THE DETERMINATION OF PYRIDINIUM CROSS-LINKS IN URINE AND SERUM AS A POSSIBLE MARKER OF CARTILAGE DEGRADATION IN RHEUMATOID-ARTHRITIS

The determination of the collagen crosslinks pyridinoline (Pyd) and de oxypyridinoline (Dpyd) seems to be a successful way of characterizing topic destructive processes in rheumatoid arthritis (RA). Dpyd is a sp ecific marker of collagen I resorption in bone, whereas Pyd is release d from types I and II collagen in bone and cartilage. Both crosslinks were examined in 38 RA patients concurrently by RP-gradient-HPLC in ur ine and serum. A positive correlation was found between the inflammato ry activity (measured by CrP) and. the level of collagen crosslinks in urine. A correlation between serum and urine concentrations was demon strable for Pyd, but not for Dpyd. Different elimination kinetics for fragments containing either Pyd or Dpyd are a possible explanation for this observation. The ratio of Pyd/Dpyd is known to be a useful marke r to distinguish between destruction of cartilage and bone collagen. B ecause the Pyd/Dpyd ratio in urine does not necessarily correspond to that in serum, probably as a result of metabolic or elimination proces ses, the usefulness of the relationship between the crosslinks in urin e as a method of differentiating between cartilage and bone degradatio n must be questioned.