Does mycophenolic acid suppress lymphocyte proliferation and can zearalenone disrupt estrogen receptor signaling?

Mycophenolic acid and zearalenone act through distinct, well-characterized biological pathways: the former is an immunosuppressive antimetabolite, whereas the latter is an estrogen-receptor-active mycotoxin.

Mycophenolic acid: immunosuppressive mechanism

• Mycophenolic acid is a selective, reversible inhibitor of inosine monophosphate dehydrogenase (IMPDH), particularly the IMPDH2 isoform relevant to activated lymphocytes.
• In isolated human lymphocytes, 2.5 µM reduced IMPDH activity by approximately 60%, and concentrations ≥10 µM reduced activity by about 85%.
• IMPDH inhibition restricts de novo guanine-nucleotide production, leading to guanine-nucleotide depletion and reduced DNA synthesis. Activated T and B cells are particularly affected because of their dependence on this pathway during proliferation.
• In phytohaemagglutinin-stimulated human T cells, proliferation was inhibited with an estimated IC50 of about 0.36 µM (0.113 mg/L), with roughly 95% inhibition reported at 2 mg/L. Thus, enzyme inhibition and suppression of lymphocyte expansion are directly linked pharmacodynamic effects.

Zearalenone: estrogen-receptor-mediated endocrine activity

• Zearalenone binds both estrogen receptor (ER) α and ERβ and produces functional, receptor-dependent signaling. It behaves as an ERα agonist and has mixed/partial agonist–antagonist activity at ERβ.
• Because ERs are ligand-activated nuclear transcription factors, this receptor modulation can alter estrogen-responsive gene expression and endocrine signaling.
• Biotransformation materially affects potency: α-zearalenol is substantially more estrogenically active than parent zearalenone—reported in some reporter assays as approximately 70-fold more potent, with an EC50 near that of estradiol—whereas β-zearalenol is weaker.
• The EFSA group tolerable daily intake is 0.25 µg/kg body weight/day, incorporating zearalenone and modified forms according to relative estrogenic potency.

Bottom line

• Both statements are strongly supported: mycophenolic acid suppresses activated lymphocyte proliferation through IMPDH inhibition and guanine-nucleotide depletion, while zearalenone can disrupt endocrine signaling through direct, subtype-dependent ERα/ERβ activity.