title: Mitochondrial coenzyme Q10 determination by isotope-dilution liquid chromatography-tandem mass spectrometry.
abstract: BACKGROUND
  Coenzyme Q10 (CoQ10) is an essential part of the mitochondrial respiratory chain. Unlike most other respiratory chain disorders, CoQ10 deficiency is potentially treatable. We aimed to develop and validate an accurate liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the determination of mitochondrial CoQ10 in clinical samples.
  
  
  METHODS
  We used mitochondria isolated from muscle biopsies of patients (n = 166) suspected to have oxidative phosphorylation deficiency. We also used fibroblast mitochondria from 1 patient with CoQ10 deficiency and 3 healthy individuals. Samples were spiked with nonphysiologic CoQ10-[(2)H6] internal standard, extracted with 1-propanol and with ethanol and hexane (2 mL/5 mL), and CoQ10 quantified by LC-MS/MS. The method and sample stability were validated. A reference interval was established from the patient data.
  
  
  RESULTS
  The method had a limit of quantification of 0.5 nmol/L. The assay range was 0.5-1000 nmol/L and the CVs were 7.5%-8.2%. CoQ10 was stable in concentrated mitochondrial suspensions. In isolated mitochondria, the mean ratio of CoQ10 to citrate synthase (CS) activity (CoQ10/CS) was 1.7 nmol/U (95% CI, 1.6-1.7 nmol/U). We suggest a CoQ10/CS reference interval of 1.1-2.8 nmol/U for both sexes and all ages. The CoQ10/CS ratio was 5-fold decreased in fibroblast mitochondria from a patient with known CoQ10 deficiency due to recessive prenyl (decaprenyl) diphosphate synthase, subunit 2 (PDSS2) mutations.
  
  
  CONCLUSIONS
  Normalization of mitochondrial CoQ10 concentration against citrate synthase activity is likely to reflect most accurately the CoQ10 content available for the respiratory chain. Our assay and the established reference range should facilitate the diagnosis of respiratory chain disorders and treatment of patients with CoQ10 deficiency.
authors: HUSLAB, Helsinki University Central Hospital, Helsinki, Finland. outi.itkonen@hus.fi
authors: Outi
authors: O
authors: Itkonen
authors: Anu
authors: A
authors: Suomalainen
authors: Ursula
authors: U
authors: Turpeinen
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002478:Cells, Cultured; D002648:Child; D002675:Child, Preschool; D002853:Chromatography, Liquid; D003903:Deuterium; D005260:Female; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D007201:Indicator Dilution Techniques; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D008875:Middle Aged; D008928:Mitochondria / Q000378:metabolism*; D008931:Mitochondria, Muscle / Q000378:metabolism; D018482:Muscle, Skeletal / Q000378:metabolism; D012016:Reference Values; D012737:Sex Factors; D012867:Skin / Q000166:cytology / Q000378:metabolism; D021241:Spectrometry, Mass, Electrospray Ionization; D053719:Tandem Mass Spectrometry; D014451:Ubiquinone / Q000031:analogs & derivatives* / Q000378:metabolism; D055815:Young Adult
chemical_list: D014451:Ubiquinone; D003903:Deuterium; C024989:coenzyme Q10