Adipose tissue loss in adjuvant arthritis is associated with a decrease in lipogenesis, but not with an increase in lipolysis

Adjuvant-induced arthritis is a model of rheumatoid arthritis that induces cachexia. In other cachectic situations, there is an increase in lipolysis resulting in a loss of adipose tissue mass. The aim of this work was to analyse the effect of chronic arthritis, induced by adjuvant injection, on white adipose tissue (WAT). For this purpose, rats were killed 10 days after adjuvant injection, when the first external symptoms appeared, on days 15 and 22 when the external signs of the illness reach their severest level. As arthritis decreases food intake, a pair-fed group was also included. Serum concentrations of insulin, leptin, adiponectin, glycerol and nitrites, as well as gene expression of leptin, adiponectin, hormone-sensitive lipase (HSL), fatty acid synthase (FAS), tumour necrosis factor alpha and zinc-alpha(2)-glycoprotein (ZAG) were determined. Arthritis decreased food intake between days 5 and 16, but not during the last 5 days of the experiment. There was a marked decrease in relative adipose tissue weight and in serum leptin and adiponectin as well as in their gene expression in WAT in arthritic rats. Arthritis decreased the gene expression of FAS in the WAT. However, none of these effects was found in pair-fed rats. Arthritis did not increase lipolysis, since arthritic rats have lower serum concentrations of glycerol, HSL mRNA in WAT, as well as liver ZAG mRNA than the pair-fed or control rats. These data suggest that in chronic arthritis the decrease in white adipose mass is secondary to a reduced adipose lipogenesis, and this effect is not mainly due to the decrease in food intake.