Inhibition of nerve growth factor signaling by peroxynitrite

Age-induced nitrative stress decreases retrograde transport of proNGF via TrkA and increases proNGF retrograde transport and neurodegeneration via p75NTR

Introduction

Axonal transport of pro nerve growth factor (proNGF) is impaired in aged basal forebrain cholinergic neurons (BFCNs), which is associated with their degeneration. ProNGF is neurotrophic in the presence of its receptor tropomyosin-related kinase A (TrkA) but induces apoptosis via the pan-neurotrophin receptor (p75NTR) when TrkA is absent. It is well established that TrkA is lost while p75NTR is maintained in aged BFCNs, but whether aging differentially affects transport of proNGF via each receptor is unknown. Nitrative stress increases during aging, but whether age-induced nitrative stress differentially affects proNGF transport via TrkA versus p75NTR has not yet been studied. Answering these questions is essential for developing an accurate understanding of the mechanisms contributing to age-induced loss of proNGF transport and BFCN degeneration.

Methods

In this study, fluorescence microscopy was used to analyze axonal transport of quantum dot labeled proNGF in rat BFCNs in vitro. Receptor specific effects were studied with proNGF mutants that selectively bind to either TrkA (proNGF-KKE) or p75NTR (proNGF-Δ9-13). Signaling factor activity was quantified via immunostaining.

Results

Young BFCNs transported proNGF-KKE but not proNGF-Δ9-13, and proNGF transport was not different in p75NTR knockout BFCNs compared to wildtype BFCNs. These results indicate that young BFCNs transport proNGF via TrkA. In vitro aging increased transport of proNGF-Δ9-13 but decreased transport of proNGF-KKE. Treatment with the nitric oxide synthase inhibitor L-NAME reduced retrograde transport of proNGF-Δ9-13 in aged BFCNs while increasing retrograde transport of proNGF-KKE but did not affect TrkA or p75NTR levels. ProNGF-Δ9-13 induced greater pro-apoptotic signaling and neurodegeneration and less pro-survival signaling relative to proNGF-KKE.

Discussion

Together, these results indicate that age-induced nitrative stress decreases proNGF transport via TrkA while increasing proNGF transport via p75NTR. These transport deficits are associated with decreased survival signaling, increased apoptotic signaling, and neurodegeneration. Our findings elucidate the receptor specificity of age-and nitrative stress-induced proNGF transport deficits. These results may help to rescue the neurotrophic signaling of proNGF in aging to reduce age-induced loss of BFCN function and cognitive decline.

An Emerging Strategy for Neuroinflammation Treatment: Combined Cannabidiol and Angiotensin Receptor Blockers Treatments Effectively Inhibit Glial Nitric Oxide Release

Cannabidiol (CBD), the major non-psychoactive phytocannabinoid found in cannabis, has anti-neuroinflammatory properties. Despite the increasing use of CBD, little is known about its effect in combination with other substances. Combination therapy has been gaining attention recently, aiming to produce more efficient effects. Angiotensin II activates the angiotensin 1 receptor and regulates neuroinflammation and cognition. Angiotensin receptor 1 blockers (ARBs) were shown to be neuroprotective and prevent cognitive decline. The present study aimed to elucidate the combined role of CBD and ARBs in the modulation of lipopolysaccharide (LPS)-induced glial inflammation. While LPS significantly enhanced nitric oxide synthesis vs. the control, telmisartan and CBD, when administered alone, attenuated this effect by 60% and 36%, respectively. Exposure of LPS-stimulated cells to both compounds resulted in the 95% inhibition of glial nitric oxide release (additive effect). A synergistic inhibitory effect on nitric oxide release was observed when cells were co-treated with losartan (5 μM) and CBD (5 μM) (by 80%) compared to exposure to each compound alone (by 22% and 26%, respectively). Telmisartan and CBD given alone increased TNFα levels by 60% and 40%, respectively. CBD and telmisartan, when given together, attenuated the LPS-induced increase in TNFα levels without statistical significance. LPS-induced IL-17 release was attenuated by CBD with or without telmisartan (by 75%) or telmisartan alone (by 60%). LPS-induced Interferon-γ release was attenuated by 80% when telmisartan was administered in the absence or presence of CBD. Anti-inflammatory effects were recorded when CBD was combined with the known anti-inflammatory agent dimethyl fumarate (DMF)/monomethyl fumarate (MMF). A synergistic inhibitory effect of CBD and MMF on glial release of nitric oxide (by 77%) was observed compared to cells exposed to MMF (by 35%) or CBD (by 12%) alone. Overall, this study highlights the potential of new combinations of CBD (5 μM) with losartan (5 μM) or MMF (1 μM) to synergistically attenuate glial NO synthesis. Additive effects on NO production were observed when telmisartan (5 μM) and CBD (5 μM) were administered together to glial cells.

Brain‑derived neurotrophic factor and nitric oxide contribute to protective effects of rosiglitazone on learning and memory in hypothyroid rats

The effects of the well‑known peroxisome proliferator‑activated receptor gamma (PPAR-γ) agonist rosiglitazone (Rosi) on brain‑derived neurotrophic factor (BDNF), nitric oxide (NO), and learning and memory were investigated in hypothyroid rats. Hypothyroidism was induced in immature Wistar rats by administration of propylthiouracil in drinking water. Rats were divided into four groups: control, hypothyroid, and hypothyroid treated with Rosi at doses of 2 mg/kg or 4 mg/kg. Memory was then assessed by the Morris water maze (MWM) and passive avoidance (PA) tests. Following anesthetization, brain samples were collected for biochemical measurements. Hypothyroidism increased the escape latency and traveled path in the learning trials of the MWM and decreased the time spent and the distance traveled in the target quadrant on the probe day. Hypothyroidism also impaired the avoidance behavior of rats in the PA test. Rosi improved the performance of rats in both MWM and PA tasks. Hypothyroidism also decreased hippocampal BDNF levels, increased NO metabolites, and induced oxidative damage in the brain. Treatment of hypothyroid rats with both doses of Rosi increased BDNF levels and decreased NO metabolites and malondialdehyde concentrations. In addition, thiol content and superoxide dismutase and catalase activities were increased in the brain regions of hypothyroid rats receiving Rosi. The administration of 4 mg/kg Rosi also significantly increased serum thyroxin levels. The results of the present study showed that BDNF and NO play a role in the protective effects of Rosi against learning and memory impairment in hypothyroid rats.

Effects of Reactive Oxygen and Nitrogen Species on TrkA Expression and Signalling: Implications for proNGF in Aging and Alzheimer's Disease

Nerve growth factor (NGF) and its precursor form, proNGF, are critical for neuronal survival and cognitive function. In the brain, proNGF is the only detectable form of NGF. Dysregulation of proNGF in the brain is implicated in age-related memory loss and Alzheimer’s disease (AD). AD is characterized by early and progressive degeneration of the basal forebrain, an area critical for learning, memory, and attention. Learning and memory deficits in AD are associated with loss of proNGF survival signalling and impaired retrograde transport of proNGF to the basal forebrain. ProNGF transport and signalling may be impaired by the increased reactive oxygen and nitrogen species (ROS/RNS) observed in the aged and AD brain. The current literature suggests that ROS/RNS nitrate proNGF and reduce the expression of the proNGF receptor tropomyosin-related kinase A (TrkA), disrupting its downstream survival signalling. ROS/RNS-induced reductions in TrkA expression reduce cell viability, as proNGF loses its neurotrophic function in the absence of TrkA and instead generates apoptotic signalling via the pan-neurotrophin receptor p75^NTR. ROS/RNS also interfere with kinesin and dynein motor functions, causing transport deficits. ROS/RNS-induced deficits in microtubule motor function and TrkA expression and signalling may contribute to the vulnerability of the basal forebrain in AD. Antioxidant treatments may be beneficial in restoring proNGF signalling and axonal transport and reducing basal forebrain neurodegeneration and related deficits in cognitive function.

Neuronal Nitric Oxide Inhibitor 7-Nitroindazole Improved Brain-Derived Neurotrophic Factor and Attenuated Brain Tissues Oxidative Damage and Learning and Memory Impairments of Hypothyroid Juvenile Rats

Hypothyroidism-associated learning and memory impairment is reported to be connected to oxidative stress and reduced levels of brain-derived neurotrophic factor (BDNF). The effects of neuronal nitric oxide inhibitor 7-nitroindazole (7NI) on brain tissues oxidative damage, nitric oxide (NO), BDNF and memory impairments in hypothyroid juvenile rats were investigated. Male Wistar juvenile rats (20 days old) were divided into five groups, including Martinez et al. (J Neurochem 78 (5):1054-1063, 2001). Control in which vehicle was injected instead of 7NI, (Jackson in Thyroid 8 (10):951-956, 1998) Propylthiouracil (PTU) where 0.05% PTU was added in drinking water and vehicle was injected instead of 7NI, (Gong et al. in BMC Neurosci 11 (1):50, 2010; Alva-Sánchez et al. in Brain Res 1271:27-35, 2009; Anaeigoudari et al. in Pharmacol Rep 68 (2): 243-249, 2016) PTU-7NI 5, PTU-7NI 10 and PTU-7NI 20 in which 5, 10, or 20 mg/kg7NI was injected intraperitoneally (i.p.). Following 6 weeks, Morris water maze (MMW) and passive avoidance learning (PAL) tests were used to evaluate the memory. Finally, the hippocampus and the cortex of the rats were removed after anesthesia by urethane to be used for future analysis. The escape latency and traveled path in MWM test was increased in PTU group (P < 0.001). PTU also reduced the latency to enter the dark box of PAL and the time spent and the distance in the target quadrant in MWM test (P < 0.001 and P < 0.01). Treatment with 7NI attenuated all adverse effects of PTU (P < 0.05 to P < 0.001). PTU lowered BDNF and thiol content and superoxide dismutase (SOD) and catalase (CAT) activities in the brain but increased malondialdehyde (MDA) and nitric oxide (NO) metabolites. In addition, 7NI improved thiol, SOD, CAT, thiol, and BDNF but attenuated MDA and NO metabolites. The results of the current study showed that 7NI improvement in the learning and memory of the hypothyroid juvenile rats, which was accompanied with improving of BDNF and attenuation of NO and brain tissues oxidative damage.

Neuroprotective and long term potentiation improving effects of vitamin E in juvenile hypothyroid rats

Abstract. Protective effects of vitamin E (Vit E) on long term potentiation (LTP) impairment, neuronal apoptosis and increase of nitric oxide (NO) metabolites in the hippocampus of juvenile rats were examined. The rats were grouped (n=13) as: (1) control; (2) hypothyroid (Hypo) and (3) Hypo-Vit E. Propylthiouracil (PTU) was given in drinking water (0.05%) during 6 weeks. Vit E (20 mg/ kg) was daily injected (IP). To evaluate synaptic plasticity, LTP from the CA1 area of the hippocampus followed by high frequency stimulation to the ipsilateral Schafer collateral pathway was carried out. The cortical and hippocampal tissues were then removed to measure NO metabolites. The brains of 5 animals in each group were removed for apoptosis study. The hypothyroidism status decreased the slope, 10–90% slope and amplitude of field excitatory post synaptic potential (fEPSP) compared to the control group (P<0.01–P<0.001). Injection of Vit E increased the slope, 10–90% slope and amplitude of the fEPSP in the Hypo-Vit E group in comparison to the Hypo group (P<0.05–P<0.01). TUNEL positive neurons and NO metabolites were higher in the hippocampus of the Hypo rats, as compared to those in the hippocampus of the control ones (P<0.001). Treatment of the Hypo rats by Vit E decreased apoptotic neurons (P<0.01–P<0.001) and NO metabolites (P<0.001) in the hippocampus compared to the Hypo rats. The results of the present study showed that Vit E prevented the LTP impairment and neuronal apoptosis in the hippocampus of juvenile hypothyroid rats.

Microglial Activation Is Modulated by Captopril: in Vitro and in Vivo Studies

The renin-angiotensin system (RAS) is an important peripheral system involved in homeostasis modulation, with angiotensin II (Ang II) serving as the main effector hormone. The main enzyme involved in Ang II formation is angiotensin-converting enzyme (ACE). ACE inhibitors (ACEIs) such as captopril (Cap) are predominantly used for the management of hypertension. All of the components of the RAS have also been identified in brain. Centrally located hormones such as Ang II can induce glial inflammation. Moreover, in Alzheimer’s disease (AD) models, where glial inflammation occurs and is thought to contribute to the propagation of the disease, increased levels of Ang II and ACE have been detected. Interestingly, ACE overexpression in monocytes, migrating to the brain was shown to prevent AD cognitive decline. However, the specific effects of captopril on glial inflammation and AD remain obscure. In the present study, we investigated the effect of captopril, given at a wide concentration range, on inflammatory mediators released by lipopolysaccharide (LPS)-treated glia. In the current study, both primary glial cells and the BV2 microglial cell line were used. Captopril decreased LPS-induced nitric oxide (NO) release from primary mixed glial cells as well as regulating inducible NO synthase (iNOS) expression, NO, tumor necrosis factor-α (TNF-α) and induced interleukin-10 (IL-10) production by BV2 microglia. We further obtained data regarding intranasal effects of captopril on cortical amyloid β (Aβ) and CD11b expression in 5XFAD cortex over three different time periods. Interestingly, we noted decreases in Aβ burden in captopril-treated mice over time which was paralleled by increased microglial activation. These results thus shed light on the neuroprotective role of captopril in AD which might be related to modulation of microglial activation.

Lung Ischaemia-Reperfusion Injury: The Role of Reactive Oxygen Species

Lung ischaemia-reperfusion injury (LIRI) occurs in many lung diseases and during surgical procedures such as lung transplantation. The re-establishment of blood flow and oxygen delivery into the previously ischaemic lung exacerbates the ischaemic injury and leads to increased microvascular permeability and pulmonary vascular resistance as well as to vigorous activation of the immune response. These events initiate the irreversible damage of the lung with subsequent oedema formation that can result in systemic hypoxaemia and multi-organ failure. Alterations in the production of reactive oxygen species (ROS) and reactive nitrogen species (RNS) have been suggested as crucial mediators of such responses during ischaemia-reperfusion in the lung. Among numerous potential sources of ROS/RNS within cells, nicotinamide adenine dinucleotide phosphate (NADPH) oxidases, xanthine oxidases, nitric oxide synthases and mitochondria have been investigated during LIRI. Against this background, we aim to review here the extensive literature about the ROS-mediated cellular signalling during LIRI, as well as the effectiveness of antioxidants as treatment option for LIRI.

Contribution of Brain Tissue Oxidative Damage in Hypothyroidism-associated Learning and Memory Impairments

The brain is a critical target organ for thyroid hormones, and modifications in memory and cognition happen with thyroid dysfunction. The exact mechanisms underlying learning and memory impairments due to hypothyroidism have not been understood yet. Therefore, this review was aimed to compress the results of previous studies which have examined the contribution of brain tissues oxidative damage in hypothyroidism-associated learning and memory impairments.

N-Propargyl Caffeamide (PACA) Ameliorates Dopaminergic Neuronal Loss and Motor Dysfunctions in MPTP Mouse Model of Parkinson's Disease and in MPP+-Induced Neurons via Promoting the Conversion of proNGF to NGF

Insufficient production of nerve growth factor (NGF) is implicated in Parkinson's disease (PD). We recently discovered that caffeic acid derivative N-propargyl caffeamide (PACA) not only potentiated NGF-induced neurite outgrowth but also attenuated 6-hydroxydopamine neurotoxicity in neuronal culture. The aim of the present study was to investigate whether PACA could increase NGF levels against 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP) neurotoxicity in a mouse PD model. We induced parkinsonism in mice by intraperitoneal injection of MPTP for seven consecutive days. Animal motor functions were assessed by rotarod test and pole test. Our results showed that PACA ameliorated motor impairments in MPTP-challenged mice. Based on Western blot analysis and/or immunofluorescence staining of NGF and tyrosine hydroxylase (TH), PACA preserved TH levels in the midbrain substantia nigra pars compacta. PACA also increased NGF expression while it decreased proNGF accumulation. Interestingly, NGF was widely induced in the midbrains including astrocytes. To elucidate the mechanisms by which PACA induces NGF, we focused on the effects of PACA on two neurotrophic signaling pathways, the PI3K and MEK pathways. We found that PACA induced the phosphorylation of Akt, ERK, and CREB against MPTP-mediated alterations. Importantly, PACA increased NGF levels and subsequently induced TrkA activation in MPTP-treated mice. Consistently, PACA also increased NGF levels in dopaminergic PC12 cells and primary rat midbrain neurons against N-methyl-4-phenylpyridinium iodide (MPP⁺) toxicity. ERK and PI3K inhibitors attenuated the effects of PACA on NGF levels. Collectively, our results suggest that PACA may rescue NGF insufficiency via sequential activation of PI3K/Akt, ERK1/2, and CREB signaling pathways. Graphical Abstract ᅟ.

The natural product 4,10-aromadendranediol induces neuritogenesis in neuronal cells in vitro through activation of the ERK pathway

Recent studies focus on promoting neurite outgrowth to remodel the central nervous network after brain injury. Currently, however, there are few drugs treating brain diseases in the clinic by enhancing neurite outgrowth. In this study, we established an NGF-induced PC12 differentiation model to screen novel compounds that have the potential to induce neuronal differentiation, and further characterized 4,10-Aromadendranediol (ARDD) isolated from the dried twigs of the Baccharis gaudichaudiana plant, which exhibited the capability of promoting neurite outgrowth in neuronal cells in vitro. ARDD (1, 10 μmol/L) significantly enhanced neurite outgrowth in NGF-treated PC12 cells and N1E115 cells in a time-dependent manner. In cultured primary cortical neurons, ARDD (5, 10 μmol/L) not only significantly increased neurite outgrowth but also increased the number of neurites on the soma and the number of bifurcations. Further analyses showed that ARDD (10 μmol/L) significantly increased the phosphorylation of ERK1/2 and the downstream GSK-3β, subsequently induced β-catenin expression and up-regulated the gene expression of the Wnt ligands Fzd1 and Wnt3a in neuronal cells. The neurite outgrowth-promoting effect of ARDD in neuronal cells was abolished by pretreatment with the specific ERK1/2 inhibitor PD98059, but was partially reversed by XAV939, an inhibitor of the Wnt/β-catenin pathway. ARDD also increased the expression of BDNF, CREB and GAP-43 in N1E115 cells, which was reversed by pretreatment with PD98059. In N1E115 cells subjected to oxygen and glucose deprivation (OGD), pretreatment with ARDD (1-10 μmol/L) significantly enhanced the phosphorylation of ERK1/2 and induced neurite outgrowth. These results demonstrated that the natural product ARDD exhibits neurite outgrowth-inducing activity in neurons via activation of the ERK signaling pathway, which may be beneficial to the treatment of brain diseases.

Protective Effect of PPARγ Agonists on Cerebellar Tissues Oxidative Damage in Hypothyroid Rats

The aim of the current study was to investigate the effects of peroxisome proliferator-activated receptor gamma (PPARγ) agonists on cerebellar tissues oxidative damage in hypothyroid rats. The animals included seven groups: group I (control), the animals received drinking water; group II, the animals received 0.05% propylthiouracil (PTU) in drinking water; besides PTU, the animals in groups III, IV, V, VI, and VII, were injected with 20 mg/kg vitamin E (Vit E), 10 or 20 mg/kg pioglitazone, and 2 or 4 mg/kg rosiglitazone, respectively. The animals were deeply anesthetized and the cerebellar tissues were removed for biochemical measurements. PTU administration reduced thiol content, superoxide dismutase (SOD), and catalase (CAT) activities in the cerebellar tissues while increasing malondialdehyde (MDA) and nitric oxide (NO) metabolites. Vit E, pioglitazone, and rosiglitazone increased thiol, SOD, and CAT in the cerebellar tissues while reducing MDA and NO metabolites. The results of present study showed that, similar to Vit E, both rosiglitazone and pioglitazone as PPARγ agonists exerted protective effects against cerebellar tissues oxidative damage in hypothyroid rats.

Genipin Derivatives Protect RGC-5 from Sodium Nitroprusside-Induced Nitrosative Stress

CHR20 and CHR21 are a pair of stable diastereoisomers derived from genipin. These stereoisomers are activators of neuronal nitric oxide synthase (nNOS) and endothelial nitric oxide synthase (eNOS). In the rat retinal ganglion (RGC-5) cell model these compounds are non-toxic. Treatment of RGC-5 with 750 μM of sodium nitroprusside (SNP) produces nitrosative stress. Both genipin derivatives, however, protect these cells against SNP-induced apoptic cell death, although CHR21 is significantly more potent than CHR20 in this regard. With Western blotting we showed that the observed neuroprotection is primarily due to the activation of protein kinase B (Akt)/eNOS and extracellular signal-regulated kinase (ERK1/2) signaling pathways. Therefore, LY294002 (a phosphatidylinositol 3-kinase (PI3K) inhibitor) or PD98059 (a MAPK-activating enzyme inhibitor) abrogated the protective effects of CHR20 and CHR21. Altogether, our results show that in our experimental setup neuroprotection by the diasteromeric pair is mediated through the PI3K/Akt/eNOS and ERK1/2 signaling pathways. Further studies are needed to establish the potential of these compounds to prevent ntric oxide (NO)-induced toxicity commonly seen in many neurodegenerative diseases.

Implications of glial nitric oxide in neurodegenerative diseases

Nitric oxide (NO) is a pleiotropic janus-faced molecule synthesized by nitric oxide synthases (NOS) which plays a critical role in a number of physiological and pathological processes in humans. The physiological roles of NO depend on its local concentrations, as well as its availability and the nature of downstream target molecules. Its double-edged sword action has been linked to neurodegenerative disorders. Excessive NO production, as the evoked by inflammatory signals, has been identified as one of the major causative reasons for the pathogenesis of several neurodegenerative diseases. Moreover, excessive NO synthesis under neuroinflammation leads to the formation of reactive nitrogen species and neuronal cell death. There is an intimate relation between microglial activation, NO and neuroinflammation in the human brain. The role of NO in neuroinflammation has been defined in animal models where this neurotransmitter can modulate the inflammatory process acting on key regulatory pathways, such as those associated with excitotoxicity processes induced by glutamate accumulation and microglial activation. Activated glia express inducible NOS and produce NO that triggers calcium mobilization from the endoplasmic reticulum, activating the release of vesicular glutamate from astroglial cells resulting in neuronal death. This change in microglia potentially contributes to the increased age-associated susceptibility and neurodegeneration. In the current review, information is provided about the role of NO, glial activation and age-related processes in the central nervous system (CNS) that may be helpful in the isolation of new therapeutic targets for aging and neurodegenerative diseases.

Botanical drug puerarin coordinates with nerve growth factor in the regulation of neuronal survival and neuritogenesis via activating ERK1/2 and PI3K/Akt signaling pathways in the neurite extension process

AIM

Nerve growth factor (NGF) regulates neuronal survival and differentiation by activating extracellular signal-regulated-kinases (ERK) 1/2 and phosphoinositide-3-kinase (PI3K)/Akt pathways in two distinct processes: latency process and neurite extension process. This study was designed to investigate whether botanical drug C-glucosylated isoflavone puerarin coordinates with NGF to regulate neuritogenesis via activating ERK1/2 and PI3K/Akt in neurite extension process.

METHODS

We investigated the neuroprotective and neurotrophic activities of puerarin in MPTP-lesioned mice and dopaminergic PC12 cells. The effects of puerarin on ERK1/2, Akt, Nrf2, and HO-1 were assessed by Western blotting. The neurite outgrowth was assayed by neurite outgrowth staining kit.

RESULTS

Puerarin protected dopaminergic cells and ameliorated the behavioral impairments in MPTP-lesioned mice. Puerarin potentiated the effect of NGF on neuritogenesis in PC12 cells by >10-fold. Mechanistic studies revealed: (1) puerarin rapidly activated ERK1/2 and Akt, leading to the activation of Nrf2/heme oxygenase-1 (HO-1) pathways; (2) ERK1/2, PI3K/Akt, and HO-1 inhibitors attenuated the neuritogenic activity of puerarin. Notably, puerarin enhanced NGF-induced neuritogenesis in a timing-dependent manner.

CONCLUSION

Puerarin effectively coordinated with NGF to stimulate neuritogenesis via activating ERK1/2 and PI3K/Akt pathways in neurite extension process. These results demonstrated a general mechanism supporting the therapeutic application of puerarin-related compounds in neurodegenerative diseases.

Oxidative and Nitrosative Stress and Immune-Inflammatory Pathways in Patients with Myalgic Encephalomyelitis (ME)/Chronic Fatigue Syndrome (CFS)

Myalgic Encephalomyelitis (ME) / Chronic Fatigue Syndrome (CFS) has been classified as a disease of the central nervous system by the WHO since 1969. Many patients carrying this diagnosis do demonstrate an almost bewildering array of biological abnormalities particularly the presence of oxidative and nitrosative stress (O&NS) and a chronically activated innate immune system. The proposal made herein is that once generated chronically activated O&NS and immune-inflammatory pathways conspire to generate a multitude of self-sustaining and self-amplifying pathological processes which are associated with the onset of ME/CFS. Sources of continuous activation of O&NS and immune-inflammatory pathways in ME/CFS are chronic, intermittent and opportunistic infections, bacterial translocation, autoimmune responses, mitochondrial dysfunctions, activation of the Toll-Like Receptor Radical Cycle, and decreased antioxidant levels. Consequences of chronically activated O&NS and immune-inflammatory pathways in ME/CFS are brain disorders, including neuroinflammation and brain hypometabolism / hypoperfusion, toxic effects of nitric oxide and peroxynitrite, lipid peroxidation and oxidative damage to DNA, secondary autoimmune responses directed against disrupted lipid membrane components and proteins, mitochondrial dysfunctions with a disruption of energy metabolism (e.g. compromised ATP production) and dysfunctional intracellular signaling pathways. The interplay between all of these factors leads to self-amplifying feed forward loops causing a chronic state of activated O&NS, immune-inflammatory and autoimmune pathways which may sustain the disease.

Peroxynitrite-An ugly biofactor?

Cellular damage occurring under oxidative conditions has been ascribed mainly to the formation of peroxynitrite (ONOOH/ONOO(-)) that originates from the reaction of NO(*) with O(2) (*-). The detrimental effects of peroxynitrite are exacerbated by the reaction with CO(2) that leads to ONOOC(O)O(-), which further decays to the strong oxidant radicals NO(2) (*) and CO(3) (*-). The reaction with CO(2), however, may redirect peroxynitrite specificity. An excessive formation of peroxynitrite represents an important mechanism contributing to the DNA damage, the inactivation of metabolic enzymes, ionic pumps, and structural proteins, and the disruption of cell membranes. Because of its ability to oxidize biomolecules, peroxynitrite is implicated in an increasing list of diseases, including neurodegenerative and cardiovascular disorders, inflammation, pain, autoimmunity, cancer, and aging. However, peroxynitrite displays also protective activities: (i) at high concentrations, it shows anti-viral, anti-microbial, and anti-parasitic actions; and (ii) at low concentrations, it stimulates protective mechanisms in the cardiovascular, nervous, and respiratory systems. The detrimental effects of peroxynitrite and related reactive species are impaired by (pseudo-) enzymatic systems, mainly represented by heme-proteins (e.g., hemoglobin and myoglobin). Here, we report biochemical aspects of peroxynitrite actions being at the root of its biomedical effects.

Peroxynitrite mediates retinal neurodegeneration by inhibiting nerve growth factor survival signaling in experimental and human diabetes

OBJECTIVE

Recently we have shown that diabetes-induced retinal neurodegeneration positively correlates with oxidative stress and peroxynitrite. Studies also show that peroxynitrite impairs nerve growth factor (NGF) survival signaling in sensory neurons. However, the causal role of peroxynitrite and the impact of tyrosine nitration on diabetes-induced retinal neurodegeneration and NGF survival signaling have not been elucidated.

RESEARCH DESIGN AND METHODS

Expression of NGF and its receptors was examined in retinas from human and streptozotocin-induced diabetic rats and retinal ganglion cells (RGCs). Diabetic animals were treated with FeTPPS (15 mg x kg(-1) x day(-1) ip), which catalytically decomposes peroxynitrite to nitrate. After 4 weeks of diabetes, retinal cell death was determined by TUNEL assay. Lipid peroxidation and nitrotyrosine were determined using MDA assay, immunofluorescence, and Slot-Blot analysis. Expression of NGF and its receptors was determined by enzyme-linked immunosorbent assay (ELISA), real-time PCR, immunoprecipitation, and Western blot analyses.

RESULTS

Analyses of retinal neuronal death and NGF showed ninefold and twofold increases, respectively, in diabetic retinas compared with controls. Diabetes also induced increases in lipid peroxidation, nitrotyrosine, and the pro-apoptotic p75(NTR) receptor in human and rat retinas. These effects were associated with tyrosine nitration of the pro-survival TrkA receptor, resulting in diminished phosphorylation of TrkA and its downstream target, Akt. Furthermore, peroxynitrite induced neuronal death, TrkA nitration, and activation of p38 mitogen-activated protein kinase (MAPK) in RGCs, even in the presence of exogenous NGF. FeTPPS prevented tyrosine nitration, restored NGF survival signal, and prevented neuronal death in vitro and in vivo.

CONCLUSIONS

Together, these data suggest that diabetes-induced peroxynitrite impairs NGF neuronal survival by nitrating TrkA receptor and enhancing p75(NTR) expression.

Peroxynitrite transforms nerve growth factor into an apoptotic factor for motor neurons

Nerve growth factor (NGF) overexpression and increased production of peroxynitrite occur in several neurodegenerative diseases. We investigated whether NGF could undergo posttranslational oxidative or nitrative modifications that would modulate its biological activity. Compared to native NGF, peroxynitrite-treated NGF showed an exceptional ability to induce p75(NTR)-dependent motor neuron apoptosis at physiologically relevant concentrations. Whereas native NGF requires an external source of nitric oxide (NO) to induce motor neuron death, peroxynitrite-treated NGF induced motor neuron apoptosis in the absence of exogenous NO. Nevertheless, NO potentiated the apoptotic activity of peroxynitrite-modified NGF. Blocking antibodies to p75(NTR) or downregulation of p75(NTR) expression by antisense treatment prevented motor neuron apoptosis induced by peroxynitrite-treated NGF. We investigated what oxidative modifications were responsible for inducing a toxic gain of function and found that peroxynitrite induced tyrosine nitration in a dose-dependent manner. Moreover, peroxynitrite triggered the formation of stable high-molecular-weight oligomers of NGF. Preventing tyrosine nitration by urate abolished the effect of peroxynitrite on NGF apoptotic activity. These results indicate that the oxidation of NGF by peroxynitrite enhances NGF apoptotic activity through p75(NTR) 10,000-fold. To our knowledge, this is the first known posttranslational modification that transforms a neurotrophin into an apoptotic agent.

The physiology and pathophysiology of nitric oxide in the brain

Nitric oxide (NO) is a molecule with pleiotropic effects in different tissues. NO is synthesized by NO synthases (NOS), a family with four major types: endothelial, neuronal, inducible and mitochondrial. They can be found in almost all the tissues and they can even co-exist in the same tissue. NO is a well-known vasorelaxant agent, but it works as a neurotransmitter when produced by neurons and is also involved in defense functions when it is produced by immune and glial cells. NO is thermodynamically unstable and tends to react with other molecules, resulting in the oxidation, nitrosylation or nitration of proteins, with the concomitant effects on many cellular mechanisms. NO intracellular signaling involves the activation of guanylate cyclase but it also interacts with MAPKs, apoptosis-related proteins, and mitochondrial respiratory chain or anti-proliferative molecules. It also plays a role in post-translational modification of proteins and protein degradation by the proteasome. However, under pathophysiological conditions NO has damaging effects. In disorders involving oxidative stress, such as Alzheimer's disease, stroke and Parkinson's disease, NO increases cell damage through the formation of highly reactive peroxynitrite. The paradox of beneficial and damaging effects of NO will be discussed in this review.

Minocycline protects basal forebrain cholinergic neurons from mu p75-saporin immunotoxic lesioning

Two prominent characteristics of Alzheimer's disease are basal forebrain cholinergic degeneration and neuroinflammation characterized by glial activation and the release of pro-inflammatory cytokines. Mu p75- saporin (SAP) is a novel immunotoxin that mimics the selective loss of basal forebrain cholinergic neurons and induces cognitive impairment in mice. We report that cholinergic cell loss in the medial septal nucleus and ventral diagonal band after i.c.v. injection of mu p75-SAP is accompanied by simultaneous activation of microglia and astrocytes in the basal forebrain region as well as significant memory loss. Consistent with a role of glial cells in the pathology of Alzheimer's disease, minocycline, a second-generation tetracycline with known anti-inflammatory and neuroprotective properties, attenuated mu p75-SAP-induced cholinergic cell loss, glial activation and transcription of downstream pro-inflammatory mediators. In addition to neuroprotection, minocycline treatment mitigated the cognitive impairment that appears to be a functional consequence of mu p75-SAP lesioning. The current study demonstrates that glial-related inflammation plays a significant role in the selective neurotoxicity of mu p75-SAP, and suggests that minocycline may provide a viable therapeutic option for degenerating cholinergic systems.

Neuroprotective efficacy and therapeutic time window of peroxynitrite decomposition catalysts in focal cerebral ischemia in rats

Free radicals have been implicated in cerebral ischemia reperfusion (IR) injury. Massive production of nitric oxide and superoxide results in continuous formation of peroxynitrite even several hours after IR insult. This can produce DNA strand nicks, hydroxylation and/or nitration of cytosolic components of neuron, leading to neuronal death. Peroxynitrite decomposition catalysts 5,10,15,20-tetrakis(N-methyl-4'-pyridyl)porphyrinato iron (III) (FeTMPyP) and 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrinato iron (III) (FeTPPS) have been demonstrated to protect neurons in in vitro cultures; however, their neuroprotective efficacy in cerebral IR injury has not been explored. In the present study, we investigated the efficacy and the therapeutic time window of FeTMPyP and FeTPPS in focal cerebral ischemia (FCI). FCI was induced according to the middle cerebral artery occlusion (MCAO) method. After 2 h of MCAO and 70 h of reperfusion, the extent of neurological deficits, infarct and edema volume were measured in Sprague-Dawley rats. FeTMPyP and FeTPPS were administered at different time points 2, 6, 9 and 12 h post MCAO. FeTMPyP and FeTPPS (3 mg kg(-1), i.v.) treatment at 2 and 6 h post MCAO produced significant reduction in infarct volume, edema volume and neurological deficits. However, treatment at latter time points did not produce significant neuroprotection. Significant reduction of peroxynitrite in blood and nitrotyrosine in brain sections was observed on FeTMPyP and FeTPPS treatment. As delayed treatment of FeTMPyP and FeTPPS produced neuroprotection, we tested whether treatment had any influence over the apoptotic neuronal death. DNA fragmentation and in situ nick end-labeling assays showed that FeTMPyP and FeTPPS treatment reduced IR injury-induced DNA fragmentation. In conclusion, peroxynitrite decomposition catalysts (FeTMPyP and FeTPPS) produced prominent neuroprotection even if administered 6 h post MCAO and the neuroprotective effect is at least in part due to the reduction of peroxynitrite and apoptosis.

Aluminum, NO, and nerve growth factor neurotoxicity in cholinergic neurons

Several neurotoxic compounds, including Al, NO, and beta-amyloid may contribute to the impairment or loss of brain cholinergic neurons in the course of various neurodegenerative diseases. Genotype and phenotypic modifications of cholinergic neurons may determine their variable functional competency and susceptibility to reported neurotoxic insults. Hybrid, immortalized SN56 cholinergic cells from mouse septum may serve as a model for in vitro cholinotoxicity studies. Differentiation by various combinations of cAMP, retinoic acid, and nerve growth factor may provide cells of different morphologic maturity as well as activities of acetylcholine and acetyl-CoA metabolism. In general, differentiated cells appear to be more susceptible to neurotoxic signals than the non-differentiated ones, as evidenced by loss of sprouting and connectivity, decreases in choline acetyltransferase and pyruvate dehydrogenase activities, disturbances in acetyl-CoA compartmentation and metabolism, insufficient or excessive acetylcholine release, as well as increased expression of apoptosis markers. Each neurotoxin impaired both acetylcholine and acetyl-CoA metabolism of these cells. Activation of p75 or trkA receptors made either acetyl-CoA or cholinergic metabolism more susceptible to neurotoxic influences, respectively. Neurotoxins aggravated detrimental effects of each other, particularly in differentiated cells. Thus brain cholinergic neurons might display a differential susceptibility to Al and other neurotoxins depending on their genotype or phenotype-dependent variability of the cholinergic and acetyl-CoA metabolism.