Prolonged effects of cholinesterase inhibition with eptastigmine on the cerebral blood flow-metabolism ratio of normal rats

Longitudinal GluCEST MRI Changes and Cerebral Blood Flow in 5xFAD Mice

Many of the focal neurological symptoms associated with Alzheimer's disease (AD) are due to synaptic loss. Glutamate chemical exchange saturation transfer (GluCEST) magnetic resonance imaging (MRI) is a candidate method to assess synaptic dysfunction. We assessed chronological changes in GluCEST in a 5xFAD mouse model of AD, comparing Glucest effects and regional cerebral blood flow (CBF). GluCEST effects and CBF in 5xFAD mice aged 1–15 months and their littermates (WT) were measured. Neurite orientation dispersion and density imaging (NODDI) MRI reflecting dendritic/axonal density was also measured and compared with GluCEST in 7-month-old mice. While regional CBF's decrease began at 7 months, GluCEST-reduction effects preceded hypoperfusion of the temporal cortex and hippocampus. While longitudinal 5xFAD mouse measurements revealed a correlation between the regional GluCEST effects and CBF, a generalized linear mixed model revealed statistically different correlations in cortical and basal brain regions. Further, NODDI-derived neurite density correlated with GluCEST effects in the parietal cortex, but not in the hippocampus, thereby revealing regional differences in pathophysiological mechanisms. Finally, GluCEST's effects correlated with regional synaptophysin. These results demonstrate that GluCEST can reflect subtle synaptic changes and may be a potential imaging method for AD diagnosis as well as serve as a biomarker of AD progression.

The nootropic and anticholinesterase activities of Clitoria ternatea Linn. root extract: Potential treatment for cognitive decline

BACKGROUND

Clitoria ternatea (CT) is an herbal plant that has been used as a memory booster in folk medicine. CT root extract has been proven to restore chronic cerebral hypoperfusion (CCH)-induced memory deficits in a rat model, but the underlying mechanisms and the toxicity profile following repeated exposure have yet to be explored.

THE AIM OF THE STUDY

To investigate the effects of the chronic (28 days) oral administration of CT root extract on CCH-induced cognitive impairment, neuronal damage and cholinergic deficit, and its toxicity profile in the CCH rat model.

MATERIALS AND METHODS

The permanent bilateral occlusion of common carotid arteries (PBOCCA) surgery method was employed to develop a CCH model in male Sprague Dawley (SD) rats. Then, these rats were given oral administration of CT root extract at doses of 100, 200, and 300 mg/kg, respectively for 28 days and subjected to behavioural tests. At the end of the experiment, the brain was harvested for histological analysis and cholinesterase activities. Then, blood samples were collected and organs such as liver, kidney, lung, heart, and spleen were procured for toxicity assessment.

RESULTS

Chronic treatment of CT root extract at doses of 200 and 300 mg/kg, restored memory impairments induced by CCH. CT root extract was also found to diminish CCH-induced neuronal damage in the CA1 region of the hippocampus. High dose (300 mg/kg) of the CT root extract was significantly inhibited the increased acetylcholinesterase (AChE) activity in the frontal cortex and hippocampus of the PBOCCA rats. In toxicity study, repeated doses of CT root extract were found to be safe in PBOCCA rats after 28 days of treatment.

CONCLUSIONS

Our findings provided scientific evidence supporting the therapeutic potential of CT root extract in the treatment of vascular dementia (VaD)-related cholinergic abnormalities and subsequent cognitive decline.

Embelin Improves the Spatial Memory and Hippocampal Long-Term Potentiation in a Rat Model of Chronic Cerebral Hypoperfusion

Alzheimer's disease (AD) is the second most occurring neurological disorder after stroke and is associated with cerebral hypoperfusion, possibly contributing to cognitive impairment. In the present study, neuroprotective and anti-AD effects of embelin were evaluated in chronic cerebral hypoperfusion (CCH) rat model using permanent bilateral common carotid artery occlusion (BCCAO) method. Rats were administered with embelin at doses of 0.3, 0.6 or 1.2 mg/kg (i.p) on day 14 post-surgery and tested in Morris water maze (MWM) followed by electrophysiological recordings to access cognitive abilities and synaptic plasticity. The hippocampal brain regions were extracted for gene expression and neurotransmitters analysis. Treatment with embelin at the doses of 0.3 and 0.6 mg/kg significantly reversed the spatial memory impairment induced by CCH in rats. Embelin treatment has significantly protected synaptic plasticity impairment as assessed by hippocampal long-term potentiation (LTP) test. The mechanism of this study demonstrated that embelin treatment alleviated the decreased expression of BDNF, CREB1, APP, Mapt, SOD1 and NFκB mRNA levels caused by CCH rats. Furthermore, treatment with embelin demonstrated neuromodulatory activity by its ability to restore hippocampal neurotransmitters. Overall these data suggest that embelin improve memory and synaptic plasticity impairment in CCH rats and can be a potential drug candidate for neurodegenerative disease-related cognitive disorders.

Visual hallucinations in Alzheimer's disease do not seem to be associated with chronic hypoperfusion of to visual processing areas V2 and V3 but may be associated with reduced cholinergic input to these areas

Background

Up to 20% of patients with AD experience hallucinations. The pathological substrate is not known. Visual hallucinations (VH) are more common in dementia with Lewy bodies (DLB). In autopsy studies, up to 60% of patients with AD have concomitant Lewy body pathology. Decreased perfusion of the occipital lobe has been implicated in DLB patients with VH, and post-mortem studies point to both decreased cholinergic activity and reduced oxygenation of the occipital cortex in DLB.

Methods

We used biochemical methods to assess microvessel density (level of von Willebrand factor, a marker of endothelial cell content), ante-mortem oxygenation (vascular endothelial growth factor, a marker of tissue hypoxia; myelin-associated glycoprotein to proteolipid protein-1 ratio, a measure of tissue oxygenation relative to metabolic demand), cholinergic innervation (acetylcholinesterase and choline acetyltransferase), butyrylcholinesterase and insoluble α-synuclein content in the BA18 and BA19 occipital cortex obtained post-mortem from 23 AD patients who had experienced visual hallucinations, 19 AD patients without hallucinations, 19 DLB patients, and 36 controls. The cohorts were matched for age, gender and post-mortem interval.

Results

There was no evidence of reduced microvessel density, hypoperfusion or reduction in ChAT activity in AD with visual hallucinations. Acetylcholinesterase activity was reduced in both BA18 and BA19, in all 3 dementia groups, and the concentration was also reduced in BA19 in the DLB and AD without visual hallucinations groups. Insoluble α-synuclein was raised in the DLB group in both areas but not in AD either with or without visual hallucinations.

Conclusions

Our results suggest that visual hallucinations in AD are associated with cholinergic denervation rather than chronic hypoperfusion or α-synuclein accumulation in visual processing areas of the occipital cortex.

Electronic supplementary material

The online version of this article (10.1186/s13195-019-0519-7) contains supplementary material, which is available to authorized users.

Chronic cerebral hypoperfusion-induced memory impairment and hippocampal long-term potentiation deficits are improved by cholinergic stimulation in rats

BACKGROUND

Chronic cerebral hypoperfusion (CCH) can induce the accumulation of reactive oxygen species, which leads to oxidative damage, neuronal injury, and central cholinergic dysfunction in vulnerable regions of the brain, such as the hippocampus and cerebral cortex. These effects can lead to significant cognitive impairments in clinical populations of vascular dementia (VaD). The present studies aimed to investigate the role of the cholinergic system in memory functions and hippocampal long-term potentiation (LTP) impairments induced by CCH in rats.

METHODS

Male Sprague Dawley rats were subjected to permanent bilateral occlusion of common carotid arteries (PBOCCA) or sham surgery. Then, PBOCCA rats received ip injections with, either vehicle (control group), the muscarinic receptor agonist oxotremorine (0.1 mg/kg), or the acetylcholinesterase inhibitor physostigmine (0.1 mg/kg). Cognitive functions were evaluated using a passive avoidance task and the Morris water maze test. In addition, hippocampal LTP was recorded in vivo under anaesthesia.

RESULTS

The PBOCCA rats exhibited significant deficits in passive avoidance retention and spatial learning and memory tests. They also showed a suppression of LTP formation in the hippocampus. Oxotremorine and physostigmine significantly improved the learning and memory deficits as well as the suppression of LTP in PBOCCA rats.

CONCLUSIONS

The present data suggest that the cholinergic system plays an important role in CCH-induced cognitive deficits and could be an effective therapeutic target for the treatment of VaD.

Clitoria ternatea L. root extract ameliorated the cognitive and hippocampal long-term potentiation deficits induced by chronic cerebral hypoperfusion in the rat

ETHNOPHARMACOLOGICAL RELEVANCE

Clitoria ternatea L. (CT), commonly known as Butterfly pea, is used in Indian Ayurvedic medicine to promote brain function and treat mental disorders. Root of CT has been proven to enhance memory, but its role in an animal model of chronic cerebral hypoperfusion (CCH), which has been considered as a major cause of brain disorders, has yet to be explored.

AIM OF THE STUDY

To assess the motor and cognitive effects of acute oral administration of CT root methanolic extract and hippocampal long-term plasticity in the CA1 region of the CCH rat model.

MATERIALS AND METHODS

Male Sprague Dawley rats (200-300 g) were subjected to permanent bilateral occlusion of common carotid arteries (PBOCCA) or sham operation. Then, these rats were given oral administration of CT root extract at doses of 100, 200 or 300 mg/kg on day 28 post-surgery and tested using behavioural tests (open-field test, passive avoidance task, and Morris water maze) and electrophysiological recordings (under urethane anaesthesia).

RESULTS

Treatment with CT root extract at the doses of 200 and 300 mg/kg resulted in a significant enhancement in memory performance in CCH rats induced by PBOCCA. Furthermore, CCH resulted in inhibition of long-term potentiation (LTP) formation in the hippocampus, and CT root extract rescued the LTP impairment. The CT root extract was confirmed to improve the glutamate-induced calcium increase via calcium imaging using primary cultured rat neurons. No significance difference was found in the CaMKII expression. These results demonstrated that CT root extract ameliorates synaptic function, which may contribute to its improving effect on cognitive behaviour.

CONCLUSIONS

Our findings demonstrated an improving effect of CT root extract on memory in the CCH rat model suggesting that CT root extract could be a potential therapeutic strategy to prevent the progression of cognitive deterioration in vascular dementia (VaD) and Alzheimer's disease (AD) patients.

Circadian rhythms of heart rate and locomotion after treatment with low-dose acetylcholinesterase inhibitors

This study tested the hypothesis that repeated exposure to low levels of sarin, pyridostigmine bromide (PB) or their combination, at doses equivalent to those possibly experienced by veterans of the 1991 Persian Gulf War, could lead to persistent or delayed autonomic effects and thus help to explain the cause of clinical findings in this population. Male Sprague-Dawley rats were treated for 3 weeks with: saline injection (0.5 ml kg(-1), s.c., 3 times weekly) with tap drinking water (control); saline injection with PB (80 mg l(-1) in drinking water); sarin injection (62.5 microg kg(-1), s.c., 0.5 x LD(50), 3 times weekly) with tap drinking water (sarin); or sarin injection with PB in drinking water (sarin + PB). At 2, 4 or 16 weeks post-treatment, heart rate (HR) and locomotor activity (LA) were studied by radiotelemetry. Two weeks posttreatment, HR in drug-treated animals was significantly lower than in controls. A decrease in low-frequency HR power spectrum (PS) was found at 00:00 h and 08:00 h with sarin + PB and at 00:00 h with sarin, while total power was enhanced with sarin + PB at 22:00 h. Minimal effects of drug treatments on HR and HR PS were detected at 4 and 16 weeks post-treatment. No significant differences in LA between control and other groups were found. Since no consistent long-term effects were found in any of the variables studied, these experiments do not support the hypothesis that repeated administration of low doses of PB and the nerve agent sarin can induce persistent or delayed alterations in autonomic function.

Preliminary findings of uncoupling of flow and metabolism in unipolar compared with bipolar affective illness and normal controls

Cerebral metabolism (CMR for glucose or oxygen) and blood flow (CBF) have been reported to be closely correlated in healthy controls. Altered relationships between CMR and CBF have been reported in some brain disease states, but not others. This study examined relationships between global and regional CMRglu vs. CBF in controls and medication-free primary affective disorder patients. Nine bipolars, eight unipolars, and nine healthy controls had [15O]-water positron emission tomography (PET) scans at rest, and [18F]-fluorodeoxyglucose PET scans during an auditory continuous performance task. Patients had [15O]-water and FDG PET scans in tandem the same day; controls had an average of 45+/-27 days between scans. Maps of regional coupling were constructed for each subject group. In controls and bipolars, global and virtually all regional correlation coefficients for CMRglu and CBF were positive, albeit more robustly so in controls. However, correlative relationships in unipolars were qualitatively different, such that global and most regional measures of flow and metabolism were not positively related. Unipolars had significantly fewer positive regional correlation coefficients than healthy controls and bipolars. These were significantly different from controls in orbital cortex, anterior cingulate, posterior cingulate, and posterior temporal cortex, and different from bipolars in pregenual anterior cingulate. In unipolars, the degree of flow-metabolism uncoupling was inversely correlated with Hamilton depression scores, indicating the severity of uncoupling was directly related to the severity of depression. These preliminary data suggest abnormal relationships between cerebral metabolism and blood flow globally and regionally in patients with unipolar depression that warrant replication and extension to potential pathophysiological implications.

Eptastigmine: ten years of pharmacology, toxicology, pharmacokinetic, and clinical studies

Eptastigmine (heptyl-physostigmine tartrate) is a carbamate derivative of physostigmine in which the carbamoylmethyl group in position 5 of the side chain has been substituted with a carbamoylheptyl group. In vitro and ex vivo results suggest that eptastigmine has a long-lasting reversible brain cholinesterase (i.e., acetylcholinesterase and butyryl-cholinesterase) inhibitory effect. When administered in vivo to rodents by various routes, eptastigmine inhibits cerebral acetylcholinesterases (AChE) and increases acetylcholine (Ach) brain levels by 2500-3000%, depending on the dose. This effect leads to an improvement in the cerebral blood flow in the ischemic brain, excitatory and inhibitory effects on the gastrointestinal tract and to a protection from acute soman and diisopropylfluorophosphate intoxication. Eptastigmine, by either acute or chronic administration, has been found to have memory enhancing effects in different species of normal, aged and lesioned animals. It also restored to normal the age-related increase of EEG power without affecting spontaneous motor activity. Clinical investigations on more than 1500 patients with Alzheimer's disease demonstrated that eptastigmine significantly improved cognitive performance (as assessed by the cognitive subscale of the Alzheimer's Disease Assessment Scale) as compared with placebo. This improvement was most evident in patients with more severe cognitive impairment at the baseline. The relationship between patient performance and average steady-state AChE inhibition was described by an inverted U-shaped dose-response curve. Pharmacokinetic studies have revealed that after oral administration eptastigmine is rapidly distributed to the tissues and readily enters the CNS, where it can be expected to inhibit AChE for a prolonged period. Eptastigmine is generally well tolerated and the majority of adverse events (cholinergic) were mild to moderate in intensity. However, the adverse hematologic (granulocytopenia) effects reported in two studies have resulted in the suspension of further clinical trials.

Cerebral microvascular pathology in aging and Alzheimer's disease

The aging of the central nervous system and the development of incapacitating neurological diseases like Alzheimer's disease (AD) are generally associated with a wide range of histological and pathophysiological changes eventually leading to a compromised cognitive status. Although the diverse triggers of the neurodegenerative processes and their interactions are still the topic of extensive debate, the possible contribution of cerebrovascular deficiencies has been vigorously promoted in recent years. Various forms of cerebrovascular insufficiency such as reduced blood supply to the brain or disrupted microvascular integrity in cortical regions may occupy an initiating or intermediate position in the chain of events ending with cognitive failure. When, for example, vasoconstriction takes over a dominating role in the cerebral vessels, the perfusion rate of the brain can considerably decrease causing directly or through structural vascular damage a drop in cerebral glucose utilization. Consequently, cerebral metabolism can suffer a setback leading to neuronal damage and a concomitant suboptimal cognitive capacity. The present review focuses on the microvascular aspects of neurodegenerative processes in aging and AD with special attention to cerebral blood flow, neural metabolic changes and the abnormalities in microvascular ultrastructure. In this context, a few of the specific triggers leading to the prominent cerebrovascular pathology, as well as the potential neurological outcome of the compromised cerebral microvascular system are also going to be touched upon to a certain extent, without aiming at total comprehensiveness. Finally, a set of animal models are going to be presented that are frequently used to uncover the functional relationship between cerebrovascular factors and the damage to neural networks.

Rivastigmine, a brain-selective acetylcholinesterase inhibitor, ameliorates cognitive and motor deficits induced by closed-head injury in the mouse

The effects of Rivastigmine, a novel centrally-acting anticholinesterase agent, were evaluated on cerebral edema, neurological and motor deficits, and impairment of spatial memory induced in mice by closed-head injury (CHI). Severe injury was induced in the left hemisphere of mice under ether anesthesia. Rivastigmine (1 or 2 mg/kg) or saline (10 ml/kg) was injected SC 5 min later. Rivastigmine (2 mg/kg) reduced cerebral edema by at least 50% (p < 0.01), 24 h after CHI and accelerated the recovery of motor function 7 and 14 days after CHI. Control mice (n = 24), previously trained to find the goal platform in a Morris water maze failed to recall or relearn its position for at least 11 days post-injury. Those given a single injection of Rivastigmine (2 mg/kg) regained their pre-test latencies by the third day after CHI. The neuroprotective effects of Rivastigmine on brain edema, neurological and motor function, and performance in the Morris water maze were completely antagonized by simultaneous SC injection of either scopolamine (0.5 mg/kg) or mecamylamine (2.5 mg/kg). The antagonists alone had no significant effect on any of these parameters. These data show that the reduction by Rivastigmine of the immediate and long-term sequelae of brain injury are mediated by increased cholinergic activity at both muscarinic and nicotinic receptors.

Autoradiographic evidence for flow-metabolism uncoupling during stimulation of the nucleus basalis of Meynert in the conscious rat

We earlier reported that electrical stimulation of the rat nucleus basalis of Meynert (NBM) induces large cerebral blood flow increases, particularly in frontal cortical areas but also in some subcortical regions. The present study was designed to address the issue of blood flow control exerted by NBM projections. To this aim, we have determined whether these flow increases were associated with proportionate changes in metabolic activity as evaluated by cerebral glucose utilization (CGU) strictly under the same experimental conditions in the conscious rat. An electrode was chronically implanted in a reactive site of the NBM as determined by laser-Doppler flowmetry (LDF) of the cortical circulation. One to two weeks later, while the cortical blood flow was monitored by LDF, we measured CGU using the [14C]2-deoxyglucose autoradiographic technique during unilateral electrical stimulation of the NBM, and analyzed the local flow-metabolism relationship. The large increases in cortical blood flow induced by NBM stimulation, exceeding 300% in various frontal areas, were associated with at most 24% increases in CGU (as compared with the control group) in one frontal area. By contrast, strong increases in CGU exceeding 150% were observed in subcortical regions ipsilateral to the stimulation, especially in extrapyramidal structures, associated with proportionate CBF changes. Thus, none of the blood flow changes observed in the cortex can be ascribed to an increased metabolic activity, whereas CBF and CGU were coupled in many subcortical areas. This result indicates that different mechanisms, which do not necessarily involve any metabolic factor, contribute to the regulation of the cerebral circulation at the cortical and subcortical level. Because the distribution of the uncoupling is coincident with that of cholinergic NBM projections directly reaching cortical microvessels, these data strongly support the hypothesis that NBM neurons are capable of exerting a neurogenic control of the cortical microcirculation.

Cholinesterase inhibition improves blood flow in the ischemic cerebral cortex

The ability of central cholinesterase inhibition to improve cerebral blood flow in the ischemic brain was tested in Sprague-Dawley rats with tandem occlusion of left middle cerebral and common carotid arteries. Cerebral blood flow was measured with lodo- 14C-antipyrine autoradiography in 170 regions of cerebral cortex. The regional distribution of blood flow was characterized in normal animals by cerebral blood flow maxima in the temporal regions. After 2 h ischemia, minimum cerebral blood flow values were found in the lateral frontal and parietal areas on the left hemisphere, and a new maximum was found in the right hemisphere in an area approximately symmetrical to the ischemic focus. Heptyl-physostigmine (eptastigmine), a carbamate cholinesterase inhibitor with prolonged time of action improved cerebral blood flow in most regions, with the exception of the ischemic core. The drug also enhanced the ischemia-induced rostral shift of cerebral blood flow maxima in the right hemisphere. The effects of eptastigmine were more marked 24 h after ischemia. Discriminant analysis showed that data from only 22 regions was sufficient to achieve 100% accuracy in classifying all cases into the various experimental conditions. The redistribution of cerebral blood flow to the sensorimotor area of the right hemisphere of animals with cerebral ischemia, a phenomenon possibly related to recovery of function, was also enhanced by eptastigmine.

Cholinergic control of cerebral blood flow in stroke, trauma and aging

Enhancing the availability of endogenous acetylcholine by inhibition of cholinesterase with physostigmine, eptastigmine or soman at sub-toxic doses increases cerebral blood flow (CBF) and the response of this variable to changes in PaCO2. These effects are not correlated with metabolic activation, suggesting that the function of the cholinergic vasodilation is not merely to supply metabolic substrates. Since choline (Ch) can exchange between blood and the brain extracellular milieu the stage is set for possible feedback interactions between ACh synthesis and CBF. A negative feedback of CBF on ACh synthesis under conditions of a negative arteriovenous (A-V) difference for Ch across cerebral capillaries may contribute to stabilize GBF in ischemia. Eptastigmine and physostigmine significantly improve perfusion in experimental models of focal cerebral ischemia and traumatic brain injury respectively. During the short periods of time in which the A-V difference for Ch across the brain is positive, a positive feedback between cerebral free Ch and CBF may enhance the ability of the brain to recover Ch from the circulation for synthesis of membrane phospholipids. A loss of cholinergic cerebrovascular control may thus impair the survival of all cells within the CNS and contribute to the pathophysiology of dementia. Perhaps the view that the loss of cholinergic cells is the end point of Alzheimer's dementia could be modified to state that a cholinergic deficit may be the starting point of a decline in cerebral phospholipid turnover and cell membrane renewal that could lead to a generalized deterioration of cerebral function.

Inhibition of acetylcholinesterase modulates the autoregulation of cerebral blood flow and attenuates ischemic brain metabolism in hypertensive rats

We designed the present study to examine whether or not the inhibition of acetylcholinesterase modulates cerebral microcirculation in hypotension and improves brain metabolism in ischemia induced by bilateral carotid artery occlusion in hypertensive rats. Blood flow to the parietal cortex was determined by the H2 clearance method. Lactate, pyruvate, and ATP were estimated by enzymatic methods. Acetylcholinesterase inhibitor (AChEI, ENA-713), at 0.05, 0.1, or 0.5 mg/kg, was intravenously injected 10 min before either hemorrhagic hypotension or cerebral ischemia. The levels of acetylcholine in the control were 29.3 +/- 8.1 (mean +/- SD) and 39.5 +/- 8.1 pmol/mg in the cortex and hippocampus, respectively, and they were significantly decreased by 15-19% after 60 min of ischemia in the vehicle-treated rats. AChEI preserved the levels to 93-98% of the control (p < 0.05 versus vehicle). The lower limit of autoregulation was 74 +/- 9% of the resting values. The administration of AChEI helped preserve blood flow and lowered the limit to 64 +/- 6% (p < 0.05 versus control). After 60 min of ischemia, lactate increased 6.5-fold and ATP decreased to 64% of the control value. The administration of AChEI dose-dependently reduced the lactate level 1.9- to 3.9-fold and well preserved the ATP level to 94-97% of the control. The inhibition of acetylcholinesterase activity may preserve cerebral autoregulation during hypotension and protect cerebral metabolism against ischemic insult.