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

Effect of dietary fats on oxidative-antioxidative status of blood in rats

This study was performed to examine the effect of different fat sources, lard, sunflower oil (SO), and fish oil (FO) in high-fat and low-fat diet on reactive oxygen species generation by blood phagocytes, glutathione redox status in erythrocytes, and total plasma antioxidant ability in rats. Whole blood chemiluminescence (CL) did not differ between three low-fat fed groups. However, baseline and phorbol myristate acetate (PMA)-stimulated CL in blood of high-lard fed rats were lower than in low-lard and high-SO fed animals. Phagocyte-stimulated oxidative burst was higher in rats fed high-SO diet than in those fed low-SO and high-FO diets. The highest level of oxidize glutathione (GSSH), the lowest reduce glutathione (GSH)/GSSG ratio in erythrocytes, and the highest plasma activity to reduce ferric ions were observed in rats fed both diets contaning linoleic acid-rich sunflower oil compared to animals fed the corresponding energy from other fats. 1,1-diphenyl-2-picrylhydrazyl radical scavenging activity of plasma was lower in high-lard and high-FO fed rats compared to the corresponding low-fat diets, and the lowest in low-FO fed rats among low-fat fed animals. We presume from our results that linoleic acid may have dual effect, prooxidative in blood cells but maintaining total antioxidant plasma ability.

Protective effects of magnesium isoglycyrrhizinate on liver function in patients after liver resection

AIM: To investigate the protective effects of magnesium isoglycyrrhizinate on liver function in patients after liver resection.

METHODS: Sixty-four patients undergoing liver resection were randomly divided into experimental group and control group. The experimental group was given magnesium isoglycyrrhizinate 150 mg at the beginning of the operation and postoperatively for 7 days, while the control group was not given the drug. The fasting ALT, AST, TBIL, DBIL, GGT and ALP levels were determined before operation and on days 1, 3 and 7 after operation.

RESULTS: Postoperative ALT and AST (except on day 3) levels in the experimental group were significantly lower than those in the control group (P < 0.05 or 0.01). On day 7 after operation, serum ALT levels returned to normal in 20 patients (64.5%) in the experimental group. Adverse reactions such as pseudohyperaldosteronism did not occur during the treatment course.

CONCLUSION: Magnesium isoglycyrrhizinate can inhibit the rapid increase in the levels of liver enzymes, particularly serum transaminase, and reduce complications in patients after hepatectomy, and is therefore suitable for perioperative use in these patients.

Differential effects of relaxation techniques on ultraweak photon emission

BACKGROUND

Evidence has accumulated favoring the possible role of oxidative stress in the pathogenesis of many chronic diseases. Meditation is utilized as an adjunct to conventional medical treatment for several clinical conditions. A few studies suggest a role of long-term meditation in the control of the free-radical metabolism. Many techniques for recording reactive oxygen species (ROS) have been made available. However, most are invasive and none are applicable to all conditions. Attention has recently been drawn to spontaneous ultraweak photon emission (UPE). However, the application of this method in meditation studies is very limited.

OBJECTIVE

The present study recorded spontaneous UPE at multiple anatomic locations of subjects with long-term experience in transcendental meditation (TM) and compared this with a group that practiced other meditation techniques (OMT) and with subjects having no meditation experience.

METHODS

The study examined the anatomic pattern of UPE of 20 subjects practicing TM, compared to 20 subjects practicing OMT, and 20 control subjects with no experience in meditation. Subjects were men who were reported to be healthy and nonsmokers. Meditation was not practiced on the day prior to recording. UPE was recorded in a dark room, using a highly sensitive, cooled photomultiplier system designed for manipulation in three directions. The protocol for the multisite registration of UPE included recording 12 anatomic locations, including the anterior torso, head, neck, and hands.

RESULTS

Data demonstrated emission intensities in the TM and OMT groups that were 27% and 17% lower, respectively, compared to the control group. The decrease was recorded at all anatomic locations. The percent emission contribution of each location to total emission was very similar for the three groups.

CONCLUSIONS

Data supported the hypothesis that persistent meditation resulted in decreased UPE. However, the determination of oxidation levels as the source of group differences needs to be verified further to confirm our hypothesis.

Effect of MG132 on proteasome activity and prooxidant/antioxidant status of rat liver subjected to ischemia/reperfusion injury

AIM

Previous studies have shown that proteasome inhibitors exerted protective effects against ischemia/reperfusion injury (IRI) of brain, heart, kidney and intestine. The aim of the present study was to investigate: (i) whether the proteasome inhibitor MG132 protects rat liver against IRI; and (ii) whether MG132 modulates prooxidant/antioxidant status of rat liver subjected to warm IRI.

METHODS

The left lateral and medial lobes (approximately 70% of the total liver volume) of livers of male Wistar rats were subjected to 30-min ischemia followed by 60-min reperfusion. Lactate dehydrogenase (LDH), aspartate aminotransferase (AST), and alanine aminotransferase (ALT) levels were measured in the plasma. Proteasome chymotryptic-like (ChT-L) activity, levels of thiobarbituric acid-reactive substances (TBARS), protein carbonyls (PC) and glutathione (GSH), as well as superoxidase dismutase (SOD), catalase (CAT), glutathionine peroxidase and glutathionine reductase activities were measured in liver fractions.

RESULTS

Thirty-min ischemia followed by 60-min reperfusion increased liver TBARS and PC, CAT and SOD activities, but decreased GSH level. Ischemia/reperfusion-induced oxidative stress was exacerbated in mitochondria, indicating that these organelles are the preferential target of IRI. Plasma LDH and AST levels were decreased by MG132 during both ischemia and reperfusion, while ALT values were decreased only after 30 min of reperfusion. MG132 did not significantly affect liver TBARS and GSH levels, but it increased PC and decreased ChT-L activity; the activities of CAT and SOD were also decreased.

CONCLUSIONS

MG132 exerts a protective effect during the early phase of reperfusion and it modulates prooxidant/antioxidant status of rat liver subjected to warm IRI.

Real time endoscopic imaging of oxyradical generation in pig stomach during ischemia-reperfusion

BACKGROUND

Oxygen-free radicals generation is considered to be a major cause of gastric injury during reperfusion. Chemiluminescence has been used to assess real-time free radical release on the surface of isolated organs.

AIMS

To evaluate the combined use of chemiluminescence and gastroendoscopy techniques and to assess the real-time production of free radicals during ischemic damage of the gastric wall in an animal model.

PATIENTS AND METHODS

For the experiment, an optical junction was set up between a fibroendoscope and a luminograph apparatus. Three pigs were submitted to gastrofibroendoscopy before, during and after 30 min of clamping of the coeliac artery. Under basal conditions, at the end of the ischemic phase and at the beginning of reperfusion, 1 mM of lucigenin, a specific superoxide enhancer, was injected in the left gastric artery of the animal. The endoscopic live images and chemiluminescence emission were recorded and successively superimposed to measure rate and spatial distribution of photon emission (photons/s).

RESULTS

Free radical production was not observed under basal conditions or during the ischemic phase, but significantly increased during reperfusion reaching a maximum peak after 15 min (0.6+/-0.2 photons x 10(5)/s) and decreased progressively thereafter. The superimposition of live and chemiluminescence images allowed the determination of the regional production rate and distribution of photons.

CONCLUSIONS

Preliminary observations, in an animal model, on an innovative imaging system which allows the visualization of rate and spatial distribution of reactive oxygen species formation are presented. This new endoscopic technique could be useful for the assessment of oxidative gastric mucosal injury in several gastric diseases; however, further studies remain necessary to determine the applicability of this technique in humans.

Kupffer cell activation after no-flow ischemia versus hemorrhagic shock

Kupffer cell-derived oxidant stress is critical for reperfusion injury after no-flow ischemia. However, the importance of Kupffer cells as source of reactive oxygen formation is unclear in a hemorrhagic shock model. Therefore, we evaluated Kupffer cell activation after 60 or 120 min of hemorrhage and 90 min of resuscitation (HS/RS) in pentobarbital-anesthetized male Fischer rats. Plasma glutathione disulfide (GSSG) as indicator for a vascular oxidant stress showed no significant changes after HS/RS. Plasma ALT activities were only moderately increased (100-200 U/L). Kupffer cells isolated from postischemic livers did not generate more superoxide than cells from sham controls. In contrast, the 10-fold increase of plasma GSSG and the 9-fold higher spontaneous superoxide formation of Kupffer cells after 60 min of hepatic no-flow ischemia followed by 90 min of reperfusion demonstrated the activation of Kupffer cells in this experimental model. Plasma ALT activities (1930 +/- 240 U/L) indicated severe liver injury. These results demonstrate a fundamental difference in the degree of Kupffer cell activation between the two models of warm hepatic ischemia. Our findings suggest that different therapeutic strategies are necessary to ameliorate the initial injury after low flow ischemia (hemorrhage) compared to cold (transplantation) or warm (Pringle maneuver) no-flow ischemia.

Increased generation of reactive oxygen species in isolated rat fatty liver during postischemic reoxygenation

BACKGROUND

Whether fatty infiltration of the liver influences the generation of reactive oxygen species (ROS) during reperfusion is unclear. Thus, this study aimed to compare the ROS formation that occurs during postanoxic reoxygenation in isolated normal and fatty livers.

METHODS

Isolated livers from fed Sprague-Dawley rats with normal or fatty livers induced by a choline-deficient diet were reperfused at 37 degrees C for 60 min with an oxygenated medium containing 10 microM of lucigenin after 1 hr of warm ischemia. Superoxide anion generation was assessed by the chemiluminescence (CLS) signal emitted from the organ surface. The hepatic content of malondialdehyde (MDA) and glutathione was determined at the end of reperfusion. Tissue injury was evaluated by the liver histology and the alanine aminotransferase (ALT) release in the perfusate.

RESULTS

CLS started rapidly with reoxygenation and it diffused to the whole organ in both groups. However, CLS emission was significantly higher in fatty liver (after 10 min: 812.425+/-39.898 vs. 294.525+/-21.068 photons/cm2/sec; P<0.01). A greater concentration of MDA was measured at the end of reoxygenation in fatty liver. Finally, the liver histology and the ALT release indicated a greater injury in steatotic than normal liver.

CONCLUSIONS

The CLS technique allows a direct visualization and comparison of ROS generation from the organ surface. Fatty infiltration increases ROS generation in the liver during postischemic reoxygenation, likely leading to the greater lipid peroxidation observed in these experiments. The increased oxidative stress may contribute to the reduced tolerance of steatotic livers to ischemia-reperfusion injury.

Marked difference in tumor necrosis factor-alpha expression in warm ischemia- and cold ischemia-reperfusion of the rat liver

Although tumor necrosis factor-alpha has been implicated in liver injury after both warm ischemia- and cold ischemia-reperfusion, it is unclear whether reactivity of the liver to these stimuli is similar with regard to cytokine expression. Here we compare the effects of warm and cold ischemia on tumor necrosis factor-alpha expression and test the hypothesis that cold ischemia preceding warm ischemia causes overexpression of this cytokine. Rat livers were flushed out with University of Wisconsin solution and subjected to varying periods of warm ischemia, cold ischemia, or cold ischemia plus warm ischemia followed by reperfusion using a blood-free perfusion model. Tumor necrosis factor-alpha and interleukin-10 release into the perfusate and bile were measured by ELISA, and expression of these cytokines and that of c-fos, c-jun, and c-myc were studied by reverse-transcriptase polymerase chain reaction. We found high levels of tumor necrosis factor-alpha in the perfusates of livers subjected to warm ischemia-reperfusion, whereas minimal or no tumor necrosis factor-alpha was detected in livers subjected to cold ischemia-reperfusion or to cold ischemia plus warm ischemia-reperfusion. Reverse-transcriptase polymerase chain reaction confirmed the above findings and showed that immediate early genes were expressed in reperfused groups of livers. Measurements of cytokine release into bile showed that neither tumor necrosis factor-alpha nor interleukin-10 were upregulated by cold ischemia-reperfusion. The results suggest that (1) warm ischemia- and cold ischemia-reperfusion of rat liver lead to very different outcomes with regard to tumor necrosis factor-alpha expression and (2) cold ischemia preceding warm ischemia prevents upregulation of tumor necrosis factor-alpha.

Effects of 5-aminoisoquinolinone, a water-soluble, potent inhibitor of the activity of poly (ADP-ribose) polymerase on the organ injury and dysfunction caused by haemorrhagic shock

Poly (ADP-ribose) synthetase (PARP) is a nuclear enzyme activated by strand breaks in DNA, which are caused inter alia by reactive oxygen species (ROS). Here we report on (i) a new synthesis of a water-soluble and potent PARP inhibitor, 5-aminoisoquinolinone (5-AIQ) and (ii) investigate the effects of 5-AIQ on the circulatory failure and the organ injury/dysfunction caused by haemorrhage and resuscitation in the anaesthetized rat. Exposure of human cardiac myoblasts (Girardi cells) to hydrogen peroxide (H(2)O(2), 3 mM for 1 h, n=9) caused a substantial increase in PARP activity. Pre-treatment of these cells with 5-AIQ (1 microM - 1 mM, 10 min prior to H(2)O(2)) caused a concentration-dependent inhibition of PARP activity (IC(50): approximately 0.01 mM, n=6). Haemorrhage and resuscitation resulted (within 4 h after resuscitation) in a delayed fall in blood pressure (circulatory failure) as well as in rises in the serum levels of (i) urea and creatinine (renal dysfunction), (ii) aspartate aminotransferase (AST), alanine aminotransferase (ALT), and gamma-glutamyl-transferase (gamma-GT) (liver injury and dysfunction), (iii) lipase (pancreatic injury) and (iv) creatine kinase (CK) (neuromuscular injury) (n=10). Administration (5 min prior to resuscitation of 5-AIQ) (0.03 mg kg(-1) i.v., n=8, or 0.3 mg kg(-1) i.v., n=10) reduced (in a dose-related fashion) the multiple organ injury and dysfunction, but did not affect the circulatory failure, associated with haemorrhagic shock. Thus, 5-AIQ abolishes the multiple organ injury caused by severe haemorrhage and resuscitation.

Effects of inhibitors of the activity of poly (ADP-ribose) synthetase on the organ injury and dysfunction caused by haemorrhagic shock

1 Poly (ADP-ribose) synthetase (PARS) is a nuclear enzyme activated by strand breaks in DNA, which are caused by reactive oxygen species (ROS). Here we investigate the effects of the PARS inhibitors 3-aminobenzamide (3-AB), nicotinamide and 1,5-dihydroxyisoquinoline (ISO) on the circulatory failure and the organ injury/dysfunction caused by haemorrhage and resuscitation in the anaesthetized rat. 2 Haemorrhage (sufficient to lower mean arterial blood pressure to 50 mmHg for 90 min) and subsequent resuscitation with shed blood resulted (within 4 h after resuscitation) in a delayed fall in blood pressure to 66+/-4 mmHg (control, n=13). This circulatory failure was not affected by administration (5 min prior to resuscitation) of 3-AB (10 mg kg-1 i.v., n=7), nicotinamide (10 mg kg-1 i.v., n=6) or ISO (3 mg kg-1 i.v., n=6). 3 Haemorrhage and resuscitation also resulted in rises in the serum levels of urea and creatinine. This renal dysfunction was attenuated by 3-AB and nicotinamide, but not by nicotinic acid (n=7), an inactive analogue of nicotinamide. Although ISO (n=6) also attenuated the renal dysfunction caused by haemorrhage and resuscitation, its vehicle (10% DMSO, n=4) had the same effect. 4 Haemorrhagic shock resulted in enhanced serum levels of aspartate aminotransferase (AST), alanine aminotransferase (ALT) and lipase, indicating the development of hepatocellular and pancreatic injury, respectively. Similarly, haemorrhagic shock also resulted in an increase in the serum levels of creatine kinase (CK) indicating the development of neuromuscular injury. This was attenuated by 3-AB and nicotinamide, but not by nicotinic acid. Although ISO also attenuated the liver, pancreatic and neuromuscular injury caused by haemorrhagic shock, its vehicle had the same effect. 5 Thus, activation of PARS contributes to the organ injury and dysfunction caused by haemorrhage and resuscitation in the rat.

Ageing affects anoxia/reoxygenation injury in rat hepatocytes

BACKGROUND

The reoxygenation phase after a period of anoxia leads to oxyradical formation, responsible for damage to cell membranes. Ageing is associated with functional and structural changes in liver cells, which modify their sensitivity to reoxygenation injury. The aim of this study was to determine the effects of ageing on the sensitivity of hepatocytes to anoxia/reoxygenation.

METHODS

Oxyradical formation and cell injury were evaluated in hepatocytes isolated from rats of different ages exposed to 2 h of anoxia and 1 h of reoxygenation. Anion superoxide was measured by lucigenin-enhanced chemiluminescence, hydrogen peroxide by luminol-enhanced chemiluminescence, and cell damage by lactate dehydrogenase (LDH) release.

RESULTS

During anoxia, oxyradical production dropped to background levels in both groups. LDH release was significantly greater in ageing hepatocytes. During reoxygenation, a massive generation of anion superoxide and hydrogen peroxide, followed by a sharp increase in LDH release, was observed in both groups. However, both oxyradicals and cell injury were significantly greater in liver cells obtained from ageing rats.

CONCLUSIONS

The data confirm that hepatocytes produce high levels of free radicals during post-ischemic reoxygenation and suggest that ageing cells are more sensitive to reperfusion injury.

Hemopexin decreases spontaneous chemiluminescence of cold preserved liver after reperfusion

Hemopexin is a plasma protein with exceptionally high affinity for heme. During liver transplantation heme is released via lysis of transfused blood. This heme may catalyze peroxidative reactions that contribute to "reperfusion" injury of the organ. Using a rat liver model of cold storage and reperfusion we tested the potential anti-oxidant effects of hemopexin. After 3 h of cold storage rat liver was reperfused with warm oxygenated buffer. Spontaneous liver chemiluminescence, which is a parameter of oxyradical production, was measured during reperfusion and expressed as an index of free radical production (IFRP). Chemiluminescence reached a maximum within 5 min of reperfusion and decreased to baseline within 30 min. Addition of hemopexin to the perfusate (5 microM) significantly decreased the IFRP. By contrast, the control proteins albumin and gamma-globulin (10 microM) had a smaller non-significant effect. The data suggest that heme could be complexed by hemopexin during reperfusion, thus inhibiting heme mediated cellular injury.

Effects of inhibitors of the activity of poly (ADP-ribose) synthetase on the liver injury caused by ischaemia-reperfusion: a comparison with radical scavengers

1. Poly (ADP-ribose) synthetase (PARS) is a nuclear enzyme activated by strand breaks in DNA which are caused by reactive oxygen species (ROS) and peroxynitrite. Excessive activation of PARS may contribute to the hepatocyte injury caused by ROS in vitro and inhibitors of PARS activity reduce the degree of reperfusion injury of the heart, skeletal muscle and brain in vivo. Here we compared the effects of various inhibitors of the activity of PARS with those of deferoxamine (an iron chelator which prevents the generation of hydroxyl radicals) and tiron (an intracellular scavenger of superoxide anion) on the degree of hepatic injury caused by ischaemia and reperfusion of the liver in the anaesthetized rat or rabbit. 2. In the rat, ischaemia (30 or 60 min) and reperfusion (120 min) of the liver resulted in significant increases in the serum levels of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) indicating the development of liver injury. Intravenous administration of the PARS inhibitors 3-aminobenzamide (3-AB, 10 mg kg(-1) or 30 mg kg(-1)), 1,5-dihydroxyisoquinoline (ISO, 1 mg kg(-1)) or 4-amino-1,8-naphthalimide (4-AN, 3 mg kg(-1)) before reperfusion did not reduce the degree of liver injury caused by ischaemia-reperfusion. 3. In contrast to the PARS inhibitors, deferoxamine (40 mg kg(-1)) or tiron (300 mg kg(-1)) significantly attenuated the rise in the serum levels of AST and ALT caused by ischaemia-reperfusion of the liver of the rat. 4. In the rabbit, the degree of liver injury caused by ischaemia (60 min) and reperfusion (120 min) was also not affected by 3-AB (10 mg kg(-1)) or ISO (1 mg kg(-1)). 5. These results support the view that the generation of oxygen-derived free radicals mediates the liver injury associated with reperfusion of the ischaemic liver by mechanism(s) which are independent of the activation of PARS.

Efeitos do alopurinol sobre a lipoperoxidação de membranas celulares renais na síndrome da isquemia e reperfusão: estudo experimental em ratos

Objetivo: Vários estudos têm demonstrado que Radicais Livres de Oxigênio (RLO) contribuem para o dano celular decorrente da isquemia e reperfusão. Este estudo foi desenvolvido como o objetivo de avaliar os efeitos da isquemia e reperfusão renal em ratos, tratados ou não com alopurinol, sobre a lipoperoxidação (LPO) das membranas celulares renais. Método: Foram usados ratos Wistar distribuídos em 4 grupos e submetidos a períodos de isquemia e reperfusão renal ou não, dependendo do grupo. Também foram submetidos ou não a tratamento com alopurinol na dose de 50 e 150 mg/Kg por via intraperitoneal, 5 e 1 horas antes do procedimento. Na avaliação da lipoperoxidação utilizou-se os métodos do TBARS e QL. Resultados: Os resultados demonstraram aumento da LPO nos animais submetidos a isquemia e reperfusão renal. No entanto, estes efeitos deletérios foram reduzidos com o pré-tratamento com alopurinol (p<0,05). Conclusão: O dano causado em animais submetidos a isquemia e reperfusão renal pode ser demonstrado e quantificado pela LPO. Além disso, o alopurinol demonstrou proteção renal contra o dano decorrente desta síndrome, diminuindo a LPO nestes animais. Estes resultados sugerem que a via da xantina oxidase é uma das mais importantes rotas metabólicas envolvidas na geração de RLO, estes responsáveis em parte pelos danos funcionais do rim na síndrome da isquemia e reperfusão deste órgão.

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.

An ethanol-extract of Ampelopsis brevipedunculata (Vitaceae) berries decreases ferrous iron-stimulated hepatocyte injury in culture

We characterized the effects of an ethanol-extract of the berries of Ampelopsis brevipedunculata (Maxim.) Trautv. (Vitaceae), a plant used in folk medicine to treat liver disease, on rat hepatocyte injury occurring spontaneously, stimulated with ferrous iron and with xanthine oxidase in combination with hypoxanthine or stimulated with ethanol in serum-free culture. Total intracellular and extracellular activities of lactate dehydrogenase (LDH) accumulating during incubation and the percentage of intracellular LDH activity released into culture medium were routinely measured, to evaluate the degree of the injury. The extract decreased a high level of LDH release spontaneously occurring and an elevated level of LDH release stimulated with ferrous iron to approximately the level caused by antioxidants, such as superoxide dismutase, pyruvate and dimethyl sulfoxide. Xanthine oxidase-stimulated LDH release was not decreased by the extract. Ethanol-stimulated LDH release was decreased by the extract when the spontaneous release level was comparatively high. These results indicate that the extract inhibits intact hepatocytes from degrading, by the toxic effect of iron released from primary injured hepatocytes through the generation of reactive oxygen species. The major antitoxic activity of the extract was found in an undialyzable fraction. Sugars were necessary to exert the activity as estimated by periodate oxidation of the extract.

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.

Endotoxin-stimulated nitric oxide production increases injury and reduces rat liver chemiluminescence during reperfusion

BACKGROUND/AIMS

Nitric oxide has many physiological functions and may play an important role in modulating tissue injury. However, the mechanism of NO action in ischemia/reperfusion injury is completely unknown. This report investigates the role of NO in hepatic reperfusion injury.

METHODS

Rat liver was oxygenated for 30 minutes, followed by 30 minutes of ischemia, and then reperfused for 30 minutes. Perfusate was sampled for aspartate aminotransferase content, as an indication of hepatic injury, and for nitrite, an index of NO production. Spontaneous organ chemiluminescence was continuously monitored as a measure of oxyradical production.

RESULTS

NO production by the perfused rat liver was induced in vivo by pretreatment with Escherichia coli lipopolysaccharide. This induction led to an increase in hepatic injury during reperfusion that was partially ameliorated by the NO synthase inhibitor NG-monomethyl-L-arginine. Chemiluminescence during reperfusion, a measure of superoxide production in this system, was also decreased in the lipopolysaccharide-treated animals, and this effect was blunted by NG-monomethyl-L-arginine.

CONCLUSIONS

These data suggest that NO may combine with superoxide formed during reperfusion to directly cause hepatocellular injury. In vitro work shows that this chemical product is the highly toxic species peroxynitrite.