The relationship between mucoadhesive polymers and surface coating in tablets for the controlled colonic delivery of a poorly water-soluble drug.

BACKGROUND: The mucoadhesive polymers play an important role in targeted and controlled drug delivery. OBJECTIVES: This study aimed to investigate the drug release behaviour and interpret the role of mucoadhesive polymers involved in the coating layer of mucoadhesive tablets for the sustained release of a poorly water-soluble drug. METHODS: A solid dispersion of prednisolone and zein was used in the core tablets created with two mucoadhesive polymers, which included Carbopol 940 and hydroxypropyl methylcellulose K4M. In addition, the properties of a single-layer coating, created from the combination of zein and Kollicoat MAE 100P to delay release through the upper parts of the gastrointestinal tract, were investigated in the presence of the above mucoadhesive polymers; these properties included drug dissolution, mucoadhesion, surface morphology, swelling and erosion. RESULTS: The mucoadhesive polymer concentrations and types were integrated not only into the core tablets through a swelling/erosion mechanism but also into the surface polymer coatings for controlled drug release. HPMC was preferred in the formulations due to the ability to form pores on the surface coating, allowing water uptake so that the coating could control drug release for a later stage via a swelling/erosion mechanism. CONCLUSION: The proposed mechanism determined in this project could be beneficial in the selection of polymers for applications targeting the colon with coated mucoadhesive tablets. Graphical abstract.

Optimization of the synthesis of a key intermediate for the preparation of glucocorticoids.

A short and efficient synthesis, based on a one-step double elimination, of a key intermediate in the synthesis of various glucocorticosteroids has been developed. This method can be carried out on large scale for further industrial applications. The synthesis allowed us to identify a novel prednisolone derivative 10 and its anti-inflammatory activity was determined in an in vivo model of inflammation. In order to understand the regioselectivity of the double elimination under various conditions, mechanistic studies were undertaken and confirmed the experimental results. We also propose a mechanism for the formation of the new steroid 10 studied by molecular modeling.

Chemical Pathways of Corticosteroids, Industrial Synthesis from Sapogenins.

Corticosteroids are products of high industrial and commercial importance. There are dozens of different synthesis published for all of them. Some are coming from academia and some from industry. Here, industrial processes for the synthesis of prednisone, prednisolone, hydrocortisone, dexamethasone, betamethasone, and methylprednisolone are described. The starting material is diosgenin and the desired molecules are reached due to a good combination of chemistry and biotechnology that was developed along the second part of the twentieth century.

Stereoisomeric Prodrugs to Improve Corneal Absorption of Prednisolone: Synthesis and In Vitro Evaluation.

A series of stereoisomeric prodrugs have been designed to examine efficacy in generating higher corneal absorption relative to prednisolone. Prodrugs have been studied and identified with LC/MS/MS and NMR analyses. Prodrugs have been characterized for aqueous solubility, buffer stability, and cytotoxicity. Cellular uptake and permeability studies have been conducted across MDCK-MDR1 cells to determine prodrug affinity towards P-glycoprotein (P-gp) and peptide transporters. Enzyme-mediated degradation of prodrugs has been determined using Statens Seruminstitut rabbit cornea (SIRC) cell homogenates. Prodrugs exhibited higher aqueous solubility relative to prednisolone. Prodrugs circumvented P-gp-mediated cellular efflux and were recognized by peptide transporters. Prodrugs (DP, DDP) produced with D-isomers (D-valine) were significantly stable against both chemical and enzymatic hydrolyses. The order of degradation rate constants observed in chemical and enzymatic hydrolyses were in the same order, i.e., L-valine-L-valine-prednisolone (LLP) > L-valine-D-valine-prednisolone (LDP) > D-valine-L-valine-prednisolone (DLP) > D-valine-D-valine-prednisolone (DDP). Results obtained from this study clearly suggest that stereoisomeric prodrug approach is an effective strategy to overcome P-gp-mediated efflux and improve transcorneal permeability of prednisolone following topical administration.

Design, synthesis, and local anti-inflammatory activity of 17ß-carboxamide derivatives of glucocorticoids.

Molecular docking studies were performed on 18 17ß-carboxamide steroids in order to select compounds with potential local anti-inflammatory activity. These derivatives are amides of cortienic acids (obtained from hydrocortisone, prednisolone, and methylprednisolone) with methyl or ethyl esters of six amino acids. Interactions with the glucocorticoid receptor (GR), binding energies and ligand efficiency values of these compounds were compared with dexamethasone and cortienic acid obtained from prednisolone (inactive metabolite). On the basis of molecular docking studies, seven compounds were selected and their binding affinities for the GR were predicted by use of the exponential model created in this study. Subsequently, selected compounds were synthesized in good yields by use of modified N,N'-dicyclohexylcarbodiimide (DCC)/1-hydroxybenzotriazole (HOBt) coupling procedure. Finally, the local anti-inflammatory activity of the synthesized compounds was examined by use of the croton oil-induced ear edema test. In vivo evaluation of systemic side effects as well as in silico prediction of metabolism were performed on the derivative with the best local anti-inflammatory activity. The combination of molecular docking studies and the exponential model for the GR binding affinity prediction could be used as an in silico tool for the rational design of novel 17ß-carboxamide steroids with potentially better biological profile than dexamethasone.

Expedient synthesis of 17α,21-dihydroxy-9ß,11ß-epoxy-16α-methylpregna-1,4-diene-3,20-dione 21-acetate from prednisolone utilising a novel Mattox rearrangement.

A six step transformation of prednisolone to 17α,21-dihydroxy-9ß,11ß-epoxy-16α-amethylpregna-1,4-diene-3,20-dione 21-acetate has been achieved in 13% unoptimised yield. Novel conditions for effecting a Mattox rearrangement and double dehydration of prednisolone were identified. Enhanced knowledge on the oxidation of silyl Δ(19,20)-enol ethers and structural factors that impact the success of the oxidation are also presented.

Low molecular weight hydroxyethyl chitosan-prednisolone conjugate for renal targeting therapy: synthesis, characterization and in vivo studies.

To further evaluate the potential renal targeting profile of low molecular weight hydroxyethyl chitosan (LMWHC) we developed before, prednisolone (Pre) was conjugated with LMWHC by EDC/NHS chemistry to improve the therapeutic effect of glucocorticoids in vivo. The conjugate was denoted as LMWHC-Pre. The prednisolone content of the conjugate was determined by reversed-phase high-performance liquid chromatography (HPLC) with Kromasil C18 column. The results showed that the average coupling degree of prednisolone to LMWHC was 76.7±3.2 µg·mg(-1). The stability and physicochemical characterization of LMWHC-Pre under various conditions were also investigated. To study the fate of LMWHC-Pre after intravenous (i.v.) administration, fluorescein isothiocyanate (FITC) was coupled to the conjugate to explore the renal targeting efficacy. The in vivo results showed that significant amount of the conjugate was accumulated into the kidneys while negligible signal could be detected when the mixture of FITC-LMWHC and prednisolone was co-administered. The preliminary pharmacodynamics study of LMWHC-Pre showed that the conjugate could effectively alleviate the nephrotic syndrome of rats induced by minimal change nephrosis (MCN) model. Toxicity study also revealed that there was little glucocorticoid-induced osteoporosis by LMWHC-Pre upon 20 days of treatment. From this study, LMWHC-Pre may be employed as an effective potential drug candidate for the treatment of chronic renal disease.

Prednisolone-glucose derivative conjugate: synthesis, biodistribution and pharmacodynamics evaluation.

This study was aimed at synthesizing and evaluating a prednisolone-glucose derivative conjugate (PDG) that was expected to increase renal biodistribution without affecting pharmacological action and to decrease the systemic side effects of prednisolone. The PDG was designed and synthesized by tethering 6-amino-6-deoxy-D-glucose (a D-glucose derivative) to prednisolone and its chemical structure was confirmed by (1) H NMR, (13) C NMR, and LC-MS. This conjugate was then subjected to in vitro and in vivo evaluation like stability studies, biological distribution, pharmacodynamics, and systemic side effects studies. In these studies, PDG not only showed significant enhancement of renal target efficiency with high values of relative uptake efficiency (RE, 24.1), concentration efficiency (CE, 8.6), and kidney targeting index (KTI, 16.3), but retained the curative potency against minimal change nephrosis (MCN). In the systemic side effects study, no osteoporosis was observed in rats after the administration of PDG for 20 days, which exhibited limited side effects. Conclusively, our findings showed a pharmacologically active conjugate with the characteristics of renal targeting and limited systemic side effects. The results implied the potential of PDG as a promising therapeutic in the treatment of renal diseases.

Recent advances in the design and synthesis of prednisolone and methylprednisolone conjugates.

Glucocorticoid drugs are commonly used in the treatment of many acute and chronic inflammatory diseases. However, application of these steroids is limited because of their physico-chemical properties, such as very low water solubility. Glucocorticoids also exhibit serious adverse side effects. Therefore, new drug delivery systems are being developed, with the aim of improving the physicochemical properties of glucocorticoids while avoiding undesirable side effects associated with systemic administration. Here we discuss the design and synthesis of conjugates of prednisolone (PD), methylprednisolone (MPD) and similar glucocorticoids. In this review, possibilities for targeting inflammatory sites, and reducing dosages and administration frequency through increasing drug circulation time are discussed. This review summarises synthetic approaches for the preparation of covalent conjugates, which are divided into two groups: low molecular weight conjugates and polymeric conjugates. These two groups are further divided into subgroups based on the chemical structure of the conjugates. Published results from in vitro and in vivo testing of prepared conjugates are also discussed.

Synthesis, transport and mechanism of a type I prodrug: L-carnitine ester of prednisolone.

Aerosol glucocorticoid medications have become more and more important in treating BA (bronchial asthma). Although these agents are dosed to directly target airway inflammation, adrenocortical suppression and other systematic effects are still seen. To tackle this problem in a novel way, two L-carnitine ester derivatives of prednisolone (as the model drug), namely, PDC and PDSC, were synthesized to increase the absorption of prednisolone across the human bronchial epithelial BEAS-2B cells by the organic cation/carnitine transporter OCTN2 (SLC22A5) and then to slowly and intracellularly release prednisolone. The transport of prednisolone, PDC and PDSC into the human bronchial epithelial BEAS-2B cells was in the order PDSC > prednisolone > PDC at 37 °C. It was found that PDSC displayed 1.79-fold increase of uptake compared to prednisolone. Transport of PDSC by BEAS-2B was temperature-, time-, and Na(+)-dependent and saturable, with an apparent K(m) value of 329.74 µM, suggesting the involvement of carrier-mediated uptake. An RT-PCR study showed that organic cation/carnitine transporters OCTN1 and OCTN2 are expressed in BEAS-2B cells, but little in HEK293T cells. The order of uptake by HEK293T was prednisolone > PDC > PDSC. In addition, the inhibitory effects of organic cations such as L-carnitine, ergothioneine, TEA(+) and ipratropium on PDSC uptake in BEAS-2B cells were in the order L-carnitine > ipratropium > TEA(+) > ergothioneine, whereas their inhibitory effects on PDSC uptake in HEK293T cells were negligible. Finally, in vitro LPS-induced IL-6 production from BEAS-2B was more and longer suppressed by PDSC than prednisolone and PDC. All of these results suggested PDSC may be an attractive candidate for asthma treatment.

Prednisolone-α-cyclodextrin-star poly(ethylene glycol) polypseudorotaxane with delayed pH-sensitivity as a targeted drug delivery system.

The acylation of prednisolone 20-hydrazone with star poly(ethylene glycol) tetracarboxylic acid (M = 20,000) has been used to prepare the corresponding pH-sensitive conjugate. With α-cyclodextrin, this conjugate forms a polypseudorotaxane, which was characterised by means of (1)H NMR spectra, powder X-ray diffraction patterns and STM microscopy. The rate of acid-catalysed hydrolysis of the conjugate was studied under in vitro conditions in model media of hydrochloric acid solutions, phosphate and acetate buffers (pH 2-5.8). The acid-catalysed hydrolysis (at pH 2) of the polypseudorotaxane was ca 3.5 times slower than that of the original conjugate. After 1h in this medium, 86% of the covalently attached prednisolone remained unchanged. The prepared polypseudorotaxane represents a promising peroral transport system of prednisolone with a pH-sensitive linker with delayed acid-catalysed hydrolysis thanks to protection at the molecular level using α-cyclodextrin.

Development of a positively charged prednicarbate nanoemulsion.

A physically and chemically stable positively charged prednicarbate nanoemulsion was developed as a carrier system for the treatment of atopic dermatitis. Phytosphingosine was used to obtain the positive charge and also because of its supportive properties for the restoration of damaged skin. As production method high pressure homogenization was employed. The optimal concentrations of phytosphingosine, the oil phase, and the emulsifiers were investigated. The production was optimized by investigating the influence of homogenization cycles, homogenization pressure, production temperature and type of homogenizer with respect to particle size, physical stability of the emulsions and chemical stability of prednicarbate. From the results the best formulation and the most appropriate production parameters were identified. In addition it could be shown that during high pressure homogenization the drug is relocated from the inner oil phase of the emulsion towards the stabilizer layer, which could be shown by an increase in chemical stability of prednicarbate. The efficiency of incorporation is influenced by the energy input during homogenization (e.g. number of homogenization cycles) but also by the production temperature. It was found that the nanoemulsions should be produced at elevated temperatures, with low homogenization pressures but higher numbers of homogenization cycles (e.g. 300 bar and 10 cycles). The results prove that the efficiency of high pressure homogenization should not only be judged by investigating the particle size and the physical stability of the emulsions alone, but also by assessing the chemical stability of the incorporated drug.

Aspirin and steroids: new mechanistic findings and avenues for drug discovery.

The inflammatory response is a life-saving protective process mounted by the body to overcome pathogen infection and injury; however, in chronic inflammatory pathologies, this response can become deregulated. Aspirin and glucocorticoids are two examples of drugs developed over the years to rectify deregulated inflammatory reactions. Interestingly, both these prototypes of anti-inflammatory therapeutics have been 'borrowed' from Mother Nature, identified from the plant and animal world, respectively. In the past century, systematic organic chemistry has been the major approach for producing new drugs, and vast quantities of aspirin and prednisolone have been synthesized, packaged and sold. However, the fascination provoked by these often life-saving drugs has not subsided, and recent work into the endogenous control of the host inflammatory response has revitalized these compounds. Thus, epi-lipoxins, produced after aspirin acetylation of inducible cyclooxygenase-2, and glucocorticoid-regulated annexin 1 appear to be important endogenous mediators of their respective anti-inflammatory effects. In addition, aspirin-triggered epi-lipoxins and glucocorticoid-regulated annexin 1 might act on the same G-protein-coupled receptor, thus rendering this shared receptor a more likely and worthwhile target for fruitful drug discovery.

Prednisolone retention in integrated liposomes by chemical approach and pharmaceutical approach.

The purpose of this study is to demonstrate a stable retention of prednisolone (PLS) in the unique liposomes integrated by lipophilic derivative approach and PEGylation approach. Palmitoyl prednisolone (Pal-PLS) was newly synthesized and used as a lipophilic derivative. The liposomes were composed of egg phosphatidylcholine (EggPC)/cholesterol (Chol) and L-alpha-distearoylphosphatidylcholine (DSPC)/Chol with or without L-alpha-distearoylphosphatidylethanolamine-polyethylene glycol 2000 (DSPE-PEG 2000) or -PEG 5000 (DSPE-PEG 5000). The retentions of PLS and Pal-PLS in the various liposomes were examined by ultrafiltration and gel filtration. Although PLS showed high trapping efficiency by all liposomes after ultrafiltration, low incorporation efficiency was observed in gel filtration. It indicates that PLS was released from the liposomes by a dilution with elution medium in gel filtration. Pal-PLS showed high incorporation into all liposomes after both ultrafiltration and gel filtration. The high incorporation of Pal-PLS into EggPC/Chol liposomes, however, was reduced by incubation with rat plasma in gel filtration. The reducing effect of rat plasma on drug incorporation into liposomes was inhibited by using DSPC and DSPE-PEGs. Thus, we systemically examined the drug retention in various liposomes and demonstrated the high retention of PLS in the liposomes integrated by lipophilic derivative approach and pharmaceutical approach using special lipids.

Synthesis of nitro esters of prednisolone, new compounds combining pharmacological properties of both glucocorticoids and nitric oxide.

Glucocorticoids (GC) are widely used in therapy for their many pharmacological properties including antiinflammatory and immunosuppressive actions. However, their use over long periods is hampered by a number of severe side effects. Given the biological properties of nitric oxide (NO) and previous experience with nonsteroidal antiinflammatory agents, we synthesized new chemical entities combining both NO and GC properties. Here we report the synthesis of nitro esters of prednisolone obtained through the esterification, with different linkers, on the hydroxy group at C-21 position of the corticosteroid structure. The alkyl chain, as of the nitrooxy derivative (2), or aromatic linkers, as of o-, m-, and p-nitrooxymethylbenzoate derivatives (3-5), respectively, furnish stable compounds that release NO and inhibit the GC receptors in biological assays. To improve solubility we introduced a more water-soluble linker such as the nitrooxyalkylpiperidine or -piperazine group (6-9). Also these compounds retained properties of both NO and prednisolone. Compound 5 (NCX 1015) was selected for its better profile: enhanced antiinflammatory properties and reduced side effects compared with prednisolone. NCX 1015 is currently under preclinical development.

Synthesis and in vitro properties of prednisolone 21-sulfate sodium as a colon-specific prodrug of prednisolone.

Colon-specific delivery of glucocorticoids is highly desirable for the efficient treatment of inflammatory bowel disease. We synthesized prednisolone 21-sulfate sodium (PDS) as a colon-specific prodrug of prednisolone (PD) and investigated its properties using rats as test animals. We expected that introduction of sulfate ester as a sodium salt might increase the hydrophilicity and restrict the absorption in the GI tract. If PDS is stable and nonabsorbable in the upper intestine, it will be delivered to the colon as an intact form, where it hydrolyze by the sulfatase to release PD. Compared with PD, the solubility of PDS increased and the apparent partition coefficient decreased greatly. PDS was stable on incubation with pH 1.2 and 6.8 buffer solutions and with the contents of the stomach and small intestine. On incubation with the cecal contents, PDS decreased to 9.6% of the dose in 10 h producing PD. The amount of PD increased to give a maximum 54% of the dose and decreased. As a control, when PD was incubated with the cecal contents, it decreased to 29% of the dose in 8 h, which implied that reduction of PD proceeded under such conditions. These results suggested that hydrolysis of PDS took place to produce and accumulate PD, which decreased by reduction as the incubation period extended. Our results suggested that PDS can be a promising colon-specific prodrug of PD, and sulfate ester group might serve as a potential colon-specific promoiety, especially for the drugs which are resistant to reduction in the colon.

Novel steroid spiro enones: condensation of prednisolone derivatives with diethyl oxalate.

In a continuing effort to discover potent anti-inflammatory steroids without systemic side effects, diethyl oxalate was condensed with the 17beta-ketol side chain of prednisolone derivatives. Prednisolone gave the most interesting result in forming a novel spiro enone with alpha-hydroxy and beta-carboxylic ester substitutions, and a facile one-pot procedure has been established for the synthesis of this highly functionalized spiro enone structure. The spiro products were tested for their binding potency to the RAW 264.7 macrophage glucocorticoid receptor, for their effect on LPS-induced nitric oxide generation in RAW 264.7 cells, and for their inhibition of rats ear edema induced by croton oil. The new compounds showed weak activities in all of the bioassays. Because the corresponding acid metabolites of two representative spiro enone esters gave no activity in either the binding assay or the nitric oxide generation test, the novel steroids are probably antedrugs. The reduced potency as compared to their parent compounds suggests that the rigid spiro structure is unfavorable to anti-inflammatory activities. Molecular modeling studies confirm that the spiro enones adopt a rigid planar geometry with the ester group in the plane.

On the formation of steroidal amidoesters of 4-[N,N-bis(2-chloroethyl)amino]benzoic acid and their cytotoxic activity.

The 4-[N,N-bis(2-chloroethyl)amino]benzoate of 17beta-acetamido-5alpha-androstan-3beta-ol, 17beta-acetamido-5-androsten-3beta-ol, 3beta-acetamido-5alpha-androstan-17beta-ol and 3alpha-acetamido-5beta-androstan-17beta-ol have been prepared and their antineoplastic effect evaluated against MIA Pa-Ca-2 pancreatic carcinoma, T47D breast carcinoma and A431 squamus cell carcinoma. Among the compounds tested, the compound 17beta-acetamido-3beta-hydroxy-5-androsten-4-[N, N-bis(2-chloroethyl)amino]benzoate appeared to possess a significant cytotoxic effect against A431 cells.

Steroidal anti-inflammatory antedrugs: synthesis and pharmacological evaluation of 16 alpha-alkoxycarbonyl-17-deoxyprednisolone derivatives.

In a continuing effort to minimize the systemic adverse effects of potent anti-inflammatory steroids, a series of 16 alpha-alkoxycarbonyl-17-deoxyprednisolone derivatives: methyl (8a), ethyl (8b), isopropyl (8c), and benzyl (8d) 11 beta,21-dihydroxy-3,20-dioxo-1,4-pregnadiene-16 alpha-carboxylate, was synthesized and evaluated for their topical and local anti-inflammatory activities. In the acute croton oil-induced ear edema dose-response bioassay, the topical anti-inflammatory potencies of these esters relative to prednisolone, 1, were: 8a:1.0, 8b:1.3, 8c:4.0, 8a:4.7 and 1:1.0. The putative metabolite, 11 beta,21-dihydroxy-3,20-dioxo-1,4-pregnadiene-16 alpha-carboxylic acid, 7, was inactive in this test. A seven day cotton pellet granuloma bioassay was employed to study the local and systemic anti-inflammatory activities of these steroids. The local anti-inflammatory potencies of these esters relative to prednisolone, 1, were 1.3, 1.5, 2.3, 2.5, and 1.0 for 8a, 8b, 8c, 8d, and 1, respectively. In this semi-chronic study, only prednisolone exhibited significant untoward side effects, such as reduction in thymus weights, normal body weight gain, and normal plasma corticosterone levels. The increase in the topical and local potencies of these steroid esters was consistent with the increase in their 1-octanol/buffer partition coefficient. The ratio of local to systemic anti-inflammatory activity of 8c and 8d was four times that of prednisolone. The effects of increasing the size of the alkoxy group of these new steroids on both topical and local anti-inflammatory activity and their concomitant decrease in untoward systemic effects were unequivocally demonstrated.(ABSTRACT TRUNCATED AT 250 WORDS)