Fungi and Mycotoxins
If you aren't familiar with the word mycotoxin it refers to secondary metabolites that are produced by microfungi that are capable of causing disease and death not only in human but in animals as well. Nevertheless, some mycotoxins have been found to have pharmacological activity. Some mycotoxins have been used as antibiotics, drugs, growth promotants, and even chemical warfare. This article will, however, focus on important mycotoxins associated with human disease including aflatoxin,and ochratoxin A as they are commonly found on coffee.
Common foods that contain the above mycotoxins include groundnuts (peanuts), maize (corn), sorghum, rice, yams, cassava, soyabeans, cotton seeds, fruits, vegetables, spices, cacao, and coffee. Many of these food stocks pose serious health risks when heavily contaminated. This quite often happens when these foods are grown under warm and humid conditions. Take a look at the picture to your left. These are coffee beans that are infected with ochratoxin A
In terms of food safety the mycotoxins and their metabolites to be concerned about include aflatoxins (B1, B2, G1, G2, and M1), ochratoxin A, patulin, and toxins produced by Fusarium molds such as fumonisins (B1, B2, and B3), trichothecenes (nivalenol and deoxynivaleonol, T-2 and HT-2 toxin) and zearalenone in terms of many foods you eat. So keep look at for these.
The symptoms of mycotoxicosis vary depending on a number of factors. These factors include what type of mycotoxin, amount and duration of exposure, health, dietary status, and genetics of the individual. The severity of mycotoxin poisoning varies depending on factors such as having a vitamin deficiency, alcohol or drug abuse, malnutrition, and any infectious disease you may have. Some mycotoxins may interact with other toxins you have in your system creating a synergistic effect.
Different mycotoxins can bring on any number of adverse health issues. For example, aflatoxins tend to be the most toxic and are referred to as genotoxic. That means they can damage DNA and by doing so can cause cancer. Other mycotoxins have been reported to cause kidney damage, gastrointestinal issues, reproductive dysfunction, and even immune system suppression. A tolerable daily intake has been established for most mycotoxins. This is based on a quantity taken in on a per day basis over a lifetime. Following those guidelines should keep you well out of harms way. For further information please visit http://www.mycotoxins.info/myco_info/consum_regu.html for mycotoxin daily allowances.
As mycotoxins are difficult to define, classifying them has been a challenge. When you're reading in the literature, you will find a number of classifications depending on the community that is writing about them. For example, clinicians often classify them by the organ they damage so they use terms like hepatotoxins, nephrotoxins, neurotoxins, and immunotoxins. Biologists often refer to them as teratogens (interferes with fetal development), mutagens, carcinogens, and allergens. Chemists refer to them by their chemical structures such as lactones and coumarins. On the other hand, mycologists refer to mycotoxins by the fungi that produce them such as Aspergillus toxins. Yet again, physicians may refer to them by a specific illness they generate such as St. Anthony's fire. So don't be surprised if you see aflatoxin referred to as a hepatotoxic, mutagenic, carcinogenic, difuran-containing, polyketide-derived Aspergillus toxin. Be patient and go with the flow.
Mycotoxins in foods can be controlled and for the most part it means taking preventive measures. This involves using good agricultural practices along with drying of crops after they are harvested and storing them properly.
Coffee Mycotoxins and What they do in the Body
There are four main aflatoxins (B1, B2, G1, and G2). This is based on their fluorescence under UV light which turns out to be blue or green. Aflatoxin B1 is the most potent carcinogen and the one most produced by microfungi. Aflatoxins are difuranocoumarin derivatives produced by a polyketide pathway by different strains of Aspergillus spp and is a common plant contaminant. Different strains of microfungi produce toxins that vary in toxigenicity. These toxins are often associated with cereals, figs, oil seeds, nuts, tobacco, and coffee. Contamination of food can occur at different times. For example aflatoxin may flourish on crops before harvest due to drought conditions. Storage is another factor. If the environment is humid, this favors mold growth. Milk products are of concern. Milk products can serve as an indirect source of aflatoxin. When feed stock is contaminated with aflatoxin that cows consume, they actually metabolically transform aflatoxin B1 into aflatoxin M1 and that gets deposited in their milk. Diseases that are caused by aflatoxins are referred to as aflatoxicoses. If this infection becomes acute death ensues. Chronic exposure develops into cancer due to immuno-suppression
Aflatoxins are metabolized by Cytochrome P450 enzymes into 8,9-epoxide. This metabolite has the ability to bind DNA as well as proteins. Specifically it binds to guanine bases which can result in GC to TA transversions according to animal studies. Nevertheless, ingestion of aflatoxins in humans has been reported to cause hepatocellular carcinoma especially if you have been exposed to hepatitis B. These cancers tend to be more common in China, Philippines, Thailand, and African countries. For those countries at risk it has been suggested to vaccinate against hepatitis B rather than removing aflatoxin from the diet. Aflatoxins have been reported to inactivate the p53 tumor suppressor gene which brings about liver cancer. This toxin causes a mutation in this gene at codon 249 which is associated with a G (guanine) to T (thymine) transversion on the genome. This mutation is a “carcinogen-specific” biomarker that remains in the tissue and easily tracked. Lung cancers have also been observed in Dutch peanut processing workers who were exposed to dust contaminated with aflatoxin B1. Due to a number of caners believed to be caused by aflatoxins The International Agency for Research on Cancer has classified aflatoxin B1 as a group I carcinogen. Group I carcinogen means that it is carcinogenic in humans.
Originally, ochratoxins were isolated from corn in the U.S. and where recognized as a potent nephrotoxin (kidney), hepatotoxin, immune suppressant, carcinogen, and a potent teratogen. Many of these toxins come from Aspergillus spp. Ochratoxins have been found in barley, oats, rye, wheat, wine, coffee beans, animal tissues (pork), blood, and milk. This toxin effects a number of metabolic pathways but in particular one that is involved with the synthesis of phenylalanine-tRNA complex. Transfer RNAs (tRNA) are involved with protein synthesis. This particular tRNA carries the essential amino acid phenylalanine to a growing polypeptide chain. This can stop synthesis of a polypeptide if it requires phenylalanine. It also inhibits ATP production in the mitochondria and stimulates lipid peroxidation (fat free radical formation).
Ochratoxin A Mechanism
The ochratoxin A mechanism is not well understood at this time. What is known is that ochratoxin accumulates in the kidneys and liver. As far as the kidney goes, ochratoxin is excreted into the urine by way of tubular secretion. This secretion process takes place by way of an organic anion transport system. Specific anion transporters, organic anion-transporting polypeptides, oligopeptide transporters, and ATP-binding cassett transports have been identified for ochratoxin A. These kidney transporters carry ochratoxin across the kidney tubule membrane and into urine. These transport systems are believed to be involved in the development of ochratoxin-induced nephrotoxicity.
For further information in the United Kingdom
If you have a question or would like further information about mycotoxins, you can contact us at:
tel: 020 7276 8716
Mycotoxins in feed
Dr Ray Smith
tel: 020 7276 8474
Constant Monitoring Needed for Aflatoxins in Chocolate - Study
Aflatoxin and ochratoxin A contamination of retail foods and intake of these mycotoxins in Japan.
Study on distribution of mycotoxins in cocoa beans