Curcumin Inhibits Thrombin-Stimulated Connective Tissue Growth Factor (CTGF/CCN2) Production Through c-Jun NH2-Terminal Kinase Suppression in Human Gingival Fibroblasts

Background: Connective tissue growth factor (CTGF/CCN2), associated with multiple human fibrotic diseases, is overexpressed in the tissue of gingival overgrowth. Although surgical excision is the current treatment modality for gingival overgrowth, the recurrent rate is high despite proper recall programs. Thrombin plays a key role in wound repair, remodeling, and fibrosis after injury and exerts profibrotic effects by activating protease-activated receptors (PARs). Curcumin [1,7-bis(4-hydroxy-3-methoxyphenyl)-1, 6-heptadiene-3,5-dione] is a natural plant phenolic compound that possesses both anti-inflammatory and antioxidant properties. This study investigates the signaling pathway of thrombin-induced CCN2 expression and inhibition of CCN2 expression by curcumin. Methods: The signaling pathway of thrombin-induced CCN2 expression in human gingival fibroblasts (HGFs) was studied using Western blot analysis. The CCN2 mRNA level was determined by quantitative reverse transcription-polymerase chain reaction. Results: Thrombin induced CCN2 expression in HGFs by activating PAR I. Pretreatment with antioxidant N-acetyl-L-cysteine, apoptosis signal-regulating kinase 1 (ASK 1) inhibitor thioredoxin, and c-Jun NH2-terminal kinase (JNK) inhibitor SP600125 (anthra[1,9-cd]pyrazol-6(2H)-one) significantly reduced thrombin-induced CCN2 expression in HGFs. Curcumin dose dependently inhibited thrombin-induced CCN2 expression through JNK suppression in HGFs. Conclusions: The results of this study suggest that thrombin-induced CCN2 expression may occur through PAR I, reactive oxygen species, ASK I, and JNK signaling in HGFs. Curcumin could effectively inhibit CCN2 expression through JNK suppression. These signaling events are important for wound healing and fibrosis. Additional research, including animal studies, is required to confirm the inhibiting role of curcumin in the development of gingival overgrowth. J Periodontol 2012;83:1546-1553.