title: Porcine liver sinusoidal endothelial cells contribute significantly to intrahepatic ammonia metabolism.
abstract: Ammonia metabolism in the liver has been largely credited to hepatocytes (HCs). We have shown that liver nonparenchymal cells that include liver sinusoidal endothelial cells (LSECs) produce ammonia. To address the limited knowledge regarding a role for LSECs in ammonia metabolism, we investigated the ammonia metabolism of isolated LSECs and HCs under three different conditions: (1) bioreactors containing LSECs (LSEC-bioreactors), (2) bioreactors containing HCs (HC-bioreactors), and (3) separate bioreactors containing LSECs and HCs connected in sequence (Seq-bioreactors). Our results showed that LSEC-bioreactors released six-fold more ammonia (22.2 nM/hour/10(6) cells) into the growth media than HC-bioreactors (3.3 nM/hour/10(6) cells) and Seq-bioreactors (3.8 nM/hour/10(6) cells). The glutamate released by LSEC-bioreactors (32.0 nM/hour/10(6) cells) was over four-fold larger than that released by HC-bioreactors and Seq-bioreactors (<7 nM/hour/10(6) cells). LSEC-bioreactors and HC-bioreactors consumed large amounts of glutamine (>25 nM/hour/10(6) cells). Glutaminase is known for catalyzing glutamine into glutamate and ammonia. To determine if this mechanism may be responsible for the large levels of glutamate and ammonia found in LSEC-bioreactors, immunolabeling of glutaminase and messenger RNA expression were tested. Our results demonstrated that glutaminase was present with colocalization of an LSEC-specific functional probe in lysosomes of LSECs. Furthermore, using a nucleotide sequence specific for kidney-type glutaminase, reverse-transcription polymerase chain reaction revealed that this isoform of glutaminase was expressed in porcine LSECs.
  
  
  CONCLUSIONS
  LSECs released large amounts of ammonia, perhaps due to the presence of glutaminase in lysosomes. The ammonia and glutamate released by LSECs in Seq-bioreactors were used by hepatocytes, suggesting an intrahepatic collaboration between these two cell types.
authors: Department of Digestive Surgery, University Hospital Northern Norway and Institute of Clinical Medicine, Norway.
authors: Geir I
authors: GI
authors: Nedredal
authors: Kjetil
authors: K
authors: Elvevold
authors: Lars M
authors: LM
authors: Ytrebø
authors: Ole-Martin
authors: OM
authors: Fuskevåg
authors: Ingvild
authors: I
authors: Pettersen
authors: Peter A G
authors: PA
authors: McCourt
authors: Kjell
authors: K
authors: Bertheussen
authors: Bård
authors: B
authors: Smedsrød
authors: Arthur
authors: A
authors: Revhaug
mesh_terms: D000641:Ammonia / Q000378:metabolism*; D000818:Animals; D019149:Bioreactors; D042783:Endothelial Cells / Q000378:metabolism*; D018698:Glutamic Acid / Q000096:biosynthesis; D005972:Glutaminase / Q000378:metabolism; D005973:Glutamine / Q000378:metabolism; D022781:Hepatocytes / Q000378:metabolism; D019344:Lactic Acid / Q000378:metabolism; D008099:Liver / Q000378:metabolism*; D008247:Lysosomes / Q000201:enzymology; D008297:Male; D034421:Sus scrofa
chemical_list: D005973:Glutamine; D019344:Lactic Acid; D018698:Glutamic Acid; D000641:Ammonia; D005972:Glutaminase