Normal function of gingival fibroblasts is essential for maintenance of the gingival extracellular matrix (ECM), but under inflammatory conditions in gingival tissue which may occur with tobacco use, they can also act in its destruction. The purpose of this study was to determine the effects of nicotine, a major component of tobacco, on gingival fibroblast proliferation, the production of fibronectin (FN), and the production and breakdown of type I collagen to elucidate its role in periodontal destruction associated with its use. A human gingival fibroblast strain derived from a healthy individual with non-inflamed gingiva was used in this study. Nicotine at concentrations > 0.075% caused cell death, and at 0.075% and 0.05% it caused transient vacuolization of the fibroblasts. At concentrations of 0.001% to 0.075%, nicotine significantly inhibited proliferation (P < or = 0.03), measured by the incorporation of [3H]-thymidine into DNA. The production of FN and type I collagen was significantly inhibited by nicotine at > or = 0.05% (P < or = 0.001), measured using specific ELISAs. On the other hand, nicotine at > or = 0.025% significantly increased collagenase activity (P < or = 0.008), using [3H]-gly and [14C]-pro-labeled type I collagen gels as substrate. The results show that, in vitro, nicotine inhibits the growth of gingival fibroblasts and their production of FN and collagen, while also promoting collagen breakdown. This suggests that nicotine itself may augment the destruction of the gingival ECM occurring during periodontal inflammation associated with smokeless tobacco use.