Background/Purpose: Recent advanced imaging studies have demonstrated that urate deposition in periarticular structures is common in gout. Urate deposition has been observed both adjacent to and within tendons, suggesting that monosodium urate monohydrate (MSU) crystals are likely to be in direct contact with tenocytes, the stromal cells of tendons.  The aim of this study was to determine the effects of MSU crystals on tenocyte viability and function.   

Methods: Cultures of primary rat tenocytes were prepared from Wistar rat tails. Primary human tenocytes were prepared from patients undergoing orthopedic surgery. MTT assays were used to assess tenocyte viability following culture with MSU crystals.  Cells cultured with MSU crystals for various times were stained with Annexin V and propidium iodide, and flow cytometry was used to determine changes in the levels of apoptosis.  Real-time PCR was used to determine changes in gene expression and Sirius red staining to detect changes in collagen deposition in tenocytes cultured with MSU crystals. 

Results: MSU crystals reduced viability in a dose-dependent manner in both primary rat and human tenocytes (Figure).  Differing MSU crystal lengths and increased serum levels in cultures did not alter this effect.  The reduction in tenocyte viability was specific to MSU crystals, as soluble uric acid did not reduce cell viability.  Flow cytometry showed that MSU crystals rapidly induced cell death, but apoptosis levels remained unchanged.  Culture with MSU crystals reduced mRNA expression of collagen types 1 and 3; and tenocytic markers, including tenomodulin, scleraxis and tenascin-C.  Collagen deposition was inhibited in tenocytes cultured with MSU crystals in a dose dependent manner.

Conclusion: These data indicate that MSU crystals directly interact with tenocytes to reduce cell viability and function.  These interactions may contribute to tendon damage in patients with chronic gout. 

Figure:  Effects of MSU crystals on primary rat and human tenocyte viability.  Cell viability was assessed using the MTT assay following 24 hours of culture with MSU crystals.  Data shown are mean (SEM); one-way ANOVA (P<0.0001) with post hoc Dunnett’s test *p<0.0001 versus control (no MSU crystals).