Mechanistic Insights into S-Allyl Cysteine's Insulin-Mimetic Role: Glucose Uptake, Receptor Kinase Interaction, and Sensitivity Recovery in Skeletal Myotubes

S-allyl cysteine (SAC), the most abundant sulfur-containing compound contained in black garlic, exerts several biological activities, including antioxidant and anti-inflammatory effects, accounting for multiple beneficial roles, among which the protection against insulin-resistance has been proposed. Despite these evidences, mechanistic study supporting its direct involvement in the modulation of insulin response and in counteracting insulin-resistance are still missing. Aim of this study is to evaluate the molecular mechanism of action of SAC on the insulin-dependent metabolic response. For this purpose, SAC effects on protein synthesis, glucose uptake, and GLUT4 translocation were assessed on C2C12 skeletal myotubes. The interaction of SAC with the insulin receptor was studied with molecular docking analyses and Differential Scanning Calorimetry. Finally, the counteracting role of SAC against insulin-resistance was studied in a C2C12 palmitic acid-induced insulin resistance model. Our results show that SAC, like insulin, stimulates protein synthesis, glucose uptake and GLUT4 plasma membrane translocation in skeletal myotubes. These last effects were reduced in the presence of the insulin receptor antagonist S961. Moreover, results from docking and calorimetry demonstrate an interaction of SAC with the insulin receptor kinase domain. Furthermore, SAC significantly both prevent and reverse the development of palmitic acid-induced insulin resistance, restoring glucose uptake to the levels detected in non-insulin-resistant cells. As a whole, these data reveal mechanistic insights into SAC insulin-mimetic role, paving the way for future research on new tools able to prevent insulin resistance and the consequent onset of metabolic syndrome.