The weight loss in the eight obese subjects who injected the highest leptin dose appeared statistically significant, almost 19 pounds on average, but it ranged widely. Two individuals lost about 35 pounds, while one patient gained nearly 20 pounds. Fortunately, UCSF now is home to a small but growing number of basic researchers who are making their own contributions to science s growing understanding of how body weight is regulated, and who keep up with the research. Among them is Christian Vaisse, who in the past has studied leptin s mechanism of action at the molecular level and who now is interested in identifying genetic variations among individuals that may play a role in obesity. After leptin was identified in 1994 and scientists showed that mice lacking the hormone got fat, Vaisse, as part of a research team that helped to confirm that leptin is essential for body weight regulation in humans, described obese patients with a rare mutation in the leptin receptor gene.
Fat cells make leptin, and in general, obese people have more leptin in their bloodstreams.
Experiments with mice show that leptin injections can reduce food intake. When the injections are halted, the mice eat more again. But single-gene mutations that cause obesity may be an exception to the rule. Vaisse suspects that mutations in numerous genes may have an influence on an individual s tendency to become fat. Considering that obese mouse strains with different defects in the leptin signaling pathways respond differently to leptin, it is not unreasonable to think humans may differ in their ability to lose weight with supplemental leptin, according to Vaisse.