Xiaoyan Chen

Rosiglitazone Attenuates the Severity of Sodium Taurocholate-induced Acute Pancreatitis and Pancreatitis-associated Lung Injury

BACKGROUND AND AIMS In addition to the effect of regulating adipocyte differentiation and insulin sensitivity, peroxisome proliferator activated receptor-gamma (PPAR-gamma) ligands also exhibit anti-inflammatory effect. However, the mechanisms concerning how PPAR-gamma ligands affect acute pancreatitis and pancreatitis-associated lung injury have not been fully elucidated. This study investigated the effect of rosiglitazone, a PPAR-gamma ligand, on acute pancreatitis and pancreatitis-associated lung injury in the rat pancreatitis model induced by sodium taurocholate. METHODS Acute pancreatitis was induced by retrograde infusion of 5% sodium taurocholate (1 mL/kg) into the bile-pancreatic duct. Rosiglitazone (6 mg/kg) was administered via the femoral vein 30 min prior to the infusion of sodium taurocholate. The severity of pancreatitis was evaluated by serum amylase level, myeloperoxidase activity, and pathology. Pancreatitis-associated lung injury was evaluated by myeloperoxidase activity, the magnitude of pulmonary edema and pathology. Intercellular adhesion molecule-1 (ICAM-1) and tumor necrosis factor-alpha mRNA expression were studied using reverse transcriptase polymerase chain reaction. ICAM-1 protein expression was studied using Western blot analysis. RESULTS Prophylactic administration of rosiglitazone attenuated (1) serum amylase level; (2) myeloperoxidase activity of pancreatic and pulmonary tissue; (3) expression of tumor necrosis factor-alpha and ICAM-1 in pancreas and lung; (4) pancreas and lung pathological damage. CONCLUSIONS Our study demonstrated that rosiglitazone exerts a protective effect against sodium taurocholate-induced pancreatic and pulmonary injury.

Inhibition of poly(ADP-ribose) polymerase attenuates acute kidney injury in sodium taurocholate-induced acute pancreatitis in rats.

Objectives The aim of our present study was to investigate the efficacy of poly(adenosine diphosphate-ribose) polymerase (PARP) inhibition in the development of acute kidney injury in an experimental model of severe acute pancreatitis induced by retrograde infusion of sodium taurocholate into the bile-pancreatic duct. Methods Severity of pancreatitis was evaluated by serum amylase, lipase, tumor necrosis factor &agr;, interleukin-1&bgr;, interleukin-6, and histological grading. The following markers of renal dysfunction and injury were measured: serum creatinine level, urea nitrogen level, myeloperoxidase activity, and histology. Activation of PARP, intercellular adhesion molecule-1, and P-selectin protein in the kidney was studied using Western blot analysis. Results 3-Aminobenzamide attenuated the following: (1) serum amylase, lipase, and renal dysfunction; (2) serum concentrations of proinflammatory cytokines; (3) pancreatic and renal pathological injury; (4) renal myeloperoxidase activity; and (5) activation of PARP, intercellular adhesion molecule-1, and P-selectin in the kidney. Conclusions Our results suggest that PARP activation may contribute to kidney injury and that PARP inhibitors may be beneficial in renal disorders associated with severe acute pancreatitis.

APPL1-Mediating Leptin Signaling Contributes to Proliferation and Migration of Cancer Cells.

Leptin has been implicated in tumorigenesis and tumor progression, particularly in obese patients. As a multifunctional adaptor protein, APPL1 (containing pleckstrin homology domain, phosphotyrosine binding domain, and a leucine zipper motif 1) plays a critical role in regulating adiponectin and insulin signaling pathways. Currently, high APPL1 level has been suggested to be related to metastases and progression of some types of cancer. However, the intercourse between leptin signaling pathway and APPL1 remains poorly understood. Here, we show that the protein levels and phosphorylation statues of APPL1were highly expressed in tissues from human hepatocellular carcinoma and triple-positive breast cancer. Leptin stimulated APPL1 phosphorylation in a time-dependent manner in both human hepatocellular carcinoma HepG2 cell and breast cancer MCF-7 cell. Overexpression or suppression of APPL1 promoted or attenuated, respectively, leptin-induced phosphorylation of STAT3, ERK1/2, and Akt in the cancer cells, accompanied with enhanced or mitigated cell proliferation and migration. In addition, we identified that APPL1 directly bound to both leptin receptor and STAT3. This interaction was significantly enhanced by leptin stimulation. Our results suggested that APPL1 positively mediated leptin signaling and promoted leptin-induced proliferation and migration of cancer cells. This finding reveals a novel mechanism by which leptin promotes the motility and growth of cancer cells.

Crucial role of group IIA phospholipase A2 in pancreatitis-associated adrenal injury in acute necrotizing pancreatitis.

This study investigated the mechanistic role of group IIA phospholipase A2 (sPLA2-IIA) in the process of pancreatitis-associated adrenal injury in acute necrotizing pancreatitis. One hundred and sixty male Wistar rats were subdivided into a sham-operated group, a sodium taurocholate-induced pancreatitis group, and a pancreatitis group pretreated with sPLA2 inhibitor (pku-mdl-101). The sPLA2 inhibitor was administered by intravenous injection 30 min before induction of pancreatitis. The severity of pancreatitis was evaluated by serum amylase and pancreatic histological score. The serum corticosterone level was measured. Adrenal injury was evaluated by histological evaluation, as well as by sPLA2 activity and sPLA2-IIA protein analysis. Pancreatitis resulted in a time-related increase in serum amylase and in the pancreatic histological score. At first, serum corticosterone increased after 3h and decreased rapidly after 6h in pancreatitis. Adrenal injury aggravated during the observation period. The sPLA2 activity in the serum and adrenal glands, as well as the expression of sPLA2-IIA protein in adrenal glands increased and peaked 6h after the induction of pancreatitis. Pretreatment of sPLA2 inhibitor significantly reduced the severity of pancreatitis and adrenal histological injury, improved the 24-h serum corticosterone levels, and effectively inhibited sPLA2 activity and sPLA2-IIA expression in adrenal glands. The sPLA2 inhibitor attenuated the severity of pancreatitis and pancreatitis-associated adrenal injury. The observations indicate that sPLA2-IIA plays a crucial role in pancreatitis-associated adrenal injury in acute necrotizing pancreatitis.

Staurosporine suppresses survival of HepG2 cancer cells through Omi/HtrA2-mediated inhibition of PI3K/Akt signaling pathway:

Staurosporine, which is an inhibitor of a broad spectrum of protein kinases, has shown cytotoxicity on several human cancer cells. However, the underlying mechanism is not well understood. In this study, we examined whether and how this compound has an inhibitory action on phosphatidylinositol 3-kinase (PI3K)/Akt pathway in vitro using HepG2 human hepatocellular carcinoma cell line. Cell viability and apoptosis were determined using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and terminal deoxyribonucleotidyl transferase–mediated dUTP-digoxigenin nick end labeling (TUNEL) assay, respectively. Glutathione S-transferase (GST) pull-down assay and co-immunoprecipitation were performed to detect protein–protein interactions. Small interfering RNA (siRNA) was used to silence the expression of targeted protein. We found that staurosporine significantly decreased cell viability and increased cell apoptosis in a concentration- and time-dependent manner in HepG2 cancer cells, along with the decreased expressions of PDK1 protein and Akt phosphorylation. Staurosporine was also found to enhance Omi/HtrA2 release from mitochondria. Furthermore, Omi/HtrA2 directly bound to PDK1. Pharmacological and genetic inhibition of Omi/HtrA2 restored protein levels of PDK1 and protected HepG2 cancer cells from staurosporine-induced cell death. In addition, staurosporine was found to activate autophagy. However, inhibition of autophagy exacerbated cell death under concomitant treatment with staurosporine. Taken together, our results indicate that staurosporine induced cytotoxicity response by inhibiting PI3K/Akt signaling pathway through Omi/HtrA2-mediated PDK1 degradation, and the process provides a novel mechanism by which staurosporine produces its therapeutic effects.

Effects of Nicotine and Vagus Nerve in Severe Acute Pancreatitis-Associated Lung Injury in Rats.

Objectives The cholinergic anti-inflammatory pathway has been elucidated as a regulator of inflammatory responses in several experimental models of diseases. This regulatory mechanism is mediated by acetylcholine, released from efferent vagus nerve, interacts with &agr;7 nicotinic acetylcholine receptors on immune cells. Experimental evidence indicates that vagus nerve stimulation or &agr;7 nicotinic acetylcholine receptor agonists control proinflammatory cytokine production and protect animals in diverse lethal models. The aim of the study was to investigate effect of the cholinergic anti-inflammatory pathway in acute lung injury in an experimental model of severe acute pancreatitis (SAP). Methods In taurocholate-induced SAP in rats, pancreatitis was preceded by pretreatment with the nicotinic receptor agonist nicotine or unilateral left cervical vagotomy. Results Pretreatment with nicotine strongly alleviated severity of SAP-associated lung injury through attenuating serum amylase, lipase, and interleukin 6 levels; pancreas and lung pathological injury; lung myeloperoxidase activity; lung tumor necrosis factor-&agr;; and high-mobility group box 1 expression. Inversely, vagotomy pretreatment resulted in an enhanced severity of pancreatitis and lung injury. Conclusions Our results reveal the role of the cholinergic anti-inflammatory pathway in experimental SAP-associated lung injury; nicotine pretreatment exerts a protective effect and vagotomy pretreatment exerts the opposite effect.

Deubiquitinase inhibitor b-AP15 activates endoplasmic reticulum (ER) stress and inhibits Wnt/Notch1 signaling pathway leading to the reduction of cell survival in hepatocellular carcinoma cells

Abstract b‐AP15, a potent and selective inhibitor of the ubiquitin‐specific peptidase 14 (USP14), displays in vitro and in vivo antitumor abilities on some types of cancer cells. However, the mechanism underlying its action is not well elucidated. The purposes of the present study are to observe the potential impacts of b‐AP15 on cell survival of hepatocellular carcinoma cells and to investigate whether and how this compound inhibits some survival‐promoting signaling pathways. We found that b‐AP15 significantly decreased cell viability and increased cell apoptosis in a dose‐dependent manner in hepatocellular carcinoma cells, along with the perturbation of cell cycle and the decreased expressions of cell cycle‐related proteins. We also demonstrated that the endoplasmic reticulum (ER) stress and the unfolded protein response (UPR) were enhanced by b‐AP15 supplementation. The inhibition of ER stress/UPR only partly attenuated the cytotoxicity of b‐AP15 on hepatocellular carcinoma cells. In addition, b‐AP15 treatment inhibited Wnt/&bgr;‐catenin and Notch1 signaling pathways, and suppressed phosphorylation of STAT3, Akt, and Erk1/2, which were not restored by the inhibition of ER stress/UPR. Furthermore, the expression levels of signaling molecules in Notch1 were reduced by specific inhibitor of Wnt/&bgr;‐catenin pathway. Notably, either Wnt or Notch1 signaling inhibitor mitigated phosphorylation of STAT3, Akt, and Erk1/2, and mimicked the cytotoxicity of b‐AP15 on hepatocellular carcinoma cells. These results clearly indicate that b‐AP15 induced cytotoxic response to hepatocellular carcinoma cells by augmenting ER stress/UPR and inhibiting Wnt/Notch1 signaling pathways. This new finding provides a novel mechanism by which b‐AP15 produces its antitumor therapeutic effects.

APPL1-mediated activation of STAT3 contributes to inhibitory effect of adiponectin on hepatic gluconeogenesis

Adiponectin has been shown to suppress hepatic gluconeogenesis. However, the signaling pathways underlying its action remain ill-defined. The purpose of this study was to examine the potential role of APPL1 in mediating anti-gluconeogenic ability of adiponectin. Primary hepatocytes were isolated from male C57BL/6 mice. Western blot and RT-PCR were performed to detect protein expression and mRNA level, respectively. The protein-protein association was determined by immunoprecipitation and GST pull-down assay. We found that APPL1 protein levels were negatively associated with expressions of proteins and mRNAs of gluconeogenesis enzymes under stimulation with adiponectin. In addition, adiponectin-stimulated STAT3 phosphorylation and acetylation were positively regulated by APPL1 and negative regulated by SirT1. Pharmacological and genetic inhibition of STAT3 mitigated impact of adiponectin on hepatic gluconeogenesis. Furthermore, adiponectin administration facilitated the binding of APPL1 to SirT1 and suppressed the association of SirT1 with STAT3. Taken together, our study showed that APPL1-SirT1-STAT3 pathway mediated adiponectin signaling in primary hepatocytes. This new finding provides a novel mechanism by which adiponectin suppresses hepatic gluconeogenesis.

Quercetin suppresses the chymotrypsin-like activity of proteasome via inhibition of MEK1/ERK1/2 signaling pathway in hepatocellular carcinoma HepG2 cells

The proteasomal system is a promising target for cancer treatment. Quercetin (Que), a flavonoid compound with antitumor ability, displays the inhibitory effect on proteasome activity. However, the underlying molecular mechanisms are ill defined. The present study found that Que treatment significantly reduced the chymotrypsin-like protease activity of proteasome whereas the trypsin- and caspase-like protease activities remained unchanged in HepG2 cancer cells, along with activation of p38 MAPK and JNK and reduction of ERK1/2 phosphorylation. Que-reduced proteasome activity could not be reverted by inhibition of p38 MAPK and JNK signaling pathway. In addition, MEK1 overexpression or knockdown upregulated or downregulated the chymotrypsin-like protease activity of proteasome, respectively. Both Que and MEK1/ERK1/2 inhibitor attenuated the expression levels of proteasome β subunits. These results indicate that Que-induced suppression of MEK1/ERK1/2 signaling and subsequent reduction of proteasome β subunits is responsible for its inhibitory impacts on proteasome activity.

Serum Gc-globulin levels are reduced in patients with severe acute pancreatitis.

Background and aim To investigate the role of group-specific component globulin (Gc-globulin) in the early process of severe acute pancreatitis (SAP). Patients and methods A total of 37 patients with SAP and 31 patients with mild acute pancreatitis (MAP) were enrolled in the study. Twenty healthy individuals served as controls. Blood samples were taken from SAP and MAP patients on the day of admission (day 1), day 7, and day 14. Serum total Gc-globulin levels were measured using an enzyme-linked immunosorbent assay. Results On admission, the total Gc-globulin levels of patients in the SAP group were 368 (270–455) mg/l (expressed as medians with interquartile range), which were significantly lower (P=0.007) compared with the control group [420 (299–585) mg/l]. In the SAP group, a significant decrease in serum total Gc-globulin was observed in patients who developed organ dysfunction [267 (242–306) mg/l] compared with patients who did not [414 (329–513) mg/l, P<0.001]. Patients with lower Gc-globulin levels were at a higher risk of developing organ dysfunction (P=0.005). Furthermore, serial measurements displayed increasing total Gc-globulin levels in survivors. Conclusion Decreased total Gc-globulin was linked to poor outcomes of SAP. These data support our hypothesis that Gc-globulin may play an important role in the early process of acute pancreatitis. Gc-globulin might be a novel target for prognosis and therapy of SAP.