Polymeric Systems for Colon-specific Mesalazine Delivery in the Intestinal Bowel Diseases Management

1875-533X/23 $65.00+.00 © 2023 Bentham Science Publishers Alberto Gomes Tavares Junior1, Jennifer Thayanne Cavalcante de Araújo1, Jonatas Lobato Duarte1, Amanda Letícia Polli Silvestre1, Leonardo Delello Di Filippo1 and Marlus Chorilli1,* 1Department of Drugs and Medicines, School of Pharmaceutical Sciences, São Paulo State University (UNESP), Araraquara, Brazil ARTICLE HISTORY Received: December 21, 2021 Revised: March 20, 2022 Accepted: April 06, 2022 DOI: 10.2174/0929867329666220707102912 Abstract: The anti-inflammatory 5-aminosalicylic acid (5-ASA) is the main therapeutic option used to prevent and treat inflammatory bowel diseases. The upper intestinal tract performs rapid and almost complete absorption of this drug when administered orally, making local therapeutic levels of the molecule in the inflamed colonic mucosa difficult to achieve. Micro and nanoparticle systems are promising for 5-ASA incorporation because the reduced dimensions of these structures can improve the drug's pharmacodynamics and contribute to more efficient and localized therapy. Together, the association of these systems with polymers will allow the release of 5-ASA through specific targeting mechanisms to the colon, as demonstrated in the mesalazine modified-release dosage form. This review will summarize and discuss the challenges for the oral administration of 5-ASA and the different colon-specific delivery strategies using polymers. Keywords: 5-ASA, polymeric systems, colonic delivery, nanoparticles systems, microparticles systems, modified-release dosage forms. 1. INTRODUCTION Inflammatory bowel disease (IBD) refers to a set of recurrent, chronic, idiopathic diseases that can injure any region of the gastrointestinal tract (GIT) extension. North America and Europe have the highest prevalence of IBD, and studies show that a significant percentage of 30 to 40% of patients with IBDs have colonic involvement [1-3]. Two defined clinical forms are included in this group: Crohn's disease (CD) and ulcerative colitis (UC) [4-7]. UC continuously involves the rectum and proximal colonic extensions (Fig. 1), whose superficial inflammatory changes restrictively affect the colonic mucosa and submucosa, resulting in cryptitis and intestinal abscesses. Unlike UC, CD mainly affects the ileum and cecum (Fig. 1), however, it can involve any region of the GIT, from the mouth to anus, manifesting stenosis, abscesses, and fistulas. Symptoms such as weight loss, *Address correspondence to this author at the School of Pharmaceutical Sciences of São Paulo State University (UNESP), 14800-903, Araraquara, São Paulo, Brazil; Tel/Fax: +55-16-3301-6998; E-mail: [email protected] chronic diarrhea, abdominal pain, and bloody stools are common in UC and CD [6, 8]. Laboratory diagnosis can be performed through the quantification of inflammation biomarkers such as Creactive protein and fecal calprotectin; however, it is not possible to distinguish UC from CD. Other biomarkers may help to distinguish IBDs, such as the presence of anti-perinuclear neutrophil cytoplasmic antibody (p-ANCA) and anti-Saccharomyces cerevisiae antibody (ASCA) with greater specificity for UC and DC, respectively. Endoscopic examinations are preferable for the conclusion of the diagnosis of IBD associated with GIT biopsies and the histological findings help to distinguish between UC and CD [ 9,10]. The treatment of IBD can be performed with anti-inflammatories (mainly 5-aminosalicylic acid (5-ASA)), corticosteroids, immunomodulators, and antibiotics [4, 11, 12]. 1.1. Mesalazine 5-ASA (Fig. 2), also known as mesalazine or mesalamine, is one of the drugs used for mild and moderate cases of IBD. The anti-inflammatory activity of Current Medicinal Chemistry ISSN: 0929-8673eISSN: 1875-533X The International Journal for Timely In-depth Reviews in Medicinal Chemistry Impact Factor: 4.184 BENTHAM SCIENCE Send Orders for Reprints to [email protected] Current Medicinal Chemistry, 2023, 30, 1351-1367 1351 REVIEW ARTICLE Polymeric Systems for Colon-specific Mesalazine Delivery in the Intestinal Bowel Diseases Management &XUUHQW0HGLFLQDO&KHPLVWU\ 1352 Current Medicinal Chemistry, 2023, Vol. 30, No. 12 Tavares Junior et al. Fig. (1). Schematic illustration of inflammatory bowel diseases evidencing the main area affected. A) Crohn’s disease and B) Ulcerative colitis. (A higher resolution / colour version of this figure is available in the electronic copy of the article). 5-ASA is proportional to its concentration in the inflamed colonic mucosa, which is normally low due to its high absorption in the small intestine, requiring high doses in the treatment [3, 13]. Currently, 5-ASA has 2 routes of administration: oral (tablets, capsules, and granules) and rectal (enemas and suppositories) [3, 14], and its mechanism is not fully elucidated, however, as it is a nonsteroidal anti-inflammatory, there is inhibition of the lipoxygenase and cyclooxygenase pathways of the arachidonic acid cascade, reducing the production of prostaglandins and leukotrienes. There is also the scavenging of free radicals and activation of PPAR-γ which reduces the proliferation of inflammatory cells [13, 15, 16]. Another pathway of action of 5-ASA is through the inhibition of NF-kB, preventing the transcription of pro-inflammatory cytokines such as IL-1 and TNF-α, that present modulation inflammation in IBD [17]. The upper intestinal tract performs rapid and almost complete absorption of 5-ASA when administered orally. and its metabolization occurs by acetylation in the intestine mucosa (in epithelial cells or by bacteria) and the liver through the enzyme N-acetyltransferase, transforming it into N-acetyl-5-ASA, which can be excreted in both feces and urine [3, 15]. Through the rectal route, it does not present good acceptability to patients and demonstrates lower absorption and systemic exposure, which contributes to the reduction of adverse effects [18, 19]. Due to these limitations, drug delivery systems are used to optimize the inherent properties of 5-ASA about its conventional form [20, 21]. For the controlled release of 5-ASA and targeted to the colon, new modifications are being developed to associate with polymers for incorporation into modified tablets or coated with polymers or encapsulated in micro/nanoparticles. Some polymers have advantages for colon-specific delivery systems due to their stability, biodegradability, non-toxicity, and ability to inhibit the degradation and early release of the drug in the gastric region, in addition to allowing mechanisms of pH-dependent solubility and specific degradation for enzymes from the colonic microbiota [3,20-26]. Therefore, this review aims to compile studies from the last decade of polymer-based systems for the colonic release of 5-ASA. Polymeric Systems for Colon-specific Mesalazine Delivery Current Medicinal Chemistry, 2023, Vol. 30, No. 12 1353 Fig. (2). Chemical structure of 5-ASA . 2. IBD PHYSIOLOGICAL AND PATHOPHYSIOLOGICAL CONSIDERATIONS FOR COLONIC DRUG DELIVERY Elucidating the pathophysiology of IBD implies understanding the interaction between immunology, genetic susceptibility, and the host's gut microbiome and its exposure to the external environment. These components determine the continuation of the pathological process. Genetic factors can affect immune system function, and environmental factors can promote microbiota imbalance, both of which cause intestinal barrier dysfunction (Fig. 3) [27-31]. Dysfunction of the intestinal barrier stimulates processes such as increased mucus production, recruitment of immune cells, ulceration, bleeding, and loss of electrolytes. The production of cytokines from macrophages accentuates the inflammatory process, generating an immune response harmful to the integrity of the mucosa and causing chronic inflammation [ 27-32]. The aforementioned pathophysiological factors mediate physiological changes in the GIT, which are natural barriers that can influence the release of orally administered drugs used in the treatment of IBD and their action in the colon. Fig. (4) summarizes the determinant factors of GIT (transit time, pH, mucus, enzymes, and microbiome) that can affect drug delivery in the colonic region [8,33,34]. GIT transit time is an essential component in designing novel strategies for colon-targeted drug delivery. The reduction of transit time affects the retention/elimination properties of the active molecule. The transit time of a pharmaceutical form varies in each region of the GIT, changing according to the physiological profile of each individual. In the stomach, it is influenced, for example, by food intake, reaching up to 6 hours when fed and ranging from 0 to 2 hours empty. About the small intestine, it usually varies from 3 to 4 hours and may present an individual variation of 2 to 6 hours in healthy organisms. The colonic region has the greatest variability, lasting from 6 to 70 hours. Pathological factors can also alter transit time, for example, patients with many episodes of diarrhea have reduced transit time in the GIT due to accelerated peristaltic movement, while UC patients have a faster colonic transit time [8, 33]. Aiming at delayed-release systems, variations in pH have been observed along with the GIT. This strategy is commonly used in delivery systems that employ polymers that are soluble at neutral pH but insoluble at acidic pH, allowing them to restrict drug release in the stomach and proximal small intestine while promoting it in the colon region. The stomach has a highly acidic environment when there is no food intake (pH 1.5-2). Depending on the region in the small intestine, the pH can range from 6 (duodenum) to 7.4 (ileum). A similar Fig. (3). Interaction between risk factors for inflammatory bowel disease. (A higher resolution / colour version of this figure is available in the electronic copy of the article). 1354 Current Medicinal Chemistry, 2023, Vol. 30, No. 12 Tavares Junior et al. Fig. (4). Physiological conditions of the gastrointestinal tract can influence the release of drugs to treat IBD. (A higher resolution / colour version of this figure is available in the electronic copy of the article). pH change is noted in the large intestine, starting at 6 (cecum) and reaching 6.7 (rectum) [8, 35]. As with intestinal transit, the pH range in the GIT can be influenced by physiological factors, such as food intake, which can vary the pH of the stomach from 3 to 6. It should be noted that the pH of the GIT is directly related to the state ionization of the drug molecules and, consequently, to its absorption [8, 33]. GIT mucus is a continuous secretion responsible for lubricating and protecting the gastrointestinal epithelium. It is a negatively charged secretion composed mainly of water and mucin. The mucus layer in the GIT is the thickest in the colon and stomach, divided into a loose luminal layer and a tightly adherent basal layer. In the stomach, mucus can protect tissue from gastric acid, while in the colon it has the function of stabilizing the resident microflora environment. The mucosal barrier limits the absorption/penetration of drugs through the intestinal epithelium in oral delivery systems, reducing the time spent in the region and limiting its therapeutic effectiveness [8, 33]. Drug and dosage forms can be degraded in any region of the GIT through enzymes from saliva, gastric juice, and intestinal juice. Enzymes in the stomach and small intestine are critical in food digestion and fat, protein, and carbohydrate metabolism. These substances sensitize certain dosage forms and drugs, compromising stability, but are advantageous when used as a strategy for targeted drug delivery in the GIT, such as prodrug systems that benefit from colonic enzymes as a mechanism for converting inactive molecules into pharmacologically active molecules and targeting the colon [8, 33]. Like enzymes, the GIT microbiome also acts in fat, proteins, and carbohydrate digestion. It is an environment with over 500 different bacteria that mostly reside in the colon. The effect of this microbiome on drug absorption and dosage forms has not been fully elucidated, but new studies highlight that the high bacterial enzymatic activities in the colon are an excellent strategy for the colonic release of loaded drugs in systems based on natural polymers (gum guar, starch, pectin, etc). These systems are advantageous for hav- Polymeric Systems for Colon-specific Mesalazine Delivery Current Medicinal Chemistry, 2023, Vol. 30, No. 12 1355 ing the ability to degrade exclusively in the presence of anaerobic bacteria in the colon [8, 33]. 3. POLYMERS USED FOR COLON-SPECIFIC DRUG DELIVERY An alternative modification of pharmaceutical forms aiming at the colonic release of 5-ASA is the use of polymers through 3 main mechanisms:(1) pHsensitive: which supports the pH changes of the acidic environment throughout the GIT to release 5-ASA in the colon; (2) time-dependent: which has a latency interval that corresponds to the passage from the mouth to the colon to begin the delayed release of 5-ASA; (3) enzymatic or bacterial degradation: there are colon bacteria that produce specific enzymes capable of degrading certain polysaccharides and thus releasing 5-ASA [13, 25, 33, 36]. Eudragit® and its variations (S100, RS, FS30D, RL, L100) are the synthetic copolymers of methacrylic acid and methyl methacrylate most used as a coating for solid pharmaceutical forms and the type of Eudragit® can confer a mechanism like pH-sensitive, dissolving at around pH 7 such as Eudragit® FS30D or S100 or time-dependent such as Eudragit® RS or RL [13, 37, 38]. Cellulose derivatives such as hydroxypropyl methylcellulose (HPMC) and ethyl cellulose (EC) are commonly used as swelling and erosion coatings of solid pharmaceutical forms aiming at colonic release a time-dependent mechanism. In some cases, there is an association with other pH-sensitive polymers to resist gastric pH [13, 25]. Chitosan (CS) is a natural polymer widely used in the colonic targeting of 5-ASA for its mucoadhesive properties, due to the interaction of charges between positive charge, coming from the amine group, and negative charge of mucoproteins, increasing the retention capacity, permeation, and absorption in the GIT Its physicochemical properties such as high molecular weight and degree of deacetylation can modulate its mucoadhesive and permeation action [39,40]. Among other interesting properties of CS, its biocompatibility, biodegradability, and in-situ gelling properties [41, 42], in addition to being degraded by colonic enzymes such as β-glycosidase and some CS derivatives such as N-succinyl-chitosan (SucCS) may also have a pH-sensitive release mechanism due to carboxylic groups [30, 36, 43-46]. Alginate (Ag) is a polysaccharide of natural origin, biocompatibility, and biodegradability [47], that is degraded by enzymes in the colon, which is also Ph-dependent and undergoes swelling and gelling in the gastric environment, preventing the early release of 5ASA. Other polysaccharides that are degraded by enzymes in the colonic microbiota and used to target 5ASA are pectin, gelatin, inulin, guar gum, starch, and dextran [13, 30]. Section 4 will address micro/nanometric scale delivery systems (Table 1) and conventional forms (Table 2) of 5-ASA with polymeric modifications for colonic targeting of IBD. 4. MESALAZINE COLON-SPECIFIC DRUG DELIVERY SYSTEMS 4.1. Polymeric Microparticles Microparticle systems have been explored as a technological strategy for specific colonic delivery of drugs providing controlled and sustained release after oral administration [48]. Mura et al. [43] developed SucCS microparticles and tested them in a 2,4,6-trinitrobenzene sulfonic acid-induced colitis model. The microparticles were obtained using a spray-drying method and presented negatively charged particles. By physical-chemical analysis, the CS and 5-ASA interactions were due to the carboxyl groups of the polymer and amino group of the drug. The release of 5-ASA from the microparticles was higher at a pH value of 7.4 (more than 90%) when compared to pH 2.0 (30%), which shows the efficiency of the delivery of 5-ASA in the colonic tissue by the microparticles [49]. The microparticles presented mucoadhesive properties in an ex vivo model using rats' GI mucosa, showing a stronger mucoadhesion in the inflamed colonic mucosa than in healthy mucosa, probably due to the concentration of positively charged proteins in the damaged tissue. Moreover, in the in vivo 2,4,6-trinitrobenzene sulfonic acid-induced colitis model, the microparticles improved the efficacy of 5-ASA by improving the gain weight and reducing the myeloperoxidase concentration. Moreover, the histological examination of the colon showed healthy tissue in the animals that received the microparticles, in comparison to damage and inflamed mucosa in animals that received the 5-ASA suspension, showing the improvement in the delivery of 5-ASA by the CS microparticles. CS microparticles coated with Eudragit® S100 were developed by Jin et al. [50]. The microparticles were prepared by the emulsion-chemical cross-linking method and presented a spherical shape and high entrapment efficiency (91.5%). in vitro, in Sprague Dawley rats, the microparticles showed controlled and pro- 1356 Current Medicinal Chemistry, 2023, Vol. 30, No. 12 Tavares Junior et al. longed release of 5-ASA from the microparticles (71% in 20 hours), presenting a different release profile than 5-ASA suspension, that showed a burst release effect, with 100% of release in 5 hours. in vivo, the microparticles demonstrated a higher half-time than the 5-ASA suspension and presented higher tissue accumulation in the colon, proving the accumulation of the microparticle in the colonic tissue. In another study, CS microparticles prepared by spray-drying were developed by Palma et al. [51]. The microparticles presented a spherical and smooth surface and an encapsulation efficiency of 64.9 ± 3.7%, with prolonged and controlled release up to 48 hours in pH 6, 7, and 8, with pH 6 favoring a more rapid release of 5-ASA from the microparticles. The microparticles presented mucoadhesion properties by interacting with mucin. Moreover, the microparticles showed high interaction and internalization with Caco-2 cells (a model of human colon carcinoma cells) and did not cause cytotoxicity to these cells. in vivo, in a sodium dextran sulfate-induced colitis model in CD1 mice, the microparticles via rectal (13 mg/kg) reduced the weight loss, being more efficient than the marketed formulation (Asamax® - 26 mg/kg). The treatment with 5-ASA formulations reduced the concentration of inflammatory markers, such as myeloperoxidase, interleukin 6, and tumor necrosis factor alfa. The anti-inflammatory effects between microparticles and Asamax® were very similar. However, the concentration of 5-ASA in the microparticles was 2-fold lower than in Asamax®, showing the greater efficiency of microparticles developed. Another strategy is the association of CS with alginate as a strategy for colonic delivery of 5-ASA. Taipa et al. [52] developed calcium (Ca) alginate (Ag) microparticles and studied the influence of CS on the release of 5-ASA from the microparticles. Obtained by ionotropic gelation, the coating with CS was made using a fluid bed reactor. The drug release of 5-ASA at pH 7.5 was faster in formulations coated with CS when compared to other formulations, presenting a high degree of swelling and erosion of the microparticles. In the presence of β-glucosidase enzymes, the microparticles of 5-ASA in the microparticles were higher in CS-coated microparticles than in the Ca-Ag microparticles. The drug release in pH (1.2 and 5.5) was different from pH 7.5, showing the influence of pH on the drug release profile. In another study, Mladenovska et al. developed CS-Ca-Ag microparticles for 5-ASA delivery. The microparticles were obtained by spray-drying associated with polymer complexation/gelation. By scanning electron microscopy, the microparticles presented as spherical but also flattened disk-shaped particles. The CS distribution was analyzed by confocal laser scanning microscopy, localized dominantly in the particle wall and the Ag throughout the particle wall and matrix [53]. in vivo, in Wistar rats, the microparticles presented high accumulation in the small intestine after 5 hours of oral administration. After 10 hours, the accumulations were higher in the colon, more prominent than the 5-ASA suspension [54]. Microparticles using the plant-derived polysaccharide inulin were developed by Walz et al. [55]. The inulin was acetylated and improves enzymatic resistance to inulinase and esterase enzymes expressed by the colon microbiota, compared to non-acetylated inulin. The release behavior of 5-ASA from the inulin microparticles showed a controlled and prolonged release. The acetylated inulin microparticles presented a less burst release effect when compared to inulin, with a release of 30% versus 100% after 52h. This behavior can be related to the hydrophobicity of acetylated inulin that prevents a break-up and fast swelling of the particles. In addition to CS, other natural polymers can be used to obtain microparticles for colonic release of 5ASA. In this context, Urtiga et al. [56] developed xylan microparticles by a cross-linking polymerization method. The microparticles presented an entrapment efficiency of 65.41 ± 3.9%. The in vitro release profile of 5-ASA from the microparticles showed rapid release in simulated gastric fluid (52% in 2h), which may be related to the formation of pores in the microparticle and the intrinsic characteristics of the polymer. To improve the colon-specific delivery of 5-ASA, microparticles were added in gastro-resistant capsules of HPMC, which delayed the release of 5-ASA from the formulation and allowed more drugs reached the colon. Microparticles coated with resistant starch (RS) were developed by Chen et al. [57]. The starch used in the microparticles presented high enzyme resistance and presented a slowed and colon-specific release compared to uncoated microparticles. The use of synthetic polymers also can be employed in microparticles intended for colonic delivery. Banabid et al. [58] described the obtention of poly(lactic acid) (PLA) microspheres for the delivery of 5ASA. Obtained by the emulsion - solvent evaporation method, the microparticles presented a spherical shape, and by thermal analysis, it was confirmed the 5-ASA encapsulation with an entrapment efficiency of 12.7%, presenting the prolonged and controlled release of 5ASA in the simulated gastric fluid. In another study, Polymeric Systems for Colon-specific Mesalazine Delivery Current Medicinal Chemistry, 2023, Vol. 30, No. 12 1357 microparticles encapsulating 5-ASA and Lactobacillus acidophilus spores were developed by Thakur et al. [59]. Eudragit® S100 spherical with wrinkled surface microparticles was obtained by a spray drying technique. Presenting 97±0.89% of entrapment efficiency, the microparticles controlled release. in vivo, in a Dinitrobenzene sulfonic acid (DNBS)-induced colitis, the microparticles reduced bleeding and diarrhea in animals with induced colitis. Moreover, the microparticles decrease myeloperoxidase levels and reduce tissue damage, showing the promising effects of these microparticles in the delivery of 5-ASA in colon inflamed tissue. Layered lipid microcapsules were developed by Balducci et al . [60]. The microcapsules were produced by spray-congealing technique and presented the controlled and prolonged release of 5-ASA at pH 7.4. The liberation of this colonic pH value was achieved using Eudragit® L100 in the composition of the microcapsules, providing gastro-resistance to the microcapsules, and protecting the 5-ASA from the acidic gastro medium. 4.2. Polymeric Nanoparticles Polymeric nanoparticles (NPs) are colloidal systems that are prepared from natural or synthetic polymers and can obtain with particle sizes up to 1000 nm, although sizes between 100 and 500 nm are commonly obtained and acceptable [61]. Therefore, several techniques are used to obtain NPs, among them, polyelectrolytic complexation and ionotropic gelation stand out, but others such as nanoprecipitation, solvent diffusion, solvent evaporation, and emulsification are also used [62, 63]. In brief, NPs are divided into a nanocapsule (shell polymer system with oil or water core) and nanospheres (polymer matrix), allowing the incorporation of water-soluble or fat-soluble drugs. On top of that, NP can be functionalized to improve particle targeting at the active site [64]. One of the main challenges of IBD is the low bioavailability of 5-ASA to reach the inflamed colon, which requires the administration of high doses and the occurrence of various toxic effects [65]. The objective of encapsulating the drug in polymeric nanocarriers is highlighted by promoting drug vectorization in the colon and thus reducing side effects, preventing degradation and absorption in the upper GIT, increasing drug bioavailability, controlling release, decreasing systemic toxicity, being able to increase the permanence time in the target site through the mucoadhesion property of some polymers, attribute that can contribute to improving the biological interaction in the affected colon site of action [8, 66]. Based on the literature, we observed several studies that use NPs for the colon-specific administration of 5ASA for the treatment of IBD. In this section of the article, we will analyze the main results of these studies. IBD is considered a chronic disease that presents a clinical condition characterized by frequent relapses, painful and uncomfortable signs, and symptoms for the patient. The work by Ahmad et al. [67] aimed to formulate polymeric nanoparticles (NPs) of gelatine containing 5-ASA coated with Eudragit®S100 through the solvent evaporation nanoprecipitation method for UC treatment. Several formulations were optimized based on variables such as gelatin concentration, Eudragit®S100 concentration, and drug concentration. The chosen NPs were characterized by a hydrodynamic diameter of 216.5 ± 60.6 nm and zeta potential (ZP) of +19.3 ± 3.2 mV for the empty NPs while the NPs with 5-ASA obtained values 󰾬󰾬of 220.2 ± 70.4 nm and ZP of +20.2 ± 3.1 mV by dynamic light scattering (DLS). After coating, the diameters were 243.8 ± 68.7 nm and ZP of +20.5 ± 3.3 mV. All samples had a low Polydispersion Index (PDI) with values 󰾬󰾬of 0.2 indicating a monodisperse system. Smooth and spherical surface morphology was also noted by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). A value of 79.11% was obtained for encapsulation efficiency (EE%). The in vitro release assay was performed in an acidic medium to mimic the conditions of the stomach with pH 2.0, KH2PO4 buffer pH 4.5, and phosphate buffer saline pH 7.4, and it can be noted that the percentage release in gastric acid medium pH 2.0 was only 1.3%, but at pH 7.4 a percentage of 50% was observed in the first 24 hours and a total release of 82% was observed in the 72h. This work also evaluated pharmacological efficacy trials in a rat model of DSS-induced colitis. Still, the authors evaluated cytotoxicity in vitro and demonstrated that NPs are cytocompatible and observed that inflammatory biomarkers such as TNF-α, IL1-β, COX-2, iNOS, myeloperoxidase, and nitrite levels were significantly decreased. Furthermore, they improve significant disease indices, such as occult bleeding, colon length, and stool consistency, thus demonstrating the great potential of these NPs for the treatment of UC. Akram and Garud developed NPs of CS and carboxymethyl inulin (CMI), which were encapsulated in 5-ASA through the ionotropic gelation method for the treatment of UC. For the development of the formulations, the authors also project using the Box-Behnken response surface method to optimize the NPs. According to the BoxBehnken design, the ideal conditions for the preparation of the NPs were obtained and from 1358 Current Medicinal Chemistry, 2023, Vol. 30, No. 12 Tavares Junior et al. that, it was characterized by the DLS technique obtaining an average diameter of 184.18 nm, ZP of +26.54 mV, and EE% of 88, 58%. NPs demonstrated spherical morphology and homogeneous distribution by TEM. The results of Differential scanning calorimeter (DSC) and Fourier-transform infrared spectroscopy (FTIR) observed that the drug indicated compatibility with NP. The in vitro release assay was performed in the acidic medium at pH 1.2 and in phosphate buffer at pH 7.4 for 24 hours and observed a release rate of minus 5% at pH 1.2. At pH 7.4, more than 80% of the drug was released after 24 hours. In conclusion, the results suggest that the proposed system is an excellent candidate for colon-specific 5-ASA release and may aid in the treatment of IBD [68]. CS has been extensively used to prepare NPs and is a great carrier for controlled drug release. The work of Markam and Bajpai was a synthesis of NPs from CS functionalized with ginger (Zingiber officinale) encapsulated with 5-ASA for evaluation of colon-specific release in vitro. FTIR data confirm the binding of ginger to CS and confirm drug incorporation into NPs. The formulations were characterized with a mean diameter of 59 nm and a ZP of −29.2 mV for the NPs without functionalization and after functionalization, it obtained a value of 78.25 nm and a ZP of −21.7 mV after the incorporation of 5-ASA the value was for 93.5 nm and ZP of -19.5 mV measured by DLS. NPs demonstrated spherical morphology and are properly dispersed by TEM. The 58.82% EE% was obtained. The in vitro release experiments were prepared in artificial fluids to mimic all GIT as gastric medium with pH 1.2, intestinal fluid pH 6.8, and phosphate-buffered saline pH 7.4. The released results indicated a higher release rate concerning the greater amount of drug in the molecule and indicated a prolonged release of the drug. Cytotoxicity assays demonstrated that the proposed system does not provide toxicity to the L-929 fibroblast cell line when kept in direct contact, even after 24 h. Therefore, accordingly, this study demonstrated the potential of NPs for colon-specific 5-ASA release in the treatment of UC [69]. NPs are being widely used due to their delivery to the target tissue, avoiding distribution to other tissues, and decreasing adverse effects. Tang et al. [70] prepared NP from CS and TPP (Sodium Tripolyphosphate) containing 5-ASA in complex with cyclodextrin by the ionotropic gelation technique for the treatment of UC. Sixteen formulations were analyzed in different proportions, concentrations, and different pH and found the optimal parameters characterized by an average diameter of 143.8 nm, PDI of 0.28 indicating a monodisperse system, and ZP of + 33.8 mV by DLS technique. The NPs demonstrated spherical morphology and uniform distribution by TEM. A value of 91.4% was obtained for EE%. The in vitro release assay was performed in pH 6.8 phosphate buffer medium and it was noted that the NPs exhibited a 70% release percentage after 24 h, which was much higher than the 20% release of the drug in solution. The study was also carried out to evaluate proinflammatory mediators such as NO, PGE2, and IL-8 in HT-29 cells. The results revealed that NPs more strongly inhibited the production of those mediators, indicating better anti-inflammatory effects compared to 5-ASA in solution. Furthermore, the cytotoxicity assay in HT-29 cells was performed and it was observed that the proposed system did not affect cell viability. Therefore, it can be concluded that the proposed system becomes a potential tool for the release of colon-specific 5-ASA for the treatment of UC. The authors Seifirad et al. [71] also developed NP from CS and TPP encapsulated with 5-ASA through an ionotropic gelation technique for the treatment of UC orally. For the development of the formulations, the authors carried out an experimental project using the Box-Behnken response surface method to optimize the NPs. A total of 26 samples were analyzed and, according to the BoxBehnken design, the ideal conditions for the preparation of the NPs were obtained and from that, it was characterized by the DLS technique obtaining an average diameter of 90 nm, PDI of 0.34, and pH 4.5. NPs demonstrated spherical morphology and homogeneous distribution by SEM. A value of 89% for EE% was obtained. The results of DSC and X-ray diffractometry (XRD) observed that the drug is molecularly dispersed in the NPs. The in vitro release assay was performed in a phosphate buffer pH 7.4 medium for 48 hours by the dialysis method and observed a prolonged release in the first hours up to a total release of 90.17 ± 2.45% in 48 hours. Finally, the results showed promise for a specific release of 5-ASA in a medium mimicked by colon pH and protect 5ASA against premature degradation in acidic stomach pH, but other studies mainly in vivo are interesting to improve the results. Based on this, another study by Mongia et al. [72] also prepared CS and TPP NPs containing 5-ASA by ionotropic gelation technique. The NP was coated with pH-dependent polymer Eudragit S-100 by solvent evaporation technique, for effective release in the colon effect by UC. Two formulations were analyzed and characterized, one without coating and the other with coating. The results found were a mean diameter of 159±4 Polymeric Systems for Colon-specific Mesalazine Delivery Current Medicinal Chemistry, 2023, Vol. 30, No. 12 1359 nm for NP-5-ASA (without coating) and 661±11 nm for NP-ES-5-ASA (after coating), ZP of 22 ±182 and −34.5±08 mV respectively, and suitable PDI. In the SEM analysis, the NPs showed spherical morphology and uniform distribution. A value of 61.5% was obtained for EE%. The DSC analysis evidenced that the drug is molecularly dispersed in NPs. The in vitro release assay was performed in a different simulated medium of gastrointestinal treats at different pH and it was noted that the coated NPs had a prolonged release at colon pH with total release within 30 hours. Compared to uncoated NPs, this full release occurs within the first 5 hours. The in vitro hemolysis assay demonstrated that the proposed system was not hemolytic. In conclusion, this study demonstrated that NPs coated with polymers have great potential, as they proved to be effective for a specific release and with less toxicity. NPs are intended to protect 5-ASA against premature degradation in the acidic pH of the stomach, causing it to be released only in the affected colon. Mahajan Sakarkar Manmode developed NPS of PLGA (poly (d, l-lactic-co-glycolic acid) encapsulated with 5-ASA through the modified spontaneous emulsification diffusion method of solvent (MSESD) for the treatment of UC. The formulations were characterized with a hydrodynamic diameter of 135 ± 3.4 nm, PDI of 0.259, and ZP of -45.2 ± 1.7 mV by the DLS technique. The NPs demonstrated spherical morphology by SEM and a value of 37.7% for EE% was obtained. The DSC analysis observed that the drug is molecularly dispersed in NPs. The in vitro release assay was performed in phosphate buffer pH 7.4 for 240 hours and demonstrated a biphasic pattern result (initial rapid release of 47.19% during the first 24 h, followed by a sustained release and up to the 10th day in 80%). Finally, the results showed a specific release of 80% of 5-ASA in a phosphate buffer medium pH 7.4, and suggest that PLGA-NPs improve the drug's bioavailability and controlled release in the target tissue [73]. Table 1. Microparticles and nanoparticles for colon-specific delivery of 5-ASA. - Polymer Targeting Mechanism Delivery Route Size Charge (mV) Refs. Microparticles SucCS pH-dependent Oral 5.1 ± 2.2 µm - 11.3 ± 3.9 [43] SucCS pH-dependent - 5.1 ± 2.2 µm -20.7 ± 4.9 [49] Eudragit® S100 coated CS pH-enzyme dependent Oral 312.2 µm -17.6 [50] CS pH-dependent Rectal 1.1-4.3 µm 50.8 ± 4.4 [51] CS-Ca-Ag pH-enzyme-dependent Oral 6.2 ± 2.2 to 8.6 + 3.2 µm −21.5 ± 1.0 to −30.7 ± 1.8 [54] CS-Ca-Ag pH-enzyme-dependent - 6.2 ± 2.2 µm −30.7 ± 1.8 [53] CS-Ca-Ag pH-enzyme-dependent - - - [52] Xylan Enzyme degradation - 14.64 ± 0.5 µm - [56] Inulin Enzyme degradation - 0.8-10 µm - [55] RS Bacterial degradation Oral 3-26 µm - [57] Eudragit® L100 pH-dependent - 50-70 µm - [60] PLA pH-dependent 100-200 µm [58] Eudragit® S100 pH-dependent Oral 4.91±0.63 µm - [59] Nanoparticles Gelatine/ Eudragit®-S100 pH-dependent Oral 243.8 ± 68.7 nm +20.5 ± 3.3 mV [67] CS/CMI pH-dependent Oral 184.18 nm +26.54 mV [68] CS/ginger pH-dependent Oral 93.5 nm -19.5 mV [69] CS/TPP pH-dependent Oral 143.8 nm +33.8 mV [70] CS/TPP pH-dependent Oral 90 nm - [71] CS/TPP/ Eudragit-S100 pH-dependent Oral 661.0 ± 11 nm -34.5± 0.8 mV [72] PLGA pH-dependent Oral 135.0 ± 34 nm -42.5± 1.7 mV [73] Abbreviations: SucCS - N-Succinyl-chitosan, CS - Chitosan, Ca - Calcium, Ag - Alginate, PLA - Poly (lactic acid), CMI - Carboxymethyl inulin, TPP - Sodium Tripolyphosphate, PLGA - Poly (d, l-lactic-co-glycolic acid), RS - Resistant starch 1366 Current Medicinal Chemistry, 2023, Vol. 30, No. 12 Tavares Junior et al. icylic acid loaded N-succinyl-chitosan microparticles for colon specific delivery. 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