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.     

THE PPAR ACTIVATOR DOCOSAHEXAENOIC ACID PREVENTS ACETAMINOPHEN HEPATOTOXICITY IN MALE CD-1 MICE

Acetaminophen (APAP)-induced hepatocellular necrosis can be prevented by treatment with peroxisome proliferators. This protection is associated with lowered protein arylation and glutathione depletion in mice. Peroxisome proliferators have been shown to activate nuclear receptors. These receptors, termed peroxisome proliferator activated receptors (PPARs), can also be activated by free fatty acids. This study was designed to determine if treatment with the PPAR activator docosahexaenoic acid (DHA) would also lower APAP toxicity. Male CD-1 mice received 250 mg DHA/kg or 500 mg clofibrate (CFB)/kg, ip, for 5 d. Controls received corn oil vehicle, ip. After overnight fasting, mice received 800 mg APAP/kg, po. At 24 h after APAP, hepatotoxicity was evident in control mice by elevated plasma sorbitol dehydrogenase activity (SDH) and histologic evidence of hepatic degeneration and necrosis. As expected, CFB pretreatment significantly decreased this. Similarly, DHA protected against APAP-induced hepatotoxicity at 24 h after challenge. However, treatment with DHA did not increase hepatic glutathione prior to APAP, as previously shown with CFB. Interestingly, DHA did not increase palmitoyl coenzyme A (CoA) oxidase activity or other biochemical parameters associated with peroxisome proliferation after 5 d of treatment at 250 mg/kg. No significant alterations in microsomal APAP glucuronidation or cytochrome P-450-mediated bioactivation were detected either. Collectively, these results show that DHA also prevents APAP-induced hepatotoxicity at 24 h after challenge. However, the association between resistance against APAP-induced liver injury, PPAR activation, and peroxisome proliferation is not clearly understood.     

The PPAR activator docosahexaenoic acid prevents acetaminophen hepatotoxicity in male CD-1 mice.

Acetaminophen (APAP)-induced hepatocellular necrosis can be prevented by treatment with peroxisome proliferators. This protection is associated with lowered protein arylation and glutathione depletion in mice. Peroxisome proliferators have been shown to activate nuclear receptors. These receptors, termed peroxisome proliferator activated receptors (PPARs), can also be activated by free fatty acids. This study was designed to determine if treatment with the PPAR activator docosahexaenoic acid (DHA) would also lower APAP toxicity. Male CD-1 mice received 250 mg DHA/kg or 500 mg clofibrate (CFB)/kg, i.p., for 5 d. Controls received corn oil vehicle, i.p. After overnight fasting, mice received 800 mg APAP/kg, p.o. At 24 h after APAP, hepatotoxicity was evident in control mice by elevated plasma sorbitol dehydrogenase activity (SDH) and histologic evidence of hepatic degeneration and necrosis. As expected, CFB pretreatment significantly decreased this. Similarly, DHA protected against APAP-induced hepatotoxicity at 24 h after challenge. However, treatment with DHA did not increase hepatic glutathione prior to APAP, as previously shown with CFB. Interestingly, DHA did not increase palmitoyl coenzyme A (CoA) oxidase activity or other biochemical parameters associated with peroxisome proliferation after 5 d of treatment at 250 mg/kg. No significant alterations in microsomal APAP glucuronidation or cytochrome P-450-mediated bioactivation were detected either. Collectively, these results show that DHA also prevents APAP-induced hepatotoxicity at 24 h after challenge. However, the association between resistance against APAP-induced liver injury, PPAR activation, and peroxisome proliferation is not clearly understood.     

Selective protein arylation and the age dependency of acetaminophen hepatotoxicity in mice

Male CD-1 mice 1, 1.5, 2, and 3 months old were given 600 mg of acetaminophen (APAP)/kg, po, and liver damage was assessed 12 hr later. The most severe hepatotoxicity was in 3-month-old mice, while the other age groups exhibited little damage. The onset of susceptibility to APAP hepatotoxicity did not correlate with the level of activity of the mixed-function oxidase system as assessed in vitro, since drug metabolizing capability was similar between 2- and 3-month-old mice. Through 4 hr after administration of APAP to 2- and 3-month-old mice in vivo, glutathione (GSH) depletion and both plasma and liver APAP concentrations were similar between ages. Additionally, 24 hr after dosing, 3-month-old mice excreted marginally more APAP-glucuronide conjugate and parent compound in urine than 2-month-old animals, while both age groups excreted similar amounts of the APAP-sulfate and GSH-derived conjugates. Even though the extent of binding of radioactive APAP to macromolecules at 4 hr was similar between 2- and 3-month-old animals, the pattern of immunochemically targetted cytosolic and microsomal proteins was different. Thus, in APAP exposure the extent of binding to specific proteins rather than the overall amount of covalent binding may be the critical determinant of the hepatotoxic response. In the present study, the age-related differences in susceptibility to APAP-induced hepatotoxicity were related to the differences in selective protein arylation.     

Green tea extract can potentiate acetaminophen-induced hepatotoxicity in mice

Green tea extract (GTE) has been advocated as a hepatoprotective compound and a possible therapeutic agent for acetaminophen (APAP) overdose. This study was conducted to determine if GTE can provide protection against APAP-induced hepatotoxicity. Three different exposure scenarios were tested. The first involved administering APAP (150 mg/kg, orally) to mice followed 6 h later by GTE (500 or 1000 mg/kg). The other two involved administering GTE prior to the APAP dose. GTE (500 or 1000 mg/kg, orally) was administered 3 h prior to APAP (200 mg/kg, orally) or for three consecutive days (once-daily) followed by APAP (300 mg/kg) on the fourth day. Indices of hepatotoxicity were assessed 24 h after the APAP dose. GTE potentiated APAP-induced hepatotoxicity when administered after the APAP dose. GTE caused significant glutathione depletion and this effect likely contributed to the observed potentiation. In contrast, GTE provided protection against APAP-induced hepatotoxicity when administered prior to the APAP dose. GTE dramatically decreased APAP covalent binding to protein indicating that less reactive metabolite was available to cause hepatocellular injury. These results highlight the potential for drug-dietary supplement interactions and the importance of testing multiple exposure scenarios to adequately model different types of potential interactions.     

Studies on the effects of l-ascorbic acid on acetaminophen-induced hepatotoxicity: II. An in vivo assessment in mice of the protection afforded by various dosage forms of ascorbate

The protection provided by various forms of ascorbate, in several dosage regimens, against acetaminophen (APAP)-induced hepatotoxicity was assessed in male MF1 mice. Hepatotoxicity was produced by treatment with 450 mg APAP/kg po and evaluated 24 hr later by the change in liver weight to body weight ratio and from a histological score of liver necrosis. All treatments were given by gavage in 0.5% tragacanth at 20 ml/kg. No significant protection was given by l-ascorbic acid (LAA) at 50, 150, or 300 mg/kg given at the same time as APAP, nor at 150 or 300 mg/kg given 1 hr afterward. A dose of 150 mg LAA/kg at the same time as, and 2 hr after APAP also failed to give protection. In contrast, other dosage forms showed a protective action. Ascorbyl palmitate provided significant protection at 300 mg/kg. After 600 and 900 mg/kg doses, the liver weight/body weight ratio and necrosis scores were not significantly greater than those in the vehicle controls. The degree of protection by a microencapsulated LAA preparation (MEAA) was related to the fate of the microcapsules in the gastrointestinal tract. This finding suggests that the pharmacokinetic profile of LAA, relative to the time scale of the hepatotoxic processes, may be critical. Sodium ascorbate gave no protection when used in combination with MEAA. The results indicate that ascorbic acid in certain biopharmaceutical forms may have potential use in the development of a safer dosage form of APAP.     

Acute acetaminophen toxicity in transgenic mice with elevated hepatic glutathione

Previous studies demonstrated that elevation of hepatic glutathione (GSH) concentrations protect against acetaminophen (APAP) hepatotoxicity in mice. Employing transgenic mice overexpressing glutathione synthetase, this study was conducted to determine if sustained elevation of hepatic GSH concentrations could ameliorate or prevent APAP toxicity. International Cancer Research transgenic mouse males and matched (ie same strain, sex, and age) control nontransgenic mice were pretreated ip with GSH synthetase substrate gamma-glutamylcysteinyl ethyl ester (gamma-GCE) or with saline. After a 16-h fast, mice received a single dose of 500 mg APAP/kg bw in saline ip and were sacrificed 4 h later. Other mice similarly pretreated were killed without APAP challenge. The elevated GSH concentrations in transgenic mice livers did not lessen APAP hepatotoxicity. Instead higher degrees of hepatotoxicity and nephrotoxicity were observed in transgenic mice than in controls as indicated by higher serum alanine aminotransferase activity and more severe histopathological lesions in transgenic mice livers and kidneys. Pretreatment with gamma-GCE did not affect either initial or post-APAP treatment tissue GSH concentrations or observed degrees of toxicity. Detection of a higher level of serum APAP in transgenic mice and the histopathological lesions found in transgenic mice kidneys together with no observable nephrotoxicity in control mice indicated early kidney damage in transgenic mice. Our findings suggest that high levels of GSH-APAP conjugates resulting from increased GSH concentrations in the livers of transgenic mice caused rapid kidney damage. Compromised excretory ability may have caused retention of APAP, which, in effect, elicited higher hepatotoxicity than that observed in nontransgenic mice.     

Immunohistochemical Localization of Acetaminophen-Bound Liver Proteins

A sensitive immunofluorescence assay was developed for localizingacetaminophen (APAP) protein adducts in liver sections fromtreated mice. Affinity-purified anti-APAP antibodies, when appliedto liver sections from mice given 600 mg APAP/kg, po, were preferentiallylocalized in cells of the centrilobular region. At 30 min afterdosing, covalently bound APAP was detected only in those cellsmost proximal to the central vein. Thereafter, binding spreadthroughout the centrilobular zone. However, by 8 hr the overallintensity of staining decreased and binding appeared more diffuse.Western blot analysis of electrophoretically resolved proteinsfrom similarly treated mice revealed a corresponding temporalarylation of cytosolic proteins by APAP and indicated that thefluorescence detected at 30 min was associated with arylationof protein(s) of 44 kDa. The findings demonstrate the sensitivityand utility of immunohistochemical techniques in the study ofcovalently bound toxicants and emphasizes the temporal linkbetween selective protein arylation in individually targettedcells to the development of APAP hepatotoxicity.     

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.     

Evidence against deacetylation and for cytochrome P450-mediated activation in acetaminophen-induced nephrotoxicity in the CD-1 mouse

Acetaminophen (APAP) administration (600 mg/kg, po) results in proximal tubular necrosis in 18-hr fasted, 3-month-old male CD-1 mice. This study was undertaken to determine if deacetylation of APAP to p-aminophenol (PAP) is a prerequisite to nephrotoxicity in the mouse, as it is in the Fischer rat. Administration of either APAP or PAP to mice resulted in significant elevations of plasma urea nitrogen and marked proximal tubular necrosis at 12 hr after dosing. Prior inhibition of APAP deacetylation by the carboxylesterase inhibitors bis(p-nitrophenyl) phosphate or tri-o-tolyl-phosphate did not alter APAP hepatotoxicity or nephrotoxicity. By contrast, pretreatment with the MFO inhibitor piperonyl butoxide decreased APAP nephrotoxicity but not that of PAP. Immunochemical analysis of kidneys from APAP-treated mice demonstrated covalently bound APAP but no binding was detected after mice were treated with a nephrotoxic dose of PAP. Since the antibody used has been characterized as being directed primarily against the N-acetyl moiety of bound APAP metabolite and since it did not react with kidney proteins of mice given a nephrotoxic dose of PAP, it is unlikely that APAP deacetylation preceded binding or that acetylation of bound PAP occurred. Taken together, these findings indicate that in the CD-1 mouse, APAP-induced nephrotoxicity differs from that previously described for the Fischer rat and likely involves cytochrome P450-dependent activation and subsequent covalent binding of a metabolite without prior deacetylation.     

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.     

Type 1 diabetic mice are protected from acetaminophen hepatotoxicity.

Streptozotocin (STZ)-induced diabetic (DB) mice challenged with single ordinarily lethal doses of acetaminophen (APAP), carbon tetrachloride (CCl4), or bromobenzene (BB) were resistant to all three hepatotoxicants. Mechanisms of protection against APAP hepatotoxicity were investigated. Plasma alanine aminotransferase, aspartate aminotransferase, and liver histopathology revealed significantly lower hepatic injury in DB mice after APAP administration. HPLC analysis of plasma and urine revealed lower plasma t1/2, increased volume of distribution (Vd), and increased plasma clearance (CLp) of APAP in the DB mice and no difference in APAP-glucuronide, a major metabolite in mice. Interestingly, covalent binding of 14C-labeled APAP to liver target proteins; arylation of APAP to 58, 56, and 44 kDa acetaminophen binding proteins (ABPs); and glutathione (GSH) depletion in the liver did not differ between nondiabetic (non-DB) and DB mice in spite of downregulated hepatic microsomal CYP2E1 and 1A2 proteins in the DB mice, known to be involved in bioactivation of APAP. Compensatory cell division measured via 3H-thymidine pulse labeling and immunohistochemical staining for proliferating cell nuclear antigen (PCNA) indicated earlier onset of S-phase in the DB mice after exposure to APAP. Antimitotic intervention of liver cell division by colchicine (CLC) after administration of APAP led to significantly higher mortality in the DB mice suggesting a pivotal role of liver cell division and tissue repair in the protection afforded by diabetes. In conclusion, the resistance of DB mice against hepatotoxic and lethal effects of APAP appears to be mediated by a combination of enhanced APAP clearance and robust compensatory tissue repair.     

Changes in susceptibility to acetaminophen-induced liver injury by the organic anion indocyanine green.

The non-metabolizable organic anion indocyanine green (ICG) has been shown previously to reduce markedly the biliary secretion of acetaminophen, particularly the glutathione conjugate of APAP (APAP-GSH), suggesting that this APAP metabolite may compete with other xenobiotics for excretion into the bile via a canalicular organic anion transport process. This study was conducted to determine whether changes in the biliary disposition of APAP induced by ICG could lead to alterations in susceptibility to APAP hepatotoxicity. To investigate this, groups of overnight-fasted male CD-1 mice received 30 micromol ICG/kg, intravenously, immediately prior to APAP dosing (500 mg/kg, ip). Controls were given propylene glycol vehicle. Mice were killed at 4 h after APAP challenge for immunochemical analysis of cytosolic protein arylation and determination of non-protein sulfhydryl (NPSH) depletion, or at 12 and 24 h for biochemical and histological assessment of liver injury. Elevated plasma sorbitol dehydrogenase activity and centrilobular hepatocellular necrosis was present in control mice receiving APAP at 12 and 24 h. Treatment with ICG did not alter susceptibility to APAP toxicity when measured at 12 h after challenge. However, the severity of histologic lesions in the ICG-APAP group was significantly lower at 24 h after challenge. Furthermore, treatment with ICG did not alter APAP-induced glutathione depletion or cytosolic protein arylation. These data suggest that the organic anion ICG has a protective effect on APAP toxicity that promotes a faster recovery from liver injury.     

Nilotinib Interferes with the Signalling Pathways Implicated in Acetaminophen Hepatotoxicity

Nilotinib, a second‐generation tyrosine kinase inhibitor, has been recently approved for the treatment for chronic myeloid leukaemia. The objective of this study was to explore the potential effects of clinically relevant doses of nilotinib against acetaminophen (APAP)‐induced hepatotoxicity in mice. To simulate the clinical application in human beings, nilotinib (25 and 50 mg/kg) was administered to mice 2 hr after APAP intoxication (500 mg/kg). The results indicated that nilotinib (25 mg/kg) (i) abolished APAP‐induced liver injury and necro‐inflammation, (ii) increased hepatic‐reduced glutathione (GSH) and its related enzymes synthesis, (iii) suppressed hepatic oxidative/nitrosative stress cascades, (iv) decreased neutrophil accumulation in the liver, and (v) prevented the over‐expression of B‐cell lymphoma‐2 (bcl‐2), cyclin‐D1 and stem cell factor receptor (c‐Kit) proteins in the liver. Although nilotinib (50 mg/kg) acted through the same mechanisms, there was severe depletion in hepatic GSH content by nilotinib itself at that dose level, rather than the potent stimulation observed by using a dose of 25 mg/kg. Consequently, the mortality rate after 18 hr was 100% for nilotinib (50 mg/kg) + APAP (750 mg/kg) versus 60% for APAP (750 mg/kg) and 40% for nilotinib (25 mg/kg) + APAP (750 mg/kg) in the survival analysis experiment. In conclusion, nilotinib can counteract the hepatotoxicity produced by a non‐lethal dose of APAP. However, there is a risk of aggravating the mortality for a lethal dose of APAP when nilotinib is co‐administered at doses relatively high, or near to the clinical range because of hepatic GSH depletion and c‐kit inhibition.     

Differential effects of daily administration of cocaine on hepatic and cerebral glutathione in mice

Twenty-four hours after acute administration of cocaine HCl (25 mg/kg, i.p.) to male C57BL/6ByJ mice, there was no hepatotoxicity as measured by plasma aspartate aminotransferase (AST) activity. In contrast, daily administration of cocaine (25 mg/kg, i.p.) for 14 days induced marked hepatotoxicity, as characterized by a greater than 400% increase in plasma AST activity when assayed 24 hr after the last injection. Concomitantly, the liver had increased levels of cysteine, gamma-glutamylcysteine, glutathione, cysteinylglycine, glutamate, methionine, taurine, and aspartate. The effect appeared to be selective for compounds of the glutathione metabolic pathways, because repeated cocaine exposure did not affect other amino acids such as leucine, isoleucine, phenylalanine, serine, and valine. There was a positive correlation between the magnitude of the elevation of cysteine and the extent of liver damage. Daily cocaine administration did not affect striatal or frontal cortex glutathione. A final cocaine challenge (50 mg/kg, i.p.) did not affect either hepatic or cerebral glutathione metabolism. The increase in hepatic cysteine and glutathione upon daily cocaine administration is a potentially important compensatory mechanism against cocaine-induced hepatotoxicity.     

Resistance to acetaminophen-induced hepatotoxicity in glutathione S-transferase Mu 1-null mice

We investigated the role of glutathione S-transferases Mu 1 (GSTM1) in acetaminophen (APAP)-induced hepatotoxicity using Gstm1-null mice. A single oral administration of APAP resulted in a marked increase in plasma alanine aminotransferase accompanied by hepatocyte necrosis 24 hr after administration in wild-type mice, but its magnitude was unexpectedly attenuated in Gstm1-null mice. Therefore, it is suggested that Gstm1-null mice are resistant to APAP-induced hepatotoxicity. To examine the mechanism of this resistance in Gstm1-null mice, we measured phosphorylation of c-jun N-terminal kinase (JNK), which mediates the signal of APAP-induced hepatocyte necrosis, by Western blot analysis 2 and 6 hr after APAP administration. A marked increase in phosphorylated JNK was observed in wild-type mice, but the increase was markedly suppressed in Gstm1-null mice. Therefore, it is suggested that suppressed phosphorylation of JNK may be a main mechanism of the resistance to APAP-induced hepatotoxicity in Gstm1-null mice, although other possibilities of the mechanism cannot be eliminated. Additionally, phosphorylation of glycogen synthase kinase-3β and mitogen-activated protein kinase kinase 4, which are upstream kinases of JNK in APAP-induced hepatotoxicity, were also suppressed in Gstm1-null mice. A decrease in liver total glutathione 2 hr after APAP administration, which is an indicator for exposure to N-acetyl-p-benzoquinoneimine, the reactive metabolite of APAP, were similar in wild-type and Gstm1-null mice. In conclusion, Gstm1-null mice are considered to be resistant to APAP-induced hepatotoxicity perhaps by the suppression of JNK phosphorylation. This study indicates the novel role of GSTM1 as a factor mediating the cellular signal for APAP-induced hepatotoxicity.     

Sex- and Age-Dependent Acetaminophen Hepato- and Nephrotoxicity in Sprague-Dawley Rats: Role of Tissue Accumulation, Nonprotein Sulfhydryl Depletion, and Covalent Binding

Acetaminophen (APAP) produces sex-dependent nephrotoxicity andhepatotoxicity in young adult Sprague-Dawley (SD) rats and age-dependenttoxicity in male rats. There is no information re garding thesusceptibility of aging female SD rats to APAP toxicity. Therefore,the present studies were designed to determine if sex-dependentdifferences in APAP toxicity persist in aging rats and to elucidatefactors contributing to sex- and age-dependent APAP hepatotoxicityand nephrotoxicity. Young adult (3 months old) and aging (18months old) male and female rats were killed from 2 through24 hr after receiving APAP (0–1250 mg/kg, ip) containing[ring-¹⁴C]APAP. Trunk blood was collected for determinationof blood urea nitrogen (BUN) concentration, serum alanine aminotransferase(ALT) activity, and plasma APAP concentration; urine was collectedfor determination of glucose and protein excretion; and liverand kidneys were removed for determination of tissue glutathione(GSH) concentration, APAP concentration, and covalent binding.APAP at 1250 mg/kg induced nephrotoxicity (as indicated by elevationsin BUN concentration) in 3-month-old females but not males,whereas APAP induced hepatotoxicity (as indicated by elevationsin serum ALT activity) in 3-month-old males but not females.Sex differences in APAP toxicity were no longer apparent in18-month-old rats. APAP at 750 mg/kg ip produced liver and kidneydamage in 18-month-old but not 3-month-old male and female rats.No consistent sex- or age-dependent differences in serum, hepatic,and renal APAP concentrations were observed that would accountfor differences in APAI toxicity. No sex- or age-dependent differencesin tissue GSH depletion or covalent binding of radiolabel fromAPAP in livers or kidneys were observed following APAP administration.Utilizing an affinity-purified polyclonal antibody raised againstAPAP, arylated proteins with electrophoretic mobility similarto those observed in mice were prominent in rat livers followingAPAP administration to 3- and 18-month-old rats of both sexes.In contrast, no arylated proteins were detected in any rat kidneysfollowing APAP administration. Absence of immunochemically detectableproteins in rat kidney following APAP administration is in directcontrast to observations in mice and supports the hypothesisthat mechanisms of APAP hepatotoxicity and nephrotoxicity inrats and mice are distinctly different. In conclusion, sex differencesin APAP toxicity are observed only in young adult (3-month-old)rats and sex differences are organ-specific with males moresusceptible to hepatotoxicity and females more susceptible tonephrotoxicity. Aging rats are more susceptible to APAP-induceddamage to both the liver and the kidney than are 3-month-oldrats but sex differences are no longer apparent in 18-month-oldrats. The mechanisms contributing to sex- and age-dependentdifferences in APAP toxicity cannot be attributed to differencesin tissue APAP concentrations, GSH depletion, or covalent binding.     

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.     

Differential gene expression in mouse liver associated with the hepatoprotective effect of clofibrate

Pretreatment of mice with the peroxisome proliferator clofibrate (CFB) protects against acetaminophen (APAP)-induced hepatotoxicity. Previous studies have shown that activation of the nuclear peroxisome proliferator activated receptor-alpha (PPARalpha) is required for this effect. The present study utilizes gene expression profile analysis to identify potential pathways contributing to PPARalpha-mediated hepatoprotection. Gene expression profiles were compared between wild type and PPARalpha-null mice pretreated with vehicle or CFB (500 mg/kg, i.p., daily for 10 days) and then challenged with APAP (400 mg/kg, p.o.). Total hepatic RNA was isolated 4 h after APAP treatment and hybridized to Affymetrix Mouse Genome MGU74 v2.0 GeneChips. Gene expression analysis was performed utilizing GeneSpring software. Our analysis identified 53 genes of interest including vanin-1, cell cycle regulators, lipid-metabolizing enzymes, and aldehyde dehydrogenase 2, an acetaminophen binding protein. Vanin-1 could be important for CFB-mediated hepatoprotection because this protein is involved in the synthesis of cysteamine and cystamine. These are potent antioxidants capable of ameliorating APAP toxicity in rodents and humans. HPLC-ESI/MS/MS analysis of liver extracts indicates that enhanced vanin-1 gene expression results in elevated cystamine levels, which could be mechanistically associated with CFB-mediated hepatoprotection.