An on-tissue parallel d₀/d₂₀-meladrazine derivatization approach for fatty acid peroxidation products imaging in...

Mass spectrometry imaging (MSI) enables the simultaneous acquisition of spatial distribution, abundance, and structural information of multiple molecules in biological tissues, yet it faces inherent challenges in detecting poorly ionizable or low-abundance analytes. Fatty aldehydes (FALs) and oxygenated fatty acids (oxo-FAs), key subclasses of fatty acid peroxidation products (FAPPs), are of profound physiological and pathological significance. However, their mass spectrometric detection remains a formidable challenge, particularly for in situ desorption and analysis in biological tissue sections.

A novel hydrogel-assisted on-tissue chemical derivatization (HCD) approach was developed, employing d₀/d₂₀-meladrazine parallel labeling coupled with airflow-assisted desorption electrospray ionization-mass spectrometry imaging (AFADESI-MSI). Through systematic optimization of hydrogel type, reaction time, reaction temperature, and concentration of the derivatization reagent, 313 FAPPs in adult zebrafish were recognized and annotated, including 176 FALs and 137 oxo-FAs. Notably, the derivatization process was performed at 4 °C with a low reagent concentration of 2 mg/mL, which is effective and more compatible with biological sample integrity. Furthermore, custom written R scripts were developed to enable rapid identification and matching of isotopically labeled peak pairs corresponding to derivative product ions. Applying this method to zebrafish whole-body sections yielded spatial distributions of 237 FAPPs. Further application to Congo red (CR)-exposed zebrafish visualized FAPPs dysregulation, indicating CR-induced oxidative stress-mediated damage in the intestine, liver and brain.

This study presents an effective tool for in situ visualization of FAPPs in adult zebrafish, and its application in water pollutant exposure research provide direct evidence of the neurotoxicity and hepatotoxicity of CR. It has broad potential for adaptation to other biological tissues and facilitates elucidating the toxicity mechanisms of environmental toxins or disease mechanisms relating to oxidative stress.