A glucocorticoid prodrug facilitates normal mucosal function in rat colitis without adrenal suppression

Glucocorticoids-based prodrug design: Current strategies and research progress

Attributing to their broad pharmacological effects encompassing anti-inflammation, antitoxin, and immunosuppression, glucocorticoids (GCs) are extensively utilized in the clinic for the treatment of diverse diseases such as lupus erythematosus, nephritis, arthritis, ulcerative colitis, asthma, keratitis, macular edema, and leukemia. However, long-term use often causes undesirable side effects, including metabolic disorders-induced Cushing's syndrome (buffalo back, full moon face, hyperglycemia, etc.), osteoporosis, aggravated infection, psychosis, glaucoma, and cataract. These notorious side effects seriously compromise patients' quality of life, especially in patients with chronic diseases. Therefore, glucocorticoid-based advanced drug delivery systems for reducing adverse effects have received extensive attention. Among them, prodrugs have the advantages of low investment, low risk, and high success rate, making them a promising strategy. In this review, we propose the strategies for the design and summarize current research progress of glucocorticoid-based prodrugs in recent decades, including polymer-based prodrugs, dendrimer-based prodrugs, antibody-drug conjugates, peptide-drug conjugates, carbohydrate-based prodrugs, aliphatic acid-based prodrugs and so on. Besides, we also raise issues that need to be focused on during the development of glucocorticoid-based prodrugs. This review is expected to be helpful for the research and development of novel GCs and prodrugs.

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.

Determination of methylprednisolone acetate in biological fluids at gold nanoparticles modified ITO electrode

The electrochemical behavior of a corticosteroid methylprednisolone (MP), used for doping, has been studied at gold nanoparticles modified indium tin oxide (nanoAu/ITO) electrode. The nanoAu/ITO electrode exhibited an effective catalytic response towards its oxidation and lowered its oxidation potential by approximately 127 mV when compared with bare ITO electrode. Oxidation of MP has been carried out in phosphate containing electrolyte in the pH range 2.13-10.00 and a well-defined oxidation peak was noticed. Linear concentration curves are obtained over the concentration range 0.01-1.0 microM with a detection limit of 2.68 x 10(-7)M at nanoAu/ITO electrode. A diffusion coefficient of 2.36 x 10(-6)cm(2)/s is calculated for MP using chronoamperometry. The proposed method is effectively applied to detect the concentration of MP in pharmaceutical formulations and human blood plasma and urine samples. A comparison of MP concentration determined in blood plasma and urine by the proposed method and GC/MS indicated that the results are essentially similar. It is believed that the method will be useful in determining this drug in case of doping.

Novel approaches to inflammatory bowel disease

Ulcerative colitis and Crohn's disease, collectively known as inflammatory bowel disease (IBD), are chronic, spontaneously relapsing disorders of unknown cause. These diseases appear to be immunologically mediated and have genetic and environmental influences. Although the cause of these diseases remains obscure, the pathogenesis of chronic intestinal inflammation is becoming clearer, due to improved animal models of enterocolitis and important advances in immunological techniques. Traditional therapy for IBD, although helping to induce and maintain disease remission, does little to alter the underlying fundamental disease process. New IBD therapy has not developed significantly over the past twenty years and includes 5-aminosalicylic acid preparations, corticosteroids and immunomodulatory agents, such as azathioprine, 6-mercaptopurine and methotrexate. There is, therefore, a need for new, specific disease-modifying therapy and the development of such therapy has been hastened by a greater understanding of the pathophysiology of IBD. This review examines the most recent novel therapies for IBD, with specific emphasis on immunomodulatory and novel anti-inflammatory therapies. Recent clinical trials are reviewed, and the potential advances and clinical impact that these novel agents may provide are discussed.

Polysaccharides in colon-specific drug delivery

Natural polysaccharides are now extensively used for the development of solid dosage forms for delivery of drug to the colon. The rationale for the development of a polysaccharide based delivery system for colon is the presence of large amounts of polysaccharidases in the human colon as the colon is inhabited by a large number and variety of bacteria which secrete many enzymes e.g. beta-D-glucosidase, beta-D-galactosidase, amylase, pectinase, xylanase, beta-D-xylosidase, dextranase, etc. Various major approaches utilizing polysaccharides for colon-specific delivery are fermentable coating of the drug core, embedding of the drug in biodegradable matrix, formulation of drug-saccharide conjugate (prodrugs). A large number of polysaccharides have already been studied for their potential as colon-specific drug carrier systems, such as chitosan, pectin, chondroitin sulphate, cyclodextrin, dextrans, guar gum, inulin, amylose and locust bean gum. Recent efforts and approaches exploiting these polysaccharides in colon-specific drug delivery are discussed.

["Targeted delivery" in the gastrointestinal tract]

Drug delivery to the intestine has become attractive to researchers with the main interest in the delivery of peptide drugs to the large intestine and the treatment of colonic diseases. There are currently 4 strategies that are pursued to reach colon specificity: 1. by relying on the pH difference between the small and the large intestine; 2. by exploiting the enzymatic activity of the colonic microflora; 3. by relying on the relatively constant small intestinal transit time and 4. by taking advantage of the increase of the luminal pressure in the colon due to strong peristaltic waves. Drug delivery to the small intestine may be achieved by pH-controlled and time-controlled drug release mechanisms. Diffusion-controlled systems allow drug delivery over the entire gastrointestinal tract.

Review article: issues in oral administration of locally acting glucocorticosteroids for treatment of inflammatory bowel disease

Inflammatory bowel diseases are treated in some cases by local administration of anti-inflammatory drugs. Local delivery of drugs in the colon following oral administration may lead to improved efficacy/side-effect profiles and may improve patient compliance. This review covers a number of issues important in the design of oral delivery systems of glucocorticosteroids for local therapy of colonic inflammation. The choice of specific glucocorticosteroids is based on the drug's physicochemical and pharmacological properties. The conditions under which an orally administered glucocorticosteroid (or other drug) must be delivered to treat ulcerative colitis are also discussed. These conditions include variations in local pH, transit throughout the gastrointestinal tract, the potential role of gut microflora, and drug dissolution in both the healthy and diseased large intestine. The effective delivery of topically-active glucocorticosteroids in ulcerative colitis and Crohn's colitis patients is complex, but if successful could improve their usefulness.

Colonic delivery of dexamethasone: a pharmacoscintigraphic evaluation

BACKGROUND

Colonic delivery of corticosteroids may reduce the side-effects commonly associated with their use. Therefore, we tested the ability of the naturally occurring polysaccharide guar gum to deliver a corticosteroid, dexamethasone, to the colon using pharmacoscintigraphy. Guar gum is metabolized in the colon by resident bacterial enzymes to trigger drug release.

MATERIALS

Each subject (eight per group, parallel study design) was administered one of four dexamethasone (9 mg) tablet formulations, radiolabelled with 153Sm using neutron activation, under fasted conditions. One formulation was designed to release drug rapidly following ingestion while the other three formulations were designed to delay release of dexamethasone to varying degrees. Progression of the formulations down the gastrointestinal tract was followed by gamma scintigraphy. Serum concentrations were measured over time to relate disintegration profiles of the tablets with pharmacokinetic observations.

RESULTS

The immediate release formulation disintegrated in the stomach, on average, within 20 min of dosing. One of the three delayed release preparations (CD1) began to disintegrate in the small intestine 1.7 +/- 1.0 h after dosing. The second and third delayed release preparations (CD2 and CD3) did not begin to disintegrate until 5.8 +/- 2.3 and 3.6 +/- 1.6 h after dosing, respectively. All three colonic delivery preparations completely disintegrated in the colon ranging from 7.8 +/- 2.7 h (CD1) to 12.4 +/- 3.2 h (CD2) following oral administration. Pharmacoscintigraphic data indicated that 72-82% of the dexamethasone was delivered into the colon although not all the dexamethasone delivered into the colon was absorbed.

CONCLUSIONS

Simple guar gum formulations are capable of delivering the corticosteroid dexamethasone to the colon of normal subjects. Locally delivered corticosteroids may be useful in the treatment of ulcerative colitis and Crohn's disease. Pharmacoscintigraphic evaluation is a useful method to discriminate between the in vivo behaviour of colonic delivery systems.

Increased permeability occurs in rat ileum following induction of pan-colitis

Acetic acid-induced pan colitis in rats leads not only to colonic injury but also to a bystander ileal injury, characterized by decreased fluid and electrolyte absorption without associated histological injury or infiltration of inflammatory cells. To examine the nature of this decreased ileal fluid and electrolyte absorption, we measured effect of acetic acid-induced pancolitis on ileal transmural sodium and chloride transport, as well as on ileal permeability to mannitol and inulin on mucosal sheets mounted in Ussing chambers. In addition, ileal tight junctional morphology was assessed by electron microscopy. In colitic animals, ileal serosal-to-mucosal sodium and chloride transmural fluxes were increased (P<0.05); compatible with the observed decrease in net fluid absorption. Mannitol and inulin ileal serosal-to-mucosal and mucosal-to-serosal ileal fluxes were similarly increased (P<0.05), suggesting that an increase in ileal permeability occurred during acetic acid-induced pancolitis. This increase in ileal permeability was not accompanied by changes in tight junctional ultrastructure. These results suggest that: (1) the decrease in ileal fluid and electrolyte absorption seen during acetic acid-induced rat pancolitis occurred in parallel with a rise in both transcellular and paracellular permeability, and (2) the ileal permeability changes were not accompanied by structural changes.

Molecular cloning of mouse intestinal trefoil factor and its expression during goblet cell changes

A cDNA encoding mouse intestinal trefoil factor (mITF) was successfully cloned and sequenced from the small intestine of C57BL/6 mouse by using the combination of reverse transcription-PCR and rapid amplification of cDNA ends methods. The gene was, similar to rat and human ITFs, mainly expressed in the small and large intestine. The mITF expression was up-regulated during the recovery phase after depletion of goblet cells in acetic acid-induced colitis. On the other hand, the expression in the jejunum was not altered, while goblet cell hyperplasia was induced by Nippostrongylus brasiliensis infection. These results suggest that the mITF expression did not simply correlate with the number of goblet cells. The mITF may play an important role in the maintenance and repair of mucosal function of the rectum. Additionally, the mITF in the jejunum may play a role in alteration of the physicochemical nature of goblet cell mucins, thereby affecting the establishment of intestinal helminths.

In vivo pharmacokinetic study for the assessment of poly(L-aspartic acid) as a drug carrier for colon-specific drug delivery

Glucocorticoids remain one of the mainstays of therapy for acute attacks of inflammatory bowel disease despite systemic side effects that limit their use. Prodrugs that selectively deliver glucocorticoids to the colon may lower the required dose and side effects. Because enzymes of gut microflora are able to cleave certain peptide and ester bonds, the ability of an ester prodrug consisting of dexamethasone (DX) as model drug and poly(L-aspartic acid) (weight-average mol wt = 30,000) as drug carrier was investigated to selectively release the drug in the large intestine. Prodrug and drug solutions (1.18 mg DX/ml DMSO) were administered to two groups of male Sprague-Dawley rats by intragastric infusion using an ALZET osmotic pump. All rats were infused for sufficient time to achieve steady state in both blood and GI-tract tissues. DX concentrations in blood and tissue samples were measured with HPLC. The steady state DX concentrations at these sites were used to calculate a drug delivery index (DDI). DX blood concentrations were significantly lower (p < 0.05) after intragastric administration of the prodrug. Moreover, prodrug administration resulted in significantly higher DX concentrations in the cecum and colon mucosa and the cecum muscle tissue compared to DX administration (p < 0.05). The prodrug led to an increase of the DX concentration in the large intestinal tissues by factors of 1.3-2.0 and to an 1.3-fold decrease of DX blood concentrations. Thus, this novel conjugate should both increase efficacy and reduce toxicity to some extent.

Colonic delivery of dexamethasone from a prodrug accelerates healing of colitis in rats without adrenal suppression

BACKGROUND/AIMS

Dexamethasone-beta-D-glucuronide, a colon-specific prodrug of dexamethasone, may be useful in the treatment of ulcerative colitis and Crohn's colitis. The aim of this study was to evaluate colonic delivery and efficacy of this prodrug in the rat.

METHODS

Distribution of dexamethasone in luminal contents and tissues of the gastrointestinal tract and in plasma was measured after oral administration of dexamethasone-beta-D-glucuronide or free dexamethasone. Efficacy of the prodrug and free drug was tested in an acetic acid-induced rat colitis model. Healing of induced colitis was assessed by measuring net intestinal fluid absorption, colonic surface area of ulceration, histology, and myeloperoxidase activity. Glucocorticosteroid toxicity was evaluated with serum corticosterone and plasma adrenocorticotropic hormone levels.

RESULTS

The drug delivery index (a measure of relative targeting efficiency) was 6.7 and 8.6 in the cecal and colonic mucosa, respectively. The prodrug was significantly more potent than free drug in improving net colonic fluid absorption while significantly reducing surface area of ulceration and histological grade in colitic rats. Treatment with free dexamethasone significantly reduced serum corticosterone levels to subnormal levels, and treatment with the prodrug maintained serum corticosterone and plasma adrenocorticotropic hormone levels near control levels.

CONCLUSIONS

The prodrug dexamethasone-beta-D-glucuronide delivers efficacious amounts of dexamethasone to the large intestine from lower doses than free dexamethasone.

A budesonide prodrug accelerates treatment of colitis in rats

Although oral glucocorticoids are the treatment of choice for moderate to severe ulcerative pancolitis, their systemic side effects and adrenal suppression account for considerable morbidity. An oral glucocorticoid-conjugate (prodrug), budesonide-beta-D-glucuronide, which is not absorbed in the small intestine but is hydrolysed by colonic bacterial and mucosal beta-glucuronidase to release free budesonide into the colon was synthesised. The objective of this study was to compare treatment with budesonide-beta-D-glucuronide with treatment with free budesonide by examining: (1) the healing of experimental colitis and (2) the extent of adrenal suppression. Pancolitis was induced with 4% acetic acid. Animals were then randomised to receive oral therapy for 72 hours with (1) budesonide-beta-D-glucuronide, (2) free budesonide, or (3) vehicle. Drug efficacy and colitic healing was determined by measuring gross colonic ulceration, myeloperoxidase activity, and in vivo colonic fluid absorption. Adrenal suppression was determined by measuring plasma adrenocorticotrophic hormone and serum corticosterone. Vehicle-treated colitis animals had gross ulceration, increased myeloperoxidase activity, and net colonic fluid secretion. Treatment with oral budesonide-beta-D-glucuronide accelerated all measures of colitis healing at a fourfold lower dose than did free budesonide. Furthermore, treatment with budesonide-beta-D-glucuronide did not result in adrenal suppression whereas free budesonide treatment did. A newly synthesised orally administered glucocorticoid-conjugate accelerates colitis healing with limited adrenal suppression. Development of an orally administered colon-specific steroid delivery system represents a novel approach to inflammatory bowel disease treatment.