Cancer anorexia: a model for the understanding and treatment of secondary anorexia

Protein calorie malnutrition, nutritional intervention and personalized cancer care

Cancer patients often experience weight loss caused by protein calorie malnutrition (PCM) during the course of the disease or treatment. PCM is expressed as severe if the patient has two or more of the following characteristics: obvious significant muscle wasting, loss of subcutaneous fat; nutritional intake of <50% of recommended intake for 2 weeks or more; bedridden or otherwise significantly reduced functional capacity; weight loss of >2% in 1 week, 5% in 1 month, or 7.5% in 3 months. Cancer anorexia-cachexia syndrome (CACS) is a multifactorial condition of advanced PCM associated with underlying illness (in this case cancer) and is characterized by loss of muscle with or without loss of fat mass. Cachexia is defined as weight loss of more than 5% of body weight in 12 months or less in the presence of chronic disease. Hence with a chronic illness on board even a small amount of weight loss can open the door to cachexia. These nutritional challenges can lead to severe morbidity and mortality in cancer patients. In the clinic, the application of personalized medicine and the ability to withstand the toxic effects of anti-cancer therapies can be optimized when the patient is in nutritional homeostasis and is free of anorexia and cachexia. Routine assessment of nutritional status and appropriate intervention are essential components of the effort to alleviate effects of malnutrition on quality of life and survival of patients.

Differences in food intake of tumour-bearing cachectic mice are associated with hypothalamic serotonin signalling

BACKGROUND

Anorexia is a common symptom among cancer patients and contributes to malnutrition and strongly impinges on quality of life. Cancer-induced anorexia is thought to be caused by an inability of food intake-regulating systems in the hypothalamus to respond adequately to negative energy balance during tumour growth. Here, we show that this impaired response of food-intake control is likely to be mediated by altered serotonin signalling and by failure in post-transcriptional neuropeptide Y (NPY) regulation.

METHODS

Two tumour cachectic mouse models with different food intake behaviours were used: a C26-colon adenocarcinoma model with increased food intake and a Lewis lung carcinoma model with decreased food intake. This contrast in food intake behaviour between tumour-bearing (TB) mice in response to growth of the two different tumours was used to distinguish between processes involved in cachexia and mechanisms that might be important in food intake regulation. The hypothalamus was used for transcriptomics (affymetrix chips).

RESULTS

In both models, hypothalamic expression of orexigenic NPY was significantly higher compared with controls, suggesting that this change does not directly reflect food intake status but might be linked to negative energy balance in cachexia. Expression of genes involved in serotonin signalling showed to be different between C26-TB mice and Lewis lung carcinoma-TB mice and was inversely associated with food intake. In vitro, using hypothalamic cell lines, serotonin repressed neuronal hypothalamic NPY secretion while not affecting messenger NPY expression, suggesting that serotonin signalling can interfere with NPY synthesis, transport, or secretion.

CONCLUSIONS

Altered serotonin signalling is associated with changes in food intake behaviour in cachectic TB mice. Serotonins' inhibitory effect on food intake under cancer cachectic conditions is probably via affecting the NPY system. Therefore, serotonin regulation might be a therapeutic target to prevent the development of cancer-induced eating disorders.

Feeding behavior in mammals including humans

The complex control of food intake and energy metabolism in mammals relies on the ability of the brain to integrate multiple signals indicating the nutritional state and the energy level of the organism and to produce appropriate responses in terms of food intake, energy expenditure, and metabolic activity. Central regulation of feeding is organized as a long-loop mechanism involving humoral signals and afferent neuronal pathways to the brain, processing in hypothalamic neuronal circuits, and descending commands using vagal and spinal neurons. Sensor mechanisms or receptors sensitive to glucose and fatty acid metabolism, neuropeptide and cannabinoid receptors, as well as neurotransmitters and neuromodulators synthesized and secreted within the brain itself are all signals integrated in the hypothalamus, which therefore functions as an integrator of signals from central and peripheral structures. Homeostatic feedback mechanisms involving afferent neuroendocrine inputs from peripheral organs, like adipose tissue, gut, stomach, endocrine pancreas, adrenal, muscle, and liver, to hypothalamic sites thus contribute to the maintenance of normal feeding behavior and energy balance. In addition to transcriptional events, peripheral hormones may also alter firing and/or connection (synaptology) of hypothalamic neuronal networks in order to modulate food intake. Moreover, intracellular energy sensing and subsequent biochemical adaptations, including an increase in AMP-activated protein kinase activity, occur in hypothalamic neurons. Understanding the regulation of appetite is clearly a major research effort but also seems promising for the development of novel therapeutic strategies for obesity.

Anorexia in cancer: role of feeding-regulatory peptides

Anorexia is one of the most common symptoms in advanced cancer and is a frequent cause of discomfort for cancer patients and their families. The pathogenesis of cancer anorexia is multi-factorial and involves most of the hypothalamic neuronal signalling pathways modulating energy homeostasis. It is considered to be the result of a failure of usual appetite and satiety signals. Loss of appetite can arise from decreased taste and smell of food, as well as from dysfunctional hypothalamic signalling pathways and cytokine production. Cytokines in particular, appear to play a key role in energy balance through persistent activation of the melanocortin system and inhibition of the neuropeptide Y pathway. The imbalance between anorexigenic and orexigenic peptides leads to suppression of appetite, and increased satiety and satiation associated with marked weight loss and decline in physical performance. High levels of serotonin also appear to contribute to these effects and recent findings implicate corticotropin-releasing factor in the pathogenesis of cancer anorexia as well. Despite significant advances in our understanding of the regulation of food intake and energy expenditure, few effective therapies are available. A better appreciation of the molecular and neuronal mechanisms that control body weight homeostasis may lead to the development of new therapies for improving the survival and quality of life of these patients.

The management of anorexia by patients with advanced cancer: a critical review of the literature

This report presents the results of a critical review of the literature on the experience of anorexia (loss of appetite) by patients with advanced cancer. Although several studies have investigated this experience, the adaptive strategies used by patients to compensate for appetite loss remain poorly elucidated. Based on the small body of extant research, it was concluded that, in many instances, a gap exists between the ability of patients and caregivers to come to terms and deal realistically with the emotional and social consequences of patient anorexia. Patients generally appear to suffer greater discord as a result of this disparity, than from the direct psychological impact of anorexia. A greater understanding of the management of anorexia by patients is essential for the development of dietary and psychosocial interventions that would aid both patients and caregivers to cope with this common symptom.