Restandardization of adjuvant-induced arthritis in rats: biochemical, radiological and histopathological characterization

Adjuvant-induced arthritis (AIA) was used to study pathobiological changes occurring in rheumatoid arthritis in humans. AIA was induced by a single 0.1 ml intradermal injection of a suspension of heat-killed Mycobacterium tuberculosis in paraffin oil at various dose levels into the footpad of male Wistar rats. The induction rate of arthritis was increased to 80-90% by using delipidated cultures. The levels of lysosomal enzymes, such as acid phosphatase and cathepsin D in serum, liver and bone increased significantly at 500 and 1,000 mu g doses. The presence of marker protein (72 kD) in the serum samples (500 and 1,000 mu g doses) together with soft tissue swelling and joint space narrowing was confirmed. Histopathology of the arthritic ankle joints showed extensive leucocyte infiltration, synovial hyperplasia and pannus formation at the highest dose levels. This model could be used for the evaluation of antiarthritic drugs with more efficacy and less toxicity.