Xanthine oxidase inhibitor in acute experimental pancreatitis in rats and mice

It has been suggested that oxygen-derived free radicals play a decisive role in the pathogenesis of acute experimental pancreatitis in a model of edematous pancreatitis. Accordingly, allopurinol, a xanthine oxidase inhibitor, was shown to mitigate the development of nonfatal acute pancreatitis in ex vivo perfusion models using dogs. For further evaluation of allopurinol, its effect was studied in two forms of fatal necrotizing acute experimental pancreatitis: sodium taurocholate-induced pancreatitis in rats and choline-deficient ethionine-supplemented diet-induced pancreatitis in mice. Allopurinol did not affect the mortality rate, pancreatic enzyme elevation in serum and ascites, the enzyme content of the pancreas, or any parameter indicating histopathological damage in the pancreas. Although these experiments did not determine the role oxygen-derived free radicals play in the development of pancreatitis, they show, none the less, the absence of any beneficial therapeutic effect of a xanthine oxidase like allopurinol on the development of the disease once it has begun.     

Studies on oxygen-derived free radicals in acute pancreatic damage in rats--pancreatic damage experimentally induced by diethyldithiocarbamate

In order to investigate the role of the oxygen-derived free radicals in the pathogenesis of acute pancreatitis, an experimentally induced pancreatic damage was prepared in rats by the injection of diethyldithiocarbamate (DDC), which was known to be an inhibitor of Cu, Zn-superoxide dismutase (SOD). Male Wistar rats weighing 200-250 g received a single subcutaneous injection of DDC at a dose of 1000 mg/kg. Serum activities of amylase were significantly increased at 3 and 5 hours after the injection of DDC. Thiobarbituric acid reactants (TBA reactants) concentrations in the pancreatic tissue were increased at 30 minutes after the injection of DDC. At 7 hours after the injections of DDC, focal necrosis and degeneration of pancreatic acinar cells were observed. Peroral administration of allopurinol, an inhibitor of xanthine oxidase, before the injection of DDC suppressed the increase of TBA reactants concentration in the pancreatic tissue, but did not suppress the increase of serum activities of amylase. These results indicate that oxygen-derived free radicals may play an important role in the pathogenesis of acute pancreatic damage. However, since allopurinol did not suppress the increase of serum activities of amylase, further examination is needed to analyze the mechanism of DDC-induced pancreatic damage.     

Oxidative stress in distant organs and the effects of allopurinol during experimental acute pancreatitis.

BACKGROUND: The present study was aimed at an assessment of the role of oxygen-derived free radicals in the development of local and systemic manifestations of L-arginine (Arg)-induced acute pancreatitis and at an evaluation of the protective effect of the xanthine oxidase inhibitor allopurinol. METHODS: Acute pancreatitis was induced in male Wistar rats by injecting 2 x 250 mg/100 g body weight of Arg intraperitoneally at an interval of 1 h, as a 20% solution in 0.15 M NaCl. Control rats received the same quantity of glycine. In a third group, 200 mg/kg of allopurinol was administered subcutaneously 30 min before the first Arg injection. Rats were killed at 6, 12, 24, or 48 h following Arg administration. Acute pancreatitis was confirmed by a serum amylase level elevation and typical inflammatory features were observed microscopically. Tissue concentrations of malonyl dialdehyde (MDA), superoxide dismutase (Mn- and Cu,Zn-SOD), glutathione peroxidase (GPx), and catalase were measured in the pancreas, liver, and kidney. RESULTS: The tissue concentration of MDA was significantly elevated in each organ. The activities of Mn-SOD, Cu,Zn-SOD, GPx, and catalase were quickly depleted in the pancreas and kidney, whereas only the Mn-SOD and GPx activities were reduced in the liver after the onset of pancreatitis. Histologic examination revealed acinar cell necrosis in the pancreas, but only mild alterations in the liver and kidney. Allopurinol pretreatment prevented the generation of reactive oxygen metabolites in the pancreas and reduced their formation in the kidney. CONCLUSION: Oxygen-derived free radicals are generated in the pancreas, liver, and kidney at an early stage of Arg-induced acute pancreatitis. The liver and the kidney, but not the pancreas, are able to defend against oxidative stress. The prophylactic application of allopurinol significantly restrains the generation of free radicals in pancreas and kidney.     

Oxidative stress in distant organs and the effects of allopurinol during experimental acute pancreatitis

Summary Background. The present study was aimed at an assessment of the role of oxygen-derived free radicals in the development of local and systemic manifestations of l-arginine (Arg)-induced acute pancreatitis and at an evaluation of the protective effect of the xanthine oxidase inhibitor allopurinol. Methods. Acute pancreatitis was induced in male Wistar rats by injecting 2×250 mg/100 g body weight of Arg intraperitoneally at an interval of 1 h, as a 20% solution in 0.15 M NaCl. Control rats received the same quantity of glycine. In a third group, 200 mg/kg of allopurinol was administered subcutaneously 30 min before the first Arg injection. Rats were killed at 6, 12, 24, or 48 h following Arg administration. Acute pancreatitis was confirmed by a serum amylase level elevation and typical inflammatory features were observed microscopically. Tissue concentrations of malonyl dialdehyde (MDA), superoxide dismutase (Mn- and Cu,Zn-SOD), glutathione peroxidase (GPx), and catalase were measured in the pancreas, liver, and kidney. Results. The tissue concentration of MDA was significantly elevated in each organ. The activities of Mn-SOD, Cu,Zn-SOD, GPx, and catalase were quickly depleted in the pancreas and kidney, whereas only the Mn-SOD and GPx activities were reduced in the liver after the onset of pancreatitis. Histologic examination revealed acinar cell necrosis in the pancreas, but only mild alterations in the liver and kidney. Allopurinol pretreatment prevented the generation of reactive oxygen metabolites in the pancreas and reduced their formation in the kidney. Conclusion. Oxygen-derived free radicals are generated in the pancreas, liver, and kidney at an early stage of Arg-induced acute pancreatitis. The liver and the kidney, but not the pancreas, are able to defend against oxidative stress. The prophylactic application of allopurinol significantly restrains the generation of free radicals in pancreas and kidney.     

Involvement of Oxygen-Derived Free Radicals in L-Arginine-Induced Acute Pancreatitis

This study was aimed at an assessment of the role of oxygen-derived free radicals in the pathogenesis of L-arginine (Arg)-induced acute pancreatitis in rat, by measuring the levels of malonyl dialdehyde (MDA), glutathione peroxidase (GPx), catalase, and superoxide dismutase (Mn- and Cu,Zn-SOD) in the pancreatic tissue, and evaluating the protective effect of the xanthine oxidase inhibitor allopurinol. Acute pancreatitis was induced in male Wistar rats by injecting 2 × 250 mg/100 g body weight of Arg intraperitoneally in a 1-hr interval, as a 20% solution in 0.15 M NaCl. Control rats received the same quantity of glycine. Allopurinol, 100 or 200 mg/kg, was administered subcutaneously 30 min before the first Arg injection. Rats were killed at 6, 12, 24, and 48 hr following Arg administration, and acute pancreatitis was confirmed by a serum amylase level elevation and typical inflammatory features observed microscopically. The serum level of amylase reached the peak level at 24 hr after the Arg injection (30,800 ± 3813 vs 6382 ± 184 units/liter in the control) and normalized at 48 hr. The tissue concentration of MDA was significantly elevated at 24 hr and reached the peak value at 48 hr (5.00 ± 1.75 vs 0.28 ± 0.05 nM/mg protein in the control). The catalase and Mn-SOD activities were significantly decreased throughout the study, while the GPx activity was significantly reduced at 6 and 12 hr, and the Cu,Zn-SOD activity was significantly lower at 12 hr after the Arg injection as compared with the controls. Allopurinol treatment markedly reduced the serum amylase elevation (12.631 ± 2.257 units/liter at 24 hr) and prevented the increase in tissue MDA concentration (0.55 ± 0.09 nM/mg protein at 48 hr). Both doses of allopurinol significantly ameliorated the pancreatic edema, necrosis, and inflammation at 48 hr after Arg administration. Oxygen-derived free radicals are generated at an early stage of Arg-induced acute pancreatitis. Prophylactic allopurinol treatment prevents the generation of reactive oxygen metabolites, reduces the serum amylase concentration, and exerts a beneficial effect on the development of histopathological changes.     

Pancreatic exocrine function in unconscious rats treated with submaximal, maximal, and supramaximal doses of bombesin tetradecapeptide

Supramaximal stimulation of the rat pancreas in vivo with caerulein elicits a sharp decline in pancreatic juice volume and protein outputs and initiates acute edematous pancreatitis within 30 min. Because of the similar effects of caerulein and bombesin on pancreatic exocrine function, we examined in unconscious rats (a) the effects of a continuous, 4-h intravenous infusion of varying doses (0.2-40.0 nmol/kg/h) of bombesin on pancreatic juice volume and protein output, and (b) whether supramaximal doses of bombesin produce acute edematous pancreatitis. A maximal, fivefold and 17-fold rise in pancreatic juice volume and protein output was achieved with intravenous doses of 1.0 and 4.0 nmol of bombesin/kg/h, respectively. Pancreas weights in rats infused with bombesin as high as 40.0 nmol/kg/h were not significantly different from control animal values (no bombesin infusion) and serum amylase concentrations were only moderately (twofold) elevated over control values in rats i.v. infused with 4.0-40.0 nmol of bombesin/kg/h. The pancreas in rats treated with the highest dose of bombesin (40.0 nmol/kg/h) revealed sparsely scattered microvacuoles in a few acinar cells and minor evidence of interacinar edema. It is concluded that supramaximal stimulation of the rat pancreas in vivo with bombesin fails to elicit acute edematous pancreatitis and appears to be related to the ability of bombesin, in contrast to supramaximal doses of caerulein, to continuously stimulate maximal pancreatic juice secretion.     

Evidence for a role of oxygen derived free radicals in the pathogenesis of caerulein induced acute pancreatitis in rats.

The effects of a polyethylene glycol linked oxygen free radical scavenger enzyme, superoxide dismutase (PEG:SOD) on caerulein induced acute pancreatitis (AP) in rats were examined. Pancreas weights and serum amylase concentrations in rats given a three hour continuous intravenous infusion of caerulein (7.5 micrograms/kg/h, n = 18) for induction of AP followed by a three hour infusion of normal saline were significantly raised by approximately 25% (p less than 0.005) and 750% (p less than 0.001), respectively, compared with values obtained in control rats (n = 7) infused for six hours with normal saline alone. A single intraperitoneal injection of either 1 X 10(4) U/kg (n = 6), 2 X 10(4) U/kg (n = 5), or 4 X 10(4) U/kg (n = 5) of PEG:SOD immediately before caerulein infusion did not significantly alter pancreas weights, serum amylase content, or pancreatic histopathology compared with rats given caerulein alone. By contrast, a single intravenous bolus injection of 4 X 10(4) U/kg (n = 9) of PEG:SOD before caerulein treatment significantly reduced serum amylase content by approximately 25% (p less than 0.05) and a continuous six hour intravenous infusion of 4 X 10(4) U/kg/h of PEG:SOD (n = 5) produced significant reductions of approximately 25% (p less than 0.001), 35% (p less than 0.05), and 50% (p less than 0.01) in pancreas weights, serum amylase concentrations, and acinar cell vacuolisation (p less than 0.01), respectively, compared with values in rats given caerulein alone. In studies using bovine serum albumin linked to polyethylene glycol and infused for six hours at protein concentrations identical to high dose PEG:SOD (n = 6), no beneficial effects against caerulein induced AP were observed. These data suggest that (a) oxygen derived free radicals are involved in the early pathogenesis of caerulein induced AP in rats, and (b) the greatly extended circulating half life of polyethylene PEG:SOD ( > 35 hours in rats compared with less than six minutes for native superoxide dismutase) may make this compound more suitable than native superoxide dismutase as a potential therapeutic agent in AP.     

Melatonin reduces pancreatic prostaglandins production and protects against caerulein-induced pancreatitis in rats

Melatonin has been used to treat experimental pancreatitis, although not all the drug's therapeutic mechanisms of melatonin have been defined. Prostaglandins (PGs) are proinflammatory mediators that exert their effects mainly locally during inflammatory diseases. The present study was undertaken to examine whether treatment with melatonin influences local PG production. An acute pancreatitis model in male Sprague-Dawley rats (225-275 g) was established by continuously infusing caerulein (15 mg/kg/hr). Mean arterial pressure and pancreatic perfusion were monitored continuously. Melatonin was delivered via the intraperitoneal route at doses of either 2 or 10 mg/kg, 30 min after caerulein injection. Malondialdehyde and glutathione levels of the pancreas and liver and the trypsinogen activation peptide levels in the serum were measured at the end of the experiment (8 hr after infusion of caerulein). Intraperitoneal injection of melatonin (2 and 10 mg/kg) reduced the reduction in systemic arterial pressure and decreased pancreatic perfusion in the rat model of caerulein pancreatitis. Moreover, melatonin treatment changed local PG production toward control level. Higher dose of melatonin was somewhat more effective in preventing the caerulein-induced alterations than was the lower dose.     

Effects of antioxidants and free radical scavengers in three different models of acute pancreatitis.

The present studies were done to evaluate the therapeutic potential of several antioxidants and free radical scavengers in three different models of acute pancreatitis. (a) Edematous pancreatitis with acinar cells necrosis was induced by seven hourly intraperitoneal injections of 50 micrograms of caerulein per kg in mice. (b) Hemorrhagic pancreatitis was induced by feeding a choline-deficient, ethionine-supplemented (CDE) diet in mice. (c) Hemorrhagic pancreatitis was induced by retrograde infusion of 0.6 ml of 5% sodium taurocholate into the pancreatic duct in rats. The following antioxidants and free radical scavengers were given at various doses intravenously, subcutaneously, or intraperitoneally before the onset of pancreatitis: Ebselen [2-phenyl-1,2-benzisoselenazol-3(2H)-one], superoxide dismutase, catalase, deferoxamine (Desferal), dimethyl sulfoxide, or allopurinol. The severity of pancreatitis was assessed at various times after its onset by determination of serum amylase and pancreatic weight (edema), by grading of histological alterations, and by determination of survival (survival determined in models of hemorrhagic pancreatitis). In general, free radical scavengers and antioxidants ameliorated edema and inflammation to a greater degree than necrosis and the increase in serum amylase. Superoxide dismutase (as did Ebselen in previous studies) exerted beneficial effects on survival in diet-induced pancreatitis in the absence of marked effects on pancreatic necrosis, suggesting that these beneficial effects are due to amelioration of extrapancreatic complications that often contribute to mortality in acute pancreatitis. None of the antioxidants had major beneficial effects in taurocholate-induced hemorrhagic pancreatitis. Thus, formation of free radicals may be important for progression and outcome in diet-induced and, to a lesser degree, in caerulein-induced pancreatitis but not at all in taurocholate-induced pancreatitis. Different models of pancreatitis may, therefore, involve different degrees and mechanisms of free radical formation. Despite the amelioration of edema and the beneficial effects on mortality seen for some antioxidants in some of the models, antioxidants and free radical scavengers appear to have only a limited potential for treatment of acute pancreatitis.     

An ultrastructural study to investigate the effect of allopurinol on cerulein-induced damage to pancreatic acinar cells in rat

Summary Conclusion Subcellular organelles and membranes were the structures most protected by allopurinol, indirectly demonstrating their role of main and early target of oxygen-derived free radicals in the pathogenesis of acute pancreatitis. Background The present work evaluates the ultrastructural changes during cerulein-induced acute pancreatitis in rat with and without treatment with allopurinol. Methods and Results Supramaximal doses of cerulein, injected intraperitoneally (50 μg/kg) twice, at 1-h interval, caused severe subcellular alterations, including zymogen distribution, pathological vacuoles, and damage to organelles and membranes. Cotreatment (40 mg/kg ip twice with 1-h interval;n=10 rats) and, most of all, pretreatment (40 mg/kg ip allopurinol, 1 h; 20 mg/kg ip allopurinol+50 μg/kg ip cerulein, 30 min; 40 mg/kg ip allopurinol, 30 min; 50 μg/kg ip cerulein;n=10 rats) with allopurinol showed significant morphological improvement.     

Effect of a new cholecystokinin receptor antagonist CR 1392 on caerulein-induced acute pancreatitis in rats

The effects of cholecystokinin receptor antagonist CR 1392 was studied in a model of mild acute pancreatitis induced in rats by four subcutaneous injections of the secretagogue caerulein. A single subcutaneous injection of 50 mg/kg body weight of CR 1392 caused a dramatic reduction in serum amylase concentration and pancreatic wet weight as well as histologic improvement of the caerulein-induced acute pancreatitis when given 30 min before the first caerulein injection. CR 1392 was also effective in reducing the elevated serum amylase activity, pancreatic weight, and histologic alterations even when administered after the pancreatitis had been induced. These present observations suggest that CR 1392 remains active for more than 3 h and blocks the action of caerulein on the pancreas.     

Role of platelet activating factor in pathogenesis of acute pancreatitis in rats.

The importance of platelet activating factor in acute pancreatitis was examined by determining the tissue content of endogenous platelet activating factor and the protective effects of TCV-309, a highly selective platelet activating factor blocker, against caerulein induced pancreatitis in rats. Infusion of caerulein (10 micrograms/kg/h) for five hours resulted in about 70% increase in pancreatic weight, 22% rise in protein content, 50% reduction in tissue blood flow, nine fold increase in tissue level of platelet activating factor and 165% rise in plasma amylase as well as histological evidence of acute pancreatitis. Such infusion of caerulein in chronic pancreatic fistula rats caused a marked increase in protein output from basal secretion of 10 mg/30 minutes to 40 mg/30 minutes in the first hour of infusion followed by a decline in protein output to 15-20 mg/30 minutes in the following hours of the experiment. Exogenous platelet activating factor (50 micrograms/kg) injected ip produced similar alterations in weight, protein content, blood flow, and histology of the pancreas but the increment in serum amylase was significantly smaller and pancreatic secretion was reduced below the basal level. TCV-309 (50 micrograms/kg) given ip before caerulein or platelet activating factor administration significantly reduced the biochemical and morphological alterations caused by caerulein and abolished those induced by exogenous platelet activating factor. These results indicate that platelet activating factor plays an important role in the pathogenesis of acute pancreatitis probably by reducing the blood flow and increasing vascular permeability in the pancreas.     

Nitric oxide regulates bacterial translocation in experimental acute edematous pancreatitis

Background/Aims: The role of nitric oxide (NO) in bacterial translocation (BT) associated with acute pancreatitis is controversial. We investigated the effects of the NO synthase substrate, L-arginine, and the NO synthase inhibitor, N-nitro-L-arginine methyl ester (L-NAME), on BT in caerulein-induced acute pancreatitis in rats. Methods: Acute pancreatitis was induced by subcutaneous injections of caerulein (12 μg/kg) at 6-hour intervals for 2 days. Subcutaneous injections of L-arginine (100 mg/kg) or L-NAME (10 mg/kg) were administered once daily for 2 days. At 48 h, pancreatic injury and BT to the mesenteric lymph nodes (MLN), liver, and peritoneum were assessed. Results: Compared with controls, rats that received caerulein injections alone had increased BT to the MLN and pancreatic inflammatory changes. L-Arginine significantly reduced the inflammation and BT caused by caerulein. L-NAME did not significantly alter pancreatic inflammation. Although caerulein + L-NAME-treated rats had increased BT to the peritoneum, MLN, and liver compared with controls, rates of BT did not significantly differ between caerulein alone- and caerulein + L-NAME-treated rats. Conclusion: In acute edematous pancreatitis, BT is increased and is regulated by NO. NO substrates limit BT and pancreatic inflammation associated with acute pancreatitis, probably by their bactericidal actions and ability to improve pancreatic blood flow.     

Electron-microscopic evidence of mitochondriae containing macroautophagy in experimental acute pancreatitis: Implications for cell death

BackgroundDysfunctional autophagy and necrosis are characteristic features of severe acute pancreatitis.ObjectiveTo unravel the cellular mechanisms underlying the pathogenesis of acute pancreatitis.MethodsWe studied the ultrastructural pancreatic morphology using electron microscopy in experimental acute pancreatitis. The control group of animals received intraperitoneal injections of normal saline. Different severity of acute pancreatitis was induced by low and high doses of caerulein in Swiss albino mice. In the low dose group, pancreatitis was induced by 4 injections of caerulein given hourly [50 μg/kg/dose – total of 200 μg/kg] and in the high dose group by 8 injections given hourly (total of 400 μg/kg). The experiments were repeated in Na-taurocholate model of acute pancreatitis in rats. The pancreatic tissue was processed and studied by transmission electron microscopy for ultrastructural changes.ResultsThe acinar cells of the pancreatitis animals revealed autophagosomes that contained cellular organelles, including mitochondria. The animals that received a higher dose of caerulein had numerous cells showing a necrotic morphology, whereas the animals in the low dose group showed a predominantly apoptotic cell morphology. The Na-taurocholate model in rats also showed similar features of severe pancreatitis with cellular necrosis and macroautophagy.ConclusionsDysfunctional mitochondria in the injured pancreatic acinar cells are degraded by macroautophagy. These observations are not model specific. Mitochondrial dysfunction and consequent energy deficit in the cells might be causally related to cellular necrosis.     

Role of endogenous platelet-activating factor in caerulein-induced acute pancreatitis in rats: Protective effects of a PAF-antagonist

The role of endogenous platelet-activating factor (PAF) in the pathogenesis of acute pancreatitis was investigated by determining whether CV-6209, a selective PAF antagonist, confers protection against caerulein-induced acute pancreatitis in rats. Continuous intravenous infusion of caerulein (5 micrograms/kg x h) induced time-dependent increase in serum pancreatic enzymes, pancreatic weight, and protein content of the pancreas, and produced histologic evidence of acute pancreatitis. Pretreatment with CV-6209 (1 mg/kg) significantly inhibited the elevation of serum pancreatic enzymes, pancreatic weight, and protein content of the pancreas. Caerulein-induced tissue oedema and recruitment of leucocytic cells were markedly ameliorated with CV-6209. Platelet-activating factor may be released endogenously and may play a role during acute pancreatitis.     

Xanthine oxidase is not a source of free radicals in the ischemic rabbit heart

The xanthine oxidase pathway has been proposed as a source of oxygen-derived free radicals in ischemic and reperfused myocardium. A spectrophotometric assay was employed to measure the xanthine oxidase activity of rat and rabbit hearts exposed to varying durations of global ischemia. In the rat 24.6 +/- 4.8 mIU/g wet wt of xanthine dehydrogenase + xanthine oxidase activity were detected in both ischemic and normally perfused myocardium. In the non-ischemic state only 6% of this activity was associated with the free radical-producing oxidase form. After 5 min of ischemia however about 25% of the enzyme was in the oxidase form, a value which remained unchanged over the following 25 min. Neither xanthine dehydrogenase nor xanthine oxidase could be detected in the rabbit heart. Failure of allopurinol, an inhibitor of xanthine oxidase, to limit infarct size in a rabbit model of ischemia/reperfusion provides further evidence that this species has insignificant amounts of xanthine oxidase in its heart. Anesthetized rabbits were subjected to coronary artery ligation for 45 min and 3 h of reperfusion. The volume of the zone of underperfusion was assessed with fluorescent microspheres and infarct size was assessed by tetrazolium staining. In control animals 67.5 +/- 3.8% of the zone of underperfusion became necrotic. In rabbits given superoxide dismutase (15000 IU/kg) + catalase (50,000 IU/kg) for 90 min starting 15 min before occlusion, infarct size was only 35.4 +/- 3.3% of the zone of underperfusion. However, in rabbits pretreated with allopurinol (75 mg p.o. 24 h before study + 30 mg/kg 5 min before occlusion) infarct size was 65.8 +/- 8.7%.(ABSTRACT TRUNCATED AT 250 WORDS)     

Free Radicals Generated by Xanthine Oxidase Mediate Pancreatitis-Associated Organ Failure

In the present study we evaluate the possibilitythat xanthine oxidase released by damaged pancreas couldact as a source of oxidative damage in systemic tissuesduring the early stages of acute pancreatitis. This was accomplished by evaluating the effectsof xanthine oxidase inhibition with oxypurinol infusedinto the portal vein. Under these conditions, weinhibited the enzyme before it reached the liver and other distant organs, without inducing changesin the severity of pancreatic damage. Results indicatethat pancreatitis parallels increases in xanthineoxidase activity in plasma. Superoxide radicalsgenerated by this enzyme appears to be involved in thedecrease of reduced glutathione levels in the plasma andliver. In addition, xanthine oxidase inhibition preventsthe infiltration of neutrophils into the lungs. We conclude that oxygen free radicals generatedby xanthine and xanthine oxidase released to thebloodstream are involved in the systemic organ failureassociated with acute pancreatitis.     

Role of xanthine oxidase in ethanol-induced lipid peroxidation in rats

To investigate a possible role of free radical production by xanthine oxidase in the pathogenesis of ethanol-induced hepatic lipid peroxidation, chow-fed rats were given ethanol (5 g/kg) and placed at 32 degrees C for 6 h, which resulted in increased hepatic malondialdehyde levels. Pretreatment with allopurinol in amounts that effectively inhibited xanthine metabolism also significantly decreased ethanol-induced lipid peroxidation, suggesting participation of free radicals produced by xanthine oxidase in the peroxidative process. Both acetaldehyde and purine can serve as substrates for xanthine oxidase. Pretreatment with cyanamide increased hepatic acetaldehyde levels 5-fold, yet this was associated with a decrease in lipid peroxidation, indicating that acetaldehyde is not the xanthine oxidase substrate involved. By contrast, ethanol increased hepatic contents of hypoxanthine and xanthine and enhanced urinary output of allantoin (a final product of xanthine metabolism), incriminating increased metabolism of purines. Ethanol administration also enhanced hepatic nicotinamide adenine dinucleotide (reduced form). A corresponding rise of nicotinamide adenine dinucleotide (reduced form) in vitro inhibited xanthine dehydrogenase activity by 60%-76%. Increased purine degradation, possibly associated with a shift from the dehydrogenase to the xanthine oxidase pathway (secondary to nicotinamide adenine dinucleotide [reduced form]-mediated inhibition of xanthine dehydrogenase activity) is proposed as a possible mechanism for ethanol-stimulated free radical production. Because allopurinol attenuates the associated lipid peroxidation, this agent might be considered for possible therapeutic use in alcohol-induced liver damage.     

Protective action of lipopolysaccharidesin rat caerulein-induced pancreatitis: role of nitric oxide

Lipopolysaccharides (LPS), the component of the cell wall of gram-negative bacteria, have been implicated in the pathogenesis of acute pancreatitis, but the mechanism of their action on the pancreas has not been fully explored. The aim of this study was to investigate the effects of various doses of LPS on the integrity of intact pancreas and that involved in acute caerulein-induced pancreatitis (CIP) in the rat and to compare these effects with those of nitric oxide (NO) donor, S-nitrose-acetylpenicillamine (SNAP). The expression of constitutive NO synthase (cNOS) and inducible NO synthase (iNOS) mRNA was also examined in the isolated pancreatic acini obtained from the inflamed pancreas of rats treated with LPS. CIP was produced by subcutaneous (s.c.) infusion of caerulein (5 microg/kg.h for 5 h) to conscious rats. Bolus injections of various doses of LPS (0.1, 1, 10, 20 or 40 mg/kg) or SNAP (1.5, 3 or 6 mg/kg) were made intraperitoneally (i.p.) either alone or 30 min prior to s.c. infusion of caerulein to induce CIP. Infusion of caerulein produced acute pancreatitis confirmed by histological examination and manifested by an increase of pancreatic mass (by about 200%). Blood levels of amylase and lipase were augmented by 400 and 800% respectively, whereas the pancreatic blood flow (PBF) was decreased by 50% in rats with CIP. Injection of low doses of LPS (0.1-1 mg/kg i.p.) or SNAP (1.5-3 mg/kg i.p.) 30 min prior to caerulein infusion reversed the harmful effects of pancreatic overstimulation with caerulein and reduced significantly the histological manifestations of CIP such as edema, neutrophil infiltration and vacuolization of the acinar cells. These protective effects of low doses of LPS pretreatment on the pancreas were completely antagonized by the suppression of the activity of NO synthase (NOS) with N(G)-nitro-L-arginine (L-NNA) applied (20 mg/kg i.p.) 15 min prior to the LPS injection. Combination of L-arginine (100 mg/kg i.p.), a substrate for NOS, with L-NNA given prior to low doses of LPS, restored the LPS-induced protection of the pancreas in rats with CIP. In contrast, higher doses of LPS (20-40 mg/kg i.p.) or SNAP (6 mg/kg i.p.), which produced a significant fall of the PBF, did not protect the pancreas against CIP. Administration of various doses of LPS to rats with CIP resulted in significant and dose-dependent stimulation of NO biosynthesis in the isolated acini obtained from the pancreas of these animals. LPS enhanced the expression of both cNOS and iNOS in the pancreatic acini obtained from rats subjected to CIP. The signal for cNOS mRNA was detected in all samples, reaching peak at the protective dose of LPS (1 mg/kg i. p.), while iNOS was overexpressed only at the highest doses of LPS that failed to exhibit the protective activity. We conclude that the pretreatment with low doses of LPS protects the pancreas against the damage provoked by CIP and this effect could be attributed, at least in part, to the activation of L-arginine-NO system in the pancreas.     

Does allopurinol reduce pain of chronic pancreatitis?

Summary Conclusion A dosage of 300 mg/d of allopurinol was not effective in reducing pain or improving activities of daily living in chronic pancreatitis. Background Allopurinol prevents the generation of oxygen-derived free radicals by inhibiting xanthine oxidase. The purpose of this study was to determine whether allopurinol is effective in reducing pain of chronic pancreatitis. Methods Thirteen patients with chronic pancreatitis who were experiencing abdominal pain requiring medication at least three times each week entered a randomized, double-blind, two-period crossover clinical trial. Patients evaluated their pain daily using a categorical pain intensity scale, numeric pain intensity scale, and a visual analog scale, and weekly completed a McGill Pain Questionnaire and activities of daily living (ADL) questionnaire. Results The mean baseline score of pain was approx 50% of most severe pain in all scoring systems. There was no significant decrease in pain associated with allopurinol compared to the placebo (p=0.24–0.75). In addition, there was no benefit in terms of ADL score associated with allopurinol compared with placebo (p=0.32). Mean uric acid level was decreased by 1.15 mg/dL while patients were taking allopurinol, compared to when they were taking placebo (p=0.007).