5-hydroxy-L-tryptophan Suppressed Food Intake in Rats Despite an Increase in the Arcuate NPY Expression

Hepatocyte steatosis activates macrophage inflammatory response accelerating atherosclerosis development

OBJECTIVES

To investigate the mechanism of comorbidity between non-alcoholic fatty liver disease (NAFLD) and atherosclerosis (AS) based on metabolomics and network pharmacology.

METHODS

Six ApoE－/－ mice were fed with a high-fat diet for 16 weeks as a comorbid model of NAFLD and AS (model group). Normal diet was given to 6 wildtype C57BL/6J mice (control group). Serum samples were taken from both groups for a non-targeted metabolomics assay to identify differential metabolites. Network pharmacology was applied to explore the possible mechanistic effects of differential metabolites on AS and NAFLD. An in vitro comorbid cell model was constructed using NCTC1469 cells and RAW264.7 macrophage. Cellular lipid accumulation, cell viability, morphology and function of mitochondria were detected with oil red O staining, CCK-8 assay, transmission electron microscopy and JC-1 staining, respectively.

RESULTS

A total of 85 differential metabolites associated with comorbidity of NAFLD and AS were identified. The top 20 differential metabolites were subjected to network pharmacology analysis, which showed that the core targets of differential metabolites related to AS and NAFLD were STAT3, EGFR, MAPK14, PPARG, NFKB1, PTGS2, ESR1, PPARA, PTPN1 and SCD. The Kyoto Encyclopedia of Genes and Genomes showed the top 10 signaling pathways were PPAR signaling pathway, AGE-RAGE signaling pathway in diabetic complications, alcoholic liver disease, prolactin signaling pathway, insulin resistance, TNF signaling pathway, hepatitis B, the relax in signaling pathway, IL-17 signaling pathway and NAFLD. Experimental validation showed that lipid metabolism-related genes PPARG, PPARA, PTPN1, and SCD were significantly changed in hepatocyte models, and steatotic hepatocytes affected the expression of macrophage inflammation-related genes STAT3, NFKB1 and PTGS2; steatotic hepatocytes promoted the formation of foam cells and exacerbated the accumulation of lipids in foam cells; the disrupted morphology, impaired function, and increased reactive oxygen species production were observed in steatotic hepatocyte mitochondria, while the formation of foam cells aggravated mitochondrial damage.

CONCLUSIONS

Abnormal lipid metabolism and inflammatory response are distinctive features of comorbid AS and NAFLD. Hepatocyte steatosis causes mitochondrial damage, which leads to mitochondrial dysfunction, increased reactive oxygen species and activation of macrophage inflammatory response, resulting in the acceleration of AS development.

Hypothalamic inflammation and food intake regulation during chronic illness

Anorexia is a common symptom in chronic illness. It contributes to malnutrition and strongly affects survival and quality of life. A common denominator of many chronic diseases is an elevated inflammatory status, which is considered to play a pivotal role in the failure of food-intake regulating systems in the hypothalamus. In this review, we summarize findings on the role of hypothalamic inflammation on food intake regulation involving hypothalamic neuropeptide Y (NPY) and pro-opiomelanocortin (POMC). Furthermore, we outline the role of serotonin in the inability of these peptide based food-intake regulating systems to respond and adapt to changes in energy metabolism during chronic disease.

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.