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

Abstract

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 α 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 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.