A unifying hypothesis of Alzheimer's disease. IV. Causation and sequence of events

Association of metabolic dysfunction with cognitive decline and Alzheimer's disease: A review of metabolomic evidence

The discovery of new biomarkers that can distinguish Alzheimer's disease (AD) from mild cognitive impairment (MCI) in the early stages will help to provide new diagnostic and therapeutic strategies and slow the transition from MCI to AD. Patients with AD may present with a concomitant metabolic disorder, such as diabetes, obesity, and dyslipidemia, as a risk factor for AD that may be involved in the onset of both AD pathology and cognitive impairment. Therefore, metabolite profiling, or metabolomics, can be very useful in diagnosing AD, developing new therapeutic targets, and evaluating both the course of treatment and the clinical course of the disease. In addition, studying the relationship between nutritional behavior and AD requires investigation of the role of conditions such as obesity, hypertension, dyslipidemia, and elevated glucose level. Based on this literature review, nutritional recommendations, including weight loss by reducing calorie and cholesterol intake and omega-3 fatty acid supplementation can prevent cognitive decline and dementia in the elderly. The underlying metabolic causes of the pathology and cognitive decline caused by AD and MCI are not well understood. In this review article, metabolomics biomarkers for diagnosis of AD and MCI and metabolic risk factors for cognitive decline in AD were evaluated.

Ageing, Age-Related Cardiovascular Risk and the Beneficial Role of Natural Components Intake

Ageing, in a natural way, leads to the gradual worsening of the functional capacity of all systems and, eventually, to death. This process is strongly associated with higher metabolic and oxidative stress, low-grade inflammation, accumulation of DNA mutations and increased levels of related damage. Detrimental changes that accumulate in body cells and tissues with time raise the vulnerability to environmental challenges and enhance the risk of major chronic diseases and mortality. There are several theses concerning the mechanisms of ageing: genetic, free radical telomerase, mitochondrial decline, metabolic damage, cellular senescence, neuroendocrine theory, Hay-flick limit and membrane theories, cellular death as well as the accumulation of toxic and non-toxic garbage. Moreover, ageing is associated with structural changes within the myocardium, cardiac conduction system, the endocardium as well as the vasculature. With time, the cardiac structures lose elasticity, and fibrotic changes occur in the heart valves. Ageing is also associated with a higher risk of atherosclerosis. The results of studies suggest that some natural compounds may slow down this process and protect against age-related diseases. Animal studies imply that some of them may prolong the lifespan; however, this trend is not so obvious in humans.

Cerebroarterial pulsatility and resistivity indices are associated with cognitive impairment and white matter hyperintensity in elderly subjects: A phase-contrast MRI study

Increased cerebroarterial pulsations are thought to be contributing factors in microvascular damage and cognitive impairment. In this study, we assessed the utility of two-dimensional (2D) phase-contrast MRI (PC-MRI) in quantifying cerebroarterial pulsations and evaluated the associations of pulsatile and non-pulsatile hemodynamic measures with cognitive performance and white matter hyperintensities (WMH). Neurocognitive assessments on 50 elderly subjects were performed using clinical dementia rating (CDR) and Montreal cognitive assessment (MoCA). An electrocardiogram-gated 2D PC-MRI sequence was used to calculate mean flow rate, pulsatility index (PI), and resistivity index (RI) of the internal carotid artery. For each subject, whole brain global cerebral blood flow (gCBF) and relative WMH volume were also quantified. Elevated RI was significantly associated with reduced cognitive performance quantified using MoCA (p = 0.04) and global CDR (p = 0.02). PI and RI were both significantly associated with relative WMH volume (p = 0.01, p < 0.01, respectively). However, non-pulsatile hemodynamic measures were not associated with cognitive impairment or relative WMH volume. This study showed that the cerebroarterial pulsatile measures obtained using PC-MRI have stronger association with the measures of cognitive impairment compared to global blood flow measurement and as such, might be useful as potential biomarkers of cerebrovascular dysfunction in preclinical populations.

Energy Metabolism Decline in the Aging Brain-Pathogenesis of Neurodegenerative Disorders

There is a growing body of evidencethat indicates that the aging of the brain results from the decline of energy metabolism. In particular, the neuronal metabolism of glucose declines steadily, resulting in a growing deficit of adenosine triphosphate (ATP) production-which, in turn, limits glucose access. This vicious circle of energy metabolism at the cellular level is evoked by a rising deficiency of nicotinamide adenine dinucleotide (NAD) in the mitochondrial salvage pathway and subsequent impairment of the Krebs cycle. A decreasing NAD level also impoverishes the activity of NAD-dependent enzymes that augments genetic errors and initiate processes of neuronal degeneration and death.This sequence of events is characteristic of several brain structures in which neurons have the highest energy metabolism. Neurons of the cerebral cortex and basal ganglia with long unmyelinated axons and these with numerous synaptic junctions are particularly prone to senescence and neurodegeneration. Unfortunately, functional deficits of neurodegeneration are initially well-compensated, therefore, clinical symptoms are recognized too late when the damages to the brain structures are already irreversible. Therefore, future treatment strategies in neurodegenerative disorders should focus on energy metabolism and compensation age-related NAD deficit in neurons. This review summarizes the complex interrelationships between metabolic processes on the systemic and cellular levels and provides directions on how to reduce the risk of neurodegeneration and protect the elderly against neurodegenerative diseases.

Peripheral serum metabolomic profiles inform central cognitive impairment

The incidence of Alzheimer's disease (AD) increases with age and is becoming a significant cause of worldwide morbidity and mortality. However, the metabolic perturbation behind the onset of AD remains unclear. In this study, we performed metabolite profiling in both brain (n = 109) and matching serum samples (n = 566) to identify differentially expressed metabolites and metabolic pathways associated with neuropathology and cognitive performance and to identify individuals at high risk of developing cognitive impairment. The abundances of 6 metabolites, glycolithocholate (GLCA), petroselinic acid, linoleic acid, myristic acid, palmitic acid, palmitoleic acid and the deoxycholate/cholate (DCA/CA) ratio, along with the dysregulation scores of 3 metabolic pathways, primary bile acid biosynthesis, fatty acid biosynthesis, and biosynthesis of unsaturated fatty acids showed significant differences across both brain and serum diagnostic groups (P-value < 0.05). Significant associations were observed between the levels of differential metabolites/pathways and cognitive performance, neurofibrillary tangles, and neuritic plaque burden. Metabolites abundances and personalized metabolic pathways scores were used to derive machine learning models, respectively, that could be used to differentiate cognitively impaired persons from those without cognitive impairment (median area under the receiver operating characteristic curve (AUC) = 0.772 for the metabolite level model; median AUC = 0.731 for the pathway level model). Utilizing these two models on the entire baseline control group, we identified those who experienced cognitive decline in the later years (AUC = 0.804, sensitivity = 0.722, specificity = 0.749 for the metabolite level model; AUC = 0.778, sensitivity = 0.633, specificity = 0.825 for the pathway level model) and demonstrated their pre-AD onset prediction potentials. Our study provides a proof-of-concept that it is possible to discriminate antecedent cognitive impairment in older adults before the onset of overt clinical symptoms using metabolomics. Our findings, if validated in future studies, could enable the earlier detection and intervention of cognitive impairment that may halt its progression.

Evidence of the Role of Omega-3 Polyunsaturated Fatty Acids in Brain Glucose Metabolism

In mammals, brain function, particularly neuronal activity, has high energy needs. When glucose is supplemented by alternative oxidative substrates under different physiological conditions, these fuels do not fully replace the functions fulfilled by glucose. Thus, it is of major importance that the brain is almost continuously supplied with glucose from the circulation. Numerous studies describe the decrease in brain glucose metabolism during healthy or pathological ageing, but little is known about the mechanisms that cause such impairment. Although it appears difficult to determine the exact role of brain glucose hypometabolism during healthy ageing or during age-related neurodegenerative diseases such as Alzheimer’s disease, uninterrupted glucose supply to the brain is still of major importance for proper brain function. Interestingly, a body of evidence suggests that dietary n-3 polyunsaturated fatty acids (PUFAs) might play significant roles in brain glucose regulation. Thus, the goal of the present review is to summarize this evidence and address the role of n-3 PUFAs in brain energy metabolism. Taken together, these data suggest that ensuring an adequate dietary supply of n-3 PUFAs could constitute an essential aspect of a promising strategy to promote optimal brain function during both healthy and pathological ageing.

GluT4: A central player in hippocampal memory and brain insulin resistance

Insulin is now well-established as playing multiple roles within the brain, and specifically as regulating hippocampal cognitive processes and metabolism. Impairments to insulin signaling, such as those seen in type 2 diabetes and Alzheimer's disease, are associated with brain hypometabolism and cognitive impairment, but the mechanisms of insulin's central effects are not determined. Several lines of research converge to suggest that the insulin-responsive glucose transporter GluT4 plays a central role in hippocampal memory processes, and that reduced activation of this transporter may underpin the cognitive impairments seen as a consequence of insulin resistance.

Is AD a Stress-Related Disorder? Focus on the HPA Axis and Its Promising Therapeutic Targets

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder that has important health and economic impacts in the elderly. Despite a better understanding of the molecular mechanisms leading to the appearance of major pathological hallmarks (senile plaques and neurofibrillary tangles), effective treatments are still lacking. Sporadic AD forms (98% of all cases) are multifactorial, and a panoply of risk factors have been identified. While the major risk factor is aging, growing evidence suggests that chronic stress or stress-related disorders increase the probability to develop AD. An early dysregulation of the hypothalamic-pituitary-adrenal axis (HPA axis or stress axis) has been observed in patients. The direct consequence of such perturbation is an oversecretion of glucocorticoids (GC) associated with an impairment of its receptors (glucocorticoid receptors, GR). These steroids hormones easily penetrate the brain and act in synergy with excitatory amino acids. An overexposure could be highly toxic in limbic structures (prefrontal cortex and hippocampus) and contribute in the cognitive decline occurring in AD. GC and GR dysregulations seem to be involved in lots of functions disturbed in AD and a vicious cycle appears, where AD induces HPA axis dysregulation, which in turn potentiates the pathology. This review article presents some preclinical and clinical studies focusing on the HPA axis hormones and their receptors to fight AD. Due to its primordial role in the maintenance of homeostasis, the HPA axis appears as a key-actor in the etiology of AD and a prime target to tackle AD by offering multiple angles of action.

Possible Clues for Brain Energy Translation via Endolysosomal Trafficking of APP-CTFs in Alzheimer's Disease

Vascular dysfunctions, hypometabolism, and insulin resistance are high and early risk factors for Alzheimer's disease (AD), a leading neurological disease associated with memory decline and cognitive dysfunctions. Early defects in glucose transporters and glycolysis occur during the course of AD progression. Hypometabolism begins well before the onset of early AD symptoms; this timing implicates the vulnerability of hypometabolic brain regions to beta-secretase 1 (BACE-1) upregulation, oxidative stress, inflammation, synaptic failure, and cell death. Despite the fact that ketone bodies, astrocyte-neuron lactate shuttle, pentose phosphate pathway (PPP), and glycogenolysis compensate to provide energy to the starving AD brain, a considerable energy crisis still persists and increases during disease progression. Studies that track brain energy metabolism in humans, animal models of AD, and in vitro studies reveal striking upregulation of beta-amyloid precursor protein (β-APP) and carboxy-terminal fragments (CTFs). Currently, the precise role of CTFs is unclear, but evidence supports increased endosomal-lysosomal trafficking of β-APP and CTFs through autophagy through a vague mechanism. While intracellular accumulation of Aβ is attributed as both the cause and consequence of a defective endolysosomal-autophagic system, much remains to be explored about the other β-APP cleavage products. Many recent works report altered amino acid catabolism and expression of several urea cycle enzymes in AD brains, but the precise cause for this dysregulation is not fully explained. In this paper, we try to connect the role of CTFs in the energy translation process in AD brain based on recent findings.

Application of Metabolomics in Alzheimer's Disease

Progress toward the development of efficacious therapies for Alzheimer’s disease (AD) is halted by a lack of understanding early underlying pathological mechanisms. Systems biology encompasses several techniques including genomics, epigenomics, transcriptomics, proteomics, and metabolomics. Metabolomics is the newest omics platform that offers great potential for the diagnosis and prognosis of neurodegenerative diseases as an individual’s metabolome reflects alterations in genetic, transcript, and protein profiles and influences from the environment. Advancements in the field of metabolomics have demonstrated the complexity of dynamic changes associated with AD progression underscoring challenges with the development of efficacious therapeutic interventions. Defining systems-level alterations in AD could provide insights into disease mechanisms, reveal sex-specific changes, advance the development of biomarker panels, and aid in monitoring therapeutic efficacy, which should advance individualized medicine. Since metabolic pathways are largely conserved between species, metabolomics could improve the translation of preclinical research conducted in animal models of AD into humans. A summary of recent developments in the application of metabolomics to advance the AD field is provided below.

Socially Housed Female Macaques: a Translational Model for the Interaction of Chronic Stress and Estrogen in Aging

PURPOSE OF REVIEW

Estrogen's role in cognitive aging remains unclear. Despite evidence implicating stress in pathological aging, the interaction of stress with estrogen on cognition in older women has received little attention, and few animal models exist with which to examine this interaction.

RECENT FINDINGS

We present evidence that aging socially subordinate female macaques that experience chronic psychosocial stress constitute a suitable model to investigate this. First, we review studies showing that estrogen modulates cognition in animal models, as well as studies demonstrating that estrogen's action on certain types of cognition is impaired by stress. Next, we discuss data showing that middle-aged socially subordinate female macaques exhibit distinct stress-induced phenotypes, and review our investigations indicating that estrogen modulates behavior and physiology differently in subordinate female monkeys. We conclude that socially housed female macaques represent a translational animal model for investigating the interplay of chronic stress and estrogen on cognitive aging in women.

Unified theory of Alzheimer's disease (UTAD): implications for prevention and curative therapy

The aim of this review is to propose a Unified Theory of Alzheimer's disease (UTAD) that integrates all key behavioural, genetic and environmental risk factors in a causal chain of etiological and pathogenetic events. It is based on three concepts that emanate from human's evolutionary history: (1) The grandmother-hypothesis (GMH), which explains human longevity due to an evolutionary advantage in reproduction by trans-generational transfer of acquired knowledge. Consequently it is argued that mental health at old-age must be the default pathway of humans' genetic program and not development of AD. (2) Therefore, mechanism like neuronal rejuvenation (NRJ) and adult hippocampal neurogenesis (AHN) that still function efficiently even at old age provide the required lifelong ability to memorize personal experiences important for survival. Cumulative evidence from a multitude of experimental and epidemiological studies indicate that behavioural and environmental risk factors, which impair productive AHN, result in reduced episodic memory performance and in reduced psychological resilience. This leads to avoidance of novelty, dysregulation of the hypothalamic-pituitary-adrenal (HPA)-axis and cortisol hypersecretion, which drives key pathogenic mechanisms of AD like the accumulation and oligomerization of synaptotoxic amyloid beta, chronic neuroinflammation and neuronal insulin resistance. (3) By applying to AHN the law of the minimum (LOM), which defines the basic requirements of biological growth processes, the UTAD explains why and how different lifestyle deficiencies initiate the AD process by impairing AHN and causing dysregulation of the HPA-axis, and how environmental and genetic risk factors such as toxins or ApoE4, respectively, turn into disease accelerators under these unnatural conditions. Consequently, the UTAD provides a rational strategy for the prevention of mental decline and a system-biological approach for the causal treatment of AD, which might even be curative if the systemic intervention is initiated early enough in the disease process. Hence an individualized system-biological treatment of patients with early AD is proposed as a test for the validity of UTAD and outlined in this review.

Alzheimer disease research in the 21st century: past and current failures, new perspectives and funding priorities

Much of Alzheimer disease (AD) research has been traditionally based on the use of animals, which have been extensively applied in an effort to both improve our understanding of the pathophysiological mechanisms of the disease and to test novel therapeutic approaches. However, decades of such research have not effectively translated into substantial therapeutic success for human patients. Here we critically discuss these issues in order to determine how existing human-based methods can be applied to study AD pathology and develop novel therapeutics. These methods, which include patient-derived cells, computational analysis and models, together with large-scale epidemiological studies represent novel and exciting tools to enhance and forward AD research. In particular, these methods are helping advance AD research by contributing multifactorial and multidimensional perspectives, especially considering the crucial role played by lifestyle risk factors in the determination of AD risk. In addition to research techniques, we also consider related pitfalls and flaws in the current research funding system. Conversely, we identify encouraging new trends in research and government policy. In light of these new research directions, we provide recommendations regarding prioritization of research funding. The goal of this document is to stimulate scientific and public discussion on the need to explore new avenues in AD research, considering outcome and ethics as core principles to reliably judge traditional research efforts and eventually undertake new research strategies.

Insulin-like growth factor 2 rescues aging-related memory loss in rats

Aging is accompanied by declines in memory performance, and particularly affects memories that rely on hippocampal-cortical systems, such as episodic and explicit. With aged populations significantly increasing, the need for preventing or rescuing memory deficits is pressing. However, effective treatments are lacking. Here, we show that the level of the mature form of insulin-like growth factor 2 (IGF-2), a peptide regulated in the hippocampus by learning, required for memory consolidation and a promoter of memory enhancement in young adult rodents, is significantly reduced in hippocampal synapses of aged rats. By contrast, the hippocampal level of the immature form proIGF-2 is increased, suggesting an aging-related deficit in IGF-2 processing. In agreement, aged compared to young adult rats are deficient in the activity of proprotein convertase 2, an enzyme that likely mediates IGF-2 posttranslational processing. Hippocampal administration of the recombinant, mature form of IGF-2 rescues hippocampal-dependent memory deficits and working memory impairment in aged rats. Thus, IGF-2 may represent a novel therapeutic avenue for preventing or reversing aging-related cognitive impairments.

Biochemical assessment of precuneus and posterior cingulate gyrus in the context of brain aging and Alzheimer's disease

Defining the biochemical alterations that occur in the brain during “normal” aging is an important part of understanding the pathophysiology of neurodegenerative diseases and of distinguishing pathological conditions from aging-associated changes. Three groups were selected based on age and on having no evidence of neurological or significant neurodegenerative disease: 1) young adult individuals, average age 26 years (n = 9); 2) middle-aged subjects, average age 59 years (n = 5); 3) oldest-old individuals, average age 93 years (n = 6). Using ELISA and Western blotting methods, we quantified and compared the levels of several key molecules associated with neurodegenerative disease in the precuneus and posterior cingulate gyrus, two brain regions known to exhibit early imaging alterations during the course of Alzheimer’s disease. Our experiments revealed that the bioindicators of emerging brain pathology remained steady or decreased with advancing age. One exception was S100B, which significantly increased with age. Along the process of aging, neurofibrillary tangle deposition increased, even in the absence of amyloid deposition, suggesting the presence of amyloid plaques is not obligatory for their development and that limited tangle density is a part of normal aging. Our study complements a previous assessment of neuropathology in oldest-old subjects, and within the limitations of the small number of individuals involved in the present investigation, it adds valuable information to the molecular and structural heterogeneity observed along the course of aging and dementia. This work underscores the need to examine through direct observation how the processes of amyloid deposition unfold or change prior to the earliest phases of dementia emergence.

Dietary antiaging phytochemicals and mechanisms associated with prolonged survival

Aging is well-known an inevitable process that is influenced by genetic, lifestyle and environmental factors. However, the exact mechanisms underlying the aging process are not well understood. Increasing evidence shows that aging is highly associated with chronic increase in reactive oxygen species (ROS), accumulation of a low-grade proinflammatory phenotype and reduction in age-related autophagy, suggesting that these factors may play important roles in promoting aging. Indeed, reduction of ROS and low-grade inflammation and promotion of autophagy by calorie restriction or other dietary manipulation can extend lifespan in a wide spectrum of model organisms. Interestingly, recent studies show that some food-derived small molecules, also called phytochemicals, can extend lifespan in various animal species. In this paper, we review several recently identified potential antiaging phytochemicals that have been studied in cells, animals and humans and further highlight the cellular and molecular mechanisms underlying the antiaging actions by these molecules.

Zn2+-Aβ40 complexes form metastable quasi-spherical oligomers that are cytotoxic to cultured hippocampal neurons

The roles of metal ions in promoting amyloid β-protein (Aβ) oligomerization associated with Alzheimer disease are increasingly recognized. However, the detailed structures dictating toxicity remain elusive for Aβ oligomers stabilized by metal ions. Here, we show that small Zn(2+)-bound Aβ1-40 (Zn(2+)-Aβ40) oligomers formed in cell culture medium exhibit quasi-spherical structures similar to native amylospheroids isolated recently from Alzheimer disease patients. These quasi-spherical Zn(2+)-Aβ40 oligomers irreversibly inhibit spontaneous neuronal activity and cause massive cell death in primary hippocampal neurons. Spectroscopic and x-ray diffraction structural analyses indicate that despite their non-fibrillar morphology, the metastable Zn(2+)-Aβ40 oligomers are rich in β-sheet and cross-β structures. Thus, Zn(2+) promotes Aβ40 neurotoxicity by structural organization mechanisms mediated by coordination chemistry.

Vascular and metabolic dysfunction in Alzheimer's disease: a review

Alzheimer's disease (AD) is thought to start years or decades prior to clinical diagnosis. Overt pathology such as protein misfolding and plaque formation occur at later stages, and factors other than amyloid misfolding contribute to the initiation of the disease. Vascular and metabolic dysfunctions are excellent candidates, as they are well-known features of AD that precede pathology or clinical dementia. While the general notion that vascular and metabolic dysfunctions contribute to the etiology of AD is becoming accepted, recent research suggests novel mechanisms by which these/such processes could possibly contribute to AD pathogenesis. Vascular dysfunction includes reduced cerebrovascular flow and cerebral amyloid angiopathy. Indeed, there appears to be an interaction between amyloid β (Aβ) and vascular pathology, where Aβ production and vascular pathology both contribute to and are affected by oxidative stress. One major player in the vascular pathology is NAD(P)H oxidase, which generates vasoactive superoxide. Metabolic dysfunction has only recently regained popularity in relation to its potential role in AD. The role of metabolic dysfunction in AD is supported by the increased epidemiological risk of AD associated with several metabolic diseases such as diabetes, dyslipidemia and hypertension, in which there is elevated oxidative damage and insulin resistance. Metabolic dysfunction is further implicated in AD as pharmacological inhibition of metabolism exacerbates pathology, and several metabolic enzymes of the glycolytic, tricarboxylic acid cycle (TCA) and oxidative phosphorylation pathways are damaged in AD. Recent studies have highlighted the role of insulin resistance, in contributing to AD. Thus, vascular and metabolic dysfunctions are key components in the AD pathology throughout the course of disease. The common denominator between vascular and metabolic dysfunction emerging from this review appears to be oxidative stress and Aβ. This review also provides a framework for evaluation of current and future therapeutics for AD.

Transcranial doppler ultrasound blood flow velocity and pulsatility index as systemic indicators for Alzheimer's disease

BACKGROUND

Multiple lines of evidence suggest that cardiovascular co-morbidities hasten the onset of Alzheimer's disease (AD) or accelerate its course.

METHODS

To evaluate the utility of cerebral vascular physical function and/or condition parameters as potential systemic indicators of AD, transcranial Doppler (TCD) ultrasound was used to assess cerebral blood flow and vascular resistance of the 16 arterial segments comprising the circle of Willis and its major tributaries.

RESULTS

Our study showed that decreased arterial mean flow velocity and increased pulsatility index are associated with a clinical diagnosis of presumptive AD. Cerebral blood flow impairment shown by these parameters reflects the global hemodynamic and structural consequences of a multifaceted disease process yielding diffuse congestive microvascular pathology, increased arterial rigidity, and decreased arterial compliance, combined with putative age-associated cardiovascular output declines.

CONCLUSIONS

TCD evaluation offers direct physical confirmation of brain perfusion impairment and might ultimately provide a convenient and a noninvasive means to assess the efficacy of medical interventions on cerebral blood flow or reveal incipient AD. In the near term, TCD-based direct assessments of brain perfusion might offer the prospect of preventing or mitigating AD simply by revealing patients who would benefit from interventions to improve circulatory system function.

A pilot study of gene/gene and gene/environment interactions in Alzheimer disease

BACKGROUND

Although some genes associated with increased risk of Alzheimer Disease (AD) have been identified, few data exist related to gene/gene and gene/environment risk of AD. The purpose of this pilot study was to explore gene/gene and gene/environment associations in AD and to obtain data for sample size estimates for larger, more definitive studies of AD.

METHODS

The effect of gene/gene and gene/environment interaction related to late onset Alzheimer Disease (LOAD) was investigated in 153 subjects with LOAD and 302 gender matched controls enrolled in the Personalized Medicine Research Project, a population-based bio-repository. Genetic risk factors examined included APOE, ACE, OLR1,and CYP46 genes, and environmental factors included smoking, total cholesterol, LDL, HDL, triglycerides, C-reactive protein, blood pressure, statin use, and body mass index.

RESULTS

The mean age of the cases was 78.2 years and the mean age of the controls was 87.2 years. APOE4 was significantly associated with LOAD (OR=3.55, 95%CL=1.70, 7.45). Cases were significantly more likely to have ever smoked cigarettes during their life (49.3% versus 38.4%, p=0.03). The highest recorded blood pressure and pulse pressure measurements were significantly higher in the controls than the cases (all P<0.005). Although not statistically significant in this pilot study, the relationship of the following factors was associated in opposite directions with LOAD based on the presence of an APOE4 allele: obesity at the age of 50, ACE, OLR1, and CYP46.

CONCLUSIONS

These pilot data suggest that gene/gene and gene/environment interactions may be important in LOAD, with APOE, a known risk factor for LOAD, affecting the relationship of ACE and OLR1 to LOAD. Replication with a larger sample size and in other racial/ethnic groups is warranted and the allele and risk factor frequencies will assist in choosing an appropriate sample size for a definitive study.

The physiological link between metabolic rate depression and tau phosphorylation in mammalian hibernation

Abnormal phosphorylation and aggregation of tau protein are hallmarks of a variety of neurological disorders, including Alzheimer's disease (AD). Increased tau phosphorylation is assumed to represent an early event in pathogenesis and a pivotal aspect for aggregation and formation of neurofibrillary tangles. However, the regulation of tau phosphorylation in vivo and the causes for its increased stage of phosphorylation in AD are still not well understood, a fact that is primarily based on the lack of adequate animal models. Recently we described the reversible formation of highly phosphorylated tau protein in hibernating European ground squirrels. Hence, mammalian hibernation represents a model system very well suited to study molecular mechanisms of both tau phosphorylation and dephosphorylation under in vivo physiological conditions. Here, we analysed the extent and kinetics of hibernation-state dependent tau phosphorylation in various brain regions of three species of hibernating mammals: arctic ground squirrels, Syrian hamsters and black bears. Overall, tau protein was highly phosphorylated in torpor states and phosphorylation levels decreased after arousal in all species. Differences between brain regions, hibernation-states and phosphosites were observed with respect to degree and kinetics of tau phosphorylation. Furthermore, we tested the phosphate net turnover of tau protein to analyse potential alterations in kinase and/or phosphatase activities during hibernation. Our results demonstrate that the hibernation-state dependent phosphorylation of tau protein is specifically regulated but involves, in addition, passive, temperature driven regulatory mechanisms. By determining the activity-state profile for key enzymes of tau phosphorylation we could identify kinases potentially involved in the differentially regulated, reversible tau phosphorylation that occurs during hibernation. We show that in black bears hibernation is associated with conformational changes of highly phosphorylated tau protein that are typically related to neuropathological alterations. The particular hibernation characteristics of black bears with a continuous torpor period and an only slightly decreased body temperature, therefore, potentially reflects the limitations of this adaptive reaction pattern and, thus, might indicate a transitional state of a physiological process.

The biochemical aftermath of anti-amyloid immunotherapy

BACKGROUND

Active and passive immunotherapy in both amyloid-beta precursor protein (APP) transgenic mice and Alzheimer's Disease (AD) patients have resulted in remarkable reductions in amyloid plaque accumulation, although the degree of amyloid regression has been highly variable. Nine individuals with a clinical diagnosis of AD dementia were actively immunized with the Aβ peptide 1-42 (AN-1792) and subjected to detailed postmortem biochemical analyses. These patients were compared to 6 non-immunized AD cases and 5 non-demented control (NDC) cases.

RESULTS

All patients were assessed for the presence of AD pathology including amyloid plaques, neurofibrillary tangles and vascular amyloidosis. This effort revealed that two immunotherapy recipients had dementia as a consequence of diseases other than AD. Direct neuropathological examination consistently demonstrated small to extensive areas in which amyloid plaques apparently were disrupted. Characterization of Aβ species remnants by ELISA suggested that total Aβ levels may have been reduced, although because the amounts of Aβ peptides among treated individuals were extremely variable, those data must be regarded as tentative. Chromatographic analysis and Western blots revealed abundant dimeric Aβ peptides. SELDI-TOF mass spectrometry demonstrated a substantive number of Aβ-related peptides, some of them with elongated C-terminal sequences. Pro-inflammatory TNF-α levels were significantly increased in the gray matter of immunized AD cases compared to the NDC and non-immunized AD groups.

CONCLUSIONS

Immunotherapy responses were characterized by extreme variability. Considering the broad range of biological variation that characterizes aging and complicates the recognition of reliable AD biomarkers, such disparities will make the interpretation of outcomes derived from epidemiologic and therapeutic investigations challenging. Although in some cases the apparent removal of amyloid plaques by AN-1792 was impressive, proportionate alterations in the clinical progression of AD were not evident. The fact that plaque elimination did not alter the trajectory of decline into dementia suggests the likelihood that these deposits alone are not the underlying cause of dementia.

Amyloid precursor protein transgenic mouse models and Alzheimer's disease: understanding the paradigms, limitations, and contributions

Transgenic (Tg) mice that overexpress mutant familial Alzheimer's disease (AD) amyloid precursor protein (APP) genes have contributed to an understanding of dementia pathology, and support the amyloid cascade hypothesis. Although many sophisticated mice APP models exist, none recapitulates AD cellular and behavioral pathology. The morphological resemblance to AD amyloidosis is impressive, but fundamental biophysical and biochemical properties of the APP/Abeta produced in Tg mice differ substantially from those of humans. The greater resilience of Tg mice in the presence of substantial Abeta burdens suggests that levels and forms deleterious to human neurons are not as noxious in these models. Transgenic mice were widely used for testing AD therapeutic agents, and demonstrated promising results. Unfortunately, clinical trials resulted in unforeseen adverse events or negative therapeutic outcomes. The disparity between success and failure is in part attributable to evolutionary divergence between humans and rodents. These observations suggest that the pathogenesis of AD is by far more intricate than can be explained by a straightforward accumulation of Abeta.

Dysregulation of the nutrient/stress sensor O-GlcNAcylation is involved in the etiology of cardiovascular disorders, type-2 diabetes and Alzheimer's disease

O-GlcNAcylation is widespread within the cytosolic and nuclear compartments of cells. This post-translational modification is likely an indicator of good health since its intracellular level correlates with the availability of extracellular glucose. Apart from its status as a nutrient sensor, O-GlcNAcylation may also act as a stress sensor since it exerts its fundamental effects in response to stress. Several studies report that the cell quickly responds to an insult by elevating O-GlcNAcylation levels and by unmasking a newly described Hsp70-GlcNAc binding property. From a more practical point of view, it has been shown that O-GlcNAcylation impairments contribute to the etiology of cardiovascular diseases, type-2 diabetes and Alzheimer's disease (AD), three illnesses common in occidental societies. Many studies have demonstrated that O-GlcNAcylation operates as a powerful cardioprotector and that by raising O-GlcNAcylation levels, the organism more successfully resists trauma-hemorrhage and ischemia/reperfusion injury. Recent data have also shown that insulin resistance and, more broadly, type-2 diabetes can be controlled by O-GlcNAcylation of the insulin pathway and O-GlcNAcylation of the gluconeogenesis transcription factors FoxO1 and CRCT2. Lastly, the finding that AD may correspond to a type-3 diabetes offers new perspectives into the knowledge of the neuropathology and into the search for new therapeutic avenues.

ReviewGenetics, lifestyle and the roles of amyloid β and oxidative stress in Alzheimer’s disease

This paper reviews a wide range of recent studies that have linked AD-associated biochemical and physiological changes with oxidative stress and damage. Some of these changes include disruptions in metal ion homeostasis, mitochondrial damage, reduced glucose metabolism, decreased intracellular pH and inflammation. Although the changes mentioned above are associated with oxidative stress, in most cases, a cause and effect relationship is not clearcut, as many changes are interlinked. Increases in the levels of Abeta peptides, the main protein components of the cerebral amyloid deposits of AD, have been demonstrated to occur in inherited early-onset forms of AD, and as a result of certain environmental and genetic risk factors. Abeta peptides have been shown to exhibit superoxide dismutase activity, producing hydrogen peroxide which may be responsible for the neurotoxicity exhibited by this peptide in vitro. This review also discusses the biochemical aspects of oxidative stress, antioxidant defence mechanisms, and possible antioxidant therapeutic measures which may be effective in counteracting increased levels of oxidative stress. In conclusion, this review provides support for the theory that damage caused by free radicals and oxidative stress is a primary cause of the neurodegeneration seen in AD with Abeta postulated as an initiator of this process.

Antibody responses, amyloid-beta peptide remnants and clinical effects of AN-1792 immunization in patients with AD in an interrupted trial

Post mortem examinations of AN-1792-vaccinated humans revealed this therapy produced focal senile plaque disruption. Despite the dispersal of substantial plaque material, vaccination did not constitute even a partial eradication of brain amyloid as water soluble amyloid-beta (Abeta) 40/42 increased in the gray matter compared to sporadic Alzheimer's disease (AD) patients and total brain Abeta levels were not decreased. Significant aspects of AD pathology were unaffected by vaccination with both vascular amyloid and hyper-phosphorylated tau deposits appeared refractory to this therapy. In addition, vaccination resulted in the consequential and drastic expansion of the white matter (WM) amyloid pool to levels without precedent in sporadic AD patients. Although vaccination disrupted amyloid plaques, this therapy did not enhance long-term cognitive function or necessarily halt neurodegeneration. The intricate involvement of vascular pathology in AD evolution and the firm recalcitrance of vessel-associated amyloid to antibody-mediated disruption suggest that immunization therapies might be more effective if administered on a prophylactic basis before vascular impairment and well ahead of any clinically evident cognitive decline. Amyloid-beta is viewed as pathological based on the postmortem correlation of senile plaques with an AD diagnosis. It remains uncertain which of the various forms of this peptide is the most toxic and whether Abeta or senile plaques themselves serve any desirable or protective functions. The long-term cognitive effects of chronic immunotherapy producing a steadily accumulating and effectively permanent pool of disrupted Abeta peptides within the human brain are unknown. In addition, the side effects of such therapy provided on a chronic basis could extend far beyond the brain. Eagerly seeking new therapies, critical knowledge gaps should prompt us to take a more wholistic perspective viewing Abeta and the amyloid cascade as aspects of complex and many-faceted physiological processes that sometimes end in AD dementia.

Nicotine and inflammatory neurological disorders

Cigarette smoke is a major health risk factor which significantly increases the incidence of diseases including lung cancer and respiratory infections. However, there is increasing evidence that smokers have a lower incidence of some inflammatory and neurodegenerative diseases. Nicotine is the main immunosuppressive constituent of cigarette smoke, which inhibits both the innate and adaptive immune responses. Unlike cigarette smoke, nicotine is not yet considered to be a carcinogen and may, in fact, have therapeutic potential as a neuroprotective and anti-inflammatory agent. This review provides a synopsis summarizing the effects of nicotine on the immune system and its (nicotine) influences on various neurological diseases.

Alzheimer's disease and natural cognitive aging may represent adaptive metabolism reduction programs

The present article examines several lines of converging evidence suggesting that the slow and insidious brain changes that accumulate over the lifespan, resulting in both natural cognitive aging and Alzheimer's disease (AD), represent a metabolism reduction program. A number of such adaptive programs are known to accompany aging and are thought to have decreased energy requirements for ancestral hunter-gatherers in their 30s, 40s and 50s. Foraging ability in modern hunter-gatherers declines rapidly, more than a decade before the average terminal age of 55 years. Given this, the human brain would have been a tremendous metabolic liability that must have been advantageously tempered by the early cellular and molecular changes of AD which begin to accumulate in all humans during early adulthood. Before the recent lengthening of life span, individuals in the ancestral environment died well before this metabolism reduction program resulted in clinical AD, thus there was never any selective pressure to keep adaptive changes from progressing to a maladaptive extent.Aging foragers may not have needed the same cognitive capacities as their younger counterparts because of the benefits of accumulated learning and life experience. It is known that during both childhood and adulthood metabolic rate in the brain decreases linearly with age. This trend is thought to reflect the fact that children have more to learn. AD "pathology" may be a natural continuation of this trend. It is characterized by decreasing cerebral metabolism, selective elimination of synapses and reliance on accumulating knowledge (especially implicit and procedural) over raw brain power (working memory). Over decades of subsistence, the behaviors of aging foragers became routinized, their motor movements automated and their expertise ingrained to a point where they no longer necessitated the first-rate working memory they possessed when younger and learning actively. Alzheimer changes selectively and precisely mediate an adaptation to this major life-history transition.AD symptomatology shares close similarities with deprivation syndromes in other animals including the starvation response. Both molecular and anatomical features of AD imitate brain changes that have been conceptualized as adaptive responses to low food availability in mammals and birds. Alzheimer's patients are known to express low overall metabolic rates and are genetically inclined to exhibit physiologically thrifty traits widely thought to allow mammals to subsist under conditions of nutritional scarcity. Additionally, AD is examined here in the contexts of anthropology, comparative neuroscience, evolutionary medicine, expertise, gerontology, neural Darwinism, neuroecology and the thrifty genotype.

Amyloid beta peptides in human plasma and tissues and their significance for Alzheimer's disease

BACKGROUND

We evaluated the amounts of amyloid beta (Abeta)) peptides in the central nervous system (CNS) and in reservoirs outside the CNS and their potential impact on Abeta plasma levels and Alzheimer's disease (AD) pathology.

METHODS

Amyloid beta levels were measured in (1) the plasma of AD and nondemented (ND) controls in a longitudinal study, (2) the plasma of a cohort of AD patients receiving a cholinesterase inhibitor, and (3) the skeletal muscle, liver, aorta, platelets, leptomeningeal arteries, and in gray and white matter of AD and ND control subjects.

RESULTS

Plasma Abeta levels fluctuated over time and among individuals, suggesting continuous contributions from brain and peripheral tissues and associations with reactive circulating proteins. Arteries with atherosclerosis had larger amounts of Abeta40 than disease-free vessels. Inactivated platelets contained more Abeta peptides than activated ones. Substantially more Abeta was present in liver samples from ND patients. Overall, AD brain and skeletal muscle contained increased levels of Abeta.

CONCLUSIONS

Efforts to use plasma levels of Abeta peptides as AD biomarkers or disease-staging scales have failed. Peripheral tissues might contribute to both the circulating amyloid pool and AD pathology within the brain and its vasculature. The wide spread of plasma Abeta values is also due in part to the ability of Abeta to bind to a variety of plasma and membrane proteins. Sources outside the CNS must be accounted for because pharmacologic interventions to reduce cerebral amyloid are assessed by monitoring Abeta plasma levels. Furthermore, the long-range impact of Abeta immunotherapy on peripheral Abeta sources should also be considered.

Histopathological and molecular heterogeneity among individuals with dementia associated with Presenilin mutations

Background

Mutations in the presenilin (PSEN) genes are associated with early-onset familial Alzheimer's disease (FAD). Biochemical characterizations and comparisons have revealed that many PSEN mutations alter γ-secretase activity to promote accumulation of toxic Aβ42 peptides. In this study, we compared the histopathologic and biochemical profiles of ten FAD cases expressing independent PSEN mutations and determined the degradation patterns of amyloid-β precursor protein (AβPP), Notch, N-cadherin and Erb-B4 by γ-secretase. In addition, the levels of Aβ40/42 peptides were quantified by ELISA.

Results

We observed a wide variation in type, number and distribution of amyloid deposits and neurofibrillary tangles. Four of the ten cases examined exhibited a substantial enrichment in the relative proportions of Aβ40 over Aβ42. The AβPP N-terminal and C-terminal fragments and Tau species, assessed by Western blots and scanning densitometry, also demonstrated a wide variation. The Notch-1 intracellular domain was negligible by Western blotting in seven PSEN cases. There was significant N-cadherin and Erb-B4 peptide heterogeneity among the different PSEN mutations.

Conclusion

These observations imply that missense mutations in PSEN genes can alter a range of key γ-secretase activities to produce an array of subtly different biochemical, neuropathological and clinical manifestations. Beyond the broad common features of dementia, plaques and tangles, the various PSEN mutations resulted in a wide heterogeneity and complexity and differed from sporadic AD.

Insulin dysfunction induces in vivo tau hyperphosphorylation through distinct mechanisms

Hyperphosphorylated tau is the major component of paired helical filaments in neurofibrillary tangles found in Alzheimer's disease (AD) brains, and tau hyperphosphorylation is thought to be a critical event in the pathogenesis of the disease. The large majority of AD cases is late onset and sporadic in origin, with aging as the most important risk factor. Insulin resistance, impaired glucose tolerance, and diabetes mellitus (DM) are other common syndromes in the elderly also strongly age dependent, and there is evidence supporting a link between insulin dysfunction and AD. To investigate the possibility that insulin dysfunction might promote tau pathology, we induced insulin deficiency and caused DM in mice with streptozotocin (STZ). A mild hyperphosphorylation of tau could be detected 10, 20, and 30 d after STZ injection, and a massive hyperphosphorylation of tau was observed after 40 d. The robust hyperphosphorylation of tau was localized in the axons and neuropil, and prevented tau binding to microtubules. Neither mild nor massive tau phosphorylation induced tau aggregation. Body temperature of the STZ-treated mice did not differ from control animals during 30 d, but dropped significantly thereafter. No change in beta-amyloid (Abeta) precursor protein (APP), APP C-terminal fragments, or Abeta levels were observed in STZ-treated mice; however, cellular protein phosphatase 2A activity was significantly decreased. Together, these data indicate that insulin dysfunction induced abnormal tau hyperphosphorylation through two distinct mechanisms: one was consequent to hypothermia; the other was temperature-independent, inherent to insulin depletion, and probably caused by inhibition of phosphatase activity.

Gene expression profiles of metabolic enzyme transcripts in Alzheimer's disease

The successfully functioning brain is a heavy user of metabolic energy. Alzheimer's disease, in which cognitive faculties decline, may be due, at least in part, to metabolic insufficiency. Using microarray analysis and quantitative RT-PCR, the expression of mRNA transcripts involved in glucose metabolism was investigated in Alzheimer's diseased post-mortem human hippocampal samples. Of the 51 members of the glycolytic, tricarboxylic acid cycle, oxidative phosphorylation, and associated pathways investigated by qPCR, 15 were confirmed to be statistically significantly (p<0.05) down-regulated in Alzheimer's disease. This finding suggests that reductions in the levels of transcripts encoded by genes that participate in energy metabolism may be involved in Alzheimer's disease.

Alzheimer' s disease, oxidative stress and gammahydroxybutyrate

Although the cause of Alzheimer's disease is unknown, oxidative stress, energy depletion, excitotoxicity and vascular endothelial pathology are all considered to play a part in its pathogenesis. In reaction to these adverse events, the Alzheimer brain appears to deploy a highly conserved biological response to tissue stress. Oxidative metabolism is turned down, the expression of antioxidative enzymes is increased and intermediary metabolism is shifted in the direction of the pentose phosphate shunt to promote reductive detoxification, repair and biosynthesis. Gathering evidence suggests that the release of beta-amyloid and the formation of neurofibrillary tangles, the two hallmarks of Alzheimer's disease, are components of this protective response. Gammahydroxybutyrate (GHB), an endogenous short chain fatty acid, may be able to buttress this response. GHB can reduce glucose utilization, shift intermediary metabolism in the direction the pentose phosphate shunt and generate NADPH, a key cofactor in the activity of many antioxidative and reductive enzymes. GHB has been shown to spare cerebral energy utilization, block excitotoxicity and maintain vascular integrity in the face of impaired perfusion. Most important, GHB has repeatedly been shown to prevent the tissue damaging effects of oxidative stress. It may therefore be possible to utilize GHB to strengthen the brain's innate defences against the pathological processes operating in the Alzheimer brain and, in this way, stem the advance of Alzheimer's disease.

Does O-GlcNAc play a role in neurodegenerative diseases?

There are several lines of evidence that the modification of proteins by cytosolic- and nuclear-specific O-linked N-acetylglucosamine (O-GlcNAc) glycosylation is closely related to neuropathologies, particularly Alzheimer's disease. Several neuronal proteins have been identified as being modified with O-GlcNAc; these proteins could form part of the inclusion bodies found, for example, in the most frequently observed neurologic disorder (i.e., Alzheimer's disease; Tau protein and beta-amyloid peptide are the well known aggregated proteins). O-GlcNAc proteins are also implicated in synaptosomal transport (e.g., synapsins and clathrin-assembly proteins). Inclusion bodies are partly characterized by a deficiency in the ubiquitin-proteasome system, avoiding the degradation of aggregated proteins. From this perspective, it appears interesting that substrate proteins could be protected against proteasomal degradation by being covalently modified with single N-acetylglucosamine on serine or threonine, and that the proteasome itself is modified and regulated by O-GlcNAc (in this case the turnover of neuronal proteins correlates with extracellular glucose). Interestingly, glucose uptake and metabolism are impaired in neuronal disorders, and this phenomenon is linked to increased phosphorylation. In view of the existence of the dynamic interplay between O-GlcNAc and phosphorylation, it is tempting to draw a parallel between the use of glucose, O-GlcNAc glycosylation and phosphorylation. Lastly, the two enzymes responsible for O-GlcNAc dynamism (i.e., O-GlcNAc transferase and glucosaminidase) are both enriched in the brain and genes that encode the two enzymes are located in two regions that are found to be frequently mutated in neurologic disorders. The data presented in this review strongly suggest that O-GlcNAc could play an active role in neurodegenerative diseases.

Characterization of the human P-type 6-phosphofructo-1-kinase gene promoter in neural cell lines

In humans three isoforms of 6-phosphofructo-1-kinase (PFK) exist. Among them platelet-type PFK (PFKP) is highly abundant in the brain. With its distinct allosteric properties PFKP is regarded to be the key enzyme for the regulation of glycolysis in this organ. We cloned 1.7 kb of the 5' upstream promoter of the human PFKP gene and analyzed the promoter activity by deletion and mutation analysis using a luciferase reporter. The transcription start point was determined at 48 bp upstream of the start codon. In deletion studies the region -65 to +48 turned out to be sufficient for promoter activity while fragment -153 to +48 showed the highest promoter activity. Sequence analysis of the region from -153 to +48 revealed a stretch of eight adjacent putative transcription factor binding sites, seven of which are Sp-family specific sites. Sp1 and Sp3 were shown to bind to most if not all of them. Additionally, an NF-Y binding site was identified. Results of deletion and mutation analysis suggest that all of these transcription factors contribute positively to promoter activity. The methylation status of the promoter region was analyzed in different neural tumor cell lines and compared with that in human leukocytes and muscle.

Glycation of the amyloid beta-protein by a nicotine metabolite: a fortuitous chemical dynamic between smoking and Alzheimer's disease

The origin of Alzheimer's disease (AD) has been subjected to an intense amount of examination; however, a clear conclusion as to the nature of this crippling disease has yet to be identified. What is readily accepted is that a definitive marker of this disease is the aggregation of the amyloid beta-peptide (A beta) into neuritic plaques. The recent observation that nicotine exposure leads to delayed onset of AD has stimulated a flurry of research into the nature of this neuroprotective effect. This phenomenon has been debated, but no consensus has been reached, and although these studies have targeted nicotine, the primary alkaloid in tobacco, few studies have considered the physiological role of nicotine metabolites in disease states. Nornicotine is a major nicotine metabolite in the CNS and has been shown to participate in the aberrant glycation of proteins in vivo in a process termed nornicotine-based glycation. Herein is detailed a potentially fortuitous role of nornicotine-based glycation in relation to the pathology of AD. Specifically, nornicotine was found to covalently alter A beta, leading to reduced peptide aggregation. Potential consequences of this reaction cascade include reduced plaque formation and/or altered clearance of the peptide, as well as attenuated toxicity of soluble A beta aggregates. The findings described provide an alternative mechanism for nicotine neuroprotection in AD and a means for the alteration of amyloid folding based on a covalent chemical event.

Prospects for antiapoptotic drug therapy of neurodegenerative diseases

The evidence for a role of apoptosis in the neurodegenerative diseases, Alzheimer's disease (AD), Parkinson's disease (PD) and amyotrophic lateral sclerosis (ALS), and in the more acute conditions of cerebral ischemia, traumatic brain injury (TBI), and spinal cord injury (SCI) is reviewed with regard to potential intervention by means of small antiapoptotic molecules. In addition, the available animal models for these diseases are discussed with respect to their relevance for testing small antiapoptotic molecules in the context of what is known about the apoptotic pathways involved in the diseases and the models. The principal issues related to pharmacotherapy by apoptosis inhibition, i.e., functionality of rescued neurons and potential interference with physiologically occurring apoptosis, are pointed out. Finally, the properties of a number of small antiapoptotic molecules currently under clinical investigation are summarized. It is concluded that the evidence for a role of apoptosis at present is more convincing for PD and ALS than for AD. In PD, damage to dopaminergic neurons may occur through oxidative stress and/or mitochondrial impairment and culminate in activation of an apoptotic, presumably p53-dependent cascade; some neurons experiencing energy failure may not be able to complete apoptosis, end up in necrosis and give rise to inflammatory processes. These events are reasonably well reflected in some of the PD animal models, notably those involving 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and rotenone. In sporadic ALS, an involvement of pathways involving p53 and Bcl-2 family members appears possible if not likely, but is not established. The issue is important for the development of antiapoptotic compounds for the treatment of this disease because of differential involvement of p53 in different mutant superoxide dismutase (SOD) mice. Most debated is the role of apoptosis in AD; this implies that little is known about potentially involved pathways. Moreover, there is a lack of suitable animal models for compound evaluation. Apoptosis or related phenomena are likely involved in secondary cell death in cerebral ischemia, TBI, and SCI. Most of the pertinent information comes from animal experiments, which have provided some evidence for prevention of cell death by antiapoptotic treatments, but little for functional benefit. Much remains to be done in this area to explore the potential of antiapoptotic drugs. There is a small number of antiapoptotic compounds in clinical development. With some of them, evidence for maintenance of functionality of the rescued neurons has been obtained in some animal models, and the fact that they made it to phase II studies in patients suggests that interference with physiological apoptosis is not an obligatory problem. The prospect that small antiapoptotic molecules will have an impact on the therapy of neurodegenerative diseases, and perhaps also of ischemia and trauma, is therefore judged cautiously positively.

Beta-amyloid and cholinergic neurons

It is generally accepted that the crucial events in the pathogeny of Alzheimer's disease (AD) are the increased accumulation of amyloidogenic peptides derived from amyloid precursor protein and the harmful actions of these peptides on neurons, which bring about neurodegeneration. The enhanced beta-amyloid accumulation is known to be caused by mutations of specific genes in patients who suffer from the familial (hereditary) form of AD but who represent just a minor group within the total population of AD patients. The reasons for beta-amyloid accumulation are not known in the much larger group of patients with the sporadic form of the disease. A biochemical feature common to either form of the disease is the preferential atrophy and degeneration of cholinergic neurons, which is probably responsible for much of the cognitive decline characteristic of the disease. We present an overview of recent investigations on the interactions between beta-amyloid and cholinergic neurons.

Immunocapture and microplate-based activity measurement of mammalian pyruvate dehydrogenase complex

Altered pyruvate dehydrogenase (PDH) functioning occurs in primary PDH deficiencies and in diabetes, starvation, sepsis, and possibly Alzheimer's disease. Currently, the activity of the enzyme complex is difficult to measure in a rapid high-throughput format. Here we describe the use of a monoclonal antibody raised against the E2 subunit to immunocapture the intact PDH complex still active when bound to 96-well plates. Enzyme turnover was measured by following NADH production spectrophotometrically or by a fluorescence assay on mitochondrial protein preparations in the range of 0.4 to 5.0 micro g per well. Activity is sensitive to known PDH inhibitors and remains regulated by phosphorylation and dephosphorylation after immunopurification because of the presence of bound PDH kinase(s) and phosphatase(s). It is shown that the immunocapture assay can be used to detect PDH deficiency in cell extracts of cultured fibroblasts from patients, making it useful in patient screens, as well as in the high-throughput format for discovery of new modulators of PDH functioning.

Neuropeptides: general characteristics and neuropharmaceutical potential in treating CNS disorders

The general characteristics of neuropeptides are discussed as a background for the understanding of their role in regulation of physiological systems. The extent of those systems that are crucially affected by neuropeptides is vast and the complexity of their interactions makes the clinical focus on a specific neuropeptide unsatisfactory. The clinical potential of neuropeptides affecting eating disorders, CNS behavioral disorders and the neuroregenerative and neuroprotective action of neuropeptides is discussed. It is probable that successful neuropeptide therapeutics will depend upon the application of translational and combinational research using various ingenious combinations of neuropeptides, their agonists and antagonists, neuropeptide receptor agonists and antagonists, improved methods of delivery and the development of peptides targeted to the genetic profile of individual patients.