ABSTRACT
Experimental and theoretical physico-chemical methods were used to investigate the interaction between several reversible monoamine oxidase A inhibitors in the oxazolidinone series and the active site of the enzyme. Phenyloxazolidinones include toloxatone and analogues, among which befloxatone was selected as drug candidate for the treatment of depression. Identification of the forces responsible for the crystal cohesion of befloxatone reveals functional groups that could interact with monoamine oxidase. Calculation of electronic properties of those compounds using ab initio molecular orbital methods lead to a description of the mode of interaction between befloxatone and the cofactor of the enzyme. Electronic absorption spectroscopy measurements confirm the hypothesis of a privileged interaction of phenyloxazolidinone-type inhibitors with the flavin cofactor of MAO. Additional sites of interaction with the protein core of MAO A are also examined with regard to the primary structure of the enzyme. As a result of this work, a model is proposed for the reversible inhibition of MAO A by befloxatone via long distance, reversible interactions with the flavin adenine dinucleotide (FAD) cofactor of the enzyme and with specific amino acids of the active site. This model is partially corroborated by experimental evidence and should be helpful in designing new potent inhibitors of monoamine oxidase.
Subject(s)
Monoamine Oxidase Inhibitors/pharmacology , Oxazoles/pharmacology , Animals , Crystallography, X-Ray , Hydrogen Bonding , Male , Molecular Conformation , Monoamine Oxidase Inhibitors/chemistry , Oxazoles/chemistry , Rats , Rats, Sprague-Dawley , Structure-Activity RelationshipABSTRACT
3-Bromobenzyloxy phenyloxy hydroxymethyl propanol was labelled with iodine-125. Labeling yield was approximately 92%. Using HPLC and an RP18 column, Iodo*MD (MW = 412) was obtained at no-carrier-added conditions (specific activity 125 Ci/mmole). Biochemical experiments were carried out in vitro and showed a Ki for MAO-B of 5.4 nM and of 5000 for MAO-A (RA/B = 926). Using ex vivo kinetic inhibition in rat (dose: 5 mg/kg p.o.), the results demonstrated a strong similarity of action with BromoMD and IodoMD, with an inhibition percentage that decreased with time (91% at 1 hour, 48% at 8 hours, 2% at 24 hours). The rat brain Iodo*MD concentration was maximal after the first pass and inhibition decreased slowly with time (T1/2 = 1.8 hours). Uptake and wash-out of Iodo*MD was studied on two-day-old rat astrocytes in culture. Half-times of uptake and efflux were respectively 2.5 minutes and 7.5 minutes. The use of metabolic inhibitors (KCN and Digoxin) suggested the absence of any active transport. Binding studies with various concentration of cold MD 360194 showed that at 10(-8) M the uptake decreased significantly. Rats were dissected at different times post i.v. injection (0-2 hours), and the principal organs and brain were obtained (the brain was separated into 7 pieces). Radioactivity was concentrated mainly in the liver (24.6 +/- 4%), fat (12.4 +/- 3.4%) and muscles (18.4 +/- 3%). In the brain the concentration was approximately 1.2 +/- 0.3% within 30 minutes post i.v. injection and 0.84 +/- 0.15% thereafter. The hypothalamus and striatum were two-fold more active than the cortex.(ABSTRACT TRUNCATED AT 250 WORDS)
Subject(s)
Astrocytes/diagnostic imaging , Brain/diagnostic imaging , Iodine Radioisotopes , Monoamine Oxidase Inhibitors , Phenyl Ethers , Propanols , Propylene Glycols , 1-Propanol/pharmacokinetics , Animals , Cells, Cultured , In Vitro Techniques , Isotope Labeling , Male , Phenyl Ethers/pharmacokinetics , Rats , Rats, Wistar , Tissue Distribution , Tomography, Emission-Computed, Single-PhotonABSTRACT
Experimental and theoretical physico-chemical methods were used to investigate the interaction between aryl-oxazolidinones and monoamine oxidase (MAO). Several arguments suggest that these compounds interact with the flavin adenine dinucleotide (FAD) cofactor of MAO. The calculation using ab initio molecular orbital methods of the electronic properties of flavin and befloxatone, a reversible inhibitor of MAO A, led to a description of the interaction between aryl-oxazolidinones and the cofactor of the enzyme. Structure activity relationship results revealed additional sites of interaction with the protein core of MAO A. As a result of this work, a model is proposed for the reversible inhibition of MAO by oxazolidinones via long distance, reversible interactions with the FAD cofactor of the enzyme.
Subject(s)
Models, Chemical , Monoamine Oxidase Inhibitors/chemistry , Monoamine Oxidase Inhibitors/pharmacology , Chemical Phenomena , Chemistry, Physical , Oxazoles/chemistry , Oxazoles/pharmacology , Structure-Activity Relationship , X-Ray DiffractionABSTRACT
It is usually postulated that the side chain attached to 17 beta position on the steroid nucleus of the cardioactive glycosides is a major determinant of their pharmacological activity. A new aminosteroid (LND 623) has been prepared. Despite the fact that the structural features quoted above are lacking, the product demonstrates a strong inotropic effect. LND 623 was active at the same range of concentrations as ouabain or digoxin. However, the maximum increase of the contractile force was significantly higher. The strength of the inotropic action is not modified in the presence of propranolol. The preliminary results suggest that the molecular requirements for the interaction of the drugs with the 'inotropic receptor' may be re-examined.
