Brown adipose tissue (BAT) is associated with improved metabolic homeostasis in humans, and studies in rodents indicate that subcutaneous white adipose tissue (SC WAT) beiging, which involves increased uncoupling protein 1 (UCP1) expression, also is associated with improved metabolism. The goal of this study was to determine the ability of mirabegron (a β3AR agonist), pioglitazone (a thiazolidinedione), or a combination of the drugs to induce brown and beige adipose tissue and to determine the effects on glucose and lipid homeostasis. We randomized obese, insulin-resistant (IR) research participants to mirabegron (50 mg/day), pioglitazone (30 mg/day), or combination therapy treatment groups. Euglycemic clamping, oral glucose tolerance tests, adipose tissue biopsies, and PET-CT scans were performed at baseline and after 10 weeks of treatment. Mirabegron improved glucose homeostasis (reduced HbA1c and improved oral glucose tolerance) to a similar extent as pioglitazone without side effects or weight gain. Although mirabegron treatment increased insulin sensitivity, the effect size was much smaller than pioglitazone, yet mirabegron treatment significantly increased the insulinogenic and disposition indexes, suggesting that a major part of the mechanism of mirabegron action involved improving β-cell function. Mirabegron treatment consistently induced SC WAT beiging as evidenced by increased UCP1 expression (2.4 fold increase; P<0.0001), but did not induce BAT, suggesting that induction of beige adipose may be part of the mechanism responsible for improved glucose homeostasis. Pioglitazone also induced beiging (1.6 fold increase in UCP1; P<0.01), but not BAT. The combination of mirabegron plus pioglitazone was not additive, with similar effects on glucose tolerance as single drug. These results suggest that mirabegron treatment has significant beneficial metabolic effects in obese, IR subjects through a distinct mechanism involving SC WAT beiging and improved pancreatic beta cell function.
B. Finlin: None. H. Memetimin: None. A.L. Confides: None. B. Zhu: None. Z.R. Johnson: None. E.E. Dupont-Versteegden: None. P.A. Kern: None.
National Institutes of Health (R01DK112282)