Figure 5. The change of protein expression in cartilage explants. (A) Immunohistochemical detection of MMP-13 and p16INK4a in cartilage explants which were stimulated with IL-1β (50 ng/mL) for 48 h, and then co-cultured with metformin (4 mM and 8 mM) for 5 days. (B) Quantification of cells positively stained for matrix metalloproteinase-13 and p16INK4a. ***P < 0.001 between the two groups.