Peptide YY: obesity's cause and cure?

Ghrelin and PYY in the regulation of energy balance and metabolism: lessons from mouse mutants

Effective control of body weight and energy homeostasis requires stringent regulation of caloric intake and energy expenditure. Gut-brain interactions comprise a central axis for the control of energy homeostasis by integrating the intake of nutrients with an effective utilization of ingested calories either by storage or by expenditure as cellular fuel. Ghrelin, a stomach-derived peptide, is the only known circulating orexigenic hormone. It is acylated with a medium-chain fatty acid by the enzyme ghrelin O-acetyltransferase (GOAT) and displays a broad range of activity, from central control of food intake to peripheral functions such as gastric emptying and insulin secretion. PYY, a peptide produced by L cells of the small intestine and rectum, has been shown to inhibit gut motility and is proposed to stimulate a powerful central satiety response. In recent years, pharmacological studies in animals and clinical studies in humans have contributed to our knowledge of principal ghrelin and PYY actions. However, valuable findings from studies using ghrelin-deficient mice, ghrelin receptor [growth hormone secretagogue receptor-1a (GHSR1a)]-deficient mice, double-knockout mice (for ghrelin and GHSR), and GOAT-deficient or -overexpressor mice, as well as mice deficient for PYY or neuropeptide Y receptors have allowed better definition of the actual physiological functions of ghrelin and PYY. This review summarizes findings from mutant mouse studies with emphasis on respective gene knockout and transgenic animals and describes how these studies contribute to the current understanding of how endogenous ghrelin and PYY as two major representatives of endocrine gut-brain communications may regulate energy and glucose homeostasis.

Ghrelin and peptide YY in postpartum lactating and nonlactating women

BACKGROUND

Epidemiologic studies suggest that childbearing is an important contributor to the development of obesity in many women and that breastfeeding may be protective. Ghrelin and peptide YY (PYY) are gut hormones involved in appetite regulation and energy homeostasis and are biological neuroendocrine signals that potentially affect body weight and adiposity.

OBJECTIVE

This study evaluated whether fasting or postprandial ghrelin or PYY is different between lactating and nonlactating postpartum women matched for age, body weight, and adiposity.

DESIGN

Ten postpartum lactating women (mean + or - SD: 28.1 + or - 4.9 y of age, 69.2 + or - 11.3 kg, 35.4 + or - 6.6% body fat) and 8 nonlactating women (28.8 + or - 7.6 y of age, 75.6 + or - 13.7 kg, 37.5 + or - 6.5% body fat) at 4-5 wk postpartum underwent measurements of body weight, body composition, and ghrelin and PYY responses to a standardized meal (350 kcal). Seven never-pregnant women served as control subjects (29.7 + or - 4.1 y of age, 60.4 + or - 4.8 kg, 25.5 + or - 2.0% body fat).

RESULTS

Ghrelin concentrations decreased, whereas PYY concentrations increased significantly (P < 0.05) in response to the meal, but fasting or meal-induced changes were not significantly different between lactating and nonlactating women. The fasting ghrelin concentration correlated with body mass index (r = -0.53, P < 0.05) and was significantly lower in postpartum than in control women (894.9 + or - 247.7 compared with 1316.9 + or - 241.0 pg/mL), even after adjustment for body mass index.

CONCLUSIONS

Our data do not support the notion that ghrelin, PYY, or both are plausible neuroendocrine signals that influence body weight regulation during lactation. They suggest, however, that ghrelin may change with increased adiposity in the postpartum state and may potentially play a role in body weight regulation after child birth.

Gut-brain axis

PURPOSE OF REVIEW

To summarize recent studies on the regulation and the functions of the gut-brain axis.

RECENT FINDINGS

Visual cues of food and food intake interact with the gut-brain axis at the level of the hypothalamus. However, the hypothalamic response to glucose intake is considerably altered in patients with type 2 diabetes mellitus, indicating involvement of the hypothalamus in the pathophysiology of this disease in humans. A large number of studies have documented the functions of gut peptides with respect to the regulation of satiety. Gut peptides are involved in the regulation of insulin secretion and sensitivity. Recent data indicate that peptide YY is a gut hormone that also modulates bone metabolism. Increasing evidence is obtained on the role of afferent gastrointestinal nerves, especially the vagal nerve, in the modulation of the functions of the gut-brain axis.

SUMMARY

The gut-brain axis is involved in a multitude of physiological processes including satiety, food intake, regulation of glucose and fat metabolism, insulin secretion and sensitivity and bone metabolism. It is likely, that more aspects of this system will be found the near future.

Anti-obesity drugs

BACKGROUND

Recent discoveries about the metabolic and genetic control systems that govern regulation of body weight and energy expenditure have afforded the opportunity to develop pharmacological agents that can be used as adjunctive treatments for patients with obesity. However, the scarcity of medications available or those that have made it to Phase III trials reflects the difficult challenge of manipulating the biology of appetite regulation.

OBJECTIVE

The aim of this study was to inform health professionals about new anti-obesity medications that target neuronal systems within the central nervous system and peripheral humoral proteins that send signals to the central nervous system.

METHODS

A critical review was conducted of information available from the medical literature.

RESULTS/CONCLUSIONS

An emerging theme is to use combination therapies that are directed towards several targets or leverage existing gastrointestinal satiety hormonal signals. By using combination therapies, it is anticipated that greater weight loss will be achieved compared to monotherapy.