Release of cartilage and bone macromolecules into synovial fluid: differences between psoriatic arthritis and rheumatoid arthritis

Objective-To elucidate whether differences in the destructive tissue proces s in cartilage and bone in psoriatic arthritis (PsA) and rheumatoid arthrit is (RA) can be recognised by different release patterns of molecular fragme nts derived from joint tissue. Methods-Aggrecan, cartilage oligomeric matrix protein (COMP), and bone sial oprotein (BSP) were quantified by immunoassays in knee joint synovial fluid samples. These were obtained early in the disease course of patients with PsA and RA. At the time of arthrocentesis radiographs of their knee and hip joints were normal. Results-At follow up no destruction had developed in the knees and hips of most patients with PsA (n=18), whereas the patients with RA could be separa ted into one "destructive" group (n=18) and one "non-destructive" group (n= 25). Patients with PsA had low synovial fluid aggrecan concentrations (p<0. 001 v the RA destructive group) but high COMP concentrations (p<0.01 and p< 0.05 v destructive and non-destructive RA groups, respectively). Consequent ly, the aggrecan/COMP ratio was lowest in the PsA group (p<0.001 and p<0.01 v the destructive and nondestructive RA group, respectively). The synovial fluid concentrations of BSP did not differ between the three patient group s. Conclusions-The release pattern of aggrecan and COMP, reflecting cartilage turnover, differed between the PsA group and, particularly the destructive RA group. This suggests that different pathophysiological mechanisms for ca rtilage involvement operate in these conditions, with different destructive potential. The BSP concentrations did not differ between the patients grou ps, which indicates similar levels of bone involvement.