Synthesis and properties of dextran-nalidixic acid ester as a colon-specific prodrug of nalidixic acid

Dextran-based Drug Delivery Approaches for Lung Diseases: A Review

Respiratory disorders, such as tuberculosis, cystic fibrosis, chronic obstructive pulmonary disease, asthma, lung cancer, and pulmonary inflammation, are among the most prevalent ailments in today's world. Dextran, an exopolysaccharide formed by Leuconostoc mesenteroides (slimeproducing bacteria), and its derivatives are investigated for several therapeutic utilities. Dextranbased drug delivery system can become an innovative strategy in the treatment of several respiratory ailments as it offers numerous advantages, such as mucolytic action, airway hydration, antiinflammatory properties, and radioprotective effect as compared to other polysaccharides. Being biocompatible, flexible hydrophilic nature, biodegradable, tasteless, odourless, non-mutagenic, watersoluble and non-toxic edible polymer, dextran-based drug delivery systems have been explored for a wide range of therapeutic applications, especially in lungs and respiratory diseases. The present article comprehensively discusses various derivatives of dextran with their attributes to be considered for drug delivery and extensive therapeutic benefits, with a special emphasis on the armamentarium of dextran-based formulations for the treatment of respiratory disorders and associated pathological conditions. The information provided will act as a platform for formulation scientists as important considerations in designing therapeutic approaches for lung and respiratory diseases. With an emphasis on lung illnesses, this article will offer an in-depth understanding of dextran-based delivery systems in respiratory illnesses.

Recent developments in natural biopolymer based drug delivery systems

Targeted delivery of drug molecules to diseased sites is a great challenge in pharmaceutical and biomedical sciences. Fabrication of drug delivery systems (DDS) to target and/or diagnose sick cells is an effective means to achieve good therapeutic results along with a minimal toxicological impact on healthy cells. Biopolymers are becoming an important class of materials owing to their biodegradability, good compatibility, non-toxicity, non-immunogenicity, and long blood circulation time and high drug loading ratio for both macros as well as micro-sized drug molecules. This review summarizes the recent trends in biopolymer-based DDS, forecasting their broad future clinical applications. Cellulose chitosan, starch, silk fibroins, collagen, albumin, gelatin, alginate, agar, proteins and peptides have shown potential applications in DDS. A range of synthetic techniques have been reported to design the DDS and are discussed in the current study which is being successfully employed in ocular, dental, transdermal and intranasal delivery systems. Different formulations of DDS are also overviewed in this review article along with synthesis techniques employed for designing the DDS. The possibility of these biopolymer applications points to a new route for creating unique DDS with enhanced therapeutic qualities for scaling up creative formulations up to the clinical level.

Recent development in fabrication and evaluation of phenolic-dietary fiber composites for potential treatment of colonic diseases

Phenolics have been shown by in vitro and animal studies to have multiple pharmacological effects against various colonic diseases. However, their efficacy against colonic diseases, such as inflammatory bowel diseases, Crohn's disease, and colorectal cancer, is significantly compromised due to their chemical instability and susceptibility to modification along the gastrointestinal tract (GIT) before reaching the colonic site. Dietary fibers are promising candidates that can form phenolic-dietary fiber composites (PDC) to carry phenolics to the colon, as they are natural polysaccharides that are non-digestible in the upper intestinal tract but can be partially or fully degradable by gut microbiota in the colon, triggering the release at this targeted site. In addition, soluble and fermentable dietary fibers confer additional health benefits as prebiotics when used in the PDC fabrication, and the possibility of synergistic relationship between phenolics and fibers in alleviating the disease conditions. The functionalities of PDC need to be characterized in terms of their particle characteristics, molecular interactions, release profiles in simulated digestion and colonic fermentation to fully understand the metabolic fate and health benefits. This review examines recent advancements regarding the approaches for fabrication, characterization, and evaluation of PDC in in vitro conditions.

Novel amphiphilic dextran esters with antimicrobial activity

New amphiphilic dextran esters were obtained by polysaccharide functionalization with different substituted 1,2,3-triazoles-4-carboxylic acid via in situ activation with N, N'-carbonyldiimidazole. Nitrogen-containing heterocyclic derivatives were achieved by copper(I)-catalyzed cycloaddition reaction between organic azides and ethyl propiolate. Structural characteristics of the compounds were studied by elemental analysis, Fourier transform infrared and nuclear magnetic resonance spectroscopy (¹H and ¹³C-NMR). Thermogravimetric analysis, differential scanning calorimetry and wide-angle X-ray diffraction were used for esters characterization. Properties of polymeric self-associates, formed in aqueous solution, were studied by dynamic light scattering and transmission electron microscopy. The critical aggregation concentration values for dextran esters, determined by fluorescence spectroscopy, were in the range of 4.1-9.5 mg/dL. Antimicrobial activity, investigated for some of the polymers by disc-diffusion method, pointed out that polysaccharide esters were active.

Conjugation of metronidazole with dextran: a potential pharmaceutical strategy to control colonic distribution of the anti-amebic drug susceptible to metabolism by colonic microbes

Metronidazole (MTDZ), the drug of choice for the treatment of protozoal infections such as luminal amebiasis, is highly susceptible to colonic metabolism, which may hinder its conversion from a colon-specific prodrug to an effective anti-amebic agent targeting the entire large intestine. Thus, in an attempt to control the colonic distribution of the drug, a polymeric colon-specific prodrug, MTDZ conjugated to dextran via a succinate linker (Dex-SA-MTDZ), was designed. Upon treatment with dextranase for 8 h, the degree of Dex-SA-MTDZ depolymerization (%) with a degree of substitution (mg of MTDZ bound in 100 mg of Dex-SA-MTDZ) of 7, 17, and 30 was 72, 38, and 8, respectively, while that of dextran was 85. Depolymerization of Dex-SA-MTDZ was found to be necessary for the release of MTDZ, because dextranase pretreatment ensures that de-esterification occurs between MTDZ and the dextran backbone. In parallel, Dex-SA-MTDZ with a degree of substitution of 17 was found not to release MTDZ upon incubation with the contents of the small intestine and stomach of rats, but it released MTDZ when incubated with rat cecal contents (including microbial dextranases). Moreover, Dex-SA-MTDZ exhibited prolonged release of MTDZ, which contrasts with drug release by small molecular colon-specific prodrugs, MTDZ sulfate and N-nicotinoyl-2-{2-(2-methyl-5-nitroimidazol-1-yl)ethyloxy}-d,l-glycine. These prodrugs were eliminated very rapidly, and no MTDZ was detected in the cecal contents. Consistent with these in vitro results, we found that oral gavage of Dex-SA-MTDZ delivered MTDZ (as MTDZ conjugated to [depolymerized] dextran) to the distal colon. However, upon oral gavage of the small molecular prodrugs, no prodrugs were detected in the distal colon. Collectively, these data suggest that dextran conjugation is a potential pharmaceutical strategy to control the colonic distribution of drugs susceptible to colonic microbial metabolism.

Synthesis, controlled release and antibacterial studies of nalidixic acid–zinc hydroxide nitrate nanocomposites

Nalidixic acid intercalated zinc hydroxide nitrate is suitable for a controlled-release formulation and the resultant nanocomposite is an effective antibacterial agent.

Dextran Carrier Macromolecules for Colon-specific Delivery of 5-Aminosalicylic Acid

Present manuscript describes the sustained and targeted delivery of 5-aminosalicylic acid to the distal ileum and proximal colon, using dextran (40 kDa) as a carrier for targeting 5-aminosalicylic acid at the colonic site by attaching p-aminobenzoic acid and benzoic acid as linkers. Prepared conjugate were characterized by UV, HPLC, FT-IR, and ¹H NMR. The degree of substitution was estimated by complete hydrolysis of conjugates in borate buffer and in vitro hydrolysis study of conjugates was performed in different biological media. It was observed that 5-aminosalicylic acid alone have produced high incidence of gastric ulcer with high ulcer index whereas lower ulcer index was found for the dextran conjugates of 5-aminosalicylic acid. The release pattern of conjugates in 3% w/v rat caecal content was confirmed the colon specificity of 5-aminosalicylic acid conjugates.

Microencapsulation of budesonide with dextran by spray drying technique for colon-targeted delivery: an in vitro/in vivo evaluation in induced colitis in rat

The aim of this study was developing colon targeted-delivery of budesonide for ulcerative colitis. Microcapsules were prepared using spray drying technique by different drug-to-dextran ratios and three molecular weights (MWs) of polymer. Differential scanning calorimetry, X-ray diffraction (XRD), drug release and loading efficiency of microcapsules were studied. In vivo efficacy of the selected formulation prepared by 1 : 10 drug-to-polymer ratio and dextran with MW 500 000 (D10M500) against acetic acid-induced colitis in rats was evaluated and compared to the control and reference groups (mesalasine and budesonide suspensions). The results showed that D10M500 microcapsules could target the drug to colon and its efficacy in reducing macroscopic damage score was higher than mesalasine suspension. Treatment with D10M500 decreased the scores of crypt damage and total colitis significantly compared to the control group which just received the vehicle and the groups treated with mesalasine and budesonide suspension which could not reduce the colitis parameters significantly.

Polysaccharides for Colon Targeted Drug Delivery

Colon targeted drug delivery has the potential to deliver bioactive agents for the treatment of a variety of colonic diseases and to deliver proteins and peptides to the colon for their systemic absorption. Various strategies, currently available to target the release of drugs to colon, include formation of prodrug, coating of pH-sensitive polymers, use of colon-specific biodegradable polymers, timed released systems, osmotic systems, and pressure controlled drug delivery systems. Among the different approaches to achieve targeted drug release to the colon, the use of polymers especially biodegradable by colonic bacteria holds great promise. Polysaccharidases are bacterial enzymes that are available in sufficient quantity to be exploited in colon targeting of drugs. Based on this approach, various polysaccharides have been investigated for colon-specific drug release. These polysaccharides include pectin, guar gum, amylose, inulin, dextran, chitosan, and chondroitin sulphate. This family of natural polymers has an appeal to drug delivery as it is comprised of polymers with a large number of derivatizable groups, a wide range of molecular weights, varying chemical compositions, and, for the most part, low toxicity and biodegradability yet high stability. The most favorable property of these materials is their approval as pharmaceutical excipients.

Degradation Kinetics of Fluorouracil-Acetic-Acid-Dextran Conjugate in Aqueous Solution

The degradation kinetics of fluorouracil-acetic-acid-dextran conjugate (FUAC-dextran) was investigated in various buffer solutions with different pH value and physiological saline solution at 60 degrees C and 37 degrees C, respectively. The hydrolytic reaction displayed pseudo-first-order degradation kinetics. Hydrolytic rate constant obtained was the function of pH value and independent of species of buffering agents. The smallest rate constant was observed at pH round 3.00. The activation energy of the hydrolytic reaction was estimated from Arrhenius equation as 88.73 +/- 6.00 kJ.mol-1. The special base catalytic degradation of the conjugate was observed from acidic to slight alkaline condition and the special base catalytic rate constants were calculated. The conjugate was more stable in physiological saline than that in buffer solution at pH 7.00 or 9.00 at 37 degrees C. The results revealed that the conjugate was stable in acidic condition and will degrade in alkaline condition.

Microbially triggered drug delivery to the colon

Increasing acceptance of protein- and peptide-based drugs necessitates an investigation into the suitability of various sites for their administration. Colon is being investigated for delivery of such molecules. Colon-specific drug delivery is designed to target drug molecules specifically to this area. Development of site-specific delivery systems may exploit a specific property of the target site for drug activation/release. The gastrointestinal tract is inhabited by over 400 bacterial species, each having a specific niche in the tract. Colon, the distal part of the intestine is inhabited by a large variety of gram negative microflora. This flora produces a vast number of enzymes which are being exploited for formulation of colon-specific drug delivery systems. A number of microbially activated systems for colon-specific drug delivery are being evaluated. These include prodrugs and synthetic or natural polymer-based delivery systems. This article aims at reviewing the various microbially activated drug delivery systems for colon-specific drug delivery with specific reference to the microflora of the various segments of the gastrointestinal tract and their role in targeting drug delivery to the colon.