The effect of lipopolysaccharide on growth factor-induced mitogenesis in human gingival fibroblasts

Quiescent and non-quiescent human gingival fibroblasts (HGF) were incubated for 24 hours with Actinobacillus actinomycetemcomitans lipopolysaccharide (LPS) and/or growth factors (interleukin-1 beta [IL-1 beta], insulin, epidermal growth factor [EGF], platelet-derived growth factor [PDGF], fibroblast growth factor [FGF], and transforming growth factor-beta [TGF-beta]) to examine the ability of LPS to modify HGF proliferation in response to these autocrine and paracrine growth factors. A. actinomycetemcomitans LPS at high concentrations (> or = 9 micrograms/well) generally resulted in a reduction in DNA synthesis in quiescent and non-quiescent fibroblasts; however, LPS at low concentrations (< 9 micrograms/well) showed a minimal enhancement of DNA synthesis (40 to 60%) in quiescent and non-quiescent cells. HGF co-incubated with mitogenic agents and LPS (9 micrograms/well) exhibited suppression of growth factor-induced 3H-Tdr uptake compared to growth factor-stimulated controls. In contrast, 3H-Tdr uptake was slightly elevated with addition of LPS at low concentrations (0.09 microgram/well). These trends were seen with all growth factors tested. Non-quiescent cells, in general, were more responsive to the growth factors and LPS/growth factor combinations when compared to the quiescent HGF. HGF were further tested for the ability of LPS to alter growth factor responsiveness by pretreating the cells with LPS prior to incubation of the growth factor, as well as, subsequent addition of LPS to growth factor-pretreated cells. Similar patterns were observed as above, except IL-1 beta-pretreated quiescent and non-quiescent HGF followed by LPS addition demonstrated a marked elevation in proliferation when compared to IL-1 beta stimulated controls. These findings suggest that LPS may potentially modulate the proliferative rate of connective tissue undergoing inflammatory or growth factor-induced reparative processes in periodontal lesions.