Anti-tumor necrosis factor agent PEG-sTNFRI improves the growth hormone/insulin-like growth factor-I system in adjuvant-induced arthritic rats

Adjuvant-induced arthritis is associated with body weight loss and decreased pituitary growth hormone (GH) and hepatic insulin-like growth factor-I (IGF-I) synthesis. Cytokines as tumor necrosis factor (TNF) mediate wasting associated with chronic inflammation. The aim of this study was to analyse whether the inhibition of TNF is able to revert the decrease in the body weight and the GH/IGF-I axis in arthritic rats. Male Wistar rats were injected with Freund's adjuvant, and 15 days later arthritic and control rats were daily injected with polyethylene glycol linked to soluble TNF receptor p55 (PEG-sTNFRI) (1 mg/kg, s.c.) or saline for 8 days. There was a significant decrease in pituitary GH mRNA (P < 0.05), hepatic IGF-I mRNA (P < 0.01) and serum concentrations of IGF-I (P < 0.01) in arthritic rats. The 8-day administration of PEG-sTNFRI resulted in an increase in food intake (P < 0.05) and body weight gain (P < 0.01) in arthritic but not in control rats. There was an increase in pituitary GH mRNA after PEG-sTNFRI treatment both in control and in arthritic rats. There was a significant increase in IGF-I serum concentrations (P < 0.05) and hepatic IGF-I mRNA expression (P < 0.05) in control rats treated with PEG-sTNFRI, whereas the effect of this anti-TNF agent in arthritic rats was only statistically significant in hepatic IGF-I mRNA expression (P < 0.05). These data suggest that TNF seems to be involved in the decrease in GH and IGF-I synthesis in arthritic rats.