An insight into role of amino acids as antioxidants via NRF2 activation.

Oxidative stress can affect the protein, lipids, and DNA of the cells and thus, play a crucial role in several pathophysiological conditions. It has already been established that oxidative stress has a close association with inflammation via nuclear factor erythroid 2-related factor 2 (NRF2) signaling pathway. Amino acids are notably the building block of proteins and constitute the major class of nitrogen-containing natural products of medicinal importance. They exhibit a broad spectrum of biological activities, including the ability to activate NRF2, a transcription factor that regulates endogenous antioxidant responses. Moreover, amino acids may act as synergistic antioxidants as part of our dietary supplementations. This has aroused research interest in the NRF2-inducing activity of amino acids. Interestingly, amino acids' activation of NRF2-Kelch-like ECH-associated protein 1 (KEAP1) signaling pathway exerts therapeutic effects in several diseases. Therefore, the present review will discuss the relationship between different amino acids and activation of NRF2-KEAP1 signaling pathway pinning their anti-inflammatory and antioxidant properties. We also discussed amino acids formulations and their applications as therapeutics. This will broaden the prospect of the therapeutic applications of amino acids in a myriad of inflammation and oxidative stress-related diseases. This will provide an insight for designing and developing new chemical entities as NRF2 activators.

In vivo and in vitro protective effects of shengmai injection against doxorubicin-induced cardiotoxicity.

CONTEXT: Shengmai injection (SMI) has been used to treat heart failure. OBJECTIVE: This study determines the molecular mechanisms of SMI against cardiotoxicity caused by doxorubicin (DOX). MATERIALS AND METHODS: In vivo, DOX (15 mg/kg) was intraperitoneally injected in model, Dex (dexrazoxane), SMI-L (2.7 mL/kg), SMI-M (5.4 mL/kg), and SMI-H (10.8 mL/kg) for 7 consecutive days. Hematoxylin-eosin (HE) and Masson staining were used to evaluate histological changes, and cardiomyocyte apoptosis was identified using TdT-mediated dUTP nick-end labelling (TUNEL). Enzymatic indexes were determined. mRNA and protein expressions were analysed through RT-qPCR and Western blotting. In vitro, H9c2 cells were divided into control group, model group (2 mL 1 µM DOX), SMI group, ML385 group, and SMI + ML385 group, the intervention lasted for 24 h. mRNA and protein expressions were analysed. RESULTS: SMI markedly improved cardiac pathology, decreased cardiomyocyte apoptosis, increased creatine kinase (CK), lactate dehydrogenase (LDH), malondialdehyde (MDA), decreased superoxide dismutase (SOD). Compared with the model group, the protein expression of nuclear factor erythroid2-related factor 2 (Nrf2) (SMI-L: 2.42-fold, SMI-M: 2.67-fold, SMI-H: 3.07-fold) and haem oxygenase-1(HO-1) (SMI-L: 1.64-fold, SMI-M: 2.01-fold, SMI-H: 2.19-fold) was increased and the protein expression of kelch-like ECH-associated protein 1 (Keap1) (SMI-L: 0.90-fold, SMI-M: 0.77-fold, SMI-H: 0.66-fold) was decreased in SMI groups and Dex group in vivo. Additionally, SMI dramatically inhibited apoptosis, decreased CK, LDH and MDA levels, and enhanced SOD activity. Our results demonstrated that SMI reduced DOX-induced cardiotoxicity via activation of the Nrf2/Keap1 signalling pathway. CONCLUSIONS: This study revealed a new mechanism by which SMI alleviates DOX-induced 45 cardiomyopathy by modulating the Nrf2/Keap1 signal pathway.

Computational Screening for the Anticancer Potential of Seed-Derived Antioxidant Peptides: A Cheminformatic Approach.

Some seed-derived antioxidant peptides are known to regulate cellular modulators of ROS production, including those proposed to be promising targets of anticancer therapy. Nevertheless, research in this direction is relatively slow owing to the inevitable time-consuming nature of wet-lab experimentations. To help expedite such explorations, we performed structure-based virtual screening on seed-derived antioxidant peptides in the literature for anticancer potential. The ability of the peptides to interact with myeloperoxidase, xanthine oxidase, Keap1, and p47phox was examined. We generated a virtual library of 677 peptides based on a database and literature search. Screening for anticancer potential, non-toxicity, non-allergenicity, non-hemolyticity narrowed down the collection to five candidates. Molecular docking found LYSPH as the most promising in targeting myeloperoxidase, xanthine oxidase, and Keap1, whereas PSYLNTPLL was the best candidate to bind stably to key residues in p47phox. Stability of the four peptide-target complexes was supported by molecular dynamics simulation. LYSPH and PSYLNTPLL were predicted to have cell- and blood-brain barrier penetrating potential, although intolerant to gastrointestinal digestion. Computational alanine scanning found tyrosine residues in both peptides as crucial to stable binding to the targets. Overall, LYSPH and PSYLNTPLL are two potential anticancer peptides that deserve deeper exploration in future.

Mining Natural Products for Macrocycles to Drug Difficult Targets.

Lead generation for difficult-to-drug targets that have large, featureless, and highly lipophilic or highly polar and/or flexible binding sites is highly challenging. Here, we describe how cores of macrocyclic natural products can serve as a high-quality in silico screening library that provides leads for difficult-to-drug targets. Two iterative rounds of docking of a carefully selected set of natural-product-derived cores led to the discovery of an uncharged macrocyclic inhibitor of the Keap1-Nrf2 protein-protein interaction, a particularly challenging target due to its highly polar binding site. The inhibitor displays cellular efficacy and is well-positioned for further optimization based on the structure of its complex with Keap1 and synthetic access. We believe that our work will spur interest in using macrocyclic cores for in silico-based lead generation and also inspire the design of future macrocycle screening collections.

Discovery of polypodiside as a Keap1-dependent Nrf2 activator attenuating oxidative stress and accumulation of extracellular matrix in glomerular mesangial cells under high glucose.

Diabetic nephropathy (DN) is a severe microvascular complication of diabetes mellitus. High glucose has resulted in oxidative stress and following renal fibrosis as the crucial nodes of this disease. Nuclear factor erythroid 2-related factor 2 (Nrf2) is a transcription factor regulating transcription of many antioxidant genes and suppressing synthesis of extracellular matrix. To discover Nrf2 activators targeting DN, we have evaluated polypodiside using cell-based assays. The results showed polypodiside inhibited the high glucose-induced self-limited proliferation of glomerular meangial cells. Activation of Nrf2 and enhanced transcription to antioxidant response elements were observed in the presence of polypodiside. Oxidative stress and accumulation of extracellular matrix induced by high glucose in glomerular meangial cells have been ameliorated by polypodiside. Further investigations revealed the effects of polypodiside on glomerular meangial cells were associated with activation of Nrf2. Co-immunoprecipitation of Nrf2 disclosed polypodiside disrupted the Kelch-like ECH-associated protein-1 (Keap1)-Nrf2 interaction. Molecular docking elucidated polypodiside could enter the Nrf2 binding cavity of Keap1 via interacting with the residues encompassing that cavity. These findings indicate polypodiside is a Keap1-dependent Nrf2 activator affording the catabatic effects against oxidative stress and accumulation of extracellular matrix in glomerular meangial cells under high glucose.

An open-source drug discovery platform enables ultra-large virtual screens.

On average, an approved drug currently costs US$2-3 billion and takes more than 10 years to develop1. In part, this is due to expensive and time-consuming wet-laboratory experiments, poor initial hit compounds and the high attrition rates in the (pre-)clinical phases. Structure-based virtual screening has the potential to mitigate these problems. With structure-based virtual screening, the quality of the hits improves with the number of compounds screened2. However, despite the fact that large databases of compounds exist, the ability to carry out large-scale structure-based virtual screening on computer clusters in an accessible, efficient and flexible manner has remained difficult. Here we describe VirtualFlow, a highly automated and versatile open-source platform with perfect scaling behaviour that is able to prepare and efficiently screen ultra-large libraries of compounds. VirtualFlow is able to use a variety of the most powerful docking programs. Using VirtualFlow, we prepared one of the largest and freely available ready-to-dock ligand libraries, with more than 1.4 billion commercially available molecules. To demonstrate the power of VirtualFlow, we screened more than 1 billion compounds and identified a set of structurally diverse molecules that bind to KEAP1 with submicromolar affinity. One of the lead inhibitors (iKeap1) engages KEAP1 with nanomolar affinity (dissociation constant (Kd) = 114 nM) and disrupts the interaction between KEAP1 and the transcription factor NRF2. This illustrates the potential of VirtualFlow to access vast regions of the chemical space and identify molecules that bind with high affinity to target proteins.

Effects of a novel biflavonoid of Lonicera japonica flower buds on modulating apoptosis under different oxidative conditions in hepatoma cells.

BACKGROUND: In our previous work, we purified a novel biflavonoid named Japoflavone D (JFD) from Lonicera japonica flower buds. Biflavonoids are chemical compounds characterized by their high levels of antioxidative activity. PURPOSE: The present study aimed to investigate the function and molecular mechanism of JFD under different oxidative conditions in hepatoma cells. METHODS: MTT assay and apoptosis assay were used to evaluate the cytotoxic effect of JFD. The activities of SOD and CAT were detected to evaluate the oxidative level. Oxidative stress was induced by H2O2 stimulation. The molecular mechanism of JFD was investigated by analyzing relative signaling pathway. RESULTS: JFD inhibited cell viability in all hepatoma cell lines we examined. Under quiescent conditions, JFD treatment of SMMC-7721 cells resulted in upregulation of AKT/mTOR signal pathway and ERK activities and downregulation of KEAP1/NRF2/ARE signaling axis, together with apoptosis. However, under oxidative stress, JFD played a quite different role. Treatment of JFD suppressed the activation of ERK and mTOR and activated the KEAP1/NRF2/ARE signaling axis, which is a predominant regulator of cytoprotective responses to oxidative stress, thereby lessening the damage caused by excess reactive oxygen species (ROS). A molecular docking analysis suggested that JFD may interrupt the interaction between KEAP1 and NRF2 by competitively anchoring to the NRF2 binding site on KEAP1. CONCLUSION: The results indicate that JFD functions as a potent antioxidant and plays dual roles in modulating apoptosis under different oxidative conditions. JFD has the potential to be developed as a protective drug for diseases related with excess ROS.

Regulation of the NRF2 transcription factor by andrographolide and organic extracts from plant endophytes.

The transcription factor NF-E2 Related Factor-2 (NRF2) is an important drug target. Activation of NRF2 has chemopreventive effects in cancer and exerts beneficial effects in a number of diseases, including neurodegenerative diseases, inflammatory diseases, hepatosteatosis, obesity and insulin resistance. Hence, there have been great efforts to discover and characterize novel NRF2 activators. One reported NRF2 activator is the labdane diterpenoid andrographolide. In this study, we identified the mechanism through which andrographolide activates NRF2. We showed that andrographolide inhibits the function of KEAP1, a protein that together with CUL3 and RBX1 forms an E3 ubiquitin ligase that polyubiquitinates NRF2. Andrographolide partially inhibits the interaction of KEAP1 with CUL3 in a manner dependent on Cys151 in KEAP1. This suggests that andrographolide forms Michael acceptor dependent adducts with Cys151 in KEAP1 in vivo, leading to inhibition of NRF2 ubiquitination and consequently accumulation of the transcription factor. Interestingly, we also showed that at higher concentrations andrographolide increases NRF2 protein expression in a Cys151 independent, but likely KEAP1 dependent manner, possibly through modification of other Cys residues in KEAP1. In this study we also screened secondary metabolites produced by endophytes isolated from non-flowering plants for NRF2-inducing properties. One of the extracts, ORX 41, increased both NRF2 protein expression and transcriptional activity markedly. These results suggest that endophytes isolated from non-flowering or other plants may be a good source of novel NRF2 inducing compounds.

Synergistic Promotion on Tyrosinase Inhibition by Antioxidants.

When exposed to ultraviolet radiation, the human skin produces profuse reactive oxygen species (ROS), which in turn activate a variety of biological responses. Mounting ROS levels activate tyrosinase by mobilizing α-melanocyte-stimulating hormone in the epidermis and finally stimulates the melanocytes to produce melanin. Meanwhile, the Keap1-Nrf2/ARE pathway, which removes ROS, is activated at increased ROS levels, and antioxidant compounds facilitates the dissociation of Nrf2. In this study, we explored the possible suppressing effects of antioxidant compounds and tyrosine inhibitors on melanin formation and the promotory effects of these compounds on ROS scavenging. The antioxidant activity of glabridin (GLA), resveratrol (RES), oxyresveratrol (OXYR), and phenylethylresorcinol (PR) were investigated via the stable free radical 2,2-diphenyl-1-picrylhydrazyl method. The inhibitory effects of the four compounds and their mixtures on tyrosinase were evaluated. l-Tyrosine or 3-(3,4-dihydroxyphenyl)-l-alanine (l-DOPA) was used as a substrate. The results showed that all mixtures did not exhibit synergistic effects with the l-tyrosine as a substrate, suggesting that l-tyrosine is not suitable as a substrate. However, the mixtures of "GLA:RES," "GLA:OXYR," "OXYR:RES," and "PR:RES" demonstrated synergistic effects (CI < 0.9, p < 0.05), whereas "GLA:RES" and "PR:OXYR" indicated an additive effect (0.9 ditive1, p < 0.05). Furthermore, we used a molecular docking strategy to study the interactions of the four compounds with tyrosinase and l-DOPA. The molecular docking result is consistent with that of the experiment. Finally, we selected RES + OXYR and used PIG1 cells to verify whether OXYR synergistically promotes RES activity on tyrosinase. The two agents had a synergistic inhibitory effect on tyrosinase activity. These results provided a novel synergistic strategy for antioxidants and tyrosinase inhibitors, and this strategy is useful in skin injury treatment.