Can toxicant and mycotoxin exposure increase reverse T3?

Exposure to environmental toxicants and mycotoxins can initiate a systemic cascade that profoundly alters peripheral thyroid hormone metabolism, shifting the balance toward the inactive metabolite reverse T3 (rT3).

Toxicant-Induced Inflammation and Oxidative Stress

• Cellular Pathogenesis: Exposure to mycotoxins such as ochratoxin A (OTA), gliotoxin, and fumonisins (FB1) generates substantial reactive oxygen and nitrogen species (ROS/RNS) and depletes cellular glutathione.
• Signaling Cascades: These toxicants suppress the master antioxidant Nrf2 pathway while promoting NF-κB nuclear translocation. This triggers the release of potent pro-inflammatory cytokines, including TNF-α, IL-6, and IL-1β, alongside lipid peroxidation (measured via malondialdehyde accumulation).

Deiodinase Shift and rT3 Accumulation

• Enzymatic Dysregulation: Systemic inflammation and oxidative stress directly alter the activity of peripheral iodothyronine deiodinases. Elevating pro-inflammatory cytokines (especially IL-6 and TNF-α) suppresses hepatic DIO1 expression and Type 1 deiodinase (D1) activity. This dual inhibition reduces both the conversion of thyroxine (T4) to active triiodothyronine (T3) and the clearance of rT3.
• Upregulation of D3: Simultaneously, oxidative stress and inflammatory mediators upregulate Type 3 deiodinase (D3) expression, which actively drives the conversion of T4 into rT3 and degrades active T3, leading to rT3 accumulation.

Clinical Implications

• Non-Thyroidal Illness Syndrome (NTIS): This shift mirrors the classic pathophysiology of NTIS. In human clinical models, the experimental infusion of recombinant IL-6 or TNF-α successfully replicates this profile, causing rapid decreases in T3 alongside a distinct, measurable rise in rT3 levels.

Bottom line

• Mycotoxin and toxicant exposure drives oxidative stress and inflammatory cytokines (IL-6, TNF-α), which suppress D1 and induce D3 deiodinase activity. This dual enzymatic shift impairs active T3 production and halts rT3 clearance, directly shifting thyroid metabolism toward elevated reverse T3.