Comparison of TiO2 photocatalysis, electrochemically assisted Fenton reaction and direct electrochemistry for simulation of phase I metabolism reactions of drugs

Online coupling of a catalytic continuous microflow reactor to mass spectrometry

Flow cell reactors used for catalyst development and applications are upcoming due to their small environmental and economic footprint. Online microflow reactor coupling with mass spectrometry (MS) opens new possibilities for monitoring catalyst performance and identifying reaction products in real time. This is demonstrated for the metabolic relevant dealkylation of lidocaine on catalytic gold micro-particles using regular liquid chromatography modules. Yields of up to 90% norlidocaine were realized under mild continuous flow conditions for up to 10 h (pH 7, 30 °C and 20 μL/min). Dissolved oxygen was shown to be a rate-limiting factor, since an inline oxygen generator allowed to increase the reactor capacity by one order of magnitude. Monitoring product time-response curve slopes after starting and ending a substrate feed, provided insights into the adsorption/desorption and conversion kinetics at the catalyst surface indicating the presence of strong adsorption sites that do not contribute substantially to substrate conversion.

Present applications of titanium dioxide for the photocatalytic removal of pollutants from water: A review

The evolution of modern technology and industrial processes has been accompanied by an increase in the utilization of chemicals to derive new products. Water bodies are frequently contaminated by the presence of conventional pollutants such as dyes and heavy metals, as well as microorganisms that are responsible for various diseases. A sharp rise has also been observed in the presence of new compounds heretofore excluded from the design and evaluation of wastewater treatment processes, categorized as "emerging pollutants". While some are harmless, certain emerging pollutants possess the ability to cause debilitating effects on a wide spectrum of living organisms. Photocatalytic degradation has emerged as an increasingly popular solution to the problem of water pollution due to its effectiveness and versatility. The primary objective of this study is to thoroughly scrutinize recent applications of titanium dioxide and its modified forms as photocatalytic materials in the removal and control of several classes of water pollutants as reported in literature. Different structural modifications are used to enhance the performance of the photocatalyst such as doping and formation of composites. The principles of these modifications have been scrutinized and evaluated in this review in order to present their advantages and drawbacks. The mechanisms involved in the removal of different pollutants through photocatalysis performed by TiO2 have been highlighted. The factors affecting the mechanism of photocatalysis and those affecting the performance of different TiO2-based photocatalysts have also been thoroughly discussed, thereby presenting a comprehensive view of all aspects involved in the application of TiO₂ to remediate and control water pollution.

Photocatalysis as a Tool for in Vitro Drug Metabolism Simulation: Multivariate Comparison of Twelve Metal Oxides on a Set of Twenty Model Drugs

The constant development in the area of medicinal substances on the market and their subsequent progress in the field of drug analysis has become one of the reasons for the search for alternative, cheaper, and faster methods to determine the metabolism pathways of new molecular entities (NMEs). The simulation of transformation processes using photocatalysis is considered to be one of the promising methods. Although its effectiveness has been proven, the research has so far focused especially on titanium dioxide, while a more accurate comparison of the suitability of different photocatalysts in terms of their use in drug metabolism studies has not been performed. For this purpose, a set of twelve metal oxides was prepared and their photocatalytic efficiency in the direction of drug metabolism mimicking was checked on a model mixture of twenty medicinal substances differing both in chemical structure and pharmacological properties. Incubation with human liver microsomes (HLMs) was used as the reference method. The metabolic profiles obtained with the use of LC-MS analysis were compared using multidimensional chemometric techniques; and the graphic presentation of the results in the form of PCA plot and cluster dendrogram enabled their detailed interpretation and discussion. All tested photocatalysts confirmed their effectiveness. However, the exact outcome of the study indicate advantage of the WO3-assisted photocatalysis over other metal oxides.

Simulation of phase I metabolism reactions of selected calcium channel blockers by human liver microsomes and photochemical methods with the use of Q-TOF LC/MS

The in vitro phase I metabolism of perhexiline and flunarizine, two calcium channel blockers was investigated during this study with the use of human liver microsomes (HLM) method compared with TiO₂, WO₃ and ZnO catalyzed photochemical reaction. In order to determine the structures of metabolites an quadrupole time-of-flight mass spectrometry combined with liquid chromatography (Q-TOF LC/MS) system was used. The obtained high resolution mass spectra enabled to identify thirteen products of metabolism of selected drugs including three not yet described metabolites of perhexiline and two new metabolites of flunarizine. The vast majority of metabolites were confirmed also with the participation of photocatalytic approach of the drug metabolism simulation. The comparison of all metabolic profiles made with the use of computational methods drew attention particularly to TiO₂ and WO₃ catalyzed photochemical reaction as similar to HLM incubation. Additionally, in silico toxicity assessment of the detected transformation products of the analyzed substances was also evaluated.

TiO2 Photocatalyzed Oxidation of Drugs Studied by Laser Ablation Electrospray Ionization Mass Spectrometry

In drug discovery, it is important to identify phase I metabolic modifications as early as possible to screen for inactivation of drugs and/or activation of prodrugs. As the major class of reactions in phase I metabolism is oxidation reactions, oxidation of drugs with TiO2 photocatalysis can be used as a simple non-biological method to initially eliminate (pro)drug candidates with an undesired phase I oxidation metabolism. Analysis of reaction products is commonly achieved with mass spectrometry coupled to chromatography. However, sample throughput can be substantially increased by eliminating pretreatment steps and exploiting the potential of ambient ionization mass spectrometry (MS). Furthermore, online monitoring of reactions in a time-resolved way would identify sequential modification steps. Here, we introduce a novel (time-resolved) TiO2-photocatalysis laser ablation electrospray ionization (LAESI) MS method for the analysis of drug candidates. This method was proven to be compatible with both TiO2-coated glass slides as well as solutions containing suspended TiO2 nanoparticles, and the results were in excellent agreement with studies on biological oxidation of verapamil, buspirone, testosterone, andarine, and ostarine. Finally, a time-resolved LAESI MS setup was developed and initial results for verapamil showed excellent analytical stability for online photocatalyzed oxidation reactions within the set-up up to at least 1 h. Graphical Abstract.

Transformation Products of Organic Contaminants and Residues-Overview of Current Simulation Methods

The formation of transformation products (TPs) from contaminants and residues is becoming an increasing focus of scientific community. All organic compounds can form different TPs, thus demonstrating the complexity and interdisciplinarity of this topic. The properties of TPs could stand in relation to the unchanged substance or be more harmful and persistent. To get important information about the generated TPs, methods are needed to simulate natural and manmade transformation processes. Current tools are based on metabolism studies, photochemical methods, electrochemical methods, and Fenton’s reagent. Finally, most transformation processes are based on redox reactions. This review aims to compare these methods for structurally different compounds. The groups of pesticides, pharmaceuticals, brominated flame retardants, and mycotoxins were selected as important residues/contaminants relating to their worldwide occurrence and impact to health, food, and environmental safety issues. Thus, there is an increasing need for investigation of transformation processes and identification of TPs by fast and reliable methods.

Digital microfluidic immobilized cytochrome P450 reactors with integrated inkjet-printed microheaters for droplet-based drug metabolism research

We report the development and characterization of digital microfluidic (DMF) immobilized enzyme reactors (IMERs) for studying cytochrome P450 (CYP)-mediated drug metabolism on droplet scale. The on-chip IMERs consist of porous polymer (thiol-ene) monolith plugs prepared in situ by photopolymerization and functionalized with recombinant CYP1A1 isoforms (an important detoxification route for many drugs and other xenobiotics). The DMF devices also incorporate inexpensive, inkjet-printed microheaters for on-demand regio-specific heating of the IMERs to physiological temperature, which is crucial for maintaining the activity of the temperature-sensitive CYP reaction. For on-chip monitoring of the CYP activity, the DMF devices were combined with a commercial well-plate reader, and a custom fluorescence quantification method was developed for detection of the chosen CYP1A1 model activity (ethoxyresorufin-O-deethylation). The reproducibility of the developed assay was examined with the help of ten parallel CYP-IMERs. All CYP-IMERs provided statistically significant difference (in fluorescence response) compared to any of the negative controls (including room-temperature reactions). The average (n = 10) turnover rate was 20.3 ± 9.0 fmol resorufin per minute. Via parallelization, the concept of the droplet-based CYP-IMER developed in this study provides a viable approach to rapid and low-cost prediction of the metabolic clearance of new chemical entities in vitro.

Investigation of the photolysis and TiO2, SrTiO3, H2O2-mediated photocatalysis of an antipsychotic drug loxapine - Evaluation of kinetics, identification of photoproducts, and in silico estimation of properties

The photolytic and photocatalytic transformation of loxapine with the use of H₂O₂, TiO₂ and SrTiO₃ under the simulated solar radiation was studied. A micro-scale method for simultaneous irradiation of multiple samples in photostability chamber was applied. RP-UHPLC-DAD coupled with ESI-Q-TOF mass spectrometer was used for the quantitative and qualitative analysis of the processes. Influence of catalysts concentration on kinetic parameters of loxapine photodecomposition was evaluated, and TiO₂ at medium concentration (100 mg L^-1) turned out to be the most effective. Sixteen transformation products were detected and their structures were elucidated. On the basis of the elucidated structures, computational evaluation of toxicity, bioconcentration and bioaccumulation factors as well as biodegradability of transformation products were conducted. The multivariate chemometric method (principal component analysis) was used to compare the calculated properties as well as the applied methods. Most of the transformation products were generally less toxic and more biodegradable than the parent compound.

Imitation of phase I metabolism reactions of MAO-A inhibitors by titanium dioxide photocatalysis

The imitation of phase I metabolism of moclobemide and toloxatone, two monoamine oxidase type A (MAO-A) inhibitors, was performed with the use of titanium dioxide photocatalytic process. Ultra high pressure liquid chromatography system coupled with an accurate hybrid ESI-Q-TOF mass spectrometer was used for the evaluation of metabolic profiles, structural elucidation of the identified transformation products and quantitative analysis of the process. Based on high resolution MS and MS/MS data, eleven transformation products were characterized in photocatalytic experiments for moclobemide and seven products for toloxatone. A significant number of these products were found as hepatic metabolites under the incubation of the selected MAO-A inhibitors with human liver microsomes (HLM). What is important, some of these HLM metabolites are not yet described in the literature. It was also found that the multivariate chemometric analysis allowed an effortless characterization of the registered metabolic profiles which can be a useful method for a fast preliminary drug metabolism study. Additionally, principal component analysis (PCA) of the registered TOF (MS) photocatalytic and HLM profiles of moclobemide and toloxatone shows that shorter irradiation time is preferred for photocatalytic metabolism experiments. A heterogeneous photocatalysis with the use of titanium dioxide was found to be a powerful tool for mimicking phase I metabolic reactions, as a fast, sensitive and inexpensive method.

TiO2 Photocatalysis-DESI-MS Rotating Array Platform for High-Throughput Investigation of Oxidation Reactions

We present a new high-throughput platform for studying titanium dioxide (TiO₂) photocatalytic oxidation reactions by performing reactions on a TiO₂-coated surface, followed by direct analysis of oxidation products from the surface by desorption electrospray ionization mass spectrometry (DESI-MS). For this purpose, we coated a round glass wafer with photocatalytically active anatase-phase TiO₂ using atomic layer deposition. Approximately 70 aqueous 1 μL samples can be injected onto the rim of the TiO₂-coated glass wafer, before the entire wafer is exposed to UV irradiation. After evaporation of water, the oxidation products can be directly analyzed from the sample spots by DESI-MS, using a commercial rotating sample platform. The method was shown to provide fast photocatalytic oxidation reactions and analysis with throughput of about four samples per minute. The feasibility of the method was examined for mimicking phase I metabolism reactions of amodiaquine, buspirone and verapamil. Their main photocatalytic reaction products were mostly similar to the products observed earlier in TiO₂ photocatalysis and in in vitro phase I metabolism assays performed using human liver microsomes.

Instrumentation and applications of electrochemistry coupled to mass spectrometry for studying xenobiotic metabolism: A review

The knowledge of metabolic pathways and biotransformation of xenobiotics, artificial substances foreign to the entire biological system, is crucial for elucidation of degradation routes of potentially toxic substances. Nowadays, there are many methods to simulate xenobiotic metabolism in the human body in vitro. In this review, the metabolism of various substances in the human body is described, followed by a summary of methods used for prediction of metabolic pathways and biotransformation. Above all, focus is placed on the coupling of electrochemistry to mass spectrometry, which is still a relatively new technique. This promising tool can mimic both oxidative phase I and conjugative phase II metabolism. Different experimental arrangements, with or without a separation step, and various applications of this technique are illustrated and critically reviewed.

Photolytic and photocatalytic degradation of tandospirone: Determination of kinetics, identification of transformation products and in silico estimation of toxicity

The photolytic and photocatalytic transformation of tandospirone with the use of TiO₂ and H₂O₂ was investigated. A micro-scale method for simultaneous irradiation with simulated full solar spectrum of multiple samples in photostability chamber was proposed. RP-UHPLC-DAD coupled with ESI-Q-TOF mass spectrometer was used for the quantitative and qualitative analysis of the processes. The developed method was fully validated and the kinetic parameters of tandospirone photodegradation were compared. The structures of eighteen photoproducts as well as phototransformation pathways were proposed. Based on the elucidated structures, computational toxicity assessment with the use of various software was performed and most of the photoproducts were found as less or similarly toxic to the parent compound. Nevertheless, several products, including one of the drug main metabolites, were significantly more toxic than the parent drug. The multivariate chemometric method (principal component analysis) was used to compare the toxicity of phototransformation products as well as the toxicity of the assessment methods.

Fenton process on single and mixture components of phenothiazine pharmaceuticals: Assessment of intermediaries, fate, and preliminary ecotoxicity

Pharmaceuticals do not occur isolated in the environment but in multi-component mixtures and may exhibit antagonist, synergistic or additive behavior. Knowledge on this is still scarce. The situation is even more complicated if effluents or potable water is treated by oxidative processes or such transformations occur in the environment. Thus, determining the fate and effects of parent compounds, metabolites and transformation products (TPs) formed by transformation and degradation processes in the environment is needed. This study investigated the fate and preliminary ecotoxicity of the phenothiazine pharmaceuticals, Promazine (PRO), Promethazine (PRM), Chlorpromazine (CPR), and Thioridazine (THI) as single and as components of the resulting mixtures obtained from their treatment by Fenton process. The Fenton process was carried out at pH7 and by using 0.5-2mgL^-1 of [Fe²⁺]₀ and 1-12.5mgL^-1 of [H₂O₂]₀ at the fixed ratio [Fe²⁺]₀:[H₂O₂]₀ of 1:10 (w:w). No complete mineralization was achieved. Constitutional isomers and some metabolite-like TPs formed were suggested based on their UHPLC-HRMSⁿ data. A degradation pathway was proposed considering interconnected mechanisms such as sulfoxidation, hydroxylation, N-dealkylation, and dechlorination steps. Aerobic biodegradation tests (OECD 301 D and OECD 301 F) were applied to the parent compounds separately, to the mixture of parent compounds, and for the cocktail of TPs present after the treatment by Fenton process. The samples were not readily biodegradable. However, LC-MS analysis revealed that abiotic transformations, such hydrolysis, and autocatalytic transformations occurred. The initial ecotoxicity tested towards Vibrio fischeri as individual compounds featured a reduction in toxicity of PRM and CPR by the treatment process, whereas PRO showed an increase in acute luminescence inhibition and THI a stable luminescence inhibition. Concerning effects of the mixture components, reduction in toxicity by the Fenton process was predicted by concentration addition and independent action models.

Oxidation of Tyrosine-Phosphopeptides by Titanium Dioxide Photocatalysis

Protein phosphorylation has a key role in cell regulation. Oxidation of proteins, in turn, is related to many diseases and to aging, but the effects of phosphorylation on the oxidation of proteins and peptides have been rarely studied. The aim of this study was to examine the mechanistic effect of phosphorylation on peptide oxidation induced by titanium dioxide photocatalysis. The effect of phosphorylation was compared between nonphosphorylated and tyrosine phosphorylated peptides using electrospray tandem mass spectrometry. We observed that tyrosine was the most preferentially oxidized amino acid, but the oxidation reaction was significantly inhibited by its phosphorylation. The study also shows that titanium dioxide photocatalysis provides a fast and easy method to study oxidation reactions of biomolecules, such as peptides.