Capillary Zone Electrophoresis with Diode-Array Detection as a Tool to Monitor Variations in the Concentration of Organic Acids from the Tricarboxylic Acid Cycle in Human Urine

The tricarboxylic acid (TCA) cycle is responsible for the generation of energy in the human body and may inform about the energy status in different physiological and pathological conditions. It was developed a method to quantify the TCA cycle intermediates (α-ketoglutaric, citric, fumaric, lactic, malic, and succinic acids) by capillary zone electrophoresis with diode array detector (CZE-DAD) in indirect mode. The background electrolyte consisted of 24 mmol L^–1 2,6-pyridine carboxylic acid, 76 mmol L^–1 β-alanine, and 4 mmol L^–1 hexadecyltrimethylammonium hydroxide (pH 4). The method was validated and presented a good linearity (R² < 0.9922) and adequate limits of detection (0.24-1.84 mg L^–1) and quantifcation (0.74-5.57 mg L^–1). The method was successfully applied to samples of individuals with obesity before being submitted to bariatric surgery and one year after the surgery. The citric, lactic, and malic acids were detected in the analyzed samples. To evaluate the changes in concentrations of the TCA intermediates, principal component analysis was carried out, and there was no signifcant difference between the two sets of samples. Altogether, the data obtained after applying this new method suggest that CZE-DAD could be used to detect and quantify the TCA cycle metabolites in human urine.

Keywords:
tricarboxylic acid cycle; organic acids; capillary zone electrophoresis; indirect method