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Aim To investigate the role of nitric oxide ( NO)-induced autophagy in human dental pulp cells ( HDPCs) and the involvement of AMP-activated protein kinase ( AMPK) pathway. Methodology The MTT assay was used to determine the cytotoxic effect of the NO donor sodium nitroprusside ( SNP) in HDPCs. Apoptosis was detected by means of the terminal deoxynucleotidyl transferase dUTP nick-end labelling ( TUNEL) assay, and apoptosis- or autophagy-related signal molecules were observed by Western blot analysis. Acidic autophagolysosomal vacuoles were stained with acridine orange to detect autophagy in the presence of 3-methyladenine (3 MA) used to inhibit autophagy. To explore the mechanism underlying autophagy and its protective role against apoptosis, compound C, the chemical AMPK inhibitor, was used. Statistical analysis was performed using Student's t-test or analysis of variance ( anova) followed by the Student-Newman-Keuls test ( P < 0.05). Results SNP decreased viability of the HDPCs in a dose- and time-dependent manner. Exposing the HDPCs to SNP increased the levels of p62 and LC3- II, the typical markers of autophagy, and increased the number of acidic autophagolysosomal vacuoles, indicating the appearance of autophagy as detected by acridine orange staining ( P < 0.05). Pre-treatment with 3 MA decreased cell viability but increased cleaved poly( ADP-ribose) polymerase ( PARP) and caspase-3, apoptosis indicators, in the SNP-treated HDPCs ( P < 0.05). SNP activated AMPK/ ULK signalling, whilst the inhibition of AMPK by compound C enhanced apoptotic cell death induced by SNP in the HDPCs ( P < 0.05). Conclusion NO induced autophagy with AMPK activation, which plays a role in the survival of HDPCs against NO-induced apoptosis. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the role of the passive layers in galvanic corrosion of Ti-Nb alloys and commercially pure titanium (cp-Ti). Ti-Nb alloys with 5, 10, 15, and 20 wt% niobium (Nb) content were prepared using an arc-melting technique under high purity Ar gas. The cp-Ti was used as a control. The electrochemical corrosion behaviors were investigated by A.C. impedance, potentiodynamic polarization, and galvanic corrosion tests. According to the results of impedance analysis, the passivation layer on Ti-Nb alloys consisted of outer, intermediate, inner, and metal defect layers, while the passivation layer on cp-Ti consisted of outer, intermediate, and inner layers. According to the results of anodic polarization tests, Ti-Nb alloys exhibited better zero potentials and reduced zero current densities. The outer layer and the inner layer of Ti-Nb alloys and cp-Ti had an effect mainly on the values of the initial galvanic current density and the sign of galvanic current density, respectively. Ti-10Nb alloy exhibited a relatively high initial galvanic current density compared to the other Ti-Nb alloys. Unlike Ti-5Nb, Ti-10Nb, and Ti-15Nb, which exhibited galvanic current densities with a minus sign, Ti-20Nb exhibited a galvanic current density with a plus sign due to its weaker inner layer than that of Ti. [ABSTRACT FROM AUTHOR]