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 Thr(172) phosphorylation of the catalytic alpha subunit of AMPK, an essential step for full kinase activation increased in a dose- and time-dependent manner. Ser(79) phosphorylation of acetyl CoA carboxylase, an intracellular substrate of AMPK, increased similarly. Analysis of isoform-specific AMPK activity revealed that MLE activated both the alpha1 and alpha2 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.