Xanthine oxidase mediates chronic stress-induced cerebrovascular dysfunction and cognitive impairment

Xanthine oxidase (XO) mediates vascular function. Chronic stress impairs cerebrovascular function and increases the risk of stroke and cognitive decline. Our study determined the role of XO on stress-induced cerebrovascular dysfunction and cognitive decline. We measured middle cerebral artery (MCA) function, free radical formation, and working memory in 6-month-old C57BL/6 mice who underwent 8 weeks of control conditions or unpredictable chronic mild stress (UCMS) with or without febuxostat (50 mg/L), a XO inhibitor. UCMS mice had an impaired MCA dilation to acetylcholine vs. controls (p < 0.0001), and increased total free radical formation, XOR protein levels, and hydrogen peroxide production in the liver compared to controls. UCMS increased hydrogen peroxide production in the brain and cerebrovasculature compared to controls. Working memory, using the y-maze test, was impaired (p < 0.05) in UCMS mice compared to control mice. However, blocking XO using febuxostat prevented the UCMS-induced impaired MCA response, while free radical production and hydrogen peroxide levels were similar to controls in the liver and brain of UCMS mice treated with febuxostat. Further, UCMS + Feb mice did not have a significant reduction in working memory. These data suggest that the cerebrovascular dysfunction associated with chronic stress may be driven by XO, which leads to a reduction in working memory.

Partial Endothelial Nitric Oxide Synthase Deficiency Exacerbates Cognitive Deficit and Amyloid Pathology in the APPswe/PS1ΔE9 Mouse Model of Alzheimer’s Disease

Increasing evidence implicates endothelial dysfunction in the pathogenesis of Alzheimer’s disease (AD). Nitric oxide (NO) derived from endothelial NO synthase (eNOS) is essential in maintaining cerebrovascular function and can modulate the production and clearance of amyloid beta (Aβ). APPswe/PSdE1 (APP/PS1) mice display age-related Aβ accumulation and memory deficits. In order to make the model more clinically relevant with an element of endothelial dysfunction, we generated APP/PS1/eNOS+/− mice by crossing complete eNOS deficient (eNOS−/−) mice and APP/PS1 mice. APP/PS1/eNOS+/− mice at 8 months of age displayed a more severe spatial working memory deficit relative to age-matched APP/PS1 mice. Moreover, immunohistochemistry and immunoblotting revealed significantly increased Aβ plaque load in the brains of APP/PS1/eNOS+/− mice, concomitant with upregulated BACE-1 (hence increased Aβ production), downregulated insulin-degrading enzyme (hence reduced Aβ clearance) and increased immunoreactivity and expression of microglia. The present study, for the first time, demonstrated that partial eNOS deficiency exacerbated behavioral dysfunction, Aβ brain deposition, and microglial pathology in APP/PS1 mice, further implicating endothelial dysfunction in the pathogenesis of AD. The present findings also provide the scientific basis for developing preventive and/or therapeutic strategies by targeting endothelial dysfunction.

Clinical Implication of Phosphodiesterase-4-Inhibition

The pleiotropic function of 3′,5′-cyclic adenosine monophosphate (cAMP)-dependent pathways in health and disease led to the development of pharmacological phosphodiesterase inhibitors (PDE-I) to attenuate cAMP degradation. While there are many isotypes of PDE, a predominant role of PDE4 is to regulate fundamental functions, including endothelial and epithelial barrier stability, modulation of inflammatory responses and cognitive and/or mood functions. This makes the use of PDE4-I an interesting tool for various therapeutic approaches. However, due to the presence of PDE4 in many tissues, there is a significant danger for serious side effects. Based on this, the aim of this review is to provide a comprehensive overview of the approaches and effects of PDE4-I for different therapeutic applications. In summary, despite many obstacles to use of PDE4-I for different therapeutic approaches, the current data warrant future research to utilize the therapeutic potential of phosphodiesterase 4 inhibition.

The role of neutrophil gelatinase-associated lipocalin and iron homeostasis in object recognition impairment in aged sepsis-survivor rats

Older adult patients with sepsis frequently experience cognitive impairment. The roles of brain neutrophil gelatinase-associated lipocalin (NGAL) and iron in older sepsis patients remain unknown. We investigated the effects of lipopolysaccharide-induced sepsis on novel object recognition test, NGAL levels, an inflammatory mediator tumor necrosis factor-α (TNFα) levels, and iron ion levels in the hippocampus and cortex of young and aged rats. The effect of an iron chelator deferoxamine pretreatment on aged sepsis rats was also examined. Young sepsis-survivor rats did not show impaired novel object recognition, TNFα responses, or a Fe2+/Fe3+ imbalance. They showed hippocampal and cortical NGAL level elevations. Aged sepsis-survivor rats displayed a decreased object discrimination index, elevation of NGAL levels and Fe2+/Fe3+ ratio, and no TNFα responses. Pretreatment with deferoxamine prevented the reduction in the object recognition of aged sepsis-survivor rats. The elevation in hippocampal and cortical NGAL levels caused by lipopolysaccharide was not influenced by deferoxamine pretreatment. The lipopolysaccharide-induced Fe2+/Fe3+ ratio elevation was blocked by deferoxamine pretreatment. In conclusion, our findings suggest that iron homeostasis in the cortex and hippocampus contributes to the maintenance of object recognition ability in older sepsis survivors.

B Vitamins Supplementation Can Improve Cognitive Functions and May Relate to the Enhancement of Transketolase Activity in A Rat Model of Cognitive Impairment Associated with High-fat Diets

OBJECTIVE

To determine whether B vitamin treatment was sufficient to reduce cognitive impairment associated with high-fat diets in rats and to modulate transketolase (TK) expression and activity.

METHODS

To test this, we separated 50 rats into five groups that were either fed a standard chow diet (controls) or a high-fat diet (experimental groups H0, H1, H2, and H3). H0 group animals received no additional dietary supplementation, while H1 group animals were administered 100 mg/kg body weight (BW) thiamine, 100 mg/kg BW riboflavin, and 250 mg/kg BW niacin each day, and group H2 animals received daily doses of 100 mg/kg BW pyridoxine, 100 mg/kg BW cobalamin, and 5 mg/kg BW folate. Animals in the H3 group received the B vitamin regimens administered to both H1 and H2 each day.

RESULTS

Over time, group H0 exhibited greater increases in BW and fat mass relative to other groups. When spatial and memory capabilities in these animals were evaluated via conditioned taste aversion (CTA) and Morris Water Maze (MWM), we found B vitamin treatment was associated with significant improvements relative to untreated H0 controls. Similarly, B vitamin supplementation was associated with elevated TK expression in erythrocytes and hypothalamus of treated animals relative to those in H0 (P<0.05).

CONCLUSION

Together, these findings suggest B vitamin can modulate hypothalamic TK activity to reduce the severity of cognitive deficits in a rat model of obesity. As such, B vitamin supplementation may be a beneficial method for reducing cognitive dysfunction in clinical settings associated with high-fat diets.

Relationship between Cerebrospinal Fluid Matrix Metalloproteinases Levels and Brain Amyloid Deposition in Mild Cognitive Impairment

This study aimed to explore whether cerebrospinal fluid (CSF) levels of matrix metalloproteinases (MMPs), and their inhibitors (TIMPs) were associated with brain amyloid deposition, cortical glucose metabolism, and white matter lesions (WMLs) in individuals with amnestic mild cognitive impairment (MCI). A total of 33 individuals with amnestic MCI (mean age, 75.6 years) underwent ¹¹C-Pittsburgh compound B positron emission tomography (PiB-PET), ¹⁸F-fluorodeoxyglucose positron emission tomography, magnetic resonance imaging or computed tomography, and CSF analysis. PET uptake of the frontal and temporoparietal lobes and posterior cingulate gyrus was assessed using the cerebellar cortex as the reference region. WMLs were assessed by the Fazekas scale. CSF levels of MMPs and TIMPs were measured with bead-based multiplex assays. After adjusting for covariates, multiple linear regression analysis showed that CSF levels of MMP-2 were negatively correlated with global PiB uptake (p = 0.035), especially in the parietotemporal lobe and posterior cingulate gyrus (p = 0.016 and p = 0.041, respectively). Moreover, CSF levels of MMP-7 were positively correlated with the severity of WMLs (p = 0.033). CSF levels of MMP-2 and MMP-7 are associated with brain amyloid deposition and severity of WMLs, respectively. These findings provide valuable insights into the role of MMPs in amyloid β catabolism and blood-brain barrier integration at the MCI stage.

Identification of Novel Positive Allosteric Modulators of Neurotrophin Receptors for the Treatment of Cognitive Dysfunction

Alzheimer's disease (AD) is the most common neurodegenerative disorder and results in severe neurodegeneration and progressive cognitive decline. Neurotrophins are growth factors involved in the development and survival of neurons, but also in underlying mechanisms for memory formation such as hippocampal long-term potentiation. Our aim was to identify small molecules with stimulatory effects on the signaling of two neurotrophins, the nerve growth factor (NGF) and the brain derived neurotrophic factor (BDNF). To identify molecules that could potentiate neurotrophin signaling, 25,000 molecules were screened, which led to the identification of the triazinetrione derivatives ACD855 (Ponazuril) and later on ACD856, as positive allosteric modulators of tropomyosin related kinase (Trk) receptors. ACD855 or ACD856 potentiated the cellular signaling of the neurotrophin receptors with EC50 values of 1.9 and 3.2 or 0.38 and 0.30 µM, respectively, for TrkA or TrkB. ACD855 increased acetylcholine levels in the hippocampus by 40% and facilitated long term potentiation in rat brain slices. The compounds acted as cognitive enhancers in a TrkB-dependent manner in several different behavioral models. Finally, the age-induced cognitive dysfunction in 18-month-old mice could be restored to the same level as found in 2-month-old mice after a single treatment of ACD856. We have identified a novel mechanism to modulate the activity of the Trk-receptors. The identification of the positive allosteric modulators of the Trk-receptors might have implications for the treatment of Alzheimer's diseases and other diseases characterized by cognitive impairment.

Cognitive effects of the GSK-3 inhibitor "lithium" in LPS/chronic mild stress rat model of depression: Hippocampal and cortical neuroinflammation and tauopathy

Low-dose repeated lipopolysaccharide pre-challenge followed by chronic mild stress (LPS/CMS) protocol has been introduced as a rodent model of depression combining the roles of immune activation and chronic psychological stress. However, the impact of this paradigm on cognitive functioning has not been investigated hitherto.

METHODS

This study evaluated LPS/CMS-induced cognitive effects and the role of glycogen synthase kinase-3β (GSK-3β) activation with subsequent neuroinflammation and pathological tau deposition in the pathogenesis of these effects using lithium (Li) as a tool for GSK-3 inhibition.

RESULTS

LPS pre-challenge reduced CMS-induced neuroinflammation, depressive-like behavior and cognitive inflexibility. It also improved spatial learning but increased GSK-3β expression and exaggerated hyperphosphorylated tau accumulation in hippocampus and prefrontal cortex. Li ameliorated CMS and LPS/CMS-induced depressive and cognitive deficits, reduced GSK-3β over-expression and tau hyperphosphorylation, impeded neuroinflammation and enhanced neuronal survival.

CONCLUSION

This study draws attention to LPS/CMS-triggered cognitive changes and highlights how prior low-dose immune challenge could develop an adaptive capacity to buffer inflammatory damage and maintain the cognitive abilities necessary to withstand threats. This work also underscores the favorable effect of Li (as a GSK-3β inhibitor) in impeding exaggerated tauopathy and neuroinflammation, rescuing neuronal survival and preserving cognitive functions. Yet, further in-depth studies utilizing different low-dose LPS challenge schedules are needed to elucidate the complex interactions between immune activation and chronic stress exposure.

Inhibition of RhoA Activity Does Not Rescue Synaptic Development Abnormalities and Long-Term Cognitive Impairment After Sevoflurane Exposure

General anesthetics interfere with dendritic development and synaptogenesis, resulting in cognitive impairment in the developing animals. RhoA signal pathway plays important roles in dendritic development by regulating cytoskeleton protein such as tubulin and actin. However, it's not clear whether RhoA pathway is involved in inhaled general anesthetics sevoflurane-induced synaptic development abnormalities and long-term cognitive dysfunction. Rats at postnatal day 7 (PND7) were injected intraperitoneally with RhoA pathway inhibitor Y27632 or saline 20 min before exposed to 2.8% sevoflurane for 4 h. The apoptosis-related proteins and RhoA/CRMP2 pathway proteins in the hippocampus were measured 6 h after sevoflurane exposure. Cognitive functions were evaluated by the open field test on PND25 rats and contextual fear conditioning test on PND32-33 rats. The dendritic morphology and density of dendritic spines in the pyramidal neurons of hippocampus were determined by Golgi staining and the synaptic plasticity-related proteins were also measured on PND33 rats. Long term potentiation (LTP) from hippocampal slices was recorded on PND34-37 rats. Sevoflurane induced caspase-3 activation, decreased the ratio of Bcl-2/Bax and increased TUNEL-positive neurons in hippocampus of PND7 rats, which were attenuated by inhibition of RhoA. However, sevoflurane had no significant effects on activity of RhoA/CRMP2 pathway. Sevoflurane disturbed dendritic morphogenesis, reduced the number of dendritic spines, decreased proteins expression of PSD-95, drebrin and synaptophysin, inhibited LTP in hippocampal slices and impaired memory ability in the adolescent rats, while inhibition of RhoA activity did not rescue the changes above induced by sevoflurane. RhoA signal pathway did not participate in sevoflurane-induced dendritic and synaptic development abnormalities and cognitive dysfunction in developing rats.

Caspase-6-cleaved Tau fails to induce Tau hyperphosphorylation and aggregation, neurodegeneration, glial inflammation, and cognitive deficits

Active Caspase-6 (Casp6) and Tau cleaved by Casp6 at amino acids 402 (Tau∆D402) and 421 (Tau∆D421) are present in early Alzheimer disease intraneuronal neurofibrillary tangles, which are made primarily of filamentous Tau aggregates. To assess whether Casp6 cleavage of Tau contributes to Tau pathology and Casp6-mediated age-dependent cognitive impairment, we generated transgenic knock-in mouse models that conditionally express full-length human Tau (hTau) 0N4R only (CTO) or together with human Casp6 (hCasp6) (CTC). Region-specific hippocampal and cortical hCasp6 and hTau expression were confirmed with western blot and immunohistochemistry in 2-25-month-old brains. Casp6 activity was confirmed with Tau∆D421 and Tubulin cleaved by Casp6 immunopositivity in 3-25-month-old CTC, but not in CTO, brains. Immunoprecipitated Tau∆D402 was detected in both CTC and CTO brains, but was more abundant in CTC brains. Intraneuronal hippocampal Tau hyperphosphorylation at S202/T205, S422, and T231, and Tau conformational change were absent in both CTC and CTO brains. A slight accumulation of Tau phosphorylated at S396/404 and S202 was observed in Cornu Ammonis 1 (CA1) hippocampal neuron soma of CTC compared to CTO brains. Eighteen-month-old CTC brains showed rare argentophilic deposits that increased by 25 months, whereas CTO brains only displayed them sparsely at 25 months. Tau microtubule binding was equivalent in CTC and CTO hippocampi. Episodic and spatial memory measured with novel object recognition and Barnes maze, respectively, remained normal in 3-25-month-old CTC and CTO mice, in contrast to previously observed impairments in ACL mice expressing equivalent levels of hCasp6 only. Consistently, the CTC and CTO hippocampal CA1 region displayed equivalent dendritic spine density and no glial inflammation. Together, these results reveal that active hCasp6 co-expression with hTau generates Tau cleavage and rare age-dependent argentophilic deposits but fails to induce cognitive deficits, neuroinflammation, and Tau pathology.

Longan (Dimocarpus longan Lour.) Aril ameliorates cognitive impairment in AD mice induced by combination of D-gal/AlCl3 and an irregular diet via RAS/MEK/ERK signaling pathway

ETHNOPHARMACOLOGICAL RELEVANCE

According to the theory of traditional Chinese medicine (TCM), Alzheimer's disease (AD) is identified as "forgetfulness" or "dementia", and it can be caused by spleen deficiency. Longan Aril (the aril of Dimocarpus longan Lour., LA) is a kind of Chinese medicine, and it can improve intelligence attributed to entering the spleen-meridian. This study aimed to explore the therapeutic effects of LA on AD mice with spleen deficiency, and to understand anti-AD mechanism of LA.

MATERIAL AND METHODS

A mouse model of AD with spleen deficiency was established by D-gal (140 mg/kg, intraperitoneal injection) and AlCl₃ (20 mg/kg, intragastrical administration) in combination with an irregular diet for 60 days, in which mice in LA group were daily given LA (0.5, 1.0 or 2.0 g/kg). The anti-AD effects of LA were evaluated by the Morris water maze, enzyme-linked immunosorbent assay (ELISA), hematoxylin and eosin (H&E), Nissl, and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assays. The anti-AD mechanism of LA was studied by using metabolomics, and the expressions of RAS/MEK/extracellular signal-regulated kinase (ERK) signaling pathway-related proteins were detected by Western blotting.

RESULTS

LA improved learning and memory abilities, superoxide dismutase (SOD) level, and form and number of Nissl bodies, while reduced the levels of Aβ₄₂, phosphorylated-tau (p-tau), reactive oxygen species (ROS), malondialdehyde (MDA), monoamine oxidase-B (MAO-B), histological injury, and apoptosis rate in AD group (P < 0.05, P < 0.01 or P < 0.001). The anti-AD mechanism of LA may be related to RAS/MEK/ERK and other signaling pathways, in which the expressions of RAS/MEK/ERK signaling pathway-related proteins significantly reduced (P < 0.05 or P < 0.01).

CONCLUSIONS

LA could improve the cognitive ability and reduce the pathologic impairment in AD mice, which might be partly mediated via inhibition of RAS/MEK/ERK singling pathway.

Dexmedetomidine Alleviates Hypoxia-Induced Synaptic Loss and Cognitive Impairment via Inhibition of Microglial NOX2 Activation in the Hippocampus of Neonatal Rats

BACKGROUND

Perinatal hypoxia is a universal cause of death and neurological deficits in neonates worldwide. Activation of microglial NADPH oxidase 2 (NOX2) leads to oxidative stress and neuroinflammation, which may contribute to hypoxic damage in the developing brain. Dexmedetomidine has been reported to exert potent neuroprotection in several neurological diseases, but the mechanism remains unclear. We investigated whether dexmedetomidine acts through microglial NOX2 to reduce neonatal hypoxic brain damage.

METHODS

The potential role of microglial NOX2 in dexmedetomidine-mediated alleviation of hypoxic damage was evaluated in cultured BV2 microglia and neonatal rats subjected to hypoxia. In vivo, neonatal rats received dexmedetomidine (25 μg/kg, i.p.) 30 min before or immediately after hypoxia (5% O2, 2 h). Apocynin-mediated NOX inhibition and lentivirus-mediated NOX2 overexpression were applied to further assess the involvement of microglial NOX2 activation.

RESULTS

Pre- or posttreatment with dexmedetomidine alleviated hypoxia-induced cognitive impairment, restored damaged synapses, and increased postsynaptic density-95 and synaptophysin protein expression following neonatal hypoxia. Importantly, dexmedetomidine treatment suppressed hypoxia-induced microglial NOX2 activation and subsequent oxidative stress and the neuroinflammatory response, as reflected by reduced 4-hydroxynonenal and ROS accumulation, and decreased nuclear NF-κB p65 and proinflammatory cytokine levels in cultured BV2 microglia and the developing hippocampus. In addition, treating primary hippocampal neurons with conditioned medium (CM) from hypoxia-activated BV2 microglia resulted in neuronal damage, which was alleviated by CM from dexmedetomidine-treated microglia. Moreover, the neuroprotective effect of dexmedetomidine was reversed in NOX2-overexpressing BV2 microglia and diminished in apocynin-pretreated neonatal rats.

CONCLUSION

Dexmedetomidine targets microglial NOX2 to reduce oxidative stress and neuroinflammation and subsequently protects against hippocampal synaptic loss following neonatal hypoxia.

Synthetic β-hydroxy ketone derivative inhibits cholinesterases, rescues oxidative stress and ameliorates cognitive deficits in 5XFAD mice model of AD

Alzheimer's disease (AD) is a progressive, chronic and age-related neurodegenerative disorder that affects millions of people across the world. In pursuit of new anti-AD remedies, 2-[Hydroxy-(4-nitrophenyl)methyl]-cyclopentanone (NMC), a β hydroxyl ketone derivative was studied to explore its neuroprotective potentials against AD. The in-vitro AChE and BuChE enzymes inhibition were evaluated by Ellman protocol and antioxidant potentials of NMC by DPPH free radical scavenging assay. In-vivo behavioral studies were performed in the transgenic 5xFAD mice model of AD using shallow water maze (SWM), Paddling Y-Maze (PYM), elevated plus maze (EPM) and balance beam (BB) tests. Also, the ex-vivo cholinesterase inhibitory effects of NMC and histopathological analysis of amyloid-β plaques were determined in the frontal cortex and hippocampal regions of the mice brain. NMC exhibited significant in vitro anti-cholinesterase enzyme potentials with an IC₅₀ value of 67 μg/ml against AChE and 96 μg/ml against BuChE respectively. Interestingly, the activities of AChE and BuChE enzymes were also significantly lower in the cortex and hippocampus of NMC-treated groups. Also, in the DPPH assessment, NMC displayed substantial antioxidant properties with an IC₅₀ value observed as 171 μg/ml. Moreover, histopathological analysis via thioflavin-s staining displayed significantly lower plaques depositions in the cortex and hippocampus region of NMC-treated mice groups. Furthermore, SWM, PYM, EPM, and BB behavioral analysis indicated that NMC enhanced spatial learning, memory consolidation and improved balance performance. Altogether, to the best of our knowledge, we believe that NMC may serve as a potential and promising anti-cholinesterase, antioxidant and neuroprotective agent against AD.

Casticin ameliorates scopolamine-induced cognitive dysfunction in mice

ETHNOPHARMACOLOGICAL RELEVANCE

The fruit of Vitex rotundifolia L. (Verbenaceae) has been used in traditional medicine as sedative or analgesic agent for headache. Recent population-based cohort studies have shown that headache including migraines is a risk factor for dementia. Thus, the fruit of V. rotundifolia may be useful for treating cognitive dysfunction observed in dementia.

AIM OF THE STUDY

We had previously found that the ethanolic extract of the fruit of V. rotundifolia ameliorated cognitive dysfunction and isolated casticin as an active compound. In the present study, we studied the effect of casticin on a mouse model of cognitive impairment induced by scopolamine.

MATERIALS AND METHODS

Mice were treated with the ethanolic extract of the fruit of V. rotundifolia (EEVR; 30, 100 or 300 mg/kg, p.o.) or casticin (0.3, 1 or 3 mg/kg, p.o.). We examined the effect of casticin or EEVR using the passive avoidance test, the Morris water maze test and the novel object recognition test. Scopolamine (1 mg/kg, i.p.) was used to induce cognitive impairment by blocking cholinergic neurotransmitter system. We investigated the effects of casticin on acetylcholinesterase (AchE) activity and the phosphorylation levels of extracellular signal-regulated kinase (ERK), cAMP response element binding protein (CREB), and the expression levels of brain-derived neurotrophic factor (BDNF).

RESULTS

EEVR (100 and 300 mg/kg, p.o.) significantly ameliorated the latency in the passive avoidance test, and casticin (1 and 3 mg/kg, p.o.) also significantly improved the latency in the passive avoidance test, novel object preference in the novel object recognition test, and swimming time in the target quadrant of the Morris water maze test. Casticin also decreased AChE activity in ex vivo analysis and increased the phosphorylation levels of memory-related signaling molecules, such as ERK, CREB and BDNF in the cortex.

CONCLUSION

These results suggest that casticin ameliorates cholinergic blockade-induced cognitive impairment, in part, through the inhibition of AChE and the activation of the ERK-CREB-BDNF signaling pathway. Taken together, the results suggest that casticin may be useful for treating the cognitive dysfunction observed during cholinergic impairment.

Reversal of peripheral nerve injury-induced neuropathic pain and cognitive dysfunction via genetic and tomivosertib targeting of MNK

Neuropathic pain caused by nerve injury presents with severe spontaneous pain and a variety of comorbidities, including deficits in higher executive functions. None of these clinical problems are adequately treated with current analgesics. Targeting of the mitogen-activated protein kinase-interacting kinase (MNK1/2) and its phosphorylation target, the mRNA cap binding protein eIF4E, attenuates many types of nociceptive plasticity induced by inflammatory mediators and chemotherapeutic drugs but inhibiting this pathway does not alter nerve injury-induced mechanical allodynia. We used genetic manipulations and pharmacology to inhibit MNK-eIF4E activity in animals with spared nerve injury, a model of peripheral nerve injury (PNI)-induced neuropathic pain. We assessed the presence of spontaneous pain using conditioned place preference. We also tested performance in a medial prefrontal cortex (mPFC)-dependent rule-shifting task. WT neuropathic animals showed signs of spontaneous pain and were significantly impaired in the rule-shifting task while genetic and pharmacological inhibition of the MNK-eIF4E signaling axis protected against and reversed spontaneous pain and PNI-mediated cognitive impairment. Additionally, pharmacological and genetic inhibition of MNK-eIF4E signaling completely blocked and reversed maladaptive shortening in the length of axon initial segments (AIS) in the mPFC of PNI mice. Surprisingly, these striking positive outcomes on neuropathic pain occurred in the absence of any effect on mechanical allodynia, a standard test for neuropathic pain efficacy. Our results illustrate new testing paradigms for determining preclinical neuropathic pain efficacy and point to the MNK inhibitor tomivosertib (eFT508) as an important drug candidate for neuropathic pain treatment.

Methylene blue inhibits Caspase-6 activity, and reverses Caspase-6-induced cognitive impairment and neuroinflammation in aged mice

Activated Caspase-6 (Casp6) is associated with age-dependent cognitive impairment and Alzheimer disease (AD). Mice expressing human Caspase-6 in hippocampal CA1 neurons develop age-dependent cognitive deficits, neurodegeneration and neuroinflammation. This study assessed if methylene blue (MB), a phenothiazine that inhibits caspases, alters Caspase-6-induced neurodegeneration and cognitive impairment in mice. Aged cognitively impaired Casp6-overexpressing mice were treated with methylene blue in drinking water for 1 month. Methylene blue treatment did not alter Caspase-6 levels, assessed by RT-PCR, western blot and immunohistochemistry, but inhibited fluorescently-labelled Caspase-6 activity in acute brain slice intact neurons. Methylene blue treatment rescued Caspase-6-induced episodic and spatial memory deficits measured by novel object recognition and Barnes maze, respectively. Methylene blue improved synaptic function of hippocampal CA1 neurons since theta-burst long-term potentiation (LTP), measured by field excitatory postsynaptic potentials (fEPSPs) in acute brain slices, was successfully induced in the Schaffer collateral-CA1 pathway in methylene blue-treated, but not in vehicle-treated, Caspase-6 mice. Increased neuroinflammation, measured by ionized calcium binding adaptor molecule 1 (Iba1)-positive microglia numbers and subtypes, and glial fibrillary acidic protein (GFAP)-positive astrocytes, were decreased by methylene blue treatment. Therefore, methylene blue reverses Caspase-6-induced cognitive deficits by inhibiting Caspase-6, and Caspase-6-mediated neurodegeneration and neuroinflammation. Our results indicate that Caspase-6-mediated damage is reversible months after the onset of cognitive deficits and suggest that methylene blue could benefit Alzheimer disease patients by reversing Caspase-6-mediated cognitive decline.

Secondary metabolite profiling, cytotoxicity, anti-inflammatory potential and in vitro inhibitory activities of Nardostachys jatamansi on key enzymes linked to hyperglycemia, hypertension and cognitive disorders

ETHNOPHARMACOLOGICAL RELEVANCE

Nardostachys jatamansi (D. Don) DC., 'Spikenard' or 'Jatamansi', a highly valued, aromatic herb from alpine Himalayas has a long history of use as ethnomedicine and dietary supplements in Ayurveda, Unani and Chinese system of medicine since Vedic ages (1000-800 BC). In Ayurveda and traditional system of medicine, the species is used as stimulant, sedative, brain tonic or mind rejuvenator, antidiabetic, cardio tonic, and in the treatment of various neurological disorders such as insomnia, epilepsy, hysteria, anxiety and depression. It is considered as Sattvic herb in Ayurveda and is now commercially marketed either as single or poly-herbal formulations by many companies in national and international markets.

AIM OF THE STUDY

The species has become threatened in its natural habitats due to over exploitation and illegal trade of its rhizomes for drug preparation in herbal and pharmaceutical industries. Considering the increasing demand and tremendous medicinal importance of this threatened plant species, a detailed study was undertaken to evaluate its antioxidant potential, secondary metabolite profiling, cytotoxicity, anti-inflammatory potential and in vitro enzyme inhibitory activities on key enzymes linked to hyperglycemia, hypertension and cognitive disorders in different plant parts of wild and in vitro-raised plants with respect to different solvent systems for its sustainable utilization.

MATERIALS AND METHODS

Anti-cholinesterase activity of leaves and rhizome of wild and cultured plant extracts was investigated against both acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) enzymes. In vitro anti-hyperglycemic (α-amylase and PTP1B), anti-hypertensive (angiotensin-converting enzyme), anti-tyrosinase and anti-inflammatory potential (5-lipoxygenase and hyaluronidase) of different plant parts of wild and in vitro-raised plants with respect to different solvent systems were also evaluated. In vitro cytotoxic effect of rootstock extracts of wild and in vitro-derived plants were against cancer (HCT-116, MCF-7 and OE33) and two normal (HEK and MEF) cell lines. Secondary metabolite profiling of rhizome segments of wild and in vitro-derived plants was carried out by quantitative gas chromatography-mass spectrometry (GC-MS).

RESULTS

In vitro-raised plantlets showed comparative higher yield of various secondary metabolites with a significantly high antioxidant activity as compared to the wild plants. Methanolic rootstock extracts of both wild and in vitro-derived plants of N. jatamansi exhibited significant AChE (IC₅₀ 36.46 ± 2.1 and 31.18 ± 2.6 µg/ml, respectively) and BuChE (IC₅₀ 64.6 ± 3.5 and 60.12 ± 3.6 µg/ml, respectively) inhibitory potential as compared to standard inhibitor galanthamine (IC₅₀ 0.94 ± 0.03 and 4.45 ± 0.5 µg/ml). Methanolic rootstock extract of in vitro-derived plants showed significant α-amylase (IC₅₀ 90.69 ± 2.1 µg/ml), PTP1B (IC₅₀ 24.56 ± 0.8 µg/ml), angiotensin-converting enzyme (IC₅₀ 42.5 ± 3.6 µg/ml) and tyrosinase (IC₅₀ 168.12 ± 3.6 µg/ml) inhibitory potential as compared to standard acarbose (IC₅₀ 52.36 ± 3.1 µg/ml), ursolic acid (IC₅₀ 5.24 ± 0.8 µg/ml), captopril (IC₅₀ 32.36 ± 2.5 µg/ml) and kojic acid (IC₅₀ = 54.44 ± 2.3 µg/ml). Both the methanolic rootstock and leaf extracts of tissue culture-derived plants exhibited promising anti-5-LOX and anti-hyaluronidase activities against the known inhibitor of 5-LOX and hyaluronidase. Furthermore, methanolic rootstock extracts of both wild and in vitro-derived plants exhibited promising cytotoxic effects to HCT-116, MCF-7 and OE33 cell lines as compared to the normal HEK and MEF after 12 h of treatment. Secondary metabolite profiling of wild and in vitro-derived plants by quantitative GC-MS analysis revealed the presence of different classes of terpenoids and phenolic acids might be responsible for its effective biological activities.

CONCLUSION

In vitro-derived plants revealed a substantial anti-cholinesterases, anti-hyperglycemic anti-inflammatory, anti-hypertensive and anti-tyrosinase potential with higher yield of various bioactive metabolites and significantly higher antioxidant activity which substantially explain medicinal importance of N. jatamansi in traditional medicine, used for centuries in different Ayurvedic formulations. The present findings suggest that cultured plants could be a promising alternative for the production of bioactive metabolites with comparative biological activities to the wild plants.

Whole-brain low-intensity pulsed ultrasound therapy markedly improves cognitive dysfunctions in mouse models of dementia - Crucial roles of endothelial nitric oxide synthase

BACKGROUND

Therapeutic focused-ultrasound to the hippocampus has been reported to exert neuroprotective effects on dementia. In the present study, we examined whether the whole-brain LIPUS (low-intensity pulsed ultrasound) therapy is effective and safe in 2 mouse models of dementia (vascular dementia, VaD and Alzheimer's disease, AD), and if so, to elucidate the common underlying mechanism(s) involved.

METHODS

We used bilateral carotid artery stenosis (BCAS) model with micro-coils in male C57BL/6 mice as a VaD model and 5XFAD transgenic mice as an AD model. We applied the LIPUS therapy (1.875 MHz, 6.0 kHz, 32cycles) to the whole brain.

RESULTS

In both models, the LIPUS therapy markedly ameliorated cognitive impairments (Y-maze test and/or passive avoidance test) associated with improved cerebral blood flow (CBF). Mechanistically, the LIPUS therapy significantly increased CD31-positive endothelial cells and Olig2-positive oligodendrocyte precursor cells (OPCs) in the VaD model, while it reduced Iba-1-positive microglias and amyloid-β (Aβ) plaque in the AD model. In both models, endothelium-related genes were significantly upregulated in RNA-sequencing, and expressions of endothelial nitric oxide synthase (eNOS) and neurotrophins were upregulated in Western blotting. Interestingly, the increases in glia cells and neurotrophin expressions showed significant correlations with eNOS expression. Importantly, these beneficial effects of LIPUS were absent in eNOS-knockout mice.

CONCLUSIONS

These results indicate that the whole-brain LIPUS is an effective and non-invasive therapy for dementia by activating specific cells corresponding to each pathology, for which eNOS activation plays an important role as a common mechanism.

A Comparison of Lysosomal Enzymes Expression Levels in Peripheral Blood of Mild- and Severe-Alzheimer's Disease and MCI Patients: Implications for Regenerative Medicine Approaches

The association of lysosomal dysfunction and neurodegeneration has been documented in several neurodegenerative diseases, including Alzheimer's Disease (AD). Herein, we investigate the association of lysosomal enzymes with AD at different stages of progression of the disease (mild and severe) or with mild cognitive impairment (MCI). We conducted a screening of two classes of lysosomal enzymes: glycohydrolases (β-Hexosaminidase, β-Galctosidase, β-Galactosylcerebrosidase, β-Glucuronidase) and proteases (Cathepsins S, D, B, L) in peripheral blood samples (blood plasma and PBMCs) from mild AD, severe AD, MCI and healthy control subjects. We confirmed the lysosomal dysfunction in severe AD patients and added new findings enhancing the association of abnormal levels of specific lysosomal enzymes with the mild AD or severe AD, and highlighting the difference of AD from MCI. Herein, we showed for the first time the specific alteration of β-Galctosidase (Gal), β-Galactosylcerebrosidase (GALC) in MCI patients. It is notable that in above peripheral biological samples the lysosomes are more sensitive to AD cellular metabolic alteration when compared to levels of Aβ-peptide or Tau proteins, similar in both AD groups analyzed. Collectively, our findings support the role of lysosomal enzymes as potential peripheral molecules that vary with the progression of AD, and make them useful for monitoring regenerative medicine approaches for AD.

Cognitive deficits induced by combined exposure of stress and alcohol mediated through oxidative stress-PARP pathway in the hippocampus

Several studies reported that stress can enhance the consumption of alcohol in humans and animals. However, the combinatorial effect of stress and alcohol on cognitive function and neurochemical alterations is quite understudied. In the present study, we have elucidated the involvement of oxidative stress-PARP cascade in alcohol and restraint stress (RS)-exposed animals using a PARP inhibitor, 1,5-isoquinolinediol (3mg/kg for 14days). Male Swiss albino mice were given alcohol (ALC) or RS (2h per day) or both in ALC+RS group for 28days. Behavioral analysis revealed cognitive dysfunction in ALC+RS group. Furthermore, oxidative stress and raised level of pro-inflammatory cytokines were found in the hippocampus region of ALC+RS group. Semi-quantitative reverse transcriptase PCR showed overactivation of PARP-1 gene in ALC+RS group. 1,5-isoquinolinediol treatment significantly prevented cognitive deficits and aforementioned neurochemical alterations. Overall, our findings showed that ALC+RS exerted deleterious effects on the hippocampus which involves oxidative stress-PARP overactivation cascade.

12/15-Lipoxygenase Inhibition Reverses Cognitive Impairment, Brain Amyloidosis, and Tau Pathology by Stimulating Autophagy in Aged Triple Transgenic Mice

BACKGROUND

The 12/15-lipoxygenase (12/15-LO) enzyme is upregulated in the brains of patients with Alzheimer's disease (AD), and its expression levels influence the onset of the AD-like phenotype in mouse models. However, whether targeting this pathway after the neuropathology and behavioral impairments have been established remains to be investigated.

METHODS

Triple transgenic (3xTg) mice received either PD146176-a selective and specific pharmacological inhibitor of 12/15-LO-or placebo starting at 12 months of age for 12 weeks. They were then assessed for the effect of the treatment on neuropathologies and behavioral impairments.

RESULTS

At the end of the study, mice in the control group showed a worsening of memory and learning abilities, whereas mice receiving PD146176 were undistinguishable from wild-type mice. The same group also had significantly lower amyloid beta levels and deposition, less tau neuropathology, increased synaptic integrity, and autophagy activation. Ex vivo and in vitro genetic and pharmacological studies found that the mechanism involved in these effects was the activation of neuronal autophagy.

CONCLUSIONS

Our findings provide new insights into the disease-modifying action of 12/15-LO pharmacological inhibition and establish it as a viable therapeutic approach for patients with AD.

Cholinergic system function and cognition in mild cognitive impairment

Evidence for cholinergic dysfunction in very early stages of neurodegeneration like mild cognitive impairment (MCI) is inconclusive. Previous positron emission tomography (PET) studies based on small samples investigated if it is related to memory impairment. We examined whether cortical acetylcholine esterase (AChE) activity is reduced at this stage and correlated with cognitive function. N-[(11)C]-methyl-4-piperidyl acetate ([11C]MP4A), a positron emission tomography tracer for measuring cerebral AChE activity in vivo, was applied in 21 controls and 17 MCI patients. Parametric images of AChE activity were analyzed using standard atlas regions. Principal components analysis (PCA) of regional values of AChE activity and correlation analysis with neuropsychological test results was performed. Cortical AChE activity showed a significant decline in MCI patients compared with controls which was most pronounced in temporal regions. They formed the main part of a principal component that was related significantly to verbal and nonverbal memory, language comprehension and executive function. Cholinergic dysfunction is an early hallmark even before onset of dementia at the clinical stage of MCI. Its impact especially on temporal neocortex is associated with impaired neuropsychological function.