Protective activity of aromatic amines and imines against oxidative nerve cell death

Variability in urinary concentrations of primary aromatic amines

Despite their known carcinogenic potential, primary aromatic amines (AAs) continue to be used in various consumer products. Human exposure to AAs is a subject of current concern. Although urinary measurements are used in the assessment of exposure, little is known about within- and between-individual temporal variability in urinary concentrations of AAs. In this study, we determined the concentrations of 30 AAs, nicotine and cotinine in 213 first morning void (FMV) urine samples collected longitudinally for over a five-week period from 15 participants residing in the Albany area of New York State, USA. Eight AAs, namely, aniline, 2-naphthylamine (2-NA), p-cresidine (p-CD), p-toluidine (p-TD), o/m-toluidine (o/m-TD), 4-chloroaniline (4-CA), 4,4'-methylenedi-o-toluidine (4,4'-MDA), and 2,6-dimethylaniline (2,6-DMA) were found in urine at a detection frequency (DF) in the range of 68-100%. Aniline and 2,6-DMA were the predominant compounds found at median concentrations of 6.0 and 3.81 ng/mL, respectively. Intraclass correlation coefficients (ICCs) of all urinary AA concentrations, except for 4-CA, showed moderate to poor predictability (ICC values ranged 0.248-0.697). Gender and ethnicity-related variations in ∑₈AA concentrations were significant. Spearman's correlations among AA concentrations suggested that the sources of exposure were not related to tobacco smoke. No significant correlations existed between AAs concentrations and oxidative stress biomarkers (OSBs). The estimated daily intakes of AAs calculated based on urinary concentrations were several orders of magnitude below the tolerable daily intakes.

O2-Mediated Dehydrogenative Phenoxazination of Phenols

Phenoxazines, in particular N-arylated phenoxazines, represent an increasingly important scaffold in the material sciences. Moreover, the oxygen-gas-mediated dehydrogenative phenochalcogenazination concept of phenols has been developed and exemplified for X = sulfur and recently for X = selenium and tellurium. The smallest chalcogen, X = oxygen, is herein exemplified with various functional groups under a likewise trivial oxygen atmosphere.

New insights into the competition between antioxidant activities and pro-oxidant risks of rosmarinic acid

Direct and indirect antioxidant activities of rosmarinic acid (RA) based on HOO˙/CH₃OO˙ radical scavenging and Fe(iii)/Fe(ii) ion chelation were theoretically studied using density functional theory at the M05-2X/6-311++G(2df,2p) level of theory. First, four antioxidant mechanisms including hydrogen atom transfer (HAT), radical adduct formation (RAF), proton loss (PL) and single electron transfer (SET) were investigated in water and pentyl ethanoate (PEA) phases. Regarding the free radical scavenging mechanism, HAT plays a decisive role with overall rate coefficients of 1.84 × 10³ M⁻¹ s⁻¹ (HOO˙) and 4.49 × 10³ M⁻¹ s⁻¹ (CH₃OO˙) in water. In contrast to PL, RAF and especially SET processes, the HAT reaction in PEA is slightly more favorable than that in water. Second, the [Fe(iii)(H₂O)₆]³⁺ and [Fe(ii)(H₂O)₆]²⁺ ion chelating processes in an aqueous phase are both favorable and spontaneous especially at the O5, site-1, and site-2 positions with large negative Δ_rG⁰ values and great formation constant K_f. Finally, the pro-oxidant risk of RA⁻ was also considered via the Fe(iii)-to-Fe(ii) complex reduction process, which may initiate Fenton-like reactions forming reactive HO˙ radicals. As a result, RA⁻ does not enhance the reduction process when ascorbate anions are present as reducing agents, whereas the pro-oxidant risk becomes remarkable when superoxide anions are found. The results encourage further attempts to verify the speculation using more powerful research implementations of the antioxidant activities of rosmarinic acid in relationship with its possible pro-oxidant risks.

Direct and indirect antioxidant activities of rosmarinic acid (RA) based on HOO˙/CH₃OO˙ radical scavenging and Fe(iii)/Fe(ii) ion chelation were theoretically studied using density functional theory at the M05-2X/6-311++G(2df,2p) level of theory.

Dihydropyrimidinone-derived selenoesters efficacy and safety in an in vivo model of Aβ aggregation

In a previous in vitro study, dihydropyrimidinone-derived selenoesteres demonstrated antioxidant properties, metal chelators and inhibitory acetylcholinesterase (AChE) activity, making these compounds promising candidates for Alzheimer's Disease (AD) treatment. However, these effects have yet to be demonstrated in an in vivo animal model; therefore, this study aimed to evaluate the safety and efficacy of eight selenoester compounds in a Caenorhabditis elegans model using transgenic strains for amyloid-beta peptide (Aβ) aggregation. The L1 stage worms were acutely exposed (30 min) to the compounds at concentrations ranging from 5 to 200 μM and after 48 h the maintenance temperature was increased to 25 ° C for Aβ expression and aggregation. After 48 h, several parameters related to phenotypic manifestations of Aβ toxicity and mechanistic elucidation were analyzed. At the concentrations tested no significant toxicity of the compounds was found. The selenoester compound FA90 significantly reduced the rate of paralyzed worms and increased the number of swimming movements compared to the untreated worms. In addition, FA90 and FA130 improved egg-laying induced by levamisole and positively modulated HSP-6 and HSP-4 expression, thereby increasing reticular and mitochondrial protein folding response in C. elegans, which could attenuate Aβ aggregation in early exposure. Therefore, our initial screening using an alternative model demonstrated that FA90, among the eight selenoesters evaluated, was the most promising compound for AD evaluation screening in more complex animals.

Structure-activity relationship studies of phenothiazine derivatives as a new class of ferroptosis inhibitors together with the therapeutic effect in an ischemic stroke model

Ferroptosis is a new type of programmed cell death discovered recently and has been demonstrated to be involved in a number of human diseases such as ischemic stroke. Ferroptosis inhibitors are expected to have potential to treat these diseases. Herein, we report the identification of promethazine derivatives as a new type of ferroptosis inhibitors. Structure-activity relationship (SAR) analyses led to the discovery of the most potent compound 2-(1-(4-(4-methylpiperazin-1-yl)phenyl)ethyl)-10H-phenothiazine (51), which showed an EC50 (half maximal effective concentration) value of 0.0005 μM in the erastin-induced HT1080 cell ferroptosis model. In the MCAO (middle cerebral artery occlusion) ischemic stroke model, 51 presented an excellent therapeutic effect. This compound also displayed favorable pharmacokinetic properties, in particular, a good ability to permeate the blood-brain barrier. Overall, 51 could be a promising lead compound for the treatment of ferroptosis related diseases and deserves further investigations.

Iminostilbene, a novel small-molecule modulator of PKM2, suppresses macrophage inflammation in myocardial ischemia-reperfusion injury

Introduction

Inflammation is a key factor in myocardial ischemia/reperfusion (MI/R) injury. Targeting leucocyte-mediated inflammation is an important strategy for MI/R therapy. Iminostilbene (ISB), a simple dibenzoazepine small molecule compound, has a strong anti-neurodegenerative effect. However, no study has shown the cardioprotective effect of ISB.

Objectives

This study aimed to investigate the role of ISB against MI/R injury and identify its molecular target.

Methods

To verify the cardiac protection of ISB in vivo and in vitro, we performed rat MI/R surgery and subjected inflammatory modeling of macrophages. In terms of molecular mechanisms, we designed and synthesized a small molecular probe of ISB and employed it on the click chemistry-activity-based protein profiling technique to fish for ISB targets in macrophages. To identify the target, we applied the competitive inhibition assay, surface-plasmon resonance (SPR), cellular thermal shift assay (CETSA), and drug affinity responsive target stability (DARTS) assay.

Results

In vivo, ISB showed robust anti-myocardial injury activity by improving cardiac function, reducing myocardial infarction, and inhibiting macrophage-mediated inflammation. In vitro, ISB strongly inhibited the transcription and the expression levels of inflammatory cytokines in macrophages. The pyruvate kinase isozyme type M2 (PKM2) was identified as the potential target of ISB through proteomic analysis and the competitive assay was performed for specific binding verification. Further thermodynamic and kinetic experiments showed that ISB was bound to PKM2 in a dose-dependent manner. Moreover, in terms of the biological function of ISB on PKM2, ISB reduced the expression of PKM2, thereby reducing the expression of HIF1α and the phosphorylation of STAT3.

Conclusion

This study for the first time demonstrated that ISB targeted PKM2 to reduce macrophage inflammation thereby significantly alleviating MI/R injury.

Mitochondrial Dysfunctions: A Red Thread across Neurodegenerative Diseases

Mitochondria play a central role in a plethora of processes related to the maintenance of cellular homeostasis and genomic integrity. They contribute to preserving the optimal functioning of cells and protecting them from potential DNA damage which could result in mutations and disease. However, perturbations of the system due to senescence or environmental factors induce alterations of the physiological balance and lead to the impairment of mitochondrial functions. After the description of the crucial roles of mitochondria for cell survival and activity, the core of this review focuses on the "mitochondrial switch" which occurs at the onset of neuronal degeneration. We dissect the pathways related to mitochondrial dysfunctions which are shared among the most frequent or disabling neurodegenerative diseases such as Alzheimer's, Parkinson's, and Huntington's, Amyotrophic Lateral Sclerosis, and Spinal Muscular Atrophy. Can mitochondrial dysfunctions (affecting their morphology and activities) represent the early event eliciting the shift towards pathological neurobiological processes? Can mitochondria represent a common target against neurodegeneration? We also review here the drugs that target mitochondria in neurodegenerative diseases.

N10 -carbonyl-substituted phenothiazines inhibiting lipid peroxidation and associated nitric oxide consumption powerfully protect brain tissue against oxidative stress

During some investigations into the mechanism of nitric oxide consumption by brain preparations, several potent inhibitors of this process were identified. Subsequent tests revealed the compounds act by inhibiting lipid peroxidation, a trigger for a form of regulated cell death known as ferroptosis. A quantitative structure–activity study together with XED (eXtended Electron Distributions) field analysis allowed a qualitative understanding of the structure–activity relationships. A representative compound N‐(3,5‐dimethyl‐4H‐1,2,4‐triazol‐4‐yl)‐10H‐phenothiazine‐10‐carboxamide (DT‐PTZ‐C) was able to inhibit completely oxidative damage brought about by two different procedures in organotypic hippocampal slice cultures, displaying a 30‐ to 100‐fold higher potency than the standard vitamin E analogue, Trolox or edaravone. The compounds are novel, small, drug‐like molecules of potential therapeutic use in neurodegenerative disorders and other conditions associated with oxidative stress.

Conjugates of methylene blue with γ-carboline derivatives as new multifunctional agents for the treatment of neurodegenerative diseases

We studied the inhibitory activity of methylene blue (MB) γ-carbolines (gC) conjugates (MB-gCs) against human erythrocyte acetylcholinesterase (AChE), equine serum butyrylcholinesterase (BChE), and a structurally related enzyme, porcine liver carboxylesterase (CaE). In addition, we determined the ability of MB-gCs to bind to the peripheral anionic site (PAS) of Electrophorus electricus AChE (EeAChE) and competitively displace propidium iodide from this site. Moreover, we examined the ability of MB-gCs to scavenge free radicals as well as their influence on mitochondrial potential and iron-induced lipid peroxidation. We found that MB-gCs effectively inhibited AChE and BChE with IC₅₀ values in the range 1.73–10.5 μM and exhibited low potencies against CaE (9.8–26% inhibition at 20 μM). Kinetic studies showed that MB-gCs were mixed-type reversible inhibitors of both cholinesterases. Molecular docking results showed that the MB-gCs could bind both to the catalytic active site and to the PAS of human AChE and BChE. Accordingly, MB-gCs effectively displaced propidium from the peripheral anionic site of EeAChE. In addition, MB-gCs were extremely active in both radical scavenging tests. Quantum mechanical DFT calculations suggested that free radical scavenging was likely mediated by the sulfur atom in the MB fragment. Furthermore, the MB-gCs, in like manner to MB, can restore mitochondrial membrane potential after depolarization with rotenone. Moreover, MB-gCs possess strong antioxidant properties, preventing iron-induced lipid peroxidation in mitochondria. Overall, the results indicate that MB-gCs are promising candidates for further optimization as multitarget therapeutic agents for neurodegenerative diseases.

Metal-free formal synthesis of phenoxazine

A transition metal-free formal synthesis of phenoxazine is presented. The key step of the sequence is a high-yielding O-arylation of a phenol with an unsymmetrical diaryliodonium salt to provide an ortho-disubstituted diaryl ether. This species was cyclized to acetylphenoxazine in moderate yield. The overall yield in the three-step sequence is 72% based on recovered diaryl ether. An interesting, unusually stable iodine(III) intermediate in the O-arylation was observed by NMR and could be converted to the product upon longer reaction time.

The Potency of Diarylamine Radical-Trapping Antioxidants as Inhibitors of Ferroptosis Underscores the Role of Autoxidation in the Mechanism of Cell Death

Two aromatic amines (ferrostatin-1 and liproxstatin-1) were recently identified from high-throughput screening efforts to uncover potent inhibitors of ferroptosis, the necrotic-like cell death induced by inhibition of glutathione peroxidase 4 (GPX4), deletion of the corresponding gpx4 gene, or starvation of GPX4 of its reducing cosubstrate, glutathione (GSH). We have since demonstrated that these two aromatic amines are highly effective radical-trapping antioxidants (RTAs) in lipid bilayers, suggesting that they subvert ferroptosis by inhibiting lipid peroxidation (autoxidation) and, thus, that this process drives the execution of ferroptosis. Herein, we show that diarylamine RTAs used to protect petroleum-derived products from autoxidation can be potent inhibitors of ferroptosis. The diarylamines investigated include representative examples of additives to engine oils, greases and rubber (4,4'-dialkyldiphenylamines), core structures of dyes and pharmaceuticals (phenoxazines and phenothiazines), and aza-analogues of these three classes of compounds that we have recently shown can be modified to achieve much greater reactivity. We find that regardless of how ferroptosis is induced (GPX4 inhibition, gpx4 deletion or GSH depletion), compounds which possess good RTA activity in organic solution (k_inh > 10⁵ M^-1 s^-1) and lipid bilayers (k_inh > 10⁴ M^-1 s^-1) are generally potent inhibitors of ferroptosis (in mouse embryonic fibroblasts). Likewise, structural analogs that do not possess RTA activity are devoid of antiferroptotic activity. These results further support the argument that lipid peroxidation (autoxidation) plays a major role in the mechanism of cell death induced by either GPX4 inhibition, gpx4 deletion, or GSH depletion. Moreover, it offers clear direction that ongoing medicinal chemistry efforts on liproxstatin and ferrostatin derivatives, which have been proposed as lead compounds for the treatment and/or prevention of ischemia/reperfusion injury, renal failure, and neurodegeneration, can be widened to include other aminic RTAs. To aid in these efforts, some relevant structure-reactivity relationships are discussed.

Phenoxazine: A Privileged Scaffold for Radical-Trapping Antioxidants

Diphenylamines are widely used to protect petroleum-derived products from autoxidation. Their efficacy as radical-trapping antioxidants (RTAs) relies on a balance of fast H-atom transfer kinetics and stability to one-electron oxidation by peroxidic species. Both H-atom transfer and one-electron oxidation are enhanced by substitution with electron-donating substituents, such as the S-atom in phenothiazines, another important class of RTA. Herein we report the results of our investigations of the RTA activity of the structurally related, but essentially ignored, phenoxazines. We find that the H-atom transfer reactivity of substituted phenoxazines follows an excellent Evans-Polanyi correlation spanning k_inh = 4.5 × 10⁶ M^-1 s^-1 and N-H BDE = 77.4 kcal mol^-1 for 3-CN,7-NO₂-phenoxazine to k_inh = 6.6 × 10⁸ M^-1 s^-1 and N-H BDE = 71.8 kcal mol^-1 for 3,7-(OMe)₂-phenoxazine (37 °C). The reactivity of the latter compound is the greatest of any RTA ever reported and is likely to represent a reaction without an enthalpic barrier since log A for this reaction is likely ∼8.5. The very high reactivity of most of the phenoxazines studied required the determination of their kinetic parameters by inhibited autoxidations in the presence of a very strong H-bonding cosolvent (DMSO), which slowed the observed rates by up to 2 orders of magnitude by dynamically reducing the equilibrium concentration of (free) phenoxazine as an H-atom donor. Despite their remarkably high reactivity toward peroxyl radicals, the phenoxazines were found to be comparatively stable to one-electron oxidation relative to diphenylamines and phenothiazines (E° ranging from 0.59 to 1.38 V vs NHE). Thus, phenoxazines with comparable oxidative stability to commonly used diphenylamine and phenothiazine RTAs had significantly greater reactivity (by up to 2 orders of magnitude). Computations suggest that this remarkable balance in H-atom transfer kinetics and stability to one-electron oxidation results from the ability of the bridging oxygen atom in phenoxazine to serve as both a π-electron donor to stabilize the aminyl radical and σ-electron acceptor to destabilize the aminyl radical cation. Perhaps most excitingly, phenoxazines have "non-classical" RTA activity, where they trap >2 peroxyl radicals each, at ambient temperatures.

Membrane protein oxidation determines neuronal degeneration

Oxidative stress is an early hallmark in neurodegenerative disorders such as Alzheimer's and Parkinson's diseases. However, the critical biochemical effector mechanisms of oxidative neurotoxicity have remained surprisingly elusive. In screening various peroxides and potential substrates of oxidation for their effect on neuronal survival, we observed that intramembrane compounds were significantly more active than aqueous or amphiphilic compounds. To better understand this result, we synthesized a series of competitive and site-specific membrane protein oxidation inhibitors termed aminoacyllipids, whose structures were designed on the basis of amino acids frequently found at the protein-lipid interface of synaptic membrane proteins. Investigating the aminoacyllipids in primary neuronal culture, we found that the targeted protection of transmembrane tyrosine and tryptophan residues was sufficient to prevent neurotoxicity evoked by hydroperoxides, kainic acid, glutathione-depleting drugs, and certain amyloidogenic peptides, but ineffective against non-oxidative inducers of apoptosis such as sphingosine or Akt kinase inhibitors. Thus, the oxidative component of different neurotoxins appears to converge on neuronal membrane proteins, irrespective of the primary mechanism of cellular oxidant generation. Our results indicate the existence of a one-electron redox cycle based on membrane protein aromatic surface amino acids, whose disturbance or overload leads to excessive membrane protein oxidation and neuronal death. Membrane proteins have rarely been investigated as potential victims of oxidative stress in the context of neurodegeneration. This study provides evidence that excessive one-electron oxidation of membrane proteins from within the lipid bilayer, depicted in the graphic, is a functionally decisive step toward neuronal cell death in response to different toxins.

Benzo[α]phenoxazines and benzo[α]phenothiazine from vitamin K3: synthesis, molecular structures, DFT studies and cytotoxic activity

Novel benzo[α]phenoxazines and benzo[α]phenothiazine from vitamin K3 are cytotoxic against HeLa, MCF-7 cell lines and potential topoisomerase II inhibitors.

High membrane protein oxidation in the human cerebral cortex

Oxidative stress is thought to be one of the main mediators of neuronal damage in human neurodegenerative disease. Still, the dissection of causal relationships has turned out to be remarkably difficult. Here, we have analyzed global protein oxidation in terms of carbonylation of membrane proteins and cytoplasmic proteins in three different mammalian species: aged human cortex and cerebellum from patients with or without Alzheimer's disease, mouse cortex and cerebellum from young and old animals, and adult rat hippocampus and cortex subjected or not subjected to cerebral ischemia. Most tissues showed relatively similar levels of protein oxidation. However, human cortex was affected by severe membrane protein oxidation, while exhibiting lower than average cytoplasmic protein oxidation. In contrast, ex vivo autooxidation of murine cortical tissue primarily induced aqueous protein oxidation, while in vivo biological aging or cerebral ischemia had no major effect on brain protein oxidation. The unusually high levels of membrane protein oxidation in the human cortex were also not predicted by lipid peroxidation, as the levels of isoprostane immunoreactivity in human samples were considerably lower than in rodent tissues. Our results indicate that the aged human cortex is under steady pressure from specific and potentially detrimental membrane protein oxidation. The pronounced difference between humans, mice and rats regarding the primary site of cortical oxidation might have contributed to the unresolved difficulties in translating into therapies the wealth of data describing successful antioxidant neuroprotection in rodents.

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Membrane proteins from the human cerebral cortex show specific and severe oxidation.

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This contrasts to human cerebellum and to mouse cortex and cerebellum of any age.

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It also contrasts to adult rat cortex and hippocampus with or without ischemia.

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Lipid peroxidation is not a predictor of membrane protein oxidation.

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Membrane protein oxidation might be related to impending neurodegeneration.

The antioxidative, non-psychoactive tricyclic phenothiazine reduces brain damage after experimental traumatic brain injury in mice

Oxidative stress due to free radical formation is an important mechanism of secondary brain damage following traumatic brain injury (TBI). Phenothiazine has been found to be a strong antioxidant in eukaryotic cells in vitro and in invertebrates in vivo. The present study was designed to determine the neuroprotective potency of unsubstituted phenothiazine in a paradigm of acute brain injury. Thirty minutes after pneumatic, controlled cortical impact (CCI) injury, C57BI6 mice were randomly assigned to "low dose" (3 mg/kg, LD) or "high dose" (30 mg/kg, HD) s.c. phenothiazine or vehicle treatment. Brain lesion, neurofunctional impairment, body weight, and markers of cerebral inflammation were determined 24h after the insult. Phenothiazine treatment dose-dependently reduced brain lesion volume (LD: -19.8%; HD: -26.1%) and posttraumatic body weight loss. There were no significant differences in the neurological function score and in markers of cerebral inflammation (Iba-1 positive cells, TNFα expression), whereas iNOS expression was significantly lower compared to vehicle-treated animals. Phenothiazine appears to modify in a post-treatment protocol certain aspects of secondary brain damage in vivo at unusually low concentrations, in particular the cortical contusion volume after TBI. The potential role of the reduced iNOS expression is unclear at present.

Antidepressants inhibit DNA methyltransferase 1 through reducing G9a levels

The discovery of epigenetic processes as possible pivotal regulatory mechanisms in psychiatric diseases raised the question of how psychoactive drugs may impact the epigenetic machinery. In the present study we set out to explore the specificity and the mode of action of the reported inhibitory effect of the TCA (tricyclic antidepressant) amitriptyline on DNMT (DNA methyltransferase) activity in primary astrocytes from the rat cortex. We found that the impact on DNMT was shared by another TCA, imipramine, and by paroxetine, but not by venlafaxine or the mood stabilizers carbamazepine and valproic acid. DNMT activity in subventricular neural stem cells was refractory to the action of ADs (antidepressants). Among the established DNMTs, ADs primarily targeted DNMT1. The reduction of enzymatic DNMT1 activity was neither due to reduced DNMT1 expression nor due to direct drug interference. We tested putative DNMT1-inhibitory mechanisms and discovered that a known stimulator of DNMT1, the histone methyltransferase G9a, exhibited decreased protein levels and interactions with DNMT1 upon AD exposure. Adding recombinant G9a completely reversed the AD repressive effect on DNMT1 function. In conclusion, the present study presents a model where distinct ADs affect DNMT1 activity via G9a with important repercussions for possible novel treatment regimes.

Transition-metal-free intramolecular N-arylations

N-Substituted phenoxazines and related aza analogs have been prepared from N-acetylated aryloxy anilides by transition-metal-free, base-catalyzed cyclization reactions. In the presence of a mixture of 10 mol % of N,N'-dimethylethylenediamine (DMEDA) and 2 equiv of K(2)CO(3) in toluene at 135 °C the products are obtained in high yields.

Neurometabolic mechanisms for memory enhancement and neuroprotection of methylene blue

This paper provides the first review of the memory-enhancing and neuroprotective metabolic mechanisms of action of methylene blue in vivo. These mechanisms have important implications as a new neurobiological approach to improve normal memory and to treat memory impairment and neurodegeneration associated with mitochondrial dysfunction. Methylene blue's action is unique because its neurobiological effects are not determined by regular drug-receptor interactions or drug-response paradigms. Methylene blue shows a hormetic dose-response, with opposite effects at low and high doses. At low doses, methylene blue is an electron cycler in the mitochondrial electron transport chain, with unparalleled antioxidant and cell respiration-enhancing properties that affect the function of the nervous system in a versatile manner. A major role of the respiratory enzyme cytochrome oxidase on the memory-enhancing effects of methylene blue is supported by available data. The memory-enhancing effects have been associated with improvement of memory consolidation in a network-specific and use-dependent fashion. In addition, low doses of methylene blue have also been used for neuroprotection against mitochondrial dysfunction in humans and experimental models of disease. The unique auto-oxidizing property of methylene blue and its pleiotropic effects on a number of tissue oxidases explain its potent neuroprotective effects at low doses. The evidence reviewed supports a mechanistic role of low-dose methylene blue as a promising and safe intervention for improving memory and for the treatment of acute and chronic conditions characterized by increased oxidative stress, neurodegeneration and memory impairment.

Antidepressant drugs diversely affect autophagy pathways in astrocytes and neurons--dissociation from cholesterol homeostasis

In the search for antidepressants' (ADs') mechanisms of action beyond their influence on monoaminergic neurotransmission, we analyzed the effects of three structurally and pharmacologically different ADs on autophagic processes in rat primary astrocytes and neurons. Autophagy has a significant role in controlling protein turnover and energy supply. Both, the tricyclic AD amitriptyline (AMI) and the selective serotonin re-uptake inhibitor citalopram (CIT) induced autophagy as mirrored by pronounced upregulation and cellular redistribution of the marker LC3B-II. Redistribution was characterized by formation of LC3B-II-positive structures indicative of autophagosomes, which associated with AVs in a time-dependent manner. Deletion of Atg5, representing a central mediator of autophagy in MEFs, led to abrogation of AMI-induced LC3B-I/II conversion. By contrast, VEN, a selective serotonin and noradrenaline reuptake inhibitor, did not promote autophagic processes in either cell type. The stimulatory impact of AMI on autophagy partly involved class-III PI3 kinase-dependent pathways as 3-methyladenine slightly diminished the effects of AMI. Autophagic flux as defined by autophagosome turnover was vastly undisturbed, and degradation of long-lived proteins was augmented upon AMI treatment. Enhanced autophagy was dissociated from drug-induced alterations in cholesterol homeostasis. Subsequent to AMI- and CIT-mediated autophagy induction, neuronal and glial viability decreased, with neurons showing signs of apoptosis. In conclusion, we report that distinct ADs promote autophagy in neural cells, with important implications on energy homeostasis.

Beneficial network effects of methylene blue in an amnestic model

Posterior cingulate/retrosplenial cortex (PCC) hypometabolism is a common feature in amnestic mild cognitive impairment and Alzheimer's disease. In rats, PCC hypometabolism induced by mitochondrial dysfunction induces oxidative damage, neurodegeneration and memory deficits. USP methylene blue (MB) is a diaminophenothiazine drug with antioxidant and metabolic-enhancing properties. In rats, MB facilitates memory and prevents neurodegeneration induced by mitochondrial dysfunction. This study tested the memory-enhancing properties of systemic MB in rats that received an infusion of sodium azide, a cytochrome oxidase inhibitor, directly into the PCC. Lesion volumes were estimated with unbiased stereology. MB's network-level mechanism of action was analyzed using graph theory and structural equation modeling based on cytochrome oxidase histochemistry-derived metabolic mapping data. Sodium azide infusions induced PCC hypometabolism and impaired visuospatial memory in a holeboard food-search task. Isolated PCC cytochrome oxidase inhibition disrupted the cingulo-thalamo-hippocampal effective connectivity, decreased the PCC functional networks and created functional redundancy within the thalamus. An intraperitoneal dose of 4 mg/kg MB prevented the memory impairment, reduced the PCC metabolic lesion volume and partially restored the cingulo-thalamo-hippocampal network effects. The effects of MB were dependent upon the local sub-network necessary for memory retrieval. The data support that MB's metabolic-enhancing effects are contingent upon the neural context, and that MB is able to boost coherent and orchestrated adaptations in response to physical alterations to the network involved in visuospatial memory. These results implicate MB as a candidate intervention to improve memory. Because of its neuroprotective properties, MB may have disease-modifying effects in amnestic conditions associated with hypometabolism.

Phenothiazines interfere with dopaminergic neurodegeneration in Caenorhabditis elegans models of Parkinson's disease

Oxidative stress is involved in the pathogenesis of various neurodegenerative disorders, conventional antioxidant strategies have yet been of limited success. We have employed transgenic Caenorhabditis elegans expressing DsRed2 in dopaminergic neurons and CFP pan-neuronally, to characterize in larval and adult animals the effects of rotenone and 1-methyl-4-phenyl-pyridinium (MPP(+)) on the dopaminergic system. Investigating the antioxidant phenothiazine and different derived antipsychotic drugs, it was found that free phenothiazine exerted strong neuroprotection at the cellular level and resulted in a better performance in behavioral assays, whereas apomorphine and other dopamine agonists only rescued adult locomotor parameters. Phenothiazine antipsychotics with dopamine antagonist properties were likewise not cytoprotective, but even induced motor deficits by themselves. Beyond phenothiazine, other tricyclic imines elicited significant neuroprotection at considerably lower doses than different natural antioxidants. Mitochondrially targeted antioxidants were more potent than these untargeted natural antioxidants, yet not as potent as the untargeted compound phenothiazine. Thus, dopaminergic toxicity of rotenone and MPP(+)in vivo can be forestalled by nanomolar concentrations of certain chain-breaking antioxidants irrespective of dopamine receptor modulation or mitochondrial targeting.

Mitochondrial optic neuropathy: In vivo model of neurodegeneration and neuroprotective strategies

This review summarizes the characteristics of a rodent toxicologic model of optic neuropathy induced by the mitochondrial complex I inhibitor rotenone. This model has been developed to fulfill the demand for a drug-screening tool providing a sound mechanistic context to address the role of mitochondrial dysfunction in the pathogenesis of neurodegenerative disorders. It features biochemical, structural, and functional retinal deficits that resemble those of patients with Leber's hereditary optic neuropathy, a mitochondrial disease characterized by selective degeneration of retinal ganglion cells, and for which an environmental component is believed to play a major triggering role. The available data support the efficiency, sensitivity, and versatility of the model for providing insights into the mechanisms of neurodegeneration, including mitochondrial dysfunction, oxidative stress and excitotoxicity. Screening work with this model has provided proof-of-principle that interventions targeting the electron transport chain, such as USP methylene blue and near-infrared light therapy, are effective at preventing neurodegeneration induced by mitochondrial dysfunction in vivo. Prospective developments of this model include the use of neuronal reporter genes for in vivo non-invasive assessment of retinal degeneration at different time points, and its combination with genetic approaches to elucidate the synergism of environmental and genetic factors in neurodegeneration.

Striatal neuroprotection with methylene blue

Recent literature indicates that low-dose Methylene Blue (MB), an autoxidizable dye with powerful antioxidant and metabolic enhancing properties, might prevent neurotoxin-induced neural damage and associated functional deficits. This study evaluated whether local MB may counteract the anatomical and functional effects of the intrastriatal infusion of the neurotoxin rotenone (Rot) in the rat. To this end, stereological analyses of striatal lesion volumes were performed and changes in oxidative energy metabolism in the striatum and related motor regions were mapped using cytochrome oxidase histochemistry. The influence of MB on striatal levels of oxidative stress induced by Rot was determined, and behavioral tests were used to investigate the effect of unilateral MB coadministration on motor asymmetry. Rot induced large anatomical lesions resembling "metabolic strokes," whose size was greatly reduced in MB-treated rats. Moreover, MB prevented the decrease in cytochrome oxidase activity and the perilesional increase in oxidative stress associated with Rot infusion in the striatum. MB also prevented the indirect effects of the Rot-induced lesion on cytochrome oxidase activity in related motor regions, such as the striatal regions rostral and caudal to the lesion, the substantia nigra compacta and reticulata, and the pedunculopontine nucleus. At a network level, MB maintained a global strengthening of functional connectivity in basal ganglia-thalamocortical motor circuits, as opposed to the functional decoupling observed in Rot-alone subjects. Finally, MB partially prevented the behavioral sensorimotor asymmetries elicited by Rot. These results are consistent with protective effects of MB against neurotoxic damage in the brain parenchyma. This study provides the first demonstration of the anatomical, metabolic and behavioral neuroprotective effects of MB in the striatum in vivo, and supports the notion that MB could be a valuable intervention against neural damage associated with oxidative stress and energy hypometabolism.

Novel imine antioxidants at low nanomolar concentrations protect dopaminergic cells from oxidative neurotoxicity

Strong evidence indicates that oxidative stress may be causally involved in the pathogenesis of Parkinson's disease. We have employed human dopaminergic neuroblastoma cells and rat primary mesencephalic neurons to assess the protective potential of three novel bisarylimine antioxidants on dopaminergic cell death induced by complex I inhibition or glutathione depletion. We have found that exceptionally low concentrations (EC(50) values approximately 20 nM) of these compounds (iminostilbene, phenothiazine, and phenoxazine) exhibited strong protective effects against the toxicities of MPP(+), rotenone, and l-buthionine sulfoximine. Investigating intracellular glutathione levels, it was found that MPP(+), L-buthionine sulfoximine, and rotenone disrupted different aspects of the native glutathione equilibrium, while the aromatic imines did not further influence glutathione levels or redox state on any baseline. However, the imines independently reduced protein oxidation and total oxidant flux, saved the mitochondrial membrane potential, and provided full cytoprotection under conditions of complete glutathione depletion. The unusually potent antioxidant effects of the bisarylimines could be reproduced in isolated mitochondria, which were instantly protected from lipid peroxidation and pathological swelling. Aromatic imines may be interesting lead structures for a potential antioxidant therapy of Parkinson's disease and other disorders accompanied by glutathione dysregulation.

Adaptive antioxidant methionine accumulation in respiratory chain complexes explains the use of a deviant genetic code in mitochondria

Humans and most other animals use 2 different genetic codes to translate their hereditary information: the standard code for nuclear-encoded proteins and a modern variant of this code in mitochondria. Despite the pivotal role of the genetic code for cell biology, the functional significance of the deviant mitochondrial code has remained enigmatic since its first description in 1979. Here, we show that profound and functionally beneficial alterations on the encoded protein level were causative for the AUA codon reassignment from isoleucine to methionine observed in most mitochondrial lineages. We demonstrate that this codon reassignment leads to a massive accumulation of the easily oxidized amino acid methionine in the highly oxidative inner mitochondrial membrane. This apparently paradoxical outcome can yet be smoothly settled if the antioxidant surface chemistry of methionine is taken into account, and we present direct experimental evidence that intramembrane accumulation of methionine exhibits antioxidant and cytoprotective properties in living cells. Our results unveil that methionine is an evolutionarily selected antioxidant building block of respiratory chain complexes. Collective protein alterations can thus constitute the selective advantage behind codon reassignments, which authenticates the "ambiguous decoding" hypothesis of genetic code evolution. Oxidative stress has shaped the mitochondrial genetic code.

Free-radical-scavenging effect of carbazole derivatives on AAPH-induced hemolysis of human erythrocytes

Since the research on antioxidants provides theoretical information for the medicinal development, and supplies some in vitro methods for quick-optimizing drugs, it attracts more scientific attention from bioorganic and medicinal chemists. In addition to the traditional O-H bond-type antioxidant, carbazole and its related tricyclic amines (Ar2NHs), in which N-H bond functioned as the antioxidant, have attracted much research attention because Ar2NHs have always been the central structure in many currently used drugs. Thus, the investigation on the structure-activity relationship (SAR) between Ar2NHs and their free-radical-scavenging capacities in detail will benefit the development of novel radical-scavenging drugs containing Ar2NHs as the central structure. Therefore, carbazole (CazNH) and its structural analogues including phenoxazine (PozNH), phenothiazine (PtzNH), iminostilbene (IsbNH) together with diphenylamine (DpaNH) were applied to protect human erythrocytes against 2,2'-azobis(2-amidinopropane hydrochloride) (AAPH)-induced hemolysis in vitro. By introducing the chemical kinetic formula related to free radical reaction, namely, the quantitative relationship between inhibition period (tinh) and the concentration of antioxidant (AH), tinh=(n/Ri)[AH], into AAPH-induced hemolysis, the values of stoichiometric factor (n) of Ar2NHs indicated that the free-radical-scavenging sequence of Ar2NHs is PozNH>DpaNH>CazNH>IsbNH>PtzNH >alpha-tocopherol (TocH). Another aim of this work was to investigate the antioxidative effect of Ar2NHs used together with other antioxidants including Trolox (TroH), VC, L-ascorbyl-6-laurate (VC-12), and TocH. The obtained data revealed that n value of PozNH when used together with all the other antioxidants decreases, whereas, n values of CazNH, DpaNH, IsbNH, and PtzNH when used in combination with TroH increase, demonstrating that two different interaction styles existed in the case of Ar(2)NHs used with other antioxidants. These findings may be useful for the development of agents for various ROS-mediated diseases in vivo.

A study on the perturbation of model lipid membranes by phenoxazines

The interactions of six newly synthesized phenoxazine derivatives with lipid bilayers were studied by means of calorimetry, fluorescence spectroscopic methods and electron spin resonance. Depending on their structure studied compounds decreased membrane fluidity and increased lipid order in liquid-crystalline bilayers to different degrees. These studies showed also that phenoxazine molecules are located close to the polar/apolar interface of bilayer. The results allow to conclude that phenoxazines rather weakly interact with lipid bilayers.

Protective effects of endomorphins, endogenous opioid peptides in the brain, on human low density lipoprotein oxidation

Neurodegenerative disorders are associated with oxidative stress. Low density lipoprotein (LDL) exists in the brain and is especially sensitive to oxidative damage. Oxidative modification of LDL has been implicated in the pathogenesis of neurodegenerative diseases. Therefore, protecting LDL from oxidation may be essential in the brain. The antioxidative effects of endomorphin 1 (EM1) and endomorphin 2 (EM2), endogenous opioid peptides in the brain, on LDL oxidation has been investigated in vitro. The peroxidation was initiated by either copper ions or a water-soluble initiator 2,2'-azobis(2-amidinopropane hydrochloride) (AAPH). Oxidation of the LDL lipid moiety was monitored by measuring conjugated dienes, thiobarbituric acid reactive substances, and the relative electrophoretic mobility. Low density lipoprotein oxidative modifications were assessed by evaluating apoB carbonylation and fragmentation. Endomorphins markedly and in a concentration-dependent manner inhibited Cu2+ and AAPH induced the oxidation of LDL, due to the free radical scavenging effects of endomorphins. In all assay systems, EM1 was more potent than EM2 and l-glutathione, a major intracellular water-soluble antioxidant. We propose that endomorphins provide protection against free radical-induced neurodegenerative disorders.

Antioxidant properties of minocycline: neuroprotection in an oxidative stress assay and direct radical-scavenging activity

Minocycline is neuroprotective in animal models of a number of acute CNS injuries and neurodegenerative diseases. While anti-inflammatory and anti-apoptotic effects of minocycline have been characterized, the molecular basis for the neuroprotective effects of minocycline remains unclear. We report here that minocycline and a number of antioxidant compounds protect mixed neuronal cultures in an oxidative stress assay. To evaluate the role of minocycline's direct antioxidant properties in neuroprotection, we determined potencies for minocycline, other tetracycline antibiotics, and reference antioxidant compounds using a panel of in vitro radical scavenging assays. Data from in vitro rat brain homogenate lipid peroxidation and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assays show that minocycline, in contrast to tetracycline, is an effective antioxidant with radical scavenging potency similar to vitamin E. Our findings suggest that the direct antioxidant activity of minocycline may contribute to its neuroprotective effects in some cell-based assays and animal models of neuronal injury.

Glycogen synthase kinase 3beta links neuroprotection by 17beta-estradiol to key Alzheimer processes

Estrogen exerts many of its receptor-mediated neuroprotective functions through the activation of various intracellular signal transduction pathways including the mitogen activating protein kinase (MAPK), phospho inositol-3 kinase and protein kinase C pathways. Here we have used a hippocampal slice culture model of kainic acid-induced neurotoxic cell death to show that estrogen can protect against oxidative cell death. We have previously shown that MAPK and glycogen synthase kinase-3beta (GSK-3beta) are involved in the cell death/cell survival induced by kainic acid. In this model and other cellular and in vivo models we have shown that estrogen can also cause the phosphorylation and hence inactivation of GSK-3beta, a known mediator of neuronal cell death. The effect of estrogen on GSK-3beta activity is estrogen receptor mediated. Further, this estrogen/GSK-3beta interaction may have functional consequences in cellular models of some key pathogenic pathways associated with Alzheimer's disease. More specifically, estrogen affects the basal levels of tau phosphorylation at a site known to be phosphorylated by GSK-3beta. Taken together, these data indicate a novel molecular and functional link between estrogen and GSK-3beta and may have implications for estrogen receptor modulation as a target for the prevention of neurodegenerative disorders.

Inactivation of glycogen synthase kinase-3β protects against kainic acid-induced neurotoxicity in vivo

Many neurodegenerative diseases involve oxidative stress and excitotoxic cell death. In an attempt to further elucidate the signal transduction pathways involved in the cell death/cell survival associated with excitotoxicity, we have used an in vivo model of excitotoxicity employing kainic acid (KA)-induced neurotoxicity. Here, we show that extracellular signal-related kinase (ERK) 2, but not ERK 1, is phosphorylated and thereby activated in the hippocampus and cerebellum of kainic acid-treated mice. Phosphorylation and hence inactivation of glycogen synthase kinase 3beta (GSK-3beta), a general survival factor, is often a downstream consequence of mitogen-activated protein kinase pathway activation. Indeed, GSK-3beta phosphorylation occurred in response to kainic acid exclusively in the affected hippocampus, but not as a consequence of ERK activation. This may represent a compensatory attempt at self-protection by the cells in this particular brain region. A role for GSK-3beta inhibition in cell survival was further supported by the fact that pharmacological inhibition of GSK-3beta using lithium chloride was protective against kainic acid-induced excitotoxicity in hippocampal slice cultures. This work supports a role for GSK-3beta in cell death in response to excitotoxins in vivo and further confirms that GSK-3beta plays a role in cell death/cell survival pathways.

Brain region-specific neuroprotective action and signaling of corticotropin-releasing hormone in primary neurons

CRH regulates the body's response to stressful stimuli by modulating the activity of the hypothalamic pituitary axis. In primary cultures and cell lines, CRH also acts as a potent neuroprotective factor in response to a number of toxins. Using primary neuronal cultures from the cerebellum, cerebral cortex, and hippocampus, we demonstrate that CRH exerts a brain region-specific neuroprotective effect on amyloid beta 25-35 toxicity. At low CRH concentrations (10(-8) M), neuroprotective effects can be observed only in cerebellar and hippocampal cultures, but a higher CRH concentration (10(-7) M) additionally led to the protection of cortical neurons. These neuroprotective effects were inhibited by H89, a specific protein kinase A inhibitor. Western blot analysis, carried out using phospho-specific antibodies directed against MAPK, cAMP response element-binding protein (CREB), and glycogen synthase kinase (GSK)3 beta also resulted in brain legion-specific differences regarding intracellular signaling. Correlating with cell survival, low CRH concentrations resulted in activation of the CREB pathway and inactivation of GSK3 beta in cerebellar and hippocampal cultures, but higher concentrations additionally resulted in activated CREB and inactivated GSK3 beta in cortical cultures. In contrast, MAPK activation occurred only in cortical neurons. Differences in signaling were found to be independent of receptor expression levels because RT-PCR analysis indicated no region-specific differences in CRHR1 mRNA expression.

Antioxidant neuroprotection in Alzheimer's disease as preventive and therapeutic approach

Various neurodegenerative disorders and syndromes are associated with oxidative stress. The deleterious consequences of excessive oxidations and the pathophysiological role of reactive oxygen species (ROS) have been intensively studied in Alzheimer's disease (AD). Neuronal cell dysfunction and oxidative cell death caused by the AD-associated amyloid beta protein may causally contribute to the pathogenesis of AD. Antioxidants that prevent the detrimental consequences of ROS are consequently considered to be a promising approach to neuroprotection. While there is ample experimental evidence demonstrating neuroprotective activities of antioxidants in vitro, the clinical evidence that antioxidant compounds act as protective drugs is still relatively scarce. Nevertheless, antioxidants constitute a major part of the panel of clinical and experimental drugs that are currently considered for AD prevention and therapy. Here, focus is put mainly on phenolic antioxidant structures that belong to the class of direct antioxidants. Experimental and clinical evidence for the neuroprotective potential of alpha-tocopherol (vitamin E) and 17beta-estradiol (estrogen) is shortly summarized and an outlook is given on possible novel antioxidant lead structures with improved pharmacological features.

Oxidative nerve cell death in Alzheimer's disease and stroke: antioxidants as neuroprotective compounds

Many neurodegenerative disorders and syndromes are associated with an excessive generation of reactive oxygen species (ROS) and oxidative stress. The pathways to nerve cell death induced by diverse potential neurotoxins such as peptides, excitatory amino acids, cytokines or synthetic drugs commonly share oxidative downstream processes, which can cause either an acute oxidative destruction or activate secondary events leading to apoptosis. The pathophysiological role of ROS has been intensively studied in in vitro and in vivo models of chronic neurodegenerative diseases such as Alzheimer's disease (AD) and of syndromes associated with rapid nerve cell loss as occuring in stroke. In AD, oxidative neuronal cell dysfunction and cell death caused by protofibrils and aggregates of the AD-associated amyloid beta protein (Abeta) may causally contribute to pathogenesis and progression. ROS and reactive nitrogen species also take part in the complex cascade of events and the detrimental effects occuring during ischemia and reperfusion in stroke. Direct antioxidants such as chain-breaking free radical scavengers can prevent oxidative nerve cell death. Although there is ample experimental evidence demonstrating neuroprotective activities of direct antioxidants in vitro, the clinical evidence for antioxidant compounds to act as protective drugs is relatively scarce. Here, the neuroprotective potential of antioxidant phenolic structures including alpha-tocopherol (vitamin E) and 17beta-estradiol (estrogen) in vitro is summarized. In addition, the antioxidant and cytoprotective activities of lipophilic tyrosine- and tryptophan-containing structures are discussed. Finally, an outlook is given on the neuroprotective potential of aromatic amines and imines, which may comprise novel lead structures for antioxidant drug design.