Mitochondrial involvement and erythronic acid as a novel biomarker in transaldolase deficiency

Abstract

Background: Sedoheptulose, arabitol, ribitol, and erythritol have been identified as key diagnostic metabolites in TALDO deficiency.

Method: Urine from 6 TALDO-deficient patients and TALDO-deficient knock-out mice were analyzed using ¹H-NMR spectroscopy and GC-mass spectrometry.

Results: Our data confirm the known metabolic characteristics in TALDO-deficient patients. The β-furanose form was the major sedoheptulose anomer in TALDO-deficient patients. Erythronic acid was identified as a major abnormal metabolite in all patients and in knock-out TALDO mice implicating an as yet unknown biochemical pathway in this disease. A putative sequence of enzymatic reactions leading to the formation of erythronic acid is presented. The urinary concentration of the citric acid cycle intermediates 2-oxoglutaric acid and fumaric acid was increased in the majority of TALDO-deficient patients but not in the knock-out mice.

Conclusion: Erythronic acid is a novel and major hallmark in TALDO deficiency. The pathway leading to its production may play a role in healthy humans as well. In TALDO-deficient patients, there is an increased flux through this pathway. The finding of increased citric acid cycle intermediates hints toward a disturbed mitochondrial metabolism in TALDO deficiency.

Fig. 1

Sedoheptulose purified from Sedum spectabile “Brillant”. (A) 500-MHz ¹H-NMR spectrum. Assignments “S” refer to the most prominent anomeric form of sedoheptulose, β-furanose. Subscript numbers refer to the carbon position in the molecule. Assignments “★” refer the other anomeric forms of sedoheptulose. (B) GC profile: Pooled urine spiked with purified sedoheptulose. Sedoheptulose anomers were present in a ratio furanose-1/furanose-2/pyranose-1/pyranose-2=22%:64%:8%:6%. In all likelihoods, furanose-1 and pyranose-1 are alpha forms and furanose-2 and pyranose-2 are the beta forms. (C₁) Mass spectrum for the peak with assignment furanose-2 (m/z values {relative abundance}: 73{100}, 217{45}, 147{27}, 204 {18}, and 359{15}). Characteristic for the furanose forms is the low ratio for m/z 204:m/z 217 [18]. (C₂) Mass spectrum for the peak with assignment pyranose-2 (m/z values {relative abundance}: 73{100}, 204{62}, 147{26}, 359{22}, and 217{12}). Characteristic for the pyranose forms is the high ratio for m/z 204:m/z 217 [18].

Fig. 2

In vitro ¹H-NMR spectra (500 MHz) of urine and model compounds measured at pH 2.50. (A) Threonic acid. (B) Erythronic acid. (C) Sedoheptulose isolated from Sedum spectabile. (D) Urine of a patient with transaldolase deficiency (S=sedoheptulose and E=erythronic acid. Subscript numbers refer to the carbon position in the molecule [Table 2]).

Fig. 3

GC–MS chromatogram of urine. (A) Pooled urine spiked with erythronic acid. (B) Urine of patient with transaldolase deficiency. (C) Control urine. (D) Mass spectrum of erythronic acid in the urine of the TALDO patient.

Fig. 4

In vitro ¹H-NMR spectra (500 MHz) of urine from mice measured at pH 2.50. (A) Urine of a control mouse. (B) Urine of a mouse with transaldolase deficiency (S=sedoheptulose and E=erythronic acid. Subscript numbers refer to the carbon position in the molecule [Table 2]).

Fig. 5

Pentose phosphate pathway. Transaldolase deficiency (solid black square) results in accumulation of sedoheptulose, erythritol, and erythronic acid. (1) Transaldolase. (2) Sedoheptulokinase. (3) Cytosolic phosphatase. (4) Fructokinase. (5) Aldolase B. (6) Aldehyde reductase. (7) Putative (after Hauschildt et al. [23]). (8) Glyceraldehyde 3-phosphate dehydrogenase [24,25]. (9) Phosphatase. (10) Putative [26]. (11) Transketolase. (12) D-Ribulose 5-phosphate epimerase. (13) Ribose 5-phosphate isomerase.