Document ID: EPA-HQ-OPP-2002-0309-0012
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2002-12-03T05:00Z

­
1­
UNITED
STATES
ENVIRONMENTAL
PROTECTION
AGENCY
WASHINGTON,
D.
C.
20460
OFFICE
OF
PREVENTION,
PESTICIDES
AND
TOXIC
SUBSTANCES
DATE:
February
28,
2001
MEMORANDUM
SUBJECT:
Oxadiazon:
Assessment
of
Mode
of
Action
on
Liver
Carcinogenicity
FROM:
Nancy
McCarroll
Toxicology
Branch
Health
Effects
Division
(
7509C)

THRU:
Pauline
Wagner,
Co­
Chair
Mechanism
of
Toxicity
Assessment
Review
Committee
(
MTARC)
Health
Effects
Division
(
7509C)

and
Karl
Baetcke,
Co­
Chair
Mechanism
of
Toxicity
Assessment
Review
Committee
(
MTARC)
Health
Effects
Division
(
7509C)

TO:
William
Burnham,
Senior
Scientist
Advisor
Chairman,
Cancer
Assessment
Review
Committee
(
CARC)
Immediate
Office
Health
Effects
Division
(
7509C)

cc:
Anna
Lowit,
Executive
Secretary,
MTARC
Veronique
LaCapra,
Chemical
Review
Manager,
SRRD
Branch
Files
Oxadiazon
­
2­
PC
Code:
109001
DP
Barcode:
D266361
Action:
The
Mechanism
of
Toxicity
Assessment
Review
Committee
(
MTARC)
met
on
February
8,
2001
to
evaluate
the
mechanistic
and
other
relevant
data
to
determine
whether
the
available
findings
support
peroxisome
proliferation
as
a
possible
mechanism
of
action
for
liver
tumors
induction
by
Oxadiazon.
The
mechanistic
data
included
one
14­
day
oral
study
in
rats
submitted
by
the
Registrant
(
MRID
No.
42310001)
and
a
journal
article
(
Richert
et
al.,
1996).

Conclusions:
Based
on
the
weight­
of­
the­
evidence,
there
are
sufficient
data
to
classify
Oxadiazon
as
a
non­
genotoxic
hepatocarcinogen.
The
available
data
also
provide
suggestive
evidence
of
peroxisome
proliferation.
There
are,
however,
weaknesses
in
the
database
that
preclude
acceptance
of
peroxisome
proliferation
as
the
mode
of
action
for
Oxadiazon­
induced
liver
tumors;
these
include:

(
1)
No
cell
proliferation
data
were
reported
for
rats
or
mice;
hence,
mitogenesis
could
not
be
mechanistically
linked
to
proliferation
of
peroxisomes.

(
2)
There
was
no
convincing
concordance
between
the
dose
response
for
peroxisomal
enzymatic
activity
and
tumor
formation.

(
3)
The
role
of
decreased
catalase
activity,
which
generally
increases
in
the
presence
of
a
proxisome
proliferator,
was
not
explained
by
the
investigators
of
the
submitted
study.

The
Committee
concluded,
therefore,
that
peroxisome
proliferation
may
be
a
possible
mode
of
action
for
Oxadiazon­
induced
liver
tumors
in
rats
and
mice.
However,
because
of
shortcomings
in
the
database,
the
available
information
do
not
support
this
proposed
non­
genotoxic
mode
of
action
for
Oxadiazon
at
this
time.
­
3­
Committee
Members
in
Attendance
Members
who
were
present
and
gave
electronic
concurrence
to
this
report
were:
Karl
Baetcke,
Mike
Ioannou,
Anna
Lowit,
Alberto
Protzel,
and
Pauline
Wagner
Data
evaluation
prepared
by:
Nancy
McCarroll,
Toxicology
Branch
Also
in
attendance
were:
Veronique
LaCapra
of
SRRD
and
HaJung
Sung
of
Rural
Development
Administration,
Korea.
­
4­
Proposed
Mechanism
of
Action
for
Oxadiazon:
Recommendations
to
the
MTARC
I.
Background:
The
relevance
of
peroxisome
proliferation
(
PP)
to
hepatocarcinogenesis
has
been
previously
discussed
(
see
HED
Memorandum:
Lactofen:
Assessment
of
Mode
of
Action
on
Liver
Carcinogenicity
from
Robert
F.
Fricke
to
Christine
Olinger,
dated
February
15,
2001).
Within
this
document,
criteria
are
presented
that
must
be
satisfied
before
a
non­
genotoxic
hepatocarcinogen
can
be
classified
as
a
PP.
These
criteria,
which
were
established
through
the
joint
efforts
of
MTARC
and
CARC,
are:

1.
Changes
in
liver
morphology
indicating
hepatomegaly
as
measured
by
increased
relative
liver
weights
and
an
increased
number
of
peroxisomes
as
measured
by
morphometric
analysis.

2.
Evidence
of
cell
proliferation
as
measured
by
increased
relative
liver
weights
and
increased
replicative
DNA
synthesis
as
measured
by
increased
hepatocellular
BrdU
nuclear
labeling
in
light
microscopy.

3.
Increased
levels
of
enzymes
involved
in
peroxisomal
fatty
acid
metabolism,
especially
acyl
or
palmitoyl
CoA
oxidase.

II.
Physical
and
Chemical
Properties
of
Oxadiazon
Oxadiazon,
2­
tert­
butyl­
4­(
2,4­
dichloro­
5­
isopropoxyphenyl)­
1,3,4­
oxadiazol­
5­
one,
is
a
selective
pre­
emergent
and
early
post
emergence
herbicide
that
is
effective
primarily
for
the
control
of
annual
grasses
and
broadleaf
weeds
in
turf.
The
trade
name
for
Oxadiazon
in
the
U.
S.
is
Ronstar.
Oxadiazon
has
no
food
or
feed
uses.
Most
of
the
usage
is
allocated
to
golf
courses.
However,
the
Registrant
is
now
supporting
use
of
Oxadiazon
on
golf
courses,
apartment/
condo
lawns,
athletic
fields,
parks,
playgrounds,
and
cemeteries.

The
mechanism
of
action
is
contact
inhibition
by
affecting
young
shoots
as
they
grow
through
the
treated
zone
(
pre­
emergence)
and
complete
coverage
(
post­
emergence).
Oxadiazon
destroys
cell
membranes
and
inhibits
photosynthesis,
probably
by
generating
oxidizing
radicals
in
light
and
is
a
powerful
inhibitor
of
plant,
yeast
and
mouse
protoporphyrinogen
oxidase,
an
enzyme
critical
in
the
biosynthesis
of
chlorophyll
and
heme
(
Matringe
et
al.,
1989).

Oxadiazon
has
the
following
structure:

Empirical
Formula:
C
15
H
18
Cl
2
N
2
O
3
III.
Classification
of
Carcinogenic
Potential
­
5­
According
to
the
Cancer
Assessment
Review
Committee
(
CARC)
report,
dated
August
27,
1987
(
HED
Document
No.
007798),
the
original
peer
review
(
November
21,
1984,
HED
Document
No.
004097)
placed
Oxadiazon
into
Group
B2
(
probable
human
carcinogen)
but
there
was
a
minority
opinion
that
the
agent
should
be
placed
in
Group
C
(
possible
human
carcinogen).
Review
of
the
weight­
of­
theevidence
on
Oxadiazon
by
the
Scientific
Advisory
Panel
(
dated
November
20,
1987)
reiterated
this
minority
view.
Consequently,
the
current
Agency
decision
on
the
carcinogenic
potential
of
Oxadiazon
concurs
with
the
Scientific
Advisory
Panel's
(
SAP)
classification
of
Oxadiazon
as
a
Group
C
carcinogen
and
the
Q1*
has
been
set
at
1.4
x
10­
1(
mg/
kg/
day)­
1
in
human
equivalents.
The
rationale
for
the
original
classification
as
group
B2
was
based
on
the
increased
incidence
of
malignant
or
combined
malignant
and
benign
liver
tumors:
a)
in
multiple
species
(
CD
­
1
mice
and
F344
rats
of
one
or
both
sexes)
and
in
multiple
experiments
(
liver
tumors
in
two
mouse
studies
and
in
one
rat
study).
The
decision
to
reclassify
Oxadiazon
as
a
Group
C
carcinogen
was
based
on
the
rationale
that
liver
tumors
were
produced
in
two
of
the
three
positive
studies
(
one
mouse
study
and
one
rat
study)
at
doses
that
exceeded
the
maximum
tolerated
dose
(
MTD).

Since
the
time
of
the
classification
of
the
oncogenic
potential
of
Oxadiazon
as
a
Group
C
carcinogen,
a
new
chronic/
oncogenicity
study
in
rats
(
MRID
No.
40993401)
and
a
new
carcinogenicity
study
in
mice
(
MRID
No.
40993301)
have
been
submitted
to
the
Agency.
The
Hazard
Identification
Assessment
Review
Committee
(
HIARC)
recommended
that
the
Q1*
be
revisited
and
that
the
Cancer
Assessment
Review
Committee
(
CARC)
reconvene
to
evaluate
these
more
recent
studies.
The
CARC
is
awaiting
the
outcome
of
the
current
MTARC
deliberations
before
evaluating
these
more
recent
chronic
studies.

IV.
Mutagenicity
Oxadiazon
is
neither
mutagenic
nor
clastogenic
but
does
cause
neoplastic
cell
transformation
in
vitro.
Acceptable
bacterial
assays
with

97.49%
Oxadiazon
were
negative
for
gene
mutations
in
Salmonella
typhimurium
and
Escherichia
coli
(
MRID
Nos.
00069893
and
41871701).
Similarly,
neither
95.5%
Oxadiazon
nor
recrystallized
Oxadiazon
(
100%)
were
mutagenic
or
clastogenic
in
cultured
mammalian
cells
and
did
not
cause
unscheduled
DNA
synthesis
(
UDS)
in
primary
rat
hepatocytes.
There
is,
however,
evidence
that
both
formulations
induced
neoplastic
transformation
in
Syrian
hamster
kidney
cells
both
in
the
presence
and
in
the
absence
of
S9
activation.
The
finding
of
positive
cell
transformation
supports
the
evidence
from
mouse
bioassays
(
MRID
Nos.
00444322,
00115733
and
40993301)
and
the
rat
long­
term
studies
(
MRID
Nos.
00149003/
00157780
and
40993401)
of
liver
tumor
induction.

V.
Evaluation
of
the
Toxicology
Database
for
Peroxisome
Proliferation
as
a
Possible
Mechanism
of
Action
for
Liver
Tumors
Induced
by
Oxadiazon
Data
submitted
by
the
Registrant
are
from
both
guideline
and
one
non­
guideline
(
mechanistic)
studies.
In
general,
the
database
for
Oxadiazon
is
complete
and
has
been
evaluated
with
respect
to
the
potential
of
Oxadiazon
to
induce
liver
tumors
via
peroxisome
proliferation.
Results
from
submitted
studies
were
selected
to
illustrate
findings
pertinent
to
peroxisome
proliferation
as
the
proposed
mechanism
of
action
of
Oxadiazon
and
are
summarized
in
Table
1.
In
addition,
a
published
study
conducted
in
rats,
mice
­
6­
and
dogs
(
Richert
et
al.,
1996)
has
also
been
considered
with
pertinent
results
presented
in
Table
1.
All
data
have
been
assessed
relative
to
the
peroxisome
proliferation
criteria
presented
earlier.

A.
Criterion
1:
Increased
Liver
Weights
and
Increased
Peroxisome
Proliferation
As
shown
in
Table
1,
increased
absolute
and
relative
liver
weights
were
seen
in
both
sexes
of
several
rat
strains
(
Sprague­
Dawley,

only
examined,
Fischer
344,
CD,
Wistar)
in
male
and
female
mice
(
CD­
1
and
ICR­
JCL)
and
Beagle
dogs.
The
length
of
exposure
ranged
from
14
days
to
2
years.
Doses
causing
increased
liver
weights
in
rats
ranged
from

200
mg/
kg/
day
(
14
days),
51
mg/
kg/
day
(
6
months)
to
6
mg/
kg/
day
(
24
months).
In
mice,
the
earliest
time
that
liver
weights
were
recorded
in
the
Guideline
studies
was
52
weeks.
At
this
interval,
significant
effects
were
seen
at
113
mg/
kg/
day.
By
104
weeks,
liver
weight
increases
were
noted
at
doses

12
mg/
kg/
day.
Similar
results
of
significantly
increased
absolute
and
relative
liver
weights
have
been
shown
by
Richert
et
al.(
1996)
in
Sprague­
Dawley
rats
(

200
mg/
kg/
day,
14
days)
and
CD­
1
mice
(

200
mg/
kg/
day,
as
early
as
28
days
post­­
treatment)
but
not
in
Beagle
dogs
after
28­
days
of
exposure.
Regardless
of
the
rodent
species,
hepatomegaly
was
generally
more
pronounced
in
males
than
in
females.
Hence,
the
data
show
convincing
evidence
pointing
to
hypertrophy
as
the
cause
of
hepatomegaly
in
rats
and
mice.
There
is
also
evidence
of
hyperplasia
in
CD­
1
mice
but
it
was
only
seen
in
one
of
two
studies
conducted
with
this
mouse
strain
and
was
not
reported
in
strain
ICRJCL

In
the
14­
day
oral
mechanism
study
(
MRID
No.
42310001)
with
Sprague
Dawley
rats,
electron
micrographs
showed
an
increase
in
peroxisomes
at
500
mg/
kg/
day
Oxadiazon.
Livers
from
lower
dose
groups
were
not
examined
microscopically.
However,
electron
microscopy
of
rat
and
mouse
liver
sections
in
the
study
of
Richert
et
al.
(
1996),
showed
a
qualitative
and
dosedependent
increase
in
peroxisomes
at
20
mg/
kg/
day
(
minimal
in
5
of
11
mice),
100
mg/
kg/
day
(
moderate
in
7
of
7
mice)
and
200
mg/
kg/
day
(
severe
in
9
of
9
mice).
Eight
of
10
rats
administered
500
mg/
kg/
day
Oxadiazon
also
showed
a
"
severe"
increase
in
peroxisomes.

B.
Criterion
2:
Evidence
of
Cell
Proliferation
As
stated
above,
there
is
ample
evidence
of
increased
relative
liver
weights;
however,
no
study
has
been
submitted
on
the
effects,
if
any,
of
Oxadiazon
on
replicative
DNA
synthesis.
It
is
of
note
that
Oxadiazon
was
tested
in
two
in
vitro
assays
(
MRID
Nos.
00115723
and
­
27)
for
UDS
in
primary
rat
hepatocytes.
Both
studies
were
negative
for
UDS,
and
cells
undergoing
DNA
replication
rather
than
DNA
repair
were
reported
to
be
evenly
distributed
among
all
groups.

C.
Criterion
3:
Evidence
of
Increased
Enzymatic
Activity
Increased
levels
of
enzymes
associated
with
liver
toxicity
(
ALP,
SGOT,
SGPT
and/
or
LDH)
were
recorded
in
subchronic
dietary
studies
lasting
90­
days
in
rats
as
well
as
chronic
studies
lasting
1­
2
years
in
rats,
mice
or
dogs
and
can
be
seen
in
many
of
the
studies
listed
in
Table
1.
In
the
14­
day
oral
mechanism
study
(
MRID
No.
42310001)
with
Sprague
Dawley
rats,
dose­
related
increases
in
palmitoyl
CoA
oxidation
(
PAO),
palmitoyl
carnitine
transferase
and
acetyl
carnitine
­
7­
transferase
(
ACT)
were
reported
at
20,
200
and
500
mg/
kg/
day;
effects
at

200
mg/
kg/
day
were
significant.
Catalase
activity
was,
however,
significantly
reduced
at
200
and
500
mg/
kg/
day.
This
decrease
in
catalase
activity,
which
is
generally
increased
in
the
presence
of
peroxisome
proliferation,
was
not
explained
by
the
investigators.

In
agreement
with
the
peroxisomal
enzyme
activity
results
from
the
submitted
14­
day
study,
Richert
et
al.
(
1996)
found
a
significant
(
p<
0.05)
and
dose­
related
increase
in
rat
(
PAO)
and
ACT
at
200
and
500
mg/
kg/
day.
In
mice,
the
same
investigators
noted
that
increases
in
PAO
were
achieved
at
100
(
174%
of
control)
and
200
mg/
kg
(
p<
0.05).
ACT
was
also
significantly
increased
at
these
levels.
No
biochemical
assays
in
dogs
were
performed.
In
vitro
studies
conducted
as
part
of
these
investigations
showed
concentration
dependent
increases
in
both
PAO
and
ACT
at
2.5­
10
x
10­
5
M
Oxadiazon
in
primary
rat
hepatocytes;
no
effect
were
seen
in
cultured
human
hepatocytes
at
comparable
doses.

While
increases
in
the
activity
of
the
two
enzyme
markers
for
peroxisome
proliferation
followed
exposure
to
Oxadiazon,
the
concordance
between
the
dose
response
for
peroxisome
enzymes
and
liver
tumor
induction
is
not
strong.
As
shown
in
Table
2,
a
dose
of
113
mg/
kg/
day
induced
significant
(
p<
0.01)
increases
in
adenomas
(+
23%)
carcinomas
(+
41%)
and
adenomas/
carcinomas
combined
(+
63%)
in
male
mouse
livers
while
a
comparable
dose
(
100
mg/
kg/
day)
caused
only
a
moderate
increase
in
the
number
of
peroxisomes
and
a
less
than
2­
fold
increase
in
PAO.
At
10.6
mg/
kg/
day
in
the
oncogenicity
study,
adenomas
(+
17%)
carcinomas
(+
16%)
and
adenomas/
carcinomas
combined
(+
33%)
were
also
significantly
increased.
However,
only
a
slight
increase
in
the
number
of
peroxisomes
and
no
increased
in
PAO
were
seen.

Similar
evidence
of
a
weak
response
in
peroxisome
enzymes
was
note
in
male
rats
dosed
with
either
200
or
500
mg/
kg/
day
Oxadiazon
in
the
submitted
mechanistic
study
or
the
published
results
of
Richert
et
al.,
(
1996).
Increases
in
PAO
only
ranged
from
1.4­
to
2.1­
fold
over
control
while
liver
tumor
induction
was
achieved
at
3.5
mg/
kg/
day.
ACT
activity,
which
is
distributed
not
only
in
the
peroxisomes
but
also
in
endoplasmic
reticulum
and
mitochondria,
only
reached
a
6­
fold
increase
in
male
rats
at
500
mg/
kg/
day.
Although
temporal
associations
were
considered,
the
Committee
acknowledged
,
based
on
its
experience
with
peroxisome
proliferators
that
increased
peroxisome
enzyme
activity
generally
occurs
(
regardless
of
the
time
interval)
at
doses
near
the
tumor
doses.
It
concluded,
therefore,
that
the
findings
with
Oxadiazon
indicate
that
tumorigenic
doses
were
substantially
lower
than
levels
inducing
peroxisome
enzymes.

VI.
Other
Modes
of
Action
As
stated
previously,
Oxadiazon
is
not
mutagenic,
and
with
the
exception
of
peroxisome
proliferation,
no
other
mode
of
action
has
been
hypothesized
for
Oxadiazon.
However,
a
possible
alternative
mode
of
action
could
be
oxidative
damage
to
DNA
through
the
production
of
hydrogen
peroxide
by
increased
fatty
acid
oxidation.
This
is
because
of
the
decreased
catalase
activity
noted
in
the
14­
day
submitted
study.
Theoretically,
the
reduction
in
catalase
activity
could
lower
the
degradation
rate
of
H
2
O
2
thus
initiating
increased
levels
of
H
2
O
2.
Cattley
et
al.
(
1998)
have
hypothesized
that
since
catalase
levels
"
are
never
increased
more
than
twofold
an
imbalance
between
generation
and
degradation
of
H
2
O
2
within
the
peroxisome"
would
exist.
The
excess
H
2
O
2,
that
would
result
from
a
loss
of
catalase
­
8­
(
as
demonstrated
in
the
Oxadiazon
study),
could
conceivably
escape
from
the
peroxisome,
react
with
transition
metals
and
form
hydroxyl
radicals.
Cattley
et
al.
note
that
if
these
radicals
form
in
the
proximity
of
macromolecules,
oxidative
damage
may
occur.

VII.
Structural
Activity
Relationships
(
SAR)

Oxadiazon
is
not
known
to
be
structurally
related
to
other
known
herbicides
that
are
also
peroxisome
proliferators
(
Richert
et
al.,
1996);
however,
a
wide
variety
of
chemical
classes
have
been
shown
to
have
the
potential
to
induce
peroxisome
proliferation.

VIII.
Conclusions
Based
on
the
weight­
of­
the­
evidence,
there
are
sufficient
data
to
classify
Oxadiazon
as
a
nongenotoxic
hepatocarcinogen.
The
available
data
also
provide
suggestive
evidence
of
peroxisome
proliferation.
There
are,
however,
weaknesses
in
the
database
that
preclude
acceptance
of
peroxisome
proliferation
as
the
mode
of
action
for
Oxadiazon­
induced
liver
tumors;
these
include:

(
1)
No
cell
proliferation
data
were
reported
for
rats
or
mice;
hence,
mitogenesis
could
not
be
mechanistically
linked
to
proliferation
of
peroxisomes.

(
2)
There
was
no
convincing
concordance
between
the
dose
response
for
peroxisomal
enzymatic
activity
and
tumor
formation.

(
3)
The
role
of
decreased
catalase
activity,
which
generally
increases
in
the
presence
of
a
proxisome
proliferator,
was
not
explained
by
the
investigators
of
the
submitted
study.

The
Committee
concluded,
therefore,
that
peroxisome
proliferation
may
be
a
possible
mode
of
action
for
Oxadiazon­
induced
liver
tumors
in
rats
and
mice.
However,
because
of
shortcomings
in
the
data
base,
the
available
information
do
not
support
this
proposed
non­
genotoxic
mode
of
action
for
Oxadiazon
at
this
time.

REFERENCE
Richert,
L.,
Price,
S.,
Chesne,
C.,
Maita,
K.
Carmichael,
N.
(
1996).
Comparison
of
the
induction
of
hepatic
peroxisome
proliferation
by
the
herbicide
oxadiazon
in
vivo
in
rats,
mice,
and
dogs
and
in
vitro
in
rat
and
human
hepatocytes.
Toxicol.
Appl.
Pharmacol
141:
35­
43.

Cattley,
R.
C.,
DeLuca,
J.,
Elcombe,
C.,
Fenner­
Crisp,
P.,
Lake,
B.
G.,
Marsman,
D.
S.,
Pastoor,
T.
A.,
Popp,
J.
A.,
Robinson,
D.
E.,
Schwetz,
B.,
Tugwood,
J.,
Wahli,
W.
(
1998).
Do
peroxisome
proliferating
compounds
pose
a
hepatocarcinogenic
hazard
to
humans?
Reg
Toxicol
and
Pharm
27:
47­
60.

Matringe,
M.,
Camadro,
J.
M.,
Labbe,
P.,
Scalla,
R.
(
1989).
Protoporphyrinogen
oxidase
inhibition
by
three
peroxidizing
herbicides:
oxadiazon,
LS
82­
556
and
M&
B
39279.
FEBS
Letters
245,
number
1,
2:
35­
38.
­
9­

Table
1
:
Summary
of
Liver
Effects
with
Oxadiazon
Study
(
MRID)
Liver
Weight
Liver
Enzymes
Liver
Histopathology
(
Nonneoplastic)
Liver
histopathology
(
Tumors)

14­
Day
Oral
Peroxisome
Proliferation
­

Rat
(
Sprague­
Dawley)

(
42310001):
0,
20,
200,

500
mg/
kg/
day
Abs
&
rel
wt

(
p<
0.05)

200
&
500
mg/
kg
(
p<
0.05)
and
dose­
related
at
200
&
500
mg/
kg

catalase,

PAO,

palmitoyl
carnitine
transferase,

ACT,

G
6
PO4ase
at
500
mg/
kg
At
500
mg/
kg:

peroxisome
proliferation;

lipids;

sinusoidal
dilation
&

rough
endoplasmic
reticulum
damage
NA
Oral
Peroxisome
Proliferation
in

Rat
(
Sprague­
Dawley):
0,
20,

200,
500
mg/
kg/
day­­
14
days
(
10/
group)

Mice
(
CD­
1):
0,
100,

200
mg/
kg/
day­­
28
days
(
12/
group)

Dogs
(
Beagles):
0,
500
mg/
kg­­
28
days
(
3/
group)

(
Richert
et
al.,
1996)
Abs
&
rel
wt

(
p<
0.05)


200
mg/
kg/
day­­
rats

100
mg/
kg/
day­­
mice
NS

500
mg/
kg/
day­­

dogs
Dose­
related

PAO
&

ACT;
(
p<
0.05)
at
200
&

500
mg/
kg/
day­­
rats
Dose­
related

PAO
&

ACT;
(
p<
0.05)
at
200
(
PAO)
&
200
&
500
mg/
kg/
day(
ACT)
­­
mice
At
500
mg/
kg
(
only
dose
tested):

peroxisome
proliferation
(
severe
in
8/
10
­
rats
Dose­
related

peroxisome
proliferation
(
minimal
at
20
5/
11;

moderate
at
100
7/
7;

severe
at
200
mg/
kg/
day
9/
9
­
mice)

No
effects­­
dogs
NA
Abbreviations:

ALP
=
Alkaline
phosphatase
LDH
=
Lactate
dehydrogenase
SGOT
=
Serum
glutamic­
oxaloacetic
transaminase
PAO
=
Palmitoyl
CoA
oxidase
SGPT
=
Serum
glutamic­
pyruvic
transaminase
ACT
=
Acetyl
carnitine
transferase
­
10­

Study
(
MRID)
Liver
Weight
Liver
Enzymes
Liver
Histopathology
(
Nonneoplastic)
Liver
Histopathology
(
Tumors)

90­
Day
Dietary


Rat
(
CD)

(
00111804):
0,
25,
100,

1000
mg/
kg/
day
Abs
&
rel
wt

(
p<
0.05)

100
&
1000
mg/
kg
(


)
wks
4
&
13:

ALP
(

100&
1000
mg/
kg;


1000
mg/
kg),
wk
13:

SGOT
(

100&
1000
mg/
kg;

1000
mg/
kg),

wks
4
&
13:

SGPT(

100&
1000
mg/
kg;


1000
mg/
kg)
At
1000
mg/
kg
(


)
&

100
mg/
kg
(

)
:
brown
pig.
Kupffer
cells
&
bile
canaliculi;
marked
variability
in
cell
size
and
staining
properties
of
hepatocytes
&

necrotic
hepatocytes
(
Above
findings
generally
seen
in

90%

&

60%

)
NA
Chronic/
Onco
Rat
(
Fischer
344)

(
00149003/
00157780):
0,

10,
100,
1000,
3000
ppm
(

0,
0.5,
4.8,
50.9,
163.1
mg/
kg/
day

;
0,
0.6,
5.9,

60.9,
192.7
mg/
kg/
day

)
Abs
&
rel
wt

(
p

0.05­

0.001)

6
mo:
1000
(

)
&
3000
ppm
(


)
;
12
mo:
1000
&
3000
ppm
(


)
;
24
mo:
100,
1000
&
3000
ppm
(


)
6
mo:
At

1000
ppm
(

)

ALP,
SGPT­­
(
at
3000
ppm

)

SGOT
(
at
3000
ppm

)

SGOT,
SGPT,

LDH,
ALP;
12
mo:
(
at

1000
ppm


)

ALP,

SGPT
;
24
mo:
(
at
3000
ppm

)

ALP,
LDH
Progressive
alterations
from
hypertrophy
through
fatty
changes
to
necrosis
(

1000
ppm

&
3000
ppm

)
(
p<
0.05)
pairwise
and
trend

adenomas
&

carcinomas
combined
(

1000
ppm

)
.
No
decrease
in
latency.

Benign
&
malignant
tumors
after
prolonged
exposure
to
hepatotoxic
doses
­
11­

Study
(
MRID)
Liver
Weight
Liver
Enzymes
Liver
Histopathology
(
Nonneoplastic)
Liver
histopathology
(
Tumors)

Chronic/
Onco
Rat
(
Wistar)
(
40993401):
0,

0,
3,
10,
100,
1000
ppm
(

0,
0.1,
0.4,
3.5,
39
mg/
kg/
day

;
0,
0.1,
0.4,

4.2,
44
mg/
kg/
day

)
Abs
&
rel
wt

(
p

0.05­

0.001)

26
wk:
1000
ppm
(


)
;

52
wk:
1000
ppm
(

)
;

78
wk:
1000
ppm
(


)
;

104
wk:
1000
ppm
(

)
wks
26:

LDH
(

1000
mg/
kg
&
wk
52);

ALP
(

1000
mg/
kg);

SGOT/
SGPT
(

1000
mg/
kg).
Wks
52,
78
&

104:
No
effects.
At
1000
ppm
(
p

0.01­

0.001):

centrilobular
hepato.
swell.(


)
;

brown
pigmentation
in
liver)
(


)
;

foci
of
cell
alteration
(

)
;

bile
duct
proliferation)

(

)
.
At
100
ppm
(
p<
0.05)
,

centrilobular
hepato.

swell.(

)
(

)
S
trend
(
p<
0.01)

&
S
pairwise
100
&

1000
ppm
(
p<
0.05­

0.01)
liver
adenomas
and/
or
carcinomas
combined.
At
1000
ppm,
S
pairwise
(
p<
0.05)
carcinomas
.

Onco
Mice
(
CD­
1)

(
00044322):
0,
300,

1000,
2000
ppm
(

0,
48,

153,
319
mg/
kg/
day

;

0,
62,
201,
417
mg/
kg/
day

)
Abs
&
rel
wt

(
p

0.05­

0.01)
at
104
wk:

300
ppm
(


)
wk
104:
(
p

0.05­

0.01)

ALP
(

300
ppm

,

1000
ppm

);

SGOT
(

1000
ppm


)
;

SGPT
(

300
ppm

,

1000
ppm

)

centrilobular
hypertrophy
(

300
ppm


)
;

diffuse
hepatocellular
hyperplasia
&

hypertrophy
(

300
ppm


)
;

nodular
hyperplasia
&

hypertrophy
(

300
ppm


)
;

focal
necrosis
(
2000
ppm


)
­­
no
stats
p<
0.01

hepatocarcinomas
(

1000
ppm


)
.
No
decrease
in
latency.
­
12­

Study
(
MRID)
Liver
Weight
Liver
Enzymes
Liver
Histopathology
(
Nonneoplastic)
Liver
histopathology
(
Tumors)

Onco
Mice
(
CD­
1)

(
00115733):
0,
100,
300,

1000,
2000
ppm
(

0,
12,

37,
122,
254
mg/
kg/
day

;
0,
14,
44,
143,
296
mg/
kg/
day

)
Abs
&
rel
wt

(
p

0.05­

0.001)
at
105
wk:

100
ppm
(

)
,

1000
ppm
(

)
Not
Done
No
detail;
terminal
sac:

lesions
listed
as
masses
(
all
dose
groups,
both
sexes),
pale
areas/
foci
(
all
dose
groups,
both
sexes),
raised
areas
(
all
dose
groups,
females
only)
unscheduled
deaths:
pigmented
Kupffer
cells,
hepatic
single
cell
necrosis
(
high­
dose
males)
p<
0.05­
0.01

liver
adenomas
(

100
ppm


)
;
p<
0.05

carcinomas
(

100
ppm

1000
ppm

)
;

p<
0.05­
0.01

combined
liver
adenomas
&

carcinomas
(

100
ppm


)
.
p<
0.05
trend
for
carcinomas
(

)
,
adenomas
(

)
&

combined
(


)

Onco
Mice
(
ICR­
JCL)

(
40993301):
0,
3,
10,

100,
1000
ppm
(

0,
0.3,

1,
11,
113
mg/
kg/
day

;

0,
0.3,
1,
9,
99
mg/
kg/
day

)
Abs
&
rel
wt

(
p

0.05­

0.001)
at
52
&
98
wk:

1000
ppm
(

)
,
98
wk:

1000
ppm
(

)
wks
52:

ALP
(

1000
mg/
kg
&
wk
98


1000
ppm);

SGOT
(


100
ppm).

SGPT
(


100
ppm
wk
52
&
at
wk
98;


1000
mg/
kg
at
wk
52)
At
1000
ppm
(
p<
0.001):

centrilobular
hepato.

swell.(

)
;

diffuse
hepatocellular
swell.(


)
;

brown
pigmentation
(


)

diffuse
hepatocellular
necrosis
(

only)
at
1000
ppm
(
p<
0.05)
but
(
p<
0.001)
at
100
ppm.

Also
in

at
100
ppm:

(
p<
0.001)

diffuse
hepatocellular
swell
and

brown
pigmentation
(

only)
p<
0.01

liver
adenomas
(

100
ppm

,
1000
ppm

)
;

p<
0.01

liver
carcinomas
(

100
ppm

,
1000
ppm

)

p<
0.01

liver
adenomas/
carcinomas
combined
(

100
ppm

,
1000
ppm

)
.


:
p<
0.05­
0.01
trend
for
liver
adenomas,
carcinomas,
and
adenomas/
carcinomas
combined.
­
13­

Study
(
MRID)
Liver
Weight
Liver
Enzymes
Liver
Histopathology
(
Nonneoplastic)
Liver
histopathology
(
Tumors)

1­
Year
Chronic
Dog
(
Beagles)
(
41326401)

0,
5,
20,
60,
200
mg/
kg/
day
Abs
&
rel
wt

(
p

0.05­

0.01)
at
necropsy:

:
rel

60
mg/
kg/
day­­
abs
at

60
mg/
kg/
day
also

but
NS;

:
abs

20
mg/
kg/
day­­
rel
also

but
S
only
at
60
mg/
kg/
day
wks
24
&
50:

SGOT
(

60
mg/
kg
(
p<
0.05)

periacinar
apoptosis
centriacinar
hepatocytic
vacuolation
None
2­
Generation
Reproduction
Rat
(
CD)

(
41239801)
0,
20,
60,

200
ppm
(

0,
1.5,
4.65,

15.5
mg/
kg/
day

;
0,

1.8,
5.6,
18.2
mg/
kg/
day

)
P
adults:
No
effect
F1
adults:
Sli

rel
wt
200
ppm

F1
and
F2
offspring:
Not
measured
Not
measured
P
adults:
No
effects
F1
adults:
periacinar
hepatocellular
hypertrophy
200
ppm

F1
or
F2
offspring:
No
effects
None
Abbreviations:

ALP
=
Alkaline
phosphatase
LDH
=
Lactate
dehydrogenase
SGOT
=
Serum
glutamic­
oxaloacetic
transaminase
PAO
=
Palmitoyl
CoA
oxidase
SGPT
=
Serum
glutamic­
pyruvic
transaminase
ACT
=
Acetyl
carnitine
transferase
a
Data
were
extracted
from
Richert
et
al.
(
1996).

b
Data
were
extracted
from
Richert
et
al.
(
1996).

c
Data
were
from
Mouse
23­
month
chronic
toxicity
and
oncogenicity
study
(
MRID
No.
40993301).

­
14­

Table
2.
Summary
of
Peroxisomal
Effects
and
Liver
Tumor
Induction
in
Male
Mice
Administered
Oxadiazon
Dose
(
mg/
kg/
day)
No.
of
Peroxisomesa
Peroxisomal
Enzyme
Activitiesb
Neoplasmsc
Palmitoyl
CoA
oxidase
(%

over
control)
Acetyl
carnitine
transferase
(%

over
control)
Adenomas
Carcinomas
Adenomas/
Carcinomas
Combined
0
0
­­
­­
2/
69
3%
3/
69
4%
5/
69
7%

0.3
­­
­­
­­
7/
71
10%
1/
71
1%
8/
71
11%

1.1
­­
­­
­­
2/
71
3%
4/
71
6%
6/
71
8%

10.6
­­
­­
­­
12/
69**

17%
11/
69*

16%
23/
69**

33%

20
Slight
(
6/
11)
106
113
­­
­­
­­

100
Moderate
(
7/
7)
174
389*
­­
­­
­­

113
­­
­­
­­
16/
71**

23%
29/
71**

41%
45/
71**

63%

200
Severe
(
9/
9)
259*
459.5*

*
Significantly
different
than
control
(
p<
0.05)

**
Significantly
different
than
control
(
p<
0.01)