Transcript BBest -- Alzheimers - Institute for Evidence

ALZHEIMER’S DISEASE
Treatment and Prevention
Ben Best
President/CEO
Cryonics Institute
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What is Alzheimer’s Disease (AD)?
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Only confirmed on autopsy
Characterized by
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Amyloid plaque
 Neurofibrillary tangles
 Neuronal loss
 Synapse loss
 Inflammation and oxidative damage
Tangles without plaque is FrontoTemporal Dementia
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Empirical versus Mechanistic
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Empirical treatment and prevention
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What appears to work
Mechanistic treatment and prevention
Understand the mechanisms
 Devise strategies based on mechanisms
 Evaluate what may work or not to understand the
mechanisms and improve strategies.
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3
Amyloid Cascade Hypothesis
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Amyloid peptide
Called Aß (amyloid beta)
 Because aggregates in ß (beta) sheets
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Simplified view
Aß formation
 ⇒ amyloid plaques
 ⇒ neuron death
 ⇒ dementia
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Amyloid cascade begins
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APP (Amyloid Precursor Protein)
 Cleaved
by secretase enzymes
 Cleavage of APP forms shorter peptides
 Cleavage by alpha or beta secretase
 Only cleavage by beta secretase forms Aß
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Two forms of Aß
After cleavage by gamma-secretase
 40 amino acid amyloid beta peptide (Aß40)
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42 amino acid amyloid beta peptide (Aß42)
⇒ amyloid plaques
STICKY!
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Amyloid cascade begins
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Damaging effects of Aß42
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Activation of microglia
Brain version of macrophages
 Produce inflammatory cytokines
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InterLeukin-1ß (IL-1ß)
 Tumor Necrosis Factor alpha (TNF−α)
 Generate peroxynitrite and oxidative stress
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Hyperphosphorylation of tau
 Tau protein stablizes cell microtubules
 Phosphorylated tau forms NFTs
 NeuroFibrillary
Tangles
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Damaging effects of NFTs
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Amyloid plaque does not cause neuron death
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NFTs are always associated with neuron death
Without microtubules neurons cannot function
NFTs become glycated
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Intimately associated with AGEs (Advanced Glycation
End-products)
 Generate free radicals contributing to neurodegeneration
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Damaging forms of Aß42
Aß42 is a 42-amino acid monomer
 Aß42 monomers can aggregate into
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 Oligomers
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(many monomers)
 Fibrils which can aggregate into plaques
Soluble oligomers are the most toxic form of Aß42
“Halos” of Aß42 oligomers around plaques
damage or destroy synapses
PNAS;Koffie,RM;106:4012 (2009)
 JOURNAL OF NEUROSCIENCE;
Lacor,PN;27:796(2007)
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Amyloid aggregation/disaggregation
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Amyloid Cascade Hypothesis
APP ⇒ Aß42 (peptide, monomer)
⇒ fibrillar Aß or oligomers
⇒ amyloid plaques
⇒ inflammation/NFTs
⇒ neuron death / synapse loss
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Amyloid Cascade Evidence
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Genetic pre-disposition to AD
 Onset
at an early age
 Most often increases gamma-secretase cleavage
 Produces increased Aß42
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Down’s Syndrome victims produce more APP
3 chromosomes with gene for APP
 Cleaved to Aß42
 Early AD
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Discussion
Choose a partner
 Tell your partner what you understood and
think while your partner silently listens – talk
for a couple of minutes
 Switch roles – partner that listened becomes
the speaker for a couple of minutes
 Short discussion
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Amyloid and NFTs in AD
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Cholesterol and the amyloid cascade
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Human brain high in myelin to facilitate axon conduction
speed
Myelin produced by oligodendrocytes (glia)
Brain contains 25% of body’s membrane cholesterol
 80% of brain cholesterol is in myelin
Cholesterol allows tight membrane packing in myelin
Cholesterol recycling and transport depends on
APOlipoprotein E (APOE)
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APOE and AD
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APOE exists in 3 alleles
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APOE2, APOE3 and APOE4
APOE4 is the only allele in non-human primates
APOE4 is less efficient than APOE3 in transporting cholesterol and
clearing the brain of Aß
APOE3 is less efficient than APOE2
14% of Caucasians have one APOE4 allele, but 40% of AD victims
have at least one APOE4 allele
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Aß42 rises markedly after head injury
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Risk of AD increases many times with head injury, but increases much
more so for those with APOE4
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APOE4 less efficient at myelin repair and Aß42 clearance after injury
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Metal toxicity and AD
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Role of aluminum is controversial
Zinc, copper and iron cause Aß aggregation
Copper particularly mediates Aß toxicity
Aß is not toxic in the absence of Cu2+
Zinc inhibits Aß toxicity
Copper enhances Aß fibril formation, an effect
potentiated by APOE4
Copper is a greater catalyst for free radicals than the other
metals
Aß binds to both copper and cholesterol causing
oxidation of cholesterol to compounds that are extremely
toxic to neurons
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Clioquinol therapy for AD
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Clioquinol binds zinc & copper (chelator)
Crosses the blood-brain barrier (BBB)
Transgenic AD-prone mice treated with clioquinol
showed a 49% decrease in Aß
AD patients treated with clioquinol for 12 weeks
 Severely demented showed slowed cognitive decline
 Moderately demented showed no effect
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ARCHIVES OF NEUROLOGY;Richie,CW;60:1685 (2003)
PBT2 is a clioquinol analog that has greater BBB
permeability, and more effectively strips copper from Aß,
without chelation, which could remove essential metals
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No adverse effects seen
Currently in clinical trials
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Copper in the diet
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Diets high in copper and saturated fats are
associated with increased risk of AD
Saturated fats increase cholesterol
Foods highest in copper content are beef liver,
oysters, molluscs, almonds, and cocoa
BRITISH JOURNAL OF NUTRITION; Loef,M;107:7
(2011)
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Discussion
Tell your partner what you understood and
think while your partner silently listens – talk
for a couple of minutes
 Switch roles – partner that listened becomes
the speaker for a couple of minutes
 Short discussion

20
NSAIDs
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Persons taking Non-Steroidal Anti-Inflammatory Drugs
(NSAIDs) for more than two years show a 50% greater
protection from AD than those not taking NSAIDs.
The same effect is not seen for cortisol, which has a more
profound anti-inflammatory effect.
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NEUROBIOLOGY OF AGING 22:799 (2001)
Older NSAIDs block both COX-1 and COX-2 enzymes
Newer NSAIDs block COX-2 (pain)
COX-1 inhibition can cause GI bleeding
Microglia express COX-1
NSAIDs (ibuprofen & indomethicin) inhibit cytokine
activation of beta-secretase (reduce Aß formation)
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JOURNAL OF NEUROSCIENCE;Sastre,M;23:9796 (2003)
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AChE Inhibitors
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Most FDA drugs for AD inhibit the enzyme
AcetylCholineEsterase (AChE)
Was assumed to work by prolonging the existence of
acetylcholine in synapses
AChE promotes Aß aggregation, which inhibition may
block
AChE inhibitors increase proportion of APP cleaved by
alpha-secretase rather than beta-secretase
AChE inhibitors cause nausea, vomiting and diarrhea
AChE inhibitors cause modest and transient slowing of
progress of AD
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Memantine
Inflammation & oxidative stress can cause
excessive glutamate release (excitotoxicity)
 Memantine protects against excitotoxicity
without interfering with glutamate signalling
 Like AChE inhibitors, benefit of memantine
therapy for AD is, although statistically
significant, nonetheless marginal
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Nicotine and smoking
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Nicotine administered to transgenic mice reduced Aß42 plaques
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Nicotine administered to the rat hippocampus enhanced
acetylcholine production and release
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PNAS;102:3046 (2005)
Many studies show more twice the risk of AD among smokers
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BIOLOGICAL PSYCHIATRY;49:200 (2001)
Transgenic mice show worsening of NFTs with nicotine
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JOURNAL OF NEUROCHEMISTRY;81:655 (2002)
THE LANCET; 351:1840 (1998)
NEUROBIOLOGY OF AGING; 24:589 (2003)
AMERICAN JOURNAL OF EPIDEMIOLOGY;166:367(2007)
Tobacco smoke contains more than just nicotine
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Insulin and Insulin sensitivity
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Diabetics have greater risk for AD
Insulin increases Aß degradation
Chromium picolinate (which increases insulin sensitivity)
improved memory performance in patients with mild AD
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NUTRITIONAL NEUROSCIENCE;13:116 (2010)
Similar benefits were seen with the insulin-sensitizing
drug metformin
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PNAS;Chen,Y;106:3907 (2009)
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Ginko biloba
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A large randomized trial showed ginko biloba improved
cognition in AD patients
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A review of a large number of studies also showed ginko
biloba improved cognition in AD patients
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BMC GERIATRICS;10:14 (2010)
A large 6-year randomized trial showed ginko biloba is
not effective in preventing AD
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JOURNAL OF NEUROLOGICAL SCIENCES;283:224 (2009)
JOURNAL OF THE AMERICAN MEDICAL ASSOCIATION;300:2253 (2008)
Does ginko biloba treat, but not prevent AD ?
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Transgenic AD-prone rodents
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Transgenic rats with gene delivery of Brain-Derived
Neurotrophic Factor (BDNF) after disease onset reversed
synapse loss and restored learning and memory
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Glycogen-Synthase Kinase 3 (GSK-3), an enzyme that
phosphorylates tau protein, when inhibited by lithium in
transgenic mice, substantially reduced NFT formation
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NATURE MEDICINE;15:331 (2009)
PNAS;102:6990 (2005)
Transgenic mice given pomegranate juice from 6 to 12.5
months of age showed 50% less accumulation of soluble
Aß and amyloid deposits in the hippocampus associated
with improved learning and memory.
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NEUROBIOLOGY OF DISEASE; 24:506 (2006)
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Cytokine antagonist
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Etanercept, an antagonist of the inflammatory
cytokine Tumor Necrosis Factor alpha (TNF−α)
has shown effectiveness in reducing symptoms in
an AD patient within hours of administration
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JOURNAL OF NEUROINFLAMMATION;5:2 (2008)
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Curcumin
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Curcumin is a phytochemical which gives curry a yellow
color
Incidence of AD is substantially lower in India
Curcumin is an antioxidant that can scavenge
peroxynitrite
Curcumin not only inhibits Aß aggregation, it
disaggregates existing plaques
Curcumin can lower insulin sensitivity
Curcumin can lower the inflammatory cytokine
InterLeukin-1ß (IL-1ß) nearly 60% in transgenic mice
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Low folate and elevated homocysteine
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Low serum folic acid and elevated plasma homocysteine
are both independent risk factors for AD
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Folic acid deficiency and excess homocysteine impair
DNA repair, sensitizing neurons to cell death from DNA
damage
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AMERICAN JOURNAL OF CLINICAL NUTRITION;82:636 (2005)
JOURNAL OF NEUROSCIENCE;22:1752 (2002)
Folic acid deficiency and excess homocysteine increase Aß
production by inducing beta-secretase – an effect that can
be overcome by administering S-Adenosyl Methionine
(SAMe)
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MOLECULAR AND CELLULAR NEUROSCIENCE;28:195 (2005)
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Exercise
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A mouse model of AD showed reduced
extracellular Aß with voluntary exercise
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A 14-year study showed a 29-50% reduction in
AD with physical activity
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JOURNAL OF NEUROSCIENCE;25:4217 (2005)
JAMA; 302:627 (2009)
A randomized study of over 4,000 men and
women over age 65 showed reduced AD with
physical activity
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ARCHIVES OF NEUROLOGY;58:498 (2001)
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Stress
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Transgenic AD-prone mice show increased Aß
accumulation, which is apparently corticosteroidrelated
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AMERICAN JOURNAL OF CLINICAL
NUTRITION;82:636 (2005)i
Glucocorticoid cascade hypothesis
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Cortisol (stress hormone) rises with age
Damages hippocampus further increasing cortisol
Destructive feedback cycle
Pacific salmon use corticosteroids to self-destruct
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Environmental enrichment
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A study of transgenic AD-prone mice showed
that environmental enrichment worsened amyloid
plaque formation
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JOURNAL OF NEUROPATHOLOGY AND
EXPERIMENTAL NEUROLOGY; 62:1220 (2003)
A subsequent study claimed that the former study
had subjected the mice to excessive stress, and
showed reduced Aß associated with environmental
enrichment
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CELL; 120:701 (2005)
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Discussion
Tell your partner what you understood and
think while your partner silently listens – talk
for a couple of minutes
 Switch roles – partner that listened becomes
the speaker for a couple of minutes
 Short discussion

34
Empirical versus Mechanistic

Empirical treatment and prevention


What appears to work
Mechanistic treatment and prevention
Understand the mechanisms
 Devise strategies based on mechanisms
 Evaluate what may work or not to understand the
mechanisms and improve strategies.

35
Amyloid and NFTs in AD
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