Individual isomers of conjugated linoleic acid reduce inflammation associated with established collagen-induced arthritis in DBA/1 mice.

Previously, dietary conjugated linoleic acid [(CLA), an equal mixture of cis-9, trans-11 (c9t11) and trans-10, cis-12 (t10c12) CLA isomers], was found to reduce inflammation in the murine collagen antibody-induced arthritis model, but less so in the murine collagen-induced arthritis (CIA) model, an arthritic model dependent upon acquired immunity. Because CLA is known to alter the acquired immune response, it was hypothesized that feeding CLA after the establishment of arthritis would reduce paw swelling in the CIA model. In this study, upon the establishment of arthritic symptoms, mice were randomized to the following dietary treatments: corn oil (CO) control (n = 6), 0.5% c9t11-CLA (n = 8), 0.5% t10c12-CLA (n = 6), or 1% combined CLA (1:1 c9t11:t10c12-CLA, n = 6). Paws were scored for severity of arthritis and measured for changes in thickness during an 84-d study period. Dietary c9t11- and combined-CLA similarly decreased the arthritic score (29%, P = 0.036, P = 0.049, respectively, when normalized to initial score) and paw thickness (0.11 mm, P = 0.027, P = 0.035, respectively) compared with CO. Dietary t10c12-CLA reduced the arthritic score (41%, P = 0.007 when normalized) and paw thickness (0.12 mm, P = 0.013) relative to CO. Reduced interleukin-1beta on d 7 and 21 for all CLA treatments (n = 3) relative to CO suggested that antiinflammatory effects of CLA isomers might work by common mechanisms of known pathways involved in chronic inflammation. In conclusion, dietary CLA reduced inflammation associated with CIA, and both c9t11-CLA and t10c12-CLA exhibited antiinflammatory effects.