Arthritis Flashcards
Define osteoarthritis
The aberrant repair and eventual degradation of articular cartilage in association with alterations in subchondral bone metabolism, periarticular osteophytosis and a variable degree of synovial inflammation
Whar percentage of adult animals have OA?
- 60% adult cats
- 20% adult dogs
What factors contribute to an individuals susceptibility to OA?
- Genetics
- Age
- Systemic factors (eg obesity)
What genes have been shown to be associated with early onset arthritis in people?
- Point mutations in type II collagen
- Mutations in genes encoding types IV, V and VI collagen
- Cartilage oligomeric matrix protein (COMP)
- Polymorphisms in the prostaglandin endoperoxidase synthase-2 (PTGS-2) which encodes COX-2 enzyme
How do chondrocytes change as they age?
- Synthesise smalled, less uniform aggregan molecules and less functional link proteins
- Mitotic and synthetic activities decline
- Responsiveness to anabolic mechanical stimuli and growth factors decreases
What is C-terminal truncation of aggregans?
An aging process in which length and uniformity of aggregan molecules is diminshed
- MMPs and aggrecanases cause c-terminal truncation
- Shorter molecules contain fewer chondroitin sulphate side chains but greater quantities of ketatin sulphate
- Therefore, have less ability in imbibe water reducing the compressive stiffness
How does obesity predispose to the formation of OA?
- Increased load on the joints
- Alters joint alignment
- Causes a systemis subclinical proinflammatory state with increased circulating adipokines such as TNF, IL-6 and leptin
TNF and IL-6 have a role in degredation of articular cartilage
What are the three overlapping phased of articular cartilage changes with OA?
- In beginning, extracellular matrix degrades on a molecular level, water content increased, size of aggregan molecules decreased and structure of collagen network is damaged leading to reduced stiffness
- Second, chondrocytes try to compensate through enhanced proliferation and metabolic activity. Cell clusters appear surrounded by newly synthesised matrix molecules.
- Finally, chondrocytes are no longer able to keep up, resulting in conplete loss of cartilage tissue
Imbalance between anabolic and catabolic processes. Initially there is an increase in cartilage thickness and swelling
What inflammatory cytokines are known to upregulate the synthesis of MMPs and other proteolytic enzymes?
- IL-1
- IL-17
- IL-18
- TNF-a
Synthesis of tissue inhibitors of metalloproteinases (TIMPS) are concomitantly decreased
What role does COX play in OA?
Chondrocytes from human OA cartilage explants express COX-2 and spontaneously produce PGE2
- PGE2 decreases proteoglycan synthesis and enhances degradation of aggercan and Type II collagen
- Upregulation of MMP-13, disintegrin and ADAMTS-5
- Downregulation of MMP-1
What role does NO play in OA?
NO is a major catabolic factor produced by chondrocytes in response to proinflammatory cytokines IL-1b and TNF-a
- Promotes chondrocyte apoptosis, most likely via mitochondrial dysfunction
What enzymes are known to degrade aggrecan, a very early event in canine OA?
- MMP-13
- Aggrecanases (ADAMTS-4, ADAMTS-5)
What enzymes can degrade the triple helix of Type II collagen?
- MMP-1 and MMP-13
- maybe MMP-8 and MMP-14
What is the most abundant noncollagenous protein in articular cartilage?
Cartilage oligomeric matric protein
What growth factors can stimulare aggrecan and collagen synthesis?
- IGF-1
- IGF-2
- TGF-b
What is the synovium?
A discontinuous layer of fibroblast-like and macrophage-like cells
What cell is a key cell in driving synovial control of cartilage metabolism?
Macrophages (through release of catabolic cytokines IL-1b and TNFa)
What are the precursors of osteophyte formation?
Mesenchymal stem cells in periosteum ot synovial lining
What fibres are found in joint nerves?
What are silent nociceptors?
- Abeta-fibers
- Adelta-fibers
- C-fibers
C-fibers are silent nociceptors because they do not respond to even noxious stimuli of the normal joint but begin to respond to mechanical stimuli during inflammation
What enzyme plays a role in central sensitisation?
COX enzymes