Protective effect of Aquilegia vulgaris (L.) on carbon tetrachloride-induced oxidative stress in rats

The ethyl ether extract of A. vulgaris inhibited in vitro microsomal lipid peroxidation (IC50 58.8 microg/ml) and showed moderate ability to scavenge superoxide radicals and to chelate iron ions. The extract (100 mg/kg body weight, po) decreased uninduced and enzymatic microsomal lipid peroxidation in the liver of male rats pretreated with CCl4 (1 ml/kg body weight) by 27 and 40%, respectively. Activity of antioxidant and related enzymes (catalase and glucose-6-phosphate dehydrogenase) inhibited by CCl4 was significantly restored after administration of the extract. The extract itself significantly enhanced superoxide dismutase activity. There was no effect of the extract on hepatic glutathione level and cytochrome P450 content, both were decreased by CCl4. Neither CCl4 nor the tested extract affected activities of NADPH-cytochrome P450 reductase and two monooxygenases, aniline hydroxylase and aminopyrine n-demethylase. It can be concluded that the protective effect of the A. vulgaris extract in CCl4-induced liver injury is mediated by inhibition of microsomal lipid peroxidation and restoring activity of some antioxidant and related enzymes.     

Hepatocyte-specific ablation of spermine/spermidine-N1-acetyltransferase gene reduces the severity of CCl4-induced acute liver injury

Activation of spermine/spermidine-N(1)-acetyltransferase (SSAT) leads to DNA damage and growth arrest in mammalian cells, and its ablation reduces the severity of ischemic and endotoxic injuries. Here we have examined the role of SSAT in the pathogenesis of toxic liver injury caused by carbon tetrachloride (CCl(4)). The expression and activity of SSAT increase in the liver subsequent to CCl(4) administration. Furthermore, the early liver injury after CCl(4) treatment was significantly attenuated in hepatocyte-specific SSAT knockout mice (Hep-SSAT-Cko) compared with wild-type (WT) mice as determined by the reduced serum alanine aminotransferase levels, decreased hepatic lipid peroxidation, and less severe liver damage. Cytochrome P450 2e1 levels remained comparable in both genotypes, suggesting that SSAT deficiency does not affect the metabolism of CCl(4). Hepatocyte-specific deficiency of SSAT also modulated the induction of cytokines involved in inflammation and repair as well as leukocyte infiltration. In addition, Noxa and activated caspase 3 levels were elevated in the livers of WT compared with Hep-SSAT-Cko mice. Interestingly, the onset of cell proliferation was significantly more robust in the WT compared with Hep-SSAT Cko mice. The inhibition of polyamine oxidases protected the animals against CCl(4)-induced liver injury. Our studies suggest that while the abrogation of polyamine back conversion or inhibition of polyamine oxidation attenuate the early injury, they may delay the onset of hepatic regeneration.     

The role of lipid peroxidation in CCl4-induced damage to liver microsomal enzymes: comparative studies in vitro using microsomes and isolated liver cells

The question as to whether CCl4 decreases the activities of glucose-6-phosphatase and cytochrome P-450 in liver endoplasmic reticulum mainly through its action in stimulating lipid peroxidation has been investigated using Promethazine to block lipid peroxidation. The investigation, moreover, has compared the effects of CCl4, with and without Promethazine, on isolated rat hepatocytes with corresponding effects on rat liver microsomal suspensions. Our data give no support for the view that products of lipid peroxidation are the main cause of the decrease in cytochrome P-450 observed in CCl4-intoxication. However, our present results are consistent with lipid peroxidation being a major contributory factor to the decrease in glucose-6-phosphatase activity observed in CCl4-induced liver injury.     

Kupffer cells inhibition prevents hepatic lipid peroxidation and damage induced by carbon tetrachloride

The aim of this work was to determine if the action mechanism of gadolinium on CCl(4)-induced liver damage is by preventing lipid peroxidation (that may be induced by Kupffer cells) and its effects on liver carbohydrate metabolism. Four groups of rats were treated with CCl(4), CCl(4)+GdCl(3), GdCl(3), and vehicles. CCl(4) was given orally (0.4 g 100 g(-1) body wt.) and GdCl(3) (0.20 g 100 g(-1) body wt.) was administered i.p. All the animals were killed 24 h after treatment with CCl(4) or vehicle. Glycogen and lipid peroxidation were measured in liver. Alkaline phosphatase, gamma-glutamyl transpeptidase, alanine amino transferase activities and bilirubins were measured in rat serum. A liver histological analysis was performed. CCl(4) induced significant elevations on enzyme activities and bilirubins; GdCl(3) completely prevented this effect. Liver lipid peroxidation increased 2.5-fold by CCl(4) treatment; this effect was also prevented by GdCl(3). Glycogen stores were depleted by acute intoxication with CCl(4). However, GdCl(3) did not prevent this effect. The present study shows that Kupffer cells may be responsible for liver damage induced by carbon tetrachloride and that lipid peroxidation is produced or stimulated by Kupffer cells, since their inhibition with GdCl(3) prevented both lipid peroxidation and CCl(4)-induced liver injury.     

Comparison of the effects of carbon tetrachloride and of 2,3,7,8-tetrachlorodibenzo-p-dioxin on the disposition of linoleic acid in rat liver in vitro

Both 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and carbon tetrachloride (CCl4) have conspicuous effects on lipid metabolism in rat liver. Although it is generally accepted that CCl4 administration leads to hepatic lipid peroxidation in vivo, conflicting reports from different laboratories make it unclear whether or not lipid peroxidation is involved in the mechanism of toxicity of TCDD. The present study involved pretreating F344 rats with CCl4 or TCDD, then at predetermined times thereafter, giving [U-14C]linoleic acid. A variety of compound classes were monitored in extracts of liver taken 30 min after the label was given. A previously unreported effect of CCl4 was a conspicuous increase in turnover of 1,2-diglycerides. That CCl4 did cause lipid peroxidation was evident from the presence of allylic hydroxyacids not seen in vehicle-treated controls, greatly increased radioactivity in protein-bound material, and decreased levels of arachidonate without decreased synthesis from linolate. Where effects of TCDD pretreatment could be seen, they were much less than the corresponding effects of CCl4. No allylic hydroxyacids were detected in livers of TCDD-treated rats. The concentration of arachidonate was not reduced, and elongation of linolate was not stimulated, indicating that TCDD did not cause extensive-but-repaired peroxidation. It is concluded that while TCDD may slightly increase hepatic lipid peroxidation in rats in vivo, the extent of such stimulation appears to be too slight to account for the toxicity of TCDD.     

Protective effect of L-theanine on carbon tetrachloride-induced acute liver injury in mice

We studied effects of L-theanine, a unique amino acid in tea, on carbon tetrachloride (CCl(4))-induced liver injury in mice. The mice were pre-treated orally with L-theanine (50, 100 or 200 mg/kg) once daily for seven days before CCl(4) (10 ml/kg of 0.2% CCl(4) solution in olive oil) injection. L-theanine dose-dependently suppressed the increase of serum activity of ALT and AST and bilirubin level as well as liver histopathological changes induced by CCl(4) in mice. L-theanine significantly prevented CCl(4)-induced production of lipid peroxidation and decrease of hepatic GSH content and antioxidant enzymes activities. Our further studies demonstrated that L-theanine inhibited metabolic activation of CCl(4) through down-regulating cytochrome P450 2E1 (CYP2E1). As a consequence, L-theanine inhibited oxidative stress-mediated inflammatory response which included the increase of TNF-α and IL-1β in sera, and expression of cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) in livers. CCl(4)-induced activation of apoptotic related proteins including caspase-3 and PARP in mouse livers was also prevented by L-theanine treatment. In summary, L-theanine protects mice against CCl(4)-induced acute liver injury through inhibiting metabolic activation of CCl(4) and preventing CCl(4)-induced reduction of anti-oxidant capacity in mouse livers to relieve inflammatory response and hepatocyte apoptosis.     

Administration of the tris salt of alpha-tocopheryl hemisuccinate inactivates CYP2E1, enhances microsomal alpha-tocopherol levels and protects against carbon tetrachloride-induced hepatotoxicity

A series of tocopherol compounds were examined for their capacity to protect against carbon tetrachloride (CCl4)-induced hepatotoxicity in rats. Of the tocopherol compounds tested in our study, only the tris salt of d-alpha-tocopheryl hemisuccinate (TS-tris) protected against CCl4-induced hepatotoxicity. The administration of d-alpha-tocopherol (alpha-T) and the nonhydrolyzable tocopherol ether, d-alpha-tocopheryloxybutyrate tris salt (TSE-tris), failed to protect against CCl4-induced hepatotoxicity. TS-tris was the only tocopherol which significantly decreased CYP2E1 activity after 18 h. This decrease in CYP2E1 activity is likely to limit the activation of CCl4 and protect against CCl4-induced hepatotoxicity. Our results also suggest that TS-tris protection against CCl4-induced hepatotoxicity correlates with the enhanced capacity of TS-tris to deliver alpha-T and increase the antioxidant status of hepatocytes. TSE-tris did not increase cellular alpha-T levels, while administration of TS-tris produced large increases in alpha-T levels in liver homogenates as well as in liver nuclei, microsomes, mitochondria and plasma membranes. This enhanced ability to deliver tocopherol equivalents to parenchymal liver cells may be related in part to the ability of TS-tris to form liposomes in aqueous solutions. TS-tris administration protected against CCl4-induced microsomal lipid peroxide formation and inactivation of the microsomal enzyme glucose-6-phosphatase (G6Pase). Supplementation of animals with alpha-T protected against microsomal lipid peroxide formation but not against the inactivation of G6Pase. Based on our findings, we propose that high cellular levels of alpha-T protect against CCl4-induced hepatotoxicity by scavenging CCl4 radicals as well as protecting against lipid peroxidation. Our results do not support the importance of microsomal lipid peroxidation as an early event in acute CCl4-induced hepatic necrosis.     

Carbon tetrachloride toxicity as a model for studying free-radical mediated liver injury

A single dose of CCl4 when administered to a rat produces centrilobular necrosis and fatty degeneration of the liver. These hepatotoxic effects of CCl4 are dependent upon its metabolic activation in the liver endoplasmic reticulum to reactive intermediates, including the trichloromethyl free radical. Positive identification of the formation of this free radical in vivo, in isolated liver cells and in microsomal suspensions in vitro has been achieved by e.s.r. spin-trapping techniques. The trichloromethyl radical has been found to be relatively unreactive in comparison with the secondarily derived peroxy radical CCl3O2., although each free radical species contributes significantly to the biological disturbances that occur. Major early perturbations produced to liver endoplasmic reticulum by exposure in vivo or in vitro to CCl4 include covalent binding and lipid peroxidation; studies of these processes occurring during CCl4 intoxication have uncovered a number of concepts of general relevance to free-radical mediated tissue injury. Lipid peroxidation produces a variety of substances that have high biological activities, including effects on cell division; many liver tumours have a much reduced rate of lipid peroxidation compared with normal liver. A discussion of this rather general feature of liver tumours is given in relation to the liver cell division that follows partial hepatectomy.     

Lipid peroxidation in purified plasma membrane fractions of rat liver in relation to the hepatoxicity of carbon tetrachloride

Preparations of rat liver sinusoidal plasma membrane have been tested for their ability to metabolize the hepatotoxin carbon tetrachloride (CCl4) to reactive free radicals in vitro and compared in this respect with standard preparations of rat liver microsomes. The sinusoidal plasma membranes were relatively free of endoplasmic reticulum-associated activities such as the enzymes of the cytochrome P450 system and glucose-6-phosphatase. CCl4 metabolism was measured as (i) covalent binding of [14C]-CCl4 to membrane protein, (ii) electron spin resonance spin-trapping of CCl3. radicals and (iii) CCl4-induced lipid peroxidation. By all of these tests, purified sinusoidal plasma membranes were found unable to metabolize CCl4. The fatty acid composition of the plasma membranes was almost identical to that of the microsomal preparation and both membrane fractions exhibited similar rates of the lipid peroxidation that was stimulated non-enzymically by gamma-radiation or incubation with ascorbate and iron. The absence of CCl4-induced lipid peroxidation in the plasma membranes seems to be due, therefore, to an absence of CCl4 activation rather than an inherent resistance to lipid peroxidation. We conclude that damage to the hepatocyte plasma membrane during CCl4 intoxication is not due to a significant local activation of CCl4 to CCl3. within that membrane.     

Identification of protein kinase C inhibitory activity associated with a polypeptide isolated from a phage display system with homology to PCM-1, the pericentriolar material-1 protein

L-arginine may aid in the liver detoxification and may benefit in the treatment of liver disorders such as liver injury. The present study was to investigate the possible protective and curative effects of L-arginine on carbon tetrachloride (CCl(4)) induced hepatotoxicity. Mice received a single dose of CCl(4). L-arginine treatment was given for 6 days prior or post to CCl(4) injection. CCl(4)-intoxication caused marked liver cell necrosis with inflammatory and apoptotic lesions. L-arginine treatment reduced hepatic necrosis and inflammation. CCl(4)-intoxication also enhanced hepatic lipid peroxidation, decreased hepatic GSH level and inhibited the activities of antioxidant enzymes. Pre-treatment and post-treatment with L-arginine decreased lipid peroxidation and restored the antioxidant status to near normal levels. These results suggest that L-arginine administration has hepatoprotective and hepatocurative effects against CCl(4) induced hepatotoxicity in mice.     

Promethazine inhibits the formation of aldehydic products of lipid peroxidation but not covalent binding resulting from the exposure of rat liver fractions to CCl4.

Promethazine is known to have protective activity in relation to CCl4-induced liver necrosis. This hepatoprotective property has been investigated with regard to the free radical scavenging and antioxidant properties of promethazine using isolated hepatocytes and microsomal suspensions. CCl4 is activated in both systems to free radical metabolites that bind covalently to lipid and protein, and initiate lipid peroxidation. A large number of carbonyl products is produced during CCl4-induced lipid peroxidation; promethazine strongly inhibits the production of all classes of carbonyl compounds in both microsomal suspensions and isolated hepatocytes. In contrast, promethazine is a very weak inhibitor of the covalent binding of metabolites of CCl4. We conclude that promethazine acts by scavenging the trichloromethylperoxyl radical and lipid peroxyl radicals, and is a weak scavenger of the trichloromethyl radical. These data, when considered together with the hepatoprotective effects of promethazine, suggest that lipid peroxidation is of relatively more importance than covalent binding in the pathogenesis of CCl4-induced liver necrosis.     

The role of iron in the paracetamol- and CCl4-induced lipid peroxidation and hepatotoxicity

Treatment of non-induced or phenobarbital-induced, glutathione-depleted mice with 400 mg/kg paracetamol led to a marked ethane exhalation as an index of in vivo lipid peroxidation (LPO) and to a significant elevation of liver-specific serum enzyme activities. Similar effects were seen with rats treated with 0.5 ml/kg CCl4. Pretreatment with the iron-chelating agent desferrioxamine (DFO) clearly suppressed lipid peroxidation in all cases, but inhibited only the CCl4-induced hepatotoxicity. Treatment of mice with desferrioxamine alone showed no hepatotoxicity at all, nor did it influence liver GSH-levels. In addition, DFO had no effect on hepatic microsomal enzyme activities responsible for the bioactivation of both paracetamol and CCl4. These findings are consistent with the theories which indicate that lipid peroxidation requires the presence of Fe2+-ions, regardless of the initiating agent, and that LPO is involved in CCl4-toxicity, but most probably not in paracetamol-induced liver damage. Furthermore, Fe2+-ions might play a role as mediators of CCl4-hepatotoxicity.     

Criteria for determination of lipid peroxidation in tissues: estimation in liver of mice intoxicated with carbon tetrachloride

The profiles of lipid peroxidation products in liver homogenates or microsomal membranes prepared from CCl4-intoxicated mice were determined by several commonly employed methods. The level of conjugated dienes peaked within 30 min and then decreased, suggesting the transitory nature of lipid peroxides in vivo. Values for thiobarbituric acid positive material peaked 30 min after CCl4 treatment, diminished thereafter for a time, and gradually rose to a new maximum at 24 h; the first peak appears to represent lipid peroxides and the second represents further degradation products including malondialdehyde. Fluorescence intensity (excitation, 360 nm; emission, 430 nm) was closely correlated with the second peak. Our findings support the involvement of lipid peroxidation in CCl4-induced hepatotoxicity in mice and emphasize the necessity for several analytical indices of lipid peroxidation performed at different time intervals.     

The effect of the administration of cobaltic protoporphyrin IX on drug metabolism, carbon tetrachloride activation and lipid peroxidation in rat liver microsomes

The effects of cobaltic protoporphyrin IX (CPP) administration on hepatic microsomal drug metabolism, carbon tetrachloride activation and lipid peroxidation have been investigated using male Wistar rats. CPP (125 mumol/kg, 72 h before sacrifice) profoundly decreased the levels of hepatic microsomal heme, particularly cytochrome P-450. Consequently, the associated mixed-function oxidase systems were equally strongly depressed. An unexpected finding was that CPP administration also greatly decreased the activity of NADPH/cytochrome c reductase, a result not generally found with the administration of the more widely used cytochrome P-450 depleting agents, cobaltous chloride. Activation of carbon tetrachloride, measured as covalent binding of [14C] CCl4, spin-trapping of CCl3 and CCl4-stimulated lipid peroxidation, was much lower in liver microsomes from CPP-treated rats. Other microsomal lipid peroxidation systems, utilising cumene hydroperoxide or NADPH/ADP-Fe2+, were also depressed in parallel with the decrease in microsomal enzyme activities.     

Carbon tetrachloride-induced lipid peroxidation dependent on an ethanol-inducible form of rabbit liver microsomal cytochrome P-450

Treatment of rats with ethanol or rabbits with either imidazole or pyrazole, agents known to induce the ethanol-inducible form of liver microsomal cytochrome P-450 (P-450 LMeb), caused, compared to controls, 3-25-fold enhanced rates of CCl4-dependent lipid peroxidation or chloroform production in isolated liver microsomes. No significant differences were seen when the rate of CCl4-dependent lipid peroxidation was expressed relative to the amount of P-450 LMeb in the various types of microsomal preparations. In reconstituted membranous systems, this type of P-450 was a 100-fold more effective catalyst of CCl4 metabolism than either of the cytochromes P-450 LM2 or P-450 LM4. It is proposed that the induction of this isozyme provides the explanation on a molecular level for the synergism seen of ethanol on CCl4-dependent hepatotoxicity.     

Lipid peroxidation and cell viability in isolated hepatocytes in a redesigned oxystat system: evaluation of the hypothesis that lipid peroxidation, preferentially induced at low oxygen partial pressures, is decisive for CCl4 liver cell injury

An oxystat system is described which is capable of maintaining steady-state oxygen partial pressures (PO2) at levels between 0.1 and 300 mm Hg for hours or even days in incubations of respiring cells. The system was used to study effects of the hepatotoxin carbon tetrachloride (CCl4) on lipid peroxidation and cell viability in isolated hepatocytes from phenobarbital-pretreated rats at various steady-state PO2. At PO2 below 35 mm Hg, with a maximum effect at 7 mm Hg, CCl4 induced an immediate lipid peroxidation, the rate of which slowed down during further incubation. AT PO2 between 35 and 70 mm Hg, CCl4 initially induced only slight lipid peroxidation, while there was a significant increase in lipid peroxidation after approximately 30 min. At PO2 above 100 mm Hg, no lipid peroxidation was induced by CCl4. At PO2 of 70 mm Hg and below, with the maximum effect at 3 mm Hg, CCl4 also induced marked losses of cell viability. Under anaerobic conditions and at PO2 greater than 70 mm Hg, CCl4 was without effect on the viability of the liver cells. Cells isolated from the pericentral area of the liver lobule showed more lipid peroxidation and loss of cell viability than cells from the periportal area of the lobule. These results provide further evidence for the decisive role of lipid peroxidation, preferentially induced at low PO2, in CCl4 liver injury.     

Alterations of the microsomal glucose-6-phosphatase system evoked by ferrous iron- and haloalkane free-radical-mediated lipid peroxidation

Alterations of catalytic activities of the microsomal glucose-6-phosphatase system were examined following either ferrous iron- or halothane (CF3CHBrCl) and carbon tetrachloride (CCl4) free-radical-mediated peroxidation of the microsomal membrane. Enzyme assays were performed in native and solubilized microsomes using either glucose 6-phosphate or mannose 6-phosphate as substrate. Lipid peroxidation was assessed by the amounts of malondialdehyde equivalents formed. Regardless of whether the experiments were performed in the presence of NADPH/Fe3+, NADPH/CF3CHBrCl, or NADPH/CCl4, with the onset of lipid peroxidation, mannose-6-phosphatase activity of the native microsomes increased immediately, while further alterations in catalytic activities were only detectable when lipid peroxidation had passed characteristic threshold values: above 2 nmol malondialdehyde/mg microsomal protein, glucose-6-phosphatase activity of the native microsomes was lost, and at 10 nmol malondialdehyde/mg microsomal protein, glucose-6-phosphatase and mannose-6-phosphatase activity of the solubilized microsomes started to decline. It is concluded that the latter alterations are due to an irreversible damage of the phosphohydrolase active site of the glucose-6-phosphatase system, while the changes observed at earlier stages of microsomal lipid peroxidation may also reflect alterations of the transporter components of the glucose-6-phosphatase system. Virtually no changes in the catalytic activities of the glucose-6-phosphatase system occurred under anaerobic conditions, indicating that CF3CHCl and CCl3 radicals are without direct damaging effect on the glucose-6-phosphatase system. Further, maximum effects of carbon tetrachloride and halothane on lipid peroxidation and enzyme activities were observed at an oxygen partial pressure (PO2) of 2 mmHg, providing additional evidence for the crucial role of low PO2 in the hepatotoxicity of both haloalkanes.     

Correlations between common tests for assessment of liver damage: indices of the hepatoprotective activity of promethazine in carbon tetrachloride hepatotoxicity

The effects of promethazine (PM) on different aspects of the hepatotoxic action of CCl4 in the rat were investigated with the objective of finding rapid and reliable indicators of hepatoprotective effects. The study was based on definitive histological assessment of liver damage caused by CCl4 in the presence and absence of PM: PM (78 mumol kg-1, i.p.) protected against CCl4-induced hepatic necrosis 24 h after a low dose of CCl4 (1.3 mmol kg-1) but not against a higher dose (13.0 mmol kg-1). The large increases in plasma activities of GOT, GPT and LDH produced by dosing with CCl4 were partially inhibited by the administration of PM. PM and CCl4 caused a synergistic and long-lasting decrease in body temperature (2-3 degrees C for 8-10 h). Modifying the toxicity with PM, together with a low dose of CCl4, helped to minimize secondary effects of CCl4, to clarify the sequence of toxic events, and to assess the sensitivity of some standard tests of hepatotoxicity. Simultaneous measurement of over 20 commonly used biochemical screening tests in individual animals 3 or 6 h after treatment permitted direct correlation of a wide variety of concentrations, activities and effects. For example, liver CHCl3 concentrations (as a measure of CCl4 metabolism) correlate strongly with increases in diene conjugation of microsomal lipids (as a measure of CCl4-induced lipid peroxidation); malonaldehyde production appears to be less sensitive as a measure of lipid peroxidation in vivo than diene conjugation. The changes induced in each parameter and the correlations between them are discussed with reference to the overall nature of the hepatotoxic reaction and its modification by PM.     

Protective effects of an extract of young radish (Raphanus sativus L) cultivated with sulfur (sulfur-radish extract) and of sulforaphane on carbon tetrachloride-induced hepatotoxicity

The protective effects of an extract of young radish (Raphanus sativus L) cultivated with sulfur (sulfur-radish extract) and of sulforaphane, an isothiocyanate, on carbon tetrachloride (CCl(4))-induced liver injury were observed in mice. CCl(4) produced a marked increase in the serum level of alanine aminotransferase (ALT), primed lipid peroxidation, and resulted in intense necrosis due to oxidative stress. Oral administration of the sulfur-radish extract and of sulforaphane after CCl(4)-induced liver injury both decreased the serum level of ALT, reduced the necrotic zones, inhibited lipid peroxidation, and induced phase 2 enzymes without affecting cytochrome P450-2E1 (CYP2E1). These results suggest that the administration of the sulfur-radish extract and of sulforaphane may partially prevent CCl(4)-induced hepatotoxicity, possibly by indirectly acting as an antioxidant by improving the detoxification system.     

The roles played by crucial free radicals like lipid free radicals, nitric oxide, and enzymes NOS and NADPH in CCl(4)-induced acute liver injury of mice

Mice were administered a single dose of carbon tetrachloride (CCl(4)) to induce acute liver injury. We found that lactate dehydrogenase (LDH) and glutamic pyruvic transaminase (GPT) levels in serum, as well as the level of thiobarbituric acid reaction substances (TBARS) in liver homogenate increased significantly in a manner both dose dependent and time dependent after CCl(4) administration. Such results suggest that the liver is susceptible to CCl(4) treatment and that lipid peroxidation is associated with CCl(4)-induced liver injury. The spin-trapping electron paramagnetic resonance (EPR) method was used to detect nitric oxide (NO) level in liver. The chemiluminescence method was also employed to measure the NO(2)(-)/NO(3)(-) concentration in serum. The NO levels in liver tissues and NO(2)(-)/NO(3)(-) concentration in serum were found to decrease significantly both in a dose-dependent manner and in time course after CCl(4) treatment. The nitric oxide synthase (NOS) II activity in the liver, in contrast, was found to increase significantly. Our study suggests that not only should the expression of NOS be analyzed but NO organ and blood concentration must be measured in the study of diseases involving nitric oxide. L-arginine treatment had no significant effect on the liver function of CCl(4)-treated mice. It was found that NO donor sodium nitroprusside (SNP; 50 or 100 microg/kg) treatment resulted in decreases of LDH, GPT, and TBARS levels, leading to a protective effect on CCl(4)-treated mice. On the other hand, N(G)-nitro-L-arginine methyl ester (L-NAME, 100 or 300 mg/kg) treatment caused more severe liver damage. Moreover, we have found in an in vitro EPR study that SNP could scavenge lipid peroxyl radical LOO&z.rad;. The above results together suggest that NO may protect CCl(4)-induced liver injury through scavenging lipid radical, inhibiting the lipid peroxidation chain reaction. On the basis of our analysis, we put forth two explanations for the stated discrepancy between NOS II and NO production: (i) NO was used up gradually in terminating lipid peroxidation and (ii) NADPH was depleted (on the basis of correlation evidence only).