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

Abstract

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.

Keywords: Anorexia; Cachexia; Cancer; Neuropeptide Y; Serotonin.

Figure 1

Effect of tumour inoculation on food intake, carcass weight and muscle, and fat weight in two cachectic models. (A) Time course of change in food intake in mice bearing the C26 tumour. (B) Carcass weight of C26 tumour-bearing mice at Day 19. (C) Weight of m. gastrocnemius and epididymal fat pads in C26 tumour-bearing mice at Day 19. (D) Time course of change in food intake of tumour-bearing mice bearing the Lewis lung carcinoma. (E) Carcass weight of Lewis lung carcinoma tumour-bearing mice at Days 10, 14, and 17. (F) Weight of m. gastrocnemius and epididymal fat pads in Lewis lung carcinoma tumour-bearing mice at Days 10, 14, and 17. *Significantly different from C (P < 0.05). Data are expressed as mean ± SEM. C, sham-injected control; TB, C26-injected tumour bearing; C-14, sham-injected control sacrificed at Day 14; TB-10, Lewis lung carcinoma-injected tumour bearing sacrificed at Day 10; TB-14, Lewis lung carcinoma-injected tumour bearing sacrificed at Day 14; and TB-17, Lewis lung-injected tumour bearing sacrificed at Day 17. Carcass weight was calculated by body weight at day of section minus tumour weight.

Figure 2

Heat map representation of gene expressions in the hypothalamus in C26 and Lewis lung carcinoma tumour-bearing mice. (A) Fold changes of orexigenic and anorexigenic genes relative to their control group were calculated and compared between C26 and Lewis lung carcinoma tumour-bearing mice. (B) Top 30 up-regulated genes in C26 tumour-bearing mice compared with their controls and top 30 up-regulated genes in Lewis lung carcinoma tumour-bearing mice compared with their controls. Twelve genes were overlapping between the C26 and Lewis lung carcinoma tumour model. Each row represents a gene, and each column represents a group of animals. Red colour indicates genes that were higher expressed as controls, and green colour indicates genes that were lower expressed as the controls. Black indicates genes whose expression was similar to compared with controls. ID: Entrez ID. C, sham-injected control; TB, C26-injected tumour-bearing; C-14, sham-injected control sacrificed at Day 14; TB-10, Lewis lung carcinoma-injected tumour bearing sacrificed at Day 10; TB-14, Lewis lung carcinoma-injected tumour bearing sacrificed at Day 14; and TB-17, Lewis lung carcinoma-injected tumour bearing sacrificed at Day 17.

Figure 3

Serotonin signalling in C26 and Lewis lung carcinoma tumour-bearing mice. (A) Schematic view of genes involved in serotonin signalling. (B) Heat map of fold changes of expressions of genes involved in serotonin signalling. (C) Serotonin level in brain relative to control mice in C26 and Lewis lung carcinoma tumour-bearing mice. Values are expressed as mean ± SEM. C, sham-injected control; tumour bearing, injected with 1 × 106 tumour cells; DNTP, 7,8-dihydroneopterin triphosphate; 6PTS, 6-pyruvoyl-tetrahydropterin; q-dbt, q-dihydrobiopterin; TRP, tryptophan; 5HT, 5-hydroxytryptamine (serotonin); MAO, monoamine oxidase; and ALDH, aldehyde dehydrogenase.

Figure 4

Effect of serotonin on messenger neuropeptide Y and neuropeptide Y secretion in hypothalamic cells. Murine-derived hypothalamic cell lines were 24 h exposed to various concentrations serotonin. Potassium chloride was used to depolarize cells (positive control). (A) Effect of serotonin on NPY secretion in hypoE-46 and hypoA-2/12 cells. (B) Effect of serotonin on neuropeptide Y gene expression in hypoE-46 and hypoA-2/12 cells. *Significantly different from C (P < 0.05). Data are expressed as mean ± SEM.