In the pathophysiology of
Alzheimer's disease (AD), the deposition of
amyloid β
protein (Aβ) is associated with oxidative stress, leading to
cognitive impairment and neurodegeneration.
Betaine (glycine betaine or trimethylglycine), known as an osmolyte and methyl donor in mammalian cells, has been reported to suppress the proinflammatory response and oxidative stress in the kidneys, but the effects of
betaine on
brain diseases remain to be determined. Here, to investigate the effects of
betaine treatment on
cognitive impairment and the increase in oxidative stress in the brain of an AD animal model, we performed a novel object recognition test and measured the
malondialdehyde (MDA; a marker of oxidative stress) levels in the frontal cortex and hippocampus of mice intracerebroventricularly injected with Aβ25-35, an active fragment of Aβ.
Betaine prevented
cognitive impairment as well as increases of the cortical and hippocampal MDA levels in Aβ25-35-injected mice. Of note,
NNC 05-2090, a selective inhibitor of
betaine/
GABA transporter-1 (GAT2/BGT-1), reduced the preventive effects of
betaine on Aβ25-35-induced
cognitive impairment without affecting the increased MDA levels in the brain of Aβ25-35-injected mice. As
betaine is used as a substrate of GAT2/BGT-1, these results suggest that
betaine is transported through GAT2/BGT-1 and prevents
cognitive impairment in Aβ25-35-injected mice, but GAT2/BGT-1 function is not required for the
antioxidant effects of
betaine.