Combination of growth factor gene-enhanced cartilage matrix synthesis with interleukin-1 receptor antagonist protein (IL-1Ra) abrogation of cartilage matrix degradation may reduce and possibly reverse cartilage loss in synovitis and osteoarthritis. The feasibility of cotransduction of synovial membrane with two such genes that may act on cartilage homeostasis was investigated in an in vitro coculture system. Cultured synoviocytes in monolayer were cotransduced with E1-deleted adenoviral vectors, one containing IGF-I coding sequence under cytomegalovirus (CMV) promoter control (200 multiplicities of infection (moi)), and the second containing IL-1Ra sequence under CMV promoter control (100 moi). Adenovirus-IGF-I (AdIGF-I) transduction and AdIGF-I/AdIL-1Ra cotransduction of synovial monolayer cultures resulted in increased IGF-I mRNA and ligand expression, and similarly AdIL-1Ra and AdIGF-I/AdIL-1Ra-transduced cultures expressed high levels of IL-1Ra. Northern analysis confirmed a single mRNA transcript of the appropriate size for both IGF-I and IL-1Ra transgene expression. Synovial cell monolayer and cartilage explant coculture experiments were used to examine the effects of IGF-I and IL-1Ra protein expressed by transduced synoviocytes on normal and IL-1-depleted cartilage. Transduced monolayer cultures produced peak medium IGF-I content of 114+/-20.2 ng/ml and IL-1Ra levels of 241.8+/-10.5 ng/ml at 48 h after transduction. These IGF-I concentrations were sufficient to produce significantly increased proteoglycan (PG) content of normal cartilage cultured in medium conditioned by AdIGF-I and AdIGF-I/AdIL-1Ra-transduced synoviocytes. Interleukin-1-exposed cartilage was markedly depleted of PG, and this catabolic state was partially reversed in AdIGF-I-transduced cultures and fully reversed by AdIGF-I/AdIL-1Ra-transduced synovial cocultures. These data indicate that cultured synoviocytes are readily cotransduced by two recombinant adenoviral vectors containing transgenes active in restoring joint health. The AdIL-1Ra and AdIGF-I transgenes were abundantly expressed and the secreted products achieved therapeutic concentrations by day 2. The resulting increase in matrix biosynthesis returned cartilage PG content to normal levels. These data suggest that there may be significant value in cotransduction of synovial membrane to attenuate cartilage malacia associated with synovitis, injury, or early arthritis.