A high omega-3 fatty acid diet mitigates murine pancreatic precancer development.

BACKGROUND: Diets containing omega-3 (ω-3) fat have been associated with decreased tumor development in the colon, breast, and prostate. We assessed the effects of a diet rich in ω-3 fat on the development of pancreatic precancer in elastase (EL)-Kras transgenic mice and examined the effect of an ω-3 fatty acid on pancreatic cancer cells in vitro. MATERIALS AND METHODS: Two cohorts of EL-Kras mice were fed a high ω-3 fat diet (23% menhaden oil) for 8 and 11 mo and compared with age-matched EL-Kras mice fed standard chow (5% fat). Pancreata from all mice were scored for incidence and frequency of precancerous lesions. Immunohistochemistry was performed for proliferating cell nuclear antigen (PCNA) to assess proliferative index in lesions of mice fed either a high ω-3 or standard diet. In vitro, the effect of the ω-3 fatty acid, docosahexaenoic acid (DHA), on two pancreatic cancer cell lines was assessed. Cancer cell proliferation was assessed with an MTT assay; cell cycle analysis was performed by flow cytometry; and apoptosis was assessed with annexin/PI staining. RESULTS: The incidence, frequency, and proliferative index of pancreatic precancer in EL-Kras mice was reduced in mice fed a high ω-3 fat diet compared with mice fed a standard chow. In vitro, DHA treatment resulted in a concentration-dependent decrease in proliferation through both G1/G0 cell cycle arrest and induction of apoptosis. CONCLUSIONS: A high ω-3 fat diet mitigates pancreatic precancer by inhibition of cellular proliferation through induction of cell cycle arrest and apoptosis.

Pancreatic stellate cells (PSCs) express cyclooxygenase-2 (COX-2) and pancreatic cancer stimulates COX-2 in PSCs.

BACKGROUND: Cyclooxygenase 2 (COX-2), the inducible form of prostaglandin G/H synthase, is associated with several human cancers including pancreatic adenocarcinoma. Pancreatic stellate cells (PSCs) play a central role in the intense desmoplasia that surrounds pancreatic adenocarcinoma. The present study examined COX-2 expression in PSCs. PSCs isolated from normal rats, were cultured and exposed to conditioned medium (CM) from the human pancreatic cell line, PANC-1. METHODS: COX-2 expression was evaluated by immunostaining and western blotting. Proliferation of PSCs was determined by thymidine incorporation and cell counting. RESULTS: COX-2 was found to be constitutively expressed in PSCs, and COX-2 protein was up-regulated by PANC-1 CM. Moreover, the induction of COX-2 by PANC-1 CM was prevented by U0126, an extracellular signal-regulated kinase (ERK) 1/2 inhibitor suggesting that activation of ERK 1/2 is needed for stimulation of COX-2. Finally, NS398, a selective COX-2 inhibitor, reduced the growth of PSCs by PANC-1 CM, indicating that activation of COX-2 is required for cancer stimulated PSC proliferation. CONCLUSION: The results suggest that COX-2 may play an important role in the regulation of PSC proliferation in response to pancreatic cancer.

Pancreatic cancer stimulates pancreatic stellate cell proliferation and TIMP-1 production through the MAP kinase pathway.

Pancreatic adenocarcinoma is characterized by an intense desmoplastic reaction that surrounds the tumor. Pancreatic stellate cells (PSCs) are thought to be responsible for production of this extracellular matrix. When activated, PSCs have a myofibroblast phenotype and produce not only components of the extracellular matrix including collagen, fibronectin, and laminin, but also matrix metalloproteinases and tissue inhibitors of metalloproteinases (TIMPs). Since PSCs are found in the stroma surrounding human pancreatic adenocarcinoma, we postulate that pancreatic cancer could impact PSC proliferation and TIMP-1 production. Rat PSCs were isolated and cultured. Isolated PSCs were exposed to PANC-1 conditioned medium (CM) and proliferation, activation of the mitogen-activated protein (MAP) kinase pathway, and TIMP-1 gene induction were determined. Exposure to PANC-1 CM increased PSC DNA synthesis, cell number, and TIMP-1 mRNA (real-time PCR) as well as activating the extracellular-regulated kinase (ERK) 1/2. Inhibition of ERK 1/2 phosphorylation (U0126) prevented the increases in growth and TIMP-1 expression. PANC-1 CM stimulates PSC proliferation and TIMP-1 through the MAP kinase (ERK 1/2) pathway.

Pancreatic stellate cell activation and MMP production in experimental pancreatic fibrosis.

BACKGROUND: The early events in pancreatic fibrosis are poorly understood. We examined the production of collagen and matrix metalloproteinases as well as the activation of pancreatic stellate cells in a rodent model of pancreatic fibrosis. MATERIALS AND METHODS: Pancreatitis was induced in rats by hyperstimulation with cerulein (50 microg/kg/day ip) and concurrent pancreatic duct obstruction (SHOP model) for 96 h (n = 48). Sham animals were injected with saline and underwent laparotomy and manipulation of the pancreas with no duct obstruction (n = 28). Rats were sacrificed daily for 18 days. Serial pancreatic sections were stained with H&E [histology], trichrome [collagen], and alpha smooth muscle actin (alpha-SMA) antibodies [activated stellate cells]. Total pancreatic matrix metalloproteinase (MMP)-2 and 9 were determined by gelatin zymography. MMP-1 production was examined using Western blotting. RESULTS: There were occasional alpha-SMA-positive cells in the pancreatic parenchyma of normal and sham animals. Within 48 h of pancreatitis induction in SHOP animals, histologic evidence of pancreatic inflammation was present, and stellate cells (alpha-SMA-positive cells) appeared surrounding pancreatic acini. The appearance of these cells was followed by collagen deposition in the same area. MMP-1 and 2 proteins increased significantly during pancreatitis while MMP-9 did not. The pancreatic architecture returned to normal by 18 days after the induction of pancreatitis. CONCLUSION: Acute pancreatic inflammation results in stellate cell activation and collagen deposition in the same area. Collagen is then resorbed at a time when MMP-1 and 2 peak. The fibrosis of acute pancreatic inflammation in this model completely resolves with restoration of normal architecture.