The aim of this study was to develop and validate a liquid chromatography–tandem mass spectrometry (LC-MS/MS) assay for the measurement of uracil (U) and dihydrouracil (UH2) concentrations in dried saliva spots (DSSs), for the evaluation of dihydropyrimidine dehydrogenase (DPD) enzyme activity.
Nine 18-mm diameter DSS discs were extracted with acetate:isopropyl alcohol (85:15, vol/vol) and analyzed by LC-MS/MS. The assay was linear in the range of 10–1000 ng·mL−1, with accuracy between 89% and 112% and precision between 5.7% and 13%. The metabolic ratio [UH2]/[U] was stable in DSS for up to 9 days at 45°C. Concentrations of U and UH2, as well as the metabolic ratio, were highly concordant between matrices. Using a metabolic ratio classification cutoff of 1.16 for the identification of slow DPD metabolizers, 98.7% concordance was achieved between SS and saliva.
DSS samples could be a useful alternative for DPD activity screening, particularly in locations with limited access to highly equipped laboratories.
*Graduate Program on Toxicology and Analytical Toxicology, Universidade Feevale, Novo Hamburgo; and
†Oncology Service, Hospital de Clínicas de Porto Alegre, Porto Alegre, Rio Grande do Sul, Brazil.
Correspondence: Marina Venzon Antunes, PhD, Universidade Feevale, ERS 239, no 2755, 93525-075 Novo Hamburgo, Rio Grande do Sul, Brazil (e-mail: email@example.com).
Supported by Universidade Feevale and Fundo de Incentivo à Pesquisa e Eventos do Hospital de Clínicas de Porto Alegre (FIPE-HCPA).
The authors declare no conflict of interest.
Received August 24, 2018
Accepted December 10, 2018