Background
The association of obesity with type 2 diabetes has been recognized for decades. Insulin resistance is a fundamental aspect of type 2 diabetes and is also linked to hypertension, hyperlipidemia, atherosclerosis and cardiometabolic syndrome. Skeletal muscle accounts for as much as 80% of insulin-sensitive glucose metabolism. An understanding of the mechanism and regulation of muscle glucose utilization is necessary to determine the nature of the defects present in metabolic diseases such as obesity and insulin-resistant diabetes. Glucose transport, the initial step in glucose utilization, is often considered rate determining in glucose utilization in muscle. Uptake of glucose and glycogen synthesis in skeletal muscle is of interest for type 2 diabetes treatment. On the other hand, Salacia extracts have been used in Ayurvedic medicine for diabetes and have been extensively consumed as a food supplement for the prevention of diabetes.
Aim
The present study aimed to determine the effects of different concentrations of proanthocyanidins-rich Salacia extract (1, 10 and 100 μg/ml) on basal and insulin stimulated 2-deoxy glucose uptake and glycogen accumulation in primary human skeletal muscle cells.
Method
Glucose uptake in human skeletal muscle cells was determined by a bioluminescent assay using a glucose uptake assay kit from Promega   (catalogue number: CS1876A01), based on the detection of 2-deoxyglucose-6-phosphate. The luminescence signal was proportional to the concentration of 2-deoxyglucose-6-phosphate in the cells, and thus the rate of glucose uptake. Glycogen synthesis was determined in cell culture lysates from human skeletal muscle cells using a colorimetric assay kit from BioVision Inc. (catalogue number: K-646-100). Absorbance was measured at 570 nm. Proanthocyanidins-rich Salacia extract was compared to two positive controls: caffeine (100μg/ml) and leucine (100μg/ml).
Results
Our results showed that proanthocyanidins-rich Salacia extract did not affect glucose uptake nor glucose synthesis in the absence of insulin. In the presence of insulin (100 nM) glucose uptake was significantly enhanced upon treatment with proanthocyanidins-rich Salacia extract at lower concentration (1µg/ml) compared to non-treated cells (p<0.05). This effect was more pronounced than caffeine or leucine. Proanthocyanidins-rich Salacia extract also significantly enhanced insulin stimulated glycogen synthesis in human skeletal muscle cells (p<0.05) compared to vehicle control. No difference was observed between proanthocyanidins-rich Salacia extract and positive controls. 
Discussion
These results suggest proanthocyanidins-rich Salacia extract may improve insulin action, increase insulin sensitivity and play a role in enhancing glucose utilization in skeletal muscles.

Proanthocyanidins-rich salacia extract enhances glucose uptake and glycogen content in human skeletal muscle cells