Quantitative lung morphology: semi-automated measurement of mean linear intercept.

BACKGROUND: Quantifying morphologic changes is critical to our understanding of the pathophysiology of the lung. Mean linear intercept (MLI) measures are important in the assessment of clinically relevant pathology, such as emphysema. However, qualitative measures are prone to error and bias, while quantitative methods such as mean linear intercept (MLI) are manually time consuming. Furthermore, a fully automated, reliable method of assessment is nontrivial and resource-intensive. METHODS: We propose a semi-automated method to quantify MLI that does not require specialized computer knowledge and uses a free, open-source image-processor (Fiji). We tested the method with a computer-generated, idealized dataset, derived an MLI usage guide, and successfully applied this method to a murine model of particulate matter (PM) exposure. Fields of randomly placed, uniform-radius circles were analyzed. Optimal numbers of chords to assess based on MLI were found via receiver-operator-characteristic (ROC)-area under the curve (AUC) analysis. Intraclass correlation coefficient (ICC) measured reliability. RESULTS: We demonstrate high accuracy (AUCROC > 0.8 for MLIactual > 63.83 pixels) and excellent reliability (ICC = 0.9998, p < 0.0001). We provide a guide to optimize the number of chords to sample based on MLI. Processing time was 0.03 s/image. We showed elevated MLI in PM-exposed mice compared to PBS-exposed controls. We have also provided the macros that were used and have made an ImageJ plugin available free for academic research use at https://med.nyu.edu/nolanlab. CONCLUSIONS: Our semi-automated method is reliable, equally fast as fully automated methods, and uses free, open-source software. Additionally, we quantified the optimal number of chords that should be measured per lung field.

Investigation of the biotransformation of melarsoprol by electrochemistry coupled to complementary LC/ESI-MS and LC/ICP-MS analysis.

Melarsoprol is the only currently available drug for treatment of the late stage of African trypanosomiasis (sleeping sickness). Unfortunately, the arsenic-containing drug causes serious side effects, for which the mechanisms have not been elucidated so far. This investigation describes the study of the melarsoprol biotransformation processes by electrochemical (EC) techniques. Based on EC, potential oxidation reactions of melarsoprol are examined. Moreover, the reactivity of melarsoprol, its metabolite melarsen oxide, and their oxidation products toward the tripeptide glutathione and the proteins hemoglobin and human serum albumin is evaluated. The combination of different analytical techniques allows the identification as well as the quantification of the biotransformation products. The hyphenation of liquid chromatography (LC) and electrospray ionization mass spectrometry (ESI-MS) is applied for identification and structure elucidation, which implies the determination of exact masses and fragmentation patterns. For the selective detection of arsenic containing metabolites, LC coupled to inductively coupled plasma mass spectrometry is utilized. Based on the obtained data, the oxidative biotransformation of melarsoprol can be predicted, revealing novel species which have been suspected, but not been identified up to now. The results of the protein studies prove that melarsen oxide, the active derivative of melarsoprol, strongly binds to human hemoglobin and forms different adducts via the free cysteinyl groups of the hemoglobin α- and ß-chain.

Combination of electrochemistry and nuclear magnetic resonance spectroscopy for metabolism studies.

During the development of new materials demonstrating biological activity, prediction and identification of reactive intermediates generated in the course of drug metabolism in the human liver is of great importance. We present a rapid and purely instrumental method for the structure elucidation of possible phase I metabolites. With electrochemical (EC) conversion adopting the oxidative function of liver-inherent enzymes and nuclear magnetic resonance (NMR) spectroscopy enabling structure elucidation, comprehensive knowledge on potential metabolites can be gained. Paracetamol (APAP) has been known to induce hepatotoxicity when exceeding therapeutic doses and was therefore selected as the test compound. The reactive metabolite N-acetyl-p-benzoquinone imine has long been proven to be responsible for the toxic side effects of APAP and can easily be generated by EC. EC coupled online to NMR is a straightforward technique for structure elucidation of reactive drug intermediates at an early stage in drug discovery.

Electrochemical oxidation and protein adduct formation of aniline: a liquid chromatography/mass spectrometry study.

Historically, skin sensitization tests are typically based on in vivo animal tests. However, for substances used in cosmetic products, these tests have to be replaced according to the European Commission regulation no. 1223/2009. Modification of skin proteins by electrophilic chemicals is a key process associated with the induction of skin sensitization. The present study investigates the capabilities of a purely instrumental setup to determine the potential of commonly used non-electrophilic chemicals to cause skin sensitization by the generation of electrophilic species from the parent compound. In this work, the electrophiles were generated by the electrochemical oxidation of aniline, a basic industrial chemical which may also be released from azo dyes in cosmetics. The compound is a known sensitizer and was oxidized in an electrochemical thin-layer cell which was coupled online to electrospray ionization-mass spectrometry. The electrochemical oxidation was performed on a boron-doped diamond working electrode, which is able to generate hydroxyl radicals in aqueous solutions at high potentials. Without any pretreatment, the oxidation products were identified by electrospray ionization/time-of-flight mass spectrometry (ESI-ToF-MS) using their exact masses. A mass voltammogram was generated by plotting the obtained mass spectra against the applied potential. Oligomerization states with up to six monomeric units in different redox states of aniline were observed using this setup. This approach was extended to generate adducts between the oxidation products of aniline and the tripeptide glutathione. Two adducts were identified with this trapping experiment. Protein modification was carried out subsequently: Aniline was oxidized at a constant potential and was allowed to react with ß-lactoglobulin A (ß-LGA) or human serum albumin (HSA), respectively. The generated adducts were analyzed by liquid chromatography coupled to ESI-ToF-MS. For both ß-LGA and HSA, aniline adducts were successfully generated and identified.

Simulation of the oxidative metabolism of diclofenac by electrochemistry/(liquid chromatography/)mass spectrometry.

Diclofenac is a frequently prescribed drug for rheumatic diseases and muscle pain. In rare cases, it may be associated with a severe hepatotoxicity. In literature, it is discussed whether this toxicity is related to the oxidative phase I metabolism, resulting in electrophilic quinone imines, which can subsequently react with nucleophiles present in the liver in form of glutathione or proteins. In this work, electrochemistry coupled to mass spectrometry is used as a tool for the simulation of the oxidative pathway of diclofenac. Using this purely instrumental approach, diclofenac was oxidized in a thin layer cell equipped with a boron doped diamond working electrode. Sum formulae of generated oxidation products were calculated based on accurate mass measurements with deviations below 2 ppm. Quinone imines from diclofenac were detected using this approach. It could be shown for the first time that these quinone imines do not react with glutathione exclusively but also with larger molecules such as the model protein ß-lactoglobulin A. A tryptic digest of the generated drug-protein adduct confirms that the protein is modified at the only free thiol-containing peptide. This simple and purely instrumental set-up offers the possibility of generating reactive metabolites of diclofenac and to assess their reactivity rapidly and easily.

Electrochemistry/liquid chromatography/mass spectrometry as a tool in metabolism studies.

Electrochemistry/liquid chromatography/mass spectrometry is a powerful complementary tool for the simulation of the oxidative metabolism of drugs and other xenobiotics.

In chemico evaluation of skin metabolism: Investigation of eugenol and isoeugenol by electrochemistry coupled to liquid chromatography and mass spectrometry.

Skin sensitization is initiated by the modification of proteins located in the skin. After oxidative activation, eugenol and isoeugenol have the potential to modify skin proteins and therefore cause sensitization processes. Despite their known skin sensitizing properties, they are of common use in cosmetic products. According to the European Commission regulation No. 1223/2009, animal tests have to be banned for substances intended for cosmetic use. Therefore, alternative methods of investigation need to be developed for the approval of future substances. For this reason, eugenol and isoeugenol were selected as model substances to be investigated in a purely instrumental approach comprising electrochemistry, liquid chromatography and mass spectrometry. In the present work, reactive oxidation products of eugenol and isoeugenol were electrochemically generated. Reactive quinones and quinone methides were formed. Surprisingly, eugenol and isoeugenol differ significantly in their oxidation behaviour. Isoeugenol exhibits the formation of quinones and quinone methides of an alkylated and dealkylated species, respectively, whereas eugenol shows the formation of quinoid species only after dealkylation. Reactive quinoid species could be trapped with glutathione and the protein ß-lactoglobulin A. The results are comparable to the ones with conventional animal studies in literature, which attribute the adverse effects of eugenol and isoeugenol to the formation of reactive quinones or quinone methides, which are reactive intermediates, able to react with proteins. Such species were successfully generated and investigated by the use of electrochemistry coupled to mass spectrometry. Above all, the investigation of adduct formation by the additional use of liquid chromatography allowed the assessment of the mechanism of oxidation, as it might happen in the skin. Both substances were proven to be trapped by the protein ß-lactoglobulin A after electrochemical oxidation. However, isoeugenol formed the larger variety of adducts compared to eugenol.

Identification and quantification of potential metabolites of Gd-based contrast agents by electrochemistry/separations/mass spectrometry.

Oxidative and potentially metabolic pathways of the five most frequently used contrast agents for magnetic resonance imaging (MRI) based on gadolinium (Gd) are examined. The oxidation of gadopentetate (Gd-DTPA) was studied with a focus on electrochemical oxidation coupled to analytical separation methods and mass spectrometric detection. Mass voltammograms generated with online electrochemistry/electrospray ionization mass spectrometry (EC/ESI-MS) gave a first overview of oxidation products. Two potential metabolites could be detected, with the major metabolite originating from an N-dealkylation (M1). Four other Gd complexes used as MRI contrast agents showed similar reactions in the EC/ESI-MS set-up. To obtain more information about the properties and the quantity of the generated products, a wide range of separation and detection techniques was applied in further experiments. Gd-DTPA and its N-dealkylation product were successfully separated by capillary electrophoresis (CE) and detected by ESI-MS and inductively coupled plasma (ICP)-MS, respectively. CE experiments indicated that the second oxidation product (M2) detected in the mass voltammogram is unstable and decomposes to M1. Employing EC/CE/ICP-MS, the quantification of the metabolites could be achieved. Under the employed conditions, 8.8% of Gd-DTPA was oxidized. Online experiments with high performance liquid chromatography (HPLC) coupled to ESI-MS confirmed the decomposition of M2. Time-resolved measurements showed a decrease of M2 and a simultaneous increase in M1 within only a few minutes, confirming the conclusion that M2 degrades to M1, while EC/LC/ICP-MS measurements provided quantitative evidence as well. The EC/MS simulation shows that a metabolic transformation should not be disregarded in further research regarding the trigger of nephrogenic systemic fibrosis (NSF), a disease exclusively observed for several hundred dialysis patients after delivery of Gd-based MRI contrast agents with linear structure. Furthermore, the used methods may allow the prediction of options for the oxidative removal of these contrast agents from wastewaters.