Plasma acylcarnitines inadequately reflect tissue acylcarnitine metabolism

Acylcarnitines have been linked to obesity-induced insulin resistance. However the majority of these studies have focused on acylcarnitines in plasma. It is currently unclear to what extent plasma levels of acylcarnitines reflect tissue acylcarnitine metabolism. We investigated the correlation of plasma acylcarnitine levels with selected tissue acylcarnitines as measured with tandem mass spectrometry, in both fed and fasted BALB/cJ (BALB) and C57BL/6N (Bl6) mice. Fasting affected acylcarnitine levels in all tissues. These changes varied substantially between the different tissue compartments. No significant correlations were found between plasma acylcarnitine species and their tissue counterparts in both mouse strains, with the exception of plasma C4OH-carnitine in BALB mice. We suggest that this lack of correlation is due to differences in acylcarnitine turnover rates between plasma and tissue compartments and the fact that the plasma acylcarnitine profile is a composition of acylcarnitines derived from different compartments. Therefore, plasma acylcarnitine levels do not reflect tissue levels and should be interpreted with caution. A focus on tissue acylcarnitine levels is warranted in metabolic studies.