The chemical biology of naphthoquinones and its environmental implications

Multiphase Radical Chemical Processes Induced by Air Pollutants and the Associated Health Effects

Air pollution is increasingly recognized as a significant health risk, yet our understanding of its underlying chemical and physiological mechanisms remains incomplete. Fine particulate matter (PM2.5) and ozone (O3) interact with biomolecules in intracellular and microenvironments, such as the epithelial lining fluid (ELF), leading to the generation of reactive oxygen species (ROS). These ROS trigger cellular inflammatory responses and oxidative stress, contributing to a spectrum of diseases affecting the respiratory, cardiovascular, and central nervous systems. Extensive epidemiological and toxicological research highlights the pivotal role of ROS in air pollution-related diseases. It is crucial to comprehend the intricate chemical processes and accompanying physiological effects of ROS from air pollutants. This review aims to systematically summarize ROS generation mechanisms in the ELF and measurement techniques of oxidative potential (OP), taking the kinetic reactions of ROS cycling in the ELF as an example, and discusses the general health implications of ROS in respiratory, cardiovascular, and central nervous systems. Understanding these processes through interdisciplinary research is essential to develop effective and precise strategies as well as air quality standards to mitigate the public health impacts of air pollution globally.

Multi-defense pathways against electrophiles through adduct formation by low molecular weight substances with sulfur atoms

There is a variety of electrophiles in the environment. In addition, there are precursor chemicals that undergo metabolic activation by enzymes and conversion to electrophiles in the body. Although electrophiles covalently bind to protein nucleophiles, they also form adducts associated with adaptive or toxic responses. Low molecular weight compounds containing sulfur are capable of blocking such adduct formation by capturing the electrophiles. In this review, we present our findings on the capture and inactivation of electrophiles by: (i) intracellular glutathione, (ii) reactive sulfur species, and (iii) extracellular cysteine (formed during the production of sulfur adducts). These actions not only substantially suppress electrophilic activity but also regulate protein adduct formation.

Fused oxazepine-naphthoquinones as novel cytotoxic agents with diverse modes of action in yeast

The naphthoquinone moiety is commonly found in numerous natural cytotoxic compounds with diverse and pleiotropic modes of action (MOAs). The moiety can exist as a standalone pharmacophore or combined with other pharmacophores to enrich their MOAs. Here, we report that the synthetic fusion of naphthoquinones and oxazepines provides potent cytotoxic compounds with diverse MOAs. Fused oxazepine-naphthoquinones were identified through a cytotoxic screen in Saccharomyces cerevisiae. The two most active compounds, CM-568 and CM-728, contained the same 3-pyridyl appendage in the oxazepine ring and were further evaluated along with close chemical derivatives. Both were highly cytotoxic, killing yeast cells in the low micromolar range; however, the role of reactive oxygen species in their MOA was significantly different. Investigations with yeast strains specifically designed to assess cell cycle, chromatin compaction, and nucleolar activity suggest that at lethal concentrations, cells die shortly after drug exposure through programmed death. Conversely, at sublethal concentrations, cell cycle progression is severely impaired. Interestingly, CM-568 labels cells with highly refractive non-fluorescent parallel rods. We conclude that the oxazepine moiety confers novel cytotoxic MOAs to naphthoquinones, which may be potentially useful in pharmacology.

Development of an at-line coupling of LC-QTOF-ESI-MS/MS to steroid 5-alpha reductase inhibition assay, a fast bioactive targeting and guided purification of natural complex sample, Impatiens balsamina Linn

This study provides a rapid and accurate method for screening steroid 5-alpha reductase (S5αR) inhibitors in Impatiens balsamina Linn (IB). using at-line LC-QTOF-ESI-MS/MS coupling S5αR inhibitory assay. IB (Balsaminaceae) is an annual herbaceous plant cultivated in tropical and subtropical regions. It has been used in traditional Chinese and Thai medicine for treatment of hair loss and various skin conditions, potentially through anti-androgenic mechanisms. A combined approach of S5αR inhibitory assay and LC-QTOF-ESI-MS/MS was developed to rapidly screen for target biomarkers and guide their isolation using preparative HPLC. The toxicity of both the extract and isolated biomarkers was evaluated on skin cells, keratinocytes, and fibroblasts. Eight bioactive compounds were identified as two naphthoquinone, two fatty acid derivatives, three nitrogenous compounds and one aromatic derivative. The most potent bioactive markers, identified as 2-methoxy-1,4-naphthoquinone (2MN) and impateinol, were targeted and isolated using preparative HPLC, yielding 5.0 % and 3.5 %, respectively. These compounds exhibited S5αR inhibitory activity higher than that of finasteride drug by 10 and 2 times, respectively. Both the isolated biomarkers and the extract demonstrated a broad therapeutic index. The developed method in this study proved to be both rapid and accurate, making it suitable for screening and targeting S5αR inhibitors in herbal plants or complex matrix samples. It facilitated the fast-guided isolation of bioactive compounds, highlighting its potential for future applications in drug discovery research.

Epigenetic Regulation of CXC Chemokine Expression by Environmental Electrophiles Through DNA Methyltransferase Inhibition

Ubiquitously distributed environmental electrophiles covalently modify DNA and proteins, potentially leading to adverse health effects. However, the impacts of specific electrophiles on target proteins and their physiological roles remain largely unknown. In the present study, we focused on DNA methylation, which regulates gene expression and physiological responses. A total of 45 environmental electrophiles were screened for inhibitory effects on the activity of DNA methyltransferase 3B (DNMT3B), a key enzyme in DNA methylation, and four compounds were identified. We focused on 1,2-naphthoquinone (1,2-NQ), an air pollutant whose toxicity has been reported previously. Interestingly, we found that 1,2-NQ modified multiple lysine and histidine residues in DNMT3B, one of which was near the active site in DNMT3B. It was found that 1,2-NQ altered gene expression and evoked inflammatory responses in lung adenocarcinoma cell lines. Furthermore, we found that 1,2-NQ upregulated CXCL8 expression through DNA demethylation of the distal enhancer and promoted cancer cell growth. Our study reveals novel mechanisms of epigenetic regulation by environmental electrophiles through the inhibition of DNMT3B activity and suggests their physiological impact.

New synergistic benzoquinone scaffolds as inhibitors of mycobacterial cytochrome bc1 complex to treat multi-drug resistant tuberculosis

Through a comprehensive molecular docking study, a unique series of naphthoquinones clubbed azetidinone scaffolds was arrived with promising binding affinity to Mycobacterial Cytbc1 complex, a drug target chosen to kill multi-drug resistant Mycobacterium tuberculosis (MDR-Mtb). Five compounds from series-2, 2a, 2c, 2g, 2h, and 2j, showcased significant in vitro anti-tubercular activities against Mtb H37Rv and MDR clinical isolates. Further, synergistic studies of these compounds in combination with INH and RIF revealed a potent bactericidal effect of compound 2a at concentration of 0.39 μg/mL, and remaining (2c, 2g, 2h, and 2j) at 0.78 μg/mL. Exploration into the mechanism study through chemo-stress assay and proteome profiling uncovered the down-regulation of key proteins of electron-transport chain and Cytbc1 inhibition pathway. Metabolomics corroborated these proteome findings, and heightened further understanding of the underlying mechanism. Notably, in vitro and in vivo animal toxicity studies demonstrated minimal toxicity, thus underscoring the potential of these compounds as promising anti-TB agents in combination with RIF and INH. These active compounds adhered to Lipinski's Rule of Five, indicating the suitability of these compounds for drug development. Particular significance of molecules NQ02, 2a, and 2h, which have been patented (Published 202141033473).

de Oliveira A, Pascoal ACRF, Cruz AL, Nascimento V. New Chalcogen-Functionalized Naphthoquinones: Design, Synthesis, and Evaluation, In Vitro and In Silico, against Squamous Cell Carcinoma

Due to the growth in the number of patients and the complexity involved in anticancer therapies, new therapeutic approaches are urgent and necessary. In this context, compounds containing the selenium atom can be employed in developing new medicines due to their potential therapeutic efficacy and unique modes of action. Furthermore, tellurium, a previously unknown element, has emerged as a promising possibility in chalcogen-containing compounds. In this study, 13 target compounds (9a-i, 10a-c, and 11) were effectively synthesized as potential anticancer agents, employing a CuI-catalyzed Csp-chalcogen bond formation procedure. The developed methodology yielded excellent results, ranging from 30 to 85%, and the compounds were carefully characterized. Eight of these compounds showed promise as potential therapeutic drugs due to their high yields and remarkable selectivity against SCC-9 cells (squamous cell carcinoma). Compound 10a, in particular, demonstrated exceptional selectivity, making it an excellent choice for cancer cell targeting while sparing healthy cells. Furthermore, complementing in silico and molecular docking studies shed light on their physical features and putative modes of action. This research highlights the potential of these compounds in anticancer treatments and lays the way for future drug development efforts.

Reaction Mechanisms of H2S Oxidation by Naphthoquinones

1,4-naphthoquinones (NQs) catalytically oxidize H2S to per- and polysufides and sulfoxides, reduce oxygen to superoxide and hydrogen peroxide, and can form NQ-SH adducts through Michael addition. Here, we measured oxygen consumption and used sulfur-specific fluorophores, liquid chromatography tandem mass spectrometry (LC-MS/MS), and UV-Vis spectrometry to examine H2S oxidation by NQs with various substituent groups. In general, the order of H2S oxidization was DCNQ ~ juglone > 1,4-NQ > plumbagin >DMNQ ~ 2-MNQ > menadione, although this order varied somewhat depending on the experimental conditions. DMNQ does not form adducts with GSH or cysteine (Cys), yet it readily oxidizes H2S to polysulfides and sulfoxides. This suggests that H2S oxidation occurs at the carbonyl moiety and not at the quinoid 2 or 3 carbons, although the latter cannot be ruled out. We found little evidence from oxygen consumption studies or LC-MS/MS that NQs directly oxidize H2S2-4, and we propose that apparent reactions of NQs with inorganic polysulfides are due to H2S impurities in the polysulfides or an equilibrium between H2S and H2Sn. Collectively, NQ oxidation of H2S forms a variety of products that include hydropersulfides, hydropolysulfides, sulfenylpolysulfides, sulfite, and thiosulfate, and some of these reactions may proceed until an insoluble S8 colloid is formed.

Unraveling the atmospheric oxidation mechanism and kinetics of naphthalene: Insights from theoretical exploration

Naphthalene, the most abundant polycyclic aromatic hydrocarbon in the atmosphere, significantly influences OH consumption and secondary organic aerosol (SOA) formation. Naphthoquinone (NQ) is a significant contributor to ring-retaining SOA from naphthalene degradation, impacting the redox properties and toxicity of ambient particles. However, inconsistencies persist regarding concentrations of its isomers, 1,2-NQ and 1,4-NQ. In present work, our theoretical investigation into naphthalene's reaction with OH and subsequent oxygenation unveils their role in SOA formation. The reaction kinetics of initial OH and subsequent O2 oxidation was extensively studied using high-level quantum chemical methods (DLPNO-CCSD(T)/aug-ccpVQZ//M052x-D3/6-311++G(d,p)) combined with RRKM/master equation simulations. The reactions mainly proceed through electrophilic addition and abstraction from the aromatic ring. The total rate coefficient of naphthalene + OH at 300 K and 1 atm from our calculation (7.2 × 10-12 cm3 molecule-1 s-1) agrees well with previous measurements (∼1 × 10-11 cm3 molecule-1 s-1). The computed branching ratios facilitate accurate product yield determination. The largest yield of 1-hydroxynaphthalen-1-yl radical (add1) producing the major precursor of RO2 is computed to be 93.8 % in the ambient environment. Our calculated total rate coefficient (5.2 × 10-16 cm3 molecule-1 s-1) for add1 + O2 closely matches that of limited experimental data (8.0 × 10-16 cm3 molecule-1 s-1). Peroxy radicals (RO2) generated from add1 + O2 include 4-cis/trans-(1-hydroxynaphthalen-1-yl)-peroxy radical (add1-4OOadd-cis/trans, 66.0 %/17.5 %), 2-cis/trans-(1-hydroxynaphthalen-1-yl)-peroxy radical (add1-2OOadd-cis/trans, 10.3 %/6.3 %). Regarding the debated predominance of 1,4-NQ (corresponding to the parent RO2, i.e., add1-4OOadd-cis/trans) and 1,2-NQ (corresponding to the parent RO2, i.e., add1-2OOadd-cis/trans) in the atmosphere, our findings substantiate the dominance of 1,4-NQ. This study also indicates potential weakening of 1,4-NQ's dominance due to competition from decomposition reactions of add1-4OOadd-cis/trans and add1-2OOadd-cis/trans. Precise reaction kinetics data are essential for characterizing SOA transformation derived from naphthalene and assessing their climatic impacts within modeling frameworks.

A new type of sulfation reaction: C-sulfonation for α,β-unsaturated carbonyl groups by a novel sulfotransferase SULT7A1

Cytosolic sulfotransferases (SULTs) are cytosolic enzymes that catalyze the transfer of sulfonate group to key endogenous compounds, altering the physiological functions of their substrates. SULT enzymes catalyze the O-sulfonation of hydroxy groups or N-sulfonation of amino groups of substrate compounds. In this study, we report the discovery of C-sulfonation of α,β-unsaturated carbonyl groups mediated by a new SULT enzyme, SULT7A1, and human SULT1C4. Enzymatic assays revealed that SULT7A1 is capable of transferring the sulfonate group from 3'-phosphoadenosine 5'-phosphosulfate to the α-carbon of α,β-unsaturated carbonyl-containing compounds, including cyclopentenone prostaglandins as representative endogenous substrates. Structural analyses of SULT7A1 suggest that the C-sulfonation reaction is catalyzed by a novel mechanism mediated by His and Cys residues in the active site. Ligand-activity assays demonstrated that sulfonated 15-deoxy prostaglandin J2 exhibits antagonist activity against the prostaglandin receptor EP2 and the prostacyclin receptor IP. Modification of α,β-unsaturated carbonyl groups via the new prostaglandin-sulfonating enzyme, SULT7A1, may regulate the physiological function of prostaglandins in the gut. Discovery of C-sulfonation of α,β-unsaturated carbonyl groups will broaden the spectrum of potential substrates and physiological functions of SULTs.

Cytosolic zinc mediates the cytotoxicity of thiol-reactive electrophiles in rat vascular smooth muscle cells

The aberrant increase or dysregulation of cytosolic Zn2+ concentration ([Zn2+]cyt) has been associated with cellular dysfunction and cytotoxicity. In this study, we postulated that Zn2+ mediates the cytotoxicity of thiol-reactive electrophiles. This notion was grounded on earlier research, which revealed that thiol-reactive electrophiles may disrupt Zn2+-binding motifs, consequently causing Zn2+ to be released from Zn2+-binding proteins, and leading to a surge in [Zn2+]cyt. The thiol-reactive electrophiles N-ethylmaleimide (NEM) and diamide were observed to induce an increase in [Zn2+]cyt, possibly through the impairment of Zn2+-binding motifs, and subsequent stimulation of reactive oxygen species (ROS) formation, resulting in cytotoxicity in primary cultured rat vascular smooth muscle cells. These processes were negated by the thiol donor N-acetyl-L-cysteine and the Zn2+ chelator TPEN. Similar outcomes were detected with co-treatment involving Zn2+ and Zn2+ ionophores such as pyrithione or disulfiram. Moreover, TPEN was found to inhibit cytotoxicity triggered by short-term exposure to various thiol-reactive electrophiles including hydrogen peroxide, acrylamide, acrylonitrile, diethyl maleate, iodoacetic acid, and iodoacetamide. In conclusion, our findings suggest that cytosolic Zn2+ acts as a universal mediator in the cytotoxic effects produced by thiol-reactive electrophiles.

Interactions between Damaged Hair Keratin and Juglone as a Possible Restoring Agent: A Vibrational and Scanning Electron Microscopy Study

Juglone, a quinonic compound present in walnut extracts, was proposed as a restoring agent for hair keratin treated with permanent or discoloration processes. The proposed mechanism of restoration by juglone involves the formation of a Michael adduct between the quinone and the thiol moieties of cysteine residues. To this purpose, the first part of the present paper involved the spectroscopic study of the product of the reaction between juglone and N-acetyl-L-cysteine as a model compound. IR spectroscopy and Scanning Electron Microscopy (SEM) monitored the chemical and morphological variations induced by applying juglone to hair keratin. In order to simulate the most common hair treatments (i.e., permanent and discoloration), juglone was applied to hair that had been previously treated with a reducing agent, i.e., methyl thioglycolate (MT) or with bleaching agents (based on hydrogen peroxide and persulfates) followed by sodium hydrogen sulfite. IR spectroscopy allowed us to monitor the formation of Michael adducts between juglone and cysteine residues: the Michael adducts' content was related to the cysteine content of the samples. In fact, MT and sodium hydrogen sulfite favored the reduction of the disulfide bonds and increased the content of free cysteine residues, which can react with juglone. SEM analyses confirmed the trend observed by IR spectroscopy since hair samples treated with juglone adopted a more regular hair surface and more imbricated scales, thus supporting the possible use of juglone as a restoring agent for damaged hair keratins.

Antimicrobial and wound healing potential of naphthoquinones encapsulated in nanochitosan

Introduction: The use of chitosan in pharmaceutical formulations is an advantageous approach due to this compound intrinsic biodegradability and biocompatibility, as well as ready availability and low polymer cost. Methods: Herein, the naphthoquinones 3- chloromethylene-menadione (NQ1) and 2,3-dichloro-1,4-naphthoquinone (NQ2) were nanoencapsulated into chitosan (CNP) by the ionotropic gelatinization technique and characterized by DLS, FTIR, SEM, TGA and DSC, and their release profiles evaluated. The antimicrobial and wound healing activities were investigated. Results and Discussion: Homogeneous chitosan nanocapsulses of about 193 nm and Z potential ranging from +30.6 to +33.1 mV loaded with NQ1 (CNP-NQ1) or NQ2 (CNPQNQ2). With nanoencapsulation efficiencies of ≥ 96%, the solubility of naphthoquinones in aqueous environments was improved, making them suitable for biological system applications. The encapsulated naphthoquinones displayed a controlled release of approximately 80% for CNP-NQ1 and 90% for CNP-NQ2 over an 8 h period at 36°C. Both CNP-NQ1 and CNP-NQ2 retained the already established free naphthoquinone antimicrobial activity against two Staphylococcus aureus strains, Staphylococcus epidermidis, Streptococcus pyogenes and Pseudomonas aeruginosa. Although presenting low toxicity to healthy human cells, only CNP-NQ1 displayed therapeutic indices above 100 for S. aureus and S. epidermidis and above 27 for S. pyogenes and P. aeruginosa, allowing for safe use in human tissues. Furthermore, CNP-NQ1 did not impair the migration of human fibroblast cells in scratch assays, adding promising wound healing properties to this formulation. These findings emphasize that CNP-NQ1 may be useful in protecting injured skin tissue from bacterial contamination, avoiding skin infections not only by reducing bacterial loads but also by accelerating the healing process until complete dermal tissue recovery.

Selective bioelectronic sensing of pharmacologically relevant quinones using extracellular electron transfer in Lactiplantibacillus plantarum

Redox-active small molecules containing quinone functional groups play important roles as pharmaceuticals, but can be toxic if overdosed. Despite the need for a fast and quantitative method to detect quinone and its derivatives, current sensing strategies are often slow and struggle to differentiate between structural analogs. Leveraging the discovery that microorganisms use certain quinones to perform extracellular electron transfer (EET), we investigated the use of Lactiplantibacillus plantarum as a whole-cell bioelectronic sensor to selectively sense quinone analogs. By tailoring the native EET pathway in L. plantarum, we enabled quantitative quinone sensing of 1,4-dihydroxy-2-naphthoic acid (DHNA) - a gut bifidogenic growth stimulator. We found that L. plantarum could respond to environmental DHNA within seconds, producing concentration-dependent electrical signals. This sensing capacity was robust in different assay media and allowed for continuous monitoring of DHNA concentrations. In a simulated gut environment containing a mixed pool of quinone derivatives, this tailored EET pathway can selectively sense pharmacologically relevant quinone analogs, such as DHNA and menadione, amongst other structurally similar quinone derivatives. We also developed a multivariate model to describe the mechanism behind this selectivity and found a predictable correlation between quinone physiochemical properties and the corresponding electrical signals. Our work presents a new concept to selectively sense quinone using whole-cell bioelectronic sensors and opens the possibility of using probiotic L. plantarum for bioelectronic applications in human health.

Assessment of the Long-Range NMR C,H Coupling of a Series of Carbazolequinone Derivatives

Synthesis, the complete 1H- and 13C-NMR assignments, and the long-range C,H coupling constants (nJC,H) of some hydrogen-deficient carbazolequinones, assessed by a J-HMBC experiment, are reported. In these molecules, the protons, used as entry points for assignments, are separated by several bonds with non-protonated atom carbons. Therefore, the use of long-range NMR experiments for the assignment of the spectra is mandatory; we used HSQC and HMBC. On the other hand, the measured heteronuclear (C,H) coupling constants 2J to 5J) allow us to choose the value of the long-range delay used in the HMBC experiment less arbitrarily in order to visualize a desired correlation in the spectrum. The chemical shifts and the coupling constant values can be used as input for assignments in related chemical structures.

Sc(OTf)3-Catalyzed Domino C-C/C-N Bond Formation of Aziridines with Quinones via Radical Pathway

Sc(III)-catalyzed domino C-C and C-N bond formation of N-sulfonyl aziridines with quinones has been accomplished to furnish functionalized indolines at a moderate temperature. The umpolung reactivity of aziridines, radical pathway, mild reaction conditions, substrate scope, and coupling of drug molecules in a postsynthetic application are the important practical features.

Potential Impacts of Energy and Vehicle Transformation Through 2050 on Oxidative Stress-Inducing PM2.5 Metals Concentration in Japan

The impacts of renewable energy shifting, passenger car electrification, and lightweighting through 2050 on the atmospheric concentrations of PM2.5 total mass and oxidative stress-inducing metals (PM2.5-Fe, Cu, and Zn) in Japan were evaluated using a regional meteorology-chemistry model. The surface concentrations of PM2.5 total mass, Fe, Cu, and Zn in the urban area decreased by 8%, 13%, 18%, and 5%, respectively. Battery electric vehicles (BEVs) have been considered to have no advantage in terms of non-exhaust PM emissions by previous studies. This is because the disadvantages (heavier weight increases tire wear, road wear, and resuspention) offset the advantages (regenerative braking system (RBS) reduces brake wear). However, the future lightweighting of drive battery and body frame were estimated to reduce all non-exhaust PM. Passenger car electrification only reduced PM2.5 concentration by 2%. However, Fe and Cu concentrations were more reduced (-8% and -13%, respectively) because they have high brake wear-derived and significantly reflects the benefits of BEV's RBS. The water-soluble fraction concentration of metals (induces oxidative stress in the body) was estimated based on aerosol acidity. The reduction of SOx, NOx, and NH3 emissions from on-road and thermal power plants slightly changed the aerosol acidity (pH ± 0.2). However, it had a negligible effect on water-soluble metal concentrations (maximum +2% for Fe and +0.5% for Cu and Zn). Therefore, the metal emissions reduction was more important than gaseous pollutants in decreasing the water-soluble metals that induces respiratory oxidative stress and passenger car electrification and lightweighting were effective means of achieving this.

Oxidized and Unsaturated: Key Organic Aerosol Traits Associated with Cellular Reactive Oxygen Species Production in the Southeastern United States

Exposure to ambient fine particulate matter (PM2.5) is associated with millions of premature deaths annually. Oxidative stress through overproduction of reactive oxygen species (ROS) is a possible mechanism for PM2.5-induced health effects. Organic aerosol (OA) is a dominant component of PM2.5 worldwide, yet its role in PM2.5 toxicity is poorly understood due to its chemical complexity. Here, through integrated cellular ROS measurements and detailed multi-instrument chemical characterization of PM in urban southeastern United States, we show that oxygenated OA (OOA), especially more-oxidized OOA, is the main OA type associated with cellular ROS production. We further reveal that highly unsaturated species containing carbon-oxygen double bonds and aromatic rings in OOA are major contributors to cellular ROS production. These results highlight the key chemical features of ambient OA driving its toxicity. As more-oxidized OOA is ubiquitous and abundant in the atmosphere, this emphasizes the need to understand its sources and chemical processing when formulating effective strategies to mitigate PM2.5 health impacts.

Fe-Based Nanomaterials and Plant Growth Promoting Rhizobacteria Synergistically Degrade Polychlorinated Biphenyls by Producing Extracellular Reactive Oxygen Species

Plant growth promoting rhizobacteria (PGPR) produce extracellular reactive oxygen species (ROS) to protect plants from external stresses. Fe-based nanomaterials can potentially interact with PGPR and synergistically degrade organic pollutants, yet they have received no study. Here, we studied how the interaction between a typical PGPR (Pseudomonas chlororaphis, JD37) and Fe-based nanomaterials facilitated the degradation of 2,4,4'-trichlorobiphenyl (PCB28), by comparing the zerovalent iron of 20 nm (nZVI20), 100 nm (nZVI100), and 5 μm; iron oxide nanomaterials (α-Fe2O3, γ-Fe2O3, and Fe3O4) of ca. 20 nm; and ferrous and ferric salts. Although all Fe materials (0.1 g L-1) alone could not degrade aqueous PCB28 (0.1 mg L-1) under dark or aerobic conditions, nZVI20, nZVI100, α-Fe2O3, and Fe2+ promoted PCB28 degradation by JD37, with the half-life of PCB28 shortened from 16.5 h by JD37 alone to 8.1 h with nZVI100 cotreatment. Mechanistically, the nanomaterials stimulated JD37 to secrete phenazine-1-carboxylic acid and accelerated the NADH/NAD+ conversion, promoting O2*- generation; JD37 increased Fe(II) dissolution from the nanomaterials, facilitating *OH generation; and the ROS gradually degraded PCB28 into benzoic acid through dihydroxy substitution, oxidation to quinone, and Michael addition. These findings provide a new strategy of nanoenabled biodegradation of organic pollutants by applying Fe-based nanomaterials and PGPR.

Bacterial responses to plant antimicrobials: the case of alkannin and shikonin derivatives

Alkannin, shikonin and their derivatives (A/S) are secondary metabolites produced in the roots of certain plants of the Boraginaceae family such as Lithospermum erythrorhizon Siebold & Zucc. and Alkanna tinctoria (L.) Tausch. These naphthoquinones express anti-cancer, wound healing, and antimicrobial activities. To study the interactions between endophytic bacteria isolated from A. tinctoria and the antimicrobials A/S, endophytic bacteria known to be resistant to the compounds were screened for their effect on A/S in liquid medium. Thereafter, the strain Pseudomonas sp. R-72008, was selected and tested for its ability to modify A/S in nutrient medium and minimal medium with A/S as sole carbon source. Bacterial growth was recorded, and high performance liquid chromatography-diode array and ultra-high performance liquid chromatography-electrospray ionization-mass spectrometry analyses were performed to detect and quantify metabolites. In nutrient medium inoculated with R-72008, a decrease in the amount of A/S monomers initially present was observed and correlated with an increase of A/S oligomers. Moreover, a significant decrease of initial A/S monomers in minimal medium was correlated with bacterial growth, showing for the first time that a bacterial strain, Pseudomonas sp. R-72008, was able to use the naphthoquinones A/S as sole carbon source. This study opens new perspectives on the interactions between bacteria and plant antimicrobials.

Distal meta-C-H functionalization of α-substituted cinnamates

Development of a novel strategy for the palladium-catalyzed selective meta-C-H activation of α-substituted cinnamates and their heterocyclic analogues with various alkenes using nitrile as a directing group (DG) has been described. Importantly, we introduced naphthoquinone, benzoquinones, maleimides and sulfolene as coupling partners in the meta-C-H activation reaction for the first time. Notably, allylation, acetoxylation and cyanation were also achieved through distal meta-C-H functionalization. This novel protocol also includes the coupling of various olefin-tethered bioactive molecules with high selectivity.

Redox and Nucleophilic Reactions of Naphthoquinones with Small Thiols and Their Effects on Oxidization of H2S to Inorganic and Organic Hydropolysulfides and Thiosulfate

Naphthoquinone (1,4-NQ) and its derivatives (NQs, juglone, plumbagin, 2-methoxy-1,4-NQ, and menadione) have a variety of therapeutic applications, many of which are attributed to redox cycling and the production of reactive oxygen species (ROS). We previously demonstrated that NQs also oxidize hydrogen sulfide (H₂S) to reactive sulfur species (RSS), potentially conveying identical benefits. Here we use RSS-specific fluorophores, mass spectroscopy, EPR and UV-Vis spectrometry, and oxygen-sensitive optodes to examine the effects of thiols and thiol-NQ adducts on H₂S-NQ reactions. In the presence of glutathione (GSH) and cysteine (Cys), 1,4-NQ oxidizes H₂S to both inorganic and organic hydroper-/hydropolysulfides (R₂S_n, R=H, Cys, GSH; n = 2-4) and organic sulfoxides (GS_nOH, n = 1, 2). These reactions reduce NQs and consume oxygen via a semiquinone intermediate. NQs are also reduced as they form adducts with GSH, Cys, protein thiols, and amines. Thiol, but not amine, adducts may increase or decrease H₂S oxidation in reactions that are both NQ- and thiol-specific. Amine adducts also inhibit the formation of thiol adducts. These results suggest that NQs may react with endogenous thiols, including GSH, Cys, and protein Cys, and that these adducts may affect both thiol reactions as well as RSS production from H₂S.

1,4-Naphthoquinone-Coated Black Carbon, a Kind of Atmospheric Fine Particulate Matter, Affects Macrophage Fate: New Insights into Crosstalk between Necroptosis and Macrophage Extracellular Traps

1,4-Naphthoquinone-coated BC (1,4 NQ-BC) is an important component of PM_2.5 and a representative secondary particle. However, there is no research on the crosstalk mechanism between necroptosis and macrophage extracellular traps (METs) after 1,4 NQ-BC exposure. In this study, we treated RAW264.7 cells with 50, 100, and 200 mg/L 1,4 NQ-BC for 24 h, with 10 μM necrostatin-1 for 24 h, and with 2.5 μM phorbol 12-myristate 13-acetate (PMA) for 3 h. Our experiment revealed that under normal physiological conditions, when macrophages receive external stimuli (such as pathogens; in this experiment, PMA), they will form METs and capture and kill pathogens, thus exerting innate immune function. However, exposure to 1,4 NQ-BC can cause necroptosis in macrophages, accompanied by increased levels of reactive oxygen species (ROS) and cytosolic calcium ions, as well as the expression disorder of inflammatory factors and chemokines, prevent the formation of METs, lead to loss of the function of capturing and killing pathogens, and weaken the innate immune function. Notably, inhibition of necroptosis restored the formation of METs, indicating that necroptosis inhibited the formation of METs. Our study was the first to explore the crosstalk mechanism between necroptosis and METs. This experiment will enrich the mechanism of macrophage injury caused by 1,4 NQ-BC exposure.

The Relevance and Insights on 1,4-Naphthoquinones as Antimicrobial and Antitumoral Molecules: A Systematic Review

Natural product derivatives are essential in searching for compounds with important chemical, biological, and medical applications. Naphthoquinones are secondary metabolites found in plants and are used in traditional medicine to treat diverse human diseases. Considering this, the synthesis of naphthoquinone derivatives has been explored to contain compounds with potential biological activity. It has been reported that the chemical modification of naphthoquinones improves their pharmacological properties by introducing amines, amino acids, furan, pyran, pyrazole, triazole, indole, among other chemical groups. In this systematic review, we summarized the preparation of nitrogen naphthoquinones derivatives and discussed their biological effect associated with redox properties and other mechanisms. Preclinical evaluation of antibacterial and/or antitumoral naphthoquinones derivatives is included because cancer is a worldwide health problem, and there is a lack of effective drugs against multidrug-resistant bacteria. The information presented herein indicates that naphthoquinone derivatives could be considered for further studies to provide drugs efficient in treating cancer and multidrug-resistant bacteria.

The Effects of 1,4-Naphthoquinone (NQ) and Naphthazarin (5,8-Dihydroxy-1,4-naphthoquinone, DHNQ) Individually and in Combination on Growth and Oxidative Stress in Maize (Zea mays L.) Seedlings

This study investigated the effects of 1,4-naphthoquinone (NQ) and naphthazarin (5,8-dihydroxy-1,4-naphthoquinone, DHNQ) individually and in combination, applied at low concentrations (0.1, 1, and 10 nM), on growth, hydrogen peroxide (H₂O₂) production, catalase activity, and lipid peroxidation in maize seedlings. It was found that NQ at 0.1 and 1 nM and DHNQ at 0.1 nM significantly stimulated the fresh weight of the aboveground parts of the seedlings (APS), while the fresh weight of the underground parts of the seedlings (UPS) was enhanced only at 0.1 nM NQ. Interestingly, DHNQ at higher concentrations (1 and 10 nM) significantly diminished the fresh weight of the APS and UPS. When NQ and DHNQ were applied together, an increase in the fresh weight of the APS at all of the concentrations studied was observed. It was also found that NQ and DHNQ individually and in combination, at all concentrations studied, decreased the H₂O₂ production in the aboveground and underground parts of maize seedlings. The presence of the DHNQ at higher concentrations (1 and 10 nM) triggered an increase in the catalase (CAT) activity of the UPS and APS compared to the control. However, NQ added at 1 nM decreased the CAT activity of both the UPS and APS, while 10 nM increased the CAT activity of UPS. NQ and DHNQ applied together at 0.1 and 10 nM almost completely inhibited catalase activity in the UPS and APS. The data that were obtained for lipid peroxidation, measured as the malondialdehyde (MDA) concentration, indicated that NQ and DHNQ at all concentrations studied decreased the MDA content of the UPS, while both naphthoquinones increased it in APS. The data presented here are discussed taking into account the mechanisms via which naphthoquinones interact with biological systems.

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.

Role of synthetical amynoquinone ethyl 2-(1,4-dioxo-1,4-dihydronaphthalen-2-ylamino) acetate in inhibition of Ehrlich's tumor

Quinones are naturally or synthetically occurring secondary metabolites that have various bio-dynamics, highlighting their antitumor potential. This has been explored through their selective cytotoxicity, and studies in medicinal chemistry about the relation between biological activity versus chemical structure may lead to the solution of the toxicity problems associated with quinones. In this context, the antitumor effect of a synthetic naphthoquinone, named Ethyl 2-(1,4-Dioxo-1,4-Dihydronaphthalen-2-Ylamino) Acetate, was tested using mice transplanted with Ehrlich ascitic tumor as an experimental model. The acute toxicity test was performed using 30 mice that received the aminoquinone at doses of 100, 200, 300, and 600 mg/kg. After evaluation of the clinical findings in the spontaneous activity tests, the LD50 calculation for the test substance showed low levels of toxicity at doses lower than 244.11 ± 23.29 mg/kg. Thus, three experimental groups were established, where animals transplanted with tumor cells received NaCl vehicle solution (control, n = 6), and the others were treated with 71.7 mg/kg of Methotrexate (n = 6) or 20 mg/kg of Aminoquinone (n = 6). All administrations were intraperitoneal, in a single dose. Three days after the implantation of the tumor cells the animals were weighed daily and evaluated for tumor biometry and development. The treatments occurred five days after the implantation of the tumor cells and were extended for 7 more days. At the end of the 12-day experimental period, all animals were euthanized for biochemical and histopathological analyses of the tumors and vital organs. The spontaneous activity test showed that the amount of responses associated with the nervous system tends to increase with the increase in dosage, highlighting the excitatory effect on the central nervous system in almost all dosages employed, followed by depressant activities on this system. There was a significant tumor reduction, both in animals treated with methotrexate (71.7 %) and in those treated with aminoquinone (91.6 %) in the control group. There was no significant difference in tumor volume between the animals treated with aminoquinone or methotrexate. The histopathological analysis revealed that in both treatments there were fewer mitoses in the tumor mass compared to the control group. However, there was apparent toxicity to the liver, heart, and left kidney in the treatment with methotrexate compared to aminoquinone. The significant capacity for tumor reduction presented by aminoquinone allows pointing it as a promising alternative for the development of a more efficient drug to control tumor development, being necessary for the development of new studies to deepen the knowledge about its mechanisms of action.

Superoxide Release by Macrophages through NADPH Oxidase Activation Dominating Chemistry by Isoprene Secondary Organic Aerosols and Quinones to Cause Oxidative Damage on Membranes

Oxidative stress mediated by reactive oxygen species (ROS) is a key process for adverse aerosol health effects. Secondary organic aerosols (SOA) account for a major fraction of fine particulate matter, and their inhalation and deposition into the respiratory tract causes the formation of ROS by chemical and cellular processes, but their relative contributions are hardly quantified and their link to oxidative stress remains uncertain. Here, we quantified cellular and chemical superoxide generation by 9,10-phenanthrenequinone (PQN) and isoprene SOA using a chemiluminescence assay combined with electron paramagnetic resonance spectroscopy as well as kinetic modeling. We also applied cellular imaging techniques to study the cellular mechanism of superoxide release and oxidative damage on cell membranes. We show that PQN and isoprene SOA activate NADPH oxidase in macrophages to release massive amounts of superoxide, overwhelming the superoxide formation by aqueous chemical reactions in the epithelial lining fluid. The activation dose for PQN is 2 orders of magnitude lower than that of isoprene SOA, suggesting that quinones are more toxic. While higher exposures trigger cellular antioxidant response elements, the released ROS induce oxidative damage to the cell membrane through lipid peroxidation. Such mechanistic and quantitative understandings provide a basis for further elucidation of adverse health effects and oxidative stress by fine particulate matter.

Oxygenated polycyclic aromatic hydrocarbons in food: toxicity, occurrence and potential sources

Oxygenated polycyclic aromatic hydrocarbons (OPAHs) are polycyclic aromatic hydrocarbons (PAHs) functionalized with at least one carbonyl group and are generally thought to be more toxic than PAHs. In this review, the physical-chemical properties, toxicity, occurrence, and potential sources of OPAHs in food were comprehensively discussed. The toxicities of 1,2-naphthoquinone, 1,4-naphthoquinone, 6H-benzo[cd]pyren-6-one, benzo[a]anthracene-7,12-quinone and 9,10-phenanthrenequinone were prominent among the OPAHs. Both 1,4-naphthoquinone and 1,2-naphthoquinone exhibited strong genotoxicity, cytotoxicity, and developmental toxicity. 6H-benzo[cd]pyren-6-one and benzo[a]anthracene-7,12-quinone showed high genotoxicity and cardiovascular toxicity. Although 9,10-phenanthrenequinone showed no genotoxicity, it exhibited almost the strongest cytotoxicity. For the majority of foods, the concentrations of OPAHs and PAHs were on the same order of magnitude. OPAHs tend to be positively correlated with the corresponding PAH concentrations in oil and fried food, while for barbequed food and seafood, no obvious correlation was found. In addition, 9-fluorenone, 9,10-anthraquinone, benzanthrone and 1,2-acenaphthenequinone had high abundance in food. Environmental pollution, food composition, storage conditions, heating methods, and other treatments influence the accumulation of OPAHs in food. Furthermore, oxygen and water played an important role in the transformation from PAHs to OPAHs. In short, this review guides the evaluation and further reduction of OPAH-related health risks in food.

In Vitro Antimicrobial Effects and Inactivation Mechanisms of 5,8-Dihydroxy-1,4-Napthoquinone

Naphthoquinones are an important class of natural organic compounds that have antimicrobial effects. However, the mechanisms of their action remain to be elucidated. Therefore, the antimicrobial activity of the chemically synthesized naphthoquinone derivative, 5,8-dihydroxy-1,4-naphthoquinone, was investigated in this study against 10 different microorganisms. Its inhibitory activity was evident against Bacillus cereus, Proteus vulgaris, Salmonella enteritidis, Staphylococcus epidermidis, S. aureus, and Candida albicans, and its MIC50 values were determined to be 14, 10, 6, 2, 4, 1.2, and <0.6 µg/mL, respectively. Moreover, the crystal violet uptake, TTC dehydrogenase activity, protein/DNA leakage, and DNA damage of the compound in these microorganisms were also investigated to reveal the antimicrobial mechanisms. In addition, scanning electron microscopy was used to detect physiological damage to the cell membrane of S. epidermidis, S. aureus, and C. albicans, which was most severe in the crystal violet uptake assay. The overall results showed that 5,8-dihydroxy-1,4-naphthoquinone exhibited its effects on S. aureus, S. epidermidis, and C. albicans by various mechanisms, especially membrane damage and membrane integrity disruption. It also caused DNA leakage and damage along with respiratory chain disruption (78%) in C. albicans. Similarly, it caused varying degrees of reduction in the respiratory activity of S. aureus (47%), S. epidermidis (16%), B. cereus (12%), S. enteritidis (9%), and P. vulgaris (8%). Therefore, 5,8-dihydroxy-1,4-naphthoquinone proved to be a very effective antifungal and antibacterial agent and could be considered a new potential drug candidate, inspiring further discoveries in these microorganisms.

Competition between In-Plane vs Above-Plane Configurations of Water with Aromatic Molecules: Non-Covalent Interactions in 1,4-Naphthoquinone-(H2O)1-3 Complexes

Non-covalent interactions between aromatic molecules and water are fundamental in many chemical and biological processes, and their accurate description is essential to understand molecular relative configurations. Here we present the rotational spectroscopy study of the water complexes of the polycyclic aromatic hydrocarbon 1,4-naphthoquinone (1,4-NQ). In 1,4-NQ-(H₂O)_1,2, water molecules bind through O-H···O and C-H···O hydrogen bonds and are located on the plane of 1,4-NQ. For 1,4-NQ-(H₂O)₃, in-plane and above-plane water configurations are observed exhibiting O-H···O, C-H···O, and lone pair···π-hole interactions. The observation of different water arrangements for 1,4-NQ-(H₂O)₃ allows benchmarking theoretical methods and shows that they have great difficulty in predicting energy orderings due to the strong competition of C-H···O binding with π and π-hole interactions. This study provides important insight into water interactions with aromatic systems and the challenges in their modeling.

Naphthoquinones and derivatives as potential anticancer agents: An updated review

One of the leading global causes of death is cancer; even though several treatment methods have improved survival rates, the incidence and fatality rates remain high. Naphthoquinones are a type of quinone that is found in nature and has vital biological roles. These chemicals have anticancer (antineoplastic), analgesic, anti-inflammatory, antimalarial, antifungal, antiviral, antitrypanosomal, antischistosomal, leishmanicidal, and anti-ulcerative effects. Direct addition of a substituent group to the 1,4-naphthoquinone ring can alter the naphthoquinone's oxidation/reduction and acid/base characteristics, and the activity can be altered. Because of their pharmacological properties, such as anticancer activity and probable therapeutic application, naphthoquinones have greatly interested the scientific community. Some chemicals having a quinone ring in malignant cells have been found to have antiproliferative effects. Naphthoquinones' deadly impact is connected with the inhibition of electron transporters, the uncoupling of oxidative phosphorylation, the creation of ROS, and the formation of protein adducts, notably with -SH enzyme groups. This review article aims to discuss naphthoquinones and their derivatives, which act against cancer and their future perspectives. This review covers several studies highlighting the potent anticancer properties of naphthoquinones. Further, various proposed mechanisms of anticancer actions of naphthoquinones have been summarized in this review.

Redox Homeostasis is Disturbed by Redox Cycling between Reactive Cysteines of Thioredoxin 1 and 9,10-Phenanthrenequinone, an Atmospheric Electron Acceptor

9,10-Phenanthrenequinone (9,10-PQ) is a toxicant in diesel exhaust particles and airborne particulate matter ≤2.5 μm in diameter. It is an efficient electron acceptor that readily reacts with dithiol compounds in vitro, resulting in the oxidation of thiol groups and concomitant generation of reactive oxygen species (ROS). However, it remains to be elucidated whether 9,10-PQ interacts with proximal protein dithiols. In the present study, we used thioredoxin 1 (Trx1) as a model of proteins with reactive proximal cysteines and examined whether it reacts with 9,10-PQ in cells and tissues, thereby affecting its catalytic activity and thiol status. Intratracheal injection of 9,10-PQ into mice resulted in protein oxidation and diminished Trx activity in the lungs. Using recombinant wild-type and C32S/C35S Trx1, we found that Cys32 and Cys35 selectively serve as electron donor sites for redox reactions with 9,10-PQ that lead to substantial inhibition of Trx activity. Addition of dithiothreitol restored the Trx activity inhibited by 9,10-PQ. Exposure of cultured cells to 9,10-PQ caused intracellular reactive oxygen species generation that led to protein oxidation, Trx1 dimerization, p38 phosphorylation, and apoptotic cell death. Overexpression of Trx1 blocked these 9,10-PQ-mediated events. These results suggest that the interaction of the reactive cysteines of Trx1 with 9,10-PQ causes oxidative stress, leading to disruption of redox homeostasis.

Molluskicidal activity of 3-aryl-2-hydroxy-1,4-naphthoquinones against Biomphalaria glabrata

Schistosomiasis is the second most prevalent parasitic infectious disease after malaria, which affects millions of people worldwide and causes health and socioeconomic problems. The snail Biomphalaria glabrata is an intermediate host for the helminth, which is the causative agent of schistosomiasis: Schistosoma mansoni. One crucial strategy for controlling the disease is the eradication of the snail host. Niclosamide is the unique molluskicide applied in large-scale control programs, but its selectivity to other species is not adequate. Therefore, there is an urgent need to develop new molluskicides that are inexpensive, safe, and selective. Quinones are ubiquitous, playing important biological roles in fungi, plants, and others. Many synthetic molecules with relevant biological activities that contain the quinone nucleus in their structure are on the market in the therapy of cancer, malaria, or toxoplasmosis, for example. Derivatives of quinones are tools in the development of new molluskicides for Abbott laboratories. In the present work, 3-aryl-2‑hydroxy-1,4-naphthoquinones (ANs) were tested for molluskicide activity against Biomphalaria glabrata. The lethal concentration was determined for 48 h of continuous exposure. The naphthoquinones were found to have molluskicide properties. AN-15 was recorded as the highest mortality. Additionally, this analog exhibited in silico reduced ambient toxicity when compared to niclosamide. The findings of this study demonstrate that 3-aryl-2‑hydroxy-1,4-naphthoquinones are effective for the management of Biomphalaria glabrata under laboratory conditions.

Antitumor Effect of Glandora rosmarinifolia (Boraginaceae) Essential Oil through Inhibition of the Activity of the Topo II Enzyme in Acute Myeloid Leukemia

It was previously shown that the antitumor and cytotoxic activity of the essential oil (EO) extracted from the aerial parts of Glandora rosmarinifolia appears to involve a pro-oxidant mechanism in hepatocellular carcinoma (HCC) and in triple-negative breast cancer (TNBC) cell lines. Its most abundant compound is a hydroxy-methyl-naphthoquinone isomer. Important pharmacological activities, such as antitumor, antibacterial, antifungal, antiviral and antiparasitic activities, are attributed to naphthoquinones, probably due to their pro-oxidant or electrophilic potential; for some naphthoquinones, a mechanism of action of topoisomerase inhibition has been reported, in which they appear to act both as catalytic inhibitors and as topoisomerase II poisons. Our aim was to evaluate the cytotoxic activity of the essential oil on an acute myeloid leukemia cell line HL-60 and on its multidrug-resistant (MDR) variant HL-60R and verify its ability to interfere with topoisomerase II activity. MTS assay showed that G. rosmarinifolia EO induced a decrease in tumor cell viability equivalent in the two cell lines; this antitumor effect could depend on the pro-oxidant activity of EO in both cell lines. Furthermore, G. rosmarinifolia EO reduced the activity of Topo II in the nuclear extracts of HL-60 and HL-60R cells, as inferred from the inability to convert the kinetoplast DNA into the decatenated form and then not inducing linear kDNA. Confirming this result, flow cytometric analysis proved that EO induced a G0-G1 phase arrest, with cell reduction in the S-phase. In addition, the combination of EO with etoposide showed a good potentiation effect in terms of cytotoxicity in both cell lines. Our results highlight the antitumor activity of EO in the HL-60 cell line and its MDR variant with a peculiar mechanism as a Topo II modulator. Unlike etoposide, EO does not cause stabilization of a covalent Topo II-DNA intermediate but acts as a catalytic inhibitor. These data make G. rosmarinifolia EO a potential anticancer drug candidate due to its cytotoxic action, which is not affected by multidrug resistance.

Halonaphthoquinones: A group of emerging disinfection byproducts of high toxicity in drinking water

Aromatic halogenated disinfection byproducts (DBPs) have received particular attention in recent years due to their high toxicity. However, most relevant researches at present focused merely on halo-monocyclic DBPs, while halo-polycyclic DBPs were scarcely explored. In this study, a new group of halo-bicyclic DBPs termed as halonaphthoquinones (HNQs) was systematically studied. By coupling with vacuum centrifugal concentrator, a SPE-UPLC-MS/MS method with high accuracy and sensitivity was developed to detect five semi-volatile HNQs in drinking water, which achieved the detection limits in the range of 0.05-0.24 ng/L. Five HNQs were identified using this method with 100% detection frequency at concentrations up to 136.7 ng/L in drinking water originated from seven water treatment plants. The cytotoxicity of the five tested HNQs in CHO-K1 cells (IC₅₀ from 3.17 to 13.18 μM) was comparable to the most toxic known carbonaceous DBP in drinking water, iodoacetic acid (IC₅₀=2.95 μM). Meanwhile, the cytotoxicity of five tested HNQs were also higher than 2,6-dichloro-1,4-benzoquinone (IC₅₀=21.73 μM) which is hundreds to thousands of times more toxic than regulated DBPs, indicating the significant toxicity risk of HNQ DBPs. To the best of our knowledge, this study presents the first analytical method for analysis of HNQ DBPs, and the first set of data on the occurrence and cytotoxicity of HNQ DBPs in drinking water. These findings are meaningful for probing deeply into the presence of varied halo-polycyclic DBPs in the aqueous environment.

A Convenient Assay to Detect Protein Oxidation Caused by Redox-Active Quinones

Redox-active quinones generate reactive oxygen species (ROS) through their redox cycling with electron donors. Hydrogen peroxide (H₂O₂) causes S-oxidation of proteins and is associated with activation of the redox signaling pathway and/or toxicity (Chem. Res. Toxicol., 30, 2017, Kumagai et al.). In the present study, we developed a convenient assay based on a combination of an enzyme-linked immunosorbent assay and a biotin-PEAC₅-maleimide assay and used it to determine protein S-oxidation by ROS during redox cycling of 9,10-phenanthrenequinone (9,10-PQ) and pyrroloquinoline quinone (PQQ). S-Oxidation of proteins in a mouse liver supernatant was detected during reaction of 9,10-PQ or PQQ with electron donors such as dithiothreitol or reduced nicotinamide adenine dinucleotide phosphate (NADPH), whereas cellular protein oxidation was not observed in the absence of electron donors. These results suggest that the developed assay is useful for the detection of S-oxidation of proteins.

Detecting Validated Intracellular ROS Generation with 18F-dihydroethidine-Based PET

PURPOSE

To determine the sensitivity of the 18F-radiolabelled dihydroethidine analogue ([18F]DHE) to ROS in a validated ex vivo model of tissue oxidative stress.

PROCEDURES

The sensitivity of [18F]DHE to various ROS-generating systems was first established in vitro. Then, isolated rat hearts were perfused under constant flow, with contractile function monitored by intraventricular balloon. Cardiac uptake of infused [18F]DHE (50-150 kBq.min-1) was monitored by γ-detection, while ROS generation was invoked by menadione infusion (0, 10, or 50 μm), validated by parallel measures of cardiac oxidative stress.

RESULTS

[18F]DHE was most sensitive to oxidation by superoxide and hydroxyl radicals. Normalised [18F]DHE uptake was significantly greater in menadione-treated hearts (1.44 ± 0.27) versus control (0.81 ± 0.07) (p < 0.05, n = 4/group), associated with concomitant cardiac contractile dysfunction, glutathione depletion, and PKG1α dimerisation.

CONCLUSION

[18F]DHE reports on ROS in a validated model of oxidative stress where perfusion (and tracer delivery) is unlikely to impact its pharmacokinetics.

Naphthoquinone-induced arylation inhibits Sirtuin 7 activity

Natural or synthetic naphthoquinones have been identified as interfering with biological systems and in particular exhibiting anticancer properties. As redox cyclers, they may first generate in cells reactive oxygen species and second, as electrophiles, they may react with nucleophiles, mainly thiols, and form covalent adducts. To further decipher the molecular mechanism of action of naphthoquinones in human cells, we have mainly analysed their effects in HeLa cells. First, we have demonstrated that menadione and plumbagin inhibit the nucleolar NAD+-dependent deacetylase Sirtuin 7 in vitro. As assessed by their inhibitions of rDNA transcription, pre-rRNA processing and formation of etoposide-induced 53BP1 foci, menadione and plumbagin inhibit also Sirtuin 7 catalytic activity in vivo. Second, we have established that in experimental conditions in which the sulfhydryl arylation by menadione or plumbagin is prevented by the thiol reducing agent N-acetyl-L-cysteine, the inhibition of Sirtuin 7 catalytic activity is also prevented. Finally, we discuss here how inhibition of Sirtuin 7 might be critical in determining menadione or plumbagin as anti-tumor agents that can be used in combination in anti-tumoral strategies.

Synthesis and evaluation of 2-phenylamino-1,4-naphthoquinones derivatives as potential hypoglycaemic agents

Due to the severe side effects revealed by most of the currently used antidiabetic medicines, search for finding new and safe drugs to manage diabetes is continued. Naphthoquinones possessing strong antioxidant properties have been employed as candidates for diabetes therapy. Present study is aimed at finding the antioxidant and hypoglycaemic potential of some novel derivatives of 2-phenylamino-1,4-naphthoquinones (PAN) including chloro, nitro, methyl and bromo (5a-d) derivatives synthesized by single pot experiment. Product crystals were purified by TLC and characterized by FT-IR. The antioxidant potential of the compounds was assayed through DPPH radical scavenging and reducing power activities noted as UV-vis. absorbance. The DPPH assay has showed the powerful antioxidant activity of nitro and bromo derivatives, while the nitro derivative showed the significant reduction potential towards FRAP assay. Hypoglycaemic potential of the compounds was studied in rat animal model. All synthesized compounds revealed better hypoglycaemic activity; however, the chloro-derivative exhibited the more potent hypoglycaemic activity showing about 43% reduction in the mean blood glucose levels of the treated animals. As the bioreduction of naphthoquinones may be influenced by changing its redox properties, it has been noticed that the e-donating resonance effect (+R) of 'chloro' group has shown the significant effects on biological activity through stabalization of its imine form which limits the potential of generation of free radicals during bioreduction of quinones and thus has been proposed as the reason of its hypoglycaemic activity. Future studies employing the properties of e-donating groups of PAN may optimize the drug-receptor interaction for better drug designing and drug development strategies against diabetes and also for the clinical trials.

Designing a Redox Noninnocent Phenalenyl-Based Copper(II) Complex: An Autotandem Catalyst for the Selective Oxidation of Polycyclic Aromatic Hydrocarbons (PAHs)

A square-planar [CuIIL] complex 1, based on the redox-active phenalenyl unit LH2 = 9,9'-(ethane-1,2-diylbis(azanediyl))bis(1H-phenalen-1-one), is prepared and structurally characterized by single-crystal X-ray diffraction analysis. Complex 1 crystallizes at room temperature with the P1 space group. The molecular structure of 1 reveals the presence of intriguing C-H···Cu intermolecular anagostic interactions of the order ∼2.7715 Å. Utilizing the presence of anagostic interactions and the free nonbonding molecular orbitals (NBMOs) of the closed-shell phenalenyl unit in 1, the oxidation reactions of some industrially important polycyclic aromatic hydrocarbons (PAHs) in the presence of the [CuIIL] complex under very mild conditions have been reported. The direct conversion of anthracene-9-carbaldehyde to 9,10-anthraquinone in one step concludes that the catalyst shows dual activity in the chemical transformations. This also includes the first report of a "single-step" catalytic transformation of pyrene-1-carbaldehyde to the synthetically difficult pyren-4-ol, a precursor for the synthesis of several novel fluorescent probes for cell imaging.

Time-Dependent Degradation of Naphthoquinones and Phenolic Compounds in Walnut Husks

The aim of the present study was to investigate how individual phenolic compounds and phenolic groups in walnut husk gratings (e.g., naphthoquinones, flavanols, flavonols, hydroxycinnamic acids) are oxidized over time, with a particular focus on the juglone synthase pathway. Walnut husk gratings were prepared and left under 'degradation' conditions (exposure to the air, room temperature) at increasing times. Following methanol extraction of these husk gratings, the HPLC profile of methanolic extract of husk gratings exhibited twenty-six compounds over time, then hydrojuglone glucoside, α-hydrojuglone, and juglone were detailed by HPLC-mass spectrometry. Initially (0-20 min), the content of hydrojuglone glucoside in the husk gratings decreased by 40.4%, while the content of α-hydrojuglone increased by 20.0%, and then decreased. After an initial delay (0-20 min), juglone increased by 47.9% from 20 to 40 min, and then decreased. This initially confirmed that hydrojuglone glucoside and α-hydrojuglone could be considered as precursors of juglone. Different phenolic groups showed different degradation processes, although they all reached their highest content after 40 min. This might arise from degradation of the phenols, increased free phenols, or activation of the plant defense mechanism due to damage to the tissue, similar to the effects of stress or a pathogen attack. Although it has been reported that the phenolic compounds decrease when food is processed or damaged, they showed increases, which were not indefinite, but time dependent. As phenolic compounds are considered highly beneficial to human health, increases upon processing indicate the need for further investigations into healthier food preparation processes. This is the first study on the degradation pathways of juglone, using a mass spectrometer, in which we suggest that hydrojuglone glucoside and α-hydrojuglone are indeed the precursors of juglone. However, it is possible that there are other degradation pathways of hydrojuglone glucoside, since less juglone is synthesized than expected.

Thioredoxin reductase 1 inhibitor shikonin promotes cell necroptosis via SecTRAPs generation and oxygen-coupled redox cycling

Shikonin, a naturally occurring naphthoquinone with potent anti-tumor activity, has been reported to induce cancer cell death via targeting selenoenzyme thioredoxin reductase 1 (TrxR1; TXNRD1). However, the interaction between shikonin and TrxR1 remains unclear, and the roles of the cellular antioxidant system in shikonin induced cell death are obscure. Here, we found that shikonin modified the Sec⁴⁹⁸ residue of TrxR1 to fully inhibit its antioxidant activity, however, the shikonin-modified TrxR1 still remained intrinsic NADPH oxidase activity, which promotes superoxide anions production. Besides, TrxR1 efficiently reduced shikonin in both selenocysteine dependent and selenocysteine independent manners, and the oxygen-coupled redox cycling of shikonin also generates excessive superoxide anions. The inhibitory effects and the redox cycling of shikonin towards TrxR1 caused cancer cell ROS-dependent necroptosis. Interestingly, as we evaluated, some cancer cell lines were insensitive to shikonin, especially kelch-like ECH associated protein 1 (KEAP1)-mutant non-small cell lung cancer (NSCLC) cells, which harbor constitutive activation of the nuclear factor-erythroid 2-related factor 2 (NRF2). NADPH bankruptcy caused by glucose starvation or glucose limitation (inhibiting glucose transporter 1 by BAY-876) could efficiently overcome the resistance of KEAP1-mutant NSCLC cells to shikonin. Glucose-6-phosphate dehydrogenase (G6PD), was known as a rate-limiting enzyme in the pentose phosphate pathway, however, the pharmacological inhibition of G6PD by 6-aminonicotinamide (6-AN), enhanced the shikonin-induced cytotoxicity but has no selectivity on KEAP1-mutant NSCLC cells. This study will be helpful in applying shikonin for potential chemotherapy, and in combinational treatment of KEAP1-mutant NSCLC.

2-Benzyllawsone protects against polymicrobial sepsis and vascular hyporeactivity in swiss albino mice

BACKGROUND

Novel naphthoquinone, 2-benzyllawsone (LT-9) was evaluated against vascular hyporeactivity and sepsis in cecal ligation and puncture (CLP) model in mice in view of its preliminary antibacterial and anti-inflammatory properties and to explore whether pretreatment with the molecule could restore vascular tone and contractile response to norepinephrine.

METHODS

Evaluation of LT-9 against vascular hyporeactivity, hypotension, and sepsis-related inflammation and infection was carried out in the CLP model in Swiss albino mice and aortic smooth muscle cells in vitro.

RESULTS

LT-9 showed potent reversal of the vascular hyporeactivity in CLP mice aorta. The increased contraction response to norepinephrine in CLP mouse aorta by LT-9 was mediated by opening of L-type voltage-dependent calcium channels (VDCC) verified by ex vivo experiment where LT-9 enhanced contraction response to CaCl2 in the aorta while abolishing the contraction response of known VDCC opener Bay K8644. LT-9 in aortic smooth muscle cells showed Fluo-4 mediated increase in calcium fluorescence. Oral administration of LT-9 at 50 and 100 mg kg-1 day-1 for 15 days significantly enhanced the mean survival time, improved hemodynamic and Electrocardiogram (ECG) profile, and aortic tissue reactivity in CLP mice. Further, LT-9 significantly reversed the perturbation of the expression profile of inflammatory cytokines, reduced the splenic microbial load, and was well tolerated in oral toxicity.

CONCLUSIONS

LT-9 showed potent biological activity against sepsis and was found to be well tolerated in the toxicity study in Swiss albino mice and showed promise for the benzyllawsone class of molecules against sepsis for the development of novel pharmacophore.

Recent Advances in Alternaria Phytotoxins: A Review of Their Occurrence, Structure, Bioactivity and Biosynthesis

Alternaria is a ubiquitous fungal genus in many ecosystems, consisting of species and strains that can be saprophytic, endophytic, or pathogenic to plants or animals, including humans. Alternaria species can produce a variety of secondary metabolites (SMs), especially low molecular weight toxins. Based on the characteristics of host plant susceptibility or resistance to the toxin, Alternaria phytotoxins are classified into host-selective toxins (HSTs) and non-host-selective toxins (NHSTs). These Alternaria toxins exhibit a variety of biological activities such as phytotoxic, cytotoxic, and antimicrobial properties. Generally, HSTs are toxic to host plants and can cause severe economic losses. Some NHSTs such as alternariol, altenariol methyl-ether, and altertoxins also show high cytotoxic and mutagenic activities in the exposed human or other vertebrate species. Thus, Alternaria toxins are meaningful for drug and pesticide development. For example, AAL-toxin, maculosin, tentoxin, and tenuazonic acid have potential to be developed as bioherbicides due to their excellent herbicidal activity. Like altersolanol A, bostrycin, and brefeldin A, they exhibit anticancer activity, and ATX V shows high activity to inhibit the HIV-1 virus. This review focuses on the classification, chemical structure, occurrence, bioactivity, and biosynthesis of the major Alternaria phytotoxins, including 30 HSTs and 50 NHSTs discovered to date.