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Impact of Mitochondrial Free Fatty Acid Overload on Hepatic Ureagenesis in Mice with Nonalcoholic Steatohepatitis
Author(s) -
Kalavalapalli Srilaxmi,
Abdo Kaitlyn I,
Murphy Zachary J,
Fernandez Jose C,
Cusi Kenneth,
Sunny Nishanth E
Publication year - 2016
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.30.1_supplement.907.17
Subject(s) - urea cycle , urea , medicine , endocrinology , beta oxidation , hepatocyte , biology , mitochondrion , chemistry , biochemistry , metabolism , amino acid , arginine , in vitro
Defects in ureagenesis are observed in several animal models with dysfunctional mitochondrial fat oxidation. The metabolic pathway of urea cycle, responsible for nitrogen disposal spans the mitochondrial and cytosolic compartments of the hepatocyte. Considering the central role of mitochondrial dysfunction in the etiology of fatty liver disease, we hypothesized that prolonged free fatty acid (FFA) overload and nonalcoholic steatohepatitis (NASH) will impair the flux through the urea cycle. To test the impact of FFA on ureagenesis, isolated primary hepatocytes from normal mice were cultured and incubated in custom media with low (0.25mM) and high (0.8mM) FFA. Urea concentration in the custom media was measured after 30mins, 3hr and 6hr incubation periods of hepatocytes by GC‐MS. Further, mice (C57/BL6) were kept on Control diet or high fructose high trans‐fat diet (TFD) for 24‐weeks to induce NASH, which was confirmed by histology. Urea turnover rates were determined after infusion of [ 15 N 2 ]urea stable isotope tracer followed by gas chromatography and mass spectrometry (GC‐MS) analysis. Liver tissues of these mice were used to quantify mRNA expression of genes involved in urea cycle. Increasing FFA concentration resulted in higher rates of urea production in isolated hepatocytes. However, onset of NASH did not alter urea turnover rates (Controls: 1.84 ±0.07 vs. NASH: 1.83 ±0.14 μmoles/min) in mice despite an induction of tricarboxylic acid (TCA) cycle activity (Controls: 2.62 ±0.47 vs. NASH: 5.39 ±0.59 μmoles/min). In spite of unaltered urea turnover, expression of genes involved in urea cycle ( CPS1, ARG1, ASL, and ASS1 ) was significantly reduced in mice with NASH. Our results demonstrate that, while a physiological increase in FFA and TCA cycle activity could stimulate ureagenesis, onset of NASH disrupts urea cycle activity. Dysfunctional ureagenesis in animals with non‐alcoholic steatohepatitis unravels a complex association between protein and FFA metabolism and may provide a snapshot into hepatic mitochondrial dysfunction. Support or Funding Information Research Opportunity Seed Fund Award, UF (N.S.)