Colon targeting with bacteria-sensitive films adapted to the disease state

Unraveling the role of pectin biodegradability and blend composition on the permeability of ethylcellulose-based blend films designed for colon targeting

Polysaccharides have often been used as the biodegradable compound in coated colon specific drug delivery systems. The selection of a specific polysaccharide is critical, as they are degraded by gut bacteria, leading to the site specific release of drugs in the colon. However, it is still not completely understood how bacterial enzymes act on the polysaccharides when they are incorporated in a coating that is primarlily made up of a hydrophobic polymer. Here, we explored to what extent pectinase degrades pectin in isolated pectin-ethylcellulose blend films by studying the film permeability. Comparison of the permeability coefficient of caffeine and the amount of pectin leakage from the blend film in the presence and absence of pectinase revealed that pectinase can still degrade the pectin in the film, on the condition that the polysaccharide is not completely encapsulated by ethylcellulose. This is different from the degradation of inulin by inulinase in the blend film of inulin in Eudragit RS as shown in our previous study (Ouyang et al., 2023). Pectin can provide a transmembrane channel for drugs due to its dissolution in water and degradation by pectinase. Pectins from apples and citrus with similar esterification degrees applied in this work had basically the same effect on film permeability and can serve as interchangeable materials for colon targeting coatings. Compatibility studies revealed a phase-separated structure of pectin-ethylcellulose films. As the proportion of pectin in the film increased, the blend film changed from a discontinuous structure to a bicontinuous structure, and the film permeability increased. Combined with the film structural characterization, the results show that the proportion of the blended components and the degradation of pectin in the film by pectinase are the determining factors affecting the permeability and microstructure of pectin-ethylcellulose blend films.

Colon targeting in rats, dogs and IBD patients with species-independent film coatings

Polysaccharides were identified, which allow for colon targeting in human Inflammatory Bowel Disease (IBD) patients, as well as in rats and dogs (which are frequently used as animals in preclinical studies). The polysaccharides are degraded by colonic enzymes (secreted by bacteria), triggering the onset of drug release at the target site. It has to be pointed out that the microbiota in rats, dogs and humans substantially differ. Thus, the performance of this type of colon targeting system observed in animals might not be predictive for patients. The aim of this study was to limit this risk. Different polysaccharides were exposed to culture medium inoculated with fecal samples from IBD patients, healthy dogs and "IBD rats" (in which colonic inflammation was induced). Dynamic changes in the pH of the culture medium were used as an indicator for the proliferation of the bacteria and, thus, the potential of the polysaccharides to serve as their substrate. Fundamental differences were observed with respect to the extent of the pH variations as well as their species-dependency. The most promising polysaccharides were used to prepare polymeric film coatings surrounding 5-aminosaliciylic acid (5-ASA)-loaded starter cores. To limit premature polysaccharide dissolution/swelling in the upper gastro intestinal tract, ethylcellulose was also included in the film coatings. Drug release was monitored upon exposure to culture medium inoculated with fecal samples from IBD patients, healthy dogs and "IBD rats". For reasons of comparison, also 5-ASA release in pure culture medium was measured. Most film coatings showed highly species-dependent drug release kinetics or limited colon targeting capacity. Interestingly, extracts from aloe vera and reishi (a mushroom) showed a promising potential for colon targeting in all species.

Film Coatings Based on Aqueous Shellac Ammonium Salt "Swanlac® ASL 10" and Inulin for Colon Targeting

Over the past decades, increasing interests took place in the realm of drug delivery systems. Beyond treating intestinal diseases such as inflammatory bowel disease, colon targeting can provide possible applications for oral administration of proteins as well as vaccines due to the lower enzymatic activity in the distal part of GIT. To date, many strategies are employed to reach the colon. This article encompasses different biomaterials tested as film coatings and highlights appropriate formulations for colonic drug delivery. A comparison of different films was made to display the most interesting drug release profiles. These films contained ethylcellulose, as a thermoplastic polymer, blended with an aqueous shellac ammonium salt solution. Different blend ratios were selected as well for thin films as for coated mini-tablets, mainly varying as follows: (80:20); (75:25); (60:40). The impact of blend ratio and coating level was examined as well as the addition of natural polysaccharide "inulin" to target the colon. In vitro drug release was measured in 0.1 M HCl for 2 h followed by phosphate buffer saline pH 6.8 to simulate gastric and intestinal fluids, respectively. Coated mini-tablets were exposed to fresh fecal samples of humans in order to simulate roughly colonic content. Several formulations were able to fully protect theophylline as a model drug up to 8 h in the upper GIT, but allowing for prolonged release kinetics in the colon. These very interesting colonic release profiles were related to the amount of the natural polysaccharide added into the system.

Microbiota-sensitive drug delivery systems based on natural polysaccharides for colon targeting

Colon targeting is an ongoing challenge, particularly for the oral administration of biological drugs or local treatment of inflammatory bowel disease (IBD). In both cases, drugs are known to be sensitive to the harsh conditions of the upper gastrointestinal tract (GIT) and, thus, must be protected. Here, we provide an overview of recently developed colonic site-specific drug delivery systems based on microbiota sensitivity of natural polysaccharides. Polysaccharides act as a substrate for enzymes secreted by the microbiota located in the distal part of GIT. The dosage form is adapted to the pathophysiology of the patient and, thus, a combination of bacteria-sensitive and time-controlled release or pH-dependent systems can be used for delivery.

Injection-molded capsule bodies and caps based on polymer blends for controlled drug delivery

A variety of polymer:polymer blends was used to prepare hot melt extrudates and empty capsules (bodies and caps) by injection-molding using a benchtop extruder (Babyplast). KollidonSR:inulin and Carbothane:inulin blends were investigated. The impact of the blend ratio on the water uptake and dry mass loss kinetics upon exposure to 0.1 MHCl, phosphate buffer pH6.8 and culture medium optionally inoculated with fecal samples from Inflammatory Bowel Disease (IBD) patients were studied. Hot melt extrudates were loaded with up to 60% theophylline, capsules were filled with drug powder. Increasing the inulin content led to increased water uptake and dry mass loss rates, resulting in accelerated drug release from the dosage forms, irrespective of the type of polymer blend. This can be attributed to the higher hydrophilicity/water-solubility of this polymer compared to KollidonSR and Carbothane. Interestingly, the presence of fecal samples in culture medium increased the water uptake and dry mass loss of hot melt extrudates to a certain extent, suggesting partial system degradation by bacterial enzymes. However, these phenomena did not translate into any noteworthy impact of the presence of colonic bacteria on theophylline release from the investigated extrudates or capsules. Hence, drug release can be expected to be independent of the location "small intestine vs. colon" from these dosage forms, which can be advantageous for long term release throughout the entire gastro intestinal tract.

Drug Disposition in the Lower Gastrointestinal Tract: Targeting and Monitoring

The increasing prevalence of colonic diseases calls for a better understanding of the various colonic drug absorption barriers of colon-targeted formulations, and for reliable in vitro tools that accurately predict local drug disposition. In vivo relevant incubation conditions have been shown to better capture the composition of the limited colonic fluid and have resulted in relevant degradation and dissolution kinetics of drugs and formulations. Furthermore, drug hurdles such as efflux transporters and metabolising enzymes, and the presence of mucus and microbiome are slowly integrated into drug stability- and permeation assays. Traditionally, the well characterized Caco-2 cell line and the Ussing chamber technique are used to assess the absorption characteristics of small drug molecules. Recently, various stem cell-derived intestinal systems have emerged, closely mimicking epithelial physiology. Models that can assess microbiome-mediated drug metabolism or enable coculturing of gut microbiome with epithelial cells are also increasingly explored. Here we provide a comprehensive overview of the colonic physiology in relation to drug absorption, and review colon-targeting formulation strategies and in vitro tools to characterize colonic drug disposition.

A novel cyanoacrylate-based matrix excipient in HPMCP capsules forms a sustained intestinal delivery system for orally administered drugs with enhanced absorption efficiency

Patients prefer oral drug delivery due to its convenience and noninvasiveness. Nevertheless, a multitude of potentially clinically important drugs will not reach the market or achieve their full potential, due to their low bioavailability and instability in gastric acid. In this study, a novel oral drug delivery system based on poly-cyanoacrylate [a polymer of 2-(2-methoxyethoxy)ethyl-2-cyanoacrylate (MECA)] and hydroxypropyl methylcellulose phthalate (HPMCP) was developed and shown to permit intestinal targeting and sustained drug release. Aspirin [acetylsalicylic acid (ASA)] was selected as a model drug for atherosclerosis treatment. It was physically dissolved in liquid MECA, and the ASA-MECA matrix was then polymerized into a solid drug-loading depot in an HPMCP shell. The delivery of the drug depot in the intestine was achieved with the HPMCP shell; then the polymerized MECA (polyMECA) provided sustained drug release. The polyMECA excipient was not absorbed by the intestine due to its high molecular weight; a fluorescein-labeled assay indicated that it was excreted completely in feces after drug release. The formulation, ASA-polyMECA-HPMCP, showed good intestinal targeting and sustained drug release in vitro and in vivo. Pharmacokinetic studies indicated that this formulation improved the bioavailability of ASA relative to commercially available controls. ASA-polyMECA-HPMCP showed desirable anti-atherosclerosis efficacy in a rabbit model, with significant enhancement of atheromatous lesion stability. Biosafety tests proved the low toxicity of ASA-polyMECA-HPMCP and the polyMECA matrix. We believe that this work has provided a practical and biocompatible system for sustained intestinal drug delivery that can be applied broadly with various drugs for specific therapeutic aims.

Robustness of Controlled Release Tablets Based on a Cross-linked Pregelatinized Potato Starch Matrix

The aim of this study was to evaluate the potential of a cross-linked pregelatinized potato starch (PREGEFLO® PI10) as matrix former for controlled release tablets. Different types of tablets loaded with diprophylline, diltiazem HCl or theophylline were prepared by direct compression of binary drug/polymer blends. The drug content was varied from 20 to 50%. Two hydroxypropyl methylcellulose grades (HPMC K100LV and K100M) were studied as alternative matrix formers. Drug release was measured in a variety of release media using different types of experimental set-ups. This includes 0.1 N HCl, phosphate buffer pH 6.8 and water, optionally containing different amounts of NaCl, sucrose, ethanol or pancreatin, fasted state simulated gastric fluid, fed state simulated gastric fluid, fasted state simulated intestinal fluid, fed state simulated intestinal fluid as well as media simulating the conditions in the colon of healthy subjects and patients suffering from Crohn's disease. The USP apparatuses I/II/III were used under a range of operating conditions and optionally coupled with the simulation of additional mechanical stress. Importantly, the drug release kinetics was not substantially affected by the investigated environmental conditions from tablets based on the cross-linked pregelatinized potato starch, similar to HPMC tablets. However, in contrast to the latter, the starch-based tablets roughly kept their shape upon exposure to the release media (they "only" increased in size) during the observation period, and the water penetration into the systems was much less pronounced. Thus, the investigated cross-linked pregelatinized potato starch offers an interesting potential as matrix former in controlled release tablets.

OPTICORE™, an innovative and accurate colonic targeting technology

Inflammatory bowel disease (IBD) is a debilitating condition, estimated to affect 7 million people worldwide. Current IBD treatment strategies are substandard, relying on colonic targeting using the pH gradient along the gastrointestinal tract. Here, we describe an innovative colonic targeting concept, OPTICORE™ coating technology. OPTICORE™ combines two release triggers (pH and enzyme: Phloral™) in the outer layer, with an inner layer promoting a release acceleration mechanism (Duocoat™). The technology comprises an inner layer of partially neutralized enteric polymer with a buffer agent and an outer layer of a mixture of Eudragit® S and resistant starch. 5-aminosalicylic acid (5-ASA) tablets were coated with different inner layers, where the type of polymer, buffer salt concentration and pH of neutralization, were investigated for drug release acceleration. Buffer capacity of polymethacrylate neutralized polymer significantly contributes to the buffer capacity of the inner layer formulation, while buffer salt concentration is a major contributor to dispersion buffer capacity in the case of hypromellose enteric polymer formulations. An interplay between buffer capacity, pH and ionic strength contributes to an accelerated drug release. Resistant starch does not impact the enteric properties but allows for drug release mediated by colonic bacterial enzymes, ensuring complete drug release. Therefore, OPTICORE™ technology is designed to offer significant advantages over standard enteric coatings, particularly allowing for more accurate colonic drug delivery in ulcerative colitis patients.

Injection Molded Capsules for Colon Delivery Combining Time-Controlled and Enzyme-Triggered Approaches

A new type of colon targeting system is presented, combining time-controlled and enzyme-triggered approaches. Empty capsule shells were prepared by injection molding of blends of a high-amylose starch and hydroxypropyl methylcellulose (HPMC) of different chain lengths. The dissolution/erosion of the HPMC network assures a time-controlled drug release, i.e., drug release starts upon sufficient shell swelling/dissolution/erosion. In addition, the presence of high-amylose starch ensures enzyme-triggered drug release. Once the colon is reached, the local highly concentrated bacterial enzymes effectively degrade this polysaccharide, resulting in accelerated drug release. Importantly, the concentration of bacterial enzymes is much lower in the upper gastrointestinal tract, thus enabling site-specific drug delivery. The proposed capsules were filled with acetaminophen and exposed to several aqueous media, simulating the contents of the gastrointestinal tract using different experimental setups. Importantly, drug release was pulsatile and occurred much faster in the presence of fecal samples from patients. The respective lag times were reduced and the release rates increased once the drug started to be released. It can be expected that variations in the device design (e.g., polymer blend ratio, capsule shell geometry and thickness) allow for a large variety of possible colon targeting release profiles.

Local delivery of macromolecules to treat diseases associated with the colon

Current treatments for intestinal diseases including inflammatory bowel diseases, irritable bowel syndrome, and colonic bacterial infections are typically small molecule oral dosage forms designed for systemic delivery. The intestinal permeability hurdle to achieve systemic delivery from oral formulations of macromolecules is challenging, but this drawback can be advantageous if an intestinal region is associated with the disease. There are some promising formulation approaches to release peptides, proteins, antibodies, antisense oligonucleotides, RNA, and probiotics in the colon to enable local delivery and efficacy. We briefly review colonic physiology in relation to the main colon-associated diseases (inflammatory bowel disease, irritable bowel syndrome, infection, and colorectal cancer), along with the impact of colon physiology on dosage form design of macromolecules. We then assess formulation strategies designed to achieve colonic delivery of small molecules and concluded that they can also be applied some extent to macromolecules. We describe examples of formulation strategies in preclinical research aimed at colonic delivery of macromolecules to achieve high local concentration in the lumen, epithelial-, or sub-epithelial tissue, depending on the target, but with the benefit of reduced systemic exposure and toxicity. Finally, the industrial challenges in developing macromolecule formulations for colon-associated diseases are presented, along with a framework for selecting appropriate delivery technologies.

Remodeling of the Candida glabrata cell wall in the gastrointestinal tract affects the gut microbiota and the immune response

The gastrointestinal (GI) microbiota acts a natural barrier to the proliferation of opportunistic pathogens. Candida glabrata is an opportunistic yeast pathogen that has adapted to colonize all segments of the human GI tract. We observed an increase in Escherichia coli, Enterococcus faecalis, and Bacteroides vulgatus populations, and a decrease in Lactobacillus johnsonii, Bacteroides thetaiotaomicron, and Bifidobacterium animalis in mice with DSS-induced colitis. This reduction was more pronounced for L. johnsonii during C. glabrata overgrowth. In addition, C. glabrata overgrowth increased mouse mortality and inflammatory parameters, and modulated the expression of intestinal receptors and signaling pathways. The C. glabrata cell wall underwent various changes during the course of C. glabrata colonization, and showed a significant increase in chitin. C. glabrata deficient in chitin synthase-3 induced fewer inflammatory parameters than the parental strain during intestinal inflammation. Oral administration of chitin attenuated the impact of colitis, and reduced the number of aerobic bacteria and C. glabrata overgrowth, while chitinase-3-like protein-1 increased. This study provides evidence that inflammation of the gut alters the microbial balance and leads to C. glabrata cell wall remodeling through an increase in chitin, which is involved in promoting persistence of C. glabrata in the gut.

Stimuli-responsive polymers for antimicrobial therapy: drug targeting, contact-killing surfaces and competitive release

INTRODUCTION

Polymers can be designed to modify their features as a function of the level and nature of the surrounding microorganisms. Such responsive polymers can endow drug delivery systems and drug-medical device combination products with improved performance against intracellular infections and biofilms.

AREAS COVERED

Knowledge on microorganism growth environment outside and inside cells and formation of biofilm communities on biological and synthetic surfaces, together with advances in materials science and drug delivery are prompting strategies with improved efficacy and safety compared to traditional systemic administration of antimicrobial agents. This review deals with antimicrobial strategies that rely on: (i) polymers that disintegrate or undergo phase-transitions in response to changes in enzymes, pH and pO2 associated to microorganism growth; (ii) stimuli-responsive polymers that expose contact-killing groups when microorganisms try to adhere; and (iii) bioinspired polymers that recognize microorganisms for triggered (competitive/affinity-driven) drug release.

EXPERT OPINION

Prophylaxis and treatment of infections may benefit from polymers that are responsive to the unique changes that microbial growth causes in the surrounding environment or that even recognize the microorganism itself or its quorum sensing signals. These polymers may offer novel tools for the design of macrophage-, bacteria- and/or biofilm-targeted nanocarriers as well as of medical devices with switchable antibiofouling properties.

Non-coated multiparticulate matrix systems for colon targeting

BACKGROUND

Colon specific drug delivery can significantly improve the efficacy of local treatments of inflammatory bowel diseases. Film coatings containing the starch derivative Nutriose have recently been reported to minimize 5-ASA release in media simulating the upper gastro intestinal tract (GIT), while releasing the drug in a time-controlled manner upon contact with feces from Crohn's Disease and Ulcerative Colitis patients. It was the aim of this study to prepare Nutriose-containing matrix pellets and mini tablets in order to avoid a film coating step.

METHODS

Highly dosed matrix pellets were prepared by extrusion-spheronization, highly dosed mini tablets by compression. Various types of lipids were added and drug release measured in 0.1 N HCl and phosphate buffer pH 6.8, optionally containing pepsin and pancreatin.

RESULTS

The type of added lipid and the preparation technique, in particular the curing conditions, significantly affected the resulting drug release kinetics. Glyceryl palmitostearate containing pellets and mini tablets showed the most promising results upon appropriate curing, minimizing premature drug release in media simulating the upper GIT.

CONCLUSION

The proposed novel multiparticulates do not require a film coating step and show an interesting potential for site-specific drug delivery to the colon of inflammatory bowel disease patients.

Enzymatically degraded Eurylon 6 HP-PG: ethylcellulose film coatings for colon targeting in inflammatory bowel disease patients

Objectives

Film coatings based on blends of Eurylon 6 HP-PG (a hydroxypropylated and pregelatinized high amylose starch) and ethylcellulose were to be evaluated as promising coating materials for site-specific drug delivery to the colon of patients suffering from inflammatory bowel diseases.

Methods

Pellet starter cores containing 60% 5-aminosalicylic acid were prepared by extrusion/spheronization and coated with different Eurylon 6 HP-PG : ethylcellulose blends at various coating levels. Drug release was measured in media simulating the contents of the upper gastrointestinal tract (in the presence and absence of enzymes) as well as in media simulating the contents of the colon.

Key findings

5-Aminosalicylic acid release could effectively be suppressed in 0.1 N HCl and phosphate buffer pH 6.8, optionally containing pepsin or pancreatin, but occurred as soon as the pellets came into contact with culture medium inoculated with faecal samples from inflammatory bowel disease patients. This can be attributed to the partial degradation of the starch derivative by enzymes secreted by bacteria present in the colon of these patients.

Conclusions

The presented drug delivery system is adapted to the pathophysiological conditions in inflammatory bowel disease patients. Furthermore, drug release remained unaltered upon 1 year open storage.