Determination of urinaryS-sulphocysteine, xanthine and hypoxanthine by liquid chromatography-electrospray tandem mass spectrometry

Abstract

Molybdenum cofactor and isolated sulphite oxidase deficiencies are two related rare autosomal recessive diseases characterized by severe neurological abnormalities, dislocated lens and mental retardation. Determination of three biochemical markers S-sulphocysteine (SSC), xanthine (XAN) and hypoxanthine (HXAN) in urine is essential for a definitive diagnosis and identification of the exact defect. We developed a rapid liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the analysis of SSC, XAN and HXAN in urine. The analysis was carried out in the negative-ion selected-reaction monitoring mode. The turnaround time for the assay was 7 min. Linear calibration curves for the three biomarkers were obtained in the range of 12-480 micromol/L. The intra- and inter-day assay variations were <2.5%. Mean recoveries of SSC, XAN and HXAN added to urine at two significantly different concentrations were in the range 94.3-107.3%. At a normal SSC urine excretion value of 3.2 micromol/mmol creatinine, the signal-to-noise ratio was 337:1. This stable isotope dilution LC-MS/MS method is specific, rapid and simple, and provides definitive diagnosis for molybdenum cofactor and isolated sulphite oxidase deficiencies in very small volumes of urine. We have identified seven new cases of isolated sulphite oxidase deficiency from four Saudi families and one Sudanese family.

Molybdenum cofactor and isolated sulphite oxidase deficiencies: Clinical and molecular spectrum among Egyptian patients

“… a S-sulphocysteine/xanthine (<10/<40 µmol/mmol creatinine) by LC–MS/MS method (Rashed et al, 2005) 15 . b Serum uric acid in children (2.0–5.5 mg/dL). …”

Molybdenum Cofactor Deficiency: A New HPLC Method for Fast Quantification of S-Sulfocysteine in Urine and Serum

“…Furthermore, most SSC analyses are performed with the classical amino acid analyzer, but quantification is limited due to the early elution of SSC. In addition, poor specificity and possible interference from other metabolites were also reported by using the amino acid analyzer (Rashed et al 2005).…”

An inlaying ultra-thin carbon paste electrode modified with functional single-wall carbon nanotubes for simultaneous determination of three purine derivatives

“…Being the precursors of UA and the intermediates in purine nucleotide or deoxynuclotide metabolism, the determination of Xa and Hxa is important in biochemical and clinical diagnosis [18]. Various techniques have been developed to determine the purine derivatives, including enzymatic methods [19,20], HPLC [21][22][23][24], HPCE [25][26][27] and electrochemistry methods [28,29], among which enzymatic approaches are valuable analytical tools and offer sensitive and specific methods for the determination of Xa, Hxa and UA. However, the xanthine oxidase can oxidize both Hxa and Xa to UA making the specific determination difficult.…”