Metabolic activity and gene expression of osteoarthritic chondrocytes in correlation with radiological and histological characteristics

The aim of this study was to analyze metabolic activity of osteoarthritic chondrocytes in correlation with radiographic, histologic and gene expression data. Six patients with osteoarthritis (OA) of the knee were analyzed clinically and radiographically (Kellgren and Lawrence, K&L). During total knee replacement surgery cartilage samples from the medial and lateral condyles and tibial plateaus were separately harvested. Specimen were analyzed histologically (Mankin Score) and total RNA was extracted. Steady state levels of stromelysin (MMP-3), aggrecan (AGG) and the house-keeping gene β-actin were measured using quantitative PCR. In order to estimate metabolic activity chondrocytes were cultured in alginate beads and proteoglycan content was measured after 1 week. PG content in cultures was dependent from degradation status of cartilage (medial compartments 20.4 ± 0.83 ng/ng, lateral compartments 29.9 ± 3.0 ng/ng P < 0.01). We found a positive correlation of PG content in cultures with Mankinʹs grading (r = 0.79; P < 0.01) and with K&L scoring (r = 0.57; P = 0.05). There was a considerable variation of expression levels of MMP-3 and AGG. PG metabolism of cultured chondrocytes correlated only with the macroscopic and microscopic degradation status of cartilage. Gene expression showed a high variability and no correlation to PG metabolism indicating a more complex regulation.