Leptin is a 16 kDa protein hormone, meaning that it weighs 16,000 Dalton, or atomic mass units. The purpose of this hormone in the body is to regulate energy intake and expenditure. Leptin regulates your appetite and metabolism through a variety of methods. Leptin is an adipose derived hormone. It is created primarily in the adipocytes in white adipose tissue (white fat), but it is also created in a variety of other places in the body. Leptin is a protein made up of 167 amino acids.
The effects of leptin were first observed in 1950 at the Jackson Laboratory. It was observed that some mice in a colony of mice were extremely obese and would eat voraciously. It turned out that they all shared a certain kind of gene mutation that either inhibited the production of leptin or inhibited leptin receptors. When the mutated mice were injected with leptin, it was observed that they began to eat less and lost weight. Leptin itself was discovered in 1994 at Rockefeller University.
The way that leptin works is very interesting. Leptin acts on the hypothalamus to inhibit appetite. It does this by counteracting the effects of feeding stimulants like neuropeptide Y or anandamine. It also promotes the production of the apetite suppressant MSH. The way that leptin does this is to bind to neurons and impede the reception of these hormones or their production.
Leptin had been studied as a treatment for obesity in humans. In studies of people with specific mutations in the production or reception of leptin, direct injections of recombinant human leptin have been shown to reduce the persons apetite and weight. In clinical trials studying the effects of leptin on obese people in general, however, the results were inconclusive. The problem was that the recombinant human leptin was not very soluble, had a short half-life in circulation, and was biologically not very potent. Another chemical has been created as a potential treatment to obesity. This other hormone is called Fc-leptin. Fc-leptin is much more soluble, has a longer half-life, and is much more potent than regular leptin. In studies on mice, Fc-leptin successfully treated obesity.