Rapid conversion to high xanthine oxidase activity in viable Kupffer cells during hypoxia

Influence of exercise on oxidative stress in patients with heart failure

Reactive oxygen species play an important role in the pathophysiology of heart failure (HF). In contrast, regular physical exercise can promote adaptations to reactive oxygen species that are beneficial for patients with HF. We completed a systematic review of randomized controlled trials that evaluate the influence of exercise on oxidative stress in patients with HF. Articles were searched in the PubMed, Cochrane, SciELO, and LILACS databases. The search was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. The quality of the included studies was assessed using the Physiotherapy Evidence Database scale. We selected 12 studies with a total of 353 participants. The included patients had a left ventricle ejection fraction of < 52% and New York Heart Association functional class II or III disease. A significant increase was observed in peak oxygen consumption (between 10 and 46%) in the group that underwent training (TG). There was an improvement in the oxidative capacity of skeletal muscles in the TG, related to the positive activity of mitochondrial cytochrome c oxidase (between 27 and 41%). An increase in the expression of the enzymes glutathione peroxidase (41%), catalase (between 14 and 42%), and superoxide dismutase (74.5%), and a decrease in lipid peroxidation (between 28.8 and 58.5%) were observed in the TG. Physical training positively influenced the cardiorespiratory capacity and enhanced the benefits of oxidant and antioxidant biomarkers in patients with HF. High-intensity training promoted a 15% increase in the plasma total antioxidant capacity, whereas moderate training had no effect.

Mitochondrial Dysfunction and Autophagy in Hepatic Ischemia/Reperfusion Injury

Ischemia/reperfusion (I/R) injury remains a major complication of liver resection, transplantation, and hemorrhagic shock. Although the mechanisms that contribute to hepatic I/R are complex and diverse involving the interaction of cell injury in hepatocytes, immune cells, and endothelium, mitochondrial dysfunction is a cardinal event culminating in hepatic reperfusion injury. Mitochondrial autophagy, so-called mitophagy, is a key cellular process that regulates mitochondrial homeostasis and eliminates damaged mitochondria in a timely manner. Growing evidence accumulates that I/R injury is attributed to defective mitophagy. This review aims to summarize the current understanding of autophagy and its role in hepatic I/R injury and highlight the various therapeutic approaches that have been studied to ameliorate injury.

Inflammasome activation in the liver: Focus on alcoholic and non-alcoholic steatohepatitis

Upregulation of the inflammatory cascade is a major element both in the progression of steatohepatitis to severe alcoholic hepatitis as well as in the progression of NASH to advanced NASH with fibrosis. The mechanisms underpinning these changes are only partially understood. Activation of the inflammatory cascade requires multiple stimuli and in this report, we discuss the role of inflammasomes that activate IL-1β as well as the sterile and pathogen-derived danger signals that results in inflammasome activation and inflammation in alcoholic and non-alcoholic steatohepatitis. The dynamics of inflammasome activation, the cell types involved and the trigger signals appear to be somewhat different between ASH and NASH. Further studies are needed to dissect the pathology-related differences between these two major forms of steatohepatitis. Clinical and therapeutic implications of inflammasome activation in steatohepatitis are also discussed.

Brain purine metabolism and xanthine dehydrogenase/oxidase conversion in hyperammonemia are under control of NMDA receptors and nitric oxide

In hyperammonemia, a decrease in brain ATP can be a result of adenine nucleotide catabolism. Xanthine dehydrogenase (XD) and xanthine oxidase (XO) are the end steps in the purine catabolic pathway and directly involved in depletion of the adenylate pool in the cell. Besides, XD can easily be converted to XO to produce reactive oxygen species in the cell. In this study, the effects of acute ammonia intoxication in vivo on brain adenine nucleotide pool and xanthine and hypoxanthine, the end degradation products of adenine nucleotides, during the conversion of XD to XO were studied. Injection of rats with ammonium acetate was shown to lead to the dramatic decrease in the ATP level, adenine nucleotide pool size and adenylate energy charge and to the great increase in hypoxanthine and xanthine 11 min after the lethal dose indicating rapid degradation of adenylates. Conversion of XD to XO in hyperammonemic rat brain was evidenced by elevated XO/XD activity ratio. Injection of MK-801, a NMDA receptor blocker, prevented ammonia-induced catabolism of adenine nucleotides and conversion of XD to XO suggesting that in vivo these processes are mediated by activation of NMDA receptors. The in vitro dose-dependent effects of sodium nitroprusside, a NO donor, on XD and XO activities are indicative of the direct modification of the enzymes by nitric oxide. This is the first report evidencing the increase in brain xanthine and hypoxanthine levels and adenine nucleotide breakdown in acute ammonia intoxication and NMDA receptor-mediated prevention of these alterations.

Xanthine oxidase-induced neuronal death via the oxidation of NADH: prevention by micromolar EDTA

The oxidation of xanthine by xanthine oxidase (XO) or xanthine dehydrogenase represents an important source of reactive oxygen species (ROS), which contribute to the damaging consequences of cerebral ischemia, inflammation, and neurodegenerative disorders. However, both enzymes are also able to act on reduced nicotinamide adenine dinucleotide (NADH). The FAD binding site to which NADH binds is distinct from that of the xanthine binding site. We report that the combination of xanthine oxidase and NADH is toxic to cultures of cerebellar granule neurons. Protection by superoxide dismutase (Cu,Zn-SOD or Mn-SOD) or catalase indicates mediation of the toxicity by superoxide and hydrogen peroxide. In addition, pre-incubating XO with EDTA at concentrations as low as 2 microM, prevented the toxicity, indicating that a metal contaminating XO is involved in producing the toxic effects of XO/NADH. It is possible that such a metal might play a role in the toxicity of XO in vivo.

Increased xanthine oxidase in the skin of preeclamptic women

Xanthine oxioreductase is the holoenzyme responsible for terminal purine catabolism. Under conditions of metabolic stress or heightened proinflammatory cytokine production, this enzyme is preferentially in its oxidized form, xanthine oxidase, with catalytic action that generates uric acid and the free radical superoxide. As preeclampsia is characterized by heightened inflammation, oxidative stress, and hyperuricemia, it has been proposed that xanthine oxidase plays a pivotal role in this hypertensive disorder of pregnancy. We sought to determine whether xanthine oxidase protein content was higher in maternal tissue of preeclamptic mothers, compared to healthy pregnant controls, using immunohistochemical analysis of skin biopsies. We further compared xanthine oxidase immunoreactivity in skin biopsies from preeclamptic women and patients with several inflammatory conditions. In preeclamptic women, intense xanthine oxidase immunoreactivity was present within the epidermis. By contrast, only very faint xanthine oxidase staining was observed in skin biopsies from healthy pregnant controls. Further, a role for inflammation in the increase of xanthine oxidase was suggested by similar findings of heightened xanthine oxidase immunoreactivity in the skin biopsies from nonpregnant individuals diagnosed with conditions of systemic inflammation. The finding of increased xanthine oxidase in maternal tissue, most likely as the result of heightened maternal inflammation, suggests maternal xanthine oxidase as a source of free radical and uric acid generation in preeclampsia.

MCI-186 (edaravone), a free radical scavenger, attenuates hepatic warm ischemia-reperfusion injury in rats

Hepatic warm ischemia-reperfusion injury (IRI) during hepatectomy and liver transplantation is a major cause of liver dysfunction in which the pathologic role of free radicals is a major concern. To assess the effect of MCI-186 (edaravone) on hepatic IRI, male Wistar rats were subjected to partial hepatic ischemia for 60 min after pretreatment with vehicle (group C) or MCI-186 (group M), or after both MCI-186 pretreatment and additional administration of MCI-186 12 h after reperfusion (group MX). Groups M and MX showed significantly lower levels of serum alanine aminotransferase and hepatic lipid peroxidation than group C, and also significantly lower expression levels of mRNA for cytokines, chemokines and intercellular adhesion molecule-1. There were fewer tissue monocytes and neutrophils in groups M and MX than in group C. These effects were more marked in group MX than in group M. Our findings suggest that treatment with MCI-186 attenuates hepatic IRI in this rat in vivo model.

Home-based exercise training modulates pro-oxidant substrates in patients with chronic heart failure

BACKGROUND

In chronic heart failure, oxidative stress is thought to lead to endothelial dysfunction. In this study, we assessed the effect of home-based exercise training on variables of the NO and purine pathways.

METHODS AND RESULTS

Eighteen patients and nine controls were randomly assigned in cross-over design to 8 weeks of exercise training (5 days/week, submaximal bicycle ergometer training, 30 min/day; calisthenics 9 min/day) and 8 weeks of sedentary lifestyle. Hypoxanthine, xanthine, l-arginine, asymmetric dimethylarginine (ADMA), symmetric DMA (SDMA) and nitrite were measured. In patients, exercise training led to an increase in peak VO(2) (p<0.003). At baseline hypoxanthine-a pro-oxidant substrate and marker of hypoxia-was higher in patients than in controls (24.6+/-4.3 vs. 11.9+/-4.2 micromol/l; p<0.05). After training there was a reduction in hypoxanthine (p<0.01). Nitrite levels were lower in patients (416+/-31 micromol/l) than in healthy controls (583+/-35 micromol/l, p<0.001). Although nitrite levels were highest after exercise, the changes did not reach statistical significance (p=n.s.). l-Arginine, ADMA, and SDMA levels were not different between groups and were not altered by exercise training.

CONCLUSIONS

Chronic heart failure is associated with increased levels of hypoxanthine and decreased levels of nitrite. This imbalance can be beneficially modulated by chronic home-based exercise training.

Alteration in some antioxidant enzymes in cardiac tissue upon monosodium glutamate [MSG] administration to adult male mice

4mg and 8mg monosodium glutamate per gram body weight was administered subcutaneously for 6 consecutive days to normal adult male mice and its effect was seen on 31(st) day after the last injection on some antioxidant enzymes in heart. A significant dose dependent increase in lipid peroxidation and xanthine oxidase level was observed, whereas the activity of free radical scavenging enzymes such as superoxide dismutase and catalase was decreased in both monosodium glutamate treated groups (Group-2 and Group-3). So, the present work suggested that monosodium glutamate at dose level of 4mg/g body weight and above induced oxidative stress in the cardiac tissue by changing the activity of free radical initiating enzyme such as xanthine oxidase and scavenging enzymes like superoxide dismutase and catalase.

Role of free radicals in failure of fatty liver grafts caused by ethanol

Alcohol is associated with accidental deaths and suicides leading to organ donation, and hepatic steatosis is an important risk factor for initial poor function and failure of human liver grafts. Mechanisms of fatty graft failure are not fully understood, but increased oxidative stress may be a major factor. To characterize the role of free radical stress and the efficacy of antioxidant treatments in fatty liver graft injury, donors for orthotopic rat liver transplantation were treated chronically (3 or more weeks) and acutely (single dose) with ethanol. After transplantation, necrosis and alanine aminotransferase release were threefold to fourfold higher in recipients of fatty grafts from donors treated with ethanol either acutely or chronically compared with findings for recipients of grafts from untreated donors. Moreover, graft survival decreased from nearly 100% to less than 20%. Free radical adducts, as measured by electron spin resonance spectroscopy, were detected in the blood and bile of rats receiving fatty grafts caused by ethanol. Markers of lipid peroxidation also increased after transplantation. Destruction of Kupffer cells with gadolinium chloride decreased free radical production and improved graft survival. Leukocyte adhesion increased beginning early after implantation, and adherent white blood cells obtained from transplanted fatty livers produced the same free radical species as were detected in blood. Therefore, Kupffer cells and adherent white blood cells are important sources of free radicals. Free radicals not only damage fatty grafts directly but also lead to enhanced inflammation and disturbed microcirculation. Delivery of superoxide dismutase-1 and superoxide dismutase-2 genes, free radical-scavenging polyphenols, and antioxidant-containing Carolina Rinse solution reduced injury and improved survival of fatty grafts caused by ethanol. Taken together, these findings indicate that free radicals increase in fatty grafts after transplantation and play an important role in injury of fatty grafts obtained from ethanol-exposed donors. Treatment of fatty donor livers with antioxidants and free radical scavengers may thus be an effective clinical therapy to prevent failure of fatty grafts.

Kupffer cells and reactive oxygen species partially mediate lipopolysaccharide-induced downregulation of nuclear receptor pregnane x receptor and its target gene CYP3a in mouse liver

Pregnane X receptor (PXR) is a member of the nuclear receptor superfamily that regulates target gene transcription in a ligand-dependent manner. The in vivo effects of lipopolysaccharide (LPS) on expression of PXR and its target gene cytochrome P450 3A (CYP3A) in mouse liver were investigated in this study. Mice were injected intraperitoneally with different doses of LPS (0.1-5.0 mg/kg). PXR and CYP3A11 mRNA levels were measured using reverse transcription polymerase chain reaction. Results indicate that LPS significantly inhibits the expression of PXR mRNA in a dose-dependent manner, followed by suppression of CYP3A11 mRNA in mouse liver. LPS also represses the upregulation of CYP3A11 mRNA levels and erythromycin N-demethylase (ERND) catalytic activity in mice pretreated with PXR ligands dexamethasone, rifampicin, mifepristone, and phenobarbital. LPS-induced downregulation of PXR and CYP3A11 mRNA in liver was significantly attenuated in mice pretreated with gadolinium chloride, a selective Kupffer cell toxicant. Pretreatment with a single dose of gadolinium chloride (10 mg/kg) also significantly attenuated LPS-induced downregulation of dexamethasone-, rifampicim-, mifepristone-, and phenobarbital-inducible, CYP3A11 mRNA expression and ERND activity in mouse liver. Furthermore, LPS-induced downregulation of PXR and CYP3A11 mRNA was significantly attenuated in mice pretreated with allopurinol, an inhibitor of xanthine oxidase, and diphenyleneiodonium chloride, an inhibitor of NADPH oxidase. Allopurinol and diphenyleneiodonium chloride pretreatment also attenuated the repressive effects of LPS on dexamethasone-, rifampicin-, mifepristone-, and phenobarbital-inducible CYP3A11 mRNA expression and ERND catalytic activity in mouse liver. However, aminoguanidine, a selective inhibitor of inducible nitric oxide synthase, has no effect on LPS-induced downregulation of PXR and CYP3A11 mRNA. Finally, LPS-induced downregulation of PXR and CYP3A11 mRNA was prevented in mice pretreated with either N-acetylcysteine or ascorbic acid. These antioxidants also prevented the repressive effects of LPS on dexamethasone-, rifampicin-, mifepristone-, and phenobarbital-inducible CYP3A11 mRNA expression and ERND catalytic activity in mouse liver. These results indicate that Kupffer cells contribute to LPS-induced downregulation of PXR and CYP3A in mouse liver. Reactive oxygen species, produced possibly by NADPH oxidase and perhaps by xanthine oxidase, are involved in LPS-induced downregulation of nuclear receptor PXR and its target gene CYP3A in mouse liver.

Dipyridamole protects the liver against warm ischemia and reperfusion injury

BACKGROUND

Adenosine, a metabolite of adenosine triphosphate degradation during ischemia, is reported to attenuate ischemia and reperfusion injury in several tissues. Dipyridamole is a nucleoside transport inhibitor that augments endogenous adenosine. In this study, we tested whether dipyridamole would attenuate hepatic I/R injury. For this purpose, dipyridamole was applied to a 2-hour total hepatic vascular exclusion model in dogs.

STUDY DESIGN

Dipyridamole (DYP) was given by continuous intravenous infusion for 1 hour before ischemia at a dose of 0.25 mg/kg (high-DYP, n = 6), 0.1 mg/kg (medium-DYP, n = 6), or 0.05 mg/kg (low-DYP, n = 6). Nontreated animals were used as ischemic controls (CT, n = 12). Two-week survival, systemic and hepatic hemodynamics, liver function tests, energy metabolism, adenosine 3', 5'-cyclic monophosphate (cyclic AMP) levels, platelet numbers, arachidonic acid metabolites, and histopathology were analyzed.

RESULTS

Two-week animal survival was 25% in CT, 17% in high-DYP, 100% in medium-DYP, and 17% in low-DYP. Dipyridamole significantly improved postreperfusion hepatic blood flow and energy metabolism, attenuated liver enzyme release and purine catabolite production, and augmented cyclic AMP levels. The medium dose of dipyridamole lessened platelet aggregation, thromboxane B2 production, and polymorphonuclear neutrophil infiltration, and improved survival.

CONCLUSIONS

We demonstrated marked hepatoprotective effects of dipyridamole against severe ischemia and reperfusion injury in canine livers. Dipyridamole is a promising agent for liver surgery and transplantation.

Posttranslational inactivation of human xanthine oxidoreductase by oxygen under standard cell culture conditions

Xanthine oxidoreductase (XOR) catalyzes the final reactions of purine catabolism and may account for cell damage by producing reactive oxygen metabolites in cells reoxygenated after hypoxia. We found a three- to eightfold higher XOR activity in cultured human bronchial epithelial cells exposed to hypoxia (0.5-3% O2) compared with cells grown in normoxia (21% O2) but no difference in XOR protein or mRNA. XOR promoter constructs failed to respond to hypoxia. The cellular XOR activity at 3% O2 returned to basal levels when the cells were returned to 21% O2, and hyperoxia (95% O2) abolished enzyme activity with no change in XOR protein. Our data suggest reversible enzyme inactivation by oxygen or its metabolites. NADH was normally oxidized by the oxygen-inactivated enzyme, which rules out damage to the flavin adenine dinucleotide cofactor. Hydrogen peroxide partially inactivated the molybdenum center of XOR, as shown by a parallel decrease in XOR-catalyzed xanthine oxidation and dichlorophenolindophenol reduction. We conclude that the transcription or translation of XOR is not influenced by hypoxia or hyperoxia. Instead, the molybdenum center of XOR is posttranslationally inactivated by oxygen metabolites in "normal" (21% O2) cell culture atmosphere. This inactivation is reversed in hypoxia and accounts for the apparent induction.

Structure and function of xanthine oxidoreductase: where are we now?

Xanthine oxidoreductase (XOR) is a complex molybdoflavoenzyme, present in milk and many other tissues, which has been studied for over 100 years. While it is generally recognized as a key enzyme in purine catabolism, its structural complexity and specialized tissue distribution suggest other functions that have never been fully identified. The publication, just over 20 years ago, of a hypothesis implicating XOR in ischemia-reperfusion injury focused research attention on the enzyme and its ability to generate reactive oxygen species (ROS). Since that time a great deal more information has been obtained concerning the tissue distribution, structure, and enzymology of XOR, particularly the human enzyme. XOR is subject to both pre- and post-translational control by a range of mechanisms in response to hormones, cytokines, and oxygen tension. Of special interest has been the finding that XOR can catalyze the reduction of nitrates and nitrites to nitric oxide (NO), acting as a source of both NO and peroxynitrite. The concept of a widely distributed and highly regulated enzyme capable of generating both ROS and NO is intriguing in both physiological and pathological contexts. The details of these recent findings, their pathophysiological implications, and the requirements for future research are addressed in this review.

Beta-galactosidase as a marker of ischemic injury and a mechanism for viability assessment in porcine liver transplantation

Glycohydrolases are a group of enzymes contained predominantly within lysosomes, which are released during Kupffer cell activation or death. One of these, beta-galactosidase, has been proposed as a marker of ischemia-reperfusion injury in the liver because Kupffer cell activation represents a primary event in the injurious reperfusion cascade. In this study, we compared B-galactosidase with more traditional indicators of liver injury and function in a porcine model of liver preservation. Porcine livers were allocated into two groups: group C (n = 5), preserved in University of Wisconsin solution by standard cold storage for 24 hours, and group W (n = 5), perfused with oxygenated autologous blood on an extracorporeal circuit for 24 hours. Both groups were subsequently tested on the circuit during a 24-hour reperfusion phase. The perfusate was sampled for levels of beta-galactosidase, as well as traditional markers of liver injury and function. A sharp increase in beta-galactosidase levels was seen on reperfusion of cold preserved livers to a level of 1,900 IU/mL. This contrasted dramatically with normothermically preserved livers, in which the level never exceeded 208 IU/mL (P =.002). beta-Galactosidase levels showed much earlier and greater increases compared with transaminase levels in livers injured by ischemia. A rapid elevation in beta-galactosidase levels corresponded well with poor liver function and more liver injury. Measurement of beta-galactosidase is a simple test that quantifies ischemia-reperfusion injury of preserved livers. It is more sensitive than transaminases, with faster and larger increases in levels after ischemic injury. It can be useful in assessing the viability of a liver during machine preservation.

Protective effect of agiotensin II type I receptor antagonist, CV-11974, on ischemia and reperfusion injury of the liver

BACKGROUND

Microcirculatory disturbance has been shown to play a critical role in hepatic ischemia and reperfusion (I/R) injury. Angiotensin II (AngII) is one of the most potent endogenous vasoconstrictors. Angiotensin II type I (AT1) receptor antagonist has been reported to have protective effects on I/R injury of the heart and kidney. However, effect on hepatic I/R injury has not been determined. In this study, we investigate our hypothesis that AT1 receptor antagonist, CV-11974, attenuates hepatic I/R injury.

METHODS

Twelve beagle dogs underwent a 2-hr total hepatic vascular exclusion with veno-venous bypass. CV-11974 was given to animals at a dose of 0.002 mg/ kg/min for 5 min followed by 0.001 mg/kg/min for 25 min via portal vein before ischemia (group II, n=6). Nontreated animals were used as the control (group I, n=6). Animal survival, hemodynamics, hepatic tissue blood flow (HTBF), liver function, platelet count, renin activity, and AngII concentration of hepatic vein, energy metabolism, and histopathology were analyzed.

RESULTS

Two-week survival was 33% in group I, in contrast, 100% in group II. Mean arterial blood pressure during early reperfusion was maintained, and HTBF after reperfusion was significantly higher in group II. Treatment attenuated liver enzyme release and decrease of platelet count, increased renin and AngII, suppressed ATP degradation during ischemia and enhanced ATP resynthesis after reperfusion. Neutrophil infiltration and histopathological damages were lessened in group II.

CONCLUSIONS

Our data demonstrated that the local renin-angiotensin system might play a role in hepatic microcirculation. AT1 receptor blockade with CV-11974 attenuated hepatic microcirculatory disturbance and ameliorated I/R injury.

Superoxide radical scavenging and attenuation of hypoxia-reoxygenation injury by neurotransmitter ferric complexes in isolated rat hepatocytes

Reactive oxygen species have been implicated in the pathogenesis of hypoxia-reoxygenation injury. Previously, we demonstrated that 2:1 catecholic iron complexes were more effective than uncomplexed catechols at (a) scavenging superoxide radicals generated enzymatically, and (b) protecting hepatocytes against hypoxia-reoxygenation injury [25]. Based on these findings, we sought to demonstrate similar effects using catecholamine neurotransmitters. Various catecholamine-iron complexes were shown to be more effective than uncomplexed catecholamines at scavenging superoxide radicals and could be used to protect cells from hypoxia-reoxygenation injury. alpha-Methyl-3, 4-dihydroxyphenylalanine (alpha-methylDOPA) complexed with ferric ion (2:1) showed the greatest superoxide scavenging potency amongst the catecholamine-iron complexes. The uncomplexed catecholamines were much less effective at scavenging superoxide radicals than the iron-catecholamine complexes. Dopamine was the most effective superoxide scavenger among the uncomplexed catecholamines. The superoxide scavenging effectiveness of the latter seemed to correlate with their reduction potentials, but not directly to their pK(a) values. Furthermore, dopamine:iron(III) complex protected isolated hepatocytes against hypoxia-reoxygenation injury at concentrations four-fold lower than that required for protection by dopamine alone.

A novel hydroxyl radical scavenger, nicaraven, protects the liver from warm ischemia and reperfusion injury

BACKGROUND

Reactive oxygen species have been considered to be involved in liver injury at the procurement, preservation, and transplantation from donors without beating hearts. A novel hydroxyl radical scavenger, nicaraven with hydrophilic and lipophilic properties, infiltrates both intracellular and extracellular spaces where it effectively scavenges reactive oxygen species. Protection by nicaraven against ischemia and reperfusion damage of the brain, heart, and kidneys has been shown. The effect of this agent on the liver remains unclear.

METHODS

Two-hour total hepatic vascular exclusion was used. Eighteen beagle dogs were randomly assigned to 2 groups: 12 animals were not treated (group I) and 6 were treated with nicaraven (group II). Nicaraven was administered intravenously (2mg/kg/min) for 60 minutes before ischemia and for 3 hours, starting 30 minutes before reperfusion.

RESULTS

Two-week survival rates were 25% in group I and 100% in group II (P <.01). Nicaraven inhibited lipid peroxidation in the liver, improved hepatic and systemic hemodynamics and energy metabolism, and suppressed liver enzyme release, endothelin-1 elevation in hepatic venous blood, histologic damage, and neutrophil infiltration into the liver.

CONCLUSIONS

Nicaraven exerted hepatic protection against warm ischemia and reperfusion injury. This may indicate nicaraven as a potential candidate to attenuate liver injury from warm ischemia and preservation in transplantation from donors without beating hearts.

Morphologic alteration of hepatocytes and sinusoidal endothelial cells in rat fatty liver during cold preservation and the protective effect of hepatocyte growth factor

BACKGROUND

Fatty liver grafts are considered to be one of the main factors of primary nonfunctioning graft in transplantation. We investigated here, the hepatic damage during cold preservation in a rat fatty liver model by ultrastructural observation, and examined the effect of human recombinant hepatocyte growth factor (hrHGF) on amelioration of the cold-preserved graft condition.

METHODS

Wistar rats were fed a choline-deficient diet (CDD) for 7 days. Livers were stored in cold University of Wisconsin (UW) solution for 0, 4, and 24 hr. We evaluated the ultrastructural alteration of the hepatocytes, sinusoidal architecture, and endothelial cells (SECs) by scanning and transmission electron microscopy. Ex vivo, we measured alanine aminotransferase (ALT) in first effluent as an index of hepatocyte injury and the hyaluronic uptake rate (HUR) as that of SEC damage. We injected hrHGF into rats fed CDD for 7 days through the portal vein and also added it to the UW solution to determine whether or not the agent ameliorated the hepatic damage in cold-preserved fatty livers.

RESULTS

In rats fed CDD for 7 days, the lesion occupied by fat deposits appeared to enlarge with the duration of cold preservation leading to the disarrangement of sinusoidal architecture. Furthermore, sinusoidal endothelial damage, in which gaps, blebs, microvilli, and sinusoid denudation were detected, appeared to be more severe in these livers than in the corresponding control livers. ALT significantly increased in the 4-hr cold-preserved livers of rats fed CDD for 7 days. HUR decreased with 4-hr cold preservation and/or with CDD feeding. Administration of hrHGF prevented the expansion of fatty droplets and reduced SEC injury as detected by morphological observations. Increase of ALT in first effluent was inhibited to about one fourth the level observed in the 4-hr cold-preserved livers of rats fed CDD. Moreover, HUR significantly increased with the pretreatment of hrHGF.

CONCLUSION

The hepatic injury in both hepatocytes and SECs in cold-preserved fatty liver graft developed more rapidly and severely than in the corresponding controls and demonstrated a protective effect of hrHGF.

Entry and integration of transplanted hepatocytes in rat liver plates occur by disruption of hepatic sinusoidal endothelium

To establish the process by which transplanted cells integrate into the liver parenchyma, we used dipeptidyl peptidase IV-deficient F344 rats as hosts. On intrasplenic injection, transplanted hepatocytes immediately entered liver sinusoids, along with attenuation of portal vein radicles on angiography. However, a large fraction of transplanted cells (>70%) was rapidly cleared from portal spaces by phagocyte/macrophage responses. On the other hand, transplanted hepatocytes entering the hepatic sinusoids showed superior survival. These cells translocated from sinusoids into liver plates between 16 and 20 hours after transplantation, during which electron microscopy showed disruption of the sinusoidal endothelium. Interestingly, production of vascular endothelial growth factor was observed in hepatocytes before endothelial disruptions. Portal hypertension and angiographic changes resulting from cell transplantation resolved promptly. Integration of transplanted hepatocytes in the liver parenchyma required cell membrane regenesis, with hybrid gap junctions and bile canaliculi forming over 3 to 7 days after cell transplantation. We propose that strategies to deposit cells into distal hepatic sinusoids, to disrupt sinusoidal endothelium for facilitating cell entry into liver plates, and to accelerate cell integrations into liver parenchyma will advance applications of hepatocyte transplantation.

Xanthine oxidase inhibition attenuates kupffer cell production of neutrophil chemoattractant following ischemia-reperfusion in rat liver

We investigated the effects of the xanthine oxidase inhibitor, BOF-4272, on the production of cytokine-induced neutrophil chemoattractant (CINC) following reperfusion injury in rat liver. Ischemia was induced for 30 minutes by portal vein occlusion. Animals were pretreated with intravenous injection of BOF-4272 (1 mg/kg) or heparin (50 U/kg) 5 minutes before vascular clamp. Both BOF-4272 and heparin limited increases in the chemoattractant compared with nonpretreated rats. Pretreatment with BOF-4272 plus heparin resulted in an additive effect. Most cells immunostained for chemoattractant were macrophages in sinusoids. In vitro chemoattractant production by Kupffer cells isolated from animals pretreated with heparin or BOF-4272 was significantly lower than by Kupffer cells from nonpretreated animals. Expression of transcripts in liver for chemoattractant peaked 3 hours after reperfusion in nonpretreated animals, while pretreatment with heparin or BOF-4272 significantly decreased chemoattractant mRNA levels. In vitro chemoattractant transcription and production could be induced in naive Kupffer cells by hypoxanthine and xanthine oxidase, but BOF-4272 prevented these increases. We conclude that Kupffer cells release chemoattractant in response to oxygen radicals reducible by xanthine oxidase inhibition.

Hypoxia-reoxygenation is as damaging as ischemia-reperfusion in the rat liver

OBJECTIVE

We hypothesized that the extent of injury and release of xanthine oxidase, an oxidant generator, into the circulation would be less in normal-flow hypoxia-reoxygenation than in equal duration no-flow ischemia-reperfusion.

DESIGN

Randomized study.

SETTING

University-based animal research facility.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

The livers were isolated, perfused, and then randomly subjected to 2 hrs of hypoxia (normal flow, low oxygen) or ischemia (no flow, no oxygen), and 2 hrs of reperfusion. Hepatocytes were also isolated, and were subjected to either: a) hypoxia (0, 2, 4, and 6 hrs); or b) hypoxia (2 and 4 hrs) with reoxygenation (2 hrs).

MEASUREMENTS AND MAIN RESULTS

The extent of liver injury (as assessed by release of hepatocellular enzymes) and the release of xanthine oxidase were measured from isolated-perfused rat livers and cultured hepatocytes. The pattern of release of xanthine oxidase in isolated-perfused liver effluent was different in hypoxia-reoxygenation compared with ischemia-reperfusion. During hypoxia, xanthine oxidase gradually increased in the effluent; then, the xanthine oxidase decreased to low concentrations during reoxygenation. After ischemia, there was a sharp spike in xanthine oxidase at 1 min of reperfusion, with a rapid decrease to low concentrations. The total release of xanthine oxidase during hypoxia-reoxygenation was similar to that during ischemia-reperfusion. Lactate dehydrogenase and other markers of liver injury showed a pattern of release that was similar to that of xanthine oxidase, but the total release of markers was not different between the two groups. In hepatocytes, most of the release of enzymes occurred in hypoxia, and the rate of release was not different between hypoxia and hypoxia-reoxygenation.

CONCLUSIONS

Hypoxia-reoxygenation results in as much damage to the liver as ischemia-reperfusion, and results in the release of a similar amount of oxidant-producing xanthine oxidase into the circulation.

Endothelial cells potentiate oxidant-mediated Kupffer cell phagocytic killing

Phagocytosis and killing of circulating organisms by Kupffer cells (KCs) are discrete, important components of host defense. However, the killing mechanism(s) are not fully understood, and the potential role of adjacent nonparenchymal cells such as hepatic endothelial cells has not been defined. Rat KCs -/+ an hepatic endothelial cell enriched cellular fraction (HECEF) were incubated with Candida parapsilosis and assayed for phagocytosis and phagocytic killing by validated fluorochromatic vital staining. The role of reactive oxygen metabolites in KC phagocytic functions was examined by inhibition with superoxide dismutase and/or catalase. Diphenyleneiodonium and allopurinol were used to examine the potential roles of NADPH oxidase and xanthine oxidase, respectively, in generating these toxic oxidants. Coculture with HECEF increased KC phagocytic activity (from 75% to 88%) and candidacidal activity (from 20% to 31%). Superoxide dismutase, catalase, diphenyleneiodonium, or allopurinol caused inhibition of candidacidal activity, but did not affect phagocytosis, and did not block the potentiation of phagocytosis or of killing caused by coculture with HECEF. Reactive oxygen intermediates generated by both NADPH oxidase and xanthine oxidase-dependent pathways are important in KC killing of Candida parapsilosis. In vitro, KC phagocytosis and killing are potentiated (via a non-oxidant-mediated mechanism) by coculture with a preparation of hepatic non-parenchymal cells composed primarily of endothelial cells.

Hydrogen peroxide derived from hepatocytes induces sinusoidal endothelial cell apoptosis in perfused hypoxic rat liver

BACKGROUND & AIMS

Evidence is accumulating that hypoxic liver injury involves not only necrosis but also apoptosis. Reactive oxygen species can cause apoptosis. This study examined the hypothesis that H2O2 induces apoptosis in hypoxic rat liver.

METHODS

Blood-perfused rat livers were made hypoxic by reducing the perfusion flow. H2O2 was detected by both 2',7'-dichlorofluorescein fluoroimaging and cerium electron-microscopic methods. To evaluate the apoptosis, the liver was stained with the terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end-labeling (TUNEL) method. To further investigate the involvement of H2O2 in hypoxia-induced liver cell apoptosis, small pieces of liver in the cultured media were exposed to 0.5 mmol/L of reagent H2O2 and stained with the TUNEL method.

RESULTS

In the hypoxic liver, H2O2 was produced predominantly by hepatocytes, and the number of apoptotic nonparenchymal cells was significantly increased, particularly in the midzone. All the apoptotic cells were positively stained with monoclonal antibody against the hepatic sinusoidal endothelial cells (SECs). In incubated liver pieces, reagent H2O2 induced apoptosis selectively in SECs.

CONCLUSIONS

Low-flow hypoxia induces H2O2 production in hepatocytes, and this H2O2 induces apoptosis selectively in SECs in the rat liver.

Decreased first trimester uric acid production in future preeclamptic patients

The relationship between first trimester uric acid production and later development of pregnancy induced hypertensive disorders (PIHD) was investigated. An anti-oxidant role for uric acid has been mentioned. Since uric acid and fibronectin (PF) are both markers of preeclampsia, the relationship between these two substances was also studied. Controls (n = 72) and patients with PIHD (n = 120) were selected. Uric acid was measured in serum and 24-hours urine samples (uric acid excretion) and PF in blood plasma in 270 nulliparous women at 13 +/- 2 weeks of gestation. Uric acid excretion was significantly lower in the first trimester in a group of patients who later develop PIHD as compared to patients who remain normotensive (p < 0.05), especially when corrected for body weight (p < 0.01). Patients with elevated PF levels in the first trimester showed a significantly lower uric acid excretion than patients with normal PF levels (p < 0.05). The data show diminished uric acid production in patients who will likely develop preeclampsia suggesting an impaired anti-oxidant production in the first trimester. This observation fits well with the hypothesis that an imbalance between anti-oxidant and oxidants plays an important role in the pathogenesis of preeclampsia.

Role of free radicals in primary nonfunction of marginal fatty grafts from rats treated acutely with ethanol

Acute treatment with one large dose of ethanol, which mimics binge drinking, causes marginal fatty liver and decreases survival significantly after liver transplantation in rats, yet mechanisms remain unclear. Therefore, we evaluated the possible role of free radicals in primary nonfunction caused by acute ethanol. Female donor rats were administered ethanol (5 g/kg orally) 20 hr before explantation, and grafts were stored in UW cold storage solution for 24-42 hr before implantation. Free radicals were trapped with alpha-(4-pyridyl 1-oxide)-N-tert-butylnitrone after transplantation, and adducts were detected using electron spin resonance spectrometry. Ethanol increased a carbon-centered radical adduct in bile approximately 2-fold and elevated serum lipid hydroperoxides approximately 4-fold. Ethanol also increased transaminase release 3.7-fold and decreased bile production by 55%. Catechin, a free radical scavenger, minimized the increase in free radicals, blunted transaminase release, and elevated bile production significantly, indicating that free radical production plays an important role in ethanol-induced fatty graft injury. GdCl3 (20 mg/kg intravenously), a selective Kupffer cell toxicant, largely blocked the increases in free radical and lipid hydroperoxide production caused by ethanol. In addition, ethanol nearly doubled white blood cell adhesion after transplantation, leading to increased superoxide production in fatty grafts. GdCl3 largely blocked leukocyte adhesion as well as superoxide production. Allopurinol, an inhibitor of xanthine oxidase, also diminished free radical production, blunted transaminase release, and improved bile production in fatty grafts significantly. Taken together, we conclude that free radical formation increases in ethanol-induced fatty grafts due mainly to activation of Kupffer cells and increased adhesion of white blood cells. Antioxidants can effectively block free radical formation and minimize injury to marginal fatty grafts caused by binge drinking.

Reperfusion injury as the mechanism of brain damage after perinatal asphyxia

Upon reperfusion of ischemic tissues, reactive oxygen metabolites are generated and are responsible for much of the organ damage. Experimental studies have revealed two main sources of these metabolites: 1) the oxidation of hypoxanthine to xanthine and on to uric acid by the oxidase form of xanthine oxidoreductase and 2) neutrophils accumulating in ischemic and reperfused tissue. Blocking either source will reduce reperfusion damage in a number of experimental situations. Although xanthine oxidoreductase activity may be unmeasurably low in organs other than liver and intestine, it may be involved in reperfusion injury elsewhere because of its localization in capillary endothelial cells. Time course considerations suggest that substrate accumulation and NADH inhibition of dehydrogenase activity may be more important in the pathogenesis than conversion of xanthine dehydrogenase into the oxidase form. Neutrophil accumulation may be partly due to oxidants in the first place, suggesting a link between the two sources of reactive oxygen metabolites. In the clinical context, many of the sequelae of perinatal asphyxia may be accounted for by reperfusion damage to organs such as brain, kidney, heart, liver, and lungs. During asphyxia, substrates of xanthine oxidase accumulate, upon resuscitation the cosubstrate oxygen is introduced, and evidence for oxidant production and effects has been obtained. In the pathogenesis of brain damage after asphyxia, both microvascular injury and parenchymal cell damage are important. Oxygen metabolites are involved in the former, but in the latter process their role is less clear because ischemia-reperfusion triggers not only oxidant production but many other phenomena, including gene activation, ATP depletion, glutamate accumulation, and increase of intracellular calcium. A severe insult results in cell necrosis, but more moderate asphyxia may cause delayed neuronal death through apoptosis. The time course of the changes in high energy phosphates as well as of selective neuronal death suggest that in the first hours of life there is a "therapeutic window," with future possibilities for prevention of permanent damage.

Attenuation of ischemic liver injury by augmentation of endogenous adenosine

Hepatic grafts from non-heartbeating donors may alleviate the organ shortage, but they inherently suffer from warm ischemia. In the present study, we tested our hypothesis that augmentation of endogenous adenosine by inhibition of nucleoside transport with R75231 attenuates ischemic liver injury. Adult female beagle dogs underwent 2-hr hepatic vascular exclusion with venovenous bypass. R75231 was given to the animals by continuous intravenous infusion for 30 min before ischemia at a dose of 0.1 mg/kg (Group 2, n=6), 0.05 mg/kg (Group 3, n=6), or 0.025 mg/kg (Group 4, n=6). Nontreated animals were used as the control (Group 1, n= 10). Animal survival, hepatic tissue blood flow, liver function, and histopathology were analyzed. Two-week animal survival was 30% in Group 1, 83% in Group 2, 100% in Group 3, and 100% in Group 4. Postreperfusion hepatic tissue blood flow was markedly improved by the treatment. Treatment significantly attenuated liver enzyme release, lipid peroxidation, and changes in adenine nucleotides and purine catabolites. Structural abnormality of the liver after reperfusion was markedly improved by R75231 treatment, showing better architecture and less neutrophil infiltration. Preischemic administration of a nucleoside transport inhibitor ameliorated ischemic liver injury due to the positive effects of augmented endogenous adenosine, and is applicable clinically when the liver is procured from a controlled non-heartbeating donor.

Glycohydrolases as markers of hepatic ischemia-reperfusion injury and recovery

Advances in liver surgery and transplantation have lead to a steady increase in the number of these interventions. Prompt quantitative assessment of hepatic of hepatic function and a patient's subsequent morbidity and mortality following surgery remain difficult despite the currently utilized historic markers of hepatic parenchymal injury (e.g., aspartate transaminase [AST], lactate dehydrogenase [LDH] gamma-glutamyl transpeptidase [GGT]). Increases in serum glycohydrolase activities appear to provide sensitive and quantitative markers of hepatic ischemia/reperfusion injury. In 10 male swine (25 to 35 kg body weight) following 30, 45, and 90 minutes of acute hepatic ischemia, the systemic release of eight different glycohydrolases and lipid peroxides into serum were determined and compared with pre- and postischemic serum levels of LDH, GGT, and AST. The rapid release of glycohydrolases into serum was directly proportional to the length of the ischemic period from 30 to 90 minutes; e.g., beta-glucosidase, mean 1.9-fold increase at 30 minutes; 8.3-fold at 45 minutes; and 22.8-fold at 90 minutes; P < .002) and the activities peaked within the first 3 hours postischemia. In constrast, AST, LDH, and GGT were released slowly and peaked 20 to 30 hours after hepatic blood flow was restored. In swine with fatal outcomes (90 minutes of ischemia), all enzyme levels increased continuously during the final hours of life. However, in swine that survived hepatic ischemia/reperfusion injury (45 minutes of ischemia) the glycohydrolases, but not AST, LDH, and GGT, declined after 2 to 3 hours' postischemia and the serum lipid peroxide levels followed the same pattern. Serum beta-galactosidase and beta-glucosidase levels are sensitive markers that rise as quickly as traditional enzyme markers (AST, LDH, GGT) following hepatic ischemic injury; moreover, the glycohydrolases have the added value of serving as predictors of survival.

Cloning and expression in vitro of human xanthine dehydrogenase/oxidase

To study the expression of human xanthine dehydrogenase/oxidase (hXDH/XO), we cloned the cDNA covering its complete coding sequence and characterized it by translation in vitro in rabbit reticulocyte lysates and by transient expression in COS-1 cells. Two specific protein products with approximate molecular masses of 150 and 130 kDa were detected in both expression systems. These products are compatible with the molecular sizes of XDH/XO, and these peptides also showed immunoreactivity with polyclonal anti-hXDH antibodies. Significant XDH/XO enzyme activity (277 +/- 54 pmol/min per mg of protein) was measured in lysates of transfected COS cells, whereas in control transfections the activities were below the detection limit of our assay (0.2 pmol/min per mg of protein). The COS cells expressed the enzyme predominantly (89.8 +/- 0.3%) in the dehydrogenase form.

Xanthine oxidase and superoxide radicals in portal triad crossclamping-induced microvascular reperfusion injury of the liver

Although reactive oxygen metabolites may play a pivotal role in mediating microvascular reperfusion injury, the source of these radicals is still a matter of controversy. With the use of spectrophotometry and intravital microscopy we studied the role of xanthine oxidase and superoxide radicals in portal triad crossclamping-induced microvascular injury in rats. After 20 min of global hepatic ischemia and splanchnic vascular congestion, followed by 40 min of reperfusion (n = 8), xanthine oxidase activities in hepatic venous (26.9 +/- 4.7 nmol/ml x min) and systemic arterial blood (16.3 +/- 2.5 nmol/ml x min) were found significantly (p < .01) increased when compared with sham-operated controls (6.8 +/- 0.9 and 6.0 +/- 0.8 nmol/ml x min, n = 8). The increase of xanthine oxidase activity was accompanied by oxygen radical-mediated intravascular hemolysis. Intravital microscopy (n = 6) revealed accumulation of leukocytes within the postischemic hepatic microvasculature with stasis in sinusoids (75.9 +/- 8.9 per liver lobule) and adherence to the endothelial lining of postsinusoidal venules (534.7 +/- 125.3 per mm2 endothelial surface). Concomitantly, compromised microvascular reperfusion was characterized by perfusion deficits of individual sinusoids (25.6 +/- 4.0% nonperfused sinusoids). The xanthine oxidase inhibitor allopurinol (50 mg/kg b.wt., orally, n = 6) and the radical scavenger superoxide dismutase (60000 IU/kg b.wt., IV, n = 6) effectively (p < .01) inhibited both sinusoidal leukostasis (16.1 +/- 2.6 and 32.1 +/- 3.1 cells/lobule) and venular leukocyte adherence (247.6 +/- 7.9 and 205.0 +/- 38.0 cells/mm2), and, hence, reduced microcirculatory deteriorations, indicated by the attenuation of sinusoidal perfusion failure (2.8 +/- 0.8 and 9.0 +/- 3.1%). Our results support the hypothesis that portal triad crossclamping-induced microvascular reperfusion injury is triggered by superoxide radicals derived from the xanthine oxidase system.

Chemiluminescent measurement of increased free radical formation after ischemia/reperfusion. Mechanisms of free radical formation in the liver

It has been proposed that xanthine oxidase-derived superoxide mediates reperfusion injury in the liver; however, there is a little direct evidence to support this hypothesis. In this paper we describe a model system to directly and noninvasively measure oxyradical formation and hepatic injury in isolated perfused rat liver. Using this sensitive chemiluminescent technique, we clearly demonstrate the theorized burst in oxygen radical production upon reperfusion of previously ischemic liver, without perturbing the system with chemical luminescence enhancers. This increase in chemiluminescence (CL) upon reperfusion was diminished by the free radical scavengers trolox and ascorbate, as well as N-2-mercaptoproprionyl-glycine (MPG), thereby confirming the oxyradical nature of this signal. Additionally, superoxide dismutase and the xanthine oxidase inhibitor allopurinol, but not catalase, attenuated the reperfusion effect, providing the most direct evidence so far that XOD derived superoxide anion is formed during liver reperfusion. Hepatic injury (AST release) did not appear to relate to increased CL, supporting the notion that the oxyradical flux may serve as a signal for other events leading to tissue injury. Further studies using this sensitive chemiluminescent technique should aid in delineating the detailed mechanism(s) of reperfusion injury.

Hepatic free radical production after cold storage: Kupffer cell-dependent and -independent mechanisms in rats

BACKGROUND/AIMS

Free radicals are important mediators of reperfusion injury; however, the mechanism(s) of oxyradical production after liver reimplantation are not well understood. A model of cold storage and reperfusion using low-level chemiluminescence to directly measure oxyradical production during reperfusion was developed.

METHODS

Rat livers were harvested and stored at 4 degrees C in University of Wisconsin cold-storage solution or Euro-Collins solution for 0-48 hours and then flushed and reperfused with warm oxygenated (37 degrees C) Krebs-Henseleit buffer. Liver chemiluminescence was measured using a sensitive photomultiplier tube, and hepatocellular injury was assessed by measuring aspartate aminotransferase release into the perfusate.

RESULTS

Chemiluminescence reached a maximum within 5 minutes of reperfusion and then decreased to a baseline within 30 minutes. There was a marked increase in chemiluminescence after only a short period of storage in University of Wisconsin cold-storage solution. Chemiluminescence decreased with longer periods of storage but steadily increased again after 16 hours of storage. Chemiluminescence after 22 hours of storage, but not after 3 hours of storage, was decreased by pretreatment with the Kupffer cell inactivator gadolinium chloride.

CONCLUSIONS

The data suggest two mechanisms of oxyradical production during cold storage and reperfusion of the rat liver. The later phase seems to be Kupffer cell dependent.