screening of anti obesity drugs
DESCRIPTION
screening of drugs and models for obesityTRANSCRIPT
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Feb 2011
SCREENING OF ANTI-OBESITY DRUGS
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ObjectivesTo understand the need for
new anti obesity drugs
To understand the
pathophysiology
To understand how to
manipulate in vivo models
To know basic in vitro tests
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Overview Introduction
Pathophysiology
Problems in animal
models
Parameters assessed
In vitro methods
In vivo methods
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ObesityEnergy intake> Energy expenditure
BMI>30 kg/m2
Multifactorial
Orexigenic peptide- NPY, AgRP, Orexin A
&B, galanin, endorphin, NE, GH-RH
Anorectic peptide- Corticotrophin-RH,
MSH, CCK, GLP1,CGRP, bombesin
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Need for anti obesity drugs?
One billion adults are
overweight
>300 million are obese
Prevalent in low income
countries.
Obesity are linked to more
deaths worldwide than
underweight.
Globally, > 42 million
children
<5y age are overweight
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Need for anti obesity drugs? Cont’d…
In late 2009, $1.1 billion
market anti-obesity drugs
could nearly triple to
reach $3.1 billion by 2016
No new anti-obesity drug
FDA approved since 1999
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Animal models
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Why mouse models ?Represenative for human disease
Genome sequenced
Acceptable reproduction time
Large numbers can be handled
Identification of disease genes
easier than in humans
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Lack of Ideal modelObesity – a complex disorderExact pathology - unknownHumans tend to enjoy eating and
are not forced to eat high fat dietHumans do not have induced
gene mutationsNo single animal model can
display interplay of behaviour, environment and genetic factors.
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Animal models- Parameters
Food intake- intake and spillage
Body weight
Adipose tissue cell size and number- osmium
fixation method
Body composition
Locomotor /physical activity
Plasma lipids, insulin and glucose levels
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Animal model
s
In vivo
Diet induce
d
Hypothalamic
Virus induce
d
Genetic
Monogenic
Polygenic
In vitro
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1.Diet Induced ObesityRationale: calorie foodsAnimal: Adult female rat
230gProcedure: Animals
given cafeteria diet. Body wt, food intake,
locomotor activity and serum insulin measured.
After 3months, rats sacrificed and adipose tissue cell size, body composition and lipid content is determined
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2.Hypothalamic ObesityRationale: Hypothalamus regulates food
intake. Venteromedial hypothalamic lesions food intake- obesity in 3-4 months.
SurgicalChemical
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a).Surgically induced hypothalamic obesityAnimal: female Sprague Dawley
rats 190g
Procedure: high fat diet for 5-9
days. The cuts are made 1mm
lateral to the midline, extended
from 8.5-5.5mm anterior to ear
bars and from 3mm dorsally from
the base of the brain.
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b). Chemically induced hypothalamic obesityAnimals: Mice/Rat (2-40 d old)Procedure: Daily inj Monosodium-L-glutamate
2g/Kg , S/C x 5dOR
Single Inj of Gold thioglucose 30-40mg/Kg , I/P
ORSingle Inj Bipiperidyl mustard 5-
50mg/Kg, I/POR
Single Inj 4-nitroquinoline l-oxide intracerebral
Obse
rvatio
n o
f para
mete
rs x
3m
onth
s
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3. Virus induced obesityRationale: Some specific viruses target
hypothalamus leading to virus induced disruption of critical brain CA pathways, leading to obesity
Animals: MiceProcedure: Mice infected with canine
distemper virus, develops obesity in 8-10 weeks.
Other viruses: Rous-associated virus-7Avian adenovirus SMAM-IAd-36Borna disease virusAvian retrovirus
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4. Genetic models of obesity
Monogenic
Polygenic
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Yellow obese mouse (Aya)Rationale: Obesity inherited through
dominant gene, on Chromosome 2 at linkage group 5, agouti locus.
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Obese mouseAutosomal recessive
mutation on
chromosome 6
Inbred stock of C57BL/6J
strain
Obesity,
hyperglycaemia, insulin
resistance
Autosomal recessive
mutation on
chromosome 4
Inbred stock of
C57BL/KsJ strain
Obesity,
hyperglycaemia, insulin
resistance
Diabetes mouse
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Fat mouseLate onset obesityAutosomal
recessive‘Fat mutation’Chromosome 8
coding for CPECPE involved in
insulin metabolismAdditional:
infertility
Late onsetAutosomal recessiveTub mutationC57BL/6J inbred
strainAdditional:
sensorineural deafness,retinal degradation
Tubby mouse
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Fatty ratZucker fatty ratMost widely usedAutosomal
recessiveFa/fa homozygous Obese by 3-5
weeks age
Mating SHR female rat (kyoto wistar)with normotensive Sprague Dawley rat
Inbred strains after several generation
SubstrainJCR: LA Corpulent rat
Vascular complications
Obese SHR rat
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WDF/TA-FA rat
Wistar fatty rat
Tranfer of fatty gene (fa) from Zucker rat
to Wistar Kyoto rat
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Polygenic ModelsJapanese KK mouse NZO mouse
Most suitableLarge body size
mice inbredYellow obesity(AY)
transferred to KK mice
KK-Ay miceDelayed onset
obesity
New Zealand obese mouse
6month age- renal disease, autoimmune disorder
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Other polygenic modelsOLETF rat
Otsuka-Long evans-Tokushima-Fatty rat
nephropathy model
BSB model
AKR/J x SWR/J model
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Transgenic modelsRationale: genes regulating energy
homeostasis are manipulatedProcedure – gene for diphtheria toxin A
chain is used to link to the gene chosen to be knocked out
KO 3 gene – in white and brown adipose tissue
KO Uncoupling protein in brown fat (thermogenesis)
KO mice lacking Steriodogenic factor I (SF-I)Overexpression of corticotropin releasing
factor gene, GLUT-4 gene, human agouti-related protein complementary DNA
Genes for leptin, leptin receptor, growth hormone, α-MSH, AgRP, Melonocortin-4 receptor, melanocortin- 3 receptor.
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In vitro assays1. To study metabolic activity in brown adipose
tissue
Assay for uncoupling protein and GLUT4 Procedure: OLETF rat, 10 weeks age are given
test drug OD S/C . Rats sacrificed at 14 weeks age. Brown and white fat removed. UCP and GLUT4 determined with western blot analysis.
2. To study 3 agonist activity
they induce wt. loss by increased thermogenesis, suppression of leptin gene expression
c-AMP response element-luciferase receptor gene assay for 3 agonist.
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In vitro assays Contd’…..3. Assay for Neuropeptide Y
It stimulates appetite. Six receptors Y 1-6Y5,Y1 antagonist- new drug targets
4. Role of leptin Ob gene product. Receptor: lepr or OB-R
a)Assay for leptin mRNA level in adipose tissue - Northern blot analysis
b) RIA for measurement of plasma leptin
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Isolated adipocyte cell lines
For leptin and leptin mRNA:
1. Rat Preadipocytes- epididymal fat pad
2. Rat primary cultured mature
adipocytes
3. 3T3-L1 adipocytes- mouse fibroblasts
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Practical ImplicationsDietary models- represent
behaviour and environmental
factors
Genetic models- for understanding
genetics of human obesity
Polygenic models- human obesity
is also polygenic
New therapeutic targets
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ReferencesDrug screening methods - S K Gupta
Drug Discovery and Evaluation - Vogel
Pharmacology- Rang and Dale
Biology of Obesity: Lessons from Animal
Models of Obesity. Journal of
Biomedicine and Biotechnology
doi:10.1155/2011/197636
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