Intramyocellular lipid

Proton NMR spectroscopy ( H MRS) has shown to offer excellent possibilities for evaluation of biochemistry in vivo. Due to its non-invasive character it is of increasing interest not only for the study of human brain diseases, which describe the majority of clinical applications, but also for metabolic characterization of organs outside the brain, as prostate, liver, heart or skeletal muscle. Studies on skeletal muscle have been of increasing interest during the last years, since it was shown that MRS enables the differentiation between two muscular lipid compartments the bulk fat components along the fasciae and muscular boundaries, which are called extramyocellular lipids (EMCL), and the metabolically highly active intramyocellular lipids (IMCL). The latter are stored in spherical droplets in the cytoplasm of muscle... 

Fig. 4. Electron myograph of skeletal muscle. The band structure caused by the sarcomeres, two capillaries (1) and several small lipid droplets (2) are shown. The intramyocellular lipid droplets (size approximately 0.1-1 pm) make up the IMCL content mentioned in the context.

Fig. 15. Comparison of a water suppressed muscle spectrum and a spectrum from yellow bone marrow containing almost pure fat (triglycerides). Measurement parameters STEAM sequence, TE=10 ms, TM=15 ms, TR = 2 s, 40 acq., VOI (11 X 11 X 20) mm. (a) Spectrum from TA muscle recorded after careful positioning of the VOI, avoiding inclusion of macroscopic fatty septa allows separation of extramyocellular (EMCL, broken lines) and intramyocellular lipid signals (IMCL, dotted lines) based on susceptibility differences. For this reason characteristic signals from fatty acids occur double. Signals of creatine (methyl, Crs, and methylene, Cr2) show triplet and doublet structure, respectively, due to dipolar coupling effects. Further signals of TMA (including carnitine and choline compartments), Taurine (Tau), esters, unsaturated fatty acids (-HC=CH-), and residual water are indicated, (b) Spectrum from yellow fatty bone marrow of the tibia with identical measuring parameters, but different amplitude scale.

Peterson et al. found an increase in intramyocellular lipid content and reduction in mitochondria phosphorylation (mitochondrial rates of ATP production) in insulin-resistant subjects versus insulin-sensitive subjects. They concluded that their results supported the h) othesis that insulin resistance is due to dysregulation of intramyocellular fatty acid metabolism, which maybe caused by an inherited defect in mitochondrial oxidative phosphorylation. 

Fig. 23.1 Body composition and lipid deposition. Data are presented as means SD. (a) There is a trend for long-chain 3-hydroxy acyl-CoA dehydrogenase (LCHAD)-deficient patients (n = 9 closed bars) to have less fat-free mass and more fat mass compared with control subjects (n = 9 open bars) when expressed as %body mass, (b) There was no difference in fat-free or fat mass expressed as mass/surface area between groups, (c) There was a trend for LCHAD-deficient patients (n = 9 closed bars) to have more extramyocellular Upid EMCL) but no difference in intramyocellular lipid IMCL) compared with...

Measurements of lipids in muscle and bone have also been made. Ye et al. found significantly higher levels of intramyocellular lipids (IMCL) in the tibialis anterior muscle of obese mice (Lep° /Lep° ) compared to control mice (Lep° / + heterozygous). Whereas, Xiao et al. have quantified the apparent diffusion coefficients (ADC) for extramyocellular lipids (EMCL) and IMCL in Sprague-Dawley rats along the direction perpendicular to muscle fibre orientation. The ADC for EMCL and IMCL were 13.8 0.9 X 10 and 4.6 0.7 x 10 mm s respectively. In bone. 

Decombaz, J., Schmitt, B., Ith, M., Decarli, B., Diem, R, ICreis, R, Hoppeler, H., and Boesch, C., Postexercise fat intake repletes intramyocellular lipids but no faster in trained than in sedentary subjects. Am. J. Physiol. Regul. Integr. Comp. Physiol. 

Larson-Meyer, D.E., Newcomer, B.R., and Hunter, G.R., Influence of endurance training and recovery diet on intramyocellular lipid content in women IH NMR study. Am. J. Physiol. Endocrin. MetaboL, 282, E95-E106, 2002. 

De Bock, K. Dresselaers, T. Kiens, B. Richter, E. A. Van Hecke, R Hespel, P. Evaluation of intramyocellular lipid breakdown during exercise by biochemical assay, NMR spectroscopy, and Oil Red O staining. Am. J. Physiol. 2007, 293, E428-E434. 

Kato et have used H MRS to assess intramyocellular lipids... 

Michael MD, Kulkami RN, Postic C et al. (2000) Loss of insulin signaling in hepatocytes leads to severe insulin resistance and progressive hepatic dysfunction. Mol Cell 6 87-97 Neumann-Haefelin C, Beha A, Kuhlmann J et al. (2004) Muscle-type specific intramyocellular and hepatic lipid metabolism during starvation in Wistar rats. Diabetes 53 528-534... 

Diffusion-weighted magnetic resonance spectroscopy has been used by Xiao and Wu to study intramyocellular and extramyocellular lipids in vivo. These studies may provide new insights in the investigation of lipid metabolism in obesity and diabetes. 

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