Mass spectrometry has been an essential technique for the investigation of the metabolic pathways of living organisms since its appearance at the beginning of the 20th century. Due to its capability to resolve isotopically labeled species, it can be applied together with stable isotope tracers to reveal the transformation of particular biologically relevant molecules. However, low-resolution techniques, which were used for decades, had limited capabilities for untargeted metabolomics, especially when a large number of compounds are labelled simultaneously. Such untargeted studies may provide new information about metabolism and can be performed with high-resolution mass spectrometry. Here, we demonstrate the capabilities of high-resolution mass spectrometry to obtain insights on the metabolism of a model plant, Lepidium sativum, germinated in D₂O and H₂¹⁸O-enriched media. In particular, we demonstrated that in vivo labeling with heavy water helps to identify if a compound is being synthesized at a particular stage of germination or if it originates from seed content, and tandem mass spectrometry allows us to highlight the substructures with incorporated isotope labels. Additionally, we found in vivo labeling useful to distinguish between isomeric compounds with identical fragmentation patterns due to the differences in their formation rates that can be compared by the extent of heavy atom incorporation.

The administration of low doses of D₂O to living organisms was used for decades for the investigation of metabolic pathways and for the measurement of the turnover rate for specific compounds. Usually, the investigation of the deuterium uptake in lipids is performed by measuring the deuteration level of the palmitic acid residue using GC-MS instruments, and to our knowledge, the application of the modern untargeted LC-MS/MS lipidomics approaches was only reported a few times. Here, we investigated the deuterium uptake for >500 lipids for 13 organs and body liquids of mice (brain, lung, heart, liver, kidney, spleen, plasma, urine, etc.) after 4 days of 100% D₂O administration. The maximum deuteration level was observed in the liver, plasma, and lung, while in the brain and heart, the deuteration level was lower. Using MS/MS, we demonstrated the incorporation of deuterium in palmitic and stearic fragments in lipids (PC, PE, TAG, PG, etc.) but not in the corresponding free forms. Our results were analyzed based on the metabolic pathways of lipids.

Synthetic cannabinoid receptor agonists (SCRAs) have become a wide group of new psychoactive substances since the 2010s. For the last few years, the X-ray structures of the complexes of cannabinoid receptor I (CB₁) with SCRAs as well as the complexes of CB₁ with its antagonist have been published. Based on those data, SCRA–CB₁ interactions are analyzed in detail, using molecular modeling and molecular dynamics simulations. The molecular mechanism of the conformational transformation of the transmembrane domain of CB₁ caused by its interaction with SCRA is studied. These conformational changes allosterically modulate the CB₁–G_i complex, providing activation of the G_i protein. Based on the X-ray-determined structures of the CB₁–ligand complexes, a stable apo conformation of inactive CB₁ with a relatively low potential barrier of receptor activation was modeled. For that model, molecular dynamic simulations of SCRA binding to CB₁ led to the active state of CB₁, which allowed us to explore the key features of this activation and the molecular mechanism of the receptor’s structural transformation. The simulated CB₁ activation is in accordance with the previously published experimental data for the activation at protein mutations or structural changes of ligands. The key feature of the suggested activation mechanism is the determination of the stiff core of the CB₁ transmembrane domain and the statement that the entire conformational transformation of the receptor to the active state is caused by a shift of alpha helix TM7 relative to this core. The shift itself is caused by protein–ligand interactions. It was verified via steered molecular dynamics simulations of the X-ray-determined structures of the inactive receptor, which resulted in the active conformation of CB₁ irrespective of the placement of agonist ligand in the receptor’s active site.

Sea buckthorn (Hippophae rhamnoides L.) is an oil crop with health benefits. Its fruits are rich in unsaturated fatty acids (FAs); however, the FA composition of the seeds and pulp differs significantly. To evaluate the expression levels of gene families that play a major role in FA biosynthesis, the transcriptomes of seeds and pulp at four fruit development stages were sequenced for five sea buckthorn varieties with diverse characteristics: Elizaveta, Inya, KP-686, Panteleevskaya, and Triumf. The results revealed that FAD3 (07426) and FAD3 (05528) are likely key genes for linolenic acid synthesis in seeds, while FAD2 (21624) is likely the main contributor to linoleic acid synthesis in both seeds and pulp. SAD (18830) primarily contributes to oleic acid synthesis in seeds, while SAD (18830) and SAD (26748) contribute to its synthesis in pulp. FATA (14745) and FATA (14109) are also implicated in FA synthesis in sea buckthorn fruits. Changes in the content of the main FAs in seeds and pulp correlated with the expression levels of the corresponding genes. KP-686 and Triumf differed the most from other varieties. These results are important for analyzing tissue-specific gene expression in seeds and pulp of sea buckthorn fruits, and they are promising for developing sea buckthorn varieties with improved oil composition.

The manuscript of a paper entitled "Interaction of Synthetic Cannabinoid Receptor Agonists with Cannabinoid Receptor I: Insights into Activation Molecular Mechanism". The work describes computer simulations of activation of the Cannabinoid Receptor I at binding of its agonist ligands. The molecular mechanism of the receptor-ligand interactions and receptor's activation is explored. The study includes theoretical models construction, intense molecular dynamics simulations, comparison with experimentally-known data. Some conclusions allow for better understanding of G-protein-copupled receptor mechanism of transmembrane allosteric modulation.

The role of phosphatidylethanol (PEth) as an alcohol consumption marker is increasing in clinical and forensic medicine. During the COVID-19 pandemic, the role of hygiene increased, and it became common practice to use disinfectants almost everywhere. This paper highlights a possible source of false positive results (by the vapors of alcohols during the blood spot drying process) in dried blood spots (DBS) by LC-MS/MS quantitation of PEth. To achieve this, the PEth quantitation method was validated according to FDA guidelines. Additionally, the synthesis of phosphatidyl derivatives by phospholipase D (PLD) in the presence of methanol and 2-propanol vapors during the DBS process was determined. Each PEth-negative sample from a healthy male patient incubated in the presence of ethanol vapor becomes PEth-positive. After 4 h of DBS drying, teetotalers become “moderate drinkers”. It is necessary to avoid using alcohol-containing disinfectants in treatment rooms, where DBS is sampled.