Electrophysiological evaluation of extracellular spermine and alkaline pH on synaptic human GABAA receptors

Polyamines have fundamental roles in brain homeostasis as key modulators of cellular excitability. Several studies have suggested alterations in polyamine metabolism in stress related disorders, suicide, depression, and neurodegeneration, making the pharmacological modulation of polyamines a highly appealing therapeutic strategy. Polyamines are small aliphatic molecules that can modulate cationic channels involved in neuronal excitability. Previous indirect evidence has suggested that polyamines can modulate anionic GABA_A receptors (GABA_ARs), which mediate inhibitory signaling and provide a direct route to reduce hyperexcitability. Here, we attempted to characterize the effect that spermine, the polyamine with the strongest reported effect on GABA_ARs, has on human postmortem native GABA_ARs. We microtransplanted human synaptic membranes from the dorsolateral prefrontal cortex of four cases with no history of mental or neurological disorders, and directly recorded spermine effects on ionic GABA_ARs responses on microtransplanted oocytes. We show that in human synapses, inhibition of GABA_ARs by spermine was better explained by alkalization of the extracellular solution. Additionally, spermine had no effect on the potentiation of GABA-currents by diazepam, indicating that even if diazepam binding is enhanced by spermine, it does not translate to changes in functional activity. Our results clearly demonstrate that while extracellular spermine does not have direct effects on human native synaptic GABA_ARs, spermine-mediated shifts of pH inhibit GABA_ARs. Potential spermine-mediated increase of pH in synapses in vivo may therefore participate in increased neuronal activity observed during physiological and pathological states, and during metabolic alterations that increase the release of spermine to the extracellular milieu.

CD34+ cell positive selection from mobilized peripheral blood by an indirect immunomagnetic method: effect of the type of mobilization and assessment of tumor depletion ability

Mobilized peripheral blood has been shown to be a suitable source of hematopoietic progenitor cells for autologous transplantation in oncologic patients. However, tumor cell contamination can potentially occur, although to a lesser extent than in the bone marrow. CD34+ cell positive selection has been developed as a system for the ex vivo purging of remaining tumor cells when used in mobilized peripheral blood. This method has shown a lower purification potential than that obtained with bone marrow or cord blood. The reason for this is not clear, but different groups have tried to improve the purity and yield of the positive selection on mobilized peripheral blood by predepletion of nonlymphoid cell populations, since they can induce nonspecific binding. The present study was designed to test an indirect immunomagnetic CD34+ cell selection method to make it reproducible, feasible, and effective for purging mobilized peripheral blood. Twenty-nine samples from mobilized peripheral blood were tested. The median starting CD34+ percentage was 0.8 (0.3%-4.2%), and the median final purity was 87% (32.7%-99.7%), with a median yield of 44.8% (15%-83.5%). The highest purity was reproducibly achieved when the starting percentage of CD34+ cells was higher than 0.65% (median purity 93.7, range 81%-99.7%, CV 6%) on samples obtained from patients primed with chemotherapy alone or chemotherapy plus recombinant human granulocyte-colony stimulating factor. No relation was found between the content of contaminating nucleated cells and the final CD34+ cell purity. This method showed a depletion capacity, assessed by PCR on samples contaminated with K562 leukemic cells, of about 3 logs. These results indicate that this indirect immunomagnetic method can produce high purity CD34+ cell fractions from mobilized peripheral blood with a high efficiency of tumor depletion.

High-performance liquid chromatographic separation of caffeine, theophylline, theobromine and paraxanthine in rat brain and serum

Caffeine and its metabolites theophylline, theobromine and paraxanthine have been determined in rat brain and serum samples by high-performance liquid chromatography with ultraviolet detection. The recovery, 85-103%, allowed quantification by external standard methods. The variability was found to be less than 3 and 7% for intra-day and inter-day assays, respectively. The detection limit, 1.57 ng of methylxanthines on column, allowed the determination of 62.5 ng/g or ml in biological material. Rats treated with 30 mg/kg caffeine (subcutaneously) were sacrificed at different times (1, 6, 12 and 24 h). Higher concentrations of methylxanthines (specially paraxanthine) were observed in the striatum than in the rest of the brain, and it was also observed that the clearance of methylxanthines was faster in serum than in brain structures.