The Role of overdose Folic Acid in Promoting Neuroinflammation, Oxidative Stress, and Apoptosis in SOD1-G93A Mice

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative condition that involves the targeted degeneration of motor neurons. The precise pathogenetic mechanisms are still largely unclear. In this study, we utilized the SOD1-G93A mouse model of ALS to investigate the effects of folic acid (FA), an important factor involved in homocysteine metabolism. Our results indicated that a little FA prolong the lifespan of the SOD1-G93A mice and medium and high dose FA significantly shortened the lifespan of the SOD1-G93A mice. Furthermore, we observed that overdose FA significantly elevated inflammation levels in the cerebellum, as evidenced by increased concentrations of tumor necrosis factor-α (TNF-α), Interleukin-1β (IL-1β), Cluster of Differentiation 68 (CD68), Cluster of Differentiation 86 (CD86), and Monocyte Chemoattractant Protein-1 (MCP-1), facilitating microglial activation. The low dose FA were the opposite of the overdose FA. Additionally, high dose FA increased the levels of phosphorylated p65 (p-p65)/p65, thereby promoting the NF-κB signaling pathway. Conversely, high dose FA inhibited the expression of total superoxide dismutase (T-SOD) while increasing the level of malondialdehyde (MDA) in the cerebellum; these effects were not observed in muscle tissue. Moreover, high dose FA elevated the levels of Bax2/Bcl-2. Concurrently, high dose FA induced increased apoptosis in SOD1-G93A mice, as demonstrated by TUNEL staining. Notably, the brain iron content of SOD1-G93A mice remained unchanged following FA treatment. These findings provide evidence that overdose FA supplementation may exert pro-inflammatory effects by promoting the NF-κB pathway, oxidative stress, and apoptosis in the context of ALS.