RESUMO
Thanks to their versatile magnetic and luminescence features, lanthanide complexes have gained a central position in biomedical imaging as magnetic resonance imaging (MRI) contrast agents and optical imaging probes. In addition, appropriate chemical design allows modification of the magnetic relaxation properties of GdIII complexes and the optical properties of visible- or near-infrared (NIR)-emitting lanthanide chelates upon interaction with various biomarkers, which makes them ideal candidates for the creation of responsive agents. In this Forum Article, we demonstrate such design principles as well as the difficulties encountered in the context of neurotransmitter (NT) detection. Lanthanide(III) complexes of a macrocyclic ligand incorporating a benzophenone chromophore and a monoazacrown ether (LnL3) have been synthesized as responsive probes to monitor amino acid NTs either in MRI (Ln = Gd) or in NIR optical detection (Ln = Nd or Yb). The parameters characterizing the water exchange and rotational dynamics of the gadolinium(III) complex were assessed by 17O NMR and 1H NMRD. In the presence of zwitterionic NTs, the inner-sphere water molecule is replaced by the carboxylate function of the NTs in the gadolinium(III) complex, leading to a decrease of the longitudinal relaxivity from 6.7 to 2-2.5 mM-1 s-1 (300 MHz and 37 °C). The apparent affinity constants range from Ka = 35 for γ-aminobutyric acid (GABA) to 80 M-1 for glycine and glutamate, and there is no selectivity with respect to hydrogen carbonate (Ka = 232; pH 7.4). The gadolinium(III) complex interacts with human serum albumin (HSA), resulting in a 60% increase in the relaxivity (20 MHz, 37 °C) in the absence of NTs. The HSA-bound complex, however, was revealed to be less responsive to NTs because of displacement of the GdIII-bound water by HSA, which was confirmed by the hydration number calculated from luminescence lifetimes of the HSA-bound europium(III) complex. The creation of an imaging agent suitable for NIR detection of NTs for an enhanced sensitivity in biological systems using the benzophenone (BP) moiety as the sensitizer of lanthanide luminescence was also attempted. Upon excitation at 300 nm of the BP chromophore in aqueous solutions of NdL3 and YbL3, characteristic NIR emissions of NdIII and YbIII were observed because of 4F3/2 â 4IJ (J = 9/2-13/2) and 2F5/2 â 2F7/2 transitions, respectively, indicating that this chromophore is a suitable antenna. Despite these promising results, luminescence titrations of NdIII and YbIII complexes with NTs were not conclusive because of chemical conversion of the ligand triggered by light, preventing quantitative analysis. The observed photochemical reaction of the ligand is strongly dependent on the nature of the lanthanide chelated; it is considerably slowed down in the presence of NdIII and EuIII.
RESUMO
A series of Gd(3+) complexes exhibiting a relaxometric response to zwitterionic amino acid neurotransmitters was synthesized. The design concept involves ditopic interactions 1)â between a positively charged and coordinatively unsaturated Gd(3+) chelate and the carboxylate group of the neurotransmitters and 2)â between an azacrown ether appended to the chelate and the amino group of the neurotransmitters. The chelates differ in the nature and length of the linker connecting the cyclen-type macrocycle that binds the Ln(3+) ion and the crown ether. The complexes are monohydrated, but they exhibit high proton relaxivities (up to 7.7â mM(-1) s(-1) at 60â MHz, 310â K) due to slow molecular tumbling. The formation of ternary complexes with neurotransmitters was monitored by (1) H relaxometric titrations of the Gd(3+) complexes and by luminescence measurements on the Eu(3+) and Tb(3+) analogues at pHâ 7.4. The remarkable relaxivity decrease (≈80 %) observed on neurotransmitter binding is related to the decrease in the hydration number, as evidenced by luminescence lifetime measurements on the Eu(3+) complexes. These complexes show affinity for amino acid neurotransmitters in the millimolar range, which can be suited to imaging concentrations of synaptically released neurotransmitters. They display good selectivity over non-amino acid neurotransmitters (acetylcholine, serotonin, and noradrenaline) and hydrogenphosphate, but selectivity over hydrogencarbonate was not achieved.
Assuntos
Complexos de Coordenação/metabolismo , Éteres de Coroa/metabolismo , Gadolínio/metabolismo , Compostos Macrocíclicos/metabolismo , Neurotransmissores/metabolismo , Aminoácidos/metabolismo , Sítios de Ligação , Complexos de Coordenação/síntese química , Complexos de Coordenação/química , Éteres de Coroa/síntese química , Éteres de Coroa/química , Gadolínio/química , Medições Luminescentes , Compostos Macrocíclicos/síntese química , Compostos Macrocíclicos/química , Espectroscopia de Ressonância Magnética , Modelos Moleculares , PotenciometriaRESUMO
Previous works have shown the interest of naturally fluorescent proflavine derivatives to label Abeta deposits in vitro. This study aimed to further characterize the properties of the proflavine 3-acetylamino-6-[3-(propargylamino)propanoyl]aminoacridine (COB231) derivative as a probe. This compound was therefore evaluated on human post-mortem and mice brain slices and in vivo in 18-month-old triple transgenic mice APPswe, PS1M146V and tauP301L (3xTgAD) mice presenting the main characteristics of Alzheimer's disease (AD). COB231 labelled amyloid plaques on brain slices of AD patients, and 3xTgAD mice at 10 and 0.1 µM respectively. However, no labelling of the neurofibrillary tangle-rich areas was observed either at high concentration or in the brain of fronto-temporal dementia patients. The specificity of this mapping was attested in mice using Thioflavin S and IMPY as positive controls of amyloid deposits. After intravenous injection of COB231 in old 3xTgAD mice, fluorescent amyloid plaques were detected in the cortex and hippocampus, demonstrating COB231 bloodbrain barrier permeability. We also controlled the cellular localization of COB231 on primary neuronal cultures and showed that COB231 accumulates into the cytoplasm and not into the nucleus. Finally, using a viability assay, we only detected a slight cytotoxic effect of COB231 (< 10%) for the highest concentration (100 µM).
Assuntos
Doença de Alzheimer/patologia , Imuno-Histoquímica/métodos , Placa Amiloide/diagnóstico , Proflavina/análogos & derivados , Aminacrina/análogos & derivados , Aminacrina/síntese química , Aminacrina/química , Animais , Autopsia , Encéfalo/patologia , Modelos Animais de Doenças , Feminino , Corantes Fluorescentes/síntese química , Corantes Fluorescentes/química , Humanos , Processamento de Imagem Assistida por Computador , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Microscopia de Fluorescência , Sensibilidade e Especificidade , Coloração e Rotulagem/métodosRESUMO
Molecular magnetic resonance imaging (MRI) approaches that detect biomarkers associated with neural activity would allow more direct observation of brain function than current functional MRI based on blood-oxygen-level-dependent contrast. Our objective was to create a synthetic molecular platform with appropriate recognition moieties for zwitterionic neurotransmitters that generate an MR signal change upon neurotransmitter binding. The gadolinium complex (GdL) we report offers ditopic binding for zwitterionic amino acid neurotransmitters, via interactions (i) between the positively charged and coordinatively unsaturated metal center and the carboxylate function and (ii) between a triazacrown ether and the amine group of the neurotransmitters. GdL discriminates zwitterionic neurotransmitters from monoamines. Neurotransmitter binding leads to a remarkable relaxivity change, related to a decrease in hydration number. GdL was successfully used to monitor neural activity in ex vivo mouse brain slices by MRI.
Assuntos
Meios de Contraste , Éteres de Coroa , Gadolínio , Imageamento por Ressonância Magnética/métodos , Neurotransmissores/metabolismo , Animais , Encéfalo/efeitos dos fármacos , Encéfalo/metabolismo , Fármacos do Sistema Nervoso Central/farmacologia , Meios de Contraste/síntese química , Meios de Contraste/química , Éteres de Coroa/síntese química , Éteres de Coroa/química , Feminino , Gadolínio/química , Imageamento Tridimensional/métodos , Camundongos , Neurotransmissores/química , Cloreto de Potássio/farmacologia , Espectroscopia de Prótons por Ressonância Magnética , Técnicas de Cultura de TecidosRESUMO
The complexation properties of H2Me-do2pa towards (nat)Bi(3+) reveal a rather fast formation of the [Bi(Me-do2pa)](+) complex, which is endowed with a very high thermodynamic stability (log K(BiL) = 34.2) and presents a single non-fluxional structure in solution. X-ray diffraction and solution NMR studies showed an octadentate binding of the ligand to the metal ion. The labelling of H2Me-do2pa with (213)Bi was performed and the resulting complex was stable in vitro, sustaining its use as an attractive alternative to taken here as a reference.
Assuntos
Bismuto/química , Quelantes/química , Complexos de Coordenação/química , Radioimunoterapia , RadioisótoposRESUMO
A series of proflavine derivatives for use to further image Aß amyloid deposits were synthesized and characterized. Aged 3xTg-AD (23 months old) mice hippocampus sections incubated with these derivatives revealed preferential labeling of amyloid plaques. Furthermore an in vitro binding study showed an inhibitory effect, although moderate, of these compounds on Aß(40) fibril formation. This study highlights the potential of proflavine as a molecular scaffold for designing new Aß imaging agents, its native fluorescence allowing in vitro neuropathological staining in AD damaged brain sections.
Assuntos
Corantes Fluorescentes/química , Placa Amiloide/patologia , Proflavina/química , Doença de Alzheimer/patologia , Peptídeos beta-Amiloides/antagonistas & inibidores , Peptídeos beta-Amiloides/metabolismo , Animais , Modelos Animais de Doenças , Camundongos , Camundongos Transgênicos , Microscopia de Fluorescência , Fragmentos de Peptídeos/antagonistas & inibidores , Fragmentos de Peptídeos/metabolismo , Proflavina/síntese químicaRESUMO
The preparation of the (1-naphthyl)(trifluoromethyl) O-carboxy-anhydride 1 and its use as a chiral derivatizing agent with several alpha-chiral primary amines are reported. The very large Delta delta(RS) values observed in (1)H NMR have been correlated with a marked preference of the corresponding alpha-hydroxy-amides for the eclipsed conformation. In comparison, the related O-methylated amides are shown to adopt staggered conformations, which substantiates the critical role of intramolecular hydrogen bonding in maximizing the anisotropic effect.