Role of xanthine oxidase and eicosanoids in development of pancreatic ischemia-reperfusion injury

Combined anti-mediator therapy for severe destructive forms of acute necrotizing pancreatitis in rats

Introduction: Inflammatory mediators play a major role in pathogenesis of acute pancreatitis with TNF (tumor necrosis factor) as the most important one. Development of effective combined therapy could help to decrease tissue damage, improve results and, finally, diminish the mortality rate in this severe pathology.

Materials and methods: All the studies were performed on 120 female white Wistar rats, weighing 250±25g. Acute pancreatitis reproduced by an intracanalicular injection of bile salts compound.

Results and discussion: The data obtained in the course of the study on the pronounced pancreatoprotective effect of infliximab are explained by its key role in the onset of the systemic inflammatory response, and, therefore, with the blockade of tumor necrosis factor alpha in the early stages, there is no pronounced secondary damage to the pancreas, which is reflected in a significant decrease in edema from 4.87±0.03 in the model up to 2.75±0.04, and as a consequence, an improvement in the blood supply of the acinar tissue from 182.38±15.92 PU up to 287.92±14.64 PU, which is expressed in a decrease in the zones of necrosis and in a decrease in mortality and, finally, efficiency coefficient from 13480.000 to 4283.348. A selective blocker of cysteinyl leukotrienes has a less pronounced protective reaction against damage to pancreatocytes, but to a much greater extent than octreotide. That is expressed by changes in the efficiency coefficient to the level of 8621.18 in montelukast group and 12767.30 in octreotide group, respectively. On the other hand, the effect of the use of infliximab does not surpass that of montelukast, and their combined use has a pronounced additive effect, which is proved by the efficiency coefficient at the level of 2390.33. This reaction is explained by the fact that TNF alpha-mediated pathway of activation of leukotriene biosynthesis is the main, but not the only one.

Conclusion: The combined anti-mediator therapy provides a great opportunity to improve the standard therapy of acute pancreatitis.

Reperfusion injury and reactive oxygen species: The evolution of a concept

Reperfusion injury, the paradoxical tissue response that is manifested by blood flow-deprived and oxygen-starved organs following the restoration of blood flow and tissue oxygenation, has been a focus of basic and clinical research for over 4-decades. While a variety of molecular mechanisms have been proposed to explain this phenomenon, excess production of reactive oxygen species (ROS) continues to receive much attention as a critical factor in the genesis of reperfusion injury. As a consequence, considerable effort has been devoted to identifying the dominant cellular and enzymatic sources of excess ROS production following ischemia-reperfusion (I/R). Of the potential ROS sources described to date, xanthine oxidase, NADPH oxidase (Nox), mitochondria, and uncoupled nitric oxide synthase have gained a status as the most likely contributors to reperfusion-induced oxidative stress and represent priority targets for therapeutic intervention against reperfusion-induced organ dysfunction and tissue damage. Although all four enzymatic sources are present in most tissues and are likely to play some role in reperfusion injury, priority and emphasis has been given to specific ROS sources that are enriched in certain tissues, such as xanthine oxidase in the gastrointestinal tract and mitochondria in the metabolically active heart and brain. The possibility that multiple ROS sources contribute to reperfusion injury in most tissues is supported by evidence demonstrating that redox-signaling enables ROS produced by one enzymatic source (e.g., Nox) to activate and enhance ROS production by a second source (e.g., mitochondria). This review provides a synopsis of the evidence implicating ROS in reperfusion injury, the clinical implications of this phenomenon, and summarizes current understanding of the four most frequently invoked enzymatic sources of ROS production in post-ischemic tissue.

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Reperfusion injury is implicated in a variety of human diseases and disorders.

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Evidence implicating ROS in reperfusion injury continues to grow.

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Several enzymes are candidate sources of ROS in post-ischemic tissue.

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Inter-enzymatic ROS-dependent signaling enhances the oxidative stress caused by I/R.

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Role of oxidative stress in pancreatic inflammation

Reactive oxygen and reactive nitrogen species (ROS/RNS) have been implicated in the pathogenesis of acute and chronic pancreatitis. Clinical and basic science studies have indicated that ROS/RNS formation processes are intimately linked to the development of the inflammatory disorders. The detrimental effects of highly reactive ROS/RNS are mediated by their direct actions on biomolecules (lipids, proteins, and nucleic acids) and activation of proinflammatory signal cascades, which subsequently lead to activation of immune responses. The present article summarizes the possible sources of ROS/RNS formation and the detailed signaling cascades implicated in the pathogenesis of pancreatic inflammation, as observed in acute and chronic pancreatitis. A therapeutic ROS/RNS-scavenging strategy has been advocated for decades; however, clinical studies examining such approaches have been inconsistent in their results. Emerging evidence indicates that pancreatitis-inducing ROS/RNS generation may be attenuated by targeting ROS/RNS-generating enzymes and upstream mediators.

Oxygen free radicals and redox biology of organelles

The presence and supposed roles of reactive oxygen species (ROS) were reported in literature in a myriad of instances. However, the breadth and depth of their involvement in cellular physiology and pathology, as well as their relationship to the redox environment can only be guessed from specialized reports. Whatever their circumstances of formation or consequences, ROS seem to be conspicuous components of intracellular milieu. We sought to verify this assertion, by collecting the available evidence derived from the most recent publications in the biomedical field. Unlike other reviews with similar objectives, we centered our analysis on the subcellular compartments, namely on organelles, grouped according to their major functions. Thus, plasma membrane is a major source of ROS through NAD(P)H oxidases located on either side. Enzymes of the same class displaying low activity, as well as their components, are also present free in cytoplasm, regulating the actin cytoskeleton and cell motility. Mitochondria can be a major source of ROS, mainly in processes leading to apoptosis. The protein synthetic pathway (endoplasmic reticulum and Golgi apparatus), including the nucleus, as well as protein turnover, are all exquisitely sensitive to ROS-related redox conditions. The same applies to the degradation pathways represented by lysosomes and peroxisomes. Therefore, ROS cannot be perceived anymore as a mere harmful consequence of external factors, or byproducts of altered cellular metabolism. This may explain why the indiscriminate use of anti-oxidants did not produce the expected "beneficial" results in many medical applications attempted so far, underlying the need for a deeper apprehension of the biological roles of ROS, particularly in the context of the higher cellular order of organelles.

Modification of oxidative stress in response to intestinal preconditioning

Previous studies have demonstrated that intestinal preconditioning protects the organ from ischemia reperfusion damage. Xanthine oxidase mediating free radical generation contributes to the development of injury associated to ischemia reperfusion. Thus, any process able to modulate the oxygen free radical generation system could attenuate the injury. Also, it is known that nitric oxide is implicated in the preconditioning response. The aim of this work is to determine: (1) the effect of intestinal preconditioning on the xanthine oxidase system, (2) the relevance of this system in the development of injury, and (3) its relationship with nitric oxide. For this purpose, we have determined the activity of the xanthine dehydrogenase/xanthine oxidase system, the levels of its substrate (xanthine), and end-product (uric acid) and oxidant stress status in rat small intestine subjected to ischemic pre-conditioning. The effects of nitric oxide inhibition have also been evaluated. Results show that the percentage of xanthine dehydrogenase to xanthine oxidase conversion, xanthine, uric acid concentration, lipoperoxides, and reduced glutathione were significantly reduced in preconditioned rats irrespectively of nitric oxide inhibition. In summary, this work shows that oxidative stress in intestinal preconditioning is reduced as consequence of the diminished conversion of xanthine dehydrogenase to xanthine oxidase, and also as a consequence of the reduced availability of xanthine.

Acute Pancreatitis Secondary to Dehydration: Case Report and Review of the Literature

Recent reports have documented the potentially catastrophic consequences of dehydration induced by vigorous exercise in otherwise healthy individuals. A case of acute pancreatitis secondary to exercise-induced dehydration is presented, and the literature of dehydration-induced syndromes, both research and clinical, is reviewed. The goal of this case report is to heighten awareness of dehydration as a potential cause of acute pancreatitis.