Membrane potential and pH-dependent accumulation of decynium-22 (1,1'-diethyl-2,2'-cyanine iodide) flourencence through OCT transporters in astrocytes (original) (raw)
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Frontiers in Pharmacology
Organic cation transporters (OCTs) are expressed in the mammalian brain, kidney, liver, placenta, and intestines, where they facilitate the transport of cations and other substrates between extracellular fluids and cells. Despite increasing reliance on ectothermic vertebrates as alternative toxicology models, properties of their OCT homologs transporting many drugs and toxins remain poorly characterized. Recently, in zebrafish (Danio rerio), two proteins with functional similarities to human OCTs were shown to be highly expressed in the liver, kidney, eye, and brain. This study is the first to characterize in vivo uptake to the brain and the high-affinity brain membrane binding of the mammalian OCT blocker 1-1′-diethyl-2,2′cyanine iodide (decynium-22 or D-22) in zebrafish. Membrane saturation binding of [3H] D-22 in pooled zebrafish whole brain versus mouse hippocampal homogenates revealed a high-affinity binding site with a KD of 5 ± 2.5 nM and Bmax of 1974 ± 410 fmol/mg protein in...
European Journal of Neuroscience, 1996
From studies on sympathetically innervated peripheral tissues it is well known that both neuronal and nonneuronal transport systems contribute to the inactivation of released monoamine transmitters. The close proximity between synapses and glia cell processes in the CNS leads to the so far unresolved question whether non-neuronal transporters are involved in the inactivation of centrally released monoamine transmitters such as noradrenaline, dopamine and 5-hydroxytryptamine. 1-Methyl-4-phenylpyridinium (MPPf) is a prototypical substrate of the extraneuronal monoamine transporter (uptake2). [3H]MPP+ was found to accumulate in various human glioma cell lines. [3H]MPP+ transport was characterized in more detail in HTZ146 human glioma cells. The K values of various compounds for the inhibition of initial rates of [3H]MPP+ transport into HTZ146 cells were closely correlated with the known K, values for the inhibition of the extraneuronal monoamine transporter (P < 0.001, f = 0.991, n = 7). The rank order of inhibitory potencies was decynium 22 > corticosterone > cyanine 863 > Omethylisoprenaline > quinine > clonidine > quinidine. [3H]MPPf accumulation was investigated not only in various CNS tumour cell lines but also in primary cultures of human astrocytes and rat cerebral cortex slices. In all tested experimental systems, accumulation was sensitive to cyanine-related inhibitors of the extraneuronal monoamine transporter. These findings suggest that the extraneuronal monoamine transporter exists in glia cells. Furthermore, it was shown that MPP' is able to make use of the extraneuronal monoamine transporter not only to enter but also to leave glia cells. This finding suggests that the extraneuronal monoamine transporter may play a key role in the mechanism of 1-rnethyl4-phenyl-l,2,3,6tetrahydropyridine (MPTP) neurotoxicity.
Life Sciences, 1997
Affinities of dopamine (DA) analogs to both granular and plasma membrane uptake transporters were measured in vitro by inhibition of [sH]DA uptake in bovine chromaffin granule ghosts and C6 glial cells transfected with cDNA for the rat presynaptic dopamine transporter, respectively. Five amines were studied: DA, 6-fluorodopamine (6FDA), m-tyramine (MTA), 6-fluoro-m-tyramine (6FMTA), and p-fluoromethylene-m-tyramine (FMMTA). Direct uptake of tsF labeled 6FDA and 6FMTA was also measured in the chromaffin granule system and compared with [sH]DA uptake. Results show that the transporter affinities of 6FDA and MTA were similar to that of DA in both transport systems while affinities of 6FMTA and FMMTA were lower. Furthermore while the direct uptake of DA and FDA in chromaffin granules were essentially identical and significantly reserpineinhibitable, the direct uptake of 6FMTA was about 15-fold less and only minimally sensitive to reserpine pretreatment.
Monoamine transporters: vulnerable and vital doorkeepers
Progress in molecular biology and translational science, 2011
Transporters of dopamine, serotonin, and norepinephrine have been empirically used as medication targets for several mental illnesses in the last decades. These protein-targeted medications are effective only for subpopulations of patients with transporter-related brain disorders. Since the cDNA clonings in early 1990s, molecular studies of these transporters have revealed a wealth of information about the transporters' structure-activity relationship (SAR), neuropharmacology, cell biology, biochemistry, pharmacogenetics, and the diseases related to the human genes encoding these transporters among related regulators. Such new information creates a unique opportunity to develop transporter-specific medications based on SAR, mRNA, DNA, and perhaps transporter trafficking regulation for a number of highly relevant diseases including substance abuse, depression, schizophrenia, and Parkinson's disease.
Journal of Nuclear Medicine, 2010
PET provides a noninvasive means to evaluate the functional integrity of the presynaptic monoaminergic system in the living human brain. Methods: In this study, a novel 18 F-labeled tetrabenazine derivative, 18 F-(1)fluoropropyldihydrotetrabenazine ( 18 F-AV-133), was used for the noninvasive assessment of the vesicular monoamine transporters type 2 (VMAT2) in 17 Parkinson disease (PD) patients and 6 healthy controls. The binding potential (BP) of 18 F-AV-133 was calculated using Logan graphical analysis. Voxel-based and volume-of-interest-based analyses of BP images were performed to examine brain regional reductions in VMAT2 density in PD. Results: VMAT2 BP was decreased by 81% in the posterior putamen, 70% in the anterior putamen, and 48% in the caudate nucleus of PD patients. Voxelbased analysis demonstrated VMAT2 reductions in the striatum and mid brain of PD patients. Furthermore, VMAT2 BPs in the caudate nuclei significantly correlated with the clinical severity of PD. Conclusion: These findings indicate that the novel 18 Flabeled ligand 18 F-AV-133 can sensitively detect monoaminergic terminal reductions in PD patients. Studies with 18 F-AV-133 may allow the presymptomatic identification of individuals with disorders characterized by degeneration of dopaminergic nigrostriatal afferents.
Journal of nuclear medicine : official publication, Society of Nuclear Medicine, 1999
The reproducibility of (+/-)-alpha-[11C] dihydrotetrabenazine (DTBZ) measures in PET was studied in 10 healthy human subjects, aged 22-76 y. The scan-to-scan variation of several measures used in PET data analysis was determined, including the radioactivity ratio (target-to-reference), plasma-input Logan total distribution volume (DV), plasma-input Logan Bmax/Kd and tissue-input Logan Bmax/Kd values. The radioactivity ratios, plasma-input Bmax/Kd and tissue-input Bmax/Kd all have higher reliability than plasma-input total DV values. In addition, measures using the occipital cortex as the reference region have higher reliability than the same measures using the cerebellum as the reference region. Our results show that DTBZ is a reliable PET tracer that provides reproducible in vivo measurement of striatal vesicular monoamine transporter density. In the selection of reference regions for DTBZ PET data analysis, caution must be exercised in circumstances when DTBZ binding in the occipi...
Synapse, 1999
Drug development in psychopharmacology has adhered to the unwritten precept that compounds targeting monoamine transporters must contain an amine nitrogen in the molecular structure. A series of non-amine-bearing aryloxatropanes that are potent inhibitors of the dopamine transporter (DAT) challenged this precept. In the present study, we investigated the brain distribution of a selective, high-affinity DAT non-amine, [ 3 H]tropoxene (2-carbomethoxy-3,4dichloro-3-aryl-8-oxabicyclo[3.2.1] octene), which binds to the DAT in monkey striatum. The autoradiographic distribution of [ 3 H]tropoxene was conducted in tissue sections of rhesus (Macaca mulatta) monkey brain. Highest accumulation of the radioligand was detected in the putamen and caudate nucleus, with significant levels also observed in the nucleus accumbens and substantia nigra. Moderate to low levels of [ 3 H]tropoxene binding were noted in the hypothalamus, amygdala, ventral tegmental area, and thalamus. The distribution of [ 3 H]tropoxene was restricted to brain regions previously identified as expressing DAT, and the relative densities of [ 3 H]tropoxene binding sites in various brain regions corresponded to those observed with other selective monoamine radioligands for the DAT. This is the first report to demonstrate that transporter-selective compounds that bear no amine nitrogen in their structure bind selectively to brain regions rich in the transporter. The results support our conclusion that an amine nitrogen is not necessary for compounds to bind to monoamine transporters and distribute in brain according to the known distribution of transporters. The findings provide further incentives to investigate the pharmacological potential of transport inhibitors lacking an amine nitrogen in the molecular structure.