Redox ticklers and beyond: Naphthoquinone repository in the spotlight against inflammation and associated maladies

Antibacterial and anti-biofilm efficacy of 1,4-naphthoquinone against Chromobacterium violaceum: an in vitro and in silico investigation

Antimicrobial resistance (AMR) is an urgent worldwide health concern, requiring the exploration for novel antimicrobial interventions. A Gram-negative bacterium, Chromobacterium violaceum, synthesizes quorum-sensing-regulated violacein pigment, develops resilient biofilms, and is often used for the screening of anti-infective drugs. The aim of this work is to assess the antibacterial and antibiofilm properties of three polyphenols: 1,4-naphthoquinone, caffeic acid, and piperine. The determination of antibacterial activity was conducted by the agar overlay and broth microdilution techniques. Analysis of membrane rupture was conducted by crystal violet uptake and β-galactosidase assay. Inhibition of biofilm was evaluated using a 96-well microtiter plate assay. Biofilm structures were visualized using light, scanning electron microscopy (SEM), and confocal laser scanning electron microscopy (CLSM). Among the phytochemicals, 1,4-naphthoquinone exhibited the highest antibacterial action (25 mm zone of inhibition). The minimum inhibitory concentration of 1,4-naphthoquinone was determined to be 405 µM. Outer and inner membrane permeability was enhanced by 52.01% and 1.28 absorbance, respectively. Violacein production was reduced by 74.85%, and biofilm formation was suppressed by 63.25% at sub-MIC levels (202.5 µM). Microscopic analyses confirmed reduced adhesion on surfaces. Hemolytic activity of 1,4-naphthoquinone showed a concentration-dependent effect, with 32.16% haemolysis at 202.5 µM. Molecular docking revealed significant interactions of 1,4-naphthoquinone with DNA gyrase followed by CviR. These findings highlight 1,4-naphthoquinone's potent antibacterial efficacy against C. violaceum, proposing its use as a surface coating agent to prevent biofilm formation on medical devices, thereby offering a promising strategy to combat bacterial infections.

Oral administration of plumbagin is beneficial in in vivo models of Duchenne muscular dystrophy through control of redox signaling

Duchenne muscular dystrophy (DMD) is a progressive muscle-wasting disease. Recently approved molecular/gene treatments do not solve the downstream inflammation-linked pathophysiological issues such that supportive therapies are required to improve therapeutic efficacy and patients' quality of life. Over the years, a plethora of bioactive natural compounds have been used for human healthcare. Among them, plumbagin, a plant-derived analog of vitamin K3, has shown interesting potential to counteract chronic inflammation with potential therapeutic significance. In this work we evaluated the effects of plumbagin on DMD by delivering it as an oral supplement within food to dystrophic mutant of the fruit fly Drosophila melanogaster and mdx mice. In both DMD models, plumbagin show no relevant adverse effect. In terms of efficacy plumbagin improved the climbing ability of the dystrophic flies and their muscle morphology also reducing oxidative stress in muscles. In mdx mice, plumbagin enhanced the running performance on the treadmill and the muscle strength along with muscle morphology. The molecular mechanism underpinning these actions was found to be the activation of nuclear factor erythroid 2-related factor 2 pathway, the re-establishment of redox homeostasis and the reduction of inflammation thus generating a more favorable environment for skeletal muscles regeneration after damage. Our data provide evidence that food supplementation with plumbagin modulates the main, evolutionary conserved, mechanistic pathophysiological hallmarks of dystrophy, thus improving muscle function in vivo; the use of plumbagin as a therapeutic in humans should thus be explored further.

Multidrug Resistant Enteric Bacteria from Cancer Patients Admitted in Douala Laquintinie Hospital, Littoral Region of Cameroon

Patients with cancer have weakened immune systems, making them more vulnerable to infections. This study was carried out to determine the bacterial origins of enteric disorders in cancer patients and noncancer patients at the Oncology Department of Laquintinie Hospital in Douala. A cross-sectional study was conducted from October 2021 to March 2023. Stool samples from 307 cancer patients with enteric disorders and 200 noncancer patients with enteric disorders were examined to diagnose the presence of bacteria using various techniques. Among all participants in this study, 62.13% were female and 37.87% were male. The average age of the participants was 46.38 ± 15.81 years, with a minimum age of 10 years and a maximum age of 84 years. The average age of participants was significantly higher (p < 0.000) in cancer patients (49.54 ± 14.65 years) compared to noncancer patients (41.53 ± 16.33 years). Proteus mirabilis, Proteus vulgaris, Salmonella typhi, Enterobacter cloacae, Klebsiella pneumoniae, Yersinia intemedia, and Klebsiella oxytoca were more frequently isolated in cancer patients than in noncancer patients, with the respective percentages of 56.25% versus 43.75%, 50.00% versus 50.00%, 61.66% versus 38.34%, 66.66% versus 33.34%, 72.22% versus 27.78%, 80.00 versus 20.00%, and 100% versus 0.00%. Most isolates were sensitive to imipenem (IMP), gentamicin (GEN), and amikacin (AMK). Proteus vulgaris, the most prevalent isolate, showed significantly high resistance (with p < 0.05) in cancer patients compared to noncancer patients at amoxicillin/clavuranic acid (AMC) (89.13% versus 41.30%), ceftriaxone (CTR) (63.04% versus 39.13%), ciprofloxacin (CIP) (65.22% versus 34.18%), and tetracycline (TET) (93.48% versus 63.04%). Multidrug resistance was observed in cancer patients compared to noncancer patients for Klebsiella pneumoniae (85.00% versus 60.00%), Salmonella typhi (84.62% versus 60.00%), and Klebsiella oxytoca (86.49% versus 43.48%). The increase in the number of Gram-negative infections among cancer patients, as shown in the present study, highlights the need for broad-spectrum therapy and effective planning of control programs to reduce bacterial diseases among cancer patients.

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.

2,3-Dichloronaphthoquinone derivatives: Synthesis, antimicrobial activity, molecular modelling and ADMET studies

In the present study, an intermediate namely 2-(3-bromopropylamino)-3-chloronaphthalene-1,4-dione was initially synthesized via the nucleophilic addition-elimination reaction between 2,3-dichloro-1,4-naphthoquinone and 3-bromo-1-aminopropane. Then a coupling reaction between the intermediate and piperazine derivatives yielded a number of 1,4-naphthoquinone derivatives. Spectroscopic analysis successfully characterized the products that were obtained in good yields. In vitro antibacterial properties of the compounds were examined against different bacterial strains. In vitro antibacterial properties of the compounds were examined against the bacterial strains S. Aureus, E. Faecalis, E. Coli and P. Aeruginosa. While compound 9 was found to be effective against all bacterial strains used, compound 12 was active against three strains and compounds 10 and 11 were effective against the two. None of the compounds are effective against C. albicans strain. In silico molecular docking studies revealed that all compounds had docking scores comparable to the antibacterial drugs ciprofloxacin and gentamicin and might be considered as DNA gyrase B inhibitors. Molecular dynamics simulations were also conducted for a better understanding of the stability and the selected docked complexes. Additionally, the drug similarity of the synthesized compounds and ADMET characteristics were examined in conjunction with the antibiotic ciprofloxacin, and drug potentials were then evaluated. Compatible predictions were found with the drug similarity and ADMET parameters.

Unlocking the potential of 1,4-naphthoquinones: A comprehensive review of their anticancer properties

Cancer encompasses a group of pathologies with common characteristics, high incidence, and prevalence in all countries. Although there are treatments available for this disease, they are not always effective or safe, often failing to achieve the desired results. This is why it is necessary to continue the search for new therapies. One of the strategies for obtaining new antitumor drugs is the use of 1,4-naphthoquinone as a scaffold in synthetic or natural products with antitumor activity. This review focuses on compiling studies related to the antitumor activity of 1,4-naphthoquinone and its natural and synthetic derivatives over the last 10 years. The work describes the main natural naphthoquinones with antitumor activity and classifies the synthetic naphthoquinones based on the structural modifications made to the scaffold. Additionally, the formation of metal complexes using naphthoquinones as a ligand is considered. After a thorough review, 197 synthetic compounds with potent biological activity against cancer have been classified according to their chemical structures and their mechanisms of action have been described.

Discovery of 5-Hydroxy-1,4-naphthoquinone (Juglone) Derivatives as Dual Effective Agents Targeting Platelet-Cancer Interplay through Protein Disulfide Isomerase Inhibition

In this study, a series of 2- and/or 3-substituted juglone derivatives were designed and synthesized. Among them, 9, 18, 22, 30, and 31 showed stronger inhibition activity against cell surface PDI or recombinant PDI and higher inhibitory effects on U46619- and/or collagen-induced platelet aggregation than juglone. The glycosylated derivatives 18 and 22 showed improved selectivity for inhibiting the proliferation of multiple myeloma RPMI 8226 cells, and the IC50 values reached 61 and 48 nM, respectively, in a 72 h cell viability test. In addition, 18 and 22 were able to prevent tumor cell-induced platelet aggregation and platelet-enhanced tumor cell proliferation. The molecular docking showed the amino acid residues Gln243, Phe440, and Leu443 are important for the compound-protein interaction. Our results reveal the potential of juglone derivatives to serve as novel antiplatelet and anticancer dual agents, which are available to interrupt platelet-cancer interplay through covalent binding to PDI catalytic active site.

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.

Synthesis, anti-inflammatory activity, inverse molecular docking, and acid dissociation constants of new naphthoquinone-thiazole hybrids

Chronic Inflammation is associated with various types of diseases that involves pro-inflammatory cytokines like IL-6 and TNF-α. High costs and serious side effects of available anti-inflammatory/immunomodulatory drugs led us to design new compounds with promising anti-inflammatory activities. Many drugs and biologically important compounds involve naphthoquinone and thiazole moieties in their core structures. Thereby, here we report the synthesis, characterization and anti-inflammatory activities of new naphthoquinone thiazole hybrids by reaction of naphthoquinone acyl thioureas with various α-bromoketone derivatives. The position of NO2 group in one of the phenyl rings of naphthoquinone thiazole hybrids was changed while different substituents were introduced at the para position of the second phenyl ring. All compounds were tested for potential immunomodulatory effect. No inflammatory cytokines were observed in the absence of LPS stimulant. On the other hand, they had promising anti-inflammatory immunomodulatory activities by being able to decrease the production of the pro-inflammatory cytokines (TNF-α and IL-6) in the LPS-stimulated cells. In an effort to find the possible mechanism of action, several enzymes involved in signalling pathways that play critical roles in inflammatory responses were screened in silico. Subsequent to inverse molecular docking approach, PI3K was predicted be the potential target. The docked complexes of the most potent compounds 5g and 5i were subjected to molecular dynamics simulation to assess the binding stability of the igands with the putative target. Acid dissociation constants (pKa) of the products were also determined potentiometrically.

Neuroprotective role of plumbagin on eye damage induced by high-sucrose diet in adult fruit fly Drosophila melanogaster

The natural compound plumbagin has a wide range of pharmacological and potential therapeutic activities, although its role in neuroretina degeneration is unknown. Here we evaluated the effects of plumbagin on retina homeostasis of the fruit fly Drosophila melanogaster fed with high glucose diet, a model of hyperglycemia-induced eye impairment to study the pathophysiology of diabetic retinopathy at the early stages. To this aim, the visual system of flies orally administered with plumbagin has been analyzed at structural, functional, and molecular/cellular level as for instance neuronal apoptosis/autophagy dysregulation and oxidative stress-related signals. Our results demonstrated that plumbagin ameliorates the visual performance of hyperglycemic flies. Drosophila eye-structure, clearly altered by hyperglycemia, i.e. defects of the pattern of ommatidia, irregular rhabdomeres, vacuoles, damaged mitochondria, and abnormal phototransduction units were rescued, at least in part, by plumbagin. In addition, it reactivated autophagy, decreased the presence of cell death/apoptotic features, and exerted antioxidant effects in the retina. In terms of mechanisms favoring death/survival ratio, Nrf2 signaling activation may be one of the strategies by which plumbagin reduced redox unbalance mainly increasing the levels of glutathione-S-transferase. Likewise, plumbagin may act additively and/or synergistically inhibiting the mitochondrial-endoplasmic reticulum stress and unfolded protein response pathways, which prevented neuronal impairment and eye damage induced by reactive oxygen species. These results provide an avenue for further studies, which may be helpful to develop novel therapeutic candidates and drug targets against eye neurotoxicity by high glucose, a key aspect in retinal complications of diabetes.

Effect of lawsone-preconditioned mesenchymal stem cells on the regeneration of pancreatic β cells in Type 1 diabetic rats

Diabetes is one of the major health issues globally. Type 1 diabetes mellitus develops due to the destruction of pancreatic β cells. Mesenchymal stem cells (MSCs) having remarkable self-renewal and differentiation potential, can regenerate β cells. MSCs preconditioned with bioactive small molecules possess enhanced biological features and therapeutic potential under in vivo environment. Interestingly, compounds of naphthoquinone class possess antidiabetic and anti-inflammatory properties, and can be explored as potential candidates for preconditioning MSCs. This study analyzed the effect of lawsone-preconditioned human umbilical cord MSCs (hUMSCs) on the regeneration of β cells in the streptozotocin (STZ)-induced Type 1 diabetes (T1D) rats. hUMSCs were isolated and characterized for the presence of surface markers. MSCs were preconditioned with optimized concentration of lawsone. T1D rat model was established by injecting 50 mg/kg of STZ intraperitoneally. Untreated and lawsone-preconditioned hUMSCs were transplanted into the diabetic rats via tail vein. Fasting blood sugar and body weight were monitored regularly for 4 weeks. Pancreas was harvested and β cell regeneration was evaluated by hematoxylin and eosin staining, and gene expression analysis. Immunohistochemistry was also done to assess the insulin expression. Lawsone-preconditioned hUMSCs showed better anti-hyperglycemic effect in comparison with untreated hUMSCs. Histological analysis presented the regeneration of islets of Langerhans with upregulated expression of βcell genes and reduced expression of inflammatory markers. Immunohistochemistry revealed strong insulin expression in the preconditioned hUMSCs compared with the untreated hUMSCs. It is concluded from the present study that lawsone-preconditioned hMSCs were able to exhibit pronounced anti-hyperglycemic effect in vivo compared with hUMSCs alone.

Plumbagin, a Natural Compound with Several Biological Effects and Anti-Inflammatory Properties

Phytochemicals from various medicinal plants are well known for their antioxidant properties and anti-cancer effects. Many of these bioactive compounds or natural products have demonstrated effects against inflammation, while some showed a role that is only approximately described as anti-inflammatory. In particular, naphthoquinones are naturally-occurring compounds with different pharmacological activities and allow easy scaffold modification for drug design approaches. Among this class of compounds, Plumbagin, a plant-derived product, has shown interesting counteracting effects in many inflammation models. However, scientific knowledge about the beneficial effect of Plumbagin should be comprehensively reported before candidating this natural molecule into a future drug against specific human diseases. In this review, the most relevant mechanisms in which Plumbagin plays a role in the process of inflammation were summarized. Other relevant bioactive effects were reviewed to provide a complete and compact scenario of Plumbagin's potential therapeutic significance.

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.

Natural Products for Pesticides Discovery: Structural Diversity Derivation and Biological Activities of Naphthoquinones Plumbagin and Juglone

Plant diseases and insect pests seriously affect the yield and quality of crops and are difficult to control. Natural products are an important source for the discovery of new pesticides. In this work, naphthoquinones plumbagin and juglone were selected as parent structures, and a series of their derivatives were designed, synthesized and evaluated for their fungicidal activities, antiviral activities and insecticidal activities. We found that the naphthoquinones have broad-spectrum anti-fungal activities against 14 types of fungus for the first time. Some of the naphthoquinones showed higher fungicidal activities than pyrimethanil. Compounds I, I-1e and II-1a emerged as new anti-fungal lead compounds with excellent fungicidal activities (EC₅₀ values: 11.35-17.70 µg/mL) against Cercospora, arachidicola Hori. Some compounds also displayed good to excellent antiviral activities against the tobacco mosaic virus (TMV). Compounds I-1f and II-1f showed similar level of anti-TMV activities with ribavirin, and could be used as new antiviral candidates. These compound also exhibited good to excellent insecticidal activities. Compounds II-1d and III-1c displayed a similar level of insecticidal activities with matrine, hexaflumuron and rotenone against Plutella xylostella. In current study, plumbagin and juglone were discovered as parent structures, which lays a foundation for their application in plant protection.

Synthetic Naphthoquinone Derivatives as Anticancer Agents in Ovarian Cancer: Cytotoxicity Assay and Investigation of Possible Biological Mechanisms Action

In this study, eight naphthoquinone derivatives were synthesized in yields ranging from 52 to 96% using easy, fast, and low-cost methodologies. All naphthoquinone derivatives were screened for their in vitro anti-proliferative activities against OVCA A2780 cancer cell lines. Amongst all analysed compounds, derivatives 3-5 presented the most prominent cytotoxic potential. Naphthoquinones 3 and 4, bearing sulfur-containing groups, were identified as having high potential for ROS production, in particular the superoxide anion. Furthermore, 3 and 4 compounds caused a decrease in the cell population in G0/G1 and induced more than 90% of the cell population to apoptosis. Compound 5 did not act in any of these processes. Finally, compounds 3-5 were tested for their inhibitory ability against PI3K and MAPK. Compounds 3 and 4 do not inhibit the PI3K enzyme. On the other hand, the naphthoquinone-polyphenol 5 was only able to inhibit the percentage of cells expressing pERK.

Chemopreventive Effects of Onosma mutabilis against Azoxymethane-Induced Colon Cancer in Rats via Amendment of Bax/Bcl-2 and NF-κB Signaling Pathways

Onosma species (Boraginaceae) are well known as medicinal plants due to their wide range of pharmaceutical potential. The present study aims to investigate the anticancer (in vitro) and chemo-protective (in vivo) efficacies of Onosma mutabilis extract (OME) in the azoxymethane (AOM)-induced aberrant crypt foci (ACF) in rats. The in vitro antiproliferative effects of OME were determined on two human tumor cell lines (Caco-2 and HT-29) via MTT assay. The in vivo chemoprotective effects of OME were investigated by performing various biochemical analyses in serum and tissue homogenates of albino rats, along with determining oxidative stress biomarkers. Inflammatory biomarkers of colon, colonic gross morphology (by methylene blue), ACF formation, and colonic histopathology (H & E stain) were determined. The immunohistochemistry of colonic tissues was also assessed by Bax and Bcl-2 protein expression. The results showed that the antitumor activity of OME against Caco-2 and HT-29 colorectal cancer cells ranged between 22.28-36.55 µg/mL. OME supplementation caused a significant drop in the ACF values and improved the immunohistochemistry of the rats shown by up-regulation of Bax and down-regulation of Bcl-2 protein expressions. These outcomes reveal that O. mutabilis may have chemoprotective efficiency against AOM-induced colon cancer represented by the attenuation of ACF formation possibly through inhibition of free radicals, inflammation, and stimulation of the colon antioxidant armory (SOD, CAT, and GPx) and positive regulation of the Nrf2-Keap1 pathway.

Asian Ancistrocladus Lianas as Creative Producers of Naphthylisoquinoline Alkaloids

This book describes a unique class of secondary metabolites, the mono- and dimeric naphthylisoquinoline alkaloids. They occur in lianas of the paleotropical Ancistrocladaceae and Dioncophyllaceae families, exclusively. Their unprecedented structures include stereogenic centers and rotationally hindered, and thus likewise stereogenic, axes. Extended recent investigations on six Ancistrocladus species from Asia, as reported in this review, shed light on their fascinating phytochemical productivity, with over 100 such intriguing natural products. This high chemodiversity arises from a likewise unique biosynthesis from acetate-malonate units, following a novel polyketidic pathway to plant-derived isoquinoline alkaloids. Some of the compounds show most promising antiparasitic activities. Likewise presented are strategies for the regio- and stereoselective total synthesis of the alkaloids, including the directed construction of the chiral axis.

Hypoglycemic and antioxidative activity evaluation of phenolic compounds derived from walnut diaphragm produced in Xinjiang

Walnut diaphragm is defined as a dry wood septum located between the walnut shell and kernel. In this work, seven phenolic compounds from walnut diaphragm were purified and characterized, and their antioxidant activities and mechanisms of hypoglycemia were investigated. Compounds 1-7 were tested for DPPH, ABTS scavenging ability, and FRAP assay to evaluate the antioxidant activity. α-Amylase inhibition assay was introduced to assess the hypoglycemic activity, and the mechanism was investigated by kinetic analysis, CD spectrum, and molecular docking. Compound 6 showed the strongest antioxidant ability, while compound 1 exhibited the strongest inhibition of α-amylase by changing the secondary structure of α-amylase in a mixed competitive inhibition mode. Molecular docking test predicted that the tetrahydropyran part in compound 1 may contribute to its hypoglycemic effect. This study furnishes a new theoretical reference for the utilization and development of walnut diaphragm into a health food with antioxidant and hypoglycemic properties. PRACTICAL APPLICATIONS: The finding of this research may serve as a basis for the subsequent development of walnut diaphragm into instant tea-based health food or added to other food carriers to achieve auxiliary antioxidant and hypoglycemic effects. This study revealed that polyphenolic components were the material basis for the antioxidant and hypoglycemic effects of walnut diaphragm, which could be identified as landmark chemical components for controlling quality standards in the development of walnut diaphragm, thus accelerating the research process of quality standards for walnut diaphragm-related products. Furthermore, the studies on the mechanism of hypoglycemic activity supply more credible data to support the development of walnut diaphragm into a safe and consumer-friendly health food. With abundant resources and clear efficacy, walnut diaphragm has great development prospect and application value.

Naphthoquinones Oxidize H2S to Polysulfides and Thiosulfate, Implications for Therapeutic Applications

1,4-Napththoquinones (NQs) are clinically relevant therapeutics that affect cell function through production of reactive oxygen species (ROS) and formation of adducts with regulatory protein thiols. Reactive sulfur species (RSS) are chemically and biologically similar to ROS and here we examine RSS production by NQ oxidation of hydrogen sulfide (H2S) using RSS-specific fluorophores, liquid chromatography-mass spectrometry, UV-Vis absorption spectrometry, oxygen-sensitive optodes, thiosulfate-specific nanoparticles, HPLC-monobromobimane derivatization, and ion chromatographic assays. We show that NQs, catalytically oxidize H2S to per- and polysulfides (H2Sn, n = 2−6), thiosulfate, sulfite and sulfate in reactions that consume oxygen and are accelerated by superoxide dismutase (SOD) and inhibited by catalase. The approximate efficacy of NQs (in decreasing order) is, 1,4-NQ ≈ juglone ≈ plumbagin > 2-methoxy-1,4-NQ ≈ menadione >> phylloquinone ≈ anthraquinone ≈ menaquinone ≈ lawsone. We propose that the most probable reactions are an initial two-electron oxidation of H2S to S0 and reduction of NQ to NQH2. S0 may react with H2S or elongate H2Sn in variety of reactions. Reoxidation of NQH2 likely involves a semiquinone radical (NQ·−) intermediate via several mechanisms involving oxygen and comproportionation to produce NQ and superoxide. Dismutation of the latter forms hydrogen peroxide which then further oxidizes RSS to sulfoxides. These findings provide the chemical background for novel sulfur-based approaches to naphthoquinone-directed therapies.

Evaluation of 1,4-naphthoquinone derivatives as antibacterial agents: activity and mechanistic studies

The diverse and large-scale application of disinfectants posed potential health risks and caused ecological damage during the 2019-nCoV pandemic, thereby increasing the demands for the development of disinfectants based on natural products, with low health risks and low aquatic toxicity. In the present study, a few natural naphthoquinones and their derivatives bearing the 1,4-naphthoquinone skeleton were synthesized, and their antibacterial activity against selected bacterial strains was evaluated. In vitro antibacterial activities of the compounds were investigated against Escherichia coli and Staphylococcus aureus. Under the minimum inhibitory concentration (MIC) of ⩽ 0.125 µmol/L for juglone (1a), 5,8-dimethoxy-1,4-naphthoquinone (1f), and 7-methyl-5-acetoxy-1,4-naphthoquinone (3c), a strong antibacterial activity against S. aureus was observed. All 1,4-naphthoquinone derivatives exhibited a strong antibacterial activity, with MIC values ranging between 15.625 and 500 µmol/L and EC₅₀ values ranging between 10.56 and 248.42 µmol/L. Most of the synthesized compounds exhibited strong antibacterial activities against S. aureus. Among these compounds, juglone (1a) showed the strongest antibacterial activity. The results from mechanistic investigations indicated that juglone, a natural naphthoquinone, caused cell death by inducing reactive oxygen species production in bacterial cells, leading to DNA damage. In addition, juglone could reduce the self-repair ability of bacterial DNA by inhibiting RecA expression. In addition to having a potent antibacterial activity, juglone exhibited low cytotoxicity in cell-based investigations. In conclusion, juglone is a strong antibacterial agent with low toxicity, indicating that its application as a bactericidal agent may be associated with low health risks and aquatic toxicity.

ELECTRONIC SUPPLEMENTARY MATERIAL

Supplementary material is available in the online version of this article at 10.1007/s11783-023-1631-2 and is accessible for authorized users.

Thioredoxin reductase selenoproteins from different organisms as potential drug targets for treatment of human diseases

Human thioredoxin reductase (TrxR) is a selenoprotein with a central role in cellular redox homeostasis, utilizing a highly reactive and solvent-exposed selenocysteine (Sec) residue in its active site. Pharmacological modulation of TrxR can be obtained with several classes of small compounds showing different mechanisms of action, but most often dependent upon interactions with its Sec residue. The clinical implications of TrxR modulation as mediated by small compounds have been studied in diverse diseases, from rheumatoid arthritis and ischemia to cancer and parasitic infections. The possible involvement of TrxR in these diseases was in some cases serendipitously discovered, by finding that existing clinically used drugs are also TrxR inhibitors. Inhibiting isoforms of human TrxR is, however, not the only strategy for human disease treatment, as some pathogenic parasites also depend upon Sec-containing TrxR variants, including S. mansoni, B. malayi or O. volvulus. Inhibiting parasite TrxR has been shown to selectively kill parasites and can thus become a promising treatment strategy, especially in the context of quickly emerging resistance towards other drugs. Here we have summarized the basis for the targeting of selenoprotein TrxR variants with small molecules for therapeutic purposes in different human disease contexts. We discuss how Sec engagement appears to be an indispensable part of treatment efficacy and how some therapeutically promising compounds have been evaluated in preclinical or clinical studies. Several research questions remain before a wider application of selenoprotein TrxR inhibition as a first-line treatment strategy might be developed. These include further mechanistic studies of downstream effects that may mediate treatment efficacy, identification of isoform-specific enzyme inhibition patterns for some given therapeutic compounds, and the further elucidation of cell-specific effects in disease contexts such as in the tumor microenvironment or in host-parasite interactions, and which of these effects may be dependent upon the specific targeting of Sec in distinct TrxR isoforms.