In Vitro and In Vivo Human Metabolism of Ostarine, a Selective Androgen Receptor Modulator and Doping Agent

Ostarine (enobasarm) is a selective androgen receptor modulator with great therapeutic potential. However, it is also used by athletes to promote muscle growth and enhance performances without the typical adverse effects of anabolic steroids. Ostarine popularity increased in recent years, and it is currently the most abused "other anabolic agent" (subclass S1.2. of the "anabolic agents" class S1) from the World Anti-Doping Agency's (WADA) prohibited list. Several cases of liver toxicity were recently reported in regular users. Detecting ostarine or markers of intake in biological matrices is essential to document ostarine use in doping. Therefore, we sought to investigate ostarine metabolism to identify optimal markers of consumption. The substance was incubated with human hepatocytes, and urine samples from six ostarine-positive cases were screened. Analyses were performed via liquid chromatography-high-resolution tandem mass spectrometry (LC-HRMS/MS) and software-assisted data mining, with in silico metabolite predictions. Ten metabolites were identified with hydroxylation, ether cleavage, dealkylation, O-glucuronidation, and/or sulfation. The production of cyanophenol-sulfate might participate in the mechanism of ostarine liver toxicity. We suggest ostarine-glucuronide (C25H22O9N3F3, diagnostic fragments at m/z 118, 185, and 269) and hydroxybenzonitrile-ostarine-glucuronide (C25H22O10N3F3, diagnostic fragments at m/z 134, 185, and 269) in non-hydrolyzed urine and ostarine and hydroxybenzonitrile-ostarine (C19H14O4N3F3, diagnostic fragments at m/z 134, 185, and 269) in hydrolyzed urine as markers to document ostarine intake in doping.

Profiling Urinary Sulfate Metabolites With Mass Spectrometry

The study of urinary phase II sulfate metabolites is central to understanding the role and fate of endogenous and exogenous compounds in biological systems. This study describes a new workflow for the untargeted metabolic profiling of sulfated metabolites in a urine matrix. Analysis was performed using ultra-high-performance liquid chromatography-high resolution tandem mass spectrometry (UHPLC-HRMS/MS) with data dependent acquisition (DDA) coupled to an automated script-based data processing pipeline and differential metabolite level analysis. Sulfates were identified through k-means clustering analysis of sulfate ester derived MS/MS fragmentation intensities. The utility of the method was highlighted in two applications. Firstly, the urinary metabolome of a thoroughbred horse was examined before and after administration of the anabolic androgenic steroid (AAS) testosterone propionate. The analysis detected elevated levels of ten sulfated steroid metabolites, three of which were identified and confirmed by comparison with synthesised reference materials. This included 5α-androstane-3β,17α-diol 3-sulfate, a previously unreported equine metabolite of testosterone propionate. Secondly, the hydrolytic activity of four sulfatase enzymes on pooled human urine was examined. This revealed that Pseudomonas aeruginosa arylsulfatases (PaS) enzymes possessed higher selectivity for the hydrolysis of sulfated metabolites than the commercially available Helix pomatia arylsulfatase (HpS). This novel method provides a rapid tool for the systematic, untargeted metabolic profiling of sulfated metabolites in a urinary matrix.

Investigation of the individual human sulfatome in plasma and urine samples reveals an age-dependency

Metabolic microbiome interaction with the human host has been linked to human physiology and disease development. The elucidation of this interspecies metabolite exchange will lead to identification of beneficial metabolites and disease modulators. Their discovery and quantitative analysis requires the development of specific tools and analysis of specific compound classes. Sulfated metabolites are considered a readout for the co-metabolism of the microbiome and their host. This compound class is part of the human phase II clearance process of xenobiotics and is the main focus in drug or doping metabolism and also includes dietary components and microbiome-derived compounds. Here, we report the targeted analysis of sulfated metabolites in plasma and urine samples in the same individuals to identify the core sulfatome and similarities between these two sample types. This analysis of 27 individuals led to the identification of the core sulfatome of 41 metabolites in plasma and urine samples as well as an age effect for 15 metabolites in both sample types.

Comparison of two arylsulfatases for targeted mass spectrometric analysis of microbiota-derived metabolites

Sulfation of metabolites is the second highest phase II modification in humans, which plays a critical role in the xenobiotics clearance process and gut microbiota-host co-metabolism. Besides the main function to remove xenobiotics from the body, sulfated metabolites have also been linked to inflammation, bacterial pathogenesis and metabolic disorders. A better understanding of how these metabolites impact the human body has turned into an important research area. Analytical methods for selective identification of this metabolite class are scarce. We have recently developed an assay utilizing the arylsulfatase from Helix pomatia due to a high substrate promiscuity combined with state-of-the-art metabolomics bioinformatic analysis for the selective identification of O-sulfated metabolites in human samples. This enzyme requires a multistep purification process as highest purity is needed for the developed mass spectrometric assay. In this study, we have utilized a new and recombinant overexpressed arylsulfatase (ASPC) for the selective identification of organic sulfate esters in human urine samples. We have compared the substrate conversion in urine samples and substrate specificity of this enzyme with purified arylsulfatase from Helix pomatia. Our analysis of urine samples revealed that both enzymes can be utilized for the selective analysis and discovery of sulfated metabolites with high promiscuity as demonstrated by equal hydrolysis of 108 substrates including sulfated conjugates of 27 metabolites of microbial origin. Importantly, we also identified 21 substrates in human urine samples that are exclusively hydrolyzed by ASPC and application of this enzyme increases the discovery of unknown sulfated metabolites with a higher scaffold diversity.

Rapid Preparation of a Large Sulfated Metabolite Library for Structure Validation in Human Samples

Metabolomics analysis of biological samples is widely applied in medical and natural sciences. Assigning the correct chemical structure in the metabolite identification process is required to draw the correct biological conclusions and still remains a major challenge in this research field. Several metabolite tandem mass spectrometry (MS/MS) fragmentation spectra libraries have been developed that are either based on computational methods or authentic libraries. These libraries are limited due to the high number of structurally diverse metabolites, low commercial availability of these compounds, and the increasing number of newly discovered metabolites. Phase II modification of xenobiotics is a compound class that is underrepresented in these databases despite their importance in diet, drug, or microbiome metabolism. The O-sulfated metabolites have been described as a signature for the co-metabolism of bacteria and their human host. Herein, we have developed a straightforward chemical synthesis method for rapid preparation of sulfated metabolite standards to obtain mass spectrometric fragmentation pattern and retention time information. We report the preparation of 38 O-sulfated alcohols and phenols for the determination of their MS/MS fragmentation pattern and chromatographic properties. Many of these metabolites are regioisomers that cannot be distinguished solely by their fragmentation pattern. We demonstrate that the versatility of this method is comparable to standard chemical synthesis. This comprehensive metabolite library can be applied for co-injection experiments to validate metabolites in different human sample types to explore microbiota-host co-metabolism, xenobiotic, and diet metabolism.

Metabolic studies of selective androgen receptor modulators RAD140 and S-23 in horses

This paper describes the studies of the in vitro biotransformation of two selective androgen receptor modulators (SARMs), namely, RAD140 and S-23, and the in vivo metabolism of RAD140 in horses using ultra-high performance liquid chromatography-high resolution mass spectrometry. in vitro metabolic studies of RAD140 and S-23 were performed using homogenised horse liver. The more prominent in vitro biotransformation pathways for RAD140 included hydrolysis, hydroxylation, glucuronidation and sulfation. Metabolic pathways for S-23 were similar to those for other arylpropionamide-based SARMs. The administration study of RAD140 was carried out using three retired thoroughbred geldings. RAD140 and the majority of the identified in vitro metabolites were detected in post-administration urine samples. For controlling the misuse of RAD140 in horses, RAD140 and its metabolite in sulfate form gave the longest detection time in hydrolysed urine and could be detected for up to 6 days post-administration. In plasma, RAD140 itself gave the longest detection time of up to 13 days. Apart from RAD140 glucuronide, the metabolites of RAD140 described herein have never been reported before.

Sensitive mass spectrometric analysis of carbonyl metabolites in human urine and fecal samples using chemoselective modification

Metabolites with ketone or aldehyde functionalities comprise a large proportion of the human metabolome, most notably in the form of sugars. However, these reactive molecules are also generated through oxidative stress or gut microbiota metabolism and have been linked to disease development. The discovery and structural validation of this class of metabolites over the large concentration range found in human samples is crucial to identify their links to pathogenesis. Herein, we have utilized an advanced chemoselective probe methodology alongside bioinformatic analysis to identify carbonyl-metabolites in urine and fecal samples. In total, 99 metabolites were identified in urine samples and the chemical structure for 40 metabolites were unambiguously validated using a co-injection procedure. We also describe the preparation of a metabolite-conjugate library of 94 compounds utilized to efficiently validate these ketones and aldehydes. This method was used to validate 33 metabolites in a pooled fecal sample extract to demonstrate the potential for rapid and efficient metabolite detection over a wide metabolite concentration range. This analysis revealed the presence of six metabolites that have not previously been detected in either sample type. The constructed library can be utilized for straightforward, large-scale, and expeditious analysis of carbonyls in any sample type.

New enzymatic and mass spectrometric methodology for the selective investigation of gut microbiota-derived metabolites

Gut microbiota significantly impact human physiology through metabolic interaction. Selective investigation of the co-metabolism of bacteria and their human host is a challenging task and methods for their analysis are limited. One class of metabolites associated with this co-metabolism are O-sulfated compounds. Herein, we describe the development of a new enzymatic assay for the selective mass spectrometric investigation of this phase II modification class. Analysis of human urine and fecal samples resulted in the detection of 206 sulfated metabolites, which is three times more than reported in the Human Metabolome Database. We confirmed the chemical structure of 36 sulfated metabolites including unknown and commonly reported microbiota-derived sulfated metabolites using synthesized internal standards and mass spectrometric fragmentation experiments. Our findings demonstrate that enzymatic sample pre-treatment combined with state-of-the-art metabolomics analysis represents a new and efficient strategy for the discovery of unknown microbiota-derived metabolites in human samples. Our described approach can be adapted for the targeted investigation of other metabolite classes as well as the discovery of biomarkers for diseases affected by microbiota.