The effects of platelet-derived growth factor-BB on periodontal cells in an in vitro wound model

Background: Platelet-derived growth factor (PDGF-BB) has been shown to enha nce periodontal regeneration. Principles of guided tissue regeneration dict ate that one of the goals of therapy is to modulate the wound healing proce sses to favor repopulation of the wound with cells derived from the periodo ntal ligament rather than from the gingival tissues. Using an in vitro woun d model, gingival fibroblasts (GF) have been shown to fill a wound space si gnificantly faster than periodontal ligament cells (PDL). There are no data reported directly comparing the response of these 2 cell types to PDGF-BB within such a wound model. Therefore, the aims of this research were: 1) to characterize both the proliferative and wound fill (WF) effects of PDGF-BB within an in vitro model and 2) to compare specific growth factor effects between GF and PDL. Methods: Primary cultures of both human PDL and GF were derived from explan ted tissues and passaged to 12-well tissue culture plates. Triplicate cultu res of both cell types were grown to confluence and in vitro wounds were me chanically created, removing a 3 mm wide band of the cell layer across the diameter of the wells. The wells were then incubated for 2, 6, and 9 days i n media containing 0.1% fetal bovine serum (FBS) and 1 of 5 concentrations of PDGF-BB. At each time point, cells were pulsed with 5-bromo, 2-deoxyurid ine (BrdU) fixed, and nuclei were stained to measure BrdU incorporation (as a measure for proliferation). Cells were counter-stained with cytoplasmic stain to measure cell number. Quantitative analyses within the wound bounda ries, marginally (area of interest [AOI] 1) and centrally (AOI 2), were acc omplished using computer-assisted histomorphometry. Results: PDL exhibited a significantly greater proliferative response to PD GF-BB in both AOI when compared to GF (P <0.0001). The PDL exhibited increa sed levels of proliferation at concentrations of PDGF-BB greater than or eq ual to 10 ng/ml. By contrast, GF displayed no increase in proliferation in response to stimulation with PDGF-BB at any of the concentrations tested wh en compared to negative controls. The wound fill (WF) responses to PDGF-BB were similar between PDL and GF, with both cell types responding in an all or none fashion when measured at day 2, and in a concentration-dependent ma nner at later time points. The only significant difference in WF between PD L and GF occurred in AOI 2 in negative control medium (0 ng/ml of PDGF-BB), with GFs having greater (P <0.01) levels of WF over the 9 days. Conclusion: The findings from this study demonstrate differing effects of P DGF-BB on the proliferation of PDL and GF in this in vitro model. These res ults suggest that there may be cell-specific differences critical to period ontal wound healing that may be exploited in the development of new therapi es.