title: Platyconic acid, a saponin from Platycodi radix, improves glucose homeostasis by enhancing insulin sensitivity in vitro and in vivo.
abstract: BACKGROUND
  Previous research demonstrated that the crude saponins of Platycodi radix improve glucose metabolism by enhancing insulin sensitivity in type 2 diabetic animals; however, which individual saponins are the most potent insulin sensitizers is unknown.
  
  
  OBJECTIVE
  This study investigated which saponin(s) have anti-diabetic action in vitro and in vivo.
  
  
  METHODS
  The insulin-stimulated glucose uptake and PPAR-γ agonistic actions of six saponins from Platycodi radix were investigated in 3T3-L1 adipocytes, and glucose-stimulated insulin secretion was determined in Min6 cells. Four individual saponins (20 mg/kg body weight) were orally administered to low-dose streptozotocin-injected diabetic mice fed a high-fat diet for 8 weeks to evaluate glucose tolerance by oral glucose tolerance testing (OGTT), insulin sensitivity by insulin tolerance testing, and insulin signaling in the liver and adipose tissues.
  
  
  RESULTS
  Platyconic acid (PA) most effectively increased insulin-stimulated glucose uptake in 3T3-L1 adipocytes, possibly in part by working as a peroxisome proliferator-activated receptors (PPAR)-γ activator; however, none of the saponins improved glucose-stimulated insulin secretion in insulinoma cells. PA-treated diabetic mice exhibited the lowest peak serum glucose levels and highest serum insulin levels during the first part of OGTT. PA also improved insulin sensitivity: PA increased glycogen accumulation and decreased triacylglycerol storage in liver, which was associated with enhanced hepatic insulin signaling, while PA potentiated the expression of adiponectin and PPAR-γ in adipose tissue, and improved insulin signaling and increased GLUT4 translocation into the membranes.
  
  
  CONCLUSIONS
  PA improves glucose homeostasis in type 2 diabetic mice, partly by enhancing hepatic and adipocyte insulin sensitivity, possibly by activating PPAR-γ.
authors.affiliation: Food Functional Research Division, Korean Food Research Institutes, Sungnam, Korea.
authors.forename: Dae Young
authors.initials: DY
authors.lastname: Kwon
authors.forename: Young Seob
authors.initials: YS
authors.lastname: Kim
authors.forename: Shi Yong
authors.initials: SY
authors.lastname: Ryu
authors.forename: Yeon Hee
authors.initials: YH
authors.lastname: Choi
authors.forename: Mi-Ran
authors.initials: MR
authors.lastname: Cha
authors.forename: Hye Jeong
authors.initials: HJ
authors.lastname: Yang
authors.forename: Sunmin
authors.initials: S
authors.lastname: Park
mesh_terms: D041721:3T3-L1 Cells; D017667:Adipocytes / Q000187:drug effects / Q000378:metabolism; D052242:Adiponectin / Q000235:genetics / Q000378:metabolism; D000818:Animals; D001786:Blood Glucose / Q000187:drug effects*; D003924:Diabetes Mellitus, Type 2 / Q000188:drug therapy / Q000473:pathology; D059305:Diet, High-Fat; D005951:Glucose Tolerance Test; D051275:Glucose Transporter Type 4 / Q000235:genetics / Q000378:metabolism; D006706:Homeostasis; D007004:Hypoglycemic Agents / Q000494:pharmacology; D007328:Insulin / Q000097:blood; D007333:Insulin Resistance; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D047495:PPAR gamma / Q000819:agonists / Q000378:metabolism; D010936:Plant Extracts / Q000494:pharmacology*; D021381:Protein Transport / Q000235:genetics; D012503:Saponins / Q000494:pharmacology*; D015398:Signal Transduction; D014315:Triterpenes / Q000494:pharmacology*
chemical_list: D052242:Adiponectin; D001786:Blood Glucose; D051275:Glucose Transporter Type 4; D007004:Hypoglycemic Agents; D007328:Insulin; D047495:PPAR gamma; D010936:Plant Extracts; D012503:Saponins; C495693:Slc2a4 protein, mouse; D014315:Triterpenes; C576414:platyconic acid