Lipolysis Rapidly Induces the Formation of N-acyl Amino Acids In Vivo
C. Gibson, S. Zaver, S. Campagna, and B. H. Voy.  2018.  The Obesity Society, T-P-3370; Obesity Week 2018.

Background Adaptive thermogenesis has re-emerged as an important component of energy expenditure. N-acyl amino acids(N-AAA), condensation products of fatty acids and amino acids, can contribute to adaptive thermogenesis by uncoupling mitochondrial respiration. Methods We tested the hypothesis that lipolysis promotes the formation of N-AAAs. We used an avian model (chickens) because lipolysis is readily induced by acute (~ 4 hr) food withdrawal. An avian model also allowed us to determine if N-AAAs are produced in the absence of brown adipose tissue, which was reported to contribute the enzyme (peptidase M20 domain containing 1 (PM20D1)) that catalyzes their synthesis. Serum was collected from 21 d-old broiler chicks that were fed ad libitum, fasted for 4, 8, or 12 h, or fasted for 12 h and then re-fed for 2 h (n=10/group). Samples were profiled for levels of 27 N-AAA species using a novel Ultra-Performance Chromatography—High Resolution Mass Spectrometry (UPLC-HRMS) method, which was validated with synthetic standards, and for non-esterified fatty acids (NEFA). Results Fasting progressively and significantly increased the serum pool of N-AAAs (p=1.8-06), in parallel with increased NEFA levels (p=0.0003). Refeeding for 2 h rapidly restored the N-AAA pool to fed levels (p=0.99; fed vs. 12 h fast-refed). Fasting also affected the N-AAA profile, with significant effects (p < 0.05) on relative abundance of 9 of the 16 N-AAA species that were detected. Abundance of some species (e.g., oleoyl-l-valine; p=2.8-04) increased with fasting while others (e.g., stearoyl-l-leucine; p=1.9-05) declined, suggesting molecule-specific regulation of N-AAA synthesis. Expression of PM20D1 in adipose tissue (subcutaneous and abdominal) and in liver was not significantly affected by fasting, suggesting there may be other routes for N-AAA formation. Conclusions In summary, these data indicate that N-AAAs are rapidly increased during lipolysis, where they may enhance energy expenditure by uncoupling cellular respiration.