ObjectivesMetformin is the most commonly used FDA approved antidiabetic drug. Emerging evidence suggest that metformin can induce browning of white adipose tissue (WAT). However, oral administration of metformin has a low level of oral bioavailability, a high level of gastrointestinal side effects, and fast renal clearance, these lower its browning WAT efficacy. Hence, localized delivery of metformin directly to subcutaneous WAT (SubQ WAT) using transdermal delivery approach is an attractive alternative. The objectives of this study are to develop metformin transdermal patch and to evaluate its anti-obesity effects in mice. MethodsWe developed a metformin-loaded patch using the combination of microneedle (MN) and Iontophoresis. Thirty male C57BL/6J mice were fed a high fat diet for 4 weeks. Then, mice were randomly divided into one of the following six groups (5/group): 1. MN + Iontophoresis (Metformin), 2. MN + Iontophoresis (Blank), 3. MN alone, 4. Iontophoresis alone, 5. Gavage (Metformin), and 6. Gavage (Saline). Metformin dose was 3 mg/kg body weight/day. All treatments were given 3 times/week for additional 5 weeks. ResultsAs compared to those in other treatment groups, MN + Iontophoresis (Metformin)-treated mice had 3.6- and 7.5-fold lower changes in body weight and body fat % (P < 0.001), lower blood glucose levels (P < 0.01), lower IgWAT and gonadal WAT masses (P < 0.05), higher energy expenditure (P < 0.05), which was associated with higher IgWAT mRNA levels of (UCP1, >3.5-fold), (PGC-1α, >1.3-fold), (CIDEA, >1.9-fold), (TMEM26, 2.6-fold) and UCP1 and phosphorylated AMPK protein expression levels (>9.5- and 9.7-fold), and lower IgWAT mRNA levels of ACC1 (1.5-), leptin (1.2-), MCP1 (1.4-) and TNFα (1.36-fold) (P < 0.001). However, no significant differences were found in food intake and plasma lipid profile. ConclusionsTransdermal delivery of metformin to SubQ WAT using MN and iontophoresis patches decreased body weight and fat gain, increased energy expenditure, lowered fat pad size and enhanced energy expenditure through browning of WAT. Funding SourcesThe project described was supported by Grant Number 1R15AT010395 from the National Center for Complementary and Integrative Health, and Grant Number 19AIREA34480011 from American Heart Association.