BPS2026 – Role of intracellular lactate on muscle tissue’s myoglobin-fatty acid/acylcarnitine interaction in cardiac ischemic conditions

Cardiac ischemia, triggered by coronary artery occlusion, induces a metabolic shift from aerobic to anaerobic respiration, elevating intracellular lactate (LAC) levels and lowering pH, positioning LAC as a critical biomarker. This study investigates molecular interactions between LAC, myoglobin (Mb) (essential for oxygen (O 2 ) storage and transport), and energy metabolism-related metabolites, free fatty acids (FA) and acylcarnitines (AC), which are pivotal for elucidating energy dynamics and cell survival under ischemic conditions. We employed isothermal titration calorimetry (ITC), UV-Vis spectroscopy, and oxytherm respirometry to analyze LAC, FA, and AC interactions with Mb and affect O 2 kinetics. The research aims to determine how these molecular interactions influence Mb’s O 2 release capacity and maintain structural integrity, potentially uncovering novel therapeutic targets for ischemia. ITC experiments demonstrated that oxy-Mb avidly binds to LAC ( Kd = 2.1 ± 0.5 μ M), palmitate PLM ( Kd = 19 ± 1.6 μ M), and palmitoylcarnitine PLC ( Kd = 1.9 ± 0.7 μ M) in one-ligand binding studies, with a 1:1 protein-ligand stoichiometry. Surprisingly, in two-ligand binding assays, no detectable interaction was recorded when second ligand (LAC or PLM or PLC) was added to the pre-bound oxy-Mb. Time resolved UV-vis spectroscopy has shown rapid structural changes to oxy-Mb characterized by a blue shift of Soret peak (435 to 422 nm) with reduced intensity and concomitant conversion of oxy-Mb to met-Mb. These changes occurred in both one- and two-ligand interactions. O 2 kinetic studies have revealed that addition of either PLM or PLC to oxy-Mb did not release O 2 . However, addition of LAC to PLM- or PLC-bound oxy-Mb rapidly releases O 2 . Collectively, these findings suggest that under elevated LAC levels, oxy-Mb undergo auto-oxidation (ferrous, Fe 2+ to ferric, Fe 3+ form), abolishing both O 2 and lipid binding, which might influence the dynamics and effectiveness of fuel transfer to mitochondria.