Histopathological changes in the liver following a paracetamol overdose: correlation with clinical and biochemical parameters

Future directions in acute liver failure

Acute liver failure (ALF) describes a clinical syndrome of rapid hepatocyte injury leading to liver failure manifested by coagulopathy and encephalopathy in the absence of pre-existing cirrhosis. The hallmark diagnostic features are a prolonged prothrombin time (ie, an international normalized ratio of prothrombin time of ≥1.5) and any degree of mental status alteration (HE). As a rare, orphan disease, it seemed an obvious target for a multicenter network. The Acute Liver Failure Study Group (ALFSG) began in 1997 to more thoroughly study and understand the causes, natural history, and management of ALF. Over the course of 22 years, 3364 adult patients were enrolled in the study registry (2614 ALF and 857 acute liver injury-international normalized ratio 2.0 but no encephalopathy-ALI) and >150,000 biosamples collected, including serum, plasma, urine, DNA, and liver tissue. Within the Registry study sites, 4 prospective substudies were conducted and published, 2 interventional ( N -acetylcysteine and ornithine phenylacetate), 1 prognostic [ 13 C-methacetin breath test (MBT)], and 1 mechanistic (rotational thromboelastometry). To review ALFSG's accomplishments and consider next steps, a 2-day in-person conference was held at UT Southwestern Medical Center, Dallas, TX, entitled "Acute Liver Failure: Science and Practice," in May 2022. To summarize the important findings in the field, this review highlights the current state of understanding of ALF and, more importantly, asks what further studies are needed to improve our understanding of the pathogenesis, natural history, and management of this unique and dramatic condition.

Mitochondria in Acetaminophen-Induced Liver Injury and Recovery: A Concise Review

Mitochondria are critical organelles responsible for the maintenance of cellular energy homeostasis. Thus, their dysfunction can have severe consequences in cells responsible for energy-intensive metabolic function, such as hepatocytes. Extensive research over the last decades have identified compromised mitochondrial function as a central feature in the pathophysiology of liver injury induced by an acetaminophen (APAP) overdose, the most common cause of acute liver failure in the United States. While hepatocyte mitochondrial oxidative and nitrosative stress coupled with induction of the mitochondrial permeability transition are well recognized after an APAP overdose, recent studies have revealed additional details about the organelle's role in APAP pathophysiology. This concise review highlights these new advances, which establish the central role of the mitochondria in APAP pathophysiology, and places them in the context of earlier information in the literature. Adaptive alterations in mitochondrial morphology as well as the role of cellular iron in mitochondrial dysfunction and the organelle's importance in liver recovery after APAP-induced injury will be discussed.

Protective Effect of Annona muricata Linn Fruit Pulp Lyophilized Powder against Paracetamol-Induced Redox Imbalance and Hepatotoxicity in Rats

In the current investigation, Annona muricata Linn. lyophilized fruit pulp powder was evaluated for its hepatoprotective activity induced by paracetamol or acetaminophen (APAP). Male Sprague Dawley rats were orally pre-treated for 15 days with A. muricata lyophilized fruit pulp powder at low (1 g/kg b.wt) and high doses (2 g/kg b.wt). Silymarin (100 mg/kg) was administered as the standard drug. Hepatotoxicity was induced using APAP, in a single oral administration of 2.5 g/kg body weight dosage on the 15th day. Aspartate transaminase (AST), alanine transaminase (ALT), and alkaline phosphatase (ALP) were elevated in the APAP group but were found to be significantly reduced in the pre-treated groups in a dose-dependent manner. APAP administration brought down the serum total protein and albumin levels significantly. The activities of superoxide dismutase (SOD), glutathione peroxidase (GPx), and catalase were reduced in the APAP administration; further, the reduced glutathione pool in the tissue was also diminished significantly. However, with the administration of Annona lyophilized fruit pulp powder, the level of antioxidant parameters was near normal. A significant increase in lipid peroxidation was observed in the APAP group, while the silymarin, AML, and AMH groups exhibited resistance to lipid peroxidation (LPO), as evident from lower levels of LPO generated. Histopathological examination also revealed considerable tissue damage in the APAP alone treatment group, which was not devastating in the silymarin, AML, and AMH groups. Altogether, the study concludes that the lyophilized fruit pulp of A. muricata is protective against APAP-induced liver injury in rats by modulating the hepatic redox systems.

Acute, chronic, and genotoxic studies on the protopine total alkaloids of the Macleaya cordata (willd.) R. Br. in rodents

The protopine alkaloids are widely distributed within the opium poppy family and have a wide range of pharmacological effects. MPTA is a product of the protopine total alkaloids extracted from the Macleaya cordata (Willd.) R. Br. Previously, we reported good anti-inflammatory activity of MPTA as well as oral acute and sub-chronic toxicity studies in rats. In order to perform a systematic toxicological safety assessment of MPTA, oral acute toxicity, genotoxicity (bone marrow cell chromosome aberration test, sperm abnormality test, bone marrow cell micronucleus test, and rat teratogenicity test), and chronic toxicity in mice were performed in this study. In the oral acute toxicity test, the LD₅₀ in ICR mice was 481.99 mg/kg, with 95% confidence limits ranging from 404.27 to 574.70 mg/kg. All three mutagenicity tests tested negative in the range of 60.25–241.00 mg/kg. The results of the teratogenicity test in rats showed no reproductive or embryonic developmental toxicity at only 7.53 mg/kg, which can be considered as a no observed effect level (NOEL) for the teratogenicity test. Therefore, MPTA is safe for use at the doses tested, but attention should be paid to the potential risk to pregnant animals and the safety evaluation and toxicity mechanisms in target animals should be further investigated.

Assessment of the biochemical pathways for acetaminophen toxicity: Implications for its carcinogenic hazard potential

In 2019 California's Office of Environmental Health Hazard Assessment (OEHHA) initiated a review of the carcinogenic hazard potential of acetaminophen. In parallel with this review, herein we evaluated the mechanistic data related to the steps and timing of cellular events following therapeutic recommended (≤4 g/day) and higher doses of acetaminophen that may cause hepatotoxicity to evaluate whether these changes indicate that acetaminophen is a carcinogenic hazard. At therapeutic recommended doses, acetaminophen forms limited amounts of N-acetyl-p-benzoquinone-imine (NAPQI) without adverse cellular effects. Following overdoses of acetaminophen, there is potential for more extensive formation of NAPQI and depletion of glutathione, which may result in mitochondrial dysfunction and DNA damage, but only at doses that result in cell death - thus making it implausible for acetaminophen to induce the kind of stable, genetic damage in the nucleus indicative of a genotoxic or carcinogenic hazard in humans. The collective data demonstrate a lack of a plausible mechanism related to carcinogenicity and are consistent with rodent cancer bioassays, epidemiological results reviewed in companion manuscripts in this issue, as well as conclusions of multiple international health authorities.

Application of the DILIsym® Quantitative Systems Toxicology drug-induced liver injury model to evaluate the carcinogenic hazard potential of acetaminophen

In 2019, the California Office of Environmental Health Hazard Assessment (OEHHA) initiated a review of the carcinogenic hazard potential of acetaminophen. The objective of the analysis herein was to inform this review by assessing whether variability in patient baseline characteristics (e.g. baseline glutathione (GSH) levels, pharmacokinetics, and capacity of hepatic antioxidants) leads to potential differences in carcinogenic hazard potential at different dosing schemes: maximum labeled doses of 4 g/day, repeated doses above the maximum labeled dose (>4-12 g/day), and acute overdoses of acetaminophen (>15 g). This was achieved by performing simulations of acetaminophen exposure in thousands of diverse virtual patients scenarios using the DILIsym® Quantitative Systems Toxicology (QST) model. Simulations included assessments of the dose and exposure response for toxicity and mode of cell death based on evaluations of the kinetics of changes of: GSH, N-acetyl-p-benzoquinone-imine (NAPQI), protein adducts, mitochondrial dysfunction, and hepatic cell death. Results support that, at therapeutic doses, cellular GSH binds to NAPQI providing sufficient buffering capacity to limit protein adduct formation and subsequent oxidative stress. Simulations evaluating repeated high-level supratherapeutic exposures or acute overdoses indicate that cell death precedes DNA damage that could result in carcinogenicity and thus acetaminophen does not present a carcinogenicity hazard to humans at any dose.

A critical review of the acetaminophen preclinical carcinogenicity and tumor promotion data and their implications for its carcinogenic hazard potential

In 2019 the California Office of Environmental Health Hazard Assessment (OEHHA) initiated a review of the carcinogenic hazard potential of acetaminophen, including an assessment of the long-term rodent carcinogenicity and tumor initiation/promotion studies. The objective of the analysis herein was to inform this review process with a weight-of-evidence assessment of these studies and an assessment of the relevance of these models to humans. In most of the 14 studies, there were no increases in the incidences of tumors in any organ system. In the few studies in which an increase in tumor incidence was observed, there were factors such as absence of a dose response and a rodent-specific tumor supporting that these findings are not relevant to human hazard identification. In addition, we performed qualitative analysis and quantitative simulations of the exposures to acetaminophen and its metabolites and its toxicity profile; the data support that the rodent models are toxicologically relevant to humans. The preclinical carcinogenicity results are consistent with the broader weight of evidence assessment and evaluations of multiple international health authorities supporting that acetaminophen is not a carcinogenic hazard.

The DILI-sim Initiative: Insights into Hepatotoxicity Mechanisms and Biomarker Interpretation

The drug‐induced liver injury (DILI)‐sim Initiative is a public‐private partnership involving scientists from industry, academia, and the US Food and Drug Administration (FDA). The Initiative uses quantitative systems toxicology (QST) to build and refine a model (DILIsym) capable of understanding and predicting liver safety liabilities in new drug candidates and to optimize interpretation of liver safety biomarkers used in clinical studies. Insights gained to date include the observation that most dose‐dependent hepatotoxicity can be accounted for by combinations of just three mechanisms (oxidative stress, interference with mitochondrial respiration, and alterations in bile acid homeostasis) and the importance of noncompetitive inhibition of bile acid transporters. The effort has also provided novel insight into species and interpatient differences in susceptibility, structure‐activity relationships, and the role of nonimmune mechanisms in delayed idiosyncratic hepatotoxicity. The model is increasingly used to evaluate new drug candidates and several clinical trials are underway that will test the model's ability to prospectively predict liver safety. With more refinement, in the future, it may be possible to use the DILIsym predictions to justify reduction in the size of some clinical trials. The mature model could also potentially assist physicians in managing the liver safety of their patients as well as aid in the diagnosis of DILI.

Fatal acetaminophen poisoning with hepatic microvesicular steatosis in a child after repeated administration of therapeutic doses

Acetaminophen is the leading cause of acute liver failure worldwide following massive ingestion. We present here a fatal acute liver failure after repeated administration of four therapeutic doses of acetaminophen at 4-h intervals in a previously healthy 9-year-old female who presented dental pain after a facial trauma during sport practice. A diagnosis of paracetamol-induced hepatitis was deduced from the clinical picture of fulminant hepatitis and tubular necrosis, the encephalopathy with oedema and without signs of trauma. Liver biopsy showed typical acetaminophen-induced necrosis and a microvesicular steatosis in periportal hepatocytes. These injuries might have been favored by pre-existing mitochondrial dysfunction related, for instance, to a deficiency in an enzyme of the mitochondrial β-oxidation pathway, or the respiratory chain. The observation of microvesicular steatosis in the periportal areas suggests an increased vulnerability via pre-existing mitochondrial dysfunction. As the liver status of patients is mostly unknown, the frequency of administration (every six hours) must be respected and the use of pharmaceutical forms allowing to adjust the dose as closely as possible to the child's weight should be promoted.

Quantitative Systems Toxicology Approaches to Understand and Predict Drug-Induced Liver Injury

The DILI-sim Initiative is a public-private partnership using quantitative systems toxicology to build a model (DILIsym) capable of understanding and predicting liver safety liabilities in drug candidates. The effort has provided insights into mechanisms underlying dose-dependent drug-induced liver injury (DILI) and interpatient differences in susceptibility to dose-dependent DILI. DILIsym may be useful in identifying drugs capable of causing idiosyncratic hepatotoxicity. DILIsym is used to optimize interpretation of traditional and newer serum biomarkers of DILI. DILIsym results are considered in drug development decisions. In the future, it may be possible to use DILsym predictions to justify reduction in size of some clinical trials.

Serum biomarkers of drug-induced liver injury: Current status and future directions

Drug-induced liver injury (DILI), which is caused by drugs and herbal or dietary supplements, remains a serious concern for drug developers, regulators, and clinicians; however, serum biomarkers utilized to detect and monitor DILI have not changed in decades and have limitations. Data-driven mathematical modeling that incorporates the release and clearance kinetics of traditional biomarkers has improved their use in the prediction of liver safety liabilities for new drug candidates. Several newer biomarkers have shown promise in terms of liver specificity, predicting the outcome of DILI events, and providing insight into its underlying mechanisms. For these new biomarkers to be qualified for regulatory acceptance, it will require their assessment in large numbers of patients who are receiving a wide range of compounds and who develop a broad spectrum of liver injuries. The ongoing and evolving international biomarker consortia should play a major role in this effort, which is likely to transform the assessment of liver safety in clinical trials and in the clinic.

GSK2881078, a SARM, Produces Dose-Dependent Increases in Lean Mass in Healthy Older Men and Women

CONTEXT

GlaxoSmithKline (GSK) 2881078 is a nonsteroidal, selective androgen receptor modulator (SARM) under investigation by GSK for treatment of reduced mobility and other functional limitation in men and women with muscle weakness associated with chronic and acute illnesses.

OBJECTIVE

This was a phase 1b study intended to explore across a dose range the pharmacokinetics (PK)-pharmacodynamics relationship and further safety and tolerability data for GSK2881078. This study also evaluated effects of CYP3A4 inhibition on PK of GSK2881078.

METHODS

This was a randomized, placebo-controlled, parallel-group, repeat-dose, dose-escalation study in healthy older males and postmenopausal females. A total of three cohorts of males and three cohorts of females were studied. Dosing at each dose level was twice daily for the first 3 days followed by once daily for up to 53 days. Repeated dual-energy X-ray absorptiometry and MRI cross-sectional thigh scans were performed. The effect of CYP3A4 inhibition on GSK2881078 PK was evaluated in a separate cohort.

RESULTS

GSK2881078 was generally well tolerated and no serious adverse events were reported. Compared with placebo, there was greater lean mass accrual with all dose levels of GSK2881078. Females exhibited a greater response at lower doses than did males. Transient elevations of alanine aminotransferase were observed. The effect of CYP3A4 inhibition on GKS2881078 PK was unlikely to be of clinical significance.

CONCLUSIONS

GSK2881078 yielded dose-dependent increases in lean mass with evidence of enhanced sensitivity in women. The compound was well tolerated.

In silico modeling to optimize interpretation of liver safety biomarkers in clinical trials

Current strategies to delineate the risk of serious drug-induced liver injury associated with drugs rely on assessment of serum biomarkers that have been utilized for many decades. In particular, serum alanine aminotransferase and total bilirubin levels are typically used to assess hepatic integrity and function, respectively. Parallel measurement of these biomarkers is utilized to identify patients with drug-induced hepatocellular jaundice ("Hy's Law" cases) which carries at least a 10% risk of death or liver transplant. However, current guidelines regarding use of these biomarkers in clinical trials can put study subjects at risk for life-threatening drug-induced liver injury, or result in over estimation of risk that may halt development of safe drugs. In addition, pharmaceutical companies are increasingly being required to conduct large and expensive clinical trials to "defend" the safety of their new drug when results from smaller trials are inconclusive. Innovative approaches and some novel biomarkers are now being employed to maximize the value of traditional biochemical tests. DILIsym®, a product of the DILIsim Initiative, utilizes serial serum alanine aminotransferase values, along with serum biomarkers of apoptosis vs necrosis, to estimate percent hepatocyte loss and total bilirubin elevations resulting from loss of global liver function. The results from analyses conducted with DILIsym have been reported to the FDA to support the safety of entolimod and cimaglermin alfa after elevations in serum alanine aminotransferase and/or bilirubin halted clinical development. DILIsym can also be utilized to determine whether rises in serum conjugated and unconjugated bilirubin are consistent with mechanisms unrelated to toxicity ( i.e. inhibition of bilirubin transport or metabolism). In silico modeling of traditional and novel drug-induced liver injury biomarker data obtained in clinical trials may be the most efficient and accurate way to define the liver safety profile of new drug candidates. Impact statement Blood tests used in clinical trials to detect and monitor drug-induced liver injury (DILI) have not changed in half a century. These tests have several shortcomings: their use has not completely prevented clinical trial participants from risk of life-threatening DILI, they can give false positive results that halt the development of safe drug candidates, and they can create liver safety "concerns" that require large additional clinical trials to accurately define DILI risk. This review highlights the use of in silico modeling to improve interpretation of the blood tests currently available to detect DILI risk in new drug candidates. This approach is increasingly being applied in clinical trials to more precisely assess the degree of hepatocellular injury and its functional impact. This new approach holds the promise of more accurately defining DILI risk in smaller clinical trials.

The transformation in biomarker detection and management of drug-induced liver injury

Drug-induced liver injury (DILI) is a major concern for patients, care givers and the pharmaceutical industry. Interpretation of the serum biomarkers routinely used to detect and monitor DILI, which have not changed in almost 50 years, can be improved with recently proposed models employing quantitative systems pharmacology. In addition, several newer serum biomarkers are showing great promise. Studies in rodents indicate that the ratio of the caspase cleaved fragment of cytokeratin 18 to total K18 in serum (termed the "apoptotic index") estimates the relative proportions of apoptosis vs necrosis during drug-induced liver injury. Glutamate dehydrogenase can reliably differentiate liver from muscle injury and, when serum is properly prepared, may also detect mitochondrial toxicity as a mechanism of liver injury. MicroRNA-122 is liver-specific, but recent data suggests it can be actively released from hepatocytes in the absence of overt toxicity limiting enthusiasm for it as a DILI biomarker. Finally, damage associated molecular patterns, particularly high mobility group box 1 and its various modified forms, are promising biomarkers of innate immune activation, which may be useful in distinguishing benign elevations in aminotransferases from those that portend clinically important liver injury. These new biomarkers are already being measured in early clinical trials, but broad acceptance will require widespread archiving of serum from diverse clinical trials and probably pre-competitive analysis efforts. We believe that utilization of a panel of traditional and newer biomarkers in conjunction with quantitative systems pharmacology modelling approaches will transform DILI detection and risk management.

Refining Liver Safety Risk Assessment: Application of Mechanistic Modeling and Serum Biomarkers to Cimaglermin Alfa (GGF2) Clinical Trials

Cimaglermin alfa (GGF2) is a recombinant human protein growth factor in development for heart failure. Phase I trials were suspended when two cimaglermin alfa‐treated subjects experienced concomitant elevations in serum aminotransferases and total bilirubin, meeting current US Food and Drug Administration criteria for a serious liver safety signal (i.e., “Hy's Law”). We assayed mechanistic biomarkers in archived clinical trial serum samples which confirmed the hepatic origin of the aminotransferase elevations in these two subjects and identified apoptosis as the major mode of hepatocyte death. Using a mathematical model of drug‐induced liver injury (DILIsym) and a simulated population, we estimated that the maximum hepatocyte loss in these two subjects was <13%, which would not result in liver dysfunction sufficient to significantly increase serum bilirubin levels. We conclude that the two subjects should not be considered Hy's Law cases and that mechanistic biomarkers and modeling can aid in refining liver safety risk assessment in clinical trials.

Is excessive acetaminophen intake associated with transaminitis in adult patients with dengue fever?

BACKGROUND

Dengue, an endemic infection causing severe flu-like symptoms and fever, is often treated with high-dose acetaminophen that can exceed recommended daily dosages. This leads to hepatotoxicity, although the underlying mechanism is poorly understood. We hypothesised that excessive acetaminophen causes hepatic toxicity in dengue patients.

AIMS

To investigate a correlation between elevated serum transaminases and excessive acetaminophen intake, and other aggravating factors of liver injury in dengue cases.

METHODS

This prospective observational study obtained blood samples from 150 participants with acute febrile illness for dengue serological tests, blood counts, and the detection of serum transaminases and acetaminophen levels. Other factors were determined by questionnaire.

RESULTS

Of 150 participants enrolled, 77 had dengue fever. Abnormally high serum aspartate transaminase and alanine transaminase levels were present in 97.0% and 75.3% of dengue cases respectively. Multivariate analysis of cases with increased serum transaminases more than threefold normal upper limits indicated that male gender (odds ratio (OR) = 3.62, 95% confidence interval (CI) 1.38-9.42) and consuming >8 g acetaminophen orally (OR = 4.62, 95% CI 1.37-13.18) correlated with transaminitis. No correlation was found for other factors such as age, fever day at presentation, body mass index, alcohol intake or dengue severity classification (all P > 0.05). Chronic alcohol consumption was higher in non-dengue (2.6%) versus dengue cases (27.8%) (P < 0.01).

CONCLUSIONS

Most dengue patients had mild-to-moderate transaminitis. Male gender and acetaminophen >8 g were associated with increased serum transaminases. Thus, 1000 mg acetaminophen every 8 h or <3000 mg/day is recommended for dengue cases. Chronic alcohol consumption might be protective against dengue infection.

A mechanistic model of drug-induced liver injury AIDS the interpretation of elevated liver transaminase levels in a phase I clinical trial

Entolimod (CBLB502) is a Toll-like receptor 5 agonist in development as a single-dose countermeasure against total body irradiation. Efficacy can be assessed from animal studies, but the “Animal Rule” does not apply to safety assessment. Marked elevations of serum aminotransferases (exceeding 1,000 IU/l) were observed in some human subjects receiving Entolimod in a safety study, threatening its continued development. The percentage of total hepatocytes undergoing necrosis in these subjects was estimated using a mechanistic, multiscale, mathematical model (DILIsym). The simulations suggested that no subject in the safety study experienced more than a modest loss of hepatocytes (<5%), which was comparable to estimates from a study of healthy volunteers receiving treatment with heparins. The predicted hepatocyte loss with Entolimod was lower than that required to cause liver dysfunction or that is routinely excised from volunteers donating for autologous liver transplantation and did not likely represent a serious health risk.

Modeling drug- and chemical-induced hepatotoxicity with systems biology approaches

We provide an overview of computational systems biology approaches as applied to the study of chemical- and drug-induced toxicity. The concept of “toxicity pathways” is described in the context of the 2007 US National Academies of Science report, “Toxicity testing in the 21st Century: A Vision and A Strategy.” Pathway mapping and modeling based on network biology concepts are a key component of the vision laid out in this report for a more biologically based analysis of dose-response behavior and the safety of chemicals and drugs. We focus on toxicity of the liver (hepatotoxicity) – a complex phenotypic response with contributions from a number of different cell types and biological processes. We describe three case studies of complementary multi-scale computational modeling approaches to understand perturbation of toxicity pathways in the human liver as a result of exposure to environmental contaminants and specific drugs. One approach involves development of a spatial, multicellular “virtual tissue” model of the liver lobule that combines molecular circuits in individual hepatocytes with cell–cell interactions and blood-mediated transport of toxicants through hepatic sinusoids, to enable quantitative, mechanistic prediction of hepatic dose-response for activation of the aryl hydrocarbon receptor toxicity pathway. Simultaneously, methods are being developing to extract quantitative maps of intracellular signaling and transcriptional regulatory networks perturbed by environmental contaminants, using a combination of gene expression and genome-wide protein-DNA interaction data. A predictive physiological model (DILIsym™) to understand drug-induced liver injury (DILI), the most common adverse event leading to termination of clinical development programs and regulatory actions on drugs, is also described. The model initially focuses on reactive metabolite-induced DILI in response to administration of acetaminophen, and spans multiple biological scales.

Correlation of MRI findings to histology of acetaminophen toxicity in the mouse

Acetaminophen (APAP) toxicity is responsible for approximately half of all cases of acute liver failure in the United States. The mouse model of APAP toxicity is widely used to examine mechanisms of APAP toxicity. Noninvasive approaches would allow for serial measurements in a single animal to study the effects of experimental interventions on the development and resolution of hepatocellular necrosis. The following study examined the time course of hepatic necrosis using small animal magnetic resonance imaging (MRI) following the administration of 200 mg/kg ip APAP given to B6C3F1 male mice. Mice treated with saline served as controls (CON). Other mice received treatment with the clinical antidote N-acetylcysteine (APAP+NAC). Mouse liver pathology was characterized using T1- and T2-weighted sequences at 2, 4, 8 and 24 h following APAP administration. Standard assays for APAP toxicity [serum alanine aminotransaminase (ALT) levels and hematoxylin and eosin (H&E) staining of liver sections] were examined relative to MRI findings. Overall, T2 sequences had a greater sensitivity for necrosis and hemorrhage than T1 (FLASH) images. Liver injury severity scoring of MR images demonstrated increased scores in the APAP mice at 4, 8 and 24 h compared to the CON mice. APAP+NAC mice had MRI scores similar to the CON mice. Semiquantitative analysis of hepatic hemorrhage strongly correlated with serum ALT. Small animal MRI can be used to monitor the evolution of APAP toxicity over time and to evaluate the response to therapy.

Carotenoid lutein protects rats from paracetamol-, carbon tetrachloride- and ethanol-induced hepatic damage

OBJECTIVES

Carotenoids are a class of natural fat-soluble pigments that are found in many fruits and vegetables. Consumption of a diet rich in carotenoids has been epidemiologically correlated with a lower risk for several diseases. In the present study the carotenoid lutein (3,3'-dihydroxy-beta,epsilon-carotene) was evaluated for its hepatoprotective activity in rats.

METHODS

Paracetamol, 20% ethanol and carbon tetrachloride were used to induce liver toxicity.

KEY FINDINGS

Levels of serum glutamate oxaloacetate transaminase, serum glutamate pyruvate transaminase and alkaline phosphatases, which were increased in the serum, were found to be significantly reduced by the treatment of lutein in a dose-dependent manner, indicating that lutein may reduce the hepatotoxicity induced by these agents(. )Serum bilirubin was also significantly lower in lutein-treated groups compared with control. Increased lipid peroxidation, conjugated diene and hydroperoxides in the liver tissue produced by the administration of paracetamol were found to be reduced in the lutein-treated groups. Levels of antioxidant enzymes, like superoxide dismutase, catalase, glutathione peroxidase and glutathione, were found to be increased in lutein-treated groups compared with control group during alcohol- and CCl(4)-induced liver toxicity. Hydroxyproline, which is an indicator of fibrosis in liver tissue, was high in the ethanol-treated control group. Hydroxyproline levels were decreased by simultaneous lutein administration.

CONCLUSIONS

Histopathological evidence confirmed the protection offered by lutein from the tissue damage caused by hepatotoxins. The hepatoprotective action may be due to lutein's ability to scavenge reactive oxygen radicals.

Long-term prognosis for transplant-free survivors of paracetamol-induced acute liver failure

BACKGROUND

The prognosis for transplant-free survivors of paracetamol-induced acute liver failure remains unknown.

AIM

To examine whether paracetamol-induced acute liver failure increases long-term mortality.

METHODS

We followed up all transplant-free survivors of paracetamol-induced acute liver injury, hospitalized in a Danish national referral centre during 1984-2004. We compared age-specific mortality rates from 1 year post-discharge through 2008 between those in whom the liver injury led to an acute liver failure and those in whom it did not.

RESULTS

We included 641 patients. On average, age-specific mortality rates were slightly higher for the 101 patients whose paracetamol-induced liver injury had caused an acute liver failure (adjusted mortality rate ratio = 1.70, 95% CI 1.02-2.85), but the association was age-dependent, and no survivors of acute liver failure died of liver disease, whereas suicides were frequent in both groups. These observations speak against long-term effects of acute liver failure. More likely, the elevated mortality rate ratio resulted from incomplete adjustment for the greater prevalence of substance abuse among survivors of acute liver failure.

CONCLUSIONS

Paracetamol-induced acute liver failure did not affect long-term mortality. Clinical follow-up may be justified by the cause of the liver failure, but not by the liver failure itself.

Auxiliary transplantation for acute liver failure: Histopathological study of native liver regeneration

Auxiliary liver transplantation (ALT) permits the serial assessment of regeneration in livers of patients with acute liver failure (ALF). Forty-nine ALF patients [32 adults (median age, 23 years; range, 16-40 years) and 17 children (median age, 12 years; range, 1-15 years)] underwent ALT between 1994 and 2004 at King's College Hospital. Twenty-four patients had seronegative liver failure, 15 had acetaminophen toxicity, 4 had hepatitis B virus (HBV) infection, 3 had drug-induced liver failure, 2 had autoimmune hepatitis, and 1 had mushroom poisoning. Nine patients without post-ALT native liver histology were excluded from review. All acetaminophen-induced, HBV, and drug-related patients had diffuse injury. Twelve seronegative patients and the autoimmune hepatitis patient had a map-like injury. On follow-up, 9 acetaminophen-induced patients, 9 seronegative patients, 2 drug-induced ALF patients, 3 HBV patients, and the autoimmune patient recovered to a near-normal native liver with inconsequential scarring. The hepatocyte proliferative rate in diffuse necrosis was 27.4% (range, 3.1%-69.4%) at hepatectomy and sharply decreased after 8 days post-ALT, being minimal months and years after ALT. In conclusion, in patients undergoing ALT for ALF with a diffuse pattern of liver injury-mainly acetaminophen toxicity-hepatocyte proliferation occurs in the native liver within a few days of transplantation. If the injury is map-like (most cases of seronegative ALF), regeneration seems to involve variable hepatocellular proliferation and potential ductular hepatopoiesis, but sequential assessment is difficult because of sampling variation. The likelihood of histological recovery appears to be minimal in livers with total hepatocyte loss at the time of ALT.

Hepatocyte nuclear factor-1 as marker of epithelial phenotype reveals marrow-derived hepatocytes, but not duct cells, after liver injury in mice

The potential bone marrow origin of hepatocytes, cholangiocytes, and ductal progenitor cells in the liver was examined in female mice after transplantation of bone marrow cells from male green fluorescent protein (GFP) transgenic donors. Following stable hematopoietic engraftment, the livers of the recipients were injured with carbon tetrachloride (CCl(4), with or without local irradiation of the liver) or 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC, with or without local irradiation of the liver). The presence of numerous marrow-derived, GFP-positive inflammatory cells had the potential to lead to erroneous interpretation of marrow-derived hepatocytes, cholangiocytes, and ductal progenitor cells. Identification of marrow-derived ductal progenitor or cholangiocyte phenotype using colocalization of GFP or Y chromosome with pancytokeratin staining also failed to distinguish epithelial cells from closely apposed inflammatory cells. To address this inadequacy, we developed a rigorous new immunofluorescence protocol to identify marrow-derived epithelial cells in the liver using Y chromosome (donor marker) and hepatocyte nuclear factor-1 (HNF1, a nuclear marker of liver epithelial, nonhematopoietic phenotype). Using the Y/HNF1 method, rare (approximately one in 20,000) hepatocytes in female mice transplanted with male bone marrow contained a donor-derived Y chromosome. On the other hand, no Y chromosomes were found in cholangiocytes or ductal progenitor cells in mice with liver injury due to DDC or CCl(4). The use of a nuclear marker of mature hepatocytes or cholangiocytes, such as HNF1, improves discrimination of marrow-derived epithelial cells in tissue sections.

Abnormal concentrations of esterified carnitine in bile: a feature of pediatric acute liver failure with poor prognosis

The etiology of acute liver failure in children is unknown in a large number of cases. Defects in fatty acid oxidation have been shown to lead to severe liver injury. This retrospective analysis examined the bile acylcarnitine profiles of 27 children with acute liver failure who underwent liver transplantation or died. Results were compared with 758 postmortem samples from individuals without acute liver failure. Cumulative amounts of free carnitine, medium- or long-chain species in excess of the 95th percentile of the control group were considered abnormal. Fourteen samples had normal profiles. Three had markedly elevated concentrations of free carnitine, whereas ten showed elevations in medium- or long-chain species. The relative risk of death was 2.86 (95% confidence interval, 1.08-7.54, P = .01) in the 10 children with elevated concentrations of medium- or long-chain species compared with those with normal analyses. Overall, medium- and long-chain acylcarnitines were increased in those patients who died compared with survivors, (dead vs. alive; medium-chain, 187 +/- 74 vs. 32 +/- 12 micromol/L, P = .008; long-chain, 146 +/- 74 vs. 15 +/- 8 micromol/L, mean +/- standard error of the mean, P = .018). These studies describe biliary free and esterified carnitine profiles in children with acute liver failure. In conclusion, the findings raise the hypothesis that abnormalities in fatty acid oxidation may predispose to a worse outcome in acute liver failure.

Contribution of acetaminophen-cysteine to acetaminophen nephrotoxicity in CD-1 mice: I. Enhancement of acetaminophen nephrotoxicity by acetaminophen-cysteine

Acetaminophen (APAP) nephrotoxicity has been observed both in humans and research animals. Recent studies suggest a contributory role for glutathione (GSH)-derived conjugates of APAP in the development of nephrotoxicity. Inhibitors of either gamma-glutamyl transpeptidase (gamma-GT) or the probenecid-sensitive organic anion transporter ameliorate APAP-induced nephrotoxicity but not hepatotoxicity in mice and inhibition of gamma-GT similarly protected rats from APAP nephrotoxicity. Protection against APAP nephrotoxicity by disruption of these GSH conjugate transport and metabolism pathways suggests that GSH conjugates are involved. APAP-induced renal injury may involve the acetaminophen-glutathione (APAP-GSH) conjugate or a metabolite derived from APAP-GSH. Acetaminophen-cysteine (APAP-CYS) is a likely candidate for involvement in APAP nephrotoxicity because it is both a product of the gamma-GT pathway and a probable substrate for the organic anion transporter. The present experiments demonstrated that APAP-CYS treatment alone depleted renal but not hepatic glutathione (GSH) in a dose-responsive manner. This depletion of renal GSH may predispose the kidney to APAP nephrotoxicity by diminishing GSH-mediated detoxification mechanisms. Indeed, pretreatment of male CD-1 mice with APAP-CYS before challenge with a threshold toxic dose of APAP resulted in significant enhancement of APAP-induced nephrotoxicity. This was evidenced by histopathology and plasma blood urea nitrogen (BUN) levels at 24 h after APAP challenge. APAP alone was minimally nephrotoxic and APAP-CYS alone produced no detectable injury. By contrast, APAP-CYS pretreatment did not alter the liver injury induced by APAP challenge. These data are consistent with there being a selective, contributory role for APAP-GSH-derived metabolites in APAP-induced renal injury that may involve renal-selective GSH depletion.

Liver death and regeneration in paracetamol toxicity

Paracetamol overdose (POD) is a major clinical problem as the commonest cause of fulminant hepatic failure (FHF) in the UK and the USA. While the main loss of liver mass occurs following hepatocyte necrosis, hepatocyte apoptosis has also been reported to occur during paracetamol toxicity in murine liver. Hepatocyte apoptosis has not previously been identified in human liver and the significance of apoptosis in paracetamol toxicity is not known. In this study of paracetamol toxicity in human liver after POD, hepatocyte apoptosis was identified at time of liver transplantation or death and was associated with striking regenerative activity. The biological significance of apoptosis is unclear but the rates of apoptosis found (0.6%) could account for a significant loss of hepatic parenchyma. The stimulus for apoptosis is not known but it is unlikely to be induced directly by paracetamol since it is absent from serum at this time. The possibility that apoptosis may be induced by Kupffer cell activation with cytokine production is raised. Patients who develop FHF after POD have a poor prognosis, with few therapeutic options apart from liver transplantation; an understanding of the dynamics of liver regeneration and ongoing cell loss by apoptosis may allow the development of new therapies in these patients.

Hepatotoxicity in acute iron poisoning

Although hepatotoxicity is a known sequela of acute iron poisoning, the literature describing it is confined to sporadic reports. Key issues such as prognosis and whether this is a dose-related phenomenon are not addressed. Review of this literature and of experimental animal studies demonstrates that it occurs early in the clinical course and has a relatively high mortality. The lowest acute serum iron concentration associated with hepatotoxicity was 1700 microg/dL (304 micromol/L). Since this greatly exceeds the reference range of 50-150 microg/dL (9-27 micromol/L), it supports a dose-related etiology. Unlike most other hepatotoxins, the periportal areas of the hepatic lobule are the primary sites of injury. As this is the principle sitefor hepatic regeneration, this accountsfor the relatively high mortality rate. An understanding of the pathogenesis of the hepatotoxicity of acute iron poisoning is central to the identification of rational and effective interventions. From the clinical perspective, the relatively high mortality rate of iron poisoning-induced hepatotoxicity requires vigilance for its onset and earlier consideration of liver transplantation.

Yang-gan-wan protects mice against apoptosis induced by anti-Fas antibody (Jo2)

We investigated the protective effect of yang-gan-wan (YGW, Pro-Liver pill), a Chinese herbal remedy, against liver apoptosis (programmed cell death) induced by anti-Fas antibody (Jo2). Mice were pretreated daily with 200 mg/kg YGW for 14 days before treatment with 10 microg/20 kg body weight Jo2. YGW significantly reduced the elevated activity of alanine aminotransferase (ALT) and also reduced the elevated activity of sorbitol dehydrogenase (SDH) produced 4 hrs after treatment with Jo2. YGW also increased the survival of mice treated with Jo2 by about 1 hr in 11 out of 16 mice (69%). Most of the mice died 9 hrs after Jo2 injection. This study demonstrates that YGW has protective effects against liver apoptosis induced by Jo2.

The value of serial Doppler ultrasound as a predictor of clinical outcome and the need for transplantation in fulminant and severe acute liver failure

The aim of this study was to document the changes in Doppler ultrasound variables of the hepatic artery and portal vein in fulminant and severe acute liver failure, and to assess their prognostic significance. 18 adult patients with fulminant and severe acute liver failure underwent serial Doppler sonography, in the early stages after presentation. 12 hourly measurements of hepatic artery resistance index (HARI), spleen length, portal vein cross-sectional area, time average velocity (TAV) and flow volume were performed. Mean HARI (p = 0.03) and mean maximum HARI (p = 0.03) were significantly higher in those who fulfilled criteria for liver transplantation. Increased portal vein flow was demonstrated, although the difference between the groups was not significant. A significant increase in portal vein cross-sectional area (p < 0.02) and spleen length (p < 0.02) was demonstrated. In summary, an increase in portal blood flow to the damaged liver has been demonstrated. The mean HARI is significantly higher in patients who fulfil transplant criteria and may possibly be used as an indicator of poorer prognosis and the need for liver transplantation in acute severe and fulminant liver failure.

Expression of the fgl2 and its protein product (prothrombinase) in tissues during murine hepatitis virus strain-3 (MHV-3) infection

Murine Hepatitis Virus Strain 3 (MHV-3) produces fulminant hepatitis with 80-90% mortality in Balb/cJ mice. Previous studies in our laboratory have shown that peritoneal macrophages from MHV-3 infected mice produce a procoagulant (PCA) which has the ability to cleave prothrombin to thrombin (prothrombinase) encoded by the gene fgl2 located on chromosome 5. PCA accounts for sinusoidal thrombosis and hepatic necrosis and the necrosis and mortality can be prevented by treatment of animals with a monoclonal antibody to PCA. These present studies were designed to examine the expression of this gene (mRNA by Northern analysis and in situ hybridization) and the gene product PCA (immunochemistry) in tissues recovered from MHV-3 infected Balb/cJ mice in an attempt to explain the liver specific nature of MHV-3 disease. Fgl2 gene expression was detected as early as 8 hours after MHV-3 infection which persisted to 48 hours in the liver, spleen and lungs whereas no gene expression was seen in the brain or kidneys despite the fact that equivalent viral titers were detected in all tissues at all times. In the liver, fgl2 gene expression was confined to endothelial and Kupffer cells with no expression in hepatocytes. Immunochemistry localized the PCA protein to Kupffer cells and endothelial cells and necrotic foci within the liver. No PCA protein was detected by immunochemistry in any other tissues at any time during the course of MHV-3 infection. These results explain the liver specific nature (fulminant hepatitis) of MHV-3 infection and provides further evidence for the role of PCA in the pathogenesis of fulminant hepatitis. MHV-3 induces selective transcription of the gene fgl2 and only hepatic reticuloendothelial cells produce functional protein (PCA) which is known to account for fulminant hepatic failure produced by MHV-3.

Fulminant hepatic failure in murine hepatitis virus strain 3 infection: tissue-specific expression of a novel fgl2 prothrombinase

Activation of the immune coagulation system has been implicated in the pathogenesis of fulminant liver failure caused by murine hepatitis virus strain 3 (MHV-3). The recent discovery of the fgl2 gene, which encodes for MHV-3-induced prothrombinase (fgl2 prothrombinase), allows for fundamental studies to determine the molecular basis for fulminant liver failure. Transcription of the fgl2 gene and translation of the protein it encodes were examined in the liver and other organs of susceptible mice following MHV-3 infection. No constitutive expression of the fgl2 gene or the fgl2 prothrombinase was detected. Within 12 to 24 h of MHV-3 infection, however, fgl2 gene transcripts were detected in large amounts in the liver, spleen, and lungs, all of which are rich in reticuloendothelial cells, but were only focally present in small amounts in the kidney and brain. There was sequential detection of fgl2 prothrombinase in the liver, where it was localized specifically to the endothelium of intrahepatic veins and hepatic sinusoids; this was allowed by fibrin deposition, which resulted in confluent hepatocellular necrosis. These results provide further evidence for the role of the selective expression of this novel fgl2 prothrombinase in the pathogenesis of MHV-3-induced fulminant liver failure.

Fulminant hepatitis associated with centrilobular hepatic necrosis in young children

OBJECTIVE

To describe fulminant hepatic failure (FHF) in children in the United States with clinical and histopathologic features distinctly different from those typical of FHF.

PATIENTS

Seven young children were seen in early 1994 with encephalopathy, coagulopathy, and elevated aminotransferase levels. Liver failure was preceded by a prodromal viral illness that resulted in a period of fasting without dehydration. Unlike the majority of children with FHF, these patients had serum bilirubin levels < 171 mumol/L (10 mg/dl). All children had received therapeutic doses of acetaminophen during the prodromal illness.

HISTOPATHOLOGIC FINDINGS

Histologic findings included zonal necrosis of hepatocytes in a centrilobular distribution, which is characteristic of toxic liver injury but is atypical for viral hepatitis and sporadic non-A non-B hepatitis.

OUTCOME

Six patients recovered spontaneously, and one died of complications of liver failure and fungal sepsis. The cause of this disorder remains unknown, but we postulate a viral or environmental insult that preferentially damages zone 3 hepatocytes. The potential for this injury may have been augmented by ingestion of therapeutic doses of acetaminophen while patients were in a fasted state. The prognosis was good compared with typical FHF in children and correlated with the degree of liver necrosis on histologic examination.

Comparison of thermally oxidized lipids and acetaminophen with concurrent consumption of ethanol as inducers of liver cirrhosis

The mechanism(s) of liver damage initiated by ingestion of toxic components of thermally oxidized lipids was compared in a rat model with the documented mechanisms of hepatic failure and necrosis initiated by acetaminophen. Acetaminophen (50 mg/kg body weight) or oxidized lipids (0.15 ml oxidized trilinolein or 1.05 ml oxidized butter oil per rat) were intubated at 12-h intervals to rats. Treated rats were allowed free access to food and water containing 3% ethanol. Changes in relative concentration of acute-phase plasma proteins, determined by two-dimensional (2D) immunoelectrophoresis, were taken as a marker of liver damage. In contrast to simple inflammation, acute-phase plasma proteins in this study disproportionately increased or decreased as histological damage of the liver due to intubation oxidized lipids or acetaminophen. Histological examination of liver of rats intoxicated with oxidized lipids revealed severe liver cirrhosis at the end of the trial, where the remaining viable hepatocytes were separated in a matrix of collagen. [3H1]Thymidine incorporation in hepatic DNA of acetaminophen or oxidized lipid intoxication increased in the early stages of intoxication, indicative of regenerative activity of the liver. Further progression of the cirrhosis inhibited continued liver regeneration and [3H1]thymidine incorporation into hepatic DNA. The cirrhotic liver at this stage failed to regenerate to the original mass upon 75% partial hepatectomy. Therefore, it may be concluded that hepatic necrosis produced by oxidized lipids or by acetaminophen may have similar mechanisms.

Nodular hyperplasia surrounding fibrolamellar carcinoma: a zone of arterialized liver parenchyma

We report a case of acetaminophen-induced liver necrosis in a 14-year-old girl. At autopsy, a 9 cm subcapsular nodule was present in the right lobe of the liver which showed distinct zonation: a central greyish white area of fibrolamellar carcinoma with a peripheral fleshy, tan-coloured rim ranging from 1 to 2 cm in thickness. This peripheral zone consisted of nodular, hyperplastic parenchyma resembling the changes seen in focal nodular hyperplasia, and stood out from the adjacent necrotic parenchyma. The sparing of this zone from the deleterious effects of acetaminophen provides indirect evidence of a predominantly arterial rather than portal blood supply to this region. The arterial supply was most probably derived from the tumour vasculature and may explain the parenchymal hyperplasia sometimes reported adjacent to a fibrolamellar carcinoma. Awareness of this phenomenon is essential when evaluating a needle biopsy, as sampling of this region may lead to a false negative diagnosis.

Non-parenchymal cell responses in paracetamol (acetaminophen)-induced liver injury

We have analysed Kupffer cell and 'activated' perisinusoidal cell populations in liver biopsies from patients with paracetamol (acetaminophen)-induced hepatic necrosis of varying degrees of severity. Kupffer cells were identified immunohistochemically using the monoclonal antibody KPJ and perisinusoidal cells by identification of alpha-smooth muscle actin expression. Material was available from four groups of individuals: (i) 11 cases with mild (grade I) injury; (ii) six cases with moderate (grade II) injury; (iii) six cases with severe (grade III) injury; and (iv) controls with normal liver histology (n = 23). Biopsies in groups (i)-(iii) were obtained within 5 days of drug ingestion. All patients in this study survived and follow-up biopsies were obtained at 4 months, by which time the histological abnormalities had fully resolved. Kupffer cells and perisinusoidal cell numbers were assessed in immunostained preparations of acute and recovery phase biopsies and in control specimens. In acute phase biopsies from patients with grade II and III injury there was expansion of the Kupffer cell and perisinusoidal cell populations within areas of injury. There was a strong correlation between the size of these two cell populations (r = 0.886). No significant difference in cell numbers was found between those with grade I injury and controls. In recovery phase biopsies from patients with paracetamol-induced injury, perisinusoidal cell numbers did not differ significantly from normal controls. Kupffer cells numbers also decreased in recovery phase biopsies compared with the acute phase, although there was persistent expansion of the Kupffer cells population in those who originally had grade III injury.(ABSTRACT TRUNCATED AT 250 WORDS)

An experimental study on the disturbance of liver circulation and the change of hemorrheology in dogs with acute liver damage

The changes of hepatic hemodynamics and hemorrheology were investigated in dogs with acute liver damage induced by acetaminophen. There were remarkable disturbance in liver circulation and hemorrheological abnormality occurring in both slight and severe liver damage. The study indicated that the degree of disturbance in liver circulation as well as in hemorheological change is positively correlated with the severity of liver damage. For example, marked increase in blood viscosity linked with elevated fibrinogen level appeared in slight liver damage, whereas reduced blood viscosity associated with decreased plasma fibrinogen level and hematocrit occurred in severe liver damage. This study also revealed that the increase of portal venous resistance (PVR) and the disturbance of liver circulation in slight liver damage were chiefly related to the increase of blood viscosity and the increase of PVR in severe liver damage was mainly associated with the reduction of the radius of portal vein.

Paracetamol (acetaminophen) poisoning

Paracetamol poisoning caused by intentional overdose remains a common cause of morbidity. In this article the mechanism of toxicity and the clinical effects and treatment of poisoning, including specific antidotal therapy, are reviewed. Areas for further research directed at reducing morbidity and mortality from paracetamol poisoning are considered.

Intrahepatic distribution of transforming growth factor-alpha (TGF alpha) during liver regeneration following carbon tetrachloride-induced necrosis

The distribution of transforming growth factor-alpha (TGF alpha) in rat liver during regeneration was studied immunohistochemically using two antibodies, one a polyclonal (26T) raised against a synthetic peptide corresponding to the 17 C-terminal amino acids of the mature rat protein, and the other a monoclonal (Ab-2) raised against recombinant human protein. In normal liver, immunoreactive TGF alpha was detected in perivenular hepatocytes using both antibodies. No sinusoidal cells were found to contain the peptide. In response to carbon tetrachloride (CCI4)-induced necrosis, an initial increase in the intensity of immunoreactivity was noted at 24 h following exposure to the toxin. This coincided with the period immediately preceding the peak of hepatocyte proliferation; Ab-2 immunoreactive cells outnumbered 26T-positive cells. Thereafter there was a reduction in the number of TGF alpha-positive cells, but by day 4 the level of immunoreactivity had returned to that of normal liver. Using bromodeoxyuridine labelling, spatial and temporal relationships between TGF alpha expression and cell proliferation were identified, supporting the concept that this peptide plays an important role in the in vivo regenerative response to hepatic injury via an autocrine mechanism.

Cocaine hepatotoxicity: influence of hepatic enzyme inducing and inhibiting agents on the site of necrosis

Cocaine-induced hepatotoxicity has been reported in human beings and is well documented in mice. One interesting feature of this toxicity that appears to be common to both species is an apparent shift in the intraacinar site of necrosis under circumstances known to alter cocaine metabolism. However, the evidence in human subjects is limited, and studies elucidating the mechanism of this phenomenon cannot be performed in human beings. Although future studies in mice may define the basis of this mechanism, the current evidence is a somewhat fragmented composite of studies using different mouse strains and enzyme-inducing agents. Therefore a comprehensive pathologic investigation was initiated for the purpose of identifying and establishing an animal model suitable for studying this phenomenon. In naive ICR mice a single 60 mg/kg dose of cocaine was found to produce midzonal (zone 2) coagulative necrosis. In mice whose oxidative metabolism had been increased with beta-ionone or in which esterase metabolism had been inhibited by diazinon, the severity of the toxicity was increased but the intraacinar origin of the lesion did not change. However, when the oxidative microsomal metabolism of ICR mice was induced by phenobarbital or beta-naphthoflavone, the acinar zone affected was dramatically different. Phenobarbital induction produced zone 1 necrosis, whereas beta-napthoflavone induction caused necrosis in zone 3. The site of necrosis corresponded with the distribution of cocaine, and its metabolites were identified with colloidal gold-conjugated antibody probes. The results of this study suggest that the agents shifting the location of cocaine-induced hepatic necrosis alter the intraacinar site of protein binding of cocaine and its metabolites.