Francisco J. López-Soriano

Tumor necrosis factor-alpha mediates changes in tissue protein turnover in a rat cancer cachexia model.

Rats bearing the Yoshida AH-130 ascites hepatoma showed enhanced fractional rates of protein degradation in gastrocnemius muscle, heart, and liver, while fractional synthesis rates were similar to those in non-tumor bearing rats. This hypercatabolic pattern was associated with marked perturbations of the hormonal homeostasis and presence of tumor necrosis factor in the circulation. The daily administration of a goat anti-murine TNF IgG to tumor-bearing rats decreased protein degradation rates in skeletal muscle, heart, and liver as compared with tumor-bearing rats receiving a nonimmune goat IgG. The anti-TNF treatment was also effective in attenuating early perturbations in insulin and corticosterone homeostasis. Although these results suggest that tumor necrosis factor plays a significant role in mediating the changes in protein turnover and hormone levels elicited by tumor growth, the inability of such treatment to prevent a reduction in body weight implies that other mediators or tumor-related events were also involved.

Cancer cachexia: understanding the molecular basis

Cancer cachexia is a devastating, multifactorial and often irreversible syndrome that affects around 50–80% of cancer patients, depending on the tumour type, and that leads to substantial weight loss, primarily from loss of skeletal muscle and body fat. Since cachexia may account for up to 20% of cancer deaths, understanding the underlying molecular mechanisms is essential. The occurrence of cachexia in cancer patients is dependent on the patient response to tumour progression, including the activation of the inflammatory response and energetic inefficiency involving the mitochondria. Interestingly, crosstalk between different cell types ultimately seems to result in muscle wasting. Some of the recent progress in understanding the molecular mechanisms of cachexia may lead to new therapeutic approaches.

The Role of Cytokines in Cancer Cachexia

A large number of observations point towards cytokines, polypeptides released mainly by immune cells, as the molecules responsible for the metabolic derangements associated with cancer‐bearing states. Indeed, these alterations lead to a pathological state known as cancer cachexia which is, unfortunately, one of the worst effects of malignancy, accounting for nearly a third of cancer deaths. It is characterized by weight loss together with anorexia, weakness, anemia, and asthenia. The complications associated with the appearance of the cachectic syndrome affect both the physiological and biochemical balance of the patient and have effects on the efficiency of the anticancer treatment, resulting in a considerably decreased survival time. At the metabolic level, cachexia is associated with loss of skeletal muscle protein together with a depletion of body lipid stores. The cachectic patient, in addition to having practically no adipose tissue, is basically subject to an important muscle wastage manifested as an excessive nitrogen loss. The metabolic changes are partially mediated by alterations in circulating hormone concentrations (insulin, glucagon, and glucocorticoids in particular) or in their effectiveness. The present study reviews the involvement of different cytokines in the metabolic and physiological alterations associated with tumor burden and cachexia. Among these cytokines, some can be considered as procachectic (such as tumor necrosis factor‐α), while others having opposite effects can be named as anticachectic cytokines. It is the balance between these two cytokine types that finally seems to have a key role in cancer cachexia.

Acute treatment with tumour necrosis factor-α induces changes in protein metabolism in rat skeletal muscle

Acute treatment of rats with recombinant tumour necrosis factor (TNF-α) caused an enhanced proteolytic rate —measured as tyrosine released in the presence of cycloheximide — insoleus muscle (34%). The cytokine treatment also decreased the rate of protein synthesis in this muscle (22%) while it had no effect upon the same parameter inextensor digitorum longus (EDL) (26%) muscle. In addition, treatment of rats with TNF-α increased amino acid uptake by transport system A in the incubated muscles both insoleus (45%) andEDL (99%) in the presence of insulin in the incubating medium. This effect was not associated with a direct action of TNF on muscle since the addition of different concentrations of the cytokine to the preparations did not alter the uptake of α-(methyl)-aminoisobutyric acid by the incubated muscles. It can be concluded that acute TNF-α treatment causes changes in protein metabolism in red-type muscles — suchsoleus — while little effects are seen in white-type muscles — such as EDL. The results presented may, to some extent, be related to the cachectic response associated with cancer and inflammation.

Anticachectic effects of formoterol: a drug for potential treatment of muscle wasting.

In cancer cachexia both cardiac and skeletal muscle suffer an important protein mobilization as a result of increased proteolysis. Administration of the β2-agonist formoterol to both rats and mice bearing highly cachectic tumors resulted in an important reversal of the muscle-wasting process. The anti-wasting effects of the drug were based on both an activation of the rate of protein synthesis and an inhibition of the rate of muscle proteolysis. Northern blot analysis revealed that formoterol treatment resulted in a decrease in the mRNA content of ubiquitin and proteasome subunits in gastrocnemius muscles; this, together with the decreased proteasome activity observed, suggest that the main anti-proteolytic action of the drug may be based on an inhibition of the ATP-ubiquitin-dependent proteolytic system. Interestingly, the β2-agonist was also able to diminish the increased rate of muscle apoptosis (measured as DNA laddering as well as caspase-3 activity) present in tumor-bearing animals. The present results indicate that formoterol exerted a selective, powerful protective action on heart and skeletal muscle by antagonizing the enhanced protein degradation that characterizes cancer cachexia, and it could be revealed as a potential therapeutic tool in pathologic states wherein muscle protein hypercatabolism is a critical feature such as cancer cachexia or other wasting diseases.

Interleukin-15 antagonizes muscle protein waste in tumour-bearing rats.

Tissue protein hypercatabolism (TPH) is an important feature in cancer cachexia, particularly with regard to the skeletal muscle. The Yoshida AH-130 rat ascites hepatoma is a model system for studying the mechanisms involved in the processes that lead to tissue depletion, since it induces in the host a rapid and progressive muscle wasting, primarily due to TPH. The present study was aimed at investigating if IL-15, which is known to favour muscle fibre hypertrophy, could antagonize the enhanced muscle protein breakdown in this cancer cachexia model. Indeed, IL-15 treatment partly inhibited skeletal muscle wasting in AH-130-bearing rats by decreasing (8-fold) protein degradative rates (as measured by14C-bicarbonate pre-loading of muscle proteins) to values even lower than those observed in non-tumour-bearing animals. These alterations in protein breakdown rates were associated with an inhibition of the ATP-ubiquitin-dependent proteolytic pathway (35% and 41% for 2.4 and 1.2 kb ubiquitin mRNA, and 57% for the C8 proteasome subunit, respectively). The cytokine did not modify the plasma levels of corticosterone and insulin in the tumour hosts. The present data give new insights into the mechanisms by which IL-15 exerts its preventive effect on muscle protein wasting and seem to warrant the implementation of experimental protocols involving the use of the cytokine in the treatment of pathological states characterized by TPH, particularly in skeletal muscle, such as in the present model of cancer cachexia.

Journey from cachexia to obesity by TNF.

Tumor necrosis factor‐α (TNF‐α) is a cytokine involved in the physiological and metabolic abnormalities found in cachectic states. Until very recently, it was inconceivable to think of TNF‐α in obesity. However, recent studies have shown that TNF‐α can also play a key role in obesity, the cytokine being overexpressed in adipose tissue of obese rodents and humans. The aim of this review is to reconcile the role of TNF‐α in these two opposite metabolic situations: obesity and cachexia. It is suggested that TNF‐α may have a key role in the control of body mass in normal weight‐controlled situations and that abnormalities in either its production (during cachexia) or action (during obesity) are responsible for the lack of control of body weight.—Argilés, J. M., López‐Soriano, J., Busquets, S., López‐Soriano, F. J. Journey from cachexia to obesity by TNF. FASEB J. 11, 743–751 (1997)

Tumour necrosis factor-α increases the ubiquitinization of rat skeletal muscle proteins

An acute intravenous administration of 100 μg/kg body weight of recombinant tumour necrosis factor‐α (TNF) resulted in a time‐dependent increase in the levels of both free and conjugated ubiquitin in rat skeletal muscle. The effects of the cytokine were more pronounced in the red muscle soleus than in the white muscle EDL. In the former muscle type, TNF‐treatment also resulted in a time‐dependent increase in the percentage of free ubiquitin. The results suggest that the ubiquitin system for non‐lysosomal protein degradation could have a very important role in the mechanism triggered by TNF which is responsible for enhanced muscle proteolysis in sepsis and other pathological states.

Interleukin-15 mediates reciprocal regulation of adipose and muscle mass: a potential role in body weight control

Interleukin (IL)-15 is a cytokine which is highly expressed in skeletal muscle. Cell culture studies have indicated that IL-15 may have an important role in muscle fiber growth and anabolism. However, data concerning the metabolic effects of this cytokine in vivo are lacking. In the present study, IL-15 was administered to adult rats for 7 days. While IL-15 did not cause changes in either muscle mass or muscle protein content, it induced significant changes in the fractional rates of both muscle protein synthesis and degradation, with no net changes in protein accumulation. Additionally, IL-15 administration resulted in a 33% decrease in white adipose tissue mass and a 20% decrease in circulating triacylglycerols; this was associated with a 47% lower hepatic lipogenic rate and a 36% lower plasma VLDL triacylglycerol content. The decrease in white fat induced by IL-15 was in adipose tissue. No changes were observed in the rate of lipolysis as a result of cytokine administration. These findings indicate that IL-15 has significant effects on both protein and lipid metabolism, and suggest that this cytokine may participate in reciprocal regulation of muscle and adipose tissue mass.

Muscle protein waste in tumor-bearing rats is effectively antagonized by a beta 2-adrenergic agonist (clenbuterol). Role of the ATP-ubiquitin-dependent proteolytic pathway.

Tissue protein hypercatabolism (TPH) is a most important feature in cancer cachexia, particularly with regard to the skeletal muscle. The rat ascites hepatoma Yoshida AH-130 is a very suitable model system for studying the mechanisms involved in the processes that lead to tissue depletion, since it induces in the host a rapid and progressive muscle waste mainly due to TPH (Tessitore, L., G. Bonelli, and F. M. Baccino. 1987. Biochem. J. 241:153-159). Detectable plasma levels of tumor necrosis factor-alpha associated with marked perturbations in the hormonal homeostasis have been shown to concur in forcing metabolism into a catabolic setting (Tessitore, L., P. Costelli, and F. M. Baccino. 1993. Br. J. Cancer. 67:15-23). The present study was directed to investigate if beta 2-adrenergic agonists, which are known to favor skeletal muscle hypertrophy, could effectively antagonize the enhanced muscle protein breakdown in this cancer cachexia model. One such agent, i.e., clenbuterol, indeed largely prevented skeletal muscle waste in AH-130-bearing rats by restoring protein degradative rates close to control values. This normalization of protein breakdown rates was achieved through a decrease of the hyperactivation of the ATP-ubiquitin-dependent proteolytic pathway, as previously demonstrated in our laboratory (Llovera, M., C. García-Martínez, N. Agell, M. Marzábal, F. J. López-Soriano, and J. M. Argilés. 1994. FEBS (Fed. Eur. Biochem. Soc.) Lett. 338:311-318). By contrast, the drug did not exert any measurable effect on various parenchymal organs, nor did it modify the plasma level of corticosterone and insulin, which were increased and decreased, respectively, in the tumor hosts. The present data give new insights into the mechanisms by which clenbuterol exerts its preventive effect on muscle protein waste and seem to warrant the implementation of experimental protocols involving the use of clenbuterol or alike drugs in the treatment of pathological states involving TPH, particularly in skeletal muscle and heart, such as in the present model of cancer cachexia.