general review of mycotoxins
TRANSCRIPT
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General Review of Mycotoxins
Dr.Kedar Karki
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Mycotoxins
• Mycotoxins are secondary metabolites produced by fungi present in feed.
• Mycotoxin's production depends on fungus specie and strand, plant specie, environmental moisture and temperature, presence of pests, etc.
• Mycotoxins cause damages in feed quality. • Their incidence depends on geographical area and
season. • Mycotoxins are toxic: they produce mycotoxicosis and
drop of performance. • Their presence in feed can be reduced by applying
Hazard Analysis and Critical Control Points.
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Mycotoxin toxicity
Main factors that influence toxicity of mycotoxins are:
• Bioavailability. • Combined effects between several mycotoxins. • Amount of mycotoxins consumed. Continuous or
intermittent ingestion of the contaminated feed. • Animal weight, age, physiological and health
status.
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Mycotoxicosis
• Mycotoxicosis (1962, Forgacs and Carl): host's intoxication as a result of ingestion of a toxic substance of fungal origin.Some cases show evident symptoms that can be easily associated to mycotoxicosis.
• In the other hand, subclinical mycotoxicosis is only recognizable by drop of performance and health status.
• Susceptibility to mycotoxicosis depends on animal specie, age, sex and coexistence with other illness.
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Mycotoxicosis can cause:
• NUTRITIONAL ASPECTS
• Feed consume decrease.
• Nutrient absorption decrease.
• HEALTH ASPECTS • Mycotoxicosis typical
of every mycotoxin.
• Immunosupression: arise of other pathologies.
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MYCOTOXINS CLASSIFICATION AND MODE OF ACTION
• Lots of described mycotoxins.
• Varied molecular weights and structures: difficult to classify.
• They keep associated to
fungus or substrate.
• Many of them are stable to chemical/physical treatments.
• Mycotoxins persist in food chain.
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Classification according to pathology
Hepatotoxins: sporidesmine, aflatoxins, luteoskirin, cycloclorotin, rubratoxins, sterigmatocistin.
Nephrotoxins: ochratoxin, citrinin.
Neurotoxins: penitrem A, patulin, fumonisins, citreoviridin.
Toxins of intestinal tract: trichotecenes, T-2 toxin, deoxynivalenol (Don, Vomitoxin), HT2 toxin, fusarenone.
Steroidal; strogenic (Zearalenone), D vitamin analogous
Haemorrhagic and circulatory toxins: Ergot alkaloids, aflatoxins.
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Classification according to chemical structure
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Chemical structure
• Chemical structure determines:
• Mycotoxin's mode of action.
• Mycotoxin's method of detoxification
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Chemical structure and mode of action Mode of action:
• specific biochemical interaction through which a substance produces its biological effect.
• In order to achieve a biological effect, an interaction with a receptor is essential.
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Chemical structure and mode of action
• Chemical groups of the receptor must interact with chemical groups of the substance, that is, chemical structures in the binding point must be complementary.
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KEY-LOCK MODEL
Mycotoxins with shared chemical structure may interact with the same receptors an thus have an alike biological effect.
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Chemical structure and mode of action
• Into practice T2 toxin, HT2 toxin, deoxynivalenol, nivalenol have a sesquiterpene group in their structure and they all have necrotic effects on mucous membranes.
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Chemical structure and mode of action
• B1, B2, G1, G2 aflatoxins, sterigmatocistin have cumarinic group in their structure and they all have haemorrhagic effects alike anticoagulant active principles used in human pharmacology: warfarine, acenocumarol. These active principles also show a cumarinic structure.
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Aflatoxin B1
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MYCOTOXIN ANALYSIS IN FEED MANUFACTURING
• Decision making in raw material purchasing
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Usual methods of analysis
• Thin layer Chromatography (TLC).
• Liquid Chromatography (HPLC).
• Gas Chromatography-Mass spectrometry (GC-MS).
• Immunoassay(ELISA).
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Maximum allowed concentration
• Gradually more countries legislate about mycotoxin limits in fodder and raw materials destined to animal nutrition.
Maximum concentrations are set depending on:• Mycotoxin's toxicity • Animal specie sensitivity and age • Fungi load characteristic of plant specie • Availability and limits of analysis method. • Maximum concentration for each mycotoxin depends on
every country.
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Maximum allowed concentration
• Maximum concentration depends on animal specie and age and on raw material or fodder.
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INTERPRETATION OF RESULTS
• Interpretation of results
Considering the results obtained in the lab, decisions are made taking into account:
• Concentration of each mycotoxin (individual effect). • Concentration of all mycotoxins analysed as a whole
(combined effects). • Possible bias of analysis. • Presence of non-analysed mycotoxins.
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COMBINED EFFECTS
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There are more possibilities of finding combined effects in
mycotoxins... • With similar molecular structure.
Synthesized by the same fungal strand or specie. Synthesized by the same fungal family.
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The appearance of combined effects depends on:
• Concentration of each mycotoxin.
• Animal sensitivity (specie, age, health status).
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Additive effect
• Combined effect of A and B mycotoxins is equal to the addition of the effect of each mycotoxins.
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Additive effect
• Aflatoxins + DeoxynivalenolPoultry: decrease in proventriculus weight, increase of DHL enzyme, indicator of tissue damage.
• Aflatoxins + Cyclopiazonic acidPoultry: growth decrease. Pigs: feed intake and growth decrease; inflammation and necrosis of the gastrointestinal tract. hepatotoxicity.
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Additive effect
• Aflatoxins + DiacetoxyscirpenolPig: Weight and growth decrease, alteration of blood parameters that indicates hepathotoxicity.
• Aflatoxins + MoniliforminPoultry: weight and efficiency decrease. Increase of heart's relative weight. Biochemical parameters indicate nephro and
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Additive effect
• Citrinin + ochratoxin APig: nephrotoxicity. They affect transport of several molecules and protein synthesis.
• FusaricPoultry: feed consumption and growth decrease. Nephro and cardiotoxicity.
• Ochratoxin A + T-2 toxin Poultry: Weight decrease, increase of kidney, liver, proventriculus and gizzard relative weight. Nephro and hepatotoxicity.
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Additive effect
• Fumonisin B1 + Diacetoxyscirpenol Turkey: Weight decrease. Hepatotoxicity.
• Fumonisin B1 + T-2 toxin Poultry: weight and efficiency decrease. Nephro and hepatotoxicity.
• Deoxynivalenol + MoliniformineTurkey: weight of kidney and heart increases. Tissular damage in myocardium.
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Synergic effect
•Combined effect of A and B mycotoxins is higher than the addition of the effect of each mycotoxin.
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Synergic effect
• Aflatoxins + Ochratoxin A Poultry: Weight decrease, mortality increase. Hepatotoxicity and severe nephrotoxicity.
• Aflatoxins + Toxin T-2 Very important because of its prevalence Poultry: weight decrease, increase of kidney, gizzard and heart relative weight; decrease of the medium corpuscular volume and of the potassium plasma levels.
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Synergic effect
• Deoxynivalenol + Fumonisin B1Pigs: great weight decrease.
• Deoxynivalenol + Zearalenone Pigs: theratogenesis in piglets.
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Antagonistic effects
• Combined effect of A and B mycotoxins is less than the addition of the effect of each mycotoxin. (but higher than the effect of each mycotoxin separately).
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Antagonistic effects
• Citrinin + ochratoxin APoultry: the presence of these mycotoxins together reduces the toxic effects of the mycotoxins separately (growth and water consumption decrease).
• Aflatoxins + diacetoxyscirpenol Poultry: the presence of these myocotoxins together reduces the toxic effects of the mycotoxins separately (growth and feed consumption decrease).
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BIAS OF THE ANALYTICAL METHOD
• 1. Not representative samplingSample not representative, because of the big sample size or the king of storage/container of the raw material.
2. Not validated analysis methodAnalysis method should have been validated by a prestigious institution like International Organization for Standardization (ISO).
3. Low quality standards Trouble to get mycotoxin standards in some countries. % recovery of solid standards by dissolution <100%.Standard solution not stable.
4. Procedure for sample extraction
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PRESENCE OF NON-ANALYSED MYCOTOXINS
• Not-analysed mycotoxins
In raw materials there could be mycotoxins whose are not analysed:
1. WELL-KNOWN MYCOTOXINS Whose analysis is not performed because of economic reasons, lack of validated methods, presence unlikely, etc.
2. LITTLE-KNOWN MYCOTOXINS Mycotoxins whose incidence and effects are little known.
THERE ARE MORE THAN 300 DESCRIBED MYCOTOXINS
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Reference:
• Interpretation of the results of mycotoxin's analysis in feed
• Author: Paper Presented at Biovet Symposium 2007 (Courtesy of Biovet SA)