Quinone-mediated induction of cytochrome P450 1A1 in HepG2 cells through increased interaction of aryl hydrocarbon receptor with aryl hydrocarbon receptor nuclear translocator

Mechanism of Laccase Induction via Emodin in Trametes versicolor

Secondary metabolites of traditional Chinese herbs can prominently stimulate the production of laccase from white rot fungi during submerged fermentation. However, the molecular mechanism through which these natural products induce the production of laccase remains unknown. In this study, the Chinese herbal medicine Polygonum cuspidatum was used to induce laccase production in Trametes versicolor, and the best inducer was identified in emodin, even under conditions of 1000-L, large-scale fermentation. Proteomics analysis identified a selection of proteins that were differentially expressed in the presence of emodin, indicating that emodin may affect the expression of laccase genes through three mechanisms: reducing bioenergy productivity, the aryl hydrocarbon receptor (AHR)/xenobiotic response element (XRE) pathway, and the nuclear erythroid 2-related factor 2 (Nrf2)/antioxidant response element (ARE) pathway. Combined with protoplast flow cytometry and fluorescence, it is revealed that emodin might reduce the synthesis of ATP by lowering the mitochondrial membrane potential, leading to the subsequent responses.

The Cellular and Molecular Determinants of Naphthoquinone-Dependent Activation of the Aryl Hydrocarbon Receptor

1,2-naphthoquinone (1,2-NQ) and 1,4-naphthoquinone (1,4-NQ) are clinically promising biologically active chemicals that have been shown to stimulate the aryl hydrocarbon receptor (AhR) signaling pathway, but whether they are direct or indirect ligands or activate the AhR in a ligand-independent manner is unknown. Given the structural diversity of AhR ligands, multiple mechanisms of AhR activation of gene expression, and species differences in AhR ligand binding and response, we examined the ability of 1,2-NQ and 1,4-NQ to bind to and activate the mouse and human AhRs using a series of in vitro AhR-specific bioassays and in silico modeling techniques. Both NQs induced AhR-dependent gene expression in mouse and human hepatoma cells, but were more potent and efficacious in human cells. 1,2-NQ and 1,4-NQ stimulated AhR transformation and DNA binding in vitro and was inhibited by AhR antagonists. Ligand binding analysis confirmed the ability of 1,2-NQ and 1,4-NQ to competitively bind to the AhR ligand binding cavity and the molecular determinants for interactions were predicted by molecular modeling methods. NQs were shown to bind distinctly differently from that of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and differences were also observed between species. Mutation of amino acid residues (F289, M334, and M342) involved in critical NQ:AhR binding interactions, decreased NQ- and AhR-dependent gene expression, consistent with a role for these residues in binding and activation of the AhR by NQs. These studies provide insights into the molecular mechanism of action of NQs and contribute to the development of emerging NQ-based therapeutics.

Molecular mechanism and health effects of 1,2-Naphtoquinone

Extensive literature regarding the health side effects of ambient pollutants (AP) are available, such as diesel exhaust particles (DEPs), but limited studies are available on their electrophilic contaminant 1,2-Naphthoquinone (1,2-NQ), enzymatically derived from naphthalene. This review summarizes relevant toxicologic and biological properties of 1,2-NQ as an environmental pollutant or to a lesser degree as a backbone in drug development to treat infectious diseases. It presents evidence of 1,2-NQ-mediated genotoxicity, neurogenic inflammation, and cytotoxicity due to several mechanistic properties, including the production of reactive oxygen species (ROS), that promote cell damage, carcinogenesis, and cell death. Many signal transduction pathways act as a vulnerable target for 1,2-NQ, including kappaB kinase b (IKKbeta) and protein tyrosine phosphatase 1B (PTP1B). Antioxidant molecules act in defense against ROS/RNS-mediated 1,2-NQ responses to injury. Nonetheless, its inhibitory effects at PTP1B, altering the insulin signaling pathway, represents a new therapeutic target to treat diabetes type 2. Questions exist whether exposure to 1,2-NQ may promote arylation of the Keap1 factor, a negative regulator of Nrf2, as well as acting on the sepiapterin reductase activity, an NADPH-dependent enzyme which catalyzes the formation of critical cofactors in aromatic amino acid metabolism and nitric oxide biosynthesis. Exposure to 1,2-NQ is linked to neurologic, behavioral, and developmental disturbances as well as increased susceptibility to asthma. Limited new knowledge exists on molecular modeling of quinones molecules as antitumoral and anti-microorganism agents. Altogether, these studies suggest that 1,2-NQ and its intermediate compounds can initiate a number of pathological pathways as AP in living organisms but it can be used to better understand molecular pathways.

Particulate matter-induced senescence of skin keratinocytes involves oxidative stress-dependent epigenetic modifications

Ambient air particulate matter (PM) induces senescence in human skin cells. However, the underlying mechanisms remain largely unknown. We investigated how epigenetic regulatory mechanisms participate in cellular senescence induced by PM with a diameter <2.5 (PM2.5) in human keratinocytes and mouse skin tissues. PM2.5-treated cells exhibited characteristics of cellular senescence. PM2.5 induced a decrease in DNA methyltransferase (DNMT) expression and an increase in DNA demethylase (ten-eleven translocation; TET) expression, leading to hypomethylation of the p16INK4A promoter region. In addition, PM2.5 led to a decrease in polycomb EZH2 histone methyltransferase expression, whereas the expression of the epigenetic transcriptional activator MLL1 increased. Furthermore, binding of DNMT1, DNMT3B, and EZH2 to the promoter region of p16INK4A decreased in PM2.5-treated keratinocytes, whereas TET1 and MLL1 binding increased, leading to decreased histone H3 lysine 27 trimethylation (H3K27Me3) and increased H3K4Me3 in the promoter of p16INK4A. PM2.5-induced senescence involved aryl hydrocarbon receptor (AhR)-induced reactive oxygen species (ROS) production. ROS scavenging dampened PM2.5-induced cellular senescence through regulation of DNA and histone methylation. Altogether, our work shows that skin senescence induced by environmental PM2.5 occurs through ROS-dependent the epigenetic modification of senescence-associated gene expression. Our findings provide information for the design of preventive and therapeutic strategies against skin senescence, particularly in light of the increasing problem of PM2.5 exposure due to air pollution.

β-Naphtoflavone and Ethanol Induce Cytochrome P450 and Protect towards MPP⁺ Toxicity in Human Neuroblastoma SH-SY5Y Cells

Cytochrome P450 (CYP) isozymes vary their expression depending on the brain area, the cell type, and the presence of drugs. Some isoforms are involved in detoxification and/or toxic activation of xenobiotics in central nervous system. However, their role in brain metabolism and neurodegeneration is still a subject of debate. We have studied the inducibility of CYP isozymes in human neuroblastoma SH-SY5Y cells, treated with β-naphtoflavone (β-NF) or ethanol (EtOH) as inducers, by qRT-PCR, Western blot (WB), and metabolic activity assays. Immunohistochemistry was used to localize the isoforms in mitochondria and/or endoplasmic reticulum (ER). Tetrazolium (MTT) assay was performed to study the role of CYPs during methylphenyl pyridine (MPP⁺) exposure. EtOH increased mRNA and protein levels of CYP2D6 by 73% and 60% respectively. Both β-NF and EtOH increased CYP2E1 mRNA (4- and 1.4-fold, respectively) and protein levels (64% both). The 7-ethoxycoumarin O-deethylation and dextromethorphan O-demethylation was greater in treatment samples than in controls. Furthermore, both treatments increased by 22% and 18%, respectively, the cell viability in MPP⁺-treated cells. Finally, CYP2D6 localized at mitochondria and ER. These data indicate that CYP is inducible in SH-SY5Y cells and underline this in vitro system for studying the role of CYPs in neurodegeneration.

In vivo exposure to hydroquinone during the early phase of collagen-induced arthritis aggravates the disease

Robust correlation between the severity of rheumatoid arthritis (RA) and cigarette smoking has been clinically demonstrated. Nevertheless, cigarette compounds responsible for this toxic effect and their mechanisms have not been described. Considering that hydroquinone (HQ) is an abundant, pro-oxidative compound of the matter particle phase of cigarette smoke, we investigated whether HQ exposure during the initial phase of collagen-induced arthritis (CIA) could aggravate the disease. For this purpose, male Wistar rats were exposed to aerosolized HQ (25 ppm), saline or 5% ethanol solution (HQ vehicle) for 1 h per day during 14 days. CIA was induced through s.c. injection of bovine collagen Type II (0.4 mg/100 μL) at days seven and 14 of exposure. Clinical signs of disease and the cell profile and chemical mediators in the synovial fluid and membrane were analysed at day 35 after the beginning of exposure. HQ exposure aggravated CIA-related paw edema and increased the cell infiltrate and interleukin-6 (IL-6) levels in the synovial fluid, promoted intense tissue collagen deposition and enhanced synoviocyte proliferation and higher frequency of aryl hydrocarbon receptor (AhR⁺) and interleukin (IL-17⁺) neutrophils in the synovial membrane. in vitro data also highlighted that neutrophils expressed increased levels of AhR, IL-17 and reactive oxygen species (ROS) generation. However, only AhR expression and ROS generation were blocked by in vitro treatment with AhR antagonist. Therefore, we conclude that in vivo HQ exposure at the early phase of AR onset worsens RA, leading to high frequency of AhR/IL-17⁺ neutrophils into the joint.

Hydroquinone exposure worsens the symptomatology of rheumatoid arthritis

The genesis of rheumatoid arthritis (RA) is complex and dependent on genetic background and exposure to environmental xenobiotic. Indeed, smoking is associated to developing and worsening pre-existing RA. Nevertheless, the mechanisms and cigarette compounds involved in the harmful processes have not been elucidated. Here, we investigated if the exposure to hydroquinone (HQ), an abundant pro-oxidative compound of cigarette and benzene metabolite, could worsen the ongoing RA. Hence, collagen-induced arthritis (CIA) was induced in male Wistar rats by s.c. injection of 400 μg (200 μL) of bovine collagen type II emulsified in complete Freund's adjuvant on day 1, and a booster injection was performed on day 7. Exposures to nebulized HQ (25 ppm), saline solution or HQ vehicle solution (5% ethanol in saline) were carried out for 1 h, once a day, on days 21-27 after CIA induction. On day 27, animals were euthanized and samples were collected for further analyses. Exposure to HQ caused loss of weight, intensified paw edema, enhanced levels of tumor necrosis factor-α (TNF-α) and anti-citrullinated protein antibody (ACPA) in the serum; augmented synoviocyte proliferation and influx of aril hydrocarbon receptor (AhR) positive cells into the synovial membrane, altered collagen fibre rearrangement in the synovia, and synoviocytes isolated from HQ exposed rats secreted higher levels of pro-inflammatory cytokines, TNF-α and interleukin-1β. Associated, we point out HQ as an environmental pollutant that aggravates RA, suggesting its participation on worsening RA in smoking patients.

Chemical toxicology of reactive species in the atmosphere: two decades of progress in an electron acceptor and an electrophile

Air pollutants such as diesel exhaust particles (DEP) are thought to cause pulmonary diseases such as asthma as a result of oxidative stress. While DEP contain a large number of polycyclic aromatic hydrocarbons, we have focused on 9,10-phenanthrenequinone (9,10-PQ) and 1,2-naphthoquinone (1,2-NQ) because of their chemical properties based on their oxidative and chemical modification capabilities. We have found that 9,10-PQ interacts with electron donors such as NADPH (in the presence of enzymes) and dithiols, resulting in generation of excess reactive oxygen species (ROS) through redox cycling. We have also shown that 1,2-NQ is able to modify protein thiols, leading to protein adducts associated with activation of redox signal transduction pathways at lower concentrations and toxicity at higher concentrations. In this review, we briefly introduce our findings from the last two decades.