Relative contribution of matrix metalloprotease and cysteine protease activities to cytokine-stimulated articular cartilage degradation

Anabolic and catabolic function of chondrocyte ex vivo is reflected by the metabolic processing of type II collagen

OBJECTIVE

The aim of the present study was to investigate collagen metabolism after anabolic and catabolic stimulation of chondrocytes ex vivo.

DESIGN

Metabolic activities in ex vivo bovine cartilage explants were stimulated with insulin-like growth factor I (IGF-I) or a combination of tumor necrosis factor alpha (TNFalpha) and oncostatin M (OSM). Supernatants were assessed for changes in biochemical markers, N-terminal propeptide of type II (PIINP) collagen and fragments of C-telopeptide of type II collagen (CTX-II). Matrix metalloproteinases (MMP) were added to metabolic inactivated cartilage and evaluated by the two biochemical markers for formation or degradation, respectively. Finally, urinary CTX-II and PIINP were evaluated for assessment of type II collagen turnover in patients with rheumatoid arthritis (RA).

RESULTS

In the bovine articular cartilage explants, IGF-I induced an increase in PIINP level up to 4.8+/-1.1[ng/ml]/mg cartilage whereas CTX-II remained below 0.1+/-0.1[ng/ml]/mg cartilage. In the catabolic stimulated explants both PIINP and CTX-II were released to the supernatant, reaching concentrations of 9.0+/-1.4 and 9.1+/-2.2[ng/ml]/mg cartilage, respectively. RA patients had significantly lower serum concentrations of PIINP (3.4+/-3.7 ng/ml) compared with those healthy individuals (18.7+/-12.41 ng/ml, P<0.001). In contrast, RA patients had significantly higher urinary CTX-II (0.8+/-0.8 mg/mmol) compared to the healthy controls (0.1+/-0.08 mg/mmol, P=0.004).

CONCLUSIONS

This study is the first to demonstrate that precursors and degradation products of type II collagen released into the supernatant can effectively reflect the anabolic and catabolic activities of stimulated cartilage explants.

Strontium ranelate reduces the urinary level of cartilage degradation biomarker CTX-II in postmenopausal women

OBJECTIVE

Strontium ranelate significantly decreases the risk of osteoporotic fractures. The objective of the present study was to investigate whether strontium ranelate (2 g/day) also affects cartilage brakedown as measured by urinary marker of cartilage degradation, designated CTX-II.

METHODS

A subgroup of 2617 postmenopausal osteoporotic women (aged 75.7+/-4.4 years) were selected from the TROPOS phase III study on the basis of a urinary sampling reported at each visit during the first three years of the study. When included in TROPOS, they were randomized to strontium ranelate or placebo in a double-blind fashion for 3 years. A calcium and vitamin D supplement was also provided to the subjects during the study. A marker of collagen type II degradation (CTX-II) corrected for urinary creatinine (CTX-II/cr.) was assessed at regular intervals throughout the study in 1310 patients in strontium ranelate group and 1307 patients in placebo group.

RESULTS

The response in CTX-II depended on time (p<0.0001), and this time dependency differed statistically significantly between groups (time x treatment) (p<0.0003). In addition, there was a statistically significant difference between treatments (p<0.0001). The difference in the response of CTX-II/cr. appeared already after three months, with the strontium ranelate-treated subjects having approximately 15-20% lower values than the placebo-treated subjects for the remaining study period (p<0.0001).

CONCLUSION

Treatment with strontium ranelate significantly decreases urinary excretion of CTX-II, a marker of cartilage destruction. Further studies are warranted to investigate an effect on cartilage formation and symptoms of osteoarthritis.