Aberrant expression and distribution of enzymes of the urea cycle and other ammonia metabolizing pathways in dogs with congenital portosystemic shunts

• Published in: PloS one 2014-06, Vol.9 (6), p.e100077
• Main Authors: van Straten, Giora, van Steenbeek, Frank G, Grinwis, Guy C M, Favier, Robert P, Kummeling, Anne, van Gils, Ingrid H, Fieten, Hille, Groot Koerkamp, Marian J A, Holstege, Frank C P, Rothuizen, Jan, Spee, Bart
• Format: Article
• Language: English
• Subjects: Aberration; Albinism; Ammonia; Ammonia - metabolism; Ammonia - pharmacology; Ammonium Chloride - pharmacology; Animals; Arginase; Argininosuccinate lyase; Biology and Life Sciences; Bypasses; Cells, Cultured; Detoxification; Dogs; Embryos; Encephalopathy; Enzymes; Gene expression; Gene Expression Regulation - drug effects; Glutamate dehydrogenase; Glutamate-ammonia ligase; Glutamate-Ammonia Ligase - metabolism; Glutamine; Hepatic encephalopathy; Hepatocytes; Hepatocytes - drug effects; Hepatocytes - enzymology; Hyperammonemia; Immunohistochemistry; Kinases; Liver; Liver - drug effects; Liver - enzymology; Medical research; Medicine and Health Sciences; Metabolic Networks and Pathways; Metabolism; Nitrogen; Oligonucleotide Array Sequence Analysis; Ornithine; Ornithine carbamoyltransferase; Portal Vein - abnormalities; Portal Vein - enzymology; RNA, Messenger - genetics; RNA, Messenger - metabolism; Rodents; Shunts; Signal Transduction - genetics; Surgery; Urea; Urea - metabolism; Vascular Malformations - enzymology; Vascular Malformations - genetics; Vascular Malformations - veterinary; Veterinary medicine; Zonal distribution
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0100077

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.