Acetaminophen-induced hepatic glycogen depletion and hyperglycemia in mice

Two hours following administration of a hepatotoxic dose of acetaminophen (500 mg/kg, i.p.) to mice, liver sections stained with periodic acid Schiff reagent showed centrilobular hepatic glycogen depletion. A chemical assay revealed that following acetaminophen administration (500 mg/kg) hepatic glycogen was depleted by 65% at 1 hr and 80% at 2 hr, whereas glutathione was depleted by 65% at 0.5 hr and 80% at 1.5 hr. Maximal glycogen depletion (85% at 2.5 hr correlated with maximal hyperglycemia (267 mg/100 ml at 2.5hr). At 4.0 hr following acetaminophen administration, blood glucose levels were not significantly different from saline-treated animals; however, glycogen levels were still maximally depleted. A comparison of the dose-response curves for hepatic glycogen depletion and glutathione depletion showed that acetaminophen (50–500 mg/kg at 2.5 hr) depleted both glycogen and glutathione by similar percentages at each dose. Since acetaminophen (100 mg/kg at 2.5 hr) depleted glutathione and glycogen by approximately 30%, evidence for hepatotoxicity was examined at this dose to determine the potential importance of hepatic necrosis in glycogen depletion. Twenty-four hours following administration of acetaminophen (100 mg/kg) to mice, histological evidence of hepatic necrosis was not detected and serum glutamate pyruvate transaminase (SGPT) levels were not significantly different from saline-treated mice. The potential role of glycogen depletion in altering the acetaminophen-induced hepatotoxicity was examined subsequently. When mice were fasted overnight, hepatic glutathione and glycogen were decreased by 40 and 75%, respectively, and fasted animals showed a dramatic increase in susceptibility to acetaminophen-induced hepatotoxicity as measured by increased SGPT levels. Availability of glucose in the drinking water (5%) overnight resulted in glycogen levels similar to those in fed animals, whereas hepatic glutathione levels were not significantly different from those of fasted animals. Fasted animals and animals given glucose water overnight were equally susceptible to acetaminophen-induced hepatotoxicity, as quantitated by increases in SGPT levels 24 hr after drug administration. The potential role of a reactive metabolite in glycogen depletion was investigated by treating mice with N-acetylcysteine to increase detoxification of the reactive metabolite. N-Acetylcysteine treatment of mice prevented acetaminophen-induced glycogen depletion.     

Effects of butylated hydroxyanisole on acetaminophen hepatotoxicity and glucuronidation in vivo

The present study examined the effects of butylated hydroxyanisole (BHA) on acetaminophen-induced hepatotoxicity and metabolism in vivo with emphasis on possible changes in the glucuronidation pathway. Female Swiss-Webster mice received BHA in the diet (1% w/w) for 12 days (600 to 800 mg/kg/day). BHA prevented acetaminophen hepatotoxicity (600 mg/kg, ip), based on serum alanine and aspartate aminotransferase activities and histopathological examination. The rate of elimination of acetaminophen from blood was 10-fold higher in BHA-fed mice (clearance, 49 ml/min/kg) than in controls (4.4 ml/min/kg). In general, the urinary metabolite excretion patterns in control and BHA-treated mice were the same. However, the rates of acetaminophen conjugation via the sulfation, glucuronidation, and mercapturic acid pathways were enhanced with the rate of glucuronide formation, the major biotransformation pathway of acetaminophen, increased sevenfold in BHA-treated mice (0.041 min-1) compared to controls (0.006 min-1). BHA increased hepatic UDP-glucuronosyltransferase activity twofold, as well as hepatic UDP-glucuronic acid concentrations. In addition, after acetaminophen administration, UDP-glucuronic acid in BHA-treated mice was depleted to a lesser extent and returned to control values more rapidly than in untreated animals. BHA had a similar but less pronounced effect on hepatic glutathione levels. The findings indicate that the rate of acetaminophen glucuronidation is increased in vivo during BHA feeding to mice. This effect appears to play a role in the enhanced excretion of acetaminophen as well as protection against acetaminophen-induced hepatotoxicity.     

Anti-hepatotoxic effects of 3,4-methylenedioxyphenol and N-acetylcysteine in acutely acetaminophen-overdosed mice

3,4-Methylenedioxyphenol (sesamol) is effective against acetaminophen-induced liver injury in rats. Whether sesamol's anti-hepatotoxic effect is comparable to that of N-acetylcysteine has never been studied. We investigated the anti-hepatotoxic effects of sesamol and N-acetylcysteine on acetaminophen-induced hepatotoxicity in mice. Equimolar doses (1 mmol/kg) of sesamol and N-acetylcysteine significantly inhibited acetaminophen (300 mg/kg)-increased serum aspartate transaminase and alanine transaminase levels 6 h post-administration. Sesamol and N-acetylcysteine maintained hepatic glutathione levels and inhibited lipid peroxidation. Moreover, the combination of sesamol and N-acetylcysteine antagonistically inhibited sesamol's protection against acetaminophen-induced liver injury. We conclude that the protective effect of sesamol against acetaminophen-induced liver damage is comparable to that of N-acetylcysteine by maintaining glutathione levels and inhibiting lipid peroxidation in mice.     

Thymoquinone supplementation reverses acetaminophen-induced oxidative stress,nitric oxide production and energy decline in mice liver

This study was undertaken to evaluate the protective effect of thymoquinone (TQ) against acetaminophen-induced hepatotoxicity. Mice were given TQ orally at three different doses (0.5, 1 and 2 mg/kg/day) for 5 days before a single hepatotoxic dose of acetaminophen (500 mg/kg i.p.). TQ supplementation dramatically reduced acetaminophen-induced hepatotoxicity, in a dose-dependent manner, as evidenced by decreased serum alanine aminotransferase (ALT) activities.Acetaminophen (500 mg/kg i.p.) resulted in a significant increase in serum ALT and total nitrate/nitrite, hepatic lipid peroxides and a significant decrease in hepatic reduced glutathione (GSH) and ATP in a time-dependent manner. Interestingly, supplementation of TQ (2 mg/kg/day) for 5 days before acetaminophen administration resulted in reversal of acetaminophen-induced increase in ALT, total nitrate/nitrite, lipid peroxide and a decrease in GSH and ATP. Moreover, TQ did not affect acetaminophen-induced early decrease in hepatic GSH indicating lack of the effect on the metabolic activation of acetaminophen.In conclusion, TQ is effective in protecting mice against acetaminophen-induced hepatotoxicity possibly via increased resistance to oxidative and nitrosative stress as well as its ability to improve the mitochondrial energy production.     

Mechanism of ketone-induced protection from acetaminophen hepatotoxicity in the rat

The effects of ketones on acetaminophen metabolism and hepatotoxicity were investigated in male rats. Ketosis was produced by oral administration of either acetone or 1,3-butanediol. Histologic studies revealed that both ketogenic agents conferred protection from acetaminophen-induced liver necrosis. Pharmacokinetic studies indicated that both acetone and 1,3-butanediol: a) increased the blood half-life of acetaminophen, b) markedly decreased the apparent rate constant for formation of acetaminophen mercapturate, and c) modestly decreased the capacities for acetaminophen sulfate formation and renal elimination of the drug. Neither acetone nor 1,3-butanediol had any effect on either the apparent rate constant for formation of acetaminophen glucuronide or on the predrug levels of hepatic glutathione. However, after a large dose of acetaminophen, the rate and percentage of glutathione depletion were markedly less in 1,3-butanediol-treated rats and modestly less in acetone-treated rats as compared with controls. These data indicate that acetone- or 1,3-butanediol-induced ketosis confers protection from hepatic necrosis due largely to decreased formation of the reactive metabolite. The effects of ketosis and of diabetes on acetaminophen metabolism and hepatotoxicity are compared.     

Anomalous susceptibility of the fasted hamster to acetaminophen hepatotoxicity

The effect of an acute fast on susceptibility to acetaminophen-induced hepatotoxicity was investigated in male Golden Syrian hamsters. Overnight starvation markedly elevated hepatic levels of glutathione throughout the diurnal cycle (peak concentration: 10.6 +/- 0.06 mM vs 7.3 +/- 0.3mM in controls). However, despite this apparent increase in the glutathione protective capacity of the liver, acetaminophen-induced hepatic necrosis was modestly potentiated by fasting, as judged by liver histology and elevation of serum transaminase (SGOT) activity. Parallel pharmacokinetic studies indicated that the overall elimination rate constant for acetaminophen was decreased in fasted animals, due largely to decreases in the apparent rate constants for formation of acetaminophen glucuronide and acetaminophen mercapturate. Formation of acetaminophen sulfate was not affected by fasting. Since the major nontoxic pathway (glucuronide) and the toxic pathway (as measured by mercapturate) decreased to a similar extent, the data indicate that the anomalous lack of protection cannot be explained on the basis of altered metabolic disposition of the drug. Measurement of hepatic glutathione levels revealed that, despite the higher initial level of glutathione in the fasted animals, the nadir to which liver glutathione levels fell after acetaminophen was the same in fed and fasted animals. Comparison of the amount of acetaminophen mercapturate in the urine with the amount of glutathione which disappeared from the liver showed close agreement for fed animals, but a major discrepancy for fasted hamsters. These data indicate that a major fraction of glutathione in the liver of the fasted hamsters is not utilized for detoxification of the acetaminophen reactive metabolite and hence does not contribute to the glutathione protective capacity.     

Effects and mechanisms of rifampin on hepatotoxicity of acetaminophen in mice

This study examined the effects and possible mechanisms of rifampin against acetaminophen-induced hepatotoxicity in mice. Rifampin significantly enhanced the biotransformation of acetaminophen, evidenced by the increase in p-aminophenol formation in rifampin-treated microsomes and the increase in plasma clearance rate of acetaminophen. Pretreatment with rifampin significantly decreased serum alanine transaminase (ALT) activities, aspartate transaminase (AST) activities and prevented severe liver necrosis following acetaminophen overdose. The contents and activities of microsomal drug-metabolizing enzyme were less affected in rifampin-pretreated mice in comparison to the animals treated with acetaminophen alone. Rifampin was capable of increasing glutathione (GSH) level and GSH reductase activity and reducing GSH depletion and the decrease in GSH reductase activity by acetaminophen in mice. In addition, it was found that the microsomal Ca²⁺-ATPase activity was not directly related to acetaminophen toxic species generated in the P450 enzyme system in vitro. These findings suggest that rifampin has species-specific effects on the liver against acetaminophen-induced hepatotoxicity in mice, which increase the level of GSH by promoting GSH regeneration.     

Zingiber officinale Roscoe prevents acetaminophen-induced acute hepatotoxicity by enhancing hepatic antioxidant status.

A large number of xenobiotics are reported to be potentially hepatotoxic. Free radicals generated from the xenobiotic metabolism can induce lesions of the liver and react with the basic cellular constituents - proteins, lipids, RNA and DNA. Hepatoprotective activity of aqueous ethanol extract of Zingiber officinale was evaluated against single dose of acetaminophen-induced (3g/kg, p.o.) acute hepatotoxicity in rat. Aqueous extract of Z. officinale significantly protected the hepatotoxicity as evident from the activities of serum transaminase and alkaline phosphatase (ALP). Serum glutamate pyruvate transaminase (SGPT), serum glutamate oxaloacetate transaminase (SGOT) and ALP activities were significantly (p<0.01) elevated in the acetaminophen alone treated animals. Antioxidant status in liver such as activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase and glutathione-S-transferase (GST), a phase II enzyme, and levels of reduced glutathione (GSH) were declined significantly (p<0.01) in the acetaminophen alone treated animals (control group). Hepatic lipid peroxidation was enhanced significantly (p<0.01) in the control group. Administration of single dose of aqueous extract of Z. officinale (200 and 400mg/kg, p.o.) prior to acetaminophen significantly declines the activities of serum transaminases and ALP. Further the hepatic antioxidant status was enhanced in the Z. officinale plus acetaminophen treated group than the control group. The results of the present study concluded that the hepatoprotective effect of aqueous ethanol extract of Z. officinale against acetaminophen-induced acute toxicity is mediated either by preventing the decline of hepatic antioxidant status or due to its direct radical scavenging capacity.     

Protective effects of selenium on acetaminophen-induced hepatotoxicity in the rat

Experiments were undertaken to examine the ability of selenium to protect against acetaminophen-induced hepatotoxicity and to examine possible mechanisms for this protective effect. Pretreatment of male, Sprague-Dawley rats with sodium selenite (12.5 mumol Se/kg, ip) 24 hr prior to acetaminophen administration produced a significant protection against the hepatotoxic effects of acetaminophen as assessed by a decrease in the plasma appearance of alanine aminotransferase and aspartate aminotransferase activities following acetaminophen. This was accompanied by an increase in the hepatic glutathione levels in selenium-treated animals and an inhibition in the decrease in hepatic glutathione content observed in animals receiving hepatotoxic doses of acetaminophen. Selenium pretreatment decreased the in vivo covalent binding of acetaminophen metabolites to hepatic protein, but did not alter hepatic microsomal cytochrome P-450 content or NADPH cytochrome c reductase activity, suggesting that selenium does not significantly alter the metabolism of acetaminophen to reactive electrophilic metabolites by the cytochrome P-450-dependent mixed-function oxidase enzyme system. Selenium produced an increase in the activity of gamma-glutamylcysteine synthetase which may account for the increased glutathione availability in selenium-treated animals and increased the activities of glutathione S-transferase and glucose-6-phosphate dehydrogenase. Examination of the urinary metabolite profile in selenium-treated animals revealed that the urinary excretion of acetaminophen and its metabolites was significantly increased over a 72-hr period. The increase occurred in the AAP-glucuronide metabolite while parent AAP and AAP-sulfate were actually decreased in selenium-treated rats. No change in recovery was observed in the AAP-glutathione or AAP-mercapturate urinary metabolites. While the glutathione conjugating system is enhanced by selenium treatment, amelioration of acetaminophen toxicity is most likely the result of enhanced glucuronidation which effectively diverts the amount of acetaminophen to be converted by the cytochrome P-450 system to the toxic metabolite.     

Role of tumor necrosis factor receptor 1 (p55) in hepatocyte proliferation during acetaminophen-induced toxicity in mice

Hepatocyte proliferation represents an important part of tissue repair. In these studies, TNF receptor 1 (TNFR1) knockout mice were used to analyze the role of TNF-alpha in hepatocyte proliferation during acetaminophen-induced hepatotoxicity. Treatment of wild-type (WT) mice with acetaminophen (300 mg/kg) resulted in centrilobular hepatic necrosis. This was associated with proliferation of hepatocytes surrounding the damaged areas, which was evident at 24 h. The cell cycle regulatory proteins, cyclin D1 and cyclin A, were also up regulated in hepatocytes. In contrast, in TNFR1-/- mice, which exhibit exaggerated acetaminophen hepatotoxicity, hepatocyte proliferation, and expression of cyclin D1 and cyclin A, as well as the cyclin dependent kinases, Cdk4 and Cdk2, were reduced. The cyclin-dependent kinase inhibitor p21 was also induced in the liver following acetaminophen administration. This was greater in TNFR1-/- mice compared to WT mice. To investigate mechanisms mediating the reduced hepatic proliferative response of TNFR1-/- mice, we analyzed phosphatidyl inositol-3-kinase (PI-3K) signaling. In both WT and TNFR1-/- mice, acetaminophen caused a rapid increase in total PI-3K within 3 h. Acetaminophen also increased phosphorylated PI-3K, but this was delayed 6-12 h in TNFR1-/- mice. Expression of Akt, a downstream target of PI-3K, was increased in both WT and TNFR1-/- mice in response to acetaminophen. However, the increase was greater in WT mice. Acetaminophen-induced expression of phosphorylated STAT3, a key regulator of cytokine-induced hepatocyte proliferation, was also delayed in TNFR1-/- mice relative to WT. These data suggest that TNF-alpha signaling through TNFR1 is important in regulating hepatocyte proliferation following acetaminophen-induced tissue injury. Delayed cytokine signaling may account for reduced hepatocyte proliferation and contribute to exaggerated acetaminophen-induced hepatotoxicity in TNFR1-/- mice.     

Effect of acetylsalicylic acid on a toxic dose of acetaminophen in the mouse

The effect of acetylsalicylic acid (ASA) on the toxicity and metabolism of [¹⁴C]acetaminophen was studied in the mouse. Pretreatment with ASA did not affect lethality, but hepatotoxicity as determined by plasma transaminases was reduced by ASA pretreatment. The blood concentration profiles of radioactivity were altered by ASA following po and ip administration. It was suggested that ASA reduced the rate of acetaminophen absorption and inhibited elimination. Paper chromatography of urine showed that following ip dosing ASA reduced the excretion of sulfate conjugate but increased the excretion of total catabolites of the glutathione conjugate. In the po study a similar inhibition of sulfation was observed, but excretion of total glutathione degradation products was not altered statistically even though excretion of mercapturate was statistically elevated by ASA pretreatment. An attempt was made to correlate the excretion of glutathione degradation products (an estimate of the toxic pathway) with toxicity. A direct correlation could not always be demonstrated, and it was concluded that factors additional to toxic metabolite formation modified acetaminophen-induced hepatotoxicity in the mouse.     

Effect of H2-receptor antagonists on acetaminophen-induced hepatic injury

The effects of H2-antagonists on acetaminophen-induced hepatic injury were examined. Rats were administered acetaminophen at the dose of 800 mg/kg body, 60 hr after injection of 3-methylcholanthrene. As an H2-antagonist, cimetidine (200 mg/kg), ranitidine (50 mg or 100 mg/kg), or famotidine (20 mg or 40 mg/kg) was administered before and after acetaminophen injection. The group administered only acetaminophen had been severely damaged as evaluated by changes in serum transaminase, P-450 content, aminopyrine demethylation, glutathione content and histological study, but administration of 200 mg cimetidine together with acetaminophen significantly reduced the hepatic injury to nearly the control level. Ranitidine had no protective effect against hepatic injury at the dose of 50 mg, which appears to have the same antacid effect as 200 mg cimetidine, whereas it had a slight but significant protective effect as evaluated by the transaminase level, glutathione content and histological study at the dose of 100 mg. Famotidine had no effect against acetaminophen induced hepatic injury. Because famotidine had no effect, the protection by H2-antagonist against acetaminophen-induced hepatic injury cannot be explained by the decrease in hepatic blood flow alone. Therefore, inhibition of P-450 activity seems to be more important for reducing the generation of the reactive metabolites of acetaminophen than hepatic blood flow decrease.     

Effect of amlodipine,lisinopril and allopurinol on acetaminophen-induced hepatotoxicity in rats

BackgroundExposure to chemotherapeutic agents such as acetaminophen may lead to serious liver injury. Calcium deregulation, angiotensin II production and xanthine oxidase activity are suggested to play mechanistic roles in such injury.ObjectiveThis study evaluates the possible protective effects of the calcium channel blocker amlodipine, the angiotensin converting enzyme inhibitor lisinopril, and the xanthine oxidase inhibitor allopurinol against experimental acetaminophen-induced hepatotoxicity, aiming to understand its underlying hepatotoxic mechanisms.Material and methodsAnimals were allocated into a normal control group, a acetaminophen hepatotoxicity control group (receiving a single oral dose of acetaminophen; 750 mg/kg/day), and four treatment groups receive N-acetylcysteine (300 mg/kg/day; a reference standard), amlodipine (10 mg/kg/day), lisinopril (20 mg/kg/day) and allopurinol (50 mg/kg/day) orally for 14 consecutive days prior to acetaminophen administration. Evaluation of hepatotoxicity was performed by the assessment of hepatocyte integrity markers (serum transaminases), oxidative stress markers (hepatic malondialdehyde, glutathione and catalase), and inflammatory markers (hepatic myeloperoxidase and nitrate/nitrite), in addition to a histopathological study.ResultsRats pre-treated with amlodipine, lisinopril or allopurinol showed significantly lower serum transaminases, significantly lower hepatic malondialdehyde, myeloperoxidase and nitrate/nitrite, as well as significantly higher hepatic glutathione and catalase levels, compared with acetaminophen control rats. Serum transaminases were normalized in the lisinopril treatment group, while hepatic myeloperoxidase was normalized in the all treatment groups. Histopathological evaluation strongly supported the results of biochemical estimations.ConclusionAmlodipine, lisinopril or allopurinol can protect against acetaminophen-induced hepatotoxicity, showing mechanistic roles of calcium channels, angiotensin converting enzyme and xanthine oxidase enzyme in the pathogenesis of hepatotoxicity induced by acetaminophen.     

Effect of nifedipine,verapamil, diltiazem and trifluoperazine on acetaminophen toxicity in mice

The hepatotoxicity of acetaminophen overdose depends on the metabolic activation to a toxic reactive metabolite by the hepatic mixed function oxidases. There is evidence that an increase in cytosolic Ca²⁺ is involved in acetaminophen hepatotoxicity. The effects of the Ca²⁺-antagonists nifedipine (NF), verapamil (V), diltiazem (DL) and of the calmodulin antagonist trifluoperazine (TFP) on the activity of some drug-metabolizing enzyme systems, lipid peroxidation and acute acetaminophen toxicity were studied in male albino mice. No changes in the drug-metabolizing enzyme activities studies and in the cytochrome P-450 and b₅ contents were observed 1 h after oral administration of V (20 mg/kg), DL (70 mg/kg) and TFP (3 mg/kg). NF (50 mg/kg) increased cytochrome P-450 content, NADPH-cytochrome c reductase and ethylmorphine-N-demethylase activities. DL and TFP significantly decreased lipid peroxidation. NF, V, DL and TFP administered 1 h before acetaminophen (700 mg/kg orally) increased the mean survival time of animals. A large increase of serum aspartate aminotransferase (AST), and liver weight and depletion of liver reduced glutathione (GSH) occurred in animals receiving toxic acetaminophen dose. NF, V and DL prevented and TFP decreased the acetaminophen-induced hepatic damage measured both by plasma AST and by liver weight. NF, V, DL and TFP changed neither the hepatic GSH level nor the GSH depletion provoked by the toxic dose of acetaminophen. This suggests that V, DL and TFP do not influence the amount of the acetaminophen toxic metabolite formed in the liver. The possible mechanism of the protective effect of NF, V, DL and TFP on the acetaminophen-induced toxicity is discussed.     

Hepatotoxicity after 3'-hydroxyacetanilide administration to buthionine sulfoximine pretreated mice.

The administration of 3'-hydroxyacetanilide, a regioisomer of acetaminophen, to mice failed to produce hepatotoxicity even after the administration of diethyl maleate. In contrast, hepatotoxicity did occur when 3'-hydroxyacetanilide was administered to buthionine sulfoximine pretreated mice. Although the administration of 3'-hydroxyacetanilide in conjunction with either diethyl maleate or buthionine sulfoximine depleted total hepatic glutathione, only the combined buthionine sulfoximine-3'-hydroxyacetanilide treatment decreased hepatic mitochondrial glutathione concentrations to below 20% of control values. In addition, pretreatment with buthionine sulfoximine increased the amount of 3'-hydroxyacetanilide bound to mitochondrial proteins. These results, in conjunction without previous results on the involvement of mitochondrial damage in the pathogenesis of hepatotoxicity caused by acetaminophen, suggest a probable relationship between mitochondrial damage caused by the buthionine sulfoximine-3'-hydroxyacetanilide treatment and hepatotoxicity caused by this treatment.     

Protective role of dietary butylated hydroxyanisole against chemical-induced acute liver damage in mice

Prior consumption of a diet containing the food antioxidant, butylated hydroxyanisole (BHA), by female mice prevented the development of or minimized the acute liver damage caused by monocrotaline, acetaminophen, or bromobenzene. In contrast, neither the incidence nor the severity of carbon tetrachloride-induced hepatotoxicity was affected by dietary BHA. Hepatotoxicity was judged by plasma alanine aminotransferase and aspartate aminotransferase levels, hepatic cytochrome P-450 content, and liver histology. The protective effect of BHA against acetaminophen-induced hepatotoxicity was not demonstrated in male mice. The observed protection by dietary BHA against acetaminophen- and bromobenzene-induced hepatotoxicity was associated with the increase of liver glutathione. It is concluded that the protective action of BHA is dependent upon the nature of the toxic agent.     

Protective effect of Platycodi radix on carbon tetrachloride-induced hepatotoxicity.

The protective effects of a Platycodi radix (Changkil: CK), the root of Platycodon grandiflorum A. DC (Campanulaceae) on carbon tetrachloride (CC14)-induced hepatotoxicity and the possible mechanisms involved in this protection were investigated in mice. Pretreatment with CK prior to the administration of CC14 significantly prevented the increased serum enzymatic activities of alanine and aspartate aminotransferase in a dose-dependent manner. In addition, pretreatment with CK also significantly prevented the elevation of hepatic malondialdehyde formation and the depletion of reduced glutathione content in the liver of CC14-intoxicated mice. However, hepatic reduced glutathione levels and glutathione S-transferase activities were not affected by treatment with CK alone. CC14-induced hepatotoxicity was also essentially prevented, as indicated by a liver histopathologic study. The effects of CK on the cytochrome P450 (P450) 2E1, the major isozyme involved in CC14 bioactivation were also investigated. Treatment of mice with CK resulted in a significant decrease of P450 2E1-dependent p-nitrophenol and aniline hydroxylation in a dose-dependent manner. CK showed antioxidant effects in FeCl2-ascorbate-induced lipid peroxidation in mice liver homogenate and in superoxide radical scavenging activity. Our results suggest that the protective effects of CK against CC14-induced hepatotoxicity possibly involve mechanisms related to its ability to block P450-mediated CC14 bioactivation and free radical scavenging effects.     

Potential role of caveolin-1 in acetaminophen-induced hepatotoxicity

Caveolin-1 (Cav-1) is a membrane scaffolding protein, which functions to regulate intracellular compartmentalization of various signaling molecules. In the present studies, transgenic mice with a targeted disruption of the Cav-1 gene (Cav-1^−/−) were used to assess the role of Cav-1 in acetaminophen-induced hepatotoxicity. Treatment of wild-type mice with acetaminophen (300 mg/kg) resulted in centrilobular hepatic necrosis and increases in serum transaminases. This was correlated with decreased expression of Cav-1 in the liver. Acetaminophen-induced hepatotoxicity was significantly attenuated in Cav-1^−/− mice, an effect that was independent of acetaminophen metabolism. Acetaminophen administration resulted in increased hepatic expression of the oxidative stress marker, lipocalin 24p3, as well as hemeoxygenase-1, but decreased glutathione and superoxide dismutase-1; no differences were noted between the genotypes suggesting that reduced toxicity in Cav-1^−/− mice is not due to alterations in antioxidant defense. In wild-type mice, acetaminophen increased mRNA expression of the pro-inflammatory cytokines, interleukin-1β, and monocyte chemoattractant protein-1 (MCP-1), as well as cyclooxygenase-2, while 15-lipoxygenase (15-LOX), which generates anti-inflammatory lipoxins, decreased. Acetaminophen-induced changes in MCP-1 and 15-LOX expression were greater in Cav-1^−/− mice. Although expression of tumor necrosis factor-α, a potent hepatocyte mitogen, was up-regulated in the liver of Cav-1^−/− mice after acetaminophen, expression of proliferating cell nuclear antigen and survivin, markers of cellular proliferation, were delayed, which may reflect the reduced need for tissue repair. Taken together, these data demonstrate that Cav-1 plays a role in promoting inflammation and toxicity during the pathogenesis of acetaminophen-induced injury.     

双环醇对扑热息痛引起小鼠肝脏能量代谢和线粒体功能障碍的影响

目的　研究双环醇对扑热息痛(对乙酰氨基酚)引起小鼠肝能量代谢紊乱和线粒体功能障碍的保护作用。方法　小鼠ip扑热息痛120mg·kg^-1 引起急性肝损伤,观察血清谷丙转氨酶(ALT)和谷草转氨酶(AST)水平、肝活体磷谱、肝线粒体膜流动性及线粒体ATPase活性的改变。结果　双环醇可显著抑制扑热息痛中毒小鼠PME/ATP及PME/PDE的升高。双环醇(200mg·kg^-1)可显著降低扑热息痛导致的线粒体膜流动性下降,并对线粒体ATPase活性降低有显著保护作用。结论　双环醇可保护扑热息痛导致的急性肝损伤,使肝脏能量代谢和磷脂代谢趋于正常,并对损伤的线粒体功能有显著的保护作用     

In vivo and in vitro hepatotoxicity and metabolism of acetaminophen in Syrian hamsters

The purpose of this investigation was to correlate the in vitro and in vivo toxicity of the hepatotoxicant, acetaminophen. Hamsters were pretreated with either phenobarbital (70 mg/kg) or 3-methylcholanthrene (20 mg/kg) or an appropriate vehicle for 3 days. In non-pretreated hamsters, single doses of acetaminophen (200-400 mg/kg i.p.) caused elevations in serum alanine aminotransferase and sorbitol dehydrogenase activities in a dose-related manner. 3-Methylcholanthrene significantly potentiated, while phenobarbital significantly reduced acetaminophen-induced elevations in serum liver enzyme activities. Both phenobarbital and 3-methylcholanthrene significantly reduced acetaminophen plasma T1/2 while only 3-methylcholanthrene increased APAP clearance. Phenobarbital pretreatment increased the urinary excretion of APAP-glucuronide. Exposure of isolated hepatocytes to acetaminophen (0.01-2.0 mM) resulted in concentration-related decreases in hepatocyte viability. Cells from 3-methylcholanthrene-pretreated hamsters were more markedly susceptible to acetaminophen toxicity than cells isolated from non-induced animals. Hepatocytes isolated from phenobarbitol pretreated animals were slightly but significantly more susceptible to acetaminophen toxicity than cells from control animals. Hepatocytes isolated from 3-methylcholanthrene pretreated animals had increased formation of an acetaminophen-glutathione conjugate compared to control. Pre-treatment with either phenobarbital or 3-methylcholanthrene enhanced glucuronidation of acetaminophen in vitro. These data demonstrate a lack of correlation between in vivo hepatotoxicity and in vitro cytotoxicity in that phenobarbital pre-treatment protected hamsters from acetaminophen-induced liver toxicity, but failed to protect hepatocytes exposed to acetaminophen in vitro.