Bone Abstracts

Delayed fracture healing is frequently experienced in patients with systemic inflammation such as during rheumatoid arthritis (RA). The reasons for this are diverse, but could also be caused by inflammatory cytokines and/or growth factors in serum from patients with active disease. We hypothesized that serum from patients with active RA contains circulating inflammatory factors that inhibit differentiation of osteochondrogenic precursors.

Serum was obtained from 15 patients with active RA (active RA-sera) and from the same patients in clinical remission 1 year later (remission RA-sera; controls). The effect of active RA-sera on osteochondrogenic differentiation of chondrogenic ATDC5 cells and primary human periosteum-derived progenitor cells was determined in micromass culture. Chondrogenic and osteogenic gene expression was analysed by qPCR. We analysed cartilage matrix accumulation by alcian blue staining, and matrix mineralization by alizarin red staining. Metabolic activity of cells was analysed by using presto blue assay.

In ATDC5 cells, active RA-sera reduced Ki67 transcription levels by 40% and cartilage matrix accumulation by 14% at day 14, and Alp transcription levels by 16%, and matrix mineralization by 17% at day 21 compared to remission RA-sera. In human periosteum-derived progenitor cells, active RA-sera inhibited metabolic activity by 8%, SOX9 transcription levels by 14%, and cartilage matrix accumulation by 7% at day 7 compared to remission RA-sera.

In conclusion, our study shows that active RA-sera inhibit osteochondrogenic differentiation of precursor cells. These findings provide important new insight regarding the role of factors present in the serum of patients with systemic inflammation in delayed fracture healing, and suggest that mitigation of systemic inflammation, by agents that do not affect fracture healing directly themselves (e.g. COX2 inhibitors), might rescue delayed fracture healing in patients with systemic inflammatory disease.