Elsevier

Carbohydrate Polymers

Volume 146, 1 August 2016, Pages 435-444
Carbohydrate Polymers

A comparative study on the efficiency of chitosan-N-acetylcysteine, chitosan oligosaccharides or carboxymethyl chitosan surface modified nanostructured lipid carrier for ophthalmic delivery of curcumin

https://doi.org/10.1016/j.carbpol.2016.03.079Get rights and content

Highlights

  • A two-step covalent binding between N-acetyl-l-cysteine (NAC) and chitosan (CS) was proposed.

  • The ophthalmic delivery of curcumin (CUR) was enhanced by elaborating nanostructured lipid carrier (NLC) decorating with CS derivatives.

  • The CS-NAC-CUR-NLC was superior to chitosan oligosaccharides (COS) or carboxymethyl chitosan (CMCS) modification in ophthalmic delivery.

  • The superiority in view of: extended release, corneal rention time and permeability through the cornea.

  • The CS-NAC coated CUR-NLC induced neither a feeling of discomfort nor irritation.

Abstract

To develop a potential nanocarrier for the topical ocular administration of curcumin (CUR), a novel thiolated chitosan was synthesized by the covalent binding between N-acetyl-l-cysteine (NAC) and chitosan (CS) to surface modify the nanostructured lipid carrier loaded CUR (CUR-NLC). And the superiorities of the CS-NAC co polymer coated CUR-NLC over chitosan oligosaccharides (COS) or carboxymethyl chitosan (CMCS) modification were also verified in detail. As expected, the increment in particle size and the reversal of zeta potential occurred after surface decorating, and the most prominent electropositivity was obtained for the CS-NAC-CUR-NLC group. Additionally, the utilization of the CS-NAC coating demonstrated an effectively controlled release over 72 h and attained a 6.4 and 18.8 fold increase in apparent permeability coefficients (Papp) compared with the CUR-NLC and the self-made eye drops, respectively. Meanwhile, the clearance rate of the NLC labeled with Rhodamine B was significantly delayed in the presence of CS-NAC. By contrast, CS-NAC-CUR-NLC was superior to the COS and CMCS coated ones in view of in vitro release, drug permeability and corneal retention. Moreover, the results of the in-vivo and in-vitro characteristics demonstrated that the promoting effect of CMCS coating was relatively weaker than COS coated ones. Ocular irritation test was executed on the CS-NAC-CUR-NLC, neither a sign of toxicity nor irritation to the external ocular tissues was observed. In conclusion, CS-NAC-CUR-NLC possesses a greater potential as an ocular drug-delivery system comparing with the COS-CUR-NLC and CMCS-CUR-NLC.

Introduction

Currently, topical application of drugs to the eye is still the main administration route for the treatment of various eye disorders as it allows for easy and painless administration, reasonably low cost production and generally high patient compliance. Nevertheless, the conventional eye drops faced the continuing problem of low bioavailability which was caused mainly by inherent defense mechanisms (Ghate & Edelhauser, 2006) in anatomical and physiological aspects, that is, the low transparency of the cornea, tear formation, blinking, and flow of the drug through nasolacrimal duct (Ludwig, 2005). Therefore, endeavors to enhance ocular bioavailability have been focused on overcoming precorneal constraints through facilitating transcorneal penetration and prolonging the precorneal retention time.

Nanostructured lipid carrier (NLC), which was able to guarantee a controlled drug release, higher drug loading and good bioavailability, appears to be a promising drug delivery system (Beloqui et al., 2013). However, the instability and anionic nature of NLC had hindered its ophthalmic application.

Among the carbohydrates generally used in the pharmaceutical field, chitosan (CS), known for its favorable biological properties such as biodegradability, nontoxicity and biocompatibility (Semwal, Singh, Archana, Verma, & Dutta, 2011; Bhatt, Singh, Archana, Verma, & Dutta, 2013), has been widely investigated as a vehicle for ophthalmic formulations and this cationic biopolymer was expected to improve the transcorneal permeability of drugs by opening the tight junctions of the epithelia (Yamamoto, Kuno, Sugimoto, Takeuchi, & Kawashima, 2005) and put off the drug elimination by interacting with the negative charged mucus (Benediktsdottir, Baldursson, & Masson, 2013). To further improve the solubility of CS and to improve its mucoadhesive and permeation enhancing properties, various derivatives such as chitosan oligosaccharides (COS), carboxymethyl chitosan (CMCS) were developed (Dutta, 2016). COS, obtained through the decomposition of CS, is a cationic polymer of low molecular weight. COS could strengthen the adherence of the formulation to the corneal surface by both electrostatic force and hydrogen bonds, and consequently facilitating the drug absorption into the cornea. Without affecting the inherent characteristic of CS, CMCS was produced by introducing carboxymethyl to the CS structure. Compared to CS, drastically increase in solubility, moisture retention ability and viscosity was achieved for CMCS and it has been considered as a promising hydrogel. Surface modification of various nanoparticles using COS or CMCS has been reported previously (Bravo-Osuna et al., 2012; Di Colo, Zambito, Burgalassi, Nardini, & Saettone, 2004; Luo, Zhao, Zhang, & Pan, 2011; Upadhyaya, Singh, Agarwal, & Tewari, 2013; Ustundag-Okur et al., 2014). However, all these systems were based on the formation of non-covalent bonds such as hydrogen bonds and ionic interactions. Accordingly, they could only provide relative weak mucoadhesion, in many cases insufficient to guarantee a valid drug delivery. As an unique cationic thiomer obtained via immobilization of thiol bearing ligands, thiolated chitosan (TCS) is able to form covalent bonds with cysteine-rich subdomains of mucus as well (Iqbal et al., 2012). In addition, the disulfide bonds are also formed within the thiomer itself, generating a gel-like property, which leads to a prolonged residence time and extended drug release behavior, therefore producing a permeation enhancing effect (Clausen & Bernkop-Schnürch, 2000).

The aim of this study was to validate the preponderance of TCS for ocular drug delivery in contrast with COS and CMCS. For this purpose, curcumin (CUR), which was known as an anti-inflammatory agent, was chosen as the model drug. Since CUR is a highly lipophilic compound which has the features of poor absorption, rapid metabolism, and fast systemic elimination, its ocular delivery is a challenging task (Allam, Komeil, & Abdallah, 2015; Siviero et al., 2015). Within this study, chitosan-N-acetyl-l-cysteine conjugate (CS-NAC) was synthesized by immobilizing the carboxylic acid group of N-acetyl-l-cysteine (NAC) on the primary amino groups of CS backbone. CUR was then encapsulated in the NLC and coated with three different CS derivatives. The resulting CS-NAC-CUR-NLC and unmodified CUR-NLC were characterized regarding their physicochemical characterizations and biocompatibility. Furthermore, the superiorities of CS-NAC-CUR-NLC versus unmodified CUR-NLC, COS-CUR-NLC and CMCS-CUR-NLC for ocular CUR delivery were evaluated concerning in vitro release study, permeation study and pre-corneal retention time.

Section snippets

Materials

Curcumin (CUR), Chitosan (CS, Mw = 179.17 kDa, deacetylation degree  95%, viscosity = 100–200 mPa s), N-acetyl-l-cysteine (NAC, molecular weight: 163.19 kDa) and Ellman’s reagent (5, 5′-dithiobis-(2-nitrobenzoic acid), DNTB) were all obtained from Aladdin® (Shanghai, China). Chitosan oligosaccharides (COS, deacetylation degree  95%) was purchased from Aoxing Biotechnology Co., Ltd. (Zhejiang, China). Carboxymethyl chitosan (CMCS, level of carboxyl  83.64%) was gifted by Isen Chemical Co., Ltd. (Jia Xing,

Synthesis and characterization of CS-NAC copolymer

The course of the reaction between CS and NAC was fulfilled according to the general scheme presented in Fig. 1. The synthesis of CS-NAC was a two-step procedure: in the first step, the activated NAC, namely the intermediate product 2, was generated. The second modification step was then achieved by amide bond formation between the primary amino groups of CS and the carboxylic acid group of the activated NAC. Obviously, the adequate conduct of the interaction between NAC and CS would rest with

Conclusion

Within this study, a novel CS-NAC conjugate had been synthesized and characterized. The CUR-NLC was produced using the melt-emulsification technique followed by coating with CS-NAC, COS or CMCS, respectively. The modification of CUR-NLC with these CS derivatives led to an increased PS and PI. Prominent zeta potential reversal from negative to positive was observed after decorating with the CS derivatives, and the CS-NAC coated ones exhibited the strongest charge. EE and DL of the NLC were both

Acknowledgments

This work was supported by the Foundation of Liaoning Educational Committee (No. L2014504) and the Doctoral Scientific Research Foundation of Liaoning Institute of Science and Technology (No. 1406B04).

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