1. Introduction

2. Experimental methods

3. Results

4. Discussion

5. Conclusions

Original Research

Enteric-coated alendronatesodium nanoliposomes: a novelformula to overcome barriers forthe treatment of osteoporosisKhaled Mohamed Hosny†, Osama Abdelhakim Aly Ahmed &Rana Tariq Al-Abdali†King Abdulaziz University, Faculty of Pharmacy, Department of Pharmaceutics, Jeddah,

Saudi Arabia

Background and objectives: Alendronate sodium (ALS) is the most common

drug used for the treatment of osteoporosis. The challenges facing ALS use

include: very poor oral bioavailability (0.6%), esophageal ulcers, and compli-

cated instructions for its use. The objective of this research is to utilize nano-

technology to formulate ALS into enteric-coated nanoliposomes (NLS) to

overcome the previously mentioned drawbacks.

Methods: NLS were prepared with lipid components of phosphatidylcholine

(PC), cholesterol (CH), and lecithin (Lec) in ratios 4:1:1, 4:2:1, 4:3:1, and 4:4:1,

respectively. Formulas that showed the highest entrapment efficiency were

prepared either alone or mixed with positive and negative charge-inducing

agents and coated with Eudragit L100. Eudragit-coated NLS (EuC-NLS) were

evaluated for particle size, zeta potential, morphological examination, and

drug release in pH 1.2 and pH 7.4 media. The pharmacokinetic study was

carried out in rabbits.

Results: Spherical NLS were successfully developed with a mean size range

from 70 to 150 nm. EuC-NLS with PC:CH:Lec:dicetyl phosphate (4:3:1:1)

successfully resist the release of ALS in acidic environments and enhanced

the bioavailability in rabbits 12-fold compared with the marketed tablets.

Conclusions: EuC-NLS is a promising novel formula for ALS with higher bio-

availability and a lower dose, avoiding the side effects of esophageal

ulceration.

Keywords: alendronate sodium, enteric coating, Eudragit, nanoliposomes

Expert Opin. Drug Deliv. (2013) 10(6):741-746

1. Introduction

Alendronate sodium (ALS) is a nitrogen-containing oral bisphosphonate used forthe treatment of osteoporosis. ALS exhibits a potent and selective inhibitory effecton osteoclast-mediated bone resorption and was approved for osteoporosis in post-menopausal females, males and also in osteoporosis due to glucocorticoid use [1,2].Approximately 50% of the patients treated with ALS showed decrease in the inci-dence of osteoporotic fracture in the hips and spine by improving bone densityand reducing bone resorption [3]. The first challenge for use of ALS is the loworal bioavailability, 0.6 -- 0.7% [4]. ALS is best absorbed when taken 2 h beforefood or after overnight fasting, as a result of ALS hydrophilicity and the negativecharges that hinder crossing of the lipoid biomembrane of the digestive tract [5].The second main challenge is the side effects of ALS which include esophagealulceration or erosion mostly with bleeding. As a result of these constraints, thedrug is subject to precautions and complicated instructions.

10.1517/17425247.2013.799136 © 2013 Informa UK, Ltd. ISSN 1742-5247, e-ISSN 1744-7593 741All rights reserved: reproduction in whole or in part not permitted

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Researchers had shown morning dosing is a major compli-ance problem with osteoporosis therapy [1,6-8]. Proper ALSadministration instructions should be given to the patient,by the physician, to avoid esophagitis and upper GI tractlesions. These instructions include: dose of ALS should betaken with a full glass of water and the patient should remainupright at least 30 min before the first food or beverage of theday. Up to 60% of patients stop taking weekly ALS during thefirst year as a result of its side effects and complicatedinstructions [8]. Different strategies were tried to improvethe bioavailability of ALS. These include the utilization ofnanotechnology to prepare biodegradable ALS nanopar-ticles [9]. Han et al. [10] delayed the residence time of ALS inthe GI tract through the preparation of a mucoadhesive lipo-somal formulation that improved the oral bioavailabilty ofALS in rats by 2.6-fold. Katsumi et al. [11] developed anALS microneedle array using hyaluronic acid that enhancedALS bioavailability by 90% in rats.Small liposomes with diameters of the order of 100 nm are

frequently used as a carrier to utilize their better absorptionand distribution [12]. In addition, NLS have the advantagesof nanoparticles, which improve the adhesion to and absorp-tion into the intestinal epithelial cells. In this case, the NLSdelivery system might be a highly effective way to improveALS absorption [13]. The technology of enteric coating isused for several applications to protect the drug from gastricfluids and enzymes, or to protect the esophagus and stomachfrom the irritant action of some drugs. Enteric coating pre-vents the drug in nanoparticles from disintegration in thestomach and it will increase the intact amount of nanoparticlesdelivered to the duodenum of the small intestine [14], whichimproves the bioavailability of ALS and reduces the mucosalirritant effect. The main objective of this work is to formulateALS in the form of NLS to improve the bioavailability of thedrug. NLS are then coated with enteric coating material(Eudragit L100) to reduce side effects on the esophagus andallow elderly patients to tolerate the drug easily.

2. Experimental methods

2.1 MaterialsALS was kindly supplied by Saja Pharmaceuticals Co. Ltd.(Jeddah, Saudi Arabia); phosphatidylcholine from egg yolk,lecithin and cholesterol were purchased from Sigma ChemicalCo. (St. Louis, Missouri, USA); stearylamine and dicetylphosphate (DP) were obtained from Fluka Chemical Co.(Buchs, Germany). Eudragit was kindly supplied by EvonikIndustries AG, (Essen, Germany) and trehalose was purchasedfrom Caesar and Loretz (Hilden, Germany). Other chemicalsand reagents were of analytical grade.

2.2 Methods2.2.1 Preparation of enteric-coated NLSNLS were prepared according to the method described byVincourt et al. [15]. Lipid components of NLS were

phosphatidylcholine (PC), cholesterol (CH), and lecithin(Lec) in gram ratios 4:1:1, 4:2:1, 4:3:1, and 4:4:1, respec-tively. Trehalose was selected as the lyoprotectant. The mini-mal trehalose/lipid ratio tested was 3, in order to avoidlyophilized cake collapse. NLS lipid components (300 mg)either alone or mixed with a positive charge-inducing agentstearylamine (SA) or negative charge-inducing agent DPwere dissolved in 10 ml chloroform and a thin lipid filmformed after removal of chloroform by rotary evaporator.The lipid film was hydrated by 10 ml phosphate bufferedsolution (pH 7.4) containing 50 mg ALS and 0.9 mg treha-lose with or without the charge-inducing agents SA and DP.Subsequently, the suspensions were sonicated using probsoni-cator (VCX750, Sonics & Materials, USA) for a time suffi-cient to obtain nanosized liposomes. The suspensions werecentrifuged for 30 min at 15,000 rpm to remove the un-entrapped ALS and then the precipitates of certain formulaewere dispersed in buffer solution (pH 7.4) in which EudragitL100 was previously dissolved and sonicated for 5 min. Thesuspensions were rendered acidic by addition of acidic solu-tion at pH 2 in order to precipitate the Eudragit. The finalsuspensions were centrifuged for 30 min at 15,000 rpm andthe EuC-NLS were then subjected to freeze--drying.

2.2.2 Determination of ALS entrapment efficiency

(EE%) in NLSThe lyophilized NLS were sonicated with methanol for15 min. The concentration of ALS in methanol was measuredat 333 nm by spectrophotometric method proposed byAl Deeb et al. [16]. EE% was calculated as shown in theequation:

(1)EE% [ALS / ALS ] 100E T= ×

where ALSE and ALST represent the encapsulated ALS andtotal ALS amount, respectively.

2.2.3 Examination of surface morphology by scanning

electron microscopeNeutral, negatively and positively charged samples of NLS weresubjected to morphological examination by using SEM. Sam-ples were reconstituted with deionized water and spread overcarbon tape. Samples were then dried in vacuum and coatedwith gold and examined under the electron microscope to deter-mine the surface morphology of the optimized lyophilized NLS.

2.2.4 Size analysis and zeta potential measurement

of NLSThe zeta potential and the mean particle size were measuredby using dynamic light scattering particle size analyzerZetatrac (Microtrac, Inc., USA).

2.2.5 In vitro gastro-resistanceTo evaluate the enteric nature of EuC-NLS, equivalent to10 mg of ALS was suspended in 1 ml of 0.1 N hydrochloric

K. M. Hosny et al.

742 Expert Opin. Drug Deliv. (2013) 10(6)

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acid (pH 1.2) in a glass cylinder with a length of 6 cm and adiameter of 2.5 cm. This cylinder was closed from one end bya presoaked dialysis membrane and suspended in a basket inthe (USP) dissolution tester containing 900 ml of 0.1 Nhydrochloric acid (pH 1.2) maintained at 37�C and100 rpm. Samples were withdrawn after 0.5, 1, 1.5 and 2 h,and assayed for ALS.

2.2.6 In vitro drug releaseThe in vitro profile for ALS from EuC-NLS was evaluated atphosphate buffer pH 7.4. ALS-NLS, equivalent to 10 mg ofALS, were suspended in 1 ml of phosphate buffer (pH 7.4) ina glass cylinder as described in the previous experiment at75 rpm. A 5 ml sample was withdrawn after 5, 10, 15, 30, 45,60, 90, 120, 150 and 180 min, and assayed for ALS at 333 nm.

2.2.7 In vivo pharmacokinetics studyHealthy albino male rabbits weighing 2 -- 2.5 kg were dividedinto two groups, six animals each, and were fasted for 12 hbefore and during the experiment. The in vivo animal studiesprotocol was revised and approved by the ethical committeeof King Abdulaziz University, Jeddah, Saudi Arabia. An oralALS formula of freeze--dried EuC-NLS was given to onegroup, and the marketed ALS tablets (10 mg) were given tothe other group. The dose of ALS was 1 mg/kg for each ani-mal group. The collection of blood samples was carried outat the following time intervals: 0.5, 0.75, 1, 1.5, 2.5, 3.5, 5,6, 12, and 24 h. Serum samples were then analyzed byHPLC. Pharmacokinetic parameters were calculated andpresented as mean ± S.D. Cmax and Tmax after oral adminis-tration were calculated directly from the plasma concentra-tion--time curve using WinNonlin� Nonlinear Estimation

Program. One-way analysis of variance (ANOVA) wasemployed to assess the significance of the difference betweenthe tested NLS formulation and the reference at a level(p £ 0.05) using the SPSS program [17]. AUC0 -- 24 was calcu-lated using the linear trapezoidal rule [18]. AUC0-¥ was deter-mined by adding the last measured plasma concentrationdivided by the elimination rate constant (Kel) to AUC0 -- 24.The relative bioavailability of enteric-coated NLS is calculatedby using the following formula [19].

(2)Relativebioavailablity [AUC Dose ]NLS Tablet= × / ×[AUC Dose ]Tablet NLS

3. Results

3.1 Factors affecting entrapment efficiencyResults in Table 1 show that the increase in the CH content ofNLS without charged additives (DP and SA) up to a ratio of4:3:1 increased the EE% of the prepared NLS. Above thisratio there was a decrease in the EE% by the increase in CHlevel. Thus, the NLS formed from lipid content in a ratio of4:3:1 (PC:CH:Lec) was selected in regards to the entrapmentefficiency (EE% = 49.39%). Incorporation of SA leads to anincrease in the EE% from 49.39% (for the neutral NLS)to 54.16%. However, the EE% decreases to 41.92% byincorporation of DP within the nanoliposomal membrane.

3.2 Morphology and size analysis of liposomesFigure 1 shows the SEM for freeze--dried ALS-NLS preparedby the lipid film hydration technique by a molar ratio of4:3:1 (PC:CH:Lec), revealing the presence of homogenous,well-identified spheres, which existed in dispersed and

Table 1. EE%, particle size, and zeta potential for different formulations of EuC-NLS.

Formula Lipid composition Ratio EE% Particle size Zeta potential

before coating

Zeta potential

after coating

F1 PC:CH:Lec 4:1:1 29.88 57 nm - 2.24 26.43F2 PC:CH:Lec 4:2:1 35.63 59 nm - 3.12 29.25F3 PC:CH:Lec 4:3:1 49.39 70 nm - 3.35 16.43F4 PC:CH:Lec 4:4:1 41.76 65 nm - 4.27 26.34F5 PC:CH:Lec:SA 4:3:1:1 54.16 150 nm 34.65 49.66F6 PC:CH:Lec:DP 4:3:1:1 41.92 110 nm - 21.45 4.92

A. B. C.

Figure 1. SEM image of freeze--dried ALS NLS, (A) Neutral NLS, (B) Negatively charged NLS, (C) Positively charged NLS.

Enteric-coated alendronate sodium nanoliposomes

Expert Opin. Drug Deliv. (2013) 10(6) 743

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aggregate collections. The particle size analysis test showedthat all prepared liposomes occurred in the nanosize range,this highlights the efficiency of the preparation method inobtaining nanosized liposomes (Table 1). The size analysiswas 70 nm for neutral NLS. In the case of charged NLS,the size increased from 70 to 150 nm in positive NLS, andto 110 nm in negative NLS.

3.3 In vitro gastro-resistanceTo evaluate the enteric nature of the coated NLS, Figure 2

shows the in vitro release profile of ALS EuC-NLS in pH1.2. The percentages of ALS released within 2 h were 3, 9,14 and 65% from negatively, neutral, positively chargedNLS, and marketed ALS tablets, respectively.

3.4 In vitro drug releaseFigure 3 shows the in vitro profile for ALS from Eudragit-coated negatively charged NLS in phosphate buffer pH 7.4.

About 30% ALS was released within 15 min, which highlightsthe rapid dissolution of the enteric coating material in pH 7.4.In addition, nearly 100% ALS was released within 3 h. Theseresults indicated that the formula composed of EuC-NLSwith lipid content PC:CH:Lec:DP (F6) in molar ratio4:3:1:1 is the optimum enteric-coated formula, and wasselected for an in vivo pharmacokinetic study.

3.5 In vivo pharmacokinetics studyThere was a statistically significant difference of the Tmax andCmax data for NLS compared with the marketed ALS product(Table 2). It was observed that the absorption of ALS was rapidand reached its peak plasma concentration in 0.75 h ± 0.09 inthe case of the commercial tablet, whereas the mean Tmax forthe tested NLS was 3.5 h ± 0.61 (Table 2). The meanAUC0-¥ for the marketed ALS tablet was significantly differentcompared with NLS. These results confirmed the enhance-ment of ALS bioavailability > 12-fold when formulated asenteric-coated NLS.

4. Discussion

EE% is used to evaluate the use of different molar ratios forPC:CH:Lec (4:1:1, 4:2:1, 4:3:1, and 4:4:1). The effect of add-ing negative and positive charge inducers, DP and SA, on theEE% of ALS within NLS was investigated. According to theresults in Table 1, by increasing the CH content in the lipidbilayer, the nanoliposomal membrane becomes more rigid,stable and less permeable, leading to more drug reten-tion [20,21]. Above certain concentrations for CH, the regularlinear structures of the membrane begin to disrupt, whichleads to a reduction in the EE%. Thus, the NLS formedfrom lipid content in a ratio of 4:3:1 (PC:CH:Lec) with EE% value of 49.39% was selected for further evaluations. Incor-poration of a positively charged inducing agent (SA) increasedthe zeta potential of liposomes from - 3.35 to 34.65, whichincreased the stability of the system against liposomal aggrega-tion and increased the EE% as a result of the electrostaticattraction between the negative phosphate group of ALS andthe positive charge of SA. The incorporation of a negativelycharged inducing agent (DP) within the nanoliposomal mem-brane reduces the zeta potential from - 3.35 to - 21.45, whichincreased the stability against liposomal aggregation, butreduced the EE%, which could be attributed to the repulsionof both negative charges for DP and ALS [22].

The increase in liposomal size after incorporation of eitherpositively or negatively charged inducing agents into the lipo-somal bilayer could be attributed to an increase in the spacingbetween the adjacent bilayers [23], resulting in the formationof liposomes larger in size compared with the neutral ver-sions [21,24]. Furthermore, the positively charged lipid, fromthe use of SA, electrostatically attracts ALS anions that wouldbe expected to push phospholipid head groups apart, henceincreasing the particles’ diameters [25]. Benech et al. [26]

reported that the improved encapsulation efficiency in

00 30 60

Time (min)

90

Marketed ALS product

Negative NLS

Neutral NLS

Positive NLS

120

10

20% A

LS

rel

ease

d

30

40

50

60

Figure 2. In vitro release of ALS from EuC-NLS formulae and

marketed ALS product in pH 1.2.

00 30 60 90

Time (min)

120 150

Positive NLS

Negative NLS

Neutral NLS

180

20

40

% o

f A

LS

rel

ease

d

60

80

100

Figure 3. In vitro release of ALS from Eudragit-coated

negatively charged, positively charged and neutral NLS in

pH 7.4.

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charged liposomes increases the effective diameter, promotescurvature changes and creates a more swollen membranestructure. In addition, the increase in particle size is attributedto the formation of multilamellar NLS. As the charge-inducing agent makes the liposomal membrane suitable tostructural rearrangement due to the repulsion which occursbetween similarly charged phospholipid head groups, it ulti-mately leads to structural transformation due to adhesion-mediated processes such as bilayer rupture and fusion [27,28].This occurred as a result of cross-linking for the NLS aggre-gates by the charge-inducing agent. Then, rapid spreading ofthe contact area deforms the liposomes as they flatten againsteach other, which places the bilayer under increased tension,which is relieved by fusion and rupture. Upon bilayer rupture,vesicles collapse, flattening against each other to formmultilamellar liposomes that increased the particle size. Simi-lar findings were also reported for incorporation of charge-inducing agents into azathioprine [29], acetazolamide [21],and indomethacin liposomes [22].

In the case of negatively charged NLS, an electrostatic attrac-tion occurred during coating between the positively chargedEudragit and the negatively charged NLS leading to improvedefficiency of Eudragit coating compared with neutral and pos-itively charged NLS. This efficient coat on negative NLS resiststhe release of ALS in acidic pH 1.2 medium. This interactionwas also confirmed by the increase in the zeta potential valueof the negatively charged NLS after coating with Eudragitfrom - 21.45 to 4.92 mV. In the case of positively chargedNLS, the repulsion of the positive charges, for Eudragit andNLS, reduced the efficiency of the enteric coating and conse-quently the gastro-resistance character of the prepared formulathat is considered undesirable in enteric-coated dosage forms.As the main aim of this work is to prevent ALS release in acidic

mediums to avoid the adverse effects of ALS, NLS composed ofPC:CH:Lec:DP (F6) in molar ratio 4:3:1:1 was selected for fur-ther evaluations. The mean pharmacokinetic parameter resultsshowed a delay in Tmax in case of NLS formula comparedwith marketed ALS tablets that is attributed to the efficientcoating with Eudragit L100, which hinders the release of ALSin the stomach (acidic pH) and releases the drug later in theintestine. The enhancement in bioavailability, > 12-fold, couldbe attributed to the size of NLS (110 nm), which have theadvantages of nanoparticles, and improve the adhesion to andabsorption into the intestinal epithelial cells [30]. In addition,the liposomal vesicles may promote the uptake by M cells inthe Peyer’s patches and increase absorption through the lym-phatic pathway [31]. Permeation of intact NLS through theintestinal epithelia pathway is considered as an additional pos-sible mechanism for the enhancement in bioavailability of theprepared NLS formula [32].

5. Conclusions

Formulation of negatively charged enteric-coated ALS-NLS,as a novel drug delivery system, provided the maximumgastro-resistant ALS release. The oral bioavailability of ALSwas enhanced by > 12-fold in relation to the commerciallyavailable product. The improved formula of ALS could elim-inate the major drawbacks of conventionally used tablets, andallow osteoporotic patients to tolerate the drug without fear ofesophageal inflammation and/or bleeding.

Declaration of interest

The authors state no conflict of interest and have received nopayment in preparation of this manuscript.

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AffiliationKhaled Mohamed Hosny†1,2,

Osama Abdelhakim Aly Ahmed1,3 &

Rana Tariq Al-Abdali4

†Author for correspondence1King Abdulaziz University, Faculty of Pharmacy,

Department of Pharmaceutics, Jeddah,

Saudi Arabia

Tel: +966592722634; Fax: +96626951696;

E-mail: Elswaify2000@yahoo.com2Beni Sueif University, Faculty of Pharmacy,

Department of Pharmaceutics and Industrial

Pharmacy, Beni Sueif, Egypt3Minia University, Faculty of Pharmacy,

Department of Pharmaceutics and Industrial

Pharmacy, Minia, Egypt4King Abdulaziz University,

Faculty of Pharmacy, Jeddah,

Saudi Arabia

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pers

onal

use

onl

y.