Extracts of irradiated mature human tooth crowns contain MMP-20 protein and activity

Objectives: We recently demonstrated a significant correlation between enamel delamination and tooth-level radiation dose in oral cancer patients. Since radiation can induce the synthesis and activation of matrix metalloproteinases, we hypothesized that irradiated teeth may contain active matrix metalloproteinases. Materials and methods: Extracted teeth from oral cancer patients treated with radiotherapy and from healthy subjects were compared. Extracted mature third molars from healthy subjects were irradiated in vitro and/or incubated for 0-6 months at 37 degrees C. All teeth were then pulverized, extracted, and extracts subjected to proteomic and enzymatic analyses. Results: Screening of irradiated crown extracts using mass spectrometry identified MMP-20 (enamelysin) which is expressed developmentally in dentine and enamel but believed to be removed prior to tooth eruption. MMP-20 was composed of catalytically active forms at Mr = 43, 41, 24 and 22 kDa and was immunolocalized predominantly to the morphological dentine enamel junction. The proportion of different sized MMP-20 forms changed with incubation and irradiation. While the pattern was not altered directly by irradiation of healthy teeth with 70 Gy, subsequent incubation at 37 degrees C for 3-6 months with or without prior irradiation caused the proportion of Mr = 24-22 kDa MMP-20 bands to increase dramatically. Extracts of teeth from oral cancer patients who received > 70 Gy radiation also contained relatively more 24 and 22 kDa MMP-20 than those of healthy age-related teeth. Conclusion: MMP-20 is a radiation-resistant component of mature tooth crowns enriched in the dentine-enamel. We speculate that MMP-20 catalyzed degradation of organic matrix at this site could lead to enamel delamination associated with oral cancer radiotherapy. (C) 2014 Elsevier Ltd. All rights reserved.