Animal models of cachexia and sarcopenia in chronic illness: Cardiac function, body composition changes and therapeutic results.

Cachexia is defined as a complex metabolic syndrome associated with underlying illness that is characterized by the loss of body weight consisting of muscle and fat mass wasting. Sarcopenia is defined as the ageing related loss of muscle mass in health and disease that may not have an effect on body weight. As millions of patients are in cachectic or sarcopenic states, both conditions contribute to high numbers to death worldwide. A number of treatments have been proposed for cachexia and sarcopenia, but these are either in the preclinical stage or in clinical trials and hence not available to the general population. Particularly in cachexia there is a massive problem of recruiting patients for trials and also with the follow-up, due to the seriousness of the disease. This underlines the importance of well-characterized animal models. Obviously, most of the widely used cachexia and sarcopenia animal models have limitations in reproducibility of the condition and novel models are warranted in this context. The key findings of developing models in the field of cachexia and sarcopenia are that more types of the conditions have been taken into the researchers' interest. In cardiac cachexia, technical issues, which limit the preciseness and reproducibility in surgical heart failure models, have been overcome by a combination of surgery and the use of transgenic mouse models or salt sensitive rat models. Fatigue is the most pronounced symptom of cachexia and may be caused by reduced cardiac function independent of the underlying disease. Sarcopenia models often suffer from the use of young animals, due to the limited availability and very high costs of using aged animals. This review will focus on rodent models designed to mimic cachexia and sarcopenia including co-morbidities such as cancer, heart failure, as well as other diseases and conditions.