Effects of naproxen on immune responses in a colchicine-induced rat model of Alzheimer's disease

Targeting NLRP3-Mediated Neuroinflammation in Alzheimer’s Disease Treatment

Alzheimer’s disease (AD) is the most common cause of dementia in the general population and, to date, constitutes a major therapeutic challenge. In the pathogenesis of AD, aggregates of amyloid β (Aβ) and neurofibrillary tangles (NFTs) containing Tau-microtubule-associated protein (tau) are known to trigger a neuroinflammatory response with subsequent formation of an inflammasome. In particular, the NOD-like receptor pyrin domain-containing 3 (NLRP3) inflammasome is thought to play a crucial role in AD-related pathology. While the mechanisms for NLRP3 activation are not fully understood, it has been demonstrated that, after detection of protein aggregates, NLRP3 induces pro-inflammatory cytokines, such as interleukin 18 (IL-18) or interleukin 1β (IL-1β), that further potentiate AD progression. Specific inhibitors of NLRP3 that exhibit various mechanisms to attenuate the activity of NLRP3 have been tested in in vivo studies and have yielded promising results, as shown by the reduced level of tau and Aβ aggregates and diminished cognitive impairment. Herein, we would like to summarize the current state of knowledge on NLRP3 inflammasome priming, activation, and its actual role in AD pathogenesis, and to characterize the NLRP3 inhibitors that have been studied most and their impact on AD-related pathology.

Naproxen as a potential candidate for promoting rivastigmine anti-Alzheimer activity against aluminum chloride-prompted Alzheimer's-like disease in rats; neurogenesis and apoptosis modulation as a possible underlying mechanism

BACKGROUND AND AIM

Alzheimer's disease (AD) is one of the leading causes of dependence and disability among the elderly worldwide. The traditional anti-Alzheimer medication, rivastigmine, one of the cholinesterase inhibitors (ChEIs), fails to achieve a definitive cure. We tested the hypothesis that naproxen administration to the rivastigmine-treated aluminum chloride (AlCl3) Alzheimer's rat model could provide an additive neuroprotective effect compared to rivastigmine alone.

MATERIALS AND METHODS

The studied groups were control (Cont), AlCl3 treated (Al), rivastigmine treated (RIVA), naproxen treated (Napro), and combined rivastigmine and naproxen treated (RIVA + Napro). Rats' memory, spatial learning, and cognitive behavior were assessed followed by evaluation of hippocampal acetylcholinesterase (AChE) activity. Hippocampal and cerebellar histopathology were thoroughly examined. Activated caspase-3 and the neuroepithelial stem cells marker; nestin expressions were immunohistochemically assayed.

RESULTS

AD rats displayed significantly impaired memory and cognitive function, augmented hippocampal AChE activity; massive neurodegeneration associated with enhanced astrogliosis, apoptosis, and impaired neurogenesis. Except for the enhancement of neurogenesis and suppression of apoptosis, the combination therapy had no additional neuroprotective benefit over rivastigmine-only therapy.

CONCLUSION

Naproxen's efficacy was established by its ability to function at the cellular level, improved neurogenesis, and decreased, apoptosis without having an additional mitigating impact on cognitive impairment in rivastigmine-treated AD rats.

Neuroinflammation in neurological disorders: pharmacotherapeutic targets from bench to bedside

Neuroinflammation is one of the host defensive mechanisms through which the nervous system protects itself from pathogenic and or infectious insults. Moreover, neuroinflammation occurs as one of the most common pathological outcomes in various neurological disorders, makes it the promising target. The present review focuses on elaborating the recent advancement in understanding molecular mechanisms of neuroinflammation and its role in the etiopathogenesis of various neurological disorders, especially Alzheimer's disease (AD), Parkinson's disease (PD), and Epilepsy. Furthermore, the current status of anti-inflammatory agents in neurological diseases has been summarized in light of different preclinical and clinical studies. Finally, possible limitations and future directions for the effective use of anti-inflammatory agents in neurological disorders have been discussed.

The protective effects of naproxen against interleukin-1β (IL-1β)- induced damage in human umbilical vein endothelial cells (HUVECs)

Non-steroidal anti-inflammatory drugs (NSAIDs) are one of the most widely used medications in the world. Naproxen is an NSAID with relatively low selectivity for cyclooxygenase-2 (COX-2), thereby having decreased risk for cardiovascular (CV) events. However, it is unclear whether naproxen might provide protection against atherosclerosis, an underlying cause of numerous cardiovascular diseases (CVDs). In the present study, we exposed human umbilical vein endothelial cells to interleukin-1β (IL-1β), a key cytokine involved in atherogenesis, with or without naproxen. Our findings indicate that naproxen could protect against IL-1β-induced damage by improving cell viability and preventing cell death. Additionally, naproxen suppressed the expression of the cytokines IL-6, IL-12, and tumor necrosis factor-α (TNF-α), and downregulated the expression of vascular endothelial growth factor (VEGF) and tissue factor (TF) induced by IL-1β. Importantly, naproxen also inhibited the attachment of monocytes to endothelial cells, which was achieved through Krüppel-like factor 6 (KLF6)-mediated reduced expression of intracellular adhesion molecule-1 (ICAM-1) and E-selectin. These findings suggest that naproxen may aid in the prevention of atherosclerosis by exerting cardioprotective effects beyond low COX-2-selectivity.

The inhibition of LSD1 via sequestration contributes to tau-mediated neurodegeneration

Tauopathies are a class of neurodegenerative diseases associated with pathological tau. Despite many advances in our understanding of these diseases, the direct mechanism through which tau contributes to neurodegeneration remains poorly understood. Previously, our laboratory implicated the histone demethylase LSD1 in tau-induced neurodegeneration by showing that LSD1 localizes to pathological tau aggregates in Alzheimer's disease cases, and that it is continuously required for the survival of hippocampal and cortical neurons in mice. Here, we utilize the P301S tauopathy mouse model to demonstrate that pathological tau can exclude LSD1 from the nucleus in neurons. In addition, we show that reducing LSD1 in these mice is sufficient to highly exacerbate tau-mediated neurodegeneration and tau-induced gene expression changes. Finally, we find that overexpressing LSD1 in the hippocampus of tauopathy mice, even after pathology has formed, is sufficient to significantly delay neurodegeneration and counteract tau-induced expression changes. These results suggest that inhibiting LSD1 via sequestration contributes to tau-mediated neurodegeneration. Thus, LSD1 is a promising therapeutic target for tauopathies such as Alzheimer's disease.

Soybean isoflavone ameliorates cognitive impairment, neuroinflammation, and amyloid β accumulation in a rat model of Alzheimer's disease

Oxidative stress and neuroinflammatory changes appear to be the early events involved in AD's development and progression. The present study was designed to assess the effect of soybean isoflavone extract (SIFE) against colchicine-induced cognitive dysfunction and oxidative stress in male rats.Fifty adult male Wistar albino rats were divided into five groups: control, ACSF-treated group, soybean isoflavones (SIF)-treated group, colchicine (COL)-treated group, and SIF + COL-treated group. We found that an intracerebroventricular (icv) injection of a single dose of colchicine (7.5 μg/rat bilaterally) resulted in learning deficits in rats subjected to the Morris water maze task associated with marked oxidative damage and decreased acetyl cholinesterase (AChE) activity. In addition, COL caused significant increase in amyloid beta peptide 1-42 (β, amyloid 1-42) interleukin-1β (IL-1β), tumor necrosis factor-α (TNFα), cyclooxygenase-2 (COX-2) and TNF-α genes expression in the brain, and glial fibrillary acidic protein (GFAP) in cortical astrocytes in the brain cortex.Treatment with SIFE (80 mg/kg b.wt) daily for 14 days followed by a single dose of COL significantly reduced the elevated oxidative stress parameters and restored the reduced antioxidant activities. Besides, the administration of SIFE reversed the overproduction of β, amyloid 1-42, pro-inflammatory cytokines, and GFAP in the brain. The obtained results were confirmed by histological observations that clearly indicate a neuroprotective effect of SIF against AD.

Effect of N-Acetyl Cysteine on Intracerebroventricular Colchicine Induced Cognitive Deficits, Beta Amyloid Pathology, and Glial Cells

Among the many factors responsible for the cognitive decline in Alzheimer's disease, beta amyloid protein and plaque formation is crucial. This amyloid pathology is associated with activation of glial cells and oxidative stress but whether oxidative stress activates beta amyloid protein in the neurons is not clear. Further the expression of microglia is also known to vary during pathogenesis of beta amyloid plaques. The aim of the present study is to evaluate the antioxidant effect of NAC on amyloid pathology and cognition and also to investigate the link between amyloid pathology and glial cells activation. Intracerebroventricular colchicine in rats known mimics human AD in many aspects including memory loss, oxidative stress, and hyper phosphorylation of tau protein. The animal groups consisted of age matched control, sham operated, AD, and NAC treated in AD models of rats. Cognitive function was evaluated in active avoidance test; beta amyloid protein, beta amyloid plaques, astrocytes, and microglia cells were quantified using immunohistochemistry in hippocampal and prefrontal cortices. Colchicine has resulted in significant cognitive loss, increased intraneuronal beta amyloid protein expression, increased reactive astrocytes, and activated microglia in all the regions of the hippocampus and prefrontal cortices. The antioxidant NAC has reversed the cognitive deficits and inhibited microglia activation but failed to inhibit BAP expression and astrocytosis. Intraneuronal BAP accumulation is deleterious and known to adversely affect cognition, but in this study in spite of intraneuronal BAP accumulation, the cognition is restored. It can be postulated that NAC might have reversed the effect of intraneuronal beta amyloid protein by acting on some downstream compensatory mechanisms which needs to be explored.

Etoricoxib inhibits peripheral inflammation and alters immune responses in intracerebroventricular colchicine injected rats

The present study was designed to investigate the effectiveness of etoricoxib induced inhibition of neuroinflammation by studying the peripheral inflammatory markers and select immune parameters in intracerebroventricular colchicine injected rats (ICIR). Results showed time dependent upregulation of the inflammatory markers in the serum along with alterations of peripheral immune parameters in ICIR and dose-dependent recovery was observed upon administration of etoricoxib to ICIR; most of these effects were greater with the longer duration of study. The present study indicates that colchicine induced neuroinflammation may cause systemic inflammation and alteration of immune responses which are mediated by increased cox- 2 activity.

Cerebral mTOR signal and pro-inflammatory cytokines in Alzheimer's disease rats

As a part of Alzheimer’s disease (AD) development the mammalian target of rapamycin (mTOR) has been reported to play a crucial role in regulating cognition and can be used as a neuronal marker. Neuro-inflammation is also a cause of the pathophysiological process in AD. Thus, we examined the protein expression levels of mTOR and its downstream pathways as well as pro-inflammatory cytokines (PICs) in the brain of AD rats. We further examined the effects of blocking mTOR on PICs, namely IL-1β, IL-6 and TNF-α. Our results showed that the protein expression of p-mTOR, mTOR-mediated phosphorylation of 4E-binding protein 4 (4E-BP1) and p70 ribosomal S6 protein kinase 1 (S6K1) pathways were amplified in the hippocampus of AD rats compared with controls. Blocking mTOR by using rapamycin selectively enhanced activities of IL-6 and TNF-α signaling pathways, which was accompanied with an increase of Caspase-3, indicating cellular apoptosis and worsened learning performance. In conclusion, our data for the first time revealed specific signaling pathways engaged in the development of AD, including a regulatory role by the activation of mTOR in PIC mechanisms. Stimulation of mTOR is likely to play a beneficial role in modulating neurological deficits in AD.Targeting one or more of these signaling molecules may present with new opportunities for treatment and clinical management of AD

Dual Role of Vitamin C on the Neuroinflammation Mediated Neurodegeneration and Memory Impairments in Colchicine Induced Rat Model of Alzheimer Disease

The neurodegeneration in colchicine induced AD rats (cAD) is mediated by cox-2 linked neuroinflammation. The importance of ROS in the inflammatory process in cAD has not been identified, which may be deciphered by blocking oxidative stress in this model by a well-known anti-oxidant vitamin C. Therefore, the present study was designed to investigate the role of vitamin C on colchicine induced oxidative stress linked neuroinflammation mediated neurodegeneration and memory impairments along with peripheral immune responses in cAD. The impairments of working and reference memory were associated with neuroinflammation and neurodegeneration in the hippocampus of cAD. Administration of vitamin C (200 and 400 mg/kg BW) in cAD resulted in recovery of memory impairments, with prevention of neurodegeneration and neuroinflammation in the hippocampus. The neuroinflammation in the hippocampus also influenced the peripheral immune responses and inflammation in the serum of cAD and all of these parameters were also recovered at 200 and 400 mg dose of vitamin C. However, cAD treated with 600 mg dose did not recover but resulted in increase of memory impairments, neurodegeneration and neuroinflammation in hippocampus along with alteration of peripheral immune responses in comparison to cAD of the present study. Therefore, the present study showed that ROS played an important role in the colchicine induced neuroinflammation linked neurodegeneration and memory impairments along with alteration of peripheral immune responses. It also appears from the results that vitamin C at lower doses showed anti-oxidant effect and at higher dose resulted in pro-oxidant effects in cAD.

Presenilin 1 transgene addition to amyloid precursor protein overexpressing transgenic rats increases amyloid beta 42 levels and results in loss of memory retention

BACKGROUND

We previously reported the production of transgenic rats (APP21 line) that over-express human amyloid precursor protein (APP) containing Swedish and Indiana mutations. In order to generate a better model for Alzheimer's disease (AD), the APP21 rat line was used to generate double transgenic line that over-expressed Presenilin 1 (PS1) with L166P mutation in addition to APP transgene (APP + PS1 line).

RESULTS

Thirty-two double transgenic founders were generated and the ultimate transgenic founder was selected based on PS1 transgene copy number and level of amyloid-beta (Aβ)42 peptide. The APP + PS1 double transgenic rats had 38 times more PS1 in brains compared to APP rats. Behavioral assessment using Barnes maze showed that APP + PS1 rats exhibited a larger learning and memory deficit than APP21 rats. Double transgenic rats also produced more Aβ42. Histological examination of the brains showed that the APP21 rat line displayed neurofibrillary tangles and in contrast, the APP + PS1 line showed chromatolysis in hippocampal neurons and neuronal loss in CA3 region of hippocampus.

CONCLUSIONS

Due to the separate segregation of APP and PS1 transgenes in APP + PS1 double transgenic rats, this transgenic line may be a valuable model for studying the effects of various levels of APP and PS1 transgenes on various aspects of brain pathologies associated with the AD phenotype.

Impairment of blood brain barrier is related with the neuroinflammation induced peripheral immune status in intracerebroventricular colchicine injected rats: An experimental study with mannitol

The neurodegeneration in AD patients may be associated with changes of peripheral immune responses. Some peripheral immune responses are altered due to neuroinflammation in colchicine induced AD (cAD) rats. The leaky blood brain barrier (BBB) in cAD-rats may be involved in inducing peripheral inflammation, though there is no report in this regard. Therefore, the present study was designed to investigate the role of BBB in cADrats by altering the BBB in a time dependent manner with injection (i.v.) of mannitol (BBB opener). The inflammatory markers in the brain and serum along with the peripheral immune responses were measured after 30 and 60min of mannitol injection in cAD rats. The results showed higher inflammatory markers in the hippocampus and serum along with alterations in peripheral immune parameters in cAD rats. Although the hippocampal inflammatory markers did not further change after mannitol injection in cAD rats, the serum inflammatory markers and peripheral immune responses were altered and these changes were greater after 60min than that of 30min of mannitol injection. The present study shows that the peripheral immune responses in cAD rats after 30 and 60min of mannitol injection are related to magnitude of impairment of BBB in these conditions. It can be concluded from this study that impairment of BBB in cAD rats is related to the changes of peripheral immune responses observed in that condition.

Cox-2 Plays a Vital Role in the Impaired Anxiety Like Behavior in Colchicine Induced Rat Model of Alzheimer Disease

The anxiety status is changed along with memory impairments in intracerebroventricular colchicine injected rat model of Alzheimer Disease (cAD) due to neurodegeneration, which has been indicated to be mediated by inflammation. Inducible cox-2, involved in inflammation, may have important role in the colchicine induced alteration of anxiety status. Therefore, the present study was designed to investigate the role of cox-2 on the anxiety behavior (response to novelty in an elevated open field space) of cAD by inhibiting it with three different doses (10, 20, and 30 mg) of etoricoxib (a cox-2 blocker) in two time points (14 and 21 days). The results showed anxiolytic behavior in cAD along with lower serum corticosterone level, both of which were recovered at all the doses of etoricoxib on day 21. On day 14 all of the anxiety parameters showed similar results to that of day 21 at high doses but not at 10 mg/kg body weight. Results indicate that the parameters of anxiety were dependent on neuronal circuitries that were probably sensitive to etoricoxib induced blocking of neurodegeneration. The present study showed that anxiolytic behavior in cADr is predominantly due to cox-2 mediated neuroinflammation induced neurodegeneration in the brain.

Role of cox-2 mediated neuroinflammation on the neurodegeneration and cognitive impairments in colchicine induced rat model of Alzheimer's Disease

The neurodegeneration in colchicine induced AD (cAD) rats is linked with neuroinflammation. The inducible cox-2 present in the brain may participate in the neuroinflammatory process related to progressive neurodegeneration in cAD rats. The aim of this study is to investigate the role of cox-2 in the neurodegeneration and cognitive impairments in cAD rats. The parameters of memory (working and reference memory), inflammatory markers [IL-1β, TNF-α, prostaglandin E2 (PGE2), cox-2 level] and histopathology of hippocampus were measured after 21-day of i.c.v. colchicine injection in rats and compared with that of control and sham operated rats. These parameters were also measured in these 3 different groups of rats after p.o. administration of 3 different doses of etoricoxib, a cox 2 inhibitor. The impairments of working and reference memory were associated with neuroinflammation and neurodegeneration in the hippocampus and increased cox-2 and PGE2 levels in hippocampus in cAD. Administration of etoricoxib in cAD rats resulted in recovery of memory impairments, neurodegeneration and neuroinflammation in hippocampus and inhibition of cox-2 and PGE2 levels in hippocampus. It appears from the results that activation of cox-2 in cAD is related to neuroinflammation involved in neurodegeneration. Colchicine induced initial neurodegeneration may trigger cascade of events for a progressive neurodegeneration where cox-2 activation plays a critical role. Moreover, this cox-2 mediated neurodegeneration is related to impairments of memory parameters. Thus, the present study showed that the impairments of memory and neurodegeneration in the hippocampus of cAD in 21-day study are mediated by cox-2 induced neuroinflammation.

Rodent models of neuroinflammation for Alzheimer's disease

Alzheimer's disease remains incurable, and the failures of current disease-modifying strategies for Alzheimer's disease could be attributed to a lack of in vivo models that recapitulate the underlying etiology of late-onset Alzheimer's disease. The etiology of late-onset Alzheimer's disease is not based on mutations related to amyloid-β (Aβ) or tau production which are currently the basis of in vivo models of Alzheimer's disease. It has recently been suggested that mechanisms like chronic neuroinflammation may occur prior to amyloid-β and tau pathologies in late-onset Alzheimer's disease. The aim of this study is to analyze the characteristics of rodent models of neuroinflammation in late-onset Alzheimer's disease. Our search criteria were based on characteristics of an idealistic disease model that should recapitulate causes, symptoms, and lesions in a chronological order similar to the actual disease. Therefore, a model based on the inflammation hypothesis of late-onset Alzheimer's disease should include the following features: (i) primary chronic neuroinflammation, (ii) manifestations of memory and cognitive impairment, and (iii) late development of tau and Aβ pathologies. The following models fit the pre-defined criteria: lipopolysaccharide- and PolyI:C-induced models of immune challenge; streptozotocin-, okadaic acid-, and colchicine neurotoxin-induced neuroinflammation models, as well as interleukin-1β, anti-nerve growth factor and p25 transgenic models. Among these models, streptozotocin, PolyI:C-induced, and p25 neuroinflammation models are compatible with the inflammation hypothesis of Alzheimer's disease.

A comparison of neurodegeneration linked with neuroinflammation in different brain areas of rats after intracerebroventricular colchicine injection

Colchicine induces neurodegeneration, but the extent of neurodegeneration in different areas of the brain in relation to neuroinflammation remains unclear. Such information may be useful to allow for the development of a model to compare colchicine-induced neurodegeneration with other neurodegenerative diseases such as Alzheimer's Disease (AD). The present study was designed to investigate the extent of neurodegeneration along with neuroinflammation in different areas of the brain, e.g. frontal cortex, parietal cortex, occipital cortex, corpus striatum, amygdala and hippocampus, in rats along with memory impairment 21 days after a single intracerebroventricular (icv) injection of colchicine. Memory parameters were measured before and after icv colchicine injection in all test groups of rats (control, sham-operated, colchicine-injected [ICIR] rats). On Day 21 post-injection, rats from all groups were anesthesized and tissues from the various brain areas were collected for assessment of biomarkers of neuroinflammation (i.e. levels of ROS, nitrite and proinflammatory cytokines TNFα and IL-1β) and neurodegeneration (assessed histologically). The single injection of colchicine resulted in impaired memory and neurodegeneration (significant presence of plaques, Nissl granule chromatolysis) in various brain areas (frontal cortex, amygdala, parietal cortex, corpus striatum), with maximum severity in the hippocampus. While IL-1β, TNFα, ROS and nitrite levels were altered in different brain areas in the ICIR rats, these parameters had their greatest change in the hippocampus. This study showed that icv injection of colchicine caused strong neurodegeneration and neuroinflammation in the hippocampus of rats and the increases in neurodegeneration were corroborated with those of neuroinflammation at the site. The present study also showed that the extent of neurodegeneration and neuroinflammation in different brain areas of the colchicine-injected rats were AD-like and supported the fact that such rats might have the ability to serve as a sporadic model of AD.