Cyclodextrins as mucosal absorption promoters of insulin. II. Effects of beta-cyclodextrin derivatives on alpha-chymotryptic degradation and enteral absorption of insulin in rats

Complexation of exenatide and cyclodextrin: An approach for the stabilization and sustained release of exenatide in PLGA microsphere

The purpose of this study was to evaluate the effects of cyclodextrins (CyDs) to stabilize exnatide in the microencapsulation medium and influence on the pharmaceutical properties of exenatide loaded PLGA microsphere. Three CyDs interacted differently with exenatide by investigation using ultraviolet, fluorescence and circular dichroism spectroscopy. The binding affinities of CyDs to the hydrophobic tryptophan residues of exenatide increased in following order: α-CyD < β-CyD < γ-CyD. It was consistent with orders of W/O interface stabilizing and anti-adsorption effects. However, the stabilizing effect of β-CyD on liquid-state and freeze-drying of exenatide was greater than that of γ-CyD. The negative values of ΔH₀, ΔS₀, and ΔG₀ indicated that the exenatide-CyDs complex formation was a favorable exothermic and spontaneous processes that increased the order in the complex with structural rigidity. Furthermore, it was also shown that β-CyD improved encapsulation efficiency, in vitro extended release, and in vivo pharmacokinetic and pharmacodynamic properties of prepared PLGA microspheres.

Sublingual insulin administration: application of hydroxypropyl beta-cyclodextrin and poloxamer188 as permeation enhancers

The objective of this investigation is to investigate the feasibility of sublingual insulin administration. Insulin solutions formulated with permeation enhancers (HPβCD/poloxamer 188) and their in-vitro and in-vivo performances were evaluated. Thereafter, insulin fast-dissolving film was further developed to have similar properties, upon dissolving the film, of the optimized insulin solution. In-vitro performance was evaluated via effect of HPβCD and/or poloxamer 188 concentration across cellulose acetate membrane and porcine esophagus. In-vivo performance was evaluated via pharmacodynamic and pharmacokinetic profiles of insulin solution administered. Cumulative amounts of insulin permeated at 60 min formulated with HPβCD (5%), poloxamer 188 (0.5%), and their combination were 1.31, 3.23, and 4.99 IU/cm², respectively, indicating an additive effect of combination of HPβCD and poloxamer 188. Insulin-induced hypoglycemic effect was observed for insulin solutions with combination of HPβCD and poloxamer 188 after sublingual administration to Sprague-Dawley rats. Microscopic evaluation of porcine oesophageal tissue indicates that HPβCD and poloxamer 188 are safe. Furthermore, the cumulative amount permeated across cellulose acetate membrane at 30 min was 1.13 and 1.00 IU/cm² for insulin solution and fast-dissolving film, respectively, demonstrating to be similar. In conclusion, the use of HPβCD/poloxamer 188 is feasible for the development of sublingual insulin solutions/films.

Selective modifications at the different positions of cyclodextrins: a review of strategies

Cyclodextrins (CDs) are natural, nontoxic, and biodegradable macrocyclic oligosaccharides. As supramolecular hosts, CDs have numerous applications in many aspects. However, nonsubstituted CDs have the disadvantages of solubility, unspecific recognition sites, and weak interactions with guest molecules. Therefore, new CD-based derivatives are successfully designed, synthesized, and widely used in various fields. This contribution outlines the research progress in CD derivatives. In particular, this review emphasizes the synthesis and application of CDs modified through functionalization in definite positions, random substitution, and reconstruction of the skeleton. At the end of this review, a summary and future directions are presented.

Development and Evaluation of pH-Responsive Cyclodextrin-Based in situ Gel of Paliperidone for Intranasal Delivery

Paliperidone (PLPD) is approved for treatment and management of schizophrenia. The current study demonstrates the potential of in situ gel of PLPD for nasal delivery. The permeation of drug through sheep nasal mucosa was analyzed since the nose-to-brain pathway has been indicated for delivering drugs to the brain. The carbopol 934 (CP)- and hydroxypropyl methyl cellulose K4M (HPMC)-based in situ gels containing 0.2% CP and 0.4% w/v HPMC were optimized using experimental design software. The use of hydroxypropyl-β-cyclodextrin (HP-β-CD) in nasal permeation of drug was investigated. Transmucosal permeation of PLPD was examined using sheep nasal mucosa. The in situ gels of PLPD exhibited satisfactory mucoadhesion and showed sustained drug release. The mucocilliary toxicity and histopathological examination confirmed that the nasal mucosa architecture remains unaffected after treatment with PLPD in situ gel. The formulation containing HP-β-CD complex of PLPD exhibited higher rate of drug permeation through sheep nasal mucosa revealing the role of HP-β-CD as nasal absorption enhancer. Thus, CP- and HPMC-based pH-triggered in situ gel containing HP-β-CD-drug inclusion complex demonstrates a novel nasal delivery of PLPD.

Microparticles, microcapsules and microspheres: A review of recent developments and prospects for oral delivery of insulin

Diabetes mellitus is a chronic metabolic health disease affecting the homeostasis of blood sugar levels. However, subcutaneous injection of insulin can lead to patient non-compliance, discomfort, pain and local infection. Sub-micron sized drug delivery systems have gained attention in oral delivery of insulin for diabetes treatment. In most of the recent literature, the terms "microparticles" and "nanoparticle" refer to particles where the dimensions of the particle are measured in micrometers and nanometers respectively. For instance, insulin-loaded particles are defined as microparticles with size larger than 1 μm by most of the research groups. The size difference between nanoparticles and microparticles proffers numerous effects on the drug loading efficiency, aggregation, permeability across the biological membranes, cell entry and tissue retention. For instance, microparticulate drug delivery systems have demonstrated a number of advantages including protective effect against enzymatic degradation, enhancement of peptide stability, site-specific and controlled drug release. Compared to nanoparticulate drug delivery systems, microparticulate formulations can facilitate oral absorption of insulin by paracellular, transcellular and lymphatic routes. In this article, we review the current status of microparticles, microcapsules and microspheres for oral administration of insulin. A number of novel techniques including layer-by-layer coating, self-polymerisation of shell, nanocomposite microparticulate drug delivery system seem to be promising for enhancing the oral bioavailability of insulin. This review draws several conclusions for future directions and challenges to be addressed for optimising the properties of microparticulate drug formulations and enhancing their hypoglycaemic effects.

Intestinal permeation enhancers for oral peptide delivery

Intestinal permeation enhancers (PEs) are one of the most widely tested strategies to improve oral delivery of therapeutic peptides. This article assesses the intestinal permeation enhancement action of over 250 PEs that have been tested in intestinal delivery models. In depth analysis of pre-clinical data is presented for PEs as components of proprietary delivery systems that have progressed to clinical trials. Given the importance of co-presentation of sufficiently high concentrations of PE and peptide at the small intestinal epithelium, there is an emphasis on studies where PEs have been formulated with poorly permeable molecules in solid dosage forms and lipoidal dispersions.

In vitro anticancer activity of Betulinic acid and derivatives thereof on equine melanoma cell lines from grey horses and in vivo safety assessment of the compound NVX-207 in two horses

Betulinic acid, a pentacyclic triterpene, and its derivatives are promising compounds for cancer treatment in humans. Melanoma is not only a problem for humans but also for grey horses as they have a high potential of developing melanoma lesions coupled to the mutation causing their phenotype. Current chemotherapeutic treatment carries the risk of adverse health effects for the horse owner or the treating veterinarian by exposure to antineoplastic compounds. Most treatments have low prospects for systemic tumor regression. Thus, a new therapy is needed. In this in vitro study, Betulinic acid and its two derivatives B10 and NVX-207, both with an improved water solubility compared to Betulinic acid, were tested on two equine melanoma cell lines (MelDuWi and MellJess/HoMelZh) and human melanoma (A375) cell line. We could demonstrate that all three compounds especially NVX-207 show high cytotoxicity on both equine melanoma cell lines. The treatment with these compounds lead to externalization of phosphatidylserines on the cell membrane (AnnexinV-staining), DNA-fragmentation (cell cycle analysis) and activation of initiator and effector caspases (Caspase assays). Our results indicate that the apoptosis is induced in the equine melanoma cells by all three compounds. Furthermore, we succeed in encapsulating the most active compound NVX-207 in 2-Hydroxyprolyl-β-cyclodextrine without a loss of its activity. This formulation can be used as a promising antitumor agent for treating grey horse melanoma. In a first tolerability evaluation in vivo the formulation was administered every one week for 19 consecutive weeks and well tolerated in two adult melanoma affected horses.

Development of acid-resistant alginate/trimethyl chitosan nanoparticles containing cationic β-cyclodextrin polymers for insulin oral delivery

In this study, the use of trimethylchitosan (TMC), by higher solubility in comparison with chitosan, in alginate/chitosan nanoparticles containing cationic β-cyclodextrin polymers (CPβCDs) has been studied, with the aim of increasing insulin uptake by nanoparticles. Firstly, TMCs were synthesized by iodomethane, and CPβCDs were synthesized within a one-step polycondensation reaction using choline chloride (CC) and epichlorohydrine (EP). Insulin-CβCDPs complex was prepared by mixing 1:1 portion of insulin and CPβCDs solutions. Then, nanoparticles prepared in a three-step procedure based on the iono-tropic pregelation method. Nanoparticles screened using experimental design and Placket Burman methodology to obtain minimum size and polydispercity index (pdI) and the highest entrapment efficiency (EE). CPβCDs and TMC solution concentration and pH and alginate and calcium chloride solution concentrations are found as the significant parameters on size, PdI, and EE. The nanoparticles with proper physicochemical properties were obtained; the size, PdI, and EE% of optimized nanoparticles were reported as 150.82 ± 21 nm, 0.362 ± 0.036, and 93.2% ± 4.1, respectively. The cumulative insulin release in intestinal condition achieved was 50.2% during 6 h. By SEM imaging, separate, spherical, and nonaggregated nanoparticles were found. In the cytotoxicity studies on Caco-2 cell culture, no significant cytotoxicity was observed in 5 h of incubation, but after 24 h of incubation, viability was decreased to 50% in 0.5 mμ of TMC concentration. Permeability studies across Caco-2 cells had been carried out, and permeability achieved in 240 min was 8.41 ± 0.39%, which shows noticeable increase in comparison with chitosan nanoparticles. Thus, according to the results, the optimized nanoparticles can be used as a new insulin oral delivery system.

Supramolecular nanoparticles constructed by balancing the forces between attractive host–guest and repulsive electrostatic interactions in two positively charged polymers

A novel type of supramolecular nanoparticle (SNP) was self-assembled based on the balance of forces including attractive supramolecular host–guest interactions and repulsive electrostatic interactions between the host and the guest polymers.

Cyclodextrins, blood-brain barrier, and treatment of neurological diseases

Biological barriers are the main defense systems of the homeostasis of the organism and protected organs. The blood-brain barrier (BBB), formed by the endothelial cells of brain capillaries, not only provides nutrients and protection to the central nervous system but also restricts the entry of drugs, emphasizing its importance in the treatment of neurological diseases. Cyclodextrins are increasingly used in human pharmacotherapy. Due to their favorable profile to form hydrophilic inclusion complexes with poorly soluble active pharmaceutical ingredients, they are present as excipients in many marketed drugs. Application of cyclodextrins is widespread in formulations for oral, parenteral, nasal, pulmonary, and skin delivery of drugs. Experimental and clinical data suggest that cyclodextrins can be used not only as excipients for centrally acting marketed drugs like antiepileptics, but also as active pharmaceutical ingredients to treat neurological diseases. Hydroxypropyl-β-cyclodextrin received orphan drug designation for the treatment of Niemann-Pick type C disease. In addition to this rare lysosomal storage disease with neurological symptoms, experimental research revealed the potential therapeutic use of cyclodextrins and cyclodextrin nanoparticles in neurodegenerative diseases, stroke, neuroinfections and brain tumors. In this context, the biological effects of cyclodextrins, their interaction with plasma membranes and extraction of different lipids are highly relevant at the level of the BBB.

Approaches for enhancing oral bioavailability of peptides and proteins

Oral delivery of peptide and protein drugs faces immense challenge partially due to the gastrointestinal (GI) environment. In spite of considerable efforts by industrial and academic laboratories, no major breakthrough in the effective oral delivery of polypeptides and proteins has been accomplished. Upon oral administration, gastrointestinal epithelium acts as a physical and biochemical barrier for absorption of proteins resulting in low bioavailability (typically less than 1-2%). An ideal oral drug delivery system should be capable of (a) maintaining the integrity of protein molecules until it reaches the site of absorption, (b) releasing the drug at the target absorption site, where the delivery system appends to that site by virtue of specific interaction, and (c) retaining inside the gastrointestinal tract irrespective of its transitory constraints. Various technologies have been explored to overcome the problems associated with the oral delivery of macromolecules such as insulin, gonadotropin-releasing hormones, calcitonin, human growth factor, vaccines, enkephalins, and interferons, all of which met with limited success. This review article intends to summarize the physiological barriers to oral delivery of peptides and proteins and novel pharmaceutical approaches to circumvent these barriers and enhance oral bioavailability of these macromolecules.

Time-action profile of an oral enteric insulin formulation in healthy Chinese volunteers

BACKGROUND

Insulin is an essential treatment for both type 1 and 2 diabetes. Among the available routes of insulin administration, oral delivery is the most appealing option.

OBJECTIVE

The purpose of this study was to evaluate the pharmacodynamic and pharmacokinetic profiles of orally administered enteric insulin and compare the time-action of these oral insulin capsules with neutral protamine Hagedorn (NPH) insulin.

METHODS

This was a single-center, randomized, 4-period, crossover study. Twelve healthy volunteers (3 per group) received 1 of 3 doses of oral enteric insulin (50, 100, or 200 U) or 1 subcutaneous injection of NPH insulin (6 U) on 4 separate days. After administration, glucose infusion rates and serum insulin concentrations were monitored for 10 hours.

RESULTS

Glucose infusion rates increased after administration of either NPH or oral enteric insulin. The mean times for maximal metabolic effects for 50, 100, and 200 U of oral enteric insulin were 250 (118), 170 (58), and 236 (132) minutes, respectively, compared with 243 (79) minutes for NPH insulin. The onset of action was slower for oral enteric insulin at 50 U (38 [10] minutes), 100 U (41 [18] minutes), and 200 U (65 [58] minutes) compared with NPH insulin (35 [8] minutes). The maximum glucose infusion rates for oral enteric insulin treatment (1.66 [0.50], 1.61 [1.00], and 1.80 [0.60] mg/kg/min for 50, 100, and 200 U, respectively) were lower compared with NPH insulin (2.06 [0.82] mg/kg/min), although these differences were not statistically significant.

CONCLUSIONS

Oral enteric insulin capsules induced significant glucodynamic effects and exhibited a time-action profile similar to that of NPH insulin in these healthy volunteers. No detectable increases in serum insulin concentration were observed in any treatment group. Trial registry number: ChiCTR-TRC-12001872.

Effective protection and controlled release of insulin by cationic beta-cyclodextrin polymers from alginate/chitosan nanoparticles

In an alginate/chitosan nanoparticle system, insulin was protected by forming complexes with cationic beta-cyclodextrin polymers (CPbetaCDs), which were synthesized from beta-cyclodextrin (beta-CD), epichlorohydrin (EP) and choline chloride (CC) through a one-step polycondensation. Due to the electrostatic attraction between insulin and CPbetaCDs, as well as the assistance of its polymeric chains, CPbetaCDs could effectively protect insulin under simulated gastrointestinal conditions. The nanoparticles have their mean size lower than 350 nm and can load insulin with the association efficiency (AE) up to 87%. It is notable that the cumulative insulin release in simulated intestinal fluid was significantly higher (40%) than that without CPbetaCDs (18%) because insulin was mainly retained in the core of the nanoparticles and well protected against degradation in simulated gastric fluid. Far-UV circular dichroism analysis also corroborated the preservation of insulin structure during the nanoparticle preparation and release process.

Poly(epsilon-caprolactone)/eudragit nanoparticles for oral delivery of aspart-insulin in the treatment of diabetes

Nanoparticles prepared with a blend of a biodegradable polyester (poly(epsilon-caprolactone)) and a polycationic nonbiodegradable acrylic polymer (Eudragit RS) have been used as a drug carrier for oral administration of a short-acting insulin analogue, aspart-insulin. Insulin-loaded nanoparticles, about 700 nm in diameter, encapsulated 97.5% of insulin and were able to release about 70% of their content in vitro in a neutral medium over 24 h. When administered orally to diabetic rats, insulin-loaded nanoparticles (50 IU/kg) decreased fasted glycemia for a prolonged period of time and improved the glycemic response to glucose in a time-dependent manner, with a maximal effect between 12 and 24 h after their administration. In parallel, plasma insulin levels increased. However, higher (100 IU/kg) and lower (25 IU/kg) doses of insulin did not exert any biological effect. It is concluded that polymeric nanoparticles composed of poly(epsilon-caprolactone)/Eudragit RS are able to preserve the biological activity of the insulin analogue aspart-insulin; however, the postprandial peak suppression was prolonged more than 24 h by comparison with regular insulin working only 6-8 h. This effect may be explained by the monomeric configuration of aspart-insulin, which is probably better taken up by the intestinal mucosa than regular insulin.

Lipophilic beta-cyclodextrin cyclic-nitrone conjugate: synthesis and spin trapping studies

Nitrone spin traps are commonly employed as probes for the identification of transient radicals in chemical and biological systems using electron paramagnetic resonance (EPR) spectroscopy. Nitrones have also found applications as therapeutic agent in the treatment of radical-mediated diseases. Therefore, a spin trap that incorporates high reactivity to superoxide radical anion (O2(*-)), more persistent superoxide adduct, enhanced bioavailability, and selective targeting in one molecular design is desirable. In this work, the synthesis of a nitrone spin trap, 4, that is tethered via amide bonds to a beta-cyclodextrin (beta-CD) and a dodecyl chain was achieved with the expectation that the beta-cyclodextrin would lead to increased reactivity to O2(*-) and persistent O2(*-) adduct while the lipophilic chain would impart membrane targeting property. The two constitutional racemic isomers, 4a and 4b, were separated using preparative HPLC, and structural analysis and self-aggregation properties were carried out using NMR, induced circular dichroism, dynamic light scattering, transmission electron microscopy, and computational approach. EPR spin trapping of O2(*-) by 4a and 4b was only successful in DMSO and not in an aqueous system, due most likely to the amphiphilic character of 4 that can favor conformations (or aggregation) hindering radical addition to nitrone. Kinetics of formation and decay of the 4a-O2H adduct in polar aprotic solvents show faster reactivity to O2(*-) and more persistent O2(*-) adduct compared to nitrones not conjugated to beta-CD. Computational analysis of 4a and 4b as well as 4a-OOH and 4b-OOH adducts were carried out, and results show that isomerism, both constitutional and stereochemical, affects the orientations of aminoxyl-NO and/or hydroperoxyl groups relative to the beta-CD annulus for optimal H-bond interaction and stability.

Effects of hydroxylpropyl-β-cyclodextrin on in vitro insulin stability

The objective of this study was to elucidate the effects of hydroxylpropyl-beta-cyclodextrin (HP-beta-CD) on the in vitro stability of insulin. It was found that HP-beta-CD had positive effects on the stability of insulin in acid and base and under high temperature conditions. Furthermore, use of HP-beta-CD could also increase the stability of disulfide bonds which are important to the conformation of insulin. Through (1)H-NMR experiments it was found that the protective effect of HP-beta-CD was due to complexation with insulin. The results suggest that the presence of HP-beta-CD could improve the stability of insulin in different environments.

Improving the stability of insulin in solutions containing intestinal proteases in vitro

Degradation of insulin was studied in this work. Casein and protamine could obviously suppress degradation of insulin by intestinal enzymes, and could protect insulin from degradation by the mechanism of competition and combination with proteolysis enzyme. What is more, co-incubated with HP-β-CD-casein or HP-β-CD-protamine, most insulin was protected from degradation by intestinal enzymes. In addition, it was found that the complexation of insulin with HP-β-CD was characterized by UV absorption spectra. These results indicated that HP-β-CD, casein and protamine could offer some positive and useful results, and could protect insulin from degradation during their transit through the intestinal tract.

Encapsulation of insulin–cyclodextrin complex in PLGA microspheres: a new approach for prolonged pulmonary insulin delivery

The insulin administration by pulmonary route has been investigated in the last years with good perspectives as alternative for parenteral administration. However, it has been reported that insulin absorption after pulmonary administration is limited by various factors. Moreover, in the related studies one daily injection of long-acting insulin was necessary for a correct glycemic control. To abolish the insulin injection, the present study aimed to develop a new formulation for prolonged pulmonary insulin delivery based on the encapsulation of an insulin:dimethyl-beta-cyclodextrin (INS:DM-beta-CD) complex into PLGA microspheres. The molar ratio of insulin/cyclodextrin in the complex was equal to 1:5. The particles were obtained by the w/o/w solvent evaporation method. The inner aqueous phase of the w/o/w multiple emulsion contained the INS:DM-beta-CD complex. The characteristics of the INS:DM-beta-CD complex obtained were assessed by 1H-NMR spectroscopy and Circular Dichroism study. The average diameter of the microspheres prepared, evaluated by laser diffractometry, was 2.53 +/- 1.8 microm and the percentage of insulin loading was 14.76 +/- 1.1. The hypoglycemic response after intratracheal administration (3.0 I.U. kg(-1)) of INS:DM-beta-CD complex-loaded microspheres to diabetic rats indicated an efficient and prolonged release of the hormone compared with others insulin formulations essayed.

Oral delivery of insulin associated to polymeric nanoparticles in diabetic rats

Nanoparticles prepared with a blend of a biodegradable polyester (poly(-epsilon-caprolactone)) and a polycationic non-biodegradable acrylic polymer (Eudragit RS) have been used as a drug carrier for oral administration of insulin. The rate of encapsulation of insulin was around 96%. The therapeutic efficiency of oral insulin nanoparticles (25, 50 and 100 IU/kg) in diabetic rats and the intestinal uptake of fluorescein isothiocyanate (FITC) labelled insulin were studied. When administered orally by force-feeding to diabetic rats, insulin nanoparticles decreased fasted glycemia in a dose dependant manner with a maximal effect observed with 100 IU/kg. These insulin nanoparticles also increased serum insulin levels and improved the glycemic response to an oral glucose challenge for a prolonged period of time. FITC-Insulin-loaded nanoparticles strongly adhered to the intestinal mucosa and labeled insulin, either released and/or still inside nanoparticles, was mainly taken up by the Peyer's patches. It is concluded that polymeric nanoparticles allows the preservation of insulin's biological activity. In addition, the antidiabetic effect can be explained by the mucoadhesive properties of the polycationic polymer (Eudragit) RS) allowing the intestinal uptake of insulin.

Lack of effect of β-cyclodextrin and its water-soluble derivatives on in vitro drug transport across rat intestinal epithelium

The present study aimed to investigate whether beta-cyclodetxrin (beta-CD) and its water-soluble derivatives, hydroxypropyl-beta-cyclodextrin (HP-beta-CD) and sulfobutyl ether beta-cyclodextrin (SBE-beta-CD), exert any effects on the permeation of two drug transport markers (propranolol and lucifer yellow) across rat intestinal epithelium. Rat ileum was stripped of its serosa and mounted inside an Ussing Chamber. Apparent permeability coefficients (P(app)) of the markers from the mucosal to serosal side of the tissue were determined at 37 degrees C in the presence and absence of the beta-cyclodextrins on the mucosal side. Potential difference (PD) was constantly monitored during each experiment to ensure maintenance of the viability and integrity of the tissue. Pre-incubation with 1% beta-CD, 1% HP-beta-CD or 1.48% SBE-beta-CD on the mucosal side for 30 min did not significantly alter the PD and the propranolol permeability (p>0.05). Co-incubation with 1% beta-CD or 1% HP-beta-CD exerted no significant effect on the P(app) of both propranolol and lucifer yellow (p>0.05), but co-incubation with 1.48% SBE-beta-CD lowered the P(app) of propranolol from (1.71+/-0.44)x10(-5) to (0.19+/-0.04)x10(-5)cm/s, which may be ascribed to the molecular complexation of propranolol with SBE-beta-CD. All three beta-cyclodextrins exert no apparent impact on both (passive) transcellar and paracellular drug transports.

Carrier-based strategies for targeting protein and peptide drugs to the lungs

With greater interest in delivery of protein and peptide-based drugs to the lungs for topical and systemic activity, a range of new devices and formulations are being investigated. While a great deal of recent research has focused on the development of novel devices, attention must now be paid to the formulation of these macromolecular drugs. The emphasis in this review will be on targeting of protein/peptide drugs by inhalation using carriers and ligands.

Membrane transporter/receptor-targeted prodrug design: strategies for human and veterinary drug development

The bioavailability of drugs is often severely limited due to the presence of biological barriers in the form of epithelial tight junctions, efflux proteins and enzymatic degradation. Physicochemical properties, such as lipophilicity, molecular weight, charge, etc., also play key roles in determining the permeation properties of drug candidates. As a result, many potential drug candidates may be dropped from the initial screening portfolio. Prodrug derivatization targeting transporters and receptors expressed on mammalian cells holds tremendous potential. Enhanced cellular delivery can significantly improve drug absorption. Such approaches of drug targeting and delivery have been the subject of intense research. Various prodrugs have been designed that demonstrate enhanced bioavailability and tissue specificity. This approach is equally applicable to human and veterinary pharmaceuticals since most of the transporters and receptors expressed by human tissues are also expressed in animals. This review highlights studies conducted on the use of transporters and receptors in an effort to improve drug bioavailability and to develop targeted drug delivery systems.

Multivalent binding of galactosylated cyclodextrin vesicles to lectin

Amphiphilic beta-cyclodextrins with alkylthio chains at the primary-hydroxyl side and galactosylthio-oligo-(ethylene glycol) units at the secondary-hydroxyl side, which form nanoparticles and vesicles, show multivalent effects in their binding to lectin.

The effect of cyclodextrins on the in vitro and in vivo properties of insulin-loaded poly (D,L-lactic-co-glycolic acid) microspheres

In this work we describe the development and characterization of a new formulation of insulin (INS). Insulin was complexed with cyclodextrins (CD) in order to improve its solubility and stability being available as a dry powder, after encapsulation into poly (D,L-lactic-co-glycolic acid) (PLGA) microspheres. The complex INS : CD was encapsulated into microspheres in order to obtain particles with an average diameter between 2 and 6 microm. This system was able to induce significant reduction of the plasma glucose level in two rodent models, normal mice and diabetic rats, after intratracheal administration.

Involvement of cholesterol in the inhibitory effect of dimethyl-beta-cyclodextrin on P-glycoprotein and MRP2 function in Caco-2 cells

We compared the inhibitory effect of various cyclodextrins (CyDs) on P-glycoprotein (P-gp) and multidrug resistance-associated protein 2 (MRP2) function and examined the contribution of cholesterol to the inhibitory effect of 2,6-di-O-methyl-beta-cyclodextrin (DM-beta-CyD) on the efflux activity of the function in Caco-2 cell monolayers. Of various CyDs, DM-beta-CyD significantly impaired the efflux activity of P-gp and MRP2. DM-beta-CyD released P-gp and MRP2 from the monolayers in the apical side's transport buffer and decreased the extent of cholesterol as well as P-gp and MRP2 in caveolae of Caco-2 cell monolayers, but not caveolin and flotillin-1. On the other hand, DM-beta-CyD did not change MDR1 and MRP2 mRNA levels. Therefore, these results suggest that the inhibitory effect of DM-beta-CyD on P-gp and MRP2 function, at least in part, could be attributed to the release of these transporters from the apical membranes into the medium as secondary effects through cholesterol-depletion in caveolae after treatment of Caco-2 cell monolayers with DM-beta-CyD.

Oral delivery of insulin from enteric-coated capsules containing sodium salicylate: effect on relative hypoglycemia of diabetic beagle dogs

The hypoglycemic effect of Eudragit S100 enteric-coated capsules containing sodium salicylate as an absorption promoter formulated with insulin in various ways: as physical mixture, by wet granulation or in suppository bases (polyethylene glycol 4000 or Witepsol W35) was studied in hyperglycemic beagle dogs. The capsules containing insulin formulated with sodium salicylate (50 mg) and prepared by either physical mixing or wet granulation using 10% polyvinyl pyrollidone gave almost the same results producing a maximum reduction in plasma glucose level (C(max)) of 81.53+/-8.21 and 79.59+/-5.75%, T(max) of 6 and 5 h, area under the curve (AUC) of 69.37+/-48.64 and 57.98+/-23.15% reduction hour (% red. h) and resulting in relative hypoglycemia (RH) of 8.73+/-6.12 and 7.29+/-2.91%, respectively. Formulation of insulin with sodium salicylate in PEG 4000 produced a lower AUC of 37.30+/-10.36% red. h and RH of 4.69+/-1.3%. While, formulation in Witepsol W35 (0.5, 1.0 and 2.0 g) that was sieved to produce particle size of 180-315 microm and filled in enteric-coated capsules showed that formulating insulin and sodium salicylate in 1 g base is the best formulation. It produced 25% reduction in plasma glucose levels of the hyperglycemic beagle dogs at T(max) of 4 h and the largest AUC of 100.10+/-25.72% red. h, resulting in the highest RH of 12.59+/-3.23%. In conclusion, 25-30% reduction in plasma glucose levels and RH of about 12.5% relative to subcutaneous injection of regular soluble insulin can be achieved by formulating insulin in Witepsol W35 (1 g) with sodium salicylate (50 mg) as an absorption promoter, reducing the resulting mass into particle size 180-315 microm, packing into hard gelatin capsules and coating with Eudragit S100.

Enhancement of absorption of insulin-loaded polyisobutylcyanoacrylate nanospheres by sodium cholate after oral and subcutaneous administration in diabetic rats

Polyisobutylcyanoacrylate (PIBCA) nanospheres were employed as biodegradable polymeric carriers for oral (p.o.) and subcutaneous (s.c.) delivery of insulin. The polymerization technique used was able to hold 65%-95% of insulin added 30 min after initiation of polymerization. The percentage drug loading was monomer concentration dependent. Insulin adsorption to the nanospheres was measured by radioimmunoassay. Although Pluronic F68 (0.5%) did not significantly alter the in vitro insulin degradation half-life T50%, sodium cholate (0.5%) increased the degradation T50% of insulin by 56% (from 13.6 +/- 1.6 to 22.1 +/- 2 min). This study also investigated the in vivo performance of insulin-loaded PIBCA in aqueous suspension with or without sodium cholate (0.5%) and Pluronic F68 (0.5%) surfactants after oral and subcutaneous administration to alloxan-induced diabetic rats. Insulin absorption was evaluated by its hypoglycemic effect. Insulin associated with PIBCA nanospheres retains its biological activity up to 15 h and 24 h after oral and subcutaneous administrations, respectively. Administered orally insulin-loaded (75 U/kg) nanospheres, in the presence of surfactants, significantly reduced the mean blood glucose level from 392 +/- 32 to 80 +/- 13 mg/dl within 2 h and maintained it at 100 mg/dl or less for more than 8 h. On the other hand, the subcutaneous administration of insulin-loaded (25 U/kg) nanospheres significantly decreased the blood glucose level from 406 +/- 33 to 88.5 +/- 12.8 mg/dl within 1 h, and the lowered glucose level was maintained at 100 mg/dl or less for more than 12 h; it returned to its initial value 24 h after administration. Insulin-loaded nanospheres with surfactants showed significant (P < .05) pharmacological availability (PA%) of 37.6% +/- 3.7% and 65.2% +/- 2.7% after oral and subcutaneous dosages, respectively. The existence of surfactants with PIBCA nanospheres improved the oral PA% by 49.2%. These findings suggest that the developed PIBCA, in the presence of surfactants, would be useful not only in improving insulin gastrointestinal absorption, but also in sustaining its systemic action by lowering the blood glucose to an acceptable level.

The effect of absorption enhancers on the initial degradation kinetics of insulin by alpha-chymotrypsin

The goal of this investigation was to establish a fast method to screen various insulin absorption enhancers by following their effect on the initial kinetics of insulin incubated with alpha-chymotrypsin at 37 degrees C. A simple, sensitive and reproducible reversed phase high performance liquid chromatography (HPLC) method has been developed to carry out this goal. Linear responses (r > 0.999) were observed over the range of 0.4-4 U/ml for insulin. There was no significant difference (P < 0.05) between inter- and intra-day studies for insulin. The mean relative standard deviations (RSD%) of the results of within-day precision and accuracy of insulin were 12%. The assay was sensitive to detect the existence of any metabolite due to the addition of any absorption enhancers, even if it was not seen with insulin alone. Three metabolites (A-C) were detected only when insulin was incubated with alpha-chymotrypsin at 37 degrees C. Metabolite D was observed when either glycocholic acid (0.5, 1%) or taurochenodeoxycholate (0.5, 1%) was incubated with insulin in the absence of alpha-chymotrypsin at 37 degrees C. The compounds that significantly increased insulin T50% were glycyrrhizic acid (0.5%) > deoxycholic acid (1%) > deoxycholic acid (0.5%) > glycyrrhizic acid (1%) > cholic acid (0.5, 1%). Capric acid (0.5%), hydroxypropyl-alpha-cyclodextrin (0.5, 1%) and dimethyl-alpha-cyclodextrin (0.5, 1, 5%) did not significantly affect insulin T50%. The bile salts increased insulin T50% in this order: deoxycholate > cholate > glycocholate > taurocholate > taurodeoxycholate > taurochenodeoxycholate > glycodeoxycholate. The results obtained would support the feasibility of utilizing such method for screening any compound incorporated in insulin formulation. These compounds should be used in the minimum possible concentration to avoid or minimize insulin degradation.

A moderate interaction of maltosyl-alpha-cyclodextrin with Caco-2 cells in comparison with the parent cyclodextrin

The cytotoxicity of maltosyl-alpha-cyclodextrin (G2-alpha-CyD) and maltosyl-beta-cyclodextrin (G2-beta-CyD) toward Caco-2 cells was compared with that of natural alpha-cyclodextrin (alpha-CyD), beta-cyclodextrin (beta-CyD) and gamma-cyclodextrin (gamma-CyD). The degree of increase in cytotoxicity was dependent on the CyD's type and the concentration: the cytotoxicity of CyDs at the same concentration increased in the order of gamma-CyD<G2-beta-CyD<G2-alpha-CyD<<alpha-CyD, although beta-CyD could not be compared to other CyDs because of low solubility in water. Alpha-CyD decreased transepithelial electrical resistance (TEER) and increased the apical-to-basolateral (AP-to-BL) transport of [3H]mannitol, a paracellular transport marker, in a concentration-dependent manner, suggesting that alpha-CyD decreased the integrity of Caco-2 cell monolayers. In addition, alpha-CyD increased the AP-to-BL transport of rhodamine 123, a transcellular transport marker, under the experimental conditions being independent of P-glycoprotein. In contrast, G2-alpha-CyD, G2-betaCyD and gamma-CyD had slight effect on both TEER and the transport of mannitol and rhodamine 123 even at relatively high concentrations up to 150 mM. The inability of G2-alpha-CyD and G2-beta-CyD to effect TEER and the transport of mannitol and rhodamine 123 could be explained by the findings that these maltosylated CyDs released only a small amount of membrane constituents from Caco-2 cell monolayers and interacted only weakly with monolayers composed of L-alpha-dipalmitoylphosphatidylcholine (DPPC) formed on water. These results indicate that G2-alpha-CyD has less cytotoxicity and less disturbing ability toward Caco-2 cell monolayers than alpha-CyD, and G2-beta-CyD has, at least, comparable cytotoxicity to beta-CyD toward them. Thus, from the safety point of view, highly water-soluble G2-alpha-CyD and G2-beta-CyD may be particularly useful in various pharmaceutical formulations.

Biological activity of insulin in GMO gels and the effect of agitation

Glyceryl monooleate (GMO)-water cubic phase gel was previously shown to protect insulin from agitation induced aggregation. However, it is not known if insulin is biologically active in the gel and what effect agitation has on insulin in the gel. Therefore, the objective was to determine the stability of insulin in cubic phase gel in terms of its biological activity in a suitable animal model such as Sprague-Dawley rats. Effect of agitation on biological activity of insulin in cubic phase GMO gel was determined by subcutaneous injections of the agitated and non-agitated gels to two groups of previously fasted rats and measuring the effect on their blood glucose levels. Two groups of rats administered with agitated insulin solution and normal saline were used as controls. The biological activity of insulin was evaluated by comparing AAC (area above the blood glucose level-time curve, in %-h), C(max) (maximum % decrease in blood glucose levels) and t(max) (time required to attain C(max), in h) values for the four groups of rats. Since cubic phase gel is highly viscous, therapeutic equivalency of insulin in the lamellar phase gel, which converts in situ into cubic phase gel, was compared to insulin solution with normal saline as the control, using AAC, C(max) and t(max) of the blood glucose profile. Insulin was biologically active in both agitated and non-agitated gels; however, upon agitation, insulin in solution totally lost its hypoglycemic activity. Agitation of insulin in the cubic phase gel was seen to have very little deleterious effect on its biological activity. Insulin in the lamellar phase gel was not only biologically active but also therapeutically equivalent to insulin solution based on AAC (327.9+/-100.8 and 431.7+/-113.3), C(max) (57. 1+/-7.0 and 70.2+/-6.5) and t(max) (2.8+/-0.7 and 4.0+/-1.7) for the lamellar phase gel and insulin solution, respectively (no significant difference, P0.05). In summary, GMO cubic phase gel protected insulin from agitation induced aggregation, and insulin was biologically active in the gel.

Hypoglycemic effect of oral insulin in diabetic rabbits using pH-dependent coated capsules containing sodium salicylate without and with sodium cholate

The hypoglycemic effect of oral insulin (20 U and 40 U) capsules coated with a pH-dependent soluble polymer (Eudragit S100) and containing sodium salicylate (50 mg) without and with sodium cholate (50 mg) was studied in alloxan-hyperglycemic rabbits and compared with that of s.c. insulin injection (20 U). The capsules containing 20 U insulin + sodium salicylate (50 mg) produced a significant reduction in plasma glucose level to 82 and 73% of initial values at 2 and 3 hr after administration, respectively. The blood glucose level slowly returned to normal values at 5 hr. The AUC0-5 hr was 73.7 +/- 43.5 mg.hr/dl compared to 242 +/- 70.5 mg.hr/dl for insulin (20 U, s.c.) with a relative hypoglycemia of 30.4%. A higher dose of oral insulin (40 U) + sodium salicylate (50 mg) was more effective in reducing plasma glucose level which steadily decreased and reached 56% of the initial value by 5 hr (AUC0-5 hr = 132 +/- 41.5 mg.hr/dl and relative hypoglycemia = 27.3%). Sodium cholate (50 mg), however, slightly improved sodium salicylate effect producing an AUC0-5 hr of 139 +/- 37.3 mg.hr/dl with relative hypoglycemia of 28.7%. The relative hypoglycemia of pH-dependent coated capsules reached in the present experiment is the highest found so far.