Page
1
of
5
April
19,
2004
FIFRA
SCIENTIFIC
ADVISORY
PANEL
(
SAP)
OPEN
MEETING
MAY
4­
6,
2004
FIFRA
SAP
WEB
SITE
http://
www.
epa.
gov/
scipoly/
sap/
OPP
Docket
Telephone:
(
703)
305­
5805
Docket
Number:
OPP­
2004­
0099
CONSULTATION
ON
DERMAL
SENSITIZATION
ISSUES
FOR
EXPOSURES
TO
PESTICIDES
CHARGE/
QUESTIONS
TO
THE
PANEL
Dermal
sensitization,
also
known
as
allergic
contact
dermatitis
(
ACD)
is
typically
characterized
by
two
phases,
termed
induction
and
elicitation.
In
the
induction
phase,
the
allergen
is
transported
to
regional
draining
lymph
nodes
where
clonal
expansion
of
allergen­
specific
T
lymphocytes
results.
The
elicitation
phase
results
from
a
subsequent
exposure
to
the
allergen,
in
which
the
allergen­
specific
T­
lymphocytes
provoke
a
cutaneous
immune
response.
Although
several
approaches
have
been
proposed
to
assess
threshold
concentrations
for
induction
and
elicitation
of
ACD
and
risk
determination
for
these
concentrations,
there
is
no
established
scientific
approach
within
the
Agency
to
do
a
quantitative
risk
assessment
associated
with
ACD.

There
are
several
accepted
methods
for
hazard
identification
of
dermal
sensitization,
including
the
Buehler
occluded
patch
test,
the
guinea
pig
maximization
test,
and
the
murine
local
lymph
node
assay
(
LLNA).
The
guinea
pig
maximization
test
as
well
as
the
Buehler
test,
while
providing
reliable
information
on
skin
sensitization,
are
best
suited
for
hazard
identification.
Several
proposals
have
been
published
regarding
quantitative
determination
of
sensitization
induction
and
elicitation
thresholds.

ISSUE
1:
Quantitative
Risk
Assessment
for
the
Induction
Phase
of
ACD
The
Mouse
Local
Lymph
Node
Assay
(
LLNA)
is
a
test
method
for
assessing
the
allergic
contact
dermatitis
(
skin
sensitization)
potential
of
chemicals,
specifically
the
induction
phase
of
sensitization.
Using
the
incorporation
of
radiolabeled
thymidine
or
iododeoxyuridine
into
DNA,
the
LLNA
measures
lymphocyte
proliferation
in
the
draining
lymph
nodes
of
mice
topically
exposed
to
the
test
article.
The
stimulation
index
(
ratio
of
lymphocyte
proliferation
in
treated
mice
compared
to
controls)
is
used
as
the
indicator
of
potential
sensitization.
In
1998,
following
review
by
the
FIFRA
SAP,
the
LLNA
was
incorporated
as
a
screening
test
in
OPPTS
Test
Guideline
870.2600
Skin
Sensitization.
In
1999,
the
Interagency
Coordinating
Committee
on
the
Validation
of
Alternative
Methods
(
ICCVAM)
Immunotoxicity
Working
Group
(
IWG)
endorsed
the
LLNA
as
an
acceptable
alternative
to
currently
accepted
guinea
pig
test
methods
for
hazard
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2
of
5
identification
of
chemicals
with
potential
to
produce
contact
hypersensitivity.
Following
additional
studies
to
validate
the
method,
the
LLNA
was
endorsed
by
the
SAP
in
December
2001
as
a
full
stand­
alone
assay.
The
OPPTS
guideline
870.2600
(
Skin
Sensitization)
has
been
revised
to
include
the
LLNA
as
a
stand­
alone
assay
for
appropriate
applications.
The
OPPTS
guideline
has
also
been
harmonized
with
OECD's
Guideline
429
for
LLNA,
which
was
adopted
in
April
2002.
Although
the
LLNA
has
not
been
validated
for
determination
of
sensitization
potency,
approaches
for
determination
of
quantitative
assessment
of
sensitization
induction
thresholds
have
been
proposed
in
the
scientific
literature
(
Gerberick
2000,
2001;
Griem
et
al.,
2003).

Gerberick
(
2000,
2001)
proposed
a
methodology
for
determination
of
a
`
sensitization
reference
dose'
for
sensitizers
in
consumer
products.
The
lower
boundary
of
the
potency
category
for
a
sensitizing
chemical
is
used
as
the
starting
point,
with
application
of
uncertainty
factors
for
interindividual
variability,
product
matrix
effects,
and
use
pattern.
This
approach
was
applied
to
the
fragrance
component
cinnamic
aldehyde
and
the
preservative
methylchloroisothiazolinone/
methylisothiazolinone
for
which
both
LLNA
and
human
sensitization
potency
were
available
(
Griem
et
al.,
2003).

Griem
et
al
(
2003)
proposed
a
quantitative
approach
in
which
identification
of
known
human
sensitizing
chemicals
used
both
an
EC3
value
(
defined
as
the
concentration
of
a
sensitizer
required
to
generate
a
threefold
stimulation
of
proliferation
in
draining
lymph
nodes)
from
an
LLNA
test
and
a
NOAEL
or
LOAEL
from
human
repeat
insult
patch
tests
(
HRIPT)
or
human
maximization
tests
(
HMT).
The
reported
concentrations
were
converted
into
specific
and
molar
area
doses.
Comparison
of
the
area
doses
of
the
LLNA
and
human
test
results
indicated
that
sensitization
thresholds
were
similar
in
mice
and
humans
despite
the
fact
that
the
area
doses
for
different
chemicals
ranged
over
several
orders
of
magnitude
(
Griem
et
al.,
2003).
It
was
concluded
from
this
analysis
that
the
LLNA
EC3
value
is
a
useful
measure
of
sensitizing
potency
in
humans,
and
that
the
EC3
value
can
be
used
as
a
surrogate
value
for
the
human
NOAEL
that
can
be
used
as
a
starting
point
in
quantitative
risk
assessment.

Uncertainty
factors
to
account
for
interspecies
variation,
intraspecies
variation,
product
matrix
effects,
and
conditions
of
exposure
(
including
repeated
exposures)
have
been
proposed
for
use
in
conduct
of
dermal
risk
assessments.
Griem
et
al.
(
2003)
have
discussed
the
application
and
magnitude
of
all
of
these
uncertainty
factors
with
respect
to
establishment
of
safe
area
doses
for
both
induction
and
elicitation,
while
Felter
et
al
(
2003)
have
proposed
the
use
of
only
the
intraspecies
variation
factor,
product
matrix
factor,
and
exposure
conditions
factor
for
determination
of
safe
area
doses
for
induction.
The
interspecies
uncertainty
factor
is
intended
to
account
for
differences
in
response
between
tests
in
animals
and
results
in
humans,
although
it
has
been
reported
(
Griem
et
al,
2003)
that
sensitizing
area
doses
are
very
similar
between
murine
and
human
data,
thus
supporting
a
potentially
reduced
uncertainty
factor
for
this
area.
The
intraspecies
uncertainty
factor
is
used
to
account
for
inherent
variability
in
the
human
population
based
on
age,
sex,
genetic
makeup,
or
health
status,
and
is
generally
agreed
that
a
factor
of
10
is
appropriate
for
this
uncertainty.
An
uncertainty
factor
may
also
be
included
for
vehicle
matrix
effects,
as
the
matrix
in
which
an
allergen
is
presented
to
the
skin
may
have
an
influence
on
the
potential
for
induction
of
ACD.
Most
experimental
data
are
generated
using
simple
vehicles,
while
Page
3
of
5
actual
exposures
are
usually
to
more
complex
formulations
that
may
contain
irritants
or
penetration
enhancers.
A
factor
of
10
may
considered
in
such
a
case,
while
a
reduced
factor
may
be
considered
for
mild
formulations.
Finally,
an
uncertainty
factor
may
be
applied
to
account
for
exposure
variables
that
may
influence
the
potential
for
induction
of
ACD,
including
the
site
of
the
body
exposed,
the
integrity
of
the
skin,
and
the
potential
for
multiple
exposures.
Using
the
above
approaches,
a
maximum
uncertainty
factor
of
1000
or
3000
could
be
derived
depending
on
the
criteria
used.
By
contrast,
a
minimum
uncertainty
factor
of
10
could
be
derived
if
results
from
human
studies
are
used.

Thresholds
for
induction
of
ACD
can
occur
following
a
single
exposure
of
sufficient
magnitude,
after
contact
with
a
large
area
of
skin,
or
as
a
consequence
of
repeated
skin
applications
(
Marzulli
and
Maibach).
Griem
et
al.
(
2003)
suggested
a
possible
higher
sensitizing
potency
of
a
chemical
upon
repeated
exposures.
This
would
make
sense
in
the
case
of
hexavalent
chromium,
as
the
significant
irritancy
of
the
chemical
could
lend
itself
to
an
increased
sensitizing
potency
by
allowing
more
chemical
to
penetrate
the
stratum
corneum.

QUESTION
1:
What
are
the
strengths
and
weaknesses
of
the
proposed
quantitative
approach
for
determination
of
induction
thresholds
to
dermal
sensitizing
chemicals?
What
other
approaches
does
the
Panel
recommend
EPA
consider?
Which
uncertainty
factors
does
the
Panel
feel
are
the
most
appropriate
for
application
to
quantitative
methods
of
induction
threshold
determination?
What
factors
should
be
included
in
the
determination
of
the
magnitude
of
each
uncertainty
factor?

ISSUE
2:
Quantitative
Risk
Assessment
for
the
Elicitation
Phase
of
ACD
Several
proposals
have
been
published
regarding
determination
of
elicitation
thresholds
in
sensitized
populations.
The
Minimum
Elicitation
Threshold
(
MET)
concept
has
been
discussed
in
previous
publications
(
Nethercott
et
al.,
1994;
Zewdie,
1998;
NJDEP,
1998;
Basketter
et
al.,
2003)
specifically
with
respect
to
hexavalent
chromium.
The
concept
behind
the
MET
is
that
there
is
an
`
elicitation
threshold'
below
which
no
sensitization
reaction
is
expected;
thus,
the
MET
is
analogous
to
an
RfD
(
Horowitz
and
Finley,
1994).
The
setting
of
an
MET
is
usually
performed
as
a
result
of
tests
in
previously
sensitized
individuals;
thus,
the
MET
is
considered
protective
of
elicitation
reactions.
However,
there
has
not
been
an
extensive
discussion
of
the
criteria
for
employing
this
concept
for
purposes
of
risk
assessment.

QUESTION
2:
What
are
the
strengths
and
weaknesses
of
the
proposed
quantitative
approaches
for
determination
of
elicitation
thresholds
to
dermal
sensitizing
chemicals?
What
other
approaches
does
the
Panel
recommend
that
EPA
consider?
Which
uncertainty
factors
does
the
Panel
feel
are
the
most
Page
4
of
5
appropriate
for
application
to
quantitative
methods
of
elicitation
threshold
determination?
What
factors
should
be
included
in
the
determination
of
the
magnitude
of
each
uncertainty
factor?

ISSUE
3:
Children
Sensitivity
Paustenbach
et
al.
(
1992)
and
Felter
et
al.
(
2002)
have
discussed
the
issue
of
whether
children
are
more
or
less
at
risk
for
development
of
ACD.
Paustenbach
et
al.
addressed
this
issue
specifically
for
hexavalent
chromium,
and
this
paper
concluded
that
risk
to
children
ages
3
to
8
is
not
likely
to
be
greater
than
adults
as
there
is
no
evidence
that
repeated
exposures
to
hexavalent
chromium
places
a
person
at
greater
risk
of
sensitization.
Felter
et
al.
suggested
that
infants
and
children
may
actually
be
at
lower
risk
for
development
of
ACD
based
on
data
gathered
from
dinitrochlorobenzene
and
pentadecylcatechol
(
poison
ivy
allergen).
However,
it
is
also
understood
that
young
children
may
not
have
been
exposed
to
different
allergens
as
compared
to
adults.
In
addition,
increased
frequency
of
exposure
in
children
may
increase
the
chance
of
induction
to
different
allergens.

QUESTION
3:
Does
the
Panel
agree
that
the
available
scientific
data
suggest
no
significant
difference
in
the
relative
sensitivity
of
children
vs.
adults
to
the
induction
and/
or
elicitation
of
ACD?
If
so,
please
provide
scientific
justification
for
this
position.
If
the
Panel
disagrees,
please
provide
scientific
justification,
including
supporting
data
and/
or
uncertainties
in
the
explanation.

ISSUE
4:
Case
Example
­
Cr(
VI)
in
treated
wood
Data
from
murine
LLNA
tests
as
well
as
from
human
patch
testing
studies
using
hexavalent
chromium
are
available
in
the
scientific
literature.
Results
of
LLNA
testing
show
EC3
values
that
indicate
area
doses
that
result
in
the
induction
of
sensitization
in
the
mouse,
while
the
results
of
patch
test
studies
in
humans
show
area
doses
that
result
in
elicitation
of
sensitization
in
already
sensitized
individuals.
In
the
Agency's
initial
assessment
seeking
to
assess
dermal
sensitization
risk
from
hexavalent
chromium,
the
lowest
dose
tested
(
0.018
ug/
cm2)
from
the
human
patch
test
study
of
Nethercott
et
al
(
1994)
was
selected
for
determination
of
dermal
risk
from
hexavalent
chromium.
A
10x
uncertainty
factor
(
3x
for
use
of
the
lowest
dose
tested
[
LOAEL]
in
this
study,
and
3x
to
account
for
the
small
size
of
the
study
population
in
the
Nethercott
study)
was
applied,
resulting
in
a
`
safe
area'
dose
of
0.0018
ug/
cm2.
Use
of
the
test
data
of
Basketter
et
al.
(
2001)
and
Hansen
et.
al
(
2003)
also
result
in
derivation
of
similar
`
safe'
area
doses
of
0.001
and
0.003

g/
cm2
respectively.
Use
of
the
murine
LLNA
test
data
and
application
of
an
uncertainty
factor
of
either
1000
or
3000
calculated
`
safe'
area
doses
of
0.01
or
0.003

g/
cm2
respectively.

QUESTION
4:
Please
comment
on
the
methods
used
for
derivation
of
`
safe'
area
doses
using
the
Page
5
of
5
available
LLNA
data
and
the
human
patch
test
data,
including
the
magnitude
of
the
applied
uncertainty
factors,
and
include
a
scientific
rationale
in
support
of
your
position.
Please
comment
on
whether
it
is
scientifically
supportable
to
derive
separate
`
safe'
area
doses
for
protection
against
induction
of
dermal
sensitization
as
well
as
elicitation
in
sensitized
individuals
by
hexavalent
chromium?
