Morus alba leaf extract stimulates 5′-AMP-activated protein kinase in isolated rat skeletal muscle

Aim of the study

Morus alba (mulberry) leaf is a natural therapeutic agent that has been shown to have an antidiabetic effect. We explored the possibility that 5′-AMP-activated protein kinase (AMPK) is involved in metabolic enhancement by the Morus alba leaf.

Materials and methods

Isolated rat epitrochlearis muscle was incubated in a buffer containing Morus alba leaf hot water extract (MLE) and the AMPK activation and related events were examined.

Results

In response to MLE treatment, the Thr¹⁷² phosphorylation of the catalytic α subunit of AMPK, an essential step for full kinase activation increased in a dose- and time-dependent manner. Ser⁷⁹ phosphorylation of acetyl CoA carboxylase, an intracellular substrate of AMPK, increased similarly. Analysis of isoform-specific AMPK activity revealed that MLE activated both the α1 and α2 isoforms of the catalytic subunit. This increase in enzyme activity was associated with an increased rate of 3-O-methyl-d-glucose transport in the absence of insulin and with phosphorylation of AS160, a signaling intermediary leading to glucose transporter 4 translocation. The intracellular energy status, estimated from the ATP and phosphocreatine concentrations, was not affected by MLE.

Conclusion

MLE stimulates skeletal muscle AMPK activity acutely without changing the intracellular energy status.