title: Liquid chromatographic-mass spectrometric method for simultaneous determination of small organic acids potentially contributing to acidosis in severe malaria.
abstract: Acidosis is an important cause of mortality in severe falciparum malaria. Lactic acid is a major contributor to metabolic acidosis, but accounts for only one-quarter of the strong anion gap. Other unidentified organic acids have an independent strong prognostic significance for a fatal outcome. In this study, a simultaneous bio-analytical method for qualitative and quantitative assessment in plasma and urine of eight small organic acids potentially contributing to acidosis in severe malaria was developed and validated. High-throughput strong anion exchange solid-phase extraction in a 96-well plate format was used for sample preparation. Hydrophilic interaction liquid chromatography (HILIC) coupled to negative mass spectroscopy was utilized for separation and detection. Eight possible small organic acids; l-lactic acid (LA), α-hydroxybutyric acid (aHBA), β-hydroxybutyric acid (bHBA), p-hydroxyphenyllactic acid (pHPLA), malonic acid (MA), methylmalonic acid (MMA), ethylmalonic acid (EMA) and α-ketoglutaric acid (aKGA) were analyzed simultaneously using a ZIC-HILIC column with an isocratic elution containing acetonitrile and ammonium acetate buffer. This method was validated according to U.S. Food and Drug Administration guidelines with additional validation procedures for endogenous substances. Accuracy for all eight acids ranged from 93.1% to 104.0%, and the within-day and between-day precisions (i.e. relative standard deviations) were lower than 5.5% at all tested concentrations. The calibration ranges were: 2.5-2500μg/mL for LA, 0.125-125μg/mL for aHBA, 7.5-375μg/mL for bHBA, 0.1-100μg/mL for pHPLA, 1-1000μg/mL for MA, 0.25-250μg/mL for MMA, 0.25-100μg/mL for EMA, and 30-1500μg/mL for aKGA. Clinical applicability was demonstrated by analyzing plasma and urine samples from five patients with severe falciparum malaria; five acids had increased concentrations in plasma (range LA=177-1169μg/mL, aHBA=4.70-38.4μg/mL, bHBA=7.70-38.0μg/mL, pHPLA=0.900-4.30μg/mL and aKGA=30.2-32.0) and seven in urine samples (range LA=11.2-513μg/mL, aHBA=1.50-69.5μg/mL, bHBA=8.10-111μg/mL, pHPLA=4.30-27.7μg/mL, MMA=0.300-13.3μg/mL, EMA=0.300-48.1μg/mL and aKGA=30.4-107μg/mL). In conclusion, a novel bioanalytical method was developed and validated which allows for simultaneous quantification of eight small organic acids in plasma and urine. This new method may be a useful tool for the assessment of acidosis in patients with severe malaria, and other conditions complicated by acidosis.
authors.affiliation: Chromatography and Separation Research Unit, Department of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand; Mahidol-Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok 10400, Thailand.
authors.forename: Natthida
authors.initials: N
authors.lastname: Sriboonvorakul
authors.forename: Natchanun
authors.initials: N
authors.lastname: Leepipatpiboon
authors.forename: Arjen M
authors.initials: AM
authors.lastname: Dondorp
authors.forename: Thomas
authors.initials: T
authors.lastname: Pouplin
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: White
authors.forename: Joel
authors.initials: J
authors.lastname: Tarning
authors.forename: Niklas
authors.initials: N
authors.lastname: Lindegardh
mesh_terms: D000138:Acidosis / Q000139:chemically induced*; D000143:Acids / Q000009:adverse effects / Q000032:analysis*; D002138:Calibration; D002853:Chromatography, Liquid / Q000379:methods*; D006801:Humans; D057230:Limit of Detection; D008288:Malaria / Q000503:physiopathology*; D013058:Mass Spectrometry / Q000379:methods*; D009930:Organic Chemicals / Q000009:adverse effects / Q000032:analysis*; D012015:Reference Standards; D015203:Reproducibility of Results
chemical_list: D000143:Acids; D009930:Organic Chemicals
keywords: Acidosis; Bio-analysis; Liquid chromatography; Mass spectrometry; Severe malaria; Unidentified acids