Can metal and mycotoxin exposures worsen amyloid and tau proteostasis?

At age 77, amyloid/tau biology and proteostasis are clinically relevant, but the proposed exposure-to-neurodegeneration pathway remains primarily mechanistic rather than established in people.

Experimental and mechanistic evidence

• Certain metals can induce oxidative-stress endpoints in experimental systems. Gadolinium oxide nanoparticles increased reactive oxygen species and lipid peroxidation in human endothelial cells; repeated gadolinium-contrast exposure in rats increased lipid peroxidation and reduced superoxide-dismutase activity. Effects depend substantially on the metal, formulation, dose, and model.
• Gliotoxin has a credible pro-oxidant mechanism: glutathione-dependent disulfide redox cycling can deplete glutathione and generate reactive oxygen species. Cell effects vary by concentration and cell type.
• Manganese reduced LC3-II autophagic flux, lysosomal abundance/catalytic capacity, and mitochondrial respiration in primary mouse astrocytes; restoring autophagy partly rescued respiration. Cadmium impaired autophagic flux in PC12 cells and primary neurons. These findings support disruption of cellular clearance systems, but do not directly establish mitophagy or other mitochondrial protein-quality-control defects.
• Gliotoxin inhibited 20S proteasomal peptide-hydrolyzing activity and, among epipolythiodioxopiperazines, inhibited 26S protein degradation through Rpn11 deubiquitinase targeting.

Relevance to amyloid and tau

• Autophagy–lysosome function clears intracellular amyloid-β and is particularly important for aggregated/phosphorylated tau; proteasomes preferentially contribute to clearance of soluble tau and intracellular amyloid-β. Therefore, impaired clearance plausibly favors protein accumulation.
• In a cross-sectional study of 128 people with mild cognitive impairment, higher cadmium was associated with lower CSF Aβ42/40 and higher tau-related biomarkers, but this cannot establish causation.

Bottom line

• Metal and mycotoxin exposures can generate oxidative stress and can disrupt selected protein-clearance pathways experimentally. It is biologically plausible that this could worsen amyloid/tau proteostasis, but exposure-driven Alzheimer pathology in humans has not been demonstrated.