Adjuvant arthritis as a model of inflammatory cachexia.

OBJECTIVE: To determine whether adjuvant arthritis (AA) leads to changes in body composition and cytokine production similar to those seen in patients with rheumatoid arthritis. METHODS: AA was induced in Lewis rats using Freund's complete adjuvant. Body cell mass was measured by determining the concentration of total exchangeable potassium using 42K gavage. Splenocyte production of interleukin-1 (IL-1) and tumor necrosis factor alpha (TNF alpha) was measured by bioassay. Weight and food intake were also measured. RESULTS: Animals that developed AA lost 6% of their body weight by the onset of clinically evident arthritis (day 14; P < 0.01) and lost 20% by the end of the inflammatory phase of AA (day 28; P < 0.0001). Body cell mass fell 24.7 +/- 8.6% (mean +/- SEM) in animals with AA, but did not change significantly in controls (increase of 6.3 +/- 7.9%) (P < 0.03). Pair-fed animals lost one-fourth of the weight lost by the animals with AA (P < 0.01), indicating that anorexia alone does not explain inflammatory cachexia. Weight loss was correlated with TNF alpha production by spleen mononuclear cells (r = 0.68, P < 0.007), and a weaker correlation was seen with IL-1 production (r = 0.45, P < 0.04). CONCLUSION: AA in rats is a useful model of inflammatory cachexia that mimics the human pathophysiology in important ways, and is consistent with cytokine-driven cachexia in chronic inflammatory arthritis.