Detection of sildenafil and its 9 metabolites in a post-race horse urine sample: A case report

The use of prohibited substances in horse racing is a major concern that jeopardizes both the fairness of competitions and the health of horses. This problem can stem from the use of licensed drugs for animal health, as well as unlicensed substances. Horse doping laboratories monitor the potential use of these substances in racehorses within the framework of regulations set by the International Federation of Horse Racing Authority. In this context, sildenafil and its major metabolite n-desmethyl sildenafil were detected in a post-race horse urine sample sent to the Pendik Veterinary Control Institute Doping Control Laboratory through a screening analysis performed with Liquid Chromatography Triple Quadrupole Mass Spectrometry. These results were confirmed by Q Exactive Orbitrap Mass Spectrometry and follow-up analyses were performed. As a result of these analyses; simultaneous detection of 9 metabolites in horse urine was reported, two of them for the first time. In addition, the pioneer and comprehensive data resulting from this study provide preliminary data for future studies and anti-doping analyses.

Integrated approach for the analysis of neonicotinoids in fruits and food matrices

We searched for five neonicotenoids (namely acetamiprid, clothianidin, imidacloprid, thiacloprid and thiamethoxam) in 67 samples of fruits, leaves, pollen and honey via HPLC-MS by employing QueChERs for extraction and purification. Clothianidin was never detected, while imidacloprid was identified in apple (9.2 µg/kg) and pollen (18-28 µg/Kg), thiacloprid in peaches (21-35 µg/kg) and acetamiprid was identified in the hazel leaves (1266 µg/kg), honey (13-26 µg /Kg) and pollen (11-24 µg/kg). Since the levels found of acetamiprid in hazel, honey and pollen were concerning, we accomplished a study to identify and characterize the possible transformation products via a laboratory simulation. The methodology exploited the analysis by HPLC-HRMS and its application in all matrices. We identify twelve transformation products, whose formation involved dimerization, hydroxylation, oxidation, demethylation and cleavage of the molecule. Three of them were also detected in hazel leaves.

Degradation and mineralization of the emerging pharmaceutical pollutant sildenafil by ozone and UV radiation using response surface methodology

Pharmaceuticals and their degradation products which are present in wastewater and superficial waters are becoming an ecological issue. This research investigated the degradation and mineralization of synthetic solutions of the pharmaceutical compound sildenafil citrate (SC) by single ozonation and ozonation jointed with UV radiation (O₃/UV). The effects of initial drug concentration (50-125 mg L^-1), inlet ozone concentration (35-125 g Nm^-3), and UV radiation on SC degradation and decrease of total organic carbon (TOC) were investigated using response surface methodology based on a central composite experimental design. Through the RSM analysis, it was possible to confirm the removal of SC for the entire experimental range. Major intermediates of SC degradation were identified and a degradation pathway was proposed. The kinetics of SC degradation was modeled as a pseudo-first-order reaction with a rate constant ranging between 0.072 and 1.250 min^-1. The SC degradation and TOC removal were strongly enhanced by increasing the concentration of gaseous ozone at the inlet and incorporating UV radiation. The highest TOC removal reached at 60 min was 75%, in the O₃/UV system, with initial SC content of 50 mg L^-1 and inlet ozone concentration of 125 g Nm^-3. The degradation rate of SC was increased 3 to 9 times in the presence of UV radiation. Ozone-based advanced oxidation processes appear as a suitable alternative for treatment of the emerging pollutant SC.

Doping detection in animals: A review of analytical methodologies published from 1990 to 2019

Despite the impressive innate physical abilities of horses, camels, greyhounds, or pigeons, doping agents might be administered to these animals to improve their performance. To control these illegal practices, anti-doping analytical methodologies have been developed. This review compiles the analytical methods that have been published for the detection of prohibited substances administered to animals involved in sports over 30 years. Relevant papers meeting the search criteria that discussed analytical methods aiming to detect and/or quantify doping substances in animal biological matrices published from 1990 to 2019 were considered. A total of 317 studies were included, of which 298 were related to horses, demonstrating significant advances toward the development of doping detection methods for equine sports. However, analytical methods for the detection of doping agents in sports involving other species are lacking. Due to enhanced accuracy and specificity, chromatographic analysis coupled to mass spectrometry detection is preferred over immunoassays. Regarding biological matrices, blood and urine remain the first choice, although alternative biological matrices, such as hair and feces, have been considered. With the increasing number and type of drugs used as doping agents, the analytes addressed in the published papers are diverse. It is very important to continue to detect and quantify these drugs, recognizing those that are most frequently used, in order to punish the abusers, protect animals' health, and ensure a healthier and genuine competition.

Characterization of lacosamide metabolites by UHPLC–ESI–HRMS method

In this study, the in vitro phase I metabolism of lacosamide was characterized with the use of ultra-high-performance liquid chromatography combined with high-resolution mass spectrometry (quadrupole time-of-flight). The use of two metabolism simulation techniques (photocatalysis and human liver microsomes) allowed the characterization of a polar metabolite of parent compound, not yet described. The experiment with the participation of HLM gave the ability to describe the full liver metabolic pathway of lacosamide. It has been proven that this molecule undergoes deacetylation, demethylation, and during liver tissue metabolism. Photocatalysis with the use of a TiO2 catalyst was proved to be a complementary technique in mimicking in vitro drug metabolism.

Mimicking of Phase I Metabolism Reactions of Molindone by HLM and Photocatalytic Methods with the Use of UHPLC-MS/MS

Establishing the metabolism pathway of the drug undergoing the hepatic biotransformation pathway is one of the most important aspects in the preclinical discovery process since the presence of toxic or reactive metabolites may result in drug withdrawal from the market. In this study, we present the structural elucidation of six, not described yet, metabolites of an antipsychotic molecule: molindone. The elucidation of metabolites was supported with a novel photocatalytical approach with the use of WO3 and WS2 assisted photochemical reactions. An UHPLC-ESI-Q-TOF combined system was used for the registration of all obtained metabolite profiles as well as to record the high resolution fragmentation spectra of the observed transformation products. As a reference in the in vitro metabolism simulation method, the incubation with human liver microsomes was used. Chemometric comparison of the obtained profiles pointed out the use of the WO3 approach as being more convenient in the field of drug metabolism studies. Moreover, the photocatalysis was used in the direction of the main drug metabolite synthesis in order to further isolation and characterization.

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.

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.

Metabolism of aildenafil in vivo in rats and in vitro in mouse, rat, dog, and human liver microsomes

Aildenafil, 1-{[3-(6, 7-dihydro-1-methyl-7-oxo-3-propyl-1H-pyrazolo [4, 3-d] primidin-5-yl)-4-ethoxyphenyl] sulfonyl}-cis-3, 5-dimethylpiperazine, a phosphodiesterase type V enzyme inhibitor (PDE5I), is under development for treatment of erectile dysfunction (ED). The purpose of this study was to elucidate metabolism of aildenafil in vivo in rats and in vitro in mouse, rat, dog, and human liver microsomes. Thirty-one phase I metabolites have been found by LTQ/Orbitrap hybrid mass spectrometry in rat urine, faeces, and bile after oral administration. Major biotransformation pathways of aildenafil included N-dealkylation of the piperazine ring, hydroxylation and dehydrogenation, aliphatic hydroxylation and loss of alkyl group of piperazine ring. Minor pathways involved hydroxylation on the phenyl ring, pyrazole N-demethylation, O-deethylation, loss of piperazine ring (cleavage of N-S bond) and dehydrogenation on the piperazine ring. Similar metabolic pathways of aildenafil were observed in the incubations of liver microsomes from mouse, rat, and dog as well as from human. The depletion rate of parent drug in mouse and rat liver microsomes was significantly different from that in human liver microsomes. The cytochrome P450 reaction phenotyping analysis was conducted using isozyme-specific inhibitors. The results indicated that CYP3A was the main isoenzyme involved in oxidative metabolism of aildenafil. Overall, these in vitro and in vivo findings should provide valuable information on possible metabolic behaviours of aildenafil in humans.

ADMET considerations for phosphodiesterase-5 inhibitors

INTRODUCTION

ADMET (absorption, distribution, metabolism, excretion, and toxicity) profiling is an important aspect of all drug developments. The pharmaceutical industry must always consider ADMET properties in order to optimize drug candidates and to introduce new formulations against existing marketed drugs. Consequently, candidate drug development may be halted early in the discovery phase or during the more costly drug development process because of their poor ADMET properties.

AREAS COVERED

The main focus of this article is ADMET profiling, pharmacokinetic (PK) drug interactions, mechanisms and possible adverse drug reactions (ADRs) for approved phosphodiesterase-5 inhibitors (PDE5Is). The authors also look at the efficacy and non-erectogenic benefits of current PDE5Is, which are widely used by patients with erectile dysfunction (ED). The authors also discuss other unapproved PDE5Is such as aildenafil and udenafil, which are currently in use in clinical trials.

EXPERT OPINION

The authors believe that the enhancing effect of PDE5Is on the nitric oxide (NO)/cyclic guanosine monophosphate (cGMP) pathway means that PDE5Is could be used to treat various conditions. An important issue in their development is 'cross-talk' between PDE5 and other PDEs and thus their specificity for other PDEs. But while it might be difficult to achieve the ideal ADMET profile, it should not necessarily prevent further development of a lead PDE5I. The risk assessment of PDE5Is, with respect to their ADMET properties, is therefore very important for predicting drug-drug interactions, possible side effects, ADRs and its future clinical applications.