The pregnane X receptor in tuberculosis therapeutics

Therapeutic Potential of Morin Hydrate Against Rifampicin Induced Hepato and Renotoxicity in Albino Wistar Rats: Modulation of Organ Function, Oxidative Stress and Inflammatory Response

Tuberculosis (TB) is a challenging public health issue, particularly in poor and developing countries. Rifampicin (RIF) is one of the most common first-line anti-TB drugs but it is known for its adverse effects on the hepato-renal system. The present study investigated the efficacy of morin hydrate (MH) in protecting hepato-renal damage inflicted by RIF in rats. RIF (50 mg/kg), and a combination of RIF (50 mg/kg) and MH (50 mg/kg) were administered orally for 4 weeks in rats. Silymarin (50 mg/kg) was used as a positive control. Increased levels of serological parameters such as AST, ALT, ALP, LDH, GGT, bilirubin, triglyceride, total cholesterol, urea, uric acid, creatinine, TNF-α, IFN-γ, IL-6 along with the decreased level of IL-10, total protein and albumin were used as markers of hepatic and renal injury. Oxidative damage in the tissues was measured by the increase in lipid peroxidation and decline in GSH, SOD and catalase activities. Histopathology of liver slices was used to study hepatic architecture. Four-week RIF treatment produced altered serological parameters with an increase in pro-inflammatory cytokines in serum suggesting hepatotoxicity and nephrotoxicity. The antioxidant status of the liver and kidney (increased lipid peroxidation and decline in GSH, SOD and catalase) was compromised. Cellular damage and necrosis were observed in liver slices. MH supplementation with RIF improved hepato-renal functions by restoring the serum and tissue markers towards normal values. Histological observations authenticated the results. MH supplementation also reduced the production of pro-inflammatory cytokines. Thus, the results revealed that MH provides protection against RIF-induced hepato-renal injury.

Microbial Metabolites as Ligands to Xenobiotic Receptors: Chemical Mimicry as Potential Drugs of the Future

Xenobiotic receptors, such as the pregnane X receptor, regulate multiple host physiologic pathways including xenobiotic metabolism, certain aspects of cellular metabolism, and innate immunity. These ligand-dependent nuclear factors regulate gene expression via genomic recognition of specific promoters and transcriptional activation of the gene. Natural or endogenous ligands are not commonly associated with this class of receptors; however, since these receptors are expressed in a cell-type specific manner in the liver and intestines, there has been significant recent effort to characterize microbially derived metabolites as ligands for these receptors. In general, these metabolites are thought to be weak micromolar affinity ligands. This journal anniversary minireview focuses on recent efforts to derive potentially nontoxic microbial metabolite chemical mimics that could one day be developed as drugs combating xenobiotic receptor-modifying pathophysiology. The review will include our perspective on the field and recommend certain directions for future research. SIGNIFICANCE STATEMENT: Xenobiotic receptors (XRs) regulate host drug metabolism, cellular metabolism, and immunity. Their presence in host intestines allows them to function not only as xenosensors but also as a response to the complex metabolic environment present in the intestines. Specifically, this review focuses on describing microbial metabolite-XR interactions and the translation of these findings toward discovery of novel chemical mimics as potential drugs of the future for diseases such as inflammatory bowel disease.

Alternatives to rifampicin: A review and perspectives on the choice of strong CYP3A inducers for clinical drug-drug interaction studies

N-Nitrosamine (NA) impurities are considered genotoxic and have gained attention due to the recall of several marketed drug products associated with higher-than-permitted limits of these impurities. Rifampicin is an index inducer of multiple cytochrome P450s (CYPs) including CYP2B6, 2C8, 2C9, 2C19, and 3A4/5 and an inhibitor of OATP1B transporters (single dose). Hence, rifampicin is used extensively in clinical studies to assess drug-drug interactions (DDIs). Despite NA impurities being reported in rifampicin and rifapentine above the acceptable limits, these critical anti-infective drugs are available for therapeutic use considering their benefit-risk profile. Reports of NA impurities in rifampicin products have created uncertainty around using rifampicin in clinical DDI studies, especially in healthy volunteers. Hence, a systematic investigation through a literature search was performed to determine possible alternative index inducer(s) to rifampicin. The available strong CYP3A inducers were selected from the University of Washington DDI Database and their in vivo DDI potential assessed using the data from clinical DDI studies with sensitive CYP3A substrates. To propose potential alternative CYP3A inducers, factors including lack of genotoxic potential, adequate safety, feasibility of multiple dose administration to healthy volunteers, and robust in vivo evidence of induction of CYP3A were considered. Based on the qualifying criteria, carbamazepine, phenytoin, and lumacaftor were identified to be the most promising alternatives to rifampicin for conducting CYP3A induction DDI studies. Strengths and limitations of the proposed alternative CYP3A inducers, the magnitude of in vivo CYP3A induction, appropriate study designs for each alternative inducer, and future perspectives are presented in this paper.

Pregnane X Receptor and the Gut-Liver Axis: A Recent Update

It is well-known that the pregnane X receptor (PXR)/Nr1i2 is a critical xenobiotic-sensing nuclear receptor enriched in liver and intestine and is responsible for drug-drug interactions, due to its versatile ligand binding domain (LBD) and target genes involved in xenobiotic biotransformation. PXR can be modulated by various xenobiotics including pharmaceuticals, nutraceuticals, dietary factors, and environmental chemicals. Microbial metabolites such as certain secondary bile acids (BAs) and the tryptophan metabolite indole-3-propionic acid (IPA) are endogenous PXR activators. Gut microbiome is increasingly recognized as an important regulator for host xenobiotic biotransformation and intermediary metabolism. PXR regulates and is regulated by the gut-liver axis. This review summarizes recent research advancements leveraging pharmaco- and toxico-metagenomic approaches that have redefined the previous understanding of PXR. Key topics covered in this review include: (1) genome-wide investigations on novel PXR-target genes, novel PXR-DNA interaction patterns, and novel PXR-targeted intestinal bacteria; (2) key PXR-modulating activators and suppressors of exogenous and endogenous sources; (3) novel bidirectional interactions between PXR and gut microbiome under physiologic, pathophysiological, pharmacological, and toxicological conditions; and (4) modifying factors of PXR-signaling including species and sex differences and time (age, critical windows of exposure, and circadian rhythm). The review also discusses critical knowledge gaps and important future research topics centering around PXR. SIGNIFICANCE STATEMENT: This review summarizes recent research advancements leveraging O'mics approaches that have redefined the previous understanding of the xenobiotic-sensing nuclear receptor pregnane X receptor (PXR). Key topics include: (1) genome-wide investigations on novel PXR-targeted host genes and intestinal bacteria as well as novel PXR-DNA interaction patterns; (2) key PXR modulators including microbial metabolites under physiological, pathophysiological, pharmacological, and toxicological conditions; and (3) modifying factors including species, sex, and time.

Something Old, Something New: Ion Channel Blockers as Potential Anti-Tuberculosis Agents

Tuberculosis (TB) remains a challenging global health concern and claims more than a million lives every year. We lack an effective vaccine and understanding of what constitutes protective immunity against TB to inform rational vaccine design. Moreover, treatment of TB requires prolonged use of multi-drug regimens and is complicated by problems of compliance and drug resistance. While most Mycobacterium tuberculosis (Mtb) bacilli are quickly killed by the drugs, the prolonged course of treatment is required to clear persistent drug-tolerant subpopulations. Mtb’s differential sensitivity to drugs is, at least in part, determined by the interaction between the bacilli and different host macrophage populations. Therefore, to design better treatment regimens for TB, we need to understand and modulate the heterogeneity and divergent responses that Mtb bacilli exhibit within macrophages. However, developing drugs de-novo is a long and expensive process. An alternative approach to expedite the development of new TB treatments is to repurpose existing drugs that were developed for other therapeutic purposes if they also possess anti-tuberculosis activity. There is growing interest in the use of immune modulators to supplement current anti-TB drugs by enhancing the host’s antimycobacterial responses. Ion channel blocking agents are among the most promising of the host-directed therapeutics. Some ion channel blockers also interfere with the activity of mycobacterial efflux pumps. In this review, we discuss some of the ion channel blockers that have shown promise as potential anti-TB agents.

Strategies for developing pregnane X receptor antagonists: Implications from metabolism to cancer

Pregnane X receptor (PXR) is a ligand-activated nuclear receptor (NR) that was originally identified as a master regulator of xenobiotic detoxification. It regulates the expression of drug-metabolizing enzymes and transporters to control the degradation and excretion of endobiotics and xenobiotics, including therapeutic agents. The metabolism and disposition of drugs might compromise their efficacy and possibly cause drug toxicity and/or drug resistance. Because many drugs can promiscuously bind and activate PXR, PXR antagonists might have therapeutic value in preventing and overcoming drug-induced PXR-mediated drug toxicity and drug resistance. Furthermore, PXR is now known to have broader cellular functions, including the regulation of cell proliferation, and glucose and lipid metabolism. Thus, PXR might be involved in human diseases such as cancer and metabolic diseases. The importance of PXR antagonists is discussed in the context of the role of PXR in xenobiotic sensing and other disease-related pathways. This review focuses on the development of PXR antagonists, which has been hampered by the promiscuity of PXR ligand binding. However, substantial progress has been made in recent years, suggesting that it is feasible to develop selective PXR antagonists. We discuss the current status, challenges, and strategies in developing selective PXR antagonists. The strategies are based on the molecular mechanisms of antagonism in related NRs that can be applied to the design of PXR antagonists, primarily driven by structural information.

Mycobacterium tuberculosis and macrophage nuclear receptors: What we do and don't know

Nuclear receptors (NRs) are ligand-activated transcription factors that are expressed in a wide variety of cells and play a major role in lipid signaling. NRs are key regulators of immune and metabolic functions in macrophages and are linked to macrophage responses to microbial pathogens. Pathogens are also known to induce the expression of specific NRs to promote their own survival. In this review, we focus on the NRs recently shown to influence macrophage responses to Mycobacterium tuberculosis (M.tb), a significant cause of morbidity and mortality worldwide. We provide an overview of NR-controlled transcriptional activity and regulation of macrophage activation. We also discuss in detail the contribution of specific NRs to macrophage responses to M.tb, including influence on macrophage phenotype, cell signaling, and cellular metabolism. We pay particular attention to PPARγ since it is required for differentiation of alveolar macrophages, an important niche for M.tb, and its role during M.tb infection is becoming increasingly appreciated. Research into NRs and M.tb is still in its early stages, therefore continuing to advance our understanding of the complex interactions between M.tb and macrophage NRs may reveal the potential of NRs as pharmacological targets for the treatment of tuberculosis.

The Influence of Pharmacogenetic Variants in HIV/Tuberculosis Coinfected Patients in Uganda in the SOUTH Study

Unsatisfactory treatment outcomes have been reported in patients coinfected with HIV/tuberculosis (TB). The aim of this study was to assess the influence of single-nucleotide polymorphisms (SNPs) in genes encoding for proteins involved in antitubercular drug disposition or effect. A pharmacogenetic study was conducted in Kampala, Uganda, where all analysis was performed. The impact of SNPs on antitubercular drug exposure, adverse events, and treatment outcomes was evaluated in patients coinfected with HIV/TB receiving treatments for both conditions. In 221 participants, N-acetyltransferase 2 (NAT2; rs1799930), solute carrier organic anion transporter family member 1B1 (SLCO1B1; rs4149032), and pregnane X receptor (PXR; rs2472677) variants affected isoniazid exposure in multivariate analysis. Most patients were deemed cured (163; 73.8%), yet PXR 63396TT carriers had a higher probability of death (P = 0.007) and of worsening peripheral neuropathy (P = 0.018). In this exploratory study in Ugandan patients coinfected with HIV/TB, genetic variants in PXR, SLCO1B1, and NAT2 were moderately associated with isoniazid exposure, whereas PXR 63396TT carriers showed worse outcomes.

Clinical and experimental research in antituberculosis drug-induced hepatotoxicity: a review

Drug-induced liver injury is the common adverse effect seen in patients receiving antituberculosis drugs (ATDs). There are several risk factors associated with the development of hepatotoxicity in such patients. Though there have been appreciable efforts taken by carrying out studies investigating the efficacy of several natural and synthetic compounds in minimising this effect, the only choice available for clinicians is withdrawal of drugs. This review would give a precise idea of ATD-induced hepatotoxicity, its underlying mechanisms and alternative therapies for the same.

Hot aqueous leaf extract of Lasianthera africana (Icacinaceae) attenuates rifampicin-isoniazid-induced hepatotoxicity

OBJECTIVES

The aim of this study is to evaluate the hepatoprotective effect of Lasianthera africana (Icacinaceae) against isoniazid (INH) and rifampicin (RIF)-induced liver damage in rats.

METHODS

The hepatoprotective effects of hot aqueous L. africana (HALA) leaf extract (0.1-1 g/kg) and silymarin (50 mg/kg) were assessed in a model of oxidative liver damage induced by RIF and INH (100 mg/kg each) in Wistar rats for 28 days. Biochemical markers of hepatic damage such as alanine aminotransferase (ALT), aspartate aminotransferase (AST) and alkaline phosphatase (ALP) were assessed. The antioxidant statuses of plasma glutathione peroxidase (GSPx), glutathione reductase (GSH), catalase (CAT) and superoxide dismutase (SOD) and lipid peroxidation were evaluated.

RESULTS

The pretreatment of INH and RIF decreased hematological indices and the antioxidant levels (P < 0.001) and increased the levels of liver marker enzymes (P < 0.001). However, pretreatment with HALA extract and silymarin provoked significant elevation of hematological indices. The levels of AST, ALT, and ALP were depressed (P < 0.001). Total triglycerides, total cholesterol, total bilirubin and low-density lipoprotein were decreased (P < 0.001). However, high-density lipoprotein, bicarbonate, and electrolytes like chloride and potassium were elevated (P < 0.001), but sodium was depressed (P < 0.05). Additionally, GSH, GSPx, SOD and CAT were elevated (P < 0.01) and malondialdehyde was depressed (P < 0.001) when compared to the RIF-INH-treated rats. Histopathological evaluations support hepatoprotective activity.

CONCLUSION

This study demonstrated that HALA leaf extract attenuated RIF-INH-induced hepatotoxicity. L. africana could be exploited in management of RIF-INH-induced hepatitis.

A human xenobiotic nuclear receptor contributes to nonresponsiveness of Mycobacterium tuberculosis to the antituberculosis drug rifampicin

Mycobacterium tuberculosis is the causative agent of tuberculosis (TB). It acquires phenotypic drug resistance inside macrophages, and this resistance mainly arises from host-induced stress. However, whether cellular drug-efflux mechanisms in macrophages contribute to nonresponsiveness of M. tuberculosis to anti-TB drugs is unclear. Here, we report that xenobiotic nuclear receptors mediate TB drug nonresponsiveness by modulating drug-efflux transporters in macrophages. This was evident from expression analysis of drug-efflux transporters in macrophages isolated from TB patients. Among patients harboring rifampicin-susceptible M. tuberculosis, we observed increased intracellular survival of M. tuberculosis upon rifampicin treatment of macrophages isolated from patients not responding to anti-TB drugs compared with macrophages from patients who did respond. Of note, M. tuberculosis infection and rifampicin exposure synergistically modulated macrophage drug-efflux transporters in vitro We also found that the xenobiotic nuclear receptor pregnane X receptor (PXR) modulates macrophage drug-efflux transporter expression and activity, which compromised the anti-TB efficacy of rifampicin. We further validated this finding in a TB mouse model in which use of the PXR antagonist ketoconazole rescued rifampicin anti-TB activity. We conclude that PXR activation in macrophages compromises the efficacy of the anti-TB drug rifampicin. Alternative therapeutic strategies, such as use of the rifampicin derivatives rifapentine and rifabutin, which do not activate PXR, or of a PXR antagonist, may be effective for tackling drug nonresponsiveness of M. tuberculosis that arises from drug-efflux systems of the host.

Functions of pregnane X receptor in self-detoxification

Pregnane X receptor (PXR, NR1I2), a member of the nuclear receptor superfamily, is a crucial regulator of nutrient metabolism and metabolic detoxification such as metabolic syndrome, xenobiotic metabolism, inflammatory responses, glucose, cholesterol and lipid metabolism, and endocrine homeostasis. Notably, much experimental and clinical evidence show that PXR senses xenobiotics and triggers the detoxification response to prevent diseases such as diabetes, obesity, intestinal inflammatory diseases and liver fibrosis. In this review we summarize recent advances on remarkable metabolic and regulatory versatility of PXR, and we emphasizes its role and potential implication as an effective modulator of self-detoxification in animals and humans.

Antiretroviral treatment in HIV-infected children who require a rifamycin-containing regimen for tuberculosis

INTRODUCTION

In high prevalence settings, tuberculosis and HIV dual infection and co-treatment is frequent. Rifamycins, especially rifampicin, in combination with isoniazid, ethambutol and pyrazinamide are key components of short-course antituberculosis therapy. Areas covered: We reviewed available data, for which articles were identified by a Pubmed search, on rifamycin-antiretroviral interactions in HIV-infected children. Rifamycins have potent inducing effects on phase I and II drug metabolising enzymes and transporters. Antiretroviral medications are often metabolised by the enzymes induced by rifamycins or may suppress specific enzyme activity leading to drug-drug interactions with rifamycins. These may cause significant alterations in their phamacokinetic and pharmacodynamic properties, and sometimes that of the rifamycin. Recommended strategies to adapt to these interactions include avoidance and dose adjustment. Expert opinion: Despite the importance and frequency of tuberculosis as an opportunistic disease in HIV-infected children, current data on the management of co-treated children is based on few studies. We need new strategies to rapidly assess the use of rifamycins, new anti-tuberculosis drugs and antiretroviral drugs together as information on safety and dosing of individual drugs becomes available.