Protection Activity of 1,4-Naphthoquinones in Rotenone-Induced Models of Neurotoxicity.

The MTS cell viability test was used to screen a mini library of natural and synthetic 1,4-naphthoquinone derivatives (1,4-NQs) from marine sources. This screening identified two highly effective compounds, U-443 and U-573, which showed potential in protecting Neuro-2a neuroblastoma cells from the toxic effects of rotenone in an in vitro model of neurotoxicity. The selected 1,4-NQs demonstrated the capability to reduce oxidative stress by decreasing the levels of reactive oxygen species (ROS) and nitric oxide (NO) in Neuro-2a neuroblastoma cells and RAW 264.7 macrophage cells and displayed significant antioxidant properties in mouse brain homogenate. Normal mitochondrial function was restored and the mitochondrial membrane potential was also regained by 1,4-NQs after exposure to neurotoxins. Furthermore, at low concentrations, these compounds were found to significantly reduce levels of proinflammatory cytokines TNF and IL-1ß and notably inhibit the activity of cyclooxygenase-2 (COX-2) in RAW 264.7 macrophages. The results of docking studies showed that the 1,4-NQs were bound to the active site of COX-2, analogically to a known inhibitor of this enzyme, SC-558. Both substances significantly improved the behavioral changes in female CD1 mice with rotenone-induced early stage of Parkinson's disease (PD) in vivo. It is proposed that the 1,4-NQs, U-443 and U-573, can protect neurons and microglia through their potent anti-ROS and anti-inflammatory activities.

Tetracyclic 1,4-Naphthoquinone Thioglucoside Conjugate U-556 Blocks the Purinergic P2X7 Receptor in Macrophages and Exhibits Anti-Inflammatory Activity In Vivo.

P2X7 receptors (P2X7Rs) are ligand-gated ion channels that play a significant role in inflammation and are considered a potential therapeutic target for some inflammatory diseases. We have previously shown that a number of synthetic 1,4-naphthoquinones are capable of blocking P2X7Rs in neuronal and macrophage cells. In the present investigation, we have demonstrated the ability of the tetracyclic quinone-thioglucoside conjugate U-556, derived from 1,4-naphthoquinone thioglucoside, to inhibit ATP-induced Ca2+ influx and YO-PRO-1 dye uptake, which indicates blocking P2X7R in RAW 264.7 macrophages. This process was accompanied by the inhibition of ATP-induced reactive oxygen species production in macrophages, as well as the macrophage survival strengthening under ATP toxic effects. Nevertheless, U-556 had no noticeable antioxidant capacity. Naphthoquinone-thioglucoside conjugate U-556 binding to the extracellular part of the P2X7R was confirmed by SPR analysis, and the kinetic characteristics of this complex formation were established. Computer modeling predicted that U-556 binds the P2X7R allosteric binding site, topographically similar to that of the specific A438079 blocker. The study of biological activity in in vivo experiments shows that tetracylic conjugate significantly reduces inflammation provoked by carrageenan. The data obtained points out that the observed physiological effects of U-556 may be due to its ability to block the functioning of the P2X7R.

Neuroprotective Effect of 1,4-Naphthoquinones in an In Vitro Model of Paraquat and 6-OHDA-Induced Neurotoxicity.

Targeted screening using the MTT cell viability test with a mini-library of natural and synthetic 1,4-naphthoquinones and their derivatives was performed in order to increase the survival of Neuro-2a neuroblastoma cells in in vitro paraquat and 6-hydroxydopamine models of Parkinson's disease. As a result, 10 compounds were selected that could protect neuronal cells from the cytotoxic effects of both paraquat and 6-hydroxydopamine. The five most active compounds at low concentrations were found to significantly protect the activity of nonspecific esterase from the inhibitory effects of neurotoxins, defend cell biomembranes from lytic destruction in the presence of paraquat and 6-hydroxydopamine, and normalize the cell cycle. The protective effects of these compounds are associated with the suppression of oxidative stress, decreased expression of reactive oxygen species and nitric oxide formation in cells and normalization of mitochondrial function, and restoration of the mitochondrial membrane potential altered by neurotoxins. It was suggested that the neuroprotective activity of the studied 1,4-NQs is attributable to their pronounced antioxidant and free radical scavenging activity and their ability to reduce the amount of reactive oxygen species formed by paraquat and 6-hydroxydopamine action on neuronal cells. The significant correlation between the neuroprotective properties of 1,4-naphthoquinones and Quantitative Structure-Activity Relationship descriptors describing the physicochemical properties of these compounds means that the hydrophobicity, polarity, charge, and shape of the molecules can be of decisive importance in determining the biological activity of studied substances.

Synthetic 1,4-Naphthoquinones inhibit P2X7 receptors in murine neuroblastoma cells.

The P2X7 receptor (P2X7R) is an ATP-gated ion channel and potential therapeutic target for new drug development. In this study, we synthesized a series of new 1,4-naphthoquinone (1,4-NQ) derivatives and investigated their antagonistic effects against mouse P2X7R. We explored the ability of the tested substances to block ATP-induced Ca2+ influx into mouse Neuro-2a cells and selected the four most effective substances: the 1,4-naphthoquinone thioglucosides U-548 and U-557 and their tetracyclic conjugates U-286 and U-556. Biological analysis of these compounds revealed significant in vitro inhibition of murine P2X7R. This inhibition resulted in marked blockade of ethidium bromide (EtBr) and YO-PRO-1 fluorescent dye uptake, pronounced decreases in ROS and NO production and protection of neuronal cell viability against the toxic action of high ATP concentrations. In silico analysis indicated favorable molecular docking results of these 1,4-NQs, pointing to their potential to bind in an allosteric site located in the extracellular region of P2X7R. These findings suggest compounds U-286, U-548, U-556 and U-557 as potential scaffolds for the design of new P2X7R blockers and drugs effective against neuropathic pain and neurodegenerative diseases.

Synthesis, Cytotoxic Activity Evaluation and Quantitative Structure-Activity Analysis of Substituted 5,8-Dihydroxy-1,4-Naphthoquinones and their O- and S-Glycoside Derivatives Tested Against Neuro-2a Cancer Cells.

Based on 6,7-substituted 2,5,8-trihydroxy-1,4-naphtoquinones (1,4-NQs) derived from sea urchins, five new acetyl-O-glucosides of NQs were prepared. A new method of conjugation of per-O-acetylated 1-mercaptosaccharides with 2-hydroxy-1,4-NQs through a methylene spacer was developed. Methylation of 2-hydroxy group of quinone core of acetylthiomethylglycosides by diazomethane and deacetylation of sugar moiety led to 28 new thiomethylglycosidesof 2-hydroxy- and 2-methoxy-1,4-NQs. The cytotoxic activity of starting 1,4-NQs (13 compounds) and their O- and S-glycoside derivatives (37 compounds) was determined by the MTT method against Neuro-2a mouse neuroblastoma cells. Cytotoxic compounds with EC50 = 2.7-87.0 µM and nontoxic compounds with EC50 > 100 µM were found. Acetylated O- and S-glycosides 1,4-NQs were the most potent, with EC50 = 2.7-16.4 µM. Methylation of the 2-OH group innaphthoquinone core led to a sharp increase in the cytotoxic activity of acetylated thioglycosidesof NQs, which was partially retained for their deacetylated derivatives. Thiomethylglycosides of 2-hydroxy-1,4-NQs with OH and MeO groups in quinone core at positions 6 and 7, resprectively formed a nontoxic set of compounds with EC50 > 100 µM. A quantitative structure-activity relationship (QSAR) model of cytotoxic activity of 22 1,4-NQ derivatives was constructed and tested. Descriptors related to the cytotoxic activity of new 1,4-NQ derivatives were determined. The QSAR model is good at predicting the activity of 1,4-NQ derivatives which are unused for QSAR models and nontoxic derivatives.

Synthesis and Evaluation of Antimicrobial and Cytotoxic Activity of Oxathiine-Fused Quinone-Thioglucoside Conjugates of Substituted 1,4-Naphthoquinones.

A series of new tetracyclic oxathiine-fused quinone-thioglycoside conjugates based on biologically active 1,4-naphthoquinones and 1-mercapto derivatives of per-O-acetyl d-glucose, d-galactose, d-xylose, and l-arabinose have been synthesized, characterized, and evaluated for their cytotoxic and antimicrobial activities. Six tetracyclic conjugates bearing a hydroxyl group in naphthoquinone core showed high cytotoxic activity with EC50 values in the range of 0.3 to 0.9 µM for various types of cancer and normal cells and no hemolytic activity up to 25 µM. The antimicrobial activity of conjugates was screened against Gram-positive bacteria (Staphylococcus aureus, Bacillus cereus), Gram-negative bacteria (Pseudomonas aeruginosa and Escherichia coli), and fungus Candida albicans by the agar diffusion method. The most effective juglone conjugates with d-xylose or l-arabinose moiety and hydroxyl group at C-7 position of naphthoquinone core at concentration 10 µg/well showed antimicrobial activity comparable with antibiotics vancomicin and gentamicin against Gram-positive bacteria strains. In liquid media, juglone-arabinosidic tetracycles showed highest activity with MIC 6.25 µM. Thus, a positive effect of heterocyclization with mercaptosugars on cytotoxic and antimicrobial activity for group of 1,4-naphthoquinones was shown.