"The nanoparticles were designed to effectively hold the drug and then gradually collapse, releasing it into nearby tissue in a sustained way instead of spreading the drug throughout the body quickly," said Zhen Gu, PhD, patch designer, study co- leader associate professor of joint biomedical engineering at the University of North Carolina at Chapel Hill and North Carolina State University.
The new treatment approach was tested in obese mice by loading the nanoparticles with one of two compounds − rosiglitazone (Avandia) or beta-adrenergic receptor agonist − known to promote browning in mice but not in humans. Each mouse was given two patches − one loaded with drug-containing nanoparticles and another without it − that were placed on either side of the lower abdomen. New patches were applied every three days for a total of four weeks. Control mice were also given two empty patches.
Mice treated with either of the two drugs had a 20 percent reduction in fat on the treated side compared to the untreated side. They also had significantly lower fasting blood glucose levels than untreated mice. Even in lean mice, the treatment with either of the two drugs increased the animals' oxygen consumption (a measure of overall metabolic activity) by about 20 percent compared to untreated controls.
Genetic analyses revealed that the treated side contained more genes associated with brown fat than on the untreated side, suggesting that the observed metabolic changes and fat reduction were due to an increase in browning in the treated mice.
The patch has not been tested in humans. The researchers are currently studying which drugs, or combination of drugs, work best to promote localized browning and increase overall metabolism.