**1. Introduction**

Brain tissue constitutes a small portion (~2%) of the total body mass [1]. With its high metabolic rate, brain tissue consumes approximately 20% of the total body oxygen [1–3]. Brain tissue rapidly metabolizes oxygen and accounts for about 25% of the body's glucose consumption, indicating a fast metabolism. Consequently, this leads to increased production of free radicals [3], making the brain tissue prone to oxidation. Hence, the presence of antioxidants becomes crucial in maintaining the redox balance in the brain tissue [4]. The high metabolic rate of brain tissue and its content

of polyunsaturated fatty acids render this organ vulnerable to oxidative damage [2]. Reactive oxygen species (ROS), produced at physiological concentrations in cells, play a role in processes such as neuromodulation, neurotransmission, and synaptic plasticity control. Additionally, brain tissue, being an organ with weak protective antioxidant mechanisms, is vulnerable to oxidative stress. It relies on high levels of antioxidants for maintaining the redox balance. Glutathione is reported to be the most abundant antioxidant in brain tissue, which is converted to vitamin C (ascorbic acid) (VC) subsequently [3]. Neurons rely on the maximal utilization of energy within the brain to maintain the neuronal membrane potential, as well as for neurotransmitter synthesis/release and axoplasmic transport [1]. In combating reactive oxygen species (ROS), neighboring astrocytes and glial cells serve as the primary defense line for neuronal cells. Neurons release ROS-oxidized vitamin C (VC) into the extracellular environment, where it is subsequently captured by adjacent glial cells. Glial cells then recycle VC, converting it back to its reduced form, ascorbate. This recycling mechanism enables the brain to sustain elevated levels of ascorbate. Ascorbate is predominantly localized within nerve cells, while glutathione is predominantly found in glial cells. The progression of aging or the development of neurodegenerative diseases often coincide with heightened oxidative stress levels and redox imbalance due to deficiencies in antioxidants such as VC [3]. The energy demands of different brain regions vary depending on neuronal functions. Age-associated cognitive decline, neurodegeneration, compromised oxygen metabolism, and impaired mitochondrial activities are linked to oxidative stress-mediated molecular pathways that contribute to neurodegeneration and associated behavioral changes [1]. The brain and neural tissues exhibit considerably higher levels of VC in comparison to other tissues [5].
