TY - JOUR A1 - Schmidt, Sebastian A1 - Holzgrabe, Ulrike T1 - Do the enantiomers of ketamine bind enantioselectively to human serum albumin? JF - European Journal of Pharmaceutical Sciences N2 - The binding of drugs to plasma proteins is an important process in the human body and has a significant influence on pharmacokinetic parameter. Human serum albumin (HSA) has the most important function as a transporter protein. The binding of ketamine to HSA has already been described in literature, but only of the racemate. The enantiomerically pure S-ketamine is used as injection solution for induction of anesthesia and has been approved by the Food and Drug Administration for the therapy of severe depression as a nasal spray in 2019. The question arises if there is enantioselective binding to HSA. Hence, the aim of this study was to investigate whether there is enantioselective binding of S-and R-ketamine to HSA or not. Ultrafiltration (UF) followed by chiral capillary electrophoretic analysis was used to determine the extent of protein binding. Bound fraction to HSA was 71.2 % and 64.9 % for enantiomerically pure R- and S-ketamine, respectively, and 66.5 % for the racemate. Detailed binding properties were studied by Saturation Transfer Difference (STD)-, waterLOGSY- and Carr-Purcell-Meiboom-Gill (CPMG)-NMR spectroscopy. With all three methods, the aromatic ring and the N-methyl group could be identified as the structural moieties most strongly involved in binding of ketamine to HSA. pK\(_{aff}\) values determined using UF and NMR indicate that ketamine is a weak affinity ligand to HSA and no significant differences in binding behavior were found between the individual enantiomers and the racemate. KW - protein binding KW - albumin KW - electrophoresis KW - nuclear magnetic resonance spectroscopy KW - ultrafiltration KW - enantioselectivity Y1 - 2024 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-349791 VL - 192 ER - TY - JOUR A1 - Schmidt, Sebastian A1 - Holzgrabe, Ulrike T1 - Method development, optimization, and validation of the separation of ketamine enantiomers by capillary electrophoresis using design of experiments JF - Chromatographia N2 - Capillary electrophoresis was chosen as cost-effective and robust method to separate ketamine enantiomers. For the method development, first different native and modified cyclodextrins were tested. The most promising chiral selector was α-cyclodextrin. A design of experiments (DoE) was carried out, which started with the screening of relevant factors. Based on these results, the method was optimized according to the significant factors (buffer, cyclodextrin concentration, pH value, voltage, temperature) of the screening based on the response resolution and migration time of the later migrating enantiomer. The optimized conditions consisted of a background electrolyte with 275 mM TRIS, adjusted with 85% phosphoric acid to a pH of 2.50, and 50 mM α-cyclodextrin, at a temperature of 15 °C, an applied voltage of 30 kV and an injection pressure of 1.0 psi for 10 s. A fused-silica capillary with a total length of 70 cm and an effective length to the detector of 60 cm was used. The method was validated according to ICH guideline Q2 R(1). The limit of quantification was 3.51 µg mL\(^{−1}\) for S-ketamine and 3.98 µg mL\(^{−1}\)for R-ketamine. The method showed good linearity for racemic ketamine with R\(^2\) of 0.9995 for S-ketamine and 0.9994 for R-ketamine. The lowest quantifiable content of S-ketamine found in R-ketamine was 0.45%. KW - ketamine KW - capillary electrophoresis KW - design of experiments KW - cyclodextrins KW - enantiomers Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-324713 SN - 0009-5893 VL - 86 IS - 1 ER - TY - JOUR A1 - Triyasmono, Liling A1 - Schollmayer, Curd A1 - Schmitz, Jens A1 - Hovah, Emilie A1 - Lombo, Cristian A1 - Schmidt, Sebastian A1 - Holzgrabe, Ulrike T1 - Simultaneous determination of the saponification value, acid value, ester value, and iodine value in commercially available red fruit oil (Pandanus conoideus, Lam.) using \(^1\)H qNMR spectroscopy JF - Food Analytical Methods N2 - Red fruit oil (RFO) can be extracted from fruits of Pandanus conoideus, Lam., an endogenous plant of Papua, Indonesia. It is a commonly used essential original traditional medicine. By applying a newly developed quantitative \(^1\)H NMR (qNMR) spectroscopy method for quality assessment, a simultaneous determination of the saponification value (SV), acid value (AV), ester value (EV), and iodine value (IV) in RFO was possible. Dimethyl sulfone (DMSO\(_2\)) was used as an internal standard. Optimization of NMR parameters, such as NMR pulse sequence, relaxation delay time, and receiver gain, finally established the \(^1\)H NMR-based quantification approach. Diagnostic signals of the internal standard at δ = 2.98 ppm, SV at δ = 2.37–2.20 ppm, AV at δ = 2.27–2.20 ppm, EV at δ = 2.37–2.27 ppm, and IV at δ = 5.37–5.27 ppm, respectively, were used for quantitative analysis. The method was validated concerning linearity (R\(^2\) = 0.999), precision (less than 0.83%), and repeatability in the range 99.17–101.17%. Furthermore, this method was successfully applied to crude RFO, crude RFO with palmitic and oleic acid addition, and nine commercial products. The qNMR results for the respective fat values are in accordance with the results of standard methods, as can be seen from the F- and t-test (< 1.65 and < 1.66, respectively). The fundamental advantages of qNMR, such as its rapidity and simplicity, make it a feasible and existing alternative to titration for the quality control of RFO. KW - quantitative 1H NMR KW - saponification Value KW - acid value KW - ester value KW - iodine value KW - red fruit oil Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-324728 SN - 1936-9751 VL - 16 IS - 1 ER - TY - JOUR A1 - Schmidt, Sebastian A1 - Zehe, Markus A1 - Holzgrabe, Ulrike T1 - Characterization of binding properties of ephedrine derivatives to human alpha-1-acid glycoprotein JF - European Journal of Pharmaceutical Sciences N2 - Most drugs, especially those with acidic or neutral moieties, are bound to the plasma protein albumin, whereas basic drugs are preferentially bound to human alpha-1-acid glycoprotein (AGP). The protein binding of the long-established drugs ephedrine and pseudoephedrine, which are used in the treatment of hypotension and colds, has so far only been studied with albumin. Since in a previous study a stereoselective binding of ephedrine and pseudoephedrine to serum but not to albumin was observed, the aim of this study was to check whether the enantioselective binding behavior of ephedrine and pseudoephedrine, in addition to the derivatives methylephedrine and norephedrine, is due to AGP and to investigate the influence of their different substituents and steric arrangement. Discontinuous ultrafiltration was used for the determination of protein binding. Characterization of ligand-protein interactions of the drugs was obtained by saturation transfer difference nuclear magnetic resonance spectroscopy. Docking experiments were performed to analyze possible ligand-protein interactions. The more basic the ephedrine derivative is, the higher is the affinity to AGP. There was no significant difference in the binding properties between the individual enantiomers and the diastereomers of ephedrine and pseudoephedrine. KW - protein binding KW - AGP KW - ultrafiltration KW - saturation transfer difference NMR KW - epitope mapping KW - ephedrine Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-300848 VL - 181 ER - TY - JOUR A1 - Schmidt, Sebastian A1 - Liu, Guoxing A1 - Liu, Guilai A1 - Yang, Wenting A1 - Honisch, Sabina A1 - Pantelakos, Stavros A1 - Stournaras, Christos A1 - Hönig, Arnd A1 - Lang, Florian T1 - Enhanced Orai1 and STIM1 expression as well as store operated \(Ca^{2+}\) entry in therapy resistant ovary carcinoma cells JF - Oncotarget N2 - Mechanisms underlying therapy resistance of tumor cells include protein kinase Akt. Putative Akt targets include store-operated \(Ca^{2+}\)-entry (SOCE) accomplished by pore forming ion channel unit Orai1 and its regulator STIM1. We explored whether therapy resistant (A2780cis) differ from therapy sensitive (A2780) ovary carcinoma cells in Akt, Orai1, and STIM1 expression, \(Ca^{2+}\)-signaling and cell survival following cisplatin (100µM) treatment. Transcript levels were quantified with RT-PCR, protein abundance with Western blotting, cytosolic \(Ca^{2+}\)-activity ([\(Ca^{2+}\)]i) with Fura-2-fluorescence, SOCE from increase of [\(Ca^{2+}\)]i following \(Ca^{2+}\)-readdition after Ca2+-store depletion, and apoptosis utilizing flow cytometry. Transcript levels of Orai1 and STIM1, protein expression of Orai1, STIM1, and phosphorylated Akt, as well as SOCE were significantly higher in A2780cis than A2780 cells. SOCE was decreased by Akt inhibitor III (SH-6, 10µM) in A2780cis but not A2780 cells and decreased in both cell lines by Orai1 inhibitor 2-aminoethoxydiphenyl borate (2-ABP, 50µM). Phosphatidylserine exposure and late apoptosis following cisplatin treatment were significantly lower in A2780cis than A2780 cells, a difference virtually abolished by SH-6 or 2-ABP. In conclusion, Orai1/STIM1 expression and function are increased in therapy resistant ovary carcinoma cells, a property at least in part due to enhanced Akt activity and contributing to therapy resistance in those cells. KW - Ca2+ release activated Ca2+ channel KW - SOCE KW - Akt KW - SH-6 KW - 2-APB KW - apoptosis Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-121423 UR - www.impactjournals.com/oncotarget VL - 5 IS - 13 ER -