Liquid extraction surface analysis mass spectrometry (LESA-MS) as a novel profiling tool for drug distribution and metabolism analysis: the terfenadine example

Liquid Extraction Surface Analysis Mass Spectrometry (LESA MS): Combining Liquid Extraction, Surface Profiling and Ambient Ionization Mass Spectrometry in One Novel Analysis Technique

In this chapter we give an overview of liquid extraction surface analysis mass spectrometry (LESA-MS), a novel analysis technique that combines liquid extraction from a surface of interest and ambient nanoelectrospray ionization combined with mass spectrometry to analyze compounds of interest. LESA MS was first described by van Berkel and Kertesz in 2009 and subsequently made commercially available by Advion Inc. by way of its TriVersa-NanoMate™ robotic nanoelectrospray ionization source. LESA was initially intended as a complementary analysis technique to MALDI imaging in pharmaceutical drug distribution and development; however, soon after the commercial availability of this technique, a broader use became apparent with applications ranging from biofilms on contact lenses, antibiotics expressed by bacteria cultured in agar, dried blood spot analysis, surface properties of aged plastics and aerosols from compactor material – to mention only a few. In this chapter, we will discuss selected applications and provide an outlook of LESA developments as they currently unfold, knowing full well that such a new technology will develop unexpectedly and in application areas not previously envisioned.

Challenges and recent advances in mass spectrometric imaging of neurotransmitters

Mass spectrometric imaging (MSI) is a powerful tool that grants the ability to investigate a broad mass range of molecules, from small molecules to large proteins, by creating detailed distribution maps of selected compounds. To date, MSI has demonstrated its versatility in the study of neurotransmitters and neuropeptides of different classes toward investigation of neurobiological functions and diseases. These studies have provided significant insight in neurobiology over the years and current technical advances are facilitating further improvements in this field. Herein, we briefly review new MSI studies of neurotransmitters, focusing specifically on the challenges and recent advances of MSI of neurotransmitters.

Liquid microjunction surface sampling of acetaminophen, terfenadine and their metabolites in thin tissue sections

Background: The aim of this work was to evaluate the analytical performance of a fully automated droplet-based surface-sampling system for determining the distribution of the drugs acetaminophen and terfenadine, and their metabolites, in rat thin tissue sections. Results: The rank order of acetaminophen concentration observed in tissues was stomach > small intestine > liver, while the concentrations of its glucuronide and sulfate metabolites were greatest in the liver and small intestine. Terfenadine was most concentrated in the liver and kidney, while its major metabolite, fexofenadine, was found in the liver and small intestine. Conclusion: The spatial distributions of both drugs and their respective metabolites observed in this work were consistent with previous studies using radiolabeled drugs.

Quantitative whole-body autoradiography, LC-MS/MS and MALDI for drug-distribution studies in biological samples: the ultimate matrix trilogy

The drug-development process requires an understanding of the ADME properties of the novel therapeutic agent. Determination of drug concentrations and identity in excreta (urine and feces) examines the products of these processes. Similar measurements made on plasma, while accurately determining exposure, show only what is being transported around the body. Both activities fail to confirm the nature of components at the pharmacologically relevant matrix - the tissue. Attention is therefore being directed towards methods that can be employed to address this lack in our current methodologies, to provide better quality data on which risk assessments can be made, so that pharmacological models can be refined, and drug safety improved. In this article, we will look at the current methods used to obtain tissue drug and drug metabolite concentrations, and their potential use in drug discovery.

Sampling reliability, spatial resolution, spatial precision, and extraction efficiency in droplet-based liquid microjunction surface sampling

RATIONALE

Droplet-based liquid extraction approaches for spatially resolved surface sampling coupled with high-performance liquid chromatography/mass spectrometry (HPLC/MS) provide the ability to deal with complex sample matrices and to identify isomeric compounds not distinguishable by MS methods alone. Improvements in sampling reliability, spatial resolution, spatial precision and extraction efficiency are required to further the analytical utility of such sampling systems.

METHODS

An autosampler capable of droplet-based liquid extraction was coupled with an HPLC/MS system. Visual inspection of the junction formation between the probe and a glass surface allowed evaluation of the liquid junction formation reliability, spatial location and size as a function of variable parameters such as solvent composition, probe-to-surface distance and droplet volume during solvent dispense and aspiration. Quantitative analysis of a component from a model surface using a weak extraction solvent was used to evaluate the effect of extraction time and number of extraction cycles on analyte extraction efficiency.

RESULTS

Reliable junction formation, independent of other variable parameters, was realized simply by maintaining a maximum distance of 0.4 mm between the probe and the sample surface. The smallest liquid junction diameter (1.6 mm) was observed when using a 1 μL dispensed volume and 90% aqueous extraction solvent with either methanol or acetonitrile. Good sampling precision was always achieved using an extraction solvent with at least 50% methanol or acetonitrile by volume. Quantitative sampling of rhodamine B from a magenta Sharpie ink surface using a weak extraction solvent showed that extraction efficiency could be improved by increasing the extraction time or the number of extraction cycles.

CONCLUSIONS

A platform employing a commercially available autosampler coupled to HPLC/MS was developed and successfully applied to investigate the effect of different sampling parameters on the reliability, spatial resolution, spatial precision and extraction efficiency of the liquid junction surface sampling process. This article is a U.S. Government work and is in the public domain in the USA.

Fully automated laser ablation liquid capture surface analysis using nanoelectrospray ionization mass spectrometry

RATIONALE

Laser ablation provides for the possibility of sampling a large variety of surfaces with high spatial resolution. This type of sampling when employed in conjunction with liquid capture followed by nanoelectrospray ionization provides the opportunity for sensitive and prolonged interrogation of samples by mass spectrometry as well as the ability to analyze surfaces not amenable to direct liquid extraction.

METHODS

A fully automated, reflection geometry, laser ablation liquid capture spot sampling system was achieved by incorporating appropriate laser fiber optics and a focusing lens into a commercially available, liquid extraction surface analysis (LESA(®))-ready Advion TriVersa NanoMate system.

RESULTS

Under optimized conditions about 10% of laser-ablated material could be captured in a droplet positioned vertically over the ablation region using the NanoMate robot-controlled pipette. The sampling spot size area with this laser ablation liquid capture surface analysis (LA/LCSA) mode of operation (typically about 120 µm × 160 µm) was approximately 50 times smaller than that achievable by direct liquid extraction using LESA(®) (ca 1 mm diameter liquid extraction spot). The setup was successfully applied for the analysis of ink on glass and paper as well as the endogenous components in Alstroemeria Yellow King flower petals. In a second mode of operation with a comparable sampling spot size, termed laser ablation/LESA(®), the laser system was used to drill through, penetrate, or otherwise expose material beneath a solvent resistant surface. Once drilled, LESA(®) was effective in sampling soluble material exposed at that location on the surface.

CONCLUSIONS

Incorporating the capability for different laser ablation liquid capture spot sampling modes of operation into a LESA(®)-ready Advion TriVersa NanoMate enhanced the spot sampling spatial resolution of this device and broadened the surface types amenable to analysis to include absorbent and solvent-resistant materials.

Using a single, high mass resolution mass spectrometry platform to investigate ion suppression effects observed during tissue imaging

RATIONALE

The signal intensity of a given molecule across a tissue section when measured using mass spectrometry imaging (MSI) is prone to changes caused by the molecular heterogeneity across the surface of the tissue. Here we propose a strategy to investigate these effects using electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI) on a single high-resolution mass spectrometry (HRMS) platform.

METHODS

A rat was administered with a single inhaled dose of a compound and sacrificed 1 h after dosing. Sections were prepared from the excised frozen lung and analysed using MALDI, liquid extraction surface analysis (LESA) nano-ESI-MS and nano-ESI liquid chromatography (LC)/MS. The ESI and MALDI ion sources were mounted either side of the ion transfer system of the same Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer.

RESULTS

MALDI MSI clearly demonstrated widespread distribution of the dosed molecule throughout the lung, with the exception of a non-lung section of tissue on the same sample surface. Comparison of the lipid signals across the sample indicated a change in signal between the lung and the adipose tissue present on the same section. Use of ESI and MALDI, with and without an internal standard, supported the evaluation of changes in the signal of the dosed molecule across the tissue section.

CONCLUSIONS

The results demonstrate the successful application of a dual ion source HRMS system to the systematic evaluation of data from MALDI MSI, used to determine the distribution of an inhaled drug in the lung. The system discussed is of great utility in investigating the effects of ion suppression and evaluating the quantitative and qualitative nature of the MSI data.

MALDI imaging mass spectrometry and analysis of endogenous peptides

In recent years, MALDI imaging mass spectrometry (MALDI-IMS) has developed as a promising tool to investigate the spatial distribution of biomolecules in intact tissue specimens. Ion densities of various molecules can be displayed as heat maps while preserving anatomical structures. In this short review, an overview of different biomolecules that can be analyzed by MALDI-IMS is given. Many reviews have covered imaging of lipids, small metabolites, whole proteins and enzymatically digested proteins in the past. However, little is known about imaging of endogenous peptides, for example, in the rat brain, and this will therefore be highlighted in this review. Furthermore, sample preparation of frozen or formalin-fixed, paraffin-embedded (FFPE) tissue is crucial for imaging experiments. Therefore, some aspects of sample preparation will be addressed, including washing and desalting, the choice of MALDI matrix and its deposition. Apart from mapping endogenous peptides, their reliable identification in situ still remains challenging and will be discussed as well.

An industry perspective on tiered approach to the investigation of metabolites in drug development

Background: A tiered approach to drug metabolite measurement and identification is often used industry wide to fulfill regulatory requirements specified in recent US FDA and European Medicines Agency guidance. Although this strategy is structured in its intent it can be customized to address unique challenges which may arise during early and late drug development activities. These unconventional methods can be applied at any stage to facilitate metabolite characterization. Results: Two case studies are described NVS 1 and 2. NVS 1: plasma concentrations, measured using a radiolabeled MS-response factor exploratory method, were comparable to those from a validated bioanalytical method. The NVS 2 example showed how in vitro analysis helped to characterize an unexpectedly abundant circulating plasma metabolite M3. Conclusion: A tiered approach incorporating many aspects of conventional and flexible analytical methodologies can be pulled together to address regulatory questions surrounding drug metabolite characterization.

Automated liquid microjunction surface sampling-HPLC-MS/MS analysis of drugs and metabolites in whole-body thin tissue sections

BACKGROUND

The aim of this work was to develop a fully automated liquid extraction-based surface sampling system utilizing a commercially available autosampler coupled with HPLC-MS/MS detection.

RESULTS

Discrete spots selected for droplet-based sampling and automated sample queue generation, for both the autosampler and MS, were enabled by using in-house developed software. In addition, co-registration of spatially resolved sampling positions and HPLC-MS information to generate heat maps of compounds monitored for subsequent data analysis was also available in the software. The system was evaluated with whole-body thin tissue sections from propranolol-dosed rats.

CONCLUSION

The spatial distributions of both the drug and its hydroxypropranolol glucuronide metabolites were consistent with previous studies employing other liquid extraction-based surface sampling methodologies.

Dithranol as a matrix for matrix assisted laser desorption/ionization imaging on a fourier transform ion cyclotron resonance mass spectrometer

Mass spectrometry imaging (MSI) determines the spatial localization and distribution patterns of compounds on the surface of a tissue section, mainly using MALDI (matrix assisted laser desorption/ionization)-based analytical techniques. New matrices for small-molecule MSI, which can improve the analysis of low-molecular weight (MW) compounds, are needed. These matrices should provide increased analyte signals while decreasing MALDI background signals. In addition, the use of ultrahigh-resolution instruments, such as Fourier transform ion cyclotron resonance (FTICR) mass spectrometers, has the ability to resolve analyte signals from matrix signals, and this can partially overcome many problems associated with the background originating from the MALDI matrix. The reduction in the intensities of the metastable matrix clusters by FTICR MS can also help to overcome some of the interferences associated with matrix peaks on other instruments. High-resolution instruments such as the FTICR mass spectrometers are advantageous as they can produce distribution patterns of many compounds simultaneously while still providing confidence in chemical identifications. Dithranol (DT; 1,8-dihydroxy-9,10-dihydroanthracen-9-one) has previously been reported as a MALDI matrix for tissue imaging. In this work, a protocol for the use of DT for MALDI imaging of endogenous lipids from the surfaces of mammalian tissue sections, by positive-ion MALDI-MS, on an ultrahigh-resolution hybrid quadrupole FTICR instrument has been provided.

Development of sheath-flow probe electrospray ionization mass spectrometry and its application to real time pesticide analysis

For the real time and direct analysis of chemical constituents from living beings and dry sample, sheath-flow probe electrospray ionization mass spectrometry (SF-PESI-MS) has been newly developed. The components from dry or semidry biological tissues can be extracted using the solvent and picked up by the needle for electrospray. This technique was applied to real-time pesticide analysis of living plants. The results have been validated with that of a well-known system, liquid extraction surface analysis mass spectrometry (LESA-MS). It is demonstrated that SF-PESI-MS can produce reasonable ionization efficiency, which is confirmed by LESA-MS.

Selected scientific topics of the 11th International Isotope Symposium on the Synthesis and Applications of Isotopes and Isotopically Labeled Compounds

This micro-review describes hot topics and new trends in isotope science discussed at the 11th International Isotope Symposium on the Synthesis and Applications of Isotopes and Isotopically Labeled Compounds from a personal perspective.

Continuous-flow liquid microjunction surface sampling probe connected on-line with high-performance liquid chromatography/mass spectrometry for spatially resolved analysis of small molecules and proteins

RATIONALE

A continuous-flow liquid microjunction surface sampling probe extracts soluble material from surfaces for direct ionization and detection by mass spectrometry. Demonstrated here is the on-line coupling of such a probe with high-performance liquid chromatography/mass spectrometry (HPLC/MS) enabling extraction, separation and detection of small molecules and proteins from surfaces in a spatially resolved (~0.5 mm diameter spots) manner.

METHODS

A continuous-flow liquid microjunction surface sampling probe was connected to a six-port, two-position valve for extract collection and injection to an HPLC column. A QTRAP® 5500 hybrid triple quadrupole linear ion trap equipped with a Turbo V™ ion source operated in positive electrospray ionization (ESI) mode was used for all experiments. The system operation was tested with the extraction, separation and detection of propranolol and associated metabolites from drug dosed tissues, caffeine from a coffee bean, cocaine from paper currency, and proteins from dried sheep blood spots on paper.

RESULTS

Confirmed in the tissue were the parent drug and two different hydroxypropranolol glucuronides. The mass spectrometric response for these compounds from different locations in the liver showed an increase with increasing extraction time (5, 20 and 40 s). For on-line separation and detection/identification of extracted proteins from dried sheep blood spots, two major protein peaks dominated the chromatogram and could be correlated with the expected masses for the hemoglobin α and β chains.

CONCLUSIONS

Spatially resolved sampling, separation, and detection of small molecules and proteins from surfaces can be accomplished using a continuous-flow liquid microjunction surface sampling probe coupled on-line with HPLC/MS detection.

Comprehensive identification of proteins from MALDI imaging

Matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI IMS) is a powerful tool for the visualization of proteins in tissues and has demonstrated considerable diagnostic and prognostic value. One main challenge is that the molecular identity of such potential biomarkers mostly remains unknown. We introduce a generic method that removes this issue by systematically identifying the proteins embedded in the MALDI matrix using a combination of bottom-up and top-down proteomics. The analyses of ten human tissues lead to the identification of 1400 abundant and soluble proteins constituting the set of proteins detectable by MALDI IMS including >90% of all IMS biomarkers reported in the literature. Top-down analysis of the matrix proteome identified 124 mostly N- and C-terminally fragmented proteins indicating considerable protein processing activity in tissues. All protein identification data from this study as well as the IMS literature has been deposited into MaTisse, a new publically available database, which we anticipate will become a valuable resource for the IMS community.

Mass spectrometry imaging under ambient conditions

Mass spectrometry imaging (MSI) has emerged as an important tool in the last decade and it is beginning to show potential to provide new information in many fields owing to its unique ability to acquire molecularly specific images and to provide multiplexed information, without the need for labeling or staining. In MSI, the chemical identity of molecules present on a surface is investigated as a function of spatial distribution. In addition to now standard methods involving MSI in vacuum, recently developed ambient ionization techniques allow MSI to be performed under atmospheric pressure on untreated samples outside the mass spectrometer. Here we review recent developments and applications of MSI emphasizing the ambient ionization techniques of desorption electrospray ionization (DESI), laser ablation electrospray ionization (LAESI), probe electrospray ionization (PESI), desorption atmospheric pressure photoionization (DAPPI), femtosecond laser desorption ionization (fs-LDI), laser electrospray mass spectrometry (LEMS), infrared laser ablation metastable-induced chemical ionization (IR-LAMICI), liquid microjunction surface sampling probe mass spectrometry (LMJ-SSP MS), nanospray desorption electrospray ionization (nano-DESI), and plasma sources such as the low temperature plasma (LTP) probe and laser ablation coupled to flowing atmospheric-pressure afterglow (LA-FAPA). Included are discussions of some of the features of ambient MSI for example the ability to implement chemical reactions with the goal of providing high abundance ions characteristic of specific compounds of interest and the use of tandem mass spectrometry to either map the distribution of targeted molecules with high specificity or to provide additional MS information on the structural identification of compounds. We also describe the role of bioinformatics in acquiring and interpreting the chemical and spatial information obtained through MSI, especially in biological applications for tissue diagnostic purposes. Finally, we discuss the challenges in ambient MSI and include perspectives on the future of the field.

Imaging nicotine in rat brain tissue by use of nanospray desorption electrospray ionization mass spectrometry

Imaging mass spectrometry offers simultaneous spatially resolved detection of drugs, drug metabolites, and endogenous substances in a single experiment. This is important when evaluating effects of a drug on a complex organ system such as the brain, where there is a need to understand how regional drug distribution impacts function. Nanospray desorption electrospray ionization, nano-DESI, is a new ambient technique that enables spatially resolved analysis of a variety of samples without special sample pretreatment. This study introduces an experimental approach for accurate spatial mapping of drugs and metabolites in tissue sections by nano-DESI imaging. In this approach, an isotopically labeled standard is added to the nano-DESI solvent to compensate for matrix effects and ion suppression. The analyte image is obtained by normalizing the analyte signal to the signal of the standard in each pixel. We demonstrate that the presence of internal standard enables online quantification of analyte molecules extracted from tissue sections. Ion images are subsequently mapped to the anatomical brain regions in the analyzed section by use of an atlas mesh deformed to match the optical image of the section. Atlas-based registration accounts for the physical variability between animals, which is important for data interpretation. The new approach was used for mapping the distribution of nicotine in rat brain tissue sections following in vivo drug administration. We demonstrate the utility of nano-DESI imaging for sensitive detection of the drug in tissue sections with subfemtomole sensitivity in each pixel of a 27 μm × 150 μm area. Such sensitivity is necessary for spatially resolved detection of low-abundance molecules in complex matrices.

Analysis of chloroquine and metabolites directly from whole-body animal tissue sections by liquid extraction surface analysis (LESA) and tandem mass spectrometry

The rapid and direct analysis of the amount and spatial distribution of exogenous chloroquine (CHQ) and CHQ metabolites from tissue sections by liquid extraction surface sampling analysis coupled with tandem mass spectrometry (LESA-MS/MS) was demonstrated. LESA-MS/MS results compared well with previously published CHQ quantification data collected by organ excision, extraction and fluorescent detection. The ability to directly sample and analyze spatially resolved exogenous molecules from tissue sections with minimal sample preparation and analytical method development has the potential to facilitate the assessment of target tissue penetration of pharmaceutical compounds, to establish pharmacokinetic/pharmacodynamic relationships, and to complement established pharmacokinetic methods used in the drug discovery process during tissue distribution assessment.