Effects of an alpha7 nicotinic receptor agonist and stress on spatial memory in an animal model of Alzheimer's disease

Molecular Signaling Pathway Targeted Therapeutic Potential of Thymoquinone in Alzheimer’s disease

Alzheimer’s disease (AD) is a neurodegenerative disease with rapid progression. Black cumin (Nigella sativa) is a nutraceutical that has been investigated as a prophylactic and therapeutic agent for this disease due to its ability to prevent or retard the progression of neurodegeneration. Thymoquinone (TQ) is the main bioactive compound isolated from the seeds of black cumin. Several reports have shown that it has promising potential in the prevention and treatment of AD due to its significant antioxidative, anti-inflammatory, and antiapoptotic properties along with several other mechanisms that target the altered signaling pathways due to the disease pathogenesis. In addition, it shows anticholinesterase activity and prevents α-synuclein induced synaptic damage. The aim of this review is to summarize the potential aspects and mechanisms by which TQ imparts its action in AD.

An Overview of the Neuropharmacological Potential of Thymoquinone and its Targeted Delivery Prospects for CNS Disorder

At present, people and patients worldwide are relying on the medicinal plant as a therapeutic agent over pharmaceuticals because the medicinal plant is considered safer, especially for chronic disorders. Several medicinal plants and their components are being researched and explored for their possible therapeutic contribution to CNS disorders. Thymoquinone (TQ) is one such molecule. Thymoquinone, one of the constituents of Plant Nigella Sativa, is effective against several neurodegenerative diseases like; Alzheimer's, Depression, Encephalomyelitis, Epilepsy, Ischemia, Parkinson's, and Traumatic. This review article presents the neuropharmacological potential of TQ's, their challenges, and delivery prospects, explicitly focusing on neurological disorders along with their chemistry, pharmacokinetics, and toxicity. Since TQ has some pharmacokinetic challenges, scientists have focused on novel formulations and delivery systems to enhance bioavailability and ultimately increase its therapeutic value. In the present work, the role of nanotechnology in neurodegenerative disease and how it improves bioavailability and delivery of a drug to the site of action has been discussed. There are a few limitations for developing novel drug formulation, including solubility, pH, and compatibility of nanomaterials. Since here we are targeting CNS disorders, the blood-brain barrier (BBB) becomes an additional challenge Hence, the review summarized the novel aspects of delivery and biocompatible nanoparticles-based approaches for targeted drug delivery into CNS, enhancing TQ bioavailability and its neurotherapeutic effects.

Activation of α7 Nicotinic Acetylcholine Receptor by its Selective Agonist Improved Learning and Memory of Amyloid Precursor Protein/Presenilin 1 (APP/PS1) Mice via the Nrf2/HO-1 Pathway

BACKGROUND To reveal the mechanism underlying the effect of alpha7 nicotinic acetylcholine receptor (nAChR) on neurodegeneration in Alzheimer disease (AD), the influence of the receptor on recognition in APP/PS1 mice was evaluated by using its selective agonist (PNU-282987). MATERIAL AND METHODS APP/PS1 and wild-type (WT) mice were treated with PNU or saline, respectively, for 7 days at the ages of 6 and 10 months. RESULTS Morris water maze analysis showed that both at 6 and 10 months of age, PNU treatment enhanced the learning and memory of APP/PS1 mice. However, PNU treatment did not alter the number of senile plaques. Furthermore, a higher protein expression of Nrf2/HO-1, ADAM10, SYP, and SNAP-25, and a lower level of oxidative stress, were observed in the hippocampus of APP/PS1 mice treated with PNU compared with the control group. CONCLUSIONS The results indicated that the activation of alpha7 nAChR by PNU improved the learning and memory of mice carrying the APP/PS1 mutation, regulated the levels of enzymes that mediate APP metabolization to reduce ß-amyloid peptide damage, and decreased the level of oxidative stress and maintained synaptic plasticity, in which the mechanism might be enhancement of the Nrf2/HO-1 pathway.

Sex influences in the preventive effects of N-acetylcysteine in a two-hit animal model of schizophrenia

BACKGROUND

Schizophrenia (SCZ) is a neurodevelopmental disorder influenced by patient sex. Mechanisms underlying sex differences in SCZ remain unknown. A two-hit model of SCZ combines the exposure to perinatal infection (first-hit) with peripubertal unpredictable stress (PUS, second-hit). N-acetylcysteine (NAC) has been tested in SCZ because of the involvement of glutathione mechanisms in its neurobiology.

AIMS

We aim to investigate whether NAC administration to peripubertal rats of both sexes could prevent behavioral and neurochemical changes induced by the two-hit model.

METHODS

Wistar rats were exposed to polyinosinic:polycytidylic acid (a viral mimetic) or saline on postnatal days (PND) 5-7. On PND30-59 they received saline or NAC 220 mg/kg and between PND40-48 were subjected to PUS or left undisturbed. On PND60 behavioral and oxidative alterations were evaluated in the prefrontal cortex (PFC) and striatum. Mechanisms of hippocampal memory regulation such as immune expression of G protein-coupled estrogen receptor 1 (GPER), α7-nAChR and parvalbumin were also evaluated.

RESULTS

NAC prevented sensorimotor gating deficits only in females, while it prevented alterations in social interaction, working memory and locomotor activity in both sexes. Again, in rats of both sexes, NAC prevented the following neurochemical alterations: glutathione (GSH) and nitrite levels in the PFC and lipid peroxidation in the PFC and striatum. Striatal oxidative alterations in GSH and nitrite were observed in females and prevented by NAC. Two-hit induced hippocampal alterations in females, namely expression of GPER-1, α7-nAChR and parvalbumin, were prevented by NAC.

CONCLUSION

Our results highlights the influences of sex in NAC preventive effects in rats exposed to a two-hit schizophrenia model.

The Neuroprotective Effects of Thymoquinone: A Review

Thymoquinone (TQ), one of the main components active of Nigella sativa, exhibited very useful biomedical effects such as anti-inflammatory, antioxidant, antimicrobial, antiparasitic, anticancer, hypoglycemic, antihypertensive, and antiasthmatic effects. There are several studies about pharmacological activities of TQ but its neuroprotection effects are not fully described. The literature search has indicated many studies pertaining to the effects of TQ in neurological problems such as epilepsy, parkinsonism, anxiety, and improvement of learning and memory, and so on. In addition, TQ protected brain cells from various injuries due to its antioxidant, anti-inflammatory, and apoptotic effects in cell line and experimental animal models. The present study has been designed to review the scientific literature about the pharmacological activities of TQ to the neurological diseases. This study purposed that although experimental studies indicated the beneficial effects of TQ against nervous system problems, better designed clinical trials in humans are needed to confirm these effects.

The p38 mitogen activated protein kinase regulates β-amyloid protein internalization through the α7 nicotinic acetylcholine receptor in mouse brain

Alzheimer's disease (AD) is one of the most devastating neurodegenerative disorders. Intracellular β-amyloid protein (Aβ) is an early event in AD. It induces the formation of amyloid plaques and neuron damage. The α7 nicotinic acetylcholine receptor (α7nAChR) has been suggested to play an important role in Aβ caused cognition. It has high affinity with Aβ and could mediate Aβ internalization in vitro. However, whether in mouse brain the p38 MAPK signaling pathway is involved in the regulation of the α7nAChR mediated Aβ internalization and their role in mitochondria remains little known. Therefore, in this study, we revealed that Aβ is internalized by cholinergic and GABAergic neurons. The internalized Aβ were found deposits in lysosomes/endosomes and mitochondria. Aβ could form Aβ-α7nAChR complex with α7nAChR, activates the p38 mitogen activated protein kinase (MAPK). And the increasing of α7nAChR could in return mediate Aβ internalization in the cortex and hippocampus. In addition, by using the α7nAChR agonist PNU282987, the p38 phosphorylation level decreases, rescues the biochemical changes which are tightly associated with Aβ-induced apoptosis, such as Bcl2/Bax level, cytochrome c (Cyt c) release. Collectively, the p38 MAPK signaling pathway could regulate the α7nAChR-mediated internalization of Aβ. The activation of α7nAChR or the inhibition of p38 MAPK signaling pathway may be a beneficial therapy to AD.

Behavioural effects of PNU-282987 and stress in an animal model of Alzheimer's disease

BACKGROUND

Cholinergic deficits play an important role in both cognitive and behavioural alterations in Alzheimer's disease. This study was aimed at evaluating the possible therapeutic role of PNU-282987 (PNU), an α7 nicotinic cholinergic receptor agonist, and the possible effects of stress in precipitating the onset of behavioural deficits in animals with susceptibility to Alzheimer's disease.

METHODS

B6C3-Tg mice with susceptibility to Alzheimer's disease and wild-type mice either with or without restraint stress received 0- or 1-mg/kg PNU. At 12 months old, mice were evaluated for activity levels, anxiety-like levels, and spatial learning and memory.

RESULTS

Data did not show the effects of PNU on activity and anxiety-like behaviour. No effect of PNU on acquisition of a spatial learning task was detected, but a reversal of stress effects on retention in the Morris water maze was observed in transgenic mice.

CONCLUSIONS

Further studies are needed in order to better understand the role of α7 nicotinic cholinergic receptor agonists in motor activity, anxiety, and spatial learning and memory and to develop more accurate pharmacological treatment of psychopathological diseases.

Redistribution of adrenomedullary nicotinic acetylcholine receptor subunits and the effect on circulating epinephrine levels in a murine model of acute asthma

The lack of circulating epinephrine (EPI) in the pathogenesis of asthma has long been attributed to the lack of adrenergic nerves in human airways. However, in this study we considered that EPI levels are regulated by EPI release in addition to synthesis. Nicotinic acetylcholine receptors (nAChRs) have been shown to control EPI release, and we hypothesized that redistribution of nAChR subunits modulates EPI release and circulating EPI levels. Using a mouse model of asthma, circulating EPI levels were measured by enzyme-linked immunosorbent assays. Changes in the expression of nAChR subunits in the adrenal medulla were observed by reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and western blot analysis. Expression of phenylethanolamine N-methyltransferase, tyrosine hydroxylase and galanin was detected by RT-qPCR. Lung pathology, airway resistance (RL) and EPI levels were also assessed after treatment with an α7 nAChR agonist or antagonist. α7 nAChR mRNA expression in the adrenal medulla was increased by more than 2-fold (P<0.05), and circulating EPI levels increased rapidly after treatment with the α7 nAChR agonist. These results indicated that increased EPI release, which was caused by the overexpression of α7 nAChR, was responsible for elevated circulating EPI levels. After treatment with an agonist of α7 nAChR, RL was significantly decreased. Serum corticosterone levels in individual mice were measured to rule out glucocorticoid as the main mediator of changes in EPI levels. On the whole, redistribution of nAChR subunits, primarily α7 nAChR, occurs in the adrenal medulla in asthmatic mice. Increased α7 nAChR expression can rapidly increase serum EPI levels and decrease airway responsiveness.

The Effect of Thymoquinone, α7 Receptor Agonist and α7 Receptor Allosteric Modulator on the Cerebral Cortex in Experimentally Induced Alzheimer's Disease in Relation to MSCs Activation

Background and Objectives

Alzheimer's disease (AD) is the most common form of dementia among older persons. Thymoquinone (TQ) has anti-inflammatory, anticonvulsant and antioxidant activity. A novel α7 nicotinic acetyl choline receptor (α7 nAChR ) agonist (PNU- 282987) have been identified to enhance the cognitive performance. An alternative treatment strategy via compounds known as nicotinic "positive allosteric modulators" (PAMs) has been reported. This study was designed to investigate the combination of PAM of α7 nAChRs with PNU- 282987 or with TQ as a possible treatment for AD in rat.

Methods

48 male albino rats were divided into 4 groups. Group І (Control), Group II received lipopolysaccharide, 0.8 mg/kg by intraperitoneal injection (IPI) once, Group III received TQ 10 mg/kg by IPI, Group IV received PNU-120596 1 mg/kg by IPI, in addition to PNU-282987 1 mg/kg by IPI in subgroup IVa and TQ in subgroup b. All treatment drugs were given for 5 days.

Results

Acidophilic masses, deformed neurons, Congo red +ve masses and reduced Phospho-CREB immunoexpression were seen in group II. All changes regressed by treatment. Some CD44 +ve cells were noticed in group II and few +ve cells in subgroup IVa, that became multiple in group III and subgroup IVb. The histological, histochemical and immunohistochemical changes were confirmed statistically and significant differences were recorded.

Conclusions

TQ or α7 nAChR agonist combined with PAM can have an important role in treatment of AD that is superior to thymoquinone alone. Exceptionally, TQ single or combined with PAM proved activation of MSC.

Behavioral effects of different enriched environments in mice treated with the cholinergic agonist PNU-282987

Environmental enrichment is an experimental model in which rodents are housed in complex environments that favor lower levels of anxiety-like behavior. PNU-282987 (PNU) is a α7 nicotinic acetylcholine receptor agonist with beneficial effects on learning though its effects on anxiety are unclear. Our main aim was to carry out a study of its effects in NMRI (n=96) mice reared in different environments: environmental enrichment (EE), Marlau™ cages (MC) and standard environment (SE). After a 4-month period, mice received acute treatment of PNU (2.5, 5 and 10mg/kg) and were evaluated in the elevated plus-maze (EPM) and hole-board (HB). In the EPM, both EE and MC reared mice showed an increase in percentage of entries into open arms while those from EE group differed from SE in time spent on open arms. Mice treated with 2.5 and 10 mg/kg of PNU devoted less time to rearing into open arms. In the HB task, MC mice displayed higher exploratory activity reflected in more head-dips (HD) during the first minute than EE and SE, whereas EE displayed low exploration levels reflected in total HD (5 min). Further research is needed in order to clarify the behavioral effects of this nicotinic agonist in interaction with different environmental conditions. This article is part of a Special Issue entitled: insert SI title.