Oxygen radical production during ischemia-reperfusion in the isolated perfused rat liver as monitored by luminol enhanced chemiluminescence

Protective effects of (6R)-5,6,7,8-tetrahydro-l-biopterin on local ischemia/reperfusion-induced suppression of reactive hyperemia in rat gingiva

We herein investigated the regulatory mechanism in the circulation responsible for rat gingival reactive hyperemia (RH) associated with ischemia/reperfusion (I/R). RH was analyzed using a laser Doppler flowmeter. RH and I/R were elicited by gingival compression and release with a laser Doppler probe. RH increased in a time-dependent manner when the duration of compression was between 30 s and 20 min. This increase was significantly suppressed by N^ω-nitro-l-arginine-methyl-ester (l-NAME), 7-nitroindazole (7-NI), and 2,4-diamino-6-hydroxypyrimidine (DAHP). However, RH was markedly inhibited following 60 min of compression. This inhibition was significantly decreased by treatments with superoxide dismutase (SOD), (6R)-5,6,7,8-tetrahydro-l-biopterin (BH₄), and sepiapterin. The luminescent intensity of superoxide anion (O₂^•−)-induced 2-methyl-6-(4-methoxyphenyl)-3,7-dihydroimidazo-[1,2-a] pyrazine-3-one (MCLA) was markedly decreased by SOD and BH₄, but only slightly by sepiapterin. BH₄ significantly decreased O₂^•− scavenging activity in a time-dependent manner. These results suggested that nitric oxide (NO) secreted by the nitrergic nerve played a role in regulating local circulation in rat gingiva. This NO-related regulation of local circulation was temporarily inhibited in the gingiva by the I/R treatment. The decrease observed in the production of NO, which was caused by suppression of NO synthase (NOS) activity subsequent to depletion of the NOS co-factor BH₄ by O₂^•−, played a partial role in this inhibition.

Effect of Monascus-fermented products on learning and memory in the SAMP8 mice

The purpose of this study was to evaluate the impact of Monascus-fermented products (MP) as regards certain changes in behavior for SAMP8 mice. Both male and female SAMP8 mice were fed a 0.03% MP diet from 3 mo of age to 11 mo of age. The results indicated that the grading score of passive avoidance behavior was significantly lower in the MP diet groups than in the control diet groups in both male and female SAMP8 mice (p < 0.05). The MP diet-augmented test-animal body weight, feed intake and feed efficiency did not differ significantly from the corresponding values for control mice. The MP diet-fed mouse group revealed significantly improved learning and memory as revealed by average escape-response testing score when comparing with control mice (p < 0.05). Further, the level of serum triglyceride and total cholesterol for the MP-fed group were shown to be significantly lower than for the control group of SAMP8 mice at 11 mo of age. The test mice fed an MP diet appeared to be significantly lower in aging score than the control group (p < 0.05). The MP diet-fed mouse group revealed significantly improved total antioxidation of liver. Subsequent to supplementation of SAMP8 mice diets with MP for a period of 8 mo, these MP-fed mice revealed significantly lower lipofuscin-cell numbers within the hippocampus (p < 0.05). The results suggest that dietary supplementation with MP might improve both learning and memory behaviour, and retard the aging process for SAMP8 mice.

Antioxidant phenolic glucosides from Gentiana piasezkii

An extract of Gentiana piasezkii afforded a new arbutin derivative 6'-O-vanilloylarbutin (1) and a new flavone-C-glucoside 7-O-feruloylorientin (2), together with four known flavonoids lutonarin (3), saponarin (4), isoorient (5) and luteolin (6). Their structures were established based on spectroscopic methods including 2D NMR (COSY and gHMBC) techniques. Compounds 1, 2, 5 and 6 were evaluated for the antioxidant activity in the 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay system.

Free radical scavenging and hepatoprotective actions of the medicinal herb, Crassocephalum crepidioides from the Okinawa Islands

Free radical scavenging and protective actions against chemically induced hepatotoxicity of Crassocephalum crepidioides were investigated. A water extract of C. crepidioides strongly scavenged superoxide anion, hydroxyl radical and also stable radical 1,1-diphenyl-2-picrylhydrazyl. Galactosamine (GalN, 400 mg/kg) and lipopolysaccharide (LPS, 0.5 microg/kg) induced hepatotoxicity of rats as seen by an elevation of serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) and of lipid peroxidation in liver homogenates was significantly depressed when the herbal extract was given intraperitoneally 1 and 15 h before GalN and LPS treatment. Similarly, carbon tetrachloride (CCl4) induced liver injury as evidenced by an increase in AST and ALT activities in serum was also inhibited by the extract pretreatment. Isochlorogenic acids, quercetin and kaempferol glycosides were identified as active components of C. crepidioides with strong free radical scavenging action. These results demonstrate that C. crepidioides is a potent antioxidant and protective against GalN plus LPS- or CCl4-induced hepatotoxicity.

Flavonol glycosides with free radical-scavenging activity of Saururus chinensis

An activity-guided fractionation procedure was used to identify the antioxidative components of the aerial parts of Saururus chinensis. The antioxidant activity was investigated with the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical- and superoxide anion-scavenging assays. Three active compounds (flavonol glycosides) were identified.

2,3,4-Trimethyl-5,7-dihydroxy-2,3-dihydrobenzofuran, a novel antioxidant, from Penicillium citrinum F5

Bioassy-directed fractionation of a culture broth of Penicillium citrinum F5 led to the isolation of a novel antioxidant 2,3,4-trimethyl-5,7-dihydroxy-2,3-dihydrobenzofuran (1), together with gentisic acid (2), and their structures were determined on the basis of spectroscopic data. In the 1,1-diphenyl-picryl-hydrazyl (DPPH) assay system, compounds 1 and 2 showed free radical scavenging activity with IC(20) values of 10.39 and 4.26 microM, respectively.

Antioxidant properties of Thonningianin A, isolated from the African medicinal herb, Thonningia sanguinea

The antioxidant properties of Thonningianin A (Th A), an ellagitannin, isolated from the methanolic extract of the African medicinal herb, Thonningia sanguinea were studied using the NADPH and Fe2+/ascorbate-induced lipid peroxidation (LPO), electron spin resonance spectrometer and the deoxyribose assay. Th A at 10 microM inhibited both the NADPH and Fe2+/ascorbate-induced LPO in rat liver microsomes by 60% without inhibitory effects on cytochrome P450 activity. Th A was similar to the synthetic antioxidant, tannic acid, as an inhibitor of both the NADPH and Fe2+/ascorbate-induced LPO but potent than gallic acid, vitamin C and vitamin E. While Th A poorly scavenged the hydroxyl radical generated by the Fenton reaction it dose-dependently scavenged 1,1-diphenyl-2-picrylhydrazyl, superoxide anion and peroxyl radicals with IC50 of 7.5, 10 and 30 microM, respectively. Furthermore, Th A showed inhibitory effects on the activity of xanthine oxidase with an IC50 of 30 microM. In the deoxyribose assay both T. sanguinea and its methanolic component Th A showed only site-specific (Fe3+ + H2O2) but not non-site-specific (Fe3+ + EDTA + H2O2) hydroxyl radical scavenging suggesting chelating ability for iron ions. Spectroscopic studies showed that Th A enhanced absorbance in the visible region in the presence of Fe2+ ions. These results indicate that the antioxidant properties of Th A involve radical scavenging, anti-superoxide formation and metal chelation.

Free radical scavenging action of the medicinal herb Limonium wrightii from the Okinawa islands

Free radical scavenging action of Limonium wrightii O. kunthe was examined in vitro and in vivo by using electron spin resonance spectrometer and chemiluminescence analyzer. A water extract of L. wrightii showed a strong scavenging action for the 1,1-diphenyl-2-picrylhydrazyl, or superoxide anion and moderate for hydroxyl radical. The extract also depressed production of reactive oxygen species from polymorphonuclear leukocytes stimulated by phorbor-12-mysistate acetate and inhibited lipid peroxidation in rat liver microsomes. When the extract was given intraperitoneally to mice prior to carbon tetrachloride (CCl4) treatment, CCl4-induced liver toxicity, as seen by an elevation of serum aspartate aminotransferase and alanine aminotransferase activities, was significantly reduced. Gallic acid was identified as the active component of L. wrightii with a strong free radical scavenging action. Our results demonstrate the free radical scavenging action of L. wrightii and that gallic acid contributes to these actions.

Sinusoidal endothelial cell injury by superoxide anion and iron in the Propionibacterium acnes-pretreated and lipopolysaccharide-stimulated rat liver

AIMS/BACKGROUND

We attempted to measure the generation of superoxide anion, examine its site of release and determine its pathological role in Propionibacterium acnes-lipopolysaccharide-induced liver injury in the rat.

METHODS

The P. acnes-pretreated (16 mg/kg i.v.) rat liver was perfused with buffer containing lipopolysaccharide (2.5 microg/ml). Chemiluminescence enhanced with Cypridina luciferin analog, MCLA, and reduction of nitro blue tetrazolium were used for detecting superoxide anion. Leakage of enzymes and release of cytokines into the perfusate, and histological specimens were also examined.

RESULTS

Superoxide dismutase-inhibitable chemiluminescence peaked at 30 min of lipopolysaccharide infusion and blue formazan precipitate was histochemically deposited mainly on hepatic macrophages. Purine nucleoside phosphorylase (PNP) activity in the perfusate, as a marker of sinusoidal endothelial cell injury, reached its maximum at 50 min and aspartate aminotransferase (AST) activity, as a marker of hepatocyte injury, reached a plateau at 90 min. Simultaneous treatment with superoxide dismutase and deferoxamine mesylate significantly suppressed the leakage of PNP and AST. Release of tumor necrosis factor-alpha and growth-related oncogene/cytokine-induced neutrophil chemoattractant-1 lagged behind PNP leakage. Light microscopy showed destruction of the sinusoids followed by hepatocyte necrosis. Electron microscopy revealed adherence of hepatic macrophages to sinusoidal endothelial cells.

CONCLUSION

These results indicate that superoxide anion released from hepatic macrophages may induce sinusoidal endothelial cell injury via interaction with iron in the P. acnes-lipopolysaccharide-treated liver.

Dimerumic acid as an antioxidant of the mold, Monascus anka

We previously reported that the mold Monascus anka, traditionally used for fermentation of food, showed antioxidant and hepatoprotective actions against chemically induced liver injuries. In the present study, the antioxidant component of M. anka was isolated and identified. The antioxidant was elucidated to be dimerumic acid. DPPH (1,1-diphenyl-2-picrylhydrazyl) radical was significantly scavenged by the antioxidant whereas hydroxyl radical and superoxide anion were moderately scavenged. When the antioxidant (12 mg/kg) was given to mice prior to carbon tetrachloride (CCl(4), 20 microl/kg, ip) treatment, the CCl(4)-induced liver toxicity in mice seen in an elevation of serum aspartate aminotransferase and alanine aminotransferase activities was depressed, suggesting the hepatoprotective action of the antioxidant. The liver microsomal glutathione S-transferase activity, which is known to be activated by oxidative stress or active metabolites, was increased by CCl(4) treatment and the increase was also depressed by pretreatment with the mold antioxidant. Thus these data confirmed that the dimerumic acid isolated from M. anka is the potential antioxidant and protective against CCl(4)-induced liver injury.

Screening of antioxidant action of various molds and protection of Monascus anka against experimentally induced liver injuries of rats

Antioxidant action of various molds, which are traditionally used for the production of foods or alcoholic beverages in Japan, was studied in vitro and in vivo. Antioxidant action was evaluated by scavenging stable free radical 1,1-diphenyl-2-picrylhydrazyl (DPPH) and lipid peroxidation of rat liver microsomes. Among 40 molds, 16 species showed the DPPH scavenging action, and the molds that can scavenge the DPPH radical inhibited lipid peroxidation. The mold with the strongest action, Monascus anka, was chosen for the investigation of a protective action against liver injury of rats. When galactosamine (GalN, 400 mg/kg) or GalN plus lipopolysaccharide (LPS, 0.5 microg/kg) was given intraperitoneally to rats (Sprague-Dawley), aspartate aminotransferase (AST) and glutathione (GSH) S-transferase (GST) activities in serum were significantly increased. However, such hepatotoxicities seen in the increase in serum enzyme levels were depressed when the extract prepared from M. anka was given 1 and 15 h before the toxic insultant. Liver microsomal GST activity, which is known to be activated by oxidative stress, was increased by GalN or GaIN plus LPS treatment and the increase was also inhibited by pretreatment with the extract. Pathomorphological changes in the liver caused by GalN treatment also were prevented by the mold extract. These results indicate that the extract of M. anka has radical scavenging action and ameliorates chemically induced hepatotoxicity.

Chemiluminescent real time imaging of post-ischemic oxygen free radicals formation in livers isolated from young and old rats

Oxygen free radicals generation is a major cause of liver injury during reperfusion. Luminescence analysis has been recently proposed to measure free radical generation by isolated cells or organs, but it allows only global tissue luminescence. Using a special Saticon videocamera with image intensifier we aimed to visualize and localize oxygen free radical generation in isolated perfused livers exposed to an oxydative stress. Livers isolated from rats aged 4 and 30 months were exposed to ischemia/reperfusion; photons emission by the organs was continuously recorded. Lucigenin was utilized as a chemiluminigenic probe to assess superoxide anion generation. In both groups, chemiluminescence was not detectable during ischemia, while it was observed after reperfusion. Photons emission started after few minutes of reperfusion, was maximal after 15-20 min and disappeared within 50-60 min. Chemiluminescence emitted by livers from younger rats however, was significantly higher when compared to chemiluminescence emitted by organs isolated from old rats (0.8 +/- 0.1 vs 0.44 +/- 0.08 photons x 10(5)/s, respectively, after 15 min; p < .01). The superimposition of chemiluminescent and live image permitted to determine the regional production rate and distribution of photons. In conclusion, the age of the rats influences significantly the amount of oxyradicals produced in the liver during post-ischemic reperfusion. The method described, allowing the visualization in real time of oxygen free radicals generation on the surface of isolated intact organs, represents a novel and potent tool for the study of oxidative stress.

Generation of free radicals during anoxia and reoxygenation in perfused osteoblastlike cells

Sensitivity to ischemia and reperfusion injury is a main problem afflicting tissues exposed to a prolonged period of oxygen deprivation. The generation of oxygen free radicals, in particular, is considered a major cause of postischemic reperfusion injury. However, studies on the mechanisms of production of free radicals are limited by the difficulty to measure in real time their formation and to discriminate between the different oxyradical species. The aim of this study was to determine whether the formation of oxygen free radicals occurs in murine osteoblastlike cells (MC3T3-E1) exposed to anoxia and reoxygenation and to explore its relation to the reoxygenation injury. Cells were cast in agarose and perfused with oxygenated Krebs-Henseleit bicarbonate buffer. Anoxia was obtained by shifting the gas phase of the media to 95% N2-5% CO2. Oxygen free radicals were detected by enhanced chemiluminescence: anion superoxide or hydrogen peroxide was measured by adding lucigenin or luminol plus horseradish peroxidase to the media, respectively. Cell injury was assessed by the rate of lactate dehydrogenase release. During the control period, lucigenin and luminol plus horseradish chemiluminescences were 15 +/- 1 nA per chamber and 20 +/- 2 nA per chamber, respectively. and lactate dehydrogenase release was 10 +/- 1 mU per minute. During anoxia, both chemiluminescences dropped to background levels, although lactate dehydrogenase release increased progressively to 38 +/- 7 mU per minute. During reoxygenation, O2 formation increased sharply to 45 +/- 6 nA and decreased to control levels; H2O2 production increased slowly, reaching 42 +/- 7 nA at the end of the reoxygenation period; lactate dehydrogenase declined progressively to control values. These results show that osteoblastlike cells produce measurable amounts of superoxide and hydrogen peroxide radicals during reoxygenation. Because lactate dehydrogenase release did not appear to relate to chemiluminescence, oxyradical flux may serve as a signal for other events that eventually lead to cell injury.

Effect of diethylmaleate on liver extracellular glutathione levels before and after global liver ischemia in anesthetized rats

Glutathione (GSH), present in a high concentration in the liver, serves important protective functions. We investigated the effect of lowered tissue GSH content, accomplished by diethylmaleate (DEM) administration, on liver extracellular GSH levels before and after global ischemia in anesthetized rats. Liver extracellular GSH levels were determined by microdialysis perfusion and an on-line high performance liquid chromatography system. Global liver ischemia was induced by ligation of the hepatic pedicles including the hepatic artery, portal vein, and bile duct. DEM (4 mmol/kg) significantly lowered both the liver tissue GSH levels (1.36 +/- 0.26 micromol/g wet wt vs 9.50 +/- 0.55 micromol/g wet wt for the untreated) and the liver extracellular GSH levels (4.3 +/- 2.4 microM vs 25.2 +/- 8.7 microM for the untreated). Global liver ischemia induced a dramatic increase in the liver extracellular GSH level. Although the liver tissue GSH level was lowered following DEM treatment, DEM administration did not affect significantly ischemia-induced elevation of extracellular GSH (when presented as fold increase relative to basal value). In conclusion, DEM showed a direct effect on liver extracellular GSH content in anesthetized rats. However, DEM treatment did not affect the relative release of GSH following global liver ischemia.

Therapeutic modulation of free radical-mediated reperfusion injury of the liver and its surgical implications

It is well known that ischemia causes functional and structural damage to liver cells, and that the status of energy metabolism provides an important means of assessing the functional viability of the ischemic organ. However, the specific sequence leading to ischemic liver cell injury is not yet fully understood; therefore, it is clinically and pathophysiologically important to elucidate the mechanism of cellular injury during hepatic ischemia and subsequent reperfusion. Whereas the conventional view attributes this injury process to the ischemia itself, recent studies have demonstrated that a variable but often substantial proportion of this injury is caused by reactive oxygen metabolites that are generated at the time of reperfusion. This article presents an outline of the mechanism of cellular injury caused during hepatic ischemia and subsequent reperfusion resulting from certain types of surgery, with special reference to the xanthine-xanthine oxidase system and the activation of neutrophils and macrophages.

Protective effect of natural flavonoids on rat peritoneal macrophages injury caused by asbestos fibers

Exposure of macrophages to asbestos fibers resulted in enhancement of the production of oxygen radicals, determined by a lucigenin enhanced chemiluminescence (LEC) assay, a formation of thiobarbituric acid reactive substances (TBARS), a LDH release into the incubation mixture, and a rapid lysis of the cells. Rutin (Rut) and quercetin (Qr) were effective in inhibiting LEC, TBARS formation, and reducing peritoneal macrophages injury caused by asbestos. The concentrations pre-treatment of antioxidants that were required to prevent the injury of peritoneal macrophages caused by asbestos by 50% (IC50) were 90 microM and 290 microM for Qr and Rut, respectively. Both flavonoids were found to be oxidized during exposure of peritoneal macrophages to asbestos and the oxidation was SOD sensitive. The efficacy of flavonoids as antioxidant agents as well as superoxide ion scavengers was also evaluated using appropriate model systems, and both quercetin and rutin were found to be effective in scavenging O2.-. These findings indicate that flavonoids are able to prevent the respiratory burst in rat peritoneal macrophages exposed to asbestos at the stage of activated oxygen species generation, mainly as superoxide scavengers. On the basis of this study it was concluded that natural flavonoids quercetin and rutin would be promising drug candidates for a prophylactic asbestos-induced disease.

Global cerebral ischemia in the rat: online monitoring of oxygen free radical production using chemiluminescence in vivo

Using online in vivo chemiluminescence (CL), we studied for the first time continuously the production of reactive oxygen species (ROS) after global cerebral ischemia and the relationship of ROS production to CBF. In anesthetized rats equipped with a closed cranial window, the CL enhancer, lucigenin (1 mM), was superfused onto the brain topically. CL was measured through the cranial window with a cooled photomultiplier, and CBF was measured simultaneously with laser-Doppler flowmetry. Reperfusion after 10 min (n = 8) of global cerebral ischemia led to a CL peak to 188 +/- 77% (baseline = 100%) within 10 +/- 4 min. After 2 h of reperfusion, CL had returned to 102 +/- 28%. Reperfusion after 20 min (n = 8) of ischemia increased CL to 225 +/- 48% within 12 +/- 3 min. After 2 h, CL was still increased (150 +/- 44%, p < 0.05 compared with 10 min of ischemia). CL after 10 min of ischemia was neither affected by brain topical free CuZn-superoxide dismutase (SOD) (100 U/ml, n = 3) nor by i.v. administration of free CuZn-SOD (104 U/kg, followed by 104 U/kg/h, n = 3). The CBF hyperfusion peak on reperfusion preceded the CL peak in all experiments by several minutes. In additional in vitro experiments we investigated the source of CL: Intracellular loading of lucigenin was demonstrated in cultured CNS cells, and a very similar pattern of CL as in the in vivo preparation after ischemia developed in rat brain slices after 15 min of hypoxia, which was unaffected by free CuZn-SOD (100 U/ml) but strongly attenuated by liposome-entrapped CuZn-SOD. We conclude that lucigenin-enhanced CL is a promising tool to study ROS production continuously from the in vivo brain of experimental animals and brain slices, and that the CL signal most likely derives from the intracellular production of superoxide. The production of ROS is preceded by reperfusion, is burst-like, and is dependent on the duration of the ischemic interval.

Hepatocyte injury resulting from the inhibition of mitochondrial respiration at low oxygen concentrations involves reductive stress and oxygen activation

By correlating lactate/pyruvate ratios and ATP levels, cytotoxicity induced by the mitochondrial respiratory inhibitors or hypoxia:reoxygenation injury can be attributed not only to ATP depletion but also to reductive stress and oxygen activation. Thus hypoxia, cyanide or antimycin markedly increases reductive stress, non-heme Fe release and H2O2 formation in hepatocytes. Cytotoxicity was partly prevented with the ferric chelator desferoxamine, the xanthine oxidase inhibitor oxypurinol and the hydrogen peroxide scavenger glutathione. No lipid peroxidation could be detected and phenolic anti-oxidants had little effect. However, polyphenolic antioxidants or the superoxide dismutase mimics TEMPO or TEMPOL partly prevented cytotoxicity. Furthermore, increasing the hepatocyte NADH/NAD+ ratio with NADH generating compounds such as ethanol, glycerol, or beta-hydroxybutyrate markedly increased cytotoxicity (prevented by desferoxamine) and further increased the intracellular release of non-heme iron. Cytotoxicity could be prevented by glycolytic substrates (eg. fructose, dihydroxyacetone, glyceraldehyde) or the NADH utilising substrates acetoacetate or acetaldehyde which decreased the reductive stress and prevented intracellular iron release. These results suggest that liver injury resulting from insufficient respiration involves reductive stress which releases intracellular Fe, converts xanthine dehydrogenase to xanthine oxidase and causes mitochondrial oxygen activation. The cell's antioxidant defences are compromised and ATP catabolism contributes to oxygen activation.

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.

Ethanol stimulates chemiluminescence from neutrophils in the liver

The production of free radicals in tissues can be continually monitored by measurement of low-level chemiluminescence. In these experiments the effects of ethanol on luminol (1 microM)-enhanced chemiluminescence were recorded in isolated perfused livers from control rats, and from rats that had undergone a 30-min period of ischemia, followed by 3 h of reinstitution of blood flow. Our previous experiments showed considerable neutrophil accumulation at this time. A routine concentration of 100 mM ethanol added after 20 min of perfusion with Krebs-Henseleit solution caused an increase in chemiluminescence of about 2000 cpm above the resting level (1600 cpm) in both control livers and livers from rats after 3 h of ischemia reperfusion in vivo. However, if ethanol was added to the perfusing medium of the isolated liver after at least 1 h of in vitro perfusion, then the magnitude of the response was very much greater (peak approximately 27000 cpm) in livers that had undergone ischemia reperfusion than in control livers (peak approximately 7000 cpm). Experiments combining addition of ethanol and the potent neutrophil stimulator, phorbol myristate acetate (PMA), plus the use of rat antineutrophil serum have shown conclusively that the very large chemiluminescent response to ethanol after prolonged in vitro perfusion is due to stimulation of neutrophil radical production.

Reactive oxygen inducing vasoconstriction in the isolated perfused rat liver

The effect of reactive oxygen generation on intact livers was studied. Production of reactive oxygen species in perfused livers isolated from normal and endotoxin-treated rats was measured using chemically enhanced chemiluminescence. The resting state chemiluminescence of the livers increased on endotoxin administration and was maximal about 6 h after treatment. Chemiluminescence from the livers was further stimulated severalfold by inclusion of phorbol myristate acetate in the perfusion medium, reaching maximum intensity 3 h after endotoxin treatment. Oxygen consumption by the endotoxin-treated liver showed a transient increase followed by a significant decrease on phorbol myristate acetate stimulation, which was inhibited by dexamethasone. These results are consistent with the occurrence of a respiratory burst followed by oxygen-radical-species-induced vasoconstriction in the intact perfused liver. The evaluation of reactive oxygen species by resident and accumulated macrophages in the intact liver is made possible by these studies, and related effects on the liver could be conveniently and quantitatively followed using this model.

Free radicals in cutaneous biology

During the past 25 years, the field of free radical biology has germinated, sprouted, and flowered. Free radicals derived from molecular oxygen, formerly of interest only to radiation chemists, are now known to play multiple roles in living systems. We will here consider the generalities of this field with some special focus on skin as a site of oxygen radical production and as a target upon which the damaging propensities of these radicals are exerted.

The first application of a chemiluminescence probe, 2-methyl-6-[p-methoxyphenyl]-3,7-dihydroimidazo[1,2-a]pyrazin-3-one (MCLA), for detecting O2- production, in vitro, from Kupffer cells stimulated by phorbol myristate acetate

The purpose of this study was to investigate the generation of superoxide anion radical, O2-, by Kupffer cells in vivo in rat liver. Phorbol myristate acetate (PMA) was infused into perfused rat liver which had been continuously infused with 2-methyl-6-[p-methoxyphenyl]-3,7-dihydroimidazo- [1,2-a]pyrazin-3-one (MCLA, a highly sensitive luminescence reagent for O2-) and the MCLA luminescence from the liver surface was detected with a sensitive photon counter. Under identical conditions, but without MCLA infusion, PMA and nitro blue tetrazolium were infused to verify generation of O2- by formation of formazan deposition. Based on MCLA luminescence and formazan deposition, both dependent on the O2- reaction, we have concluded that liver Kupffer cells generate O2- in vivo in response to stimuli such as PMA. Further, the generation of O2- by Kupffer cells may be by the same mechanism as displayed by macrophages.

Chemiluminescent response to PMA in isolated rat liver after in situ ischemia-reperfusion

The median and left lateral lobes of rat liver in situ were rendered ischemic for 30 min, then blood flow reinstituted. After 1, 3, 6, 24, or 48 h, livers were removed and set up for isolated perfused organ study. Luminol enhanced chemiluminescence (LEC) was recorded from the surface of the median and left lateral lobes before and for 90 min following phorbol myristate acetate (PMA, 1.6 x 10(-8) M) perfusion. An increase in PMA induced LEC was evident at 1 h and continued to increase up to 6 h. By 24 h the magnitude of the PMA response had returned to within control values. This indicates that a large influx of inflammatory cells had occurred in the liver following the in vivo ischemia-reperfusion insult and that these cells were well fixed in the tissue and capable of mounting a very large and sustained burst of radical production on stimulation with PMA. This combined in vivo/in vitro technique is ideally suited for the assessment of interventions designed to ameliorate damage following oxidative stress.

Oxidative stress-induced activation of microsomal glutathione S-transferase in isolated rat liver

The activation of microsomal glutathione (GSH) S-transferase in isolated rat liver by oxidative stress was investigated using both ischemia/reperfusion and perfusion with hydrogen peroxide. When the isolated liver was reperfused for 30 min and 60 min after 90 min ischemia, microsomal GSH S-transferase activity, but not cytosolic transferase activity, was increased 1.2-fold and 1.3-fold, respectively. In addition, microsomal GSH peroxidase activity was also significantly increased after 60 min reperfusion following ischemia. The increase in microsomal GSH S-transferase activity by ischemia/reperfusion was reversed by dithiothreitol. When N-ethylmaleimide, which activates microsomal GSH S-transferase by covalent binding to the cysteine residue of the enzyme, was incubated with microsomes, transferase activity was increased to 526% in control microsomes and to 399% in liver that underwent ischemia/reperfusion liver. These data indicate that microsomal GSH S-transferase is activated by ischemia/reperfusion of the liver by means of disulfide bond formation. When rats were pretreated with a catalase inhibitor 3-amino-1,2,4-triazole for 6 weeks, microsomal GSH S-transferase activity was increased 1.4-fold by ischemia/reperfusion, corresponding to a 1.8-fold increase as compared to the non-perfused liver of untreated rats. Perfusion of the isolated liver with hydrogen peroxide (1 mM, 15 min) also caused a significant increase in microsomal GSH S-transferase activity with a concomitant decrease in GSH content, confirming that liver microsomal GSH S-transferase in rats was activated in vivo by oxidative stress.

Parenchymal and vascular endothelial cell injury in the hypoxic and reperfused rat liver. Evidence for superoxide anion generation by perfusion with ferricytochrome c

Isolated perfused livers from rats fasted overnight were subjected to 90 min of low-flow hypoxia followed by reoxygenation for 30 min. Intra-hepatic generation of superoxide anion was analysed by continuous perfusion with 40 mumol/l of oxidized cytochrome c, the reduction of which was measured spectrophotometrically in the effluate. Reduction of cytochrome c as an indicator for hepatic superoxide anion generation remained constant during pre-hypoxic perfusion and during hypoxia. Upon reperfusion, an initial peak was observed to 47.2 +/- 3.8 nmol/g/min followed by a stable plateau above pre-hypoxic values. Both peak and plateau were significantly attenuated in the presence of 80,000 U/l superoxide dismutase (SOD). Accordingly, tissue contents of lipid peroxides were significantly lower at the end of reperfusion (976 +/- 73 vs 1153 +/- 71 nmol/g*), enzyme leakage [U/g/min] from the endothelium (PNP: 8.4 +/- 4.2 vs 17.2 +/- 3.4**) and from the hepatic parenchyma (Alt: 108 +/- 35 vs 170 +/- 23*) was significantly reduced during reperfusion and oxygen consumption was elevated in the presence of SOD (3.27 +/- 0.34 vs 2.71 +/- 0.37*). It is concluded that reactive oxygen species arise in the vascular lumen or the space of Disse after prolonged hypoxia of the liver, altering the functional outcome of the organ upon reoxygenation. SOD is able to protect against these alterations. * P < 0.05; ** P < 0.01.

Effect of antioxidants on hypoxia/reoxygenation-induced injury in isolated perfused rat liver

Isolated perfused livers from rats fasted overnight were subjected to 30 min. of hypoxia followed by reoxygenation for 60 min., resulting in marked cytotoxicity as evidenced by an enhanced release of cytosolic enzymes (lactate dehydrogenase: 14-fold over controls, glutamate-pyruvate-transaminase: 12-fold over controls) and glutathione (twofold over controls) into the perfusate, by calcium accumulation (by a factor of 1.4) in the tissue and by an 80% inhibition of bile secretion. Virtually no mitochondrial injury became apparent and no evidence for lipid peroxidation could be found. In the presence of ascorbate, an augmentation of hepatic injury was observed. This might be due to the pro-oxidant activity of ascorbate in the presence of ionized iron, which is easily released from high molecular weight stores under reductive (e.g. hypoxic) conditions. The water soluble vitamin E analogue trolox C as well as propyl gallate clearly protected the liver against hypoxia/reoxygenation injury, yielding further evidence for a causative role of oxidative stress in this model. Due to their water solubility and their high efficacy as free radical scavengers, these antioxidants might be of therapeutic value.

Comparison of the effect of a mitochondrial uncoupler, 2,4-dinitrophenol and adrenaline on oxygen radical production in the isolated perfused rat liver

Using the isolated perfused rat liver, we examined the effect of stimulation of mitochondrial respiration by 2,4-dinitrophenol (2,4-DNP) and adrenaline on reactive oxygen species (ROS) production, liver damage and lipid peroxidation. ROS production was monitored by luminol- and lucigenin-enhanced chemiluminescence and oxygen uptake was measured simultaneously. Liver damage and lipid peroxidation were evaluated by measuring hepatic lactate dehydrogenase (LDH) and thiobarbituric acid reacting substances (TBARS) release. Tissue ROS level decreased and oxygen uptake increased soon after 2,4-DNP infusion. On termination of 2,4-DNP infusion, there was a sharp increase in lucigenin-enhanced chemiluminescence, which declined slowly, but luminol-enhanced chemiluminescence did not change prominently. Hepatic LDH and TBARS release increased gradually during 2,4-DNP infusion and were manifested by termination of the infusion. Allopurinol did not affect ROS production and TBARS release, but delayed increases in LDH release after termination of 2,4-DNP infusion. Adrenaline, which stimulates mitochondrial respiration without uncoupling caused similar but smaller ROS changes observed in 2,4-DNP. LDH and TBARS release were not affected significantly by adrenaline infusion. These results indicate that uncoupling of oxidative phosphorylation decreases ROS production and restoration of oxidative phosphorylation enhances ROS production and liver damage. Xanthine oxidase is unlikely to contribute to enhanced ROS production after termination of 2,4-DNP but has some protective effect during uncoupling.

Glutathione and ischemia-reperfusion injury in the perfused rat liver

Using the isolated perfused rat liver, we investigated the relationship of glutathione (GSH) with reactive oxygen species (ROS) generation and liver cell damage during ischemia/reperfusion in normal and GSH-depleted conditions. Lucigenin-enhanced chemiluminescence was used as a sensitive index of tissue ROS generation. After 30 minutes of equilibration, livers were subjected to global ischemia for various times (60 or 90 minutes) and then reperfused for another 120 minutes. Intracellular ROS levels increased sharply at the onset of reperfusion and then declined slowly. After 30 to 60 minutes of reperfusion, ROS levels started to increase progressively in a linear fashion. However, sinusoidal glutathione disulfide release did not increase during reperfusion in the same livers, suggesting that intracellular ROS generation is too low to cause a significant increase in GSH oxidation. Pretreatment with phorone (300 mg/kg intrapentoneally [ip]), which reduced hepatic GSH by 90%, did not cause any difference in intracellular ROS generation compared with the control livers. There were also no significant differences in lactate dehydrogenase and thiobarbituric acid reactive substances (TBARS) release between the control and phorone-treated livers during reperfusion after various times of ischemia. These data indicate that ROS generation in the normal isolated perfused liver during ischemia/reperfusion is extremely low and intracellular GSH does not serve as a major intracellular defense system against such a low oxidative stress.