title: Trigonella foenum-graecum Seed Extract, 4-Hydroxyisoleucine, and Metformin Stimulate Proximal Insulin Signaling and Increase Expression of Glycogenic Enzymes and GLUT2 in HepG2 Cells.
abstract: BACKGROUND
  Fenugreek (Trigonella foenum-graecum) is globally recognized for its medicinal properties and hypoglycemic effects. The seed extract as well as its active compound, 4-hydroxyisoleucine (4-OH-Ile), have been shown to reduce hyperglycemic insulin resistance. The mechanism by which this occurs has not been investigated in human liver cells (HepG2) in comparison to the antihyperglycemic drug, metformin.
  
  
  METHODS
  We investigated the effects of an aqueous fenugreek seed extract (FSE), 4-OH-Ile, and metformin in HepG2 cells relative to insulin as a positive control. Cells were treated with FSE and 4-OH-Ile at 100 ng/mL under normoglycemic (5 mM glucose) and hyperglycemic (30 mM glucose) conditions for 72 hr. Tyrosine phosphorylation of insulin receptor-β (IR-β), protein kinase B (Akt), glycogen synthase kinase-3α/β (GSK-3α/β), and glucose transporter 2 (GLUT2) was determined by western blotting. Gene expression of sterol regulatory element-binding protein 1c (SREBP1c), GLUT2, glycogen synthase (GS), and glucokinase (GK) was evaluated by quantitative polymerase chain reaction, and supernatant glucose levels were measured using the Piccolo biochemistry analyzer.
  
  
  RESULTS
  Under normo- and hyperglycemic conditions, FSE, 4-OH-Ile, insulin (100 ng/mL), and metformin (2 mM) caused a significant increase in phosphorylation of IR-β, Akt, GSK-3α/β, and GLUT2. Glucose uptake, however, was most significantly increased in FSE-treated cells during both conditions. FSE induced the most significant changes in downstream insulin signaling, GS, GK, SREBP1c, and GLUT2 expression compared to 4-OH-Ile, metformin, and insulin. In addition, FSE significantly increased glucose uptake.
  
  
  CONCLUSIONS
  Collectively, these findings provide a mechanism by which FSE exerts antihyperglycemic effects similar to metformin and insulin that occurs via enhanced insulin signaling, gene expression, and increasing glucose uptake.
authors.affiliation: 1 Discipline of Medical Biochemistry, Faculty of Health Science, School of Laboratory Medicine and Medical Sciences, University of KwaZulu-Natal , Durban, South Africa .
authors.forename: Nikita
authors.initials: N
authors.lastname: Naicker
authors.affiliation: 1 Discipline of Medical Biochemistry, Faculty of Health Science, School of Laboratory Medicine and Medical Sciences, University of KwaZulu-Natal , Durban, South Africa .
authors.forename: Savania
authors.initials: S
authors.lastname: Nagiah
authors.affiliation: 2 Department of Physiology, Faculty of Health Sciences, School of Medicine, Prinshof Campus, University of Pretoria , Pretoria, South Africa .
authors.forename: Alisa
authors.initials: A
authors.lastname: Phulukdaree
authors.affiliation: 1 Discipline of Medical Biochemistry, Faculty of Health Science, School of Laboratory Medicine and Medical Sciences, University of KwaZulu-Natal , Durban, South Africa .
authors.forename: Anil
authors.initials: A
authors.lastname: Chuturgoon
mesh_terms: D015703:Antigens, CD / Q000378:metabolism; D004798:Enzymes / Q000235:genetics / Q000378:metabolism*; D051273:Glucose Transporter Type 2 / Q000235:genetics / Q000378:metabolism*; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism; D000071679:Glycogen Synthase Kinase 3 beta / Q000378:metabolism; D056945:Hep G2 Cells; D022781:Hepatocytes / Q000187:drug effects* / Q000201:enzymology; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D007328:Insulin / Q000378:metabolism*; D007532:Isoleucine / Q000031:analogs & derivatives* / Q000302:isolation & purification / Q000494:pharmacology; D008687:Metformin / Q000494:pharmacology*; D010766:Phosphorylation; D008517:Phytotherapy; D010936:Plant Extracts / Q000494:pharmacology*; D010946:Plants, Medicinal; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D011972:Receptor, Insulin / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D029910:Trigonella; D015854:Up-Regulation
chemical_list: C104672:4-hydroxyisoleucine; D015703:Antigens, CD; D004798:Enzymes; D051273:Glucose Transporter Type 2; D007004:Hypoglycemic Agents; D007328:Insulin; D010936:Plant Extracts; C495680:SLC2A2 protein, human; D007532:Isoleucine; C056164:fenugreek seed meal; D008687:Metformin; C435941:INSR protein, human; D011972:Receptor, Insulin; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; D051057:Proto-Oncogene Proteins c-akt; D038362:Glycogen Synthase Kinase 3; C448021:glycogen synthase kinase 3 alpha