Metallothionein Is Inappropriate to Neutralise Excess Hepatic Copper in Wilson’s Disease

Mutations in ATP7B impair biliary copper excretion and copper–ceruloplasmin release, causing hepatic copper overload in Wilson’s disease (WD). Metallothionein (MT), a key intracellular copper buffering agent, is overexpressed in WD liver. We evaluated the diagnostic significance of MT immunostaining in explanted livers from hepatic and neurological WD, including untreated cases and those receiving short- versus long-term chelation. Histochemical and immunohistochemical analyses were performed. Our results show that MT overexpression progresses to irreversible accumulation. Sustained copper-induced redox cycles promote MT polymerisation, aggregation, and resistance to proteolysis, accompanied by oxidative stress, lysosomal dysfunction, and hepatocellular injury. MT localises to bile canaliculus membranes, hepatocyte nuclei, lysosomes, and mesenchymal cells, suggesting discrete roles in disease mechanisms. Given the persistent MT accumulation despite prolonged chelation, we propose that MT fails to neutralise excess copper in WD; instead, polymerised MT traps Cu+, depleting the cytosolic copper pool destined to ATP7B-mediated ceruloplasmin loading, plasma secretion, and biliary export. Accordingly, MT dysregulation emerges as central to WD pathogenesis and supports MT immunohistochemistry as a sensitive diagnostic adjunct. These findings provide a rationale for developing more efficient chelators that mobilise hepatic copper stores without causing MT build-up, potentially improving outcomes.