1,2-Naphthoquinone activates vanilloid receptor 1 through increased protein tyrosine phosphorylation, leading to contraction of guinea pig trachea

Disruption of Atrial Rhythmicity by the Air Pollutant 1,2-Naphthoquinone: Role of Beta-Adrenergic and Sensory Receptors

The combustion of fossil fuels contributes to air pollution (AP), which was linked to about 8.79 million global deaths in 2018, mainly due to respiratory and cardiovascular-related effects. Among these, particulate air pollution (PM2.5) stands out as a major risk factor for heart health, especially during vulnerable phases. Our prior study showed that premature exposure to 1,2-naphthoquinone (1,2-NQ), a chemical found in diesel exhaust particles (DEP), exacerbated asthma in adulthood. Moreover, increased concentration of 1,2-NQ contributed to airway inflammation triggered by PM2.5, employing neurogenic pathways related to the up-regulation of transient receptor potential vanilloid 1 (TRPV1). However, the potential impact of early-life exposure to 1,2-naphthoquinone (1,2-NQ) on atrial fibrillation (AF) has not yet been investigated. This study aims to investigate how inhaling 1,2-NQ in early life affects the autonomic adrenergic system and the role played by TRPV1 in these heart disturbances. C57Bl/6 neonate male mice were exposed to 1,2-NQ (100 nM) or its vehicle at 6, 8, and 10 days of life. Early exposure to 1,2-NQ impairs adrenergic responses in the right atria without markedly affecting cholinergic responses. ECG analysis revealed altered rhythmicity in young mice, suggesting increased sympathetic nervous system activity. Furthermore, 1,2-NQ affected β1-adrenergic receptor agonist-mediated positive chronotropism, which was prevented by metoprolol, a β1 receptor blocker. Capsazepine, a TRPV1 blocker but not a TRPC5 blocker, reversed 1,2-NQ-induced cardiac changes. In conclusion, neonate mice exposure to AP 1,2-NQ results in an elevated risk of developing cardiac adrenergic dysfunction, potentially leading to atrial arrhythmia at a young age.

Capture of Electrophilic Quinones in the Extracellular Space: Evidence for a Phase Zero Reaction

Electrophilic quinones are produced during the combustion of gasoline in the atmosphere. Although these reactive species covalently bind to protein-based nucleophiles in cells, resulting in the formation of protein adducts involved in the modulation of redox signaling pathways and cytotoxicity, the extracellular regulation of quinones is not understood. In this study, incubation of 1,2-naphthoquinone (1,2-NQ) with the low-molecular-weight fraction of mouse plasma resulted in the consumption of cysteine (CysSH) in the plasma in a concentration-dependent manner. Covalent modification of albumin was markedly repressed by the addition of either the low-molecular-weight fraction of mouse plasma or CysSH, suggesting that CysSH protects by forming a conjugate with 1,2-NQ. Similar phenomena also occurred for other atmospheric quinones 1,4-NQ and 1,4-benzoquinone (1,4-BQ). The addition of cystine to a culture medium without amino acids enhanced the release of CysSH from A431 cells and blocked 1,2-NQ-mediated arylation of intracellular proteins, suggesting that 1,2-NQ interacts with extracellular CysSH. Liquid chromatography-tandem mass spectrometry analysis revealed that 1,2-NQ and 1,4-BQ undergoes nucleophilic attack by CysSH, yielding a 1,2-NQH₂-SCys adduct and 1,4-BQH₂-SCys adduct, respectively. Unlike 1,2-NQ and 1,4-BQ, the authentic 1,2-NQH₂-SCys adduct and 1,4-BQH₂-SCys adduct had little effect on the covalent modification of cellular proteins and viability of A431 cells. These results suggest that electrophilic quinones are readily trapped by CysSH released from A431 cells, forming less-toxic CysSH adducts and thereby repressing covalent modification of cellular proteins. These findings provide evidence for the existence of a "phase zero" reaction of electrophiles prior to their uptake by cells.

Activation of PTP1B/EGFR signaling and cytotoxicity during combined exposure to ambient electrophiles in A431 cells

Chemical modification of the thiol group on protein tyrosine phosphatase (PTP) 1B triggers an activation of epidermal growth factor receptor (EGFR) signaling that is mimicked by environmental electrophiles through S-modification of PTP1B. While activation of PTP1B/EGFR by a single exposure to an electrophile has been established, the effects of combined exposure to electrophiles are unknown. Here, we examined the activation of EGFR signaling by combined exposure to ambient electrophiles in human epithelial carcinoma A431 cells. Simultaneous exposure to 1,2- and 1,4-naphthoquinone (NQ) augmented the S-modification of endogenous and recombinant human PTP1B (hPTP1B). Combined exposure of hPTP1B or A431 cells to 1,2- and 1,4-NQ escalated the inactivation of PTP compared with individual exposure. Phosphorylation of EGFR and its downstream kinase extracellular signal-regulated kinase (ERK) 1/2 by 1,2-NQ exposure was facilitated by simultaneous exposure to 1,2-NQ with 10 µM 1,4-NQ. An EGFR inhibitor diminished the phosphorylation of ERK1/2, indicating that ERK was phosphorylated following EGFR activation by the NQ cocktail. The combined exposure to NQs also accelerated cell death in A431 cells compared with each NQ alone. While no EGFR/ERK activation was seen following 1,4-benzoquinone (BQ) treatment, exposure to 1,4-NQ in the presence of 1,4-BQ increased 1,4-NQ-mediated activation of EGFR. This suggests that the enhancement of 1,4-NQ-dependent EGFR activation by 1,4-BQ is caused by a different mechanism than 1,2-NQ with 1,4-NQ. These results suggest that combined exposure to ambient electrophiles, even at low concentrations, can induce stronger activation of redox signaling than individual exposure. Our findings indicate that combining different electrophiles may produce unexpected effects.

Potential Interplay between Nrf2, TRPA1, and TRPV1 in Nutrients for the Control of COVID-19

In this article, we propose that differences in COVID-19 morbidity may be associated with transient receptor potential ankyrin 1 (TRPA1) and/or transient receptor potential vanilloid 1 (TRPV1) activation as well as desensitization. TRPA1 and TRPV1 induce inflammation and play a key role in the physiology of almost all organs. They may augment sensory or vagal nerve discharges to evoke pain and several symptoms of COVID-19, including cough, nasal obstruction, vomiting, diarrhea, and, at least partly, sudden and severe loss of smell and taste. TRPA1 can be activated by reactive oxygen species and may therefore be up-regulated in COVID-19. TRPA1 and TRPV1 channels can be activated by pungent compounds including many nuclear factor (erythroid-derived 2) (Nrf2)-interacting foods leading to channel desensitization. Interactions between Nrf2-associated nutrients and TRPA1/TRPV1 may be partly responsible for the severity of some of the COVID-19 symptoms. The regulation by Nrf2 of TRPA1/TRPV1 is still unclear, but suggested from very limited clinical evidence. In COVID-19, it is proposed that rapid desensitization of TRAP1/TRPV1 by some ingredients in foods could reduce symptom severity and provide new therapeutic strategies.

Nrf2-interacting nutrients and COVID-19: time for research to develop adaptation strategies

There are large between- and within-country variations in COVID-19 death rates. Some very low death rate settings such as Eastern Asia, Central Europe, the Balkans and Africa have a common feature of eating large quantities of fermented foods whose intake is associated with the activation of the Nrf2 (Nuclear factor (erythroid-derived 2)-like 2) anti-oxidant transcription factor. There are many Nrf2-interacting nutrients (berberine, curcumin, epigallocatechin gallate, genistein, quercetin, resveratrol, sulforaphane) that all act similarly to reduce insulin resistance, endothelial damage, lung injury and cytokine storm. They also act on the same mechanisms (mTOR: Mammalian target of rapamycin, PPARγ:Peroxisome proliferator-activated receptor, NFκB: Nuclear factor kappa B, ERK: Extracellular signal-regulated kinases and eIF2α:Elongation initiation factor 2α). They may as a result be important in mitigating the severity of COVID-19, acting through the endoplasmic reticulum stress or ACE-Angiotensin-II-AT₁R axis (AT₁R) pathway. Many Nrf2-interacting nutrients are also interacting with TRPA1 and/or TRPV1. Interestingly, geographical areas with very low COVID-19 mortality are those with the lowest prevalence of obesity (Sub-Saharan Africa and Asia). It is tempting to propose that Nrf2-interacting foods and nutrients can re-balance insulin resistance and have a significant effect on COVID-19 severity. It is therefore possible that the intake of these foods may restore an optimal natural balance for the Nrf2 pathway and may be of interest in the mitigation of COVID-19 severity.

[Redox Signaling and Reactive Sulfur Species to Regulate Electrophilic Stress]

Humans are exposed to various xenobiotic electrophiles on a daily basis. Electrophiles form covalent adducts with nucleophilic residues of proteins. Redox signaling, which consists of effector molecules (e.g., kinases and transcription factors) and redox sensor proteins with low pK_a cysteine residues, is involved in cell survival, cell proliferation, quality control of cellular proteins and oxidative stress response. Herein, we showed that at a low dose, xenobiotic electrophiles selectively modified redox sensor proteins through covalent modification of their reactive thiols, resulting in activation of a variety of redox signaling pathways. However, increasing the dose of xenobiotic electrophiles caused non-selective and extensive modification of cellular proteins involved in toxicity. Of interest, reactive sulfur species (RSS), such as hydrogen sulfide (H₂S), cysteine persulfide (CysSSH), glutathione persulfide (GSSH) and even synthetic polysulfide (e.g., Na₂S₄), readily captured xenobiotic electrophiles, forming their sulfur adducts, which was associated with inactivation of the electrophiles. Our findings suggest that an adaptive response through redox signaling activation and RSS-mediated electrophile capturing is involved in the regulation of electrophilic stress.

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.

Transient Receptor Potential Channels and Chronic Airway Inflammatory Diseases: A Comprehensive Review

Chronic airway inflammatory diseases remain a major problem worldwide, such that there is a need for additional therapeutic targets and novel drugs. Transient receptor potential (TRP) channels are a group of non-selective cation channels expressed throughout the body that are regulated by various stimuli. TRP channels have been identified in numerous cell types in the respiratory tract, including sensory neurons, airway epithelial cells, airway smooth muscle cells, and fibroblasts. Different types of TRP channels induce cough in sensory neurons via the vagus nerve. Permeability and cytokine production are also regulated by TRP channels in airway epithelial cells, and these channels also contribute to the modulation of bronchoconstriction. TRP channels may cooperate with other TRP channels, or act in concert with calcium-dependent potassium channels and calcium-activated chloride channel. Hence, TRP channels could be the potential therapeutic targets for chronic airway inflammatory diseases. In this review, we aim to discuss the expression profiles and physiological functions of TRP channels in the airway, and the roles they play in chronic airway inflammatory diseases.

A Chemical Perspective of Pharmacology and Toxicology

My chemical training provided a somewhat different perspective of biolo-gical problems, in the problem itself and approaches to its solution. I was fortunate to have in my laboratory postdocs and students who shared this perspective and used appropriate tools to address problems in amphetamine pharmacology and air pollution toxicology. These apparently disparate areas of research shared two chemical reactions: prooxidant-based generation of reactive oxygen and formation of covalent bonds between electrophiles and biological nucleophiles. This article is an attempt to summarize that research and to identify those individuals who made the contributions.

Experimental and Theoretical Studies on Iron-Promoted Oxidative Annulation of Arylglyoxal with Alkyne: Unusual Addition and Migration on the Aryl Ring

An Fe(III)-promoted oxidative annulation reaction was developed for the synthesis of 1,2-naphthoquinones. A variety of substituted arylglyoxals and internal alkynes undergo the transformation in the presence of FeCl₃ at room temperature to afford the 1,2-naphthoquinone products in good yields in a short reaction time. Interestingly, the products show unusual pseudomigration of the substituent on the arene ring of arylglyoxals. A possible mechanism involving Fe(III)-promoted formation of a vinyl cation from arylglyoxal and alkyne, electrophilic addition of the vinyl cation to the ipso carbon of the aryl group to give a spiral intermediate, and then migration of the keto carbon to the ortho carbon was proposed as key steps and verified using quantum mechanics.

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.

An environmental pollutant, 9,10-phenanthrenequinone, activates human TRPA1 via critical cysteines 621 and 665

Transient receptor potential ankyrin 1 (TRPA1) is activated by noxious cold, mechanical stimulation, and irritant chemicals. In our recent study, 9, 10‐phenanthrenequinone (9,10‐PQ) is the most potent irritant for activation of NRF2 among 1395 cigarette smoke components and it may be, therefore, important to find its additional targets. Here, we show that 9,10‐PQ functions as an activator of TRPA1 in human embryonic kidney (HEK) cells expressing human wild‐type TRPA1 (HEK‐wTRPA1) and human alveolar A549 (A549) cells. Application of 9,10‐PQ at 0.1–10 μmol/L induced a concentration‐dependent Ca²⁺ response as well as inward currents at −50 mV in HEK‐wTRPA1 cells. The current response was blocked by TRPA1 antagonists, HC‐030031 (HC) and A‐967079. To test whether 9,10‐PQ affects the cysteine residues of TRPA1, we expressed mutant TRPA1 channels in HEK cells (HEK‐muTRPA1) in which six different cysteine residues were replaced with serine. Among them, a mutation of cysteine 621 (C621S) abolished the 9,10‐PQ‐induced Ca²⁺ and current responses. The channel activity induced by 9,10‐PQ was also abolished in excised inside‐out patches isolated from HEK‐muTRPA1 cells with the C621S substitution. Although a mutation of cysteine 665 (C665S) reduced the 9,10‐PQ‐induced response, channel sensitization by pretreatment with Cu²⁺ plus 1,10‐phenanthroline and by internal dialysis of 3 μmol/L Ca²⁺ restored the response. However, a double mutant with C621S and C665S substitutions had little response to 9,10‐PQ, even when sensitized by Ca²⁺ dialysis. In A549 cells, 9,10‐PQ induced an HC‐sensitive Ca²⁺ response. Our findings demonstrate that 9,10‐PQ activation of human TRA1 is dependent on cysteine residues 621 and 665.

Airborne quinones induce cytotoxicity and DNA damage in human lung epithelial A549 cells: the role of reactive oxygen species

Ambient particulate matter (PM) is associated with adverse health effects. Quinones present in PM are hypothesized to contribute to these harmful effects through the generation of reactive oxygen species (ROS). However, whether the ROS induced by quinones is involved in mediating DNA damage as well as other biological responses in pulmonary cells is less well known. In this study, the toxic effects of five typical airborne quinones, including 1,2-naphthoquinone, 2-methylanthraquinone, 9,10-phenanthrenequinone, 2-methyl-1,4-naphthoquinone, and acenaphthenequinone, on cytotoxicity, DNA damage, intracellular calcium homeostasis, and ROS generation, were studied in human lung epithelial A549 cells. An antioxidant N-acetylcysteine (NAC) was used to examine the involvement of ROS in adverse biological responses induced by quinones. The quinones caused a concentration-dependent viability decrease, cellular LDH release, DNA damage, and ROS production in A549 cells. 1,2-Naphthoquinone, but not the other four quinones, increased intracellular calcium (Ca(2+)) levels in a dose-dependent manner. These toxic effects were abolished by administration of NAC, suggesting that ROS played a key role in the observed toxic effects of quinones in A549 cells. These results emphasize the importance of quinones in PM on the adverse health effects of PMs, which has been underestimated in the past few years, and highlight the need, when evaluating the effects on health and exposure management, to always consider their qualitative chemical compositions in addition to the size and concentration of PMs.

Activation of EGFR/MEK/ERK/AP-1 signaling mediated by 1,2-naphthoquinone, an atmospheric electrophile, in human pulmonary A549 cells

1,2-Naphthoquinone (1,2-NQ) is found to be an electrophile contaminated in the atmosphere. Although we found that 1,2-NQ activates epidermal growth factor receptor (EGFR) coupled to inhibition of protein tyrosine phosphatase 1B (PTP1B) activity through covalent modification of Cys121 in human epithelial A431 cells, modulation of its downstream signal transduction pathway caused by 1,2-NQ remains to be elucidated. In the present study, we examined whether 1,2-NQ could affect such cellular signaling in human pulmonary A549 cells. Exposure of A549 cells to 1,2-NQ increased EGFR phosphorylation, resulting in activation of MEK/ERK signaling that was blocked by either PD15035 or PD98059. As a result, DNA binding activity of transcription factor AP-1 was enhanced during exposure to 1,2-NQ in the cells. These results suggest that the atmospheric electrophile phosphorylates EGFR, thereby activating the MEK/ERK/AP-1 signal transduction pathway in A549 cells.

Early postnatal, but not late, exposure to chemical ambient pollutant 1,2-naphthoquinone increases susceptibility to pulmonary allergic inflammation at adulthood

High diesel exhaust particle levels are associated with increased health effects; however, knowledge on the impact of its chemical contaminant 1,2-naphthoquinone (1,2-NQ) is limited. We investigated whether postnatal and adult exposures to 1,2-NQ influence allergic reaction and the roles of innate and adaptive immunity. Male neonate (6 days) and adult (56 days) C57Bl/6 mice were exposed to 1,2-NQ (100 nM; 15 min) for 3 days, and on day 59, they were sensitized and later challenged with ovalbumin (OVA). Airway hyper-responsiveness (AHR) and production of cytokines, immunoglobulin E (IgE) and leukotriene B4 (LTB4) were measured in the airways. Postnatal exposure to 1,2-NQ activated dendritic cells in splenocytes by increasing expressing cell surface molecules (e.g., CD11c). Co-exposure to OVA effectively polarized T helper (Th) type 2 (Th2) by secreting Th2-mediated cytokines. Re-stimulation with unspecific stimuli (PMA and ionomycin) generated a mixed Th1 (CD4(+)/IFN-γ(+)) and Th17 (CD4(+)/IL-17(+)) phenotype in comparison with the vehicle-matched group. Postnatal exposure to 1,2-NQ did not induce eosinophilia in the airways at adulthood, although it evoked neutrophilia and exacerbated OVA-induced eosinophilia, Th2 cytokines, IgE and LTB4 production without affecting AHR and mast cell degranulation. At adulthood, 1,2-NQ exposure evoked neutrophilia and increased Th1/Th2 cytokine levels, but failed to affect OVA-induced eosinophilia. In conclusion, postnatal exposure to 1,2-NQ increases the susceptibility to antigen-induced asthma. The mechanism appears to be dependent on increased expression of co-stimulatory molecules, which leads to cell presentation amplification, Th2 polarization and enhanced LTB4, humoral response and Th1/Th2 cytokines. These findings may be useful for future investigations on treatments focused on pulmonary illnesses observed in children living in heavy polluted areas.

Inflammation-related effects of diesel engine exhaust particles: studies on lung cells in vitro

Diesel exhaust and its particles (DEP) have been under scrutiny for health effects in humans. In the development of these effects inflammation is regarded as a key process. Overall, in vitro studies report similar DEP-induced changes in markers of inflammation, including cytokines and chemokines, as studies in vivo. In vitro studies suggest that soluble extracts of DEP have the greatest impact on the expression and release of proinflammatory markers. Main DEP mediators of effects have still not been identified and are difficult to find, as fuel and engine technology developments lead to continuously altered characteristics of emissions. Involved mechanisms remain somewhat unclear. DEP extracts appear to comprise components that are able to activate various membrane and cytosolic receptors. Through interactions with receptors, ion channels, and phosphorylation enzymes, molecules in the particle extract will trigger various cell signaling pathways that may lead to the release of inflammatory markers directly or indirectly by causing cell death. In vitro studies represent a fast and convenient system which may have implications for technology development. Furthermore, knowledge regarding how particles elicit their effects may contribute to understanding of DEP-induced health effects in vivo, with possible implications for identifying susceptible groups of people and effect biomarkers.

Hydroxyl radical generation mechanism during the redox cycling process of 1,4-naphthoquinone

Airborne quinones contribute to adverse health effects of ambient particles probably because of their ability to generate hydroxyl radicals (·OH) via redox cycling, but the mechanisms remain unclear. We examined the chemical mechanisms through which 1,4-naphthoquinone (1,4-NQ) induced ·OH, and the redox interactions between 1,4-NQ and ascorbate acid (AscH(2)). First, ·OH formation by 1,4-NQ was observed in cellular and acellular systems, and was enhanced by AscH(2). AscH(2) also exacerbated the cytotoxicity of 1,4-NQ in Ana-1 macrophages, at least partially due to enhanced ·OH generation. The detailed mechanism was studied in an AscH(2)/H(2)O(2) physiological system. The existence of a cyclic 1,4-NQ process was shown by detecting the corresponding semiquinone radical (NSQ·-) and hydroquinone (NQH(2)). 1,4-NQ was reduced primarily to NSQ·- by O2·- (which was from AscH(2) reacting with H(2)O(2)), not by AscH(2) as normally thought. At lower doses, 1,4-NQ consumed O2·- to suppress ·OH; however, at higher doses, 1,4-NQ presented a positive association with ·OH. The reaction of NSQ·- with H(2)O(2) to release ·OH was another important channel for OH radical formation except for Haber-Weiss reaction. As a reaction precursor for O2·-, the enhanced ·OH response to 1,4-NQ by AscH(2) was indirect. Reducing substrates were necessary to sustain the redox cycling of 1,4-NQ, leading to more ·OH and a deleterious end point.

Linking oxidative events to inflammatory and adaptive gene expression induced by exposure to an organic particulate matter component

BACKGROUND

Toxicological studies have correlated inflammatory effects of diesel exhaust particles (DEP) with its organic constituents, such as the organic electrophile 1,2-naphthoquinone (1,2-NQ).

OBJECTIVE

To elucidate the mechanisms involved in 1,2-NQ-induced inflammatory responses, we examined the role of oxidant stress in 1,2-NQ-induced expression of inflammatory and adaptive genes in a human airway epithelial cell line.

METHODS

We measured cytosolic redox status and hydrogen peroxide (H2O2) in living cells using the genetically encoded green fluorescent protein (GFP)-based fluorescent indicators roGFP2 and HyPer, respectively. Expression of interleukin-8 (IL-8), cyclooxygenase-2 (COX-2), and heme oxygenase-1 (HO-1) mRNA was measured in BEAS-2B cells exposed to 1,2-NQ for 1-4 hr. Catalase overexpression and metabolic inhibitors were used to determine the role of redox changes and H2O2 in 1,2-NQ-induced gene expression.

RESULTS

Cells expressing roGFP2 and HyPer showed a rapid loss of redox potential and an increase in H2O2 of mitochondrial origin following exposure to 1,2-NQ. Overexpression of catalase diminished the H2O2-dependent signal but not the 1,2-NQ-induced loss of reducing potential. Catalase overexpression and inhibitors of mitochondrial respiration diminished elevations in IL-8 and COX-2 induced by exposure to 1,2-NQ, but potentiated HO-1 mRNA levels in BEAS cells.

CONCLUSION

These data show that 1,2-NQ exposure induces mitochondrial production of H2O2 that mediates the expression of inflammatory genes, but not the concurrent loss of reducing redox potential in BEAS cells. 1,2-NQ exposure also causes marked expression of HO-1 that appears to be enhanced by suppression of H2O2. These findings shed light into the oxidant-dependent events that underlie cellular responses to environmental electrophiles.

The chemical biology of naphthoquinones and its environmental implications

Quinones are a group of highly reactive organic chemical species that interact with biological systems to promote inflammatory, anti-inflammatory, and anticancer actions and to induce toxicities. This review describes the chemistry, biochemistry, and cellular effects of 1,2- and 1,4-naphthoquinones and their derivatives. The naphthoquinones are of particular interest because of their prevalence as natural products and as environmental chemicals, present in the atmosphere as products of fuel and tobacco combustion. 1,2- and 1,4-naphthoquinones are also toxic metabolites of naphthalene, the major polynuclear aromatic hydrocarbon present in ambient air. Quinones exert their actions through two reactions: as prooxidants, reducing oxygen to reactive oxygen species; and as electrophiles, forming covalent bonds with tissue nucleophiles. The targets for these reactions include regulatory proteins such as protein tyrosine phosphatases; Kelch-like ECH-associated protein 1, the regulatory protein for NF-E2-related factor 2; and the glycolysis enzyme glyceraldehyde-3-phosphate dehydrogenase. Through their actions on regulatory proteins, quinones affect various cell signaling pathways that promote and protect against inflammatory responses and cell damage. These actions vary with the specific quinone and its concentration. Effects of exposure to naphthoquinones as environmental chemicals can vary with the physical state, i.e., whether the quinone is particle bound or is in the vapor state. The exacerbation of pulmonary diseases by air pollutants can, in part, be attributed to quinone action.

Inhibition of DNA binding activity of cAMP response element-binding protein by 1,2-naphthoquinone through chemical modification of Cys-286

1,2-Naphthoquinone (1,2-NQ) is an atmospheric electrophile that reacts covalently with protein thiols. Our previous study revealed that exposure of bovine aortic endothelial cells to 1,2-NQ causes covalent modification of cAMP response element-binding protein (CREB), thereby inhibiting its DNA binding activity and substantial gene expression of B-cell lymphoma-2 (Bcl-2) that is regulated by this transcription factor. In this study, we identified the modification sites of CREB that are associated with the decreased transcriptional activity. Matrix-assisted laser desorption and ionization time-of-flight mass spectrometry (MALDI-TOF/MS) analysis indicated that three amino acids (Cys-286, Lys-290, and Lys-319) were irreversibly modified by 1,2-NQ. Mutational analysis revealed that electrophilic modification of Cys-286, but not the other two amino acids, at the DNA binding domain is essential for the reduced CREB activity. Substitution of Cys-286 with tryptophan (C286W), which mimics CREB modification by 1,2-NQ, supported this notion. These results suggest that the covalent interaction of CREB with 1,2-NQ through Cys-286 blocks the DNA binding activity of CREB, resulting in the repression of CREB-regulated genes.

Immunochemical method to detect proteins that undergo selective modification by 1,2-naphthoquinone derived from naphthalene through metabolic activation

Naphthalene undergoes biotransformation by a variety of enzymes to yield 1,2-naphthoquinone (1,2-NQ), a reactive metabolite that binds covalently to proteins. Because this covalent modification is thought to account for naphthalene toxicity, a procedure to detect 1,2-NQ bound to macromolecules is required. In this study, we prepared a polyclonal antibody against 1,2-NQ and examined the specificities of the antibody for various aromatic structures and for the regiochemistry of the quinone functionality. Western blot analysis revealed that the antibody prepared against 1,2-NQ recognized the naphthalene moiety with the ortho-dicarbonyl group, but not with the para-dicarbonyl group; in addition, little cross-reactivity of ortho-quinones with different numbers of aromatic rings (n = 1, 3, 4, 5, 6) was seen. Dot blot and Western blot analyses with the polyclonal antibody enabled quantitative determination of the formation of protein-bound 1,2-NQ during the metabolic activation of naphthalene. The present method can be expected to applicable for the identification of the molecular targets of 1,2-NQ derived from naphthalene in cells and tissues.

Toxicological disruption of signaling homeostasis: tyrosine phosphatases as targets

The protein tyrosine phosphatases (PTPs) consist of a diverse group of enzymes whose activity opposes that of the tyrosine kinases. As such, the PTPs have critical roles in maintaining signaling quiescence in resting cells and in restoring homeostasis by effecting signal termination. Interest in these enzymes has increased in recent years following the discovery that the activity of PTPs is modulated through redox mechanisms during signaling. The molecular features that enable redox regulation of PTPs during physiological signaling also render them highly susceptible to oxidative and electrophilic inactivation by a broad spectrum of structurally disparate xenobiotic compounds. The loss of PTP activity results in a profound disregulation of protein phosphotyrosine metabolism, leading to widespread and persistent activation of signaling cascades in the cell.

Involvement of sensory nerves and TRPV1 receptors in the rat airway inflammatory response to two environment pollutants: diesel exhaust particles (DEP) and 1,2-naphthoquinone (1,2-NQ)

The environmental chemical 1,2-naphthoquinone (1,2-NQ) is implicated in the exacerbation of airways diseases induced by exposure to diesel exhaust particles (DEP), which involves a neurogenic-mediated mechanism. Plasma extravasation in trachea, main bronchus and lung was measured as the local (125)I-bovine albumin accumulation. RT-PCR quantification of TRPV1 and tachykinin (NK(1) and NK(2)) receptor gene expression were investigated in main bronchus. Intratracheal injection of DEP (1 and 5 mg/kg) or 1,2-NQ (35 and 100 nmol/kg) caused oedema in trachea and bronchus. 1,2-NQ markedly increased the DEP-induced responses in the rat airways in an additive rather than synergistic manner. This effect that was significantly reduced by L-732,138, an NK(1) receptor antagonist, and in a lesser extent by SR48968, an NK(2) antagonist. Neonatal capsaicin treatment also markedly reduced DEP and 1,2-NQ-induced oedema. Exposure to pollutants increased the TRPV1, NK(1) and NK(2) receptors gene expression in bronchus, an effect was partially suppressed by capsaicin treatment. In conclusion, our results are consistent with the hypothesis that DEP-induced airways oedema is highly influenced by increased ambient levels of 1,2-NQ and takes place by neurogenic mechanisms involving up-regulation of TRPV1 and tachykinin receptors.

Epidermal growth factor receptor activation by diesel particles is mediated by tyrosine phosphatase inhibition

Exposure to particulate matter (PM) is associated with increased cardiopulmonary morbidity and mortality. Diesel exhaust particles (DEP) are a major component of ambient PM and may contribute to PM-induced pulmonary inflammation. Proinflammatory signaling is mediated by phosphorylation-dependent signaling pathways whose activation is opposed by the activity of protein tyrosine phosphatases (PTPases) which thereby function to maintain signaling quiescence. PTPases contain an invariant catalytic cysteine that is susceptible to electrophilic attack. DEP contain electrophilic oxy-organic compounds that may contribute to the oxidant effects of PM. Therefore, we hypothesized that exposure to DEP impairs PTPase activity allowing for unopposed basal kinase activity. Here we report that exposure to 30 microg/cm(2) DEP for 4 h induces differential activation of signaling in primary cultures of human airway epithelial cells (HAEC), a primary target cell in PM inhalation. In-gel kinase activity assay of HAEC exposed to DEPs of low (L-DEP), intermediate (I-DEP) or high (H-DEP) organic content showed differential activation of intracellular kinases. Exposure to these DEP also induced varying levels of phosphorylation of the receptor tyrosine kinase EGFR in a manner that requires EGFR kinase activity but does not involve receptor dimerization. We demonstrate that treatment with DEP results in an impairment of total and EGFR-directed PTPase activity in HAEC with a potency that is independent of the organic content of these particles. These data show that DEP-induced EGFR phosphorylation in HAEC is the result of a loss of PTPase activities which normally function to dephosphorylate EGFR in opposition to baseline EGFR kinase activity.

Transient receptor potential vanilloid channels in hypertension, inflammation, and end organ damage: an imminent target of therapy for cardiovascular disease?

PURPOSE OF REVIEW

The possible role of several neurohormonal factors in pathogenesis of hypertension has been studied extensively both in humans and in experimental animal models. However, controversial data from some previous studies are indecisive and call for reassessment and development of new targets. This mini-review presents some of the most recent findings about the role of transient receptor potential vanilloid type 1 channels in the development of hypertension and its pathology.

RECENT FINDINGS

The transient receptor potential vanilloid type 1, channel activated by novel endovanilloids or altered pH, temperature, and/or local hemodynamics, may serve as a distinct molecular sensor detecting sodium and water balance and may play a role in preventing salt-induced hypertension and tissue damage. Impairment of the function of the transient receptor potential vanilloid type 1 channels may contribute to increased salt sensitivity, inflammation, and end organ damage.

SUMMARY

Emerging evidence indicates that the transient receptor potential vanilloid type 1 channel plays a key role in cardiovascular health and disease by acting as a sensor and regulator of cardiovascular homeostasis and a protector against cardiovascular injury. Given the huge population who suffers from cardiovascular disease, the study of the transient receptor potential vanilloid channels may improve our understanding of pathogenesis of several common cardiovascular disorders and may lead to the development of therapy for hypertension, inflammation, and organ damage.

Diesel exhaust increases EGFR and phosphorylated C-terminal Tyr 1173 in the bronchial epithelium

Background

Epidemiological studies have demonstrated adverse health effects of environmental pollution. Diesel exhaust (DE) is a major contributor to particulate matter pollution. DE exposure has been shown to induce a pronounced inflammatory response in the airways, together with an enhanced epithelial expression of cytokines such as IL-8, Gro-α, IL-13 and activation of redox sensitive transcription factors (NFκB, AP-1), and MAP kinases (p38, JNK). The aim of the present investigation was to elucidate the involvement of the epidermal growth factor receptor (EGFR) signalling pathway in the epithelial response to DE in-vivo.

Results

Immunohistochemical staining was used to quantify the expression of the EGFR, phosphorylated Tyrosine residues, MEK and ERK in the bronchial epithelium of archived biopsies from 15 healthy subjects following exposure to DE (PM₁₀, 300 μg/m³) and air. DE induced a significant increases in the expression of EGFR (p = 0.004) and phosphorylated C-terminal Tyr 1173 (p = 0.02). Other investigated EGFR tyrosine residues, Src related tyrosine (Tyr 416), MEK and ERK pathway were not changed significantly by DE.

Conclusion

Exposure to DE (PM₁₀, 300 μg/m³) caused enhanced EGFR expression and phosphorylation of the tyrosine residue (Tyr 1173) which is in accordance with the previously demonstrated activation of the JNK, AP-1, p38 MAPK and NFkB pathways and associated downstream signalling and cytokine production. No effects were seen on the MEK and ERK pathway suggesting that at the investigated time point (6 hours post exposure) there was no proliferative/differentiation signalling in the bronchial epithelium. The present findings suggest a key role for EGFR in the bronchial response to diesel exhaust.

[Chemical biology of 1,2-naphthoquinone, a novel air pollutant that affects signal transduction pathways]

Prolonged exposure of humans to ambient particulate matter such as diesel exhaust particles (DEP) induces a variety of adverse health effects including cardiovascular diseases, asthma and cancer. Polycyclic aromatic hydrocarbons (PAHs) and their derivatives in DEP are thought to be potential candidates for the deleterious effects of DEP. We have identified 1,2-naphthoquinone (1,2-NQ) as a novel PAH quinone that contaminates DEP. Because 1,2-NQ is covalently bound to macromolecules through reactive thiols (thiolate ions), our rationale was that cellular proteins modified by 1,2-NQ seem to act as a redox-sensor and thus the interaction of thiol proteins with 1,2-NQ may disrupt their functions. To address our hypothesis, we prepared specific antibody against 1,2-NQ bound to proteins. In this review, we introduce an inhibitor of kappaB kinasebeta (IKKbeta) and protein tyrosine phosphatase 1B (PTP1B) as target molecules for 1,2-NQ. Although IKKbeta activates transcription factor NF-kappaB and PTP1B negatively regulates the receptor-protein tyrosine kinase, such as epidermal growth factor receptor (EGFR) in cells, covalent modification of these proteins caused by 1,2-NQ results in inhibition of NF-kappaB activity and transactivation of EGFR.

Comparison of the effect of phenol and its derivatives on protein and free radical formation in human erythrocytes (in vitro)

The effect of phenolic compounds: phenol, 2,4-dichlorophenol (2,4-DCP), 2,4-dimethylphenol (2,4-DMP) and catechol on human erythrocytes was studied. The level of fluorescent label - 6-carboxy-2',7'-dichlorodihydrofluorescein diacetate (H(2)DCFDA) oxidation by phenolic compounds in erythrocytes as well as the carbonyl group content and hemoglobin denaturation were monitored. H(2)DCFDA has been utilized extensively as a marker for studies of oxidative stress at the cellular level. We noted that 2,4-DCP, 2,4-DMP and catechol induced an increase in the concentration- and time-dependent H(2)DCFDA oxidation. We also observed an increase in carbonyl group content and the changes in parameter T (denaturation of hemoglobin) in erythrocytes incubated with 2,4-DCP, catechol and 2,4-DMP. The highest level of H(2)DCFDA oxidation was provoked by 2,4-DCP. The biggest changes of proteins in erythrocytes measured as the carbonyl group content were induced by 2,4-DMP, but measured as parameter T they were induced by catechol. It was observed that phenol did not oxidize H(2)DCFDA up to the concentration of 2.5 mM after 3 h of incubation. Phenol did not affect the carbonyl group content but decreased parameter T (induced denaturation of hemoglobin). To sum up, the kind of the substituent in a phenolic ring determines the molecular mechanism of action of the individual compound and the capacity of reactive oxygen species generation and thus damages the specified structures in human erythrocytes.

Chemical knockdown of protein-tyrosine phosphatase 1B by 1,2-naphthoquinone through covalent modification causes persistent transactivation of epidermal growth factor receptor

1,2-Naphthoquinone (1,2-NQ), an atmospheric contaminant, causes the contraction of guinea pig trachea through the activation of epidermal growth factor receptor (EGFR) by inhibiting protein-tyrosine phosphatases (PTPs). Phosphorylation of EGFR is negatively regulated by PTPs, but details of the mechanism by which 1,2-NQ inhibits PTPs have not been elucidated. Results described in this report demonstrate that 1,2-NQ forms covalent bonds with PTP1B after exposure to human epithelial A431 cells. In this study, a concentration-dependent phosphorylation of EGFR was found to be coupled to the reduction of PTP activity in the cells. The reduction in PTP activity was due to the irreversible modification of PTP1B, and when PTP1B was overexpressed by the cells, the 1,2-NQ-mediated EGFR phosphorylation was suppressed. Studies with purified PTP1B and 1,2-NQ showed that the reduction in enzyme activity was due to a nucleophilic attack by the quinone on the enzyme, to form covalent bonds. Matrix-assisted laser desorption and ionization time-of-flight mass spectrometry analysis and mutation experiments revealed that PTP1B inactivation was primarily due to covalent attachment of the quinone to Cys-121 of the enzyme, with binding to His-25 and Cys-215 as well. Collectively, the results show that covalent attachment of 1,2-NQ to PTP1B is at least partially responsible for the reduction of PTP activity, which leads to prolonged transactivation of EGFR in the cells.

Relationship between redox activity and chemical speciation of size-fractionated particulate matter

BACKGROUND

Although the mechanisms of airborne particulate matter (PM) related health effects remain incompletely understood, one emerging hypothesis is that these adverse effects derive from oxidative stress, initiated by the formation of reactive oxygen species (ROS) within affected cells. Typically, ROS are formed in cells through the reduction of oxygen by biological reducing agents, with the catalytic assistance of electron transfer enzymes and redox active chemical species such as redox active organic chemicals and metals. The purpose of this study was to relate the electron transfer ability, or redox activity, of the PM samples to their content in polycyclic aromatic hydrocarbons and various inorganic species. The redox activity of the samples has been shown to correlate with the induction of the stress protein, hemeoxygenase-1.

RESULTS

Size-fractionated (i.e. < 0.15; < 2.5 and 2.5 - 10 microm in diameter) ambient PM samples were collected from four different locations in the period from June 2003 to July 2005, and were chemically analyzed for elemental and organic carbon, ions, elements and trace metals and polycyclic aromatic hydrocarbons. The redox activity of the samples was evaluated by means of the dithiothreitol activity assay and was related to their chemical speciation by means of correlation analysis. Our analysis indicated a higher redox activity on a per PM mass basis for ultrafine (< 0.15 microm) particles compared to those of larger sizes. The PM redox activity was highly correlated with the organic carbon (OC) content of PM as well as the mass fractions of species such as polycyclic aromatic hydrocarbons (PAH), and selected metals.

CONCLUSION

The results of this work demonstrate the utility of the dithiothreitol assay for quantitatively assessing the redox potential of airborne particulate matter from a wide range of sources. Studies to characterize the redox activity of PM from various sources throughout the Los Angeles basin are currently underway.

Effects of naphthoquinone on airway responsiveness in the presence or absence of antigen in mice

We have recently demonstrated that naphthoquinone (NQ), one of extractable chemical compounds of diesel exhaust particles (DEP), enhances antigen-related airway inflammation with goblet cell hyperplasia in mice (Inoue et al. in Eur Respir J 209(2):259-267, 2007). Further, NQ has enhanced lung expressions of interleukin (IL)-4 and IL-5. However, the effects of NQ on other cardinal features of asthma have not been completely investigated. The aim of the present study was to evaluate the effects of NQ on airway responsiveness on the model. Vehicle, NQ, ovalbumin (OVA), or NQ + OVA was administered intratarcheally to ICR mice for 6 weeks. Twenty-four hours after the last instillation, lung histology, lung functions such as total respiratory system resistance (R) and Newtonian resistance (R (n)), and protein level of IL-13 and mRNA level for MUC5AC in the lung were examined. Repetitive exposure to NQ aggravated antigen-related lung inflammation. NQ alone enhanced R and R (n) as compared to vehicle without statistical significance. OVA alone or NQ plus OVA showed increases in R and R (n), which was prominent in NQ plus OVA (P < 0.05 vs. vehicle). Combined exposure to NQ and OVA elevated the levels of IL-13 and MUC5AC in the lung as compared with exposure to NQ or OVA alone. These results indicate that NQ can enhance airway hyperresponsiveness in the presence or absence of an antigen. Also, amplified lung expressions of IL-13 and MUC5AC might partly contribute to the deterioration of asthma features by NQ.

An environmental quinoid polycyclic aromatic hydrocarbon, acenaphthenequinone, modulates cyclooxygenase-2 expression through reactive oxygen species generation and nuclear factor kappa B activation in A549 cells

Diesel exhaust particles (DEPs) contain oxygen-containing polycyclic aromatic hydrocarbons (PAHs) called quinoid PAHs. Some quinoid PAHs generate free radicals as they undergo enzymatic and nonenzymatic redox cycling with their corresponding semiquinone radicals. Reactive oxygen species (ROS) produced by these reactions can cause severe oxidative stress connected with inflammatory processing. Although humans and animals are continuously exposed to these chemicals in the environment, little is known about which quinoid PAHs are active. In this study, we estimated the intracellular ROS production and nuclear factor kappa B (NF-kappaB) translocation in A549 cells exposed to isomers of quinoid PAHs having two to four rings. We found that both acenaphthenequinone (AcQ) and 9,10-phenanthrenequinone (PQ) enhanced ROS generation and that AcQ translocated NF-kappaB from the cytosol to the nucleus. However, PQ, which has been reported to induce apoptosis, did not influence NF-kappaB activation. In addition, AcQ induced cyclooxygenase-2 (COX-2) expression which is a key enzyme in the inflammatory processing involved in the activation of NF-kappaB. Upregulation of NF-kappaB and COX-2 expression by AcQ treatment was suppressed by the antioxidant N-acetylcysteine (NAC). These results provide that AcQ might play an important role in human lung inflammatory diseases as an air pollutant.