Metallothionein is a Potential Therapeutic Strategy for Amyotrophic Lateral Sclerosis

Lou Gehrig's disease, a synonym of amyotrophic lateral sclerosis, is an adult-onset lethal neurodegenerative disorder. Irrespective of extensive efforts to elucidate the pathogenesis of the disease and searches for therapies, no favorable pharmacotherapeutic strategies have yet to be proposed. In a popular rodent model of ALS, G93A SOD1 strain of mouse, intracellular copper conditions were geared toward copper accumulation inside cells, resulting in an acceleration of oxidative stress and apoptotic process. Disruption of intracellular copper homeostasis was common to transgenic mice expressing human mutant SOD1s. In this review, the novel hypothesis that disruption of intracellular copper homeostasis could be involved in the development of the disease was introduced. Based upon the hypothesis, therapeutic outcomes of agents that are capable of correcting and/or modifying intracellular copper homeostasis are described. Administration of ammonium tetrathiomolybdate, a selective intracellular copper chelator, delayed onset, slowed progression, and prolonged survival of a rodent model of the disease (G93A SOD1 mice). Metallothionein is a low molecular weight, cysteine-rich, metal-binding cytoplasmic protein that has beneficial properties in detoxification of toxic heavy metals, homeostatic regulation of intracellular essential trace elements, including copper, antioxidant, and antiapoptotic roles. In animal experiments of the G93A SOD1 mice, an increase of metallothionein proteins by means of induction by exercise or dexamethasone, genetic overexpression, or intraperitoneal administration, all resulted in a preferable outcome. The therapeutic effects were not inferior to those of approved drugs for ALS in humans. These observations suggest that metallothionein could be worth investigating the therapeutic potential in clinical use. Keywords: Metallothionein, intracellular Cu homeostasis, SOD1 mutation, cysteine111, Cu chaperons, Cu secretion.