The Effect of Metals on Spatial Memory in a Transgenic Mouse Model of Alzheimer's Disease

The amyloid-beta protein (A beta) is a metalloprotein with affinity for the metal ions zinc (Zn), copper (Cu), and iron (Fe), which are found in high concentrations in the plaques of Alzheimer's disease (AD). Increasing attention is focused on the role of these metals in AD, and much of the evidence suggests a dyshomeostasis between these metal ions may significantly affect A beta aggregation and deposition in the brain. While the effect of these metals on A beta has been shown in vitro, there is less behavioral data supporting a direct role in cognitive impairment. In order to investigate the cognitive consequences of metal dyshomeostasis, we sought to directly increase metal levels in the brain by dietary means in a transgenic mouse model (Tg2576). We have now examined the effect of increased Zn (10 ppm) and Fe (10 ppm) levels in the drinking water in the Tg2576 mouse. Since increased dietary Zn can lead to Cu deficiency, a Zn group supplemented with copper was also examined (Zn (10 ppm) + Cu (0.025 ppm)). Significant increases in latency and fewer platform crossings on probe trials, which are considered measures of spatial memory impairment, were seen in both Fe and Zn supplemented transgenic mice, compared to those raised on lab water. No significant differences were seen between the Zn + Cu group and in transgenic mice raised on lab water. These data suggest that the negative consequences of Zn may be due to a reduction in copper levels and, therefore, an imbalance between these metal ions rather than a direct effect of increased Zn.