Fenoterol Hydrobromide

Hepatic organic cation transporter 1 (OCT1, SLC22A1) has a broad spectrum of structurally diverse substrates, including drugs like morphine, metformin, sumatriptan, and fenoterol. Here, we leveraged existing cryo-EM data to identify amino acids that constrain the binding pocket toward the intracellular lumen and performed functional analyses to determine their roles in OCT1 transport, in general, and in substrate specificity, in particular. We mutated W217, W354, and I446 and analyzed their effects on the transport of 27 structurally highly diverse substrates in HEK293 cells. The W354A mutant resulted in a complete loss of function for all tested substrates, whereas only the W354Y mutant partially retained OCT1 activity. Molecular dynamics simulations and functional analyses suggest that W354 affects OCT1 transport by forming a hydrogen bond with N453 in transmembrane helix 10, thereby stabilizing OCT1 in its outward open conformation. W217A showed strongly substrate-dependent effects, with the aromatic ring of tryptophan being the key property affecting transport. Smaller, less lipophilic substrates were more strongly affected. The substrate-specific effects of the W217A mutant correlated significantly with those of the F244A mutant. The double mutant W217A/F244A strongly reduced uptake of all tested substrates, indicating a compensatory mechanism between these two amino acids. I446 showed only marginal effects on OCT1 transport. Our data suggest that W354 is crucial for OCT1 function by mediating the switch from an inward-occluded to inward-open conformation but is not directly involved in substrate interaction. In contrast, W217, along with the previously known F244, contributes to the substrate specificity of OCT1.

The misuse of beta‐agonist drugs as growth promoters in livestock production, highlighted by the cases of intoxication in Europe in the 1990s, has resulted in strict regulations in the European Union. These restrictions have required the development of increasingly sensitive analytical methods. In June 2022, the European Union Reference Laboratory (EURL BVL Berlin) released the Guidance Document on Minimum Method Performance Requirements (MMPRs), a technical guidance for analytical methods in residue control. The MMPRs represent the minimum concentrations that official laboratories should be able to reliably identify to analyze prohibited substances in different animal matrices. In this work, a qualitative screening method for 21 beta‐agonists at half of MMPRs was developed and validated in animal lung and liver by UPLC–MS/MS technique according to Commission Implementing Regulation (EU) 2021/808 requirements. With regard to detection capability CCβ, the results obtained permitted the qualitative determination of 11 clenbuterol‐like beta‐agonists (Clenbuterol, Bromchlorbuterol, Brombuterol, Cimaterol, Cimbuterol, Clenpenterol, Clenproperol, Hydroxymethylclenbuterol, Mabuterol, Mapenterol, Tulobuterol) at 0.05 μg/kg and for 10 salbutamol‐like beta‐agonists (Carbuterol, Isoxsuprine, Clencyclohexerol, Ractopamine, Ritodrine, Salbutamol, Terbutaline, Zilpaterol, Fenoterol, Salmeterol) at 0.25 μg/kg. The method was validated for lungs and livers of different animal species (cattle, chicken, sheep, and swine): following the requirements of the above‐mentioned Regulation. The method was found to be robust and specific.