Several studies have demonstrated that inflammation in the subacromial bursa is an important component in the pathogenesis of impingement syndrome. We have demonstrated in a previous study that many inflammatory cytokines, including stromal cell-derived factor 1 (SDF-1, CXCL12), are increased in the subacromial bursa [Blaine et al. 2005. J Shoulder Elbow Surg 14(Suppl 1):84S-89S]. SDF-1 is a potent chemotactic and angiogenic factor that stimulates recruitment of inflammatory cells. In the current study, we proposed that the resident cells in subacromial bursal tissue produce SDF-1, which can play a role in the inflammatory reponse of bursal tissue, and that this chemokine can be regulated by steroid (dexamethasone) and nonsteroidal anti-inflammatory medications (NSAIDs).
Twenty-two subacromial bursa tissues (18 bursitis and 4 normal bursa) were obtained intraoperatively from patients during shoulder surgery and analyzed using the cDNA Array technique in accordance with an IRB approved protocol. cDNA array results were confirmed with real-time reverse transcription-polymerase chain reaction (RT-PCR). Bursal cells (from 4 normal bursa, 3 bursitis) and two normal bone marrow with whole tissue explants were cultured for one passage. Cell culture supernatants were collected and SDF-1 protein was detected with enzyme-linked immunosorbent assay (ELISA). Cultured bursal cells were treated with a COX-2 inhibitor and dexamethasone, and cells was harvested at 1-day and 4-day intervals. SDF-1 expression was evaluated by real-time RT-PCR and ELISA. cDNA Array analysis demonstrated that the gene expression of SDF-1 was increased in patients with subacromial bursitis compared to controls (p<0.05). Real-time RT-PCR also revealed that the mRNA expression of SDF-1 in bursitis tissue is increased 10-fold over control tissue. While the normal bursal cells produced negligible amounts of SDF-1 protein, cultured cells derived from bursitis lesion released as much SDF-1 protein (235 pg/100,000 cells) as normal bone marrow stromal cells (283 pg/100,000 cells) as measured by ELISA. The addition of a COX-2 inhibitor and dexamethasone to bursitis cell lines led to decreased SDF-1 expression levels compared to untreated bursitis cell lines. These studies demonstrate that there is a significant elevation of SDF-1 expression in the subacromial bursa of patients with rotator cuff disease. Furthermore, this chemokine can be downregulated by COX-2 inhibitors and steroids. These results provide biologic evidence for the use of steroid and NSAIDs in the treatment of subacromial bursitis. In the future, targeted inhibition of molecules such as SDF-1 in the subacromial bursa may present a therapeutic strategy that may avoid the side effects of these other (steroid and NSAID) medications.