Catabolic factors in tumour-induced cachexia
A transplantable colon adenocarcinoma of the mouse (MAC16) was utilized as a model of human cancer cachexia. The MAC16 tumour produced extensive weight loss in the host at small tumour burdens and without a reduction in either food or fluid intake. The weight loss was characterised by a decrease in both carcass fat and muscle mass which were directly proportional to the weight of the tumour. The weight loss has been correlated with the production of circulatory catabolic factors by the tumour, which degrade host muscle and adipose tissue in vitro. These factors were further characterised and have been shown to be distinct and separable by gel exclusion chromatography. The proteolytic factors (molecular weight > 150k daltons) were distinguishable from the lipolytic factors which appeared related with molecular weights of approximately 3.0, 1.5 and 0.7k daltons. Lipolytic factors of the same molecular weights were identified in other tumour models and in the body fluids of tumour-bearing animals and cancer patients. These factors were not present in healthy individuals or in patients with other weight-losing conditions. Various temperatures studied reversed the weight loss seen in the cachexia induced by the MAC16 adenocarcinoma in vivo. The effects of these treatments could be linked in vitro to the inhibition of the catabolic factors produced by the tumour. These results suggest that these factors may be responsible for the cachexia the tumour confers on its host. These factors may be useful in the understanding and therapy of cancer cachexia.