Colonic drug delivery

Carbohydrate Polymer-Based Targeted Pharmaceutical Formulations for Colorectal Cancer: Systematic Review of the Literature

Colon cancer is the third most diagnosed cancer worldwide, followed by lung and breast cancer. Conventional treatment methods are associated with numerous side effects and compliance issues. Thus, colon targeted drug delivery has gained much attention due to its evident advantages. Although many technologies have been explored, the use of pH-sensitive polymers, especially biodegradable polymers, holds exceptional promise. This review aims to collate research articles concerning recent advances in this area. A systematic search using multiple databases (Google Scholar, EMBASE, PubMed, MEDLINE and Scopus) was carried out following the preferred reported items for systematic reviews and meta-analyses (PRISMA) guidelines with an aim to explore the use of pH-sensitive carbohydrate polymers in developing colon targeted pharmaceutical formulations. Following screening and quality assessment for eligibility, 42 studies were included, exploring either single or a combination of carbohydrate polymers to develop targeted formulations for colon cancer therapy. Pectin (11) is the most widely used of these biopolymers, followed by chitosan (09), alginate (09) and guar gum (08). This systematic review has successfully gathered experimental evidence highlighting the importance of employing carbohydrate polymers in developing targeting formulations to manage colon cancer.

Cellulose Nanofibers Improve the Performance of Retrograded Starch/Pectin Microparticles for Colon-Specific Delivery of 5-ASA

Cellulose nanofibers (CNF) were employed as the nanoreinforcement of a retrograded starch/pectin (RS/P) excipient to optimize its colon-specific properties. Although starch retrogradation ranged from 32 to 73%, CNF addition discretely disfavored the RS yield. This result agrees with the finding that in situ CNF reduces the presence of the RS crystallinity pattern. A thermal analysis revealed that the contribution of pectin improves the thermal stability of the RS/CNF mixture. Through a complete factorial design, it was possible to optimize the spray-drying conditions to obtain powders with high yield (57%) and low moisture content (1.2%). The powders observed by Field Emission Gum Scanning Electron Microscopy (FEG-SEM) had 1–10 µm and a circular shape. The developed methodology allowed us to obtain 5-aminosalicilic acid-loaded microparticles with high encapsulation efficiency (16–98%) and drug loading (1.97–26.63%). The presence of CNF in RS/P samples was responsible for decreasing the burst effect of release in simulated gastric and duodenal media, allowing the greatest mass of drug to be targeted to the colon. Considering that spray-drying is a scalable process, widely used by the pharmaceutical industry, the results obtained indicate the potential of these microparticles as raw material for obtaining other dosage forms to deliver 5-ASA to the distal parts of gastrointestinal tract, affected by inflammatory bowel disease.

Preparation, development and characterization of Leucaena leucocephala galactomannan (LLG) conjugated sinapic acid: A potential colon targeted prodrug

Sinapic acid (SA), a widely prevalent hydroxycinnamic acid, possess numerous biological activities owing to its antioxidant property. The present study was aimed to prepare colon targeted polysaccharidic/polymeric ester prodrug of SA (a microbially triggered system) using Leucaena leucocephala galactomannan (LLG) as a polysaccharidic carrier. The polymeric conjugates of SA-LLG were found to exhibit an increase in % yield and DS with increase in amount of SA and volume of thionyl chloride. The degree of depolymerization of SA-LLG prodrug batches were evaluated using optimized concentration of galactomannase. The SA-LLG prodrug was characterized employing UV and FTIR spectroscopy, ¹H NMR and XRD. In vitro release study of the optimized prodrug batch (SL10) suggested stable nature of SA-LLG conjugate under acidic (pH 1.2) and alkaline conditions (pH 6.8). The treatment of prodrug with galactomannase (15 mg/mL) followed by esterase (10 U/mL) enzyme released approximately 81% of SA after 24 h. The cell viability results revealed that free SA and SA-LLG were found to have similar antiproliferative potential against human colon cancer cell lines (HCT-116 cells). Our investigation revealed that polysaccharidic prodrug, SA-LLG, has the potential for colon targeting of SA and thus can be employed for the treatment of Inflammatory Bowel Diseases (IBDs).

Eudragit®-S100 Coated PLGA Nanoparticles for Colon Targeting of Etoricoxib: Optimization and Pharmacokinetic Assessments in Healthy Human Volunteers

Aim

Etoricoxib is a selective inhibitor of COX-2 enzyme. It is proposed as a potent anti-inflammatory drug intended for the control of irritable bowel syndrome. The current work aimed at developing etoricoxib-loaded nanoparticles for colon- targeting.

Materials and Methods

PLGA nanoparticles were developed via nano-spray drying technique. The D-optimal design was adopted for the investigation of the influence of i) DL-lactide-coglycolide (PLGA) concentration, ii) polyvinylpyrrolidone K30 (PVP K30) concentration and iii) lactide:glycolide ratio in the copolymer chain on the yield%, the encapsulation efficiency (EE%), particle size (PS) and percentage of drug release after 2h (P_2h), 4h (P_4h) and 12h (P_12h). To promote colon targeting of the systems, the best achieved system (M14) was either directly coated with poly(methacrylic acid-co-methyl methacrylate) [Eudragit^®-S100] or loaded into hard gelatin capsules and the capsules were coated with poly(methacrylic acid-co-methyl methacrylate) (E-M14C). The pharmacokinetic parameters of etoricoxib following oral administration of E-M14C in healthy volunteers were assessed relative to commercial etoricoxib tablets.

Results

M14 system was prepared using PLGA (0.5% w/v) at a lactide:glycolide ratio of 100:0, in the presence of PVP K30 (2% w/v). M14 system was nano-spherical particles of 488 nm size possessing promising yield% (63.5%) and EE% (91.2%). The percentage drug released after 2, 4 and 12 hours were 43.41%, 47.34 and 64.96%, respectively. Following M14-loading into hard gelatin capsules and coating with poly(methacrylic acid-co-methyl methacrylate) [Eudragit-S100], the respective P_2h, P_4h and P_12h were 10.1%, 28.60% and 65.45%. Significant (p < 0.05) differences between the pharmacokinetic parameter of E-M14C in comparison with the commercial product were revealed with a delay in T_max (from 2.5h to 6h), a prolongation in MRT_0-∞ (from 24.4h to 34.7h) and an increase in the relative oral bioavailability (4.23 folds).

Conclusion

E-M14C is a potential system for possible colon targeting of etoricoxib.

Colon-targeting of progesterone using hybrid polymeric microspheres improves its bioavailability and in vivo biological efficacy

This study aims to enhance progesterone (PG) oral bioavailability via its incorporation into hybrid colon-targeted pectin/NaCMC microspheres (MS) cross-linked with Zn²⁺ and Al³⁺. The MS were characterized for particle morphology, encapsulation efficiency, swelling behavior, drug release, mucoadhesivity and colon-specific degradability. Response-surface methodology was adopted to optimize the fabrication conditions. Enhancement of in vivo drug performance was evaluated through pharmacokinetic and pharmacodynamic studies. The optimized formulation was typically spherical with a mean diameter of 1031 µm and drug entrapment efficiency of 88.8%. This formulation exhibited pH-dependent swelling, negligible drug release in simulated gastric fluid and sustained-release pattern in simulated small intestinal fluid with a mean t_50% of 26.5 h. It also showed prolonged and preferential adhesion to rat colonic mucosa, as well as expedited degradation in presence of rat caecal contents. The MS significantly increased the area under the curve and mean residence time by 1.8 and 2.3-fold, respectively compared to the free drug. Orally administered MS showed ~10 times increase in myometrial thickness compared with the drug suspension and elicited uterine responses very similar to that obtained parenterally. These results confirm the ability of this new carrier system to improve the oral bioavailability of PG and attain adequate clinical efficacy.

Bioresponsive drug delivery systems in intestinal inflammation: State-of-the-art and future perspectives

Oral colon-specific delivery systems emerged as the main therapeutic cargos by making a significant impact in the field of modern medicine for local drug delivery in intestinal inflammation. The site-specific delivery of therapeutics (aminosalicylates, glucocorticoids, biologics) to the ulcerative mucus tissue can provide prominent advantages in mucosal healing (MH). Attaining gut mucosal healing and anti-fibrosis are main treatment outcomes in inflammatory bowel disease (IBD). The pharmaceutical strategies that are commonly used to achieve a colon-specific drug delivery system include time, pH-dependent polymer coating, prodrug, colonic microbiota-activated delivery systems and a combination of these approaches. Amongst the different approaches reported, the use of biodegradable polysaccharide coated systems holds great promise in delivering drugs to the ulcerative regions. The present review focuses on major physiological gastro-intestinal tract challenges involved in altering the pharmacokinetics of delivery systems, pathophysiology of MH and fibrosis, reported drug-polysaccharide cargos and focusing on conventional to advanced disease responsive delivery strategies, highlighting their limitations and future perspectives in intestinal inflammation therapy.

Impact of Pore-Walls Ligand Assembly on the Biodegradation of Mesoporous Organosilica Nanoparticles for Controlled Drug Delivery

Porous materials with molecular-scale ordering have attracted major attention mainly because of the possibility to engineer their pores for selective applications. Periodic mesoporous organosilica is a class of hybrid materials where self-assembly of the organic linkers provides a crystal-like pore wall. However, unlike metal coordination, specific geometries cannot be predicted because of the competitive and dynamic nature of noncovalent interactions. Herein, we study the influence of competing noncovalent interactions in the pore walls on the biodegradation of organosilica frameworks for drug delivery application. These results support the importance of studying self-assembly patterns in hybrid frameworks to better engineer the next generation of dynamic or "soft" porous materials.

Pressure responsive nanogel base on Alginate-Cyclodextrin with enhanced apoptosis mechanism for colon cancer delivery

5-Fluorouracil (5-Fu) commonly use in the treatment of different kinds of cancer, but limited cellular uptake and death is still a problem. Herein, we report a simple process for the synthesis of pressure-sensitive nanogels that indicate to be appropriate in the delivery of 5-Fu. The hydrogels (Al-CD) prepare by crosslinking of alginate (Al) with modified beta Cyclodextrin (β-CD) as Crosslinker. Next, nanoparticles obtaine by an emulsification method. 5-Fu as model drug loades into the Al-CD nanogels easily by mixing it in aqueous solution with the nanoparticles. The results revealed that the Al-CD nanogels are cytocompatible. They have also a noticeable drug encapsulation (82.1 ±5.7%) while they can release (in vitro controlled) 5-Fu in conditions that imitate the intravascular pressure conditions. These nanogels can rapidly be taken up by HT-29 cells (a colon cell line). In addition, a higher 5-Fu intracellular accumulation and a significant cell death extension by apoptosis mechanism is notice when compare with free 5-Fu. Accordingly, the developed nanogels can be employe as an excellent candidate to overcome the inefficiency of 5-Fu in anticancer treatments and possibly can employe for further evaluation as a chemotherapical agent in applications beyond cancer. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 349-359, 2018.

Current status of selected oral peptide technologies in advanced preclinical development and in clinical trials

The development of oral dosage forms that allows absorption of therapeutic peptides to the systemic circulation is one of the greatest challenges for the pharmaceutical industry. Currently, a number of technologies including either mixtures of penetration enhancers or protease inhibitors and/or nanotechnology-based products are under clinical development. Typically, these formulations are presented in the form of enteric-coated tablets or capsules. Systems undergoing preclinical investigation include further advances in nanotechnology, including intestinal microneedle patches, as well as their combination with regional delivery to the colon. This review critically examines four selected promising oral peptide technologies at preclinical stage and the twelve that have progressed to clinical trials, as indicated in www.clinicaltrials.gov. We examined these technologies under the criteria of peptide selection, formulation design, system components and excipients, intestinal mechanism of action, efficacy in man, and safety issues. The conclusion is that most of the technologies in clinical trials are incremental rather than paradigm-shifting and that even the more clinically advanced oral peptide drugs examples of oral bioavailability appear to yield oral bioavailability values of only 1-2% and are, therefore, only currently suitable for a limited range of peptides.

Oral Bifidobacterium longum expressing alpha-melanocyte-stimulating hormone to fight experimental colitis

The oral delivery of peptides is a highly attractive treatment approach. However, the harsh environment of the gastrointestinal tract limits its application. Here, we utilize Bifidobacterium as a delivery system to orally deliver a potent anti-inflammatory but short duration peptide alpha-melanocyte-stimulating hormone (α-MSH) against experimental colitis. The aim of our study was to facilitate the efficient oral delivery of α-MSH. We designed a vector of pBDMSH and used it to construct a Bifidobacterium longum expressing α-MSH. We then determined the bioactivity of recombinant Bifidobacterium in lipopolysaccharide-induced inflammatory models of HT-29 cells. Finally, we used Bifidobacterium expressing α-MSH against dextran sulfate sodium (DSS)-induced ulcerative colitis mice. Results based on the myeloperoxidase activity, the levels of inflammatory cytokines TNF-α, IL-1β, IL-6, and IL-10 and the histological injury of colon tissue reveal recombinant Bifidobacterium was efficient in attenuating DSS-induced ulcerative colitis, suggesting an alternative way to use Bifidobacterium as a delivery system to deliver α-MSH for DSS-induced ulcerative colitis therapy.

Translating Human Effective Jejunal Intestinal Permeability to Surface-Dependent Intrinsic Permeability: a Pragmatic Method for a More Mechanistic Prediction of Regional Oral Drug Absorption

Regional intestinal effective permeability (P(eff)) values are key for the understanding of drug absorption along the whole length of the human gastrointestinal (GI) tract. The distal regions of the GI tract (i.e. ileum, ascending-transverse colon) represent the main sites for GI absorption when there is incomplete absorption in the upper GI tract, e.g. for modified release formulations. In this work, a new and pragmatic method for the estimation of (passive) intestinal permeability in the different intestinal regions is being proposed, by translating the observed differences in the available mucosal surface area along the human GI tract into corrections of the historical determined jejunal P(eff) values. These new intestinal P(eff) values or "intrinsic" P(eff)(P(eff,int)) were subsequently employed for the prediction of the ileal absorption clearance (CL(abs,ileum)) for a set of structurally diverse compounds. Additionally, the method was combined with a semi-mechanistic absorption PBPK model for the prediction of the fraction absorbed (f(abs)). The results showed that P(eff,int) can successfully be employed for the prediction of the ileal CL(abs) and the f(abs). P(eff,int) also showed to be a robust predictor of the f(abs) when the colonic absorption was allowed in the PBPK model, reducing the overprediction of f(abs) observed for lowly permeable compounds when using the historical P(eff) values. Due to its simplicity, this approach provides a useful alternative for the bottom-up prediction of GI drug absorption, especially when the distal GI tract plays a crucial role for a drug's GI absorption.

Analysis of the impact of controlled release formulations on oral drug absorption, gut wall metabolism and relative bioavailability of CYP3A substrates using a physiologically-based pharmacokinetic model

Controlled release (CR) formulations are usually designed to achieve similar exposure (AUC) levels as the marketed immediate release (IR) formulation. However, the AUC is often lower following CR compared to IR formulations. There are a few exceptions when the CR formulations have shown higher AUC. This study investigated the impact of CR formulations on oral drug absorption and CYP3A4-mediated gut wall metabolism. A review of the current literature on relative bioavailability (Frel) between CR and IR formulations of CYP3A substrates was conducted. This was followed by a systematic analysis to assess the impact of the release characteristics and the drug-specific factors (including metabolism and permeability) on oral bioavailability employing a physiologically-based pharmacokinetic (PBPK) modelling and simulation approach. From the literature review, only three CYP3A4 substrates showed higher Frel when formulated as CR. Several scenarios were investigated using the PBPK approach; in most of them, the oral absorption of CR formulations was lower as compared to the IR formulations. However, for highly permeable compounds that were CYP3A4 substrates the reduction in absorption was compensated by an increase in the fraction that escapes from first pass metabolism in the gut wall (FG), where the magnitude was dependent on CYP3A4 affinity. The systematic simulations of various interplays between different parameters demonstrated that BCS class 1 highly-cleared CYP3A4 substrates can display up to 220% higher relative bioavailability when formulated as CR compared to IR, in agreement with the observed data collected from the literature. The results and methodology of this study can be employed during the formulation development process in order to optimize drug absorption, especially for CYP3A4 substrates.

Enzymatically synthesized dextran nanoparticles and their use as carriers for nutraceuticals

This study evaluated the use of enzymatically synthesized dextran nanoparticles to entrap a hydrophobic nutraceutical, the isoflavone genistein.

Strategies of targeting oral drug delivery systems to the colon and their potential use for the treatment of colorectal cancer

Colorectal cancer (CRC) is the third most common cause of cancer-related death in both men and women. Often, surgical intervention remains the choice in treating CRC. Traditional dosage forms used for treating CRC deliver drug to wanted as well as unwanted sites of drug action resulting in several adverse side effects. Targeted oral drug delivery systems are being investigated to target and deliver chemotherapeutic and chemopreventive agents directly to colon and rectum. Site-specific delivery of a drug to colon increases its concentration at the target site, and thus requires a lower dose with reduced incidence of side effects. The major obstacle to be overcome for successful targeting of drug to colon through oral route is that drug absorption/degradation must be avoided in stomach and small intestine before the dosage form reaches colon. The review includes discussion of physiological factors that must be considered when targeting drugs directly to colorectal region, an outline on drugs used for treatment and prevention of CRC, and a brief description of various types of colon-targeted oral drug delivery systems. The focus is on the assessment of various formulation approaches being investigated for oral colon-specific delivery of drugs used in the treatment and prevention of CRC.

A pH/enzyme-responsive polymer film consisting of Eudragit FS 30 D and arabinoxylane as a potential material formulation for colon-specific drug delivery system

Polymer film based on pH-dependent Eudragit FS 30 D acrylic polymer in association with arabinoxylane, a polysaccharide issued from gum psyllium, was produced by way of solvent casting. Physical-chemical characterization of the polymer film samples was performed by means of thermogravimetry (TGA), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). Furthermore, water-equilibrium swelling index (I(s)) and weight loss of the films in KCl buffer solution of pH 1.2, in KH(2)PO(4) buffer solution of pH 5.0, or in KH(2)PO(4) buffer solution of pH 5.0 consisting of 4% enzyme Pectinex 3X-L (w/v) were also carried out for the film characterization. No chemical interactions between the Eudragit FS 30 D and the arabinoxylane polymer chains were evidenced, thus suggesting that the film-forming polymer structure was obtained from a physical mixture of both polymers. The arabinoxylane-loader films showed a more pronounced weight loss after their immersion in buffer solution containing enzyme Pectinex 3X-L. The introduction of the arabinoxylane makes the film more susceptible to undergo an enzymatic degradation. This meant that the enzyme-dependent propriety issued from the arabinoxylane has been imprinted into the film formulation. This type of polymer film is an interesting system for applications in colon-specific drug delivery system.

Novel salicylazo polymers for colon drug delivery: dissolving polymers by means of bacterial degradation

Novel azo polymers were prepared for colonic drug delivery with a release mechanism based on structural features of azo derivatives designed for rapid bacterial degradation leading to soluble polymers. Two Salicylazo derivatives were prepared and conjugated as side chains at different ratios to methacrylic acid-methyl methacrylate copolymers (Eudragits). The azo compounds were designed to have a hydrophilic and a hydrophobic part on opposite sides of the azo bond. Upon reduction of the azo bonds, the hydrophobic part is released, resulting in a more water soluble polymer. The solubility of the polymeric films was studied relative to Eudragit S known to dissolve toward the end of the small intestine. One of the two azo derivatives prepared gave rise to polymers, which showed reduced solubility relative to Eudragit S. These polymers were subjected to reduction tests in anaerobic rat cecal suspensions by following the release of the hydrophobic product. Reduction rate was found to be rapid, comparable to that of Sulfasalazine. Studies on the azopolymeric films in anaerobic rat cecal suspensions, showed that these polymers dissolve faster than in sterilized suspensions. Solid dosage forms may be coated with these polymers to provide an efficient delivery system to the colon with a rapid release mechanism.

Chitosan-carboxymethyl tamarind kernel powder interpolymer complexation: investigations for colon drug delivery

The present study was aimed at evaluating the possible use of inter polymer complexed (IPC) films of chitosan (CH) and carboxymethyl tamarind kernel powder (CMTKP) for colon release of budesonide. Viscosity analysis of the supernatant liquid obtained after reacting CH and CMTKP in different proportions revealed 40:60 to be the optimum stoichiometric ratio. The FTIR spectra of IPC films formed from 50:50 or 40:60 ratio of CH:CMTKP did not reveal any reduction in the peaks at 1560cm(â1) and 1407cm(â1) after exposure to pH 1.2, suggesting resistance of the interaction between âCOO(â) groups of CMTKP and âNH(3) (+) groups of CH to gastric pH. Tablets containing Avicel pH 102 as diluent and coated to a weight gain of 10%, w/w with aqueous solutions of 40:60 or 50:50 ratio of CH:CMTKP did not release budesonide in pH 1.2 buffer. Histopathology of the rat colon after oral administration of these IPC film coated tablets revealed significantly greater (p<0.05) reduction in TNBS-induced ulcerative colitis as compared to that after administration of uncoated tablets. The Cmax of budesonide achieved after oral administration of these IPC film coated tablets was comparable to that observed after administration of uncoated tablets. The results strongly indicate versatility of CH-CMTKP IPC films to deliver budesonide in the colon.

Colon specific delivery of indomethacin: effect of incorporating pH sensitive polymers in xanthan gum matrix bases

In the present study, an attempt has been made to design controlled release colon-specific formulations of indomethacin by employing pH responsive polymers Eudragit (L100 or S100) in matrix bases comprised of xanthan gum. The prepared tablets were found to be of acceptable quality with low-weight variation and uniform drug content. In vitro release studies indicated rapid swelling and release of significant percentage of drug in the initial period from matrix tablets composed of xanthan gum alone. Addition of pH responsive polymers Eudragit (L100 or S100) to xanthan gum matrix resulted in negligible to very low drug release in the initial period in acidic to weakly acidic medium. Furthermore, with increase in pH of the dissolution medium due to dissolution of Eudragit L100/Eudragit S100 that resulted in the formation of a porous matrix, faster but controlled drug release pattern was observed. Thus, a sigmoidal release pattern was observed from the designed formulations suitable for colonic delivery. Drug release mechanism in all cases was found to be of super case II type, indicating erosion to be the primary cause of drug release. Since the drug release from almost all the matrix bases in the initial phase was negligibly low and followed with controlled release for about 14-16 h, it was concluded that a matrix design of this composition could have potential applications as a colon-specific drug delivery device with additional advantage of easy scale-up and avoidance of all-or-none phenomenon associated with coated colon-specific systems.

Development of time-, pH-, and enzyme-controlled colonic drug delivery using spray-dried chitosan acetate and hydroxypropyl methylcellulose

A colonic drug delivery with a new concept based on a combination of time-, pH-, and enzyme-controlled system was developed. Spray-dried chitosan acetate (CSA) prepared from low molecular weight chitosan was characterized. A combination of CSA and hydroxypropyl methylcellulose (HPMC) was used as new compression-coats for 5-aminosalicylic acid (5-ASA) tablets. Factors affecting in-vitro drug release, i.e. % weight ratio of coating polymers, enzyme activity, pH of media, and excipients in core tablets, were evaluated. The tablets compression-coated with HPMC:CSA at 60:40 and 50:50% weight ratio providing lag times about 5-6h were able to pass through the stomach (stage I, 0.1N HCl) and small intestine (stage II, pH 6.8, Tris-HCl). The delayed release was time- and pH-controlled owing to the swelling with gradual dissolving of CSA and HPMC in 0.1N HCl and the less solubility of CSA at higher pH. After reaching the colon (stage III, pH 5.0, acetate buffer), the dissolution of CSA at low pH triggered the drug release over 90% within 14h. Furthermore, the degradation of CSA by beta-glucosidase in the colonic fluid enhanced the drug release while adding the disintegrant or the osmotic agent in the core tablets would affect the drug release.

Azo compounds in colon-specific drug delivery

Azo compounds have the potential to act as drug carriers that facilitate the selective release of therapeutic agents to the colon, and also to effect the oral administration of those macromolecular drugs that require colon-specific drug delivery. With some further research-driven refinements, these materials may lead to more efficient treatments for local conditions, such as colonic cancer or inflammatory bowel disease. This article provides an overview of the azo-based systems developed to date, identifies the requirements for an ideal carrier, and highlights the directions for further developments in the field of azo group-facilitated colonic delivery.

Chitosan-pentaglycine-phenylboronic acid conjugate: a potential colon-specific platform for calcitonin

Novel drug delivery vehicles based on the biodegradable, mucoadhesive polysaccharide chitosan covalently linked to a boronic acid protease inhibitor have been prepared and characterized. It was anticipated that these conjugates could protect a proteinaceous drug, such as salmon calcitonin, against proteolysis by serine proteases, an obstacle that prevents its oral administration. Specifically, 4-formylphenylboronic acid was linked to chitosan. Three types of conjugates were prepared. In the first, 4-formylphenylboronic acid was directly linked to chitosan. The other two conjugates employed glycylglycine and pentaglycine spacers. Enzyme-inhibition assays toward trypsin and elastase, in the presence of the enzyme chitosanase, demonstrated a strong inhibitory effect for the chitosan-pentaglycine-phenylboronic acid conjugates, while no inhibitory effect could be detected without chitosanase. The chitosan-pentaglycine-phenylboronic acid conjugate with the highest degree of substitution of 4-formylphenylboronic acid was able to decrease the salmon calcitonin degradation rate by trypsin. It is concluded that chitosan-pentaglycine-phenylboronic acid conjugates are a potential multifunctional, colon-specific vehicle for orally administered salmon calcitonin.

Time-controlled oral delivery systems for colon targeting

In recent years, many research efforts have been spent in the achievement of selective delivery of drugs into the colon following oral administration. Indeed, colonic release is regarded as a beneficial approach to the pharmacological treatment or prevention of widespread large bowel pathologies, such as inflammatory bowel disease and adenocarcinoma. In addition, it is extensively explored as a potential means of enhancing the oral bioavailability of peptides, proteins and other biotechnological molecules, which are known to be less prone to enzymatic degradation in the large, rather than in the small, intestine. Based on these premises, several formulation strategies have been attempted in pursuit of colonic release, chiefly including microflora-, pH-, pressure- and time-dependent delivery technologies. In particular, this review is focused on the main design features and release performances of time-controlled devices, which rely on the relative constancy that is observed in the small intestinal transit time of dosage forms.