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Animal Models in Bipolar Animal Models in Bipolar DisorderDisorderBy Jakob Avi ShimshoniBy Jakob Avi Shimshoni
I.I. IntroductionIntroduction
Bipolar Disorder (BD) is common, affecting Bipolar Disorder (BD) is common, affecting approximately 4 million persons in the USA.approximately 4 million persons in the USA.
BD is characterized by unpredictable swings in BD is characterized by unpredictable swings in mood from mania to depressionmood from mania to depression
BD can be divided into bipolar manic-depression BD can be divided into bipolar manic-depression and unipolar disorderand unipolar disorder
Clinical FeaturesClinical Features
Depressed, miserableElevated,labileMood
Retardation or agitation, poverty of movements and expression
Disinhibition, hypersexuality, excessive spending
Behavior
Fatigue. Loss of libidoInsomnia, weight lossPhysical
Guilt, unworthinessGrandiose, self confidentIdeation
Lacking, apatheticExcessive, increased psychomotor activity, distractable
Energy
Slow, monotonousFast, flight of ideasTalk
DepressionMania
Manic episodes emerge graduallyManic episodes emerge gradually
They can last as long as several months to years They can last as long as several months to years when untreatedwhen untreated
Frequent age of onset: 20-30 yearsFrequent age of onset: 20-30 years
I.I. PathophysiologyPathophysiology
Alterations in Brain StructureAlterations in Brain Structure
- - Ventricular enlargementVentricular enlargement
- Glial density reduction in - Glial density reduction in prefrontal cortexprefrontal cortex
- MRI of BD patients reveal - MRI of BD patients reveal vascular diseasesvascular diseases
Alteration in Brain functionAlteration in Brain function
- - Lower cortical metabolism in depressed BDLower cortical metabolism in depressed BD
- Decreased metabolism and blood flow in prefrontal - Decreased metabolism and blood flow in prefrontal cortex in depressed BD cortex in depressed BD
Alterations in Signal TransductionAlterations in Signal Transduction
cAMP/PK-A systemcAMP/PK-A system
- - increased Adenylyl cyclase activityincreased Adenylyl cyclase activity
- higher Gs levels- higher Gs levels - increased PK-A activity- increased PK-A activity
PIP2-PathwayPIP2-Pathway
- - increased platelet PIP2 concentration increased platelet PIP2 concentration
- increased PK-C membrane/cytosol partitioning- increased PK-C membrane/cytosol partitioning - increased PK-C activity- increased PK-C activity - Li decreases inositol levels in brain tissue- Li decreases inositol levels in brain tissue
Abnormalities of Ca 2+ signaling - Higher Ca2+ levels in platelets, neutrophils and
lymphocytes
- Increased PK-C activity may be responsible for abnormal Ca2+ levels
Na +/K +-ATPase hypothesis - Reduced Na+/K+-ATPase activity
- Lower Na+/K+-ATPase protein α2 subunit
- Intraventricular Quabain administration to animals, increases motor activity
NeurotransmittersNeurotransmitters
The Dopamine-HypothesisThe Dopamine-HypothesisIs based on the following
findings: Dysfunctional neural circuitry
of reward and incentive motivation
Decreased CSF Homovanilic acid in depressed compared to
manic patients Antidepressants enhance the
activity of the mesolimbic DA-system
Acute administration of psychostimulants like amphetamine
produce effects similar to mania Acute mania is treated with
neuroleptic drugs
Norepinephrine-SystemNorepinephrine-System
Increased NE turnover Increased NE turnover Higher urinary MHPG (methoxy-4-hydroxyphenylglycol) Higher urinary MHPG (methoxy-4-hydroxyphenylglycol)
in mania as compared to depressionin mania as compared to depression
5-HT-System5-HT-System
Decreased 5-Hydroxyindolacetic acid levels in frontal and parietal cortex
Reduced 5-HT transportes in frontal cortex
Hypothalamic-Pituitary-Adrenocortical AxisHypothalamic-Pituitary-Adrenocortical Axis
Increased HPA activity in depressed and mixed BD patientsIncreased HPA activity in depressed and mixed BD patients
Chronic hypercortisolemia is toxic to hippocampal neuronsChronic hypercortisolemia is toxic to hippocampal neurons
The Circadian RhythmThe Circadian Rhythm
Sleep-wake cycle is determined by external and internal rhythms
The internal rhythm is coordinated by a master clock in the supra-chiasmatic nucleus
Two transcriptional factors determine its function:
CLOCK and BMAL1
In BD patients subtle disturbances in circadian rhythms precede the full-scale shift in mood state
I.I. PharmacotherapyPharmacotherapy
Newer Antiepileptic drugs in BDNewer Antiepileptic drugs in BD LamotrigineLamotrigine :: Dosage: 100-300mg/day Lamotrigine shows significant benefit as monotherapy
or as adjunctive agent in bipolar depression as well as rapid cycling. Efficacy in acute mania is unclear.
Gabapentin Dosage: 900-3600mg/day Gabapentin is often prescribed for patients with BD as
adjunctive, in spite of negative results in clinical trials. Topiramate Dosage: 200-600mg/day Open-label studies suggest improvement in the manic
phase of BD patients.
Mechanism of action of mood stabilizersMechanism of action of mood stabilizers
LiLi ++:: LiLi++ reduces cAMP fluctuations, by G-protein inhibition reduces cAMP fluctuations, by G-protein inhibition Attenuation of Receptor coupled PIP2-signalling, by Attenuation of Receptor coupled PIP2-signalling, by
inhibition of IMP (Ki=0.8mM)inhibition of IMP (Ki=0.8mM) Down-regulation of PK-C isozymes and reduction in PK-C Down-regulation of PK-C isozymes and reduction in PK-C
bound to plasma-membranebound to plasma-membrane NeuroprotectionNeuroprotection Increase growth cone area of neuronsIncrease growth cone area of neurons Decreased adrenergic and dopaminergic super sensitivityDecreased adrenergic and dopaminergic super sensitivity
CBZCBZ Increase growth cone areaIncrease growth cone area Reduces basal levels of cAMP as well as levels after Reduces basal levels of cAMP as well as levels after
Adenylyl-cyclase activationAdenylyl-cyclase activation Stabilization of NaStabilization of Na++-channels-channels
VPAVPA Decrease inositol biosynthesis, by MIP-synthase Decrease inositol biosynthesis, by MIP-synthase
inhibitioninhibition Increase growth cone areaIncrease growth cone area NeuroprotectionNeuroprotection PK-C isozymes down regulation and reduced PK-C PK-C isozymes down regulation and reduced PK-C
bonding to plasma membranebonding to plasma membrane Block of voltage-dependent NaBlock of voltage-dependent Na++-channels-channels
Mechanism of Inositol Biosynthesis
NeuroprotectionNeuroprotection
Increased Bcl-2 and BDNF
Reduction in p53 proapoptotic protein
Inhibition of GSK-3β results in an increased gene transcription
Rational for the use of AED’s in BDRational for the use of AED’s in BD Gradual progression in intensity and frequency of Gradual progression in intensity and frequency of
epileptic seizuresepileptic seizures and manic-depressive episodes.and manic-depressive episodes.
Manic-depressive episodes are neither random nor Manic-depressive episodes are neither random nor predictable; epileptic seizures occurs randomly.predictable; epileptic seizures occurs randomly.
Kindling –HypothesisKindling –Hypothesis: Phenomenon whereby repeated : Phenomenon whereby repeated administration of an initially sub-convulsive electrical administration of an initially sub-convulsive electrical stimulus results in progressive intensification of seizure stimulus results in progressive intensification of seizure activity, culminating in spontaneous seizures.activity, culminating in spontaneous seizures.
Both disorders respond to several identical drugs.Both disorders respond to several identical drugs.
I.I. Animal ModelsAnimal Models IntroductionIntroduction
Animal models in psychiatry are controversial, due to the Animal models in psychiatry are controversial, due to the difficulties of trying to mimic higher cognitive functioning difficulties of trying to mimic higher cognitive functioning in animalsin animals
We classify behavioral changes in:We classify behavioral changes in: - Subjective changes: fear, euphoria, dysphoria, - Subjective changes: fear, euphoria, dysphoria,
depressed mooddepressed mood
- Objective changes: locomotor activity, circadian rhythm- Objective changes: locomotor activity, circadian rhythm
Validity of Animal Models
Face-Validity: Refers to similarity in behavior between the model and
the disorder Construct-Validity: Evaluates the correlation of the model with molecular
changes described in illness pathophysiology Predictive-Validity: Evaluates the responsiveness of the model to the drugs
used to treat the illness modeled
Animal Models of ManiaAnimal Models of Mania
There are 4 major features of mania that could be There are 4 major features of mania that could be modeled:modeled:
HyperactivityHyperactivity ElationElation IrritabilityIrritability InsomniaInsomnia
A viable model will have to demonstrate positive effects A viable model will have to demonstrate positive effects of Liof Li++ and no effect of drugs ineffective in mania and no effect of drugs ineffective in mania
Operational approach for evaluating elation:Operational approach for evaluating elation:Intracranial self stimulationIntracranial self stimulation
Sleep Deprivation Model
The rat is kept on a small platform surrounded by water for 72h
At the end of the period, it is returns to its home cage and doesn’t readily fall asleep
Symptoms presented during this time: insomnia, hyperactivity, aggressiveness, hypersexuality
Benefits: effective, economic, no invasive manipulation
Drug-screening-test In this test the latency to sleep and motor activity are measured.Example:
Acute Psychomotorstimulant Model
Hyperactivity is induced by a mixture of amphetamine (1.2mg/kg) and chlordiazepoxide (12.5mg/kg) injected s.c. 35min before the test.
Activity was assessed by recording the number of entries into the arms of a maze during a 5min period.
Brain lesion modelBrain lesion model Lesions in hippocampus and amygdala during the first
weeks after birth induce increased locomotor activity, decreased investigatory behavior and decreased seizure threshold
Induction: Injection of cholera toxin
Social Isolation Isolation of rats in the neonatal period produces
syndrome in which hyperactivity is a major component Additional changes: increased aggressiveness,
stereotypy
Animal Models of DepressionAnimal Models of Depression
IntroductionIntroduction
The largest animal models of depression is based on the The largest animal models of depression is based on the application of stressapplication of stress
Stressors used: foot shock, restraint, water immersionStressors used: foot shock, restraint, water immersion
Depressed behavior is characterized by: reduced Depressed behavior is characterized by: reduced locomotor activity and reward behaviorlocomotor activity and reward behavior
Basic requirements for validated animal modelBasic requirements for validated animal model Predictive validityPredictive validity Responsiveness to Tricyclics and MAO-A inhibitors
Face validity The model must demonstrate resemblance to clinically
defined core symptoms of the disorder Core symptoms are: loss of pleasure (anhedonia) depressed mood Construct validity limited evaluation because of lack of basic knowledge
Chronic mild stress model (CMS)
Rats are exposed sequentially to a variety of mild stressors over a period of weeks
This procedure causes a decrease in sensitivity to reward
CMS induced behavioral deficits may be maintained for several months
Normal behavior is restored by chronic treatment with Tricyclics during continual CMS
CMS-Procedure: CMS-Procedure:
Results:Results:
Forced Swim testForced Swim test
Developed by Porsolt in 1978 as a Developed by Porsolt in 1978 as a screening test for antidepressants screening test for antidepressants in rodentsin rodents
The rats are placed in a water tank The rats are placed in a water tank that doesn’t permit escapethat doesn’t permit escape
After a short struggle time they After a short struggle time they display an immobile posture display an immobile posture reflecting a state of behavioral reflecting a state of behavioral despair (helplessness) despair (helplessness)
Effect of reboxetine treatment on immobility and Effect of reboxetine treatment on immobility and defecation defecation
Reserpine ModelReserpine Model
Pharmacologically induced model, which is most frequently used for drug screening
Reserpine causes depletion of catecholamines
In humans it causes depression, sedation, parkinsonism and in animals hypoactivity
Animals are treated with the test drug prior to Reserpine injection(0.25mg/kg)
Rats are tested for activity levels and immobility time
Genetic model: Flinders sensitive line of rats (FSL)
Selective breed for increased sensitivity of muscarinic agents
FSL rats show reduced locomotor activity, reduced weight, increased REM sleep and anhedonia
High responsiveness to Tricyclics, SSRI’s, but not to psychostimmulants
Good face, construct and predictive validity
I. Conclusions
No validated model incorporate both components of bipolar disorder
The animal models for mania and depression are used currently in research as well as in the industry for drug screening
In the last few years a new in-vitro model is developed in neural cells, as a research tool as well as a screening test
I. In-Vitro Screening Approach for new ant-bipolar drugs
Dictyostelium Discoideum Model Dictyostelium D. is a soil living amoeba It is used to measure the effects of drugs on inositol
levels, using a direct IP3-binding protein assay
Dorsal root ganglion Are used to measure the effect of drugs on the growth
cone area. This effect is mediated through inositol depletion.
VPA-induced teratogenicity
• Congenital malformations – 11.1%• Neural tube defects – 2%
Structural requirements to teratogenic molecule:
1. Presence of α-hydrogen2. Presence of carboxylic function3. Branching on α-carbon with two side chains containing three carbon atoms each CH3CH2CH2
CHCH3CH2CH2
COOH
I. Promising VPA-Derivatives as Anti-BD drugs
VPA-Derivatives depleting IP3 more strongly than Li+
Not teratogenic(>3mM)
76.5%
Not teratogenic (>3mM)
78%
At 2-3mM25-60%
62%
At 0.25-1mM40-60%
88%
Teratogenicity%IP3 reductionat 0.5mM
Drug
Maximal Electroshock Seizures (MES)
(60Hz, 50mA, 0.2s)
Animal Models of Epilepsy
sc Metrazole (scMet)
Kindled rat model
Identifies drugs effective against tonic\clonic seizures seizure spread inhibition
Identifies drugs effective against absence seizures increase in seizure threshold
Identifies drugs effective against partial and seconarily generalized
seizures
Chemical Structure of Chemical Structure of Cyclic Analogs of VPA
CONH2
CONHCH3
CONHCONH2
CONHOCH3
M-TMCD
TMCU
Methoxy-TMCD
CONH
N N
S
SO2NH2
TMC-thiadiazole
TMCD
Antiepileptic activity and toxicity of cyclic analogs of VPA
333mg: 6.5% resorption 0% alformation
538171NT9229TMC-urea
660mg: 54% resorption 34%malformation330mg: 27% malformation
>500NTNT>5009TMC-Thiadiazole(ip)
300mg: 8% resorption 1% malformation
38185>100;C52>250TMCD
300mg: 15% resorption 1% alformation
1634140;h4582MTMCD
NT333150NT35108Methoxy-TMCD
600mg:8% resorption 41% alformation
78426980<646485VPA
TeratogenicityTD50mgkg
Chungmg/kg
Kindlingmg/kg
scMETmg/kg
MES mg/kg
Drug
NT>500Inactive<160NT>25082TMC-glycinamide
NT>500NTNT>25041N-Acetyl-tmc-urea
TeratogenicityTD50-Chungmg/kg
Kindlingmg/kg
scMETmg/kg
MES mg/kg
Drug
CONHCONHOCCH3
N-Acetyl-tmc-urea
CONHCH2CONH2
TMC-glycinamide
Structure of VPA-Derivatives
CONH2
COOH
CONHCH3
CONH2
COOHCONH2
CONHCH2CONH2
VPD
M-VPD
VGD
VCA VCD
DIADID
CONHCONH2
Isovaleroylurea
COOH
VPA
CONHCH2COOH
VGA
Antiepileptic activity and Toxicity of VPA-Derivatives
600mg: 10.4% resorbtion 0% malformation
63NTNT3716R-PID
NT500NTNT83>250Isovaleroylurea
600mg: 6.3%resorbtion 0%malformation
68NTNT3731PID (racemic)
not teratogenic87NTNT5932Valpromide
not teratogenic>1000226161;C300;h
>75073Valrocemide (VGD)
TeratogenicityTD50-Chungmg/kg
Kindlingmg/kg
scMETmg/kg
MES mg/kg
Drug
Results of antiepileptic activity and toxicity of drugs given ip to mice
188225200TMCA
279240269Valnoctic acid
813258Valnoctamide
633731PID
574187DID
303156238DIA
TD50scMET mg/kg
MES mg/kg
Drug
Thank you very much for your attentionThank you very much for your attention , , hopefully I didn’t induce a manic episode upon hopefully I didn’t induce a manic episode upon you !you !