Bioanalytical and Mass Spectrometric Methods for Aldehyde Profiling in Biological Fluids

Abstract

Human exposure to aldehydes is implicated in multiple diseases including diabetes, cardiovascular diseases, neurodegenerative disorders (i.e., Alzheimer's and Parkinson's Diseases), and cancer. Because these compounds are strong electrophiles, they can react with nucleophilic sites in DNA and proteins to form reversible and irreversible modifications. These modifications, if not eliminated or repaired, can lead to alteration in cellular homeostasis, cell death and ultimately contribute to disease pathogenesis. This review provides an overview of the current knowledge of the methods and applications of aldehyde exposure measurements, with a particular focus on bioanalytical and mass spectrometric techniques, including recent advances in mass spectrometry (MS)-based profiling methods for identifying potential biomarkers of aldehyde exposure. We discuss the various derivatization reagents used to capture small polar aldehydes and methods to quantify these compounds in biological matrices. In addition, we present emerging mass spectrometry-based methods, which use high-resolution accurate mass (HR/AM) analysis for characterizing carbonyl compounds and their potential applications in molecular epidemiology studies. With the availability of diverse bioanalytical methods presented here including simple and rapid techniques allowing remote monitoring of aldehydes, real-time imaging of aldehydic load in cells, advances in MS instrumentation, high performance chromatographic separation, and improved bioinformatics tools, the data acquired enable increased sensitivity for identifying specific aldehydes and new biomarkers of aldehyde exposure. Finally, the combination of these techniques with exciting new methods for single cell analysis provides the potential for detection and profiling of aldehydes at a cellular level, opening up the opportunity to minutely dissect their roles and biological consequences in cellular metabolism and diseases pathogenesis.

Keywords: aldehydes; biological fluids; cancer; data-dependent profiling; derivatization; diseases; exposure biomarkers; genotoxicity; high-resolution mass spectrometry; isotope labeling; oxidative stress.

Figure 1

Exogenous and endogenous sources of human exposure to aldehydes.

Figure 2

Structures of common aldehydes associated with various human diseases.

Figure 3

Reaction of 2-thiobarbituric acid (2-TBA) with malondialdehyde (MDA), a biomarker of oxidative stress. 2-TBA reacts with MDA to form a colored product, which is measured spectrophotometrically at 532 nm. The intensity of the colored product reflects the level of lipid peroxidation in the sample.

Figure 4

Reaction of MBTH with aldehydes to form an intense blue-colored complex. Figure adapted from Reference [131] (Copyright 2016, Elsevier).

Figure 5

Real-time imaging of total aldehydic load in cells. Cellular aldehyde labeling fluorescence images and flow cytometry data. Hela cells were exposed to varying concentrations of: (a) formaldehyde; (b) glycolaldehyde; (c) acrolein; and (d) acetaldehyde along with 20 μM of the dye AFDZ and 10 mM catalyst (2,4-dimethoxyaniline) with images taken after 1 h of incubation. Note that 50 μM was used with acrolein and 100 μM for the other aldehydes tested. (e) K562 cells pretreated with 250 μM daidzin and incubated with 40 μM of AFDZ dye, 10 mM catalyst (2,4-dimethoxyaniline), and with/without 20 mM ethanol. (f) Flow cytometry data monitoring the production of aldehyde over time in K562 cells with/without ethanol. The fluorescence intensities were compared to that obtained from t = 0 without added ethanol and daidzin. Scale bars (20 μM) are shown. Reprinted from [171] (Copyright 2016, American Chemical Society).

Figure 6

Commonly used differential isotope labeling reagents for profiling and relative quantitation of carbonyl compounds.

Figure 7

Development of a high-resolution accurate mass data-dependent MS³ neutral loss screening strategy for profiling and quantitative analysis of aldehydes in biological fluids. (a) The high-resolution accurate mass of ^•OH (17.0027 Da) was used to screen for all DNPH-derivatized aldehydes. (b) Monitoring of specific fragment ions (m/z 78.0332 and m/z 164.0323) minimizes possible false positive identification. (c) Representative MS, MS², and MS³ spectra of DNPH-derivatized acetaldehyde and proposed structures of major fragment ions. Reprinted with permission from Ref. [218] (Copyright 2017, Springer).