Osteoarthritis is a common type of arthritis that causes the breakdown of cartilage in joints. It is characterized by loss of cartilage, thickening of bones, and formation of bone spurs. Risk factors include age, obesity, injury, and genetics. While NSAIDs are commonly used to treat symptoms, there are no approved disease-modifying drugs for osteoarthritis. Various animal models are used in research to study the disease process and potential treatments, but they all have limitations in mimicking human osteoarthritis. Further research is still needed to develop effective disease-modifying therapies.

1. Dr. Shouvik Choudhury
PGT, Dept. of Pharmacology
IPGME&R, Kolkata

2.  Most common type of arthritis
 Slowly progressing deterioration of articular cartilage with
intermittent painful inflammation
 Pathologic changes are-
• Loss of hyaline articular cartilage
• Thickening and sclerosis of subchondral bony plate
• Outgrowth of osteophyte at margin
• Synovitis and weakness of muscles

3.  Second most common rheumatologic problem
 Prevalence of 22% to 39% in India*
 Estimated to be the 10th leading cause of nonfatal burden
 Risk factors: female, increasing age, obesity, sedentary
lifestyle,trauma
 Worldwide prevalence of symptomatic knee OA 25.4%#
 4th leading cause of years lived with disability (YLD)
leading to 3% YLD in 2000 *
*- Pal et al. Epidemiology of knee osteoarthritis in India and related factors, Indian J Orthop. 2016 Sep; 50(5):
518–22.
#- Allen et al, Epidemiology of osteoarthritis: state of the evidence, Curr Opin Rheumatol. 2015 May ; 27(3):
276–83

4. Cartilage injury,
chondrocyte
mitosis
Proteoglycan
depletion
Osteoblast and
osteoclast in
subchondral bone
activated
Synovial
inflammation,
macrophage
migration
Cartilage loss
and Osteophyte
formation
Synovial joints components affected
meniscus, cartilage, subchondral bone, synovial membrane

7. OARSI (osteoarthritis research society international) guideline 2014

8. Limitations:
 No animal model sufficiently mimic the slow progressive
pathology of human OA
 Paucity of reliable parameters and lack of validation to
asses disease progression
 Animal models have a wide range of severity and rate of
progression of pathogenic changes
 Still no FDA approved disease-modifying OA drugs
(DMOADs) to validate pharmacological effect
Commonly used animals: Dog (pond nuki), Guinea pig
(dunkin-hartley), Mice, Rat, Rabbit, Sheep, Horse

9. USFDA draft guidelines for industry for use in the development of drugs, devices, and biological
products intended for the treatment of osteoarthritis (OA),1999

10. Small animal models
• First screening model for
therapeutic intervention
• Results may not be
translatable to human
with equal efficacy
• Now used to study
pathogenesis of OA mainly
• Relatively quicker,
cheaper, easier to use
Large animal models
• Anatomy markedly similar
to that of humans
• Used to confirm efficacy of
drugs before clinical trial
• Cost , ethical issues and
feasibility to use a big
challenge

11. Ref : hindwai

13.  Simulates natural progression of human osteoarthritis
 Rely on pathological changes rather than post-traumatic
alterations
 Drawback - long time requirement to develop injury , cost
a) Naturally occurring – dunkin hartley guinea pig is most
widely used, others are- STR/ort mice, Rabbit, Dog, Horse
b) Genetically modified- gene mutations are designed
either to protect from OA or to worsen change
Helped to establish specific genetic contribution or
molecular basis , eg- Col9a1 (−/−) mice, knock-out mice

14.  Used to see effect of drug on disease process
 Rapid induction of OA ensures shorter time frame
a) Surgically induced- commnly used models are ACLT
(anterior cruciate ligament transection) in dog/goat,
menisectomy in guinea pig, ovariectomy in rabbit
b) Chemically induced- injection of inflammatory compound
at joint to induce OA
 Non invasive model- closed fracture or dislocation
induced from outside, less chance of infection, not done
regularly

15.  Minimum age needed 10weeks
 Easy to use and low cost
 Common strain- STR/1N, STR/ort
 Recently used transgenic mice with mutated GDF5 allele
was susceptible to OA in collagenase model
 Limitation – very thin cartilage/ post operative
management difficult/ routine MRI inaccessible
 Metalloproteinase and IL inhibitors tested

16.  Minimum age 3 months
 Easy to care, cartilage thicker, low cost
 Post operative management difficult
 Iodoacetate model used to study pain in OA
 Drugs evaluated- Diacerin in rat menisectomy model
Alendronate (bisphophonates) in ACL
model
Glucosamine

17.  Minimum age 6 months
 Histopathology remarkably similar to human OA
 Varus alignment lead to load on medial copartment as in
human
 Risk factors as age, BMI can be studied
 Common strains- dunkin-hartley, GOHI, strain 13
 Drugs evaluated- MMP inhibitor in menisectomy model,
bisphosphonate, glucosamine, hyaluronan, chondroitin
sulfate in spontaneous models

18.  Minimum age 8-9 months
 Commonly used ACL and meniscus transection model
 Drugs evaluated- bisphosphonate, hyaluronic acid, MMP
inhibitors etc
 Limitaion- different knee biomechanics, regenerable
articular cartilage, absence of lamellar collagen layer, post
operative mangement difficult

19.  Closest to gold standard model
 First developed by Pond and Nuki as ACL model
 Other models used- menisectomy, focal defect creation,
chemical induction
 All treatments modality can be evaluated- oral, intra
articular injection, arthoscopic surgery, knee replacement
 Licofelone (a novel COX inhibitor) evaluated – reuction in
cartilage lesion size
 Used as a translational model

20.  Horse- largest available model
 Minimum age – 2 years
 Therapy evaluated- hyaluronic acid, triamcinolone,
chondrocyte implantation
 Single trauma may lead to OA
 Ovine models also used for implantation
 Sheep/goat not prone to spontaneous OA
 Ruminant nature prevent enteral thearpy evaluation

21. Some commonly used in vivo methods are-
 Canine Anterior Cruciate Ligament (ACL) Transection
Model
 Chymopapain-Induced Cartilage Degeneration in the
Rabbit
 Spontaneous OA Model in STR/1N Mice
 Transgenic Mice as Models of Osteoarthritis

22.  ACL transection in dog knee leads to progressive cartilage
erosion and osteophyte formation
Method : dog anesthetised knee bent at 90° ACL dissected
and wound closed sham operation in the contralateral
knee marked osteophytosis and subchondral sclerosis at
8-12 weeks
Evaluation : macroscopic inspection and Mankin score
grading reported after treatment for 7 weeks…glycosamino
glycan and intra articular hyaluronic acid injection
evaluated
Modification : done in rabbit, hartley guinea pig, wistar rat

23.  Intraarticular injection of chymopapain into rabbit knee
joint results in cartilage degradation with rapid loss of
proteoglycans
Method : male New Zealand white rabbit anesthetised1.8mg
chymopapain in 0.1ml injected into joint space animal
sacrificed after 10-14 days histology of full thickness
cartilage sample done
Evaluation : proteoglycan content determined hyaluronic
acid and MMP inhibitors evaluated
Modification : rat model of pain, rabbit model of arthrosis

24.  Gradual development of OA
 Method : male mice trained to walk on rotating cylinder
from 10 weeks drug applied systemically for 8 weeks
mean walking time recorded and compared animal
sacrificed, joint histology done
 Evaluation : mean walking time decreases with age and
disease progression anti inflammatory drugs increase
the mean time
 Modification : interleukin inhibitor in Balb/c mouse,
collagenase inhibitor in STR/ort mouse

25.  Transgenic mice with collagen mutations include different
types of collagen
 As mutation in type II collagen, type IX and type XI
collagen
 Some models with mutations in non-collagenous
molecules were described
 Involvement of MMP also demonstrated indegradation of
cartilage and development of OA in mice
 Deletion of active ADAMTS5 prevents cartilage
degradation in a murine model

26.  Performed mainly with chondrocytes
 Vital role in degradation and reduced synthesis of matrix
 Two main components- proteoglycan attached to
hyaluronic acid filament (aggrecan) and type II collagen
 Enzymatic degradation involving metallo-proteinases
considered the main events
 Most of drug of OA- not been primarily selected and
optimized by in vitro assays
 Chondrocyte and cartilage explant culture systems used
for several years

27. Commonly used ones-
 Modulation of Cellular Proteoglycan Metabolism
 Cellular Chondrocytic Chondrolysis
 Cartilage Explant Chondrolysis
 Influence on Matrix Metalloproteases
 Aggrecanase Inhibition

28.  Articular cartilage grown in artificial matrix
 Matrix staining reveals the amount of newly formed matrix
remaining around the cells
 Agarose cell culture prepared from cell suspension and 2%
agarose gel….kept in multiwell plate
 Test compounds added to see effect on cartilage function
 Extinction is expressed in percentage as staining density
 Adv- suitable for 50 test drugs at a moment
 Limitation- radiolabelling better, preperation difficult

29.  IL-1, known proteogycan suppressor, added to articular
chondrocytes grown in agarose gel
 Test done to detect potential interference of a drug with
pathological process
 Radiolabelling done to see degradation or reduced synthesis
 Test drugs added in various concentration in multiwell plate
 Assessment done by β-scintillation counter and counts per
minute measured
 Human chondrocytes can be used now a days

30.  Chondrocytes vary in their metabolic activity and cytokine
response depends on the relative location
 Cellular assays are a homogeneous mixture of an
otherwise heterogeneous cell population
 Chondrocytes are more reactive after isolation compared
to those in tissue culture
 IL-1 and test compounds are added
 Assessment in β-scintillation
 Disadvantage- greater amount of cartilage required

31.  MMPs can degrade all components of the extracellular
matrix and have been implicated in a number of
pathological conditions
 Produced in response to pro-inflammatory cytokines
 Influence of test substances on recombinant MMP-2, MMP-
3, and MMP-9 activity was determined using the
fluorescent quenched substrate
 Test drugs are mixed in different concentration and
substrate hydrolysis measured
 Several modification of this tests done

32.  Aggrecan,a multidomain proteoglycan, is a major
component of cartilage and provides compressive
resistance to articular cartilage
 Inhibition may be a potential therapy to alter the
progression of osteoarthritis
 Measured proteoglycan was expressed per weight of
cartilage
 Concentration of ADAMTS4, ADAMTS5 also measured
 Modifications done as microplate method, high-throughput
screening assay ( alfa screen)

33.  OA is a multifactorial disease causing joint pain and
disability in most countries
 Analgesic and anti-inflammatory drugs are mainstay of
therapy (NSAID still mostly used drug)
 No approved DMOAD available
 Anti –oxidative drug, MMP inhibitor, hyaluronic acid
derivatives are showing promising result to prevent
cartilage degradation, but still not confirmed
 Further research in both preclinical and clinical setting
required for developing OA therapy

34. Thank You