Ex Vivo Proton NMR Analysis and Characterization of Thymus Lipid Metabolites and their Variation with Age in C57BL/6 Mice

Application 1H NMR spectroscopy techniques to the ex vivo study of thymus of 0.5-24 month-old C57BL/6 mice allowed the identification, the quantification and the estimation of some structural parameters (length and unsaturation) of various lipids in the thymus and their changes with age. An initial decrease of lipid metabolites in the thymus from 0.5 to 1 month of age was followed by large raises on further ageing, with 14, 8, and 4 fold increases for the total lipid content, fatty acids and glycerides, respectively, which correlated positively with age and negatively with thymus involution. The estimated average number of methylene groups per lipid chain essentially doubled its value from approximately 4-5 for the youngest mice to around 8 for the elderly, while the values obtained for the average number of double bonds per chain decreased with age from about 1-0.9 at 0.5/1 months of age to 0.6-0.7 for 18/24 months-old mice. The combination of NMR and histological data allowed studying the age-associated changes of the contribution of adipose- derived lipids to the total lipid content of the thymus and the amount of adipose tissue infiltrating the thymus. Both parameters initially showed a decrease from 0.5 months of age to (the adipose-free thymus at) 1 month of age. Afterwards, a continuous increase was observed on ageing: at 2 months about 55% of the lipids in the thymus were adipose-derived, while at 24 months they amounted to as much as about 95% of the total lipid content; for the same age-period, the estimated minimum adipose lipid content in the thymus changed from about 0.26% to 4.5%.