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Hepatic iodothyronine 5'-deiodinase. The role of selenium

Authors:
J R Arthur
J R Arthur
J R Arthur
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Fergus Nicol at École Polytechnique
Fergus Nicol
Geoff J Beckett at The University of Edinburgh
Geoff J Beckett
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Abstract and Figures

Selenium (Se) deficiency decreased by 8-fold the activity of type 1 iodothyronine 5'-deiodinase (ID-I) in hepatic microsomal fractions from rats. Solubilized hepatic microsomes from rats injected with 75Se-labelled Na2SeO3 4 days before killing were found by chromatography on agarose gels to contain a 75Se-containing fraction with ID-I activity. PAGE of this fraction under reducing conditions, followed by autoradiography, revealed a single 75Se-containing protein (Mr 27,400 +/- 300). This protein could also be labelled with 125I-bromoacetyl reverse tri-iodothyronine, an affinity label for ID-I. The results suggest that hepatic ID-I is a selenoprotein or has an Se-containing subunit essential for activity.
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BiQchem.
J.
(1990)
272,
537-540
(Printed
in
Great
Britain)
Hepatic
iodothyronine
5'-deiodinase
The
role
of
selenium
John
R.
ARTHUR,*
Fergus
NICOL*
and
Geoffrey
J.
BECKETTt
*Division
of
Biochemical
Sciences,
Rowett
Research
Institute,
Greenburn
Road,
Bucksburn,
Aberdeen
AB2
9SB,
and
tUniversity
Department
of
Clinical
Chemistry,
Royal
Infirmary,
Edinburgh
EH3
9YW,
Scotland,
U.K.
Selenium
(Se)
deficiency
decreased
by
8-fold
the
activity
of
type
I
iodothyronine
5'-deiodinase
(ID-I)
in
hepatic
microsomal
fractions
from
rats.
Solubilized
hepatic
microsomes
from
rats
injected
with
75Se-labelled
Na'SeO3
4
days
before
killing
were
found
by
chromatography
on
agarose
gels
to
contain
a
75Se-containing
fraction
with
ID-I
activity.
PAGE
of
this
fraction
under
reducing
conditions,
followed
by
autoradiography,
revealed
a
single
75Se-containing
protein
(Mr
27400
+
300).
This
protein
could
also
be
labelled
with
125I-bromoacetyl
reverse
tri-iodothyronine,
an
affinity
label
for
ID-I.
The
results
suggest
that
hepatic
ID-I
is
a
selenoprotein
or
has
an
Se-containing
subunit
essential
for
activity.
INTRODUCTION
The
only
well-characterized
function
for
selenium
(Se)
in
animal
cells
is
as
a
component
of
the
glutathione
peroxidase
[1,2],
although
at
least
13
selenoproteins
have
been
identified
in
animal
cells.
It
has
been
suggested
that
some
of
these
have
a
role
in
endocrine-organ
metabolism,
particularly
in
the
thyroid
gland
[3,4].
Thyroxine
(T4)
is
produced
in
the
thyroid
gland
and
is
considered
to
be
a
prohormone,
since
it
is
converted
into
the
more
metabolically
active
3,3',5-tri-iodothyronine
(T3)
by
iodo-
thyronine
deiodinases
(IDs)
in
the
organs
of
the
body.
Two
forms
of
ID
can
perform
this
5'-monodeiodination
of
T4
to
T3.
The
type
I
enzyme
(ID-I)
is
present
in
liver
and
kidney
and
is
involved
in
the
production
of
plasma
T3,
whereas
the
brain,
pituitary
and
brown
adipose
tissue
contain
the
type
II
enzyme
(ID-IT).
Se
deficiency
inhibits
the
conversion
of
T4
into
T3
by
both
ID-I
and
ID-Il
[5-8].
Loss
of
ID
activity
appears
to
be
responsible
for
the
impaired
thyroid-hormone
metabolism
observed
in
Se-deficient
animals,
and
we
have
therefore
suggested
that
ID-I
and
ID-II
are
Se-containing
or
Se-dependent
proteins
[5,9].
Here
we
produce
further
evidence
of
an
association
of
Se
with
hepatic
ID-I.
MATERIALS
AND
METHODS
Reagents
7Se-labelled
Na2SeO3
(sp.
radioactivity
2.67
,uCi/,ug),
125I-labelled
reverse
tri-iodothyronine
(rT3;
sp.
radioactivity
<
1200
,uCi/,ug)
and
Hyperfilm-MP
were
from
Amersham
Inter-
national
(Amersham,
Bucks.,
U.K.).
Amino
acids
for
rat
diets
were
supplied
by
Forum
Chemicals,
Reigate,
Surrey,
U.K.
Heat-
inactivated
donor
horse
serum
was
obtained
from
Flow
Labora-
tories,
Rickmansworth,
Herts.,
U.K.
All
other
reagents
were
from
Sigma
Chemical
Co.
or
BDH
(both
of
Poole,
Dorset,
U.K.).
Animals
and
diets
Weanling
male
Hooded
Lister
rats
of
the
Rowett
Institute
strain
were
maintained
on
semisynthetic
diets
based
on
amino
acids
containing
either
<
0.005
mg
of
Se/kg
(basal;
-Se
diet')
or
supplemented
with
0.1
mg
of
Se/kg
(as
Na2SeO3;
'+
Se
diet')
[10].
The
rats
were
individually
housed
in
plastic
cages
with
stainless-steel
grid
tops
and
floors;
food
and
distilled
water
were
available
ad
libitum.
After
6
weeks,
rats
were
anaesthetized
with
diethyl
ether,
and
blood
was
collected
into
heparinized
tubes
by
cardiac
puncture.
Thereafter
livers
were
perfused
via
the
hepatic
portal
vein
with
0.15
mol
of
KCl/l
at
4
°C
to
remove
residual
blood.
The
livers
were
then
homogenized
in
potassium
phosphate
(0.125
mol/l)/EDTA
(1
mmol/l),
pH
7.4,
using
four
passes
of
a
Teflon-pestle/glass-body
Potter-Elvehjem
homogenizer.
Homo-
genates
were
centrifuged
at
12000
g
for
20
min
(at
4
°C),
and
the
resulting
supernatants
were
further
centrifuged
at
105
000
g
for
60
min
(at
4
°C)
in
an
MSE
65
high-speed
ultracentrifuge.
The
microsomal
fraction
was
resuspended
to
a
final
protein
con-
centration
of
approx.
10
mg/ml
in
the
homogenization
buffer.
For
'in
vivo'
labelling
studies,
male
Hood
Lister
rats
(250
g
body
wt.)
were
given
intraperitoneal
injections
of
250
,uCi
of
75Se
as
Na2Se3
containing
93.6
,ug
of
Se.
After
4
days
the
livers
were
removed
under
diethyl
ether
anaesthesia,
and
microsomal
frac-
tions
were
prepared
as
described
above.
Enzyme
assays
After
activation
with
the
105000
g
supernatant
from
liver
homogenates,
the
ID-I
activity
in
microsomal
fraction
was
determined
by
using
the
method
described
by
Sawada
et
al.
[11],
except
that
horse
rather
than
human
serum
was
used
to
pre-
cipitate
thyroid
hormones.
Glutathione
peroxidase
activity
was
assayed
using
H202
(0.25
mmol/l)
as
substrate
in
the
presence
of
GSH
(5
mmol/l)
[10].
Affinity
labelling
of
ID-I
N-Bromoacetyl-['25I]rT3
was
synthesized
from
[1251]rT3
using
the
method
of
Nikodem
et
al.
[12]
for
T3.
After
synthesis
the
1251.
containing
affinity
label
was
stored
in
ethyl
acetate/methanol
(7:3, v/v).
The
solvent
was
evaporated
from
0.6
,uCi
of
affinity
label
under
a
stream
of
dry
N2
before
the
addition
of
the
ID-I-
containing
fraction
and
incubation
of
the
mixture
for
15
min
at
37
°C
with
dithiothreitol
(DTT;
3
mmol/l)
and
EDTA
(3
mmol/l).
Abbreviations
used:
ID(-I),
(type
I)
5'-deiodinase;
T4,
thyroxine;
iodothyronine);
DTT,
dithiothreitol.
T3,
3,3',5-tri-iodothyronine;
rT3,
reverse
tri-iodothyronine
(3,3',5'-tri-
Vol.
272
537
J.
R.
Arthur,
F.
Nicol
and
G.
J.
Beckett
Solubilization
of
ID-I
Microsomal
suspension
(2
ml)
was
mixed
with
1
ml
of
pot-
assium
phosphate
(0.125
mol/l),
pH
7.4,
containing
CHAPS
(18
g/1),
EDTA
(1
mmol/l)
and
DTT
(3
mmol/l).
Thereafter
the
mixture
was
centrifuged
at
105
000
g
for
I
h
at
4
°C
and
the
supernatant,
which
contained
70
%
of
the
original
microsomal
ID-I
activity,
was
retained
for
subsequent
fractionation.
Fractionation
of
ID-I
The
solubilized
microsomal
fraction
(2
ml)
was
applied
to
an
85
cm
x
2
cm
column
packed
with
Sepharose
CL-6B.
The
column
was
eluted
with
potassium
phosphate
(125
mmol/l)/DTT
(1
mmol/l)/CHAPS
(1.0
g/1)/EDTA
(1
mmol/l),
pH
7.4;
2
ml
fractions
were
collected.
Each
fraction
was
assayed
for
ID-I
activity,
glutathione
peroxidase
activity,
total
protein
and
75Se
radioactivity.
Two
0.5
ml
subsamples
were
taken
from
the
column
fraction
containing
maximum
ID
activity
(tube
26;
see
Fig.
1
below).
One
subsample
was
allowed
to
react4
with
label
N-
bromoacetyl-[125I]rT3
for
15
min
then
both
subsamples
were
dialysed
for
18
h
twice
against
500
ml
of
Tris
(50
mmol/l)/EDTA
(0.5
mmol/l)/DTT
(1.0
mmol/l),
pH
7.4.
Thereafter
the
samples
were
concentrated
by
using
Centricon
filters
(10000-M,
cut-off;
Amicon)
and
treated
with
glycerol,
SDS
and
DTT
to
give
final
concentrations
of
20%
(v/v),
4%
(w/v)
and
50
mmol/l
re-
spectively.
The
solution
was
then
boiled
for
2
min
and
subjected
to
electrophoresis
[13]
(1.5
mm;
12%
acrylamide
gel/4
%
stack-
ing
gel)
using
a
Bio-Rad
Miniprotean
II
system
(Bio-Rad,
Watford,
Herts.,
U.K.).
Gels
were
fixed,
stained
with
Coomassie
Blue
and
dried
under
vacuum.
Proteins
labelled
with
75Se
or
1251
were
detected
by
autoradiography,
with
exposure
being
carried
out
at
-70
°C
for
72
h.
Further
quantitative
information
on
the
distribution
of
radioactivity
was
obtained
by
cutting
gels
after
autoradiography
into
1
mm
bands
and
counting
their
75Se
or
126I
activity
using
a
Packard
Cobra
y-radiation
counter
with
channel
settings
to
allow
dual-isotope
counting.
RESULTS
Microsomal
fraction
ID-I
activity
After
6
weeks
of
experiment,
Se-containing
glutathione
per-
oxidase
activity
was
1.28
+
0.09
units/mg
of
protein
(means
+
S.E.M.)
in
liver
from
the
Se-supplemented
group
compared
with
0.007
+
0.001
unit/mg
of
protein
in
the
rats
consuming
an
Se-
deficient
diet,
confirming
that
the
latter
animals
were
Se-deficient.
Table
1.
ID-I.
activity
in
microsomal
fractions
from
Se-deficient
and
Se-supplemented
rats
ID-I
activity
in
liver
microsomal
fractions
from
rats
which
had
consumed
Se-deficient
diet
for
6
weeks
from
weaning
was
approx.
10
%
of
that
in
fractions
from
Se-supplemented
control
rats
with
or
without
activation
by
liver
supernatant
(Table
1).
The
addition
of
the
105
000
g
liver
supernatants
from
+
Se
or
-
Se
rats
were
equally
effective
in
activating
the
ID-I
activity
in
microsomes
from
+
Se
or
-
Se
rats
(Table
1).
In
Hooded
Lister
rats,
main-
tained
on
a
standard
laboratory
diet
(Labsure,
Cambridge,
U.K.)
and
the
same
age
as
the
Se-supplemented
animals,
hepatic-
microsomal-fraction
ID-I
activity
was
323
+
8
fmol
of
iodine
liberated/min
per
mg
of
protein
(mean
+
S.E.M.)
from
activation
with
cytosol.
This
is
similar
to
the
activity
in
Se-supplemented
rats,
which
is,
therefore,
not
abnormally
elevated
(Table
1).
Solubilization
and
chromatography
of
microsomal-fraction
ID-I
activity
When
the
microsomal
fraction
was
solubilized
with
CHAPS
(6
mg/ml)
in
the
presence
of
DTT
(2
mmol/l)
and
centrifuged,
70
%
of
the
initial
ID-I
activity
was
recovered
in
the
supernatant.
It
was
established
in
preliminary
studies
that
this
was
the
optimal
concentration
of
CHAPS
for
solubilization
of
ID-I
activity.
When
the
solubilized
hepatic
microsomal
fraction
from
75Se-
treated
rats
was
subjected
to
exclusion
chromatography
on
an
agarose-gel
column,
two
peaks
of
75Se
radioactivity
were
obtained
U)
2.5
2.0]
1.5
C
1.0
0.5
CL
x
Z
0
0.
1
cn4
x
Hepatic
microsomal
and
105000
g
supernatant
fractions
were
pre-
pared
from
+
Se
and
-
Se
rats
as
described
in
the
Materials
and
methods
section.
The
Table
shows
microsomal
ID-I
activity
in
the
presence
and
absence
of
supernatant.
Results
are
means
+
S.E.M.
for
three
rats/group.
Significant
differences
from
the+
Se
activity
are
shown:
*
P
<
0.00
1.
ID-I
activity
(fmol
of
iodine
liberated/min
per
mg
of
protein)
Microsomal
Activator
fraction
...
+
Se
-
Se
None
+
Se
supernatant
-Se
supernatant
18+2.1
342
+
33
342
+40
2.1
+0.6*
33
+
27*
44+
24*
Z-.
0
E
a
60
-
45
-
30
-
15
-
0
-
I
20
30
40
50 60
70
Fraction
no.
Fig.
1.
Chromatography
of
solubilized
75Se-labelled
hepatic
nicrosomes
(microsomal
fraction)
on
Sepharose
6B-CL
Hepatic
microsomes
were
prepared
from
rats
injected
4
days
previously
with
75Se-labelled
Na2SeO3.
The
microsomes
were
solu-
bilized
and
chromatographed
on
Sepharose
6B-Cl;
thereafter
ID-I
and
glutathione
peroxidase
activity
were
determined
in
2
ml
column
fractions,
as
described
in
the
Materials
and
methods
section.
1990
------
1
1
--4
538
Hepatic
iodothyronine
5'-deiodinase
(Fig.
1).
One
was
eluted
at
the
void
volume
and
corresponded
to
the
single
peak
of
ID-I
activity.
The
second
peak
coincided
with
the
single
peak
of
glutathione
peroxidase
activity.
Two
samples
were
taken
from
the
central
fraction
of
the
deiodinase
peak,
and
one
of
these
was
allowed
to
react
with
N-bromoacetyl-[1251]rT3
to
label
the
enzyme.
The
samples
were
separated
by
SDS/PAGE
and
were
shown
by
autoradiography
to
contain
a
radioactive
band
corresponding
to
a
protein
with
Mr
27400+
300
(mean
+
S.E.M.,
five
determinations).
The
intensity
of
this
band
was
considerably
increased
in
the
subsample
that
was
treated
with
the
125I-containing
affinity
label
(Fig.
2).
Determination
of
the
Origin
-
M,
27400-
.:
....:;
:.
1
2
Fig.
2.
Autoradiograph
of
ID-I-containing
column
separation
of
proteins
by
SDS/PAGE
fractions
after
After
treatment
of
rats
with
7"Se-labelled
Na2SeO3
and
chromato-
graphy
of
solubilized
hepatic
microsomal
fraction
(Fig.
1),
the
column
fraction
with
the
greatest
ID-I
activity
was
separated
by
SDS/PAGE.
Lane
2,
fraction
before
reaction
with
N-bromoacctyl-
[125I]rT3;
lane
1,
fraction
after
reaction
with
N-bromoacetyl-[125IIrT3.
i
6
z-
v
20
16
12
-8
-4
L0
20
-16
-12
-
8
-
4
-
0
0
017
E
tn
r-
E
n
r-
0
10
20
30
40
Fraction
no.
Fig.
3.
7"Se
and
125I
radioactivity
in
fractions
of
the
polyacrylamide
gel
used
to
separate
ID-I-containing
column
fractions
The
results
were
obtained
from
the
gel
used
to
produce
the
autoradiograph
shown
in
Fig.
2.
(a)
Lane
1;
sample
from
column
after
reaction
with
N-bromoacetyl-['25I]rT3;
(b)
lane
2;
sample
before
reaction
with
N-bromoacetyl-[I5I]rT3.
radioactivity
in
subsections
of
the
gels
showed
that
the
1251
from
the
affinity
label
co-migrated
with
the
"'Se
resulting
from
treatment
of
the
rats
in
vivo
(Fig.
3).
DISCUSSION
Se
deficiency
adversely
affects
thyroid-hormone
metabolism
and
decreases
5'-deiodination
of
T4
in
tissue
homogenates
from
rats
[5-9,14,15].
These
changes
are
consistent
with
an
essential
role
for
Se
in
the
IDs,
and
we
have
suggested
that
these
enzymes
may
be
selenoproteins
[5,6].
Decreased
tissue
ID
activities
in
Se
deficiency
could
in
theory
result
from
a
defect
in
either
the
microsomal
ID
or
the
cytoplasmic
factors
[11]
necessary
for
activation
of
the
enzyme.
However,
the
equal
abilities
of
liver
supernatants
from
Se-deficient
or
Se-supplemented
rats
to
acti-
vate
ID-I
activity
in
hepatic
microsomal
fractions
(Table
1)
shows
clearly
that
the
effect
of
Se
deficiency
on
ID
activity
occurs
in
the
particulate
fraction.
This
conclusion
is
supported
by
decreased
ID-I
activity
in
hepatic
microsomes
from
Se-deficient
rats
(Table
1).
More
direct
evidence
for
an
association
between
Se
and
ID-I
was
obtained
on
exclusion
chromatography
of
solubilized
hepatic
microsomes
from
75Se-treated
rats,
since
both
75Se
and
ID-I
activity
were
present
in
the
fraction
eluted
at
the
void
volume
(Fig.
1).
The
Mr
of
this
75Se-labelled
protein
as
established
by
SDS/PAGE
was
27400+300
and
therefore
similar
to
that
of
hepatic
ID-I
[16].
Since
hepatic
ID-I
represents
only
0.01
%
of
the
total
protein
in
the
microsomal
fraction
[16]
and
is,
moreover,
very
labile,
it
is
difficult
to
purify
by
conventional
techniques
[17].
However,
it
was
possible
to
overcome
these
problems
by
use
of
an
125I-containing
affinity
label
to
determine
directly
the
relation-
ships
between
ID-I
and
Se
in
the
partially
purified
fraction.
The
occurrence
of
75Se,
from
'in
vivo'
labelling
of
the
enzyme,
and
of
1251,
from
'in
vitro'
affinity
labelling,
in
the
same
fraction
separated
by
electrophoresis
provides
convincing
evidence
that
ID-I
is
indeed
an
Se-containing
enzyme.
This
therefore
extends
the
previous
indirect
evident
based
on
greatly
decreased
ID
activity
in
Se-deficient
rats
[5-7].
The
stoichiometry
of
Se
incorporation
into
hepatic
ID-I
and
elucidation
of
its
role
in
the
expression
of
enzyme
activity
will
have
to
await
purification
of
the
protein
in
sufficient
quantities
for
Se
analysis
and
mechanistic
studies.
By
use
of
a
75Se-labelling
procedure,
Behne
and
co-workers
[3,4]
have
identified
up
to 13
selenoproteins
in
homogenates
of
rat
tissues.
One
of
these,
selenoprotein
7,
had
M,
27800+400
and
was
found
in
liver,
kidney
and
thyroid
gland.
It
is
therefore
similar
in
M,
to
the
Se-containing
protein
which
bound
the
ID
affinity
label,
bromoacetyl-rT3
(Fig.
2),
and
also
has
similar
tissue
distribution
to
ID-I
[18].
The
present
results
support
the
conclusion
that
hepatic
ID-I
is
an
Se-containing
protein.
The
loss
of
hepatic
and
other
ID-I
activities
in
Se
deficiency
explains
the
associated
adverse
effects
on
thyroid-hormone
metabolism.
Since
the
activities
of
the
two
Se-containing
enzymes
glutathione
peroxidase
and
ID-I
are
lost
at
similar
stages
of
Se
depletion
[7],
changes
in
thyroid-hormone
metabolism
as
well
as
impairment
of
peroxide
metabolism
should
be
considered
as
the
origins
of
the
biochemical,
metabolic
and
pathological
consequences
of
Se
deficiency.
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540
... This is attributed to selenium's role as a cofactor for enzymes engaged in digestive enzyme synthesis, leading to the heightened activity of these enzymes and an improved absorption rate, directly fostering growth [28]. Furthermore, selenium's presence as a key constituent in the deiodinase enzyme indirectly stimulates the growth of hormone synthesis and secretion, thus expediting animal growth and protein synthesis [29,30]. Additionally, research has underscored variances in the impacts of diverse selenium sources on aquatic animal growth. ...
Dietary Nanometer Selenium Enhances the Selenium Accumulation, Nutrient Composition and Antioxidant Status of Paramisgurnus dabryanus spp.
Article
Full-text available
  • Jan 2024
Selenium, an essential trace element, exerts beneficial effects on aquatic animals when present in suitable concentrations. This study investigates the effect of dietary nanometer selenium (Nano-Se) on the muscle selenium accumulation, nutrient composition, and antioxidant ability of Paramisgurnus dabryanus spp. Nano-Se was supplemented in the basal diets at levels of 0, 0.1, 0.2, 0.4, and 0.6 mg/kg. Three hundred fish, averaging 5.21 ± 0.06 g, were randomly divided into five groups and fed the experimental diet for 6 weeks. Fish with a dietary Nano-Se supplement of 0.2 mg/kg exhibited activities of SOD, GSH-Px, AKP, and CAT in the liver, which were significantly higher (p < 0.05) compared to the control diet, while MDA content was significantly lower (p < 0.05) in the 0.2 mg/kg group. The muscle selenium content significantly increased (p < 0.05) at ≥0.2 mg/kg Nano-Se levels. The highest levels of essential amino acids, EAA/TAA, and EAA/NEAA ratios were observed in fish fed 0.2 mg of Nano-Se. Thus, this study recommends incorporating 0.2 mg of Nano-Se per kg in the diet to enhance antioxidant defense, selenium content, and nutrient composition.
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... The research results also showed the superiority of T7, T6 and nano-selenium transactions in terms of live weight, feed conversion rate, fatality rate, and the ratio vitality %.This result is consistent with Vish et al. [21] and Abdel-Moneim et al. [22] who reported that nanoselenium supplementation resulted in increased production traits in broiler chickens. The reason for this is that nanoselenium affects the growth of birds through the metabolism of thyroid hormones, which play an important role in growth, protein production and metabolism by increasing the active hormone Tryodothyronine (T3) and decreasing the hormone Tetraiodothyronine (T4), thereby improving feed conversion to promote growth and live weight gain [23,24]. Jamima et al. [25] reported that adding 0.15 mg/kg of nanoselenium particles to the feed could improve the weight gain and live weight of broiler chickens. ...
Effect Add Different Concentrations of Organic, Inorganic, and Nano-Selenium to Diet of Broiler Chickens (Ross 308) that Exposed to Heat Stress on Certain Productive Traits
Article
Full-text available
  • Nov 2023
This study was conducted at Al-Anwar Poultry Station in Babil Governorate Iraq for 35 days, from July 10, 2022 to August 17, 2022, in order to demonstrate the effects of supplementing broiler diets with varying concentrations of organic, inorganic and nano-selenium (Se) on certain production traits and under conditions of heat stress, 560 chicks of one day old (Ross 308) were used without identifying their sex and divided randomly into 7 transactions with 4 replicates for each transaction, and each replicate included 20 chicks. The first transaction, T1, was the control transaction without addition, and organic selenium was added in the second and third transactions (T2 and T3) at a concentration of 1 and 1.5 mg / kg, respectively, while the fourth and fifth transaction (T4 and T5) inorganic selenium was added at a concentration of 1 and 1. 5 mg / kg, respectively, while the sixth and seventh transaction (T6 and T7) included the addition of nano-Se at a concentration of 1 and 1.5 mg / kg, respectively. The results of the study showed the following: (1) Highly significant (P≤0.01) superiority of T2 transaction over all studied transactions in live body weight and overweight. (2) There was a significant (P≤0.01) superiority of the rate of feed consumption for the transactions T2, T5 over the T1, T3, T4, T6, T7. As for the food conversion coefficient, the transaction T4, T6 was more “significant” improvement at a level of (P≤0.01) than the rest of the transactions. The control transaction was the least improved transaction. (3)The data recorded a “significant” decrease for all addition transactions in the percentage of total deaths compared to the control transaction. T5 was similar to T1, but with a lower rate.
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... In higher organisms, selenoproteins and selenoenzymes play important biological roles and are pivotal for survival. Glutathione peroxidases and thioredoxin reductases remove reactive oxygen species and protect the cell membrane and DNA from oxidative damage (8)(9)(10), iodothyronine deiodinases maintain thyroid hormone homeostasis (11)(12)(13), and SelenoP regulates selenium (Se) levels (14)(15)(16). The systemic deletion of the cognate tRNA (tRNA Sec ) is embryonically lethal in mice (17), and replacement of Sec with L-serine (Ser) or Cys compromises selenoenzyme activity and selenoprotein folding (18)(19)(20). ...
Structural basis for the tRNA-dependent activation of the terminal complex of selenocysteine synthesis in humans
Article
Full-text available
  • Mar 2023
O-Phosphoseryl-tRNASec selenium transferase (SepSecS) catalyzes the terminal step of selenocysteine (Sec) synthesis in archaea and eukaryotes. How the Sec synthetic machinery recognizes and discriminates tRNASec from the tRNA pool is essential to the integrity of the selenoproteome. Previously, we suggested that SepSecS adopts a competent conformation that is pre-ordered for catalysis. Herein, using high-resolution X-ray crystallography, we visualized tRNA-dependent conformational changes in human SepSecS that may be a prerequisite for achieving catalytic competency. We show that tRNASec binding organizes the active sites of the catalytic protomer, while stabilizing the N- and C-termini of the non-catalytic protomer. Binding of large anions to the catalytic groove may further optimize the catalytic site for substrate binding and catalysis. Our biochemical and mutational analyses demonstrate that productive SepSecS•tRNASec complex formation is enthalpically driven and primarily governed by electrostatic interactions between the acceptor-, TΨC-, and variable arms of tRNASec and helices α1 and α14 of SepSecS. The detailed visualization of the tRNA-dependent activation of SepSecS provides a structural basis for a revised model of the terminal reaction of Sec formation in archaea and eukaryotes.
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Selenoprotein P – Selenium transport protein, enzyme and biomarker of selenium status
Article
Full-text available
  • Sep 2022
  • FREE RADICAL BIO MED
The habitual intake of selenium (Se) varies strongly around the world, and many people are at risk of inadequate supply and health risks from Se deficiency. Within the human organism, efficient transport mechanisms ensure that organs with a high demand and relevance for reproduction and survival are preferentially supplied. To this end, selenoprotein P (SELENOP) is synthesized in the liver and mediates Se transport to essential tissues such as the endocrine glands and the brain, where the “SELENOP cycle” maintains a privileged Se status. Mouse models indicate that SELENOP is not essential for life, as supplemental Se supply was capable of preventing the development of severe symptoms. However, knockout mice died under limiting supply, arguing for an essential role of SELENOP in Se deficiency. Many clinical studies support this notion, pointing to close links between health risks and low SELENOP levels. Accordingly, circulating SELENOP concentrations serve as a functional biomarker of Se supply, at least until a saturated status is achieved and SELENOP levels reach a plateau. Upon toxic intake, a further increase in SELENOP is observed, i.e., SELENOP provides information about possible selenosis. The SELENOP transcripts predict an insertion of ten selenocysteine residues. However, the decoding is imperfect, and not all these positions are ultimately occupied by selenocysteine. In addition to the selenocysteine residues near the C-terminus, one selenocysteine resides central within an enzyme-like environment. SELENOP proved capable of catalyzing peroxide degradation in vitro and protecting e.g. LDL particles from oxidation. An enzymatic activity in the intact organism is unclear, but an increasing number of clinical studies provides evidence for a direct involvement of SELENOP-dependent Se transport as an important and modifiable risk factor of disease. This interaction is particularly strong for cardiovascular and critical disease including COVID-19, cancer at various sites and autoimmune thyroiditis. This review briefly highlights the links between the growing knowledge of Se in health and disease over the last 50 years and the specific advances that have been made in our understanding of the physiological and clinical contribution of SELENOP to the current picture.
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Selenoproteins in brain development and function
Article
  • Aug 2022
  • FREE RADICAL BIO MED
Expression of selenoproteins is widespread in neurons of the central nervous system. There is continuous evidence presented over decades that low levels of selenium or selenoproteins are linked to seizures and epilepsy indicating a failure of the inhibitory system. Many developmental processes in the brain depend on the thyroid hormone T3. T3 levels can be locally increased by the action of iodothyronine deiodinases on the prohormone T4. Since deiodinases are selenoproteins, it is expected that selenoprotein deficiency may affect development of the central nervous system. Studies in genetically modified mice or clinical observations of patients with rare diseases point to a role of selenoproteins in brain development and degeneration. In particular selenoprotein P is central to brain function by virtue of its selenium transport function into and within the brain. We summarize which selenoproteins are essential for the brain, which processes depend on selenoproteins, and what is known about genetic deficiencies of selenoproteins in humans. This review is not intended to cover the potential influence of selenium or selenoproteins on major neurodegenerative disorders in human.
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Functional Mimics of Glutathione Peroxidase: Spirochalcogenuranes, Mechanism and Its Antioxidant Activity
Chapter
Full-text available
  • Apr 2022
The present chapter describe a series of synthetic organoselenium compounds such as ebselen analogues, diaryl selenides, spirodioxyselenurane, spirodiazaselenuranes and its Glutathione peroxidise (GPx) catalytic activity. These ebselen related compounds either by modifying the basic structure of ebselen or incorporating some structural features of the native enzyme, a number of small-molecules of selenium compounds as functional mimics of GPx are discussed. In addition to this, spirodioxyselenuranes and spirodiazaselenuranes are important class of hypervalent selenium compounds, whose stability highly depends on the nature of the substituents attached to the nitrogen atom. The glutathione peroxidase (GPx) mimetic activity of all the selenium compounds showed significantly by facilitating the oxidation of the selenium centre. In contrast to this, ebselen analogue shows significant antioxidant activity compared with spirodiazaselenuranes and its derivatives.
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Selenium-containing Peptides and their Biological Applications
Article
  • Feb 2022
Selenium (Se) is known for its beneficial biological roles for several years but interest in this trace element has seen significant increase in the past couple of decades. It has been reported to be a part of important bioactive organic compounds, such as selenoproteins and amino acids including selenocysteine (SeCys), selenomethionine (SeMet), selenazolidine (SeAzo), and selenoneine. The traditional Se supplementations (primarily as selenite, and selenomethionine), though have been shown to carry some benefits, also have associated toxicities thereby paving the way for the organoselenium compounds, especially the selenoproteins and peptides (SePs/SePPs) that offer several health benefits beyond fulfilling the elementary nutritional Se needs. This review aims to showcase the applications of selenium-containing peptides that have been reported in recent decades. Herein this article summarize their bioactivities including neuroprotective, antiinflammatory, anticancer, antioxidant, hepatoprotective, and immunomodulatory roles. This will offer the readers a sneak peek into the current advancements to invoke further developments in this emerging research area.
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The changes in hepatic enzyme expression caused by selenium deficiency and hypothyroidism in rats are produced by independent mechanisms
Article
Full-text available
  • Apr 1990
Selenium (Se) deficiency for 5 weeks in rats produced changes in the activity of a number of hepatic, renal and plasma enzymes. In animals whose food intake was restricted to 75% of normal for 2 weeks, Se deficiency produced significant increases in the activity of hepatic cytosolic 'malic' enzyme and mitochondrial alpha-glycerophosphate dehydrogenase (GPD), two enzymes that are particular sensitive to the thyroid-hormone concentrations in tissue. Propylthiouracil-induced hypothyroidism produced significant decreases in 'malic' enzyme and GPD activities. The effect of hypothyroidism on the activity of 'malic' enzyme, GPD and other enzymes studied in liver and plasma was often opposite to that seen in Se deficiency. Glutathione S-transferase (GST) activity was increased by both Se deficiency and hypothyroidism, but in hypothyroid animals further significant increases in GST were produced by Se deficiency. These data suggest that the changes in enzyme expression observed in Se deficiency are not caused by decreased tissue exposure to thyroid hormones.
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Inhibition of type I and type II iodothyronine deiodinase activity in rat liver, kidney and brain produced by selenium deficiency
Article
Full-text available
  • Jun 1989
Selenium deficiency for periods of 5 or 6 weeks in rats produced an inhibition of tri-iodothyronine (T3) production from added thyroxine (T4) in brain, liver and kidney homogenate. This inhibition was reflected in plasma T4 and T3 concentrations, which were respectively increased and decreased in selenium-deficient animals. Although plasma T4 levels increased in selenium-deficient animals, this did not produce the normal feedback inhibition on thyrotropin release from the pituitary. Selenium deficiency was confirmed in the animals by decreased selenium-dependent glutathione peroxidase (Se-GSH-Px) activity in all of these tissues. Administration of selenium, as a single intraperitoneal injection of 200 micrograms of selenium (as Na2SeO3)/kg body weight completely reversed the effects of selenium deficiency on thyroid-hormone metabolism and partly restored the activity of Se-GSH-Px. Selenium administration at 10 micrograms/kg body weight had no significant effect on thyroid-hormone metabolism or on Se-GSH-Px activity in any of the tissues studied. The characteristic changes in plasma thyroid-hormone levels that occurred in selenium deficiency appeared not to be due to non-specific stress factors, since food restriction to 75% of normal intake or vitamin E deficiency produced no significant changes in plasma T4 or T3 concentration. These data are consistent with the view that the Type I and Type II iodothyronine deiodinase enzymes are seleno-enzymes or require selenium-containing cofactors for activity.
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The effects of selenium and copper deficiencies on glutathione S -transferase and glutathione peroxidase in rat liver
Article
Full-text available
  • Jan 1988
Selenium (Se) deficiency in rats produced significant increases in the activity of hepatic glutathione S-transferase (GST) with 1-chloro-2,4-dinitrobenzene as substrate and in various GST isoenzymes when determined by radioimmunoassay. These changes is GST activity and concentration were associated with Se deficiency that was severe enough to provoke decreases of over 98% in hepatic Se-containing glutathione peroxidase activity (Se-GSHpx). However, decreases in hepatic Se-GSHpx of 60% induced by copper (Cu) deficiency had no effect on GST activity or concentration. Increased GST activity in Se deficiency has previously been postulated to be a compensatory response to loss of Se-GSHpx, since some GSTs have a non-Se-glutathione peroxidase (non-Se-GSHpx) activity. However, the GST isoenzymes determined in this study, GST Yb1Yb1, GST YcYc and GST YaYa, are known to have up to 30-fold differences in non-Se-GSHpx activity, but they were all significantly increased to a similar extent in the Se-deficient rats.
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Subcellular distribution of selenoproteins in the liver of the rat
Article
  • Apr 1990
  • Biochim Biophys Acta
After in vivo labeling with [75Se]selenite, the intracellular distribution of selenoproteins in the liver was investigated in selenium-adequate and selenium-deficient rats. In the subcellular fractions, which were obtained by differential centrifugation, the proteins were separated by means of SDS-PAGE and the selenium compounds were identified via their 75Se activity. In this way twelve selenium-containing proteins or protein subunits with molecular weights between 12,100 and 75,400 were found. Glutathione peroxidase was concentrated in the cytosol and in the mitochondria. With the newly detected selenoproteins, some were enriched in the cytosol, one was mainly found in the nuclear fraction and some, which were present mainly in the mitochondrial and microsomal fractions, are most probably membrane-bound. In the liver of selenium-depleted rats the selenium administered was used predominantly to restore the levels of some of the newly found selenoproteins, while in the liver of selenium-adequate animals most of the selenium retained was incorporated into the glutathione peroxidase. The differences in the distribution among the subcellular fractions and the specific incorporation of the element in selenium deficiency into certain compounds suggest that there are several metabolic pathways for selenium and that the selenoproteins are involved in several different processes of intracellular metabolism.
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The effects of selenium depletion and repletion on the metabolism of thyroid hormones in the rat
Article
  • Jul 1990
  • J INORG BIOCHEM
Rats were fed selenium-deficient (less than 0.005 mg selenium/kg) or selenium-supplemented diets (0.1 mg selenium/kg, as Na2SeO2) for up to five wks from weaning to assess the effects of developing selenium deficiency on the metabolism of thyroid hormones. Within two wks 3:5,3'-triiodothyronine (T3) production from thyroxine (T4) in liver homogenates from selenium-deficient rats was significantly lower compared with the activity in liver homogenates from selenium-supplemented rats. This decreased activity was probably responsible, in part, for the higher T4 and lower T3 concentrations in plasma from the selenium-deficient rats after 3, 4, and 5 weeks of experiment. Repletion of selenium-deficient rats with single intra-peritoneal injections of 200 micrograms selenium/kg body wt. (as Na2SeO3) 5 days before sampling reversed the effects of the deficiency on thyroid hormone metabolism and significantly increased liver and plasma glutathione peroxidase activities. However a dose of 10 micrograms selenium/kg body wt given to rats of similar low selenium status had no effect on thyroid hormone metabolism or glutathione peroxidase activity but did reverse the increase in hepatic glutathione S-transferase activity characteristic of severe selenium deficiency. Imbalances in thyroid hormone metabolism are an early consequence of selenium deficiency and are probably not related to changes in hepatic xenobiotic metabolizing enzymes associated with severe deficiency.
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Rat liver type I iodothyronine deiodinase is not identical to protein disulfide isomerase
Article
  • Aug 1989
This study was done to test the recent hypothesis (Boado et al. (1988) Biochem. Biophys. Res. Commun. 155, 1297-1304) that type I iodothyronine deiodinase (ID-I) is identical to protein disulfide isomerase (PDI). Autoradiograms of rat liver microsomal proteins, labeled with N-bromoacetyl-[125I]triiodothyronine (BrAc[125I]T3) and separated by SDS-PAGE, show predominantly 2 radioactive bands of Mr 27 and 56 kDa. Substrates and inhibitors of ID-I inhibited labeling of the 27 kDa band but not that of the 56 kDa band. Treatment of microsomes with trypsin abolished labeling of the 27 kDa protein and destroyed the activity of ID-I but did not prevent labeling of the 56 kDa protein. Following treatment of microsomes at pH 8.0-9.5 or with 0.05% deoxycholate (DOC) PDI content and labeling of the 56 kDa protein were strongly diminished but ID-I activity and labeling of the 27 kDa protein were not affected. The latter decreased in parallel after treatment at pH greater than or equal to 10. Rat pancreas microsomes contain high amounts of PDI but show no ID-I activity. Reaction of these microsomes with BrAc[125I]T3 results in extensive labeling of a 56 kDa protein but no labeling of a 27 kDa protein. Pure PDI (Mr 56 kDa) was readily labeled by BrAc[125I]T3 but showed no deiodinase activity. These results strongly suggest that the 27 kDa band represents (a subunit of) ID-I while the 56 kDa band represents PDI. From these and other data it is concluded that PDI and ID-I are not identical proteins.
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Phospholipid hydroperoxide glutathione peroxidase: Specific activity in tissues of rats of different age and comparison with other glutathione peroxidases
Article
  • Dec 1989
  • Biochim Biophys Acta
The tissue distribution of phospholipid hydroperoxide glutathione peroxidase (PHGPX) was studied in rats of different ages. In the same samples the activities of Se-dependent glutathione peroxidase (GPX), and non-Se-dependent glutathione peroxidase (non Se-GPX) were also determined using specific substrates for each enzyme. Enzymatically generated phospholipid hydroperoxides were used as substrate for PHGPX, hydrogen peroxide for GPX, and cumene hydroperoxide for non-Se-GPX (after correction for the activity of GPX on this substrate). PHGPX specific activity in different organs is as follows: liver = kidney greater than heart = lung = brain greater than muscle. Furthermore, this activity is reasonably constant in different age groups, with a lower specific activity observed only in kidney and liver of young animals. GPX activity is expressed as follows: liver greater than kidney greater than heart greater than lung greater than brain = muscle, and substantial age-dependent differences have been observed (adult greater than old greater than young). Non-Se-GPX activity was present in significant amount only in liver greater than lung greater than heart and only in adult animals. These results suggest a tissue- and age-specific expression of different peroxidases.
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Partial purification of the microsomal rat liver iodothyronine deiodinase I. Solubilization and ion-exchange chromatography
Article
  • Mar 1988
  • MOL CELL ENDOCRINOL
Rat liver microsomal fraction was treated with several non-ionic, anionic or zwitterionic detergents in order to investigate which is most suitable for subsequent purification of the iodothyronine deiodinase. Criteria for effective solubilization were (a) no or little inhibitory effect of the detergent on deiodinase activity, (b) non-sedimentable activity by centrifugation at 105,000 X g, and (c) a low molecular weight of the soluble complex as determined by Sephacryl S-300 gel filtration in the presence of detergent. Optimal solubilization was obtained by treatment of the microsomes with cholate and subsequent precipitation of dispersed protein with 30% ammonium sulfate, resulting in the removal of adhering phospholipids. Enzyme was resolubilized best with the non-ionic detergents Brij 56 or Emulgen 911 in the presence of 0.5 M NaCl. This deiodinase preparation had an isoelectric point at pH 9.3 and was further purified by subsequent chromatography on DEAE-Sephacel and CM-Sepharose. Only the Emulgen 911-dispersed enzyme was retained by the CM-Sepharose column. Further purification was investigated by chromatofocusing. This resulted in a rapid inactivation of the Emulgen 911 preparation whereas the Brij 56-soluble enzyme was ultimately purified 400 times after DEAE-Sephacel and chromatofocusing.
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Evidence for Spesific Selenium Target Tissues and New Biologically Important Selenoproteins
Article
  • Aug 1988
  • Biochim Biophys Acta
After in-vivo labeling with [75Se]selenite the Se-containing proteins present in rat tissues were investigated by means of SDS-polyacrylamide gel electrophoresis. Thirteen Se-containing proteins or protein subunits with relative molecular weights of 12,100, 15,600, 18,000, 19,700, 22,200, 23,700, 27,800, 33,300, 55,500, 59,900, 64,900, 70,100 and 75,400 were detected in the tissue homogenates. The protein with the molecular weight of 23,700 was the subunit of glutathione peroxidase, which is the only selenoprotein so far known to have biological functions in animals. Most of these proteins were found in all tissues investigated but one was only detected in the testes and the spermatozoa and one was present mainly in the thyroid. With inadequate selenium intake there was a priority supply of the element to the brain, the reproductive and the endocrine organs, and at a molecular level to Se-containing proteins other than glutathione peroxidase. The results suggest important biological functions of these selenoproteins, especially in the specific target tissues.
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