caerulein (10(-7) M) also downregulated NEP activity and mRNA expression in isolated pancreatic acinar cells. The role of NEP in AP was examined in two opposite ways: inhibition of NEP (phosphoramidon [5 mg/kg] or thiorphan [10 mg/kg]) followed by 6 hourly caerulein injections) or supplementation with exogenous NEP (10 hourly caerulein injections, treatment of recombinant mouse NEP [1 mg/kg] during second caerulein injection). Inhibition of NEP raised SP levels and exacerbated inflammatory conditions in mice. Meanwhile, the severity of AP, determined by histological examination, tissue water content, myeloperoxidase activity, and plasma amylase activity, was markedly better in mice that received exogenous NEP treatment. Our results suggest that NEP is anti-inflammatory in caerulein-induced AP. Acute inhibition of NEP contributes to increased SP levels in caerulein-induced AP, which leads to augmented inflammatory responses in the pancreas and associated lung injury.     

The role of the CC chemokine, RANTES, in acute lung allograft rejection

Lung transplantation is a therapeutic option for patients with end-stage lung disease. Acute allograft rejection is a major complication of lung transplantation and is characterized by the infiltration of activated mononuclear cells. The specific mechanisms that recruit these leukocytes have not been fully elucidated. The CC chemokine, RANTES, is a potent mononuclear cell chemoattractant. In this study we investigated RANTES involvement during acute lung allograft rejection in humans and in a rat model system. Patients with allograft rejection had a 2.3-fold increase in RANTES in their bronchoalveolar lavages compared with healthy allograft recipients. Rat lung allografts demonstrated a marked time-dependent increase in levels of RANTES compared with syngeneic control lungs. RANTES levels correlated with the temporal recruitment of mononuclear cells and the expression of RANTES receptors CCR1 and CCR5. To determine RANTES involvement in lung allograft rejection, lung allograft recipients were passively immunized with either anti-RANTES or control Abs. In vivo neutralization of RANTES attenuated acute lung allograft rejection and reduced allospecific responsiveness by markedly decreasing mononuclear cell recruitment. These experiments support the idea that RANTES, and the expression of its receptors have an important role in the pathogenesis of acute lung allograft rejection.     

Pancreatic acinar cell: its role in acute pancreatitis

The pancreatic acinar cell is the functional unit of the exocrine pancreas. It synthesizes, stores, and secretes digestive enzymes. Under normal physiological conditions, digestive enzymes are activated only once they have reached the duodenum. Premature activation of these enzymes within pancreatic acinar cells leads to the onset of acute pancreatitis; it is the major clinical disorder associated with pancreatic acinar cells. Although there have been major advances in our understanding of the pathogenesis of this disease in recent years, available treatment options are still limited to traditional nonspecific and palliative interventions. Novel therapeutic strategies have been suggested based on ongoing research in the physiology and pathophysiology of the disease; these include the administration of systemic antibiotics, antioxidants, cytokine antagonists, and more recently, inhibition of the renin-angiotensin system. Notwithstanding this promising development, most of these potential therapies are still in an experimental stage or clinical trial. Further investigation is needed to prove the efficacy of these novel treatment modalities.     

Differential role for TLR3 in respiratory syncytial virus-induced chemokine expression

Respiratory syncytial virus (RSV) is the leading cause of lower respiratory tract infection in young infants worldwide. Previous studies have reported that the induction of interleukin-8/CXCL8 and RANTES/CCL5 correlates with disease severity in humans. The production of these chemokines is elicited by viral replication and is NF-kappaB dependent. RSV, a negative-sense single-stranded RNA virus, requires full-length positive-sense RNA for synthesis of new viral RNA. The aim of our studies was to investigate whether active viral replication by RSV could evoke chemokine production through TLR3-mediated signaling pathways. In TLR3-transfected HEK 293 cells, live RSV preferentially activated chemokines in both a time- and dose-dependent manner compared to vector controls. RSV was also shown to upregulate TLR3 in human lung fibroblasts and epithelial cells (MRC-5 and A549). Targeting the expression of TLR3 with small interfering RNA decreased synthesis of IP-10/CXCL10 and CCL5 but did not significantly reduce levels of CXCL8. Blocking the expression of the adapter protein MyD88 established a role for MyD88 in CXCL8 production, whereas CCL5 synthesis was found to be MyD88 independent. Production of CCL5 by RSV was induced directly through TLR3 signaling pathways and did not require interferon (IFN) signaling through the IFN-alpha/beta receptor. TLR3 did not affect viral replication, since equivalent viral loads were recovered from RSV-infected cells despite altered TLR3 expression. Taken together, our studies indicate that TLR3 mediates inflammatory cytokine and chemokine production in RSV-infected epithelial cells.     

Regulation of CD20 expression by radiation-induced changes in intracellular redox status

Increasing the levels of CD20 expression in cells that harbor low CD20 levels may enhance their responsiveness to CD20-specific antibody therapies. Here, we examined the regulation of CD20 expression after treatment with 0.5-2.0 Gy X-irradiation and hydrogen peroxide (H(2)O(2)), in the presence or absence of known antioxidants, in the Burkitt lymphoma cell lines Daudi and Raji. Irradiation of cells enhanced cell-surface CD20 expression; the kinetics and extent of this change were cell-type specific and time-dependent. The kinetics of reactive oxygen species generation and changes in mitochondrial membrane potential after irradiation were also correlated with changes in CD20 expression. Raji and Daudi cells treated with H(2)O(2) showed a 2-to 2.5-fold increase in CD20 expression at 12 and 20 h, respectively. Buthionine sulfoximine, which depletes glutathione, also increased surface CD20, whereas antioxidants, such as PEG-catalase, PEG-SOD, vitamin C, and amifostine, decreased CD20 expression induced by radiation or H(2)O(2). The antioxidant-mediated decrease in CD20 expression induced by radiation or H(2)O(2) suggests a mechanism involving redox regulation. These results demonstrate the critical role of radiation-induced oxidative stress in CD20 expression and may have implications for defining and improving the efficacy of CD20-targeted antibody therapy and radioimmunotherapy.     

Gene dosage-dependent effects of bcl-2 expression on cellular survival and redox status

The human oncogene bcl-2 exerts protective functions in numerous models of apoptotic cell death and increased oxidative stress. We investigated the effects of inducible bcl-2 overexpression on cellular survival and redox status in dopaminergic rat pheochromocytoma PC 12 cells. Induction of high-level expression of bcl-2 in PC 12 cells resulted in generation of oxidative stress and cessation of growth by cell cycle arrest. Cell cycle arrest in bcl-2-overexpressing PC 12 cells was prevented by an inhibitor of extracellular signal-related kinase (ERK 1/2) activation. Protective effects of bcl-2 expression against L-DOPA neurotoxicity decreased with increasing amounts of bcl-2. Furthermore, high-level bcl-2 overexpression sensitized cells towards oxidative stress and glutathione depletion. Our data suggest that bcl-2 expression is beneficial only in a limited gene dosage range and that high-level expression of bcl-2 exerts potential deleterious effects.     

Zinc and copper status in acute pancreatitis: an experimental study

Metal ions are required as active components of several proteins, including pancreatic enzymes, and they can play important roles in the etiopathogenesis of acute pancreatitis. In the present study, we measured the concentrations of zinc (Zn) and copper (Cu) in both serum and pancreatic tissue, as markers of trace element status in an experimental acute pancreatitis model. Twenty-four male Wistar rats were divided into two groups: the experimental group (N=24) and the control group (N=10). Acute pancreatitis was induced by injection of 48% ethyl alcohol into the common biliary duct. The animals were sacrificed 24 h later to detect the concentrations of Zn and Cu. There was no significant difference in tissue Zn and Cu concentrations between control and experimental groups (p<0.05). However, in the acute pancreatitis group, serum Zn and Culevels were very significantly lower (p<0.001 and p<0.0001, respectively). In conclusuion, these findings suggested that altered mineral metabolism in serum and pancreatic tissue may have contributed to the pathophysiology of acute pancreatitis.     

The chemokine system and its role in obesity

The chemokine system is a complex arrangement of molecules that attract leukocytes to the site of injury or inflammation. This chemotactic behavior gives the system the name “Chemokine.” The intricate and redundant nature of the chemokine system has made it a subject of ongoing scientific investigation. Obesity is characterized as low-grade systemic or chronic inflammation that is responsible for the release of cytokines, adipokines, and chemokines. Excessive tissue fat expansion triggers the release of chemokines, which in turn attract various leukocytes and activate the resident immune surveillance system, eventually leading to worsening of obesity and other related comorbidities. To date, 50 chemokines and 20 chemokine receptors that belong to the G-protein-coupled receptor family have been discovered, and over the past two decades, the physiological and pathological roles of many of these chemokines and their receptors have been elucidated. The objective of this review is to present an update on the link between chemokines and obesity under the light of recent knowledge.     

Central role of neutrophil in the pathogenesis of severe acute pancreatitis

Severe acute pancreatitis (SAP) is an acute abdominal disease with the strong systemic inflammatory response, and rapidly progresses from a local pancreatic damage into multiple organ dysfunction. For many decades, the contributions of neutrophils to the pathology of SAP were traditionally thought to be the chemokine and cytokine cascades that accompany inflammation. In this review, we focus mainly on those recently recognized aspects of neutrophils in SAP processes. First, emerging evidence suggests that therapeutic interventions targeting neutrophils significantly lower tissue damage and protect against the occurrence of pancreatitis. Second, trypsin activation promotes the initial neutrophils recruitment into local pancreas, and subsequently neutrophils infiltration in turn triggers trypsin production. Finally, neutrophils have the unique ability to release neutrophil extracellular traps even in the absence of pathogens.     

The role of sirtuins in modulating redox stressors

For much of the time since their discovery, the sirtuin family of deacetylase enzymes has been associated with extension of life span. This longevity-promoting capacity in numerous model systems has enabled the sirtuins to gain "celebrity status" in the field of aging research. However, the mechanisms underpinning these changes remain incompletely defined. A general phenotype long associated with aging is the dysregulation of biological systems, which partly occurs via the accumulation of damage over time. One of the major sources of this damage is oxidative stress, which can harm both biological structures and the mechanisms with which they are repaired. It is now becoming clear that the beneficial life-span effects of sirtuins, along with many of their other functions, are closely linked to their ability to regulate systems that control the redox environment. Here we investigate the links between sirtuins and their oxidative/redox environment and review the control mechanisms that are regulated by the activity of sirtuin deacetylase proteins.     

The extracellular microenvironment plays a key role in regulating the redox status of cell surface proteins in HIV-infected subjects

There is an overwhelming interest in the study of the redox status of the cell surface affecting redox signaling in the cells and also predicting the total redox status of the cells. Measuring the total surface thiols (cell surface molecule thiols, csm-SH) we have shown that the overall level of surface thiols is tightly controlled. In vitro, the total concentration of intracellular glutathione (iGSH) seems to play a regulatory role in determination of the amounts of reduced proteins on cells. In addition, short term exposure of the cell surface to glutathione disulfide (GSSG, oxidized GSH) seems to reduce the overall levels of csm-SH suggesting that the function of some cysteine containing proteins on the cell surface may be regulated by the amount of GSSG secreted from the cells or the GSSG available in the extracellular environment. Examination of peripheral blood mononuclear cells (PBMCs) from healthy or HIV-infected subjects failed to reveal a similar correlation between the intra- and extracellular thiol status of cells. Although there is a relatively wide variation between individuals in both csm-SH and iGSH there is no correlation between the iGSH and csm-SH levels measured for healthy and HIV-infected individuals. There are many reports suggesting different redox active proteins on the cell surface to be the key players in the total cell surface redox regulation. However, we suggest that the redox status of the cells is regulated through a complex and tightly regulated mechanism that needs further investigation. In the mean time, overall surface thiol measurements together with case specific protein determinations may offer the most informative approach. In this review, we discuss our own results as well as results from other laboratories to argue that the overall levels of surface thiols on the exofacial membrane are regulated primarily by redox status of the cell surface microenvironment.