Glutamate increases toxicity of inorganic lead in GT1-7 neurons: partial protection induced by flunarizine

Abstract

Recent studies point to an interaction between the glutamatergic neurotransmitter system and inorganic lead (Pb) neurotoxicity. Pb (1-100 microM) evoked cytotoxicity over the period of 72 h in mouse hypothalamic GT1-7 neurons. Glutamate (0.1 or 1 mM) on its own did not have any effect on cell viability. However, 1 mM glutamate clearly increased Pb-induced cell death at 48 and 72 h. Although flunarizine (0.1-10 microM), an antagonist of L- and T-type voltage-sensitive calcium channels (VSCCs), partially protected from the cytotoxicity induced by co-exposure to Pb (10 or 100 micro M) and glutamate (1 mM), it had no protective effect on cytotoxicity induced by Pb alone. The flunarizine-induced protection was dependent on time and observed only at 48 h. Neither verapamil, an antagonist of L-type VSCCs, nor DIDS, an inhibitor of anion exchange, at non-toxic concentrations (0.1-10 microM) had any effect on cytotoxicity induced by Pb alone or together with glutamate at any studied time point. Co-exposure to Pb and glutamate also resulted in more prominent production of reactive oxygen species (ROS) than either of the compounds alone. Interestingly, we observed an increase in intracellular glutathione (GSH) levels in cells exposed to micromolar concentrations of Pb. Glutamate decreased the levels of intracellular GSH and also partially reduced the Pb-induced increase in GSH levels. These results suggest that the interaction of glutamate and Pb results in increased neuronal cell death via mechanisms that involve an increase in ROS production, a decrease in intracellular GSH defense against oxidative stress and probably T-type VSCCs.

Clinical perspective on oxidative stress in sporadic amyotrophic lateral sclerosis

“…In experimental models, combined exposure to glutamate and lead as compared to either agent alone increased neuronal cell death via mechanisms involving an elevation in the production of oxygen radicals and a decrease in intracellular GSH defenses against oxidative stress (217). Exposure of mouse embryonic (day 12) spinal cord and dorsal root ganglion cells to low levels of paraquat, exogenous glutamate, and thermal stress, both singly and in combination (218), revealed that paraquat administered alone was associated with cell death in a dose-dependent manner, an effect that was multiplied by heat shock.…”

Comparative evaluation of N-acetylcysteine (NAC) and N-acetylcysteine amide (NACA) on glutamate and lead-induced toxicity in CD-1 mice

“…The toxicity of glutamate generally involves increased Ca 2+ influx, increased generation of ROS, mitochondrial dysfunction, and oxidative stress which, in turn, may cause apoptosis (Chandra et al ., 2000). In a nutshell, glutamate excitotoxicity, lead neurotoxicity, and oxidative stress are considered to be related phenomena causing neuronal damage (Naarala et al ., 1995; Loikkanen et al ., 2003). …”

Copper Enhances Zinc-Induced Neurotoxicity and the Endoplasmic Reticulum Stress Response in a Neuronal Model of Vascular Dementia

“…However, both glutamate and Zn 2+ are neurotoxic, distinguishing the effects of Zn 2+ and glutamate by using neuronal cells that possess glutamate receptors has proved difficult. GT1-7 cells either lack or possess low levels of ionotropic glutamate receptors and do not exhibit glutamate toxicity (Mahesh et al, 1999 ; Loikkanen et al, 2003 ). Furthermore, we found that GT1-7 cells are much more sensitive to Zn 2+ than other neuronal cells, including PC-12 cells, B-50 cells (a neuroblastoma cell line), or primary cultured neurons of the rat cerebral cortex or hippocampus (Koyama et al, 2011 ).…”