Carbamazepine-Induced Liver Injury Requires CYP3A-Mediated Metabolism and Glutathione Depletion in Rats

Preclinical liver toxicity models: Advantages, limitations and recommendations

Experimental animal models are crucial for elucidating the pathophysiology of liver injuries and for assessing new hepatoprotective agents. Drugs and chemicals such as acetaminophen, isoniazid, valproic acid, ethanol, carbon tetrachloride (CCl4), dimethylnitrosamine (DMN), and thioacetamide (TAA) are metabolized by the CYP2E1 enzyme, producing hepatotoxic metabolites that lead to both acute and chronic liver injuries. In experimental settings, acetaminophen (centrilobular necrosis), carbamazepine (centrilobular necrosis and inflammation), sodium valproate (necrosis, hydropic degeneration and mild inflammation), methotrexate (sinusoidal congestion and inflammation), and TAA (centrilobular necrosis and inflammation) are commonly used to induce various types of acute liver injuries. Repeated and intermittent low-dose administration of CCl4, TAA, and DMN activates quiescent hepatic stellate cells, transdifferentiating them into myofibroblasts, which results in abnormal extracellular matrix production and fibrosis induction, more rapidly with DMN and CCL4 than TAA (DMN > CCl4 > TAA). Regarding toxicity and mortality, CCl4 is more toxic than DMN and TAA (CCl4 > DMN > TAA). Models used to induce metabolic dysfunction-associated liver disease (MAFLD) vary, but MAFLD's multifactorial nature driven by factors like obesity, fatty liver, dyslipidaemia, type II diabetes, hypertension, and cardiovascular disease makes it challenging to replicate human metabolic dysfunction-associated steatohepatitis accurately. From an experimental point of view, the degree and pattern of liver injury are influenced by various factors, including the type of hepatotoxic agent, exposure duration, route of exposure, dosage, frequency of administration, and the animal model utilized. Therefore, there is a pressing need for standardized protocols and regulatory guidelines to streamline the selection of animal models in preclinical studies.

Metabolic Activation and Cytotoxicity of Gramine Mediated by CYP3A in Rats

Gramine (GRM), which occurs in Gramineae plants, has been developed to be a biological insecticide. Exposure to GRM was reported to induce elevations of serum ALT and AST in rats, but the mechanisms of the observed hepatotoxicity have not been elucidated. The present study aimed to identify reactive metabolites that potentially participate in the toxicity. In rat liver microsomal incubations fortified with glutathione or N-acetylcysteine, one oxidative metabolite (M1), one glutathione conjugate (M2), and one N-acetylcysteine conjugate (M3) were detected after exposure to GRM. The corresponding conjugates were detected in the bile and urine of rats after GRM administration. CYP3A was the main enzyme mediating the metabolic activation of GRM. The detected GSH and NAC conjugates suggest that GRM was metabolized to a quinone imine intermediate. Both GRM and M1 showed significant toxicity to rat primary hepatocytes.

Carbamazepine-induced renal toxicity may be associated with oxidative stress and apoptosis in male rat

Carbamazepine (CBZ) is the antiepileptic drug used in epilepsy and some psychiatric disorders. Besides its widely used, many adverse effects have been reported including hematotoxicity, hepatotoxicity, endocrine disorders, and testicular damages due to oxidative stress. However, the role of CBZ on renal toxicity is not fully known. In this study, we attempted to explain the connected mechanisms by focusing on the metabolism of CBZ-induced renal toxicity in rats. Twenty male Wistar-Albino rats were randomized into 2 groups (n = 10); control (1 mL/day distilled water, orally) and CBZ (25 mg/kg/day CBZ, orally) groups. After 60 days, TAS (total oxidant status) and TOS (total oxidant status) levels, histopathological features, some genes involved in apoptosis, 8-hydroxy-2-deoxyguanosine (8-OHdG) activity, and apoptotic cells were assessed of kidney tissue. The oxidative stress index (OSI) was measured from TAS and TOS levels. TOS levels and OSI significantly increased, while TAS levels decreased in the CBZ group relative to the control group. Histopathological observations, Caspase-3 (Casp3), Poly [ADP-ribose] polymerase-1 (PARP-1), 8-OHdG immunoreactivities, and apoptotic cells markedly raised in the CBZ group compared with the control group. Also, mRNA expression of Cytochrome c (Cytc) and CASP3 significantly increased in the CBZ group compared to the control group. In conclusion, long-term use of CBZ may promote renal damage in rats by inducing oxidative stress and apoptosis.

Inhibition of autophagy with expression of NADPH oxidase subunit p22phox in preneoplastic lesions in a high-fat diet and streptozotocin-related hepatocarcinogenesis rat model

To study the effects of autophagy inducer carbamazepine (CBZ) in a high-fat diet (HFD)/streptozotocin (STZ)-related early hepatocarcinogenesis model, we determined autophagic flux by immunohistochemical analysis of autophagy marker expression in preneoplastic liver foci and compared that with the expression of the NADPH oxidase subunit. Male F344 rats were fed a basal diet or HFD and subjected to two-stage hepatocarcinogenesis; diabetes mellitus was induced via STZ administration. Several STZ-treated, HFD-fed rats were administered CBZ (a total of five doses every one or two days) at week 7 and 8. STZ-treated, HFD-fed rats decreased β cells in the islet of Langerhans and increased adipophilin-positive lipid droplets in the liver; moreover, they had a larger area of glutathione S-transferase placental form-immunopositive preneoplastic liver foci, which was associated with inhibition of autophagy and induction of the NADPH oxidase subunit, as demonstrated by increased immunohistochemical expression of an autophagosome receptor marker microtubule-associated protein light chain 3 (LC3)-binding protein p62, and of an NADPH oxidase subunit p22phox in the preneoplastic foci. An increased trend of an autophagy phagophore marker LC3 in preneoplastic foci was also detected. CBZ administration could induce autophagy and impair p22phox expression, as shown by altered expression of autophagy regulators (Atg5, Atg6, Lamp1, Lamp2, and Lc3), NADPH oxidase subunits (P22phox and P67phox), and antioxidant enzymes Gpx1 and Gpx2. These results suggest that inhibition of autophagy and induction of p22phox might contribute to HFD/STZ-related early hepatocarcinogenesis in rats; however, the effects of CBZ administration on the STZ/HFD-increased preneoplastic foci were marginal in this study.

Pharmacokinetic and toxicodynamic concepts in idiosyncratic, drug-induced liver injury

INTRODUCTION

Idiosyncratic drug-induced liver injury (IDILI) causes morbidity and mortality in patients and leads to curtailed use of efficacious pharmaceuticals. Unlike intrinsically toxic reactions, which depend on dose, IDILI occurs in a minority of patients at therapeutic doses. Much remains unknown about causal links among drug exposure, a mode of action, and liver injury. Consequently, numerous hypotheses about IDILI pathogenesis have arisen.

AREAS COVERED

Pharmacokinetic and toxicodynamic characteristics underlying current hypotheses of IDILI etiology are discussed and illustrated graphically.

EXPERT OPINION

Hypotheses to explain IDILI etiology all involve alterations in pharmacokinetics, which lead to plasma drug concentrations that rise above a threshold for toxicity, or in toxicodynamics, which result in a lowering of the toxicity threshold. Altered pharmacokinetics arise, for example, from changes in drug metabolism or from transporter polymorphisms. A lowered toxicity threshold can arise from drug-induced mitochondrial injury, accumulation of toxic endogenous factors or harmful immune responses. Newly developed, interactive freeware (DemoTox-PK; https://bit.ly/DemoTox-PK) allows the user to visualize how such alterations might lead to a toxic reaction. The illustrations presented provide a framework for conceptualizing idiosyncratic reactions and could serve as a stimulus for future discussion, education, and research into modes of action of IDILI.

Assessment of hepatic prostaglandin E2 level in carbamazepine induced liver injury

Objective. Carbamazepine (CBZ), a widely used antiepileptic drug, is one major cause of the idiosyncratic liver injury along with immune reactions. Conversely, prostaglandin E₂ (PGE2) demonstrates a hepatoprotective effect by regulating immune reactions and promoting liver repair in various types of liver injury. However, the amount of hepatic PGE₂ during CBZ-induced liver injury remains elusive. In this study, we aimed to evaluate the hepatic PGE₂ levels during CBZ-induced liver injury using a mouse model. Methods. Mice were orally administered with CBZ at a dose of 400 mg/kg for 4 days, and 800 mg/kg on the 5th day. Results. Plasma alanine transaminase (ALT) level increased in some of mice 24 h after the last CBZ administration. Although median value of hepatic PGE₂ amount in the CBZ-treated mice showed same extent as vehicle-treated control mice, it exhibited significant elevated level in mice with severe liver injury presented by a plasma ALT level >1000 IU/L. According to these results, mice had a plasma ALT level >1000 IU/L were defined as responders and the others as non-responders in this study. Even though, the hepatic PGE₂ levels increased in responders, the hepatic expression and enzyme activity related to PGE₂ production were not upregulated when compared with vehicle-treated control mice. However, the hepatic 15-hydroxyprostaglandin dehydrogenase (15-PGDH) expression and activity decreased significantly in responders when compared with control mice. Conclusions. These results indicate that elevated hepatic PGE₂ levels can be attributed to the downregulation of 15-PGDH expression under CBZ-induced liver injury.

Preclinical models of idiosyncratic drug-induced liver injury (iDILI): Moving towards prediction

Idiosyncratic drug-induced liver injury (iDILI) encompasses the unexpected harms that prescription and non-prescription drugs, herbal and dietary supplements can cause to the liver. iDILI remains a major public health problem and a major cause of drug attrition. Given the lack of biomarkers for iDILI prediction, diagnosis and prognosis, searching new models to predict and study mechanisms of iDILI is necessary. One of the major limitations of iDILI preclinical assessment has been the lack of correlation between the markers of hepatotoxicity in animal toxicological studies and clinically significant iDILI. Thus, major advances in the understanding of iDILI susceptibility and pathogenesis have come from the study of well-phenotyped iDILI patients. However, there are many gaps for explaining all the complexity of iDILI susceptibility and mechanisms. Therefore, there is a need to optimize preclinical human in vitro models to reduce the risk of iDILI during drug development. Here, the current experimental models and the future directions in iDILI modelling are thoroughly discussed, focusing on the human cellular models available to study the pathophysiological mechanisms of the disease and the most used in vivo animal iDILI models. We also comment about in silico approaches and the increasing relevance of patient-derived cellular models.

Noninvasive monitoring of hepatic glutathione depletion through fluorescence imaging and blood testing

Hepatic glutathione plays a key role in regulating redox potential of the entire body, and its depletion is known to increase susceptibility to oxidative stress involved in many diseases. However, this crucial pathophysiological event can only be detected noninvasively with high-end instrumentation or invasively with surgical biopsy, limiting both preclinical research and clinical prevention of oxidative stress-related diseases. Here, we report that both in vivo fluorescence imaging and blood testing (the first-line detection in the clinics) can be used for noninvasive and consecutive monitoring of hepatic glutathione depletion at high specificity and accuracy with assistance of a body-clearable nanoprobe, of which emission and surface chemistries are selectively activated and transformed by hepatic glutathione in the liver sinusoids. These findings open a new avenue to designing exogenous blood markers that can carry information of local disease through specific nanobiochemical interactions back to the bloodstream for facile and rapid disease detection.

Graded doses of grape seed methanol extract attenuated hepato-toxicity following chronic carbamazepine treatment in male Wistar rats

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Chronic carbamazepine treatment decreased the body weight and relative liver weight of male Wistar rats.

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Carbamazepine induced the activities of liver enzymes in male Wistar rats.

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Carbamazepine increased the product of lipid peroxidation (malondialdehyde) of the liver.

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Carbamazepine induced various hepatic histomorphological alterations in male Wistar rats.

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Most of these derangements were attenuated by grape seed methanolic extract.

Aim

This study investigated the effects of co-administration of carbamazepine (CBZ) with grape (Vitis vinifera) seed methanolic extract (GSME) on liver toxicity.

Method

Thirty-five male rats (145−155 g) were randomized into 5 groups (n = 7) and administered with propylene glycol (PG 0.1 mL/day), CBZ (25 mg/kg), CBZ (25 mg/kg) + GSME (200 mg/kg), CBZ (25 mg/kg) + GSME (100 mg/kg), or CBZ (25 mg/kg) + GSME (50 mg/kg) orally for 28 days. Twenty-four hours after the last dose, changes in the body weights were determined. The rats were euthanized by cervical dislocation. The liver was weighed and later homogenized; while the supernatant was analyzed biochemically. The liver tissues were preserved in 10 % neutral-buffered formalin for the histomorphological investigation.

Result

There was significant (p = 0.0001) decrease in the body weight following carbamazepine treatment. The relative liver weight also decreased significantly (p = 0.0004) across the treatment group compared with control. The activities of the liver enzymes (aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, and glutathione activities), including the concentrations of malondialdehyde, increased significantly (p ≤ 0.0004) following carbamazepine treatment. Various morphological alterations were observed, especially in the photomicrograph of the CBZ treated rats. However, these derangements were attenuated significantly in the CBZ - GSME co-treated group.

Conclusion

This study concludes that GSME treatment may serve as a potential therapeutic agent in carbamazepine-induced hepatotoxicity/ dysfunction.

Models of Idiosyncratic Drug-Induced Liver Injury

Drug-induced liver injury (DILI) is a leading cause of attrition during the early and late stages of drug development and after a drug is marketed. DILI is generally classified as either intrinsic or idiosyncratic. Intrinsic DILI is dose dependent and predictable (e.g., acetaminophen toxicity). However, predicting the occurrence of idiosyncratic DILI, which has a very low incidence and is associated with severe liver damage, is difficult because of its complex nature and the poor understanding of its mechanism. Considering drug metabolism and pharmacokinetics, we established experimental animal models of DILI for 14 clinical drugs that cause idiosyncratic DILI in humans, which is characterized by the formation of reactive metabolites and the involvement of both innate and adaptive immunity. On the basis of the biomarker data obtained from the animal models, we developed a cell-based assay system that predicts the potential risks of drugs for inducing DILI. These findings increase our understanding of the mechanisms of DILI and may help predict and prevent idiosyncratic DILI due to certain drugs.

[Recent advances in evaluation studies for drug-induced liver injury]

With the recent progress in drug metabolism and pharmacokinetics studies, the attrition due to pharmacokinetics in clinical trials and post-marketing was reduced to less than 1%. On the other hand, attrition of clinical trials due to adverse effects and toxicity has remained high. In particular, drug-induced liver injury (DILI) is a major cause of discontinuation of clinical trials and withdrawal of drug candidates after marketing. DILI is roughly divided into intrinsic and idiosyncratic. The former is relatively easy to predict its onset in preclinical drug development, but the latter's onset mechanism is still unknown and its onset prediction is difficult. We are investigating to develop an experimental animal model of idiosyncratic DILI (iDILI), clarify the pathogenic mechanism, and apply the obtained biomarker information to the establishment of an in vitro cell-based prediction test system. In this paper, we will introduce various animal models of iDILI, present status of pathogenic mechanism study, and classification of iDILI drugs, and introduce the recent progress of in vitro cell-based prediction test system and new causative factors of iDILI.

Hypoxia/reoxygenation exacerbates drug-induced cytotoxicity by opening mitochondrial permeability transition pore: Possible application for toxicity screening

Recently, mitochondrial dysfunction is thought of as an important factor leading to a drug-induced liver injury. Our previous reports show that mitochondria-related toxicity, including respiratory chain inhibition (RCI) and reactive oxygen species (ROS) induction, can be detected by the modification of sugar resource substitution and high oxygen condition. However, this in vitro model does not detect mitochondrial permeability transition (MPT)-induced toxicity. Another study with a lipopolysaccharide-pre-administered rodent model showed that ischemia/reperfusion induced ROS, sensitized the susceptibility of MPT pore opening and, finally developed drug-induced liver toxicity. Based on this result, the present study investigated the effect of hypoxia/reoxygenation (H/R) treatment mimicking the ischemia/reperfusion on MPT-dependent toxicity, aiming to construct a system that can evaluate MPT by drugs in hepatocytes. Mitochondrial ROS were enhanced by H/R treatment only in the galactose culture condition. Amiodarone, benzbromarone, flutamide and troglitazone which induced MPT pore opening led to hepatocyte death only in combination with H/R and galactose. Moreover, this alteration was significantly suppressed in hepatocytes lacking cyclophilin D. In conclusion, MPT-induced cytotoxicity can be detected by activating mitochondrial function and H/R. This cell-based assay system could evaluate MPT induced-cytotoxicity by drugs, besides RCI and ROS induction.

PXR-mediated idiosyncratic drug-induced liver injury: mechanistic insights and targeting approaches

INTRODUCTION

The human liver is the center for drug metabolism and detoxification and is, therefore, constantly exposed to toxic chemicals. The loss of liver function as a result of this exposure is referred to as drug-induced liver injury (DILI). The pregnane X receptor (PXR) is the primary regulator of the hepatic drug-clearance system, which plays a critical role in mediating idiosyncratic DILI.

AREAS COVERED

This review is focused on common mechanisms of PXR-mediated DILI and on in vitro and in vivo models developed to predict and assess DILI. It also provides an update on the development of PXR antagonists that may manage PXR-mediated DILI.

EXPERT OPINION

DILI can be caused by many factors, and PXR is clearly linked to DILI. Although emerging data illustrate how PXR mediates DILI and how PXR activity can be modulated, many questions concerning the development of effective PXR modulators remain. Future research should be focused on determining the mechanisms regulating PXR functions in different cellular contexts.

Establishment of a mouse model of troglitazone-induced liver injury and analysis of its hepatotoxic mechanism

Drug-induced liver injury is a major problem in drug development and clinical drug therapy. Troglitazone (TGZ), a thiazolidinedione antidiabetic drug for the treatment of type II diabetes mellitus, was found to induce rare idiosyncratic severe liver injury in patients, which led to its withdrawal in 2000. However, in normal experimental animals in vivo TGZ has never induced liver injury. To explore TGZ hepatotoxic mechanism, we established a novel mouse model of TGZ-induced liver injury. Administration of BALB/c female mice with a single intraperitoneal TGZ dose (300 mg/kg) significantly elevated alanine aminotransferase and aspartate aminotransferase levels 6 hours after the treatment. The ratio of oxidative stress marker glutathione/disulfide glutathione was significantly decreased. The increased hepatic mRNA levels of inflammation- and oxidative stress-related factors were observed in TGZ-treated mice. Subsequently, hepatic transcriptome profiles of TGZ-exposed liver were compared with those of non-hepatotoxic rosiglitazone. The Janus kinase/signal transducer and activator of transcription (JAK/STAT) signaling pathway was activated in TGZ-induced liver injury. The activation of the JAK/STAT pathway promoted phosphorylation of STAT3 in TGZ-treated mice. Consequently, upregulation of STAT3 activation increased mRNA levels of its downstream genes. In conclusion, a single intraperitoneal dose of TGZ exposure could induce liver injury in BALB/c female mice and, by a hepatic transcriptomic analysis, we found that the activation of JAK/STAT pathway might be related to TGZ-induced hepatotoxicity.

Strain and interindividual differences in lamotrigine-induced liver injury in mice

Lamotrigine (LTG) has been widely prescribed as an antipsychotic drug, although it causes idiosyncratic drug-induced liver injury in humans. LTG is mainly metabolized by UDP-glucuronosyltransferase, while LTG undergoes bioactivation by cytochrome P450 to a reactive metabolite; it is subsequently conjugated with glutathione, suggesting that reactive metabolite would be one of the causes for LTG-induced liver injury. However, there is little information regarding the mechanism of LTG-induced liver injury in both humans and rodents. In this study, we established an LTG-induced liver injury mouse model through co-administration with LTG and a glutathione synthesis inhibitor, l-buthionine-(S,R)-sulfoximine. We found an increase in alanine aminotransferase (ALT) levels (>10 000 U/L) in C57BL/6J mice, with apparent interindividual differences. On the other hand, a drastic increase in ALT was not noted in BALB/c mice, suggesting that the initiation mechanism would be different between the two strains. To examine the cause of interindividual differences, C57BL/6J mice that were co-administered LTG and l-buthionine-(S,R)-sulfoximine were categorized into three groups based on ALT values: no-responder (ALT <100 U/L), low-responder (100 U/L < ALT < 1000 U/L) and high-responder (ALT >1000 U/L). In the high-responder group, induction of hepatic oxidative stress, inflammation and damage-associated molecular pattern molecules in mRNA was associated with vacuolation and karyorrhexis in hepatocytes. In conclusion, we demonstrated that LTG showed apparent strain and interindividual differences in liver injuries from the aspects of initiation and exacerbation mechanisms. These results would support interpretation of the mechanism of LTG-induced liver injury observed in humans.

CYP3A Activation and Glutathione Depletion Aggravate Emodin-Induced Liver Injury

1,3,8-Trihydroxy-6-methylanthraquinone (emodin), a widely existing natural product in herbal medicines, has been reported to be hepatotoxic, but the exact underlying mechanism is still not fully understood. The objective of the present study was to evaluate the role of CYP3A and glutathione (GSH) in emodin-induced liver injury. Primary human hepatocytes were exposed to emodin with and without addition of CYP3A inducer/inhibitor and GSH synthesis inhibitor. It was found that emodin-mediated cytotoxicity increased when CYP3A was activated and GSH was depleted. Hepatotoxicity induced by emodin in rats by activation/inhibition of CYP3A and depletion of GSH was further investigated. Administration of emodin in combination with l-buthionine sulfoximine (BSO) or dexamethasone (DEX) resulted in aggravated liver injury, whereas pretreatment with ketoconazole (KTZ) suppressed the side effects caused by emodin. In addition, plasma exposure of emodin and its glucuronide metabolite were measured by ultraperformance liquid chromatography triple quadrupole mass spectrometry. Emodin and its glucuronide were lower in BSO-, DEX-, and KTZ- co-treated rats compared with those administered with emodin alone. In conclusion, these mentioned results suggested that CYP3A induction and GSH depletion might be involved in hepatotoxicity induced by emodin. This study may help to understand the risk factors and the mechanism of hepatotoxicity of emodin in humans.

The Modulatory Role of CYP3A4 in Dictamnine-Induced Hepatotoxicity

Dictamni Cortex (DC) has been reported to be associated with acute hepatitis in clinic and may lead to a selective sub-chronic hepatotoxicity in rats. Nevertheless, the potent toxic ingredient and the underlying mechanism remain unknown. Dictamnine (DTN), the main alkaloid from DC, possesses a furan ring which was suspected of being responsible for hepatotoxicity via metabolic activation primarily by CYP3A4. Herein, the present study aimed to evaluate the role of CYP3A4 in DTN-induced liver injury. The in vitro results showed that the EC₅₀ values in primary human hepatocytes (PHH), L02, HepG2 and NIH3T3 cells were correlated with the CYP3A4 expression levels in corresponding cells. Furthermore, the toxicity was increased in CYP3A4-induced PHH by rifampicin, and CYP3A4 over-expressed (OE) HepG2 and L02 cells. Contrarily, the cytotoxicity was decreased in CYP3A4-inhibited PHH and CYP3A4 OE HepG2 and L02 cells inhibited by ketoconazole (KTZ). In addition, the hepatotoxicity of DTN in enzyme induction/inhibition mice was further investigated in the aspects of biochemistry, histopathology, and pharmacokinetics. Administration of DTN in combination with KTZ resulted in attenuated liver injury, including lower alanine transaminase and aspartate transaminase activities and greater AUC and C_max of serum DTN, whereas, pretreatment with dexamethasone aggravated the injury. Collectively, our findings illustrated that DTN-induced hepatotoxicity correlated well with the expression of CYP3A4, namely inhibition of CYP3A4 alleviated the toxicity both in vitro and in vivo, and induction aggravated the toxicity effects.

Role of cytochrome P450-mediated metabolism and involvement of reactive metabolite formations on antiepileptic drug-induced liver injuries

Several drugs have been withdrawn from the market or restricted to avoid unexpected adverse outcomes. Drug-induced liver injury (DILI) is a serious issue for drug development. Among DILIs, idiosyncratic DILIs have been a serious problem in drug development and clinical uses. Idiosyncratic DILI is most often unrelated to pharmacological effects or the dosing amount of a drug. The number of drugs that cause idiosyncratic DILI continue to grow in part because no practical preclinical tests have emerged that can identify drug candidates with the potential for developing idiosyncratic DILIs. Nevertheless, the implications of drug metabolism-related factors and immune-related factors on idiosyncratic DILIs has not been fully clarified because this toxicity can not be reproduced in animals. Therefore, accumulated evidence for the mechanisms of the idiosyncratic toxicity has been limited to only in vitro studies. This review describes current knowledge of the effects of cytochrome P450 (CYP)-mediated metabolism and its detoxification abilities based on studies of idiosyncratic DILI animal models developed recently. This review also focused on antiepileptic drugs, phenytoin (diphenyl hydantoin, DPH) and carbamazepine (CBZ), which have rarely caused severe adverse reactions, such as fulminant hepatitis, and have been recognized as sources of idiosyncratic DILI. The studies of animal models of idiosyncratic DILIs have produced new knowledge of chronic administration, CYP inductions/inhibitions, glutathione contents, and immune-related factors for the initiation of idiosyncratic DILIs. Considering changes in the drug metabolic profile and detoxification abilities, idiosyncratic DILIs caused by antiepileptic drugs will lead to understanding the mechanisms of these DILIs.

Association of a reactive intermediate derived from 1',6-dihydroxy metabolite with benzbromarone-induced hepatotoxicity

Treatment with benzbromarone can be associated with liver injury, but the detailed mechanism remains unknown. Our recent studies demonstrated that benzbromarone was metabolized to 1',6-dihydroxybenzbromarone and followed by formation of reactive intermediates that were trapped by glutathione, suggesting that the reactive intermediates may be responsible for the liver injury. The aim of this study was to clarify whether the reactive intermediates derived from 1',6-dihydroxybenzbromarone is a risk factor of liver injury in mice. An incubation study using mouse liver microsomes showed that the rates of formation of 1',6-dihydroxybenzbromarone from benzbromarone were increased by pretreatment with dexamethasone. Levels of a hepatic glutathione adduct derived from 1',6-dihydroxybenzbromarone were increased by pretreatment with dexamethasone. Furthermore, plasma alanine amino transferase activities were increased in mice treated with benzbromarone after pretreatment with dexamethasone. The results suggest that the reactive intermediate derived from 1',6-dihydroxybenzbromarone may be associated with liver injury.

In Silico Identification of Bioremediation Potential: Carbamazepine and Other Recalcitrant Personal Care Products

Emerging contaminants are principally personal care products not readily removed by conventional wastewater treatment and, with an increasing reliance on water recycling, become disseminated in drinking water supplies. Carbamazepine, a widely used neuroactive pharmaceutical, increasingly escapes wastewater treatment and is found in potable water. In this study, a mechanism is proposed by which carbamazepine resists biodegradation, and a previously unknown microbial biodegradation was predicted computationally. The prediction identified biphenyl dioxygenase from Paraburkholderia xenovorans LB400 as the best candidate enzyme for metabolizing carbamazepine. The rate of degradation described here is 40 times greater than the best reported rates. The metabolites cis-10,11-dihydroxy-10,11-dihydrocarbamazepine and cis-2,3-dihydroxy-2,3-dihydrocarbamazepine were demonstrated with the native organism and a recombinant host. The metabolites are considered nonharmful and mitigate the generation of carcinogenic acridine products known to form when advanced oxidation methods are used in water treatment. Other recalcitrant personal care products were subjected to prediction by the Pathway Prediction System and tested experimentally with P. xenovorans LB400. It was shown to biodegrade structurally diverse compounds. Predictions indicated hydrolase or oxygenase enzymes catalyzed the initial reactions. This study highlights the potential for using the growing body of enzyme-structural and genomic information with computational methods to rapidly identify enzymes and microorganisms that biodegrade emerging contaminants.

Pathogenetic analyses of carbamazepine-induced liver injury in F344 rats focused on immune- and inflammation-related factors

Drug-induced liver injury is one of the major reasons for a drug to be withdrawn postmarketing. Carbamazepine (CBZ), an anticonvulsant agent, has been reported rarely to cause liver failure in humans. We recently generated a rat model of CBZ-induced liver injury using F344 rats for five consecutive days of CBZ administration combined with a glutathione (GSH) depletor, L-buthionine S,R-sulfoximine, treatment. The involvement of metabolic activation was demonstrated in developing CBZ-induced liver injury, and a difference in metabolic activation reactions between mice and rats was indicated. In this study, we analyzed the pathogenetic mechanism of CBZ-induced liver injury, primarily focusing on immune- and inflammation-related factors using the rat model for CBZ-induced liver injury. After the last CBZ administration, plasma alanine aminotransfearase (ALT) levels were drastically increased. In the histopathological evaluation, time-dependent hepatocellular degeneration and necrosis were observed in the centrilobular region. Different from mice, although hepatic mRNA expression levels of inflammation-related genes were increased, T-helper cell-related genes were not predominantly changed in rats. The number of ED1- and ED2-positive macrophages was increased in injured centrilobular areas in the liver with CBZ-induced liver injury. Treatment with a Kupffer cell depletor, gadolinium chloride, prevented the elevation of plasma ALT levels and an increase in the hepatic mRNA expression levels of inflammation-related genes. Hepatic adenosine triphosphate (ATP) contents were significantly decreased 24 h after CBZ administration. Therefore, the Kupffer cells-mediated inflammation was predominant in the development of the CBZ-induced liver injury in rats.