Hepatic expression of heme oxygenase-1 and antioxidant response element-mediated genes following administration of ethinyl estradiol to rats

Heme oxygenase-1 (HO-1) is one of several enzymes induced by hepatotoxicants, and is thought to have an important protective role against cellular stress during liver inflammation and injury. The objective of the present study was to evaluate the role of HO-1 in estradiol-induced liver injury. A single dose of ethinyl estradiol (500 mg/kg, po) resulted in mild liver injury. Repeated administration of ethinyl estradiol (500 mg/kg/day for 4 days, po) resulted in no detectable liver injury or dysfunction. Using RT-PCR analysis, we demonstrate that HO-1 gene expression in whole liver tissue is elevated (>20-fold) after the single dose of ethinyl estradiol. The number and intensity of HO-1 immunoreactive macrophages were increased after the single dose of ethinyl estradiol. HO-1 expression was undetectable in hepatic parenchymal cells from rats receiving Methocel control or a single dose of ethinyl estradiol, however cytosolic HO-1 immunoreactivity in these cells after repeated dosing of ethinyl estradiol was pronounced. The increases in HO-1 mRNA and HO-1 immunoreactivity following administration of a single dose of ethinyl estradiol suggested that this enzyme might be responsible for the observed protection of the liver during repeated dosing. To investigate the effect of HO-1 expression on ethinyl estradiol-induced hepatotoxicity, rats were pretreated with hemin (50 micromol/kg, ip, a substrate and inducer of HO-1), with tin protoporphyrin IX (60 micromol/kg, ip, an HO-1 inhibitor), or with gadolinium chloride (10 mg/kg, iv, an inhibitor/toxin of Kupffer cells) 24 h before ethinyl estradiol treatment. Pretreatment with modulators of HO-1 expression and activity had generally minimal effects on ethinyl estradiol-induced liver injury. These data suggest that HO-1 plays a limited role in antioxidant defense against ethinyl estradiol-induced oxidative stress and hepatotoxicity, and suggests that other coordinately induced enzymes are responsible for protection observed with repeated administration of high doses of this compound.     

Dynamic changes of heme oxygenase-1 and carbon monoxide production in acute liver injury induced by carbon tetrachloride in rats

Heme oxygenase-1, a stress-responsive enzyme that catabolizes hemes into carbon monoxide, biliverdin, and iron, has been shown to play a pivotal role in many physiological and pathological situations. Here we investigated changes in HO-1 enzyme activity and protein expression, and its end product carbon monoxide concentrations in the liver of rats after CCl(4) treatment. We found that CCl(4) administration not only induced severe liver damage in rats, as demonstrated by dramatic elevation of ALT, AST levels and severe histopathological changes, but also resulted in a prominent up-regulation of HO-1 enzyme activity. Western blot and immunohistochemical analysis confirmed that expression of HO-1 protein was also increased significantly in a time-dependent manner following CCl(4) treatment, and localized mainly in liver cells around the central vein. In addition, CO concentrations in the liver of CCl(4)-treated rats were elevated remarkably in the same time-dependent way as HO-1 induction in contrast to the control rats. These data indicated that HO-1/CO pathway was greatly up regulated in the liver of rats after CCl(4) treatment, which might play an important protective role in the pathophysiological mechanism underlying CCl(4)-induced hepatotoxicity. It therefore suggested that more relevant studies should be carried out in the future to clarify the detailed mechanisms.     

Therapeutic potential of hemin in acetaminophen nephrotoxicity in rats

The therapeutic potential of hemin, the heme oxygenase-1 inducer, was investigated against renal damage induced by acute acetaminophen overdose in rats. Nephrotoxicity was induced by a single oral dose of acetaminophen (2.5g/kg). Hemin was given as a single s.c. injection (40μmol/kg), 1h following acetaminophen administration. Hemin treatment restored blood urea nitrogen and serum creatinine levels that were elevated by acetaminophen. Hemin also compensated deficits in the antioxidant defense mechanisms (reduced glutathione, and catalase and superoxide dismutase activities), and suppressed lipid peroxidation in renal tissue resulted from acetaminophen administration. Hemin attenuated the acetaminophen-induced elevations in renal tumor necrosis factor-α and nitric oxide levels, and caspase-3 activity. Additionally, hemin ameliorated acetaminophen-induced renal damage observed by light microscopic examination. The therapeutic effect afforded by hemin was abolished by prior administration of zinc protoporphyrin-IX, the heme oxygenase-1 inhibitor. It was concluded that hemin represents a potential therapeutic option to protect renal tissue from the detrimental effects of acute acetaminophen overdose.     

Heme oxygenase/carbon monoxide-biliverdin pathway may be involved in the antinociceptive activity of etoricoxib, a selective COX-2 inhibitor

The aim of this study was to assess the interaction between the heme oxygenase-1/ biliverdin/carbon monoxide (HO-1/BVD/CO) and cyclooxygenase-2 (COX-2) pathways in the writhing test. Mice were pretreated with 0.1, 1 or 10 mg/kg, ip etoricoxib, a selective COX-2 inhibitor, or with one of the following HO-1/BVD/CO pathway modulators: 1, 3 or 9 mg/kg, sc ZnPP IX, a specific HO-1 inhibitor, 0.3, 1 or 3 mg/kg, sc hemin, a substrate of the HO-1/BVD/CO pathway; or 0.00025, 0.025 or 2.5 μmol/kg, sc DMDC, a CO donor. Mice pretreated with etoricoxib or one of the HO-1/BVD/CO pathway modulators received an injection of acetic acid (ip) after 30 and 60 min, respectively. Next, the number of writhes was quantified between 0 and 30 min after stimulus injection. In another series of experiments, ineffective doses of etoricoxib were co-administered with hemin or DMDC and an effective dose of etoricoxib with ZnPP IX, followed by an acetic acid injection. Four hours after the acetic acid injection, levels of bilirubin, which is a product of BVD conversion by the BVD reductase enzyme, in the peritoneal lavage were determined. Hemin or DMDC reduced (p<0.05) the number of writhes, but ZnPP IX potentiated (p<0.05) the effect of acetic acid by increasing (p < 0.05) the number of writhes. The co-administration of etoricoxib with hemin or DMDC reduced (p<0.05) the number of writhes. However, the analgesic effect of etoricoxib was not observed in the presence of ZnPP IX. Pretreatment with ZnPP IX reduced bilirubin levels, but etoricoxib pretreatment significantly increased the bilirubin concentration in peritoneal exudates. The data obtained from these experiments showed that the HO-1/BVD/CO pathway was activated in the acetic acid-induced abdominal writhing model. The analgesic effect of etoricoxib was at least partially dependent on the participation of the HO-1/BVD/CO pathway.     

Failure of exogenous prostaglandin to afford complete protection against acetaminophen-induced hepatotoxicity in the rat

The protective effect of 16, 16-dimethylprostaglandin E2 (dm-PGE2) against acetaminophen-induced hepatotoxicity was determined in the rat. The dm-PGE2 was administered at two dose levels both before and after acetaminophen administration. The hepatotoxicity was evaluated by a rise in serum transaminases 24 h after acetaminophen administration and by histological examination of liver preparations. The urinary acetaminophen and its metabolites were determined by high-pressure liquid chromatography. The results suggest that exogenous dm-PGE2 administration had a modest protection against acetaminophen-induced hepatotoxicity, in contrast to its well established cytoprotective effect against many noxious agents in the gastrointestinal tract. Prostaglandin treatment had little effect on acetaminophen metabolites excretion in the urine, suggesting that it did not affect the cytochrome P-450-dependent mixed-function oxidase drug-metabolizing enzyme system. The livers from dm-PGE2-acetaminophen-treated rats showed less advanced necrosis compared to those from saline-acetaminophen-treated rats. Whereas only 2 of 13 rats died in the prostaglandin-treated group, 4 of 13 rats died in the saline-treated group.     

Sulforaphane protects against acetaminophen-induced hepatotoxicity

Oxidative stress is closely associated with acetaminophen (APAP)-induced toxicity. Heme oxygenase-1 (HO-1), an antioxidant defense enzyme, has been shown to protect against oxidant-induced tissue injury. This study investigated whether sulforaphane (SFN), as a HO-1 inducer, plays a protective role against APAP hepatotoxicity in vitro and in vivo. Pretreatment of primary hepatocyte with SFN induced nuclear factor E2-factor related factor (Nrf2) target gene expression, especially HO-1 mRNA and protein expression, and suppressed APAP-induced glutathione (GSH) depletion and lipid peroxidation, which eventually leads to hepatocyte cell death. A comparable effect was observed in mice treated with APAP. Mice were treated with 300 mg/kg APAP 30 min after SFN (5 mg/kg) administration and were then sacrificed after 6 h. APAP alone caused severe liver injuries as characterized by increased plasma AST and ALT levels, GSH depletion, apoptosis, and 4-hydroxynonenal (4-HNE) formations. This APAP-induced liver damage was significantly attenuated by pretreatment with SFN. Furthermore, while hepatic reactive oxygen species (ROS) levels were increased by APAP exposure, pretreatment with SFN completely blocked ROS formation. These results suggest that SFN plays a protective role against APAP-mediated hepatotoxicity through antioxidant effects mediated by HO-1 induction. SFN has preventive action in oxidative stress-mediated liver injury.     

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.     

Hepatoprotective effect of coenzyme Q10 in rats with acetaminophen toxicity

The potential protective effect of coenzyme Q10 against acute liver injury induced by a single dose of acetaminophen (700 mg/kg, p.o.) was investigated in rats. Coenzyme Q10 treatment was given as two i.p. injections, 10 mg/kg each, at 1 and 12 h following acetaminophen administration. Coenzyme Q10 significantly reduced the levels of serum aminotransferases, suppressed lipid peroxidation, prevented the decreases of reduced glutathione and catalase activity, decreased the elevations of tumor necrosis factor-α and nitric oxide as well as attenuating the reductions of selenium and zinc ions in liver tissue resulting from acetaminophen administration. Histopathological liver tissue damage mediated by acetaminophen was ameliorated by coenzyme Q10. Immunohistochemical analysis revealed that coenzyme Q10 significantly decreased the acetaminophen-induced overexpression of inducible nitric oxide synthase, nuclear factor-κB, caspase-3 and p53 in liver tissue. It was concluded that coenzyme Q10 protects rat liver against acute acetaminophen hepatotoxicity, most probably through its antioxidant, anti-inflammatory and antiapoptotic effects.     

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.     

Modulation by heme and zinc protoporphyrin of colonic heme oxygenase-1 and experimental inflammatory bowel disease in the rat

Reactive oxygen species, suggested to be involved in inflammatory bowel disease, may be modulated by endogenous anti-oxidant products of heme oxygenase-1 (HO-1). In the present work, HO-1 expression in trinitrobenzene sulphonic acid (TNBS)-induced colitis in the rat and the effects of HO-1 modulation, particularly by the HO-1 inducer, heme, were further evaluated. Colitis was induced by intracolonic challenge with TNBS and assessed macroscopically and by myeloperoxidase (MPO) assay. Heme oxygenase activity was determined by measurement of bilirubin formation and HO-1 protein expression was determined by Western blotting. TNBS challenge led to an early and substantial induction of HO-1 protein expression and heme oxygenase activity in the colon that peaked after 48-72 h and declined over 10 days. Heme (30 micromol/kg/day, s.c) increased colonic HO-1 protein expression and enzyme activity and decreased colonic damage and myeloperoxidase activity. Short-term administration of cadmium chloride (2 mg/kg, s.c.), another known HO-1 inducer, also reduced the colonic injury and myeloperoxidase levels. In contrast, the HO-1 inhibitor, zinc protoporphyrin (50 micromol/kg/day, s.c) significantly increased the colonic damage and myeloperoxidase activity over 10 days, as did tin protoporphyrin (30 micromol/kg/day, s.c). These results support the proposal that induction of HO-1 provides a protective mechanism in this model under both acute and more-chronic conditions, and that its selective up-regulation could thus be of therapeutic potential in colitis.     

Protective effect of arabic gum against acetaminophen-induced hepatotoxicity in mice

Overdose of acetaminophen, a widely used analgesic drug, can result in severe hepatotoxicity and is often fatal. This study was undertaken to examine the effects of arabic gum (AG), which is commonly used in processed foods, on acetaminophen-induced hepatotoxicity in mice. Mice were given arabic gum orally (100 g l(-1)) 5 days before a hepatotoxic dose of acetaminophen (500 mg kg(-1)) intraperitoneally. Arabic gum administration dramatically reduced acetaminophen-induced hepatotoxicity as evidenced by reduced serum alanine (ALT) and aspartate aminotransferase (AST) activities. Acetaminophen-induced hepatic lipid peroxidation was reduced significantly by arabic gum pretreatment. The protection offered by arabic gum does not appear to be caused by a decrease in the formation of toxic acetaminophen metabolites, which consumes glutathione, because arabic gum did not alter acetaminophen-induced hepatic glutathione depletion. Acetaminophen increased nitric oxide synthesis as measured by serum nitrate plus nitrite at 4 and 6 h after administration and arabic gum pretreatment significantly reduced their formation. In conclusion, arabic gum is effective in protecting mice against acetaminophen-induced hepatotoxicity. This protection may involve the reduction of oxidative stress.     

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.     

血红素加氧酶-1的表达对实验性肝硬化内毒素血症大鼠的影响

目的:探讨血红素加氧酶-1(HO-1)的表达对实验性肝硬化内毒素血症大鼠的影响。方法:32只健康雄性wistar大鼠,随机分为4组,正常+脂多糖(LPS)(对照组)、肝硬化+生理盐水对照组(TAA组)、肝硬化+LPS组(TAA+LPS组)、肝硬化+LPS+hemin(氯化高铁血红素)(HM组)。用硫代乙酰胺(TAA)诱导肝硬化模型时间共计10周,对照组自由饮清水。于模型造成后,向对照组、TAA+LPS组、HM组大鼠腹腔内注入LPS3 mg/kg;TAA组大鼠腹腔内注入等量的生理盐水;HM组于注射LPS 12 h前,腹腔注射HM(40 mg/kg),并在注入LPS 6 h后,各组动物经腹主动脉穿刺采全血观察血浆中丙氨酸氨基转移酶(ALT)、天门冬氨基酸转移酶(AST)、一氧化氮(NO)及丙二醛(MDA)的表达。留肝组织用免疫组织化学法观察HO-1的表达。结果:对照组、TAA组、TAA+LPS组、HM组血浆中的ALT/AST、MDA、NO依次升高差异有显著性(P<0.05),对照组、TAA、TAA+LPS、HM组各组大鼠的灰阶值显著依次降低,且有明显差别(P<0.05)。结论:在实验性的肝硬化内毒素中尽管HO-1的表达增加,但它未起到保护作用,它与内毒素对机体的损伤有关。     

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.     

Examination of the protective effect of ICRF-187 and dimethyl sulfoxide against acetaminophen-induced hepatotoxicity in Syrian golden hamsters

The protective activity of 1,2-bis(3,5-dioxopiperazin-l-yl)propane (ICRF-187) and dimethyl sulfoxide (DMSO) was tested against acetaminophen-induced hepatotoxicity. Male Syrian golden hamsters injected intraperitoneally between 18:00 h and 20:00 h for 2 consecutive days with acetaminophen (N-acetyl-p-aminophenol) (300 mg/kg) displayed signs of hepatotoxicity as evidenced by increases in enzyme activity and cellular damage. Forty-eight hours after the second acetaminophen dose, the activities of serum glutamic-pyruvic transaminase and alkaline phosphatase were increased compared with levels found in hamsters given only saline. In addition, hepatocellular necrosis was evident in acetaminophen-treated animals. ICRF-187 (300 mg/kg) given 1 h before acetaminophen attenuated the increases in enzyme activities, and both DMSO (7.3 g/kg) and ICRF-187 reduced the incidence and severity of acetaminophen-induced hepatocellular injury. Both ICRF-187 and DMSO are capable of altering free radical-mediated toxicity in other experimental systems. Whether these compounds reduce acetaminophen-induced liver toxicity by a similar mechanism remains to be determined.     

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 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.     

Retinol potentiates acetaminophen-induced hepatotoxicity in the mouse: mechanistic studies.

This study was designed to elucidate the mechanism of retinol's potentiation of acetaminophen-induced hepatotoxicity. To accomplish this, the major bioactivation and detoxification pathways for acetaminophen were investigated following retinol (75 mg/kg/day, 4 days), acetaminophen (400 mg/kg), and retinol + acetaminophen treatment. Hepatic microsomes were used to determine the catalytic activity and polypeptide levels of cytochrome P450 enzymes involved in the murine metabolism of acetaminophen. Results showed that the catalytic activity and polypeptide levels of CYP1A2, CYP2E1, and CYP3A were unchanged in the treatment groups compared to vehicle and untreated controls. In combination, retinol + acetaminophen caused a significantly greater depletion of GSH compared to corn oil + acetaminophen (0.36 +/- 0.11 vs 0.89 +/- 0.19 micromol/g, respectively, p < 0.05). This greater GSH depletion correlated with a higher degree of hepatic injury in the retinol + acetaminophen-treated animals but is probably not the cause of the potentiated injury since the results showed that retinol treatment itself did not alter hepatic glutathione (3.34 +/- 0.43 vs 3.44 +/- 0.46 micromol/g for retinol vs vehicle, respectively). However, hepatic UDPGA stores were decreased in the retinol-treated group compared to untreated and corn oil controls (54.6 +/- 10.6 vs 200.6 +/- 17.6 nmol/g for retinol and untreated control, respectively, p < 0.001). This demonstrates that there is significantly less hepatic UDPGA available for conjugation following retinol administration. The results suggest that decreased hepatic UDPGA is likely the cause of retinol's potentiation of acetaminophen-induced hepatic injury.