A biomimetic chitosan derivates: Preparation, characterization and transdermal enhancement studies of n-arginine chitosan

Article abstract of DOI:10.3390/molecules16086778

A novel arginine-rich chitosan (CS) derivates mimicked cell penetration peptides; N-Arginine chitosan (N-Arg-CS) was prepared by two reaction methods involving activated L-arginine and the amine group on the chitosan. FTIR spectra showed that arginine was chemically coupled with CS. Elemental analysis estimated that the degrees of substitution (DS) of arginine in CS were 6%, 31.3% and 61.5%, respectively. The drug adefovir was chosen as model and its permeation flux across excised mice skin was investigated using a Franz diffusion cell. The results showed that the most effective enhancer was 2% (w/v) concentration of 10 kDa N-Arg-CS with 6% DS. At neutral pH, the cumulative amount of adefovir permeated after 12 hours was 2.63 ± 0.19 mg cm ^-2 which was 5.83-fold more than adefovir aqueous solution. Meanwhile N-Arg-CS was 1.83, 2.22, and 2.45 times more effective than Azone, eucalyptus and peppermint, respectively. The obtained results suggest that N-Arg-CS could be a promising transdermal enhancer.

Full text of DOI:10.3390/molecules16086778

Molecules 2011, 16, 6778-6790; doi:10.3390/molecules16086778
OPEN ACCESS
molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Article
A Biomimetic Chitosan Derivates: Preparation,
Characterization and Transdermal Enhancement Studies of
N-Arginine Chitosan
1
,†
2,†
1
1
1
Hui-Xia Lv , Zhen-Hai Zhang , Xiao-Pan Wang , Qing-Qing Cheng , Wei Wang ,
3
,
1,
4
5
5
Xu-Hui Huang *, Jian-Ping Zhou *, Qiang Zhang , Lu-Lu Hou and Wei Huo
1
Department of Pharmaceutics, China Pharmaceutical University, No. 24 tongjiaxiang Nanjing,
China; E-Mail: lvhuixia@163.com (H.-X.L.)
2
Jiangsu Province Academy of Traditional Chinese Medicine, Nanjing, No. 100 shizhijie Nanjing,
China; E-Mail: davidpharm@yeah.net
3
4
Department of Pharmacy, Fujian Provincial Hospital, China. No.134 dongjie Fuzhou, China
State Key Laboratory of Natural and Biomimetic Drugs, School of Pharmaceutical Sciences, Peking
University, No.38 Xueyuan Road Haidian District, Beijing, China;
E-Mail: zhangqiangdodo@bjmu.edu.cn
5
Jiangxi Xierkangtai Pharmaceutical Co. Ltd., North Zone, High-New Technology Industrial Zone,
Pingxiang, Jiangxi, China; E-Mail: hoululu_12345@hotmail.com (L.-L.H.)
†
These authors contributed equally to this work.
*
Authors to whom correspondence should be addressed; E-Mails: iamzhoujianping@163.com
(
J.-P.Z.); huangys1024@163.com (X.-H.H.); Tel.: +86 25 83271102 (J.-P.Z.);
Fax: +86-25-83301606 (J.-P.Z.); Tel.: +86-0591-87557768-2040(X.-H.H.).
Received: 11 July 2011; in revised form: 25 July 2011 / Accepted: 1 August 2011 /
Published: 9 August 2011
Abstract: A novel arginine-rich chitosan (CS) derivates mimicked cell penetration
peptides; N-Arginine chitosan (N-Arg-CS) was prepared by two reaction methods
involving activated L-arginine and the amine group on the chitosan. FTIR spectra showed
that arginine was chemically coupled with CS. Elemental analysis estimated that the
degrees of substitution (DS) of arginine in CS were 6%, 31.3% and 61.5%, respectively.
The drug adefovir was chosen as model and its permeation flux across excised mice skin
was investigated using a Franz diffusion cell. The results showed that the most effective
enhancer was 2% (w/v) concentration of 10 kDa N-Arg-CS with 6% DS. At neutral pH, the

Molecules 2011, 16
6779
−2
cumulative amount of adefovir permeated after 12 hours was 2.63 ± 0.19 mg cm which
was 5.83-fold more than adefovir aqueous solution. Meanwhile N-Arg-CS was 1.83, 2.22,
and 2.45 times more effective than Azone, eucalyptus and peppermint, respectively. The
obtained results suggest that N-Arg-CS could be a promising transdermal enhancer.
Keywords: biomimetic chitosan derivates; arginine-rich; cell penetration peptides;
N-arginine chitosan; transdermal enhancer; adefovir
1
. Introduction
Cell-penetrating peptides (CPPs) are short cationic peptides such as Transactivator of Transcription
(
(
TAT), penetratin and oligoarginine that facilitate the cellular uptake of various molecular cargos
from small chemical molecules to nanoparticles and large fragments of genes or proteins). CPPs
typically have an amino acid-based composition that contains positively charged amino acids such as
arginine or lysine. In the case of oligoarginine and related peptides, the salient structural feature is that
they are very rich in arginin in general. There has been no real consensus as to the mechanism of CPP
translocation, but there was no doubt that an arginine with a guanidinium group is critical to the
translocation process [1,2]. Since arginine is abundant in cell-penetrating peptides which are highly
cationic, they strongly adsorb on the membrane surfaces via hydrogen bond-induced formations of the
guanidino moieties in arginine with anionic phosphates, sulfates, and carboxylates of cellular
components [3].
Notably, chitosan (CS) is a nontoxic biopolymer that are produced by the deacetylation of chitin,
and currently CS and its derivatives are receiving considerable attention in pharmaceutical and
commercial applications due to their biological activities and properties [4-7]. Because of their
permeation enhancing effect, enzyme inhibitory capabilities, mucoadhesive properties [8], CS and its
derivatives are important excipients for delivery systems.
In this study, N-Arg-CSs, which we call biomimetic chitosan derivatives, prepared by chemical
coupling of L-arginine, mimicked the argnine-rich peptides in order to get the cellular uptake functions
of typical CPPs. N-ArgCSs were first reported in 2004 as novel anticoagulant biomaterials [9]. From
then on some other functions of N-Arg-CS were investigated. These functions include antibacterial
action [10,11], gene transfection efficiency enhancement [12] and siRNA delivery [13]. Meanwhile
our previous study (not published yet) has shown that N-Arg-CS can effectively enhance the oral
absorption and the transdermal delivery of some drugs. To date, no report has ever describved the
above function of N-Arg-CS.
Adefovir [9-(2-phosphonomethoxyethyl) adenine] is an acyclic nucleoside phosphonate used as a
broad-spectrum antiviral that is highly effective against herpes-, retro-, and hepadnaviruses.
Meanwhile other studies have shown that a 1–5 mg dosage of adefovir is effective against
filterable virus which causes skin disease [14]. The major drawbacks of adefovir with regard to
oral administration are its low oral bioavailability, dose-dependent nephrotoxicity and
gastrointestinal disturbance. Transdermal drug delivery offers numerous advantages over conventional
routes of administration, by supplying a sustained release of drug to provide a steady plasma profile

Molecules 2011, 16
6780
and hence reduce side effects, avoid the first-pass metabolism and circumvent the gastrointestinal tract.
The aforementioned facts show that transdermal delivery of adefovir might be necessary as an
alternative to the oral administration. Inspired by the aforementioned research work we have prepared
a series of N-Arg-CS with different molecular weights and DS values and explored their transdermal
enhancement of adefovir absorption.
2
. Results and Discussion
2
.1. Characterization of N-ArgCS samples
The FTIR spectra of L-Arg, CS and N-Arg-CS-B samples are shown in Figure 1. For arginine, the
−
1
−1
absorption band at 1623.15 cm is assigned to the guanido group, and the band at 1403 cm is
–
–
attributed to COO symmetric bending. The C-C-N asymmetric bending and COO scissioning modes
−1
−1
are found at 1137 cm and 773 cm , respectively [15,16]. Chitosan exhibits the characteristic bands
−1
−1
2
of NH scissoring vibrations at 1669 cm , carbonyl asymmetric stretching vibrations at 1563 cm ,
−1
−1
and C-O stretching vibrations of the pyranose ring at 1068 cm and 1010 cm [17]. Comparing with
those of chitosan and arginine, several noticeable changes are apparent in the spectra of N-Arg-CS
−1
samples. The band of guanido group appears at 1615.97 cm and the band of C-C-N asymmetric
−1
–1
bending at 1149 cm . The new band at 1526.23 cm is most likely due to an amide bond linking
chitosan and arginine [9].
Figure 1. FTIR spectrums of the CS, L-Arg and N-Arg-CS-B.
The substitution degrees of arginine in CS estimated from elemental analysis were about 6%
(
N-Arg-CS-A, N-Arg-CS-B, and N-Arg-CS-C), 31.3% (N-Arg-CS-D) and 61.5% (N-Arg-CS-E),
respectively, as presented in Table 1.

Molecules 2011, 16
6781
Table 1. The elemental analysis of CS and N-Arg-CS.
MW C(%) N(%) C/N DD(%) DS(%)
10kD 32.12 ± 0.02 6.06 ± 0.05
Samples
CS
5.30
4.49
4.52
4.53
91.0
-
N-ArgCS-A 5kD 36.68 ± 0.01 8.17 ± 0.03
N-ArgCS-B 10kD 36.52 ± 0.03 8.08 ± 0.05
N-ArgCS-C 20kD 36.56 ± 0.06 8.07 ± 002
-
-
-
-
-
6.3%
6.0%
5.9%
31.3%
61.5%
N-ArgCS-D 10kD 37.64 ± 0.02 12.26 ± 0.08 3.07
N-ArgCS-E 10kD 48.95 ± 0.04 19.98 ± 0.06 2.45
Notes: MW is molecular weight; DD is the degree of deacetylation; DS is the degree of
substitution.
TG curves of chitosan and N-Arg-CS samples are shown in Figure 2. The thermogram of N-Arg-CS
has three weight loss stages. The first stage ranges between 30 and 90 °C and shows about 11.15%
loss in weight, corresponding to the evaporation of adsorbed and bound water. The second one starts at
90 °C and continues up to 180 °C during which there is no significant weight loss. The weight is
abruptly decreased when the temperature reaches 250 °C due to the degradation of N-Arg-CS together
with the breakage of the amide linkage of N-Arg-CS. Compared to N-Arg-CS, the first stage of
chitosan decomposition occurs between 0 and 60 °C, associated with the loss of bound water in the
samples. The second one ranging from 60 to 300 °C corresponds to further dehydration and
degradation of the samples.
Figure 2. TG thermogravimetric of CS and N-Arg-CS-B.
2.2. In vitro skin permeation
2
.2.1. Skin penetration of Adefovir with N-Arg-CS of different MWs in various pH values
Table 2 presents the accumulative percutaneous amount (Q) and steady-state permeation rate of
adefovir with 60.0 mg N-Arg-CS of different MWs in 3 mL adefovir solutions (containing 6.0 mg of
adefovir) at various pH values.

Molecules 2011, 16
Table 2. Effect of N-Arg-CS at various pH values on the skin penetration of adefovir.
6782
–2
−2 −1
Samples
pH
Qn(µg·cm )
Jss(µg·cm ·h )
3
5
7
9
3
5
7
9
3
5
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
457.08 ± 17.15
457.69 ± 21.00
450.82 ± 23.02
330.65 ± 24.38
1714.07 ± 7.79
1826.66 ± 28.61
2125.53 ± 118.48
1815.55 ± 39.10
2306.56 ± 23.61
2333.18 ± 15.31
2628.86 ± 71. 50
2318.23 ± 26. 54
1386.08 ± 33. 82
1388.28 ± 141.75
2064.91 ± 65. 13
1861.52 ± 24. 11
37.70
38.16
35.53
Control
26.75
144.23
148.61
173.53
149.32
189.47
191.60
208.87
191.35
109.52
110.69
169.17
149.78
N-Arg-CS-A
N-Arg-CS-B
N-Arg-CS-C
7
9
. 0
. 0
3
5
7
9
.0
.0
.0
.0
The results showed that both transdermal permeation profile of adefovir with or without N-Arg-CS
followed zero-order kinetics. Meanwhile, compared to those of adefovir solutions without enhancer,
both the Q and Jss of adefovir solutions with 2% N-Arg-CS-A, N-Arg-CS-B, N-Arg-CS-C as enhancer,
respectively, had significant difference (P < 0.05). The effects of different N-Arg-CS specimens
depended on the pH. As for N-Arg-CS-A and N-Arg-CS-B, the cumulative percutaneous amount
increased in the order QpH3 < QpH5 ≈ QpH9 < QpH7, and QpH7 is higher than other three Qs (P < 0.05).
However, the result of N-Arg-CS-C is a little different with the order QpH3 ≈ QpH5 < QpH9 < QpH7 and QpH7
is also higher than other three Qs (P < 0.05). This result supports the observation of Vávrova [18,19].
The results obtained were likely due to different dissociation states of adefovir and N-Arg-CS in at
a
the different pH values. Adefovir is an ionic compound with three pK s, 1.2 (loss of a proton from the
dihydrogenphosphonate and formation of a zwitterion), 4.2 (release of the free base at N1 and
formation of a monoanion) and 6.8 (formation of a phosphonate dianion) [20]. At pH 7 adefovir exists
in the form of a monoanion and a dianion with an almost equal 1:1 molar ratio. N-Arg-CS is a
positively charged polymer due to the existence of a different state of the guanido group of arginine in
acidic, neutral and basic solutions. A complex of N-Arg-CS and adefovir might be formed by the
interaction between positive and negative charge to enhance drug transdermal delivery.
Meanwhile different molecular weight N-Arg-CS with the same DS had different accumulative
percutaneous amounts. The results showed that the accumulative percutaneous amount with N-Arg-
CS-B (Mw, 10 kDa) was higher than that of N-Arg-CS-A (Mw, 5kDa) and N-Arg-CS-C (Mw, 20 kDa)
under all pH circumstances.
3.2.2. Effect of N-ArgCS DS and concentration on the skin penetration of adefovir
The effect of N-Arg-CS substitution value on adefovir transdermal delivery is presented in Figure
(A). The results showed that the cumulative percutaneous amount with N-Arg-CS-B was significantly
3

Molecules 2011, 16
6783
higher than that of N-Arg-CS-D and N-Arg-CS-E (P < 0.05). Meanwhile, there is no significant
difference between N-Arg-CS-D and N-Arg-CS-E (P > 0.05). It was unexpected that the increase in
DS of the N-Arg-CSs did not enhance their penetration properties.
Figure 3. Effect of N-Arg-CS with different substitution values (A) and concentrations (B)
on the skin penetration of adefovir after 12 h (n = 6) (A: The samples are N-Arg-CS-B,
N-Arg-CS-D and N-Arg-CS-E and the concentration is 2%; B: The sample is N-Arg-CS-B).
Regarding the use of different concentrations of N-Arg-CS, the situation is the same as in the case
of DS. The increase in concentration of N-Arg-CS did not lead to an increase in the penetration
enhancement properties of N-Arg-CS as presented in Figure 3(B). 2% of N-Arg-CS seemed to be the
optimum concentration.
2
.2.3. Comparison of different enhancers
Table 3 and Figure 4 present the accumulative percutaneous amount (Q) of adefovir with 60 mg
arginine, different MW chitosans, physical mixtures of arginine and chitosan (1:1) and N-Arg-CS
in 3 mL natural pH adefovir solution (contains 6.0 mg of adefovir).

Molecules 2011, 16
Table 3. The accumulated transportation of adefovir across mice skins with various
6784
enhancers after 12 h (n = 6).
−
2
−2 −1
Enhancer
Control
Qn/µg·cm
Jss/µg·cm ·h
450.82 ± 23.02
701.16 ± 27.99
652.41 ± 29.65
729.82 ± 35.45
660.89 ± 21.02
975.12 ± 47.37
1097.58 ± 49.88
819.91 ± 26.08
2125.53 ± 118.48
2628.86 ± 71.50
2064.91 ± 65.13
1439.04 ± 59.51
1182.55 ± 76.43
1072.81 ± 55.82
35.53
60.13
51.83
55.08
59.13
79.13
93.30
64.02
173.53
208.87
169.17
124.59
98.47
73.51
L-Arg
CS5000
CS10000
CS20000
Mixture of CS5000& L-Arg
Mixture of CS10000& L-Arg
Mixture of CS20000& L-Arg
N-Arg-CS-A
N-Arg-CS-B
N-Arg-CS-C
Azone
Eucalyptus
Peppermint
Figure 4. The accumulated transportation of adefovir across mice skins with various
enhancers after 12 h (n = 6).
The results show that the cumulative amount of adefovir with arginine, different MWs CS and the
physical mixture of arginine and CS after 12 hour were 1.53, 1.43, 1.60, 1.44, 2.13, 2.40, 1.79 folds
more than control sample, respectively. The transdermal enhancement of the arginine is likely due to
its guanidino group. It was reported that guanidino group had the ability to open the tight junctions
between cells and to reduce the membrane potential [21]; the chitosan can open the tight junctions of
the epithelia [8]. The enhancement of arginine and CS mixture could be of the addition effect of both
materials. Furthermore the cumulative amount of adefovir with N-Arg-CS-A, B, C after 12 hours was
4
.71, 5.83, 4.58 times that of the control, respectively The above shows that N-Arg-CS, chemical
coupling of arginine and CS could be an promising transdermal enhancer for adefovir.
Azone (1-dodecylazacycloheptaN-2-one or laurocapram) was the first molecular that was
specifically designed as a skin penetration enhancer. It probably exerts its penetration enhancing
effects through the interactions with the lipid domains of the stratum corneum. Eucalyptus and

Molecules 2011, 16
6785
peppermint are essential oils, and they can impact membrane fluidity to exert their penetration
enhancement [22]. Comparison of N-Arg-CS enhancement with that provided by azone, eucalyptus
and peppermint is presented in Table 3 and Figure 5. The results show that cumulative amount drug
permeated by azone, eucalyptus and peppermint after 12 hours was 2.14, 1.58, 1.34-fold more than
control, respectively. The enhancement of N-Arg-CS-B was found to be 1.83, 2.22, 2.45 folds more
than that of azone, eucalyptus and peppermint, respectively. These results show that N-Arg-CS is
slightly superior to typical penetration enhancers.
Figure 5. The accumulated transportation of adefovir across mice skins with various
enhancers after 12 h (n = 6).
3. Experimental
3.1. Materials
CS (MW5 kDa, 10 kDa, 20 kD, DD > 90%) from shrimp was purchased from GoldeN-shell
Biochemical Co., Ltd. (Zhejiang, China). L-Arg was purchased from Shanghai HuiXing Biochemistry
Reagent Limited Company. (Shanghai, China). Adefovir was purchased from Nanjing Chia-Tai
Tianqing Pharmacy Co. Ltd. (Nanjing, China). All the other chemicals were of analytical grade and
can be used without further purification. Healthy male Kunming species mice (25–30 g) were supplied
by Qinglongshan Laboratory Animal Center. (Nanjing, China). All animal experiments complied with
the rules that are set forth in the NHI Guide of the Care and Use of Laboratory Animals.
3
.2. Synthesis of N-ArgCS with different DS
3
.2.1. Synthesis of N-ArgCS with low DS
The N-ArgCS samples with low DS were synthesized by a modified method described elsewhere[9],
as shown in the Scheme 1(1). First L-Arg (0.3 g) was dissolved in distilled water (10 mL). N-hydroxy-
succinimide (NHS) and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) were added to the
solution, respectively, at a fixed molar ratio of 1:1:3, to activate the carboxyl group of L-Arg. The pH
of the resultant solution was adjusted to 6 with 1% acetic acid and 1% NaOH solution. The carboxyl
group of L-Arg was activated for 2 h. Secondly; chitosan (1 g, MW 5 kDa) was dissolved in 1% acetic

Molecules 2011, 16
6786
acid solution (100 mL). The pH was adjusted in the same manner as L-Arg solution with 1% NaOH
solution. The activated L-Arg solution was added to the chitosan solution to react at ambient
temperature with continuous stirring for 48 h. The resultant solution was dialyzed (MWCO = 3,500)
against distilled water for 48 h, then lyophilized. The final product was named as N-ArgCS-A. Using
the same method for preparation of N-ArgCS-A, and other chitosans (MW 10 kDa and 20 kDa) N-
ArgCS-B and N-ArgCS-C, were produced, respectively.
Scheme 1. Two methods of N-ArgCS synthesis.
3
.2.2. Synthesis of N-ArgCS with high DS
In order to increase the DS, dicarbonic acid bis (1,1-dimethylethyl)ester (Boc 20) was used to
prevent the reaction of activated L-Arg molecules with each other, as shown in Scheme 1(2). L-Arg

Molecules 2011, 16
6787
(
0.44 g) was dissolved in distilled water (20 mL). Boc (0.54 g) was dissolved in tetrahydrofuran (THF,
2
0 mL), and then added to the L-Arg solution. The pH was adjusted to 6 with 1M NaOH solution and
allowed to react at ambient temperature for 24 h. The product was isolated by removing the THF under
reduced pressure using a rotary evaporator. The final product from the evaporation process was
dissolved again in distilled water (20 mL). NHS and EDC were added at fixed molar ratio of 1:1:3
(
g/g/g) as L-Arg/NHS/EDC, respectively. The pH of the resultant solution was adjusted to 6 with 1%
acetic acid and 1% NaOH solution. The Boc carboxyl group of the protected L-Arg was activated for
h. Exactly 1 g of chitosan (MW 10 kDa) was dissolved in 1% acetic acid solution (100 mL) and the
2
pH was adjusted to 6. The activated Boc protected L-Arg solution was added into chitosan solution to
react at ambient temperature with continuous stirring for 48 h. After the reaction was complete, the Boc
groups were deprotected with 1% CF COOH. The obtained solution was dialyzed (MW cutoff = 3,500)
3
against distilled water for 48 h and then lyophilized. The final product was named as N-Arg-CS-D.
N-ArgCS-E was prepared in the same manner with the ratio of 1:1.31:1.63 (g/g/g, CS/L-Arg /Boc).
3
.3. Characterization of N-ArgCS
FTIR spectra of chitosan, L-Arg and N-ArgCS-B were measured by using a FT-IT Nicolet Impact
4
10 spectrophotometer. Powder samples were mixed with KBr, and pressed into disks for
measurement. The DS of N-Arg-CS sample was determined by elemental analysis (C, N) using a Vario
EL III elemental analysis instrument. Thermal degradation (TG) of samples was monitored using a
thermal analyzer. Chitosan and N-ArgCS-B were heated from ambient temperature to 400 °C at a
constant heating rate of 10 °/min under a nitrogen atmosphere.
3
.4. In vitro permeation experiments
Abdominal skins were obtained from male Kunming species mice weighing 25–30 g. After its hair
was shaved carefully with an electric clipper, the skin was excised from the abdominal region of each
scarified mouse and the subcutaneous fat and other extraneous tissues were trimmed out with
physiologic saline. The excised mice skins were washed, then stored at 4 and used within 12 h after the
skin was harvested. The permeation experiments were performed using Franz diffusion cells fitted with
−2
excised mice skins at 32 °C. The effective diffusion area was 1.54 cm and the receptor chamber was
filled with 16 mL of physiologic saline which was constantly stirred at 400 rpm throughout the
experiment. After adefovir and N-Arg-CS mixture solution was applied on the epidermal surface of the
skin, 2 mL of medium in receptor chamber was withdrawn at specific time intervals for up to 12 h. An
equal volume of the fresh physiologic saline was immediately replenished after each sampling process.
Collected samples were filtered through 0.22 μm microporous membrane filter and adefovir was
quantified by HPLC analysis.
3
.5. Drug analysis
Samples were analyzed by LC - 10AT VP HPLC system with a SPD - 10A VP variable-wavelength
ultraviolet absorbance detector and a reverse phase Licrosphere C column (250 mm × 4.6 mm i. d, 5 µm)
18
operating at room temperature. The sample (1 mL) was precipitated by 1 mL methanol and filtered by

Molecules 2011, 16
6788
using 0.22 μm filter membrane. The mobile phase composed of a mixture of methanol/phosphate
−1
buffer at pH 2.5 in a ratio of 80:20 v/v, respectively, the flow rate was 0.5 mL·min . Adefovir was
detected at 261 nm with the retention time of 5.3 min. The standard curve was linear over the
−1
2
concentration range 1–90 µg·mL (R = 0. 9999). The coefficients of variation (RSD) for inter- and
intraday variation was both below 1%.
3
.6. Data analysis
The cumulative amount of adefovir permeating through the skin was plotted as a function of time.
The skin flux was determined from Fick’s law of diffusion: J = dQ /Adt. Where, J is the steady-state
ss
n
ss
−
2
−1
skin flux in μg·cm ·h , dQ
n
is change in quantity of the drug passing through the skin into the
2
receptor chamber in dt hours, A is the active diffusion area in cm and dt is the change in time [23].
The cumulative amount of drug permeating through the skin at different time intervals was calculated
by equation (1):
n−1
(
1)
Cn×Vo + Ci ×V
∑
i=1
Qn =
A
where Cn is the drug concentration of the receiver solution at each sampling time, Ci the drug
concentration of the i (h) sample, and V and V the volumes of the receiver solution and the sample,
0
respectively, A represents the skin surface area. The flux was calculated from the slope of the linear
portion of the profile. All parameters were reported as the mean ± S.D. Statistical analysis was carried
out by using analysis of variance (ANOVA). The level of significant was taken as P < 0.05. A
correlation analysis was performed with the aid of the SPSS program, and correlation co-efficient were
examined for significance (P < 0.05) by using Student’s t-test.
4
. Conclusions
In summary, the above experimental results show that different molecular weights of N-Arg-CS
with different degrees of substitution have the potential to enhance the rate of adefovir transdermal
delivery. In particular, the most effective transdermal enhancer is 2% (2 mg/mL) N-Arg-CS (MW
1
0 kDa) with 6% substitution degree. Chemically a complex of arginine and CS can significantly
enhance the transdermal penetration compared to arginine and CS used singly, which was considered
to be a result of strong interaction between positive and negative charge in N-Arg-CS and adefovir,
then the guanidinium groups and amino groups of N-Arg-CS are strongly adsorbed on the cell
membrane surfaces to open the tight junctions of the epithelia, allowing for the paracellular transport.
These N-Arg-CS simulated arginine-rich cell penetration peptides have potential as a novel
transdermal enhancer, although the mechanism of action needs further investigation.
Acknowledgments
The National Natural Science Foundation of China (No. 30901867 and No. 30973649) is gratefully
acknowledged for financial support. This work was also supported by the National Basic Research
Program of China (973 Program, No. 2009CB903300).

Molecules 2011, 16
6789
Conflict of Interest
The authors declare no conflict of interest.
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