Current Alzheimer Research - Volume 4, Issue 4, 2007

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Cholinergic nucleus basalis (NB) neurons provide the major cholinergic innervation to the cortical mantle, are selectively vulnerable in late stage Alzheimer's disease (AD) and require the neurotrophin, nerve growth factor (NGF) and its receptors (TrkA and p75NTR), for their survival. The molecular events underlying the demise of these neurons in AD were investigated using tissue harvested from participants in a longitudinal clinical pathological study of aging and AD who agreed to an annual clinical evaluation providing a categorization of no cognitive impairment (NCI), mild cognitive impairment (MCI) or AD and postmortem brain donation. Although the number of choline acetyltransferase (ChAT)- positive neurons was unchanged, TrkA and p75NTR receptor-containing neurons, which co-localize with ChAT, were significantly reduced in the NB of subjects with MCI and AD compared to those with NCI. These observations indicate a phenotypic down-regulation rather than frank NB neuronal degeneration in MCI. Expression profiling of single cholinergic NB neurons revealed TrkA but not p75NTR mRNA is reduced in MCI, suggesting that decreased neurotrophin responsiveness may be an early biomarker for AD. The NGF precursor molecule, proNGF, is increased in the cortex in MCI and AD. Since proNGF accumulates in the presence of reduced cortical TrkA and sustained levels of p75NTR, a shift in the balance between cell survival and death molecules may occur in prodromal AD. Coincident with these phenomena, brain derived neurotrophic factor (BDNF) and its precursor molecule, proBDNF, are reduced in the MCI cortex, potentially depriving CBF neurons of additional trophic factor support. Moreover, there is a shift in the ratio of 3 repeat tau to 4 repeat tau gene expression, whereas total tau message is stable in NB neurons during the disease process. These data suggest there is a shift in cholinotrophic molecular events in MCI and early AD which may lead to cell dysfunction and eventual cell death over the course of the disease. These findings support the concept that from a neurotrophic pathobiologic perspective, MCI is already early AD.

Forebrain cholinergic neurons are highly dependent on nerve growth factor (NGF) for phenotype maintenance. We have established that in addition to “target-derived” NGF neurotrophic stimulation, cholinergic neurons also respond dose-dependently, to intra-parenchymal NGF administration in the somato-dendritic region of the nucleus Basalis [1], thus illustrating the potential of alternative reparative therapies which would by-pass the undesirable effects of diffuse neurotrophin application. Moreover, our lab has also observed that the steady-state number of cortical cholinergic synapses is dependent on continuous NGF supply, as anti-NGF monoclonal antibodies and TrkA receptor antagonists deplete pre-existing cholinergic bouton numbers [2]. Furthermore, the application of either NGF or TrkA NGF-mimetic agonists successfully rescues the age-dependent loss of cortical cholinergic boutons in aged-impaired rats [3]. The vulnerability of the cortical cholinergic system has also been demonstrated in transgenic animal models of the Alzheimer's disease (AD) amyloid pathology [4-6]. It is of interest to note however, that an up-regulation of cholinergic presynaptic boutons has been observed in certain transgenic mouse models prior to plaque formation [6]. This observation is similar to the visibly increased immunoreactivity of cortical and hippocampal choline acetyltransferase (ChAT) fibers in patients with Mild Cognitive Impairment (MCI, [7]). A series of ex-vivo experiments conducted by our group have demonstrated that contrary to popular belief, proNGF, as opposed to mature NGF, is released from the cerebral cortex in an activity-dependent manner. In addition, proNGF appears to be released with a series of pro-enzymes and enzymes, which are involved in its subsequent maturation to NGF and degradation in the extracellular space [8]. Given that proNGF is known to be upregulated in AD patients [9] a dysregulation in the maturation or degradation of mature NGF might explain the preferential vulnerability of the cholinergic system in the AD pathology.

Alzheimer disease (AD) is a neurodegenerative disease that affects cognition, behavior and function. The etiology of the disease is unknown, however, the Primary Risk Factors for AD are aging, and family history. Neurofibrillary tangles (NFT) and amyloid-bearing neuritic plaques in the limbic and cerebral cortices are the characteristic neuropathologic lesions in brains of patients with AD. The NFT is mainly composed of hyprephosphorylated tau, whereas the major component of the neuritic plaques is the amyloid beta (Aβ) protein. The clinical diagnosis of probable AD is based on history, physical examination, neuropsychological testing, laboratory studies and neuroimaging techniques. However, there is no specific laboratory marker to support the diagnosis of definite AD or monitoring the progression of the disease. Several biochemical markers related to neuropathology have been identified in cerebrospinal fluid (CSF). We describe the studies of CSF or blood levels of amyloid β protein in patients with AD and age-matched nondemented controls. Due to the heterogeneity and complex nature of the disease, it is highly unlikely that that a single marker specific for AD will be found.

Computerized administration of neuropsychological tests can be an objective, sensitive and efficient way to screen for and monitor cognitive changes in the elderly. However, current computer software still suffers from limitations in both the administration of those tests and the interpretation of their results, which might severely hamper their usability. In this paper qualitative aspects of current methods and their use in the prediction of dementia are discussed, guidelines for correct design and usage of computerized methods are suggested and a solution that overcomes several of the methodological limitations is proposed.

We have demonstrated that aged animals show significant improvements in cognitive function and neurogenesis after brain transplantation of human neural stem cells or of human adult mesenchymal stem cells that have been dedifferentiated by transfection of the embryonic stem cell gene. We have also demonstrated that peripheral administration of a pyrimidine derivative increased cognition, endogenous brain stem cell proliferation and neurogenesis. These results indicate a bright future for stem cell therapies in Alzheimer's disease (AD). Before this is realized, however, we need to consider the affect of AD pathology on stem cell biology to establish an effective stem cell therapy for this disease. Although amyloid-β (Aβ) deposition is a hallmark of AD, an absence of a phenotype in the β-amyloid precursor protein (APP) knockout mouse, might lead one to underestimate the potential physiological functions of APP and suggest that it is unessential or can be compensated for. We have found, however, that APP is needed for differentiation of neural stem cells (NSCs) in vitro, and that NSCs transplanted into a APP-knockout mouse did not migrate or differentiate - indicating that APP plays an important role in differentiation or migration process of NSCs in the brain. Then again, treatment with high a concentration of APP or its over-expression increased glial differentiation of NSCs. Human NSCs transplanted into APP-transgenic mouse brain exhibited less neurogenesis and active gliosis around the plaque like formations. Treatment of such animals with the compound, (+)-phenserine, that is known to reduce APP protein levels, increased neurogenesis and suppressed gliosis. These results suggest APP levels can regulate NSC biology in the adult brain, that altered APP metabolism in Down syndrome or AD may have implications for the pathophysiology of these diseases, and that a combination of stem cell therapy and regulation of APP levels could provide a treatment strategy for these disorders.

As the average ages of North Americans and Europeans continue to rise; similarly the incidence of “old age” associated illnesses likewise increases. Most notably among these ailments are conditions linked to dementia-related neurodegenerative disorders, such as Alzheimer's disease (AD), Parkinson's disease (PD) and stroke. While in the early stages, these conditions are associated with cellular dysfunction in distinctly different brain regions, thus affecting different neuronal cell types; it is most likely that the final stages share similar cellular and molecular processes leading to neuronal death and ultimately overt clinical symptoms. In this regard, different environmental and genetic triggers ranging from head trauma to protein mutations and toxicological exposure may instigate a cascade of intracellular events that ultimately lead to neuronal death. One strong candidate trigger protein, and thus a potential target for therapeutic manipulation is the potent pro-inflammatory / pro-apoptotic cytokine, tumor necrosis factor-α (TNF-α). TNF-α is secreted by the brain resident marcophage (the microglial cell) in response to various stimuli. It has been demonstrated to play a major role in central nervous system (CNS) neuroinflammation-mediated cell death in AD, PD and amyotrophic lateral sclerosis (ALS) as well as several other CNS complications. Recently, agents that modulate the levels of circulating peripheral TNF-α protein have been shown to be worthwhile therapeutic agents with the use of Enbrel (Etanercept) and Remicade (Infliximab), both of which display beneficial properties against rheumatoid arthritis and other peripheral inflammatory diseases. Unfortunately, these agents are largely unable to penetrate the blood-brain barrier, which severely limits their use in the setting of neuroinflammation in the CNS. However, thalidomide, a small molecule drug, can inhibit TNF-α protein synthesis and, unlike larger molecules, is readily capable of crossing the blood-brain barrier. Thus thalidomide and its analogs are excellent candidate agents for use in determining the potential value of anti-TNF-α therapies in a variety of diseases underpinned by inflammation within the nervous system. Consequently, we have chosen to discuss the relevance of unregulated TNF-α expression in illnesses of the CNS and, to an extent, the peripheral nervous system. Additionally, we consider the utilization of thalidomide-derived agents as anti-TNF-α therapeutics in the setting of neuroinflammation.

Alzheimer's disease (AD) is linked to cholinergic deficiency and the overactivation of glutamate receptors. The acetylcholinesterase (AChE) inhibition treatment approach has produced the most encouraging results in clinical practice, and memantine, a moderate antagonist of N-methyl-D-aspartate (NMDA) receptors, has been approved for treating AD. However, AChE inhibitors have limited success as they only improve memory in mild dementia but cannot stop the process of neurodegeneration; while memantine possesses neuroprotective effects only with a little ability in memory enhancement. There has been a major rush among neuroscience research institutions and pharmaceutical firms worldwide to search for safer and more effective therapeutic agents for AD. The novel dimers, derived from tacrine and the fragment of huperzine A (HA'), have been demonstrated to be potent and selective reversible inhibitors of AChE. Bis(7)-tacrine, bis(12)-hupyridone (E12E) and HA'(10)-tacrine, are representatives of three series of novel dimers. According to the preclinical studies, these compounds have been shown to have low toxicity and high efficacy for improving cognitive deficits in several animal models. More interestingly, bis(7)-tacrine, similar to memantine, prevents glutamate-induced neurotoxicity by moderately blocking glutamate receptor NMDA subtype. Furthermore, bis(7)-tacrine, as well as E12E, possesses multiple neuroprotective effects in vitro and in vivo. Taking together, these dimeric AChE inhibitors, especially bis(7)- tacrine, E12E and HA'(10)-tacrine, may provide beneficial effects in AD and other neurodegenerative diseases.

Cell models of tauopathy were generated in order to study mechanisms of neurodegeneration involving abnormal changes of tau. They are based on neuroblastoma cell lines (N2a) that inducibly express different forms of the repeat domain of tau (tauRD), e.g. the 4-repeat domain of tau with the wild-type sequence, the repeat domain with the ΔK280 mutation (“pro-aggregation mutant”), or the repeat domain with ΔK280 and two proline point mutations (“anti-aggregation mutant”). The data indicate that the aggregation of tauRD is toxic, and that aggregation and toxicity can be prevented by low molecular weight compounds, notably compounds based on the N-phenylamine core. Thus the cell models are suitable for developing aggregation inhibitor drugs.

Accumulation of iron at sites where neurons degenerate in Parkinson's disease (PD) and Alzheimer's disease (AD) is thought to have a major role in oxidative stress induced process of neurodegeneration. The novel non-toxic lipophilic brain- permeable iron chelators, VK-28 (5- [4- (2- hydroxyethyl) piperazine- 1- ylmethyl]- quinoline- 8- ol) and its multi-functional derivative, M-30 (5-[N-methyl-N-propargylaminomethyl]-8-hydroxyquinoline), as well as the main polyphenol constituent of green tea (-)-epigallocatechin-3-gallate (EGCG), which possesses iron metal chelating, radical scavenging and neuroprotective properties, offer potential therapeutic benefits for these diseases. M-30 and EGCG decreased apoptosis of human SH-SY5Y neuroblastoma cells in a neurorescue, serum deprivation model, via multiple protection mechanisms including: reduction of the pro-apoptotic proteins, Bad and Bax, reduction of apoptosis-associated Ser139 phosphorylated H2A.X and inhibition of the cleavage and activation of caspase-3. M-30 and EGCG also promoted morphological changes, resulting in axonal growth-associated protein-43 (GAP-43) implicating neuronal differentiation. Both compounds significantly reduced the levels of cellular holo-amyloid precursor protein (APP) in SH-SY5Y cells. The ability of theses novel iron chelators and EGCG to regulate APP are in line with the presence of an iron-responsive element (IRE) in the 5'-untranslated region (5'UTR) of APP. Also, EGCG reduced the levels of toxic amyloid-beta peptides in CHO cells over-expressing the APP “Swedish” mutation. The diverse molecular mechanisms and cell signaling pathways participating in the neuroprotective/neurorescue and APP regulation/processing actions of M-30 and EGCG, make these multifunctional compounds potential neuroprotective drugs for the treatment of neurodegenerative diseases, such as PD, AD, Huntington's disease and amyotrophic lateral sclerosis.

In the non-amyloidogenic pathway the α-secretase cleaves the amyloid precursor protein (APP) within the sequence of Aβ-peptides and precludes their formation. In addition, α-secretase cleavage releases an N-terminal extracellular domain with neurotrophic and neuroprotective properties. The disintegrin metalloproteinase ADAM10 has been shown to act as α-secretase in vivo, to prevent amyloid plaque formation and hippocampal defects in an Alzheimer disease mouse model. An increase in α-secretase activity therefore is an attractive strategy for treatment of AD and may be achieved by modulating selective signalling pathways. Functional characterization of the human ADAM10 promoter showed that it contains several binding elements for transcription factors which are regulated by extracellular ligands. Retinoic acid (RA) was identified as an inducer of human ADAM10 promoter activity. In human neuroblastoma cell lines RA treatment upregulated the expression of both the α-secretase ADAM10 and its substrates APP and the related APP-like-protein 2 (APLP2), and led to an enhanced secretion of their extracellular domains. Furthermore, G protein-coupled receptors (GPCRs) localized in brain areas affected by AD were investigated. Activation of the PAC1 receptor by the neuropeptide PACAP was identified as an approach for upregulation of the α-secretase pathway.

A major strategy for the development of a disease-modifying therapy against Alzheimer's disease is pharmacological intervention designed to reduce levels of β-amyloid in the brain. Among various ways of reducing β-amyloid production, the inhibition of β-secretase (memapsin 2, BACE) is particularly attractive. Not only does β-secretase initiates the amyloid cascade, it also is an aspartic protease, a class of proteases for which successful inhibitor drugs have been developed to treat AIDS patients. Extensive efforts in research and development of a β-secretase inhibitor drug have taken place in many laboratories during the past few years. However, no drug candidate is currently in clinical trials. In spite of the lack of obvious success, much progress has been made to incorporate the drug-like properties in the evolution of better inhibitors. The inhibitors from more recent generations are indeed similar in characteristics to other protease inhibitor drugs. This progress permits optimism that development of clinical candidates of β-secretase inhibitor drugs is a realistic goal.

Amyloid β-peptide (Aβ), which plays a central role in Alzheimer Disease, is generated by presenilin-dependent and presenilin-independent γ-secretase cleavages of β-amyloid precursor protein (βAPP). We report that the presenilins (PS1 and PS2) also regulate p53-associated cell death Thus, we established that PS deficiency, catalytically inactive PS mutants, γ-secretase inhibitors and βAPP or APLP2 depletion reduced the expression and activity of p53, and lowered the transactivation of its promoter and mRNA levels. p53 expression was also reduced in the brains or βAPP-deficient mice or in brains where both PS had been invalidated by double conditional knock out. AICDC59 and AICDC50, the γ- and η- secretase-derived C-terminal fragments of βAPP, respectively, trigger the activation of caspase-3, p53-dependent cell death, and increase p53 activity and mRNA. Finally, HEK293 cells expressing PS1 harboring familial AD (FAD) mutations or FAD-affected brains, all display enhanced p53 activity and p53 expression. Our studies demonstrate that AICDs control p53 at a transcriptional level, in vitro and in vivo and unravel a still unknown function for presenilins.

Active and passive Aβ immunotherapy in Alzheimer's disease (AD)-like mouse models lowers cerebral amyloid- β protein (Aβ) levels, especially if given early in the disease process, and improves cognitive deficits. In 2002, a Phase IIa clinical trial was halted due to meningoencephalitis in ∼6% of the AD patients. It is hypothesized that the immunogen, full-length Aβ1-42, may have led to an autoimmune response. Currently, we are developing novel Aβ peptide immunogens for active immunization in amyloid precursor protein transgenic mice (APP Tg) to target Aβ B cell epitopes (within Aβ1-15) and avoid Aβ-specific T cell epitopes (Aβ16-42) so as to generate a safe and effective AD vaccine. Intranasal immunization with dendrimeric Aβ1-15 (16 copies of Aβ1-15 on a lysine core) or a tandem repeat of Aβ1-15 joined by 2 lysines and conjugated to an RGD motif with a mutated form of an E. coli-derived adjuvant generated robust Aβ titers in both wildtype and APP Tg mice. The Aβ antibodies recognized a B cell epitope within Aβ1-7, were mostly T-helper 2 associated immunoglobulin isotypes, bound human AD and APP Tg plaques, and detected Aβ oligomers. Splenic T cells reacted to the immunogens but not full-length Aβ. Six months of intranasal immunization (from 6-to-12 months of age) of J20 mice with each immunogen lowered insoluble Aβ42 by 50%, reduced plaque burden and gliosis, and increased Aβ in plasma. Interestingly, Aβ antibody generation was influenced by route of immunization. Transcutaneous immunization with dβ1-15, but not full-length Abeta, led to high Aβ titers. In summary, our short Aβ immunogens induced robust titers of predominantly Th2 antibodies that were able to clear cerebral Aβ in the absence of Aβ-specific T cell reactivity, indicating the potential for a safer vaccine. We remain optimistic about the potential of such a vaccine for prevention and treatment of AD.

One of the main neuropathological lesions observed at brain autopsy of Alzheimer's disease (AD) patients are the extracellular senile plaques mainly composed of amyloid-β (Aβ) peptides. Aβ is generated by proteolytic processing of amyloid precursor protein (APP) via β and γ-secretases. The β-secretase APP cleaving enzyme 1 (BACE1) has become a target of intense research aimed at blocking the enzyme activity. Recent studies showed that BACE1 is involved in processing other non-APP substrates, and that other proteases are involved in APP processing. We have recently established a novel approach to inhibit Aβ production via antibodies against the β-secretase cleavage site of APP. These antibodies bind wild type and Swedish mutated APP expressed in transgenic mice brain tissues. The isolated antibodies do not bind any form of Aβ peptides. Antibody up-take experiments, using Chinese hamster ovary cells expressing wild-type APP, suggest that antibody internalization and trafficking are mediated via the endocytic pathway. Administration of antibodies to the cells growing media resulted in a considerable decrease in intracellular Aβ levels, as well as in the levels of the corresponding C-terminal fragment (C99). The relevance of intra-neuronal accumulation of mainly Aβ42 as an early event in AD pathogenesis suggests that this approach may be applicable as a novel therapeutic strategy in AD treatment.

Alpha-synuclein is the main constituent of intra-neuronal Lewy bodies, which are characteristic of Parkinson's disease, but aggregates are also found as axonal inclusions. Alpha-synuclein pathology is found together with betaamyloid plaques and neurofibrillary tangles in Alzheimer's disease and other neurodegenerative disorders. In spite of the fact that the biological function of this synaptic protein is not known so far, there is an increasing body of evidence indicating an interaction with amyloid peptides, but also with tau-hyperphosphorylation. A high proportion of alpha-synuclein purified from Lewy bodies is phosphorylated on Ser129. There are still different opinions about the toxicity of the alphasynuclein aggregates. Alpha-synuclein seems to influence different intracellular signaling pathways which are in direct relation to defense mechanisms against reactive oxygen species or apoptosis. It is obvious that overproduction of alphasynuclein, but also different mutations, are inducing the formation of aggregates. Because of the possible link to neurodegeneration, different attempts have been made to counteract alpha-synuclein aggregation. An interesting approach is utilizing beta-synuclein, a biological factor, with an aminoacid sequence closely resembling that of alpha-synuclein. Proof of concept studies indicated that overexpression of beta-synuclein is able to counteract alpha-synuclein aggregation in a transgenic animal model, while also ameliorating functional deficits. As an alternative approach, the use of low molecular beta-synuclein N-terminal peptide derivatives has been considered. Several of these structures displayed clear neuroprotective activities in tissue culture models of neurodegeneration, including beta-amyloid toxicity. Therefore it has been speculated that these compounds might have a broad therapeutic efficacy in different neurodegenerative disorders. A proof of concept study in hAPP-transgenic animals resulted in a highly significant decrease in beta-amyloid plaque load, an increase in soluble beta-amyloid peptides and a decrease in insoluble forms. There was also significant improvement of cognitive deficits in this APP transgenic mouse model following intranasal but also peripheral treatment with three of these compounds. From this study it is concluded that the observed effects of the peptides derived from beta-synuclein Nterminus are depending on both, a direct interaction with aggregation of proteins, but also with stimulation of antiapoptotic and anti-oxidative intracellular signaling pathways.

What are the resources needed by clinical pharmacology to test drugs in ways that model how the practitioner achieves optimal effectiveness and safety with each patient? I describe the applications of test-retest standard error of measurement, clinical decision rules, means or other statistical summaries of observations, clinical trial designs that use each patient as her own control, and methods to control observer and site variance as steps for developing a CT tested model for optimal clinical uses of an Alzheimer's drug by a practitioner. Many investigators and clinicians have been concerned with clinical judgments being scientifically uncontrolled and unsystematic. The methods I describe demonstrate how clinical trials can be used to overcome these limitations in current patient care. “Darwin showed that one simply could not understand evolution as long as one accepted essentialism. Species and populations are not types, they are not essentialistically defined classes, but rather are biopopulations composed of genetically unique individuals” E. Mayr [1].

Advances in the treatment of demented individuals is critically dependent upon experimental administration of new drugs to such people, who, by definition, frequently cannot provide informed consent. Ethical problems associated with studies on demented individuals are therefore of great importance. While there is some similarity to other groups (children, psychotic individuals and patients in coma) there also exist several differences. Obtaining an informed consent from a dementing individual is always problematic. Advance directives are helpful to caregivers and patients should be encouraged, at early stages of the disease, to provide them. Participation in drug studies carries inherent benefits to patients, but at the same time exposes them to risks and discomforts which should be monitored and reviewed more intensively than in studies on cognitively intact individuals. The vulnerability of demented people and their dependence requires special attention by the institutional review board (IRB), unique items to be included in the study protocols and consent forms, etc. Representatives of patients' advocacy groups can make important contributions to the IRB, to serve the best interests of the patient and prevent exploitation by the industry as well as by researchers, and honoring the autonomy of the patients. It would be helpful and justified to enable subjects to continue in the study in an open-label design in this situation, once they sign a suitable informed consent. A no-fault insurance could be provided to the patient in this situation.

As a potential disease-modifying treatment for AD, Alzhemed (tramiprosate) is a compound that binds to soluble amyloid-beta peptide (Aβ) and inhibits the formation of neurotoxic aggregates that lead to amyloid plaque deposition in the brain. The safety, tolerability, and pharmacodynamic effects of Alzhemed were assessed in a double-blind study in which 58 individuals with mild-to-moderate AD (MMSE 13-25) were randomized to receive placebo or Alzhemed 50, 100 or 150 mg BID for 3 months. At the end of the double-blind phase, 42 of these subjects entered a 36-month openlabel (OL) phase in which they received Alzhemed 150 mg BID. Assessments included plasma and cerebrospinal fluid (CSF) Alzhemed concentrations, CSF levels of Aβ, as well as cognitive (Alzheimer's Disease Assessment Scale-cognitive subscale, Mini-Mental State Examination) and clinical performance (Clinical Dementia Rating scale, Sum-of-Boxes) measures. Alzhemed was safe and well tolerated, crossed the blood-brain barrier, and dose-dependently reduced CSF Aβ42 levels after 3 months of treatment. Mild AD subjects (MMSE 19-25 at entry) displayed greater reduction of CSF Aβ42 levels than moderate AD participants (MMSE 13-18 at entry). There was no effect of Alzhemed on the cognitive or clinical measures after 3 months of treatment. The OL follow-up suggested a stabilization of cognitive function especially in mild AD subjects over the 36-month study period. Alzhemed thus appears to be well tolerated with long-term exposure and reduces CSF Aβ42 levels in mild-to-moderate AD subjects. These findings will be discussed in the context of two large-scale randomized, double-blind, placebo-controlled Phase III clinical trials that are currently being conducted to test the long-term safety and efficacy of Alzhemed.

Recent studies demonstrate that the therapeutic response in Alzheimer's disease (AD) is genotype-specific. More than 200 genes are potentially associated with AD pathogenesis and neurodegeneration, and approximately 1,400 genes distributed across the human genome account for 20 to 95% of variability in drug disposition and pharmacodynamics. Cytochrome P450 enzymes encoded by genes of the CYP superfamily, such as CYP1A1 (15q22-q24), CYP2A6 (19q13.2), CYP2C8 (10q24), CYP2C9 (10q24), CYP2C19 (10q24.1-q24.3), CYP2D6 (22q13.1), CYP2E1 (10q24.3-qter), and CYP3A5 (7q22.1), acting as terminal oxidases in multicomponent electron transfer chains which are called P450- containing monooxygenase systems, metabolize more than 90% of drugs. Some of the enzymatic products of the CYP gene superfamily can share substrates, inhibitors and inducers whereas others are quite specific for their substrates and interacting drugs. Some cholinesterase inhibitors (tacrine, donepezil, galantamine) are metabolized via CYP-related enzymes, especially CYP2D6, CYP3A4, and CYP1A2. The distribution of CYP2D6 genotypes in the Spanish population is the following: (a) Extensive Metabolizers (EM)(51.61%): *1/*1, 47.10%; and *1/*10, 4.52%; (b) Intermediate Metabolizers (IM)(32.26%): *1/*3, 1.95%; *1/*4, 17.42%; *1/*5, 3.87%; *1/*6, 2.58%; *1/*7, 0.75%; *10/*10, 1.30%; *4/*10, 3.23%; *6/*10, 0.65%; and *7/*10, 0.65%; (b) Poor Metabolizers (PM)(9.03%): *4/*4, 8.37%; and *5/*5, 0.65%; and (c) Ultrarapid Metabolizers (UM)(7.10%): *1xN/*1, 4.52%; *1xN/*4, 1.95%; and CYP2D6 gene duplications, 0.65%. PMs and UMs also accumulate genotypes of risk associated with APOE-, PS-, ACE-, and PRNP-related genes. Approximately, 15% of the AD population may exhibit an abnormal metabolism of cholinesterase inhibitors; about 50% of this population cluster would show an ultrarapid metabolism, requiring higher doses of cholinesterase inhibitors to reach a therapeutic threshold, whereas the other 50% of the cluster would exhibit a poor metabolism, displaying potential adverse events at low doses. In AD patients treated with a multifactorial therapy, including cholinesterase inhibitors (e.g., donepezil), the best responders are the CYP2D6-related EMs and IMs, and the worst responders are PMs and UMs. In addition, the presence of the APOE-4 allele in genetic clusters integrating CYP2D6 and APOE genotypes contributes to deteriorate the therapeutic outcome. From these data, it can be postulated that pharmacogenetic and pharmacogenomic factors are responsible for 75-85% of the therapeutic response in AD patients treated with conventional drugs.