Chemical Research in Toxicology最新文献

Apurinic/apyrimidinic endonuclease 1 (APE1) is a central enzyme in the base excision repair (BER) pathway. APE1 catalyzes incision of the phosphodiester linkage on the 5'-side of apurinic/apyrimidinic (AP) sites during the repair of damaged nucleobases in cellular DNA. Inhibition of this enzyme can potentiate the action of DNA-damaging chemotherapeutic agents. The antihypertensive drug hydralazine generates covalent AP adducts that block the catalytic action of APE1. Hydralazine was found to be superior to the investigational drug methoxyamine in its capacity to covalently capture AP sites in duplex DNA and inhibit the action of APE1. It was further shown that hydralazine sensitized SF295 glioblastoma cells to the cytotoxic action of the anticancer drug Temozolomide, which generates alkylpurine residues requiring APE1 for repair. The results suggest that the FDA-approved drug hydralazine might be repurposed in oncology to potentiate the activity of existing chemotherapeutic agents that induce AP sites in cellular DNA.

The scale of nanoparticle use in consumer goods has grown exponentially over several decades owing to the unique properties of materials in this size range. At the same time, well-defined end of life cycle disposal strategies have not been developed for most materials, meaning that we are approaching the potential for a new ecological disaster with the release of millions of metric tons of nanoparticles into the waste stream. The field of nanotoxicology has grown to meet the challenge of investigating the potential hazards of these materials and has already identified toxicity mechanisms that affect multiple tropes of life. However, there are stipulations on how applicable many of these results are to real world applications. These limitations largely arise from the complex network of variables that must be considered during these investigations. Herein, we focus on the challenges posed by the transformations that nanoparticles undergo when they are introduced into a biological environment. For example, biomolecules, such as proteins, rapidly coat nanoparticles with a shell, called a corona, that can modulate the toxicity of the core materials and/or aid its internalization into cells. As such, unlike in the evaluation of small molecule toxicity, one cannot assume that they know the composition of the nanoparticle-biomolecule species at any given time. This additional layer of complication, as well as the noncovalent nature of the corona, have made it difficult to identify consistent toxicity trends. In this Perspective, we highlight current analysis strategies and the difficulties in studying nanotoxicity, recent advances to aid in these studies, and efforts to reduce nanotoxicity and outline remaining challenges.

Biological polyamines, such as spermine, spermidine, and putrescine, are abundant intracellular compounds mostly bound to nucleic acids. Due to their nucleophilic nature, polyamines easily react with apurinic/apyrimidinic (AP) sites, DNA lesions that are constantly formed in DNA by spontaneous base loss and as intermediates of base excision repair. A covalent intermediate is formed, promoting DNA strand cleavage at the AP site, and is later hydrolyzed regenerating the polyamine. Here we have investigated formation of AP site adducts with spermine and spermidine using sodium borohydride trapping technique and shown that they could persist in DNA for long enough to possibly interfere with cell's replication and transcription machinery. We demonstrate that both adducts placed internally into DNA are strongly blocking for DNA polymerases (Klenow fragment, phage RB69 polymerase, human polymerases β and κ) and direct dAMP incorporation in the rare bypass events. The internal AP site adducts with polyamines can be repaired, albeit rather slowly, by Escherichia coli endonuclease IV and yeast Apn1 but not by human AP endonuclease APE1 or E. coli exonuclease III, whereas the 3'-terminal adducts are substrates for the phosphodiesterase activities of all these AP endonucleases.

The β-amyloid precursor protein-cleaving enzyme 1 (BACE1) inhibitor JNJ-54861911, a candidate for the treatment of Alzheimer's disease, was withdrawn from clinical trials due to drug-induced liver injury (DILI). This paper describes our investigation of the metabolism of JNJ-54861911 to understand the potential contribution to the observed DILI. In human hepatocytes, JNJ-54861911 is metabolized by CYP450 3A4 to a reactive intermediate (RI), which undergoes glutathione (GSH) addition at C6 of the 2-amino-4-methyl-1,3-thiazin-4-yl moiety via glutathione S-transferase α1 (GSTA1) catalysis. Despite the preponderant role of CYP3A4 as an enabler, the adduct has the same level of oxidation as that of JNJ-54861911. The exact mechanism of RI formation might involve a sulfoxide (with further reduction) or tautomeric forms of JNJ-54861911 bearing a reactive thiazinium cation activating both the C2 and C6 positions. The cell pellet from the human hepatocyte incubated with ¹⁴C-JNJ-54861911 was analyzed via gel electrophoresis, resulting in the identification of a major protein adduct on GSTA1, a cross-link resulting from the addition of GSH and lysine 120 to JNJ-54861911, most likely on position C6 and on the nitrile, respectively. Ultimately, this major adduct might only account for 15-25% of the total covalent binding (CVB). Other important contributors to CVB might exist, like the bioactivation of the major diaminothiazine metabolite (DIAT). The level of covalent binding (CVB) burden (fraction of the dose resulting in CVB) is clearly below 1 mg/day, with a low daily dose of 25 mg. Despite this limited magnitude of CVB, it could still contribute to the liver enzyme elevations observed in approximately 20% of the patients and to the few cases of severe immune-mediated DILI. The latter could occur through a haptenization phenomenon and/or by inducing stress in hepatocytes. Such stress may activate an innate immune response, which, in turn, promotes the adaptive immune response.

A series of novel oxadiazole derivatives were designed, synthesized, and evaluated for their pharmacological effects. All target compounds were subjected to analysis using ¹H NMR, ¹³C NMR, and mass spectrometry. They showed a strong affinity to the AT1 receptor and effectively lowered blood pressure in spontaneously hypertensive rats at a nanomolar level. Compounds IV₁ and IV₂ were particularly effective, demonstrating comparable or greater potency in reducing blood pressure compared to Losartan. Therefore, compounds IV₁ and IV₂ have the potential to be developed as antihypertension medications.

E-cigarette emissions, which contain a variety of hazardous compounds, contribute significantly to indoor air pollution and raise concerns about secondhand exposure to vaping byproducts. Compared to fresh vape emissions, our understanding of chemically aged products in indoor environments remains incomplete. Terpenes are commonly used as flavoring agents in e-liquids, which have the ability to react with the dominant indoor oxidant ozone (O₃) to produce reactive oxygenated byproducts and result in new particle formation. In this study, mixtures of propylene glycol (PG), vegetable glycerin (VG), and terpenes as e-liquids were injected into a 2 m³ FEP chamber to simulate the indoor aging process. 100 ppbv O₃ was introduced into the chamber and allowed to react with the fresh vape emissions for 1 h. Complementary online and offline analytical techniques were used to characterize the changes in the aerosol size distribution and chemical composition during the aging processes. We observed more ultrafine particles and a greater abundance of highly oxygenated species, such as carbonyls, in aged e-cigarette aerosols. Compared with their fresh counterparts, the aged emissions exhibited greater cytotoxic potential, which can be attributed to the formation of these highly oxygenated compounds that are not present in the fresh emissions. This work highlights the dynamic chemistry and toxicity of e-cigarette aerosols in the indoor environment as well as the indirect risks of secondhand exposure.

Defining the underlying toxicological mechanisms of various small molecules is of utmost importance in understanding the pathogenesis of chemical exposure-related human diseases and developing safe and effective therapeutics. Herein, we discuss the toxicological mechanisms of different small molecules utilizing the different tools of chemical biology.

The analytical quality of compounds subjected to high-throughput screening (HTS) impacts accurate interpretation of assay results, with poor quality samples potentially leading to false negatives or positives. The Tox21 "10K" library consists of over 8900 unique compounds, spanning a diverse landscape of environmental and pharmaceutical chemicals, posing opportunities and challenges for analytical quality control (QC) determinations. Tox21 sample plates stored in DMSO at ambient conditions for 0 (T0) and/or 4 months (T4), totaling more than 13K unique sample identifiers (Tox21 IDs), were subjected to various analyses, including liquid and gas chromatography mass spectrometry (LC-MS, GC-MS) and nuclear magnetic resonance (NMR). Results for each sample at T0 or T4 underwent expert review and, where possible, a QC grade conveying purity, identity, and concentration was assigned. Herein, we relate details of the methods applied and report on the original (v0) Tox21 ID level results. Thirteen QC grades were condensed to 5 quality scores to aid global analysis, resulting in reinterpretation and improvement of >700 sample grades. Of the 92% T0 samples successfully graded, 76% exceeded 90% purity. For 76% of samples that were also tested at T4, 89% showed no evidence of sample loss or degradation. Prioritized quality bins were used to summarize thousands of replicate sample-level QC results to a compound-level QC score to support structure-based analyses. ToxPrint chemotype analysis identified structural features enriched in unstable compounds, as well as in high and low quality T0 subsets. Predicted vapor pressure was weakly correlated with low-concentration QC indicators, reflecting likely entanglement with method amenability and quality issues. Finally, an ongoing EPA effort to re-evaluate the original QC spectra is generating insights that will further modify QC grades. Tox21 QC spectra and results will be made available in a new public QC browser, facilitating further evaluation to support HTS interpretation and modeling applications.

Ferroptosis is regarded as a promising cancer therapeutic target. As a major bioactive compound from traditional Chinese medicine (TCM) herb Sophora flavescens Aiton, oxymatrine (OMT) can depress inflammatory factors, reduce iron deposition, and suppress the hub gene or protein expression involved in ferroptosis and inflammation. Additionally, OMT can control collagen deposition in the liver and has a therapeutic effect on liver cancer. This research investigated the action mechanism of the mechanism of the effect of OMT on the process of liver cancer. OMT triggered cell death and restrained cell proliferation in liver cancer cells, along with downregulated levels of Yin Yang 1 (YY1) and glutathione peroxidase 4 (GPX4) and elevated expression of silent information regulator 1 (SIRT1). Moreover, ferroptosis is the main method leading to OMT-induced liver cancer cell death. OMT-induced ferroptosis was reversed after GPX4 and YY1 overexpression or inhibition of SIRT1. Furthermore, the OMT restrained tumor growth through the SIRT1/YY1/GPX4 axis in liver cancer transplantation models. These results indicated that OMT inhibited cell viability and induced ferroptosis of liver cancer cells, involving the regulatory mechanism of the SIRT1/YY1/GPX4 axis.

Nucleotide excision repair is a crucial cellular mechanism that ensures genomic stability, thereby preventing mutations that can lead to cancer. The human XPC and its yeast ortholog Rad4 protein complexes are central to this process and were the focus of the study. We used surface plasmon resonance and differential scanning fluorimetry to study the binding characteristics of XPC and Rad4 when bound to the bulky cluster di-FAAF-containing 55-mer duplex DNA. Our findings revealed that XPC binds 10 times more significant affinity to control and di-FAAF-modified DNA than Rad4 with greater protein-DNA interactions. Differential scanning fluorimetry indicates that Rad4 causes comparatively more significant conformational changes upon complexation with the damaged DNA. We conducted DNase I footprinting of the Rad4/DNA complex for the first time by determining the regions protected from DNase I digestion. The DNA at the lesion is entirely resistant to digestion by DNase I in the absence of Rad4 several nucleotides to the 3'-side of the first FAAF lesion. The lack of DNase I cleavage at the lesions did not change upon adding Rad4. However, in the presence of Rad4, a footprint is observed on the 7-nucleotide region (5'-TGGTGAT-3') of the complementary strand to the 3' side of the lesion.