Inefficient substrate utilization: a mechanism of cachexia in cancer

Efficiency of oxidative phosphorylation in liver mitochondria is decreased in a rat model of peritoneal carcinosis

BACKGROUND & AIMS

Cancer cachexia is a dynamic process characterized by a negative energy balance induced by anorexia and hypermetabolism. The mechanisms leading to hypermetabolism are not totally elucidated. This study examines the efficiency of oxidative phosphorylation and energy wasting in liver mitochondria isolated from rats with cancer cachexia induced by peritoneal carcinosis (PC).

METHODS

PC was generated by an intraperitoneal injection of cancer cells (PROb) in BDIX rats. The efficiency of oxidative phosphorylation and energy wasting as well as the role played by reactive oxygen species (ROS) and cardiolipin (mitochondrial inner membrane phospholipid) in these processes were assessed in liver mitochondria of PC and pair-fed control rats.

RESULTS

The efficiency of oxidative phosphorylation decreased (-26%) while energy wasting increased (+22%) in liver mitochondria from PC compared to control rats. The increased energy wasting was associated with a higher cardiolipin content (+55%, p<0.05; R(2)=0.64, p<0.05) and with a lower n-6/n-3 polyunsaturated fatty acid ratio in cardiolipin (-45%, p<0.05; R(2)=0.21, p<0.05) in PC rats. ROS production was increased by 12-fold in liver mitochondria from PC rats.

CONCLUSIONS

The efficiency of ATP synthesis was reduced and energy wasting processes were increased in liver mitochondria of PC rats. This suggests that liver mitochondria from PC rats request more nutrients than liver mitochondria from control rats to maintain the same ATP production. These alterations were associated to the content and fatty acid composition of cardiolipin.

Etiology of anorexia in cancer

Although the causes of cancer anorexia remain poorly understood, it now seems evident that the symptoms of appetite and weight loss which occur in cancer patients are multiply-determined. Thus, the actual causes of specific clinical problems will depend on the type of disease and treatment involved. This report examines research aimed at understanding the mechanisms responsible for cancer anorexia. Particular emphasis is placed on studies examining the contribution of learned food aversions to the anorexia induced by tumors and antitumor therapy. Evidence from the clinic and the laboratory indicates that learned food aversions occur as a result of the association of foods with symptoms induced by chemotherapy and/or tumor growth. The role these aversions play in the etiology of cancer anorexia is discussed and studies aimed at developing methods for preventing them are described.

The influence of intravenous hyperalimentation (IVH) on wound healing in tumor-bearing rats

Two studies were conducted to measure the metabolic influence of tumor growth in rats. Parameters for the metabolic state were wound-healing qualities of colon and skin. Both early and later stages of tumor growth lowered wound healing qualities to a statistically significant degree. No anorexia or weight loss was found in this rat-tumor model during the study period. Intravenous hyperalimentation (IVH; with proteins and carbohydrates) of tumor-bearing rats stimulates tumor growth but at the same time restores wound-healing qualities to control levels, both during early and later stages of tumor growth. It is suggested that tumor growth leads to an as yet not measurable disturbance of the metabolic equilibrium but that IVH can replenish the tumor-bearing host and restore the metabolic equilibrium.