Mild-photothermal and nanocatalytic therapy for obesity and associated diseases

Background: Current anti-obesity medications suffer from limited efficacy and side-effects because they act indirectly on either the central nervous system or gastrointestinal system. Herein, this work aims to introduce a transdermal photothermal and nanocatalytic therapy enabled by Prussian blue nanoparticles, which directly act on obese subcutaneous white adipose tissue (sWAT) to induce its beneficial remodeling including stimulation of browning, lipolysis, secretion of adiponectin, as well as reduction of oxidative stress, hypoxia, and inflammation. Methods: Prussian blue nanoparticles were synthesized and incorporated into silk fibroin hydrogel for sustained retention. The efficacy of mild photothermal (808 nm, 0.4 W/cm², 5 min) and nanocatalytic therapy (mPTT-NCT) was assessed both in vitro (3T3-L1 adipocytes) and in vivo (obese mice). The underlying signaling pathways are carefully revealed. Additionally, biosafety studies were conducted to further validate the potential of this therapy for practical application. Results: On 3T3-L1 adipocytes, mPTT-NCT was able to induce browning, enhance lipolysis, and alleviate oxidative stress. On obese mice model, the synergistic treatment led to not only large mass reduction of the targeted sWAT (53.95%) but also significant improvement of whole-body metabolism as evidenced by the substantial decrease of visceral fat (65.37%), body weight (9.78%), hyperlipidemia, and systemic inflammation, as well as total relief of type 2 diabetes. Conclusions: By directly targeting obese sWAT to induce its beneficial remodeling, this synergistic therapy leads to significant improvements in whole-body metabolism and the alleviation of obesity-related conditions, including type 2 diabetes. The elucidation of underlying signaling pathways provides fundamental insights and shall inspire new strategies to combat obesity and its associated diseases.