In situ metabolism of 1,omega medium chain dicarboxylic acids in the liver of intact rats as detected by 13C and 1H NMR

The hepatic metabolism of 1,omega-dodecanedioic acid, a physiologically relevant representative of the medium-chain dicarboxylic acid family, has been studied by a combination of in vivo and in vitro 13C and 1H NMR spectroscopic techniques. Rats in different nutritional or hormonal situations were infused with [1,12-13C2]- or [1,2,11,12-13C4]dodecanedioic acid, and the kinetics of 13C label appearance as well as the final relative concentrations of metabolic products were measured noninvasively in the liver of the intact rat by 13C NMR spectroscopy. Perchloric acid and chloroform/methanol extracts of liver biopsies obtained at the end of the infusion period were further analyzed by high resolution 13C NMR and one-dimensional and two-dimensional COSY and J-resolved 1H NMR. [1-13C]- and [1,2-13C2]adipic acids were the main end products of the in vivo metabolism of [1,12-13C2]- or [1,2,11,12-13C4]dodecanedioic acids, respectively, indicating that the beta-oxidation pathway of medium-chain dicarboxylic acids proceeds in situ monodirectionally. [1-13C]Adipic acid, the main product of peroxisomal beta-oxidation, could also be detected in situ. This finding, together with the in vivo and in vitro absence of signals characteristic of intramitochondrial oxidation of [1-13C]acetyl-coenzyme A, provide a strong evidence supporting a predominant contribution of the peroxisomal beta-oxidation system to the overall oxidation of these compounds in vivo. Homonuclear two-dimensional COSY 1H NMR spectra of acid extracts from rat liver provided a convenient method of analyzing the metabolic repercussions of dicarboxylic acid accumulation, revealing a decrease in the hepatic concentration of beta-hydroxybutyrate and an accumulation of adipic acid and the amino acid L-lysine.