Neurodegenerative diseases are characterized by chronic microglial over-activation and oxidative stress. It is now beginning to be recognized that reactive oxygen species (ROS) produced by either ...microglia or the surrounding environment not only impact neurons but also modulate microglial activity. In this review, we first analyze the hallmarks of pro-inflammatory and anti-inflammatory phenotypes of microglia and their regulation by ROS. Then, we consider the production of reactive oxygen and nitrogen species by NADPH oxidases and nitric oxide synthases and the new findings that also indicate an essential role of glutathione (γ-glutamyl-l-cysteinylglycine) in redox homeostasis of microglia. The effect of oxidant modification of macromolecules on signaling is analyzed at the level of oxidized lipid by-products and sulfhydryl modification of microglial proteins. Redox signaling has a profound impact on two transcription factors that modulate microglial fate, nuclear factor kappa-light-chain-enhancer of activated B cells, and nuclear factor (erythroid-derived 2)-like 2, master regulators of the pro-inflammatory and antioxidant responses of microglia, respectively. The relevance of these proteins in the modulation of microglial activity and the interplay between them will be evaluated. Finally, the relevance of ROS in altering blood brain barrier permeability is discussed. Recent examples of the importance of these findings in the onset or progression of neurodegenerative diseases are also discussed. This review should provide a profound insight into the role of redox homeostasis in microglial activity and help in the identification of new promising targets to control neuroinflammation through redox control of the brain.
All metazoans depend on the consumption of O
by the mitochondrial oxidative phosphorylation system (OXPHOS) to produce energy. In addition, the OXPHOS uses O
to produce reactive oxygen species that ...can drive cell adaptations
, a phenomenon that occurs in hypoxia
and whose precise mechanism remains unknown. Ca
is the best known ion that acts as a second messenger
, yet the role ascribed to Na
is to serve as a mere mediator of membrane potential
. Here we show that Na
acts as a second messenger that regulates OXPHOS function and the production of reactive oxygen species by modulating the fluidity of the inner mitochondrial membrane. A conformational shift in mitochondrial complex I during acute hypoxia
drives acidification of the matrix and the release of free Ca
from calcium phosphate (CaP) precipitates. The concomitant activation of the mitochondrial Na
/Ca
exchanger promotes the import of Na
into the matrix. Na
interacts with phospholipids, reducing inner mitochondrial membrane fluidity and the mobility of free ubiquinone between complex II and complex III, but not inside supercomplexes. As a consequence, superoxide is produced at complex III. The inhibition of Na
import through the Na
/Ca
exchanger is sufficient to block this pathway, preventing adaptation to hypoxia. These results reveal that Na
controls OXPHOS function and redox signalling through an unexpected interaction with phospholipids, with profound consequences for cellular metabolism.
Drug discovery faces an efficacy crisis to which ineffective mainly single-target and symptom-based rather than mechanistic approaches have contributed. We here explore a mechanism-based disease ...definition for network pharmacology. Beginning with a primary causal target, we extend this to a second using guilt-by-association analysis. We then validate our prediction and explore synergy using both cellular in vitro and mouse in vivo models. As a disease model we chose ischemic stroke, one of the highest unmet medical need indications in medicine, and reactive oxygen species forming NADPH oxidase type 4 (Nox4) as a primary causal therapeutic target. For network analysis, we use classical protein–protein interactions but also metabolite-dependent interactions. Based on this protein–metabolite network, we conduct a gene ontology-based semantic similarity ranking to find suitable synergistic cotargets for network pharmacology. We identify the nitric oxide synthase (Nos1 to 3) gene family as the closest target to Nox4. Indeed, when combining a NOS and a NOX inhibitor at subthreshold concentrations, we observe pharmacological synergy as evidenced by reduced cell death, reduced infarct size, stabilized blood–brain barrier, reduced reoxygenation-induced leakage, and preserved neuromotor function, all in a supraadditive manner. Thus, protein–metabolite network analysis, for example guilt by association, can predict and pair synergistic mechanistic disease targets for systems medicine-driven network pharmacology. Such approaches may in the future reduce the risk of failure in single-target and symptom-based drug discovery and therapy.
Guanosine (GUO) is an endogenous modulator of glutamatergic excitotoxicity and has been shown to promote neuroprotection in in vivo and in vitro models of neurotoxicity. This study was designed to ...understand the neuroprotective mechanism of GUO against oxidative damage promoted by oxygen/glucose deprivation and reoxygenation (OGD). GUO (100 μM) reduced reactive oxygen species production and prevented mitochondrial membrane depolarization induced by OGD. GUO also exhibited anti‐inflammatory actions as inhibition of nuclear factor kappa B activation and reduction of inducible nitric oxide synthase induction induced by OGD. These GUO neuroprotective effects were mediated by adenosine A1 receptor, phosphatidylinositol‐3 kinase and MAPK/ERK. Furthermore, GUO recovered the impairment of glutamate uptake caused by OGD, an effect that occurred via a Pertussis toxin‐sensitive G‐protein‐coupled signaling, blockade of adenosine A2A receptors (A2AR), but not via A1 receptor. The modulation of glutamate uptake by GUO also involved MAPK/ERK activation. In conclusion, GUO, by modulating adenosine receptor function and activating MAPK/ERK, affords neuroprotection of hippocampal slices subjected to OGD by a mechanism that implicates the following: (i) prevention of mitochondrial membrane depolarization, (ii) reduction of oxidative stress, (iii) regulation of inflammation by inhibition of nuclear factor kappa B and inducible nitric oxide synthase, and (iv) promoting glutamate uptake.
Guanosine (GUO) promotes neuroprotection against oxygen and glucose deprivation in hippocampal slices via a mechanism that involves modulation of adenosine receptors and activation of PI3K/AKT and MAPK/ERK. These signaling pathways are implicated in the prevention of mitochondrial membrane depolarization, reduction of oxidative stress, regulation of inflammation by inhibition of NF‐κB and inducible nitric oxide synthase (iNOS), and the promotion of glutamate uptake. EAAT: excitatory amino acid transporter, ROS: reactive oxygen species.
Read the Editorial Highlight for this article on doi: 10.1111/jnc.12328.
Tacripyrines (1−14) have been designed by combining an AChE inhibitor (tacrine) with a calcium antagonist such as nimodipine and are targeted to develop a multitarget therapeutic strategy to confront ...AD. Tacripyrines are selective and potent AChE inhibitors in the nanomolar range. The mixed type inhibition of hAChE activity of compound 11 (IC50 105 ± 15 nM) is associated to a 30.7 ± 8.6% inhibition of the proaggregating action of AChE on the Aβ and a moderate inhibition of Aβ self-aggregation (34.9 ± 5.4%). Molecular modeling indicates that binding of compound 11 to the AChE PAS mainly involves the (R)-11 enantiomer, which also agrees with the noncompetitive inhibition mechanism exhibited by p-methoxytacripyrine 11. Tacripyrines are neuroprotective agents, show moderate Ca2+ channel blocking effect, and cross the blood−brain barrier, emerging as lead candidates for treating AD.
Heme oxygenase-1 (HO-1) is an inducible enzyme known for its anti-inflammatory, antioxidant and neuroprotective effects. However, increased expression of HO-1 during aging and age-related ...neurodegenerative diseases have been associated to neurotoxic ferric iron deposits. Being microglia responsible for the brain's innate immune response, the aim of this study was to understand the role of microglial HO-1 under inflammatory conditions in aged mice. For this purpose, aged wild type (WT) and LysMCreHmox1△△ (HMOX1M-KO) mice that lack HO-1 in microglial cells, were used. Aged WT mice showed higher basal expression levels of microglial HO-1 in the brain than adult mice. This increase was even higher when exposed to an inflammatory stimulus (LPS via i.p.) and was accompanied by alterations in different iron-related metabolism proteins, resulting in an increase of iron deposits, oxidative stress, ferroptosis and cognitive decline. Furthermore, microglia exhibited a primed phenotype and increased levels of inflammatory markers such as iNOS, p65, IL-1β, TNF-α, Caspase-1 and NLRP3. Interestingly, all these alterations were prevented in aged HMOX1M-KO and WT mice treated with the HO-1 inhibitor ZnPPIX. In order to determine the effects of microglial HO-1-dependent iron overload, aged WT mice were treated with the iron chelator deferoxamine (DFX). DFX caused major improvements in iron, inflammatory and behavioral alterations found in aged mice exposed to LPS. In conclusion, this study highlights how microglial HO-1 overexpression contributes to neurotoxic iron accumulation providing deleterious effects in aged mice exposed to an inflammatory insult.
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•Microglial HO-1 increases with aging and under an acute inflammatory stimulus.•LPS-dependent microglial HO-1 upregulation during aging leads to iron overload.•Microglial HO-1-dependent iron accumulation leads to ferroptosis.•HO-1-dependent iron alterations lead to neuroinflammation.•HO-1 inhibitors/iron chelators reduce iron accumulation and neuroinflammation.
Systems medicine has a mechanism-based rather than a symptom- or organ-based approach to disease and identifies therapeutic targets in a nonhypothesis-driven manner. In this work, we apply this to ...transcription factor nuclear factor (erythroid-derived 2)-like 2 (NRF2) by cross-validating its position in a protein-protein interaction network (the NRF2 interactome) functionally linked to cytoprotection in low-grade stress, chronic inflammation, metabolic alterations, and reactive oxygen species formation. Multiscale network analysis of these molecular profiles suggests alterations of NRF2 expression and activity as a common mechanism in a subnetwork of diseases (the NRF2 diseasome). This network joins apparently heterogeneous phenotypes such as autoimmune, respiratory, digestive, cardiovascular, metabolic, and neurodegenerative diseases, along with cancer. Importantly, this approach matches and confirms in silico several applications for NRF2-modulating drugs validated in vivo at different phases of clinical development. Pharmacologically, their profile is as diverse as electrophilic dimethyl fumarate, synthetic triterpenoids like bardoxolone methyl and sulforaphane, protein-protein or DNA-protein interaction inhibitors, and even registered drugs such as metformin and statins, which activate NRF2 and may be repurposed for indications within the NRF2 cluster of disease phenotypes. Thus, NRF2 represents one of the first targets fully embraced by classic and systems medicine approaches to facilitate both drug development and drug repurposing by focusing on a set of disease phenotypes that appear to be mechanistically linked. The resulting NRF2 drugome may therefore rapidly advance several surprising clinical options for this subset of chronic diseases.
SCOPE: We have studied if curcumin can protect glial cells under an oxidative stress and inflammatory environment, which is known to be deleterious in neurodegeneration. METHODS AND RESULTS: Primary ...rat glial cultures exposed to the combination of an oxidative (rotenone/oligomycin A) and a proinflammatory LPS stimuli reduced by 50% glial viability. Under these experimental conditions, curcumin afforded significant glial protection and reduction of reactive oxygen species; these effects were blocked by the HO‐1 inhibitor tin protoporphyrin‐IX (SnPP). These findings correlate with the observation that curcumin induced the antioxidative protein HO‐1. Most interesting was the observation that the glial protective effects related to HO‐1 induction were microglial specific as shown in glial cultures from LysMCʳᵉHmox∆/∆ mice where curcumin lost its protective effect. Under LPS conditions, curcumin reduced the microglial proinflammatory markers iNOS and tumor necrosis factor, but increased the anti‐inflammatory cytokine IL4. Analysis of the microglial phenotype showed that curcumin favored a ramified morphology toward a microglial alternative activated state against LPS insult also by a HO‐1‐dependent mechanism. CONCLUSION: The curry constituent curcumin protects glial cells and promotes a microglial anti‐inflammatory phenotype by a mechanism that implicates HO‐1 induction; these effects may have impact on brain protection under oxidative and inflammatory conditions.
The transcription factor nuclear factor erythroid 2‐related factor 2 (NRF2) is considered the master regulator of the phase II antioxidant response. It controls a plethora of cytoprotective genes ...related to oxidative stress, inflammation, and protein homeostasis, among other processes. Activation of these pathways has been described in numerous pathologies including cancer, cardiovascular, respiratory, renal, digestive, metabolic, autoimmune, and neurodegenerative diseases. Considering the increasing interest of discovering novel NRF2 activators due to its clinical application, initial efforts were devoted to the development of electrophilic drugs able to induce NRF2 nuclear accumulation by targeting its natural repressor protein Kelch‐like ECH‐associated protein 1 (KEAP1) through covalent modifications on cysteine residues. However, off‐target effects of these drugs prompted the development of an innovative strategy, the search of KEAP1‐NRF2 protein–protein interaction (PPI) inhibitors. These innovative activators are proposed to target NRF2 in a more selective way, leading to potentially improved drugs with the application for a variety of diseases that are currently under investigation. In this review, we summarize known KEAP1‐NRF2 PPI inhibitors to date and the bases of their design highlighting the most important features of their respective interactions. We also discuss the preclinical pharmacological properties described for the most promising compounds.
Novel multifunctional compounds have been designed, synthesized, and evaluated as potential drugs for the treatment of Alzheimer’s disease (AD). With an l-glutamic moiety as a suitable biocompatible ...linker, three pharmacophoric groups were joined: (1) an N-benzylpiperidine fragment selected to inhibit acetylcholinesterase by interacting with the catalytic active site (CAS), (2) an N-protecting group of the amino acid, capable of interacting with the acetylcholinesterase (AChE)-peripheral anionic site (PAS) and protecting neurons against oxidative stress, and (3) a lipophilic alkyl ester that would facilitate penetration into the central nervous system by crossing the blood−brain barrier. At submicromolar concentration, they inhibit AChE and butyrylcholinesterase (BuChE) of human origin, displace the binding of propidium iodide from the PAS of AChE, and could thus inhibit Aβ aggregation promoted by AChE. They also display neuroprotective properties against mitochondrial free radicals, show low toxicity, and could be able to penetrate into the CNS.
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