Curcumin prevents leptin raising glucose levels in hepatic stellate cells by blocking translocation of glucose transporter-4 and increasing glucokinase.
OBJECTIVE
Hyperleptinemia is commonly found in obese patients, associated with non-alcoholic steatohepatitis and hepatic fibrosis. Hepatic stellate cells (HSCs) are the most relevant effectors during hepatic fibrogenesis. We recently reported that leptin stimulated HSC activation, which was eliminated by curcumin, a phytochemical from turmeric. This study was designed to explore the underlying mechanisms, focusing on their effects on intracellular glucose in HSCs. We hypothesized that leptin stimulated HSC activation by elevating the level of intracellular glucose, which was eliminated by curcumin by inhibiting the membrane translocation of glucose transporter-4 (GLUT4) and inducing the conversion of glucose to glucose-6-phosphate (G-6-P).


METHODS
Levels of intracellular glucose were measured in rat HSCs and immortalized human hepatocytes. Contents of GLUT4 in cell fractions were analysed by Western blotting analyses. Activation of signalling pathways was assessed by comparing phosphorylation levels of protein kinases.


RESULTS
Leptin elevated the level of intracellular glucose in cultured HSCs, which was diminished by curcumin. Curcumin suppressed the leptin-induced membrane translocation of GLUT4 by interrupting the insulin receptor substrates/phosphatidyl inositol 3-kinase/AKT signalling pathway. Furthermore, curcumin stimulated glucokinase activity, increasing conversion of glucose to G-6-P.


CONCLUSIONS
Curcumin prevented leptin from elevating levels of intracellular glucose in activated HSCs in vitro by inhibiting the membrane translocation of GLUT4 and stimulating glucose conversion, leading to the inhibition of HSC activation. Our results provide novel insights into mechanisms of curcumin in inhibiting leptin-induced HSC activation.
Department of Pathology, School of Medicine, Saint Louis University, 1100 S.Grand Boulevard, St Louis, MO 63104, USA.
Youcai
Y
Tang
Anping
A
Chen
D000818:Animals; D015153:Blotting, Western; D002478:Cells, Cultured; D003474:Curcumin / Q000494:pharmacology*; D005941:Glucokinase / Q000187:drug effects* / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D051275:Glucose Transporter Type 4 / Q000378:metabolism*; D055166:Hepatic Stellate Cells / Q000187:drug effects / Q000378:metabolism; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D020738:Leptin / Q000378:metabolism*; D008297:Male; D010766:Phosphorylation / Q000187:drug effects; D021381:Protein Transport; D051381:Rats; D017207:Rats, Sprague-Dawley; D011924:Rats, Zucker
D051275:Glucose Transporter Type 4; D020738:Leptin; D005941:Glucokinase; D003474:Curcumin; D005947:Glucose