Ellagic acid blocks activation of pancreatic stellate cells
Introduction
In 1998, star-shaped cells in the pancreas, namely pancreatic stellate cells (PSCs), were identified and characterized [1], [2]. In normal pancreas, stellate cells are quiescent and can be identified by the presence of Vitamin A-containing lipid droplets in the cytoplasm. In response to pancreatic injury or inflammation, they are transformed (“activated”) from their quiescent phenotype into myofibroblast-like cells which actively proliferate, express α-smooth muscle actin (α-SMA), and produce type I collagen and other extracellular matrix components. Many of the morphological and metabolic changes associated with the activation of PSCs in animal models of fibrosis also occur when these cells are grown in serum-containing medium in culture on plastic. There is accumulating evidence that PSCs play a pivotal role in the development of pancreatic fibrosis [1], [2], [3], [4]. In addition, PSCs may participate in the pathogenesis of acute pancreatitis [3], [5]. The activation of signaling pathways such as p38 MAP kinase [6], Rho-Rho kinase [7] and JNK [8] might play a role in the activation process. Obviously, control of the activation of PSCs and their cell functions are potential targets for the development of new treatments for pancreatic fibrosis and inflammation.
Ellagic acid (2,3,7,8-tetrahydroxy[1]benzopyrano[5,4,3,–cde][1] benzopyran-5,10-dione) (Fig. 1) is a plant-derived polyphenol found in a wide variety of fruits and nuts such as raspberries, strawberries, walnuts, grapes and black currants [9]. Ellagic acid has a variety of biological activities including anti-oxidant [9], anti-inflammatory [10], anti-fibrosis [11] and anti-cancer [12], [13] properties. Ellagic acid protected against ischemia/reperfusion-induced gastric injury [10] and carbon tetrachloride-induced liver fibrosis [11]. The anti-cancer properties of ellagic acid include induction of cell cycle arrest and apoptosis [12], and inhibition of tumor formation and growth in vivo [13]. The molecular mechanisms responsible for these effects remain largely unknown. But its potent scavenging action on both superoxide anion and hydroxy anion might be involved [9], [10]. Because oxidative stress plays a role in the development of pancreatic fibrosis and inflammation [14], it would be interesting to see whether ellagic acid affects the activation and cell functions of PSCs. But, little is known about the effects of ellagic acid on PSCs as well as on the activation of signal transduction pathways. We here report that ellagic acid inhibited key cell functions of PSCs and spontaneous activation of freshly isolated PSCs in culture.
Section snippets
Materials
Ellagic acid (m.w. = 338.2) was dissolved in DMSO, and stocked at 10 mg/ml. Poly(dI-dC)-poly(dI-dC) and [γ-32P]ATP were obtained from Amersham Biosciences, UK, Ltd. (Buckinghamshire, Little Chalfont, UK). Rat recombinant PDGF-BB was purchased from R&D Systems (Minneapolis, MN). Recombinant human IL-1β and TNF-α were obtained from Roche Diagnostics (Mannheim, Germany). Double-stranded oligonucleotides probes for activator protein-1 (AP-1) or NF-κB were purchased from Promega (Madison, WI). Rabbit
Ellagic acid inhibited PDGF-induced proliferation and migration
As previously reported [15], PDGF-BB significantly increased proliferation of PSCs (Fig. 2A). PDGF-induced proliferation was inhibited by ellagic acid in a dose-dependent manner. The inhibitory effect was significant at as low as 1 μg/ml. Ellagic acid at 25 μg/ml (in 0.25% DMSO) virtually abolished the cell proliferation induced by PDGF-BB, whereas the vehicle (DMSO) did not. In these experiments, ellagic acid up to these concentrations did not affect cell viability during the incubation as
Discussion
Control of the activation of PSCs and their cell functions is a potential target for the development of new treatments for pancreatic fibrosis and inflammation. The present study demonstrated that a plant polyphenol ellagic acid inhibited several key functions of PSCs including PDGF-induced proliferation, migration, α-SMA gene expression, MCP-1 production and collagen gene expression. In addition, ellagic acid inhibited transformation of freshly isolated cells to activated, myofibroblast-like
Acknowledgements
This work was supported in part by Grant-in-Aid for Encouragement of Young Scientists from Japan Society for the Promotion of Science (to A.M.), by the Pancreas Research Foundation of Japan (to A.M. and to K. K.), by the Kanae Foundation for Life and Socio-Medical Science (to A.M.) and by the Uehara Memorial Foundation (to A.M.).
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