Abstract
AimPrevious research recognizes that NADPH can produce reduced glutathione (GSH) as a coenzyme and produce ROS as a substrate of NADPH oxidase (NOX). Besides, excessive activation of glutamate receptors results in mitochondrial impairment. The study aims at spelling out the effects of NADPH and Mito-apocynin, a NOX inhibitor which specifically targets the mitochondria, on the excitotoxicity induced by Kainic acid (KA) and its mechanism.MethodsThe in vivo neuronal excitotoxicity model was constructed by stereotypically injecting KA into the unilateral striatum of mice. Administrated NADPH (i.v, intravenous) 30 min prior and Mito-apocynin (i.g, intragastric) 1 day prior, respectively, then kept administrating daily until mice were sacrificed 14 days later. Nissl staining measured the lesion of striatum and survival status of neurons. Cylinder test of forelimb asymmetry and the adhesive removal test reflected the behavioral deficit caused by neural dysfunction. Determined Total superoxide dismutase (T-SOD), malondialdehyde (MDA), and GSH indicated oxidative stress. Western blot presented the expression levels of LC3-II/LC3-I, SQSTM1/p62, TIGAR, and NOX4. Assessed oxygen consumption rate using High-Resolution Respirometry. In vitro, the MitoSOX Indicator reflected superoxide released by neuron mitochondria. JC-1 and ATP assay Kit were used to detect mitochondrial membrane potential (MMP) and energy metabolism, respectively.ResultsIn this study, we have successfully established excitotoxic model by KA in vivo and in vitro. KA induced decreased SOD activity and increased MDA concentration. KA cause the change of LC3-II/LC3-I, SQSTM1/p62, and TIGAR expression, indicating the autophagy activation. NADPH plays a protective role in vivo and in vitro. It reversed the KA-mediated changes in LC3, SQSTM1/p62, TIGAR, and NOX4 protein expression. Mito-apocynin inhibited KA-induced increases in mitochondrial NOX4 expression and activity. Compared with NADPH, the combination showed more significant neuroprotective effects, presenting more neurons survive and better motor function recovery. The combination also better inhibited the over-activated autophagy. In vitro, combination of NADPH and Mito-apocynin performed better in restoring mitochondria membrane potential.ConclusionIn summary, combined administration of NADPH and NOX inhibitors offers better neuroprotection by reducing NADPH as a NOX substrate to generate ROS. The combined use of NADPH and Mito-apocynin can better restore neurons and mitochondrial function through autophagy pathway.
Highlights
Glutamate is an important excitatory neurotransmitter in the central nervous system and plays a crucial role in a variety of neural processes including cognition, learning and memory (Barker-Haliski and White, 2015; Reiner and Levitz, 2018)
NADPH has two biological roles in the regulation of redox: the first is as a pivotal component of cellular antioxidant system; the second is to act as a substrate for NADPH oxidase (NOX), which plays a key role in many biological and pathological processes by producing ROS
It is necessary to investigate whether NOX inhibitors such as apocynin can be used in combination with NADPH to better protect neurons from kainic acid (KA)-induced excitotoxicity
Summary
Glutamate is an important excitatory neurotransmitter in the central nervous system and plays a crucial role in a variety of neural processes including cognition, learning and memory (Barker-Haliski and White, 2015; Reiner and Levitz, 2018). NADPH supplementation significantly increased TIGAR expression, inhibited ROS levels and autophagy/lysosomal pathways, and protected neurons from KA-induced excitotoxicity in vivo and in vitro (Liu et al, 2020). NOX1, NOX2, and NOX4 are the major subtypes of NOX in the central system that play a major role in brain injury and neurodegenerative diseases. They can produce superoxide anion or hydrogen peroxide from NADPH as substrate (Liu et al, 2020). It is necessary to investigate whether NOX inhibitors such as apocynin can be used in combination with NADPH to better protect neurons from KA-induced excitotoxicity
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