1583-P: Measuring Mitochondrial Metabolism In Vivo with [1,2-¹³C₂]-L-Glutamine Mass Isotopomers

Background:Accuracy of tracer-based measurements of in vivo metabolic rates rely on assumptions, i.e., tracer non-interference with metabolism

Aim: [1,2-¹³C₂]-L-glutamine was evaluated to trace hepatic (H) & renal (K) metabolism in rats fed control vs. highfat-highsucrose diets (HFHSD) with validation by independent models and compared to lactate, propionate, and acetate tracing

Methods: Sprague-Dawley rats underwent primed, continuous infusions of [1,2-¹³C₂]-L-glutamine vis-à-vis lactate, propionate, acetate infusions.Plasma/freeze-clamped tissues were obtained at 7 timepoints. Isotopomers were interpreted by steady-state and kinetic Mass Isotopomer Multi-Ordinate Spectral Analysis (MIMOSA)

Results:[1,2-¹³C₂]-L-glutamine equilibrated without significant impact on intermediary/glucose metabolism. Transaminase exchange (v_x) was >> citrate synthase (v_CS). v_PEPCK/v_CS was 1.5 in (H) and 1.9 in (K). Pyruvate contributed 76% of anaplerosis in (H) and 90% in (K) with the remainder from propionate (v_PCC) (H) and glutamate (v_GDH) (H, K)). Citrate lyase (v_ACLY/v_CS) was significant only in (H) (18%) increasing on HFHSD. Plasma insulin ([i]), glucose ([g]), and/or glucose turnover (R_a) were increased by acetate ([i]=1.5x, p=0.015; [g]=129mg/dl, p=0.021), lactate ([i]=2.03x, p=0.0001; [g]=156mg/dl, p=0.0001, R_a=7.2mg/kg/min, p=0.006), and propionate ([i]=1.7x, p=0.0013; [g]=165mg/dl, p=0.0001, R_a=7.8mg/kg/min, p=0.0017). Lactate, acetate, and propionate increased cataplerosis > HFHSD

Conclusion: [1,2-¹³C₂]-L-glutamine MIMOSA provided unaltered, direct measurements of mitochondrial metabolism validated by independent kinetic and steady-state models and demonstrated comparable v_PEPCK and v_CS, fast transaminase, substantial v_ACLY, v_PCC, and minimal v_GDH. Metabolic changes induced by HFHSD were less than those caused by lactate, propionate, acetate.