ACS Nano 11, 9223–9230 (2017 )

Brown adipose tissue (BAT) is a heat-generating organ abundant in hibernating animals and newborn babies. While white adipose tissue (WAT) stores excessive energy in the form of fatty molecules, BAT consumes energy through non-shivering thermogenesis. Conversion of WAT into BAT, defined as a 'browning' process, could offer treatment options for obesity and its associated pathologies, such as type-2 diabetes. However, the use of browning agents in the clinic is stymied by the existence of side effects affecting unrelated organs.

Now Zhang et al. engineer a biocompatible microneedle patch for local delivery of browning molecules encapsulated in dextran nanoparticles. The nanoparticles also contain glucose oxidase (GOx) and catalase, which allow controlled release of the browning drugs. In the presence of a physiological concentration of glucose, GOx produces gluconic acid, while catalase neutralizes the hydrogen peroxide produced by the reaction. The resulting decrease of the local pH triggers degradation of the nanoparticles and subsequent drug release.

After confirming that the nanoparticles induce in vitro reprogramming of white adipocytes into brown adipocytes, the researchers apply the nanoparticle-loaded microneedle patch to the inguinal region of lean and obese mouse models. Six days post-treatment, lean mice show local browning of visceral white fat pads and improved systemic metabolism, an indication of the sustained effect of the browning agents. After four weeks, diet-induced obese mice lose 30% of their visceral WAT and display increased energy consumption, higher fatty acid oxidation, improved body weight control and higher insulin sensitivity. These observations support the anti-obesity and anti-diabetic potential of the designed microneedle patch.