Damiana ( <i>Turnera diffusa</i> ) Reduces Adipocyte Cell Differentiation and Ameliorates Myocyte Glucose Uptake

<i>Turnera diffusa</i> Willd. ex Schult. leaf has been used in traditional medicine as an aphrodisiac, tonic, and in the management of diabetes. Based on the traditional use and recent evidence of antidiabetic activity, we investigated the effects of a 95% ethanolic extract of <i>T. diffusa</i> leaf (TDE) on a series of ligand-activated transcription factors, namely PPARα, PPARγ, LXR and NRF2, which are involved in the regulation of metabolic pathways associated with obesity, diabetes and inflammation. Further, the effects of TDE on α-glucosidase enzyme, lipid accumulation in adipocytes (adipogenesis) and glucose uptake in myocytes were also evaluated. Phytochemical analysis of TDE was performed by mass spectrometry. TDE (50 μg/mL) demonstrated a strong agonistic effect on LXR (2.7-fold) and NRF2 (21.6-fold), while the activation of PPARα, and PPARγ was in the range of 1.4-1.8-folds under similar experimental conditions. At a concentration of 100 μg/mL TDE decreased lipid accumulation in adipocytes by 55.3% and increased glucose uptake in muscle cells by 91.3%. The adipogenic effect induced by a full PPARγ agonist (rosiglitazone) was antagonized by TDE showing a decrease of 57.6% in lipid accumulation. This is the first report to reveal the agonistic action of TDE on multiple nuclear receptors along with its glucose uptake enhancing and antiadipogenic effects. The results indicate the potential utility of TDE in alleviating the symptoms of metabolic syndrome and in preventing the undesired adipogenic effects of antidiabetic drugs of the glitazone class. Phytochemical analysis of TDE indicated the presence of flavonoids as major constituents. Further studies in animal models of type II diabetes and obesity are warranted to explore its utility as an anti-diabetic and anti-obesity supplement.