Endocrine Abstracts

Background: Obesity is strongly associated with insulin resistance (IR). IR at the molecular level may be defined as a diminished activation of PI3K/Akt signaling and its related molecules (IRS-1/Akt/AS160) as well as reduced glucose uptake. Subjects with obesity have elevated plasma levels of saturated fatty acids, such as palmitic acid (PA), which triggers insulin signaling disruption in vivo and in vitro. Oregano (Origanum vulgare L.) is a plant used as a food component worldwide. Interestingly, the main constituents of oregano have shown protective effects on obesity-related dysfunctions. The Origanum vulgare L. essential oil (O-EO) contains considerable amounts of phenolic monoterpenes, such as carvacrol and thymol, which may explain the biological activity of the plant. The aim of this study was to assess whether O-EO exposure protects against PA-induced disruption of IRS-1/Akt/AS160 signaling and glucose uptake in human adipose cells.

Methods: Cytotoxicity of a range of O-EO concentrations (0.01–20 µg/ml) was evaluated by MTS assay in in vitro differentiated adipocytes from the adipose cell line SW872. Adipocytes were incubated or not with PA for 24 h in the presence or not of O-EO (2-h preincubation), and thereafter stimulated with insulin or vehicle. Thereby, experimental conditions were: control (untreated cells), 0.4 mM PA, 0.1 µg/ml of O-EO, 10 µg/ml of O-EO, 0.1 µg/ml of O-EO (2 h before) + 0.4 mM PA for 24 h, 10 µg/ml of O-EO (2 h before) + 0.4 mM PA for 24 h, and incubated with 100 nM insulin for 10 min. Phosphorylation of Tyr-IRS-1, Ser-Akt and Thr-AS160 were evaluated by Western blot and glucose uptake was assessed using the 2-NBDG analogue.

Results: In SW872 adipocytes, O-EO was not cytotoxic at any concentration assessed. Insulin-stimulated phosphorylation of IRS-1, Akt, AS160 and glucose uptake were not affected by treatment with 0.1 and 10 μg/ml O-EO compared with vehicle-treated cells. PA-treated adipocytes showed a reduction in insulin-stimulated phosphorylation of IRS-1, Akt, AS160 and glucose uptake compared to control (P<0.05). Interestingly, these effects were prevented by O-EO treatment.

Conclusion: These findings give new insights into the effect of O-EO ameliorating PA-impaired insulin signaling and glucose uptake in adipocytes. More studies should focus on Origanum vulgare L., since might represent a preventive approach in individuals whose circulating PA levels contribute to IR.