RESUMO
Doping agents are widely and illicitly distributed through the Internet. Analysis of these preparations is useful in order to monitor the availability of prohibited substances on the market, and more importantly to predict which substances are expected to be found in urine samples collected from athletes and to aid clinical and forensic investigations. Based on a close collaboration with the Norwegian police and the Norwegian custom authorities, the Norwegian Doping Control Laboratory has performed analyses of confiscated material suspected of containing doping agents. The analyses were performed using gas chromatography (GC) and liquid chromatography (LC) combined with mass spectrometry (MS). The majority (67%) of the analyzed black market products contained anabolic- androgenic steroids (AAS) as expected, whereas peptide- and protein-based doping substances were identified in 28% of the preparations. The Norwegian Doping Control Laboratory receives samples collected from recreational and elite athletes in addition to samples collected in clinical and forensic investigations. The findings in the seized material reflected the findings in the urine samples analyzed regarding the anabolic steroids. Thus, analyzing material seized in Norway may give a good indication of doping agents available on the local market.
Assuntos
Dopagem Esportivo , Tráfico de Drogas , Drogas Ilícitas/análise , Substâncias para Melhoria do Desempenho/urina , Detecção do Abuso de Substâncias/métodos , Anabolizantes/urina , Cromatografia Gasosa , Cromatografia Líquida , Espectrometria de Massas , Noruega , Peptídeos/urina , Esteroides/urina , Fatores de Tempo , UrináliseRESUMO
The dopamine transporter (DAT), a member of the neurotransmitter:sodium symporter family, mediates the reuptake of dopamine at the synaptic cleft. DAT is the primary target for psychostimulants such as cocaine and amphetamine. We previously demonstrated that cocaine binding and dopamine transport alter the accessibility of Cys342 in the third intracellular loop (IL3). To study the conformational changes associated with the functional mechanism of the transporter, we made cysteine substitution mutants, one at a time, from Phe332 to Ser351 in IL3 of the background DAT construct, X7C, in which 7 endogenous cysteines were mutated. The accessibility of the 20 engineered cysteines to polar charged sulfhydryl reagents was studied in the absence and presence of cocaine or dopamine. Of the 11 positions that reacted with methanethiosulfonate ethyl ammonium, as evidenced by inhibition of ligand binding, 5 were protected against this inhibition by cocaine and dopamine (S333C, S334C, N336C, M342C and T349C), indicating that reagent accessibility is affected by conformational changes associated with inhibitor and substrate binding. In some of the cysteine mutants, transport activity is disrupted, but can be rescued by the presence of zinc, most likely because the distribution between inward- and outward-facing conformations is restored by zinc binding. The experimental data were interpreted in the context of molecular models of DAT in both the inward- and outward-facing conformations. Differences in the solvent accessible surface area for individual IL3 residues calculated for these states correlate well with the experimental accessibility data, and suggest that protection by ligand binding results from the stabilization of the outward-facing configuration. Changes in the residue interaction networks observed from the molecular dynamics simulations also revealed the critical roles of several positions during the conformational transitions. We conclude that the IL3 region of DAT undergoes significant conformational changes in transitions necessary for both cocaine binding and substrate transport.
Assuntos
Cocaína/metabolismo , Proteínas da Membrana Plasmática de Transporte de Dopamina/metabolismo , Inibidores da Captação de Dopamina/metabolismo , Dopamina/metabolismo , Clonagem Molecular , Cisteína/genética , Cisteína/metabolismo , Proteínas da Membrana Plasmática de Transporte de Dopamina/química , Células HEK293 , Humanos , Conformação Proteica , Transporte Proteico , Reagentes de Sulfidrila/farmacologia , Tropanos/metabolismo , Tropanos/farmacologia , Tiramina/metabolismo , Zinco/farmacologiaRESUMO
OBJECTIVES: Loss of glutamate from cardiomyocytes during ischaemia may aggravate ischaemia-reperfusion injury in open heart surgery. This may be due to reversal of excitatory amino acid transporters (EAATs). However, the expression of such transporters in cardiomyocytes is ambiguous and quantitative data are lacking. Our objective was to study whether EAATs were expressed in the rat heart and to study whether blocking of transporter operation during cardiac ischaemia could be beneficial. METHODS: We used TaqMan real-time PCR and immunoisolation followed by western blotting to unequivocally identify EAAT subtypes in rat hearts. We used a novel high-affinity non-transportable competitive inhibitor, named LL-TBOA [(2S,3S)-3-(3-(6-(6-(2-(2-(2-(2-(2-aminoethoxy)ethoxy)-ethoxy)ethoxy) acetamido)hexanamido)- hexanamido)-5-(4-(trifluoromethyl)benzamido)benzyloxy) aspartic acid], to block EAAT-mediated transport during global ischaemia and reperfusion of isolated rat hearts. RESULTS: Rat hearts expressed EAAT subtypes 1 and 3, while subtypes 2 and 4 were not detected. Hearts were isolated and perfused with 1.6 µM LL-TBOA for 5 min before 30 min of induced global ischaemia and 60 min of reperfusion (n = 8). Control hearts were perfused either with the solvent dimethylsulfoxide 3.5 mM (n = 7) or with no pretreatment (n = 8). Infarct size was evaluated by triphenyl tetrazolium chloride (TTC) staining. LL-TBOA reduced infarct size from 33 ± 14 to 20 ± 5% (mean ± SD) (P = 0.015). Dimethylsulfoxide alone had no effect (35 ± 2%). Reperfusion arrhythmias were reduced by LL-TBOA (P = 0.009), but not by dimethylsulfoxide alone. CONCLUSION: Rat hearts express EAAT1 and EAAT3, but the mRNA levels are, respectively, â¼ 25 and 200 times lower than in the brain. Addition of LL-TBOA has a beneficial effect against ischaemia-reperfusion injury.