VEGF and CD31 expression in arthritic synovium and cartilage of human knee joints

To determine the histological differences and the particular aspects of local angiogenesis in knee joint of the patients with osteoarthritis (OA) and rheumatoid arthritis (RA).

In 10 cases with RA and five OA, immunohistochemical stains were performed with CD31 and VEGF-A (Vascular Endothelial Growth Factor). All surgical samples provided from total knee joint arthroplasty. Angiogenesis was quantified in both synovial membrane and cartilage.

In patients with OA, villous proliferation of the synovial membrane was more prominent that in RA. In the last, invasion of the cartilage by the proliferated synovial tissue was more characteristic. The neovascularization was more intense in RA than in OA, in both synovium and degenerated cartilage. In RA, the vessels were immature in the superficial areas and became larger in the deep synovium. The local angiogenesis was characterized by sprouting and splitting (intussusceptions) mechanisms. In OA, the mature vessels predominated in the subintimal zones. Sprouting or non-sprouting mechanisms of local angiogenesis, which can indicate vascular formation from the resident mature vessels, were not identified in OA.

Angiogenesis seems to have particular behavior in RA and OA. In RA, local active angiogenesis seems to predominate but in OA up taking of the circulating precursors may be more intensely involved. Intra-articular inhibition of local angiogenesis could have therapeutically impact in RA but not in OA. Finally, we can conclude that there probably are many different pathways leading to the same joint damage having certain therapeutic consequences.