Nevirapine Biotransformation Insights: An Integrated In Vitro Approach Unveils the Biocompetence and Glutathiolomic Profile of a Human Hepatocyte-Like Cell 3D Model

The need for competent in vitro liver models for toxicological assessment persists. The differentiation of stem cells into hepatocyte-like cells (HLC) has been adopted due to its human origin and availability. Our aim was to study the usefulness of an in vitro 3D model of mesenchymal stem cell-derived HLCs. 3D spheroids (3D-HLC) or monolayer (2D-HLC) cultures of HLCs were treated with the hepatotoxic drug nevirapine (NVP) for 3 and 10 days followed by analyses of Phase I and II metabolites, biotransformation enzymes and drug transporters involved in NVP disposition. To ascertain the toxic effects of NVP and its major metabolites, the changes in the glutathione net flux were also investigated. Phase I enzymes were induced in both systems yielding all known correspondent NVP metabolites. However, 3D-HLCs showed higher biocompetence in producing Phase II NVP metabolites and upregulating Phase II enzymes and MRP7. Accordingly, NVP-exposure led to decreased glutathione availability and alterations in the intracellular dynamics disfavoring free reduced glutathione and glutathionylated protein pools. Overall, these results demonstrate the adequacy of the 3D-HLC model for studying the bioactivation/metabolism of NVP representing a further step to unveil toxicity mechanisms associated with glutathione net flux changes.

Determinants of virological outcome and adverse events in African children treated with paediatric nevirapine fixed-dose-combination tablets

BACKGROUND

Nevirapine is the only nonnucleoside reverse transcriptase inhibitor currently available as a paediatric fixed-dose-combination tablet and is widely used in African children. Nonetheless, the number of investigations into pharmacokinetic determinants of virological suppression in African children is limited, and the predictive power of the current therapeutic range was never evaluated in this population, thereby limiting treatment optimization.

METHODS

We analysed data from 322 African children (aged 0.3-13 years) treated with nevirapine, lamivudine, and either abacavir, stavudine, or zidovudine, and followed up to 144 weeks. Nevirapine trough concentration (Cmin) and other factors were tested for associations with viral load more than 100 copies/ml and transaminase increases more than grade 1 using proportional hazard and logistic models in 219 initially antiretroviral treatment (ART)-naive children.

RESULTS

Pre-ART viral load, adherence, and nevirapine Cmin were associated with viral load nonsuppression [hazard ratio = 2.08 (95% confidence interval (CI): 1.50-2.90, P < 0.001) for 10-fold higher pre-ART viral load, hazard ratio = 0.78 (95% CI: 0.68-0.90, P < 0.001) for 10% improvement in adherence, and hazard ratio = 0.94 (95% CI: 0.90-0.99, P = 0.014) for a 1 mg/l increase in nevirapine Cmin]. There were additional effects of pre-ART CD4 cell percentage and clinical site. The risk of virological nonsuppression decreased with increasing nevirapine Cmin, and there was no clear Cmin threshold predictive of virological nonsuppression. Transient transaminase elevations more than grade 1 were associated with high Cmin (>12.4 mg/l), hazard ratio = 5.18 (95% CI 1.95-13.80, P < 0.001).

CONCLUSION

Treatment initiation at lower pre-ART viral load and higher pre-ART CD4 cell percentage, increased adherence, and maintaining average Cmin higher than current target could improve virological suppression of African children treated with nevirapine without increasing toxicity.

Mechanisms of Drug-Induced Hepatotoxicity

Drug-induced hepatotoxicity (DIH) is a significant cause of acute liver failure and liver transplantation. Diagnosis is challenging due to the idiosyncratic nature, its presentation in the form of other liver disease, and the lack of a definite diagnostic criteria. Generation of reactive metabolites, oxidative stress, and mitochondrial dysfunction are common mechanisms involved in DIH. Certain risk factors associated with a drug and within an individual further predispose patients to DIH.

Antiretroviral drug toxicity in relation to pharmacokinetics, metabolic profile and pharmacogenetics

INTRODUCTION

Besides therapeutic effectiveness, drug tolerability is a key issue for treatments that must be taken indefinitely. Given the high prevalence of toxicity in HIV therapy, the factors implicated in drug-induced morbidities should be identified in order to improve the safety, tolerability and adherence to the treatments. Current approaches have focused almost exclusively on parent drug concentrations; whereas recent evidence suggests that drug metabolites resulting from complex genetic and environmental influences can also contribute to treatment outcome. Pharmacogenetic variations have shown to play a relevant role in the variability observed in antiretroviral drug exposure, clinical response and sometimes toxicity. The integration of pharmacokinetic, pharmacogenetic and metabolic determinants will more probably address current therapeutic needs in patients.

AREAS COVERED

This review offers a concise description of three classes of antiretroviral drugs. The review looks at the metabolic profile of these drugs and gives a comprehensive summary of the existing literature on the influence of pharmacogenetics on their pharmacokinetics and metabolic pathways, and the associated drug or metabolite toxicity.

EXPERT OPINION

Due to the high prevalence of toxicity and the related risk of low adherence to the treatments, association of kinetic, genetic and metabolic markers predictive of therapeutic or toxicity outcomes could represent a more complete approach for optimizing antiretroviral therapy.

The Combination of Anti-CTLA-4 and PD1-/- Mice Unmasks the Potential of Isoniazid and Nevirapine To Cause Liver Injury

Our laboratory recently reported what we believe is the first valid animal model of idiosyncratic drug-induced liver injury (IDILI) by treating PD1-/- mice with an anti-CTLA-4 antibody and amodiaquine (AQ). PD1 and CTLA-4 are important immune checkpoint receptors that are involved in inducing immune tolerance. This model was able to produce significant liver injury that looks very similar to the liver injury seen in humans. Although this model was shown to work with AQ, the question becomes whether blocking immune tolerance would unmask the potential of other drugs to cause IDILI. In this study, we tested isoniazid and nevirapine, both drugs with significant histories of causing IDILI in humans even though they do not cause significant injury in animals with doses that result in therapeutic blood levels. Both drugs in combination with these immune checkpoint inhibitors caused mild but significant delayed onset liver injury, which is similar to the mild injury that they can cause in humans. INH-induced liver injury in this model was associated with an increase in NK cells, while NVP-induced liver injury was associated with a greater increase in CD8 T cells. Although the liver injury caused by these drugs in this model was mild, these results suggest that impairing immune tolerance may be a general method for unmasking the potential of drugs to cause IDILI and therefore provide a screening tool for drug development.

Differences in nevirapine biotransformation as a factor for its sex-dependent dimorphic profile of adverse drug reactions

OBJECTIVES

Nevirapine is widely used for the treatment of HIV-1 infection; however, its chronic use has been associated with severe liver and skin toxicity. Women are at increased risk for these toxic events, but the reasons for the sex-related differences are unclear. Disparities in the biotransformation of nevirapine and the generation of toxic metabolites between men and women might be the underlying cause. The present work aimed to explore sex differences in nevirapine biotransformation as a potential factor in nevirapine-induced toxicity.

METHODS

All included subjects were adults who had been receiving 400 mg of nevirapine once daily for at least 1 month. Blood samples were collected and the levels of nevirapine and its phase I metabolites were quantified by HPLC. Anthropometric and clinical data, and nevirapine metabolite profiles, were assessed for sex-related differences.

RESULTS

A total of 52 patients were included (63% were men). Body weight was lower in women (P = 0.028) and female sex was associated with higher alkaline phosphatase (P = 0.036) and lactate dehydrogenase (P = 0.037) levels. The plasma concentrations of nevirapine (P = 0.030) and the metabolite 3-hydroxy-nevirapine (P = 0.035), as well as the proportions of the metabolites 12-hydroxy-nevirapine (P = 0.037) and 3-hydroxy-nevirapine (P = 0.001), were higher in women, when adjusted for body weight.

CONCLUSIONS

There was a sex-dependent variation in nevirapine biotransformation, particularly in the generation of the 12-hydroxy-nevirapine and 3-hydroxy-nevirapine metabolites. These data are consistent with the sex-dependent formation of toxic reactive metabolites, which may contribute to the sex-dependent dimorphic profile of nevirapine toxicity.

Pharmacokinetics of phase I nevirapine metabolites following a single dose and at steady state

Nevirapine is one of the most extensively prescribed antiretrovirals worldwide. The present analyses used data and specimens from two prior studies to characterize and compare plasma nevirapine phase I metabolite profiles following a single 200-mg oral dose of nevirapine in 10 HIV-negative African Americans and a steady-state 200-mg twice-daily dose in 10 HIV-infected Cambodians. Nevirapine was assayed by high-performance liquid chromatography (HPLC). The 2-, 3-, 8- and 12-hydroxy and 4-carboxy metabolites of nevirapine were assayed by liquid chromatography-tandem mass spectrometry (LC/MS/MS). Pharmacokinetic parameters were calculated by noncompartmental analysis. The metabolic index for each metabolite was defined as the ratio of the metabolite area under the concentration-time curve (AUC) to the nevirapine AUC. Every metabolite concentration was much less than the corresponding nevirapine concentration. The predominant metabolite after single dose and at steady state was 12-hydroxynevirapine. From single dose to steady state, the metabolic index increased for 3-hydroxynevirapine (P < 0.01) but decreased for 2-hydroxynevirapine (P < 0.001). The 3-hydroxynevirapine metabolic index was correlated with nevirapine apparent clearance (P < 0.001). These findings are consistent with induction of CYP2B6 (3-hydroxy metabolite) and a possible inhibition of CYP3A (2-hydroxy metabolite), although these are preliminary data. There were no such changes in metabolic indexes for 12-hydroxynevirapine or 4-carboxynevirapine. Two subjects with the CYP2B6 *6*6 genetic polymorphism had metabolic indexes in the same range as other subjects. These results suggest that nevirapine metabolite profiles change over time under the influence of enzyme induction, enzyme inhibition, and host genetics. Further work is warranted to elucidate nevirapine biotransformation pathways and implications for drug efficacy and toxicity.

Bioactivation of nevirapine to a reactive quinone methide: implications for liver injury

Nevirapine (NVP) treatment is associated with a significant incidence of liver injury. We developed an anti-NVP antiserum to determine the presence and pattern of covalent binding of NVP to mouse, rat, and human hepatic tissues. Covalent binding to hepatic microsomes from male C57BL/6 mice and male Brown Norway rats was detected on Western blots; the major protein had a mass of ~55 kDa. Incubation of NVP with rat CYP3A1 and 2C11 or human CYP3A4 also led to covalent binding. Treatment of female Brown Norway rats or C57BL/6 mice with NVP led to extensive covalent binding to a wide range of proteins. Co-treatment with 1-aminobenzotriazole dramatically changed the pattern of binding. The covalent binding of 12-hydroxy-NVP, the pathway that leads to a skin rash, was much less than that of NVP, both in vitro and in vivo. An analogue of NVP in which the methyl hydrogens were replaced by deuterium also produced less covalent binding than NVP. These data provide strong evidence that covalent binding of NVP in the liver is due to a quinone methide formed by oxidation of the methyl group. Attempts were made to develop an animal model of NVP-induced liver injury in mice. There was a small increase in ALT in some NVP-treated male C57BL/6 mice at 3 weeks that resolved despite continued treatment. Male Cbl-b(-/-) mice dosed with NVP had an increase in ALT of >200 U/L, which also resolved despite continued treatment. Liver histology in these animals showed focal areas of complete necrosis, while most of the liver appeared normal. This is a different pattern from the histology of NVP-induced liver injury in humans. This is the first study to report hepatic covalent binding of NVP and also liver injury in mice. It is likely that the quinone methide metabolite is responsible for NVP-induced liver injury.

Nevirapine pharmacokinetics and risk of rash and hepatitis among HIV-infected sub-Saharan African women

OBJECTIVES

To estimate nevirapine (NVP) pharmacokinetics and examine its association with rash and/or hepatotoxicity in women starting antiretroviral treatment in the AIDS Clinical Trials Group A5208/OCTANE study in Africa.

DESIGN

In HIV-infected, nonpregnant women with screening CD4 cell count less than 200 cells/μl randomized to NVP (twice daily, after 14-day once-daily lead-in period) and tenofovir/emtricitabine, single NVP blood samples were collected 14 and 28 days following randomization. Rash and hepatotoxicity that occurred during therapy, or within 7 days after the last dose of NVP, were defined as toxicity.

METHODS

NVP pharmacokinetics were modeled by population pharmacokinetic analysis. Individual Bayesian pharmacokinetic estimates were used to calculate clearance, 24-h area under the curve, and predicted plasma concentrations.

RESULTS

Median week 4 NVP clearance was 2 l/h. Among the 359 women, 194 (54%) developed a rash of any grade; 82 (23%) had grade 2+ and nine (3%) had grade 3+ rash. Median clearance was 1.7 l/h for participants exhibiting 3+ rash versus 2 l/h in women without 3+ rash (P = 0.046). The odds of developing 3+ rash was 50% higher for every 20% decrease in clearance (P = 0.046). NVP discontinuation due to rash/liver toxicity was significantly more common among women with pretreatment CD4 cell count more than 250 cells/μl (P = 0.003).

CONCLUSION

In this study, HIV-infected African women starting a NVP-based antiretroviral regimen had a lower NVP clearance compared to previous reports. Severe rash, but not hepatotoxicity, was associated with higher NVP exposure. Albeit observed in a small number of women, baseline CD4 cell count at least 250 cells/μl was significantly associated with NVP toxicity.

Persistent high nevirapine blood level with DRESS syndrome 12 days after interruption of antiretroviral therapy

Nevirapine is an antiretroviral agent associated with drug reaction with eosinophilia and systemic symptoms (DRESS) syndrome. Such a case in an immunocompetent woman recently treated with nevirapine for postexposure HIV prophylaxis is reported here. Despite a period of 12 days after interruption of treatment, a high blood level of nevirapine was still observed.

Demonstration of the metabolic pathway responsible for nevirapine-induced skin rash

The reverse transcriptase inhibitor, nevirapine (NVP), causes skin rashes and hepatotoxicity. We used a rat model to determine if the rash is caused by the parent drug or a reactive metabolite. By manipulation of metabolic pathways and testing analogues, we eliminated all but one pathway, 12-hydroxylation, which involves the oxidation of an exocyclic methyl group, as being responsible for the rash. Treatment with 12-OH-NVP caused a rash, and an analogue in which the methyl hydrogens were replaced by deuterium to inhibit the 12-OH pathway did not cause a rash; however, quite unexpectedly, blood levels of the deuterated analogue were very low. This is due to partitioning of the benzylic free radial intermediate between oxygen rebound to form 12-OH-NVP and loss of another hydrogen atom to form a reactive quinone methide, which inactivates P450. Cotreatment with the P450 inhibitor, 1-aminobenzotriazole, led to comparable levels of NVP and the deuterated analogue, and the deuterated analogue still caused a lower rash incidence. These data clearly point to the 12-hydroxy pathway being responsible for NVP skin rash. We propose that the hepatotoxicity of NVP in humans is due to the quinone methide formed by P450 in the liver, while the skin rash may be due to the quinone methide formed in the skin by sulfation of 12-OH metabolite followed by loss of sulfate. This is the first example in which a valid animal model of an idiosyncratic drug reaction was used to determine the metabolic pathway responsible for the reaction.

Current awareness: Pharmacoepidemiology and drug safety

In order to keep subscribers up‐to‐date with the latest developments in their field, John Wiley & Sons are providing a current awareness service in each issue of the journal. The bibliography contains newly published material in the field of pharmacoepidemiology and drug safety. Each bibliography is divided into 20 sections: 1 Reviews; 2 General; 3 Anti‐infective Agents; 4 Cardiovascular System Agents; 5 CNS Depressive Agents; 6 Non‐steroidal Anti‐inflammatory Agents; 7 CNS Agents; 8 Anti‐neoplastic Agents; 9 Haematological Agents; 10 Neuroregulator‐Blocking Agents; 11 Dermatological Agents; 12 Immunosuppressive Agents; 13 Autonomic Agents; 14 Respiratory System Agents; 15 Neuromuscular Agents; 16 Reproductive System Agents; 17 Gastrointestinal System Agents; 18 Anti‐inflammatory Agents ‐ Steroidal; 19 Teratogens/fetal exposure; 20 Others. Within each section, articles are listed in alphabetical order with respect to author. If, in the preceding period, no publications are located relevant to any one of these headings, that section will be omitted.