Abstract
Tea catechins promote glucose uptake in skeletal muscle cells. In this study, we investigated whether the addition of an acyl group to the C-3 position of catechins to generate 3-O-acyl-catechins promoted glucose uptake in L6 myotubes. 3-O-Myristoyl-(−)-epicatechin (EC-C14) and 3-O-palmitoyl-(−)-epicatechin (EC-C16) promoted glucose uptake and translocation of glucose transporter (GLUT) 4 in the cells. The effect of 3-O-acyl-(−)-epicatechins was stronger than that of (−)-epicatechin (EC), whereas neither 3-O-myristoyl-(+)-catechin (C-C14) nor 3-O-palmitoyl-(+)catechin (C-C16) promoted glucose uptake or GLUT4 translocation as well as (+)-catechin (C). We further investigated an affinity of catechins and 3-O-acyl-catechins to the lipid bilayer membrane by using surface plasma resonance analysis. Maximum binding amounts of EC-C16 and C-C16 to the lipid bilayer clearly increased compared with that of (−)-EC and (+)-C, respectively. We also examined the mechanism of GLUT4 translocation and found EC-C14 and EC-C16 induced the phosphorylation of PI3K, but did not affect phosphorylation of Akt or IR. In conclusion, the addition of an acyl group to the C-3 position of (−)-EC increases its affinity for the lipid bilayer membrane and promotes GLUT4 translocation through PI3K-dependent pathways in L6 myotubes.
Highlights
Catechins and their gallate esters are a class of polyphenols that includes the subclass known as flavan-3-ols
It was demonstrated that green tea and tea catechins possessed a regulatory effect on glucose metabolism [6,7], especially, (−)-epigallocatechin gallate (EGCg), the major compound derived from green tea
Because insulin-induced translocation of GLUT4 requires the activation of several proteins in the insulin signaling pathway, such as IR, phosphatidylinositol 3ʹ-kinase (PI3K), and Akt [8], we investigated whether 3-O-acyl-(−)epicatechins activate the insulin signaling pathway in L6 myotubes
Summary
Catechins and their gallate esters are a class of polyphenols that includes the subclass known as flavan-3-ols. EGCg promoted glucose uptake, along with glucose transporter (GLUT) 4 translocation in skeletal muscle cells [6]. The translocation is regulated by insulin and AMP-activated protein kinase signaling pathways [9]. (−)-EC conjugated with fatty acid strongly inhibited DNA polymerase activity and angiogenesis in human endothelial cells [13] These reports suggest natural catechin derivatives and synthesized catechin derivatives increase the lipophilicity, which may contribute to the increase their bioactivities. Our previous study showed that tea catechins, except for (+)-C and (−)-catechin gallate, significantly increased glucose uptake activity in skeletal muscle cells [6]. We investigated whether synthesized 3-O-acyl-catechins increase glucose uptake activity in L6 myotubes. Investigated an affinity of 3-O-acyl-catechins for lipid bilayer membrane using surface plasmon resonance (SPR) analysis
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