Repeated dosing with the peroxisome proliferator clofibrate decreases the toxicity of model hepatotoxic agents in male mice

Deciphering Acetaminophen-Induced Hepatotoxicity: The Crucial Role of Transcription Factors like Nuclear Factor Erythroid 2-Related Factor 2 as Genetic Determinants of Susceptibility to Drug-Induced Liver Injury

Acetaminophen (APAP) is the most commonly used over-the-counter medication throughout the world. At therapeutic doses, APAP has potent analgesic and antipyretic effects. The efficacy and safety of APAP are influenced by multifactorial processes dependent upon dosing, namely frequency and total dose. APAP poisoning by repeated ingestion of supratherapeutic doses, depletes glutathione stores in the liver and other organs capable of metabolic bioactivation, leading to hepatocellular death due to exhausted antioxidant defenses. Numerous genes, encompassing transcription factors and signaling pathways, have been identified as playing pivotal roles in APAP toxicity, with the liver being the primary organ studied due to its central role in APAP metabolism and injury. Nuclear factor erythroid 2-related factor 2 (NRF2) and its array of downstream responsive genes are crucial in counteracting APAP toxicity. NRF2, along with its negative regulator Kelch-like ECH-associated protein 1, plays a vital role in regulating intracellular redox homeostasis. This regulation is significant in modulating the oxidative stress, inflammation, and hepatocellular death induced by APAP. In this review, we provide an updated overview of the mechanisms through which NRF2 activation and signaling critically influence the threshold for developing APAP toxicity. We also describe how genetically modified rodent models for NRF2 and related genes have been pivotal in underscoring the significance of this antioxidant response pathway. While NRF2 is a primary focus, the article comprehensively explores other genetic factors involved in phase I and phase II metabolism of APAP, inflammation, oxidative stress, and related pathways that contribute to APAP toxicity, thereby providing a holistic understanding of the genetic landscape influencing susceptibility to this condition. SIGNIFICANCE STATEMENT: This review summarizes the genetic elements and signaling pathways underlying APAP-induced liver toxicity, focusing on the crucial protective role of the transcription factor NRF2. This review also delves into the genetic intricacies influencing APAP safety and potential liver harm. It also emphasizes the need for deeper insight into the molecular mechanisms of hepatotoxicity, especially the interplay of NRF2 with other pathways.

Conventional versus drug-eluting embolic transarterial chemoembolization with doxorubicin: comparative drug delivery, pharmacokinetics, and treatment response in a rabbit VX2 tumor model

The purpose of this study was to compare intra-tumoral drug delivery, pharmacokinetics, and treatment response after doxorubicin (DOX) conventional (c-) versus drug-eluting embolic (DEE-) transarterial chemoembolization (TACE) in a rabbit VX2 liver tumor model. Twenty-four rabbits with solitary liver tumors underwent c-TACE (n = 12) (1:2 water-in-oil emulsion, 0.6 mL volume, 2 mg DOX) or DEE-TACE (n = 12) (130,000 70-150 µm 2 mg DOX-loaded microspheres). Systemic, intra-tumoral, and liver DOX levels were measured using mass spectrometry up to 7-day post-procedure. Intra-tumoral DOX distribution was quantified using fluorescence imaging. Percent tumor necrosis was quantified by a pathologist blinded to treatment group. Lobar TACE was successfully performed in all cases. Peak concentration (C_MAX, µg/mL) for plasma, tumor tissue, and liver were 0.666, 4.232, and 0.270 for c-TACE versus 0.103, 8.988, and 0.610 for DEE-TACE. Area under the concentration versus time curve (AUC, µg/mL ∗ min) for plasma, tumor tissue, and liver were 18.3, 27,078.8, and 1339.1 for c-TACE versus 16.4, 26,204.8, and 1969.6 for DEE-TACE. A single dose of intra-tumoral DOX maintained cytotoxic levels through 7-day post-procedure for both TACE varieties, with a half-life of 1.8 (c-TACE) and 0.8 (DEE-TACE) days. Tumor-to-normal liver DOX ratio was high (c-TACE, 20.2; DEE-TACE, 13.3). c-TACE achieved significantly higher DOX coverage of tumor vs. DEE-TACE (10.8% vs. 2.3%; P = 0.003). Percent tumor necrosis was similar (39% vs. 37%; P = 0.806). In conclusion, in a rabbit VX2 liver tumor model, both c-TACE and DEE-TACE achieved tumoricidal intra-tumoral DOX levels and high tumor-to-normal liver drug ratios, though c-TACE resulted in significantly greater tumor coverage.

A single pretreatment with clofibric acid attenuates carbon tetrachloride-induced necrosis, but not steatosis, in rat liver

The present study investigated whether a single pretreatment with clofibric acid suppresses liver injury in rats after CCl₄ intoxication. Rats received a single pretreatment with clofibric acid (100 mg/kg, i.p.) 1 h prior to a CCl₄ (1 mL/kg, p.o.) challenge, and were euthanized 24 h after the CCl₄ administration. A single pretreatment with clofibric acid effectively suppressed increases in the serum aminotransferase activities and the severity of necrosis following the CCl₄ challenge, whereas the pretreatment did not protect against CCl₄-induced fatty liver. The clofibric acid pretreatment did not affect blood concentrations of CCl₄ in the early stage after CCl₄ dosing, or the level of the CCl₄ reaching the liver 1 h after the CCl₄ challenge. Moreover, the clofibric acid pretreatment did not affect the intensity of the covalent binding of the [¹⁴C]CCl₄ metabolite to microsomal proteins and lipids. The clofibric acid pretreatment did not alter microsomal cytochrome P450 2E1 activity. Based on these results, we conclude that protection against CCl₄-induced hepatocellular necrosis by a clofibric acid pretreatment does not require its repeated administration, and that a single and brief pre-exposure to clofibric acid prior to CCl₄ dosing markedly suppresses necrosis without affecting the development and progression of steatosis.

From hepatoprotection models to new therapeutic modalities for treating liver diseases: a personal perspective

A variety of rodent models of hepatoprotection have been developed in which tolerance to acetaminophen-induced hepatotoxicity occurs. Autoprotection/heteroprotection is a phenomenon where prior exposure to a mildly toxic dose of toxicant confers protection against a subsequently administered higher dose of the same toxicant (as in the case of autoprotection) or to a different toxicant (referred to as heteroprotection). Multiple mechanisms regulate this adaptive response, including hepatocellular proliferation, proteostasis, enhanced expression of cytoprotective genes, and altered tissue immune response. In this review, we will discuss recent findings that highlight the complexity of these adaptive mechanisms and we also outline the usefulness of these findings to devise therapeutic and/or diagnostic tools for acetaminophen-induced liver damage in patients.

MDR1 transporter protects against paraquat-induced toxicity in human and mouse proximal tubule cells

Paraquat is a herbicide that is highly toxic to the lungs and kidneys following acute exposures. Prior studies have demonstrated that the organic cation transporter 2 and multidrug and toxin extrusion protein 1 contribute to the urinary secretion of paraquat in the kidneys. The purpose of this study was to determine whether the multidrug resistance protein 1 (MDR1/Mdr1, ABCB1, or P-glycoprotein) also participates in the removal of paraquat from the kidneys and protects against renal injury. Paraquat transport and toxicity were quantified in human renal proximal tubule epithelial cells (RPTEC) that endogenously express MDR1, HEK293 cells overexpressing MDR1, and Mdr1a/1b knockout mice. In RPTEC cells, reduction of MDR1 activity using the antagonist PSC833 or siRNA transfection increased the cellular accumulation of paraquat by 50%. Reduced efflux of paraquat corresponded with enhanced cytotoxicity in PSC833-treated cells. Likewise, stable overexpression of the human MDR1 gene in HEK293 cells reduced intracellular levels of paraquat by 50%. In vivo studies assessed the renal accumulation and subsequent nephrotoxicity of paraquat (10 or 30 mg/kg ip) in wild-type and Mdr1a/1b knockout mice. At 4 h after paraquat treatment, renal concentrations of paraquat in the kidneys of Mdr1a/1b knockout mice were 750% higher than wild-type mice. By 72 h, paraquat-treated Mdr1a/1b knockout mice had more extensive tubular degeneration and significantly greater mRNA expression of kidney injury-responsive genes, including kidney injury molecule-1, lipocalin-2, and NAD(P)H quinone oxidoreductase 1, compared with wild-type mice. In conclusion, MDR1/Mdr1 participates in the elimination of paraquat from the kidneys and protects against subsequent toxicity.

Transgenic expression of the human MRP2 transporter reduces cisplatin accumulation and nephrotoxicity in Mrp2-null mice

The chemotherapeutic drug cisplatin is actively transported into proximal tubules, leading to acute renal injury. Previous studies suggest that the multidrug resistance-associated protein 2 (Mrp2) transporter may efflux cisplatin conjugates from cells. We sought to determine whether the absence of Mrp2 alters the accumulation and toxicity of platinum in the kidneys of mice and whether transgenic expression of the human MRP2 gene could protect against cisplatin injury in vivo. Plasma, kidneys, and livers from vehicle- and cisplatin-treated wild-type and Mrp2-null mice were collected for quantification of platinum and toxicity. By 24 hours, twofold higher concentrations of platinum were detected in the kidneys and livers of Mrp2-null mice compared with wild types. Enhanced platinum concentrations in Mrp2-null mice were observed in DNA and cytosolic fractions of the kidneys. Four days after cisplatin treatment, more extensive proximal tubule injury was observed in Mrp2-null mice compared with wild-type mice. Kidneys from naive Mrp2-null mice had elevated glutathione S-transferase mRNA levels, which could increase the formation of cisplatin-glutathione conjugates that may be metabolized to toxic thiol intermediates. Transgenic expression of the human MRP2 gene in Mrp2-null mice reduced the accumulation and nephrotoxicity of cisplatin to levels observed in wild-type mice. These data suggest that deficiency in Mrp2 lowers platinum excretion and increases susceptibility to kidney injury, which can be rescued by the human MRP2 ortholog.

GW501516-activated PPARβ/δ promotes liver fibrosis via p38-JNK MAPK-induced hepatic stellate cell proliferation

BACKGROUND

After liver injury, the repair process comprises activation and proliferation of hepatic stellate cells (HSCs), which produce extracellular matrix (ECM) proteins. Peroxisome proliferator-activated receptor beta/delta (PPARβ/δ) is highly expressed in these cells, but its function in liver repair remains incompletely understood. This study investigated whether activation of PPARβ/δ with the ligand GW501516 influenced the fibrotic response to injury from chronic carbon tetrachloride (CCl4) treatment in mice. Wild type and PPARβ/δ-null mice were treated with CCl4 alone or CCl4 co-administered with GW501516. To unveil mechanisms underlying the PPARβ/δ-dependent effects, we analyzed the proliferative response of human LX-2 HSCs to GW501516 in the presence or absence of PPARβ/δ.

RESULTS

We found that GW501516 treatment enhanced the fibrotic response. Compared to the other experimental groups, CCl4/GW501516-treated wild type mice exhibited increased expression of various profibrotic and pro-inflammatory genes, such as those involved in extracellular matrix deposition and macrophage recruitment. Importantly, compared to healthy liver, hepatic fibrotic tissues from alcoholic patients showed increased expression of several PPAR target genes, including phosphoinositide-dependent kinase-1, transforming growth factor beta-1, and monocyte chemoattractant protein-1. GW501516 stimulated HSC proliferation that caused enhanced fibrotic and inflammatory responses, by increasing the phosphorylation of p38 and c-Jun N-terminal kinases through the phosphoinositide-3 kinase/protein kinase-C alpha/beta mixed lineage kinase-3 pathway.

CONCLUSIONS

This study clarified the mechanism underlying GW501516-dependent promotion of hepatic repair by stimulating proliferation of HSCs via the p38 and JNK MAPK pathways.

Protective effect of Cassia fistula fruit extract on bromobenzene-induced nephrotoxicity in mice

The efficacy of a crude hydro-alcoholic extract of Cassia fistula (golden shower tree) fruit to protect the kidney against bromobenzene-induced toxicity was studied. Negative control mice received normal saline; positive control mice were given 460 mg/kg of bromobenzene; Cassia fistula treated mice received 200, 400, 600 and 800 mg/kg of Cassia fistula fruit extract followed by 460 mg/kg bromobenzene (daily by oral gavage for 10 days). On the 11th day, the mice were sacrificed, blood samples were obtained to assess blood urea nitrogen (BUN) and creatinine levels, and kidneys were removed for histological examination. We found that bromobenzene induced significant nephrotoxicity reflected by an increase in levels of BUN and creatinine that was dose dependently prevented by the Cassia fistula fruit extract. The nephroprotective effect of the Cassia fistula fruit extract was confirmed by the histological examination of the kidneys. To the best of our knowledge, this is the first study to demonstrate the protective effect of Cassia fistula in nephrotoxicity.

Transcriptional regulation of renal cytoprotective genes by Nrf2 and its potential use as a therapeutic target to mitigate cisplatin-induced nephrotoxicity

The use of the chemotherapeutic drug cisplatin is limited in part by nephrotoxicity. Cisplatin causes renal DNA adducts and oxidative stress in rodents. The transcription factor Nrf2 (nuclear factor E2-related factor 2) induces expression of cytoprotective genes, including Nqo1 (NADPH:quinone oxidoreductase 1), Ho-1 (heme oxygenase-1), and Gclc (glutamate cysteine ligase catalytic subunit), in response to electrophilic and oxidative stress. In the present study, plasma and kidneys from wild-type and Nrf2-null mice were collected after receiving cisplatin for evaluation of renal injury, inflammation, mRNA, and protein expression. Compared with wild types, more extensive nephrotoxicity was observed in Nrf2-null mice after cisplatin treatment. Kidneys from Nrf2-null mice treated with cisplatin had more neutrophil infiltration accompanied by increased p65 nuclear factor κB binding and elevated inflammatory mediator mRNA levels. Cisplatin increased renal mRNA and protein expression of cytoprotective genes (Nqo1, Ho-1, Gclc) and transporters Mrp2 and Mrp4 in wild-type but not in Nrf2-null mice. Lastly, the Nrf2 activator, CDDO-Im [2-cyano-3,12-dioxooleana-1,9-dien-28-oic imidazolide], increased Nrf2 signaling in kidneys from wild-type mice and protected them from cisplatin toxicity. Collectively, these data indicate that the absence of Nrf2 exacerbates cisplatin renal damage and that pharmacological activation of Nrf2 may represent a novel therapy to prevent kidney injury. Coordinated regulation of detoxification enzymes and drug transporters and suppression of inflammation by Nrf2 during cisplatin nephrotoxicity are probable defense mechanisms to eliminate toxic mediators and promote proximal tubule recovery.

The influence of alpha-, beta-, and gamma-melanocyte stimulating hormone on acetaminophen induced liver lesions in male CBA mice

Research over the past decade has indicated that melanocortin peptides are potent inhibitors of inflammation and a promising source of new anti-inflammatory and cytoprotective therapies. The purpose of the present paper is to compare protective effects of α-, β-, and γ-melanocyte stimulating hormone on acetaminophen induced liver lesions in male CBA mice. Acetaminophen was applied intragastrically in a dose of 150 mg/kg, and tested substances were applied intraperitoneally 1 hour before acetaminophen. Mice were sacrificed after 24 hours and intensity of liver injury was estimated by measurement of plasma transaminase activity (AST and ALT) and histopathological grading of lesions. It was found that α-, β-, and γ-MSH decrease intensity of lesions by both criteria in a dose-dependent manner.

Urolithiasis and hepatotoxicity are linked to the anion transporter Sat1 in mice

Urolithiasis, a condition in which stones are present in the urinary system, including the kidneys and bladder, is a poorly understood yet common disorder worldwide that leads to significant health care costs, morbidity, and work loss. Acetaminophen-induced liver damage is a major cause of death in patients with acute liver failure. Kidney and urinary stones and liver toxicity are disturbances linked to alterations in oxalate and sulfate homeostasis, respectively. The sulfate anion transporter-1 (Sat1; also known as Slc26a1) mediates epithelial transport of oxalate and sulfate, and its localization in the kidney, liver, and intestine suggests that it may play a role in oxalate and sulfate homeostasis. To determine the physiological roles of Sat1, we created Sat1-/- mice by gene disruption. These mice exhibited hyperoxaluria with hyperoxalemia, nephrocalcinosis, and calcium oxalate stones in their renal tubules and bladder. Sat1-/- mice also displayed hypersulfaturia, hyposulfatemia, and enhanced acetaminophen-induced liver toxicity. These data suggest that Sat1 regulates both oxalate and sulfate homeostasis and may be critical to the development of calcium oxalate urolithiasis and hepatotoxicity.

Peroxisome proliferator-activated receptor-beta/delta protects against chemically induced liver toxicity in mice

Potential functional roles for the peroxisome proliferator-activated receptor-beta/delta (PPARbeta/delta) in skeletal muscle fatty acid catabolism and epithelial carcinogenesis have recently been described. Whereas PPARbeta/delta is expressed in liver, its function in this tissue is less clear. To determine the role of PPARbeta/delta in chemically induced liver toxicity, wild-type and PPARbeta/delta-null mice were treated with azoxymethane (AOM) and markers of liver toxicity examined. Bile duct hyperplasia, regenerative hyperplasia, and increased serum alanine aminotransferase (ALT) were found in AOM-treated PPARbeta/delta-null mice, and these effects were not observed in similarly treated wild-type mice. Exacerbated carbon tetrachloride (CCl(4)) hepatoxicity was also observed in PPARbeta/delta-null as compared with wild-type mice. No differences in messenger RNAs (mRNAs) encoding cytochrome2E1 required for the metabolic activation of AOM and CCl(4) were observed between wild-type or PPARbeta/delta-null mice in response to CCl(4). Significant differences in the expression of genes reflecting enhanced nuclear factor kappa B (NF-kappaB) activity were noted in PPARbeta/delta-null mice.

CONCLUSION

Results from these studies show that PPARbeta/delta is protective against liver toxicity induced by AOM and CCl(4), suggesting that this receptor is hepatoprotective against environmental chemicals that are metabolized in this tissue.

Mechanisms and outcomes of drug- and toxicant-induced liver toxicity in diabetes

Increase dincidences of hepatotoxicity have been observed in diabetic patients receiving drug therapies. Neither the mechanisms nor the predisposing factors underlying hepatotoxicity in diabetics are clearly understood. Animal studies designed to examine the mechanisms of diabetes-modulated hepatotoxicity have traditionally focused only on bioactivation/detoxification of drugs and toxicants. It is becoming clear that once injury is initiated, additional events determine the final outcome of liver injury. Foremost among them are two leading mechanisms: first, biochemical mechanisms that lead to progression or regression of injury; and second, whether or not timely and adequate liver tissue repair occurs to mitigate injury and restore liver function. The liver has a remarkable ability to repair and restore its structure and function after physical or chemical-induced damage. The dynamic interaction between biotransformation-based liver injury and compensatory tissue repair plays a pivotal role in determining the ultimate outcome of hepatotoxicity initiated by drugs or toxicants. In this review, mechanisms underlying altered hepatotoxicity in diabetes with emphasis on both altered bioactivation and liver tissue repair are discussed. Animal models of both marked sensitivity (diabetic rats) and equally marked protection (diabetic mice) from drug-induced hepatotoxicity are described. These examples represent a remarkable species difference. Availability of the rodent diabetic models offers a unique opportunity to uncover mechanisms of clinical interest in averting human diabetic sensitivity to drug-induced hepatotoxicities. While the rat diabetic models appear to be suitable, the diabetic mouse models might not be suitable in preclinical testing for potential hepatotoxic effects of drugs or toxicants, because regardless of type 1 or type2 diabetes, mice are resistant to acute drug-or toxicant-induced toxicities.

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

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

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.

Role of cytosolic liver fatty acid binding protein in hepatocellular oxidative stress: effect of dexamethasone and clofibrate treatment

The presence of cysteine and methionine groups together with an ability to bind long-chain fatty acid (LCFA) oxidation products makes liver fatty acid binding protein (L-FABP) an attractive candidate against hepatocellular oxidative stress. In this report, we show that pharmacological treatment directed at modulating L-FABP level affected hepatocellular oxidant status. L-FABP expressing 1548-hepatoma cells, treated with dexamethasone or clofibrate, decreased and increased intracellular L-FABP levels, respectively. Oxidative stress was induced by H2O2 incubation or hypoxia-reoxygenation. The fluorescent marker, dichlorofluorescein (DCF), was employed to measure intracellular reactive oxygen species (ROS). Hepatocellular damage was assessed by lactate dehydrogenase (LDH) level. Dexamethasone treatment resulted in a significant increase in DCF fluorescence with higher LDH release compared to control cells. Clofibrate treatment, however, resulted in a significant decrease in both parameters (p<0.05). Drug treatments did not affect cytosolic activities of glutathione peroxidase (GPx), superoxide dismutase (SOD), or catalase suggesting that the differences between treated and control cells may likely be associated with varying L-FABP levels. We conclude that L-FABP may act as an effective endogenous cytoprotectant against hepatocellular oxidative stress.

Oxidative stress in experimental liver microvesicular steatosis: role of mitochondria and peroxisomes

BACKGROUND

Hepatic microvesicular steatosis is a clinical manifestation seen in a number of liver diseases. Although the role of mitochondrial beta-oxidation in the development of the disease has been well studied, information on lipid peroxidative damage in liver subcellular organelles is scarce. The present study looked at oxidative stress in hepatic peroxisomes and microsomes in microvesicular steatosis, using an animal model of the disease.

METHODS

Rats were given i.p. injections of sodium valproate (700 mg/kg bodyweight) to induce microvesicular steatosis, which was confirmed by histology.

RESULTS

Oxidative stress was evident in liver in steatosis, accompanied by structural and functional alterations in hepatic mitochondria. Alterations in lipid composition, with decreased phosphatidyl choline and ethanolamine and increased lysophosphatidyl choline and ethanolamine, were seen. An increase in triglyceride content was also seen. In addition, increased lipid peroxidation was also evident in peroxisomes and microsomes from steatotic rats. Pretreatment with clofibrate results in partial reversal of changes produced by valproate.

CONCLUSIONS

These results suggest that in addition to impaired mitochondrial beta-oxidation, oxidative stress is also seen in the hepatic peroxisomes and microsomes during microvesicular steatosis.

Disruption of NaS1 sulfate transport function in mice leads to enhanced acetaminophen-induced hepatotoxicity

Sulfate is required for detoxification of xenobiotics such as acetaminophen (APAP), a leading cause of liver failure in humans. The NaS1 sulfate transporter maintains blood sulfate levels sufficiently high for sulfonation reactions to work effectively for drug detoxification. In the present study, we identified two loss-of-function polymorphisms in the human NaS1 gene and showed the Nas1-null mouse to be hypersensitive to APAP hepatotoxicity. APAP treatment led to increased liver damage and decreased hepatic glutathione levels in the hyposulfatemic Nas1-null mice compared with that in normosulfatemic wild-type mice. Analysis of urinary APAP metabolites revealed a significantly lower ratio of APAP-sulfate to APAP-glucuronide in the Nas1-null mice. These results suggest hyposulfatemia increases sensitivity to APAP-induced hepatotoxicity by decreasing the sulfonation capacity to metabolize APAP. In conclusion, the results of this study highlight the importance of plasma sulfate level as a key modulator of acetaminophen metabolism and suggest that individuals with reduced NaS1 sulfate transporter function would be more sensitive to hepatotoxic agents.

Erdosteine Against Acetaminophen Induced Renal Toxicity

Acetaminophen (APAP) induced toxicities have been a major problem in clinical practice. The aim of the present study was to demonstrate a possible protective role of erdosteine, a mucolytic agent having antioxidant properties via its active metabolites, on APAP induced renal damage in rats. Female Wistar Albino rats were divided into groups including control, erdosteine (150 mg/kg, oral), APAP (1 g/kg, oral) APAP+erdosteine (150 mg/kg, oral) and APAP+erdosteine (300 mg/kg, oral). APAP treatment caused lipid peroxidation as well as high NO level in renal tissue. Also, APAP treated rats had decreased activities of CAT and GSH-Px, but not SOD. In addition, tubular epithelial degeneration, vacuolization and cell desquamation were clearly observed in the APAP treated rats. The cellular debris in the proximal tubules and cortical interstitial congestions were prominent in the kidneys of APAP treated rats. BUN and creatinine levels were increased after APAP administration. All these pathological changes were reversed after erdosteine treatments. Erdosteine treated APAP groups showed milder tubular degeneration, epithelial vacuolization in the proximal tubules, lesser cellular desquamation and better morphology when compared with APAP groups. In conclusion, erdosteine may be a choice of preventive treatment against APAP induced nephrotoxicity.

Transport deficient (TR−) hyperbilirubinemic rats are resistant to acetaminophen hepatotoxicity

The biliary excretion of acetaminophen (APAP) is reduced in transport deficient (TR-) hyperbilirubinemic rats lacking the multidrug resistance-associated protein 2 (Mrp2). This mutant strain of Wistar rats has impaired biliary excretion of organic anions and increased hepatic glutathione. The rational for this study was to determine if there is an altered risk for liver damage by APAP in the absence of Mrp2. Therefore, the susceptibility of TR- rats to APAP hepatotoxicity was investigated. Male Wistar and TR- rats were fasted overnight before APAP treatment (1 g/kg). Hepatotoxicity was assessed 24 h later by plasma sorbitol dehydrogenase activity and histopathology. In other studies, TR- rats received buthionine sulfoximine before APAP to reduce hepatic glutathione to values similar to those in Wistar rats. mRNA expression of APAP metabolizing enzymes was also measured in naïve animals. Wistar rats treated with APAP showed significant elevations in plasma sorbitol dehydrogenase activity, while no increases in enzyme activity were observed in TR- rats. Histopathology was in agreement. Hepatic non-protein sulfhydryls were significantly lower in Wistar rats receiving APAP than in TR- rats. TR- rats treated with buthionine sulfoximine and APAP showed dramatic increases in hepatotoxicity. TR- rats had increased mRNA expression of several APAP metabolizing enzymes. Mrp2 expression not only is important in biliary excretion, but also influences the toxic potential of reactive intermediates by controlling intrahepatic GSH and possibly drug metabolism.

Altered disposition of acetaminophen in mice with a disruption of the Mrp3 gene

MRP3 is an ABC transporter localized in the basolateral membrane of epithelial cells such as hepatocytes and enterocytes. In this study, the role of Mrp3 in drug disposition was investigated. Because Mrp3 preferentially transports glucuronide conjugates, we investigated the in vivo disposition of acetaminophen (APAP) and its metabolites. Mrp3+/+ and Mrp3-/- knockout mice received APAP (150 mg/kg), and bile was collected. Basolateral and canalicular excretion of APAP was also assessed in the isolated perfused liver. In separate studies, mice received 400 mg APAP/kg for assessment of hepatotoxicity. No differences were found in the biliary excretion of APAP, APAP-sulfate, and APAP-glutathione between Mrp3+/+ and Mrp3-/- mice. However, 20-fold higher accumulation of APAP-glucuronide (APAP-GLUC) was found in the liver of Mrp3-/- mice. Concomitantly, plasma APAP-GLUC content in Mrp3-/- mice was less than 10% of that in Mrp3+/+ mice. In addition, APAP-GLUC excretion in bile of Mrp3-/- mice was tenfold higher than in Mrp3+/+ mice. In the isolated perfused liver, we also found a strong decrease of APAP-GLUC secretion into the perfusate of Mrp3-/- livers. Plasma alanine aminotransferase (ALT), aspartate aminotransferase (AST), and histopathology showed that Mrp3-/- mice are more resistant to APAP hepatotoxicity than Mrp3+/+ mice, which is most likely a result of the faster repletion of hepatic GSH. In conclusion, basolateral excretion of APAP-GLUC in mice is nearly completely dependent on the function of Mrp3. In its absence, sufficient hepatic accumulation occurs to redirect some of the APAP-GLUC to bile. This altered disposition in Mrp3-/- mice is associated with reduced hepatotoxicity.

Effect of fermentation on Sweetpotato (Ipomoea batatas) toxicity in mice

Unfortunate bovine fatalities occurring after ingestion of mold-damaged sweetpotatoes preclude the use of the culled tubers in livestock feed. In cattle, mold-damaged sweetpotatoes induce an acute respiratory distress syndrome resulting in asphyxiation. Because of this potential toxicity and the general abundance of culled sweetpotatoes, the detoxification efficacy of ensiling was explored since it is an easy and economically viable technique often applied to preserve livestock feed. Sweetpotato slices with or without mold damage were stored either frozen (to represent unfermented samples) or fermented for 6 weeks at room temperature. Following fermentation, organic extracts were generated for administration to mice. Thirty hours following administration of the extracts, mice were evaluated for gross and microscopic lesions affecting the lungs, liver, and kidneys. Fermentation of 6 weeks duration was observed to inadequately eliminate the lung, liver, and kidney toxicity caused by mold-damaged sweetpotatoes. In fact, fermentation exacerbated the hepatotoxicity of mold-damaged sweetpotatoes. This is also the first demonstration that sweetpotato regions lacking visible mold damage can induce lung and kidney injury, which, however, is preventable by fermentation.

Activation of PPAR-alpha in streptozotocin-induced diabetes is essential for resistance against acetaminophen toxicity

Diabetic (DB) mice exhibit significant resistance to hepatotoxicants. The role of peroxisome proliferator receptor (PPAR)-alpha activation in diabetes, in protection against lethal acetaminophen (APAP) challenge, was investigated. Upon treatment with APAP (600 mg/kg, i.p., a LD100 dose in wild-type [WT] non-DB mice), WT-DB mice showed only 30% mortality and 40% less liver injury as measured by alanine aminotransferase and histopathology. In contrast, diabetes in PPAR knockout (PPAR-alpha-/-) mice failed to protect against APAP toxicity, suggesting the importance of PPAR-alpha in diabetes-induced protection. S-phase DNA synthesis and PCNA immunohistochemical staining after injury showed early and robust tissue repair in WT-DB mice, but not in the PPAR-alpha-/--DB mice. Microarray analyses were performed on livers from non-DB and DB (WT and PPAR-alpha-/-) mice at 0 and 12 h after APAP. Microarray data were confirmed via real-time polymerase chain reaction analysis of several genes, including stress response, immediate early genes, DNA damage, heat shock proteins, and cell cycle regulators, followed by Western analyses of selected proteins. Gel shift assays revealed higher activation of nuclear factor-kappaB in WT-DB mice after APAP treatment. These findings suggest PPAR-alpha activation as a hepatoprotective adaptive response mediating protection against APAP in diabetes.

Protection against acetaminophen hepatotoxicity by clofibrate pretreatment: role of catalase induction

Mice pretreated with the peroxisome proliferator clofibrate (CFB) are highly resistant to acetaminophen (APAP)-induced hepatotoxicity. The objective of the present study was to investigate whether the increase in hepatic catalase activity following CFB pretreatment plays a role in this hepatoprotection. An irreversible inhibitor, 3-amino-1,2,4-triazole (3-AT), was used to modulate catalase activity. Hepatic catalase activity in mice pretreated with CFB (500 mg/kg, i.p., for 10 days) was significantly inhibited by 3-AT (100 or 500 mg/kg, i.p.). In addition, the lower dose of 3-AT (100 mg/kg) had minimal effect on biliary and urinary excretion of APAP metabolites generated from a nontoxic dose, suggesting that APAP metabolism was not modulated by this dose of 3-AT. The mortality rate of corn-oil-pretreated mice challenged with APAP (800 mg/kg, p.o.) was significantly increased by 3-AT (100 mg/kg, i.p.) given 1 h before APAP. As expected, CFB pretreatment conferred full protection against APAP-induced hepatotoxicity. The same 3-AT treatment, however, did not abolish hepatoprotection in CFB-pretreated mice, despite the marked inhibition of hepatic catalase activity. In conclusion, these results indicate that elevated catalase activity in mice exposed to CFB does not appear to mediate the hepatoprotection, suggesting that other cellular defense mechanisms are involved.

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.

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

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

Clofibric acid or diethylmaleate supplemented diet decrease blood pressure in DOCA-salt treated male Sprague Dawley rats--relation with liver antioxidant status

The effects of 8-week diethylmaleate (DEM) and clofibric acid (CFA) supplemented diet on blood pressure, body and liver weights, liver antioxidant status and nitric oxide synthase (NOS) activity were investigated in 8-week DOCA-salt treated and untreated Sprague-Dawley male rats. It appeared that DEM and particularly CFA treatments were associated with a significant decrease in blood pressure in DOCA-salt treated rats, and an accentuation of the decreases in body weights in both diet supplemented groups. This was not associated with increases in NO production in the liver. In contrast, hepatic lipid peroxidation was significantly decreased in both DOCA-salt treated and untreated groups on DEM and particularly on CFA supplemented diet. The protective effects of CFA and DEM against hepatic cellular damage could be involved in the decreases in blood pressure in DOCA-salt treated rats, where CFA was more efficient than DEM. In CFA supplemented groups, there was a strong increase in hepatic superoxide dismutase (SOD), glutathione-peroxidase (GSH-Px), and catalase (CAT) activities and in DEM supplemented groups, increases in SOD and CAT activities and in GSH levels were observed. Our data suggest that normalization of blood pressure in DOCA-salt treated rats by CFA was due to an enhancement of the half-life of NO while DEM increased its availability.