CYP2E1-dependent elevation of serum cholesterol, triglycerides, and hepatic bile acids by isoniazid

Effects of compound Anoectochilus roxburghii (Wall.) Lindl. oral liquid on relative metabolic enzymes and various biochemical indices in Wistar rats with isoniazid-induced liver injury

Isoniazid (INH) is the first-line anti-tuberculosis drug in clinical practice, and its main adverse effect is drug-induced liver injury (DILI). This study aimed to investigate the hepatoprotective effect of Compound Anoectochilus roxburghii (Wall.) Lindl. Oral Liquid (CAROL) and to provide a new strategy for the search of potential drugs against INH-induced liver injury in Wistar rats. Animal experiment was based on INH (100 mg/kg) induced liver injury to explore the intervention effects of CAROL at doses of 1.35, 2.70, and 5.40 mL/kg. LC-QTOF-MS/MS was used to identify hepatoprotective components in CAROL and its' exposed components in rat serum. The hepatoprotective effect of CAROL was evaluated by pathological observation of rat liver tissue and changes in levels of biochemical indices and cytokines in serum or liver tissue. Of the 58 hepatoprotective components identified, 15 were detected in the serum of rats with liver-injured treated by high-dose CAROL. Results of animal experiments showed that the levels of various biochemical indexes and cytokines were significantly reversed with CAROL intervention. In particular, the expression level of cytokeratin-18 and high-mobility group box 1, as specific and sensitive indicators of DILI, was significantly reduced in the serum of rats with CAROL intervention compared with the INH model group. The same reversal was observed in the levels of TBIL, ALP, ALT, and AST in serum, as well as in the levels of TNF-α, IL-6, SOD, and MDA in liver tissue. For INH-metabolizing enzymes, an evident expression inhibition was observed in N-acetyltransferase 2 and glutathione S-transferases with CAROL intervention, which may be the key to controlling INH hepatotoxicity. CAROL has a favorable hepatoprotective effect on INH-induced liver injury. This study takes the first step in studying the hepatoprotective mechanism of CAROL against INH hepatotoxicity and provides reference for wider clinical applications.

Precision Medicine Strategies to Improve Isoniazid Therapy in Patients with Tuberculosis

Due to interindividual variability in drug metabolism and pharmacokinetics, traditional isoniazid fixed-dose regimens may lead to suboptimal or toxic isoniazid concentrations in the plasma of patients with tuberculosis, contributing to adverse drug reactions, therapeutic failure, or the development of drug resistance. Achieving precision therapy for isoniazid requires a multifaceted approach that could integrate various clinical and genomic factors to tailor the isoniazid dose to individual patient characteristics. This includes leveraging molecular diagnostics to perform the comprehensive profiling of host pharmacogenomics to determine how it affects isoniazid metabolism, such as its metabolism by N-acetyltransferase 2 (NAT2), and studying drug-resistant mutations in the Mycobacterium tuberculosis genome for enabling targeted therapy selection. Several other molecular signatures identified from the host pharmacogenomics as well as other omics-based approaches such as gut microbiome, epigenomic, proteomic, metabolomic, and lipidomic approaches have provided mechanistic explanations for isoniazid pharmacokinetic variability and/or adverse drug reactions and thereby may facilitate precision therapy of isoniazid, though further validations in larger and diverse populations with tuberculosis are required for clinical applications. Therapeutic drug monitoring and population pharmacokinetic approaches allow for the adjustment of isoniazid dosages based on patient-specific pharmacokinetic profiles, optimizing drug exposure while minimizing toxicity and the risk of resistance. Current evidence has shown that with the integration of the host pharmacogenomics-particularly NAT2 and Mycobacterium tuberculosis genomics data along with isoniazid pharmacokinetic concentrations in the blood and patient factors such as anthropometric measurements, comorbidities, and type and timing of food administered-precision therapy approaches in isoniazid therapy can be tailored to the specific characteristics of both the host and the pathogen for improving tuberculosis treatment outcomes.

Metabolism-dependent inhibition of CYP2E1 by isoniazid, a mediator of idiosyncratic liver injury

Liver injury is a well-known adverse effect of the anti-tuberculosis drug isoniazid (INH); however, animal models that accurately replicate this effect as seen in humans have not been constructed, and the mechanism of its pathogenesis remains unclear. Recently, an immune-mediated mechanism have been proposed based on clinical studies, suggesting the involvement of cytochrome P450-mediated formation of reactive metabolites and covalent adducts in severe cases. In the present study, we investigated the role of CYP2E1 in this mechanism. Liver microsomes from humans, rats, and mice were preincubated with INH and NADPH; thereafter, residual CYP2E1 activity was measured. The inhibition of CYP2E1 by INH was potentiated by preincubation, indicating time-dependent inhibition. There were no major species-based differences in inhibition among humans, rats, and mice. Further to our findings on the inhibition kinetics, resistance of the inhibition to glutathione and catalase indicated that the reactive metabolites of INH covalently bonded to CYP2E1 in a suicidal manner. A similar time-dependent inhibition was also observed for the known metabolites acetylhydrazine and hydrazine; however, the conditions that inhibited the hydrolysis or activated the acetylation of INH did not affect inhibition by INH, suggesting that the reactive metabolites contributing to the inhibition were generated via alternative pathways. This indicates that CYP2E1 alone generates reactive INH metabolites and that haptenized CYP2E1 may be involved in immune-mediated liver injury.

Effect of NAT2, GSTM1 and CYP2E1 genetic polymorphisms on plasma concentration of isoniazid and its metabolites in patients with tuberculosis, and the assessment of exposure-response relationships

Objectives: Isoniazid is a key drug in the chemotherapy of tuberculosis (TB), however, interindividual variability in pharmacokinetic parameters and drug plasma levels may affect drug responses including drug induced hepatotoxicity. The current study investigated the relationships between isoniazid exposure and isoniazid metabolism-related genetic factors in the context of occurrence of drug induced hepatotoxicity and TB treatment outcomes. Methods: Demographic characteristics and clinical information were collected in a prospective TB cohort study in Latvia (N = 34). Time to sputum culture conversion (tSCC) was used as a treatment response marker. Blood plasma concentrations of isoniazid (INH) and its metabolites acetylisoniazid (AcINH) and isonicotinic acid (INA) were determined at three time points (pre-dose (0 h), 2 h and 6 h after drug intake) using liquid chromatography-tandem mass spectrometry. Genetic variations of three key INH-metabolizing enzymes (NAT2, CYP2E1, and GSTM1) were investigated by application PCR- and Next-generation sequencing-based methods. Depending on variables, group comparisons were performed by Student's t-test, one-way ANOVA, Mann-Whitney-Wilcoxon, and Kruskal-Wallis tests. Pearson correlation coefficient was calculated for the pairs of normally distributed variables; model with rank transformations were used for non-normally distributed variables. Time-to-event analysis was performed to analyze the tSCC data. The cumulative probability of tSCC was obtained using Kaplan-Meier estimators. Cox proportional hazards models were fitted to estimate hazard rate ratios of successful tSCC. Results: High TB treatment success rate (94.1%) was achieved despite the variability in INH exposure. Clinical and demographic factors were not associated with either tSCC, hepatotoxicity, or INH pharmacokinetics parameters. Correlations between plasma concentrations of INH and its metabolites were NAT2 phenotype-dependent, while GSTM1 genetic variants did not showed any effects. CYP2E1*6 (T > A) allelic variant was associated with INH pharmacokinetic parameters. Decreased level of AcINH was associated with hepatotoxicity, while decreased values of INA/INH and AcINH/INH were associated with month two sputum culture positivity. Conclusion: Our findings suggest that CYP2E1, but not GSTM1, significantly affects the INH pharmacokinetics along with NAT2. AcINH plasma level could serve as a biomarker for INH-related hepatotoxicity, and the inclusion of INH metabolite screening in TB therapeutic drug monitoring could be beneficial in clinical studies for determination of optimal dosing strategies.

Human Cytochrome P450 1, 2, 3 Families as Pharmacogenes with Emphases on Their Antimalarial and Antituberculosis Drugs and Prevalent African Alleles

Precision medicine gives individuals tailored medical treatment, with the genotype determining the therapeutic strategy, the appropriate dosage, and the likelihood of benefit or toxicity. Cytochrome P450 (CYP) enzyme families 1, 2, and 3 play a pivotal role in eliminating most drugs. Factors that affect CYP function and expression have a major impact on treatment outcomes. Therefore, polymorphisms of these enzymes result in alleles with diverse enzymatic activity and drug metabolism phenotypes. Africa has the highest CYP genetic diversity and also the highest burden of malaria and tuberculosis, and this review presents current general information on CYP enzymes together with variation data concerning antimalarial and antituberculosis drugs, while focusing on the first three CYP families. Afrocentric alleles such as CYP2A6*17, CYP2A6*23, CYP2A6*25, CYP2A6*28, CYP2B6*6, CYP2B6*18, CYP2C8*2, CYP2C9*5, CYP2C9*8, CYP2C9*9, CYP2C19*9, CYP2C19*13, CYP2C19*15, CYP2D6*2, CYP2D6*17, CYP2D6*29, and CYP3A4*15 are implicated in diverse metabolic phenotypes of different antimalarials such as artesunate, mefloquine, quinine, primaquine, and chloroquine. Moreover, CYP3A4, CYP1A1, CYP2C8, CYP2C18, CYP2C19, CYP2J2, and CYP1B1 are implicated in the metabolism of some second-line antituberculosis drugs such as bedaquiline and linezolid. Drug-drug interactions, induction/inhibition, and enzyme polymorphisms that influence the metabolism of antituberculosis, antimalarial, and other drugs, are explored. Moreover, a mapping of Afrocentric missense mutations to CYP structures and a documentation of their known effects provided structural insights, as understanding the mechanism of action of these enzymes and how the different alleles influence enzyme function is invaluable to the advancement of precision medicine.

Genetic Variants and Drug Efficacy in Tuberculosis: A Step toward Personalized Therapy

Tuberculosis (TB) continues to be a major infectious disease affecting individuals worldwide. Current TB treatment strategy recommends the standard short-course chemotherapy regimen containing first-line drug, i.e., isoniazid, rifampicin, pyrazinamide, and ethambutol to treat patients suffering from drug-susceptible TB. Although Mycobacterium tuberculosis, the causing agent, is susceptible to drugs, some patients do not respond to the treatment or treatment may result in serious adverse reactions. Many studies revealed that anti-TB drug-related toxicity is associated with genetic variations, and these variations may also influence attaining maximum drug concentration. Thus, inter-individual diversities play a characteristic role by influencing the genes involved in drug metabolism pathways. The development of pharmacogenomics could bring a revolution in the field of treatment, and the understanding of germline variants may give rise to optimized targeted treatments and refine the response to standard therapy. In this review, we briefly introduced the field of pharmacogenomics with the evolution in genetics and discussed the pharmacogenetic impact of genetic variations on genes involved in the activities, such as anti-TB drug transportation, metabolism, and gene regulation.

Hepatoprotective Effect of Corm of Ensete ventricosum (Welw.) Cheesman Extract against Isoniazid and Rifampicin Induced Hepatotoxicity in Swiss Albino Mice

Drug-induced liver injury (DILI) is one of the cumbersome health-related problems which render approximately 50% of liver failure and patients to receiving liver transplantation every year. Antituberculosis drugs such as isoniazid and rifampicin are potentially rendering hepatotoxicity. Ensete ventricosum (Welw.) Cheesman is an herbaceous perennial plant that contributes to the indigenous ethnomedicinal values for the society. This study aimed to investigate the hepatoprotective effect of corm of Ensete ventricosum (Welw.) Cheesman extracts against isoniazid and rifampicin induced hepatotoxicity in Swiss albino mice. The study was conducted on 30 Swiss albino mice randomly allocated into five groups. Group I, group II, group III, group IV, and group V were the groups in which mice were given distilled water, only isoniazid and rifampicin, isoniazid and rifampicin along with 200 mg/kg corm of Ensete ventricosum (Welw.) Cheesman extract, isoniazid and rifampicin along with 400 mg/kg corm of Ensete ventricosum (Welw.) Cheesman extract, and isoniazid and rifampicin along with silymarin per oral per day, respectively. On the 30th day of the experiment, mice were sacrificed after anesthetized, and blood was drawn for the liver function test, and the liver was also taken from each experimental mouse for histopathological evaluation. Data were entered into EpiData version 3.1 subsequently exported to SPSS version 25 for analysis by using one-way ANOVA. Plasma alanine aminotransferase (ALT) levels, aspartate aminotransferase (AST), alkaline phosphatase (ALP), and total bilirubin (TBIL) of group II mice were significantly (p < 0.05) elevated as compared to group I. The group of mice treated with a corm of Ensete ventricosum (Welw.) Cheesman at a dose of 400 mg/kg (group IV) and silymarin100 mg/kg (group V) showed a significant (p < 0.05) decrease in ALT, AST, ALP, and TBIL as compared to the group II. The liver section of group II showed a change in liver architecture; however, these deformities were not noticed in group IV mice. The result showed corm of Ensete ventricosum (Welw.) Cheesman extract has a very promising hepatoprotective potential against isoniazid and rifampicin induced liver injury.

Cell Type-Specific Roles of CD38 in the Interactions of Isoniazid with NAD+ in the Liver

NAD⁺ is a critical molecule that is involved in multiple cellular functions. CD38 is a multifunctional enzyme with NAD⁺ nucleosidase activity. Our previous work revealed the CD38-dependent interactions of isoniazid (INH), an antituberculosis drug, with NAD⁺ to form INH-NAD adduct. In the current work, our metabolomic analysis discovered a novel NAD⁺ adduct with acetylisoniazid (AcINH), a primary INH metabolite mediated by N-acetyltransferase (NAT), and we named it AcINH-NAD. Using Nat1/2(-/-) and Cd38(-/-) mice, we determined that AcINH-NAD formation is dependent on both NAT and CD38. Because NAT is expressed in hepatocytes (HP), whereas CD38 is expressed in Kupffer cells (KC) and hepatic stellate cells (HSC), we explored cell type-specific roles of CD38 in the formation of AcINH-NAD as well as INH-NAD. We found that both INH-NAD and AcINH-NAD were produced in the incubation of INH or AcINH with KC and HSC but not in HP. These data suggest that hepatic nonparenchymal cells, such as KC and HSC, are the major cell types responsible for the CD38-dependent interactions of INH with NAD⁺ in the liver. SIGNIFICANCE STATEMENT: The current study identified AcINH-NAD as a novel metabolite of INH in the liver. Our work also revealed the essential roles of nonparenchymal cells, including Kupffer cells and hepatic stellate cells, in the CD38-dependent interactions of NAD⁺ with INH, leading to the formation of both INH-NAD and AcINH-NAD in the liver. These data can be used to guide the future studies on the mechanisms of INH and NAD⁺ interactions and their contributions to INH-induced liver injury.

Toxicoproteomic Profiling of hPXR Transgenic Mice Treated with Rifampicin and Isoniazid

Tuberculosis is a global health threat that affects millions of people every year, and treatment-limiting toxicity remains a considerable source of treatment failure. Recent reports have characterized the nature of hPXR-mediated hepatotoxicity and the systemic toxicity of antitubercular drugs. The antitubercular drug isoniazid plays a role in such pathologic states as acute intermittent porphyria, anemia, hepatotoxicity, hypercoagulable states (deep vein thrombosis, pulmonary embolism, or ischemic stroke), pellagra (vitamin B₃ deficiency), peripheral neuropathy, and vitamin B₆ deficiency. However, the mechanisms by which isoniazid administration leads to these states are unclear. To elucidate the mechanism of rifampicin- and isoniazid-induced liver and systemic injury, we performed tandem mass tag mass spectrometry-based proteomic screening of mPxr^-/- and hPXR mice treated with combinations of rifampicin and isoniazid. Proteomic profiling analysis suggested that the hPXR liver proteome is affected by antitubercular therapy to disrupt [Fe-S] cluster assembly machinery, [2Fe-2S] cluster-containing proteins, cytochrome P450 enzymes, heme biosynthesis, homocysteine catabolism, oxidative stress responses, vitamin B₃ metabolism, and vitamin B₆ metabolism. These novel findings provide insight into the etiology of some of these processes and potential targets for subsequent investigations. Data are available via ProteomeXchange with identifier PXD019505.

Determination of isoniazid acetylation patterns in tuberculosis patients receiving DOT therapy under the Revised National tuberculosis Control Program (RNTCP) in India

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Monitoring of liver function tests is very important in patient receiving DOT therapy.

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There was no significance difference reported in the differential leucocytes count.

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We define mechanisms underlying the adverse drug reactions observed following DOTS.

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The plasma INH concentration was reported to be high in slow acetylation.

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Plasma INH concentration greater than the antimode are slow acetylator.

Isoniazid is the most commonly used drug for treatment of tuberculosis, and is administered individually or in combination with other drugs as standard first line therapy. Offsetting its efficacy, severe adverse effects, especially peripheral neuropathy and hepatotoxicity, are associated with isoniazid therapy, limiting its use in tuberculosis. Isoniazid is acetylated in vivo producing hydrazine and acetyl hydrazine, which are responsible for hepatotoxicity. Marked pharmacogenetic differences in acetylation have been reported among different population across the globe. This study evaluates isoniazid acetylation patterns in tuberculosis patients receiving DOT therapy under the Revised National Tuberculosis Control Program (RNTCP) in a specialized tuberculosis hospital in north India. Of 351 patients from whom samples were taken for biochemical analysis of adverse events, 36 were assessed for acetylation patterns. Blood samples were taken 1 h after administration of a 600 mg dose of isoniazid, and plasma concentrations of isoniazid were determined using a validated HPLC method. Of these 36 patients, 20 (55.56%) were slow acetylators and 16 (44.44%) were fast acetylators. Our results are consistent with those of an earlier study conducted in a different region of India. Most biochemical changes produced during long-term isoniazid therapy resolve after therapy is terminated.

Increased hepatic acylcarnitines after oral administration of amiodarone in rats

Amiodarone is known to induce hepatic injury in some recipients. We applied an untargeted metabolomics approach to identify endogenous metabolites with potential as biomarkers for amiodarone-induced liver injury. Oral amiodarone administration for 1 week in rats resulted in significant elevation of acylcarnitines and phospholipids in the liver. Hepatic short- and medium-chain acylcarnitines were dramatically increased in a dose-dependent manner, while the serum levels of these acylcarnitines did not change substantially. In addition, glucose levels were significantly increased in both the serum and liver. Gene expression profiling showed that the hepatic mRNA levels of Cpt1, Cpt2, and Acat1 were significantly suppressed, whereas those of Acot1, Acly, Acss2, and Acsl3 were increased. These results suggest that hepatic acylcarnitines and glucose levels might be increased due to disruption of mitochondrial function and suppression of glucose metabolism. Perturbation of energy metabolism might be associated with amiodarone-induced hepatotoxicity.

A comprehensive review of cytochrome P450 2E1 for xenobiotic metabolism

Cytochrome P450 2E1 (CYP2E1) plays a vital role in drug-induced hepatotoxicity and cancers (e.g. lung and bladder cancer), since it is responsible for metabolizing a number of medications and environmental toxins to reactive intermediate metabolites. CYP2E1 was recently found to be the highest expressed CYP enzyme in human livers using a proteomics approach, and CYP2E1-related toxicity is strongly associated with its protein level that shows significant inter-individual variability related to ethnicity, age, and sex. Furthermore, the expression of CYP2E1 demonstrates regulation by extensive genetic polymorphism, endogenous hormones, cytokines, xenobiotics, and varying pathological states. Over the past decade, the knowledge of pharmacology, toxicology, and biology about CYP2E1 has grown remarkably, but the research progress has yet to be summarized. This study presents a timely systematic review on CYP2E1's xenobiotic metabolism, genetic polymorphism, and inhibitors, with the focus on their clinical relevance for the efficacy and toxicity of various CYP2E1 substrates. Moreover, several knowledge gaps have been identified towards fully understanding the potential interactions among different CYP2E1 substrates in clinical settings. Through in-depth analyses of these knowns and unknowns, we expect this review will aid in future drug development and improve management of CYP2E1 related clinical toxicity.

The application of metabolomics toward pulmonary tuberculosis research

In the quest to identify novel biomarkers for pulmonary tuberculosis (TB), high-throughput systems biology approaches such as metabolomics has become increasingly widespread. Such biomarkers have not only successfully been used for better disease characterization, but have also provided new insights toward the future development of improved diagnostic and therapeutic approaches. In this review, we give a summary of the metabolomics studies done to date, with a specific focus on those investigating various aspects of pulmonary TB, and the infectious agent responsible, Mycobacterium tuberculosis. These studies, done on a variety of sample matrices, including bacteriological culture, sputum, blood, urine, tissue, and breath, are discussed in terms of their intended research outcomes or future clinical applications. Additionally, a summary of the research model, sample cohort, analytical apparatus and statistical methods used for biomarker identification in each of these studies, is provided.

Exposure of Infants to Isoniazid via Breast Milk After Maternal Drug Intake of Recommended Doses Is Clinically Insignificant Irrespective of Metaboliser Status. A Physiologically-Based Pharmacokinetic (PBPK) Modelling Approach to Estimate Drug Exposure of Infants via Breast-Feeding

Isoniazid is a first-line anti-tuberculosis drug recommended for treatment of drug-susceptible Mycobacterium tuberculosis infections. Breast-feeding is not contra-indicated while undergoing isoniazid therapy, even though isoniazid was found to migrate into breast milk, leading to infant drug exposure. Exposure assessment of isoniazid in infants exposed to the drug via breast milk has so far not accounted for the polymorphic expression of the isoniazid metabolising enzyme N-acetyltransferase 2. The aim of this study was to re-visit the safety assessment of maternal isoniazid therapy for infants exposed to the drug via breast milk, while accounting for fast and slow metabolisers in the adult and infant population, as well as for slower metabolism in small infants than in adults. We applied a physiologically-based pharmacokinetic (PBPK) modelling approach to estimate mother and infant external and internal drug exposure non-invasively. Validity of our PBPK models was confirmed through comparison of simulated results with experimental data. Highest recommended oral doses for mothers are daily 300 mg or 900 mg every 3 days. Simulation of maternal intake of 300 mg resulted in oral exposures of 0.58 (95%CI: 0.42-0.69) mg/day and 1.49 (1.22-1.50) mg/day for infants of fast and slow metabolising mothers, respectively. Oral exposures of infants within the first 24 h after maternal intake of 900 mg were 1.75 (1.25-2.06) mg/day and 4.46 (4.00-4.50) mg/day. Maximal drug concentrations in infant plasma ranged between 0.04 and 0.78 mg/L for the two dosing regimens. We therefore conclude that infant exposure to isoniazid via breast milk after maternal drug intake of highest recommended doses is very low. We expect that such low exposure levels most likely do not cause any clinically significant adverse effects in nursed infants.

Prominence of Oxidative Stress in the Management of Anti-tuberculosis Drugs Related Hepatotoxicity

Advanced medical services and treatments are available for treating Tuberculosis. Related prevalence has increased in recent times. Unfortunately, the continuous consumption of related drugs is also known for inducing hepatotoxicity which is a critical condition and cannot be overlooked. The present review article has focused on the pathways causing these toxicities and also the role of enzyme CYP2E1, hepatic glutathione, Nrf2-ARE signaling pathway, and Membrane Permeability Transition as possible targets which may help in preventing the hepatotoxicity induced by the drugs used in the treatment of tuberculosis.

Telfairia occidentalis (Cucurbitaceae) pulp extract mitigates rifampicin-isoniazid-induced hepatotoxicity in an in vivo rat model of oxidative stress

OBJECTIVE

Drug-induced liver injury complicates antituberculosis drug treatment and is a leading cause of death worldwide. The aim of this study is to establish the ethnomedicinal claim of hepatoprotective effects of fruit pulp extract of Telfairia occidentalis against rifampicin (RIF) and isoniazid (INH)-induced oxidative stress in rats.

METHODS

T. occidentalis pulp extract (TOPE) (125-500 mg/kg) and silymarin (50 mg/kg) were evaluated in an induced hepatotoxicity model of oxidative stress in Wistar rats by intoxication with RIF and INH (100 mg/kg each) orally for 60 d. Markers indicating oxidative stress and hepatic damage such as alanine aminotransferase (ALT), aspartate aminotransferase (AST) and alkaline phosphatase (ALP) were assessed. Biomarkers of antioxidant status, including catalase, glutathione reductase, glutathione peroxidase and superoxide dismutase, and marker of lipid peroxidation, malondialdehyde (MDA), were assayed using standard procedures. The hematological profile, lipid profile, serum markers for kidney function and histopathological examination were also assessed.

RESULTS

Intoxication with RIF and INH markedly reduced the hematological indices and elevated the biochemical enzyme markers (AST, ALT and ALP, P < 0.001) and lipid profile (P < 0.001), while antioxidant biomarkers were significantly (P < 0.01) depressed and MDA was elevated. However, pretreatment with TOPE significantly (P < 0.001) alleviated this alteration and sustained the antioxidant potentials. The histopathological morphology supports the biochemical evidence of hepatoprotection.

CONCLUSION

Current study is indicative of potential antioxidant activity, hepatoprotective effects and plausible therapeutic alleviation of RIF-INH-induced hepatotoxicity of TOPE in laboratory animals.

Mass spectrometry-based metabolomics for tuberculosis meningitis

Tuberculosis meningitis (TBM) is a prevalent form of extra-pulmonary tuberculosis that causes substantial morbidity and mortality. Diagnosis of TBM is difficult because of the limited sensitivity of existing laboratory techniques. A metabolomics approach can be used to investigate the sets of metabolites of both bacteria and host, and has been used to clarify the mechanisms underlying disease development, and identify metabolic changes, leadings to improved methods for diagnosis, treatment, and prognostication. Mass spectrometry (MS) is a major analysis platform used in metabolomics, and MS-based metabolomics provides wide metabolite coverage, because of its high sensitivity, and is useful for the investigation of Mycobacterium tuberculosis (Mtb) and related diseases. It has been used to investigate TBM diagnosis; however, the processes involved in the MS-based metabolomics approach are complex and flexible, and often consist of several steps, and small changes in the methods used can have a huge impact on the final results. Here, the process of MS-based metabolomics is summarized and its applications in Mtb and Mtb-related diseases discussed. Moreover, the current status of TBM metabolomics is described.

Genetic Variations Associated with Anti-Tuberculosis Drug-Induced Liver Injury

Purpose of this Review

In order to combat the development of drug resistance, the clinical treatment of tuberculosis requires the combined use of several anti-tuberculosis (anti-TB) drugs, including isoniazid and rifampicin. Combinational treatment approaches are suggested by the World Health Organization (WHO) and are widely accepted throughout the world. Unfortunately, a major side effect of the treatment is the development of anti-tuberculosis drug-induced liver injury (AT-DILI). Many factors contribute to isoniazid- and rifampicin-mediated AT-DILI and genetic variations are among the most common factors. The purpose of this review is to provide information on genetic variations associated with isoniazid- and rifampicin-mediated AT-DILI.

Recent Findings

The genetic variations associated with AT-DILI have been identified in the genomic regions within or near genes encoding proteins in the following pathways: drug metabolizing enzymes (NAT2, CYP2E1, and GSTs), accumulation of bile acids, lipids, and heme metabolites (CYP7A1, BSEP, UGTs, and PXR), immune adaptation (HLAs and TNF-α), and oxidant challenge (TXNRD1, SOD1, BACH1, and MAFK).

Summary

The information summarized in this review considers the genetic bases of risk factors contributing to AT-DILI and provides information that may help for future studies. Some of the implicated genetic variations can be used in the design of genetic tests and serve as biomarkers for the prediction of isoniazid- and rifampicin-mediated AT-DILI risk in personalized medicine.

Investigating the CYP2E1 Potential Role in the Mechanisms Behind INH/LPS-Induced Hepatotoxicity

Tuberculosis (TB) is one of the oldest infectious diseases that affected humankind and remains one of the world's deadliest communicable diseases that could be considered as global emergency, but the discovery and development of isoniazid (INH) in the 1950s paved the way to an effective single and/or combined first-line anti-TB therapy. However, administration of INH induces severe hepatic toxicity in some patients. Previously, we establish a rat model of INH hepatotoxicity utilizing the inflammatory stress theory, in which bacterial lipopolysaccharide (LPS) potentially enhanced INH toxicity. These enhancing activities ranged between augmenting the inflammatory stress, oxidative stress, alteration of bile acid homeostasis, and CYP2E1 over-expression. Although pre-treatment with dexamethasone (DEX) helped overcome both inflammatory and oxidative stress which ended-up in alleviation of LPS augmenting effects, but still minor toxicities were being detected, alongside with CYP2E1 over expression. This finding positively indicated the corner-stone role played by CYP2E1 in the pathogenesis of INH/LPS-induced liver damage. Therefore, we examined whether INH/LPS co-treatment with CYP2E1 inhibitor diallyl sulfide (DAS) and DEX can protect against the INH/LPS-induced hepatotoxicity. Our results showed that pre-administration of both DAS and DEX caused significant reduction in serum TBA, TBil, and gamma-glutamyl transferase levels. Furthermore, the histopathological analysis showed that DAS and DEX could effectively reverse the liver lesions seen following INH/LPS treatment and protect against hepatic steatosis as indicated by absence of lipid accumulation. Pre-treatment with DAS alone could not completely block the CYP2E1 protein expression following INH/LPS treatment, as appeared in the immunoblotting and immunohistochemistry results. This is probably due to the fact that the combined enhancement activities of both INH and LPS on CYP2E1 protein expression levels might resist the blocking probabilities of DAS. In the meantime, addition of DEX to the DAS/INH/LPS combination caused a significant reduction in CYP2E1 protein expression as revealed by the immunoblotting and fading coloration in immunohistochemistry results. Thus, addition of DEX and DAS together caused strong protection against INH/LPS-induced hepatic damage. These findings reveal the potential therapeutic value of combining DAS and DEX with INH in TB management for reducing the potential risk and incidences of hepatotoxicity.

Cell-based assay using glutathione-depleted HepaRG and HepG2 human liver cells for predicting drug-induced liver injury

Immortalized liver cells have been used for evaluating the toxicity of compounds; however, excessive glutathione is considered to lessen cytotoxicity. In this study, we compared the effects of glutathione depletion on cytotoxicities of drugs using HepaRG and HepG2 cells, which express and lack drug-metabolizing enzymes, respectively, for predicting drug-induced liver injury (DILI) risks. These cells were pre-incubated with L-buthionine-S,R-sulfoximine (BSO) and then exposed to 34 test compounds with various DILI risks for 24 h. ATP level exhibited the highest predictability of DILI among tested parameters. BSO treatment rendered cells susceptible to drug-induced cytotoxicity when evaluated by cell viability and caspase 3/7 activity with the sensitivity of cell viability from 50% in non-treated HepaRG cells to 71% in BSO-treated HepaRG cells. These results indicate that cytotoxicity assays using GSH-depleted HepaRG cells improve the predictability of DILI risks. However, HepaRG cells were not always superior to HepG2 cells when assessed by ATP level. The combination of HepG2 and HepaRG cells index produced the best prediction in the cases of caspase 3/7 acitivity and ATP level. In conclusions, the developed highly sensitive cell-based assay using GSH-reduced cells would be useful for predicting potential DILI risks at an early stage of drug development.

Deficiency of N-acetyltransferase increases the interactions of isoniazid with endobiotics in mouse liver

Acetylation is the major metabolic pathway of isoniazid (INH) mediated by N-acetyltransferases (NATs). Previous reports suggest that slow acetylators have higher risks of INH hepatotoxicity than rapid acetylators, but the detailed mechanisms remain elusive. The current study used Nat1/2(-/-) mice to mimic NAT slow metabolizers and to investigate INH metabolism in the liver. We found that INH acetylation is abolished in the liver of Nat1/2(-/-) mice, suggesting that INH acetylation is fully dependent on NAT1/2. In addition to the acetylation pathway, INH can be hydrolyzed to form hydrazine (Hz) and isonicotinic acid (INA). We found that INA level was not altered in the liver of Nat1/2(-/-) mice, indicating that deficiency of NAT1/2 has no effect on INH hydrolysis. Because INH acetylation was abolished and INH hydrolysis was not altered in Nat1/2(-/-) mice, we expected an extremely high level of INH in the liver. However, we only observed a modest accumulation of INH in the liver of Nat1/2(-/-) mice, suggesting that there are alternative pathways in INH metabolism in NAT1/2 deficient condition. Our further studies revealed that the conjugated metabolites of INH with endobiotics, including fatty acids and vitamin B6, were significantly increased in the liver of Nat1/2(-/-) mice. In summary, this study illustrated that deficiency of NAT1/2 decreases INH acetylation, but increases the interactions of INH with endobiotics in the liver. These findings can be used to guide future studies on the mechanisms of INH hepatotoxicity in NAT slow metabolizers.

Impairment of Mitochondrial Biogenesis and Dynamics Involved in Isoniazid-Induced Apoptosis of HepG2 Cells Was Alleviated by p38 MAPK Pathway

Isoniazid (INH), a widely used first-line antitubercular drug, has been noted to be associated with hepatotoxicity. In spite of extensive researches over many decades, the mechanism of INH-induced hepatotoxicity still remains poorly understood. Recently, mitochondrial toxicity has been emerging as a new paradigm for INH-induced hepatotoxicity. In this study, we showed that INH impaired mitochondrial biogenesis and dynamics in human hepatocarcinoma HepG2 cells. INH reduced mitochondrial membrane potential (MMP) and induced mitochondria swelling. INH also inhibited the protein expressions of three major mitochondrial biogenesis regulators, SIRT1, PGC1α and NRF1, along with increased acetylation of PGC1α. Meanwhile, INH decreased the number of mitochondria, accompanied by decreased expression of mitochondrial protein COX IV. INH caused mitochondrial fragmentation involving decreased levels of the fusion protein MFN2 as well as the fission protein DRP1. INH-reduced DRP1 expression was associated with the increase of apoptosis, suggesting the existence of pro-survival fission and its involvement in mitochondrial quality control. INH activated p38 MAPK, whereas inhibition of p38 MAPK aggravated INH-induced decreases of SIRT1, PGC1α, NRF1, COX IV and DRP1 expressions. P38 MAPK inhibition also further up-regulated the acetylation of PGC1α and exacerbated INH-induced MMP loss, mitochondrial swelling and apoptosis. Taken together, INH-activated p38 MAPK induced mitochondrial biogenesis to alleviate apoptosis through partly recovering SIRT1-PGC1α pathway activation. In the meantime, p38 MAPK activation by INH promoted protective mitochondrial fission to alleviate apoptosis by partial recovery of DRP1 expression.

The role of metabolomics in tuberculosis treatment research

Despite the fact that tuberculosis (TB) is a curable disease, it still results in approximately 1.8 million deaths annually. Various inadequacies in the current TB treatment strategies are major contributors to this high disease prevalence, including the long duration of therapy, the severe side effects associated with TB drugs, treatment failure due to drug resistance, post-treatment disease relapse, and HIV co-infection. In this review, we describe how metabolomics has contributed toward better explaining/elucidating the mechanisms of drug action/metabolism, drug toxicity and microbial drug resistance, and how metabolite biomarkers may serve as prognostic indicators for predicting treatment outcome as well as for the development of new TB drugs. We also discuss possible future contributions that metabolomics can make toward more efficient, less toxic TB treatment strategies.

Evaluation of ameliorative ability of Silibinin against zidovudine and isoniazid-induced hepatotoxicity and hyperlipidaemia in rats: Role of Silibinin in Phase I and II drug metabolism

HIV/AIDS patients have suppressed immune system, making them vulnerable to many opportunistic infections including tuberculosis (TB). The patients who are co-infected with TB undergo combined regimens with anti-retroviral drugs such as zidovudine (AZT) and anti-tubercular drug such as isoniazid (INH) for therapy leading to hepatotoxicty. Silibinin (SBN), extracted from Silybum marianum commonly called as "Milk thistle" is used against several drugs-induced hepatotoxicity. The present study evaluates the ameliorative effect of SBN against AZT alone, INH alone, and INH + AZT-induced toxic insults to liver of rats. Wistar albino rats (n = 6/groups) were given INH and AZT (25 and 50 mg mg/kg b.w.) respectively either alone or in combination for a sub-chronic period of 45 days orally. Another group of rats received SBN (100 mg/kg b.w.) along with INH and AZT. The group that received propylene glycol served as control. AZT alone, INH alone and INH + AZT treatments showed parenchymal cell injury and cholestasis by highly significant increase in the activities of marker enzymes (aspartate and alanine transaminase, alkaline phosphatase, argino succinic acid lyase), bilirubin and protein. The presence of hyperlipidaemia was observed by analyzing lipid profiles in serum/liver/adipose tissue, gene expression (RT-PCR) of Phase-I and II metabolizing enzymes and western blot. Transmission electron microscopy study also revealed large vacuoles with membraneous debri, pleomorphic mitochondria, disruption of endoplasmic reticulum, presence of lipid droplets, breakage in cellular and nuclear membrane. SBN simultaneous treatment showed ameliorative effect against INH + AZT-induced hepatotoxicity and hyperlipidemia in rats.

Dexamethasone Pretreatment Alleviates Isoniazid/Lipopolysaccharide Hepatotoxicity: Inhibition of Inflammatory and Oxidative Stress

Isoniazid (INH) remains a cornerstone key constitute of the current tuberculosis management strategy, but its hepatotoxic potentiality remains a significant clinical problem. Our previous findings succeed to establish a rat model of INH hepatotoxicity employing the inflammatory stress theory in which non-injurious doses of inflammatory-mediating agent bacterial lipopolysaccharides (LPS) augmented the toxicity of INH that assist to uncover the mechanisms behind INH hepatotoxicity. Following LPS exposure, several inflammatory cells are activated and it is likely that the consequences of this activation rather than direct hepatocellular effects of LPS underlie the ability of LPS to augment toxic responses. In this study, we investigated the potential protective role of the anti-inflammatory agent dexamethasone (DEX), a potent synthetic glucocorticoid, in INH/LPS hepatotoxic rat model. DEX pre-treatment successfully eliminates the components of the inflammatory stress as shown through analysis of blood biochemistry and liver histopathology. DEX potentiated hepatic anti-oxidant mechanisms while serum and hepatic lipid profiles were reduced. However, DEX administration was not able to revoke the principal effects of cytochrome P450 2E1 (CYP2E1) in INH/LPS-induced liver damage. In conclusion, this study illustrated the DEX-preventive capabilities on INH/LPS-induced hepatotoxicity model through DEX-induced potent anti-inflammatory activity whereas the partial toxicity seen in the model could be attributed to the expression of hepatic CYP2E1. These findings potentiate the clinical applications of DEX co-administration with INH therapy in order to reduce the potential incidences of hepatotoxicity.

Isoniazid metabolism and hepatotoxicity

Isoniazid (INH) is highly effective for the management of tuberculosis. However, it can cause liver injury and even liver failure. INH metabolism has been thought to be associated with INH-induced liver injury. This review summarized the metabolic pathways of INH and discussed their associations with INH-induced liver injury.

Role of Inflammatory and Oxidative Stress, Cytochrome P450 2E1, and Bile Acid Disturbance in Rat Liver Injury Induced by Isoniazid and Lipopolysaccharide Cotreatment

Isoniazid (INH) remains the core drug in tuberculosis management, but serious hepatotoxicity and potentially fatal liver injury continue to accompany INH consumption. Among numerous theories that have been established to explain INH-induced liver injury, an inflammatory stress theory has recently been widely used to explain the idiosyncrasy. Inflammatory stress usually sensitizes tissues to a drug's toxic consequences. Therefore, the present study was conducted to verify whether bacterial lipopolysaccharide (LPS)-induced inflammation may have a role in enhancing INH hepatotoxicity. While single INH or LPS administration showed no major toxicity signs, INH-LPS cotreatment intensified liver toxicity. Both blood biomarkers and histological evaluations clearly showed positive signs of severe liver damage accompanied by massive necrosis, inflammatory infiltration, and hepatic steatosis. Furthermore, elevated serum levels of bile acid associated with the repression of bile acid synthesis and transport regulatory parameters were observed. Moreover, the principal impact of cytochrome P450 2E1 (CYP2E1) on INH toxicity could be anticipated, as its protein expression showed enormous increases in INH-LPS-cotreated animals. Furthermore, the crucial role of CYP2E1 in the production of reactive oxygen species (ROS) was clearly obvious in the repression of hepatic antioxidant parameters. In summary, these results confirmed that this LPS-induced inflammation model might prove valuable in revealing the hepatotoxic mechanisms of INH and the crucial role played by CYP2E1 in the initiation and propagation of INH-induced liver damage, information which could be very useful to clinicians in understanding the pathogenesis of drug-induced liver injury.

A High Dose of Isoniazid Disturbs Endobiotic Homeostasis in Mouse Liver

Overdose of isoniazid (INH), an antituberculosis drug, can be life-threatening because of neurotoxicity. In clinical practice for management of INH overdose and acute toxicity, the potential of INH-induced hepatotoxicity is also considered. However, the biochemical basis of acute INH toxicity in the liver remains elusive. In the current study, we used an untargeted metabolomic approach to explore the acute effects of INH on endobiotic homeostasis in mouse liver. We found that overdose of INH resulted in accumulation of oleoyl-l-carnitine and linoleoyl-l-carnitine in the liver, indicating mitochondrial dysfunction. We also revealed the interactions between INH and fatty acyl-CoAs by identifying INH-fatty acid amides. In addition, we found that overdose of INH led to the accumulation of heme and oxidized NAD in the liver. We also identified an INH and NAD adduct in the liver. In this adduct, the nicotinamide moiety in NAD was replaced by INH. Furthermore, we illustrated that overdose of INH depleted vitamin B6 in the liver and blocked vitamin B6-dependent cystathionine degradation. These data suggest that INH interacts with multiple biochemical pathways in the liver during acute poisoning caused by INH overdose.

Repeated administration of ethambutol in therapeutic dose causes testes alteration and spermatogenesis disruption in Wistar rats

Ethambutol (EMB) is conventionally used to treat tuberculosis and atypical Mycobacterium infections in combination with other antimycobacterial drugs. Eventually, EMB testicular toxicity has not been explored extensively yet. The aim of the study is to evaluate testicular toxicity of EMB. We explored the impact of EMB on male rats' fertility, testosterone level and germ cells state, testicular pro- and anti-oxidant status and DNA damage, as well as identified EMB effects on cytochrome P-450 2E1 (CYP2E1) both with computer simulation and in vivo. We demonstrated that EMB administration to male rats decreased in epididymal sperm count (19%) and fertility index (53%). These events were accompanied by reduction in serum testosterone content (1.6 times) and appearance of spermatogenic epithelium damages. It was also found in testes the intensification of lipid peroxidation, decrease in reduced glutathione content and changes in DNA fragmentation. Additionally, computer simulation showed direct interaction of EMB with CYP2E1 active site and heme. On the top of this, we demonstrated that level of testicular CYP2E1 messenger RNA in EMB-treated rats was increased 8.7 folds and p-nitrophenol hydroxylase activity in testes rose three folds. As this shows, EMB-caused CYP2E1 induction, oxidative stress, and apoptosis in the testes contribute to inhibition of steroidogenesis enzymes and spermatogenesis disruption.

Induction of protective autophagy against apoptosis in HepG2 cells by isoniazid independent of the p38 signaling pathway

Isoniazid (INH), one of the first-line anti-tuberculosis drugs, is adversely associated with hepatotoxicity in the clinic. However, the detailed mechanism of this side effect is still unclear. The traditional theory that cytochrome P450 2E1 is involved in INH-induced hepatotoxicity remains controversial, therefore other mechanisms by which INH exerts hepatotoxicity need to be investigated. In the current study, we showed that in vitro treatment of human hepatocarcinoma HepG2 cells with INH induced caspase-dependent apoptosis through extrinsic and intrinsic pathways. It was characterized by the increased population of apoptotic cells using Annexin V/propidium iodide (PI) double staining by flow cytometry, and by the activation of caspases 8, 9, 3 and poly (ADP-ribose)-polymerase (PARP) proteins by western blotting. INH treatment also induced autophagy as shown by the upregulated levels of microtubule-associated protein 1 light chain 3-II (LC3-II), increased GFP-LC3 punctates, and elevated monodansylcadaverine (MDC) fluorescence intensity. The measurement of the autophagic flux using chloroquine (CQ) confirmed that INH stimulated autophagy but did not inhibit it by impairing lysosomal degradation. The blockage of autophagy with CQ exacerbated INH-induced apoptosis significantly. Further study showed that INH treatment down-regulated the protein phosphorylation of the mammalian target of rapamycin (mTOR), the key negative regulator of autophagy. In addition, INH induced p38 signaling activation. SB203580, a p38 inhibitor, effectively enhanced INH-induced apoptosis by increasing the cleavages of caspases 9, 3 and PARP, but did not affect autophagy. In summary, we firstly found that INH induced a protective autophagy which was associated with the inhibition of the mTOR pathway, and that INH induced p38 signaling activation to inhibit apoptosis by down-regulation of caspases 9, 3 and PARP pathways, but not that of autophagy. Thus, activation of autophagy and p38 signaling is presumably a therapeutic strategy for INH-induced hepatotoxicity.

Analysis of serum metabolic profile by ultra-performance liquid chromatography-mass spectrometry for biomarkers discovery: application in a pilot study to discriminate patients with tuberculosis

BACKGROUND

Tuberculosis (TB) is a chronic wasting inflammatory disease characterized by multisystem involvement, which can cause metabolic derangements in afflicted patients. Metabolic signatures have been exploited in the study of several diseases. However, the serum that is successfully used in TB diagnosis on the basis of metabolic profiling is not by much.

METHODS

Orthogonal partial least-squares discriminant analysis was capable of distinguishing TB patients from both healthy subjects and patients with conditions other than TB. Therefore, TB-specific metabolic profiling was established. Clusters of potential biomarkers for differentiating TB active from non-TB diseases were identified using Mann-Whitney U-test. Multiple logistic regression analysis of metabolites was calculated to determine the suitable biomarker group that allows the efficient differentiation of patients with TB active from the control subjects.

RESULTS

From among 271 participants, 12 metabolites were found to contribute to the distinction between the TB active group and the control groups. These metabolites were mainly involved in the metabolic pathways of the following three biomolecules: Fatty acids, amino acids, and lipids. The receiver operating characteristic curves of 3D, 7D, and 11D-phytanic acid, behenic acid, and threoninyl-γ-glutamate exhibited excellent efficiency with area under the curve (AUC) values of 0.904 (95% confidence interval [CI]: 0863-0.944), 0.93 (95% CI: 0.893-0.966), and 0.964 (95% CI: 00.941-0.988), respectively. The largest and smallest resulting AUCs were 0.964 and 0.720, indicating that these biomarkers may be involved in the disease mechanisms. The combination of lysophosphatidylcholine (18:0), behenic acid, threoninyl-γ-glutamate, and presqualene diphosphate was used to represent the most suitable biomarker group for the differentiation of patients with TB active from the control subjects, with an AUC value of 0.991.

CONCLUSION

The metabolic analysis results identified new serum biomarkers that can distinguish TB from non-TB diseases. The metabolomics-based analysis provides specific insights into the biology of TB and may offer new avenues for TB diagnosis.

Increased serum bile acid concentration following low-dose chronic administration of thioacetamide in rats, as evidenced by metabolomic analysis

A liquid chromatography/time-of-flight mass spectrometry (LC/TOF-MS)-based metabolomics approach was employed to identify endogenous metabolites as potential biomarkers for thioacetamide (TAA)-induced liver injury. TAA (10 and 30mg/kg), a well-known hepatotoxic agent, was administered daily to male Sprague-Dawley (SD) rats for 28days. We then conducted untargeted analyses of endogenous serum and liver metabolites. Partial least squares discriminant analysis (PLS-DA) was performed on serum and liver samples to evaluate metabolites associated with TAA-induced perturbation. TAA administration resulted in altered levels of bile acids, acyl carnitines, and phospholipids in serum and in the liver. We subsequently demonstrated and confirmed the occurrence of compromised bile acid homeostasis. TAA treatment significantly increased serum levels of conjugated bile acids in a dose-dependent manner, which correlated well with toxicity. However, hepatic levels of these metabolites were not substantially changed. Gene expression profiling showed that the hepatic mRNA levels of Ntcp, Bsep, and Oatp1b2 were significantly suppressed, whereas those of basolateral Mrp3 and Mrp4 were increased. Decreased levels of Ntcp, Oatp1b2, and Ostα proteins in the liver were confirmed by western blot analysis. These results suggest that serum bile acids might be increased due to the inhibition of bile acid enterohepatic circulation rather than increased endogenous bile acid synthesis. Moreover, serum bile acids are a good indicator of TAA-induced hepatotoxicity.

Activation of the Nrf2 response by intrinsic hepatotoxic drugs correlates with suppression of NF-κB activation and sensitizes toward TNFα-induced cytotoxicity

Drug-induced liver injury (DILI) is an important problem both in the clinic and in the development of new safer medicines. Two pivotal adaptation and survival responses to adverse drug reactions are oxidative stress and cytokine signaling based on the activation of the transcription factors Nrf2 and NF-κB, respectively. Here, we systematically investigated Nrf2 and NF-κB signaling upon DILI-related drug exposure. Transcriptomics analyses of 90 DILI compounds in primary human hepatocytes revealed that a strong Nrf2 activation is associated with a suppression of endogenous NF-κB activity. These responses were translated into quantitative high-content live-cell imaging of induction of a selective Nrf2 target, GFP-tagged Srxn1, and the altered nuclear translocation dynamics of a subunit of NF-κB, GFP-tagged p65, upon TNFR signaling induced by TNFα using HepG2 cells. Strong activation of GFP-Srxn1 expression by DILI compounds typically correlated with suppression of NF-κB nuclear translocation, yet reversely, activation of NF-κB by TNFα did not affect the Nrf2 response. DILI compounds that provided strong Nrf2 activation, including diclofenac, carbamazepine and ketoconazole, sensitized toward TNFα-mediated cytotoxicity. This was related to an adaptive primary protective response of Nrf2, since loss of Nrf2 enhanced this cytotoxic synergy with TNFα, while KEAP1 downregulation was cytoprotective. These data indicate that both Nrf2 and NF-κB signaling may be pivotal in the regulation of DILI. We propose that the NF-κB-inhibiting effects that coincide with a strong Nrf2 stress response likely sensitize liver cells to pro-apoptotic signaling cascades induced by intrinsic cytotoxic pro-inflammatory cytokines.

Polymorphisms in CYP2E1, GSTM1 and GSTT1 and anti-tuberculosis drug-induced hepatotoxicity

Anti-tuberculosis drug-induced hepatitis (ATD- induced hepatitis) has been linked to polymorphisms in genes encoding drug metabolizing enzymes. N-acetyltransferase 2 (NAT2), cytochrome P450 2E1 (CYP2E1) and glutathione S-transferase (loci GSTM1 and GSTT1) are involved in the metabolism of isoniazid, the most toxic drug for the treatment of tuberculosis (TB). This study was designed to determine the frequency and to evaluate whether polymorphisms at CYP2E1, GSTM1 and GSTT1 genes are associated with drug response, as well as to identify clinical risk factors for ATD-induced hepatitis. A total of 245 Brazilian patients undergoing treatment for TB were genotyped using polymerase chain reaction and restriction fragment length polymorphism and sequencing methods. The frequencies of the CYP2E1 polymorphic alleles RsaI, PstI and DraI are 8%, 8.5% and 12%, respectively. GSTM1 and GSTT1 genes are deleted in 42.9% and 12.4% of the population, respectively. Fifteen patients (6.1%) developed hepatotoxicity. Clinical (HIV, female sex and extrapulmonary TB) and genetic characteristics (CYP2E1 without any mutations, having NAT2 slow acetylator profile) are at higher risk of developing ATD-induced hepatitis in this population. Genotyping for GSTM1 and GSTT1 showed no influence on drug response.

LC-MS-based metabolomics: an update

Liquid chromatography-mass spectrometry (LC-MS)-based metabolomics can have a major impact in multiple research fields, especially when combined with other technologies, such as stable isotope tracers and genetically modified mice. This review highlights recent applications of metabolomic technology in the study of xenobiotic metabolism and toxicity, and the understanding of disease pathogenesis and therapeutics. Metabolomics has been employed to study metabolism of noscapine, an aryl hydrocarbon receptor antagonist, and to determine the mechanisms of liver toxicities of rifampicin and isoniazid, trichloroethylene, and gemfibrozil. Metabolomics-based insights into the pathogenesis of inflammatory bowel disease, alcohol-induced liver diseases, non-alcoholic steatohepatitis, and farnesoid X receptor signaling pathway-based therapeutic target discovery will also be discussed. Limitations in metabolomics technology such as sample preparation and lack of LC-MS databases and metabolite standards, need to be resolved in order to improve and broaden the application of metabolomic studies.

Mechanisms of isoniazid-induced idiosyncratic liver injury: emerging role of mitochondrial stress

Idiosyncratic drug-induced liver injury (DILI) is a significant adverse effect of antitubercular therapy with isoniazid (INH). Although the drug has been used for many decades, the underlying mode of action (both patient-specific and drug-specific mechanisms) leading to DILI are poorly understood. Among the patient-specific determinants of susceptibility to INH-associated DILI, the importance of HLA genetic variants has been increasingly recognized, whereas the role of polymorphisms of drug-metabolizing enzymes (NAT2 and CYP2E1) has become less important and remains controversial. However, these polymorphisms are merely correlative, and other molecular determinants of susceptibility have remained largely unknown. Regarding the drug-specific mechanisms underlying INH-induced liver injury, novel concepts have been emerging. Among these are covalent protein adduct formation via novel reactive intermediates, leading to hapten formation and a potential immune response, and interference with endogenous metabolism. Furthermore, INH and/or INH metabolites (e.g. hydrazine) can cause mitochondrial injury, which can lead to mitochondrial oxidant stress and impairment of energy homeostasis. Recent studies have revealed that underlying impairment of complex I function can trigger massive hepatocellular injury induced by otherwise nontoxic concentrations of INH superimposed on these mitochondrial deficiencies. This review discusses these emerging new paradigms of INH-induced DILI and highlights recent insights into the mechanisms, as well as points to the existing large gaps in our understanding of the pathogenesis.

Loss of von Hippel-Lindau protein (VHL) increases systemic cholesterol levels through targeting hypoxia-inducible factor 2α and regulation of bile acid homeostasis

Cholesterol synthesis is a highly oxygen-dependent process. Paradoxically, hypoxia is correlated with an increase in cellular and systemic cholesterol levels and risk of cardiovascular diseases. The mechanism for the increase in cholesterol during hypoxia is unclear. Hypoxia signaling is mediated through hypoxia-inducible factor 1α (HIF-1α) and HIF-2α. The present study demonstrates that activation of HIF signaling in the liver increases hepatic and systemic cholesterol levels due to a decrease in the expression of cholesterol hydroxylase CYP7A1 and other enzymes involved in bile acid synthesis. Specifically, activation of hepatic HIF-2α (but not HIF-1α) led to hypercholesterolemia. HIF-2α repressed the circadian expression of Rev-erbα, resulting in increased expression of E4BP4, a negative regulator of Cyp7a1. To understand if HIF-mediated decrease in bile acid synthesis is a physiologically relevant pathway by which hypoxia maintains or increases systemic cholesterol levels, two hypoxic mouse models were assessed, an acute lung injury model and mice exposed to 10% O2 for 3 weeks. In both models, cholesterol levels increased with a concomitant decrease in expression of genes involved in bile acid synthesis. The present study demonstrates that hypoxic activation of hepatic HIF-2α leads to an adaptive increase in cholesterol levels through inhibition of bile acid synthesis.

Isoniazid-induced cell death is precipitated by underlying mitochondrial complex I dysfunction in mouse hepatocytes

Isoniazid (INH) is an antituberculosis drug that has been associated with idiosyncratic liver injury in susceptible patients. The underlying mechanisms are still unclear, but there is growing evidence that INH and/or its major metabolite, hydrazine, may interfere with mitochondrial function. However, hepatic mitochondria have a large reserve capacity, and minor disruption of energy homeostasis does not necessarily induce cell death. We explored whether pharmacologic or genetic impairment of mitochondrial complex I may amplify mitochondrial dysfunction and precipitate INH-induced hepatocellular injury. We found that INH (≤ 3000 μM) did not induce cell injury in cultured mouse hepatocytes, although it decreased hepatocellular respiration and ATP levels in a concentration-dependent fashion. However, coexposure of hepatocytes to INH and nontoxic concentrations of the complex I inhibitors rotenone (3 μM) or piericidin A (30 nM) resulted in massive ATP depletion and cell death. Although both rotenone and piericidin A increased MitoSox-reactive fluorescence, Mito-TEMPO or N-acetylcysteine did not attenuate the extent of cytotoxicity. However, preincubation of cells with the acylamidase inhibitor bis-p-nitrophenol phosphate provided protection from hepatocyte injury induced by rotenone/INH (but not rotenone/hydrazine), suggesting that hydrazine was the cell-damaging species. Indeed, we found that hydrazine directly inhibited the activity of solubilized complex II. Hepatocytes isolated from mutant Ndufs4(+/-) mice, although featuring moderately lower protein expression levels of this complex I subunit in liver mitochondria, exhibited unchanged hepatic complex I activity and were therefore not sensitized to INH. These data indicate that underlying inhibition of complex I, which alone is not acutely toxic, can trigger INH-induced hepatocellular injury.

Protective effects of metallothionein on isoniazid and rifampicin-induced hepatotoxicity in mice

Isoniazid (INH) and Rifampicin (RFP) are widely used in the world for the treatment of tuberculosis, but the hepatotoxicity is a major concern during clinical therapy. Previous studies showed that these drugs induced oxidative stress in liver, and several antioxidants abated this effect. Metallothionein (MT), a member of cysteine-rich protein, has been proposed as a potent antioxidant. This study attempts to determine whether endogenous expression of MT protects against INH and RFP-induced hepatic oxidative stress in mice. Wild type (MT+/+) and MT-null (MT−/−) mice were treated intragastrically with INH (150 mg/kg), RFP (300 mg/kg), or the combination (150 mg/kg INH +300 mg/kg RFP) for 21 days. The results showed that MT−/− mice were more sensitive than MT+/+ mice to INH and RFP-induced hepatic injuries as evidenced by hepatic histopathological alterations, increased serum AST levels and liver index, and hepatic oxidative stress as evidenced by the increase of MDA production and the change of liver antioxidant status. Furthermore, INH increased the protein expression of hepatic CYP2E1 and INH/RFP (alone or in combination) decreased the expression of hepatic CYP1A2. These findings clearly demonstrate that basal MT provides protection against INH and RFP-induced toxicity in hepatocytes. The CYP2E1 and CYP1A2 were involved in the pathogenesis of INH and RFP-induced hepatotoxicity.