Provided are siRNA molecules that are particularly efficient in their ability to reduce transcription and expression of TNF or IL-1β in canine macrophage and synovial cells. The siRNA molecules demonstrate improved silencing of TNF or IL-1β as compared to siRNA molecules disclosed prior to the present invention. These properties are demonstrated in accepted experimental models of osteoarthritis, and particularly canine osteoarthritis. The siRNA molecules of the invention, may be employed in pharmaceutical compositions for use in the prevention and/or reduction of osteoarthritis in dogs. The inventors have found that encapsulation of the siRNAs in small PLGA microspheres confers surprisingly advantageous properties.
