Intramyocellular lipids versus intramyocellular triglycerides

Zhou, Dequan; Guo, Zhao

doi:10.1002/mrm.23255

Cited by 6 publications

(5 citation statements)

References 24 publications

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“…We agree that any reports of the concentration of intramyocellular triglycerides measured by 1 H magnetic resonance spectroscopy should be interpreted cautiously and in light of the remarks by Zhou and Guo (2). When these methods are applied to healthy subjects under different physiological conditions or to patients with real disease, it is possible that the simplifying assumptions described above about the concentration of diglycerides, acylcarnitines, and other metabolites may not apply.…”

supporting

confidence: 76%

“…Zhou and Guo have questioned our assignment of the 1 H fat signals observed in human skeletal muscle at 7 T to the methyl protons (∼0.84 ppm) and the methylene protons (∼1.24 ppm) of intracellular triglycerides (1, 2). In our study, we assumed that the 1 H signal in the methyl region could be assigned exclusively to the methyl group of long chain fatty acids in triglycerides.…”

mentioning

confidence: 97%

“…The 1 H spectrum of phospholipids produces very broad lines, on the order of 1 kHz (3, 4), and the T 2 's are very short, ranging from 1 to 10 μs. As noted (2), we assumed ‐ but did not demonstrate ‐ that the contribution of phospholipids was negligible because the methyl signal was relatively sharp and symmetric, and because the observations were made at very long echo times. The total concentration of nonesterified fatty acids, monoglycerides, and diglycerides in rat soleus muscle is about 1% of the concentration of triglycerides (5).…”

mentioning

confidence: 99%

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Ren

Sherry

Malloy

2011

Magnetic Resonance in Med

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supporting

confidence: 76%

mentioning

confidence: 97%

mentioning

confidence: 99%

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Reply to: Intramyocellular lipids vs. intramyocellular triglycerides

Ren

Sherry

Malloy

2011

Magnetic Resonance in Med

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“…imcTG is detected at 1.3 ppm simultaneously and termed as intramyocellular lipids. However, the accuracy of these terms is debatable (27). The subcutaneous fat, residing outside the deep fascia, is drained by separate veins (the great saphenous vein and its tributaries) and thus can be in theory excluded from the gross skeletal muscle compartment by careful catheter placement (see below).…”

Section: Four Pools Of Triglycerides In the Legmentioning

confidence: 99%

Arterio-venous balance studies of skeletal muscle fatty acid metabolism: what can we believe?

Guo

Jensen

2013

American Journal of Physiology-Endocrinology and Metabolism

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Guo Z, Jensen MD. Arterio-venous balance studies of skeletal muscle fatty acid metabolism: what can we believe? Am J Physiol Endocrinol Metab 305: E925-E930, 2013. First published August 13, 2013; doi:10.1152/ajpendo.00346.2013.-The arterio-venous balance (A-V balance/difference) technique has been used by a number of groups, including ours, to study skeletal muscle fatty acid metabolism. Several lines of evidence indicate that, like glycogen, intramyocellular triglycerides (imcTG) are an energy source for local use. As such, the report that increased release of free fatty acids (FFA) via lipolysis from skeletal muscle, but not from adipose tissue, is responsible for the increased systemic lipolysis during IL-6 infusion in healthy humans is somewhat unexpected (26). It appears that given the complex anatomy of human limbs, as to be discussed in this review, it is virtually impossible to determine whether any fatty acids being released into the venous circulation of an arm or leg derive from the lipolysis of intermuscular fat residing between muscle groups, intramuscular fat residing within muscle groups (between epimysium and perimysium, or bundles), or the intramyocellular triglyceride droplets (imcTG). In many cases, it may even be difficult to be confident that there is no contribution of FFA from subcutaneous adipose tissue. This question is fundamentally important as one attempts to interpret the results of skeletal muscle fatty acid metabolism studies using the A-V balance technique. In this Perspectives article, we examine the reported results of fatty acid kinetics obtained using the techniques to evaluate the degree of and how to minimize contamination when attempting to sample skeletal muscle-specific fatty acids. arterio-venous difference; arterio-venous balance; leg; forearm; skeletal muscle; adipose; fatty acids Terminology and ExpressionsFOR THE STUDY OF MUSCLE FATTY ACID METABOLISM, the leg arterio-venous (A-V) balance technique is commonly employed (17,19,20,22,26). It employs flexible catheters to collect blood samples from the femoral artery and femoral vein for the purpose of measuring the concentration of fatty acids. This information allows one to determine the net uptake or net release of fatty acids (mmol/l) based on the A-V concentration difference. If the difference is positive, it is a net uptake. If it is negative, it is a net release. Often, plasma or blood flow rate is determined simultaneously to calculate the rates of net uptake and net release of fatty acids across the leg (mmol/min). These parameters only provide one-way information, either release or uptake, but not both. To measure both directions, free fatty acid (FFA) tracers are required. By combining plasma flow, fatty acid concentrations, and the isotopic enrichment (with stable isotope) or specific activity (with radioactive isotope), the unidirectional uptake as well as the unidirectional release of fatty acids can be quantified (13,25). The term release and uptake with or without a preceding adjective "net" confers qui...

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“…Near infrared spectroscopy is subject to certain assumptions and limitations and many of the following concerns about NIRS methodology are areas of active Adipose tissue thickness (subcutaneous) is the main source of betweensubjects STT variance, and is a major confounding factor of NIRS muscle Hb data because light is highly scattered in adipose tissue 30 . The contributions of intramyocellular lipids are typically disregarded because the concentrations are low enough 31,32 to be deemed negligible. Larger STT is associated with an underestimation of Hb concentrations (O2Hb, HHb, and tHb) 33,34 .…”

Section: 21assumptions and Limitationsmentioning

confidence: 99%

Quantifying contact force artefact in near infrared spectroscopy

Schwab¹

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Transcutaneous near infrared spectroscopy (NIRS) of muscle requires coupling between the device and the skin. An unfortunate by-product of this coupling is contact force artefact, where the amount of contact force between the device and the skin affects measurements. Contact force artefact is well known, but largely ignored in most NIRS research. We performed preliminary investigations of contact force artefact to quantify tissue behaviour to inform future NIRS designs. Specifically, we conducted three studies on contact force artefact: (i) an experimental investigation of static load at varied levels of contact force and muscle activation, (ii) an experimental investigation of oscillating load at varied levels of contact force and frequency, and (iii) a Monte Carlo simulation of photon propagation through skin, adipose tissue, and muscle. Our results confirmed that contact force artefact is a confounding factor in NIRS muscle measurements because contact force affects measured hemoglobin concentrations in a manner consistent with muscle contractions. Further, the effects of contact force are not altered by muscle contraction and a likely candidate for the mechanism responsible for contact force artefact is the viscoelastic compression of superficial tissues (skin and adipose) during loading. Simulation data suggests that adipose tissue plays a key role in diffuse reflectance of photons, so any compression of the superficial tissues will affect the reflected signal. Further research is required to fully understand the mechanisms behind contact force artefact, which will, in turn, inform future NIRS device designs.

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Intramyocellular lipids versus intramyocellular triglycerides

Cited by 6 publications

References 24 publications

Reply to: Intramyocellular lipids vs. intramyocellular triglycerides

Reply to: Intramyocellular lipids vs. intramyocellular triglycerides

Arterio-venous balance studies of skeletal muscle fatty acid metabolism: what can we believe?

Quantifying contact force artefact in near infrared spectroscopy

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