Scientific Committee on Food
Outcome of discussions
Opinion of the
Scientific Committee on Food on Ochratoxin A (expressed on
17 September 1998)
1. Terms of reference
The Committee is asked to review and
revise as necessary its opinion of 22 September 1994 1 on
ochratoxin A in the light of results of toxicological
studies published since that time.
In making its review the Committee is
asked to take note of the recently published Scientific
Co-operation report "Assessment of the dietary intake of
ochratoxin A by the population of the EU Member States"
Ochratoxin A is a mycotoxin produced by
several fungi (
Aspergillus species), and occurs naturally in a
variety of plant products such as cereals, coffee beans,
beans, pulses and dried fruit all over the world. It has
been detected also in products such as coffee, wine, beer
and grape juice. It occurs also in kidney, liver and blood
from mammals by transfer from animal feed. Investigations
of the frequency and levels of occurrence of ochratoxin A
in food and human blood samples indicate that foodstuffs
are frequently contaminated.
Ochratoxin A is a nephrotoxic mycotoxin
which is carcinogenic to rodents and possesses teratogenic,
immunotoxic 3 4 5 and possibly neurotoxic 6 7 properties.
Further, it may be implicated as a factor in the human
disease Balkan Endemic Nephropathy and the development of
urinary tract tumours in humans 8 9. Also, recent data from
France and North Africa point towards a correlation between
chronic interstitial nephritis and high exposure to
ochratoxin A 10 11 12 13 14.
In its opinion in 1994 the Committee
stated that ochratoxin A is a potent nephrotoxic agent, a
carcinogen and that it has genotoxic properties. The
genotoxic effect may be explained by an indirect mechanism
involving impaired protein synthesis. The Committee
provisionally concluded that an acceptable safe level of
daily exposure would fall in the range of a few ng/kg
b.w./day and it proposed to reconsider its opinion in the
light of new information 1.
The Joint FAO/WHO Expert Committee on
Food Additives (JECFA) has evaluated ochratoxin A at its
37th meeting in 1991 15 and at the 44th meeting in 1995 16.
In its assessments, JECFA addressed the carcinogenic
effect, but based its assessments on the nephrotoxic effect
in pigs (the most sensitive species). With a Lowest
Observed Adverse Effect Level (LOAEL) of 8 µg/kg b.w. and
applying a safety factor of 500, the Committee in 1991
arrived at a Tolerable Daily Intake (TDI) of 16 ng/kg b.w.,
which was converted to a Provisional Tolerable Weekly
Intake (PTWI) of 112 ng/kg b.w.. This value was rounded off
to 100 ng/kg b.w. at the 1995 meeting (i.e. not a change in
the toxicological evaluation).
The Canadian authorities have evaluated
ochratoxin A in 1989, ´90, ´91 and ´96 17 18 19 20 and
suggested a Provisional Tolerable Daily Intake (PTDI) of
1.2-5.7 ng ochratoxin A/kg b.w./day for a lifetime risk
level of 10-5. The evaluations were based on ochratoxin As
carcinogenic properties and both a safety factor- and
model-based approach were used in the calculations.
A Nordic expert group on food toxicology
made an assessment in 1991 and proposed a highest tolerable
daily intake of 5 ng/kg b.w./day, based on the carcinogenic
properties of ochratoxin A. Model-based approaches were
used in the calculations 21.
In 1993, the International Agency for
Research on Cancer (IARC) classified ochratoxin A as a
possible human carcinogen (group 2B), based on sufficient
evidence for carcinogenicity in animal studies and
inadequate evidence in humans 22.
Since many reviews on ochratoxin A are
available and there is general agreement about the toxicity
profile, the present report focuses primarily on the mode
of action of ochratoxin A carcinogenicity.
An assessment of dietary intake of
ochratoxin A by the population of EU Member States was
published2 in the framework of the Scientific
Co-operation23 of the European Commission. Thirteen
countries provided data on occurrence of ochratoxin A in
food products, on consumption of these food products and on
occurrence of ochratoxin A in human blood plasma and human
There were large differences in the
amount, detail and quality of the data from the
participating countries; the judgement as to whether the
occurrence data were representative or not, and thus
relevant for the intake estimations, was made by the
participating countries for their own data. Eight countries
were able to estimate mean dietary intake for an average
adult person based on food occurrence and consumption data,
and these mean dietary intakes were in the range from 0.7
to 4.6 ng/kg b.w./day. Of these eight, five also gave an
estimate of mean dietary intake for an average adult person
based on human blood plasma data, and these were in the
range from 0.2 to 2.4 ng/kg b.w./day .These values
corresponded to average blood plasma concentrations of 0.18
to 1.8 ng/ml, respectively. Thus, all the estimates of mean
dietary intakes of ochratoxin A for average adult persons
fell in the range from close to zero to a few ng/kg
b.w./day. Since the dietary intake data are mean values it
is understood that some individuals will be exposed to
higher levels of ochratoxin A.
The main contributor to the dietary
intake of ochratoxin A seems to be cereals and cereal
4. Evaluation of the mode of action of ochratoxin A
The carcinogenicity of ochratoxin A in
both rats and mice is well established. Ochratoxin A
induces renal tumours in rats of both sexes and in male
mice. In the rat kidney, tumour induction is seen at a very
low dose level (70 µg/kg b.w.). Moreover, in mice
ochratoxin A gives rise to liver tumours in both sexes
A correlation between carcinogenicity
and exposure to ochratoxin A is not established in humans.
However, a correlation has been described between high
exposure to ochratoxin A (high level of ochratoxin A in the
blood) and high frequency of Balkan Endemic Nephropathy,
and it has been found that urinary tract tumours are
present with very high incidence in regions affected by
Balkan Endemic Nephropathy 8.
Ochratoxin A is negative in conventional
mutagenicity tests carried out according to standard
protocols, i.e. Ames test and tests for gene mutations and
chromosomal aberrations in mammalian cell cultures.
However, using different test conditions and/or different
endpoints, ochratoxin A is reported to be able to cause
in vitro and
in vivo, micronuclei, unscheduled DNA synthesis,
sister chromatid exchanges
in vitro, gene mutations in bacterial cells
(modified Ames test) and in NIH/3T3 cell lines 24 25 26 27
It has to be noted that the covalent
binding of chemicals or their reactive metabolites to DNA
is generally believed to be a key step in the initiation of
carcinogenesis by genotoxic agents. It has been reported
that, after administration of 3H labelled ochratoxin A to
rats, no radioactivity was found in liver DNA or kidney
DNA. From these negative results, covalent binding indexes
(CBI) of <0.25 for kidney and of <0.1 for liver DNA
were calculated 29, which are considered to be of no
On the other hand, it has been shown
repeatedly that ochratoxin A induces DNA-adducts in
kidneys, liver and spleen from mice and rats
in vitro as well
in vivo. The highest DNA-adduct levels were found in
the target organs (kidney and bladder), being most
persistent in the kidney 30 31. In addition ochratoxin A
has also been shown to induce DNA-adducts in monkey kidney
cells and human bronchial cells
in vitro 32 33
. However, in all the above mentioned studies, the
adducts have been measured by use of 32P-post-labelling
techniques, which cannot give a final proof for ochratoxin
Therefore, at present, it remains to be
established whether the DNA-adducts represent direct,
covalent binding of ochratoxin A/ochratoxin A metabolites
or represent secondary base changes due to indirect
mechanisms. Such mechanisms could include oxidative damage,
increased binding of endogenous compounds or tissue injury
and sustained hyperplasia 34 35 36 29 37 38 39.
Metabolism and kinetics
The biotransformation of ochratoxin A
has not yet been elucidated in detail and the possible
contribution of metabolites, especially to genotoxicity, is
currently unclear. However, recent studies have shown that,
in vitro, ochratoxin A is converted into
DNA-reactive metabolites 40 33. Experiments have indicated
that the toxicity of ochratoxin A is related to its
isocoumarin moiety 41.
Studies in rats have shown that
ochratoxin A is cleared at a much slower rate from the body
than its metabolites 42.
Only one study on one subject is
available on the metabolic disposition of ochratoxin A in
humans. This study indicated that the half-life of
ochratoxin A in humans is comparable with the one in
monkeys but is about ten times longer than that seen in
Ochratoxin A is a mycotoxin which
possesses carcinogenic, nephrotoxic, teratogenic,
immunotoxic and possibly neurotoxic properties. It has also
been linked to nephropathy in humans. Ochratoxin A may have
a long half-life in humans.
Ochratoxin A is carcinogenic in rodents.
In conventional mutagenicity tests it is negative. However,
recent data from
in vitro and
in vivo tests using less conventional methods have
provided evidence of the genotoxic potential of ochratoxin
The Committee is aware that further
studies are on-going to elucidate the mechanisms involved
in ochratoxin A carcinogenicity.
Estimates of tolerable daily intake by
other bodies (see background), based on non-threshold
mathematical modelling approaches or a safety
factor/threshold approach, have ranged from 1.2 to 14 ng/kg
The Committee notes that the higher
figure of 14 ng/kg b.w./day was derived using
nephrotoxicity as the endpoint. However there is now an
increasing concern about potential genotoxicity of
ochratoxin A and its mechanism of action as a carcinogen.
Therefore the Committee considers it would be prudent to
reduce exposure to ochratoxin A as much as possible,
ensuring that exposures are towards the lower end of the
range of tolerable daily intakes of 1.2-14 ng/kg b.w./day
which have been estimated by other bodies, e.g. below 5
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