Introduction:
Osteoarthritis is a chronic degenerative process of multifactor etiology, still largely unexplained. The activity of antioxidant enzymes and concentration of lipid peroxidation products in synovial membrane can be indirectly inferred from its oxidation-reduction status. The role of synovial membrane in the pathogenesis of osteoarthritis is relatively poorly understood, probably due to the difficulties in the acquisition of the material.

Aim of the research:
We sought to understand the association between osteoarthritis development and the activities of several antioxidant enzymes and levels of selected oxidative stress biomarkers in synovial membranes of osteoarthritic patients.

Material and methods:
The synovial tissue samples were collected from 67 patients. Of these patients, 48 underwent endoprosthetic total hip replacement due to osteoarthritis (the examined group), while 19 underwent surgical repair of a traumatic femoral neck fracture (the control group). Homogenates of synovial membrane were prepared according to our published method. The biochemical analysis included: activity of copper-zinc superoxide dismutase (CuZn-SOD), glutathione peroxidase (GPx), glutathione reductase (GR), catalase (CAT), concentrations of protein, malondialdehyde (MDA), thiol groups, and total oxidant status (TOS).

Results:
When comparing the examined group with the control group, the activity of CuZn-SOD was significantly elevated and the activity of GPx and the level of thiol groups were significantly decreased, whereas the activities of GR, CAT, the levels of protein, MDA, and TOS remained unaltered.

Conclusions:
Osteoarthritis is associated with oxidative stress and altered activities of the antioxidant enzymes in synovial membrane. However, lipid peroxidation seems not to be important for the etiology and development of osteoarthritis.