AFTER HEPATIC METABOLISM-- biotransformation ACTIVATES them
where do aflatoxins come from?
produced by fungi-- Aspergillus ﬂavus - Aspergillus parasiticus - Aspergillus niger group
what is the PRIMARY target organ of the aflatoxins? what is the secondary target?
PRIMARY: LIVER!!!! (they are bioactivated there, so liver is at ground 0 for damage) .... SECONDARY: immune suppression and reduced performance
what is a co-toxin associated with aflatoxins, and how does it happen?
Cyclopiazonic acid= CPA= co-toxin produced by Aspergillus spp
so aspergillus is everywhere, but there is a tendency for aflatoxin to be in particular climates.. what climate, and why is this the case?
toxins usually produced in tropical/subtropical areas (the climate encourages them to produce the toxins)
aflatoxins can start be a problem at what two different times-- and which is easier to fix?
(1) preharvest (2) storage <---easier to fix storage problem (preharvest requires fixing environment)
Biotransformation of aﬂatoxin B 1--> how is this AB1 metabolized? what are the products? how do they differ/what influences this process?
Phase 1: cytochrome P450 catalyzed bioactivation breaks the aflatoxin B1 down into B1 endo epoxide and B1 exo epoxide. BOTH are toxic, but endo is more toxic than exo. How the liver decides which to produce more of depends on: (1) Relative expression of P450 isoenzymes (diff enzymes break it down differently) (2) Substrate (AFB 1 ) affinity
does biotransformation or conjugation decide whether or not aflatoxin becomes the endo epoxidase or exo epoxidase product?
biotransformation decides that (diff CYP450 enzymes= diff results) and remember that both are toxic but endo is moreso.
GSTs (Glutathione S-transferase)--> what is this? what variations does it have, and what are the implications of that?
These are phase II metabolism proteins (conjugation! Zone 3) so first the aflatoxin is biotransformed (make epoxide) and then conjugation (can deactivate them again) . GST's are species specific in expression and affinity, therefore they would be good targets for chemoprevention of aflatoxicosis (GSTs are both conjugation and antioxidant)
what is Aﬂatoxin M 1 like after metabolism? how is it metabolized?
metabolized by oxidation, it is less carcinogenic and mutagenic, but equally toxic (milk and urine excretion).
what are the two most toxic aflatoxin products?
B1 and M1 (A1 and P1 are not that toxic or not at all)
which aflatoxin is associated with causing cancer?
what is the major thing about M1 and its toxicity?
biggest difficulty is that its elim with milk-- esp harmful to kids (and kids are more sensitive). ((also just as toxic as B1- so these are the most toxic)
how is Aﬂatoxin Q 1 metabolized, and what happens to it?
metabolized by hydroxylation, which detoxifies it (NOT TOXIC) and then it is excreted with the urine
Aﬂatoxin P 1- how is this metabolized, what happens to it?
Metabolized by demethylation, causes reduced toxicity (urinary excretion) (so maybe some production loss but not a killer like B1 and M1)
so aside from the metabolic pathways which metabolize aflatoxin into B1, M1, P1, and Q1.. it can also be transformed into aflatoxicol, which is not toxic (happens in rumen of rumis)...so how come we don't like aflatoxicol still?
aflatoxicol is not toxic- but if re-absorbed absorbed, can be converted back to B1 and be toxic again
so big take-away with aflatoxin metabolism is...
diff enzymes and paths result in different toxins, or even substances which are not toxic!
Factors affecting the biotransformation of aﬂatoxin? (4)
(1) Genetic polymorphisms-- ie: species (breed) differences of age / gender (2) Nutrients (3) Non-nutrients, natural compounds (4) Synthetic compounds
what are 3 nutritional states which affect the biotransformation of aﬂatoxin....and what are the results?
(1) Low protein diet - increased acute toxicity (2) High protein diet - increased neoplastic foci (3) Low vitamine A - increased DNA adducts (which means inc carcinogenecity)
what is a Non-nutrient, natural compounds that has an affect on the biotransformation of aflatoxin, and how?
ﬂavonoids induce GST and are antioxidants
what is a synthetic compound that has an affect on the biotransformation of aflatoxin, and how?
oltipraz (dithio-thiols) are inhibitors of CYP450 and inducers of GST/GSH (antioxidant enzymes)
which type of aflatoxin causes cancer? what kinda cancer is it? what happens (specific metabolism) to cause this situation?
B1 can cause cancer-- specifically, hepatocellular carcinomas. Cytochromep450, specifically 1A2 (also responsible for making M1) and 3A4 (these were the ones he said in class- ppt says 1A, 2A, 2B, 2C, 3A) result in epoxide formation that leads to Non CYP450 dependent oxidations turn DNA (guanine) into a pro-mutagenic DNA adduct (AFB 1 epo-epoxide - DNA (N7-guanine) adducts - mutations of p53 (activation of ras-protooncogenes) - HCC IARC group 1A) (so has direct effect on portions of DNA, leading to mutagenecity). Ultimately, the DNA adduct (epodixe+guanine in the DNA adduct) is pretty unstable and it rapidly elim with urine. the other form of wlim is glutathione transferase (conjugation rxn), which also makes it elim in urine
why do we care about CYP1A2 and CYP3A4?
these are the 2 that lead to DNA adducts/ high mutagenicity
why do we care about Glutathione-S-transferase?
the harmful aflatoxin epoxides can be congugated with GST to AFLATOXIN GLUTATHIONE/ AFLATOXIN N-ACETYLCYSTEIN which are then non-toxically passed in the kidney
the whole pic of aflatoxin bioactivation and bioinactivation...
what does he mean by oral toxicity?
oral uptake leads to breast milk intixication of children
what kinda food are aflatoxins on?
Cereals, grains, nuts and products thereof (Carry-over into meat and eggs is negligable- milk (M1) is a concern tho)
Carry-over of AFB 1 into milk (AFM 1 )-- this is esp a high risk in?
(1) In high producing animals (2) Animals with subclinical mastitis are at risk (altered metabolism, inflammation, inc elim... why inc elim? bc of inflammation.there is a blood milk barrier. subclinical mastitis interferes with blood milk barrier, which means it (M1) goes into milk more easily ) (there is some species diffs- and water buffalo more prone for some reason)
Human exposure to aﬂatoxins--> Children exposed to aﬂatoxins from food supplies present how?
show poor growth and immune suppression, making them susceptible to HIV and malaria
Fungal metabolite (Aspergillus ﬂavus and A. parasiticus)
what are the types of aflatoxins and which is most toxic?
Aﬂatoxin B 1 , B 2 , G 1 , G 2 with aﬂatoxin B 1 being the most toxic
what food does aflatoxin infect, and what regions of the world are most affected?
World-wide contaminant of corn, all nuts, peanuts (history), cotton seed in tropical and subtropical climate zones. Highest levels in screenings/broken grains and damaged nuts
which aflatoxin do you find in milk?
In milk alfatoxin M 1 and M 2 - hepatic metabolites
which animals are sensitive to aflatoxin/ which are most sensitive?
all animal species, including companion animals due to diet changes in modern pet animal nutrition (more grains). The most sensitive species is ﬁsh, followed by geese (bioassay), other poultry species, cattle, sheep, horses and humans
what are the main CSs of aflatoxin toxicity?
hepatotoxicity (biotransformation dependent epoxide formation) -- can cause neoplasia as well (B1 biotransformed through 1A2 and 3A4)
how does B1 induce hepatocellular carcinoma?
if biotransformed through CYP1A2 and CYP3A4 which results in epoxide formation that leads to a non-CYP450 dependant oxidation which causes the epoxide to bind with the DNA and induces adducts to form--- DNA adducts= DNA damage= inc mutagenecity/carcinogenecity
which species are suspetible to aflatoxins?
humans, ﬁsh (salmon, trout, tilapia) and all other animals tested
what are the clinical symptoms of aflatoxicosis?
loss of appetite, reduced weight gain, decreased production, icterus. Increased transaminases (ALT, AST, AP) and total bilirubin, decreased albumin... and Secondary immunosuppression (increased risk for infections)
what will you see on post-mortem with aflatoxicosis?
Bile duct proliferation with pale livers (fatty liver syndrome), Karyomegaly in hepatocytes, Preneoplastic lesions
what would your possible work-up for aflatoxins be like?
you are necropsying an animal which was icteric, has a fatty liver, and the liver has tumors on it. you suspect aflatoxicosis-- which sample should you send in?
no need to send in animal tissues for B1 analysis-- its rapidly elim from system but can look for preneoplastic lesions tec. but dont bother trying to sample B1 in the tissue-- send in the food to be checked.
what are the 3 main biotransformation pathways of pyrrolizidine alkaloids?
(1) Hydrolysis: carboxylesterases (2) N-oxidation: mainly FMOs (flavin-containing monooxygenase (FMO) protein family specializes in the oxidation of xeno-substrates) (3) Dehydrogenation: CYP450 (3A, 2B/2C)
which cytochrome P450's mainly biotransform PA?
when are PAs most toxic?
AFTER BIOACTIVATION IN THE LIVER
what is the target organ of PAs, and why?
THE LIVER. bc they don't become toxic till bioactivation, and that occurs in the liver, so liver is ground 0
which path bioactivities Pyrrolizidine alkaloids to toxic substances? which pathways can detoxify them again? What determines this balance?
activated by CYP450, 3A, 2B/2C. iNACTIVATED by N-oxidation and hydrolysis (if you shut down one path or the other, etc)
which zone will you see liver tox in with PAs?
ZONE 3 because activated into toxic compounds by CYP450 3A, 2B/2C (bioactivation)
what is Pyrrolozidine tox in horses called?
is PA tox usually acute or chronic? Why?
usually gradual inc of toxin-- not acute exposure. never see acute form bc these plants taste foul, horse wont eat unless there is nothing else to eat. Horses geneally wont eat toxic plants until they have nothing else left to eat. these particular plants are very bitter- they eat small amounts-- develop tox over time.
the toxicity of PAs depends on... (general)
time and dose...also species differences
how do you dx PA tox?
only way to dx is bx!!
what does pathology/intoxication look like with acute(high dose) tox? Chronic(low dose)?
HIGH DOSE/ACUTE: Liver cell and endothelial cell injury (Acute=/=common). other side says: massive liver cirrhosis.....LOW DOSE/CHRONIC: (MUCH more common presentation) Intrahepatic hemorrhages and veno-occlusion (low dose/chronic) - liver cirrhosis. Other slide says: liver cirrhosis
what species are sensitive to PAs? which are resistant?
horses! Cattle and sheep with copper toxicosis.... and then on the same slide it ALSO says: Biotransformation based toxicity: Sensitive species: horses, cattle, rat, chicken, human. Resistant species: sheep, guinea pig, hamster, gerbil
CSs of ACUTE PA tox? what does post-mortem look like with acute?
(remember acute is the rare presentation) liver failure (generally lethal)= Icterus/jaundice, Depression (hepato- encephalopathy), Edema, ascites... POST-MORTEM: extensive centrilobular necrosis and hemorrhages, karyomegaly
CSs of CHRONIC PA tox? what will PE and lab results show? how will you work them up?
(more common presentation) Rough coat, weight loss, weakness, anorexia, production losses (milk), photosensitization. Liver is small and dense upon palpation. AST/ALT slightly increased, GGT high. WORKUP: identiﬁcation of exposure, PA analysis, histological examination of the liver (karyomegaly, portal necrosis)
what is prog of PAs and why?
poor (liver cirrhosis progresses even after cessation of exposure)
so although humans arent gonna go out and eat some wild plants (well...most. here's looking at you, Darwin awards) why are humans at risk for PA tox?
PA’s are excreted in (dairy) milk and accumulate in honey
how does PA tox affect humans?
progressive veno-occlusive liver injury with liver cirrhosis, no convincing evidence for carcinogenicity
what animal products are PAs excreted into?
milk and honey (sorry Jewish friends)
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