Search

Glucuronidation is a common phase II metabolic process for drugs and xenobiotics which increases their solubility for excretion. Acyl glucuronides (glucuronides of carboxylic acids) present concerns as they have been implicated in gastrointestinal toxicity and hepatic failure. Despite the substantial success in the bulk analysis of these species, previous attempts using traditional mass spectrometry imaging (MSI) techniques have completely or partially failed and therefore little is known about their localization in tissues. Herein, we use nanospray desorption electrospray ionization mass spectrometry imaging (nano-DESI MSI), an ambient liquid extraction-based ionization technique, as a viable alternative to other MSI techniques to examine the localization of diclofenac, a widely used nonsteroidal anti-inflammatory drug, and its metabolites in mouse kidney and liver tissues. MSI data acquired over a broad m/z range showed low signals of the drug and its metabolites resulting from the low ionization efficiency and substantial signal suppression on the tissue. Significant improvements in the signal-to-noise were obtained using selected ion monitoring (SIM) with m/z windows centered around the low-abundance ions of interest. Using nano-DESI MSI in SIM mode, we observed that diclofenac acyl glucuronide and hydroxydiclofenac are localized to the inner medulla and cortex of the kidney, respectively, which is consistent with the previously reported localization of enzymes that process diclofenac into its respective metabolites. In contrast, a uniform distribution of diclofenac and its metabolites was observed in the liver tissue. Concentration ratios of diclofenac and hydroxydiclofenac calculated from nano-DESI MSI data are generally in agreement to those obtained using liquid chromatography tandem mass spectrometry (LC-MS/MS) analysis. Collectively, our results demonstrate that nano-DESI MSI can be successfully used to image diclofenac and its primary metabolites and derive relative quantitative data from different tissue regions. Our approach will enable a better understanding of metabolic processes associated with diclofenac and other drugs that are difficult to analyze using commercially available MSI platforms., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Peptides have become a fast-growing segment of the pharmaceutical industry over the past few decades. It is essential to develop cutting edge analytical techniques to support the discovery and development of peptide therapeutics, especially to examine their absorption, distribution, metabolism and excretion (ADME) properties. Herein, we utilized two label-free mass spectrometry (MS) based techniques to investigate representative challenges in developing therapeutic peptides, such as tissue distribution, metabolic stability and clearance. A tool proof-of-concept cyclic peptide, melanotan II, was used in this study. Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI), which is a well-developed label-free imaging technique, was used to map the detailed molecular distribution of melanotan II and its metabolites. Droplet-based liquid microjunction surface sampling liquid chromatography-high resolution mass spectrometry (LMJ-SSP-LC-HRMS) was used in combination with MALDI-MSI to rapidly profile molecular information and provide structural insights on drug and metabolites. Using both techniques in parallel allowed a more comprehensive and complementary data set than using either technique independently. We envision MALDI-MSI and droplet-based LMJ-SSP-LC-HRMS, which can be used in combination or as standalone techniques, to become valuable tools for assessing the in vivo fate of peptide therapeutics in support of drug discovery and development., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)