BiomaterialsScience

PAPER

Cite this: Biomater. Sci., 2014, 2, 522

Received 2nd October 2013,Accepted 4th December 2013

DOI: 10.1039/c3bm60236b

www.rsc.org/biomaterialsscience

Design and use of silica-containing redoxnanoparticles, siRNPs, for high-performanceperitoneal dialysis†

Yukio Nagasaki,*a,b,c Tatsuya Yaguchi,a Takuma Matsumura,a Toru Yoshitomi,a

Yutaka Ikeda,a Atsushi Uedad and Aki Hirayamae

The prevention of encapsulating peritoneal sclerosis (EPS) and the enhancement of dialysis efficiency are

two important strategies that can improve the quality of life of patients undergoing peritoneal dialysis. We

have thus far developed bionanoparticles that effectively scavenge reactive oxygen species (redox nano-

particles; RNPs). The objective of this study was to apply RNPs as a component of dialysate to reduce oxi-

dative stress. Porous silica nanoparticles were combined with RNPs to enhance the effective adsorption

capacity of low-molecular weight (LMW) compounds. The silica-containing RNPs (siRNPs) were confirmed

to statistically decrease the level of creatinine and blood urea nitrogen in vivo. EPS model rats that under-

went an intraperitoneal injection of chlorhexidine gluconate exhibited dysfunction of the peritoneal mem-

brane. siRNP administration did not result in dysfunction of the peritoneal membrane. An LMW nitroxide

compound, TEMPOL, also showed a weak peritoneal protective effect, although its efficiency was limited.

No blood uptake of siRNPs was observed when they were administered into the peritoneal cavity. However,

LMW-TEMPOL diffused into the blood stream, which might have decreased its effective concentration in

the peritoneal cavity and led to adverse effects across the entire body. Considering these results, siRNPs are

expected to be a new multi-functional nanomaterial for high performance peritoneal dialysis.

1. Introduction

Recently, technological developments in renal replacementtherapy (RRT) have been used to successfully treat patientswith renal failure. By the end of 2010, 2.03 million patientswere undergoing RRT. Nearly 90% of these patients receivedhemodialysis (HD) therapy, while worldwide only 8.4–11%were treated with peritoneal dialysis (PD).1 Although HD sub-stitutes for a portion of renal function, there still remainseveral issues such as (1) the continuous need for hospital

attendance, which limits the social activities of patients; (2)insufficient removal of medium molecular weight uremictoxins; and (3) the removal of body fluid in a short timethereby leading to cardiac overload and vascular damage.2

These issues increase the patient risk for several seriousdiseases such as stroke and myocardial infarction.3 In con-trast, the following reasons make PD the first choice of RRT inmany countries: (1) low load in terms of medical economies;4

(2) social precedence during domiciliary treatment; and (3)medical advantages with respect to patient outcome.5 For thelast reason in particular, current studies are successivelyrevealing the advantages of the PD-first policy as they relate toresidual renal function and survival rates.6 For example, dia-lysate can be changed by oneself. In addition, rehabilitation iseasy, it maintains renal function, and the risk of stroke andmyocardial dysfunction is low. Thus, PD has much potential toprovide a high quality of life to patients who are undergoingRRT.

However, the long-term outcome of PD is still poorer thanthat of HD. Two major reasons for this are (1) the insufficiencyof dialysis due to the loss of peritoneal function, which thusincreases changes in dialysate; and (2) the occurrence ofencapsulating peritoneal sclerosis (EPS), which is a fatal com-plication of PD.7 Chronic inflammation of the peritoneal

†Electronic supplementary information (ESI) available. See DOI:10.1039/c3bm60236b

aDepartment of Materials Science, Graduate School of Pure and Applied Sciences,

University of Tsukuba, Tennodai 1-1-1, Tsukuba, Ibaraki 305-8573, JapanbMaster’s School of Medical Sciences, Graduate School of Comprehensive Human

Sciences, University of Tsukuba, Tennodai 1-1-1, Tsukuba, Ibaraki 305-8573, JapancSatellite Laboratory, International Center for Materials Nanoarchitectonics

(WPI-MANA), National Institute for Materials Science, University of Tsukuba,

Tsukuba, Tennodai 1-1-1, Ibaraki 305-8573, Japan. E-mail: yukio@nagalabo.jp;

Tel: +81 29 853 5749dTsukuba University Hospital Hitachi Medical Education and Research Center,

Jyonan-chou 2-1-1, Hitachi, Ibaraki 317-0077, JapaneCenter for Integrative Medicine, Tsukuba University of Technology, Kasuga 4-12-7,

Tsukuba 305-8521, Japan

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membrane leads to encapsulation of the intestine, which thenresults in severe ileus and malnutrition in EPS patients.8 Theduration of PD is intricately related to EPS, whereby more than3–8 years of PD history remarkably enhances the risk of EPSand leads to the termination of PD and switching over to HD.9

Dialysate with a high glucose concentration causes oxidativestress to the peritoneum and results in EPS over the course ofseveral years.10 Frequent changes in dialysate increase the riskof contracting infectious diseases.11 Resolving these would notonly increase the quality of life for the patient, but also reducemedical costs worldwide. For these objectives to be met, botha decrease in oxidative stress to the peritoneal membrane andan increase in the adsorption capacity of blood wastes arerequired.

We have previously developed novel nanotherapeutics withredox nanoparticles (RNPs) containing nitroxide radicals asfree radical scavengers for treating cerebral and renal ische-mia–reperfusion, as well as brain hemorrhage.12 Typicalcharacteristics of RNPs are (1) because nitroxide radicals arecovalently conjugated to the nanoparticle backbone, they arenot leaked to the outside of the nanoparticle;13 (2) the sizes ofRNPs are ca. 40 nm in diameter and thus they are not interna-lized into healthy cells;14 and (3) as a consequence RNPs donot interfere with normal redox reactions inside the cell. Thesecharacteristics help RNPs selectively scavenge over-producedreactive oxygen species (ROS), especially outside the cell. Wehave so far confirmed the therapeutic effects of RNPs withrespect to several disease models such as cerebral15 andrenal16 ischemia–reperfusion injuries, cerebral hemorrhage,17

cancer,18 ulcerative colitis,19 and small intestinalinflammation.20

The objective of this study was to apply RNPs as one of thecomponents in dialysate to reduce oxidative stress. Poroussilica nanoparticles were combined with RNPs in order toenhance the adsorption capacity of creatinine and other LMWcompounds effectively (Fig. 1). The silica-containing RNPs(siRNPs) thus prepared were confirmed to increase the adsorp-tion capacity of uremic toxins in vivo. EPS model rats were

prepared by injecting them daily with chlorhexidine gluconate(CH) intraperitoneally (i.p.) for a week. siRNPs were adminis-tered to the peritoneal cavity of the rats at the same time toconfirm that they were protected against CH-induced inflam-mation. CH-induced dysfunction of the peritoneal membranesuch as disruption of the mesothelial cell layer and vascularityof the expanded submesothelial compact zone was notobserved for the siRNP treatments. These results show poten-tial for siRNPs to be used as a new multi-functional nano-material in peritoneal dialysis.

2. Materials and methods2.1. Materials

2,2′-Azobisisobutyronitrile (Kanto Chemical Co., Inc., Tokyo,Japan) was purified by performing recrystallization frommethanol. Chloromethylstyrene (CMS) was kindly provided bySeimi Chemical Co., Ltd (Kanagawa, Japan) and purified bywashing with alkaline to remove the inhibitor, dehydratingwith sodium sulfate, and vacuum distilled under a nitrogenatmosphere. 4-Amino-2,2,6,6-tetramethylpiperidine-1-oxy(4-amino-TEMPO) (Aldrich Chemical Co., Inc., U.S.A.), 2-propa-nol, diethyl ether, dimethyl sulfoxide, N,N-dimethylformamide(DMF), and tetraethoxysilane (TEOS) (Wako Pure ChemicalIndustries, Ltd, Osaka, Japan) were used without further purifi-cation. Colloidal silica 10–20 nm in diameter (Snowtech-O,SiO2 = 20 wt%; pH = 2–4; viscosity = 1.0–3.0 mPa s) was kindlyprovided by Nissan Chemical Co., Ltd (Tokyo, Japan) and usedwithout further purification. PEG possessing a methoxy groupat the α-chain end and a sulfanyl group at the ω-chainend (MeO-PEG-SH) (NOF CORPORATION Co., Ltd, Japan),2-methyl-6-p-methoxyphenylethynyl-imidazopyrazinone (MPEC,Atto, Corp. Tokyo, Japan), and methyl orange (MO) (KantoChemical, Tokyo, Japan) were used without further purification.Twenty percent chlorhexidine gluconate (CH; Wako, Tokyo,Japan) was used after dilution to 0.1% by the addition of saline.

Fig. 1 Schematic illustration of silica-containing redox nanoparticles (siRNPs). (a) Structure of siRNPs and (b) siRNPs for peritoneal dialysis.

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2.2. Preparation of MeO-PEG-b-PMNT

Block copolymer (MeO-PEG-b-PMNT) composed of the hydro-philic PEG segment and the hydrophobic poly(4-methyl-styrene) segment possessing nitroxide radicals as a side chainvia an amine linkage was synthesized according to our pre-vious studies.21 Briefly, poly(ethylene glycol)-b-poly(chloro-methylstyrene) (MeO-PEG-b-PCMS) was synthesized by theconventional radical telomerization of CMS using MeO--PEG-SH as a telogen. The chloromethyl groups were convertedto 2,2,6,6-tetramethylpiperidinyl-1-oxyls via an amination re-action of benzyl chloride in the MeO-PEG-b-PCMS blockcopolymer with 4-amino-TEMPO in DMF.

2.3. Preparation of siRNPs

Preparation of siRNPs was carried out by following twomethods.

2.3.1. Preparation of siRNPs using commercially availablecolloidal silica (siRNPs(1)). To an aqueous solution of PEG-b-PMNT under acidic conditions (pH = 3.0–4.0; 5 mg mL−1)different amounts of colloidal silica were added (1, 5, and10 wt% against polymer weight). The mixture was stirred usinga magnetic stirrer and the pH was increased to 9 by addingNaOHaq. The zeta potential and particle sizes of the siRNPswere measured by employing laser doppler velocimetry anddynamic light scattering (DLS), respectively, using a ZetasizerNanoseries ZEN3600 (Malvern Instruments Ltd, Worcester-shire, UK). Incorporation of silica into the RNPs was deter-mined by transmission electron microscopy (TEM: JEOLJEM-100CX; acceleration voltage = 100 kV).

2.3.2. Preparation of siRNPs by a TEOS sol–gel method(siRNPs(2)). RNP was prepared by performing dialysis,whereby 5 mg of the MeO-PEG-b-PMNT was dissolved in 1 mLof N,N-dimethylformamide (DMF; Wako Pure Chemicals,Osaka, Japan). It was then transferred into a membrane tube(Spectra/Por, molecular weight cut-off size: 3500 Da, SpectrumLaboratories Inc., Savannah, GA, USA) and then dialyzed for24 h against 2 L of distilled water, which was changed after 2,4, 8, 12, and 20 h. A predetermined amount of TEOS (Si/polymer ratios were in the range of 0–30 wt%) was added tothe reaction mixture and it was stirred for 24 h at 80 °C undera nitrogen atmosphere. Following this, it was transferred intoa membrane tube (Spectra/Por, molecular weight cut-off size:12–14 000 Da, Spectrum Laboratories Inc., Savannah, GA, USA)and dialyzed for 48 h against 2 L of distilled water, which waschanged after 1, 2, 4, 8, 20, and 32 h. The sizes, surfacecharge, silica content, and electron spin resonance (ESR)intensity of the obtained siRNPs were analyzed using DLS,laser Doppler viscometer, an inductively coupled plasmaoptical emission spectrometer (ICPS-8100 (Shimadzu, TokyoJapan, 1.2 kW), and ESR (Burker EMXPlus, Germany, centerfield: 3500.00 G; sweep width: 400.000 G; MW Attenuator: 30dB; temperature: 300.00 K; receiver gain: 1.00 × 103; modu-lation frequency: 100.00 kHz; modulation amplitude: 2.00 G;modulation phase: 0.00°; offset: 0.00%; time constant

20.48 ms; conversion time: 40 ms; harmonic: 1; and dualdetection mode: Phase).

2.4. Animal experiments

Blood uptake tests of siRNPs and their protective effect againstEPS injury were carried out using 6 weeks old male SD rats(approximately 200 g) that were purchased from Charles RiverJapan, Inc. (Yokohama, Japan). PD experiments using siRNPswere carried out using 6 weeks old male ICR mice (approxi-mately 30 g) that were purchased from Charles River Japan,Inc. (Yokohama, Japan). The animals were maintained in theexperimental animal facilities of the University of Tsukuba. Allof the experiments were performed according to the Guide forthe Care and Use of Laboratory Animals Resource Center ofthe University of Tsukuba.

2.5. Blood uptake of siRNPs in vivo

Three milliliters of an aqueous solution of siRNPs(1) (polymerconcentration = 20 mg mL−1; 6.66 mg mL−1; 42.6 mM nitro-xide radicals) or TEMPOL (6.66 mg mL−1; 42.6 mM nitroxideradicals) was administered into the peritoneal cavity of the 6weeks old male SD rats. After predetermined time intervals,100 µL of blood was drawn from the tip of the tail while eachrat was under anesthesia induced by isoflurane (4% induction,2% maintenance). Serum samples were obtained by carryingout centrifugation (5000 g) and the ESR intensity was analyzedafter the addition of potassium ferricyanide (K3[Fe(CN)6])(100 mM, 10 μL) to the plasma (200 μL) to re-oxidize the hydro-xylamines to nitroxide radicals.

2.6. Protective effect of siRNPs against EPS injury

EPS model rats were prepared according to a prior article byBozkurt et al.22 To 6 weeks old male SD rats, 2 mL of 0.1% CHand 15% ethanol in saline were given by i.p. administrationonce a day for 1 week to prepare the EPS model rats. Simul-taneously, 2 mL of saline, 3 mL of siRNPs(1) (polymer concen-tration, 20 mg mL−1; 42.6 mM nitroxide radicals), or 3 mL ofTEMPOL (6.66 mg mL−1; 42.6 mM nitroxide radicals) wasgiven in the peritoneal cavity once a day for 1 week. After1 week, the rats were sacrificed and the peritoneum removed.The generation of superoxide in the peritoneum was moni-tored by chemiluminescence using MPEC. Histological assayswere carried out using the Masson trichrome (MT) stainingmethod23 and were analyzed using an optical microscope (DMRXA2; Leica, Tokyo, Japan).

2.7. Effect of siRNPs on peritoneal dialysis

2.7.1. Adsorption profile of siRNPs in vitro. To a 990 µL ofMO solution 10 µL of sample solution was added and thesolution was stirred for 1 h at r.t. (initial concentrations of MOand siRNPs(2) were 9.82 µg mL−1 and 1.7 mg mL−1 (2.8 mMnitroxide radicals), respectively). This was followed by perform-ing centrifugal filtration of the mixture (MWCO: 300 000;2580 g; 10 min; 25 °C). The filtrate was monitored using aUV/Vis apparatus at 466 nm (Shimadzu UV2500).

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2.7.2. Decrease in blood creatinine and blood urea nitro-gen by siRNPs in vivo. Renal failure mice were prepared byischemic treatment of both kidneys. After 6-week-old ICR micewere anesthetized with pentobarbital sodium (40 mg kg−1),both renal pedicles were bound with sutures to produce renalischemia model mice. After the peritoneum was sewed up,2.4 mL of 4.25 wt%/vol% glucose solution containing siRNPs(2)(100 mg mL−1) was introduced into the peritoneal cavity andblood was drawn via cardiocentesis into a tube using a hepari-nized syringe after predetermined time intervals. Plasmasamples were obtained by performing centrifugation (2000 g),and creatinine and blood urea nitrogen (BUN) levels were ana-lyzed using a Fuji DRI-CHEM 3500 (Fuji Film, Tokyo, Japan).

2.8. Statistical analysis

All data are expressed as the mean ± S.E.M. from 8 to 10animals per group. Statistical analysis using SPSS (IBM Corp.,NY, USA) was performed by one-way analysis of variance fol-lowed by Tukey’s post-hoc test.

3. Results and discussion3.1. Preparation of siRNPs

Preparation of siRNPs was carried out according to Scheme 1.MeO-PEG-b-PMNT was synthesized by a two-step reaction start-ing from MeO-PEG-SH. The molecular weight and compositionof the obtained PEG-b-PMNT are described in the ESI.† Theincorporation of silica into the core of the redox nanoparticleswas carried out by following two methods. Commercially avail-able silica nanoparticles are negatively charged due to the dis-sociation of silanols on their surface. Because the PMNTsegment in PEG-b-PMNT possesses repeating amino groups asside chains, it causes electrostatic interaction with silica par-ticles. After PEG-b-PMNT was dissolved in acidic media alongwith silica nanoparticles followed by increasing the pH toneutral, about half of the amino groups in the PMNT segmentdeprotonate to form core–shell type polymer micelles.13 Fig. 2shows DLS and TEM data. Average size of the micelles wasapproximately 40 nm (silica content of 5 wt%), which was

slightly increased compared with empty RNPs (22 nm, silicacontent of 0 wt%). From the TEM analysis, silica particles wereobserved in the micelle core and their number increased withincreasing initial ratio (silica/polymer). For example, 5 and 15average number of silica in the core of RNPs were observed for1 and 5 wt% of the initial silica dose, respectively. More than5 wt% silica content tended to coagulate the particles asshown in Fig. 2.

Because the core of RNPs is hydrophobic under neutral con-ditions, hydrophobic compounds can be solubilized. WhenTEOS was added to the RNP solution, the solution becamecompletely transparent due to the solubilization of TEOS inthe core of the RNPs. This was followed by a base-mediatedhydrolysis–condensation reaction that took place to form silicananoparticles in the core of RNPs, which was catalyzed by theamino groups located in it. It is interesting to note that thestable siRNPs with much higher silica content could be pre-pared by this sol–gel method in contrast to those that were pre-pared using commercially available silica (data not shown).The DLS data are shown in the ESI.† Silica contents in thenanoparticle increased in a TEOS dose dependent manner,which is summarized in Table S2.† Though the high amount ofsilica was entrapped in the nanoparticle, the surface charge of theobtained nanoparticle (siRNP(2)(Si/polymer = 20 wt%)) was ca.−4.03 mV, which is similar to that of siRNP(1) as shown inTable S1.† The shielding of the surface charge of siRNP(2) denotesconfinement of silica in the core of the nanoparticle.

3.2. Blood uptake of siRNPs

Since the size of the prepared siRNPs in this study was ca.40 nm, the solution was completely transparent as shown inthe insert of Fig. 3. This is a better characteristic of an additiveof dialysate. However, if siRNPs are absorbed into the bloodvia the peritoneum, adverse effects to the entire body have tobe taken into consideration. After siRNPs were administeredinto the peritoneal cavity, the ESR signal of nitroxide radicalsin the serum was monitored as a function of time. When low-molecular weight TEMPOL was administered, a typical tripletsignal based on nitroxide radicals was observed at 10 min afteradministration and observed until 30 min as shown in Fig. 3.In contrast, no ESR signal was observed in the blood stream inthe case of siRNPs(1) and siRNP(2). It was reported that thethreshold of the peritoneum is ca. 30 kDa.24 Thus, a 40 nmsize prevents penetration through the peritoneum membrane.Considering these results, specifically the transparent nano-particle solution preventing blood-stream adsorption, it can beconcluded that siRNPs are highly safe as an additive of perito-neal dialysate.

3.3. Protective effect of siRNPs against EPS injury

We have so far confirmed that our RNPs effectively suppressoxidative stress by scavenging ROS, which shows their remark-able therapeutic effects against several diseases as statedabove. If the siRNPs prepared in this study also work effectivelyas ROS scavengers, they may prevent EPS because the oxidativestress is believed to be an inducer of EPS.25 EPS model rats

Scheme 1 Synthetic scheme for nitroxide radical containing blockcopolymer, PEG-b-PMNT.

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were prepared by administering CH. As can be seen in Fig. 4,following the administration of CH into the peritoneal cavityfor 1 week, the ROS level significantly increased. WhensiRNPs(1) were administered, the ROS level was the same as

Fig. 2 Size distributions of silica-containing redox nanoparticles (siRNPs)(1) prepared by different silica/PEG-b-PMNT ratios determined usingdynamic light scattering (a) and transmission electron microscopy (TEM) data (b).

Fig. 3 Blood uptake of TEMPOL (open circles) and silica-containingredox nanoparticles (siRNPs)(1) (closed circles, SiO2 = 5 wt%) as a func-tion of time. The samples were administered into the peritoneal cavity(3 mL of siRNPs) at 6.66 mg mL−1 or TEMPOL (6.66 mg mL−1). The con-centration of the nitroxide radicals was 42.6 mM for both cases. Theinsert is a photo of the siRNP(1) solution (20 mg mL−1).

Fig. 4 Amount of superoxide anion in the peritoneum due to treatmentvia PD. (20 mg mL−1 of silica-containing redox nanoparticles (siRNPs) or6.66 mg mL−1 of TEMPOL was added to the dialysate.).

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that of the control. The administration of low molecularweight TEMPOL also decreased the ROS level but not to thesame level as that of siRNPs. Rapid adsorption of TEMPOLinto the blood stream (which may cause adverse effects acrossthe entire body) might decrease the effective concentration inthe peritoneal cavity.

Fig. 5 shows the results of MT staining after the treatments.The CH-treated rats showed dysfunction of the peritoneumsuch as disruption of the mesothelial cell layer and vascularityof the expanded submesothelial compact zone (Fig. 5b), whilethe normal rats did not exhibit these symptoms (Fig. 5a). Forexample, the thickness became 269 ± 48 µm when CH wasintraperitoneally administered, while for the normal rats it wasonly 29 ± 13 µm. When siRNPs were administered, the thick-ness was 42 ± 18 µm, which indicates its extremely strongtherapeutic effect (Fig. 5c). We again observed a limited effectfor low molecular weight TEMPOL (thickness was 87.8 ±34.1 µm) as shown in Fig. 5d.

3.4. Effect of siRNPs on peritoneal dialysis

3.4.1. Adsorption profile of siRNPs in vitro. In vitro adsorp-tion capacity of siRNPs was evaluated using MO. BecauseRNPs possess a hydrophobic core, the maximum adsorption ofMO was 6.4 wt%. As can be seen in Fig. 6, the adsorptioncapacity increased with the increasing amount of silica andattained 9.2 wt% for siRNPs(2) (silica content 2.3%). siRNPsthus increased 50% in the adsorption capacity compared withthat of RNPs in vitro.

3.4.2. Decrease in blood creatinine and BUN by siRNPsin vivo. Since siRNPs(2) showed high adsorption of low mole-cular weight compounds, they were anticipated to improve thetherapeutic effects in PD when mixed in the dialysate. AftersiRNPs-containing dialysate was administered to the perito-neal cavities of acute renal failure model mice, blood levels ofcreatinine and BUN were monitored (Fig. 7). Both the creati-nine and BUN levels significantly increased for therenal failure model mice after 6 and 9 h, respectively. A4.25 vol%/wt% glucose solution decreased these levels to someextent for the complete bilateral renal ischemia. When RNPsor siRNPs(2) were mixed with the dialysate, the blood levels of

creatinine and BUN decreased significantly. In particular, BUNafter 6 h and creatinine after 9 h showed a strong effect forsiRNPs(2). The increased adsorption capacity of siRNPs(2)worked effectively in this case.

4. Conclusions

We have improved the peritoneal dialysis system using a newlydesigned siRNP. Silica particles 10–20 nm in diameter wereincorporated into RNPs in order to improve the colloidal dis-persion stability of silica in the physiological environment andthe adsorption capacity of low molecular weight compoundspresent as waste in blood. When siRNPs were administeredinto the peritoneal cavity, no blood adsorption was observed,which was in sharp contrast to a low molecular weight antioxi-dant. Negligible or no blood uptake of siRNPs would likely notbe detrimental to the entire body. The ROS scavenging charac-teristic of the siRNPs prevented oxidative damage of the perito-neum in EPS model rats. The addition of siRNPs to dialysate

Fig. 5 Histological assessments by performing Masson trichrome (MT) staining of peritoneum treated with saline (2 mL) (a), chlorhexidine gluconate(CH) (2 mL at 0.1%) (b), CH + silica-containing redox nanoparticles (siRNP(1), SiO2 = 5 wt%) (CH: 2 mL at 0.1%; siRNP(1): 3 mL of 20 mg mL−1 solution)(c) and CH + TEMPOL (CH: 2 mL at 0.1%; and TEMPOL: 3 mL of 6.66 mg mL−1 solution) (d). These solutions were administered into the peritonealcavity once a day for 1 week. The arrows indicate the thickness of the peritoneum. Scale bars = 200 μm.

Fig. 6 Adsorption capacity of silica-containing redox nanoparticles(siRNPs)(2) in vitro. The horizontal axis denotes the silica content of thesiRNPs(2). The initial concentrations of methyl orange (MO) and siRNPs(2) were 9.82 μg mL−1 and 1.7 mg mL−1, respectively.

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also improved the therapeutic efficiency of acute renal failuremodel mice. These results suggest that siRNPs are suitablenanobiomaterials for patient friendly peritoneal dialysis.

Acknowledgements

This work was partially supported by a Grant-in-Aid for Scienti-fic Research on Innovative Areas “Fusion Materials”(#25107707) from the Ministry of Education, Culture, Sports,Science and Technology of Japan (MEXT), a Grant-in-Aid forScientific Research(C) from the JSPS (#24591224), and a grantfrom the Japanese Association of Dialysis Physicians(JADP2012-09).

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Fig. 7 Therapeutic effect of silica-containing redox nanoparticles (siRNPs(2)) as an additive of peritoneal dialysis (PD)–dialysate against renal failuremodel mice. Vehicle: 2.4 mL of 4.25 wt%/vol% glucose solution; RNP: 2.4 mL of 4.25 wt%/vol% glucose solution containing RNPs (100 mg mL−1)and siRNPs (2, SiO2 = 3.77 wt%): 2.4 mL of 4.25 wt%/vol% glucose solution containing siRNPs(2) (2.4 m of 100 mg mL−1) for 6 h (a) and 9 h (b). *p <0.05; **p < 0.01; ***p < 0.005.

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Biomaterials Science Paper

This journal is © The Royal Society of Chemistry 2014 Biomater. Sci., 2014, 2, 522–529 | 529

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