Oxidative stress in a rat model of chronic gliosis

Low-intensity pulsed ultrasound stimulation (LIPUS) modulates microglial activation following intracortical microelectrode implantation

Microglia are important players in surveillance and repair of the brain. Implanting an electrode into the cortex activates microglia, produces an inflammatory cascade, triggers the foreign body response, and opens the blood-brain barrier. These changes can impede intracortical brain-computer interfaces performance. Using two-photon imaging of implanted microelectrodes, we test the hypothesis that low-intensity pulsed ultrasound stimulation can reduce microglia-mediated neuroinflammation following the implantation of microelectrodes. In the first week of treatment, we found that low-intensity pulsed ultrasound stimulation increased microglia migration speed by 128%, enhanced microglia expansion area by 109%, and a reduction in microglial activation by 17%, indicating improved tissue healing and surveillance. Microglial coverage of the microelectrode was reduced by 50% and astrocytic scarring by 36% resulting in an increase in recording performance at chronic time. The data indicate that low-intensity pulsed ultrasound stimulation helps reduce the foreign body response around chronic intracortical microelectrodes.

Oxidative damage in neurodegeneration: roles in the pathogenesis and progression of Alzheimer disease

Alzheimer disease (AD) is associated with multiple etiologies and pathological mechanisms, among which oxidative stress (OS) appears as a major determinant. Intriguingly, OS arises in various pathways regulating brain functions, and it seems to link different hypotheses and mechanisms of AD neuropathology with high fidelity. The brain is particularly vulnerable to oxidative damage, mainly because of its unique lipid composition, resulting in an amplified cascade of redox reactions that target several cellular components/functions ultimately leading to neurodegeneration. The present review highlights the "OS hypothesis of AD," including amyloid beta-peptide-associated mechanisms, the role of lipid and protein oxidation unraveled by redox proteomics, and the antioxidant strategies that have been investigated to modulate the progression of AD. Collected studies from our groups and others have contributed to unraveling the close relationships between perturbation of redox homeostasis in the brain and AD neuropathology by elucidating redox-regulated events potentially involved in both the pathogenesis and progression of AD. However, the complexity of AD pathological mechanisms requires an in-depth understanding of several major intracellular pathways affecting redox homeostasis and relevant for brain functions. This understanding is crucial to developing pharmacological strategies targeting OS-mediated toxicity that may potentially contribute to slow AD progression as well as improve the quality of life of persons with this severe dementing disorder.

Low-intensity pulsed ultrasound stimulation (LIPUS) modulates microglial activation following intracortical microelectrode implantation

Microglia are important players in surveillance and repair of the brain. Their activation mediates neuroinflammation caused by intracortical microelectrode implantation, which impedes the application of intracortical brain-computer interfaces (BCIs). While low-intensity pulsed ultrasound stimulation (LIPUS) can attenuate microglial activation, its potential to modulate the microglia-mediated neuroinflammation and enhance the bio-integration of microelectrodes remains insufficiently explored. We found that LIPUS increased microglia migration speed from 0.59±0.04 to 1.35±0.07 µm/hr on day 1 and enhanced microglia expansion area from 44.50±6.86 to 93.15±8.77 µm 2 /min on day 7, indicating improved tissue healing and surveillance. Furthermore, LIPUS reduced microglial activation by 17% on day 6, vessel-associated microglia ratio from 70.67±6.15 to 40.43±3.87% on day 7, and vessel diameter by 20% on day 28. Additionally, microglial coverage of the microelectrode was reduced by 50% in week 1, indicating better tissue-microelectrode integration. These data reveal that LIPUS helps resolve neuroinflammation around chronic intracortical microelectrodes.

The relationships between neuroglial and neuronal changes in Alzheimer's disease, and the related controversies II:

Since the original description of Alzheimer´s disease (AD), research into this condition has mainly focused on assessing the alterations to neurons associated with dementia, and those to the circuits in which they are involved. In most of the studies on human brains and in many models of AD, the glial cells accompanying these neurons undergo concomitant alterations that aggravate the course of neurodegeneration. As a result, these changes to neuroglial cells are now included in all the "pathogenic cascades" described in AD. Accordingly, astrogliosis and microgliosis, the main components of neuroinflammation, have been integrated into all the pathogenic theories of this disease, as discussed in this part of the two-part monograph that follows an accompanying article on gliopathogenesis and glioprotection. This initial reflection verified the implication of alterations to the neuroglia in AD, suggesting that these cells may also represent therapeutic targets to prevent neurodegeneration. In this second part of the monograph, we will analyze the possibilities of acting on glial cells to prevent or treat the neurodegeneration that is the hallmark of AD and other pathologies. Evidence of the potential of different pharmacological, non-pharmacological, cell and gene therapies (widely treated) to prevent or treat this disease is now forthcoming, in most cases as adjuncts to other therapies. A comprehensive AD multimodal therapy is proposed in which neuronal and neuroglial pharmacological treatments are jointly considered, as well as the use of new cell and gene therapies and non-pharmacological therapies that tend to slow down the progress of dementia.

Molecular insights of NADPH oxidases and its pathological consequences

Reactive oxygen species (ROS), formed by the partial reduction of oxygen, were for a long time considered to be a byproduct of cellular metabolism. Since, increase in cellular levels of ROS results in oxidative stress leading to damage of nucleic acids, proteins, and lipids resulting in numerous pathological conditions; ROS was considered a bane for aerobic species. Hence, the discovery of NADPH oxidases (NOX), an enzyme family that specifically generates ROS as its prime product came as a surprise to redox biologists. NOX family proteins participate in various cellular functions including cell proliferation and differentiation, regulation of genes and protein expression, apoptosis, and host defence immunological response. Balanced expression and activation of NOX with subsequent production of ROS are critically important to regulate various genes and proteins to maintain homeostasis of the cell. However, dysregulation of NOX activation leading to enhanced ROS levels is associated with various pathophysiologies including diabetes, cardiovascular diseases, neurodegenerative diseases, ageing, atherosclerosis, and cancer. Although our current knowledge on NOX signifies its importance in the normal functioning of various cellular pathways; yet the choice of ROS producing enzymes which can tip the scale from homeostasis toward damage, as mediators of biological functions remain an oddity. Though the role of NOX in maintaining normal cellular functions is now deemed essential, yet its dysregulation leading to catastrophic events cannot be denied. Hence, this review focuses on the involvement of NOX enzymes in various pathological conditions imploring them as possible targets for therapies. SIGNIFICANCE OF THE STUDY: The NOXs are multi-subunit enzymes that generate ROS as a prime product. NOX generated ROS are usually regulated by various molecular factors and play a vital role in different physiological processes. The dysregulation of NOX activity is associated with pathological consequences. Recently, the dynamic proximity of NOX enzymes with different molecular signatures of pathologies has been studied extensively. It is essential to identify the precise role of NOX machinery in its niche during the progression of pathology. Although inhibition of NOX could be a promising approach for therapeutic interventions, it is critical to expand the current understanding of NOX's dynamicity and shed light on their molecular partners and regulators.

Amitriptyline Reduces Sepsis-Induced Brain Damage Through TrkA Signaling Pathway

Sepsis can induce acute and chronic changes in the central nervous system termed sepsis-associated encephalopathy (SAE). Not only cognitive deficits but also anxiety, depression, and post-traumatic stress disorder are common in severe sepsis survivors. In this study, we demonstrated that amitriptyline, a classic tricyclic antidepressant, reduced sepsis-induced brain damage through the tropomyosin receptor kinase A (TrkA) signaling pathway. Amitriptyline ameliorated neuronal loss assessed by Nissl staining in a mouse cecal ligation and puncture (CLP)-induced sepsis model. Furthermore, amitriptyline reduced early gliosis assessed by immunofluorescence and late cognitive deficits assessed by the Morris water maze (MWM) test. Moreover, amitriptyline treatment attenuated oxidative stress indicated by less superoxide dismutase (SOD) and catalase (CAT) activity consumption and malondialdehyde (MDA) accumulation. Interestingly, those protective effects of amitriptyline could be abolished by GW441756, a TrkA signaling pathway inhibitor. Immunoblot directly showed that TrkA signaling pathway-associated proteins, such as Akt and GSK3β, were involved in the neuroprotective effects of amitriptyline. Thus, amitriptyline appears to be an encouraging candidate to treat cognitive deficits and depression after severe sepsis.

The role of astrocytes in oxidative stress of central nervous system: A mixed blessing

Central nervous system (CNS) maintains a high level of metabolism, which leads to the generation of large amounts of free radicals, and it is also one of the most vulnerable organs to oxidative stress. Emerging evidences have shown that, as the key homeostatic cells in CNS, astrocytes are deeply involved in multiple aspects of CNS function including oxidative stress regulation. Besides, the redox level in CNS can in turn affect astrocytes in morphology and function. The complex and multiple roles of astrocytes indicate that their correct performance is crucial for the normal functioning of the CNS, and its dysfunction may result in the occurrence and progression of various neurological disorders. To date, the influence of astrocytes in CNS oxidative stress is rarely reviewed. Therefore, in this review we sum up the roles of astrocytes in redox regulation and the corresponding mechanisms under both normal and different pathological conditions.

Nonsteroidal anti-inflammatory drug, indomethacin improves spatial memory and NMDA receptor function in aged animals

A redox-mediated decrease in N-methyl-D-aspartate (NMDA) receptor function contributes to psychiatric diseases and impaired cognition during aging. Inflammation provides a potential source of reactive oxygen species for inducing NMDA receptor hypofunction. The present study tested the hypothesis that the nonsteroidal anti-inflammatory drug indomethacin, which improves spatial episodic memory in aging rats, would enhance NMDA receptor function through a shift in the redox state. Male F344 young and aged rats were prescreened using a 1-day version of the water maze task. Animals were then treated with the indomethacin or vehicle, delivered in a frozen milk treat (orally, twice per day, 18 days), and retested on the water maze. Indomethacin treatment enhanced water maze performance. Hippocampal slices were prepared for examination of CA3-CA1 synaptic responses, long-term potentiation, and NMDA receptor-mediated synaptic responses. No effect of treatment was observed for the total synaptic response. Long-term potentiation magnitude and NMDA receptor input-output curves were enhanced for aged indomethacin-treated animals. To examine redox regulation of NMDA receptors, a second group of aged animals was treated with indomethacin or vehicle, and the effect of the reducing agent, dithiothreitol ([DTT], 0.5 mM) on NMDA receptor-mediated synaptic responses was evaluated. As expected, DTT increased the NMDA receptor response and the effect of DTT was reduced by indomethacin treatment. The results indicate that indomethacin acted to diminish the age-related and redox-mediated NMDA receptor hypofunction and suggest that inflammation contributes to cognitive impairment through an increase in redox stress.

Pretreatment with N-acetyl cysteine suppresses chronic reactive astrogliosis following maternal nanoparticle exposure during gestational period

Early pregnant employees are potentially and unintendedly exposed to industrial chemicals including nanoparticles. Developmental toxicity of nanoparticle exposure has been concerned because exposure to fine particle including carbon black nanoparticle (CB-NP) during the brain developmental stage enhances the risk of brain disorders. Maternal CB-NP exposure dose-dependently induces astrogliosis, which is an abnormal increase in the reactive astrocytes with glial fibrillary acidic protein (GFAP) and aquaporin-4 overexpression due to the destruction of nearby neurons and blood vessels. The present study aimed to investigate protective effects of antioxidants on the histopathological denaturation with astrogliosis following maternal CB-NP exposure in offspring mice, thereby to evaluate the role of oxidative stress on the developmental toxicity. Pregnant ICR mice were treated with CB-NP by intranasal instillation on gestational days 5 and 9. N-acetyl cysteine (NAC) or ascorbic acid was intraperitoneally administered to the pregnant mice 1 h prior to CB-NP instillation. The brains were collected from 6- to 12-week-old offspring mice and analyzed using western blotting and immunohistochemistry. NAC suppressed GFAP overexpression in 6- and 12-week-old offspring mice following maternal CB-NP exposure. However, NAC did not suppress aquaporin-4 overexpression following maternal CB-NP exposure. Ascorbic acid did not suppress, but rather slightly and significantly enhanced the expression of GFAP and aquaporin-4. These results indicate that astrogliosis by maternal CB-NP exposure is partially prevented by NAC pretreatment. Oxidative stress is a possible key factor of developmental neurotoxicity of maternal NP exposure. This study will contribute to elucidating the mechanisms underlying the effects of developmental neurotoxicity of NPs.

Vascular insufficiency, not inflammation, contributes to chronic gliosis in a rat CNS transplantation model

PURPOSE

There is considerable variability in the extent and nature of the glial response to injury and neurodegeneration. Transplantation of fetal cortical tissue onto the brain of neonatal host rats or mice results in region-specific changes dependent on where the fetal tissue is placed. These changes include chronic astrocytic and microglial gliosis, oxidative stress, and altered metabolism of a number of proteins associated with the pathogenesis of Alzheimer's disease. Such changes are only observed in heterotopic (cortex-to-midbrain) grafts and are not observed in homotopic cortex-to-cortex grafts. We investigated two possible triggers for the region-specific gliosis observed in our transplant model hypothesizing that either i) poor vascularization and lack of blood brain barrier integrity or ii) an inflammatory response initiated by the transplantation process, contributed to establishing chronic pathological changes.

METHODS

We analyzed the time course of neovascularization, blood brain barrier permeability and inflammation using a combination of immunohistochemistry, enzyme-linked immunosorbant assay and Evan's blue dye extravasation techniques.

RESULTS

Blood brain barrier permeability and altered neovascularization occurred prior to the onset of gliosis in heterotopic grafts.

CONCLUSION

These data suggest that ischemic conditions and blood brain barrier damage can be a primary mechanism that initiates chronic gliosis and associated inflammatory changes in central nervous system tissue.

Aging, cortical injury and Alzheimer's disease-like pathology in the guinea pig brain

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized histopathologically by the abnormal deposition of the proteins amyloid-beta (Aβ) and tau. A major issue for AD research is the lack of an animal model that accurately replicates the human disease, thus making it difficult to investigate potential risk factors for AD such as head injury. Furthermore, as age remains the strongest risk factor for most of the AD cases, transgenic models in which mutant human genes are expressed throughout the life span of the animal provide only limited insight into age-related factors in disease development. Guinea pigs (Cavia porcellus) are of interest in AD research because they have a similar Aβ sequence to humans and thus may present a useful non-transgenic animal model of AD. Brains from guinea pigs aged 3-48 months were examined to determine the presence of age-associated AD-like pathology. In addition, fluid percussion-induced brain injury was performed to characterize mechanisms underlying the association between AD risk and head injury. No statistically significant changes were detected in the overall response to aging, although we did observe some region-specific changes. Diffuse deposits of Aβ were found in the hippocampal region of the oldest animals and alterations in amyloid precursor protein processing and tau immunoreactivity were observed with age. Brain injury resulted in a strong and sustained increase in amyloid precursor protein and tau immunoreactivity without Aβ deposition, over 7 days. Guinea pigs may therefore provide a useful model for investigating the influence of environmental and non-genetic risk factors on the pathogenesis of AD.

Astrogliosis in the brain of obese Zucker rat: a model of metabolic syndrome

Metabolic syndrome (MetS) is a disorder characterized primarily by the development of insulin resistance. Insulin resistance and subsequent hyperinsulinemia, originating from abdominal obesity, increases the risk of cerebrovascular and cardiovascular disease and all-cause mortality. Obesity is probably a risk factor for Alzheimer's disease and vascular dementia and is associated with impaired cognitive function. The obese Zucker rat (OZR) represents a model of type 2 diabetes exhibiting a moderate degree of arterial hypertension and of increased oxidative stress. To clarify the possible relationships between MetS and brain damage, the present study has investigated brain microanatomy in OZRs compared with their littermate controls lean Zucker rats (LZRs). Male OZRs and LZRs of 12 weeks of age were used. Their brain was processed for immunochemical and immunohistochemical analysis of glial fibrillary acidic protein (GFAP). In frontal and parietal cortex of OZRs a significant increase in the number of GFAP immunoreactive astrocytes was observed. Similar findings were found in the hippocampus, where an increased number of GFAP immunoreactive astrocytes were detected in the CA1 and CA3 subfields and dentate gyrus of OZRs compared to the LZRs. These findings indicating the occurrence of brain injury accompanied by astrogliosis in OZRs suggest that these rats, developed as an animal model of type 2 diabetes, may also represent a model for assessing the influence of MetS on brain. The identification of neurodegenerative changes in OZRs may represent the first step for better characterizing neuronal involvement in this model of MetS and possible treatment for countering it.

Ovariectomy and 17beta-estradiol replacement do not alter beta-amyloid levels in sheep brain

The benefits of estrogen replacement as a preventative treatment for Alzheimer's disease (AD) are subject to debate. Because the effects of estrogen depletion and replacement on accumulation of the neurotoxic beta-amyloid (A beta) peptide in transgenic animal models of AD have been variable, we examined A beta levels and oxidative stress in a nontransgenic animal model. Sheep have traditionally been used as a model for human reproduction; however because they share 100% sequence homology with the human form of A beta, they may also have potential as a nontransgenic model for A beta biology. The effect of ovariectomy and estrogen replacement administered for 6 months via slow-release implant was examined in the brain of 4.5-yr-old sheep. A beta levels were measured by ELISA, and protein levels of the amyloid precursor protein (APP), APP C-terminal fragments (C100), and presenilin-1 were examined semiquantitatively by Western blot as markers of APP processing. Markers of oxidative stress were examined semiquantitatively by Western blot [4-hydroxy-2(E)-nonenal] and oxyblot (protein carbonyls). We found no effects of estrogen depletion and supplementation in terms of AD-related biochemical markers, including A beta levels, APP processing, and oxidative stress levels. Evidence of a trend toward increased P450 side-chain cleavage enzyme levels in the hippocampus of ovariectomized and estrogen supplemented sheep suggests that neurosteroidogenesis may compensate for gonadal estrogen depletion; however, these findings cannot explain the lack of effect of estrogen supplementation on APP processing. It is possible that supraphysiological doses of estrogen are necessary to yield antiamyloidogenic and antioxidative benefits in ovariectomized sheep.