Sterigmatocystin
Encyclopedia
Sterigmatocystin is a poison
of the type dermatoxin
, from the fungi genus Aspergillus
. It appears on crusts of cheese
with mold.
, ethanol
, acetonitrile
, benzene
, and chloroform
. It reacts with hot ethanolic KOH and is methylated by methyl sulphate and methyl iodide. Methanol or ethanol in acid produces dihydroethoxysterigmatocystin.
, mutagen
, and teratogen. It is less acutely toxic to rodents and monkeys but appears to be slightly more toxic to zebra fish. The LD50 in mice is in excess of 800 mg/kg. The 10 day LD50 in Wistar rats is 166 mg/kg in males, 120 mg/kg in females, and 60-65 mg/kg for ip. administration in males. The ip. 10 day LD50 for vervet monkeys is 32 mg/kg.
Chronic symptoms include induction of hepatomas in rats, pulmonary tumours in mice, renal lesions and alterations in the liver and kidneys of African Green monkeys. Rats fed 5-10 mg/kg of sterigmatocystin for two years showed a 90% incidence of liver tumours. It has been suggested that sterigmatocystin is about 1/10 as potent a carcinogen as aflatoxin B1.
Toxic effects of sterigmatocystin-fed laboratory animals have included kidney and liver damage and diarrhoea. Skin and hepatic tumours are induced in rats by dermal application. Cattle exhibiting bloody diarrhoea, loss of milk production and in some cases death were found to have ingested feed containing Aspergillus versicolor and high levels of sterigmatocystin of about 8 mg/kg. The acute toxicity, carcinogenicity, and metabolism of sterigmatocystin has been compared with those for aflatoxin and several other hepatotoxic mycotoxins.
The IARC-classification
of sterigmatocystin is group 2B, which means it is likely carcinogenic to humans. In practice, the risk is quite low however, as this substance only appears on cheese crusts with mold, and because of that the chance of daily exposure is very low. A molded crust is best not to be consumed in whole, but after removing the crust, the cheese can still be consumed; Sterigmatocystin is a different kind of mold than that which appears on cheese itself, which can simply be removed before further consumption.
and 4% aqueous potassium chloride
. Methods for detection using TLC are not very sensitive having a limit of detection in the range 20-50 microgrammes/kg. TLC plates must be sprayed with aluminium chloride and heated. Analytical methods for the determination of sterigmatocystin have been reported using HPLC but again these are not very sensitive because of lack of UV absorbance or fluorescence, although a post column reaction with aluminium chloride has been used to increase sensitivity. More recently, methods using HPLC linked with atmospheric pressure ionisation mass spectrometric detection have been developed for foods such as cheese, bread and corn products.
Poison
In the context of biology, poisons are substances that can cause disturbances to organisms, usually by chemical reaction or other activity on the molecular scale, when a sufficient quantity is absorbed by an organism....
of the type dermatoxin
Dermatoxin
A dermatoxin is a toxic chemical that damages skin, mucous membranes, or both, often leading to necrosis. Dermatoxins can be drugs, natural chemicals, or artificial chemicals....
, from the fungi genus Aspergillus
Aspergillus
Aspergillus is a genus consisting of several hundred mold species found in various climates worldwide. Aspergillus was first catalogued in 1729 by the Italian priest and biologist Pier Antonio Micheli...
. It appears on crusts of cheese
Cheese
Cheese is a generic term for a diverse group of milk-based food products. Cheese is produced throughout the world in wide-ranging flavors, textures, and forms....
with mold.
Introduction
Sterigmatocystin is a toxic metabolite structurally closely related to the aflatoxins (compare general fact sheet number 2), and consists of a xanthone nucleus attached to a bifuran structure. Sterigmatocystin is mainly produced by the fungi Aspergillus nidulans and A. versicolor. It has been reported in mouldy grain, green coffee beans and cheese although information on its occurrence in foods is limited. It appears to occur much less frequently than the aflatoxins, although analytical methods for its determination have not been as sensitive until recently, and so it is possible that small concentrations in food commodities may not always have been detected. Although it is a potent liver carcinogen similar to aflatoxin B1, current knowledge suggests that it is nowhere near as widespread in its occurrence. If this is the true situation it would be justified to consider sterigmatocystin as no more than a risk to consumers in special or unusual circumstances. A number of closely related compounds such as o-methyl sterigmatocystin are known, and some may also occur naturally.Chemical and Physical Properties
Sterigmatocystin crystallises as pale yellow needles and is readily soluble in methanolMethanol
Methanol, also known as methyl alcohol, wood alcohol, wood naphtha or wood spirits, is a chemical with the formula CH3OH . It is the simplest alcohol, and is a light, volatile, colorless, flammable liquid with a distinctive odor very similar to, but slightly sweeter than, ethanol...
, ethanol
Ethanol
Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...
, acetonitrile
Acetonitrile
Acetonitrile is the chemical compound with formula . This colourless liquid is the simplest organic nitrile. It is produced mainly as a byproduct of acrylonitrile manufacture...
, benzene
Benzene
Benzene is an organic chemical compound. It is composed of 6 carbon atoms in a ring, with 1 hydrogen atom attached to each carbon atom, with the molecular formula C6H6....
, and chloroform
Chloroform
Chloroform is an organic compound with formula CHCl3. It is one of the four chloromethanes. The colorless, sweet-smelling, dense liquid is a trihalomethane, and is considered somewhat hazardous...
. It reacts with hot ethanolic KOH and is methylated by methyl sulphate and methyl iodide. Methanol or ethanol in acid produces dihydroethoxysterigmatocystin.
Toxicity and Importance
The toxic effects of sterigmatocystin are much the same as those of aflatoxin B1. It is thus considered as a potent carcinogenCarcinogen
A carcinogen is any substance, radionuclide, or radiation that is an agent directly involved in causing cancer. This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes...
, mutagen
Mutagen
In genetics, a mutagen is a physical or chemical agent that changes the genetic material, usually DNA, of an organism and thus increases the frequency of mutations above the natural background level. As many mutations cause cancer, mutagens are therefore also likely to be carcinogens...
, and teratogen. It is less acutely toxic to rodents and monkeys but appears to be slightly more toxic to zebra fish. The LD50 in mice is in excess of 800 mg/kg. The 10 day LD50 in Wistar rats is 166 mg/kg in males, 120 mg/kg in females, and 60-65 mg/kg for ip. administration in males. The ip. 10 day LD50 for vervet monkeys is 32 mg/kg.
Chronic symptoms include induction of hepatomas in rats, pulmonary tumours in mice, renal lesions and alterations in the liver and kidneys of African Green monkeys. Rats fed 5-10 mg/kg of sterigmatocystin for two years showed a 90% incidence of liver tumours. It has been suggested that sterigmatocystin is about 1/10 as potent a carcinogen as aflatoxin B1.
Toxic effects of sterigmatocystin-fed laboratory animals have included kidney and liver damage and diarrhoea. Skin and hepatic tumours are induced in rats by dermal application. Cattle exhibiting bloody diarrhoea, loss of milk production and in some cases death were found to have ingested feed containing Aspergillus versicolor and high levels of sterigmatocystin of about 8 mg/kg. The acute toxicity, carcinogenicity, and metabolism of sterigmatocystin has been compared with those for aflatoxin and several other hepatotoxic mycotoxins.
The IARC-classification
International Agency for Research on Cancer
The International Agency for Research on Cancer is an intergovernmental agency forming part of the World Health Organisation of the United Nations....
of sterigmatocystin is group 2B, which means it is likely carcinogenic to humans. In practice, the risk is quite low however, as this substance only appears on cheese crusts with mold, and because of that the chance of daily exposure is very low. A molded crust is best not to be consumed in whole, but after removing the crust, the cheese can still be consumed; Sterigmatocystin is a different kind of mold than that which appears on cheese itself, which can simply be removed before further consumption.
Products affected and Natural Occurrence
The occurrence of sterigmatocystin in raw materials and foods has not been reported often. The instances reported have usually been on mouldy, or poor quality materials such as wheat, maize, animal feed, hard cheese, pecan nuts and green coffee beans. While this lack of information may be due to deficiencies in the analytical methods, where surveys of good quality products have been carried out with reliable methodology, sterigmatocystin has rarely if ever been found. However, further assurance is required before sterigmatocystin can finally be dismissed as a risk because A. versicolor has been isolated frequently from cereals, grain products, fruits and marmalade, dried meat products and grapefruit juice. Relatively high levels of sterigmatocystin have been formed in bread, cured ham and salami after inoculation with A. versicolor.Sampling and Analysis
Methods for extraction of sterigmatocystin have been commonly based on a mixture of acetonitrileAcetonitrile
Acetonitrile is the chemical compound with formula . This colourless liquid is the simplest organic nitrile. It is produced mainly as a byproduct of acrylonitrile manufacture...
and 4% aqueous potassium chloride
Potassium chloride
The chemical compound potassium chloride is a metal halide salt composed of potassium and chlorine. In its pure state, it is odorless and has a white or colorless vitreous crystal appearance, with a crystal structure that cleaves easily in three directions. Potassium chloride crystals are...
. Methods for detection using TLC are not very sensitive having a limit of detection in the range 20-50 microgrammes/kg. TLC plates must be sprayed with aluminium chloride and heated. Analytical methods for the determination of sterigmatocystin have been reported using HPLC but again these are not very sensitive because of lack of UV absorbance or fluorescence, although a post column reaction with aluminium chloride has been used to increase sensitivity. More recently, methods using HPLC linked with atmospheric pressure ionisation mass spectrometric detection have been developed for foods such as cheese, bread and corn products.