An Exploratory Study on the Development of an Animal Model of Acute Pancreatitis Following Nicotine Exposure

Cigarette smoking is known to be a major risk factor for pancreatic cancer and pancreatitis is believed to be a predisposed condition for pancreatic cancer. As of this date, there is no established experimental animal model to conduct detailed studies on these two deadly diseases. Our aim is to establish a rodent model by which we can systematically study the pathogenesis of pancreatitis and pancreatic cancer.

Adult Male Sprague Dawley rats were exposed to graded doses of nicotine by various routes for periods of three to 16 weeks. Blood samples were measured for hormonal and metabolic parameters. The pancreas was evaluated for histopathological changes and its function was assessed in isolated pancreatic acini upon stimulation with cholecystokinin (CCK) or carbachol (Cch). The pancreatic tissue was evaluated further for oncogene expression.

Body weight, food and fluid intakes, plasma glucose and insulin levels were significantly reduced in animals with nicotine exposure when compared to control. However, CCK and gastrin levels in the blood were significantly elevated. Pancreatic function was decreased significantly with no alteration in CCK receptor binding. Pancreatic histology revealed vacuolation, swelling, cellular pyknosis and karyorrhexis. Mutant oncogene, H-ras, was overexpressed in nicotine-treated pancreatic tissue.

The results suggest that alterations in metabolic, hormonal and pathologic parameters following nicotine-treatment appear consistent with diagnostic criteria of human pancreatitis. It is proposed that rats could be considered as a potential animal model to study the pathogenesis of pancreatitis.

An exploratory study on the development of an animal model of acute pancreatitis following nicotine exposure

Cigarette smoking is known to be a major risk factor for pancreatic cancer and pancreatitis is believed to be a predisposed condition for pancreatic cancer. As of this date, there is no established experimental animal model to conduct detailed studies on these two deadly diseases. Our aim is to establish a rodent model by which we can systematically study the pathogenesis of pancreatitis and pancreatic cancer.

Adult Male Sprague Dawley rats were exposed to graded doses of nicotine by various routes for periods of three to 16 weeks. Blood samples were measured for hormonal and metabolic parameters. The pancreas was evaluated for histopathological changes and its function was assessed in isolated pancreatic acini upon stimulation with cholecystokinin (CCK) or carbachol (Cch). The pancreatic tissue was evaluated further for oncogene expression.

Body weight, food and fluid intakes, plasma glucose and insulin levels were significantly reduced in animals with nicotine exposure when compared to control. However, CCK and gastrin levels in the blood were significantly elevated. Pancreatic function was decreased significantly with no alteration in CCK receptor binding. Pancreatic histology revealed vacuolation, swelling, cellular pyknosis and karyorrhexis. Mutant oncogene, H-ras, was overexpressed in nicotine-treated pancreatic tissue.

The results suggest that alterations in metabolic, hormonal and pathologic parameters following nicotine-treatment appear consistent with diagnostic criteria of human pancreatitis. It is proposed that rats could be considered as a potential animal model to study the pathogenesis of pancreatitis.

Does solvent influence the ground-state tautomeric population of hypericin?

Nuclear magnetic resonance measurements indicate that hypericin exists in the same "normal" tautomeric form irrespective of whether the solvent is dimethyl sulfoxide or tetrahydrofuran. This result is discussed in the context of previous experimental and theoretical work. It is concluded that solvent perturbations cannot induce tautomerization in hypericin.

Lipid peroxidation in rat brain is increased by simulated weightlessness and decreased by a soy-protein diet

This study tested whether or not simulated weightlessness by tail-suspension increases the levels of lipid peroxidation products in rat brain. The brain tissues of rats on a soybean diet were also assayed for lipid peroxidation products to evaluate the possible role of soy-protein as a dietary anti-oxidant. Male Sprague-Dawley rats were used. Group 1 rats were fed standard Purina rat chow ad libidum and served as controls. Group 2 rats were fed a soybean diet containing 37% soy-protein and were not tail-suspended. Group 3 rats were fed standard Purina rat chow ad libidum and were tail-suspended to induce simulated weightlessness. After 2 wk, all of the rats were killed. Each whole brain was segmented into frontal cortex, cerebellum, and brain stem. After a specific weight of each segment was excised, the residual tissues were combined and used as a whole brain sample. The samples were analyzed for lipid peroxidation products by a chromogenic assay that reacts with malondialdehyde (MDA) and 4-hydroxyalkenals (4-HNE). The mean concentrations of lipid peroxidation products (MDA plus 4-HNE) in whole brain, frontal cortex, cerebellum, and brain stem of the control rats ranged from 16 to 18 micromol/g; the corresponding means ranged from 10 to 13 micromol/g in rats fed the soybean diet, and from 22 to 26 micromol/g in the tail-suspended rats. Thus, the mean levels of lipid peroxidation products in brain tissues were decreased in the rats fed the soy diet and were increased in the rats that were tail-suspended to simulate weightlessness, when compared to those of rats fed a regular diet.

Pathophysiological effects of nicotine on the pancreas: an update

Epidemiological evidence strongly suggests an association between cigarette smoking and pancreatic diseases. It is well recognized that nicotine, a major component in cigarette smoke, is an addictive agent and, therefore, reinforces smoking behavior. The current review update focuses on the genetics of nicotine dependence and its role on the development of pancreatic diseases. The role of smoking and nicotine in pancreatitis and pancreatic cancer development is also discussed. Exposure of laboratory animals to nicotine clearly supports the notion that nicotine can induce pancreatic injury. The mechanism by which nicotine induces such effects is perhaps mediated via signal transduction pathways in the pancreatic acinar cell, leading to enhanced levels of intracellular calcium release, resulting in cytotoxicity and eventual cell death. The induction of pancreatic injury by nicotine may also involve activation and expression of protooncogene, H-ras, which can increase cytosolic calcium via second messenger pathways. Development of pancreatic carcinoma in cigarette smokers as observed in human populations may be the result of activation and mutation of the H-ras gene. A possible pathogenetic mechanism of nicotine in the pancreas activating multiple signal transduction pathways is schematically summarized in Figure 1.

Bivalent disulfide-stabilized fragment variable immunotoxin directed against mesotheliomas and ovarian cancer

We have used protein engineering to generate a stable bivalent fragment variable (Fv) molecule from the antimesothelin antibody SS, in which the VH and VL domains of the Fv are linked to each other by a disulfide bond, and the two Fvs are connected by a flexible 15-amino acid (Gly4-Ser)3 linker. The SS (dsFv)2 molecule is fused to a M(r) 38,000 truncated form of Pseudomonas exotoxin to generate a bivalent, disulfide stabilized, (dsFv)2 immunotoxin. The immunotoxin was expressed in Escherichia coli, refolded in vitro, and purified to approximately 95% purity with a high yield of > 10%. Binding studies demonstrated that the (dsFv)2 molecule has 40 times higher apparent affinity for recombinant mesothelin than a monovalent dsFv molecule. The (dsFv)2 immunotoxin was 4-10-fold more cytotoxic to three mesothelin antigen-positive cell lines than the monovalent dsFv immunotoxin. However, when tested in mice bearing tumor cells expressing mesothelin, the antitumor activity of the bivalent immunotoxin is very similar to the activity of the lower affinity monovalent immunotoxin. Our data indicate that increasing affinity of an antibody fragment does not necessarily lead to higher antitumor activity of an immunotoxin in vivo.

Effect of food restriction on plasma cholecystokinin levels and exocrine pancreatic function in rats

The objective of this study was to examine the effects of 10% food restriction on body weight, plasma cholecystokinin (CCK) levels, and exocrine pancreatic function in male Sprague-Dawley rats. A matched group of rats with unrestricted access to food served as controls. After ingesting the diets for 32 da, the rats were killed and blood obtained for plasma cholecystokinin, glucose, and insulin determinations. To evaluate pancreatic function, the pancreases were removed, weighed, and digested with collagenase to isolate pancreatic acini, which were incubated with maximal stimulating dose of CCK. The fraction of amylase that was released into the medium was measured. To explore the role of membrane receptors in exocrine pancreatic secretion, CCK receptor affinity and CCK receptor capacity were determined by radioligand binding assays in isolated, purified membranes from pancreatic acini. Compared to the control group, rats with 10% food restriction showed (a) reduced body weight gain, (b) increased pancreatic weight, (c) increased plasma CCK level, and (d) no significant changes in plasma glucose or insulin levels. The food-restricted group showed a reduction of pancreatic function, assessed by measuring amylase release in response to maximal CCK stimulation; the amylase release was diminished by 35% in the food-restricted group. In isolated acinar cell membranes from food-restricted rats, CCK receptor affinity and capacity were reduced by 23% and 16%, respectively, compared to controls. These results indicate that consumption of less food than normal affects pancreatic function by a mechanism that evidently involves CCK release and downregulation of CCK receptors. The data suggest that CCK plays an important physiological role in the adaptation to eating less food, and thereby to the lowering of body weight in rats and, possibly, in other animals.

Molecular comparison of toxigenic clinical & non-toxigenic environmental strains of Vibrio cholerae O1 Ogawa isolated during an outbreak of cholera in south India

BACKGROUND & OBJECTIVES

While investigating a cholera outbreak in south India, toxigenic and nontoxigenic strains of Vibrio cholerae O1 were isolated from patients and from the environment, respectively. This study was performed to compare the genetic relatedness of the patient and environmental strains to determine clonal relationships among these strains and thereby determine the source of the cholera outbreak.

METHODS

The 16 strains of V. cholerae isolated from hospitalized patients and 8 environmental V. cholerae strains isolated from the environment were phenotypically and genotypically characterized using a variety of standard techniques.

RESULTS

Sixteen toxigenic clinical strains and 2 nontoxigenic environmental strains belonged to O1 serogroup, Ogawa serotype and El Tor biotype. The remaining 6 nontoxigenic environmental strains were classified as non-O1, non-O139 V. cholerae. The drug resistance pattern of the clinical and environmental strains of V. cholerae showed marked differences with the patient strains being resistant to more number of drugs as compared to the environmental strains. DNA fingerprinting of the strains showed considerable diversity between toxigenic clinical and nontoxigenic environmental O1 Ogawa isolates and between the O1 and non-O1, non-O139 isolates.

INTERPRETATION & CONCLUSION

In this outbreak of cholera, the O1 strains of V. cholerae from clinical and environmental sources belonged to two different clones and the environmental strains could perhaps be the future cholera outbreak causing clones.

Self-assembly and binding of a sorting nexin to sorting endosomes

The fate of endocytosed membrane proteins and luminal contents is determined by a materials processing system in sorting endosomes. Endosomal retention is a mechanism that traps specific proteins within this compartment, and thereby prevents their recycling. We report that a sorting nexin SNX1, a candidate endosomal retention protein, self-assembles in vitro and in vivo, and has this property in common with its yeast homologue Vps5p. A comparison of SNX1 expressed in bacterial and in mammalian systems and analyzed by size-exclusion chromatography indicates that in cytosol SNX1 tetramers are part of a larger complex with additional proteins. An endosomal retention function would require that SNX1 bind to endosomal membranes, yet the complexes that we analyzed were largely soluble and little SNX1 was found in pellet fractions. Using green fluorescent protein fusions, endocytic compartment markers and fluorescence recovery after photobleaching, we found that there is an equilibrium between free cytoplasmic and early/sorting endosome-bound pools of green fluorescent protein-SNX1. Fluorescence resonance energy transfer indicated that spectral variants of green fluorescent protein-SNX1 were oligomeric in vivo. In cell extracts, these green fluorescent protein-SNX1 oligomers corresponded to tetrameric and larger complexes of green fluorescent protein-SNX1. Using video microscopy, we observed small vesicle docking and tubule budding from large green fluorescent protein-SNX1 coated endosomes, which are features consistent with their role as sorting endosomes. http://www.biologists.com/JCS/movies/jcs2058.html

Effects of diversion and reperfusion of pancreaticobiliary juice on amylase release from isolated rat pancreas

Diversion of pancreaticobiliary juice from the small intestine results in resetting of the normal negative-feedback regulation of exocrine pancreatic secretion. The mechanism by which this process occurs is not well understood. To examine this regulatory process, we investigated the effects of pancreaticobiliary juice diversion and reperfusion on exocrine pancreas using isolated rat pancreatic acini. Two groups of rats were surgically prepared for pancreaticobiliary juice diversion and reperfusion. Both groups received a liquid diet via a duodenal cannula and saline by intravenous infusion for 24 hours following surgery. Forty-eight hours after the surgery and infusions, the rats were sacrificed, and acinar cells were quickly isolated from each pancreas. Amylase release from isolated acini was measured in response to doses of cholecystokinin octapeptide (CCK-8) and carbachol. Acinar cell receptor binding was measured by using CCK-8 labeled with iodine 125 and N-tritium-methscopolamine bromide as radioligands. Amylase release in response to both CCK-8 and carbachol was significantly decreased in the diversion group when compared with that of the reperfusion group. Receptor binding sites of CCK-8 and methscopolamine bromide were similar in the diversion and reperfusion groups. The results suggest that cholecystokinin- and carbachol-mediated amylase response is affected by pancreaticobiliary juice diversion through a process that most likely involves alteration of post-receptor-mediated intracellular signaling pathways.

Mecamylamine, a nicotinic receptor channel antagonist, affects amylase secretion by isolated pancreatic acinar cells

It is well established that CCK is a potent stimulator of amylase secretion from the pancreatic acinar cells, while nicotine is an effective inhibitor of such secretion. The present study was conducted to determine whether mecamylamine, a well-established ganglionic blocker drug, could influence amylase secretion from the pancreas. Male Sprague-Dawley rats were fasted, sacrificed, the pancreas removed, and pancreatic acinar cells isolated and purified. The cells were equally divided into 4 different flasks and treated with the following solutions: (control), 10 mM nicotine, 10 microM mecamylamine or 100 microM mecamylamine. The cells were washed twice after 30 min incubation at 37 degrees C, resuspended in HR buffer, and amylase release in response to graded doses of CCK-8 was measured in cells from each flask. The study was repeated four times. Basal amylase release was not different by treatment with nicotine or different doses of mecamylamine. In response to CCK-8, amylase release was decreased by nicotine and by mecamylamine (100 microM) when compared with control. Amylase release was similar between control and mecamylamine (10 microM). Peak amylase released with the maximal dose of CCK-8 (1 x 10(-10) M) was less in cells treated with nicotine when compared with those measured cells treated with saline or with the two doses of mecamylamine. The release of amylase was suppressed in a similar manner in all treatment groups in response to supramaximal (3 x 10(-10) to 1 x 10(-9) M) doses of CCK-8. Mecamylamine, at the high dose, acts on isolated pancreatic acinar cells to decrease amylase release in a manner similar to that found with nicotine. Both of these drugs, nicotine and mecamylamine, may act via CCK receptors via two different intracellular mechanisms.

Chronic dietary Cu(2+)-deficiency alters cholecystokinin signal transduction in isolated rat pancreatic acini

This study tested the hypothesis that diminished exocrine pancreatic function observed in Cu(2+)-deficient rats is associated with alterations in the cholecystokinin (CCK) signal transduction pathway. Male Sprague-Dawley rats were maintained on either a control diet (11 ppm Cu2+) or a Cu(2+)-deficient diet containing 6000 ppm triethylenetetramine tetrahydrochloride. For the duration of the study rats had free access to water and food. After 4 weeks, rats were sacrificed and pancreatic acini isolated for measurement of amylase content, cholecystokinin-stimulated amylase release and total inositol phosphate formation. Plasma Cu2+ levels were significantly (P < 0.05) decreased in rats on a Cu(2+)-deficient diet (19.2 +/- 3.4 micrograms Cu2+/dL), compared with the control diet (77.0 +/- 3.5 micrograms Cu2+/dL). Both amylase content of pancreatic acini and total CCK-8-stimulated amylase release were significantly decreased in Cu(2+)-deficient rats. In addition, Cu(2+)-deficient rats exhibited a decrease (153.5 +/- 30.9%) in the magnitude of CCK-8-stimulated total inositol phosphate formation compared with control rats (220.8 +/- 11.9%). Moreover, CCKA receptor affinity on pancreatic membranes was not significantly altered by Cu(2+)-deficiency, while CCKA receptor density was significantly (P < 0.05) decreased in Cu(2+)-deficient rats. The addition of Cu2+ to the binding assay of Cu(2+)-deficient rats did not restore receptor density to control values. The data demonstrates that adequate dietary intake of Cu2+ is important to maintain the functional integrity of the exocrine pancreas.

Smoking and pancreatic disorders

Cigarette smoking is a major risk factor for pancreatic cancer and probably pancreatitis. It has been reported that patients with chronic pancreatitis are 16 times more likely to develop pancreatic cancer than normal individuals. Nicotine, a major component of tobacco and an addicted drug of abuse in humans, appears to play a role in the aetiology of both pancreatic cancer and pancreatitis. This review discusses major published reports pertaining to the influence of nicotine on these diseases in humans and the probable effects of nicotine on the pathophysiology of the pancreas in animal models. A hypothetical pancreatic acinar cell model showing multiple signal transduction pathways is presented relating to possible mechanisms of action of nicotine on the pathophysiology of the pancreas.

Immunotoxins with increased activity against epidermal growth factor receptor vIII-expressing cells produced by antibody phage display

Recombinant immunotoxins are fusion proteins composed of Fv regions of antibodies and bacterial or plant toxins that are being developed for the targeted therapy of cancer. MR1(Fv)-PE38 is a single-chain recombinant immunotoxin that targets a mutant form of the epidermal growth factor receptor (EGFR), EGFRvIII, that is frequently overexpressed in malignant glioblastomas. We have used random complementarity determining region (CDR) mutagenesis to obtain mutants of MR1(Fv) with an increased affinity for EGFRvIII and an increased activity when converted to a recombinant immunotoxin. Initially, nine residues of heavy chain CDR3 were randomly mutagenized, and several mutants with increased binding affinity were isolated. All mutations were located at amino acids 98 and 99, which correspond to a DNA hot spot, a DNA sequence that mutates at high frequency during natural antibody maturation. A specific region of variable region of antibody light chain CDR3 was mutagenized that corresponded to a hot spot and a mutant (MR1-1) with an additional increase in affinity, and cytotoxic activity was isolated. These studies show that targeting hot spots in the CDRs of Fvs is an effective approach to obtaining Fvs with increased affinity. The increased affinity of MR1-1(Fv) makes it an attractive candidate for the targeted therapy of glioblastomas.

Response of rat exocrine pancreas to high-fat and high-carbohydrate diets

Intake of diets with high fat content is a risk factor for acute pancreatitis and pancreatic cancer. The underlying mechanisms leading to the development of these diseases due to high fat intake are currently unknown. The current study was designed in rats to determine the physiologic and pathological consequences of a highfat diet that contained excess amounts of cottonseed oil or a high-carbohydrate diet that contained high amounts of sucrose on the exocrine pancreas. Rats were maintained on the diets for 4 weeks, and a cannula was inserted into the right jugular vein and one into the pancreatic duct for collection of pancreatic juice. Volume of the pancreatic juice and concentrations of amylase, lipase, and trypsinogen in the pancreatic juice were measured before and after infusions of CCK-8. Results showed that basal and CCK-stimulated pancreatic outputs of volume, amylase and lipase but not trypsinogen, were significantly elevated in intact rats given a high-fat diet when compared with rats given a high-carbohydrate diet. Forty-eight hours later, rats were sacrificed, and parts of the pancreas were removed for isolation of pancreatic acinar cells and for histopathologic studies. Pancreatic acini isolated from rats on a high-fat diet showed significantly lower basal and CCK-stimulated amylase release when compared with those on a high-carbohydrate diet. Histology of the pancreas of rats on a high-carbohydrate diet appeared normal; however, the pancreas of rats on high-fat diet showed significant alterations in exocrine pancreas. These results showed abnormalities in the exocrine pancreas of rats on a high-fat diet, that were not found in rats on a high-carbohydrate diet; further, they support the contention that a high-fat diet has a deleterious effect on the pancreas.

Distribution of 3H-nicotine in rat tissues under the influence of simulated microgravity

Rat tail suspension offers a useful model to reproduce physiologic responses to weightlessness. The present study was conducted in the head-down-tilt (HDT) rat model to assess changes in metabolism of body tissues employing 3H-nicotine. Twelve male rats were used in the study. Half of the rats were tail suspended at 30 degrees for two weeks on a 12/12 light/dark cycle. During this period, body weight, food and fluid intakes were measured. At term, animals were anesthetized and injected i.v. with a solution containing 4 microcuries of nicotine. After 90 min the animals were sacrificed, exsanguinated and tissues (brain, blood, trachea, salivary gland, lung, heart, esophagus, spleen, kidneys and testes) were harvested. The distribution of 3H-nicotine per gram of each tissue was determined and calculated as percent of total injected radioactivity. Final body weights of suspended animals were significantly (P < 0.05) lower than those of controls (309 +/- 21 vs 350 +/- 11 g). 3H-Nicotine was retained in greatest amounts by the kidneys, followed in order by salivary glands, spleen, and gastrointestinal tissues. Compared to non-suspended control, the tissue retention of nicotine in suspended animals was decreased in the following tissues: esophagus (25%), aorta (25%), fundus (25%), trachea (22%), adrenals (18%), spleen (17%), and pancreas (12%). The decreased retention of nicotine in tissues from suspended animals may be indicative of the fluid shifts and changes in blood flow to those tissue beds. The lack of differences in nicotine retention in liver and kidney between control and suspended groups may implicate a normal metabolic function of these organs even under simulated weightlessness.

Estradiol alters cholecystokinin stimulus-response coupling in rat pancreatic acini

We have previously demonstrated that altered exocrine pancreatic stimulus-secretion coupling is associated with ovariectomy and chronic estradiol administration. To elucidate possible mechanisms underlying those effects we examined the ability of chronic administration of different doses of estradiol to regulate the CCK signal transduction pathway in isolated rat pancreatic acini. Doses of estradiol ranging from 0.5 to 119 micrograms/day were administered to ovariectomized rats for 18 days. Ovariectomy was associated with enhanced CCK-stimulated pancreatic amylase release, whereas estradiol dose dependently decreased the magnitude of CCK-stimulated amylase release. Ovariectomy was also associated with enhanced CCK receptor numbers on acinar cell membranes. Estradiol administration was associated with dose-dependent decreases in CCK receptor numbers. Neither ovariectomy nor estradiol administration affected CCK receptor affinity. Moreover, estradiol administration was associated with increased expression of the alpha-subunit of the heterotrimeric G protein Gq/11 (Galphaq/11). Recent findings (H. Ohnishi, S. A. Ernst, D. I. Yule, C. W. Baker, and J. A. Williams. J. Biol. Chem. 272: 16056-16061, 1997) demonstrate that Galphaq/11 may exert a tonic inhibitory effect on pancreatic enzyme release. In view of these findings, the increased expression of Galphaq/11 induced by estradiol likely contributes to the inhibition of pancreatic enzyme release. We conclude that the effect of estradiol to decrease pancreatic secretion is mediated through regulation of CCK receptor density and Galphaq/11 expression.