Impaired hepatic fatty acid oxidation in rats with short-term cholestasis: characterization and mechanism

Abstract

Rats with long-term cholestasis have reduced ketosis during starvation. Because it is unclear whether this is also the case in short-term cholestasis, we investigated hepatic fatty acid metabolism in rats with bile duct ligation for 5 days (BDL5, n ‫؍‬ 11) or 10 days (BDL10, n ‫؍‬ 11) and compared the findings with those made with pair-fed control rats (CON5 and CON10, n ‫؍‬ 11). The plasma ␤ -hydroxybutyrate concentration was reduced in BDL rats (0.54 ؎ 0.10 vs. 0.83 ؎ 0.30 mM at 5 days and 0.59 ؎ 0.24 vs. 0.88 ؎ 0.09 mM at 10 days in BDL and control rats, respectively). In isolated liver mitochondria, state 3 oxidation rates for various substrates were not different between BDL and control rats. Production of ketone bodies from [ 14 C]palmitate was reduced by 40% in mitochondria from BDL rats at both time points, whereas production of 14 CO 2 was maintained. These findings indicated intact function of the respiratory chain, Krebs cycle, and ␤ -oxidation and suggested impaired ketogenesis (HMG-CoA pathway). Accordingly, the formation of acetoacetate from acetyl-CoA by disrupted mitochondria was reduced in BDL rats at 5 days (2.1 ؎ 1.0 vs. 4.8 ؎ 1.9 nmol/min per mg protein) and at 10 days (1.7 ؎ 1.0 vs. 6.2 ؎ 1.9 nmol/min per mg protein). The principal defect could be localized at the rate-limiting enzyme of the HMG-CoA pathway, HMG-CoA synthase, which revealed decreased activity, and reduced hepatic mRNA and protein levels. We conclude that short-term cholestasis in rats leads to impaired hepatic fatty acid metabolism due to impaired ketogenesis. Ketogenesis is impaired because of decreased mRNA levels of HMG-CoA synthase, leading to reduced hepatic protein levels and to decreased activity of this key enzyme of ketogenesis.

Coactivation of Foxa2 through Pgc-1β promotes liver fatty acid oxidation and triglyceride/VLDL secretion

“…An aliquot of freshly isolated mitochondria was used to determine mitochondrial protein. The b oxidation of [1-14 C]palmitic acid by liver mitochondria was assessed as described by Lang et al (2001). CO 2 trapped on the filter papers was counted for 1-14 C activity using a scintillation counter.…”