Development and initial evaluation of a novel method for assessing tissue-specific plasma free fatty acid utilization in vivo using (R)-2-bromopalmitate tracer

We describe a method for assessing tissue-specific plasma free fatty acid ( FFA) utilization in vivo using a non-beta-oxidizable FFA analog, [9,10-H-3] -(R)-2-bromopalmitate (H-3-R-BrP), Ideally 3H-R-BrP would be transported in plasma, taken up by tissues and activated by the enzyme acyl-CoA synthetas e (ACS) like native FFA, but then H-3-labeled metabolites would be trapped. In vitro we found that 2-bromopalmitate and palmitate compete equivalently for the same ligand binding sites on albumin and intestinal fatty acid bin ding protein, and activation by ACS was stereoselective for the R-isomer, I n vivo, oxidative and non-oxidative FFA metabolism was assessed in anesthet ized Wistar rats by infusing, over 4 min, a mixture of 3H-R-BrP and [U-C-14 ] palmitate (C-14-palmitate), Indices of total FFA utilization (R*(f)) and incorporation into storage products (R-fs') were defined, based on tissue c oncentrations of H-3 and C-14, respectively 16 min after the start of trace r infusion. R*(f), but not ', was substantially increased in contracting (s ciatic nerve stimulated) hindlimb muscles compared with contralateral non-c ontracting muscles. The contraction-induced increases in R*(f) were complet ely prevented by blockade of beta-oxidation with etomoxir, These results ve rify that 3H-R-BrP traces local total FFA utilization, including oxidative and non-oxidative metabolism. Separate estimates of the rates of loss of 3H activity indicated effective H-3 metabolite retention in most tissues over a 16-min period, but appeared less effective in liver and heart. j/r In co nclusion, simultaneous use of 3H-R-BrP and [C-14]palmitate tracers provides a new useful tool for in vivo studies of tissue-specific FFA transport, ut ilization and metabolic fate, especially in skeletal muscle and adipose tis sue., Development and initial evaluation of a novel method for assessing ti ssue-specific plasma free fatty acid utilization in vivo using (R)-2-bromop almitate tracer.