Structural and biochemical characterization of maximal and supramaximal hormonal stimulation of rat exocrine pancreas

Myrtus communis leaf extract protects against cerulein-induced acute pancreatitis in rats

In this study, the aim was to examine the potential protective effects of Myrtus communis subsp. communis leaf ethanol extract (MC) treatment against acute pancreatitis (AP) in rats. Thirty-two rats were grouped as the saline-pretreated control (C), MC-pretreated control (MC), saline-pretreated AP (AP), and MC-pretreated AP (MC + AP) groups. To induce AP, cerulein was administered (50 µg/kg) two times. The rats were given MC for 14 days before cerulein injection. Six hours after the final cerulein injection, the rats were sacrificed. Pancreatic damage was associated with an increase in the serum activity of lipase and amylase, the pancreatic activity of myeloperoxidase, and the pancreatic level of malondialdehyde, interleukin-1β, and interleukin-6. AP also led to a decrease in the pancreatic level of anti-inflammatory interleukin-10 and glutathione. Pretreatment with MC before the induction of AP significantly reduced the pancreatic damage observed during the histological examination as well as reversed the biochemical changes evoked by AP. PRACTICAL APPLICATIONS: Acute pancreatitis is characterized by high mortality (average about 5%; severe cases may reach about 30%). The current treatment for acute pancreatitis is mainly symptomatic. The introduction of herbal drugs may lead to the development of a new strategy in the treatment of this disease. This study revealed that MC reduced pancreatic injury by decreasing pro-inflammatory cytokines, increasing antioxidant capacity and anti-inflammatory cytokine, IL-10. To the authors' knowledge, this research is the first report showing that MC inhibits the development of AP. This observation suggests that MC may be useful in the prevention and the treatment of AP in clinical settings.

The econobiology of pancreatic acinar cells granule inventory and the stealthy nano-machine behind it

The pancreatic gland secretes most of the enzymes and many other macromolecules needed for food digestion in the gastrointestinal tract. These molecules play an important role in digestion, host defense and lubrication. The secretion of pancreatic proteins ensures the availability of the correct mix of proteins when needed. This review describes model systems available for the study of the econobiology of secretory granule content. The secretory pancreatic molecules are stored in large dense-core secretory granules that may undergo either constitutive or evoked secretion, and constitute the granule inventory of the cell. It is proposed that the Golgi complex functions as a distribution center for secretory proteins in pancreatic acinar cells, packing the newly formed secretory molecules into maturing secretory granules, also known functionally as condensing vacuoles. Mathematical modelling brings forward a process underlying granule inventory maintenance at various physiological states of condensation and aggregation by homotypic fusion. These models suggest unique but simple mechanisms accountable for inventory buildup and size, as well as for the distribution of secretory molecules into different secretory pathways in pancreatic acinar cells.

Autophagy in pancreatic acinar cells in caerulein-treated mice: immunolocalization of related proteins and their potential as markers of pancreatitis

Drug-induced pancreatitis (DIP) is an underdiagnosed condition that lacks sensitive and specific biomarkers. To better understand the mechanisms of DIP and to identify potential tissue biomarkers, we studied experimental pancreatitis induced in male C57BL/6 mice by intraperitoneal injection of caerulein (10 or 50 μg/kg) at 1-hr intervals for a total of 7 injections. Pancreata from caerulein-treated mice exhibited consistent acinar cell autophagy and apoptosis with infrequent necrosis. Kinetic assays for serum amylase and lipase also showed a dose-dependent increase. Terminal deoxynucleotidyl transferase-mediated biotin-dNTP nick labeling (TUNEL) detected dose-dependent acinar cell apoptosis. By light microscopy, autophagy was characterized by the formation of autophagosomes and autolysosomes (ALs) within the cytoplasm of acinar cells. Immunohistochemical studies with specific antibodies for proteins related to autophagy and pancreatic stress were conducted to evaluate these proteins as potential biomarkers of pancreatitis. Western blots were used to confirm immunohistochemical results using pancreatic lysates from control and treated animals. Autophagy was identified as a contributing process in caerulein-induced pancreatitis and proteins previously associated with autophagy were upregulated following caerulein treatment. Autophagosomes and ALs were found to be a common pathway, in which cathepsins, lysosome-associated membrane protein 2, vacuole membrane protein 1, microtubule-associated protein 1 light chain 3 (LC3), autophagy-related protein 9, Beclin1, and pancreatitis-associated proteins were simultaneously involved in response to caerulein stimulus. Regenerating islet-derived 3 gamma (Reg3γ), a pancreatic acute response protein, was dose-dependently induced in caerulein-treated mice and colocalized with the autophagosomal marker, LC3. This finding supports Reg3γ as a candidate biomarker for pancreatic injury.

Review of experimental animal models of acute pancreatitis

The underlying mechanisms involved in the pathogenesis of acute pancreatitis are ill understood. The mortality rate of this disease has not significantly improved over the past few decades. Current treatment options are limited, and predominantly aimed at supportive therapy. A key feature of severe acute pancreatitis is the presence of extensive tissue necrosis with both local and systemic manifestations of inflammatory response syndromes. A better understanding of the underlying pathophysiology of severe acute pancreatitis may lead to more targeted therapeutic options, potentially leading to improved survival. Animal models of acute pancreatitis are therefore an essential investigative tool for these aims to be achieved. This review discusses the suitability of recent non-invasive models of acute pancreatitis such as hormone-induced, alcohol-induced, immune-mediated, diet-induced, gene knockout and L-arginine; and invasive models including closed duodenal loop, antegrade pancreatic duct perfusion, biliopancreatic duct injection, combination of secretory hyperstimulation with minimal intraductal bile acid exposure, vascular-induced, ischaemia/reperfusion and duct ligation.

Caerulein-induced acute pancreatitis inhibits protein synthesis through effects on eIF2B and eIF4F

Acute pancreatitis (AP) has been shown in some studies to inhibit total protein synthesis in the pancreas, whereas in other studies, protein synthesis was not affected. Previous in vitro work has shown that high concentrations of cholecystokinin both inhibit protein synthesis and inhibit the activity of the guanine nucleotide exchange factor eukaryotic initiation factor (eIF)2B by increasing the phosphorylation of eIF2alpha. We therefore evaluated in C57BL/6 mice the effects of caerulein-induced AP on pancreatic protein synthesis, eIF2B activity and other protein translation regulatory mechanisms. Repetitive hourly injections of caerulein were administered at 50 microg/kg ip. Pancreatic protein synthesis was reduced 10 min after the initial caerulein administration and was further inhibited after three and five hourly injections. Caerulein inhibited the two major regulatory points of translation initiation: the activity of the guanine nucleotide exchange factor eIF2B (with an increase of eIF2alpha phosphorylation) and the formation of the eIF4F complex due, in part, to degradation of eIF4G. This inhibition was not accounted for by changes in the upstream stimulatory pathway, because caerulein activated Akt as well as phosphorylating the downstream effectors of mTOR, 4E-BP1, and ribosomal protein S6. Caerulein also decreased the phosphorylation of the eukaryotic elongation factor 2, implying that this translation factor was not inhibited in AP. Thus the inhibition of pancreatic protein synthesis in this model of AP most likely results from the inhibition of translation initiation as a result of increased eIF2alpha phosphorylation, reduction of eIF2B activity, and the inhibition of eIF4F complex formation.

Alterations in the glycoconjugates of pancreatic cell membrane induced by acute pancreatitis

The alterations that progressively appear in plasma membrane glycoconjugates of rat pancreatic cells at different stages of acute pancreatitis induced by duct obstruction have been analyzed on individual cells by flow cytometry using the fluoresceinated lectins, wheat germ agglutinin (WGA), Tetragonolobus purpureus agglutinin (TP) and Concanavalin A (Con A), which specifically bind to N-acetyl D-glucosamine, L-fucose and D-mannose, respectively. Two populations of pancreatic cells were differentiated according to the forward scatter (size), which showed different density of saccharidic terminals located at external positions in the glycoconjugates of the plasma membrane. A significant increase in WGA and TP binding was found 1.5 h after pancreatic obstruction, which could be due to the fusion of zymogen granules with the plasma membrane as suggested by the basolateral exocytosis observed by electron microscopy at this stage. The most external sugar residues of membrane glycoconjugates are removed 12 h after pancreatic duct obstruction as a consequence of an advanced state of pancreatitis. The hydrolytic process reaches greater depths in the membrane 48 h after obstruction. At this stage a significant decrease in WGA, TP and ConA binding was found in all pancreatic cells, indicating the loss of N-acetyl D-glucosamine and/or sialic acid, L-fucose and even D-mannose which is located in the core of the glycan. The results provide information about the progressive degradation induced by acute pancreatitis in pancreatic cell membrane glycoconjugates.

Nonesterified fatty acids in acute cerulein-induced pancreatitis in the rat. Are they really deleterious in vivo?

During acute pancreatitis, experimental data obtained in vitro suggested that pancreatic lipase generates nonesterified fatty acids (NEFA), noxious for acinar cells, by hydrolysis of pancreatic or circulating triglycerides. The purpose of this work was to determine whether experimentally induced high plasma NEFA levels do indeed aggravate in vivo cerulein-induced pancreatitis. Anesthetized Sprague-Dawley rats received cerulein and were simultaneously infused intravenously with either saline or a triglyceride + heparin mixture (TGH) in order to increase the amount of circulating NEFA. Plasma NEFA increased about fourfold (3.02 +/- 0.28 mumol/liter) in animals infused with TGH with respect to controls (0.75 +/- 0.05 mumol/liter). In rats receiving cerulein + TGH, pancreatic enzyme levels in plasma, ascites, and histological alterations of the pancreas did not differ from those observed in the rats receiving cerulein + saline. There was less macroscopic pancreatic edema (P < 0.01) in the cerulein + TGH group than in the cerulein + saline group. Separate infusion of either heparin alone or of triglycerides alone had no effect. We conclude that high levels of circulating NEFA do not aggravate cerulein pancreatitis in rats and may even induce a protective effect.

Impact of microcirculatory flow pattern changes on the development of acute edematous and necrotizing pancreatitis in rabbit pancreas

Impairment of pancreatic microcirculation has often been advocated as one pathogenic mechanism in necrotizing pancreatitis. In contrast, data on pancreatic capillary perfusion in edematous pancreatitis are scarce. It was the aim of this experimental study to compare changes in pancreatic microcirculation in edematous and necrotizing pancreatitis. Twelve rabbits were allocated to two groups. Two different models of acute pancreatitis were used. Edematous pancreatitis was elicited by intravenous administration of cerulein (25 micrograms/kg/hr) (N = 6). Necrotizing pancreatitis of the biliary type was induced by pressure-controlled intraductal infusion of a mixture of taurocholate, trypsin, and blood (N = 6). Pancreatic microcirculation was quantified by means of intravital microscopy assessing functional capillary density, blood cell velocity, and distribution of the plasma marker FITC-dextran 70. Systemic hemodynamics were maintained at baseline values by fluid administration. Regardless of edema or necrosis, pronounced extravasation of FITC-dextran was recorded in the early stage of pancreatitis. In cerulein-induced pancreatitis, hyperemia developed as indicated by an increase in blood cell velocity in the presence of homogeneous capillary perfusion. In contrast, a progressive reduction of the number of perfused capillaries was detected in necrotizing pancreatitis. In conclusion, pancreatic microvascular perfusion may be regarded as an important pathogenetic factor for the determination of acute pancreatitis.

The lysosomal hydrolases in the rat pancreas after maximal or supramaximal stimulation with cerulein

The decompartmentation of lysosomal compartment in pancreatic acinar cells with consecutive activation of zymogens might play an important role as a "trigger mechanism" in acute pancreatitis. The admixture of lysosomal hydrolases to secretory enzymes in pancreatic juice was found, but their role in pancreatic secretion remains obscure. The aim of the present study was to assess the fragility of pancreatic lysosomal structure after maximal (optimal) or supramaximal stimulation of rats with cerulein during 3, 6, 12 h, and after recovery. In the mitochondrial-lysosomal (M-L) and in the supernatant (S) of pancreases free (F) total (T), and fractional free (%F/T) activities of beta-glucuronidase (beta G), acid phosphatase (AcP), cathepsins (Cs), and beta-N-acetyl-hexosaminidase (NAH) were estimated. In edematous pancreatitis following supramaximal stimulation with cerulein, a significant increase of %F/T of beta G in whole homogenate began at 6 h of hyperstimulation in comparison to the control (93 vs 42% p < 0.01). This increment persisted until 12 h of hyperstimulation and declined after 24 and 48 h of recovery to 67-69%. The changes of %F/T of beta G in M-L followed those in whole homogenate, and additionally the increase free activity in S after 6 h of hyperstimulation and after 24 h recovery occurred. The respective activities of other hydrolases showed a similar pattern of changes. It is of interest that fragility of lysosomal membranes increases significantly also after maximal stimulation when inflammatory changes were absent. Our results suggest that the increase of lysosomal fragility of the pancreas is most unlikely pathological in itself, but also occurs during stimulated pancreatic secretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Localization of lysosomal and digestive enzymes in cytoplasmic vacuoles in caerulein-pancreatitis

Intracellular localization and enzymatic activities of lysosomal enzymes (cathepsin B, N-acetyl-beta-glucosaminidase, and beta-glucuronidase) were studied in control rats and after induction of caerulein pancreatitis. In control rats high enzymatic activities were found in the postnuclear 1000 g fraction (purified zymogen granules). The corresponding subcellular fraction in pancreatitis animals additionally contained larger secretory vacuoles and autophagosomes and revealed a marked increase in lysosomal enzyme activities. Immunolabelling studies at the ultrastructural level for trypsinogen and cathepsin B demonstrated a colocalization of lysosomal and digestive enzymes in zymogen granules in healthy controls. After induction of pancreatitis immunolabelling still demonstrated a colocalisation of cathepsin B and trypsinogen in secretory granules and newly formed Golgi-derived secretory vacuoles. Concomitantly appearing autophagosomes were, however, only labelled for cathepsin B. It is concluded that segregation of lysosomal and digestive enzymes is incomplete in normal acinar cells resulting in a colocalization in zymogen granules. In pancreatitis colocalization in secretory granules is maintained, whereas only lysosomal enzymes were sufficiently transferred into autophagic vacuoles. No indication for impaired mechanisms of molecular sorting of lysosomal and digestive enzymes in caerulein-induced pancreatitis was found.

Oxygen-derived free radicals in cerulein-induced acute pancreatitis

Conscious rats were treated with a supramaximal dose of 5.10(-6)g.kg-1.h-1 of cerulein for periods of 3 and 12 h. In both groups of animals typical features of acute oedematous pancreatitis were proved by biochemical and histologic examinations. The most important finding of our study was the decrease of superoxide dismutase (SOD) activity in pancreatic tissue, accompanied by a slight increase of this scavenger enzyme in serum of rats stimulated with cerulein during 3 h. Parallelly, evident elevation of malondialdehyde (MDA) concentration in pancreatic tissue was noted. After the 12-h infusion of cerulein we were not able to detect any SOD activity in pancreatic tissue, whereas this activity appeared in ascitic fluid of tested animals. Further increase of MDA concentration in pancreatic tissue, in comparison with 3-h pancreatitis, was found. These data suggest that in 3-h and 12-h cerulein-induced pancreatitis the oxygen-derived free radicals mediate the increased lipid peroxidation in pancreatic tissue. We think that the depletion of the scavenger enzyme SOD may be responsible for such a disturbance of lipid metabolism.

Translational control of anionic trypsinogen and amylase synthesis in rat pancreas in response to caerulein stimulation

Infusion of rats with optimal doses of caerulein for up to 24 hr resulted in divergent changes in protein synthesis in the exocrine pancreas: a 3-fold increase in synthesis of anionic trypsinogen and a 75% decrease in synthesis of amylase. Lipase synthesis showed no change. Rates of total protein synthesis increased 2-fold, while DNA, RNA, and poly(A)+ mRNA concentrations were unchanged during hormonal stimulation. mRNA concentrations for anionic trypsinogen, lipase, and amylase were determined by dot blot hybridization analysis with cDNA and cRNA probes. Despite 12-fold changes in the ratio of synthesis of anionic trypsinogen to amylase at 24 hr of caerulein stimulation, changes in levels of mRNA encoding these two proteins were not observed. The slight decreases observed in amylase mRNA concentrations were found in both hormone and saline-infused animals. In vitro pulse-chase experiments after 12 hr of saline or caerulein infusion indicated that differential turnover of anionic trypsinogen and amylase did not occur during hormone stimulation. These data demonstrate that the differential regulation observed in protein synthesis that results from a single period of hormone stimulation is mediated by differential regulation of mRNA translation. The high degree of conservation observed in the 5' terminal sequences of both amylase and anionic trypsinogen mRNAs between mouse, rat, and dog suggests that sequence-specific mechanisms and secondary structure may play a role in the translational control of these two mRNAs.

Effect of live and heat-killed bacteria on the secretory activity of Paneth cells in germ-free mice

Germ-free mice were given live or heat-killed facultative anaerobes, and the ultrastructure of ileal Paneth cells was quantitatively examined with special reference to secretory granules showing a bipartite substructure (central core and peripheral halo). After administering live or heat-killed bacteria, there was a decrease in the area occupied by the cores of secretory granules in Paneth cells, and exocytosed core material was observed in the crypt lumen. There were no changes in the area occupied by the halo of secretory granules. None of the examined Paneth cells phagocytosed bacteria. It is concluded that certain bacteria may affect the secretion of antibacterial agents contained in the secretory granules of Paneth cells.

Stimulation of pancreatic secretory process in the rat by low-molecular weight proteinase inhibitor. I. Dose-response study on enzyme content and secretion, cholecystokinin release and pancreatic fine structure

Application of a single dose of a new type of proteinase inhibitor camostate (FOY-305) via orogastric tube was used in rats to study the dose-response relationship of resulting pancreatic stimulation. Doses up to 10 mg/kg failed to elicit any response, while significant decrease in enzyme content and increase in serum CCK-levels were observed with doses ranging from 25 to 400 mg/kg. A single dose of 100 mg/kg was selected for a time-sequence analysis, which revealed a 60 to 70% depletion of enzyme stores persisting over 6 h and reverting to control levels by 12 h. Peak increases in serum CCK-levels (15-fold above the elevation observed after regular food intake) were found after 30 min and persisted as an 8- to 10-fold elevation for at least 3 h, then declined to control levels by 9 h. This prolonged endogenous hormone release and resulting pancreatic stimulation were also verified in a separate group of animals in which volume, protein, and enzyme output were measured after cannulation of the pancreatic duct. While volume secretion was not altered by feeding a single dose of 100 mg/kg FOY-305, protein and enzyme output increased 2- to 3-fold over a period of 7 h. Fine-structural analysis of the pancreas demonstrated efficient depletion of zymogen granules from acinar cells with all doses between 50 and 400 mg/kg, accompanied by the appearance of membrane material in the acinar lumina at 3 and 6 h. The same transient increase in the number of lysosomal bodies predominantly containing mitochondria with all doses above 50 mg/kg was interpreted as increased organelle turnover due to persisting hormonal stimulation.

Stimulating effect of bombesin on the growth of gastrointestinal tract and pancreas in suckling rats

The current study examines the effects of bombesin on gastrointestinal and pancreatic growth in suckling rats. During a period of 6 days, 7-day-old rats were injected twice daily with bombesin tetradecapeptide (20 micrograms/kg) in hydrolyzed gelatin or with gelatin alone. At the end of bombesin treatment, the weights of stomach, intestine, and pancreas; the heights of fundic and antral mucosae; and the density of parietal cells were significantly increased over control values. The gastrin cell population also tended to be augmented. The surface of glandular stomach, the duodenal mucosal height, and the somatostatin cell population were not modified as compared to controls. Electron morphometric analysis indicates that the increase in pancreatic weight under bombesin treatment was partly due to hypertrophy of acinar cells. This was confirmed by biochemical data that also showed that hypertrophy was associated with hyperplasia. Storage of secretory granules in acinar cells of the neonate rat pancreas under bombesin treatment seemed probable. Chymotrypsinogen and trypsinogen pancreatic contents were greatly augmented; lipase and colipase contents were not affected, whereas the amylase content tended to decrease. All these findings suggest that bombesin might be a general trophic factor for the neonatal digestive system in the rat. The mechanism of its action, however, remains to be determined.