title: Aberrant expression and distribution of enzymes of the urea cycle and other ammonia metabolizing pathways in dogs with congenital portosystemic shunts.
abstract: The detoxification of ammonia occurs mainly through conversion of ammonia to urea in the liver via the urea cycle and glutamine synthesis. Congenital portosystemic shunts (CPSS) in dogs cause hyperammonemia eventually leading to hepatic encephalopathy. In this study, the gene expression of urea cycle enzymes (carbamoylphosphate synthetase (CPS1), ornithine carbamoyltransferase (OTC), argininosuccinate synthetase (ASS1), argininosuccinate lyase (ASL), and arginase (ARG1)), N-acetylglutamate synthase (NAGS), Glutamate dehydrogenase (GLUD1), and glutamate-ammonia ligase (GLUL) was evaluated in dogs with CPSS before and after surgical closure of the shunt. Additionally, immunohistochemistry was performed on urea cycle enzymes and GLUL on liver samples of healthy dogs and dogs with CPSS to investigate a possible zonal distribution of these enzymes within the liver lobule and to investigate possible differences in distribution in dogs with CPSS compared to healthy dogs. Furthermore, the effect of increasing ammonia concentrations on the expression of the urea cycle enzymes was investigated in primary hepatocytes in vitro. Gene-expression of CPS1, OTC, ASL, GLUD1 and NAGS was down regulated in dogs with CPSS and did not normalize after surgical closure of the shunt. In all dogs GLUL distribution was localized pericentrally. CPS1, OTC and ASS1 were localized periportally in healthy dogs, whereas in CPSS dogs, these enzymes lacked a clear zonal distribution. In primary hepatocytes higher ammonia concentrations induced mRNA levels of CPS1. We hypothesize that the reduction in expression of urea cycle enzymes, NAGS and GLUD1 as well as the alterations in zonal distribution in dogs with CPSS may be caused by a developmental arrest of these enzymes during the embryonic or early postnatal phase.
authors.affiliation: Department of Clinical Sciences of Companion Animals, Faculty of Veterinary Medicine, Utrecht University, Utrecht, the Netherlands.
authors.forename: Giora
authors.initials: G
authors.lastname: van Straten
authors.affiliation: Department of Clinical Sciences of Companion Animals, Faculty of Veterinary Medicine, Utrecht University, Utrecht, the Netherlands.
authors.forename: Frank G
authors.initials: FG
authors.lastname: van Steenbeek
authors.affiliation: Department of Pathobiology, Faculty of Veterinary Medicine, Utrecht University, Utrecht, the Netherlands.
authors.forename: Guy C M
authors.initials: GC
authors.lastname: Grinwis
authors.affiliation: Department of Clinical Sciences of Companion Animals, Faculty of Veterinary Medicine, Utrecht University, Utrecht, the Netherlands.
authors.forename: Robert P
authors.initials: RP
authors.lastname: Favier
authors.affiliation: Department of Clinical Sciences of Companion Animals, Faculty of Veterinary Medicine, Utrecht University, Utrecht, the Netherlands.
authors.forename: Anne
authors.initials: A
authors.lastname: Kummeling
authors.affiliation: Department of Clinical Sciences of Companion Animals, Faculty of Veterinary Medicine, Utrecht University, Utrecht, the Netherlands.
authors.forename: Ingrid H
authors.initials: IH
authors.lastname: van Gils
authors.affiliation: Department of Clinical Sciences of Companion Animals, Faculty of Veterinary Medicine, Utrecht University, Utrecht, the Netherlands.
authors.forename: Hille
authors.initials: H
authors.lastname: Fieten
authors.affiliation: Molecular Cancer Research, University Medical Centre Utrecht, Utrecht, the Netherlands.
authors.forename: Marian J A
authors.initials: MJ
authors.lastname: Groot Koerkamp
authors.affiliation: Molecular Cancer Research, University Medical Centre Utrecht, Utrecht, the Netherlands.
authors.forename: Frank C P
authors.initials: FC
authors.lastname: Holstege
authors.affiliation: Department of Clinical Sciences of Companion Animals, Faculty of Veterinary Medicine, Utrecht University, Utrecht, the Netherlands.
authors.forename: Jan
authors.initials: J
authors.lastname: Rothuizen
authors.affiliation: Department of Clinical Sciences of Companion Animals, Faculty of Veterinary Medicine, Utrecht University, Utrecht, the Netherlands.
authors.forename: Bart
authors.initials: B
authors.lastname: Spee
mesh_terms: D000641:Ammonia / Q000378:metabolism* / Q000494:pharmacology; D000643:Ammonium Chloride / Q000494:pharmacology; D000818:Animals; D002478:Cells, Cultured; D004285:Dogs; D005786:Gene Expression Regulation / Q000187:drug effects; D005974:Glutamate-Ammonia Ligase / Q000378:metabolism; D022781:Hepatocytes / Q000187:drug effects / Q000201:enzymology; D007150:Immunohistochemistry; D008099:Liver / Q000187:drug effects / Q000201:enzymology; D053858:Metabolic Networks and Pathways; D020411:Oligonucleotide Array Sequence Analysis; D011169:Portal Vein / Q000002:abnormalities* / Q000201:enzymology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000235:genetics; D014508:Urea / Q000378:metabolism*; D054079:Vascular Malformations / Q000201:enzymology* / Q000235:genetics / Q000662:veterinary*
chemical_list: D012333:RNA, Messenger; D000643:Ammonium Chloride; D000641:Ammonia; D014508:Urea; D005974:Glutamate-Ammonia Ligase