Metallothionein synthesis increased by Ninjin-yoei-to, a Kampo medicine protects neuronal death and memory loss after exposure to amyloid β1-42

It is possible that increased synthesis of metallothioneins (MTs), Zn2+-binding proteins is linked with the protective effect of Ninjin-yoei-to (NYT) on Zn2+ toxicity ferried by amyloid β1-42 (Aβ1-42).

The present study indicates that pre-administration of NYT diet for 2 days increases synthesis of MTs, which reduces intracellular Zn2+ toxicity ferried by extracellular Aβ1-42, resulting in protecting neuronal death in the dentate gyrus and memory loss after exposure to Aβ1-42.

Judging from the biological half-life (18-20 h) of MTs, the effective period of newly synthesized MT on capturing Zn2+ is estimated to be approximately 2 days. In the present paper, a diet containing 3% NYT was administered to mice for 2 days and then Aβ1-42 was injected into the lateral ventricle of mice.

MT level in the dentate granule cell layer was elevated 2 days after administration of NYT diet, while the administration reduced intracellular Zn2+ level increased 1 h after Aβ1-42 injection, resulting in rescuing neuronal death in the dentate granule cell layer, which was observed 14 days after Aβ1-42 injection. Furthermore, Pre-administration of NYT diet rescued object recognition memory loss via affected perforant pathway long-term potentiation after local injection of Aβ1-42 into the dentate granule cell layer of rats.