RESUMO
We investigated the effect of Pd and Ni dopants on the formation and desorption of tritiated water (T2O) molecules from the Li2TiO3 (001) surface using first-principles calculations coupled with the climbing-image nudged elastic band method. We calculated the energy barriers for T2O production and desorption on the pure Li2TiO3 surface to be 0.94 and 0.64 eV, respectively. The Pd and Ni dopants enhanced T2O formation by reducing the formation energy of O vacancies, and T2O generated spontaneously on the dopant surface. Moreover, we found that dopant atoms affect the charge transfer of neighboring atoms, which leads to orbital hybridization and the generation of a chemical bond between the O and T on the doped Li2TiO3 surface. In addition, desorption of T2O from the doped Li2TiO3 surface requires a relatively low energy (<0.50 eV). This theoretical study suggests that doping the Li2TiO3 surface with metal atoms is an effective strategy for producing T2O molecules and is beneficial to T release.
RESUMO
AIM: Cigarette smoking is a risk factor in the development of periodontal diseases. In addition, a delayed healing process has been shown in smokers compared with non-smokers after periodontal treatment. Cell migration is a key process of wound healing and it is highly regulated by a variety of signalling pathways. The small G protein, Rac, is necessary for cell migration. Our aim was to determine if nicotine disrupted Rac and its downstream signalling proteins, p21-activated kinase 1/2 (PAK1/2), and p44/42 mitogen-activated protein kinase (MAPK) (extracellular regulated kinase 1/2). MATERIAL AND METHODS: Primary human fibroblasts from healthy gingival tissues were cultured and grown to confluence. Cells were serum starved for 24 h, and then treated with nicotine (0 or 0.5 microM) prior to in vitro wounding. Cell migration was analysed in live cell assays following in vitro wounds. Rac activity, phosphorylation levels of PAK1/2, and p44/42 MAPK were assessed in cultures treated with or without nicotine after multiple wounds. RESULTS: Nicotine decreased cell migration rates by 50% compared with controls. In addition, nicotine altered the activation patterns of Rac and PAK 1/2 and up-regulated p44/42 MAPK. CONCLUSION: Decreased cell migration in periodontal wounds exposed to nicotine may be mediated through the Rac and PAK1/2 signalling pathways.
Assuntos
Movimento Celular/efeitos dos fármacos , Nicotina/efeitos adversos , Agonistas Nicotínicos/efeitos adversos , Cicatrização/efeitos dos fármacos , Proteínas rac de Ligação ao GTP/efeitos dos fármacos , Análise de Variância , Polaridade Celular/efeitos dos fármacos , Fibroblastos/efeitos dos fármacos , Fibroblastos/fisiologia , Gengiva/efeitos dos fármacos , Gengiva/lesões , Humanos , Proteína Quinase 3 Ativada por Mitógeno/efeitos dos fármacos , Proteína Quinase 3 Ativada por Mitógeno/metabolismo , Proteínas Serina-Treonina Quinases/efeitos dos fármacos , Proteínas Serina-Treonina Quinases/metabolismo , Quinases Ativadas por p21 , Proteínas rac de Ligação ao GTP/metabolismoRESUMO
Cigarette smoking has been suggested as a risk factor for several periodontal diseases. It has also been found that smokers respond less favorably than non-smokers to periodontal therapy. Previous work in our lab has shown that nicotine inhibits human gingival cell migration. Since myofibroblasts play an important role in wound closure, we asked if nicotine affects gingival wound healing process by regulating myofibroblast differentiation. Human gingival fibroblasts (HGFs) from two patients were cultured in 10% fetal bovine serum cell culture medium. Cells were pretreated with different doses of nicotine (0, 0.01, 0.1, and 1 mM) for 2 h, and then incubated with transforming growth factor beta (TGF-beta1) (0, 0.25, 0.5, and 1 ng/ml) with or without nicotine for 30 h. The expression level of alpha-smooth muscle actin (alpha-SMA), a specific marker for myofibroblasts, was analyzed by Western blots, immunocytochemistry, and real-time polymerase chain reaction (real-time PCR). Phosphorylated p38 mitogen-activated protein kinase (Phospho-p38 MAPK) activity was analyzed by Western blots. TGF-beta1 induced an increase of alpha-SMA protein and mRNA expression, while nicotine (1 mM) inhibited the TGF-beta1-induced expression of alpha-SMA but not beta-actin. Nicotine treatment down-regulated TGF-beta1-induced p38 MAPK phosphorylation. Our results demonstrated for the first time that nicotine inhibits myofibroblast differentiation in human gingival fibroblasts in vitro; supporting the hypothesis that delayed wound healing in smokers may be due to decreased wound contraction by myofibroblasts.
