Dynamic Influence of pH on Metalloproteinase Activity in Human Coronal and Radicular Dentin

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The aim of this study was to evaluate the effect of pH on the activation of matrix metalloproteinases (MMPs) of human coronal (CD) and radicular dentin (RD). CD and RD were pulverized to powder, and proteins were extracted with 1% phosphoric acid. The extracted proteins and the demineralized powder were separately incubated in the following solutions: 4-aminophenylmercuric acetate (control) or a buffer solution at different pHs (2.5, 4.5, 5.0, 6.0, and 7.0). After incubation, proteins were separated by electrophoresis to measure MMP activities by zymography. To assess the solubilized dentin collagen, the demineralized dentin powder was sustained in incubation buffer, and the amount of hydroxyproline (HYP) released was measured. Zymography revealed MMP-2 gelatinolytic activities for CD and RD in all experimental groups. For both substrates, the lowest pH solutions (2.5, 4.5, and 5.0) yielded higher gelatinolytic activity than those obtained by the highest pH solutions (6.0 and 7.0). For HYP analysis, no detectable absorbance values were observed for pHs of 2.5 and 4.5. The amount of HYP was higher for pH 7.0 than those of all other groups (p < 0.05), except for pH 6.0. No statistical differences were found between pHs 6.0 and 5.0 and control (p > 0.05). The MMP-2 enzyme from human CD and RD is dynamically influenced by pH: at low pH, the extracted enzyme activates this latent form, whereas collagen degradation by the matrix-bound enzyme is only observed when pHs are close to neutral.

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