PD: Animal Models and Drug Development Flashcards
Describe features of toxin based models of PD?
Toxins are injected into nigrostriatal system/systemically to kill DA neurons
NB: route of delivery depends on if toxin can cross BBB
Examples of toxin-based models of PD?
- 6-OHDA
- MPTP
- Lactacystin
6-hydroxydopamine (6-OHDA) features and properties?
[oxidative product of dpoamine found in small amounts]
Can’t cross BBB so must be administered as unilateral stereotaxic injection in anaesthetised animals
Dose responsive loss of nigrostriatal DA neurons
This is ideal to model different stages of cell loss (e.g. 60-70%)
Outcome of 6-hydroxydopamine (6-OHDA) injection into different regions of animal brain?
Injection into SNpc -> rapid cell loss (3-4 days)
Inject into medial forebrain bundle -> cell loss 7 days
Inject into striatum -> cell loss over 2 weeks
Compare features of 6-OHDA and PD?
- mitochondrial inhibition
- selective neuronal loss
- oxidative stress
(BUT no altered proteins)
How to assess outcomes using 6-OHDA model?
- behaviour
- immunohistochemistry (neuronal counts and glial activity)
- High Performance Liquid Chromatography (HPLC)]- detect neurotransmitters
- tyrosine hydroxylase immunopositive neurons (general neuron stain -> cell loss)]- compare loss of neurons in lesion vs control
Environmental mimics of PD
- Manganese -> Parkinson-like syndrome w/ fixed gaze, bradykinesia, postural difficulties, rigidity, dystonia]- from mining manganese ore
- Carbon disulphide (from rubber processing)
- Cycad seeds (from Guam) -> Parkinson-like syndrome w/ dementia
MPTP features and properties?
Lipophilic i.e. penetrates BBB]- can be given systematically
Compare features of MPTP and PD
- mitochondrial inhibition
- oxidative stress
(BUT no protein inclusions…but yes if given with probenicid)
Which species are susceptible to MPTP?
Humans, primates, mice (C57black)
Mice, rats, cats and dogs are relatively resistant to MPTP
MPTP in non-human primates?
3 doses of MPTP produces persisten behavioural syndrome: akinetic, flexed posture, increased limb rigidity, tremor, clumsy movement, freezing episodes
MPTP in primate brain?
MPTP rapidly converted to MPP+, which remains for several days
NB: in other species, both MPP+ and MPTP are rapidly removed from the brain
Outcome of MPTP administration?
Loss in SNpc but not VTA/NAc
Behavioural changes are reversed w/ L-DOPA + carbidopa (or DA agnoists)
What are Proteasome Inhibitor (PSI) Models?
Proteasome degrades altered proteins. Build up of altered proteins intracellularly -> oxidative stress + cell death
How to administer PSI?
Peripheral (systemic) administration
2 injections/week over 5 weeks
Disadvantages of PSI model for PD?
Not reproducible
Lactacystine features and properties?
Proteasome inhibitor
Doesn’t cross BBB
(more stable model than PSI)
Lactacystin method of administration?
Stereotactic injection into SNpc/MFB
Lactacystin compared to 6-OHDA and MPTP?
Chronic progressive model and spread
(compared to rapid cell loss seen in 6-OHDA and MPTP
Compare features of Lactacystin and PD?
- selective neuronal loss
- oxidative stress
- altered proteins
(BUT no mitochondrial inhibition)
Outcome of a-syn in drosophiliae?
- Selective DA neuronal death
- Lewy body-like structures
- movement disorder (change in climbing behaviour)
Outcome of increased wild-type a-syn in transgenic mice?
- neuronal inclusions (hLB sunflower structure, rLB is disorganised)
- no neuronal loss
Outcome of expressing A30P/A53T double mutant
- age dependent decrease in SNpc TH cell number
- decreased motor function
- no inclusions
Disadvantages of using transgenic mice w/ a-syn to model PD?
- need to wait 18 months for pathology
- transgenic mice expensive
- mice require 2-3 mutations of a-syn, but no human has >1 a-syn mutation
Outcome of rAAV a-syn overexpression (viral vector delivers wild-type or mutated a-syn)?
- deficits in motor behaviour
- decreased DA striatal terminalis and cell bodies
Disadvantages of using rAAV a-syn overexpression?
Have to wait 6 months for pathology]- it is a progressive model
Mechanism of injecting pre-formed a-syn fibrils?
Braak hypothesis: injecting protofibrils in SNpc mirrors spread of altered proteins in similar pattern to PD
Taken up by striatal neurons -> Lewy bodies
- fibrils cause native a-syn to misfold
- inclusions spread across brain over time
Outcome of injecting pre-formed a-syn fibrils?
Small amount of nigrostriatal DA cell loss (30%) which doesn’t translate to behavioural deficits
Outcome of using LRRK2 Transgenic mice?
Cell death in neuroblastoma cells and mouse cortical neurons
Compare LRRK2 model and PD
- movement dysfynction
- abnormal proteins
(BUT no neuronal loss in SNpc)
NB: you can add MPTP to induce stress or neurodegeneration
Function of mtDNA?
Encodes 13 key subunits of respiratory chain. It is critical for mitochondrial biogenesis
Relationship between mtDNA and age?
mtDNA mutations increase with age
What regulates mtDNA transcription?
Mitochondrial transcription factor A (Tfam)
Outcome of Tfam KO mice (MitoPark Mouse)
Reduced mtDNA expression and mitochondrial respiratory chain deficiency in DA neurons
List some ways of assessing behaviour in PD models
- Forepaw reaching behaviour
- Amphetamine-induced rotational assessment
- Walking on a beam (no. of falls)
Outcome of unilateral lesion in:
forepaw reaching behaviour
amphetamine-induced rotational assessment
forepaw reaching: assymetry in paw use
amphetamine-induced rotation: [unilateral DA release (inhibition on intact side)] -> turn towards
|
assymetry causes animals to walk in circles (no. of turns corresponds to lesion size)
Evaluation of PD models?
- Rodents don’t have stresses of human cells synapses (require E) per DA neuron is greater in humans
- PD has mixed motor and non-motor symptoms]- cannot mirror all of these
Drug development from models example in PD?
Deferiprone (iron chelator) for PD
PD has increased iron in SNpc (iron redox -> ROS)
Animal model (ferrocene deposits iron globally, not just in SNpc): shows iron chelators to be neuroprotective
Ways of assessing animal models with PD?
- behavioural tests
- tyrosine hydroxylase immunopositive neurons (general neuronal stain to look for cell loss)
- high pressure fluid chromatography (detect NTs)
