Abstract Body: Background: The heart primarily uses long-chain fatty acids (FA), specifically palmitate (P), to fuel ATP synthesis. FA taken-up by transporters (e.g. CD36 and FATP3) are first attached to carnitine by CPT1 to form acyl-carnitines (AC), such as palmitoyl-carnitine (PC), that can then be imported into mitochondria. FA metabolism is reduced in heart failure (HF) with ACs found lower in myocardium but increased in plasma. In normal human plasma PC is ~1uM while P is 400mM. Whether cardiomyocytes (CMs) can take up PC and oxidize it for use in the TCA remains unknown.

Research Question/Aim: To test whether exogenous PCs can be (a) taken up and (b) oxidized by CMs independent of CPT1.

Methods: Neonatal rat cardiomyocytes (NRVMs), cardiac fibroblasts (NRVFs), adult mouse cardiomyocytes (AMs), and human endothelial coronary artery cells (HECAs) were cultured with 5uM C¹⁴ PC or C¹⁴ P and oxidation assayed by radioactive CO₂ release.

Results: C¹⁴ PC is taken up by AM (5% PC vs 21% of C¹⁴ Palmitate), NRVMs (35% vs 65%), NRVFs (6% vs 30%), HECA (9% vs 23%), as well as various other organ derived cells. The uptake of PC vs P is distinct and not competitive within each cell type. AM and NRVM metabolize PC at <5%. NRVM metabolism of PC can be increased from 1.5 to 2.5% by high lipid treatment prior to C¹⁴ PC exposure. The increase is lost by CPT1 inhibition (via 20uM etomoxir), indicating exogenous PC metabolism in heart cells occurs via intracellular division to carnitine and P. In cardiomyocytes, we found extracellular PC concentration above 30µM resulted in cytotoxicity. We show CD36, FATP3, and CPT1b protein levels are reduced in human failing myocardium.

Conclusion: Exogenous PC is taken up by heart cells to a much greater extent than metabolized. As protein expression of key FA transporters is decreased, we propose an alternative form of FA uptake through an AC specific plasma membrane transporter and a cytoplasmic mechanism for division to mitigate toxicity. Whether cardiac cells in HF are similarly able to take up or metabolize PC and if this contributes to toxicity in HF is unknown.