Citrinin

Citrinin is a polyketide-derived yellow nephrotoxic pigment produced by several Penicillium species, most notably P. citrinum (the namesake) and P. expansum, and by Aspergillus terreus. It frequently co-occurs with ochratoxin A in cereal-grain contamination because the producer-organism overlap is substantial, and the two toxins target overlapping renal pathways.

Citrinin is a pentaketide-derived quinone methide with a yellow chromophore that gives the molecule its name and the colored appearance of substrates supporting its production. The reactive quinone methide is the structural feature underlying its biological activity. It can alkylate cellular nucleophiles, particularly thiols and amines.

Citrinin is a nephrotoxin. The molecule disrupts mitochondrial function in renal tubular cells, induces oxidative stress, and at higher doses produces apoptosis of tubular epithelium. Potential nephrotoxic synergy with ochratoxin A in co-exposure scenarios is documented in animal studies. Mechanism description is cellular only.

Production occurs at A_w ≥ 0.80, broader than the OTA production threshold for most producer organisms, which means citrinin is often produced at conditions slightly below those that favor OTA. Temperature optimum is 20–30 °C. Substrates include stored cereal grains, red yeast rice (from Monascus species, outside the indoor mycology context), and cheese rinds.

Stored cereals, fermented foods (Asian red yeast rice products via Monascus purpureus), cheese rinds. Often co-occurs with OTA in cereal contamination.

IARC carcinogen classification: Group 3 (not classifiable as to human carcinogenicity)^[2].

Ochratoxin A. Frequently co-produced; nephrotoxic synergy documented. See ochratoxin A.