Trichothecenes

The trichothecenes are a family of more than 200 sesquiterpenoid mycotoxins sharing a tetracyclic 12,13-epoxytrichothec-9-ene skeleton. They inhibit eukaryotic protein synthesis by binding the ribosome's peptidyl transferase center and are among the most potently cytotoxic mycotoxins characterized. Two functional groupings dominate indoor and food relevance: macrocyclic (Type D) trichothecenes from Stachybotrys (satratoxins, roridins, verrucarins) and simple (Type A and B) trichothecenes from Fusarium (T-2, HT-2, deoxynivalenol, nivalenol) and Trichoderma / Memnoniella (trichodermin, trichodermol).

The shared skeleton is a 12,13-epoxide tetracyclic sesquiterpenoid. The four conventional groupings (A, B, C, D) differ by substitution pattern:

• Type A (e.g., T-2, HT-2, diacetoxyscirpenol): no carbonyl at C8; widely produced by Fusarium sporotrichioides and F. poae
• Type B (e.g., DON, NIV, fusarenone X): carbonyl at C8; the principal cereal trichothecenes from F. graminearum and F. culmorum
• Type C: second epoxide at C7,8; rare
• Type D: macrocyclic ring between C4 and C15; the satratoxins, roridins, and verrucarins from Stachybotrys and Myrothecium; the most cytotoxic class per unit mass

Trichothecenes bind the 60S ribosomal subunit at the peptidyl transferase center and inhibit eukaryotic protein synthesis^[1]. The mechanism is highly conserved across cell types, which underlies the family's broad cytotoxicity. Translation inhibition triggers the ribotoxic stress response: MAP kinase activation, transcription factor induction, and at higher exposures apoptosis. Immunosuppression at low doses and cytotoxicity at higher doses are both well-characterized. Mechanism description is cellular only; no clinical interpretation.

Production conditions vary sharply by genus and toxin type:

• Stachybotrys macrocyclic trichothecenes: require A_w ≥ 0.94 on cellulose substrate; sustained moisture over weeks; the species and toxin production are tightly linked to building water damage on drywall paper, ceiling tile, and gypsum board
• Fusarium simple trichothecenes: variable by species; field-spike (preharvest) production by F. graminearum favors cooler temperatures than vegetative growth; storage-period production differs
• Memnoniella simple trichothecenes: produced on cellulose substrates in tandem with Stachybotrys; literature on cardinal A_w for M. echinata is incomplete

Two distinct natural-occurrence patterns:

• Indoor water damage: macrocyclic trichothecenes from Stachybotrys and simple trichothecenes from Memnoniella on water-damaged cellulose substrates (drywall paper, ceiling tile, paper, cardboard)
• Cereal grains: DON, NIV, T-2, HT-2 from Fusarium in wheat, corn, barley; field-spike (preharvest) and storage contamination patterns differ

IARC carcinogen classification: not classified for most trichothecenes (insufficient data). Deoxynivalenol (DON) specifically is classified as Group 3 (not classifiable as to human carcinogenicity).

Trichothecenes are not directly biosynthetically related to other indoor mycotoxin families at this level. Within the family, the macrocyclic and simple variants are biosynthetic divergences from a shared tetracyclic precursor.