Dexamethasone and Aβ₂₅-₃₅ accelerate learning and memory impairments due to elevate amyloid precursor protein expression and neuronal apoptosis in 12-month male rats

Mitochondrial Treatment Improves Cognitive Impairment Induced by Lipopolysaccharide in Mice

Neuroinflammation has been proven to drive cognitive impairment associated with neurodegenerative diseases. It has been demonstrated that mitochondrial dysfunction is associated with cognitive impairment caused by neuroinflammation. We hypothesized that the transfer of exogenous mitochondria may be beneficial to the therapy of cognitive impairment induced by neuroinflammation. In the study, the effect of exogenous mitochondria on cognitive impairment induced by neuroinflammation was investigated. The results showed that mitochondrial treatment ameliorated the cognitive performance of lipopolysaccharide (LPS)-treated mice. Additionally, mitochondrial therapy attenuated neuronal injury and down-regulated the expression of proinflammatory cytokines, including TNF-α and pro- and cleaved IL-1β, and the expression of Iba-1 and GFAP in the hippocampus and cortex of LPS-treated mice. Additionally, mitochondrial treatment increased mitochondrial ΔΨm, ATP level, and SOD activity and attenuated MDA level and ROS production in the brains of LPS-treated mice. The study reports the beneficial effect of mitochondrial treatment against cognitive impairment of LPS-treated mice, thereby providing a potential strategy for the treatment of cognitive impairment caused by neuroinflammation.

Jiedu-Yizhi Formula Improves Cognitive Impairment in an Aβ 25-35-Induced Rat Model of Alzheimer's Disease by Inhibiting Pyroptosis

Jiedu-Yizhi formula (JDYZF) is prescribed for the treatment of Alzheimer's disease (AD) and was created by Jixue Ren, a master of traditional Chinese medicine, based on the "marrow deficiency and toxin damage" theory. In our clinic, this formula has been used for the treatment of AD for many years and has achieved good results. However, the mechanism by which JDYZF improves cognitive impairment has not been determined. In this study, we confirmed that orally administered JDYZF reversed the cognitive deficits in an Aβ _25-35-induced rat model, increased the number of neurons in the hippocampal CA1 area, improved their structure, decreased the deposition of β-amyloid (Aβ), reduced the expression of proteins related to the NLRP3/Caspase-1/GSDMD and LPS/Caspase-11/GSDMD pyroptosis pathways, and reduced the levels of interleukin 1β (IL-1β) and IL-18, thereby inhibiting the inflammatory response. In addition, JDYZF exerted no hepatotoxicity in rats. In short, these results provide scientific support for the clinical use of JDYZF to improve the cognitive function of patients with AD.

Hydrogen Sulfide Ameliorates Cognitive Dysfunction in Formaldehyde-Exposed Rats: Involvement in the Upregulation of Brain-Derived Neurotrophic Factor

OBJECTIVE

To investigate whether hydrogen sulfide (H2S) counteracts formaldehyde (FA)-induced cognitive defects and whether the underlying mechanism is involved in the upregulation of hippocampal brain-derived neurotrophic factor (BDNF) expression.

METHODS

The cognitive function of rats was evaluated by the Morris water maze (MWM) test and the novel object recognition test. The content of superoxide dismutase (SOD) and malondialdehyde (MDA) in the hippocampus were detected by enzyme-linked immunosorbent assay (ELISA). The neuronal apoptosis in the hippocampal CA1 region was detected by terminal deoxynucleotidyl transferase-mediated dUTP nick-end (TUNEL) staining. The expression of the BDNF protein was detected by Western blot and immunohistochemistry.

RESULTS

We found that sodium hydrosulfide (NaHS, a donor of H2S) significantly reversed the impairment in the function of learning and memory in the MWM test and the novel objective recognition task induced by intracerebroventricular injection of FA. We also showed that NaHS significantly reduced the level of MDA, elevated the level of SOD, and decreased the amount of TUNEL-positive neurons in the hippocampus of FA-exposed rats. Moreover, NaHS markedly increased the expression of hippocampal BDNF in FA-exposed rats.

CONCLUSIONS

H2S attenuates FA-induced dysfunction of cognition and the underlying mechanism is involved in the reduction of hippocampal oxidative damage and apoptosis as well as upregulation of hippocampal BDNF.

5,6,7,4'-Tetramethoxyflavanone protects against neuronal degeneration induced by dexamethasone by attenuating amyloidogenesis in mice

Long-term exposure to high glucocorticoid levels induces memory impairment and neurodegeneration in Alzheimer's disease (AD) by increasing the expression of amyloid β and tau hyperphosphorylation (pTau). Previous studies showed beneficial effects of flavonoids in neurodegenerative models. 5,6,7,4'-tetramethoxyflavanone (TMF) is one of the active ingredients in Chromolaena odorata (L.), which R. M. King and H. Rob discovered in Thailand. This study focused on the effects of TMF on dexamethasone (DEX)-induced neurodegeneration, amyloidogenesis, pTau expression, neuron synaptic function, and cognitive impairment and the potential mechanisms involved. Mice were intraperitoneally administered DEX for 28 days before being treated with TMF for 30 days. The mice were randomly divided into six groups (twelve mice per group): control; TMF administration (40 mg/kg); pioglitazone administration (20 mg/kg); DEX administration (60 mg/kg); DEX administration plus TMF; and DEX administration plus pioglitazone. Behavioral tests showed that TMF significantly attenuated the memory impairment triggered by DEX. Consistently, TMF reduced DEX-induced amyloid beta production by reducing the expression of beta-site APP cleaving enzyme 1 (BACE1) and presenilin 1 (PS1), whereas it increased the gene expression of a disintegrin and metalloprotease 10 (ADAM10). TMF treatment also decreased pTau expression, inhibited phosphonuclear factor-kappa B (pNF-kB) and inhibited glycogen synthase kinase 3 (GSK-3) activity by increasing GSK3 phosphorylation (pGSK3). In addition, TMF also improved synaptic function by increasing the expression of synaptophysin (Syn) and postsynaptic density protein 95 (PSD95) while decreasing acetylcholine esterase activity. Conclusively, TMF provided neuroprotection against DEX-induced neurodegeneration. These findings suggest that TMF might have potential as a therapeutic drug for AD.

Hippocampal Injections of Oligomeric Amyloid β-peptide (1-42) Induce Selective Working Memory Deficits and Long-lasting Alterations of ERK Signaling Pathway

Increasing evidence suggests that abnormal brain accumulation of soluble rather than aggregated amyloid-β1-42 oligomers (Aβo(1-42)) plays a causal role in Alzheimer's disease (AD). However, as yet, animal's models of AD based on oligomeric amyloid-β1-42 injections in the brain have not investigated their long-lasting impacts on molecular and cognitive functions. In addition, the injections have been most often performed in ventricles, but not in the hippocampus, in spite of the fact that the hippocampus is importantly involved in memory processes and is strongly and precociously affected during the early stages of AD. Thus, in the present study, we investigated the long-lasting impacts of intra-hippocampal injections of oligomeric forms of Aβo(1-42) on working and spatial memory and on the related activation of ERK1/2. Indeed, the extracellular signal-regulated kinase (ERK) which is involved in memory function had been found to be activated by amyloid peptides. We found that repeated bilateral injections (1injection/day over 4 successive days) of oligomeric forms of Aβo(1-42) into the dorsal hippocampus lead to long-lasting impairments in two working memory tasks, these deficits being observed 7 days after the last injection, while spatial memory remained unaffected. Moreover, the working memory deficits were correlated with sustained impairments of ERK1/2 activation in the medial prefrontal cortex (mPFC) and the septum, two brain areas tightly connected with the hippocampus and involved in working memory. Thus, our study is first to evidence that sub-chronic injections of oligomeric forms of Aβo(1-42) into the dorsal hippocampus produces the main sign of cognitive impairments corresponding to the early stages of AD, via long-lasting alterations of an ERK/MAPK pathway in an interconnected brain networks.

NADPH oxidase-derived production of reactive oxygen species is involved in learning and memory impairments in 16-month-old female rats

Women undergoing the natural menopause can experience progressive cognitive dysfunction, particularly in the form of memory impairment. However, the mechanisms underlying memory impairments in the menopause remain to be elucidated. There is increasing evidence that oxidative damage caused by excessive reactive oxygen species (ROS) production may correlate with age‑associated cognitive impairment. The nicotinamide adenosine dinucleotide phosphate oxidase (NOX) family is important in the generation of ROS in the brain. It has been hypothesized that the accumulation of ROS, derived from NOX, may be involved in menopause‑associated learning and memory impairments. The present study investigated whether NOX‑derived ROS generation affected the learning and memory ability in 3‑month and 16‑month‑old female rats. The results of a morris water maze assessment revealed that there were significant learning and memory impairments in the 16‑month‑old female rats. Furthermore, the activity of superoxide dismutase (SOD), level of malondialdehyde (MDA), production of ROS and expression levels of NOX2, p47phox, Ras‑related C3 botulinum toxin substrate 1 (RAC1) and protein kinase C α (PKCα) were investigated in the cortex and hippocampus of 3‑month and 16‑month old female rats. The results demonstrated that the activity of SOD was significantly decreased, whereas the levels of MDA, production of ROS and expression levels of NOX2, p47phox, RAC1 and PKCα were significantly increased in the 16‑month old female rats. These results suggested that NOX‑mediated oxidative stress may be important in menopause‑associated learning and memory impairments.

Simvastatin pretreatment protects cerebrum from neuronal injury by decreasing the expressions of phosphor-CaMK II and AQP4 in ischemic stroke rats

Excitotoxicity and cytotoxic edema are the two major factors resulting in neuronal injury during brain ischemia and reperfusion. Ca2+/calmodulin-dependent protein kinase II (CaMK II), the downstream signal molecular of N-methyl-D-aspartate receptors (NMDARs), is a mediator in the excitotoxicity. Aquaporin 4 (AQP4), expressed mainly in the brain, is an important aquaporin to control the flux of water. In a previous study, we had reported that pretreatment of simvastatin protected the cerebrum from ischemia and reperfusion injury by decreasing neurological deficit score and infarct area (Zhu et al. PLoS One 7:e51552, 2012). The present study used a middle cerebral artery occlusion (MCAO) model to further explore the pleiotropic effect of simvastatin via CaMK II and AQP4. The results showed that simvastatin reduced degenerated cells and brain edema while decreasing the protein expressions of phosphor-CaMK II and AQP4, and increasing the ratios of Bcl-2/Bax, which was independent of cholesterol-lowering effect. Immunocomplexes formed between the subunit of NMDARs-NR3A and AQP4 were detected for the first time. It was concluded that simvastatin could protect the cerebrum from neuronal excitotoxicity and cytotoxic edema by downregulating the expressions of phosphor-CaMK II and AQP4, and that the interaction between NR3A and AQP4 might provide the base for AQP4 involving in the signaling pathways mediated by NMDARs.

Melatonin protects against amyloid-β-induced impairments of hippocampal LTP and spatial learning in rats

Alzheimer's disease (AD), the most prevalent neurodegenerative disease in the elderly, leads to progressive loss of memory and cognitive deficits. Amyloid-β protein (Aβ) in the brain is thought to be the main cause of memory loss in AD. Melatonin, an indole hormone secreted by the pineal gland, has been reported to produce neuroprotective effects. We examined whether melatonin could protect Aβ-induced impairments of hippocampal synaptic plasticity, neuronal cooperative activity, and learning and memory. Rats received bilateral intrahippocampal injection of Aβ1-42 or Aβ31-35 followed by intraperitoneal application of melatonin for 10 days, and the effects of chronic melatonin treatment on in vivo hippocampal long-term potentiation (LTP) and theta rhythm and Morris water maze performance were examined. We showed that intrahippocampal injection of Aβ1-42 or Aβ31-35 impaired hippocampal LTP in vivo, while chronic melatonin treatment reversed Aβ1-42- or Aβ31-35-induced impairments in LTP induction. Intrahippocampal injection of Aβ31-35 impaired spatial learning and decreased the power of theta rhythm in the CA1 region induced by tail pinch, and these synaptic, circuit, and learning deficits were rescued by chronic melatonin treatment. These results provide evidence for the neuroprotective action of melatonin against Aβ insults and suggest a strategy for alleviating cognition deficits of AD.

Intensive protein synthesis in neurons and phosphorylation of beta-amyloid precursor protein and tau-protein are triggering factors of neuronal amyloidosis and Alzheimer's disease

Recently the studies of Alzheimer’s disease have become particularly actual and have attracted scientists from all over the world to this problem as a result of dissemination of this dangerous disorder. The reason for such pathogenesis is not known, but the final image, for the first time obtained on microscopic brain sections from patients with this disease more than a hundred years ago, is well known to clinicists. This is the deposition of Ab amyloid in the brain tissue of senile plaques and fibrils. Many authors suppose that the deposition of beta-amyloid provokes secondary neuronal changes which are the reason of neuron death. Other authors associate the death of neurons with hyperphosphorylation of tau-proteins which form neurofibrillar coils inside nerve cells and lead to their death. For creation of methods of preclinical diagnostics and effective treatment of Alzheimer’s disease novel knowledge is required on the nature of triggering factors of sporadic isoforms of Alzheimer’s disease, on cause-effect relationships of phosphorylation of amyloid precursor protein with formation of pathogenic beta-amyloids, on the relationship with these factors of hyperphosphorylation of tau-protein and neuron death. In this review we analyze the papers describing the increasing of intensity of biosynthesis in neurons in normal conditions and under the stress, the possibility of development of energetic unbalanced neurons and activation of their protective systems. Phosphorylation and hyperphosphorylation of tau-proteins is also tightly connected with protective mechanisms of cells and with processes of evacuation of phosphates, adenosine mono-phosphates and pyrophosphates from the region of protein synthesis. Upon long and high intensity of protein synthesis the protective mechanisms are overloaded and the complementarity of metabolitic processes is disturbed. This results in dysfunction of neurons, transport collapse, and neuron death.

Formaldehyde impairs learning and memory involving the disturbance of hydrogen sulfide generation in the hippocampus of rats

Formaldehyde (FA), a well-known indoor and outdoor pollutant, has been implicated as the responsible agent in the development of neurocognitive disorders. Hydrogen sulfide (H(2)S), the third gasotransimitter, is an endogenous neuromodulator, which facilitates the induction of hippocampal long-term potentiation, involving the functions of learning and memory. In the present study, we analyzed the effects of intracerebroventricular injection of FA on the formation of learning and memory and the generation of endogenous H(2)S in the hippocampus of rats. We found that the intracerebroventricular injection of FA in rats impairs the function of learning and memory in the Morris water maze and novel object recognition test and increases the formation of apoptosis and lipid peroxidation in the hippocampus. We also showed that FA exposure inhibits the expression of cystathionine β-synthase, the major enzyme responsible for endogenous H(2)S generation in hippocampus and decreases the production of endogenous H(2)S in hippocampus in rats. These results suggested that FA-disturbed generation of endogenous H(2)S in hippocampus leads to the oxidative stress-mediated neuron damage, ultimately impairing the function of learning and memory. Our findings imply that the disturbance of endogenous H(2)S generation in hippocampus is a potential contributing mechanism underling FA-caused learning and memory impairment.