RESUMO
The efflux of purine nucleobases and their nucleosides from the rat brain was investigated using the brain efflux index (BEI) method. Calculated BEI values showed that purine nucleobases had very rapid initial efflux after the intracerebral injection, which was followed by the slower efflux due to the intracellular trapping of labelled molecules and confirmed by the capillary depletion technique. The efflux of ribonucleosides was much slower than the efflux of nucleobases and the structure of the sugar moiety seemed to be important, since a significant difference in the efflux velocity between ribo- and deoxyribonucleosides was observed. The results of self- and cross-inhibition studies suggested that the efflux of test molecules was saturable and that purines shared the same transport system on the abluminal side of the blood-brain barrier.
Assuntos
Barreira Hematoencefálica/efeitos dos fármacos , Encéfalo/efeitos dos fármacos , Proteínas de Transporte/efeitos dos fármacos , Nucleosídeos de Purina/metabolismo , Purinas/metabolismo , Adenosina/sangue , Adenosina/líquido cefalorraquidiano , Animais , Barreira Hematoencefálica/fisiologia , Encéfalo/metabolismo , Radioisótopos de Carbono/metabolismo , Proteínas de Transporte/fisiologia , Desoxirribonucleosídeos/sangue , Desoxirribonucleosídeos/líquido cefalorraquidiano , Espaço Extracelular/efeitos dos fármacos , Espaço Extracelular/metabolismo , Guanosina/sangue , Guanosina/líquido cefalorraquidiano , Hipoxantina/sangue , Hipoxantina/líquido cefalorraquidiano , Injeções Intraventriculares , Inosina/sangue , Inosina/líquido cefalorraquidiano , Nucleosídeos de Purina/sangue , Nucleosídeos de Purina/líquido cefalorraquidiano , Ratos , Ratos WistarRESUMO
The aim of this study was to analyse the uptake of the synthetic nucleoside tiazofurin and glucoso-linker-tiazofurin conjugate (GLTC) into rat C6 glioma cells in vitro. Results indicated that C6 cells accumulated [3H] tiazofurin slowly with time and that accumulation was reduced by the presence of unlabelled GLTC in the medium which implies that GLTC competes with tiazofurin for transport sites. Uptake of [14C] 2 deoxy-glucose into these cells was very rapid and was not affected by the presence of unlabelled GLTC. To prove the true rate of uptake, the HPLC analysis of cellular extract was performed. After the 360 min of incubation in medium that contained 0.15 mM of tiazofurin, the sum of the concentration of tiazofurin and it's metabolite thiazole-adenine dinucleotide (TAD) in the cells was a total of approximately 4.8% of the amount added to each flask. After the same period of incubation in medium which contained 0.15 mM of GLTC, the sum of concentrations of conjugate, free tiazofurin and TAD represented less than 1/3 of the total concentration measured after the incubation with free tiazofurin and was further reduced in the presence of dipyridamole. Therefore, it can be concluded that GLTC shows some affinity for the nucleoside transporter, but the actual rate of uptake is low.
