Lipids are a large class of biomolecules naturally occurring in different forms throughout the body. As many lipid species tend to exist in high concentrations, they are an abundant source of MR-observable nuclei. This presentation will review the measurements of lipids that have been made successfully with MRS-based approaches and highlight the important findings from MRS studies of lipids. Specifically, focus will be on the following areas: (1) Introduction to characteristics of lipids, (2) Detection and quantification of lipid levels with 1H MRS, (3) Assessment of lipid composition with 1H MRS and 13C MRS too, (4) Measurement of the kinetics of lipid metabolism with 13C MRS.
Target Audience
This talk is directed at MR scientists with a basic background in MRS who would like to learn more about the capabilities of MRS in regards to studying lipid species in vivo.Methods
This presentation will focus on the use of 1H MRS and 13C MRS to study the amounts and composition of lipid species in vivo. Additionally, the use of 13C MRS ex-vivo will be discussed in regards to its ability to elucidate various aspects of lipid metabolism.Results
Some key highlights of the application of MRS to the study of lipids are as follows:
- Localized 1H MRS can detect multiple NMR resonances from lipids in various organs in vivo. The relative amounts of these different resonances can be used to infer properties of lipid composition.
- Using the ratio of the repeating methylene (-CH2)n- resonance to the water resonance as an index of lipid content, localized 1H MRS can detect lipid levels in tissue down to approximately 1%.
- Localized 1H MRS can be used to discriminate brown adipose tissue from other types of less metabolically active adipose tissue.
- 13C MRS, when combined with appropriate 13C-labeled substrates, can be used to measure the kinetics of lipid synthesis and lipid breakdown, as well as the interaction of lipid metabolism with other metabolic pathways. This approach is particularly useful to assess the acute effects of pharmacological effectors of lipid metabolism.
- The ability to quantify lipid levels in different tissues in vivo has led to significant findings and improved our understanding of the pathophysiology of metabolic diseases.
Conclusion
MRS studies of lipids have yielded generally translatable approaches and have greatly improved our understanding of lipid function in both healthy and diseased states.Hwang, JH & Choi, CS. Experimental & Molecular Medicine (47), 2015.
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