Neuroinflammation and cerebrovascular disease in old age: a translational medicine perspective

Early Brain Injury After Subarachnoid Hemorrhage: Incidence and Mechanisms

Aneurysmal subarachnoid hemorrhage is a devastating condition causing significant morbidity and mortality. While outcomes from subarachnoid hemorrhage have improved in recent years, there continues to be significant interest in identifying therapeutic targets for this disease. In particular, there has been a shift in emphasis toward secondary brain injury that develops in the first 72 hours after subarachnoid hemorrhage. This time period of interest is referred to as the early brain injury period and comprises processes including microcirculatory dysfunction, blood-brain-barrier breakdown, neuroinflammation, cerebral edema, oxidative cascades, and neuronal death. Advances in our understanding of the mechanisms defining the early brain injury period have been accompanied by improved imaging and nonimaging biomarkers for identifying early brain injury, leading to the recognition of an elevated clinical incidence of early brain injury compared with prior estimates. With the frequency, impact, and mechanisms of early brain injury better defined, there is a need to review the literature in this area to guide preclinical and clinical study.

Age-Associated Resilience Against Ischemic Injury in Mice Exposed to Transient Middle Cerebral Artery Occlusion

Ischemic stroke is the leading cause of death and disability. Although stroke mainly affects aged individuals, animal research is mostly one on young rodents. Here, we examined the development of ischemic injury in young (9-12-week-old) and adult (72-week-old) C57BL/6 and BALB/c mice exposed to 30 min of intraluminal middle cerebral artery occlusion (MCAo). Post-ischemic reperfusion did not differ between young and adult mice. Ischemic injury assessed by infarct area and blood-brain barrier (BBB) integrity assessed by IgG extravasation analysis was smaller in adult compared with young mice. Microvascular viability and neuronal survival assessed by CD31 and NeuN immunohistochemistry were higher in adult than young mice. Tissue protection was associated with stronger activation of cell survival pathways in adult than young mice. Microglial/macrophage accumulation and activation assessed by F4/80 immunohistochemistry were more restricted in adult than young mice, and pro- and anti-inflammatory cytokine and chemokine responses were reduced by aging. By means of liquid chromatography-mass spectrometry, we identified a hitherto unknown proteome profile comprising the upregulation of glycogen degradation-related pathways and the downregulation of mitochondrial dysfunction-related pathways, which distinguished post-ischemic responses of the aged compared with the young brain. Our study suggests that aging increases the brain's resilience against ischemic injury.

HIV Promotes Neurocognitive Impairment by Damaging the Hippocampal Microvessels

Current evidence suggests that mild cerebrovascular changes could induce neurodegeneration and contribute to HIV-associated neurocognitive disease (HAND) in HIV patients. We investigated both the quantitative and qualitative impact of HIV infection on brain microvessels, especially on hippocampal microvessels, which are crucial for optimal O2 supply, and thus for maintaining memory and cognitive abilities. The results obtained using cultured human brain microvascular endothelial cells (HBMEC) were reproduced using a suitable mouse model and autopsied human HIV hippocampus. In HBMEC, we found significantly higher oxidative stress-dependent apoptotic cell loss following 5 h of treatment of GST-Tat (1 µg/ml) compared to GST (1 µg/ml) control. We noticed complete recovery of HBMEC cells after 24 h of GST-Tat treatment, due to temporal degradation or inactivation of GST-Tat. Interestingly, we found a sustained increase in mitochondrial oxidative DNA damage marker 8-OHdG, as well as an increase in hypoxia-inducible factor hypoxia-inducible factor-1α (HIF-1α). In our mouse studies, upon short-term injection of GST-Tat, we found the loss of small microvessels (mostly capillaries) and vascular endothelial growth factor (VEGF), but not large microvessels (arterioles and venules) in the hippocampus. In addition to capillary loss, in the post-mortem HIV-infected human hippocampus, we observed large microvessels with increased wall cells and perivascular tissue degeneration. Together, our data show a crucial role of Tat in inducing HIF-1α-dependent inhibition of mitochondrial transcriptional factor A (TFAM) and dilated perivascular space. Thus, our results further define the underlying molecular mechanism promoting mild cerebrovascular disease, neuropathy, and HAND pathogenesis in HIV patients.

Molecular Mechanisms of Neuroimmune Crosstalk in the Pathogenesis of Stroke

Stroke disrupts the homeostatic balance within the brain and is associated with a significant accumulation of necrotic cellular debris, fluid, and peripheral immune cells in the central nervous system (CNS). Additionally, cells, antigens, and other factors exit the brain into the periphery via damaged blood–brain barrier cells, glymphatic transport mechanisms, and lymphatic vessels, which dramatically influence the systemic immune response and lead to complex neuroimmune communication. As a result, the immunological response after stroke is a highly dynamic event that involves communication between multiple organ systems and cell types, with significant consequences on not only the initial stroke tissue injury but long-term recovery in the CNS. In this review, we discuss the complex immunological and physiological interactions that occur after stroke with a focus on how the peripheral immune system and CNS communicate to regulate post-stroke brain homeostasis. First, we discuss the post-stroke immune cascade across different contexts as well as homeostatic regulation within the brain. Then, we focus on the lymphatic vessels surrounding the brain and their ability to coordinate both immune response and fluid homeostasis within the brain after stroke. Finally, we discuss how therapeutic manipulation of peripheral systems may provide new mechanisms to treat stroke injury.

Cell senescence in neuropathology: A focus on neurodegeneration and tumours

The study of cell senescence is a burgeoning field. Senescent cells can modify the cellular microenvironment through the secretion of a plethora of biologically active products referred to as the senescence-associated secretory phenotype (SASP). The consequences of these paracrine signals can be either beneficial for tissue homeostasis, if senescent cells are properly cleared and SASP activation is transient, or result in organ dysfunction, when senescent cells accumulate within the tissues and SASP activation is persistent. Several studies have provided evidence for the role of senescence and SASP in promoting age-related diseases or driving organismal ageing. The hype about senescence has been further amplified by the fact that a group of drugs, named senolytics, have been used to successfully ameliorate the burden of age-related diseases and increase health and life span in mice. Ablation of senescent cells in the brain prevents disease progression and improves cognition in murine models of neurodegenerative conditions. The role of senescence in cancer has been more thoroughly investigated, and it is now accepted that senescence is a double-edged sword that can paradoxically prevent or promote tumourigenesis in a context-dependent manner. In addition, senescence induction followed by senolytic treatment is starting to emerge as a novel therapeutic avenue that could improve current anti-cancer therapies and reduce tumour recurrence. In this review, we discuss recent findings supporting the role of cell senescence in the pathogenesis of neurodegenerative diseases and in brain tumours. A better understanding of senescence is likely to result in the development of novel and efficacious anti-senescence therapies against these brain pathologies.

The Role of Oxidative Stress in Early Brain Injury after Subarachnoid Hemorrhage

This review focuses on the problem of oxidative stress in early brain injury (EBI) after spontaneous subarachnoid hemorrhage (SAH). EBI involves complex pathophysiological mechanisms, including oxidative stress. In the first section, we describe the main sources of free radicals in EBI. There are several sources of excessive generation of free radicals from mitochondrial free radicals’ generation and endoplasmic reticulum stress, to hemoglobin and enzymatic free radicals’ generation. The second part focuses on the disruption of antioxidant mechanisms in EBI. The third section describes some newly found molecular mechanisms and pathway involved in oxidative stress after EBI. The last section is dedicated to the pathophysiological mechanisms through which free radicals mediate early brain injury.

Efficacy and safety of vascular intervention combined with intravenous thrombolysis in treatment of acute intracranial arterial occlusion

Efficacy and safety of vascular intervention combined with intravenous thrombolysis (IVT) was investigated in the treatment of acute intracranial arterial occlusion (AIAO). Ninety-two patients with AIAO treated in People's Hospital of Tongchuan from January 2014 to February 2016 were enrolled in this retrospective study. Forty-two patients were treated with vascular intervention (control group), while another 50 patients were treated with vascular intervention combined with IVT (study group). They were observed in terms of the improvement of clinical efficacy after treatment, the comparison of complications after treatment, the National Institute of Health Stroke Scale (NIHSS) score after treatment, the modified Rankin Scale (mRS) score at 3 months after treatment, and the Mini-Mental State Examination (MMSE) score at 3 months after treatment. Compared with those in the control group, patients in the study group had statistically significantly higher marked effectiveness and statistically significantly lower ineffectiveness (P=0.018), and a statistically significantly higher overall effective rate (P=0.042). The NIHSS score in the study group was statistically significantly lower than that in the control group after treatment (P=0.001). There was a statistically significant difference between the two groups in the mRS score at 3 months after treatment (Z=8.764, P>0.05). Compared with those in the control group, patients in the study group had a statistically significantly higher MMSE score after treatment, and a statistically significantly lower total incidence of postoperative complications (P=0.001). Vascular intervention combined with IVT has good efficacy and high safety in the treatment of AIAO, and the combination can statistically significantly improve patients' quality of life, so it has a good clinical application value.

Protective role of diosgenin against hyperglycaemia-mediated cerebral ischemic brain injury in zebrafish model of type II diabetes mellitus

Impairment in glucose regulation is an indicatory effect capable of mediating multiple dysfunction such as cerebrovascular disorder with ischemia and brain damage inclusive. This study aims at investigating the glucose-lowering and neuroprotective capability of Diosgenin (DG) towards hyperglycemia-induced cerebral injury in a developed type 2 diabetes mellitus (T2DM) Zebrafish (ZF) model. T2DM was developed in ZF with 20 mg/kg body weight (b.w) multiple-low dose (MLD) Streptozotocin (STZ) for 28 days. Different doses of 20 mg/kg b.w (DG1) and 40 mg/kg b.w (DG2) DG was intraperitoneally administered twice in 7 days for a period of 28 days after T2DM was completely developed. Weight and behavioral changes were monitored and the catalytic activity including the plasma glucose level of diseased and treated ZF was spectrometrically estimated. Histopathological studies were employed to image the brain pathological condition during disease and treatment. SPSS was used as the statistical tool for result analysis and comparison of data obtained. STZ significantly (^###p < 0.001) induced hyperglycemia when compared to control as plasma glucose increases from 101.56 ± 4.52 mgdL⁻¹ to 175.87 ± 6.00 mg/dL. Our results have indicated a marked reduction in glucose concentration from a mean average of 175.87 ± 6.00 mgdL⁻¹ to 105.68 ± 4.48 mgdL⁻¹ and 82.06 ± 7.27 mgdL⁻¹ in DG 1 and DG 2 respectively. Catalytic activity significantly decreases (p < 0.05) from 206.42 ± 30.77 unit/mL to 123.85 ± 29.99 unit/mL at a minimum and maximum value of 103.21 and 275.23 in diseased ZF respectively. On DG treatment, catalytic activity significantly (p < 0.01) rise from 101.58 ± 11.29 and 130.73 ± 27.52 to 130.98 ± 17.13 and 255.96 ± 30.34 with DG1 and DG2 treatment respectively. Studies on the behavioral pattern of STZ-induced anxiolytic effect on ZF confirmed changes in the number of transitions and time spent in both Novel tank test (NTT) and Dark/light test (LDT). Histopathological analysis confirmed the cerebral cortex with inflammatory brain cells in the diseased condition and an attenuation of damage posed revealed in diseased state was largely reversed with DG. As compared to the normal control, a significant (^#p < 0.05 and ^###p < 0.001) changes in weight of fishes were recorded and DG1 and DG2 significantly promotes (***p < 0.001) body weight and improves the irregularities in weight of ZF during disease progression. Our study confirms that the potential of DG towards the management of hyperglycemia and hyperglycemia–mediated cerebral ischemic injury is through its blood glucose-lowering properties, anti-inflammatory activity, antioxidant effect, and anxiolytic capabilities.

Exosome-shuttled miR-92b-3p from ischemic preconditioned astrocytes protects neurons against oxygen and glucose deprivation

Ischemic preconditioning (IPC) exerts protective effects against ischemic cerebral injury. In the present study, an in vitro model of cerebral ischemia (oxygen and glucose deprivation, OGD) was established to investigate the neuroprotective mechanism of IPC. We found that conditioned medium (C.M.) from astrocytes rather than neurons nor microglia cell line BV2 exerted neuroprotection. Moreover, exosomes derived from OGD preconditioned astrocytes can be taken up by neurons and attenuated OGD-induced neuron death and apoptosis. High-throughput microRNA (miRNA) sequencing revealed that miR-92b-3p levels in exosomes released from preconditioned astrocytes were increased. Overexpression of miR-92b-3p in neurons with miR-92b-3p mimic achieved the same protective effects as C.M. from astrocytes. Thus, we propose that the mechanism of IPC may associate with astrocytes, and that exosome-mediated miR-92b-3p shuttle from preconditioned astrocytes to neurons participate in these process.

Dysfunction of Cerebrovascular Endothelial Cells: Prelude to Vascular Dementia

Vascular dementia (VaD) is the second most common type of dementia after Alzheimer's disease (AD), characterized by progressive cognitive impairment, memory loss, and thinking or speech problems. VaD is usually caused by cerebrovascular disease, during which, cerebrovascular endothelial cells (CECs) are vulnerable. CEC dysfunction occurs before the onset of VaD and can eventually lead to dysregulation of cerebral blood flow and blood-brain barrier damage, followed by the activation of glia and inflammatory environment in the brain. White matter, neuronal axons, and synapses are compromised in this process, leading to cognitive impairment. The present review summarizes the mechanisms underlying CEC impairment during hypoperfusion and pathological role of CECs in VaD. Through the comprehensive examination and summarization, endothelial nitric oxide synthase (eNOS)/nitric oxide (NO) signaling pathway, Ras homolog gene family member A (RhoA) signaling pathway, and CEC-derived caveolin-1 (CAV-1) are proposed to serve as targets of new drugs for the treatment of VaD.

Task-related changes in degree centrality and local coherence of the posterior cingulate cortex after major cardiac surgery in older adults

OBJECTIVES

Older adults often display postoperative cognitive decline (POCD) after surgery, yet it is unclear to what extent functional connectivity (FC) alterations may underlie these deficits. We examined for postoperative voxel-wise FC changes in response to increased working memory load demands in cardiac surgery patients and nonsurgical controls.

EXPERIMENTAL DESIGN

Older cardiac surgery patients (n = 25) completed a verbal N-back working memory task during MRI scanning and cognitive testing before and 6 weeks after surgery; nonsurgical controls with cardiac disease (n = 26) underwent these assessments at identical time intervals. We measured postoperative changes in degree centrality, the number of edges attached to a brain node, and local coherence, the temporal homogeneity of regional functional correlations, using voxel-wise graph theory-based FC metrics. Group × time differences were evaluated in these FC metrics associated with increased N-back working memory load (2-back > 1-back), using a two-stage partitioned variance, mixed ANCOVA.

PRINCIPAL OBSERVATIONS

Cardiac surgery patients demonstrated postoperative working memory load-related degree centrality increases in the left dorsal posterior cingulate cortex (dPCC; p < .001, cluster p-FWE < .05). The dPCC also showed a postoperative increase in working memory load-associated local coherence (p < .001, cluster p-FWE < .05). dPCC degree centrality and local coherence increases were inversely associated with global cognitive change in surgery patients (p < .01), but not in controls.

CONCLUSIONS

Cardiac surgery patients showed postoperative increases in working memory load-associated degree centrality and local coherence of the dPCC that were inversely associated with postoperative global cognitive outcomes and independent of perioperative cerebrovascular damage.

Inhibition of leukotriene B4 synthesis protects against early brain injury possibly via reducing the neutrophil-generated inflammatory response and oxidative stress after subarachnoid hemorrhage in rats

Leukotriene B4 (LTB4) is a highly potent neutrophil chemoattractant and neutrophils induces inflammatory response and oxidative stress when they recruit to and infiltrate in the injuried/inflamed site, such as the brain parenchyma after aneurysmal subarachnoid hemorrhage (SAH). This study is to investigate the potential effects of inhibition of LTB4 synthesis on neutrophil recruitment, inflammatory response and oxidative stress, as well as early brain injury (EBI) in rats after SAH. A pre-chiasmatic cistern SAH model of rats was used in this experiment. SC 57461A was used to inhibit LTB4 synthesis via intracerebroventricular injection. The brain tissues of temporal lobe after SAH were analyzed. Neuronal injury, brain edema and neurological function were evaluated to investigate the development of EBI. We found that inhibition of LTB4 synthesis after SAH could reduce the level of myeloperoxidase, alleviate the inflammatory response and oxidative stress, and reduce neuronal death in the brain parenchyma, and ameliorate brain edema and neurological behavior impairment at 24h after SAH. These results suggest that inhibition of LTB4 synthesis might alleviate EBI after SAH possibly via reducing the neutrophil-generated inflammatory response and oxidative stress.

Bridging Type 2 Diabetes and Alzheimer's Disease: Assembling the Puzzle Pieces in the Quest for the Molecules With Therapeutic and Preventive Potential

Type 2 diabetes (T2D) and Alzheimer's disease (AD) are two age-related amyloid diseases that affect millions of people worldwide. Broadly supported by epidemiological data, the higher incidence of AD among type 2 diabetic patients led to the recognition of T2D as a tangible risk factor for the development of AD. Indeed, there is now growing evidence on brain structural and functional abnormalities arising from brain insulin resistance and deficiency, ultimately highlighting the need for new approaches capable of preventing the development of AD in type 2 diabetic patients. This review provides an update on overlapping pathophysiological mechanisms and pathways in T2D and AD, such as amyloidogenic events, oxidative stress, endothelial dysfunction, aberrant enzymatic activity, and even shared genetic background. These events will be presented as puzzle pieces put together, thus establishing potential therapeutic targets for drug discovery and development against T2D and diabetes-induced cognitive decline-a heavyweight contributor to the increasing incidence of dementia in developed countries. Hoping to pave the way in this direction, we will present some of the most promising and well-studied drug leads with potential against both pathologies, including their respective bioactivity reports, mechanisms of action, and structure-activity relationships.

Dysfunction of the neurovascular unit in ischemic stroke and neurodegenerative diseases: An aging effect

Current understanding on the mechanisms of brain injury and neurodegeneration highlights an appreciation of multicellular interactions within the neurovascular unit (NVU), which include the evolution of blood-brain barrier (BBB) damage, neuronal cell death or degeneration, glial reaction, and immune cell infiltration. Aging is an important factor that influences the integrity of the NVU. The age-related physiological or pathological changes in the cellular components of the NVU have been shown to increase the vulnerability of the NVU to ischemia/reperfusion injury or neurodegeneration, and to result in deteriorated brain damage. This review describes the impacts of aging on each NVU component and discusses the mechanisms by which aging increases NVU sensitivity to stroke and neurodegenerative diseases. Prophylactic or therapeutic perspectives that may delay or diminish aging and thus prevent the incidence of these neurological disorders will also be reviewed.

Cerebral ischemic damage in diabetes: an inflammatory perspective

Stroke is one of the leading causes of death worldwide. A strong inflammatory response characterized by activation and release of cytokines, chemokines, adhesion molecules, and proteolytic enzymes contributes to brain damage following stroke. Stroke outcomes are worse among diabetics, resulting in increased mortality and disabilities. Diabetes involves chronic inflammation manifested by reactive oxygen species generation, expression of proinflammatory cytokines, and activation/expression of other inflammatory mediators. It appears that increased proinflammatory processes due to diabetes are further accelerated after cerebral ischemia, leading to increased ischemic damage. Hypoglycemia is an intrinsic side effect owing to glucose-lowering therapy in diabetics, and is known to induce proinflammatory changes as well as exacerbate cerebral damage in experimental stroke. Here, we present a review of available literature on the contribution of neuroinflammation to increased cerebral ischemic damage in diabetics. We also describe the role of hypoglycemia in neuroinflammation and cerebral ischemic damage in diabetics. Understanding the role of neuroinflammatory mechanisms in worsening stroke outcome in diabetics may help limit ischemic brain injury and improve clinical outcomes.

Resting-State Cardiac Workload is Related to Both Increased Neocortical Aggregation of Amyloid-β and Relative Impairments in Spatial Working Memory in Pre-Clinical Alzheimer's Disease

We sought to determine whether there is any association between a cardiac workload marker, rate pressure product (RPP), working memory, and cortical amyloid-β (Aβ) burden in 63 cognitively normal midlife adults (Mage = 62.8 years; range = 55 to 75 years) at risk for Alzheimer's disease (AD). The results show a small-to-moderate relationship between increasing cardiac workload (at rest) and neocortical amyloidosis in individuals at the preclinical stage of AD. Moreover, increasing RPP was linearly related to increasing relative impairments on a spatial working memory task (R2 = 0.30), but only for those individuals with neuroimaging evidence suggestive of preclinical AD. These results support a relationship between the aggregation of Aβ protein plaques in the neocortex, increased cognitive impairment, and more inefficient myocardial oxygen use in the absence of significant metabolic demands.

Notch signaling in cerebrovascular diseases (Review)

The Notch signaling pathway is a crucial regulator of numerous fundamental cellular processes. Increasing evidence suggests that Notch signaling is involved in inflammation and oxidative stress, and thus in the progress of cerebrovascular diseases. In addition, Notch signaling in cerebrovascular diseases is associated with apoptosis, angiogenesis and the function of blood-brain barrier. Despite the contradictory results obtained to date as to whether Notch signaling is harmful or beneficial, the regulation of Notch signaling may provide a novel strategy for the treatment of cerebrovascular diseases.

Neuroprotective effect of paeoniflorin on H2O2-induced apoptosis in PC12 cells by modulation of reactive oxygen species and the inflammatory response

Paeoniflorin (PF) is a product derived from Paeoniae Radix and is commonly prescribed in traditional Chinese medicine. PF has been reported to exhibit neuroprotective, anti-ischemic, antioxidant, anti-inflammatory and anticancer effects. The neuroprotective properties of PF have been demonstrated in animal models of various neuropathologies. The present study investigated the effects of PF on hydrogen peroxide (H₂O₂)-induced apoptosis in PC12 cells, to improve the understanding of the mechanisms underlying its neuroprotective properties. The H₂O₂-induced apoptosis of PC12 cells resulted in a reduction in the B-cell lymphoma 2 (Bcl-2)/Bcl-2-associated X protein ratio and the activation of caspase-3. PF treatment was observed to reverse the apoptotic process and to modulate the expression levels of a number of apoptosis-associated proteins. Furthermore, PF significantly mitigated the H₂O₂-induced reduction in cell viability, in addition to scavenging reactive oxygen species and preventing the release of lactate dehydrogenase from the PC12 cells. In addition, the apoptosis-associated activation of nuclear factor (NF)-κB was inhibited in the PF-treated cells, and the expression levels of tumor necrosis factor α and interleukin (IL)-1β were reduced. In conclusion, the present study demonstrated that PF was able to reduce H₂O₂-induced toxicity by blocking the activation of the neuroinflammatory factor NF-κB. These results suggest that PF may be a valuable neuroprotective agent for the treatment of neurological disease and injury.

Effects of high-fat diet on neuronal damage, gliosis, inflammatory process and oxidative stress in the hippocampus induced by transient cerebral ischemia

In this study, we investigated the effects of a normal diet (ND) and high-fat diet (HFD) on delayed neuronal death in the gerbil hippocampal CA1 region after transient cerebral ischemia. In the HFD-fed gerbils, ischemia-induced hyperactivity was significantly increased and neuronal damage was represented more severely compared to the ND-fed gerbils. Ischemia-induced glial activation was accelerated in the HFD-fed gerbils. Cytokines including interleukin-2 and -4 were more sensitive in the hippocampal CA1 region of the HFD-fed gerbils after ischemia-reperfusion. Additionally, we found that decreased 4-HNE and SODs immunoreactivity and protein levels in the hippocampal CA1 region of the HFD-fed gerbils after ischemia-reperfusion. These results indicate that HFD may lead to the exacerbated effects on ischemia-induced neuronal death in the hippocampal CA1 region after ischemia-reperfusion. These effects of HFD may be associated with more accelerated activations of glial cells and imbalance of pro- and anti-inflammatory cytokines and/or antioxidants after transient cerebral ischemia.

Alzheimer's disease and immunotherapy

Alzheimer's disease (AD) is a growing health care epidemic. It is the most common cause of dementia and its incidence is rising. Age, which influences the oxidative and inflammatory states of the brain, is the most important risk factor. Currently there is no disease modifying treatments available for this irreversible, progressive debilitating disease. Immunotherapy represents an emerging, potentially disease modifying strategy aimed at reducing the pathological lesions of AD and facilitating cognitive improvement. Many clinical trials are currently underway. This literature review highlights current knowledge regarding the physiology of aging and how it relates to the pathogenesis of AD. In addition, immunotherapy is discussed in the context of its mechanism, current studies and future goals.

Effects of different doses of doxepin on passive avoidance learning in rats

BACKGROUND

Studies have shown that Doxepin has anti-inflammatory effects and reduces oxidative stress. Due to the fact that other tricyclic antidepressants have been shown to have neuroprotective effects, this study aimed to investigate the effects of different doses of doxepin on passive avoidance learning in rats.

MATERIALS AND METHODS

Old male Wistar rats were used in this study. Doxepin was administered intraperitoneally (1, 5 and 10 mg/kg) for 21 days. Passive avoidance learning test was used for evaluation of learning and memory. Rats received foot electrical shock on fifteen day, and step through latencies were evaluated one week after the electrical shock in retention phase.

RESULTS

Administration of Doxepin considerably increased the step through latencies in the rats that received the doses of 1 and 5 mg/kg (P < 0.05). However, in the dose of 10 mg/kg, there wasn't any significant change comparing to control group.

CONCLUSION

These results indicate that Doxepin has desirable effects on cognitive functions in low doses. Therefore, Doxepin can be considered as memory enhancers that understanding the underling mechanisms need further investigation.

Long-term estrogen deprivation leads to elevation of Dickkopf-1 and dysregulation of Wnt/β-Catenin signaling in hippocampal CA1 neurons

Surgically menopausal women incur a 2- to 5-fold increased risk for dementia and mortality from neurological diseases, but the mechanisms underlying these increased risks remain unclear. Previously, we demonstrated that after global cerebral ischemia (GCI), 17β-estradiol (E2 or estrogen) suppresses hippocampal elevation of the Wnt antagonist Dickkopf-1 (Dkk1), a neurodegenerative factor. We, thus, hypothesized that prolonged loss of E2 may lead to dysregulation of neural Dkk1 and Wnt/β-Catenin signaling, which could contribute to an increased risk of neurodegeneration. To test this hypothesis, we examined the effect of short-term (1 week - STED) and long-term E2 deprivation (10 weeks - LTED) via ovariectomy upon basal and E2-regulated Dkk1 levels and Wnt/β-Catenin signaling in the hippocampal CA1 region following GCI. In STED rats, E2 exerted robust neuroprotection against GCI, suppressed post-ischemic elevation of Dkk1, and enhanced pro-survival Wnt/β-Catenin signaling, effects that were lost in LTED rats. Intriguingly, LTED rats displayed modest basal changes in Dkk1 and survivin expression. Further work showed that c-Jun N-terminal Kinase (JNK) mediated GCI-induced changes in Dkk1 and survivin, and JNK inhibition afforded neuroprotection in LTED rats. Finally, we extended our findings to natural aging, as 24-month-old, reproductively senescent female rats also displayed a modest increase in basal Dkk1 in the CA1, which consistently co-localized with the apoptotic marker TUNEL after GCI and coincided with a loss of E2 neuroprotection. As a whole, this study supports the "critical period hypothesis" and further suggests that perimenopausal estradiol replacement may prevent neurodegenerative changes in the hippocampus by maintaining favorable Wnt/β-Catenin signaling.

Triggers and effectors of oxidative stress at blood-brain barrier level: relevance for brain ageing and neurodegeneration

As fundamental research advances, it is becoming increasingly clear that a clinically expressed disease implies a mixture of intertwining molecular disturbances. Oxidative stress is one of such pathogenic pathways involved in virtually all central nervous system pathologies, infectious, inflammatory, or degenerative in nature. Since brain homeostasis largely depends on integrity of blood-brain barrier (BBB), many studies focused lately on BBB alteration in a wide spectrum of brain diseases. The proper two-way molecular transfer through BBB depends on several factors, including the functional status of its tight junction (TJ) complexes of proteins sealing neighbour endothelial cells. Although there is abundant experimental work showing that oxidative stress associates BBB permeability alteration, less is known about its implications, at molecular level, in TJ protein expression or TJ-related cell signalling. In this paper, oxidative stress is presented as a common pathway for different brain pathogenic mechanisms which lead to BBB dysregulation. We revise here oxidative-induced molecular mechanisms of BBB disruption and TJ protein expression alteration, in relation to ageing and neurodegeneration.

Age-related decrease in cerebrovascular-derived neuroprotective proteins: effect of acetaminophen

As the population ages, the need for effective methods to maintain brain function in older adults is increasingly pressing. Vascular disease and neurodegenerative disorders commonly co-occur in older persons. Cerebrovascular products contribute to the neuronal milieu and have important consequences for neuronal viability. In this regard vascular derived neuroprotective proteins, Such as vascular endothelial growth factor (VEGF), pigment epithelium-derived factor (PEDF), and pituitary adenylate cyclase activating peptide (PACAP) are important for maintaining neuronal viability, especially in the face of injury and disease. The objective of this study is to measure and compare levels of VEGF, PEDF and PACAP released from isolated brain microvessels of Fischer 344 rats at 6, 12, 18, and 24 months of age. Addition of acetaminophen to isolated brain microvessels is employed to determine whether this drug affects vascular expression of these neuroprotective proteins. Experiments on cultured brain endothelial cells are performed to explore the mechanisms/mediators that regulate the effect of acetaminophen on endothelial cells. The data indicate cerebrovascular expression of VEGF, PEDF and PACAP significantly decreases with age. The age-associated decrease in VEGF and PEDF is ameliorated by addition of acetaminophen to isolated brain microvessels. Also, release of VEGF, PEDF, and PACAP from cultured brain endothelial cells decreases with exposure to the oxidant stressor menadione. Acetaminophen treatment upregulates VEGF, PEDF and PACAP in brain endothelial cells exposed to oxidative stress. The effect of acetaminophen on cultured endothelial cells is in part inhibited by the selective thrombin inhibitor hirudin. The results of this study suggest that acetaminophen may be a useful agent for preserving cerebrovascular function. If a low dose of acetaminophen can counteract the decrease in vascular-derived neurotrophic factors evoked by age and oxidative stress, this drug might be useful for improving brain function in the elderly.

The sensorimotor and cognitive deficits in rats following 90- and 120-min transient occlusion of the middle cerebral artery

Middle cerebral artery occlusion (MCAO) is the most commonly used method to study the neurological and histological outcomes and the pathological mechanisms of ischaemic stroke. The current work compares sensorimotor and cognitive deficits and the infarct volume in rats following a transient 90- or 120-min MCAO, which allows the appropriate behavioural tests to be chosen based on the goal and design of the experiment. In the beam-walking test, we found significant differences between the 90- and 120-min MCAO groups in the number of foot faults made with the impaired hindlimb on post-stroke days 3, 7 and 14. In the cylinder test, a difference between the 90- and 120-min groups was observed on post-operation day 14. The responses to tactile and proprioceptive stimulation were impaired to a similar extent after 90- and 120-min MCAO in the vibrissae-evoked forelimb-placing and limb-placing tests. Moreover, we found significant memory impairment in the 120-min MCAO group 6 days after the acquisition trial. The brain tissue damage was significantly higher after 120-min occlusion of the MCA compared with 90-min occlusion; the infarct volumes were 13% and 25% of the contralateral hemispheres, respectively. In conclusion, both the 90- and 120-min occlusion models result in a significant impairment of sensorimotor, tactile and proprioceptive function, but memory impairment is only observed in the 120-min MCAO group. The beam-walking and cylinder tests detected neurological dysfunction after the 120-min MCAO, whereas the limb-placing and vibrissae-evoked forelimb-placing tests were able to evaluate the neurological dysfunction in rats after 90- and 120-min MCAO.