Abstract

Objective - To evaluate the antioxidant effects of synovial fluid (SF) pooled from metacarpophalangeal joints of healthy horses or horses with various pathological conditions, and to compare them with the antioxidant effects of hyaluronic acid (HA) and chondroitin sulfate (CS). Sample Population - SF from 1 metacarpophalangeal joint was obtained from 42 horses immediately after humane slaughter. Samples were classified into 3 groups on the basis of origin: healthy joints or joints with chronically damaged cartilage or vascularly congested synovial membranes as detected via macroscopic evaluation. Procedures - Antioxidant effects were evaluated by use of rat liver microsomal fractions treated with Fe3+-ascorbate as a free radical generator system leading to oxidative stress. Amounts of thiobarbituric-reactive substances and glutathione transferase (GSH-T) conjugation activity were measured. Results - SF from healthy and chronically damaged joints inhibited microsomal lipid peroxidation, whereas SF from joints with congested synovial membranes had only a slight effect. Hyaluronic acid and CS did not inhibit microsomal lipid peroxidation. Moreover, GSH-T activity was detected in all SF samples, which had similar activity regardless of disease status. All SF samples as well as HA and CS protected rat microsomal GSH-T activity against oxidative damage. Only SF samples from joints with congested synovial membranes protected microsomal thiols against oxidation, an effect also evident with HA and CS. Conclusions and Clinical Relevance - The antioxidant mechanisms associated with the response to metacarpophalangeal joint damage in horses appeared to act on different targets, depending on whether the damage was acute or chronic.