Less Is More: A Physiological Dose of Vitamin B12 Enhances Neural Recovery Compared to a High Dose in an H₂O₂-Stressed SH-SY5Y Neural-Like Cell Model

Vitamin B12 (VitB12) plays a crucial role in neural homeostasis, and a high dose is preferred as treatment to support recovery from neural impairments. However, a significant knowledge gap remains regarding its dose-dependent effects, particularly in its influence on cellular recovery following neural damage. To address this, we utilized retinoic acid-differentiated SH-SY5Y cells, as an in vitro neural model, where we induced neural damage using hydrogen peroxide (H2O2), followed by recovery in either a physiological or high dose of VitB12. Our findings reveal that a physiological dose of VitB12 promotes more efficient recovery by enhancing cell survival and promoting neurite elongation after H2O2 insult, compared to a high dose. Recovery with a physiological dose of VitB12 was associated with an early-stage (2 h) activation of antioxidant defenses, suggesting a quicker cellular response to oxidative stress than the high dose. At later stages (24 h), recovery with a physiological dose of VitB12 enhances mitochondrial metabolic activity and morphodynamics, alongside promoting lipid remodeling and increased formation of lipid droplets (LDs). These lipid-related processes may collectively contribute to mitigating oxidative damage and reinforcing cellular resilience during recovery. Overall, our study highlights that a physiological dose of VitB12 not only activates antioxidant defenses earlier than the high dose but also induces later-stage lipid remodeling, potentially supporting neural recovery and homeostasis.