Creatine synthesis: hepatic metabolism of guanidinoacetate and creatine in the rat in vitro and in vivo

• Published in: American journal of physiology: endocrinology and metabolism 2009-02, Vol.296 (2), p.E256-E261
• Main Authors: da Silva, Robin P, Nissim, Itzhak, Brosnan, Margaret E, Brosnan, John T
• Format: Article
• Language: English
• Subjects: Amidinotransferases - metabolism; Amino acids; Animals; Biochemistry; Cells, Cultured; Creatine - biosynthesis; Creatine - blood; Creatine - pharmacokinetics; Enzymes; Glycine - analogs & derivatives; Glycine - blood; Glycine - metabolism; Guanidinoacetate N-Methyltransferase - metabolism; Hepatocytes - metabolism; Liver - enzymology; Liver - metabolism; Male; Metabolism; Models, Biological; Nitrogen Isotopes - pharmacokinetics; Phosphates; Rats; Rats, Sprague-Dawley; Rodents
• ISSN: 0193-1849; 1522-1555
• DOI: 10.1152/ajpendo.90547.2008

1 Department of Biochemistry, Memorial University of Newfoundland, St. John's, Newfoundland and Labrador, Canada; and 2 Division of Child Development, Abramson Pediatric Research Center, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania Submitted 27 June 2008 ; accepted in final form 10 November 2008 Since creatinine excretion reflects a continuous loss of creatine and creatine phosphate, there is a need for creatine replacement, from the diet and/or by de novo synthesis. Creatine synthesis requires three amino acids, methionine, glycine, and arginine, and two enzymes, L -arginine:glycine amidinotransferase (AGAT), which produces guanidinoacetate acid (GAA), and guanidinoacetate methyltransferase (GAMT), which methylates GAA to produce creatine. In the rat, high activities of AGAT are found in the kidney, whereas high activities of GAMT occur in the liver. Rat hepatocytes readily convert GAA to creatine; this synthesis is stimulated by the addition of methionine, which increases cellular S -adenosylmethionine concentrations. These same hepatocytes are unable to produce creatine from methionine, arginine, and glycine. 15 N from 15 NH 4 Cl is readily incorporated into urea but not into creatine. Hepatic uptake of GAA is evident in vivo by livers of rats fed a creatine-free diet but not when rats were fed a creatine-supplemented diet. Rats fed the creatine-supplemented diet had greatly decreased renal AGAT activity and greatly decreased plasma [GAA] but no decrease in hepatic GAMT or in the capacity of hepatocytes to produce creatine from GAA. These studies indicate that hepatocytes are incapable of the entire synthesis of creatine but are capable of producing it from GAA. They also illustrate the interplay between the dietary provision of creatine and its de novo synthesis and point to the crucial role of renal AGAT expression in regulating creatine synthesis in the rat. interorgan metabolism; in vivo hepatic fluxes; S -adenosylhomocysteine hydrolase; methylation demand Address for reprint requests and other correspondence: J. T. (Sean) Brosnan, Dept. of Biochemistry, Memorial Univ. of Newfoundland, St. John's, NL, Canada A1B3X9 (e-mail: jbrosnan{at}mun.ca )