Erythritol and xylitol differentially impact brain networks involved in appetite regulation in healthy volunteers

BACKGROUND

There is a growing consensus that sugar consumption should be reduced and the naturally occurring, low-calorie sweeteners xylitol and erythritol are gaining popularity as substitutes, but their effect on brain circuitry regulating appetite is unknown.

AIM

The study's objective was to examine the effects of the two sweeteners on cerebral blood flow (rCBF) and resting functional connectivity in brain networks involved in appetite regulation, and test whether these effects are related to gut hormone release.

METHODS

The study was performed as a randomized, double-blind, placebo-controlled, cross-over trial. Twenty volunteers received intragastric (ig) loads of 50g xylitol, 75g erythritol, 75g glucose dissolved in 300mL tap water or 300mL tap water. Resting perfusion and blood oxygenation level-dependent data were acquired to assess rCBF and functional connectivity. Blood samples were collected for determination of CCK, PYY, insulin and glucose.

RESULTS

We found: (i) xylitol, but not erythritol, increased rCBF in the hypothalamus, whereas glucose had the opposite effect; (ii) graph analysis of resting functional connectivity revealed a complex pattern of similarities and differences in brain network properties following xylitol, erythritol, and glucose; (iii) erythritol and xylitol induced a rise in CCK and PYY, (iv) erythritol had no and xylitol only minimal effects on glucose and insulin.

CONCLUSION

Xylitol and erythritol have a unique combination of properties: no calories, virtually no effect on glucose and insulin while promoting the release of gut hormones, and impacting appetite-regulating neurocircuitry consisting of both similarities and differences with glucose.

Gut Hormones in Health and Obesity: The Upcoming Role of Short Chain Fatty Acids

We are currently facing an obesity pandemic, with worldwide obesity rates having tripled since 1975. Obesity is one of the main risk factors for the development of non-communicable diseases, which are now the leading cause of death worldwide. This calls for urgent action towards understanding the underlying mechanisms behind the development of obesity as well as developing more effective treatments and interventions. Appetite is carefully regulated in humans via the interaction between the central nervous system and peripheral hormones. This involves a delicate balance in external stimuli, circulating satiating and appetite stimulating hormones, and correct functioning of neuronal signals. Any changes in this equilibrium can lead to an imbalance in energy intake versus expenditure, which often leads to overeating, and potentially weight gain resulting in overweight or obesity. Several lines of research have shown imbalances in gut hormones are found in those who are overweight or obese, which may be contributing to their condition. Therefore, this review examines the evidence for targeting gut hormones in the treatment of obesity by discussing how their dysregulation influences food intake, the potential possibility of altering the circulating levels of these hormones for treating obesity, as well as the role of short chain fatty acids and protein as novel treatments.

Dietary macronutrient regulation of acyl and desacyl ghrelin concentrations in children with Prader-Willi syndrome (PWS)

BACKGROUND

The effects of dietary macronutrients on orexigenic and anorexigenic hormones in children are poorly understood.

OBJECTIVE

To explore effects of varying dietary macronutrients on appetite-regulating hormones [acyl ghrelin (AG) and desacyl ghrelin (DAG), glucagon-like peptide 1 (GLP-1), peptide tyrosine tyrosine (PYY) and insulin] in children with PWS and healthy children (HC).

DESIGN

Randomized, cross-over experiments compared two test diets [high protein-low carbohydrate (HP-LC) and high protein-low fat (HP-LF)] to a STANDARD meal (55% carbohydrate, 30% fat, 15% protein). Experiment 1 included ten children with PWS (median age 6.63 years; BMI z 1.05); experiment 2 had seven HC (median age 12.54 years; BMI z 0.95). Blood samples were collected at baseline and at 60-minute intervals for 4 hours. Independent linear mixed models were adjusted for age, sex and BMI z-score.

RESULTS

Fasting and post-prandial AG and DAG concentrations are elevated in PWS children; the ratio of AG/DAG is normal. Food consumption reduced AG and DAG concentrations in both PWS and HC. GLP-1 levels were higher in PWS after the HP-LC and HP-LF meals than the STANDARD meal (P = .02-0.04). The fasting proinsulin to insulin ratio (0.08 vs 0.05) was higher in children with PWS (P = .05) than in HC. Average appetite scores in HC declined after all three meals (P = .02) but were lower after the HP-LC and HP-LF meals than the STANDARD meal.

CONCLUSION

Altered processing of proinsulin and increased GLP-1 secretion in children with PWS after a high protein meal intake might enhance satiety and reduce energy intake.

Nutritive, Post-ingestive Signals Are the Primary Regulators of AgRP Neuron Activity

The brain regulates food intake by processing sensory cues and peripheral physiological signals, but the neural basis of this integration remains unclear. Hypothalamic, agouti-related protein (AgRP)-expressing neurons are critical regulators of food intake. AgRP neuron activity is high during hunger and is rapidly reduced by the sight and smell of food. Here, we reveal two distinct components of AgRP neuron activity regulation: a rapid but transient sensory-driven signal and a slower, sustained calorie-dependent signal. We discovered that nutrients are necessary and sufficient for sustained reductions in AgRP neuron activity and that activity reductions are proportional to the calories obtained. This change in activity is recapitulated by exogenous administration of gut-derived satiation signals. Furthermore, we showed that the nutritive value of food trains sensory systems-in a single trial-to drive rapid, anticipatory AgRP neuron activity inhibition. Together, these data demonstrate that nutrients are the primary regulators of AgRP neuron activity.

Sitagliptin and Roux-en-Y gastric bypass modulate insulin secretion via regulation of intra-islet PYY

AIMS

The gut hormone peptide tyrosine tyrosine (PYY) is critical for maintaining islet integrity and restoring islet function following Roux-en-Y gastric bypass (RYGB). The expression of PYY and its receptors (NPYRs) in islets has been documented but not fully characterized. Modulation of islet PYY by the proteolytic enzyme dipeptidyl peptidase IV (DPP-IV) has not been investigated and the impact of DPP-IV inhibition on islet PYY function remains unexplored. Here we have addressed these gaps and their effects on glucose-stimulated insulin secretion (GSIS). We have also investigated changes in pancreatic PYY in diabetes and following RYGB.

METHODS

Immunohistochemistry and gene expression analysis were used to assess PYY, NPYRs and DPP-IV expression in rodent and human islets. DPP-IV activity inhibition was achieved by sitagliptin. Secretion studies were used to test PYY and the effects of sitagliptin on insulin release, and the involvement of GLP-1. Radioimmunoassays were used to measure hormone content in islets.

RESULTS

PYY and DPP-IV localized in different cell types in islets while NPYR expression was confined to the beta-cells. Chronic PYY application enhanced GSIS in rodent and diabetic human islets. DPP-IV inhibition by sitagliptin potentiated GSIS; this was mediated by locally-produced PYY, and not GLP-1. Pancreatic PYY was markedly reduced in diabetes. RYGB strongly increased islet PYY content, but did not lead to full restoration of pancreatic GLP-1 levels.

CONCLUSION

Local regulation of pancreatic PYY, rather than GLP-1, by DPP-IV inhibition or RYGB can directly modulate the insulin secretory response to glucose, indicating a novel role of pancreatic PYY in diabetes and weight-loss surgery.

The role of gut hormones in appetite regulation (review)

Eating process is an aggregate of complex and different forms of behavior. Its regulation is based on energy homeostasis and appetite control which includes two components: the homeostatic and the hedonistic control. Important signals in appetite regulation are gut-derived hormones. They are produced by enteroendocrine cells in response to nutrient and energy intake, and achieve their effects by influencing brain structures involved in food intake regulation. The key brain structure involved in this process is the hypothalamus. Gut hormones reach the hypothalamus from the circulation or by the vagal nerve via the nucleus of the solitary tract. Among gut peptides, ghrelin is the only orexigenic hormone, leading to an increase in food intake and body weight. All others, such as cholecystokinin, glucagon like peptide-1, oxyntomodulin, peptide tyrosine tyrosine or pancreatic polypeptide, are anorexigenic, leading to decrease in food intake. Also, gut-derived endocannabinoids exert orexigenic effect on appetite. Keeping in mind the growing problem of obesity, the crucial issue when considering gut derived peptides is to understand their mechanisms of acting because of potential role in clinical therapy, and discovering long-lasting gut peptides or their analogues, with no or minimal side effects.

Obesity in the ageing man

As the population is ageing globally, both ageing and obesity are recognized as major public health challenges. The aim of this narrative review is to present and discuss the current evidence on the changes in body composition, energy balance and endocrine environment that occur in the ageing man. Obesity in the ageing man is related to changes in both body weight and composition due to alterations in energy intake and total energy expenditure. In addition, somatopenia (decreased GH secretion), late-onset hypogonadism (LOH), changes in thyroid and adrenal function, as well as changes in appetite-related peptides (leptin, ghrelin) and, most importantly, insulin action are related to obesity, abnormal energy balance, redistribution of the adipose tissue and sarcopenia (decreased muscle mass). A better understanding of the complex relationship of ageing-related endocrine changes and obesity could lead to more effective interventions for elderly men.