title: Protective effects of marein on high glucose-induced glucose metabolic disorder in HepG2 cells.
abstract: BACKGROUND
  Our previous study has shown that Coreopsis tinctoria increases insulin sensitivity and regulates hepatic metabolism in high-fat diet (HFD)-induced insulin resistance rats. However, it is unclear whether or not marein, a major compound of C. tinctoria, could improve insulin resistance. Here we investigate the effect and mechanism of action of marein on improving insulin resistance in HepG2 cells.
  
  
  METHODS
  We investigated the protective effects of marein in high glucose-induced human liver carcinoma cell HepG2. In kinase inhibitor studies, genistein, LY294002, STO-609 and compound C were added to HepG2 cells 1h before the addition of marein. Transfection with siRNA was used to knock down LKB1, and 2-(N-(7-nitrobenz-2-oxa-1, 3-diazol-4-yl) amino)-2-deoxyglucose (2-NBDG), an effective tracer, was used to detect glucose uptake.
  
  
  RESULTS
  The results showed for the first time that marein significantly stimulates the phosphorylation of AMP-activated protein kinase (AMPK) and the Akt substrate of 160kDa (AS160) and enhanced the translocation of glucose transporter 1 (GLUT1) to the plasma membrane. Further study indicated that genistein (an insulin receptor tyrosine kinase inhibitor) altered the effect of marein on glucose uptake, and both LY294002 (a phosphatidylinositol 3-kinase inhibitor) and compound C (an AMP-activated protein kinase inhibitor) significantly decreased marein-stimulated 2-NBDG uptake. Additionally, marein-stimulated glucose uptake was blocked in the presence of STO-609, a CaMKK inhibitor; however, marein-stimulated AMPK phosphorylation was not blocked by LKB1 siRNA in HepG2 cells. Marein also inhibited the phosphorylation of insulin receptor substrate (IRS-1) at Ser 612, but inhibited GSK-3β phosphorylation and increased glycogen synthesis. Moreover, marein significantly decreased the expression levels of FoxO1, G6Pase and PEPCK.
  
  
  CONCLUSIONS
  Consequently, marein improved insulin resistance induced by high glucose in HepG2 cells through CaMKK/AMPK/GLUT1 to promote glucose uptake, through IRS/Akt/GSK-3β to increase glycogen synthesis, and through Akt/FoxO1 to decrease gluconeogenesis. Marein could be a promising leading compound for the development of hypoglycemic agent or developed as an adjuvant drug for diabetes mellitus.
authors.affiliation: Institute of Medicinal Plant Development, Chinese Academy of Medical Sciences, Peking Union Medical College, Beijing, 151 Malianwa North, Haidian District, Beijing 100193, China; Key Laboratory of Bioactive Substances and Resources Utilization of Chinese Herbal Medicine, Ministry of Education, Beijing, China.
authors.forename: Baoping
authors.initials: B
authors.lastname: Jiang
authors.affiliation: Institute of Medicinal Plant Development, Chinese Academy of Medical Sciences, Peking Union Medical College, Beijing, 151 Malianwa North, Haidian District, Beijing 100193, China.
authors.forename: Liang
authors.initials: L
authors.lastname: Le
authors.affiliation: Institute of Medicinal Plant Development, Chinese Academy of Medical Sciences, Peking Union Medical College, Beijing, 151 Malianwa North, Haidian District, Beijing 100193, China.
authors.forename: Wei
authors.initials: W
authors.lastname: Zhai
authors.affiliation: Institute of Medicinal Plant Development, Chinese Academy of Medical Sciences, Peking Union Medical College, Beijing, 151 Malianwa North, Haidian District, Beijing 100193, China; Key Laboratory of Bioactive Substances and Resources Utilization of Chinese Herbal Medicine, Ministry of Education, Beijing, China.
authors.forename: Wenting
authors.initials: W
authors.lastname: Wan
authors.affiliation: Institute of Medicinal Plant Development, Chinese Academy of Medical Sciences, Peking Union Medical College, Beijing, 151 Malianwa North, Haidian District, Beijing 100193, China.
authors.forename: Keping
authors.initials: K
authors.lastname: Hu
authors.affiliation: Institute of Medicinal Plant Development, Chinese Academy of Medical Sciences, Peking Union Medical College, Beijing, 151 Malianwa North, Haidian District, Beijing 100193, China; Key Laboratory of Bioactive Substances and Resources Utilization of Chinese Herbal Medicine, Ministry of Education, Beijing, China.
authors.forename: Peng
authors.initials: P
authors.lastname: Yong
authors.affiliation: Institute of Medicinal Plant Development, Chinese Academy of Medical Sciences, Peking Union Medical College, Beijing, 151 Malianwa North, Haidian District, Beijing 100193, China; Key Laboratory of Bioactive Substances and Resources Utilization of Chinese Herbal Medicine, Ministry of Education, Beijing, China.
authors.forename: Chunnian
authors.initials: C
authors.lastname: He
authors.affiliation: Institute of Medicinal Plant Development, Chinese Academy of Medical Sciences, Peking Union Medical College, Beijing, 151 Malianwa North, Haidian District, Beijing 100193, China; Key Laboratory of Bioactive Substances and Resources Utilization of Chinese Herbal Medicine, Ministry of Education, Beijing, China.
authors.forename: Lijia
authors.initials: L
authors.lastname: Xu
authors.affiliation: Institute of Medicinal Plant Development, Chinese Academy of Medical Sciences, Peking Union Medical College, Beijing, 151 Malianwa North, Haidian District, Beijing 100193, China; Key Laboratory of Bioactive Substances and Resources Utilization of Chinese Herbal Medicine, Ministry of Education, Beijing, China. Electronic address: pgxiao@implad.ac.cn.
authors.forename: Peigen
authors.initials: P
authors.lastname: Xiao
mesh_terms: D000091162:AMP-Activated Protein Kinase Kinases; D000818:Animals; D045744:Cell Line, Tumor; D047188:Chalcones / Q000494:pharmacology*; D055785:Gene Knockdown Techniques; D005943:Gluconeogenesis / Q000187:drug effects; D005947:Glucose / Q000378:metabolism / Q000633:toxicity*; D044882:Glucose Metabolism Disorders / Q000139:chemically induced* / Q000517:prevention & control*; D051272:Glucose Transporter Type 1 / Q000378:metabolism; D056945:Hep G2 Cells; D006801:Humans; D007333:Insulin Resistance; D010766:Phosphorylation / Q000187:drug effects; D020011:Protective Agents / Q000494:pharmacology*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D017346:Protein Serine-Threonine Kinases / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics; D051381:Rats
chemical_list: D047188:Chalcones; D051272:Glucose Transporter Type 1; D020011:Protective Agents; D047428:Protein Kinase Inhibitors; D034741:RNA, Small Interfering; C495677:SLC2A1 protein, human; C550306:marein; D017346:Protein Serine-Threonine Kinases; C109790:STK11 protein, human; D000091162:AMP-Activated Protein Kinase Kinases; D005947:Glucose
keywords: Akt; FoxO1; Gluconeogenesis; Glycogen synthesis; HepG2 cells; Marein