Abstract

Creatine uptake by muscle cells is increased in the presence of insulin. Accordingly, compounds with insulin-like actions may also augment creatine uptake. The aim of this study was to investigate whether Trigonella foenum-graecum (fenugreek), an insulin mimetic, increases total intracellular creatine levels in vitro. Total cellular creatine content was measured fluorometrically in L6C11 muscle myotubes treated for 1, 4, and 24h with 0.5mM creatine (CR), CR and 20μg/mL fenugreek seed extract (CR+FEN), CR and 100nM insulin (CR+INS), and CR+INS+FEN (n=6 per treatment group). Alterations in the expression of the sodium- and chloride-dependent creatine transporter, SLC6A8, and key signaling proteins in the PI3-K/Akt pathway were determined. Compared to control (CON), CR+INS+FEN increased total creatine content after 4h (P<0.05), whereas all conditions increased SLC6A8 protein expression above CON at this time (P<0.05). Changes in insulin signaling were demonstrated via increases in AktThr308 phosphorylation, with CR+INS>CON and CR at 1h (P<0.05) and with CR+INS+FEN>CON, CR, and CR+INS at 4h (P<0.05). In contrast, no changes in PKCζ/λ or GLUT4 phosphorylation were detected. Fenugreek, when combined with insulin, modulates creatine content via a mechanism which is independent of the activity of SLC6A8, suggesting that an alternative mechanism is responsible for the regulation and facilitation of insulin-mediated creatine uptake in skeletal muscle cells.

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