Determination of nitrofuran metabolites and nifurpirinol in animal tissues and eggs by ultra-high performance liquid chromatography-tandem mass spectrometry validated according to Regulation (EU) 2021/808

In this work, an analytical method for the determination of eight non-allowed nitrofurans, including nifurpirinol and the metabolites of furazolidone, furaltadone, nitrofurantoin, nitrofurazone, nifursol, nitrovin, and nifuroxazide in animal tissues, including muscle (poultry, bovine, ovine, porcine, rabbit, and fish), kidney (bovine, ovine, porcine), and eggs, has been developed and validated according to Regulation (EU) 2021/808. The method was based on derivatization with 2-nitrobenzaldehyde in acid medium, followed by vortex-assisted liquid-liquid extraction and solid phase extraction for sample purification prior to ultra-high performance liquid chromatography-tandem mass spectrometry. Under selected conditions, the method was validated showing satisfactory relative matrix effects (CV ≤ 20 %), linearity (R2 ≥ 0.98), trueness (≤20 %, expressed as bias), accuracy (83-120 %), repeatability (1.7-19.9 %), reproducibility (1.9-25.7 %), specificity (blank signal ≤30 % at the LCL), and ruggedness. The decision limit for confirmation (CCα) for the target analytes ranged from 0.27 to 0.35 μg kg-1, all below the current reference point for action (RPA) of 0.5 μg kg-1 for the studied compounds. This validated method is currently accredited according to UNE-EN ISO/IEC 17025 by the Spanish National Accreditation Body (ENAC) to be implemented for official control analyses in the Public Health Laboratory of Valencia (Spain).

Selective Cell Ablation Using an Improved Prodrug-Converting Nitroreductase

Selective cell ablation is an invaluable tool to investigate the function of cell types, the regeneration of cells, and the modeling of diseases associated with cell loss. The nitroreductase (NTR)-mediated cell ablation system is a simple method enabling the elimination of targeted cells through the expression of a nitroreductase enzyme and the application of a prodrug (such as metronidazole). The prodrug is reduced to a cytotoxic product by nitroreductase, thereby leading to DNA damage-induced cell death. In species with elevated regenerative capacity such as zebrafish, removing the prodrug allows endogenous tissue to replace the lost cells. Herein, we describe a method for the use of a markedly improved nitroreductase enzyme for spatially and temporally controlled targeted cell ablation in the zebrafish. Recently, we identified an NTR variant (NTR 2.0) that achieves effective targeted cell ablation at concentrations of metronidazole well below those causing toxic side effects. NTR 2.0 thereby enables the ablation of "resistant" cell types and novel cell ablation paradigms. These advances simplify investigations of cell function, enable interrogations of the effects of chronic inflammation on regenerative processes and facilitate modeling of degenerative diseases associated with chronic cell loss. Techniques for transgenic nitroreductase expression and prodrug application are discussed.