Nutritional status modifies pregnane X receptor regulated transcriptome

Evaluation of FXR Activity in Pollutants Identified in Sewage Sludge and Subsequent in Vitro and in Vivo Characterization of Metabolic Effects of Triphenyl Phosphate

BACKGROUND

Metabolic dysfunction-associated steatotic liver disease (MASLD) is the most common liver disease worldwide, and increasing evidence suggests that exposure to environmental pollutants is associated with the increased incidence of MASLD. The farnesoid X receptor (FXR) plays an important role in the development of MASLD by regulating bile acids (BAs) and lipid metabolism. However, whether FXR-active pollutants are the environmental drivers of MASLD remains unclear.

OBJECTIVES

This study aimed to determine whether FXR-active pollutants exist in the environment and evaluate their ability to trigger MASLD development in mice.

METHODS

An FXR protein affinity pull-down assay and nontargeted mass spectrometry (MS) analysis were used to identify environmental FXR ligands in sewage sludge. A homogeneous time-resolved fluorescence coactivator recruitment assay and cell-based dual-luciferase reporter assay were used to determine the FXR activities of the identified pollutants. Targeted analysis of BAs, MS imaging, lipidomic analysis, 16S rRNA sequencing, and quantitative polymerase chain reaction were conducted to assess the ability of FXR-active pollutants to induce metabolic disorders of BAs and lipids and to contribute to MASLD development in C57BL/6N mice.

RESULTS

We identified 19 compounds in the sewage sludge that had FXR-antagonistic activity, and triphenyl phosphate (TPHP) was the FXR antagonist with the highest efficacy. Mice exposed to either 10 or 50 mg / kg TPHP for 30 d had higher levels of conjugated primary BAs in enterohepatic circulation, and the BA pool showed FXR antagonistic activities. The exposed mice also had greater lipogenesis (more Oil Red O staining and high triglyceride levels) in liver.

CONCLUSIONS

Nineteen FXR-antagonistic pollutants were identified in sewage sludge. FXR inhibition by the strongest antagonist TPHP may have a role in promoting MASLD development in mice by inducing a positive feedback loop between the FXR and BAs. https://doi.org/10.1289/EHP15435.

Advances in antitumor activity and mechanism of natural steroidal saponins: A review of advances, challenges, and future prospects

BACKGROUND

Cancer, the second leading cause of death worldwide following cardiovascular diseases, presents a formidable challenge in clinical settings due to the extensive toxic side effects associated with primary chemotherapy drugs employed for cancer treatment. Furthermore, the emergence of drug resistance against specific chemotherapeutic agents has further complicated the situation. Consequently, there exists an urgent imperative to investigate novel anticancer drugs. Steroidal saponins, a class of natural compounds, have demonstrated notable antitumor efficacy. Nonetheless, their translation into clinical applications has remained unrealized thus far. In light of this, we conducted a comprehensive systematic review elucidating the antitumor activity, underlying mechanisms, and inherent limitations of steroidal saponins. Additionally, we propose a series of strategic approaches and recommendations to augment the antitumor potential of steroidal saponin compounds, thereby offering prospective insights for their eventual clinical implementation.

PURPOSE

This review summarizes steroidal saponins' antitumor activity, mechanisms, and limitations.

METHODS

The data included in this review are sourced from authoritative databases such as PubMed, Web of Science, ScienceDirect, and others.

RESULTS

A comprehensive summary of over 40 steroidal saponin compounds with proven antitumor activity, including their applicable tumor types and structural characteristics, has been compiled. These steroidal saponins can be primarily classified into five categories: spirostanol, isospirostanol, furostanol, steroidal alkaloids, and cholestanol. The isospirostanol and cholestanol saponins are found to have more potent antitumor activity. The primary antitumor mechanisms of these saponins include tumor cell apoptosis, autophagy induction, inhibition of tumor migration, overcoming drug resistance, and cell cycle arrest. However, steroidal saponins have limitations, such as higher cytotoxicity and lower bioavailability. Furthermore, strategies to address these drawbacks have been proposed.

CONCLUSION

In summary, isospirostanol and cholestanol steroidal saponins demonstrate notable antitumor activity and different structural categories of steroidal saponins exhibit variations in their antitumor signaling pathways. However, the clinical application of steroidal saponins in cancer treatment still faces limitations, and further research and development are necessary to advance their potential in tumor therapy.

Investigation of TGF-α-overexpressing mouse hepatocytes (TAMH) cultured as spheroids for use in hepatotoxicity screening of drug candidates

The immortalized mouse liver cell line TAMH has been described as a valuable tool for studying hepatotoxic mechanisms, but until now, it has only been reported to grow as a monolayer in culture. However, culturing hepatocytes as three-dimensional (3D) spheroids has been shown to result in improved liver-specific functions (e.g., metabolic capacity) by better mimicking the in vivo environment. This approach may lead to more reliable detection of drug-induced liver injury (DILI) in the early phase of drug discovery, preventing post-marketing drug withdrawals. Here, we investigated the cultivation of TAMH as 3D spheroids, characterizing them with optical and transmission electron microscopy as well as analyzing their gene expression at mRNA level (especially drug-metabolizing enzymes) compared to TAMH monolayer. In addition, comparisons were made with spheroids grown from the human hepatoblastoma cell line HepG2, another current spheroid model. The results indicate that TAMH spheroids express hepatic structures and show elevated levels of some of the key phase I and II drug-metabolizing enzymes, in contrast to TAMH monolayer. The in vitro hepatotoxic potencies of the drugs acetaminophen and flupirtine maleate were found to be very similar between TAMH spheroidal and the monolayer cultures. Both the advantages and disadvantages of TAMH spheroids as an in vitro hepatotoxicity model compared to monolayer model are discussed.

Adverse outcome pathway for pregnane X receptor-induced hypercholesterolemia

Pharmaceuticals and environmental contaminants contribute to hypercholesterolemia. Several chemicals known to cause hypercholesterolemia, activate pregnane X receptor (PXR). PXR is a nuclear receptor, classically identified as a sensor of chemical environment and regulator of detoxification processes. Later, PXR activation has been shown to disrupt metabolic functions such as lipid metabolism and recent findings have shown PXR activation to promote hypercholesterolemia through multiple mechanisms. Hypercholesterolemia is a major causative risk factor for atherosclerosis and greatly promotes global health burden. Metabolic disruption by PXR activating chemicals leading to hypercholesterolemia represents a novel toxicity pathway of concern and requires further attention. Therefore, we constructed an adverse outcome pathway (AOP) by collecting the available knowledge considering the molecular mechanisms for PXR-mediated hypercholesterolemia. AOPs are tools of modern toxicology for systematizing mechanistic knowledge to assist health risk assessment of chemicals. AOPs are formalized and structured linear concepts describing a link between molecular initiating event (MIE) and adverse outcome (AO). MIE and AO are connected via key events (KE) through key event relationships (KER). We present a plausible route of how PXR activation (MIE) leads to hypercholesterolemia (AO) through direct regulation of cholesterol synthesis and via activation of sterol regulatory element binding protein 2-pathway.

The Function of Xenobiotic Receptors in Metabolic Diseases

Metabolic diseases are a series of metabolic disorders that include obesity, diabetes, insulin resistance, hypertension, and hyperlipidemia. The increased prevalence of metabolic diseases has resulted in higher mortality and mobility rates over the past decades, and this has led to extensive research focusing on the underlying mechanisms. Xenobiotic receptors (XRs) are a series of xenobiotic-sensing nuclear receptors that regulate their downstream target genes expression, thus defending the body from xenobiotic and endotoxin attacks. XR activation is associated with the development of a number of metabolic diseases such as obesity, nonalcoholic fatty liver disease, type 2 diabetes, and cardiovascular diseases, thus suggesting an important role for XRs in modulating metabolic diseases. However, the regulatory mechanism of XRs in the context of metabolic disorders under different nutrient conditions is complex and remains controversial. This review summarizes the effects of XRs on different metabolic components (cholesterol, lipids, glucose, and bile acids) in different tissues during metabolic diseases. As chronic inflammation plays a critical role in the initiation and progression of metabolic diseases, we also discuss the impact of XRs on inflammation to comprehensively recognize the role of XRs in metabolic diseases. This will provide new ideas for treating metabolic diseases by targeting XRs. SIGNIFICANCE STATEMENT: This review outlines the current understanding of xenobiotic receptors on nutrient metabolism and inflammation during metabolic diseases. This work also highlights the gaps in this field, which can be used to direct the future investigations on metabolic diseases treatment by targeting xenobiotic receptors.

Bile Acids: Physiological Activity and Perspectives of Using in Clinical and Laboratory Diagnostics

Bile acids play a significant role in the digestion of nutrients. In addition, bile acids perform a signaling function through their blood-circulating fraction. They regulate the activity of nuclear and membrane receptors, located in many tissues. The gut microbiota is an important factor influencing the effects of bile acids via enzymatic modification. Depending on the rate of healthy and pathogenic microbiota, a number of bile acids may support lipid and glucose homeostasis as well as shift to more toxic compounds participating in many pathological conditions. Thus, bile acids can be possible biomarkers of human pathology. However, the chemical structure of bile acids is similar and their analysis requires sensitive and specific methods of analysis. In this review, we provide information on the chemical structure and the biosynthesis of bile acids, their regulation, and their physiological role. In addition, the review describes the involvement of bile acids in various diseases of the digestive system, the approaches and challenges in the analysis of bile acids, and the prospects of their use in omics technologies.

Mice blocking Ser347 phosphorylation of pregnane x receptor develop hepatic fasting-induced steatosis and hypertriglyceridemia

Nuclear receptor Pregnane X Receptor (PXR; NR1I2) has transcriptional regulation functions for energy homeostasis in the liver. Mouse PXR has a conserved phosphorylation motif at serine 347 (serine 350 in humans) within the ligand-binding domain. PXR phosphorylated at this motif is expressed in mouse livers in response to fasting. Mice with a PXR∗Ser347Ala knockin mutation (PXR KI) were generated to block phosphorylation, and utilized to investigate the role of Ser347 phosphorylation in vivo. PXR KI mice had decreased body weight at 8-weeks of age and had much greater weight loss after fasting compared with PXR WT mice. The cDNA microarray analysis of hepatic mRNAs showed that cell death or apoptotic signaling was induced in fasting PXR KI mice. Moreover, increasing hepatic lipids, triglycerides and the development of hypertriglyceridemia were observed in fasting PXR KI mice. These findings are indicative that blocking phosphorylation prevents mice from maintaining hepatic energy homeostasis. Thus, phosphorylated PXR may be an essential factor to prevent the liver from developing damage caused by fasting.

Nuclear Receptor PXR in Drug-Induced Hypercholesterolemia

Atherosclerosis is a major global health concern. The central modifiable risk factors and causative agents of the disease are high total and low-density lipoprotein (LDL) cholesterol. To reduce morbidity and mortality, a thorough understanding of the factors that influence an individual’s cholesterol status during the decades when the arteria-narrowing arteriosclerotic plaques are forming is critical. Several drugs are known to increase cholesterol levels; however, the mechanisms are poorly understood. Activation of pregnane X receptor (PXR), the major regulator of drug metabolism and molecular mediator of clinically significant drug–drug interactions, has been shown to induce hypercholesterolemia. As a major sensor of the chemical environment, PXR may in part mediate hypercholesterolemic effects of drug treatment. This review compiles the current knowledge of PXR in cholesterol homeostasis and discusses the role of PXR in drug-induced hypercholesterolemia.

Activation of pregnane X receptor induces atherogenic lipids and PCSK9 by a SREBP2-mediated mechanism

BACKGROUND AND PURPOSE

Many drugs and environmental contaminants induce hypercholesterolemia and promote the risk of atherosclerotic cardiovascular disease. We tested the hypothesis that pregnane X receptor (PXR), a xenobiotic-sensing nuclear receptor, regulates the level of circulating atherogenic lipids in humans and utilized mouse experiments to identify the mechanisms involved.

EXPERIMENTAL APPROACH

We performed serum NMR metabolomics in healthy volunteers administered rifampicin, a prototypical human PXR ligand or placebo in a crossover setting. We used high-fat diet fed wild-type and PXR knockout mice to investigate the mechanisms mediating the PXR-induced alterations in cholesterol homeostasis.

KEY RESULTS

Activation of PXR induced cholesterogenesis both in pre-clinical and clinical settings. In human volunteers, rifampicin increased intermediate-density lipoprotein (IDL), low-density lipoprotein (LDL) and total cholesterol and lathosterol-cholesterol ratio, a marker of cholesterol synthesis, suggesting increased cholesterol synthesis. Experiments in mice indicated that PXR activation causes widespread induction of the cholesterol synthesis genes including the rate-limiting Hmgcr and upregulates the intermediates in the Kandutsch-Russell cholesterol synthesis pathway in the liver. Additionally, PXR activation induced plasma proprotein convertase subtilisin/kexin type 9 (PCSK9), a negative regulator of hepatic LDL uptake, in both mice and humans. We propose that these effects were mediated through increased proteolytic activation of sterol regulatory element-binding protein 2 (SREBP2) in response to PXR activation.

CONCLUSION AND IMPLICATIONS

PXR activation induces cholesterol synthesis, elevating LDL and total cholesterol in humans. The PXR-SREBP2 pathway is a novel regulator of the cholesterol and PCSK9 synthesis and a molecular mechanism for drug- and chemical-induced hypercholesterolemia.

PXR and 4β-Hydroxycholesterol Axis and the Components of Metabolic Syndrome

Pregnane X receptor (PXR) activation has been found to regulate glucose and lipid metabolism and affect obesity in response to high-fat diets. PXR also modulates vascular tone. In fact, PXR appears to regulate multiple components of metabolic syndrome. In most cases, the effect of PXR action is harmful to metabolic health, and PXR can be hypothesized to play an important role in metabolic disruption elicited by exposure to endocrine-disrupting chemicals. The majority of the data on the effects of PXR activation on metabolic health come from animal and cell culture experiments. However, randomized, placebo-controlled, human trials indicate that the treatment with PXR ligands impairs glucose tolerance and increases 24-h blood pressure and heart rate. In addition, plasma 4β-hydroxycholesterol (4βHC), formed under the control of PXR in the liver, is associated with lower blood pressure in healthy volunteers. Furthermore, 4βHC regulates cholesterol transporters in peripheral tissues and may activate the beneficial reverse HDL cholesterol transport. In this review, we discuss the current knowledge on the role of PXR and the PXR–4βHC axis in the regulation of components of metabolic syndrome.

Metabolism-Disrupting Chemicals and the Constitutive Androstane Receptor CAR

During the last two decades, the constitutive androstane receptor (CAR; NR1I3) has emerged as a master activator of drug- and xenobiotic-metabolizing enzymes and transporters that govern the clearance of both exogenous and endogenous small molecules. Recent studies indicate that CAR participates, together with other nuclear receptors (NRs) and transcription factors, in regulation of hepatic glucose and lipid metabolism, hepatocyte communication, proliferation and toxicity, and liver tumor development in rodents. Endocrine-disrupting chemicals (EDCs) constitute a wide range of persistent organic compounds that have been associated with aberrations of hormone-dependent physiological processes. Their adverse health effects include metabolic alterations such as diabetes, obesity, and fatty liver disease in animal models and humans exposed to EDCs. As numerous xenobiotics can activate CAR, its role in EDC-elicited adverse metabolic effects has gained much interest. Here, we review the key features and mechanisms of CAR as a xenobiotic-sensing receptor, species differences and selectivity of CAR ligands, contribution of CAR to regulation hepatic metabolism, and evidence for CAR-dependent EDC action therein.

Vitamin K in Vertebrates' Reproduction: Further Puzzling Pieces of Evidence from Teleost Fish Species

Vitamin K (VK) is a fat-soluble vitamin that vertebrates have to acquire from the diet, since they are not able to de novo synthesize it. VK has been historically known to be required for the control of blood coagulation, and more recently, bone development and homeostasis. Our understanding of the VK metabolism and the VK-related molecular pathways has been also increased, and the two main VK-related pathways-the pregnane X receptor (PXR) transactivation and the co-factor role on the γ-glutamyl carboxylation of the VK dependent proteins-have been thoroughly investigated during the last decades. Although several studies evidenced how VK may have a broader VK biological function than previously thought, including the reproduction, little is known about the specific molecular pathways. In vertebrates, sex differentiation and gametogenesis are tightly regulated processes through a highly complex molecular, cellular and tissue crosstalk. Here, VK metabolism and related pathways, as well as how gametogenesis might be impacted by VK nutritional status, will be reviewed. Critical knowledge gaps and future perspectives on how the different VK-related pathways come into play on vertebrate's reproduction will be identified and proposed. The present review will pave the research progress to warrant a successful reproductive status through VK nutritional interventions as well as towards the establishment of reliable biomarkers for determining proper nutritional VK status in vertebrates.

The Other Obesity Epidemic-Of Drugs and Bugs

Chronic psychiatric patients with schizophrenia and related disorders are frequently treatment-resistant and may require higher doses of psychotropic drugs to remain stable. Prolonged exposure to these agents increases the risk of weight gain and cardiometabolic disorders, leading to poorer outcomes and higher medical cost. It is well-established that obesity has reached epidemic proportions throughout the world, however it is less known that its rates are two to three times higher in mentally ill patients compared to the general population. Psychotropic drugs have emerged as a major cause of weight gain, pointing to an urgent need for novel interventions to attenuate this unintended consequence. Recently, the gut microbial community has been linked to psychotropic drugs-induced obesity as these agents were found to possess antimicrobial properties and trigger intestinal dysbiosis, depleting Bacteroidetes phylum. Since germ-free animals exposed to psychotropics have not demonstrated weight gain, altered commensal flora composition is believed to be necessary and sufficient to induce dysmetabolism. Conversely, not only do psychotropics disrupt the composition of gut microbiota but the later alter the metabolism of the former. Here we review the role of gut bacterial community in psychotropic drugs metabolism and dysbiosis. We discuss potential biomarkers reflecting the status of Bacteroidetes phylum and take a closer look at nutritional interventions, fecal microbiota transplantation, and transcranial magnetic stimulation, strategies that may lower obesity rates in chronic psychiatric patients.