Pyridoxine Inhibits Depolarization-Evoked Glutamate Release in Nerve Terminals from Rat Cerebral Cortex: a Possible Neuroprotective Mechanism?

Abstract

Pyridoxine (vitamin B 6 ) protects neurons against neurotoxicity. An excessive release of glutamate is widely considered to be one of the molecular mechanisms of neuronal damage in several neurological diseases. We investigated whether pyridoxine affected glutamate release in rat cerebral cortex nerve terminals (synaptosomes). Pyridoxine inhibited the release of glutamate that was evoked by exposing synaptosomes to the K ϩ channel blocker 4-aminopyridine (4-AP), and this phenomenon was concentration-dependent. Inhibition of glutamate release by pyridoxine was prevented by the vesicular transporter inhibitor bafilomycin A1, or by chelating intraterminal Ca 2ϩ , but was insensitive to DL-threo-␤-benzyl-oxyaspartate, a glutamate transporter inhibitor. Pyridoxine did not alter the resting synaptosomal membrane potential or 4-AP-mediated depolarization. Examination of the effect of pyridoxine on cytosolic [Ca 2ϩ ] revealed that diminution of glutamate release could be attributed to a reduction in voltage-dependent Ca 2ϩ influx. Consistent with this, the pyridoxine-mediated inhibition of glutamate release was completely prevented by blocking the Nand P/Q-type Ca 2ϩ channels, but not by blocking intracellular Ca 2ϩ release or Na ϩ /Ca 2ϩ exchange. Furthermore, the pyridoxine effect on 4-AP-evoked glutamate release was abolished by the protein kinase C (PKC) inhibitors bisindolylmaleimide I (GF109203X) or bisindolylmaleimide IX (Ro318220), and pyridoxine significantly decreased the 4-AP-induced phosphorylation of PKC, PKC␣, and myristoylated alanine-rich C kinase substrate. Together, these results suggest that pyridoxine inhibits glutamate release from rat cortical synaptosomes, through the suppression of presynaptic voltage-dependent Ca 2ϩ entry and PKC activity.

Treatment of oxaliplatin-induced peripheral neuropathy by intravenous mangafodipir

“…Vitamin B6 is known for its ability to maintain normal neurological functions and for its neuroprotective activity (15). In addition, given that mangafodipir is endowed with SOD-, catalase-, and glutathione reductase-like (GR-like) properties, it can target multiple steps of the ROS cascade by detoxifying superoxide anions and hydrogen peroxide and by restoring GSH (16,17).…”

Berberine Inhibits the Release of Glutamate in Nerve Terminals from Rat Cerebral Cortex

“…Glutamate release was assayed by on-line fluorometry [22], [23]. Pelleted synaptosomes were resuspended at a protein concentration of 0.5mg/ml in HBM containing 16 µM bovine serum albumin (BSA) and incubated in a stirred and thermostatted cuvette at 37 °C in a Perkin-Elmer LS-55 spectrofluorimeter (PerkinElmer Life and Analytical Sciences, Waltham, Mass., USA.).…”

“…The [Ca 2+ ] C was assayed by on-line fluorimetry as described previously [22]. Synaptosomes (0.5mg/ml) were resuspended in 1ml of HBM containing 0.1mM CaCl 2 and loaded with 5 µM fura-2-acetoxymethyl ester (Fura-2-AM) for 30min at 37 °C.…”

Idebenone inhibition of glutamate release from rat cerebral cortex nerve endings by suppression of voltage-dependent calcium influx and protein kinase A

“…Initial rates of glutamate release associated with depolarization may be underestimated as corrections for this delay were not incorporated (Rawls et al 1999). Actually, this online enzyme-linked fluorescent detection from synaptosomes has long been considered an approach particularly appropriate to investigate the presynaptic regulation of neurotransmitter release by drugs (Nicholls and Sihra 1986;Yang and Wang 2009). In brief, synaptosomes (0.5 mg/ml) were resuspended in HBM that contained 16 μM BSA and incubated in an LS-50B spectrofluorimeter (Perkin-Elmer Life Sciences) at 37°C with stirring.…”