Background: Gingival overgrowth is a common side-effect following administration of cyclosporin A. We reported previously that lysosomal protease cathepsin-L activity, but not cathepsin-B, was significantly suppressed by short-term cyclosporin A exposure in human gingival fibroblasts. Although this suppression may lead to decreased degradation of gingival connective tissue, a net increase in matrix proteins, and gingival overgrowth, the effects of cyclosporin A need to be more elucidated, considering the long-term use for patients following organ transplantation. Objective: The aim of the present study was to evaluate the effects of clinically relevant doses of cyclosporin A on cultured human gingival fibroblasts. We evaluated the effects of long-term cyclosporin A exposure on cell proliferation, mRNA expression of various proteases and both cathepsin-B and -L activity in human gingival fibroblasts. Materials and Methods: Human gingival fibroblasts were isolated from three donors' healthy gingiva and cultured from five to eight passages with or without 200 ng/ml of cyclosporin A. Proliferative activity of cyclosporin A-treated cells was examined using MTT assay. Total RNA and cellular proteins were collected for semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) analysis and for measurement of the cathepsin-B and -L activity. Results: Long-term cyclosporin A exposure had no effects on cell proliferation. Accumulation of cathepsin-B, -H and -L mRNA was markedly suppressed by long-term cyclosporin A exposure, whereas accumulation of another lysosomal enzyme N-acetyl-β-D-glucosaminidase mRNA, which is involved in remodeling of gingival epithelium, was not apparently impaired in cyclosporin A-treated cells. Accumulation of matrix metalloprotease-1 (MMP-1) and tissue inhibitor of matrix metalloprotease-1 (TIMP-1) mRNA, which are involved in remodeling of extracellular matrix, also was not impaired. In addition, we demonstrated that long-term cyclosporin A exposure significantly suppressed not only the activity of the active form of cathepsin-(B + L) compared to the activity in non-treated cells (p = 0.0458), but also the activity of the active form of cathepsin-B (p < 0.0001) in human gingival fibroblasts. Conclusion: The decreased ability of protein degradation by not only cathepsin-L but also cathepsin-B is, at least, one of the several factors developing the cyclosporin A-induced gingival overgrowth.
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