Involvement of cytochrome P450-mediated metabolism in tienilic acid hepatotoxicity in rats

Tienilic acid is reported to be converted into electrophilic metabolites by cytochrome P450 (CYP) in vitro. In vivo, however, the metabolites have not been detected and their effect on liver function is unknown. We previously demonstrated that tienilic acid decreased the GSH level and upregulated genes responsive to oxidative/electrophilic stresses, such as heme oxygenase-1 (Ho-1), glutamate-cysteine ligase modifier subunit (Gclm) and NAD(P)H dehydrogenase quinone 1 (Nqo1), in rat liver, as well as inducing hepatotoxicity by co-treatment with the glutathione biosynthesis inhibitor l-buthionine-(S,R)-sulfoximine (BSO). In this study, for the first time, we identified a glutathione-tienilic acid adduct, a stable conjugate of putative electrophilic metabolites with glutathione (GSH), in the bile of rats given a single oral dose of tienilic acid (300mg/kg). Furthermore, a tienilic acid-induced decrease in the GSH level and upregulation of Ho-1, Gclm and Nqo1 were completely blocked by pretreatment with the CYP inhibitor 1-aminobenzotriazole (ABT, 66mg/kg, i.p.). The increase in the serum ALT level and hepatocyte necrosis resulting from the combined dosing of BSO and tienilic acid was prevented by ABT, despite a low hepatic GSH level. These findings suggest that the electrophilic metabolites of tienilic acid produced by CYP induce electrophilic/oxidative stresses in the rat liver and this contributes to the hepatotoxicity of tienilic acid under impaired GSH biosynthesis.     

Evaluation of hepatotoxicity and oxidative stress in rats treated with tert-butyl hydroperoxide

Although tert-butyl hydroperoxide (t-BHP) is commonly used to induce oxidative stress, little is known about the time- or dose-dependence of its oxidative effects. In this study, we examined hepatotoxicity and oxidative stress in male rats at various times (0–24 h) after t-BHP (0, 0.2, 0.5, 1 or 3 mmol/kg, ip) treatment. Serum hepatotoxicity parameters were increased from 2 h following 1 mmol/kg t-BHP and reached their maximum values at 8 h. Plasma malondialdehyde levels were maximally elevated by 62% at 0.5 h and returned to control levels by 4 h. Hepatic glutathione levels were decreased between 0.5 and 2 h, and hepatic glutathione disulfide levels were increased at 2 h. Interestingly, hepatic glutathione levels were increased at 24 h, which may be attributed to up-regulation of glutathione synthesis through induction of gamma-glutamylcysteine ligase expression. The elevation of hepatotoxic parameters and plasma MDA was observed from 0.5 to 1 mmol/kg t-BHP, respectively, in a dose-dependent manner. Considering that the maximal dose resulted in 20% lethality, 1 mmol/kg of t-BHP may be suitable for evaluating antioxidant activity of tested compounds. Our results provide essential information to characterize the t-BHP-induced oxidative stress and hepatotoxicity.     

Effects of buthionine sulfoximine and cysteine on the hepatotoxicity of butylated hydroxytoluene in rats

Pretreatment with buthionine sulfoximine (BSO; 900 mg/kg) induced the elevation of serum GOT and GPT activities in a non-toxic dose of butylated hydroxytoluene (BHT; 250-500 mg/kg) in rats. The elevation of serum enzyme activities was accompanied by a remarked depletion of the hepatic glutathione (GSH) concentration. In contrast, pretreatment with cysteine (100-200 mg/kg) inhibited the elevation of serum enzyme activities at a toxic dose of BHT (1000 mg/kg). The effects of BSO and cysteine on BHT-induced hepatotoxicity in rats are discussed.     

Hepatotoxicity of butylated hydroxytoluene and its analogs in mice depleted of hepatic glutathione

Butylated hydroxytoluene (2,6-di-tert-butyl-4-methylphenol, BHT) has been reported to be a lung toxicant. Mice treated with BHT (200-800 mg/kg, po) in combination with an inhibitor of glutathione (GSH) synthesis, buthionine sulfoximine (BOS; 1 hr before and 2 hr after BHT, 4 mmol/kg per dose, ip) developed hepatotoxicity characterized by an increase in serum glutamic pyruvic transaminase (GPT) activity and centrilobular necrosis of hepatocytes. The hepatotoxic response was both time- and dose-dependent. BHT (up to 800 mg/kg) alone produced no evidence of liver injury. As judged by the observation of normal serum GPT, drug metabolism inhibitors such as SKF-525A, piperonyl butoxide, and carbon disulfide prevented the hepatotoxic effect of BHT given in combination with BSO. On the other hand, pretreatment with cedar wood oil resulted in increased hepatic injury in mice treated with both BHT and BSO. Pretreatment with phenobarbital also tended to increase hepatic injury as judged by changes in serum GPT. These results suggest that BHT is activated by a cytochrome-P-450-dependent metabolic reaction and that the hepatotoxic effect is caused by inadequate rates of detoxification of the reactive metabolite in mice depleted of hepatic GSH by BSO administration. The hepatotoxic potencies of BHT-related compounds also were examined in BSO-treated animals. For hepatotoxicity, the phenolic ring must have benzylic hydrogen atoms at the 4 position and an ortho-alkyl group(s) that moderately hinders the hydroxyl group. These structural requirements essentially are the same as those for the toxic potency in the lung (T. Mizutani, I. Ishida, K. Yamamoto, and K. Tajima (1982), 62, 273-281) and support the hypothesis that BHT-quinone methide plays a role in producing liver damage in mice with depressed hepatic GSH levels.     

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.     

Protective mechanisms of anthocyanins from purple sweet potato against tert-butyl hydroperoxide-induced hepatotoxicity

Anthocyanins have been shown to exert anti-proliferative, anti-inflammatory effects and anti-carcinogenic activity. In the present work, we investigated the protective effects of anthocyanin fraction (AF) from purple sweet potato on tert-butyl hydroperoxide (t-BHP)-induced hepatotoxicity in HepG2 cell line and in rat liver. The result showed that the oral pretreatment of AF before t-BHP treatment significantly lowered the serum levels of the hepatic enzyme markers (ALT and AST) and reduced oxidative stress of the liver by evaluation of malondialdehyde and glutathione. Histopathological evaluation of the livers also revealed that AF reduced the incidence of liver lesions. The in vitro result showed that AF significantly reduced t-BHP-induced oxidative injury, as determined by cell cytotoxicity, intracellular glutathione content, lipid peroxidation, reactive oxygen species (ROS) levels, and caspases activation. Also, AF up-regulated antioxidant enzymes including heme oxygenase-1 (HO-1), NAD(P)H:quinone reductase, and glutathione S-transferase. Moreover, AF induced Nrf2 nuclear translocation and Akt and ERK1/2 activation, pathways that are involved in inducing Nrf2 nuclear translocation. Taken together, these results suggest that the protective effects of AF against t-BHP-induced hepatotoxicity may, at least in part, be due to its ability to scavenge ROS and to regulate the antioxidant enzyme HO-1 via the Akt and ERK1/2/Nrf2 signaling pathways.     

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.     

Ticlopidine-induced hepatotoxicity in a GSH-depleted rat model

We investigated hepatotoxicity induced by ticlopidine (TIC) in glutathione (GSH)-depleted rats by pre-treatment of a well-known GSH synthesis inhibitor, l-buthionine-S,R-sulfoxinine (BSO). Although sole administration of either TIC or BSO showed no signs of hepatotoxicity, combined administration of TIC with BSO induced hepatotoxicity, which was characterized by centrilobular necrosis of the hepatocytes and an elevation of plasma alanine aminotransferase activity. Administration of radio-labeled TIC in combination with BSO resulted in significantly higher covalent binding to rat liver proteins than that observed after sole dosing of radio-labeled TIC. Pre-treatment of 1-Aminobenzotriazole, a non-specific inhibitor of P450s, completely suppressed both hepatotoxicity and the increased hepatic covalent binding caused by TIC co-treatment with BSO. The results obtained in this animal model suggest that GSH depletion and covalent binding may be involved in hepatotoxicity induced by TIC. These observations may help to understand the risk factors and the mechanism of hepatotoxicity of TIC in humans.     

Metabolism-dependent hepatotoxicity of amodiaquine in glutathione-depleted mice

We investigated the hepatotoxicity induced by AQ using a glutathione (GSH)-depleted mice model. Although sole administration of either AQ or l-buthionine-S,R-sulfoxinine (BSO), a well-known GSH synthesis inhibitor, produced no significant hepatotoxicity, combined administration of AQ with BSO induced hepatotoxicity characterized by centrilobular necrosis of the hepatocytes and an elevation of plasma alanine aminotransferase activity. Pretreatment of aminobenzotriazole, a nonspecific inhibitor for P450s, completely suppressed the above hepatotoxicity caused by AQ co-treatment with BSO. Administration of radiolabeled AQ in combination with BSO exhibited significantly higher covalent binding to mice liver proteins than that observed after sole dosing of radiolabeled AQ. The results obtained in this GSH-depleted animal model suggest that the reactive metabolite of AQ formed by hepatic P450 binds to liver proteins, and then finally leads to hepatotoxicity. These observations may help to understand the risk factors and the mechanism for idiosyncratic hepatotoxicity of AQ in humans.     

Alleviation of hepatic injury by chrysin in cisplatin administered rats: Probable role of oxidative and inflammatory markers

BackgroundCisplatin is an effective and extensively used chemotherapeutic agent to treat range of malignancies, but its therapeutic use is limited because of dose-dependent nephrotoxicity and hepatotoxicity. Several published reports advocate that supplementation with antioxidant can influence cisplatin induced hepatic damage.MethodIn the present study the Wistar rats were subjected to concurrent prophylactic oral treatment of chrysin (25 and 50 mg/kg b.wt.) against the hepatotoxicity induced by intraperitoneal administration of cisplatin (7.5 mg/kg b.wt.). Efficacy of chrysin against the hepatotoxicity was evaluated in terms of biochemical estimation of antioxidant enzyme activities, histopathological changes and expression levels of molecular markers of inflammation.ResultsChrysin ameliorated cisplatin-induced lipid peroxidation, xanthine oxidase activity, glutathione depletion, decrease in antioxidant (catalase, glutathione reductase, superoxide dismutase, glutathione peroxidase and glucose-6 phosphate dehydrogenase) and phase-II detoxifying (glutathione-S-transferase and quinone reductase) enzyme activities. Chrysin also attenuated expression of COX-2, iNOS and levels of NFκB and TNF-α, and hepatic tissue damage which were induced by cisplatin. Histological findings further supported the protective effects of chrysin against cisplatin-induced hepatic damage.ConclusionThe results of the present study demonstrate that oxidative stress and inflammation are closely associated with cisplatin-induced toxicity and chrysin shows the protective efficacy against cisplatin-induced hepatotoxicity possibly via attenuating the oxidative stress and inflammatory response.     

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.     

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.     

Protective mechanisms of Aralia continentalis extract against tert-butyl hydroperoxide-induced hepatotoxicity: in vivo and in vitro studies

In the present work, we investigated the protective effects of the ethanol extract of Aralia continentalis roots (AC) on tert-butyl hydroperoxide (t-BHP)-induced hepatotoxicity in a cultured Hepa1c1c7 cell line and in mouse liver. Pretreatment with AC prior to the administration of t-BHP significantly prevented the increase in serum levels of hepatic enzyme markers (ALT, AST) and lipid peroxidation and reduced oxidative stress, as measured by glutathione content, in the liver. Histopathological evaluation of the livers also revealed that AC reduced the incidence of liver lesions. The in vitro study showed that AC significantly reduced t-BHP-induced oxidative injury in Hepa1c1c7 cells, as determined by cell cytotoxicity, intracellular glutathione content, lipid peroxidation, reactive oxygen species (ROS) levels, and caspase-3 activation. Also, AC up-regulated phase II genes including heme oxygenase-1 (HO-1), NAD(P)H:quinone reductase, and glutathione S-transferase. Moreover, AC induced Nrf2 nuclear translocation and ERK1/2 and p38 activation, pathways that are involved in inducing Nrf2 nuclear translocation. Taken together, these results suggest that the protective effects of AC against t-BHP-induced hepatotoxicity may, at least in part, be due to its ability to scavenge ROS and to regulate the antioxidant enzyme HO-1 via the ERK1/2 and p38/Nrf2 signaling pathways.     

Caffeic acid phenethyl ester protects against tamoxifen-induced hepatotoxicity in rats

Tamoxifen (TAM) is widely used in the treatment and prevention of breast cancer. Adverse effects of TAM include hepatotoxicity. Caffeic acid phenethyl ester (CAPE), an active component of propolis, has been used in folk medicine for diverse ailments. In the current study, the protective effects of CAPE against TAM-induced hepatotoxicity in female rats were evaluated. TAM (45 mg/kg/day, i.p., for 10 consecutive days) resulted in an elevation of serum alanine aminotransferase (ALT), aspartate aminotransferase (AST) and alkaline phosphatase (ALP), depletion of liver reduced glutathione (GSH) and accumulation of oxidized glutathione (GSSG) and lipid peroxidation (LPO). Also, TAM treatment resulted in inhibition of hepatic activity of glutathione reductase (GR), glutathione peroxidase (GPx), superoxide dismutase (SOD) and catalase (CAT). Further, it raised liver tumor necrosis factor-alpha (TNF-α) level and induced histopathological changes. Pretreatment with CAPE (2.84 mg/kg/day; i.p., for 20 consecutive days, starting 10 days before TAM injection) significantly prevented the elevation in serum activity of the assessed enzymes. CAPE significantly inhibited TAM-induced hepatic GSH depletion and GSSG and LPO accumulation. Consistently, CAPE normalized the activity of GR, GPx, SOD and CAT, inhibited the rise in TNF-α and ameliorated the histopathological changes. In conclusion, CAPE protects against TAM-induced hepatotoxicity.     

Multi-targeted protection of acetaminophen-induced hepatotoxicity in mice by tannic acid

Tannic acid (TA) is the polyphenol that has beneficial health effects against oxidative stress. However, the hepatoprotective effects of TA are still relatively unknown. In the present study, we evaluated the effects of TA on an acetaminophen (APAP)-induced hepatotoxicity model, which was established by administration of 400 mg/kg of APAP. The levels of alanine transferase (ALT), aspartate transferase (AST), dendothelin-1 (ET-1), nitric oxide (NO) and malondialdehyde (MDA) in the APAP-induced hepatotoxicity mice were significantly increased (up to ~ 200%), while their levels were reduced by pretreatment with TA (25 and 50 mg/kg) (P < 0.05). The activities of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH-Px) in the APAP-induced hepatotoxicity mice were significantly reduced (lower to ~ 65%), while their activities were increased by pretreatment with TA (25 and 50 mg/kg) (P < 0.05). In addition, pretreatment with oral TA (25 and 50 mg/kg) for 3 days before the APAP administration dose-dependently ameliorated changes in hepatic histopathology, suppressed overexpression of interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), c-fos, c-jun, NF-κB (p65) and caspase-3 (all P < 0.05), downregulated bax and upregulated bcl-2, nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) (all P < 0.05) in the liver. These results indicate that TA exhibits significant hepatoprotective effects against APAP-induced hepatotoxicity and suggest that the hepatoprotective mechanisms of TA may be related to anti-oxidation, anti-inflammation and anti-apoptosis.     

Failure of recovery from lead induced hepatoxicity and disruption of erythrocyte antioxidant defence system in Wistar rats

Lead acetate (PbA) is one of the major environmental contaminants with grave toxicological consequences both in the developing and developed countries. The liver and erythrocyte antioxidant status and markers of oxidative were assessed. Exposure of rats to PbA led to significant decline (p < 0.05) in hepatic and erythrocyte glutathione peroxidase (GPx), glutathione S-transferase (GST), catalase (CAT), superoxide dismutase (SOD), and reduced glutathione (GSH) content. Similarly, malondialdehyde (MDA) and H₂O₂ concentrations were significantly (p < 0.05) elevated. Histopathology and immunohistology of liver of rats exposed to PbA showed focal areas of necrosis and COX-2 expression after 6 weeks of PbA withdrawal. Taken together, hepatic and erythrocytes antioxidant defence system failed to recover after withdrawal of the exposed PbA for the period of the study. In conclusion, experimental animals exposed to PbA did not recover from hepatotoxicity and disruption of erythrocyte antioxidant defence system via free radical generation and oxidative stress.