Protease-activated receptor-2 regulates bicarbonate secretion by pancreatic duct cells in vitro

BACKGROUND

Pancreatic duct cells (PDCs) are responsible for bicarbonate production by the pancreas. The trypsin-sensitive protease-activated receptor (PAR-2), also known as the trypsin receptor, is highly expressed in the pancreatic duct system and has been shown to regulate PDC ion transport. The possible role of this receptor on bicarbonate secretion, the central function of duct cells, is unknown. We hypothesize that PAR-2 may regulate pancreatic bicarbonate secretion during times of inappropriate pancreatic enzyme activation.

METHODS

To study this hypothesis in vitro, explants of the bovine main pancreatic duct were isolated and maintained in primary culture. They were then mounted in Ussing chambers, and bicarbonate secretion was determined with an autoburette titration. The response to luminal or serosal trypsin (10 micromol/L) and the synthetic trypsin receptor activating peptide (TRAP) (30 micromol/L) on spontaneous and secretin-stimulated bicarbonate secretion (10 nmol/L) was examined.

RESULTS

Serosal trypsin had no effect. Both luminal trypsin and TRAP significantly reduced the spontaneous bicarbonate secretion observed at luminal pH 7.4 (2.8 +/- 0.2 - 0.4 +/- 0.1 micromol/hr/cm(2) and 4.0 +/- 1.2 - 1.6 +/- 0.4 micromol/hr/cm(2), respectively) in a reversible manner. Baseline bicarbonate secretion at luminal pH 8.0 was reduced by trypsin and TRAP, but the increase in response to secretin stimulation observed with controls was unaffected.

CONCLUSIONS

PAR-2 activation may be the mechanism by which pancreatic juice secretion is inhibited during pancreatitis. We suggest that pharmacologic activation of PAR-2 receptors could suppress pancreatic exocrine secretion and thus serve as a potential agent in the treatment and prevention of pancreatic fistulas.

In vitro cultivation of human fetal pancreatic ductal stem cells and their differentiation into insulin-producing cells

AIM: To isolate, culture and identify the human fetal pancreatic ductal stem cells in vitro, and to observe the potency of these multipotential cells differentiation into insulin-producing cells.

METHODS: The human fetal pancreas was digested by 1 g/L collagease type IV and then 2.5 g/L trypsin was used to isolate the pancreatic ductal stem cells, followed by culture in serum-free, glucose-free DMEM media with some additional chemical substrates in vitro (according to the different stage). The cells were induced by glucose-free (control), 5 mmol/L, 17.8 mmol/L and 25 mmol/L glucose, respectively. The cell types of differentiated cells were identified using immunocytochemical staining.

RESULTS: The shape of human fetal pancreatic ductal stem cells cultured in vitro was firstly fusiform in the first 2 wk, and became monolayer and cobblestone pattern after another 3 to 4 wk. After induced and differentiated by the glucose of different concentrations for another 1 to 2 wk, the cells formed the pancreatic islet-like structures. The identification and potency of these cells were then identified by using the pancreatic ductal stem cell marker, cytokeratin-19 (CK-19), pancreatic β cell marker, insulin and pancreatic α cell marker, glucagons with immunocytochemical staining. At the end of the second week, 95.2% of the cells were positive for CK-19 immunoreactivity. Up to 22.7% of the cells induced by glucose were positive for insulin immunoreactivity, and less than 3.8% of the cells were positive for glucagon immunoreactivity in pancreatic islet-like structures. The positive ratio of immunoreactive staining was dependent on the concentration of glucose, and it was observed that the 17.8 mmol/L glucose stimulated effectively to produce insulin- and glucagons-producing cells.

CONCLUSION: The human fetal pancreatic ductal stem cells are capable of proliferation in vitro. These cells have multidifferentiation potential and can be induced by glucose and differentiated into insulin-producing cells in vitro.

Basolateral anion transport mechanisms underlying fluid secretion by mouse, rat and guinea-pig pancreatic ducts

Fluid secretion by interlobular pancreatic ducts was determined by using video microscopy to measure the rate of swelling of isolated duct segments that had sealed following overnight culture. The aim was to compare the HCO(3)(-) requirement for secretin-evoked secretion in mouse, rat and guinea-pig pancreas. In mouse and rat ducts, fluid secretion could be evoked by 10 nm secretin and 5 microm forskolin in the absence of extracellular HCO(3)(-). In guinea-pig ducts, however, fluid secretion was totally dependent on HCO(3)(-). Forskolin-stimulated fluid secretion by mouse and rat ducts in the absence of HCO(3)(-) was dependent on extracellular Cl(-) and was completely inhibited by bumetanide (30 microm). It was therefore probably mediated by a basolateral Na(+)-K(+)-2Cl(-) cotransporter. In the presence of HCO(3)(-), forskolin-stimulated fluid secretion was reduced approximately 40% by bumetanide, approximately 50% by inhibitors of basolateral HCO(3)(-) uptake (3 microm EIPA and 500 microm H(2)DIDS), and was totally abolished by simultaneous application of all three inhibitors. We conclude that the driving force for secretin-evoked fluid secretion by mouse and rat ducts is provided by parallel basolateral mechanisms: Na(+)-H(+) exchange and Na(+)-HCO(3)(-) cotransport mediating HCO(3)(-) uptake, and Na(+)-K(+)-2Cl(-) cotransport mediating Cl(-) uptake. The absence or inactivity of the Cl(-) uptake pathway in the guinea-pig pancreatic ducts may help to account for the much higher concentrations of HCO(3)(-) secreted in this species.

Effect of Bak Foong pills on exocrine pancreatic-bile secretion

We have recently demonstrated that Bak Foong Pills (BFP), a well-known Chinese medicine widely used for treating gynecological disorders, stimulates human colonic epithelial anion secretion, which was mediated by intracellular cAMP and Ca(2+). The present study further investigated the effect of BFP on exocrine pancreatic-bile secretion using in vivo and in vitro approaches. Duodenal infusion of BFP ethanol extract (1 g/kg) in rats produced increases in the volume and protein output of pancreatic-bile juice, but did not affect its pH. Surgical ablation of vagal neural pathway slightly reduced the effect of BFP on the protein output and volume, indicating that the vagal nerve pathway was not the major player in medicating the effect of BFP on exocrine pancreatic-bile secretion. Using CAPAN-1 cell line, a human pancreatic duct cell line, in conjunction with the short-circuit current (I(SC)) measurements, we further demonstrated that BFP could directly stimulate pancreatic HCO(3)(-) secretion. Basolateral addition of BFP (600 microg/ml) produced averaged charges transported of 2100+/-382.5 microC/cm(2), which was blocked by apical addition of Cl(-) channel blocker. Removal of HCO(3)(-) from the Krebs-Henseleit (K-H) solution inhibited the BFP-induced I(SC) by more than 95%. The present results suggest that BFP could improve digestive function by stimulating pancreatic protein and HCO(3)(-) secretion.

Combined gastrin and epidermal growth factor treatment induces islet regeneration and restores normoglycaemia in C57Bl6/J mice treated with alloxan

AIMS/HYPOTHESIS

Increasing beta-cell mass and/or function could restore glucose homeostasis in diabetes mellitus. Hitherto, trophic factors for beta-cell regeneration after toxic events have been difficult to identify. We evaluated the application of gastrin and epidermal growth factor after alloxan-induced pancreatic beta-cell damage.

METHODS

After alloxan treatment (70 mg/kg), mice were implanted with Alzet osmotic minipumps releasing gastrin and epidermal growth factor for one week. We monitored glycaemia, did histological analyses of the pancreata and quantified pancreatic beta-cell mass and insulin content.

RESULTS

Alloxan treatment alone resulted in a persisting hyperglycaemic state. Combined gastrin and epidermal growth factor treatment restored normoglycaemia in 3 days, an effect which seemed permanent. Glucose tolerance tests showed normal glucose responsiveness. Gastrin on its own and epidermal growth factor on its own did not alleviate hyperglycaemia. Islet mass, islet density and pancreatic insulin content were higher in mice treated with gastrin and epidermal growth factor than in untreated mice with persisting hyperglycaemia. In normoglycaemic control mice treatment with gastrin and epidermal growth factor did not affect these parameters. We detected transitional cytokeratin-positive ductal to endocrine insulin-expressing cells and noted increased ductal but not beta-cell proliferation.

CONCLUSIONS/INTERPRETATION

Our results show that combined treatment with gastrin and epidermal growth factor can induce sufficient regeneration of a functional islet mass to restore glucose homeostasis.

Expression of Nestin and IGF-1 in Rat Pancreas after Streptozotocin Administration

The present study examines whether centroacinar (CA) and intercalated duct (ICD) cells can serve as stem cells, after administration of the diabetogenic agent streptozotocin (STZ). Thirty rats were divided into five experimental groups: (1) control, (2) 1 day after STZ (STZ-1), (3) 3 days after STZ (STZ-3), (4) 7 days after STZ (STZ-7) and (5) 14 days after STZ (STZ-14). Many small pancreatic islets were observed in the STZ-7 group than in the other experimental groups, and many of these small islets were in close contact with ICD and CA cells. A higher number of nestin, insulin-like growth factor-1 (IGF-1) and IGF-1-receptor positive ICD and CA cells were observed at STZ-3 and STZ-7 than at the others. These expression patterns coincided well with the proliferating cell nuclear antigen pattern. The results suggest that rat pancreatic endocrine cells after damage by STZ administration might be recovered from newly generated cells derived from ICD and CA cells.

Effect of secretin on serum pancreatic enzymes and on the Wirsung duct in chronic nonpathological pancreatic hyperenzymemia

AIM

Chronic nonpathological pancreatic hyperenzymemia (CNPH) is a new syndrome characterized by an increase in serum pancreatic enzymes in the absence of pancreatic disease. The aim of this study was to increase our understanding of this condition by determining the serum pancreatic enzyme response as well as changes in the caliber of the Wirsung duct after secretin stimulation.

METHODS

Twenty subjects with CNPH and 9 healthy subjects without CNPH were studied. Blood samples were drawn 5 and 0 min before and 5, 10, 15, 30, 45, and 60 min after intravenous injection of secretin (1 U/kg). Amylase, pancreatic isoamylase, and lipase concentrations were determined. The caliber of the Wirsung duct was measured by ultrasonography.

RESULTS

The injection of secretin caused a marked and statistically significant (p < 0.05) increase in serum pancreatic enzymes in the subjects with CNPH that persisted for the duration of the study. The increase over the basal value was in the range of 1.2- to 1.6-fold for amylase, 1.4- to 2.1-fold for pancreatic isoamylase, and 2.6- to 4.2-fold for lipase. In the control subjects the increase was mild, but statistically significant (p < 0.05), ranging from 1.1- to 1.2-fold for amylase, 1.2- to 1.4-fold for pancreatic isoamylase, and 1.5- to 2.2-fold for lipase. The injection of secretin caused a slight increase in the diameter of the Wirsung duct in both groups of subjects, but this was statistically significant only during the first 30 min of the study.

CONCLUSIONS

The serum pancreatic enzyme response to secretin was more marked in CNPH than in controls. The Wirsung duct showed no alterations after secretin injection that would help to explain the hyperenzymemia.

Expression of galectin-3 in the rat pancreas during regeneration following hormone-induced pancreatitis

Supramaximal dosage of the cholecystokinin analog caerulein leads to edematous pancreatitis with subsequent acinar cell destruction predominantly by apoptosis. We have used immunohistochemistry to reveal the expression of the anti-apoptotic protein galectin-3 in pancreatic acinar cells. Galectin-3, which occurs only in duct cells under physiological conditions, is expressed in a subset of acinar cells after the end of a 12-h caerulein infusion, giving rise to a "patchy" staining pattern. During the subsequent period of inflammation and regeneration, galectin-3 expression increases in those acinar cells that undergo apoptosis. By 48 h after the end of caerulein infusion, morphologically normal cells do not contain galectin-3 and participate in regeneration by proliferation. Tubular complexes, being transient structures from degenerative acini, accumulate galectin-3 in the remnants of the epithelium cells. Stimulation with supramaximal dosages of caerulein of the cell line AR4-2J, which is derived from rat pancreatic acinar cells, also results in a marked increase of galectin-3, confirming the in vivo results. We postulate that the high expression of the anti-apoptotic protein galectin-3 regulates the time course of the apoptotic process in pancreatic acinar cells.

Differentially up-regulated genes in proliferating porcine neonatal pancreas cells caused by epidermal growth factor

Pancreatic duct cells are considered to be a major source for beta-cell regeneration or neogenesis. Although epidermal growth factor (EGF) is a well-known important growth factor for pancreas development, the control of pancreatic duct cell growth and differentiation by EGF is poorly understood. In this study, we focused on identifying the genes that were differentially up-regulated in response to EGF stimulation using monolayer cultured porcine neonatal pancreas cells. Cells were obtained from 1 to 3 day old pigs, dispersed and cultured for 8 days. Monolayer cultured porcine pancreas cells were comprised of duct cells and some endocrine and mesenchymal cells (75.2 +/- 15.1, 19.6 +/- 4.9, and 9.5 +/- 3.1%, respectively). After 16 h in serum free media, cells were treated with 100 microg/L EGF for 24 h. Differentially expressed genes were screened by subtractive hybridization. (3)H-thymidine uptake was significantly increased by EGF with time (untreated vs. 24 h treated, untreated vs. 48 h treated: 305.5 +/- 3.5 cpm vs. 380.3 +/- 17.3 cpm (P < 0.05), 309.2 +/- 4.51 vs. 929 +/- 9.19 cpm, (P < 0.005), respectively). Three hundred and fifty cDNA clones were obtained by subtractive hybridization and the inserts were confirmed in 161 colonies and then sequenced. Finally, we found increased mRNA expression of five unknown and five known genes, including cytochrome c oxidase subunit I (COI), cyclooxygenase-2 (COX-2), matrix metalloproteinase-13 (MMP-13), Wiskott-Aldrich syndrome protein interacting protein (WASPIP), and hyaluronan synthase-2 (HAS-2). We confirmed the up-regulation of these genes by Northern blot and semi-quantitative RT-PCR at various time points. The present findings opened new targets for the research on the mechanisms of pancreatic duct cell proliferation by EGF.

Effect of tetramethylpyrazine on exocrine pancreatic and bile secretion

AIM: To investigate the effect of tetramethylpyrazine (ligustrazine, TMP) on the secretion of exocrine pancreas (and biliary).

METHODS: In in vivo study, we investigated the effect of TMP on the secretion of pancreatic-bile juice (PBJ) in rats. Using human pancreatic duct cell line, CAPAN-1, combined with the short-circuit current (I_SC) technique we further studied the effect of TMP on the pancreatic anion secretion.

RESULTS: Administration of TMP (80 mg/kg, ip) significantly increased the secretion of PBJ (P < 0.05), but the pH of PBJ and the secretion of pancreatic protein were not significantly affected. Basolateral addition of TMP produced a dose-dependent increase in I_SC (EC₅₀ = 1.56 mmol/L), which contained a fast transient I_SC response followed by a slow decay. Apical application of Cl^- channel blockers, DPC (1 mmol/L), decreased the response by about 67.1% (P < 0.001), whereas amiloride (100 μmol/L), a epithelial sodium channel blockers, had no effect. Removal of extracellular HCO₃^- abolished TMP-induced increase in I_SC by about 74.4% (P < 0.001), but the removal of external Cl^- did not. Pretreatment with phosphodiesterase inhibitor, IBMX (0.5 mmol/L), decreased the TMP-induced I_SC by 91% (P < 0.001).

CONCLUSION: TMP could stimulate the secretion of PBJ, especially pancreatic ductal HCO₃^- secretion via cAMP or cGMP-dependent pathway. It need further study to investigate the roles of cAMP or cGMP in the effect of TMP on the secretion of exocrine pancreas.

N-acetylcysteine prevents intra-acinar oxygen free radical production in pancreatic duct obstruction-induced acute pancreatitis

Although oxygen free radicals (OFR) are considered to be one of the pathophysiological mechanisms involved in acute pancreatitis (AP), the contribution of acinar cells to their production is not well established. The aim of the present study was to determine the effect of N-acetylcysteine (NAC) in the course of AP induced by pancreatic duct obstruction (PDO) in rats, directly analysing by flow cytometry the quantity of OFR generated in acinar cells. NAC (50 mg/kg) was administered 1 h before and 1 h after PDO. Measurements by flow cytometry of OFR generated in acinar cells were taken at different PDO times over 24 h, using dihydrorhodamine-123 as fluorescent dye. Histological studies of pancreas and measurements of neutrophil infiltration in the pancreas, pancreatic glutathione (GSH), malondialdehyde (MDA) levels, plasma amylase activity and hemoconcentration were carried out in order to assess the severity of AP at different stages. NAC effectively blunted GSH depletion at early AP stages and prevented OFR generation found in acinar cells as a consequence of AP induced by PDO. This attenuation of the redox state impairment reduced cellular oxidative damage, as reflected by less severe pancreatic lesions, normal pancreatic MDA levels, as well as diminished neutrophil infiltration in pancreas. Hyperamylasemia and hemoconcentration following AP induction were ameliorated by NAC administration at early stages, when oxidative stress seems to be critical in the development of pancreatitis. In conclusion, NAC reinforces the antioxidant defences in acinar cells, preventing OFR generation therefore attenuating oxidative damage and subsequently reducing the severity of PDO-induced AP at early stages of the disease.

Effect of orlistat on fat absorption in rats: A comparison of normal rats and rats with diverted bile and pancreatic juice

Orlistat is a specific inhibitor of pancreatic and gastric lipases leading to decreased absorption of fat. In the present study, we measured the effect of orlistat on lymphatic fat transport in rats following intake of oils very different in FA composition and TAG structure, and compared this with the transport in normal rats and rats with fat malabsorption. Rats were subjected to cannulation of the main mesenteric lymph duct, and a feeding catheter was inserted into the stomach. In addition, malabsorbing rats were cannulated in the common bile and pancreatic duct. Emulsified safflower, fish, and randomized oils were administered, and lymph was collected for 24 h and analyzed for FA composition. Administration of 25 mg orlistat together with the dietary oils resulted in very small changes from baseline lymphatic transport, indicating that inhibition of the fat absorption was almost complete and furthermore that the source of fat had no influence on the inhibitory effect of orlistat. Orlistat did not interfere with the absorption of the hydrolysis products, since high absorption of sn-2 MAG and FFA (oleic acid) mixed with orlistat was observed. The baseline lymphatic transport in the orlistat group was higher than in the malabsorbing group, but this was the result of generally lower transport of endogenous FA in the malabsorbing group, presumably caused by the absence of bile FA. The transport of FA in normal rats was several-fold higher than the transport after orlistat addition and in malabsorbing rats. Thus, this study showed that orlistat inhibited fat hydrolysis, and thereby lymphatic absorption, almost completely independently of the fat administered.

Ethanol induces fluid hypersecretion from guinea-pig pancreatic duct cells

Ethanol is the leading cause of pancreatitis; however, its cellular effects are poorly understood. We examined the direct effects of ethanol in the concentration range 0.1-30 mM, i.e. relevant to usual levels of drinking, on fluid secretion from guinea-pig pancreatic duct cells. Fluid secretion was continuously measured by monitoring the luminal volume of interlobular duct segments isolated from the guinea-pig pancreas. [Ca2+]i was estimated by microfluorometry in duct cells loaded with fura-2. Ethanol at 0.3-30 mM significantly augmented fluid secretion stimulated by physiological (1 pM) or pharmacological (1 nM) concentrations of secretin. It augmented dibutyryl cAMP-stimulated fluid secretion but failed to affect spontaneous or acethylcholine-stimulated secretion. Ethanol at 1 mM shifted the secretin concentration-fluid secretion response curve upwards and raised the maximal secretory response significantly by 41%. In secretin-stimulated ducts, 1 mM ethanol induced a transient increase in [Ca2+]i that was dependent on the presence of extracellular Ca2+. Ethanol failed to augment secretin-stimulated secretion from ducts pretreated with an intracellular Ca2+ buffer (BAPTA) or a protein kinase A inhibitor (H89). In conclusion, low concentrations of ethanol directly augment pancreatic ductal fluid secretion stimulated by physiological and pharmacological concentrations of secretin, and this appears to be mediated by the activation of both the intracellular cAMP pathway and Ca2+ mobilization.

Substance P inhibits bicarbonate secretion from guinea pig pancreatic ducts by modulating an anion exchanger

The stimulatory pathways controlling HCO3- secretion by the pancreatic ductal epithelium are well described. However, only a few data are available concerning inhibitory mechanisms, which may play an important role in the physiological control of the pancreas. The aim of this study was to investigate the cellular mechanism by which substance P (SP) inhibits pancreatic ductal HCO3- secretion. Small intra/interlobular ducts were isolated from the pancreas of guinea pigs. During overnight culture the ducts seal to form a closed sac. Transmembrane HCO3- fluxes were calculated from changes in intracellular pH (measured using the pH-sensitive dye BCECF) and the buffering capacity of the cells. We found that secretin can stimulate HCO3- secretion in guinea pig pancreatic ducts about fivefold and that this effect could be totally blocked by SP. The inhibitory effect of SP was relieved by spantide, an SP receptor antagonist. SP had no effect on the activity of basolateral Na+-HCO3- cotransporters and Na+/H+ exchangers. However, the peptide did inhibit a Cl--dependent HCO3- efflux (secretory) mechanism, most probably the Cl-/HCO3 exchanger on the apical membrane of the duct cell.

Keratinocyte growth factor and beta-cell differentiation in human fetal pancreatic endocrine precursor cells

AIMS AND HYPOTHESIS

Keratinocyte growth factor (KGF) is a member of the heparin-binding fibroblast growth factor family with a high degree of specificity for epithelial cells in vitro and in vivo. Our aim was to study the effect of KGF on beta-cell growth and differentiation on islet-like cell clusters derived from human fetal pancreas.

METHODS

We investigated the effects of KGF, in vitro, on beta-cell differentiation from undifferentiated pancreatic precursor cells and in vivo after transplantating human fetal pancreatic cells into athymic rats treated with KGF.

RESULTS

Treatment of islet-like cell clusters with KGF in vitro did not change the number of insulin producing cells, as measured by the measurement of insulin content or DNA. The in vivo treatment of recipient rats with KGF increased the number of beta cells within the grafts 8 weeks after transplantation. At this time, glucose-stimulated insulin secretion was evaluated by glucose stimulation tests in rats bearing the transplants. Measurements of human C-peptide concentrations after glucose challenge showed that the newly differentiated beta cells in the KGF-treated group were functionally competent as opposed to the control group, where the graft failed to release insulin appropriately.

CONCLUSION/INTERPRETATION

These findings suggest that in vivo, KGF is capable of inducing human fetal beta-cell expansion. The growth promoting effect of KGF on beta cells occurred mainly through the activation of ductal cell proliferation and their subsequent differentiation into beta cells.

Origin and development of the precursor lesions in experimental pancreatic cancer in rats

Notwithstanding the importance of understanding how pancreatic ductal adenocarcinoma develops, the process remains controversial. A key question is whether the cells of origin of the tubular complexes that constitute precursor lesions are derived from a single cell type or from multiple types. Suggestions that they arise solely from centroacinar cells or ductal cells have been based on inference due to their morphologic appearance in tissue from patients or investigation of limited numbers of tubular complexes in animal models later in the carcinogenic process. The present study establishes clearly that two steps are involved; rapid transdifferentiation to produce tubular complexes followed later by transformation of the component cells. Animals were killed at intervals beginning 1 day after implantation of the carcinogen dimethylbenzanthracene. Transdifferentiation of acinar cells to ductal cells does not require cell division. Transition of lobules to tubular complexes begins by 2 days after implantation of carcinogen. Within 4 days after implantation well-developed tubular complexes are present. Islets participate in the process. Ductal adenocarcinoma is observed by 1 month after implantation of carcinogen. Chymotrypsin and cytokeratin localized by immunocytochemistry indicate acinar and ductal cell characteristics. Acino-ductal transdifferentiation persists in carcinogen-implanted animals, but not in controls implanted with sodium chloride crystals or subjected to sham implantation. The precursor lesions (tubular complexes) are formed by the transdifferentiation of acinar cells and to a lesser extent islet cells, with the incorporation of the duct cells pre-existing in the lobules. Therefore, cells that at one time were acinar cells, islet cells, and duct cells, provide the precursor cells for the ductal adenocarcinoma that develops from tubular complexes. The results raise the question whether the transdifferentiated cells in the tubular complexes of patients with chronic pancreatitis are more susceptible to carcinogenic influences, resulting in the increased rate of pancreatic cancer.

Centroacinar and intercalated duct cells as potential precursors of pancreatic endocrine cells in rats treated with streptozotocin

The present study examined the possibility for regeneration of pancreatic endocrine cells from centroacinar (CA) and intercalated duct (ICD) cells in rat pancreas after 5 days of continuous streptozotocin (STZ) administration. Nine rats were divided into 3 experimental groups: 1) Control group, 2) Short term recovery group; three days after STZ administration (STZ 3), and 3) Long term recovery group; ten days post-STZ administration (STZ 10). The CA and ICD cells in the STZ 3 group had swollen cytoplasm, and sometimes contained a vesicle within the core. An insulin positive signal was detected in and around the CA and ICD cells. In the STZ 3 group, cytokeratin 20 signals were co-localized with insulin signals in both CA and ICD cells. Electron microscopically, endocrine cells and small pancreatic islets were in close contact with CA and ICD cells. Systemic biophysical serum data reflected these immunohistological results. The present results suggest that CA and ICD cells are involved in the regeneration of pancreatic B cells in rats following a lesion produced by five consecutive days of STZ administration.

Bak Foong Pills stimulate anion secretion across normal and cystic fibrosis pancreatic duct epithelia

The present study examined the effect of Bak Foong Pills (BFP), an over-the-counter traditional Chinese medicine (China registration no. Z980035), on anion secretion and the underlying signaling pathways in normal and cystic fibrosis pancreatic duct cell lines, CAPAN-1 and CFPAC-1, respectively, using the short-circuit current technique. Apical addition of BFP ethanol extract (600 microg/ml) induced a fast transient I(SC) peak that was followed by a slower but more sustained increase in I(SC) in CAPAN-1 cells. However, the response to BFP in CFPAC-1 was predominantly the first transient peak. Apical addition of DIDS (200 microM) inhibited the first peak by more than 60% in both cell lines without significantly affecting the second I(SC) rise. More than 85% of the BFP-induced first transient in both cell lines was inhibited when extra and intracellular Ca(2+) was chelated or emptied by pre-treatment with BAPTA (100 microM) and thapsigargin (10 microM), respectively. Acute addition of PMA (1 microM), a PKC activator, blocked more than 95% of the BFP-induced first peak in both cell lines, consistent with previously reported PKC modulation of Ca(2+)-dependent pancreatic anion secretion. The BFP-induced second I(SC) rise in CAPAN-1 could be inhibited by 73.6% and 71.13% by pretreatment of the cells with MDL-12330A (20 microM), an adenylate cyclase inhibitor and Rp-cAMP (200 microM), a cyclic AMP antagonist, respectively. However, less than 25% of the I(SC) was inhibited by combined treatment with BAPTA and thapsigargin. The second rise was also completely blocked by DPC (2mM) or Glibenclamide (1mM). The results indicate that BFP ethanol extract stimulates pancreatic duct anion secretion in normal and CF cells via different signaling pathways involving both Ca(2+) and cAMP.

Retinoic acid increases the length and volume density of ducts in the rat embryonic pancreas

In this study, the role of all-trans retinoic acid (RA) on the proliferation of rat embryonic pancreas ducts and on the proportion of insulin cells was investigated. All-trans RA (10-6 m) was added to Ham's F12.ITS serum-free medium in which 12.5 day rat dorsal pancreatic buds were cultured on Matrigel. Control explants were cultured on Matrigel in Ham's F12.ITS alone or in Ham's F12.ITS containing ethanol (the diluent for RA). After a 7 day culture period, explants were incubated with bromodeoxyuridine (BrdU) for assessment of cell proliferation. Explants were processed for both morphometry and immunocytochemistry. The length density and volume density of the pancreatic ducts were assessed using an image analysis system. Cells positive for insulin, BrdU and glucagon were localized on adjacent serial sections. RA treatment caused a statistically significant increase in the volume density (P < 0.007) and length density (P < 0.008) of the ducts, as well as a 1.2-fold increase (P < 0.0001) in the proportion of insulin to glucagon cells, compared to both control groups. Few insulin cells were BrdU positive, indicating that cells had a low proliferation rate. The increased proportion of insulin cells may relate to the increased volume density and length density of the ducts in RA-treated explants. It is suggested that RA stimulated the production of additional progenitor cells and not proliferation of existing insulin cells.

Morphological relationship between intercalated duct and pancreatic islet in streptozotocin and/or camostat mesilate administrations in the chicken

Present electron microscopical and immunocytochemistrical studies elucidated some morphological relationship between intercalated duct (ICD) and pancreatic islet cells in the chicken in streptozotocin (STZ) and/or camostat mesilate (CM) administrations. Twenty-one chickens were set into four experimental groups: (1) control group, (2) STZ administration group, (3) CM administration group, and (4) STZ + CM administration group. Cytoplasms of ICD cells stained more strongly with eosin in STZ administration group than other groups, and electron-dense materials and intercalated processes between ICD and islet cells were also increasing in time dependence in STZ administration. Number of pancreatic islet in STZ + CM co-administration was about 3.1 times larger than other groups. Many small sized cells were detected at surrounding area of ICD and they incorporated 5-bromo-2'-deoxyuridine better than other experimental groups. Present morphological data suggested that ICD cells might support some tolerances of pancreatic endocrine cells against toxic substances and also involve in regeneration of new pancreatic islet cells in STZ + CM co-administration.

Cultured pancreatic ductal cells undergo cell cycle re-distribution and beta-cell-like differentiation in response to glucagon-like peptide-1

The intestinal hormone glucagon-like peptide-1 (GLP-1) has been shown to promote an increase in pancreatic beta-cell mass via proliferation of islet cells and differentiation of non-insulin-secreting cells. In this study, we have characterized some of the events that lead to the differentiation of pancreatic ductal cells in response to treatment with human GLP-1. Rat pancreatic ductal (ARIP) cells were cultured in the presence of GLP-1 and analyzed for cell counting, cell cycle distribution, expression of cyclin-dependent-kinase (Cdk) inhibitors, transcription of beta-cell-specific genes, loss of ductal-like phenotype and acquisition of beta-cell-like gene expression profile. Exposure of ARIP cells to 10 nM GLP-1 induced a significant reduction in the cell replication rate and a significant decrease in the percentage of cells in S phase of the cell cycle. This was associated with an increase in the number of cells in G0-G1 phase and a reduction of cells in G2-M phase. Western blot analysis for the Cdk inhibitors, kinase inhibitor protein 1 (p27(Kip1)) and Cdk-interacting protein 1 (p21(Cip1)), demonstrated a significant increase in p27(Kip1) and p21(Cip1) levels within the first 24 h from the beginning of GLP-1 treatment. As cells slowed down their proliferation rate, GLP-1 also induced a time-dependent expression of various beta-cell-specific mRNAs. The glucose transporter GLUT-2 was the first of those factors to be expressed (24 h treatment), followed by insulin (44 h) and finally by the enzyme glucokinase (56 h). In addition, immunocytochemistry analysis showed that GLP-1 induced a time-dependent down-regulation of the ductal marker cytokeratin-20 (CK-20) and a time-dependent induction of insulin expression. Finally, GLP-1 promoted a glucose-dependent secretion of insulin, as demonstrated by HPLC and RIA analyses of the cell culture medium. The present study has demonstrated that GLP-1 induces a cell cycle re-distribution with a decrease in cell proliferation rate prior to promoting the differentiation of cells towards an endocrine-like phenotype.

Where have all the Na+ channels gone? In search of functional ENaC in exocrine pancreas

Many epithelia express specific Na(+) channels (ENaC) together with the cystic fibrosis regulator (CFTR) Cl(-) channels. Pancreatic ducts secrete HCO(3)(-)-rich fluid and express CFTR. However, the question whether they possess ENaC has not been consistently addressed. The aim of the present study was to investigate if pancreatic ducts express functional ENaC. Membrane voltages (V) of ducts isolated from rat pancreas were measured with microelectrodes or whole-cell patch-clamp technique. Amiloride and benzamil given from bath or luminal sides did not hyperpolarize V. Lowering of extracellular Na(+) concentrations had effects that were not consistent with a simple Na(+) conductance, but rather with a Na(+)/Ca(2+) exchange. Acute or long-lasting treatment of pancreatic ducts with mineralocorticoids had no effect on V of unstimulated or secretin-stimulated preparations. Furthermore, pre-treatment of animals with glucocorticoids had no effect on pancreatic fluid secretion evoked from ducts, or from acini. Hence, our study shows that pancreas especially pancreatic ducts do not express functional ENaC.

Effects of bile acids on dog pancreatic duct epithelial cell secretion and monolayer resistance

Pancreatic duct epithelial cells (PDEC) mediate the secretion of fluid and electrolytes and are exposed to refluxed bile. In nontransformed cultured dog PDEC, which express many ion transport pathways of PDEC, 1 mM taurodeoxycholic acid (TDCA) stimulated an (125)I(-) efflux inhibited by DIDS and 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB) and a (86)Rb(+) efflux inhibited by charybdotoxin. Inhibition by 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA)-AM suggests mediation via increased intracellular Ca(2+) concentration, whereas the absence of lactate dehydrogenase release excludes cellular toxicity. At 1 mM, TDCA stimulated a larger (125)I(-) efflux than glycodeoxycholate; two dihydroxy bile acids, taurochenodeoxycholate and TDCA, were similarly effective, whereas a trihydroxy bile acid, taurocholate, was ineffective. In Ussing chambers, 1 mM serosal or 2 mM luminal TDCA stimulated an I(sc) increase from confluent PDEC monolayers. TDCA also stimulated 1) a short-circuit current (I(sc)) increase from basolaterally permeabilized PDEC subject to a serosal-to-luminal Cl(-) gradient that was inhibited by BAPTA-AM, DIDS, and NPPB and 2) an I(sc) increase from apically permeabilized PDEC subject to a luminal-to-serosal K(+) gradient inhibited by BAPTA-AM and charybdotoxin. Along with the efflux studies, these findings suggest that TDCA interacts directly with PDEC to stimulate Ca(2+)-activated apical Cl(-) channels and basolateral K(+) channels. Monolayer transepithelial resistance was only minimally affected by 1 mM serosal and 2 mM luminal TDCA but decreased after exposure to higher TDCA concentrations (2 mM serosal and 4 mM luminal). A secretory role for bile acids should be considered in pancreatic diseases associated with bile reflux.

Exendin-4 differentiation of a human pancreatic duct cell line into endocrine cells: involvement of PDX-1 and HNF3beta transcription factors

Exendin-4 (EX-4), a long acting agonist of GLP-1, induces an endocrine phenotype in Capan-1 cells. Under culture conditions which include serum, approximately 10% of the cells contain insulin and glucagon. When exposed to EX-4 (0.1 nM, up to 5 days), the number of cells containing insulin and glucagon increased to approximately 40%. Western blot analysis detected a progressive increase in protein levels of glucokinase and GLUT2 over 3 days of EX-4 treatment. We explored the sequence of activation of certain transcription factors known to be essential for the beta cell phenotype: PDX-1, Beta2/NeuroD, and hepatocyte nuclear factor 3beta (HNF3beta). Double immunostaining showed that PDX-1 coexisted with insulin and glucagon in EX-4-treated cells. Treatment caused an increase in PDX-1 protein levels by 24 h and induced its nuclear translocation. Beta2/NeuroD protein levels also increased progressively over 24 h. HNF3beta protein level increased twofold as early as 6 h after EX-4 treatment. EMSA results indicated that EX-4 caused a 12-fold increase in HNF3beta binding to PDX-1 promoter area II. Beta2/NeuroD protein levels progressively increased after 24 h treatment. Differentiation to insulin-producing cells was also seen when Capan-1 cells were transfected with pdx-1, with 80% of these cells expressing insulin 3 days after transfection. PDX-1 antisense totally inhibited such conversion. During the differentiation of duct cells to endocrine cells, cAMP levels (EX-4 is a ligand for the GLP-1, G-protein coupled receptor) and MAP kinase activity increased. Our results indicate that EX-4 activates adenylyl cyclase and MAP kinase which, in turn, may lead to activation of transcription factors necessary for an endocrine phenotype.

Expression of the IIIc variant of FGF receptor-1 confers mitogenic responsiveness to heparin and FGF-5 in TAKA-1 pancreatic ductal cells

BACKGROUND

Fibroblast growth factors (FGFs) contribute to angiogenesis and mitogenesis by binding to tyrosine kinase receptors termed FGF receptors (FGFRs). FGF-5 is a secreted FGF that is believed to preferentially act via the IIIc splice variant of FGFR-1. Human pancreatic ductal carcinoma cells express FGF-5 and FGFR-1IIIc, implying a potential for autocrine growth modulation.

AIM

In this study we investigated the importance of FGFR-1 IIIc expression for FGF-5 mitogenic signaling in a pancreatic ductal cell line.

METHODS

A cDNA encoding FGFR-1 IIIc was expressed in the well-differentiated TAKA-1 Syrian hamster pancreatic ductal cell line.

RESULTS

TAKA-1 cells secrete FGF-5, but were found not to express FGFR-1 and to be unresponsive to exogenous FGF-5. In contrast, TAKA-1 clones expressing FGFR-1 IIIc were growth stimulated in the presence of FGF-5 and displayed enhanced mitogen-activated protein kinase (MAPK) activity in the presence of FGF-5. PD98059, an inhibitor of this pathway, inhibited FGF-5-induced growth in these clones.

CONCLUSION

Our data demonstrate that FGFR-1 IIIc can mediate FGF-5-induced mitogenesis via the MAPK pathway in pancreatic ductal cells, and suggest that expression of FGFR-1 IIIc in conjunction with FGF-5 may contribute to the pathobiology of human pancreatic cancer.