General Review of Mycotoxins

General Review of Mycotoxins

Dr.Kedar Karki

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.

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.

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.

Mycotoxicosis can cause:

NUTRITIONAL ASPECTS

Feed consume decrease.

Nutrient absorption decrease.

HEALTH ASPECTS Mycotoxicosis typical

of every mycotoxin.

Immunosupression: arise of other pathologies.

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.

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.

Classification according to chemical structure

Chemical structure

Chemical structure determines: Mycotoxin's mode of action. Mycotoxin's method of detoxification

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.

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.

KEY-LOCK MODEL

Mycotoxins with shared chemical structure may interact with the same receptors an thus have an alike biological effect.

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.

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.

Aflatoxin B1

MYCOTOXIN ANALYSIS IN FEED MANUFACTURING Decision making in raw material

purchasing

Usual methods of analysis

Thin layer Chromatography (TLC). Liquid Chromatography (HPLC). Gas Chromatography-Mass

spectrometry (GC-MS). Immunoassay(ELISA).

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.

Maximum allowed concentration Maximum concentration depends on

animal specie and age and on raw material or fodder.

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.

COMBINED EFFECTS

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.

The appearance of combined effects depends on:

Concentration of each mycotoxin. Animal sensitivity (specie, age, health

status).

Additive effect

Combined effect of A and B mycotoxins is equal to the addition of the effect of each mycotoxins.

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.

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

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.

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.

Synergic effect

Combined effect of A and B mycotoxins is higher than the addition of the effect of each mycotoxin.

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.

Synergic effect

Deoxynivalenol + Fumonisin B1Pigs: great weight decrease.

Deoxynivalenol + Zearalenone Pigs: theratogenesis in piglets.

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).

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).

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

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

Reference:

Interpretation of the results of mycotoxin's analysis in feed

Author: Paper Presented at Biovet Symposium 2007 (Courtesy of Biovet SA)