Parkinson's Disease Flashcards
A deficiency in substantia nigra is known as…
Parkinson’s Disease
In someone who has died of PD, what are not found in the substantial nigra?
The cell bodies
How much of brain dopamine is found in the basal ganglia?
80%
What is the most common neurogenerative motor disorder? What percent of the population does this hit after age 60? After age 85?
Lewy body PD. 1% and 5%, respectively.
What is the average age of onset of PD?
55-60, although 10% is <40 years
How much striatal dopamine loss do you have before you start noticing the symptoms?
70-80% due to some redundancy in the system
Why is there a therapeutic window for treating PD?
Because we don’t treat until symptoms are seen at 70-80% loss, but treatment doesn’t improve symptoms past 85% loss. The rate at which this stratal dopamine loss occurs is different for each person depending on the progression and how aggressive the onset is.
akinetic
the absence of movement
Bradykinesia
movement is slow.
PD is considered a what kind of kinetic disorder?
A hypo kinetic disorder
Movement disorders include:
Hyperkinetic - increased movement
Hypokinetic - decreased movement
Dystonia - involuntary muscle spasms leading to sustained, painful postures
Myoclonus - rapid jerking movements
Chorea - dyskinesia (dance-like flowing movements)
What are two major pathological characteristics of PD?
- Degeneration of the nigrostriatal pathway (dopaminergic neurons of the SNc that enervate the caudate and putamen are lost)
- Appearance of Lewy bodies
What is a major component of Lewy bodies?
Alpha-synuclein. Mutations in alpha-synuclein gene lead to misfolding of the protein, leaky vesicles, and then an accumulation of cytoplasmic DNA.
If PD seems to have been inherited, what could you look for genetically?
mutations in the alpha-synuclein
Lewy bodies are in what neurodegenerative diseases?
multiple system atrophy (in oligodendrocytes)
Dementia with Lewy bodies (in neurons)
PD (in neurons)
Is alpha-SYN found mainly in pre- or post-synaptic neurons?
Presynaptic terminal, used for maintaining synaptic vesicles
What are the clinical manifestations?
A. Tremor at rest
B. Bradykinesia progressing to akinesia
C. Rigidity
Also…
D. Diminished sense of smell, changes in handwriting
E. Mask-like face (later symptom)
F. Excessive salivation/swallowing difficulties
G. Depression (co-morbidity, treated separately)
H. Sleep disturbances (due to medication or muscle rigidity)
I. Anxiety
J. Dementia (30% / more advanced pts)
What was the main drug used to treat PD until the 1960’s?
Anticholinergics, for excessive drooling
In true PD, do the symptoms start symmetrically or asymmetrically?
Asymmetrically
What distinguishes idiopathic PD from PD from other causes?
asymmetry of symptoms and resting tremor. Also response to L-dopa therapy
What can cause symptoms of PD?
stroke, infection, drug-induced toxicity (DA antagonists, MPTP)
What hereditary forms of PD are there?
- Alpha-synuclein (familial)
- PARKIN (familial, juvenile and early onset)
- UCH-L1
- PINK1
- LRRK2
What gene is associated with juvenile onset PD?
PARK2
What is the three-step process of tagging a protein with UBIQUITIN?
- E1 activates UBIQUITIN
- E2 transports UBIQUITIN
- E3 ligase protein complex (PARKIN) recruits substrate and UBIQUITIN is transferred to the target protein.
How else is the UBIQUITIN-proteasome system implicated in PD?
- Unfolded proteins enter the 20S proteasome cylinder to be degraded
- Cap proteins facilitate unfolding and release Ub chain. Ubiquitin carboxy-terminal hydrolase (UCH-L1) degrades chain to free Ub. Alpha-synuclein aggregates cannot be unfolded. Thought to interfere with 26S proteasome normal function.
What is required to release the monomeric form of Ub?
UCH-L1
What are the accumulated mis-folded proteins called?
Lewy-bodies
What organelle is implicated with this energy crisis?
The mitochondria
Where are the Lewy bodies located?
In the cytoplasm, but they spread to the dendrites
What gene implicated in PD is also known as Dardarin?
Leucine Rich Repeat Kinase 2 (LRRK2)
What gene links idiopathic and familial PD?
LRRK2
What was discovered when LRRK2 mutations were examined in different types of patients?
A link was discovered between familial and idiopathic PD.
Of the genes implicated in PD, which is the greatest known contributor to PD?
LRRK2. It has multiple pathogenic mutations.
In a dose-response curve of kinase activity, what is the difference between a high IC50 number and a low IC50 number?
The lower the IC50 number, the more potent the inhibitor.
What is MPTP?
It is a pro-toxin that is converted into MPP+ by MAO-B in glia, that produces PD-like neurological effects.
How does MPP+ enter the neuron?
Via the dopamine transporter (DAT)
What does MPP+ bind to within the neuron?
Neuromelanin. Levels of melanin are high within the nigrostriatal tract.
What can protect against MPTP effects?
- A selective MAO-B inhibitor such as Selegiline will prevent conversion from MPTP to MPP+ (and MPDP in between)
- DAT inhibitors protect against neurotoxicity (bringing in bad things via the DAT)
What form of the chemical creating “frozen addicts” crosses the blood brain barrier?
MPTP
Where does MPP+ concentrate once it gets into the neuron? What is the primary cause of MPTP toxicity?
It concentrates in the mitochondria where it inhibits oxidative phosphorylation. This depletes ATP, which leads to cell death. Mitochondrial damage is the primary cause of toxicity.
Does MPTP produce Lewy bodies?
No, although it does produce irreversible damage and acute PD-like symptoms.
What is the pesticide hypothesis?
The link between environment toxins and the subsequent development of PD to account for some fraction of idiopathic PD.
What does the normal function of Parkin and PINK1 appear to maintain?
Mitochondrial function and promote clearance of dysfunctional mitochondria.
What was the impact of the discovery of MPTP?
That the focus is on the mitochondria, and how dysfunction can affect the neuron.
What are the autosomal dominant and autosomal recessive genetic risk factors involved in PD?
Dominant: LRRK2, alpha-synuclein
Recessive: Parkin, PINK1
What are the five nuclei in the basal ganglia?
- Caudate
- Putamen
- Globus Pallidus
- Subthalamic
- Substantia nigra
What nuclei form the striata?
caudate and putamen
What do the basal ganglia do?
They regulate the flow of information from the motor cortex to the motor neurons of the spinal cord.
How many types of dopamine receptors are there? Which are similar to each other?
- D1 and D5 are coupled similarly.
Dopamine pathway: What is the pathway of dopamine in from aa to vesicle release?
Dietary phenylalanine is converted to tyrosine by hepatic PH. Tyrosine is transported into the neuron and then converted to L-DOPA by tyrosine hydroxylase. AADC/AAAD catalyzes L-DOPA to dopamine. Dopamine is packaged and released from vesicles into the synaptic terminal mediated by Ca2+.
Dopamine pathway: what does the dopamine in the synaptic cleft do?
It can affect dopamine auto receptors at the presynaptic terminal, receptors at the postsynaptic terminal, or be transported by the DAT presynaptically (which terminates the DA response, has 12 domains, and is target for cocaine).
Dopamine pathway: After transport by DAT….
Once DA has been transported inside by DAT, it can be stored via VMAT2, or metabolized. Metabolism options include MAO and then COMT, or COMT and then MAO. (Remember COMT adds methyl group, MAO removes NH2 and adds O2H). Homovanillic acid (HVA) is the product of either way. DOPAC is one of the bi-products.
What is the direct pathway from the basal ganglia to the motor cortex?
substantia nigra –> striatum –> substantia nigra –> thalamus –> cortex
What is the indirect pathway from the basal ganglia to the motor cortex?
substantia nigra –> striatum –> globus pallidus –> subthalamic –> substantia nigra –> thalamus –> cortex
Is D1 receptor activating or inhibitory?
Activating
Is D2-like receptors activating or inhibitory?
Inhibitory
If the normal direct or indirect pathways are working, what happens to the cortex?
It has a normal activating signal from the thalamus.
If the normal direct or indirect pathways have a loss of dopamine, what happens to the cortex?
The thalamus is inhibited from sending a signal to the cortex.
Does the loss of dopamine have the same effect on the direct and indirect pathways?
Both pathways inhibit the cortex, although the effect is unequal. The indirect pathway seems to actively inhibit the motor cortex stimulation. The difference allows drug design ideas.
What is the goal of medication therapy for PD?
Treat symptoms, not alter disease. Maintain functional mobility.
What are the four strategies?
- Replace DA
- Mimic dopamine action
- Inhibit breakdown of DA
- Modulate GABA (via anti-muscarinic agents)
What is the single most effective agent is PD treatment?
L-Dopa therapy
How is L-dopa given?
In mono therapy, only 1-3% enters CNS. Would have to give 2-8 g/day to reach therapeutic levels. Usually given with decarboxylase inhibitor such as carbidopa, to inhibit AAAD reactions in the periphery. (In periphery, L-Dopa would be converted into dopamine and not enter the CNS). This way, more can enter CNS.