The role of amino acids in appetite regulation

There is currently a lack of safe and effective treatment options for obesity. A high protein diet is an effective weight loss and weight maintenance strategy. However, like many diets, high protein diets can be difficult to adhere to. The mechanisms by which protein exerts its weight-reducing effect remain unclear. However, it has been reported that different types of protein exert different effects on appetite. One possible explanation for these differences is the varied amino acid constituents of the protein. Preliminary data from our group investigated the effect of a range of amino acids on food intake in rodents. L-cysteine was identified as the most anorexigenic amino acid. This thesis has investigated the effect of L-cysteine on food intake and explored possible mechanisms by which it mediates this effect. L-cysteine dose dependently decreased food intake in both rats and mice following oral gavage and intraperitoneal administration. This reduction in food intake did not appear to be secondary to behavioural side effects or feelings of nausea. L-cysteine increased neuronal activation in the area postrema and nucleus tractus solitarius, delayed gastric emptying and suppressed plasma acyl-ghrelin levels. However, the anorectic effect of L-cysteine did not appear to depend on NMDA, GPRC6A or CCK-A receptors, nor on subdiaphragmatic vagal afferent signalling. Repeated administration of L-cysteine also decreased food intake in rats and diet-induced obese mice. The studies described in this thesis demonstrate the anorectic effects of L-cysteine and identify possible sites of action. It is likely that different amino acids exert different effects on appetite through a number of mechanisms, the combination of which contributes towards the success of high protein diets on body weight and appetite. This thesis provides a framework for future studies to investigate the therapeutic potential of combinations of amino acids that could provide a safe and practical therapeutic treatment for obesity.Open Acces

Publisher Correction: Enhanced β-adrenergic signalling underlies an age-dependent beneficial metabolic effect of PI3K p110α inactivation in adipose tissue.

An amendment to this paper has been published and can be accessed via a link at the top of the paper

Publisher Correction: Enhanced β-adrenergic signalling underlies an age-dependent beneficial metabolic effect of PI3K p110α inactivation in adipose tissue.

An amendment to this paper has been published and can be accessed via a link at the top of the paper

Important Role of the GLP-1 Axis for Glucose Homeostasis after Bariatric Surgery.

Bariatric surgery is widely used to treat obesity and improves type 2 diabetes beyond expectations from the degree of weight loss. Elevated post-prandial concentrations of glucagon-like peptide 1 (GLP-1), peptide YY (PYY), and insulin are widely reported, but the importance of GLP-1 in post-bariatric physiology remains debated. Here, we show that GLP-1 is a major driver of insulin secretion after bariatric surgery, as demonstrated by blocking GLP-1 receptors (GLP1Rs) post-gastrectomy in lean humans using Exendin-9 or in mice using an anti-GLP1R antibody. Transcriptomics and peptidomics analyses revealed that human and mouse enteroendocrine cells were unaltered post-surgery; instead, we found that elevated plasma GLP-1 and PYY correlated with increased nutrient delivery to the distal gut in mice. We conclude that increased GLP-1 secretion after bariatric surgery arises from rapid nutrient delivery to the distal gut and is a key driver of enhanced insulin secretion.RNA-sequencing was undertaken at the CRUK Cambridge Institute Genomics Core. Cell sorting was performed at the NIHR Cambridge BRC Cell Phenotyping Hub. PL received a Society for Endocrinology Early Career Grant. GR received an Addenbrooke’s Charitable Trust / Evelyn Trust Cambridge Clinical Research Fellowship [16-69] and a Royal College of Surgeons Research Fellowship. The work was partially funded by a project grant from the EFSD/Novo Nordisk Programme for Diabetes Research in Europe

GPRC6a is not required for the effects of a high-protein diet on body weight in mice

Objective: The G-protein coupled receptor family C group 6 member A (GPRC6A) is activated by proteinogenic amino acids and may sense amino acids in the gastrointestinal tract and the brain. The study investigated whether GPRC6A was necessary for the effects of low- and high-protein diets on body weight and food intake in mice. Methods: The role of GPRC6A in mediating the effects of a low-protein diet on body weight was investi-gated in GPRC6a knockout (GPRC6a-KO) and wild-type (WT) mice fed a control diet (18 % protein) or a low-protein diet (6 % protein) for 9 days. The role of GPRC6A in mediating the effects of a high-protein diet on body weight was investigated in GPRC6a-KO and WT mice fed a control diet (18 % protein) or a high-protein diet (50 % protein) for 5 weeks. Results: A high-protein diet reduced body weight gain and food intake compared with a control diet in both WT and GPRC6a-KO mice. A low-protein diet decreased body weight gain in GPRC6a-KO mice. Conclusions: GPRC6A was not necessary for the effects of a low- or high-protein diet on body weight and likely does not play a role in protein-induced satiety

Hepatocyte p53 ablation induces metabolic dysregulation that is corrected by food restriction and vertical sleeve gastrectomy in mice.

P53 has been implicated in the pathogenesis of obesity and diabetes; however, the mechanisms and tissue sites of action are incompletely defined. Therefore, we investigated the role of hepatocyte p53 in metabolic homeostasis using a hepatocyte-specific p53 knockout mouse model. To gain further mechanistic insight, we studied mice under two complementary conditions of restricted weight gain: vertical sleeve gastrectomy (VSG) or food restriction. VSG or sham surgery was performed in high-fat diet-fed male hepatocyte-specific p53 wild-type and knockout littermates. Sham-operated mice were fed ad libitum or food restricted to match their body weight to VSG-operated mice. Hepatocyte-specific p53 ablation in sham-operated ad libitum-fed mice impaired glucose homeostasis, increased body weight, and decreased energy expenditure without changing food intake. The metabolic deficits induced by hepatocyte-specific p53 ablation were corrected, in part by food restriction, and completely by VSG. Unlike food restriction, VSG corrected the effect of hepatocyte p53 ablation to lower energy expenditure, resulting in a greater improvement in glucose homeostasis compared with food restricted mice. These data reveal an important new role for hepatocyte p53 in the regulation of energy expenditure and body weight and suggest that VSG can improve alterations in energetics associated with p53 dysregulation

Peptidomics of enteroendocrine cells and characterisation of potential effects of a novel preprogastrin derived-peptide on glucose tolerance in lean mice.

OBJECTIVES: To analyse the peptidomics of mouse enteroendocrine cells (EECs) and human gastrointestinal (GI) tissue and identify novel gut derived peptides. METHODS: High resolution nano-flow liquid chromatography mass spectrometry (LC-MS/MS) was performed on (i) flow-cytometry purified NeuroD1 positive cells from mouse and homogenised human intestinal biopsies, (ii) supernatants from primary murine intestinal cultures, (iii) intestinal homogenates from mice fed high fat diet. Candidate bioactive peptides were selected on the basis of species conservation, high expression/biosynthesis in EECs and evidence of regulated secretionin vitro. Candidate novel gut-derived peptides were chronically administered to mice to assess effects on food intake and glucose tolerance. RESULTS: A large number of peptide fragments were identified from human and mouse, including known full-length gut hormones and enzymatic degradation products. EEC-specific peptides were largely from vesicular proteins, particularly prohormones, granins and processing enzymes, of which several exhibited regulated secretion in vitro. No regulated peptides were identified from previously unknown genes. High fat feeding particularly affected the distal colon, resulting in reduced peptide levels from GCG, PYY and INSL5. Of the two candidate novel peptides tested in vivo, a peptide from Chromogranin A (ChgA 435-462a) had no measurable effect, but a progastrin-derived peptide (Gast p59-79), modestly improved glucose tolerance in lean mice. CONCLUSION: LC-MS/MS peptidomic analysis of murine EECs and human GI tissue identified the spectrum of peptides produced by EECs, including a potential novel gut hormone, Gast p59-79, with minor effects on glucose tolerance.AstraZenec