Bariatric surgery and the gut-brain communication--the state of the art three years later

Comparison of surgical versus diet-induced weight loss on appetite regulation and metabolic health outcomes

Bariatric surgery is associated with significant and sustained weight loss and improved metabolic outcomes. It is unclear if weight loss alone is the main mechanism of improved metabolic health. The purpose of this trial was to compare indices of appetite regulation, insulin sensitivity and energy intake (EI) between participants achieving 10 kg of weight loss via Roux-en-Y Gastric Bypass (RYGB) or dietary restriction (DIET); intake of a very low calorie liquid diet (800 kcal/d; 40% protein, 40% fat, 20% carbohydrate that matched the post-RYGB dietary protocol). Adults qualifying for bariatric surgery were studied before and after 10 kg of weight loss (RYGB [n = 6]) or DIET [n = 17]). Appetite (hunger, satiety, and prospective food consumption [PFC]), appetite-related hormones, and metabolites (ghrelin, PYY, GLP-1, insulin, glucose, free fatty acids [FFA], and triglycerides [TG]) were measured in the fasting state and every 30 min for 180 min following breakfast. Participants were provided lunch to evaluate acute ad libitum EI, which was similarly reduced in both groups from pre to post weight loss. Fasting ghrelin was reduced to a greater extent following RYGB compared to DIET (P = 0.04). Area under the curve (AUC) for ghrelin (P = 0.01), hunger (P < 0.01) and PFC (P < 0.01) increased after DIET compared to RYGB, following 10 kg weight loss. Satiety AUC increased after RYGB and decreased after DIET (P < 0.01). Glucose and insulin (fasting and AUC) decreased in both groups. FFA increased in both groups, with a greater increase in AUC seen after RYGB versus DIET (P = 0.02). In summary, appetite-related indices were altered in a manner that, if maintained, may promote a sustained reduction in energy intake with RYGB compared to DIET. Future work with a larger sample size and longer follow-up will be important to confirm and extend these findings.

Rational design of dual peptides targeting ghrelin and Y2 receptors to regulate food intake and body weight

Ghrelin and Y2 receptors play a central role in appetite regulation inducing opposite effects. The Y2 receptor induces satiety, while the ghrelin receptor promotes hunger and weight gain. However, the food regulating system is tightly controlled by interconnected pathways where redundancies can lead to poor efficacy and drug tolerance when addressing a single molecule. We developed a multitarget strategy to synthesize dual peptides simultaneously inhibiting the ghrelin receptor and stimulating the Y2 receptor. Dual peptides showed dual activity in vitro, and one compound induced a slight diminution of food intake in a rodent model of obesity. In addition, stability studies in rats revealed different behaviors between the dual peptide and its corresponding monomers. The Y2 receptor agonist was unstable in blood, while the dual peptide showed an intermediate stability compared to that of the highly stable ghrelin receptor inverse agonist.

Neuropsychiatric features associated with nutritional and metabolic status in a gastric bypass patient

Bariatric patients may present for psychiatric evaluation due to exacerbation of preexisting psychiatric disorders, new onset psychiatric disorders and/or neuropsychiatric complications associated with abnormal nutritional and metabolic states following the surgical procedure. These neuropsychiatric complications can be insidious, and clinical manifestations may vary, possibly due to the individual central nervous system (CNS) vulnerability to nutritional decline. Lack of awareness of these complications and their symptoms can result in delays in diagnosis and treatment. Identifying and correcting underlying pathophysiologic processes that lead to such neuropsychiatric syndromes can be challenging. We report a case of a patient who developed a protracted course of mood and cognitive disorder after gastric bypass surgery, which illustrates some of the complexities encountered in diagnosing and managing these patients.

Brief report: approaches to 31P-MRS in awake, non-sedated children with and without autism spectrum disorder

We piloted a suite of approaches aimed to facilitate a successful series of up to four brain and muscle (31)Phosphorus-Magnetic Resonance Spectroscopy ((31)P-MRS) scans performed in one session in 12 awake, non-sedated subjects (ages 6-18), 6 with autism spectrum disorders (ASD) and 6 controls. We targeted advanced preparation, parental input, physical comfort, short scan protocols, allocation of extra time, and subject emotional support. 100% of subjects completed at least one brain scan and one leg muscle scan: 42 of 46 attempted scans were completed (91%), with failures dominated by exercise muscle scans (completed in 6/6 controls but 3/6 cases). One completed scan lacked usable data unrelated to subject/scan procedure (orthodonture affected a frontal brain scan). As a group, these methods provide a foundation for conduct and enhancement of future MR studies in pediatric subjects with ASD.

Physiology of weight loss surgery

The clinical outcomes achieved by bariatric surgery have been impressive. However, the physiologic mechanisms and complex metabolic effects of bariatric surgery are only now beginning to be understood. Ongoing research has contributed a large amount of data and shed new light on the science behind obesity and its treatment, and this article reviews the current understanding of metabolic and bariatric surgery physiology.

Peripheral signals modifying food reward

The pleasure derived from eating may feel like a simple emotion, but the decision to eat, and perhaps more importantly what to eat, involves central pathways linking energy homeostasis and reward and their regulation by metabolic and endocrine factors. Evidence is mounting that modulation of the hedonic aspects of energy balance is under the control of peripheral neuropeptides conventionally associated with homeostatic appetite control. Here, we describe the significance of reward in feeding, the neural substrates underlying the reward pathway and their modification by peptides released into the circulation from peripheral tissues.

Mechanisms responsible for excess weight loss after bariatric surgery

Obesity has increased alarmingly in the United States and is increasing in many countries of the world. Because obesity is an important risk factor for type 2 diabetes and other chronic diseases, it is important to develop approaches to counter the rapid increase in adiposity. One approach is bariatric surgery, the most successful clinical intervention known for treating obesity. Surgery can result in impressive weight loss and improvement of obesity-related comorbidities. Yet the mechanisms responsible for this remarkable effect of surgery remain controversial. It is now clear that caloric restriction, per se, does not explain all the reduction in stored fat mass after surgery. A number of gastrointestinal hormones, including glucagon-like peptide (GLP)-1, peptide YY, oxyntomodulin, GLP-2, glucose-dependent insulinotropic polypeptide, ghrelin, and others, can play roles in energy homeostasis and could be involved in bariatric-surgery-related weight loss and weight loss maintenance. Vagal innervation may play a role. In addition, there may be other yet-uncharacterized factors that could participate. This review discusses the possible roles of these hormonal mechanisms in various types of bariatric surgery to help elucidate some of the potential mechanisms at play in short-term and long-term post-bariatric surgery weight loss. Understanding such mechanisms could lead to new and efficacious means to control or even reduce the epidemic of obesity.

Bariatric surgical anatomy and mechanisms of action

Because bariatric surgery is becoming increasingly common, gastroenterologists need to be familiar with the surgical and endoscopic anatomy of the operations in use today. This review focuses on the 4 most commonly performed bariatric operations in the United States: Roux-en-Y gastric bypass, adjustable gastric band, sleeve gastrectomy, and biliopancreatic diversion with duodenal switch. The anatomy and mechanism of action of each procedure is discussed and illustrated. Emphasis is placed on the endoscopic anatomy, with review of the commonly encountered complications. Emerging techniques and devices are reviewed.

New approaches to the pharmacological treatment of obesity: can they break through the efficacy barrier?

In this review we assess the range of centrally active anorectics that are either in human clinical trials, or are likely to be so in the near future. We describe their weight loss efficacy, mode of action at both pharmacological and behavioural levels, where understood, together with the range of side effects that might be expected in clinical use. We have however evaluated these compounds against the considerably more rigorous criteria that are now being used by the Federal Drugs Agency and European Medicines Agency to decide approvals and market withdrawals. Several trends are evident. Recent advances in the understanding of energy balance control have resulted in the exploitation of a number of new targets, some of which have yielded promising data in clinical trials for weight loss. A second major trend is derived from the hypothesis that improved weight loss efficacy over current therapy is most likely to emerge from treatments targeting multiple mechanisms of energy balance control. This reasoning has led to the development of a number of new treatments for obesity where multiple mechanisms are targeted, either by a single molecule, such as tesofensine, or through drug combinations such as qnexa, contrave, empatic, and pramlintide+metreleptin. Many of these approaches also utilise advances in formulation technology to widen safety margins. Finally, the practicality of peptide therapies for obesity has become better validated in recent studies and this may allow more rapid exploitation of novel targets, rather than awaiting the development of orally available small molecules. We conclude that novel, more efficacious and better tolerated treatments for obesity may become available in the near future.