An enhanced bioactive chitosan-modified microemulsion for mucosal healing of ulcerative colitis

The intestinal mucus layer plays a crucial role in the systemic absorption of drugs. While penetration through this layer traditionally constitutes a pivotal phase in drug absorption, the approach for treating ulcerative colitis (UC) shifts towards facilitating the direct delivery of drugs to the colon. In this study, we engineered a chitosan-modified microemulsion encapsulated nobiletin (NOB-CS-ME) characterized by small particle dimensions and positive charge specifically, designed to enable targeted delivery. In vitro experiments demonstrated that this NOB-CS-ME effectively became less into the intestinal mucus layer, thus achieving successful escape of the intestinal mucus barrier absorption. After circumventing this barrier, NOB-CS-ME exhibited heightened cellular uptake by colonic epithelial cells, displaying an approximately 1.3-fold increase compared to the unmodified microemulsion. Collectively, these observations imply enhanced drug bioavailability, potentially resulting in more efficacious mucosal healing, providing a promising avenue for natural small-molecule drug delivery in UC treatment.

Introduction

The intestinal mucus layer, serving as a barrier against pathogens, also constrain drug absorption [1,2]. Extensive research has investigated mucopenetrating assemblies to enhance drug delivery to intestinal cells [3]. However, it is essential to recognize that inflammatory bowel diseases (IBD), which encompass conditions like Crohn’s disease (CD) and UC, are lifelong progressive disorders characterized by chronic, recurrent, and alternating phases of illness affecting the gastrointestinal system [4]. In the context of UC, the disruption of the mucosal epithelial barrier integrity necessitates efficient mucosal healing as a prerequisite for effective therapy [5,6]. However, conventional non-targeted therapies often face challenges, such as undesirable side effects and reduced efficacy, primarily due to drug entrapment of the intestinal mucus layer before reaching the intended target site [7,8]. In contemporary research, there is a growing emphasis on strategies that facilitate drug escape from the intestinal mucus layer, thus preventing premature penetration and enabling targeted delivery to the colon, where the therapeutic payload can be released [9]. Consequently, achieving intestinal mucus escape in drug delivery systems has gained increased attention to enhance drug release, specifically in the colon site, particularly in the context of UC therapy.

Nano-drug delivery systems designed for colon drug delivery are of paramount importance in research targeting diseases affecting this region [10,11]. Mucus constitutes a complex matrix comprised of large biomolecules including mucin and glycoproteins, characterized by the presence of multiple negatively charged functional groups [12]. The negative charge surface can penetrate the intestinal mucus, that is pores between the mucin fibers forming the entangled network, due to the electrostatic exclusion with mucins [13]. Recent studies have revealed that negative charges on the surface of nanoparticles were penetrating the intestinal mucus, and finally being absorbed into the system recycle [14]. Conversely, nanoparticles with a positive surface charge can accomplish intestinal mucus escape, thereby reaching the colon directly rather than penetrating the intestinal mucus barrier. Chitosan (CS), a naturally occurring cationic polysaccharide, remains undigested in the upper portion of the gastrointestinal tract (GIT) [15,16]. However, CS is readily degraded by specific enzymes produced by the colonic microbiota [17]. Additionally, CS can open the intercellular tight junction reversibly [18]. Thus, due to these characteristics above, CS is widely used in colon drug delivery strategies. Furthermore, inflammation of the colonic mucosa often coincides with a thinner even depletion of the mucus layer [19,20]. Consequently, small-sized nanoparticles tend to accumulate at inflammatory sites, primarily due to the enhanced permeability and retention (eEPR) effect in the inflamed tissues, ultimately facilitating their uptake by intestinal cells [21]. Overall, CS-modified nanoparticles featuring small particle sizes can effectively evade the intestinal mucus, reach the inflammatory colon, and successfully traverse trans-colonic epithelial cells to complete the drug delivery process.

In this study, we introduce a small-sized NOB-CS-ME. Microemulsion is a unique drug delivery system with a particle size ranging from 10 nm to 100 nm [22]. It can solubilize lipophilic drugs, has thermodynamic stability, and is relatively simple to prepare. The composition of NOB-CS-ME includes nobiletin (NOB), Cremophor EL, Transcutol HP, and Capryol 90, with further modification using CS (Fig. 1A). NOB, derived from Citri Reticulatae Pericarpium, is known for its anti-inflammatory properties [23]. However, NOB is characterized by poor water solubility [24]. The design strategy posits that NOB-CS-ME exhibits a reduced propensity for infiltration and penetration of the intestinal mucus layer, thereby facilitating successful evasion of intestinal mucus (Fig. 1B). This mechanism underpins the observed superior efficacy in the treatment of inflammation. Through systematic evaluation, we observe the intestinal mucus escape ability and cellular uptake of NOB-CS-ME. In addition, the orally administered NOB-CS-ME was investigated for the anti-inflammatory and barrier repairment effects by both in vitro and in vivo experiments.

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Materials

NOB was obtained from Shanghai Standard Technology Co., Ltd. (Shanghai, China). Cremophor EL was obtained from BASF (China) Co., Ltd. (Shanghai, China). Capryol 90 and Transcutol HP were kind gifts obtained from Gattefosse China Trading Co., Ltd. (Shanghai, China). Chitosan (<3000 Da) and chlorpromazine were obtained from Shanghai yuanye Bio-Technology Co., Ltd. (Shanghai, China). Dulbecco’s modified Eagle’s medium (DMEM) and fetal bovine serum (FBS) were obtained from Thermo Fisher Scientific.

Lixia Yue, Ping Ye, Yi Zhang, Ru Guo, Weihua Xu, Shaogang Huang, Yanfeng Xiu, Yongzhuo Huang, Bing Wang,
An enhanced bioactive chitosan-modified microemulsion for mucosal healing of ulcerative colitis, International Journal of Biological Macromolecules, 2024, 137847, ISSN 0141-8130, https://doi.org/10.1016/j.ijbiomac.2024.137847.

Read also our introduction article on Chitosan here: