A polyamine analog bismethylspermine ameliorates severe pancreatitis induced by intraductal infusion of taurodeoxycholate

Experimental Acute Pancreatitis Models: History, Current Status, and Role in Translational Research

Acute pancreatitis is a potentially severe inflammatory disease that may be associated with a substantial morbidity and mortality. Currently there is no specific treatment for the disease, which indicates an ongoing demand for research into its pathogenesis and development of new therapeutic strategies. Due to the unpredictable course of acute pancreatitis and relatively concealed anatomical site in the retro-peritoneum, research on the human pancreas remains challenging. As a result, for over the last 100 years studies on the pathogenesis of this disease have heavily relied on animal models. This review aims to summarize different animal models of acute pancreatitis from the past to present and discuss their main characteristics and applications. It identifies key studies that have enhanced our current understanding of the pathogenesis of acute pancreatitis and highlights the instrumental role of animal models in translational research for developing novel therapies.

Selective regulation of polyamine metabolism with methylated polyamine analogues

Polyamine metabolism is intimately linked to the physiological state of the cell. Low polyamines levels promote growth cessation, while increased concentrations are often associated with rapid proliferation or cancer. Delicately balanced biosynthesis, catabolism, uptake and excretion are very important for maintaining the intracellular polyamine homeostasis, and deregulated polyamine metabolism is associated with imbalanced metabolic red/ox state. Although many cellular targets of polyamines have been described, the precise molecular mechanisms in these interactions are largely unknown. Polyamines are readily interconvertible which complicate studies on the functions of the individual polyamines. Thus, non-metabolizable polyamine analogues, like carbon-methylated analogues, are needed to circumvent that problem. This review focuses on methylated putrescine, spermidine and spermine analogues in which at least one hydrogen atom attached to polyamine carbon backbone has been replaced by a methyl group. These analogues allow the regulation of both metabolic and catabolic fates of the parent molecule. Substituting the natural polyamines with methylated analogue(s) offers means to study either the functions of an individual polyamine or the effects of altered polyamine metabolism on cell physiology. In general, gem-dimethylated analogues are considered to be non-metabolizable by polyamine catabolizing enzymes spermidine/spermine-N¹-acetyltransferase and acetylpolyamine oxidase and they support short-term cellular proliferation in many experimental models. Monomethylation renders the analogues chiral, offering some advantage over gem-dimethylated analogues in the specific regulation of polyamine metabolism. Thus, methylated polyamine analogues are practical tools to meet existing biological challenges in solving the physiological functions of polyamines.

Review of experimental animal models of biliary acute pancreatitis and recent advances in basic research

Acute pancreatitis (AP) is a formidable disease, which, in severe forms, causes significant mortality. Biliary AP, or gallstone obstruction-associated AP, accounts for 30-50% of all clinical cases of AP. In biliary AP, pancreatic acinar cell (PAC) death (the initiating event in the disease) is believed to occur as acinar cells make contact with bile salts when bile refluxes into the pancreatic duct. Recent advances have unveiled an important receptor responsible for the major function of bile acids on acinar cells, namely, the cell surface G-protein-coupled bile acid receptor-1 (Gpbar1), located in the apical pole of the PAC. High concentrations of bile acids induce cytosolic Ca(2+) overload and inhibit mitochondrial adenosine triphosphate (ATP) production, resulting in cell injury to both PACs and pancreatic ductal epithelial cells. Various bile salts are employed to induce experimental AP, most commonly sodium taurocholate. Recent characterization of taurolithocholic acid 3-sulphate on PACs has led researchers to focus on this bile salt because of its potency in causing acinar cell injury at relatively low, sub-detergent concentrations, which strongly implicates action via the receptor Gpbar1. Improved surgical techniques have enabled the infusion of bile salts into the pancreatic duct to induce experimental biliary AP in mice, which allows the use of these transgenic animals as powerful tools. This review summarizes recent findings using transgenic mice in experimental biliary AP.

Overexpression of spermidine/spermine N1-acetyltransferase or treatment with N1-N11-diethylnorspermine attenuates the severity of zinc-induced pancreatitis in mouse

Depletion of pancreatic intracellular polyamine pools has been observed in acute pancreatitis both in the animal models and in humans. In this study, the wild-type mice, polyamine catabolic enzyme spermidine/spermine N(1)-acetyltransferase overexpressing (SSAT mice) and SSAT-deficient mice were used to characterize the new zinc-induced acute pancreatitis mouse model and study the role of polyamines and polyamine catabolism in this model. Intraperitoneal zinc injection induced acute necrotizing pancreatitis in wild-type mice as well as in SSAT-overexpressing and SSAT-deficient mice. Serum α-amylase activity was significantly increased in all zinc-treated mice compared with the untreated controls. However, the α-amylase activities in SSAT mice were constantly lower than those in the other groups. Histopathological examination of pancreatic tissue revealed edema, acinar cell necrosis and necrotizing inflammation, typical for acute pancreatitis. Compared with the other zinc-treated mice less damage according to the histopathological analysis was observed in the pancreatic tissue of SSAT mice. Levels of intracellular spermidine, and occasionally spermine, were significantly decreased in pancreases of all zinc-treated animals and SSAT enzyme activity was enhanced both in wild-type and SSAT mice. Interestingly, a spermine analog, N(1), N(11)-diethylnorspermine (DENSpm), enhanced the proliferation of pancreatic cells and reduced the severity of zinc-induced pancreatitis in wild-type mice. The results show that in mice a single intraperitoneal zinc injection causes acute necrotizing pancreatitis accompanied by decrease of intracellular polyamine pools. The study supports the important role of polyamines for the integrity and function of the pancreas. In addition, the study suggests that whole body overexpression of SSAT obtained in SSAT mice reduces inflammatory pancreatic cell injury.

Polyamine catabolism in relation to trypsin activation and apoptosis in experimental acute pancreatitis

BACKGROUND

Overinduced polyamine catabolism (PC) in a transgenic rat model has been suggested to be a mediator of trypsin activation which is important in acinar cell necrosis. PC has also been observed in experimental taurodeoxycholate pancreatitis. We hypothesized that PC may be a mediator of trypsin activation in taurodeoxycholate pancreatitis.

METHODS

Pancreatitis was induced in wild-type rats by 2 or 6% taurodeoxycholate infusion or in transgenic rats by overexpressing spermidine/spermine N(1)-acetyltransferase (SSAT). The time courses of necrosis, caspase-3 immunostaining, SSAT, polyamine levels, and trypsinogen activation peptide (TAP) were monitored. The effect of the polyamine analogue bismethylspermine (Me(2)Spm) was investigated.

RESULTS

In a transgenic pancreatitis model, TAP and acinar necrosis increased simultaneously after the activation of SSAT, depletion of spermidine, and development of apoptosis. In taurodeoxycholate pancreatitis, necrosis developed along with the accumulation of TAP. SSAT was activated simultaneously or after TAP accumulation and less than in the transgenic model, with less depletion of spermidine than in the transgenic model. Supplementation with Me(2)Spm ameliorated the extent of acinar necrosis at 24 h, but contrary to previous findings in the transgenic model, in the taurodeoxycholate model it did not affect trypsin activation. Compared with the transgenic model, no extensive apoptosis was found in taurodeoxycholate pancreatitis.

CONCLUSIONS

Contrary to transgenic SSAT-overinduced pancreatitis, PC may not be a mediator of trypsin activation in taurodeoxycholate pancreatitis. The beneficial effect of polyamine supplementation on necrosis in taurodeoxycholate pancreatitis may rather be mediated by other mechanisms than amelioration of trypsin activation. and IAP.

Current status of the polyamine research field

This chapter provides an overview of the polyamine field and introduces the 32 other chapters that make up this volume. These chapters provide a wide range of methods, advice, and background relevant to studies of the function of polyamines, the regulation of their content, their role in disease, and the therapeutic potential of drugs targeting polyamine content and function. The methodology provided in this new volume will enable laboratories already working in this area to expand their experimental techniques and facilitate the entry of additional workers into this rapidly expanding field.

Characterization of polyamine homeostasis in l-ornithine-induced acute pancreatitis in rats

OBJECTIVES

l-Ornithine is a precursor of polyamine synthesis that is essential for cell survival. In contrast, intraperitoneal (IP) administration of a large dose of l-ornithine results in death of pancreatic acinar cells in rats. We investigated changes in pancreatic and extrapancreatic polyamine homeostasis after injection of l-ornithine and tested the effects of the stable polyamine analogue methylspermidine (MeSpd) on l-ornithine-induced pancreatitis.

METHODS

Male Wistar rats were injected IP with 3 g/kg l-ornithine and were untreated, pretreated, or treated with 50 mg/kg MeSpd IP. Rats were killed after 0 to 168 hours for determinations of polyamines and activities of ornithine decarboxylase and spermidine/spermine N(1)-acetyltransferase (SSAT). Pancreatitis severity was assessed by measuring standard laboratory and histological parameters.

RESULTS

Injection of l-ornithine paradoxically induced pancreatic spermidine catabolism, possibly via activation of SSAT, after (>6 hours) appearance of the first histological signs of acute pancreatitis. Polyamine levels generally increased in the lung and liver with the exception of lung spermidine levels, which decreased. Methylspermidine did not influence polyamine levels and SSAT activity and did not ameliorate the severity of l-ornithine-induced pancreatitis.

CONCLUSIONS

l-Ornithine-induced pancreatitis was associated with activation of pancreatic polyamine catabolism. However, administration of a metabolically stable polyamine analogue did not affect disease severity.

Changes in blood polyamine levels in human acute pancreatitis

OBJECTIVE

Experimental studies have shown that pancreatic activation of polyamine catabolism occurs during the early stage of acute pancreatitis. Changes in pancreatic polyamines are reflected in the red blood cell (RBC) polyamine contents, correlating with the extent of pancreatic necrosis. The aim of this human study was to examine the changes in polyamine levels in the RBCs of patients with acute pancreatitis.

MATERIAL AND METHODS

Twenty-four patients with acute pancreatitis (7 alcoholic, 10 gallstone and 7 of unknown etiology) were recruited in the study. Eighteen patients with non-pancreatic acute abdominal diseases were included as controls, and 6 volunteers were studied as references. Blood samples were collected on admission and during hospitalization to assess polyamine levels. After clinical recovery, the patients revisited the clinic, and RBC polyamine levels were measured again. For comparison, plasma interleukin-6 (IL-6), IL-10 and C-reactive protein (CRP) were measured.

RESULTS

In acute pancreatitis patients, there was no difference in RBC polyamine levels on admission compared with those in controls or in volunteers. Putrescine levels on admission were higher in patients with pancreatic necrosis than in patients without necrosis, but there was no difference in spermidine and spermine levels. Patients with pancreatitis of unknown etiology had significantly higher levels of polyamines on admission and throughout hospitalization, but they also had more necrosis, which explained the difference in multivariate analysis. Spermidine and spermine levels increased after clinical recovery. RBC putrescine correlated with IL-6 and IL-10, and spermine correlated with CRP.

CONCLUSIONS

The results of this study suggest that RBC polyamines change in human acute pancreatitis in several respects, as has been previously observed in experimental pancreatitis.

alpha-Methylspermidine protects against carbon tetrachloride-induced hepatic and pancreatic damage

The role of polyamines in carbon tetrachloride (CCl(4))-induced organ injury was studied in syngenic rats and transgenic rats with activated polyamine catabolism. In syngenic rats, administration of CCl(4) resulted in the induction of hepatic spermidine/spermine N(1)-acetyltransferase (SSAT), accumulation of putrescine, reduction in spermine level and appearance of moderate hepatic injury within 24 h. Upon treatment with CCl(4), transgenic rats overexpressing SSAT displayed induction of both hepatic and pancreatic SSAT, with subsequent accumulation of putrescine and decrease of both spermidine and spermine pools. Administration of CCl(4) in SSAT transgenic rats induced not only massive hepatic injury, but also severe acute necrotizing pancreatitis. Pretreatment of the animals with catabolically stable functional polyamine mimetic, alpha-methylspermidine (MeSpd) prevented pancreatic and hepatic injury in SSAT rats and markedly reduced liver damage in syngenic animals. As assessed by immunostaining of proliferating cell nuclear antigen, MeSpd increased the amount of regenerating hepatocytes in both genotypes. These results show that CCl(4) induces hepatic and pancreatic polyamine catabolism, and the extent of organ damage correlates with the degree of polyamine depletion. Furthermore, MeSpd protects against CCl(4)-induced hepatic and pancreatic damage and promotes tissue regeneration.

Transgenic animals modelling polyamine metabolism-related diseases

Cloning of genes related to polyamine metabolism has enabled the generation of genetically modified mice and rats overproducing or devoid of proteins encoded by these genes. Our first transgenic mice overexpressing ODC (ornithine decarboxylase) were generated in 1991 and, thereafter, most genes involved in polyamine metabolism have been used for overproduction of the respective proteins, either ubiquitously or in a tissue-specific fashion in transgenic animals. Phenotypic characterization of these animals has revealed a multitude of changes, many of which could not have been predicted based on the previous knowledge of the polyamine requirements and functions. Animals that overexpress the genes encoding the inducible key enzymes of biosynthesis and catabolism, ODC and SSAT (spermidine/spermine N1-acetyltransferase) respectively, appear to possess the most pleiotropic phenotypes. Mice overexpressing ODC have particularly been used as cancer research models. Transgenic mice and rats with enhanced polyamine catabolism have revealed an association of rapidly depleted polyamine pools and accelerated metabolic cycle with development of acute pancreatitis and a fatless phenotype respectively. The latter phenotype with improved glucose tolerance and insulin sensitivity is useful in uncovering the mechanisms that lead to the opposite phenotype in humans, Type 2 diabetes. Disruption of the ODC or AdoMetDC [AdoMet (S-adenosylmethionine) decarboxylase] gene is not compatible with mouse embryogenesis, whereas mice with a disrupted SSAT gene are viable and show no harmful phenotypic changes, except insulin resistance at a late age. Ultimately, the mice with genetically altered polyamine metabolism can be used to develop targeted means to treat human disease conditions that they relevantly model.