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Screening of antiobesity 23may2012


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screening of drugs/ agents for obesity. the models are described here

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Screening of antiobesity 23may2012

  1. 1. SCREENING OF ANTI- OBESITY DRUGS Dr. Akanksha William 23 May 2012
  2. 2. Objectives• To review the patho physiology of obesity• Need for new anti obesity drugs• To understand the basis of using animal models• To know in vitro tests
  3. 3. • Introduction• Burden of the disease• Pathophysiology• Ideal animal model• Problems in animal models• Parameters assessed• In vitro methods
  4. 4. Obesity• Energy intake> Energy expenditure BMI(wt/m2) CLASSIFICATION 18.5-24.9 NORMAL 25-29.9 Over weight/PRE OBESE 30-34.9 OBESE class I 35-39.9 Obese class II >40 Obese class III
  5. 5. Disease burden• WHO -1.5 billion obese• U.S. 68% (largest market)• India-60% affected Children- 14.3% boys - 9.3% girls
  6. 6. Need for anti obesity drugs• 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
  7. 7. Pathophysiology
  8. 8. Life styleEnvironment Multifactorial Genetics Diet
  9. 9. Ideal animal model• Representative for human disease• Genome sequenced• Acceptable reproduction time• Large numbers can be handled• Placebo subtracted weight loss >5% maintained for >1 year is the efficacy end point for approval.
  10. 10. Lack of Ideal model• Obesity – a complex disorder• Exact pathology - unknown• Humans tend to enjoy eating and are not forced to eat high fat diet• No single animal model can display interplay of behavior, environment and genetic factors.
  11. 11. Parameters assessed• Food intake- intake and spillage• Body weight• Adipose tissue cell size and number• Body composition• Locomotor /physical activity• Plasma lipids, insulin and glucose levels
  12. 12. HypothalamicDiet induced Virus induced Genetic models obesity• Normal vs. • Surgical • Canine • Spontaneously high fat diet • Chemical distemper obese rat • Modification virus(antigenic • WBN/KOB ally related to • Zukar fatty rat • Gold measles) thioglucose • WDF/TA-FA induced • Borna disease RAT • Monosodium- • Rous • OLETF RAT associated glutamate • Obese SHR induced virus 7 • JCR:LA- obesity • Avian Corpulent adenovirus • Spontaneously • Ad 36 human obese mouse adenovirus • Growth hormone deficient dwarf rat
  14. 14. • Rationale: calorie foods• Animal: Adult female rat 230-250gms
  15. 15. Animals given cafeteria diet.Body wt, food intake, locomotor activity and serum insulin measured. After 3months, rats sacrificedAdipose tissue cell size, body composition and lipid content is determined
  16. 16. Disadvantages-acute food intake model• Stimulating food intake by fasting• Insensitive to drugs that have delayed onset of action• Drugs that increase energy expenditure• Lipase inhibitors
  17. 17. Hypothalamic Obesity
  18. 18. • Rationale: Hypothalamus regulates food intake. Surgical Chemical
  19. 19. Surgically induced obesity• Animal: 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.
  20. 20. Chemically induced obesity• Animals: Mice/Rat (2-40 d old)
  21. 21. Inj Monosodium-L-glutamate2g/kg , s/c x 5 days Inj of Gold thioglucose 30- 40mg/kg , i/p Inj Bipiperidyl mustard 5- 50mg/kg, i/p Inj 4-nitroquinoline l-oxide intracerebral
  22. 22. Virus induced obesity
  23. 23. • Rationale: Some specific viruses target hypothalamus leading to virus induced disruption of feedback pathways, leading to obesity• Animals: Mice
  24. 24. Procedure• Mice infected with canine distemper virus, develops obesity in 8-10 weeks.• Other viruses: Rous-associated virus-7 Avian adenovirus SMAM-I Ad-36 Borna disease virus Avian retrovirus
  25. 25. Genetic models of obesity Monogenic Polygenic
  26. 26. Yellow obese mouse (Aya)• Rationale: Obesity inherited through dominant gene, on Ch- 2 at linkage group 5, agouti locus.
  27. 27. Obese mouse• Autosomal recessive mutation on chromosome 6• Inbred stock of C57BL/6J strain• Obesity, hyperglycaemia, insulin resistance
  28. 28. Diabetes mouse• Autosomal recessive mutation on chromosome 4• Inbred stock of C57BL/KsJ strain• Obesity, hyperglycaemia, insulin resistance
  29. 29. Fat mouse• Late onset obesity• Autosomal recessive• ‘Fat mutation’• Chromosome 8• Additional: infertility
  30. 30. Tubby Mouse• Autosomal recessive• Late onset• Tub mutation• C57BL/6J inbred strain• Additional: sensorineural deafness, retinal degeneration
  31. 31. Fatty rat• Zucker fatty rat• Most widely used• Autosomal recessive• Fa/fa homozygous• Obese by 3-5 weeks age
  32. 32. Obese SHR rat• Mating SHR female rat (kyoto wistar)with normotensive Sprague Dawley rat• Inbred strains after several generation• Substrain-JCR: LA Corpulent rat• Vascular complications
  33. 33. WDF/ta-fa rat• Wistar fatty rat• Tranfer of fatty gene (fa) from Zucker rat to Wistar Kyoto rat
  34. 34. Polygenic Models Japanese KK mouse• Most suitable• Large body size mice inbred• Yellow obesity(AY) - KK mice• KK-Ay mice• Delayed onset obesity
  35. 35. NZO mouse• New Zealand obese mouse• 6month age- renal disease, autoimmune disorder
  36. 36. Other polygenic models• OLETF rat -Otsuka-Long Evans-Tokushima-Fatty rat nephropathy model• BSB model• AKR/J x SWR/J model• M 16- to study genetics of growth and obesity
  37. 37. Transgenic modelsRationale: genes regulating energy homeostasis are manipulated• KO 3 gene – in white and brown adipose tissue• KO Uncoupling protein -thermogenesis• KO mice lacking Steriodogenic factor I (SF-I)
  38. 38. • 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.
  40. 40. To study metabolic activity in brown adipose tissue Male fatty rat, 10 weeks age are given test drug od s/c Rats sacrificed after 14 weeks. Brown and white fat removed UCP and GLUT4 determined with western blot analysis
  41. 41. To study 3 agonist activityInduce weight loss by increased thermogenesis,suppression of leptin gene expression
  42. 42. Assay for Neuropeptide Y It stimulates appetite. Six receptors Y 1-6 Y5,Y1 antagonist- new drug targetsRole of leptin Ob gene product. Receptor: lepr or OB-R - Northern blot analysis - RIA
  43. 43. Isolated adipocyte cell linesFor leptin and leptin mRNA:1. Rat Preadipocytes- epididymal fat pad2. Rat primary cultured mature adipocytes3. 3T3-L1 adipocytes- mouse fibroblasts
  44. 44. Practical Implications• Dietary models- represent behavior and environmental factors• Genetic models- for understanding genetics of human obesity• Polygenic models- human obesity is also polygenic• New therapeutic targets
  45. 45. References Drug screening methods - S K Gupta Drug Discovery and Evaluation - Vogel Pharmacology- Rang and Dale Steven P Vickers.The utility of animal modelsto evaluate novelanti-obesity agents. British Journal of Pharmacology.2011; 164: 1248–1262. Biology of Obesity: Lessons from Animal Models of Obesity. Journal of Biomedicine and Biotechnology doi:10.1155/2011/197636
  46. 46. • Animal models and their value in predicting drug efficacy and toxicity. 2011; 15 - 16.
  47. 47. THANK YOU