Benzo(a)pyrene phenol production by perfused rat liver and its inhibition by ethanol.

A rapid and inexpensive method has been developed to estimate rates of benzo(a)pyrene phenol production by perfused rat liver. This method is based on the measurement of benzo(a)pyrene phenols utilizing a simple fluorometric procedure. Within 2 to 3 min after infusion of benzo(a)pyrene bound to serum albumin, phenols are excreted into the perfusate, primarily as glucuronide and sulfate conjugates. Maximal rates of phenol release were 8 to 10 nmol/g/hr in livers from control rats and 40 to 42 nmol/g/hr in livers from 3-methylcholanthrene-treated rats. Fasting of 3-methylcholanthrene-treated rats for 24 hr prior to perfusion experiments did not affect either the rate of phenol production or the extent of their conjugation. Ethanol (20 mM) inhibited rates of phenol formation by 50% in livers from fasted, 3-methylcholanthrene-treated rats but had no effect on benzo(a)pyrene hydroxylase activity in isolated hepatic microsomes. These data indicate that ethanol inhibits phenol formation from benzo(a)pyrene in intact liver, probably by diminishing the supply of the cofactor reduced nicotinamide adenine dinucleotide phosphate.

Enhancement of carbon tetrachloride-induced liver injury by a single dose of ethanol: proton magnetic resonance imaging (MRI) studies in vivo.

Magnetic resonance imaging (MRI) and localized magnetic resonance spectroscopy (MRS) were used to study the effects of a single dose of ethanol, given 18 h prior to experiments, on CC14-induced acute hepatotoxicity in rats in situ. Localized edema in the centrilobular region of the liver, following exposure to ethanol and CCl4, was detected by 1H-MRI techniques. The edema was characterized by a volume selective spectroscopy (VOSY) method, which measured an increase in water concentration from ethanol and CCl4-treated rat livers, in comparison to control livers. Electron microscopy (EM) of the high intensity regions of the ethanol/CCl4 treated liver sections revealed dramatic subcellular changes such as fragmentation of the granular endoplasmic reticulum (ER), formation of large vacuoles and lipid droplets in the cytoplasmic matrix and extensive swelling of the mitochondria as well as disruption of the cristae. Pretreatment with alpha-phenyl tert-butyl nitrone (PBN), a free radical spin trap, prior to halocarbon exposure, was found to reduce the CC14-mediated high intensity region in the liver images. Electron microscopy of the PBN pretreated CCl4 exposed rat liver sections revealed only minor observable differences in subcellular organization, such as some swelling of the mitochondria, when compared to controls. In addition, these data suggest that ethanol may potentiate CCl4 hepatotoxicity by increased formation of free radical intermediates. Inhibition of the CCl4-induced edematous response in rat liver by PBN demonstrates that free radical intermediates, arising from the metabolism of CCl4, are possibly the causal factor in the initiation of the edema.

In vivo detection of aflatoxin-induced lipid free radicals in rat bile.

Aflatoxin B1 (AFB1), a potent hepatotoxin and hepatocarcinogen, is metabolized in the liver via cytochrome P-450 to an AFB1-8,9-epoxide intermediate. The formation of the AFB1-8,9-epoxide correlates with the pathological changes observed in numerous mammalian species. Oxidative damage has been postulated to play a major role in the mechanisms associated with AFB1-induced cytotoxicity and carcinogenecity in mammalian species. The aim of this study was to detect and identify free radical intermediates from the hepatic metabolism of AFB1 in vivo. Rat bile ducts were cannulated and rats were treated simultaneously with AFB1 (3 mg/kg i.p.) and the spin trapping agent 4-POBN (alpha-(4-pyridyl-1-oxide)-N-tert-butyl nitrone) (1 g/kg i.p.), and bile was collected over a period of 2 h at 20-min intervals. ESR spectroscopy was used to detect a carbon-centered radical adduct of 4-POBN in rat bile. The effect of metabolic inhibitors, such as deferoxamine mesylate (DFO), an iron chelator, and SKF 525A, a cytochrome P-450 inhibitor, on in vivo aflatoxin-induced free radical formation were also studied. It was found that there was a significant decrease in free radical formation by pre-treatment with both DFO and SKF 525A. This indicates that oxidation of AFB1 generates free radical species via CYP metabolism and an iron-mediated redox mechanism.

Spin trapping of superoxide radicals following stimulation of neutrophils with fMLP is temperature dependent.

Oxygen radical formation by human neutrophils stimulated with a chemotactic peptide, formyl-methionyl-leucyl-phenylalanine (fMLP), was studied through the use of spin trapping and superoxide dismutase-inhibitable reduction of oxidized cytochrome c. Both methods provided comparable data on temperature-dependent kinetics of superoxide radical formation, but hydroxyl radicals were also detected in spin-trapping experiments. When superoxide generation was monitored at 37 degrees C, the respiratory burst lasted only a few minutes. If the neutrophils were stimulated at 37 degrees C, but superoxide measurements were done at room temperature, the respiratory burst was again transient. However, neutrophils persistently generated superoxide when both stimulation and subsequent measurements were performed at room temperature. In the presence of the actin polymerization inhibitor, cytochalasin B, superoxide generation was persistent, even when measurements were conducted at 37 degrees C. A possible explanation for these observations is that the fMLP receptor complexes quickly aggregate and are internalized at physiological temperature, but not at room temperature. Very little superoxide was formed if cells were kept at a temperature of 4 degrees C for 1 h prior to fMLP addition, which is consistent with decreased expression of the fMLP receptor at cold temperatures.

Spin-trapping studies of hepatic free radicals formed following the acute administration of ethanol to rats: in vivo detection of 1-hydroxyethyl radicals with PBN.

The generation of free radicals in rat liver following the acute oral administration of ethanol was studied with the spin-trapping method, using a deuterated derivative of phenyl-N-tert-butylnitrone (PBN-d14) as the spin-trapping agent. After administration of ethanol and PBN-d14 to rats, organic extracts of the liver were prepared and subjected to ESR spectroscopy. In the case of ethanol-treated rats, the ESR spectra indicated that mixtures of radicals had been trapped, while spectra from control rats were essentially negative. The predominant spin adduct detected after ethanol treatment is proposed to be from a carbon-centered, primary alkyl radical, based on gamma-hydrogen hyperfine splitting patterns observed with PBN-d14. Oxygen-centered radicals also contributed to the ESR spectra. Liver extracts also contained low concentrations of the 1-hydroxyethyl radical spin adduct, which was indicated by weak spectral lines corresponding to those of the 1-13C-ethanol adduct. These data confirm previous suggestions that ethanol is metabolized to a free radical metabolite in rat liver. In addition, some information on types of lipid radicals generated during alcohol intoxication has been obtained.

Determination of the rate of superoxide generation from biological systems by spin trapping: use of rapid oxygen depletion to measure the decay rate of spin adducts.

A method was developed to measure the superoxide generation rate from biological systems using the spin trapping method. Kinetic treatment of the decay rate of the superoxide adduct of 5,5-dimethylpyrroline N-oxide (DMPO) revealed that the EPR signal intensity of the system is proportional to the superoxide generation rate. Rapid depletion of oxygen in the sample was utilized to terminate superoxide generation so that the decay rate of the DMPO superoxide adduct (DMPO-OOH) could be determined. For this decay measurement, a controlled atmosphere EPR cavity was developed and was used with an open-air sample cell. Superoxide generation rates determined with this method for stimulated neutrophils and for the hypoxanthine-xanthine oxidase system were comparable to those obtained with the cytochrome c reduction method. This method is specifically applicable to the system in which dissolved oxygen supplied from the gas phase is utilized as a source of superoxide.

Characteristics of an oxidant formed during iron (II) autoxidation.

When ethanol (100 mM) and the spin trapping agent DMPO were added to a solution of FeSO4 (0.1 mM) in phosphate buffer (40 mM), pH 7.4, the spectrum of the 1-hydroxyethyl radical spin adduct of DMPO could be detected by ESR spectroscopy. The ESR signal intensity of the 1-hydroxyethyl radical increased with higher concentrations of phosphate. Under these conditions, hydroxyl radical adducts could not be detected. However, if H2O2 (0.1 mM) was also added, the ESR spectra contained signals from both the hydroxyl and 1-hydroxyethyl radical adducts of DMPO. When ethanol was replaced with azide (100 mM) in these experiments, strong ESR signals from the azidyl radical adduct of DMPO were observed only in the Fenton system. The absence of hydroxyl radical adduct signals in the Fe(2+)-PO4 reaction could not be explained by instability of the hydroxyl radical adduct in the presence of Fe2+ or superoxide. Experiments with oxygen radical scavengers indicated that the oxidant formed during Fe2+ autoxidation was less reactive to benzoate, DMSO and tert-butanol than the hydroxyl radical. The available data indicate that the primary oxidant formed during Fe2+ autoxidation in phosphate buffer is not the hydroxyl radical, but may be an iron-oxygen complex such as a ferryl species.

Free radical formation during ketamine anesthesia in rats: a cautionary note.

Ketamine is a useful anesthetic agent with good analgesic properties; however, when ketamine was used to anesthetize rats for spin trapping studies of alcohol-induced free radicals, liver extracts contained a strong electron paramagnetic resonance (EPR) signal of a novel radical. The same EPR signal was observed in liver extracts when rats which had not received alcohol were anesthetized with ketamine. When ketamine was added to liver microsomes and NADPH, a nitroxide radical derived from ketamine could be detected in organic extracts. When the spin trapping agent POBN was also added, microsomes produced both a ketamine nitroxide radical and a spin adduct. Similar results were obtained during ketamine oxidation by hydrogen peroxide in a tungstate-catalyzed reaction, or in a Fenton reaction system. The data suggest that the secondary amine group of ketamine can be oxidized to a stable nitroxide which produces an EPR spectrum in the absence of a spin trapping agent. The POBN spin adduct detected may be from a carbon-centered radical in the cyclohexanone ring of ketamine. Because several types of radicals can be formed from ketamine, this agent may not be appropriate as an anesthetic for many types of in vivo spin trapping experiments.

Aromatic hydroxylation in PBN spin trapping by hydroxyl radicals and cytochrome P-450.

Phenyl N-tert-butylnitrone (PBN) is widely used as a spin trapping agent, but is not useful detecting hydroxyl radicals because the resulting spin adduct is unstable. However, hydroxyl radicals could attack the phenyl ring to form stable phenolic products with no electron paramagnetic resonance signal, and this possibility was investigated in the present studies. When PBN was added to a Fenton reaction system composed of 25 mM H(2)O(2) and 0.1 mM FeSO(4), 4-hydroxyPBN was the primary product detected, and benzoic acid was a minor product. When the Fe(2+) concentration was increased to 1.0 mM, 4-hydroxyPBN concentrations increased dramatically, and smaller amounts of benzoic acid and 2-hydroxyPBN were also formed. Although PBN is extensively metabolized after administration to animals, its metabolites have not been identified. When PBN was incubated with rat liver microsomes and a reduced nicotinamide adenine dinculeotide phosphate (NADPH)-generating system, 4-hydroxyPBN was the only metabolite detected. When PBN was given to rats, both free and conjugated 4-hydroxyPBN were readily detected in liver extracts, bile, urine, and plasma. Because 4-hydroxyPBN is the major metabolite of PBN and circulates in body fluids, it may contribute to the pharmacological properties of PBN. But 4-hydroxyPBN formation cannot be used to demonstrate hydroxyl radical formation in vivo because of its enzymatic formation.

Diminished rates of glucuronidation and sulfation in perfused rat liver after chronic ethanol administration.

Rates of glucuronidation and sulfation of 7-hydroxycoumarin were studied in perfused livers from normal chow-fed rats, or in livers from rats that had been fed liquid control or ethanol-containing diets. During infusion of 100 microM 7-hydroxycoumarin, rates of glucuronidation were similar in livers from chow-fed or control diet rats, but were 34% less in livers from ethanol-fed rats. These rates of glucuronidation in perfused livers could not be explained by changes of UDP-glucuronyltransferase activity, which was highest in hepatic microsomes from ethanol-treated rats and lowest in microsomes from chow-fed rats. The low rates of glucuronidation in livers from ethanol-treated rats were correlated with low hepatic concentrations of UDP-glucuronic acid, which were less than 70% of the levels measured in the other treatment groups. However, the diminished UDP-glucuronic acid levels could not be explained by alterations in adenine nucleotides, NAD+/NADH ratios, glycogen, UDP-glucose, or activity of UDP-glucose dehydrogenase. Rates of sulfation declined during prolonged 7-hydroxycoumarin infusion in livers from ethanol-treated rats, but not in livers from rats that had received the control diet. Similarly, hepatic concentrations of adenosine-3'-phosphate 5'-sulfatophosphate (PAPS) also decreased with time only in livers from ethanol-treated rats. Thus, chronic ethanol feeding impairs glucuronidation and sulfation in perfused livers as a result of diminished availability of the required cofactors for these conjugation pathways.

Inhibition of p-nitroanisole O-demethylation in perfused rat liver by oleate.

p-Nitroanisole O-demethylation in perfused livers from fasted, phenobarbital-treated rats was rapidly and reversibly inhibited by sodium oleate (0.3 to 0.6 mM). Xylitol partially reversed this inhibitory effect. The inhibition was not mediated by a direct effect of oleate on microsomal components since concentrations of oleate ranging up to 1.0 mM did not affect p-nitroanisole O-demethylation by isolated microsomes. Infusion of 0.6 mM oleate did not alter the measured intracellular NAD+/NADH ratio but did cause a significant increase in the intracellular NADP+/NADPH ratio. A significant decrease in the ATP/ADP ratio was also observed. Oleoyl CoA inhibited p-nitroanisole O-demethylation in microsomes (Ki about 30 microM), and both oleoyl CoA and palmitoyl CoA inhibited the energy-linked nicotinamide nucleotide transhydrogenase in submitochondrial particles (Ki about 1 microM). Thus, inhibition of mixed-function oxidation in the intact liver by oleate is most likely mediated by oleoyl CoA. Oleoyl CoA inhibits mixed-function oxidation in the intact liver by acting directly on cytochrome P-450 and by decreasing generation of NADPH via inhibition of key enzymes of the citric acid cycle and the energy-linked transhydrogenase.

p-Nitroanisole O-demethylation in perfused hamster liver. High rates of pentose cycle-independent mixed-function oxidation.

Rates of p-nitroanisole O-demethylation in perfused livers from Syrian golden hamsters were three to four times greater than comparable rates measured in preparations from Sprague-Dawley rats. Hamsters also had greater microsomal p-nitroanisole O-demethylase activity and cytochrome P-450 contents than rats. In general, phenobarbital caused similar increases in these properties in both species. Fasting of hamsters for 24 hr increased p-nitroanisole O-demethylase activity in microsomes but did not affect rates in perfused livers. Rates were also unaffected in the perfused liver by pretreatment with 6-aminonicotinamide, an inhibitor of the pentose phosphate shunt. Hamster livers had low activities of pentose cycle enzymes but high activities of malic enzyme and isocitrate dehydrogenase compared to rats. In hamster livers, maximal rates of p-nitroanisole O-demethylation were not maintained but declined steadily over 40 min with prolonged p-nitroanisole infusion. The decreased rates of mixed-function oxidation in the non-recirculating perfusion system could not be explained by diminished tissue viability or degradation of cytochrome P-450 but were likely due to a decline in the formation of reduced cofactor. Hepatic concentrations of alpha-ketoglutarate and malate increased during p-nitroanisole infusion. Furthermore, rates of p-nitroanisole O-demethylation were inhibited by ethanol and aminooxyacetate, agents which inhibit the generation and/or movement of mitochondrial reducing equivalents into the cytosol. The infusion of pyruvate stimulated p-nitroanisole O-demethylation in perfused livers from fasted hamsters. This effect was maximal with 0.1 mM pyruvate, did not require gluconeogenesis, and was insensitive to 6-aminonicotinamide treatment. Thus, stimulation of p-nitroanisole metabolism by pyruvate in hamster livers is likely related to the mitochondrial oxidation of pyruvate, rather than to increased NADPH generation via the pentose phosphate cycle. These data indicate that mitochondrial sources of NADPH supply reducing equivalents for mixed-function oxidation in hamster liver.

Regulation of NADPH-dependent mixed-function oxidation in perfused livers. Comparative studies with sorbitol and ethanol.

Sorbitol and ethanol were shown to have opposite effects on p-nitroanisole O-demethylation in perfused livers from fasted, phenobarbital-treated rats. Sorbitol (2 mM) stimulated drug metabolism by 50% while ethanol (20 mM) caused 80% inhibition. Both sorbitol and ethanol infusion decreased the NAD+/NADH ratio and increased fluorescence of pyridine nucleotides monitored from the liver surface; however, the NADP+/NADPH ratio was decreased by sorbitol but tended to be increased by ethanol. Stimulation of drug metabolism by sorbitol was abolished by pretreatment of fasted rats with 6-aminonicotinamide, an inhibitor of the pentose phosphate shunt, but was not affected by aminooxyacetate, a transaminase inhibitor. These results indicate that sorbitol stimulated p-nitroanisole metabolism by providing NADPH via the pentose phosphate shunt. Ethanol and sorbitol caused changes in intracellular concentrations of NADPH in livers from fasted rats which correlated directly with changes in hepatic levels of citrate and aspartate. Furthermore, aspartate infusion reduced the inhibition of p-nitroanisole O-demethylation by ethanol. This inhibition was also reversed partially by sorbitol in livers from 6-aminonicotinamide-treated rats. It is concluded that ethanol inhibits mixed-function oxidation primarily by decreasing the concentrations of citric acid cycle intermediates which leads to depletion of cytosolic NADPH.

Maintenance of nicotinamide dinucleotide phosphate content and oxidation-reduction state during mixed-function oxidation of p-nitroanisole in isolated perfused livers of various species.

The influence of p-nitroanisole, a substrate for mixed-function oxidation, on total NADP+ and NADPH and NADP+/NADPH ratios was examined in perfused livers from three different species. Studies were performed using livers from Sprague-Dawley rats, Syrian golden hamsters and C57BL/6J mice. Although rates of p-nitroanisole O-demethylation varied more than 16-fold in perfused livers from these species, NADP+/NADPH ratios calculated from measured concentrations of NADP+ and NADPH and from ratios calculated from substrate pairs assumed to be in near equilibrium with NADP+-dependent dehydrogenases remained remarkably constant under most conditions. Thus, rates of NADPH utilization and generation must be tightly coupled in perfused livers during high rates of mixed-function oxidation. Exceptions to the general pattern noted above occurred in livers of fasted, phenobarbital-treated rats where carbohydrate reserves were depleted and in livers from 3-methyl-cholanthrene-treated mice where rates of p-nitroanisole O-demethylation were exceptionally high. Livers from fed phenobarbital-treated rats displayed a paradoxical decrease in NADP+/NADPH ratios reflecting reduction calculated from substrates assumed to be in near equilibrium with 6-phosphogluconate dehydrogenase during mixed-function oxidation, suggesting that NADPH generation exceeded NADPH utilization in the rat in the fed state. In contrast, the NADP+/NADPH ratio calculated from measured pyridine nucleotides increased in livers of 3-methylcholanthrene-treated mice perfused with p-nitroanisole, reflecting oxidation. Moreover, the NADP+/NADPH ratio calculated from substrates assumed to be near equilibrium with 6-phosphogluconate dehydrogenase increased in livers of fasted rats, suggesting that utilization of NADPH exceeded generation. Thus, adequate carbohydrate reserves appear essential for maintenance of NADPH during high rates of mixed-function oxidation.

Antioxidants and gadolinium chloride attenuate hepatic parenchymal and endothelial cell injury induced by low flow ischemia and reperfusion in perfused rat livers.

The objective of this study was to determine whether Kupffer cells contribute to parenchymal and endothelial cell damage induced by ischemia-reperfusion in perfused rat livers. Parenchymal and endothelial cell injury were determined by measuring activities of lactate dehydrogenase (LDH) and purine nucleoside phosphorylase (PNP), respectively, in the effluent perfusate of livers subjected to 60 min of low flow ischemia followed by 30 min of reperfusion. Upon reperfusion, LDH and PNP activities increased significantly within the first 10 min of reperfusion and remained elevated over control values throughout the duration of reperfusion. Pretreatment with gadolinium chloride, an inhibitor of Kupffer cell function, significantly decreased LDH and PNP efflux during reperfusion by approximately 60% and 50%, respectively. When Kupffer cells were stimulated by vitamin A pretreatment, PNP efflux was doubled during reperfusion. Vitamin E pretreatment attenuated LDH and PNP release by approximately 70% during reperfusion compared to enzyme release in untreated livers. Moreover, the water-soluble antioxidants superoxide dismutase and desferrioxamine reduced reperfusion injury, whereas catalase had no effect on enzyme release. These results demonstrate that superoxide anions released from Kupffer cells are involved in oxidative damage to endothelial cells as well as hepatocytes during the early stages of hepatic reperfusion.

Degradation of DMPO adducts from hydroxyl and 1-hydroxyethyl radicals by rat liver microsomes.

Hydroxyl and 1-hydroxyethyl radical adducts of 5,5-dimethylpyrroline N-oxide (DMPO) were prepared by photolysis, and mechanisms for loss of their EPR signals in rat liver microsomal suspensions were evaluated. Rates of NADPH-dependent EPR signal loss were more rapid in phosphate buffer than in Tris buffer. Addition of superoxide dismutase (SOD) partially protected the adducts when Tris was used as a buffer, but was relatively ineffective in the presence of phosphate. The ferrous iron chelator bathophenan-throlene partially protected the spin adducts in the presence and absence of phosphate, but complete protection was observed when SOD was also added. The spin adducts were unstable in the presence of Fe+2 and K3Fe(CN)6, but Fe+3 alone had little effect on the EPR signals. The data are consistent with two mechanisms for microsomal degradation of DMPO spin adducts under these conditions. Microsomes from superoxide in the presence of oxygen and NADPH, which attacks these DMPO spin adducts directly. The spin adducts are also degraded in the presence of Fe+2, and phosphate stimulates this iron-dependent destruction of DMPO spin adducts.

Mutual contact of adherent polymorphonuclear leukocytes inhibits their generation of superoxide.

Superoxide generation by polymorphonuclear leukocytes (PMNs) in suspension, or adherent to glass or plastic, after stimulation with N-formylmethionyl-leucyl-phenylalanine or phorbol myristate acetate was measured by cytochrome c reduction and spin trapping. Amounts of superoxide generated by adherent PMNs were inversely related to cell density. The generation of hydrogen peroxide was also inhibited at higher cell densities. In contrast to adherent cells, superoxide released by PMNs in suspension linearly increased with respect to cell number over a wider range. Microscopic observation indicated that the number of cells in mutual contact increased rapidly at cell densities higher than 4 x 10(4) cells/cm2, and inhibition of superoxide became apparent at higher cell densities. Mediators which could be released by PMNs, such as NO and adenosine, were not the cause of inhibition. These data suggest that mutual contact of PMNs suppresses their generation of superoxide. Survival rates of PMNs after stimulation increased at higher densities, indicating that the mutual contact-induced inhibition of superoxide generation by PMNs may be physiologically relevant at sites of inflammation.

Metabolism of ethanol to 1-hydroxyethyl radicals in rat liver microsomes: comparative studies with three spin trapping agents.

Metabolism of ethanol to 1-hydroxyethyl radicals by rat liver microsomes was studied with three nitrone spin trapping agents (POBN, PBN, and DMPO) under essentially comparable conditions. The data indicate that POBN was the superior spin trapping agent for 1-hydroxyethyl radicals, and that DMPO was least efficient. Addition of deferoxamine completely prevented detection of 1-hydroxyethyl radicals with PBN or DMPO, but caused only 50% decrease in EPR signals when POBN was the spin trap. However, superoxide dismutase only decreased 1-hydroxyethyl radical formation when POBN was the spin trap. Other experiments demonstrated that POBN was the most effective of these nitrones for reduction of Fe(III) in aqueous solutions. Furthermore, 1-hydroxyethyl radical adducts were formed when POBN was added to mixtures of ethanol, phosphate buffer, POBN and FeCl3, but this effect did not occur with either PBN or DMPO. Thus, these data indicate that undesirable effects of POBN on iron chemistry may influence results of spin trapping experiments, and complicate interpretation of the resulting data.

Oxygen radical formation in well-washed rat liver microsomes: spin trapping studies.

The generation of hydroxyl radicals by rat liver microsomes was monitored by spin trapping with 5,5-dimethylpyrroline N-oxide (DMPO). The results confirm and extend previous data which demonstrated that hydroxyl radicals are produced by microsomes in the presence of NADPH and O2, and without the exogenous addition of iron. No EPR signals could be detected unless catalase activity which was associated with the microsomes could be substantially diminished. Addition of azide was the most effective means of eliminating catalase activity, but azide also reacted rapidly with hydroxyl radicals, forming azidyl radicals which were in turn trapped by DMPO. Extensive washing and preincubation of microsomes with 3-amino-1,2,4-triazole in the presence of H2O2 were evaluated as alternative methods of decreasing the catalase contamination of microsomes. Although neither method completely eliminated microsomal catalase activity, addition of azide was no longer necessary for hydroxyl radical detection with DMPO. When highly washed microsomal preparations were tested, weak signals of the superoxide radical adduct of DMPO could also be detected. These data indicate that the sensitivity of spin trapping in microsomal systems can be improved substantially when care is taken to eliminate cytosolic contaminants such as catalase.

Effect of low flow ischemia-reperfusion injury on liver function.

The release of liver enzymes is typically used to assess tissue damage following ischemia-reperfusion. The present study was designed to determine the impact of ischemia-reperfusion on liver function and compare these findings with enzyme release. Isolated, perfused rat livers were subjected to low flow ischemia followed by reperfusion. Alterations in liver function were determined by comparing rates of oxygen consumption, gluconeogenesis, ureagenesis, and ketogenesis before and after ischemia. Lactate dehydrogenase (LDH) and purine nucleoside phosphorylase (PNP) activities in effluent perfusate were used as markers of parenchymal and endothelial cell injury, respectively. Trypan blue staining was used to localize necrosis. Total glutathione (GSH + GSSG) and oxidized glutathione (GSSG) were measured in the perfusate as indicators of intracellular oxidative stress. LDH activity was increased 2-fold during reperfusion compared to livers kept normoxic for the same time period whereas PNP activity was elevated 5-fold under comparable conditions. Rates of oxygen consumption, gluconeogenesis, and ureagenesis were unchanged after ischemia, but ketogenesis was decreased 40% following 90 min ischemia. During reperfusion, the efflux rates of total glutathione and GSSG were unchanged from pre-ischemic values. Significant midzonal staining of hepatocyte nuclei was observed following ischemia-reperfusion, whereas normoxic livers had only scattered staining of individual cells. Reperfusion of ischemic liver caused release of hepatic enzymes and midzonal cell death, however, several major liver functions were unaffected under these experimental conditions. These data indicate that there were negligible changes in liver function in this model of ischemia and reperfusion despite substantial enzyme release from the liver and midzonal cell death.