Division of Endocrinology, Diabetology, Angiology, Nephrology, Pathobiochemistry, and Clinical Chemistry, Department of Internal Medicine, University Tübingen, 72076 Tübingen, Germany.
J Clin Endocrinol Metab. 2013 Jun;98(6):E1137-42. doi: 10.1210/jc.2012-3976. Epub 2013 Apr 30.
Acylcarnitines are biomarkers of incomplete β-oxidation and mitochondrial lipid overload but indicate also high rates of mitochondrial fatty acid oxidation. It is unknown whether the production of acylcarnitines in primary human myotubes obtained from lean, metabolically healthy subjects reflects the fat oxidation in vivo.
Our objective was to quantify the acylcarnitine production in myotubes obtained from subjects with low and high fasting respiratory quotient (RQ).
Fasting RQ was determined by indirect calorimetry. Muscle biopsies from the vastus lateralis muscle were taken from 6 subjects with low fasting RQ (mean 0.79 ± 0.03) and 6 with high fasting RQ (0.90 ± 0.03), and satellite cells were isolated, cultured, and differentiated to myotubes. Myotubes were cultivated with 125 μM (13)C-labeled palmitate for 30 minutes and 4 and 24 hours. Quantitative profiling of 42 intracellular and 31 extracellular acylcarnitines was performed by stable isotope dilution-based metabolomics analysis by liquid chromatography coupled to mass spectrometry.
Myotubes from donors with high fasting RQ produced and released significant higher amounts of medium-chain acylcarnitines. High (13)C8 and (13)C10 acylcarnitine levels in the extracellular compartment correlated with high fasting RQ. The decreased expression of medium-chain acyl-coenzyme A dehydrogenase (MCAD) in these myotubes can explain the higher rate of incomplete fatty acid oxidation. A lower intracellular [(13)C]acetylcarnitine to carnitine and lower intracellular (13)C16/(13)C18 acylcarnitine to carnitine ratio indicate reduced fatty acid oxidation capacity in these myotubes. Mitochondrial DNA content was not different.
Acylcarnitine production and release from primary human myotubes of donors with high fasting RQ indicate a reduced fatty acid oxidation capacity and a higher rate of incomplete fatty acid oxidation. Thus, quantitative profiling of acylcarnitine production in human myotubes can be a suitable tool to identify muscular determinants of fat oxidation in vivo.
酰基辅酶 A 是不完全β-氧化和线粒体脂质过载的生物标志物，但也表明线粒体脂肪酸氧化率很高。目前尚不清楚从瘦的、代谢健康的受试者中获得的原代人肌管产生酰基辅酶 A 是否反映了体内脂肪氧化。
我们的目的是定量测定来自低和高空腹呼吸商（RQ）的肌管中酰基辅酶 A 的产生。
通过间接热量法测定空腹 RQ。从股外侧肌中取 6 名空腹 RQ 低（平均 0.79 ± 0.03）和 6 名空腹 RQ 高（0.90 ± 0.03）的受试者的肌肉活检，分离、培养和分化成肌管。用 125 μM（13）C 标记的棕榈酸培养肌管 30 分钟、4 小时和 24 小时。通过液相色谱-质谱联用的稳定同位素稀释代谢组学分析定量分析 42 种细胞内和 31 种细胞外酰基辅酶 A。
空腹 RQ 高的供体的肌管产生和释放的中链酰基辅酶 A 明显更多。细胞外高（13）C8 和（13）C10 酰基辅酶 A 水平与空腹 RQ 高相关。这些肌管中中链酰基辅酶 A 脱氢酶（MCAD）的表达降低可以解释不完全脂肪酸氧化率较高的原因。这些肌管中较低的细胞内[（13）C]乙酰基辅酶 A 与肉碱和较低的细胞内（13）C16/（13）C18 酰基辅酶 A 与肉碱的比值表明脂肪酸氧化能力降低。线粒体 DNA 含量无差异。
高空腹 RQ 供体的原代人肌管产生和释放酰基辅酶 A 表明脂肪酸氧化能力降低和不完全脂肪酸氧化率增加。因此，定量分析人肌管中酰基辅酶 A 的产生可以作为一种合适的工具来识别体内脂肪氧化的肌肉决定因素。
