Leptin was first described in 1994 by scientist Jeffrey Friedman. The word leptin, which comes from the Greek, literally means “thin.” Assigned to the proteohormones, leptin is responsible for appetite regulation.
What is leptin?
Proteohormones are the hormones that are structured like proteins but still perform typical tasks of hormones – such as messenger functions and regulatory mechanisms. Leptin is a typical such protein compound with hormone function. Leptin is mainly produced and released in fat cells (adipocytes). In much smaller quantities, leptin is also formed in bone marrow, placenta and gastric mucosa. Leptin has an appetite-suppressing effect in the human body and is thus actively involved in the regulation of the amount of food consumed.
Production, manufacture, and formation
Leptin is a fat-insoluble protein compound that is produced in the fat cells of the human body. In very small amounts, the placenta, spinal cord, and skeletal muscle also produce leptin. The neuropeptides released via the hypothalamus, which stimulate appetite and encourage people to eat, are inhibited by leptin. Accordingly, the most important function of leptin is to act as a receptor for neuropeptides. Leptin also serves as a receptor for POMC (proopiomelanocortin) and KART (cocaine– and amphetamine-regulated transcript). Here, however, leptin acts in a quasi-inverted manner: POMC and CART have an appetite-suppressing effect per se, but they must first be activated by leptin. As soon as fat depots in the adipocytes are reduced, the leptin level in the blood drops. The low concentration in turn ensures that appetite is stimulated. This, among other reasons, is why humans experience a feeling of hunger.
Function, effect and properties
Leptin is a hormone produced naturally in the body, predominantly in fat cells. By inhibiting appetite-stimulating neuropeptides on the one hand, and by activating appetite-inhibiting transmitters such as POMC and KART, leptin directly affects the amount of food a person eats. The amount of leptin in the blood is directly dependent on the amount of fat depots. If the body’s adipocytes are full, the fat cells produce leptin, which suppresses appetite. If the amount of fat in the adipocytes decreases, they stop producing leptin; appetite develops. The described fluctuation in the fat content is not externally perceptible for humans, i.e. corpulent people are just as little constantly appetite-less as thin people constantly suffer from hunger. Whether leptin performs other tasks has not yet been adequately demonstrated.
Diseases, ailments, and disorders
Leptin can cause high blood pressure and increase heart rate by stimulating the nervous system. However, this is rather uncommon and not a medical condition worthy of treatment as such. Moreover, the symptoms usually subside quickly. Soon after the discovery of leptin, scientists were able to identify the function of the hormone, which is a regulation of appetite. For years, the diet industry, as well as medical research, tried to take advantage of the appetite-suppressing effect of leptin. It was assumed that obese people suffer from a leptin deficiency and therefore have a perpetual appetite, which ultimately leads to massive obesity. From then on, attempts were made to artificially supply this assumed deficiency in the form of a leptin-containing tablet. However, extensive tests showed that obese people did not suffer from a leptin deficiency; on the contrary, many obese people actually had very high leptin levels (leptin paradox). It was subsequently demonstrated that obese people in many cases do not suffer from leptin deficiency but from leptin resistance. The body’s own leptin cannot inhibit the appetite-stimulating neuropeptides and at the same time cannot activate the appetite-inhibiting transmitters POMC and CART. Patients suffering from leptin resistance are thus very often obese and can only achieve and maintain a healthy body weight with enormous willpower and discipline. However, recent research gives reason for hope. A group of researchers from Boston was able to show which regions in the brain or hypothalamus are responsible for leptin resistance. They were able – at least in animal experiments – to stimulate the hypothalamus to produce chaperones. Chaperones are proteins that support hormones in their activity.Leptin resistance could thus be at least partially reversed, so that perhaps a remedy for obesity, which has its origin in leptin resistance, could be found in the near future after all. An interesting line of research is trying to establish a link between eating disorders and leptin. It seems that some people can control their appetite in a more disciplined way than others. Patients suffering from anorexia even seem to be able to eliminate their appetite altogether. However, it has not yet been possible to answer satisfactorily whether there is a connection between such disorders and a disturbed leptin balance.
