Effect of ethanol on brain metallothionein in transgenic mice

Three isoforms of metallothionein (MT-I, -II, and -III) have been detected in mice brain but little is known on their inducibility. Therefore, changes in MT levels in brain were investigated in MT-I overexpressing transgenic mice (MT-I*) and wild type mice of the same strain (C57BL/6J) after oral administration of ethanol.

All experimental mice were given 4 g/kg of ethanol by gastric intubation. In addition, to account for the stress of animal handling, both groups of mice (MT-I* and C57) were given distilled water by gastric intubation and used as controls. At different times after ethanol/water treatment, the mice were killed and the brains were dissected into six regions. The total amount of MT in the brain and different regions were measured by a cadmium-binding assay. Zinc and copper were measured by atomic absorption spectrometry. The results were compared with untreated mice and corresponding control mice.

In C57BL/6J mice, the whole brain MT was increased by approximately 1.29-fold at 12 hr and approximately 1.27-fold at 18 hr after ethanol administration compared with basal levels. In MT-I* male mice, the whole brain MT was increased by approximately 1.64-fold at 12 hr and approximately 1.62-fold at 18 hr after ethanol administration, whereas in MT-I* female mice, it was increased by approximately 1.57-fold at 12 hr and approximately 1.61-fold at 18 hr after ethanol administration. Although the zinc and copper levels in the whole brain were not altered, the zinc level in the cerebellum at 12 and 18 hr in male and female MT-I* mice were increased, and zinc levels in the hippocampus of male MT-I* mice were increased at 12 and 18 hr after ethanol treatment.

Acute or chronic ethanol administration can cause generation of oxygen free radical and oxidative stress to the brain. The generation of free radicals is thought to be one of the causes of cell injury after ethanol administration. The mechanism of induction of MT in brain after oral ethanol administration may be associated with oxidative stress caused by ethanol or its metabolites, and can be considered as a protective mechanism against ethanol toxicity.