Vitamin B12 deficiency results in severe oxidative stress, leading to memory retention impairment in Caenorhabditis elegans

Oxidative stress is implicated in various human diseases and conditions, such as a neurodegeneration, which is the major symptom of vitamin B12 deficiency, although the underlying disease mechanisms associated with vitamin B12 deficiency are poorly understood. Vitamin B12 deficiency was found to significantly increase cellular H2O2 and NO content in Caenorhabditis elegans and significantly decrease low molecular antioxidant [reduced glutathione (GSH) and L-ascorbic acid] levels and antioxidant enzyme (superoxide dismutase and catalase) activities, indicating that vitamin B12 deficiency induces severe oxidative stress leading to oxidative damage of various cellular components in worms. An NaCl chemotaxis associative learning assay indicated that vitamin B12 deficiency did not affect learning ability but impaired memory retention ability, which decreased to approximately 58% of the control value. When worms were treated with 1 mmol/L GSH, L-ascorbic acid, or vitamin E for three generations during vitamin B12 deficiency, cellular malondialdehyde content as an index of oxidative stress decreased to the control level, but the impairment of memory retention ability was not completely reversed (up to approximately 50%). These results suggest that memory retention impairment formed during vitamin B12 deficiency is partially attributable to oxidative stress.