The role of Kupffer cell oxidant production in early ethanol-induced liver disease

Considerable evidence for a role of Kupffer cells in alcoholic liver disease has accumulated and they have recently been shown to be a predominant source of free radicals. Several approaches including pharmacological agents, knockout mice, and viral gene transfer have been used to fill critical gaps in understanding key mechanisms by which Kupffer cell activation, oxidant formation, and cytokine production lead to liver damage and subsequent pathogenesis. This review highlights new data in support of the hypothesis that Kupffer cells play a pivotal role in hepatotoxicity due to ethanol by producing oxidants via NADPH oxidase.

Overexpression of manganese superoxide dismutase prevents alcohol-induced liver injury in the rat

Mitochondria are thought to play a major role in hepatic oxidative stress associated with alcohol-induced liver injury. Thus, the hypothesis that delivery of the mitochondrial isoform of superoxide dismutase (Mn-SOD) via recombinant adenovirus would reduce alcohol-induced liver injury was tested. Rats were given recombinant adenovirus containing Mn-SOD (Ad.SOD2) or beta-galactosidase (Ad.lacZ) and then fed alcohol enterally for 4 weeks. Mn-SOD expression and activity of Ad.SOD2 in liver mitochondria of infected animals was increased nearly 3-fold compared with Ad.lacZ-infected controls. Mitochondrial glutathione levels in Ad.lacZ-infected animals were decreased after 4 weeks of chronic ethanol, as expected, but were unchanged in Ad.SOD2-infected animals. Alanine aminotransferase was elevated significantly by ethanol, an effect that was prevented by Ad.SOD2. Moreover, pathology (e.g. the sum of steatosis, inflammation, and necrosis) was elevated dramatically by ethanol in Ad.lacZ-treated rats. This effect was also blunted in animals infected with Ad.SOD2. Neutrophil infiltration was increased about 3-fold in livers from both Ad.lacZ- and Ad.SOD2-infected rats by ethanol treatment. Moreover, ESR-detectable free radical adducts in bile were increased about 8-fold by ethanol. Using (13)C-labeled ethanol, it was determined that nearly 60% of total adducts were due to the alpha-hydroxyethyl radical adduct. This increase in radical formation was blocked completely by Ad.SOD2 infection. Furthermore, apoptosis of hepatocytes was increased about 5-fold by ethanol, an effect also blocked by Ad.SOD2. Interestingly, tumor necrosis factor-alpha mRNA was elevated to the same extent in both Ad.lacZ- and Ad.SOD2-infected animals follows ethanol exposure. These data suggest that hepatocyte mitochondrial oxidative stress is involved in alcohol-induced liver damage and likely follows Kupffer cell activation, cytokine production, and neutrophil infiltration. These results also support the hypothesis that mitochondrial oxidant production is a critical factor in parenchymal cell death caused by alcohol.

Development of an animal model of chronic alcohol-induced pancreatitis in the rat

This study was designed to develop an animal model of alcoholic pancreatitis and to test the hypothesis that the dose of ethanol and the type of dietary fat affect free radical formation and pancreatic pathology. Female Wistar rats were fed liquid diets rich in corn oil (unsaturated fat), with or without a standard or high dose of ethanol, and medium-chain triglycerides (saturated fat) with a high dose of ethanol for 8 wk enterally. The dose of ethanol was increased as tolerance developed, which allowed approximately twice as much alcohol to be delivered in the high-dose group. Serum pancreatic enzymes and histology were normal after 4 wk of diets rich in unsaturated fat, with or without the standard dose of ethanol. In contrast, enzyme levels were elevated significantly by the high ethanol dose. Increases were blunted significantly by dietary saturated fat. Fibrosis and collagen alpha1(I) expression in the pancreas were not detectable after 4 wk of enteral ethanol feeding; however, they were enhanced significantly by the high dose after 8 wk. Furthermore, radical adducts detected by electron spin resonance were minimal with the standard dose; however, the high dose increased carbon-centered radical adducts as well as 4-hydroxynonenal, an index of lipid peroxidation, significantly. Radical adducts were also blunted by approximately 70% by dietary saturated fat. The animal model presented here is the first to demonstrate chronic alcohol-induced pancreatitis in a reproducible manner. The key factors responsible for pathology are the amount of ethanol administered and the type of dietary fat.

Diphenyleneiodonium sulfate, an NADPH oxidase inhibitor, prevents early alcohol-induced liver injury in the rat

The oxidant source in alcohol-induced liver disease remains unclear. NADPH oxidase (mainly in liver Kupffer cells and infiltrating neutrophils) could be a potential free radical source. We aimed to determine if NADPH oxidase inhibitor diphenyleneiodonium sulfate (DPI) affects nuclear factor-kappaB (NF-kappaB) activation, liver tumor necrosis factor-alpha (TNF-alpha) mRNA expression, and early alcohol-induced liver injury in rats. Male Wistar rats were fed high-fat liquid diets with or without ethanol (10-16 g. kg(-1). day(-1)) continuously for up to 4 wk, using the Tsukamoto-French intragastric enteral feeding protocol. DPI or saline vehicle was administered by subcutaneous injection for 4 wk. Mean urine ethanol concentrations were similar between the ethanol- and ethanol plus DPI-treated groups. Enteral ethanol feeding caused severe fat accumulation, mild inflammation, and necrosis in the liver (pathology score, 4.3 +/- 0.3). In contrast, DPI significantly blunted these changes (pathology score, 0.8 +/- 0.4). Enteral ethanol administration for 4 wk also significantly increased free radical adduct formation, NF-kappaB activity, and TNF-alpha expression in the liver. DPI almost completely blunted these parameters. These results indicate that DPI prevents early alcohol-induced liver injury, most likely by inhibiting free radical formation via NADPH oxidase, thereby preventing NF-kappaB activation and TNF-alpha mRNA expression in the liver.

SPC-100270, a protein kinase C inhibitor, reduced hypoxic injury due to reperfusion following orthotopic liver transplantation in the rat

Recently, we reported that SPC-100270, a sphingosine derivative and inhibitor of protein kinase C (50-90 microM) in mixed micelle assays, reduced reperfusion injury resulting from hypoxia in a low-flow, reflow model of liver perfusion. Here we report that SPC-100270 has similar beneficial effects following liver transplantation in vivo. Rat liver transplantation was performed using nonarterial and rearterial techniques. Livers from syngenic rats were harvested surgically, prepared with vascular cuffs and a splint, and stored for 24 or 48 h in University of Wisconsin (UW) cold storage solution. Just prior to completion of vascular reconstruction, the organ was rinsed with 3 or 10 ml of Ringer's solution, vehicle, or a solution containing SPC-100270 (up to 500 microM). Following implantation surgery, low doses of SPC-100270 were ineffective at reducing both parenchymal and nonparenchymal cell death, yet significant (P < 0.05) reductions were observed with 500 microM. Further, nonparechnymal cell viability was improved nearly four fold by the drug. SPC-100270 (500 microM) tended to increase survival following 48 h cold storage in UW solution, but the improvement was not statistically significant. SPC-100270 also did not diminish carbon-centered free radical formation in transplanted livers from alcohol-treated rats. Collectively, these data support the hypothesis that pretreatment of donor livers with an inhibitor of protein kinase C is effective in vivo at reducing reperfusion injury, particularly to nonparenchymal cells, following orthotopic liver transplantation in the rat.

Delivery of the Cu/Zn-superoxide dismutase gene with adenovirus reduces early alcohol-induced liver injury in rats

BACKGROUND AND AIMS

Alcohol-induced liver injury is associated with an increase in oxidants from a variety of possible sources. Therefore, it was hypothesized that increased and stable expression of the antioxidant enzyme Cu/Zn-superoxide dismutase (SOD1) would diminish oxygen free radicals and reduce alcohol-induced liver injury.

METHODS

To test this hypothesis, rats were given recombinant adenovirus containing Cu/Zn-superoxide dismutase (Ad.SOD1) or beta-galactosidase (Ad.lacZ) and fed ethanol enterally for 3 weeks.

RESULTS

SOD was increased significantly 3-5-fold over endogenous levels in both hepatocytes as well as Kupffer cells 3 weeks after infection. Serum transaminase levels and pathology were elevated significantly in Ad.lacZ-treated animals by using an intragastric feeding model. This effect was blunted significantly in Ad.SOD1-infected animals. Importantly, electron spin resonance-detectable free-radical adducts caused by ethanol were also decreased by SOD1 overexpression. Moreover, the increase in nuclear factor kappaB (NFkappaB), tumor necrosis factor alpha (TNF-alpha), and interleukin 1 messenger RNA (mRNA) caused by ethanol was blunted in animals treated with Ad.SOD1.

CONCLUSIONS

These data support the hypothesis that oxidant production is critical in early alcohol-induced liver injury and that gene delivery of antioxidant enzymes may be useful in prevention and treatment.

Viral delivery of superoxide dismutase gene reduces cyclosporine A-induced nephrotoxicity

BACKGROUND

Cyclosporine A (CsA) increases free radical formation in the kidney. Accordingly, this study investigated whether gene delivery of superoxide dismutase (SOD) reduced radical production and nephrotoxicity caused by CsA.

METHODS

Rats were given adenovirus (Ad) carrying lacZ or Cu/Zn-SOD genes three days prior to CsA treatment. Histology, glomerular filtration rates (GFRs) and free radical adducts in urine were assessed.

RESULTS

SOD activity was increased 2.5-fold three days after viral infection and remained at 2- and 1.6-fold higher 10 and 17 days later. Treatment with CsA for seven days decreased GFR by 70% in rats infected with Ad-lacZ as expected; however, the decrease was diminished significantly in rats receiving Ad-SOD. CsA treatment for two weeks caused a loss of brush border and dilation of proximal tubules, necrosis, and increased leukocyte infiltration into the kidney; these effects were minimized by SOD. Dimethyl sulfoxide (DMSO) was attacked by the hydroxyl radical to produce a methyl radical. Indeed, administration of CsA with 12C-DMSO in rats infected with Ad-lacZ produced a radical adduct with hyperfine coupling constants similar to 4-POBN/methyl radical adduct and another unknown radical adduct. CsA given with 13C-DMSO produced a 12-line spectrum, confirming the involvement of hydroxyl radicals. Free radical adducts detected in urine were increased approximately fivefold by CsA, an effect blocked completely by SOD.

CONCLUSIONS

CsA increases free radical formation. Gene delivery of SOD blocks formation of free radicals, thereby minimizing nephrotoxicity caused by CsA.

Gene delivery of Cu/Zn-superoxide dismutase improves graft function after transplantation of fatty livers in the rat

Oxygen-derived free radicals play a central role in reperfusion injury after organ transplantation, and fatty livers are particularly susceptible. Endogenous radical scavengers such as superoxide dismutase (SOD) degrade these radicals; however, SOD is destroyed rapidly when given exogenously. Therefore, an adenoviral vector encoding the Cu/Zn-SOD gene (Ad.SOD1) was used here to test the hypothesis that organ injury would be reduced and survival increased in a rat model of transplantation of fatty livers. Donors received chow diet (untreated), high-fat diet, or ethanol-containing high-fat diet. Some of the ethanol-fed donors were infected either with the gene lacZ encoding bacterial beta-galactosidase (Ad.lacZ), or Ad.SOD1. After liver transplantation, SOD activity and protein expression in liver, survival, histopathology, release of transaminases, free radical adducts in bile, and activation of NF-kappaB, IkappaB kinase (IKK), Jun-N-terminal kinase (JNK), and TNFalpha were evaluated. Ad.SOD1 treatment increased survival dramatically, blunted transaminase release, and reduced necrosis and apoptosis significantly. Free radical adducts were increased two-fold in the ethanol group compared with untreated controls. Ad. SOD1 blunted this increase and reduced the activation of NF-kappaB. However, release of TNFalpha was not affected. Ad.SOD1 also blunted JNK activity after transplantation. This study shows that gene therapy with Ad.SOD1 protects marginal livers from failure after transplantation because of decreased oxygen radical production. Genetic modification of fatty livers using viral vectors represents a new approach to protect marginal grafts against primary nonfunction.

NADPH oxidase-derived free radicals are key oxidants in alcohol-induced liver disease

In North America, liver disease due to alcohol consumption is an important cause of death in adults, although its pathogenesis remains obscure. Despite the fact that resident hepatic macrophages are known to contribute to early alcohol-induced liver injury via oxidative stress, the exact source of free radicals has remained a mystery. To test the hypothesis that NADPH oxidase is the major source of oxidants due to ethanol, we used p47(phox) knockout mice, which lack a critical subunit of this major source of reactive oxygen species in activated phagocytes. Mice were treated with ethanol chronically, using a Tsukamoto-French protocol, for 4 weeks. In wild-type mice, ethanol caused severe liver injury via a mechanism involving gut-derived endotoxin, CD14 receptor, production of electron spin resonance-detectable free radicals, activation of the transcription factor NF-kappaB, and release of cytotoxic TNF-alpha from activated Kupffer cells. In NADPH oxidase-deficient mice, neither an increase in free radical production, activation of NF-kappaB, an increase in TNF-alpha mRNA, nor liver pathology was observed. These data strongly support the hypothesis that free radicals from NADPH oxidase in hepatic Kupffer cells play a predominant role in the pathogenesis of early alcohol-induced hepatitis by activating NF-kappaB, which activates production of cytotoxic TNF-alpha.

Allopurinol prevents early alcohol-induced liver injury in rats

Free radical formation caused by chronic ethanol administration could activate transcription factors such as nuclear factor-kappaB (NF-kappaB), which regulates production of inflammatory cytokines. Xanthine oxidase is one potential source of reactive oxygen species. Therefore, the purpose of this study is to determine whether allopurinol, a xanthine oxidase inhibitor and scavenger of free radicals, would affect free radical formation, NF-kappaB activation, and early alcohol-induced liver injury in rats. Male Wistar rats were fed a high-fat diet with or without ethanol (10-16 g/kg/day) continuously for up to 4 weeks with the Tsukamoto-French enteral protocol. Either allopurinol or saline vehicle was administered daily. Allopurinol had no effect on body weight or the cyclic pattern of ethanol in urine. Mean urine ethanol concentrations were 271 +/- 38 and 252 +/- 33 mg/dl in ethanol- and ethanol + allopurinol-treated rats, respectively. In the control group, serum aspartate aminotransferase and alanine aminotransferase levels were approximately 40 I.U./l and 25 U/l, respectively. Administration of enteral ethanol for 4 weeks increased serum transaminases approximately 5-fold. Allopurinol blunted these increases significantly by approximately 50%. Ethanol treatment also caused severe fatty infiltration, mild inflammation, and necrosis. These pathological changes also were blunted significantly by allopurinol. Furthermore, enteral ethanol caused free radical adduct formation, values that were reduced by approximately 40% by allopurinol. NF-kappaB binding was minimal in the control group but was increased significantly nearly 2.5-fold by ethanol. This increase was blunted to similar values as control by allopurinol. These results indicate that allopurinol prevents early alcohol-induced liver injury, most likely by preventing oxidant-dependent activation of NF-kappaB.

Medium-chain triglycerides inhibit free radical formation and TNF-alpha production in rats given enteral ethanol

This study determined whether free radical formation by the liver, tumor necrosis factor (TNF)-alpha production by isolated Kupffer cells, and plasma endotoxin are affected by dietary saturated fat. Rats were fed enteral ethanol and corn oil (E-CO) or medium-chain triglycerides (E-MCT) and control rats received corn oil (C-CO) or medium-chain triglycerides (C-MCT) for 2 wk. E-CO rats developed moderate fatty infiltration and slight inflammation; however, E-MCT prevented liver injury. Serum aspartate aminotransferase levels, gut permeability, and plasma endotoxin doubled with E-CO but were blunted approximately 50% with E-MCT. In Kupffer cells from E-CO rats, intracellular calcium was elevated by lipopolysaccharide (LPS) in a dose-dependent manner. In cells from E-MCT rats, increases were blunted by approximately 40-50% at all concentrations of LPS. The LPS-induced increase in TNF-alpha production by Kupffer cells was dose dependent and was blunted by 40% by MCT. E-CO increased radical adducts and was reduced approximately 50% by MCT. MCT prevent early alcohol-induced liver injury, in part, by inhibition of free radical formation and TNF-alpha production by inhibition of endotoxin-mediated activation of Kupffer cells.

Dietary glycine and renal denervation prevents cyclosporin A-induced hydroxyl radical production in rat kidney

Cyclosporin A (CsA) nephrotoxicity is associated with renal hypoxia and increases in free radicals in the urine. This study was designed to elucidate the mechanism of radical production caused by CsA. Pretreatment of rats with CsA (25 mg/kg, i.g.) for 5 days decreased glomerular filtration rates by 65%, an effect largely prevented by both dietary glycine (5%) or renal denervation. CsA dissolved in olive oil produced a 6-line alpha-(4-pyridyl 1-oxide)-N-tert-butylnitrone (4-POBN)/free radical signal in the urine, which partitioned predominantly into the aqueous phase after chloroform extraction (i.e., it is water soluble). Dimethyl sulfoxide (DMSO) is attacked by the hydroxyl radical to produce a methyl radical; administration of CsA with [(12)C]DMSO produced two radical species in urine, one with hyperfine coupling constants similar to the 4-POBN/methyl radical adduct found in aqueous solution. CsA given with [(13)C]DMSO produced a 12-line spectrum, confirming the formation of hydroxyl radicals. The methyl radical produced by the hydroxyl radical represented 62% of radicals detected in urine but only 15% in bile. Therefore, hydroxyl radicals are produced largely in the kidney. Free radicals in urine were increased about 5-fold by CsA, an effect completely blocked by the inhibitory neurotransmitter, glycine, or by renal denervation. CsA infusion for 30 min increased efferent renal nerve activity 2-fold, and dietary glycine (5%) totally blocked this phenomenon. Taken together, these data are consistent with the hypothesis that CsA increases hydroxyl radical formation by increasing renal nerve activity resulting in vasoconstriction and hypoxia-reoxygenation. Glycine blunts the effect of CsA on the renal nerve, which explains, in part, prevention of nephrotoxicity.

Binge drinking disturbs hepatic microcirculation after transplantation: prevention with free radical scavengers

Disturbances in hepatic microcirculation increase graft injury and failure; therefore, this study evaluates the effects of ethanol on microcirculation after liver transplantation. Donor rats were given one dose of ethanol (5 g/kg) by gavage 20 h before explantation, and grafts were stored in University of Wisconsin solution for 24 h before implantation. Acute ethanol treatment decreased 7-day survival of grafts from about 90 to 30%, increased transaminase release nearly 4-fold, and decreased bile production by 60%. Moreover, portal pressure increased significantly and liver surface oxygen tension decreased about 50%, indicating that ethanol disturbs hepatic microcirculation. Pimonidazole, a 2-nitroimidazole hypoxia marker, was given i.v. to recipients 30 min after implantation, and grafts were harvested 1 h later. Ethanol increased hepatic pimonidazole binding about 3-fold, indicating that ethanol led to hypoxia in fatty grafts. Ethanol also significantly increased free radicals in bile. Catechin (30 mg/kg i.v. upon reperfusion), a free radical scavenger, and Carolina Rinse solution, which contains several agents that inhibit free radical formation, minimized disturbances in microcirculation and prevented pimonidazole adduct formation significantly. These treatments also blunted increases in transaminase release and improved survival of fatty grafts. Destruction of Kupffer cells with GdCl(3) (20 mg/kg i.v. 24 h before explantation) or inhibition of formation of leukotrienes with MK-886 (50 microM in University of Wisconsin or rinse solution) also minimized hypoxia and improved survival after transplantation. Taken together, these results demonstrate that ethanol disturbs hepatic microcirculation, leading to graft hypoxia after transplantation, most likely by activating Kupffer cells and increasing free radical production.

Mechanisms of alcohol-induced hepatotoxicity: studies in rats

Alcohol treatment results in increases in the release of endotoxin from gut bacteria and membrane permeability of the gut to endotoxin, or both. Females are more sensitive to these changes. Elevated levels of endotoxin activate Kupffer cells to release substances such as eicosanoids, TNF-alpha and free radicals. Prostaglandins increase oxygen uptake and most likely are responsible for the hypermetabolic state in the liver. The increase in oxygen demand leads to hypoxia in the liver, and on reperfusion, alpha-hydroxyethyl free radicals are formed which lead to tissue damage in oxygen-poor pericentral regions of the liver lobule.

Reperfusion injury in livers due to gentle in situ organ manipulation during harvest involves hypoxia and free radicals

Kupffer cell-dependent injury in livers gently manipulated during harvest develops upon transplantation; however, underlying mechanisms remain unknown. Thus, the purpose of this study was to identify factors involved in mechanisms of injury. Livers from female Sprague-Dawley rats (200-230 g) were cold stored for 24 h in University of Wisconsin solution. Subsequently, livers were perfused at 37 degrees C with oxygen-saturated Krebs-Henseleit buffer containing fluorescein-dextran to assess microcirculation. Cell death was assessed by uptake of trypan blue, a vital dye. Minimal dissection during harvest had no effects on sinusoidal lining cells; however, gentle organ manipulation dramatically increased trypan blue uptake about 5-fold (p <.05). In contrast, perfusion with N2-saturated buffer after cold storage totally prevented cell death due to manipulation. At harvest, portal venous pressure was increased significantly by 70% due to manipulation. Furthermore, vascular space and microcirculation were decreased by more than 50% (p <.05), reflecting the rate of entry and exit of fluorescein-dextran. Pimonidazole, a 2-nitroimidazole marker, was given to rats before harvest to detect hypoxia in liver. Pimonidazole adduct binding was increased significantly about 2-fold by manipulation. To detect free radical adducts by electron spin resonance (ESR) spectroscopy in bile, C-phenyl-N-tert-butylnitrone was given as spin trapping reagent to the donor before operation. Free radical formation was increased about 3-fold by organ manipulation (p <.05). Donors given gadolinium chloride, a selective Kupffer cell toxicant, or dietary glycine, which prevents activation of Kupffer cells, significantly blunted microcirculatory disturbances, hypoxia, and death of endothelial lining cells. These data indicate for the first time that gentle organ manipulation during harvest causes oxygen-dependent reperfusion injury to endothelial lining cells via mechanisms involving hepatic microcirculation, hypoxia, and Kupffer cells.

Glycine improves survival after hemorrhagic shock in the rat

This study investigated the effect of glycine on hemorrhagic shock in the rat. Rats were bled to maintain mean arterial pressure at 30-35 mm Hg for 1 h and subsequently resuscitated with 60% shed blood and lactated Ringer's solution. Only 20% of rats receiving saline just prior to resuscitation survived 72 h after shock. Survival was increased by glycine (11.2-90.0 mg/kg, i.v.) in a dose-dependent manner (half-maximal effect = 25 mg/kg) and reached maximal values of 78% at 45 mg/kg. Eighteen hours after resuscitation, creatinine phosphokinase increased 23-fold, transaminases increased 33-fold, and creatinine was elevated 2.4-fold, indicating injury to the heart, liver, and kidney, respectively. Pulmonary edema, leukocyte infiltration, and hemorrhage were also observed. In the kidney, proximal tubular necrosis, leukocyte infiltration, and severe hemorrhage in the outer medullary area occurred in rats receiving saline. Glycine reduced these pathological alterations significantly. It has been reported that oxidative stress and tumor necrosis factor(TNF)-alpha-production are involved in the pathophysiology of multiple-organ injury after shock. In this study, free radical production was increased 4-fold during shock, an effect blocked largely by glycine. Increases in intracellular calcium and production of TNF-alpha by isolated Kupffer cells stimulated by endotoxin were elevated significantly by hemorrhagic shock, alterations which were totally prevented by glycine. Taken together, it is concluded that glycine reduces organ injury and mortality caused by hemorrhagic shock by preventing free radical production and TNF-alpha formation.

Ethanol, not fat accumulation per se, increases free radical production in a low-flow, reflow liver perfusion model

BACKGROUND

Ethanol increases primary graft failure after liver transplantation, yet whether it acts via mechanisms involving fat accumulation remains unclear.

METHODS

Rats were pair-fed a modified Lieber-DeCarli liquid diet containing 35% (high-fat) or 12% (low-fat) of calories as fat combined with 36% of calories as ethanol or isocaloric maltose-dextrin for 4-5 weeks. Reperfusion injury to the liver was studied using a low-flow, reflow perfusion model and a liver transplantation model, and free radicals were detected using electron spin resonance and the spin trapping technique.

RESULTS

As expected, basal hepatic triglycerides were similar in livers from rats fed low- and high-fat control diets. Ethanol did not alter triglyceride levels significantly in rats fed a low-fat diet, but increased values about 2.4-fold in rats fed a high-fat diet. Ethanol increased lactate dehydrogenase release during reperfusion from 10 to 26 IU/g/h in rats fed a low-fat diet and from 17 to 34 IU/g/h in rats fed a high-fat diet, respectively. Portal pressure increased from about 3 to 10.5 cm H2O upon reperfusion in livers from high-fat, ethanol-fed rats, but only reached values of 9.1 in the low-fat, ethanol-fed group. A free radical adduct signal was detected in the bile of livers from ethanol-treated rats, and the magnitude of this signal was similar in livers of ethanol-treated rats fed high- or low-fat diets. However, radical adducts could not be detected in either group in the absence of dietary ethanol. Moreover, 67-77% rats given low-fat or high-fat control diets survived after liver transplantation, but only 11% survived if treated with ethanol.

CONCLUSIONS

It is concluded that ethanol plays a major role in hepatic reperfusion injury, most likely via mechanisms involving free radicals. Increased hepatic fat content alone plays only a minor role, probably by causing slight disturbances in the hepatic microcirculation.

Generation of lipid free radicals by adherent leukocytes from transplanted rat liver

The production of free radicals in blood correlates with primary nonfunction of transplanted livers, but the source of the free radicals is unknown. The purpose of this study was to determine if adherent leukocytes in the transplanted liver are responsible for the radicals detected in blood. First, a new method to harvest adherent leukocytes from the liver without enzymatic digestion was developed and characterized by transplanting livers from ethanol-treated rats, which increases primary nonfunction, and from saline-treated controls. Free radicals were then detected in isolated leukocytes using the spin-trapping technique and electron spin resonance (ESR) spin spectroscopy. Livers were perfused with a balanced salt solution (200 ml), followed by a Ca(2+)-free solution containing EGTA and heparin (400 ml). Perfusion with Ca(2+)-free buffer removed greater than 90% of all adherent leukocytes from saline-treated livers and nearly 80% of all leukocytes from fatty livers without removing Kupffer cells. Transplanted fatty livers from rats given ethanol contained significantly more adherent leukocytes (5.0 x 10(7) cells/liver) than grafts from control donors (3.2 x 10(7) cells/liver) and almost double the number of adherent neutrophils and monocytes. Moreover, adherent white blood cells from transplanted livers produced the same three free radical species that have been detected previously in blood; however, cells from ethanol-treated livers produced about five times more radical adducts. These data show that adherent white blood cells produce free radicals that are important in the mechanism of primary graft nonfunction.

Cyclosporin A increases hypoxia and free radical production in rat kidneys: prevention by dietary glycine

The major side effect of cyclosporin A is severe nephrotoxicity. It is likely that cyclosporin A causes vasoconstriction leading to hypoxia-reperfusion injury; therefore, these experiments were designed to attempt to obtain physical evidence for hypoxia and free radical production in kidney following cyclosporin A. Rats were treated daily with cyclosporin A (25 mg/kg ig) for 5 days, and pimonidazole, a hypoxia marker, was injected 2 h after the last dose of cyclosporin A. A dose of alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone (4-POBN) was injected 3 h after cyclosporin A to trap free radicals. Cyclosporin A doubled serum creatinine and decreased glomerular filtration rates by 65% as expected. Pimonidazole adduct binding in the kidney was increased nearly threefold by cyclosporin A, providing physical evidence for tissue hypoxia. Moreover, cyclosporin A increased 4-POBN/radical adducts nearly sixfold in the urine but did not alter levels in the serum. Glycine, which causes vasodilatation and prevents cyclosporin A toxicity, minimized hypoxia and blocked free radical production; however, it did not alter cyclosporin A blood levels. These results demonstrate for the first time that cyclosporin A causes hypoxia and increases production of a new free radical species exclusively in the kidney. Therefore, it is concluded that cyclosporin A causes renal injury by mechanisms involving hypoxia-reoxygenation, effects which can be prevented effectively by dietary glycine.

The role of gut-derived bacterial toxins and free radicals in alcohol-induced liver injury

Previous research from this laboratory using a continuous enteral ethanol (EtOH) administration model demonstrated that Kupffer cells are pivotal in the development of EtOH-induced liver injury. When Kupffer cells were destroyed using gadolinium chloride (GdCl3) or the gut was sterilized with polymyxin B and neomycin, early inflammation due to EtOH was blocked. Anti-tumour necrosis factor (TNF)-alpha antibody markedly decreased EtOH-induced liver injury and increased TNF-mRNA. These findings led to the hypothesis that EtOH-induced liver injury involves increases in circulating endotoxin leading to activation of Kupffer cells. Pimonidazole, a nitro-imidazole marker, was used to detect hypoxia in downstream pericentral regions of the lobule. Following one large dose of EtOH or chronic enteral EtOH for 1 month, pimonidazole binding was increased significantly in pericentral regions of the liver lobule, which was diminished with GdCl3. Enteral EtOH increased free radical generation detected with electron spin resonance (ESR). These radical species had coupling constants matching alpha-hydroxyethyl radical and were shown conclusively to arise from EtOH based on a doubling of the ESR lines when 13C-EtOH was given. Alpha-hydroxyethyl radical production was also blocked by the destruction of Kupffer cells with GdCl3. It is known that females develop more severe EtOH-induced liver injury more rapidly and with less EtOH than males. Female rats on the enteral protocol exhibited more rapid injury and more widespread fatty changes over a larger portion of the liver lobule than males. Plasma endotoxin, ICAM-1, free radical adducts, infiltrating neutrophils and transcription factor NFkappaB were approximately two-fold greater in livers from females than males after 4 weeks of enteral EtOH treatment. Furthermore, oestrogen treatment increased the sensitivity of Kupffer cells to endotoxin. These data are consistent with the hypothesis that Kupffer cells participate in important gender differences in liver injury caused by ethanol.

Clarification of the relationship between free radical spin trapping and carbon tetrachloride metabolism in microsomal systems

It has been proposed that the C-phenyl-N-tert-butylnitrone/trichloromethyl radical adduct (PBN/.CCl3) is metabolized to either the C-phenyl-N-tert-butylnitrone/carbon dioxide anion radical adduct (PBN/.CO2-) or the glutathione (GSH) and CCl4-dependent PBN radical adduct (PBN/[GSH-.CCl3]). Inclusion of PBN/.CCl3 in microsomal incubations containing GSH, nicotinamide adenine dinucleotide phosphate (NADPH), or GSH plus NADPH produced no electron spin resonance (ESR) spectral data indicative of the formation of either the PBN/[GSH-.CCl3] or PBN/.CO2- radical adducts. Microsomes alone or with GSH had no effect on the PBN/.CCl3 radical adduct. Addition of NADPH to a microsomal system containing PBN/.CCl3 presumably reduced the radical adduct to its ESR-silent hydroxylamine because no ESR signal was observed. The Folch extract of this system produced an ESR spectrum that was a composite of two radicals, one of which had hyperfine coupling constants identical to those of PBN/.CCl3. We conclude that PBN/.CCl3 is not metabolized into either PBN/[GSH-.CCl3] or PBN/.CO2- in microsomal systems.

Development and characterization of a new model of tacrine-induced hepatotoxicity: role of the sympathetic nervous system and hypoxia-reoxygenation

Tacrine is an acetylcholinesterase inhibitor approved for the treatment of Alzheimer's disease. Unfortunately, reversible hepatotoxicity in about 30% of patients at therapeutic doses limits clinical use. The purpose of this study was to develop and characterize a model of tacrine hepatotoxicity to begin to understand the mechanisms of injury. Rats were given tacrine (10-50 mg/kg, intragatrically) and killed 24 hr later. An increase in serum aspartate aminotransferase was observed up to 35 mg/kg and histology revealed pericentral necrosis and fatty changes. Aspartate aminotransferase was increased from 12 to 24 hr and returned to control values by 32 hr. Livers were perfused in a nonrecirculating system to measure oxygen uptake and trypan blue was infused at the end of each experiment to evaluate tissue perfusion. Time for trypan blue to distribute evenly throughout the liver 3 hr after tacrine treatment was significantly increased (6.9 +/- 1.3 min) compared to controls (1.0 +/- 0.3 min) reflecting decreased tissue perfusion. Tacrine also significantly increased the binding of a hypoxia marker, pimonidazole, in pericentral regions almost 3-fold, and increased portal pressure in vivo significantly. It is hypothesized that tacrine, by inhibiting acetylcholine breakdown in the celiac ganglion, increases sympathetic activity in the liver leading to vascular constriction, hypoxia and liver injury. To test this hypothesis, the hepatic nerve was severed and animals were allowed to recover before tacrine treatment. This procedure significantly reduced serum aspartate aminotransferase, time of dye distribution, pimonidazole binding and portal pressure. Furthermore, a free radical adduct was detected with spin trapping and electron spin resonance spectroscopy 8 hr after tacrine treatment, providing evidence for reoxygenation. When catechin (100 mg/kg, i.p.), a free radical scavenger, was given before tacrine, injury was decreased by about 45%. Furthermore, feeding 5% arginine in the diet significantly reduced portal pressure and time of dye distribution. These data are consistent with the hypothesis that tacrine hepatotoxicity is a hypoxia-reoxygenation injury mediated through the sympathetic nervous system.

Role of Kupffer cells, endotoxin and free radicals in hepatotoxicity due to prolonged alcohol consumption: studies in female and male rats

Alcohol ingestion results in increases in the release of endotoxin from gut bacteria or membrane permeability of the gut to endotoxin, or both. Female rats are more sensitive to these changes. Elevated levels of endotoxin activate Kupffer cells to release substances such as eicosanoids, tumor necrosis factor-alpha and free radicals. Prostaglandins increase oxygen uptake and most likely are responsible for the hypermetabolic state in the liver. The increase in oxygen demand leads to hypoxia in the liver, and on reperfusion, alpha-hydroxyethyl free radicals are formed that lead to tissue damage in oxygen-poor pericentral regions of the liver lobule.

Role of Kupffer cells in reperfusion injury in fat-loaded livers from ethanol-treated rats

Reperfusion injury was studied in blood-free perfused livers from fat-loaded, ethanol-treated rats. Rats were pair-fed a modified Lieber-DeCarli liquid diet containing 36% calories as ethanol or isocaloric maltose-dextrin for 4 to 5 weeks. Reperfusion injury to the liver, which occurs in previously hypoxic regions upon reintroduction of oxygen, was studied in a low-flow, reflow perfusion model. Lactate dehydrogenase in effluent perfusate increased from basal levels of < 1 to 17 IU/g/h in livers from controls, whereas prior alcohol treatment elevated values to 37 IU/g/h. Pretreatment of rats with gadolinium chloride (GdCl3, 20 mg/kg i.v.), a selective Kupffer cell toxicant, minimized lactate dehydrogenase release during reperfusion to 7 to 8 IU/g/h in livers from both groups. Rates of malondialdehyde production were 144 and 166 nmol/g/h during reperfusion in control and alcohol-treated rats, respectively, but values reached only 54 and 79 nmol/g/h after GdCl3 treatment. Interestingly, a typical PBN/carbon-centered free radical adduct signal was detected in bile of livers from ethanol-treated rats, but not in controls or ethanol-treated rats given GdCl3. Portal pressure increased during the reperfusion period in livers from alcohol-treated rats, although not in controls, and GdCl3 reduced it significantly. Taken together, these data indicate that reperfusion injury is greater in fatty livers from alcohol-treated rats in a blood-free model. Inactivation of Kupffer cells minimized reperfusion injury in both control and alcohol-treated rats, most likely by diminishing lipid peroxidation thereby improving hepatic microcirculation.

Role of Kupffer cells in failure of fatty livers following liver transplantation and alcoholic liver injury

Kupffer cells have been implicated in mechanisms of pathophysiology following liver transplantation. Recently, postoperative injury in ethanol-induced fatty liver has been evaluated because fatty livers often fail following transplantation. The low-flow, reflow liver perfusion model was used to study the role of Kupffer cells (KC) in reperfusion injury to fatty livers from rats fed a diet containing ethanol for 4-5 weeks. Treatment with GdCl3, which selectively destroys KC, decreased cell death significantly. Thus, destruction of KC minimized hepatic reperfusion injury, most likely by inhibiting free radical formation and improving microcirculation. Since it was demonstrated recently that destruction of KC prevented the hypermetabolic state observed with acute alcohol exposure, their involvement in events leading to alcohol-induced liver disease was investigated. In rats exposed to ethanol continuously via intragastric feeding for up to 4 weeks, GdCl3 treatment prevented elevation of aspartate aminotransferase (AST) and dramatically reduced the average hepatic pathological score. These results indicate that KC participate in the early phases of alcohol-induced liver injury. Endotoxaemia occurs in alcoholics and activates KC; therefore, we evaluated the effect of minimizing bacterial endotoxin by intestinal sterilization with the antibiotics polymyxin B and neomycin. Antibiotics diminished plasma endotoxin levels significantly and prevented ethanol-induced increases in AST values. These results indicate that endotoxin is involved in the mechanism of ethanol-induced liver injury. A six-line radical spectrum was detected with electron paramagnetic resonance spectroscopy in bile from alcohol-treated rats which was blocked by GdCl3. The free radical adducts had hyperfine coupling constants characteristic of lipid-derived free radical products. In conclusion, these studies demonstrate that KC are involved in reperfusion injury to ethanol-induced fatty livers and hepatic injury due to long-term treatment with ethanol.

Primary nonfunction of fatty livers produced by alcohol is associated with a new, antioxidant-insensitive free radical species

The formation of free radicals after orthotopic liver transplantation in the rat correlates with graft failure. Fatty livers from alcoholics transplant poorly, so these studies were designed to examine the effect of alcohol on free radical formation in a rearterialized rat liver transplantation model. Treatment of rats for 3-5 weeks with either a high-fat or an ethanol-containing liquid diet caused characteristic pericentral lipid accumulation. After storage in University of Wisconsin cold storage solution (UW) and transplantation, a reperfusion injury characterized by increased postoperative AST levels (greater than 1500 U/l in about 3 hours) was observed in rats fed high-fat or alcohol-containing diets, whereas parenchymal cell injury was seen much less in low-fat controls. Survival was around 63% in the low-fat group but decreased to 12 and 18% in the high-fat and alcohol groups, respectively. Furthermore, intracellular lipid content correlated inversely with survival. In untransplanted livers, the spin trap alpha-phenyl N-tert-butylnitrone (PBN) was infused, and blood samples were collected and extracted with chloroform:methanol. Signals indicative of carbon-centered PBN radical adducts were barely detectable in all untransplanted groups studied by electron paramagnetic resonance. In contrast, a robust 6-line complex spectrum was obtained from all groups studied immediately after 48 hours of cold storage in UW solution and transplantation. A mixture of 3 radical species was identified. Two had coupling constants similar to lipid-derived free radicals, whereas the third is a new species with unique coupling constants and is most likely oxygen derived. In low-fat controls, the signal was reduced significantly by superoxide dismutase (SOD)/catalase; however, SOD/catalase had no effect on free radicals in lipid-loaded livers. Thus, both dietary high fat and alcohol exposure produce a unique SOD/catalase-insensitive free radical species that may be involved in the mechanism of failure of fatty livers after orthotopic liver transplantation.

Role of Kupffer cells in the pathogenesis of hepatic reperfusion injury

The purpose of this study was to evaluate the role of Kupffer cell activation in the pathogenesis of reperfusion injury. In a blood-free liver perfusion model, pericentral hypoxia and reperfusion injury occurred. Lactate dehydrogenase (LDH) and malondialdehyde (MDA) release, oxygen uptake, and trypan blue staining were assessed. Within the first 10 min of reflow, LDH and MDA release reached maximal values of 44 U.g-1.h-1 and 115 nmol.g-1.h-1, respectively. Trypan blue cell staining was confined to pericentral regions of the liver lobule. When Kupffer cells were inactivated with GdCl3, release of enzymes and MDA was reduced significantly by > 50%, and hepatic cell death was almost completely absent. Since increases in MDA suggested involvement of free radicals, livers were perfused with phenyl N-t-butylnitrone (5 mM), a spin-trapping agent. Analysis of liver tissue by electron paramagnetic resonance spectroscopy revealed a typical six-line spectrum, providing direct evidence that carbon-centered radicals were generated on reflow. GdCl3 treatment decreased radical adduct formation by approximately 50%. Collectively, these results strongly support the hypothesis that activation of Kupffer cells plays an important role in the pathogenesis of hepatic reperfusion injury.

New reactive oxidizing species causes formation of carbon-centered radical adducts in organic extracts of blood following liver transplantation

alpha-(4-pyridyl-1-oxide)-N-t-butylnitrone (4-POBN) radical adducts from Folch (chloroform:methanol) extraction of blood of transplanted livers exhibited a large 6-line electron paramagnetic resonance (EPR) spectrum. Slow EPR sample preparation involving freezing and thawing prior to extraction over 15 min yielded a spectrum assigned as a lipid-derived free radical species, whereas rapid (< 1 min) extraction without a freeze-thaw cycle yielded a mixture of radicals, one with coupling constants similar to the alpha-hydroxymethyl-4-POBN adduct (4-POBN/.CH2OH). Extraction with purified chloroform, however, yielded a much weaker, probably lipid-derived signal. Use of 13C-methanol in the Folch extracting solution yielded a 12-line EPR spectrum, indicating that a new, highly reactive oxidant species from blood following liver transplantation can convert organic solvents used in tissue extractions to free radicals. This hypothesis was supported by simulation of EPR spectra of free radicals extracted rapidly with Folch, which indicated that the spectrum contained two carbon-centered species, one with hyperfine coupling constants similar to the alpha-methylhydroxyl-4-POBN adduct, the other probably lipid-derived. Because the former originates from methanol in the Folch, extraction of samples with alcohol-free organic solvent is most likely superior when the potential for formation of stable oxidant species exists, such as after liver transplantation.

Evidence that free radicals are involved in graft failure following orthotopic liver transplantation in the rat--an electron paramagnetic resonance spin trapping study

The purpose of these studies was to determine whether free radicals were formed as a consequence of reperfusion during orthotopic liver transplantation and whether their formation was related to graft failure. Grafts were stored for 18 hr in Euro-Collins solution or for 48 hr in University of Wisconsin solution (nonsurvival conditions) and reperfused with blood containing the spin trap alpha-phenyl N-tert-butylnitrone (PBN). Venous blood samples (4-5 ml) were collected, and serum was extracted with chloroform and methanol (2:1) and analyzed for radical adducts by electron paramagnetic resonance (EPR) spectroscopy. In samples from livers stored under nonsurvival conditions, EPR spectra were detected indicating the presence of PBN radical adducts. In contrast, radical adduct formation was 3- to 4-fold lower in similar experiments performed with untransplanted livers or with livers stored under survival conditions (1 hr in Ringer's solution or 24 hr in UW solution). Oxygen radicals are more likely involved in the production of radical adducts because formation was nearly completely prevented by superoxide dismutase plus catalase or Carolina rinse, which contains glutathione, desferrioxamine mesylate, and allopurinol. Radical adduct formation was much greater in a blood-free perfusion system where oxygen delivery was high, suggesting that blood elements are not necessary for radical adduct formation. An inverse correlation between survival of livers stored in UW solution and radical adduct signal was observed in this study. Thus, it is concluded that free radicals formed during reperfusion are involved in the mechanism of graft failure following liver transplantation in the rat.

Reperfusion rather than storage injury predominates following long-term (48 h) cold storage of grafts in UW solution: studies with Carolina Rinse in transplanted rat liver

Both storage injury and reperfusion injury have been reported in association with liver transplantation; however, which predominates is not clear. Therefore, these studies were designed to evaluate whether Carolina Rinse, which minimizes reperfusion injury following orthotopic liver transplantation in the rat, would be effective after long-term (48 h) storage of grafts in University of Wisconsin (UW) cold storage solution where sufficient time for development of storage injury exists. Livers were rinsed with either Ringer's solution or Carolina Rinse solution immediately prior to completion of implantation surgery. In the Ringer's group, 30-day survival was high following 24 h of cold storage (4/5) but was very low after 48 h (1/16). Importantly, survival was increased significantly (5/14) when grafts were rinsed with Carolina Rinse following 48 h of cold storage. In both groups, parenchymal cells appeared normal by scanning electron microscopy, excluded trypan blue, and released SGOT at values only slightly above the normal range immediately (i.e., less than 5 min) after 48 h of cold storage. However, SGOT values rose steadily during the 1st hour postoperatively following reperfusion in the Ringer's rinse group and reached levels around 1,000 U/l. In addition, nonparenchymal cells were not labelled with trypan blue following storage, but significant labelling occurred within 1 h. Both SGOT release and nonparenchymal cell injury were reduced significantly when grafts were rinsed with Carolina Rinse prior to completion of surgery. Liver injury assessed histologically 24 h postoperatively was also reduced about 50% by Carolina Rinse. Oxidative stress appeared to be involved, since radical adducts, most likely of lipid origin, were trapped during the first 5 min after reperfusion with the spin trapping technique and detected by electron paramagnetic resonance spectroscopy. Lipid radical formation was reduced nearly completely on reperfusion by Carolina Rinse. Since Carolina Rinse improved survival of liver grafts following long periods of cold storage and reduced lipid radical formation and hepatocellular injury, we concluded that a reperfusion injury rather than a storage injury predominates following orthotopic transplantation of livers stored for long periods of time in cold UW solution.

Reaction of glutathione with a free radical metabolite of carbon tetrachloride

Carbon tetrachloride and bromotrichloromethane are both metabolized by cytochrome P-450 in the presence of phenyl-N-t-butyl nitrone PBN) to the PBN/trichloromethyl (PBN/.CCl3) and the PBN carbon dioxide anion (PBN/.CO2-) radical adducts in the liver. The formation of the latter but not the former species in perfused liver was reduced markedly by prior depletion of hepatic glutathione with either diethyl maleate or buthionine sulfoximine treatments. In microsomal incubations, the PBN/.CO2- radical adduct was detected only upon the addition of cytosol. In microsomal incubations containing PBN, CCl4, and GSH, but no added cytosol, a novel radical adduct with distinctive coupling constants was detected. This radical adduct's ESR spectrum exhibited 13C isotope effects when it was formed in an incubation containing 13CCl4 or Br13CCl3. The presence of GSH in the radical adduct is postulated based on the radical adduct's hydrophilicity and slow rate of rotation in solution. The detection of this new radical adduct, PBN/[GSH-.CCl3], establishes the reaction of GSH with a CCl4-derived free radical as a significant event in the metabolism of CBrCl3 and CCl4. The cytosolic conversion of PBN/[GSH-.CCl3] into PBN/.CO2- has been demonstrated and characterizes the PBN/.CO2- radical adduct as the product of metabolism of PBN/[GSH-.CCl3], a primary radical adduct. Thus, it is concluded that GSH rather than oxygen is obligatory for the formation of PBN/.CO2- from .CCl3 in intact cells.

The carbon dioxide anion radical adduct in the perfused rat liver: relationship to halocarbon-induced toxicity

CCl4 has been shown previously to be metabolized to the trichloromethyl radical (.CCl3) and to a novel oxygen-containing carbon dioxide anion radical (.CO2-) in the perfused rat liver and in vivo. Since the role of free radicals in CCl4-induced hepatotoxicity is unclear, these studies were designed to determine if a relationship between .CO2- formation and halocarbon-induced hepatotoxicity exists. CCl4 or bromotrichloromethane (CBrCl3) was infused into livers from control or phenobarbital-treated rats perfused with either nitrogen- or oxygen-saturated Krebs-Henseleit bicarbonate buffer. Samples of effluent perfusate and chloroform/methanol extracts of liver were analyzed by ESR spectroscopy for free radical adducts following infusion of halocarbon and the spin trap, phenyl-t-butylnitrone (PBN). Hyperfine coupling constants and 13C-isotope effects observed in the ESR spectra of organic extracts of liver demonstrated the presence of the PBN radical adduct of .CCl3 from both halocarbons. Radical adducts in aqueous extracts of liver and effluent perfusate had hyperfine coupling constants and 13C-isotope effects identical to those of PBN/.CO2- generated chemically from formate. The PBN/.CO2- radical adduct was also observed in urine following the intragastric administration of CBrCl3 and PBN. Detection of PBN/.CO2- adducts in the effluent perfusate was decreased 3- to 4-fold by DIDS (0.2 mM), an inhibitor of the plasma membrane anion transport system. The rate of formation of PBN/.CO2- was decreased 2- to 3-fold following inhibition of cytochrome P-450-dependent monooxygenases by metyrapone (0.5 mM) and was increased about 2-fold by induction of cytochrome P-450 by phenobarbital pretreatment. Toxicity of halocarbons in the perfused liver was assessed by measuring the release of lactate dehydrogenase (LDH) into the effluent perfusate in livers from phenobarbital-treated rats under conditions identical to those employed to detect radical adducts (i.e., during the infusion of CCl4 or CBrCl3 into livers perfused with either nitrogen- or oxygen-saturated perfusate). Under all conditions studied, PBN/.CO2- was detected in the effluent perfusate within 2-4 min. Metabolism of halocarbons to PBN/.CO2- was 6- to 8-fold faster during perfusion with nitrogen-saturated rather than with oxygen-saturated perfusate. Concomitantly, liver damage detected from LDH release occurred much sooner during halocarbon infusion in the presence of nitrogen-saturated rather than oxygen-saturated perfusate. A good correlation between the rate of formation of PBN/.CO2- and the time of onset of LDH release following halocarbon infusion was observed.(ABSTRACT TRUNCATED AT 400 WORDS)

A search for oxygen-centered free radicals in the lipoxygenase/linoleic acid system

Studies of the oxygenation of linoleic acid by soybean lipoxygenase utilizing electron spin resonance spectroscopy and oxygen uptake have been undertaken. The spin trap, alpha-(4-pyridyl-1-oxide)-N-t-butylnitrone (4-POBN) was included in the lipoxygenase system to capture short-lived free radicals. Correlation of radical adduct formation rates with oxygen uptake studies indicated that the major portion of radical adduct formation occurred when the system was nearly anaerobic. Incubations containing [17O]oxygen with nuclear spin of 5/2 did not have additional ESR lines as would be expected if an oxygen-centered 4-POBN-lipid peroxyl radical adduct were formed indicating that the trapped radical must be reassigned as a carbon-centered species. To establish the presence of [17O2]oxygen in our incubations, a portion of the gas from the lipoxygenase/linoleate experiments was used to prepare the 4-POBN-superoxide radical adduct utilizing a superoxide producing microsomal/paraquat/NADPH system.

[17O]oxygen hyperfine structure for the hydroxyl and superoxide radical adducts of the spin traps DMPO, PBN and 4-POBN

[17O]oxygen hyperfine coupling constants are reported for the superoxide and hydroxyl radical adducts with the spin traps 5,5-dimethyl-1-pyrroline N-oxide, N-t-butyl-alpha-phenylnitrone and alpha-(4-pyridyl 1-oxide)-N-t-butylnitrone. These couplings provide spectroscopic evidence that the spin adducts have been correctly identified.

The formation of a novel free radical metabolite from CCl4 in the perfused rat liver and in vivo

Electron spin resonance spectroscopy has been used to monitor free radicals formed during CCl4 metabolism by perfused livers from phenobarbital-treated rats. Livers were perfused simultaneously with the spin trap phenyl N-t-butylnitrone and with either 12CCl4 or 13CCl4. Perfusate samples and CHCl3:CH3OH extracts of perfusate and liver samples were analyzed for phenyl N-t-butylnitrone radical adducts of reactive free radicals. In the organic extracts, hyperfine coupling constants and 13C isotope effects observed in the ESR spectra indicated the presence of the radical adduct of the trichloromethyl radical. Surprisingly, an additional free radical signal about two orders of magnitude more intense than that of the phenyl N-t-butylnitrone/CCl.3 radical adduct was observed in the aqueous liver perfusate. This adduct was also detected by ESR in rat urine 2 h after intragastric addition of spin trap and CCl4. This radical adduct had hyperfine coupling constants and 13C isotope effects identical with the radical adduct of the carbon dioxide anion radical (CO2-.). Analysis of the pH dependence of the coupling constants yielded a pK alpha of 2.8 for the CO2-. radical adduct formed either in the perfused liver or chemically. Carbon tetrachloride is converted into CCl.3 by cytochrome P-450 through a reductive dehalogenation. The trichloromethyl free radical reacts with oxygen to form the trichloromethyl peroxyl radical, CCl3OO., which may be converted into .COCl and then trapped. This radical adduct would hydrolyze to the carboxylic acid form, which is detected spectroscopically. Alternatively, the carbon dioxide anion free radical could form through complete dechlorination and then react with the spin trap to give the CO2-. radical adduct directly.