Wasting in adjuvant-induced arthritis and its relationship to plasma zinc, copper and liver metallothionein.

The appearance of joint inflammation (JI) 14 days after the injection of adjuvant (AJ) in the tail of rats is associated with a cachectic syndrome which is characterised by marked weight loss (WL). The degree of weight loss was examined in relation to the extent of change in other markers of inflammation including increased plasma copper (pCu), decreased plasma zinc (pZn) and increased hepatic metallothionein (hMT). At 14 days post-AJ injection, arthritic rats showed the following changes, relative to the controls: body weight, 12% decrease, pZn, 50% decrease; pCu, 90% increase and hMT, 11-fold increase (all p < 0.001). Significant relationships were observed between JI, WL, pZn and hMT. The following coefficients of determination (r2) were observed; JI and WL, -0.530, JI and pZn, -0.485; JI and hMT, 0.286; WL and hMT, -0.510 (all p < 0.007). There was a strong relationship between the decreased pZn and increased hMT; r2 = 0.456 (p < 0.001). While increased pCu was clearly associated with AJ-arthritis in these rats, there was no quantitative relationship between the extent of change in pCu and the other parameters measured (r2 all < 0.01). The highest correlation observed was between pZn and WL (r2 = 0.637, p < 0.001). While the initial depression of pZn may be the result of increased hepatic hMT levels, longer term reductions in pZn levels are linked to systemic inflammation, the degree of arthritis and associated weight loss.