Coenzyme Q sub(10) quantification in muscle, fibroblasts and cerebrospinal fluid by liquid chromatography/tandem mass spectrometry using a novel deuterated internal standard

RATIONALE Neurological dysfunction is common in primary coenzyme Q sub(10) (2,3-dimethoxy, 5-methyl, 6-polyisoprene parabenzoquinone; CoQ sub(10); ubiquinone) deficiencies, the most readily treatable subgroup of mitochondrial disorders. Therapeutic benefit from CoQ sub(10) supplementation has also been noted in other neurodegenerative diseases. CoQ sub(10) can be measured by high-performance liquid chromatography (HPLC) in plasma, muscle or leucocytes; however, there is no reliable method to quantify CoQ sub(10) in cerebrospinal fluid (CSF). Additionally, many methods use CoQ sub(9), an endogenous ubiquinone in humans, as an internal standard. METHODS Deuterated CoQ sub(10) (d sub(6)-CoQ sub(10)) was synthesised by a novel, simple, method. Total CoQ sub(10) was measured by liquid chromatography/tandem mass spectrometry (LC/MS/MS) using d sub(6)-CoQ sub(10) as internal standard and 5mM methylamine as an ion-pairing reagent. Chromatography was performed using a Hypsersil GOLD C4 column (1503mm, 3 mu m). RESULTS CoQ sub(10) levels were linear over a concentration range of 0-200 nM (R super(2)=0.9995). The lower limit of detection was 2 nM. The inter-assay coefficient of variation (CV) was 3.6% (10 nM) and 4.3% (20 nM), and intra-assay CV 3.4% (10 nM) and 3.6% (20 nM). Reference ranges were established for CoQ sub(10) in CSF (5.7-8.7 nM; n=17), fibroblasts (57.0-121.6 pmol/mg; n = 50) and muscle (187.3-430.1 pmol/mg; n=15). CONCLUSIONS Use of d sub(6)-CoQ sub(10) internal standard has enabled the development of a sensitive LC/MS/MS method to accurately determine total CoQ sub(10) levels. Clinical applications of CSF CoQ sub(10) determination include identification of patients with cerebral CoQ sub(10) deficiency, and monitoring CSF CoQ sub(10) levels following supplementation. Copyright [copy 2013 John Wiley & Sons, Ltd.