Muscarinic binding and choline acetyltransferase in postmortem brains of demented patients

Benefits of Treatment with Ginkgo Biloba Extract EGb 761 Alone or Combined with Acetylcholinesterase Inhibitors in Vascular Dementia

BACKGROUND

Vascular dementia (VaD) is the most severe manifestation of cognitive impairment caused by cerebrovascular disease. There are currently no specific drug treatments approved for VaD, with cholinesterase inhibitors (AChEI) being frequently used in VaD. However, the benefits they provide are small and short-lived. The standardized extract of Ginkgo biloba EGb 761 has demonstrated protective properties against neuronal and vascular damage and has been used as a pharmacological treatment for VaD.

OBJECTIVES

This study aims to study the efficacy of EGb 761 alone and in combination with AChEI in a real-life setting. We carried out a retrospective analysis of data over a 12-month period in a sample of people suffering from VaD.

METHODS

We retrospectively identified 77 patients with a diagnosis of VaD who had received treatment with any of the following drugs: Ginkgo biloba extract EGb 761 (240 mg daily), donepezil (10 mg daily), galantamine (16 or 24 mg daily), or rivastigmine patch (9.5 or 13.3 mg daily). Subjects were divided into three groups according to the treatment they had received: EGb 761 alone (n = 25), AChEI alone (n = 26), and EGb 761+AChEI (n = 26). Cognitive functioning was assessed by Mini-Mental State Examination (MMSE), Rey Auditory Verbal Learning Test (RAVLT), Symbol Digit Modalities Test (SDMT), Boston Naming Test (BNT), Trail Making Test forms A (TMTA) and B (TMTB), Letter (LFT) and Category Fluency Test (CFT); neuropsychiatric symptoms were assessed by the Neuropsychiatric Inventory (NPI); functional capacity was assessed by Interview for Deterioration in Daily Living (IDDD).

RESULTS

A statistically significant improvement was observed in the EGb 761 group versus the AChEI group at 12 months' follow-up in CFT (+1.74, p < 0.001), TMTA (-17.91, p = 0.031) and NPI (-5.89, p < 0.001). With regard to the combined treatment, a statistically significant improvement was shown in the EGb 761 plus AChEI treatment group versus AChEI group at the 12-month follow-up in MMSE (+2.0, p = 0.001), RAVLT (+2.23, p = 0.007), CFT (+1.15, p = 0.013), TMTA (-19.92, p = 0.012), TMTB (-46.50, p < 0.001) and NPI (-6.77, p < 0.001). In the same line, a statistically significant improvement was observed in the EGb 761 plus AChEI treatment group versus EGb 761 at 12-month follow-up regarding MMSE (+2.11, p = 0.001), RAVLT (+2.35, p = 0.004) and TMTB (-25.25, p = 0.015).

CONCLUSION

After 12 months of treatment EGb 761 alone or combined with AChEI showed cognitive and behavioral benefits in patients suffering from VaD. This study thus provides additional real-world evidence for the combined use of EGb 761 and anti-dementia drugs in VaD patients.

The Effects of Statins on Neurotransmission and Their Neuroprotective Role in Neurological and Psychiatric Disorders

Statins are among the most widely used drug classes in the world. Apart from their basic mechanism of action, which is lowering cholesterol levels, many pleiotropic effects have been described so far, such as anti-inflammatory and antiatherosclerotic effects. A growing number of scientific reports have proven that these drugs have a beneficial effect on the functioning of the nervous system. The first reports proving that lipid-lowering therapy can influence the development of neurological and psychiatric diseases appeared in the 1990s. Despite numerous studies about the mechanisms by which statins may affect the functioning of the central nervous system (CNS), there are still no clear data explaining this effect. Most studies have focused on the metabolic effects of this group of drugs, however authors have also described the pleiotropic effects of statins, pointing to their probable impact on the neurotransmitter system and neuroprotective effects. The aim of this paper was to review the literature describing the impacts of statins on dopamine, serotonin, acetylcholine, and glutamate neurotransmission, as well as their neuroprotective role. This paper focuses on the mechanisms by which statins affect neurotransmission, as well as on their impacts on neurological and psychiatric diseases such as Parkinson's disease (PD), Alzheimer's disease (AD), vascular dementia (VD), stroke, and depression. The pleiotropic effects of statin usage could potentially open floodgates for research in these treatment domains, catching the attention of researchers and clinicians across the globe.

Oral administration of grape seed polyphenol extract restores memory deficits in chronic cerebral hypoperfusion rats

Chronic cerebral hypoperfusion (CCH) has been recognized as an important cause of both vascular dementia and Alzheimer's disease (AD), the two most prominent neurodegenerative diseases causing memory impairment in the elderly. However, an effective therapy for CCH-induced memory impairment has not yet been established. Grape seed polyphenol extract (GSPE) has powerful antioxidant properties and protects neurons and glia during ischemic injury, but its potential use in the prevention of CCH-induced memory impairment has not yet been investigated. Here, CCH-related memory impairment was modeled in rats using permanent bilateral occlusion of the common carotid artery. A Morris water maze task was used to evaluate memory, the levels of acetylcholinesterase, choline acetyltransferase, acetylcholine were used to evaluate cholinergic function, and oxidative stress was assessed by measuring the enzyme activity of superoxide dismutase, glutathione peroxidase, malonic dialdehyde, and catalase. We found that oral administration of GSPE for 1 month can rescue memory deficits. We also found that GSPE restores cholinergic neuronal function and represses oxidative damage in the hippocampus of CCH rats. We propose that GSPE protects memory in CCH rats by reducing ischemia-induced oxidative stress and cholinergic dysfunction. These findings provide a novel application of GSPE in CCH-related memory impairments.

Vitamin B6 prevents isocarbophos-induced vascular dementia in rats through N-methyl-D-aspartate receptor signaling

BACKGROUND

We have previously reported that the long-term exposure of organophosphorus induces vascular dementia (VD) in rats. As a coenzyme, vitamin B6 is mainly involved in the regulation of metabolisms. Whether vitamin B6 improves VD remains unknown.

METHODS

The model of VD was induced by feeding rats with isocarbophos (0.5 mg/kg per two day, 12 weeks). The blood flow of the posterior cerebral artery (PCA) in rat was assessed by transcranial Doppler (TCD). The learning and memory were evaluated by the Morris Water Maze (MWM) test.

RESULTS

Administration of vitamin B6 increased the blood flow in the right and left posterior cerebral arteries and improved the functions of learning and memory in isocarbophos-treated rats. Vitamin B6 increased the protein levels of N-methyl-D-aspartate receptor (NMDAR) 2B, postsynaptic densities (PSDs) protein 95, and calmodulin-dependent protein kinase II (CaMK-II) in the hippocampus, which were decreased by isocarbophos in rats. Morphological analysis by light microscope and electronic microscope indicated disruptions of the hippocampus caused by isocarbophos were normalized by vitamin B6. Importantly, the antagonist of NMDAR signaling by eliprodil abolished these beneficial effects produced by vitamin B6 on PCA blood flow, learning, memory, and hippocampus structure in rats, as well as the protein expression of NMDAR 2B, PSDs protein 95, and CaMK-II in the hippocampus.

CONCLUSION

Vitamin B6 activates NMDAR signaling to prevent isocarbophos-induced VD in rats.

Erythropoietin Rescues Memory Impairment in a Rat Model of Chronic Cerebral Hypoperfusion via the EPO-R/JAK2/STAT5/PI3K/Akt/GSK-3β Pathway

Vascular dementia is the second most common cause of dementia in older people and is characterized by the sudden onset of impairments in thinking skills and behavior, which generally occur following a stroke. Unfortunately, effective therapy for vascular dementia remains inadequate. Erythropoietin (EPO) is a glycoprotein hormone that controls erythropoiesis, or red blood cell production. Recently, a prominent role for EPO has been defined in the nervous system, and there is growing interest in the potential therapeutic use of EPO for neuroprotection. However, whether it is protective from memory impairments and the underlying mechanisms of vascular dementia (VD) remains unknown. In the current study, we reported that supplements with exogenous erythropoietin (EPO) for 4 weeks could restore impaired memory in 2-vessel occlusion (2VO) rats, a well-established vascular dementia animal model. EPO also rescued impairments in dendritic spines and cholinergic dysfunctions in the hippocampus. Moreover, EPO suppressed the overactivation of GSK-3β in the hippocampus by stimulating the JAK2/STAT5/PI3K/Akt signal pathway. Furthermore, we found that genetic knockdown of the EPO receptor (EPO-R) by shRNA blocks the neuroprotection conferred by EPO on memory in VD. We hypothesized that EPO treatment is able to rescue the memory impairments in VD by stimulating the EPO-R/JAK2/STAT5/PI3K/Akt/GSK-3β pathway and suggest the potential usage of EPO in the therapy for VD.

Chronic administration of isocarbophos induces vascular cognitive impairment in rats

Vascular dementia, being the most severe form of vascular cognitive impairment (VCI), is caused by cerebrovascular disease. Whether organophosphorus causes VCI remains unknown. Isocarbophos (0.5 mg/kg per 2 days) was intragastrically administrated to rats for 16 weeks. The structure and function of cerebral arteries were assayed. The learning and memory were evaluated by serial tests of step-down, step-through and morris water maze. Long-term administration of isocarbophos reduced the hippocampal acetylcholinesterase (AChE) activity and acetylcholine (ACh) content but did not alter the plasma AChE activity, and significantly damaged the functions of learning and memory. Moreover, isocarbophos remarkably induced endothelial dysfunction in the middle cerebral artery and the expressions of ICAM-1 and VCAM-1 in the posterior cerebral artery. Morphological analysis by light microscopy and electron microscopy indicated disruptions of the hippocampus and vascular wall in the cerebral arteries from isocarbophos-treated rats. Treatment of isocarbophos injured primary neuronal and astroglial cells isolated from rats. Correlation analysis demonstrated that there was a high correlation between vascular function of cerebral artery and hippocampal AChE activity or ACh content in rats. In conclusion, chronic administration of isocarbophos induces impairments of memory and learning, which is possibly related to cerebral vascular dysfunction.

The history of the cholinergic hypothesis

The cholinergic hypothesis of cognitive impairment and Alzheimer's disease has been for decades a "polar star" for studies on dementia and neurodegenerative diseases. Aim of the present article is to briefly summarize its birth and its evolution throughout years and discoveries. Putting the cholinergic hypothesis in an historical perspective, allows to appreciate the enormous amount of experimental and clinical research that it has stimulated over years and the impressive extent of knowledge generated by this research. While some of the assumptions at the basis of its original formulation are disputable in the light of recent developments, the cholinergic hypothesis has, however, constituted an invaluable stimulus to better understand not only the anatomy and the biochemistry of the cholinergic systems of brain connections but also its developmental biology, its complex relationships with trophic factors, its role in cognitive functions. Thus, rather than being consigned to history, the cholinergic hypothesis will likely contribute to further understanding dementia and neurodegenerative diseases and will hopefully be integrated in novel therapies and treatments.

Cholinergic deficiency involved in vascular dementia: possible mechanism and strategy of treatment

Vascular dementia (VaD) is a progressive neurodegenerative disease with a high prevalence. Several studies have recently reported that VaD patients present cholinergic deficits in the brain and cerebrospinal fluid (CSF) that may be closely related to the pathophysiology of cognitive impairment. Moreover, cholinergic therapies have shown promising effects on cognitive improvement in VaD patients. The precise mechanisms of these cholinergic agents are currently not fully understood; however, accumulating evidence indicates that these drugs may act through the cholinergic anti-inflammatory pathway, in which the efferent vagus nerve signals suppress pro-inflammatory cytokine release and inhibit inflammation, although regulation of oxidative stress and energy metabolism, alleviation of apoptosis may also be involved. In this paper, we provide a brief overview of the cholinergic treatment strategy for VaD and its relevant mechanisms of anti-inflammation.Acta Pharmacologica Sinica (2009) 30: 879-888; doi: 10.1038/aps.2009.82.

Mechanism of action of the nicotinic acetylcholine receptor

Nicotinic acetylcholine receptors at peripheral synapses mediate rapid and effective excitatory synaptic transmission. The functional properties of peripheral and central nicotinic acetylcholine receptors are similar, yet in the central nervous system nicotinic receptors do not appear to occur postsynaptically at many excitatory synapses. Two properties of nicotinic receptors are that significant Ca2+ influx can occur through the receptor channel and that at low agonist concentrations steady activation of nicotinic receptors can occur. These are discussed in the context of presynaptic and postsynaptic localizations of nicotinic receptors.

Vascular determinants of cholinergic deficits in Alzheimer disease and vascular dementia

Alzheimer's disease (AD) and vascular dementia (VaD) are widely accepted as the most common forms of dementia. Cerebrovascular lesions frequently coexist with AD, creating an overlap in the clinical and pathological features of VaD and AD. This review assembles evidence for a role for cholinergic mechanisms in the pathogenesis of VaD, as has been established for AD. We first consider the anatomy and vascularization of the basal forebrain cholinergic neuronal system, emphasizing its susceptibility to the effects of arterial hypertension, sustained hypoperfusion, and ischemic cerebrovascular disease. The impact of aging and consequences of disruption of the cholinergic system in cognition and in control of cerebral blood flow are further discussed. We also summarize preclinical and clinical evidence supporting cholinergic deficits and the use of cholinesterase inhibitors in patients with VaD. We postulate that vascular pathology likely plays a common role in initiating cholinergic neuronal abnormalities in VaD and AD.

Dementia with cerebrovascular disease: the benefits of early treatment

Patients with vascular dementia (VaD) and Alzheimer's disease with cerebrovascular disease (AD + CVD) have dementia associated with underlying CVD. Although diagnosis of VaD is challenging, VaD is typically characterized by a stepwise progression of dementia that is closely associated with stroke and focal neurological findings, and a symptom profile that often includes executive dysfunction leading to decreased ability to perform instrumental activities of daily living (IADL). In contrast, AD + CVD patients typically present with progressive deterioration of cognition/memory that may also be influenced by concurrent cerebrovascular events. Early diagnosis and intervention are desirable to prevent further decline due to subsequent vascular events. Management of CVD can limit deterioration of cognitive symptoms in VaD patients, and treatment benefits with cholinesterase inhibitors may be realized as improvement above baseline levels in dementia symptoms. Results from a combined analysis of two 24-week, placebo-controlled clinical trials show that donepezil-treated VaD patients improve in cognition, global function, and performance of IADL. In contrast, AD + CVD patients may continue to decline despite management of CVD, and treatment benefits should be recognized as initial improvements followed by stabilization or slowed decline of dementia symptoms over time. In post-marketing studies, donepezil-treated AD and AD + CVD patients show similar benefits in cognition, global function, and quality of life. The results of these studies support the use of donepezil in treatment of patients with VaD or AD + CVD.

Donepezil: a clinical review of current and emerging indications

This article reviews the piperidine derivative, donepezil hydrochloride (E2020, Aricept), a reversible central acetylcholinesterase inhibitor currently approved for treatment of mild-to-moderate Alzheimer's disease. Donepezil is well absorbed orally, unaffected by food or by time of administration; it reaches therapeutic levels in doses of 5-10 mg/day and peak plasma concentrations are obtained 3-4 h after oral administration. A single bedtime dose is recommended due to the long elimination half-life of the drug (70 h). Donepezil does not cause liver toxicity or significant drug interactions and is relatively well-tolerated. Initial side effects include nausea, vomiting, diarrhoea, insomnia, muscle cramps, fatigue, anorexia and syncope. Caution is advised in patients with bradycardia. Long-term use of donepezil in AD has been found to delay nursing-home placement and to result in caregiver respite. Donepezil also slows deterioration of cognition and global function in patients with moderate-to-severe AD, with improvement of abnormal behaviours. In addition to AD, donepezil demonstrates significant improvement in cognition, global function and activities of daily living in comparison with placebo-treated patients with vascular dementia and has potential therapeutic benefit for other neurological conditions.

Higher in vivo muscarinic-2 receptor distribution volumes in aging subjects with an apolipoprotein E-epsilon4 allele

The apolipoprotein E-epsilon4 allele confers an increased susceptibility to age-related memory problems and Alzheimer's disease. Abnormalities in the cholinergic system are also likely contributors to memory deficits associated with aging and AD. To determine the effect of the APOE-epsilon4 allele on the muscarinic component of the cholinergic system of aging subjects, 10 healthy subjects with APOE-epsilon4 alleles (APOE-epsilon4+) and 10 without (APOE-epsilon4-), ranging in age from 52 to 75 years, were tomographically scanned with the F-18-labeled muscarinic-2 (M2) selective agonist, 3-(3-(3-[(18)F]Flouropropyl)thio)-1,2,5-thiadiazol-4-yl)-1,2,5,6-tetrahydro-1-methylpyridine ([(18)F]FP-TZTP). The distribution volumes (V(T)) of [(18)F]FP-TZTP were determined by compartmental modeling of partial volume and free fraction corrected PET scans. Regional cerebral blood flow (rCBF) measurements with H(2) (15)O were also performed. Global Gray V(T) (840 +/- 155 ml plasma/ml tissue) was greater in APOE-epsilon4+ subjects than APOE-epsilon4- subjects (660 +/- 113 ml plasma/ml tissue, P = 0.01), and previously studied younger subjects. There were no significant differences between the groups with respect to rCBF, but within the APOE-epsilon4+ group there was a trend for subjects with the higher Global Gray V(T)s to have lower Global Gray CBFs (r = -0.65, P < 0.06). A lower concentration of acetylcholine in the synapse of APOE-epsilon4+ older individuals is a likely explanation for the greater [(18)F]FP-TZTP distribution volumes.

Patient populations in clinical trials of the efficacy and tolerability of donepezil in patients with vascular dementia

There is increasing evidence to suggest that patients with vascular dementia (VaD) exhibit a cholinergic deficit. These patients may therefore benefit from treatment with cholinesterase (ChE) inhibitors such as donepezil. However, there are difficulties in accurately defining patients with VaD. Clinical trials to assess the efficacy and tolerability of donepezil in patients with VaD have been completed. National Institute of Neurological Disorders and Stroke and the Association Internationale pour la Recherche et l'Enseignement en Neurosciences (NINDS-AIREN) criteria were used to establish inclusion and exclusion criteria: evidence of dementia (impaired memory and two other cognitive domains), and evidence of cerebrovascular disease (CVD) from neuroimaging and physical examination and a possible or probable relationship between dementia and CVD were required for enrollment. Patients with a diagnosis of Alzheimer's disease (AD) or dementia caused by other conditions not associated with the cardiovascular system (e.g., MS, chronic infections, hypothyroidism) were excluded. These criteria ensured that only patients with probable or possible VaD were enrolled. Enrolled patients had a mean Hachinski score of 9.7, with memory impairment the most prominent feature of their dementia. Sixty percent of patients had a history of at least one stroke and 18% of patients had a history of transient ischemic attack (TIA) pre-dementia. Cortical and subcortical infarcts were among the lesions observed on computer-assisted tomography and magnetic resonance imaging scans with significant white matter lesions also present in some patients. Placebo-treated patients demonstrated stable cognitive and global function over the 24 weeks of the study. These observations suggest that the patients enrolled in these trials have a broad range of CVD, and are different from those enrolled in AD trials.

The cholinergic system in Alzheimer's disease

The past decade has witnessed an enormous increase in our knowledge of the variety and complexity of neuropathological and neurochemical changes in Alzheimer's disease. Although the disease is characterized by multiple deficits of neurotransmitters in the brain, this overview emphasizes the structural and neurochemical localization of the elements of the acetylcholine system (choline acetyltransferase, acetylcholinesterase, and muscarinic and nicotinic acetylcholine receptors) in the non-demented brain and in Alzheimer's disease brain samples. The results demonstrate a great variation in the distribution of acetylcholinesterase, choline acetyltransferase, and the nicotinic and muscarinic acetylcholine receptors in the different brain areas, nuclei and subnuclei. When stratification is present in certain brain regions (olfactory bulb, cortex, hippocampus, etc.), differences can be detected as regards the laminar distribution of the elements of the acetylcholine system. Alzheimer's disease involves a substantial loss of the elements of the cholinergic system. There is evidence that the most affected areas include the cortex, the entorhinal area, the hippocampus, the ventral striatum and the basal part of the forebrain. Other brain areas are less affected. The fact that the acetylcholine system, which plays a significant role in the memory function, is seriously impaired in Alzheimer's disease has accelerated work on the development of new drugs for treatment of the disease of the 20th century.

Demonstration of a reduction in muscarinic receptor binding in early Alzheimer's disease using iodine-123 dexetimide single-photon emission tomography

Decreased muscarinic receptor binding has been suggested in single-photon emission tomography (SPET) studies of Alzheimer's disease. However, it remains unclear whether these changes are present in mildly demented patients, and the role of cortical atrophy in receptor binding assessment has not been investigated. We studied muscarinic receptor binding normalized to neostriatum with SPET using [123I]4-iododexetimide in five mildly affected patients with probable Alzheimer's disease and in five age-matched control subjects. Region of interest (ROI) analysis was performed in a consensus procedure blind to clinical diagnosis using matched magnetic resonance (MRI) images. Cortical atrophy was assessed by calculating percentages of cerebrospinal fluid in each ROI. An observer study with three observers was conducted to validate this method. Alzheimer patients showed statistically significantly less [123I]4-iododexetimide binding in left temporal and right temporo-parietal cortex compared with controls, independent of age, sex and cortical atrophy. Mean intra-observer variability was 3.6% and inter-observer results showed consistent differences in [123I]4-iododexetimide binding between observers. However, differences between patients and controls were comparable among observers and statistically significant in the same regions as in the consensus procedure. Using an MRI-SPET matching technique, we conclude that [123I]4-iododexetimide binding is reduced in patients with mild probable Alzheimer's disease in areas of temporal and temporo-parietal cortex.

In vitro pharmacological properties of 4-bromodexetimide for muscarinic receptors

The decrease of m-AChR density observed in neurodegenerative disorders has generated considerable interest in non-invasive mapping of muscarinic acetylcholine receptors (m-AChR) in the central nervous system. The aim of our study was to evaluate the selectivity of 4-bromodexetimide for the M1, M2, M3 and M4 m-AChR subtypes using in vitro binding analysis to determine the potential use of the bromine-76 labelled 4-bromodexetimide in the investigation of m-AChR subtypes in human brain with Positron Emission Tomography. Subtype selectivity of 4-bromodexetimide was determined in competition studies against tritiated subtype selective ligands using various rat or rabbit structure homogenates reflecting a single binding site and in optimal saturation and low non specific binding conditions. These conditions were reached for every subtype studied by analyzing the data from the saturation experiments of the tritiated ligands. 4-bromodexetimide displayed nanomolar affinities for the four m-AChR subtypes and a preferential selectivity for the M1 and M4 subtypes. The saturation analysis of [76Br]4-bromodexetimide, performed with rat cortex membranes showed high affinity for m-AChR receptors (Kd = 1.8 nM). As in vivo studies of [76Br]4-bromodexetimide showed preferential localization in the cortex and the striatum which are M1 and M4 rich structures and since it binds preferentially to the M1 and M4 subtypes, this radiotracer can still allow a combined subtype specific measurement of these muscarinic receptors.

The neurochemistry of Alzheimer type, vascular type and mixed type dementias compared

We present the results of a meta-analysis of neurochemical changes in human post mortem brains of Alzheimer type (AD), vascular type (VD) and mixed type (MF) dementias, and matched controls based on 275 articles published between January 1980 and February 1994. Severity of degeneration between the different neurochemical systems is as follows, although ranking is difficult with regard to limited numbers of investigations in some neurochemical systems: Cholinergic system > serotonergic system > excitatory amino acids > GABAergic system > energy metabolism > NA > oxidative stress parameters > neuropeptides > DA. But, within a neurochemical system, degeneration is not evenly distributed. Spared parameters, e.g. muscarinic receptors and MAO-B, allow to make some suggestions for future therapeutic strategies.

Differential cholinergic regulation in Alzheimer's patients compared to controls following chronic blockade with scopolamine: a SPECT study

The effects of low-dose chronic scopolamine on measures of cerebral perfusion and muscarinic receptors were tested in eight Alzheimer's disease (AD) subjects and eight elderly controls. Single photon emission computed tomography (SPECT) scans using technetium-labelled hexamethypropylene amine oxide (99mTc-HMPAO) to measure cerebral perfusion before and after chronic scopolamine revealed a significant 12% increase in the normal controls (P < 0.01) while the AD subjects showed no significant change. In contrast, the controls showed decreased muscarinic binding as evidenced by 123I-quinuclidinyl-4-iodobenzilate (123I-QNB) labelling after chronic drug (-10%, P < 0.01) whereas the AD subjects showed increased 123I-QNB labelling (+8%, P < 0.05). The difference between AD and control subjects was even more marked when the ratio of I-QNB to HMPAO uptake was compared, pointing to a double dissociation in the SPECT results. These data cannot be explained by group differences in cerebral perfusion alone and suggest a differential sensitivity between AD and elderly controls to chronic cholinergic blockade.

Safety and tolerability of CI-979 in patients with Alzheimer's disease

CI-979 ((E)-1,2,5,6-tetrahydro-1-methyl-3-pyridinecarboxaldehyde, O-methyloxime monohydrochloride), a novel muscarinic agonist, is being investigated as a potential treatment for Alzheimer's disease (AD). The objective of the present study was to determine the safety and tolerance of multiple, rising, oral doses of CI-979 in patients with AD. Ten male patients aged 59 to 74 years (mean 65 years) who met NINCDS criteria for AD were randomized to receive either CI-979 (eight patients) or placebo (two patients) according to a double-blind, parallel-group, rising-dose design. Doses were 0.5-mg q6h, 1-mg q12h, 1-mg q6h, 2-mg q12h, 2-mg q6h, 2.5-mg q6h, and 3-mg q6h. All doses were to be administered sequentially for 3 days each with the exception of the 2.5-mg q6h dose, which was to be administered for 1.5 days. Five patients receiving CI-979 discontinued study medication because of adverse events; two after receiving 2-mg q6h (10 doses), two after 2.5-mg q6h (5 doses), and one after 3-mg q6h (4 doses). The study was terminated following administration of the fourth 3-mg dose due to the nature and intensity of adverse events. Cholinergic symptoms including diaphoresis, hypersalivation, nausea, diarrhea, hypotension, chills, headache, flatulence, and urinary frequency and signs suggestive of parkinsonism (cogwheeling, tremor, pillrolling, posturing, and shuffling gait) were dose-limiting. The frequency and intensity of adverse events increased with increasing CI-979 dose. No other clinically significant CI-979-related changes occurred in physical examinations, clinical laboratory measurements, electrocardiograms, or ophthalmologic examinations. Steady-state trough plasma CI-979 concentrations increased in proportion to dose. In summary, CI-979 doses of 1-mg q6h were well tolerated by all patients; 2-mg q6h was tolerated by most patients, and 2.5-mg and 3-mg doses were poorly tolerated, Dose titration to a maximum of 2-mg q6h will therefore be used in initial efficacy trials of CI-979 in patients with AD.

Lack of effect of tacrine administration on the anticoagulant activity of warfarin

The effect of tacrine administration on prothrombin time was studied in 13 patients receiving prolonged warfarin therapy. After a 3-week baseline period and 5 days of placebo administration, patients received 20 mg tacrine four times daily for 5 days. Prothrombin times were determined during baseline, daily before the morning doses of placebo and tacrine, and 14 days after the last tacrine dose (closeout). Mean (+/- SD) prothrombin times were 16.2 +/- 2.8 seconds at baseline, 15.1 +/- 2.6 seconds during the placebo phase, 15.8 +/- 3.6 seconds during the tacrine phase, and 15.3 +/- 3.6 seconds at closeout, indicating that tacrine has no effect on the anticoagulant activity of warfarin. Alteration of warfarin dosage should not be required in patients receiving concurrent tacrine therapy.

In vivo measurement of acetylcholinesterase activity in the brain with a radioactive acetylcholine analog

A novel method for visualization of brain acetylcholinesterase (AChE) in vivo has been developed. Following intravenous administration of a radiolabelled acetylcholine analog, N-methyl-3-piperidyl acetate, there was very good agreement between the distribution of radioactivity and AChE activity in the brain of rat and monkey. The method would be applicable for in vivo studies of human brain AChE activity in disorders of central cholinergic systems such as Alzheimer's disease.

A multiple-dose safety trial of eptastigmine in Alzheimer's disease, with pharmacodynamic observations of red blood cell cholinesterase

A placebo-controlled multiple dose study was conducted to evaluate the safety, tolerability, and pharmacodynamics of multiple dose levels of eptastigmine in 25 patients with probable Alzheimer's disease (AD). Twenty patients (12 M, 8 F; mean age 74, range 57-84) were randomized to receive 12mg (N = 3), 20mg (N = 6), 28mg (N = 6) or placebo (N = 5) tid on a double-blind basis for 14 days, followed by seven days of single blind placebo, in successively rising dose groups. All patients completed the study without intolerable or severe adverse events. All doses significantly (p < 0.001) reduced peak and trough RBC cholinesterase (AChE) activity as compared to baseline. Percent inhibition for Day 14 peak and trough RBC AChE peak and trough values, respectively, appeared proportional to dose: 18% and 21% (12mg); 36% and 35% (20mg); 40% and 44% (28mg). In order to determine the maximum tolerated dose of eptastigmine, an additional single-blind study was performed in five patients (2 M, 3 F; mean age 78, range 72-80) utilizing a rising dose schedule of eptastigmine (N = 4) or placebo (N = 1), starting with the previously tolerated 28mg tid dose and increasing by 4mg tid up to a potential maximum of 56mg tid. Dose-limiting adverse events occurred requiring discontinuation of medication in one patient at 48mg tid and two patients at 52mg tid; RBC AChE inhibition was proportional to dose, with peak values up to 70% inhibition at 48mg tid. The maximum tolerated dose of 48mg tid was identified as a basis for potential Phase II multicenter efficacy trials.

Intermediary metabolism disturbance in AD/SDAT and its relation to molecular events

1. Early-onset dementia of Alzheimer type (EODAT; AD) and late-onset dementia of Alzheimer type (LODAT; SDAT) are heterogenous in origin. 2. A common superordinate pathobiochemical principle in the etiopathogenesis of both types of dementia is neuronal energy failure with subsequent abnormalities in cellular Ca2+ homeostasis and glucose-related amino acid metabolism. 3. These metabolic abnormalities are assumed to occur first at axodendritic terminals of the acetylcholinergic-glutamatergic circuit and to cause morphological damage at synaptic sites. 4. Metabolic stress and structural damage at synaptic sites may induce enhanced formation of APP and its cleavage product amyloid. 5. Energy-metabolism related abnormalities along with functional and structural changes at synaptic sites of the acetylcholinergic-glutamatergic circuit may precede the formation of amyloid in DAT brain.

Alterations in cortical muscarinic receptors following cholinotoxin (AF64A) lesion of the rat nucleus basalis magnocellularis

Cortical choline acetyltransferase (ChAT), tyrosine hydroxylase (TH), tryptophan hydroxylase (TPH), muscarinic receptors and sodium-dependent, high-affinity, choline uptake (SDHACU) sites were examined in the rat brain following unilateral stereotaxic injection of the cholinotoxin, AF64A, into the nucleus basalis magnocellularis (NBM). Injection of AF64A resulted in a significant loss of presynaptic cholinergic markers in the cortex without alteration in TH and TPH activity. The binding to SDHACU sites was reduced to background values in the NBM and increased in the central amygdala (Ce) and cortex. The increase in cortical [3H]QNB binding was the result of a change in muscarinic receptor number (BMAX) and not a change in receptor affinity (KD). Examination of muscarinic receptor subtypes demonstrated a reduction of M1 receptor binding in the cortex and NBM without any alteration in the Ce. Non-M1 binding was significantly increased in all the laminae of the cortex and in the Ce, but decreased in the NBM. These data suggest that there exists a population of M1 receptors on NBM projections to the cortex and that NBM projections influence a population of postsynaptic receptors in the cortex and Ce which are not of the M1 subtype.

The potential for muscarinic receptor subtype-specific pharmacotherapy for Alzheimer's disease

In several neurodegenerative disorders, including Alzheimer's disease, a loss of the cholinergic projections of the basal forebrain to the cerebral cortex and hippocampus occurs. Studies of the anatomic and physiologic characteristics of these ascending cholinergic systems suggest that they are important in processing information and in memory function. Muscarinic receptors are situated at various critical control points in these pathways. Activation of postsynaptic muscarinic receptors often increases the excitability of neurons; thus, the signal-to-noise ratio for sensory processing is enhanced. In addition, muscarinic receptors negatively control cholinergic tone at presynaptic sites. Molecular biologic methods have disclosed the existence of five muscarinic receptors, which are coupled to different second messenger systems. The evidence reviewed suggests that at least four of the five muscarinic receptor genes are expressed as functional receptor proteins in the neocortex and hippocampal formation. On the basis of the current information about their pharmacologic properties and coupling mechanisms in nervous tissue, drugs that selectively affect subtypes of muscarinic receptors could enhance cortical cholinergic function and thereby ameliorate certain cognitive impairments in Alzheimer's disease.

Cholinergic receptors in human brain: effects of aging and Alzheimer disease

A general review of cholinergic receptors in human brain is presented. The paper focuses upon changes in normal aging brain and in Alzheimer disease. Studies from five different approaches are reported: 1) molecular biology; 2) receptor binding studies; 3) studies with specific neurotoxins; 4) immunocytochemistry; and 5) PET scan. These studies document profound and characteristic differences between the normal aging and the pathological Alzheimer brain with regard to cholinergic receptor localization, distribution, and function.

Multiple dose pharmacokinetics, safety, and tolerance of velnacrine (HP 029) in healthy elderly subjects: a potential therapeutic agent for Alzheimer's disease

The pharmacokinetics, safety, and tolerance of 1,2,3,4-tetrahydro-9-aminoacridin-1-olmaleate (HP 029) a potential therapeutic agent for Alzheimer's disease, were assessed after multiple oral doses in a randomized double-blind, placebo controlled, ascending dose study in 56 healthy elderly men (14 per dose group). The subjects in the first three groups received 25, 50, or 100 mg two times a day and a fourth group was administered 100 mg velnacrine tid for 28 days. All subjects received a final dose on day 29. Subjects were confined for continuous observation during the 36-day study period. Blood and urine samples were collected for the pharmacokinetic assessment. There were no clinically important changes in the safety variables in both age groups after any dose. There was no evidence of hepatotoxicity when elderly men were given 100 mg tid for 28 days. Nine subjects reported one or two episodes of gastrointestinal (diarrhea) side effects (6 in the 100 mg bid group and 3 in the 100 mg tid dose group) during a 29-day trial. None required treatment or were discontinued from study. These results indicate that the safety and tolerance up to 100 mg tid for 28 days in healthy elderly men are acceptable. Velnacrine was rapidly absorbed after oral administration. There were dose-related increases in Cmax, AUCs, and amount of drug excreted in urine. During multiple dosing, the Cmax increased as a function of dose. The tmax and t1/2 were not affected by dosage nor multiple dosing. Steady state levels of velnacrine were reached between days 2 and 3 with no evidence of further accumulation of velnacrine thereafter. Approximately 11-30% of the administered dose was excreted in the urine over the course of the study. The favorable pharmacokinetic characteristics and acceptable safety and tolerance of multiple dosing oral doses of velnacrine support further testing of this compound for efficacy and safety in Alzheimer's patients.

Clinical safety, tolerance, and plasma levels of the oral anticholinesterase 1,2,3,4-tetrahydro-9-aminoacridin-1-oL-maleate (HP 029) in Alzheimer's disease: preliminary findings

HP 029 (1,2,3,4-tetrahydro-9-aminoacridin-1-oL-maleate), an oral anticholinesterase, enhances memory in rodents and may be useful in treating Alzheimer's disease (AD). To assess adverse events in relation to dosage and plasma drug levels, 24 hospitalized AD subjects were randomly assigned to receive placebo or HP 029 for 10 days in a double-blind, sequential escalation study. Maximum daily dosages were 450 mg (group 1), 300 mg (group 2), and 225 mg (group 3), divided into three doses per day. The group 1 trial was discontinued on day 5 because one subject, 6 hours following the second of three scheduled 150-mg doses, had a tonic seizure after protracted vomiting and hyperventilation; adverse events in other patients included nausea, vomiting, abdominal cramps, diarrhea, dizziness, and syncope. Adverse events were generally less severe in group 2, but only two of six HP 029 subjects could complete the trial at 300 mg/day. All group 3 subjects completed the trial at 225 mg/day with drug related, mild adverse events (nausea, vomiting, lacrimation, rhinorrhea) in only two subjects. Although mean plasma drug levels were related to adverse events across dosage groups, they did not adequately predict the occurrence or severity of adverse events in individual subjects. The 225 mg/day dose appears to be safe for use in multicenter outpatient trials of HP 029 efficacy in AD. Further patient studies are ongoing to determine the relation of specific subject characteristics to the metabolic profile of HP 029 and biological response.

Excitatory amino acid binding sites in the hippocampal region of Alzheimer's disease and other dementias

Quantitative receptor autoradiography was used to measure muscarinic cholinergic, benzodiazepine, kainate, phencyclidine (PCP), N-methyl-D-aspartate (NMDA) (measured in Tris acetate), quisqualate-sensitive, non-quisqualate-sensitive and total glutamate (measured in Tris chloride buffer) binding sites in adjacent sections of the hippocampal region of 10 Alzheimer's disease, nine control, and six demented, non-Alzheimer's disease postmortem human brains. The measurements were compared to the number of neurofibrillary tangles as revealed by Congo red staining of adjacent sections. All assays and measurements were done by observers blinded to the clinical diagnoses. Binding was decreased significantly for all ligands except quisqualate in stratum pyramidale of CA1 of the Alzheimer's disease brains. The binding loss was significantly greater for the non-quisqualate and NMDA sites than for the muscarinic, benzodiazepine and kainate sites with the total glutamate and PCP site losses being intermediate. Only the loss of benzodiazepine binding was significantly correlated with the number of neurofibrillary tangles. Lesser binding losses were seen in adjacent areas. This difference in the degree of binding decrease is consistent with the hypothesis that NMDA receptors are located on more distal dendrites of hippocampal neurons. There they may be relatively more vulnerable than the other receptors to the pathological process.

Selective alterations of high affinity [3H]forskolin binding sites in Alzheimer's disease: a quantitative autoradiographic study

Quantitative autoradiographic analysis of high affinity [3H]forskolin binding sites was carried out in postmortem brains from normal controls and patients dying with Alzheimer's disease. Choline acetyltransferase (ChAT) activity and senile plaque formation were also quantified. [3H]Forskolin binding was markedly reduced in all layers of middle frontal gyrus in the Alzheimer brains and the deficit correlated with the deficit in ChAT activity in this area. In the hippocampal region [3H]forskolin binding was no different in the Alzheimer brains compared to controls, although ChAT activity was significantly reduced. There was an inconsistent reduction in [3H]forskolin binding in all layers of middle temporal gyrus which did not correlate with the cholinergic deficit. Significant senile plaque formation was observed in all 3 brain regions examined and [3H]forskolin binding did not correlate with plaque formation in any brain region. Thus, while all 3 brain regions were affected by the pathological correlates of Alzheimer's disease, [3H]forskolin binding was consistently reduced only in frontal cortex.

Alzheimer's disease: changes in hippocampal N-methyl-D-aspartate, quisqualate, neurotensin, adenosine, benzodiazepine, serotonin and opioid receptors--an autoradiographic study

The following receptors were assessed post-mortem in the hippocampi (anterior region) of eight patients with Alzheimer's disease and nine age-matched controls, using autoradiography: N-methyl-D-aspartate (including glutamate, phencyclidine and glycine binding sites), quisqualate, kainic acid, adenosine A1, benzodiazepine, serotonin (1 and 2), muscarinic cholinergic, beta-adrenergic, neurotensin and opioid receptors. In CA1 there were significant parallel losses of binding to the three N-methyl-D-aspartate-linked sites (average reduction 46%) and also losses of quisqualate (38%) and serotonin2 (58%) receptor binding, with a 47% loss of binding to A1 sites. Binding to all of these receptors was also reduced in CA3 (except binding to A1 sites which was normal) but only the serotonin2 receptor binding loss reached significance (52%). A significant reduction in binding was also observed in the entorhinal area to the N-methyl-D-aspartate receptor-linked sites (average reduction = 39%), benzodiazepine (40%) and serotonin2 receptors (45%), and there was a loss of binding to neurotensin (57%) and opioid receptors (42%). Significant reductions in the dentate gyrus molecular layer were seen for serotonin2 receptors (44%), and binding to opioid (44%) and A1 receptors (46%). Levels of ligand binding to muscarinic cholinergic, serotonin1, beta-adrenergic and kainic acid receptors were not significantly different from control values in any of the four areas examined. These results provide support for observations of selective receptor changes in Alzheimer's disease involving a broad range of receptor types which encompass both excitatory amino acid and other receptors (notably serotonin2, A1, benzodiazepine, neurotensin and opioid receptors). The implications of the pattern of receptor changes for the suggestion that excitotoxicity plays a role in the disease are discussed, as is the possible contribution of the receptor changes to the symptomatology of Alzheimer's disease.

Non-Alzheimer-type pattern of brain cholineacetyltransferase reduction in dominantly inherited olivopontocerebellar atrophy

We recently reported reduced activity of the cholinergic marker enzyme cholineacetyltransferase (ChAT) in several brain regions of patients with dominantly inherited olivopontocerebellar atrophy (OPCA). To document the regional extent of these changes we performed a comprehensive examination of the behavior of ChAT throughout both cerebral cortical and subcortical brain areas in 5 patients from one large OPCA pedigree. As compared with the controls, mean ChAT activities in OPCA were reduced by 39 to 72% in all (n = 27) cerebral cortical areas examined and in several thalamic subdivisions, caudate head, globus pallidus, red nucleus, and medial olfactory area. In contradistinction to findings in Alzheimer's disease (AD), mean ChAT levels in OPCA amygdala and hippocampal subdivisions were either normal or only mildly reduced. The lack of severe disabling dementia in our OPCA patients compared with AD patients having a similar cortical cholinergic reduction could be explained by an absence of either a marked cholinergic loss in amygdala or hippocampus or significant loss of noncholinergic cerebral cortical and limbic neurons as occurs in AD brain. We suggest that this and other OPCA pedigrees having a cortical cholinergic reduction represent a unique model for the study of behavioral consequences of a more selective cerebral cortical cholinergic lesion rather than a limbic cholinergic lesion.

Nicotinic binding sites in cerebral cortex and hippocampus in Alzheimer's dementia

Postmortem cerebral neocortical and hippocampal samples were taken from patients who died with dementia of the Alzheimer type (DAT) and individuals without diagnoses of neurological or psychiatric disease (control). Nicotinic binding was assayed with 20 nM [3H]acetylcholine [( 3H]ACh) in the presence of atropine, or with 4 nM (-)-[3H]nicotine ((-)-[3H]Nic). Binding of both ligands was lower in the following regions from DAT vs. control brains (P less than or equal to 0.05): superior, middle and inferior temporal gyri, orbital frontal gyrus, middle frontal gyrus, pre- and postcentral gyri, inferior parietal lobule, and hippocampal endplate. Values of the correlation coefficient (r's) for binding of the nicotinic cholinergic ligands in these regions ranged from 0.70 to 0.93 (P's less than 0.05), suggesting that [3H]ACh and (-)-[3H]Nic labeled the same sites in human brain. There was no difference in nicotinic binding in the presubiculum, comparing DAT and control samples (P greater than 0.05). Here too, correlations between binding of the two ligands were statistically significant in control and DAT groups (r's = 0.92, P's less than 0.05). Nicotinic binding measured with [3H]ACh, but not (-)-[3H]Nic, was significantly lower in the H2 (field of Rose) and H1-subiculum areas of DAT samples compared to control. Correlations between binding of the two ligands in these regions ranged from 0.21 to 0.34 for the two groups (P's greater than 0.05). The findings support a loss of neocortical and hippocampal nicotinic cholinergic binding sites in DAT.(ABSTRACT TRUNCATED AT 250 WORDS)

(+-)-cis-2-methyl-spiro(1,3-oxathiolane-5,3') quinuclidine (AF102B): a new M1 agonist attenuates cognitive dysfunctions in AF64A-treated rats

(+-)-cis-2-Methyl-spiro(1,3-oxathiolane-5,3')quinuclidine (AF102B), a new muscarinic agonist of utmost rigidity, exhibits a high selectivity for M1 muscarinic receptors. In rats having a cholinergic hypofunction induced by the intracerebroventricular administration of ethylcholine aziridinium (AF64A), AF102B reversed cognitive impairments in a step-through passive avoidance task and in an 8-arm radial maze. AF102B reversed cognitive impairments at significantly lower doses than those needed to induce side-effects. In addition, AF102B exhibited low toxicity. The results suggest that AF102B may prove useful for treatments of cholinergic deficiencies and cognitive impairments, like those reported in Alzheimer's disease.

Single dose safety, tolerance, and pharmacokinetics of HP 029 in healthy young men: a potential Alzheimer agent

1,2,3,4-tetrahydro-9-aminoacridin-1-ol maleate (HP 029) is a new cholinergic compound that has been shown to enhance memory in animals and therefore may be potentially effective in humans for the treatment of Alzheimer's disease (AD). The initial safety, tolerance, and pharmacokinetics of HP 029 after single oral doses were assessed in a randomized, double-blind, placebo controlled study in 70 healthy young men (eight dose groups). The test doses ranged from 5 to 200 mg. There were 9 subjects per dose group, 6 on HP 029 and 3 on placebo. The 5 and 100 mg dose groups had only 8 subjects. Plasma and urine samples were analyzed for nonconjugated HP 029 using an HPLC assay with a detection limit of 1 ng/ml. HP 029 was rapidly absorbed after oral dosing with mean peak plasma levels occurring between 0.75 and 1.2 hours. The mean peak levels ranged from 12.7 and 234.7 ng/ml after the 10 and 200 mg doses, respectively. There were dose related increases in peak plasma levels, AUCs, and the amounts of drug excreted in the urine. The mean plasma half-life was about 2.0 hours and was not affected by dose. About 6 to 11% of the dose was eliminated in the urine. HP 029 was renally cleared at a high rate and independent of dose. There were no clinically important or drug-related changes in any of the physical examinations, audiograms, or ophthalmologic examinations. There were only minor within-subject fluctuations in vital signs, ECGs, and laboratory values, none of which were clinically meaningful or drug related after any of the doses of HP 029.(ABSTRACT TRUNCATED AT 250 WORDS)

Selective influence of rat genotype on age-related regional changes in forebrain muscarinic binding

Muscarinic binding was analyzed in the hippocampus and frontal cerebral cortex of 3 (young) and 24-month-old (aged) inbred Wistar-Kyoto (WKY), Brown-Norway (BN) and Lewis rats, by the specific binding of the antagonist quinuclidinylbenzilate (QNB). While no age-related changes were detected in the hippocampus of all strains, complex changes were found in the cortex. Maximal binding capacity (Bmax) of [3H]QNB was decreased in the cortex of aged WKY rats, remained unchanged in the BN strain and was elevated in Lewis rats. We conclude that regional differences exist in age-related changes in forebrain muscarinic binding which are probably due to differences in the types and connections of cholinoceptive neurons in these regions. The results suggest that it is the rate of these changes which is affected by the rat genotype.