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Background: Transforming growth factor (TGF)-β1 is involved in the pathogenesis of both drug-induced gingival overgrowth and hereditary gingival fibromatosis. Ribozymes enzymatically cleave target mRNAs and are expected to be utilized as the basis of novel nucleic acid-based therapies. We designed a chimeric DNA-RNA ribozyme targeting TGF-β1 mRNA and examined its effect on growth of gingival fibroblasts in culture. Methods: Chimeric DNA-RNA hammerhead ribozyme with sequence complementary to the loop structure of human TGF-β1 mRNA was used. We evaluated transfer of the chimeric ribozyme by hemagglutinating virus of Japan (HVJ)-envelope into cultured human gingival fibroblasts in vitro and rat gingival tissues in viva. We then examined effects of the chimeric ribozyme to TGF-β1 on proliferation and DNA synthesis in human gingival fibroblasts. We also examined effects of the chimeric ribozyme to TGF-β1 on expression of TGF-β1, type IV collagens, and fibronectin mRNAs and expression of TGF-β1 protein in human gingival fibroblasts. Results: Chimeric ribozyme was sufficiently distributed into human fibroblasts in vitro and rat gingivae in vivo. Chimeric ribozyme to TGF-β1 significantly inhibited expression of TGF-β1, type IV collagen, and fibronectin mRNAs and TGF-β1 protein in human gingival fibroblasts. Mismatch ribozyme had no effect on expression of these molecules. Chimeric ribozyme to TGF-β1 also significantly inhibited proliferation and DNA synthesis in gingival fibroblasts. Conclusion: Chimeric DNA-RNA ribozyme targeting TGF-β1 may be a useful gene therapy agent for treatment of gingival hyperplasia. [ABSTRACT FROM AUTHOR]