title: Anaplerosis from glucose, alpha-ketoisocaproate, and pyruvate in pancreatic islets, INS-1 cells and liver mitochondria.
abstract: Methyl succinate (MS) and alpha-ketoisocaproate (KIC) when applied alone to cultured pancreatic islets or INS-1 832/13 cells do not stimulate insulin release. However, when the two metabolites are combined together they strongly stimulate insulin release. Studying the possible explanations for this complementarity has provided clues to the pathways involved in insulin secretion. MS increased carbon incorporation of KIC into acid-precipitable material and lipid in INS-1 cells. In isolated mitochondria, MS alone increased malate, but MS plus KIC increased citrate, alpha-ketoglutarate, and isocitrate. These data and the known pathways of their metabolism suggest that MS supplies the oxaloacetate component of citrate and KIC supplies the acetate component of citrate. Other citric acid cycle intermediates can be formed from citrate enabling anaplerosis to supply precursors for extramitochondrial pathways. In addition, KIC, glucose and pyruvate can be metabolized to acetoacetate. In an INS-1 cell line deficient in ATP citrate lyase, incorporation of carbon from pyruvate into acid-precipitable material and lipid was not lowered. This negative result is in agreement with our recent discovery that citrate is not the only carrier of acyl groups from the mitochondria to the cytosol in the beta cell and that acetoacetate can also transfer acyl carbon to the cytosol.
authors.affiliation: Childrens Diabetes Center, School of Medicine and Public Health, University of Wisconsin, Rm. 3459 Medical Science Center, 1300 University Ave., Madison, WI 53706, USA. mjmacdon@wisc.edu
authors.forename: Michael J
authors.initials: MJ
authors.lastname: MacDonald
authors.forename: Scott W
authors.initials: SW
authors.lastname: Stoker
authors.forename: Noaman M
authors.initials: NM
authors.lastname: Hasan
mesh_terms: D001275:ATP Citrate (pro-S)-Lyase / Q000378:metabolism; D000818:Animals; D002245:Carbon Dioxide / Q000378:metabolism; D002247:Carbon Isotopes; D002460:Cell Line; D011232:Chemical Precipitation; D005947:Glucose / Q000378:metabolism* / Q000494:pharmacology; D007515:Islets of Langerhans / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D007651:Keto Acids / Q000378:metabolism* / Q000494:pharmacology; D008930:Mitochondria, Liver / Q000187:drug effects / Q000378:metabolism*; D011773:Pyruvates / Q000378:metabolism* / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013347:Subcellular Fractions / Q000187:drug effects; D013379:Substrate Specificity / Q000187:drug effects
chemical_list: D002247:Carbon Isotopes; D007651:Keto Acids; D011773:Pyruvates; D002245:Carbon Dioxide; C013082:alpha-ketoisocaproic acid; D001275:ATP Citrate (pro-S)-Lyase; D005947:Glucose