The effects of fluoride on proliferation and apoptosis of primary cultured rat ameloblast / 中华地方病学杂志

ABSTRACT

Objective To investigate the effects of fluoride at different concentrations on proliferation and apoptosis of primary rat ameloblast in vitro.Methods Ameloblasts were isolated from tooth germ of 4 days SD rat maxillomandibular molar and cultured in vitro.Cells were treated with NaF at 0.0 (control group),0.4,0.8,1.6,3.2 and 6.4 mmol/L for 24,48 and 72 h,respectively.Inverted microscope was used to observe cell morphology;immunochemistry method was used to identify ameloblasts;3-(4,5-dimethylthiazole-2)-2,5-diphenyl tetrazolium bromide (MTT) assay was applied to measure cell viability at each time point.The cells were treated with 1.6 mmol/L NaF for 24 and 48 h,or after 50 mol/L caspase pan-inhibitor Z-VAD-FMK pretreatment 1 h,1.6 mmol/L NaF treatment for 48 h.Cell apoptosis was then tested by flow cytometry.In addition,activation of caspase-3 and poly (ADP-ribose) polymerase (PARP) were assessed by Western blotting to explore potential involvement of caspase activation in NaF-induced apoptosis.All data analysis was performed using SigmaStat V 3.5 software.Results ①Primary rat ameloblasts were in polygonal shape at low density and appeared like paving stone at high density with obvious nucleus,showing typical morphological characteristics of cells with epithelial origin.②The results of immunochemistry assay indicated that the cultured cells were positive in cytokeratin 14 (CK14) and ameloblastin (AMBN) staining,in accordance with the immunocytochemical characteristics of ameloblasts.③The effects of NaF on ameloblast proliferation were in a dose-and time-dependent manner.For low dose NaF (0.4 and 0.8 mmol/L) groups,cells treated for 24 h had significantly higher cell proliferation rates than that of the control group (0.0 mmol/L,P ＜0.05),the proliferation indexes for 0.0,0.4 and 0.8 mmol/L groups were 1.00 ± 0.00,1.38 ± 0.11 and 1.29 ± 0.13,respectively;the same doses of NaF had no obvious influence on cell proliferation at 48 h (1.00 ± 0.00,1.16 ± 0.14 and 0.94 ± 0.07,P ＞ 0.05);cell proliferation indexes at 72 h were significantly lower than that of the control group (0.87 ± 0.03 and 0.80 ± 0.04,P ＜ 0.05).Medium dose of NaF (1.6 mmol/L) did not cause obvious alterations in cell proliferation at 24 h (0.90 ± 0.08,P ＞ 0.05);while cell proliferation indexes at 48 and 72 h were obviously reduced than that of the control group (0.38 ± 0.03 and 0.26 ± 0.04,P ＜ 0.01).For high NaF concentration (3.2 and 6.4 mmo]/L) groups,cell proliferation indexes were significantly decreased at all time points compared with control cells,the rates for 3.2 mmol/L groups were 0.57 ± 0.14,0.08 ± 0.03 and 0.00 ± 0.00,respectively,and the rates for 6.4 mmol/L groups were 0.11 ± 0.04,0.00 ± 0.00 and 0.00 ± 0.00,respectively (P ＜ 0.01).④Flow cytometry was used to detect apoptosis.The results showed that treatment with 1.6 mmol/L NaF resulted in significantly increased apoptosis in ameloblasts at both 24 h [(5.80 ± 2.03)％] and 48 h [(17.45 ± 4.97)％] compared to the control group [(2.59 ± 0.95)％,P ＜ 0.05].In cells pre-treated with pan-caspase inhibitor Z-VAD-FMK,NaF-induced apoptosis was significantly lower than that of cells treated with only 1.6 mmol/L NaF [(9.43 ± 3.79)％ vs (18.26 ± 3.39)％,P ＜ 0.05].⑤Cleavage of caspase-3 and PARP was detected in ameloblasts treated with 1.6 mmol/L NaF for 48 h.Conclusion Overdose fluoride could inhibit proliferation and induce apoptosis via activation of caspase cascade in primary cultured rat ameloblasts.