Yoko Nomiyama

Green tea polyphenol (–)-epigallocatechin-3-gallate inhibits ethanol-induced activation of pancreatic stellate cells

Background  Activated pancreatic stellate cells (PSCs) play a central role in the pathogenesis of pancreatic fibrogenesis and inflammation. Ethanol, a major cause of chronic pancreatitis, directly induces PSC activation and oxidative stress. Inhibition of PSC activation or stimulation to PSC might be an effective therapeutic strategy for the prevention of pancreatic fibrosis, and (–)‐epigallocatechin‐3‐gallate (EGCG), a major component of green tea extracts, is a potent antioxidant of polyphenols. Therefore, we examined the mechanisms through which ethanol induces oxidative stress on PSCs and evaluated the effect of EGCG on activation and cell functions of ethanol‐stimulated PSCs.

High glucose activates rat pancreatic stellate cells through protein kinase C and p38 mitogen-activated protein kinase pathway.

Objective: Hyperglycemia is implicated in fibrosis in many organs. Exocrine and endocrine pancreas are closely linked both anatomically and physiologically, and pathological conditions in the exocrine gland can cause impairment of endocrine function and vice versa. Chronic pancreatitis causes pancreatic fibrosis and sometimes results in diabetes mellitus. Pancreatic stellate cells (PSCs) play a pivotal role in pancreatic fibrogenesis. However, the effects of high glucose concentrations on PSC activation have not been fully elucidated. Methods: Cultured PSCs were incubated in the presence of various concentrations of glucose. Pancreatic stellate cell proliferation, &agr;-smooth muscle actin (&agr;-SMA) expression, and collagen production were determined by colorimetric conversion assay, Western blot analysis, and Sirius red dye binding assay, respectively. Results: High glucose concentrations significantly increased PSC proliferation, &agr;-SMA expression, and collagen type I production in PSCs. High glucose concentrations activated protein kinase C (PKC) in PSCs, and PKC inhibitor GF109203X inhibited glucose-stimulated PSC proliferation, &agr;-SMA expression, and collagen secretion. High glucose also activated p38 mitogen-activated protein kinase (MAPK) in PSCs, and p38 MAPK inhibitor SB203580 inhibited glucose-stimulated collagen secretion. Conclusions: Our results indicate that high glucose concentrations stimulate PSC activation via PKC-p38 MAP kinase pathway and suggest that high glucose may aggravate pancreatic fibrosis.

Preferential increase of extracellular matrix expression relative to transforming growth factor beta1 in the pancreas during the early stage of acute hemorrhagic pancreatitis in rats.

Objectives: To elucidate the role of transforming growth factor (TGF) β1 and extracellular matrix (ECM) after acute necrotizing pancreatitis, we studied the regulation of TGF-β1 and ECM after induction of pancreatitis. Methods: We examined the serial changes of levels of plasma TGF-β1 by enzyme-linked immunoassay and expression of TGF-β1 and ECM by Northern and Western blot analyses, respectively, in the pancreas after induction of sodium taurocholate-induced acute pancreatitis. Results: Plasma total (active and inactive) TGF-β1 levels at 3 hours after induction of pancreatitis were significantly increased compared with baseline values. The levels of TGF-β1 messenger RNA (mRNA) were unaltered by day 2. Levels of fibronectin mRNA at 3 hours after induction of pancreatitis were already higher than the baseline values. Latency-associated peptide-TGF-β1 showed a peak on day 7. Thus, the expression of ECM mRNA increased earlier than that of TGF-β1 mRNA. Conclusions: These results suggest that the increase in plasma TGF-β1 concentration probably results from the elevated secretion of TGF-β1 from several cells and/or the redistribution of TGF-β1 protein and that the increase in expression of ECM probably is associated with the activation of TGF-β1. It is conceivable that both increased plasma concentration and focal activation of TGF-β1 play an important role in ECM production during the early stage of acute pancreatitis.Abbreviations: AP - acute pancreatitis, ECM - extracellular matrix, EDTA - ethylene diamine tetraacetic acid, FN - fibronectin, NaTc - sodium taurocholate, PBS - phosphate buffered saline, SDS - sodiumdodecyl sulfate, SSC - saline sodium-citrate solution, TGF-β1 - transforming growth factor-β1

Increased expression of Smad6 deteriorates murine acute experimental pancreatitis in two models

Background: Smad6 is implicated in the inhibition of bone morphogenetic protein signalling. However, the function of Smad6 in the pancreas remains obscure. Methods: To elucidate the unknown function of Smad6, we developed transgenic mice selectively expressing Smad6 in pancreatic acinar cells using a plasmid construct coding rat elastase 1 enhancer/promoter. Results: Smad6 transgenic mice had no specific distinguishing phenotype such as body weight, pancreatic wet weight and concentrations of pancreatic protein. However, Smad6 transgenic mice reacted to hyperstimulation by caerulein injection or a diet containing 0.5% ethionine. Maximal amylase release stimulated by CCK-8 was significantly decreased in Smad6 transgenic mice acini, and trypsin activities in transgenic mice acini were significantly increased after stimulation of CCK-8. There was no difference in effect of CCK-8 stimulation on the subsequent increase in intracellular free Ca2+ concentration ([Ca2+]i) between wild-type and transgenic mice acini. These findings suggest that reduced pancreatic enzyme secretion was caused by the disorder of its downstream signal transduction pathways in acinar cells. The amino acid sequence at the N-terminus of Smad6 was similar to that of synaptosome-associated protein (SNAP) 25 interacting protein, which plays an important role in regulating exocytosis of pancreatic enzymes in acinar cells. Pancreatic SNAP25 protein levels in transgenic mice were decreased after caerulein-induced pancreatitis. Conclusions: These results suggest that elevated expression of Smad6 inhibits normal function of SNAP25-interacting protein and SNAP25, reduces amylase secretion in acinar cells, and increases the susceptibility of acinar cells to the onset of pancreatitis.