Structural changes by sulfoxidation of phenothiazine drugs

A putative three-dimensional arrangement of the human serotonin transporter transmembrane helices: a tool to aid experimental studies

The human serotonin transporter is the molecular target for selective serotonin reuptake inhibitor drugs which are being used for treatment of depression. A three-dimensional model of the membrane spanning parts of the transporter was constructed. The transporter was assumed to consist of 12 transmembrane alpha-helices. The model was based on published experimental data of cocaine binding to mutant transporters, amino acid sequence analysis, and interactive molecular graphics. The model suggests that a high affinity cocaine binding site is situated in a region of the model where Asp98 acts like an anchor, while a putative low affinity site is situated in another region with Glu508 as the anchoring amino acid. A series of docking experiments with various reuptake inhibitors were conducted, using interactive molecular graphics techniques combined with energy calculations and analysis of the transporter-ligand complexes. Experiments involving molecular mapping of ligand binding areas may benefit from using the current model in experimental design. From the current model, several amino acids were proposed as prime candidates for mutagenesis and subsequent ligand binding studies. Also for evaluation of results from site directed mutagenesis experiments with SERT and similar transporters we assume the model will be helpful.

Chlorpromazine-induced increase in dipalmitoylphosphatidylserine surface area in monolayers at room temperature

The Langmuir technique revealed that the surface area of acidic glycerophospholipids (dipalmitoylphosphatidylserine, -glycerol, and dipalmitoylphosphatidic acid) in monolayers increased dramatically when micromolar concentrations of the antipsychotic drug chlorpromazine (CPZ) were present in the subphase. Monolayers of neutral glycerophospholipids (dipalmitoylphosphatidylcholine and -ethanolamine) did not show such a large effect with CPZ. Compared to CPZ, millimolar concentrations of the monovalent cations Li+, K+, Na+, Rb+, and Cs+ did not appear to influence the dipalmitoylphosphatidylserine monolayer, suggesting that the effect of CPZ, a monovalent cationic amphophile, was due to an interaction with the acyl chains of the lipids. In addition, the effect of CPZ was reduced by 150 mM Na+, suggesting that the sodium cations might screen the negatively charged headgroups from an electrostatic interaction with the positively charged drug molecule. Two CPZ analogs, chlorpromazine sulfoxide and CPZ with 2 carbons in the side chain, were also studied. These observations suggest that part of the biological effects of CPZ, being antipsychotic and/or side effects, may be due to CPZ's action on the acidic glycerophospholipids in nerve cell membranes.

Horseradish peroxidase-catalyzed sulfoxidation of promethazine and properties of promethazine sulfoxide

Promethazine sulfoxide was obtained with a quantitative yield in a horse radish peroxidase-catalyzed reaction of promethazine and hydrogen peroxide and was also prepared by direct chemical synthesis. The enzymatic sulfoxidation of promethazine was studied in vitro as a function of pH, promethazine, and hydrogen peroxide concentration. Promethazine sulfoxide inhibits with an apparent K(i) of 59.7 microM at pH 5.5 the enzymatic reaction, followed spectrophotometrically, polarographically, potentiometrically, and luminometrically. The reaction was also inhibited by ascorbic acid (K(i) 26.8 microM) and glutathione (K(i) 41.8 microM). The spectrophotometric techniques employed, together with ESR spectrometry, allowed the identification of at least three radical species formed in the course of the reaction. Promethazine sulfoxide is devoid of the antioxidant effect exhibited by promethazine on rat brain synaptosomes. The sulfoxide also lacks photosensitizing action, while retaining the neuroleptic effect of the parent compound.