Influence of ascorbic acid esters on acetaminophen-induced hepatotoxicity in mice

Groups of male Swiss-Webster mice were gavaged with acetaminophen (APAP), APAP + ascorbyl stearate (AS), or APAP + ascorbyl palmitate (AP) at a dose of 600 mg/kg for each chemical. APAP alone caused a significant increase in liver weight/body weight ratio and hepatic glutathione (GSH) depletion. Co-administration of the ascorbate esters AP or AS with APAP prevented an increase in liver weight/body weight ratios and hepatic glutathione depletion. APAP + AS treatments caused significantly greater reductions in rectal temperature at 15-30 min post-dosing periods when compared to APAP + AP or AS treatments. Blood levels of APAP had the same relationship. The study indicates a correlation between APAP blood levels and antipyretic effect of APAP + AS and APAP + AP coadministrations. While both ascorbate esters probably afford protection against APAP-induced hepatotoxicity in mice by reducing the reactive intermediate back to the parent compound, the APAP + AS combination provides better therapeutic efficacy as an antipyretic at the 15-30 min post-dosing periods.     

Protection against Acetaminophen Hepatotoxicity by a Single Dose of Clofibrate: Effects on Selective Protein Arylation and Glutathione Depletion

Previous reports demonstrated that repeated administration ofperoxisome proliferators protects against acetaminophen (APAP)hepatotoxicity in mice. This protection was associated witha decrease in APAP's selective protein arylation and glutathionedepletion. This study was conducted to determine if a singledose of clofibrate (CFB), rather than repeated doses, wouldsimilarly prevent APAP toxicity. CD-1 male mice received a singledose of 500 mg CFB/kg and controls were given corn oil 24 hrprior to APAP challenge. After an 18-hr fast, mice were challengedwith 800 mg APAP/kg (in 50% propylene glycol) and killed at4 or 12 hr. Other mice similarly pretreated were killed withoutAPAP challenge. The results showed that pretreatment with asingle CFB dose significantly decreased APAP-induced hepatotoxicity.At 12 hr after APAP plasma sorbitol dehydrogenase activity andthe severity of hepatocellular necrosis were decreased in CFBpretreated mice. Surprisingly, no differences in hepatic nonproteinsulfhydryl (NPSH) depletion or selective arylation of targetproteins in cytosol were observed at 4 hr after APAP challenge.Neither did a single dose of CFB significantly alter hepaticNPSH content prior to APAP challenge. These results indicatethat protection against APAP hepatotoxicity by CFB does notrequire repeated administration, and the absence of significantalterations in APAP's selective protein arylation or glutathionedepletion suggests that the protection against APAP hepatotoxicityafter a single treatment with CFB may differ mechanisticallyfrom the protection observed after repeted CFB dosing.     

Cholestasis induced by model organic anions protects from acetaminophen hepatotoxicity in male CD-1 mice

Administration of the non-metabolizable organic anion indocyanine green (ICG) prior to a toxic dose of acetaminophen (4-acetamidophenol; APAP) reduces liver injury 24 h after dosing. ICG also produces a dose-dependent decrease in bile flow in mice and rats. Studies in bile duct-cannulated rats suggest that cholestasis can play a role in this protection. This study was conducted to determine if the ability of model organic anions to produce cholestasis is relevant to the protection against APAP hepatotoxicity afforded by ICG. In these studies, overnight fasted male CD-1 mice were dosed (i.v.) with the cholestatic dyes bromcresol green (BCG, 30 μmol/kg) and rose bengal (RB, 60 μmol/kg) immediately prior APAP administration (500 mg/kg, i.p.). Other groups of mice received the non-cholestatic dyes dibromosulphthalein (DBSP, 150 μmol/kg) and amaranth (AM, 300 μmol/kg) prior to APAP. Controls were given vehicle only. Hepatocellular necrosis was evident at 24 h in control mice receiving APAP. Pretreatment with the cholestatic dyes BCG and RB decreased the severity of hepatocellular necrosis induced by APAP. However, administration of the non-cholestatic dyes DBSP and AM did not alter APAP-induced liver damage. Glutathione replenishment was not altered by pretreatment with any of these dyes. Furthermore, ICG protected mice against carbon tetrachloride (CCl₄) hepatotoxicity. Since CCl₄ undergoes minimal biliary excretion and does not compete for biliary transport fuction, this finding supports the notion that cholestasis itself rather than competition for canalicular transporters is central to the hepatoprotection by ICG and other cholephilic dyes.     

The toxicity and biotransformation of single doses of acetaminophen in dogs and cats

The biotransformation of single oral doses of acetaminophen (APAP) was studied in dogs an cats. Each animal received APAP at a no-effect (low), mildly toxic (medium), and severely toxic (high) dosage; dosages for each species were selected to produce similar clinical effects at each respective dosage. For dogs, these dosages were 100, 200, and 500 mg APAP/kg, while for cats, the similar effective dosages were 20, 60, and 120 mg APAP/kg. Plasma half-lives in dogs remained constant at the lower two dosages, but nearly tripled at the high dosage. The plasma half-lives in cats rose with increased dosage. Although the cats were given lower APAP dosages than the dogs, the plasma half-lives of cats were greater than those of the dogs at the medium and high dosages. Both species excreted about 85% of the administered single dose within the first 24 hr. APAP-glucuronide was the principal metabolite excreted in the urine of dogs; its fraction of the total metabolites excreted in urine remained constant at the three dose levels. In cats, APAP-sulfate was the major metabolite in urine at all three dosage levels, but the fraction of the total urinary metabolites represented by APAP-sulfate decreased as the dosage increased. Hepatic centrilobular pathology was seen in dogs, while cats had more diffuse liver pathologic changes. The results indicate that the cat is at increased risk from APAP exposure because of impaired glucuronidation and saturation of its sulfate conjugation pathway.     

Lysosomal Instability and Cathepsin B Release during Acetaminophen Hepatotoxicity

Acetaminophen (APAP) overdose is currently the most frequent cause of drug‐induced liver failure in the United States. Recently, it was shown that lysosomal iron translocates to mitochondria where it contributes to the collapse of the mitochondrial membrane potential. Therefore, the purpose of this study was to investigate whether cathepsin B, a lysosomal protease, is involved in APAP‐induced hepatotoxicity. Cathepsin B activity was measured in subcellular liver fractions of C57Bl/6 mice 3 hr after 300 mg/kg APAP treatment. There was a significant increase in cytoplasmic cathepsin activity, concurrent with a decrease in microsomal activity, indicative of lysosomal cathepsin B release. To investigate the effect of cathepsin B on hepatotoxicity, the cathepsin inhibitor AC‐LVK‐CHO was given 1 hr prior to 300 mg/kg APAP treatment along with vehicle control. There was no difference between groups in serum alanine aminotransferase (ALT) values, or by histological evaluation of necrosis, although cathepsin B activity was inhibited by 70–80% compared with controls. These findings were confirmed with a different inhibitor (z‐FA‐fmk) in vivo and in vitro. Hepatocytes were exposed to 5 mM acetaminophen. Lysotracker staining confirmed lysosomal instability and cathepsin B release, but there was no reduction in cell death after treatment with cathepsin B inhibitors. Finally, cathepsin B release was measured in clinical samples from patients with APAP‐induced liver injury. Low levels of cathepsin B were released into plasma from overdose patients. APAP overdose causes lysosomal instability and release of cathepsin B into the cytosol but does not contribute to liver injury under these conditions.     

Hepatoprotective Effects of the Shark Bile Salt 5{beta}-Scymnol on Acetaminophen-Induced Liver Damage in Mice

The hepatoprotective effect of the shark bile salt 5ß-Scymnolhas been studied in the model of acute hepatotoxicity inducedby administration of acetaminophen (APAP, paracetamol). 5ß-Scymnolat doses of 20, 35, and 70 mg/kg intraperitoneally (ip) decreasedsignificantly the serum activity of alanine aminotransferase,sorbitol dehydrogenase, and lactate dehydrogenase (p < 0.05)caused by APAP treatment (350 mg/kg ip) alone. The highest doseof 5ß-Scymnol remained hepatoprotective when administered4 hr after the APAP overdose. N-Acetylcysteine (NAC) is protectiveagainst APAP-induced hepatotoxicity at 250 and 500 mg/kg (ip)when administered up to 3 hr after APAP overdose, as shown bya significant reduction in serum enzyme activity. Coadministrationof 5ß-Scymnol (70 mg/kg) and NAC (250 mg/kg) alsoreduced serum enzyme levels and histopathological effects; however,a similar level of hepatoprotection was conferred by 5ß-Scymnoltreatment alone. In addition, 5ß-scymnol has potenthydroxyl radical quenching activity as it markedly inhibiteddeoxyribose degradation in a ferrous/ascorbate Fenton reactionsystem. These results indicate a possible role for the use of5ß-scymnol, either alone or concomitant with NAC,in the prevention of hepatic necrosis following toxic dosesof APAP.     

Antioxidative and Hepatoprotective Effects of Physalis peruviana Extract against Acetaminophen-Induced Liver Injury in Rats

The aim of this study was to examine the antioxidant activities of Physalis peruviana L. (Solanaceae) aqueous extract (PPWE) and its protective effect against acetaminophen (APAP)-induced hepatotoxicity in rats. Using different models of antioxidant assay, namely ferric thiocyanate, 2,2-diphenyl-1-picrylhydrazyl (DPPH), and reducing power, PPWE showed a dose-dependent increase in antioxidant activities, with total antioxidant activity (IC₅₀: 0.81 μ g/ml) close to that of vitamin C (IC₅₀: 0.89 μ g/ml). APAP at 850 mg/kg significantly increased the levels of serum glutamic pyruvic transaminase (sGPT), glutamic oxaloacetic transaminase (sGOT) and alkaline phosphatase (sALP). However, pre-treatment with PPWE at doses 150, 300, and 600 mg/kg body weight significantly prevented the increase in these enzymes, which are the major indicators of liver hepatitis. Biochemical assays of liver homogenate showed that PPWE at 150～ 600 mg/kg significantly enhanced superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) concentrations, and diminished the level of thiobarbituric acid reactive substances (TBARS). Furthermore, liver histological observation also showed an obvious amelioration in the liver cell necrosis, liver lesion, and fatty changes in PP-treated groups. High performance liquid chromatographic analysis showed that ellagic acid (ca. 0.2%) but not others could be the major component contributing to the antioxidant and hepatoprotective activities of PPWE. The present study concludes that PPWE possesses antioxidant activity and potent hepatoprotective effect against APAP-induced liver injury in rats.     

S-Adenosylmethionine (SAMe) attenuates acetaminophen hepatotoxicity in C57BL/6 mice

Hepatic toxicity is associated with excessive dosages of the over the counter analgesic, acetaminophen (APAP). The aim of this study was to explore protection by the nutritional agent S-adenosylmethionine (SAMe) on APAP hepatotoxicity. Male C57BL/6 mice were injected intraperitoneal (i.p.) with 500 mg/kg (15 ml/kg) APAP or water vehicle (VEH). SAMe was injected i.p. at a dose of either 1000 mg/kg (5 ml/kg) just prior or 500 mg/kg SAMe 15 min prior to administration of VEH or APAP. Comparison of groups showed that SAMe reduced APAP toxicity. Plasma alanine aminotransferase (ALT) levels were increased 2 and 4 h after APAP administration when compared to vehicle (VEH) controls. Liver weight was increased relative to the VEH group within 4 h after APAP treatment. Histological examination by light microscopy confirmed small changes in morphology within 2 h after APAP injection and marked centrilobular necrosis within 4 h in the APAP group. In contrast, when APAP was administered to SAMe pretreated mice, ALT and liver weights were comparable to the VEH and SAMe groups. Histological examination also showed that SAMe produced a marked protection in APAP mediated centrilobular necrosis at 4 h after APAP injection. APAP administration depressed hepatic glutathione levels when monitored at 2 and 4 h. Lipid peroxidation was induced above VEH values 2 and 4 h after APAP injection. Consistent with the SAMe protection of APAP hepatic toxicity, the expected depletion of hepatic glutathione (GSH) levels by APAP was prevented by SAMe pretreatment. SAMe pretreatment also prevented the induction of lipid peroxidation at 2 and 4 h post-APAP administration. In conclusion, SAMe provides protection from APAP hepatic toxicity at 2 and 4 h post-APAP injection. SAMe pretreatment prevented APAP associated depletion in hepatic glutathione and induction of lipid peroxidation as part of its mechanism of protection.     

Limited hepatotoxic potential of acrylonitrile in rats

The possible hepatotoxicity of acrylonitrile (ACN) was investigated based on reports of decreased hepatic glutathione in rats and liver abnormalities in man after exposure to ACN. Male and female rats pretreated po daily for 3 days with sodium phenobarbital (400 μmol/kg) or with Aroclor 1254 (300 μmol/kg) were given ACN (50, 75, 100, or 150 mg/kg) po for 1, 2, or 3 days, or 100 or 500 ppm ACN in drinking water for 21 days. Rats were killed 30 min or 24 hr after one dose of ACN or on Day 22 in the subacute study. Hepatic nonprotein sulfhydryl (NP-SH) concentration and the activities in serum of sorbitol dehydrogenase (SDH) and transminase (GPT) were measured. The liver was examined grossly and microscopically. Hepatic NP-SH decreased significantly (39, 60, 74, and 81%) at 30 min after 50, 75, 100, or 150 mg ACN, respectively. In some experiments serum SDH was significantly elevated (approximately fourfold) 24 hr after 150/mg/kg ACN. Pretreatment with phenobarbital and Aroclor 1254 resulted in only a slight enhancement of the ACN-induced elevation in serum SDH or GPT activities. Serum SDH increased 60% in rats given 500 ppm ACN in drinking water. Focal superficial necrosis of the liver associated (p < 0.001) with hemorrhagic gastritis of a distended forestomach was found in rats necropsied 24 hr after administration of 150 mg/kg ACN. Other than this superficial necrosis, light microscopy revealed only minor changes in liver tissue. Electron microscopy disclosed no changes in the organelles of hepatocytes of rats treated for 21 days with ACN.     

Role of pharmacokinetics and metabolism in the enhanced susceptibility of middle-aged male Sprague-Dawley rats to acetaminophen nephrotoxicity

Middle-aged male Sprague-Dawley (SD) rats (9-12 months) are more susceptible to acetaminophen (APAP)-induced nephrotoxicity than are young (2-3 months) adult males. The present studies were designed to evaluate the role of pharmacokinetics and renal and hepatic metabolism of APAP in age-dependent nephrotoxicity. Following 750 mg/kg APAP, ip, a nephrotoxic dosage in 12-month-old but not 3-month-old rats, renal cortical APAP concentrations were significantly greater in 12-month-old compared with 3-month-old SD rats at 3, 4, and 6 hr after treatment. Renal medullary APAP concentrations in 12 month-old rats were significantly greater than in 3-month-old rats at 2, 3, and 5 hr after treatment. Serum APAP concentrations were significantly elevated in 12-month-old compared with 3-month-old rats from 2 through 5 hr after APAP (750 mg/kg ip). However, APAP tissue/serum concentration ratios were similar in 3- and 12-month-old rats, indicating that differences in tissue concentration were secondary to increased serum concentrations in older rats. Conjugated APAP metabolites in blood were similar in 3- and 12-month-olds during the initial 2-3 hr after 750 mg/kg APAP, ip, but began to accumulate in 12-month-old but not 3-month-old rats within 6-8 hr after APAP administration, perhaps secondary to declining renal function. After 500 mg/kg APAP, iv, blood APAP concentrations were markedly elevated in 12-month-old compared with 3-month-old rats during the entire course of the experiment.(ABSTRACT TRUNCATED AT 250 WORDS)     

Astaxanthin pretreatment attenuates acetaminophen-induced liver injury in mice

BackgroundAcetaminophen (APAP) is a conventional drug widely used in the clinic because of its antipyretic-analgesic effects. However, accidental or intentional APAP overdoses induce liver injury and even acute liver failure (ALF). Astaxanthin (ASX) is the strongest antioxidant in nature that shows preventive and therapeutic properties, such as ocular protection, anti-tumor, anti-diabetes, anti-inflammatory, and immunomodulatory effects. The aim of present study was to determine whether ASX pretreatment provides protection against APAP-induced liver failure.MethodsMale C57BL/6 mice were randomly divided into 7 groups, including control, oil, ASX (30 mg/kg or 60 mg/kg), APAP and APAP + ASX (30 mg/kg or 60 mg/kg) groups. Saline, olive oil and ASX were administered for 14 days. The APAP and APAP + ASX groups were given a peritoneal injection of 700 mg/kg or 300 mg/kg APAP to determine the 5-day survival rate and for further observation, respectively. Blood and liver samples were collected to detect alanine transaminase (ALT), aspartate transaminase (AST), inflammation, oxidative stress and antioxidant systems, and to observe histopathologic changes and key proteins in the mitogen-activated protein kinase (MAPK) family.ResultsASX pretreatment before APAP increased the 5-day survival rate in a dose-dependent manner and reduced the ALT, AST, hepatic necrosis, reactive oxygen species (ROS) generation, lipid peroxidation (LPO), oxidative stress and pro-inflammatory factors. ASX protected against APAP toxicity by inhibiting the depletion of glutathione (GSH) and superoxide dismutase (SOD). Administration of ASX did not change the expression of c-Jun N-terminal kinase (JNK), extracellular signal-regulated kinase (ERK) and P38. However, phosphorylation of JNK, ERK and P38 was reduced, consistent with the level of tumor necrosis factor alpha (TNF-α) and TNF receptor-associated factor 2 (TRAF2).ConclusionASX provided protection for the liver against APAP hepatotoxicity by alleviating hepatocyte necrosis, blocking ROS generation, inhibiting oxidative stress, and reducing apoptosis by inhibiting the TNF-α-mediated JNK signal pathway and by phosphorylation of ERK and P38, which made sense in preventing and treating liver damage.     

Prevention of acetaminophen-induced liver toxicity by 2(R,S)-n-propylthiazolidine-4(R)-carboxylic acid in mice

The cysteine (Cys) precursor 2(R,S)-n-propylthiazolidine-4(R)-carboxylic acid (PTCA) was shown previously to maintain near normal levels of hepatic GSH and GSSG at 24 hr and to protect against hepatic necrosis and mortality at 48 hr after toxic doses of acetaminophen (APAP) in mice. Studies were performed in C57BL/6 mice to determine: (a) the time course of APAP-induced hepatic sulfhydryl depletion, and (b) the effectiveness of PTCA in preventing APAP-induced decreases in sulfhydryl concentrations at the time of maximal depletion. APAP (400-800 mg/kg in 50% propylene glycol; 2.65-5.29 mmol/kg) and PTCA (1-5 mmol/kg 30 min after APAP) were administered i.p. Hepatic GSH, GSSG, and Cys concentrations were determined by HPLC. Hepatocellular damage was assessed by elevations in serum glutamate-pyruvate transaminase (SGPT) activity and histopathologic examination. APAP and PTCA produced dose-dependent effects. At 4 hr after the highest dose of APAP, hepatic GSH and Cys concentrations were reduced to 5 and 14%, respectively, of values in vehicle-treated controls, and the GSSG concentration was below the sensitivity of the analytical method. At 24 hr, recovery of hepatic sulfhydryls was incomplete, and there was hepatic necrosis with an approximately 100-fold increase in SGPT activity. At the highest dose of PTCA, the concentrations of GSH, Cys, and GSSG at 4 hr after APAP (800 mg/kg) were 66, 116, and 111%, respectively, of vehicle controls. PTCA in doses of 1.75 to 5 mmol/kg attenuated the APAP-induced increases in SGPT activity. It was concluded that the protective effect of PTCA is most likely related to prevention of hepatic sulfhydryl depletion.     

Protective effects of salidroside against acetaminophen-induced toxicity in mice

The protective effect of salidroside (SDS) isolated from Rhodiola sachalinensis A. BOR. (Crassulaceae), was investigated in acetaminophen (APAP)-induced hepatic toxicity mouse model in comparison to N-acetylcysteine (NAC). Drug-induced hepatotoxicity was induced by an intraperitoneal (i.p.) injection of 300 mg/kg (sub-lethal dose) of APAP. SDS was given orally to mice at a dose of 50 or 100 mg/kg 2 h before the APAP administration in parallel with NAC. Mice were sacrificed 12 h after the APAP injection to determine aspartate aminotransferase (AST), alanine aminotransferase (ALT), and tumor necrosis factor-alpha (TNF-alpha) levels in serum and glutathione (GSH) depletion, malondialdehyde (MDA) accumulation, and caspase-3 expression in liver tissues. SDS significantly protected APAP-induced hepatotoxicity for SDS improved mouse survival rates better than NAC against a lethal dose of APAP and significantly blocked not only APAP-induced increases of AST, ALT, and TNF-alpha but also APAP-induced GSH depletion and MDA accumulation. Histopathological and immunohistochemical analyses also demonstrated that SDS could reduce the appearance of necrosis regions as well as caspase-3 and hypoxia inducible factor-1alpha (HIF-1alpha) expression in liver tissue. Our results indicated that SDS protected liver tissue from the APAP-induced oxidative damage via preventing or alleviating intracellular GSH depletion and oxidation damage, which suggested that SDS would be a potential antidote against APAP-induced hepatotoxicity.     

Protective effect of ethanol against acetaminophen-induced hepatotoxicity in mice: role of NADH:quinone reductase.

The role of NAD(P)H:quinone reductase (QR; EC 1.6.99.2) in the alcohol-derived protective effect against hepatotoxicity caused by acetaminophen (APAP) was studied. In mice pretreated with dicoumarol (30 mg/kg), an inhibitor of QR, hepatic necrosis caused by APAP (400 mg/kg) was potentiated. Hepatocellular injuries induced by APAP, as assessed by liver histology, serum aminotransferase activities, hepatic glutathione (reduced and oxidized) contents, and liver microsomal aminopyrine N-demethylase activities, all were potentiated by pretreatment of mice with dicoumarol. Even in mice given APAP and ethanol (4 g/kg), in which APAP-inducible hepatic necrosis was abolished, the dicoumarol pretreatment again produced moderate hepatotoxicity and reversed the protective effect of ethanol. In mice pretreated with dicoumarol and ethanol, levels of APAP in blood and bile fluid between 90 and 240 min were higher than those in mice given ethanol. However, the biliary contents of sulfate and glucuronide conjugates of APAP were much lower than those in the ethanol group, particularly at early time points. In contrast, the biliary level of APAP-cysteine conjugate, which in the ethanol group was at its basal level, was increased maximally in the dicoumarol-pretreated mice. In the mice given dicoumarol and ethanol, the biliary APAP-cysteine conjugate level was increased moderately. These results suggest that ethanol inhibited not only the microsomal (CYP2E1 mediated) formation of a toxic quinone metabolite from APAP, but also accelerated the conversion of the toxic quinone metabolite produced back to APAP by stimulating cytoplasmic QR activity. In the presence of dicoumarol, however, QR activity was inhibited, and conversion of the toxic quinone metabolite back to APAP became inhibited and diminished the alcohol-dependent protective effect against APAP-induced hepatic injury.     

Temporal and Dose-Response Features of Monochlorobenzene HepatotoxicityBN in Rats

Temporal and Dose–Response Features of MonochlorobenzeneHepatotoxicity in Rats. DALICH, G. M., AND LARSON, R. E. (1985).Fundam. Appl. Toxicol. 5, 105–116. Time- and dose-dependentcorrelations of monochlorobenzene (CB) hepatotoxic effects werestudied in view of (1) assumed mechanistic similarities to bromobenzene(BB), (2) the paucity of these data for CB, and (3) the relativelygreater environmental importance of CB compared with BB. Anip dosage of 9.8 mmol/kg CB (LD10) produced evidence of livertoxicity over a 72-hr time course. Sulfobromophthalein (BSP)retention was maximized 3–16 hr post-treatment and normalizedafter 72 hr, whereas plasma alanine aminotransferase activity(ALT) and morphological evidence of damage were maximized about48 hr after dosing. Maximal covalent binding to liver protein(3.07 nmol/mg) had occurred by 24 hr and approximately 36% ofthe administered dose had appeared in the urine by 48 hr. Liverand plasma CB concentrations were proportionally increased overthe dosage range 2.0–14.7 mmol/kg but marked centrolobularnecrosis and ALT elevations were seen only at the two highestdosages (9.8 and 14.7 mmol/ kg). On the other hand, all dosesdepressed hepatic glutathione (GSH) to between 30 and 40% ofcontrol by 4 hr. Evidence of rapid recovery was evident at 2.0and 4.9 mmol/kg but GSH levels remained low through 8 hr after9.8 or 14.7 mmol/kg. Liver/body weight ratios were increasedto a similar extent at all dosages when measured 24 hr post-treatment.Urinary excretion ranged from 59% at the low dosage to only19% at the highest dosage by 24 hr. Dose-related covalent bindingto liver protein at 24 hr occurred up to 9.8 mmol/kg but thebinding associated with 14.7 mmol/kg was equivalent to thatseen with the 4.9 mmol/kg dosage (1.6 nmol/mg protein). CytochromeP-450 levels were depressed to between 50 and 80% of control24 hr post-treatment with no clear dose relationship. Whilethe hepatotoxic effects of CB and BB appear similar, these datasuggest that some mechanistic differences are involved.     

Peroxisome proliferator-activated receptor alpha-null mice lack resistance to acetaminophen hepatotoxicity following clofibrate exposure.

The purpose of this study was to investigate whether activation of the nuclear receptor PPARalpha is needed for protection from acetaminophen (APAP) hepatotoxicity produced by repeated administration of the peroxisome proliferator clofibrate (CFB). Female wild-type and PPARalpha-null mice received corn oil vehicle or 500 mg CFB/kg, ip, daily for 10 days. They were then fasted overnight (18 h) and either killed at 4 or 24 h after challenge with 400 mg APAP/kg. Controls received 50% propylene glycol vehicle only. In this model of CFB hepatoprotection, liver injury was assessed by measuring plasma sorbitol dehydrogenase activity and by histopathology at 24 h after APAP challenge. Significant hepatocellular necrosis was evident in both corn oil-pretreated PPARalpha-null and wild-type mice at 24 h after APAP challenge. In agreement with previous studies, CFB-pretreated wild-type mice showed marked protection against APAP toxicity. In contrast, CFB did not provide protection against APAP hepatotoxicity in the PPARalpha-null mice. Similarly, at 4 h after APAP challenge, hepatic glutathione depletion and selective arylation of cytosolic proteins were reduced significantly in CFB-pretreated wild-type mice, but not in PPARalpha-null mice. The lack of changes in APAP binding and NPSH depletion in CFB-pretreated, PPARalpha-null mice is consistent with the presence of significant liver injury at 24 h in this treatment group. These findings demonstrate that the protection against APAP hepatotoxicity by peroxisome proliferator treatment is mediated by the activation of PPARalpha.     

Echinomycin decreases induction of vascular endothelial growth factor and hepatocyte regeneration in acetaminophen toxicity in mice

Up-regulation of vascular endothelial growth factor (VEGF) is important to hepatocyte regeneration in the late stages of acetaminophen (APAP) toxicity in the mouse. This study was conducted to examine the relationship of hypoxia-inducible factor 1α (HIF-1α) to VEGF and hepatocyte regeneration in APAP toxicity using an inhibitor of HIF-1α DNA-binding activity, echinomycin (EC). B6C3F1 male mice were treated with APAP (200 mg/kg IP), followed by EC (0.15 mg IP) and killed at 4 hr. Serum alanine aminotransferase (ALT), necrosis, hepatic glutathione (GSH) and APAP protein adducts were comparable in the APAP/EC and the APAP/veh mice at 4 hr. Additional studies showed that high dose EC (0.3 mg) reduced hepatic VEGF but also lowered hepatic GSH. Subsequent studies were performed using the 0.15-mg dose of EC. Although EC 0.15 mg had no effect on hepatic VEGF levels at 8 hr, by 24 hr VEGF levels were decreased by 40%. Toxicity (ALT and histopathology) was comparable in the APAP and APAP/EC groups at 24 and 48 hr. Proliferating cell nuclear antigen expression was reduced by both Western blot analysis and immunohistochemical staining in the APAP/EC mice at 48 hr. The data support the hypothesis that induction of HIF-1α, its binding to DNA and subsequent expression of VEGF are important factors in hepatocyte regeneration in APAP toxicity in the mouse.     

Citrinin mycotoxicosis in the rabbit

In three trials, single or multiple doses of citrinin dissolved in 0.5 N-NaOH and adjusted to neutral pH with HCl were given to rabbits by either the oral or intraperitoneal route. The 72-hr LD50 was 50 mg/kg body weight by intraperitoneal administration and 134 mg/kg by the oral route. The primary clinical sign in rabbits receiving a single oral dose of 125-150 mg citrinin/kg was fluid diarrhoea commencing 8 hr after dosing. Pathological alterations were generally confined to the kidney and consisted of degeneration and necrosis of proximal convoluted tubules and straight segments. In rabbits given a single oral dose of citrinin (130 mg/kg) the earliest histopathological change, seen 8 hr after dosing, was cytoplasmic vacuolation of tubular epithelial cells. Rabbits given a single oral dose of 120 mg citrinin/kg had regeneration of renal tubular epithelium accompanied by slight tubular cell necrosis when examined 7 days after dosing. Rabbits given multiple sublethal doses of citrinin (33.5 or 77 mg/kg daily for 7 days) had renal alterations of mild tubular degeneration and necrosis, and tubular regeneration.     

A NO-releasing derivative of acetaminophen spares the liver by acting at several checkpoints in the Fas pathway

NCX-701 is a nitric oxide (NO)-releasing acetaminophen (APAP) derivative. In the present study we demonstrated that NCX-701 is as effective as APAP in controlling body temperature in a rat model of endotoxin-induced fever. Liver toxicity is a major complication of APAP overdosing. To investigate whether NCX-701 is hepatotoxic, BALB/C mice were injected with 100 - 500 mg kg(-1) APAP or NCX-701 alone or in combination (i.e. 500 mg kg(-1) of both compounds). Our results demonstrated that although APAP caused a dose-dependent liver injury, NCX-701 was completely devoid of liver toxicity. At the dose of 500 mg kg(-1) APAP caused an approximately 40 fold increase of AST plasma levels and extensive centrilobular necrosis. APAP and NCX-701 share the same metabolic pathway as demonstrated by the time-course of APAP-glucuronide concentrations in plasma and liver. NCX-701 was safe in mice with pre-existing chronic liver disease. Indeed, while C57BL6 transgenic mice expressing the hepatitis B virus (HBV) at the age of 8 months were significantly more susceptible to liver damage induced by APAP (500 mg kg(-1)) than their congenic littermates, treating HBV-transgenic mice with NCX-701, 500 mg kg(-1), caused no damage. Co-administration of NCX-701 at the dose 500 mg kg(-1) to mice treated with APAP, 500 mg kg(-1), completely protected against liver damage induced by APAP. APAP, but not NCX-701, upregulated liver Fas and Fas Ligand mRNA expression in vivo. Incubating mouse hepatocytes with APAP, but not with NCX-701, increased cell surface Fas expression and sensitized hepatocytes to death induced by challenge with a Fas-agonistic antibody. Collectively, these observations suggest that APAP toxicity is Fas mediated and that NCX-701 spares the liver by acting at several checkpoints in the Fas pathway.