Hepatic Enzyme Induction Research Articles

Next Generation Risk Assessment to Address Disease-Related Vulnerability—A Proof of Concept for the Sunscreen Octocrylene

Risk assessment for cosmetics in the European Union (EU) are triggered by a ban on animal testing and concerns of endocrine disruption (ED). The risk assessment focuses on healthy populations and, for potential ED, includes specific developmental stages as vulnerable due to specific concerns on endocrine effects. However, the assessment focuses on healthy individuals and does not consider that some pathologies may increase dermal absorption and even vulnerability to endocrine disruptors. Data from the EU risk assessment, human pharmacokinetic studies and ToxCast bioactivity were combined in a hypothesis-driven Next-Generation Risk Assessment to identify possible risk drivers for vulnerable populations including oncological patients and atopic dermatitis. In vitro effects are observed at concentration in the order of measured plasmatic levels under normal use patterns. The induction of hepatic enzymes is the most relevant bioactivity endpoint, in line with animal findings. The information on endocrine potential is inconclusive, and the possibility for skin effects and endocrine mechanism linked to tumor induction require further elucidation. The information on octocrylene (CAS number: 6197-30-4) bioactivity is limited, lacking information on the metabolites and the immunotoxicity potential, particularly relevant for oncological patients.

Kinetically-derived maximal dose (KMD) confirms lack of human relevance for high-dose effects of octamethylcyclotetrasiloxane (D4)

The kinetically-derived maximal dose (KMD) is defined as the maximum external dose at which kinetics are unchanged relative to lower doses, e.g., doses at which kinetic processes are not saturated. Toxicity produced at doses above the KMD can be qualitatively different from toxicity produced at lower doses. Here, we test the hypothesis that high-dose-dependent toxicological effects of octamethylcyclotetrasiloxane (D4) occur secondary to kinetic overload. Octamethylcyclotetrasiloxane (D4) is a volatile, highly lipophilic monomer used to produce silicone polymers, which are ingredients in many consumer products and used widely in industrial applications and processes. Chronic inhalation at D4 concentrations 104 times greater than human exposures produces mild effects in rat respiratory tract, liver weight increase and pigment accumulation, nephropathy, uterine endometrial epithelial hyperplasia, non-significant increased uterine endometrial adenomas, and reduced fertility secondary to inhibition of rat-specific luteinizing hormone (LH) surge. Mechanistic studies indicate a lack of human relevance for most of these effects. Respiratory tract effects arise in rats due to direct epithelial contact with mixed vapor/aerosols and increased liver weight is a rodent-specific adaptative induction of drug-metabolizing hepatic enzymes. D4 is not mutagenic or genotoxic, does not interact with dopamine receptors, and interacts at ERα with potency insufficient to cause uterine effects or to alter the LH surge in rats. These mechanistic findings suggest high-dose-dependence of the toxicological effects secondary to kinetic overload, a hypothesis that can be tested when appropriate kinetic data are available that can be probed for the existence of a KMD. We applied Bayesian analysis with differential equations to information from kinetic studies on D4 to build statistical distributions of plausible values of the Km and Vmax for D4 elimination. From those distributions of likely Km and Vmax values, a set of Michaelis–Menten equations were generated that are likely to represent the slope function for the relationship between D4 exposure and blood concentration. The resulting Michaelis–Menten functions were then investigated using a change-point methodology known as the “kneedle” algorithm to identify the probable KMD range. We validated our Km and Vmax using out of sample data. Analysis of the Michaelis–Menten elimination curve generated from those Vmax and Km values indicates a KMD with an interquartile range of 230.0–488.0 ppm [2790–5920 mg/m3; 9.41–19.96 µM]. The KMD determined here for D4 is consistent with prior work indicating saturation of D4 metabolism at approximately 300 ppm [3640 mg/m3; 12.27 µM] and supports the hypothesis that many adverse effects of D4 arise secondary to high-dose-dependent events, likely due to mechanisms of action that cannot occur at concentrations below the KMD. Regulatory methods to evaluate D4 for human health protection should avoid endpoint data from rodents exposed to D4 above the KMD range and future toxicological testing should focus on doses below the KMD range.

Effects of One-Year Anti-seizure Treatment with Add-On Cenobamate on Bone Density and Bone Turnover in Adults with Drug-Resistant Focal Epilepsy: An Observational Study.

Cenobamate is a novel anti-seizure medication (ASM) with unusually high responder rates even in patients with refractory epilepsy. Due to its enzyme-inducing properties, cenobamate could negatively affect bone metabolism, similar to other ASMs; however, effects of long-term cenobamate treatment on bone health have not yet been investigated. The aim of this longitudinal observational study was to assess the effects of 1 year of continuous, adjunctive cenobamate treatment on bone health in patients with drug-resistant, focal epilepsy. Adult patients from a tertiary epilepsy centre received cenobamate add-on to their concomitant anti-seizure medication. Bone mineral density at femoral neck and lumbar spine, as well as bone formation biomarkers, electrolytes and liver enzymes in serum were assessed at baseline and after 12 months of continuous cenobamate therapy. Forty-seven patients (29 male, median age 40 years) were included in the study. Median daily dose of cenobamate at 12 months was 250 mg. Moderate, yet statistically significant reduction of the T-score at femoral neck but not lumbar spine was found after 1 year of cenobamate treatment, also in a subgroup of patients (n = 37) without enzyme inducers in the comedication. Additionally, we observed statistically significant changes in bone formation biomarkers: decreased serum level of osteocalcin and increased bone-specific alkaline phosphatase. Bone minerals (calcium and phosphorus) as well as vitamin D3 remained unchanged. Parathormone was statistically significantly reduced. There was a highly statistically significant increase in serum gamma-glutamyl transferase (GGT) levels after 12 months of treatment, reflecting an underlying hepatic enzyme induction by cenobamate. A statistically significant decrease of the T-score at femoral neck, as well as prominent alterations in the bone formation biomarkers, suggest an increase in bone turnover after 1 year of cenobamate treatment. The underlying mechanism is most likely attributed to the hepatic enzyme activation, indicated by a prominent elevation of serum GGT. The results alert for bone density control in susceptible patient groups. DRKS00027568, March 2, 2022 retrospectively registered.

Hepatic enzyme induction and its potential effect on thyroid hormone metabolism in the metamorphosing tadpole of Xenopus laevis (African clawed frog).

Hepatic enzyme induction, an inherent defense system against xenobiotics, is known to simultaneously affect endocrine system functions in mammals under specific conditions, particularly thyroid hormone (TH) regulation. While this phenomenon has been studied extensively, the pathway leading to this indirect thyroid effect in mammals has unclear applicability to amphibians, despite the importance of amphibian species in assessing thyroid-disruptive chemicals. Here, we investigated the effects of three well-known mammalian enzyme inducers-β-naphthoflavone (BNF), pregnenolone carbonitrile (PCN), and sodium phenobarbital (NaPB)-on the gene expression of phase-I and phase-II metabolizing enzymes in Xenopus laevis tadpoles. Waterborne exposure to BNF and PCN significantly induced the expression of both phase-I (cytochrome P450, CYP) and phase-II enzymes (UDP-glucuronosyltransferase, UGT and sulfotransferase, SULT), but in different patterns, while NaPB exposure induced CYP2B expression without affecting phase-II enzymes in tadpoles, in contrast to mammals. Furthermore, an ex vivo hepatic enzyme activity assay confirmed that BNF treatment significantly increased phase-II metabolic activity (glucuronidation and sulfation) toward TH. These results suggest the potential for certain mammalian enzyme inducers to influence TH clearance in X. laevis tadpoles. Our findings provide insights into the profiles of xenosensing activity and enzyme induction in amphibians, which can facilitate a better understanding of the mechanisms of indirect effects on the thyroid system via hepatic enzyme induction in nonmammalian species.

Coadministration of Voriconazole and Rifabutin Can Increase the Risk of Adverse Drug Reactions in Patients with Multiple Infections.

Coinfection of tuberculosis or nontuberculous mycobacteria and Aspergillus presents a challenge in medication selection because of the pharmacokinetic interactions between rifampin and voriconazole. Some researchers have suggested the use of rifabutin as an alternative to rifampin because of its lower hepatic cytochrome P450 enzyme induction potency despite its contraindication to drug labels. This study presents clinical cases of voriconazole and rifabutin coadministration and their potential risks. This retrospective study was conducted using clinical data from patients who met the following criteria: (1) admitted to Seoul National University Hospital between July 2014 and August 2023 and (2) concurrently administered rifabutin and voriconazole for more than 5 days. Among the 6 patients analyzed, 4 experienced adverse drug reactions (ADRs). Three patients experienced visual and auditory hallucinations, lower extremity numbness, or delirious behavior. Two patients had prolonged the time from the start of the Q wave to the end of the T wave intervals, and 1 had elevated aspartate aminotransferase and alanine aminotransferase levels. In addition, 2 patients experienced severe nausea, poor oral intake, and weight loss. Despite receiving 1.81-fold the recommended voriconazole dosage, a therapeutic concentration (1.0-5.5 mg/L) was not achieved because of cytochrome P450 induction by rifabutin. However, during septic shock, the voriconazole concentration increased by 13.7- to 36-fold. Concurrent use of rifabutin and voriconazole was associated with ADRs, including the time from the start of the Q wave to the end of the T wave prolongation, hallucinations, and severe nausea. Moreover, initially, there was a significant decrease in voriconazole concentrations; however, these concentrations substantially increased during septic shock. Therefore, it is essential to monitor drug concentrations and ADRs during concurrent use of voriconazole and rifabutin.

Rifampin – Risperidone and Divalproex Drug-drug Interaction: A Case Report

Rifampin is a potent hepatic cytochrome enzyme inducer, promoting the metabolism of many drugs. Here, we describe a case wherein rifampin-induced drug interactions affected the clinical improvement of a patient on psychiatric drugs for bipolar disorder. He was administered divalproex, risperidone, quetiapine, and clonazepam, along with anti-tuberculosis drugs HERZ, containing 600 mg rifampin. Despite taking 900 mg/day divalproex, his serum valproate levels were below 2 μg/ml, and his manic symptom persisted. Therefore, the antipsychotic risperidone (5 mg) was replaced with olanzapine (20 mg). Following this, his manic symptoms improved rapidly. Rifampin is a potent CYP3A and CYP2D6 inducer and is known to significantly reduce serum risperidone levels. Thus, even a high dose of risperidone did not induce a significant clinical effect, which was observed immediately after replacing with olanzapine. Therefore, drug interactions may have had a significant effect on clinical outcomes. Clinicians should be cognizant of drug interactions when treating psychiatric patients on rifampin therapy. The case has been sufficiently revised to protect the patient's personal information.

Treatment of Tuberculosis in special situations

Treatment of Tuberculosis in special situations implies overcoming special challenges in patients with diabetes, pregnant women, people aged over 65 years, and those with chronic kidney or liver disease.Rifampicin is a potent hepatic enzyme inducer, may lower plasma levels of sulphonyl urea and can increase the hypoglycemic effect of metformin. Since insulin is not metabolized, no pharmacokinetic interactions with anti-TB drugs occur. Gastrointestinal upset and hepatitis are reported as the most frequent adverse events in older people. In patients >80 years,pyrazinamide may be omitted. In TB patients with chronic kidney disease (CKD), an inappropriate dosage of anti-TB drugs can result in unsuccessful treatment or side effects. Current guidelines for first-line anti-TB drugs therefore recommend that dosages of ethambutol (EMB) and pyrazinamide (PZA) be adjusted according to patient renal function and body weight, although no change in dosage is necessary for patients with mild renal insufficiency . However, it remains unknown how the renal function-based dosage adjustments recommended by the guidelines affect efficacy outcomes for TB patients with CKD. In chronic liver disease (CLD) patients, The Child–Turcotte–Pugh (CTP) score can be used as a guide for designing appropriate regimens. In stable CLD (CTP d”7), a treatment regimen including isoniazid, rifampicin, and ethambutol is recommended, a 2-month intensive phase with the three drugs, followed by isoniazid and rifampicin continuation phase for 7 months partially liver-sparing regimen consisting of Ethambutol, Rifampicin, and a quinolone for 9 months is advisable in case of more severe CLD (CTP 8–10).If CLD is very advanced (CTP £11), a total liver-sparing regimen consisting of Ethambutol and a quinolone (Levofloxacin or Moxifloxacin) for 12 months. Bangladesh J Medicine 2023; Vol. 34, No. 2(1) Supplement: 196-197

3D Spheroid Primary Human Hepatocytes for Prediction of Cytochrome P450 and Drug Transporter Induction.

Primary human hepatocytes (PHHs) have been the gold standard in vitro model for the human liver and are crucial to predict hepatic drug-drug interactions. The aim of this work was to assess the utility of 3D spheroid PHHs to study induction of important cytochrome P450 (CYP) enzymes and drug transporters. 3D spheroid PHHs from three different donors were treated for four days with rifampicin, dicloxacillin, flucloxacillin, phenobarbital, carbamazepine, efavirenz, omeprazole or β-naphthoflavone. Induction of CYP1A1, CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP3A4, and transporters P-glycoprotein (P-gp)/ABCB1, multidrug resistance-associated protein 2 (MRP2)/ABCC2, ABCG2, organic cation transporter 1 (OCT1)/SLC22A1, SLC22A7, SLCO1B1 and SLCO1B3 were evaluated at mRNA and protein levels. Enzyme activity of CYP3A4, CYP2B6, CYP2C19 and CYP2D6 were also assessed. Induction of CYP3A4 protein and mRNA correlated well for all donors and compounds and had a maximal induction of 5- to 6-fold for rifampicin, which closely correlates to induction observed in clinical studies. Rifampicin induced the mRNA of CYP2B6 and CYP2C8 by 9- and 12-fold, while the protein levels of these CYPs reached 2- and 3-fold induction, respectively. Rifampicin induced CYP2C9 protein by 1.4-fold, while the induction of CYP2C9 mRNA was over 2-fold in all donors. Rifampicin induced ABCB1, ABCC2 and ABCG2 by 2-fold. In conclusion, 3D spheroid PHHs is a valid model to investigate mRNA and protein induction of hepatic drug-metabolizing enzymes and transporters, and this model provides a solid basis to study induction of CYPs and transporters, which translates to clinical relevance.

Phenobarbital, a hepatic metabolic enzyme inducer, inhibits preneoplastic hepatic lesions with expression of selective autophagy receptor p62 and ER-phagy receptor FAM134B in high-fat diet-fed rats through the inhibition of ER stress.

We investigated the role of endoplasmic reticulum (ER)-phagy in NAFLD-related hepatocarcinogenesis in high-fat diet (HFD)-fed and/or phenobarbital (PB)-treated rats by clustering the expression levels of the selective autophagy receptor p62 and the ER-phagy-specific receptor FAM134B in preneoplastic hepatic lesions. We obtained four clusters with variable expression levels of p62 and FAM134B in preneoplastic lesions, and a variable population of clusters in each group. PB administration increased the clusters with high expression levels of p62 while HFD feeding increased the clusters with high expression levels of both p62 and FAM134B. The areas of preneoplastic lesions of these clusters were significantly increased than those of other clusters with low expression levels of p62 and FAM134B. The combination of HFD feeding with PB counteracted the effects of each other, and the cluster composition was similar to that in the control group. The results were associated with decreased gene expression of ER stress, inflammatory cytokine, autophagy, and increased expression of antioxidant enzyme. The present study demonstrated that clustering analysis is useful for understanding the role of autophagy in each preneoplastic lesion, and that HFD feeding increased preneoplastic lesions through the inhibition of ER-phagy, which was cancelled with PB administration through the induction of ER-phagy.

PD29 Systematic Review With Meta-analysis Of Pharmacokinetic Parameters Of Tyrosine Kinase Inhibitors Used In Chronic Myeloid Leukemia

IntroductionTherapeutic drug monitoring (TDM) is a cost-effective tool to increase treatments’ efficacy and safety. Analyses of pharmacokinetics proprieties of tyrosine kinase inhibitors (TKI) used for chronic myeloid leukemia (CML) can contribute towards effective TDM, development of tailored treatments and new dosing regimens. We aimed to synthesize the available evidence on pharmacokinetic parameters of imatinib, nilotinib, bosutinib, ponatinib in healthy individuals vs. CML patients.MethodsSystematic searches were conducted in PubMed, Scopus and Web of Science. We included in vivo studies addressing TKIs’ pharmacokinetics, including maximum observed concentration (Cmax), time of maximum observed concentration (Tmax) and half-life (t1/2). Meta-analyses of event rates (mixed-effect models) were performed for the parameters of interest: area under the concentration-time curve from time zero to the last measurable concentration (AUC0-t) and from time zero to infinity (AUC 0-∞). Results were presented as event rates with 95 percent confidence intervals. Heterogeneity was assessed using chi-square and I2 statistical tests and considered significant when p<0.05 and high when I2>75 percent (Comprehensive Meta-Analysis v.2 Biostat-Englewood, NJ).ResultsOverall, 50 articles were included for analyses (n=26 imatinib, n=11 nilotinib, n=8 bosutinib, n=5 ponatinib). Most studies were performed in the United States (46.0%), designed as open-label trials (70.0%). Several significant interactions between TKI with enzyme inhibitors (ketoconazole, midazolam, aprepitant, metoprolol, grapefruit juice), proton pump inhibitors (esomeprazole, lanzoprazole, omeprazole), antacids, H2 antagonists (famotidine) and enzyme inducers (St. John’s, rifampicin) were found (p<0.001). Given the significant increase in AUC and Cmax in patients with hepatic/liver impairments currently using TKI, strict therapeutic monitoring is paramount to maintain safety. The between study heterogeneity was rated as moderate to high (I2=75-90%) due the limited number of trials for some drugs, different study design, and populations.ConclusionsThe co-administration of TKI with hepatic enzyme inducers or inhibitors, proton pump inhibitors, antacids, H2 antagonists, as well as in patients with hepatic/liver failures requires caution and additional monitoring. Further well-designed trials are needed to strengthen this evidence for some TKIs, namely bosutinib and ponatinib.

LBODP105 A Case of Significantly Increased Levothyroxine Requirement With Rifampin Therapy

Abstract Introduction Rifampin has a wide range of drug interactions through increased hepatic microsomal enzyme activity. We are reporting a case of a patient with post-surgical hypothyroidism on stable thyroid hormone replacement therapy who required significantly higher doses of levothyroxine after starting rifampin. Case Report Patient is a 78-year-old woman with history of Papillary Thyroid Cancer (PTC) in remission status post thyroidectomy in 1994 and radioactive iodine therapy in 1997. Patient had been on a stable dose of Levothyroxine of 75-88mcg daily until a visit in January 2013 when her TSH was found to be 39 despite compliance with levothyroxine. Further history revealed that she was diagnosed with Mycobacterium Avium Intracellulare (MAI) infection of the lungs for which she was given rifampin therapy. Her Levothyroxine dose was progressively increased to 150mcg daily. She received rifampin therapy for 18 months, from August 2012 until April 2013. Her Levothyroxine dose was later changed to average 139 mcg /day based on TSH levels and continued to be the same through the rifampin course. In April 2014, and following discontinuation of rifampin, Levothyroxine was decreased to 100mcg daily and subsequently 75mcg daily. During a relapse of MAI in March 2016, her levothyroxine dosage was similarly again increased to 125mcg daily for TSH of 24.58. In June 2017, rifampin was discontinued after completion of second course of MAI treatment, and Levothyroxine dose decreased to 88 mcg daily, and subsequently 75 mcg in September 2017, and average daily 64mcg most recently given age and long-term remission with target mid normal TSH. Discussion Rifampin is used to treat active tuberculosis and MAI infection among other uses. It is a hepatic enzyme inducer which significantly interacts with other drugs. It has been reported previously to cause hypothyroidism in patients with underlying thyroid disorder and increased serum TSH while on levothyroxine, but its impact range on thyroid function has not been clearly described. Our patient was on stable levothyroxine dose following thyroidectomy, and required almost a 100% increase of levothyroxine dose when started on rifampin therapy, returning to baseline levothyroxine requirements off rifampin. This case highlights the severe hypothyroidism and significant impact on levothyroxine dose requirements following rifampin therapy, and the importance of close thyroid function monitoring in patients with hypothyroidism and on rifampin, especially in context of post-surgical hypothyroidism. Presentation: No date and time listed

Massive adrenocortical carcinoma presenting as peripheral edema: a case report

BackgroundAdrenocortical carcinoma is a rare, but potentially lethal, malignancy that is usually detected as an incidental finding on abdominal imaging studies or owing to hormonal complications. This report recounts an unusual presentation with leg edema due to compression of the inferior vena cava. The dearth of proven effective treatment is also addressed.Case presentationA 65-year-old White male physician presented with severe, bilateral pitting edema that extended from the toes to the thighs. It progressed over several months. He also experienced paroxysmal dyspnea. Evaluation of cardiac, hepatic, and renal function failed to determine a cause. Computed tomography revealed a tumor above the right kidney, with compression of the intrahepatic inferior vena cava and upstream distension. Serum cortisol and dehydroepiandrosterone sulfate concentrations were elevated, 24-hour urinary cortisol level was elevated, and serum adrenocorticotropic hormone and testosterone concentrations were suppressed. A 27-cm tumor, the right lobe of the liver, the right kidney, and 26 lymph nodes were resected. Histological study confirmed the diagnosis of adrenocortical carcinoma. Ki67 proliferation index was 26.7% (worse prognosis associated with index > 10%). Lymph nodes were negative for malignancy, but a separate 2.7-cm tumor was found near the renal hilum. Adjuvant mitotane chemotherapy was prescribed. Serum testosterone concentration returned to normal. High-dose hydrocortisone administration was needed because of adrenal suppression and CYP 3A4 induction by mitotane.ConclusionImaging of the abdomen and pelvis should be conducted in cases of unexplained leg edema. In this case, a large adrenal cancer compressed the vena cava. Iron deficiency followed resection of the large tumor. Advanced stages of adrenocortical carcinoma are associated with poor prognosis. Mitotane chemotherapy is a standard but unproven adjuvant treatment that is associated with many complications, and its induction of hepatic CYP 3A4 enzymes necessitates adjustment of other medications.

Treatment of epilepsy associated with primary and metastatic brain tumors

There is a number of unsolved issues in management of epilepsy associated with primary and metastatic brain tumors (BTs). In particular, no consensus approaches to treatment of patients with epilepsy associated with BTs have been proposed regarding use of current anti-epileptic drugs (AEDs). The review presents the relevant data on epidemiology, features of clinically manifested epilepsy at varying stages of BTs, aspects of drug-drug interaction between AEDs and anti-tumor agents, AED-related effects on cognitive functions as well as quality of life in patients with epilepsy associated with BTs. Levetiracetam and valproic acid comprise the first-line drugs for treating seizures in patients with BTs. It is unreasonable to use AEDs acting as hepatic microsomal enzyme inducers for therapy of epileptic seizures in BTs, because it may decrease efficacy of chemotherapy agents and glucocorticoids along with elevated rate of side effects. Perampanel acting as a selective noncompetitive AMPA receptor antagonist, may be one of the drugs of choice for the adjunctive therapy of epileptic seizures associated with BTs.

Evaluation of the effect of phenobarbital administration on the biochemistry profile, with a focus on serum liver values, in epileptic cats.

Phenobarbital (PB) is the most common antiseizure drug (ASD) used for the management of feline epilepsy. In dogs, PB is known to cause serum liver enzyme induction and hepatotoxicity, especially after administration long term or in high concentrations. In cats, insufficient evidence is available to draw similar conclusions. The aim of this study was to evaluate the effect of PB administration on the serum biochemistry profile of epileptic cats. As an additional objective, other adverse effects arising, related to PB treatment, were recorded. Medical records of four veterinary centres were retrospectively reviewed for epileptic cats receiving PB treatment. Cats were included if they had a diagnosis of idiopathic epilepsy or structural epilepsy; a normal baseline serum biochemistry profile; at least one follow-up serum biochemistry profile; no concurrent disease or had not received medication that could possibly influence liver function or lead to serum liver enzyme induction. Alkaline phosphatase, alanine aminotransferase (ALT), aspartate transaminase and gamma-glutamyl transferase activities, and total bilirubin, bile acids, glucose, albumin, total protein, urea and creatinine concentrations before and during PB administration were recorded. PB serum concentration was also recorded, when available. Thirty-three cats (24 males, nine females) with a median age of 3 years (range 2 months to 12 years) met the inclusion criteria. Idiopathic or structural epilepsy was diagnosed in 25 (76%) and eight (24%) cats, respectively. The follow-up period ranged from 9 to 62 months. This study found an increase in ALT in three cats, possibly related to a PB serum concentration >30 µg/ml. No statistically significant increase in serum liver enzymes or other evaluated biochemistry parameters was found by comparing pre- and post-treatment parameters. PB administration did not result in hepatic enzyme induction or other biochemical abnormalities in cats. This strengthens the safety profile of PB as an ASD in cats.

Effects of Xiaochaihu decoction on the expression of cytochrome P450s in rats.

Xiaochaihu decoction is one of the most important traditional Chinese medicines that is widely used with other drugs in clinical practice, and may cause drug-drug interactions. However, there is not sufficient experimental evidence for the effects of Xiaochaihu decoction on cytochrome P450s (CYPs). The aim of the present study was to investigate the effects of Xiaochaihu decoction on the mRNA and protein levels of hepatic CYPs. Eighty normal male Sprague-Dawley (SD) rats were randomly divided into two groups based on body weight and duration of drug administration (3 and 6 days). Each group was further divided into subgroups: Control group (2 ml 5‰ CMC-Na); hepatic enzyme inducer group (50 mg/kg/day rifampicin); and experimental groups (Xiaochaihu decoction: Low dose, 1.7 g/kg/day; medium dose, 3.4 g/kg/day; high dose, 6.8 g/kg/day). The effects of Xiaochaihu decoction on Cyp1a2, Cyp3a1, Cyp2d6, and Cyp1b1 mRNA and protein expression in rats were evaluated using reverse transcription quantitative reverse transcription polymerase chain reaction and western blot analysis. After 3 days, medium dose of Xiaochaihu decoction inhibited the mRNA and protein expression of Cyp1a2, Cyp3a1 and Cyp1b1. In addition, after 6 days, Xiaochaihu decoction induced Cyp3a1 mRNA expression at low and medium doses; Cyp2d6 mRNA expression at low and high doses; and Cyp2d6 protein expression at high doses. Nonetheless, the gene and protein expression of Cyp1b1 was not affected at any dose. The findings of the present study may provide insights into potential drug-drug interactions associated with Xiaochaihu decoction.

Levofloxacin based non-rifampicin anti-tuberculous therapy: An effective alternative in renal transplant recipients in resource limited setting.

Rifampicin is one of the most effective components of anti-tuberculous therapy (ATT). Since rifampicin is a hepatic enzyme (CYP3A4) inducer, in a post-renal transplant recipient, the dose of calcineurin inhibitors needs to be up-regulated and frequently monitored. In resource-limited (low- and lower-middle-income countries) setting this is not always feasible. Therefore, we evaluated a non-rifampicin-based ATT using levofloxacin in kidney transplant recipients. We retrospectively studied the medical records of renal transplant recipients diagnosed with tuberculosis in our institute between 2014 and 2017. After a brief discussion with patients regarding the nature and course of ATT, those who opted for a non-rifampicin based therapy due to financial constraints were included in the study and followed for a minimum of 6 months period after the completion of ATT. Out of the 550 renal transplant recipients, 67 (12.2%) developed tuberculosis after a median period of 24 (1-228) months following transplantation, of them, 64 patients opted for non-rifampicin-based ATT. The mean age was 37.6 years. Only 25% were given anti-thymocyte globulin based induction, while the majority (56; 87.5%) of them were on tacrolimus-based triple-drug maintenance therapy. Extrapulmonary tuberculosis was noted in 33% of cases, while 12 (18.7%) had disseminated disease. The median duration of treatment was 12 months and the cure rate of 93.7% (n = 60) was achieved at the end of therapy. Levofloxacin based ATT appears to be a safe and effective alternative of rifampicin in kidney transplant recipients who cannot afford heightened tacrolimus dosage.

Species differences in phenobarbital-mediated UGT gene induction in rat and human liver microtissues.

Species differences in hepatic metabolism of thyroxine (T4) by uridine diphosphate glucuronosyl transferase (UGT) and susceptibility to thyroid hormone imbalance could underlie differences in thyroid carcinogenesis caused by hepatic enzyme inducers in rats and humans. To investigate this hypothesis we examined profiles of hepatic UGT induction by the prototypical CAR activator phenobarbital (PB) in rat and human liver 3D microtissues. The rationale for this approach was that 3D microtissues would generate data more relevant to humans. Rat and human liver 3D microtissues were exposed to PB over a range of concentrations (500 u M - 2000 u M) and times (24-96 hr). Microarray and proteomics analyses were performed on parallel samples to generate integrated differentially expressed gene (DEG) datasets. Bioinformatics analysis of DEG data, including CAR response element (CRE) sequence analysis of UGT promoters, was used to assess species differences in UGT induction relative to CAR-mediated transactivation potential. A higher proportion of human UGT promoters were found to contain consensus CREs compared to the rat homologs. UGTs 1a6, 2b17 and 2b37 were upregulated by PB in rat liver 3D microtissues, but unaltered in human liver 3D microtissues. By contrast, human UGTs 1A8, 1A10 and 2B10 showed higher levels of induction (RNA and /or protein) compared to the rat homologs. There was general concordance between the presence of CREs and the induction of UGT RNA. As UGT1A and 2B isoforms metabolise T4, these results suggest that differences in UGT induction could contribute to differential susceptibility to CAR-mediated thyroid carcinogenesis in rats and humans.

T4-mediated rescue of aortic malformations in hypothyroid rats indicates maternal thyroid status can affect great vessel development

Pexacerfont is a corticotrophin-releasing factor subtype 1 receptor (CRF-1) antagonist developed for potential treatment of anxiety and stress-related disorders. In male rats, pexacerfont caused hepatic enzyme induction leading to increased thyroxine (T4) clearance. When administered to pregnant rats on gestation day 6 to 15, pexacerfont at 300 mg/kg/day (30× mean AUC in humans at 100 mg/day) produced similar effects on thyroid homeostasis with serum T4 and thyroid-stimulating hormone levels that were 0.3–0.5× and 3.3–3.7× of controls, respectively. At this dose, fetuses of pexacerfont-treated dams presented findings associated with maternal hypothyroidism including growth retardation and increased skeletal alterations. Additionally, there were unexpected great vessel malformations that were mostly derived from the 4th pharyngeal arch artery in 5 (4.3%) fetuses from 3 (15.8%) litters. The etiology was unclear whether the vascular malformations were related to insufficient thyroid hormones or another mechanism. To better understand this relationship, pregnant rats were implanted with a subcutaneous L-thyroxine pellet designed to provide a sustained release of T4 throughout organogenesis in rat embryos (GD 6 to 15; the dosing period of pexacerfont). T4 supplementation produced a near euthyroid state in pexacerfont-treated dams and completely prevented the fetal vascular malformations. These results suggest maternal T4 levels during organogenesis may have a role in great vessel morphogenesis associated with patterning and/or regression of pharyngeal arch arteries. Although previous clinical reports have speculated a potential relationship between thyroid hormone homeostasis and early cardiovascular development, this is the first report to experimentally demonstrate this relationship in great vessel morphogenesis.

Nrf2 in liver toxicology

Liver plays essential roles in the metabolism of many endogenous chemicals and exogenous toxicants. Mechanistic studies in liver have been at the forefront of efforts to probe the roles of bioactivation and detoxication of environmental toxins and toxicants in hepatotoxicity. Moreover, idiosyncratic hepatoxicity remains a key barrier in the clinical development of drugs. The now vast Nrf2 field emerged in part from biochemical and molecular studies on chemical inducers of hepatic detoxication enzymes and subsequent characterization of the modulation of drug/toxicant induced hepatotoxicities in mice through disruption of either Nrf2 or Keap1 genes. In general, loss of Nrf2 increases the sensitivity to such toxic chemicals, highlighting a central role of this transcription factor and its downstream target genes as a modifier to chemical stress. In this review, we summarize the impact of Nrf2 on the toxicology of multiple hepatotoxicants, and discuss efforts to utilize the Nrf2 response in predictive toxicology.

Toxicity of Pexacerfont, a Corticotropin-Releasing Factor Type 1 Receptor Antagonist, in Rats and Dogs.

Pexacerfont is a corticotropin-releasing factor subtype 1 receptor antagonist that was developed for the treatment of anxiety- and stress-related disorders. This report describes the results of repeat-dose oral toxicity studies in rats (3 and 6 months) and dogs (3 months and 1 year). Pexacerfont was well tolerated in all of these studies at exposures equal to or greater than areas under the curve in humans (clinical dose of 100 mg). Microscopic changes in the liver (hepatocellular hypertrophy), thyroid glands (hypertrophy/hyperplasia and adenomas of follicular cells), and pituitary (hypertrophy/hyperplasia and vacuolation of thyrotrophs) were only observed in rats and were considered adaptive changes in response to hepatic enzyme induction and subsequent alterations in serum thyroid hormone levels. Evidence for hepatic enzyme induction in dogs was limited to increased liver weights and reduced thyroxine (T4) levels. Mammary gland hyperplasia and altered female estrous cycling were only observed in rats, whereas adverse testicular effects (consistent with minimal to moderate degeneration of the germinal epithelium) were only noted following chronic dosing in dogs. The testicular effects were reversible changes with exposure margins of 8× at the no observed adverse effect level. It is not clear whether the changes in mammary gland, estrous cycling, and testes represent secondary hormonal changes due to perturbation of the hypothalamic-pituitary-adrenal axis or are off-target effects. In conclusion, the results of chronic toxicity studies in rats and dogs show that pexacerfont has an acceptable safety profile to support further clinical testing.