Appetite suppressant... for mice
‘Chemical that can stop you eating for pleasure is discovered by British scientists,’ the Daily Mail reported. It said that an appetite suppressant that takes away the desire for post-pub kebabs and calorific late-night snacks has been discovered by British scientists.
What is not immediately apparent from the news report is that this was an experiment in rodents and its relevance to the human desire for kebabs is limited. The chemical hemopressin does appear to work in a similar way to rimonabant, a synthetic appetite suppressant for humans. However, rimonabant (Acomplia) is no longer available in the UK as its risks (potentially depression and increased suicide risk) were considered to be greater than its benefits.
A lot more research in animals and then humans is needed to determine whether hemopressin suppresses appetite in humans, but without these side effects. At present, a healthy balanced diet and regular exercise remain the best way to lose weight.
Where did the story come from?
The study was carried out by researchers from the University of Manchester in the UK and the University of Mainz, Germany. It was funded by the British Society for Neuroendocrinology and the European Foundation for the Study of Diabetes. The study was published in the peer-reviewed The Journal of Neuroscience.
The Daily Mail did not mention until half way through the article that this was an experiment in mice.
What kind of research was this?
This was a laboratory and animal study investigating the effect of hemopressin, a chemical produced in the rodent brain that affects blood pressure and pain sensation. Hemopressin also affects the cannabinoid receptor (CB1), a part of the brain associated with appetite. Here, the researchers wanted to test the theory that hemopressin is a naturally occurring appetite suppressant.
What did the research involve?
Firstly, the researchers carried out a laboratory experiment on cells to confirm that hemopressin does actually bind to and block the CB1 receptor. They also carried out tests involving normal mice and rats, and mice genetically engineered to be obese or to lack a functioning CB1 receptor. All the rodents were male, housed in similar conditions and fed a fixed amount of food each evening. In one of the experiments, the rodents were randomly selected to receive either hemopressin or a saline injection into their abdomen or a region of their brain. The rodents’ food intake was then assessed one, two, four and 24 hours after the injection.
What were the basic results?
The researchers found that in the normal rats and mice, injecting hemopressin into the brain or the abdomen was associated with a decrease in the amount of food eaten overnight, with greater appetite suppression with greater doses of hemopressin. The effects were demonstrated up to four hours after brain injection and at two hours after abdominal injection. Appetite returned to normal after a further 12 hours.
Obese mice also demonstrated a similar pattern of appetite reduction at one and two hours after hemopressin injection into the abdomen, with appetite returning to normal afterwards. However, in mice genetically engineered to lack a functioning CB1 receptor, there was no reduction in appetite following hemopressin injection.
Hemopressin did not cause any obvious adverse effects such as nausea, sedation or aversion to food. Mice injected with hemopressin displayed no behavioural difference or signs of illness compared to mice given the placebo injection.
How did the researchers interpret the results?
The authors conclude that hemopressin appears to be a natural chemical that blocks CB1 receptors in the brain, and therefore reduces appetite.
Conclusion
Although of scientific interest, this animal research currently has limited direct implications for humans. As the newspaper reports, hemopressin works in a similar way to rimonabant, a synthetic appetite suppressant for humans that also targets the CB1 receptor. However, rimonabant (Acomplia) was withdrawn from the UK market as the European Medicines Agency considered that the drug’s benefits did not outweigh its potential risks, notably depression and possibly increased suicide risk.
It is possible that in the longer-term, hemopressin may be tested as a possible appetite suppressant in humans, but this would require further animal research illustrating efficacy and safety before human studies could begin. In particular, researchers would want to determine whether hemopressin has similar side effects to rimonabant.
Research into appetite stimulants and suppressants is likely to continue. At present, the advice for humans remains the same: that a healthy balanced diet and regular exercise are the best way to reduce the risk of overweight and obesity and their related disease risks.
