J. Nutr.
Absorption
and
Metabolism
II. Transformation
Sci.
of Pyridoxamine
of Pyridoxamine in Intestinal
Vitaminol.,
38, 227-233,
1992
in Mice
to Pyridoxal
Tissues
Tae SAKURAI, Tadashi ASAKURA, Aritake MIZUNO, and Makoto MATSUDA Department of Biochemistry, The Jikei University School of Medicine, Nishi-Shinbashi, Minato-ku, Tokyo 105, Japan (Received December 2, 1991)
Summary The absorption of pyridoxamine from the intestine of the mouse was studied in whole animals. [3H]Pyridoxamine was orally administered and the distribution of isotope between the six recognized forms of vitamin B6 was determined in portal blood after the adminis tration. When small doses (1.4 or 14 nmol) were administered, labeled pyridoxamine could hardly be found in the portal blood, although labeled pyridoxal and pyridoxal phosphate were found in the same blood. However, when a large amount (46 or 140nmol) was given, a significant amount of labeled pyridoxamine was found with labeled pyridoxal and pyridoxal phosphate in the portal blood. These results suggest that a physiological dose of pyridoxamine is rapidly transformed to pyridoxal in the intestial tissues and then released in the form of pyridoxal into the portal blood. Key Words pyridoxamine, pyridoxal phosphate, pyridoxal kinase, pyri doxine phosphate oxidase, intestine
Pyridoxamine (PM) and pyridoxamine phosphate (PMP) are the forms of vitamin B6 found in foods; PMP is completely hydrolyzed to PM before absorption. Therefore, the absorption and metabolism of PM to the active coenzyme (pyridoxal phosphate, PLP) in the various organs and tissues are important in the management of nutrition. The general pathway for the conversion of PM to PLP is well known. Briefly, PM is phosphorylated to PMP by pyridoxal (PL) kinase, which has been detected in all mammalian tissues investigated (1). PMP is converted to PLP by pyridoxine phosphate (PNP) oxidase (2) which, in contrast to the wide distribution of PL kinase, is confined to a few tissues (3-8). PLP can be hydrolyzed to PL by phosphatase (9), and PL is converted again to PLP by PL kinase or metabolized to pyridoxic acid by aldehyde oxidase (4). 227
228
T. SAKURAI
Since these
PL
two
PM
to
and
of
phosphatase
by
of
source
of The
is the
the
B6
problem
of
of
evaluate
PM
to
the
circulating
by
administration
in
recent to
PL
[3H]
from
the
shown is
that
may
7, 8),
dietary
when
a
PNP
be
(S,
physio
converted
kinase,
PL
liver
converting
completely
PL
thus
and of
to
oxidase
used
as
the
and
principal
to
be
of
or solved.
The
intestine
in
metabolites
liver-is
of
mainly
purpose
the
PM
of
involved
the
present
conversion
in
portal
in
of
blood
the
study
dietary
was
PM
following
to
the
oral
was
obt
PM.
Chemicals.
Amberlite
has PM of
and
intestine means
(10).
MATERIALS
ained
study
organ-intestine
remains
in a
mice,
liver,
tissue
which
active provide
participation
and/or most
analyzing
of
our given
sequential
participation
PL,
are may
fact,
orally
intestine
vitamin
conversion
In
PM
PL
oxidase
phosphatases
PL.
dose
circulating
PNP
plus
circulating
logical
to
kinase
enzymes
et al.
PM,
with
specific
Radiochemical
column
AND
activity
Centre
(11).
Acid
METHODS
of
about
(Amersham,
phosphatase
3.87Ci/mmol,
England)
was
purchased
mice,
weighing
and
purified
from
with
Sigma
an
Chemical
Co. Experimental
procedures.
experimental
animals.
experiment. [3H] of
The
PM
was
portal
performed.
followed
in
neutralized
for
5 min
to
acid
as
described
[3H]
(12).
B6
acid
PM
in
the
sequentially
and
described
PM.
The
and
the
extracts
The to
again
isotope
in
7 min
3-4,
and
and
EDTA
of blood
at
PM
1N
perchloric
acid,
collected
from
The
blood
was
supernatant
20,000•~g
for
centrifuged
were
surgery [3H]
was
The
and
as the
removal
after
administration.
mg)
which
the and
times
centrifuged.
few
cells,
before
used
before containing
diethylether,
9 volumes
centrifuged (a
minute
different
the
were 6 h
solution
Portal
after
acid
blood
extracts
first
were
to
content
was 5 min.
at
extracted
onto
the
with
an
each
PLP,
fractions
(11)
with
Amberlite
In
3,000•~g perchloric
PLP, and
PNP, were
to
and PL,
column and
collected
chromatographic
PNP,
PMP
to in
the
PL,
PMP, PN,
chrom
modification
column,
vitamers,
PMP
Amberlite
by some
CG-120
phosphorylated
PNP
same
into
Badger
containing
(0.25ml) of
separated and
elute
PLP,
from
Fractions
Loo
put to
effluent,
hydrolyze
applied
were
by
washed
respectively, above.
pH with
described
was
derived,
to
at
20g, for
saline
with
15 min).
10s
of One
removed
perchloric
plasma
vitamers
phosphatase
tively,
cavity.
about animals
here.
Briefly,
and
1N
100ƒÊl
homogenized
for
mixed
procedures
column (PN),
was
separate
atographic
of
5 N NaOH
blood
then
the
anesthetized
was
vein
9 vol.
with
cases,
gastric
(20,000•~g,
mesenteric
homogenized
some
and
from with
were
intestine
weighed
intestinal
the
they
centrifugation
DDY withheld
injected
into
blood, The
by
was
were
a cannula
or
administration,
the
animals
through
intestine
Male
Food
and
was and
separate
the
pyridoxine treated PM, PL,
PN,
the
same
was
determined
by
respec and
manner
as
throughout. fraction
J. Nutr.
Sci.
by Vitaminol.
a
ABSORPTION
liquid
scintillation
OF PYRIDOXAMINE
FROM
INTESTINE
229
spectrometer.
RESULTS
After of
[3H]
after
1.4nmol
PM the
by oral
absorbed
at
of
blood Fig.
Considerable
but
[3H]
PM
the
portal
PM. [3H]
labeled
was
hardly for
When
nmol,
peak
than
amount
PLP
of those
of
1.
[3H]
of
isotope PM
pmol
(Fig.
the
absorbed from
the
time in
absorption
1).
By
intestine
from
the
of
3, 1992
[3H]
slope
of of
and
PL
and nmol,
[3H] the
[3H] various
[3H]
PM [3H]
3 experiments.
of
the of
7min
had
been
intestine
the
for
progression
PLP
remaining vitamer
[3H]
B6
5.4ƒÊCi)
labeled
labeled
in
PM
in
PM [3H]
the
was
PM
found
intestine
in
a
to
33-fold
found
at Each
as
when (Fig.
various point
small
together
detected
chromatograms
(1.4nmol/mouse).
examined,
only
was
administered
of
administered,
increased
was
5.4ƒÊCi
were
was
PM
in
1. saturation
to
was
administration
in
blood,
appearing Table with
cold
portal
shown
in the
in
of
nmol,
is
vitamers
summarized investigated
the
in
PM
present
was
Moreover,
5.4ƒÊCi)
[3H]
were
administered of
metabolites
amounts (14
3H
amount PLP.
of
after with
B6 of
PLP
are
PM
PM
7min
[3H]
[3H]
point
of
amount
PL
and
of
amount
amounts
predominant,
(140
of
PL
same
of
of
a considerable
column
time
blood
the
labeled
Amount
mean•}SD
38, No.
[3H]
the
The same
addition
were
PM
[3H]
amount
when
administration
Vol.
the
Amberlite
transport
in portal
5.4ƒÊCi),
amounts
administered,
of
5.92
of
the
the
a 10-fold
and
an
of
at
of
However,
large
as
orally
a function
of
detected.
10s
vitamers
PL
amount.
Fig.
from
amounts
blood
B6
amount
administration
involving
[3H]
(46
the
mechanism
and
half
calculated
pattern
after
2a.
The
The
was
was as
absorption.
elution
experiments
(5.4ƒÊCi) presented about
rate.
point
PM
7 min
PM was
administration,
time
The
[3H]
intestine
a steady
10 s at this curve
of
the
a
2b).
times represents
with a larger 100-fold Figure
3
after the
230
T. SAKURAI
Table
1.
portal
blood
* This in
Disappearance
value
intestine.
at 7 min
was The
of following
calculated other
PM
from
intestine
administration
from values
et al.
the are
slope
means•}SD
and
appearance
of B6 vitamers
in
of PM.
of
the of
progression three
curve
of
PM
absorption
experiments.
Fig. 2. Elution patterns from Amberlite column of [3H]B6 vitamers in portal blood 7 min after oral administration of 1.4 nmol (a) and 140 nmol (b) of [3H]PM per mouse. The data shown here are representative of 3 experiments.
shows the relationships between the ratios of [3H]PL, PLP, and PM to all [3H]B6 vitamers in portal blood, and the amounts of [3H]PM administered. Labeled PL in the portal blood was mainly located in the plasma, while labeled PLP was mainly located in the blood cells, regardless of the dosage of labeled PM. Moreover, labeled PM found after the administration of a large amount of labeled PM was located entirely in the plasma. J. Nutr.Sci. Vitaminol.
ABSORPTION
OF
PYRIDOXAMINE
FROM
INTESTINE
231
Fig. 3. Relationship between various dosages of [3H] PM and relative levels of [3H]B6 vitamers in portal blood at 7 min after oral administration.
DISCUSSION Although
the
established, on
the
nmol
it has basis
of
of
as
portal
two
during
absorbed
from
[3H]
through
the
unable
to
of
the
also
of
et the
appeared
in
administered the
liver
[3H] but
in
the
had
intestinal
al.
(14)
PN
PL
and
PM
the
to
PL
system, may
was
the
tissue portal
this
though
isotope
of
the PM
These
to
[3H]
active
completely
may of
in
PL
possibly
however, because
into
[3H]
of
blood,
blood,
is
10s from
blood.
portal
pathway blood
a means
for
converted or
could clearly
absorbed
portal
completely
The
even
in
PM
were
released PM
the
PLP
PLP
1.4-14 weight.
[3H]
PM [3H]
weight/day The
body
[3H]
contrast,
through
provide
[3H] the
intestinal
pathway. PM
portal
indicated
taken
high
PL that
tissue
PL
is synthesized
PL
may that
of
In
body
nmol/kg
and
definitely
(13).
administered, PL
of
1).
been
the
the
be
short
pathway.
converting
dietary
L.
observed
38, No.
(Table
nmol/kg
70-700
[3H]
percent
not
mammalia
orally
amount
a few
B6 has
70-700
to
was
small
than
period
be
various
whereas
The
intestine
[3H]
Vol.
blood,
convert
the
tissues
PM/mouse
vitamin
equivalent
PM•¨PMP•¨PLP•¨PL
[3H]
all
[3H]
more
the in
to of
was
portal
intestine
circulating P.
intestine we
same
that
time
Tsuji most
the
not
Accordingly, to
no
completely
circulation
PM
20g)
peaks.
was
the
PLP
estimated
for
B6 requirements
the
large
suggest
and
tentatively
of in
blood
intestine
requirement
(about
found
observed
dietary
vitamin
1.4nmol
be
results
been
the
PM/mouse
When hardly
the
mouse
be
contain
3, 1992
was
kinase
and of
3H
from into PL
when
PN
was
to
PLP
converted
the
following
released
that
up
PNP [3H]
the [3H] the kinase,
oxidase PN
oral PN
whether
and
rapidly
administration
blood
the and they
of above may contain
with
PMP,
activities.
appeared
through
portal
incubated
intestinal
In
agreement
in
PNP,
[3H]
PNP
with
them,
and
PL
product of
or
in
that
The
a source oxidase
the
suggesting
(12). as
that
PLP,
PN,
pathway serve
rings,
suggesting
PLP
not.
in
232
T. SAKURAI
et al.
When amounts of [3H] PM larger than 46 nmol were administered, a consid erable amount of [3H] PM appeared in the portal blood without being efficiently transformed to [3H] PL (Figs. 2b, 3). This result suggests that the ability of intestine to efficiently convert dietary PM to circulating PL is limited and that the limit is between 14 and 46 nmol of PM per mouse. The PM that leaked out to the portal circulation was mainly located in blood plasma. Plasma PM may serve as a source of the coenzyme PLP in tissues that contain both PL kinase and PNP oxidase. Our previous report showed that when an excess of PM was given orally to mice, a considerable amount of PM appeared in the heart blood and that the ability of the intestine and/or liver to convert PM to PL had also a limit between 14 and 46 nmol of PM per mouse (10). The fact that these two limits are almost the same suggests that the liver does not participate very actively in the conversion of PM to PL, though the organ has no less than 4-fold the activity of PNP oxidase in the intestine (liver: 155 pmol/min/mg protein; intestine: 35 pmol/min/mg protein) (8). It is not so easy to interpret this contradiction. In any case, it is important to note that when a physiological level of PM is orally administered to mice, PM is almost entirely transformed to PL in the intestine, which may be the major source of vitamin B6 for most tissues and organs including blood and liver, and that even when a large quantity of PM is adminis tered, a considerable amount of PL in the blood originates from the PL produced by intestinal tissue. REFERENCES
1)
McCormick, nases.
D.
I.
B.,
Assay,
Gregory,
M.
distribution,
E.,
and
Snell,
purification,
E.
and
E.
(1961):
properties.
Pyridoxal
J.
Biol.
phosphoki
Chem.,
236,
2076
- 2084. 2)
Wada,
H.,
and
pyridoxamine 3)
Pogell,
B.
M.
phosphate 4)
5)
T.,
Morino,
H.,
L.
L.,
radiometric chem., 8)
125,
9)
Turner,
(in J.
of
Hamm,
M.
in
rat
and
liver.
K.
Rol,
pyridoxamine
D.
and
to
pyridoxal
L.
studies
Biochem., M.
48,
(1980):
Acta,
28-36.
Transport
631,
phosphate
112-123.
oxidase
activity
in
731-737.
and
(pyridoxine)
Enzymatic
J.
Biophys.
90B, A.,
(1960):
Henderson,
Biochim.
Physiol.,
phosphate
oxidase.
(pyridoxine)
Biochem. M.,
pyridoxamine
Ichihara,
W.,
pyridoxine
761-776.
phosphate
Pyridoxamine
B.
of
and
of
Kazarinoff,
M.
5•L-phosphate
N.
(1982):
oxidase.
Anal.
A Bio
329-334. M.,
Vitamins
Y.,
oxidation
2089-2095.
232,
Pyridoxine
pyridoxine
Garber,
assay
Matsuda,
Sakamoto,
Comp.
enzymatic 236,
oxidation Chem.,
D.,
(1988):
tissues.
Langham,
The Chem.,
Biol.
III. D.
of
M.
(1961): Biol.
J.
Y.,
Buss,
metabolism
mammalian 7)
liver.
metabolism.
Mehansho,
Fonda,
E. J.
Enzymatic
rabbit
pyridoxine
and 6)
E.
(1958):
in
Morisue, on
Snell, phosphate.
and Japanese),
M.
(1961):
Mizuno,
A. 63,
(1989):
Absorption
and
metabolism
of
vitamin
443-448.
Pyridoxal
phosphate
breakdown
by
an
alkaline-phosphatase
J.
Nutr.
Sci.
Vitaminol.
B6.
ABSORPTIONOF PYRIDOXAMINE FROM INTESTINE
10)
11) 12) 13)
14)
Vol.
233
preparation. Biochem. J., 80, 663-668. Sakurai, T., Asakura, T., Mizuno, A., and Matsuda, M. (1.991): Absorption and metabolism of pyridoxamine in mice. I. Pyridoxal as the only form of transport in blood. J. Nutr. Sci. Vitaminol., 37, 341-348. Loo, Y. H., and Badger, L. (1969): Spectrofluorometric assay of vitamin B6 analogues in brain tissue. J. Neurochem., 16, 801-804. Sakurai, T., Asakura, T., and Matsuda, M. (1987): Transport and metabolism of pyridoxine and pyridoxal in mice. J. Nutr. Sci. Vitaminol., 33, 11-19. Weiser, H., Reusser, P., and Wiss, O. (1968): XIII. Requirements of animals and microbes, in The Vitamins II, ed. by Sebrell, W. H., Jr., and Harris, R. S., Academic Press, New York and London, pp. 109-117. Tsuji, T., Yamada, R., and Nose, Y. (1973): Intestinal absorption of vitamin B6. I. Pyridoxal uptake by rat intestinal tissue. J. Nutr. Sci. Vitaminol., 19, 401-417.
38, No.
3, 1992
Absorption
and
Metabolism
II. Transformation
Sci.
of Pyridoxamine
of Pyridoxamine in Intestinal
Vitaminol.,
38, 227-233,
1992
in Mice
to Pyridoxal
Tissues
Tae SAKURAI, Tadashi ASAKURA, Aritake MIZUNO, and Makoto MATSUDA Department of Biochemistry, The Jikei University School of Medicine, Nishi-Shinbashi, Minato-ku, Tokyo 105, Japan (Received December 2, 1991)
Summary The absorption of pyridoxamine from the intestine of the mouse was studied in whole animals. [3H]Pyridoxamine was orally administered and the distribution of isotope between the six recognized forms of vitamin B6 was determined in portal blood after the adminis tration. When small doses (1.4 or 14 nmol) were administered, labeled pyridoxamine could hardly be found in the portal blood, although labeled pyridoxal and pyridoxal phosphate were found in the same blood. However, when a large amount (46 or 140nmol) was given, a significant amount of labeled pyridoxamine was found with labeled pyridoxal and pyridoxal phosphate in the portal blood. These results suggest that a physiological dose of pyridoxamine is rapidly transformed to pyridoxal in the intestial tissues and then released in the form of pyridoxal into the portal blood. Key Words pyridoxamine, pyridoxal phosphate, pyridoxal kinase, pyri doxine phosphate oxidase, intestine
Pyridoxamine (PM) and pyridoxamine phosphate (PMP) are the forms of vitamin B6 found in foods; PMP is completely hydrolyzed to PM before absorption. Therefore, the absorption and metabolism of PM to the active coenzyme (pyridoxal phosphate, PLP) in the various organs and tissues are important in the management of nutrition. The general pathway for the conversion of PM to PLP is well known. Briefly, PM is phosphorylated to PMP by pyridoxal (PL) kinase, which has been detected in all mammalian tissues investigated (1). PMP is converted to PLP by pyridoxine phosphate (PNP) oxidase (2) which, in contrast to the wide distribution of PL kinase, is confined to a few tissues (3-8). PLP can be hydrolyzed to PL by phosphatase (9), and PL is converted again to PLP by PL kinase or metabolized to pyridoxic acid by aldehyde oxidase (4). 227
228
T. SAKURAI
Since these
PL
two
PM
to
and
of
phosphatase
by
of
source
of The
is the
the
B6
problem
of
of
evaluate
PM
to
the
circulating
by
administration
in
recent to
PL
[3H]
from
the
shown is
that
may
7, 8),
dietary
when
a
PNP
be
(S,
physio
converted
kinase,
PL
liver
converting
completely
PL
thus
and of
to
oxidase
used
as
the
and
principal
to
be
of
or solved.
The
intestine
in
metabolites
liver-is
of
mainly
purpose
the
PM
of
involved
the
present
conversion
in
portal
in
of
blood
the
study
dietary
was
PM
following
to
the
oral
was
obt
PM.
Chemicals.
Amberlite
has PM of
and
intestine means
(10).
MATERIALS
ained
study
organ-intestine
remains
in a
mice,
liver,
tissue
which
active provide
participation
and/or most
analyzing
of
our given
sequential
participation
PL,
are may
fact,
orally
intestine
vitamin
conversion
In
PM
PL
oxidase
phosphatases
PL.
dose
circulating
PNP
plus
circulating
logical
to
kinase
enzymes
et al.
PM,
with
specific
Radiochemical
column
AND
activity
Centre
(11).
Acid
METHODS
of
about
(Amersham,
phosphatase
3.87Ci/mmol,
England)
was
purchased
mice,
weighing
and
purified
from
with
Sigma
an
Chemical
Co. Experimental
procedures.
experimental
animals.
experiment. [3H] of
The
PM
was
portal
performed.
followed
in
neutralized
for
5 min
to
acid
as
described
[3H]
(12).
B6
acid
PM
in
the
sequentially
and
described
PM.
The
and
the
extracts
The to
again
isotope
in
7 min
3-4,
and
and
EDTA
of blood
at
PM
1N
perchloric
acid,
collected
from
The
blood
was
supernatant
20,000•~g
for
centrifuged
were
surgery [3H]
was
The
and
as the
removal
after
administration.
mg)
which
the and
times
centrifuged.
few
cells,
before
used
before containing
diethylether,
9 volumes
centrifuged (a
minute
different
the
were 6 h
solution
Portal
after
acid
blood
extracts
first
were
to
content
was 5 min.
at
extracted
onto
the
with
an
each
PLP,
fractions
(11)
with
Amberlite
In
3,000•~g perchloric
PLP, and
PNP, were
to
and PL,
column and
collected
chromatographic
PNP,
PMP
to in
the
PL,
PMP, PN,
chrom
modification
column,
vitamers,
PMP
Amberlite
by some
CG-120
phosphorylated
PNP
same
into
Badger
containing
(0.25ml) of
separated and
elute
PLP,
from
Fractions
Loo
put to
effluent,
hydrolyze
applied
were
by
washed
respectively, above.
pH with
described
was
derived,
to
at
20g, for
saline
with
15 min).
10s
of One
removed
perchloric
plasma
vitamers
phosphatase
tively,
cavity.
about animals
here.
Briefly,
and
1N
100ƒÊl
homogenized
for
mixed
procedures
column (PN),
was
separate
atographic
of
5 N NaOH
blood
then
the
anesthetized
was
vein
9 vol.
with
cases,
gastric
(20,000•~g,
mesenteric
homogenized
some
and
from with
were
intestine
weighed
intestinal
the
they
centrifugation
DDY withheld
injected
into
blood, The
by
was
were
a cannula
or
administration,
the
animals
through
intestine
Male
Food
and
was and
separate
the
pyridoxine treated PM, PL,
PN,
the
same
was
determined
by
respec and
manner
as
throughout. fraction
J. Nutr.
Sci.
by Vitaminol.
a
ABSORPTION
liquid
scintillation
OF PYRIDOXAMINE
FROM
INTESTINE
229
spectrometer.
RESULTS
After of
[3H]
after
1.4nmol
PM the
by oral
absorbed
at
of
blood Fig.
Considerable
but
[3H]
PM
the
portal
PM. [3H]
labeled
was
hardly for
When
nmol,
peak
than
amount
PLP
of those
of
1.
[3H]
of
isotope PM
pmol
(Fig.
the
absorbed from
the
time in
absorption
1).
By
intestine
from
the
of
3, 1992
[3H]
slope
of of
and
PL
and nmol,
[3H] the
[3H] various
[3H]
PM [3H]
3 experiments.
of
the of
7min
had
been
intestine
the
for
progression
PLP
remaining vitamer
[3H]
B6
5.4ƒÊCi)
labeled
labeled
in
PM
in
PM [3H]
the
was
PM
found
intestine
in
a
to
33-fold
found
at Each
as
when (Fig.
various point
small
together
detected
chromatograms
(1.4nmol/mouse).
examined,
only
was
administered
of
administered,
increased
was
5.4ƒÊCi
were
was
PM
in
1. saturation
to
was
administration
in
blood,
appearing Table with
cold
portal
shown
in the
in
of
nmol,
is
vitamers
summarized investigated
the
in
PM
present
was
Moreover,
5.4ƒÊCi)
[3H]
were
administered of
metabolites
amounts (14
3H
amount PLP.
of
after with
B6 of
PLP
are
PM
PM
7min
[3H]
[3H]
point
of
amount
PL
and
of
amount
amounts
predominant,
(140
of
PL
same
of
of
a considerable
column
time
blood
the
labeled
Amount
mean•}SD
38, No.
[3H]
the
The same
addition
were
PM
[3H]
amount
when
administration
Vol.
the
Amberlite
transport
in portal
5.4ƒÊCi),
amounts
administered,
of
5.92
of
the
the
a 10-fold
and
an
of
at
of
However,
large
as
orally
a function
of
detected.
10s
vitamers
PL
amount.
Fig.
from
amounts
blood
B6
amount
administration
involving
[3H]
(46
the
mechanism
and
half
calculated
pattern
after
2a.
The
The
was
was as
absorption.
elution
experiments
(5.4ƒÊCi) presented about
rate.
point
PM
7 min
PM was
administration,
time
The
[3H]
intestine
a steady
10 s at this curve
of
the
a
2b).
times represents
with a larger 100-fold Figure
3
after the
230
T. SAKURAI
Table
1.
portal
blood
* This in
Disappearance
value
intestine.
at 7 min
was The
of following
calculated other
PM
from
intestine
administration
from values
et al.
the are
slope
means•}SD
and
appearance
of B6 vitamers
in
of PM.
of
the of
progression three
curve
of
PM
absorption
experiments.
Fig. 2. Elution patterns from Amberlite column of [3H]B6 vitamers in portal blood 7 min after oral administration of 1.4 nmol (a) and 140 nmol (b) of [3H]PM per mouse. The data shown here are representative of 3 experiments.
shows the relationships between the ratios of [3H]PL, PLP, and PM to all [3H]B6 vitamers in portal blood, and the amounts of [3H]PM administered. Labeled PL in the portal blood was mainly located in the plasma, while labeled PLP was mainly located in the blood cells, regardless of the dosage of labeled PM. Moreover, labeled PM found after the administration of a large amount of labeled PM was located entirely in the plasma. J. Nutr.Sci. Vitaminol.
ABSORPTION
OF
PYRIDOXAMINE
FROM
INTESTINE
231
Fig. 3. Relationship between various dosages of [3H] PM and relative levels of [3H]B6 vitamers in portal blood at 7 min after oral administration.
DISCUSSION Although
the
established, on
the
nmol
it has basis
of
of
as
portal
two
during
absorbed
from
[3H]
through
the
unable
to
of
the
also
of
et the
appeared
in
administered the
liver
[3H] but
in
the
had
intestinal
al.
(14)
PN
PL
and
PM
the
to
PL
system, may
was
the
tissue portal
this
though
isotope
of
the PM
These
to
[3H]
active
completely
may of
in
PL
possibly
however, because
into
[3H]
of
blood,
blood,
is
10s from
blood.
portal
pathway blood
a means
for
converted or
could clearly
absorbed
portal
completely
The
even
in
PM
were
released PM
the
PLP
PLP
1.4-14 weight.
[3H]
PM [3H]
weight/day The
body
[3H]
contrast,
through
provide
[3H] the
intestinal
pathway. PM
portal
indicated
taken
high
PL that
tissue
PL
is synthesized
PL
may that
of
In
body
nmol/kg
and
definitely
(13).
administered, PL
of
1).
been
the
the
be
short
pathway.
converting
dietary
L.
observed
38, No.
(Table
nmol/kg
70-700
[3H]
percent
not
mammalia
orally
amount
a few
B6 has
70-700
to
was
small
than
period
be
various
whereas
The
intestine
[3H]
Vol.
blood,
convert
the
tissues
PM/mouse
vitamin
equivalent
PM•¨PMP•¨PLP•¨PL
[3H]
all
[3H]
more
the in
to of
was
portal
intestine
circulating P.
intestine we
same
that
time
Tsuji most
the
not
Accordingly, to
no
completely
circulation
PM
20g)
peaks.
was
the
PLP
estimated
for
B6 requirements
the
large
suggest
and
tentatively
of in
blood
intestine
requirement
(about
found
observed
dietary
vitamin
1.4nmol
be
results
been
the
PM/mouse
When hardly
the
mouse
be
contain
3, 1992
was
kinase
and of
3H
from into PL
when
PN
was
to
PLP
converted
the
following
released
that
up
PNP [3H]
the [3H] the kinase,
oxidase PN
oral PN
whether
and
rapidly
administration
blood
the and they
of above may contain
with
PMP,
activities.
appeared
through
portal
incubated
intestinal
In
agreement
in
PNP,
[3H]
PNP
with
them,
and
PL
product of
or
in
that
The
a source oxidase
the
suggesting
(12). as
that
PLP,
PN,
pathway serve
rings,
suggesting
PLP
not.
in
232
T. SAKURAI
et al.
When amounts of [3H] PM larger than 46 nmol were administered, a consid erable amount of [3H] PM appeared in the portal blood without being efficiently transformed to [3H] PL (Figs. 2b, 3). This result suggests that the ability of intestine to efficiently convert dietary PM to circulating PL is limited and that the limit is between 14 and 46 nmol of PM per mouse. The PM that leaked out to the portal circulation was mainly located in blood plasma. Plasma PM may serve as a source of the coenzyme PLP in tissues that contain both PL kinase and PNP oxidase. Our previous report showed that when an excess of PM was given orally to mice, a considerable amount of PM appeared in the heart blood and that the ability of the intestine and/or liver to convert PM to PL had also a limit between 14 and 46 nmol of PM per mouse (10). The fact that these two limits are almost the same suggests that the liver does not participate very actively in the conversion of PM to PL, though the organ has no less than 4-fold the activity of PNP oxidase in the intestine (liver: 155 pmol/min/mg protein; intestine: 35 pmol/min/mg protein) (8). It is not so easy to interpret this contradiction. In any case, it is important to note that when a physiological level of PM is orally administered to mice, PM is almost entirely transformed to PL in the intestine, which may be the major source of vitamin B6 for most tissues and organs including blood and liver, and that even when a large quantity of PM is adminis tered, a considerable amount of PL in the blood originates from the PL produced by intestinal tissue. REFERENCES
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38, No.
3, 1992
