(P11-020-24) Development of an Albumin-Free Formulation for Administering Isotopically Labeled Palmitate for Measuring Free Fatty Acid Kinetics in Mice

Objectives: Free fatty acid (FFA) flux is an essential metabolic parameter, representing FFA transport between body compartments. The measurement of FFA flux through serum/plasma has been widely conducted using isotopically labeled FFA complexed with albumin. However, using albumin to promote the tracer’s solubility is problematic for researchers who are studying an albumin-deficient condition. Thus, we aimed to develop an albumin-free formulation of isotopically labeled palmitate for studies of FFA kinetics in mice. We also examined if the new formulation can detect the differences of metabolically distinct mice using albumin knockout (Alb^-/-) mice.

Methods: [U-¹³C]palmitate tracer was prepared as a traditional albumin formulation or as a novel formulation using a combination of polyvinylpyrrolidone (PVP) and dimethyl sulfoxide (DMSO). 8 week old male wildtype (WT) mice were intravenously injected with tracer in albumin or PVP/DMSO formulations following a 16-h fast, then blood was collected from the tail at 0, 2.5, 5.0, and 7.5-min time points. Using liquid chromatography/mass spectrometry for the analysis of serum, a single exponential equation for the time-related dilution of the tracer isotopic enrichment was determined for the calculation of serum FFA flux. Additionally, hematocrit was tested as a proxy measure for plasma volume. Throughout the experiment, each mouse was monitored for distress or acute illness. We then applied PVP/DMSO formulation for assessment of FFA flux in Alb^-/- and WT mice of both sexes by using the procedure above.

Results: The mice showed no signs of distress or acute illness following the injection of PVP/DMSO or albumin formulations. Hematocrit, serum FFA flux rate, and FFA concentration were not significantly different between the two formulations. When comparing WT to Alb^-/- mice, serum FFA flux rate and concentration were significantly lower in Alb^-/- mice than WT mice (genotype main effect, P < 0.05), and there were no significant group differences for hematocrit.

Conclusions: A novel albumin-free formulation for administering isotopically labeled palmitate was developed, which can be used to determine serum FFA flux. This formulation is valuable for enabling studies of FFA flux in albumin-deficient animals.

Funding Sources: McKinley Educational Initiative