Toward Revealing Microcystin Distribution in Mouse Liver Tissue Using MALDI-MS Imaging.

Daria Kucheriavaia,Judy A Westrick,Dragan Isailovic,Nicholas Peraino,David J Kennedy,Steven T Haller,Dušan Veličković,Apurva Lad

doi:10.3390/toxins13100709

Abstract

Cyanotoxins can be found in water and air during cyanobacterial harmful algal blooms (cHABs) in lakes and rivers. Therefore, it is very important to monitor their potential uptake by animals and humans as well as their health effects and distribution in affected organs. Herein, the distribution of hepatotoxic peptide microcystin-LR (MC-LR) is investigated in liver tissues of mice gavaged with this most common MC congener. Preliminary matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) imaging experiments performed using a non-automated MALDI matrix deposition device and a MALDI-time-of-flight (TOF) mass spectrometer yielded ambiguous results in terms of MC-LR distribution in liver samples obtained from MC-LR-gavaged mice. The tissue preparation for MALDI-MS imaging was improved by using an automated sprayer for matrix deposition, and liver sections were imaged using an Nd:YAG MALDI laser coupled to a 15 Tesla Fourier-transform ion cyclotron resonance (FT-ICR)-mass spectrometer. MALDI-FT-ICR-MS imaging provided unambiguous detection of protonated MC-LR (calculated m/z 995.5560, z = +1) and the sodium adduct of MC-LR (m/z 1017.5380, z = +1) in liver sections from gavaged mice with great mass accuracy and ultra-high mass resolution. Since both covalently bound and free MC-LR can be found in liver of mice exposed to this toxin, the present results indicate that the distribution of free microcystins in tissue sections from affected organs, such as liver, can be monitored with high-resolution MALDI-MS imaging.

Highlights

Cyanotoxins contaminate lakes, rivers, and reservoirs during cyanobacterial harmful algal blooms (cHABs) and create hazards for water consumption and recreational activities
MALDI-MS imaging was used to localize unbound MC-LR in liver tissue sections from mice gavaged with this cyanotoxin
While MC-LR was detected by MALDI-TOF MS, MS imaging was only efficient after an automated matrix sprayer and MALDI-Fourier-transform ion cyclotron resonance (FT-ICR)-MS were used for MC-LR detection

Summary

Introduction

Cyanotoxins contaminate lakes, rivers, and reservoirs during cHABs and create hazards for water consumption and recreational activities. Microcystins (MCs) are of major concern due to their high toxicity and abundance in freshwater bodies during cHABs [1]. MCs are cyclic heptapeptides that contain the unusual amino acid ADDA (3-amino-9-methoxy-2,6,8-trimethyl-10-phenyldeca-4(E),6(E)-dienoic acid), which is found in the related cyanotoxins nodularins [2]. The general structure of MCs is often presented as cyclo-(D-alanine-X-D-methyl aspartic acid-Y-ADDA-D-glutamic acid-methyl dehydroalanine), where X and Y are two variable L-amino acids at positions 2 and 4 (e.g., leucine and arginine in the case of MC-LR) [2]. ADDA is primarily responsible for the high toxicity of MCs, which mainly affect the liver by inhibiting protein phosphatases 1 and 2A (PP1 and PP2A) and have been shown to exacerbate the development of pre-existing gastrointestinal and liver disease [6,7,8,9,10,11]. Some of the MCs may remain unbound in the liver and kidney, and MC excretion has been favored by formation of glutathione and cysteine adducts [12,13,14]

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Results

Conclusion