Human experimental medicine studies of gut hormone LEAP2, an endogenous ghrelin antagonist and target for obesity, diabetes, cachexia and addiction

Obesity, and alcohol dependence are major health burdens, with significant economic, social and societal impacts. After people lose weight it is common for them to regain this weight over time, and this is driven in part by changes in hormones producd by the gut and fat cells in the body which act on the brain to influence behaviour and appetite. One of these is ghrelin, a hormone produced by the stomach, that increases in the blood when people fast or lose weight, and falls when they eat food or gain weight. Ghrelin stimulates appetite, food intake and the brain's responses to seeing food by acting on the hunger and reward circuits, and is also thought to cause stress-induced overeating.

Ghrelin also stimulates consumption and motivation to seek alcohol. Similar circuits in the brain reglate our behaviours to food as well as alcohol and other drugs of abuse. Blocking the action of ghrelin in the body may therefore be a potential treatment to help people lose weight initially or particularly to maintain their weight loss, as well as reducing alcohol consumption and preventing relapse in those with alcohol dependence.

Recently a new hormone has been discovered called LEAP2, that is produced in the gut, and in animal studies LEAP2 blocks the action of ghrelin at its receptor. Levels of LEAP2 in the blood move in the opposite direction to ghrelin as people lose or gain weight, or fast or eat food. However, little is currently known about whether LEAP2 has the same effects in humans, or if it may have a potential as a treatment for obesity and addiction.

To understand what LEAP2 does in humans this study will perform the following:

(i) for the first time give LEAP2 hormone to healthy participants to assess safety and how much one needs to give to increase blood levels to a slightly higher than normal level:

(ii) see if giving this hormone over several hours only, as an infusion into a vein, to healthy people who are not obese, reduces their appetite and how much they eat, and whether it also changes sugar levels in the blood and the levels of other hormones (the hormone infusion will be compared with placebo water infusion);

(iii) use brain MRI scanning to see if giving this hormone reduces brain activation when they see pictures of food or alcohol, or play a game where they can win points towards money, food or alcohol rewards, or see unpleasant images (as a stressor); and

(iv) see what things change LEAP2 levels in the blood by measuring the levels in people who have already had blood samples stored from previous studies, before and after they have lost weight, either from dieting, having obesity surgery or other procedures to aid weight loss, and also when they eat a meal, or are given other gut hormones that can affect appetite.

This information will enable us to see if targeting LEAP2 will be a worthwhile approach to develop new medicines for the treatment of obesity, diabetes, and addiction to alcohol, and also in the reverse situation, for people with illnesses that cause them to lose appetite and their weight.

In mice, the novel gut hormone LEAP2, an endogenous GHSR (ghrelin receptor) antagonist/inverse agonist, attenuates signaling by the biologically active stomach-derived hormone, acyl ghrelin (AG).

This first study in humans, examines if LEAP2:
(i) reduces appetite and food intake,
(ii) lowers plasma glucose via stimulation of insulin secretion and decreasing GH secretion, and
(iii) reduces brain cue reactivity and reward anticipatory responses to high-energy foods, money and alcohol, and negative emotional reactivity, while
(iv) regulation of plasma LEAP2 is reciprocal to AG, possibly through direct interactions between the two hormones.

This first-in-human experimental medicine study will address these hypotheses by first performing a dose finding pilot study, and a double-blind placebo-controlled cross-over study administering an acute intravenous infusion of LEAP2 (compared to placebo) to healthy, non-obese adults, and assessing the above outcome measures, through ratings of appetite and craving, ad libitum test meals, blood sampling for metabolites and hormones, and functional MRI brain scans during a food and alcohol evaluation task, an incentive delay task for money, food and alcohol, and a negative emotional reactivity task.

Plasma LEAP2 and AG concentrations will also be assayed from studies involing weight loss through different dietary, surgical and endoscopic means, as well as after eating food and administration of other appetitive gut hormones including AG, desacyl ghrelin and GLP-1.

There is a pressing need to develop novel pharmacotherapies for obesity, metabolic diseases and addiction, and an approach derived alterations of gut hormones provides many opportunities. The increasing evidence of gut-hormone-brain pathways affecting both food and alcohol consumption and reward means that we will see increasing cross-over in pharmacological approches for treatments between the disciplines, with hormone-based therapies and targets having potential in both spheres.

As with the discovery of any new hormone, such as LEAP2, there is much classical physiology, endocrinology, metabolism and neuroscience to investigate, before this can be pursued as a drug target in obesity, diabetes and addiction. However, knowedge about its safety and potential biological efficacy in humans is an essential first step to compliment measurement of its plasma concentrations under a variety of manipulations, diseases and clinical interventions, and associations with other metabolites and hormone levels. Furthermore, the discovery of a ghrelin antagonist that could be used in humans by mimicking a naturally occuring hormone, can be of great utility in exploring the physiological (as opposed to pharmacological) actions of ghrelin in a wide variety of body systems. The pleiotropic effects of exogenous ghrelin mean that this research will be of interst to many scientific and clinical disciplines as a way of probing the role of endogenous ghrelin in humans.

If efficacy is seen in this study, future experimental medicine studies will need to study the action of LEAP2 in patients, including obesity, type 2 diabetes mellitus, and relevant addicted populations e.g. alcohol use disorder, smokers, problem gamblers etc. Such proof-of-concept experimental medicine study (as with our ICCAM and GHADD studies) provides a Go-NoGo decision gateway to pursue clinical trials once appropriate pharmaceutical formulations are available. Other fields in which further investigation of ghrelin antagonists, and LEAP2-mimetics, may be of benefit include: weight regain after bariatric surgery, and genetic forms of obesity including Prader-Willi syndrome, where AG is markedly elevated.

As a first-in-human peptide hormone study, this study has elected to use intravenous infusions in this initial study to allow fine tuning of dose finding and avoid any safety concerns with a bolus subcutaneous dose. Future studies could switch to using subcutaneous injections after this initial intravenous study as previous done with the first ghrelin administration studies at Imperial (Wren et al. 2001; Druce et al. 2005, 2006; Ashby et al. 2009, Goldstone et al. 2014). Pharmacological advances through academic and pharmaceutical company research are likely to find modified versions of LEAP2 with improved ability to bind and block GHSR (AG receptor) and have longer lasting duration of action to avoid need for once daily or more frequent subcutaneous injections, as has been seen in the GLP-1 therapeutic space for obesity and type 2 diabetes mellitus.

In addition to these other beneficial effects of gut hormones, their action through replication of endogenous hormonal changes which occur regularly as we eat meals may also help avoid side effects seen with drugs targeting neurotransmitter systems.

Recently, N-terminal fragments of LEAP2, including LEAP2(1-12-NH2), have been found to maintain biological activity to that of full length LEAP2, binding to GHSR, and acting as an antagonist to AG, blocking its effects to increase food intake, and in vitro acting as an antagonist to AG, and as an inverse agonist at the constitutively active GHSR receptor. This will facilitate the development of smaller peptide molecules to mimic effects of LEAP2 for clincial use. Indeed, replication of the findings of this study using LEAP2(1-12-NH2) in humans would be an obvious next step towards impact.