Sketches of some mycotoxins produced by indoor fungi.
BY JOHN NEVILLE AND KRISTINE KURTZ
Mycotoxins are included in a range of secondary metabolites
produced by growing fungi that have varying degrees of toxicity. Significant deficiencies exist in the scientific knowledge of
the health effects of mycotoxins. Limited information is available regarding acute toxic responses of various mycotoxins
from animal studies. The rate of production of an individual
mycotoxin, or even the ability of a specific species to produce a
particular mycotoxin, is subject to a wide number of environmental variables. And although environmental stimuli for mycotoxin production have been well characterized for certain
fungi, this information is still needed for other common indoor
fungi. The presence of a specific species of fungi growing in a
building does not automatically equate to either the production
of a mycotoxin or exposure of a building occupant.
Presently, more than 1,000 mycotoxins are reported in the literature. New mycotoxins are being found as research continues.
Current knowledge of mycotoxin health effects is primarily focused on ingestion of contaminated foods. Research pertaining to
health effects of mycotoxin exposure from breathing spores and
other fungal structures in contaminated buildings is currently
underway in Canada, Europe, the United States, and Japan.
Following are brief descriptions of several mycotoxins.
Aflatoxin was discovered in 1960 when an outbreak of “Turkey
X Disease” occurred in England, which resulted in over 100,000
turkey deaths. Aflatoxin was found to be the common suspect
of death and originated from animal feed that had mold-conta-minated Brazilian peanut meal. The aflatoxin-producing mold
was Aspergillus flavus. The “Turkey X Disease” was so severe
that it initiated investigations in mycotoxin research.
Aflatoxin has been shown to produce liver cancer in many
animals, including calves, pigs, rabbits, cats, rats, sheep, and
various birds. Aflatoxins are acutely toxic, carcinogenic, mutagenic, and teratogenic. Of all the different types of aflatoxins,
aflatoxin B1 is the most toxic. Other fungi that produce aflatoxin include Aspergillus parasiticus and Apergillus nomius.
Aflatoxin has been found in cereal grains, cotton, and milk.
Chaetoglobosins are produced by Chaetomium globosum (the
most common Chaetomium species found indoors). Chaetoglo-bosin A, B, and C are cytotoxic to HeLa cells. They inhibit cytoplasmic cleavage and, thereby, cause cells to be polynucleate.
Toxicity information on the chaetoglobosins is sparse.
Citrinin is a yellow mycotoxin that was first isolated in 1931
from a culture of Penicillium citrinum. In 1951, yellow-colored
rice imported from Thailand to Japan was contaminated with P.
citinum that was producing citrinin. Citrinin and Ochratoxin A
often co-occur. It is thought that citrinin caused nephrotoxico-sis in pigs in Denmark, Ireland, Norway, and Sweden. It is also
believed that citrinin was associated with Balkan Endemic
Nephropathy, a human kidney disease (see Ochratoxin A). It is
also implicated in causing renal damage, vasodilation,
bronchial constriction, and increased muscular tone. Citrinin is
produced by various Aspergillus and Penicillum species.
Cyclopiazonic acid was first isolated from Penicillium cyclopium.
This mycotoxin is suspected to be the cause of kodua poisoning
in people of India who consumed kodo millet seed. Cyclopiazonic acid caused necrosis in the spleen and lymph nodes of
dogs. It is believed to be a neurotoxin and to cause necrosis in
the liver, spleen, and kidneys. Cyclopiazonic acid is produced
by various Aspergillus and Penicillum species. Toxicity properties of cyclopiaznic acid have not been thoroughly appraised.
Griseofulvin was first isolated from a Penicillium species in
1939. Griseofulvin is thought to be potentially hepatotoxic,
neurotoxic, tumorgenic, and teratogenic. Griseofulvin may
block mitotic division in cells within bone marrow, intestinal
lining, and tumors. It is produced by Memnoniella echinata and
various Penicillium species. Dechologriseofulvin and epi-dechlorogriseofulvin were first isolated from Memnoniella echinata in 1996. This is the first record for griseofulvins to be
isolated from other fungi outside of Penicillium. Toxicity properties of griseofulvins have not been thoroughly investigated.
In 1983, mycophenolic acid was the first fungal metabolite to
be purified and crystallized. Mycophenolic acid is produced by
various Penicillium species. In one study, 35 people received
oral doses of 2.4 to 7.2 g of mycophenolic acid daily for 52 to
104 weeks. Reactions included cramps, diarrhea, and nausea.
Mycophenolic acid may have some anti-cancer properties. This
compound is considered to be a mycotoxin because it displays
toxic effects on mice and rats. Mycophenolic acid toxicity has not
been thoroughly assessed but is believed to be relatively low.