Acetaminophen-induced hepatic injury in mice: the role of lipid peroxidation and effects of pretreatment with coenzyme Q10 and alpha-tocopherol

Understanding coenzyme Q

Coenzyme Q (CoQ), also known as ubiquinone, comprises a benzoquinone head group and a long isoprenoid side chain. It is thus extremely hydrophobic and resides in membranes. It is best known for its complex function as an electron transporter in the mitochondrial electron transport chain (ETC) but is also required for several other crucial cellular processes. In fact, CoQ appears to be central to the entire redox balance of the cell. Remarkably, its structure and therefore its properties have not changed from bacteria to vertebrates. In metazoans, it is synthesized in all cells and is found in most, and maybe all, biological membranes. CoQ is also known as a nutritional supplement, mostly because of its involvement with antioxidant defenses. However, whether there is any health benefit from oral consumption of CoQ is not well established. Here we review the function of CoQ as a redox-active molecule in the ETC and other enzymatic systems, its role as a prooxidant in reactive oxygen species generation, and its separate involvement in antioxidant mechanisms. We also review CoQ biosynthesis, which is particularly complex because of its extreme hydrophobicity, as well as the biological consequences of primary and secondary CoQ deficiency, including in human patients. Primary CoQ deficiency is a rare inborn condition due to mutation in CoQ biosynthetic genes. Secondary CoQ deficiency is much more common, as it accompanies a variety of pathological conditions, including mitochondrial disorders as well as aging. In this context, we discuss the importance, but also the great difficulty, of alleviating CoQ deficiency by CoQ supplementation.

Mitoquinone protects against acetaminophen-induced liver injury in an FSP1-dependent and GPX4-independent manner

Mitochondrial oxidative stress has been a crucial mediator in acetaminophen (APAP)-induced hepatotoxicity. MitoQ, an analog of coenzyme Q10, is targeted towards mitochondria and acts as a potent antioxidant. This study aimed to explore the effect of MitoQ on APAP-induced liver injury and its possible mechanisms. To investigate this, CD-1 mice and AML-12 cells were treated with APAP. Hepatic MDA and 4-HNE, two markers of lipid peroxidation (LPO), were elevated as early as 2 h after APAP. Oxidized lipids were rapidly upregulated in APAP-exposed AML-12 cells. Hepatocyte death and mitochondrial ultrastructure alterations were observed in APAP-induced acute liver injury. The in vitro experiments showed that mitochondrial membrane potentials and OXPHOS subunits were downregulated in APAP-exposed hepatocytes. MtROS and oxidized lipids were elevated in APAP-exposed hepatocytes. We discovered that APAP-induced hepatocyte death and liver injury were ameliorated by attenuation of protein nitration and LPO in MitoQ-pretreated mice. Mechanistically, knockdown of GPX4, a key enzyme for LPO defense systems, exacerbated APAP-induced oxidized lipids, but did not influence the protective effect of MitoQ on APAP-induced LPO and hepatocyte death. Whereas knockdown of FSP1, another key enzyme for LPO defense systems, had little effect on APAP-induced lipid oxidation but partially weakened the protection of MitoQ on APAP-induced LPO and hepatocyte death. These results suggest that MitoQ may alleviate APAP-evoked hepatotoxicity by eliminating protein nitration and suppressing hepatic LPO. MitoQ prevents APAP-induced liver injury partially dependent of FSP1 and independent of GPX4.

Preclinical and Clinical Role of Coenzyme Q10 Supplementation in Various Pathological States

Coenzyme Q10 (CoQ10) is an efficient antioxidant produced endogenously in a living organism. It acts as an important cofactor in the electron transport system of mitochondria and reported as a safe supplement in humans and animals with minimal adverse effect. CoQ10 is found naturally, as a trans configuration, chemical nomenclature of which is 2,3- dimethoxy-5- methyl-6-decaprenyle -1,4-benzoquinone. It is found in the body in two forms. In quinone form (oxidized form), it serves as an electron transporter that transfers the electrons in the electron transport chain between various complexes, and in ubiquinol form (reduced form), it serves as potent antioxidants by scavenging free radicals or by tocopherol regeneration in the living organism. Its primary roles include synthesis of adenosine triphosphate (ATP), stabilizes lipid membrane, antioxidant activity, cell growth stimulation, and cell death inhibition. CoQ10 has shown a variety of pharmacological and clinical effects including neuroprotective, hepatoprotective, anti-atherosclerotic, anticonvulsant, antidepressant, anti-inflammatory, antinociceptive, cardiovascular, antimicrobial, immunomodulatory, and various effects on the central nervous system. Present review has set about to bring updated information regarding to clinical and preclinical activities of CoQ10, which may be helpful to researchers to explore a new bioactive molecules for various therapeutic application.

Molecular mechanisms underlying the promotion of wound repair by coenzyme Q10: PI3K/Akt signal activation via alterations to cell membrane domains

Coenzyme Q10 (CoQ10) promotes wound healing in vitro and in vivo. However, the molecular mechanisms underlying the promoting effects of CoQ10 on wound repair remain unknown. In the present study, we investigated the molecular mechanisms through which CoQ10 induces wound repair using a cellular wound-healing model. CoQ10 promoted wound closure in a dose-dependent manner and wound-mediated cell polarization after wounding in HaCaT cells. A comparison with other CoQ homologs, benzoquinone derivatives, and polyisoprenyl compounds suggested that the whole structure of CoQ10 is required for potent wound repair. The phosphorylation of Akt after wounding and the plasma membrane translocation of Akt were elevated in CoQ10-treated cells. The promoting effect of CoQ10 on wound repair was abrogated by co-treatment with a phosphatidylinositol 3-kinase (PI3K) inhibitor. Immuno­histochemical and biochemical analyses showed that CoQ10 increased the localization of caveolin-1 (Cav-1) to the apical membrane domains of the cells and the Cav-1 content in the membrane-rich fractions. Depletion of Cav-1 suppressed CoQ10-mediated wound repair and PI3K/Akt signaling activation in HaCaT cells. These results indicated that CoQ10 increases the translocation of Cav-1 to the plasma membranes, activating the downstream PI3K/Akt signaling pathway, and resulting in wound closure in HaCaT cells.

Recommendations for the use of the acetaminophen hepatotoxicity model for mechanistic studies and how to avoid common pitfalls

Acetaminophen (APAP) is a widely used analgesic and antipyretic drug, which is safe at therapeutic doses but can cause severe liver injury and even liver failure after overdoses. The mouse model of APAP hepatotoxicity recapitulates closely the human pathophysiology. As a result, this clinically relevant model is frequently used to study mechanisms of drug-induced liver injury and even more so to test potential therapeutic interventions. However, the complexity of the model requires a thorough understanding of the pathophysiology to obtain valid results and mechanistic information that is translatable to the clinic. However, many studies using this model are flawed, which jeopardizes the scientific and clinical relevance. The purpose of this review is to provide a framework of the model where mechanistically sound and clinically relevant data can be obtained. The discussion provides insight into the injury mechanisms and how to study it including the critical roles of drug metabolism, mitochondrial dysfunction, necrotic cell death, autophagy and the sterile inflammatory response. In addition, the most frequently made mistakes when using this model are discussed. Thus, considering these recommendations when studying APAP hepatotoxicity will facilitate the discovery of more clinically relevant interventions.

CoQ10 promotes resolution of necrosis and liver regeneration after acetaminophen-induced liver injury

Coenzyme Q10 (CoQ10) which acts as an electron transporter in the mitochondrial respiratory chain has many beneficial effects on liver diseases. In our previous research, CoQ10 has been found to attenuate acetaminophen (APAP) induced acute liver injury (ALI). However, whether CoQ10 administration is still effective at the late stage of APAP overdose is still unknown. In this study, we aimed to test CoQ10 efficacy at the late stage of APAP overdose. C57BL/6J mice were intraperitoneally treated with APAP to induce liver injury. CoQ10 (5 mg/kg) was given to mice at 16 hours after APAP treatment. The results showed that while CoQ10 treatment at 16 hours post-APAP overdose had no effects on the expression of ROS generated genes or scavenged genes, it still significantly decreased necrosis of hepatocytes following APAP-induced ALI. Moreover, CoQ10 increased MerTK+ macrophages accumulation in the APAP-overdose liver and inhibition of MerTK signaling partly abrogated the protective role of CoQ10 treatment on the hepatic necrosis. CoQ10 treatment also significantly enhanced hepatocytes proliferation as shown in the increased BrdU incorporation in the APAP-intoxicated mice liver section. In addition, CoQ10 treatment increased hepatic PCNA and Cyclin D1 expression and promoted activation of the β-catenin signaling in APAP-overdose mice. To conclude, these data provide evidence that CoQ10 treatment is still effective at the late stage of APAP-induced ALI and promotes resolution of necrosis and liver regeneration following ALI.

Ferroptosis and Acetaminophen Hepatotoxicity: Are We Going Down Another Rabbit Hole?

Acetaminophen (APAP) hepatotoxicity is the most frequent cause of acute liver failure in the US. The mechanisms of APAP-induced liver injury have been under extensive investigations for decades, and many key events of this necrotic cell death are known today. Initially, two opposing hypotheses for cell death were proposed: reactive metabolite and protein adduct formation versus reactive oxygen and lipid peroxidation (LPO). In the end, both mechanisms were reconciled, and it is now generally accepted that the toxicity starts with formation of reactive metabolites that, after glutathione depletion, bind to cellular proteins, especially on mitochondria. This results in a mitochondrial oxidant stress, which requires amplification through a mitogen-activated protein kinase cascade, leading ultimately to enough reactive oxygen and peroxynitrite formation to trigger the mitochondrial membrane permeability transition and cell death. However, the earlier rejected LPO hypothesis seems to make a comeback recently under a different name: ferroptosis. Therefore, the objective of this review was to critically evaluate the available information about intracellular signaling mechanisms of APAP-induced cell death and those of ferroptosis. Under pathophysiologically relevant conditions, there is no evidence for quantitatively enough LPO to cause cell death, and thus APAP hepatotoxicity is not caused by ferroptosis. However, the role of mitochondria-localized minor LPO remains to be further investigated.

CoQ10 protects against acetaminophen-induced liver injury by enhancing mitophagy

Coenzyme Q10 (CoQ10), which is a key cofactor of the electron transport chain in the mitochondria has shown many beneficial effects on liver diseases. However, the mechanisms of CoQ10 protective role on the acetaminophen (APAP)-induced liver injury are elusive and unclear. In this study, we further investigated the CoQ10 therapeutic effects on APAP-overdose liver injury. C57BL/6 J mice were intraperitoneally treated with APAP to induce liver injury. CoQ10 (5 mg/kg) was given to mice at 1.5 h after APAP treatment. The results showed that hepatic CoQ10 levels were decreased during the APAP-induced hepatotoxicity and preceded serum ALT elevation. Treatment of CoQ10 significantly improved the liver injury induced by APAP. Moreover, CoQ10 treatment decreased the ROS levels and promoted the antioxidative related gene expression in APAP overdose mice. Importantly, results showed that even though CoQ10 had no effects on the mtDNA copy number and the expression of genes related to mitochondrial biogenesis, it significantly improved the mitochondrial complex I and V activities and promoted the mitophagy in APAP-overdose mice. To further authenticate mitophagy role in CoQ10-mediated improved liver injury in vivo, we administrated APAP-overdose mice with chloroquine 1 h prior to APAP treatment and found that chloroquine treatment functionally abrogated the CoQ10 protective role on APAP overdose mice. To conclude, this study provides evidence that CoQ10 activates mitophagy to protect against APAP-induced liver injury. Therefore, CoQ10 may represent a novel therapeutic option for the prevention and treatment of drug-induced liver injury.

Iron loading exerts synergistic action via a different mechanistic pathway from that of acetaminophen-induced hepatic injury in mice

Acetaminophen (APAP) overdose is a major cause of drug-induced acute liver failure. In such cases, free iron is released from lysosomes and is transported to mitochondria where it plays a pivotal role in APAP-induced liver injury. We previously reported that ascorbic acid (Asc) markedly mitigates APAP-induced hepatic damage in aldehyde reductase (Akr1a)-knockout (KO) mice that produce about 10% Asc as wild-type (WT) mice. However, the issue of the protective mechanism of Asc in association with the status of iron remains ambiguous. To gain additional insights into this issue, we examined effects of APAP (500 mg/kg) on female KO mice under conditions of iron loading. While the KO mice without AsA supplementation were more sensitive to APAP toxicity than the WT mice, FeSO₄ loading (25 mg/kg) to WT mice aggravated the hepatic injury, which was a similar extent to that of the KO mice. Supplementation of Asc (1.5 mg/ml in the drinking water) ameliorated KO mice irrespective of iron status but did not change the iron-mediated increase in the lethality in the WT mice. Hepatic cysteine and glutathione levels declined to similar extents in all mouse groups at 3 h irrespective of the iron status and largely recovered at 18 h after the APAP treatment when liver damage was evident. Asc prominently mitigated APAP toxicity in KO mice irrespective of the iron status but had no effect on the synergistic action of iron and APAP in the WT mice, suggesting that the mechanism for the deteriorating action of loaded iron is different from that of APAP toxicity.

Some in vitro/in vivo chemically-induced experimental models of liver oxidative stress in rats

Oxidative stress is critically involved in a variety of diseases. Reactive oxygen species (ROS) are highly toxic molecules that are generated during the body's metabolic reactions and can react with and damage some cellular molecules such as lipids, proteins, or DNA. Liver is an important target of the oxidative stress because of its exposure to various prooxidant toxic compounds as well as of its metabolic function and ability to transform some xenobiotics to reactive toxic metabolites (as ROS). To investigate the processes of liver injuries and especially liver oxidative damages there are many experimental models, some of which we discuss further.

Genistein protection against acetaminophen-induced liver injury via its potential impact on the activation of UDP-glucuronosyltransferase and antioxidant enzymes

The purpose of this study was to investigate genistein's influence on the relationship between the activation of uridine diphosphate glucuronosyltransferase (UGTs) and the protection against acetaminophen-induced liver toxicity. Animal experimental results revealed that genistein (50, 100 or 200mg/BWkg) significantly ameliorated the biomarkers alanine aminotransferase, alanine aminotransferase, lactate dehydrogenase and malondialdehyde, as indicators of acute liver damage caused by APAP (200mg/BWkg). The level of GSH declined sharply after treatment with APAP within 1h in both the liver and blood with and without genistein. However, after 16h, the levels approached or returned to the original level. Genistein may accelerate and promote APAP glucuronidation as the results showed that APAP-glucuronide increased by 18.44%, 46.79%, and 66.49% for 4h of treatment with genistein dosages of 50, 100 or 200mg/BWkg, respectively, compared with the APAP-only treatment. The activation of UGTs and glutathione peroxidase and the inhibition of CYP2E1 by genistein were observed, and UGTs mRNA expression level with genistein was measured. These findings suggest that genistein can prevent and protect against APAP-induced liver toxicity due to the inhibition of APAP biotransformation and the resistance to oxidative stress via the modulation of the activities of metabolism and the antioxidant enzyme.

Role of Grape Seed Extract on Methotrexate Induced Oxidative Stress in Rat Liver

The efficacy of methotrexate (MTX), a widely used cytotoxic chemotherapeutic agent, is often limited by its severe hepatotoxicity. Regarding the mechanisms of these adverse effects, several hypotheses have been put forward, among which oxidative stress is noticeable. The present study was undertaken to determine whether grape seed extract (GSE), a new natural free radical scavenger, could ameliorate the MTX-induced oxidative injury in the rat liver. The animals were divided into 3 groups. Each group consisted of 12 animals. MTX-GSE group: rats were given GSE (100mg/kg body weight) orally for 15 days, and a single dose of MTX (20mg/kg, intraperitoneally) was added on the 10th day. MTX group: these received placebo distilled water (orally) instead of GSE for 15 days and the same MTX protocol applied to this group on the 10th day. Control group: rats were given distilled water (orally) through 15 days and physiological saline (intraperitoneally) instead of MTX was administered on the 10th day in a similar manner. On the 16th day, liver tissue samples were obtained under deep anaesthesia. The level of malondialdehyde (MDA), an end product of lipid peroxidation, and the activities of süperoxide dismutase (SOD) and catalase (CAT), two important endogenous antioxidants, were evaluated in the tissue homogenates. MTX administration increased the MDA level and decreased the SOD and CAT activities in the liver homogenates ( p < 0.001), while these alterations were significantly reversed by GSE treatment ( p < 0.001). MTX led to significantly reduced whole blood count parameters ( p < 0.05). When GSE was supplemented, no significant changes in blood count parameters were noted. It appears that GSE protects the rat liver and inhibits methotrexate-induced oxidative stress. These data indicate that GSE may be of therapeutic benefit when used with MTX.

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 hepatotoxicity and protein nitration in neuronal nitric-oxide synthase knockout mice

In overdose acetaminophen (APAP) is hepatotoxic. Toxicity occurs by metabolism to N-acetyl-p-benzoquinone imine, which depletes GSH and covalently binds to proteins followed by protein nitration. Nitration can occur via the strong oxidant and nitrating agent peroxynitrite, formed from superoxide and nitric oxide (NO). In hepatocyte suspensions we reported that an inhibitor of neuronal nitric-oxide synthase (nNOS; NOS1), which has been reported to be in mitochondria, inhibited toxicity and protein nitration. We recently showed that manganese superoxide dismutase (MnSOD; SOD2) was nitrated and inactivated in APAP-treated mice. To understand the role of nNOS in APAP toxicity and MnSOD nitration, nNOS knockout (KO) and wild-type (WT) mice were administered APAP (300 mg/kg). In WT mice serum alanine aminotransferase (ALT) significantly increased at 6 and 8 h, and serum aspartate aminotransferase (AST) significantly increased at 4, 6 and 8 h; however, in KO mice neither ALT nor AST significantly increased until 8 h. There were no significant differences in hepatic GSH depletion, APAP protein binding, hydroxynonenal covalent binding, or histopathological assessment of toxicity. The activity of hepatic MnSOD was significantly lower at 1 to 2 h in WT mice and subsequently increased at 8 h. MnSOD activity was not altered at 0 to 6 h in KO mice but was significantly decreased at 8 h. There were significant increases in MnSOD nitration at 1 to 8 h in WT mice and 6 to 8 h in KO mice. Significantly more nitration occurred at 1 to 6 h in WT than in KO mice. MnSOD was the only observed nitrated protein after APAP treatment. These data indicate a role for nNOS with inactivation of MnSOD and ALT release during APAP toxicity.

Plasmid DNA linearization in the antibacterial action of a new fluorescent Ag nanoparticle-paracetamol dimer composite

Herein, we report the generation of a composite comprised of p-hydroxyacetanilide dimer and Ag nanoparticles (NPs) by reaction of AgNO(3) and p-hydroxyacetanilide. The formation of the composite was established by UV-vis, FTIR and NMR spectroscopy, transmission electron microscopy and X-ray diffraction along with substantiation by mass spectrometry. Interestingly, the composite exhibited an emission spectrum with a peak at 435 nm when excited by light of wavelength 320 nm. The composite showed superior antimicrobial activity with respect to its individual components against a wide range of Gram positive and Gram negative bacteria at relatively low concentrations of Ag NPs and at which there was no apparent cytotoxicity against mammalian cells. Our results suggest that the composite strongly interacted with the bacterial cell walls leading to cell bursting. Interestingly, enhancement in the reactive oxygen species (ROS) generation in bacteria was observed in the presence of the composite. It is proposed that the ROS generation led to oxidation of the dimer to N-acetyl-p-benzoquinone imine (NAPQI). The generated NAPQI acted as a DNA gyrase inhibitor causing cell death following linearization of DNA.

Repeated preexposure or coexposure to arsenic differentially alters acetaminophen-induced oxidative stress in rat kidney

Acetaminophen (AP) is a widely used, cheap, and over-the-counter nonsteroidal anti-inflammatory drug. Its toxicity depends on the cytochrome P-450 (CYP)-mediated oxidation to the toxic metabolite N-acetyl-p-benzoquinoneimine. On the other hand, arsenic, a global groundwater and environmental contaminant of major public health concern, decreases hepatic CYP content and its dependent monoxygenase activities. We hypothesized that arsenic exposure would reduce the AP toxicity. Our aim was to evaluate the effects of repeated preexposure or coexposure to arsenic on the oxidative stress induced by a single or repeated oral administration of AP in rat kidney and its possible relationship with the effects of arsenic on certain antioxidants. Rats were exposed to arsenic through drinking water at 25 ppm for 28 days. The dosages of AP used for a single administration after arsenic preexposure for 28 days were 420 and 1000 mg kg(-1) , while for daily concurrent administration with arsenic for 28 days were 105 and 420 mg kg(-1) body weight. AP increased lipid peroxidation (LPO) in rat kidney where its acute administration caused more LPO than its subacute dosing. Repeated arsenic exposure differentially altered the AP-induced LPO. Arsenic preexposure antagonized LPO induced by the acute AP administration; in contrast, arsenic coexposure aggravated the repeated dose (AP)-mediated LPO. Arsenic-mediated alterations in renal sensitivity to LPO did not appear to be linked to the antioxidants such as reduced glutathione, superoxide dismutase, catalase, glutathione peroxidase, and glutathione reductase; nor could it be related to glutathione-S-transferase activity. The results indicated that repeated arsenic preexposure decreased susceptibility of rat kidney to acute AP-mediated oxidative stress; on the contrary, its coexposure rendered the rat kidney more vulnerable to oxidative stress induced by the repeated dosing of AP.

Protection by Exogenously Added Coenzyme Q(9) against Free Radical-Induced Injuries in Human Liver Cells

Reduced coenzyme Q(10) (CoQ(10)H(2)) is known as a potent antioxidant in biological systems. However, it is not yet known whether CoQ(9)H(2) could act as an antioxidant in human cells. The aim of this study is to assess whether exogenously added CoQ(9) can protect human liver cells against injuries induced by a water-soluble radical initiator, 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH) and a lipid-soluble radical initiator, 2,2'-azobis(2,4-dimethylvaleronitrile) (AMVN). CoQ(9)-enriched cells were obtained by treatment of HepG2 cells with 10 microM CoQ(9) liposomes for 24 h. CoQ(9)-enriched cells were exposed to 10 mM AAPH and 500 microM AMVN over 4 h and 24 h, respectively. The loss of viability after treatment with AAPH or AMVN was much less in CoQ(9)-enriched cells than in naive HepG2 cells. The decrease in glutathione and the increase in thiobarbituric acid-reactive substance after treatment with AAPH or AMVN were also suppressed in CoQ(9)-enriched cells. The incubation of CoQ(9)-enriched cells with AAPH or AMVN led to a decrease in cellular CoQ(9)H(2) and reciprocal increase in cellular CoQ(9) resulting from its antioxidant function. Taken together, it was demonstrated for the first time that exogenously added CoQ(9) could prevent oxidative stress-mediated damage to human cells by virtue of its antioxidant activity.

Acute exposure to ozone exacerbates acetaminophen-induced liver injury in mice

Ozone (O(3)), an oxidant air pollutant in photochemical smog, principally targets epithelial cells lining the respiratory tract. However, changes in gene expression have also been reported in livers of O(3)-exposed mice. The principal aim of the present study was to determine if acute exposure to environmentally relevant concentrations of O(3) could cause exacerbation of drug-induced liver injury in mice. Overdose with acetaminophen (APAP) is the most common cause of drug-induced liver injury in developed countries. In the present study, we examined the hepatic effects of acute O(3) exposure in mice pretreated with a hepatotoxic dose of APAP. C57BL/6 male mice were fasted overnight and then given APAP (300 mg/kg ip) or saline vehicle (0 mg/kg APAP). Two hours later, mice were exposed to 0, 0.25, or 0.5 ppm O(3) for 6 h and then sacrificed 9 or 32 h after APAP administration (1 or 24 h after O(3) exposure, respectively). Animals euthanized at 32 h were given 5-bromo-2-deoxyuridine 2 h before sacrifice to identify hepatocytes undergoing reparative DNA synthesis. Saline-treated mice exposed to either air or O(3) had no liver injury. All APAP-treated mice developed marked centrilobular hepatocellular necrosis that increased in severity with time after APAP exposure. O(3) exposure increased the severity of APAP-induced liver injury as indicated by an increase in necrotic hepatic tissue and plasma alanine aminotransferase activity. O(3) also caused an increase in neutrophil accumulation in livers of APAP-treated animals. APAP induced a 10-fold increase in the number of bromodeoxyuridine-labeled hepatocytes that was markedly attenuated by O(3) exposure. Gene expression analysis 9 h after APAP revealed differential expression of genes involved in inflammation, oxidative stress, and cellular regeneration in mice treated with APAP and O(3) compared to APAP or O(3) alone, providing some indications of the mechanisms behind the APAP and O(3) potentiation. These results suggest that acute exposure to near ambient concentrations of this oxidant air pollutant may exacerbate drug-induced liver injury by delaying hepatic repair.

Zinc Supplementation with Polaprezinc Protects Mouse Hepatocytes against Acetaminophen-Induced Toxicity via Induction of Heat Shock Protein 70

Polaprezinc, a chelate compound consisting of zinc and l-carnosine, is clinically used as a medicine for gastric ulcers. It has been shown that induction of heat shock protein (HSP) is involved in protective effects of polaprezinc against gastric mucosal injury. In the present study, we investigated whether polaprezinc and its components could induce HSP70 and prevent acetaminophen (APAP) toxicity in mouse primary cultured hepatocytes. Hepatocytes were treated with polaprezinc, zinc sulfate or l-carnosine at the concentration of 100 microM for 9 h, and then exposed to 10 mM APAP. Polaprezinc or zinc sulfate increased cellular HSP70 expression. However, l-carnosine had no influence on it. Pretreatment of the cells with polaprezinc or zinc sulfate significantly suppressed cell death as well as cellular lipid peroxidation after APAP treatment. In contrast, pretreatment with polaprezinc did not affect decrease in intracellular glutathione after APAP. Furthermore, treatment with KNK437, an HSP inhibitor, attenuated increase in HSP70 expression induced by polaprezinc, and abolished protective effect of polaprezinc on cell death after APAP. These results suggested that polaprezinc, in particular its zinc component, induces HSP70 expression in mouse primary cultured hepatocytes, and inhibits lipid peroxidation after APAP treatment, resulting in protection against APAP toxicity.

The protective effects of garlic extract against acetaminophen-induced oxidative stress and glutathione depletion

Acetaminophen, the most commonly sold over-the-counter antipyretic analgesic, is capable of causing severe and sometimes fatal hepatic damage in humans and experimental animals. The incidence of liver injury due to acetaminophen overdose, either with suicidal intent or by accident, is increasing. Garlic is among those medicinal plants famous for its different health protective effects. In this study, the protective effects of garlic extract on acute acetaminophen-induced liver injury were investigated using freshly isolated rat hepatocytes. The hepatocytes were isolated from Sprague-Dawley male rats by a two step collagenase model. Formation of Reactive Oxygen Species (ROS) and Glutathione (GSH) depletion were studied after addition of acetaminophen to cell suspensions. The effects of garlic extract on prevention of ROS formation as well as GSH depletion was investigated and compared with the effects of N-Acetyl Cysteine (NAC) as the standard treatment. Reactive oxygen species formation was assessed by a spectrofluorometry method and garlic extract was shown to be as effective as NAC in decreasing ROS formation induced by acetaminophen. Glutathione (GSH) levels of hepatocytes were determined using HPLC. Garlic extract was effective in preventing GSH depletion significantly (p < 0.05). It is concluded that garlic extract has an antioxidant effect and can protect hepatocytes from GSH depletion following NAPQI production.

Inhibition of liver fibrosis by solubilized coenzyme Q10: Role of Nrf2 activation in inhibiting transforming growth factor-beta1 expression

Coenzyme Q10 (CoQ10), an endogenous antioxidant, is important in oxidative phosphorylation in mitochondria. It has anti-diabetic and anti-cardiovascular disease effects, but its ability to protect against liver fibrosis has not been studied. Here, we assessed the ability of solubilized CoQ10 to improve dimethylnitrosamine (DMN)-induced liver fibrogenesis in mice. DMN treatments for 3 weeks produced a marked liver fibrosis as assessed by histopathological examination and tissue 4-hydroxyproline content. Solubilized CoQ10 (10 and 30 mg/kg) significantly inhibited both the increases in fibrosis score and 4-hydroxyproline content induced by DMN. Reverse transcription-polymerase chain reaction and Western blot analyses revealed that solubilized CoQ10 inhibited increases in the transforming growth factor-beta1 (TGF-beta1) mRNA and alpha-smooth muscle actin (alpha-SMA) protein by DMN. Interestingly, hepatic glutamate-cysteine ligase (GCL) and glutathione S-transferase A2 (GSTA2) were up-regulated in mice treated with CoQ10. Solubilized CoQ10 also up-regulated antioxidant enzymes such as catalytic subunits of GCL and GSTA2 via activating NF-E2 related factor2 (Nrf2)/antioxidant response element (ARE) in H4IIE hepatoma cells. Moreover, CoQ10's inhibition of alpha-SMA and TGF-beta1 expressions disappeared in Nrf2-null MEF cells. In contrast, Nrf2 overexpression significantly decreased the basal expression levels of alpha-SMA and TGF-beta1 in Nrf2-null MEF cells. These results demonstrated that solubilized CoQ10 inhibited DMN-induced liver fibrosis through suppression of TGF-beta1 expression via Nrf2/ARE activation.

Efficacy of royal jelly against the oxidative stress of fumonisin in rats

Fumonisins (FB) are mycotoxins produced by Fusarium verticillioides, frequently associated with corn. It produces toxicity, including teratogenicity, equine leukoencephalomalacia, porcine pulmonary edema, hepatic or renal damage in most animal species and perturb sphingolipid metabolism. The aim of the present study was to evaluate the protective effects of royal jelly (RJ) against FB toxicity. Sixty male Sprague-Dawley rats were divided into six treatment groups including the control group; group fed FB-contaminated diet (200mg/kg diet) and the groups treated orally with RJ (100 or 150mg/kg body weight) with or without FB for 3 weeks. FB alone decreased body weight gain, feed intake, GPX and SOD. Whereas it increased in ALT, AST, triglycerides, cholesterol, HDL, LDL, createnine and uric acid levels. Animals received FB showed severe histological and histochemical changes in liver and kidney tissues. Cotreatment with FB plus RJ resulted in a significant improvement in all the tested parameters and the histological and histochemical pictures of the liver and kidney. These improvements were pronounced in animals fed FB-contaminated diet plus the high dose of RJ. It could be concluded that RJ have a protective effects against FB toxicity and this protection was dose dependent.

Role of NAD(P)H:quinone oxidoreductase 1 in clofibrate-mediated hepatoprotection from acetaminophen

Mice pretreated with the peroxisome proliferator clofibrate (CFB) are resistant to acetaminophen (APAP) hepatotoxicity. Whereas the mechanism of protection is not entirely known, CFB decreases protein adducts formed by the reactive metabolite of APAP, N-acetyl-p-benzoquinone imine (NAPQI). NAD(P)H:quinone oxidoreductase 1 (NQO1) is an enzyme with antioxidant properties that is responsible for the reduction of cellular quinones. We hypothesized that CFB increases NQO1 activity, which in turn enhances the conversion of NAPQI back to the parent APAP. This could explain the decreases in APAP covalent binding and glutathione depletion produced by CFB without affecting APAP bioactivation to NAPQI. Administration of CFB (500mg/kg, i.p.) to male CD-1 mice for 5 or 10 days increased NQO1 protein and activity levels. To evaluate the capacity of NQO1 to reduce NAPQI back to APAP, we utilized a microsomal activating system. Cytochrome P450 enzymes present in microsomes bioactivate APAP to NAPQI, which binds the electrophile trapping agent, N-acetyl cysteine (NAC). We analyzed the formation of APAP-NAC metabolite in the presence of human recombinant NQO1. Results indicate that NQO1 is capable of reducing NAPQI. The capacity of NQO1 to amelioriate APAP toxicity was then evaluated in primary hepatocytes. Primary hepatocytes isolated from mice dosed with CFB are resistant to APAP toxicity. These hepatocytes were also exposed to ES936, a high affinity, and irreversible inhibitor of NQO1 in the presence of APAP. Concentrations of ES936 that resulted in over 94% inhibition of NQO1 activity did not increase the susceptibility of hepatocytes from CFB treated mice to APAP. Whereas NQO1 is mechanistically capable of reducing NAPQI, CFB-mediated hepatoprotection does not appear to be dependent upon enhanced expression of NQO1.

Cytoprotective effects of carvedilol against oxygen free radical generation in rat liver

The protective effects of carvedilol, an antihypertensive agent, against oxidative injury caused by acetaminophen were studied in rat liver. Male Wistar rats (250 +/- 30 g) were pre-treated with carvedilol (3.6 mg/kg, p.o.) for 10 days and on the 11th day received an overdose of acetaminophen (800 mg/kg, p.o.). Four hours after acetaminophen administration, blood was collected to determine serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT). After that, rats were killed and the livers were excised to determine reduced glutathione (GSH), thiobarbituric acid reactive substances (TBARS) and carbonyl protein contents, and the activity of the antioxidant enzymes catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx), and glutathione S-transferase (GST), and also the DNA damage index. Acetaminophen significantly increased the levels of TBARS, the DNA damage and SOD, AST and ALT activities. Carvedilol was able to prevent lipid peroxidation, protein carbonilation and DNA fragmentation caused by acetaminophen. Moreover, this drug prevented increases in SOD, AST and ALT activities. These results show that carvedilol exerts cytoprotective effects against oxidative injury caused by acetaminophen in rat liver. These effects are probably related to the O2*- scavenging property of carvedilol or its metabolites.

Mechanisms of protection by melatonin against acetaminophen-induced liver injury in mice

The present study was performed to determine whether melatonin protects mouse liver against severe damage induced by acetaminophen (APAP) administration and where melatonin primarily functions in the metabolic pathway of APAP to protect mouse liver against APAP-induced injury. Treatment of mice with melatonin (50 or 100 mg/kg, p.o.) 8 or 4 hr before APAP administration (750 mg/kg, p.o.) suppressed the increase in plasma alanine aminotransferase and aspartate aminotransferase activities in a dose- and a time-dependent manner. Melatonin treatment (100 mg/kg, p.o.) 4 hr before APAP administration remarkably inhibited centrilobular hepatic necrosis with inflammatory cell infiltration and increases in hepatic lipid peroxidation and myeloperoxidase activity, an index of tissue neutrophil infiltration, as well as release of nitric oxide and interleukin-6 into blood circulation at 9 hr after APAP administration. However, melatonin neither affected hepatic reduced glutathione (GSH) content nor spared hepatic GSH consumption by APAP treatment. Moreover, pretreatment with melatonin 4 hr before APAP administration did not influence the induction of hepatic heat shock protein 70 (HSP70) by APAP and melatonin alone did not induce HSP70 in mouse liver. These results indicate that exogenously administered melatonin exhibits a potent hepatoprotective effect against APAP-induced hepatic damage probably downstream of the activity of cytochrome P450 2E1, which works upstream of GSH conjugation in the pathway of APAP metabolism, via its anti-nitrosative and anti-inflammatory activities in addition to its antioxidant activity.

Attenuation of tamoxifen-induced hepatotoxicity by taurine in mice

BACKGROUND

One of the most attractive approaches to disease prevention involves the use of natural antioxidants to protect tissue against toxic injury. We investigated the modulatory effects of exogenously administered taurine on the toxicity of the anticancer drug tamoxifen with special reference to protection against disruption of drug metabolizing and antioxidant enzymes in Swiss albino mice.

METHODS

Male Swiss albino mice were divided into 4 groups. The extent of lipid peroxidation was evaluated in terms of thiobarbituric acid reactive substances formed. The following assays were performed in the hepatic tissue (a) antioxidant enzymes such as superoxide dismutase and catalase, (b) cytochrome P450 content, (c) glutathione-metabolizing enzymes such as glutathione peroxidase, glutathione reductase, glutathione-S-transferase and glucose 6-phosphate dehydrogenase, and (d) low molecular weight antioxidants (reduced glutathione, ascorbic acid) and protein carbonyl content.

RESULTS

Tamoxifen induced lipid peroxidation, protein carbonyl content and inhibited the enzymes of antioxidant defense system. It was also observed that the activities of antioxidant enzymes and glutathione-metabolizing enzymes were considerably stabilized in mice pretreated with taurine.

CONCLUSION

Taurine protects the integrity of the hepatic tissue by stabilizing the reactive oxygen species mediated lipid peroxidation and protein carbonyl formation. Additionally taurine may prove to be efficacious as an antioxidant in tamoxifen-induced hepatotoxicity.

Geranylgeranylacetone protects against acetaminophen-induced hepatotoxicity by inducing heat shock protein 70

Geranylgeranylacetone (GGA), an anti-ulcer drug, has been reported to induce heat shock protein (HSP) 70 in several animal organs. The present study was performed to determine whether GGA protects mouse liver against acetaminophen (APAP)-induced injury and whether it has potential as a therapeutic agent for APAP overdose. Hepatic damage was induced by single oral administration of APAP (500 mg/kg). GGA at 400 mg/kg was given orally 4 or 8h before, or 0.5h after APAP administration. Treatment of mice with GGA 4h before or 0.5h after APAP administration suppressed increases in transaminase activities and ammonia content in blood as well as hepatic necrosis. Such GGA treatment significantly increased hepatic HSP70 accumulation after APAP administration. Furthermore, GGA inhibited increases in hepatic lipid peroxide content and hepatic myeloperoxidase activity after APAP administration. In contrast, GGA neither inhibited hepatic cytochrome P450 2E1 activity nor suppressed hepatic glutathione depletion after APAP administration. The protective effect of GGA treatment 4h before APAP on hepatotoxicity induced by APAP was completely inhibited with quercetin, known as an HSP inhibitor. In conclusion, GGA has been identified as a new antidote to APAP injury, acting by induction of HSP70. The potential of GGA as a therapeutic tool is strongly supported by its ability to inhibit hepatic injury even when administered after ingestion of APAP.

Retinoid X receptor alpha Regulates the expression of glutathione s-transferase genes and modulates acetaminophen-glutathione conjugation in mouse liver

Nuclear receptors, including constitutive androstane receptor, pregnane X receptor, and retinoid X receptor (RXR), modulate acetaminophen (APAP)-induced hepatotoxicity by regulating the expression of phase I cytochrome P450 (P450) genes. It has not been fully resolved, however, whether they regulate APAP detoxification at the phase II level. The aim of the current study was to evaluate the role of RXRalpha in phase II enzyme-mediated detoxification of APAP. Wild-type and hepatocyte-specific RXRalpha knockout mice were treated with a toxic dose of APAP (500 mg/kg i.p.). Mutant mice were protected from APAP-induced hepatotoxicity, even though basal liver glutathione (GSH) levels were significantly lower in mutant mice compared with those of wild-type mice. High-performance liquid chromatography analysis of APAP metabolites revealed significantly greater levels of APAP-GSH conjugates in livers and bile of mutant mice compared with those of wild-type mice. Furthermore, hepatocyte RXRalpha deficiency altered the gene expression profile of the glutathione S-transferase (Gst) family. Basal expression of 13 of 15 Gst genes studied was altered in hepatocyte-specific RXRalpha-deficient mice. This probably led to enhanced APAP-GSH conjugation and reduced accumulation of N-acetyl-p-benzoquinone imine, a toxic electrophile that is produced by biotransformation of APAP by phase I P450 enzymes. In conclusion, the data presented in this study define an RXRalpha-Gst regulatory network that controls APAP-GSH conjugation. This report reveals a potential novel strategy to enhance the detoxification of APAP or other xenobiotics by manipulating Gst activity through RXRalpha-mediated pathways.

Fibroblast cell lines from young adult mice of long-lived mutant strains are resistant to multiple forms of stress

Previous studies have shown that dermal fibroblast cell lines derived from young adult mice of the long-lived Snell dwarf mutant stock are resistant, in vitro, to the cytotoxic effects of H(2)O(2), cadmium, UV light, paraquat, and heat. We show here that similar resistance profiles are seen in fibroblast cells derived from a related mutant, the Ames dwarf mouse, and that cells from growth hormone receptor-null mice are resistant to H(2)O(2), paraquat, and UV but not to cadmium. Resistance to UV light, cadmium, and H(2)O(2) are similar in cells derived from 1-wk-old Snell dwarf or normal mice, and thus the resistance of cell lines derived from young adult donors reflects developmental processes, presumably hormone dependent, that take place in the first few months of life. The resistance of cells from Snell dwarf mice to these stresses does not reflect merely antioxidant defenses: dwarf-derived cells are also resistant to the DNA-alkylating agent methyl methanesulfonate. Furthermore, inhibitor studies show that fibroblast resistance to UV light is unaffected by the antioxidants ascorbic acid and N-acetyl-L-cysteine. These data suggest that postnatal exposure to altered levels of pituitary hormones leads to development of cellular resistance to oxidative and nonoxidative stressors, which are stable through many rounds of in vitro cell division and could contribute to the remarkable disease resistance of long-lived mutant mice.

Glutathione depletion and anaesthesia in mice alter heme and drug metabolising enzymes

The effects of enflurane and isoflurane on heme metabolism, its regulation, and on some parameters involved in the hepatic drug metabolising system in animals under GSH depletion were investigated. A single dose of the anaesthethics (1 ml kg(-1), i.p.) was administered to control and GSH depleted mice, animals were sacrificed 20 min after. As a consequence of GSH depletion, a significant inhibition in delta-Aminolevulinic acid synthetase activity, the first enzyme of heme biosynthesis, and a striking induction in Heme oxygenase activity, the main enzyme of heme metabolism, were observed. Cytochrome P-450 levels and the activities of P-4502E1 and glutathione S-transferase were increased. These changes in heme metabolism and drug metabolising enzyme system were not altered further by the administration of enflurane or isoflurane. These findings would indicate that the status of oxidative stress produced by GSH depletion could not be affected by these anaesthetics and/or that disturbances in heme metabolism were already too important to undergo further variations.

Ebselen and diphenyl diselenide change biochemical hepatic responses to overdosage with paracetamol

The toxicity of paracetamol is largely related to its conversion to the reactive intermediate alkylating metabolite N-acetyl-para-benzo-quinoneimine (NAPQI). δ-Aminolevulinate dehydratase (δ-ALA-D) is a sulfhydril containing enzyme which is extremely sensitive to oxidizing and alkylating agents. In the present study, we examined whether acute treatment with paracetamol changes δ-ALA-D activity. The influence of two organochalcogenides with glutathione peroxidase-like activity, diphenyl diselenide [(PhSe)(2)] and ebselen was also assessed as potential protecting agents against paracetamol toxicity. Paracetamol (1200mg/kg for three days 4h after the injection of DMSO, diphenyl diselenide (100μmol/kg) or ebselen (100μmol/kg) caused an inhibition of about 40% (P < 0.01) in hepatic δ-ALA-D. Ebselen restored enzyme activity to control values. Non-protein-SH and ascorbic acid were diminished to 50% of control value by paracetamol, independent of chalcogenides treatment (all P values <0.05). In view of the fact that paracetamol caused a massive reduction in non-protein-SH and ascorbic acid, we realize that the protective effect of ebselen on δ-ALA-D activity is mediated by its thiol peroxidase-like activity or by a direct interaction with NAPQI and other reactive species formed during paracetamol metabolism.

Hepatoprotective and antioxidant effects ofAlnus japonica extracts on acetaminophen-induced hepatotoxicity in rats

The stem bark of the Betulaceae plant Alnus japonica, which is indigenous to Korea, has been used as a popular folk medicine for hepatitis and cancer. In this study, the antioxidant activity of the crude extract and the hepatoprotective activities on acetaminophen (AAP)-induced toxicity in the rat liver were evaluated. We investigated the effect of the methanol (AJM) and solvent fracton of the stem bark of Alnus japonica (AJ) on AAP-induced hepatotoxicity in rats. In rat hepatocyte culture, pretreatment with AJM (50, 100, 150 and 200 microg/ml) significantly decreased the cytotoxicity of AAP in a dose-dependent manner. The pretreated with EtOAc and BuOH fraction led to an increase in free radical scavenging activity and a decrease in inhibition of lipid peroxidation, both superoxide dismutase and catalase prevent the hepatotoxicity by AAP in the treatment of A. japonica fraction. We conclude that AJ is an important antioxidant in AAP-induced live hepatotoxicity and that extract of AJM plays a hepatoprotective effects in the against AAP-induced cytotoxicity in cultured rat hepatocytes in vitro. Pending more evaluation for safety and efficacy, AJ can potentially be used in mitigating AAP-induced hepatotoxicity.

Preventive effect of Thea sinensis melanin against acetaminophen-induced hepatic injury in mice

The preventive effect of Thea sinensis melanin (TSM) against overdoses of N-acetyl-p-aminophenol (NAPAP) was studied on ICR mice. Animals were given 400 mg/kg intraperitoneally (i.p.) of NAPAP, and TSM was injected i.p. in doses 10-40 mg/kg 2 h before intoxication. The protective effects were evidenced by a complete blockage of the NAPAP-induced elevation of plasma alanine aminotransferase (ALT) activity, decreased concentration of thiobarbituric acid reactive substances (TBARS) to the control level, and a partial prevention of reduced glutathione (GSH) depletion in the liver tissue. Preadministration of TSM also caused restoration of superoxide dismutase (SOD) activity and resumed content of coenzymes Q9 and Q10. TSM by itself, however, did not affect the hepatic functional parameters, including serum ALT, TBARS, GSH, SOD, or coenzymes Q in the liver. Administration of TSM caused a dose-dependent inhibition of N-nitrosodimethylamine demethylase activity with ED50 of 15.8 mg/kg. Activities of ethoxyresorufin O-dealkylase and pentoxyresorufin O-alkylase isozymes were changed insignificantly. The immune suppressive effect of NAPAP on the in vivo antibody-forming cell responses was demonstrated using ICR-sensitized mice with sheep red blood cells. The joint effect of TSM and NAPAP indicated the capability of TSM to recover immunity of the animals to the level of intact mice. Results obtained demonstrate that TSM preadministration can prevent the multiple toxic effects of NAPAP.

Potential roles of hepatic heat shock protein 25 and 70i in protection of mice against acetaminophen-induced liver injury

The aim of the present study was to assess the contribution of the level of expression of heat shock protein 25 (HSP25), 60 (HSP60), 70 (HSC70) and 70i (HSP70i) in mouse livers after a lethal dose of acetaminophen (APAP) to their survival. We examined changes in survival ratio, plasma APAP level and alanine aminotransferase (ALT) activity, and hepatic reduced glutathione (GSH), HSP25, HSP60, HSC70 and HSP70i levels following treatment of mice with APAP (500 mg/kg, p.o.). The plasma APAP level increased rapidly, and reached a maximum 0.5 h after APAP treatment. Hepatic GSH decreased rapidly, and was almost completely depleted 1 h after APAP treatment. Plasma ALT activity, an index of liver injury, significantly increased from 3 h onwards after APAP treatment. The survival ratios 9 h, 24 h and 48 h after APAP treatment were 96%, 38% and 36%, respectively. We found a remarkable difference in the patterns of hepatic HSP25 and HSP70i induction in mice that survived after APAP treatment. HSP70i levels increased from 1 h onwards after APAP treatment in a time-dependent manner, and reached a maximum at 9 h. In contrast, HSP25 could be detected just 24 h after APAP treatment, and maximal accumulation was observed at 48 h. Other HSPs examined were unchanged. Notably, the survival ratio dropped by only 2% after HSP25 expression. Recently, a novel role for HSP25 as an anti-inflammatory factor was suggested. We have already shown that 48-h treatment with APAP induces severe centrilobular necrosis with inflammatory cell infiltration in mouse livers. Taken together, the level of expression of hepatic HSP25 may be a crucial determinant of the fate of mice exposed to APAP insult.

Antioxidants protect primary rat hepatocyte cultures against acetaminophen-induced DNA strand breaks but not against acetaminophen-induced cytotoxicity

Acetaminophen, a safe analgesic when dosed properly but hepatotoxic at overdoses, has been reported to induce DNA strand breaks but it is unclear whether this event preceeds hepatocyte toxicity or is only obvious in case of overt cytotoxicity. Moreover, it is not known whether the formation of reactive oxygen species (ROS) is involved in the formation of the DNA strand breaks. In the present study, the dose-response curves for cytotoxicity and DNA strand breaks and the response to antioxidant protection have been compared. In primary hepatocytes from untreated male rats, cytotoxicity as measured by the MTT test and by Neutral Red accumulation was obvious at 10 mM acetaminophen but DNA strand breaks as measured by the comet assay were only found at 25-30 mM acetaminophen. Non-cytotoxic concentrations of three compounds with antioxidant activity, the glutathione precursor N-acetylcysteine (100 micro M), the plant polyphenol silibin (25 micro M) and the antioxidant vitamin alpha-tocopherol (50 micro M), were not able to inhibit acetaminophen toxicity at any acetaminophen concentration, while they completely prevented the formation of DNA strand breaks at 25-30 mM acetaminophen. The occurrence of oxidative stress in our experiments was indicated by a slight increase of malondialdehyde formation at 40 mM acetaminophen and by an adaptive increase in catalase mRNA concentration. We conclude that in acetaminophen-treated hepatocytes ROS-independent cell death and ROS-dependent DNA strand breaks occur which appear not to be causally related as judged from their dose dependency and their response to antioxidants.

Protective effects of melatonin, vitamin E and N-acetylcysteine against acetaminophen toxicity in mice: a comparative study

Acetaminophen (AA) is a commonly used analgesic and antipyretic drug; however, when used in high doses, it causes fulminant hepatic necrosis and nephrotoxic effects in both humans and experimental animals. It has been reported that the toxic effects of AA are the result of oxidative reactions that take place during its metabolism. In this study we investigated if melatonin, vitamin E or N-acetylcysteine (NAC) are protective against AA toxicity in mice. The doses of the antioxidants used were as follows: melatonin (10 mg/kg), vitamin E (30 mg/kg) and NAC (150 mg/kg). Blood urea nitrogen (BUN), serum creatinine, alanine aminotransferase (ALT), aspartate aminotransferase (AST) levels in blood, and glutathione (GSH), malondialdehyde (MDA), oxidized protein levels and myeloperoxidase (MPO) activity in liver and kidney tissues were measured. BUN and serum creatinine, ALT and AST levels which were increased significantly following AA treatment decreased significantly after pretreatment with either vitamin E, melatonin or NAC; however, they were not reduced to control levels. ALT and AST levels were significantly higher at 4 hr compared with the 24 hr levels after AA administration. However, BUN and creatinine levels were significantly elevated only at 24 hr. GSH levels were reduced while MDA, MPO and oxidized protein levels were increased significantly following AA administration. These changes were reversed by pretreatment with either melatonin, vitamin E or NAC. Liver toxicity was higher at 4 hr, whereas nephrotoxicity appeared to be more severe 24 hr after treatment with AA. Vitamin E was the least efficient agent in reversing AA toxicity while melatonin, considering it was given as at lower dose than either vitamin E or NAC, was the most effective. This may be the result of the higher efficacy of melatonin in scavenging various free radicals and also because of its ability in stimulating the antioxidant enzymes.

Therapeutic effect of S-allylmercaptocysteine on acetaminophen-induced liver injury in mice

S-allylmercaptocysteine is one of the water-soluble organosulfur compounds in ethanol extracts of garlic (Allium sativum L.). We had demonstrated earlier that treatment with S-allylmercaptocysteine before acetaminophen administration protects mice against acetaminophen-induced hepatotoxicity. In this study, we examined the therapeutic effect of S-allylmercaptocysteine treatment after acetaminophen administration. A single dose of S-allylmercaptocysteine (200 mg/kg, p.o.) to mice 0.5 h after acetaminophen administration (500 mg/kg, p.o.) significantly suppressed both the increase in plasma alanine aminotransferase activity and the hepatic necrosis, and also reduced acetaminophen-induced mortality from 43% to 0%. These data indicate that S-allylmercaptocysteine is useful as an antidote for acetaminophen overdose. S-allylmercaptocysteine significantly suppressed hepatic cytochrome P450 2E1 (CYP2E1) activity and induction of inducible 70-kDa heat shock protein, a marker of acetaminophen arylation of protein. These results suggest that S-allylmercaptocysteine exerts its protective effect by inhibition of CYP2E1 activity, which leads to the suppression of acetaminophen arylation of hepatic protein.

Ca(2+)-calmodulin antagonist chlorpromazine and poly(ADP-ribose) polymerase modulators 4-aminobenzamide and nicotinamide influence hepatic expression of BCL-XL and P53 and protect against acetaminophen-induced programmed and unprogrammed cell death in mice

Acetaminophen (AAP), the analgesic hepatotoxicant, is a powerful inducer of oxidative stress, DNA fragmentation, and apoptosis. The anti-apoptotic oncogene bcl-XL, and the pro-apoptotic oncogene p53 are two key regulators of cell cycle progression and/or apoptosis subsequent to DNA damage in vitro and in vivo. This study investigated the effect of AAP on the expression of these oncogenes and whether agents that modulate DNA fragmentation (chlorpromazine, CPZ) and DNA repair through poly(ADP-Ribose) polymerase (PARP) activity (4-AB: 4-aminobenzamide) can protect against AAP-induced hepatotoxicity by inhibiting oxidative stress, DNA fragmentation, and/or by altering the expression of bcl-XL and p53. In addition, the protective effect of supplemental nicotinamide (NICO), known to be depleted in cells with high PARP activity during DNA repair, is similarly evaluated. Male ICR mice (3 months old) were administered vehicle alone; nontoxic doses of 4-AB (400 mg/kg, ip), NICO (250 mg/kg, ip) or CPZ (25 mg/kg, ip), hepatotoxic dose of AAP alone (500 mg/kg, ip), or AAP plus one of the protective agents 1 h later. All animals were sacrificed 24 h following AAP administration. Serum alanine aminotransferase activity (ALT), hepatic histopathology and lipid peroxidation, DNA damage, and expression of bcl-XL and p53 (western blot analysis) were compared in various groups. All of the three agents significantly prevented AAP-induced liver injury, lipid peroxidation, DNA damage, and associated apoptotic and necrotic cell deaths, 4-AB being the most effective and NICO the least. Compared to control, there was a considerable decrease in bcl-XL expression, and an increase in p53 expression in AAP-exposed livers. The effect of AAP on bcl-XL was antagonized and that on p53 was synergized by the PARP-modulator 4-AB as well as NICO, whereas the endonuclease inhibitor CPZ was without effect on either bcl-XL or p53 expression. These results suggest that the hepatotoxic effect of AAP involves multiple mechanisms including oxidative stress, upregulation of endonuclease (or caspase-activated DNAse) and alteration of pro- and anti-apoptotic oncogenes. The observed antagonism of AAP-induced hepatocellular apoptosis and/or necrosis by modulators of multiple processes including DNA repair suggests the likelihood that a more effective therapy against AAP intoxication should involve a combination of antidotes.

Clofibrate pretreatment in mice confers resistance against hepatic lipid peroxidation

Pretreatment with peroxisome proliferators protects mice against various hepatotoxicants. Since our previous work suggested that the hepatoprotection may involve an increased ability to cope with oxidative stress, the present work directly addressed this possibility. Several observations indicated a heightened defense against oxidative stress accompanies the hepatoprotection produced by clofibrate. Firstly, the carbonyl content of hepatic proteins from clofibrate-pretreated mice was 40% lower than those from vehicle-treated controls. Secondly, liver homogenates from clofibrate-pretreated mice produced less thiobarbituric acid reactive substances upon incubation under aerobic conditions or exposure to ferrous sulfate. This effect was not due to lower levels of peroxidation-prone polyunsaturated fatty acids in clofibrate-treated livers. Thirdly, in vitro experiments indicated that the antioxidant factor in liver homogenates from clofibrate-pretreated mice was not glutathione. Rather, since it was inactivated by proteases and heat treatment, we concluded that a protein is involved. Collectively, our results suggest that a resistance to lipid peroxidation develops in mouse liver during exposure to clofibrate. The identity of the putative antioxidant protein and its contribution to the protection against liver toxicity observed in this and other laboratories awaits future investigation.

Transcriptional activation of heme oxygenase-1 and its functional significance in acetaminophen-induced hepatitis and hepatocellular injury in the rat

BACKGROUND/AIM

Glutathione depletion contributes to acetaminophen hepatotoxicity and is known to induce the oxidative stress reactant heme oxygenase-1. The metabolites of the heme oxygenase pathway, biliverdin, carbon monoxide, and iron may modulate acetaminophen toxicity. The aim of this study was to assess cell-type specific expression of heme oxygenase-1 and its impact on liver injury and microcirculatory disturbances in a model of acetaminophen-induced hepatitis.

METHODS

Gene expression of heme oxygenase-1 was studied by Northern- and Western analysis as well as immunohistochemistry. The time course of heme oxygenase-1 and -2, cytokine-induced neutrophil chemoattractant-1, and intercellular adhesion molecule-1 was studied by Northern analysis. DNA-binding activity of nuclear factor-kappaB was determined by electrophoretic mobility shift assay. Sinusoidal perfusion and leukocyte-endothelial interactions were assessed by intravital microscopy.

RESULTS

Acetaminophen caused a moderate sinusoidal perfusion failure (-15%) and infiltration of neutrophils along with activation of nuclear factor-kappaB and intercellular adhesion molecule-1 and cytokine-induced neutrophil chemoattractant-1 mRNAs. Induction of heme oxygenase-1 mRNA and protein (approximately 30-fold) in hepatocytes and non-parenchymal cells paralleled the inflammatory response. Blockade of heme oxygenase activity with tin-protoporphyrin-IX abrogated acetaminophen-induced hepatic neutrophil accumulation and nuclear factor-kappaB activation, but failed to affect sinusoidal perfusion and liver injury.

CONCLUSIONS

The inflammatory response associated with acetaminophen hepatotoxicity is modulated by the parallel induction of the heme oxygenase-1 gene. However, heme oxygenase-1 has no permissive effect on sinusoidal perfusion and does not affect liver injury in this model. These data argue against a central role of nuclear factor-kappaB activation and neutrophil infiltration as perpetuating factors of liver injury in acetaminophen toxicity.

Repeated acetaminophen dosing in rats: adaptation of hepatic antioxidant system

Repeated dosing of acetaminophen (paracetamol) to rats is reported to decrease their sensitivity to its hepatotoxic effects, which are associated with oxidative stress and glutathione depletion. We determined if repeated acetaminophen dosing produced adaptive response of key antioxidant system enzymes. Male rats (Sprague-Dawley, 10 weeks) were given 800, 1200, or 1600 mg/kg/day acetaminophen by oral gavage for 4 days. Liver was assayed for oxidative stress and antioxidant markers: malondialdehyde (MDA), thiobarbituric acid reactive substance (TBARS), total antioxidant status (TAS), glutathione (GSH), glutathione reductase (GR), glutathione peroxidase (GPx), glucose-6-phosphate dehydrogenase (G6PD), catalase (CAT), and superoxide dismutase (SOD), and alanine transaminase (ALT) as a marker of hepatocellular injury. Acetaminophen at 1200/1600 mg/kg decreased GSH 26/47%, GPx 21/26%, CAT 35/28%, SOD 21/12%; and TAS 28/18% (correlated with CAT, r=0.91; SOD, r=0.66; GPx, r=0.45). Despite antioxidant deficiencies, and no TBARS change, MDA decreased 26%/33%/37% at 800/1200/1600 mg/kg, which correlated with increased GR (61%/62%/76%, r=0.77) and G6PD (130%/110%/190%, r=0.78). Both MDA (r=0.68) and G6PD (r=0.71) correlated with hepatic ALT, which decreased 27%/43%/48%, respectively. Resistance to acetaminophen hepatotoxicity produced by repeated exposure is partially attributable to upregulation of hepatic G6PD and GR activity as an adaptive and protective response to oxidative stress and glutathione depletion.

Effects of halothane reexposure in female mice and their offspring

Female CBi mice subjected to multiple exposures to halothane inhalation anesthesia before mating were investigated for the potential effects of such intervention on a specific antibody response mounted by them and their offspring. An assessment of the toxicologic and reproductive performance of female mice undergoing anesthesia was also performed. Adult female mice received three episodes of halothane anesthesia at weekly intervals. Seventy-two hours after the last dose, mice were subjected to the following procedures: 1) study of the specific humoral immune response to sheep red blood cells (SRBC); 2) hematologic, hepatologic, and histopathologic studies; and 3) mating with syngeneic sires. Halothane-treated females had increased amounts of specific antibody secreting B cells, with liver studies showing evidence of microscopic fatty changes and decreased lipid peroxidation. Anesthesia did not alter reproductive performance but lowered offspring survival. Offspring displayed depressed antibody response after challenge with SRBC at weaning and at 60 d of age. The anti-SRBC antibody response that was found to be enhanced in halothane anesthetized females, seemed to be conversely impaired when studied in the offspring.