Determination of the GABA analogue succinic semialdehyde in urine and cerebrospinal fluid by dinitrophenylhydrazine derivatization and liquid chromatography–tandem mass spectrometry: Application to SSADH deficiency

Summary

Succinic semialdehyde (SSA) accumulates in the inborn error of meta- bolism succinic semialdehyde dehydrogenase deficiency owing to impaired enzymatic conversion to succinic acid. We developed a stable-isotope dilution liquid chromato- graphy–tandem mass spectrometry method for the determination of SSA in urine and cerebrospinal fluid samples. Stable-isotope-labelled [¹³C₄]SSA, serving as internal standard, was prepared by reaction of ninhydrin with L-[¹³C₅]glutamic acid. SSA in body fluids was converted to its dinitrophenylhydrazine (DNPH) derivative, without sample purification prior to the derivatization procedure. The DNPH derivative of SSA was injected onto a C₁₈ analytical column and chromatography was performed by isocratic elution. Detection was accomplished by tandem mass spectrometry operating in the negative multiple-reaction monitoring mode. The limit of detection was 10 nmol/L and the calibration curves over the range 0–500 pmol of SSA showed good linearity (r² > 0.99). The intra-day coefficient of variation (n = 10) for urine was 2.7% and inter-day coefficient of variation (n = 5) for urine was 8.5%. The average recoveries performed on two levels by enriching urine and cerebrospinal fluid samples ranged between 85 and 115%, with coefficients of variation < 8%. The method enabled the first determination of normal values for SSA in urine and pathological values of SSA in urine and cerebrospinal fluid samples derived from patients with succinic semialdehyde dehydrogenase deficiency.