Accumulation of long-chain acylcarnitine and 3-hydroxy acylcarnitine molecular species in diabetic myocardium: Identification of alterations in mitochondrial fatty acid processing in diabetic myocardium by shotgun lipidomics

Diabetic cardiomyopathy is the result of maladaptive changes in energy homeostasis. However, the biochemical mechanisms underlying dysfunctional lipid metabolism in diabetic myocardium are incompletely understood. Herein, we exploit shotgun lipidomics to demonstrate a 4-fold increase in acylcarnitines in diabetic myocardium, which was reversible upon insulin treatment. Analysis of acylcarnitine molecular species in myocardium unexpectedly identified acylcarnitine molecular species containing a mass shift of 16 amu in comparison to the anticipated molecular species. Synthesis of 3-hydroxy acylcarnitine identified the natural products as the 3-hydroxylated acylcarnitines through comparisons of diagnostic fragmentation patterns of synthetic and naturally occurring constituents using tandem mass spectrometry. Diabetes induced an increase of both calcium-independent phospholipase A₂ (iPLA ₂) mRNA and iPLA₂ activity in rat myocardium. Cardiac ischemia in myocardium genetically engineered to overexpress iPLA₂ dramatically increased the amount of acylcarnitine present in myocardium. Moreover, mechanism-based inactivation of iPLA₂ in either wild-type or transgenic myocardium ablated a substantial portion of the acylcarnitine increase. Collectively, these results identify discrete insulin remediable abnormalities in mitochondrial fatty acid processing in diabetic myocardium and identify iPLA₂ as an important enzymatic contributor to the pool of fatty acids that can be used for acylcarnitine synthesis and energy production in myocardium.