Nitric oxide inhibits androgen receptor-mediated collagen production in human gingival fibroblasts

Lin S‐J, Lu H‐K, Lee H‐W, Chen Y‐C, Li C‐L, Wang L‐F. Nitric oxide inhibits androgen receptor‐mediated collagen production in human gingival fibroblasts. J Periodont Res 2012; 47: 701–710. © 2012 John Wiley & Sons A/S Background and Objective: In our previous study, we found that flutamide an androgen receptor (AR) antagonist] inhibited the up‐regulation of collagen induced by interleukin (IL)‐1β and/or nifedipine in gingival fibroblasts. The present study attempted to verify the role of nitric oxide (NO) in the IL‐1β/nifedipine‐AR pathway in gingival overgrowth. Material and Methods: Confluent gingival fibroblasts derived from healthy individuals (n = 4) and those with dihydropyridine‐induced gingival overgrowth (DIGO) (n = 6) were stimulated for 48 h with IL‐1β (10 ng/mL), nifedipine (0.34 μm ) or IL‐1β + nifedipine. Gene and protein expression were analyzed with real‐time RT‐PCR and western blot analyses, respectively. Meanwhile, Sircol dye‐binding and the Griess reagent were, respectively, used to detect the concentrations of total soluble collagen and nitrite in the medium. Results: IL‐1β and nifedipine simultaneously up‐regulated the expression of the AR and type‐I collagen α1 Colα1(I)] genes and the total collagen concentration in DIGO cells (p < 0.05). IL‐1β strongly increased the expression of inducible nitric oxide synthase (iNOS) mRNA and the nitrite concentration in both healthy and DIGO cells (p < 0.05). However, co‐administration of IL‐1β and nifedipine largely abrogated the expression of iNOS mRNA and the nitrite concentration with the same treatment. Spearman’s correlation coefficients revealed a positive correlation between the AR and total collagen (p < 0.001), but they both showed a negative correlation with iNOS expression and the NO concentration (p < 0.001). The iNOS inhibitor, 1400W, enhanced IL‐1β‐induced AR expression; furthermore, the NO donor, NONOate, diminished the expression of the AR to a similar extent in gingival fibroblasts derived from both healthy patients and DIGO patients (p < 0.05). Conclusion: IL‐1β‐induced NO attenuated AR‐mediated collagen production in human gingival fibroblasts. The iNOS/NO system down‐regulated the axis of AR/Colα1(I) mRNA expression and the production of AR/total collagen proteins by DIGO cells.