Dietary Hyaluronic Acid Migrates into the Skin of Rats

Abstract

Hyaluronic acid is a constituent of the skin and helps to maintain hydration. The oral intake of hyaluronic acid increases water in the horny layer as demonstrated by human trials, but in vivo kinetics has not been shown. This study confirmed the absorption, migration, and excretion of (14)C-labeled hyaluronic acid ((14)C-hyaluronic acid). (14)C-hyaluronic acid was orally or intravenously administered to male SD rats aged 7 to 8 weeks. Plasma radioactivity after oral administration showed the highest level 8 hours after administration, and orally administered (14)C-hyaluronic acid was found in the blood. Approximately 90% of (14)C-hyaluronic acid was absorbed from the digestive tract and used as an energy source or a structural constituent of tissues based on tests of the urine, feces, expired air, and cadaver up to 168 hours (one week) after administration. The autoradiographic results suggested that radioactivity was distributed systematically and then reduced over time. The radioactivity was higher in the skin than in the blood at 24 and 96 hours after administration. The results show the possibility that orally administered hyaluronic acid migrated into the skin. No excessive accumulation was observed and more than 90% of the hyaluronic acid was excreted in expired air or urine.

Full text

Research Article
Dietary Hyaluronic Acid Migrates into the Skin of Rats
Mariko Oe,1Koichi Mitsugi,2Wataru Odanaka,1Hideto Yoshida,1Ryosuke Matsuoka,1
Satoshi Seino,1Tomoyuki Kanemitsu,1and Yasunobu Masuda1
1R&D Division, Kewpie Corporation, 2-5-7 Sengawa Kewport, Sengawa, Chofu, Tokyo 182-0002, Japan
2ADME & Tox. Research Institute, Sekisui Medical Co., Ltd., 2117 Muramatsu, Tokai-mura, Naka-gun, Ibaraki 319-1182, Japan
Correspondence should be addressed to Ryosuke Matsuoka; ryosuke matsuoka@kewpie.co.jp
Received  May ; Revised  July ; Accepted  July ; Published  October 
Academic Editor: Enzo Berardesca
Copyright ©  Mariko Oe et al. is is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Hyaluronic acid is a constituent of the skin and helps to maintain hydration. e oral intake of hyaluronic acid increases water in
the horny layer as demonstrated by human trials, but in vivo kinetics has not been shown. is study conrmed the absorption,
migration, and excretion of 14C-labeledhyaluronicacid(
14C-hyaluronic acid). 14C-hyaluronic acid was orally or intravenously
administered to male SD rats aged  to  weeks. Plasma radioactivity aer oral administration showed the highest level  hours
aer administration, and orally administered 14C-hyaluronic acid was found in the blood. Approximately % of 14C-hyaluronic
acid was absorbed from the digestive tract and used as an energy source or a structural constituent of tissues based on tests of the
urine, feces, expired air, and cadaver up to  hours (one week) aer administration. e autoradiographic results suggested that
radioactivity was distributed systematically and then reduced over time. e radioactivity was higher in the skin than in the blood
at  and  hours aer administration. e results show the possibility that orally administered hyaluronic acid migrated into the
skin. No excessive accumulation was observed and more than % of the hyaluronic acid was excreted in expired air or urine.
1. Introduction
Hyaluronic acid is a high molecular mass linear polysac-
charide composed of D-glucuronic acid and N-acetyl-D-
glucosamine []. Hyaluronic acid is well known and was rst
isolatedandidentiedfromcattleeyesbyMeyerandPalmer
in  []. Hyaluronic acid is synthesized by all animals and
in some microbes, existing in all connective tissues of the
body, including the skin, joint uid, blood vessels, serum,
brain, cartilage, heart valves, and umbilical cord. e total
volume of hyaluronic acid in the body is about  g for an
adult weighing  kg, replacing one third of the hyaluronic
acid aer degradation and synthesis everyday [].
Hyaluronic acid is used in medicines, cosmetics, and
foods and is a material receiving attention worldwide. Mixed
into supplements, confectioneries, beverages, and processed
foods, hyaluronic acid is approved as health food material
for new resource foods in China, food additives and health
function food in Korea, and as a food additive in Japan.
Hyaluronic acid is marketed as a supplement in the USA,
Canada, Italy, and Belgium.
Safetytestsofhyaluronicacidincludedrepeateddose
oral toxicity tests [], chronic toxicity tests [], acute toxicity
tests [–], subacute toxicity tests [–], reproductive and
developmental toxicity studies [–], antigenicity tests [,
], mutagenicity tests [–], and micronucleus assays [,
]. Safety was conrmed; hence, hyaluronic acid is a food
ingredient that can be ingested with condence.
Hyaluronic acid supplements are used to treat joint pain
in Europe and America, whereas it is known as a moisturizer
for the skin in addition to treating joint pain in Japan. e
oral intake of hyaluronic acid is reported to increase water
in the horny layer as demonstrated in human trials [–].
On the other hand, further study is required whether orally
administered high-molecular hyaluronic acid is taken up into
the body and exerts eects.
Starch, a high molecular polysaccharide, is degraded
into disaccharides by saliva and pancreatic juice and further
Hindawi Publishing Corporation
e Scientific World Journal
Volume 2014, Article ID 378024, 8 pages
http://dx.doi.org/10.1155/2014/378024

e Scientic World Journal
O
O
O
O
OH
OH
OH H
H
H
H
H
H
H
H
H
H
n
14C
NHCOCH3
14COONa 14 CH2OH
F : Structure of 14C hyaluronic acid.
degraded into monosaccharides to be absorbed by the small-
intestinal epithelial cells in the small intestine.
Orally ingested ber, such as cellulose, was not typically
considered to be absorbed into the body but this ber was
reported to ferment in the presence of intestinal bacteria and
was then taken up by the body []. In contrast, studies using
Caco- cells reported that hyaluronic acid permeated the
intestinal epithelium while retaining the chemical structure
[],andhyaluronicacidwastakenupintothebodyviaoral
administration [,]butthestudyresultswerefewinnum-
ber, and thus there was controversy over in vivo absorption.
In articles that investigated in vivo absorption of hyaluronic
acid [,], a complex of radiolabeled technetium and
hyaluronic acid was used via the oral route; therefore, the
absorption results of technetium-hyaluronic acid molecular
architecture may not be obtained due to separation of
the complex or progression of ligand substitution reaction
between the complex and the biological constituents [].
Orally administered hyaluronic acid migrates into con-
nective tissues, such as skin [,],butmetabolismand
excretion aer migration into the connective tissue have not
been adequately examined.
In order to conrm the series of biokinetic processes of
hyaluronic acid from absorption to excretion, we measured
theplasmaradioactivitylevel;excretionrateinurine,feces,
and expired air; the residual rate in the body; and examined
14C distribution in each tissue with whole body autoradiogra-
phy for single oral or single intravenous administration in rats
using 14C-hyaluronic acid, a stable molecular architecture
with 14C incorporated into the carbon skeleton.
2. Materials and Methods
2.1. Radiolabeled Compounds. We synthesized 14C-
hyaluronic acid based on the tissue culture method
(14C glucose was added in the culture medium) using the
crista galli in the ADME/TOX Research Institute, Daiichi
Pure Chemicals Co., Ltd., Ibaraki Prefecture, Japan. 14C-
hyaluronic acid (Figure )wasobtainedbyvacuumdrying
aer purifying with hydrous ethanol. e average molecular
weight was , from measuring with the limiting
viscosity method. Specic radioactivity was . kBq/mg,
and radiochemical purity was .%.
2.2. Laboratory Animals. WepurchasedmaleSDratsaged-
 weeks (weighing .–. g, Charles River Laboratories
Japan, Inc.), reared under temperature conditions of ∘C
±∘Candrelativehumidityof%±%, and then fed
food (MF for rats, Oriental Yeast Co., Ltd.) and tap water ad
libitum. Rats were used for study aer preliminary breeding
for  days or more.
2.3. Blood Radioactivity Measurement. e 14C-hyaluronic
acid was administered orally at  mg/kg (𝑛=3)and
intravenously at  mg/kg (𝑛=3)forplasmaradioactivity
measurement, which is an index of bioavailability. Consider
the following:
Bioavailability (%)=[AUC]p.o./DOSEp.o.
[AUC]i.v. /DOSEi.v.
× 100, ()
where [AUC]p.o.is oral administration [AUC]i.v./DOSEi.v. is
oral dose, [AUC]i.v.is intravenous administration AUC, and
DOSEi.v.is intravenous dose.
e test material dissolved in injectable distilled water
was administered by single oral gavage to rats using a syringe
with the oral probe into the stomach. Administered radioac-
tivity was . MBq/kg body weight. Intravenous injection
was performed in the femoral vein using a needle syringe.
e administered radioactivity dose was . MBq/kg body
weight. e transition of plasma 14C radioactivity was inves-
tigated by collecting blood over time from the tail vein of
animals that received the single administration.
Aer collecting about  𝜇Lofbloodfromthetailvein
using a heparin-treated capillary tube (Terumo Corporation)
at , , and  minutes and , , , , , , , ,
, , and  hours aer administrating 14C-hyaluronic
acid, followed by centrifugation (at  ×gforminutes
at room temperature), the obtained  𝜇Lofplasmawas
transferred to vials as radioactivity samples and dissolved by
adding  mL of the tissue solubilizer Soluene- (Packard
Instrument Company). Aer adding  mL of scintillator
Hionic-Fluor (Packard Instrument Company) and standing
at room temperature, the 14C-hyaluronic acid concentration
was calculated by measuring radioactivity using the LSC
(Liquid Scintillation Counter, TR, Packard Instrument
Company).
2.4. Measuring Excretion Rate in Urine, Feces, and Expired
Air and Residual Rate in the Body. e animals that received
14C-hyaluronic acid in a single oral administration at a dose
of  mg/kg (𝑛=3)werehousedinmetaboliccages,and
the 14C-excretion rates in the urine, feces, and expired air
were determined from the collected urine, feces, and expired
air samples at predetermined times. Aer the last sampling,
animals were killed under ether anesthesia to measure the
residual rate in the body.
For measuring the urinary excretion rate, the cage was
washed with a small amount of distilled water during  to ,
to,to,to,to,to,to,to
, and  to  hours aer 14C-hyaluronic acid adminis-
tration,andthewaterusedforwashingwasputtogetherwith

e Scientic World Journal 
theurine,followedbyfurtherdilutiontomLwithdistilled
water. Aer transferring the collected  mL of diluent to
vials as radioactivity samples,  mL of scintillator HIONIC-
FLUOR was added and urinary excretion rate was calculated
fromtheradioactivityvaluemeasuredusingtheLSC.
For measuring the fecal excretion rate, weighing the feces
collected during –, –, –, –, –, –,
and – hours aer 14C-hyaluronic acid administration,
adding distilled water, stirring to make homogeneous with
the Polytron homogenizer (Kinematica Inc.), and further
diluting to  mL with distilled water, the . mL was
transferred to vials as radioactivity samples. Aer dissolving
with heat by adding  mL of tissue solubilizer Soluene-,
adding  mL of scintillator Hionic-Fluor, and standing at
room temperature, the feces excretion rate was calculated
fromtheradioactivityvaluemeasuredusingtheLSC.
For measuring the excretion rate in expired air, the excre-
tion rate in expired air was calculated from the radioactivity
value measured using the LSC aer collecting expired air in
two trap bottles linked in series that were lled with  mL
of % monoethanolamine solution while venting air into a
metaboliccage,transferringeachmLtovialsasradioactivity
samples and adding  mL of scintillator Hionic-Fluor.
Formeasuringtheresidualrateinthebody,theresidual
rate in the body was calculated from the radioactivity value
measuredusingtheLSCaeraddingmLof.mol/L
sodium hydroxide solution and  mL of toluene to cadaver
tissues, dissolving with heat to reux, diluting to  mL with
water, and stirring to make homogeneous, and the . mL was
transferred to vial aer adding  mL of scintillator Hionic-
Fluor.
2.5. Whole Body Autoradiography. Aer animals that
received 14C-hyaluronic acid in a single oral administration
at a dose of  mg/kg were killed under ether paralysis
at a predetermined time, radioactivity distributions and
time-dependent changes to various tissues were examined
by preparing whole body autoradiograms.
e animals were killed under ether anesthesia at , ,
and  hours aer 14C-hyaluronic acid administration (𝑛=
1each), the hair coat was sheared immediately, and the
nasal cavity and anus were blocked with % sodium carboxyl
methyl cellulose (CMC-Na). e body was frozen in dry ice-
acetone,separatingthefrontandhindlimbsandtailfromthe
frozen cadaver, embedding with % CMC-Na on microtome
stages, freezing in dry ice-acetone, xing on cryomicrotome
(PMV MP, Sweden PMV), and scraping o by sticking
cryosections at a thickness  𝜇monadhesivetape(no.
, Sumitomo M Co., Ltd.) to be freeze dried. Predried
sections were covered with a protective coat ( 𝜇mdiagram
foil, Mitsubishi Chemical Corp. polyester lm Co., Ltd.) and
tightly adhered to the imaging plate (Type-BAS SR, Fuji
PhotoFilmCo.,Ltd.)tobeexposedforacertainperiod
oftimeinaleadshieldbox.Aerexposure,wholebody
autoradiograms were prepared from radioactivity images
recorded on imaging plates using BAS (Fujix BAS, Fuji
Photo Film Co., Ltd.). Reading conditions for the imaging
T : Radioactivity concentration in plasma aer single oral or
intravenous administration of C hyaluronic acid to rats (dose: p.o.;
 mg/kg, IV;  mg/kg).
Time
Radioactivity concentration
(𝜇g eq. of hyaluronic acid/mL)
p.o. i.v.
 min N.D. 233.0 ± 22.1
 N.D. 222.5 ± 15.7
 N.D. 211.7 ± 8.4
hr N.D. 180.1 ± 2.6
N.D.123.1 ± 2.0
1.1 ± 0.8 47.8 ± 9.4
7.6 ± 0.6 3.6 ± 0.3
 3.5 ± 0.3 1.7 ± 0.1
 2.0 ± 0.1 0.9 ± 0.1
 1.3 ± 0.1 0.6 ± 0.1
 0.9 ± 0.0 0.4 ± 0.1
 0.7 ± 0.1 0.3 ± 0.0
 0.5 ± 0.0 0.2 ± 0.0
 0.4 ± 0.1 0.1 ± 0.1
Detection limit . .
𝑇max (hr) 8±0 —
𝐶max (𝜇g eq./mL) 7.6 ± 0.6 —
𝐶0(𝜇g eq./mL) — 238.4 ± 25.5
𝑇1/2
( min– hr) (hr) — 1.3 ± 0.1
(– hr) (day) 1.9 ± 0.1 1.7 ± 0.1
AUC (𝜇geq.⋅hr/mL)
(– hr) 284 ± 16 757 ± 37
(–∞)309 ± 20 765 ± 40
Data are expressed as the mean values ±S.D. of three animals.
N.D.: not detected.
—: not determined.
platewerearesolutionof𝜇m, gradation of , sensitivity
of ,, and latitude of .
3. Results
3.1. Plasma Radioactivity Level
3.1.1. Oral Administration Group. At the time of the sin-
gle oral administration of 14C-hyaluronic acid at a dose
of  mg/kg in male SD rats aged  to  weeks, plasma
radioactivity rose slowly, 𝐶max (peak plasma radioactivity
level) was . 𝜇g eq/mL, 𝑇max (time at 𝐶max)washours,
𝑇1/2 (– h) (half-life) was . days, and AUC (–∞)(area
under the concentration-time curves of plasma) was  𝜇g
of eq/mL/h (Tab l e  ). 14C-hyaluronic acid migrated into the
bloodwhenorallyadministered.
3.1.2. Intravenous Administration Group. At the time of single
intravenous injection of 14C-hyaluronic acid at a dose of

e Scientic World Journal
T : Cumulative excretion of radioactivity in urine, feces, and expired air as COaer single oral administration of C hyaluronic acid
to rats (dose:  mg/kg).
Time (hr) Excretion of radioactivity (% of dose)
Urine Feces Expried air Total
– . ±. — . ±. —
.±. — . ±. —
 . ±. . ±. . ±. . ±.
 . ±. . ±. . ±. . ±.
 . ±. . ±. . ±. . ±.
 . ±. . ±. . ±. . ±.
 . ±. . ±. . ±. . ±.
 . ±. . ±. . ±. . ±.
 . ±. . ±. . ±. . ±.
Carcass ( hr) . ±.
Data are expressed as the mean values ±S.D. of three animals.
—: not determined.
mg/kginmaleSDratsagedtoweeks,theplasma
radioactivity level was . 𝜇g of eq/mL at  minutes aer
administration, which was the rst measurement time, and
𝑇1/2 ( minutes to  hours) decreased in . hours. 𝑇1/2 (–
 hours) was . days, and AUC (–∞)was𝜇gof
eq/mL/h (Table ). Bioavailability calculated from the AUC
of the oral administration group and intravenous adminis-
tration group was %.
3.2. Excretion Rate in Urine, Feces, and Expired Air and Resid-
ual Rate in the Body. At the time of single oral administration
of 14C-hyaluronicacidatadoseofmg/kginmaleSDrats
aged  to  weeks, radioactivity was excreted in urine: .% of
the dose by  hours, .% by  hours, and .% by  hours
aer administration. In feces, 14C was excreted as follows:
.% of the dose by  hours, .% by  hours, and .% by
 hours. In expired air, radioactivity was excreted as follows:
.% of the dose by  hours, .% by  hours, and .%
by  hours. Total excretion rate in urine, feces, and expired
air was .% of the dose by  hours aer administration,
whereas .% of the dose remained in the cadaver at this point
of time (Ta b l e  ).
3.3. Whole Body Autoradiogram. At the time of single oral
administration of 14C-hyaluronic acid at a dose of  mg/kg in
male SD rats aged  to  weeks, 14C was detected in the skin as
follows: . PSL/mm2at  hours, . PSL/mm2at  hours,
and . PSL/mm2at  hours aer administration. 14Cwas
detected in the blood as follows: . PSL/mm2at  hours,
. PSL/mm2at  hours, and . PSL/mm2at  hours
aer administration. e 14Clevelintheskinwassimilar
to that in the blood at  hours aer administration, whereas
ahigher14C level was detected in the skin compared with
the blood at  hours or more aer administration (Ta b l e  ,
Figures –).
In the other tissues, the highest radioactivity was
observed in the intestinal contents at  hours aer admin-
istration; subsequently, readings in the pancreas, harderian
gland, liver, and mandibular gland were high. e radioac-
tivity in the following was higher than in the blood: the
bowels, intravesical urine, spleen, kidney, thyroid gland,
stomach, bone marrow, brown fat, lungs, seminal vesicle,
adrenal gland, pituitary gland, thymus, heart, and prostate.
Radioactivityatasimilarlevelasinthebloodwasfoundinthe
epididymis, skeletal muscles, and the brain. e testes, white
fat, gastric contents, and eyeballs showed lower radioactivity
levels than in the blood (Tab l e  and Figure ). At  hours
aer administration, high radioactivity was observed in
intestinal contents, and the harderian gland was subsequently
high. Radioactivity in the following was higher than in the
blood: bowels, bone marrow, adrenal gland, thyroid gland,
liver, spleen, kidney, stomach, brown fat, pituitary gland,
prostate, thymus, lungs, mandibular gland, and seminal
vesicle. Radioactivity at a similar level to the blood was found
in the pancreas and heart. e skeletal muscle, epididymis,
brain, testes, white fat, eyeballs, intravesical urine, and gastric
contents showed lower radioactivity levels than in the blood
(Table  and Figure ). At  hours aer administration, all
radioactivity dropped. Radioactivity in the following was
higher than in the blood: harderian gland, seminal vesicle,
adrenal gland, kidney, liver, brown fat, and bowels. Other
tissues showed similar levels of radioactivity to the blood
or lower levels of radioactivity than the blood (Table  and
Figure ).
4. Discussion
At the time of single oral administration of 14C-hyaluronic
acid at a dose of  mg/kg in male SD rats aged  to  weeks,
the plasma radioactivity level was less than the detection limit
by  hours aer administration. Four hours or more aer that,
14C began to be detected and reached the maximum level at
 hours aer administration; therefore, hyaluronic acid was
absorbed slowly from the digestive tract. At  hours or more
aer administration, 𝑇1/2 (– hours) disappeared in .
days, and this elimination half-life period was similar to that
of the intravenous administration group at a dose of  mg/kg.

e Scientic World Journal 
T : e distribution of radioactivity in selected organs and
tissues as [(photostimulated luminescence-background)/area]aer
single oral administration of C hyaluronic acid to rats at a dose of
 mg/kg.
No. Tssue Distribution of radio activity (PSL/mm)
hr hr hr
Adrenal gland . . .
Blood . . .
Bone marrow . . .
Brain . . .
Brown fat . . .
Epididymis . . .
Eyeball . . .
Fat . . .
Gastric contents . . .
 Harderian gland . . .
 Heart . . .
 Intestinal contents . . .
 Intestine . . .
 Kidney . . .
 Liver . . .
 Lung . . .
 Mandibular gland .    .    .  
 Pancreas . . .
 Pituitary gland . . .
 Prostate gland . . .
 Seminal vesicle . . .
 Skeletal muscle . . .
 Skin . . .
 Spleen . . .
 Stomach . . .
 Teste s . . .
 ymus . . .
 yroid gland . . .
 Urine in bladder . . .
Namely,hyaluronicacidwastakenupbythebodyviatheoral
administration route.
For migration to the skin, hyaluronic acid reached the
skin in this study though the molecular weight was unknown.
e 14C derived from hyaluronic acid that reached the tissues
via the oral route decreased over time, but there was similar
or higher radioactivity distributed in the skin than in the
blood even at  hours aer administration; thus, this was
considered a useful nding for the eect of hyaluronic acid
on the skin.
Low-molecular-weight hyaluronic acid is reported to
promote the growth of broblasts and to elevate hyaluronic
acid synthesis [,]. If orally administered hyaluronic acid
should reach the skin in the form of low-molecular-weight
hyaluronic acid, the phenomenon described above occurs
andisconsideredtoactonskinmoistureimprovement.
Right axis aspect
Le axis aspect
Center axis aspect
419285221
17 27 25 13 29 20 8
22
1424
23
716
626
10 15
112 3
11 189
F : Whole body radioluminograms  hours aer single oral
administration of 14C hyaluronic acid to a rat (dose:  mg/kg). ()
Adrenalgland.()Blood.()Bonemarrow.()Brain.()Brown
fat. () Epididymis. () Eyeball. () Fat. () Gastric contents. ()
Harderian gland. () Heart. () Intestinal contents. () Intestine.
() Kidney. () Liver. () Lung. () Mandibular gland. ()
Pancreas. () Pituitary gland. () Prostate gland. () Seminal
vesicle. () Skeletal muscle. () Skin. () Spleen. () Stomach.
()Testes.()ymus.()yroidgland.()Urineinbladder.
Hydroxyproline and ceramide, which are the components
present in the skin as hyaluronic acid, are known to be
transferred to the skin by ingestion. It is reported that .% of
ceramide was transferred to the skin  hours aer ingestion
[]. Although the amount of hydroxyproline transferred to
the skin by ingestion is unclear, it has been shown to reach the
skin []. us it is well known that the components present
intheskinreachtheskinbyingestion.However,thereisno
other report on the transfer of macromolecular polysaccha-
ride such as hyaluronic acid to the skin by ingestion than that
of hyaluronic acid.
In regard to pharmacokinetics of ingested hyaluronic
acid, it has been reported that low molecular hyaluronic acid
passes through the intestine [], endogenous hyaluronic
acid is present in the blood, and hyaluronic acid is stable in
the body [,]. ere is a report showing that hyaluronic
acid labeled with 99Tc reached the skin []. In this report
where movements of free 99Tc and 99Tc-hyaluronic acid to
the skin were studied, free 99Tc reached the skin  min
aer administration and disappeared  min aer admin-
istration, whereas 99Tc-hyaluronic acid reached the skin 
hours aer administration and remained in the skin even
 hours aer administration []. It was considered that, in
the study, the compound reached the skin with maintaining
the hyaluronic acid structure to some extent since 99Tc

e Scientic World Journal
19
16 122
26
12
15
17
10
4
28 27
7
11 189
23 24 14 3
25 13 29 20 8 6
5212
Right axis aspect
Le axis aspect
Center axis aspect
F : Whole body radioluminograms  hours aer single oral
administration of 14C hyaluronic acid to a rat (dose:  mg/kg). ()
Adrenal gland. () Blood. () Bone marrow. () Brain. () Brown
fat. () Epididymis. () Eyeball. () Fat. () Gastric contents. ()
Harderian gland. () Heart. () Intestinal contents. () Intestine.
() Kidney. () Liver. () Lung. () Mandibular gland. ()
Pancreas. () Pituitary gland. () Prostate gland. () Seminal
vesicle. () Skeletal muscle. () Skin. () Spleen. () Stomach.
()Testes.()ymus.()yroidgland.()Urineinbladder.
was administered as a chelate complex. In our study, 14C-
radioactivity was detected in the skin  to  hours aer
administration. erefore, it is possible that ingested 14C-
hyaluronic acid reached the skin as a form of hyaluronic
acid. However, the existence form of 14Cintheskinwasnot
directly analyzed in the current study. us, the identication
of substance containing 14C which reached the skin and the
involvement of this substance in the skin moisture retention
eect needs to be addressed in the future.
Formetabolism,apartofthehyaluronicacidusedin
body tissues is physiologically subject to keratinization and
subsequent desquamation in the epidermis [], and the
rest is subject to degradation by hyaluronidase [,]
or fragmentation by oxygen radicals in each tissue [–
]. Partially degraded hyaluronic acid is reported to enter
local lymph nodes through lymphatic vessels following a
fragmentation process and subsequently enters the blood
circulation system, going through nal hydrolysis in the liver
[,] and then eliminated from the body. is study
examined extracorporeal excretion at the time of single oral
administration of 14C-hyaluronic acid at a dose of  mg/kg
in male SD rats aged  to  weeks; consequently, the main
excretion route was via expired air, resulting in .% of
the dose being excreted by  hours aer administration.
Urinary and fecal excretion rates were .% and .% of the
dose, respectively, by  hours aer administration, whereas
212
Right axis aspect
Le axis aspect
Center axis aspect
16
10 15 6
419 28 5
17 27
23 24 14 22
1813
25
11 9 12 29 20 826
1
73
F : Whole body radioluminograms  hours aer single oral
administration of 14C hyaluronic acid to a rat (dose:  mg/kg). ()
Adrenalgland.()Blood.()Bonemarrow.()Brain.()Brown
fat. () Epididymis. () Eyeball. () Fat. () Gastric contents. ()
Harderian gland. () Heart. () Intestinal contents. () Intestine.
() Kidney. () Liver. () Lung. () Mandibular gland. ()
Pancreas. () Pituitary gland. () Prostate gland. () Seminal
vesicle. () Skeletal muscle. () Skin. () Spleen. () Stomach.
()Testes.()ymus.()yroidgland.()Urineinbladder.
radioactivity remained at .% of the dose in the body at this
time.
Approximately % of 14C-hyaluronic acid was absorbed
from the digestive tract and used as an energy source or a
structuralconstituentofthebody.Atotalof%bioavailabil-
ity determined from AUC was a low value compared with the
% absorption rate. Typically, high-molecular polysaccha-
rides, such as starch, are absorbed from the small intestine
and then carried to the liver via the hepatic portal vein from
the capillary bed and are known to be metabolized in the
liver. Orally ingested hyaluronic acid is mostly metabolized
in the liver and degraded into carbon dioxide (rst-pass
eect); bioavailability was low because hyaluronic acid was
eliminated as expired air from the lungs before entering
whole-body blood circulation [].
In recent years, an aging society is advancing in Japan,
USA,andEurope.Hyaluronicacidinthebodydecreases
with age, and accordingly, the hyaluronic acid content in the
skin of -year-old elderly persons is lower than one-quarter
compared with that of a -year-old youth []. us, the
need in food applications for hyaluronic acid is increasing to
supplement decient hyaluronic acid. is study can support
the nding that hyaluronic acid reaches the skin and that
hyaluronic acid does not accumulate excessively. We hope
this will lead to QOL improvement and relief for the elderly
and people suering from dry skin.

e Scientic World Journal 
5. Conclusions
isstudy’sresultshaveshownthepossibilitythatorally
ingested 14C-hyaluronic acid was taken up into the body and
migrated into the skin. Further study is required, includ-
ing the molecular weight in the blood of orally ingested
hyaluronic acid and conrmation by skin tissue extraction.
Also,aerorallyingestedhyaluronicacidwasusedby
tissues, % or more was metabolized and eliminated in
expired air and urine, suggesting that there was no excessive
accumulation in the body.
Conflict of Interests
e authors declare that there is no conict of interests
regarding the publication of this paper.
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