Glutathione (GSH) is a major intracellular thiol-containing antioxidant that plays an important role in protecting neurons from oxidative stress. In addition, the thiol group of GSH can act as a major Zn²⁺ chelator and maintain Zn²⁺ homeostasis in neurons. This evidence suggests that neuronal GSH levels may be a key factor in neuronal survival after stroke. A therapeutic role for exogenous glutathione has been demonstrated in ischemic stroke rats.

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Overview of GSH

GSH – the main low molecular weight aminothiol in cells – is a tripeptide made up of -glutamyl, cysteinyl, and glycine. It is involved in many biological processes, including antioxidants that guard protein thiol groups against oxidative damage and the removal of reactive oxygen species (ROS).

GSH kills harmful ROS (superoxide radicals, hydroxyl radicals, peroxynitrites) either by itself or in conjunction with enzymes. If GSH levels go down, ROS builds up, and calcium peaks, programmed cell death takes place, not apoptosis. Cell redox reactions require a healthy cell's level of GSH to be in equilibrium with the ratio of reduction to oxidation. Furthermore, GSH contributes to endothelial functions by defending endothelial cells from oxidative injury and controlling proliferation in endothelial repair and wound healing.

In the brain, GSH is only ever found in a reduced form at high concentrations (between 1-3mM), so it functions as a storehouse for the glutamate neurotransmitter. But it is found far less, in blood plasma, as low as 3 μM, and mostly as an oxidized disulfide.

Antioxidant Role of GSH in Oxidative Stress Induced by Cerebral Ischemia

Oxidative stress is a major mediator of cerebral ischemia/reperfusion-induced injury. On the one hand, GSH directly scavenges ROS. On the other hand, GSH acts as a substrate for various glutathione peroxidases to eliminate ROS. In these reactions, glutathione is oxidized to glutathione disulfide (GSSG), which is reduced back into GSH via glutathione reductase. Inflammatory oxidative damage from ischemia/reperfusion has been reported to decrease brain endogenous GSH levels and to be lowered by exogenous GSH or glutathione monoethyl ester treatment after ischemia.

Fig. 1 Mechanisms of GSH protection against hippocampal neuron damage following brain ischemia. (Higashi, et al., 2021)

GSH Protects Neurons from Ischemia-induced Disruption of Intracellular Zn²⁺ Homeostasis

While most Zn²⁺ in the brain is bound to proteins, a smaller portion is concentrated in presynaptic vesicles, especially in hippocampal glutamatergic neurons. The intracellular levels of Zn²⁺ in the hippocampus are low during the natural course of things, but under ischemia and reperfusion Zn²⁺ gets released and pools in hippocampal neurons, causing neurodegeneration. Zn²⁺ chelators have been protective against this accumulation. GSH defends neurons against ischemia-induced Zn²⁺ build-up by binding Zn²⁺ with its thiol group. Resupplementing GSH with N-acetyl cysteine (NAC) stops the buildup of Zn²⁺ and prevents neurodegeneration. So, GSH regulates intracellular Zn²⁺ homeostasis and offers neuroprotection as well as antioxidant effects. But the accumulation of too much Zn²⁺ can silence some of the most important enzymes in the GSH redox cycle, and compromise the protective function of GSH.

GSH Exerts a Therapeutic Effect on Ischemic Stroke by Interacting With Intrastriatal Dopamine

Dopamine (a precursor of catecholamines, norepinephrine, and epinephrine) is a neurotransmitter and signaling molecule produced by the parasympathetic ganglia and involved in a multitude of sensorimotor processes in the brain. In recent years, dopamine boosters have been injected to aid stroke recovery. Exogenous GSH has been found to lower inflammatory factors, inhibit oxidative stress, and prevent microglia activation by increasing dopamine in the striatum, thus acting as a treatment for ischemic stroke.

Fig. 2 Effects of exogenous dopamine on the levels of GSH and its related substances. (Wang, et al., 2022)

EAAC1-mediated Neuronal GSH Synthesis Protects Blood-Brain Barrier Integrity

GSH levels are controlled primarily by excitatory amino acid carrier 1 (EAAC1), a transmitter of cysteine, a GSH substrate, in neurons. We now know more than ever that EAAC1 deficiencies enhance ischemia-induced hippocampal damage via deregulated Zn²⁺ homeostasis and oxidative stress, and that daily fluctuations in EAAC1 modulate hippocampus responses to ischemia-induced neuronal cell death. Therefore, intracellular GSH physiology through EAAC1 is vital to the survival of neurons in cerebral ischemia and could be a therapeutic target.

1. Higashi, Y., et al. (2021). Protective role of glutathione in the hippocampus after brain ischemia. International journal of molecular sciences, 22(15), 7765.
2. Wang, H., et al. (2022). Exogenous glutathione exerts a therapeutic effect in ischemic stroke rats by interacting with intrastriatal dopamine. Acta Pharmacologica Sinica, 43(3), 541-551.