Chronic exendin-4 treatment prevents the development of cancer cachexia symptoms in male rats bearing the Yoshida sarcoma.

Cancer cachexia is the syndrome of weight loss, loss of appetite, and wasting of skeletal muscle and adipose tissue experienced by many individuals with cancer. Currently, few effective treatment and prevention strategies are available for these patients, due in part to a poor understanding of the mechanisms contributing to cachexia. Insulin resistance has been associated with cancer cachexia in epidemiological, human, and animal research. The present experiment was designed to examine the ability of Exendin-4, a GLP-1 agonist and insulin sensitizing agent, to prevent the development of cachexia symptoms in male Sprague Dawley rats bearing the Yoshida sarcoma. Following tumor implantation or sham surgery, rats were treated daily with saline or Exendin-4 (3 µg/kg body weight/day) and were monitored for tumor growth and cachexia symptoms for 21-23 days. As a result of large variability in treatment effects, data were analyzed separately for animals with large and small tumors. Exendin-4 treatment reduced tumor growth and prevented the development of cancer cachexia symptoms in animals with small, but not large, tumors. In addition, insulin levels were preserved in Exendin-4-treated tumor-bearing animals. The results of this experiment demonstrate a novel preventative therapy for cancer cachexia and a novel use of Exendin-4. Further research is necessary to determine the mechanisms through which Exendin-4 exerts these potent effects.

Mitochondrial and sarcoplasmic reticulum abnormalities in cancer cachexia: altered energetic efficiency?

BACKGROUND: Cachexia is a wasting condition that manifests in several types of cancer, and the main characteristic is the profound loss of muscle mass. METHODS: The Yoshida AH-130 tumor model has been used and the samples have been analyzed using transmission electronic microscopy, real-time PCR and Western blot techniques. RESULTS: Using in vivo cancer cachectic model in rats, here we show that skeletal muscle loss is accompanied by fiber morphologic alterations such as mitochondrial disruption, dilatation of sarcoplasmic reticulum and apoptotic nuclei. Analyzing the expression of some factors related to proteolytic and thermogenic processes, we observed in tumor-bearing animals an increased expression of genes involved in proteolysis such as ubiquitin ligases Muscle Ring Finger 1 (MuRF-1) and Muscle Atrophy F-box protein (MAFBx). Moreover, an overexpression of both sarco/endoplasmic Ca(2+)-ATPase (SERCA1) and adenine nucleotide translocator (ANT1), both factors related to cellular energetic efficiency, was observed. Tumor burden also leads to a marked decreased in muscle ATP content. CONCLUSIONS: In addition to muscle proteolysis, other ATP-related pathways may have a key role in muscle wasting, both directly by increasing energetic inefficiency, and indirectly, by affecting the sarcoplasmic reticulum-mitochondrial assembly that is essential for muscle function and homeostasis. GENERAL SIGNIFICANCE: The present study reports profound morphological changes in cancer cachectic muscle, which are visualized mainly in alterations in sarcoplasmic reticulum and mitochondria. These alterations are linked to pathways that can account for energy inefficiency associated with cancer cachexia.

Cancer-related anemia in a rat model: alpha2-macroglobulin from Yoshida sarcoma shortens erythrocyte survival.

Implantation of Yoshida ascites sarcoma in rats was found to lead to a reduction in the hemoglobin content, the erythrocyte count and the packed cell volume of blood to 30% of normal in 4 d; however, there was no decrease in the mean cell hemoglobin, the mean cell volume and the mean corpuscular hemoglobin concentration, or suppression of erythropoiesis. The red cells from the circulation of tumor-bearing animals, tagged with (51)Cr and injected intravenously in normal rats, showed significantly faster clearance than normal. The erythrocytes contaminating the tumor ascites exhibited extremely short survival, suggesting that one or more secreted tumor product(s) may be responsible for the effect. Incubation of red cells from normal rats in the cell-free ascites fluid, or with an isoform of alpha2-macroglobulin purified from it, also led to reduction in the survival; but the ascites fluid depleted specifically of alpha2-macroglobulin was without any effect. The erythrocytes exhibiting reduced survival showed a proportionate decrease in their cellular deformability. The study identifies a tumor product that is directly responsible for the causation of anemia in the host, and the mechanism by which it does so.

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 by 14C-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.

Lack of effect of the cytokine suppressive agent FR167653 on tumour growth and cachexia in rats bearing the Yoshida AH-130 ascites hepatoma.

Daily s.c. administration of 6 mg/kg of FR167653 (an inhibitor of the synthesis of interleukin-1 and tumour necrosis factor-alpha) to rats bearing the ascites hepatoma Yoshida AH-130 (a highly cachectic tumour) did not prevent either the anorexia or the massive weight loss - affecting both adipose tissue and skeletal muscle - present in the cachectic animals. The compound did not affect the circulating levels of triacylglycerols or other metabolites such as glucose or lactate. Nor did the administration of FR167653 influence tumour growth. It is concluded that the drug is unable to reverse the cachectic state in this particular experimental tumour model.

Stimulation of brown adipose tissue activity in tumor-bearing rats.

Despite anorexia, cancer development is frequently accompanied by an increase of energy expenditure. Considering the pivotal role played by brown adipose tissue (BAT) in the energy metabolism of small mammals, we investigated the functional and compositional modification in BAT of anorexic tumor-bearing (Yoshida sarcoma) and pair-fed control rats. BAT thermogenic activity (assessed by maximal mitochondrial GDP binding) was 1.8-fold greater in tumor-bearing rats than in controls, while the thermogenic capacity (assessed by measurement of uncoupling protein) was unchanged. This suggests that tumor bearing had induced an unmasking of uncoupling protein sites. BAT hypertrophy and hyperplasia, characteristic of full-fledged BAT activation, did not occur. The mitochondrial oxidative capacity of BAT (assessed by cytochrome c oxidase activity) was 1.6-fold lower in tumor-bearing than in control rats. The main compositional modification observed in BAT of tumor-bearing rats was an increase in the saturation of cardiolipin fatty acids. These results suggest that the BAT stimulation induced by tumor bearing after 10 days is almost exclusively functional and that the tissue development is limited, probably by anorexia. However, a suppressive effect of anorexia inhibition by tumor bearing cannot be excluded.

Increased ATP-ubiquitin-dependent proteolysis in skeletal muscles of tumor-bearing rats.

Little information is available on proteolytic pathways responsible for muscle wasting in cancer cachexia. Experiments were carried out in young rats to demonstrate whether a small (< 0.3% body weight) tumor may activate the lysosomal, Ca(2+)-dependent, and/or ATP-ubiquitin-dependent proteolytic pathway(s) in skeletal muscle. Five days after tumor implantation, protein mass of extensor digitorum longus and tibialis anterior muscles close to a Yoshida sarcoma was significantly reduced compared to the contralateral muscles. According to in vitro measurements, protein loss totally resulted from increased proteolysis and not from depressed protein synthesis. Inhibitors of lysosomal and Ca(2+)-dependent proteases did not attenuate increased rates of proteolysis in the atrophying extensor digitorum longus. Accordingly, cathepsin B and B+L activities, and mRNA levels for cathepsin B were unchanged. By contrast, ATP depletion almost totally suppressed the increased protein breakdown. Furthermore, mRNA levels for ubiquitin, 14 kDa ubiquitin carrier protein E2, and the C8 or C9 proteasome subunits increased in the atrophying muscles. Similar adaptations occurred in the muscles from cachectic animals 12 days after tumor implantation. These data strongly suggest that the activation of the ATP-ubiquitin-dependent proteolytic pathway is mainly responsible for muscle atrophy in Yoshida sarcoma-bearing rats.

Effect of Yoshida ascites tumour on the circulation in rats.

The circulation in anaesthetized rats with Yoshida ascites tumour was studied. Cardiac output was determined according to the reference flow method, while the distribution of cardiac output by labelled microspheres 15 mu in diameter. Arterial blood pressure decreased by 39 mm Hg and TPR by 23% at unaltered cardiac output. Blood flow of the brain and the coronaries increased by 39-43% while that of the kidney and the intestines decreased by 43 and 28%, respectively. The cardiac output fractions of the brain, the coronaries and the hepatic artery increased considerably, while that of the kidney decreased. The haematocrit decreased from 43 to 23%. It is assumed that part of the circulatory alterations (redistribution of cardiac output) were due to the anaemia and its consequences, while the others (arterial hypotension, lack of increase in cardiac output) should be regarded as an effect of a factor reaching the circulation from the cells of the ascites tumour.