Living cells maintain a balance between oxidation and reduction, and perturbations of this redox balance are thought to contribute to various diseases. Recent attempts to regulate redox state have ...focused on electrophiles (EPs), which activate potent cellular defense systems against oxidative stress. One example of this approach is exemplified by carnosic acid (CA) and carnosol (CS), compounds that are found in the herb rosemary (Rosmarinus officinalis). Importantly, CA and CS themselves are not electrophilic, but in response to oxidation, become electrophilic, and then activate the Keap1/Nrf2/ARE (antioxidant-response element) transcription pathway to synthesize endogenous antioxidant “phase 2” enzymes. As a result of our efforts to develop these compounds as therapeutics for brain health, we have formulated two innovative criteria for drug development: the first concept is the use of pro-electrophilic drugs (PEDs) that are innocuous in and of themselves; and the second concept involves the use of compounds that are pathologically activated therapeutics (PATs);i.e., these small molecules are chemically converted to their active form by the very oxidative stress that they are designed to then combat. The chemical basis for PED and PAT drugs is embodied in the ortho- and para-hydroquinone electrophilic cores of the molecules, which are oxidized by the Cu²⁺/Cu⁺ cycling system (or potentially by other transition metals). Importantly, this cycling pathway is under stringent regulation by the cell redox state. We propose that redox-dependent quinone formation is the predominant mechanism for formation of PED and PAT drugs from their precursor compounds. In fact, redox-dependent generation of the active form of drug from the “pro-form” distinguishes this therapeutic approach from traditional EPs such as curcumin, and results in a decrease in clinical side effects at therapeutic concentrations, e.g., lack of reaction with other thiols such as glutathione (GSH), which can result in lowering GSH and inducing oxidative stress in normal cells. We consider this pro-drug quality of PED/PAT compoundsto be a key factor for generating drugs to be used to combat neurodegenerative diseases that will be clinically tolerated. Given the contribution of oxidative stress to the pathology of multiple neurodegenerative diseases, the Keap1/Nrf2/ARE pathway represents a promising drug target for these PED/PAT agents.
Excitatory inhibitory (E I) balance, defined as the balance between excitation and inhibition of synaptic activity in a neuronal network, accounts in part for the normal functioning of the brain, ...controlling, for example, normal spike rate. In many pathological conditions, this fine balance is perturbed, leading to excessive or diminished excitation relative to inhibition, termed E I imbalance, reflected in network dysfunction. E I imbalance has emerged as a contributor to neurological disorders that occur particularly at the extremes of life, including autism spectrum disorder and Alzheimer's disease, pointing to the vulnerability of neuronal networks at these critical life stages. Hence, it is important to develop approaches to rebalance neural networks. In this review, we describe emerging therapies that can normalize the E I ratio or the underlying abnormality that contributes to the imbalance in electrical activity, thus improving neurological function in these maladies.
Abstract Nitric oxide (NO) is a gasotransmitter that impacts fundamental aspects of neuronal function in large measure through S -nitrosylation, a redox reaction that occurs on regulatory cysteine ...thiol groups. For instance, S -nitrosylation regulates enzymatic activity of target proteins via inhibition of active site cysteine residues or via allosteric regulation of protein structure. During normal brain function, protein S -nitrosylation serves as an important cellular mechanism that modulates a diverse array of physiological processes, including transcriptional activity, synaptic plasticity, and neuronal survival. In contrast, emerging evidence suggests that aging and disease-linked environmental risk factors exacerbate nitrosative stress via excessive production of NO. Consequently, aberrant S -nitrosylation occurs and represents a common pathological feature that contributes to the onset and progression of multiple neurodegenerative disorders, including Alzheimer's, Parkinson's, and Huntington's diseases. In the current review, we highlight recent key findings on aberrant protein S -nitrosylation showing that this reaction triggers protein misfolding, mitochondrial dysfunction, transcriptional dysregulation, synaptic damage, and neuronal injury. Specifically, we discuss the pathological consequences of S -nitrosylated parkin, myocyte enhancer factor 2 (MEF2), dynamin-related protein 1 (Drp1), protein disulfide isomerase (PDI), X-linked inhibitor of apoptosis protein (XIAP), and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) under neurodegenerative conditions. We also speculate that intervention to prevent these aberrant S -nitrosylation events may produce novel therapeutic agents to combat neurodegenerative diseases.
The activity of Cdk5 and its regulatory subunit p35 is thought to be important in both normal brain function and neurodegenerative disease pathogenesis. Increased Cdk5 activity, via proteolytic ...cleavage of p35 to a p25 fragment by the calcium-activated protease calpain or by phosphorylation at Cdk5(Tyr15), can contribute to neurotoxicity. Nonetheless, our knowledge of regulation of Cdk5 activity in disease states is still emerging. Here we demonstrate that Cdk5 is activated by S-nitrosylation or reaction of nitric oxide (NO)-related species with the thiol groups of cysteine residues 83 and 157, to form SNO-Cdk5. We then show that S-nitrosylation of Cdk5 contributes to amyloid-β (Aβ) peptide-induced dendritic spine loss. Furthermore, we observed significant levels of SNO-Cdk5 in postmortem Alzheimer’s disease (AD) but not in normal human brains. These findings suggest that S-nitrosylation of Cdk5 is an aberrant regulatory mechanism of enzyme activity that may contribute to the pathogenesis of AD.
Metabolic syndrome (MetS) and Type 2 diabetes mellitus (T2DM) increase risk for Alzheimer's disease (AD). The molecular mechanism for this association remains poorly defined. Here we report in human ...and rodent tissues that elevated glucose, as found in MetS/T2DM, and oligomeric β-amyloid (Aβ) peptide, thought to be a key mediator of AD, coordinately increase neuronal Ca(2+) and nitric oxide (NO) in an NMDA receptor-dependent manner. The increase in NO results in S-nitrosylation of insulin-degrading enzyme (IDE) and dynamin-related protein 1 (Drp1), thus inhibiting insulin and Aβ catabolism as well as hyperactivating mitochondrial fission machinery. Consequent elevation in Aβ levels and compromise in mitochondrial bioenergetics result in dysfunctional synaptic plasticity and synapse loss in cortical and hippocampal neurons. The NMDA receptor antagonist memantine attenuates these effects. Our studies show that redox-mediated posttranslational modification of brain proteins link Aβ and hyperglycaemia to cognitive dysfunction in MetS/T2DM and AD.
The most common inherited form of amyotrophic lateral sclerosis (ALS), a neurodegenerative disease affecting adult motoneurons, is caused by dominant mutations in the ubiquitously expressed Cu²⁺/Zn²⁺ ...superoxide dismutase (SOD1). Recent studies suggest that glia may contribute to motoneuron injury in animal models of familial ALS. To determine whether the expression of mutant SOD1 ($mSOD1^{G93A}$) in CNS microglia contributes to motoneuron injury,$PU.1^{-/-}$mice that are unable to develop myeloid and lymphoid cells received bone marrow transplants resulting in donor-derived microglia. Donor-derived microglia from mice overexpressing$mSOD1^{G93A}$, an animal model of familial ALS, transplanted into$PU.1^{-/-}$mice could not induce weakness, motoneuron injury, or an ALS-like disease. To determine whether expression of$mSOD1^{G93A}$in motoneurons and astroglia, as well as microglia, was required to produce motoneuron disease,$PU.1^{-/-}$mice were bred with$mSOD1^{G93A}$mice. In$mSOD1^{G93A}/PU.1^{-/-}$mice, wild-type donorderived microglia slowed motoneuron loss and prolonged disease duration and survival when compared with mice receiving$mSOD1^{G93A}$expressing cells or$mSOD1^{G93A}$mice. In vitro studies confirmed that wild-type microglia were less neurotoxic than similarly cultured$mSOD1^{G93A}$microglia. Compared with wild-type microglia,$mSOD1^{G93A}$microglia produced and released more superoxide and nitrite+nitrate, and induced more neuronal death. These data demonstrate that the expression of$mSOD1^{G93A}$results in activated and neurotoxic microglia, and suggests that the lack of$mSOD1^{G93A}$expression in microglia may contribute to motoneuron protection. This study confirms the importance of microglia as a double-edged sword, and focuses on the importance of targeting microglia to minimize cytotoxicity and maximize neuroprotection in neurodegenerative diseases.
Bone marrow stem cells give rise to a variety of hematopoietic lineages and repopulate the blood throughout adult life. We show that, in a strain of mice incapable of developing cells of the myeloid ...and lymphoid lineages, transplanted adult bone marrow cells migrated into the brain and differentiated into cells that expressed neuron-specific antigens. These findings raise the possibility that bone marrow-derived cells may provide an alternative source of neurons in patients with neurodegenerative diseases or central nervous system injury.
Transcription factor MEF2C regulates multiple genes linked to autism spectrum disorder (ASD), and human MEF2C haploinsufficiency results in ASD, intellectual disability, and epilepsy. However, ...molecular mechanisms underlying MEF2C haploinsufficiency syndrome remain poorly understood. Here we report that Mef2c
(Mef2c-het) mice exhibit behavioral deficits resembling those of human patients. Gene expression analyses on brains from these mice show changes in genes associated with neurogenesis, synapse formation, and neuronal cell death. Accordingly, Mef2c-het mice exhibit decreased neurogenesis, enhanced neuronal apoptosis, and an increased ratio of excitatory to inhibitory (E/I) neurotransmission. Importantly, neurobehavioral deficits, E/I imbalance, and histological damage are all ameliorated by treatment with NitroSynapsin, a new dual-action compound related to the FDA-approved drug memantine, representing an uncompetitive/fast off-rate antagonist of NMDA-type glutamate receptors. These results suggest that MEF2C haploinsufficiency leads to abnormal brain development, E/I imbalance, and neurobehavioral dysfunction, which may be mitigated by pharmacological intervention.
Living cells maintain a balance between oxidation and reduction, and perturbations of this redox balance are thought to contribute to various diseases. Recent attemptsto regulate redox state have ...focused on electrophiles (EPs), which activate potent cellular defense systems against oxidative stress. One example of this approach is exemplified by carnosic acid (CA) and carnosol (CS), compounds that are found in the herb rosemary (Rosmarinus officinalis). Importantly, CA and CS themselves are not electrophilic, but in response to oxidation, become electrophilic, and then activate the Keap1/Nrf2/ARE (antioxidant-response element) transcription pathway to synthesize endogenous antioxidant “phase 2”enzymes. As a result of our efforts to develop these compounds as therapeutics for brain health, we have formulated two innovative criteria fordrug development: the first conceptis the use of pro-electrophilic drugs (PEDs) that are innocuous in and of themselves; and the second concept involves the use of compounds that are pathologically activated therapeutics (PATs); i.e., these small molecules are chemically converted to their active form by the very oxidative stress that they are designed to then combat. The chemical basis for PED and PAT drugs is embodied in the ortho- and para-hydroquinone electrophilic cores of the molecules, which are oxidized by the Cu2+/Cu+ cycling system (or potentially by other transition metals). Importantly, this cycling pathway is under stringent regulation bythe cell redox state. We propose that redox-dependent quinone formation is the predominant mechanism for formation of PED and PAT drugs from their precursor compounds. In fact, redox-dependent generation of the active form of drugfrom the “pro-form” distinguishes this therapeutic approach from traditional EPs such as curcumin, and results in a decrease in clinical side effects at therapeutic concentrations, e.g., lack of reaction with other thiols such as glutathione (GSH), which can result in lowering GSH and inducing oxidative stress in normal cells. We consider this pro-drug quality of PED/PAT compounds to be a key factor for generating drugs to be used to combat neurodegenerative diseases that will be clinically tolerated. Given the contribution of oxidative stress to the pathology of multiple neurodegenerative diseases, the Keap1/Nrf2/ARE pathway represents a promising drug target for these PED/PAT agents.
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•We propose two novel types of clinicallytolerated drugs.•Pro-electrophilic drugs (PEDs) and pathologically activated therapeutics (PATs).•PEDs/PATs can manifest pro-drugs because of the presence of an ortho- or para-hydroquinone.•PEDs are converted by oxidative stress to electrophiles, which activate the Nrf2/ARE pathway.•PEDs produce antioxidant phase 2 enzymes to combat cellular redox stress.
Alzheimer's disease (AD) is characterized by synaptic and neuronal loss, which occurs at least partially through oxidative stress induced by oligomeric amyloid-β (Aβ)-peptide. Carnosic acid (CA), a ...chemical found in rosemary and sage, is a pro-electrophilic compound that is converted to its active form by oxidative stress. The active form stimulates the Keap1/Nrf2 transcriptional pathway and thus production of phase 2 antioxidant enzymes. We used both in vitro and in vivo models. For in vitro studies, we evaluated protective effects of CA on primary neurons exposed to oligomeric Aβ. For in vivo studies, we used two transgenic mouse models of AD, human amyloid precursor protein (hAPP)-J20 mice and triple transgenic (3xTg AD) mice. We treated these mice trans-nasally with CA twice weekly for 3 months. Subsequently, we performed neurobehavioral tests and quantitative immunohistochemistry to assess effects on AD-related phenotypes, including learning and memory, and synaptic damage. In vitro, CA reduced dendritic spine loss in rat neurons exposed to oligomeric Aβ. In vivo, CA treatment of hAPP-J20 mice improved learning and memory in the Morris water maze test. Histologically, CA increased dendritic and synaptic markers, and decreased astrogliosis, Aβ plaque number, and phospho-tau staining in the hippocampus. We conclude that CA exhibits therapeutic benefits in rodent AD models and since the FDA has placed CA on the 'generally regarded as safe' (GRAS) list, thus obviating the need for safety studies, human clinical trials will be greatly expedited.
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