Real Time Measurement of Hepatic β‐oxidation with Deuterium Magnetic Resonance in Murine Models on a High Fat Diet

Abstract

Non‐alcoholic fatty liver disease (NAFLD) is characterized by >5% hepatic fat by mass. As one of the most common liver diseases, with a prevalence of roughly 24% in the U.S. adult population, NAFLD related morbidities account for a striking ~300 billion dollars a year in healthcare costs for the U.S. alone [Shetty, A., & Syn, W. K. Federal practitioner: for the health care professionals of the VA, DoD, and PHS, (2019), 36(1), 14–19]. NAFLD, both in humans and murine models of the disease, has been associated with increased rates of hepatic β‐oxidation and reactive oxygen species production [Sunny, N. E., Parks, E. J., Browning, J. D., & Burgess, S. C. Cell metabolism, (2011). 14(6), 804–810]. These characteristics are thought to drive a pro‐inflammatory state that causes hepatic damage, and can transition to the much more serious malady nonalcoholic steatohepatitis. To directly quantify hepatic β‐oxidation as a potential biomarker of NAFLD disease development and progression, we are developing deuterium magnetic resonance (DMR) techniques to monitor oxidation of D15‐octanoate. In the perfused mouse liver, we demonstrate that DMR measures of HDO production, as a direct byproduct of β‐oxidation, estimate hepatic β‐oxidation rates within 5% of standard quantitation by mass spectrometry of fatty acid depletion from perfusate. In a dietary model of NAFLD (60% fat by kcal, HFD) we observed increased overall b‐oxidation, but when normalized to the total liver weight, the HFD liver oxidized less than the low‐fat diet control. By coupling DMR spectroscopy, gas chromatography‐mass spectrometry and metabolic modelling, we were able to identify increases in total ketogenesis and FADH2 oxidation in high fat diet perfused livers. When normalizing metabolic flux to liver protein, both octanoate and FADH2 oxidation were significantly lower in high fat diet livers. Increased total fatty acid oxidation and ketogenesis implicate activation of compensatory mechanisms by the liver during NAFLD to address higher levels of circulating lipids. Decreases in efficiency/relative oxidation indicate an accrual of hepatic damage that hinders the efficient clearance of excess lipids. These results demonstrate the utility of DMR as a sensitive measure for detecting changes in metabolic activity during NAFLD progression, and suggests that a clinical imaging paradigm might be feasible.