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Porcine liver sinusoidal endothelial cells contribute significantly to intrahepatic ammonia metabolism
Author(s) -
Nedredal Geir I.,
Elvevold Kjetil,
Ytrebø Lars M.,
Fuskevåg OleMartin,
Pettersen Ingvild,
McCourt Peter A. G.,
Bertheussen Kjell,
Smedsrød Bård,
Revhaug Arthur
Publication year - 2009
Publication title -
hepatology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.488
H-Index - 361
eISSN - 1527-3350
pISSN - 0270-9139
DOI - 10.1002/hep.23076
Subject(s) - bioreactor , glutaminase , biology , glutamine , metabolism , biochemistry , liver cytology , glutamine synthetase , microbiology and biotechnology , amino acid , botany , liver metabolism
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. Conclusion: 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. (H EPATOLOGY 2009.)