Increasing doses of CDDO inhibit the expression of MMP-1, MMP-13, and Bcl-3 in human primary chondrocytes. Human primary chondrocytes (passage 1) were treated for 24 hours with 300 nM to 5 μM CDDO before the addition of 10 ng/ml IL-1. After a further 18 hours of culture, RNA was harvested, reverse transcribed and subjected to quantitative real-time PCR for MMP-1 (a), MMP-13 (b), and Bcl-3 (c). Results were normalized to GAPDH, and are means of culture triplicates. They are expressed as molecules per molecule of GAPDH. Two-tailed Student's t-tests were performed on the data, and significance is indicated as follows: *P < 0.1; **0.01 <P < 0.05; ***P < 0.01.