Signal enhancement in laser diode thermal desorption-triple quadrupole mass spectrometry analysis using microwell surface coatings

Characterization of laccases from Trametes hirsuta in the context of bioremediation of wastewater treatment plant effluent

The bioremediation of pharmaceutical compounds contained in wastewater, in an ecological and sustainable way, is possible via the oxidative action of fungal laccases. The discovery of new fungal laccases with unique physico-chemical characteristics pushes researchers to identify suitable laccases for specific applications. The aim of this study is to purify and characterize laccase isoenzymes produced from the Trametes hirsuta IBB450 strain for the bioremediation of pharmaceutical compounds. Two main laccases mixtures were observed and purified in the extracts and were called Yn and Yg. Peptide fingerprinting analysis suggested that Yn was constituted mainly of laccase Q02497 and Yg of laccase A0A6M5CX58, respectively. Robustness tests, based on tolerance and stability, showed that both laccases were affected in a relatively similar way by salts (KCl, NaCl), organic solvents (ACN, MeOH), denaturing compounds (urea, trypsin, copper) and were virtually unaffected and stable in wastewater. Determination of kinetic constants (Michaelis (KM), catalytic constant (kcat) and kinetic efficiency (K=kcat/KM)) for the transformation of synthetic hormone 17α-ethynylestradiol and the anti-inflammatory agent diclofenac indicates a lower KM and kcat for laccase Yn but relative similar K constant compared to Yg. Synergistic effects were observed for the transformation of diclofenac, unlike 17α-ethynylestradiol. Transformation studies of 17α-ethynylestradiol at different temperatures (4 and 21 °C) indicate a transformation rate reduction of approximately 75-80% at 4 °C against 25% for diclofenac in less than an hour. Finally, the classification of laccases Yg and Yn into one of eight groups (group A-H) suggests that laccase Yg belongs to group A (constitutive laccase) and laccase Yn belongs to group B (inducible laccase).

Ultrafast analysis of peptides by laser diode thermal desorption-triple quadrupole mass spectrometry

RATIONALE

The COVID-19 pandemic demonstrated the importance of high-throughput analysis for public health. Given the importance of surface viral proteins for interactions with healthy tissue, they are targets of interest for mass spectrometry-based analysis. For that reason, the possibility of detecting and quantifying peptides using a high-throughput technique, laser diode thermal desorption-triple quadrupole mass spectrometry (LDTD-QqQMS), was explored.

METHODS

Two peptides used as models for small peptides (leu-enkephalin and endomorphin-2) and four tryptic peptides (GVYYPDK, NIDGYFK, IADYNYK, and QIAPGQTGK) specific to the SARS-CoV-2 Spike protein were employed. Target peptides were analyzed individually in the positive mode by LDTD-QqQMS. Peptides were quantified by internal calibration using selected reaction monitoring transitions in pure solvents and in samples spiked with 20 μg mL^-1 of a bovine serum albumin tryptic digest to represent real analysis conditions.

RESULTS

Low-energy fragment ions (b and y ions) as well as high-energy fragment ions (c and x ions) and some of their corresponding water or ammonia losses were detected in the full mass spectra. Only for the smallest peptides, leu-enkephalin and endomorphin-2, were [M + H]⁺ ions observed. Product ion spectra confirmed that, with the experimental conditions used in the present study, LDTD transfers a considerable amount of energy to the target peptides. Quantitative analysis showed that it was possible to quantify peptides using LDTD-QqQMS with acceptable calibration curve linearity (R²  > 0.99), precision (RSD < 18.2%), and trueness (bias < 8.3%).

CONCLUSIONS

This study demonstrated for the first time that linear peptides can be qualitatively and quantitatively analyzed using LDTD-QqQMS. Limits of quantification and dynamic ranges are still inadequate for clinical applications, but other applications where higher levels of proteins must be detected could be possible with LDTD. Given the high-throughput capabilities of LDTD-QqQMS (>15 000 samples in less than 43 h), more studies are needed to improve the sensitivity for peptide analysis of this technique.

Current status and future directions of high-throughput ADME screening in drug discovery

During the last decade high-throughput in vitro absorption, distribution, metabolism and excretion (HT-ADME) screening has become an essential part of any drug discovery effort of synthetic molecules. The conduct of HT-ADME screening has been "industrialized" due to the extensive development of software and automation tools in cell culture, assay incubation, sample analysis and data analysis. The HT-ADME assay portfolio continues to expand in emerging areas such as drug-transporter interactions, early soft spot identification, and ADME screening of peptide drug candidates. Additionally, thanks to the very large and high-quality HT-ADME data sets available in many biopharma companies, in silico prediction of ADME properties using machine learning has also gained much momentum in recent years. In this review, we discuss the current state-of-the-art practices in HT-ADME screening including assay portfolio, assay automation, sample analysis, data processing, and prediction model building. In addition, we also offer perspectives in future development of this exciting field.

Ultrafast laser diode thermal desorption method for analysis of representative pharmaceuticals in soil leachate samples

We developed and evaluated a novel analytical method combining ambient ionization technique - laser diode thermal desorption with chemical ionization (LDTD-APCI) and tandem mass spectrometry detection. The LDTD/APCI-MS/MS method was developed for determination of representative pharmaceuticals from different classes (carbamazepine, sulfamethoxazole, irbesartan, fexofenadine) in leachate samples from soil sorption experimentation. We then optimized laser pattern, laser energy and spiked sample volume, which are crucial parameters for this LDTD/APCI-MS/MS method. We further identified utility of a chelating agent (Na₂-EDTA) to obtain the highest achievable and reproducible signal of target analytes. Achieved method performance parameters (LODs, LOQs, trueness and precision) were comparable with those obtained from LC-MS/MS. However, application of this novel LDTD/APCI-MS/MS method reduced analysis time by two orders of magnitude (to 12 s), compared to more conventional LC-MS/MS approaches, without use of organic solvents. We expect this novel method will reduce costs and increase throughput for future analyses of pharmaceuticals in the environment while advancing a timely principle of green chemistry.

Further studies on the signal enhancement effect in laser diode thermal desorption-triple quadrupole mass spectrometry using microwell surface coatings

The laser diode thermal desorption (LDTD) ionization source allows ultrafast and sensitive analysis of small molecules by mass spectrometry. Signal enhancement in LDTD has been observed when coating the surface of sample microwells with a solution of ethylenediaminetetraacetic acid (EDTA) or nitrilotriacetic acid. Here we present a quantitative analysis of signal enhancement using solutions of diverse commercial proteins (lysozyme, immunoglobulin G, albumin, and fibrinogen) as coatings. Results showed that compounds with polar chemical functions such as carboxylic acid, sulfonyl, and nitro had signal enhancement factors, in most cases higher than 10, when using any of the tested proteins as coating agent. Analysis of variance revealed that immunoglobulin G and fibrinogen gave the best results. However, the signal enhancement factors obtained with these proteins were not superior to those observed with EDTA. To explain the signal enhancement effect of proteins, analysis by scanning electron microscopy of dried samples on the microwell sample plates was carried out. Images showed that salicylic acid, one of the compounds with the highest observed signal enhancement, formed a thick layer when applied directly on the uncoated surface, but it formed small crystals (<1 μm) in the presence of protein or EDTA coatings. Further crystallographic studies using powder X-ray diffraction showed that the crystalline form of salicylic acid is modified in the presence of EDTA. Salicylic acid when mixed with EDTA had a higher percentage of amorphous phase (38.1%) than without EDTA (23.1%). These results appear to confirm that the diminution of crystal size of analytes and the increase of amorphous phase are implicated in signal enhancement effect observed in LDTD using microwell surface coatings. To design better coatings and completely elucidate the signal enhancement effect in LDTD, more studies are necessary to understand the effects of coatings on the ionization of analytes.