Ginkgo biloba extract (GbE) has been indicated as an efficient
medicine for the treatment of diabetes mellitus type 2. It remains unclear if its
effects are due to an improvement of the insulin signaling cascade, especially in
obese subjects. The aim of the present study was to evaluate the effect of GbE on
insulin tolerance, food intake, body adiposity, lipid profile, fasting insulin, and
muscle levels of insulin receptor substrate 1 (IRS-1), protein tyrosine phosphatase
1B (PTP-1B), and protein kinase B (Akt), as well as Akt phosphorylation, in
diet-induced obese rats. Rats were fed with a high-fat diet (HFD) or a normal fat
diet (NFD) for 8 weeks. After that, the HFD group was divided into two groups: rats
gavaged with a saline vehicle (HFD+V), and rats gavaged with 500 mg/kg of GbE diluted
in the saline vehicle (HFD+Gb). NFD rats were gavaged with the saline vehicle only.
At the end of the treatment, the rats were anesthetized, insulin was injected into
the portal vein, and after 90s, the gastrocnemius muscle was removed. The
quantification of IRS-1, Akt, and Akt phosphorylation was performed using Western
blotting. Serum levels of fasting insulin and glucose, triacylglycerols and total
cholesterol, and LDL and HDL fractions were measured. An insulin tolerance test was
also performed. Ingestion of a hyperlipidic diet promoted loss of insulin sensitivity
and also resulted in a significant increase in body adiposity, plasma
triacylglycerol, and glucose levels. In addition, GbE treatment significantly reduced
food intake and body adiposity while it protected against hyperglycemia and
dyslipidemia in diet-induced obesity rats. It also enhanced insulin sensitivity in
comparison to HFD+V rats, while it restored insulin-induced Akt phosphorylation,
increased IRS-1, and reduced PTP-1B levels in gastrocnemius muscle. The present
findings suggest that G. biloba might be efficient in preventing and
treating obesity-induced insulin signaling impairment.