Poison Of The Month

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By Jack Dwayne. Thrasher, Ph.D.

(505) 937-1150 - Cell

Email: toxicologist@...

http://www.drthrasher.org/Aflatoxins_and_Aflatoxicosis.html

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Poison Of The Month

AFLATOXINS AND AFLATOXICOSIS

INTRODUCTION

Aflatoxins were initially isolated and identified as the causative

toxins in Turkey X disease (necrosis of the liver) in 1960 when over

100,000 turkeys died in England.1 They are the most studied

mycotoxins with over 5,000 research papers published through 2002.

There are four generally recognized Aflatoxins, designated B1, B2,

G1 and G2 (Figures 1 and 2). The metabolites, M1 & M2, which are

found in milk,2 are shown in Figure 3. The order of toxicity is B1

greater than G1, greater than G2, greater than B2.3 However,

aflatoxin B1 is the major mycotoxin produced by most species under

culture conditions4 Because of this and its toxicity, B1 is the most

frequently studied of the four.

Aflatoxins are produced by different species of Aspergillus,

particularly flavus and parasiticus, as well as members of the

Genera Penicillium and Rhizopus.5,6 Strains of Aspergillus flavus

and parasiticus produce mycotoxins under favorable conditions.

Aflatoxins can contaminate corn, cereals, sorghum, peanuts, and

other oil-seed crops. Thus, food contamination by this group of

mycotoxins has been implicated in both animal and human

aflatoxicoses. In addition, inhalation of aflatoxins is associated

with disease and injury in both animals and humans. Finally,

aflatoxins are known animal carcinogens and have been linked to

cancer of the liver in humans.

AFLATOXINS AND CANCER IN HUMANS

Aflatoxins are carcinogenic to humans and animals. Sufficient

evidence exists for humans and animals. Overall summary evaluation

of carcinogenic risk to humans is Group 1.3,5,22

Aflatoxin B1 is a potent liver carcinogen in a variety of

experimental animals. It causes liver tumors in mice, rats, fish,

marmosets, tree shrews and monkeys following administration by

various routes. Types of cancers described in research animals

include; hepatocellular carcinoma (rats) colon and kidney (rats),

cholangiocellular cancer (hamsters), lung adenomas (mice), and

osteogenic sarcoma, adenocarcinoma of the gall bladder and carcinoma

of the pancreas (monkeys).3

In humans, aflatoxin B1 has been linked to hepatocellular carcinoma

from three studies reported in the medical literature as follows:

An increased incident (10 % excess) of hepatocellular carcinoma was

reported in south-eastern portion the U.S. in areas of high daily

intake of aflatoxin B1. The daily intake of B1 in the south-eastern

subjects was 13-197 ug/kg body weight as compared to those in

northern and western areas with a daily intake of 0.2-0.3 ug/kg body

weight.7

In China a strong correlation between the intake of peanut, peanut

oil, and corn and increased mortality rates for liver cancer were

reported in five groups of inhabitants from four villages. The

mortality rates were 125, 97.40, 41.65, 24.01 and 1.05,

respectively. The median intake of aflatoxin B1 for each group was

6.05, 6.36, 2.69, 1.83 and 0 ug/day. The median daily urine

concentrations of M1 metabolite were 16.46, 8, 29, 4.78 and 1.21

ng/person. A significant correlation was found between the mortality

rates of primary liver cancer and intake of aflatoxin B1. Further,

analysis of M1 in the urine can be used as an index for human

exposure to aflatoxin B1 in an epidemiological study (cited in

reference 6).

Cancer in 67 men who had inhaled particles contaminated with

aflatoxin were reported in an 11 year followup study. They worked in

a mill crushing peanuts and other oil seeds. Two of the men

developed fatal liver disease, while eleven developed cancers of

various organs. The 13 men had inhaled doses estimated to be between

160 to 395 ug/cubic meter/man/wk. In 55 matched control men, 4

developed cancer and none died from liver disease. The excess

cancers in this study was not significant, however the number of

subjects was insufficient to exclude a significant positive

correlation.6,8

Finally, it was reported that in hepatocellular carcinoma cases

exposed to aflatoxin B1, mutation of p53 gene is fixed at codon 249

third base and takes the form of G to T transversion. It appears

from the reported observations that it is a definate marker of

mutation, which is induced by aflatoxin B1 mutagen and is applicable

for molecular epiemiology survey of sufferers of aflatoxin B1

exposure among heptacellular carcinoma cases.24

AFLATOXICOSIS IN HUMANS

Suspected cases of aflatoxicosis have been reported in India. Over

200 villages in western India experienced an outbreak of disease

affecting humans and dogs. The illness was characterized by

jaundice, rapidly developing ascites, portal hypertension and a high

mortality rate. Death usually occurred from massive gastrointestinal

bleeding. The disease was confined to the very poor who ate badly

molded corn containing aflatoxin at a concentration of 6.25 to 15.6

ppm. The average daily intake was 1-6 mg of aflatoxin.6,9

Reye's syndrome is characterized by symptoms of encephalopathy and

fatty degeneration of the viscera. It occurs in children under 16

and is believed to follow nonspecific viral illness, influenza B and

varicella. Abnormalities are present in mitochondrial structure and

function, including defective oxidative phosphorylation.10

Aflatoxins have been reported to be associated with a Reye-like

Syndrome in Thailand, New Zealand, Czechoslovakia, the United

States,6,15,Malaysia,11 Venezuela,12 Europe.13 An incident of 106

fatal cases of hepatic disease among 397 individuals who became ill

after eating maize contaminated with aflatoxin also suggests that

acute aflatoxicosis can occur in human beings.16

The Reye-like syndrome reported in various places around the world

was characterized by multiple symptoms and clinical findings that

included: disturbed consciousness, fever, convulsions, vomiting,

disturbed respiratory rhythm, altered muscle tone, and altered

reflexes. Serum glutamic-pyruvic transaminase and glutamic-

oxalacetic acid transaminase (mitochondrial) enzymes levels were

elevated. Hypoglycemia and low cerebrospinal fluid glucose were

observed. The onset of the illness included coughing, rhinorrhea,

sore throat, earache, slightly enlarged, firm yellow liver, and a

pale, slightly widened renal cortex. A high rate of mortality

occurred, 81 % of the diagnosed cases. Since Reye's Syndrome is

characterized by abnormal mitochondrial structure and function, it

is of interest to note that aflatoxin B1 causes abnormal

mitochondrial structure and function.17-21

Aflatoxins have been demonstrated in human cord blood and sera of

women immediately after birth. These result demonstrated the

transplacental transfer and concentration of aflatoxin by the feto-

placental unit.6 Moreover, neonates with and without jaundice were

investigated for the presence of aflatoxins in the cord blood.

Jaundice and decreased birth weight were correlated with a higher

concentration of alflatoxin B1. The observations showed that

neonates are exposed to aflatoxin prenatally and that high incidence

of jaundice occurred in wet warm months.29 These observations are of

biological significance for humans because aflatoxins are mutagenic,

carcinogenic, teratogenic, and immunosuppressive in animals. The

implications of these findings are potentially profound and deserve

further study.6

Three cases of pulmonary insterstitial fibrosis, two agriculatural

workers and one textile worker, with exposure to aflatoxins have

been reported.42 Lung samples from the three workers contain

aflatoxin B1 suggesting a possible occupational of aflatoxin

exposure via the respiratory tract and lung disease.

IMMUNE RESPONSE IN HUMANS AND AFLATOXINS

Antibodies to aflatoxin B1 have been reported in humans. At present,

these antibodies are considered indicative of exposure and may or

may not be related to disease.15,27

Workers handling animal-feed exposed to mycotoxins, including

aflatoxins, were examined for alterations in plasma alpha tumor

necrosing factor (TNF-alpha). Airborne concentration of aflatoxin

was 0.99 ng/m3. Exposed workers had increased levels of TNF-alpha

and concomitant changes in serum lactate dehyrogenase isoenzyme

activity.28

AFLATOXICOSIS IN ANIMALS

Domestic animals (pets and agricultural), monkeys and laboratory

rats and mice have been the subject of a large body of research on

the adverse effects of aflatoxins (particularly B1). These effects

include adducts and mutations, cancer, immunosuppression, lung

injury and birth defects. Also, aflatoxins have been shown to

interact with DNA (nuclear and mitochonndrial adducts) and

polymerases responsible for DNA and RNA synthesis. The literature is

voluminous and can be researched through the National Library of

Medicine. Thus, aflatoxicosis in animals will be briefly reviewed

here.

Aflatoxins are immunosuppressive in a variety of animals making them

more susceptible to infection by various microorganisms. The animals

include sheep, cattle, mice, rats rabbits, pigs, poultry among

others.6,30-33

Aflatoxicosis in horses, cows and dogs has been described.

Essentially, the disease process is similar to that seen in humans.

However, because of ability to study animals in more detail in the

laboratory, considerable more scientific information has accumulated

regarding the course of the disease.

Calves develop a disease that features blindness, circling and

falling down, twitching of ears and grinding of teeth. Spasm of the

rectum is seen in most cases. Death usually follows within two days

of onset of severe clinical signs. Postmortem findings revealed

pale, firm and fibrosed liver. Histologically the main liver changes

are centrilobular necrosing, bile duct proliferation and veno-

occlusive disease. The kidneys are yellow and surrounded by wet fat.

Ascites and edema of the mesentery (enteritis) and rectal eversion

are common findings.

Other pathological features in cattle are blood coagulation defects,

which may involve impairment of prothrombin, factors VII and X and

possibly factor IX. A single dose of alflatoxin causes increases in

plama enzymes (aspartate aminotransferase, lactate dehydrogenase,

glutamate dehyrogenase, gamma-glutamyltransferase and alkaline

phosphatase) and in bilirubin, probably reflecting liver damage.

Other abnormal clinical findings are proteinura, ketonuria,

glycosuria and hematuria.6 Similar changes in blood coagulation

parameters have been reported in dogs.6

Horses are more susceptible to the adverse effects of aflatoxins

than are cattle. The disease in horses is characterized by decreased

feed intake, loss of body weight, liver damage, centrilobular

hepatic disease, brain, kidney and heart damage. Behavioral changes

before death include belligerence, somnolence, excessive yawning,

head pressing, circling, aimless walking and even blindness.34

MITOCHONDRIAL DAMAGE AND AFLATOXINS

Damage to mitochondria can lead to mitochondrial diseases and may be

responsible for aging mechanisms. The damage can be to mitochondrial

DNA (adducts and mutations), mitochondrial membranes, increased cell

death (apoptosis) as well as to disruption of energy production

(production of ATP).43,44 Aflatoxin B1 preferentially attacks

mitochondrial DNA (mtDNA) during heptocarcinogenesis vs nuclear

DNA;45 mtDNA is protected in aflatoxicosis resistant rodents from

DNA adducts that effect mitochondrial transcription and

translation;46 the mycotoxin alters energy-linked functions of ADP

phosphorylation and FAD- and NAD-linked oxidizing substrates21 and a-

ketoglutarate-succinate cytochrome reductases;19 it causes

ultrastuctural changes in mitochondria;17,18 and also induces

mitchondrial directed apoptosis.20,47,48 Thus, disruption of

mitochondria may well lead to dysfunction of various organs and

concomitant symptoms that escape standard medical diagnostics. For

example, it is believed that certain mitochondrial diseases result

from the the ability of the nucleus to detect energetic deficits in

its area. The nucleus attempts to compensate for the power shortages

(e.g. lack of ATP) by triggering athe replication of any nearby

mitochondria. Unfortunately, this response promotes replication of

the very mitochondria that are casuing the local energy shortage,

futher aggravating the problem (see Wallace, reference 43 for

further detailed information).

CONCLUSIONS

Aflatoxicosis, be it humans or animals, is characterized by liver

damage. What information is available with respect to human

exposure, encephalopathy can occur and is also observed in domestic

animals. In addition, preliminary evidence from human studies

demonstrates that aflatoxins cause an increase in circulating alpha

tumor necrosing factor, suggesting that these mycotoxins are also

immunotoxic in humans. In animals, immunosuppression does occur in a

variety of different species.

Aflaxtoxins are present in the food chain. They have been found in

human cord blood and apparently can enter the developing fetus in

humans and animals.35,36 In addition, aflatoxins have been found in

human breast milk37, cow's milk and dairy products38,39 and infant

formula.40 Not only has exposure to aflatoxins been implicated in

hepatocellular carcinoma, hepatic failure, encephalopathy and Reye's

syndrome, such exposure may also be important in the health and well

being of the fetus and neonates. Thus, it has been postulated that

intra-uterine and neonate exposure from contaminated food products

may play an etiology in (1) Kwashiorkor, (2) neonatal susceptibility

to infection and jaundice, (3) childhood infections and malignant

disease and compromised response to phrohylatic immunizations in

children.41

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