title: Characterization of hepatic fatty acids in mice with reduced liver fat by ultra-short echo time (1)H-MRS at 14.1 T in vivo.
abstract: Alterations in the hepatic lipid content (HLC) and fatty acid composition are associated with disruptions in whole body metabolism, both in humans and in rodent models, and can be non-invasively assessed by (1)H-MRS in vivo. We used (1)H-MRS to characterize the hepatic fatty-acyl chains of healthy mice and to follow changes caused by streptozotocin (STZ) injection. Using STEAM at 14.1 T with an ultra-short TE of 2.8 ms, confounding effects from T2 relaxation and J-coupling were avoided, allowing for accurate estimations of the contribution of unsaturated (UFA), saturated (SFA), mono-unsaturated (MUFA) and poly-unsaturated (PUFA) fatty-acyl chains, number of double bonds, PU bonds and mean chain length. Compared with in vivo (1) H-MRS, high resolution NMR performed in vitro in hepatic lipid extracts reported longer fatty-acyl chains (18 versus 15 carbons) with a lower contribution from UFA (61 ± 1% versus 80 ± 5%) but a higher number of PU bonds per UFA (1.39 ± 0.03 versus 0.58 ± 0.08), driven by the presence of membrane species in the extracts. STZ injection caused a decrease of HLC (from 1.7 ± 0.3% to 0.7 ± 0.1%), an increase in the contribution of SFA (from 21 ± 2% to 45 ± 6%) and a reduction of the mean length (from 15 to 13 carbons) of cytosolic fatty-acyl chains. In addition, SFAs were also likely to have increased in membrane lipids of STZ-induced diabetic mice, along with a decrease of the mean chain length. These studies show the applicability of (1)H-MRS in vivo to monitor changes in the composition of the hepatic fatty-acyl chains in mice even when they exhibit reduced HLC, pointing to the value of this methodology to evaluate lipid-lowering interventions in the scope of metabolic disorders.
authors.affiliation: Laboratory for Functional and Metabolic Imaging (LIFMET), École Polytechinque Fédérale de Lausanne (EPFL), Lausanne, Switzerland.
authors.forename: Ana Francisca
authors.initials: AF
authors.lastname: Soares
authors.affiliation: Center for Biomedical Imaging (CIBM), Lausanne, Switzerland.|Department of Radiology, University of Geneva (UNIGE), Geneva, Switzerland.
authors.forename: Hongxia
authors.initials: H
authors.lastname: Lei
authors.affiliation: Laboratory for Functional and Metabolic Imaging (LIFMET), École Polytechinque Fédérale de Lausanne (EPFL), Lausanne, Switzerland.|Department of Radiology, University of Geneva (UNIGE), Geneva, Switzerland.|Department of Radiology, Faculty of Biology and Medicine, University of Lausanne, Lausanne, Switzerland.
authors.forename: Rolf
authors.initials: R
authors.lastname: Gruetter
mesh_terms: D000273:Adipose Tissue / Q000378:metabolism*; D050154:Adiposity; D000818:Animals; D015415:Biomarkers / Q000378:metabolism; D003921:Diabetes Mellitus, Experimental / Q000139:chemically induced / Q000378:metabolism*; D005227:Fatty Acids / Q000378:metabolism*; D008099:Liver / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D066244:Proton Magnetic Resonance Spectroscopy / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013311:Streptozocin; D014018:Tissue Distribution
chemical_list: D015415:Biomarkers; D005227:Fatty Acids; D013311:Streptozocin
keywords: fatty acids; magnetic resonance spectroscopy (MRS); mouse liver; poly-unsaturated fatty acids (PUFA); streptozotocin (STZ)