@phdthesis{Knoche2022,
  author    = {Knoche, Lisa},
  title     = {Untersuchung von Transformationsprodukten ausgew{\"a}hlter Tierarzneimittel generiert durch Elektrochemie, Mikrosomal Assay, Hydrolyse und Photolyse},
  pages     = {163, III},
  year      = {2022},
  abstract  = {The knowledge of transformation pathways and transformation products of veterinary drugs is important for health, food and environmental matters. Residues, consisting of original veterinary drug and transformation products, are found in food products of animal origin as well as the environment (e.g., soil or surface water). Several transformation processes can alter the original veterinary drug, ranging from biotransformation in living organism to environmental degradation processes like photolysis, hydrolysis, or microbial processes. In this thesis, four veterinary drugs were investigated, three ionophore antibiotics Monensin, Salinomycin and Lasalocid and the macrocyclic lactone Moxidectin. Ionophore antibiotics are mainly used to cure and prevent coccidiosis in poultry especially prophylactic in broiler farming. Moxidectin is an antiparasitic drug that is used for the treatment of internal and external parasites in food-producing and companion animals. The main objective of this work is to employ different laboratory approaches to generate and identify transformation products. The identification was conducted using high-resolution mass spectrometry (HRMS). A major focus was placed on the application of electrochemistry for simulation of transformation processes. The electrochemical reactor - equipped with a three-electrode flow-through cell - enabled the oxidation or reduction by applying a potential. The transformation products derived were analyzed by online coupling of the electrochemical reactor and a HRMS and offline by liquid chromatography (LC) combined with HRMS. The main modification reaction of the identified transformation products differed for each investigated veterinary drug. Monensin showed decarboxylation and demethylation as the main modification reactions, for Salinomycin mostly decarbonylation occurred and for Lasalocid methylation was prevalent. For Moxidectin, I observed an oxidation (hydroxylation) reaction and adduct formation with solvent. In general, for Salinomycin and Lasalocid, more transient transformation products (online measurement) than stable transformation products (offline measurements) were detected. By contrast, the number of transformation products using online and offline measurements were identical for Monensin and Moxidectin. As a complementary approach, metabolism tests with rat or human liver microsomes were conducted for the ionophore antibiotics. Monensin was investigated by using rat liver microsomes and the transformation products identified were based on decarboxylation and demethylation. Salinomycin and Lasalocid were converted by human and rat liver microsomes. For both substances, more transformation products were found by using human liver microsomes. The transformation products of the rat liver microsome conversion were redundant, and the transformation products were also found at the human liver microsome assay. Oxidation (hydroxylation) was found to be the main modification reaction for both. In addition, a frequent ion exchange between sodium and potassium was identified. The final two experiments were performed for one substance each, whereby the hydrolysis of Monensin and the photolysis of Moxidectin was investigated. The transformation products of the pH-dependent hydrolysis were based on ring-opening and dehydration. Moxidectin formed several transformation products by irradiation with UV-C light and the main modification reactions were isomeric changes, (de-)hydration and changes of the methoxime moiety. In summary, transformation products of the four investigated veterinary drugs were generated by the different laboratory approaches. Most of the transformation products were identified for the first time. The resulting findings provide an improved understanding of clarifying the transformation behavior.},
  language  = {en}
}
@article{KnocheLisecKoch2022,
  author    = {Knoche, Lisa and Lisec, Jan and Koch, Matthias},
  title     = {Analysis of electrochemical and liver microsomal transformation products of lasalocid by LC/HRMS},
  series = {Rapid communications in mass spectrometry : RCM},
  volume    = {36},
  journal   = {Rapid communications in mass spectrometry : RCM},
  number    = {18},
  publisher = {Wiley},
  address   = {New York, NY},
  issn      = {0951-4198},
  doi       = {10.1002/rcm.9349},
  pages     = {10},
  year      = {2022},
  abstract  = {Rationale: Lasalocid (LAS), an ionophore, is used in cattle and poultry farming as feed additive for its antibiotic and growth-promoting properties. Literature on transformation products (TP) resulting from LAS degradation is limited. So far, only hydroxylation is found to occur as the metabolic reaction during the LAS degradation. To investigate potential TPs of LAS, we used electrochemistry (EC) and liver microsome (LM) assays to synthesize TPs, which were identified using liquid chromatography high-resolution mass spectrometry (LC/HRMS). Methods: Electrochemically produced TPs were analyzed online by direct coupling of the electrochemical cell to the electrospray ionization (ESI) source of a Sciex Triple-TOF high resolution mass spectrometer. Then, EC-treated LAS solution was collected and analyzed offline using LC/HRMS to confirm stable TPs and improve their annotation with a chemical structure due to informative MS/MS spectra. In a complementary approach, TPs formed by rat and human microsomal incubation were investigated using LC/HRMS. The resulting data were used to investigate LAS modification reactions and elucidate the chemical structure of obtained TPs. Results: The online measurements identified a broad variety of TPs, resulting from modification reactions like (de-)hydrogenation, hydration, methylation, oxidation as well as adduct formation with methanol. We consistently observed different ion complexations of LAS and LAS-TPs (Na+; 2Na(+) K+; NaNH4+; KNH4+). Two stable methylated EC-TPs were found, structurally annotated, and assigned to a likely modification reaction. Using LM incubation, seven TPs were formed, mostly by oxidation/hydroxylation. After the identification of LM-TPs as Na+-complexes, we identified LM-TPs as K+-complexes. Conclusion: We identified and characterized TPs of LAS using EC- and LM-based methods. Moreover, we found different ion complexes of LAS-based TPs. This knowledge, especially the different ion complexes, may help elucidate the metabolic and environmental degradation pathways of LAS.},
  language  = {en}
}
@article{KnocheLisecSchwerdtleetal.2022,
  author    = {Knoche, Lisa and Lisec, Jan and Schwerdtle, Tanja and Koch, Matthias},
  title     = {LC-HRMS-Based identification of transformation products of the drug salinomycin generated by electrochemistry and liver microsome},
  series = {Antibiotics},
  volume    = {11},
  journal   = {Antibiotics},
  number    = {2},
  publisher = {MDPI},
  address   = {Basel},
  issn      = {2079-6382},
  doi       = {10.3390/antibiotics11020155},
  pages     = {12},
  year      = {2022},
  abstract  = {The drug salinomycin (SAL) is a polyether antibiotic and used in veterinary medicine as coccidiostat and growth promoter. Recently, SAL was suggested as a potential anticancer drug. However, transformation products (TPs) resulting from metabolic and environmental degradation of SAL are incompletely known and structural information is missing. In this study, we therefore systematically investigated the formation and identification of SAL derived TPs using electrochemistry (EC) in an electrochemical reactor and rat and human liver microsome incubation (RLM and HLM) as TP generating methods. Liquid chromatography (LC) coupled to high-resolution mass spectrometry (HRMS) was applied to determine accurate masses in a suspected target analysis to identify TPs and to deduce occurring modification reactions of derived TPs. A total of 14 new, structurally different TPs were found (two EC-TPs, five RLM-TPs, and 11 HLM-TPs). The main modification reactions are decarbonylation for EC-TPs and oxidation (hydroxylation) for RLM/HLM-TPs. Of particular interest are potassium-based TPs identified after liver microsome incubation because these might have been overlooked or declared as oxidated sodium adducts in previous, non-HRMS-based studies due to the small mass difference between K and O + Na of 21 mDa. The MS fragmentation pattern of TPs was used to predict the position of identified modifications in the SAL molecule. The obtained knowledge regarding transformation reactions and novel TPs of SAL will contribute to elucidate SAL-metabolites with regards to structural prediction.},
  language  = {en}
}