João Frade

Publications of João Frade

• Glutamate induces release of glutathione from cultured rat astrocytes--a possible neuroprotective mechanism?

  Authors: João Frade, Simon Pope, Maike Schmidt, Ralf Dringen, Rui Barbosa, Jennifer Pocock, João Laranjinha, Simon Heales

  Journal of neurochemistry. 06/2008; 105(4):1144-52.

  Glutamate is the major excitatory amino acid of the mammalian brain but can be toxic to neurones if its extracellular levels are not tightly controlled. Astrocytes have a key role in the protectionGlutamate is the major excitatory amino acid of the mammalian brain but can be toxic to neurones if its extracellular levels are not tightly controlled. Astrocytes have a key role in the protection of neurones from glutamate toxicity, through regulation of extracellular glutamate levels via glutamate transporters and metabolic and antioxidant support. In this study, we report that cultures of rat astrocytes incubated with high extracellular glutamate (5 mM) exhibit a twofold increase in the extracellular concentration of the tripeptide antioxidant glutathione (GSH) over 4 h. Incubation with glutamate did not result in an increased release of lactate dehydrogenase, indicating that the rise in GSH was not because of membrane damage and leakage of intracellular pools. Glutamate-induced increase in extracellular GSH was also independent of de novo GSH synthesis, activation of NMDA and non-NMDA glutamate receptors or inhibition of extracellular GSH breakdown. Dose-response curves indicate that GSH release from rat astrocytes is significantly stimulated even at 0.1 mM glutamate. The ability of astrocytes to increase GSH release in the presence of extracellular glutamate could be an important neuroprotective mechanism enabling neurones to maintain levels of the key antioxidant, GSH, under conditions of glutamate toxicity.

• Nitric oxide monitoring in hippocampal brain slices using electrochemical methods.

  Authors: Ana Ledo, Rui M Barbosa, João Frade, João Laranjinha

  Methods in enzymology. 02/2002; 359:111-25.

• Nitric oxide in brain: diffusion, targets and concentration dynamics in hippocampal subregions.

  Authors: Ana Ledo, João Frade, Rui M Barbosa, João Laranjinha

  Molecular aspects of medicine. 25(1-2):75-89.

  Nitric oxide (NO(*)) is a diffusible regulatory molecule involved in a wide range of physiological and pathological events. At the tissue level, a local and temporary increase in NO(*) concentrationNitric oxide (NO(*)) is a diffusible regulatory molecule involved in a wide range of physiological and pathological events. At the tissue level, a local and temporary increase in NO(*) concentration is translated into a cellular signal. From our current knowledge of biological synthesis and decay, the kinetics and mechanisms that determine NO(*) concentration dynamics in tissues are poorly understood. Generally, NO(*) mediates its effects by stimulating (e.g., guanylate cyclase) or inhibiting (e.g., cytochrome oxidase) transition metal-containing proteins and by post-translational modification of proteins (e.g., formation of nitrosothiol adducts). The borderline between the physiological and pathological activities of NO(*) is a matter of controversy, but tissue redox environment, supramolecular organization and compartmentalisation of NO(*) targets are important features in determining NO(*) actions. In brain, NO(*) synthesis in the dependency of glutamate NMDA receptor is a paradigmatic example; the NMDA-subtype glutamate receptor triggers intracellular signalling pathways that govern neuronal plasticity, development, senescence and disease, suggesting a role for NO(*) in these processes. Measurements of NO(*) in the different subregions of hippocampus, in a glutamate NMDA receptor-dependent fashion, by means of electrochemical selective microsensors illustrate the concentration dynamics of NO(*) in the sub-regions of this brain area. The analysis of NO(*) concentration-time profiles in the hippocampus requires consideration of at least two interrelated issues, also addressed in this review. NO(*) diffusion in a biological medium and regulation of NO(*) activity.