Our bodies function according to a cycle close to 24 hours. Sleep, appetite, body temperature and many hormones follow this internal clock. Traveling across several time zones suddenly shifts the external light cycle relative to this rhythm. The body then takes time to readjust, causing jet lag.
Researchers from Rice University and Northwestern University tested a way to act on this clock. Their approach relies on leptin, a hormone best known for its role in regulating appetite and metabolism. Earlier studies had already indicated that it could also play a role in the body's daily rhythms.
To deliver this hormone, the team modified human cells so that they would continuously produce leptin. These cells were then enclosed in small protective capsules and implanted in animals. Encapsulation allows the molecules produced to escape while isolating the cells from the host's immune system.
The researchers then shifted the periods of light and darkness to reproduce a disturbance comparable to a time-zone change. In rodents, the animals receiving leptin adapted more quickly to the new schedule. The team then observed a comparable effect in non-human primates.
The result is interesting because it directly links metabolism to the biological clock. In other words, regulating our daily rhythm does not depend solely on the light received by the eyes. Chemical signals circulating in the body can also alter how quickly this rhythm readjusts.
The researchers now want to better understand how this hormone acts on the mechanisms that regulate the internal clock. They are also studying versions capable of controlling the amount produced or repeating the action on demand.
These studies will have to precede any experimentation in humans.