Effects of Alzheimer's Disease

A Healthy Brain The healthy brain is made up of millions of interconnecting nerve cells, called neurons. Neurons constantly communicate with each other by sending signals through tentacle-like connections called axons and dendrites. How Alzheimer's Disease Affects the Brain The brain of a patient with Alzheimer's disease is much different. The orderly, organized arrangement of nerve cells found in a healthy brain become entangled, full of senile plaques and neurofibrillary tangles. The plaques and tangles interfere with the normal activity between neurons in the area of the brain responsible for intellectual thought. Symptoms of Alzheimer's Disease Alzheimer's disease affects people in different ways. The disease is slowly progressive from onset. Memory loss, confusion, disorientation, and poor judgment are a few of the symptoms of Alzheimer's disease.

Alzheimer's disease

The first readily identified symptoms of Alzheimer's disease are usually short-term memory loss and visual-spatial confusion. These initial symptoms progress from seemingly simple and often fluctuating forgetfulness and difficulty orienting oneself in space such as in a traffic lane while driving, to a more pervasive loss of short-term memory and difficulty navigating through familiar areas such as one's neighborhood, then to loss of other familiar and well-known skills as well as recognition of objects and persons.

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Since family members are often the first to notice changes that might indicate the onset of Alzheimer's they should learn the early warning signs and serve as informants during initial evaluation of patients clinically. Aphasia, disorientation and disinhibition often accompany the loss of memory. Alzheimer's disease (AD) may also include behavioral changes, such as outbursts of violence or excessive passivity in people who have no previous history of such behavior.

In the later stages of the disease, deterioration of musculature and mobility, leading to bedfastness, inability to feed oneself, and incontinence, will be seen if death from some external cause (e.g. heart attack or pneumonia) does not intervene. Once identified, the average lifespan of patients living with Alzheimer's disease is approximately 7-10 years, although cases are known where reaching the final stage occurs within 4-5 years or at the other extreme they may survive up to 21 years.


Stages and symptoms

Mild — In the early stage of the disease, patients have a tendency to become less energetic or spontaneous, though changes in their behavior often go unnoticed even by the patients' immediate family. This stage of the disease has also been termed Minor Cognitive Impairment (MCI), when the patient does not meet the criteria for a diagnosis of dementia.

Moderate — As the disease progresses to the middle stage, patients might still be able to perform tasks independently (such as using the bathroom), but may need assistance with more complicated activities (such as paying bills).

Severe — As the disease progresses from the middle to the late stage, patients will not be able to perform even simple tasks independently and will require constant supervision. They become incontinent of bladder and then incontinent of bowel. They will eventually lose the ability to walk and eat without assistance. Language becomes severely disorganized, and then is lost altogether. They may eventually lose the ability to swallow food and fluid, and this can ultimately lead to death.

Diagnosis

No medical tests are available to diagnose Alzheimer's disease conclusively pre-mortem. A definitive diagnosis of Alzheimer's disease must await microscopic examination of brain tissue which generally occurs at autopsy therefore Alzheimer's disease (AD) is primarily a clinically diagnosed condition based on the presence of characteristic neurological and neuropsychological features and the absence of alternative diagnoses. Determination of neurological characteristics is made utilizing patient history and clinical observation, while neuropsychological evaluation includes memory testing and assessment of intellectual functioning over a series of weeks or months. Supplemental physical testing, including blood tests and neuroimaging, is utilized to rule out other diagnoses. Psychological testing, to include screening for depression and a mini mental state examination, can be helpful in establishing the presence and severity of dementia. Although certain clues from history may suggest a diagnosis of vascular dementias instead of, or in addition to, AD, the ability of certain neuroimaging modalities such as SPECT to differentiate vascular type from Alzheimer disease types of dementias, appears to be superior to clinical exam (PMID 15545324). Differential diagnosis should also include dementia with Lewy bodies and frontotemporal dementia.

Interviews with family members and/or caregivers are also utilized in the initial assessment of the disease, as a patient with Alzheimer's may tend to minimize his or her symptoms, or may undergo evaluation at a time when his or her symptoms are less apparent, as quotidian fluctuations ("good days and bad days") are a common feature of the disease. Observations noting that a patient's good memory function decreases over time plays a critical role in the diagnosis of Alzheimer's.

Biochemical characteristics

Alzheimer's disease has been identified as a protein misfolding disease, or proteopathy, due to the accumulation of abnormally folded A-beta and tau proteins in the brains of AD patients. A-beta, also written Aβ, is a short peptide that is a proteolytic byproduct of the transmembrane protein amyloid precursor protein (APP), whose function is unclear but thought to be involved in neuronal development. The presenilins are components of a proteolytic complex involved in APP processing and degradation. Although amyloid beta monomers are soluble and harmless, they undergo a dramatic conformational change at sufficiently high concentration to form a beta sheet-rich tertiary structure that aggregates to form amyloid fibrils that deposit outside neurons in dense formations known as senile plaques or neuritic plaques, in less dense aggregates as diffuse plaques, and sometimes in the walls of small blood vessels in the brain in a process called amyloid angiopathy or congophilic angiopathy.

AD is also considered a tauopathy due to abnormal aggregation of the tau protein, a microtubule-associated protein expressed in neurons that normally acts to stabilize microtubules in the cell cytoskeleton. Like most microtubule-associated proteins, tau is normally regulated by phosphorylation; however, in AD patients, hyperphosphorylated tau accumulates as paired helical filaments that in turn aggregate into masses inside nerve cell bodies known as neurofibrillary tangles and as dystrophic neurites associated with amyloid plaques.

Neuropathology

Both amyloid plaques and neurofibrillary tangles are clearly visible by microscopy in AD brains. At an anatomical level, AD is characterized by gross diffuse atrophy of the brain and loss of neurons, neuronal processes and synapses in the cerebral cortex and certain subcortical regions. This results in gross atrophy of the affected regions, including degeneration in the temporal lobe and parietal lobe, and parts of the frontal cortex and cingulate gyrus. Levels of the neurotransmitter acetylcholine are reduced. Levels of the neurotransmitters serotonin, norepinephrine, and somatostatin are also often reduced. Glutamate levels are usually elevated

Disease mechanism

Three major competing hypotheses exist to explain the cause of the disease. The oldest, on which most currently available drug therapies are based, is known as the "cholinergic hypothesis" and suggests that AD is due to reduced biosynthesis of the neurotransmitter acetylcholine. The medications that treat acetylcholine deficiency have served to only treat symptoms of the disease and have neither halted nor reversed it. The cholinergic hypothesis has not maintained widespread support in the face of this evidence, although cholingeric effects have been proposed to initiate large-scale aggregation leading to generalized neuroinflammation.

Research after 2000 includes hypotheses centered on the effects of the misfolded and aggregated proteins, amyloid beta and tau. The two positions differ with one stating that the tau protein abnormalities initiate the disease cascade, while the other states that amyloid beta (Aβ) deposits are the causative factor in the disease. The tau hypothesis is supported by the long-standing observation that deposition of amyloid plaques do not correlate well with neuron loss; however, a majority of researchers support the alternative hypothesis that Aβ is the primary causative agent.

The amyloid hypothesis is initially compelling because the gene for the amyloid beta precursor (APP) is located on chromosome 21, and patients with trisomy 21 (Down Syndrome) who thus have an extra gene copy almost universally exhibit AD-like disorders by 40 years of age. The traditional formulation of the amyloid hypothesis points to the cytotoxicity of mature aggregated amyloid fibrils, which are believed to be the toxic form of the protein responsible for disrupting the cell's calcium ion homeostasis and thus inducing apoptosis. A more recent and widely supported hypothesis suggests that the cytotoxic species is an intermediate misfolded form of Aβ, neither a soluble monomer nor a mature aggregated polymer but an oligomeric species. Relevantly, much early development work on lead compounds has focused on the inhibition of fibrillization, but the toxic-oligomer theory would imply that prevention of oligomeric assembly is the more important process or that a better target lies upstream, for example in the inhibition of APP processing to amyloid beta.

It should be noted further that ApoE4, the major genetic risk factor for AD, leads to excess amyloid build up in the brain before AD symptoms arise. Thus, Aβ deposition precedes clinical AD. Another strong support for the amyloid hypothesis, which looks at Aβ as the common initiating factor for Alzheimer's disease, is that transgenic mice solely expressing a mutant human APP gene develop first diffuse and then fibrillar amyloid plaques, associated with neuronal and microglial damage

Epidemiology

Alzheimer's disease is the most frequent type of dementia in the elderly and affects almost half of all patients with dementia. Correspondingly, advancing age is the primary risk factor for Alzheimer's. Among people aged 65, 2-3% show signs of the disease, while 25–50% of people aged 85 have symptoms of Alzheimer's and an even greater number have some of the pathological hallmarks of the disease without the characteristic symptoms. Every five years after the age of 65, the probability of having the disease doubles. The share of Alzheimer's patients over the age of 85 is the fastest growing segment of the Alzheimer's disease population in the US, although current estimates suggest the 75-84 population has about the same number of patients as the over 85 population

Prevention

Aging itself cannot be prevented, but the senescence of it can be mitigated. However, the evidence relating certain behaviors, dietary intakes, environmental exposures, and diseases to the likelihood of developing Alzheimer's varies in quality and its acceptance by the medical community. It is important to understand that interventions that reduce the risk of developing the disease in the first place may not alter its progression after symptoms become apparent. Due to their observational design, studies examining disease risk factors are often at risk from confounding variables. Several recent large randomized controlled trials—in particular the Women's Health Initiative—have called into question preventive measures based on cross-sectional studies. Some proposed preventive measures are even based on studies conducted solely in animals or in cell cultures but are not listed here.

Adults with damaged blood vessels in the brain or atrophy in their temporal lobe are more likely to develop Alzheimer's disease. It is known that blood vessel damage in the brain is more likely to occur in patients with high blood pressure, high cholesterol or diabetes. Therefore, prevention of these conditions can lower the risk of developing Alzheimer's, as well as heart attack and stroke.

Exploring Alzheimer's Disease

Alzheimer's disease affects one in 10 Americans over the age of 65. Most of us will know someone in our lifetime with this disease. Leon J. Thal, M.D., Chairman, Department of Neurosciences at UCSD explains how this disease manifests and explores the latest research available.

Inflammation in Alzheimer's Disease

Cynthia A. Lemere, Ph.D. Associate Professor of Neurology at Harvard Medical School and an Associate Neuroscientist at Brigham & Women’s Hospital in the Center for Neurologic Diseases (CND). She has been an active participant in the research field of Alzheimer's disease (AD) for more than sixteen years. Dr. Lemere received her B.A. from Mount Holyoke College, her M.S. in Neurobiology from State University of New York at Albany, and her Ph.D. in Pathology from Boston University School of Medicine. Her thesis research, conducted in the laboratory of Dr. Dennis Selkoe at the CND, focused on mechanisms of ß-amyloid generation and deposition in Alzheimer’s disease and models thereof, particularly in Down syndrome. During her years as Postdoctoral Fellow and Instructor at the CND, her research focused on the role of inflammation in Alzheimer’s disease. In particular, these studies involved examining brain tissue from APP transgenic mice, a transgenic or genetically-engineered mouse model of AD, and Down syndrome to examine the temporal accrual of amyloid-associated inflammatory proteins, such as complement protein, in relation to Aß deposition, gliosis and neuritic changes. In addition, she collaborated with scientists in Medellin, Colombia, to confirm in vivo that which was already known in vitro, that mutations in the presenilin 1 gene lead to overproduction of Aß42.

Cynthia Lemere of Harvard Medical School shares her findings on the link between inflammation and Alzheimer's disease.

About Speaker:

In 1997, she founded an independent laboratory at the CND and continued her research on the role of inflammation in AD by examining strategies for reducing amyloid ß-protein (Aß) protein, cerebral deposits of which are a key feature of AD, and its resultant inflammation in the AD brain. Her results showed that chronic nasal immunization with Aß peptide in APP transgenic mice led to anti-Aß antibody production and a lowering of the Aß burden in the brain. Dr. Lemere and her colleagues have optimized various treatment protocols in non-transgenic mice and then employed them to lower cerebral Aß levels in APP transgenic mice. In addition to pursuing the mechanism of these effects, much of her laboratory's work focuses on the humoral and cellular immune responses to Aß immunization in APP tg mice and in non-human primates. Recently, her lab completed a 10 month Aß immunization trial in Caribbean vervet monkeys and found a lowering of Aß protein in both CSF and brain.

Other projects in her laboratory have involved examining the temporal appearance of both intraneuronal Aß and P25 (the regulatory subunit for cdk5) in Down syndrome brain, characterization of a-synuclein following traumatic brain injury and characterization of sonic hedgehog in aged human control and AD brain.

Alzheimer's Disease

Bruce Reed, the Associate Director of the Alzheimer's Disease Research Center at UC Davis presents a comprehensive update on Alzhemier's Disease. What is Alzhemier's Disease and can it be cured or treated? Can one predict who will ultimately be afflicted by this disease? What is the current research being done on Alzheimier's Disease

Alzheimer's Disease Neuropathology

Clinical differentiation of neurodegenerative diseases that produce dementia is imprecise. Neuropathology offers the only way to make a definite diagnosis. The CNS autopsy is also important for clinical quality control and for providing tissue that furthers research into these disabling disorders. This brief article summarizes the major neuropathologic features of largely sporadic disorders that present with late-life dementia. The common causes of dementia discussed are Alzheimer's disease, Lewy body disease, and vascular dementia; less common disorders described are dementia lacking distinctive histopathology, Pick's disease, progressive supranuclear palsy, corticobasal degeneration, and Creutzfeldt-Jakob disease.

Green Fluorescent Protein(GFP)

Green florescent protein (GFP) has revolutionized research in medicine and biology, enabling scientist to get a visual fix on how organs function on the spread of disease and the response of infected cells to treatment,

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In 2008 Nobel Chemsitry prize was announced to Osamu Shimomura of Japan and American duo Martin chalfie and Roger Tsien for deriving Florescent protein from a jellyfish Aequorea Victoria.

The GFP is composed of 238 amino acids; it is isolated from jellyfish Aequorea Victoria that fluoresces green when exposed to blue light.It was discovered

GFP has a typical beta barrel structure, consisting of one β-sheet with a alpha helix containing the fluorophore running through the center, while the tightly packed barrel shell protects the flurophore from quenching by the surrounding microenviornment,the inward facing side chains of the barrel induce specific cyclization reactions on the tripeptide Ser65-Tyr66-Gly67 that lead to fluorophore formation. This occurs in a series of discrete steps with distinct excitation and emission properties.

GFP has functioned has a guiding star for bichemist, biologist and medical scientist, The gene to make GFP is inserted into the DNA of lab animals, bacteria or other cells, where it is switched on by other genes, the glow becomes apparent under ultraviolet light, The telltale protein gives researchers an instant way of monitoring process that were previously invisible.

By targeting nerve cells in Alzheimer’s disease person scientist can follow the, destruction caused by disease, Tumour progression can be followed by adding GFP to cancer cells, By adding GFP to a growing mouse embryo, they can see how the pancreas generates insulin-producing beta cells. Today GFP is a standard tool for thousands of researchers all over the world

GFP derivatives

Due to the potential for widespread usage and the evolving needs of researchers, many different mutants of GFP have been engineered. The first major improvement was a single point mutation (S65T) reported in 1995 in Nature by Roger Tsien This mutation dramatically improved the spectral characteristics of GFP, resulting in increased fluorescence, photostability and a shift of the major excitation peak to 488nm with the peak emission kept at 509 nm. This matched the spectral characteristics of commonly available FITC filter sets, increasing the practicality of use by the general researcher. The addition of the 37 °C folding efficiency (F64L) point mutant to this scaffold yielded enhanced GFP (EGFP). EGFP has an extinction coefficient (denoted ε), also known as its optical cross section of 9.13×10−21 m²/molecule, also quoted as 55,000 M−1cm−1. The quantum yield (QY) of EGFP is 0.60. The relative brightness, expressed as ε•QY, is 33,000 M−1cm−1. Superfolder GFP, a series of mutations that allow GFP to rapidly fold and mature even when fused to poorly folding peptides, was reported in 2006.

Many other mutations have been made, including color mutants; in particular blue fluorescent protein(EBFP, EBFP2, Azurite, mKalama1), cyan fluorescent protein (ECFP, Cerulean, CyPet) and yellow fluorescent protein derivatives (YFP, Citrine, Venus, YPet). BFP derivatives (except mKalama1) contain the Y66H substitution. The critical mutation in cyan derivatives is the Y66W substitution, which causes the chromophore to form with an indole rather than phenol component. Several additional compensatory mutations in the surrounding barrel are required to restore brightness to this modified chromophore due to the increased bulk of the indole group. The red-shifted wavelength of the YFP derivatives is accomplished by the T203Y mutation and is due to π-electron stacking interactions between the substituted tyrosine residue and the chromophore.These two classes of spectral variants are often employed for fluorescence resonance energy transfer (FRET) experiments. Genetically-encoded FRET reporters sensitive to cell signaling molecules, such as calcium or glutamate, protein phosphorylation state, protein complementation, receptor dimerization and other processes provide highly specific optical readouts of cell activity in real time.

Semirational mutagenesis of a number of residues led to pH-sensitve mutants known as pHluorins, and later super-ecliptic pHluorins. By exploiting the rapid change in pH upon synaptic vesicle fusion, pHluorins tagged to synaptobrevin have been used to visualize synaptic activity in neurons.

The nomenclature of modified GFPs is often confusing due to overlapping mapping of several GFP versions onto a single name. For example,mGFP often refers to a GFP with an N-terminal palmitoylation that causes the GFP to bind to cell membranes. However, the same term is also used to refer to monomeric GFP, which is often achieved by the dimer interface breaking A206K mutation. Wild-type GFP has a weakdimerization tendency at concentrations above 5 mg/mL. mGFP also stands for "modified GFP" which has been optimized through amino acid exchange for stable expression in plant cells.

Use

The availability of GFP and its derivatives has thoroughly redefined fluorescence microscopy and the way it is used in cell biology and other biological disciplines. While most small fluorescent molecules such as FITC (fluorescein isothiocyanate) are strongly phototoxic when used in live cells, fluorescent proteins such as GFP are usually much less harmful when illuminated in living cells. This has triggered the development of highly automated live cell fluorescence microscopy systems which can be used to observe cells over time expressing one or more proteins tagged with fluorescent proteins. Analysis of such time lapse movies has redefined the understanding of many biological processes including protein folding, protein transport, and RNA dynamics, which in the past had been studied using fixed (i.e. dead) material.

Another powerful use of GFP is to express the protein in small sets of specific cells. This allows researchers to optically detect specific types of cells in vitro (in a dish), or even in vivo (in the living organism).