Quantifying fatty acid synthesis using heavy water: Enabling back‐to‐back studies

Abstract

Studies aimed at modulating the contribution of de novo lipogenesis (DNL) to lipid homeostasis are of interest. For example, there appears to be an increased contribution of DNL in cases of dyslipidemia and adipose accretion suggesting that the inhibition of fatty acid synthesis may affect clinical phenotypes. Unfortunately, it is unclear whether inhibition of one specific step in the lipogenic pathway is more important than another. Heavy water (D2O) is generally considered to be a reliable isotopic tracer for quantifying DNL. In contrast to other tracers, D2O yields a homogeneous and quantifiable precursor labeling. However, a drawback of using D2O centers on the relatively long half‐life of water implying that one must wait a substantial time before performing repeat studies in the same subjects; this can create a bottleneck in the development and evaluation of novel therapeutics for inhibiting DNL especially in cases where one aims to use subjects as their own controls. We previously demonstrated the ability to perform back‐to‐back studies of glucose and cholesterol flux by administering multiple doses of D2O and therein circumvent an extensive washout time; presumably these “tricks” can help minimize resources and decrease the turnaround time when testing hypotheses. Herein we now demonstrate the ability to perform back‐to‐back studies of DNL using D2O. However, we have identified special circumstances that limit some aspects of the data analysis, i.e. it is possible to obtain what appear to be negative values for DNL. Using a rodent model we have identified the physiological mechanism that explains the data. We show that one can use D2O to test inhibitors of DNL by performing back‐to‐back studies in higher species (i.e. treat non‐human primates with platensimycin, an inhibitor of fatty acid synthase).Support or Funding InformationAll authors were employed by Merck while this work was being done.